Krypton chemistry

The chemistry of krypton is less extensive than that of xenon, and the well-established characteristics, summarized in detail in the book chapters in 1973 by Bartlett and Sladky (4) and in 1984 by Selig and Holloway (12) are dealt with in outline here, but the new developments since 1979 are referenced in detail. 

The only stable binary fluoride of krypton is the difluoride, KrF2, and all the known chemistry derives from this molecule. Early reports of the preparation of KrF4 have not been substantiated, and no simple stable oxides or oxide fluorides have been isolated. However, small amounts of the violet free radical, KrF, have been observed following y-irradiation of KrF2 (.2—4). There has also now been direct observation of [KrO ]+ (n = 1, 2) and [KrOH]+ by Fourier-transform ion cyclotron resonance (FT-ICR) mass spectrometry, for which ab initio theoretical calculations suggest that the two species are covalently bonded with bond dissociation enthalpies of 237.7 and 169.5 kJ mol1 respectively (21). 

Krypton difluoride has now been shown to exist in two crystallographic forms, a low-temperature ( —196°C) phase, referred to as a-RrF2, and a high-temperature (-78°C) phase, /3-KrF2 (23). Study of the vibrational spectra has shown that the X-ray structure reported 

XeOF4 (44). It is also noteworthy that XeOF4 is not fluorinated by PtF6 (45). 

Pyrolysis of the krypton complex at between 60 and 65°C gave gold pentafluoride, AuF5  

Perhaps even more remarkable is the extension of krypton chemistry to include Kr-N-bonded species in the cations [HC=N—KrF]  

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Recent Review Literature The Possibility of Argon Chemistry Krypton Chemistry Xenon Chemistry... 

Figure Bl.26.4. The adsorption of argon and krypton on graphitized carbon black at 77 K (Eggers D F Jr, Gregory N W, Halsey G D Jr and Rabinovitch B S 1964 Physical Chemistry (New York Wiley) eh 18).

Following Bartlett s discovery of xenon hexafluoroplatinate(VI), xenon and fluorine were found to combine to give several volatile, essentially covalent fluorides, and at least one fluoride of krypton has been obtained. From the xenon fluorides, compounds containing xenon-oxygen bonds have been made much of the known chemistry of xenon is set out in Figure 12.1. 

The chemistry of xenon is much more extensive than that of any other noble gas. Only one binary compound of krypton. KrF2, has been prepared. It is a colorless solid that decomposes at room temperature. The chemistry of radon is difficult to study because all its isotopes are radioactive. Indeed, the radiation given off is so intense that it decomposes any reagent added to radon in an attempt to bring about a reaction. 

Since the discovery of the first noble gas compound, Xe PtF (Bartlett, 1962), a number of compounds of krypton, xenon, and radon have been prepared. Xenon has been shown to have a very rich chemistry, encompassing simple fluorides, XeF2> XeF, and XeF oxides, XeO and XeO oxyf luorides, XeOF2> XeOF, and Xe02 2 perxenates perchlorates fluorosulfates and many adducts with Lewis acids and bases (Bartlett and Sladky, 1973). Krypton compounds are less stable than xenon compounds, hence only about a dozen have been prepared KrF and derivatives of KrF2> such as KrF+SbF, KrF+VF, and KrF+Ta2F11. The chemistry of radon has been studied by radioactive tracer methods, since there are no stable isotopes of this element, and it has been deduced that radon also forms a difluoride and several complex salts. In this paper, some of the methods of preparation and properties of radon compounds are described. For further information concerning the chemistry, the reader is referred to a recent review (Stein, 1983). 

Bartlett, N. and Sladky, F. 0., The Chemistry of Krypton, Xenon, and Radon, in Comprehensive Inorganic Chemistry (A. F. Trotman-Dickenson, ed), Vol. 1, pp. 213-330, Pergamon Press, Oxford,... 

The difference in the ionization potentials of xenon and krypton (1170 versus 1351 kj/mol) indicates that krypton should be the less the reactive of the two. Some indication of the difference can be seen from the bond energies, which are 133 kj/mol for the Xe-F bond but only 50 kj/mol for the Kr-F bond. As a result, XeF2 is considerably more stable of the difluorides, and KrF2 is much more reactive. Krypton difluoride has been prepared from the elements, but only at low temperature using electric discharge. When irradiated with ultraviolet light, a mixture of liquid krypton and fluorine reacts to produce KF2. As expected, radon difluoride can be obtained, but because all isotopes of radon undergo rapid decay, there is not much interest in the compound. In this survey of noble gas chemistry, the... 

Numerous other reactions of krypton difluoride are known, but they will not be reviewed here. The chemistry of krypton is well established, but it is still much less extensive than that of xenon. Although a rather extensive chemistry of the noble gases has developed, the vast majority of the studies have dealt with the xenon compounds. 

The principal laws for the fluorination of polymeric hydrocarbons are the same as those described above for the simple case. Direct fluorination has been used extensively in organic chemistry (but only since the early 1970s) in low-temperature methods, where the fluorine is strongly diluted with some inert gas (helium, argon, nitrogen, krypton). One can note the La Mar, aerosol-based, and liquid-phase fluorination methods. 

For convenience, the even rarer and less stable krypton compounds are also covered in this entry. All xenon compounds are very strong oxidants and many are also explosively unstable. For a now obsolete review, see [1]. A recent compact review of noble gas chemistry is found in [2], A series of alkali xenates, MH0Xe03.1.5H20 are unstable explosive solids. The equivalent fluoroxenates MFXe03are far more stable. Individually indexed compounds are ... 

Table 6.18 contains the small amount of data for the + 6 and + 7 states of Xe. All four species are extremely unstable and must be handled very carefully. It is probable that radon has a similar chemistry, and there is a possibility that some higher oxidation states of krypton exist. 

As stated above, noble gas chemistry is almost restricted to that of xenon, with a few krypton compounds of lower stability and with the chemistry of radon largely unexplored, due to the short half-lives of its isotopes. Two reviews1,6 give good coverage of more recent noble gas chemistry. 

Both theory and experiment indicate that the electronic structures of the noble gases [helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and radon (Rn)] are especially nonreactive these atoms are said to contain filled shells (Table 2.1). Much of the chemistry of the elements present in organic molecules is understandable in terms of a simple model describing the tendencies of the atoms to attain such filled-shell conditions by gaining, losing, or, most importantly, sharing electrons. 

The chemistry of krypton is much more limited Hum that of xenon. Apparently only the difluonde forms directly from the elements. Attempts to make helium, neon, and argon fluorides have been unsuccessful. Radon should react even more readily than xenon, but its chemistry is complicated by the difficulty of working with a... 

Reviews about the chemistry of noble gases including the cations of xenon and krypton... 

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