Themochemical and SPECTROSCOPIC STUDIES of SOME GOLD and TELLURIUM COMPLEXES -R V . E^Vc by Michael John Baker. a Thesis Present

THEmOCHEMICAL AND SPECTROSCOPIC -r STUDIES OF SOME V . e^vc

GOLD AND TELLURIUM COMPLEXES

Michael John Baker.

A thesis presented for the degree of

Doctor of Philosophy

in the University of London

Chemistry Department,

Royal Holloway College 1982

RHC bGMSaa Ô

a302 14 006045828b ProQuest Number: 10097505

INFORMATION TO ALL USERS The quality of this reproduction is dependent upon the quality of the copy submitted.

In the unlikely event that the author did not send a complete manuscript and there are missing pages, these will be noted. Also, if material had to be removed, a note will indicate the deletion. uest.

ProQuest 10097505

Published by ProQuest LLC(2016). Copyright of the Dissertation is held by the Author.

ProQuest LLC 789 East Eisenhower Parkway P.O. Box 1346 Ann Arbor, Ml 48106-1346 I wish to express my sincere thanks to Dr. Arthur Finch and Dr. Peter Gates for their great help and patient counselling throughout my three years of research at Holloway.

Also, my thanks to the past and present Heads of Department at Scunthorpe College of Science and Technology, Mr, Hopkinson and Mr. Watts, and to North Humberside County Council for enabling this research to be undertaken.

Finally, my deepest thanks and affection to my mother, whose typing of this work and constant encouragement have been invaluable (as has the encouragement of her colleague-typistÎ).

M.J. Baker. CONTENTS. 1. ABSTRACT 16 THERMOCHEMISTRY OF SOLD TETRAHALIDES. 2. INTRODUCTION 19

2a." General chemistry 19

2b. Halides of gold 26 2c. Thermodynamic properties of gold/halogen compounds 3k

2d. Background to gold thermodynamic data contained 36 in N.B.S. Circular 500

3 . EXPERIMENTAL SECTION 3a. Synthesis and analysis of the compounds used 40 3b. Aurochloric acid 40 3c. Potassium, rubidium and caesium tetrachloroaurate 40 3d. Potassium, rubidium and caesium tetrabromoaurate 41

3e. Tétraméthylammonium and tetraethylammonium 43 dibromoaurate

3f. Tétraméthylammonium and tetraethylammonium 44 dichloroaurate 3g. Tétraméthylammonium, triethylammonium and 46 tetraethylammonium diiodoaurate 3h. Reclamation of gold 50

3j. Details of reactions studied 50

3k. Calorimetry 67

3 1 . Brief description of procedure 6? 3m. Calculation of the heat of reaction ?4

3n. Titration calorimetry 76

4. RESULTS SECTION 4a. Tetrahaloaurate results (heat of solution) 85

4b. KAuCl^ 85

4c. RbAuCl^^ 88

4d. KAuBr^^ 90

4e. RbAuBrj^ 93

DISCUSSION OF RESULTS.

4f. Tetrahaloaurate results (heat of solution) 103

4g, Raman spectra IO3 4h. Calorimetric results 108

4 j. Calculations II3 4k. Summary of tetrahaloaurate results 121 Tetraalkylammonium dibromoaurate results. 122 41. Raman spectra 122

4m. Heat of reaction of Mej^NAuBr2 with FeSO^^ solution 129

4n. Heat of reaction of Et^NAuBrg with FeSOj^ solution I30

4o. Calculations I33

4p. Summary of dihaloaurate results I37

Tetraalkylammonium dihaloaurates. I38

4q. The Raman spectra of the dichloroaurates 138 4r. The Raman spectra of the diiodoaurates 144 4s. Calorimetric results of Etj^^NAuI^ with SOg (aq) 147

4t. Calculations I50

4u. Calorimetric titration results. 152

4v. KAuClj^ with aqueous ferrous sulphate I52 4w. KAuBrj[^ with aqueous ferrous sulphate 154

4x. Mechanism of the ferrous reduction of gold (III) 159

4y. Mechanism of the hydrolysis of gold (III) I63 4z. Kinetics and mechanism of the sulphite reduction 165

gold (III) 5. Antimony pentachloride and Arsenic trichloride i j q complexes of Auric Chloride.

5a. Experimental. I70 5b. Results and discussion.

6. APPENDIX III.

6a. Calculation of lattice energies by the ^ 1 7 7 Kapustinskii method

6b. Errors in lattice energy calculations via the 180 Kapustinskii equn.

7 . APPENDIX IV. Estimation of experimental errors. 182

8. APPENDIX V. Calorimetric reaction stoichiometries. 185

8a. FeSOj^ with Et^^NAuBr^ 185

8b. SO2 with Etj^NAuI^ 186

8c. FeSO^ with KAuClj^ I87

9. APPENDIX VI. Calculation of the ionic radii of the complex 188 anions

10.APPENDIX VII.

THAM calibrations. I92

11.APPENDIX VIII.

Activity coefficients of the calorimetric solvents 1 9 5 used SPECTROSCOPY OF TELLURIUM HALIDES AND COMPLEXES. 12. INTRODUCTION.

12a. General Chemistry. I99 12b. Halides of the Gp VI elements. 202 12c. Tellurium (II) and (IV) chlorides and bromides. 206 12d. Lewis acid complexes of tellurium tetrahalides. 214

1 3 . EXPERIMENTAL SECTION.

13a. 'Tellurium tetrachloride. 217

13b. Tellurium tetrabroraide. 219

13c. Tellurium dichloride dibromide. 220

13d. Tellurium dichloride dibromide/aluminium 222 chloride complex Tellurium Tetrabromide Complexes. 223 13e. Tellurium tetrabromide/aluminium tribromide 223 complex 13f. Tellurium tetrabromide/aluminium trichloride 226 complex 13g. Tellurium tetrabromide/antimony pentabromide 227 complex 13h. Tellurium tetrabromide/antimony pentachloride 227 complex Tellurium Tetrachloride Complexes. 228

1 3 i. Tellurium tetrachloride/aluminium tribromide 229 complex 13k. Tellurium tetrachloride/aluminium trichloride 229 complex 1 3 1. Tellurium tetrachloride/antimony penta(^lo^ide 230

14. RESULTS AND DISCUSSION SECTION. l4a. Tellurium tetrabromide and tetrachloride. 231 l4b. Tellurium dichloride dibromide. 241 I4c. Tellurium dichloride dibromide/aluminium 245 trichloride complex.

14 . Tellurium tetrabromide complexes. 247 l4d. Tellurium tetrabromide/aluminium tribromide 257 complex l4e. Tellurium tetrabromide/aluminium trichloride 273 complex l4f. Tellurium tetrabromide/antimony pentabromide 273 complex l4g. Tellurium tetrabromide/antimony pentachloride 278 complex 14_ . Tellurium Tetrachloride Complexes. 281 l4h. Tellurium tetrachloride/aluminium tribromide 281 complex 14j. Tellurium tetrachloride/aluminium trichloride 289 complex l4k. Tellurium tetrachloride/antimony pentachloride 292 complex

1 5 . APPENDIX I Characterisation and analysis of tellurium 297 compounds

16. APPENDIX II Solvent purification and drying.and tellupium 299 toxjLcity

1 7. REFERENCES. 300 18. ADDENDUM. 313 8

List of Tables. Page .

2al). Ionisation energies of group IB elements. 20 2a2). Some standard redox potentials of Au corapds. 22 2bl). Halides of gold and thermodynamic data at 27

298 K for crystalline compounds. 2cl). Examples of chemical thermodynamic properties 35 of gold halides, 3nl).. Syringe calibration for titration 80 calorimetry. 3n2). Enthalpy of neutralisation of HCl(l.OM) 81

with Na0H(0.03M). 4bl). Enthalpy of solution of KAuCl^ in water. 85

4b2). Enthalpy of solution of KAuCl^^ in HCl soins. 86 4b3). Enthalpy of solution of KAuCl^ in KNO^ soins. 87

4cl). Enthalpy of solution of RbAuCl^ in water. 88

4c2). Enthalpy of solution of RbAuCl^ in HCl soins. 89 4dl). Enthalpy of solution of KAuBr^ in water. 90 4d2). Enthalpy of solution of KAuBr^^ in HBr soins. 91 4d3). Enthalpy of solution of KAuBr^ in NaC10|^ 92 soins. 4el). Enthalpy of solution.of RbAuBr^ in water. 93 4e2). Enthalpy of solution of RbAuBr^ in HBr soins. 94 4gl). Vibrational spectra of AuCl^. 4g2). Vibratipnal spectra of AuBr^. e 4jl). Estimation of AH^y^^ and AH^^^ values for 120

AuCl^ and AuBr^ (R.M. de Jonge). 4j2). AH^y^^ and AH^^^ values for AuCI^ and AuBr^ 120 (this work). 4k). Summary of the tetrahaloaurate results. 121 411). Vibrational spectra of the tetraalkylammonium 123 dibromoaurate. 4m). Enthalpy of reaction of Me^NAuBrg with FeSO^. 12?

4n). Enthalpy of reaction of Et^NAuBr2 with FeSO^. I30

4p). Summary of the dihaloaurate results. 137

4ql). Raman spectrum of Etji^NAuCl2 (s ). 141 4s). Enthalpy of reaction of Et^NAuIg in SO^ soins. 147 4v). Calorimetric KAuCl^ results(titration). 152 4wl). Calorimetric KAuBr^ results(titration). 15^ 5bl). Raman spectrum of auric chloride (Adams and 173 Churchill).

8al). Stoichiometry of the FeS0 ^/Et^NAuBr2 reaction. 185

8bl). Stoichiometry of the S02 /Et^NAul2 reaction. 186

8cl). Stoichiometry of the FeSO^^KAuCl^^ reaction. 187 loal). Endothermie tham calibrations. 192 lobl). Exothermic tham calibrations. 193

12 al). Ionisation energies of the group VI elements. 201

12 bl). Halides of the group VI elements (& structures 203 of the halides).

I4al). Raman spectra of the solid tellurium tetra 232 halides .

I4bl). Raman spectrum of solid TeCl2 ,Br2 . 246 l4cl). Raman spectra of the TeCl2 Br2 /AlCl^ salts. 252 I4dl). Raman spectra of the TeBr^/AlBr^ products. 260 I4el). Raman spectrum of the TeBr^/AlCl^ product. 270 I4fl), Raman spectrum of the TeBr^SbBr^ product. 276

I4gl). Raman spectrum of the TeBr^SbCl^ product. 279 I4hl). Raman spectrum of the TeCl^/AlBr^ product. 285 10

14jl). Raman spectrum of the TeCl^/AlCl^ product. 2 9 I l4kl). Raman spectrum of the TeCl^SbCl^ product. 295 11

List of Figures. Page

2 bl). Au^Clg 29 2b2). Electronic absorption spectra of KAuCl^ in KCl,32 KAüBr^ in KBr and KAuCl/^KAuBr^ in KI. 2b3). Electronic absorption spectra of AuGl” , AuBr^ 33

and AUI2 in acetonitrile.

3 jl). Raman spectra of RbAuBr^ in aq. NaOH soins. 60

3j2). Raman spectrum of CsAuCl^AgNO^ precipitate. 6l 3j3). U.V./vis. spectra of AuBrJJ/AgNO^ reactants 62 and products. 3j4). Chart of transmittance at 381 nm on addition of&3 AgNO^(excess) to CsAuBr^(aq) + HNO^(aq). 3j5). Potentiometric trace of the AgNO^/CsAuCl^(aq) 64 reaction.

3 1 1). The calorimeter. 68

3 1 2 ). The experimental apparatus. 69 3ml). Exothermic reaction trace (eg tham with HCl) 77 and calibration trace. 3m2). Endothermie reaction trace (eg Me^NAuBr^ reactn?^ with FeSO^) and calibration trace. 3nl). Example exothermic titration trace and ^ calibration. 4el). Graph of AH^^^(KAuCl^(s)) v Molarity of the 9^ resulting solution. 4e2). Graph of AH^^^(KAuBr^(s)) v Molarity of the 95 resulting solution. 4e3). Graph of (RbAuGlj^(s ) ) v Molarity of the 97 resulting solution. 12

4e4). Graph of (RbAuBr^^ (s ) ) v Molarity of the 98 resulting solution.

4e5). Graph of (KAuCl^(s ) ) v Activity of HCl 99 or KNO^ solvent. 4e6). Graph of AH^^^^(RbAuCl/^ (s ) ) v Activity of HCl 100 solvent.

4e7). Graph of AH^^^ (KAuBr^^ (s ) ) v Activity of 101 NaClO^ or HBr solvent.

4e8). Graph of AH'^^j^(RbAuBr^(s) ) v Activity of HBr 102 solvent. 4gl). Raman spectrum of the AuCl^ ion. 104

4g2). Raman spectrum of the AuBr]^ ion. 106

4g3). Raman spectrum of the CsBr/AuBr^(aq) product 107 (CsAu^Br^).

4hl). Raman spectra of NaAuCl^ in H2 O and conc. HCl. 110

4h2). Raman spectra of RbAuBr^ in H2 O and conc. HBr. 111 411). Raman and I.R. spectra of AuBr" (I.R. spectrum) 124

412). Raman spectrum of AuBr^. 125 4ml). Graph of AH^ of Me^NAuBr2 with FeSO^ v Weight 128 of Me^NAuBr^ used. 4m2). Graph of AH^ of Me^NAuBrg with FeSO^ v Molarity 129 of FeSO^ used.

4nl). Graph of AH'^ of Et^NAuBr^ with FeSO^^ v Weight 131 of Et^NAuBr taken.

4n2). Graph of AH"^ of Et^NAuBr2 with FeSO^ v Molarityl32 of FeSO^ used.

4ql). Raman spectrum of the Et^NAuCl2 product. 139 4q2). Raman spectrum of the Et^NHAuBr^ product. 140

4q3). .Raman spectrum of the Et^NHAuBr2 product. 143 13

4q4). Raman spectrum of the Et^NHAuIg product. 144

4rl). Raman spectrum of the Et^NAul2 Product. 145 4r2). Raman spectrum of the Me^NAuIg product. 146

4sl). Graph of of Et^NAul2 with SO2 v Molarity 148

of the SO2 solution.

4s2). Graph of of Et^NAul2 with SO2 v Sample 149 weight. 4vl). Graph of of KAuCl^ with FeSO^ v Molarity 153 of the KAuCl^ solution. 4wl). Graph of AH^ of KAuBr^ with FeSO^ v Molarity 155 of the KAuBr^ solution. 4w2). Specimen calorimetric FeSOjy^KAuCl^ reaction 156 trace. 4w3). Specimen calorimetric FeSO^KAuBr^^ reaction 157 trace. 5bl). Raman spectrum of the solid AuCl^ product. 174 5b2). Raman spectrum of the AuCl^/SbCl^ reaction 175 product. 5b3). Raman spectrum of the AuCl^/AsCl^/Cfg 176 reaction product.

9 1). The square planar tetrahaloaurate anion. 189

9 2 ). The linear dihaloaurate anion. . 190 lObl). Tham calibration graphs. 194 111). Graph of S'- of HCl solutions of various 195 molarities. 112). Graph of J- of HBr solutions of various 196 molarities.

1 13). Graph of of KNO^ solutions of various 197 molarities. 14

114). Graph of of NaClO^ solutions of various 198 molarities.

l4al). Raman spectrum of the solid TeCl^ product. 233 I4a2). Raman spectrum of the solid TeCl^ product 234 (white sublimation product).

I4a3). Raman spectrum of the solid TeCl^ product 235 (yellow sublimation product). I4a4). Raman spectrum of the solid TeBr^ product. 236 l4a5). Raman spectra of the TeBr^ solid sublimation 237 fractions.

I4bl). The structure of a cubic unit of TeCl2 Br2 . 244

I4b2). Raman spectrum of solid TeCl2 Br2 prepared at 24? one atmosphere.

I4b3). Raman spectrum of TeCl2 Br2 (sealed tube expt.) 248 I4b4). Raman spectrum of 1*1 TeCl^TeBr^^ reactant 249 mixture (Raman-tube expt.).

I4b5). Raman spectrum of TeCl2 Br2 product (Raman- 250 - tube expt.).

I4cl). Raman spectrum of solid TeCl2 Br2 reactant. 253

I4c2). Raman spectrum of the TeCl2 Br2 /AlCl^ (3 hrs. ) 254 product.

I4c3). Raman spectrum of the TeCl2 Br2 /AlCl^ (1 day) 255 product.

I4c4). Raman spectrum of the TeCl2 Br2 /AlCl^ (8 days) 256 product. I4dl). Raman spectrum of the TeBr^/AlBr^ product 261 (CCl^)-first preparation. I4d2). Raman spectrum of the TeBr^/AlBr^ product 262

(CCI4 ). 15 l4d3). Raman spectrum of the TeBr^AlBr^ product . 263

(CC1|^)-residue from CH2 CI2 recrystallisation. - l4d4). Raman spectrum of the TeBr^/AlBr^ product 264

(CCl^)-filtrate from CH2 CI2 recrystn. I4d5). Raman spectrum of the TeBr^/AlBr^ product 265

(CS2 ). I4d6). Raman spectrum of the TeBr^/AlBr^ product 266

(CS2 ). I4d7). Raman spectrum of the TeBr^/AlBr^ product 267

(CS2 )-residue from CH2 CI2 recrystn. I4d8). Raman spectrum of the TeBr^/AlBr^ product 268

l4d9). Raman spectrum of the TeBr^/AlBr^ product 269

(C^H^/C^H^2 )-2 ^^ prep.-filtrate

recrystallised from CH2 CI2 . l4el). Raman spectrum of the TeBr^/AlCl^ product. ^75 l4fl). Raman spectrum of the TeBr|ySbBr^/Br2 277 product. l4gl). Raman spectrum of the TeBr^/SbCl^ product. 280 l4hl). Structure of the complex TeCl^.MX^. 284 l4h2). Raman spectrum of TeCl^^AlBr^ product from 286

the C^H^/C^H^2 preparation. I4h3). Raman-active vibrational modes of AlClBr^. 287 l4jl). Raman-active vibrational modes of AlCl^. 290 l4kl). Raman-active vibrations of the octahedral 292 SbCl^ ion.

I4k2). Raman-active vibrational modes of SbCl^. 293 l4k3). Raman spectrum of the solid TeCl^/SbCl^ 296 product. 16

1. ABSTRACT.

Using an isoperibol solution reaction calorimeter the enthalpies of aquation of selected anhydrous alkali tetrahaloaurates were measured and

AH^(MAuX2^(s) ) derived from this and ancillary data as follows* (AH^(KAuCl^(s)) =- 608.8 + 0.3 kJ AH^(RbAuCl^(s)) = - 613.9 ± 1.0 kJ mol"^î AfÇ(lüluBr;^(s)) = -486.1 + I.3 kJ mol"^;

AH^(RbAuBr2^(s) ) = - 497.5 ± 1.8 kj mol"^)

From the measured enthalpies of reduction of Me^NAuBrg and Et^NAuBr2 (with aqueous FeSOji^ soln.), and Et/^NAul2 (with aqueous SO2 soln.), the standard enthalpies of formation of the dihaloaurates were calculated. (AH'J (Me^NAuBrgfs)) = - 291.3 ±0.1 kJ mol“^; AH^ (Et^NAuBrgfs)) = -428.4 - O.lkJ mol”^i AH^fEt^MAuIgts)): -353.92 i 0.20 kj mol'l).

"Thermochemical radii" of the ions

AuCl^, AuBr^ and AuBr2 have been calculated by the Kapustinskii- Yatsirairskii procedure in order to estimate the lattice energies of the above salts, and the standard enthalpies of formation of the gaseous AuCl^, AuBrj^ and AuBrg ions. Additional standard enthalpies of formation and lattice energies of alkali metal salts containing these ions have been calculated. 17

The reaction between aqueous tetrahaloaurate and ferrous sulphate in acid medium (X = Cl, Br) has been investigated by means of a thermometric titration; this was found to have only one rate limiting step in agreement with the induced chloride exchange of the AuCl^ (aq.) data reported by Rich and Taube.

Raman investigations revealed no reaction between AuCl^ and SbCl^, or AuCl^ and AsCl^.

The syntheses of tellurium dichloride dibromide and the tellurium tetrahalide salts TeCl^BrÂlCl^; TeBrÂlBr^ TeBrÂlCl^, TeBr^SbBr^, TeBr^SbCl^; TeClÂlBr^, TeClÂlCl^ and TeCl^SbCl^ were attempted, using a technique involving halogénation and complexation in a number of chlorinated solvents. Raman investigations of the isolated products revealed 1. the formation of an impure TeClBr^Cl (s) product.

2 . the possible formation of an impure, covalent

TeCl2 BrAlBr2 Cl2 product. 3. the formation of an impure TeBr^ AlBr^ (s) product

from CS2 medium. 4. no reaction of TeBr^ with AlCl^.

5 . no reaction of TeBr^ with SbBr^.

6 . chlorination of tellurium tetrabromide by antimony pentachloride to yield a product with BrtCl ratio of 1*2

7 . no complexation between the tellurium tetrachloride and

AlBrj. 18

8. an unidentified product from TeCl^ and AlCl^ which thermally decomposed in a laser beam of wavelength 647.1 nm. 9. the formation of an impure TeCl^ SbCl^ product.

Purification of the tetrahalides and complexes by distillation under reduced pressure and recrystallisation from glacial acetic acid/ acetic anhydride or toluene was attempted. In all cases thermal decomposition took place. 19

The Thermochemistry of Gold Tetrahalides.

/ 2. Introduction.

2a). General Chemistry.-

Gold is a group IB metal, atomic number 79» and

electronic configuration (Xe) 4f^^ 5d^^ 6s^. The outer 6s-

electron is poorly shielded by both the 4f and 5d electrons, and therefore feels a high effective nuclear charge (calcd. from Slater's Rules) (Puddephatt,1978). It is a combination of high ionisation energy and high binding energy which gives gold its noble character (Puddephatt,1978).

Variations in the second and third ionisation

energies account for the dominance of the +1 and +111 oxidation

states for this element, the +111 state being the preferred. Subsequent ionisation energies are also lowest for gold, explaining the existence of the +V oxidation state for gold but not for silver or copper.(Table 2al).(Puddephatt,1978). Accurate values of the electron affinities of the group IB elements are difficult to obtain, but it is generally held that gold has the highest value. Values of 226 and 270 kJ mol”^ have been proposed by different workers ( Puddephatt,

1978).

Most of the chemistry of gold is therefore concerned with the +1 and +111 oxidation states. Although there have been several reports of Au(ll) compounds, many of 20

Table 2al).-

lonisation Energies of Group IB Elements (kJ mol~^).

(Puddephatt,1978).

Element. ^ ^ ^ ^

Cu 745 1958 3554 5330

Ag ' 731 2074 3361 5020

Au 890 1980 2943 4200 21

these are in error (eg. AUX2 ) (Engelhard, I9 6 9). Walters and

Gray (JAGS, 3534 (I9 6 5)), however, demonstrated the existence of dithiomaleonitrile complexes of gold (II), Most aqueous species of gold (I) and gold (III) are unstable with respect to disproportionation and reduction. Gold (I) is stable in contact with water only in the form of complexes such as Au(CN)2 (aq) or slightly soluble compounds such as

Aul(c) (Engelhard, I9 6 9). The oxidised forms of gold exist only at redox potentials greater than the oxidation potential of water. Under these conditions gold cannot be oxidised by dissolved oxygen in the presence of either strong acids or alkalis (Puddephatt,1978).

The reason for the high electrode potentials for oxidation of gold in the presence of complexlng ligands lies in the very low stability of the aquo ions (Au(H2 O )2 )^ and (Au (H2 O )j[^)^^ ( Puddephatt, I978). The potentials are lower in the presence of complexing ligands, but standard potentials indicate only whether the reaction is feasible thermo dynamically, not kinetically (puddephatt,I978).

Whether oxidation to the complex (AuL^)^ or (AuL^)^* occurs in the presence of a ligand depends on the relative magnitudes of E^ q and E"^ ^ and on the strength of the oxidising agent. Both gold (I) and gold (III) form more stable compounds with I"than with Br” , and with Br“ than with

Cl” ; behaving as a class b metal and preferring to bond to large polarisable ligands (Sadler, I9 7 6). Copper (I) and silver (1 ) are also soft acids, but gold (1 ) discriminates to a greater extent between the ligands. This is in agreement 22

Table 2a2).-

Some Standard Redox Potentials.

(Puddephatt,1978 ) (See also Peshchevitskii, 19 67b).)

+ Au + 2 L — 1,0 — (AuL^) + e‘

Au + 4l -Et ^ , 0 — (AuL,,)"^ + 3e'

Ligand ^ 1 ,0 ^3.0 ^3.1

HgO +1.7 +1 .5 0 +1 .4 (+2.12)

Cl" +1 .1 5 +1 .0 0 +0 ,9 3

Br" +0 .9 6 +0.86 +0.81

I" +0 .5 6 +0 .5 7 +0 .5 7

SON" +0 .6 7 +0.64 +0 .6 2

ON" -0 .6 1 23 with the prediction that large metal ions in low oxidation . states will have the greatest class b character (Puddephatt,

1978 )• If gold is complexed with ambidentate ligands, then both gold (I) and gold (III) almost invariably bond to the softer end of the ligand (Puddephatt,1 9 78).

The electron configurations of Au (III) and Au (I) are 5d^6s^6p^ and 5d^^6s^6p^, respectively, but the orbital populations calculated from SCCC-LCA0-M3 methods show that considerable covalency exists in the metal-ligand bonds for both complexes. The 6s and 6p orbitals of gold engage in bonding and the charge on gold is always less than +1 . The extent of this covalency, due largely to cr-bonding, increases as expected on passing from fluoride through to iodide complexes (Puddephatt,I978).

For linear gold (1) complexes the simple bonding schemes suggest that the filled 5d orbitals play no part in bonding, and that the o'-bonding will use 6sp-hybrid orbitals on gold. The MO calculations show that 6s and 6p orbitals on gold are strongly involved in bonding in (AuX^)” , but also show that the 5d-orbitals contribute significantly to the gold-halide cr-bonds, in accordance with Orgel 's comments on d-s mixing in linear gold (1 ) complexes (Puddephatt,I978 )

For square-planar gold (111) complexes,

Q Valence Bond theory predicts that gold (111) will have the 3d configuration and that c-bonds will be formed using the four 24

3d X 2 -y 2, 6s, 6p^, X 6p^, y hybrid orbitals. The M3 calculations support this. (Puddephatt,1978)

Some of the compounds formed by gold, in particular those which were produced for use in this study will now be discussed.

Hydrides of Gold.-

AuH and AuH^ may be prepared at low temperatures in ether, but decompose to the elements on heating (E.

Wiberg, I9 6 3). The bond dissociation energy of the mono hydride has been calculated at 310 kJ mol”^ from

spectroscopic studies (Ringstrom, I963 ; Desclaux, I9 7 6), and the monomer exists in the gas phase when gold is heated to 1400°C in hydrogen.

Sulphides, Selenides and Tellurides of Gold.-

Gold does not react directly with sulphur, V but the compounds Au^S and Au2 S^ can be prepared (Puddeph -

att,l978 ). In the gas phase at high temperature AU2 S molecules apparently exist (Smoes et al., 1972), the

standard Gibbs free energy of formation AG^ of solid AU2 S being +29 kJ mol"^ (Puddephatt,1978)•

Both AuSe and Au^Se^ are known. Two crystalline forms of the monoselenide exist , one form of which is best represented as Au(1)Au(lll)Se2 . (Puddephatt,

1978 )• 25

Gold reacts directly with tellurium to form

AuTe2 » which occurs naturally (Puddephatt,I978 ). The crystals contain linear Te-Au-Te units, and the standard enthalpy of formation, AH ^ is -18.6 kJ mol“^ (Andon, I97I). Au^Te^ also occurs naturally, and a compound of composition

AuTCf is formed by reducing a solution containing gold (III) and tellurium (IV) with hydrazine (Howie and Veale,

19 6 6). In addition, the mixed compounds AuBrSe, AuITe and AuXTe2 (X = Cl, Br or I) are known. (Rabenau and Rau,

1973; Rabenau et al., I9 6 9; Haendler, 197^; and Mootz,l973).

Oxides and Hydroxides of Gold.-

Gold (III) hydroxide, Au(OH)^ is formed by addition of sodium hydroxide to solutions containing (AuCl^) This hydroxide can be dehydrated to give first Au(0)0H and then Au20 ^, which decomposes to the elements above l6o°C. The heat of formation of the auric oxide, (Au2 Û^) is -I3 .O kJ mol”^ (Puddephatt,1978). Gold (III) hydroxide, auric acid, behaves as a weak acid and neutralisation of solutions in KDH leads to reprecipitation of gold (III) hydroxide. The hydroxide is also soluble in sulphuric or nitric acid, and there is evidence that the species (B^AuO^)", (HAuO^)^” and (AuO^)^” are formed on treating with stronger hydroxide solutions (Johnston and Leland,

1938).

The lower oxide of gold, Au^O, does not exist, but the oxidation of CsAu at 400°C gives the aurate (I) derivative CsAuO (Hestermann and Hoppe, I9 6 8). ' 26

Oxy-acids of Gold.-

As well as the trihydroxide described prev iously, there exists what Schottlânder described as "auryl hydrosulphate", AuHSO^^. When this compound is treated with l/lO of its weight of potassium hydrogen sulphate, potassium disulphatoaurate is formed (Schottlânder, Raschig Annalen, 1883» 21?» 312).

The corresponding silver salt can be formed. Since gold does not yield salts containing either aurous or auric ions the existence of aurous sulphate, auric sulphate and auric chromate is doubtful ( Puddephatt,I978 ). For similar reasons reports of the existence of both aurous and auric nitrates are doubtful, but Schottlânder reported the acid H**’(Au(M3^ )j^)~ ,3H20 (analogous to H (AuX^) ,3H20 , but which decomposed in water). (Schottlânder, Raschig Annalen, 1883» 217 » 312; and Jeffrey, Trans. Faraday Soc.,

1 9 1 6, 1 1 , 1 7 2 ).

2b). Halides of Gold.-

The known halides of gold, together with some thermochemical data, are listed below. As can be seen; only fluorine gives a gold (V) derivative (Schmidbaur, I9 7 6) while iodine yields only a gold (I) compound. 27

Table 2bl)

Halides of Gold and Thermodynamic Data at 298K for

Compound Colour -1

Oxidation State (I)i-

(Au F) . -7 5 est. Au Cl yellow-white -35 -1 6

AuBr light yellow -1 9 -1 5

Au I lemon yellow +1 .7 -3.3

Oxidation State (III)*-

AuF^ golden yellow -3 6 0

AuClj red -1 2 1 -5 4

AuBr^ dark brown -6 7 .3 -3 6

Oxidation State (V).-

AuF^ dark red — — — — 28

Brewer et al (See Quill, 1950) cited AH^ = -75.3 kJ mol”^ for the formation of AuF(c)i however thermodynamic data suggest that it would be unstable with respect to disproportionation to gold and gold trifluoride

(Engelhard, I9 6 9), and there is no other evidence for the existence of this compound. AuF^ is a powerful fluorinating agent and forms adducts; eg. AuF^.BrF^,

AuF^SeF^ and NO(AuF^) (Puddephatt,I978 ). Gold (III) has o the usual low spin d configuration in AuF^, and the compound adopts a fluorine-bridged helical chain polyraer-

-structure (Schmidbaur, I9 7 6). The chains are linked with weaker fluorine bridges; each gold being at the centre of a square planar arrangement of fluorine atoms. Additional weak cross-linking gives an approximately tetragonally distorted octahedral environment about each gold atom

( Puddephatt,1978 ).

Gold (V) fluoride can be prepared by thermal decomposition of either (KrF)"*^(AuF^)“ or of (0 2 )"*^(AuF^)“

(Holloway, 1975; Sokolov, 1976; Vasile, I9 7 6). Gold (V) has the low spin 5d^ electron configuration. Fluorine bridging also takes place in this solid, the gold having approximately octahedral stereochemistry (Holloway, 1975;

Edwards, 1974; Vasile I9 7 6). Reaction with oxygen and fluorine forms (OgJfAuF^), with XeF2 yields (Xe2 F^)(AuF^), and with NOF leads to (NO)(AuF^). ( Puddephatt,I978 ).

Reaction of chlorine with gold may yield either gold (I) chloride or gold (III) chloride depending upon the conditions." At room temperature gold (I) chloride 29

is metastable and slowly disproportionates to gold and

gold (IIIJ chloride (Puddephatt, I9 7 8).

The trichloride can be prepared by reaction with chlorine below 254°C, and vapour transport of gaseous auric chloride in a chlorine atmosphere yields large crystals of AuCl (Diag.A), Other methods of formation

exist. (Puddephatt,1 9 7 8) (Dell'Amico and Calderazzo, 1973).

A convenient method of production of gold trichloride is to heat pure hydrochloroauric acid at 200°C

in a current of dry chlorine (Lenher, I9 1 3). The molecular weight of the trichloride between 150°and 26o°C corresponds

with the formula (AuCl^)2 » a dimer analagous to gold tribromide (Diagram B) (Mundorf and Dehnicke, 1973). Gold trichloride decomposes into aurous chloride and chlorine at 254-236°G, further decomposition of the aurous compound taking place at 290^0 (Puddephatt,I978 ).

A black compound of the empirical formula

"AUCI2 " is formed by reaction of gold (III) chloride in thionyl chloride with a deficiency of carbon monoxide.

The reaction gives (Au(CO)Gl) which reacts with AU2 C1^ to give Au2 (C0 )Cl^, and eventually "AUCI2 ". The product is a mixture of gold (1) and gold (III) species, with cyclic (Au^CIq) molecules containing linear gold (I) and square planar gold (III) centres as shown below (Dell'Amico, I9 7 6). K / ' Fig 2bl).- Au,,Cl„ Au n-\— Au-— q (Dell'Amico, 1976 and 1977) XI— Au-^Cl

A, 30

A number of coordination compounds of gold monochloride have been described, examples being the compound with phosphorus trichloride, Cl^P-AuCl; and compounds of the gener^ formulae R^P-AuCl and R^As-AuCl, where R=alkyl group (Rawson and Rawcliffe, 1973)

,A\ / \ Dl.sr.. A. \^^V" 1,76,

Cl ^01. _ o .01 straehle, 19?4). Diagram B. (Puddephatt, I978 ) ^ \(33pm ooP^ < 9 0 Cl Cl 01 Theoretically, the chloroaurates are obtain able by neutralisation of a solution of hydrochloroauric acid with the appropriate base. In practice, however, the chloroaurate is most easily formed when an excess of the appropriate cation is present as provided by a solution of the chloride. The least soluble salt (the chloroaurate)

(Mellor, 1 9 2 3 ) is precipitated. A large number of chloro aurates have been described. The sodium and potassium salts, NaAuCl^.PH^O and KAuC1^.2 H2 0 , are both used in the photographic industry as film toners (Puddephatt, 1978).

The ammonium salt has the composition NH^AuC1^.3H2 0 , and the calcium, barium and strontium salts all have the general formula M(AuCl^)2 .6H2 O . (Rawson and Rawcliffe, I9 7 3).

The salts are characterised by being highly crystalline, soluble in water, and deep yellow or orange in colour. Chloroaurates of many organic bases have been prepared, and these latter compounds have, in many cases, been identified through their salts with hydrochloroauric acid (Puddephatt, 1978 ). 31

Gold (III) bromide is formed by the exothermic reaction of gold powder with liquid bromine (Meyer,I9 0 9). The structure is dimeric like that of (AUgCl^) , its properties resembling those of the trichloride (Straehle,

1 9 7 4). On heating to about 200°C the tribromide decomposes to bromine and gold (I) monobromide (with structure analogous to AuCl). AuBr decomposes to the elements on being heated above 250 °C; and, like the corresponding chloride, decomposes in contact with water to yield gold and gold (III) species (Puddephatt, 1978).

The bromoaurates can be obtained by addition of an excess of the appropriate cation (the bromide) to an aqueous solution of hydrobromoauric acid (AuBr^ in HBr solution). The tetrabromoaurate is precipitated as the least soluble salt on reduction of the volume of the solution. Addition of a bromide to a tetrachloroaurate solution will result in halide exchange to form the bromo- aurate (Mellor,I9 2 3 ) (Peshchevitskii, I9 6 7; Pouradier, I9 6 6;

Louw, 1974; and Almgren, I97I).

Tetraalkylammonium salts of both the tetrachloroaurates and tetrabromoaurates can be reduced by phenylhydrazinium chloride to yield the dihaloaurate (R^N^ AuX^). Acetone will also reduce the tetrabromoaurate anion (Braunstein and Clark, 1973).

Because of the high polarising power of gold (III), Aul^ spontaneously disproportionates in aqueous solution, (Ryan, I9 6 9). 32

Aui; Aul^ + ( lAu(Ij)-?)

KAuI^ forms a black solid, but spectro scopic studies confirm-a thermal disproportionation of

Aul^, liberating iodine by autoreduction, (Sadler, I9 7 6). However, when HI is condensed on (CgH^j^NAuCl^, the tetraiodoaurate salt is formed. This is moderately stable to

hydrolysis. (Ryan, I9 6 9). Little is known about the stability of AuI” in aqueous solution. In acetonitrile it is pale yellow and very stable. However, it appears

that (n-Buji^N) (AUI2 ) immediately deposits metallic Au when

HgO is added to ethanolic solutions. (Puddephatt,I978 ).

Fig 2b2). Electronic absorption spectra of KAuCl^ in IN KCl (-) KAuBrj^ in IN KBr (>--) and KAuCl^ or KAuBr^.ZH^O in IN KI (--)■* Aul^ disproportionates to liberate I^.

(A.K. Gangopadhayhay and

A. Ghakravorty, I9 6I).

\jj. cn' V

260 nm 33

Fie. 2b3). Electronic absorption spectra of the colourless ions I.- Au^Cl2 and Au'^’Br^f and pale yellow ion Au^I^ in aceto nitrile at 20 ^C, prepared by mixing in li3 mole ratios of AufMeCNjgClO^ with Et^NCl and Bu^^NBr, and AuBr^ with excess Bu^NI.

(Sadler, I9 7 6)

Lu 100

200 300 nm

Some of the thermodynamic properties of selected haloaurate compounds will now be discussed. 34

2c). Thermodynamic Properties of Gold/Halogen Compounds.-

Data exists in the literature for the thermo dynamic properties of some AuX, AuX^ and HAuX^ compounds (both crystalline, and in aqueous solution), where X = Cl or Br (N.B.S. Circular 500, 1952). However, the crystalline HAuX^ compounds studied contain waters of crystallisation (Table 2cl). It was therefore decided to determine the standard heats of formation of a number of anhydrous alkali metal/gold tetrahalide salts. This would allow calculation of the thermochemical radii of the tetrahaloaurate anions, from the Kapustinskii equation for the lattice energy of a crystalline compound (Kapustinskii,

1 9 3 3). The lattice energy of each salt could then be derived.

As shown in the Results section, if the thermo chemical radii of any two cations and anions are known, the lattice energy and so the heat of formation of the corresponding salt can be calculated.

The gold (III) salts KAuCl^, RbAuCl^, KAuBr^ and RbAuBr^ were studied. The gold (I) salts

Et^NAuBr2 and Me^NAuBrg have also been investigated calorimetrically, to determine the thermochemical radius of the dibromoaurate ion.

These salts were chosen as they can be obtained in the anhydrous form. The ionic radii of the ions K*, Rb"*"; and thermochemical radii of Me^N^ and Et^N^ are known 35

Table 2cl).-

Examples of Chemical Thermodynamic Properties of Gold Halides.

(Values quoted in Tech. Note 270-4, I9 6 9).

Formula. State AHJ f kjmol'l J deg~^mol~^

AuCl . c -35.1 AuClj c -1 1 7 .6

in 900 HgO aq -137.24

AuC1 ^.2 H20 c -7 1 5 .0

AUCI4 aq -3 2 2 .2 -2 3 5 .2 2 +2 6 6 .9

Au2 C1^ & -97.1 HAuCl^ aq -3 2 2 .2 -2 3 5 .2 2 +2 6 6 .9

HAuCl^.jHgO c -1 1 9 2 .0

HAUCI4 .4H2 O c -1489.1

AuBr c -1 3 .9 7 AuBr” aq -128.4 1 1 5 .0 2 +2 1 9 .7 AuClg aq 1 5 1 .1 7 AuBr^ c -53.26

aq -3 9 .2 9 AuBr^ aq -1 9 1 .6 1 6 7 .4 +3 3 6 .0 HAuBr^ aq -1 9 1 .6 1 6 7 .4 +3 3 6 .0

HAuBr^.5H2 O c -1 6 6 8 .2 36 along with other, necessary ancillary data (N.B.S. Circular 500, 1952),

2d). Background to Gold Thermodynamic Data Contained in Circular 500 (1952).

Fischer and Biltz (I9 2 8) measured the heats of solution in aqueous ICl^ of Cl2 (g). Au(s), AuCl(s),

AuCl^(s), Br2 (l), AuBr(s) and AuBr^(s); and calculated the heats of formation; AH^(AuCl(s))=-35.1 KJ mol"^, AH*(AuCl2(s))=-118.4 KJ AH|(AuBr(s))=-l4.2 J mol"^ and AH^(AuBr^(s))=-6o.7 KJ mol”^ (Bichowsky, I9 3 6).

The dissociation pressure data of Fischer and

Biltz (1 9 2 8) and of Ephraim (I9I9) yield for AuCl(s) AH^=

-3 6 .8 KJ mol”^ and -34.6 J mol“^ respectively (Bichowsky,

1 9 3 6). The Au-Cl system has been widely investigated and the equilibrium dissociation pressures of CI2 for

2AuCl(s) = 2Au(s) + Cl2 (g)

have been measured using static methods by Ephraim (I9I9)

(24?-287°C), by Meyer (I90I) (170-24o°C), by Fischer and

Biltz (1 9 2 8) (156-231 ^0 ), and by Shchukarev, Oranskayov and Tsintsius (I9 5 6) (152-253°C). Of these results, those of Meyer, Fischer and Biltz, and Shchukarev et al, agree well. The of reaction 2AuCl(s ) =2Au(s ) + 0 1 2 (g) determined by Fischer and Biltz=+?0.3-1.7 J mol”^ of CI2

(Hager and Hill, I9 7 0). From the results of Shchukarev 3?

et al (1 9 5 6), the standard heats of formation of AuCl(s)

(-3 5 .2 -1 .1 kJ mol"^) and AuCl^Cs) (-114.9±3.2 kJ mol“^) could be calculated (Hager and Hill, 1970).

The dissolution of gold in chlorine water, to form AuCl, is probably due to its reaction with atomic chlorine rather than molecular chlorine, and Sviturov et

al (1 9 7 0) calculated the free energy change of the AuCl

formation reaction as -122.98 kJ mol”^ at 25°C and 760 torr.

The dissociation pressure data of Fischer and

Biltz (1 9 2 8), Petit (1925)1 and Pellaton (I9 1 5) yield for

AuCl^(c), AH^=-11?.6, -1 1 1 .3 , and -123.4 kJ mol"^ resp-

ectively (Bichowsky and Rossini, I9 3 6). Au2 d^(g) was identified as the vapour transport species in the Au-Cl

system at low temperature (T<450°C) (Hager and Hill, I97O).

2Au(s) + 3 0 1 2 (g) = Au2 Cl^(g)

for which AhJ(Au2 C1^(g))=-1 0 2 .926-I8 .4 kj mol"^ was obtained

by J.P. Hager and R.B. Hill (I9 7 0) from the data of Fischer and Biltz (1928).

Thomsen (Thermochemische Untersuchungen Barth, Leipzig, 1882-1886) measured the heat of solution of the anhydrous gold trichloride in water to be 18.62 kJ mol”^.

The heat of reaction of 2AuCl^(500) with 3 5 0 2 (5 0 0 ) was found by Thomsen to be 349.8 kj mol”^, giving aH^(AuCl^(aq))=

-I2 3 .3 mol”^. Combination with Fischer and Biltz's 38

value for A>Ç(AuC1^(s)) yields mean AH^(AuCl^(aq))=-1 3 7 .0 kl mol”^ (Bichowsky and Rossini, I9 3 6).

The heat of solution of AuCl^(s) in aqueous hydrochloric acid was determined by Thomsen (Thermochemische Untersuchungen Barth, Leipzig, 1882-1886), and Fischer and

Biltz (1 9 2 8) as 3 7 .6 and 42.3 kJ mol”^ respectively.

Using the Fischer and Biltz (I9 2 8) value of 118.4 kJ mol”^ as the value of AH^(AuCl^(s)), this gives AH^(HAuCl^(aq))=

-3 2 0 .9 and -3 2 5 .5 kJ mol”^ respectively. The heats of solution of the tri- and tetrahÿdrates of aurochloric acid, and the heat of solution of AuBr^(s) in aqueous hydrobromic acid and H250 ^(aq), were measured by Thomsen (Thermo chemische Untersuchungen Barth, Leipzig, 1882-1886) and yielded values of AH^(AuBr^(s))=-2 0 .92 and -24.3 kJ mol”^ respectively. Fischer and Biltz (I9 2 8) studied the equi librium

AuBr(s) + Br2 (g) = AuBr^(s)

to give AH^(AuBr(s))=-71^4 kj mol”^ (Bichowsky, I9 3 6).

Thomsen (Thermochemische Untersuchungen, Barth, Leipzig, 1882-1886) determined the heat of solution of AuBr^(s) to be -15.73 kJ mol”^, and the heat of mixing of AuBr^(aq) with aqueous hydrobromic acid to be 32.2 kJ mol— ^ , g i v i n g AH‘^(HAuBr^(aq) )=-197.1 kJ mol”^. The heat of solution of HAuBr^.5H20 (s ) was also measured by the same author. (See Bichowsky and Rossini,- I9 3 6). 39

These are examples of the studies used to calculate the thermodynamic values of halo-gold compounds listed in the National Bureau of Standards Circular 500. These values have since been revised in some cases, in N.B.S. Tech. Note 270-4 (See Table 2cl). However, this publication has no reference index, and so a discussion of the data sources is not possible. The values contained in N.B.S. Tech. Notes 270-4 and 270-3 (1966-79) (for ancillary data on the halide ions) have been used in calculations, where possible t in this work. 40

3. EXPERIMENTAL SECTION

3a) Synthesis and analysis of the compounds used.

Below are descriptions of the methods used to produce the compounds thermochemically investigated, and any intermediate products.

3b) Aurochloric acid, HAuCl^.x HgO

The aurochloric acid was formed by boiling an aqua regia solution of elemental gold with aliquots of conc. hydrochloric acid (to remove nitric),(Cotton and Wilkinson, I9 6 9). The resulting yellow solution was dried on a water bath. The aurochloric acid (Yield = 7 9 % \ Volhard for Cl, 34.6#: Calc, for HAuCl^.^HzO; Cl, 34.4#) contained an unknown quantity of water of crystallisation, but a slight excess of the acid reacted with alkali metal halides to form the alkali metal tetrahaloaurates.

3c) Potassium, rubidium and caesium tetrachloroaurate. . M'*' AuCl^ {!«■'■ = K'*', Rb+Cs^).

HAuCl^(aq) + KCl(aq) = KAuCl^(s) + HCl(aq) Potassium tetrachloroaurate was prepared by addition of aqueous potassium chloride to an approximately equimolar quantity of aqueous aurochloric acid. On removal of excess solvent, crystals of potassium tetrachloroaurate dihydrate were obtained (Yield = 6?#:

Cl, 3 1 .4^1 Calc, for KAuCl^. ZH^O; 01,34-3 %).. These were recrystallised from dry ethanol (Bonamico & Dessy,l973) 41

and the resulting anhydrous chloroaurate was dried at 100°C. (Yield = 60#, Cl, 3?.5#i Calc, for

KAuCl^, Cl, 37.5#).

Analysis of the product was by Raman spectroscopy (using a Coherent Radiation model 52 Krypton gas laser (647.1 nm) for excitation) with the sample powdered and sealed in glass capillary tubes.

Percentage halide was determined by reduction with SO2 and a potentiometric titration with silver nitrate (see Tellurium Experimental section). Unless this gave the product to be within one per cent of absolute purity, a further recrystallisation from dry ethanol was carried out. Karl-Fischer reagent could not be used due to its reducing properties; however, further drying of the products at lOO^C. in a vacuum pistol resulted in no further loss of weight, indicating the absence of water in the sample.

A similar synthesis using rubidium or caesium chloride was used to produce anhydrous rubidium tetrachloroaurate. (Yield = 74#, Cl, 33.3#: Calc, for

RbAuCl^; Cl, 3 3.4#) and anhydrous caesium tetrachloroaurate (Yield = 80#; Cl, 2 9 .8#: Calc, for

CsAuCl^ : Cl, 3 0 .1#).

3d). Potassium, rubidium and caesium tetrabromoaurate.

M+AuBr^ (m "^ = K+,Rb+,C3+) 42

KBr(aq) + Au(s) + ^2 Br^ (1) = KAuBr/^(aq).

Potassium tetrabromoaurate was formed from an aqueous slurry of gold, potassium bromide and bromine held at 55^C. for 6 h (Block, 1953). This solution was evaporated to dryness at 55^G and the residue was dissolved in methanol, filtered and washed through a medium glass sinter. After evaporation at 40°C, the product was dried at 80^C in a vacuum oven and analysed. (Yield = 79#; Br, 5?-3#« Calc, for KAuBr^^; Br, 57«5#)* (For Raman spectrum, see

Results section). (See also Ann, 217, 312 (I8 8 3)).

AuBr^(aq) + RbBr (aq) = RbAuBr^^(s)

Rubidium tetrabromide was produced on mixing equimolar solutions of gold tribromide (produced from the elements) (Puddephatt, 1978 and Fattens, I97O), M and rubidium bromide in hydrobromic acid (Schottlânder, 1883). The precipitate was recrystallised from methanol and dried at 80°C in a vacuum oven. (Yield = 81#;

Br 5 3 .4 #* Calc, for RbAuBr^; Br, 53*1#)• (See Results Section for Raman).

Caesium tetrabromoaurate was formed on mixing an aqueous solution of caesium bromide with the equimolar quantity of potassium tetrabromoaurate in aqueous HBr soln.. (Higher mole ratios of the 43

tetrabromoaurate lead to a black mixed- valence salt T TTT " Cs^Au Au Br^). (Brauer and Sleater, I97O). The red/brown product was filtered, recrystallised from dry ethanol, and dried in a vacuum oven at 80°C.

(Yield = 68#: Br, 49.1#; Calc, for CsAuBr^^; Br,

4 9.2 #). (See Results section for Raman spectrum).

A synthesis for caesium tetrabromoaurate similar to that used to form the rubidium salt, and involving the mixing of AuBr^ and CsBr solutions in aqueous hydrobromic acid, led to the formation of the double salt, CqAu2 Br^. (Yield = 4l#i Br, 40.4#;

Calc, for Cs2 Au^Au^^^Br^; Br, 42.1#). (See Results section for Raman spectrum). Analysis of the caesium salts was by Volhard titration and potentiometric titration. The aqueous salt was reduced with SO2 gas, boiled and filtered. The bromide solution was mixed with I50 cm^ of acetic acid/sodium acetate buffer

(pH 4 .9) and titrated against a standard O.IM AgNO^ solution, using a silver billet electrode, and saturated KNO^ bridge to a calomel standard (3-8M K Cl electrolyte solution).

3e) Tetramethvlammonium and tetraethvlammonium

dibromoaurate, R^N^AuBr2 ( R = Et, Me).

On treating an ethanolic solution of

HAuCl^.x H2 O at 50 - 60°C with an eight- to ten-fold 44

excess of tetraethylammonium bromide, tetraethylammonium tetrabromoaurate (Etj^N^AuBrj^ ) was formed as a maroon

precipitate. (Braunstein and Clark, 1973). This was recrystallised from ethanol and analysed. (Yield = 79#;

Br, 4 9.2 #: Calc, for Et^^NAuBr^^; Br, 49.4#). Pure tetrabromoaurate was partly dissolved in absolute

ethanol and heated with acetone at 60 - 70^C. (P.Braunstein & R.J.H.Clark, 1973)• On refrigeration, long needles of the dibromoaurate were obtained. The Raman and infra-red spectra (Results section) and the bromine content of the product were recorded. (Yield = 60#j

Br, 3 2 .6#: Calc, for Et^NAuBr^; Br, 32.8#).

The tétraméthylammonium salt was produced as above, using Me NBr. (Yield = 61#; Br, 37.1#; Calc. 4 for Mej^NAuBr^; Br, 37.1#).

HAuCl/^.x H^O + 4Et^NBr = Et^NAuBr^^ + 3Et^NCl

+ HCl

Et^NAuBr^ + Me^CO = Et^^NAuBr^ + CH^BrCOMe + H Br

3f) Tetramethvlammonium and Tetraethylammonium dichloroaurate R^N^AuClg (R = Me, Et).

The synthesis of the two gold I chlorides,

Et^NAuClg and Me^NAuCl2 was attempted. Using the method of Braunstein and Clark,(1973) where an ethanolic 45

slurry of Et^NAuCl^ (1.62g in 30 cm^) is reduced with

phenylhydrazinium chloride (0 .25 g in 10 cm^) for l^hrs in the warm, only approximately O.lg of tetraethylammonium dichloroaurate was isolated. Characterisation was by Raman spectroscopy and halogen analysis. (Cl, 16.6#»

Calc, for Et^NAuCl2 ; Cl, I7 .8#). Repeated attempts at synthesis proved unsuccessful and a similar method employing Me^NAuCl^ did not yield the dichloroaurate product.

Au (III) is a typical Chatt-Ahrland B group acceptor and as such should form very strong iodo

complexes. Several 1 9th. century references to gold (III) iodide and iodoaurates exist (J.W. Mellor, 1946). All these involved evaporation of aqueous iodide solutions thought to contain Au(III). However, it is known that Au(III) is not stable in aqueous iodide solutions,

(A.K. Gangopadhayay & A. Chakrovorty, I9 6 I) and so these products probably consisted of mixtures of gold (I) iodide or complex iodides and salts of I^.

When (C2 H^)^NAuC1^ is treated with liquid anhydrous HI, quantitative conversion to the black

crystalline tetraiodoaurate occurs (J .L . Ryan, I969) . The salt is reported to be moderately stable to air, apparently because of its extreme water insolubility. This insolubility is related to the strength of the 46

Aul|^ complex and its lack of tendency to hydrolyse (B group behaviour). The salt dissolves with immediate decomposition in nonaqueous solvents such as acetone, acetonitrile, and nitroraethane. At -78°C the salt dissolves to a very slight extent in acetone and to a greater extent in propylene carbonate. However, the complex rapidly liberates iodine.

Several insoluble 'double auric iodides' have reportedly been prepared by adding auric chloride to an aqueous solution of the appropriate iodide. However, the same cations which give insoluble Aul^ salts will give insoluble salts and the resulting mixture of AuI and MI^ will appear analytically to be a tetraiodiaurate. The aqueous method cannot be expected to yield pure salts of Aul^ , but instead will give mixed chloro-iodo complexes generally contaminated with 1^ and Aui or salts of AUI2 .

3g) Tetramethvlammonium. triethylammonium and tetraethvlammonium diiodoaurate.

R^N~^Aul2 (R = Me, Et), and Et^NH~*'AuI~

With only the reported synthesis of tetraethylammonium tetraiodoaurate (J.L.Ryan, I969 and 1 9 74) and despite the number of possibly useful calorimetric reactions being severely limited by the decomposition of the Aul^ anion in solution (and the possible coordination of the I^ so produced), the 47

diiodoaurates were considered for calorimetric study. Tetraethylammonium di-iodoaurate was prepared via the method of Braunstein and Clark, by mixing Et^NAuBrg with Et^NI in the molar ratio of 1 i 2, in absolute ethanol, at 4o°C. (Yield = ]0#; I, 4-3.6#i Calc, for

Et^NAuIg* I, 4 3 .7#). (See Results section for Raman spectrum).

The Braunstein paper also details the synthesis of tetra- n - butylammonium di-iodoaurate. However, this compound could not be used as the second Aulg salt for the determination of the thermochemical radius of the complex anion. This was due to lack of data concerning the radius of the n-Bu^w'*’ ion and the heats of formation of the gaseous and aqueous cation.

The synthesis of tétraméthylammonium di-iodoaurate was attempted (all necessary ancillary data for the tétraméthylammonium ion being known). The preparation was carried out as for the tetraethylammonium salt, using Me^NAuBr£ and Me^Nl in absolute ethanol. No crystals were isolated and on reduction of the volume of the solution and subsequent cooling in a salt/ice bath, the tétraméthylammonium iodide was isolated (I, 6 3.0#: Calc, for Me^NI;

I, 6 3.1#).

It may be that the formation of 48

tétraméthylammonium diiodoaurate is energetically unfavourable due to the small size of the tétraméthylammonium cation compared to the Et^N - The synthesis of triethylammonium di-iodoaurate was therefore attempted. Production of this compound via the Braunstein and Clark route required Et^NHAuBr2 and Et^NHIas precursors.

Triethylammonium iodide was formed by addition of HI solution ( BDH) to triethylamine in carbon tetrachloride, at 0°C, when white crystals of the product were precipitated (Yield = 85#; I* 55'*0# : Calc, for Et^NHIi I, 55*4#).

Mixing of ethanolic solutions of gold trichloride and triethylammonium bromide in the mole ratio 1 I 4 yielded triethylammonium tetrabromoaurate, and 4.1g of this in 3 6cm^ of dry ethanol was treated at 60 - 70°C with 2.4 ml. of acetone, leading to the formation of the dibromoaurate (Yield = 41.6#;

Br. 42.5#: Calc, for Et^NHAuBr2 , 34.8#). 2g of this "3 prodqct (4.4 mmol) in lOcra^ of dry ethanol was reacted with 2 g of triethylammonium iodide (8 .7 mmol) in 10ml of dry ethanol at 3 0°C for 30 mins, and was then left to cool slowly, while being shaken continuously for 2 hours. The solution was refrigerated (10 - 12 hrs.) and the white crystals were filtered off and washed with ethanol and diethyl ether (Yield = 39#» I» 53-6#; 49

Calc, for Et^NHAul^; 1, 45.9#)* Further crystals were obtained by addition of ether to the filtrate.

(Yield = 86#; I, 51.9#)* (See Results section for Raman spectra). The isolated product was mainly Et^NHI.

Triethylammonium bromide was prepared by reacting hydrogen bromide gas with triethylamine vapour in a slush bath of acetone and dry ice (B. Derahkshan,

1 9 8 0). Hydrogen bromide was prepared by reacting bromine with tetralin (tetrahydronaphthalene) containing pure iron filings. The reaction vessel was cooled in

a water bath which was heated to approx. 3 5°C upon the reaction becoming sluggish. The gas was passed through

a trap of tetralin to eliminate traces of Br2 and was then dried by means of a liquid nitrogen trap before entering the reaction vessel. Triethylamine vapour entered the vessel on nitrogen carrier gas bubbled through the liquid amine. The reaction vessel was

protected by a CaCl2 drying tube, and cn cooling to -?0°C Et^NHBr was formed. This was filtered under

suction and dried in a vacuum desiccator over CaCl2 .

(Yield = 4 9#; Br, 4].8#: Calc, for Et^NHBr; Br,4].9#).

A similar technique, using HI (from addition of iodine in tetralin to boiling tetralin) and triethylamine in carbon tetrachloride was originally employed to produce Et^NHI. (I, 54.4#: Calc, for

Et^NHI; I, 5 5 .4#). 50

The yield of pure iodide was too low for use in further synthesis.

3h) Reclamation of gold - (T. Page, 19?8) Gold residues were dissolved in water and treated with SOg until the formation of a dark brown gold precipitate. The suspension was boiled until coagulation occurred, and filtered through a coarse sinter. The solid was boiled with aliquots of distilled water until addition of AgNO^ showed no halide present. The gold was boiled with two samples of nitric acid to remove other metals (e.g. tellurium or selenium; and then filtered, washed with water, and dried. (Yield ^

3j) Details of reactions studied. The enthalpies of solution of the metal tetrahaloaurates in water were measured, using various sample weights in order to find any dependence on the concentration of the salt in the final solution. However, the aqueous tetrahaloaurate ions partake in a series of equilibria involving hydroxide exchange with the halide ionsi- (Engelhard, I9 6 9).

AuX^ (aq) + H2 0 (l) AuX^OH'(aq) + X”(aq) + H*(aq)

X = Cl K = 7 X 10”^mol^l ^ (complete in "^1 minute) X = Br K = 7 X 10 ^mol^l ^

AuX^OH”(aq) + H2 0 (l) ^ A u X 2 (0H )2 (aq)+Xleq) +H%q) 51

X = Cl K = 3x10 ^ mol^l ^ (complete i n -^1 hour). X = Br K = lxlO"9 mol^l'Z

(see also Peshchevitskii, 1 9 6 9? Dubinskii, I9 6 8;Bjerrum

(Bull Soc. Chim Belg), 1948; Chateau, I9 6 6; Cotton &

Wilkinson, I9 6 9; Carlsson, 196?; and Fry, I9 6 6). Further exchange equilibria result in the

formation of Au(OH)^ (Bjerrum, 1948; Dubinskii, I9 7 1).

A series of standard solutions of HBr or HCl were then used as solvents, in order to inhibit the hydroxide exchange equilibria. The resulting enthalpies of solution were plotted against activity of the solvent used.

Due to the disproportionation of the gold (I) compounds in water (A) to gold and gold (III), a reduction reaction was employed.

(A) I- 3 Et^^NAuBr^ — 2 Au(0) (s) + Et^NAuBr^(aq)+2Et^NBr (aq) A number of reducing agents were investigated. (Mellor, 1967). These included aqueous solutions of sulphur dioxide, hydroquinone, phenylhydrazine, potassium nitrite, tin dichloride, oxalic acid, and ferrous sulphate (Mellor,1967 »

Lenher, I9I3 ). Only the ferrous sulphate solution led to the formation of a gold precipitate, and not a sol, in the cold, and within a minute of being added. (Tobe, 1972; see also

Miller & Fisher, 1974).

Using ferrous sulphate on samples of the 52

dihaloaurates, a gravimetric analysis of the gold precipitate was carried out. The dibromoaurate was reacted with a ten-fold excess of sulphate, followed by filtration of the gold, which was then washed with water and dried at 130°C. The gold was found to be

precipitated quantitatively. (Table 8 al)).

To determine the ferrous sulphate consumed in the reaction, a known excess of previously standardised ferrous solution was reacted with a given weight of the dibromoaurate. Bromide ions interfere with permanganate and dichromate titrations with ferrous ions, and so an analytical technique involving ICI (from KIO^ and KI in HCl soln) was attempted. The iodine released from reaction of the ICI with the ferrous ions could be titrated against a standard iodate solution. This method gave inconsistent results.

The dichromate titration with ferrous ions is unaffected by chloride ions. (Vogel, I96O). Therefore the dibromoaurate sample was reacted with a known excess of standard ferrous sulphate solution. - The gold precipitate was isolated and weighed, while the bromide ions were removed with excess silver nitrate solution which was boiled, filtered and weighed. The silver nitrate was reacted with excess sodium chloride solution, was boiled and the chloride filtered off. The remaining ferrous ions were titrated against a standard potassium 53

dichromate solution, using N - phenylanthranilic acid as indicator. The number of ferrous ions found to

be removed in the reaction (Table 8 al)) agreed well with that predicted from the proposed stoichiometry of_ the reaction*-

3 M“^AuBr“(s) + 3 FeSO^(aq) = 3 Au(o)(s) + ^ { a q ) + FeBr^(aq) + 3M^Br"(aq) M^= Me^N^ or Et^N^ (See Appendix V )

The heat of reaction of tetraethylammonium diiodoauratels) with aqueous sulphur dioxide was measured.

Aqueous sulphur dioxide has often been referred to as a solution of 'sulphurous acid'. is present in very small quantities,if at all,

in such solutions and the equilibria in aqueous SO2 solutions are reported to be best represented as:

(Peake, I9 7 6).

SO 2 + XH 2 O = SOg JCH20

SO2 + H2 O = K « 1

SOg. xHgO = HSO^(aq) + H^O‘*'(aq>f(x-2 )H20

The first acid dissociation constant for 'Sulphurous acid'is defined as*

K = [HSQ-] [H+]______= l.jxKfZmoU-l [Total dissolved SOg] - [HSO^] - [So|”] and so the major species in an aqueous solution of sulphur dioxide is SO2 .XH2 O. (KaZakov, I968 b)). 54

Solutions of SO2 are often used as reducing agents*

2 H2 O + SO2 = S 0 ^ ~ + + 2 e" = - 0 .1?V. The reaction studied was found to be:

2 Et^NAul2 (aq) + SO^faq) = 2Et^Nl(aq) + 2Au(s) + 2HI(aq) + 2 H20(1) + H^iSO^Oaq)

Sulphur dioxide solution at 25°C. was prepared by passing the gas (B.D.H.Ltd.) into 5OO cm^ of freshly boiled distilled water. The solution was then diluted ten times with distilled water and stored in the dark under nitrogen gas. The concentration of the solution was determined by reacting aliquots (20cra^) with excess standard iodine solution (B.D.H. O.IM A.V.S.) and back-titrating with standard sodium thiosulphate solution (B.D.H. O.IM A.V.S.) using freshly prepared starch indicator-solution.

The dilute solutions were quickly pipetted into the calorimeter vessel, and the air space above t this solution was flushed with dry nitrogen.

Ferrous sulphate solution could not be used to reduce the diiodoaurate salt as a redox reaction between gold (I) and iodide ions releases metallic gold and tetraethylammonium tri-iodide.

3Et^NAul2 (s) + 3FeS0^(aq) = 3Au(o)(s) + Fe2 (S0^)^(aq) + Fel^(aq)

+ 3Et^M+l"(aq)

Et^MAuIgfs) + I”(aq) = Au(o) + Et^NI^(aq) 55

Uncertainty in the degree of associa üon between the liberated iodine and aqueous tetraethylammonium iodide (e.g. see Ford-Smith et al, 1972), and the absence of thermodynamic data concerning the triiodide necessitated the use of another calorimetric reaction.

One aqueous reaction leading quantitatively to clearly defined products is the sulphur dioxide reduction of the gold (I) salt. It has been reported that on such a reduction of an aqueous gold (III) salt, a relatively stable solution of gold (I) is formed which

requires a large excess of aqueous SO2 before full quantitative reduction to the metal takes p l a c e . (Lenher,

1 9 13). However, on breaking an ampoule containing

O.lg of solid Etji^NAul2 in 100 cm^ of aqueous O.IM SO2 solution, the stoichiometry of the reaction was determined to bei-

2 Et^NAul2 (s) + S0 2 (aq) + Z K ^ O U ) = 2 Et;^NI (aq)+2Au(s )+2HI (aq)

+ H2 S0j^(aq). This was confirmed by gravimetric analysis of the gold released, a potentiometric titration of the total iodide released ,(after removal of excess SO2 by boiling), and an iodine/thiosulphate back-titration (after removal of iodide produced in the reaction, with silver nitrate solution) giving the moles of SO2 reacted (see Appendix ?).

An investigation of a calorimetric reaction using caesium tetrabromoaurate was carried out. The 56

reaction investigated was that between aq. CsAuBr^ acidified with nitric acid (10# by volume) and an excess of aqueous silver nitrate solution. 3cm^ of the tetrabromoaurate (2.46 x 10 M), plus O.lcm^ of cone HNO^ were placed in a U.V.cell, and the visible spectrum of the AuBr^ ion was followed at 3 8 1m" , immediately after the addition of 0 .5 cm^ of silver nitrate solution (0.1 M). Some AgNO^ photodecomposed, leading to decreased transmittance, however the coagulation of a white precipitate led to an increasing transmittance, at 381nm with time. The white precipitate was formed within 30 seconds of nitrate addition and the subsequent coagulation was complete within three minutes. Precipitate coagulation also took place in the dark. This was followed potentiometrically using the Ag billet electrode with a KHO^ bridge and calomel reference. (See Figs 3j2 to 3j^« The reaction was thus sufficiently rapid to be useful calorimetrically

The stoichiometry of the reaction was then ft studied. 30cm^ of aqueous CsAuBr^(2.46 x 10 M) were mixed with 4 cm^ of conc. HNO^ and of a standardised aqueous AgNO^ solution (O.IM), allowed to stand in darkness for three minutes, and the solution was then filtered through a Whatman 542 ashless filter paper. The paper was ignited to constant weight to determine the weight of Ag + Au in the precipitate, and was then treated with nitric acid to remove only the silver. The filtrate was titrated against thiocyanate either 57

potentiometrically or via the Volhard method, in order to determine the moles of silver nitrate remaining. Both gravimetric and titriraetric results indicated a gold I silver reaction ratio of 1 i 5-

Using the caesium tetrachloroaurate, a reaction stoichiometry of lAu(lII) i 5 Ag(I) was again observed. The gold was precipitated quantitatively. To confirm this, aliquots of CsAuCl^ stock solution were reacted with excess AgNO^ in the presence of HNO^. The precipitate was filtered off. The gold precipitate and the remaining solution were then subjected to a number of tests in order to determine, qualitatively, the chemical species present. Tests used:- (Vogel, 1954). 1) Kl/starch test for chlorate. This test reacted with both the control solution (a solution of silver nitrate and nitric acid), and the filtrate. 2) D - dimethvlamino - benzylidlne - rhodanine reagent test for %old. On masking the silver with potassium cyanide it was found that gold was not present in solution 3) Indigo test for chlorate. The control (silver nitrate, nitric acid and sodium sulphate) and the filtrate both

bleached the indigo. 4) Aniline sulphate test for chlorate. A negative result

was obtained for the filtrate. 5) Manganous sulphate - ohosphoric acid test_ for _bromate (CsAuBr^ used). Both the control and the filtrate

gave a positive test. 58

J. Pelletier noted that AgNO^ or Ag^SO^ precipitated a mixture of auric oxide and silver chloride from a neutral solution of gold chloride (J. Pelletier, Ann. Chim. Phys., (2),' 13, 5, 1820). According to Jacobsen the pale brown precipitate is 4AgCl.Au(OH)^.

(J. Jacobsen, Corapt. Rend., 146, 1213, I908). (See also Rawson and Rawcliffe, "Principles of Inorganic and Theoretical Chemistry", Heinmann Education, 1973).

In this study an acidified solution of the chloroaurate was used. Assuming a similar precipitate to be formedi- CsAuCl^ (aq) + 4 AgNO^ (aq) = 4 AgCl[(s) + Au(OH)^|(s)

+ 3H2 O (1) + 3HN0^ (aq) + CsNO^ (aq)

However, a reaction stoichiometry of 3AgN0j % 1 CsAuCl^ was found in this study. This may have been due to decomposition of some silver nitrate during the reaction; due to the errors incurred by using a small sample weight of gold salt; or due to acidification of the reactants with nitric acid.

From fig. 3j2)., the Raman spectrum of the precipitate, it can be seen that the peaks are not consistent with the presence of gold-chlorine bonds (which would be observed above 300 cm ^). AgCl (NaCl structure) has an i.r. active transverse optic mode (184 cm“^), but no Raman-active vibrations. Thus, unless the symmetry of the AgCl lattice is lowered, the bands in 3j2). cannot be assigned to the silver halide. 59

Therefore it appears that the precipitate consisted of halide, Ag and Au. No chlorate or bromate were formed and no gold remained in solution. As the composition of the precipitate, the final products, and their states remained unclear, it was decided to use the heat of solution of the tetrahaloaurate in water, as the calorimetric reaction. The potassium and rubidium salts were used, as they could be obtained easily in an anhydrous form.

Gold hydroxide can be formed by addition of sodium hydroxide to solutions containing AuXj^

(Mellor, 1967) (X = Cl, or Br). Fig. 3 jl) shows the Raman spectra of rubidium tetrabromoaurate in sodium hydroxide solutions of different strengths. It can be seen that by IM NaOH all tetrabromoaurate has reacted, to give the gold hydroxide. The use of this as a calorimetric reaction was considered. With IM NaOH solution , Au(OH)^ was formed as a brown solid, and not as a sol, immediately upon mixing the solutions at 25 °C. Auric hydroxide is generally known as auric acid since it behaves as a weak acid (Liptrot, 1977). Thus, it readily dissolves in NaOH solution. Johnston and Leland (1938) found that the solubility curve of auric -6 hydroxide rose continuously from the value 3 x 10 moles of gold per 1000 g of water to a maximum of approx.

1 X 10“^ moles per lOOOg of water at 0.42M sodium 60

Fig. 3.11). Raman Spectra of RbAuBr^ 'in Aqueous NaOH Solutions

100

M N jiOH

NaO

cr> o o o vO s CO m CM s WAYENUM3ER (cm ^). 61

Fig. Tj? ) Raman Spectrum of CsAuCl.^/AgNO^ Precipitate.

100

O o o

WAVENUMBER(cm'l) 62

CsAu:3r,, in

Decante i liquid f rom CsAuBr /AgNO- Rea ction

Changeover to U

WAVELENGT

Reactants and Products. 63

iOTq.onpojq.ui -e

CO c •H O

I—I

o I— I,

cz> 64

( *>i'Kva) nyso moog

e 0) en >1 en 0) o -P O c 0) o I—I •H (D -P ü 0) (Ü ü (U c cr; Q) . î-t a k I—I iH

ü •H X5 ■H 0> en B •—{o -p c Q) P> O o CL, o

b£ •H o 65

hydroxide, fell steeply to a minimum solubility at IM hydroxide (1.5 x 10“^ moles per lOOOg of water) and rose nearly linearly with higher concentrations of base.

The stable solid below 0.42M NaOH had the composition Au(OH)^ and, above 0.42M NaOH, the composition Na2 HAuO^. The data could be well accounted for, to the minimum at IM alkali, by the equilibria Au(OH)j + oh" - H^AuO^ + H^O

Au(OH) 2 + 20H" - HAuOj" + 2 H2 O

NagHAuOj - 2Na* + HAuO^" This interpretation was confirmed by measurements in alkaline solution of potassium sulphate.

To account qualitatively for the observed rise in the solubility above IM NaOH, the equilibrium

Na^ HAuOj + oh" = 2Na+ + AuO^" + HgO was introduced.

Therefore, with O.lg (1.8 x 1 0 moles) of KAuBr^^ in 100 cm^ of IM NaOH, approximately 1.5 x lO"^ moles of Au(OH)^ (8^ of the product) would be dissolved in the hydroxide solution as H^AuO^ (aq) and HAuO^ (aq) ions, the heats of formation of which are known. However, with the resulting difficulty in defining the thermodynamic states of the final reaction products, and in determining

/ the stoichiometry of the reaction, it was decided to investigate by means of a calorimetric titration, the 66

aqueous tetrahaloaurate/ferrous sulphate reaction.

(see also Kazakov and Konovalova, I968),

A measured volume of stock KAuCl^ solution in 1M was reacted with a known excess of ferrous sulphate solution (in 1M The gold precipitate was weighed, while chloride was removed with excess silver nitrate solution which waa boiled, filtered and weighed. The calorimetric titration of ferrous sulphate stock solution into a known volume of potassium tetrachloroaurate solution gave a reaction ratio of 1 kAuCl^ 1 3 FeSO^. (See Appendix V).

The tetrahaloaurate/ferrous sulphate reaction was investigated by means of a thermometric titration, using the same calorimeter as that used to measure of the tetrahaloaurates.

A strong aqueous solution of ferrous sulphate (acidified with to stabilise the solution), was titrated into a dilute aqueous solution of the tetra haloaurate (likewise acidified with to inhibit hydrolysis of the tetrahaloaurate anion). The heat evolved was then monitored against time (and volume of reactant titrated). (See section 3m).

The form of such an evolved heat v titrant graph would yield information on the mechanism of the reaction studied. E.g.- 67

Moles of titrant (T) The above indicates a reaction with three distinct steps. The enthalpy of each simple reaction can be calculated from &T, and the stoichiometry calculated from the number of moles of titrant (&T) consumed in each simple reaction.

3k) . CAIDRIMETRY»-

31). Brief Description of Procedure.

The reactions studied were carried out in a calorimeter consisting of a thin-walled Dewar vessel operating in the isoperibol mode, at 298.2K. The solid sample (approx. 0.2 g) was accurately weighed into a glass ampoule which possessed two thin-walled bulbs. The solvent or reacting solution (100 cra^) was introduced into the Dewar vessel at a temperature close to 25 ^0 , and was allowed to equilibrate with the surrounding water bath (23 .0- 0 .005^0 ), the solution being stirred at approximately 3000 rpm. On thermal equilibration, which was determined by the reading on the thermistor bridge attaining a previously 68

FÎK. 311). The Calorimeter.

S ide. Adhes ive -Crocodile clip

.mpoule- breaker Paddr i n Thermistor

Heater

Ocm/ Dewar-vessel

The Thermistor.

Leads. Plan. Adhes ive. Calibration heater. Nut.

Thermistor. AmoouleXholder.

Thin-walled Glass tube. Stirrer Ampoule-bregker.

Unusad. Bead of S erniconductor.

Oil, /or good thermal contact between the thermistor and the surrounding glass. 69

Fig. 312). The Experimental Apparatus.

CMART- RECORDER

GAHWYN mV BACK-OFF. THFRÎ.IISTU R- BRIDGE

AMPLIFIER

REFERENCE

CAIDRirviETER 10/v

STANDA WATER- -3ATH

2982 K THERMISTOR HEATER

REACTION CALORIIvIETER. 70

calibrated position (Fig. 3ra 1)), a fore-period was recorded on a chart recorder. The ampoule bulbs were then broken, allowing the sample to mix intimately with the solution. The heat either released or absorbed in this process caused a change in the temperature of the solution which was detected by the thermistor (100 K n , in a thin -walled glass tube) in the reaction vessel. The resistance change of this thermistor was balanced,using a Carwyn a.c. differential thermistor bridge (which could be used either in a direct (resistance), or in a comparative (differential, A/B) mode), with that of another thermistor in a reference calorimeter, thus nullifying signals due to changes in the bath temperature. The voltage due to the resistance difference between these two thermistors was amplified and fed with a back-off (millivolt) voltage, via a summing operational amplifier, to a chart recorder to be plotted with time. An after period was then recorded.

On plotting the reaction graph (the solution being cooled back to 25^0 only after an exothermic reaction), a calibration run was carried out using the 0 .3W, 100 n. solid state heater in the reaction vessel. For a similar temperature interval, the time for which the heater was run (- 0 .01s), the power of the heater (the voltage across the heater and a standard

10 resistance in series), and a corresponding chart v/as recorded. 71

From an analysis of these runs a heat of reaction per mole of sample could be calculated. Regular checks on the accuracy of the experimental system were carried out by measuring the heat of solution of fham (Tris (hydroxymethyl) siminomethane - B.D.H., Aristar) in excess 0.05M NaOH (endothermie) and in excess 0.05M HCl (exothermic), one tham being run before, and one after a series of runs.

For a more detailed description of the apparatus, see Dr. Stuart Peake's thesis (I976). A typical calorimetric run for ffiam is described below to explain the operation of the calorimeter.

An empty sumpoule was weighed together with a B5 stopper. The ampoule was then filled with powdered dry tham up to the level of the top bulb of the ampoule. (With hygroscopic samples, ampoule filling was carried out in a dry box). The stoppered ampoule and tham sample were reweighed. The ampoule was then attached to the ampoule-holder(a 3mm. precision-ground glass rod with a B5 cone attached to one end), by means of an elastic band and the calorimeter screwed carefully into its aluminium cap. The hydrochloric acid solution was warmed to approximately 25^ G, and pipetted into the reaction calorimeter. An identical volume (100 cm.) of solution was introduced into the reference calorimeter. The vessels were placed in the thermostatted bath and the stirrers were connected to precision motors. 72

By using the tiermistor bridge in the single channel mode the voltage across a single thermistor could be read and compared with the value obtained for the thermistor at 25®C.. The calorimeter could then either be heated (by means of the resistance-heater),

or cooled (by a flow of dry nitrogen gas) to 25 ^C. The calorimeters were then left for an hour until full equilibration with the surrounding water bath was achieved. This corresponded to a flat, level trace being obtained on the chart recorder, with the bridge in the differential mode (allowing a comparison of the reaction and reference thermistors).

A fore-period of 15 mins. was then recorded on the chart recorder. The ampoule bulbs were fractured against the spike of the ampoule-breaker, and the bottom of the calorimeter vessel. The effect of ampoule- breaking was negligible. As the temperature of the calorimeter rose, the recorder pen was brought back onto scale by adjustment of the millivolt source. An after period of fifteen mins. was then recorded. With the thermistor bridge switched to the single channel-mode, monitoring the resistance of the thermistor in the reaction vessel, the calorimeter was cooled to 25 °C,. The calorimeters were left to equilibrate for one hour.

The -thermistor bridge was set to the differential mode and the millivolt source set to the 73 initial value used in the reaction run. A fore-period of 15 rains, was recorded. The time of heating was sufficient to give a pen displacement approximately equal to that recorded in the reaction. The potentials across the heater (P}{)and the 10_a standard resistance (Pr ) were measured. The heating time was noted and an after-period of 15 rains, was recorded.

The Carwyn thermistor bridge is detailed elsewhere .(PeakelThis was a unit ratio bridge where one element was slightly unbalanced. In general, the out-of-balance voltage was not directly proportional to the thermistor temperature. The electrical calibration experiment was arranged to result in the same heat output as that obtained in the reaction. Non-linearity errors then cancelled on calculating the ratio of these voltage changes.

The corrected temperature changes for the reaction and calibration experiments could be calculated from the out-of-balance potential displayed by the thermistor bridge.

All reactions studied were moderately fast (i.e. complete in under 5 rains.), and so the voltage values for the fore-and after-periods were obtained by linear extrapolation of the reaction fore- and after-periods to the time of ampoule breaking. 74

The value of the after-period voltage should be found by extrapolation of the after-period to the time

(to corresponding to O .63 of the voltage change

(Wadso, 1966). Although the position of could not be estimated, the difference between the after-period voltage value at this time and at the time of ampoule breaking for a than reaction (complete in under two minutes) was negligible, and for a reaction of five minutes duration was equal to the uncertainty in estimation of t^

Due to the linearity of the voltage-time graphs, a simplified form of the Dickinson equal area method could be used to extrapolate the traces. Thus, the fore- and after-period voltages of the calibration experiment were extrapolated to the time corresponding to half the voltage change.

After an endothermie reaction, the calibration experiment was carried out as described above but was done so immediately following the after-period of the reaction run, raising the temperature of the reaction vessel to approximately 25 °C.. The traces were treated as above.

3m) Calculation of the heat of reaction^ Considering the" heating circuit - If V is the voltage across the standard 1 0 ^ resistance s (Rg) and is the voltage across the heater, for a current I 75

flowing through the circuit:- Vg = IRg (from Ohm's law). = IQ-a

■••I = (Vs/io ) -- ® = Power of heater = = (Vs” CE)

The heat energy (AQc ) released from the heater during calibration is given by%-

AQc = F#' (where t^ = time of heating) This heat release is directly proportional to the chart recorder pen displacement (ATc) during calibration.

AQc = K. ATc - (£) Yielding the calibration constant, K = AQc -

ATc From^^ and^?^i -

V — D + " ■ '■h - *h - © ATc Similarly, the heat energy ( ) released during reaction is directly proportional to the chart recorder pen displacement (AT^) during reaction.

AQ r = K. ATjj - ®

F r o m ® - AQ r = AT^ _ ®

AT c The enthalpy per mole ( AH ^ ^ of this reaction = AQfj - "V (where = moles of reactant). = Weight of reactant taken (g) = W - (lO Molecular weight of reactant M.W.

Zrpmj^jandJ^) -

AH^^ = A Q r - M.W. - ®

W 76

Substituting from(^^ for AQ j^ i AHjj®" = P%.t%. ATj^. M.W. J mol'l

W. A T c AHjj®" = AT^. M.W. KJ mol"^

1000'. W. A T c

3n) Titration Calorimetry:- The calorimeter described in the previous section was adapted to form a titration calorimeter.

A tapered glass tube, approximately 6 cm. long and formed into a capillary at one end, was cemented with epoxy resin into an unused ferrule screwed into the reaction calorimeter cap. The capillary end of the tube dipped 5 mm below the surface of the reactant solution. A twelve metre length of 1 mm. diameter polythene tubing was fitted, one end to the titrant delivery tube, and the "3 other to a 10 cm precision syringe. ("Re-Pette", Jencons Ltd.), actuated by an electric drive. The tubing was coiled around a section of 5 cm diameter brass tubing immersed in the constant temperature bath. The titrant was therefore delivered into the reaction vessel at the same temperature as the caloriraetric fluid. The motor speed of the pipette-pump could be adjusted from a setting of 0 to 50* A setting of 15 was used throughout the experiments. In a calibration of the syringe, the weight of water delivered with time was measured. The water was collected at 25^0 in a 10 cm^ volumetric flask positioned below the titrant delivery tube. (Table 3n 1). 11

Fig. Im X)

Exothermic reaction trace (eg.) tham with HCl.

Bridge out-of-balance voltage, Y.

Ampoule broken. Time

ATr = V^- Vp = Chart recorder pen displacement (mm.), after reaction.

Calibration trace -

Bridge out-of-balance voltage, V.

Heating stopped.

Time.

0.5 I I

Heating started.

ATq = Y^ - Vp = Chart recorder pen displacement (mm.), after calibration. 78

Fie, Im Z)

Endothermie reaction trace (eg.Me|^NA.uBr2 reaction with FeSO^)

Bridge out-of-balance voltage, V.

I Ampoule broken. 8 1 . 0 --- 100.5 Time.

Back-off voltage=2600 mV (Reverse ).

ATR = 19. 5 nim.

Calibration for Me^i^NAuErg/ Fe SOj^ reaction -

_____ Bridge out-of-balance voltage, V.

260 OR

AT_=21.0mm. Stop heating

83.5 Time.

start heating Back-off=2600R

10 AH M.W t A TF,

1000 X W X AT

Me^NAuBrg in 0 .05% FeSO^ t AH^ = + 16.10 kj raol“^ 79

The accuracy of the calorimeter was checked by measurement of the heat of neutralisation of aqueous HCl with aqueous NaOH. (Table 3n 2). A typical titration is described as followsi- The syringe and titrant reservoir were filled with aqueous hydrochloric acid (1.00 M B.D.H.), care being taken to exclude air bubbles. By withdrawing the syringe plunger a small air bubble was produced at the tip of the capillary. This bubble prevented premature mixing of titrant and titrand solutions. 100 cm^. of carbonate-free aqueous NaOH ( 0.03M) at

25 °C. was pipetted into the reaction calorimeter, and the cap of the calorimeter was screwed into the neck of the Dewar. A charge of 100 cm/, of distilled water was introduced in a similar manner into the reference calorimeter. The temperature of each calorimeter was

adjusted to 25 °C, and the calorimeters were left to stir and equilibrate for thirty minutes.

Using the millivolt back-off source, 10cm. of chart paper was checked to correspond to 0.4000 V. The millivolt source was then switched off and remained inoperative while recording a titration trace, which was accommodated within one chart-width. A chart speed of

1 cm. min ^ was used.

With the thermistor bridge in the differential

A/b mode the recorder pen was unbalanced by use of the 80

t- Syringe calibration for titration calorimetrv-

Time of pump operation Mass of water Rate o f titrant (s) delivered (g) delivery by syringe

300.12 0.5853 1.950 X 10"3

791.72 1.5372 1.942 X 10"3

427.95 0.8328 1.946 X 10"3

307.35 0.6024 1.960 X 10"3

361.30 0.7002 1.938 X 10"3

256.00 0.4951 1.934 X 10"^

422.40 0.8246 1.952 X 10“3

Meari = 1.946- O.OO9 X 10 ^ cm^s ^

= 0 .117- 0.001 cm^ min 81

Table In 2) - ENTHALPY OF NEUTRALIZATION OF HCl (l.QM) WITH NaOH(0-03M)

55.93

AHo mean = -55.6? (- O.56) kJ mol"^ (literature = R

_ 55.90 - 0.10 kJ raol"^ for 1.2 MHCl with O .05 M NaOH)

(Vanderzee, I963, and Pitzer, 1937). 82

coarse back-off control, to O.3V. The chart recorder pen was positioned on the left-hand side of the chart paper by adjustment of the pen zero control. A base line of 5 mins. duration was recorded, when the syringe drive was activated to deliver titrant and was stopped approximately 100 secs, after the end-point was observed on the chart.

The reaction calorimeter was cooled back to the original base-line and allowed to equilibrate for thirty minutes. A base-line of five minutes was again recorded, when the calibration heater was switched on to give a chart displacement equivalent to that obtained in the reaction. Typical reaction and calibration voltage-time plots are shown in fig. 3n 1 ), together with the extrapolation technique used.

The chart-recorder displacement ( Z\T^) was proportional to the heat evolved during the titration. For the calibration experiment, the extrapolated pen- displacement (AT^) at the mid-point of the voltage-time plot was a measure of the heat evolved during calibration. The number of moles of titrant reacted in the titration was calculated from the distance on the abscissa of the chart.

The enthalpy change for the titration reaction was calculated using the expression:- 83

= Pji' mol“^. and = V^. V,

N. AT^.IOOO 10 where is the power of the heater, t^ is the time of heating, AT^ and AT^ are as shown on the above traces, N is the number of moles of titrant reacted, and and Vg are the voltages across the heater and the

standard IOjt. resistance, respectively.

The mechanism of the reaction between aqueous KAuCl^ (or KAuBr^^) and ferrous sulphate solution was investigated calorimetrically. In each case the titrant was aqueous FeSO^ solution (0.400 M B.D.H., in

1MH 2 S0^) and the titrand was a charge of O.OI3M KAuX^ solution (in 1M H^SO^). 84

Fig. 3n 1)

Reaction.

Bridge out-of-balance voltage V

Time of reaction. Time, (and -\ --- ATr volume of titrant).

Calibration t -

Bridge out-of-balance voltage V

Time .5 85

k ) RESULTS SECTION 4a) TETRAHALOAÜRATE RESULTS ( A H'%olution)

4b) KAuClj^ - i) Enthalpy of solution of KAuClj^ in water (at 298K)

Table 4b 1)

Purity by analysis 1 Run number KAuCli, (aq) -s -3 (for Cl") + AH ^ ( k j mol" '■) & date /x 10 moldffl

39.25 1. 4 .3.79 8.44

38.30 2 . 6.3.79 13.72

39.13 3 . 6.3.79 10.81

99.8# 38.89 4. 7.3.79 8.66

39.03 6. 8.3.79 12.43

39.47 7. 9.3.79 8.87

39.40 8.10.3.79 8.86

100.5"Â 39.09 12 . 3 .5.79 12.10

39.79 13. 8.5.79 7.31

99.2 # 39.43 19.11.6.79 5.16

39.34 26 .15.6.79 13.99

L.K.B.runs [for L.K.S, detdils see Wadso , ' 9664

9 9 . 8% 40.37 9.20 .3.79 6.76

37.96 10.21 .3.79 9.06

= + 39.19- 0.26 kj mol”^ Mean AH sol 86

4).b)ii) Table 4b)2) Enthalpy of solution of KAuCl^^ in hydrochloric acid solutions (at 298%) -

Purity by Run number Activity of KAuCl^(aq) Analysis and date HCl soln /xlO”^ mol (for Cl”) (mol dm ^) dm”3

100. 1# 39.19 (-0.39) 1-13 4 .3.79 0 - 15.6.79

100.5# ' 35.91 14. 11.5.79 0.05 3.65

99.8# 34.95 11. 7.3.79 0.1 11.72

100.5# 34.82 15. 10.5.79 0.1 9.13

32.56 16. 11.5.79 1.0 7.04

100.6# 30.23 17. 6.6.79 2.0 4.80

29.20 18. 6.6.79 3.0 6.79

29.13 20. 11.6.79 3.0 5.82

‘100.2# 22.29 21. 12 .6.79 6.0 4.73

26.05 22. 12 .6.79 4.0 2.87

33.76 23 . 13.6.79 0.75 1.91

35-16 24. 14.6.79 0.5 7.28

99.2# 31.98 25 . 14.6.79 1.9 5.97

35.07 27 . 18.6.79 0.5 5.06 87

Table 4b 3)

Enthalpy of solution of KAuCl,. in KUO solutions (at 2Q8K) 3

Purity by Run number Activity of (KAuCl^(aq)

Analysis and date KKOj soln. /X 1 0 ”^ mol (for Cl”) mol dm dm”3

39.00 2 8 .1 9.6 .7 9 0 2.13

34.10 2 9 .2 0 .6.7 9 1.0 4 .6 2

99.2#

29.29 3 0 .22 .6 .79 2.0 3.51

26.83 3 1 .22 .6.79 2 .5 2.22 88

4c) RbAuCl^

Table 4c 1 )

4c)i) Enthalpy of solution of RbAuCl^ in water (at 298K)

1.1 Purity by 1) Run number RbAuCl^(aq) analysis and date / X 10 ^ mol dm (for Cl")

53-39 1. 4.2.80 4 .5 2

9 9.2 # 53.46 2 . 5 .2.80 4.11

5 1 .1 1 7. 1 1 .2.80 1.11

51.63 10. 1 9.6.79 6.61

100.3#

51.97 1 1. 2 0 .6.79 2 .2 9

51.98 1 2 . 2 0 .6.79 6.34

1.0 kJ mol ^ Mean AH sol^ = +52.3 - 89

4c) ii) Table 4c 2 Enthalpy of solution of RbAuCl^ in hydrochloric acid solutions (at 298K)

Purity by I Run number Activity of (RbAuCl^(a^) analysis and date HClsoln. /xlO (for Cl") mol dm”3

43 .14 3 . 6.2.80 0.080 5 .45

42.62 4. 7.2.80 0.811 4 .7 1

9 9.2 #

4 1 .5 4 5 . 8.2.80 2.022 6 .1 5

33.83 6. 8.2.80 12.55 5.20

39.76 8. 12.2.80 3.948 6.26

41.13 9. 12 .2.80 2.913 7 .65 90

4d) KAuBr/^

Table 4d 1) 4d i) Enthalpy of solution of KAuBr^^ in water (at 298K)

Purity by Run number (KAuBr2^(aq) ) Analysis and date /x 10”3 mol.dm"3 (for Br )

35.27 1. 11.1.80 2.97

9 9.6# 34.77 2, 14.1.80 6 .35

35.94 7. 2 1 .1.80 4.01

34.23 8. 2 3 .1.80 4.42

100.4% 36.61 9. 2 3 .1.80 3 .04

34.19 1 0 . 2 7 .1.80 4 .9 1

35.29 16. 3.2.80 4 .1 5

-1 = + 35.19 - 0.82 kj mol Mean AH sol 91

4d) ii). ■ Table 4d 2) Enthalpy of solution of KAuBr^ in hydrobromic acid solutions (at 298K).

Purity by L) Run number Activity of (KAuBr^(aq analysis and date HBr soln. /X 10 ^ moh (for Br ) mol dm dm’3

+ 33.94 3 . 1 5 .1.80 0.043 4.42

9 9.6# + 31.68 4. 1 6.1.80 0.467 4 .30

+ 29.21 5 . 1 6.1.80 1.052 5.92

+ 24.23 6. 18.1.80 1.550 4.24

1 00.4# + 26.68 11. 28.1.60 2.905 4.64 (molarity) 92

4d) Table 4d. 3)

Enthalpy of solution of KAuBr^ in NaClO^ solutions (at 298K)

Purity by ' Run number Activityof (KAuBr^ta# analysis and date iaClO^ soln. /x 10 3 -3 (for Br ) Dol. dm”^ mol dm ^

29.32 12.29,1 .8 0 1.156 4.66

27.30 1 3 .2 9.1.80 2.024 3 .4 4 100.4%

23.32 14.30.1.80 5.101 3.80

22.22 15.3 1.1.80 3.406 3 .01 93

4e). RbAuBr^

4e) i) Table 4e I)

Enthaloy of solution of RbAuBr^^ in water (at 298K)

1 Purity by + mol" *■) Run number (RbAuBr^(aq))

Analysis and date / X 10 3 0OX dm 3 (For Br”)

48.68 5 . 18.2.8 0 7 .9 8

50.78 3 . 1 7.2.80 1 .7 6

100. s i o 48.84 4. 1 7.2.80 4 .6 9

51.41 2. 16.2.80 2.28

46.61 1 . 15.2.80 6 .2 6

100.1% 50.22 1 2 . 2 7 .2.80 5.1 9

48.41 13. 2 .3.80 8.66

-1 MeanAHg^^ = + 49-3 “ 1*5 mol 94

4e)ii)

Table 4e 2 )

Enthalpy of solution of RbAuBr^^ in hydrobromic acid

solutions (at 298K)

Purity by + mo]J') Run number Activityof (RbAuBr^(aq)] Analysis and date HBr soln. /x 10"3 (for Br ) mol dm"3 mol dm 3

44.94 7. 2 2 .2.80 0.467 4.66

40.86 8. 22.2.80 1.029 3.34

100.5#

4 7.6 5 6. 21.2.80 0.048 4.04

39.82 9. 25 .2.80 0.738 3.4 4

100.1 % 43.60 1 1 . 2 7 .2.80 0.738 5.00

46.75 10. 26.2.80 0.226 4.80

(See Figs. 4e 1) to 4e 8), and for a discussion of the error bars in these figures see Appendix IV ). 95

Fig. 4el). Graph of of KAuCl^^

V the Molarity of the Resulting Solution.

h40-5

- 4 0 0 0

-39 5

G G -690 0

- 3 8 5 Ô

- 3 8 0

“375 Q

r370

-365

Concentration of KAuci^^Caq) (io“ ^ mol dm,-3 -^)

40 60 80 1&0” 120 14Ô 16^0 l8^ 96

Fig. 4e2). Graph of for KAuBr^(s)-*KAuBr^(aq.)

V the Molarity of the resulting solution.

+AHg^^(kJ mol"l)

-39

^38

-37 Ô

-36 6

0 Ô Ô

y 6 r34

-33

-32

-31

Concentration of KAuBr^ soln. (xlO"^mol dm"^)-3

30. . 1. 0-0 10 2 0 3 0 4 0 5 0 6-0 7 0 97

Fig. 4e3). Graph of of RbAuGl^ V the molarity of the resulting solution.

-54 Q

-53

-52 0 0

-51 Ô

-50

-49

-48

-47

-46

_ 3 Concentration of RbAuCl^ soln.(xlO”^ AS _ 1______, _ _L ____ I ______L L moil dm”-^ 10 20 3*0 4 0 S'O 6 0 7 0 98

Fig. 4e4). Graph of of RbAuBj^(s) V Molarity of Resulting Solution,

(kJ mol"^ of Au)

-53

r52

-51

0 hSO

-49 0 0 k 8

-47

-46

Concentration of RbAuBr^ (lO'^mol3 dm"^) - 3 45 L L 20 4 0 ô'o 8 0 n Ô 12 0 140 ‘ 99

Fig. 4e5). Graph of KAuCl,^ Results (AHsol)

V Activity of HCl or KNO^ Used as Solvent (See notes on page 313)-

+ Hsol (kJ mol” of Au)

-36

o HCl L34 a K N O h32

-30

-28

-26

-24

Activity of HCl or KNO. I'"°‘ 4 0 6 0 100

Fie. 4e6). Graph of AH^ ^ of RbAuCl^ y Activity of HGl used as Solvent.

-45 (When activity of HC1=0,

AHgoi=+52.3 kj mol"^.)

-40

-37

-36 -35 h33

-32

-30 -29

-28

-27 Activity of HCl (mol dm ^).

10-0 12 0 101

Fig. 4e7). Graph of KAuBr,j SPl— T Activity of NaClOij or HBr Solution Used. (See notes on page 313).

-32 o H Br

G NaClO

-30

-29

1-28

-27

-26

-2S

Activity of MaClO^ or HBr (mol dm"^) 102

Fig. 4e8). Graph of of RbAuBr

V Activity of HBr Used.

(kJmol" )

H50

-49

Activity of HBr (mol dm ) 0-8 103

DISCUSSION OF RESULTS

4f). The metal tetrahaloaurates

4g). Raman spectra:- i). AuCl^ 1-

In the solid state, the AuCl^ ion is square planar and therefore belongs to the symmetry point group. The ion possesses three Raman-active fundamentals,

O^(a^g), ^2^^1g^’ ^^4 (b2 g); three infra-red fundamentals, '^3•'^6*^7’ one inactive mode, ^(Table 4g 1)).

v)^ and 0^ are both pure stretching vibrations while a pure in-plane bending mode, occurs at much lower wavenumber. Table 4g 1;. Vibrational spectra of AuCl^

AuCl^ KAuCl, RbAuCl,

Raman i.r. (cm ) Raman spectrum (cm (lit,) (This study)

0:i 348 351 350

325 327 327

142

0, 172 174 180

0. 361

166 104

Fig. 4gl). Raman Spectrum of the AuCl^ Ion. (Square Planar lon-D^^^ Symmetry).

100 1 Lit. Spectrum (cm ^ 348

142

361

A u C

O o m m CM C sl OJ

WAVENUMBER (cm"^) 105

ii) AuBr^

The AuBr^ ion is again a square planar ion in the solid and in solution and so belongs to the symmetry point group, with three Raman active fundamentals

(^1# 4+) '

Table 4g 2) Vibrational spectra of AuBr^ .

AuBr, KAuBr, RbAuBr,

Raman i.r. / (cm “1 \ ) Raman spectrum (cm~^) (lit.) (This study)

214 _ 211 212

O 2 196 195 195

101

102 100 102

^6 249 110 ^7 106

Raman Spectrum of the AuBrlj Ion. (Square-Planar ion, Symmetry.)

100 Lit. Spectrum(Bosworth & Clark)' (cm~ ') I_

---

s A u B r

uBr,

o o o O o oo CS( O ry oo oo

WAVENUMBER (cra“^) 107

Fig. ) . Raman Spectrum of CsBr/AuBr^ (aq ) Product (Shown by Halide Analysis to be Cs^AupBr£).

■n

CZ> <=> O cz> O s / m m s s

WAVENUMBER(cm"^) 108

4h). Calorimetric résultat-

As can be seen, there is no simple dependence of the measured heat of solution with the molarity of the resulting tetrahaloaurate solution (Figs. 4e 1) to 4e 4))

The graph of heat of solution plotted against the activity of acid (either HCl or HBr) used as solvent is a straight line plot with a sharp decrease in the endothermie heat of solution when passing from pure water to the acid solvent. It was thought that this initial drop was due to the inhibition of the hydroxide/halide ion exchange equilibria of the aqueous tetrahaloaurate anion. From the equilibrium constant — 7 ? — ? — of 7 X 10 ^ mol 1 for AuCl^ (aq), in pure water at

25 °C, 19^ of the anions exchange one chloride for a hydroxide ion, whereas, in 0.05 M HCl, only 0.028# of the anions exchange. Therefore, the above supposition that the exchange equilibria have a significant effect on the measured heat of solution of the tetrachloroaurates, seems reasonable.

The further linear decrease of the heat of solution with the activity of acid used could have been due to association of chloride ions from solution with tetrachloroaurate anions. However, Raman spectra of sodium tetrachloroaurate in various strengths of hydrochloric acid solutions (and even in conc. hydrochloric acid) showed no disparities with the literature spectrum. 109

The same result was obtained with tetrabromoaurate in

HBr(aq). (Figs. j^^l and 4^2. )•

It was therefore assumed that the decrease in heat of solution was due to a simple activity effect of the hydrochloric acid solution, the gold salt becoming less soluble with increase of the activity of the acid used. This assumption was tested by measuring the heat of-solution of potassium tetrachloroaurate in a series of potassium nitrate solutions of differing molarities .. On plotting the measured heats of solution against the activity of nitrate used, a straight line was again obtained. However, there was no initial drop in the value of the heat on passing from pure water to potassium nitrate solution. This, presumably, was due to no chloride or hydrogen ions being present to inhibit the exchange equilibria of the tetrachloroaurate anion.

Therefore, by extrapolating the linear section of the heat of solution V acid activity graph, to zero concentration of acid, the standard heat of solution of potassium tetrachloroaurate in water could be estimated. A similar estimation was made for the other tetrahaloaurates studied.

The final values for these standard heats of solution, for the process MAuXj^(s) + nH20(l) = M**’(aq) + AuX^ (aq) + n H20(l) 110

Fig. 4hl). Haman Spectra of NaAuCI^^ in H qG. and conc. HGl.

100

in conc

in H-0

o o CN g s m m m m M _ § ,

WAVtNUivlBciR (cm ^). Ill

Fig. 4h2). Raman Spectra of RbAuBr,^ in H^O and conc. HBr.

100

•1M Nq OI-

— in 1 HEr

WAVnNUMBER (cm”^). 112

are as follows*- + (kJ mol~^)

KAuCl^ + 3 5.49 - 0.2 6 RbAuCl^ + 43.2 - 1.0 KAiiBr^j, + 34.04 - 0.82

' RbAuBrj^ + 48.2 t 1 .5

From these values, and the known heats of formation of the aqueous ions, the heats of formation of the anhydrous gold salts were calculated. Using the Yatsimirskii procedure and the Kapustinskii equation, a "thermochemical radius" for the ions AuCl^ and AuBr^i^ was calculated. These were then used in the Kapustinskii equation to calculate the lattice energies of the tetrahaloaurates studied. An accurate calculation of the lattice energies at 298.2K from the values at 0 K requires a knowledge of the change of the specific heat capacities of the salts with temperature (between 0 - 298.2K). Assuming the calculated values at 0 K to almost equal the corresponding lattice energies at 298.2K, these could be inserted into a thermochemical cycle to calculate the standard heat of formation of the gaseous anion. This procedure was carried out for KAuClj^, RbAuCl^; KAuBr/^ and RbAuBr^. An average value of this standard heat of formation was calculated from the two results obtained for each tetrahaloaurate anion.

Similarly, the lattice energy of any haloaurate comoound for which the ionic radius of the 113

cation is also known, can be calculated from the Kapustinskii equation (e.g. CsAuX^^ ; X = Br, or Cl) The standard heat of formation of the compound can then be calculated, either by the Yatsimirskii method, or by means of a thermochemical cycle involving the heat of formation of the relevant gaseous tetrahaloaurate anion.

4j). Calculations -

From the measured heats of solution - n H2 O (1) + KAuCl^(s) = KAuCl^(aq)

AHgl'j^CKAuCXi^Cs)) = +35.49 kjmol"^ n H2 O (1) + RbAuCl^(s) = RbAuCl^(aq) AHg|j^(RbAuCl4(s))- +43.20 kJ mol'l and from the literature values (NBS Circular 500, 1952)s-

A H f (K+ (g)) + 514.63 kj mol'l

ù . y ^ (Rb+(g)) + 4 9 1.2 0 kj mol"^

A K | (K+. (aq)) - 251.21 kj mol'l

A h |" (Rb+(aq)) - 248.53 kj mol'l

= ionic radius of the K"*" ion = 0.133 nm

= thermochemical radius(Greenwood,I9 68)

= ionic radius of the Rb^ion = 0.14? nm

= thermochemical radius(Greenwood,1968)

(AUCI4 (aq)) = - 32 2 .2 kJ mol'l (AuBr^ (aq)) = - 191.7 kJ mol"^

(MAuCli^(s)) nHgOd) + MAuCIk (s ) MAuCl^(aq)

AHf^(MAuCli^(s) )\ y^^(M"^(aq) )+AH|(AuCl^(aq) )

M(s) + Au(s) + 2 Cl-Xg) 114

(KAuClj^(s)) =

= (K+(aq)) + AH^ (AuCl^faq))- AHg^j^(KAuClj^(s) )

= -251.21 - 322.17 - 3 5.49 = - 608.87 kj mol'l

Ah| 2 = AH^ (RbAuCl^(s))

= AH^ (Rb+(aq) + AH^ (AuCi;^(aq)) - AHg^3^{RbAuClj^,(s J )

= - 248.53 - 322.17 - 4 3 .2 0 = - 613.90 kj mol'l Using the Yatsimirskii. method -

Ui - 82 = AH'^ (Mi+(g)) - A H ^ (Mgfg)) - AK^(M^X(s))+AH^(M2X(s)) where = Rb^ and X = AuCl^

- Ug = + 514.63 - 491.20 + 608.87 - 613.90 = + 18.4 kj môi~^ From the quartic equation derived from the Kapustinskii equation (Appendix III) - r^ + 2r^(m^+m2) +r^ (m^ + + 4m^m2 + c(m^ - ^2 ))

+r (2 m^m2 + c(m^ - m^ ) - 0.069c (m^^ - m2 ))

+ (m^mg + c (m^m2 - m^m^) + 0.0345 c (m^ - m^)) = 0. of the form r4 + 2Ar^ + Br^ + Cr + D = 0 : - c = a constant = 242.8 = 242.8 = 13.20 U1-U2 1874

“ 1 = ^K+ = 0 -133M 1. mg = rRb+ = 0.147 nm. r = r^_ =

Inserting these values into the equation we obtain I-

+ 0 .56r^ - 6.729800 x 10"^r^ - 2.804424 x lO'^r

- 1.445615 X 10"3 = 0

This quartic can be solved on a Hewlett-Packard HP 65 programmable calculator (See Dr. S. Peake's thesis, 1976) 115

Four roots are obtained; r = 3*109960 x 10“^

r = - 6.592562 X 10"2

r = 8 + it) 8= -2.625332 X 10~1

) t* 3 .9751 # X 10~2 r « s - it )

The only positive real root obtained, r ■ 0.3 1 1 nm., is taken to be the thermochemical radius of the AuCl^ ion.

.From -thft. Jtapygtir.skiL,, Uo = Lattice energy of MX(s) at OK = 242.8 /1 - 0.0345 \

+rm+)l + V V

KAuCl^-

»'m+ = = 0 .133nm. = O O l l m .

Uo(KAuCl.(s; ) « 242.8______(1 - 0.0T45 I ------— .10.311 + 0 .133) I 10.311 + 0 .133} -1 + 504x .36-Kj iBfil RbAuCl^ -

= fRb+ = 0.l47na r^- = r^^ci^- '

Oo(RbAuCK(3)) = 242.8 ■■ ■ (1 - 0.0345 ) r — r- . (O.3II + 0.147) ( (O.3 II + 0.147)) ■= + 490,20 kj niQl'^.. Assuming Uo(MAuCl^(s)) 3^ U^^gtMAuCl^Cs))

From the thermochemical cycle 1- 116

M*(g) AuCl^ (g) UggglMAuCl^ls))

+ 2 RT AH|'(M‘^(g)) + AH^(AuCi;j;(g))

MAuCl^ s)

AH|'(MAu C1^(8))

M(s) + Au(s) + 2012(g) where, 2RT ” Work done in expanding one mole of M*(g) and one mole of AuCl^(g) to zero pressure.

^hen = K*:-

AH^(AuCi;;;(g)) = AH|T(KAu C1^(8)) + U2|g(KAuCl^(s))

+ 2RT -AH^(K'^(g))

= -608.87 + 504.36 - 514.63+ (2x 8.314 x 298.2) ( 1 0 0 0 J

= -614.18 kj mol'l

When M'*' » «2 » Rb~*~t-

AH^(AuClj^(g)) = AH^(RbAuCl;^(s)) + U2^g(RbAuCl^(s))

+ 2 RT - AHj(Rb'^(g))

= -6I3 .9 0 + 4 90.20 - 491.20 +(2z 8.314 X 298.2) ( 1000 )

•= -609.94 kJ mol'l

Average AH^(AuCir(g)) ■= - 612.06=^ - 612 kj mol"^

From the literature valuesi- r + = Ionic radius of Cs^ * 0.168nm. = thermochemical cs radius.

(CB+(g)) = + 4 59.93 kj mol"l(NBS Circular 500,1952)

And from the Kapustinskii equatlon_«-

Uo (CsAu CU(8)) = 242.8 ■ Il - iU23l5______) ------(0.168 + 0 .3IÏ) (0.168 + 0 .311)) = 242.8 (1- 9.0345) = ■+ 479.38. kpjmail^ 07479 ( 0.479 ) 117

From the thermochemical cycle -

AH^(CsAuCli^(s))= AK^(AuCi;^(g))+ Art|'(Cs‘^(g) )-U^g(CsAuCl^(s) ) - 2 RT = -612.07 + 459.93 - 4 70.38 - 4 .9 5 3 ° 627,47 kJ mol'l

Using the literature values already listed, the same calculations may be carried out for the potassium and rubidium tetrabromoaurate.

R.M. de Jonge (1976) has used a computer . program to derive the Madelung energy, van der Waals energy term, and zero-point energy of some tetrahalogenoraetallates (II). The pseudo-lattice energies at 0 K of several alkali palladium and platinum chlorides and bromides were then evaluated (AH^^). The heats of complexation (AH?om) were calculated from the relevant literature data. ^ P - AH com p_ 2A (g) + MT^(g) + 4x”(g) -2A (g) + MX^ (g)

AHp^jjj=2 AHp(A'^(g))+AH^(M^'^(g))+ 4 AHp(X"(g)) -AHp(AgMX^^(8)) -AH ^

The values of the heats of hydration of the ions were also calculated. A H^ MX^"(g) ------(aq).

^«h^dr - AHp(M^+(g)) - 4AHp(X-(g)) + A H ^ where A H ^ is equal to the heat of formation of the aqueous ion.

An estimation of ^H^^^ of the corresponding 118

gold complexes (AuCl^ and AuBrj^) was attempted.

A H ^ d r ^218 estimated first. According to the Born charging equation the heats of hydration are proportional to the square of the charge and inversely proportional to the "effective" radius of the ion (George & McClure,

1959). Thus A of both gold complexes were considered to be approximately one quarter of the iso-electronic platinum complexes (both having the same size). The third ionization potential of gold was estimated at

28.5 V, so giving the resulting calculated heats of complexation only a relative meaning.

The estimated hydration energies were not considered to be correct, but in comparing both heats of complexation they followed the expected order AuCl^ AuBr^, the difference being equal to

7 0.6 - 8.4 kJ mole”^. Expressed as a percental difference, this was approximately equal to the percental difference between the corresponding platinum complexes. The heats of formation of the gaseous anions, AuCl^ and AuBr^ were calculated from these values.

AH^(AuXj^(g) ) = AH^(Au‘*'(g) ) + 4 A H p ( X ”(g)) - and were compared with results from this study. Unfortunately, the lattice energies of alkali tetrahaloaurates are not reported by de Jonge. Therefore, the quantities and were calculated from the potassium tetrahaloaurate heats of formation, and lattice energies, reported here.

These can be seen in Table 4 j. 2) 119

It will be noted that the AuCl^ and AuBr^ values reported here (Table 4 j 2)),are much closer than those of de Jonge (Table 4 j 1)). Indeed, in the case o f A H ^ ^ and ’ the trend between the chloride and bromide is reversed, the heat of hydration and heat of complexation of the tetrabromoaurate seeming higher than the tetrachloroaurate. However, if we calculate the errors involved in the A h ^com calculation, from experimental results the AuCl^ result has an associated error of - 8 .1 kj mol ^ and the AuBr^^ result has an error of - 8 .6 kj mol The two com results are not significantly different and the reverse in trend from that of de Jonge, may be due to the inaccuracies inherent in the Kapustinskii method of calculating lattice energies (See Appendix III).

The major difference betweenAH^^^

(this work) and ^ ^hydr Jonge), appears to be due to the inequality of the standard heats of formation of the aqueous anions as taken in this work,from standard thermodynamic tables and as recorded by De Jonge. This inequality results from the expression used by de Jonge to calculate A H ^ AHf(MX^(aq))

M(s) + 2 X2 (6)+ ?2 H2 (g) ----- H+(aq) + MX^^ (aq)

= 6H»(MXj^(aq)) _ (H+(aq)) -1 AH^(H^(aq)) was taken to have a value of + 434.8 kJ mol

(L.L.Quill, 1950). Thevalues calculated in this aq work are equal to the standard heat of formation of the 120

Table 4i 1)

(numbers between brackets are relative values)-R.M.de Jonge

- (1967) AuCl^ AuBr^ (kJ mol“^)

A -756.21 -625.7

- ) -5980.7 -5980.7

-4AH^(X'(g) ) +983.1 +9 34.6

corn +(5571.5) +(5500.9) ) > relative (-182.2) ^ » h V (-171.0 ) ) values AHpAuX^fg)) -573.9 -4 5 4 .8

Table 4i 2)

A H - , r values for AuCl^ and AuBr^ - This work.

AuCl^ AuBr^ (kJ mol'l)

^»aq -322.17 -191.7 - AK|r (M^+fg)) -6085.0 -6085.0

- 4 A h|' (X“(g)l +984.3 +935.8

^ r o m +5719.7 +5739.6 ^ C y d r + 296.8 + 3 98.7 . A h"^ (AuX^fg)) -612.1 -584.7 121

4 k) SUMMARY OF TETRAHALOAURATE RESULTS

HEATS OF FORMATION (kJ mol~^) -

Calçd Expt^l Caici KAuCl^(s) -608.8 - 0.3 KAuBr;^(s) -486.1-1.3

RbAuCl^fs) -613.9 - 1.0 RbAuBr^ls) -497-5 + 1.8

CsAuCl^(s) -627 .5- 3 .0 CsAuBr^(s) -517.2 +4 .0

THERMOCHEMICAL RADII(nml IONIC RADII (nm)

AuCl 0.311 0.409 (Appendix SI) AuBr, 0.422 0 .4 5 2

LATTICE ENERGIES (kj mol~^). AT 0 K . -

KAuCln +504.4 - 1.1 KAuBr 4 +410.3-2.8 RbAuCl, +4 9 0 .2 - 1.0 RbAuBr, +400.8-2.6

CsAuCli +4 7 0 .4 - 2 .7 CsAuBr^ +3 8 7.5-2 .4

HEATS OF FORMATION OF THE GASEOUS ANIONS Tkj mol -1 )

+ AuCl^ (g) - 612.1 1 1 .3

AuBr^ (g) - 584.7 - 3 .2 122

aqueous tetrahaloaurate ion in a hypothetically ideal

solution of unit molality (N.B.S.Tech - Note 27 O-3 , I968). This involves the usual convention that the values of

A AG^, AS ^ a n d for (aq std. state, molality = 1 ) are zero.

If we apply.this assumption to de Jonge'3 figures . this leads to calculated values forAH^(AuClZ) aq 4" and AH^(AuBr^) of - 321.41 kj mol”^ aind - I9O.9O kj mol*"^ in good agreement with the values used in this study. Revised values of for the tetrahaloaurates are

+252.49 kj mol”^ and + 263.90 kJ mol'^ for AuCl^ and AuBr^ respectively. From the values of this study, theAHj^^^ of the tetrabromoaurate is also more endothermie than that of the tetrachloroaurate, but the difference is much greater (102 kJ mol"^).

The tetraalkvlammonium dibrorooaurates. -

4.1) Raman spectra : -

The Au%2 ion is linear and is therefore assigned to the symmetry group Only three bands can be observed, (5g*) being Raman-active, and and 0^ (&u^) infra-red active. These stringent selection rules are not expected to be obeyed in the solid state. The and 0^ bands have been reported as not being significantly dependent on the counter-ion. The ^ 2 fundamental (TTy) is split into a doublet in the infra-red spectrum, with the lower-frequency component being more intense. In this study only the 0^ of Et^NAuBr2 123

Table 41 1) -

The vibrational spectra of the tetraalkvlammonium

Braunstein and Clark (cm"^) This study (cm”^)

Et^N AuBr^ Et^NAuBr^ Me^N AuBr“

Saman Infra-red Raman Infra-red Ra^an

252 vs 252

208vs 210 207

0. ca 9 5 m ,b r 83s,br 124

FÎR. 4ll). Raman and Infra-red Spectra of AuBr%. Infra-red Spectrum. (Linear lon-IL, Symmetry). CÛ fl Lit. Spectrum(Braunstein & Clark). m Raman(cm ) I.R.

252 vs 00 vs

ca S5 m,br

o Csl

WAVENUMBER (cm"^). 125

Pig. 412). Raman Spectrum of AuBr%.

100

o g S o m OJ CNJ §

WAVENUMB£R (cm"^). 126

could be detected in the far-infrared region (210 -4 50cm , using a nujol mull between Csl plates. (Table 4l 1 ).

2). Calorimetric resultst-

As in the case of the tetrahaloaurates, on plotting the measured heat of reaction against the weight of gold salt taken, no dependence between these two quantities can be seen. Similarly, there is no trend of. heat of reaction with the molarity of ferrous sulphate used.

The mean of the results shown give the heat of reaction ( kj mol”^ of Au (I)). 3w\uXg (s) + 3FeS0j^(aq) = 3 Au(0)(s)| +Fe2(S0^)2(aq)+ FeBi^ (aq)+3M''’X~(aq)

= + 16.36 + 0 .1 6 kj mol"^

= Et^N* AH^'^ = - 6,26 - 0.23 kj mol"^

The procedure for calculating the heats of formation of the solid dihaloaurates, the thermochemical radius of the anion and the lattice energies of.the salts studied was similar to that used in treating the tetrahaloaurate results. Again, the heat of formation of the gaseous dibroraoaurate anion was estimated and used to calculate the lattice energy, and heat of formation of a dibromoaurate of a cation (in this case K'*’) of known ionic radius. KAuBr^ has not been synthesised or isolated. 127

4 m). Enthalpy of reaction of Me^NAuBr2 with FeSO^ -

3Me^NAuBr2 (s) + ]FeSO^(aq) = 3Au(0)(s) ) + Fe2 (S0^)^(aq) + FeBr^(aq) + 3Me^NBr(aq).

Table 4m 1)■

>urity by analysis Run number Me^NAuBr2 (FeSC^aq) for Br ) (kJmol'^of Au) and date sample(g) (mol da”^j

+ 16.62 2 1 .5 .80 0.0488g 0.0502

+ 16.31 2 2 .5.80 0 .0132 g 0.0502

9 9.9* + 16.10 11.6.80 0 .0622 g 0.0509

+ 16.10 11.6.80 0 .0606g 0.0525

+ 16.43 12.6.80 0 .0576g 0.1013

+ 16.54 12.6.80 0.0688g 0.0260

+ 16.46 14.6.80 0.0474g 0.0776

9 9.8% + 16.31 2 2 .7.8 0 0 .0928g 0.0260

Mean = + 16.36 - O.I6 kj mol ^ Au 128

Fig. 4ml). Graph o f o f Me^NAuBr^ w ith Fesb^^ V Weight of Me^NAuBr^ used

+ AH^(kJ mol'l)

-20

-19

-18

-17

-16

-IS

-14

Weight of Me^NAu3r2(g) J3 1 I J I- 1 1 1____ J_____ I______0 0O1 0-02 003 0 04 005 0-0 6 0 07 0 0 8 0 09 0 10 129

Fig. 4m2). Graph of AH ^ o f Me^NAuBr^ with FeSO

V Molarity of FeSOused.

+AHp(kJ mol'l)

-19

-18

-17

-16

-15

-K

_ Q Molarity of FeSO^ used (mol dm"^) 13 0 0 02 5 0050 0 075 0100 130

4n). Enthalpy of reaction of Et^NAuBrg with FeSO^(at 298K)

3 Et^NAuBr2 (s) + 3FeS0^(aq) = 3Au(0)(s)j + Fe^O^)^(aq)

+FeBr^(aq) + 3Et^NBr(aq).

Table 4n 1)

Purity by analysis AH|- Run number Et^NAuBrg (FeSO^(aq) (for Br ) ( kJ mol ^Au ) and date sample (g) (mol dm^)

- 6.26 13.5.80 0.1808 0.0521

99.4# - 5.95 13.5.80 0.2435 0.0521

- 6.06 20.5.80 0.2644 0.0502

' - 5.93 20.5.80 0.1570 0.0502

- 6.45 22.5.80 0.1754 0.1007

- 6.18 22.5.80 0.1925 0.0252

- 6.26 23.5.80 0.0799 0.0760

- 6.93 23.5.80 0.2827 0.0502

100.3% - 6.29 21.7 .80 0.1620 0.0260

Mean = 6.26 - 0.23 kj mol ^Au 131

Fig. 4nl). Graph ofAH^ of Et^NAuBr^ with FeSO,^

V Weight of Et/jNAuBrp Taken.

AH* (kj mol'l of Et^NAuBTg)

— 15'0

-440

-13-0

42 0

41-0

-40 0

-9-0

-60

-7-0 ^

.6.0 ^ ^ ^ ^ ÿ

- 5 0 $

- 4 0

-3-0

--20

h-1-0 Q Weight of Et^NAuBrg (g) & 0 T 0-08“ Ô1Ô“ “Ô i r ^ 1 î T ‘ 016 018 " &20^0-22 024 ' 026 ‘ 028 132

Fig. 4n2). Graph of AH? of Et^NAuBr^ with FeSO^ V Molarity of FeSO,^ Used.

6H^(kJ mol'l)

4 2 0

41 0

-10 0

-90

-80

-70

-60

-5 0

-4-0

'3 0

-20

-10 Molarity of FeSO^ (mol dm'^) 0025 ' 0Ô50 aO^' 01ÔO 133

4 q ) Calculations -

From the measured heats of reaction, and the literature values*-

(Me^N+Caq)) = - 103.34 kJ mol"^ (B. Derahkshan, I98O)

AH ^ (Br"(aq)) = - 121.57 kj mol"^ (NBS Giro 500, I9 5 2 ) and so, AH^(Me^NBr(aq) ) = - 224.91 kj mol ^

^Me^N* = thermochemical radius of Me^N^ ion = 0 .210 nm.

(B. Derahkshan, I98O)

'*Et^N'*’ ~ thermochemical radius of Et^N^ ion = 0 .160nm.

(B. Derahkshan, I98O) Ah'!" (FegfSO^Ijtaq)) = - 2734-7 kj mol“^

(in 3000 HgO)

AH^ (FeBr^(aq)) = - 372.4 kj mol'l (Tech Note 270-4, 1969) (in 40,000 HgO)

A h'J (FeSO^(aq)) = - 992.0 kj mol”^

(in 200 HgO)

The following thermochemical cycle may be drawn*- A h 3FeS0i^(aq) + 3Me^NAuBr3(s) . _ 3Au(s) + Fe2(S0^)^(aq)

3 (FeS0 4(*q))

3 A H | ( A u (s ))

+3 AH|'(Me^NAuBr2(s)) +AH^(Fe2(S0^)^(aq)) +AH|(FeBr^(aq))

+3 AH^(Me^NBr(aq))

3 Fe(s) + 3S(s) + 602 (g) + 12 C(s) + 18H2(g) + + 3Au(s) + JBrvXg) 134

This gives,

3Ah|:(M8i^NAuBr2(s))= 3Ah| ( Au(s) ) +AH^(Fe2(SO^)^(aq) ) + AH^(F*Br^(aq)) + 3AH|(Mej^NBr(aq) )

-AhJ - 3AH^ (FeSO^(aq))

- 3 x 0 - 2734.7 - 3 72.4 - 3 I 2 24.91 - 16 .3 6 + 3 X 9 92.0

.*.3 %AH^(Me^NAuBr2 (a)) - - 822.19 kJmol"^

AK^(Me^NAuBr2 (s)) ° - 274.06 kJmol"^

Taking.the following literature values,

AH^(Et^N'^(aq)) - - 248.00 kjmol"^ (B.Derahkshan.,I98O)

AH^(Br"(aq)) - - 121.55 kJmol"^ (NBS Clrc 500,1952)

then,

AK^(Et^NBr(aq))“ - 369-55 kJmol”^ and constructing

a similar cycle for the Eti^tiAuBr^ reaction#- 3 AH^(Eti^NAuBr2(s))-3AH^(Au(s))+AH|rPe2(S0^)^(aq))

+AH^(FeBr^(aq))

+ 3^H^(Et^NBr(aq))-AMj - 3AH|((FeS0^(aq) )

= 3 x 0 - 2734.7 - 3 72.4 - 3 X 36 9.55 + 6 .2 6 + 3 X 992.0

» - 1233.49 kJmol'l

AH^(Et^NAuBr2 (s) ) = - 411.-16 kJmol~^

U i- U2=AK^Mj^'*’(g ))-A H |'(M 2 ‘^(g))-A K |:{M ^X (s)) ‘

+ AH|(M2X( s ))

From the literature values#-

A H ^ ( M e X ( g ) ) = + 580 kjmol-^ (B.Derahkshan.I98O) and, AK^(Et^N'^(g)) = + 463 kJ mol"^

«2 = Me^N+, = Et^N* and X = AuBr^

Ui - U^= 463 - 580 + 411.16 - 2 7 4.0 6 = + 20.10kJmol~^

giving £ = 242.8 = g42.8 = 12.08.in the quartic equation. (Uj-Ug) 20.10 135

This leads to

+ 2 X 0.3?r3 - 0 . 3 9 9 4 - 0.156?895r - 0.0114449 which has the real positive root

r = 0 .6 5 2 nn = the thernochemical radius of the

AuBr- ion

Ppom the Kapustinekii. Born-Maver equation -

Ug - 242.8 (1 - 0.0345 ) (in kj mol"^) ('m+ +"x-)) i). Me^WAuBr^-

01 (Me^NAuBr-fs)) = 242.8 (0 .210+0 .652)1 (0 .210+0 .652 )) = + 270.40 kjmol-1 ii). Et^NAuBrg -

U„(Etj.NAuBrp(s)) = 242.8 _ _ U - 0.0345 .. ) ° ^ (0 .160+0 .652 ) ( (0 .160+0 .652 )) -1 = + 286.31 kjmol

Assuming U^(MAuBr2 (s) )^U^g(MAuBr2 (s) ) and from the thermochemical cycles#-

M*(g) + AuBr^tg)

U^g(MAuBr2(s) )

+ 2 RT AH^(M'*’(g)) MAuBrpCs) +AH^Au3r2(g))

AH|'(MAuBr2(s))

M(s) + Au(s) + Br^tg) 136

i) When M* =

AH^^AuBrgtg)) = AH^(Et^NAuBr2(s)) + D2^|'(Et;^NAuBr2(s) )+ 2RT - AH|(Et^N‘^(g))

= -411.16 + 286.31 + (2 X 8.314 x 298.2) - 463 ( 1000 )

•= -582.89 kj mol-1

ii) When = Me^N* -

AH^CAuBrjtg)) » AHj(M8;^hAuBr2(s)) + U2^(Me^NAuBr2(8))+ 2RT - AH|(Me^N‘^(g))

-274.06 + 270.40 + (2 x 6.314.x 298.2) - 580 ' 1000 ^ = -578.70 kj mol'l

From these values.

Mean AH^ÇAuBr^lg) ) = ~ 560-60 5^1 kj mol ^

From the literature values

» Ionic radius of ion = 0,133

andAH%(K*(g)) = +514.63 kjmol"^ (NBS Circular 5OO, 1952).

and using the Kaoustinskii equation -

U„(KAuBr,(s) ) = 242.8_____ (1 - 0.0345 ) ° (0 .133+0 .652 )( (0 .133+0 .652 )

= +295.71^+ 296 kJaol~^

From the Bom-Haher cycle -

AH^(KAuBr2(s)) = AH^(AuBr2(g)) + AH^(K+(g)) - U^^g(KAuBr2(s)) - 2 RT

= -580.80 + 514.63 - 295-71 - (2 x 8.314 x 298.2) ( 1000 ) = -366.84 kj mol ^ 137

4p). SUMMARY OF

HEATS OF FORMATION (kj.mpl~^) -

Calc? Me/^N'^^AuBr^Cs) -2 7 4.1 - 0 .1 Et^N'*^AuBr2(s) -411.2 Î 0.1

K^AuBrg(s) -367 - 10

IONIC RADIUS (nm)

AuBr. 0 .652 0 .43 0 (See Appendix VI)

LATTICE ENERGIES (kj mol'^) -

Mej^NAuBr2 + 2 70.4 - 2 .1

Etj^NAuBr2 + 286.3 - 2.4

KAuSro + 295-7 - 2 .5

GASEOUS ANION (kJ mol'^)

AuBr^Cg) - 581 ” 10 138

The te tra a l^ Ia m iQ n luni-dihaloaurataa -

4q) paman spectra i-

The Raman spectrum of the tetraethylammonium dichloroaurate product can be seen in Fig. 4q 1). This can be compared with the spectrum reported by Braunstein and Clark.

The spectrum is poor due to burning of the sample, the presence of some elemental gold giving the product a slight brown discolouration. A cold cell was used to prevent burning, with little improvement of the spectrum. The linear AuCl^ anion belongs to the symmetry point group Dooh, and so only one of the three observed vibrational modes should be Raman active. (For a fuller discussion of the AuX^ spectrum, see Etji^NA\iBr2 ).

However, in the solid state, the selection rules are not stringently obeyed, as strong lattice forces are present in the tetraethylammonium salt. AuCl^ is not a very good scatterer and gives rise to only medium Raman intensities as compared with the AuBr^ and Au%2 ions.

Despite only partial resolution of the

Raman spectrum, the agreement of this with Braunstein and

Clark and the halide analysis confirms the product to be

Et;^NAuCl2.

Fig. 4q 2). shows the Raman spectrum of the triethylamraoniura tetrabromoaurate product. Two bands are 139

Fig. 4ql). Raman Spectrum of Et^NAuCl^ Product.

--5 0 5^ ,--

E ^ w 00 m m un m

s o o s o o 0 m m rn CVJ § s 8

WAVENUKBER(cm”^) 140

Fig. 4q2). Raman Spectrum of £t-NHAu3r,^ (3 )

100

O) <0 o o Csl s s S s m m R WAVJHU.4B3.^ {cn ") 141

.1) Raman spectrum of Etji^NAuCl^Cs) (cmT^)

Brauniatelû and. Giark This study

353 w 355 w

( 334 333 sh vw

«■*■) ( 329 328 w

( 324

119 02(^u) j 116 111 142

observed at 213cm~^ and I96cm”^, corresponding to the

Raman-active fundamentals g ) and (b^g), respectively

(See Discussion of the AuCl^ and AuBr^ Raman spectra).

The spectrum was not followed below 160 cm"^ sind so the

^ 4 ( b2 g) vibration at 102 cm"^ was not observed.

This correspondence with the literature spectrum and the halide analysis result shows the solid to be pure triethylammoniurn tetrabromoaurate.

It can be seen from Fig.4q 3) that the

Raman spectrum of the reduction product is not that of a dibromoaurate (a very strong Raman band at approximately

208 cm"^); the halide analysis result and the spectrum indicate the isolated solid to be triethylammonium bromide. Thus, the final product does not exhibit the

Raman spectrum (Fig. 4q 4) of a diiodoaurate (a very strong band at I56 cm"^ corresponding to the fundamental

, but a mixture of the triethylammonium bromide and iodide spectra. The composition of the product is confirmed by halide analysis. 14]

Fig. 4q3). Raman S,jectrum of Kt^NHAuBr^ ,

100

CN CO LT

30_

1/5

C75 ro V

o o CD CD

WAVFNU.MBFR (cm 144

Fig. 4q4). Raman Spectrum of the Et^NHAuIo Product (solid)

o O <=> S CD Csl 0 s m L cs CSI CSI WAVENUMBER (cm"^) 1^5

Fie. 4rl). Raman Spectrum of Et^NAuI^ Product

100

o o o o o o oo o oo NO -J- NO o> m m m CnJ _ QnJ| OsJ WAVENUMBER (cm” -^) 146

Pie. 4r2). Raman Spectrum of Mej.NAuIo Product.

100

o CD o o o o CD C s l vO ^ oo m m Csl ÇNJ Csl WAVENUMBER ( cm"-^) 147

Calorimetric Results. 4s). Enthalpy of Reaction of Et^NAuI^ in SO^ Solutions (at 298K).- 2 Et^NAuIgfaq) + SOgfaq) = 2Et^NI(aq) + 2Au(s) + 2HI(aq)

+ 2 H2 O ( 1 ) + H-iSO^faq) Table 4s 1)

Purity by analysis a h J Run numbei • Molarity of jEt^NAuIg

(for I”) ( kJ mo 1” ^Au ) and date. SO 2 ( mo 1 dm“- sample(g

-13.55 1. 5.8.80 0.032 0,0811

-13.40 2. 5.8.80 0.098 0.1135

-13.34 3. 6.8.80 0 .0 9 8 0.0714

9 9.7% -13.63 4. 6.8 .80 0.098 0.1152

-12.99 5 . 6.8.80 0.098 0.1081

-13.19 6. 7.8.80 0 .0 9 4 0.124?

-13.84 ?. 7.8.80 0 .1 6 8 0.1221

Mean AH* = -13.42 -0.26 kj mol~^Au. 148

Fig. 4sl). Graph of AHjT of Et^NAuI^ with SO^ (aq) V Molarity of SO^ Solution.

n16'0 -1 AHp (kJ mol"^ of Et^NAul2 ) k15-0 pi 40 Ô z13 0 a

=120

=110

=10-0

=90

-’80

=70

=60

=5 0

=40

=30

=20

=10 Molarity of SO, (mol dm”^) J L ______I J____ .1 J______I______£ ___ 0 01 0 03 0 05 0 07 0 09 Oil 013 015 017 019 021 023 149

Fig. 4s 2). Graph of AH^ of EtjjNAuIp with SO^ V Sample Weight.

AHp(kj mol 1)

■ -150

0 Ô 0 0 --1 i O Ô

42 0

■1T0

-100

-9-0

-8 0

“■7-0

--6 0

-5 0

--40

-60

—20

— TO

0 , Et^NAuIp^sample weight (g) 007 008 009 010 0-11 0-12 150

Tetraalkylammon:

4r). Raman spectra i.-

As previously described, only three

bands can be observed in the vibrational spectrum of

the linear Au%2 ion (Dooh)i being Raman-active

a n d ^ 2 ( ^ u ^ and \>^(E infra-red active. The \) 2 fundamental is split into a doublet in the infra-red

region. In this study 0^^ of Et2^NAul2 was detected

in the Raman spectrum of the solid (Fig. 4r1)

In the tétraméthylammonium salt, only one

peak is recorded in the Raman spectrum of the solid.

However, this occurs at 120 cm“^, well below the frequency

of the 0 ^ vibrational mode of the diiodoaurate anion

(which is not significantly dependent on the counter-ion).

It appears that the isolated solid was unreacted

tétraméthylammonium iodide.

4t). Calculations - From the measured heat of reaction -

2Et;i^NAul2(s) + S02(aq) + 2H20(i)= 2Et^NI(aq) + 2Au( s)+2HI(aq)

A H ^ = - 13.42(± 0 .26) kj mol'l (of Au) and from the literature values 1-

AH^(Et2^N‘^(aq) ) = - 248.00 kj mol"^ (B.Derahkshan,I96O)

AH^(l"(aq)) «= - 55.20 kJ mol"^ (NBS Circ.500,1952)

AH^(SOg(aq)) = - 329.82 kJ mol"^ (in 500 HgO) -1 AH^^HgOfl)) = -285.90 kJ mol 151

AHt(HI(aq)) = - 55-12 kJ mol“^ ^(20,000 HgO)

A H^CHoSOi, (aq) ) " -906.24 kj mol'l (50,000 HgO)

2 AH|(Et^lW ul2(s)) = AJI^(H2S0j^(aq)) + 2 Z1H^(Et^NI (aq) +2Z\H^(Au(8) )

+ 2 AH^(HI(aq)) - - AK^(S02(aq) ) - 2 AH ^ (Hg^ (1))

= - 906.24 - 2 X 303.20 + 2 X 0 - 2 X 55.12

+ 1 3.42 + 329.82 + 2 X 285.90 = - 707.84 kj mol"^

Thus, AHp[Et^^RAul2 (s) ) = - 353-92- 0.20 kj aol~^ of Au

It can be seen from figures 4. s 1) and 4.s 2) that there is no dependence of the measured heat of reaction, A H ^ o n either the molarity of SO^ solution used or the weight of iodoaurate sample reacted.

As the exothermic reaction-heat was small, and small samples of the compound were reacted (owing to a shortage of the pure product), an error of - has been arbitrarily assigned to each data point in the graphs.

In the absence of data referring to a second diiodoaurate salt, then no calculation of the thermochemical radius of the anion, or of the lattice energy of this salt, can be carried out. 152

4u). CALORIMETBIC. I -

KAiiXj^CM HgSO^ ) +3?eS0^^ (1M )^KX(1M ) +PeX^(1M ) +Au( s )

(X = Cl or Br) + ?e2(S0^)^(IM RgSO,^)

4v). KAuClj^

Table 4y 1) Run Date PeSOi^ in 1M HgSO^ KAuCl|^ in 1M SOj^ ^ reaction fia.- nolarity(mol dm”^’ molarity (mol dm~^) (kJ mol"^;

1 10.9.80 0.400 3.64 X 10"3 170.46

2 11.9.80 0.400 2.12 X 10"3 170.28

3 12.9.80 0.400 2.12 X 10"3 167.25

4 1 5 .9 .8 0 0.400 1.16 X 10"3 175.17

5 15 .9 .8 0 0.400 2.12 X 10"3 172.05

6 16.9 .8 0 0.400 2.94 X 10"3 165.74

7 1 6.9 .8 0 0.400 2.94 X 10"3 166.46

8 1 7.9 .8 0 0.400 2.12 X 10"3 163.28

9 1 8.9 .8 0 0.400 , 3.64 X 10"3 153.48

10 1 8.9 .8 0 0.400 2.12 X 10"3 172.52

AH Mean R - 167.7 - 4.4 kJ mol'l 153

Graph of

Fig. 4vl). AH^ o f KAuCl;, with FeSQ,j(aq)

V Molarity of the KAuCl,^ Solution,

( kJ mol"^ of Au)

-180

--170 0

--160

--ISO

Molarity of KAuCl/, (lO'^mol dm ^ ) I 1______20 3-0 4-0 154

4w) KAuBrj^

Table 4w 1)

Run Date PeSO^ inIM HgSO^ KAuBr^^ inIM -AH^eacrtion

So. molarity (mol.da”^] molarity (mol.dm”^) (kJ mol*^)

1 20.9.80 0.400 1.74 X 10"3 65.13

2 20.9.80 0.400 0.95 X 10"3 61.83

3 21.9.80 0.400 1.74 X 10"3 60.36

4 22.9.80 0.400 2.98 X 10"3 65.90

# 5 22.9.80 0.400 1.74 X 10"^ 62.73

6 23.9.80 0.400 2.98 X 10"3 66.33

7 25 .9.80 0.400 2.98 X 10"3 68.60

8 25 .9.80 0.400 2.98 X 10"3 64.21

9 27.9.80 0.400 2.41 X 10"] 59.03

10 27.9.80 0.400 2.98 X 10*] 61.67

-1 Mean = - 63.6 - 2.1 kj.mol 155

Fig. 4wl). Graph of AH^ of KAuBr^^ with FeSO^(aq)

V Molarity of the KAuBr,j Solution.

A H ^ ( kj mol"^ of Au)

r~70 Ô

--60 Ô I

h-50

--40

Molarity of KAuBr^^ (ICT^mol dm”])

-30 _l . - 10 20 3 0 156

Fig. 4w 2) SPECIMEN CALORIMETRIC FeSOi./KAuCl,

SS&CTIQf< T B m i

\ V, - 0 .5790V

\ = 5.892V 0.341W

tjj = 68.77s

Pump speed 0.117 cm^ min ^ Chart speed 1 cm min"^

N. .1000

N = moles o:^\ Au reacted

=p.117x14.70x0.400 =^2 .293 x10 3 X 1000

Time

19 5 mm "XvoTumro reactant)

241.5 nun

Molarity of FeSO^^ used «= 0.400M

= 2 c34l_;L6g_:^2 X - 2 4 U - 175.1? kJ mol'l

2.293 X 10 X 141.0 X 1000 a f.M 157

\ Fig. 4w 3). SPECIMEN CALORi;^METRIC FeSO^yKAuBr^

REACTION TRACE

V, - Ü5791V / Fh* 0.341W _V. _V, - 5.692V ------/\^ ^ 77.0mm 3 "“1 Pump speed = 0.11? cmrmin \tjj^l.72s \ Chart speed = 1 cm min AH F Fj^.tjj. ATjj

\ N, AT" c.1000 \ N = 'moles of Au Reacted \ \ Ui : 7.839 X 10 ^ ^ 2.613% -4 10 moles

Time (volume of reactant)

aTq 9 7.5mm \ A \ \

4 Umm lïrmü Molarity “of FeSO^’used ~ ^ ~ o 7 ‘i 0 o a \l37^0min

Q.341 X 41.72 X 92.5 ■ -68.60 kjmol-1 2.613 X 10"^ X 77.0 X 1000 of Au 158

It can be seen from the specimen reaction traces shown that aqueous ferrous sulphate reduction of the tetrahaloaurates is rapid (complete in under 15 minutes) and involves only one rate-limiting step.

The ferrous sulphate and potassium tetrahaloaurate solutions were made up using 1M sulphuric acid solution. The hydrogen ions from the acid inhibited the tetrahaloaurate-hydroxide exchange equilibria, so that the initial calorimetric solution contained K*(aq), AuCl^ (aq), I 2“ H (aq) and SO^"(aq) ions, and no other species.

It was noted in the heats of solution determinations for the tetrahaloaurates, that addition of acid (hydrochloric or hydrobromic acid) resulted not only in the inhibition of the exchange equilibria, but also in what was assumed to be an activity effect of the acid. This caused the endothermie heat of solution of the alkali tetrahaloaurate to decrease linearly as the total ionic content of the calorimetric solution was increased. Similarly, the exothermic standard heats of formation of

FeCl^(aq) and Fe2 (S0j^)^(aq) decrease on addition of acid to the aqueous solution. Therefore, the heats of reaction measured for the reduction of a 1M solution of potassium tetrahaloaurate with a similarly acidic solution of ferrous sulphate are not in agreement with those predicted from the heats of formation of the solid tetrahaloaurates.

This, however, does not detract from the fact 159

that the reduction-reaction trace is not "stepped", and therefore indicates that the reaction mechanism involves one slow step.

4x). - Mechanism of the ferrous reduction of gold (III)

A likely mechanism of the reduction reaction was proposed in the kinetic study of Rich and Taube. As the reduction of AuCl^ by Fe(II) induces a rapid exchange of Cl" and AuCl^, the rate of exchange of 01^^(aq) with the Cl^^ in the tetrachloroaurate anion was therefore followed during the reaction along with (Fe^^), [Cl ') and (AuC1^3

The kinetic data supports the conclusion that Au(II) is the catalyst for the reduction. The inhibition of Fe(IH) formed during the reaction on the chloride exchange of the tetrachloroaurate anion is only very slight, as is a four-fold change in the acidity of the solution. The mechanism proposed by Rich and Taube to explain the variation of the induced chloride exchange with concentration of Fe(II), Cl" and AuCl^ was as follows:-

1). Fe^‘*’+ AuCl^ Fe^'^+ 1 (II). CAuClj^)

2). AUgi+ Cl* T AUg^* + Cl" Very rapid. *_ 3). AUg^* + AuCl^. AUgl- + AuCl^ kgCAu(II)] (AuCip

4). 2Au(II)------Au(I) + Au(III) K4Ca u (i i )3^

5) 3Au (I) ----► Au(II] + 2Au K^CAud))^ 160

The data did not establish the formula of X T 2 — — the catalyst but the formulations AuCl^" or AuCl" were suggested. It seems likely that the great lability of Au^^Cl" as compared to AuCl^^ is due to the possibility of states of different coordination number for Au(II) having nearly the same energy. Some compensation in energy for the loss of Cl" is expected from the increase in average stability of the hybridized orbitals, from increase in stability, of the electron in the atomic orbital, and from the decrease in repulsion of negative ions. The phenomenon of an intermediate oxidation state having high lability to substitution appears to be the explanation for some induced exchanges observed with Pt Cl^^, with Pt^^^Cl being more labile than PtCl^~ or PtCl^".

The rate constant was found to be

1.8 X 10^1 mole"^ min"^, and the limits 6x10^1 mole ^ i n } and nK^> 5 x 10® 1 mole"^ min ^ were determined (n = 3 or 4). The consumption of Fe^^ was sufficiently complete in 5 seconds, except at low (AuCl^) concentrations, but the rate limiting step was found to be K^,for chloride e^changei

The single slow step indicated by the calorimetric titration results found in this study is in accordance with this proposed mechanism; a slow rate of intermediate Au(II) formation followed by rapid reaction steps leading to formation of elemental gold. I6l

The heat of reaction of the ferrous

reduction can be calculated from the thermochemical cycle-

AH R KAuX^dM HzSO^)* 3FeS0^(1MH 2S0^)-^KXQM HzSO^)* FeX^ClM H^SO^)

Ari|:(KAuX^(1M HgSO^)) + Au(s) + Fe2 (S0^)^ClMH2S0^) +3 X AH^lFeSO^dM H^SO^))

AHf(KXClM H 2SO4 ))

t AH|'(FeX^GM H2SO4 ))

+ AH|(Fe2(S0i^)^(lM H^SO^) )

1 K(s) + 1 Au(s) + 2X,(g or 1) + 3Fe(s) + 3S(s) + 60,(g)

f . g r radvption in the. of acid -

AH^ = AH^(KX(aq)) + AH^(FeX^(aq)) + AH|'(Fe2(S0j^)^(aq) )

- Art|'(KAuXj^(aq)) - 3 x AH^(FeSO^(aq) )

AHt(K'^(aq) ) = -251.21 kjmol"^ (NBS Circ.500 , 1952) -1 AH^(Cl"(aq)) » -167.20 kJmol - ) -1 AH^(Br~(aq)) = -121.57 kJnol " )

AH|'(FeCl^{aq))= -5 I8.8 kjmol"^ (NBS Tech Note 270-4,1969) (in 50,000 H2O) AH|(FeBr^(aq))= - 372.4 kjmol"^ ) (in 40,000 H2O)

AH|T(FeSO^(aq) )= - 992.0 kjmol"^ (in 200 H2O) -1 AH^XFe2(S0%)j(aq)) = - 2734.7 kJmol (in 3,000 H2O) 162

AH^(AuCi;^(aq)) = -322.2 kJmol"^ (NBÿ Tech Note 270-4,1969)

AH^^(AuBr^(aq)) = - 191-7 kj mol"^ ( " ) ( )

For the ferrous sulphate reduction of KAuCl/j in aqueous soln.-

AHjj^ = -2 5 1.21 - 167.20 - 518.8 - 2734.7 + 25 1.2 1 + 322.2

' + 3 % 9 92.0 = -122.5(^1.0)kjaol“^of Au

For the ferrous sulphate reduction__of KAuBr^j in aqueous aoln.

= -251.21 - 121.57 - 372.4 - 2734.7 + 25 1.2 1 + 191.7

• + 3 X 9 92.0 = ~6l^g(-0.3) kjmol ^of Au

It seems likely that, as with the potassium and rubidium tetrachloroaurates and FeCl^, acidification will lead to a reduction of the exothermic standard heats of formation of aqueous solutions of FeSO^, FegtSO^)^, KX and FeX_ (X = Cl or Br). Unfortunately, the heats of * V formation of these acidic solutions are not known, and so a full prediction of the heats of reaction between ferrous sulphate and the potassium tetrahaloaurates cannot be calculated.

Mechanisms of other reactions studied calorimetrically - The following reactions were not investigated by means of the titration calorimeter in this study, but were used as calorimetric reactions in the gplution calorimeter. Therefore, the following mechanistic data is taken from literature sources and is included for interest only. 163

4y). Mechanism of the hvdrolvsls of gold (III).

The rate of hydrolysis of tetrachloroaurate in aqueous solution was investigated by a spectrophotometric method at a number of different Cl” and concentrations, by Fry, Hamilton and Turkevich, (F.H. Fry, G.A. Hamilton and J. Turkevich, 1966), It was found that when excess of chloride ion was present, and the hydrogen ion concentration was kept constant, the change of absorbance at 360 nm . followed first order kinetics. The first order rate constants calculated from the absorbancy change were independent of the initial tetrachloroaurate concentration, the phosphate buffer concentration and the ionic strength, but they varied with chloride and hydrogen ion concentrations.

A plot of the observed first order rate constant v the product of hydrogen ion and chloride concentrations was linear at high concentrations. On the basis of the experimental data. Fry et al., eliminated the possibility of hydrolysis proceeding via a direct displacement of oh” on AuClj^, or by means of a rapid initial reversible aquation of AuCl^ (AuClj^ + H20=i=^AuC1^H20 + Cl”), followed by some slow reactions of AuCl^H20. HAuCl^ was found not to be an intermediate in the hydrolysis.

The mechanisms found to be most consistent with the data were ones involving as the initial step a slow reversible aquation of AuCl^. The simplest of these involves rapid equilibration between AuCl^H20 and its ionized form. 164

AuCl^ + HgO EZZZZZTAuCl^H^O + Cl" ^2 K AuCljHgO^ ' " ^ Au CI^OH" + H Rapid, giving a rate equation of '

«obsd'. “ «1 + CCl") . for high _

A rapid subsequent ionization of the trichloroaquoaurate (III) acid most closely agreed with the rate data. In the chloride exchange study of AuCl^ conducted by Rich and Taube, a rate of exchange (K) was found, such that

K = h'CAuCip + k " (AuCljp Cci"; .

Two general mechanisms were proposed, consistent with the first term: 1). the reversible reaction of AuCl^ with water to give Cl" and AuCl^.Hj^O as an intermediate, and 2). As in 1)., but with a rapid exchange between AuCl^.H20 and Cl” before the reverse of the first step, to reconstitute AuCl^. Fry et al deduced that mechanism 1) would yield â value o f R ' in the Rich and Taube study equal to that of obtained in their work; mechanism 2) would give a value for k' equal to . The former correspondence was found, and so it was proposed that all Cl -independent exchange took place by the reversible aquation of AuCl^. At 26^C, the observed first order rate constants in the spectrophotometric study of tetracloroaurate hydrolysis fell in the range 3.0 - 1.2 x lO”^ sec”^ when the chloride 165

ion concentration was varied from 0,5 to 005M, and the hydrogen ion concentration was varied from 1 2 .6 to

1.1 X 10 ^M. (See also W. Robb, I9671 Y.I. Dubinakii et al,

19681 and A.J. Hall and D.P.N. Satchell, I9 77).

4z). Kinetics and Mechanism of the sulphite reduction of , aqueous AuBr^

The mechanism of the sulphite reduction of aqueous AuBr^ has been investigated by V.P. Kazakov and

M.V. Konovalova (I9 68). Solutions of AuBr^ (5 - 3 x 10“®M) in aqueous bromide (0.1 - O.OIM) were prepared. Aqueous SOg^lO^^to 10”®M) was added to the solution in a thermostatted bath, and the absorbance of the aqueous tetrabromoaurate ion, at 254 nm, was followed (€ = 4 x 10^).

As the acidity of the solution was varied between 10 ^ - 10"^M, by addition of perchloric acid, the reaction rate changed by a factor of two. Ionic strength was varied by altering the concentration of sodium perchlorate in the initial solution. It was also found that-the reaction rate increased slightly with temperature.

The reaction of AuBrj^ with sulphite at these concentrations of SO2 , was reported by Kazakov and Konovalova as being reduction to gold (I). AuBr^ + So|"------AuBr^ + SO^"

It was also stated that the AuBr,, 166

concentration can only be reduced as far as a limit determined by the spontaneous reduction:-

AuBrj^ ^ AuBr2 + Br ; Br2 + Br Br^" K = 3 X mol'l. and that this limit is dependent upon the concentrations of AuBr^ and Br” in the solution. Increase in Br* concentration displaces the equilibrium to the right, since Br” combines with the Br2 ' Therefore, at concentrations (AuBr|^”3 * 10 and (Br ] = IM, 10^ of the AuBr^^ undergoes spontaneous reduction

However, no mention is made in this paper of the hydrolysis reactions of the tetrabromoaurate ion. Addition of bromide to an aqueous tetrabromoaurate solution acts to decrease the number of AuBr^” ions undergoing exchange equilibria with water. There is no mention, in all but the Russian papers, of this spontaneous tetrabromoaurate reduction.

This aside, the results of this kinetic study of aqueous tetrabromoaurate reduction by sulphite led to the following conclusions. The influence of hydrogen ion concentration on reaction rate was attributed to the displacement of the equilibrium for the dissociation of sulphurous acid and the change in HSO^” concentration. Fiom the conclusion that the upper limit for the H^SO^ concentration should be V i O times the SO2 concentration, the equilibrium constant for the sulphurous acid dissociation determined by electrochemical methods relates to the equilibrium 167

At 20°C ( I = 0.1) I-

SO2 + H^f> . ' — HSO~ + h'*’ •= 3-4 X 10^1 mole'^s"^ Kj = 2 X 10® 1 mole"^s"^ and the expression for the constant

K - Ch s o ^") (H+D ___0

CS02 + H2 S0P includes in the denominator the sum of the concentrations of dissolved SO^ and H2 S0^. The assumption that it is the HSOj” ion which reacts with the AuBr^” was justified by the fact that the values of the reaction rate constant calculated from equation (a) were fairly constant. The rate equations used werei-

d(AuBr^ ] / dt = (AuBr2^ 3 CSO2 + HSO^ 3

d(AuBr2^“3 = K CHS0^”3 “Tt

k = k' CH'") K

HSO^” concentrations were calculated from the results of the determination of K = (HS0^”3 CH^3 / ^ 280 ^ (Johnstone and Leppa,

1934» Robe and Harris, I963).

Therefore it was concluded that the HSO^ ion reacts with AuBr^^" much more rapidly than SO2 and the H^SO^ in equilibrium with it. The reduction scheme proposed was t -

SO2 + H20:r=T:H2S0g — ir Hso^ + H^

+ (AuBr^”)

k I 2 Au + SO 4 168

the HSO^" ion apparently being able to form intermediate coordination compounds with AuBr^^”, unlike the sterically hindered H^SO^. The rate of total reduction of AuBr/^” could not be determined due

to the rapid equilibration of SO2 with HSO^”. Second order kinetics were not observed throughout the reduction, but after approximately three-quarters of the AuBr^^” had reacted, the reaction rate began to rise spontaneously.

This was not due to SO^”. Kazakov and Konovalova (I968), proposed that this was due to a different form of gold (I) than that present at the start of the reaction. K 3: 10^^ AuBrg + 2S0j" = = Au(S0^)3" + 2Br"

The complex of Au^ with sulphite is so stable that at a Br” concentration of 2.37 x 10~^M, from the moment that gold (I) appears in solution and so long as the sulphite concentration is sufficient to combine with the gold (I), the gold will exist in the form of the sulphito-complex. As the reduction proceeds and the sulphite ion concentration falls, it was surmised that a mixed complex, AuBr(SO^) should be formed. In the last stages of the reaction the mixed bromosulphita complex disappears as sulphite

reduces AuBr^^” to AuBr^.

It was thought that catalysis involved one of the gold (I) complexes. Au^ complexes are kinetically labile and so their participation in such a catalysis is quite probable. 169

At higher concentrations of aqueous sulphur dioxide solution reduction of gold (III) is complete.

However, the last stage in reduction from gold (I) to the element was not investigated by Kazakov and Konovalova.

On the reduction of an aqueous gold (III) solution with a stream of sulphur dioxide gas, it is apparent that the clear gold (I) solution is formed before further reduction to the element takes place. It is most likely therefore, that final reduction occurs after the formation of the univalent salt, assuming the same mechanism to hold at the high sulphite concentrations used in this work. 170

5. AuCl^/ SbCl^ and AuClV AsCl, COMPLEXES

5a). E^PEEIMENTAIl -

The synthesis of a complex between gold trichloride and antimony pentachloride was attempted. If, in such a complex, the antimony acts as a Lewis acid and the gold as a Lewis base, a chloride-shift to form

AUCI2 SbCl^” may occur. If the antimony acts as a Lewis base, and the gold as an acid, SbCl^^AuCl^” may be formed

(as in PCl^^AuCl^”). As neither a AuCl2 ^ nor a SbCl^* species has been reported to date, the Raman investigation of such a AuCl^/SbCl^ complex would be of great interest.

Anhydrous gold trichloride was formed by heating aurochloric acid (Ig) for 30 mins. at 200°C in a stream of dry chlorine. The reaction was complete upon the cessation of water-formation. After cooling in the chlorine stream, the product was stored over CaCl2 (Yield

= 7 9 % , Cl, 34.31 Calc, for AuCl^j Cl, 35-06%). (For Raman spectrum of product, see Results section).

1.2g of the trichloride was added to a solution of antimony pentachloride (1.2g) in dry dichlororaethane and stirred, slightly warm, for several hours. The resulting deep maroon solid was filtered under dry nitrogen and analysed. (Yield = 68%; Cl,35.0%: Calc, for AuCljf SbCl^, 4?.1%). (For Raman spectrum of product, see Results section). The product was found to 171

be unreacted gold trichloride. Repeated attempts at this synthesis using excess antimony pentachloride and mixing gold trichloride with pure antimony pentachloride, failed to produce the desired complex.

The complexation of gold trichloride with arsenic trichloride was attempted. The solid AuCl^(lg) was dissolved in arsenic trichloride and chlorine passed through the solution for several hours. The mixture was then stirred for twenty four hours. The dark red solid recrystallised from the solution and filtered under dry nitrogen (Yield = 71%; Cl, 37-5%* Calc, for AuCl^.AsCl^;

Cl, 4 3 .9%) rapidly decomposed, with release of HCl, on exposure to air. A Raman spectrum of the product is indentical to the gold trichloride reactant.

5b). pesultg and Discussipn_-

The Raman spectra of the starting material, gold trichloride and the solid products from the antimony pentachloride and arsenic trichloride reactions,'can be seen in Figs. 5b 1), 5b 2) and 5b 3) respectively. In Table 5b 1) are listed the Raman bands observed in the spectrum of solid auric chloride by D.M. Adams and R.G, Churchill 11965) Also shown are frequencies calculated by Adams from a normal coordinate analysis using force constants optimised to fit the experimentally observed vibrational bands. 172

Auric chloride exists as a planar dimer.

The Raman spectrum should show four stretching modes.

Three (at 380 cm"^, 331 and 291 ca"^, were found by Adams and Churchill, the fourth not being observed due to its coincidence with the frequency

(calculated 376 cm ^). \)2 was assigned at 331cm"^ due to the high intensity of the observed band. Remaining modes were assigned by comparison with AuCl^ .

It can be seen that the Raman spectra of the solids isolated in this study (Figs. $ b 2 and 5b 3)# closely resemble that of Adams and Churchill for Au^Cl^. Therefore, the band at 380 cm”^ has been assigned to the

O^(A^g) vibration; 366 cm”^ to 0 ^ (B^^); 329 cm”^ to

0 2 (Aig); and the band at 292 cm"^ tov)^(Bj^). No SbCl^, SbCl^, AsCl^, or AsCl^ Raman peaks are visible, and the reaction products are unreacted gold trichloride. 173

shlsridf (As assigned bv Adams and Churchill. 19M)

(cm-1 * Au-Cl terminal + bridge stretch 380 381 ig Au-Cl bridge + terminal stretch 331 322 Skeletal deformation 168 183 Skeletal deformation 99 96 Au-Cl terminal stretch not obs. B 376 Ig Bridge stretch 291 291 124 124 8 AUCI2 rock B.2 g AUCI2 terminal wag not obs.

B AUCI2 terminal twist 106 3g 15 174

Fig. 5bl). Raman Spectrum of Solid AuCl^ Product.

100

m m

vO m

vO>o

O CD CD o O OO OOm m m WAVENUMflER(cm"-^) 175

Fig. 5b2) Raman Spectrum of AuCl^/SbCl^ Reaction Product.

• o I n

~*_rso ISO

O o o oo csl m m m m WAV£NUMBER(cm"^) 176

F ig. 5b3) Raman Spectrum of AuGl^/AsGl^/Clq Reaction

Product.

100

o> CD s CDm vOm m WAVENUMBER(cm”^) 177

6. APPENDIX III.

6a). CALCULATION OF LATTICE ENERGIES BY THE KAPUSTINSKII METHOD - Bom-Waver Equation for the lattice energy of an ionic crystal: U - AN, (1 - P/ ) - (T) ------/ j. r (where and e are the ionic and electronic charges, N is Avogadro's constant, r is the inter-ionic distance^Al, A is the structurally dependent Madelung constant, p is a constant characterising the interionic repulsive forces (equal to a value of 0.3^5 for most crystals), and Vis the number of ions in the molecule).

It can be seen that the detailed calculation of the lattice energy of a compound requires a full knowledge of the crystal structure. The structure may contain non-spherical ions or be so complex as to render precise Madelung constant-calculations impracticable.

For the solution of this problem, Kapustinskii used his empirically found parallelism connecting the differences between the TÆadelung constant for a given crystal and that of the sodium chloride structure and the differences between the corresponding actual interionic distances and those calculated from tables of 6 - coordinate ionic radii. This made it possible to reconstruct an imaginary, "iso-energetic" rebinding of a crystal of any given type into a sodium 176

chloride structure, which could be readily computed from the known ionic radii ( r_ and r_). C BL

This approach permits equation (f) to be transformed.

2, "*c + fa where r^c and r_ a are the formal 6- coordinate radii of the cation and anion (in A)

Summing all the constants in this expressioni-

U = 121.4 V ^1^2 1 - 0 .3 4 5

+ fa) (fc+fa)

(This may be expanded into a quartic equation (see Section 4j)) In cases where it can be checked against precise calculations of lattice energy, this generalised equation has proved approximately as accurate as the Born-Mayer equation,

(Kapustinskii, I9 5 6 ) . Kapustinskii verified the accuracy of this equation by comparing the results of calculations with experimental results obtained by summing the thermochenical values already known from the Bom-Haber cycle. When such data were available and the radius of one of the ions was lacking, it was possible to reverse the calculation and using equation obtain from the thermal data the radius of a simple or complex ion. Such values were named "thermochemical radii". While 179

some complex radicals, especially those of octahedral configuration, may be considered as spheres whose dimensions are directly determined by their radii, there are a good many ions whose structure is far from spherical. In all cases one may speak of effective ionic radii as spherical particles which can equivalently (i.e. without changing the energy of the lattice as a whole) replace in the solid an ion of any configuration.

However, it is important to recognise I that these radii only have significance in lattice-energy calculations by means of the Kapustinskii equation and do not carry any normal stereochemical significance (for instance, r^ for CHS > CNO”< CN ; CIO^ > BrO^ > 10^ ; and (NOz)^ < BF^‘ ).

Kapustinskii*s equation has been criticised for emphasising the sum of the radii (r_ + r.) whereas in many ionic lattices the interatomic distances are predominantly determined by anion-anion contacts.

However, it has proved an effective guide to lattice energies of complex ionic compounds, in the absence of data necessary for more detailed calculations.

Yatsimirskii in his book (K.B. Yatsimirskii, I95I), computed the thermochemical radii for 36 complex anions and 67 complex cations, showing their consistency and additivity, and used equation ( 2) to establish many binding energies (heats of hydration, entropies of complex ions in solution, and alkyl 180 affinities) and to calculate the heats of solution of salts. The Kapustinskii equation has also been used to predict the stable existence of several compounds, including the lower-valent halides and chalcogenides of the lanthanide elements.

For condensed states the entropy factor can be neglected and the free energy changes, determining the chemical reaction, closely approach thermal effects. By means of the relevant "thermochemical" radii and equation @ , an approximation to the free energy changes can be made. A positive value for the thermal effect thus found indicates that a synthesis is energetically possible. In such a way the chemical syntheses of (Mg(CO, CSnCl^), (Ca (CO, CSn 01^, and [Co (C^H^N)^ Cl^] CFbCl^O were predicted and successfully completed.

6b). Errors in lattice-energy calculations via the Kapustinskii equation - The more complete expression for lattice energy

U = AN ( 1 - Py^)+ c + & ^ - (3)

T "73 contains additional terms, the zero-point energy, and the van der Waals forces, cy^6, with the constant c computed by the London method. Comparison with experimental data from the Bom-Haber cycle indicates that for purely ionic crystals the second and the third term have little significance. The crystal lattice energy equation dealt 181

with here is reduced to taking account precisely of the first term of equation (3) # and so it is important to have some idea of the accuracy of the expression.

In Kapustinskii*s monograph w were

plotted against V(r + r ) experimental c a data for metal halides, oxides and chalcogenides. The curve corresponded to equation(?> the accuracy of which is of the order of 2 - 3%« In most cases, the ionic radii themselves are known to the same accuracy.

When necessary the accuracy of the value of the coefficient p can be increased by the introduction of Kapustinskii*s empirically found dependence of p on the sum of the ionic radii i- (Kapustinskii, 1956).

P = 0.3^5 - 0.00435 (Tg + When this is substituted into the Kapustinskii equation for the crystal lattice energy ( @ ) i -

U = 121.4 V (1 - 0 .345 + 0 .00435(r^+r^j) ^

]

In this case, a comparison of calculated results with experimental data shows the errors to be distributed statistically, the quadratic mean deviation for

MX salts being 3*36 kj (approx. O.5#), and for the MX2 salts, 21.8 kj (approx. 1 % ) . This more accurate expression is unfortunately more cumbersome. 182

7. APZENDIX_iy.

ESTIMATION OP EX^Efi^MEHTAL gRpORS. - (N.T.J. Bailey. I969)

Although the solution calorimeter used in determining the heats of solution and reaction of the gold salts

should give an accuracy of - 1^, the necessarily small samples taken and the resulting low heats of reaction, lead to a higher associated error. The error in the measured heat of solution increases with increasing time for complete solution, and decreasing sample weight. (leading to an increased extrapolation of after-period to zero reaction time, and a decreased temperature change of the reaction calorimeter, respectively). Thus in the graphs of measured heat of tetrahaloaurate solution versus the activity of acid or salt solution used as solvent, each data point has associated with it an error bar of - 2 % (estimated).

The precision of experimentally determined enthalpies of reaction are usually quoted as twice the standard deviation of the mean, s i

— \ 2 8 = (X - X)

n (n - 1 ) (where x is the arithmetic mean of n results), assuming a normal distribution at the 95^ confidence interval. However, for n < 20 the error is more correctly assessed by the "students t" distribution. In the solution of the tetrahaloaurates in water, the reaction of the dihaloaurates 183

with aqueous FeSO^ or SO^, and the reaction of the tetrahaloaurates with aqueous FeSO^, the error associated with the quoted mean heat of reaction refers to a 95# confidence interval. This is calculated assuming a Student's t - distribution. The results are reported as X - ts/ /h.

where *= 1 ( Y. - 1 ( Z x)^ n - 1 { n j and X * 1/ Z X Yn (n * number of results (x), and t * the "student's t" value for (n - 1) degrees of freedom at the 95# confidence interval).

An error bar equal to the 95# confidence interval has therefore been drawn for each point plotted in the tetrahaloaurate heat of solution/molarity of gold solution* dihaloaurate heat of solution/weight of sample (and FeSO^ or SO^ molarity); and tetrahaloaurate/FeSO^^ titration graphs.

For a series of values

A H = AH j^ + AH^ + ______+ZlH^. where AH, has an uncertainty interval of - x, then the ^ + ( n 2 error for AH was taken as - ( zZ (x, ) ) . Ancillary ( i=l ^ ) data were taken from National Bureau of Standards Tech. notes which have unlisted sources. The procedure followed in assigning an uncertainty interval is identical to that used in "CATCH" tables, i.e., the uncertainty interval is assumed to be ten times the last figure given. 184

The intercepts in the AHg^j^(MAuX2^(s) ) v molarity of acid solvent graphs have been assigned an error equal to the 95^ confidence interval of the heat of solution of the corresponding alkali tetrahaloaurate in pure water. The calculated anion thennocheaiical radii have an associated error of -1#. This is adequate as a comparatively large change in the measured heats of reaction has a much smaller effect on the calculated thermochemical radius. 165

8. APPENDIX V - CALORIBŒTRIC REACTION STOICHIOMETRIES

Evidence for stoichiometries of the aqueous ferrous sulphate and sulphur dioxide reduction of gold (III) and gold (I) salts.

8a) FeSO^^ with Et^NAuBrg - Table 8a 1)

Purity of Moles Moles Moles Au Moles Moles Br Et^NAuBr2 Etj|^NAuBr2 PeSO^ collected FeSO^ in by Br” taken taken (10-4) reacted solution anal.(#) (10-4) (10-3) (10-4) (10^)

4.54 1.041 4.58 - 8.49

99.4# 4.55 1.041 4.55 - 8.88

3.40 I.0I3 - 3.48 -

2.84 0.998 - 2.85 -

2.92 0.995 - 2.94 -

Me^NAuBr2 \ -

99.8# 2.81 1.146 - 2.83

Therefore, nH^O + xEt;^NAuBr2 (s) + x FeSO^(aq) = x Au(s) + 2x Br (aq) + ? leads to the equationi- ^Et^NAuBrgfs) + 3FeS0^(aq) * 3Au(s) + Fe2(S0ji^)^(aq)+FeBr^(aq) +3Et^NBr(aq) 186

8b.). SO^ with Et^NAul^ - Table 8b 1)

Purity of Moles of Moles SO2 Moles Au Moles of I" Moles of SO2 Et^HAul2 Et2+RAul2 taken collected in solution reacted by 1“ taken Uo"3) (10-4) 1 10-4 , (10-^) anal. (10-4,

1.73 1.92 1.74 3.46 -

1.73 3.23 . 1.75 3.50 -

99.7

1.56 1.96 1.57 3.08 0.77

1.17 1.96 1.20 - 0.57

1.18 1.94 1.98 2.40 0.60

Titration of the liberated acid with standard sodium hydroxide solution gave inconsistent results, possibly due to the very dilute solutions used.

Therefore,

2xEt2^NAul2 + I SO2 + 1^ 2^ - 2xAu + ? loads to the equation;-

2Et2^NAul2(s) + S02(aq) + 2 H^OCl) = 2 Et^NI(aq) + 2Au(s)

+ 2 HI (aq) + H2S0;^(aq) 187

8c). FeSOji^ with KAuCl^ - Table 8c 1)

Purity of Moles of Moles Au Holes Cl From the titration KAuCl|^ KAuCl^ collected in calorimetry the by Cl" taken (10-4) solution FeSOj^i KAuCl^^ anal.(#) (10-4) (10-4) ratio was found as

2.42 2.40 9.56 3 1 1

100.3*

4.00 3-93 16.00

KAuBrj^ FeSûj^i KAuBr/^ ratio

99.8* 5.02 4.91 20.26 3 I 1

Therefore,

nH^O + xKAuCl^(aq) + 3xFeS0^(aq) * xAu(s) + 4xCl*(aq) + ?

leads to the equationi-

KAuCl^(aq) + 3FeS0^(aq) = KCl(aq) +F$Cyiaq)+Au(s)+Fe2(^0j^)^(aq) 186

9. APPENDIX VI - CALCULATION OF THE IONIC RADII OF THE COMPLEX ANIONS. The gold (III) tetrahalide anion is square planar in structure, and has been studied by X-ray crystallography in both anhydrous potassium tetrachloroaurate and potassium tetrabromoaurate dihydrate. (See also

Sleater, I9 7 0).

Bonamico and Dessy (1973) found two crystallographically independent tetrachloroaurate ions present in the cell of the anhydrous compound. The mean

Au - Cl internuclear distance was found to be 2 .2 9 (- 0.02)A. This is comparable with a gold-chlorine bond length of

2.2 7 A in the (Ph^As) (AuCl^) complex (Jones et al, I973), and a value of 2.29 A in the aqueous tetrachloroaurate anion (Maeda, 1974).

Cox and Webster ( 1936 ) , in their X-ray investigation of the dihydrate, found no coordination between the water molecules and the gold atoms and a mean Au - Br internuclear distance of 2.37 A. In the aqueous anion, Masunobi Maeda (1974) et al, determined a mean value of 2.43 A. The radius of the sphere circumscribing the tetrahaloaurate anion can therefore be calculated*- 189

/ X“ / / anion îs I

\ \ \

The, square JDl&nar tetrahaloaurate anion

It can be seen that - x the internuclear distance of the Au - X atoms in the relevant anion. As the Au - X bonds in the tetrachloroaurate and

tetrabromoaurate show marked covalent character (E.J. Bara,

1975? Sasana, I97I)» r^ is taken as the van der Waals radius of the X atom. With Cl and Br, this figure is so close to the ionic radius that no significant error can be incurred by this assumption.

Therefore,

^Anion * ^Au - ^x becomes, ■= 2.29 + 1.80 « 4 .09^

o AuBrr « 2.57 + 1.9 5 4 .52 A 190

The gold (I) dihalide anion adopts a

linear structure and a single crystal X-ray diffraction

study on (Au (bdtcjg) AuBr2 (bdtc = Bu^ NCS^)» has

revealed the presence of discrete, linear, centrosymmetric o AuBr2 anions with an Au - Br bond length of 2.35 A. (Bowmaker

and Whiting, 1976) (also Beurskens, et al, I968).

\ / \ anion

Again, the distance r^ is taken to be equal to the van der Waal's radius of the bromine atom. (See Bowmaker and Whiting,

1976).

So, + r. Anion Au - X 191

becomes,

' AuBr “ 2.35 + 1.95 = 4.30 A

It is clear that the thermo chemical radii determined in this work do not follow the same trend

(ÂuBrg ^ ÂuBrj^ » ÂuBrj^ ^ ^ AuClj^ ^ the ionic radii calculated above > ÂuCl^'^

However, it must be remembered that thermo chemical radii are for use in the Kapustinskii - lattice energy calculation and have no physical significance (see Appendix III). As the anions are non-spherical, the calculation of a physical ionic radii is highly approximate and of doubtful validity.

However, it can be seen that in both thermo chemical and ionic radii, r _ > r AuBr^ AuCl^ 192

10). APPENDIX n i - THAM CALIBRATIOMS a ). Endo thaiïi. -

The heat of solution of tris (hydroxymethyl) aminofflethane in excess 0 . 0^ sodium hydroxide solution. Table 10 a) 1).

Date of Run Weight of fham taken (g) + (kJ mol"^:

2.4.79 0.1118 17.22

11.6.79 ■ 0.5205 1 7.2 4

22.6.79 0.3058 17.16

2 5 .6.79 0.2429 1 7 .1 6

2 0 .7.79 0.3224 1 7.1 0

4 .9 .7 9 0.2350 1 7.1 3

10.1.80 0.2656 1 7 .2 7

10.1.80 0.2326 1 7.17

2 3 .1.80 0.4970 1 7.2 7

19.2 .8 0 0.4270 1 7 .1 6

28.2.80 0.3382 1 7.2 8

2 3 .5.80 0.4409 1 7 .2 5

1 9.7 .80 0.4725 1 7.2 1

2 0 .9 .8 0 0.3162 . 1 7 .1 6

2 6 .9 .8 0 0.1304 1 7 .2 3

Mean = + 17.20- 0.06 kj mol“^

(Literature value: = + 17.18 kJ mol (Pro38n,l973) See Figure 10b 1); where the mean value of the endo tham solution is shown, - 0.5% experimental error limits 193

b). Exo tham -

The heat of solution of tris (hydroxymethyl) aminomethane in excess O.lM hydrochloric acid solution.

I).

Date of Run Weight of tham taken (g) -AHjj (kJ mol"l|

1 7.3 .7 9 0.1564g 2 9 .7 4

2 0 .3 .7 9 0.2785g 2 9 .7 5

6.1.80 0.3487g 2 9 .8 5

r. 29,29 -1-.0aQO«7

(Literature valueiAHp= -29*79 kJ mol (Prosen,I973)

See Figure 10b 1) : where the mean value of the exo than, solution is shown, - 0 .5% experimental error limits. o CD 194 es

e » iCD

( ) ^

S CN (T

CD CP

CD 10 C3D Û (Tj U Ü es C r- o es •H -4- -P O ctJ u •HJ=> .H (ti O CNgCD E eu X E Eh Gj es X N3 H un 1 0CN 0 X X w O CD R fH cp vO X .R b£ ' ^ O O 'ri es rn ô CN f= G 0 " ë _sc: -4- U" 0 ^ oc ^ c- vO un X 0 G7^ C> • cS cK gK t Cv Csl 4f + g 1 X - T _.l . 1 JT@_L _1__ î ! 195 11). APPENDIX VIII.-ACTIVITY COEFFICIENTS OF THE SOLVENTS

Fig. 111). Graph of the Activity/ Coefficient ( ^ + ) of HCl Solutions of various Molarities.

at 25°C. ^^/experimental iHarned and Owen,

-16 mol. dm 1 9 6 7 ). of HCl(aq) y+

0.796

0.757

0.809

0.896

1.009

1.316

1.762

Molarity of HCl soln. (mol dm~^)

4 0 196 Fig. 112). Graph of the Activity Coefficient(^î ) of HBr Solutions of Various Molarities at 25°G. y +(experimental) crO-93 mo 1 dm of HBr -092 0.001

-091 0.930 0.01 0.906 -090 0.02 0.879

0 .0 5 0.838

0.805 0.2 0.782

0 8 7 0.5

- 0-8;

-0-81

-080

-079

Molarity of HBr solution. 0 7 7 _ l .._ 197

Fig. 113. Graph of the Activity Coefficient(y+) of KNO^ Solutions of Various Molarities,

at 25°C.

Y +/experimental

mo 1. dm^.

of KNO^(aq) Y +

0.1 0.733

0.2 0.659

0.3 0.607 0.5 0.542 0.7 0.494 1.0 0.441

1.5 0.378

1-0-5 2.0 0.327

2.5 0.293 3.0 0.266 3.5 0.244

-04

- 0 3

Molarity of KNO^ solution (mol dra"^) __i_ 0 .05 10 i s ' 2 0 ^ ' .. 25 198

Fig. Il4). Graph of the Activity Coefficient(X+) of NaClO^ Solutions of Various Molarities, at 25°C. ^/experimental mol, dm,-3 of NaClO^(aq)

0.1 0.775

0.2 0.729

0.3 0.701

0.5 0.668 0.7 0.648

1.0 0.629

1.4 0.616

2.0 0.609

2.5 0.609

3.0 0.611

3.5 0.617

4.0 0.626 5.0 0.649

6.0 0.677

Molarity of NaClO^ soln. (mol dm”^) 0-60 2-Ô 3-0 40 5 0 199

SPECTROSCOPY OF THE TELLURIUM HALIDES AND COMPLEXES. 12) INTRODUCTION. 12a) General Chemistry

In this introduction, some of the general chemistry of tellurium will be discussedi in particular, in relation to the chemistry of the other group VI elements (oxygen, sulphur, selenium and polonium). Both sulphur and selenium adopt Mg rings or polymeric chains in their allotropie forms (Massey, I972). In sulphur, the eight membered ring is the stable form at normal temperatures; with selenium the chain polymer found in grey selenium is most stable (Powell and Timms, 1974). Tellurium exists in only one modification, consisting of long spiral chains of tellurium atoms, isomorphous with trigonal

(grey) selenium and rhombohedral sulphur (Massey, I972).

The study of polonium chemistry is complicated by the radio activity of all its known isotopes, but elemental polonium has a metallic lattice (Massey, I972).

This trend in the structures of the elements is a reflection of the gradually increasing metallic character of the elements, on passing down the group VI, due to the increased shielding effect of the inner electrons on the outer ns and np electrons as quantum number n varies from two to six. The electrical properties of the elements vary accordingly down the group, oxygen and sulphur being insulators, selenium and tellurium semiconductors, and polonium showing metallic conduction (Massey, 1972).

Chemically, this increase in the metallic 200

character is manifested in various ways; such as an increasing tendency to form positive ions, a decreasing stability of the 2 _ M " ions and a weakening of the M-X bond (Massey, I972).

Considering the electronic configurations for the group VI elements, as shown in Table 12al); energy considerations for these elements rule out the possibility of their gaining an inert-gas configuration produced by loss of all six valence electrons, to form ions (Massey, 1972). Te and Po , both having an ns electron configuration, are known; for instance in tellurium dioxide (TeO^) and polonium

dioxide (P0O 2) (Mellor, I9 67). In addition, some poly

atomic cations have been reported (Massey, I9 7 2 ). As with sulphur, both selenium and tellurium can be oxidised to cationic forms in the presence of Lewis acid, and X-ray

structure determinations on Se^^ (H520ÿ)2 and Tej^ (A1C1^)2 show both these cations to be square planar with inter- chalcogen bonds shorter than those in the solid selenium or tellurium. This is consistent with a bonding picture of six T&electrons delocalised over the four atoms of the cation (Powell and Timms, 1974).

The most usual ways for the group VI elements to obtain a rare-gas electronic configuration are as follows 2 a). Forming M ” ions, as in the alkali-metal oxides, sulphides, selenides,tellurides and polonides. b). Forming two covalent bonds, as in water and dimethyl sulphide. c). Forming MR" ions, as in hydroxide and thiosulphide ions

(Massey, 1972). 201

Table 12a 1)

Ionization Energies of the Group VI Elements, (Massey, 1972)

I.E. 2 ’^ ^ I.E. 3^'^ I.E. I.E. Covalent kJ mo 1~^ KJ mol~^ kj Diol~^ kj mo 1~^ radius/A 0

Is2s2p 1314 3393 5301 7469 0.66 S (Ne)

3s3p 1000 2260 3379 4564 1.04 Se (Ar)

3d4s4^ 941.4 2075 3088 4138 1.17 Te (Kr)

4d%s5p 870.4 1795 3012 3683 1.37 Po (Xe) IQ 2 L ^f3d6s6p 811.7 ——— —— — ———— —--- 202

12b) Halides of the Group VI Elements.- The following table lists the known halides of this group.

Normally, M-X bonds decrease in strength as the atomic weight of M increases; however, only the iodides of tellurium and polonium are stable. Similarly, the only tetrachloride which is stable in the gaseous state is that of tellurium (Massey, 1972).

In most cases the halides can be synthesised from the elements, using carefully controlled conditions where necessary (Thorpe, 19^3). The extent of halide bridge bonding increases down a group as the halide acceptor power of the elements increases. The tellurium tetrahalides have structures tending towards a TeX^X” form, although some degree of covalent halogen bridging is preserved, especially in the fluoride.

From simple valency considerations it might be predicted that sulphur, selenium and tellurium would form stable dihalides, with tetra- and hexa-halides as possible higher oxidation states. The difluorides rapidly dis proportionate to the elements and the corresponding tetra- fluoride (Powell and Timms, 1974). Selenium dichloride is a gaseous decomposition product of SeCl^ and can be complexed with (NMe2 )2^=^* • It is reported that the most stable of the dihalides are SClg, a red liquid, and TeCl2 . a black solid (Powell and Timms, 1974). The former gives 1 % 1 complexes with strong Lewis acids, eg AlGlj or SbCl^, and 203

Table 12b 1)

Halides of the Group VI Elements.

- Oxygen Sulphur Selenium Tellurium Polonium M^X OgCl 0 2Br

"2*2 °2^2 SpFp^^ isomers) S2 CI2 Se^Cl^

^2®^2 SSgBrz

M^X2 0 ^F2 S^Cl2 (Short chains of S atoms)

MX2 OF2 SF,

OCl. SC12 SeCl2 TeCl2 PoCl

OBr. TeBr2 PoBr

Sel2

MX; SF^ SeF^ TeF^

SCI4 SeCl^ TeCl^ PoCl SeBr^ TeBr^ PoBr

Tel^ P0 I4

MX SF.

MX SF. SeFV TeF

* (Unstable at room temperature). ^2*10 ^2^10 204

Table 12b 1) (continued).

Oxygen also forms ClÔ^# ClÔ^, IÔ^, 12^5 OCl.

Tellurium subhalides Te^Cl2 . Te2 Cl, Te2 Br, Te2 l, /^-Tel

and o<-TeI are also known (Rabenau, I9 7 6).

The Te2 % compounds have a double-chain structure, with

3 and 4-coordinate Te atoms. Te^Cl2 has a single-chain structure with 2 and 4-coordinate Te atoms (Angew Chem, Internat. Ed., 1973, 1^2, 499).

[ Structures of the Halides. (Massey, 1972).

‘M- M s x*^ w M M2 X2 (1 ) (as H2 O 2 ) (S2 F2 only adopts this form).

M X-

MX^ (trigonal bipyramidal) MX^ (octahedral) -X X^ ^x X" CM-

^2^10 (two octahedra sharing one apex). 205

also with Lewis bases such as pyridine. Tellurium di chloride is a stronger Lewis acid than SCI2 and forms a stable cis square planar complex with thiourea (Powell and Timms,

19 74). However, it has been strongly suggested by

Christensen (1973) that the tellurium compound TeCl2 is only stable at low temperatures, and disproportionates to give elemental tellurium and the tetrachloride at room temperature.

and SeF^ are gases, whereas TeF^ is a crystalline solid with a fluorine-bridged structure in which there is square pyramidal coordination about tellurium. All the tetrafluorides complex with BF^ and strong Lewis bases (eg. pyridine or trimethylaraine), and with F” donors such as CsF to give MF^“ and the MF^” ions respectively (Powell and Timms, 1974).

Other tetrahalides are less stable. SCl^ decomposes below -15^0, and SeBr^ decomposes at room teraperature( Powell and Timms, 1974). TeCl^ in benzene forms Te^Cl^^ which may have a cubane-like structure, as in the solid. Complex anions such as SeCl^^", Tel^ and Te^Cl^^ are more stable (Powell and Timms, 1974). TeF^ is slowly hydrolysed by water to telluric acid, unlike the extremely inert SF^. Also unlike the sulphur or selenium hexafluoride, tellurium hexafluoride behaves as a weak Lewis acid (Powell and Timms,

1 9 7 4).

The compounds TeF^Cl and TeF^Br (similar to mixed halide compounds such as SF^Cl and SF^Br) have been reported, but, unlike their sulphur analogues do not readily 206

release the TeF^ radical (Powell and Timms, 1974).

12c) Tellurium (II) and (IV) Chlorides and Bromidest- In this section the halides of tellurium which are "of specific interest to this work will be considered, ie. tellurium dibromide and tetrabromide, tellurium dichloride and tetrachloride and the dichloride dibromide, as well as Lewis acid salts of the tetrahalides.

Tellurium Dichloride;- This was first prepared by Aynsley (1953)» and exists at liquid nitrogen temperatures as brown crystals. However Christensen and Alstad, in 1973» proposed that above this temperature it consists of a mixture of the element and the tetrachloride. Their study of tellurium dichloride from two commercial sources and a sample formed by the authors using the method of Aynsley involved analyses using infra red, Raman and X-ray techniques, and also gravimetric and neutron activation analysis. Their analyses were more consistent with those of mixtures of elementary tellurium (possibly in an amorphous form) and the tetrachloride, than with that expected for tellurium dichloride.

Aynsley reported that on addition of bromine to the dichloride, the dichloride dibromide was formed; and a similar reaction using iodine yielded the dichloride di-iodide.

Tellurium Tetrachloridet -

This can be prepared by direct treatment of

the element with pure dry chlorine at I5 OC -300C (Thorpe, 1943)» 207

or by the action of sulphur monochloride on warm tellurium or tellurium dioxide (Thorpe, 1943). The crystals can be washed with carbon disulphide to remove sulphur, final purification being effected by distillation in a current of Cl^ and HCl. Tellurium tetrachloride forms large white crystals (m.p.225°C), which melt to give an amber liquid (b.p.390°C). The substance behaves in solutions as a salt-like compound of polar character. On exposure to the air it deliquesces rapidly, and the dioxide slowly separates, (Thorpe, 1943).

Tellurium tetrachloride reacts with boron tribromide to give a yellow solid, (tellurium tetrabromide), melting above 3 6o°C. ^C1 TeCl^+BBr^ = Cl^Te^ J)BBi^ = ClgTeClBr+BBrgCl (1), 3r

TeCljBr+BBr^ = Cl^BrTe^^ ^Br^ = TeCl2Br2+BBr2Cl (2).

3BBr2Cl = ZBBr^+BClj

Repetition of step (2) leads to a quantitative conversion of the tetrachloride to tellurium tetrabromide. That no reaction occurs, either in benzene or in the absence, of solvent, may reflect a significantly lower lattice energy for a tetrabromoborate relative to tellurium tetrabromide, (Chen and George, 1972).

The compounds SCl^, SeCl^ and TeCl^are well known for their donor and acceptor properties towards other chlorides. Depending on the differences in Lewis acidity cationic (such as SeCl^ ) and anionic species (eg. TeCl^ ) 208

can be formed, (Beattie, I9 6 7). It has been shown by X-ray, NQR and Raman investigations that the structures of the crystalline compounds MCl^.AlCl^, M=S, Se and Te, essentially consist of pyramidal MCl^ and tetrahedral A1G1^“ ions, which also seems to be the case in the molten state, (Beattie,

1 9 6 7; Paul, 1 9 6 9; Gerding, I9 7O; Okuda, 1975; Krebs, I9 7 1). Similar results have been deduced for SeCl^.GaCl^ by Raman spectroscopy.

The compound 2SCl^.SnCl^, which was formulated

+ 2— as (SCl^)2 SnCl^ , seems to be the only example of a reaction among two tetrachlorides (F.W.Poulsen and R.W.Berg, I9 7 8).

Various types of compounds are formed between the tetrachlorides and different pentachlorides. An X-ray study has shown TeCl^.PCl^ to contain tetrahedral PCl^ and polymeric (TeCl^) chains with octahedrally coordinated Te(IV) (Krebs, 1973). For compounds MCl^.SbCl^, M=S, Se, Te, two alternative structures have been suggested (Beattie,

1 9 6 7; Morishita, 1974). For sulphur an ionic description

SCl^SbCl^ was adequate (Beattie, I9 6 7), whereas a neutral binuclear chloride-bridged structure was claimed for the selenium and tellurium compounds (Gerding, I9 6 9).

SCl^.NbCl^ and SCl^.TaCl^ have been mentioned as byproducts formed during the chlorination of Nb2 0 ^ and

Te2 Û^ in SOCI2 (Poulsen and Berg, I9 7 8). The two phase' diagram studies of Poulsen and Berg (I9 7 8) showed the existence of the four 1x1 compounds (Se, Te)Cl^.(Nb, Ta)Cl^ as slightly incongruently low melting materials (m.p. near I9Û C), 209

A thermo chemical investigation indicates that the 1*1 compounds dissociate to give gaseous TeCl^ and MCl^ in the vapour phase at 375°-379°C. All the six compounds MCl^.MCl^

(M=S,Se,Te and m '= Nb,Ta) are quite hygroscopic solids (Poulsen and Berg, 1978). The sulphur and selenium compounds show decomposition on melting in sealed ampoules, chlorine and lower valent sulphur and selenium chlorides probably being formed. In benzene, known to be a moderately good solvent for TeCl^ and the.pentachlorides, the addition compounds are quickly decomposed, probably by chlorinating the benzene (Poulsen and Berg, 1978).

Most metals are rapidly attacked on heating with TeCl^, the most resistant metal tetrachloride seeming to be tantalum. With platinum, platinous chloride is formed; and with an excess silver, silver telluride and chloride are produced (Thorpe, 1943).

Tellurium tetrachloride can be recrystalliseed (at -30^C.) from concentrated hydrochloric acid to yield TeCl^,

HCl, 5 ^ 2 ^ (m.p.-20^C). Evaporation of this medium with solutions of the alkali halides leads to the formation of chlorotellurates of the type M^TeCl^. The tetrachloride dissolves in ether, and can be recovered as TeCl^, Et^O crystals on evaporation (Thorpe, 1943).

Tellurium Dibromide%- Tellurium dibromide as produced by Aynsley (1955)» at liquid nitrogen temperature, was a chocolate-coloured powder.

This readily disproportionated into tellurium and the 210

tetrabromide, and addition of chlorine to the dibromide yielded tellurium tetrachloride.

Previous syntheses of the dibromide involved the'sublimation of a mixture of tellurium and tellurium tetrabromide; the condensation of TeBr2 vapour in a vacuum at

-80°C; or the reduction of tellurium tetrabromide in dry ethereal solution in the dark with finely divided tellurium (Aynsley, 1955). However, Aynsley suggested that other workers in this field did not handle solid tellurium dibromide but a solid solution of the element and its tetrabromide.

In view of the lower thermal stability of tellurium dichloride compared with the dibromide, and the findings of Christensen and Alstad (1973) indicating the non existence of solid tellurium dichloride; it is possible that the brown solid isolated by Aynsley was a mixture of elemental tellurium and tellurium tetrabromide.

Tellurium Tetrabromidei- Telluriura tetrabromide can be obtained by direct union of the elements at room temperature, excess bromine being removed by gently heating the product in a current of dry carbon dioxide (Thorpe, 1943). The yellow product sublimes at 420°C, and condenses to give orange crystals. Chemical properties parallel those of the tetrachloride. With hydrobromic acid, it affords TeBr^, HBr, 5H2 O . With tellurium, the tetrabromide forms a eutectic at 200°C, containing ' } 6 % of bromine; bromotellurates of the alkali metals have also been isolated, (Thorpe, 1943). 211

Tellurium Dichloride Dibromide (TeCloBro)!- A common method of preparing this compound is that employed by Aynsley in 1953- This involves the condensation of the dichloride of tellurium on a nitrogen cold- finger, and addition of the stoichiometric quantity of liquid bromine, to form the mixed halide, tellurium dichloride dibromide.

Beattie, in 19?4, questioned the existence of tellurium dichloride as a stable crystalline compound under normal conditions. This doubt was founded on the results of Rabenau and Rau (1973). G.C,Christensen, in 1973. reported Raman, infra-red, gravimetric, and neutron activation studies of tellurium, tellurium tetrachloride and "tellurium dichloride", and concluded that tellurium dichloride is nonexistent in the solid phase.

For this reason, Beattie et al, (1974) produced the dichloride dibromide of tellurium by mixing equimolar quantities of the tetrachloride and tetrabromide in a sealed ampoule, and heating this mixture to 3 00^0 . for a few minutes. Beattie's synthesis of the mixed halide (1974) by a), bromination of "tellurium dichloride" and b). heating a mixture of tellurium tetrachloride and tellurium tetrabromide in a sealed tube at 300^C. for a few minutes, yielded products, the observed melting points of which (a). 305-309*^0 , b). 304-307°C) agreed well with Aynsley's reported melting point of 292^C.,

(Aynsley, 1953). 212

Until 1968 the literature was devoid of structural information concerning this mixed halide. Tellurium dichloride dibromide represents the only known example of a group VI mixed tetrahalide which is stable enough in the vapour phase to allow a structural investigation by gas phase laser Raman spectroscopy (Ozin and Van der Voet, Canadian J, .

Chem. 1 9 7 1). By analogy with tellurium tetrachloride, the species present in the vapour of tellurium dichloride dibromide would be expected to be molecular. Ozin and Vander Voet (Canadian J. Chem, 1971), in their gas phase Raman spectrum study, concluded that molecular tellurium dichloride dibromide yields Raman data consistent with either of the low symmetry ([^) structures, ] Cl Cl .-Br I ^ Br Te.^^ or Te Cl ! ,r I I rather than the predicted C^^ structure Cl I ^ 3 r T < 2 I Cl It was also suggested that the spectrum could also be consistent with a mixture of the two C£y isomers Cl Br I I ^ 0 1 Te^ and Te, I ^ B r I "Cl Cl Br and possibly the C^ structures, where relative amounts of each depend on the solid structure (Ozin and Vander Voet, j. Mol.

S truct., 1 9 7 1)•

Hence the structure of molecular Tecl2Br2 has 213 still not been satisfactorily ascertained, and the structure may depend on that of the solid tellurium dichloride dibromide. There was for some time uncertainty about the structure of the tellurium tetrahalides. In 19?0, it was shown by Buss and Krebs^ that they adopt the structure-

X—|e— (X= Cl or Br)

V—L- (B. Buss and B. Krebs, 1970) __L X— Té-----

With each tellurium atom surrounded by three chlorine atoms at normal TeCl distances of 2.3% and one at a further distance 6- of 2 .9A, giving a structure approaching the ionic TeCl^ Cl

Assuming the TeCl2Br2 solid structure to be analogous to that of the solid tetrachloride and tetrabromide,

(Ozin and Van der Voet, J. Mol. Struct., I97I), the solid mixed halide may therefore exist as:- Br - /Cl Br I^—-— ^ ^ ^ Cl-

Br- le - C l [f or

Br No Lewis acid salts of tellurium dichloride dibromide have been reported in the literature, but many such salts of tellurium tetrachloride (and, to a lesser extent, the tetrabromide) have been studied spectroscopically. (See Section 12d). It was therefore proposed to carry out a similar reaction with TeCl2Br2 in order to determine which halide ion was transferred to the Lewis acid. 214

12d). Lewis Acid Complexes of the Tellurium Tetrahalides

The Raman and infra-red spectra of solid TeCl2 Br2

(Minkin, 1973; Ozin and Vander Voet, I9 7I; Katsaros and George,

1 9 6 9; Ozin and Vander Voet, I9 7I(p.704)), TeCl^ (Beattie et al,_1974; Gerding and Houtgraaf, 1954; Ozin and Vander Voet,

1 9 7 1; Katsaros and George, I9 6 9; Greenwood et al, I9 6 6; Adams

and Lock, I9 6 7; Hayward and Hendra, I9 6 7; Morishita, 1974; Christensen, 1973), TeBr^^ (Ozin and Vander Voet, 1971;

Katsaros and George, I9 6 9; Greenwood et al, I9 6 6; Adams and

Lock, 1 9 6 7; Hayward and Hendra, I9 6 7), and solutions of these substances, have been reported. Nuclear quadrupole resonance studies of the tetrachloride and tetrabromide have also been carried out (Morishita, 1974; Okuda, 1975). A gas phase Raman spectrum of tellurium dichloride dibromide is to be found in the literature (Ozin and Vander Voet, 1971 (p.?04)); as are the solution characteristics of the parent tetra halides and the mixed tetrahalide (Katsaros and George,

1 9 6 9).

Neither the tetrachloride nor the tetrabromide reacts with boron tribromide to give a complex (Chen and George, 19?2). However, Raman spectra have been reported for TeCl^GaCl^ (Gol'dshtein, 1973, Hamada, 1973), TeCl^SbCl^

(Morishita, 1974, and Beattie, I9 6 7), TeCl^AsF^ (Beattie,

1 9 6 7), TeCl^PCl^ (Beattie, I9 6 7), TeCl^AlCl^ (Beattie, I9 6 7),

and TeCl^ (Beattie, I9 6 7), as well as for a solution of

TeCl^SbCl^ in nitromethané (Gerding and Stuftens, I9 6 9), Infra-red spectra and dipole moments have been recorded for TeCl^AlBr^, TeCl^GaBr^ and TeCl^GaCl^ (Gol'dshtein, 1973 & 197.2), tellurium tetrachloride acting as a Cl" donor to the Lewis 215

acid. The Raman spectrum of liquid TeCl^AlCl^ (Gerding and Houtgraaf, 1954) has also been recorded, as well as quantitative polarization measurements on this and the solid state spectrum (The solid consisting of a cooled melt) (Gerding and Houtgraaf, 1954). The specific conductivities of melts of TeCl^TaCl^ and TeCl^NbCl^ and the Raman shifts of the melts at 230°G have been measured (Poulsen and Berg,

1 9 78). Conductimetric studies of TeCl^/group VA chloride melts (TeCl^-AsCl^, TeCl^-BCl^, TeCl^-PCl^ and TeCl^-POCl^) have also been undertaken (Konov, 1974); along with conductimetric studies of solutions of TeCl^SO^, TeCl^BCl^,

TeCl^SbCl^, TeCl^PCl^ and TeCl^AlCl^ in benzene (Paul, I9 6 9).

X-ray, N.Q.R. and Raman data (Beattie, I967 ; Gerding, 1970; Okuda, 1975; Krebs, 1971; Gol'dshtein, 1972) have allowed the crystal structures of TeCl^AlCl^ and TeBr^AlBr^ to be investigated; and have shown them to consist of pyramidal MX^ ions and tetrahedral AIX^ ions, which also seems to persist in the molten state. An X-ray study (Krebs, 1973) has shown TeCl^PCl^ to contain tetrahedral PCl^ and polymeric (TeCl^) - chains with octahedrally coordinated Te(IV). For the MCl^SbCl^ compounds (M=S, Se, Te), two alternative

structures have been suggested (Beattie, I9 6 7). For sulphur an ionic description SCl^SbCl^ proved adequate, whereas a neutral binuclear chlorine-bridged structure was claimed for the selenium and tellurium compounds (Morishita, 1974). The TeCl^ /TlCl^was formulated as the ionic complex TeCl^TlCl^

(Malhotra, 1977).

Apart-’from the N.Q.R. study of the tellurium 216 tetrabromide/alurainiura tribromide complex (Okuda, 1975), there appears to have been very little work done on the bromine analogues of the tetrachloride complexes previously mentioned.

The original intention of the present work was to synthesise and study by Raman (and, possibly, infra-red and N.Q.R.) spectroscopy, the Lewis acid complexes of tellurium dichloride dibromide. However, since all attempts to prepare pure TeCl2 Br2 failed, an attempt was made to investigate by Raman spectroscopy, Lewis acid complexes of the parent tellurium tetrachloride and tetrabromide.

The tellurium tetrahalide/Lewis acid complex syntheses attempted were those of TeBr^AlBr^, TeBr^AlCl^, TeBr^SbBr^ and TeBr^SbCl^; there being no report in the literature of the Raman spectrum of any of these complexes.

Also attempted were the syntheses of the chlorine analogues TeClÂlBr^, TeClÂlCl^, and TeCl^SbCl^. The Raman spectra of TeClÂlCl^ (Gerding and Houtgraaf, 1954) and

TeClySbCl^ (Beattie et al., I9 6 7) have been previously reported, but that of TeCl^AlBr^ is unknown. These syntheses were carried out in an effort to ascertain the usefulness of the synthetic routes. 217

13). EXPERIMENTAL SECTION

Initially, the synthesis of tellurium dichloride dibromide from the tetrachloride and

tetrabromide was attempted (I.R. Beattie et al. 1974). A pure product of the mixed halide could not be isolated (possibly due to the impurity of the starting materials, which decomposed on attempts to purify them).

The synthesis and investigation of the Lewis acid complexes of tellurium tetrachloride and tetrabromide was, in the main, unsuccessful. Hence, most of the section on tellurium compounds is concerned with experimental procedures and the results of these.

As the sequence of reactions carried out, in order to synthesise a required product, depends on the outcome of previous reactions, the analysis results are given in this section. To simplify the description of the experimental procedure, this section has been divided into subsections according to the compound being discussed.

13 a). Tellurium tetrachloride (TeCl^)

Tellurium tetrachloride was produced,(as M previously described by Brauer, 1965) from the elements

by heating tellurium powder at 3 90^C in a current of dry chlorine, when white tellurium tetrachloride distilled over. Most of the tellurium, however, remained unreacted

(Yield = l i f e , Cl, 48.7#. Calc for TeCl^ i Cl, 52.6#). 218

A second method of synthesis was attempted, to try and increase this low yield. Dry chlorine (Mattheson) was bubbled into a slurry of tellurium in dry carbon tetrachloride. The much improved yield (85#) of white product was then filtered off in an atmosphere of dry nitrogen, using a thoroughly dried closed filtration apparatus. All transference operations were carried out in a dry box, owing to the marked water sensitivity of the product.

Volhard titrations (Vogel, i9 6 0) of the products obtained using this method gave results for percentage chloride varying from 48.?# to 51.2# (Calc, value 5 2 .6#). The low values presumably resulted from the presence of metallic tellurium. A Raman spectrum of the impure product (Results section) closely corresponds to the literature tellurium tetrachloride spectrum.(Hayward and Hendra, I9 6 7).

The product was purified using a vacuum distillation apparatus. In all cases a black solid fraction was collected. This was followed in one case by a white crystalline substance (TeCl^), leaving a light brown residue. The black material was possibly a decomposition product such as tellurium oxychloride, M (Brauer, I9 6 5), and gave no Raman spectrum. Insufficient white solid for analysis was obtained, but the characteristic

TeCl^ Raman spectrum (Hayward and Hendra, I9 6 7) was observed

(Results section). This sample was later used in a synthesis of tellurium dichloride dibromide. 219

A recrystallisation of the crude tetrachloride from dry toluene was attempted (Brader, 1965). However, it was found necessary to reduce the volume of the solution under reduced pressure, when a dark brown solid was precipitated.

In further syntheses employing tellurium tetrachloride it was therefore found necessary to use the crude product ( of known purity) and to attempt to purify the final, desired product.

13 b). Tellurium tetrabromide (TeBrj^) Tellurium tetrabromide was produced from the elements by condensing bromine vapour onto tellurium n powder (Brauer, I9 6 5). The product was sublimed over at 0 .3 5 mm Hg and ?6^C. Most of the tellurium remained unreacted (Yield = 15#, Br, 6 7.3#, Calc, for TeBr^ :

Br, 7 1.5#).

A similar method to that used for TeCl^ was employed by passing dry bromine vapour in a current of nitrogen into a slurry of tellurium powder in dry carbon tetrachloride. The slurry was occasionally warmed during the reaction time of several hours to ensure reaction. The yellow solid (Yield = 81#. Br, 66.2#, Calc, for

TeBr^, Br, 71.5#) was filtered and collected in an atmosphere of dry nitrogen. The deficit of bromine is ascribed to the presence of unreacted tellurium. A Raman spectrum of the product (Results section) compares well with the literature sprectrum of tellurium tetrabromide. 220

(Hayward and Hendra, I9 6 7).

Sublimation of the product under reduced n pressure (Brauer, I9 6 5), yielded firstly a black solid fraction, followed by an orange, then a yellow solid, leaving a buff residue. In one such sublimation, the yellow fraction was isolated, powdered and used for the

synthesis of TeCl2 Br2 . It displayed the Raman spectrum characteristic of TeBr^ (Results section), whereas the black solid gave no observable spectrum and was possibly tellurium oxybromide.

Recrystallisation of the crude product from

glacial acetic acid in acetic anhydride (50# by volume)

ft (Brauer, I9 6 5) yielded no crystals. On reduction of the volume of the solution under reduced pressure, a brown solid was obtained.

Therefore, in further syntheses employing tellurium tetrabromide the impure product (of known purity) was used.

13 c)- Tellurium dichloride dibromide (TeCl2 Br2 ) Tellurium dichloride dibromide was produced in this study from the tetrachloride and the tetrabromide, Aynsley formed this compound from tellurium dichloride as a precursor (Aynsley, 1953), but it has been reported that it could not exist as a stable crystalline compound under normal conditions (Rabenau, 1973 and Christensen,

1 9 7 3). 221

Using Beattie's method (I.R. Beattie et al,

1 9 7 4), equimolar quantities of tetrachloride and tetrabromide were mixed and heated to 3 0 0°C for up to one hour in either l).a one-atmosphere vessel or 2). a sealed glass tube. At approximately 90^C in the one- atmosphere vessel, and below 200°C in the sealed tube, a black solid sublimed off leaving a yellow and buff solid as residue. By 300°C all the solid in both types of vessel had sublimed. On cooling, a black/yellow solid condensed (Yield 9I#). No Raman spectrum of this product could be recorded, either due to photodecomposition, or due to the black solid acting as a mirror for the laser beam.

The analyses were as follows 1- One-atraosphere tube Cl, 16.2#, Br 40.?#, CliBr = 1:1.12

Sealed tube Cl, I9.3#, Br 48.4#, CliBr = 1:1.11

(Calc, for TeCl2 Br2 : Cl,19.8#, Br 44.6#, Cl:Br = 1:1).

Equimolar quantities of resublimed TeCl^ and

TeBr^ were heated to 300°C in a sealed Raman tube. The Raman spectra of the mixture before heating, and the yellow residue remaining after sublimation of the black fraction are given in the Results section. Insufficient product was collected to enable a percentage halide determination. , The black fraction gave no Raman spectrum.

Sublimation under reduced pressure of the products obtained in these experiments yielded a large quantity of black solid, a small yellow fraction and a buff residue. 222

Samples of 1). TeCl^, 2). TeBr^ sind 3). a

111 mixture of these, were investigated between 25 ^C and 3 00°C using a differential scanning calorimeter to determine if any reaction took place between the tetrahalides. Unfortunately, the volatile black fraction ruptured the sealed sample pans, well below 200°C.

13cl). Tellurium dichloride dibromide/aluminium trichloride

complex (TeClgBrg/AlCl^)

It would appear that Beattie's method of

TeCl2 Br2 synthesis (Beattie, 19?4) was, to some extent, successful, yielding an impure dichloride dibromide product. From the Raman spectrum of the solid product (see Results section), it can be seen that the Te-Br and Te-Cl vibrations occur at higher wavenumbers than in the tetrachloride and tetrabromide, and the recorded spectrum agrees well with that reported by Van der Voet and Ozin (Ozin and Van der Voet, 1971).

The impure tellurium dichloride-dibromide product (l.lOg) was stirred with aluminium trichloride (0.44g) in dry dichloromethane (5cm^) for three hours. The resulting pale yellow solid was filtered under dry nitrogen, analysed and gave the Raman spectrum shown (Fig.l4c2.) (Yield = 58#; Cl, 33.3#; Br, 34.1#% Calc for TeBr2 Cl2 /AlCl^; Cl, 36.1#; Br, 32.5#). The experiment was repeated, gently warming the mixture and 223 stirring for one day and then with excess AlCl^ for eight days,a reaction occurring to give a solid product

(Yield = 51#; Cl, 2 9 .5#; Br, 4o.6#t Calc for TeBr2 Cl2 /

AlCl^j Cl, 3 6.1#; Br, 3 2 .5#) (See Results suid Discussion section).

TeBr^AlCl^,TeBr^SbBr^,TeBr^SbCl^)

13 el- Tellurium tetrabromide/aluminium tribromide complex (TeBr^AlBr^)

(i) In Carbon Tetrachloride

Te + 2 Br2 + AlBr^ = TeBr^ AlBr^

Stoichiometric quantities of aluminium tribromide, elemental bromine and tellurium (powder) were mixed in dry carbon tetrachloride. No reaction was discernible and so a three-fold excess of bromine was added.

An orange/buff solid (yield = 65#, Br, by Volhard,IO3 .O#) was collected, and the Raman spectrum of this product was recorded (Results section).

In order to find an explanation for this high bromine analysis the silver nitrate solution was standardised against sodium chloride (the Mohr titration) (Vogel, I96O) and the thiocyanate solution against the silver nitrate. The solutions proved to be accurately O.IM. A second analysis of the product gave Br,103*5# (Calc, for TeBr^AlBr^i Br, 78.3#). The complex was synthesised twice more in dry carbon tetrachloride, and the Raman spectrum of 224

one of these products can be seen in the Results section. Now Raman bands are clearly visible near 340 cm and suggest the presence of Te-Cl bonds in the sample. These peaks are of low intensity and had been overlooked in the spectrum of the first product. A second Raman spectrum showed them to be present.

Potentiometric titrations were therefore performed on the original complex and gave Cl, 24.3#;

Br, 4 7.5#; Br 1 Cl = I1I.I5 (Calc for TeBr^AlBr^ t

Cl, 0#; Br, 7 8.3#) with the second end-point of the titration occurring at the correct potential for chloride ions. Potentiometric titration on two samples of the second synthesis product gave Cl, 24.3#; Br, 47.5#;

BrxCl = 1 I 1 .1 5 .

Silver nitrate showed no chloride ions present in the carbon tetrachloride, distilled water, molecular sieve, or aluminium tribromide (Vogel, 1954). A potentiometric titration of a hydrolysed sample of the aluminium tribromide gave the correct percentage of Br.

A synthesis of the complex was carried out in carbon tetrachloride freshly dried with molecular sieve. A further synthesis employed bromine dried over PgO^.

Analysis of this last product gave Cl, 2 3 .6#; Br 47.1#;

Bri Cl = 111. 13 (Calc, for TeBr^AlBr^ 1 C1,0#; Br, 78,3#).

No crystals were obtained on attempted 225

recrystallisation from dichloromethane, reduction of the volume of the solution yielding a small amount of yellow/ black solid. The Raman spectrum was recorded, but the product burned in the laser beam (64?.Inm) (Results section)

It was surmised that the chlorine in the complex could only originate from the carbon tetrachloride.

Hence the possibility of halide exchange between CCl^ and

AlBr^ must be considered

3CC1^ + AlBr^ = jCBrClj + AlCl^

This would explain the absence of AlBr^ bands in the Raman spectra, no aluminium tribromide remaining to react with the tellurium tetrabromide.

(ii) In Carbon Disulohide

Stoichiometric quantities of tellurium powder, bromine and aluminium tribromide were mixed in dry carbon disulphide. The Raman spectrum of the resulting orange powder (Yield = 7 3 > 5 % » Br, by Volhard, 71.8^. Calc, for

TeAlBry: Br, 78.3^) can be found in the Results section.

The low percentage bromine is presumably due .to the presence of unreacted tellurium. A second synthesis of the complex in CSg gave Br, 73.0%, and the Raman spectrum shown

(Results section).

An insoluble fraction (Yield = 91%; Br, 67.2%. Calc, for TeAlBry* Br, 7^-3%) was collected on recrystallisation of the product from freshly purified

CSg, and a dark orange/yellow solid (Yield = 9%, Br,59.9%) which fumed on exposure to air, was obtained on removal of 226

the solvent.

A recrystallisation from hot dichlororaethane

yielded an insoluble orange powder (Yield = 85%; Br, 6 9.0%. Calc, for TeAlBr^i Br, 78.3%), and yellow crystals. (Yield = 5%i Br, 6.0%).

It appeared that the use of carbon disulphide as a reaction medium was not leading to the formation of TeAlBry in a pure form. This could well have been due

to decomposition of the CS2 to form reactive sulphur species during the reaction, and recrystallisation.

(iii) In Benzene/Cvclohexane

This method was used by Gol'dshtein (Gol'dshtein et al, 1973) to produce the tellurium tetrachloride/aluminium tribromide complex. A dry cyclohexane solution of AlBr- was added to a dry benzene j * solution of an equiraolar amount of TeBr^^. The Raman spectrum of the green precipitate (Yield 52%) was recorded (Results section), although it burned badly in the laser beam (647.1 nm).

A second dark yellow product (Yield 30%) was recrystallised from dichlororaethane, yielding a product

(Raman spectrum in Results section) with Br = 7 6.8%

(Calc, for TeAlBry i Br, 78.3%)«

13 f). Tellurium omide/aluminium_trichIpride _como 1 ex (TeBr^AlCl^)'

Te + 2 BT 2 AlClj = TeBr^. AlCl^ 227

Stoichiometric quantities of tellurium powder, aluminium trichloride and bromine were mixed in dry carbon tetrachloride. A yellow product was obtained I Yield = 79%: Br, 65.4%; Cl, 0.0%, Calc, for TeBr^AlCl^. Br, 55.1%: Cl, 18.3%). (See Results section for Raman spectrum;.

13 g ). Tellurium tetrabromide/antimony oentabromide complex

(TeBr^.SbBr^)

3Br2 + Te + SbBr^ = TeBr^.SbBr^

Antimony tribromide was recrystallised from dry toluene (D.D. Perrin, I9 6 6) and mixed with stoichiometric quantities of tellurium and bromine in dry dichlororaethane. The Raman spectrum of the yellow precipitate (Yield = 80%; Br, 64.6%. Calc, for TeBr^.SbBr^i Br, 74.2%) shows it to be tellurium tetrabromide. (See Results section). (Hayward and Rendra, I9 6 7).

^13 h). Tellurium tetrabromide/antimonv oentachloride complex (TeBr^.SbCl^)

Te + 2 Br2 = TeBr^^ TeBr^^ + SbClj = TeBr^.SbCl^

Stoichiometric quantities of tellurium powder and bromine were mixed in dry dichloromethane followed by an equimolar quantity of antimony pentachloride. The Raman spectrum of the resulting green solid (Yield 43%; Br, 27.3%;

Cl, 2 5 .2 %. Calc, for TeBr^SbCl^: Br, 42.8%; Cl, 23-8%) resembles that of tellurium dichloride dibromide (Ozin and Van der Voet, 1971), despite the low Bri Cl ratio found of 228

1 I 2.1. Evaporation of the dichloromethane yielded a solid (Br, 1.9%; Cl, 38.6%; BriCl = 1:46) high in chlorine. Due to the low bromine and high chlorine content of the product, bromine was added after the Lewis acid in a second synthesis. Again a green solid

(Br, 29.7%; Cl, 24.9%; B n Cl = 1 i I.8 9. Calc, for

TeBr^SbCl^; Br, 42.8%; Cl, 2 3 .8%) was filtered off and the filtrate yielded a yellow solid (Br, 2.7%; Cl, 44.8%; B n Cl = 1 I 3^.8) on evaporation. Liquid nitrogen was used as desiccant on handling the extremely moisture-sensitive product.

From the low bromine content of the products and the absence of SbCl^ bands in their Raman spectra

(337cm 277 cm"}v^; 172 cm }\^). (See Results Section), it would seem that chlorination of the tellurium by antimony pentachloride has occurred, to form a tellurium mixed halide.

Tellurium tetrachloride complexes(TeCl^ AlBr^, TeCl^ AlCl^ and TeCl^ SbCl^ )

More literature exists on the vibrational spectra of tellurium tetrachloride/Lewis acid complexes than on the corresponding tetrabromide complexes. (PCl^/TeClji^ - Ozin and Van der Voet, 1972; TeCl^ AlBr^,TeCl^ Ga Br^, TeCl^ GaCl^ - I.P.Gol'dshtein et al, 1973; TeCl^.AlCl^ - Gerding and Houtgraaf,1954;

TeCl^AsF^, TeCl^SbCl^ - Beattie and Chud z. ynska, I9 67 ; TeCl^AlCl^ (NQR) - T. Okuda et al., 1975; TeCl^NbCl^, 229

TeCl^TaCl^ - Poulsen & Berg, 1978; TeCl^AlCl^ (X - ray)- Krebbs; TeCl^SbCl^ (NQR) - Morishita; TeCl^. SO^ - Gerding et al., 1970; TeCl^SbCl^ - Gerding & Stuftuns,

1 9 6 9; as compared with TeBr^AlBr^ (NQR) - T. Okuda, et al., 1 9 7 5).

13 j )' Tellurium tetrachloride/aluminium tribromide complex (TeCl^AlBr-) —— ■■ ■■ I ■■ On addition of a dry cyclohexane solution of aluminium tribromide to a dry benzene solution of the tetrachloride (the Gol'dshtein synthesis), a white suspension was formed, turning to grey with time. The Raman spectrum (Results section) of the grey solid (Yield = 59%) was recorded.

On using a sealed reaction vessel, a dark green powder (Yield = 42%; Cl, 16.5%; Br, 50«3%* Calc, for TeCl^AlBr^; Cl, 2 6 .5%; Br, 44.7%) was deposited, and the Raman spectrum of this product agreed closely with that of the first. There was a surfeit of bromine and a deficit of chlorine in the product (Cl; Br

= 1 I 1 .3 5 . Calc, for TeCl^AlBr^; Cl; Br. = 1 ; 0.75).

13 k)- Tellurium tetrachloride/aluminium trichloride complex (TeCl^. AlCl^)

TeCl^ + AlClj = TeCl^. AlCl^

Stoichiometric quantities of TeCl^ and AlCl^ were mixed in dry carbon tetrachloride to yield a white precipitate (Yield = 66%), which decomposed in 230 the laser beam. A cold cell was used but no Raman spectrum could be recorded, even at liquid nitrogen temperature. (Cl, 55«7%* Calc, for TeCl^AlCl^; Cl, 61.6%).

13 D* Tellurium tetrachloride/antimony pentachloride complex. (TeCl^SbCl^)

Tellurium tetrachloride and antimony pentachloride (approximately 1 cm^ excess) were mixed in dry dichloromethane. The Raman spectrum of the pale yellow precipitate (Yield = 98%) can be seen in the Results section. (Cl, 57.1%* Calc, for TeCl^/

SbCl^î Cl, 56.1%) 231

14. RESULTS AND DISCUSSION SECTION^

14.a) Tellurium tetrabromide (TeBr^) and Tellurium tetrachloride (TeCl^).

Raman Spectra. The Raman spectra of the solid tetrahalides can be seen in Table 14 al). The structure of the tetrahalides of the elements of group VI B was, at least \ until 1966, a subject of considerable controversy. If the lone pair on the central chalcogen atom is stereochemically active, valency theory predicts a trigonal bipyramidal arrangement of the bonding pairs and lone pair, with the lone pair in an equatorial position. The result would be a molecule of Q,2\/ symmetry X .X O T e : I X with ten valence electrons, and two pairs of equivalent axial and equatorial halogen atoms. Electron diffraction suggests this to be so for the tellurium tetrahalides in the vapour state. A molecule of this symmetry would exhibit nine Raman active modes;

4Aj^ + 2 B2 + 2 B - ^ + A2 '

However, compounds which are monomeric in the vapour can rearrange into ion aggregates on condensation as solids.

As recorded by Hayward and Hendra (I9 6 7), 232

TABLE 14 a 1)

Raman Spectra of the solid tellurium tetrahalides

TeCl, TeBr, -1 -1 -1 This work (cm~^) Hayward (cm"^)This work(cm '^) Havwardfcm /) & Hendra(19671 & Hendra(1967)

376s 376s 246s 2 5 0 s 0^ A^

351s 351s 2 31 s 227 s 2 26 SIO33 E 344 s 343s 222s 220sJ

133vw 133v w V>2 A]_

153* 150w 125 vw 1 2 5 y y j i ^ E 106vw 233

Fig. I4al). Raman Spectrum of Solid TeCl^

Lit SpectrumCcm ) 376

vO 351 3 % 150

m LO

O o O o vO Osl s s; m m m

WAVENUHBER (cm”^) 2j4

Fig. I4a2). Raman Spectrum of solid TeGl;^ (White sublimation nroduct).

unG m rr

o o C5 O O s m LTI rn m m m m CNI

WAVENUMBER (cm"^). 235

Pig. I4a3). Raman Spectrum of solid TeCl;^ (Yellow sublimation

p r o d u c t ) .

’E

os m

o CD o O o o CD OsO o mCNI m CM oo _ 1 V/AVEMUiuSER (cm ^). 2]6

Fie. I4a4). Raman Spectrum of solid TeBr,j.

100

Csl

v O

o o O 8

Fie. I4a5). Raman Spectra of the TeBr^ solid sublimation

fractions.

100

f r a c t i o n

6 0-’.

w un n.

o CNI 8 s s g s CNI 0 rn CnI CNI ^ L_ T L_n_ - 238

the Raman spectra of the tetrahalides show a close similarity to the spectra of the group VB trihalides An anionic structure containing cations (X = Br or Cl) of symmetry and halide anions has been suggested:

+ X“ Te

An isolated molecule of this type should show four Raman active vibrational modes :- 2 A^ + 2E.

The experimental Raman spectra of the tetrahalides reported here correspond closely with those

of Hayward and Hendra (I9 6 7).

According to these authors neither of the two suggested structures and 0^^ ) are consistent with the number of stretching modes observed in the

Raman spectra (occurring in the 3OO - 400 cm. ^ range

for TeCl^ and in the 200 - '}QQ cm ^ range for TeBr^). The structure should yield four bands corresponding to the chalcogen - halogen stretching vibrations in the Raman spectrum, and the ionic structure should give only two. In this study of tellurium tetrabromide, four stretching frequencies are observed at 246, 2 3 1 , 227 and 222 cra”^, whereas Hay/zard and Hendra reported three at 250, 226, 220 cm ^. In this study 239

of tellurium tetrachloride three stretching frequencies

are seen (3 7 6, 351 and 3^4 cm which agrees closely

with Hayward's spectrum (3 7 6, 351» 3^3 cra”^).

A possible explanation of the number of bands observed is that the degenerate modes of the pyramidal TeX^^ ion are split by the crystal symmetry A structure similar to that of trimethylselenoniura iodide has been suggested.

Halogen atoms 1 and 2 and the lone pair of the chalcogen atom occupy equatorial positions of a trigonal bipyramidal arrangement, while halogen atom

3 and the halide ion 4 occupy the axial positions, with a charge-transfer interaction between the halide-ion donor and the chalcogen acceptor atom of the cation. The chalcogen atom is bonded to three electron - withdrawing halogen atoms and should be a strong acceptor The tv/o equatorial halogen atoms would be expected to be slightly closer to the tellurium atom than the axial halogen 3 . This leads to a reduction of the symmetry,

from to C2 » causing the previously degenerate vibrations to be solit in two; the splitting of the 240 antisymmetric stretching frequency ( would thus give rise to the lower-frequency Raman doublet.

The Raman (and infra-red) active modes of vibration of a species are shown belowi-

O ^ A E )

For the majority of the pyramidal MX^ species the symmetric stretching and deformation modes lie at higher frequencies than the corresponding antisymmetric modes. The bands at 345 a.nd 145 cm ^ in the infra-red spectrum of tellurium tetrachloride have been assigned to the degenerate E modes, on the basis of depolarisation ratios in the Raman spectrum of the liquid.

The Te^Cl^^ molecular unit in the tellurium tetrachloride crystal has been shown, by X-ray crystallography, to have a two-fold symmetry axis passing vertically through the unit cell (B.Buss & B. Krebs,I97O).

A o- I . 2-9A) 1 - --p I y 6A------C) 241

On the basis of the reasonable assumption of a similar crystal symmetry for the tetrabromide (Cordes et al, 1964), assignment of the observed Raman bands to the ionic structure is given in Table 14 a 1).

The analysis results (Experimental Section) show a deficit of halogen in the tetrahalides, presumably due to the presence of unreacted tellurium.

14.b) Tellurium dichloride dibromide (TeCl2 Br2 )

Raman Spectrum

A molecular system such as tellurium dichloride dibromide containing ten valence electrons is stereochemically interesting. Katsaros and George

(1 9 6 9) made an infra-red study of the solid and of solutions in benzene and in dimethylformamide, which suggested a TeClBr2 ^ Cl ionic structure in the crystal.

The first report of a gas phase Raman spectrum of the dichloride dibromide was by Ozin and Van der Voet (1971,704). Their gas and solution phase data favoured the structure Br .Cl

All Raman bands were polarised and the four 242 polarised Raman active stretching modes observed corresponded closely in frequency with those expected for equatorial and axial Te -Cl stretching modes

(3 7 0, 285 cm”^) and equatorial and axial TeBr stretching modes (242, I98 cm . The spectra obtained could also be explained on the basis of a distorted trigonal bipyramid with a vacant equatorial position.

I__ Cl Br Te: Cl Br

However, a later report by Beattie et al

(1 9 7 4) suggests that it is unlikely for TeCl2 Br2 to be the only component present under the somewhat extreme conditions necessary for a gas phase Raman spectrum

(3 1 0‘^C). A mixture of the configurations,

Cl Br Br ,Br .Cl Cl Te 'Br Cl Br Cl Br Cl

(C2v) (C2v) (C^) A. B. C. where the relative amounts of each depend on the solid structure, could also explain the data.

The Raman data for TeCl2 Br2 parallel that 243 for the tetrachloride and shows the structure in the solid state differs from that in the vapour and in solution, in which a molecular form, as shown above, is probable. Assuming .therefore the solid structure of the dichloride dibromide to be similar to that of

TeCl^, a hypothetical cubic unit csf TeCl2 Br2 could be drawn, with either a chlorine or bromine atom at the end of the "long" bond. (G.A. Ozin & A. Van der Voet

1971, 397).

Neglecting the possibility of distortion and rearrangement, the structure of the vapour molecule will depend on which tellurium atom remains bonded to the bridging halogen atom on vaporisation. From normal coordinate analyses of the three molecular structures A,B, and C, Ozin and Van der Voet (I97I) ascribed the Raman spectrum of gaseous TeCl2 Br2 to a mixture of configurations A and B.

As reported by Katsaros and George CI9 6 9;, the infrared absorptions of solid tellurium dichloride dibromide correspond to one Te - Cl stretching mode (340 cra“^ (vs)) and two Te - Br modes (247 (vs) and

230 cm~^(vs)). Two other absorptions, perhaps due to bending modes, are also present (l46(s) and 131cm ^(s)) The suggested stretching frequencies are therefore in agreement with those predicted for a pyramidal TeClBr^ ion of Cq symmetry. 244

Fie. l4bl). The Structure of a Cubic Unit of TeCl^Bro.

Br T,

— Br

B r Te

cu_^

Br Br

Br- - T é — Tl "Te -Cl

Ci / 2k s

s )^ (a'i) ) VgtA') Os (A' ) 0 ^ (a') 0 ^(a")

O3 (xz) ig(YXZ) Jg(XY) 0 ^ 3 (XY) SgfYXY) S^^(YXZ) i.e., the degenerate vibrations of the group are split into two bands, to give six vibrations observable in both the Raman and infra-red spectrum. The relationship between C^.. and C is shown below jV s

(XYj) 0 ^ (A^) VgCA,) O3 (E) (E)

Os (XY) gg(YXY) Vj(XY) (YXY)

Cg (ZXYg) Oj_ ’(A' ) O3 '(A' ) ^(A' ) 0^(a" ) N)^(A' ) 0^(a" ) Og (XZ) &g(YXZ) Og(XY) Og(XY) Sg(YXY) S^g(YXZ)

Presumably the degenerate vibrational modes of the pyramidal Z X Y ^ ion are split, as in TeX^, due to the charge-transfer interaction of the halide-ion donor (either Br or Cl ) and the chalcogen acceptor atom of the cation.

As can be seen from Table 14 b 1), there is good agreement between the Raman spectrum recorded in this study and that of Ozin and Van der Voet (I9 7I) for TeCl2 Br2 . The analysis results, however, show a slight deficit of chlorine and surfeit of bromine in the product, possibly due to the presence of some unreacted tetrabromide.

14c. Tellurium dichloride dibromide/aluminium trichloride complex (TeCl23r2 / AlCl^). 2k 6

Table 14 b 1)

Raman spectrum of solid tellurium dichloride dibromide

TeClgBrgfs) TeCl^(s) TeBr^ (3) TeCl2Br2 (Iliia_wark) (This work) (This work) (Ozin & Van der Voet.1971)

376 3

351 3 357 mwsh O3E 340 w 343 3 338 s

249 3 250 3 A A 242 vs 235 msh 233 sh

228 s 226 3 226 mwsh S a E 220 s

158 w

15OW 148 w

136 w 132 w

109 w

77 s 74 s

52 6 ■51 s 247

Fi#. l4b2). Raman Spectrum of solid TeCl^Br^ prepared at One Atmosphere.

ifr--

o o o O o o o O O CN CO vO) CM 8 CO vO m m CNJ (N / _i WAVENUMBER (cm“^) 24e

Fig. I4b3). Raman Spectrum of TeCl^Br^ (Sealed Tube)

o o O o o <0 o> m o m i_n m rn _ _rSj CV| WAVENUMBER(cm" 24?

Fig. I4b4). Raman Spectrum of the 1:1 TeCl^/TeBr^ mixture used in TeCl^Br^ synthesis. (Raman-tube Experiment)

100

U*l

o o O O OJ 8 GO ki m 0 4 WAVENUM32R (cm"^) 250

Fig. I4b5). Raman Spectrum of the TeGIoBr^ Product of the Raman-Tube Experiment.

O s o> R LO P o m m m C\l OJ i_n WAYENUMBSR (cra“^). 251

Raman Spectra The Raman spectrum of the starting material is that of tellurium dichloride dibromide, (See previous discussion section). It can be seen that the solid state spectra are similar for both the one-day and eight-day reactions, indicating the completion of reaction. The lack of a strong band at 506 cm ^ indicates the absence of unreacted

Al2 Cl^ in the products. The AlCl^Br^_^^ (x = 0 to 4) Raman spectra were recorded by Bradley, Brier and Jones, using the tétraméthylammonium salts. It is possible that the Raman bands observed at 263 and 256 cm ^ may be due to the mixed bromochloroaluminate vibrations at 308 cm ^ and 2?8 cm ^ respectively, shifted to lower frequency in the tellurium dichloride dibromide complex.

The presence of a Raman band at 3IO cm"^ in the product for the three hour reaction implies the presence of either AlCl^Br” or AlCl2 Br2 . The absence of a strong band at 24? cra”^ suggests the former, whereas the absence of the TeCl2 Br2 vibration at 226 cm”^ suggests that h a l o g e n exchange has occurred around the chalcogen atom.

The later products (one and eight days) also display strong Raman bands at 263 and 257cm ^

(as well as TeCl2 Br2 bands at 24?, 233 226 cm ^). 252 tn > fi > m s vr\0 owo CsJ O M •H C ^ CVJ

m u > > > > fi 03 03 ,0 w GONAOCM GOGO A- cj- On GO CM 0 VA 0 A - r—1 r^iH en en CM CM CM 1-4 I—I

f i 03 03 GO 0 0 CM GO GO o- g . GO 0 VA 0 CN- -=}■ r 4 CNi en en CM CM CM

03 k , a OQ fi ,Û GO 0 CM 00 00 e n vn 00 VA 0 A - 00 CM m en CM CM r—I

03 03 fi 0 0 CM GO VA GO CM 03 en r - i I—I cd NO co N O N O 00 O CN- GO o o en zj- iH NO NO CM NO NA CM I— J I— I I—1 O rH I—I 4 03

03 03 03 03 41 NO M [N- CM mu-\\o r - f C ^C M CM en CM o O CM CM CM CM i-H I—I 1-4 EH0>

03 w 03 S 03 o Cn- Cn-C^nO vn c n ^ e n CM en £ m CM CM CM -H ü03 enO 03 03 03 5 c NO r H c J- en (t3 O- VA fi r ~ \ c ^ H (d K rm x : x : 1 >> 03 03 03 r-4 cd > > 03 03 03 g g 5 cd 'U A- GO CnNONQ r4 0 en 4- 3 vo MD vA_j- en CM CM rH C 00 en CM CM CM CM CM CM 1—1 0)

•H >j x : x i x : o ^ Cd 03 03 03 0) Tj 03 03 03 6 03 > 3: A 0 encN-MO CM MO CM 0 X r4 NO v A ^ en CM cnr4 w en CM CM CM CM CM 1—1 1-4 a> 03 r-l P( x03 : (d 0 > f i 03 03 ^ > Eh x : VA - j - 0 enes- cm A- MO r-4 MO VA en 0 '- en en en CM CM CM CM 253

Fig. l4cl). Raman Spectrum of Solid TeCl^Br^ Reactant

C/3

O O O CD OO oo m m m 8

WAVENUMBER(cm“^) 254

FIr . 14c2) Raman Spectrum of TeCloBro/AlCl^ Product, After Three Hours Stirring. lOO

CD CD CO S m ml m

WAVENUMBER(cm“^) 255

cv c\i o o OOL

OZL

Oil

09Z

ooe

"^■■TTOTS; TW S K T Y H I ' ,*9 ^ o o o ' " o S LO ^ m 5 ? 1 E /H 1 Ol 3 < I Q L • -♦-■» •4J o o f : 0) bC . o o. CNi t}£ K m rH w C M f H O •fH m C 0 L, • Eh 0 ti£ E -P •H oJ «M 4n -p a K o cti w < 3 : OOL OZL

091

0 8 1

(EZ

09Z 09Z

HOIS' mO o 257

There is no strong band at nor at 214 cm"^ and so the SLnion cannot be AlClBr^ or AlBr^^". The intensities of the two bands 308, 2?8 cm ^ are reversed in the AlCl^Br ion, from that observed in the two products, the higher frequency band being the stronger. Also, there is no observable scattering at 352 cm"^. The presence of AlCl^Br is not indicated and the best agreement with the experimental spectra is obtained by assuming a structure TeCl2 Br AlCl2 Br2 . V,e must then assume some chlorination of the tellurium, during reaction. This is unlikely, and the fit of the experimental Raman spectra to those of the bromochloroaluminate ions remains poor. A more likely explanation is that the complex formed is covalent in structure (as in TeCl^.AlBr^ - Gol'dshtein, 1973)• At present there are not enough data to determine this. Time did not allow for further investigation.

Tellurium Tetrabromide Complexes l4d. Tellurium tetrabromide/aluminium tribromide complex (TeBry^AlBr^)

There has been no report of the Raman spectrum of the solid 1 : 1 tellurium tetrabromide/ aluminium tribromide complex. However, analogies between this and the chloro-complex TeCl^AlCl^ can reasonably be drawn, and the NQR study by Okuda (1975) indicated an ionic structure for the complex (similar to the chlorine analogue). 258

We have (i) for a Te Br^^ species the following normal modes»-

(Siebert I9 6 6)

e Te Raman active modes = 2 k ^ + 2E OBr and (11) for a Td A1 Br^ species, the following normal modes I -

• A1 Raman active modes = A^ + E + ?2 OBr Assignments for these species are summarised in Tablei^ d 1)

The TeBr^ and AlBr^ 0 ^ vibrational modes may overlie to show only one Raman band, as in the TeCl^ AlCl^ spectrum recorded by Gerding and Houtgraaf (195^)• Also, as in the spectrum of TeCl^'*’AlCl^, the stretching frequencies of the TeBr^ ion may be increased in TeBr^^AlBr^^ (relative to tellurium tétrabromide). Thus, 0 ^ TeBr^ and V^TeBr^ will then be observed at approximately 261 cm ^ and

(2 5 5 , 2 5 1 , 2^6 cm"^)respectively. 259

1). Product from the synthesis in carbon tetrachloride

In this synthesis it is apparent that some halogen exchange with solvent occurred, yielding a product in which the Cl i Br ratio = 1.15 * 1. (See Experimental Section). The Raman spectrum is shown in Fig 14 d .1) and the wavenumbers listed in Table 14 d.l).

The Raman spectra of the starting materials, tellurium tetrabromide and aluminium tribromide, have

been given for comparative purposes. The Al2 Br^ molecule is a dimer with bromine bridges, and all assignments have been made on the basis of a planar and centrosymmetric molecule of the point group

Br Br Raman active modes =

Ag + 2 + 2 B^g + B ^

'^1 "^6 ^11 ^15 XYgtwist

\)g \)g(XY^,ip) \)y XYg wag ^ ^ 2 XY^ rock (parallel)

O 3 SfXYg^.ip) Ring def.

As can be seen, and as was expected from the analysis results (see Experimental section), there is little correspondence between the experimentally recorded 260

I-P N CVJ C I—I Cv.00 04 C^VO CO 00 04 CO •H •H Jh 'AOVJ' 0^04 O O N 0) o\ 0 ^ m 0 4 04 04 EH(D O T3 rH

N U o PP 04 04 OnU^OO SO 0--CS4 •H ro ^ 0^04 ( n Cv-VT\ O •H (\4 04 N H (D x : Eh Eh

SO U » a> V hO M PP o o rH I—I 5 > ^ rs 04 04 CO o - ctf (D x: 04 04 04 04 M rH f~l EH Eh VO p o Ü X— 0.) c n p ÎH ^- -s. tn PP 0 4 rH CO C < O O ctf E i- E O 0 4 Os 0 4 r H 0 4 ctf k w o 04 04 rH 0 4 O OsOO O- P: PP •H f-l 04 04 04 04 04 rH I—I

• c n XJ k pq 1—1 -zy fH Ü rf < O Ü 04 00 0-04 SO O S 0 ^ 0 0> E Jj- oo_2h 0^04 SO^C)- t-( to o 010^04 04 04 rH r H i H x> PP •H k ctf 0) X P» E< EH E-1 261

Pig. I4dl) Raman Spectrum of TeBr^^/AlBr^ Product

from CCl;p Solvent Preparation. First Preparation.

100

O O o o CNI

Fig;. l4d2). Raman Spectrum of Te3r;^/A13r^ Product from the

CCIjj-Solvent Preparation.

100

jCDJ N

o o o

WAVENUHBBR (cm”^) 263

Fig. I4d3). Raman Spectrum of the TeBr^j/AlBr^ Product

(CCl^ Prep.). Residue from the CH^Glp

Recrystallisation 100

(in

O o o o o

Fie. I4d4). Raman Spectrum of TeBr^/AlBr^Product (CClf, Prep.) Filtrate from CH^C1^ Recrystallisation

1--

o O

Fig. I4d5) Raman Spectrum of TeBr^^/AlBr^ Product from CSo-Solvent Preparation.

O CD CD s S O CD OO 0 m __ §1 WAVENUMBER (cra”^) 266

Fig. I4d6). Raman Spectrum of TeBr/j/AlBr^ Product from CS^-Solvent Preparation.

GO,

—r , H.

O o CD o CDo> o §1 „ M - i WAVENUMBER ( cm"-^) 267

FiK. Raman Spectrum of TeBr^/AlBr^ product(CS^ prep.) Residue from the CHpCln Recrystallisation (Parallel Polarisation)

1---

XTT O]

O o oR 8 o O oR m m c>i|__ WAVENUMBER (cra"^) 266

Fig. I4d8). Raman Spectrum of TeBr^^/AlBr^ Product, Filtered from Solvent (C^H^/C^Hj^o-Preparation)

o o o o o s o 8 m O'j WAVENUMBER(cm"^) 269

Fig;. I4d9). Raman Spectrum of 2^^ TeBr^/AlBr^ Product

(C^H^/C^Hj_2 Preparation). Filtrate, Recrystallised from CHqGIq»

o o

o 8 s 8 8 8 mL_jcnj__ WAVENUM3ER(cm”^) 270

spectrum of the product synthesised in CCl^ and that predicted for TeBr^AlBr^ (an amalgamation of the experimental spectrum of TeBr^ Br” (this study) and

the literature spectrum of AlBr^ (Brown, I9 7 0)).

From fig. I4d2). it is apparent that there are three strong'ong peaks at 342, I6 9, and 143 cra”^ in the product spectrum.

These bands cannot be assigned to either the TeBr^ (fig. I4a4) or AlBr^ (tablt l4dl) spectrum. It is suggested that chlorination of the aluminium tri bromide has taken place, resulting in the formation of aluminium trichloride.

3CCI4 + AlBr^ = 3CBrClj + AlCl^ (Encyclopaedia of Chemical Reactions? Jacobson, vol 1, 1946). (This is from an original reference to Vesper and Rollefson, J.A.C.S., ^ , 1456 (1934), where bromotri- chloromethane was prepared by treating carbon tetra chloride with aluminium bromide and this mixture was allowed to stand at room temperature for three days.)

The peak, at 342 cm”^ is most consistent with that in the Raman spectrum of Al2 Cl^ (see table l4cl). It would appear that the AlCl^ formed has not reacted with the tellurium tetrabromide reactant (See section l4e). 271

The found Cl:Br ratio of the product (1,15* 1) will depend on the reactant ratios, as the Raman spectrum indicates that no complex has been formed (in which case a stoichiometric ratio of TeBr^^AlCl^ would be found),

2 ). Product from the synthesis in carbon disulphide.

When comparing the spectrum of the product with that predicted for TeBr^ AlBr^ (Table 14 d.l) it can be seen that there is a close correspondence. There is no band at approximately 39^ cm“^ (AlBr^ vibration) in the Raman spectrum of the solid from

CS2 » and the bands at 81 cm“^ and 72 cm“^ are weak and may be lattice vibrations, although they are not observed in the spectrum of either TeBr^ or Al2 Br^.

There are no observable bands above 300 cm”^ in the Raman spectrum of the product indicating the absence of unreacted Al2 Br^.

Analysis for bromide is low, possibly due to the presence of elemental tellurium. However, the evidence seems to indicate the product to be TeBr* AlBr^, albeit impure. (Note that excess AlBr^ and bromine will remain in solution as AlBr^.Br^^. CS2 -Jacobson, "Encycl opaedia of Chem. Reactions", vol. 1, 1946).

Recrystallisation from CS2 or CH2 CI2 resulted in a reduction of the bromine content. It was surmised that reactive sulphur species formed in CS2 over reaction 272

times used (24 hours or more). These could then react with the tellurium species, interfering with the addition reaction, and lead to a low bromine content of the isolated product. A simple test for any solvent interference was to perform the same TeBr^/AlBr^ reaction in a different medium.

3) Product from the synthesis in benzene/cvclohexane

The best correlation is between the Raman spectrum of tellurium tetrabromide and that of this recrystallised product. (See Table 14 d.l). The -1 very strong AlBr^^ at 212 cm is absent from the spectrum of the product (unlike the CS^ product), indicating that it is not TeBr^ AlBr^.

The solid residue filtered from the reaction medium was significantly decomposed in the laser beam, the only observable Raman band being shifts at 250(s), 234(sh), 228(s), 222(sh) cra”^. This is consistent with the Raman spectrum of TeBr^^, although the and frequencies occur in the product at slightly higher values than in the tetrabromide, (Table 14 a.l). No band at 212 cm was recorded, indicating the absence of AlBr^ in the product.

The solid contained too little bromine to be the desired product (7 6.8^1 calc, for TeBr^^AlBr^ ;

7 8.3^). The high percentage bromine as compared with 273

that calculated for TeBr^ (7 1.5^) may be due to the presence of a small quantity of unreacted Al2 Br^.

14. e Tellurium tetrabromid^al,umlnium trichlp j j ^ complex (TeBr/j/AlCl^)

As with TeCl^.AlBr^, a number of structures for the solid may be suggested, e.g. in ionic forms such as TeSr^ AlCl^Br or in molecular complexes such as TeBr^.AlCl^. However, the analysis result of

6 5.4 % bromine and 0 % chlorine together with the product spectrum (Table 14 e. 1), indicates that the product is tellurium tetrabromide with a deficit of bromine (Calc, for TeBr^; Br, 71*5^)» probably due to the presence of unreacted, elemental tellurium (from the impure TeBr^ reactant).

14.f Reaction of tellurium with antimony tribromide and bromine (TeBr^ySbBr,) , ■■■■■.■- ■■■■r ■ — rrr-r=r.i-=. There is no previous result for the complex TeBr^^ SbBr^ and the above reaction (see Experimental Section for details) yielded a product which was confirmed as TeBr^ by the Raman spectrum, although the bromine analysis was low due to the presence of unreacted tellurium (64.6^1 Calc, for

TeBr^^SbBr^"; Br, 7 k . 2 ^ i t Calc, for TeBr^; Br, 7I.5?;).

The Raman spectrum of the starting material SbBr^ (C^y) is shown in Table 14 f.l). The molecule exhibits four Raman active vibrational modes (2A^ + 2E). (see section 14 d, *5b o Br). 274

Table 14 e.l)

Raman spectrum of TeBr^/AlCl^ reaction product

TeBr^, AlCl^ product TeBr^ (This work)______(This work)

244 s 246 O j A

230 s sh 231

223 s 227 O3E

222

128 w 133

120 w 125 ; i 103 w 106 !

74 m

52 w sh 46 m 275

Fig. l4el). Raman Spectrum of Solid TeBr^/AlCl^ Product

100

rs i LD

wl m

o o o o CD o CNI s Ln m

WAVENUMBER(cm"^) 276

Table 14 f. 1)

Raman spectrum of the TeBr^/SbBr^ reaction product

TeBr^SbBr^ product TeBr^^ SbBr^

(This work) (This work) (Evans. I960)

247 m 246 s 242 Vj

232 w sh 231 s

225 w 227 s

222 s

205 0 ^

133 vw

125 VH 125 v^

106 VW 105 ^ 2 86 0%, 277

FiR. Raman Spectrum of TeBr^/SbBr^/Br^ Product

a snail p e a l : a t 125

o o o o o v£> o s m m

WAVENUMBER(cra”^) 276

The SbBr^ anion would exhibit octahedral symmetry (0^) and, as with the chloro-analogue, three Raman active vibrations should be observed. The stretching frequencies of the TeBr^ ion in the complex TeBr^ Sb Br^ should occur at higher wavenumber than in the tetrabromide.

14 g . Reaction of tellurium with antimony pentachloride and bromine. (TeBr^.SbCl^)

The product gave a ClxBr ratio of 1 % 1.99 (Calc, for TeBr^.SbCl^ = li 1.25). Two plausible formulations for the complex may be envisaged i an ionic type (TeBr^ SbCl^Br) or donor - acceptor type (TeBr^SbCl^) with a donor acceptor bond between the Te and Sb atoms.

The spectrum of the ionic form may be calculated as a summation of the Raman spectra of the free ions TeBr^ and SbCl^Br. For the TeBr^ spectrum see Results Section, TeBr^. The SbCl^Br spectrum shown in Table 14 g.l) is that recorded in PCl^ SbCl^Br by Bentley, Finch, Gates and Ryan(1972). A conceivable structure of the covalent form would be

Cl 01

— 01 Br ;Cl / vCl Br a molecule with a total of 27 vibrational modes. 279

Table 14 g.l)

Raman spectrum of the TeBr^/SbCl^ reaction product

TeBr^SbCl^ product SbCl^Br TeBr- SbCl

(This work) Bentley (This work) (Carlson,I963 et al Wilmhurst,I9 6O)

396 v).

361 msh 357

341 m br 332 V 3

310 m 30? ^ 2

2 9 0 ffl

244 s 246 0-

231

224 s 227

218 s sh 222 s,br 222y

175 s 1 7 5 ^ 6

157 w 165 ^ 8 134 w 133 0 ,

126 V w sh

104 w sh 1 0 6) 74 260

Fig. l4gl). Raman Spectrum of TeBr^/SbClf Product

100

m ni

o o> O o CD CM s s o CD m m m m _ rvj| CN oo WAVENUMBER(era" 281

It should be remembered that the stretching frequencies ( ^ and 0^) of the TeBr^* ion are shifted to higher wavenumbers on complexation with an electron acceptor, compared to in the tetrabromide.

It can be seen from Table 14 g.l) that there are not enough observed bands in the ç>ectrum of the product to support the view either of an ionic or covalent structure. Nor, it would seem, is there any unreacted Te3r^ or SbCl^ in the product.

Comparing the spectrum of the product with that of TeCl2 Br2 (See Table 14 b.l)), there is a strong similarity. It is possible that SbCl^ has chlorinated the tetrabromide rather than complexing with it. It is also possible that both chlorination and complexation has taken place, but it is difficult to explain how the percentages of bromine and chlorine in the product have the values 28.5% and 2 5 *1% respectively, and a Br* Cl ratio of 1 * 2. (Found for TeCl2 Br2 product, this study; Br, 48.4^; Cl, 1 9.3%; Br * Cl = 1 : 1.1)

Tellurium Tetrachloride_Co_mplexe

14 h . Reaction of tellurium tetrachloride with aluminium tribromide (TeCl^/AlBr^)

Some previous investigations of the compounds, TeCl^.AlBr^, TeCl^. GaBr^ and TeCl^. GaCl^ have been reported (Gol'dshtein, Gur’yanova, Peisakhova and Shifrina), 282

(1973). Different views have been expressed about the nature of the intermolecular bond in dimetal complexes of the type TeX^^.MX^ (in which M is a group III element and X is a halogen). From an analysis of I.R. and Raman spectral data it was concluded that such complexes are ionic in structure, TeX^ MXj^. Gol'dshtein et al. concluded, however, that the intermolecular bonds in such complexes are donor-acceptor in nature, the bond being formed by the interaction of the unshared electron pair of the tellurium atom with the vacant orbital of the central atom of MX^.

The complex TeCl^.AlBr^ was isolated by Gol*dshtein on mixing equimolar quantities of AlBr^ in cyclohexane and TeCl^ in benzene. The product was described as a yellow crystalline solid melting at 260°C with decomposition. The conductivity of a benzene solution, the I.R. spectrum, the dipole moment, and the heat of formation of the complex was measured. The investigation showed that with group III metal halide TeCl^ forms fairly stable and highly polar 1 : 1 complexes. Their weak dissociation in benzene suggested that the equilibrium constants of reaction 1 or, if the complexes have an ionic structure reaction 2, are extremely high.

TeX^^.MX^ ----- TeX^^ + MX^ q ^

TeX+.MX^ -T " TeX+ + MXj^ 2. 28]

Beattie and co-workers compared the

vibrational spectra in the region 250 - 550 cra”^ of molecules of type MX^ (M = P, As, Sb) with the spectra of the complexes of TeCl^ with group III metal halides

(1 9 6 7) and concluded that the complexes have an ionic structure of the type TeCl^^ AlCl^.

In Gol'dshtein's work, following the view that a donor-acceptor bond Te — M is present in the complex, the I.R. spectra of the complexes TeCl^.MX^ were compared with the spectra of other typically

donor-acceptor complexes R2 S-MX^.

The similarity of these spectra in the region of raetal(III) - halogen stretching vibrations led to the conclusion that the AlBr^ configuration was the same in both types of complexes. In other words, in the complex TeCl^.AlBr^, as in typical donor-acceptor complexes, the metal (III) atom has a tetrahedral configuration with symmetry and acts as an electron acceptor. Gol*dshtein*reported "Here the TeCl^ molecule being an electron donor of the type which does not usually alter its configuration substantially on complex formation, retains its trigonal bipyramidal structure, in which four hybrid 5sp d orbitals of tellurium are occupied by chlorine atoms, and the fifth by an unshared electron pair". The structure proposed by Gol'dshtein was as shown in 264

figure 14 h .1).

Figure 14 h.l) Structure of Br the complex TeCl^.MX^.

Cl The spectra of the complex TeCl^.AlBr^ in benzene and in the solid state showed very few differences in relative intensities. These were attributed by Gol'dshtein (1973) to a change in state of aggregation and it was concluded that the complex has the same structure in solution and in the solid.

The donor-acceptor nature of the coordinate links in the complex TeCl^.AlBr^ was supported by the magnitude of the dipole moment. The formation of the intermolecular Te-^Al is associated with a considerable transfer of charge from the donor (TeCl^) to the acceptor (AlBr^). This was in keeping with the data on the heat of formation of the complex, the same order of acceptor power of being preserved; AlBr^ > GaBr^ > GaCl^

Gol'dshtein concluded that the compounds

TeCl^.KX^ are donor-acceptor complexes of the nv type, with the TeCl^ molecule behaving as an n - donor towards MX^. The intermolecular bond being formed was 285

Table 14 h.l)

Raman spectrum of the TeCl^/AlBr^ reaction product. TeCl^AlBry TeBr^ TeCl+ AlgBr^fs) AlBr^ AlCl^ AlClBr^ product This I (This workjThis)(Miller) Brown)(Nanis)(Bradley et' work j ( jwork][1966 j 1920 575Ji

^850ii 47a0^(a^) (calc) 417^^1 400^i^(e) 394

376

351 354 34 9O.

341 mbr 344) 264 msh

256 msh 247 s 246^1 247^^(ai)

232 ssh 2 3 1 ; 226 s 227! ^3 2 7 2 ! 210^2 212 0 1 172 w 180^^

163 w 153^4 140^^ 146^^2 I44\^(e) 134^l(e) 133'^2 125 V, 1 1 4 ^ )4 106

98^2 90 "^(e) 85^ (calc) 79^15 70^4 266

Fig. I4h2). Raman Spectrum of TeCl^AlBr^ from the C^H^/C^^Hio Preparation.

100

CD CD CD CD o o o O OJ 8 CNj oo vO Csl oo m m m CNI c\j OJ OJ WAVENUiMBîiR (cm -1 X ) 267

considered a result of the unshared electron pair of the tellurium atom with the vacant sp^ orbital of the central metal (III) atom. This interpretation proposed in 1972, for TeCl^.AlBr^ is contradictory to the ionic structure for the complex TeCl^ AlCl^ proposed by Gerding and Houtgraaf in 195^.

Twenty-one (3N - 6) vibrational nodes are predicted for the donor-acceptor form of the complex (TeCl^.AlBr^), whereas the bands predicted for the ionic form (TeCl^ AlBr^Cl ) are shown in Table 14 h.l). The (AlCl^) ion has been shown by X-ray crystallography to have tetrahedral symmetry. The normal modes of these ions will therefore be given by a^(R) + e (H) + Zf^ (ln,R) . Substitution of a bromine atom into (AlCl^)” or a chlorine atom into (AlBr^) reduces the symmetry to and changes the vibrational representation to ]a^ (ir,R) + 3e(iJ3R). (Pig. 14 h.3). In the complex the stretching frequencies of the TeX^ ion are raised to a higher wavenumber than in the tellurium tetrahalide. Fig. 14 h.3).

Although the Raman spectrum shown (Fig. 14 h.l) only covers the frequency range 140 cm”^, to 400 cm no peaks were seen on a preliminary investigation of the product, between 400 cm”^ and 500 cm That is, no Raman peaks corresponding to the i.r. absorptions at 400, 450 and 490 cm~^ (reported by Gol'dshtein) were observed. There are not enough bands present in the spectrum of the product it seems, to support the covalent structure TeCl^.AlBr^ proposed by Gol'dshtein. It can also be seen from Table 14 h.l) that the absence of bands at 41? cm ^

and 3 ? 6 cm ^ indicates that no Al£Br^ or TeCl^ remains unreacted in the product. The absence of any observed Raman frequencies above 540 cm ^ suggests that there are no TeCl^ units in the isolated solid. However,

a portion of the spectrum (24? cm 232 cm ^ and 226 cm”^) closely corresponds to that of TeBr^. It may be, therefore, that halide exchange has occurred between the tellurium tetrachloride and aluminium tribromide, to form TeBr^. Several possibilities exist. A full exchange would result in formation of TeBr^Br and

Nine Raman bands are predicted from the symmetry point group of the planar, chlorine-

bridged Al2 Cl^ molecule. (5063^0 2170^, 112\^(Ag);

4 3 8^, 1680^ (B^g); ^0 6 I64cm ^'^2^®2g^'— ^15^^3g^^ 269

(Siebert, I9 6 6). This could therefore be the case, the peak at 34o cm“^ being the stretching vibration of

Al2 Cl^, and the 163 cm“^ and 172 cra“^ peaks in the product spectrum being due to the type V ^2 snd type V ^ vibrations of the Al2 Cl^ molecule. It seems that the complex TeCl^.AlBr^, either in the ionic or covalent form has not been isolated. The Raman spectrum of the product consistent with that of TeBr^AlCl^ (the frequencies at

3 4 7, 232 and 226 cm“^ being assigned to the TeBr^ and 0^ vib. modes and the frequencies at 341 and 1?2 cm”^ being assigned to and of the AlCl^ ion). (Table 14hl). Halide exchange between the reactants does not seem unreasonable. (See Section l4dl).

14 j). Reaction of tellurium tetrachloride with aluminium trichloride (TeCl^/AlCl^) An ionic structure, TeCl^AlCl^, was assumed to exist in the complex, to explain the number and polarities of the Raman bands observed by Gerding (1954). (This is in accordance with the X-ray study of Krebs

(I9 7I) which concluded an ionic structure). The full assignments macfe in their study are shown in Table l4 jl). The bands were assigned on the basis of the TeCl^ and NO'*’AlCl]j^ Raman spectra recorded by the same authors, the pyramidal TeCl^ ion and tetrahedral AlCl^ ion both exhibiting four Raman active vibrational modes (2A^ +

2E and A^ + E + 2 F ^ respectively). (See Section l4a. and

Fig.. 14 j. 1) . 290

Raman active vibrational modes of the AlCl^ ion (Td)

(Siebert, I9 6 6) o A1 • Cl

Although no Raman spectrum of the complex could be recorded in this study, it is interesting to note that the TeCl^ spectrum recorded by Hayward and Kendra (196?) and in this study (Table 14 j.l), differs from that reported by Gerding and Houtgraaf (I9 5 4). (The triply-degenerate 0^ mode being split into two Raman bands). This may slightly alter the TeCl^^AlCl^ assignment reported by the latter. The shift at 342 cm”^ may be due to a combination of the AlCl^ and the split TeCl^ \)^ modes of vibration. The ionic structure proposed by Gerding and Houtgraaf

(19 54) was later endorsed by the HQR studies of Okuda et al (1 9 7 5) who suggested the structure.

O = 01

The product isolated in this study remains unidentified 291

Table 14 i. 1)

Raman spectrum of the TeCl^/AlCl^ reaction product

TeCl+AlCl^ TeClÂlCl^ TeCl^ TeClj TeCl' (This study)(Gerding & iGerding &)(This (Hayward & (Houtâaf) (Hoy^^âaf) (study!

(581)-A1C1^0^

Sample 528 burnt in 506 laser light 487 492 464 ms

434 418 415

391sp-TeC1^0^ 3 7 4^ 3760^ 376

367sdp-TeCl^\)-j 342"^ 351) v l 351 Ü. 342sp-AlCl^^^ 344 343 J (290) (246) (228)ms 208

185ms-TeCl^191^2 168

139 br-TeCl+VV 143^ 153"^ 150^^ and ^ ^ AlC l^V^ 87 292

14.k. Reaction of tellurium tetrachloride with antimony pentachloride (TeCl^/SbCl^)____

In a study made in I967 the Raman spectrum of solid 1 I 1 tellurium tetrachloride/antimony pentachloride complex was recorded using green excitation light (mercury line ). (Table 14 k.l). The bands marked * were assigned as probably due to SbCl^ ). Neglecting lattice and combination bands, it is possible to predict approximately the Raman spectrum of TeCl^SbCl^ by considering only the Raman active vibrations of the two component ions. The antimony hexachloride anion (0^) exhibits three Raman active vibrational modes (1 + 1 + 1 and these frequencies are given in Fig. 14 k.l).

Figure 14 k.l) Raman active vibrations of the octahedral SbCl^ ion.

• Cl

o Sb (siebert, I9 6 6)

As in the spectrum of TeCl^ AlCl^ recorded by Gerding and Houtgraaf (1954)# the stretching frequencies of the TeClj ion may be raised to a higher wavenumber 293

(^20cm -In in . TeCl^ SbCl^ than in TeCl^

The most likely structure for the binuclear donor-acceptor covalent complex isi-

A total of twenty-seven (3N - modes are predicted for this complex. Many more Raman bands would be predicted for a covalent structure than the number experimentally recorded for the product (Table 14 k.l). Again, the Raman spectrum of the starting material (SbCl^) has been tabulated. The trigonal bipyramidal SbCl^ (D^^) molecule exhibits eight vibrations, six of which are Raman active.

Vy(E')

Fig. 14 k. 2) - Raman active vibrational modes of

SbCl^. (Siebert, I9 6 6).

If, as evidence for other octahedral species suggests, the free ion selection rules 294

still apply in the complex, the SbCl^ Raman bands are shifted to lower frequencies than in the AsCl^ SbCl^ spectrum, to 312 cm ^ (0^), 257 cm ^ and 165 cm”^ (^^). The TeCl^ stretching vibrations are raised to higher frequencies (compared to the TeCl^ Cl” Raman bands) by complexation with SbCl^, to occur at 399 cm ^

(^^), 385 cm”^ and 358 cm”^ (^^), in accordance with the spectrum of Fig. 14 k. 3). The TeCl^ O 2 and vibrations in TeClj^AlCl^ occur at 185cm”^ and

139 cm ^ respectively (Gerding and Houtgraaf) (1954), and so the bands at 186cm ^ and 147 cm ^ in the product spectrum are assigned accordingly.

It is possible that the product may be contaminated with unreacted antimony pentachloride, but the Raman spectrum of the complex is consistent with an ionic structure TeCl^ SbCl^ . 295

Table 14 k.l)

Raman spectrum of the TeCl^/SbCl^ reaction product

TeCl^/SbCl^ TeCljSbCl^ (AsCl^)SbCl^ TeCl^Cl SbCl^ product

(This work) (Beattie (Beattie & ) (This ) (Wilmshurst) ( 1967 (webster j |study) | I96O j i 1963 )

399 395 396 v \ 385 385 376

367 358 355 357 344) 3

337\^

312 310 307 J

2 7 7 - ^ 2 257 256 244 Gerding (1954)- 186 (185)^2 (not observed ) 172 172 v> in this 175-^6 163 0, 165 166 8 147 153'^. 74 0 296

Fig. l4k3). Raman Spectrum of Solid TeCl^/SbClr Product.

100

CD CD ' C D C D o O s OO CN I C D m m 11 m | m Osl

WAVENUMBER(cm” 297

15). AJPPENDIX I.

The characterisation and analysis of the tellurium compounds was carried out by two means*- 1). Raman spectroscopy and comparison, where possible, with literature spectra. 2) Quantitative analysis for halogen content using;-

a), the standard Volhard procedure, (Vogel,I96O), and b). potentiometric titration with a silver electrode (containing an internal reference, calomel electrode (Metrohm, Switzerland)), against a standard silver nitrate solution. In the presence

of 150 ml. of a p.H. 4 .9 acetic acid/ sodium acetate buffer, this allowed separate chlorine and bromine analysis of the sample. Care was taken to protect the solution from light during the titration.

These procedures were performed on a halide solution obtained by dissolving a known weight of the product in water. This was then reduced with sulphur dioxide gas, boiled to expel the gas, and filtered to remove the elemental tellurium. The resulting halide solution could then be titrated with silver nitrate.

For the antimony-containing complexes TeCl^.SbCl^ and TeBr^.SbCl^, the reduction procedure was modified. The sample of product was added to an excess of 0 .1 M, sodium hydroxide solution, causing 296

formation of the insoluble antimony hydroxide and reduction to elemental tellurium. 299

16). APPENDIX II

Due to the water and light-sensitivity of the tellurium compounds, all transfer operations were carried out in a dry box. The compounds were stored in a desiccator above phosphorus pentoxide, in the absence of light.

Tellurium is a cumulative poison if ingested or inhaled (T.L.Y. 0.1 mg m and causes a foul body odour if absorbed through the skin. All operations were therefore carried out in a fume cupboard or dry box,and gloves were worn.

Solvents used in the preparations (carbon tetrachloride, toluene, dichloromethane, benzene and cyclohexane) were dried prior to use with 4A molecular sieve. Acetic acid employed in the tellurium tetrabromide recrystallisation was dried by mixing

5 0 /5 0 by volume with acetic anhydride. Carbon disulphide used in the TeBr^.AlBr^ synthesis was purified immediately before use and kept in the dark in a sealed vessel. Purification involved standing the solvent with bromine (0.5 cm^/1) for three to four hours, followed by shaking with potassium hydroxide solution. Copper turnings were then added (to remove unreacted bromine) and the solvent was dried over calcium chloride.(Perrin,

1 9 6 6). 300

Adams, D.M., & Churchill, R.G J. Chem.Soc.(A),1 9 6 8 pp 2141 - 2144

Adams, D.M., & Lock, P.J. JCS(A) 1 9 6 7,pp.145-146

Almgrem, L., Acta Chem Scand 2 ^

3713 - 3720 (I97I)

Andon, R.F.L., Martin,J.P., JCS(A) (I9 7I), 1788

& Mills, K.C. Aynslay, E.E., JCS (1953)• 3016

Aynsley, E.E., & Watson,R.H., JCS (1955), 2603 Bailey, N.T.J., "Statistical Methods in

Biology". 5th.Ed. I9 6 9, English Universities Press) Ltd) Ba ra, E • J •, Spectrosc.Lett, 1975,

8(2-3), 1 5 1 -5 Beattie, I.R.,& Chudzynska,H. JCS(AU967), 984-90 Beattie, I.R., Bizri,0., JCS (Dalton) 1974,1747-8 Blayden,H.E., Gibson, .T.R., Moss,R., & Phillips, B.A.

Beattie, I.R., & Webster, M. JCS (19 63), 38. Belevantsev, V.I., Kolonin,G.R., Zhur. Nforg Khia 12,

& Ryakhovskaya, S.K. 2492 - 2497 (1972) Bentley, P.P., Pinch, A., Inorg. Chem. 11, 413, 1972 Gates, P.M. & Ryan, P.J.

Beurskens, P.T., Blaauw, H.J.A., Inorg. Chem. 7 (I9 6 8) 8O5 Cras,J.A.,& Steggerda,J.J.

Bichowsky A Rossini "Thermochemistry of Chemical Substances", Reinhold (1936). 301

Bjerrum, N., Bull Soc. Chim. Belg.

i2, '♦3 2 -4 4 5 (1948) Block, B.P. Inorg. Syntheses, vol IV - ed, J.C. failar, McGraw Hill,London, p.14 (1953)

Bonamico, M., & Descy.G., Acta Cryst. B g S .

1 7 35 -3 6 (1 9 7 3) Booth, H.S. "Inorganic Synthesis", vol IV p.16 (1953)

Bosworth,Y.M.,A Clark,R.J.H. Inorg. Chem. I9 6 5# 14(1),

171 - 6 Bosworth, Y.M., A Clark,R.J.H JCS Dalton, 1975,361-385 Bowaaker, G.A., A Whiting, R. Aust. J. Chem. 1976 22, 1407 - 12 Bradley, R.H. Brier» P.N., A J. Chem. Soc.(A), 1971,

Jones, D.E.H. p. 1397 - 1400 M Brauer, C, "Handbook of Preparative Inorganic Chemistry, vol 2, Academic Press. Brauer.G., A Sleater, G. Journal of Less Common Metals, vol.21, Part (3),

pp 283 - 291 (1 9 7 0) Braunstein, P.,A Clark,R.J.H. JCS Dalton, 1973,1845-1848. Brovm, D.H., A Stewart, D.T. Spectrochim.Acta 26A,

1344 (I97O)

Buss, B ., A Krebs, B Angew Chem. Int. Ed. Engl

9 (I97O), 463.

Carlson, G.L., Spectrochim. Acta Ig,

1529 (1 9 6 2 ) 302

Carlsson, L., A Lundgren,G. Acta Chem.Scand, 21

(1967) No. 3, 819

Chateau,H.,Gad*t, M.C. A J. Chim. Phys.63,269

Pouradier, J. (1 9 6 6)

Chen, M.T., A George, J.W. J. Inorg. Nucl. Chem,

1 9 7 2 .Vol pp.3261-3262

Christensen, G.C. A Alstad,J. Radiochena Radioanal Lett.

1973 13(4), 227-34.

Cordes, A.W., Kruh, R.F., Acta Crystallogr. 12,

Gordon,E.K. A Kemp, U.K. 756 (1964)

Cotton, F.A., A Wilkinson, C. "Advanced Inorg. Chem".

2 nd. ed.,Wiley(1 9 69),

Cox and Webster J.C.S., 1 9 3 6, 1635-7.

De Jonge, R.M., J . Inorg. Nucl. Chem.

1 9 76,Vol.38,pp 1821-1826

Dell •Amico,D.B.ACalderazzo,F. Gazz.Chim.Ital.103 (1973)

1 0 9 9.

Dell •Amico, D.B.,Calderazzo,F., JCS, Dalton Trans.

A Karchetti, F. (1 9 7 6) 1829

Dell 'Amico, D.B.,Calderazzo,F., J. Chem.Soc. Chem.Commun.

Marchetti, F., Merlino, S., (1977), 31

A Perego, G.

Derahkshan B., Thesis submitted for the Doctorate of Philosophy

rR.H.C,London U, I98O

Desclaux, J.P.A Pyykko, P., Chem. Phys.Lett 39

(1 9 7 6), 3 0 0 .

Dubinskii, V.I., Shul'man A Zh. Neorg. Khim, 13 (1),

Peshchevitskii, B.I. 5 4 - 7, 1969. 303

Dubinskii, V.I. & Demidova,G.V. Zh.Neorg.Khim. 16,

2636 - 2639 (1971) Edwards, A.J..Falconer,W.E., JCS Dalton, 1974, 1129. Griffiths, J.E.,Sander W.A.,

& Vasile K.J.

Engelhard Industries Tech. Vol X, No.l. 1969 pp 5 -9 Bulletin,(Gedansky & Hepler) (L_;M.Gedansky A L.G.Hepler)

Ephraim, P., Chem.Ber.1 9 1 9,vol 52.

pp. 241 - 54

Evans, J.C., J.Mol.Spectry.4,4 3 5(1 9 6 0)

Pattens, M.O. J. Chem. Phys. I9 7 0, 63 (11), 4249-64

Fischer,W., & Biltz,W. Z.Anorg. Allgem. Chem.3928,

vol.1 7 6,pp 81-111 Pord-Snith, M.H., Hobeeb,J.J. JCS Dalton, 1972, & Rawsthome, J.H. p. 2116 - 2120 Friend, J. Newton, "Man and the Chemical

Elements 71951,Griff in.

Fry, F.H., Hamilton, G.A. Inorg.Chem.vol 5 , No.11

& Turkevich, J., Nov.1 9 6 6. 1 9 4 3.

Gangopadhayay, A.K., J .Chera .-Phys .36,2 2 0 6 & Chakravorty, A. (1961) George,?., & McClure, D.S. Prog.Inorg.Chen.i, 381

(1959)

Gerding, H., & Houtgraaf,H., Recueil 2 1 (1954),759-770

Gerding, H., A Stuftuns, D.J., Rev.Chim.Hung.(1 9 6 9), £

795 - 815 Gerding, H., Stuftuns, D.J. Rec.Tray.Chim, (1970) £2

A Gijben, H., (6), pp 6 1 9 -2 4

Goggin, P.L., A Mink, J.,. JCS Dalton,1 9 7 4,1 479-8 3 304

Ool*dshtein,I.P.,Peisakhova,M.E. Dokl.Akad.Nauk.SSSR(1972)

Gur'yanova.E.N.A Kocheshkov,K.A 2 2 3 .(6 ), 1316 - 19

Gol*dshtein,I.P.,Gur*yanova,E.N., Zh.Obshch.KhiB. &3 (11),

Peisakhova,M.E.,A Shifrina.R.R. 1973, 2347-51

Greenwood, N.N., Straughan, B.P. JCS (A), 1966,

A Wilson, A.E. pp 1479 ~ 80

Greenwood, N.N. "Ionic Crystals",

Butterworths,London,I 9 6 8 .

Haendler, H.M., Mootz, D., J. Solid State Chen 10 Rabenau,A.,A Rosenstein,G. (1974), 175.

Hager, J.P.,A Hill, R.B. Met. Trans.1,2723-31(1970)

Hall, A.J., A Satchell, D.P.N. JCS Dalton,1977.PP 1403-09

Hamada,K., Morishita, H., Nagasaki, Daigaku

A Higashi, Y., Kyoikugakubu Shizen

Koyaku Kenkyu Hokoku

(1973) 2i, pp 41 - 6

H a m e d , H.S. A Owen, B.B., "The Phys.Chem.of

electrolytic Soins", 3rd.ed,

1967 - Reinhold N.Y.

Hayward, G.C., A Hendra, P.J. JCS (A), 1967, 643.

Hestermann, K., A Hoppe, R., Z.Anorg.Allg.Chea. 360 (1968) 113.

Holloway, J.H.,A Schrobilgen,G.J, J. Chem.Soc.Chem.Commun.

1975. 623.

Howie, F.H., A Veale, C.R., J.inorg.Nucl.Chen. 2 S (1966) 1149

Jannsen, E.M.W., Folmer, J.C.W. J.Less-Common Metals,J#

A Wiegers, G.A. (1974) 71

Johnson,H.L., A Leland, H.L., jacs,22, 1439-45 (1938) 305

Jones, P.G., Guy, J.J. Acta Crystallogr.,Sect.B.

& Sheldrick, O.M. 31 (1975) 2687 Kapustinskii, A.P. Z.Phys.Chem.22 B,26l

(l933)fZeitshrifte.

Kapustinskii, A.F., Quarterly Reviews jjQ, I956 London Chem.Soc.pp 263-94 Katsaros, N,, A George, J.W. Inorg.Chia Acta Vol.3

Part 1 (I9 6 9; 1 6 5-16 6 a) Kazakov,V.P.A Konovalova,M.Y. Zh.Neorg Khia.1968.I3

(1), 66-70 b) Kazakov,V.P.A Konovalova,M.Y. Zh.Neorg Khim.1 9 6 8 ,1 3

(2), 4 4 7 -5 3 Korov, A.V., Zh.Neorg.Khim, 1974,19

(4), 1134 - 5 .

Krebs, B., Z. Anorg. Allg.Chem.1 9 7 1,

386 (3) 2 5 7-6 9 Krebs, B., Buss, B., A Berger,W., Z. Anorg.Allg.Chem. 397.

1 (1973) Lenher, JACS, 15, 546 (1 9 1 3) Liptrot, G.F., "Modem Inorganic Chemistry" - Mills A Boon, London (1977)

Louw , W.J. A Robb, W., Inorganics Chim.Acta, 9 (1974),33 - 37 Maeda, M., Ohtaki H., Bull Chem.Soc. Japan,

A Johansson, G., 1 9 7 4, 49(7) 2 2 9-3 7

Malhotra, K.C., Indian Journal of Chemistry,Sect.A.,1977,

15A (1), 53 - 5 . 306

Massey, A.G. "The Typical Elements",

1 9 7 2 , Penguin.

Mellor, J.W., "A Comprehensive Treatise on Inorg. and Theor. Chemistry", Vol III,

Longmans,Green & Co,

New York, 1923 pp 586-610

Kellor, ■Mellor's Modem Inorganic Chem",revised ed.

G.D.Parkes,Longmans,I967

Meyer, F . , Compt .'Rend. 1 9 0 1, vol 133, pp 815 - 818

Meyer, F., Academic des Sciences,

8th.Feb, 1909 pp 346-348

Miller, A.D., A Fisher, E.I. Izv.Sib. Otd. Akad. Nauk. SSSR, Ser.Khim.Nauk.1974 (2), 77 - 80 (Russ).

Miller, R.H., Diss. Abs. 26, 5744 (I9 6 6)

Minkin, V.J., Sadekov, J.D., Zh.Obshch.Khim,I9 7 3, &3,

Sayapina,L.M. & Minyaev,R.M., 8O9 Mootz,D., Rabenau A., J.Solid State Chem. & Wunderlich,H.,A Rosenstein,G., (1973), 5^3 Morishita, H., Nagasaki Daigaku Kijoikugakubu Shizen Koyaku Kenkyu Hokoku,

1 9 7 4 , (15), 61-7 Mu5r, G.D. ed., "Hazards in the Chem. Laboratory",2nd.ed.1977 The Chem.Soc. Alden Press 307

Mundorf T., & Dehnicke,K., Z.Naturforsch,Teil B,

IS (1973) 506 Nanis, L,, & Balasubramanyam,K., J. Chem.Phys. 42,676(1965) NBS Circular 500, 1952,- "Selected Values of Chemical Thermodynamic Properties". NBS Tech. Note 270-4 "A Bulletin of Thermo dynamics & Thermochem. (Chem.Thermodynamics). 1966 - 79 Okuda, T., Yamada, K., Bull Chem.Soc.Japan, Purukawa, Y.,A Negita, H., 1975,48 (2),392-5

Ozin, G.A., & Voet.A.Van der Canad.J.Chem.1 9 7 1,4 9 ,7 0 4 Ozin,G.A., & Voet,A.Van der J.Mol.Structure 10(1971)

397 - 403 Ozin, G.A., & Voet,A.Van der J.Mol.Structure 13(1972)

435

Page, T., Ph.D. Thesis, R.H.C. London,1 9 78,p.208

Paul R.C., Paul,K.K. Aust.J,Chem.(1 9 6 9) g g

& Malhotra, K.C. 847 - 52 Peake, S.J., Thesis submitted for Doctorate of Philosophy,

1 9 7 6,London University RHC.

Pellaton, M., J. Chim.Phys.1 9 1 5,vol I3 pp 426- 64

Perrin, D.D., Armarego,W.L.F. "Purification of Laboratory

& Perrin, D.R., Chemicals", I9 6 6, Pergamon Press. 306

a) Peshchevitskii,B.I. Zh.Neorg.Khim. 12

& Belevantsev, V.I., 312-318 (196?) b) Peshchevitskii,B.I., Izv.Technol.Proc,Int. Brenburg,A.M, Belevantsev,V.I.Congr.Refrig., 12th, 1, A Kazakov, V.P. 383-385(1967) Peshchevitskii, B.I., Zh. Neorg.Khim. 14

A Belevantsev, V.I., 2393 - 2396 Peshchevitskii, B.I., Izv.Sib.Otd.Akad.Nauk.

A Belevantsev, V.I., SSSRiser.Khlm.Nauk.i9 6 9,

No. 2, 82 - 89 Peshchevitskii, B.I., Izv.Sib.Otd.Akad.Nauk.

A Belevantser, Y.I., SSSR.ser,Khim.Nauk.19 71,

No. 6 , 26 - 3 1 .

Petit, M., Bull Soc. Chim.France,

1 9 2 5 ,Y0I.3 2 ,pp.6 1 5 -2 3

Pitzer, K.S., J.Am.Chea.Soc.,62, 2365 (1937) Poulsen, F.W. A Berg, R.W. J.Inor.Nucl.Chem, 1978,

v o l . 4 7 1 -7 6

Pouradier, J., A Goquard, M., J.Chim.Phys.6 3,IO7 2 -7 8

(I9 6 6)

Powell, P., A Timms, P.L., "The Chem.of the Non-,

metals",1 9 74,Chapman AKaU.

Prosen, E.J. A Kilday, M.V., Joum.of Res.N.B.S.1973,

22A. 599 Puddephatt, R.J., "The Chemistry of Gold", Monograph 16, R.J.Puddephatt,Topics in Inorg.A Gen.Chem. A collection of Monographs - R.J.H.ClarkU978j 309

Quill, L.L., "The Chemistry and Metallurgy of Miscellan eous Materials"! Thermodynamics (Ed. by L.L.Qui11)McGraw-Ki11, New York(1950) P.157 Rabenau, A., Rau, H., Angew Chem.Int.Ed.Eng.g

& Rosenstein, G,, (1969) 145. Rabenau, A,, A Rau, H., Inorg.Synth.14,(1973)»l60 Rabenau, A., 8th.Int.Syap. on Reactivity of Solids - ed.John Wood et al,l976. Proceedings P.731-735 Plenum. Rabenau, Y.A., Zh.Anorg.Chea.1973 %

325, 273 Rich, R.L. A Taube, H., J.Phys.Chem.Yol 62, 1

(1 9 5 4) P 6 - 11

Ringstrom, U., Nature,I2 S,(I9 6 3),981.

Robb, W., Inorg.Chem.6 7,6(2),382-6

Ryan, J.L., Inorg.Chem.Yol 8, No.IQ

1 9 6 9,pp. 205a - 2062

Ryan, J.L., Inorg. Synth. 1974, 15,

225 - 35 (Eng). Sadler, P.J., Reprint from "Structure

and Bonding", Yol.2 9 ,

1 9 7 6. 310

Sasana, A., Matuo, T., J. Magn.Resonance,1 9 7 1,

Nakamura,D., & Kubo, M. 4(2), 257 - 73 Schmidbaur, H., Angew Chem.Int.ed.Engl.

Vol. 15 (1976) No.12 p. 728-40

Schottlander, Ann. 212, 312 (I8 8 3)

Shchukarev, S.A., Oranskaya,M.A., Zh.Neorg.Khim.I9 5 6,vol 1,

A Tsintsius, V.M. pp. 881 - 86 Siebert, H., Anwendurgen und Allgemeine Chemie in Einzeldarstellurgen - Band VII - Springer - Verbg,Berlin - Anwendurgen der Schwingusspektroskopie inder Anorganischen

Chemie - I9 6 6. Simm, G.H., A Sutton, L.E., •Molecular Structure by diffraction Methods",

19761Chem.Soc.(pp 476-83)

Sleater, G., Baeminghausen Z. Anorg. Allgem. Chem.2Û, M A Brauer, G., 372 (1 ), 9 - 13 Sinoes, S., Kandy, P., Bull Soc.Chim.Belg.81 Auwera-Mahieu,A.V. A Drowart, J. (1972) 45.

Sokdov, Y.B., Prusakov,Y.N., Dokl.Akad.Nauk,SSSR,229

Ryzhkov,A.V.,A Drobyshevskii Yu Y,(I9 7 6) 884 Sporter, R., A Johnson, J.F. Analytical Calorimetry, Plenum press, 1968,p.203- 208(J.Jordon A P.W.Carr) 311

Stecher, P.O. éd., "The Merck Index", 8th. Edition,Merck & Co.

1 9 6 9, U.S.A. Straehle J., & Loercher,K.P. Z.Naturforsch, Teil £. 29 (1974 i 266. also

Straehle J., Z.Naturforsch,2 (1 9 7 0),

25 (1 0 ), 1186 - 7 and Straehle, J., & Loercher, K ,P. Z. Naturforsch, B. t Anorg., Org.

Chem.1 9 7 5. 30B(9-10),662-4 Sviturov, N.Y., Izv.Yyssh.Ucheb.Zaved., Tsvet.Met.36, No. 5,

69 - 71 (I9 7O) Thorpe - "Thorpe's Dictionary of Applied Chemistry",4th.ed.

Yol.XI,1 9 4 3, Longmans, Green & Co.

Tobe, M.L., Inorganic Reaction Mechanisms (Nelson),

1 9 7 2 , P. 54 -

Yanderzee, C.E. & Swanson,J.A. J.Phys.Chem.62 2 6 0 8 (1 9 63)

Yasile, M.J., Richardson, T.J., JCS Dalton,I9 7 6, 351* Stevie,F.A.,& Falconer,W.E. Yogel, A.I., "Textbook of Quantitative Inorganic Analysis,

Longmans, i9 6 0. 312

V og ©1, A #I#, "Macro A Semimicro Qualitative Inorganic Analysis",1954,4th.ed. Wadso, I., Science Tools, the LKB Instrument Journal,vol 13,

pp 3 3 -3 9 (1 9 6 6) - Lieb- Produkter AB., Sweden. Wiberg E., A Neumaier, H., Inorg.Nucl.Chem.Lett.,1

(1965), 3 5 .

Wllmshiiret, J.K., J.Mol.Spect. 6 ,3 4 3(19 60) (see also G.L.Carlson,

19 62 ). Yatsimirskii, K.B. "The Thermochemistry of complex Compounds" -

1951 - Moscow. Yatsimirskii, Y.B., Izvest.Akad.Nauk.SSSR,

Otdel.Khim.Nauk.1 9 47,4 5 3 . 313

18 ADDENDUM. Notes to Graphs 4e5 and 4e?.- The differences in the (KAuX^ (s ) ) v solvent activity graphs for aqueous acid and salt solutions may be due to two factors,- a). A physical effect; i.e. the increase in activity of the solvent and ion-pairing in the solution, causing incomplete dissociation of the sample in the solution. (The resulting inter actions in such a system are difficult to discuss). b). A chemical effect; i.e. reaction of the solvent with sample. It was thought that the initial decrease of AH'ôi(ÂuBrî^Cs) ) on passing from water to HBr(aq) (Fig. 4e?) was due to a chemical effect, the acid inhibiting hydroxide exchange of the tetrahaloaurate. Hence, no initial drop of is seen in the perchlorate results. An activity effect of the

solvent then causes a further linear decrease in in both acid and salt results. (Note that AH^^ 1^ dependent on the total activity of the resulting solution, but at high acid/ salt concentrations this should approximate to the activity of acid or salt used.) The same features may be seen in Fig. 4e5, where (KAuCl^(s ) ) is plotted against activity of HCl solvent used. The very large decrease in with activity of KNO^ solution used may possibly be due also to complexation equilibria of the gold (III) with nitrate ions. Nitrate ions

are unidentate to gold (Cotton and Wilkinson, I9 6 9), and may either replace 01” or lead to a hexacoordinate structure, A test for such substitution would be a Raman investigation of the nitrate solutions, when D^h Au(NO^)]^ (full nitration) or lower symmetry AuCl^(NC^)j^_^ species may be formed.