This dissertation has been 64—9598 microfilmed exactly as received

WEED, Emily Davis, 1925- A STUDY OF THE PALLADIUM II—CHLORIDE COMPLEXES IN AQUEOUS SOLUTION,

The Ohio State University, Ph.D., 1964 Chemistry, analytical

University Microfilms, Inc., Ann Arbor, Michigan. A STUDY OF THE PALLADIUM II-CHLORIDE COMPLEXES III

AQUEOUS SOLUTION

DISSERTATION

Presented in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in the Graduate School of The Ohio State University

3sr

Emily Davis Weeds B. S<

The Ohio State University 196*}-

Approved by

~ f \ ~ Adviser Department of Chemistry ACKNOWLEDGMENTS

The author wishes to express her sincere appreciation to

her advisers Dr. James I. Watters, for his interest and guidance

during the course of this investigation. I also wish to thank The

Ohio State University for the assistantships and scholarships and the National Science Foundation, the Standard Oil Company of

Indianas the Visking Corporation, and E. I. du Pont de Nemours

for financial assistance during the course of my studieso CONTENTS

Page

INTRODUCTION 9....ft«..G..o.«oooo..eo.o 1

CHAPTER I - THE PALLADIUM (II)-PERCHLORATE SYSTEM

HlS^OinCdX I*£VXSW • ® . . o » o fl.oe.»eo o « » • .. 10

Preparation and study of palladium (II) perchlorate solutions ....a.®..®.... 10

Perchlorate complexes of metal ions ...... 14

Experimental techniques and results . » . „ ...... 19

General discussion .oao.®...... 19

Apparatus . . . & sa«®soa« .o.o..... 22

Preparation of reagents ...... 25

Spectrophotometric procedures and results ..... 38

Stepwise potentiometric titration of palladium (II) perchlorate solutions with sodium bicarbonate and sodium hydroxide ...... 105

Dialysis of palladium (II) perchlorate solutions ° . 110

Nuclear magnetic resonance study of palladium perchlorate solutions ...... Ill

Discussion of results ...... o... 115

CHAPTER II - THE PALLADIUM (II)-CHLORIDE SYSTEM

Historical review ©«o ...... o...o 123

'The chloride complexes of palladium (II) ...... 3.23

Theoretical ...... ooo... 129

Experimental techniques and results © . 141

ueneral discussion .a...... ®.®...© 141

iii CONTENTS (ContcU)

Page

Preparation of reagents ...... 143

Spectrophotometrie studies ...... o 145

Discussion of results ...... 231

APPENDIX ...... 261

REFERENCES ' . . . . 291

iv TABLES

Table '' Page

1. Comparison of Average Molar Absorptivities and Average Deviation from the Mean Absorptivity for Various Palladium (II) Perchlorate Preparations ooo®®.®®® 41

2 o Change in Molar Absorptivity with Time s. for Palladium (II) Perchlorate Solutions Prepared from Standard Solution NO e 15 «e9«»tB44ooeooieo}ee e e t c s

3® Increase in Absorbance from One Day after Mixing to One Month after Mixing? for Solutions Prepared from Standard Palladium (II) Perchlorate Solution No® 6 ® * ® 47

4. Change in Absorbance of Palladium (II) Perchlorate Solutions with Temperature 49

5® Change in the Molar Absorptivity of Palladium (II) Perchlorate Solutions with Perchloric Acid Concen­ tration in the 0©2 to 1®0 M Range 53

6 o Molar Absorptivity of Palladium (II) Perchlorate Solu~ tions Having a Constant Mole Ratio of Perchlorate to Palladium • ® ® 9®«o»co®®o«oooeaoao 54

7® Molar Absorptivity of Palladium (II) Perchlorate Solu­ tions Prepared from Standard Solution No® l6 ® . * <, » . 55

80 Effect of Sodium Chlorate on the Molar Absorptivity of Palladium (II) Perchlorate Solutions . * » ® ...... 57

9o Effect of Perchloric Acid on the Absorption Parameters of Palladium (II) Perchlorate Solutions Prepared from Standard Solution Ho® 10 * ® •<> o »«»9oeoo«« o 6l

10® Effect of Perchloric Acid on the Absorption Parameters of Palladium (II) Perchlorate Solutions Prepared from Standard Solution No® 6 ® . „ . . „ . . . ® „ . . . . » 64

11® Molar Absorptivity of Palladium (II) Perchlorate Con­ taining 5 Molar Perchloric acids Validity of Beer's Law . 65

12® Effect of Various Samples of Perchloric Acid on the Molar Absorptivity of Palladium (II) Perchlorate in 7°9 Molar Perchloric Acid ®®©®®aoo9«oo»9o©»o®®o 66

1 3 . Effect of Various Preparations of Palladium (II) Per­ chlorate on the Molar Absorptivity of Palladium (II) Perchlorate in 9*6 Molar Perchloric Acid . = . « * . . ® 67 v TABLES (Contdo)

Table Page

14. Average Molar Absorptivity vs. Time* for Palladium (II) Perchlorate Solutions Containing 5 .10 Molar Perchloric acid ...... 70

15<» Comparison of Observed Molar Absorptivity of Palladium (II) Perchlorate Solutions with Values Calculated by Extrapolation to Zero Perchlorate Concentration . . . . 73

16. Effect of Sodium Perchlorate on the Molar Absorptivity of Palladium (II) Perchlorate Solutions ......

1?. Effect of Barium Perchlorate on the Molar Absorptivity of Palladium (II) Perchlorate Solutions...... 78

18. Effect of Perchloric Acid on the Absorption Parameters of Palladium (II) Perchlorate Solutions Containing ; 0.6l6 Mole Ratio of Chloride to Palladium ...... 82

19® Molar Absorptivity of Palladium (II) in Concentrated Sodium Hydroxide Solutions ...... 86

20. Effect of Silicic Acid on the Molar Absorptivity of Palladium (II) Solutions Prepared from Standard Solution No. 13 ...... 90

21. Effect of Perchloric Acid on the Absorption Parameters of Copper (II) Perchlorate Solutions...... 100

22. Effect of Sodium Perchlorate on the Absorption Parameters of Copper (II) Perchlorate Solutions .... 104

2 3 . Stepwise Titration of Palladium (II) Perchlorate Solu­ tions with Sodium Hydroxide and Sodium Bicarbonate .... 108

24. Nuclear Magnetic Resonance Absorption of Chlorine-35 in Concentrated Perchloric Acid Solutions Containing Various Metal I o n s ...... 114

25. Comparison of the Absorption Parameters for Palladium (II)-Perchlorate and Palladium (II)-Hydroxide Solutions by Various Investigators ...... 116

260 Comparison of Values for the Molar Absorptivity of Palladium (II) Perchlorate Solutions by Various Investigators...... 117

vi TABLES (Contdo)

Table Page

27® Data for Formation Curve of the Palladium (II)-Chloride System at ^1*10 ? ^f20 $ & and mp* o.»©ooo..o© l6l

28o Change in Absorbance of Palladium (II) Perchlorate x-.ath Chloride Concentration at Selected Wavelengths © « . . . 169

29o Molar Absorptivity of Palladium (II) in 1 Molar Hydro­ chloric Acids Validity of Beer9s Law ...... 173

30 c Data for the Calculation of at h-10 mu by the Slope- Intercept Method .. o * © .o..©. « » o 17^*

31o Evaluation of at Various Wavelengths Using the Slope-Intercept Method ...... 177

32. Change in Calculated Molar Absorptivity of Trichloro- palladate (II) Ion with Various Assumed Values of K. . « 183

33® Maximum Error in Free Chloride Concentration Produced by an Error of 0.002 Units in Absorbance at Various Regions of the Hole Ratio Curves at 4-30 mu ...... 186

3^o Stability Constants for the Palladium (II)-Chloride System with Errors Estimated by Graphical and by Analytical Methods ...... 0 ...... 187

35® Distribution of Pa3_ladium (II) Chloride Complexes as a Function of -Log SCI and Mole"Ratio of Chloride to Palladium ...... 189

369 Molar Absorptivity of Palladium (II) Chloride Complexes in the 360 to 560 mu Wavelength Region ...... © 19^

3 7 9 Comparison of the Molar Absorptive.ty of the Mono- cnloropalladium (II) Ion Obtained by Various Methods o © ...... 199

380 Comparison of the Molar Absorptivity of the Dichloro- palladium (II) Ion Obtained by Various Methods . . . © . 201

39® Comparison of the Values for the Molar Absorptivity of the Trichloropalladate (II) Ion by Various Methods ©o©...... o©«.*ooo‘o©#e«. 202 i(00 Comparison of the Molar Absorptivity of the Tetra- chloropalladate (II) Ion Obtained by Various Methods .©...... Co...... 20 3

vii TABLES (Contdo)

Table Page

41-480 Comparison of Calculated and Observed Values for the Molar Absorptivity of Palladium (II) Chloride Solutions ...... o • • 206-213

49® Theoretical Composition of Palladium (II) Chloride Solutions • 214

50o Effect of Ionic Strength on the Molar Absorptivity of Palladium (II) in Chloride Solutions ...... 221

51• Effect of Substituting Sodium and Potassium Chlorides for Hydrochloric Acid on the Molar Absorptivity of Palladium (II) in 1 Molar Chloride Solutions . . * 0 223

520 Effect of Acid Concentration on the Molar Absorptivity of Palladium (II) in 1 Molar Chloride Solutions * . 224

53® Relative Effect of Hydrochloric Acid and Perchloric Acid on the Molar Absorptivity of Palladium (II) in 1 to 4 Molar Chloride Solutions ...... 226

5 4 ® Comparison of the Formation Constants Obtained by Various Investigators for the Palladium (II)- Chloride System ...... 232

55® Comparison of Molar Absorptivity Values at Selected Mole Ratios of Chloride to Palladium by Various Investigators for the Palladium (II)-Chloride System ...... 234

560 Comparison of Values for the Molar Absorptivity of Palladium (II) in 1 Molar Hydrochloric Acid by Various Investigators « 238

57® Comparison of Values for the Molar Absorptivity of Palladium (II) in Concentrated Hydrochloric Acid Solutions by Various Investigators ...... 242

580 Comparison of the Absorption Parameters for Palladium (II) Chloride Complexes in Aqueous Solution by Various Investigators . 0 0 252

59® Stability Constants of Chloride Complexes of Various Metal Ions in Aqueous Solution . 255

viii FIGURES

Figure Page

1© Change in Absorbance of Palladium (II) Perchlorate Solutions with Temperature . © o © o o o © © © © © © • © © 5^*

2o Effect of Perchloric Acid Concentration on the Molar Absorbtivity of Standard Palladium (II) Perchlorate Solution No© 10 «©©•»©©©© ©©©©aoo©©©© © 59

3© Effect of Perchloric Acid Concentration on the Absorbance of Standard Palladium (II) Perchlorate Solution No© 6 0 « 63

4© Molar '.hciorptivity of Palladium (II) Perchlorate vs© Perchlorate Concentration at Selected Wavelengths in the Visxble Region o©»©©©®©©©©©o©©©o© 72

3© Molar Absorptivity of Palladium (II) Perchlorate vs© Perchlorate Concentration at Selected Wavelengths m the Ultraviolet Region ©©©© »•©©«©©«©©•© 78

6» Effect of Perchloric Acid Concentration on the Absorbance of Palladium (II) Perchlorate Solutions Containing 0»6l6 Mole Ratio of Chloride to Palladium ©.>©©©.©©.© 81

7® Effect of Perchloric Acid Concentration o p . the Absorbance of Nickel (II) Perchlorate Solutions « . . .©=..».© 94

8© Change in Molar Absorptivity of 0©0476 M Copper (II) Perchlorate Solutions with Perchloric Acid Concen­ tration at Various Wavelengths 99

9© Change in Molar Absorptivity of 0©0476 M Copper (II) Perchlorate Solutions with Sodium Perchlorate Concen­ tration at Various Wavelengths 103

10© Molar Absorptivity vs. Wavelength Curves for Palladium (II) Perchlorate Solutions by Various Investigators © © © 118

11© Effect of Chloride Concentration on the Absorbance of 4©35 Millimolar Palladium (II) Perchlorate Solutions © © © 148

12© Effect of Chloride Concentration on the Absorbance of 0.869 Millimolar Palladium (II) Perchlorate Solutions © © © 150

13° Effect of Chloride Concentration on the Absorbance of 0.218 Millimolar Palladium (II) Perchlorate Solutions © © © 132

14© Mole Ratio Curves for the Palladium (II)-Chloride System in the Zero to 0©5 Mole Ratio Range at 430 mp. «©..©«, 135

ix FlG URES (Contd o)

Page 15o Mole Ratio Curves for the Palladium (Il)-Chloride System in the Zero to 1.2 Mole Ratio Range at 4-30 raw ...... 157

16. Mole Ratio Curves for the Palladium (Il)-Chloride System in the Zero to 10 .5 Mole Ratio Range at 430 mw ..... 159

17. Theoretical Formation Curves of the Palladium (II)- Chloride System for n Values from Zero to 2.0 and Experimental Values of n at Various Wavelengths ...... 163

I80 Absorbance vs. Chloride Concentration for 4«35 and 0.870 Millimolar Palladium (II) Perchlorate Solutions at 430 m w ...... 1&5

19° Slope-Intercept Plot of Corresponding Solutions for the Estimation of Maximum Coordination Number of Palladium . . 168

20. Absorbance vs. Chloride Concentration for the Palladium (II)-Chloride System at Selected Wavelengths ...... 171

21. Slope-Intercept Plot of the Palladium (Il)-Chloride System at 410 mW5 Determination of ...... 176

22. Slope-Intercept Plot at 400 mw for the Calculation of at Various Values of ...... 180

2 3 . Change in the Calculated Molar Absorptivity of the Trichloropalladate (II) Ion with Various Values of ...... i...... 182 L

25® Distribution of Palladium (II) Chloride Complexes as a Function of Total Chloride Concentration ...... 193

26. Molar Absorptivity of Palladium (II) Chloride Complexes vs. Wavelength...... 196

27. Molar Absorptivity of PdCl4* and PdC^ Calculated by Various Methods ...... 198

28. Relative Effects of Hydrochloric and Perchloric Acids on the Molar Absorptivity of Palladium (II) in 1 to 4 MoDar Chloride Solutions ...... 228

x FIGURES (Contdo)

Figure Page

29° Comparison of Mole Ratio Curves for the Palladium (II)-Ghloride Syst^™ by Various Investigators at 380 liljii 0000000000000000000 o 237

30o Comparison of Mole Ratio Curves for the Palladium (II)-Chloride System by Various Investigators at 460 rrp <= 0 ® 0 . . , ...... 0 . 0 237

31o Molar Absorptivity vs» Wavelength Curves for Palladium (II) Chloride in 1 Molar Hydrochloric Acid by

Various Investigators ..>.....>...0.0... 240

32o Molar Absorptivity vs 0 Wavelength Curves for Palladium (II) Chloride in Concentrated Hydrochloric Acid Solutions by Various Investigators » ...... 244

33° Formation Curve for the Palladium (il)-Chloride System at 470 and 480 mM- by Shchukarev et al® o ® 0 ® . ® ® 248

34o Theoretical Formation Curves for the Palladium (II)- Chloride System Calculated from the Stabiliiy Constants of Shchukarev et al® and from the Present Investigation 250

xi INTRODUCTION

The objective of this investigation was to study the equilibria between palladium (II) and chloride in aqueous solution and to provide a basis for the quantitative study of other palladium (II) complexes in solution. It was initially part of a long range program in this laboratory instigated by Dr. W. M. MacNevin and designed to elucidate the analytical chemistry of the platinum group metalso

U) vi. M. MacNevin and 0. H. Krieges Anal. Chem.p 27? 535 (1955)? W. M. MacNevin and E. A. Hakkila? ibid.9 29? 1019 (1957)? Vi". M. MacNevin and M. L. Bunton? ibid. ? 29 $ 1806 (1957).

The coordination chemistry of metals is becoming an increasingly important part of inorganic and analytical chemistry. Many investi­ gations have been concerned with the solution chemistry of uranium*, thoriums the actinidesj and the first transition series; however9 most of the research on palladium complexes has involved the prepara­ tion and structure of the solid compounds and their use in analytical chemistry. Few quantitative investigations of palladium (II) com­ plexes in aqueous solution have been reported. This may be attributed to the lack of information on the general chemistry and the experi­ mental difficulties encountered? such as ease of reduction to the free metalj hydrolysis? and in some cases slow attainment of equilib­ rium.

Important theoretical advances in recent years have resulted in a better understanding of the bonding forces? spectra? and magnetic 2 properties of coordination compounds. Paulings interpretation of 2 chemical bonding in terms of hybridized atomic orbitals is useful

(2) L. Pauling? '"The Mature of the Chemical Bonds” Cornell University Press? I960© in predicting the favored stereochemical configuration for palladium compounds? but is unable to explain the electronic transitions re­

sponsible for the near infrared? visible? and ultraviolet spectral 3-5 bands. The crystal field theory of bonding which uses an essen-

(3) J. S. Griffith? nThe Theory of Transition Metal Ions?" Cambridge University Press? 1961. (4) L. E. Orgel? "An Introduction to Transition-Element Chemis­ try: Ligand Field Theory?" Methuen? London? I960. (5) C. J. Ballhausen? "Introduction to Ligand Field Theory?" McGraw-Hill? Mew York? 1962®

tially electrostatic model? deals primarily with electron repulsions

and makes no assumptions about electron pair bonding. For the first

row transition series where the bonding is primarily electrostatic

and the spin orbit coupling is negligible? this theory has been suc­

cessful in predicting stereochemical? magnetic? and some thermodynamic

properties as well as energy levels in the unfilled d orbitals of

the metal ion. However? for diamagnetic square-planar and tetragonal O d complexes formed by palladium (II) in which a considerable amount

of covalent bonding is present? the crystal field theory gives an

incorrect ordering of the d orbitals and does not explain the spectro-

chemical series. Currently the molecular orbital theory seems most

promising? Jorgensen? Gray? and Ballhausen have applied molecular 3 orbital calculations to the complexes of palladium (II) and are con­ tributing to a greater understanding of the thermodynamic ? stereo­ chemical? magnetic? kinetic* and spectral properties of these complexeso 6 9 Since this research is concerned with the application

(6) H. B. Gray* J. Chem. Educ = ? ^1? 2 (196^) . (7) H. B. Gray and G. J. Ballhausen? J. Am. Chem. Soc.? 85? 260 (1963). (8) C. K-i Jorgensen? "Advances in Chemical Physics?" Vol. 5» I. Prigogine? editor? Interscience Publishers? New York? 1963® (9) C. K. Jorgensen? "Absorption Spectra and Chemical Bonding in Complexes?" Pergamon? New York? 1961. of absorption measurements to elucidate the equilibria in aqueous solutions of palladium (II) complexes? an analysis of the energy levels responsible for the spectra is beyond the scope of this in­ vestigation.

In the solid state bivalent palladium usually forms square-planar complexes which are isomorphous with their platinum (II) analogues

(10) A. ?. Wells? "Structural Inorganic Chemistry?" 2d ed.? Oxford University Press? London? 1950* (11) R. S. Nyholm? Quart. Rev.? ji? 321 (19^9)°

Hovrever? in the past few years there has been an increasing amount of evidence for the existence of the penta- and hexacoordinated ion in the solid state and in solution. The absorption spectra of palla dium (II) complexes in solution indicate that most species have 12 tetragonal symmetryo Interpretation of exchange studies and the

(12) C. K. Jorgensen? "Absorption Spectra of Complexes of Heavy Metals?" Contract No. DA-91-508-SUC-2h7? Report? European Research Office? U. S. Army Dept.? Fra-kfurt am Main (1958)o kin8t-5.cs of displacement reactions of palladium (II) complexes whereby one ligand replaces another in the complex ion involve the assumption that two solvent molecules are weakly bound in the remaining (trans) 13-14 positions of an octahedron about the metal ion« Only a few stable

(13) F. Basolo and R. G. Pearson* “Mechanisms of Inorganic Reactions *,s John Wiley and Sons* Inc.* New York* 1958. p. 207o (1*0 A. A. Grinberg and N. V. Kiseleva* J. Inorg. Chem. USSR* 119 (1958). octahedral complexes of palladium (II) are known. Harris et al.^ have

(15) C. M. Harris* R. S. Nyholm* and D. J. Phillips* J. Chem. Soe., ^379 (I960). prepared bis(diarsine) complexes of the general type [Pd(DA)2-X]X» inhere DA is o-phenylenebis(dimethylarsine) and X is a halogen* nitro or thiocyanate group. These complexes have a tetragonally distorted octahedral structure in the solid state and are 1 j1 electrolytes in nitrobenzene. Tris-o~diphenylarsine* (QAS)» forms complexes of the type [Pd(QAS)X]*r which have trigonal b5.pyramidai coordination in the solid state and in benzene solution^ Absorption spectra of colloidal

(16) C. A. Savage and L. M. Vananzi, J. Chem. Soe.* 15^ (1962). suspensions of the dimethylglyoxime complex of palladium (II)*

[PdtDngJg]# visible region indicate the presence of strong 17 intermolecular metal-metal bonds.

(17) G. V. Banks and D. W. Barnum* J. Am. Chem. Soe.* 80* 4767 (1958)o 5

The magnetic behavior of palladiums like that of other platinum group metalss has been found to be very complicated. This situation 18 has been summarized by Van Vleck. Divalent palladium has a magnetic

(18) Van VLecks "The Theory of Electric and Magnetic Suscept­ ibilities?'1 Oxford University Press? Oxford? 1932?p. 3 H ° susceptibility of from 0.07 to 0.3.3 Bohr magnetons in most of its compounds except in the difluoride? with an octahedrally coordinated rutile structure and magnetic moment of 1.84 Bohr magnetons

(19) D. P. Mellor? J. Proc. Roy. Soe.? N. 5. Wales9 2Z» 145 (1944). (20) N. Bartlett and R. Maitland* Acta Cryst.? 11? 747 (1958)®

This indicates that in most palladium (II) complexes there is electron pairing in the d orbitals and suggests covalent bond formation. There may also be some exchange interaction between neighboring metal ions ? as was found to be present in concentrated salt solutions of para- 21 magnetic ions of the platinum group. Nuclear quadrupole resonance

(21) J. H. E® Griffiths? J. Owen? and I. M. Ward? Proc. Roy. Soc.? A 219? 526 (1953)• measurements on a number of palladium and platinum halides have shox-in 22 a considerable amount of covalency in the metal halide bonds®

(22) Kazuo Ito» K. Nakamura? Y. Kurita? Kaji Ito? and M. Kubo? J. Am. Chem. Soc.? 8 2? 4526 (1961)® 6

There has been a concerted effort to associate the ability of a 23-25 metal to form complexes with its position in the periodic table®

(23) J. Bjerrum, Chem. Rev., 46* 38I (1950)® (24) S. Ahrland, J. Chatt* and W. R. Davies» Quart. Rev., 12) 265 (1958). (25) H. Irving and R. J. P. Williams* Nature* 162* 746 (1948)0

26 Irving and Williams have shown that there is an increase in the stability of complexes formed by divalent metal ions of the first transition series as the atomic number of the metal increases toward a maximum at copper* but with zinc the stability decreases again.

This trend of relative stabilities remains valid for the second and third transition series* as may be seen by comparison of the stability constants of the chloride complexes of divalent palladium and plati­ num xcith those of cadmium and mercury* respectively. ■j The factors which determine the relative tendencies of various elements to form complexes may be divided into two groups: (1 ) the i onic forces which are dependent upon the ratio of effective cationic nuclear charge to cation crystal radius and (2 ) the covalent forces which depend on the particular number of d electrons in the transition 26 metal ion. One measure of the effective nuclear charge is the

(26) M. C. Day and J. Selbin* "Theoretical Inorganic Chemistry*" Reinhold Publishing Corporation, New York, 1962. ionization potential. The second ionization potential of the elements in the three transition series increases with atomic number towards a maximum at copper, silver, and gold* respectively. The covalent forces depend on crystal-field stabilization energy, stereochemistry, availability of empty d orbitals for acceptance IX bonding and avail­ ability of d-electron pairs for back-donation XT bonding. For the important complex geometries Gray^ has shown that the crystal-field stabilization energy for the same ligand follows the order square- planar) octahedral) tetrahedral. The planar configuration is most common among the elements in oxidation states for which the resulting complex contains no unpaired electrons [i'Ji(II)s Pd(II), Au(III)], or 27 one unpaired electron [Cu(ll), Ag(II), O(ll)]o The availability

(27) D. P. Mellor, Chem. Rev., 137 ( W 3 ) « of d orbitals of palladium (II) for acceptance XT bonding as well as for back-donation IT bonding is shown by the relatively great stability of the iodide and cyanide complexes, respectively, and by the strong bonding of heavy atom donors.

Several investigators have reported stability constants for 28 99 palladium (II) complexes. Maley and Mellor have determined the

(28) L. E. Maley and D. P. Mellor, Aust. J. Sci. Res., A-2, 92 (1949). (29) Ibid., p. 579«

stepwise stability constants for the salicylaldehyde and glycine com­ plexes of palladium (II) from pH measurements of perchloric acid

solutions containing potassium tetrachloropalladate (II). They cal­

culated the following values at 25°C.s log K]_ = 7.7^- and log Kg = 7<>03

for the salicylaldehyde complexes in 50 percent dioxanej and log Kj_ = 9»12 and log Kg = 8.A-3 for the glycine complexes. These

30 , authors reported a value of log B2 = 26 for diethylenediamme-

(30) D. P. Mellor and L. E. Maley? Nature? l6l? 436 (19^8). palladium (II) however? no information was given as to the method em­ ployed. MacNevin and Kriege'^*^ investigated the complex species

(31) W. M. MacNevin a:nd 0. H. Kriege? J-. Am. Chem. Soc.? 7Z> 61^9 (1955). (32) W. M. MacNevin and 0. H. Kriege? Anal. Chem.? 26? 1768 (195*0. present in aqueous solutions of palladium (II) and ethylenediamine- tetraacetic acid by speetrophotometric? potentioraetric? and migration methods. They found H^PdY? PdY^” ? and PdOHI predominate in the pH regions 1.6 to 2.0? ^ .5 to 9.5s and H ° 5 to 13®5s respectively. From e.m.f. measurements using a spongy palladium electrode? these authors obtained a value of 18.5 for log K of the following reaction at 25°C« and at an ionic strength of 0.2: Pd^+ + Y^ «=*■ PdY^” . A thermodynamic study of the reactions between palladium (II) and acetylacetone was made by Droll? Block? and Fernelius.33 Values of the stability constants

(33) H. A. Droll? B. P. Block? and W. C. Fernelius? J. Phys. Chem., 61, 1000 (1957)« of the reactions 2+ — + 4. — Pd + acac Pd(acac) ? and Pd(acac) + acac Pd(acac)g at three chloride concentrations from 0®102 to 0.0278 M were deter- o mined at 20s 30s and 40 C® from a static pH titration procedure and corrected to the apparent thermodynamic constants with the aid of the Debye-Huckel equation. The thermodynamic constants were obtained

by extrapolation of the apparent log K values to zero chloride con­

centration. The folloitfing values were reporteds log K]_ = 16*5 at

20°G. i log K-j_ = 16.2 and log K2 = 10 ®9 at 30°C.; log = 15 °3 and

log Kg = 10®5 at 40°C. Maley and Mellor found values of 8 .7I and

8 .I3 for log and log Kgs respectively? for this system at 2.5°Co

in 50 percent dioxane solutions containing potassium tetrachloro-

palladate (II) and acetylacetone.

Comparison of the stability constants for the salicylaldehyde?

acetylacetone? and ethylenediamine complexes of palladium (II) x-jith

those for the formation of analogous complexes of other divalent metals gives the following decreasing order of stability% Pd(IX)§

Cu(II)s Ni(lI)* Pb(II), CCo(II)* Zn(II)], Cd(II)» Fe(II), Mn(II)s

Mg(ll). In solutions free of chloride the stability constants of these

palladium (II) complexes would probably be greater than those of

mercury (II). The stability constant reported for the palladium (II) 2— complex with ethylenediaminetetraacetic acid? PdY ? is the same

order of magnitude as those reported for Ni(II)9 Pb(II)* and Co(II).

Further comparison of the stability constants of palladium (II)

complexes with those of other metal ions will not be attempted because

of lack of quantitative information and apparent inconsistencies in

some of the constants reported. CHAPTER I

THE PALLADIUM (II)-PERCHLORATE SYSTEM

Historical Review

Palladium perchlorate solutions

The strong coordinating tendencies of palladium (II) and the acidity of its aquo ion make its existence as the free hydrated ion 'kh. doubtful;-' however* the results of recent studies have indicated

(3^) W. C. Fernelius, Record of Chemical Progress* Kresge- Hooker Science Library* 11* 21 (1950)® the presence of this ion in perchlorate media at acid concentrations greater than 0.1 M. Solutions have been prepared by dissolution of the hydrous oxide and Pd^gO^^ClO^)^ in perchloric acid* by thermal conversion of nitrate solutions to the perchlorate* and by meta- thetical reactions of palladium (II) chloride with mercuric perchlorate and silver oxide. They have been investigated by spectrophotometric* conductometric* e.m.f.* ion exchange* and migration methods. The lack of agreement among various investigators concerning the absorbance of palladium (II) perchlorate solutions prepared by the same method as well as by differeht methods illustrates the difficulty in obtaining pure solutions® 35 Templeton* Watt* and Garner"^ precipitated Pd0®xH,~,0 from a

10 11

(35) Ho Templeton? G. Watt* and C. S. Garner? J. Am. Chem. Soc.? 1608 (1943).

hydrochloric acid solution with sodium hydroxide and dissolved the partially dried oxide in perchloric acid at room temperature. From

e.m.f. measurements using a spongy palladium electrode and reference

hydrogen electrode these authors established a value of E°q3 for the

reaction

Pd(s) Pd2H'(aq) (4.00 formal HCIO^) + 2e~

31 as -0.987 volt. MacNevin and Kriege measured the equilibrium

potential of this couple against a calomel half cell and calculated

a value of -0.93810.002 volt at 298 K in dilute perchloric acid

solutions- in which the ionic strength was 0.2 M. Droll prepared

(38) H« A. Droll? thesis? The Pennsylvania State University (1958)? pp. 8 and 47»

palladium oxide by neutralization of a hydrochloric acid solution of

palladium (II) chloride with sodium hydroxide. The oxide was refluxed

for 12 hours with 4 N perchloric acid and the resulting solution

neutralized to an acid concentration of 0.4 M with tetramethylammonium

hydroxide. The absorbance of palladium (II) perchlorate solutions con­

tain^ z from 0 o5243 to 1.573 ^ palladium (II)? and from 0.139 to

0.416 M perchloric acid at ionic strengths 0.22? 0.43? and 0.71 was

measured in the 320 to 700 mix itfavelength region at 2 1 ? 29»5s and

38°C ■> The molar absorptivity was found to be independent of the

ClO^/Pd ratio but varied with hydrogen ion concentration. 12

The latter effect was attributed to the equilibrium

Pd2+ + H20 ^PdOH+ + H+ ; % = — — 2 H (Pd2+) and values for the molar absorptivity of Pd2+ in the 3&5 to 480 mp. wavelength region were calculated by algebraic solution of simul­ taneous equations of the following forms

ePdOH e = epd + (H+)

37 Sundaram and Sandell dissolved palladium sponge in hot fuming nitric

(37) A» K« Sundaram and E. 3. Sandell* J. Am. Chem. 3oc.» 77 > Q55 (1955)• acid and converted the resulting palladium (II) nitrate to the per­ chlorate by evaporation of the solution with concentrated perchloric acid. These authors measured the absorption of palladium (II) per­ chlorate solutions containing from 1.8 to 4.4 mM palladium (II) and from 0.1 to 1.0 M perchloric acid in the 360 to 520 mp. wavelength region and found no evidence for hydrolysis or complex formation with perchlorate ion at these concentrations. Livingston^® dissolved

(38) S. E. Livingston* J. Chem. Soc.» 5091 (1957)® palladium sponge in concentrated nitric acid. After addition of

concentrated perchloric acid* the solution was heated until it fumed

strongly; brown needles were deposited on cooling. The precipitate was washed with perchloric acid and subsequently dried in vacuo over 13 P40i0 . Thesbsorption spectra of solutions of the perchlorate in 1 M perchloric acid and in water were measured; the conductivity and pH of aqueous solutions of the compound xrere also reported. Since and K£ of the mercury (II) chloride complexes are 10^°^and 10^°^s 19 12 respectivelyJorgensen and co-workers were able to prepare

(39) L. G. Sillens Acta Chem. 3cand.;> 539 (1949)® solutions of the aquo palladium (II) ion utilizing the following re­ action ;

PdCl^ + 4 Hg2+ Pd2+ + 4 HgCl+.

They also used silver oxide to remove the chloride from a concen­ trated sodium hydroxide solution of the tetrachloropalladate (ll)e

Quantum-mechanical calculations were applied to the absorption data 40 and band assignments xtfere made. Stevenson» Franke® Berg? and Kervik

(40) P. C. Stevenson j A. A. Frankes R. Berg; and VJ. Nervik* J. Am. Chem. Soc. s 25? 4876 (1953)® reported that palladium showed excellent absorption on Dowex $0 in

0«5 to 1 N perchloric acid solutions. Electrolysis of solutions con­ taining 1*3 mM palladium (II) perchlorate in 0.8 and 6«8 M perchloric acid revealed that palladium was present as a cationo 41

(41) H. B. Sommerville» thesis; The Ohio State University; 1958. 14

Perchlorate complexes of metal ions

Perchlorate media have been -used frequently for the study of complex equilibria in aqueous solution since the perchlorate ion is considered to have less tendency to complex with metal ions than any other common anion. Recently the existence of both inner and outer orbital complexes of metal ions with perchlorate have been demon­ strated by conductometrie, potentiometrie , kinetic, and optical 42 methods. G. F. Smith and his students observed changes in the

(42) G. F. Smith and 0. A. Getz? Ind. Eng. Chem.j Anal. Ed.» 10, 191 (1938). oxidation potential of the Ce(IV)/Ce(III) couple with perchloric acid concentration and concluded that one or both species combine with per­ chlorate. Blaustein and Gryder^ studied this couple in nitric acid

(43) B. D. Blaustein and J. VI • Gryder, J. Am. Chem. Soc., 79, 540 (1957). solution by extraction and e.m.f. methods and interpreted their data as indicating the existence of Ge(lV)-Ce(lIl) and Ce(lV)~Ce(lV) 44 polymers even in 5®5 formal nitric acid. King and Pandow postulated

(44) E. L. King and M. L. Pandow, J. Am. Chem. Soc., 74, 1966 (1952).

the existence of perchlorate complexes of cerium (IV) based on the

changes produced by concentrated solutions of perchloric acid and sodium perchlorate in the ultraviolet absorption of cerium (IV) 15 solutions. Heidt and Berestecki^ and Sutcliffe and Weber^ attributed

(45) L. J. Keidt and J. Berestecki? ibid.? 22 s 2049 (1955)° (46) L. H. Sutcliffe and J. R. Weber? Trans. Faraday Soc.? 5 2 s 1225 (1956)o the observed variations of the absorptivity of the 296 mu peak of

cerium (III) perchlorate solutions with temperature and with per- chlorate anion concentration to the reaction

Ca3+ + CIO" GeClO^o

The molar absorptivity of the free cerium (III) ion? eo ? and of the complex? e^» were assumed to be independent of the temperature and

of the medium. Sutcliffe and Weber calculated association constants

of 2.4 and 0.28 at 18 and 40.2°C« respectively? at an ionic strength {3 of 1.14 M. Heidt and Berestecki used the Debye-Huckel equation to

extrapolate log K to zero ionic strength at temperatures between 15

and 55°C.? and reported the following values for the thermodynamic

constants at 25°C.; AF° - -2.61 kcal.? AH° = -11.82 kcal.? and

As° = -31 e.u. The negative value of ^3° was interpreted as evidence

for the existence of an outer orbital type complex in which hydrogen

bonds are formed between two or more oxygen atoms of the perchlorate

ligand and the oxygen atoms of water molecules associated i-Jlth the

cerium (III) ion. This interpretation is consistent with R a m a n ^

(47) M. M. Jones? E. A. Jones? D. F. Harmon? and R. T. Semmes? J. Am. Chem. Soc.? 8 3? 2038 (1961). 16 48 and n.m.r. studies which revealed no e/ldence for the existence of

(48) F« Klanberg, J. P. Hunt, and H. W. Dodgen, Inorg. Chem., 2, 139 (1963).

49 covalent complexes* Sutton measured the absorption spectra of

(4-9) J* Sutton, Nature, 169, 71 (1952) ® aqueous solutions of iron (ill) perchlorate containing perchloric acid in concentrations from 1 to 7 M» He assumed that molar absorp- tivities vie re invariant with the composition of the reaction medium, and that the known activity coefficients of chromium (III) and mag­ nesium (II) were approximately those of iron (III) and the perchlorate complex in unmixed solutions. Using the empirical equation of uuechauf, he calculated a value of = 0.475^0°075 for the stability constant of the ferric perchlorate complex at infinite dilution. <50 Using the activity function of Davies, Sykes^ obtained a value of

(50) K. W. §ykes, "Kinetics and Mechanism of Inorganic Reac­ tions in Solution," Special Publication No. 1, The Chem. Soc., London, 1957s P» 84.

19 at 19°C. and 14 at 250C. for the association constant of ferric perchlorate complex at zero ionic strength, from the data of Richards 51 52 and Sykes, and Olson and Simonson, respectively. Fromherz and Libr

(51) A* R. Olson and T. R. Simonson, J. Chem. Phys., 1£, 1322 (1949). (52) H. Fromherz and K. H. Lih, Z» Phys. Chem., A 1 6 7, 103 (1933)® observed that although the absorption of mercury (II) solutions was independent of the perchloric acid concentration in the 180-235 wavelength region? at longer wavelengths a new band appeared whose intensity Increased with perchloric acid concentration. These authors postulated the existence of undissociated HgCClO^^o Raman spectra of saturated mercury (II) perchlorate solutions'obtained by Murray and

Cleveland-53 gave evidence of covalent bond formation^ on the other

(58) 1* I* Murray and F. F. Cleveland? J. Am. Chem. Soc.? 6 5? 2110 (19^3)o

47 hand? Raman spectra obtained by Jones et al° did not exhibit lines which could be attributed to covalent complexes. In their study of o 2-f / 2+ the formal potentials of the Hg^ /Hg and the Hg /Hcouples 54 Heitanen and Sillen concluded that association between mercurous

(54) S. Hietanen and L» G. Sillen? Arkiv Kemi? 10? 103 (1956)0 and perchlorate ions is greater than that between mercuric and per­ chlorate ions. Conductometric and ion exchange studies5^ showed that

(55) V. Krishnan and C. C. Patel? Chem. and Ind.? 14? 321 (196l)o

TiO(ClO^)2 ®6H20 dissociates into 2 ions? TiO(ClO^)4' and CIO”? with an average dissociation constant of 2.471 x 10"^. Murthy and Patel*^

(5 6) P. R. Murthy and C. C. Patel? Katurvdss.? 48? 693 (1961)® 18 studied, the conductance of aqueous solutions of Zr02(Cl0^)2 «2H20 and postulated dissociation of the solid into Zr0(C10^)+ and C10£ ions, with a dissociation constant K=0.00l856. However, ion exchange data indicated that even in 2 M solutions of perchloric acid the

ZrO^**’ ion was adsorbed on Dowex 50. Rogers and W a i n d ^ observed the

(5?) T. E. Rogers and G. M. Waind, Trans. Faraday Soc.» S l» 1360 (1961)o

effects of perchloric acid and sodium and barium perchlorates on the

absorption of thallium (III) perchlorate solutions in the 240 to

280 mu- wavelength range at 25, 33«5> and 40°C. and postulated the

existence of thallium (III) perchlorate complexes. The bathochromic,

hypochromic shift in the absorption maxima of neodymium (III) per­

chlorate solutions at 522 and 427 mp produced by a concentration 58 increase from 6 to 11.8 M perchloric acid was interpreted by Krumholz

_ (58) P. Krumholz, J. Phys. Chem., 63., 1313 (1959)«

as evidence of complex formation between perchlorate and neodymium ^-r (III) ions. Both n.m.r* '8 and Raman studies have indicated the

existence of covalent bonding between manganese (II) and perchlorate

ions® Hathaway and Underhill-'59 found that infrared spectra of

(59) B. J. Hathaway and A. E. Underhill* J. Chem. Soc«, 3091 (1961).

Fe(Cl0i}.)2.9H20fNi(Cl0^)2 «6H20 , Cu(C10ij_)2 ®6H20, Ag(C10i),) .H20, and 19

Th(C10^)^o6H20 were consistent with the existence of the simple perchlorate ion in these solutions; however* they found increasing coordination of perchlorate as a monodentate ligand in

Cu(Cl0^)2o^ eCN» Mn(ClO^)|MeCN* and ZnCciO^J^MeCN. Spectra of the lower hydrates FeCClO^^^I^O* NiCclO^) and GuCclO^goSH^O led the authors to conclude that perchlorate acts as a monodentate ligand while that of anhydrous Cu(C1 0 ^ )2 and Fe(G10ij.)^ were interpreted as evidence of bidentate coordination through two of the oxygen atomso

Barker* Harris and McKenzie isolated the five-coordinated species

(60) N. T. Barker* C. M. Harris* and E° D. McKenzie* Proc. Chem. Soc.* 335 (1961).

[CuCchel^CClO^)]+ (where chel=phenyl or bipyridyl) as the hexafluoro- phosphate* [CuCchel^CClO^) jPF^s Changes in the visible spectrum of

[Cu(bipy)g]PFg in anhydrous nitrobenzene produced by additional per­

chlorate were interpreted as evidence for the entrance of perchlorate ion into the inner coordination sphere of copper (11)©

Experimental Techniques and Piesults

General discussion

In order to study the complex-forming tendencies of palladium

(II) it was necessary to prepare solutions in which the acidity was sufficiently high to repress hydrolysis* and in which the anion present had little tendency to complex with the metal ion. Nitrate* sulfate?

and perchlorate media have frequently been used for the study of com­ plex formation since they have less affinity for metal ions because 20 2 61 of their saturation of charge* * Although it is sometimes stated

(61) K* Fajans and G. Joos? Z. Physik. 22? 1 (192^). that oxyanions do not enter into complex formation} proof for the existence of inner sphere complexes containing nitrate® sulfate? and 62 j63 perchlorate has been established* Since the relative coordinating

(62) J. C. Bailar? Jr.? "The Chemistry of the Coordination Compounds?" Reinhold Publishing Corporation? New York? 1956. (63) "Stability Constants? Part II? Inorganic Ligands?" The Chemical Society? London? 1958* tendencies of these ions depend on the specific metal ion under con­ sideration? it was of interest to examine spectrophotometrically the nitrate? sulfate? and perchlorate solutions of palladium (II) to determine which of these anions had the least affinity for palladium

(II).

The absorbance of a solution containing 4 mM palladium (II) in

1 M nitric acid (stored under air) was measured at intervals from

1 day to 2 weeks after preparation. The absorbance did not change during this period? indicating that the solution was stable. Nitrate produced a shift in the wavelength of maximum absorption of palladium

(II) perchlorate to higher wavelengths (bathochromic shift) with a corresponding increase in the intensity of absorption at the maximum

(hyperchromic shift). This indicated complex formation between palladium (II) and nitrate ion and agrees with the results of Sunda- 37 ram and Sandell* The extent of complex formation is not known? but 21 even if it were* the nitrate medium would not be suitable for the investigation of complex formation between palladium (II) and many other ligands because of the absorption of the nitrate ion around

300 mM-e6^®65

(64) Eugene Rabinowitch? Rev. Modern Physics? 14? 112 (1942) (6 5) H. L. Friedman? J. Chem. Phys.? 21? 319 (1952)®

The absorbance of a solution containing 1 mM palladium (Ii) in

0 .0 3 N sulfuric acid at wavelengths in the 210 to 300 mp region^as 66 reported by Chapman and Sherwood, was very similar to that of

(6 6) F. W. Chapman? Jr. and R, M. Sherwood? Anal. Chem.? 29? 172 (1957)® palladium (II) perchlorate solutions prepared by the present workers.

It was subsequently found that solutions containing 4.35 mM palladium

(II)» 0 .3 6 M perchloric acid? and from zero to 0.0944 M sodium sulfate had the same absorption spectrum in the 600 to 320 mp. wavelength region. Hence it appeared that sulfate ion did not complex with palladium (II) under these conditions. Sulfate would not interfere in the spectrophotometric investigation of palladium (II) complexes? since it does not absorb in the 600 to 220 mp, wavelength region % however? the calculation of hydrogen ion concentration at the rela­ tively high acid concentrations necessary to prevent hydrolysis of palladium (II) would be complicated due to the presence of bisulfate.

Although it has been shown that perchlorate can form complexes with metal ions and preliminary spectrophotometric results of the 22 present investigation indicated interaction between palladium (II) and perchlorates a perchlorate medium was used in further investi­ gations because it appeared that this anion has less affinity for palladium (II) than any other common anion. Standard palladium (II) perchlorate solutions were prepared by a variety of methods in order to determine the optimum experimental conditions for preparation of these solutions without contamination by chloride* nitroso complexes* silicic acid and/or colloidal oxide. Properties of these solutions were studied by spectrophotometric* potentiometric> ion exchange* chromatographic* dialysis* and nuclear magnetic resonance methods.

During the course of the experimental work it was necessary to ex­ plore the effect of various factors such as temperature* hydrogen ion concentration* and perchlorate concentration.

Apparatus

Spectrophotometers. Two Beckman DU quartz spectrophotometers were used with 1 and 10 cm. cell compartments. The temperature of

the cell compartments was controlled during absorption measurements

by circulating x^ater from a constant temperature bath. The 1 cm.

cell compartment was used with Beckman standard thermospacers * Cat.

No. 2075® 'The 10 cm. cell compartment was modified by soldering

? ft. of 6 mm. copper tubing to the outside walls and covering the

compartment and cover with a mixture of asbestos and plaster of paris.

One junction of a calibrated chromel-alumel thermocouple xtfas placed

against the upper surface of the sample cell and the other immersed

in the constant temperature bath. Imbalance in the thermocouple 23 circuit was measured by a Rublicon Model 2700 potentiometer with external Leeds and Northrup galvanometer (Type 2^4-20 C)o

Constant temperature equipment. Precision Scientific Company heaterss thermoregulators and electronic relay assemblies9 Cat. Mo.

6 2 9 0 ? were used to maintain 2 fifteen-gallon capacity water baths a't

25l0ol°C. Palladium perchlorate solutions were kept in these baths except during the summer months when they Xirere refrigerated = A

Sargent constant temperature bath? Cat. No. S-8L05s with mercury thermos

regulator and electronic relay was used in conjunction with an Eastman

centrifugal pump* Model A-l* for maintaining constant temperature in the cell compartments during absorption measurementso

l'j.R.Ro spectrometero This instrument was a high-resolution type 6*7 described by Farringer; samples were sealed in Pyrex tubes (8 m m 0

(67) L. D. Farringerj thesis? The Ohio State University? 1958®

o.do and 6 in length) before examinationo

Potentiometric equipment. The potentiometric assembly used in

measuring the potential of palladium electrodes in perchloric and

hydrochloric acid solutions consisted of the followings A Leeds and

Northrup Type K-2 potentiometer (Cat. No. S-70656I) with Type R

galvanometer (Cat. No. S-612421) and nickel-cadmium cells; a Rublicon

B potentiometer (Cat. No. S-5733®) with spotlight galvanometer (Cat.

No. S-569- / ? o Burgess No. 6 dry cells connected in series-parallel

and an Eppley standard cell. The uniformity of the slide itfire of the

K-2 potentiometer was determined with resistors in ’’dial D” £S reference. Zk

The resistors were checked against a Leeds and Northrup Wheatstone bridge (Cat. No. W]Z^). The standard cell was checked against a similar cell calibrated by the National Bureau of Standards and was kept in an insulated compartment in order to prevent hysteresis ef­ fects caused by sudden temperature changes.

Spectrograph. The emission spectra of sodium, hydroxide? sodium chloride? palladium sponge? palladium chloride? and palladium oxide prepared by evaporation of palladium perchlorate solutions were taken on an A.R.L.-Dietert spectrograph? using National Spectrographic carbon electrodes and Kodak SA-1 emulsion.

Electroanalysis apparatus. Copper was determined electrogravi- metrically by means of an Eberbach electro-analysis apparatus? Cat.

No. 32-5^0? with platinum gauze cathode and stationary platinum wire

anode.

pH meter. A Beckman Model G. pH meter with a general purpose

glass electrode? Cat. No. 1190-80? and a reference calomel electrode?

Cat. No. 1170? was used to measure the pH of the solutions. The

various bridge arrangements are described in the section on experi­

mental methods.

Electron microscope. Suspensions of palladium oxide were evaporated

on copper grids covered by a collodion membrane and the resulting mat­

erial examined in a Hitachi Type HU 10 electron microscope at about

80?000 x magnification. Diffraction patterns were obtained with the

60?000 x probe.

Optical microscope. Palladium oxide precipitates were examined in

the 15-3° x magnification range with a Bausch and Lomb Type LC microscope. 25

Centrifuges» Two International Equipment Company centrifuges were used for some of the separations of silica and palladium oxide during this invesrigation: a size 2* 3/^ analytical types with pyrex test tubes 6 in. long and 1 in. outside diameter; and a micro­ chemical type with 5 ml. test tubes®

Millipore filter» Solutions having a perchloric acic concentra­ tion of 1 M or less were clarified by filtration through a Type HA.

Millipore filter of 0*45 M- pore size* used according to the procedure 68 described by Heilweil. This technique is referred to as filtration

(68) I. J . Heilweil? thesis* The Ohio State University* 195^9 P o 6 3® through “the Millipore filter

Balance weights. Balance weights were class S* calibrated against a set of class M weights certified by the National Bureau of Standards®

yplumetric glasswareo All pipets $ burets and volumetric flasks were Byrex and individually calibrated by weight using distilled water® o Temperature corrections to 25 G. were applied whenever necessary®

Thermometers. The mercury-in-glass thermometers used in this investigation were calibrated against a standard thermometer certified by the National Bureau of Standards®

Preparation of reagents

Palladium (II) perchlorate solutions. Seventeen standard solu­

tions of palladium (II) perchlorate were prepared by dissolution of

the hydrous oxide in perchloric acid and by thermal conversion of nitrate solutions to the perchlorate* The preparation and study of several of these solutions serve to illustrate pertinent principles.

The use of silver oxide to remove chloride from strongly basic solutions of palladium (II) was not attempted as pure perchloric acid solutions of palladium (II)> free from large amounts of sodium and traces of heavy metal ions* were desired for these studies. Attempts to remove chloride from perchloric acid solutions of palladium (II) chloride by volatilization were unseceessful because of the remarkable stability of palladium (II) chloride in concentrated solutions of perchloric acid even at high temperatures.

Tests for chloride with silver nitrate 69 and for nitrate with

(6 9) J. Rosir.j "Reagent Chemical and Standards}" 3d ed.} D* Van Nostrand Co.} Inc.} New York} 1955» sodium iodide and carbon tetrachloride were made on each standard solution. Tests for nitrate were negative in all the preparations described below; tests for chloride were positive for standard solu­ tions Nos. 9 and 13.

Palladium (II) chloride obtained from Coleman and Bell} Norwood*

Ohio was used as starting material for all the preparations unless otherwise specified. This material was purified by the least two precipitations with dirnethylglyoxirne Spectrographic analysis of

(70) G. H. Ayres and 2. W. Berg* Anal. Chem.} 2j5} 980 (1953)°

the purified material revealed only traces of platinum and nickel» and 27 showed the material to be of about the same purity as a sample of pall?dium sponge obtained from Johnson I\ at they and Company ? London ?

England .

Standard solutions prepared by dissolution of palladium oxide in perchloric acids Preliminary experiments concerned with the pre«> cipitation of the hydrous oxide from hydrochloric acid and perchloric acid solutions under varying conditions of acidity? palladium (II) concentrations rate of addition of sodium carbonate or sodium hydroxides as well as the effects of aging? showed that only small changes in these variables produced significant differences in the solubility of the product in perchloric acid. In general the material precipi­ tated from hydrochloric acid solutions was darker? more compact? less soluble? and less easily peptized by water than the oxide pre­ cipitated from perchloric acid solutions. Solutions of the oxide precipitated from hydrochloric acid solutions always contained small amounts of chloride? as shown by tests of the perchloric acid solutions with silver nitrate. The pronounced tendency of the hydrous oxide to be peptized by water was demonstrated in the above experiments. The positive charge of colloidal palladium oxide was deduced from its tendency to adhere to the walls of glass containers and the relative effects of sodium sulfate? barium chloride? and sodium perchlorate on its coagulation.

Standard palladium (II) perchlorate solution No. 14-» Purified palladium (II) chloride (1.5 g») was dissolved in 200 ml. of 3*36 M perchloric acid on heating. After filtration through an ultra-fine sintered glass filter the solution was diluted to 2 liters with distilled water and. M3 g. of sodium carbonate dissolved in 1 liter of distilled water was slowly added to the solution from a buret.

The chocolate-brown precipitate was transferred to a medium-porosity sintered glass filter and washed successively with 1 liter of 1 N sodium perchlorate (Fisher* purified) and 1 liter of distilled water.

It was then dissolved on the filter by addition of 66 ml. of 72 percent perchloric acid and the resulting solution diluted to 188 ml. with distilled water. The almost black colloidal solution of oxide was transferred to a J00 ml. round bottom flask and refluxed for 12 hourso

After filtration through an ultra-fine sintered glass, filter the solu­ tion was diluted to 2 liters and the oxide reprecipitated with sodium carbonate* washed and dissolved in 72 percent perchloric acid as described above. The product from the third precipitation* an orange* flocculent precipitate* was transferred to a medium porosity sintered glass filter and washed successively with 400 ml. of purified sodium perchlorate and 300 ml. of distilled water. The precipitate was im­ mediately dissolved in 60 ml. of 72 percent perchloric acid and allowed

to remain for 12 hours at room temperature before dilution with distilled water to an acid concentration of 1 M. The yellow solution was filtered

through the Millipore filter.

Standard palladium (II) perchlorate solution No. 15« This solu­

tion was prepared in a manner similar to that of No. 14 except that

final dilution of the 11.3 M perchloric acid solution of palladium

oxide to an acid concentration of 1 M with distilled water was com­

pleted in 2 hours. The yellow solution appeared perfectly transparent

and initially exhibited no visible Tyndall effect. 29

Standard palladium (II) perchlorate solution Moo 9° Palladium oxide prepared by successive precipitation from 1 M hydrochloric acid and 1 M perchloric acid solutions with sodium carbonates as described previouslys was refluxed x^ith b M perchloric acid for 12 hours. After

2b hours the supernatant liquid was decanted from the undissolved. oxide

and filtered through an ultra-fine sintered glass filter. Approximate­

ly half of the solutions designated as Wo® 9as> was diluted to 500 ml.

with distilled water and a filtered solution of potassium hydroxide

added until the acidity of the solution was 0»b M. The potassium per­

chlorate which crystallized from the solution at 0°C® was removed by

filtration. After 2b hours the solution was refiltered through the

Millipore filter. Aliquot No. 9b was diluted with distilled water to

an acid concentration of 0®5 ^ before filtration through the Milli­

pore filter. The perchloric acid solution used as reference was pre­

pared by refluxing b M perchloric acid for 12 hours before dilution

to 0.5 M with distilled water. A negative test for chloride with

silver nitrate indicated there was no thermal decomposition of the

reference solution of perchloric acid under these conditionso

Standard solutions prepared by conversion of palladium nitrate

to the perchlorate. Standard palladium (II) perchlorate solution

Wo. 6 . Palladium dimethylglyoxime precipitated from a 1 M perchloric

acid solution of purified palladium was washed successively with 2

liters of 0.1 M perchloric acid and 2 liters of distilled water. The

organic material was destroyed on heating with nitric acid and the

nitrate removed by fuming with 72 percent perchloric acid in a 2 liter 30

Vycor evaporating dish. The final solution containing palladium in

400 ml. of 72 percent perchloric acid was evaporated to 130 ml.* fil­ tered through an ultra-fine sintered glass filter, and diluted to

1440 ml. with distilled water. After 6 days the solution was refil­ tered through the Millipore filter.

Standard palladium (II) perchlorate solution Mo. 7°' Speetro- graphieally pure palladium sponge (l gm.) obtained from Johnson Matthey and Company, was dissolved in hot concentrated nitric acid and the acid removed by repeated evaporations almost to dryness with 70 percent double distilled perchloric acid. The residue after 3 evaporations was dissolved in 20 ml. of 70 percent perchloric acid and transferred to a 25 ml. stoppered volumetric flask where it remained for 3 years before use.

Palladium and perchloric acid concentrations were determined by analysis of weighed amounts of the solution using the same procedures as described for the standardization of palladium perchlorate solu­ tions. The volumetric concentration was calculated from the measured density.

The absorbance of this solution after dilution with double distil­ led water to a perchloric acid concentration of 1 M was measured from

220 to 600 m|J.. The molar absorptivity (Table 1) appears to be in good agreement with that obtained for preparation No. 16.

Standard palladium (II) perchlorate solution No. 10. This solu-

tion was prepared as described for No. 6 except that the concentrated

nitric acid solution containing palladium was evaporated almost to dry­

ness three times with 70.percent perchloric acid. The final residue 31 was dissolved in concentrated perchloric acid and the solution filtered through an ultra-fine sintered glass filter.. Dilution with distilled water to an acid concentration of 1 M was made 3 months later.

Standard palladium (II) perchlorate solution No. 16. Palladium sponge (99 °5 Per cent palladium) obtained from Goldsmith Brothers?

Chicago? Illinois? was purified by two successive precipitations of the palladium with diiuethylglyoxime ? followed by destruction of the organic material with nitric acid and conversion of palladium to the chloride by repeated evaporation to dryness with hydrochloric acid.

The palladium was further purified by electrolysis of a 0.1 M hydro­ chloric acid solution of the chloride in an H cell containing 2 palla­ dium electrodes separated by a medium-porosity sintered glass plate.

The deposited palladium was dissolved by hot concentrated nitric acid

in a Vycor evaporating dish and the nitric acid removed by repeated

evaporation almost to dryness with 72 per cent perchloric acid. The

residue was partially dissolved in concentrated perchloric acid and

transferred to a stoppered? Ityrex volumetric flask. Distilled water

was added until the acid concentration was 4 M and the solution heated

for h days at ?9°C. After filtration of the supernatant liquid through

an ultra-fine sintered glass filter? the solution was further diluted

xtfith distilled water and 1 M perchloric acid until the palladium and

perchloric acid concentrations were in the desired range.

Standard palladium (II) perchlorate solution No. 17. This was

prepared as described for No. 16 except that the solution of palladium

perchlorate in 11*3 M perchloric acid was not diluted with distilled water before it was heated in an enclosed flask at 79°Co for 12 hours. 32

Standardization of palladium (II) perchlorate solutions. The palladium concentration of all the standard palladium (II) perchlorate solutions except No. 9 was determined gravimetrically by precipitation of palladium dimethyIglyoxime from three 50-ml. aliquots containing

0.2 M sodium chloride, according to the method of Wunder and 71-73 74 T'huringer o The spectrophotometric method of Ayres and Tuffly

(71) M. Wunder and V. Thuringer, Z. Anal. Chem., j?2» 101 (1913)« (72) W. F. Hillebrand, G. E. F. Lundell, H. A. Bright, and J. I. Hoffman, ’’Applied Inorganic Analysis,” 2d ed., John Wiley and Sons, Inc., New York, 1953* (73) F* E. Beamish, Talanta, 1, 10 (1953)* (74) G. H. Ayres and B. L. Tuffly, Anal. Chem., 24, 949 (1952)* was used to determine the palladium concentration of standard solution

No* 9 as well as to make periodic checks on the other standard solu­ tions during the course of the experiments.

The perchlorate concentration was determined by an ion exchange method using purified Dowex 50 X-3, 20-40 mesh, converted to the hydrogen form with 4 h perchloric acid.' Aliquots of 10 ml. each were placed on a 240 x 40 mm. column and the resin washed with 60 ml. of distilled xtfater at the rate of l/2 ml. per minute. The eluate was titrated with 0 .2 M standard sodium hydroxide using phenolphthalein

indicator. Purified sodium chloride was used as a standard. The

perchloric acid concentration was calculated from the total perchlorate

and palladium concentrations, except in the case of standard solution

No. 9a, which contained potassium perchlorate. The perchloric acid

concentration in this solution was ascertained by reduction of the palladium with silver, precipitation of silver with an equivalent 33 amount of chloride? and subsequent titration of the perchloric acid with standard 0»2 M sodium hydroxide? using phenolphthalein indicator*

All of the palladium (II) perchlorate solutions were kept in con­ stant temperature baths at 25°Co except during the summer monthss when they were refrigerated.

Copper (II) perchlorate solutionso Three stock solutions of copper (II) perchlorate were prepared as follows; Reagent copper oxide obtained from the J. T. Baker Company was dissolved in an excess of 70 percent perchloric acid? and the solution evaporated until in­ cipient precipitation of CutClO^g^I^O. After dilution with distilled water? the solution was filtered through the Millipore filter and then further evaporated until copper perchlorate fomed. The crystals separating from the solution at 0°C<> were transferred to a sintered glass filter and washed with distilled water. The final product ot>- tained after two additional reciystallizations from dilute perchloric acid was dissolved in 1 M perchloric acid. The copper concentration 72 was determined by an electrogravimetric method; and the perchloric acid concentration by an Ion exchange method similar to that described for the standardization of palladium (II) perchlorate solutions. Nickel (II) perchlorate solutions. Stock solutions of nickel (II) perchlorate were prepared from nickel carbonate (Baker and Adamson) and perchloric acid (G. F. Smith). The solutions contained about 0.1 14 perchloric acid to prevent hydrolysis of the nickel ion. Although the nickel carbonate contained 0.6 percent cobalt (II) 2 the presence of

this impurity was not expected to present any difficulties in inter- pretation of the absorption spectra for purposes of this investigation? c> 3^

(75) A* Vo Kiss and M. Gerendasj Z. Physik. Chem.j A 180? 117 (1937)c

The solution was clarified by filtration through an ultra-fine sintered glass filter* The nickel concentration was determined gravimetrically by precipitation of nickel glyoxime from homogeneous solutionj ac­ cording to the procedure of Bickerdikeo^ Perchloric acid concentration

(76) E. LoEickerdike» Anal. Chem.j 24j 1026 (1952)o was ascertained by an ion exchange method similar to that described for the standardization of palladium (II) perchlorate solutionse

Sodium perchlorate solutionso These solutions were among the most difficult to prepare in adequate purity because of the tendency of

rj *^3 sodium perchlorate to decompose to chlorate and chloride when heated®

(77) M. M. Markowitzj J. Phys. Chem.j 6l» 5^5 (1957)® (78) M. M. Markowitz> J. Inorg. Hucl. Chem.j 2j5j 407 (1963) ®

Chloride was the main decomposition product which interfered j since it was so completely complexed by palladium (II) in the palladium (II) solutions containing sodium perchlorate.

Several preparations were tested. Aqueous solutions (1) were made up from solid sodium perchlorate and sodium perchlorate monohydrate obtained from G. F. Smith Chemical Company. A 2 M solution of sodium

perchlorate (2 ) was prepared by neutralization of 70 percent double distilled perchloric acid (G. F. Smith) with primary standard sodium carbonate (Mallinekrodt). Fisher purified sodium perchlorate was

(3a) dissolved in double distilled water and used with no further purificationor (3b) recrystallized successively from double dis­ tilled water and redistilled ethanol and then dried in a vacuum oven at 92°G«; or (3c) recrystallized twice from redistilled ethanol and

then dried at 85°C® for 3& hours; or (3d) recrystallised twice from double distilled water to give a saturated solution which was stored

in a polyethylene bottle®

The perchlorate concentration was determined by an ion exchange

method using Dowex 50 X-8 ? 20-40 mesh? converted to the hydrogen form

x«rith perchloric acid? as in the standardization of palladium (II)

perchlorate solutions.

Several tests were made on saturated aqueous solutions of the

preparations to establish the purity of the sodium perchlorate. Spot

tests were made for silicas chlorates chloride? iron (III)? and other

heavy metals® s The pH and absorbance from 220 to 600 mM- in 5 cm®

(79) Fritz Feigl? ''Qualitative Analysis by Spot Tests?" 3dsl»? Elsevier? New York? 1946®

cells were measured. None of the preparations were completely satis­

factory since sufficient chloride was present to cause interference

in the interpretation of the effect of perchlorate on the absorbance

of palladium (II) perchlorate solutions. However? preparation (3d)

above contained the least chloride and was therefore used as the

standard solution for adding sodium perchlorate to palladium (II)

i perchlorate solutions. Weighed amounts of preparation (3d) were used to establish the sodium perchlorate concentration.

Barium perchlorate solutions. Barium perchlorate trihydrate» prepared from barium hydroxide octahydrate (J. T. Baker Co.) and double distilled perchloric acid (G. F. Smith Co.), was recrystallized 80 twice from dilute perchloric acido A saturated aqueous solution

(80) E. Hayek and E* Schnell, Monatsh. Chem., 8£> h-72 (195+ )• contained 0«001 M perchloric acid and less than 0.001 percent chloride.

After filtration through the Millipore filter, the solution was stan­ dardized by an ion exchange method similar to that described for palladium perchlorate solutions. Further solutions x^ere prepared

from this solution on a weight basis.

Silica gel. Merk 60-80 mesh silica gel was digested alternately

with 5 M hydrochloric acid and 5 M nitric acid at 80-90°C« until tests

for iron (III) in the supernatant liquid were negative. After treat­

ment with 5 M perchloric acid, the gel was washed with distilled water

until the supernatant liquid was neutral to litmus. The gel x^as then

dried for 2k hours at 110°C. and stored in a bottle xvith a tightly

fitting ground glass stopper.

Perchloric acid solutions. All of the perchloric acid solutions

were prepared by dilution of 72 percent double distilled acid with

distilled water unless otherwise specified. Solutions 1 M or less in

perchloric acid were standardized volumentrically against Mallinekrodt

primary standard sodium carbonate using methyl red as indicator. 37 Solutions containing concentrations of perchloric acid greater than

1 M were standardized try weight against standard scdium hydroxide using phenolphthalein as indicatoro

Hydrochloric acid solutionso All standard hydrochloric acid solutions were prepared from reagent-grade acid (E = I® duPont) and standardized against primary standard sodium carbonate (Mallinekrodt) using methyl red as indicator. The titer was checked against stand­ ard sodium hydroxide using phenolphthalein as indicator.

Sodium hydroxide solutions. Stock solutions of 20 N sodium hydroxide were prepared by dissolving reagent-grade pellets in boiled distilled water. These solutions were aged for at least 2 months to remove sodium carbonate and then filtered under nitrogen through a medium-porosity sintered glass filter. They were standardized against standard hydrochloric acid using phenolphthalein as indicator. In the

solutions for determining the effect of sodium hydroxide on palladium

(II) perchlorate? weighed amounts of two different 20 N stock solutions were used to establish the sodium hydroxide concentration.

Aliquots of the aged solutions were diluted with boiled? nitrogexi deaerated distilled water? to which several grams of barium hydroxide had been added to precipitate any remaining carbonate° These solu­

tions were standardized against National Bureau of Standards potassium

acid phthalate using phenolphthalein as indicator and x-fere used for

standardization of hydrochloric acid and perchloric acid. All stand­

ard solutions were kept in polyethylene bottles equipped with poly­

ethylene siphon tubes and protected from the atmosphere with guard

tubes containing ascarite and anhydrone. Distilled waters The distilled water used in all of the experi» ments was deionized double distilled water and contained less than

0.1 ppm impuritieso

Spectrophotometric procedures and results

General spectrophotometric procedure. In what follows a series is an array of measurements taken to determine the effect of any one variable on the absorbance of a palladium (II) standard solution. In each series the spectrophotometer} the sample and reference cells# and the programing of the slit width with wavelength were maintained constant. Two Beckman DU quartz spectrophotometers were used during the course of these experiments. The difference in absorbance readings on potassium chromate spectral standards^ for the 2 instruments was

(81) M. G. Mellon} "Analytical Absorption Spectroscopy's" John Wiley and Sonss Inc.} New York} 195° s P° 26lo within ±0.002 in the 600 to 320 rap. wavelength region. Wavelength

calibration was performed at 5 points in the 600 to 265 mp region 82 using a mercury discharge source. Since the maximum deviation was

(82) Ian K. Walker and Hariy J. Todd} Anal. Chem.} Jl} 1602 (1959)o

0.2 mp.} corrections were not applied to the observed readings. The

temperature of the cell compartments was controlled during absorption

measurements by circulating water from a constant temperature bath. Absorbance measurements were made with fused quartz cells of ls> 5s and 10 cm. nominal length® The relative cell lengths were determined using solutions of tetrabromopalladate (11)^ and copper

(II) perchlorate® Before measuring the absorbance of a solution the sample and reference cells were cleaned in warm dilute nitric acid? rinsed well with distilled waters dried at 110°C®s and cooled for 30 minutes. Unless otherwise indicateds solutions were transferred from volumetric flasks to the absorption cells by pipet with the minimum amount of agitation to prevent inclusion of solid material such as silicic acid. Absorbance of the sample was measured against the refer­ ence solution containing everything but palladium (II) in equal concentrations and cell corrections were applied for the difference in light loss at the windows of the sample and reference cells. The measurements were made at approximately constant sensitivity and the slit width was varied with wavelength according to a fixed program.

About once a week the cells were also cleaned with a dilute solu­ tion of Tide and the cell corrections checked. These corrections seldom varied more than 0.001 absorbance unit in the 240 to 600 mu

i wavelength region over a period of several years and provided a check on instrument performance.

Absorbance of palladium perchlorate solutions in I M perchloric acid. The absorbances of solutions prepared from standard palladium

(IX) perchlorate solutions Nos. 6 S 9s 10p 14 9 and 16 in the 260 to

600 mu wavelength region at 2j5°C. are given in the Appendix. The average molar absorptivity and average deviation from the mean absorp­ tivity for solutions prepared from each of these standard solutions

and for standard solution No. 7» used in the nuclear magnetic resonance experiment? are compared in Table 1® The maximum absorbance was observed at 380 mM. for all of the palladium (II) perchlorate solutions containing 1 M perchloric acid. However? standard solutions 9 s l^s and 1 5 ? prepared try dissolution of hydrous palladium oxide in per­ chloric acid? had higher molar absorptivities at every wavelength than standard solutions Nos. 6 ? 7s 10? l6 ? and 17? prepared by con­ version of palladium nitrate to the perchlorate.

The absorbance of solutions prepared from standard solution No.

14 did not change from 0 to 21 days after preparation? but a consider­ able amount of colloidal palladium (II) oxide was formed in this standard solution within three years after preparation. The colloidal material was not removed by filtration through the millipore filter or by centrifugation for fifteen minutes. The stability of colloidal palladium oxide and the slowness with which its perchloric acid solu­ tions reach equilibrium is shown by the change in molar absorptivity of - :lutions prepared from standard palladium solution No. 15 with time? as given in Table 2. The presence of colloidal material in

standard solution No. 9b was inferred from its relatively high molar

absorptivity in the ultraviolet region. This solution gave a positive

test for chloride as did No. 9a to which no sodium hydroxide was added

for partial neutralization of the perchloric acid. Since the stability

of perchloric acid under the conditions used to prepare standard

solution No. 9 was proved? it was not known whether catalytic decompo­

sition^ of the acid by palladium occurred or whether chloride

(8 3) VJ. R. King and C. S. Garner? J. Phys. Chem.? j)8? 29 (195^)« (84) G. A. Rechnitz? thesis? University of Illinois? 1961.

------:------_j------:------:------. ------41 TABLE 1

COMPARISON OF AVERAGE MOLAR ABSORPTIVITIES AND AVERAGE DEVIATION FROM THE MEAN ABSORPTIVITY FOR VARIOUS PALLADIUM (II) PERCHLORATE PREPARATIONS

(HC10,)=lo0 M T=25°C o

Std» Soln . 10 16 17 7

Spd x 103 1 g96 to 9*83 0.951 to 19.04 0.4357 to 1 8 .7 3 6066

No . of Diff o Pd Cones. Used 5 4 5 1

A sinix e i&e e e iAe e 240 —— 27.7 0 o2 2 6 .5 250 asnmn 7*5 .2 6.9 260 --- ... 3 .8 ol 3.2 270 8 1 .0 2 .1 0 .2 2.7 .2 2 .3 280 4*7 0 .5 2 .0 .2 2 .0 .2 2 .1 290 3.6 .4 2.5 .2 2.3 ol 2 .6 300 5 o0 .5 4.3 .2 3.8 .2 «3 310 8 ®5 .4 8 .0 .2 7.5 .1 8 .2 320 15*5 .4 14.8 .2 14.5 .2 1 5 .0 330 2506 .5 25.5 .2 2 5 .6 o3 25 »7 340 40 ol .4 39.8 .2 40.2 o3 40.5 350 c * m i q ... 56.4 *3 56.9 o2 5 6 .4 360 71.9 .4 70.9 .2 71.6 o2 71.1 370 8106 .4 80.4 .1 81.4 o2 80.9 3 75 83 o9 o3 82.9 .1 BOS 8 3 .2 380 84*5 •3 8 3 .6 .1 84.2 ol 8 3 .9 385 84 o2 o3 82.9 .1 8 3 .2 390 82 03 .3 81.2 ol 82.2 .2 81.4 395 79 08 ©2 78.6 .1 5 ans ...... 78.7 400 76 .2 .2 75«2 .1 76.0 ol 750 3 410 67 ®6 ol 66.8 ol 67.5 o2 66.6 420 57 06 .0 57°3 .2 57.9 .2 56.9 430 46 ®5 .1 46.4 .2 46.8 ol 4 6 ,>3 440 35.5 .2 3 5 0 .15 35.9 .1 35.5 460 17*2 o2 17.2 a a * * 17.6 .2 17 o3 480 7o9 o3 7.7 ------7.9 .1 7.8 500 4o7 o2 4.5 ------4.9 .2 4.8 520 3*7 o2 3 .8 .1 3.8 540 3.2 o2 — » 3.2 .1 3*2 560 2.6 .2 2^6 580 ... 0 warn e s 2.6 . 1 2.0 600 1.4 0 2 — * = " » • » 1*5 TABLE 1 (Conto)

COMPARISON OF AVERAGE MOLAR ABSORPTIVITIES AND AVERAGE DEVIATION FROM THE KEAN ABSORPTIVITY FOR VARIOUS PALLADIUM (II) PERCHLORATE PREPARATIONS

(HC10^ )=1oO M T=25°C o

Std. Soln« 9-b 14 6* 6**

S Pd x 103 0*650 to 6*83 1*36 to 13*62 1*72 to 13.1 4»53 22.6

No. of Diffo Pd Cones« Used 3 7 8 3

e e t i p e i e e

240 41« 3. a i M a i M«S«S 30* MMM 250 -- o . . 16.5 2. ' «•—«> MMM 10 s MMM 260 15*4 3 .7 11.5 1 . 5*7 0.5 270 10 *6 3 .2 8*5 2. — a , — 3*3 .2 280 7*0 2 .5 5*4 0*3 2.5 *5 290 5.5 1*5 4.8 .4 M a t e s M—. 2.6 .5 300 6.2 1 .0 5 .8 .4 O i M M 4.3 .6 310 9*4 0 .7 9*4 .4 « . — « • 7*9 •3 320 16.0 .6 16.0 .7 •SMM 14.8 •3 330 26.5 .2 26.5 .5 25.8 0.2 25.7 .2 340 40*9 .4 41.2 .4 40.7 .2 40.4 .1 350 57 «0 .2 57*6 .2 57.1 .2 5608 .1 360 71.9 .1 72.4 .1 72.1 *2 71*7 .1 370 81*4 .1 82.0 .6 8I .7 .2 81.1 .0 375 83.8 .2 84.2 •5 .MO* 83.4 .2 380 84*5 .1 85*2 .3 84*6 •3 84.2 .1 385 84.1 .1 84.9 •3 83.8 .2 390 82.2 .1 83.0 .4 82.2 .4 8I .5 .2 395 79.8 •3 80.2 79.5 .2 79*2 .2 400 76.0 .7 76.9 .3 75*7 *3 75*4 .1 410 67-6 •7 67.9 .3 67.0 *3 67.2 .1 420 57.8 .6 58.2 *3 57 «1 .2 57-2 •3 430 46 .7 ®6 47.0 .5 MBS a M a 46.3 .1 440 35*6 .6 36*0 .4 34.8 .2 35*1 .3 460 17.1 • .2 17.8 .4 16.6 .1 17.0 .2 480 7.6 .1 8.1 •3 7.6 .1 7*9 • 3 500 4*5 .1 4*9 .2 4*6 .1 4.6 .1 520 — » —>(XS 4.0 .15 M—M a w e t 3.6 .1 540 — —— 3.4 •3 — M 3.1 .2 560 — 2.6 .2 2.6 .1 2*5 .1 580 ... 2.0 *2 _ < » « > 1.9 .2 600 — 1.5 .2 1.3 .1 1.3 •3 ^Solutions mixed one year after preparation of standard palladium solutiono * "'Solutions mixed two years after preparation of s tandard palladium solution® 4 3 TABLE 2

CHANGE IN MOLAR ABSORPTIVITY WITH TIME® FOR PALLADIUM (II) PERCHLORATE SOLUTIONS PREPARED FROM STANDARD SOLUTION NOo 15

(HC10^)=1.00 M T=25°C* 0.998 era. cell length

S'bdl« Soln.© 15 15 15 13 13 15 15 15 13 Solrw 1 2 3 4 3 1 2 8 5 rpd x 103 16® 90 8=45 6*76 3=38 1®69 16 ®9 8 .45 6.76 1®69 At® days 21 0 0 0 0 23 2 2 2

A9mp- e e e e e e e e "e

270 78 ®0 75=1 7 4=8 75=1 79=1 74=5 74=8 7 2 .8 280 71 =4 69=5 6 8 .9 69=2 73=5 68=7 6 8 .8 65=4 290 64.6 62.6 62.1 62.1 64 66.6 62 oO 6 2 .1 59=2 300 59 *3 57 ol 5 6 .7 57=1 58 6 0 .7 57=1 5 6 .8 54.1 310 56 06 55-0 54.5 54.8 55 5 8 .3 54.8 54=5 52.4 320 58 ®0 5 6 .7 5 6.I 5 6 .5 57 59=8 56=7 5 6 .2 54=1 330 6 4 .5 62.9 63 = 2 6 2 .6 6 2 .5 66.1 6 2 .3 62.4 6 1 .5 340 7 5 .1 73.7 74.0 73=4 73 76.3 73=2 74.1 7 2 .2 350 87 oO 87=3 86.6 86 ...... 86.6 86.6 8 5 .O 360 98 ®5 9 8 .8 98.2 98 **»■» ~ 98=3 98.1 97 363 103 ®6 103=4 103=0 102 103 ®0 102.8 102 370 —- 106 ®4 1 0 6 .2 105=9 106 106 ®4 105=9 105 375 107=5 107=8 107=6 108 107=3 107=1 107 378 108 ®0 108.0 107=3 107 107=4 107=4 107 380 --- 107=4 107=7 107=1 107 104.4 107=4 107 382 •»*»«» 107=1 107=2 1 0 6 .8 107 107=1 1 0 6 .8 1 0 6 .5 385 — 106 .0 IO60 2 105=6 106 1 0 6 .2 105=9 106 390 -»— 103=7 103=7 103=3 103 105=6 103=5 1 0 3 .2 103 400 ...... 95=3 95=4 95=0 95 96=4 95=2 95*0 95 410 84.9 85=2 84.6 24 86=9 84.8 84.7 84 420 73=5 73=5 72=9 73 74.6 73=3 73=1 73 430 6 1 ,3 60=7 60=9 60 oO 61 6 2 .1 60 06 60.5 61 440 48 ®5 48.3 48.2 47.8 48 49=2 48.1 4 7 .8 48 460 27.4 27=2 27=1 26=9 27 27=9 27=2 26=9 27 480 15.8 15=6 15=6 15=4 15 16.2 15=7 1 5 .2 15 500 11.0 10.9 10.8 10.7 11 11=3 11.0 10.6 11 520 8 .7 8.6 8=6 8 .3 8 8=9 8.8 8.5 8 540 7*0 6.9 7»0 6.8 7 7=2 7=1 7=0 7 560 5®4 5=5 5=5 5=5 6 5 .6 5=7 5=3 6 TABLE 2 (Contdo)

CHANGE IN MOLAR ABSORPTIVITY WITH TIME j FOR PALLADIUM (II) PERCHLORATE SOLUTIONS PREPARED FROM STANDARD SOLUTION NO* 15

(HClO^)-l.OO M T=25°C. 0*998 cm. cell length

Std. Soln . 15 15 15 15 15 15 15 15 Soln. i 2 4 5 1* 2* 4 * 5* £Pd x 103 1 6 .9 8.45 3*40 1 .6 9 1 6 .6 8.58 3-40 1.69 days 61 40 40 40 82 61 61 61

Ajiraii e e e e e e e ~e

270 78.4 6 3 .O 5 6 .8 64.3 54.6 48.8 45 .6 280 113*7 71.3 56.7 48.8 5 6 .0 46.9 41.9 37.3 290 107.7 64.7 5 0 .6 43.2 5 0 .8 41.1 36.4 3 2 .0 300 103-5 6 0 .0 4-7.0 39.6 48.1 38.5 34.2 3 0 .2 310 96.4 58.1 4 6 .5 39.9 48.0 3 8 .6 34.6 3 0 .8 320 9 6 .6 6 0 .0 . 49.1 43-5 51.1 42.3 3 8 .8 35.5 330 98.6 • 6 6 .5 55-9 49*4 5 8 .6 50.5 46.3 4 3 .8 340 —. 77.1 6 7 .6 6 1 ,5 70.3 62.1 58.0 55.6 330 —— 90.4 81.8 84.0 76.2 72.8 70.4 360 — «... 102.4 94.4 88.8 96.9 89.4 8 6 .3 83.7 363 106 .4 98.5 94.1 ——— 94.2 91.4 88.8 370 ——— 109*9 102.4 97.6 98.4 95.0 92.9 3 75 111.8 104.2 99*4 -- - 99.6 97.1 95.3 378 — 111.8 104.2 99.7 -- - 99.9 97.4 95-6 380 111.7 104.2 99.7 99.9 97.4- 95.6 382 ——. 111.1 103.9 99.7 —« 99.6 97.1 95.3 385 109.9 1 0 3 .0 98.8 98.9 96.5 94.7 390 107.5 100.3 97.0 -- 96.9 94-.7 92.6 400 --- 99.0 89.1 93.7 89.5 8 7 .6 8 5 .8 bio 102.8 79-3 84.2 79.6 77.8 76.9 420 90.6 75.9 71-3 68.6 72.5 68.6 66.9 66 oO 430 75-9 6 3 .2 58.6 55-9 60 .2 56.3 54.7 53*8 440 6 2 .2 5 0 .2 46.2 4 3 .8 4-7.7 44.2 43.1 42.0 4-60 37-9 28.4 2 5 .6 23.4 26.7 24.0 22.8 21.6 480 2 4 .3 16.6 13.9 1 3 .0 1 5 .2 13.1 12.1 11.8 500 17.6 11.5 9.5 8 .3 10.4 8.8 7.8 7.1 520 13-9 9.0 7.7 7.1 8.2 6.9 6.4 6.5 540 10.9 7.2 6.4 5*6 6 .5 5.6 5.0 4.7 560 8 .5 5-7 4.9 4 .7 5.2 4.3 4.0 3.8 * After filtration through a Millipore filter of 0.45 M* porosity 4 5 TABLE 2 (Contdo)

CHANGE IN MOLAR ABSORPTIVITY WITH TIME* FOR PALLADIUM (II) PERCHLORATE SOLUTION PREPARED FROM STANDARD SOLUTION SO. 15

(HC10^)=lo00 M T=250C. 0.998 cm. cell length

Std. Soln. 15 15 15 15 Soln® 2** 4 *$ 6** SPd x 103 15 .6 8.43 3.40 3-38 A^* days 259 238 238 246

e e e e

270 22.9 4 3 .8 40.6 40.2 280 17.2 34.1 32.4 31.4 290 14.5 28.4 26.8 25-9 300 15.5 27.6 25.7 24.4 310 19.0 30.1 27.4 26.0 320 25.2 35 oO 32.0 30.8 330 34.4 42.5 40.7 39.4 340 47.0 53-9 52.6 51.6 350 62.0 67.5 67 .3 66.7 360 75 °0 80.0 81.0 8 0 .8 365 8 5 .4 85.7 8 5 .5 370 88.8 89-7 8 9 .6 375 90.0 91-8 91.4 378 ----- 91.8 92.2 92.3 380 91.9 92.2 92.5 382 91.8 92.2 92.3 385 91.5 91.8 91.6 390 84.4 90.2 89.7 90.0 400 78.0 82.5 83.1 83.3 410 69.4 75-3 73-8 73-7 420 59.5 64.9 63 .2 63.1 430 48.3 53-4 51-7 51-5 440 37.3 41.1 40.1 40.2 460 18.4 20.9 20 .6 20.4 480 8 .5 10.3 10.2 10.3 500 5.2 6 .5 6.6 6 .5 520 4.0 5.2 5-1 5«0 540 3.4 4.3 4.1 4.1 560 2.7 3.4 3°5 3.6

**After refiltration through a Millipore filter of 0.45 P- porosity 46 was introduced as a contaminant in the palladium oxide®

The molar absorptivity of standard solutions Nos® 6 * 10* 16* and

17 did not change during a two year period after preparation; however* an increase in the absorbance with time was observed for palladium perchlorate solutions prepared by dilution of standard solution No. 6 with 1 M perchloric acid. The increase in absorbance*A A? from 1 day to 1 month after preparation is given for 6 solutions in Table 3® An attempt was made to measure the scattering directly by using the re­ flectance attachment for the Beckman DU* but the precision attained was so poor that this technique was abandoned after a few experiments.

Within a week after preparation* a small amount of finely divided*

colorless precipitate appeared in all these solutions. Similar pre­

cipitates were formed by dilution of once distilled ?2 percent per­

chloric acid with double distilled water. Spot tests using ammonium 79 molybdate and benzidine' revealed that the precipitate was silicic

acid. The increase in observed absorbance of palladium (II) perchlorate

and perchloric acid solutions on addition of silicic acid and the at­

tempt to remove this impurity from palladium perchlorate solutions by

dialysis are discussed in subsequent sections®

The use of double-distilled 70 percent perchloric acid and the

partial dehydration of silicic acid in this reagent by evaporation of

the palladium perchlorate solutions almost to dryness in the prepara­

tion of standard solutions Nos. 7* 10* 13s 16> and 17 were effective

in reducing spectrophotometric interference from this impurity. Since

the silicic acid could not be completely removed* solutions whose

absorbance was measured more than 12 hours after preparation were 47 TABLE 3

INCREASE IN ABSORBANCE FROM ONE DAY AFTER MIXING TO ONE MONTH AFTER MIXING, FOR SOLUTIONS PREPARED FROM STANDARD PALLADIUM (II) PERCHLORATE SOLUTION NO* 6*

(h c i o ^)=o <>956 m loOO cm 0 cell length

S P d x 103 8®73 8 .8 3 6®97 3o 48 2.62 l.?2

Ajmp a A A A A A AA A A A A

330 OoOlO OoOlO 0.007 o®oi3 0 .0 0 9 5 0 .003

340 oOlO ®010 «oo6 ®oi2 ®009 .004

350 oOlO ®012 oOlO ®0125 .010 .0043

360 .0 1 1 .0 1 1 ®008 ®0125 .0095 o0035

370 .012 .0 1 1 oOlO .014 .010 .003

380 «012 .0 1 1 ®009 o017 .0095 .008 0 H 0 390 VO ®013 o009 ®021 .0 1 1 .009

400 ®014 ®014 ®0085 ®020 .0083 .0095

420 oOlO ®010 ®010 o0225 .0 0 8 3 o0105

440 .0 1 1 ®0095 ®009 0OI8 .0063 .0095

460 •0075 ® 006 o0055 ®014 .0063 .OO63

480 0OO6 .0 0 3 ®006 .010 .0 0 3 .0 0 3 5

500 .0063 ®004 ®0045 .009 .0045 .003 00 »r\ O VA 0 O 550 ®006 .0035 ®005 0 9 .004

600 o003 .0025 o0025 .0 0 6 .0035 .003 ^The solutions were thoroughly shaken before transfer to the absorption cell® The only precipitate present was finely divided silicic acid which x-r as also present in the reference solutions® The solutions were kept at room temperature during the summer months ® k3 transferred from the volumetric flasks to the absorption cells by pipet with the minimum amount of agitation to prevent inclusion of the precipitated material*

Effect of temperature on the absorbance of palladium (II) perchlorate solutions * The temperature coefficient of absorption for palladium (II) perchlorate solutions was studied in order to determine the degree of temperature control necessary to obtain the required precision in absorption measurements and to prevent hydrolysis of the palladium* Solutions containing 0.01 M palladium (II) and 1.0 M

perchloric acid were prepared from standard palladium (II) perchlorate

solutions 9s 10* lh* and 15* The absorbance was measured at h0 wave­

lengths in the 270 to 600 mp. region in the temperature sequence 25>

17s 25s 35s and 25°G. The solutions were kept in a constant tempera­

ture bath at a given temperature for a minimum of 8 hours before the

absorbance at that temperature was measured.

Irreversible changes in the absorbance at 35°C» were noteds

after five days at this temperature a small amount of hydrous palla­

dium (II) oxide was precipitated. The change in absorbance* AA? from

25 to 17+0o2°C. for a solution containing 10.26 mM palladium (II)

and 1.00 M perchloric acid is given in Table h and Figure 1. The

temperature coefficient of molar absorptivity was found to be within

0.2°C. from 270 to 600 mp in the 25 to 17°G. temperature range.

Effect of perchlorate concentration on the absorbance of palla­

dium (II) perchlorate solutions. The absorbance of palladium (II) in

perchloric acid solutions containing less than 1 M perchloric acid

was investigated in order to determine the stability of palladium (II) 49 TABLE 4

CHANGE IE ABSORBANCE OF PALLADIUM (II) PERCHLORATE SOLUTIONS WITH TEMPERATURE*

HPd=10o26 mM (HC10^)=lo00 M 1,000 cm, cell length

Tj°Co 25 17 AA A A 10© AA/A^JjO A e/°Co

270 0,1145 0ol07 -0 ,0 0 6 5 ~5»7 -0 ,1 0 275 ,076 ,0705 -,0055 ©2 - ,0 6 280 <>0525 o049 ■=,0035 — ,04 290 0036 o0345 =.,0015 ssij'gO - ,0 1 300 o049 o0485 "•,0005 -loO - .0 1 305 ,0625 0O635 ,001 1 ,6 ,03 310 o084 0O86 ,0 0 2 2,4 ,0 3 315 ,1145 ,1175 ,003 2 ,6 ,04 320 ol535 ol57 ,0035 2 ,3 ,04 325 ,2025 ,2065 ,004 2 ,0 ,05 330 ,2625 ,2695 ,005 1,9 ,09 340 ,413 o422 ,009 2 0 2 ol0 350 ©582 °593 ,0 1 1 1,9 ,14 355 0657 ,669 ,011 1.7 ,1 0 360 o733 ,741 ,0 0 8 1 ,1 ,1 0 365 *789 ,8 0 0 ,010 1.3 ,14 370 0832 ,838 ,006 0 o7 *0 75 375 0858 ,861 ,003 0 ,3 ,04 380 0869 ,870 ,0 0 1 0 ,1 ,0 1 385 0863 ,861 — ,0 0 2 —0 ,2 -o025 390 ,846 ,840 — ,006 -0,7 - ,0 7 5 395 08I8 ,811 - ,0 0 7 -0,9 — o09 400 ,780 ,7695 -,0 0 9 5 -lo2 - ,1 5 410 ,695 ,681 -,014 —2,0 - ,1 6 420 ,596 ,580 -,0l6 —2o7 — ,20 430 ,481 ,465 -,0l6 -3 «3 -,20 440 ,368 o352 -,0l6 -4,3 -,20 460 ,179 ,167 -o012 -6,7 — ol4 480 ,0815 ,0745 -,007 -9o -,075 500 ,049 ,047 -,002 —4o ~,04 540 ,032 o031 -,001 —3 © -.01 560 ,026 ,024s? -,0015 -6, -,01 600 d 4 5 ,0135 -,001 -7o «3,01 ^Solution prepared from standard palladium perchlorate No, 10 FIGURE 1

CHANGE IN ABSORBANCE OF PALLADIUM (II) PERCHLORATE SOLUTIONS WITH TEMPERATURE*

* AA values correspond to the difference in absorbance? a 25°Co s for a solution containing 10*26 mM palladium (II) perchlorate in 1 M perchloric acid and are tabulated in Table 4-o

50 AA

-.020

-.030

-.040 200 250 300 350 400 450 500 550 600 Wavelength, mju. Ol Figure with respect to hydrolysis. Molar absorptivities of solutions pre­ pared from standard palladium (II) perchlorate solutions Nos. 9 s 13s

6 p and 10 containing from 0 .2 to 1 M perchloric acid are given in

Table 5» An increase in perchloric acid concentration in this range produced a decrease in the molar absorptivity of these solutions at wavelengths below 395 ^ s but the wavelength of maximum absorbance was unchanged.

In order to determine whether this effect was a function of the hydrogen ion concentration or perchlorate ion concentrations six solu­ tions containing from 0.951 bo 19*04 mi-1 palladium (II) and a constant mole ratio of perchlorate to palladium equal to 50.8 were prepared.

The absorbance of these solutions was measured immediately after mixing in order to minimize any effects produced by colloidal hydroly­ sis products. The molar absorptivity of these solutions in the wave­

length range from 265 to 5°0 mu is given in Table 6. The molar

absorptivity of solutions containing from 0.1932 to O .967 M perchloric

acid and from 3 .81 to 19*0h- mM palladiums respectively* was constant

at any given wavelength in this region. Comparison of the molar ab­

sorptivities of each of these solutions with the values obtained for

corresponding solutions containing the same concentration of palladium

in 1 M perchloric acid (Table 7) shows that an increase in perchlorate

concentration produced, a decrease in the molar absorptivity of these

solutions below 395 mu and an increase at wavelengths above 400 mu

with an isosbestic around 395 MUo

The possibility that chlorate* present as an impurity in the per­

chloric acid* was responsible for the change in absorbance of 53 TABLE 5

CHANGE IN THE MOLAR ABSORPTIVITY OF PALLADIUM (II) PERCHLORATE SOLUTIONS WITH PERCHLORIC ACID CONCENTRATION IN THE 0*2 TO 1.0 M RANGE

T=25°C, 1,00 cmo cell length

Std.Soln, 9=a* 9- 13* 6 10 £Pd x 103 3*57 6,33 3,26 3,80 4,36 ,63

H 3* 0 0 (HCIO4 ) 0*401 1*01 0o482 e 0,388 0.194 1.12 0.186 0.97 0.19* days 5 1 2 1=6 0,125 4 0c,125

e e "e e e "e e e e e

260 mumm* 10 .0 11.1 11.8 14,9 1 2,9 c=»e>«» ca«*c=* 15*6 SBB3CB. 270 16.1 6®3 7.7 9 ,0 9 ,5 9 .4 9*6 a»cajQ 280 10 08 4,0 5.1 6 ,4 7,9 6 .3 CO 6 .1 290 7 .4 3 ,4 4 .2 5,1 5*1 4 .8 O B o 5*5 6 .2 300 4 .9 4,8 5*5 5*4 5.8 5*6 6 ,2 606 310 10*8 8,3 9*1 8,7 9 ,0 9*1 tn»e=,e» i=H31K» 9*2 10.2 320 ■17.3 15*2 16 ol 15*4 15*5 16.0 14.9 17*0 15*7 17*1 330 28,4 26c? 28,6 25.8 26,5 26.9 25.8 28.4 25.? 27.3 340 43*5 41,5 44,0 40,2 4 1 ,4 4 2 .0 40,8 43 06 40.4 41.9 350 59*5 57*2 6o.2 56.8 58.1 58.9 57*3 60,6 5606 59,5 360 74,1 71,9 74.7 71.8 73*1 73*9 72*0 75*0 71,6 74,9 370 83,4 81*5 84,2 81 o4 82.6 83.1 81.7 83 *8 81.3 83.1 375 85*3 83*8 86,2 84,9 84,9 85*6 86.0 83*7 85,6 380 85*9 84 0 5 86,7 83,1 85.5 86.0 84,6 860 2 84 0 2 86,0. 385 85.2 83.9 86.1 84,6 85,2 8 5*5 84,2 85.2 83*9 85*5 390 82*3 84,2 8 3 .O 83,2 83.4 82.1 83,0 82.1 83,4 395 80 «6 79*7 81,4 80e? 80.4 80,6 7908 80,3 79*6 80,6 400 75*8 75*1 75*6 77*2 76,8 76.9 75*6 76,1 75*9 76,9 410 67.. 4 66.8 67.3 68,6 68.3 68.2 67.0 67,2 6 7*5 68,2 420 57«0 57*1 56.9 5 8,6 57,9 57*7 56*7 56,7 57 *4 57*7 430 46,1 45*5 47,5 46,9 4 6 .4 45,6 45*5 4 6 ,4 46,6 440 34,8 34,9 34,4 36,4 35*9 35*5 34.6 34.4 35*3 35*5 460 I 608 17,0 l6 ,6 17,6 17*3 17*0 16.7 17*0 17*2 17,1 480 7 .9 7 06 7*7 8.1 8 .0 7*9 7,6 7,8 8.0 7*9 500 4 ,8 4»7 4 ,9 4 ,9 4 ,9 5 ,0 4 .7 5.0 4 .7 5.0

^Solution gave a positive test for chloride with silver nitrate TABLE 6

MOLAR ABSORPTIVITY OF PALLADIUM (II) PERCHLORATE SOLUTIONS HAVING A CONSTANT MOLE RATIO OF PERCHLORATE TO PALLADIUM *

Stdo Soln«. 16 16 16 16 16 16 SPd x io3 19.04 11.42 7.62 3.81 1.904 0.951 (HCIO^) 0.967 0.5196 0.3864 0.1932 0 .0 9 6 6 0.0483 8, cm. 0.998 0.998 0.998 0.998 5 *oo 5.00 # *

Agmp. e e e "e e e

265 2.0 2.1 2„5 2.4 4.4 4.9 270 1*7 1.7 2.0 1.9 3*5 4.4 275 1.5 1.6 1.9 2.0 3*1 4.1 280 1.6 1.6 1.9 1.8 2.9 4.0 285 1.8 1.7 2.0 2.1 3.0 3*9 290 2.2 2.2 2.4 2.5 2.3 4.2 295 2.9 2.8 3*0 2.9 3*9 4.6 300 3.9 3.9 4.0 3.9 5 .0 5*7 305 5*5 5.4 5.6 5*5 6.6 7*1 310 7.7 7.7 7.8 7.8 8.8 9«0 315 10 .6 10.8 11.0 10.9 11.9 12.3 320 14.4 14.7 14.8 14.7 1 6 .0 16.2 325 19*7 19.9 19.8 21.7 21.2 330 2 5 .I 2 5 .8 2 6.0) 25*9 2 7 .8 27 .1 340 39.5 40.5 40.9 41.3 42.8 42.1 350 56,0 56.9 57.4 57.8 m a n w 59*4 355 64.8 6 5 .2 6 5 .7 57.1 66.8 360 70*9 71.7 7 2 .2 72.9 73*9 73*6 365 77 o5 77.8 7 8 .0 79*4 78.9 370 8 1 .3 81.4 81.8 83.2 82.4 375 8 3 .7 83.4 83*8 85.0 84.5 378 ——— 84.3 83.9 84.1 85.3 84.7 380 84.5 83.9 84.1 85*3 84.7 382 «a> « « i 84.3 83.7 83.9 8 5 ,1 84.5 385 8 3 .6 83.1 83*3 84.4 8 3 .5 390 ----- 8 1 .5 81*2 81 <>2 82.6 81.1 395 78.8 7 8 .5 78.1 79*2 78.3 400 — — » 74 08 74.4 74.3 75 o2 75*5 410 66.8 66.0 65.7 65«4 66.0 6 6 .3 420 57.1 56.2 55.9 55*2 5 6 .0 5 6 .3 430 46.3 45«4 44.8 44.3 4 5 .I 45*1 440 35 o4 34.7 34.1 33*7 34.3 34*3 460 17.2 1 6 .5 1 6 .2 1 5 .8 16.5 1 6 .5 480 7*7 7.4 7..2 6 .7 7*6 7 .6 500 4.6 4.4 4.2 3*9 — — ^Absorbance measured directly after mixing ❖^Visible turbidity in solutions containing 1.904 and 0o951 ciM palladium TABLE 7 55

MOLAR ABSORPTIVITY OF PALLADIUM (II) PERCHLORATE SOLUTIONS PREPARED MO M STANDARD SOLUTION NOo 16

(HC10^=lo00 M T=25°Co

Std. Solno 16 16 16 16 Solnc 1 2 3 4 £ Pd x 103 19*04 7©62 1.904 0,951 dj cm© 0©998 0,998 5 .0 0 5=00

265 2«0 2 ©5 2.5 3=0 270 1=7 2 ,2 2 .2 2 .5 275 1*5 1.9 1.9 2,3 280 1 .6 1.9 2 o0 2 .3 285 1 ,8 2 ,2 2,3 2.4 290 2,2 2.6 2.6 2,7 295 2,9 3.1 3.4 3=5 300 4,0 4.2 4,4 4«7 305 5*5 5 ®8 5*9 6 .1 310 7*7 7*9 7*9 8«3 315 1 0 ,6 10.9 1 1 .0 llr.2 320 14,5 14.5 14.9 1 5 .1 330 2 5 .I 25*4 25,5 2 5 ©8 340 39*5 3 9 .8 39=7 40.1 350 5 6 .1 56.3 56 ol 56=9 360 7 0 .8 71.1 70o6 71=0 365 7 6 ,8 7 6 .3 76.7 370 80.7 80.2 80 ©4 375 83*0 82.9 82 08 378 ... 83 o4 83 ©2 83,6 380 o a (Sk*4 83*7 83*5 83.5 382 m m » n 83,6 83©2 83=5 385 ...—. 82.8 83=0 390 a n g b 81.4 81,0 81,2 395 «iu imwa 78,8 78.3 78.7 400 75*3 75 <=4 75=0 410 66,8 66.8 6 6 .9 6 6 ,7 420 57.1 57*1 57=2 57=7 430 46,3 46.2 4 6 .5 46.7 440 35*4 35*4 35=5 35=9 460 17,2 17.2 17=3 17=6 480 7,7 7,6 7 .8 8.1 500 4 ,5 4.5 4.7 4.8 520 3*5 3*5 3=8 4=0 540 3,0 3 .0 3 .2 3=3 palladium (II) perchlorate solutions produced by perchlorate was investigated. The absorbance of 3°63 mM palladium perchlorate solu­ tions containing 0.97 and 0.194 M perchloric acid? respectively? with various amounts of sodium chlorate was measured at 40 wavelengths in the 325 to 600 mM- wavelength region. In Table 8 the molar absorp- tivities of two of these solutions having 0.08 and 0.8 M sodium chlorate are compared with solutions containing the same concentration of palladium and perchloric acid but with no chlorate added. The presence of 0.08 M sodium chlorate produced no significant change in the molar absorptivity in this wavelength range. The small batho- chromic? hyperehromic shift in the wavelength of maximum absorption produced by 0.8 M sodium chlorate was attributed to the presence of chloride as an impurity in the sodium chlorate.

In order to further investigate the nature of the effect of per­ chlorate concentration on the absorbance of palladium (II) solutions containing 3®93 wM palladium and from 1 to 11 M perchloric acid were prepared from standard palladium (II) perchlorate solution No. 10» distilled water and weighed amounts of standard perchloric acid. The standard perchloric acid solution was stored in a closed system buret protected against moisture by means of drying tubes charged with an­ hydrous magnesium perchlorate. Molar absorptivities of 7 of these

solutions in the 300 to 600 mu wavelength region are given in Figure 2o

These curves showed a progressive bathochromic shift in the wavelength

of maximum absorption of palladium (II) from 380 to 410 mu as the con­

centration of perchloric acid was increased from 1 to 11 M. The molar absorptivity at the maximum decreased from 84.5 to 74 in the 57 TABLE 8

EFFECT OF SODIUM CHLORATE OH THE MOLAR ABSORPTIVITY OF PALLADIUM (II) PERCHLORATE SOLUTIONS

£ P d = 3 o 6 3 mM T=25c'Go 0o998 cm . cell length

Stdo Soln. 10 10 10 10 (HClOij,) 0«■97 0 .■97 0 . ,194 0.194 (NaClO^) Oc,00 Oc,080 0 .00 0.80

A sia|i. A e A e A e- A e

325 0o0725 20 oO 0 o072 19.8 0.075 20.9 0.0695 19.1 330 o0935 25 c7 o0935 25o8 .098 27*3 o0915 25.2 335 *119 32 08 “>•»■» .1245 34 o4 oll75 32.4 340 ol465 4 0.4 .1465 4 0.4 *1515 4 1 0 9 *1455 40.1 3*4-5 .1765 48 06 .1845 51 oO .1765 47*0 350 o2055 5606 .2055 56.6 *2155 59*5 .206 56 .8 355 02345 64 06 —- .2455 67.8 .2365 65.2 360 <,260 7106 o2595 71.5 .2715 74.9 .262 72.2 365 o2805 77*3 o2795 77 oO .294 81 oO .2855 78.7 370 <>295 8103 ®295 81.3 .3016 83.1 .300 82.7 375 «304 83 o7 ©304 83.8 o3105 85.6 .312 86.0 378 0 0 5 5 84.2 *3115 85.8 *315 86.8 380 .3055 84=2 o307 84o6 .3122 86.0 o3152 86.9 382 -3055 84o2 -— .2115 85.8 .316 87 ol 385 »3045 83*9 o305 84.0 .3104 85*5 *315 8608 390 o298 82 ol o299 82.4 .3027 83.4 o309 85.1 395 .289 79 *6 .2895 79 08 .2925 80.6 .300 82.7 400 *2755 75*9 .27 7 76.3 *279 76.9 .288 79 0 3 44-10 o245 67*5 .246 67.8 *2475 68.2 o2575 70.9 *4-20 .2085 57-4 .209 57*7 .2095 57* ? .220 60.6 *4-30 0I685 46 ©4 .1695 46.7 .1692 46.6 .1778 49*0 440 .128 35-3 .1295 35*7 .129 35*5 0I36 37*5 450 o093 25 06 «** “ca .099 27 »3 460 a0625 17 *2 0O625 17 ®2 .062 17*1 .0663 18.3 4?0 .042 11.6 ■=»“<=» «... .045 12.4 480 .029 8.0 .029 8.0 .0285 8.0 .0305 8o4 500 .017 4.7 .0175 5®0 .0175 5*0 .0182 5.0 520 *014 3.8 .014 3.8 .0145 4.0 o0137 3*8 540 <,012 3.3 .012 3°3 .0125 3.4 .0118 3.2 560 0OO85 2.3 .009 2.5 .010 2.7 .0087 2.4 580 .007 1.9 .007 1.9 -— «=. .0068 1.9 600 .0055 1.5 o0055 lo5 .005 1 o4 *005 1 . 4 FIGURE 2

EFFECT OF PERCHLORIC ACID CONCENTRATION ON THE MOLAR ABSORPTIVITY OF PALLADIUM (II) PERCHLORATE SOLUTIONS PREPARED FROM STANDARD SOLUTION NOo 10

ZPd=0,00393 M T=25°C» 1.000 cm. cell length

Curve No. (HCIO^) Molar

1 1.048

2 3 .60

3 5.16 4 7<>90

5 9.59

6 10.63

? 1 1 .3

58 901

80 '

70'

60'

ex \ o 50' tp J3

40

50'

Z0

600 550 500 --- 450 1 to 9*5 M perchloric acid range* but increased from 74 to 78 as the perchloric acid was increased from 9*5 to 11.3 M» Isosbestics were

observed at 395 and 408 m|J< for solutions containing 0.2 to 4o6 M and

from 5 to 9»6 M perchloric acid* respectively. The half-intensity

band width* & * was relatively constant for solutions containing from

1 to 5 M perchloric acid. An increase from 6.2 to 6.5 kK was observed

as the acid concentration was increased from 5 to 11 M* These results are summarized in Table 9®

Similar results x^ere obtained from a study of the effect of per- L. chloric acid concentration on the absorbance of palladium (II)

perchlorate solutions prepared from standard solution No. 6* as illus­

trated in Figure 3 and Table 10. Average molar absorptivities at

395 and 408 mM- were 0.4 and 0.7 units higher for solutions prepared

from standard palladium (XI) perchlorate No. 6 than for those prepared

from standard solution No. 10.

The possibility that impurities other than chlorate in the per­

chloric acid and/or palladium perchlorate standard solutions were

responsible for these changes in absorbance was eliminated by the

following experiments? The validity of Beer’s law for 4 palladium

perchlorate solutions containing from 1.96 to 7*87 M palladium in

5.16 K perchloric acid* Table 11* the molar absorptivity of palladium

(II) in 4 samples of 7 .9 M perchloric acid* Table 12; and the molar

absorptivity of 9®6 M perchloric acid solutions of palladium perchlor­

ate prepared from 5 preparations of standard palladium (II) perchlorate*

Table 13® 61 TABLE 9

EFFECT OF PERCHLORIC ACID ON THE ABSORPTION PARAMETERS OF PALLADIUM PERCHLORATE SOLUTIONS PREPARED FROM STANDARD SOLUTION NOo 10

EPd=3°93 inM T=25°Co loOOO cm* cell length

(HClOj*) X max emax e 395mu- e408mM> *(+) 6 (« Molar kK kK

1*048 380 8 4 «5 80 oO 70 oO 2o97 3 o22

3.60 383 81o9 79 06 71*2 2o92 3o2

5 «l6 386 80 ol 78 0? 72«4 2o95 3 o26

7-90 393 76 *5 7606 72*7 3°09 3=17

9°59 398 74 oO 74o0 72o7 3 o2 0 3ol5

10 063 405 74*5 72 08 74.4 3o32 3*14

i i o 3 410 78 75 77 0 7 3o43 3.11 FIGURE 3;

EFFECT OF PERCHLORIC ACID CONCENTRATION ON THE ABSORBANCE OF PALLADIUM (II) PERCHLORATE SOLUTIONS PREPARED FROM STANDARD SOLUTION NOo 6

HPd=0.00435 M T=26°C» 1.00 cm. cell length

Curve (HClO^) Molar

1 0.186

2 1.13

3 2.06

4 3.94

5 4.87

6 5.81

7 6.74

8 8.61

62 Absorbance 30 h .300 .000 .200 .500 .400 .100 iue 3 Figure Wavelength, m ju 0 425 400 5 500 450 c a> - j 64 TABLE 10

EFFECT OF PERCHLORIC ACID ON THE ABSORPTION PARAMETERS OF PALLADIUM PERCHLORATE SOLUTIONS PREPARED FROM STANDARD SOLUTION NO. 6

T. P d = 4 036 mM T=26°Co loOO cm. cell length

Imax (HC104 ) eraa:t 6 ( + ) 6 (~) Molar mp. e395mn e408mP kK kK

0.1 8 6 379 8 6 .2 8 0 .3 69.3 3.0 3 0

1.13 380 84.4 79.6 69.3 3.0 3.2

2 .0 6 382.5 84.2 8 0 .3 7 0 .2 3.1 3.1

3*94 385 82.5 80.5 72.2 3*1 3.2

4.87 3 8 6 .5 8 1 .2 80.3 72.9 3.1 3.2

5 .8 1 389 80.7 8 0 .0 73«4 3 .1 3.1

6 .74 390 78.7 78.4 73-4 3-1 3®3

8 .6 1 395 75 <>9 75.7 73.4 3-1 3 .2 65 TABLE 11

THE MOLAR ABSORPTIVITY OF PALLADIUM (II) PERCHLORATE CONTAINING 5 MOLAR PERCHLORIC ACIDs THE VALIDITY OF BEER5S LAW

(HC10^)=5*l6 M T=25°C o 1,000 cm* cell length

Std, Soln® 10 10; 10 10 SPd x 103 7 087 5*91 3*94 1,9 6 1 At g days 1 1 1 1 Ajmp. A e A e A e A © 270 0*030 3*8 0.024 4.1 0*014 3*6 0.0 1 0 5*1 280 *0185 2*4 *0153 2,6 *0095 2,4 .007 3*6 290 *017 2 *2 *0147 2*5 *009 2*3 .006 3*1 300 .0245 3*1 ,020 3*4 .0 1 3 3*3 *0065 3*3 310 *045 5*7 *0355 6,0 *0235 6,0 .0105 5*4 320 *086 10*9 ,0663 11,2 ,043 10,9 .0225 11*5 330 *149 19*6 *114 19*3 ,0755 19,2 .0385 19*6 340 *243 30.9 *185 31*3 ,1225 31*1 ,0605 30*8 350 •3585 45*6 .270 45*7 ,180 45*7 .090 45*9 360 .4 75 60 *4 *3592 6 0 ,8 ,238 6 0 ,5 *1195 60*9 370 .563 71*6 *4255 72,0 ,285 72,4 .145 73*9 375 *5985 76 ol *^533 76*7 *300 7 6 ,2 *151 77*0 380 *615 78*2 .4655 78,8 * 3 H 79 oO ,156 79*5 384 0627 79 o7 ...... *315 80,0 .158 8 0 ,5 385 *626 79*6 *473 8 0 ,0 ... ,159 81.1 386 ...... *315 80 *0 ... 388 ... *474 8 0 ,2 *315 80 ,0 .1585 8 0 ,8 390 *621 78 o9 *470 79*5 *3148 79*9 *1575 80*3 395 a 6l6 78 03 *4657 ?8,8 *310 78,7 .156 79*5 400 o603 76 e6 *456 77*2 *3042 77*2 *153 ?8 ,0 410 *556 70*7 ,422 71,4 *2813 71*4 ,1415 7 2 ,1 420 *493 62*7 *372 6 3 ,0 ,248 62,9 *1245 63*5 430 *417 53*0 *3145 53*2 *2075 52*7 .105 53*5 440 *331 42ol *2495 42.2 ,1663 42.2 *0845 4 3 ,0 460 .173 22*0 .131 22,2 .087 22,1 ,044 22.4 480 *079 10 *0 0O60 10.1 *041 10 *4 ,020 10.2 500 *043 5*5 *033 5*6 *0225 5*7 ,010 5*1 550 o024 3*1 ,019 3*2 *012 3*0 .007 3.6 600 *012. 1*5 ,009 1,5 ... — ,0025 1.3 TABLE 12 66

EFFECT OF VARIOUS SAMPLES OF PERCHLORIC ACID ON THE MOLAR ABSORPTIVITY OF PALLADIUM (II) PERCHLORATE IN 7*9 MOLAR PERCHLORIC ACID

23*1*3.93 ffiM T=25°Co 0.998 cm. cell length

Std. Soln. 10 10 10 10 Soln.'’5 1 2 3 4 e e e e

270 5.6 4,1 5.9 6 .2 280 3.4 2,9 4.2 4.2 290 3.4 2 .8 3®6 3 .6 300 3 .8 3.4 4.1 4.3 310 5«9 5.3 5«6 5 .9 320 9.2 8.8 9.3 -9.7 330 15.5 1 5 .0 1 5 .0 15.5 340 2 5 .2 24.7 24.7 2 5 .6 350 37.7 37.1 36.9 38.3 360 51.7 51.1 5 0 .9 52.4 370 63.9 6 3 .1 6 3 .1 64.4 380 72.3 7 2 .0 71.2 72.8 385 _— 75.3 388 75.8 75.2 — — 390 76.3 75 *8 75 c 3 76.3 392 76.3 75.7 75.6 76.5 394 76«3 75.7 7 6 .0 76.5 396 76.3 75.7 75.7 76.7 398 76.1 75.7 75*4 76.5 400 75.7 75.4 75.2 75.8 402 75.2 74.8 74.9 75.3 406 73.8 --- 73*8 410 72.0 72.0 71.8 72.3 414 7 0 .0 — -- — «— - — 420 66*2 66.2 6 6 .7 66.0 430 58.0 58.0 5 8 .5 57.9 440 48*6 48.9 49.6 48.1 460 28.4 28.4 29.0 27.9 500 7*2 7.0 7.5 7.3

* lo Mallenckrodt analytical reagent 60$ HCIO^ 2. Baker and Adamson anaytical reagent 60% HCIO^ 3» G. F. Smith analytical reagent 6ofo HCIO^ 4. G. F. Smith double distilled 70% HCIO^ TABLE 13

EFFECT OF VARIOUS PREPARATIONS OF PALLADIUM (II) PERCHLORATE ON THE MOLAR ABSORPTIVITY OF PALLADIUM (II) PERCHLORATE IN 9»6 MOLAR PERCHLORIC ACID t 0 0 0 —3 0

T=25°C0 cm. c e l l len gth

Stdo Solno 6 6 14 S oln 0 1 1* 2 SPd x 103 4 o95 4*95 2.73 ( hcio4 ) 9*58 9*58 9*6 A e A e A e

275 0o037 7*5 0*0335 608 0*024 8.8 280 o0295 60O o0255 5*2 o0195 7*1 285 o024 4®9 o020 4o0 0OI55 5*7 290 o022 4«5 .014 5 .1 295 o021 4®3 0OI6 3*2 .013 4 .8 300 o0215 4o3 .018 3*6 .014 5.1 305 .024 4 .9 o020 4 .0 o014 5.1 310 o027 5®5 . 0^5 5°1 .0155 5*7 315 0O32 6 .5 0032 6 .5 .019 7 .0 320 .042 8»5 O04l5 8 .4 .024 8®8 325 o0525 10 06 0O525 10 06 .029 10.6 330 «066 13*3 .067 13*5 *035 1 2 .8 340 ®lo6 21 ®4 „108 21o8 .0585 2 1 .4 350 ®161 32*5 .1635 33 oO .089 32.6 360 .226 45*7 »226 45*7 .1255 46.0 370 o285 57 oo o284 57*4 *1575 57®? 380 *3315 67.0 .3295 6 6 .6 .183 6?.0 390 *3575 72®2 *356 71 *9 *197 72.2 396 03645 73*6 ®360 72o7 .2005 73 ®4 298 *3645 73 ®6 .201 73*6 400 o3645 73*6 ®362 73*1 .202 74 oO 406 -— —- --- .200 73 ®3 410 «357 72.1 *355 71 0? *197 72.2 420 *337 68.1 ®334 67*5 0I 86 68.1 430 .304 6 1 .4 *303 61.2 0I68 61.5 440 0265 53*5 .263 53*1 .146 53.5 460 0I69 34.1 0I 675 33*8 o0925 33 ®9 480 o0905 I 8 .3 .088 17*8 o048 l? .6 500 .047 9 .5 o046 9*3 .0245 9 a0 520 0O285 5.8 .028 5*7 <>015 5®5 540 .0236 4 .7 .022 4 .4 .0125 4 .6 560 .020 4 .0 .018 3 .6 o010 3®7 ’"'Six months after preparation 68 TABLE 13 (Contdc)

EFFECT OF VARIOUS PREPARATIONS OF PALLADIUM (II) PERCHLORATE ON THE MOLAR ABSORPTIVITY OF PALLADIUM (II) PERCHLORATE IN 9«6 MOLAR PERCHLORIC ACID

T=25°C« 1.000 cm. cell length

Std. Soln. 10 13* Soln® 3 4 E P d x 103 3*93 3.87 (HCIO4 ) 9*57 9.60

A e A e

275 0.023 5.9 . 0.038 9.8 280 *0175 4.5 .030 7.8 285 *015 3.8 .0245 6.3 290 *0135 3.4 .019 4 .9 295 .015 3.8 .016 4.1 300 *0175 4.5 .015 3.9 305 *0165 4.2 .015 3.9 310 .021 5.3 .019 4.9

315 ' .026 6.6 .023 5.9 320 .0325 8.3 .0295 7.6 325 .040 10.2 .036 9.3 330 .051 13.0 .048 12.4 340 .085 21.6 .079 20.4 350 .1285 32.8 .1235 31.9 360 .180 45.8 .174 45.0 370 .2285 58.1 .222 57.4 380 .265 67,4 .2595 67 .I 390 .2855 72.6 .281 7 2.6 396 .292 74.5 .286 73.9 398 .2925 74.4 --- 400 .2915 74.2 .287 ?4.2 406 .288 73.3 .286 73.9 410 .2845 72.4 .2825 73.0 420 .269 68.4 .268 69.3 430 .243 61.8 .2425 62.7 440 .2095 53*3 .210 5^*3 460 .133 3^.3 .134 34.6 480 .072: 18.3 .070 18.1 500 .036 9.2 .036 9.3 520 .023 5*9 .0225 5*8 540 .018 4.6 .017 4.4 560 .014 3.5 .013 3.4 "This preparation gave a positive test for chloride with AgNO^ 69

Oxidation of palladium (II) to palladium (IV) by the perchloric acid at room temperature was thought improbable from free energy con-

Q £ siderationso These calculations were substantiated by spectro-

(8 5) W. M. Latimer, "The Oxidation States of the Elements and Their Potentials in Aqueous Solutions9" 2d ed«, Prentice-Hall, Inca, 1952. photometric experiments concerned with the stability of palladium

(II) in 5 ‘16 M perchloric acid over a 184 day interval (Table 14) and the stability of palladium (II) in 11.4 M perchloric acid over a

3 year interval (Table 1).

Plots of molar absorptivity versus total perchlorate concentra­ tion in the 320 to 460 mu wavelength region for solutions prepared from standard palladium (II) perchlorate solutions Nos<> 6 and 10 showed distinct breaks in the 5 M perchlorate region. An additional change in slope of the curves at some wavelengths was observed in the

10 M region. Plots at 4 wavelengths are given in Figure 4. Extra­ polation of the molar absorptivity values obtained for solutions con­ taining from 1 to 4 06 K perchlorate to zero perchlorate concentration gave the values listed in Table 15* The maximum decrease in molar absorptivity of palladium (II) produced by increasing perchlorate concentrations in this range occurred in the 360 mu wavelength region.

The rate of decrease in molar absorptivity with perchlorate concen­ tration was 4 percent at 360 mu.

The ultraviolet absorption spectrum of palladium (II) in 1 H perchloric acid had a minimum around 2?8 mu (e=1 .9 )| at lower 2 wavelengths the absorbance increased rapidly to a value of 6 x 10 70 TABLE 14 i AVERAGE MOLAR ABSORPTIVITY vs® TIME, FOR PALLADIUM (II) PERCHLORATE SOLUTIONS CONTAINING 5*10 MOLAR PERCHLORIC ACID (HC10^)=5«6 M T=25°C» loOOO cm. cell length

Std. Soln® 10 10 10 IPdx 103 1®96 to 7087 1.96 to 7087 1.96 to 7.87 At, days 1 53 184

eav0 + A © e ;£ &es e t Ae

270 4®3 0.03 * t o n 4.3 0®4 275 3-3 ®2 — 3*4 .4 280 2.7 .1 2.3 0.8 2.9 .4 285 2 ,5 .1 1*9 .8 2.6 .3 290 2,4 .1 1.9 .6 2.6 *3 295 2.7 .15 2.2 .4 2.6 .2 300 3.4 •1 * 2.9 0 2 3*3 .1 305 — ---- 3*9 o l 4.3 .1 310 6.0 .2 5»4 .1 5*7 .2 315 8 .3 .1 7.7 .2 8.2 .2 320 11.0 .2 1 10.4 .1 11.2 .2 325 14® 6 .2 13*9 *3 14.5 o2 330 19.0 .2 18.5 .2 19.2 .2 340 30 ®8 .1 30.2 .1 31.0 .2 350 45.4 *15 45*2 *3 45.7 .1 360 60.1 .15 59.9 .2 60.6 .2 370 72,0 *3 71.7 .2 72.0 *3 375 — -— --- 76.5 *35 380 78.5 .1 78*3 .2 78.9 *3 385 79.8 .2 79*5 .2 ---- 386 79 *9 .1 80.0 .0 390 79*8 .2 79*5 .2 79*7 *3 395 79*0 .2 78.5 .2 78.8 *3 400 77*1 *3 76,6 .1 77.3 .25 410 —_ 70.9 .4 71.4 *25 420 62.9 .1 62.7 *3 63.0 .2 430 . ---- 53*0 .1 53*1 .2 440 42.2 .1 42.2 .1 42.2 .0 460 22.2 .1 22.2 .1 22.2 .1 480 10.0 .1 9.9 .2 10.2 .1 500 5*3 .03 5.2 *3 5.6 o l FIGURE 4

THE MOLAR ABSORPTIVITY OF PALLADIUM (II) PERCHLORATE VSo PERCHLORATE CONCENTRATION AT SELECTED WAVELENGTHS IN THE VISIBLE REGION

71 9 0 • Std Pd Solrr^S

0 Std Pd Soln^lO 80 50

70 40 e

60 30

460m 50 20

40

30

Figure 4 73 TABLE 15

COMPARISON GF OBSERVED MOLAR ABSORPTIVITY OF PALLADIUM (II) PERCHLORATE SOLUTIONS WITH VALUES CALCULATED BY EXTRAPOLATION TO ZERO PERCHLORATE CONCENTRATION

S t d . S o l n . 10 10 10 6 6 6 6 XTPd x 10^ 3*93 3 .6 3 3 .6 3 4 .3 6 4 .3 6 4 .3 6 4 .3 6 (h c i o 4 ) 0.00 0.97 0.194 0.00 1.12 0.00 ! 0.998 E N a C l x l O 3 0.00 0.00 0.00 0.00 0.00 2.68 2.68

AamjJ. e e x t . eobs. ®obs 0 ee x t 0 e o b s . eext. eobs0

320 16 15 *7 17.1 16 14.9 —

330 27 25.7 27.3 27.3 2 5 .8 2 3 .2 22.9

340 42.5 40.4 41.9 42.9 40.8 31*7 3 0 .5

350 59 «4 5 6.6 59 o5 60 .2 57 *3 4 6 .3 44.4

360 74.4 7 1 .6 74.9 74.4 72.0 65.9 63.2

370 84.3 8I .3 83.1 84.4 8 1 .7 87.2 84.3

380 86.0 84.2 86.0 86.0 84.6 107.2 104.6

385 84.8 84.2 ---

390 83 82.1 8 3 .4 82.4 82.1 123.9 121.6

395 80 79 06 8 0 .6 80 79.8

400 76 75*9 76.9 74.8 75*8 131.2 129*9

410 6 6 .7 67.5 68.2 6 5 .6 6 7 .0 127.7 128.4

420 5 6 .O 57.4 57.7 55 0 4 5 6 .7 115.6 117*9

430 44.0 46.4 46.6 43 o4 4 5 .6 97.6 100.1

440 32.7 3 5 0 35 °5 42.6 45®6 77.2 80.5

460 14.7 1 7 .2 17 •! 15 ®4 16.7 43.4 4 5 .6 at 220 mM-j the lower limit of the wavelength region which was measured.

This indicated the presence of a charge-transfer band whose maximum absorbance was at wavelengths below 220 ihm-. It is well known that the intensity and position of charge-transfer bands are veiy sensitive to temperature and general medium effects as well as to changes occurring in the inner coordination sphere of the metal ion. In order to study the effect of perchloric acid on the ultraviolet spectra of palladium

(II) in this regions solutions containing from 1.9 to 3*8 mM palladium and from 0.1 to 10.8 M perchloric acid were prepared from standard palladium solution No. l6 and standard 11.3 M perchloric acid. The molar absorptivity of these solutions in the 220 to 250 mM- region was a continuous function of the perchloric acid concentration from

1 to 10.8 M» as is shown in Figure 5» The magnitude of the effect of perchloric acid concentration on the absorbance of palladium (II) in 1 K perchloric acid increased with decreasing wavelength below

250 m^ and was much larger than that observed inlhe 400 mM- region.

Iiolar absorptivities of palladium (II) perchlorate solutions containing various concentrations of sodium and barium perchlorates

are given in Tables 16 and 17* respectively. The effect of these

salts on the molar absorptivity of palladium (II) in the 320 to 600 mM* wavelength region was comparable with that of perchloric acid if the

latter were shifted to somewhat lower molalities in the 1 to 4.6 ranges

but at wavelengths below 250 mM- a significant difference in the effect

of perchloric acid and sodium and barium perchlorates was observed$

as shown in Figure 5« There appeared to be no maxima or minima in FIGURE 5

THE MOLAR ABSORPTIVITY OF PALLADIUM (II) PERCHLORATE VSo PERCHLORATE CONCENTRATION AT SELECTED WAVELENGTHS IN THE ULTRAVIOLET REGION

75 200

Std. Pd Soln, 16 175

150 24 0 m/x

125 e 100

75 250 m^,

240mp, 50

25

I Clo4

Figure 5 77 TABLE 16

EFFECT OF SODIUM PERCHLORATE OH THE MOLAR ABSORPTIVITY OF PALLADIUM (II) PERCHLORATE SOLUTIONS

Std.Solns 16 16 16 6 6 £Pd x 103 1*905 1*905 4*36 4.3 6 4 .3 6 (HCIO^) O 0O966 0*0966 1.12 2o06 0 .96 (NaClO^) 0.000 7.46* 0.000 0.000 1.04- ^jCB l o 5*00 5*00 1*00 1.00 1*00 A t 30 min.» 30 min* 1 d. 1 d 0 1 d*

Ajmia. A Q A e A e A e A e VO O O 320 0 d 5 7 16 .0 ■O v 0*065 14.9 0 14.8 0*062 14.2 330 o265 24.8 0 .17? 18 .6 *1125 25*8 *109 2 5 .O .106 2.4*3 340 »4o8 42.8 *288 3 0 .2 *178 40.8 .171 39*2 .168 38*5 350 -- — *4235 44*5 .250 57*3 .242 55*5 *238 54*6 360 o704 73*9 *560 5 8 .8 *314 72.0 *306 7 0 .2 .304 69*7 365 *756 79*4 06195 65*0 *3375 77*4 *331 75*9 *328 75*2 370 *792 83*2 .668 70.1 *356 81*7 *350 80*3 *347 79*6 375 o8095 8 5 .0 *708 74*3 .361 82.8 *359 82*3 378 0802 85*3 — — Owta *364 83*5 380 0812 35*3 *730 7 6*7 *369 84.6 0366 83*9 *365 83*7 382 o800 8 5 .1 *738 77*5 ___ *367 84.2 *365 83*7 385 <>8o4 84.4 *735 77*2 *367 84.2 .3655 83*8 .3645 83 06 390 *48? 82.6 *735 77*2 *358 82.1 .360 82.6 *359 82*3 395 *754 79 ®2 *735 77 oZ *348 79*8 *350 80*3 *351 80*5 400 o4l6 75*2 *723 75 0 9 *3295 75*6 *335 7608 *335 76.8 410 *629 66.0 0667 70 oO *292 67*0 .298 6 8 .3 .300 68.8 420 *533 56.0 *599 62.9 *247 96*3 *2555 5 8 .6 *259 59*4 430 o430 45.1 *5075 53*3 *199 45*6 .207 47*5 *210 48*2 440 .•327 34*3 *408 42.8 *151 34.6 *1595 36*6 .163 37 *4 460 ol572 1 6 .5 *2177 22.9 *073 1 6 .7 *078 17*9 *080 18*3 480 0O72 7.6 *099 10.4 *033 7*6 .034 7*8 *036 8*3 500 *045 4.7 *0 515 5*4 *0205 4*7 .020 4.6 .021 4*8 520 *037 3*9 *037 3*9 —-

^Prepared from sodium perchlorate preparation 3 do **Prepared from sodium perchlorate preparation 3 Co 78 TABLE 1?

EFFECT OF BARIUM PERCHLORATE ON THE MOLAR ABSORPTIVITY OF PALLADIUM (II) PERCHLORATE SOLUTIONS*

Std a Soln a 16 16 16 16 2-Pd x lO3 3.81 3 .8I 1.905 1.905 (HC10J 0,1932 0.1932 0.09658 0.09658 (BaClO^) 0 .0000 2.98 0 .0000 2.98 bj cm. 0.998 0.998 5 .00 5.00 Agixi^t A e A e A e A e 265 0 a009 2.4 0,0145 3.8 0 .0415 4.4 0.0535 5*6 270 ,0072 1.9 0OI25 3-3 •0335 3-5 .042 4.4 275 .0075 2 .0 .011 2.9 .0295 3.1 .035 3.7 280 .00? 1 .8 .0105 2 .8 .028 2.9 .032 3.4 285 .008 2 .1 .0105 2 .8 .029 3.0 .0277 2.9 290 .0095 2.5 .0115 3.0 .022 2.3 .033 3-5 295 .011 2.9 .014 3-7 .0375 3-9 .0373 4.9 300 .015 3.9 0OI65 4 .3 .0475 5.0 .045 4.7 305 .021 5-5 .020 5 .3 .0625 6.6 .055 5 .8 310 .0298 7 .8 .0255 6 ,7 .0835 8.8 0O695 7.3 315 .0415 1 0 .9 .0335 8.8 .1135 11.9 ,089 9.3 320 ,056 14.7 .0435 11.4 -.157 16.0 .117 12.3 325 .0755 19.8 .058 15 .2 .207 21.7 .152 16.0 330 .0985 25.9 .0755 19.8 .265 24.8 .195 20.5 340 *157 41.3 .123 32.3 .408 42.8 .309 32.4 350 .220 57.8 •1785 46.9 — ----- — 355 .250 65.7 .2075 54.5 .639 6 7 ol •5195 54.5 360 o27? 72.9 o2357 61.9 .704 73.9 .589 61.8 365 .2963 78.0 .2593 68.1 .756 79.4 .646 67.8 370 •311 81.8 •2795 73 *4 .792 83.2 .695 73.O 375 •3185 83 .8 °2935 77-0 .8095 85.0 .730 76.7 380 •3195 84.1 .3025 79.4 .812 85.3 .752 79.0 385 .3165 8 3 0 .3065 8O .5 ,804 84.4 . .762 80.0 390 .3085 81.2 •3945 79.9 .787 82.6 ' .760 79.8 395 .297 78.1 .3015 79.2 .754 79.2 .750 78.8 400 .2825 74.3 • .293 76.9 .716 75.2 .734 77.1 410 .2485 6 5 .4 .2702 70.9 .629 66.0 .6725 70.6 420 .2098 55-2 .2385 62.6 .533 56.0 .600 63.0 430 .1685 4 4.3 .200 52.5 .430 4 5 .I .502 52.7 440 .128 33-7 •1595 41.9 .327 34.3 .399 41.9 460 .0602 1 5 .8 .0837 22.0 .1572 16.5 .2092 22.0 480 .0254 6 .7 .0357 9 »4 .072 7.6 — 500 .015 3-9 .0197 5.2 ,045 4.7 ,0985 5.2 520 .0112 2.9 .014 3-7 •037 3-9 .0365 3.8 vAbsorbance of solutions measured immediately after preparation 79 in the plots of molar absorptivity versus perchlorate concentration for solutions containing as high as 5°96 N barium perchlorate or

7 06 M sodium perchlorate. Absorbance at the 395 mix isosbestic point

(e=79o0) remained constant for the barium perchlorate solutions over the range of concentrations used. The presence of chloride ion in the sodium perchlorate preparations caused a bathochromic shift in the absorbance curve in addition to that produced by perchlorate.

In order'to determine the significance of the isosbestics at

395 and 408 mns a series of solutions having 4 .3 6 mM palladium*

0.00268 M hydrochloric acid and from 1 to 6«3 M perchloric acid were prepared as described for the palladium perchlorate solutions. The

O , 1 M perchloric acid solution contained 45s 50s and 5 percent Pd *

PdCl+? and PdCU^s respectively* as calculated from the stability

constants obtained as described in Chapter II. Molar absorbtivity

curves for these solutions in the 3^0 to 500 mp. wavelength region are

given in Figure 6 . These curves showed a progressive infrared shift

as the concentration of perchloric acid increased from 1 to 6 .3 M;

however * the molar absorptivity at the wavelength of maximum abso rption

remained relatively constant. Isosbestics were observed at 407 mix for

solutions having frorn 1 to 5°3^ M perchloric acid and at 415 mix for

those containing from 5*3^ to 6 .3 M acid. These results are summarized

in Table 18.

Plots of molar absorptivity of these solutions versus total per­

chlorate concentration shox-jed changes in slope in the 4 to 6 M region of perchlorate concentrations but the changes in slope were not as well defined as those observed for the solutions having no chloride. FIGURE 6

EFFECT OF PERCHLORIC ACID CONCENTRATION ON THE ABSORBANCE OF PALLADIUM (II) PERCHLORATE SOLUTIONS CONTAINING 0.6l6 MOLE RATIO OF CHLORIDE TO PALLADIUM

2Pd=0.00435 M HC1=0.00268 M T=26°C« 1.00 cm. cell length

Curve (HCIO^) Molar

1 1 .1 3

2 2.06

3 3 «oo

4 3*94

5 .5.34

6 6 . 2 ?

7 6 .7 4

Solutions prepared from standard palladium perchlorate solu­ tion No. 6 Orange precipitate (PdG^) formed within one day after preparation

80 Absorbance .500 .300 400 .000 .600 .200 .100 300 iue 6 Figure 350 W a v e l e n g t h ,my u 400 400 5 500 450 82

TABLE 18

EFFECT OF PERCHLORIC ACID ON THE ABSORPTION PARAMETERS OF PALLADIUM (I]) PERCHLORATE SOLUTIONS CONTAINING 0o6l6 MOLE RATIO OF CHLORIDE TO PALLADIUM*

Xpd=4«36 mM £HC1:=0.00268 M T=26°C. 1.00 cm. cell length

Amax (HC10J emax e407mp. e4l5mM. 6 (-) Molar 5 ( + ) mp* kK kK

1 .1 3 405 131.0 130.7 120.0 3.0 2.4

2.06 405 130.3 130.3 125.7 3.0 2.4

3.00 407 130.5 130.3 127.1 2.9 2.4

3*94 409 130.5 130.3 128.9 2.9 2.4

5.34 412 131.2 130.3 131.2 2.9 2.4

6.27 415 131.2 128.4 131.2 3.1 2.4 6.74 3jC

Solutions prepared from standard palladium (II) perchlorate solution No. 6

** Orange precipitate formed within one day after preparation Extrapolation of the molar absorptivity valves obtained for the palla­ dium perchlorate solutions containing chloride and from 1 to 5 M perchloric acid to zero perchlorate concentration gave the values listed in Table 15 • The maximum decrease in molar absorptivity- produced by increasing perchloric acid concentration occured in the

375 rap. wavelength region. The rate of decrease was about 3 .4* percent at 375

An increase in perchloric acid concentration would be expected

to produce an increase in the stability constant for PdCl+ ; however^ a large increase in K]_ would not change the concentration of PdCl+

in the above solutions to any appreciable extent since KqJ=2o4 x 10^ 86 in 1 M perchloric acid solution (Chapter II)o Comparison of the

(86) H. Colls R. V. Naumans and ?• W. Wests -J. Am. Chem. Soc.s 81s 128^ (1959)o

absorbance curves for palladium perchlorate solutions containing

O 0OO268 M hydrochloric acid with the curves for corresponding solu­

tions at the same perchloric acid concentration but having no chloride

revealed that the wavelength of intersection of each pair of solutions

increased with perchloric acid concentration. This indicated that an

increase in the perchloric acid concentration from 1 to 5 M produced

a bathochromics hyperchromic shift in the wavelength of maximum

absorbance of PdCl+ o

These results showed that the effect of perchloric acid concen­

tration on the absorbance of palladium perchlorate solutions was

probably a medium effect rather than an effect produced by complex 84 formation between palladium (II) and perchlorate ions. The presence of isosbestic points in both series of solutions and the alteration in molar absorptivities of Pd and PdCl demonstrate the caution which should be exercised in the interpretation of spectrophotometric

data when an appreciable change in the concentration of medium ions occurs®

The effect of sodium hydroxide on the molar absorptivity of

palladium (II). The effect of sodium hydroxide on the molar absorp­

tivity of palladium (II) was studied in order to determine if the

presence of mononuclear hydrolysis products such as [Pd(H20^(OH)]+

in palladium (II) perchlorate solutions could be detected by spectro­

photometric measurements. The successive replacement of water in the

first coordination sphere of palladium (II) by chloride and ethylene-

diamines as well as the replacement of chloride in the tetrachloro-

palladate (II) ion by ethylenediamines produces progressively increas­

ing or d ecreasing effects on the ligand field parameter A • The re­

placement of H^O in the inner coordination sphere of Pd(H20)j~+ by

(0H)”° should be expected to produce similar effects. If the frequency

of maximum absorption of the tetraaquo- and tetrahydroxo-eomplexes

are known* approximate values for the absorption maximum of the

monohydroxo complex can be calculated from the rule of average environ- 87 3-X merit* as used by Tsuchida for [Co^H^cdG complexes.

(87) R« Tsuchida* Bull. Chem. Soc. Japan* 13* 436 (1938)°

Solutions were prepared from two aged preparations of 20 M sodium

hydroxide* standard palladium perchlorate solutions Nos. 13 and 10* and carbon dioxide-free double distilled water. An aliquot of the palladium perchlorate solution was added to a weighed amount of sodium hydroxide solution in a volumetric flask and the flask filled to the mark at 25°C« with distilled water. Reference solutions were prepared in a similar manner except that 1 M perchloric acid was substituted for the palladium solution. Care was exercised to exclude carbon dioxide from the solutions by performing the operations in a nitrogen atmosphere«

The effects of palladium concentrations sodium hydroxide concen­ tration and time on the absorption of 8 palladium (II) hydroxide solutions in the 260 to 560 my. wavelength region are presented in Table

19* The wavelength of maximum absorption for the tetrahydroxopalladate

(II) ion appears to be in the 360 to 365 my- wavelength region. It x»ras not possible to obtain the absorption spectrum of this ion with any degree of certainty from these experiments because of the progressive hypsochromic shift of the wavelength of maximum absorption of palladium

(II) produced by increasing sodium hydroxide concentration from 2.2 to 15*8 M and the failure to obtain constant values for the absorbances of these solutions within a 6 day period after preparation. These ef­ fects may be caused by the presence of polynuclear species of palladium hydroxides which are slow to attain equilibrium. There is also the probability that impurities in the sodium hydroxide may be complexing with the palladium.

If the law of average environment is applied to the palladium hydroxide system? then

a [Pd(H2G)3(0H)]+ = § a [Pd(H^]2+ + o[Pd(0H)4]2" 86 TABLE 19

MOLAR ABSORPTIVITY OF PALLADIUM (II) IN CONCENTRATED SODIUM HYDROXIDE SOLUTIONS

(KaC10^)=0o204 M T=25°Co

Std. Soln,• 13 13 13 13 13 13 13 13 Soln. No# 1 2 3 3 4 5 6 7 £Ed x 103 3-87 3-87 0 .7 7 6 0.776 0.776 0.776 3-87 3-87 NaOH 2e2 2.2 2 .2 2 .2 4.6 4.6 7.8 1 5 .8 ^ 5 crru Go 998 0.998 5 .0 0 5-00 5.00 5-00 0.998 0.998 t J 'i days 4 5 1 4 1 6 5 4 e e e e e e e e

260 31 ®1 31-5 37-4- 36.9 3 4 .3 33-2 3 4 .6 2?0 7.1 6.9 9-7 8 .5 4-5 — * 9 -4 7-5 280 4.8 4.0 6 .7 6 .3 1-9 ------«. 7-1 4 .9 290 7.0 6 .3 8.0 8.0 4.4 2.8 9-3 7 .8 300 12.9 12.7 12.6 13-4 10.1, 9-8 1 5 .4 15-4 310 24.0 2 3 .8 22.0 24.0 20.5 21.3 27-1 29-5 320 42.4 42.0 37-9 41.5 37.4 39-3 46.3 51-3 330 66.4 65.9 6 0 .8 6 5 .8 61.7 63.5 72.1 79-8 340 94.2 93-9 89-3 93-9 90 .8 93-3 102.1 11 0 .6 343 1 0 8 .5 — 103.9 107-8 1 05-8 108.1 11 6 .5 122.7 350 120.4 120.7 117*4 119-7 119-2 121.0 129*0 132-6 355 130.0 13 0 .1 128.5 130.3 130-3 131-3 138*8 139-0 360 136.2 136.2 1 3 6 .5 136.5 138.4 138.8 144.4 140.8 365 139.0 139-3 141.2 139-7 142.6 146.8 139-0 370 137-7 138.1 141.5 139-2 142.6 141.7 145-0 134.1 375 133-6 134.1 138.6 135-0 139-2 138.5 139-8 127-4 380 127-4 137-1 132.7 128.6 132.8 131-4 132.3 119-1 390 109.7 109-0 116.0 110 08 115-2 113-6 113-4 101-6 400 87-3 8 7 .2 94.1 89.2 94.1 91.2 91-0 83-5 410 6 6 .7 66 «5 72.4 6 7 .6 72.3 6 9 .6 69-3 65-9 420 47-5 *4-7-3 5 2 .1 48.2 51-3 49.2 49-6 49-5 430 31-7 31-5 35-3 31-7 34.1 32.1 32.9 34.2 440 20.0 19-6 2 2 .5 19.8 21.6 19-8 21.2 22.6 460 8 .3 7-9 9-5 7-5 8.6 7-1 8.9 9-7 480 4-7 4.4 5 .8 4.1 5.4 3.4 5-7 5-7 500 3.4 3-1 4.4 2.8 4.1 2.1 4.0 3.9 520 2.7 2.1 3-4 1-7 3-1 1-3 3-1 3-1 540 1.8 1.6 2.8 1-3 2-3 0.5 2.1 2.1 560 1.2 0.8 2.0 0.6 1.8 1-7 1.8 87 and a value of 26®6 kK or 37& ron is calculated for the absorbance maximum of [Pd(H20)^(0H)]':'® The concentration of this species would be expected to be small compared to that of pdCf^O)^* since Kjj for the first hydrolysis of analogous systems such as cobalt and nickel are 1 x 10”^ and k x 10“^ ? respectively®^9^ Therefore? unless

(88) S® Chaberek? R® C. Courtney? and A® E® Ifertell? J® Am® Chem, Soc®? 2±t» 5057 (1952)® ePdOH significantly different from ep^s the presence of mononuclear hydrolysis products in the palladium perchlorate solutions would not be expected to produce any significant effects on the absorption spectrum®

Effect of silicic acid on the absorbance of palladium (II) per™- chlorate solutions® The initial increase with time in absorbance of palladium perchlorate solutions prepared by dilution of standard solu­ tion Ho® 6 with 1 M perchloric acid or distilled x*ater followed by a decrease in absorbance on the appearance of a finely divided colorless precipitate was thought to be caused by the formation and slow precipi­ tation of silicic acid® This hypothesis was based on the following observationss (1) the precipitate gave a positive test for silicic 77 acid with ammonium molybdate and benzidine? (2) a similar precipi­

tate appeared in the perchloric acid reference solutions prepared by

dilution of once-distilled perchloric acid with distilled water;

(3) a greater amount of precipitate appeared in the 0®2 M perchloric

acid solutions than in the 1 M acid solutionsa as would be expected

since the solubility of silicic acid has a minimum at a pH of around 8 8

I,®'* and (4-) the palladium concentration} as determined spectrophoto-

(89) H. To 5. Britton, "Hydrogen Ions," 3d ed., Vol« 2, Chapman and Hall, Ltd., London, 195& s p o 131»

74 metrically with sodium bromide, did not change with time.

Further investigation of the effect of silicic acid on the absorb­

ance of palladium perchlorate solutions appeared desirable since there was a possibility that a small amount of palladium was adsorbed on the

silica. It is known that acidified solutions of cobalt (II), zinc

(II), and copper (II) salts react with silicates to liberate colloidal

silica which then acts as a protective colloid by forming a protective 90 layer on the metal hydroxide.

(90) R. K« Iler, "The Colloid Chemistry of Silica and Silicates," Cornell University Press, Ithaca, New York, 1955» P« 68.

The effect of silicic acid on the absorbance of palladium (II)

perchlorate solutions was investigated by batch and column experi­

ments at concentrations of 3*8 to 0.2 mM palladium perchlorate and

from 0.2 to 1 M perchloric acid, and at contact times of 30 minutes

to 3 days. The columns (38 cm. length, 1 cm. diameter) contained

2h gms. of the oven dried gel. a.nd had solution volumes of 25 ml.

They were first saturated with perchloric acid of the desired concen­

tration. Then a given volume of the palladium (II) perchlorate solu­

tion was placed on top of the column and eluted with 0.2 or 1 M

perchloric acid into volumetric flasks.

Solutions for the batch experiments were prepared as 89 follows: the required amounts of oven dried silica gel and standard perchloric acid solution were added to an aliquot of the palladium

(II) perchlorate standard solution in a 50 or 100-ml. calibrated volumetric flasks and then diluted to the mark with distilled water®

The solutions were then shaken for intervals of from 1 hour to 6 days®

Reference solutions of perchloric acid were prepared and treated in the same manner as the palladium (II) perchlorate solutions® The molar absorptivities of 3

1.02? 0.4-0s and 0.20 M perchloric acid? respectively? before and after treatment m t h silicic acid are given in Table 20o

Eluates from the column experiments and suspensions from the batch experiments were allowed to stand for at least 3 days before removal of aliquots for spectrophotometric examination in order to allow silicic acid to settle out. Some of these aliquots were also centrifugated for 15 minutes in an International Equipment Company centrifuge (size 2? j/U- hp) after which aliquots were removed from the centrifuge tubes for spectrophotometric examination. Aliquots containing palladium (II) perchlorate were converted to the tetra- bromopalladate (II)j as in the case of standard palladium perchlorate solutionsand the concentrations determined from the absorbance of the tetrabromopalladate (II) ion at 500 mp..

Comparison of the absorbance of palladium (II) perchlorate solu­ tions before and after silicic acid treatment showed the following effects; (1) no change in the wavelength of the absorption maximum for palladium (II) perchlorate nor in the general shape of the ab­ sorbance curve? (2) a maximum in the 390 mp region and a shoulder 90

TABLE 20

EFFECT OF SILICIC ACID ON THE MOLAR ABSORPTIVITY OF PALLADIUM (II) PERCHLORATE SOLUTIONS PREPARED FROM STANDARD SOLUTION NOo 13

EPd x 103 3 080 3 .80* 3 .8 0 3 .8O* 3*80 3 .80* (HCIO^) 1 .0 2 1 .0 2 0.40 0.40 0 .2 0 0 .2 0 ^ s d a y s 6 6 6

A smp e "eavo eav„ av. eav. eav. eav.

260 11.5 15 12*9 13.1 13.1 13*7 265 1 0 .0 13 1 1 .3 1 1 .6 1 1 .2 1 2 .0 270 8 .1 11 9*4 9*6 9.4 10 oO 275 6 .5 -- 7*9 7*9 7*7 8 .2 280 5.1 8 6 .5 6 .5 6 .3 6 .7 290 3.9 6 5*1 5*2 4.8 5*1 300 5*0 6 .9 5 .8 5 *8 5*6 5.8 310 8 .2 9*5 9 .0 9*2 9*1 9*3 320 14.8 15*9 15*5 1 5 .6 1 5 .8 1 6 .2 330 25*5 2 6 .6 2 6 .5 2 6 .5 2 6 .8 27.6 340 40.1 40.8 41.4 41.5 42.0 42.3 350 5 6 .6 57*5 5 8 .1 58.4 5808 59*6 360 7 1 .6 72.7 73*1 73*4 73*8 74.6 365 77*2 7 8 .3 78.4 , 78.9 79*2 8 0 .1 370 8 1 .3 82.4 82.5 8 3.O 83 d 84.0 375 83*7 8 5 .2 84.9 8 5 .2 85*5 8 6 .1 380 84.9 8 6 .2 8 5 .4 8 6 .0 8 6 .0 8 6 ,9 385 84.5 85.9 8 5 .2 85 *6 8 5*5 8 6 .3 390 8 3 .0 84.5 8 3 .2 83*9 8 3 .4 84.4 395 ___ 81.7 80 *4 8 0 .8 8 0 .6 81.7 400 77*1 78.3 7 6 .8 77*2 76.9 77*6 410 6 8 .6 70.0 6 8 .3 6 8 .5 6 8 .1 6 8 .7 420 5 8 .8 6 0 .0 57*9 58.1 57*7 5 8 .3 430 4 7 .6 48.6 46*9 47*0 4606 47*1 440 3 6 .5 37*3 35*8 35*8 35*4 35*8 460 17.8 1 8 .5 17*2 17.1 17*0 17*1 480 8.0 8.4 7*9 7*7 7*8 7*9 500 4.9 5*3 4.9 4.7 4.9 5*0 520 3 .8 4.2 3 .8 3*7 3*7 3*9 540 3*2 3*5 3*1 3*0 3*1 3*2 560 2 .5 2.9 2.6 2.4 2.6 2.8 580 2.0 2.3 1.9 1.8 1*9 2.1 600 1.4 1.6 1,4 1.3 1.4 1.6

*Batch experiment with 0*5 Sm * silica gel/5 0 ml. solution 91 at 280 mu for plots of the change in absorbance s Aes versus wave” length; and (3 ) a maximum at the fractional molar absorptivitys

Ae/e* at about 280 mu® From (1) it was concluded that complexation of the silica by palladium (II) seems unlikely® Light scattering or absorption by colloidal silicic acid in the palladium perchlorate solutions appears to be responsible for (2 ) ? since the perchloric acid solutions after treatment with silicic acid showed absorption maxima in the 270 to 280 mu wavelength region® Absorption curves of hydro­ chloric acid? sodium hydroxides sodium chlorides sodium bicarbonates sodium perchlorates and other solutions used in this investigation also had maxima in this region®

The analytical results on the tetrabromopalladate (II) solutions indicated that there was no significant change in palladium (II) con­ centration with silicic acid treatment® Since palladium (II) was not

sorbed by silicic acids it is probable that it was not significantly hydrolyzed in the 0®2 to 1 M perchloric acid solutions and in the 0.1 to 0.2 mM palladium (II) concentration range® These conclusions are 91 based on the results of Hazel et a.l® who have shown that silicic

(91) F® Hazels R® V® Schocks Jr. s and M® Gordons J. Am. Chem. Soc®, £1# 2256 (19*4-9) •

acid does not combine with a normal metal ion such as I-KHgO)]^" until

a hydroxyl ion enters the coordination sphere of the metal ions 92 forming a basic ion. Britton found that combination of metal ions

(92) H® T® S® Brittons J® Chern® Soc®s *4-25 (1927) o 92 with silicic acid occurs in the pH region at which the metal hydroxide would be formed (either as a sol or as a precipitate) on prolonged standing®

Effect of perchlorate concentration on the absorbance of copper

(II) perchlorate solutions® Although shifts in the absorbance curves of several ‘tri- and tetravalent metal ions produced by perchlorate have 4 6 .49 s58 been reported, there have been few comparable studies for divalent metal ions® The effect of perchloric acid, sodium perchlor­ ates and barium perchlorate on the absorption spectrum of the hydrated copper (II) ion was investigated in order to provide a basis of com­ parison for the palladium (II) system. Nickel (II) and rhodium (III) perchlorate solutions were also studied. An increase in perchlorate concentration from 0.1 to 5«8 M by addition of perchloric acid or sodium perchlorate produced no change in the wavelengths of maximum absorption of nickel (II) or rhodium (III) within 2 mp-o The maximum decrease in intensity of absorption for nickel (II) in the 1200 to

240 mp wavelength region with increasing concentration of perchloric acid from 1 to 5*8 M> as is shown in Figure 7» was 2 percent. At­ tempts to prepare the hydrated platinum (II) ion were unsuccessful.

The absorption spectrum of the aquo-copper (II) ion, as well as

the spectra of many copper (II) complexes in the visible and ultra­ violet regions j is well known®^-95 xhe tetragonal structure of the

(93) D. A. L. Hope» R. J. Otter, and J. E. Prue, J. Chem. Soc., 5226 (1960)o (94) J. Ferguson, Spectrochim. Acta, 12, J lS (1961)® (95) E® Doehlemann and H. Fromherz, Z. Physik. Chem., A 171, 353 (195*0* FIGURE 7

EFFECT OF PERCHLORIC ACID CONCENTRATION ON THE ABSORBANCE OF NlCKSL(ll) PERCHLORATE SOLUTIONS

Curve SNi (HCIO^)

1 X OoZ^rO 0o8 W 2 0 0®2440 5o8^

93 Absorbance .000 .200 1.000 .300 .400 .500 .600 .800 .900 .700 .100 Figure 450 7 550 650 W avelength ( m m ( avelength W 750

jli 850 ) 950 1050 1150 94 aquo-copper (II) ion is similar to that of the palladium (II) ion? howeverj the energy levels in the d shells of these two ions are very 8 ?96 different® Evidence for the entrance of perchlorate ion into the

(96) J. Bjerrum? C. J. Ballhausen? and C. K. Jorgensen? Acta Chem. Scand.j 85 1275 (195*0 ® inner coordination sphere of copper (II) has been obtained by Hathaway and Underhill 59 from infrared measurements of Cu(ClQ^g"2^0 and 60 CuCClO^)^? and by Barker et al® from changes in the visible absorp­ tion spectrum of [Cu(bipy)^]PF^ produced by perchlorate® Williams^

(97) R« P» Williams ? Disc. Faraday Soc»? 2*b 238 (1957)® reported that the absorbance of copper (II) perchlorate solutions was unaffected by large changes in perchlorate concentration. Zagorets 98 et alo7 studied the dependence of the visible and ultraviolet spectrum

(98) P. A. Zagorets and G. P. Bulgakova? Russ. J. Phys. Chem.? J6S 11*4-9 (1962)o of copper (II) perchlorate solutions on the concentration of various alkali and alkaline earth perchlorates from 0 .1 to 2 M perchlorate.

These authors found that perchloric acid produced no change in the absorbance? however? on addition of perchlorate salts? a bathochromic shift occurred in the absorbance band of the aquo-copper (II) ion at

2*44 mp*. At a given concentration of perchlorate? the relative mag­ nitude of the shift produced by the metal perchlorates was as follows?

Cs? Rb> K> Li> Na ? Ba> Be> Mg> Sr> Ca. Zagorets et alo proposed 96 that the energy of the shift of the hydrated copper (II) band depends directly upon the bonding energy of the alkali metal and alkaline earth metal ions with water molecules in the hydration zone. The magnetic susceptibility of copper (II) perchlorate solutions also

gives evidence of some type of interionic interaction. Berthier 99 et alo reported that copper (II) perchlorate solutions* as well as

(99) P« Berthier, C. Courty, and J. Gauthier, Compt. Rend., 239, 241 (1954).

other copper (II) salt solutions, show a large increase in the para­

magnetism of copper at concentrations below 0«l6 molal. At concen­

trations above 0 .1 6 molal the magnetic susceptibility corresponds to

a magnetic moment of 2.007 Bohr magnetons.

Copper perchlorate solutions were prepared by addition of stand­

ard perchloric acid and/or a given weight of standard sodium perchlor­

ate solution (3d) to an aliquot of the standard copper (II) perchlorate

solution in a calibrated volumetric flask, followed by dilution to the

desired volume at 25°C. with distilled water. For solutions containing

greater than 1 M perchlorate, an aliquot of the standard copper (II)

perchlorate solution was added to the desired weight of standard 1 1 .3 M

perchloric acid, barium perchlorate solution and/or sodium perchlorate

(Fisher reagent) in a calibrated volumetric flask and the solution

diluted to the mark at 25°C. with distilled water. Reference solutions

were prepared in the same manner except that 1.019 M perchloric acid

was substituted for the standard copper (II) perchlorate solutionso The effects of copper? perchloric acid? sodium perchlorate? and barium perchlorate concentrations on the absorption curve of the aquo- copper (II) ion at 25°C. were studied at 45 wavelengths in the 240 to

1150 mp wavelength region. At constant perchlorate to copper ratios from 2c23 to 25*55 copper concentrations from 0.02379 to 1.078 M? and perchloric acid concentrations from 0.0332 to 1.011 M? Beer's law was obeyed. An increase in the ratio of perchlorate to copper produced a small hypsochromic shift in the absorption curve of the

copper (II) in the 810 mp region. The effect of perchloric acid con­

centration on the molar absorptivity of copper (II) perchlorate solu­

tions at several wavelengths is given in Figure 8. The change in

absorbance produced by perchloric acid was greatest in the 240 to

265 mp region at perchloric acid concentrations above 5 A pro­ nounced change in slope of the molar absorptivity versus wavelength

curves in the 5 to 6 M perchlorate region was observed at wavelengths

above 740 mp. Similar changes were noted in the effect of perchloric

acid on the wavelength of maximum absorption and the intensity of ab­

sorption at the maximum? in the 810 mp region? as is shown in Table 21o

The validity of Beer's law for solutions containing from 0.0238 to

0.1426 K copper in 4.83 M perchloric acid indicated that the change

in absorption curve of the hydrated copper (II) ion with perchloric

acid concentration was probably not caused by impurities in the per­

chloric acid. A hypsochromic? hyperchromic shift in the wavelength

of maximum absorption of copper (II) at 810 mp occurred t'jith an in­

crease in sodium and barium perchlorate concentration from 1 to 7°5 ho

From 1 to 4 M perchlorate ion concentrations the effect of sodium and FIGURE 8

CHANGE IN MOLAR ABSORPTIVITY OF 0*0476 Ml COPPER (II) PERCHLORATE SOLUTIONS WITH PERCHLORIC ACID CONCENTRATION AT VARIOUS WAVELENGTHS

98 99

13.0 265 mp, 265 mu 65 0 mp, 6 5 0 m p 12.5, 3.5

12.0 3.0

2.5

8 0 0 m p

no 2.0

10.5

10.0

9.5 0.5

9.0; 2.0 4.0 8.0 10.0 12.0

Figure 8 100

TABLE 21

EFFECT OF PERCHLORIC ACID OH THE ABSORPTION PARAMETERS OF COPPER (II) PERCHLORATE SOLUTIONS

T=25°C® loOO cm. cell length

Solru ECu (HCIOk ) V a x 6(+) 6 (-) mil M mM- M** cm” kK kK

1 47° 62 0 d 536 810 11 .6 1 2.1 1 2 .8 3

2 47 062 .965 810 11.61 2.13 2.81

3 47° 59 1*95 809 11.66 2 .1 3 2.77

4 47°59 2 .8 3 807.5 11 .6 8 2.13 2.78

5 47.59 3*73 805 11.78 2.13 2.77

6 47.59 # .6 2 80 2 .5 11.84 2.1 2 2.7 8

7 47° 59 5°52 800 11.94 2.1 3 2.7 8

8 47 °59 6.41 800 11 .8 6 2.15

9 47.59 7°69 798 11.67 2.18 2 .7 8

10 47.59 9*07 794 11 .3 2 2 .2 0 2 .8 2 li 23 °79 1 0 .1 2 794 11.18 2.20 2 .8 2 1 0 1 barium perchlorates on the absorbance of copper (II) corresponded to that of perchloric acid displaced to somewhat lower molalities® The molar absorptivity at any given wavelengths the wavelength of maximum absorptions and the intensity of absorption at the maximum for copper

(II) perchlorate solutions containing sodium perchlorate were con­

tinuous functions of the total perchlorate concentration at all wave­ lengths as can be seen in Figure 9 and Table 22 o

The absorption spectrum of hydrated copper (II) ion in the 300 to 1250 mp wavelength region consists of 3 overlapping bands produced

by electronic transitions in the d orbitals of the ion. A charge

-3 8 transfer band is found around 200 mM- (e=l<>6 x lCK)o The effect of

complex formation on the absorbance of the aquo-copper ion would be

expected to be large in the region where electron transfer between

the metal ion and coordinated ligands occurs® The relatively small

change in molar absorptivities of the hydrated copper (II) ion in the

2h0 to 1200 mp wavelength region produced by sodium and barium per­

chlorates from 1 to 4<>4- as well as perchloric acid at concentra­

tions below h Ms indicated that replacement of water in the inner

coordination sphere of copper (II) by perchlorate did not occur under

the experimental conditions.. Complex formation between copper (II)

and anions such as the halides» nitrates and sulfate results in a

decrease in the separation of the energy levels in the hydrated ion.

Coordination of copper (II) with perchlorate would be expected to pro­

duce similar effects. The rapid increase in absorbance of copper (II)

in the 2^+0 to 265 mp region and the change in slope of the molar ab­

sorptivity versus wavelength curves at xjavelengths above ?40 mp with FIGURE 9

CHANGE IN MOLAR ABSORPTIVITY OF O.OR7 6 M COPPER (II) PERCHLORATE SOLUTIONS WITH SODIUM PERCHLORATE CONCENTRATION AT VARIOUS WAVELENGTHS

102 103

650 mu 265 mjx

12.5 6 5 0 mjj. 3.5

8 0 0 mjA

12.0 3.0

2.5

750 1.0 2.0

10.5

2 6 5 m jx

10.0 9 0 0 m

9.5 0.5

9.0 4 6 8 i: cio4 Figure 9 104

TABLE 22

EFFECT OF SODIUM PERCHLORATE ON THE ABSORPTION PARAMETERS OF COPPER(II) PERCHLORATE SOLUTIONS

T=25°Ca 1.00 cm. cell length

Soln. 2Cu (HC104 ) (NaClO. ) ^ _%ax_ s (+) 5 (« uiM M M 4 mu- M" cm kK kK

1 4 7 .5 3 0.153 0.000 810 11 .6 1 2 .11 2.8 2

2 4 7 .5 3 .153 0815 808 11.62 2.11 2.32

3 47.53 ol53 1.804 806 II.65 2.11 2.82

4 47.53 .153 3.072 805 11.74 2.11 2.81

5 47.53 .153 4.682 803 11.86 2.12 2.78

6 47.53 .153 5.382 802 11.90 2.13 2.77

7 23.79 .153 6 .5 7 800 12.01 2.12 2.79

8 23.79 .153 7.47 800 12.11 2.13 2.77 105 increasing perchloric acid concentration from 5 to 10o2 M was evidence that a specific effect on the energy levels of the copper (II) ion was produced by perchloric acid in this concentration range? as was found for palladium (II)o

Stepwise potentiometric titration of palladium (II) perchlorate solutions with standard sodium bicarbonate and sodium hydroxide

The purpose of these experiments was to s tudy potentiometrically the equilibria and rate of attainment of equilibrium between palladium

(II) and hydroxide ions by means of the glass electrode? and to cor­ relate these results with spectrophotometric measurements. Since the change in pH with hydrogen ion concentration is too small to be deter­ mined with sufficient accuracy using the present method in the pH region where appreciable hydro'-~ sis of palladium (II) occurs? it x^as not expected that the solubility product or hydrolysis constants could be calculated.

The undersaturation approach to equilibrium could not be used be­ cause the rate of attainment of equilibrium was too slow to be of any practical use. A microcrystalline modification of palladium oxide 100 prepared by the method of Schreiner and Adams was not easily purified

(100) R. L. Schreiner and R. Adams? J. Am. Chem. Soc. ? 46? 1684 (1924). and was insoluble in perchloric acid; the precipitate dissolved in hydrobromic acid only on prolonged boiling® as reported by these investigators. The composition of the hydrous oxide precipitated 1 0 6 from perchloric acid solutions was too uncertain for use in experi­ ments of this kindo"^^ A stepwise or static titration procedure was

(101) 0. Glemser and G. Peuschel» Z. Anorg. Allgem. Chem., 2 8 1, 44 (1955) • adopted, since it was found that the equilibrium pH was established too slowly for use of a more dynamic method.

Solutions were prepared by addition of appropriate amounts of

003858 M sodium hydroxide or 0.5704 M sodium bicarbonate from cali­ brated burets to aliquots of the standard palladium perchlorate solution in a calibrated volumetric flask and diluting to the mark with carbon dioxide free distilled water. These solutions contained

4.35 mM paDladium (II) and 0.23 M perchlorate ion at hydrogen ion concentrations from 0.23 to 10~^. The pH readings were made on cells of the following general type at intervals from 1 day to 1 month a fter mixing the solutionsi

Pd(Cl0i,,)? hS2c12 Ag AgCl HCl Glass HClOij. 1 M4 M Satd. Electrode NaClO^ HaClO^ NaCl KC1

A Beckman Model G pH meter was used with glass and calomel electrodes.

The pH meter was standardized at a pH of 1.10 with 0.100 M hydrochloric acid and at pH values of 4.01, 6 .8 5, and 9»18 with standard buffers obtained from the National Bureau of Standards. High purity, oil- pumped nitrogen, saturated with water vapor, was employed to remove

the carbon dioxide from the solutions containing sodium bicarbonate

and to prevent absorption of carbon dioxide by the sodium hydroxide

solutions at pH values greater than 3*5®

./ / 10?

The hydrogen ion concentration in the palladium (II) perchlorate solutions was determined from the observed pH by interpolation on a plot of pH (observed) versus hydrogen ion concentration obtained from the stepwise titration of 0 .2 3 perchloric acid with sodium hydroxide.

The use of these reference solutions automatically corrected for all liquid junction potentials except those due to palladium (II) ion| these were assumed to be negligible. The perchloric acid concentration of the standard palladium (II) perchlorate solution was calculated from the stepwise titration of aliquots of this solution with sodium hydrox­ ide » assuming that palladium (II) combines with 2 moles of sodium hydroxide per mole of palladium below a pH of 9®

The pH was observed for solutions containing from 0.2 to 0.01 M hydrogen ion concentration at 5 intervals from 1 day to 1 month after mixing. Since the pH of these solutions showed only small random

fluctuations during this period? the average of 5 readings was taken

as the equilibrium value® These average pH values? together with the

ratio of hydroxyl ion bound per palladium (II) ion? [CH-(H+)]/Cp^=ns

and the error in the ratio produced by an error of 0.01 unit in pH

are given in Table 23® If an error of 0.01 unit in the pH is assumed

also for the reference solutions containing perchloric acid and sodium

perchlorate? then the error in n would be twi.ce that given in Table 23«

Since adsorption of hydrogen ions by the precipitate probably occurred?

these results can only be considered an approximationo

Precipitates from the sodium hydroxide and sodium bicarbonate

solutions were examined in an electron microscope (Hitachi HU 10)

and were found to be amorphous. The absorbance of the supernatant TABLE 23

STEPWISE TITRATION OF PALLADIUM (II) PERCHLORATE SOLUTIONS WITH SODIUM HYDROXIDE AND SODIUM BICARBONATE

EPd=4« 35 mM (C10^)“=0e23 M T=30°C.

Titrant Sodium Hydroxide Sodium Bicarbonate

A(H + ) n CH P^obs. (H +) A(H + ) n CH P^o'os . (h +) to 0 0.0394 1.43 0.051 0 .0 1 1 6 2 .8 1 0 .6 0.0649 1.28 0.072 0.007 1.7 1 J .0318 1.51 .0415 .0 1 0 2 .4 .3 .0363 1.47 .0 4 6 .0 1 0 2.4 O £f> .0 1 6 $ 1 .6 8 .027 .0105 2.5 .2 5 .0249 1.58 .0343 .0094 2 .2 .2 .0127 1.75 .023 .0103 2 .4 .25 .0192 1 .6 6 .028 .009 2 .1 .2 .0 0 88 1.82 .0195 .0107 2.5 .25 .0157 1.69 .026 .0 1 0 2 .4 .3 .0 0 5 0 1.92 .0155 .0105 2.5 .2 .0135 1.765 .0225 .009 2 .1 .2 .0035 2 .0 0 .0127 .009 2 .1 .2 .0077 1.89 .0165 .009 2 .1 .2 .0 0 1 2 2.09 .0 1 0 4 .009 2 .1 .1 .0 0 2 0 2 .075 .011 ,009 2 .1 .1

H O 00 109 liquids after centrifugation for JO minutes in the microchemical centrifuges was measured in the 260 to 600 mp. wavelength i&giono

The wavelength of the maximum was 380 mu for all the solutions; the absorbance was higher at all wavelengths than the absorbance of the corresponding palladium (II) perchlorate solution with the same initial concentration of palladium but containing no sodium hydroxideo

The BA©/increased with decreasing wavelength which indicated the presence of polynuclear hydrolysis products whose absorbance was greater than that of the aquo palladium ion*

This preliminary study of the hydrolysis of palladium (II) in­ dicated that the hydrolysis occurs relatively rapidly (within 24 hours) for Ho25 mM palladium (II) solutions in the pH region below 2 and is followed by the slow formation of polynuclear species. Neither the potentiometric nor spectrophotometric methods were useful in further elucidating the nature of the hydrolysis of palladium. Measurement of a property of the palladium perchlorate solutions which is a linear function of the hydrogen ion concentration rather than a logarithmic function would probably yield more significant results. A3.though conductivity measurements have been used successfully by Biedermann 102 et al« for the investigation of hydrolytic equilibrias in general

(102) C® Berecki Biedermann and Go Biedermanns International Conference on Coordihation Chemistry» Londons 1959s ’’Special Publica­ tion 139 *’ The Chemical Society, London, 1959s P° 190 o there is poor agreement between e quilibrium constants obtained by the conductivity method and those obtained by other methdso 110

Dialysis of palladium (II) perchlorate solutions

The removal of silicic acid and colloidal palladium oxide in palladium (II) perchlorate solutions was investigated by dialysis8

A Visking cellulose acetate membrane (1 in diameter) i*as immersed in distilled water for 3 days and in 1 M perchloric acid for 2 days prior to the experiments in order to remove foreign material«• The stability of the membrane in 1 II perchloric acid was tested by dialysis of 100 ml. of 0.4312 K copper perchlorate in 1 M perchloric acid. After 12

hours aliquots were taken both inside and outside the membrane and

their absorption was measured at 44 wavelengths in the 250 to 1250 mp wavelength region. The copper concentration was deduced from the ab­

sorption at 890 mp. Since the molar absorptivity of these solutions

and that of a copper perchlorate solution not exposed to the membrane

agreed within 0«05 unitsj it was concluded that hydrolysis of the

cellulose acetate under these conditions probably would not cause any

interference* but that the molecular itfeight of the silicic acid in

these solutions was less than 30>000 and that silica therefore could

not be removed using this technique.

A 25-ml. aliquot of standard palladium perchlorate solution No. 13

containing 0.0192 M palladium in 1.019 M perchloric acid vras placed

inside the dialyzer which was suspended in 75 ml* of 1.019 M perchloric

acid. After 4 hours a 10-ml. aliquot was taken from the outer solu­

tion and its absorption measured at 48 wavelengths in the 220 to 600 mp

wavelength range. The palladium concentration was determined spectro-

photometrically and found to be 0.00402 M. The molar absorptivity of

the dialyzed solution at every wavelength was significantly greater Ill than that of the solution not exposed to the membrane® Since the wavelength of maximum absorption was not affected and e increased itfith decreasing wavelengths it was concluded that polymeric material was introduced into the solution.

The absorption and scattering of light by molecular linear col­ loids such as cellulose is generally small? however? there was a possibility that the hydrolysis products might react with palladium

(II). Because of this possibility? and also because silica Twas not removed by dialysis ? this technique could not be used for purifying palladium solutions and was not investigated any further®

Nuclear magnetic resonance study of palladium (II) perchlorate solutions

This technique was used in an attempt to detect complex formation between palladium (II) and perchlorate ion by measuring the effect of palladium (II) on the chlorine-35 nuclear magnetic resonance in the perchlorate anion in concentrated perchloric acid solutions® Nuclear magnetic resonance studies have been very useful for the investiga­

tion of interactions between metal ions with chlorine-3 5 s fluorine-19s 103-105 48 and oxygen-1? in water® ^ Klanberg et al® have measured the

(103) D« B® Chesnut? J. Chem. Phys.? ^2? 1234 (i960)® (104) R« E® Connick and R. E. Poulson? J. Phys® Chem.? 6 3? 568 (1959)® (105) H. Taube? ’'Progress in Stereochemistry? 8 ® 8 * D® de la flare and W. Klyne editors? Butterworth Inc®? Washington? D. C®? 1962? p. 53®

effects of divalent manganese? cobalt? nickel? copper? beryllium? and trivalent cerium and iron on the chlorine-3 5 nuclear magnetic resonance

absorption of perchlorate ion in perchloric acid solutions. On the 132 basis of their data? these authors postulated the existence of an inner-sphere complex between manganese (II) and perchlorate ion.

Although palladium (II) is diamagnetic in all of its known com- pounds except the difluorides 20 there exists the possibility that the perchlorate might also be paramagnetic and therefore produce an observable effect on the electron spin relaxation time of chlorine-35 in the perchlorate anion if the exchange of perchlorate ion between the complex and the solution is slow. Manganese (II) and copper (II) interactions were also studied to afford a basis for comparisono

Weighed amounts of manganese (II) perchlorate dihydrate (G. F*

Smith Chemical Co.)9 standard copper (II) perchlorate solutions and standard perchloric acid were used to prepare the manganese (II) and copper (II) perchlorate solutions and the perchloric acid reference solutions. They were diluted to a predetermined volume with distilled water and then reweighed to determine the amount of water. Palladium

(II) perchlorate standard solution No. 7 was used without further dilution.

The magnetic field intensity during measurements was standardized

by measuring the field strength at which the chlorine-35 resonance

line appeared for a saturated aqueous sodium chloride solution; this

was found to be 7886o4 gauss. The absorption lines of the perchlorate

solutions were observed at 27°C. under conditions of slow passage and

a radiofrequency of 3 0 Mc/sec. to produce side bands for the accurate

determination of line widths.

A chemical shift of 1268 ppm» relative to saturated sodium

chloride solutions was observed for the chlorine-35 nucleus in 10.^0 113 to 11=27 M perchloric acid solutions - None of the added metal ions produced any additional shifts®

The widths of the resonance peaks® 6 ? observed for the chlorine-

35 nucleus in palladium (II) and copper (II) perchlorate solutions are compared with the line widths obtained for perchloric acid solu­ tions in Table 24® The width of the peak in the manganese (II) perchlorate solution was so large that it could not be measured®

Reproducibility of line widths for modulation frequencies from 100 to 400 c/sec® was itfithin 0®02 gauss® The line boradenings j> A ® were calculated by subtracting the line width observed for the perchloric acid solution from the line width of the metal perchlorate solution measured under the same conditions®

Neither palladium (II) nor copper (II) showed a detectable broadening of the chlorine-35 resonance line in concentrated perchloric acid solutions % hence® it may be concluded that the quadrapcle effects are small under the conditions of the experiment® The results found for copper (II) and manganese perchlorate solutions agree with those 4-8 reported by Klanberg et al® Possibly the use of oxygen-17 as indicator in perchlorate solutions measured at lox%rer temperatures and at high concentrations of metal ions will yield information on the interaction between metal ions* water molecules 9 and perchloric acid in concentrated perchlorate solutions®. 114

TABLE 24

NUCLEAR MAGNETIC RESONANCE ABSORPTION OF CHLORINE-35 IN CONCENTRATED ' PERCHLORIC ACID SOLUTIONS CONTAINING VARIOUS METAL IONS

Metal K(C 10. ) (HC10,) Mod® Freq. 6 M M c/sec» Gauss

Pd (II) 0.330 10.40 200 0.29 CM Pd (II) ®330 10.40 400 0

Cu (II) 0I 078 11.24 88 .24

Mn (II) •99 10.80 400 &

------— 10.40 200 *29

— 11.06 400 .41

— 11.27 88 o22

——_ 11.27 400 •39

& Width of ine resonance peak was so large that it could not be measured Discussion of Results

Comparison of the absorption parameters for palladium perchlorate solutions by various investigators is given in Table 25° Although there is fairly good agreement in the xravelength of maximum absorbance? except for. the solutions prepared by D r o l l there are large differences in the values obtained for the molar absorptivity at the maximum and the half-width of the absorption curve which cannot be explained bjr the differences in temperature? palladium concentration? acidity? and per­ chlorate concentration? according to the results of this investigationo

Molar absorptivities for palladium (II) perchlorate solutions in the 320 to 600 mn> wavelength region obtained by the present workers agree closely with the values by Sundaram and Sandell?^^ as seen in

(106) A. K. Sundaram and E. B« Sandell? private communication.

Table 26 and Figure 10. Analysis of the absorbance data of Droll indicated the presence of O.b mole ratio of chloride to palladium and colloidal palladium oxide in his solutions. Current experiments showed that palladium oxide precipitated from chloride solutions usua3.1y con­ tained small amounts of chloride which resulted in a bathochromic? hyperchromic shift in the wavelength of maximum absorptivity of the palladium (II) perchlorate solutions. Standard solutions of palladium

(II) perchlorate prepared by dissolution of palladium oxide in perchloric acid under various conditions such as temperature? concentration? acidity? etc. in this investigation often contained colloidal oxide xdiich produced

an increase in the absorbance at every wavelength in the 220 to 600 mp

115 TABLE 25

COMPARISON OF THE ABSORPTION PARAMETERS FOR PALLADIUM (II)-PERCHLORATE AND PALLADIUM (II)-HYDROXIDE SOLUTIONS BX VARIOUS INVESTIGATORS

Species T s°C 0 Amax CT max ^ax 6 + 6 = References mp. kK kK kK

Pd (II) (0o4 Pi HC10J 29 o5 400 25,0 127 3«? 2.7 Droll36 ( 1 M HCLO.) 25 379 26 o4 86 2.8 3.0 Jorgensen ^ ( 1 M HC10 ) 25 382 26 o2 200 Livingston et al 38 (O06 Pi HCIO^) 20 380 26,3 101,1 3.2 Shchukarev et al 107 ( 1 M HClOi ) 25 380 26.3 84 3.0 3°2 Sundaram et al. H0 106 ( 1 M HCIO^) 25 380 26.3 85 3.0 3.2 Present work

Pd (II) 1 9 ( 2 h NaOH) 25 368 27.2 165 3*4 3 .0 Jorgensen c (2.2 M NaOH) 25 366 2 7 0 139 3.0 3.1 Present work 11?

TABLE 26

COMPARISON OF VALUES FOR THE MOLAR ABSORPTIVITY OF PALLADIUM (II) PERCHLORATE SOLUTIONS OBTAINED BY VARIOUS INVESTIGATORS

Investi­ gator* 1 2 3 4 S>d x 103 7 ©62 7 ’.62 4.41 1.841 1.573 0.7865 0.00135 EHClOi 003864 1.00 1.00 1.00 0.416 .416 06 Tj°Co 25 25 25 25 29*5 29*5 20:

Aainp. e e e e e e e

320 14.8 14.5 51*7 56.4 <_Q.— 330 25.9 25.4 48 51.8 -- - 340 40.8 39.8 ------« -- 53*2 55*8 — 350 57-4 56.3 57.4 ----- 65.8 69*2 ---- 360 72.0 71.1 71.9 71*7 82.4 85.6 ----- 370 81.2 80.7 81.0 82.0 99*4 102 ----- 380 83-7 83.7 83.7 84.7 113 117 101 390 81.0 81.4 81.2 81.5 123 127 97 400 74.3 73.3 ?4.6 75*0 127 132 91 410 65.6 66.8 67.1 67.4 123 128 81 420 55.8 57.1 56.5 57*0 112 118 69 430 44.7 46.2 46.0 45*6 96.2 102 55 440 34.1 35*4 34.9 35*3 ?8o 5 83*7 40 450 — 27.0 25.0 62.1 56.2 32 46o 1 6 .2 17.2 16.6 16.8 46.3 48.2 25 4?0 —- 11.3 11.4 34.2 35.8 19 480 7.2 7.6 8 .6 7.6 25*2 2606 14 490 5*9 — 19*3 21.8 10 500 4.2 4 .5 — 15.8 16 .5 9 520 3.2 3*5 —— 1048 12.4 7 540 2.7 3.0 — 8.2 8.2 6 560 2.0 2.4 .— 6.6 8.2 5 580 1.4 1.7 5*7 3 .8 4 600 1.0 1.3 ——— 4.8 3 .8 3

* 1 Present investigation 2 Sundaram and Sandell^06 3 Droll36 (ppo 132-133) 4 Shchukarev8 Molar Absorbancy 100 150 125 50 75 25 iue 10 Figure VOLAR ABSORPTIVITY VS. WAVELENGTH CURVES FOR PALLADIUM PALLADIUM FOR CURVES WAVELENGTH VS. ABSORPTIVITY VOLAR PERCHLORATE SOLUTIONS BY VARIOUS INVESTIGATORS VARIOUS BY SOLUTIONS PERCHLORATE 0 0 4 aeegh rn Wavelength, 450 Sundca n Sandell and cran d n u -S O Droll - A -Shchukarev X Peet investigation Present - o jjl 500 550 118 ) I I ( 0350 0 6 119 wavelength region® Precipitation of the oxide from, solution occurred only after prolonged periods of time. It is probable that colloidal oxide was responsible for the relatively large molar absorptivities ob- ~o 107 served by Livingston-5 and Shchukarev et al. The band width reported

(107) S. A. Shchukarevj 0. A. Lobaneva? M. Ac Ivanova? and M. A. Kononova? Vestnik Leningrad Univ.? 16? No. 10? Ser. Fiz. i Khim.? No. 2? 152, (196l)o

by Jorgensen for palladium (II) perchlorate solutions is significantly

smaller than that observed by other investigators. This difference is

not understood in view- of the agreement in absorption parameters obtained

by the present workers for different preparations of palladium per­

chlorate as well as by dissolution of palladium oxide in perchloric

acid (solution No. Ih) ,unless the slit widths used by Jorgensen were

very much smaller than those employed by the present workers. ^6 a Droll^ attributed the change in absorbance of 10”^ M palladium

(II) perchlorate solutions produced by an increase in perchloric acid

concentration from 0.139 to 0.^16 M to the formation of Pd(0H)+ .

Chromatographic? spectrophotometric? and potentiometric measurements of

this investigation indicated that solutions containing 0 .2 to 20 mil

palladium perchlorate in 1 M perchloric acid were stable toward hydroly­

sis at 25°C« Small amounts of species such as Pd(OH)'*’ could have been

present at lower acidities; however? their contribution to the absorbance

at hydrogen ion concentrations as low as 0 .2 M was not detected by

spectrophotometric measurements ® The effect of perchloric acid on the absorbance of metal perchlorates

has been attributed to (1 ) hydrolysis of the cation; (2 ) association or 120 complex formstion between the perchlorate anion and the metal ion; and

(3 ) alterations in the hydration sphere of the cation produced by the dehydrating effect of perchlorates. The change in the absorbance of palladium (II) produced by perchloric acid and sodium and barium per­

chlorates at concentrations from 0.1 to M could not be attributed 108 to any of these factors. It has been shown by McRae that the molar

(108) E. G. McRae a J. Phys. Chem.j 61? 562 (1957)°

absorptivity of a non-polar solute in a non-polar solvent is proportional

to (AL0+B)(n^-l)/(2n^+l)s where A and B are constants for a given sol­

vent? Lq is constant for a given metal ion? and n is the refractive

index of the solution. The dipole interaction between solute and solvent

for solutions of polar solutes in polar solventswould be expected to

produce further pertubations of the energy levels of the metal ion.

The specific influence of perchloric acid on the absorption curve

of palladium (II) 2 as contrasted with the effect of sodium and barium

perchlorates» at perchlorate concentrations greater than 5 M was believed

to be associated with changes in the hydration sphere of the palladium

(II) ion. Although the term solvation has remained somewhat vague? cur­

rent X-ray diffraction measurements of aqueous solutions and experiments

concerned with the exchange of labeled water beW een the solution and

the hydration sphere of the metal ion are leading to a greater under­

standing of the structure of these solutions generaq^y

(109) G. ¥. Brady? J. Chem. Physics8 28? (1958)« 121 agreed, that there are several different types of interactions between cations and solvent.. Non-neighbor interactions in a crystal lattice cause departures from the simple nearest neighbor field and Van Vleck 110 has shown that these may be important in the spectrao Intermolecular

(110) T. M. Dunns " M odem Coordination ChemistryJ. Lewis and R. G. Wilkinsseds.j Interscience» Mew Yorks 1960)o forces between water molecules in the "second hydration sphere" of the palladium ion and chemically inert medium ions may also result in de­ partures from the fields exerted by the water molecules on the palladium ion. Nuclear magnetic resonance measurements have indicated that the magnetic influence of the hexaaquochromium (II) ion extends beyond the water in the primary solvation sphere of the ion® 111 Although the

(111) Mo AJLeis Jr.;) Inorg. Chem.s M+ (196^4-)® enthalpy of hydration at infinite dilution for Ba > H > Na » the associa­ tion of water molecules with hydrogen ion in perchlorate solutions at concentrations greater than 5 M must be greater than for barium and sodium ions since the perchloric acid solutions are hydroscopicoX In

(112) V. P. Vasilev9 E. K. Zalotarev® A. F. Kapustinskiis Ko Po Mishchenkos E. A. Podgornaya s> and K. Bo Yalsimirskiis Russ. J. Phys. Ghem.j 8^0 (1960)® view of the mean activity coefficients of perchloric acid and sodium and barium perchlorates as well as conductivity and diffusion measurements in concentrated solutions of these electrolytes» it would be expected

that the effect of barium perchlorate on the absorbance of palladium (II) 122 T13,114 be greater than that of sodium perchlorate*

(113) R» A. Robinson and R. H. Stokes s “Electrolyte Solutions?" Academic Press? New York? 1955* (114) H. S. Hamed and B. B. Owen? "The Physical Chemistry of Electrolytic Solutions ?" 2d ed. ? Reinhold Publishing Corp.? New York ? 1950 c

An unequivocal interpretation of medium effects on the properties of solutes in solutions having a high concentration of inert salts is often difficulto^^ However? it is probable that effect of perchlorate

(115) "Interactions in Ionic Solutions.g" Discussions Faraday Soc.? 24? 17-238 (1957)* concentration on the absorption spectrum of the hydrated palladium (II) ion is an environmental effect rather than a chemical change in the prim­

ary species. These effects are important in the interpretation of absorp­

tion measurements? especially in the spectrophotometric determination

of stability constants.

Absorption parameters for palladium (II) hydroxide solutions from

the present investigation are compared with the values reported by Jor- 12 gensen in Table 2 5 ® Although the wavelength of maximum absorptivity

observed by the present workers for solutions containing 0.776 and 3*87

mivi palladium (II) perchlorate in 2.2 M sodium hydroxide agrees within 2 mp- 2— with the value reported by Jorgensen for Pd(OH)^ ? there is considerable

disagreement in the values for and 6 ■^le sl°w dissolution of

polynuclear hydroxy-compounds is a possible explanation for this dif­

ference? as well as for the bathochromic? hypochromic? shift in the

absorbance maximum of these solutions with time which was found in the

present investigation0 c h a p t e r II

THE PALLADIUM (II)-CHLORIDE SYSTEM

Historical Review

The ehloride complexes of palladium (II)

The chloride complexes of divalent palladium have played an important part in the refinings purification and atomic weight determination of this elementhowever$ until recent years there

(1) Ro Gilchrist* Che-m. Rev.? 32s 277 (19^3)® have been few quantitative studies of the equilibria or identifi- o cation of the species present in aqueous solutiono Even among

(2) Gmelin? "Handbuch der Anorganischen Chemie?*'3 Teil 65 ? Verlag Chemie? Berlin? 19^2® recent studies there is rather poor agreement. Spectrophotometric

studies have indicated the stepwise addition of four chloride ions but there is considerable disagreement concerning the addition of

two more chloride ions in concentrated solutions® This disagreement

may originate in part from contamination? as indicated by relatively

high absorbancies obtained in some of the studies* Investigation of

this system has been hampered by the difficulty of obtaining revers­

ible indicator electrodes? the ease of reducing palladium to the free

123 124 metal} the acidic properties of the ion* and the fact that pH measure­

ments cannot be used to establish the ligand concentrations®

Sundaram and Sandell^ applied the mole ratio method to spectro-

(3) A. K. Sundaram and E. B. Sandell» J. Am. Chem. Soc.j 77s 855 (1955)®

photometric measurments of solutions containing palladium perchlorate

and varying amounts of chloride® Their data confirm the existence of

PdCl+ p PdClg? PdCl^“ ? and higher complexes® Evidence for the presence O of PdCl^” in aqueous solutions containing PdClg and sodium chloride

has been reported by Ayres who applied the method of continuous

(4) G. H. Ayres, Anal® Chem® > 2£> 1622 (1953)®

variations to spectrophotometric data. Droll} Block} and Fernelius^

(5) H. A® Drolls B. P« Blocks and VI. C® Ferneliuss J. Phys® Chem.} 6jLs 1000 (1957)®

calculated the stepwise stability constants for the first four

palladium chloride complexes at 21 * 29®5» and 38°G® from spectro­

photometric measurements of palladium perchlorate solutions containing

ratios of chloride to palladium from zero to 4.2® Values for these

constants at zero ionic strength were calculated using the equation

of Debye and Huckelj they are given in Table 53® S. A® Shchukarev 7 et al. used Bjerrum’s' corresponding solution method to calculate 123

(6 ) S. A« Shchukarev; 0. A. Lobaneva? M. A. Ivanovas and M. A. Kononova? Vestnik Leningrad Univ.? 16 No. 10? Ser. Fiz. i Khim? Noo 2? 152 (1961)o (7) J® Bjerrum? Kgle Danske Videnskab. Selskabo Mate Bys ° Meddo? 21? (19^) No. 4° the free ligand concentration from spectrophotometric measurements of the palladium chloride system at 470 and 480 mM-s 20°G<>? an ionic strength of 0*8 and hydrogen ion concentration of 0.6 Mo Values for Q the consecutive formation constants were calculated by Bjerrum’s

(8 ) J. Bjerrum? "Metal Aramine Formation in Aqueous Solution?*’ P. Hasse and Son? Copenhagen? 1941e approximation Kn=l/ (A)|j=n-l/2 and are given in Table 53. Templeton et al«^ measured the potential of spongy palladium electrodes in

(9) D. H. Templeton? G. W. Watt? and C. S. Garner? J. Am. Chemo Soc.j 6*5? 1608 (1943). hydrochloric acid solutions and in solutions containing both hydro=> chloric and perchloric acids at concentrations from 1 to 4 formal.

Using the value of ->0.987 volt which they obtained for the formal potential of the Pd/Pd^+ couple in 4 formal perchloric acid? these o 10 authors calculated a value of 13*22 for log at 25 C. Latimer

(10) W. Latimer? "Oxidation Potentials?" 2nd ed.? Prentice Hall? Inc.? New York? 1952°

gave a value of 12*3 for log £4 which was calculated from the standard 126 free energy data on PdCl^“ (aq) from the National Bureau of Standards and the free energy value for Pd (aq) calculated from the value of Templeton et ale

In the past few years there has been an increasing amount of evidence for the existence of the penta- and hexa-coordination in the solid state and in solution from spectrophotometric} conductometric® 2+ crystallographies and kinetic data® It is known that Pd can combine with 6 bromide ions in nitrobenzene solution^; however® there is some

(11) C. M. Harris} S. E» Livingston? and la Ha Reece? J> Chem® Soc.® 1505 (1959)o

2+ controversy as to the maximum number of chloride ions bound to Pd 12 in aqueous solution® Samuel and Udden explained the bathochromic

(12) R. Samuel and M. Udden> Trans. Faraday Soc.® 31? ^23 (,1935)o

shift in the absorption of potassium tetrachloropalladate (II) produced

by excess potassium and sodium chlorides as due to the bonding of two

additional halogen atoms. Sundaram and Sandell^ have given a similar

interpretation to their spectrophotometric data. Grinberg and

Kiseleva-^ studied the absorption of aqueous solutions containing

(13) A. A . Grinberg and N. Y. Kiseleva® Zhur. Neorg. Khim.® 2 s 180^ (1958)®

potassium tetrachloropalladate (II) at various concentrations of

chloride and hjdrogen ion as a function of time. These authors found 127 that, only small changes in the wavelength of maximum absorption were produced by hydrolysis and concluded that the shift in the wavelength of maximum absorbance produced by excess chloride was evidence for

the presence of chloride complexes with a coordination number greater

than 4 at high chloride concentrations. Harris et sl.^ measured the

visible and ultraviolet spectra of the tetraethylamino- and triphenyl-

methylarsonium salts of tetrachloropalladate (II) and tetrachloro-u-

dichlorodipalladate (II) ions in various solvents and in the solid

state. They observed pronounced blue shifts on dissolution of these

salts, the shift increasing in the following order; nitrobenzene,

nitromethane, acetone, methanol, acetonitrile, and water. The authors

attributed the shifts in absorption to solvation of the tetrachloro­

palladate (II) ion, with water having the strongest donor property.

Droll‘d obtained a value of 8 x 10”-^ at 25°C. for the thermodynamic

(14-) H. A. Droll, thesis, The Pennsylvania State University, 1956.

stability constants of the reactions

PdCl^" + Cl" ^ PdCl|~

and

PdCl'j?" + Cl" ^ PdCl^“

These constants were obtained from spectrophotometric measurements of

palladium chloride solutions containing from 1 .6 2 to 8 .0 7 M hydro­

chloric acid, with chloride ion activities as given by Harned and 128

Owen‘S and by Akorlof and Teareo^ Jorgensen and co-workers^"'7

(15) H. S. H a m e d and B. B. Owen* ’’The Physical Chemistry of Electrolytic Solutionsf " 2d ed.» Reinhold Publishing Corp.? New York* 1950® (16) G. Akerlof and J. W. Teare? J. Am. Chem. Soc.j j>9? 1859 (1937)® (17) C. K. Jorgensen? ’’Absorption Spectra of Heavy Metals?11 Contract No. D.A® 91“508~E®U.C.-247* Report European Research Office? U. S. A m y Dept.? Frankfort am Main? 195®* (18) C. K. Jorgensen* ’’Absorption Spectra and Chemical Bonding in Complexes>" Addison-Wesley Publishing Co. Inc.j Readings Mass.? 1962.

7 applied Bjerrum’s' method of continuous variations to spectrophoto­ metric data and obtained a maximum coordination number of 4 and an

equilibrium constant of 6 for the reaction

PdCl" + Cl” -s=* PdCl|~

o at 25 C« in 1 M perchloric acid. They state that even in 12 M hjdro-

2- chloric acid no further bonding of chloride ions to FdCl^ occurs;

however? they have not published the data used in arriving at their £ conclusions. Shchukarev et al. obtained formation curves for the

palladium chloride system between values of n=0 and 4. They concluded

that no more than four chlorides are bound to palladium? since the

wavelength of maximum absorption for the tetrachloropalladate (II) ion

at 475 mp. was not changed by further addition of chloride. Theoretical

The stepxcLse formation of complexes was first proved by Morse^

(19) H« Morses Z. Physiko Chem®* ^la ?09 (1902)o in 1902 for the successive association of four chloride ions with 20 mercury (II)» In 1921 Bjerrum observed the stepwise addition of

(20) N. Bjerrum, Z. Anorg. Chem®s 119s 179 (1921)=.

six thiocyanate ions to chromium (III)o The publication in 19^1

of J. Bjerrum’s thesis”'7 on equilibria involving metal ion-amine com­

plexes resulted in a resurgence of interest in this area. It has

subsequently been shown that step equilibria are of wide occurrence

and include not only complex formation but oxidation-reduction and

acid-base systems® For a monodentate ligand the steps are

M + L 5=i ML (1)

ML + L ^ ML2 (2)

M L ^ + L ?=± ML. (3)

where M indicates the metal ion and L indicates the ligand® Ionic

charges are usually omitted for convenience® Stepwise formation

constants? and overall complexity constantsj B •s are as follows s J J 130 (ML2 ) K2 “ (ML) (L) (5)

(ML*) K3 " (MLW>- (L) (6)

h = % (7)

(m l 2 ) po = K-1K0 = v (8) 2 12 (M) (L)2

J (MLi) pi =ir\ = — C9) J nal (M) (L)J where parentheses are used to express the concentration of the species in moles per liter*. The maximum number of ligands in the complex is indicated ly H. The following expressions are used in the calcula­ tions; The total central ion concentration» G^s in moles per liter is

CM = (M) + \ ( I V (10) n=l and the total ligand concentration 3 is

J CL = (L) + S n(MLn) . (11) n=l

In modem practice these equilibrium constants expressed in terms

of concentrations are valid because the activity coefficients are maintained constant by the presence of a constant large excess concen­

tration of a supporting electrolyte whose interaction with the species

involved is neglected. Thus a species described as M2+ in perchloric

acid medium may be M(HC10^)x (H+)y (ClO^)” (HgO)^ The main reason

for this practice is that concentrations but not activities of many 131 species can be calculated readily® The activities of hydrogen and hydroxide ions are frequently used in these expressions since these activities are easily measured potentiometrically using the glass electrode® The practice of obtaining thermodynamic constants in terms of activities by using conventional approximations and extra- polating to infinite dilution is not feasible for systems involving weak complexes} hydrolyzable cations® and very complicated equilibria®

Many such systems exists however} too little is known about the

structure of solutions at ionic strengths above 0.1 Ms where specific

ionic interactions invalidate the interionic attraction theory® Most

of the work concerning measurements of activity coefficients in strong

acid solutions is limited to acids and hydroxides in the presence of

simple salts® g In order to facilitate analysis of complex equilibria} Bjerrum

introduced an important new concept. He defined n as the average

number of ligands attached to the metal and was able to obtain his

so called formation function in which n could be solved experimentally

and then expressed in terms of only stepwise equilibrium constants

and the free ligand concentration. Thus j E n(MLn) n=l CL - (L) (12) (M> + E (MLn) CM n=l

Combination of equations (12^) and (9) with the elimination of (M) gives

^ ( L ) + 2£2 (L)2 + (13) 132 which may be rearranged into the form

n + (n - l)^(L) + (n - 2)P2 (L)2 h* “ ‘(n - j)3j(L)^ = 0 (Ik)

It is possible to determine the equilibrium constants of the system by solution of simultaneous equations for several solutions having values of n between zero and N, provided the concentration of free ligand is known or can be calculated*

Examination of equation (13) reveals that for a system containing only mononuclear complexes, n is a function of the free ligand concen­

tration and is independent of the total metal ion concentration* 7 Bjerrum has utilized his formation function for the calculation of

concentrations of free ligands which are not necessarily basic in

his method of "corresponding solutions." The method has been applied

to the spectrophotometric and potentiometric study of complexes of

iron (III)*^®22 copper (II),^2j2^ uranyl ( I I ) ,^>25 mercury (II)

(21) J. Badoz-Lambling, Ann. Chim. (Paris), 8, 586 (1953)* (22) H. Irving and Q. H. Mellor, J. Chem. 3oc.» 3^57 (1955)° (23) S. Fronaeus, Acta Chem. Scand., 139 (1951)« (2k) 3. Ahrland, ibid., 2* 783 (19^9); £> 199, 1151 (195U« (25) Kuan Yee-boon and Hsu Kwand-Hsiew, Acta Chim. Sinica, 29, 37 (1963)c (26) T. G. Spiro and D. N. Hume, Inorg. Chem., 2, 3^0 (1963)*

and silver (I)©2^

(27) L. V. Nazarova and A. V. Ablov, Zhur. Neorg. Khim., 1305 (1963)»

Bjerrum defined solutions containing different total 133- concentrations of the same metal ion and ligands but the same concen­ tration of ligand as corresponding solutions since he was able to show that they contained the same ratio of the various complex species as follows * In two solutions indicated by the subscripts 1 and 2 which have the same free ligand concentrations

(15) and

(16)

Rearrangement and combination of equations similar to (15) and (16) gives

(M)2 (ML)2 (ML2 )2 (>2Lj ) 2

Corresponding solutions have the same relative proportions of complexes and consequently identical values of n is evident from equation (13)<* From equation (12) one obtains

Cla - (L) CLe - (L) (18) which may be rearranged to give the following equations

(19) ( % - GM2 ) Substitution of the value of (L) in equation (19) into (18) gives

- V n = ------(20)

If a property of the system which depends on the relative proportion of the complexes can be measured* and only mononuclear complexes are present, the free ligand concentration can be determined and the stability constants of the system calculated. Such properties in­ clude the potential of an e3-ectrode, the half wave potential, or the molar absorption spectrum of the system.

Bjerrum’s method of corresponding solutions is readily adaptable to spectrophotometric measurements. If the optical absorbance of a solution containing M, ML, ML9, ••••ML. can be expressed by the Beer- ^ J Lambert law, and no polynuclear species are present then at a given wavelength

T A = log ^2 = [e0 (M) + e1 (ML) + e2(ML2) + •••e;j(ML;j) + eL (L)]b, (21) where A = the observed absorbance of the solution, b = the optical

path length, en = the molar absorptivity of the nth species expressed -1 -1 in M cm , and = the molar absorptivity of the ligand. If the

absorbance of the ligand is negligible, division of equation (21) by

CM and b gives

_1_ = 1K1 + ei Cm.) + X P . (22) °Hb ch J °M i

Provided that eQ X e-^ X e2 X eL = ^ an(^ ^ / ^ ^ L ^as no ra3-ximum

or minimum, only corresponding solutions have equal molar absorptivities.

The composition of corresponding solutions are best obtained by plotting 135 e as a function of C iJC ^ for a series of solutions having different total metal concentrations* The spectrophotometric error can be minimized if the path length is varied so that (C^b) is maintained constant from one series of measurements to another* If the dis­ placement method is used it is not necessary that BeerBs law be obeyed by the complex whose absorbance is measured* 17 Jorgensen has shown that the maximum number of ligands3 Nj> attached to the metal. ion can also be determined from data obtained for corresponding solutions. By rearrangement of equation (12) one

obtains

- = H o (23 ) CM CM . For a series of corresponding solutions a plot of C p / v e r s u s gives a limiting value of n as -* 0. Values of (L) are obtained from the slope of these lines and utilized for the determination of K^T*

If the complexity constants of a system are of such a large magnitude that is independent of then equation (1 2 ) becomes

n = Si- (2d)

and it is not possible to obtain (L)* The other limiting case exists when the complexity constants are so small that and (L) are of

nearly the same magnitude and their difference cannot be determined with sufficient accuracy for the calculation of 1 * The absolute

magnitude of these limitations is dependent on

[ Spc j a « k / c M ) as a function of where Fc is the property of the system being measured *

When corresponding solutions are determined from spectrophoto­ metric data by interpolation from mole ratio curves for a series of solutions at different total concentrations of metal ion* the differ­ ence ^L in free ligand concentration produced by an error j bA in absorbance is

ACM |S 2 " Sl J” VS2 &L

Where 3 is the slope of the mole rati;;) curve at A. Thus greater accuracy in determining the free ligand concentration is obtained from corresponding solutions having the greatest relative difference in metal ion concentration# The error in a given stability constants APn » produced by a given error in absorbance may be calculated at a

given value of n from a combination of equation (25) with the differen­

tial form of equation (9 ) as follows:

a£n = - w D (26) a(L) (M)(L)n+1

and

(27) tt)n + 1 S2 3]_

If R is the relative error in KnJ> (L) must be known with R percent

accuracy since at any given value of YI When (L) is relatively large so that it is approximately equal to Cl » slope-intercept treatments of spectrophotometric data are particularly useful for calculating the first or last stepwise con- 28 29 stantso A modification of the graphic method proposed by Lewis

(28) F« J » C. Rossotti and He Rossotti? nThe Determination of Stability Constants?" McGraw-Hill Book Co.} New Yorks I96I 0 (29) ¥• B. Lewis s thesis s University of California at Los Angeles » 19^2* has been used in this work for the calculation of K^ for the palladium

(Il)-chloride system* This method has been employed by Newton and

Arcand-^ in studying the cerium (III) sulfate complexes as t«js11 as by

(30) T» W. Newton and G. M* Arcands J* Am* Chem* Sac*? 23* 24^9 (1953)o

Whiteker and Davidson-^ for studying the iron (III) sulfate complexes*

(31) R. A. VJhiteker and N. Davidson? ibid*s 23* 3083 (1953)®

It has the advantage over the Benesi and Hildebrand method in that

the equilibrium constant and molar absorptivity of the complex species

are obtained independently*

Consider the following equilibrium and the corresponding forma­

tion constants % If there is no appreciable concentration of anjr other complex species in the solution, then

CM = (MLn-l> + (KL)o (30)

VJhen the absorbance of the ligand is negligible* these quantities may be substituted in the expression for Beer’s law to give the following equation;

| = e CM = en-1 (MLn_i) + en (MLn ) (31) where e is the observed mean molar absorptivity of the metal ion in a given solution without regard to the species actually present*

Substitution of equation (30) into (31) gives

® ^ n - l ^ + ® ^vELn^ = en-l (IvjLn-l^ + en (Iu£Ln) ° (3 2 )

Substituting the value of (HLn_^) from equation (6) into (32) and

rearranging yields

(e - en )(L) = j P - l - j L - (3 3)

The left-hand term can be calculated if en is known and (L) can be

determined* since (e-en) is the change in the mean molar absorbtivity

over that due to pure MI^. If a plot of (e-en)(L) on the Y axis

against e on the X axis gives a straight line* the validity of the

above assumptions is confirmed and Kn as well as en-l can be deter­

mined from the slope and the X intercept, respectively. If an ap­

preciable proportion of the ligand is complex bound more accurate 139 values of (L) can be calculated from the relationship

(L) = (CL - nCM ) + x + (34) and substituted into equation (33)® This process of successive ap­ proximation can be repeated until a constant value of Kn is obtainedo

The use of high speed digital computers and methods of data

reduction for the calculation of stability constants have been dis­

cussed by several investigators,32-3^ programs have been written

(32) J. G. Sullivan? J® Rydberg? and ¥. Fo Miller? Acta Chem® Scand., 1^, 2023 (1959)® (33) Z® Z» Hugus? Jr.? ’’Advances in the Chemistry of the Coordination Compounds?” So Kirschner? editor? Macmillan? New York? 1961, p. 379c (3^) So ¥. Rabideau and Ro Ho Moore? J« Phys« Chem®? 6^? 371 (1961)?

for the treatment of data obtained from the solubility and potentio-

metric measurements?^ ^ and for the constants which appear in the

(33) J® Rydberg and J• C. Sullivan? Acta Chem® Scand.? ljl? 2057 (1959)® (36) Ro S. Tobias and Z. Z® Hugus? Jo Phys® Chem®? 6£? 2165 (196l)o (37) No Ingri and L. G. Sillen? ibid.? l6? 159 ? 173 (1962)o (38) W® J. Randall? D. F. Martin? and To Moeller? Proc® Chem® Soc«? 340 (1961)0

39 40 Beer’s law equation®^ Rabideau and Kline have used high speed

(39) P« A. D* de Maine and N. Bo Jurenski? "Abstracts 140th AoCoS« Meeting/ 26 T? Chicago? 196le (40) So ¥. Rabideau and R® Jo Kline? J® Phys«> Chem.? 64? 680 (1960)o 140 computers to calculate the first hydrolysis constants of plutonium (IV)

from spectrophotometric data by a least squares method; howevers the

relationships between spectrophotometric measurements and thermodynamic

quantities are so diverse that for more complex systems no program

has been developed at this time. Absorbance data for the palladium (II)-

chloride system are given in the Appendix in the hope that at some

future time evaluation of the stability constants can be performed

by computer methodso Experimental Techniques and Results

General discussion

Most of the methods generally employed for the quantitative study of complex equilibria in solutions are not applicable to the palladium

(II)“Chloride system in view of the strong oxidizing power* coordi­ nating abilitys and hydrolytic tendencies of divalent palladium. It was hoped that the concentration of free chloride in these solutions could be obtained using e®nwfo measurements of the following concen­ tration cell? extrapolated to zero times

y M HCIO^ AgCl Pd(C10^)2 Ag (1 - y) M HCI x M HC10 AgCl Ag 4 (1 - x) M HCl

Silver chloride electrodes prepared by the thermal electrolytic 41*42 method gave steady and reproducible potentials in dilute hydro*

(41) G. N» Lewis* J. Am. Chem. Soc.* 28 s 158 (1906). (42) H. S. H a m e d and R. W* Ehlers* J. Am. Chem. Soc«s 55s 21?9 (1933)o

chloric acid solution; however* when palladium was introduced into

the solution as the perchlorate or tetrachloropalladate (II) the

potential fluctuated so rapidly that it xras not possible to use this 43 method for the estimation of the free chloride. Transpiration and

(4 3 ) S. J. Bates and H. D« Kirschman* ibid«* 41* 1991 (1919)°

141 142 pH measurements were made to determine the partial pressure of HCl (g) above solutions containing 1 M hydrogen ion and from 0.1 to 1 M hydro- o chloric acid. Since the vapor pressure of hydrochloric acid at 25 C. 44 is so low this method was not sufficiently sensitive to yield any

(44) J. T. Dunn and E. K. Rideal? J. Chem. Soc.? 125? 676 (1924)*

28 significant results. The solvent extraction technique for deter­

mining the concentration of the uncharged species? PdClg? was expbred

unsuccessfully using a series of purified ethers and halogenated hydrocarbons. Palladium (II) chloride was found to be relatively

insoluble in organic solvents apparently as a result of polymerization

in the solid and hydration of the aqueous species. It has been found

that although the tetrachloroplatinate (II) ion can readily be ex­

tracted by ethyl acetate and ethers from hydrochloric acid solutions

of 1 M or greater acid concentrations? the corresponding palladium 415.46 complex has an extremely low solubility in these solvents* J

(45) E« B. Sandell? "Colorimetric Determination of Traces of Metals?" 2d ed.? Interscience Publishers? Inc.? New York? 1950° (46) G. H. Ayres and A. S. Meyer? Anal. Chem.? 2^? 299 (1951)®

Spectrophotometric methods for the investigation of equilibria

in solution have been employed with increasing frequency in the past

twenty yearsAlthough the inherent accuracy of this technique

(47) "Stability Constants? Part I: Organic Ligands?" The Chemical Society? London? 1957? "Stability Constants? Part IIs Inorganic Ligands?" The Chemical Society? London? 1956® 143 is limited? it has been most fruitful in the investigation of complex equilibria of multicomponent systems involving many coexisting species? and in cases inhere the potentiometric method is inapplicable® The spectrum of a given complex is much more constant than most other physico-chemical properties? particularly in organic solvents and 18 strong acid solutionso

Preparation of the reagents

Solutions prepared for the palladium (II)-perchlorate system

(Chapter I)® The standard palladium (II) perchlorate? sodium

hydroxide? and perchloric acid solutions used in the investigation

of the palladium (Il)-chloride system were prepared and standardized

as described in Chapter I* Standard palladium (II) perchlorate solu­

tions Nos. 6 and 17 were used to prepare solutions containing chloride

in concentrations less than 1 M; Nos® 17 and 13 were used to prepare

solutions 1 M or greater in chloride® The double distilled water was

also the same as described in Chapter I®

Standard palladium (II) chloride solutiona Palladium (II)

chloride was purified as described in the preparation of standard

palladium (II) perchlorate solutions. The final product after three

evaporations to dryness with hydrochl©ric acid was dissolved in stan­

dard 1 M hydrochloric acid? transferred to a 2-liter volumetric flask?

and heated at 80°C. for 12 hours before filtration through the

Millipore filter*

The palladium concentration in three 50-ml. aliquots was deter­

mined gravimetrically by precipitation with dimethylglyoxime as

described in the standardization of palladium (II) perchlorate Ikk- solutions. There was no significant change in the titer of this solution before and after the experiments.

The hydrochloric acid concentration was determined by titration of 10-mi. aliquots, diluted to 100 ml. with distilled waters against standard 0.2 M sodium hydroxide using phenolphthalein indicator. At the first appearance of the alkaline color of the indicators the solution was boiled for at least 15 minutes» cooled to room tempera­ ture in a constant temperature bath, and immediately titrated to the

end point. The accuracy of this method, as checked with standard

palladium (II) perchlorate solutions which had been standardized by

an ion exchange method before the addition of sodium chloride, was

estimated to be within 0.1 percent. A method utilizing spectro-

graphically pure magnesium to reduce the palladium prior to titration

with sodium hydroxide gave results 0.3 percent low, presumably be­

cause of incomplete precipitation of magnesium hydroxide under these

conditions. Silver was also used to precipitate metallic palladium

but results were not reproducible at the relatively high ratios of

chloride to silver present in the solutions.

Hydrochloric acid solutions. Reagent-grade acid was twice dis­

tilled in an all-glass apparatus and the middle third fraction of

the distillate, after dilution with distilled water to an acid con­

centration of 5.7 M» was stored in a Vycor flask. The acid concen­

tration was ascertained from the measured density and the titer, as

determined by potentiometric titration of a weighed amount of the acid

with standard sodium hydroxide. Standard solutions containing 1 M

and 0.2 M hydrochloric acid per liter were prepared by dilution of 145

■weighed amounts of the purified acid with distilled water-, The acid concentration YJas checked by titration against Mallinckrodt primary standard sodium carbonate using methyl red indicator-, A similar procedure was used to prepare hydrochloric acid solutions from reagent- grade acid e

Solutions containing hydrochloric and perchloric acid at unit ionic strength were prepared by volumetric dilution of the respective standard acid solutions * assuming no volume change on mixing ®

Sodium chloride solutions. Reagent-grade sodium chloride was 48 purified according to the procedure of Pinching and Bates®

(48) G« D. Pinching and R. G® Bates, J. Res® Nat® Bur® Std®, 32, 311 (1946)®

Spectrographic analysis and spectrophotometric measurements of an aqueous saturated solution revealed that small quantities of silica were present® The chloride concentration x»ras determined gravimetri-

cally by precipitation with silver nitrate® Standard sodium chloride

solutions were prepared from weighed amounts of the purified salt®

Spectrophotometric studies

Five series of solutions containing from 0»217 to 7®23 mM

palladium (II) and from zero to 9»2 M hydrochloric acid were pre­

pared for the determination of the stability constants of the

palladium-chloride system. Solutions having less than 0®7 M hydro­

chloric acid vjere prepared by volume from standard palladium

perchlorate solution No. 17, 1.003 M perchloric acid, and solutions 146 containing X M hydrochloric acid or sodium chloride and (1 - X) M perchloric acid. For chloride concentrations from 0.7 to 4 M* pre­ determined weights of 6.310 M hydrochloric (double distilled) or

6.032 M hydrochloric acid were added to aliquots of the palladium perchlorate solution and then the solutions were diluted to the

required volume with distilled water; solutions having greater than

4 M hydrochloric acid were prepared in a similar manner from 12.4 M

reagent-grade acid.

The absorbance of 236 solutions was measured in 1> 5s or 10 cm.

cells at about 40 selected wavelengths in the 320 to 600 dim- wavelength o region at 25 C« against a reference solution containing everything

but palladium. The techniques used are described in Chapter I9 page 38

The effect of chloride concentration on the absorbance of 4»35»

0.869j and 0.218 mM palladium (II) solutions in the 320 to 550 mp

region is shown in Figures 11s 12» and 13o

series a shift in the wavelength of maximum absorption to higher wave­

lengths (bathochromic shift) with a corresponding increase in the

intensity of absorption at the maximum (hyperchromic shift) occurred

as the chloride concentration was increased until a limiting value

in the 423 mp region was reached. Further addition of chloride produced

s. decrease in the intensity of absorption at the maximum (hypochromic

shift) and a further increase in the wavelength of maximum absorption

to a limiting x-ravelength of 474 mp. An isosbestic was observed at

466 mp (e = 156*7) for solutions containing from 0.05 to 2 M chloride*

The absence of any isosbestic point before that at 466 mp indicated

that for smaller chloride concentrations at least three different FIGURE 11

EFFECT OF CHLORIDE CONCENTRATION ON THE ABSORBANCE OF 4,35 MILLIKOLAR PALLADIUM (II)-PERCHLORATE SOLUTIONS*

C u r v e SC 1 m M L “ 1 1 0 ,0 0 0 2 0,864 3 2 ,1 5 8 4 3 ,0 2 2 5 4,316 6 5 ,1 8 0 7 6,474 8 8 0638 9 10,79 10 12,95 11 1 5 ,1 1 12 19»97 13 29,96 14 39,97 15 49,89 16 6 9 ,8 5 17 99,76 18 200 ,4 19 399,3 20 1027 . 21 9 ,2 0 x 105

*A11 solutions contain 4,35^0,01 mM palladium (Ii) and loOO M hydrogen ion .900

.800

.700 -

.600

.500

.400 -

.300

.200

.100

300 325 350 375

Wavelength (mjj,)

Figure ii FIGURE 12

EFFECT OF CHLORIDE CONCENTRATION ON THE ABSORBANCE OF O 0 8 6 9 KILLIMOLAR PALLADIUM (II)-PERGHLORATE SOLUTIONS-

Curve ECl^-l

1 0 o000 2 01729 3 »3500 4 O6o47 5 0863 6 1-295 7 1-729 8 2-159 9 3-024 10 4*157 11 8 o004 12 15-98 13 24*02 14 32*02 15 59-9 16 99-9 17 199-9 18 599-7

*A11 solutions contain 0o869±0o001 mM palladium (II) and loOO M hydrogen ion

149 .200 .000 .300 Absorbance .400 - 0 0 5 IOOO p .100 .800 .900 .600 .700 300 Figurs 12 325 350 375 425 0 0 4 aeegh m/i.) (m Wavelength 450 475 500 FIGURE 13

EFFECT OF CHLORIDE CONCENTRATION ON THE ABSORBANCE OF 0©218 MILLIMOLAR PALLADIUM (II)-PERCHLORATE SOLUTIONS*

Curve 3-aiML"

1 0*000 2 ©04868; 3 0IO8O 4 o2l6l 5 8 32^3 6 <,4321 7 ©6479 8 08646 9 1 o296 10 1 ©947 11 3*023 12 lOoOO 13 2 0 o32 14 30©41 15 40©63 16 79©89 17 120 ©2 18 239©9 19 498*8

*A11 solutions contained 0 ©218 mM palladium and loOO M hydrogen ion

151 .000 .050 Absorbance .200 . .300 .250 .350 .150 10 .400 .500 450 ! 0 2 400 325 300 iu e 13Figure 350 375 Wavelength Wavelength (mpj) 450425 475 500 no oi 153 palladium species were present in significant concentrations«

In order to compare the absorbances for different concentrations and different cell lengths *» the experimental absorbance was corrected to that which would be obtained in a 1 cm. cell if the palladium (II) concentration were exactly 4.35 mM. This normalized absorbance?

A° = .00435 Ij was used so that the change in n and (Cl ) produced by a given experimental error in the observed absorbance could be more readily calculated.

A° was calculated for each of the four series as a function of the mole ratio of chloride to palladium and plotted on large size graph paper with a smooth curve drawn through the points. A series of corresponding solutions plots in the 3&0 to 440 mu. wavelength region revealed that the change in absorbance produced by dilution was greatest in the 420 to 430 mp. region. Therefore? most of the calculations of n and (Cl”) were made from data in this wavelength region. A mole ratio plot for solutions containing 4.35 palladium

(II) showed three distinct breaks at ratios of 1? 2 3 and 3 which indicated that e^e-^eg^e^s a necessary condition for the inter­ pretation of the data by the method of corresponding solutions.

Figure 14 shows a corresponding solutions plot at 430 mp for solutions containing 7.23? ^°35s 0.870? 0.435? and 0.218 mM palladium

(II) and from zero to 0 .5 mole ratios of chloride to palladium. The extremely small difference in the curve for solutions containing 7 .2 3 and 4.35 nM palladium illustrates the small degree of dissociation of

PdCl+. Figures 15 and 16 are continuations of the corresponding solu­

tions plot at 430 mp for the four series of solutions containing FIGURE lb

MOLE RATIO CURVES FOR THE PALLADIUM (II)-CHLORIDE SYSTEM IN THE ZERO TO 0.5 MOLE RATIO RANGE AT k-30 mM,

Curve S P d m M

1. 7.23

2 **•35

3 ■ 0 .8 7 0

b •^35

5 *218

15^ .000 .100 .200 .300 400 .500

I C | _ I P d

Figure 14 FIGURE 15

MOLE RATIO CURVES FOR THE PALLADIUM (II)-CHLORIDE SYSTEM IN THE ZERO TO 1.2 MOLE RATIO RANGE AT 430 Bp

Curve sPdmM 1 ^*35

2 0.870

3 .435

4 «218

156 Absorbance .300 .500 .200 .400 .600 .700 Figure .000 15 .200 40.600 .400 Z Pd ICI_ .800 1.000

1.200 157 FIGURE 16

MOLE RATIO CURVES FOR THE PALLADIUM (II)-CHLORIDE SYSTEM IN THE ZERO TO 10 c 5 MOLE RATIO RANGE AT 430 mp.

Curve 2PdmM

1 4 <>35

2 0,870

3 ,435

4 ,218

158 .200 A bsorbance 1.000 .600 .400 .800 1.200 0.00 Figure 16 1.00 3.00 4.00 5.00 Y Pd 6.00 7.00 8.00 9.00

10.00 159 l6o

4.35* 0.870» 0.435 and 0.218 mM palladium (II), respectively. The decrease in slope of these curves with decreasing palladium concen­ tration illustrates the increasing extent of dissociation as additional chloride is bound to the palladium.

Corresponding solutions were selected by graphical interpolation from these plots and values of n and (Cl“) for each of the six pairs of solutions were then calculated by algebraic solution of equations similar to (19) and (20)o Values of n and pCl obtained from corres­ ponding solutions having the following palladium (II) concentrations were used to construct formation curves for the systems (l) 4.35 and 0.870 mM, (2) 4.35 and 0.435 mM, (3) 4«35 and 0.218 mM, and (4)

O.87O and 0.218 mM® The maximum deviation of pCl for combinations

(2) and (3 ) at 430 mp in the n range from 0 .6 0 to I .50 was 0.1 unit

at n = 0.95® At lower values of n, (2) indicated a greater degree

of dissociation in the system than did (1), (3), or (4). Since there

appeared to be no other systematic deviations in the formation curves

below n = 1.8, values of Cq-^ were plotted against Cp^ and values for

K and (Cl"”) were determined from the best straight lines drawn through

each set of points. The results of these calculations at 410, 420,

430? and 440 mp are presented in Table 27 and Figure 17. Jorgensen*s

modification of the meuhod of corresponding solutions was used to ob­

tain the limiting value of n in the palladium (II.)-chloride system.

Corresponding solutions were obtained by interpolation on a plot of

A0 versus Eel" at 430 mp (Figure 18) for solutions containing 4.35

and 0.870 mM palladium and from 0.059 to 0.127 M chloride. A plot 1 6 1 TABLE 27

DA.?A. FOR. THE FORMATION CURVE OF THE PALLADIUM (II)-CHLORIDE SYSTEM BY BJERRUM’S METHOD OF CORRESPONDING SOLUTIONS

AjirijJ. A° n PCI

440 Os 285 0*377 4*633 o315 *470 4*490 *483 *968 3*860 0696 1*566 3-271 .774 I 0820 3*001 *800 1*920 2*915 430 o250 *117 5-198 =2825 .198 4*955 03195 *296 4*814 o357 *395 4*686 o374 *438 4*611 -395 *496 4.488 *420 *546 4*43 .440 *609 4*334 *4?2 *685 4*216 o503 *793 4*100 o531 *828 4*009 s585 *966 3.851 0607 1*024 3.804 ,630 1*092 3-758 0655 1*148 3*684 0689 1*246 3*602 *720 1*326 3*504 *742 1*380 3*448 »?68 1*449 3 0 5 8 o820 1*6075 3*220 0851 1*710 3*126 0865 1-763 3*0805 0882 1*827 3 .OI32 420 *300 *107 5*270 ,338 *191 5.0 2 8 €.4625 *487 4*508 <.4905 °537 4.412 *520 *616 4*319 *7325 1*1485 3*716 *844 1*493 3-374 *919 1.790 3*063 *941 1*914 2*938 410 *382 *194 5*081 *4655 *381 4*700 *577 *648 4.144 ®?53 1*118 3-747 *822 1*409 3*454 *980 1*798 3.0 5 6 FIGURE 1?

THEORETICAL FORMATION CURVES OF THE PALLADIUM (II)-CHLORIDE SYSTEM FOR n VALUES FROM ZERO TO 2®0 AND EXPERIMENTAL VALUES OF n AT VARIOUS WAVELENGTHS

162 163

zooo 2.0x 10^ 4.1 xIO7, 1.00x10',0 2.40x10" 2.4x 104 5.0xl07 I.IOxlO10 2.64x10" 2.8xl04 5.7xIO7 I.25xl010 3.00x10"

° 410 m u x . 42 0 mjo. o 430mj4. A 4 4 0 mju, 1.000

0.500

0.000 3.0 3.5 4.0 4.5 5.0 pci Figure 17 FIGURE 18

ABSORBANCE vs, CHLORIDE CONCENTRATION FOR 4.35 AND 0.080 MILLIMOLAR PALLADIUM (II) PERCHLORATE SOLUTIONS AT 430 mil

Curve S PdmM ^scm 1 4.35 1.000 2 0.870 5.00

164 Absorbanoe .200 .300 .500 400 .600 1.000 .800 .700 .900 0.00 iue 18 Figure 005 ^fCI)rn/L 010 015

0.20 165 1 6 6

G-J against Cjvf’^ according to equation (23) gave an average

' W x as shorn in Figure 19® Consistent values of n and (Cl“ ) in the n region above 1.8 could not be obtained for this sy±em by the method of corresponding solutions because of the relatively small change in A° with G j J for the more dilute solutions. The formation curve could have been extended to higher values of n by increasing C^j however, in the present investi­ gation Cjyi was limited by the intensity of absorption which could be accurately measured using the cells available. This data was sufficient to calculate good values for Kj_, K^, e-j_, e£, and preliminary values for K-j and e^o It will be shown that reliable values could be obtained for the addition of the terminal chloride ion as well as values for ejj and by the slope-intercept method. It will also be shown that all of the data could be accounted for by assigning the value of 4 to No

The presence of an isosbestic at 466 mp. at chloride concentra­ tions in the 0.2 to 1.0 M range, the limiting value of n = 4, and the relatively small change in absorbance with increasing chloride con­ centration in this region indicated that the value of was suffici­ ently small so that a slope-intercept method could be employed for its

eva3.uation. Data obtained for the meet concentrated solutions of

palladium (II) (4»35 M) whose absorbances passed through the isosbestic

point were used for these calculations. The absorbance of palladium

(II) in chloride solutions, as illustrated in Table 28 and Figure 20

did not attain a constant value at high chloride concentrations.

However, preliminary values of were calculated at 410, 420, 430,

440, and 450 mp. from the minimum values of e in the 1 to 4 M chloride FIGURE 19

SLOPE-INTERCEPT PLOT OF CORRESPONDING SOLUTIONS FOR ESTIMATION OF THE MAXIMUM COORDINATION NUMBER OF PALLADIUM

1 6 7 14 0

120

100

80

60

40j

20

0 100 500 1500 2000

Figure 19 168 TABLE 28

CHANGE IN ABSORBANCE OF PALLADIUM (II) PERCHLORATE WITH CHLORIDE CONCENTRATION AT SELECTED WAVELENGTHS*

EPd~4e35 ^ T=25°Cc. loOOO cm. cell length

Agiap. 360 380 440 466 520 474 (hciojj,) m c i A° A° A° A° A° A°

1 0«96 0«0499 0 .4 4 5 3 0.1923 0.?41 0.2279 a > 0 3 3 S » 2 o92 .07984 .4884 .1705 o6797 0.683 o2444 QUO 3 o90 .0999 .5054. .1611 .6438 .682 o250? c » a a -e 3 > 4 .89 .1 2 0 1 .5145 .1534 062O8 0682 .2597 d a t a 5 .87 ol399 .5245 .1496 .6 0 5 2 .683 o2597 6 .81 .1999 .550 .1424 .5 6 7 6 0682 o2?03 e u s e i FT# t ®6l .3993 .5796 .1323 .5213 .6 8 3 .2838 1 9 0 a 8 .5 1 .499 .5807 .1303 e>5102 .6 8 3 0 2348 e a e = » « » 9 .41 .599 .5872, .1293 .5032 .683 .2 8 8 3 0.6974 10 o31 0698 .5932 .1288 • 5012 .683 .2883 .701 11 .2 5 2 .797 — .1 2 8 0 .496 «682 .2871 .6 9 8 8 12 .252 1.002 .5924 ol270 .4895 .6 8 2 .2 8 7 1 06998 13 .252 1 .0 2 ? .5929 .1270 <>4900 .6 8 2 ©2876 .6998 11* .2 5 2 1 .496 .5899 .1240 .4819 .684 .2881 .7018 15 .252 1.997 .5924 .1230 .4799 ®686 .2876 .7 0 3 8 16 .252 2.998 .5848 .1225 o4S14 .690 .2376 ©7078 17 .2 5 2 3.995 o576? .1205 .4829 .693 ©2878 .7108 18 .2 5 2 3 .8 8 8 .5758 .1205 o4839 o694 .2846 o?X0S 19 .2 5 2 4 .6 2 .5708 .1210 .4369 0695 .2841 .7113 20 .252 9.2 .5336 .1 2 2 .5100 .720 *2846 o7344

‘'Absorbance values are given to the fourth decimal place although the limit of accuracy is probably 1 in the third decimal place FIGURE 20

ABSORBANCE vs. CHLORIDE CONCENTRATION FOR THE PALLADIUM (II)-CHLORIDE SYSTEM. AT SELECTED WAVELENGTHS

170 Absorbance .0 0.300 0.500 0.400 0.600 .5 0.350 0.550 0.450 0.650 0.700 0.750 0.800 0.0 Figure 20 1.0 2.0 3.0 . 5.0 4.0 d I M/L 6.0 7.0 8.0 6 m jx 466 6 mju, 360 2 mju, 520 9.0 10.0 0.250 0.200 0.400 0.450 0.500

soubqjosqv 172 ranges The validity of Beer's law for solutions containing from

19«30 to 0.922 xnM palladium (II) in 1.00 M hydrochloric acid (Table 293 shows that the palladium is present in these solutions largely as the tetrachloropalladate (II) ion. Preliminary values of (Cl”) were cal- 2- culated with the assumption that only PdCl^ existed in the solutions.

Using the equation

(A° - B^)(cr>K^ = E3 - A°9 (35)

(A° *>■ E^)(G1‘") was plotted on the Y axis against A° along the X axis.

The negative reciprocal of the slope was equal to the X intercept was equal to E^$ and the Y intercept multiplied by was also equal to Data for the determination of at 410 mu by this method are given in Table 30« The linearity of the function was somewhat sensi­ tive to the values of used* as is illustrated in Figure 21„ That an incorrect value of should produce a curved lines especially for A° values approaching E^s might be anticipated. Since slight curvatures in opposite directions were detected for E^ values of 0.221 and 0.223> their mean 0.222 was considered the optimum value. This

corresponds to e. = 51 M^'cm^ . The Y intercept was equal to H r 0.0327 and the X intercept (not shown) was equal to 0.875s yielding

a value of 26 for and 201 if^cm for e^o Data obtained at several

wavelengths in this manner after successive corrections for bound

chloride (equation 3^) are summarized in Table 31 ° An average value

of 24YL was calculated from data in the 420 to 450 my. wavelength

region. 173 TABLE 29

MOLAR ABSORPTIVITY OF PALLADIUM (II) IN 1 MOLAR HYDROCHLORIC ACID5 VALIDITY OF BEER6S LAW

£HC1=1„00 M T=25°Co

Std s Soln s 19 19 19 13 13 13 irPd x io3 1 9 .3 0 3 .8 6 3 0.7733 3.84 0,9606 0.1922 (HC104 ) 0.00 0 .0 0 0.00 0.204 0.204 0.204 0.104 ( 0 .9 9 7 (5 »oo (0.997 (5.00 (10.00 8s>cin ( 0.500 (2.0 0 (O.5OO (2.00 ( 5 .0 0

A.§iri4 6 e 0 e e e

320 726 732 728 734 330 556 563 562 565 560 562 340 452 455 456 458 454 457 330 283.4 284.1 28 6 .5 285 285 286.4 360 134.8 134.4 13 6 .5 135 135 138.0 370 5 6 .2 55 °8 57.0 5 6 .7 57-0 57*9 380 29.4 2 9 .I 29.7 29.4 29-3 3 0 .2 385 26,65 2 6 .5 2 6 ,8 2606 2 6 .7 27-6 390 27.9 28.0 28.2 27.9 28.0 2.8.6 400 39-9 39.8 39.5 3 9 0 39-5 40 o2 410 57.1 56.9 56 .9 5 6 .5 56.4 56.7 4l6 6 7 .5 67.7 6 7 .8 6 7 .5 6 7 .1 6 7 .6 420 75.0 75.1 75-2 74.7 74.4 74.9 426 8 6 .7 86.2 86.4 86.0 85.5 86.4 430 94.6 93-9 94.0 93.6 94.2 A40 114.1 113.4 113.5 112.9 112.4 112.9 450 133-9 132.3 132.1 132.2 131.6 133-4 460 1 5 0 .2 149.8 1 5 0 o0 149.7 149.2 149.6 466 158.9 156.7 157.0 156.7 155-9 157.1 470 159 e 7 160.0 159.8 159.4 159.2 159.7 474 1 6 0 .3 1 6 0 .5 1 6 0 .3 1 6 0 .0 1 6 0 .3 1 6 0.5 480 157.4 158.0 157.8 158.0 157-5 1 5 8 .2 490 14-3.5 144.4 144.6 144.2 144.2 145,1 500 119.6 119.6 120.2 120.3 120.? 121.5 520 6 5 .0 6506 65.9 66.0 6 6 .0 66.1 540 28.5 2 8 .5 28.6 28.7 29-1 28.6 560 14.3 14.4 14.2 14.2 14 ;o 13.9 580 10 ol 10.2 10.1 10.1 10.2 9-7 600 8.6 8.7 8.6 8 .7 8.4 7 .6 174-

TABLE 30

DATA FOR THE CALCULATION OF AT 410 m BY THE SLOPE-INTERCEPT METHOD

SPd=4o35 mM T=25°Co 1.000 cm. cell length

(A°-E^)(Cl~) (A°t % ) ( C 1 “) k° SCI (Cl“ ) A°=0.223 A°=0.221

0 .4217 0 o0999 0o0839 O.I67 0.168

.3931 ol201 .1039 .177 .179

o3721 .1399 .1236 .184 .187

.3320 .1990 .1824 .199 .202

°2959 .2993 .2824 .206 .212

.2923 ®3999 .3829 .227 .235

,,2682 .499 .482 .218 .22?

.2606 *599 .582 .219 .230

o2556 •698 .681 .222 .236

.2507 .797 .780 .216 .232 FIGURE 21

SLOFE-INTERCEPT PLOT OF THE PALLADIUM (II)-CHLORIDE SYSTEM AT 410 k m -? DETERMINATION OF

175 410 mu,

.0 2 0 -

^ E4>CI

.010 G-E40 221

.005 a-E4=223

.001 - -J 1 I L- i i i -i------1—----1------1------1------1------1____L ___I____I____I____I____I_____I____I____I____L 100 200 3 0 0 4 0 0 500 6 0 0

Figure 21 176 /

TABLE 31

EVALUATION OF % AT VARIOUS WAVELENGTHS USING THE 3LQPMNTERCEPT MEUiOD

Z P d ^ o 3 5 raM 2 (Cl + C10^)=lo00 U T=25°C.

Agmtj. V u T 1 ® 3 9i'r1cm”3-

420 68 *? 24*8 227*9

430 8? 06 24*3 24104

440 108.5 24.2 230.9

450 1 2 9 «7 22.9 200.0 178

In order to illustrate the dependence of e^ on equation (35) was rearranged to give

A° (36)

Assuming 10 values of from 6 to 70 s the free ligand concentration was calculated according to equation (32). The quantity on the left- hand side of equation (3 6) was then calculated from the observed absorbance of the eleven solutions at 4-00, 420, 430, and 4-50 mM- and plotted against l/K^(Cl”)j as illustrated in Figure 22 for 400 m|J.

The values of corresponding to a of 24 which were obtained by interpolation from Figure 23 are in good agreement with the values of e j calculated from plots similar to Figure 21. and those which were 4 3 calculated from the stability constants K]_ = 2.4 x 10 , K£ = 2<>2 x 10^, 2 1 K-j = 2.2 x 10 , = 2.4 x 10 , and the molar absorptivities of solu­ tions containing 4.35 palladium at n values of 0.488, 0 .6 8 1, 0 .963*

1.404, 1.781, 3*244, 3*488, and 3*960. The values of calculated

from the Y intercepts of plots similar to Figure 22 using a value of

24 for ( T a b l e 32) a r e j_n good agreement with the values of e^

obtained from plots similar to Figure 21 and the values which were

calculated from the stability constants 8-j_ = 2.4 x 10^, 82 “ 5*0 x 10?*

83 = 1 .1 0 x 1010, 8^ = 2.64 x 1011j and the molar absorptivities of

solutions containing 4®35 palladium at n values of 0.488, 0.681*

0.963* 1.404, 1.781, 3.244, 3.488, and 3 *9 6 0 .

The remaining stability constants K-^, I^* and Kj were calculated

by substitution of 11 and (Cl ) values found by Bjerrum’s correspond­

ing solution method in equation (14-). The value of = 24 was FIGURE 22

SLOPE-INTERCEPT PLOT AT 400 mu FOR THE CALCULATION OF e~ AT VARIOUS ASSUMED VALUES OF *

179 180

.7 0 0 -

.600

.5 0 0 -

(A°+A°)

.400

.300

.2 0 0 -

.1401 20 30 40 50 Figure 22 FIGURE 23

CHANGE IN THE CALCULATED MOLAR ABSORPTIVITY OF THE TRICHLORO- PALLADATE (II) ION WITH VARIOUS ASSUMED VALUES OF K,;_

181 400

350 -

300

250

200

El

40 50 60 70 182 K4

Figure 23 183 TABLE 32

CHANGE IN CALCULATED MOLAR ABSORPTIVITIES OF THE TRI- CHLOROPALLADATE (II) ION WITH VARIOUS ASSUMED VALUES OF

£Pd=4o35 mil S (C1 + 010^)=! o00 M T=25°C*

A smiJ» k4 e4

400 6 3 4 o0 71 *3 20 34=9 123 °7 24 35 136* 25 35 «4 139 o7 30 35 o9 156 35 36 cO 172 40 3602 187 46 35 »9 20? 50 3605 215 60 3602 247 70 3608 273

420 6 62*5 137 20 6 8 .3 208 24 69 221* 25 69 03 227 30 69 *9 256 35 70 ol 270 40 70 08 291 46 70 ol 319 50 71°5 328 60 70 08 383 70 7 1 0? 433

430 6 80 o9 154 20 88 »3 214 24 88 2 3 6* 25 87<»7 244 30 8 9 .O 261 35 88 05 291 40 88*5 310 46 89 o? 336 50 89*7 360 60 89*7 395 70 90o2 438 184

TABLE 32 (Contdc)

Ajinp. K4 e4 e3

6 1 2 8o 7 159 20 129.5 194 24 130 202* 25 130 204 30 1 3 0 .7 211 35 130.5 228 40 13 1 .0 235 46 1 3 0 .8 249 50 13 1 .0 252 60 13 1 .0 279 70 13 1 .0 297

^Obtained b y interpolation from Figure included as a known quantity* Preliminary constants were refined by successive approximation. The limits of error in the stability con­ stants were determined graphically by comparison of the experimental formation curve with a series of formation curves calculated from different sets of stability constants * as illustrated in Figure 17®

In order to relate errors in the stability constants to the experi­ mentally measured variable Aj equation (25) was used to calculate the change in free chloride concentration produced by an error of 0*002 units in the absorbance at various regions of the mole ratio curves*

The results of these calculations a> given in Table 33 * Using these values for a(Cl“)9 the values for (PdCl^~n)s (Pd2*)s and (Cl") which were calculated from the stability constants at n = 0*^88» l*h045 and

1*781j the corresponding (Anal*) was obtained by substitution into equation (28) o These values are given with the stability con­ stants found for the system in Table 3^ 9 and demonstrate that for the palladium-chloride system Bjerrurn's method of corresponding solu­ tions can be used to calculate values of Ki greater than 5 times the reciprocal of the largest concentration of metal ion used* Theoretical mole ratio curves were constructed for 4-*35 and 0*218 mM palladium (II) solutions using various assumed values of and the molar absorptivity values calculated for the pure species. The corresponding solutions plots at mia. indicated a value of 10-^ was the largest value of which could be calculated for this system using Bjerrum8s corresponding solution methodo

The distribution of the various palladium chloride species for solutions containing b«35 mM palladium (II) as functions of the mole TABLE 33

MAXIMUM ERROR IN FREE CHLORIDE CONCENTRATION PRODUCED BY AN ERROR OF 0.002 UNITS IN ABSORBANCE AT VARIOUS REGIONS OF THE MOLE RATIO CURVES

Range ECl/DPd 0 to 0.1 1 .2 to 1 .5 1.7 to 2.0

Pdn1 Pdp 2 W i Pd2 a (or)* A(Cl")* A(Cl")* A Pd

(1 ) 0 .00435 0.000870 1.088 x 101"3 1.126 x 10"5 1.537 x 10"5 2.353 x 10"-5

(2 ) .00435 9000435 4.833 x 10"^ 5.132 x 10“6 7 .3^ x 10"6 1.000 x 10"5

(3) o00435 .0002175 2.289 x 10"^ 4.023 x 10~6 6.832 x 10~6 7.684 x 10”6

(4) .000870 .000435 8.700 x 10"^ 9.492 x 10"6 1.504 x 10"5 1.989 x 10"5

(5) .000870 .0002175 2.900 x 10“^ 5.179 X 1 0 ~ 6 9.261 x 10-6 I .036 x 10“5

(6) .000435 .0002175 4.350 x 10"4 7.887 x 10"6 1.435 x 10"5 1.515 x 10"-5

* Calculated from equation (25) using Aa =0o002 and values for S^ and S~ obtained from the mole i?atio curves at 430 miJ. IS? TABLE- 34

STABILITY CONSTANTS FOR THE PALLADIUM (II) CHLORIDE SYSTEM WITH ERRORS ESTIMATED BY GRAPHICAL AND BY ANALYTICAL METHODS

n region V (Graph) & £ PltisOl 0 ^ 1 2.4 x 10^ ±0.4 x 10* ±0.4 x 10^ 0.488

2 2.2 x 103 ±0.2 x lO^ ±0.04 x io3 1.404

3 2.2 x 102 -0o2 x 102 ±0 *02 x 102 1.781

4 2.4 x 101 ±0.2 x 101

rThese values correspond to the following values for the overall complexity constants; £-,=204x10^5 P?=5 «OxlO^; $3=!.10x10^-°; and (3^-2. 64xl0±^ 188 ratio of chloride to palladium (II) and total chloride is given in

Table 35 and presented in Figures 24 and 25 » respectivelyo

The molar absorptivity of the complexes at eighteen wavelengths in the 3^0 to 460 trp region was calculated in the follovdng manner:

The composition of solutions containing 4*35 palladium (II) at values of n = 0.488* 0.681* 0.963* 1«404» 1.781* 3.244* 3.448* and

3<,960 was calculated from the stability constants; then these values and the observed absorbance were substituted into a series of simul­ taneous equations similar to equation (22) and the series solved algebraically for e^s and e^ by the method of determinants©

The values so obtained are given in Table 3.6 and plotted in Figure 2 6 .

The molar absorptivity curves for PdCl+ and P d C ^ are also plotted in Figure 27* curves 1 and 6 * respectively.

In Table 37 the values for e^ calculated by the foregoing pro­ cedure are compared with the observed molar absorptivities at n = 1 and with the values calculated for solutions at low mole ratios of chloride to palladium* assuming complete conversion to.the mono- chloropalladium (II) ion. This comparison is shown graphically in

curves 1* 2* and 4 of Figure 27 « These curves indicate (a) there

is some dissociation of PdCl+ and formation of higher complexes whose molar absorptivities are larger than those of PdCl+ at wavelengths

greater than 400 even at mole ratios of chloride to palladium

of 0.2 in 4o35 roM palladium (II) solutions and (b) that considerably

more dissociation of PdCl+j accompanied by an increase in the con­

centration of complexes such as PdC^s occurs as the chloride to

palladium ratio was increased to 1.0o 169 TABLE 35 DISTRIBUTION OF PALLADIUM (II)-CHLORIDE COMPLEXES AS A FUNCTION OF -LOG £01 AND MOLE RATIO OF CHLORIDE TO PALLADIUM*

■£Pd«ir.35 mm E (01+010^)=!*00 M T=25°Co

ECl/EPd -LogSCl $ Pd2+ $ PdCl+ $ PdCl2 $ PdCl” % PdClJ”

0*0238 3.989 97.65 2.344 0 .0 0 5 M l — .0466 3*693 95*40 4.579 o*D19 .-- .0680 3.525 93*24 6.714 .042 *1104 3.319 89.19 10.70 .112 --- .1678 3*137 8 3 .6 7 I60O6 .268 ~ ~ ~ .203 3 .0 5 4 80*32 19.28 *402 ----- *282 2.911 72.92 2 6 .2 5 .804 *351 2.816 6 6 .6 1 32.00 1*333 --- — *496 2.666 54.15 42.88 2.948 0.021 --- - 0694 2 .5 2 0 38.80 54.48 6 .6 3 9 .085 _• --- *901 2.407 25.57 61.37 12.78 .281 0=001 *992 2.365 20.82 62.46 16*27 *447 .001 1.195 2*284 12.68 60*85 25-35 1.116 .005 1.489 2.189 5.785 51*37 39*60 3*223 *029 1.785 2.110 2.515 38.62 51*50 7*251 .111 1.993 2 .0 6 2 1.403 30*30 5 6 .8 1 11.25 *243 2.353 1.990 0*532 19*14 59*82 19*74 *711 2*596 1.947 .293 14.07 58.61 25*79 1.238 3 .0 0 6 1.884 *119 8.557 53*48 35*30 2*542 3.693 1.794 *034 4.122 42*94 4-7*24 5*668 4*004 1*759 .021 3*088 38.60 50=95 7*337 4*306 1.727 *014 2.395 34.92 5 3 .7 8 9*034 4.591 1.700 *010 1.900 3 1 .6 6 55*73 10*70 5*148 1.649 .005 1.271 26.48 58*26 13*98 8 .7 3 2 1.420 ------0*214 10.715 56*52 32 .5 6 11.40 1.304 .093 6 .5 8 7 50*72 42.60 13.79 1.222 ------*049 4.629 4 5 .8 3 49 *49 16.16 1.153 ------.030 3*439 41*61 54*92 22.95 1.001 —— *010 1 .7 6 2 3 2 .6 0 65 *66 27.61 0.921 *006 1*235 28.25 70*51 31.78 *859 -« --- .004 0.940 25*22 7 3 .8 4 49*80 o664 .001 *390 17*17 82.44 72.84 .499 — ------.184 12.17 87* 67 91.72 *399 .11? 9*823 90 *06 114*7 *302 ------*750 7-951 91*97 141.9 .206 ------— .049 6.490 93*46 187*9 .088 ------.028 4.9 4 9 95*02 210*9 .037 ---- - .022 4.424 95*55 233*8 -.007 ------.018 3*999 95*98 46*3*8 -.695 .005 2.041 97*96

^Accuracy probably limited to three significant figures FIGURE 24

DISTRIBUTION OF PALLADIUM (II) CHLORIDE COMPLEXES AS A FUNCTION OF THE MOLE RATIO OF CHLORIDE TO PALLADIUM

190 ( PdCIn) EPd .000 .200 .400 1.000 600 .800 00 0 iue 4 2 Figure 0.50 1.00 .025 3.00 2.50 1.50 EPd ECI. 2.00 3.50 4.00 FIGURE 25

DISTRIBUTION OF PALLADIUM (II) CHLORIDE COMPLEXES AS A FUNCTION OF TOTAL CHLORIDE CONCENTRATION

192 (PdCI„)

i P d 1.000 .000 .400 .800 .600 .03.50 4.00 iue 25 Figure 3.00 2.00 lg Cl E log - 1.50 1.00 0.50

0.00 193 194

TABLE 36

MOLAR ABSORPTIVITY OF PALLADIUM (II) CHLORIDE COMPLEXES IN THE 36 0 TO 5 6 0 mix WAVELENGTH REGION *+

ePdCl+ ePdCl2 ePdCl“ ePdCl^“

360 55-9 30 .5 83 134.3 370 87 50 46 56 380 122 84.? 53 28.4 390 151 ®6 132 84 25 40Q 171 o4 184 132 35.8 410 173 225 180 52 420 158o9 243 217 69.4 430 136 233*5 232.8 8 8 .6 440 109.5 205.5 226 108.6 450 85 169 204 130 460 6 2 ,3 134 177 149 4?0 4 5 .2 1 0 1 .8 150.5 159 480 32.5 76.4 126.3 159 490 22.5 58 103 145.7 500 18 ®2 39.5 8I .5 121 520 12.4 21 .1 45 66 540 1 0 .6 13*4 22.6 29 560 9 11 15 14 ^Deviations in the molar absorptivity for the various species ares PdCl+ j PdClg* PdCl^“ j tl unit; PdCl^* *2 units®

^The data are presented in Figure 26 the numbers above the curves indicate the value of (n+1) in PdCl£j”n . FIGURE 26

MOLAR ABSORPTIVITY OF PALLADIUM (II) CHLORIDE COMPLEXES vs. WAVELENGTH

Curve Species „ 24- 1 Pd

2 PdCl+

3 PdCl2 PdCl^

5 PdClJ

195 sOo

■9ot FIGURE 27*

MOLAR ABSORPTIVITY OF PdCI+ AND PdClg CALCULATED BY VARIOUS METHODS

~ ’ " Curve numbers refer to column numbers in Tables 37 and 38

197 198

225

200

175

ISO

100

75

50

25

350 400 500 Wavelength, m/j. Figure 2 7 199

TABLE 37

COMPARISON OF THE MOLAR ABSORPTIVITY OF THE MOKOCHLOROPALLADIUM (II) ION OBTAINED BY VARIOUS METHODS

Method* 1 2 3 4 5 SPd 0.00435 0.00435 0.00723 0o00434 0.000865 SCl/sPd 0 to 230 0«99 0 to 0.1798 0 to 0.200 0 to 0.200 aei / a M ±1 +0.23 +0.86 +1.15 +I0I5 \jrny. el el el el el

340 29.8 18.9 19.3 19*0 350 --- 37.5 31.5 33°2 36.6 360 55 »9 5^-7 55.6 55 o9 59.9 370 87 79.6 8 5 .4 8 6 .2 89.4 380 122 107.4 118.6 120.2 122.6 390 15106 133 146.7 149.3 152.0 400 171.4 152.9 168.7 167.2 166.7 410 173 159.7 172.4 167.9 420. 159 152.0 158.8 1 5 8.O -- 430 136 134.1 137*2 137.2 134.3 440 109.5 110.1 109.0 109.4 109*4 450 85 86.1 86.2 85 08 84.1 460 62*3 6 5 .2 6 3 .4 64.0 6 3 .4 470 4 5 .2 47.7 47.6 46.4 480 32.5 34.6 32.7 33.7 3606 490 2 2 .5 25.7 24.2 25.3 25 *5 500 18.2 19.0 18.7 18.5 19.7 520 12.4 12.4 12.4 13«5 14.4 540 10.6 9*6 10.4 12.2 11.8 560 9 7 .8 8.8 9.2 11.2

* 1 Calculated using K-, =2.4x10^5 K?=2.2xlo3s K =2.2x10^ and 1^=2. .4X101 ' J 2 Observed molar absorptivity 3 Weighted mean calculated from solutions having Scl/SPd 0 to O o1196j 0 to 0.0599s and 0 to 0.1798 assuming only Pd and PdGl+ to be present in these solutions» and PdCl= SCI 4 Calculated as in 3 5 Calculated as in 3 2 0 0

Values for were calculated by assuming that only PdCl+ and

PdC^ existed in solutions containing mole ratios of chloride to palladium of lo20 to 1.50 and I .78 to 1 «99 ? respectively* and that all the chloride was bound to palladium (II). In Table 37 these values are compared with the molar absorptivities observed for a solution containing 4»35 palladium (II) and 8.64 mM chloride* and with the values for given in Table 38* The formation of complexes higher than PdClg which have a greater molar absorptivity than Pd 2+ * + PdCl s or PdClg at wavelengths less than 38O mp is especially evident from comparison of the molar absorptivities in columns 6 * 7s and 9 of Table 380 The increasing amount of dissociation and formation of complexes higher than PdCl£ as the chloride concentration was increased is shown graphically in Figure 27 o

A comparison of curves 1* 2* and 4 as well as those of 6 * 7s and 8 constitute a good qualitative confirmation of the validity of the molar absorptivity curves for these pure species. Further con­

firmation is given by the good agreement of the molar absorptivities of the trichloropalladate and tetrachloropalladate (II) ions obtained

by different methods* as shown in Table 39 and columns 1 and 3 °f

Table 40 respectively* and the agreement between the observed and

calculated chloride concentrations and molar absorptivity at the

wavelength of maximum absorption for the system. A maximum molar

absorptivity of 221.6 M“^cm”^ at 430 mp should be obtained for 4.35

and 0.870 mM palladium at 0.014 and 0.006 M chloride concentrations

respectively. The observed value of e was 220.2 at 430 mji. max and at the pi’edieted chloride concentrations o 2 0 1

TABLE 38

COMPARISON OF THE MOLAR ABSORPTIVITY- OF THE DICHLOROPALLADIUM (II) ION OBTAINED BY VARIOUS METHODS

Method* ~ 6 7 8 9 EPd x K K 4 .3 4 4 .3 4 4.34 4 .3 4 SCl/SPd 0 to 230 1=99 0 to 0.200 0 to 0.200 1 1.20 to 1 .5 0 1.78 to 1.99 dsg/SAA ±1 -0 .2 3 £2 12

IjmtJt e2 e2 e2 e2

350 — 51.8 40.8 60.5 360 30.5 45=0 42.8 52 = 7 370 50 6l»5 67=9 7 0 .6 380 84-7 92=7 1 0 6 .7 101.4 390 132 132=3 150.1 134.9 400 184 173=1 194=9 1 7 2 .1 410 225 203 220.6 420 243 211.4 224.9 192.9 430 233=5 200.6 211.8 184.? 440 205=5 175=6 1 8 0 .3 153=9 450 169 144.9 146.5 1 2 6 .0 460 134 114.9 117.1 101.4 470 101.8 88.1 89=6 78.0 480 76.4 67 = 3 6 6 .7 59=7 490 58 - ~ - 50=7 47=2 500 39=5 37=4 — 35=2 520 21.1 20.7 — 21.0 540 13=4 13=5 ---- - 15=1 560 11 10.8 11.0

" *6 Calculated using K-i =2.4x10^ K?=2.2xl0 j> Ko=2«2x10 and K^=2.4xl0l

7 Observed molar absorptivity

8 Calculated from solutions having ECl/EPd as indicateds assuming Pd (II) was quantitatively converted to PdCl+ at the lower mole ratio and PdCl* itfas quantitatively converted to FdCl2 at the higher mole ratio

9 Calculated as explained in 8 202

TABLE 39

COMPARISON OF THE VALUES OBTAINED FOR TIE MOLAR ABSORPTIVITY OF THE TRICHLOROPALLADATE (II) ION BY VARIOUS METHODS

SPd=405 mM £ H +=1.00 M T=25°C,

Method* 1 2

AsW|i. e3 °3

400 136 132

420 221 217

430 236 233

450 202 204

*1 Interpolated from Figure 23 at K^=24; based on slope- intercept data*

2 Calculated from the formation constants K]_=2«4xl0 s K2~2o2xlOs Ko=2.2xl0 s K^=2.4xl0 y and the mean molar absorptivities observed for solutions containing 4*35 mM palladium (II) at n values of 0*488* 0,681s 0 ,963s 1*404* 1,781s 3.244, 3.448, and 3.960 TABLE 40

COMPARISON OF THE MOLAR ABSORPTIVITY OF THE TETRACHLOROPALLADATE (II) ION OBTAINED BY VARIOUS METHODS

Method* 1 2 3 k 5

\sra|JL e4 e4 e 4 e4 e4

___ 350 284 — 283 360 134 136 136 370 56 56 —— 36 380 28 28 — ----- 29 390 23 26 ------28 400 36 37 — 35 37 410 52 53 3103 52 56 420 69 71 68<>7 69 75 430 89 90 8706 88 94 440 109 ill 1 08„5 109 113 450 130 131 129 8 7 130 132 460 149 130 — 150 470 139 160 . ------1 6 0 480 139 159 --- 138 490 146 146 143 500 121 122 121 320 66 66 66 340 29 29 - ~ — 29 560 14 14 ——— 14

1 Calculated from the observed molar absorptivities of 4<»35 mM palladium (II) solutions and the following formation constantss K1 =2 .^xlOi|'; K2=2.2x103; K3=2 *2x102 ; and K ^ B ^ x l O 1 2 Limiting molar absorptivity observed for 4<>35 mM palladium (II) in 1 to 4 M hydrochloric acid 3 Values of obtained using the slope-intercept method. (Figure 21) 4 Values of e^ obtained using the slope-intercept method (Figure 22) 5 Molar absorptivity observed for 4*33 mM palladium (II) in 1»027 M hydrochloric acid Except for an unfavorable charge factor there is no reason to exclude possible species in which chloride ions act as bridging uq groups between two palladium (II) ions® 7 In view of the polymeric

(49) J« C« Bailar, Jr., "Chemistry of Coordination Compounds," Reinhold Publishing Corp., New York, 1956® structure of many palladium compounds in the solid statetheir

(50) A. F. Wells, "Structural Inorganic Chemistry," 2d ed.» Oxford University Press, London, 19 5^° presence would not be surprising. Although the existence of ternary complexes in the copper (II)-, nickel (XI)-» and cobalt (Il)-chloride systems has been postulated on the basis of spectrophotometric and e.m.f. measurements,^ previous investigators of the palladium (II)-

(5D Ivl. W. Lister and P. Rosenblum, Can. J. Chem., J8» 182? (1960)o chloride system have not discussed the possible presence of such com­ plexes. If such complexes were formed their presence would be favored by high palladium concentrations and low ratios of chloride to palladium.

One would expect e p ^ d to be much greater than since the forma­ tion of polynuclear complexes is usually accompanied by an enhancement in the absorbance of a systemThus if Pd^Cl^ were present, values

for at low mole ratios of chloride to palladium would increase with palladium (II) concentration. Agreement among the values for

epdci calculated at low mole ratios of chloride to palladium at total 205 palladium concentrations of 0 .8 6 5® *4-®3^s and 7*23 niM palladium (II)

(columns 3 j b? and 5 °f Table 37 is evidence that polynuclear species such as Pd£Cl 3+ were not present in significant concentrations in the solutions studied® These conclusions were substantiated by the ab­ sence of significant trends in the formation curves with palladium 52 concentration or wavelength® and the agreement between experimental

(52) H. J. Go Hayman® J® Chem. Phys.® 2290 (1962)0 and calculated molar absorptivities at low values of n for solutions containing from 0.218 to 7®23 mM palladium (II)«

Harris et al.~^ have measured the absorbance of the tetrabromo- and tetrachloropalladate (II) ions as x^ell as that of the halogen bridged dimers tetrabromo-u-dibromodipaHadate (II) and tetrachloro-u- dichlorodipalladate (II) ions in a number of solvents and in the crystalline state® They found that the monomeric and dimeric species generally exhibit maxima at the same wavelengths in the same solvent? however® the molar absorptivity of the dimer at the maxima was approxi­ mately- double that of the monomer® These authors give no evidence 2— for the existence of Pd£Cl^ in aqueous solution and demonstrate the

strong coordinating ability of water® relative to a number of polar

and nonpolar solvents in the case of the tetrabromo- and tetrachloro­ palladate (II) ions® Agreement between the values of calculated

by different methods (Table 39 and the absence of any trend between

calculated and observed values for the molar absorptivities of chloride

solutions containing from 0 .2 1 8 to h <>35 mM palladium and from zero to

0.6 M hydrochloric acid (Tables to *4-8® is evidence that species TABLE 41.

COMPARISON OF CALCULATED AND OBSERVED VALUES FOR THE MOLAR ABSORPTIVITY OF PALLADIUM (II) CHLORIDE SOLUTIONS*

1 2 3 4 5 sPd X 103 4 .3 4 4 .3 4 4 .3 4 4 .3 4 4 .3 4 E Cl/EPd 0.199 0.497 0,696 0.999 1,49 n 0*1964 0.4882 006812 0.9934 1 .404

AjmM- eobs.» ecalc« eobs« ecalc. eobs. ecalc. eobse ecalc. cobs0 ecalc 0

360 68«5 68.4 6 3 .6 63.6 6 0 .2 60.3 55.1 55.1 47.6 47.6 370 82*1 82.0 82.8 82.7 8 2 .1 81.7 79.6 79.6 70.7 70.7 380 9 1 0 90*9 100.4 100.3 104.1 104.8 107.4 107.7 102 06 102 08 390 95 o4 95*2 113.2 1 1 3 0 123.1 123.2 133.7 133.6 137.8 138.6 400 94.4 94 0 5 120.1 120.2 135° 3 135.1 152.9 153.4 169.7 169.6 410 87-7 88.0 117.5 117.4 136.0 135.0 159.7 159*5 18? ..9 187.7 420 77*7 77.5 106 «6 106.6 119.2 119.4 152.0 151.8 188.1 188.2 430 64*8 64.3 90.6 90.6 108.0 108.0 134.1 133.6 172.6 172,6 440 50*7 50.3 72.4 72.4 87.4 87.4 110.1 110.2 147.0 146.7 450 37 08 37*5 '55*2 55.4 68.0 67.8 86.1 86 o9 119.0 118.7 460 2 6 .6 26.3 40.1 40.1 50.0 49.8 65.2 65.1 91.9 91.7 4?0 18*5 18.1 28.6 28.6 3 6,2 35.9 47.7 47.8 69.1 68.9 480 1 3 .0 12.9 20.5 ■20-* 4 ■ < ■ 25.9 25.8 34.6 34.9 51.4 51.5 490 9 ®6 9.1 14.5 14.4 19.1 18.4 25.7 25.I 38.2 38.2 500 7.4 7.4 11.4 11.5 14.3 14.4 19.0 19.1 27.9 27.9 520 5°7 5.4 8.0 8,0 10.0 9.7 12.4 12.0 16.4 16.4 540 4 .9 4 .5 6 .7 6.6 7 .8 7.9 9.6 9.5 11.7 .11.7 560 3*7 3.8 5.4 5.5 6 .3 6.6 7.8 8.0 9.6 9,6

^Calculated using "fo =2.4x10^; K2=2.2x103; K^=2o2xl02? K/^2.4x10-1

tv> o o\ TABLE 42

COMPARISON OF CALCULATED AND OBSERVED VALUES FOR THE MOLAR ABSORPTIVITY OF PALLADIUM (II) CHLORIDE SOLUTIONS*

6 7 8 9 10 SPd x 10-* 4«3?4 4 .3 4 4.34 4.35 4.34 SCl/SPd 1.778 1.99 2.98 4.59 9,21 n 1,640 1,781 2 ,3 0 5 2.752 3.244

eobs® ecalc<> eobs, ecalco eobs. ecalc, eobs, ecalc, eobs. ®calco

360 45*8 45.3 45.03 44,9 53.7 50.3 71,4 71.3 98.1 95,5 370 6 5,1 64.7 6105 61 ,3 5 1 ,8 52.1 47.9 49.1 49.1 50.8 380 96.8 96.7 92,7 92,5 75.07 74.9 60.4 61,7 46,2 47.7 390 13 5 «6 134,7 132.3 131.7 114,1 114,4 92,3 94.2 6?,4 68,4 400 172,2 172,5 173.1 172,5 160.3 161,1 137.1 138.9 102.3 103.9 410 197.4 197.6 202,9 201,4 200,1 200,4 177.1 180.4 139.1 140.2 420 203,6 203,9 211 o 5 211,3 220.2 222.1 205.6 208.3 166.8 168,5 430 190.5 191.1 200.6 200,6 220.0 220,8 212.6 215.7 180.1 182.9 440 165.5 165.4 175.6 175.5 200,3 201,3 202.9 204,7 182,0 183.3 450 135.9 135.6 144,9 145.1 171.4 172,6 182,6 182.7 174.3 174.8 460 106,1 106,4 114.9 114.9 142,3 142.5 157«9 158.0 162,7 162.9 470 81.2 81,1 88.1 88,4 115.0 114,7 134.6 133,8 148,4 148.5 480 61 ,3 61,5 67.3 6?,7 91.4 91.8 112.4 112.2 132.4 132.6 490 45.8 4 6,4 51,6 71.7 72,5 91.6 91.8 112.8 113.2 500 33.7 33.6 37.4 37,4 54,2 54,1 71.3 71,2 90.5 90.9 520 19.1 19.6 20.7 20.9 28,8 29.7 38,0 39.1 48.5 49.9 540 12.9 12.8 13.5 13.5 16,2 16 o7 19.6 20.1 23.2 23*9 560 10 o4 10,3 10,8 10,7 11.8 12,3 12,6 13.5 13.4 14.2

^Calculated using K]_~2,4x10^% K2"2,2x105j 1^=2,2x102; Kif=2o4xl0l

•>3 TABLE 43

COMPARISON OF CALCULATED AND OBSSR¥ED VALUES FOR THE MOLAR ABSORPTIVITY OF PALLADIUM (II) CHLORIDE SOLUTIONS*

11 12 13 14 15 ^Pd x io3 4-355 4.355 4.355 4.35 4.35 ic ifc P d 1308 1 8 ,3 32 .1 236 459 n 3o448 3.563 3.732 3,960 3.979

A»m|i e0bSe ecalco eobs0 e calc. eobs 0 ecalco eobso ecalc. ®Obs. ecalc p

360 106 .0 106.0 112.3 111.3 120.6 120.5 136 132 136.1 133.2 370 51*7 51.2 52.3 52.0 53.4 53.4 56 .6 55.6 56.0 55.8 380 42 .5 42.3 39.2 39.3 34.4 35.1 29.2. 29.4 28.3 28.9 390 58.0 57-0 51.1 50.5 41.2 40.7 27.6 27.4 26.0 26.2 400 86.7 86.7 76.5 76.6 61 »o 61.2 39.1 39.7 36.9 37*8 410 119.2 118.6 105.9 105.6 85.5 85.6 53.0 --- 53.1 54.6 420 145.2 145.0 131.0 130.5 108.0 107.9 74.6 75.3 71.4 ?2»4 430 161.1 161.3 147.3 147.7 126.3 125.9 93°5 94.4 90.4 91.6 440 16608 166.8 156o3 156.1 139.1 138.8 112.6 1 1 3 0 110.6 110.8 450 165.9 165.7 159.5 159.3 148.6 148.8 132.5 133.0 131.3 131.5 460 161,4 161.1 159 03 159 0 2 155.6 155.9 149.6 150.1 149.8 149 06' 470 153.0 153.0 154.5 154.2 156.5 156.3 160.2 158.7 161.1 158.8 480 140.3 140.3 143.7 144.2 149.4 150.1 158.8 157.7 159.6 158.3 490 122.3 122.3 126.7 127.0 134.2 134.2 145.I 144.0 145*6 144.8 300 99.2 99.2 103.4 103.7 110.0 110.1 121 <>2 119.4 121.9 120.2 520 54.1 54.1 56 .2 56.7 59.7 60.3 66.1 65.2 66.1 65 .6 540 2 5 0 2 5 0 25 .8 26.1 26.8 27.3 29.1 28.7 28.9 2 8.9 560 14.3 14*3 14.1 14.3 13.7 14.2 14.2 14.0 14.2 14.0

Calculated using K^=2 .4x10^5 K2 =2 .2xlo3 ; 1(3=2 .2x 1 0 ^ 5 K^=2o4xl0l TABLE 44

COMPARISON OF CALCULATED AND OBSERVED VALUES FOR THE MOLAR ABSORPTIVITY OF PALLADIUM (II) CHIORIDE SOLUTIONS*

16 17 18 19 20 ^Pd x 10^ 0*870 0.868 0.8 6 8 0.868 0.868 ECl/SPd 0*000 0.199 0.498 0.992 1-99 n 0.000 0.188 0.462 0.878 1-477 A mu< 8 eobs<> ecalc 0 eobs. ecalc. eobs. ecalc. eobs. ecalc. eobs. ecalc 0

360 71-5 71.5 68.6 68.5 65.2 64.0 58.2* 56.7 48.2 46 .7 370 81.0 81.0 81.9 81.9 84.2 82.7 82.3 80.6 70,2 68 .8 380 83.8 84.0 91.0 90.8 100.7 99.6 IO8 .3 107-3 102.5 101 o0 390 81.7 81.9 94.9 94.7 112 08 111.8 132.5 131.1 139-4 137-0 400 75-9 76.1 94.1 93-7 118.9 117-9 148.4 148.5 172-5 170.9 410 67.7 67.5 87.2 87.2 116.0 114.8 152.5 152.7 191-8 191-3 420 58.0 57-7 77.5 76.7 105-7 104.0 144,7 143.9 193-9 193-6 430 46.9 46.7 64.4 63.5 89.6 88.2 126,3 125.9 178*4 178.8 *l40 35.8 35-7 50.4 49-7 72.1 ' 70.4 IO3 .3 103-3 152.3 153.2 450 25.8 25.8 37.3 37.0 55.2 53-8 82.1 81.9 123-5 124.2 460 17.7 17.4 26.4 25-9 40.0 38.8 6 0 .6 6 0 .3 95-9 9606 470 11.5 11.4 18.4 17.8 28.4 27.6 43.9 44.1 72.1 73-0 480 7*9 7.8 13*5 12.3 20.6 19-7 32.1 32.1 53-8 54-7 490 6.1 5-7 9.8 8.9 15-3 13-9 23-7 2 3 .O 40.0 40,8 500 5.0 4.7 7=7 7-3 11.7 1101 17-5 17-7 29-4 29-7 520 3-9 3-7 5.8 5.4 8.5 7-7 11.7 110 4 17-2 17-2 340 3.2 3 .1 4.8 4.5 6 .9 6.4 9-2 9-1 12.4 12-0 360 2.6 2 .5 4.0 3.7 5-7 5-4 7-5 7 .6 9-9 9-8

^Calculated using Ki=2o4xl0^: K2=2.2xl0-^s Kj=2.2xlO^; K^=2o4xl0-*-

ro VOo TABLE 45

COMPARISON OF GALGUUTED AND OBSERVED VALUES FOR THE MOLAR ABSORPTIVITY OF PALLADIUM (II) CHLORIDE SOLUTIONS*

A 21 22 23 24 25 £Pd x 10-* 0 1.870 0 ,.868 0 ,.870 0,,870 0,,868 SCI/ Pd 2 .48 2..98 9<.20 32,,2 69..0 ii I..677 1 1.831 2,.605 3<.233 3-.525

A®mp eobs 0 ecalc * eobs«> ecalc<> eobs. ecalc. eobs 0 ecalc 0 eobs. % a l c .

360 48.2 46.7 46.4 4 5 .I 63.9 64.8 94.8 95.0 109.2 109.9 3?o 70.2 68.8 61.4 60 .2 48.5 49.6 49.4 49.9 50.8 51.7 380 102.5 101.0 ■91.7 90.9 64.9 66.2 • 47.5 48.0 • 38.6 40.3 390 139.4 137.0 131.7 130.5 99.8 101.2 68.8 6 9 .I 51.2 52.7 400 172 o5 170.9 172.7 172.2 145.7 147.3 IO3 .8 104.8 78.5 80,0 410 191.8 191.3 203.2 202.4 187.6 188.8 140.6 141.3 108.6 110.0 420 193.9 193.6 213.0 213.6 212.9 215.2 169.0 169.7 13^.2 135.5 430 178.4 178.8 203.5 203.6 217.7 219.9 182.9 184.0 150.8 152.3 440 152.3 153.2 177.9 179.1 203.7 205.9 I8 3.O 184.1 158.8 159.8 450 123.5 124.2 147.2 148.3 180.0 181.0 175.2 175.2 161,4 I6I .5 460 95.9 96.6 119.1 118.2 153.3 154.2 I6 3.O I6 3.O 159.2 159.8 4?0 82.9 83.3 90.1 91.3 128,0 127.4 148.3 148.3 153.6 158.6 480 62.9 63.I 68.8 '7 0.0 IO5 .3 IO5 .6 131-7 132.1 142.9 142.9 490 47.2 47.7 52.0 53.5 84.3 84.3 85,4 112.4 125.8 125.3 500 34.6 34.5 38.3 38.? 65.3 6 5 .4 9 0.4 90.5 100,7 102.1 520 19.8 19.6 21.3 21.7 3 4.8 35.9 48.5 49.6 56.2 55.9 540 13.3 12.9 13.8 13.7 18.6 19.0 23.5 23.8 25.9 25.9 560 10.8 10.4 10.8 10.9 12.5 1 3 .1 13-7 13.8 14.3

*Calculated using K1=2.^-xl0^; K2=2.2xlo3; Kj =2,2x 10^; K^=2o4xl0^ TABLE 46

COMPARISON OF CALCULATED AND OBSERVED VALUES FOR THE MOLAR ABSORPTIVITY OF PALLADIUM (II) CHLORIDE SOLUTIONS*

26 27 28 29 30 SPd x 103 0.870 0.4357 0.4357 0.4358 O .435 SCl/^Pd 334 0.000 0.620 1.116 2.73 n 3*873 0.000 0.533 0.884 1.544

\smu 9obs. ecalc. eobSo ecalc. eobs. ecalc. eobs. ecalc. eobs. ecalc.

360 129.2 127 08 72.1 71.5 63.9 62.8 57 »0 56.5 48.9 46.0 370 54.9 54.8 81.5 81.0 83.7 82.6 81.1 80.5 69.8 6 7.I 380 30 o9 31.5 84.4 84.0 102.5 101.5 107.3 107 «3 102.6 99.3 390 32.7 32.5 82.5 81.9 116.9 II5 .8 132.1 131 »2 139.7 136.2 400 47.6 47.9 76.2 ?6.1 124.4 123.8 148.5 148.8 175*1 171.8 410 68.1 68.1 67.9 67.5 .122.1 121.8 153 a 153*0 197.1 194.1 420 87.7 87.9 58.3 57 °7 111.6 111.0 144 o4 144.3 200 oX 198.0 430 106 cO 106.6 47.0 46.7 95 °o 94 06 126.2 126.3 18^ o7 185.0 440 123.O 123.2 36.I 35.7 76.1 75 »9 103.4 103.5 158.7 158.3 450 138.4 139.2 26.2 25.8 58.8 58.3 8 0 .8 81.1 129.2 128.9 460 151*5 152.4 17.8 17.4 42.9 42.3 6 0.6 60.5 100.6 100.7 470 158.2 157.8 11.6 11.4 30.5 30.3 . 44.1 44.2 76.4 76.4 480 154.5 154.8 8.0 7 .8 21.9 21.7 31.8 32.1 57.8 57.5 490 140.2 140.3 5°7 15.3 23.0 43.6 43.0 500 II6 .5 116 oO 5.0 4 .7 12.4 12.2 17o3 17 o? 31.8 31.2 520 63.7 63.3 4.0 3«7 8.6 8.4 11.4 11.4 18.8 18.0 540 28.0 28.2 3 0 3.1 7.0 6 .9 8.8 9.1 13.2 12 0 560 13 °7 14.1 2.8 2 .5 5 06 5 .8 7.2 7.6 9.7 10.1

^Calculated, using K-^ =2.4x10^ K2=2o2xl0^; Kj=2.2xl02 ; 1(^=2«4xl0^ TABLE 47

COMPARISON OF CALCULATED AND OBSERVED VALUES FOR THE MOLAR ABSORPTIVITY OF PALLADIUM (II) CHLORIDE SOLUTIONS*

31 22 33 34 35 EPd x 103 0,435 0.435 0.2180 0.2181 0.2180 SCl/SPd 13 *8 45.8 0.000 0.620 2.97 n 2*535 3 a i 2 0.000 0.476 1.378

Ajmy. eobs. ecalc. eobs. ecalc. eobS e calc 0 eobs<> ecalc 0 eobs. ecalco

360 62 03 60.6 88.5 88.8 72 o2 71.5 64.4 63.8 48,3 48.0 370 50 o4 49.5 49.9 49 ®4 81,9 81.0 83.7 82,7 72.2 71*3 380 68.8 68.1 51*7 51*3 84.9 84,0 100.9 100.0 104.4 IO3.3 390 105*1 104 o2 76.3 75*6 82.7 8I .9 113.7 112.6 139.0 137.7 400 151.1 150.6 114.3 114.3 76.4 76.1 119.4 119.1 I69.O I69.O 410 191*4 191*6 152.4 152*7 67.8 67.5 116.9 116.2 186,9 186.4 420 216*2 216.9 180.7 181.7 58.4 57.7 IO6.3 105 o4 186,0 186,3 430 220.1 22081 192.7 194.6 47 a 46.7 89.4 89.5 168.6 170.4 440 204.3 204.5 190.0 191.7 36.5 35*7 71.5 71.5 143.6 144.9 450 178,8 I78.3 178.8 179.0 26.4 25.8 54.3 54.7 115.6 11608 460 151.1 150.4 162.9 I63.O 17.3 17.4 39.7 39.5 88.4 90.2 470 125.4 123.7 145.3 145*4 11.6 11.4 28.1 65,8 67,8 480 104.2 100.8 127.1 127.4 8,0 7.8 20.2 20.1 48.4 50.5 490 81.9 80.9 106,9 107.5 6.0 5*7 --- 14.2 36.0 37.4 500 62.9 61.5 84.7 . 85.6 4.8 4.7 11.0 11.4 26.4 27*3 5 20 33.4 33*7 45.9 47.O 3.9 3*7 7.9 7.9 15.2 16 a 540 18.3 18.2 22.7 22.9 3*4 3 a 6.1 6.5 11.0 11*5 560 12.? 12.8 13*7 14 a 2.6 2.5 4,8 5.5 9 a 9*5

^Calculated using K-j_=2«4xl0^; K2=2.2xlo3; K^=2o2xl0^; K^=2o4xl0^ TABLE 48

COMPARISON OF CALCULATED AND OBSERVED VALUES FOR THE MOLAR ABSORPTIVITY OF PALLADIUM (II) CHLORIDE SOLUTIONS*

36 37 38 39 40 £Pd x 103 0.2181 0,2181 0.2180 0,2181 0.2181 ECl/sPd 15 o4 45 »8 214 3 66 I .83 x 103 n 2,293 2,2822 3*455 3.622 3-903

Ajmfi e n 6 obs 0 ecalc» eobs 0 calc. eobs. calco eobs 0 ecalc. eobs. wcalc<>

360 54,4 53-2 74,5 74,6 10 5 ,5 106 .3 117*9 114,9 132.5 129.4 370 53-2 52 .2 49,3 49.0 5 0 .3 51 .2 54.3 53-5 56.6 55.1 380 76,9 76 pO 59.8 59.6 41.3 42.2 39 ol 37 08 31,6 30'. 8 390 116.7 114,9 90,8 90.7 5 6 .7 56.7 48.8 47,0 32,1 30.7 400 162,7 161.5 134,1 134.6 86.0 8 6 ,3 72,2 71.2 44,8 4 5 .O 410 201,6 200 0 7 175.2 175.8 118.6 118.1 99,9 98.7 63.9 64,3 420 221,0 222,2 202,9 204.3 144.4 144.4 124.9 122.7 83 g2 83 ,5 430 219.2 220,7 210.2 212,9 1 6 0 .3 160,7 141.2 140.2 101,9 102.4 440 200,4 201,2 201,5 203,4 1 6 5 ,4 166,4 151.1 150.2 119-4 119.8 450 171.0 172,1 182,5 182.9 165.0 16 5 .4 1 5 6 .4 155*8 136.3 137.0 460 141,9 142,3 159.7 159.7 160.4 161.0 158.9 158,2 150.2 151.6 4?0 114,4 114.4 137.3 13 6 .3 151.5 152.5 155 o5 155.0 158.1 158.2 480 90,8 91.2 115,8 115.3 139.0 140.3 146.7 146.3 154,8 155-8 490 71.1 72,0 94.4 94,8 121,1 122,3 129.3 129.5 141,0 141,6 500 53.8 53.7 74 ol 74o 0 97*5 99 °3 106.8 106,0 117.6 117,2 520 28,8 29.5 3 9 .4 40,6 52,5 5 5 .4 5 8 .5 5 8.O 63.2 64.0 540 16,5 16,7 2 0 .5 20.7 24.1 2 5 .4 2 6 ,8 2 6 ,5 27-6 28.4 360 12,4 11.7 13.1 13.3 12.8 1 3 .8 14.2 1 3 .8 13.8 13 .6

^Calculated using Kj=2<>4x10^5 K2=2 ,2xl0 ^; Ky=2o2xl02; K^=2o4xl0^ TABLE 49

COMPOSITION OF PALLADIUM (II) CHLORIDE SOLUTIONS**

_ 2ct SPd x 103 xCl/lPd n i Pd + $> PdCl+ $ PdCl2 $ PdCl^" % PdCl^ “

1 4 ,3 4 0.199 0.196 80.75 18.87 0.383 0.008 ...... 2 4 .3 4 .497 .488 54.15 42.88 2,948 0.021 3 4 .3 4 .696 .681 38.72 54.53 6.667 .086 0.0001 4 4 .3 4 .990 .963 20.82 62.46 16.27 .448 .0013 5 4.3? 1.49 1.404 5.773 51.34 39.63 3.230 .0287 6 4.37 1.78 1,640 2,497 38,52 51.58 ?»293 .1125 7 4 .3 4 1.99 1.781 1,432 30,58 56.67 1 1 .0 9 .2368 8 4.34 2.98 2.305 0.126 8.8 46 53.91 34.69 ,2435 9 4.35 4.59 2.752 0.001 1,900 31.67 55,73 1 0 .7 0 10 4.34 9.21 3.244 -— 0.181 9.755 55*55 34.52 11 4,35 1 3 o8 3.448 .049 4.613 45.78 49,56 12 4.35 18„3 3.563 — ... .020 2.701 38.24 59.04 13 4.35 32.1 3.732 -- .004 • 0.918 24.97 74,11 14 4 .3 5 236 3.960 -- --- .018 3 “999 95.98 15 4.35 4 59 8.970 -- --- .005 2.060 97.94

16 0.870 0.000 0 . 0 0 0 100.0 mmammm _ w _ , m » -» ^ 17 0.868 .199 .188 81.48 18.110 0.351 0.001 .... 18 0.868 ,498 .462 56.44 40.97 2,581 .017 19 .868 «992 .878 25.57 61.37 12,78 .281 0.0007 20 .868 1.99 1.477 4.475 47.48 43.74 4.255 .0352 21 .870 2.48 I 0677 2.168 36.41 53.10 8.178 .1374 22 .868 2.98 I .831 1.164 27,87 57.94 12.72 .3046 23 .870 9-20 2.605 3.320 39.68 50.08 6.897 24 .870 32.2 3.233 —_ 0,193 10.10 55,93 33.78 25 .868 69.O 3.525 -— .028 3.272 40.91 55.80 26 .870 344 3.873 — — 1 0.189 12.31 84o50 TABLE 49 (contdo)

SEd x 103 SCl/EPd n $ m 2+ j> PdCl+ $ Pd&2 $ PdCl3~ $ PdCl^'

27 0*4357 0,000 0,000 100,00 28 ,4357 *620 -533 50,38 45*95 3,638 0*030 29 A 358 1,116 *884 25*24 61.47 13,00 *029 30 *435 2*73 1*544 3° 554 43 0 92' 47*12 5*337 0.0660 31 *435 13.8 2*535 0.036 4.248 43,40 46,81 5.509 32 *435 45*8 3*112 ,001 0,370 14*38 58,91 26*34

33 *2180 0,000 0,000 100,00 n o ^ • • M M a m a m a m 34 *2181 *620 ,476 • 55*19 42.02 2*777 0*019 ■■ a 35 *2180 2*97 1*378 62.95 52.60 38*16 ■ 2*923 0.0258 36 ,2181 15*4 2.293 0.134 9*153 54.33 34*05 2.329 37 ,2181 45*8 2,822 ,006 1.428 27*92 57.66 12.99 38 *2180 214 3*455 *0,047 4*512 45*49 49*98 39 ,2181 366 3*622 0.012 1.944 33*82 64.22 40 ,2181 1,83 x 10*3 3*903 —— 0,108 9*444 90,46

^Calculated using ^=2*4x10^; Kg=5.CxlO?; K^l.lOxlO10; I^=2o64x 101;L* ^Percentage composition given to four significant figures; however? accuracy probably limited to three« 2 1 6 such as Pc^Cl^” were not present in the solutions studied. Analogous species in the ruthenium (III) and rhodium-^ chloride systems

(53) H. H. Cady and R» E. Connick, J. Am. Ghem. Soc», 80s 2.646 (1958)o (54) R. E. Connick and D. A. Fines ibid., 82, 4187 (I960). (55) R» E. Connick and D. A. Fine, ibid., 83 , 3414 (196l)0 (56) W. C. Wolsey, C. A. Reynolds, and J. Kleinberg, Inorg. Chem.j 2, 463 (1963). also have been shown to be monomeric.

Apriori there is no reason to believe that the complex designated as P d C ^ does not exist in both cis and trans forms in the solutions

C.r7 Q studied, 8 since the replacement of coordinated water by chloride

(57) R* S. Nyholm, Quart. Rev., 2* 321 (1949)» (5 8) J. V. Quagliano and L. Schubert, Chem. Rev., j>0, 201 (1952)c

ion occurs very rapidly. Although there are relatively few examples

of cis-trans isomerism of palladium compounds in the crystalline phase,

the predominance of the trans form in the solid state has no neces­

sary connection between the thermodynamic stability of these complexes 59 in aqueous solutionsoJ The stability constants of t rans complexes

(59) A. A. Grinberg and V. M. Shulman, Bokl. Akad. Nauk. SSSR, 215 (1933)o

of platinum (II) are generally greater than those of the cis isomers«,

(60) A. A. Grinberg, G. A. Shagisuitanova, and M. I. Gelfman, Svensk Kern. Tidskr®, 22.* (1961) o 21? 4* The existence of geometrical isomers of RuGX? and RuOX« in aqueous solution has been reported by Connick and Fineo'^'8'^ Violsey et a l o ^ found no evidence for the presence of isomers for RhCl^a but iso» lated two uncharged species which they proposed to bo cis and trans in a concentration ratio of 1 to 3° Although the trans effect has much less influence in the reactions of palladium (II) than in the case of platinum (II) and other ions of the platinum group metals which have a greater amount of XT b o n d i n g 9^'”^ one t-;ould expect a

(6 1) F® Basolo and R . G« Pearson0 Mechanisms of Inorganic Reactions9s3 John Wiley and Sons® Mew Yorks 1958s p° 20?« (62) Fo Basolo2 He B® Grays a n d R® G» Pearsons J® Am* Chen® Socos 8 2 s 4200 ( 1 9 6 0) o (53) Fo Basolo and R. G. Pearsons "Progress in Inorganic Chemistryp" 4# Interscisnce Publishers9 Hew Yorks 1962s pp® 381-4530 greater concentration of the trans PdGlg than of the cis isomer in aqueous solution due to the electrostatic stabilization of the trans form® From statistical considerations the concentration of cis isomer would be expected to be twice as large as that of the trans form®

(64) S® Wo Benson® J® Am* Chenu Soc®j> 80s 5151 (1958)®

Absorption parameters calculated for PdCl^ (page25>2 ) indicate that if both cis and trans isomers exist in this system their spectral characteristics are very similaro Very small differences in the posi° tion of the absorption maxima were found for both the ruthenium (III) *54 9 *26 and rhodium (lIl)®»chloride isomers respectively9 however few deductions can be made on the basis of these results since 'idle 218 electronic transitions of these 4d-* and 4d^ ions are very different 6 6 3 from those of palladium (II)? having a 4d electronic structure#

(65) C. K. Jorgensen? ”Advances in Chemical PhysicsJj? Inter­ science Publishers? New York? 1963? PP° 33-146#

From a consideration of the relative symmetry of the cis and trans isomers one would expect the total a rea under the absorption curve 66 of the trans isomer would be less than that of the cis isomero

(66) F. Basolo? C. J. Ballhausen? and J. Bjerrum? Acta Chem. Scand.? 9? 810 (1955)®

Comparison of the experimentally observed molar absorptivities

with the calculated values for forty palladium chloride solutions at

eighteen wavelengths in the 360 to 560 mu wavelength region is given

in Tables 4l to 48# The composition of the solutions is given in

Table 49# In general the observed and theoretical molar absorptiv­

ities agree within 1 unit or 1 percent except for the following cases;

The deviation was 3 units for a 4#35 palladium solution at n = 2#75

in the 410 to 430 mp. wavelength region and for a 0©435 palladium

solution at n = 1#54 at x-avelengths below 430 m|i.« Deviations in the

region of n = 3 at these wavelengths were not unexpected because of

the large concentration of the trichloropalladate (II) ion in these

solutions and the relatively greater uncertainty in the molar ab-

sorbtivity values calculated for this pure species. This greater

uncertainty was attributed to the large changes in the composition

of the medium. The values of e]_ and e2 represent the molar absorpti- 219 vities of PdCl+ and PdClg in loO M perchloric acid, values for e^ and e^ were calculated for solutions containing from 0®06 to 0*6 M hydrochloric acid and from 0.9^ to 0*^ M perchloric acid at a total hydrogen ion concentration of 1 M. The deviation in the case of the

0.^35 palladium solution at n = 1«^4 and the larger deviations in general for solutions at this palladium concentration may reflect the limits of errors in the complexity constantso

Studies of palladium (Il)-chloride solutions at ionic strengths greater than 1 M» In the evaluation of the stability constants for the palladium (Il)-chloride system it was assumed that the activity coefficients of all species and the molar absorptivities of the palladium chloride complexes remained essentially constant while hydrochloric acid was substituted for perchloric acid over the range from zero to 0*6 M hydrochloric acid and from 0*218 to ij-*35 diM pallad­ ium (II), at a total hydrogen ion concentration of 1=00 M. The agreement between the calculated and observed values of e in this concentration range constitutes good evidence that no appreciable absorptivity changes resulted from this change in the composition of the supporting electrolyteo Since the complexation of chloride by

palladium (II) was not complete in 1 H hydrochloric acid, it was

necessary to exceed this ionic strengtho

As the concentration of hydrochloric acid was increased from

1 to 2 li there was no change in the molar absorptivity of the solu­

tions at the isosbestic (466 mu)| however, there appeared to be a

definite trend in the difference between observed and calculated molar

absorptivities which indicated a greater concentration of the 22G tetrachloropalladate (II) ion than would be predicted from the stability constants calculated for the system at lower ionic strengths.

As the hydrochloric acid concentration was increased from 2 to 9 M the wavelength of maximum absorption of the palladium (II)-chloride solutions was displaced to 472 my- and there was a continuous change in absorbance at most wavelengths in the 320 to 600 my- wavelength region» as seen in Figure 20© These phenomena could not be explained on the basis of previous experimental results and suggested studies on the effect of concentration and nature of the medium ions on the stability constants and molar absorptivities of the system.

The effect of perchloric acid concentration on the molar ab­

sorptivities of two solutions containing 0.2 and 0.4 M hydrochloric

acid is seen in Table 5Q« The decreases in concentration of perchloric

acid from 0 .6 0 to 0 .0 5 and 0.80 to C-.05 M* respectively5 at constant

chloride concentrations resulted in a blue shift in the wavelengths

of maximum absorptivity and corresponding decreases in the intensity

of absorption at the maximum for both solutionso At wavelengths

greater than 400 my- curves for the solutions containing 0.2 and 0.4 M

chloride at the lower perchloric acid concentration corresponded to

those obtained for solutions containing around 0 .1 3 and 0.3 M hydro­

chloric acid* respectively* at a total hydrogen ion concentration of

1 lio Below 380 my- a decrease in perchloric acid concentration resulted

in a small increase in molar absorptivity greater than that which

would be expected from an increase in the concentration of PdCl^ and

lower species. This indicated that the activity coefficients and

molar absorptivities of the palladium-chloride species were affected 221 TABLE 50

EFFECT OF IONIC STRENGTH ON THE MOLAR ABSORPTIVITY OF PALLADIUM (II) IN CHLORIDE SOLUTIONS

T=25°Co 5o00 cm* cell length

Std. Soln. 17 17 17 17 SPd x io3 O .870 0.865 0.870 0*871 SHCl 0 o2006 0.2055 0.3998 0.3998 (HCIO^) 0 .8 0 0.050 0 .6 0 0.050

Ajmu. F ■© e e

355 188 0 5 195*6 196.1 360 126.6 12 3 .0 130*9 131*8 365 82 ol --- 84*0 86.4 370 54*5 53*8 54.4 55 ol 375 39*0 —- 37*4 40*9 380 3 2 .2 34.2 29*3 33*4 385 32.0 35*0 30 *0 32.4 390 55*8 4 0 .5 29*8 35.2 395 42 08 48.? 35*6 41*3 400 52o6 59*9 44*6 49*0 410 74 o4 84.5 6308 68.8 420 95*2 106.4 8 3 .3 65*6 430 112.9 124*6 101.9 107*5 440 128o 9 137*8 119*1 123*6 450 142 o2 147*6 1 3 6 .4 139*6 460 152.9 154.6 150.6 151.4 4 66 156.6 1 5 6 .8 156.2 1 5 6 .8 4?0 157*7 15606 158*5 1 5 8 .6 472 157.6 —_ ----- 158*6 480 152*4 149*9 155*5 154*6 490 138.3 134*9 142*0 141*1 500 114.6 111.3 117.8 117*2 510 8 7 .8 —— 90.8 90.4 520 6 2 .5 61*0 64.1 64*3 540 27*7 26*9 27*9 28*7 222 by the perchloric acid concentration. There was also a possibility that some hydrolysis had occurred in the solutions containing 0 .0 5 ^ perchloric acid.

In order to determine the effect of hydrogen ion concentration on the molar absorptivity curves? palladium (II) solutions containing from zero to 0.939 M sodium chloride and 0«0608 to 1.0 M hydrochloric acid at a total chloride concentration of 1.0 M were prepared. Table

51 and the first two columns of Table 52 illustrate that substitution

of sodium chloride for hydrochloric acid in these solutions produced

no measurable effect on the molar absorptivity curves of these solu­

tions in the 320 to 600 nH-A wavelength region. Substitution of 0»?91 M

hydrochloric acid by potassium chloride in 1 M chloride solutions of

palladium (II)'produced a decrease in the molar absorptivities at

wavelengths below 3&0 mM-s as is seen in Table 51® The absorbance of

a solution containing 0 .0 6 0 8 M hydrochloric acid and 0 .9 3 9 M sodium o chloride (Table 52 was unchanged after heating for 4 days at 60 C.

These results indicated that an increase in with ionic strength

and not hydrolysis of the palladium (II)-chloride complexes was chiefly

responsible for the change in the molar absorptivity curve of the

palladium-chloride solution containing 0.4 M hydrochloric acid as

the perchloric acid was decreased from 0.60 to 0.05 M and suggested

the possibility that the difference between the calculated and ob­

served molar absorptivities of palladium (Il)-chloride solutions at

ionic strengths up to 2 M could be attributed to an ionic strength

effect. The fact that the equilibria and molar absorptivities of the

palladium (II)-chloride species present in 1 M chloride solutions TABLE 51 2 2 3

EFFECT OF SUBSTITUTING SODIUM AND POTASSIUM CHLORIDES FOR HYDROCHLORIC ACID ON THE MOLAR ABSORPTIVITY OF PALLADIUM (II) IN CHLORIDE SOLUTIONS

T*25°C. 0.997 cm. cell length IS >S>S Std. Soln. 17 17 19 19 19 E P d x IO3 4.34 4,35 3 .8 6 3 3 .8 6 3 3.863 SHC1 0 e00864 0.0 0 0 1 .0 0 0 0.2018 0.2018 EMG 1 0 .000 0.00864 0.000 0.791 0.791 (hcio4 ) 1 .0 0 1 .0 0 0.000 0 ©000 0.000

A pmi-t e e "e e e

330 170.5 171.0 — « s * w a a 340 92o3 92.8 454 ■«*“>*» 345 - — 6 7 .8 373 372 369 350 5 1 .8 52.4 2 8 3 .1 283 27?o9 355 45.0 45.2 200.7 200 .8 197.0 360 45.0 45 oO 1 3 4 .4 134.4 131*7 365 50.9 5 1 .2 8 6 .8 86.7 8 5 .5 370 61.5 6106 55 ®8 55.8 55.4 375 —_ -— 3 8 .1 3 8.O 3 8 .2 380 92.7 93-0 2 9 .2 2 8 .8 29 -7 385 .— 1 1 2 .2 2 6 .5 26 .1 27 .2 390 1 3 2 .3 132*7 2 8 .0 27.6 28 .8 395 — 15 2 .9 3 2 .6 32.4 33.6 400 1 7 3 .2 1 7 2 .9 39.8 39.4 40.4 410 203.2 202.6 56.9 5 6 .9 57*4 420 211.4 210.7 75*1 75-1 75*5 430 200.6 200 .1 93°9 94.0 94.4 440 175.6 175 oO 113.4 113.3 1 1 3 .8 450 144.9 144.7 1 3 2 .3 1 3 2 .3 133»2 460 114.9 114.4 149.8 1 5 0 .2 1 5 0 .6 466 —— 156.7 157.2 158.0 470 88.1 88.0 160.0 159.7 I6 0 .5 474 — » ~ 1 6 0 .5 160.5 160 0 7 480 67*3 67.3 158.0 158.1 158.0 490 5 0 .6 144.4. 144.7 144.3 500 37.4 3 7 0 1 1 9 .6 12 0 .5 119.6 510 «*•»«* 92.5 93.0 92.0 520 20.8 20.8 6 5 .6 65.9 64.8 540 13.5 I3 .7 2 8 .5 28.6 28 03 560 10.8 11.1 14.4 14.1 14.0 580 9.1 9.5 10.2 10.1 10.2 600 7 .5 7 .6 8 .7 8 ,7 8.6

*M=Na **M=K 224 TABLE 52

EFFECT OF ACID CONCENTRATION ON THE MOLAR ABSORPTIVITY OF PALLADIUM (II) IN 1 MOLAR CHLORIDE SOLUTIONS

T=25°C« 0.997 cm. cell length

Std. Soln. 19 19 * 19 19 19 EPd x K K 1 .1 6 2 1 .1 6 2 3 .8 6 2 3.8 6 5 3.8 6 5 EHCl 0.2069 0.0608 0.2 0 1 8 0.2018 0.2018 (NaCl) 0.791 0.791 0.791 0.791 0.791 (HCIO^) 0.000 0.000 0 .0 0 0 1.798 3-798

e e e e e

340 457 457 453 447 3 45 377 377 371 371 363 350 288 286 283 282 272 355 206 206 200,8 199-9 191.6 360 137 0 7 137-5 134.4 133.7 126.7 365 8 9 .6 89.6 8 6 .7 86.6 81.5 370 57.2 5 6 .4 550 8 5 5 .6 51-9 375 39.5 39.1 3 8 .0 37-8 35-2 380 29.6 2 9 .6 28.8 2 8 .3 27-0 385 2 7.O 2 6 .6 2 6 .1 2 5 .6 24.5 390 29.0 2 8 .5 27-6 26o7 2 5 .8 395 3 2 .6 3 2 .2 32.4 30-9 30 .0 400 40.2 39.8 39.4 37.4 36.4 410 56 .1 55-9 56.9 54.1 52.9 420 7 6.O 76.0 75-1 72.4 71.4 430 94.5 94.3 94.0 91-4 9 0 ,8 440 114.6 114.4 113.3 111.5 111.8 450 133-5 133-4 1 3 2 .3 13 2 .0 13 2 ,8 460 150.9 150.7 1 5 0 .2 150o3 152.7 466 158.8 158.8 157.2 158.1 159.4 470 161.4 161.0 159.7 160.8 162.4 474 16 2 .7 162.7 1 6 0 .5 161.8 I6 3 .2 480 158.9 158.8 15 8 .1 159.3 160.3 490 145.7 14 5 .7 144.7 145-7 145-5 500 120.9 121.5 120.5 121*5 121.0 510 93-9 94.8 93.0 93-8 92.9 520 6 6 .7 67.4 6 5 .9 6 6 .3 6 5 .0 540 29.2 29.2 2 8 .6 29 ol 28.2 560 1 4 .5 15.4 14.1 14.1 14.0 580 10.8 11.2 10.1 10 ol 10.0 600 8 .7 8 .7 8 .7 8.8 806

^Heated 4 days at 60°C. with no change in absorbance 225 were not changed when the hydrochloric acid was largely replaced by sodium chloride was of some importance also in subsequent studies of replacement reactions involving the stepwise substitution of chloride in the tetrachloropalladate (II) ion by ethylenediaminea

The relative effects of perchloric and hydrochloric acids in the 1 to k M range on the molar absorptivities of palladium (II)- chloride solutions are given in Table 53 and Figure 28o Comparison of curves 1 and 2 shows that perchloric acid up to a concentration of 2 M. was not as effective as hydrochloric acid in increasing the concentration tetrachloropalladate (II) ion in the solutions con­

taining 2 M hydrogen ion® This result would be expected since an

increase in hydrochloric acid concentration not only produced an in­

crease in ionic strength but also an increase in chloride activity®

Comparison of curves 2s 3s and h- which represent the changes in molar

absorptivities of palladium (Il)-chloride solutions when the ionic

strength of the medium was increased from 1 to 2<.8® and h.8 M s

respectively» showed that the effects of perchloric acid and hydro­

chloric acid were qualitatively similar and that there was a roughly

linear dependence of on the ionic strength in the '380 to h-50 mp

wavelength region® Solutions at ionic strengths from 2®8 to h-®8 no

longer passed through an isosbestic at if-66 rap as did the solutions

containing from 0»1 to 2 M hydrochloric acid5 but intersected around

lf-38 mp. The maximum increase in molar absorptivity produced by an

increase in ionic strength from 1 to 4.8 K occurred in the 4?0 mp

wavelength region and represented an increase of around 1 percent®

On the basis of these results it was concluded that an increase TABLE 53

RELATIVE EFFECT OF HYDROCHLORIC AND PERCHLORIC ACIDS ON THE MOLAR ABSORPTIVITY OF PALLADIUM (II) IN 1 TO 4 MOLAR CHLORIDE SOLUTIONS T=25°C• 0.99? cm. cell length

1 2 3 4 Prep. No. 17 19 17 19 EPd x 10"3 4.35 3.86 4.35 3.86 EHCl 1.027 to 1.997 0.2018 1.027 to 3.995 0.2018 (NaCl) 0.00 0.791 0 .0 0 0.791 (HC104 ) 0 b20 0 .0 0 to 1.798 0.20 0.0 0 to 3*7 e e e e

345 0 .0 0 0 .0 -2.3 -8 350 0.00 -1 .0 -3.2 -11 355 0.00 -0.9 -3°2 -9.2 360 0 .0 0 -0.7 -3.7 -7*7 365 -0 .5 0 .0 -2.9 -5*2 370 -0 .5 —0 .2 -1.7 -3*9 375 -0 .6 -0.5 -1.4 -2 .8 380 -0 .9 -0.5 -1.5 -1 .8 385 -1 .3 -0.5 -1.3 -1.6 390 -1 .4 5 -0.9 -1.6 -1.8 395 -106 -I .5 -1.64 -2.4 400 -2.2 -2.0 -2.2 -3 .0 410 -3.2 -2.8 -3-2 —4.0 420 -3-35 -2.7 -3-2 -3*7 430 -3 .2 -2.6 -3.1 -3 .2 440 -2 .3 -1.8 -1.6 -1 .5 450 -1.15 -0.3 -0.1 0 .5 460 0.00 0.1 1 .3 2*5 466 1 .0 0 .9 2.5 2 .2 470 0 .9 1.1 2.1 2.7 474 — 1.3 2.5 2*7 480 0«9 1.2 2.1 2.2 490 0.7 1.0 1.7 0.8 500 0.8 1.0 1.0 0.5 520 0 .5 0.4 0.5 -0.9 540 0.0 0 .5 0.1 -0.4 560 0.0 0 .0 0.1 -0.1 580 0.0 0 .0 0.0 -0.1 600 0.0 0 .1 0.0 -0 .1 FIGURE 28*

RELATIVE EFFECTS OF HYDROCHLORIC AND PERCHLORIC ACIDS ON THE MOLAR ABSORPTIVITY OF PALLADIUM (II) IN 1 TO k MOLAR CHLORIDE SOLUTIONS

& Curve numbers refer to column numbers in Table 52

227 I

Ae

360 4 00 450 500 550 A m i l

Figure 28 228 229 in with ionic strength in the 1 to 2 M region was responsible for the trend in the difference between observed and calculated molar absorptivities and at ionic strengths from 2 to 4®8 M there was an additional small medium effect on the molar absorptivity curves®

Similar effects of ionic strength on the stability constants of the- silver (I)-^?s^® cadmium (11)-?^ iron (III)-?^ and thorium (IV)-^

(6 7) I® Leden? Svensk Kern. Tidskr.? 64? 249 (1952)® (68) E» Berne and I , Leden? ibid®? 6^$ 88 (1953)® (6 9 ) C. E. Vandersee and H* J. Dawson? Jr«j J® Am® Chem. Sac®? 5659 (1953)® (70) E. Rabincwitch and W. H® Stockmayer? ibid.? 64? 335 (194-2)® (71) W. C. Waggener and R. W® Stoughton? J® Phys ® Chem®? 56? 1 (1952)o

chloride stability constants have also been reported®

The further increase in hydrochloric acid concentration from

4 ®8 to 9 M produced an increase in the molar absorptivity curves of palladium (II)-chloride solutions in the wavelength range from 385

to 500 rap. and a decrease at wavelengths below 3®0 mir? as seen in

Figure 20o The maximum increase in molar absorptivity was 5 percent

at 460 mp.? however there was no significant change in the band width

or the appearance of any new absorption bands* These results indicated

2- that the changes in molar absorptivity of PdCl^ produced by an in­

crease in hydrochloric acid concentration in this concentration range

was a medium effect. This effect could be attributed to a pertuba-

tion in the energy levels of the electrons in the pa orbitals of

palladium (II) produced by interaction of the medium with the two sigma

bonded water molecules in the inner coordination sphere® This is 230

(72) N. S. Bayliss and E. G. McRae* J. Chem. Phys.* j$8j> 1002 (195*0 • (73) H. B. Gray and C. J. Ballhausen* J. Am. Chem. Soc.j 85* 260 (1963)0

74- in accord with the results of Bjerrum* Adamson* and Bolstrup who

(74-) J. Bjerrum* A. W. Adamson* and 0. Bolstrup* Acta Chem. Scand.* 10* 329 (1956)»

found that changes of solvent do not effect the position of maximum

absorption of spin forbidden bands in saturated complexes* but usually

produce changes in the intensity of absorption. Discussion of Results

A. comparison of the formation constants obtained by various investigators for the palladium (II)-chloride system is given in

Table 5^° Values for the stepwise formation constants were all ob­ tained by the speetrophotometric method but generally under different experimental conditions such as temperature and ionic strength so that one should not expect complete agreement; however? a comparison of the speetrophotometric data does lead to some general conclusions concerning possible sources of error.

The effects of colloidal palladium oxide and chloride on the molar absorptivity of palladium (II) in 1 M perchlorate solutions was shown in Chapter I. The presence of these impurities is further demonstrated by a comparison of the speetrophotometric data for the palladium chloride system. Values for the molar absorptivity of palladium perchlorate solutions having mole ratios of chloride to I palladixun equal to 1.0 and 2.2 are given in Table 35" The data obtained in the present investigation 'agree with that of Sundaram 3»75 and Sandell* Molar absorptivity curves obtained by Droll"' are

(75) A. K. Sundaram and E* B. Sandell? Private communication. much higher at every wavelength and the maxima are displaced toward

longer wavelengths. These differences between the data of Droll and

that of the present investigators continue to exist in palladium (II)

231 TABLE 54

COMPARISON OF THE FORMATION CONSTANTS OBTAINED BY VARIOUS INVESTIGATORS.FOR THE PALLADIUM (II)-CHLORIDE SYSTEM

Reaction Tj>°Co Medium Log K Log P/^ References

Pd2 + Cl" ^ PdCl* 21° --- 5> 0 6 .2 t 0 .1 -- Droll14 29®5 --- .£> 0 60O ol Droll^4 20 0 .8(010/,) 4 .3 4 — — Shchukarev et al, 6 25 loO H (CIO^) 4.4 .1 Present work

PdCl+ + Cl" PdCl2 21° --- o- 0 4.7 t 0.1 Droll14 14 29-5 --- & 0 4.5 .1 Droll" £ 20 O 08 (CIO/,) 3.54 - -- Shchukarev et al® 25 1.0 H (CIO/,.) 3®34 .04 Present work

PdCl£ + Cl” ^ PdCl" 21° --- * 0 2 .5 t 0.1 Droll1'4 3 29*5 ——> 0 2.4 .1 Droll14 20 0.8 (C104 ) 2.68 — -- Shchukarev et al< 25 1.0 H (ClO^) 2.34 .04 Present work

PdCl^ + Cl” PdClf” 21° 0 Droll 14 2.6 t 0.1 14 4 29.5 — — 0 2 06 ol Droll' 20 0.8 (CIO/,) 1 .6 8 — Shchukarev et al. 25 1.0 H (CIO/,.) 0 .8 — Jorgensen1? 25 1.0 H (CIO4 ) I .38 .04 Present work

PdCl|" + Cl"«=fc PdCl3" 21° — — > 0 -2.1 + 0ol Droll14 5 29.5 -- 0 -2..1 ol Droll14 Z£Z TABLE 5^ (Contdo)

Reaction T,°C. Medium Log K Log % References

4 — 14 PdCl?” + Cl“ z ? PdCl7 21° --- ^ 0 -2.1 + 0.1 B r o l l y j 29 o 5 — — > 0 -2.1 ol — Droll

Pd2 + 4 Cl” Z T PdCl|‘ 25° ^J-oO H (CIO^) •mrnrntm 13o22 Templeton et alo^ 25 -- 12.30 Latimer-^ 21 — — «» 0 _ 16.0 Drolll^ 29.5 ,— -■> o « —„ 15o5 Droll ^ , 20 0o8 (CIOk ) 12 e 2^ Shchekarev et als 25 1.0 H (C10^) llo^J-2 Present work TAELE 55

COMPARISON OF MOLAR ABSORPTIVITY VALUES AT SELECTED MOLE RATIOS OF CHLORIDE TO PALLADIUM BY VARIOUS INVESTIGATORS FOR THE PALLADIUM (II)-CHLORIDE SYSTEM

Investi­ 1 2 4 gator* 3 LSl/EPd ^ 0.992 2.18 1 .0 1 .0 0 2 .2 2 .2 1 .0 LPd x 103 0.8 6 8 0 .8 7 0 1.841 0 .7865 0 .7 8 6 5 0.7865 1.35 (HClOi+) 1 .0 0 1 .0 0 1 .0 0 0 .2 0 8 0 .2 0 8 0 .2 0 8 O 06 T» °Cc 25 25 25 29.5 21 29.5 20

Xpmii e 0 'e e e e e

330 30 05 1 1 3 .7 m M ,_ 73.5 165 l6l — a*. 340 3 0 .3 64.8 6 0 .2 105 101 .... 350 40.0 44.0 -- 6 1 .7 74.2 ...... 360 58 o2 —— 59 74.2 -- -- 370 82.3 6 8 .3 84 97.6 8 6 .5 ——- -- 380 1 0 8 .3 100.4 112 127 116 - - 390 1 3 2 .5 139.7 136 ------174 LOO 148.4 173*0 154 177 190 -- 185 410 152.5 195.3 158 188 218 .... 194 420 144.7 199 150 184 226 226 188 430 1 2 6 .3 185 130 167 214 214 166 440 103.3 159 107 143 186 188 141 450 8 0 .6 130 82 117 155 ... 118 460 6 0 .6 101 61 9 0 .6 123 12? 94 470 43*9 7 6 .7 45 6 7 .8 95.7 98.3 74 480 3 2 .1 57.3 33 5 1 .0 74.2 7 7 .6 60 490 23.7 43.1 24 39.3 -— — 51 500 17.5 —— 30.4 ——— ——— 45

* 1 Present investigation n n c 2 Sundaram and Sandell 14 3 Droll, pp. 144, 150, 152

4 S. A. Shchukarev, et al. 235 perchlorate solutions at high chloride concentrationss as is shown in the mole ratio curves in Figures 29 and JO at 380 and 460 mpj respectively. This indicates the presence of impurities (presumably chloride and colloidal oxide) whose concentration appears to be rela­ tively constant at chloride to palladium ratios from zero to 10.

Comparison of the data given in Tables 55s 69 shows that ZSe/A(Cl” )/(Pd) reported by Schukarev et al.®^ in the range of chloride to palladium concentrations of zero to 1.00 was greater at all wavelengths than that obtained by other investigators and at palladium concentrations threefold those used by Shchukarev et al® The latter investigators did not give more experimental data at chloride concentrations less than 0.0135 M so that further comparisons could be made at low ratios of chloride to palladium.

Since the data for the calculation of and by Droll^ was based on the absorbance of palladium (II)-chloride solutions contain­ ing from 1 to 8 M hydrochloric acidj it is important to compare the speetrophotometric data obtained by various investigators for solu­ tions in this concentration range. Most of the solutions were prepared by addition of concentrated solutions of hydrochloric acid to standard solutions of palladium (II) chloride or potassium tetrachloropalladate

(II) in dilute hydrochloric acids rather than addition of hydrochloric acid to the standard palladium (II) perchlorate solutions.

The results of five investigations concerning the molar ab­ sorptivity of palladium (II) in 1 M hydrochloric acid solutions in the 350 to 600 mp wavelength region is given in Table56 and Figure 31® FIGURES 29 AND 30

COMPARISON OF MOLE RATIO CURVES FOR THE PALLADIUM (II)-CHLORIDE SYSTEM BY VARIOUS INVESTIGATORS AT 3 8 O AND k60 mp.

2 3 6 Molor Absorptivity ^ Molar Absorptivity 100 100 MO 130- 70 60 80 40 80 20 80 sc-y- 40 20 60 Figure 29 Figure 30 -Droll - A Peet investigation —Present G -rsn investigation G-Present 460 mju. 460 A-Droll A . 237 2 3 8

TABLE 56

COMPARISONi OF VALUES FOR THE MOLAR .ABSORPTIVITY OF PALLADIUM (II) IN 1 MOLAR HYDROCHLORIC ACID BY VARIOUS INVESTIGATORS

Investi­ gator* 1 2 3 4 5 EPd x 103 4®35 1.841 118 1.049 1*35 (HC10.) 0.24 0.100 0.0000 0.0000 0 oOOOO SCI 1.027 1 .0 0.998 1 .6 2 1 .0 0 T s °C® 25 25 25 29.7 20 bj. cm 1 .0 0 0 1 .0 0 0 .0 1 1.003 —

Ijmii. e e e e e

350 285 275 368 360 136 -- 135 197 —. 370 56.4 55 59*1 95*8 — - 380 2 9 .2 30 33*8 54.7 --- 390 2 7 .6 29 33*0 4 3 .2 -- 400 39®0 39 43*0 49.8 61 410 5 6 .2 5 6 .5 59*1 6 2 .7 69 420 74.6 74.4 77*6 7 8 .8 80 430 93*5 94.5 94.6 97.8 90 440 112.5 113*5 113 120 106 450 132.4 134.7 131 138 125 460 149.8 152 148 159 142 470 160 161 156 173 151 480 158 160 155 176 146 490 145 145 143 I65 133 300 121 121.6 118 144 112 510 93*8 9 4 .5 93*9 116 87 520 66.1 67.4 6 7 .5 86.6 63 530 —. 4 5 .I 4 7 .4 6 1 .0 42 540 29=1 29*3 3 0 .4 39*9 24 350 19*0 22.0 — 17 560 14 ___ 14-9 1 8 .5 12 570 ------12.2 9 380 10 ___ 10.5 12.2 6 590 -.I- —- 9*5 5 600 8 .3 — 8.8 10.4 5

1 Present investigation 75 £ Sundaram and Sandell ^ 3 Cohen and Davidson’ 4 Droll3^ p. 158 5 Shchukarev et al® FIGURE 31

MOLAR ABSORPTIVITY vs. WAVELENGTH CURVES FOR PALLADIUM (II)- CHLORIDE IN 1 MOLAR HYDROCHLORIC ACID BY VARIOUS INVESTIGATORS

239 Molar Absorbancy 200 100 150 175 125 50 75 25 o Figure 31 350 375 0 0 4 0 5 4 5 2 4 Wavelength, m -oe od Davidson ond O-Cohen A 'D ro ll and Fernelm s s Fernelm and ll ro 'D A Peet investigation Present • - -udrm n Sandell and x-Sundaram - Shchukarev jx 475 525 0 0 5 240 2 4 1 7*5 76 The data of Sundaram and Sandell? J Cohen and Davidson?‘ and that of

(76) A. J® Cohen and Norman Davidson? Document 3044? American Documentation Institute? 1719 N Street? Washington? D»C.| J» Am* Chem® Soc, 21* 1955 (1951)» the present investigators at 25°C<> agree reasonably well? but that of Droll^ at 29 °5°C» and Shchukarev et al°^ at 20°Co are not within the spectrophotometric error» The change in molar absorptivity of palladium (II)-chloride solutions with temperature was not invest!- 77 gated in this study? but the results of A y res and Tuffly ' on the

(77) G* Ho Ayres and B. L<> Tuffly? Analo Chem»? 2 k s 949 (1952)® palladium (II)-bromide system at high concentrations of hydrobromic acid and sodium bromide indicate that temperature effects are negli­ gible at the wavelength of maximum absorption» In view of the

relatively small temperature coefficient of absorption observed in the palladium (II)-bromide system? the validity of Beer5s law for palladium (II) solutions in 1 M hydrochloric acid? and the agreement in the molar absorptivity curves of palladium (II) which were prepared

from standard palladium (II) perchlorate solutions and those prepared

from the standard palladium (II) chloride solution (Table 28)? it is difficult to understand the lack of agreement among these investigators®

Comparison of the molar absorptivity curves of palladium (II) by

several investigators for hydrochloric acid solutions in the 4 to 9 K

range is given in Table 37 and Figure 32 o The relatively high molar

absorptivities reported by Shchukarev et al and by Droll^ suggest 242

TABLE 57

COMPARISON OF VALUES FOR THE MOLAR ABSORPTIVITY OF PALLADIUM (II) IN CONCENTRATED HYDROCHLORIC ACID SOLUTIONS BY VARIOUS INVESTIGATORS

Investi­ gator 1 2 3 4 5 E P d x 4 0 5 4.35 1.049 0.5243 1*35 (HCIOO 0.24 0.24 0 .0 0 0 0 0 .0 0 0 0 0 .0000 S C I 3*995 9-2 4.4 8.07 4.0 Tj °C. 25 25 2 9 0 2 9 0 20 b> cm 1 .0 0 1 .0 0 1 .0 0 1 .0 0

¥ e e e ~e

350 282 0 9 269 394 798 355 1 9 9 0 186 300 733 - — — 360 1 3 2 .6 123 222 676 ~ — 36 5 84.7 78.9 160 625 ---— 3?o 54.8 51-2 118 583 — --- 375 36.9 35*7 91*2 5^7 ----- 380 27.7 2 8 .0 73*1 505 — 385 24.9 2 6 .0 64.6 467 390 2 6 .1 2 7 .8 6l .8 ^33 196 395 30 0 3 2 .1 70*3 395 171 400 3 6 .9 38.9 64.6 369 141

410 53*1 55*7 73*1 315 124 420 7 1 0 74.6 84.5 276 120 430 90.4 9 5 0 107 247 124 440 111.0 117 0 120 232 136 450 132.4 1 3 9 0 141 218 150 460 1 5 0 .8 1 5 8 .3 165 218 164 470 1 6 2 .3 1 6 8 .3 177 213 169 480 I6 0 .9 164.8 181 205 165 490 146.8 149*0 171 186 147 500 1 2 2 .2 1 2 3 .0 141 151 119

510 94.3 93*9 108 125 92 520 6 6 .2 6 5 .4 8 2 .7 92.2 68 540 29.0 2 8.4 37*0 4 3 0 26 560 14.1 11.4 14.2 2 0 .9 14 58O 1 0 .2 1 0 .2 9 0 1 5 .2 7 600 8 .3 8.4 5*7 9 0 5 * lj>2 Present investigation 3 »4 Droll*1^ p. 169 £ 5 Shchukarev et ale PIG UR.3 32

MOLAR ABSORPTIVITY vs« WAVELENGTH CURVES FOR PALLADIUM (II)- CHLOEIDE IN CONCENTRATED HYDROCHLORIC ACID SOLUTION BY VARIOUS INVESTIGATORS

2 4 3 Molar Absorbancy 400 0 0 3 0 5 2 0 5 3 200 150 100 0 5 Figure 32 0 5 3

0 0 4 Wavelength, m ^ -rsn ivsiain . M 9.2 investigation ©-Present h -Droll - Shchukarev Shchukarev - Peet netgto 4.001V? investigation -Present 0 5 4 0 0 5 4.04 HCI 8.07 JV!8.07 0 5 5 24 4 0 0 6 245

"the presence of an impurity in their solutions whose absorbance in­

creased significantly with hydrochloric acid concentration® Hydro-

chloric acid'78 sr 79 does not absorb at wavelengths above 220 md? however

(78) E. Rabinowitehj Rev. Modem Physicsa 14? 112 (194-2)® (79) J» Jortner and A. Treinins Trans® Faraday Soc.j 58? 15^3 (1962).

small amounts of’ an impurity in the hydrochloric acid such as iron 80 (III) should be expected to produce such an effect® The results

(80) D® E. Metzler and R® J. layers» J0 Am® Chem® Soc®9 72 » 3776 (1950)®

of this investigation showed that the absorbance of iron (ill) in

reagent-grade acid is negligible. The absorption of aqueous solutions

of 12®4j lo09 and 0®01 M hydrochloric acid prepared by dilution of

reagent-grade acid vjith double distilled water showed no absorbance

at wavelengths above 400 mp.; but as the wavelength decreased the ab­

sorbance gradually increased to a maximum at 275 m iJ's followed by a

decrease to a miniraum at 355» and then increased sharply with decreas­

ing wavelength. The absorbance above 255 mu- was attributed to the

presence of silicic acid since most of the reagents used in this work

displayed similar absorption curves. The presence of an impurity in

reagent hydrochloric acid which reacted with the palladium to produce

a significant increase in absorbance of palladium-chloride solutions

prepared by Droll and Shchukarev et a_l. was discarded in view of the

fact that the molar absorptivity curves of palladium chloride solutions

prepared from reagent hydrochloric acid did not differ from those 2^6 prepared from the double distilled ^oid. In the present investi­ gation reference solutions containing the same concentration and source of hydrochloric acid were used in the reference cells so that the effect of silicic acid on the absorbance was cancelled. Common impurities in the palladium such as nickel®"*" and platinum^’ have

(81) A. v. Kiss and P. Cookan* Z. Anorg. Chem., 2^5? 355 (19^1) (82) J* Chattj G. A. Gamlen, and L. E. Orgel.-i J. Chem. Soc., h86 (1958)« relatively low molar absorptivities in this wavelength region. If the palladium chloride was prepared by dissolution of palladium in aqua regia there is a possibility that nitroso compounds might be present} however they should not be expected to produce an effect of this magnitude on the absorbance-. 6 The formation curves reported by Shchukarev et al» for the palladium (Il)-chloride system at 20°C.> an ionic strength of 0.8 and hydrogen ion concentration of 0.6 M are reproduced in Figure 330

These curves xjere obtained by applying Bjerrum's''7 method of corres­ ponding solutions to the spectrophotometric measurements of 0.1 to

0.2 mM palladium (II) perchlorate solutions containing from zero to

0.6 M hydrochloric acid. Values for the stepwise formation constants 8 were calculated from the formation curve at MB0 mu using Bjerrum’s

approximation Kn = 1/ (Cl“)_ _ ^ \ j 2* "theoretical formation curves

calculated from the constants reported by Shchukarev et al. and those

from the present investigation are compared in Figure 3 4 c The ratios

of successive constants should be about ten times as large as those 8 reported in order to produce the large inflections at the midpoint. FIGURE 33

FORMATION CURVE FOR THE PALLADIUM (II)-CHLORIDE SYSTEM AT 470 AND 480 m\i BY SHCHUKAREV etaLo

247 248

' f - -

n

log (CD Figure 33 FIGURE 34

THEORETICAL FORMATION CURVES FOR THE PALLADIUM (II)-CHLORIDE SYSTEM CALCULATED FROM THE STABILITY CONSTANTS OF SHCHUKAREV et alo AND FROM THE PRESENT INVESTIGATION 250

log K(, log K2. log K., logK — Shchukarev 4.34 3.54 2.68 1.68 v— -Present work 4.40 3.34 2.34 1.38

3.0

n 2.0

- log (CD Figure 34 251

The above method is very useful for calculation of approximate forma­ tion constants; however9 further refinements are desirable for systems 83 in which the ratios of successive constants are about 20 o

(8 3) H. Mo N« Ho Irving and Ho Rossottis J« Chem® Soc«s 3397 (1953 ) and references therein#

The results of the present investigation indicate that a maximum

of 4 chloride ions are coordinated to palladium (II) in aqueous hydro­

chloric acid solutions* Shchukarev et al* ^reported similar results3

however; there is a considerable disagreement in the values for K^

found by various investigators# Shchukarev et al» calculated a value

of 48 from the formation curve of the system at n = 3°5 and a value g£, of 68 using the graphical method of Newman and Hume in conjunction

(84) Lo Newman and D. Humes J» Am» Chem* Soc.j J?9s 4571 (1957)°

with Bjerrum’s corresponding solution method for determination of the

free chloride* These authors assumed that palladium (II) was almost

completely converted to the tetrachloro-complex in 0*12 M hydrochloric

acid and used values for which were much smaller than those re­

ported by other investigators» as seen in Table 580 They gave no

explanation for the change in absorbance of their solutions as the

hydrochloric acid concentration increased* The difference in these

results and those at 25°G* cannot be explained on the basis of tempera­

ture 9 since for this system has been found to be relatively indepen­

dent of temperature in the 20 to 30°Co range The results of the 252

TABLE 58

COMPARISON OF THE ABSORPTION PARAMETERS FOR PALLADIUM (II) CHLORIDE COMPLEXES IN AQUEOUS SOLUTION BY VARIOUS INVESTIGATORS*

A. Species 0 max ^max Tj.°C .1 6M 6 (-) Reference my- kK meT cm - kK kK

Pd2+ (1 M HCIO^) 25 379 2606 86 2.8 3»0 Jorgensen^-7 (0,6 M HClOij.) 20 380 26*3 101 cl — 3.2 Shchukarevj et al.° (1 M HClOif.) 25 38O 26*3 85 3.0 3-2 Present work

PdCl+ 25 606 26.6 176 2.38 2.36 Present -work

PdCl2 25 618 23.9 210 2.3 2.3 Jorgensen^? 25 621 23-7 266 2.07 2.13 Present work

PdCl” 25 633 23.1 233 2.09 2.66 Present work

PdCl2” 25 676 21,10 166 2*5 1.6 Jorgensen-^-7 6 20 676. 21.10 166. 2.8 1.6 Shchukarev , et al. 2ci 676 21.10 160 2.62 1.6 Present work

’''The absorption parameters for palladium (II) perchlorate solu­ tions are given for purposes of comparison

! 253 present investigation indicated a smaller value of would be expected at an ionic strength of 0.80 than at an ionic strength of 1.00. X7 o Jorgensen ^ calculated a value of 6 for % at 25 C. by applying

Bjerrum’s method of corresponding solutions to solutions containing

3 and 10 mM palladium (II)s respectivelys in 1 M perchloric acid.

Values for in the 400 to 450 mu wavelength region which correspond to a value of 6 may be obtained from Table 32o Comparison of these values with those obtained by the two methods used in this investi­ gation (Table 39) indicated that a value of 6 is inconsistent with the values of Kqs and found by the present workers. Kq and

K£ would have to be much larger and Kj smaller so that the principal species existing at a Cl/ Pd ratio of 2 would be PdCl?. The absorp­ tion parameters for PdCl^, reported by Jorgensen^ (Table 58) were apparently calculated on this assumption. These is considerable dis­ sociation of PdClgg as shown by a comparison of mole ratio curves at different total palladium (II) concentrations given in Figure l6«

It appears likely that some of the difficulty in interpretation of spectrophotometrie measurements of the palladium (II)-chloride system arises from the presence of a ,!pseudo-isosbestic point” at

456 m,u which has been attributed to an equilibrium between PdCl2 and

PdCl^» Results of the present investigation indicated that such an isosbestic point should occur when the percentage of PdCl^j in the solution is in the vicinity of the maximum. Figure 25 shows that in this range of chloride concentrations ^(PdCip/^ZXci”) is a mini­ mum while ^(PdC^J/^lCCl”) and >(PdCljq )/^S(Cl ) are large. There should be relatively no change in the absorbance of the system as Z5k 2 - PdCl2 is replaced by PdCl. , since these species have the same molar absorptivity at mp (Figure 26)»

Stability constants for the chloride complexes os other metal ions are given in Table 59» Comparison of these constants shows

(a) The elements which have the greatest affinity for chlorides gold? platinums mercury, iridiums thorium, rhodium, palladium, silver, and oopper, are neighboring elements occupying an area of more or less triangular shape in the periodic table® (b) The stability con­ stants generally become larger when an increase in oxidation number for a given element and with an increase in atomic weight for iso- electronic ions® (Copper is a notable exception.) (c) for these complexes is greater than K2 in all cases. TABLE 59

STABILITY CONSTANTS OF CHLORIDE COMPLEXES OF VARIOUS METAL IONS IN AQUEOUS SOLUTION

Metal t ,°c 9 ion Medium Log K1 Log Kg Log Log K4 Log Log K 6 L°S Pn

Sc (III) 25 0.5(010^) 1 o07 1 o 04 __ — 85

Or (III) 25 5(HC104 ) -0,65 -1.54 — -- 86

Mn(Il) 20 0o69l(HC104 ) 0.59 -0.51 -0,43 — — —— 87

Mn(lll) 2 5 0 2 2(HC10A) 0.95 — — — 88

2 H(C1°4 ) —__ Fe(ll) 20 0 . 3 6 0 .0 4 — — 89

Fe (ill) 25 _ > 0 1.48 0 .0 5 - 1 .0 - 1 .9 2 — 70.90

C o ( I I ) 2 5; 2 (NaClO^) -0.18 -0.56* •aoa a an — __ — 51

Ni(II) — 25 2(NaC104 ) -0.24 -0.05 . ----- 51.91

Gu(l) / 25 CSS Ctt. — 0.20 ca esa — P 3= 5 o 70 8, p06i

20 t v -»« __ Cu(ll) 0.691 H(C104 ) 1.98 «0.29 -0.15 -O.oo -=>- 92

Zn(ll) 25 2 H (C104 ) -0.49 ■>«« —n m — — __ 91 Ga(III) 25 -*0 -0.6 -1.7 - 2 . 2 - 1 . 3 *4a 93

I(III) o c u n t 25 0 5(C104 ) 0 . 3 6 — --- 85 v« yn.

Zr(IV) 25 2( H G 1 0 4 ) 0 . 3 0 pan* tarn m m —- n « R 9 *••• «s as 94 TABLE 59 (Contdo)

Metal R e f e r - ion T,°C. Me d i um Log K-j_ Log K 2 Log Log Log Log Log ences

Ru(lll) 25 0.1 to 5(C104) — 1 .4 8 0.43 - 0.10 -0.85 - 1 .0 — 54

Rh(lll) 12 0 6H(C104 ) 3 3 3 2.4 1.4 ”0.25 — 56

P d ( I I ) 25 i h (c i o 4 ) 4.1 3.34 2.34 1.38 11.4 Pres. work A g ( l ) 25 - 0 3.04 2 .0 0 0 .0 0 0.26 67,68, 95

Cd(Il) 25 -*o 2 .0 0 0.70 -0.59 __ — — 6 9 ,9 6

In(lII) 20 0.69H(C104 ) 2 .3 6 1.27 0.32

Sn(II) 25 3 (EaG1 0 4 ) 1 .0 6 o. 66 - 0 ,2 2 — — — 98,34

Sb(IIl) 25 4 h(cio4) 2.26 1 .2 4 0 .6 8 0.55 -0.01 - 0.60 — 99

L a ( I I I ) 25 l(UaC104 ) •0 .1 2 — 100

Lu(III) 20 o .i k (n o 3 ) 1.45 — — 101

Ir(lll) 50 2 .2H(C104 ) — — -0.9 p0=14 102

Pt(ll) 25 -»0 3 .0 0 1 .5 2 — — — 3 ; = 1 6 . 6 103, 104,60

Au (I) 25 p2=9 10,p. 193 Ox On TABLE 59 (Contdo)

Metal Refer ion t ,°c . Medium Log K1 Log K2 Log Log Log Log L °S Pn ences

AB (III) 18 0 «x» «e» «tt» 9MB — p^= 2 1 030 105

Hg(ll) 25 0 o5 NaClO^ 6,74 8*48 0,85 1,00 — CM MO 1 0 6 ? 107

T1(I) 25 4-? 0,00 ■”•0, 80 — — — — 108

TI(III) 25 0, 5H(CIO^) 6,7 8 5«26 2,52 1,72 ----- 109

Pb(Il) 25 -»0 1 .6 0 0,18 "0 0 1 -0„3 — 110

Bi(III) 25 4Na?lH(C10^) 2,43 2.0 1,35 0,43 0,48 -«• 111

ws» a a a u(iv) 21 2 (NaClO^ ) 0 e26 <”0 0 19 ““ .----- 112 0 i-t 0 1 Pu(IIl) RT V a r « 0 -0.41 — — 113

Am(lll) 25 -»0 1 017 — — — m m co 114

Cm(lll) 25 ->0 1*17 —- —» « _ = 115

*Dimerization (85) A« D, Paul? J. Phys, Chem,? 66? 1248 (1962)9 (86) H. S. Gates? thesis? University of Wisconsin (1956)« (87) D. F. C. Morris and E. L« Shorts J. Chem. Soc.j 5148 (1961), (88) H« Taube? J. Amo Chem, Soco? 3928 (1948)® (89) Ho Olerupj thesis? Lund (1944)• . (90) Yo Marcuss J. Inorg„ Nucl, Chemo? 12; 28? (I960), v)r (91) P« Kivalo and R. Luotoj Suomen Kemistilehti? 30B? 163 (1957) <> TABLE 59 (Contdo)

(92) D. F. C. Morris and E. L. Short, J. Chem. Soc.,2672 (1962)0 (93) K. A. Kraus, F.Nelson and G. W. Smith, J. Phys. Chem., j>8 , 11 (1956). (94) W. H. McVey, J. Ain. Chem. Soc., 3182 (1949)® (95) J® H. Jonte and D. S. Martin, Jr., J. Am. Chem. Soc*, 2.052 (1952)* (96) C. E. Vanderzee and H. J. Dawson, Jr. ,ibido, 80, 5048 (1958)* (97) B. G. F. Carleson and H. Irving, J. Chem. Soc., 4390 (1954). (98) A. I. Busev and N. A. Kanaev, C. A., 5 3 , 21067b (1959)® (99) F. Pantani and P. Desideri, Gazz. Chim. Ital.» 89, I36O (1959)* (100) 1(. L. Mattern, UCRL Report 1407 (1951)* (101) E® J. Wheelitfright, F. H. Spedding, and G. Schwarzenbach, J. Am. Chem. Soc., 75, 4196 (1953)® (102) I. A* Poulsen and C. S. Gamer, J. Am. Chem. Soc., 84, 2032 (1962)0 (103) C. I. Sanders and D. S. Martin, Jr., J. Am. Chem. Soc., 8^, 807 (1961). (104) A. A. Grinberg and G. A. Shagisultanova, Zhur. Neorg. Khim., 5* 280 (i960). (105) N® Bjerrum and A. Kirschner, Kgl. Danske Videnskab. Selskab Skrifter, Nat.-: . mat. Afd., 5 , No. 1, 8 (1918). (106) L. G. Sillen, Acta Chem. Scand., j), 539 (1949)* (107) L. D. Hansen, R. M. Izatt, and J. J. Christensen, Inorg. Chem., 2, 1243 (1963)* (108) B. Baysal, "The Catalytic Effect of Chloride on the Rate of T1(I)-T1(III) Electron-Exchange," Actes Intern. Congr. Catalyse, 2e.» Vol. I, Paris, I960, p. 559® (109) Sister Mary J. M. Woods, thesis, University of Wisconsin, Diss. Abs., 21, 3259 (1961). (110) F. Nelson and K. A* Kraus, J. Am. Chem. Soc., 76, 5916 (1954)* (111) L. Newman and D. Hume, J. Am. Chem. Soc., 79, 4576 (1957)® (112) R. A. Day, R. N. White, F. 0. Hamilton, J. Am. Chem. Soc., 77» 3180 (1955)® (113) 0. L. Kabanova and P. N. Palei, Zhur. Neorg. Khim., 31 (I960). (114) M. Ward and G. A® Welch, J. Inorg. Nucl. Chem., 2, 395 (1956)0 259

Extensive studies^ have been made of the stability of

(115) S. Ahrland? Acta Chem. Scand.? 10? 723 (1956)» (116) A. J. Poe and M. S. Vaidya? J. Chem. Soc»? 1023 (1961). halide complexes in aqueous solution. Correlation of these stabilities with periodic properties such as ionization potential? electronegativ­ ity? valence or oxidation number? and ionic or covalent radii have not given a completely satisfactory explanation. Recent investigations have indicated that the stability of metal-halogen complexes is di- 117 rectly related to the degree of covalent character of the bond.

(117) Ho M. No H. Irving? International Conference of Coordina­ tion Chemistry? London? 1959° Special Publication Mo. 1 3 ? The Chemical Society? London? 1959s p° 13°

Evidence for the covalency of metal-ligand bonds in KgPdBr^? KgPdBr^?

KgPtCl^? i^PtCl^ ? and KgPtBr^ was found by Ito et alo~~^ from the

(118) Kazuo Ito? D. Nakamura? f. Kurita? Kaji Ito? and M. Kubo? J. Am. Chem. Soc.? 83? 4526 (1961).

quadrupole coupling constants of the halogens. Further direct proof

for the covalency of chloride complexes of paramagnetic platinum

group metals is given by the paramagnetic resonance experiments of 119 120 Gwen and Stevens? x ■ Ito? Nakamura and Kubos and. by Marram?

(119) J* Owen and K. W. H. Stevens? Nature? 1£1? 836 (1953)= (120) K. Ito? D. Nakamura? and M. Kubo? Inorg. Chem.? 2? 690 (1963). 260

McNiff? and Ragle.121

(121) E. P. Marram? E. J. McNiff? and J. L. Ragle? J. Phys. Chem., 6 7? 1?19 (1963)•

Although this evidence indicates an increased thermal stability would be expected for the platinum group elements as a result of a relatively large amount of covavalency, factors other than the stability of the metal-halogen bond must be considered in order to explain the relative stability of complex ions in solution. An equilibrium con­ stant measured in aqueous solution is essentially a ratio of the stability constant of the complex ion? ML^> to the stability constant of the solvated ion? MS . The change in energy in the process is determined by the difference in energies of formation of the gaseous particles? ML^ and MS^? by the difference in their solvation energies? by the energy of solvation of L? and by the heat of vaporization of the solvent? S. Quantative thermodynamic data needed to evaluate

theories in the case of complex ions in aqueous solution are? in many cases? not known. Correlation of Af ° values with calorimetric-

ally determined £H° and corresponding AS° values for metal

complex formation in aqueous solution should lead to a greater under­

standing of the nature of metal-ligand interaction. The calorimetric 122 study of Christensen et al. of the mercury (II)-halide systems

(122) J. J. Christensen? R. M. Izatt? L. D. Hansen? and J. D« Hale? Inorg0 Chem.? 130 (1964-).

has emphasized the importance of ion solvation as well as bond

energies in determining the relative stability constants® APPENDIX

Absorbance of Palladium (II) Perchlorate Solutions

Absorbance of Palladium (II) Perchlorate Solutions Containing Chloride

2 6 1 2 6 2 TABLE 60

ABSORBANCE OF PALLADIUM (II) PERCHLORATE SOLUTIONS PREPARED FROM STANDARD SOLUTION NO* 9

Std.Soln. 9 9 9 9 9 9 9 9 Solno 1 1 2 4 3 3 3 5 MO 0 UPdxlO^ 3.5? 3*57 6 .8 3 3*26 3.26 3*33 1*30 0 (HO%) 0*401 0.401 1.012 0*482 04482 0.489 1.13 1.14 (KClOij.) 0*045 0.045 0.00 0.00 0.00 0.00 0*00 0.00 cm* 0*998 0.998 0*998 0.998 0.998 0.998 5,00 5*00 days 5 181 1 2 181 363 4 3

AjmM, A A AAA AA A

260 lam — O 0O68 0.036 0.044 0.0545 0.099 0*068 270 0*0575 0.051 .043 .025 .0305 .0395 .0655 .050 280 .0385 .0365 .027 .0165 .0215 .0275 .0445 .0335 290 .0265 .0305 .0235 *0135 .0145 .022 .035 .02 5 300 *028 .032 .0325 .018 .0205 .023 .041 .0245 310 .0385 .0425 .0565 .0295 .0315 o0335 .0615 .0335 320 .0615 .0645 .1035 .0525 .0545 .058 .1045 .0545 330 .101 .102 .182 .093 .0895 .0925 ol715 .0855 340 .155 *1545 .283 .143 *1395 .141 .2645 .132 350 .212 .2125 •390 *196 .194 .196 .369 .185 360 .264 .264 .490 .243 .241 .244 .466 .234 365 .282 ------.531 .262 .269 *261 *501 *252 370 *297 .2965 *5555 .274 .2705 .2745 *528 .265 3 75 *304 *571 .2805 .2?8 .281 .543 *273 378 *306 .305 .576 .281 — .2825 *548 *275 380 .306 *305 .576 *282 *279 *2835 *549 o2?5 382 .306 —, •575 .281 .283 *549 *2755 385 .3035 .572 .280 .276 .281 *5465 .274 390 *2975 *2955 .561 .274 .271 *275 •5335 395 .287 .5435 .265 .261 .265 *517 .2605 400 .270 .272 .512 .246 .248 .252 *4925 .2505 410 *240 .241 .4555 .219 .2195 .223 .4385 .223 420 .203 .204 *389 .185 .186 *1905 *3745 .191 430 — —- .314 .148 .150 *152 .3025 .1545 440 .124 .1245 .238 .112 .113 .115 .230 .1185 460 .060 .062 .116 .054 *053 0O56 n ac .0565 480 .028 .030 *052 .025 .025 .025 .0485 .025 500 .017 .0185 .032 .016 .016 .015 .029 .014 550 .018 .008 .009 .008 .017 .008 600 *009 .005 ■005„ .0035 .008 .002 263 TABLE 6 1

ABSORBANCE OF PALLADIUM (II) PERCHLORATE SOLUTIONS PREPARED FROM STANDARD SOLUTION NO, 14

(HC10^)=lo02 M T=23°C

Stde Soln. 14 14 14 14 14 14 14 Soln. 1 1 2 2 3 4 5 £'Fd x 103 13.62 13.8 8.16 7*96 5*45 2.717 0.681 t>j cm. 1.000 1.000 1,000 1.000 1,000 1,000 5<>00 At 21 d. 13 mo. 1 hr. 12 mo. 1 hr, 1 hr, 5 brs 21 d. 24 d. X A AA A A A A

270 0.099 0.1195 0.0424 0,2043 0.041 0 .022 0.0295 280 ,0695 ,0968 .0432 . 2048 .028 .016 .0195 290 .060 .100 .0367 , 2415 .027 .014 *0175 300 ,074 ,1285 .0473 . 298 ,032 .017 .0225 310 .120 .1835 o0751 *3557 ,0515 .026 .034 315 .159 ,2245 .0987 .381 .0665 .034 .0455 320 .210 .2755 .130 .404 .087 .0455 *057 325 ,276 .334 .168 ,420 .114 *057 .0725 330 .354 .410 .2154 . 4405 .1455 .0734 .0925 340 .550 .596 *333 • 503 .224 .0112 .1415 350 .772 .8035 .4684 * 5795 .314 .1565 .1965 355 .3312 _ — _ • 355 •177 a 22 2 360 .973 .998 *590 .646 *395 .1965 ,247 365 .633 .6703 .426 ,211 ,2675 370 ,665 .6875 .446 .223 .281 375 1.150 ,6846 .6895 .4585 .288 378 1.160 .6928 .6875 .463 .2315 .291 380 1.160 . *693 .6825 .464 .2318 .292 382 — 1.160 *693 • 6795 .4635 .2315 ,291 385 ..... — .6895 . 670 .4605 .2305 .290 390 .674 . 6495 ,451 ,2255 ,2845 395 1.089 .632 .624 *437 .218 .276 400 1,040 .6226 *5945 .418 ,208 .2625 410 .916 ®923 *5563 .5235 .370 .185 •2345 420 .7 85 .788 *4733 .4445 .318 ol603 .200 430 .634 .6385 *3835 . 360 o258 .129 .1625 440 .485 ,488 .2945 . 2752 .196 *099 .125 460 .2365 .2365 .1445 .134 .0965 .049 .0615 480 ,1065 .1067 .0633 .0602 .043 .022 ,028 500 .0635 o064 .038 .0367 .026 .013 *0175 264 TABLE 62

ABSORBANCE OF PALLADIUM (II) PERCHLORATE SOLUTIONS PREPARED FROM STANDARD SOLUTION NO* 6

(HCIO^O.956 M T=25°C« 1,00 cm. cell length

EPdxlO3 2 1 .8 13.1 8,73 6.97 3.48 2 ,6 2 1.72

Agmii. AA AA AA A

330 0,5 6 0 0.337 0 ,2 2 6 0 .1 8 2 0.091 0.067 0.045 340 0*877 .530 •359 .284 .142 .106 .070 350 1,24 .735 .499 .399 .1995 .149 .098 360 1.57 .940 ,6 2 8 .502 .252 .1895 .124 365 1 .6 8 1 .0 1 0 .675 ,540 ,271 .203 .134 370 1.78 1,064 ,7105 o569 .285 .214 ,141 376 1 ,8 0 1.095 .732 ,585 .2945 .221 .145 378 1.81 1 .1 0 2 .736 ,589 .2955 .222 .1455 380 1.82 1 .1 0 2 .737 .590 .296 .222 .146 3821 1.82 1.100 .736 .588 *2955 .222 .1455 384 1.81 1.098 .7325 0586 ,2945 .221 .145 386 1,8 0 1,091 •729 .582 .294 .219 .144 388 1.80 1.082 .7215 ,5785 .290 ,217 ,143 390 1.78 1 .0 6 8 .717 •5725 ,288 .215 .1425 395 1.73 1.035 .693 .554 ,279 .2075 .13? 400 1 .6 2 0,984 .6 5 9 .528 .266 .1995 .1295 410 1.45 ,873 .583 .466 o235 .177 .1145 420 1.24 o745 .498 .399 .200 .1495 .097 440 0.751 ,4525 ,3043 .243 .123 .0915 .058 460 0.3615 .2195 .1465 .1165 .058 .0425 .027 480 .1645 .0995 .067 .053 .027 .0195 .011 500 .0995 ,060 .0405 .032 .01? .0115 .007 550 .058 .036 .024 .018 .009 .006 .003 600 .027 .017 .012 .009 .005 .0025 .0005 265 TABLE 6 3

ABSORBANCE OF PALLADIUM (II) PERCHLORATE SOLUTIONS PREPARED FROM STANDARD SOLUTION NO. 10

(HC104)=1o04 m T=25°Co 1.0 0 0 cm. cell length

Std. Soln. 10 10 10 10 10 10 10 H T d x 10^ 19*65 9-83 7-87 3*94 3ol4 1.96 3.70*

XjmM- AA AA A A A

275 0 0O645 0.0515 0 .0 2 6 0.018 0.013 280 •""“9 .0445 .036 .021 .015 .0115 0.013 285 0o091 •033 .029 .018 .013 .0105 .011 290 *070 .029 0O275 .018 .0125 .0098 .0115 295 0O675 *033 .030 .019 .014 .011 300 *0815 .041 0O36 ,0225 .0165 .012 .018 310 <>149 .078 .064 • 037 .028 .018 .032 320 o?.84 .146 .119 .063 .049 5 o0315 •057 325 •377 .190 ol55 • 079 .0625 ,,038 .0725 330 *4935 .249 .2005 .102 o032 .0505 .094 340 •782 •393 *318 ol59 .128 .079 .148 350 ___ •557 .448 .224 .179 .111 .2095 360 *702 *565 .2825 .2255 .1425 .265 365 ---- .762 .610 •305 .2435 .1525 .285 370 — •797 .640 .322 •3565 .1605 .302 375 .822 .660 • 330 .265 .165 .311 378 •— - .830 .666 • 332 .2665 .1665 380 .834 .667 • 334 .2665 .1665 •3135 382 .832 .666 .2665 0I665 385 .828 .660 .332 .2655 0I655 •311 390 — .815 .649 .325 .259 .161 •3055 395 »792 .628 • 3155 .250 •1565 •2955 400 »■-— •754 .600 .3005 .2395 .1505 .283 410 — 9673 •533 .268 .212 •133 .250 420 I.I67 *572 •453 .229 .181 .112 .213 430 .946 •4575 .366 .1855 .146 .091 .172 440 .7225 *354 - .142 olli .068 .1315 460 • 3535 .170 •137 .0675 .053 o0325 .0635 480 .1605 .078 .062 o0315 .0245 .015 .0285 500 •0955 .048 •037 .019 .0145 .008 .017

^Absorbance measured o months after mixing TABLE 64 266

ABSORBANCE OF PALLADIUM (II) PERCHLORATE SOLUTIONS PREPARED FROM STANDARD SOLUTION NO® 16

(HC10^)=la00 M T=25°Ce

Std c fioln. 16 16 16 16 Soln® 1 2 3 4 T f d x 103 19.04 7 .6 2 1.904 0.951 b? cm. 0.998 0.998 5.00 5.00 Ajmn A ■flA AA

265 0.0383 0.0193 0.0235 0.0145 270 .032 .0165 .0205 .012 275 o0292 .0147 .0185 .011 280 o030 .0145 .019 .011 285 .0335 .0165 .0215 .0115 290 .0416 .020 .0245 .013 295 .0547 .024 .032 .0165 300 .075 .032 .042 .0225 305 .1037 .0445 .056 .029 310 .146 .060 .0755 00395 315 .2017 .083 .105 .0535 320 .2 75 .1105 .142 .072 330 .477 .193 .2433 .123 340 .751 o303 o3783 .191- 350 1 .066 .4285 o5345 .2705 360 1.345 •5405 0673 .338 365 .5845 .727 .365 370 06135 .?64 .3825 375 06315 •789 .394 378 «... <.6345 .792 .3975 380 .6365 .795 »3975 382 06355 «7925 .3975 385 .789 .395 390 —- .6195 .771 .3865 395 •5995 .746 .3745 boo *5725 .718 .361 410 1 .2 6 8 .508 0637 .321 420 1.084 *4345 o545 .2745 430 .8805 .3515 .4425 .222 440 .672 .2695 o338 .171 460 .3263 .1305 .1647 .0837 480 .1455 .058 .0745 .0385 500 .0865 .0345 .0445 .023 520 ,067 .027 .0365 .019 540 .0565 .0225 .030 o0155 2 6 ? TABLE 6 $

EFFECT OF PERCHLORIC ACID CONCENTR. 'ION ON THE MOLAR ABSORPTIVITY OF PALLADIUM (II) PERCHLORATE SOLUTIONS PREPARED FROM STANDARD SOLUTION NO. 10

T=25°Cc 1.000 cm. cell length

Std. Soln. 10 10 1 0 10 E'Pd x 103 3^94 3->93 3=93 3=93 (H C IO ^ ) 1 . 0 4 2.75 3=60 4.46

Ajmix A e A e A e A e .

270 « = .«=» 0.012 3.1 0.018 4.6 0.0145 3.4 280: 0 .021 5=3 .0095 2.4 .0155 4.0 .0 1 1 2.8 290 .018 4.6 .011 2.8 .011 .28 300 .0225 5=7 .013 3.3 .017 4.3 .015 3 .8 310 <>037 9.4 .026 6.6 .026 6.6 .025 .6.4 320 .063 16.0 ,0505 12.9 .0485 12.4 .0475 12.1 330 .102 25o9 .0905 23.O .088 22.3 .083 21.1 340 .159 40.6 .142 3 6.I .139 35=4 .129 3 2 .8 350 .224 57=1 .207 52.7 .1985 50.4 .1 9 1 48.6 360 .2825 70.2 .266 67.7 .2565 65 .2 .250 6 3 .6 363 . 3 0 5 77 o7 .2895 73=7 .280 710 2 ... —.. 370 .322 81.? .306 77=9 .298 75=8 =295 75=1 375 •330 8 3 .8 .319 81.2 =313 79=6 .311 79=1 378 .332 84.5 .322 81.9 =317 80.7 =313 79=6 380 .334 84.8 .325 82.7 .321 81.7 =317 80.7 382 _—— °325 82.7 .322 81.9 .318 80.9 384 --- o325 82.7 .322 81.9 .320 81.4 386 — o325 82.7 .321 81.7 .321 81.7 388 — .3245 82.6 =3195 81.3 .322 81.9 390 .325 82.5 .3225 82.1 .318 80.9 .321 81.7 395 •3155 80.0 .312 79=4 =313 79=6 =3135 79=8 400 .3005 76.3 .299 76.1 .300 76.3 .304 77=4 410 .268 68.0 .270 680? .274 69=7 .276 70.2 420 .229 58.1 =235 59.8 =2395 6o.9 .244 62 ©0 4 3 0 .1855 47.1 .193 49.1 .197 50 .1 .203 5I oD 440 .142 36 .0 .149 37=9 =153 38.9 .161 41.0 460 .0695 17.1 .074 18.9 .078 19=8 .083 21.1 480 o0315 8.0 .033 8.4 .036 9.2 .038 9 = 7 500 .019 4.8 .0195 5.0 .021 5.4 .022 5.6 55 0 ■ Q M S .0125 3.2 .013 3.1 .0135 3 .4 600 .0 0 7 1 . 8 .007 1.8 .008 2.0 268 TABLE 65 (Contdo)

EFFECT OF PERCHLORIC ACID CONCENTRATION ON THE MOLAR ABSORPTIVITY OF PALLADIUM (II) PERCHLORATE SOLUTIONS PREPARED FROM STANDARD SOLUTION NOe 10

T=25°Cc 1.00 era. eell length

Stdo Soln0 10 10 : 10 SPd x 103 3*94 3«93 3*96 (HC104 ) 5.16 7o 9 9.57 days 1 1 1

OB* A smii A e A e A e

270 .014 3.6 .0155 6.2 « M n « o 280 o0095 2.4 .0105 4.2 .0175 4.5 290 .009 2.3 .0092 3.6 o0135 3.4 300 .013 3*3 . 0 1 1 4.3 .0175 4.5 310 00235 6.0 .015 5.9 .021 5®3 320 .043 10.9 .0245 9.7 .0325 8.3 330 °o?55 19.2 o0395 15.5 .051 13.0 340 .1225 31.1 .0653 25.6 .08$ 21.6 350 .180 45.7 .0975 38.3 .1285 32.8 360 .238 60.5 *1335 52.4 .180 45.8 370 .285 72.4 .1642 64.4 .2285 58.1 380 .311 79.0 *1855 72.8 .265 67.4 385 .192 75.3 --- 390 .3148 79.9 .1945 76.3 .2855 72.6 394 — — .195 76.5 — t o * 396 — .1955 76.7 .292 74.3 398 W M Q i M i a a a .195 76.5 .2925 74.4 400 .3042 77 o2 .1933 75.8 .2915 74.2 406 — n w w .288 73.3 410 .2813 71.4 .1843 72.3 .2845 72.4 420 .248 62.9 0I683 66.0 .269 68.4 430 .2075 52.7 .1475 57.9 .243 61.8 440 ..1663 42.2 .1225 48.1 .2095 5 3 0 460 .08? 22.1 .071 27.9 .135 34.3 480 .041 10.4 .0355 13.9 .072 I8.3 500 .0225 5.7 .0183 7*3 o036 9.2 269 TABLE 65 (Contdo)

EFFECT OF PERCHLORIC ACID CONCENTRATION ON THE MOLAR ABSORPTIVITY OF PALLADIUM (II) PERCHLORATE SOLUTIONS PREPARED FROM STANDARD SOLUTION NO. 10 T=25°C. 5.00 cm. cell length

Std. Soln. 10 10 Y’Pd x 103 1.965 0.794 (HC104) 10 06 11.3 At j days 5 1-5

A'jinp. A e A e

270 0*182 18*5 0.167 42 280 c,0 6l 6.2 .060 15 290 *024 2.4 .024 6 300 •0185 1.9 .016 4 310 *0295 3.0 o,0l6 4 320 *0565 5*7 .024 6 330 elDO 1C. 2 .036 9 340 *173 17 06 .0635 16 350 o276 28.1 .107 27 360 o402 40.9 .156 39.4 370 o525 53 «4 .206 52 380 0628 63 o9 .254 64 385 *665 67 o7 cnma « 390 0696 70.8 .286 72 395 o715 72.8 .298 75 400 *728 74.1 .304 76.5 402 *729 74.2 406 o732 74*5 .308 78 410 *?28 74.1 .310 78 420 »705 71.8 .304 77 430 06 55 66 *7 .290 73 440 °590 60.1 .267 6? 460 .407 41.4 *195 49 480 *230 23.4 .117 29 500 0I21 12.3 .064 16 600 o0245 2.5 .011 3 270 TABLE 66

EFFECT OF PERCHLORIC ACID CONCENTRATION ON THE ABSORBANCE OF PALLADIUM (II) PERCHLORATE SOLUTIONS PREPARED FROM STANDARD SOLUTION NOo 6

IPd=4«36 mM T=26°C. loOO cm. cell length

Std.Soln« 6 6 6 6 6 6 6 6 (HCIO^) 0*186 1*12 2.06 3 4*89 5*81 6.74 8.61

A A A A AAA A

320 0.074 O0O65 0.0645 0.061 O.O565 0.0545 0*0445 0.039 330 *124 .1125 *109 .100 ,092 .088 .076 *0655 340 *190 . 178 .171 .155 *146 .138 *124 *106 350 *264 C.250 .242 .222 . 210 .1995 .184 *158 360 .32? *314 .306 *287 •275 *2635 .245 .2175 365 ,352 *3375 •331 *315 .302 .291 .2745 .245 370 .3655 • 356 *350 *335 .324 •3155 *306 *2705 372 «>370 .366 ... *341 *331 —- ... 375 *375 .361 *348 .3405 *332 *318 .292 380 .376 .369 *386 *3575 •351 •3435 •330 .3085 382 *374 *367 *3 59 *354 .>7 •335 a m i d 384 *3725 ------...— *3 55 .338 385 *3715 *367 *3655 .360 ... •350 ... *320 386 *3^9 *363 *3605 *356 •3505 *340 .3225 388 *366 .361 •359 •355 *352 *342 •3255 390 0362 *358 .360 ®358 •355 •352 .343 .328 395 *350 *348 .350 •351 *3505 *349 *341 .331 400 *332 *3295 •335 *338 •339 •3395 •3345 •329 406 — ... .326 *324 •323 408 — a™ — M .321 *320 .320 410 ®293 .292 .298 *309 •313 •3155 .3145 *3175 415 — .290 .300 *3005 .306 420 *247 *247 *2555 *271 •375 *281 *284 *2945 430 *1985 *199 .207 .223 .232 *2395 *244 .261 4^0 *150 * 1*51 ol595 •1755 .184 •1925 .1985 o221 450 *1075 *1075 .1145 *129 .138 •1455 •1535 .178 460 *074 *073 .078 *089 • 097 *103 .110 .134 470 .048 .048 *050 *059 .065 *0705 *076 .097 480 *034 *033 .034 .041 .045 .048 o053 *068 490 *026 *025 .025 .029 .032 .0345 .037 .048 500 .022 *0205 .020 *024 * 0245 .026 .0275 .036 271 TABLE 6?

EFFECT OF PERCHLORIC ACID CONCENTRATION ON THE ABSORBANCE OF PALLADIUM (II) PERCHLORATE SOLUTIONS CONTAIN BIG CHLORIDE

EBd=4<>36 igM 233aCl=2*68 mM T=26°C* loOOO cm* cell length;

Std. Soln*. 6 6 6 6 6 6 6 (h c i o 4 ) 0*998 1*40 2 o06 3*00 3 ©94 5«34 6*27

A AA A A A, A

320 0o097 0 S0965 0*0995 0*1015 0*101 O 0IO3 0*101 330 ©100 o098 .098 .098 ©094 ©092 *0885 340 -133 *129 .1265 ol23 ©115 *108 *1024 350 *1935 0I885 *183 ©177 0I65 ©153 *143 360 *2755 ©2?0 *262 ©253 ©238 *222 .2065 365 *322 *315 *306 o2965 *282 s26l *2455 370 0 6 7 5 *361 ©3525 ©342 ©325 *305 ©286 375 *413 *408 ©3975 ©387 ©370 *3495 *330 380 *456 *450 *440 *432 *416 ©3925 ©373 382 *472 *46?5 ...... ©391 CO 385 ©472 0 *436 o419 386 *501 ©497 390 *53 0 *523 .5165 0508 *496 *476 *458 395 *556 *538 ©529 *510 *494 396 *557 ©5535 *5435 400 *5665 ©564 ©561 ©556 ©550 *542 ©5275 402 *^69 *5675 .565 *561 405 *569 ©569 ©569 ©567 406 *569 *568 --- *568 .565 ©555 408 *567 *566 *568 *568 ©570 ... ©5625 410 ©560 *561 *564 ©568 ©569 ©572 ©567 415 *54-25 *543 ----- ©5585 420 ©514 *518 *525 ©535 ©543 .562 *5 69 430 .4365 .441 *454 *4665 *4835 *511 *529 440 •351 ©355 ©369 ©383 *404 *438 *458 450 *270 *276 *287 *300 .320 *354 ©375 460 ©199 *201 .212 *223 ©2395 *270 *292 470 *1425 .145 ©154 *162 *174 *199 *217 480 *103 *104 *110 .116 .125 .144 *159 490 *076 o0775 .081 *084 *0905 *105 *115 500 *058 *0585 .062 *064 .068 ©0775 *085 272 TABLE 6 8

THE ABSORBANCE OF PALLADIUM PERCHLORATE SOLUTIONS CONTAINING CHLORIDE

(H*)=loOO M T=25°C © 0«996 cm. cell length

O 1 2 3 4 5 SPd x 10J 7.23 7*23 7o23 7.23 7*23 SCl/SPd 0 0,0599 0,1193 0,1196 0,1798 A.j.my> AAAA A

325 0 *1405 0 .136' 0,131 0,1325 0,1293 330 81835 •177 ■ •169 ,170 •I65 340 *2887 *2795 ,269? ,270 ,,2617 330 *408 •3977 •3845 •385 •3763 360 *514 •507 ,498 •500 <-495 370 *5868 ©588 •589 •590 •5935 38O ,607 •622 0636 0637 •653 390 -593 0620 •647 o648 0679 400 o5475 •589 0626 •628 0667 410 •485 •5317 •5755 •5785 0620 420 *4155 •4585 •503 •5035 •548 430 •3355 •3735 ,415 •417 •4525 440 •2585 •288 •323 •3245 •354 430 . *1843 •209 .2383 •239 ,263 460 •124? •144 .1655 .1663 .1843 470 •0825 0O967 .113 .114 .±2? 480 .0565 .066 .078? •0793 .0892 490 •0417 o0393 ,058 .0589 ,0653 300 •0338 •0403 •0463 .0465 .0517 520 .027 .0305 0O345 *035 .0383 540 .022 •025 •0285 .0293 ,0317 560 .018 •021 .0235 •0237 ,026 TABLE 6 9

THE ABSORBANCE OF PALLADIUM PERCHLORATE SOLUTIONS CONTAINING- CHLORIDE + Hi Tf 0 0 0 M T=:250 C O 0*996 cm. cell length

2 3 4 5 6 7* 8 EPd x 103 4 o374 4*34 4*34 4*34 4*34 4*34 4*374 4*34 2Cl/sPd 0 O d 9 9 0*403 0*497 0*696 0*99 1*48 1*49 Aginy< A A AAA A AA

320 0o064 O 0O6O « . « ■ » 0*0745 0*105 0*210 0*5955 0*584 330 .1115 <,098 0.090 *091 *0995 *145 o365 *357 340 *1748 0I547 *1375 ol32 *1235 *128 .2168 *2125 350 *247 *2243 .203 *194 *179 *1615 *1698 *167 360 *3107 o296 *2795 *275 .260 »237 .2073 *206 370 *353 *355 .356 *358 o355 *344 *308 *3063 380 *3658 *3945 *4195 *433 *450 *464 *44? *4445 390 •3571 *4125 *465 *4895 ->532 05775 06005 *597 fj-oo *3298 <,408 *481 *519 *592 *66l *7395 *736 410 0 294 ®379 *465 *508 *588 *6905 *8185 *8165 420 *252 *336 *7215 *461 *544 *657 *8195 .815 430 *2038 *280 ?356 o3915 *467 o5795 *752 *745 440 0I563 c219 *2835 *313 *3?8 *476 *6405 *635

450 oll24 0I635 *2143 *2387 .294 *372 ’ *5185 *511 460 *0767 .115 *155 -1735 *216 *282 *4005 *3955 470 0O50 *080 *109 *1235 ol 565 *206 *301 .2967 480 o0345 0O56 ,078 0O885 *112 *1495 *224 *220 490 .0255 *0425 *0565 *0625 *0825 *111 *1663 .1637 500 o0213 o032 *0445 *0495 *062 *083 *1217 .1205 520 0OI66 e0245 *0315 *0345 *043 *0535 o0715 *071 540 0OI38 .021 *0255 .0288 *0338 *0415 *051 o050 560 0*115 ,016 *021 *0235 *027 *0338 *0418 *0413

^Prepared from reagent-grade hydrochloric acid m - TABLE 70

THE ABSORBANCE OF PALLADIUM PERCHLORATE SOLUTIONS CONTAINING CHLORIDE

(H+)=1.00 M T=25°C. 0.996 cm. cell length

10 11 12 13 14 15 16 IPd x lo3 4.374 4.34 4.35 4.35 4.35 4*34 4.35 4.3 5 ECl/SPd 1.778 1.99 2.184 2.48 2.68 2.98 3.47 4.59 Lpmp A AA •it* AA A A

330 0.582 0.737 0.9215 1.2.07 1.38 1.63 ... 340 .322 .399 o4975 0.646 0.743 0.895 1.14 1.50 350 .2005 .224 .264 .321 .521 .426 0.525 0.672 360 .1995 .194? .1997 ,207 .5595 .232 .262 .3094 370 .2835 .266 .2565 .2395 .2315 .224 .2167 .207j 380 .4215 ,4005 .384 . 359 .342 .3245 o300 .261' 390 .5898 *572 .560 .535 .519 .493 .458 .400 400 .7503 .7485 .745 .731 .715 .693 .657 410 .8598 08785 0883 .881 .865 .837 .770 420 • .8868 .914 »937 .957 .959 ... .941 .891 426 ®$6l8 .923 .951 .958 .958 .961 .919 430 ,8298 0867 .900 .929 .939 .951 .954 .921 440 .7208 .759 .7955 .829 .847 .866 .883 .879 450 .5922 .6265 .660 .700 .720 .741 .772 .791 460 .4622 .4965 .529 0568 .589 .615 06485 .684 470 *3538 .381 .412 .448 .466 .497 °535 .583 480 ,2672 .291 .3167 .3497 0366 «395 .434 .487 490 .1995 .219 ' .2415 .270 .2845 .310 .3463 .397 300 .1468 .1615 .179 .1995 .213 .2345 .2653 .309 520 .0833 .090 .0985 .108 .115 ,1245 .1415 .164^ 540 .0563 .0585 .0617 .0645 .0667 .0705 .0775 .085 560 .0453 .0465 .0488 .049 .050 ,0513 .10535 ,054:

^Prepared irora reagent-grade hydrochloric acid 275 TABLE 71

THE ABSORBANCE OF PALLADIUM PERCHLORATE SOLUTIONS CONTAINING CHLORIDE

(H+)*1.00 M T=25:°c. 0.996 cm. cell length

17 18 19 20* 21* 22* 23* 24* EPd x lO^ 4 .3 4 4 .34 4 .3 5 4*355 4.355 4.355 4.355 4.355 ICl/LPd 6 .8 9 9 o21 1 1 .3 1 3 .8 I 8 .3 22.9 27.6 32.1

A jmii, A A A AA A A A

350 0*8335 0.925 0.9845 1.016 1.066 1.099 1.113 1.138 360 *3698 .412 .4435 0.460 0.487 0.504 0.513 0c523 370 »2075 ' .2125 .2195 .2242 .227 .229 .229 .2315 380 *2205 .200 .1915 .1845 .170 .1607 .153 .1492 390 •330 .292 .2675 .2515 .2215 .2013 .187 0I 788 400 *4955 .443 .404 •3 ?6 *332 .3015 .2815 . 26? 410 .6695 .6025 .5525 .517 .4595 .4205 .392 .371 420 <•7935 .7225 .6685 .630 0568 .522 .490 .4685 426 0834 .7665 .7165 .6765 0615 .571 •539 .518 430 .844 .784 *738 .699 .639 .598 .5675 .548 436 .843 o793 .7515 .7185 0665 .628 .6005 .684 440 .831 .7885 *751 .7235 06778 .642 .619 .6035 450 °7 77 *755 •738 .7195 .692 0669 .653 06445 460 .704 *705 .705 o?00 .691 0683 0677 .675 466 0636 0669 .679 .6805 068I 068O .680 .681 470 0624 .643 0658 06635 .670 .674 06765 0679 480 .5425 •5735 .598 .6085 .6245 0634 .6415 .648 490 .455 .4887 .5165 ,5305 .5495 .564 •5745 0582 500 .360 .392 .419 .4305 .4485 .461 .4715 .477 520 *1938 .210 .227 .2348 .2437 .250 .259 .259 540 o0943 .1005 .10? .1098 .112 .114 .117 .1164 560 .0565 .058 o0597 .062 .061 0O60 .060 .0595

^Prepared from reagent-grade hydrochloric acid 276

TABLE 72

THE ABSORBANCE OF PALLADIUM PERCHLORATE SOLUTIONS CONTAINING’ CHLORIDE

T=25°Ce 0o966 cm. cell length

25* 26 27* 28 29 30 31 32 EPd x lo3 4.355 4 .3 4 4.355 4 .3 4 4.34 4,34 4.34 4.35 2Cl/lPd 4 5 .9 69.O 91.8 192.0 0,155 O 0I38 0.161 1 ,8 3 (H+) 1 ,01 1 ,0 1 1.0 1 1.01 1 .0 1 1.01 1,01 1 .0 5

A AA AA A A A

355 0.819 0 0847 0.852 O .857 O .865 0.873 0.879 0.879 360 .5485 .56 7 .5705 .576 *577 .5835 .5395 .588 370 .238 o241 .242 .242 .2435 • 2455 .2465 .2445 380 .142 ol345 .1337 •1315 ,1295 .1285 .128 .1275 390 .160 .142 .137 .133 .1295 .1265 .124 .1223 400 .235 .206 •197 .1935 •1855 . 181 .1765 .174 410 6 331 .294 .2815 .278 .2665 •259 ,254 .2497 420 •^235 .379 .3645 .362 .3485 .340 .128 ,330 430 .500 .4595 *4455 .4415 .430 .4225 .418 .4125 440 .566 .532 .5215 .518 •507 .500 ,498 ,498 450 .6215 .599 •5955 •593 .586 .5815 •579 .578 460 «665 o6555 .6555 .654 ,650 .649 ,649 .6488 466 .680 .678 .680 0679 .679 .679 ,679 •679 470 .683 .685 .690 .689 .689 .690 ,692 06925 476 .6?? .681 .6885 ,688 .690 ,6915 •6935 .694 480 o6595 .669 .6745 .675 .678 .681 .683 .683 490 o5975 .610 .6145 .6165 .619 ,623 ,624 .626 500 .4927 .508 .5105 .514 .5165 .521 •523 o523 310 .379 .393 .396 .398 .400 .405 .406 ,405 520 o2695 o2795 .2798 .282 .283 .2865 .2865 .286 540 .1205 .124 .1243 .1245 .125 .127 .1265 .1265 560 .061 .0615 .0615 ,0613 .0615 .0617 .0615 .0615

& Prepared fl’om reagent-grade hydrochloric acid TABLE 73 I THE ABSORBANCE OF PALLADIUM PERCHLORATE SOLUTIONS CONTAINING CHLORIDE

T=25°Ce O o966 cm© cell length

33 34 35 36 37 38 39 40 EPd x 103 A ©35 4 ©35 4 ©35 L©35 4.35 4 ©35 4©35 4*35. ECiyfePd 236 344 459 459 689 918 1062 2 « llx l(y (H+) 1©28 1.75 2 ©25 2 ©25 3-25 4 ©25 4 ©87 9=5 355 008775 0.8845 0©8775 008795 O 08705 008635 0.8515 0 ©8045 360 o5905 ©5875 ©590 ©5895 ©5825 o5745 ©5685 o53l5 370 ©245 *2435 ©243 ©2L25 .2402 •2375 ©234 ©2218 38O 0I265 •12 35 ©1225 ©1225 ©122 ©120 ©1205 *1215 390 •©1198 0II5 •1135 .1125 ©114 ©113 oll45 ©1205 LOO ,1695 0I635 ©1605 ©160 ©160 ©l6o ©162 ©1685 410 ©244 ©235 ©2305 ©230 ©230 ©230 ©232 ©2415 420 •323 ©3125 .309 =3093 ©308 •309 ©311 ©3232 L30 ©405 •3955 ©3913 ©3915 •3915 •3917 •396 ©413 440 ©488 ©480 ©478 *479 •4795 ©481 ©485 ©508 450 =574 •569 •569 •569 ©5217 •5735 •578 ©6045 460 ©648 ©648 ©648 ©649 0650 o6535 ©658 ©686 466 ©679 ©681 ©6835 ©6835 ©687 ©690 «692 =717 470 ©694 0695 ©698 0698 ©700 •703 ©705 ©729 476 06965 •699 *701 ©701 ©704 ©708 •707 ©729 480 0688 0689 ©692 ©6915 •695 0697 . 0696 ©714 490 06285 . 629 06315 0631 o6337 0636 0634 06455 500 *525 ©526 ©5285 ©528 •529 •5295 ©5255 =533 510 0L065 0L065 .4085 ©40? 0L085 ©408? ©4045 ©4067 520 02865 ©287 ©2865 ©2865 ©2865 ©2867 ©283 ©2835 540 ©126 •12 55 .126 ©125 ©1245 ©1257 ©123 0I23 560 ©0613 ©0613 ©0613 ©0613 ©061 ©0613 <>0605 ©0493

^Prepared Jtom reagent-gra.de hydrochloric a cid 2?8:

TABLE ?4

THE ABSORBANCE OF PALLADIUM PERCHLORATE SOLUTIONS CONTAINING CHLORIDE

(H+)=loOO M T=25°C. 5.00 cm. cell length

1=!= L 2* 3 4 5 6 7 8* T, Pd x 10H 8.72 8.72 8.68 8.68 8.68 8.70 8.70 8.76 ICl/SPd 0 0.149 0.199 0.403 0.498 0.992 1.195 1.48

AAAAAAA A

325 0o0877 O.O835 0.0795 0.0715 0.088 0.2025 0.3153 330 .1125 .1057 .1025 .098 .100 0.1327 .1675 .2476 340 .1765 .1648 •157 .1443 .142 .131? .139 .1663 350 .2487 o2357 .2265 .2115 .206 .174 .165 .1633 360 .2228

.285 3 •3125 .3047 .2975 .2897 •253 .23900 C^\ 370 »355 059 0553 .3643 .3653 .3578 .3301 38O 0673 091 095 .425 .07 .471 .471 .4645 390 0 5 8 .401 .412 .467 .4895 .5763 .692 .604 400 0312 .3892 .4085 .4795 .516 .6455 .6795 .719 410 .2952 «3594 0785 .4625 .5035 .6635 .7145 .776 420 .2532 0157 .3363 .4178 .459 .6292 .6835 •759 430 .2037 .2607 .2793 .3508 .3888 0492 .2073 .6825 440 .1567 .2027 .2185 .280 .313 .4493 ■ .500 .5735 450 .1127 .1495 .162 .2113 .2395 .3505 .394 .456 460 .0772 .105 .1145 .153 •1735 .2635 .296 .348 470 .0507 .0724 .080 .108 .1232 .191 .2175 .2598 480 .0349 .0507 .0585 .0765 .0895 .1395 .158 .1905 490 .0^67 .0425 .0578 .0665 .103 .1175 .1405 500 .022 .0303 .0335 .0435 .050? .076 .0865 .1043 520 .0172 .0232 .0253 .0325 .03? .051 .056 .0638 540 .0144 . .0195 .021 .02? .030 .040 .0422 ,0477 560 .012 .0152. .0175 .0215 .0247 .0325 .0347 .0385

^Prepared from reagent-grade hydrochloric acid 279

TABLE 75

THE ABSORBANCE OF PALLADIUM PERCHLORATE SOLUTIONS CONTAINING CHLORIDE

(H+)=1«>00 M T=25°C» 5oOO cm. cell length

1. 9 10* 11* 12 13 14 15 16* EPd X icn 8 .6 8 8 .7 6 8 ,7 6 8 .6 8 8 .6 8 8068 8 . ?Q: 8=71 s Cl/£Pd 1*49 1 ,7 8 I >97 2 .1 8 2.48 2=98 3.47 3=67

Apmn AAA A A AA A

330 0 a2472 003456 0 .4198 0,4945 0.6125 0.8045 0.9985 1.177 340 ol67 o208 .2428 .282 .3385 .445 =5375 0 ,6 3 5 350 a 165 al688 .1783 =1913 .2085 .241 .2838 .321 360 o225 a 2103 .2068 .2075 .2025 .2015 .2087 .215 370 .3323 ,3128 *3033 .2973 .2843 .2663 =2593 .2503 380 ,4655 ,4502 .4425 .437 .4205 =393 .3845 =3715 390 ,6055 ,604 .6025 .6023 .5883 .5715 .5625 =549 400 »7185 a 740 =749 =7525 .752 =7495 .7485 =7422 410 *7735 0815 .836 .8495 .8675 .8817 .8925 08967 420 07575 ,814 ,842 08673 .8963 =9243 =9495 .9617 430 .6793 *7435 =778 .8043 .8413 .8833 .9103 =9317 440 «572 0631 .665 =6923 =7318 =772 .806 .829? 450 «4 55 *509 =5398 .564 =6025 0639 .672 .7002 460 *346 .3925 =420 .4392 .4705 =517 =5395 .587? 470 02582 *2955 =316 *3335 .3605 =391 .4215 .4472 480 d8 9 8 o21?8 .2363 .2495 .2735 .2985 .326 =3494 490 a 141 .1627 =1757 .1375 .2055 .2255 .2488 ,2697 500 al035 .1197 .1297 .1375 .1505 .166 0I832 =2002 520 0065 o0711 •0753 .0795 .086 0O925 .102 ol099 540 o048 0O507 <>0527 0O55 .058 .060 .0645 .0677 560 .0395 ,042 .0437 .0443 .047 .04? o0515 .0532

^Prepared from reagent-grade hydrochloric acid TABLE 76-

THE ABSORBANCE OF PALLADIUM PERCHLORATE SOLUTIONS CONTAINING CHLORIDE

(H+)=1.00 K T=25°Co 5.00 cm. cell length

I. 17* 18* ;19* 20 21 22 23* SPd x 1(T 8 .7 6 8.7 6 8.76 8 .7 0 8.70 8.70 8.71 SCl/EPd 4o45 5.2 3 5°92 6.8 9 9.20 11 a5 13.8

A smii A A A A A A A

340 0.7193 0.8223 0.9408 1.036 1.246 1.383 cb 350 *3538 .4068 .4478 0.486 O .383 0.660 0.7042 360 .2173 .2293 .2408 .248 .278 .3083 •3197 370 .2393 .2298 .2235 .216 .211 .2147 .2082 380 .354 •335 o324 .3072 .2825 •2705 .2567 390 o5297 .3067 .491 .4693 .4343 .4103 .3907 400 .728 .7095 o6935 .6715 — .6015 •5777 410 .888 .978 .857 .849 .816 •783 o756? 420 .962 .962 .960 .949 .926 .899 .876? 430 .941 .952 .9585 .955 .947 •92? •9107 440 .845 .862 .878 .879 .886 .883 o8737 450 .719 <-7395 .754 .764 .783 •791 •7897 460 .385 .609 .624 0639 .667 .684 .6903 466 .5095 .536 •5525 .569 .601 .622 .6312 470 .4625 .4275 .306 .5225 •557 .581 o5937 480 .3647 .3873 .406 .423 .458 .483 .4987 490 .283 .303 .320 •3337 .3667 o3955 .4097 300 .210 .228 .2413 .236 .284 .306 .3187 520 .1143 .1228 .1296 .1363 .1513 .164 .1694 540 .0674 o0707 .0737 .0757 .081 .0813 .0967 560 o0507 .0322 .0524 .0537 .0545 .0565 .0552

^Prepared from reagent-grade hydrochloric acid TABLE 77

THE ABSORBANCE OF PALLADIUM PERCHLORATE SOLUTIONS CONTAINING CHLORIDE

(H+)=1«00 M T=25°C. 5*00 cm. cell length

24 25* 2 6* 27* 28 29* 30 31* SPd x 10^ 8®?0 8 .7 1 8.71 8.71 8 .7 0 8.71 8 .6 8 8.71 Lcl/SPd 16 *1 1 8 .3 22.9 27.6 3 2 .2 3 6 .8 69.0 91.9

AAA AA AA A

345 1.093 1.145 1.214 1 .2 7 0 1.321 1.33 350 0.741 0.7817 008327 0 08767 0.916 0.9327 1.045 1 .0 8 3 360 0 3 3 5 .3502 .3687 .3917 .4125 .4182 0 .4 7 4 0.4967 370 *2062 .2075 .2082 .2125 .215 .2142 .2202 .2275 38O *2425 .2352 .2227 .2142 .2065 .2002 .1675 .1642 390 .3673 .3567 .3327 .3157 .2993 .2877 . 2223 .2092 400 .54 95 .5342 .5017 .4752 .4515 .4347 *3405 .315 410 .7285 .7092 o6717 .6392 06H 5 .5927 .4715 .4367 420 .848 .8297 .7937 .7617 .735 .7092 .5823 .5412 430 .893 08787 .8437 .8177 .7955 .7707 06543 .6142 440 .859' <.8527 .8297 .8127 .796 .7767 . 689 .6567 450 .788 .786? .7757 .7677 .762 .7497 .7005 06787 460 .695 .7027 .7042 .7072 .709 =7057 o691 06867 466 0639 o6477 06567 06652 .671 06717 .6795 .6827 470 .60 35 .6142 06252 06367 0645 .6477 .6665 .6747 480 .512 .5267 .5^52 .5612 .573 <=5797 .620 06317 490 .426 .438 .4567 .4737 o489 .4967 <>546 .5592 500 .332 .3452 .3602 .3757 .393 .3972 .437 .4567 520 0I78 .1837 .1931 .2017 .211 .2127 .2437 .2462 540 .089 .0914 o0947 .0977 .102 0IOO5 .1125 .1122 560 .0557 .0557 .0567 .0577 .059? =058 .060 o060

^Prepared from reagent-grade hydrochloric acid 282

TABLE 78

THE ABSORBANCE OF PALLADIUM PERCHLORATE SOLUTIONS CONTAINING CHLORIDE

(H"'r)- 1 6Q0 M T=25°GJ 5.00 cm. cell length

L 32* 33 34 35 36 37* 38 39 SPd x K T 8.75 8 .68 8 .6 8 8.70 8.70 8.70 8.70 8.70 ECl/EPd 115 138 161 184 230 344 460 689

A jBui AAA A AAAA

355 0 o7803 0.7845 0.797 0.800 0.825 O .839 0.850 0.860 360 o5203 .521 .532 .534 •552 .562 .568 •577 370 .2358 .2293 .2338 .233 .2403 .2387 •2373 .238 380 .1605 .149 .147 .1432 .1425 .1345 .129 .1245 390 .196 .179 .1728 .1853 .1593 .1423 .132 .1223 400 *2915 .269 •2555 .245 .230 .207 •1923 .180 410 *406 •3755 •3575 .3455 .326 .2963 .2763 •2595 420 .5065 .4728 .4523 .438 7 •4173 •3813 •3598 .340 430 *5825 .5518 •5313 .5167 .4953 .461 .4413 .423 440 06315 •608 •5915 •5795 .5625 •535 o517 .502 450 0664 .648 .637 06295 .620 .602 •5925 --- 460 068 5 06745 06705 .6685 0665 0659 .6535 .650 466 *687 .6815 .6805 ,680 .682 .680 06785 •680 470 *681 06785 .6805 .6815 06855 ,688 ,6875 .692 476 0662 06655 -- --- 480 *644 .6485 •6535 0656 .6635 .672 .6735 0683 490 ■>577 .5825 05885 •593 .6022 .610 .6145 .623 500 .471 . .479 .484 ,4985 .496 .507 .510 •519 520 •2593 •2635 .266 .2665 .271 •277 .278 .283 540 .1187 *1185 .1195 .1185 .122 .1217 .122 .1237 560 .0622 0O62 .062 •0595 .062 .0595 .0575 o06l

*Prepared from reagent-grade hydrochloric acid 283

TABLE 79

THE ABSORBANCE OF PALLADIUM PERCHLORATE SOLUTIONS CONTAINING CHLORIDE

(H+)=loOO M T=25°Co 10.00 cm. cell length

1 2 3 4 5 6 7 8 SPd x 10^ 4.357 4 0 5 8 4 .3 5 8 4.357 4.357 4.357 4.357 4.357 S c i/S P d 0 0.0992 0 .2 2 3 0.248 0 .3 7 2 0 .4 9 6 0 .6 2 0 0.744

A jiriMi A A A A A A AA

320 O 0O68 0.065 0.0637 0.069 0 .0 6 7 5 0.0748 0 .0 8 5 0.0998 330 .1148 .108 .101 .1042 0 9 7 7 .095 o0963 .0995 340 .1777 .1675 .1575 * 0 5 9 .148 .140 •133 .1295 350 .249 .240 .2277 0 2 9 8 .2155 .204 .1955 .1875 360 .314 0 0 8 .2998 .302 .2915 .284 .2775 .2697 370 0 5 5 05 7 5 0 5 9 .363 .3825 .3625 0632 .3605 380 .3675 0 8 3 0 9 9 8 .4075 .42.0 .432 .445 .452 390 0 5 9 5 08 5 5 .418 .428 .455 .481 .5072 .529 400 0 3 2 O 665 .412 .4255 .463 .5025 .540 .572 mo .2957 0 3 4 083 5 097 5 .442 .488 .5298 06 9 5 420 .254 .292 .038 .3522 0 9 6 5 ‘ .441 .4845 .524 430 .2048 .239 .282 .2925 .332 0 7 1 .4125 .4495 440 *1575 .I85 .2202 .2302 .264 *2975 o3305 .361 450 .114 .135 .164 .1715 .1977 .225 .255 .2798 460 oO 775 .0745 .116 .1222 .142 .1635 0I85 .2043 470 .0507 .063 .080 —_ .1155 <1325 .1465 480 •035 .045 .056 .060 .0705 .0825 .0952 0IO53 500 4.022 .0265 .0325 .035 .0405 .047 .0538 .058 520 .0175 .0202 .0245 .02? .0295 .0326 .0373 .0398 540 .0143 .017 .0198 .0223 .0245 .0264 .0302 .032 560 .012 .0128 .0155 0.OI8 .0197 .0218 .0245 .0255

^Prepared from reagent-grade hydrochloric acid 28**

TABLE 80'

THE ABSORBANCE OF PALLADIUM PERCHLORATE SOLUTIONS CONTAINING CHLORIDE

(H+ )*1.0Q M T=25°C. 10.00 cm. cell length

9 10 11 12 13 14 15 16 £Pd x 10/+ 4.358 4.355 4 0 5 5 4 0 5 5 4.355 4*355 4 <055 4.35 SCl/SPd 1.116 1.98 2.72 3*47 4#96 5.95 7.44 8.93

A?, mu AAAA A A AA

320 0.1755 0.480 0.774 I .050 1 0 3 330 .130 .3005 .4805 0.659 0.990 I.I83 1.43 1.64 340 .1272 ”1935 ®277 .3615 0 33 0.637 0.777 0.8967 350 .1685 .1723 .1928 .2178 .280 0215 077 .4325 360 .2485 .2249 .2125 .2055 .2055 .2138 aCCO .2425 370 0535 0295 0055 .285 ®259 .250 .2395 ®2355 380 .4675 .466 .4465 .4245 087 070 .3507 0375 390 .5655 .612 .6075 0 97 0645 *548 0 23 .5075 400 .6473 .739 • .7615 .7665 .750 .7435 .724 .7095 410 .6673 .801 .8575 .8815 .895 .8965 .888 <•8795 420 .6295 0925 .8705 .9115 .950 .9645 .967 „8?15 430 050 .719 .8035 .8555 .912 .9365 .952 *9595 440 .4505 .6075 .6905 .7445 .807 .8325 .858 .8765 450 052 .4875 .562 .6105 .673 .7025 .730 0515 460 9264 073 .4375 »4795 .540 .657 5 098 .6205 470 .1923 .2805 0325 067 .421 .4475 .476 .5005 480 .1385 .208 .2512 .2805 025 .3495 0752 .3995 500 .0755 .115 .1382 •1555 .184-5 .2005 .2197 *2375 520 .0495 .0705 .0818 •1555 .102 .110 .1193 .1285 540 .0385 .053 .0575 . .088 .064 .0677 .0705 .0745 560 ,0315 .0445 .0422 .060 .0502 .0525 .053 ■.055

^Prepared from reagent-grade hydrochloric acid TABLE 81

THE ABSORBANCE OF PALLADIUM PERCHLORATE SOLUTIONS CONTAINING CHLORIDE

(H+)=1«00 M T=25°C« lOoOO cm0 cell length

1 17 18 19 20 21 22 23 24- E P d x 104 4o35 4*35 4.35 4*35 4-35 4-35 4-35 4*35 SCl/SPd 9c92 1 3 -8 18.4 2 2 .9 2 7 .6 32.1 3608 4 5 .8

Ljmu. AA AAA A AA

345 0 <.6705 0o8075 0.940 1 .0 1 3 1 .0 8 2' lol35 1.178 1.243 350 o46 q -3475 06375 O 06S3 0 *7325 0.7725 0 .8 0 0 0 .8 6 0 355 0-324 o372 -433 *4575 .4905 -5175 -538 .5 8 0 360 -2475 .2705 .305 .3 1 4 c.334 -3495 .360 -3855 370 *2305 o2l88 .222 .2105 .2145 .213 .2127 .2173 380 -3273 -299 .2847 <>263 *2573 o2455 -2365 .2255 390 -4955 .4565 .431 .403 o3875 .3685 *3555 -3325 400 -695 .6565 0622 -5925 *571 .6475 *5285 .498 410 08695 08315 .8 0 1 .7725 *7475 .7225 .7035 0664 420 -9645 •9395 .914 0888 08655 .8425 08235 .7875 430 -9635 o9565 .940 -919 .9045 .8845 08755 .840 440 *8815 .8 8 75 .8 8 8 0878 08675 o8595 08505 0828 450 07625 ®777 .791 ®?90 *790 .7 8 8 5 .7875 *779 460 06345 .6565 .681 .687 .6965 -7015 *7075 .710 470 -5155 .5 4 5 ®573 -589 .600 .6155 .6215 0633 480 .4135 .445 *475 *492 -5075 -527 o5365 .554 490 -3265 -3555 -385 •404 .423 .4365 .4475 .466 500 .248 -2735 *■299 *314 o3295 .34-35 *353 *369 520 ol342 .145 0I605 *1675 *1765 .184 *1905 .2 0 0 2 540 o07 65 -0795 0O855 .0865 .0895 .093 .095 o099 360 o055 .055 0O573 o0573 o0575 0O592 0O585 -0597

^Prepared from reagent-grade hydrochloric acid 286 TABLE 82

THE ABS3RBANCE OF PALLADIUM PERCHLORATE SOLUTIONS CONTAINING CHLORIDE

(H+)=leOO M T=25°C. 10*00 cm. cell length

2* 3* 4* 7* 8* h 1* 5* 6* SPd x 10^ 2.180 2.181 2.181 2.181 2.181 2.181 2.181 2.181 ECl/lPd 0 0.0992 0.124 0.149 0.223 0.372 0.496 0.620 A2m|Ji A AA AAAA A

120 0.035 0.0348 0.0353 0.031 0.0325 0.0305 0.0375 0.0395 330 .0577 .0565 .057 .0515 .051 .045 o0502 .0485 340 .0895 .0865 .087 .081 .0792 .0693 .0745 .068 350 .125 .1217 .1217 .1168 .115 .104 .107 .1005 360 -1573 .155 .1553 .1565 .1505 .1435 .1455 .1405 370 .178 .180 .181 .1785 .1815 .1845 .184 .1825 380 .185 .1925 .195 -1935 .1995 .2098 .215 .220 390 .1803 .193 .197 .1975 .207 .226 .2377 .248 400 *1665 .1835 .189 .1918 .203 .228 *2455 .2605 410 .1477 .166 .172 ■1755 .190 .216 .237 •255 420 .1273 .1445 .149 •1535 .1665 .1947 .2125 .2318 430 .1027 .118 .1225 .126 .1375 ,1625 .180 .195 440 .0795 .091 .0955 .0975 .107 .129 .1425 .156 450 oO 575 .0665 .0695 .0718 .080 .0973 .1077 .1185 460 <>037? .047 o049 .049 .056 .070 .078 .0865 470 .0253 ... .033 .033 .038 .0493 .0555 480 .0175 .0223 .023 .023 .027 .035 .039 .044 500 0OIO5 .013 .0135 .013 .015 .0205 .023 .024 520 .OO85 .010 -.0105 .010 .0115 .015 .016 .0173 540 .0075 w a p s .009 .008 .0095 .0125 .0135 .0132 560 .0057 .007 .0073 .0075 .0072 .0105 .0105 .0105

^Prepared from reagent-grade hydrochloric acid 287

TABLE 8 3

THE ABSORBANCE OF PALLADIUM PERCHLORATE SOLUTIONS CONTAINING CHLORIDE

(H+)=1«00 M T=25°Co 10o00 cm0 cell length

1, 10* 11* 12* 13* 14* 15* 16* SPd x 104 2.181 2*181 2*18 2*181 2*182 2*180 2*180 2*180 Ecl/EPd 0*?44 0*868 0*991 1.485 1*98 2 *L8 2*72 2*97

AA AAA A A A

320 0 0OL85 0 »o545 0*059 0*0975 0*1643 0*215 0*252 0*2698 330 o0515 .033 .0515 *0663 *1073 0I3L *158 .1645 340 .0685 .0667 *0615 *0595 *0815 *0878 *1005 .0992 350 olOO .096 *0887 *078 *0 877 *0835 *0895 *0828 360 *140 *1367 *1295 *1173 *1225 *1125 *115 .1053 370 *185 0I833 •17 77 *1712 *1773 *1655 .1665 •1575 380 .227 *2297 .2275 *232 *2L25 *235 .2365 *2275 390 .260 o269 *2705 *2873 *3073 *307 *309 *303 LOO <>2.775 *289 *297 *3278 *3573 *3645 *3705 *3685 410 o2?L5 *2873 *2995 *340 *3775 *3955 *4065 *4075 420 •2505 *266 *278 *3228 *3648 *3875 *402 *4055 430 .2128 .2273 *239 *2825 *3265 *3502 *363 *3675 440 .1718 *183 .193 .2325 *2732 *2948 *308 *313 L50 .1315 *141 .148 *180 *2155 *236 .247 5 *252 460 *0968 *1035 *108 .133 .164 *180 .1905 0I927 470 .0698 *0745 *0777 *097 *122.2 ol332 *1425 •1435 480 o050 .0535 *0552 0O69 *0898 o0985 *10 55 .1055 500 .028 *0298 *0295 *035 o050 *054 *0588 *0785 520 *020 *020 *019 *0215 o032 *0325 *0355 o0575 540 .0153 *016 .014 *015 *0245 *0245 *027 *0332 360 *0123 *0135 .011 *0115 *0202 *020 *0222 *024

^Prepared from reagent-grade hydrochloric acid TABLE 84

THE ABSORBANCE OF PALLADIUM PERCHLORATE SOLUTIONS CONTAINING CHLORIDE

(H+)=a.00 M T=25°Co 10,00 cm. cell length

17* 18* 19* 20* 21* 22* 23* 24* EPd x 10^ 2,180 2.181 2.179 2,178 2.178 2.182 2.180 2.180 2Cl/ajd 3.47 3*96 4.06 4.96 5.95 7.44 8.93 9.92

A-smti AAA A AAA A

320 0.3373 0.3935 0.400 0.496 0.593 0.726 0.842 0.901 330 ,2095 .2455 ,250 •3115 .37^ .469 .5515 .596 340 ,1245 .140 .142 .1725 .2035 .2557 .300 .3212 350 .094 .098 .0975 .1065 .1175 .1373 .15^7 .1612 360 .1093 .1075 .105 .1035 .103 .106 .1077 .1073 370 •1575 .154 .1498 .1445 .1392 .1345 .1298 .1238 380 .2277 .225 .220 .214 .2073 .200 .1925 .185 390 ,3065 .3065 o3025 .2995 •29^5 .2877 .2807 .27^5 400 •3775 .381 •3775 .381 .382 .3795 •3747 .3685 410 .422 .430 .4295 •^39 .445 .450 .450 .447 420 .424 .4365 .437 .4505 M 25 .473 .480 .4795 430 .388 .4045 .406 .424 .^375 .4 55 .463 .4665 440 .3325 •3^75 •3^95 .366 .382 .4025 .413 ,4185 450 .2702 .2825 .2848 .301 .3165 .335 .3^7 .3525 460 .2077 .220 .2205 .2367 .251 '.2698 .2798 .2845 470 •1573 .1662 .1675 .1802 .193 .2085 .219 .2242 480 .1175 .1258 .1255 .136 .1465 .161 .1697 .1752 490 .0877 .0945 ,0945 .103 .111 .124 .1305 500 .0647 .070 .0697 .0757 .0822 .091 o0975 .100 520 .0375 .041 .0398 .0435 .046 .051 ,053 .0548 540 .0275 0O285 .028 .0295 .0299 .0335 .033 .0325 560 ...______♦Prepared from reagent-grade hydrochloric acid 289

TABLE 8 5 I THE ABSORBANCE OF PALLADIUM PERCHLORATE SOLUTIONS CONTAINING CHLORIDE

(H+ )=1<>00 M T=25°C«> lOoOO cm* cell length

1. 25* 26* 27* 28* 29* 30* 31* 32- E Pd x K r 2*179 2,181 2.181 2.181 2.180 2.181 2.180 2ol80 I Cl/rPd 13*4 1 5 0 5 4508 55.1 67*2 93°2 ' 139*5 186

A AA A ■ A A AA

340 0 *408 0 0^.45 0*7375 0*789 0.8105 O086O 0*912 0*933 34S *285 *310 *5205 .560 *5815 06225 *6725 9699 350 ol99 *2125 02545 038I *398 *431 .4725 *496 360 ol73 •1515 0I 625 ol725 *178 ol92 .114 o2248 370 *120 0I I 6 .1075 0I06 .105 ol052 .1123 0IIO7 380 ol75 .1677 0I 305 ' 0I 225 *1173 0IO85 *1035 -0953 390 o2625 o2545 *198 0I 852 .1773 0I625 ol47 91325 400 03625 o35^ *2925 .2 775 .2655 o2448 *220 .199 410 «445 *4397 .3822 *3645 03528 c3285 .298 .2725 420 *4845 <>482 .4425 9 427 *4145 *3895 •3573 o3295 430 *477 .478 .4585 .448 ->4375 *418 *3885 *3625 440 *433 o43 7 .4395 o433 .4275 *4125 .392 <>3655 450 *3678 •373 .398 0 3965 *3942 03873 0 7 7 *3657 460 <>3035 ,3095 «3482 0 5 1 o3525 *3548 •3558 .3535 466 *2675 o274 03185 o324 *3265 0 3 2 5 0 3 8 .3405 4?0 *243 o2495 .2995 .305 *309 *3175 *3075 ■>331 480 ol927 e 198 *2525 *3605 .267 *2785 *2928 *3013 490 ol927 •155 *2058 0215 o2205 * 235 *248 *2623 500 o ll4 .oll73 .1615 9 168 *1735 *1853 *2005 *2102 520 o06l? o0627 .086 o090 <>0925 *0995 a o ? 8 .114 540 0O36 o036 *04^8 O0455 00458 *048 0O523 0O545

--Prepared, from reagent-grade hydrochloric acid 290

TABLE 8 6

THE ABSORBANCE OF PALLADIUM PERCHLORATE SOLUTIONS CONTAINING CHLORIDE

(H+)=l.00 M T=25°Co 10.00 cm. cell length1 & 00 33* 34* 35* 36* 37* UJ 39* L’Pd x 104 2.180 2.181 2.181 2.181 2.181 2.181 2.181 S c i/S P d 213 05 366 551 1.10x103 1.38x103 1.83x103 2.29x105

A?mu, AA A AA A A

340 0.944 0.9755 0.984 0.9955 0.9855 0.98^5 1.00 350 -5075 o5505 .572 •5935 .604 06065 0.6145 360 .230 .2572 .269 .2802 .286 .289 •293 370 .1097 .1185 .1185 .1212 .123 •1235 .124 380 .090 .0852 *0775 .0705 .0705 .069 .067 390 .1235 .1065 0O915 .0765 .0743 .070 0O665 400 -1875 •1575 •135 .1098 .1053 .0978 .0947 410 o2585 .2178 .1895 .155 .1485 •1393 .1347 420 .3148 .2723 .239 •1985 •1925 .1815 •1753 430 <>3295 .308 .2785 .2392 .233 .2222 •2155 44-0 .3605 o3295 .305 .2748 .270 .2605 .2565 450 o3597 •341 o325 •305 .303 .2972 .2947 460 o3497 .3465 •3375 •330 •331 •3275 .3275 466 *339 .3445 .3407 •3392, •3217, •3398 •340 4?G .3303 .3392 9 340 .3422 •345 ♦3448 .345 476 o3l57 — •333 •338 .343 .3435 •345 480 .303 .320 .325 .332 •3365 •3375 •3395 490 .264 .283 .2905 .3012 •3057 .3075 .3103 500 .2125 *233 .240 .250 •255 .2565 •259 520 .1145 ol275 .1305 .1348 •1377 .1378 .140 540 0O525 .0585 0O583 .0598 .061 .0602 0O6I

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Chapter II

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107. Hansen* L. D.» Izatt* R. M.* and Christensen* J. J.* Incrg0 Chem.* 2* 1243 (1963)«

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112.0 Bay* R. A.* White, R. N.» and Hamilton* F. 0.* ibid. * 77* 3180 (1955)°

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114c Ward, M.» and. Welch, G. A.* J. Inorg. Nucl. Chem., 2* 395 (1956)*

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I) M l y Sgvis seed vias born in Huntsville, Alabama on iiarch 5, 1925. 1 receiyed my primary and secondary education in the public schools of Huntsvillej Alabama, liy undergraduate training was received at Vanderbilt University and The Ohio State

University which granted me the Bachelor of Science degree cue,

laude December, I5I1], I entered the graduate school at The .Ohio

State University in June, 19^2 and was a member of the junior

staff of the Department of Chemistry during the academic years

1952-1953 and 1953-15$1|. I 'ra avardea a Standard Oil of Indiana

Fellowship in 1555) a Visking Research Fellowship in 1556)'and a

Rational Science Foundation Fellowship in 1957 and 1959. t i l e

completing requirements for the Ph.D. degree, I received additional

grants from S. I. du Pont and the Ohio State University.

30ii