THE FLUORIDES of PLATINUM and R E L a T E D Compounds by DEREK HARRY LOHMANN B.Sc, University of London, 1953 M.Sc, Queen's Univ
and related compounds
by
DEREK HARRY LOHMANN
B.Sc, University of London, 1953 M.Sc, Queen's University, Ontario, 1959
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OF THE REQUIREMENTS FOR THE DEGREE OF
DOCTOR OF PHILOSOPHY
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CHEMISTRY
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THE UNIVERSITY OF BRITISH COLUMBIA
October 1961, In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of
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Department of CHEMISTRY
The University of British Columbia, Vancouver 8, Canada.
Date 31st October 1961. %\\t Pntesttg of ^irtttslj Columbia
FACULTY OF GRADUATE STUDIES
PROGRAMME OF THE
FINAL ORAL EXAMINATION
FOR THE DEGREE OF
DOCTOR OF PHILOSOPHY
PUBLICATIONS oi
. I. "Polar effects in Hydrogen abstraction reactions," M. P. Godsay, DEREK HARRY LOHMANN D. H. Lohmann and K. E. Russell, Chem. and Ind., 1959, 1603. B.Sc, University of London, 1953 M.Sc, Queen's University, Ontario, 1959 2. "Two new fluorides of Platinum," N. Bartlett and D. H. Lohmann,
Proc. Chem. Soc, 1960, 14. TUESDAY, NOVEMBER 28th, 1961, AT 1:00 P.M.
3. "The reaction of 2,2-Diphenyl-l-Picrylhydrazyl with 9,10-Dihy- droanthracene and 1,4-Dihydronaphthalene," I. S. Hogg, D. H. IN ROOM 342, CHEMISTRY BUILDING Lohmann and K. E. Russell, Canad. J. Chem., 1961, 39, 1394.
4. "The kinetics of reaction of 2,2-Diphenyl-l-Picrylhydrazyl with COMMITTEE IN CHARGE phenols," I. S. Hogg, D. H. Lohmann and K. E. Russell, Canad. Chairman: F. H. SOWARD J. Chem. 1961, 39, 1588. N. BARTLETT C. A. McDOWELL K. B. HARVEY V. J. OKULITCH L. D. HAYWARD E. TEGHTSOONIAN
External Examiner: H. J. EMELEUS Cambridge University THE FLUORIDES OF PLATINUM AND RELATED The crystal structures of the tetrafluorides of platinum rhodium, COMPOUNDS tin and lead were investigated. No similarity in structure was found. A brief investigation into the fluorides of rhodium has led to ABSTRACT the suggestion that a pentafluoride, in addition to a terafluoride, The fluorides of platinum have been reinvestigated. Attempts exists. to prepare a difluoride were unsuccessful. It is suggested that this is due to it being unstable towards disproportionation. X-ray Crystallographic evidence is presented as evidence for a trifluoride of platinum although a pure sample has not been isolated. GRADUATE STUDY This trifluoride is shown to be isostructural with the rhombo- hedral trifluorides of palladium, iridium and rhodium. Field of Study: Chemistry Platinum tetrafluoride has been reinvestigated. It was found to be diamagnetic and to have a lattice of slightly-distorted, tetra• Topics in Inorganic Chemistry N. Bartlett, H. C. Clark, gonal uranium tetrachloride type. The adducts of platinum tetra• fluoride with bromine trifluoride and selenium tetrafluoride were W. R. Cullen, G. J. Willis investigated further and found to be diamagnetic. The platinum tetrafluoride, selenium tetrafluoride adduct was shown to be iso• Advanced Inorganic Chemistry N. Bartlett, H. C. Clark structural with the corresponding palladium and germanium com• pounds. An ionic lattice is suggested for these compounds. Bromine Crystal Structures K. B. Harvey, L. W. Reeves trifluoride adducts do not form a similar series and this, combined with their physical properties, led to the suggestion that these com• Molecular Structure L. W. Reeves, C. Reid, J. Trotter pounds are more covalent in nature. Seminar in Chemistry N. Bartlett, K. B. Harvey The previously unknown pentapositive state of platinum has bein established. Platinum pentafluoride is a deep-red, reactive Other Studies: solid which readily disproportionates on heating. It gives rise to 1:1 adducts with iodine pentafluoride and chlorine trifluoride. These, Differential Equations C. Froese like the bromine trifluoride adducts, are low-melting solids. Potas• sium fluoroplatinate (V) was prepared as a deep-yellow solid, Digital Computers H. Dempster crystallizing with the rhombohedral potassium fluorosmate lattice. A pentapositive oxyfluoride, platinum oxytrifluoride, was found; it Nuclear Physics J. B. Warren is suggested that this is polymeric. Platinum hexafluoride has been briefly investigated.
A very reactive oxyfluoride, of formula PtO„F6, has been pre• pared and investigated. It is a deep-red solid which can be sublimed at 90° in a vacuum. It melts with decomposition at 219°. It is paramagnetic and crystallizes in a cubic lattice. Many of its chemi• cal properties were studied. It is suggested that this compound is platinum peroxidehexafluoride. ,1
British Columbia * REQUEST *
Transaction Number 4642692
Patmn Name
PaLrM. Number
Item Number 39424050651303 Lille Fluorides of platinum and related coi
Pickup Location I.K. BARBER circulat
Qgto/Ti mp (ii)
ABSTRACT
The fluorides of platinum have been.reinvestigated. Attempts to
prepare a difluoride were unsuccessful. It is suggested that this is-
due to it being unstable towards disproportionation.
X-ray Crystallographic evidence is presented as evidence for a
trifluoride of platinum although a pure sample has not been, isolated.
This trifluoride is shown to be isostructural with the rhombohedital
trifluorides of palladium, iridiumi and rhodium.
Platinum tetrafluoride has been reinvestigated. It was found
to be diamagnetic and to have a lattice of slightly-distorted, tetragonal
uranium tetrachloride type. The adducts of platinum tetrafluoride with
bromine trifluoride and selenium tetrafluoride were investigated further
and found to be diamagnetic. The platinum tetrafluoride, seleniumi tetra•
fluoride adduct was shown* to be isostructural with the corresponding
palladium and germanium compounds. An ionic lattice is suggested for
these compounds. Bromine trifluoride adducts do not form a similar-
series and this, combined with their- physical properties lead to the
suggestion that these compounds are more covalent in nature.
The previously unknown pentapositive state of platinum has been
established. Platinum pentafluoride is a deep-red, reactive solid which
readily disproportionates on heating. It gives rise to 1:1 adducts with
iodine pentafluoride and chlorine trifluoride. These, like the bromine
trifluoride adducts, are low-melting solids. Potassium fluoroplatinate (v)
was prepared as a deep-yellow solid, crystallizing with the rhombohedral potassium fluorosmate lattice. A pentapositive oxyfluoride, platinum
oxytrifluoride was found, it is suggested that this is polymeric.
Platinum hexafluoride has been briefly investigated. (iii)
A very reactive oxyfluoride, of formula PtO^Fg, has been prepared and investigated. It is a deep-red solid which can be sublimed at
90° in a vacuum. It melts with decomposition! at 219°. It is para• magnetic and crystallizes in a cubic lattice. Many of its chemical properties were studied. It is suggested that this compound is platinum peroxidehexafluoride.
The crystal structures of the tetrafluorides of platinum rhodium, tin and lead were investigated. No similarity in structure was found.
A brief investigation into the fluorides of rhodium has lead to; the suggestion! that a pentafluoride, in addition to a tetrafluoride, exists. (iv)
TABLE OF CONTENTS
Page ABSTRACT ii TABLE OF CONTENTS iv LIST OF TABLES vi LIST OF FIGURES vii LIST OF PLATES vii ACKNOWLEDGEMENTS viii INTRODUCTION 1
EXPERIMENTAL
ANALYSIS 11 PHYSICAL METHODS 18 MATERIALS 20 APPARATUS FOR HANDLING FLUORINE 25; FLUORINATION REACTIONS 26 PLATINUM DIFLUORIDE 30 PLATINUM TRIFLUORIDE 31 PLATINUM TETRAFLUORIDE 32 THE PLATINUM TETRAFLUORIDE, BROMINE TRIFLUORIDE ADDUCT . . 39 THE PLATINUM TETRAFLUORIDE, SELENIUM TETRAFLUORIDE ADDUCT 39 PLATINUM PENTAFLUORIDE 44 POTASSIUM FLUOROPLATINATE (V) 46 THE PLATINUM PENTAFLUORIDE, IODINE PENTAFLUORIDE ADDUCT. . 50 THE PLATINUM PENTAFLUORIDE, CHLORINE TRIFLUORIDE ADDUCT. . 50 PLATINUM OXYTRIFLUORIDE 52 PLATINUM HEXAFLUORIDE 53
PtO„Fc PLATINUM PEROXIDEHEXAFLUORIDE? 2 o Preparation, 53 Purification 55 Properties 56 Crystal Structure 5:7 Mass spectrum 59 Infra—red spectrum...... 59 Ultra violet and visible spectrumi 60 Magnetic study 60 Vapour pressure study ...... 61 Reactions 61 RHODIUM TETRAFLUORIDE 66 RHODIUM PENTAFLUORIDE? 69 POTASSIUM FLUORORHODATE (V) 70 TIN TETRAFLUORIDE 72 LEAD TETRAFLUORIDE 75. Page DISCUSSION
THE VALENCY STATES OF PLATINUM 7.6 PLATINUM DI FLUORIDE 79 PLATINUM TRIFLUORIDE 82 PLATINUM TETRAFLUORIDE . . . 84 PLATINUM PENTAFLUORIDE 87 POTASSIUM HEXAFLUOROPLATINATE (V) 90 PLATINUM OXYTRIFLUORIDE 92 PLATINUM HEXAFLUORIDE 93 PtO F PLATINUM PEROXIDEHEXAFLUORIDE? 94 THE COMPLEXES OF QUADRIPOSITIVE PLATINUM 100 THE TETRAFLUORIDES 103 THE FLUORIDES OF PALLADIUM 106 THE FLUORIDES OF RHODIUM 107 GENERAL DISCUSSION 108 SUGGESTIONS FOR FURTHER INVESTIGATIONS 109
SUMMARY
SUMMARY OF THE KNOWN FLUORIDES OF PLATINUM 110
APPENDICES
1. AN ALT/AC HIE COMPUTER PROGRAMME FOR THE DETERMINATION OF USEFUL FUNCTIONS FROM X-RAY POWDER PHOTOGRAPHS. . . 112 2. AN ALWAC HIE COMPUTER PROGRAMME FOR THE GRAPHICAL DETERMINATION OF ACCURATE LATTICE PARAMETERS FOR TETRAGONAL CRYSTALS 111
REFERENCES 121 (vi)
LIST OF TABLES Page .•
TABLE I. Tbe simple fluorides of Group VIII 10
TABLE II. Calculated and observed x-ray diffr&ctiom data for platinum, trifluoride. • 31
TABLE III. Calculated and observed x-ray diffractiom data for platinum tetrafluoride. 36
TABLE IV. Calculated and observed x-ray diffractiom
data for PtF4 (SeF4)2 41
TABLE V. Calculated and observed x-ray diffraction.
data for PdF. (SeF„)0 42 4 4' 2 TABLE VI. Calculated and observed x-ray diffractiom
data for GeF^ (SeF4)2 43
TABLE VII. Calculated and observed x-ray diffraction data for KPtF„ 49) 6 TABLE VIII. Calculated and observed x-ray diffraction data for JPtO- F„ 58 2 o
TABLE IX. Mass spectrum of PtOgEg 59
TABLE X. Infra-red spectrum of PWgFg 60
TABLE XI. Molar susceptibilites of PtO F x 10 " c.g.s. units 60
TABLE XII. Calculated and observed x-ray diffractiom data for RhF^ 68 TABLE XIII. Calculated and observed x-ray diffraction
data for SnF4 73
TABLE XIV. Unit cell dimensions of the trifluoride of Group VIII83
TABLE XV. Knowm pentafluorides of the second and third
transition series 87
TABLE XVI. Potassium salts, of the MF ~ ion 90
TABLE XVII' Lattice constants of some KMFC structures .... 91 o TABLE XVIII. The known saline tetraf luorides 104 TABLE XLX. Infra-red spectra of some tetraf luorides 105) (vii)
LIST OF FIGURES
Fo11owing page
FIGURE 1. Apparatus used for pyrohydrolysis ...... 11
FIGURE 2. Apparatus for handling fluorine . . 25s
FIGURE 3. Apparatus for reactions involving bromine trifluoride? selenium, tetrafluoride or iodine pentafluoride ...» 27
FIGURE 4. Apparatus for reactions involving oxygem difluoridej sulphur tetrafluoride or chlorine trifluoride...... 28
FIGURE 5:. Apparatus used for studying thermal
decomposition reactions 33
FIGURE 6. Apparatus used for preparation of PtO^Fg . . 53
FIGURE 7. Apparatus used for purification, of PtOgFg ... 55,
FIGURE 8. Apparatus used for measuring gas evolution . 61
LIST OF PLATES
PLATE 1. Platinum trifluoride 82
PLATE 2. Some Tetraf luorides 103
PLATE 3. Potassium Fluoroplatinate (V) 91 (Vi i i)
ACKNOWLEDGEMENTS
The author wishes to express his sincere appreciation to Br. N. Bartlett, for his encouragement and helpful discussion, throughout the course of this study.
The author is grateful to Mrs. M. Zell for assistance with some of the spectraj to Dr. J. Bloor and the British Columbia Research Council for use of the Perkin-Elmer 21 spectrophotometer employing caesium bromide opticsj; to Dr. D. Frost and Mr. F». Bloss for the mass spectrometer analyses and to;
Messrs. H. Dempster and W. Betweiler of the Computing Centre for helpful discussion on computer programming.
The author thanks the Consolidated Mining and Smelting Company of
Canada Limited for the award of the COMINCO Fellowship for 1960-61. INTRODUCTION The history of inorganic fluorine chemistry falls into three distinct
phases:-
1) The isolation of elemental fluorine and early exploratory work carried
out by Moissan, between 1886 and 1900.
2) The systematic investigation of a wide range of metallic and non
metallic fluorides by Ruff and his associates, between 1910 and 1935.
3) The renewed interest in fluorine chemistry since the early 1940's,
initiated by the separation of the isotopes of uranium as their volatile
hexafluorides. This led to the development of a safe and reliable
generator of fluorine and more recently to the availability of fluorine
commercially.
Investigation of the simple fluorides of platinum was started by
Moissan. In 1889(l), he reported platinum tetrafluoride and in 1891(2),
platinum difluoride. The existence of the former compound has been well
substantiated, but the existence of the latter is still questionable.
Moissan prepared platinum tetrafluoride by heating bundles of platinum wire, contained in thick-walled platinum or fluorspar boats* to a dull-red heat in a stream of fluorine. He found that the reaction proceeded better
in the presence of hydrogen fluoride gas, and suggested that the reaction went through the intermediate compound PtF^, nHF. Moissan claimed that platinum difluoride remained behind as an insoluble residue when the tetra• fluoride was extracted with water, but gave no analytical evidence to support this.
Subsequent reports of the preparation of platinum tetrafluoride have been made by Ruff and Zedner(3), who heated a mixture of fluorine and oxygen or nitrogen in an electric discharge between platinum electrodes. 2
Buff(4) obtained it by heating the compound PbF^, 3HF to above 200 in a
platinum vessel; by the action of free fluorine on platinum metal at a dull red heat(5) and, together with platinum difluoride, as a thin layer on the platinum anode when liquid hydrogen fluoride, treated with potassium bifluoride, was electrolysed(6). Sharpe(7) prepared platinum tetra•
fluoride by heating the compound PtBrgF^Q to a temperature of 200° under vacuum.
Platinum tetrafluoride has also been reported as a by-product in
several fluorination reactions performed in platinum apparatus (8, 9, 10).
Attempts to prepare platinum tetrafluoride by the action of liquid or
gaseous hydrogen fluoride on platinum tetrachloride failed (ll, 12) as did the reaction between molten potassium bifluoride and platinum metal(ll).
Attempts to prepare platinum tetrafluoride from aqueous solution have also
failed (2, 13, 14, 15).
Moissan described platinum tetrafluoride as a dark red mass and as
small, brown-yellow, very hygroscopic crystals which needed to be sealed
in well-dried, glass vessels for their preservation. It is said to be volatile and to decompose at red heat into fluorine and platinum metal.
When it is heated in a glass tube, the glass is attacked to produce platinums metal and silicon tetrafluoride. It dissolves readily in water to give
a yellow-brown solution which decomposes exothermally into hydrofluoric acid
and the orange, hydrated dioxide of platinum, this decomposition is greatly
accelerated by boiling. It readily combines with the fluorides and chlorides
of phosphorous and boron to give well-crystalline volatile compounds. It has also been found to form adducts with bromine trifluoride(7) and seleniumi tetrafluoride(l6). Nyholm and Sharpe(l7) reported it as being paramagnetic
= 1.1 Bohr magnetons). 3.
Claims to hare prepared the difluoride of platinum have been made by workers other than Moissan. Poulenc(l2) heated ammonium fluoraplatinate
in a stream of hydrogen fluoride to a temperature in excess of 300°.
Ruff(6) claimed to have prepared it as a thin layer on the platinum anode when liquid potassium bifluoride containing hydrogen fluoride was electrolysed.
Platinum difluoride is described (l, 2) as a greenish-yellow crust that is insoluble in water and which on heating decomposes into platinum and fluorine. Little else is known about it. (it is felt that some confusion may have arisen in the early literature due to Moissan (l, 2) describing platinum tetrafluoride as "platinum bifluoride (PtFIg)" and platinum difluoride as "platinum protofluoride (PtFl)". With the revision of atomic weights, this was subsequently corrected(l8)).
The only other fluoride of platinum reported hitherto, was the volatile platinum hexafluoride, described recently by Weinstock, Claasen and
Malm(l9). They prepared this by electrically heating a platinum spiral in an atmosphere of fluorine gas maintained at a pressure of 300 mm.
The main product of the reaction was platinum tetrafluoride? which remained as a non-volatile, yellow-brown solid. In addition, a yellow-brown, volatile solid condensed on a surface? directly above the platinum spiral, which was cooled with liquid nitrogen. This compound was shown to be platinum hexafluoride by chemical analysis and vapour density measurements. It is described as a dark-red solid of melting point 56.7° that appears black ini its massive form. Its vapour is brown-red, similar to bromine. It was described as the least stable and most reactive of the then known hexa- fluorides,slowly decomposing when stored in glass or quartz? leaving a red-brown residue, which the authors state must be due either to photo- 4.
decomposition or to reaction with the glass. It can however be stored
indefinitely, at room temperature, in clean nickel containers. The
solid was reported to be isostructural with osmium and iridium hexa-
fluorides but no X-ray data has been published. The same authors(20)
have subsequently observed the vibrational spectrum in the infra-red
region, and find that the main features of the spectrum are similar to
those observed for the other, known hexaf luorides, being interpreted in: terms of the octahedral point group 0^.
The history of the complex fluorides of platinum;goes back beyond that
of the simple fluorides. The first report of salts of fluoroplatinic acid was made by Berzelius(2l), who prepared potassium fluoroplatinate(lV) by treating a solution of potassium fluoride with a less than equivalent
quantity of chloroplatinic acid, decanting the liquid from the precipitated potassium chloroplatinate and evaporating. Berzelius also prepared the
ammonium salt in a similar manner. Schlesinger and co-workers (22, 23) prepared the potassium salt by fusing finely divided platinum metal with
the complex fluoride 3KF.HF.PbF4 (or K^PbEg) (HFg)) , extracting with 48$ hydrofluoric acid, precipitating the lead as lead sulphate and evaporating to induce crystallization. Sharpe and Emeleus(24) prepared potassium
fluoroplatinate in low yield by the thermal decomposition of potassiumi tetrafluorobromite in a platinum crucible. Sharpe(7, 25) prepared the potassium, rubidium and caesium salts by treating the corresponding chloro- platinates or bromoplatinates with bromine trifluoride. Pernos, Naeserr and co-workers(26, 27, 28, 29) were the first to isolate fluoroplatinic acid. They first prepared a series of rare earth fluoroplatinates, by 5.
heating the corresponding rare earth fluoride with platinum foil in a stream of dry air to a temperature of 525° for five hours and leaching the water-soluble rare-earth fluoroplatinate from the mixture. The free acid was prepared by passing an aqueous solution of lanthanum fluoroplatinate through a column of Dowex 50 (strong acid) ion exchange resin, and evapo• rating the eluate to dryness in a polyethylene beaker by vacuum desiccatiom over sodium hydroxide pellets. The same authors prepared the sparingly soluble potassium, rubidium and caesium salts by simple metathetical re• actions of the corresponding alkali nitrate with lanthanum fluoroplatinate solution, the salts being purified by recrystallization from hot water.
Sodium and ammonium fluoroplatinate were prepared by "titrating" lanthanum; fluoroplatinate solution with the corresponding hydroxide solution until no more lanthanum hydroxide precipitated. The lanthanum hydroxide was centrifuged off, the solution evaporated almost to dryness under reduced pressure and cooled to 5° until precipitation was complete. Attempts to prepare lithium fluoroplatinate in a similar manner were unsuccessful as hydrolysis of the fluoroplatinate ion occurred. Magnesium, calcium and strontium salts were prepared by the reaction of fluoroplatinic acid with the oxide> hydroxide and carbonate of the respective metals. The sparingly soluble barium salt was prepared by the metathetical reaction of lanthanum fluoroplatinate with barium chloride.
Fluoroplatinic acid is obtained in the hydrated form and consists of yellow, hygroscopic crystals (27). Its titration curve with sodium* hydroxide solution shows it to be a strong acid. The salts of fluoroplatinic acid are all pale yellow in colour; those of the rare eaths, alkaline earths;
(with the exception of barium), sodium and ammonium are soluble in water 6.
and those of potassium, rubidium, caesium and barium are insoluble*
Potassium fluoroplatinate has been shown to be diamagnetic(l7). The crystal structures of these compounds, as indeed with many compounds of the type A^MXg, consist of close-packed layers of A and X atoms with the
M atoms occupying some of the octahedral holes (30> 31). The octahedral arrangement of the fluorines around the platinum has been shown by the complete structure determination of potassium fluoroplatinate by Mellor and Stephenson, (32). The sodium salt is isomorphous with sodium fluoro- silicate, which has a hexagonal structure. The potassiumi (25, 32) rubidium and caesium compounds have the trigonal potassium fluorogermanate structure. The strontium and barium salts have been interpreted on the basis of a rhonbohedral unit cell (33). The ultra violet and visible absorption spectrum of the fluoroplatinate ion was shown to have maxima at
245? and 318 m/u (22, 26). The infra-red absorption spectrum of potassium! fluoroplatinate has been mentioned by Peacock and Sharp (34), who note a single maximum, which they assign, as J 3, at 583 cm The fluoroplatinate ion is relatively stable (22, 35), being stable to hydrolysis (this is in marked contrast to the rapid hydrolysis of the related fluoropalladate ion) and undergoing substitution reactions with the other halogem acids only very slowly (7). It has been found difficult to reduce the fluoroplatinate ion, but when reduction does occur platinum metal is precipitated. Perros et al(35) tried a wide variety of reducing agents in attempting to reduce the fluoro• platinate ion to the fluoroplatinite ion, but they were unsuccessful, either, getting no reduction at all or getting complete reduction to platinum metal.
By estimating the electrode potentials, by extrapolation from those of the other complex halides of platinum in aqueous solution, they concluded that 7.
the fluoroplatinite ion is probably unstable with respect to dispropor• tionation into platinum metal and the fluoroplatinate ion. The only other complex fluorides of platinum known were the bromine trifluoride(7) and selenium tetrafluoride(16) adducts of platinum tetrafluoride, both of which could be prepared by the interaction of platinum tetrafluoride with the appropriate solvent.
The foregoing has briefly summarized the known fluorides of platinum before the present work was started. The fluorides of platinum known at that time are compared with those of the other group VIII elements in
Table 1. We see that the stability of higher valency states decreases as we go from left to right in any one triad and that the stability of higher valency states increases with transition series number. Thus, iron forms two stable fluorides, a difluoride and a trifluoride; in cobalt, the tri• fluoride is readily reduced to the very stable difluoride and is therefore useful as a fluorinating agent; the only known simple fluoride of nickel is the difluoride.
In the second triad, ruthenium attains the highest valency in forming a pentafluoride also a trifluoride (36, 37) and in addition, Ruff and Vidic have reported the doubtful existence of ruthenium octafluoride (36). Two fluorides of rhodium have been established, the trifluoride (38) and the tetrafluoride (33, 7). Ruff and Ascher could not establish whether the compound they had prepared by the action of fluorine on rhodium at 500° was the tetrafluoride or the pentafluoride, but Sharpe(7), who prepared rhodium tetrafluoride by the action of bromine trifluoride on rhodium tetrabromide has stated that the properties of this compound are identical 8..
with those given by Ruff and Ascher (38). In palladium, the trifluoride is the highest known simple fluoride. The difluoride and the trifluoride have been well established (38, 39) but it was not until the work of
Bartlett and Hepworth that palladium difluoride was obtained in the pure state.
In the third triad, although all the metals form hexafluorides, the stability decreases in the order osmium, iridium, platinum. The octa- fluoride of osmium reported by Ruff and Tschirch (40) has been shown by
Weinstock and Malm (4l) and by Hargreaves and Peacock (42) to be identical with the hexafluoride. Ruff and Tschirch had also reported a hexafluoride and a tetrafluoride, their "hexafluoride', by the nature of its properties? is here tentatively assigned as being the pentafluoride. Osmium trioxy- difluoride (43) is the only established oxyfluoride of the group, though an oxytetrafluoride of iridium had been claimed by Ruff and Fischer (44), but this has since been denied by Robinson and Westland (45). The trifluoride, tetrafluoride and hexafluoride of iridium are well established, though the similarity between the properties of the tetrafluoride and neighbouring penta- fluorides had been noted (45).
With the complex fluorides> the same tendencies are noticed, though in this respect iron is somewhat; anomalous in that it does not form tetravalent complexes. Platinum too seems somewhat anomalous in that it does not form pentavalent complexes, the remainder of the third transition series from tantalum to platinum all forming the MF^ ion.
At the onset of this work then, several gaps remained in the expected series of platinum-fluorine compounds. The tetravalent state was well characterized and the hexavalent state had only just been established. 9.
The divalent state had been reported but not confirmed. The trivalent state, very stable in palladium which has the same electronic structure as platinum in its valence shell and exhibited by most of the members of the group, had not been reported. The pentavalent state, shown by osmium and ruthenium and possibly iridium, again had not been reported. Accord• ingly, it was decided to reinvestigate the fluorides of platinum with a view to trying to prepare and characterize those then unknown valency states. 10
TABLE I
The Simple Fluorides of Group VIII
Iron Cobalt Nickel
FeF^ CoF2 NiF,
FeF, CoF3
Ruthenium Rhodium Palladium
PdF2
RuF, RhF„ PdF„
RhF 4 m.l06°, b.313° RuF_
RuFg(?)
Iridium Platinum Osmium
PtF2(?)
IrFg
OsF4 m.230°, b.280-300° IrF^ m.l06-lo7°, b.300° PtF, 4
0sF5(?) m.70°, b.225.5°
IrFc m.44 , b.53.6 PtF- m.56.7 OsF. m.32.1°,b.45.9° o o
OsOgFg m.170 Ir0F4(?) EXPERIMENTAL 11.
ANALYSIS
AH weighings were performed using a Mettler "Gramatic", constant- load balance. Unless otherwise stated, all quantitative filtrations were carried out on medium-porosity, sintered-glass crucibles. The re• agents were of ANALAR grade. Standard analytical techniques were followed throughout (46).
INTRODUCTION
The analysis of platinum fluorides was complicated by the formation in solution of the stable fluoroplatinate (IV) ion. Before either platinum or fluorine could be estimated quantitatively this ion had to be broken down. The following analytical schemes effected this:-
(1) Willard and Winter distillation (47)
A known weight of material) containing 0.05. to 0.3g. of fluorine, was added to a long-necked distillation flask and 25 mis. of concentrated sulphuric acid or preferably 60fi phosphoric acid were added. The mixture was distilled with the temperature kept in the range 130-135? by the addition of water from a dropping funnel. Approximately 200 mis. of distillate were collected. The fluorine was recovered as hydrofluoric and fluorosilicic acids.
(2) Pyrohydrolysis (48, 49)
The apparatus used was similar to that described by earlier workers and is shown in Figure 1. The essential part of the apparatus was a silica tube, 2 cm. diameter and 40 cm. long, having a 35/20 B.S. silica socket at one end and a B.10 ground silica cone at the other. The steam condenser, of Pyrex glass, was attached to this by way of a B.10 ground cone. FIGURE 1 Apparatus used for pyrohydrolysis 12.
The steam preheater and steam trap, made of ^ in. int. diam. copper tubing, were attached to the other end of the silica tube by means of a brass ball, machined to fit the 35/20 B.S. silica socket. Both the brass ball and the B.10 silica cone were provided with inset tubes to prevent the occur• rence of seepage at the joints. The pyrohydrolysis tube was heated in an electric furnace. Temperature measurements were made using a high tempera• ture thermometer. Steam was generated in a 1 litre, three-necked flask; one neck taking the air inlet bubbler, one the moist-air/steam outlet and the third a thermometer.
Details of the conditions will be found under the compounds concerned.
Essentially, a platinum boat was weighed to constant weight after being heated to 300° in a stream of steam followed by heating to the same tempera• ture in a stream of hydrogen. The fluoride sample, approximately 0.2 g, was transferred to the platinum boat in a dry-box and the boat reweighed.
The boat was quickly transferred to the pyrohydrolysis tube, initially at room temperature. The hydrolysis was carried out by first passing moist air over the sample, then slowly raising the temperature of the water in. the bubbler together with the temperature of the furnace until eventually steam was passed over the sample at 300°. The distillate was collected by bubbling through 50 mis. of water contained in a conical flask. Washings from the condenser were collectedwith the distillate. The fluoride iom concentration was estimated by titration with 0.1 N sodium hydroxide using phenolphthalein as indicator. Earlier workers (48) claimed that the titra• tion should be carried out at 60° to decompose any fluorosilicic: acid, but this was found to be an unnecessary precaution.
_ Titration (mis.) x 0.19 fo F Wt. of sample (g.) 13.
To check the titration, the fluoride ion was precipitated as lead
chlorofluoride.
To determine platinum, the condenser was replaced by a silica tube
10 mm. diameter tapering to 5 mm. diameter. The apparatus was flushed
with nitrogen, then hydrogen was passed, the emergent gas being burned.
The boat and platinum.residue were heated to constant weight.
For all weighings, the platinumi boat was contained in a horizontal
weighing bottle fitted with a close-fitting ground glass stopper.
(3} Parr bomb method (50, 51)
A known weight of material containing approximately 0.1 g. of fluorine
was transferred to a 02 gelatine capsule in. a dry-box. The capsule was
placed inside a Parr bomb together with approximately 0.2 g. of metallic
sodium. The bomb, was screwed together in the dry-box:. It was placed
inside an iron shield and heated for 1 hr. over a Meker burner. The bomb;
was allowed to cool to room temperature, then the excess sodium was des• troyed by boiling with absolute ethyl alcohol. The fluorine was extracted,
as sodium fluoride, with water and estimated as lead chlorofluoride.
(4) Reduction methods
Reduction methods generally lead to the precipitation of platinum as
the metal. A variety of reducing agents have been tried with varying
success. Beamish in his review (52) states that when using organic re•
ducing agents, precipitation is never complete, and these are not to be
recommended; reduction with zinc metal in hydrochloric acid solution gives;
a quantitative precipitation of platinum metal, but unless extreme care is
taken, some zinc becomes platinum coated leading to a high result. 14.
Conclusion
The Willard and Winter method and the reductive methods suffer from the disadvantage that pretreatment. of the sample is necessary and that:, only one component can be estimated at a time. The Willard and Winter method also suffers from the disadvantage that bumping often occurs during distillation, and when sulphuric acid is used this can lead to erronious results due to the precipitation of lead sulphate.
The pyrohydrolysis method does not suffer from these disadvantages; and was used whenever possible.
ESTIMATION OF FLUORINE
Introduction
Fluorine may be estimated by many methods, of which precipitation as calcium fluoride (53), lithium fluoride (54), triphenyltin fluoride (55) or lead chlorofluoride (56) and titration with thorium nitrate solution using sodium alizarin sulphate as indicator (47) are the most common.
The yellow to pink end point in the titration of fluoride with thoriumi nitrate is very difficult to detect. Precipitation with calcium fluoride gives a precipitate that is very difficult to filter and wash. Pre• cipitation as lithium fluoride gives a well-crystalline and easily filter• able precipitate but the conversion factor in this case is not favourable.
Precipitation as triphenyltin fluoride suffers from the disadvantage that the estimation must be performed in a 60-70^ alcoholic solution under carefully controlled conditions. Precipitation as lead chlorofluoride relies largely on a rigid adherence to empirical procedures, but the pre• cipitate is granular, settles readily and is easily filtered. In addition, the conversion factor is favourable. Accordingly this last precipitation 15.
method was used exclusively for the estimation of the fluoride ion in
this investigation.
Estimation of fluorine by precipitation as lead chlorofluoride
The distillate from either a pyrohydrolysis or from a Willard and
Winter distillation was made just alkaline to bromophenol blue with lQfi
sodium hydroxide solution. Concentrated hydrochloric acid, 1 ml., was
added and the solution heated to 80°; lead nitrate, 5 g., was added with
stirring and the heating was continued until all the lead nitrate had dis•
solved and the solution was just below boiling point. Sodium acetate,
5 g., was added with stirring, resulting in the precipitation*, of lead chlorofluoride. The heavy, white precipitate was digested for one hour
at 95-100° and allowed to cool overnight. The precipitate was collected
on a sintered-glass crucible, washed with a saturated solution of lead
chlorofluoride and finally with two small quantities of water. The pre•
cipitate was dried to constant weights at 130—140°.
= Wt. of PbClF x 7.261 j* Fluorine Wt. of Sample
Because of the possibility of precipitating other ions under these
conditions? particularly when the solution to be estimated was the dis•
tillate from a Willard and Winter distillation performed in the presence
of sulphuric acid, it was the practice to check the composition of the
lead chlorofluoride by dissolution in dilute nitric acid followed by pre•
cipitation of the chloride as silver chloride.
= Wt. of AgCl x 13.26 Fluorine Wt. of Sample ESTIMATION OF PLATINUM
Introduction
Any of the methods mentioned earlier for the precipitation of platinum as metal from the fluoroplatinate ion may be used for the estimation of platinum with the reservations made there. The claim of Beamish (52), that there is incomplete precipitation of platinum when using organic re• ducing agents, has been substantiated in this work. Reduction with fine, granular zinc, added slowly, followed by washing of the precipitated platinum with 10^ hydrochloric acid gives quantitative precipitation of platinum with no contamination by the zinc.
Other methods used to estimate platinum include, precipitation as platinum disulphide (57), precipitation as ammonium hexachloroplatinate(58), and precipitation as dimethylphenylbenzyl bromoplatinate (59, 60).
The disadvantage of the sulphide method is that sulphur is occluded by the precipitate, causing an uncertainty of composition. Precipitation as ammonium hexachloroplatinate suffers from the disadvantage that the precipitate is appreciably soluble in water (0.5 g./lOO g. water) (61), this may be offset to some extent by performing the estimation in a solu• tion containing an excess of ammonium chloride. The hydration energy, and hence solubility, of compounds of this type has been found to be de• creased by increasing the size of the anions. A variety of compounds with large anions were tried (59) and dimethylphenylbenzyl ammonium chloride was found to be the most satisfactory. Accordingly, throughout this investigation platinum was estimated from solution by first precipi• tating as the metal with zinc, then dissolving the metal in aqua regia and re-precipitating as dimethylphenylbenzyl bromoplatinate. 17.
Estimation of platinum by precipitation with dimethylphenylbenzylammonium chloride
Preparation of reagent (62)
Dimethylphenylbenzylammonium chloride was prepared, by mixing equimolar
quantities of freshly distilled benzyl chloride (176-178°) (28 mis.)
and dimethyl aniline (191-194°) (31 mis.)? as a white crystalline mass.
Excess reactants were removed by washing with ether and the material was
recrystallized, as a white crystalline solid, from alcohol by the addition
of ethyl acetate (m.p. 116° (sealed tube)).
A bf> aqueous solution and a 0.1^> aqueous solution were prepared from
the solid. Both were stored in dark bottles and were satisfactory after
many months storage.
Estimation
A known quantity of a solution containing platinum, usually in the form
of the fluoroplatinate ion, was taken, made acid with 10^ hydrochloric acid
and fine? granular zinc added in small amounts until reduction was complete.
The precipitated platinum was digested at 40-50° for one hour, then collected
in a sintered glass crucible. It was washed with 10^ hydrochloric acid
and dried to constant weight at, 110°.
The platinum was dissolved in the minimum quantity of aqua regia and
the solution was twice evaporated to dryness with 48^ hydrobromic acid and solid sodium bromide. The residue was dissolved in hydrobromic acid, 4 mis. of hydrobromic acid being added for each 10 mg. of platinum.
The solution was diluted to 100 mis. and 5 mis. of 5/& dimethylphenylbenzyl- ammonium chloride per 10 mg. of platinum were added with stirring. The 18.
flocculent, orange precipitate was allowed to stand for 3 hours, and then collected in a sintered-glass crucible, washed with the 0.1^ solution of dimethylphenylbenzylammonium chloride followed by 3 mis. of dioxane and
4 mis. of cyclohexane. The precipitate was dried to constant weight at 80°.
Wt. of ppt. x 0.1776 $ Pt. Wt. of Sample
The methods used in the pretreatment of the compounds and estimation of other elements will be mentioned under the compounds concerned.
PHYSICAL METHODS
X-ray powder photographs
These were taken using nickel-filtered copper K radiation (K<* ,
1.5443; Mot, 1.5405; K «=< (£ (2K<*X + K«*2)) , 1.5418 £). The nickel filter,
0.089 mm. thick, was placed in the collimator of a General Electric model
XRP-SF11 X-ray diffraction unit and removed most of the Sy3 radiation.
The diffraction pattern was recorded photographically using a 14.32 cm. camera of the Straumanis type. With the target operated at 40 KV and 15 mA required exposure times varied between 4 and 20 hours.
Specimen capillaries, 0.5 mm. diameter, of either quartz or Lindemann glass (as supplied by Pantak Ltd., Windsor) were used. Hygroscopic materials were loaded in the dry box. The capillaries were sealed using a small» hot flame and the seal was covered with picein wax. The dis*- tances between symmetrical pairs of arcs were measured using an accurate . 2 2 scale and vernier. Bragg angles, interplanar spacings, 1/d values, sin © values and the Nelson-Riley extrapolation function (63) were obtained from these using an ALWAC III E digital computer (Appendix I). Intensities were estimated visually. 19.
Magnetic Measurements
Magnetic susceptibilities were measured using a Guoy balance? des•
cribed in detail by Clark and O'Brien (64). The magnetic balance con•
sisted of a Varian 4-inch electromagnet, model Y4084, having 2-inch
tapered pole caps? producing a field of approximately 15 kilogauss, with
a current of 2 amperes. The current was regulated by a Varian, model
U2300 A» power supply with model 2301 A current regulator. Weighings
were made on a Spoerhase, Model 10M, microbalance having a sensitivity
of - 0.01 mg. Temperature control was provided by a cryostat similar
to that described by Figgis and Nyholm (65), which allowed the temperatur
to be controlled at any point in the range 78-300°K by suitable control o
the current passing through an electrically heated coil and the pressure
within the inner Dewar flask.
The sample, contained in a glass tube 12 cms. x 5 mm. was suspended
from the bottom of the sample pan, and between the pole pieces of the mag•
net, by means of a thin gold chain. The sample was weighed with the
field off and then with the field on. The tube was emptied and re-
weighed. This procedure was repeated with the tube filled with an. equal
volume of mercury (ii) cobaltitetr.athiocyanate (66).
Magnetic moments were calculated using the formula.
Where, the subscripts I and II refer to sample and standard respectively.
W Weight of material
&W Increase in weight of the material in the magnetic field. 20.
A g Gram susceptibility V -6
A gll 16.4 x 10 c.g.s. units
T Temperature (°K)
0 Curie Temperature
Ultra-violet and visible spectra
Ultra-violet and visible spectra were recorded using either a CARY 11
or a CARY 14 instrument. In the solution work matched 1 cm. quartz cells
were used.
Infra-red spectra
Infra-red spectra were recorded using either a PERKIN ELMER "Infracord"'
spectrophotometer or a PERKIN ELMER 21, spectrophotometer.
Specific Gravity measurement
Specific gravities were measured using a 1 ml. capacity bottle pro• vided with a ground glass cap. Hygroscopic materials were loaded in the dry box. Carbon Tetrachloride was employed on the displacement fluid.
MATERIALS
Platinum metals
All platinum metals were obtained from Johnson, Matthey and Mallary
Ltd., Toronto, grades of at least 99.99^ purity being used.
Fluorine
Fluorine was obtained from Allied Chemicals, General Chemicals.
Division, New York.
Platinum-metal salts
Ammonium Hexachloroplatinate
All residues and solutions from experiments were bulked together.
Periodically, they were evaporated to dryness and extracted with aqua regia. 21.
Excess nitric acid was removed by evaporating to dryness twice with con•
centrated hydrochloric acid. The residue was dissolved in concentrated
hydrochloric acid, diluted four times with water and treated with an equal
bulk of saturated ammonium chloride solution. The pale-orange precipitate
was allowed to settle overnight, filtered, washed twice with saturated,
ammonium chloride solution, and finally with water.
Found* Pt, 43.95^ Calc. for (NH4)2 Pt C16:- Pt, 43.97^.
Hexachloroplatinic acid
Hexachloroplatinic acid was prepared by treating a hot (80°) sus•
pension of ammonium hexachloroplatinate with an excess of acid-washed
Dowex 50 (strong acid) ion-exchange resin. The conversion was completed
by passing the solution through a column of the same resin. The golden-
yellow solution was evaporated to dryness under an infra red lamp to give
red-brown deliquescent crystals of hexachloroplatinic acid hexahydrate
(m.p. 60°). The crystals were recrystallized from water.
Found: Pt, 38.21/& Calc. for H2PtC16, 6H20: Pt, 37.70^.
Platinum Tetrachloride (67)
Platinum tetrachloride was prepared by heating hexachloroplatinic
acid to 275° in a stream of chlorine for two hours, allowing to cool to
150°, grinding, re-heating to 275° for a further one hour and finally
allowing to cool in a stream of nitrogen. Platinum tetrachloride obtained
in this manner consists of deep, red-brown, hygroscopic crystals which
readily form the yellow pentahydrate. It was therefore stored in sealed
tubes.
Found: Pt, 57.78^ Calc. for PtCl4, 57.92^. 22.
Platinum Dichloride (68)
Platinum dichloride was prepared by heating hexachloroplatinic
acid to 450° in a stream of chlorine for two hours. The residue was;
boiled with a 0.5$ aqueous solution of hydrochloric acid, to remove any
platinum tetrachloride, then dried at 360° for 30 minutes. Platinum;
dichloride obtained in this way was green brown.
Found: Pt, 73.22. Calc. for PtCl :- Pt, 73.36$,
Platinum Tetrabromide
Platinum tetrabromide was prepared by Halberstadt1s modification of
the method of Meyer and Zublin (69, 70).
Platinum sponge was heated to 180° in a sealed tube with an excess
of 2:1, hydrobromic acid (48$) : bromine, for 12 hours. The solution was
filtered, to remove any platinum dibromide, evaporated to dryness then-
heated to 180°. The residue was re-dissolved in water and the evapo•
ration and drying repeated. Platinum tetrabromide was obtained as deep
violet crystals.
Found: Pt, 54.95. Calc. for PtBr4:- Pt, 55.0$.
Platinum Dioxide
Platinum dioxide monohydrate was obtained by the method of Adams
et al. (71, 72, 73)
A solution of 8 g. of hexachloroplatinic acid hexahydrate in 20 mis.
of water was added to 78 g. of sodium nitrate in a silica evaporating basin. The solution was heated slowly with constant stirring. At 300°,
the sodium nitrate melted and reacted with the hexachloroplatinic acid; resulting in the evolution of nitrogen dioxide and the precipitation of platinum dioxide. Heating was continued to 480°, and this temperature 23.
was maintained for 15 minutes. The mixture was allowed to cool and was then leached with water. The insoluble platinum dioxide was washed
first by decantation, then by filtration, until free from nitrates. It was dried at 110°.
The monohydrate was dehydrated by heating, 280°, in a stream of oxygen for 48 hours.
Found: Pt, 85.38. Calc. for Pt02: -Pt, 85.92$.
Rhodium Trichloride
Rhodium metal was heated to 600° in a stream of chlorine for 24 hours.
Rhodium trichloride prepared in this way was a deep red-brown crystalline
solid.
Found: Rh, 49.3. Calc. for RhCl_: Rh, 49.2$.
Rhodium tribromide
Rhodium tribromide was prepared by refluxing rhodium metal with an excess of a bromine/faydrobromic acid mixture for 48 hours. The excess bromine/hydrobromic acid was distilled off at 15-20 mm. pressure and the solution was slowly evaporated under an infra-red lamp. The crystals obtained were dried in a vacuum desiccator to yield deep-red-violet crystals of rhodium tribromide dihydrate.
Found: Rh, 27.0. Calc. for RhBr3> 2H20: Rh, 27.2$.
Tin metal and lead acetate
British Drug Houses ANALAR grade were used.
Hafnium Metal
Material of 99.9$ grade from Bios Laboratories Inc., New York, was used. 24.
Selenium Tetrafluoride
Selenium tetrafluoride was prepared by the method of Aynsley,
Peacock and Robinson (74).
Selenium metal was sublimed on to the walls of a flask of approximately
2 litres capacity. The flask was cooled to 0° in an ice bath and the
selenium fluorinatedj using a low rate of flow of fluorine. The seleniumi
tetrafluoride produced was condensed in a train of traps cooled in alcohol/
solid carbon dioxide. Purification was by trap to trap distillation.
Sulphur Tetrafluoride
Sulphur tetrafluoride was obtained from Du Pont and Nemours Inc.,
Wilmington.
Bromine Trifluoride, Iodine Pentafluoride and Chlorine Trifluoride
These were obtained from the Mattheson Co. Inc., Newark and were used after trap to trap distillation.
Oxygen Difluoride
Oxygen difluoride was prepared by the method of Ruff and Menzel (75).
Fluorine was slowly bubbled through 250 mis. of a 2$ aqueous sodium hydroxide solution, oxygeni difluoride together with some oxygeni was evolved.
The gases were washed by bubbling through water, and water vapour and hydrogen fluoride were removed by passing the gases through a trap cooled to -78° in alcohol/solid carbon dioxide. Oxygen difluoride was condensed as a pale yellow liquid in a trap cooled to -183° by liquid oxygen. The reaction was allowed to proceed until approximately 5 mis. of oxygen di• fluoride had condensed. The oxygen difluoride was; sealed off at atmos• pheric pressure and stored at liquid oxygen temperature until needed. 25.
APPARATUS FOR HANDLING FLUORINE
The apparatus that was used for handling fluorine is shown dia- grammatically in Figure 2. It was contained in a wide, well-ventilated fume-hood. The cylinder was clamped in a vertical position and shielded on two sides by bricks and on the other sides by the walls of the fume- hood. The cylinder valve was opened by a key, which was welded to a four-foot long handle manipulated through a slot in the brick shield.
The base of the valve was held firmly by means of a wrench attached to a four-foot handle.
The pressure of the fluorine, which was 400 lbs. per sq. inch in the cylinder, was reduced by using two Hoke stainless-steel, needle valves in series. The high-pressure side, which was constructed from half-inch, stainless steel pressure tubing, was connected to the cylinder by a com• pression fitting, a teflon gasket being employed. A stainless-steel)
Bourden-type, pressure gauge was screwed and silver-saldered into this part of the system. The low pressure side was constructed from quarter- inch copper tubing with the exception of the sodium fluoride-pellet: chamber,
A, which was of half-inch diameter copper tubing. All valves on the low- pressure side of the system were brass-bodied, bellows-sealed needle valves.
There was no flow meter in the system, though an estimation of the rate of flow was obtained from the bubble rate in the low-viscosity, fluorocarbon-oil (Hooker Chemicals, FS-5) blow-off. Earlier attempts to measure the flow rate using a pin-hole flow meter were unsuccessful due to blockage of the pin-hole.
The sodium fluoride pellets served to remove any hydrogen fluoride contained in the fluorine. The diluent gas was dried by passage through FIGURE 2 Apparatus for handling fluorine
•3
o a. a. o
3 N2"°2
H K
ONI 26.
a Brechsel bottle containing sulphuric acid.
Reaction systems were attached to the fluorine supply by means of
"teflon" tubing (i" i.d., f" o.d.)
FLUORINATION REACTIONS
In all fluorination reactions, the apparatus used must be dry, other•
wise hydrolysis, with the consequent generation of hydrogen fluoride will
occur. The avoidance of hydrolysis is particularly important wheni working
in glass or silica systems, for the hydrogen fluoride produced then, reacts
to produce silicontetrafluoride and water, which then generates more
hydrogen fluoride. This combination of reactions continues until the material supplying the hydrogen, fluoride or the glass are consumed.
Rigorous drying of the apparatus was achieved by heating the apparatus, while under vaccum, with a non-luminous flame. When the system was to be open to the atmosphere, nitrogen gas was admitted via a bubbler con•
taining concentrated sulphuric acid and a trap cooled in liquid oxygen.
Reactions involving elemental fluorine
In these reactions} the apparatus was dried and nitrogen gas, which was used as a diluent, introduced as described. A single trap was attached
to the apparatus before the reaction zone? this was cooled with liquid
oxygen to remove hydrogen fluoride and moisture from the fluorine/nitrogen mixture. A train of traps was attached beyond the reaction zone, and these too were cooled with liquid oxygen. Liquid oxygen (b. -183°) was the most suitable refrigerant as it condensed most volatile reaction*pro• ducts but not fluorine (b. -188°). Liquid nitrogen (b. -196°) is less
suitable in that it does condense fluorine. High temperature fluorination reactions in glass or silica apparatus produced silicon tetrafluoride which 27.
also condensed in the traps cooled with liquid oxygen. In such cases,
it was found more convenient to employ alcohol/solid carbon dioxide
(-78°) cooled traps in which silicon tetrafluoride did not collect.
The reaction zone was heated by calibrated, wire-wound heaters*
Reactions involving bromine trifluoride, selenium tetrafluoride
or iodine pentafluoride
These solvents have convenient liquid ranges (BrF , m. 9°, b. 126°, o
IF , m. 10°, b. 100°, SeF. , m. -10°, b. 100°) and can be handled easily
in systems similar to that shown in Figure 3.
The solvent was stored in a break-seal bottle, 1. The material to be fluorinated or brought into solution was placed in a silica reaction bulb, 2, which was attached to the system through a graded-seal. Hygro•
scopic materials were also placed in break-seal bottles. The loading was
carried out in a dry-box, and the bottles were sealed under vacuum. The
leading limb of trap 3 was constricted slightly.
In a typical procedure, the traps of the dried, apparatus were cooled with liquid oxygen, them the break-seal was broken by moving the nickel balls with a magnet. The liquid oxygem was removed from around trap 1 and the contents were allowed to warm up, any ice condensing on the out• side was removed by gentle warming using a hot-air blower. The first material to distil condensed in the constriction in trap 3 forming a plug of solid which prevented further material distilling into this trap. The remainder of the material distilled smoothly into trap 2. It was found preferable not to heat trap 1 other than to remove the ice formed on the outside, otherwise attack on the glass occurred with the consequent formation of silicon tetrafluoride. This caused a loss of vacuum which resulted in FIGURE 3 Apparatus for reactions involving bromine trifluoride. selenium tetrafluoride or iodine pentafluoride
a—-* 2Z&
o in o o >N r— > Wi 28.
a decrease in the rate of distillation.
When all the solvent had been transferred? the liquid oxygeni around
trap 3 was lowered and the plug removed by melting with a hot-air blower.
The storage trap was removed by sealing the apparatus at "a". Dry air
was slowly admitted and the liquid oxygen was removed from around the
reaction bulb; the reaction bulb was then allowed to warm up to room
temperature. The reactants were refluxed? when necessary? by warming the
reaction bulb with a small? luminous flame. When reaction was complete?
the vessel was cooled with liquid oxygen and the system was re-evacuated.
The liquid oxygen was removed from around the bulb? which was allowed to
slowly warm up to room temperature? excess reactant and any volatile
products distilling into trap 3. When the transferrence was complete?
the bulb was sealed off at "b".
Excess bromine trifluoride was destroyed by pouring into an excess
of dry carbon tetrachloride. Excesses of selenium tetrafluoride and
iodine pentaf luoride were destroyed by pouring into an excess of concenr-
trated sulphuric acid. This solution was then poured? in a thin stream?
into a copious quantity of water.
Reactions involving oxygen,, difluoride? sulphur tetrafluoride
or chlorine trifluoride
These compounds are not liquid at room temperature (SF^? m. -121°? b. -40°, QFg* m. -224°, b. 145°, ClFg, m. -76°? b. 12°) and had to be manipulated in closed systems? similar to that shown in Figure 4. The material to be fluorinated was contained in a nickel boat inside the re• action tube? which could be heated by means of a wire-wound heater. The apparatus was dried? then the. volatile reactant was transferred to trap 1? FIGURE 4
FIGURE k Apparatus for reactions involving oxygen difluoride, sulphur tetrafluoride or chlorine trifluoride OJ
t a Q; O I_ Ul «- o
a 4f
ZD
CJ v-
CM
ro
3
_a — E E 3 OJ I o o tn > 0) 29.
which was cooled with liquid nitrogen, and the apparatus was sealed at
"a" and "b". Trap 4 was surrounded with liquid nitrogen, and the re• action zone was heated to the desired temperature. Trap 1 was allowed to warm up, with a consequent distillation of the reactant through the reaction zone to trap 4. The volatile reactant was transferred back to trap 1 in a similar manner, after first cooling the reaction zone to room temperature. The temperature of the reaction zone was raised and the above procedure repeated. When the reaction was judged to be com• plete, the excess of volatile reactant was condensed into trap 2, which was then removed from the system by sealing at "c" and "d1*. Any non• volatile product and unreacted starting material were sealed into the reaction tube by sealing at "e,,;. Any volatile product, not volatile at room temperature was retained in trap 3 by sealing at "f".
Excess reactants were disposed of by allowing them to slowly evapo• rate in a well-ventilated flume hood. 30.
PREPARATION AND PROPERTIES OF THE
FLUORIDES OF PLATINUM
PLATINUM DIFLUORIDE
All attempts to reduce platinum tetrafluoride to prepare a lower fluoride of platinum were unsuccessful.
Attempted fluorination of platinum dichloride using anhydrous hydrogen fluoride
Platinum dichloride, contained in a nickel boat, was heated in a stream of anhydrous hydrogen fluoride in a nickel reactor. There was no interaction at temperatures below 200° and the only identifiable products obtained at temperatures above this were platinum metal and platinum tetrafluoride.
Reaction of platinum dichloride with sulphur tetrafluoride
Platinum dichloride, contained in a nickel boat, was reacted with sulphur tetrafluoride in an all-glass, closed system. Initially the reaction was carried out at room temperature, then the temperature was raised in 50° intervals. No apparent reaction occurred up to a tempera• ture of 400°, when fluorination of the containing tube occurred.
An x-ray powder photograph of the residue revealed no lines other than those of platinum dichloride. 31.
PLATINUM TRIFLUORIDE
All attempts to reduce platinum tetrafluoride to yield a lower fluoride were unsuccessful. However, x-ray powder photographs of the residues from the fluorination of platinum metal in the presence of powdered glass, at
400°j showed a pattern of lines that corresponded very closely to those of palladium trifluoride.
These lines were indexed on the basis of a bimoleculor rhombohedral unit cell with a = 5.41 t 0.01A*, ^=54.3 £ 0.1°, V-97A*3, Dc=8.6 g. cm"3.
Calculated and observed values of l/d^ are given in Table II.
Residues from these reactions were inhomogeneous, consisting mainly of pale-yellow to orange material containing some black specks. It is significant that specimens having the more intense platinum trifluoride pattern also contained a greater proportion of black material.
TABLE II. Calculated and observed x-ray diffraction data for platinum trifluoride.
1/jlf hkl Calc. Obs. 110 0.0760 0.0775 211 0.1391 0.1418 IOT 0.1648 0.1666 222 0.1893 0.1895 210 0.2121 0.2121 200 0.2408 0.2425 220 0.3039 0.3064 321 0.3541 0.3588 332 0.3914 0.3973 211 0.4056 0.4071 310 0.4687 0.4702 211 0.4945 0.4946 431 0.7331 0.7295> 420 0.8486 0.8483 32.
QUADRIPOSITIVE PLATINUM
PLATINUM TETRAFLUORIDE, PtF4
Preparation
1. Fluorination of platinum metal
Fluorination of platinum metal using a low concentration of elemental fluorine at 300° produced platinum tetrafluoride as the non-volatile re• action product. When, produced in this way it was pale-yellow and well crystalline, but some platinum metal always remained under a protective coating of the tetrafluoride, which was involatile at this temperature.
2. Thermal decomposition of the platinum tetrafluoride bromine trifluoride adduct (7)
(i) Preparation of the platinum tetrafluoride, bromine trifluoride adduct
Platinum tetrabromide was dried overnight, at 70°, in the silica bulb of a bromine trifluoride reaction system. Reaction with bromine trifluoride occurred immediately the bromine trifluoride melted and had to be moderated by cooling with liquid oxygen. Bromine was rapidly evolved and a deep red solution was obtained. This was refluxed for fifteen minutes, then excess bromine trifluoride and any bromine remaining were removed by vacuum distillation at room temperature. The platinum tetrafluoride, bromine trifluoride adduct remained as a pale, red-brown solid.
Analysis was by pyrohydrolysis to a temperature of 300°.
Founds Pt, 36.7; F, 35.1. Calc. for PtF4 (BrFg) . Pt, 35.9; F, 34.9$ 33.
(ii) Thermal decomposition
The platinum tetrafluoride, bromine trifluoride adduct was heated, under vacuum, in a nickel boat contained in an all glass-apparatus as shown in Figure 5. The temperature was held constant for six-hour periods and was raised by intervals of 50°. Decomposition started at
130° and bromine trifluoride collected in the first trap. All of the bromine trifluoride was not removed until 300°, at which temperature the platinum tetrafluoride sublimed and started to decompose into platinum metal and fluorine. To overcome this* a sample of the adduct was o heated, under vacuum, at 200 for twelve hours. The platinum tetrafluoride containing some residual bromine was then heated to 250° in a stream of fluorine, when all the residual bromine was eliminated as a mixture of bromine trifluoride and bromine pentafluoride.
Platinum tetrafluoride produced in this manner was light brown, but x-ray powder photographs were poor, showing that the crystallites of the material were smaller than, the ideal for sharp-line photographs. Analysis was by pyrohydrolysis to a temperature of 300°.
Found: Pt, 71.7; F, 27.8; Bromine absent. Calc. for PtF4:- Pt, 72.0;
F, 28$.
Properties
Platinum tetrafluoride varies in colour from pale yellow to brown.
The higher the temperature of preparation, the paler the colour.
It was not very hygroscopic and could be handled for short periods of time in the atmosphere) without significant decomposition. On pro• longed exposure to moist air, however, hydrolysis occurred with the forma• tion of the pale-yellow fluoroplatinic acid and a precipitate of hydrated FIGURE 5 Apparatus used for studing decomposition reaction.
B19 Cone & socket
1
8
To vacuum system 34.
platinum dioxide.
It reacted slowly with hydrochloric acid with the formation of chloro-
platinic acid.
The presence of fluoroplatinic acid and chloroplatinic acid in these
reactions were shown by examinations of their ultra-violet spectra. The
spectrum of the fluoroplatinate ion is not very pronounced, consisting of. two
shallow peaks on the edge of a very strong charge-transfer band. This species
was confirmed by converting it to the deep-red hexaiodoplatinate (IV) ion by
reaction with potassium iodide. The reaction is very slow in sharp contrast
to the reaction of bromoplatinic acid and chloroplatinic acid with potassium
iodide.
The absorption peaks (m/f) for the halogenoplatinic acid are as follows.-
PtC1 Ptl PtFg" 6~" PtBr6~"(26) 6~~ 275,315 263 305~ 341,226
A magnetic moment study showed, the tetrafluoride to be diamagnetic.
Infra-red spectrum
The infra-red spectrum of the material in a nujol mull was recorded! using
both sodium chloride and caesium bromide optics. A sharp peak at 675i cmi *
and a broad peak at 576 cm * were observed.
The crystal structure of Platinum Tetrafluoride
X-ray powder photographs of the material prepared by fluorination of
platinum metal were interpreted on the basis of a pseudo-tetragonal unit cell,
J a = b =6.668 £ 0.005A\ C = 5.708; £ 0.005A\ ot* y3 = 90°, 92.02 *r0.05° ,
Z = 4, V =s 253.5A>3, Dc =7.10 g.cm 3, Dm =6.12 g.cm 3 (the discrepancy between
the observed and calculated values is attributed to the specimen not being perfectly crystalline).
Observed and calculated values for l/d^ are given, in Table III. 35.
TABLE III. Calculated and observed x-ray diffraction data for platinum tetrafluoride
hkl Calc. Obs. Ions. 101 0.0532 0.0545 10 200 0.0899 0.0922 9 211 0.1399 0.1425 8 211 0.1463 0.1483 8 112 0.1661 0.1680 7 112 0.1693 0.1705 7 220 0.1735 0.1764 3 220 0.1863 0.1887 3 202 0.2127 0.2141 2 301 0.2331 0.2356 8 103 0.2987 0.3007 5 321 0.3134 0.3170 6 321 0.3329 0.3348 5 312 0.3429 0.3456 7 312 0.3525 0.3543 8 400 0.3598 0.3630 6 213 0.3854 0.3873 5 213 0.3918 0.3932 4 411 0.4065 0.4104 6 411 0.4193 0.4205 6 420 0.4369 0.4409 6 420 0.4625 0.4639 4 303 0.4786 0.4802 3 402 0.4826 - 004 0.4910 0.4913 3 332 0.5131 0.5151 4 332 0.5419 0.5420 6 422 0.5697 - — 431 0.5736 - — 323 0.5781] 0.5800 7 204 0.5809/ 501 0.5928 - — 422 0.5953 0.5953 55 431 0.6120 0.6118 6 413 0.6520 0.6529 3 224 0.6646] 413 0.6648 I 0.6663 & 521 0.6668J
224 0.6784 — 521 0.6988] 0.7004 7 512 0.6994 / 314 0.7111 - - 512 0.7154 0.7163 9 TABLE III cont'd
hkl Calc. Obs. lob 440 0.7164 314 0.7207 - — 440 0.7675 — — 105 0.7898 — 600 0 . 8095 0.811- 1 5 433 0.8191 0.8216 5 503 0.8383 0.8403 1 404 0.8508 0.8504 6 611 0.8530 0.8549 6 433 0.8575 — - 532 0.8633 0.8654 3 611 0.8722 0.8707 3 815 0.8765 — — 620 0.8802? 0.8806 2 215 0.8829J 523 0.9123 0.9127 5 620 0.9186 — — 541 0.9206 - — 532 0.9213 - - 424 0.9279 0.9278 4 602 0.9323 - - 523 0.9443 0.9435 3 424 0.9535 0.9504 3 305 0.9697 0.9655 1 541 0.9846 0.9819 4 37.
The following regularities in reflections were noted,
hkl present if h + k + 1 = 2n
hko present if h 2n and k = 2n
Okl present if k +• 1 » 2n hhl present if 1 = 2n and 2h +- 1 = 4n these indicate that the lattice is body-centred and 001, 150 and 110 are glide planes. The regularities place the molecule in a space group re•
lated to the tetragonal space group D4^-I4j/amd.
Reaction of platinum tetrafluoride
(i) With selenium tetrafluoride (16)
A suspension of platinum tetrafluoride in selenium tetrafluoride was refluxed for fifteen minutes at atmospheric pressure. The platinum tetra• fluoride partially dissolved, with the formation of a pale, yellow-pink solution, which after removal of excess solvent under vacuum yielded a pale, yellow solid, which had a pink fluorescence.
The material was analysed by first decomposing a known weight of material in a 5$ sodium carbonate solution. It dissolved completely to give a pale-yellow solution. Aliquots were taken; selenium was estimated by precipitation as the metal from a solution acidified with concentrated hydrochloric acid. Platinum was determined on the filtrate from this determination. Fluorine was estimated as lead chlorofluoride after a
Willard and Winter distillation.
Founds Pt, 34.92; Se, 25.5; F, 36.5. Calc. for PtF4 (Se F^: Pt, 33.5;
Se, 27.2; F, 39.3$. 38.
(ii) With iodine pentafluoride
Platinum tetrafluoride did not dissolve in iodine pentafluoride when
the mixture was refluxed and no apparent reaction occurred. Removal of
the solvent left a light-brown solid. Chemical analysis showed this to be platinum tetrafluoride and an x-ray powder photograph showed no lines other than those of platinum tetrafluoride.
(iii) With sulphur tetrafluoride
Platinum tetrafluoride was heated in a stream of sulphur tetrafluoride
in a closed system. No apparent reaction occurred until a temperature of 300°, when platinum tetrafluoride sublimed on to the walls of the apparatus. Chemical analysis of the residue showed it to be platinum tetrafluoride and an x-ray powder photograph revealed no lines other than those of platinum tetrafluoride.
(iv) With chlorine trifluoride
Chlorine trifluoride did not interact with platinum tetrafluoride, in a closed system, below 300°. At this temperature, an orange solid condensed on the cooler walls beyond the heated zone and a pale yellow solid collected in the traps cooled with liquid nitrogen. The orange and yellow materials were shown by melting point determination (m. 170°) and by x-ray powder photographs to be identical with the material pro•
duced by the reaction of chlorine trifluoride with Pt0J?o. 2 o (v) With powdered glass
A mixture of equal quantities of platinum tetrafluoride and powdered glass, placed in a nickel boat, was heated in an atmosphere of nitrogen in an apparatus similar to that shown in Figure 5. The traps were cooled with liquid nitrogen. 39.
The material was heated, for six hour periods, at a series of
temperatures .and at 50° intervals, samples were taken for x-ray powder
analysis. No apparent reaction occurred until a temperature of 350°
when silicon tetrafluoride condensed in the first trap, and the x-ray
powder photograph showed lines due to platinum metal. Further heating
resulted in the reduction of further platinum tetrafluoride to platinum metal with no intermediate fluoride produced.
THE PLATINUM TETRAFLUORIDE, BROMINE TRIFLUORIDE ADDUCT, PtF4(BrFg>2
Preparation
The bromine trifluoride adduct of platinum tetrafluoride was pre•
pared as described under the preparation of platinum tetrafluoride.
It was also prepared by the reaction of bromine trifluoride with PtO^Fg
or platinum pentafluoride.
Properties
The adduct was found to be a pale, red-browm solid (m. 132° (sealed
tube)). The melt was deep-red and viscous and slowly attacked the glass
container. The solid was rapidly hydrolysed and gave a clear orange
solution containing the fluoroplatinate ion. An x-ray powder photograph
showed it to be crystalline* but the pattern was somewhat complex and dif•
fuse, and no attempt was made to index it. The solid was diamagnetic.
An attempt was made to displace the bromine trifluoride with iodine pentafluoride, but no replacement occurred even on prolonged refluxing.
THE PLfflNUM TETRAFLUORIDE, SELENIUM TETRAFLUORIDE ADDUCT, PtF (SeF ) —" •—~——————— 4* 472 Preparation
The platinum tetrafluoride, selenium tetrafluoride adduct was prepared 40.
as described under the reaction of platinum tetrafluoride. It was obtained by the action of selenium tetrafluoride on PtO^Fg or platinum hexafluoride.
Properties
The adduct was found to be a palej yellow solid which did not melt, but decomposed on heating to 350° into platinum metal and selenium tetra• fluoride. It reacted exothermally with water to give a solution con• taining the fluoroplatinate ion. It was found to be diamagnetic.
A sharp x-ray powder pattern was obtained. This was almost identical with the patterns previously obtained from the germanium (77) and palladium- analogues (78, 79). These photographs were indexed on the basis of hexag• onal unit cells containing four molecules:-
PtF4(SeF4)2 PdF4(SeF4)2 GeF^SeF^ a 15.74 t 0.01 15.47 t 0.01 15.60 ± 0.01 c 4.93 £ 0.01 4.88 ± 0.01 4.93 f 0.01 X 3 V 1055 1015 1040 ; X
Dc 3.66 3.26 2.93 g.cm"3
Observed and calculated values for l/d^ are given in Tables IV, V and
VI.
POTASSIUM FLU0R0PLATINATE (IV)
Potassium fluoroplatinate (IV) was prepared by the method of Sharpe(7).
The infra-red spectrum of a nujol mull of the material was recorded over the range 400—4000 cm *. The following peaks were observed:-
488(m), 528(w), 538(w), 583(s), 730(m), 1050(v.s. broad), 1308(w) (32). 41.
TABLE IV. Calculated and observed x-ray diffraction
data for PtF. (SeFj0 4 4 2
ui hkl Calc. Obs. lobs. 110 0.0166 0.0177 10 210 0.0388 0.0388 8 001 0.0415 0.0446 10 220 0.0665 0.0680 9 310 0.0720 0.0735 9 211 0.0803 0.0805 6 400 0.0886 0.0886 4 301 0.0912 0.0926 5 320 0.1053. 0.1065 3 311 0.1135. 0.1127 9 401 0.1309 0.1310 5 330 0.1496 0.1516 9 004 0.1660 0.1659 5 510 0.17171 0.1700 6 102 0.1715J 421 0.1966 0.1971 3 600 0.1994 0.2016 3 430 0.2050 0.2077 2 402 - 0.2546 0.2552 4 440 0.2659 0.2659 8 700 0.2715 0.2717 3 620 0.2880 0.2869 7 502 0.3045 0.3027 6 602 0.3651 0.3641 5) 003 0.3735S 0.3733 7 42.
TABLE V. Calculated and observed x-ray diffractioni
data for PdF, (SeF4)2 4
I/ hkl Calc. Obs. 110 0.0167 0.0166 210 0.0390 0.0388; 001 0.0419 0.0441 220 0.0668 0.0672 310 0.0724 0.0731 211 0.0809 0.0810 400 0.0891 0.0892 301 0.0920 0.0926 311 0.1143 0.1138, 401 0.1310 0.13353 330 0.1504 0.1518 411 0.1616 0.1597 002 0.1676 0.1662 510 0.17271 0.1718 102 0.1732J 501 0.1812 0.1797 440 0.1899 0.1866 421 0.1979 0.1966 600 0.2005 0.2023 402 0.2576 0.2559 440 0.2674 0.2675> 700 0.2729 0.2764 620 0.2896, 0.2897 441 0.3093 0.306,7 422 0.3236 0.3221 540 0.3398 0.3412 630 0.3509 0.3513 711 0.3594 0.3582 602 0.3681 0.3679 003 0.3771 0.3771 43,
TABLE VI. Calculated and observed x-ray diffractiom
data for GeF (SeF„)n 4 4'2
bkl Calc. Obs. 110 0.0165 0.0165 210 0.0385 0.0389 001 0.0419 0.0430 300 0.04953 0.0497, 220 0.0660 0.0675; 310 0.0715 0.0730 211 0.0795 0.0800 400 0.0880 0,0864 301 0.0905 0.0910 320 0.1045; 0.1050 311 0.1125 0.1134 410 0.1155 0.1168 401 0.1290 0.1324 330 0.1485 0.1501 411 0.15653 0.1572 002 0.1640 0.1637 102 0.1695\ 0.1706 510 0.1705U 501 0.1785) 0.1782: 202 0.1860 0.1859 600 0.1980 0.1997 402 0.2520 0.2540 440 0.2640 0.2641 700 0.2695 0.2725 332 0.3125 0.3111 621 0.3270 0.3264 540 0.3355 0.3400 630 0.34653 0.34963 602 0.3620 0.3655, 44.
PENTAPOSITIVE PLATINUM
PLATINUM PENTAFLUORIDE, PtFg.
Preparation
Platinum pentafluoride was prepared, at 350°, by the fluorinationi of platinum dichloride, contained in a nickel boat, in a silica apparatus.
It collected as a deep-red solid just beyond the reaction zone. When fluorination was complete, the apparatus was sealed off at both ends of the reaction tube. The material was transferred, in a dry-box, to a
10 mm. silica tube tapering into a 5 mm. silica tube. The platinum penta• fluoride was warmed, under vacuum, in an attempt to melt it into the narrower tube and at the same time sublime off any PtO^Fg that had been formed simultaneously with the pentafluoride. Because of the high sur• face tension and viscosity of the melt and the production, of silicon tetra• fluoride by interaction with the container, it was not possible to obtain a continuous column of the material in the narrow tube. Instead, several bands were formed at different levels in the tube.
Analysis was carried out by decomposing a known weight of material in. a 5$ solution of sodium carbonate and determining the platinum, precipitated and in solution, and the fluorine as previously described.
Found: Pt, 65.0; F, 32.8. PtF_ requires Pt, 67.2; F, 32.8$. o
It was also formed in fluorination reactions involving platinum metal and other platinum compounds where the temperature of fluorination was greater thani350°, but the yields in these instances were not as good as. with the fluorination of the dichloride.
It was also formed by the photolysis of platinum hexafluoride. 45.
Properties
The investigation of the properties of platinum pentafluoride was
severely limited by its high surface tension and its ready disproportionationi
into platinumi tetrafluoride and platinum hexafluoride.
It was found to be a deep-red, glassy solid (m. 80°). The melt, which
was deep-red, had a very high surface tension and viscosity. The boiling
point could not be estimated because of its ready disproportionation.
That this disproportionation occurs even at the melting point was shown by
the decrease in melting point on subsequent determinations. Disproportion•
ation was found to be very rapid at 200°, in a vacuum, platinum: hexafluoride was condensed out in a trap cooled with liquid nitrogem and the residue of platinum tetrafluoride was recognized by its x-ray powder photograph.
A magnetic study, which was necessarily qualitative due to the irregular packing of the tube, showed it to be paramagnetic.
An x-ray powder photography taken of the material melted into a silica x-ray capillary, did not give a pattern of lines.
Reactions of platinum pentafluoride
(i) With water
It reacted exothermally with water, approximately 25$ of the platinum, being precipitated as the hydrated dioxide, the remainder going into solution,
as the fluoroplatinate ion.
(ii) With bromine trifluoride
It reacted with bromine trifluoride only on prolonged refluxing, to give a deep orange solution. On removing the excess solvent, pale-orange crystals were obtained. These were shown, by an x-ray powder photograph to be the lj.2 platinum tetrafluoride, bromine trifluoride adduct described above. 46.
2. With potassium bromide in bromine trifluoride solution.
Interaction with potassium fluoride in bromine trifluoride was tried
in an attempt to prepare potassium fluoroplatinate (v). Because the
platinum pentafluoride could not be weighed out accurately, an^ estimated
excess was taken. Reaction was more rapid than the reaction between!
bromine trifluoride and platinum pentafluoride alone. Some bromine was
evolved and a deep red solution* remained. Removal of excess solvent:, left
a pale-yellow solid. An x-ray powder photograph of this revealed only
lines due to potassium fluoroplatinate (IV) and the platinum tetrafluoride,
bromine trifluoride adduct.
3. With iodine pentafluoride.
It reacted very slowly with iodine pentafluoride, dissolving on pro•
longed refluxing, with the formation of a cloudy red solution. Removal
of excess solvent, overnight, left a pale orange solid. The product gave
an x-ray powder pattern identical with that obtained for the reaction bet• ween iodine pentafluoride and PtO F„. This material proved to be PtF_, IF .
4. With sulphur tetrafluoride.
No reaction occurred between platinum pentafluoride and gaseous sulphur tetrafluoride, even on, heating to the melting point of platinum pentafluoride.
POTASSIUM FLUOROPLATINATE.(V), KPtFg
Preparation
1. Reaction of potassium fluoride with PtO_F„ in iodine _ 2 o pentafluoride solution.
Equimolar quantities of potassium fluoride (0.093g) and ^^O^Fg (o.534g) were weighed in a dry-box, into a silica bulb attached, by a graded; seal, to a breakseal. The bulb was sealed under vacuum and joined to an iodine 47.
pentafluoride-reaction system. Reaction occurred immediately the iodine
pentafluoride melted. There was a slow evolution of gas and a cloudy-
red solution was formed. Some material (presumably the potassium fluoride, which isnot very soluble in iodine pentafluoride) did not react in the cold.
The solution was refluxed for fifteen minutes. On removal of the excess;
iodine pentafluoride at room temperature, a mustard-yellow, solid remained.
Analysis was by pyrohydrolysis to 300°.
Found: F, 32.0; Residue, 69.0. KPtFg requires F, 32.7; Pt, 56.0; K,11.3$.
2. Fluorination of a mixture of platinum tetrachloride and
potassium chloride.
A finely-ground, equimolar mixture of platinum tetrachloride(0.47g.) and potassium chloride (o.lg.) contained in a nickel boat was heated in a
stream of fluorine. The temperature was slowly raised, no reaction'. o occurred until a temperature of 120 , when the material blackened in patches, with apparent sintering. The temperature was slowly raised to 300°, above this temperature volatile platinum fluorides were produced. The residue appeared heterogeneous, consisting of a mixture of black and yellow specks.
An x-ray powder photograph showed that the material was a mixture of potassium fluoroplatinate (IV) and potassium fluoroplatinate (v).
3. Subliming PtO^Fg on to potassium fluoride under vacuum.
Potassium fluoride, contained in a nickel boat, was heated to 70°.
PtOgFg was sublimed over this under vacuum. A deep yellow residue re• mained, this was shown by an x-ray powder photograph to contain mostly potassium fluoroplatinate (V) with smaller quantities of potassium! fluoro- platinate (IV) and unreacted potassium fluoride. 4'8.
Other, unsuccessful, attempts to prepare potassium hexafluoro• platinate (V) were made as follows:-
1) Heating an equimolar mixture of potassium?fluoride and platinum di•
chloride to 200° in a stream of fluorine.
2) Heating an equimolar mixture of potassium fluoride and PtO^Fg in an atmosphere of nitrogen.
3) By the action of excess bromine trifluoride on an equimolar mixture of platinum metal and potassiumi fluoride.
4) By the action of excess bromine trifluoride on an equimolar mixture of potassium fluoride and platinumi tetrachloride.
Properties
Potassium hexafluoroplatinate (V) is a deep-yellow crystalline solid.
It could be stored indefinitely in well-dried, sealed tubes. In moist air, however, it slowly decomposed, evolving ozone smelling gases. It reacted exothermally with water evolving ozone smelling gases and giving a pale yellow precipitate, which was shown, by an x-rray powder photograph to be potassium fluoroplatinate (IV). A magnetic study showed it to be para• magnetic ( Ms. 0.87 Bohr magnetons). An infra-red spectrum, of a nujol mull, recorded using both sodium! chloride and caesium bromide optics, showed a single broad absorption band that had peaks at 590 and 640 cm
The Crystal Structure of potassiumi fluoroplatinate (v).
X-ray powder photographs of potassium fluoroplatinate were interpreted on the basis of a rhombohedral unit cell, a - 4.87 ± 0.02 X;
3 cx = 97.7 ± 0.2°; V = 113 X . Dc = 5.11 g. cm"3. Calculated and observed values for l/d are given in Table VII. 49.
TABLE VII. Calculated and observed x-ray diffraction
data for KPtF„
ui hkl Calc. Obs. lobs. 100 0.0421 0.0421 10 101 0.0714 0.0717 10 110 0.0971 0.0974 8 111 0.1134 0.1139 7 200 0.1684 0.1691 6 201 0.1847 0.1850 3 211 0.2140 0.2150 5 211 0.2397 0.2396 9 202 0.2853 0.2867 4 211 0.3170 0.3180 2. 212 0.3274 0.3288 3 301 0.3824i 0.3811 7 310 0.4597 0.4591 6 302 0.4700 0.4690 6 312 0.4992, 0.5000 5, 312 0.5250 0.5254 4 311 0.5533 0.5521 1 321 0.6023 0.6061 2 322 0.6642 0.6639 3 50.
THE PLATINUM PENTAFLUORIBE, IODINE PENTAFLUORIBE ABDUCT, PtFK,lF_ 5 5
Preparation
The platinum pentafluoride, iodine pentafluoride adduct was prepared as described under the reactions of platinum pentafluoride and PtO F„. 2 6
Properties
It was found to be a pale-orange crystalline solid. It reacted vigorously with water, evolving acid gases and giving a solution con• taining the fluoroplatinate ion. It reacted vigorously with concentrated hydrochloric acid, giving a solution which was found to contain the chloroplatinate ion. Vigorous reaction occurred with most organic solvents, with the precipitation of platinum metal. No reaction occurred with carbon tetrachloride. It melted, though not sharply, at about 140° with attack on the glass container. A decomposition study showed that: the material started to decompose at about 180° and decomposition was com• plete at 300°, platinum tetrafluoride remained as the residue.
A magnetic moment., study showed the material to be paramagnetic
( ^=0.65 Bohr magnetons). An x-ray powder photograph showed that the material was crystalline, but the patterm was complex and no attempt was made to index it.
THE PLATINUM PENTAFLUORIBE, CHLORINE TRIFLUORIDE ADDUCT, PtFC1F„ 5 3
Preparation l) Fluorination of platinum dichloride
In the fluorination of platinum dichloride to prepare platinumi penta- fluoride, a platinum pentafluoride, chlorine trifluoride adduct condensed in the traps of the fluorination apparatus as a pale-yellow powder and in 51.
the zone after the platinum pentafluoride and before the traps as an iridescent film.
2) Reaction of chlorine trifluoride with platinum tetrafluoride
Chlorine trifluoride was passed, over platinum tetrafluoride, contained in a nickel boat in a closed system. The temperature of the reaction zone was raised in 50° intervals. No reaction occunred until a tempera• ture of 350° when the platinum pentafluoride, chlorine trifluoride adduct condensed as a light yellow solid in the first trap, and as a light orange solid on the tube following the reaction zone.
3) Reaction of chlorine trifluoride with Ptp Fg
Chlorine trifluoride was condensed on to PtO^Fg in a closed system.
A vigorous evolution of gas occurred on warming with the formation of a solution which was deep-red at first; as the reaction proceeded, the colour became paler, and was finally pale-orange. The trap was them cooled in liquid oxygen. The end trap of the system was cooled in liquid nitrogen and sealed off. The gas in this end trap was analysed on the mass spectrometer, oxygen difluoride, fluorine, oxygen, ozone and nitrogen were sought. Only oxygen, in high concentration, was found. The excess chlorine trifluoride was distilled from the solutioni under vacuum and a deep red volatile material transferred with it. The latter could possibly be chlorine monoxide. The chlorine trifluoride adduct^ remained behind as a pale-orange residue.
Analysis was performed by pyrohydrolysis to 300°.
(Found: Pt, 51.9; F, 38.4. PtFgClFg requires Pt, 51.0; Cl, 9.3;
F, 39.7$,). 52.
Properties
The platinum pentafluoride. chlorine trifluoride adduct varied in colour from bright-yellow to orange depending on its mode of preparation.
X-ray powder photographs showed it to be well crystalline, but the pattern, obtained was complex and no attempt was made to index it. It melted sharply at 170-171° to a deep red liquid. It sublimed readily in a good vacuum at 100°, leaving an iridescent film on the cooler parts of the apparatus. It reacted vigorously with water with the evolution of pungent gases and gave a pale yellow solution which contained the fluoroplatinate ion but not the chloroplatinate ion.
PLATINUM OXYTRIFLUORIDE, Pt0Fo ______y
Preparation
Platinum oxytrifluoride was prepared by the fluorination of platinum dioxide at 200°.
Analysis was by pyrohydrolysis to 500°.
Found: Pt, 73.1; F, 21.4. Pt0Fg requires Pt, 72.8; F, 21.3$.
It was also prepared, together with some platinum trifluoride, by the fluorination of platinum metal in the presence of powdered glass.
Properties
Platinum trifluoride was found to be a light brown solid.. It was, stable to hydrolysis, and could be boiled with water without apparent, re• action. X-ray powder photographs were sharp but complex, showing it to be well crystalline. Samples were always contaminated with some platinum tetrafluoride. 53.
HEXAPOSITIVE PLATINUM
PLATINUM HEXAFLUORIDE, PtFg
Platinum hexafluoride was observed in the fluorination of platinum metal at temperatures in excess of 300°. It was best formed by fluorinating o platinum metal initially at 300 in a very rapid stream of fluorine in a nickel apparatus. It formed as deep-red (bromine-coloured) vapours directly above the reaction zone, these if swept away in a rapid stream of gas could be condensed out as a deep-red (almost-black) solid.
Reactions
It was readily photolysed by visible light, and gave a material which behaved as platinum pentafluoride.
The hexafluoride hydrolysed very rapidly to give a black precipitate and a pale orange solution containing the fluoroplatinate ion.
It reacted vigorously with selenium tetrafluoride to give a pale-yellow solid, which was shown by an x-ray powder photograph to be the platinum tetrafluoride, selenium tetrafluoride adduct.
PtOgFg. PLATINUM PEROXIDE HEXAFLU0RIDE(?)
Preparation
1. PtOgFg was best prepared by the action of mixed fluorine and oxygeni o. gases in platinum metal at 450 . The apparatus used is as showni in Figure
6. The reaction chamber was made of thicfc-walled silica tubing,, which was joined to the remainder of the apparatus through graded seals. Many dif• ferent designs of traps, to maintain a turbulent gas flow through the appara• tus were tried. The arrangement shown in Figure 6 proved to be the most successful. The platinum sponge to be fluorinated was contained in a nickel boat. FIGURE 6 Apparatus used for preparation of Pt 0^
, F2,N2o^02
o
A
_a
CM D
ro D
-D j
0) i> 54.
The apparatus was evacuated and dried in the usual manner, then.with
traps 1 and 5 cooled with alcohol/solid carbon dioxide, oxygen, was admitted
to the system through a sulphuric acid bubbler. The remainder of the
traps were cooled with alcohol/solid carbon dioxide, then after first dis•
connecting the system from the vacuum line, fluorine was passed, at a rapid
rate over the platinum metal, initially at room temperature. The tempera•
ture of the reaction zone was slowly raised. Reaction first began at 350°
when a surface coating of platinum tetrafluoride was observed. At 400°,
deep-red vapours of platinum hexafluoride were seen and simultaneously
the deep red platinum pentafluoride was deposited on the cooler walls of o
the reaction.vessel beyond the heated, zone. At 425-450 , PtO^Fg was
noticed as a deep red filmi beyond the reaction zone and as a fine pale-
orange powder in the traps. At this temperature, the silica reaction as,
chamber was fluorinated, /was evident by the etching which occurred and by
the condensation of silicon tetrafluoride by liquid oxygen, when this was used as a coolant for the traps. The fluorination was terminated when
the platinum metal in the boat had been consumed, or when the attack on.
the silica tube had become extensive. The apparatus was flushed with
oxygen until a test with a filter paper moistened with potassium iodide
showed the emergent, gas to be free from fluorine (usually it was necessary
to flush for about one hour). The apparatus was then evacuated and sealed
off at points a, b, c, d and-e.
2. The volatile oxyfluoride was also prepared in a similar manner to the
above with nitrogen replacing oxygen as the carrier gas. This method 55.
however, gave a lower yield and gram quantities were obtained only after very extensive attack on the silica of the reaction tube.
3. It was also prepared with the platinum metal contained in. a nickel reaction tube, which was attached to a train of traps by means of com• pression fittings. The volatile oxyfluoride was produced wheni oxygeni was used as the carrier gas but not with nitrogent as carrier gas. Alter• natively it could be prepared when a mixture of platinum metal and platinum dioxide was fluorinated in this manner even with nitrogen as carrier gas.
The disadvantage with this method of preparation was that the glass tube leading into the nickel reaction tube rapidly became plugged.with product.
4. It was also produced when oxygen difluoride was passed oven heated platinum metal in a closed system. No reaction occurred until 350° when the platinum metal was attacked to produce a pale-yellow crust of platinum tetrafluoride. No further reaction occurred until 400°, when PtO. F con- densed as a deep-red film beyond the reaction zone. Because of the dif• ficulties attendant in the preparation of oxygen difluoride, this method is not., of practical value.
5. It was produced in low. yield by fluorinating other platinum compounds in glass or silica apparatus.
Purification
It was purified by trap to trap distillation ini the apparatus shown, in
Figure 7. Three traps containing PtO^Fg were usually joined to a manifold and the system beyond them dried under vacuum. Trap 6 was cooled with liquid oxygen and the break-seals on traps 1, 2 and 3 were broken. Any volatile impurities were pumped off at room temperature, and these were collected in trap 6. Trap 4 was surrounded with liquid oxygen and traps FIGURE 7 Apparatus used for purification of Pj. 02Fg
CNI
G: CO ~r
O LZJ -C
LO 33-
O
CO —* .•-» O oi 3 O O h- > 01 1 56.
I, 2 and 3 were heated to 90 . The oxyfluoride sublimed from them into trap 4. When all the material volatile at this temperature had sublimed, the apparatus was sealed at a. The coolant was removed from trap 4 which was allowed to warm up to room temperature, any volatile material being transferred to trap 6. Trap 5 was surrounded with liquid oxygen and the oxyfluoride was transferred to it in a similar manner. The apparatus was sealed at b and c. The PtO^Fg condensed on the cooler parts of the appara• tus as a deep red solid. It was removed from the walls and powdered by moving the nickel balls with a magnet. It was then shaken: into the tubes x and y for magnetic moment studies, analyses etc.
Analysis
Analysis for both fluorine and platinum was effected by pyrohydrolysis* which proceeded very readily even at room temperature.
pt0 F (Found: Pt, 57.5; F, 32.4. 2 6 requires Pt, 57.2; F, 33.4$).
Platinum metal was determined separately by ignition of a known weight of material in a platinum crucible in an atmosphere of hydrogen:
(Found: Pt, 57.4$).
Fluorine was determined separately by fusion of the material with sodium in a Parr bomb followed by precipitation as lead chlorofluoride
(Found: F, 32.7$). Oxygen was determined by displacement with bromine
triflunride. Found: 0, 10.4. PtO„Fc requires 0, 9.4$. 2 o
Properties
PtOgFg, depending on its state of division, existed either as a fine, orange-brown powder or as a deep red film. On cooling, there was: a reversable colour change from red-brown at about -120° to bright orange below this temperature. It sublimed readily in a good vacuum at 90° and 57.
melted in a sealed tube at 219 , to a deep-red, viscous liquid, with the evolution of gas. It hydrolysed rapidly in moist air, and so had to be handled in sealed systems and stored in sealed, dry pyrex bulbs. It, could be stored indefinitely under these conditions.
It reacted violently with most organic solvents, but not with carbon. tetrachloride, in which it did not dissolve.
Crystal structure for PtO„Fc 2 Q-' The x-ray powder pattern was interpreted on the basis of a body-centred.' cubic unit cell containing eight molecules:
3 3 3 a a 10.032 ± 0.002 X; V - 1009.6 X ; Dc = 4.48 g.cnf* ; Dm = 4.20 g.cm" .
Observed and calculated values for l/d are given in Table VIII.
The observed indices of the reflection show the following relationship,
hkl present only when h + k + 1 = 2n indicating that the lattice is body centred. A suitable space group could not be found.
The platinum atoms, which have a high scattering factor must be situated on a simple cubic lattice, a = 5.016 ± 0.001 X since all of the lines, with the exception of four week ones, can be indexed on the basis of this simple 58.
TABLE VIII. Calculated and Observed x-ray diffraction
data for Pt0nF„ 2 6
1/d2 hkl Calc. Obs. lobs
110 0.0199 — — 200 0.0398 0.0413 8 211 0.0597 220 0.0795 0.081- 8 1-0 222 0.1193 0.1217 5 321 0.1391 0.1410 1 400 0.1590 0.1614 4 411 0.1799 0.1808 2 420 0.1988 0.2020 7 332 0.2287 0.2216 2 422 0.2385 0.2415 9 431 0.25:84 0.2606 1 440 0.3180 0.3209 6 600, 442 0.3578 0.3613 9 620 0.3975 0.4010 7 622 0.4372 0.4406 6 444 0.4770 0.4800 4 640 0.5167 0.5198 6 642 0.55.64 0.5600 9 800 0.6359 0.6390 2 820, 644 0.6757 0.6787 7 822, 660 0.7154 0.7190 6 662 0.7552 0.7582 4 840 0.7949 0.7984 5 842 0.8347 0.8381 6 664 0.8744 0.8761 4 844 0.9539 0.9558 3. 10,0,0; 860 0.9938 0.&95:7 4 10,2,0; 862 0.0340 1.0361 7 . 10,2,2; 666 1.0731 1.0768 4 10,4,0; 864 1.1526 1.1549 6 10,4,2 1.1924* 1.1936 5 880 1.2718, — 10,4,4; 882 1.3116 1.3134 4- 10,6,0; 866 1.35:14 1.3525 4 10,6,2 1.3911 1.3925; 4 12,0,0; 884 1.4309 1.4313 3 12,2,0 1.4706 1.4721 2 12,2,2;10,6,4 1.5103 1,5118 5 12,4,0 1.5898 1^5902 3 ,2; 10,8,0;886 1.6296 1.6300 6 &y.
Mass Spectrum
A mass spectrum of PtO^Fg was recorded by subliming the material into
a mass spectrometer. The observed peaks and their assignments are given,
in Table IX.
TABLE IX. Mass spectrum of PtOgFg
Mass Assignment. 196 Pt*"
210 + 211 PtO 212
22 ? r PtO + 227 2
229 + 230 PtOF 231
242 PtO *
243 3
Species of greater mass number could not be detected on the mass
spectrometers available.
Infra-Red Spectrum
The infra red spectrum was recorded using three different cellss-
1. A stainless-steel-bodied cell with calcium fluoride windows. The
spectrum was recorded both in the vapour phase, with the cell heated to
100°, and with the material sublimed on to the cell windows.
2. A glass-bodied cell with sodium chloride windows. A spectrum of material sublimed on to the windows was recorded.
3. As in 2, using potassium bromide windows.
The observed absorption frequencies and their relative intensities are given in Table X. 60.
TABLE X. Infra-red spectrum of PtfigFg
(CM"1) Intensity 631 v.s. 680 w 725 v.w. 975 v.w. 1308 w 1448 m 1458 m 1495i m.w. 1505 m.w.
Ultra-violet and visible spectrum
The ultra-violet and visible spectrum of PtO^Fg was recorded of^material that had been sublimed on to the quartz windows of a glass bodied cell.
The absorption steadily increased with decrease in wavelength, rising sharply at 4000 A* and showing a single maximum at 3500 X.
Magnetic study
A magnetic study was carnied out in the range 88-300°K. Values for the molar susceptibilities in this range are given, in Table XI. A plot of l/'Ku versus temperature obeyed the Curie-Weiss law and gave a value of -6° for the Weiss constant. The effective magnetic moment at 20° is
2.45 Bohr magnetons.
TABLE XI. Molar, susceptibilities of PtOgFg x 10 c.g.s. units
T(°K) 88 116 133 146 175 204 233 261 XM 6066 4809 4290 4107 3670 3209 2801 2557
271 294 2498 2313 FIGURE 8 Apparatus used for measuring gas evolution 61.
Vapour-pressure studies
A preliminary vapour-pressure study was carried out, using a simple isoteniscope with a low-viscosity, fluorolube oil in the differential man- nometer. At temperatures in excess of 150°, however, attack on the glass apparatus occurred.
A nickel diaphram gauge has been designed for this study and it is hoped that satisfactory measurements can be made in the near future.
Reactions of Pt0oFft 2 o
1) With water
It reacted violently with water. Oxygen was evolved, a black: pre• cipitate and a pale yellow solution were obtained. The black precipitate,
which was very finely divided, was shown, by x-ray analysis to contain some platinum metal and in addition some amorphous material, which was soluble in hydrochloric acid. The pale yellow solution was found to con• tain the fluoroplatinate ion. That the gas evolved was oxygen was shown by (i) its mass spectrum (ii) being absorbed by alkaline pyrogallol (iii) the absence of absorption bands in its infra-red spectrum. The oxyfluoride also reacted vigourously with water vapour to give an orange-yellow pre• cipitate of hydrated platinum dioxide and a golden yellow solution con• taining the fluoroplatinate ion. This reaction with water vapour was followed quantitatively, the gas volumes being measured using a TtJpler pump.
The arrangement used was similar to that used by Emeleus and Woolf (8l) and is shown diagramatically in Figure 8.
Bulb 1 contained water which had previously been degassed, bulb 2 con• tained a known weight of PtO F„. Both bulbs had been sealed under vacuum. 62.
Tap A lead to a high vacuum system and tap B to a Toplec pump.
The apparatus was evacuated overnight through A. Tap A was closed and the two break seals broken. Water vapour soon reacted with the material in bulb 2, with the formation of hydrated platinum dioxide and fluoroplatinic acid. When all the material had reacted, both bulbs were cooled in liquid oxygen, and any gases pumped through B and their' volumes measured by the Topler pump. Immediately the gas entered the pump, attack of the mercury occurred with the formation of a black scum. Analysis of the gas, by mass spectrum, however, showed only oxygen: to be present. A further sample when opened under alkaline pyrogallol was almost completely absorbed.
Results
i) 0.8872 g 70.5) mis. oxygeni
or 1 gm. mole. 27.1 1.
ii) 0.1908 g 14.8 mis. oxygeni
or 1 gm. mole. 26.5 1.
2) With bromine trifluoride
It reacted vigourously with bromine trifluoride, at room temperature, in an open system to give a deep red solution. On removal of the excess bromine trifluoride under vacuum-, at room temperature,; a pale-orange com• pound remained. This was shown, by x-ray analysis to be identical with the platinum.tetrafluoride, bromine trifluoride adduct.
The reaction was followed quantitatively in a similar manner to the reaction with water. In this case the bromine trifluoride was transferred under vacuum to the PtO^Fg cooled with liquid oxygeni. Any gases formed 63.
during the transfer, of bromine trifluoride were removed through A before allowing the materials to warm up and react. The gas evolved again attacked the mercury of the Tdpler pump* and again, was shown by mass spectrumi analysis and absorption in alkaline pyrogallol to be oxygen.
Results
i) 0.1112 g- 8.0 mis. oxygeni
or 1 gm1. ml. 24.5: 1.
ii) 0.30493 g 22.5 mis.
or 1 gm, ml. 25.1 1.
3) Wiith selenium tetrafluoride
It reacted vigourously and with much effervescence with selenium; tetra- fluoride> at atmospheric pressure, to give a pale, yellow solution and a deeper yellow solid. Evaporation of the selenium) tetrafluoride under- vacuum, at room temperature, left a pale yellow solid. This was showni by x-ray powder photographs to consist mainly of the platinum tetrafluoride,; selenium tetrafluoride adduct, there being in addition, a faint pattern of another phase. The gaseous products from this reaction, were collected for infra-red and mass spectrometer analysis*
The infra-red analysis showed the following peaks:
664 (w), 717 (w), 780 (v.s.), 842 (m) , 9253 (m), 1030 (v.s.), 1182 (w),
1286 (m.w.), 1438 (s), 1484 (s) cm All of which may be accounted for by selenium hexafluoride (82) with the exception of the peak at 1030 cm * which can be accounted for as a silicon, tetrafluoride peak (83). 64.
A mass spectrum of the gas evolved showed only selenium hexafluoride and a small quantity of siliconi tetrafluoride to be present.
Thus, it was concluded that selenium hexafluoride and a small amount of silicon tetrafluoride were the maim gaseous products of this reactions.
The reaction was again studied quantitatively using a Tttpler pump.
Again, the mercury of the pump suffered attack by the gases evolved.
Result
0.134 g. 18 mis. selenium hexafluoride
or 341 g. 45.8 1.
4) With Iodine pentafluoride
It was reacted with iodine pentafluoride at atmospheric pressure.
The reaction, in contrast to the reactions with selenium; tetrafluoride and with bromine trifluoride, was slow. No reaction occurred at room temperature, but on warming to about 35° a gas was slowly evolved and a deep-red solution formed. As the reactiom proceeded, the solution be• came paler and eventually a pale-orange solution remained. Removal of the excess iodine pentafluoride, under vacuum, at room temperature, left an orange solid. This was shown to be a platinum pentafluoride, iodine pentafluoride adduct.
Analysis was by pyrohydrolysis to 250°.
Found: Pt, 38.9; F, 34.2. 2tFg, 1F5 requires Pt, 38.1; F,37.1.
5) With sulphur tetrafluoride
It was reacted with sulphur tetrafluoride in a closed system. No reaction occurred until 90°, when; the materials reacted in the vapour phase to give a buff powder. X-ray powder photographs of this material showed it 65.
to be crystalline and to contain essentially one phase.
Analysis, by pyrohydrolysis,showed it to contain 57.4$. platinumi and 29.0$ fluorine.
The experiment was repeated using a larger quantity- of PtO^Fg.
Reaction occurred at a lower temperature, with great evolution of gas.
An x^ray powder photograph of the residue showed it to consist of a mixr- ture of the material obtained in the earlier experiment, and platinumi tetrafluoride.
6) For reactions with potassium fluoride and potassium fluoride in_ iodine pentafluoride solution, see under preparation of potassium fluoro- platinate (v).
7) For reaction with chlorine trifluoride, see under the preparation, of the platinum pentafluoride, iodine pentafluoride adduct. 66.
THE FLUORIDES OF RHODIUM
RHODIUM TETRAFLUORIDE
Preparation (7)
a) Preparation of a rhodium fluoride, bromine trifluoride adduct, RhF_,BrE„?
Rhodium tribromide was dried at 110°, overnight, in the bulb; of a
bromine trifluoride-reaction apparatus. Reaction with bromine trifluoride
was slow at first, a greensolutioni being obtained. On prolonged refluxrng,,
however, complete reaction occurred with the evolution of a large quantity
of bromine and the formation of a deep red solution. Excess bromine tri•
fluoride was distilled off, under vacuum, over a period of 24 hours. The
adduct remained as a pale-pink powder.
No reaction occurred between.rhodium trichloride and bromine tri•
fluoride under similar conditions.
Properties of the adduct
The adduct is a pale-pink solid. An x-ray diffraction photograph
showed a complex pattern of lines and no attempt was made to index this.
It was found to be diamagnetic. It reacted vigorously with water to
give first a deep-red solution and precipitate, then reacted further to
give an olive-green solution and precipitate of hydrated rhodium dioxide.
The bromine trifluoride adduct reacted vigorously with concentrated hydro•
chloric acid to give a pale-orange solution.
b) Decomposition of the adduct
The adduct was heated in a nickel boat in the decomposition apparatus
(Figure 5). It began to evolve bromine trifluoride even on warming to
50°, at the same time the material became amorphous. However, all of the 67.
bromine trifluoride was not removed until a temperature of 300 . At this
temperature an x-ray powder photograph indicated that the material was o
crystalline again. On heating to 350 the x-ray patterm was sharper,,
though heating beyond this temperature did not improve the sharpness of
further x-ray pictures.
Analysis was carried out by pyrohydrolysis to 500?.
Found: Rh, 57.0; F, 40.8. Calc. for RhF^: Rh, 57.5; F, 42.5$.
Properties
Rhodium tetrafluoride was a deep-violet solid. It was moderately
stable in moist air and could be handled for short periods of time in, the
atmosphere, without hydrolysis occurring. That is was fairly stable to• wards moisture was also shown by the fact that a temperature of 500° had to be reached before pyrohydrolysis was complete. It reacted with water, to give an olive-green solution and precipitate.
The infra-red spectrum, of a nujol mull of the material, was recorded using both sodium chloride and caesium bromide optics. It showed a single very broad peak extending over the range 576-678 cm
Crystal structure for rhodium tetrafluoride
X-ray powder photographs of rhodium tetrafluoride were indexed on,the- basis of a face-centred cubic cell containing sixteen molecules: a -» 10.292 £ 0.0021; V - 1090 A*3; Dc = 4.37 g. cm"3; Dm - 3.60 g. cm"3.
Calculated and observed values for l/d. are given in Table XII.
The observed indices of the reflections show the following relation*- ship: hkl present only when h, k, 1 all even or;,.all odd which indicates that the lattice is face-centred.
These extinctions are compatable with either of the space groups
F23 or F43m. 68.
TABLE XII. Calculated and observed x-ray diffraction
data for RhF„
1/d2 hkl Calc. Obs. lobs. 111 0.0283 0.0287 10 220 0.0755 0.0793 3 311 0.1038 0.1051 8 222 0.1133 0.1142. 9 400 0.1510 0.1538 5 311 0.1794 0.1809. 4 422: 0.2266 0.22853 3 511f 333 0.2549 0.2568 7 x 440 0.3021 0.3038 8, 531 0.33041 0.3319 8 533 0.4059J 0.4068 5 622 0.4154 0.4176 8 444 0.4531 0.4547 5. 7115 551 0.4814 0.4837 7 7315 553 0.5&7.0 0.5591 8 800 0.6042 0.6077, 4 820 5 644't 0.6419 0.6396; 3 822; 660 0.6797 0.6826 4 751; 555 0.7080 0.7171 5: 840 0.7552 0.75653 6. 911; 753 0.7835; 0.7868. 6. 921; 761; 655$ 0.8118 0.8125= 4 931 0.8590 0.8610 5 844: 0.9062 0.9076. 6 933; 771; 755 0.9346 0.935.5; 5 10,2,2; 666. 1.0195 1.0205> 6 955 1.0856. 1.0871 5 11,1,1; 755S 1.1611 1.1600 4 880 1.20831 1.2096 3 1,3,1; 971; 955; 1.2366: 1.2377 5 10,6,2 1.3216 1.3223 8 12,4,0 1.5104 1.5112 3 10,6,6 1.6237 1.6290 4 12,4,4 1.6614 1.6593 3 69.
Reaction of rhodium tetrafluoride with sulphur tetrafluoride
Rhodium tetrafluoride was reacted with sulphur tetrafluoride in a
closed system. No reaction occurred even on taking the temperature to
350°.
PENTAPOSITIVE RHODIUM
RHODIUM PENTAFLUORIDE?
Preparation
1. Fluorination of rhodium tetrafluoride
Rhodium tetrafluoride was heated in a stream of fluorine in an attempt
to obtains a more crystalline sample. No reaction occurred until a temera-
ture of 260°, when a deep-brown.vapour was noticed above the heated material
and a pale-red film condensed on the cooler walls of the apparatus. This material on warming with a non-luminous flame tended to ball together ini a
similar manner to platinum pentafluoride. The rhodium tetrafluoride re• maining in the boat was found to still be amorphous.
2. Fluorination of rhodium metal
Rhodium metal contained in a nickel boat, was fluorinated in a silica< reaction tube. No reaction was observed;, until 375;° when; deep red vapours were observed! above the heated metal. Almost simultaneously an orange film,, deep red in bulk.began to form on the cooler parts of the apparatus. This material behaved in a similar manner to that, produced irul. It attacked the silica apparatus very readily; because of this, the reaction was
stopped. The violet, residue remaining in the boat was showni by x-ray analysis to be a mixture of rhodiumi metal and rhodium trifluoride.
In a subsequent experiment a trap cooled with liquid oxygen, was arranged! so that it was very close to the reactiont zone, but no compound, volatile 70.
at room temperature} similar to platinum hexafluoride was observed.
On no occasion was sufficient volatile material obtained for analysis..
Properties
The material exists as a pale-orange film, (nwvyO0) which is deep red
in bulk. It has a high surface tension as shown by its tendency to "ball".
It reacted very vigorously with water to give a deep-blue precipitate
and solution and evolved acid gases. With concentrated hydrochloric acid
a blue-violet precipitate was obtained, this turned green, on standing.
POTASSIUM FLU0RORH0DATE (V)
An attempt was made to prepare this material by the reaction between, equimolar quantities of potassium bromide (o#348 g.) and rhodium tribromide
(l g) in bromine trifluoride solution. The reaction occurred with much more vigour than the reaction between bromine trifluoride and rhodium) tri• bromide alone, giving a deep red solution. Excess bromine trifluoride was. distilled off, under vacuum, overnight, leaving a pale-pink solid. An x-ray powder photograph of this material indicated that there were two phases present. One was identified as potassiumi fluororhodate (IV), the other could not be identified. 71.
THE FLUORIDES OF PALLADIUM
FLUORINATION. OF PALLADIUM METAL
A rapid stream of fluorine was passed over palladium metal sponge, contained in a nickel boat, in a silica reaction tube. The temperature was slowly raised; no reactioni occurred until 150°, when the metal in• candesced and sintered to give a black residue which contained some light- brown patches. The temperature was slowly raised to a maximum of 500°, but no furthen- reaction occurred.
An x-ray powder photograph showed that the material was principally palladium trifluoride with a trace of palladium difluoride.
FLUORINATION OF PALLADIUM DIBROMIDE
A rapid stream of fluorine was passed over palladium dibromide, con• tained in a nickel boat, in a silica reaction tube. Reaction occurred at room temperature, when a glowing zone passed down the boat, leaving a black: homogeneous residue. A pale-yellow solid, presumably a mixture of bromine trifluoride and bromine pentafluoride, condensed in a trap cooled with an alcohol/solid carbon dioxide mixture situated after the reaction zone. The temperature was then slowly raised to a maximum of 500° but no further reaction occurred.
An x-ray powder photograph of the residue showed only lines attribu• table to palladium trifluoride. 72.
TIN TETRAFLUORIDE, SnF4
Preparation (84)
Tin metal, contained in a nickel boat, was heated to just above its
melting point in a stream of fluorine. Tin tetrafluoride formed as a
white powder which was not volatile in the fluorine stream at this
temperature.
Analysis was by pyrohydrolysis at 350°. Fluorine was estimated both
by titration- against standard alkali' and by precipitation as lead chloro-
fluoride. Tin was estimated by heating the residue from pyrohydrolysis
in a stream of air and weighing to constant weight as stannic oxide.
Eound: Sn, 61.10; F, 36,65. Calc. for SnF4: Sn, 60.97; F, 39.03$.
Properties
The infra red-spectrum, of a nujol mull of the material, was recorded using both sodium chloride and caesium bromide optics. A single, very/
broad, absorption band, extending over the range 575-694 cm * was observed.
The crystal structure of tin tetrafluoride
The x-ray powder pattern of tin tetrafluoride has been interpreted om
the basis of a tetragonal unit cell containing eight molecules,
3 3 a a 8.773 £ 0.005X, c = 7.187 ± 0.005X, V = 554A*, Dc = 4.66 g. cm" , —3
Dm = 4.68 g. cm .
Calculated and observed values for l/d2 are given, in Table XIII.
The observed indices of the reflections show the following relation•
ship:
001 present only when 1 2n
hhl present only when h - 2n.
These indicate the presence of two screw axes. A suitable space
group could not be found. 73.
TABLE XIII. Calculated and observed x-ray diffraction;
data for SnF„
2
hkl Calc. Obs. lobs. 210 0.0651 0.0655i 7 002 0.0776 0.0789 10 0.1041^ 220 0.1032 1 112 0.1026J 221 0.1235 0.1247 7 321 0.18861 0.1892 3 103 0.1875 J 302 0.1947 0.1942 1 312 0.2077 0.2069 9 322 0.2468, 0.2476 9 420 0.2603 0.2577 7 004 0.3102.1 0.311 5> 332 0.3120 J 1104 0.3232 "1 0.3246. 9 430, 500 0.325.4 J 520 0.3774 0.3796 7. 531 0.4619 0.4615 6 442 0.4941 0.4913 4 0.4999"! 433, 503 0.5025, 6 611 0.5010J 0.5519T 523 0.5552 4 541 0.5530 ) 424 0.5705> 0.5682 4 305 0.6019 0.5988 1 315 0.6151 0.6134 4 640 0.6768 0.6763 4 006 0.6980 0.6952 3 306 0.81511 0.8117 4 651 0.8133J 326 0.8672 0.8676 3 660 0.9371 0.9376 3 830 0.9501 0.9492 1 117 0.9761 0.9787 2 506 1.0234] 1.0207 1 813 1.0205J 840 1.0412 1.04193 1 900 1.0542 1.0560 4 922, 762 1.1839 1.1834 4 931 1.1918 1.1931 2 646 1.2186 1.2221 4 546 1.23i6 1.2325 2 TABLE XIII cont'd:.
hkl Calc. Obs. lobs. 940 1.2625; 1.2623 517 1.2885 1.2848 527 1.3275) 1.3290 2 844 1.3514") 1.3494 2 772 1.3531J 1.4380*1 10,3,1 1.4355; 7 943 1.4370J 10,0,3 1.4760 1.4748 8; 10,4,0 1.5097 1.5057 6i 961 1.5422"! 1.5411 & 816; 1.5.440 / 915. 1.5520 1.548& 4 11,0,0 1.5748T 1.5719 6j 944 1.5729J 11,1*0 1.567&S 707 1.5878 J 1.5864 5 10,4,2 1.5873J 119 1.5966i) 1.592.7, 3 10,3,3 1.5931J 10,5,0 1.6269 1.6270 5 11,0,2 1.6524 1.6497 5. 880 1.6659 1.6680 7 7&.
LEAD TETRAFLUORIBE
Preparation
(i) Preparation of lead difluoride (85)
Lead difluoride was prepared as a white powder by repeatedly evaporati
lead acetate with aqueous hydrofluoric acid under ani infra-red lamp.
(ii) Preparation of lead tetrafluoride (85)
Lead difluoride, contained in a nickel boat was fluorinated in a silic o
tube. No reaction occurred until 300 , when, the material became deep yellow, and on further reaction became white once more. No volatile
products were observed.
Analysis was by pyrohydrolysis at 150°, lead being estimated as; lead dioxide.
Founds Pb, 73.8; E, 26.0. Calc. for PbF4$ Pb, 73.2; F, 26.8$.
Properties
Lead tetrafluoride is a white powder, which hydrolyses rapidly in moist air to give lead dioxide.
A very complex x-ray powder pattern was obtained; and no attempt, was made to index it. It is probable that the crystal lattice is of low sym• metry or the unit cell large. The pattern showed: some similarity to the hafnium tetrafluoride pattern.
An infra-red spectrumi recorded in the sodium chloride and caesium bromide regions showed a strong peak at 525: cm * and a weaker peak at
640 cm"1. DISCUSSION 76.
THE VALENCY STATES OF PLATINUM
Platinum, as with other transitiom metals, is capable of existing in.
a wide range of oxidatiom states. In common with most of the elements,
the highest oxidation states occur in the fluorides and oxides. The
energy required to excifee any oxidation state must be offset by the energy
gained im bond formation and, if the compound is a solid, the energy liber•
ated in forming a crystal lattice.
The lattice energy of am ionic; compound is directly proportional to the square of the anionic charge and inversely proportional to the inter-
ionic distance, which for* a given oxidation state of the cation depends on the ionic radius of the anion. Now, anionic radii are at a minimum with fluorine (r = 1.36A*) (86) and we would therefore expect fluorides to have higher lattice energies tham compounds of any other monovalent, ligand.
The only ion of comparable size is the 0^ (r •= 1.4oX)(86) ion; because of its double cha rge, this gives rise to, compounds having even greater lattice energies tham the corresponding fluorides.
The energy required to dissociate a fluorine molecule into fluorine atoms is low (AH = 38 k. cals) (87) whereas the dissociation of an oxygeni molecule into atoms requires three times this energy ( H =. 118 k. cals)
(88). The formation of a bond to a fluorine atom therefore liberates much, more energy than the combination with am oxygeni atom. This difference offsets the more favourable lattice energy in. the oxides. These are the factors which cause the elements to exhibit their highest oxidatiom states whem coordinated by oxygem or fluorine atoms. Oxygen and fluorine are almost equally effective in this respect. 77.
The oxidation state may, however,; be limited by the allowed coordination
of the central atom. Oxygen, because of its double charge, is capable of
bringing out the same oxidation state with half the coordination which
fluorine demands. This may well be the reason why an octafluoride of
osmium has not been found, although osmium attains an oxidation state of + 8
in osmium tetroxide and osmium trioxydifluoride (43).
Although fluorine is capable of exciting the high oxidation states, this does not exclude the possibility of preparing fluorides in which- lower oxidation states exist. However, a very high enthalpy of formation', of a higher fluoride may in some cases favour the disproportionation, of a lower fluoride into the metal and a high, fluoride. Waddington (89) has. shown:, from thermodynamical considerations, that cuprous fluoride would: have a low enthalpy of formation and would be unstable towards dispropontion- atiion to the difluoride and copper metal.
Returning to platinum, a platinum atom in its ground state has the electronic configurationi
5 6
s p d 4 B
2 6 9 - 1 and would in theory be capable of attaining a maximum oxidation state of ten. In practice, however, this has not been obtained, but as we would expect the highest oxidation, obtained has been with fluorine and oxygen.
At the onset of this work, the highest oxidation state of platinum was six, which existed in both the poorly-characterized, trioxide and the:';: unstable hexafluoride. Of the lower oxidation states, the tetrapositive state was established in platinum, tetrafluoride, but a trifluoride was 78.
unknowns and a difluoride was reported but unconfirmed. However, these
oxidation states were known for a variety of other ligands. The penta• positive state was unknown at that time* 79.
PLATINUM DIFLUORIDE
In the platinum group of metals, the only known difluoride is that of palladium, though difluorides are known for most of the elements of the first transition series. It was thought, that by virtue of its similar atomic size and electronic configuration*platinum; might resemble palladium! in this respect.
The structures of the known transition metaL difluorides fall into two groups (90), those crystallizing with a rutile, or distorted rutile
lattice (chromium, manganese, iron, cobalt, nickel, copper,: zinc and palladium!) and those crystallizing with the fluorite arrangement (cadmium and mercury).
By analogy, then, we would expect platinum difluoride to crystalline with a rutile or possibly a fluorite lattice. The octahedral coordination which. the platinum atom would have in a rutile lattice would only be compatable 6 2 with the electronic configuration: d^ dl^, with the d^ electrons unpaired
(90). A pairing of these electrons would lead to distortion of the octa• hedron, such as is found in the dichlorides of platinum and palladiumi (91), where infinite chains of planar MCl^ groups share chlorine atoms. Now, 2+ palladium difluoride is the only paramagnetic Pd compound known, even 2 + palladium monoxide being diamagnetic; thus we see the paramagnetic Pd ioni is not a very stable species and it may well prove to; be impossible to stabilize the platinum! analogue. It should also be mentioned that the isoelectronic Au ion is diamagnetic in potassium fluoroaurate and it has
beem suggested (92) that the AuE4 ion has a square planar- shape. Although auric trifluoride is paramagnetic, it is not isomorphous with palladium trifluoride, as would be expected if the gold atom had a regular octahedral coordination of fluorine atoms. 80.
Morris (93) , using a simple Born-Lande' expression, calculated the lattice energies of the them known difluorides using crystallographic interatomic distances. The values he obtained compared favourably with those obtained practically from the Born^-Haber cycle.
Making similar calculations for the difluorides of platinum and palladium, assuming platinum difluoride to be isostructural with palladium; difluoride,gives values of 643 and 634 K cals per mole respectively for the lattice energies and corresponding values of 18 and 32 K cals per mole for the heat of formation of the compounds from their elements.
Palladium difluoride has been prepared and well characterized (38, 39).
The various attempts in this work to prepare platinum difluoride have all been; unsuccessful. Other workers have attempted, unsuccessfully, to reduce platinum tetrafluoride by different methods. Moissan; (2) tried to obtain the difluoride from; the phosphorus trifluoride complexes with platinum: tetrafluoride, but was unsuccessful. Bartlett (16) attempted to reduce platinum tetrafluoride by similar means to those used for the reduction; of palladium trifluoride. With sulphur tetrafluoride, he obtained a rust-
coloured solid,: which was shown; to contain platinum metal together with a phase which was not identified, but which; did not have a rutile structure.
The selenium tetrafluoride adduct PtF^SeE^Jg showed no signs of decomposition, on heating, until 350° when it decomposed rapidly into platinum' metal and selenium: hexafluoride. Robinson; and Hair (76) also attempted to reduce platinum tetrafluoride using selenium: tetrafluoride. They claim to have isolated the compound PtE (seF.) which decomposed on heating (no temperature was quoted) to give platinum metal. It would appear that their compound which was incorrectly formulated (94), was the same as that reported by 81.
Bartlett and in this work.Sharp (95) heated platinum tetrafluoride with carbon monoxide under pressure and obtained a mixture of the volatile platinum dicarbonyl octafluoride and platinum metal.
Although platinum difluoride, is thermodynamically possible when coit- sidered to have a rutile lattice, it could prefer another lattice.
However, all attempts to prepare it have failed, a possible explanation! for this is that it is unstable towards disproportionation. into platinum tetrafluoride and platinum metal.
2PtFrt *PtE;, + Pt -2 4
As no thermochemical data is at present available for platinum tetra• fluoride, it is not possible to confirm or reject this possibility. 82.
PLATINUM TRIFLUORIDE
As shown in Table I, trifluorides are known for all members of the platinum group except platinum and osmium. For palladium and rhodium, they may be prepared by the fluorination of the respective metal with elemental fluorine. For iridium and ruthenium, they are best prepared by reduction of the higher fluorides.
Now, structurally the trifluorides of the transition metals may be divided into three main groups:-
1) Those having the rhenium trioxide lattice, this is adopted by the trifluorides of niobium, tantalum and molybdenum.
2) Those having the palladium trifluoride structure, this is adopted by the trifluorides of palladium, rhodium and iridium.
3) Those having the vanadium trifluoride lattice, this is adopted by the trifluorides of vanadium, iron, cobalt and ruthenium.
Jack et al (96) in their investigations of the trifluorides of types
2 and 3 have shown the fluorides of group 2 to be hexagonal close packed arrangements of fluorine atoms with the metal atoms in octahedral hole sites, and those of group 3 to be intermediate between these and the more open structure of rhenium trioxide type.
It was supposed that if a trifluoride of platinum did exist, it would crystallize in a lattice of either group 2 or group 3. A lattice of this type was found in residues from the fluorination of platinum metal in the presence of powdered glass (see plate 1) the compound could not, however, be isolated. This lattice was indexed on the basis of a bimolecular rhonbohedral unit cell, the dimensions of which are compared with those PLATE 1.
1.PdF3 2.Residues 3.PtOF3 83.
obtained by Jack et al (95) for the trifluorides of the other Group VIII metals, in Table XIV.
TABLE XIV. Unit-cell dimensions of the trifluorides;
of Group VIII •0)
FeF3 5J.362 57.99
CoF3 5.279 56.97
RuF3 5.408 54.67
EhF3 5.330 54.42
PdF3 5.5234: 53.925.
IrF 5,. 418 54.13 3
PtF3 5.41 .54.'3 84.
PLATINUM TETRAFLUORIDE
Platinum tetrafluoride is the easiest platinum fluoride to prepare and is the most stable thermally. It does, however, decompose on heating above
350° to give the metal, no intermediate lower fluorides have been observed in this thermal decomposition. This behaviour contrasts with the pyrolysis of the corresponding tetrachloride and tetrabromide (97, 98);
390 440 590 ptm — ° - PtciQ— ° - Ptci — ° -PtCl -Pt 4 3 2 ocn° 490°
PtBr, - PtBn_ — - PtBrn -PtBr -Pft.
4 3 2
If platinum tetrafluoride is heated in a stream of fluorine, then oxidation occurs with the formation of a mixture of the penta- and hexa• fluoride.
Nyholm and Sharpe (17) have reported platinum tetrafluoride to be para• magnetic (yU'» 1.1 Bohr magnetons). Q Now, quadripositive platinum is a d system; if the platinum were 6^ octahedrally coordinated, there would be a d^, configuration and a conse• quent, diamagnetism. The paramagnetism of Nyholm and Sharpe therefore sug• gested a coordination number different from six. Both the bromine tri• fluoride and selenium tetrafluoride \adducts of platinum tetrafluoride, were investigated and found to be diamagnetic. Nyholm and Sharpe (17) had found potassium fluoroplatinate (IV), in which the platinum atom is octahedrally co• ordinated by fluorine atoms, to be diamagnetic. Accordingly, the magnetic properties of platinum tetrafluoride were reinvestigated. The fluoride as prepared by the thermal decomposition of the bromine trifluoride adduct,
(which was the method used by Sharpe and Nyholm in preparing theiir- sample Unit cell and bonding about one platinum in PtF^
Shaded fluorine atoms represent the inner coordination sph< 85.
for magnetic moment determination) was found to contain some bromine,
probably combined as bromine trifluoride. This was removed by heating
the solid in a stream of fluorine gas. A sample, prepared in this manner,
giving a good analysis and x-ray pattern which was completely indexed, was found to be diamagnetic. It must therefore be supposed that the para•
magnetism of the compound of Sharpe and Nyholm was due to a paramagnetic
impurity, in all probability a bromine trifluoride adduct.
The uncomplicated x-ray powder pattern was indexed on the basis of a
body-centred monoclinic unit cell which is closely related to the tetragonal 19
unit cell with space group - I4/amd. This is the space group which
Mooney (99) had assigned to the tetrachlorides of uranium and thorium.
The relative intensities of the lines of the platinic: tetrafluoride pattern
show a close resemblance to those of the uranium tetrachloride and thorium'
tetrachloride patterns, though it must be emphasized that the monpclinic
distortion only allows comparison to be made for the low angle lines. There
is little doubt, however, that the structure adopted by platinum.tetra•
fluoride is very similar to that of uraniumi tetrachloride.
Mooney (99) interpreted the structure of uranium tetrachloride and
thorium tetrachloride on the basis of eight coordination, of the metal atom
by the chlorine atoms. The chlorine atoms are in two sets of flattened
tetrahedra} one set being at 2.46A* and the other set at 3.11A* from the
metal atom. Each chlorine in the closely coordinated set is one of the
more distantly coordinated tetrahedron on another platinum atom and vice
versa. In this way, each uranium or thorium atom is coordinated to, eight
other metal atoms via the chlorine atoms. It would be expected that the
long chlorine-metal bonds could be easily brokeni with the separation of 86,
discrete uranium tetrachloride and thorium tetrachloride molecules.
Both uranium tetrachloride and thorium tetrachloride can be sublimed and Mooney (99) pointed to this being consistant with the structure.
That this structure is the one found in platinum tetrafluoride is also supported by the ready sublimati on of this material above 300°.
A full structure determination! was not attempted for platinum;tetra• fluoride, because of the difficulty of locating the very light fluorine atoms in the presence of the very heavy platinum atoms. However, assuming the coordination of platinum atoms by fluorine atoms was similar to the coordination of thorium and uranium; atoms by chlorine atoms, bond lengths were calculated and found to be 1.90A* for the short bonds and 2.14% for the long bonds. The short-bond length of 1. 90X compares very favourably with the value of 1.91A* for the Pt(lV)-F bond found by Mellor and Stephenson.(32) in potassium fluoroplatinate (IV). 87
PLATINUM PENTAFLUORIDE
TABLE XV. Known pentafluorides of the second
and third transition series
NbFs (100) MoF& (101) RuFfi. (46>) RhFg ?^ m. ~80°" ~67°" 107°" b. 235° 273.6 313°
TaFg (100) ReF5 (103) OsF& (103) IrF4 (45) FtFg/ m. 95° 48° 70° 106° 80« b. 229° 221.3 J 225.9° 300°
/ this work.
Table XV lists the pentafluoride of the second and third; transition.series together with their melting and boiling points. Of. the platinum group, the pentafluoride of ruthenium has been established since 1925 (36). The penta• fluoride of osmium has been, known since 1912 (40), but it was only recently (104) that it was characterized as such. Iridium tetrafluoride has been, tentatively classified here with the pentafluorides, because its properties and mode of preparation justify the suspicion that it is a pentafluoride (103). It cant be seen that the pentafluoride of platinum: and the, as yet poorly characterized, pentafluoride of rhodium fit into this scheme.
Platinum pentafluoride is produced by the photolysis of platinum hexa• fluoride, osmium pentafluoride and iridium tetrafluoride are produced in a similar manner.
Above its melting point (80°), platinum pentafluoride undergoes dispropor• tionation into platinum hexafluoride and platinum: tetrafluoride:
2PtF_ »- PtF„ + PtF. 5J 6 4 88.
Cady and Hargreaves (103) have shown this to be typical of the transition; metal pentafluorides.
The noble metal pentafluorides and rhenium pentafluoride all exhibit very high surface tension effects. The molten fluorides resemble molten; sulphur in forming spheres which do not "wet" glass. They are also generally viscous and after having been melted, crystallize very slowly, often forming glasses. Platinum pentafluoride is no exception to this behaviour.
Edwards and Peacock (103) have made the only structural investigation! of these compounds by x-ray diffraction-methods. They investigated molybdenum pentafluoride by single crystal methods and found that it was monoclinic with two molecules per unit cell. They found two different, types of fluorine atom, and as there was no evidence for a bimolecular species suggested an ionic structure of the type (MoF*) (MoFg ). This would be consistent- with the ready disproportionation of the species. They suggest that; this might be a general pentafluoride structure. Conductivity measure• ments on vanadium pentaf luoride and certain* non-metallic pentaf luorides (105,) have demonstrated the» existence of autoioniizationi iin the melts:
2 XF&; XE* •*- XFg"
It is probable that platinum pentafluoride would also ionize in this manner.
If we now consider the chemicalxproperties of these compounds, the pentafluorides of niobium, tantalum, ruthenium, osmium and iridium have all been shown, to form 1:1 adducts with bromine trifluoride (106). The platinumi compound is somewhat different in that it reacts to form.a 2:1 bromine trifluoride, platinum tetrafluoride adduct. On heating, this adduct. decomposes into platinum tetrafluoride and bromine trifluoride. This 89.
reaction! with bromine trifluoride shows that the pentafluoride of platinum; is more reactive than the pentafluorides of the other members of the group, and can act as a fluorinating agent, towards bromine trifluoride, oxidizing this to bromine pentafluoride. The reaction between platinumi pentafluoride and selenium tetrafluoride was not studied, but the corresponding reactions with platinum tetrafluoride, platinum-hexafluoride and PtO^Fg all yielded the 2:1, selenium tetrafluoride, platinumi tetrafluoride adduct. It is probable that platinumi pentafluoride would do the same. Corresponding
1:1 metal pentafluoride, seleniumi tetrafluoride adducts are knowni for the pentafluorides of osmium and iridium,: these are both low melting solids
which decompose at their melting points into (MF&)2 SeF4 adducts (107).
Adducts corresponding to the iodine pentafluoride and chlorine tri• fluoride adducts of platinum pentafluoride have not been, reported for other members of the platinum group. Similar adducts are however known for the pentafluorides of antimony, with both iodine pentafluoride and chlorine trifluoride, and arsenic with chlorine trifluoride. The formation of platinum pentafluoride complexes with these donors reflects the greater resistance of iodine pentafluoride and chlorine trifluoride to fluorinatiom compared to bromine trifluoride.
The great reactivity of platinum pentafluoride has hindered work on this compound considerably, as it has on the other known pentafluorides.
Unless great strides are made for handling such compounds, it seems unlikely that any further structural information will be obtained. 90.
POTASSIUM FLUOROPLATINATE (V)
TABLE XVI. Potassium salts of the MF„o ion.
KVF,
KNbF KMoF 6 6
KTaF KWF. KReF, KOsF, KlrF, KPtF, 6 6 ""6 6
The known potassium salts of the MFg (v) ioni are listed im Table XVI.
Those of niobium, tantalum, molybdenum, tungsten and rhenium all have the potassium fluoroniobate (v) structure - this has a tetragonal (pseudo-cubic) unit cell (103). Those of vanadium, ruthenium, osmium, iridiumi and plati• num have the rhombohedral barium fluorosilicate, or distorted caesiumi chloride, structure (109); with regular, , or near regular, octahedral co• ordination of the metal by fluorine atoms.
Potassium fluorosmate (V), fluoriiridate (v) and fluororuthenate (V) all interact rapidly with water with the^ evolution of oxygen, and the forma• tion of the corresponding fluorometallate (IV) ion; hydrolysis to the hydrated dioxide of the metal concerned occurs slowly. A similar behaviour is found with potassium fluoroplatinate (V). The reduction.of the MFg~~ (y), ion presumably occurs by an electron being transferred from the water through the coordination, sphere of fluorines around the metal:
F F
F F'
\.V/ IV 1 M 2H 1/2 0c \ < F 91.
Any other mechanism must invoke either- temporary reduction of the
coordination sphere to 5.. (S^) or an increase to 7 (S^2) , both of which would be expected to lead to a complete break-dowm of the ion rather than, a reformation of the fluorine octahedron. Further, the MFg anion, can• not be formed in aqueous solution and the hydrolysis of this species is an exothermic process (7).
The lattice constants, of the potassium salts of the noble-metal fluorometallate (v) ion, listed in Table XVII indicate that the fluoro- platinate V ion is approximately the same size as the corresponding MFg ions for ruthenium, osmium and iridium. This similarity in size is further demonstrated by the near identity of the powder patterns as can be seen in Plate 3, where the x-ray powder photographs of potassium fluoro- ruthenate (V) and potassium fluoroplatinate (v) are compared.
TABLE XVI1. Lattice constant_ s of some KMF„ structures
KRuFg (109) 4.97 97.4
KOsFg (109) 4.991 97.18,
KlrFg (109) 4.98. 97.4 . .
KPtFg / 4.87 9,7.7
4 - this work.
A similar resemblance is seen.when comparing the infra-red absorption peaks of potassium fluoroplatinate (v) with those of potassium fluoro- sinate (V) and potassium fluori. ridate (v)s 3. 2. 1.
PLATE3.
1.K2PtF6 2.KPtF6 3.KRuF6 92.
KOsFg (34) KlrFg (34) KPtFg
0 3 616 667 640,590 cm"1
Thus, in both its physical and chemical properties, potassium fluoro-
platinate (v) behaves as we would expect:, from its position in the group.
PLATINUM OXYTRIFLUORIBE
This compound is characterized by its great, inertness. For a penta• valent compound this can. only be explained in.terms of the material being polymeries
F F F F
0 —Pt— 0 -^Pt — 0 I I F F
It bears no resemblance to the other MOF compounds VoF (llO) and o o ReOF (HI). y3
PLATINUM HEXAFLUORIDE
The preparation and properti.es. of platinum hexafluoride, and a number
of other hexafluorides of the heavier transition.metals, have been fully- described in a series of papers by Weinstock and his coworkers (19, 20,
112, 41, 113, 114).
They found platinum hexafluoride to be one of the least, stable of the hexafluorides and, because of its great reactivity, have found working with it very difficult. It is a very powerful oxidizing agent and they report (112) that it will oxidize neptunium and plutonium tetrafluorides to their respective hexafluorides and bromine trifluoride to bromine penta- fluoride. They did not state what the non-volatile reaction product.in the last reaction was, but by analogy to the experiment performed with selenium, tetrafluoride in this work it is likely that they obtained the bromine trifluoride adduct of platinum tetrafluoride. Likewise in the reaction performed between platinum.hexafluoride and selenium, tetrafluoride in this investigation., where the selenium tetrafluoride, platinum tetra• fluoride adduct was obtained, it is probable that the selenium, tetra• fluoride was oxidized to selenium hexafluoride. The reactions beings
PtF_ + 3 BrF_ - PtF. (BrF0)0 •+- BrE_
PtFe 3 SeF. -PtF. (SeF.)n + SeFfi
6 4 4 47 2 6.
The physical properties of platinum hexafluoride have been showni to follow the pattern set by the other hexafluorides of the group (112). 94.
PtOJFc PLATINUM PEROXIDEHBXAFLUORIDE 2 o
Whenever high temperature fluorinations of platinum metal were carried
out in glass or silica apparatus, or in the presence of oxygen, high, yields
of a deep red volatile solid were obtained. This material sublimed in a vacuum at 90°. It reacted, with extreme vigour, with water to liberate
ozone smelling gases. Benzene and other organic solvents immediately caught
fire in contact with the solid, but it neither reacted with nor dissolved ini
carbon tetrachloride. These properties and the mode of preparation! indicated that it was a fluoride or oxy fluoride of platinum with the platinum in a very high oxidation state.
Great difficulty, however, was experienced in characterizing this com• pound because of its great reactivity and the problems associated with its analysis.
Initially analyses were carried out by dropping a weighed quantity of the material into a 5$ sodium carbonate solution and quickly stoppering the flask, when all reaction was considered to be complete, the precipitate was filtered off ignited and weighed as platinum metal. The solution was made up to a standard volume, aliquots were taken and these were analysed for fluorine, by precipitation as lead chlorofluoride after a Willard and Winter distillation, and for platinum by precipitation with zinc in hydrochloric acid solution. Inconsistant results were obtained, the most consistant of which suggested the formula PtOF^ (115). Whem the physical and chemical properties were investigated further, they were found to be inconsistant
with this formulation. Further analytical schemes were then sought. 95.
First the compound was decomposed by breaking a frail bulb containing a known weight of material into 5$ sodium carbonate solution in a sealed jar, allowing this to stand overnight and them analysing as above, using finely granulated zinc for the precipitation of the platinum metal. The results obtained by this method were agaim inconsistant but showed am increase in the percentage fluorine and a decrease in; the percentage platinum.
The pyrohydrolysis method was then tried and it gave consistant results.
It was felt however, that due to the greats reactivity of the compound, some fluorine could be lost in transferring the material to the apparatus.
Accordingly the fluorine composition was checked by fusion with sodium metal in a Parr bomb. The fluorine analysis by this method agreed with that from the pyrohydrolysis. As a safeguard against low platinum, analyses due to platinum being lost as a volatile higher oxide (52) during the pyrohydrolysis, the platinum' was checked by weighing a quantity of material into a platinum crucible and them roasting this in an atmosphere of hydrogen to constant weight. The results obtained by this method were in very good agreement with those obtained from the pyrohydrolysis. Having established the percentage platinum and fluorine present, the other element present had to be established. From the mode of preparation; of the compound, this could only be oxygen; or silicon. The analyses were consistant with the formulation PtOJ?„ or PtSiF^. The latter seemed unlikely because no silica 2 o o was observed on hydrolysis. That the other element present, was oxygen was shown firstly by synthesis, by fluorination of platinum dioxide in a nickel apparatus using oxygen as the diluent gas; and then quantitatively by dis• placing the oxygen with bromine trifluoride in a silica apparatus. The 96i. evolution of approximately one mole of oxygen per gram mole of material
confirmed the formulation PtO_Fe. 2 6
Attempts were made to ascertain the valency state of the compound using the method of Crowell and Yost (116) but this could not be applied due to the variety of valency states produced on hydrolysis.
It was hoped that an indication of the valency state could be obtained from a magnetic moment study. However, no simple theory is at present, capable of explaining magnetic data, especially in the second and third transition series. Magnetic data in the first transition series have been largely explained by the theory of Kotani (117), but more recently
(118) it has been shown that two of the basic assumptions of the Kotani theory,
(i) that Coulomb repulsion is much stronger than spin-orbit coupling, and (ii) that magnetic interaction between ions is negligible,; are not satisfied by 4d and 5d electrons.
The magnetic moment obtained (yU ^ 2.45. Bohr-magnetons) is consistant with either two or three unpaired electrons,, the former being the most, likely.
The quantitative gas evolution experiments are consistant with the empirical formula PtO^Fg, although the oxidation of water with the conse• quent, reduction of platinum to the quadripositive state would be expected to liberate 1_- moles of oxygen, per gram mole of material according to the equation:
A PtOgFg + H20 * J?t * + 6F" 1- 2H* +1% 0^ 97.
In practice, however, less than this quantity was obtained, this is pos• sibly explained by the formation of hydrogen peroxide under the conditions of the experiment.
The x-ray crystallographic data clearly indicates that the platinumi atoms are at the points of a simple cubic lattice, a -s. 5.016°i. Faints superlattice reflections, however, show that- the oxygens and fluorines cannot have such a simple lattice. They can, however, be represented by a unit cell eight times this size (p.58). This situation is akin to that; described by Zachariesen (119), who found that in the lanthanum oxyfluoride structure, the lanthanum atoms were on the points of a cubic lattice but the oxygens and fluorines were on a lattice of lower symmetry. In the platinum oxyfluoride structure, the average volume occupied by the oxygen: o3 and fluorine atoms is 15;.9A , which indicates very close packing. Zachariesen
(120) reports values varying from 16.9 to 19.4&3 for the volume of the fluoride ion in the uranium fluorides.
The mass spectrographic evidence was of limited value as mass numbers above 245, could not be observed on the instruments available. However, a definite indication of two oxygen* atoms linked to one platinum atom was- obtained.
The infra-red spectrum is complex,, and no attempt was made to assign frequencies. It does, however, indicate that the molecule of low symmetry and the spectrum shows very little resemblence either to that of platinum hexafluoride (20) or that of the hexafluoroplatinate (V) ion. There is also; no peak, in the region* between 700 and 1000 cm""*, which is the region where
one would expect to find an 0-F stretch (0-F s OF , 928 (121, 122); SpoF0F
879(123); SF OF, 888(124); SeF OF, 925 cm-1 (125)). 98.
It seems, then unlikely that the compound contains at. Pt-O-F bonds.
In its chemical behaviour, PtO^F^ behaves as a very powerful oxidizing agent. The reaction with bromine trifluoride has been mentioned earlier in connection with its value in the confirmation of the formula. The other product of the reaction is the 2:1 bromine trifluoride platinum, tetrafluoride adduct, in this instance then the bromine trifluoride must, be acting as a reducing agent. Similarly selenium tetrafluoride acts as a reducing agent in reacting with PtO^F^ to form the 2:1 selenium tetra• fluoride, platinumi tetrafluoride adduct. Iodine pentafluoride reacts to give a platinum pentafluoride adduct, however, and the best way to prepare potassium hexafluoroplatinate (v) is by interaction of the oxyfluoride and potassium fluoride in this solvent.. This salt is also produced when, the oxyfluoride is sublimed over potassium fluoride under vacuum.
What then are the likely structures for this compound?
The following have been considered:-
OF This structure is consistant with the magnetic 1. F\ | ^ F Pt, data in that six valent platinum is likely to F^"^ | ^ F
OF be paramagnetic with two unpaired electrons.
It is however inconsistant with the fact that no 0-F stretching frequency is observed, in the infra-red spectrum. This.also does not explaini immediately why platinumi coordinated by six fluorines is found in the fluoroplatinate ion in solution.
2. The ionic formulation VtF^Q* . Thisraost unlikely formulation .could explaini the magnetic properties of the compound, for although the platinum. 99.
in this compound would be in the five-valent state the singly charged 0*
ion would also have one unpaired electron. With such a compound, however,
dissociation into the components 0,oF and PtF_ would be expected on sublima-
tion. The fact that the compound sublimed completely and could be quanti•
tatively transferred argues against this.
This formulation is inconsistant with both the magnetic 3. FgPt ^
properties and with the infna-red spectrum. Such, a
structure would involve all ten. valence electrons in bonds with the result', that it would be diamagnetic.
4. F_PtC ^0 on- F_P*r ^0 0^ >ptFft» 6 6 6 \0 \0—0^
- i.e. platinum peroxidehexafluoride.
This formulation, either as a monomer, or as a polymen, would account for most of the properties of the compound. It would involve octa-positive platinum, which would necessitate two unpaired electrons - this is consistent with the magnetic data. The fact that the material sublimes readily suggests that it is compos.ed of discrete low molecular weight molecules. The x-ray evidence allows the monomeric. formulation only. The great reactivity and oxidizing properties of the compound and the existence of ozone smelling gases on hydrolysis - though no ozone was detected in the infra-red spectrum «f the gases evolved - are also consistent, with this formulation. A molecular- weight, determination on.the material was not possible.
This compound will then, be knowm as "platinum peroxide hexafluoride". 100
THE COMPLEXES OF QUADRIPOSITIVE PLATINUM
Writing, once more the lattice dimensions of the selenium tetrafluoride
adducts of platinum tetrafluoride, palladiumi tetrafluoride and germaniums
tetrafluoride*
PtF4 (SeF4)2 PdF4 (SeF4)2 GeF4 (SeF4)2
a 15.74 15.47. 15.60 i c. 4.93 4.88 4.93 i It is seen that these form an isomorphous series, similar to the iso-
morphous series of the salts of fluoroplatinic, fluoropalladic and fluoro-
germanic acids;
e.g. K2PtF6 (32) K2PdF6} (78,79) K2GeF6(l26) a 5.76 5.72 5.62, 1 c 4.641 4.67 4.65 1 It would appear, then, that the selenium tetrafluoride complexes can be
regarded as salts of the respective fluorometallate (IV) anion with the cation
SeF* - i.e. (SeFg)2 PtF&, (SeF^ PdFg, (SeFg)2 GeFg.
The salt-like character of these compounds is evid ent in tha t they do not melt on heating, but on heating to a sufficiently high temperature,, they, break-down, into their components.-
That selenium tetrafluoride is capable of autoionization to give the
SeF* cation.
2SeF. ___ SeF* + SeF ~ 4 3 5> has been shown by conductivity studies. (94).
Bromine trifluoride and iodine pentafluoride have also been showni to be ionizing solvents by conductivity measurements. (127): 2BrF ' BrF * + BrF " 3 2 4
+ 2 IF, . 1F. 1- IF " 5 4 6 101
These solvents also form.adducts from solution. The adducts formed with these compounds} however, are usually found to be low-melting, to
crystallize only with difficulty and to decompose at relatively low tempera• tures, usually evolving the respective solvent, and leaving behind a fluoride
of the metal concerned. The 2:1 bromine trifluoride platinumi tetrafluoride
adduct is typical in this respect in that it melts at 130° and readily de•
composes above this temperature to yield platinum tetrafluoride, %yith the
evolution of BrF„. o
These solvents do not appear to form salts of isomorphous acids as do
the selenium tetrafluoride compounds - e.g. (BrEg)2 P^Fg, (BrF2)2 GeF,g but (BrFg) PdF^. In the case of the palladium compound, this fact is particularly striking, as the 1:1 bromine trifluoride palladium tribromide
compound reacts with potassium, fluoride and with selenium tetrafluoride to yield the potassium and fluoroselenonium salts of fluoropalladic acid respectively (78):
6 BrFQ, PdF. +12 KBrF- 6 K PdF„ + Br + 16 BrF„
6 BrF } PdF_ 12 SeF.- 6(SeF3)2 PdFg + Br2 -f- 4 BrFg. o o 4 Thus, the bromine trifluoride complexes would appear to be considerably more covalent in nature than the corresponding selenium compounds.. The fact that the platinum compound gives rise to the fluoroplatinate (IV) iom in solution, however, shows that the platinum, must be coordinated by six fluorines. It would seem, then- that these compounds are best written! ini terms of the covalent structures:- F
F 102.
This is in contrast to the ionic structures proposed for the selenium tetrafluoride compounds!-
F I Pt E Se | ^F F F J 2 etc.
These formulations would best be checked by a nuclear, magnetic: moment study of the compounds. 103.
THE TETRAFLUORIDES
Zachariesen (128) had shown that the tetrafluorides of ceriunr, terbium*
zirconium, hafnium and the actinide elements were isomorphous and crystall•
ized in the monoclinic system, and a complete structure determination! of
zirconium tetrafluoride had been made by Burbank and Bensey (129). When,
it was found that platinum tetrafluoride did not crystallize in this system,
but had a uranium; tetrachloride-type of structure, it was decided to investi•
gate the other- knowni tetraf luorides to determine the importance of this- lattice.
The known saline tetrafluorides are listed in\ Table XV111. Those of manganese and osmiums had not beem established at that time, that of iridiumi was thought to resemble the pentafluorides more tham the tetrafluorides and those of chromium and vanadium were under investigation, in other parts of these laboratories. As a start; to this project, the tetrafluorides of rhodium.,tin and lead were investigated and it was found that no two structures were alike (see Plate 2). Crystalline samples of rhodium tetrafluoride were obtained only with great; difficulty, and the x-ray pattern was indexed on the basis of a face-centred, cubic unit cell containing 16 molecules.
Tin tetrafluoride was found to be tetragonal, the unit cell containing 8.. molecules. Lead tetrafluoride, despite earlier reports (85.), which indicated that it was tetragonal, gave a complex powder pattern andno attempt, was made to index it.
Subsequent reports have indicated that the structure of rhenium*tetra• fluoride is complex (ill) and although osmium.tetrafluoride has been con• firmed, no structural data has been given (104). PLATE 2. SOME TETRAFLUOR IDES
1.PtF4 2.RhF4 3.SnF4 4.PbF4 104.
TABLE XVI11. The known.saline tetrafluorides
TiF4(l30) VF4(131) CrF4(l32)
ZrF4(l28) MoF4(l0l)
HfF.(l28) WJ134)
Rare Earth: CeF4, TbF4 (128)
Transuranic: ThF4, UF4, NpF4, PuF4, AmF4 (128) .
Thus, we see that the tetrafluorides are capable of crystallizing in a variety of different, lattices, and no set lattice type, other than that of zirconium tetrafluoride is predominent.
The infra-red spectra of the tetrafluorides investigated are tabulated, together with those of the previously investigated tetrafluorides in Table XIX.
The peaks obtained are tentatively assigned as being \)g , the assymetric stretching frequency. Direct comparison between the sets is not real how• ever because the earlier results were of materials in the gas phase, while those reported here are for nujol mulls of the materials concerned. The latter method results in a vast broadening of the bands as compared with the sharp peaks- obtained for the spectra of materials in the gas phase. 105.
TABLE XIX. Infra-red spectra of some tetrafluorides
-*1 >) 3
CF4 (135) 904 435, 1283 634
SiF4 (135, 83) 800 268 1031 391
GeF4 (135) 740 200 800 260
ZrF4 (136) 668, 670 190
HfF4 (136) 645), 650
TbF4 (136) 520
PtF„ ^ 576, 674 4 PbF„ ^ 4 4552, 640
SnF4 ^ 5.75-6941
RhF. ^ 4 550-678 / this v/ork. 10.6.
THE FLUORIDES OF PALLADIUM
The lower fluorides of palladium have recently been reported in; detail
(78). The attempts made in. this, work to prepare a higher fluoride of palla• dium than the well characterized trifluoride resulted in, failure, the same products being obtained as were obtained by Ruff and Ascher (38). It is felt however, that'the formation of some palladium difluoride in the fluorin• ation* of palladium metal is due to sintering, not to localized heating as ascribed by Ruff and Ascher. Weinstock et al (114) were also unable to prepare a higher fluoride of palladium than.the trifluoride. These workers tried heating palladium metal, with an induction heater, in; ani atmosphere of fluorine in a liquid nitrogen-cooled quartz reacter. This was the same method that had been successful in the preparation of the other hexafluorides: of the group.
It would seem, then, that a hexafluoride of palladium cannot be pre• pared. This is not too surprising in view of the instability of the hexafluoride of its nearest neighbour, rhodium (114). However, from its position in the Periodic Table, a higher fluoride than; the trifluoride of palladium would be expected. 10 T.
THE FLUORIDES OF RHODIUM
The brief investigation of the fluorides of rhodium resulted from attempts to obtain, a sample of rhodium tetrafluoride crystalline enough; for structural determination.
The pale-pink rhodium fluoride, bromine trifluoride adduct formed by reacting rhodium tribromine with bromine trifluoride had been mentioned earlier by Sharpe (7), but he was unable to isolate it. This compound was isolated during this investigation, but analyses of it were inconsis• tent. They did, however, suggest that it was a lsl complex between bromine trifluoride and a fluoride of rhodium. The diamagnetism of the compound indicates the formulation RhE , BrF . Tripositive rhodium has Q a d configuration, and this would be consistent with the observed diamag- netism. Quadripositive rhodium, on the other hand, has a d configuration and so would be expected to be paramagnetic.
The volatile, orange compound produced by the fluorination of rhodium metal or rhodium tetrafluoride is very reactive. During its preparation, it attacked the silica tube very readily. It also reacted violently with water to yield a deep-blue solution and precipitate. Unfortunately in• sufficient, of this material was available for analysis. The behaviour of this compound is in marked contrast to the behaviour of rhodium tetrafluoride prepared by the method of Sharpe (7). The latter does not melt, and iis not volatile, it can be handled in moist air for short periods of time without decomposition. It does react with water, however, to give a green solution! and precipitate. It would seem then, ithat the volatile red-brown compound obtained on fluorination of rhodium metal, and as described earlier by Ruff and Ascher (38), was in fact rhodium pentafluoride and not rhodiumt tetrafluoride as designated by Sharpe (7). 10 8.
That the deep red vapours seen above rhodium metal and rhodium tetra•
fluoride on fluorination were rhodium hexafluoride has been given support,
by the recent isolation of the very unstable rhodium hexafluoride by Weinstock,
Claasen and Cbernick. (114), who prepared it by burning rhodium metal in an
atmosphere of fluorine and condensing the vapours on a surface cooled with
liquid nitrogen situated directly above the reaction zone. They describe
this compound as existing as deep-red vapours or as a black solid, which
rapidly decomposes at room temperature into a lower fluoride and fluorine.
GENERAL DISCUSSION
Since this work was started, several important contributions concerning
the fluorides of the neighbouring elements to platinum have been; made.
Hargreaves and Peacock (104), have characterized the fluorides of osmium:
and have proved that the compound tentatively assigned as osmium: pentafluoride
in Table 1 is in fact the pentafluoride, they also suggest that the compound
that Ruff and Tschirch (40) referred to as osmium^pentafluoride is in. fact
osmium dioxydifluoride or osmium; trifluoride. Weinstock et al (113, 114)
have, prepared and characterized the two very reactive hexafluorides of
ruthenium and rhodium.
Further advances have also been made in the fluorine chemistry of the
other transition metals. Malm, Selig and Fried (137) have succeeded in.
preparing the first simple septavalent fluoride, that of rhenium. Hargreaves
and Peacock (103) have described the preparation! and properties of a penta-
fluoride, tetrafluoride, oxytetrafluoride and oxytrifluoride of rhenium.
More recently, Klemm et al (133) have prepared manganese tetrafluoride, a
compound that had been suspected for some time but which had not previously been.isolated. Prior to this the drop in maximum valency from five for 10S.
vanadium and chromium to three for manganese in its simple fluorides had
seemed rather great, though manganese had previously exhibited the septa- positive state in forming permanganyl fluoride.
In spite of these recent, changes, the overall trend in the. fluorine
chemistry of the transition metals outlined in the introduction remain unchanged. The position of the maximum oxidation state in each transition,
series is shifted to higher atomic number as we pass from the first to the second to the third transition series. The fact that there is a change in maximum valency of three units in;moving from rhodium to palladium, and again from platinum to gold, seems rather anomalous. Further investigation may however reveal higher fluorides for. these metals.
SUGGESTIONS FOR FURTHER INVESTIGATIONS
From this investigation, certain topics at once suggest themselves as being fruitful for further study:-
1) An attempt to prepare further adducts of iodine pentafluoride and chlorine trifluoride with other transition metal fluorides. This should be accompanied by a study of all adducts of this type using nuclear-magnetic resonance techniques to ascertain the types of bonding in these compounds.
2) A reinvestigation of the fluorides of rhodium, with a particular- view to characterizing the suggested pentafluoride - this may prove very difficult.due to the great reactivity of the compound. An oxyfluoride analogous to platinum peroxidehexafluoride should also be looked for.
3) An investigation into the possibility of forming peroxidehexafluorides with all those elements forming volatile hexafluorides, by carrying out the fluorinations using oxygen, as the carrier gas.
4) The preparation and structure determination of other salts of fluoro^ platinic acid (v). SUMMARY 110.
SUMMARY OF THE KNOWN FLUORIDES OF PLATINUM
Magnetic Other 3 Formula Colour rr-- —T- — Structure Ref. Moment properties —— PtF, Gn.-yellow 1,2,6,12
PtF, Black Rhombohedral a = 5.41:
I- A „0
PtF. Yellow Diamag. Monoclinic Sublimes 300 1-17, 7/ a _ 6.668; c _5.708s if =92.02
PtFe Deep red Paramag, m. 80
PtF, Red-bn. 0 b.c.c. m. 56.7 vapour 19.20,112? a -6.209 black solid PtOF„
p Light, bn. t02F6 2.45B.M. Cubic m.2l9°(d) Orange-red a = 5.016 Sublimes 90*
Adducts m. 130 (d) 7,/ PtF4(BrFg)2 Red; Diamag. .'Hexagonal Dec. 350° 16, PtF4(SeF4)2 Lt.-orange Diamag. a _ 15.74'; c =4.93
PtF_,lE_ Orange 0.65B.M. m. 160 (d)
PtF_,ClF„ Yellow-orange m. 171°(d) o o 7*
PtF5,SF4? Buff Dec. 180°
Pt(C0)2Fg Pale-Yellow Sublimes 70 95 Magnetic Solubility/ Formula Colour Structure S.G. Ref. Salts Moment 100g H20 27 H2 PtF6 Pale-yellow
n Diamag. Trigonal 4.83 0.750 7,17,21- K2 PtF6 a a, 5.76 25, 28, c =4.64 30-32,3'
it Rb0 PtFft — Trigonal 6.00 0.278 7,2S, 28. 2 o a = 5.96 30-32!. c x4.83
II — Cs2 PtF6 Trigonal 5.39 0.484 7,25), 28 a = 6.22 30-32 C; =5.61
tt! Na2 PtF6 — Hexagonal 4.21 20.49 28,30 a = 9.41 c •= 5.165
- - - - - 28 Li2 PtF6
(NH4)2 PtF6 Pale-yellow - - 3.59 7.32 21, 28>
tt. La2 (PtF6)3 - - 2.63 7.5, 26
tt. Pr,2 (PtF6)3 - - 2.64 7.1 26:
tt. Nd2 (PtF6)3 - - 2.66, 6.6 26
Ce2 (PtF6)3 - - - - - 26i
Mg PtFg 6H20 Pale-yellow - - 2.65. 67.9 29
It; Ca PtFft 6H 0 - - 4.13 104.9 29 o. 2 Sr PtF„ 2H 0 II: Rhombohedral 4.42 98.6 29, 33 o 2 a = 4.74 ««• =97.8,
Ba PtFg tt: — Rhombohedral 6.04 0.171 29, 33 a =4.88 oc =98°
E PtFc Yellow 0.87 B.M. Rhombohedral 5.11 Dec. o a = 4.87
oc = 97.70
/ this work. APPENDICES .112-
APPENDIX 1.
AN ALWAC HIE COMPUTER PROGRAMME FOR DETERMINING USEFUL
FUNCTIONS FROM X-RAY POWDER PHOTOGRAPHS
Introduction
The "reflection" of x-rays by a crystal lattice only occurs when; the
Bragg equation,
2 d sin 6 = A is satisfied.
6 angle of incidence
d interplaner spacing
h warelength of radiation used.,
If we consider an x-ray powder photograph, the distance between; any pair of lines; (x< > - will correspond to 4 6 and is related to the radius of the film (R) by,
Xg - ij = 4 6. R. where 6 here is measured in.radians.
Thus, 0 may be determined from a knowledge of R. and the measured
v/alues of and x^# By substituting this value of © in the Bragg equation* d may be determined.
From a consideration of the reciprocal lattice, it can be shown; that,
^ ^, r.2 *2 „2. .*2 ,2 *2 C = ha +• K b + 1 c; * 2hka*b*cos + 2klbfc*cos + 21hc c a cos^S Where, c5" hkl is the reciprocal lattice vector and a*, b*, c*, <=**, jS and 8 are the reciprocal lattice dimensions* Now, _fhkl - l/dhkl 2 Qhkl = l/d hkl or, combining with the Bragg equation^ 2 2 2 2 ©hkl ~ l/d hkl = 4 sin 6hkl/?> _ const, x sin ehkl. Now, each line of a powder photograph corresponds to a reciprocal lattice vector. Thus, the first step in interpreting a powder photograph is to select, from the list of Q values, values of the reciprocal cell edges a , b , c . These values are then checked against the experimental values by using these to compute a complete set, of Qhkl values according to the above equation. This may be carried out by a comparison of either aim 6 values or 1/d values. The actual cell edges may theni be computed from the reciprocal cell edges. Nelson and Riley (63) have sho.wni that for cubic crystals, the main, source of error in the determinatiiont of the lattice parameter is due to absorption, and found empirically that this could be best overcome by cos2B cos2© plotting values of a againstL the functional.- ( . . H —) and extrapo- sm D o lating the value to 90°', where the error due to absorption is zero. This function has since been used by other workers (138, 139, 140) for the determination of accurate lattice parameters for tetragonal and hexagonal systems. The programme to be described was written to process data obtained from x-ray powder photographs. Values of the wavelength, of radiation used, radius of the film and values of pairs of x^ and Xg are input into the computer and values of x^> Xg» x^ Xg» © (in degrees) sin2©, d, l/d2 and the Nelson-Riley function, are output. Input routine The programme, which is to be stored in channels de-eo of the com• puter, is first read into the computer from the programme tape. The computer then, halts and awaits the input, of numerical- data, which is then read in by a separate data tape. The data tape should be punched out on. the Flexowriter in the following form, deOO CR ft SP. R CR. x1 SP. Xg SP. x1« SP. Xg * SP CR. etc. Where, Xg is the greater of the two values in each case. The numbers may be punched in. in any convenient form - 5.000, 5i, 0.125;, .125> etc. - and terminated either by a space (SP.) or a carriage return* (CR.) . Five sets of x^, Xg values can conveniently be accommodated on one line. Any number of Xj, xg values can be processed im this manner, the data should be terminated by a stop code. When a change of wavelength is required - e.g. for Ko^ and K«g values - a fresh data tape must be punched. Output The computer will output results on the high-speed punch if this is on, otherwise results will be output on the Flexowriter. It is preferable to 115 output, data on the high-speed punch, then print the results from this later. Data is output in columns in the form: R 2 2 xx xg %1 +• x2 6° sin © d 1/d N.R. fn. A typical calculation involving 50 x^, xg pairs takes about six minutes to compute. The data tape for this takes about ten minutes to punch and check. The programme is giveni overleaf: PJI7UPH7O 09 oooooooo-oooooooo 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 oooooooo-oooooooo •oooooooo-oooooooo- 6«nootzo tgoooioo *lHlOOlEO ^ooootoo oooooooo-oooooooo •oooooooo-£q.qi76£oo 00002000 00090000 OOOtyXXX) 0000I000 03 JO£2 oooooooo-oooooooo •00000000-'B^6i70l£,B OOOOOOOO-OOOOOOOO' •OOOOOOOO-lrt^OfiHi OOOOOOOO-OOOOOOOO' •oooooooo-9^6t[Oi oooooooo-oooooooo •000086U zfi_9£iiqs oooooooo-oooooooo •B^jp^zli 2£2,9ooo£ OOOOOOOO-OOOOOOOO' •00JP09U ^i9ooo£ , oooooooo-oooooooo lQq?ol£v c_6i70t£T2 21820^^3 si_6Hl8-l 008ZO+7ti7 Ifi_ai5tl7 280£1£2.9 09ll6ip_ 0t£«0092 09U6l<_ 8^6i6^6-tj JU&LSgn O+IHT£^6+T oiE^gogz Ol&eoQLs o^l-tTt^6-n 90i8°6it 9U8£^^ o^oi^qp olC^lt 6S8+T09U O^QJPtQ 3P J0£2 117. APPENDIX 2. AN ALWAC HIE COMPUTER PROGRAMME FOR THE GRAPHICAL DETERMINATION OF ACCURATE LATTICE PARAMETERS FOR TETRAGONAL CRYSTALS. Introduction When attempts are made to determine lattice parameters for tetragonal or hexagonal crystals, there are three unknowns, a, c and the drift or systematic error. Methods for determining these include Cohens's least; squares method (141) and the graphical methods of Taylor and Floyd (138) and Myers and Davies (139). This programme was devised to assist im using the last method. The direct graphical method of Myers and Davies depends om finding the line best fit for a series of straight lines ini three dimensional, space, each straight line being derived from a particular crystal lattice reflection. In practice, a two dimensional projection of the three dimensional situation is adopted. The Bragg equation when, applied to tetragonal crystals may be written in the following forms: 2 si 2 2 & 2 q2 k2 2 (a/c) s 3 » ©/ * *f7 " ( + )/! (general form) and a2 s ft 2 (h2 +- k2)/4 sin2 0 (for hkO planes) 2 2 These are equations of straight lines ini variables a and (a/c) . These may; be plotted for a givemO after indexing. Ideally, the lines would all intersect, at a point, but drift and scatter must be taken into; consideration and the line of best fit has to. be found. This is done by constructing a fan diagram of the extrapolation function of the angles om 118. transparent paper and moving this around on the plot until the line of best fit is found. The horizontal line gives the (a/c)2 value and the o # . 2 extrapolated value of 0 s90 (from the fan diagram) gives the a value. The drift is found by a subsequent plot - the third dimensional: 2 representation!- of the derived a values against the Nelson-Riley extrapolation function. Input routine This programme, which is to be stored ini channels el and e2 of the computer, is read into.* the computer, by the high-speed reader, from the programme tape. The computer halts and then awaits the input of numerical data, which is input from; a separate data tape. The data tape should be punched out on. the Flexowriter int the following from', elOO CR. hx SP. SP. lx SP. 61° CR h2 SP. k2 SP. 12 SP. 82° CR. etc. and the data terminated by a stop code. Output routine The computer tests for 1 _. 0, computes the data and outputs the results in the form:- 2 2 2 2 2 2 hx kx lx 4 sin 8/ >, 1 (h fc )/l for hkl and }\2 (h2 + k2) /4 sin2 £> 0 for hkO etc. 119. A typical computation involving fifteen planes took approximately thirty seconds to compute. The data tape for this took approximately three minutes to punch, and check. The programme is given overleaf. LtfVlSBQ. 23 00000000 00000000 00000000 00000000 00000000 00000000 oooooooo-oooooooo- 00000000 00000000 00000000 00000000 00000000 00000000 oooooooo oooooooo- oooooooo-oooooooo-00000000-6000011 1 oooooooo-oooooooo g^ootno 1122.10911 96000100 02000120 oHrooi2o 6Z<&Q£QL 90000100 9M00000 oooonooo lo££q6Ll 29 Jo£2 L&cayzL 19 ££990092 90^9176^1 $£QLlo^ 1£6IT0092 ££0-1712^ 9£9*i09H PSqaoil'B v£Lzooo£ 12A90092 siLQ^IP o£t9q£61 o£l9<\£6L OlW£i.3 0911^2^ 9£&v£q? z66ivzl9 j£^0liv nLQl£6ii ol£«oo82 *i£6L66Ll •^sttozqi 09lt£2q£ 22lseoo£ sU929£9 19 J0£2 f REFERENCES 121. 1. H. Moissan, Compt. rend., 1889, 109, 807. 2. H. Moissan, Ann. Chim. Phys., 1891(6), 24, 282. 3. 0. Ruff- and J. Zedner, Ber., 1909, 42, 1037. 4. 0. Ruff, Z.anorg. Chem., 1916, 98, 27. 5. 0. Ruff., Z. angew. Chem., 1928, 41, 738;. 6. 0. Ruff, Ber., 1936, 69, A 181. 7. A. G. Sharpe, J. Chem. Soc, 1950, 3444. 8. 0. Ruff and J. Zedner, Ber., 1909, 42, 493. 9. G. Gore, Chem. N., 1871, 23, 13. 10. 0. Ruff and J. Fischer, Z. anorg. 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"X-ray diffraction procedures", Wiley, New York, 1954, p.485. FIGURE 1 Apparatus used for pyrohydrolysis FIGURE 2 Apparatus for handling fluorine Zi o Q. Q. O N2-°2 (Nl LL FIGURE 3 Apparatus for reactions involving bromine trifluoride, selenium tetrafluoride or iodine pentafluoride •a a— I I I ID Ii O CO a >s\ > cnJi FIGURE A FIGURE 4 Apparatus for reactions involving oxygen difluoride, sulphur tetrafluoride or chlorine trifluoride o>—• £ o Q) V) > o 3 CM CO 3T 3 JQ E E ZJ HM O o I/) I J— o >» FIGURE 5 Apparatus used for studing decomposition reaction. B19 Cone & socket 1 To vacuum system FIGURE 6 Apparatus used for preparation of P^ W -Q— CM O CO D EZ3 ai FIGURE 7 Apparatus used for purification of 02Fg Q: "0= —o _Q LO if o« °o w>* „ I— > (/» 1 FIGURE 8 Apparatus used for measuring gas evolution