Noble Gas Chemistry

Ramsay and Rayleigh succeeded in isolating all of the noble gases except radon and in showing that they were inert to all common reagents. They also discovered the identity of alpha particles and ionized helium. 

If an aqueous solution of hydroquinone is cooled while under a pressure of several hundred kilopascals (equals several atmospheres) of a noble gas [X = Ar, Kr. XeJ, a crystalline solid of approximate composition [ClsHs(OH)-,])X is obtained. These solids are -hydroquinone clathrates with noble gas atoms filling most of the cavities.3 Similar noble gas hydrates are known (Fig. 17.1). These clathrates are of some importance since they provide a stable, solid source of the noble gases. They have also been used to effect separations of the noble gases since there is a certain selectivity exhibited by the clathrates. 

Of particular interest is the effect of noble gases in biological systems. For example, xenon has an anesthetic effect. This is somewhat surprising in that the conditions present in biological systems are obviously not sufficiently severe to effect chemical combination of the noble gas (in the ordinary sense of that word). It has been proposed that the structure of water might be altered via a clathrate-type interaction. 

Although clathrate formation and dipole interactions are perfectly acceptable subjects for chemical discussions, chemists feel more at ease when they can find stable compounds formed from the species being studied. A logical approach would be the 

4 For a discussion of the earliest work on the noble gases, see WoMenden. J. H. J. Client. EJuc. 1969. 46, 369 Hiebert, E. N. In Noble-Gas Compauitdsi Hyman. H. H.. Ed. University of Chicago Chicago. 1963 p 3. 

Thonotigh studies of solutions of xenon in boron trichloride and boron tiibromide were undertaken. A phase study of the melting point of these systems as a function of composition showed no evidence of compound formation. The Raman spectra of these mixtures are identical to those of pure BXj indicating no noble gas-boron trihalide interactions. 

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J. H. Holloway, Noble-gas Chemistry, Methuen, London, 1968, 213 pp. See also Chem. in Britain, July 1987, pp. 658-64. 

Xe is comparable to, that of molecular oxygen (1175kJmol for O2 -> 02 + e )- He quickly proceeded to show that deep-red PtFe vapour spontaneously oxidized Xe to produce an orange-yellow solid and announced this in a brief note/ Within a few months Xep4 and Xep2 had been synthesized in other laboratories/ Noble-gas chemistry had begun. 

Whilst the great bulk of noble-gas chemistry concerns Xe-F or Xe-O bonds, attempts to bond Xe to certain other atoms have also been successful. Compounds containing Xe-N bonds have been produced by the replacement of F... 

Until about 40 years ago, these elements were referred to as "inert gases" they were believed to be entirely unreactive toward other substances. In 1962 Neil Bartlett, a 29-year-old chemist at the University of British Columbia, shook up the world of chemistry by preparing the first noble-gas compound. In the course of his research on platinum-fluorine compounds, he isolated a reddish solid that he showed to be 02+(PtFB-). Bartlett realized that the ionization energy of Xe (1170 kJ/mol) is virtually identical to that of the 02 molecule (1165 kJ/mol). This encouraged him to attempt to make the analogous compound XePtF6. His success opened up a new era in noble-gas chemistry. 

Important to recognize limitations of this concept [Lewis octet] in relation with the noble gas chemistry. ... 

At first, noble gas chemistry had almost no practical applications. Recently, however, lasers have been developed that are based on the chemical reactions of noble gases. 

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... 

Holloway, J. H. (1968). Noble-Gas Chemistry. Methuen, London. A thorough discussion of some of the early work on noble gas chemistry. A good introductory reference. 

Recent Advances in Noble-Gas Chemistry John H. Holloway and Eric G. Hope... 

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 ... 

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. 

Xenon Dioxide Difluoride. Xe02F2 mw 201.30 colorl solid, liq vap mp 30.80°.Prepn is by distilling Xe oxytetrafluoride into Xe trioxide at dry ice temp, and then fractionally distilling off the unreacted Xe oxytetrafluoride along with the by-product Xe difluoride, leaving the product. According to Holloway, samples of Xe dioxide-difluoride have expld Refs 1) J.H. Holloway, Noble Gas Chemistry , Methuen, London (1968), 132-34 2) J.C. 

According to Klimov (Ref 2) the tetrafluoride is resistant to deton. However, because of its high reactivity, very sensitive explns result from contact with flammable materials such as acet, polyethylene, wool, paper, sawdust, Al foil, ferric carbonyl, lubricants or styrene Refs 1) J.H. Holloway, Noble-Gas Chemistry , Methuen, London (1968), 95 ff 2) BD. Klimov et al, Explosion Hazard During Work With Fluorine Containing Xenon Compounds , Zh Prikl Khim (Leningrad) 42 (12), 2822-24 (1969) CA 72, 85784 (1970) 3) T.C. 

Seppelt, Konrad and Lentz, Dieter, Novel Developments in Noble Gas Chemistry 29 167... 

It is now well known that despite their name the noble gases (at least Rn, Xe, and Kr) do, in fact, participate in interactions normally considered chemical, notably with F but also with other elements, and the Xe-F bond strength is a substantial 30kcal/mole. Noble gas chemistry is accordingly a subject of considerable theoretical interest. Nevertheless, it is extremely unlikely that conditions resulting in the formation of noble gas compounds would be encountered outside the laboratory, so noble gas chemistry will not be important in geochemistry and will not be discussed here. Treatments of noble gas chemistry are presented by Hyman (1963), Classen (1966), Dean (1985), and Pyykko (1997). 

Greenwood, N. N., Eamshaw, A. (1997). Chemistry of the Elements (2nd ed.). Oxford Butterworth-Heinemann. Chapter 18 gives an excellent overview of noble gas chemistry. 

Seppelt, Konrad and Lentz, Dieter, Novel Developments in Noble Gas Chemistry Serpone, N. and Bickley, D. G., Kinetics and Mechanisms of Isomerization and... 

Within a year of the discovery of XePtFe and as a result of worldwide activity, it was clear that the chemistry of the noble gases would be limited to the heavier elements as set out in my Noranda Lecture (see Ref. S2). Because of the dangerous radioactivity associated with all of the radon isotopes, this meant that the bulk of noble-gas chemistry would be that of xenon. The chemistry of krypton appeared to be limited to KrF2 and compounds that could be derived from it. In all cases, it was clear, the range of accessible noble-gas chemistry was dictated by lower ionization potentials at the noble-gas atom, and high electronegativity and small size of the ligand atoms, as discussed in Ref. 45. 

The author is an emeritus professor of chemistry and a principal investigator in the Division of Chemical Sciences, Lawrence Berkeley National Laboratory. His research interests have largely been concerned with the highest attainable oxidation states of the noble metals, and noble-gas chemistry. 

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