Platinum hexafluoride reactions

THE XENON-PLATINUM HEXAFLUORIDE REACTION AND RELATED REACTIONS... 

Table 6. — Some results for the xenon -F platinum hexafluoride REACTION...

N. Bartlett and N. K. Jha, The Xenon-Platinum Hexafluoride Reaction and Related Reactions, Noble Gas Compounds, ed. H. H. Hyman, University of Chicago Press (1963) 23-30. 

In 1962, the English chemist Neil Bartlett overturned the conventional wisdom. Bartlett was exploring the reactions of platinum hexafluoride, an extremely reactive molecule. He found that PtFg reacted cleanly and rapidly with molecular oxygen O2 FPIFg —> O2 FPlFg ... 

Although xenon has the stable octet configuration and is thought to be as inert as other noble gases, several xenon compounds have been prepared. The first xenon compound synthesized by N. Bartlett in 1962 was a red sohd, XePtFe, made by the reaction of xenon with platinum hexafluoride undergoing the following oxidation sequence (Cotton, F. A., Wilkinson G., Murillo, C. A. and M. Bochmann. 1999. Advanced Inorganic Chemistry, ed., pp. 588. New York John Wiley Sons) ... 

The same authors showed that platinum hexafluoride, which is a somewhat weaker oxidative fluorinating agent than KrF+, can also oxidize NF3, though the yield and purity of the NF4+ fluoroplatinate formed as a dark red solid were low. The pure salt was prepared for purposes of comparison by the thermal reaction at 125°C between NF3, F2, and PtF6. The reaction between NF3 and the hexafluoride was carried out either in HF solution at 25°C or under ultraviolet irradiation in the gas phase, also at ambient temperature. In each case the vibrational spectrum of the product showed the presence of a tetraflu-oroammonium salt, but the product was a mixture of fluoroplatinate and polyfluoroplatinate which could not be purified by extraction with liquid HF. 

Reagents.—Platinum hexafluoride and rhodium hexafluoride were prepared from 0.03-in. diameter pure metal wire supplied by Johnson, Matthey, and Mallory Ltd., Toronto. The reaction with fluorine was initiated by electrical heating of the wire, the metal reactor used being similar to that described by Weinstock, Malm, and Weaver [2]. Airco Reagent Grade xenon was used. 

In their early studies of the oxidation of xenon by platinum hexafluoride Bartlett and Jha found [1] that the stoichiometry of the product of that spontaneous reaction varied between XePtF and Xe(PtFg)2. Chemical and physical evidence Indicated that the oxidation state of the platinum in Xe(PtFg)jj was +5. Pyrolysis of XeCPtFg), at 165°, yielded xenon tetra-fluorlde as the only identified volatile product, (xenon itself was not... 

The reaction of xenon with platinum hexafluoride yields at least two distinct quinquevalent platinum products, XePtF, and Xe(PtFj)j. A third compound XePtjFij which is diamagnetic, is produced by heating the former. During continuing investigations of the reaction between xenon, fluorine, and platinum pentafluoride, at least two different compounds have been detected. The better characterized compound is produced when 1 1 molar ratios of xenon and platinum pentafluoride are employed in admixture with 80 p.s.i. 

The spontaneous oxidation of molecular oxygen and of atomic xenon, each of which has a first ionization potential of 281 kcal. mole , by platinum hexafluoride, has estabhshed the remarkable oxidizing power of the hexafluoride. None of the other third-transition-series hexafluorides will oxidize these species. Since it is well established - that the platinum hexafluoride-oxygen adduct is the salt Oj+[PtFe] , the lattice energy of which is estimated, employing Kapustinskii s second equation to be 125 kcal. moIe, the electron affinity of the PtF, molecule is required to be >156 kcal. mole, to ar count for the observed exothermic reaction [Pg.244]

Nitric oxide is readily oxidized by platinum hexafluoride but it has not proved possible to control the reaction to produce a pure product. A mixture of NOPtF, and (NO)jPtF, is always produced. Platinum hexafluoride is, however, able to oxidize nitrosyl fluoride with the elimination of fluorine ONF - - PtF, - ON+[PtF8J - -iFj. In a typical experiment, platinum hexafluoride (5-20 mmoles), prepared by Weinstock, Malm, and Weaver s method, was warmed to room temperature, in a closed nickel vessel, with... 

The reaction of selenium tetrafluoride with platinum hexafluoride. When selenium tetrafluoride and platinum hexafluoride were mixed in a silica bulb, there was an immediate and vigorous reaction at —9°, which evolved much gas, presumed to be selenium hexafluoride. Selenium tetrafluoride, which was present in a large excess, was removed by vacuum distillation. X-Ray examination showed the yellow residue to be the 2 1 selenium tetrafluoride-platinum tetrafluoride adduct. 

It occurred to Bartlett that the ionization energies of the oxygen molecule (1180 kj/mol) and the xenon atom (1167 kj/mol) were remarkably similar. He decided to try the same reaction as above with xenon replacing the diatomic oxygen. He prepared known volumes of xenon (in slight excess) and platinum hexafluoride and carefully noted the pressure of each. When he allowed the two gases to mix. 

Further investigation demonstrated that the reaction was more complicated than Bartlett had originally thought. In fact, this reaction is still not well-understood. Equation (19.3) is probably more representative of what happens when xenon and platinum hexafluoride come together ... 

Bartlett s original reaction between xenon and platinum hexafluoride is now... 

The octahedral hexafluorides are obtained directly from the elements and both are volatile, extremely reactive and corrosive solids, RhFg being the least stable of the platinum metal hexafluorides and reacting with glass even when carefully dried. They are thermally unstable and must be frozen out from the hot gaseous reaction mixtures, otherwise they dissociate. 

The hexafluoride is a very powerful oxidizing agent reacting violently with most oxidizable substances. Reaction with liquid water is violent forming HF, oxygen, lower fluorides of platinum, and other products. In vapor phase hydrolysis occurs more smoothly. 

The chemistry in this area is greatly limited. During the period of the Manhattan Project considerable study was devoted to the synthesis of volatile heavy metal fluorides. PoFs has been prepared by the reaction between 20 po electroplated on platinum and elemental fluorine. Analytical data were never obtained for the hexafluoride, which is reported to be stable in the vapor phase but disproportionates to the tetrafluoride on cooling. 

The departure from the 1 1 reaction stoichiometry in the xenon-rhodium hexafluoride system is less than for the platinum system. This is surprising in view of the greater instability and chemical reactivity of the rhodium fluoride. Ruthenium hexafluoride, which is less reactive than rhodium hexafluoride, has been reported [7] to react non-stoichiometrically with xenon. Perhaps the use of small quantities of rhodium fluoride favored the 1 1 addition. There is as yet no evidence for the oxidation state of rhodium in the adduct, although the formulation Xe -1- [RhFe] would, as in the corresponding platinum case, appear to be energetically more favorable than Xe +[RhF6] . 

The way in which the oxidizing power of the hexafluorides increases with atomic number in the third transition series is demonstrated by the nature of the reactions with nitric oxide which are summarized in Figure 7. Since the ionization potential of nitric oxide is 62 kcal. mole lower than for oxygen it can reduce osmium hexafluoride to the quinquevalent and platinum to the quadrivalent... 

Sulfur hexafluoride accelerates the pyrolysis of paraffin hydrocarbons (164), lowers the octane number of gasoline containing lead tetraethyl (189), removes silicon from a platinum catalyst when heated to 800 to 1000° (206) and catalyzes the reaction of ammonia with a ketone and aldehyde to give a substituted pyridine (196). It may be used at high pressure to fill a fuse. When the fuse blows an arc is prevented (210). 

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