OF PALLADIUM

by

JOHN WILSON QUAIL B. Sc., University of British Columbia, 1959

A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE

in the Department

of

CHEMISTRY

We accept this thesis as conforming to the required standard

THE UNIVERSITY OF BRITISH COLUMBIA April, 1961 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University

of British Columbia, I agree that the Library shall make

it freely available for reference and study. I further

agree that permission for extensive copying of this thesis

for scholarly purposes may be granted by the Head of my

Department or by his representatives. It is understood that copying or publication of this thesis for financial

gain shall not be allowed without my written permission.

Department of

The University of British^Columbia Vancouver $, Canada. ii

ABSTRACT

The preparation and reactions of simple and complex fluorides of palladium and gold using solvents have been studied.

Two new compounds, fluoselenonium hexaf luo- palladate (IV) and fluoselenonium tetrafluoaurate (III), have been prepared. Both are in the tetrafluoride solvent system. Fluoselenonium hexafluo- palladate (17) reacts with a base, pentafluo- selenate (IV), to form a salt, potassium hexafluopalladate (IV) which crystallizes in a trigonal modification, a = 5.717 ±

.003 i? , c . 4.667 + .003 A* .

Pure palladium difluoride has been produced in two reactions. These reactions are: (1) the thermal decomposition of fluoselenonium hexafluopalladate (IV), and (2) the reduction of palladium trifluoride with selenium tetrafluoride.

The magnetic moment of the adduct of palladium trifluoride has been measured and found to be 2.2 B.M.

Evidence is presented for the existence of a potassium salt of the trifluopalladate (II) . It has iii

not been possible to prepare complex fluorides of terpositive palladium in selenium tetrafluoride solution. iv

TABLE OF CONTENTS

PAGE

List of Figures vi

List of Tables vi

Chapter

1. Introduction 1

2. Discussion 8

3. Conclusion 22

4. Experimental 25

I General Techniques 25

a) Glassware 25

b) X-Ray Photographs 26

c) Magnetic Measurements '. 26

II Analytical Methods 28

a) 28

b) Palladium 30

c) Selenium 31

d) Gold and Selenium 31

e) Bromine 31

III Reactants 31

a) Fluorine Supply • 31

b) Bromine Trifluoride 33

c) Palladium Diiodide and Dibromide 34

d) Gold 34

e) 35 V PAGE

IV The Preparation of Selenium Tetrafluoride ... 35 V The Preparation of Palladium Trifluoride and Its Adduct ¥ith Bromine Trifluoride 36 VI The Preparation of Fluoselenonium Hexafluopalladate (IV) 38 VII The Reaction of Fluoselenonium Hexafluo• palladate (IV) With Bromine Trifluoride 39

VIII Reactions of Fluoselenonium Hexafluo• palladate (IV) 39 IX The Preparation of Palladium Difluoride 40

X Potassium Fluoride and Palladium Difluoride in Selenium Tetrafluoride 41 XI Potassium Fluoride and Palladium Trifluoride in Selenium Tetrafluoride 42 XII The Preparation of Potassium Hexafluo• palladate (IV) 44 XIII The of Potassium Hexafluo• palladate (IV) 47

5. Bibliography 52 6. Vita 54 vi

LIST OF FIGURES

To Follow Page

1. Apparatus for the Preparation of SeF^ 35

2. Apparatus for the Preparation of KgPdF^ 44

LIST OF TABLES

Page

1. Known Simple Fluorides of Group VIII Metals .... 2

2. The Physical Properties of Some Fluoride Solvents 6

3. Trigonal Modifications of Potassium Salts of Hexafluo-, Quadripositive Ge, Pd and Pt 14

4. Fluorides of Palladium 23

5. X-Ray Data for a Potassium Salt of Fluo- palladate (II) (CuK^ radiation) 43

6. Assignment of the X-Ray Reflections of K2PdF£ (CuK^. radiation) 48

7. Observed and Calculated X-Ray Intensities for

K2PdF6 (CuK^ radiation) 51 vii

ACKNOWLEDGEMENT

The author wishes to express his sincere appreciation to Dr. N. Bartlett for his guidance and encouragement throughout the course of this work.

He also wishes to thank the other members of the staff and his fellow graduate students for their helpful suggestions.

The author is grateful to the National

Research Council for financial assistance, in the form of a Studentship, during the period from May I960 to

April 1961. INTRODUCTION

Immediately after the Second World War commercial

supplies of fluorine became readily available. This was

the result of wartime interest in uranium .

The availability of fluorine stimulated interest in fluorine

compounds.

The pioneering studies of Moissan and Ruff had

layed a foundation to the chemistry of fluorine and fluorides, but much of the early work is contradictory and unreliable.

The recent proof1 that the long accepted osmium octafluoride2

is in fact osmium hexafluoride points both to the need for

caution in accepting earlier results and the difficulty

inherent in the experimental work.

Despite the great activity in all branches of

fluorine chemistry during the past fifteen years, large

gaps remain in our knowledge. As long as such gaps remain,

interest in this field will remain at a high level.

The fluorides of transition metals have been the

center of a great deal of interest because of the wide

range of valence states which are encountered. The known

simple fluorides of group VIII metals are shown in Table 1.

Nickel tends toward the lowest oxidation state. In going down and across the group from nickel a tendency toward

higher oxidation states is noted.

Fluorine compounds of palladium have been prepared

in the t2, +3 and «-4 oxidation states. Two simple fluorides 2

TABLE I

Known Simple Fluorides of Group VIII Metals

Fe Co Ni

FeF2 CoF2 NiF2

FeF^ CoF3 sa m m PdF 2

RUF3 RhF3 PdF3

RhF4

RuFtj

Os Ir £t [PtF^J

0sF4 IrF4 PtF4

OsF5 [irF^ PtF^

OsF, Ir'F, PtF,

Compounds given in brackets are not established with certainty 3 of palladium have been prepared, the difluoride and the trifluoride. It is interesting that the tetrafluoride cannot be made although platinum tetrafluoride is easily prepared. The trifluoride was first prepared in 1928 by

Ruff and Ascher,^ by heating palladium metal to 500° in a stream of fluorine. The black crystalline powder is very hygroscopic and it hydrolyzes rapidly when exposed to moist air. Other methods of preparing the trifluoride have been 4 discovered. Sharpe has prepared palladium trifluoride by reacting palladium dibromide with bromine trifluoride to give a bromine trifluoride adduct of palladium trifluoride which was decomposed under vacuum at 220° to give pure palladium trifluoride.

Berzelius^ claimed to have made palladium difluoride by the action of fluorides upon palladous salts in aqueous solution. This claim is invalid since palladium difluoride is readily and irreversibly hydrolyzed. The trifluoride is easily reduced to palladium difluoride and to palladium metal by such reagents as hydrogen, sulfur dioxide and iodine vapour. If appropriate quantities of palladium trifluoride and palladium metal powder are heated together a reaction occurs and palladium difluoride is formed. None of the above reactions gives pure palladium difluoride. Palladium metal Is always present. Palladium difluoride was first prepared pure by Bartlett and Hepworth, 4 who reduced the bromine trifluoride complex of palladium trifluoride with selenium tetrafluoride at approximately

150°. Palladium difluoride Is a violet to light brown powder, the color depending on its origin. It is hydrolyzed by moisture to the monoxide, but It can easily be kept for long periods in a dry sealed glass tube,

A complex fluoride of palladium was not prepared until 1950, when Sharpe4 prepared the bromine trifluoride complex of palladium trifluoride as described above, o Hoppe and Klemm soon afterward prepared the hexafluo- palladates (IV) of potassium, and rubidium by the fluorination of the corresponding chloropalladates. The only complex dipositive fluoride which Is known is caesium 9 trifluopalladate (II), which has been prepared by Bartlett.

The main reason for the difficulty in preparing fluorides of palladium is their instability toward hydrolysis.

For the quadripositive hexafluopalladates this behavior is unusual when compared to the quadripositive hexafluo- platinates, which can be recrystallized from aqueous solution.

The work which is described in this thesis was directed toward preparing complex fluorides of dl- and terpositive palladium. Complete success was not achieved in this area. However, the paths of several interesting reactions have been established. Also, a new crystal modifi• cation of potassium hexafluopalladate (IV) has been prepared 5 and evidence is presented for the existence of a potassium salt of dispositve palladium.

Dry methods of preparation are often unsatis• factory because reaction is usually incomplete and an inhomo- geneous product is obtained. An ideal situation would be to have a solvent which was chemically inert but highly polar and capable of dissolving fluorides. No such solvent is known. However, a number of solvents are known which combine varying proportions of the desired qualities of inertness and polar nature. Some of these solvents and their physical properties are tabulated in

Table 2.

The extremely high Trouton's constant for selenium tetrafluoride suggests that it would be a very polar solvent.

It has mild reducing properties and it also fluorinates by exchange. Chemical evidence suggests that selenium tetra• fluoride behaves as an ionizing solvent according to the equilibrium

s f 2 SeF4 N SeF3 • SeF^~

Complexes are formed with some transition metal 12 fluorides, such as SeF^ OsF^, which can be considered as an "" in the selenium tetrafluoride solvent system.

Bromine trifluoride also has a high Trouton's constant. It has good solvent properties but it is an extremely powerful fluorinating agent, which greatly limits its usefulness. It is believed to ionize according to the 6

TABLE 2

The Physical Properties of Some Fluoride Solvents

m.pt. b.pt. Trouton's Reference Constant

BrF3 8.8° 125° 25.7 10

BrF5 -61.3° 40.5 23.2 10

IF 9.6 98° 26.3 10 5 o o 10 SF4 -121 -40 27.1

SeF. 106 30.0 10 4 -9.3° © HF -83° 20 20.6 11 7

equilibrium

2BrF_ - ^ BrF * * BrF ~ 3 ^ 2 4

Evidence for ionization is found in the isolation of such

1 "acids" as BrF^ SbF^ and BrF2AuF4 ^ and such "bases" as

14 KBrF4 and AgBrF4.

None of the above solvents could be considered ideal. Each has its own advantages and shortcomings. The particular reaction to be studied will determine the choice of the most appropriate solvent. DISCUSSION

The only fluoride complex of terpositive palladium which has been prepared is the lsl bromine tri• fluoride complex of palladium trifluoride.4- This complex has been found to possess a magnetic momenty^^ • 2.2 B.M. at 21°, which is very close to Nyholm and Sharpe's value1^

for palladium trifluoride ^eff » 2.0 B.M.). The magnetic moment of palladium trifluoride could be due to either one or three unpaired electron spins. The value is large for one unpaired electron spin, but could be accounted for by three. Low values are usual in the second and third transition series1^? ^7 and can be explained by spin-orbit 18 coupling. The crystal structure is rhombohedral, being made up of a hexagonal close packing of the fluorine atoms with palladium atoms in octahedral hole sites. In the cubic electrostatic field of the , the five degenerate

4d orbitals of the palladium are split into a lower triplet

u of de" orbitals (dXy> <3XZ> <3yz) which are orientated between the three axes on which the fluorines are situated and an

upper doublet of "d^" orbitals (dx2ly2, dz2> orientated along the axes. The magnitude of this splitting is directly proportional to the charge or dipole moment of the ligand, the number of ligands and the average value of the fourth power of the radius of the "d" electrons. It is inversely proportional to the fifth or sixth power of the distance from the center of the ion to the center of the ligand. As 9 electrons are added to the "d" orbitals Hund's rules are obeyed. That is, two electrons avoid being in the same orbit if possible, and their spins are parallel if they are in different singly occupied orbits of the same energy.

In an octahedral complex the first three 11 d" electrons will then go into the lower set of three orbitals. The next few electrons will either fill the higher pair of levels or pair up and occupy the lower levels doubly. The choice will depend on the splitting between the upper and lower levels and on the pairing energy required. If the splitting is large, then pairing will occur and a reduced magnetism will result. If the splitting is small, then the electrons will occupy different orbitals and the maximum paramag• netism will be observed.

For palladium trifluoride the electronic con• figuration is probably^

All Pd-F bond lengths are of equal length In a near perfect octahedron.1® Ligand Field Theory predicts that the filling of the dy orbitals must be symmetrical. Any unsymmetrieal filling of the dy orbitals would result in unequal repulsion on the six surrounding fluorines and an imperfect octahedron.

It is probable that the electron configuration is the same in the bromine trifluoride complex. 10

Palladium difluoride has a rutile structure which places six fluorines octahedrally around each palladium. The Pd-F bond distances are Identical within experimental error. Ligand Field Theory predicts a sym• metric filling of the d^, orbitals.

+2 Pd H H H V- V- Palladium difluorlde has a magnetic momenty^.^, « 1.84 B.M.

at room temperature.20 This value indicates two unpaired

electrons in the d shell. The spin only value for two unpaired electron spins is 2.83 B.M. The low value can be explained by spin orbit coupling. Further lowering can be attributed to antiferromagnetlsm.

The preparation of palladium difluoride by 7 Bartlett and Hepwortir suggested the existence of a selenium

tetrafluoride derivative of palladium trifluoride. In their

preparation they reacted the bromine trifluoride complex of

palladium trifluoride with selenium tetrafluoride. The

compound which resulted was decomposed at 150 , in an

atmosphere of selenium tetrafluoride, to palladium difluorlde .

An attempt was made to prepare the supposed terpositive

intermediate complex by displacing the bromine trifluoride

from the 1:1 bromine trifluoride-palladium trifluoride

complex with selenium tetrafluoride. Wien the selenium

tetrafluoride was added to the complex, copious quantities

of bromine were evolved. This was unusual in view of the 11 fact that no reaction is observed between bromine tri• fluoride and selenium tetrafluoride when they are boiled together. The appearance of bromine was indicative, of reduction of the bromine trifluoride. The isolation of the solid product fluoselenonium hexafluopalladate (IV) proved that the palladium had been further oxidized to the quadripositive state:

6 BrF , PdF- «• 12 SeF >6 (SeF.)_ PdFc «• Br «• 4 BrF_

In this reaction selenium tetrafluoride acts like an alkali fluoride. This reaction is similar to the oxidation of palladium to the quadripositive state by bromine trifluoride in the presence of potassium, rubidium and caesium fluorides as reported by Sharpe.21 The selenium tetrafluoride appears to be a fluoride ion donor, and it stabilizes the palladium in the quadripositive state by the formation of PdF^~ octahedra.

Fluoselenonium hexafluopalladate (IV) is dia• magnetic. All of the electrons must therefore be paired.

The six 4d electrons of the quadripositive palladium fill the 4d orbitals,/ The 4d orbitals are available to form d spJ hybrid orbitals for octahedral coordination to the six fluorines.

It 'is possible that the quadripositive palladium could be stabilized by the donation of electron pairs from the selenium tetrafluoride molecules to vacant orbitals of

V 12 the palladium. Linkage through fluorine atom bridges could also occur. These possibilities appear unlikely in view of the fact that similar compounds of quadripositive platinum7 and germanium have been prepared and are iso- structural with the quadripositive palladium compound. It is known, however, that the PdF^= , PtFg= and GeF^~ octahedra are extremely similar in si2e and shape. This will be substantiated in the following discussion.

Fluoselenonium hexafluopalladate (IV) is an

"acid" in the selenium tetrafluoride solvent system. It can be "neutralized" by a "base" such as potassium pentafluo- selenate(IV) in selenium tetrafluoride to yield a "salt" - potassium hexafluopalladate (IV):

K PdF 4SeF (SeF3)2PdF£ 4- 2KSeF^ > 2 6 * 4

An X-ray powder photograph of the product can be wholly indexed on the basis of a trigonal unit cell. When potassium hexafluopalladate (IV) was prepared in bromine trifluoride Pl by the method of Sharpe it yielded an X-ray powder photo• graph which contained the lines of the trigonal modification along with strong lines which were associated with another phase. This is in agreement with Sharpe*s observation that some bromine trifluoride was solvated and could not be removed from the compound. Potassium hexafluopalladate (IV) o was first prepared by Hoppe and Klemm in a hexagonal

modification, a = 5.75, c = 9.51 A° , by fluorination of the corresponding chloride at 270° . 13

Compounds of the type A2MF£, where A s K, Rb, Cs ' and M • Pd, Pt, Ge are found in three energetically similar crystal structures which are:

(i) the trigonal or K2GeF£ type structure

(ii) the hexagonal or K2MnF£ type structure

(iii) the cubic or K2SiF£ type structure

Much ambiguity exists in the previous classification of these structures. Compounds which have been used to typify a structure have been found to exist in more than one modification. This is further complicated by the frequent

description of the trigonal K2GeF^ type structure as hexa• gonal. The only unambiguous system of classification would be to refer directly to the space group concerned. This is not practical, however, because in many cases sufficient information is not available.

Only a trigonal modification of potassium hexa- fluoplatinate (IV) J has been reported. The structural data for this and the isostructural potassium hexafluo- 24 germanate are compared in Table 3 with the new modification of the hexafluopalladate.

The similarity of the PtF^~ and PdF^* units in shape and size is striking. The presumed electronic con•

4 4 6 6 figurations in the Pt* and Pd* ions (5<3g and 4d^ respect• ively) is also very similar. In view of this, the difference in lability of the complex ions is surprising. In water, 14

TABLE 3

Trigonal Modifications of Potassium Salts of

Hexafluo-, Quadripositive Ge, Pd and Pt

a c c/a Xf Zf Z^ M-F Reference

K2GeF6 5.62A° 4.65A° .827 0.148 0.220 0.700 1.77A° 24

0 K0PdF/r 5.72A° 4.67A .8l6 0.15 0.24 0.70 1.86A° Present d ° Work

K2PtF6 5.76A" 4.64A° .806 0.15 0.25 0.74 1.91A° 23

Atomic positions of space group are

1 Pd (Pt, Ge) in 0, 0, 0;

2 K in 1/3, 2/3, Z; 2/3, 1/3, Z ;

6 F in X, 2X, Z; X, X, Z; 2X, X, Z;

X, 2X, Z; X, X, Z; 2X, X, Z. 15 hexafluopalladate (IV) is instantly hydrolyzed to the dioxide and hydro gen fluoride. The hydrolysis of hexafluo- platinate is extremely slow, and hexafluoplatinate may even be recrystallized from water.

Bromine trifluoride does not appear to be capable of stabilizing quadripositive palladium, laftien a sample of fluoselenonium hexafluopalladate (IV) was reacted with bromine trifluoride, it dissolved to give a solution of terpositive palladium. The reaction can probably be repre• sented by the equation:

2 (SeF3)2PdF6 «• 3BrF^—> 4SeF4 2 BrF^, PdF^ * BrF^

An alternative to the formation of would be the formation of . Since quadripositive selenium does not appear to reduce quadri• positive palladium below 150° , it is reasonable to suggest that bromine trifluoride is the reducing agent. Bromine trifluoride has been observed to act as a reducing agent, in other reactions with transition metals in high oxidation 25 states, by other workers. J The reaction goes to completion because selenium tetrafluoride, which stabilizes quadri• positive palladium, has a boiling point appreciably lower than the boiling point of bromine trifluoride and Is, therefore, driven out of the solution. A possible explan• ation for the above reaction is that bromine trifluoride does not act as a fluoride ion donor in this system and so cannot stabilize quadripositive palladium as hexaf luo palla- date (IV). The linkage may take place through a fluorine 16 bridge. Fluoselenonium hexafluopalladate (IV) decomposes at 155° to palladium difluoride. The palladium appears to be reduced directly from the quadripositive state to the dispositive state according to the reaction

(SeF3)2PdF£ > PdF2 *• SeF$ * SeF4 A terpositive palladium compound was not detected. The reduction did not depend on an atmosphere of selenium tetrafluoride being present since the difluoride was formed even when the decomposition was carried out in a vacuum. A further attempt was made to prepare a selenium tetrafluoride derivative of terpositive palladium by reacting palladium trifluoride with selenium tetrafluoride. At room temperature there was no apparent reaction. At the boiling point of selenium tetrafluoride the palladium trifluoride was reduced to pure palladium difluoride

2 PdF^ * SeF4 ->> 2 PdF2 «• SeF^

The selenium tetrafluoride was removed in a vacuum just above room temperature and there was no sign of a selenium tetrafluoride derivative of palladium di• fluoride. It appears that the intermediate observed by

Bartlett and Hepworth , and assumed to be a 1:1 selenium tetrafluoride - palladium trifluoride adduct, was actually a mixture of palladium difluoride and fluoselenonium 17

hexafluopalladate (17).

Selenium tetrafluoride reduces palladium tri•

fluoride at a much lower temperature than previously-

reported. It possesses properties which may make it very

useful as a reducing agent in the preparation of metal

fluorides. It is one of the few available reducing agents

for fluorides iwkich is a liquid at room temperature..The

relatively high boiling point (10(?) is an added convenience.

Selenium tetrafluoride is also one of the best ionizing

solvents for fluorides and as observed earlier the fluoride

ion donor properties are effective in the stabilization of

certain oxidation states of transition metals. The non oxidizing properties of this solvent are also of value in

the preparation of derivatives of elements in low and easily oxidized oxidation states.

Caesium trifluopalladate (II) has been prepared by Bartlett^ by reacting and palladium

difluorlde in selenium tetrafluoride solution. When potas•

sium fluoride is substituted for the caesium fluoride no

reaction occurs. Caesium fluoride would be expected to be

a stronger base than potassium fluoride in a fluoride solvent

system and caesium fluoride is much more soluble than potas•

sium fluoride in fluoride solvents.

An attempt was made to prepare a complex fluoride

of terpositive palladium by reacting palladium trifluoride 18 and potassium fluoride in selenium tetrafluoride. The possibility existed that a strong base such as potassium fluoride might stabilize terpositive palladium in selenium tetrafluoride as it stabilizes quadripositive palladium in the same solvent.

The reaction between equimolar quantities of potassium fluoride and palladium trifluoride in selenium tetrafluoride yielded a mixture of palladium difluorlde, potassium hexafluopalladate (IV) and some other phase which gave an X-ray pattern of very diffuse lines.

The reaction between two molar parts of potassium fluoride and one molar part of palladium trifluoride did not yield palladium difluorlde. The major phase was a magenta solid which gave an X-ray powder photograph pattern of diffuse lines identical to that observed in the product from the 1:1 mixture. The magenta solid could not be obtained free of impurities. The main impurities appeared to be potassium pentafluoselenate (IV) and potassium hexa- fluosilicate (IV). The solid Impure product had zero magnetic moment, strongly indicating that the product was a dipositive complex of palladium, since any terpositive complex would have at least one unpaired electron spin, lalhen the magenta solid was treated with hydrochloric acid, yellow potassium tetrachloro-palladate (II) was formed. 19

Two possibilities exist for the composition of the magenta product. These are KPdF. and K PdF„. If the 3 2 4 reaction were a straight foreward reduction and complexing of the palladium, the decision would be simple. A 1:1 molar ratio of reactents would react in one of two ways

2 KF * 2PdF3 * SeF4 > PdF2 * K2PdF4 * SeF^

2 KF 4- 2PdF3 + SeF4 > 2KPdF3 f SeF£ in the same manner, a 2:1 molar ratio would react in one of two ways

4 KF * 2PdF3 «• SeF4 > 2K2PdF4 + SeF6

4 KF * 2PdF3 * 3SeF4 > 2KPdF3 * 2KSeF^ «• SeF6

Neither a 1:1 nor 2:1 ratio resulted in a pure product.

PdF2 was present in the 1:1 reaction, but large quantities of KSeFjj were produced in the 2:1 reaction. The presence of potassium hexafluopalladate (IV) in the product was also unusual. To explain the results, it is necessary to postulate the formation of an intermediate complex of terpositive

palladium of formula K2PdF^. The reaction then proceeds by reduction of the complex or disproportionation. Both pro• cesses probably occur.

PdF3 + 2KF V K2PdF^

2K2PdF^ 3SeF4 > -KPdF3 2KSeF^ * SeF^

mF 2K2PdF6 1- SeF4 y &2 6 * KPdF3 KSeF^ 20

In the 1:1 reaction, enough potassium fluoride is present to complex only half of the palladium trifluoride. The other half is vulnerable to reduction to palladium di- fluoride, which will not react with potassium fluoride.

The formation of the terpositive palladium complex appears to be a rapid process, while the reduction or dis- proportionation of the complex is a slower process, the rate of which is comparable to the rate of reduction of palladium trifluoride by selenium tetrafluoride.

The absence of paramagnetism and the indexing of the X-ray powder photograph lines on the basis of a tetragonal unit cell, a s 4.36, c = 3.46 - .03A , unfortun• ately give no definite indications of the composition of the dipositive complex. For KPdF^ a Perovskite type structure

would be expected and for K2PdF4 a Spinel type structure would be expected. With all electron spins paired, a dis• tortion would be expected in both structures which could result in a tetragonal distortion of the unit cell.

When the bromine trifluoride, auric fluoride complex is treated with selenium tetrafluoride, the bromine trifluoride is displaced by the selenium tetrafluoride to form an orange-yellow solid which is a 1:1 selenium tetra• fluoride adduct of auric fluoride.

AuF^jBrF^ «• SeF4 >AuF3,SeF4 *• BrF^ 21

o

The complex is diamagnetic and is stable up to 200 . The high thermal stability of the compound contrasts with the bromine trifluoride adduct which is decomposed to bromine trifluoride and auric fluoride at 180 . This is an indication that there is a difference in the bonding. The selenium tetrafluoride complex Is probably a fluoselenonium salt.

Terpositive gold is pseudoisoelectronic with dipositive palladium, but whereas the latter exhibits para• magnetism, terpositive gold is diamagnetic. The diamag- netism could be the result of a square planar or tetragonal

splitting of the 5d orbitals, in which one orbital (dxa_ y4> is of much higher energy than any of the others. The electron configuration would be dxz dyz dz2 dxy dx2-yz Au*3

A study of the pyrolysis products of the complex using X-ray powder techniques may reveal a lower fluoride.

To date, only the terpositive valence state has been observed in fluorides. It is also probable that a higher fluoride will be made in the future. CONCLUSION

The terpositive state of palladium is unstable in selenium tetrafluoride. Selenium tetrafluoride acts as a reducing agent to reduce palladium trifluoride to palladium difluorlde. In the presence of a fluorinating agent, selenium tetrafluoride stabilizes the quadripositive state of palladium. Strong evidence exists which shows that selenium tetrafluoride acts as a fluoride ion donor, resulting in the SeF^*" ion and such ions as hexafluo• palladate (IV) and tetrafluoaurate (III).

The hexafluopalladate (IV) ion very closely resembles the hexafluoplatinate (IV) ion in size, shape, and M-F distances. Despite this similarity and the similar electron configurations of the metal ions, hydrolysis of the two complex ions proceeds at vastly differing rates.

This behavior cannot be accounted for in terms of structure and must be related to some other property of the ions.

The slow hydrolysis of the hexafluoplatinate (IV) is character• istic of an SN.^ mechanism, the slow unimolecular dissociation into a five coordinate ion and a fluoride ion being the rate determining step. It is probable tha$ the hydrolysis of the hexafluopalladate (IV) ion is also a first order process, the unimolecular dissociation being much more rapid than

in the platinum case. An SN2 mechanism is unlikely to apply in either case since the required seven coordinate inter• mediate would necessitate the availability of a vacant bonding 23

TABLE 4

Fluorides of Palladium 24 orbital. The electronic configurations of the platinum and palladium ions in these complexes do not provide for

such an orbital.

Few complex fluoride derivatives of di- and terpositive palladium have been prepared, but it is probable that other compounds of this type will be prepared by the use of other fluoride solvents, such as fluosulfonic acid or . Magnetic susceptibility studies

and crystal structure determinations of such complex lower fluorides would prove very interesting. EXPERIMENTAL

I General Techniques

a) Glassware

Most volatile fluorides attack Pyrex glass. The

attack is often due to the presence of which is sometimes formed by the hydrolysis of the fluoride by the water which is invariably present on the surface of the glass. The hydrolysis is autocatalytic in nature, and

in theory, one molecule of water could completely decompose

a sample of fluoride and badly attack the glass container.

MFn «• H20 >> M0Fn_2 * 2HF

4HF f Si02 > SiF4 * 2H20

MFn * H2O y etc.

Because of this, steps must be taken to

thoroughly dry all apparatus. This is best done by

"flaming out" under vacuum. It is also necessary to insure

that the fluorides to be handled are free from hydrogen

fluoride.

Since the reactive volatile fluorides attack

hydrocarbon vacuum tap greases, grease must

be used on all ground glass surfaces. Even fluorocarbon

grease is attacked to some extent by such reagents as

bromine trifluoride and selenium tetrafluoride. In this

work, therefore, the use of glass stopcocks and ground glass i joints has been kept to a minimum. 26

Silica is more resistant than Pyrex to attack by hydrogen fluoride and it would be advantageous to use an apparatus constructed entirely in silica but the added inconvenience entailed in its construction outweighs the advantage. Silica reaction bulbs which were connected to the Pyrex systems by means of graded seals were used. These seals stood up very well to thermal shock but fractured when subjected to mechanical strains.

b) X-Ray Photographs

X-ray powder photographs of the solid products were taken using a 14.32 cm. General Electric camera. The radiation was filtered using nickel foil (.089 mm.) to remove radiation. The X-ray tube was operated at 40 kilovolts and 20 milliamps and an average exposure under these conditions was 12 hours. The dry-box technique was employed in preparing samples. A portion of the substance was finely powdered and charged into thin walled capillaries

(0.5 mm. diameter) of Pyrex glass or silica. The capillaries were quickly sealed using a small, very hot flame.

c) Magnetic Measurements

Magnetic susceptibilities of the solids were obtained using a Gouy balance. A Varian #4004 magnet with

2 inch tapered pole faces provided a magnetic field of approximately 15 kilogauss with a coil current of 2 amperes.

For the determination of magnetic susceptibilities 27 by the Gouy method, the specimen tube is so placed that the bottom of the sample is in the center of the homo• geneous portion of the magnetic field. Also, the length of the sample is such that its top is in a region of negligible field.

The molar susceptibility is given by the expression

Xm sAW.M.C W where

Xm - molar susceptibility of sample

W • weight of sample

AW B change in weight of sample on application of field

M B molecular weight of sample

C s the apparatus constant

The apparatus constant can be determined accurately by using standard substances of known susceptibility. Two standards are commonly used. They are

-6

Benzene Xg - Xrn^ = -0.702 x 10" c.g.s. (27)

6 HgCo (SCN)4 X* » Xrn^ B 16.44 x io" c.g.s. (28) where X^ is the gram susceptibility. All susceptibilities were measured at room temperature.

Some of the magnetic moment samples were made up in a dry-box in dry Pyrex glass tubes which were quickly sealed. Since the other material encountered was loose and 28 finely powdered It could be handled in a closed system. In this preferred procedure, a side-arm of the glass tubing used for magnetic moments was sealed on to the reaction bulb prior to the reaction. The reaction bulb was sealed off under reduced pressure. Some of the product was then transferred to the arm which was sealed off.

II Analytical Methods

The composition of solid products encountered in the reactions which were studied was determined by chemical analysis. Standard procedures were used. X-ray powder photography was used to identify compounds and detect mixtures. A library of X-ray powder photographs of known substances was built up to facilitate this,

a) Fluorine

The main problem in an analysis for fluorine is interference from other ions. This is overcome by first separating the fluoride by distillation as . The fluoride can be precipitated as triphenyl tin fluoride, , or lead chlorofluoride. The lead chlorofluoride method was used in this work because of its simplicity and the favourable multiplication factor.

Volumetric determination of fluoride by titration with thorium nitrate was not favoured because of the subtle colour change at the end point with the consequent need of much practise to obtain reliable results. 29

The fluorine compound was weighed by difference

into a slightly alkaline solution (50 ml). This solution was placed in a distillation flask fitted with a side arm

and dropping funnel, a thermometer and a condenser. About 29 25 ml. of concentrated sulfuric acid or 70% perchloric acid were added. The solution was boiled and the temperature of o o the boiling mixture was maintained between 130 C. and 135 C. by adding water dropwise as the distillation proceeded.

Approximately 250 ml. of the distillate, (which presumably

contained the fluoride as hydrofluoric and hexafluosilicic acids) was collected. Perchloric acid was found to give more

consistent results than sulfuric acid. It is believed that

small amounts of the acid sometimes splash into the condenser

and are washed into the distillate. In the precipitation of lead chlorofluoride, lead sulphate will also precipitate whereas lead perchlorate is soluble.

To precipitate the fluoride, the distillate was neutralized and made faintly alkaline with sodium hydroxide, using bromphenol blue as an indicator. Concentrated hydro•

chloric acid (1 ml.) was added, the solution heated to 80°C. and lead .nitrate (5 gm.) added. The solution was then heated

almost to the boiling point and hydrated sodium acetate (5 gm) was added. The solution was kept at the boiling point for one hour and was allowed to cool overnight. The precipitate was filtered on a sintered glass crucible, washed with 30

o saturated lead chlorofluoride solution and dried at 140 -

150°C. for two hours,

b) Palladium

A solid weighed sample was placed in a beaker and dissolved in concentrated hydrochloric acid. The solution was evaporated several times to near dryness with hydrochloric acid to remove all traces of fluoride, which would interfere with most quantitative analyses. The evaporation product and 26 ml. of concentrated hydrochloric acid were made up to 250 ml.

Two different methods were used to determine palladium. In the first method, aliquots of palladium solution or weighed samples of compounds were placed in an alkaline carbonate solution. The hydrated oxide precipitated.

It was filtered on a quantitative paper and was ignited to palladium metal. It was heated to constant weight in a stream of hydrogen.

The most reliable analytical method was to pre• cipitate the palladium from a hot dilute solution as the dimethyl glyoxime complex. A minimum volume of one percent dimethylglyoxime in was used. The yellow complex was filtered on a sintered glass crucible, washed with hot water, dried at 155°C, and weighed. 31

c) Selenium

Selenium was precipitated as the element by passing sulfur dioxide into a strong hydrochloric acid solution. It was filtered on a sintered glass crucible and was washed with alcohol and ether and then dried at

110°.

d) Gold and Selenium

Gold and selenium are precipitated simultaneously by almost any reducing agent. Separation can be accomplished by filtering the gold-selenium mixture on a sintered glass crucible, weighing, and then dissolving the selenium in nitric acid of specific gravity 1.25.

e) Bromine

Bromine was precipitated from acid solution as the silver salt.

Ill Reactants

a) Fluorine Supply

Fluorine was supplied in a steel gas cylinder con• taining six pounds of fluorine at 400 p.s.i. by the Allied

Chemical Company. The cylinder was installed in an upright position in a walk-in fume hood and was shielded with a brick safety screen. Reduction of the gas pressure was achieved with two stainless steel needle valves (Hoke type

316 No. Y 343H) in series. The high pressure gas line was 32

constructed from ^ inch stainless steel pressure tube,

threaded and silver soldered at all joints.

On the low pressure side of the needle valves

\ inch copper tubing connected with brass compression

fittings was used. In the low pressure line, directly after

the pressure reducing needle valves, was a blow-off con•

sisting of a silver soldered T-joint of \ inch copper

tubing with its outlet dipping into a test-tube containing

"Fluorolube oil" (Hooker Chemical Co., FS-5.) The blow-

off was both a safety device and a crude flow meter. The

flow-rate was measured by counting bubbles emerging at

the blow-off when the needle valve (Hoke No. 431) at the

exit of the low pressure line was closed.

To permit dilution of the fluorine, with dry

nitrogen, a brass T-joint was provided in the line. A brass needle valve (Hoke No. 431) controlled the nitrogen inlet.

A copper tube containing pellets was Inter•

posed between the blow-off and the nitrogen inlet. The

sodium fluoride removed hydrogen fluoride present in the

fluorine gas. Diluted fluorine passed from the low pressure

line through a brass needle valve (Hoke No. 431) into the

reaction systems which were connected to the line either with

brass compression fittings or with teflon tubing sealed with

Kel-F fluorocarbon grease. 33

b) Bromine trifluoride

Bromine trifluoride was supplied, in fifteen

pound stainless steel cylinders containing five pounds of

the liquid, by The Matheson Company Inc. A needle valve

(Matheson No. 55-670) was used in series with the valve

on the cylinder. The second valve was connected to pieces of apparatus by means of a short length of teflon tubing

of appropriate diameter sealed with "Kel-F" fluorocarbon

grease.

The bromine trifluoride was used in portions of

5 mis, to 15 mis. from break-seal bottles. It was trans•

ferred from the cylinder to individual bottles by vacuum

distillation in an all-glass apparatus. This consisted

of a manifold with four to six break-seal bottles with a

pair of traps at each end. Both ends of the glass apparatus

were open. One end was attached to the cylinder and the other to a vacuum pump. Bromine trifluoride was distilled

into the traps nearer the cylinder. When sufficient bromine

trifluoride had been transferred, the valves on the cylinder

were closed and the glass tubing was drawn down and sealed

with a flame near the teflon connection. A liquid nitrogen

trap was placed around one of the traps at the other end -of

the apparatus and the level of nitrogen kept as high as

possible. The bromine trifluoride was allowed to distil

and a small quantity of it quickly plugged the entrance to 34 the trap and made an effective vacuum seal. Liquid nitrogen baths were placed around each of the breakseal bottles and bromine trifluoride distilled into them. If the transference of bromine trifluoride slowed down because of loss of vacuum, usually arising from interaction of bromine tri• fluoride with the glass to form oxygen and tetra• fluoride, the plug of bromine trifluoride could easily be melted and the vacuum re-established, the seal being renewed as before. The breakseal bottles were drawn off and stored

in dry-ice in a large Dewar flask.

c) Palladium Diiodide and Dibromide

Palladium diiodide is prepared by adding the

stoichiometric quantity of iodide (as potassium iodide

solution) to a solution of bivalent palladium. The in•

soluble palladium diiodide is filtered off, washed with water and alcohol, and dried.

Palladium dibromide was prepared by evaporating an aqua regia solution of palladium with concentrated hydro- bromic acid or by dissolving palladium in hydrobromic acid containing elemental bromine. The bromide was recovered after evaporation to dryness.

d) Gold

Gold metal was used in the form of a very fine powder. 35

e) Potassium Fluoride

Anhydrous potassium fluoride was prepared by

the reaction of AR grade potassium carbonate with AR grade hydrofluoric acid. The product, which is the hydrate, was

then heated to approximately 800 C in a platinum crucible

to obtain the unsolvated salt. It was allowed to cool in

a desiccator and was then transferred to a dry-box to be

powdered and was stored In a desicator.

IV The Preparation of Selenium Tetrafluoride

Selenium tetrafluoride was prepared by the method

described by Aynsley, Peacock and Robinson,"^0 A Pyrex

glass apparatus as shown in Fig. 1 was used. Selenium

pellets (100 gms.) were placed in the reaction bulb between

traps 1 and 2. The selenium was sublimed under vacuum on

to the walls of the reaction vessel. Dry nitrogen was allowed

to enter the system at A and a slow stream of dry nitrogen

was passed from A to D. Dry-ice-alcohol baths, or pre•

ferably liquid oxygen baths, were placed around all traps.

Liquid nitrogen is not used as a refrigerant since it con•

denses fluorine. An ice bath was placed around the reaction

vessel. Fluorine was introduced into the nitrogen stream

and it reacted with the cold selenium to give selenium tetra•

fluoride, which collected as a liquid in the bottom of the

vessel. When most of the selenium had been consumed, the CO •oo

c o

w « Q:

w o

«0

fC < 36 fluorine stream was cut off and the system was purged of fluorine with dry nitrogen. The system was sealed at B and then evacuated through D. The selenium tetrafluoride was distilled into traps 2 and 3, then the system was sealed at C. A liquid nitrogen bath was placed around each of the break-seal bottles and one as high up on trap 4 as possible.

The selenium tetrafluoride in traps 2 and 3 was allowed to warm up} Some selenium tetrafluoride immediately distilled into the opening of trap 4, where it condensed and formed a plug. The remainder distilled into the break-seal bottles.

When the transference was complete the break-seal bottles were drawn off under vacuum and stored until needed in "dry- ice."

There is a definite advantage to using a plug of the reactant to seal the system during a distillation. If the vacuum in the system is lost through the formation of volatile products, such as oxygen, by attack of the reactant on the glass, it is a simple matter to open the plug and re-evacuate the system. Opening of the system after a distillation is also simplified.

V The Preparation of Palladium Trifluoride and Its Adduct With Bromine Trifluoride

In order to save time and conserve materials, two or more related preparations were often done in a single apparatus. Palladium trifluoride and its adduct with bromine 37 trifluoride were simultaneously prepared after the method 4 described by Sharpe. An apparatus was constructed of Pyrex glass and consisted of a manifold connected to a line of two traps which were in turn connected to a vacuum pump.

The manifold had a side tube containing nickel balls.

Attached to the manifold were a break-seal bottle of selenium tetrafluoride and two bulbs, each containing about three grams of palladium dibromide.

The apparatus was evacuated and the bromine tri• fluoride break-seal was opened. By placing a liquid nitrogen trap as high as possible on one of the traps, a plug of bromine trifluoride was made to form in the narrow neck of the trap. The bromine trifluoride was then distilled on to both of the palladium dibromide samples. When the trans• ference was complete, the plug of bromine trifluoride was removed and the two bulbs were allowed to warm slowly to room temperature at atmospheric pressure. The vigorous reaction between bromine trifluoride and palladium dibromide was controlled by occasionally cooling the bulbs with liquid nitrogen. Large quantities of bromine were formed in the course of the reaction. After the palladium dibromide was completely dissolved, the bromine and excess bromine tri• fluoride were pumped into the two traps. When all of the volatile substances had been removed, a dark brown solid remained. One of the reaction bulbs was sealed off at this 38 time to obtain a sample of the complex fluoride. This was the bromine trifluoride adduct of palladium trifluoride.

A sample was taken for analysis.

Found: Br, 25.3$; P, 39.0$; Pd, 33.9$.

Calculated for BrF^, PdF3: Br, 26.5$; F, 38.0$; Pd, 35.5$

It was paramagnetic^/Weff = 2.24 B.M. at 20°C.

The complex fluoride in the remaining bulb was heated to 220°C. in a vacuum to remove all of the bromine trifluoride. The residue was black palladium trifluoride.

VI The Preparation of Fluoselenonium Hexafluopalladate (IV)

For the preparation of fluoselenonium hexafluo• palladate (IV) an apparatus very similiar to that shown in

Fig. 2 was used. Only one reaction bulb was used, however.

The apparatus consisted of two traps connected to a manifold with three branches: one branch to the reaction bulb, one branch to a bromine trifluoride break-seal bottle and the remaining branch to a selenium tetrafluoride break-seal bottle.

Palladium dibromide (3 gm.), contained in the bulb was converted to the bromine trifluoride - palladium trifluoride adduct in the manner described above. Selenium tetrafluoride was added to this adduct and the mixture was refluxed for two hours. Copious quantities of bromine were evolved. Removal of the volatile substances at 100°C. under vacuum left a yellow product, which was fluoselenonium 39 hexaf luopalladate (IV).

Found F, 45.6$; Pd, 21.9$; Se, 31.3$

(SeF3)2PdF6 requires F, 46.3$; Pd, 21.6$; Se, 32.1$ -6

The solid was diamagnetic, Xg = -.36 x 10 c.g.s. units.

VII The Reaction of Fluoselenonium Hexafluopalladate (IV) with Bromine Trifluoride

Yellow fluoselenonium hexaf luopalladate dissolved

In bromine trifluoride on warming to give a red solution.

The bromine trifluoride was removed under vacuum to leave the paramagnetic bromine trifluoride - palladium trifluoride adduct. '

VIII Reactions of Fluoselenonium Hexafluopalladate (IV)

The temperature of decomposition and the thermal decomposition products of fluoselenonium hexaf luopalladate (IV) were studied by keeping samples of the compound at set temperatures for periods of approximately one hour. Decom• position was carried out both under vacuum and at atmospheric pressure. X-ray powder photographs of the products showed decomposition to be complete in one hour at 155° (atmospheric pressure), the product being palladium difluoride. At 135°

(atmospheric pressure) decomposition was slow and incomplete.

After 30 minutes a mixture of palladium difluoride and fluoselenonium hexafluopalladate (IV) remained.

The complex fluoride reacted rapidly with water, 40 resulting in the precipitation of a brown solid containing palladium and selenium, probably palladous selenate. Hydro• chloric acid dissolved the hexaf luopallad ate and when this solution was mixed with potassium chloride a red precipitate of potassium hexachloropalladate (IV) was formed.

IX The Preparation of Palladium Difluoride

Palladium difluorlde was prepared by the re• duction of palladium trifluoride with selenium tetrafluoride.

A single Pyrex glass apparatus was used for the preparation of palladium trifluoride and its subsequent reduction with selenium tetrafluoride.

The apparatus consisted of a. manifold connected to a line of four traps. To the manifold were attached a bromine trifluoride breakseal, a selenium tetrafluoride breakseal and a bulb containing palladium dibromide (circa

3g.)

Palladium trifluoride was prepared as described above. The volatiles from this preparation were pumped into the two traps farthest from the reaction bulb. The two traps were drawn off under vacuum after the selenium tetra• fluoride break-seal had been opened. The selenium tetra• fluoride was distilled onto the palladium trifluoride and the apparatus was then opened to dry air. The reaction bulb was warmed and the selenium tetrafluoride refluxed at atmospheric pressure. The black palladium trifluoride 41 turned brown. After a two hour reflux, the excess selenium tetrafluoride was vacuum distilled at approximately 50°C.

Into the two remaining traps. The residue, which was a light brown solid was palladium difluoride.

Found: F, 26.1$; Pd, 73.1$;

Calculated for PdF2 F, 26.3$; Pd, 73.7$.

An X-ray powder photograph showed only the lines character•

istic of palladium difluoride.

X Potassium Fluoride and Palladium Difluoride in Selenium Tetrafluoride

Palladium difluoride (.440 gm.) and potassium fluoride (.353 gm.) were weighed into a breakseal bottle

in a 1:2 molar ratio. The tube through which the materials were placed in the breakseal bottle was immediately sealed.

The breakseal bottle containing the palladium difluoride

and potassium fluoride and another breakseal bottle contain•

ing about 10 mis. of selenium tetrafluoride were both sealed on to a Pyrex glass manifold which was connected to a vacumm

pump through two traps.

The apparatus was evacuated. Both breakseals were

then broken and the selenium tetrafluoride was vacuum distilled on to the palladium difluoride and potassium fluoride

mixture with the system sealed by a plug of selenium tetra•

fluoride in the neck of one of the traps. After the transfer of the selenium tetrafluoride, the plug was removed and 42 dry air was admitted into the apparatus. The mixture was warmed and refluxed for four hours, after which the selenium

tetrafluoride was removed into the t\m traps. The residue was dried in a vacuum at approximately 80°C.

The product was a mixture of a white and a very dark or black solid. It was paramagnetic. An X-ray powder

photograph showed it to be a mixture of palladium difluoride

and potassium pent af luo selenate CEV) .

XI Potassium Fluoride and Palladium Trifluoride in Selenium Tetrafluoride

a) In Molar Ratio 2:1

The preceding reaction was repeated using potassium

fluoride (.348 gm.) and palladium trifluoride (.490 gm.)

in a 2:1 molar ratio. On warming the reaction mixture, a black suspension was formed. The color changed on refluxing

and after one hour was purple. Two phases appeared to be

present: a dense purple solid which sedimented quickly and

a white solid which settled more slowly in admixture with

some of the purple solid. The selenium tetrafluoride was

removed slowly under vacuum and the natural separation of

the phases was maintained. The residue was dried under

vacuum at approximately 80°. Small quantities of the two

phases were separated mechanically in a dry-box. X-ray

powder photographs of these two samples were taken. A

mixture of the two phases was found to have zero magnetic 43

TABLE 5

X-Ray Data for a Potassium Salt of Fluopalladate (II) (CuK^ radiation)

A2

lobs Obs. Calc. hkl

W 0.0526 0.0530 100

M 0.0835 0.0835 001

V.S. 0.1071 0.1060 110

M 0.1403 0.1365 101

V.W. 0.1840 0.1895 111

¥ 0.2699 0.2650 210

W 0.2854 0.2955 201

M 0.3420 0.3485 211

V.W. 0.3901 0.3870 102

Possible v.w. 0.4244 0.4240 220 doublet 0.4400 112

V.W. 0.5109 0.5075 221

v.v.w. 0.5586 0.5605 301

v.w. 0.6785 0.6890 320

Possible v.w. 0.9518 0.9540 330 doublet 0.9560 411

V.S. > S.y M.S. y M. ^> M.W. y W. y V.W. ^ V.V.W. 44 moment. The dense purple phase gave a powder photograph consisting of a series of blurred lines, indicative of poor crystallinity (i.e. small particle size). The poor quality of the photographs has made unambiguous indexing of the lines impossible, but they are consistant with a tetragonal unit cell: a = 4.36, c = 3.4-6 - .03A. The calculated and found values for 1/d2 are given in Table 5.

The pink phase contained strong lines due to potassium pentafluoselenate (IV) and also a pattern character• istic of potassium hexafluosicicate (IV). Lines due to the trigonal form of potassium hexafluopalladate (IV) were also observed.

b) In Molar Ratio 1:1

The above reaction was carried out using a 1:1 molar ratio of palladium trifluoride and potassium fluoride.

An X-ray powder photograph of the product showed palladium difluoride, potassium hexafluosilicate and the series of blurred lines characteristic of the dense purple-red phase described above.

XII The Preparation of Potassium Hexafluopalladate (IV)

An apparatus was constructed as shown in Fig. 2.

Potassium bromide (1.688 g.) and palladium dibromide (1.892g.) were accurately weighed in a 2:1 molar ratio into separate bulbs. The bulbs were silica and were joined to the Pyrex

45 system through graded seals. After the system was evacuated the bromine trifluoride breakseal was opened.

Liquid nitrogen baths were placed on the two reaction bulbs.

A liquid nitrogen bath was placed on the left hand trap with the nitrogen level as high as possible. Bromine tri• fluoride condensed in the tube above the trap and formed a plug. The remaining bromine trifluoride distilled into the two reaction bulbs. The plug was then removed and dry air was allowed into the system. The bromine trifluoride was allowed to melt, and a reaction took place in each bulb.

Both reactions liberated copious quantities of bromine:

3KBr r 4BrF3 y 3KBrF4 • 2Br2

2PdBr2 «• 4BrF^ »2PdF^, BrF^ • 3Br2

Both solutions were refluxed for a few minutes to insure complete reaction. The bromine and bromine trifluoride were distilled into the two traps. The bulbs were warmed to 10G C. to completely remove the excess bromine tri• fluoride. The selenium tetrafluoride breakseal was then opened and a plug of selenium tetrafluoride was formed in the entrance of the left hand trap. After transference to the two bulbs was complete, the system was again opened to an atmosphere of dry air and the selenium tetrafluoride was melted and warmed. The bromine trifluoride in the potassium tetrafluobromite (III) was easily displaced by the selenium 46

tetrafluoride:

KBrF, + SeF. • .KSeF^ + BrF0

- 4 4 ^ 5 ' 3

The brown bromine trifluoride complex of palladium tri• fluoride assumed the yellow-brown colour of fluoselenonium hexafluopalladate (IV). Bromine was evolved:

6PdF3, BrF3 «• 12SeF4 > 6(SeF3)2PdF6 <• Br2 * 4BrF^

After prolonged refluxing (1-2 hours) of the mixtures in the separate bulbs the apparatus was tipped and the potassium pentafluoselenate (IV) solution was poured into the palladium fluoride suspension. The yellow-brown colour of the latter changed to a bright canary yellow. Complete transference of the potassium pentafluoselenate (IV) was achieved by distilling selenium tetrafluoride into the reaction bulb and tipping the apparatus again. After a reflux of one hour the

product appeared homogenous. The volatiles were removed under vacuum, at 100°, to leave a fine yellow powder. This was potassium hexafluopalladate (IV).

Found: Pd, 34.6$; F, 37.9$; yield, 2.166 g.

K2PdF6 requires Pd, 35.7$; F, 38.1$; yield, 2.125 g. A preparation of potassium hexaf luopalladate (IV) was carried out in bromine trifluoride by the method of 21

Sharpe. A 2:1 molar ratio of potassium bromide and

palladium dibromide was placed in a reaction bulb. This

mixture was reacted with bromine trifluoride using the same 47 techniques described above. The volatiles were removed under vacuum at 100° to leave a yellow powder. X-ray

powder photographs showed a complex pattern of lines, among which were the lines characteristic of the trigonal mod•

ification of potassium hexafluopalladate (IV).

XIII The Crystal Structure of Potassium Hexafluopalladate (IV)

Debye X-ray powder photographs of the potassium hexafluopalladate (IV) were taken as described. Arc lengths on a selected photograph were measured with an accurate

scale and vernier. Arc lengths were converted into d

spacings and Vd2 values with the aid of an Alwac III E digital computer. The pattern was indixed on the basis of

a trigonal unit cell, a= 5.7*17 ± .003 A° , c = 4.667 t .003A0 .

For the determination of unit cell dimensions the Nelson,

Riley extrapolation function-^1 was employed. The calculated

and found values of Vd2 are given in Table 6.

Comparison of the unit cell dimensions of tri•

gonal potassium hexaf luopallad ate (IV) with those of the

trigonal forms of potassium hexafluoplatinate (IV) and

potassium hexafluogermanate (IV) suggested that the symmetry of these three compounds was the same. The space group

chosen, therefore, was C 3m - with the following special

positions

Pd in (a): (0, 0, 0)-,

2K in 2(d): (1/3, 2/3, z), (2/3, 1/3, 2)5 48 - TABLE 6 Assignment of the X-Ray Reflections of lyPdF^

h k 1 Calc. 0bst h k 1 Calc. OPS.

100 0.0408 0.0424 313 0.9435 0.9439

001 0.0459 0.0475 322 0.9589 0.9607

101 0.0867 0.0889 500 1.0200 1.0215 110 0.1223 0.1251 214 1.0202

Ul 0.1683 0.1706 412 1.0404 1.0415

201 0.2091 0.2116 501 1.0659 1.0687 102 0.2244 0.2266 403 1.0659

210 0.2856 0.2889 330 1.1016 1.1029

112 0.3060 0.3092 331 1.1475 1.1493 211 0.3315 0.3342 005 1.1478

202 0.3469 0.3495 421 1.1884

300 0.3672 0.3696 323 1.1884 1.1895

301 0.4131 105 1.1884 0.4158 003 0.4132 502 1.2036 1.2055

103 ' 0.4539 0.4567 224 1.2242 1.2254

212 0.4693 0.4716 510 1.2648 I.2670 220 0.4896 0.4916 314 1.2650

310 0.5304 0.5343 115 1.2701 1.2715 113 0.5355 413 1.2699 0.5381 211 0.5355 511 1.3106 1.3116 302 0.5509 0.5534 205 1.3110 48A

TABLE 6 (cont1d)

h k 1 Calc. ObsOPS.t h k 1 Calc. Obs.

203 0.5764 422 1.3260 1.3270 0.5777 311 0.5763 503 1.4331 1.4338 401 0.6987 215 1.4333 0.7005 213 O.6987 600 1.4688 1.4698

312 0.7140 0.7158 430 1.5095 1.5105 004 0.7345 0.7372 324 1.5097 320 0.7752 0.7779 305 1.5150 321 0.8213 0.8245 1.5150 333 1.5147 402 0.8364 0.8379 423 1.5556 410 0.8568 0.8595 1.5560 431 1.5555 223 0.9027 0.9056 520 1.5912 1.5914 411 0.9027 225 1.6374 1.6376 49

6F in 6(i): (x, x, z ), (x, 2x,z ), (2x, x, z ),

(x, x,z), (x, 2x,z), (2x, x,Z).

The intensities of lines were calculated with the

formula 2 P 1 1- cos22$ I <*C F hkl sin 6 cosO

where F, , _ is the calculated structure factor for the set hkl 2 of planes hkl, p is the permutation factor, and 1 » cos 2Q

sin2© cos©

is a combination polarization, Lorentz and geometric factor.

A problem arose, when it was found that the X-ray

powder photograph of the sample which was considered purest

and most crystalline showed anomalous intensities which did not correspond to any reasonable structure. Close Inspection of the photograph showed that the lines which were much

stronger than expected were all due to planes of atoms parallel

to the C axis. The 001 line was weaker than expected and uneven in this photograph. The intensity of the 100 line was very strong in the equatorial zone of the photograph, but faded appreciably at its edges. This evidence established that preferred orientation of the crystallites in the glass

capillary had occured. The crystals are presumably needle

shaped, the C axis being parallel to the axis of the crystal.

When packed into a fine capillary the crystals next to the wall of the tube tend to line up parallel to the wall with

their long axes along the length of the capillary. Since

potassium hexaf luopalladate (IV) has a high absorption 50 coefficient, the intensity of X-ray powder photograph lines is determined largely by the outermost layer of the cylinder of material.

An X-ray powder photograph of another preparation which had been more carefully powdered gave a pattern in which the preferred orientation effects were absent. The relative intensities were estimated visually on a scale v.s.^ s. m.s.^ m. ^ m.w. ^ w. ^ v.w. ^ v.v.w.

The final positions of the atoms were obtained by trial and

error methods. The structure factor Fnkl for a plane of atoms is the algebraic sum of the structure factors of the various atoms in that plane. phki= Wpd> *ww *WF>

F^^(Pd) is independent of any variables because of the unique position assigned to the Pd atom. The value

F K is de en<3ent of Fhkl(Pd) is therefore constant. hkJ.( ) P

F F is de enderrfc on 0 on only one variable, Z. nk.x( ) P "k™

variables, Xp and Zp. Intensities due to planes of the hkO series will be independent of Z, and will therefore depend

only on Xp. Using an Alwac III E digital computer, values

2 F pd F (K for p^ (1 ,^cos 2e) ^ hkl( ) * hkl ^ ^ (sin © cos©) ' '

P^ (1 t cos22 ) £(F (F)) were calculated and

(Mrreedse ) ( hK1 %)

tabulated for a range of possible values of ZK, XF and Zp. 51

Values of the parameters were arrived at by comparison of the calculated intensities of all possible combinations of parameters with the observed values of the intensities.

The final values for the parameters were: .70 .02 m .15 Zk z t xF t .01 Z .24 * .02 P -

The observed and calculated intensities for this structure are listed in Table 7.

TABLE 7

Observed and Calculated Intensities for K2 PdP6 hkl hkl I . *calc ''"calc obs obs 100 S 721 211 M.S. 275 001 M 244 202 S. 346

101 V.S. 949 300 w. 81

110 s 427 301,003 w. 69

200 Nil .5 103 v.v.w. 15

111 M.W. 153 212 M.S. 259

002 Nil 8 220 M. 145

201 V.S. 794 310 V.W. 31

102 M 210 113,221 M. 137

210 W 42 302 V.W. 23

112 W 57 203,311 M.S. 189 400 Nil 2 BIBLIOGRAPHY

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