UBC Theses and Dissertations

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UBC Theses and Dissertations

New flourides of the noble metals. Rao, Ramesh Pathur

Abstract

The compound previously identified as palladium trifluoride and as such accepted as the only unambiguous tervalent palladium compound, has been shown to be the mixed valence compound Pd²⁺[PdF₆]²⁻. This has resolved difficulties associated with the description of PdF₃ in terms of crystal field theory. The synthesis of a new series of compounds of general formula Pd²⁺[MF₆]²⁻, isomorphous with Pd²⁺[PdF₆]²⁻and magnetically similar to the latter has been achieved. The oxidation state of palladium excited by bromine trifluoride has been shown to be +4 when good fluoride ion donors are available (i.e.when the solution is basic) and +2 when good fluoride ion acceptors are present in solution (i.e. in acid conditions). Reasons for the instability of Pd(III) in a fluorine ligand environment are discussed. Antiferromagnetic ordering has been observed in palladium difluoride. -This has accounted for the low value of the room temperature magnetic moment of the compound. A less tedious synthesis of palladium difluoride has been accomplished by the pyrolysis of the new palladium(II) hexafluorogermanate(IV), at temperatures above 350°. A tetrafluoride of palladium has been prepared for the first time. It is the highest valence binary palladium fluoride now known. It has a body centered tetragonal lattice and is isostructural with uranium and thorium tetrachlorides. The adduct of palladium tetrafluoride with bromine trifluoride, (BrF₃)₂PdF₄, has been prepared and was found to be isomorphic with the corresponding platinum compound. The magnetic susceptibility of gold trifluoride has been reinvestigated. Analytically pure AuF₃ has been shown to be diamagnetic. This has unambiguously assigned a low spin d⁸ configuration for Au(III) in gold trifluoride. Fluoroaurates(III) of sodium, potassium, nitrosyl, rubidium and caesium have been found to be diamagnetic. The salts with the exception of CsAuF₄ proved to be isomorphous. Also NOAuF₄ has been found to be isomorphous with NOBrF₄. The existence of a tetrapositive state of gold has been indicated. Gold tetrafluoride is a pale yellow, highly reactive solid. This first paramagnetic compound of gold is amorphous to x-rays. The previously unknown pentapositive state of rhodium has been established. Rhodium pentafluoride is a deep red solid, m.p. 95.5°, and is highly reactive. It reacts with carbon tetrachloride, chlorine monofluoride being among the products. It is structurally similar to ruthenium pentafluoride, but has a smaller molecular volume. A hexafluororhodate(V) has been prepared for the first time by reacting rhodium pentafluoride with stoichiometric amount of caesium fluoride in iodine pentafluoride. It is structurally similar to the other caesium hexafluorometallates(V) of the noble metals. The hitherto unknown iridium pentafluoride has been established and its identity with the previously known iridium tetrafluoride has been revealed. Iridium pentafluoride is structurally similar to the other noble metal pentafluorides, and is almost isodimensional with ruthenium pentafluoride. It has magnetic properties typical of a third transition series d⁴ electronic configuration in an octahedral or near octahedral environment. It is suggested that in both rhodium and iridium pentafluoride the structural unit is a fluorine bridged tetramer as in ruthenium pentafluoride.

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