Krypton difluoride

As mentioned, krypton difluoride is an exceedingly powerful oxidizing and fluorinating agent, far more potent than Xep2. Thus, it oxidizes xenon to XeF and gold to the unique Au(V) compound KrF+AuFg  

At 60 °C, the gold-containing salt decomposes to yield the molecular fluoride AU2F10  

KtF2 transfers a fluoride ion to strong Lewis acids such as SbF5, forming the KrF+ cation  

The KrF+ cation is one of the strongest oxidants known. As mentioned in Section 7.8, it oxidizes CIF5 and BrF5 to ClFg and BrFg+, respectively  

Recall that, unlike iodine, chlorine and bromine do not form uncharged XF7 molecules. 

Submitted by ANDREJ SMALC, KAREL LUTAR, and BORIS ZEMVA Checked by SCOTT A. KINKEADf 

The commonly used method for the preparation of krypton difluoride, which is based on passing an electric discharge through a gaseous mixture of krypton and fluorine at low temperature and reduced pressure, is rather tedious because of the relatively low yield. However, the irradiation of a liquid krypton-fluorine mixture at — 196°C proved to be a very successful method for the preparation of krypton difluoride in quantities up to 10 g in a single run. 

The synthesis of krypton difluoride is carried out in a 150-mL low-temperature photochemical reactor (Fig. 1). The reactor consists of a ring-shaped 

To avoid the possible overpressure in the system due to coolant loss that could consequently cause the bursting of the reactor, it is highly recommended to attach a large buffer reservoir to the system e.g., instead of the 2-L vessel in Fig. 2 in Section I). The volume of this vessel should be sufficient about 40 L to contain all of the gas at room temperature and at a pressure of 2 bar. The vessel should be pressure-tested and resistant to fluorine [e.g., an empty fluorine gas cylinder would be the most appropriate) filled with fluorine to 400 mbar (vapor pressure of fluorine at — 196°C). The buffer reservoir should be opened to the reactor immediately after condensation of fluorine in the reactor. After the synthesis is finished and excess fluorine distilled off, the buffer reservoir should be closed again. 

Instead of the buffer reservoir a proper vacuumtight pressure-reliff valve could be installed onto a vacuum line, which opens automatically at just above atmospheric pressure and is, of course, vented to a proper hood. 

---

Naturally occurring krypton contains six stable isotopes. Seventeen other unstable isotopes are now recognized. The spectral lines of krypton are easily produced and some are very sharp. While krypton is generally thought of as a rare gas that normally does not combine with other elements to form compounds, it now appears that the existence of some krypton compounds is established. Krypton difluoride has been prepared in gram quantities and can be made by several methods. A higher fluoride of krypton and a salt of an oxyacid of krypton also have been... 

Krypton Difluoride. Krypton difluoride [13773-81 -4] KrF is a colorless crystalline solid which can be sublimed under vacuum at 0°C but is thermodynamically unstable and slowly decomposes to the elements at ambient temperatures (Table 1). It can, however, be stored for indefinite periods of time at —78° C. The KrF molecule has been shown, like XeF2, to be linear in the gas phase, in the sofld state, and in solution. The standard enthalpy of... 

Krypton difluoride cannot be synthesized by the standard high pressure-high temperature means used to prepare xenon fluorides because of the low thermal stabitity of KrF. There are three low temperature methods which have proven practical for the preparation of gram and greater amounts of KrF (141—143). Radon fluoride is most conveniently prepared by reaction of radon gas with a tiquid halogen fluoride (CIE, CIE, CIE, BrE, or lE ) at room temperature (144,145). 

Krypton difluoride is a fluorinating agent some 50 kJ/mol more powerful than fluorine itself. It forms adducts, salts of FKr+, with high valency fluorides such as AsF5 and SbF5, these react explosively with organic compounds. 

Radon difluoride is quantitatively reduced to elemental radon by water in a reaction which is analogous to the reactions of krypton difluoride and xenon difluoride with water. Complex salts of radon also hydrolyze in this fashion. 

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. 

Kroll process, 13 84-85 15 337 17 140 in titanium manufacture, 24 851-853 Kroll zirconium reduction process, 26 631 KRW gasifier, 6 797-798, 828 Krypton (Kr), 17 344 commercial, 17 368t complex salts of, 17 333-334 doubly ionized, 14 685 hydroquinone clathrate of, 14 183 in light sources, 17 371-372 from nuclear power plants, 17 362 physical properties of, 17 350 Krypton-85, 17 375, 376 Krypton compounds, 17 333-334 Krypton derivatives, 17 334 Krypton difluoride, 17 333, 336 uses for, 17 336... 

We now have three substances remaining methane, CH4, methyl fluoride, CH3F, and krypton difluoride, KrF2. We also have two types of intermolecular force remaining dipole-dipole forces and London forces. In order to match these substances and forces we must know which of the substances are polar and which are nonpolar. Polar substances utilize dipole-dipole forces, while nonpolar substances utilize London forces. To determine the polarity of each substance, we must draw a Lewis structure for the substance (Chapter 9) and use valence-shell electron pair repulsion (VSEPR) (Chapter 10). The Lewis structures for these substances are ... 

The krypton atom in krypton difluoride does not obey the octet rule. The presence of five pair around the krypton leads to a trigonal bipyramidal electron-group geometry. The presence of three lone pairs and two bonding pairs around the krypton makes the molecule linear. The two krypton-fluorine bonds are polar covalent. However, in a linear molecule, the bond polarities pull directly against each other and cancel. Cancelled bond polarities make the molecule nonpolar. The strongest intermolecular force in the nonpolar krypton difluoride is London force. 

Ammonium fluoride, NH4F, Krypton difluoride, KrF2, Sodium chloride, NaCl,... 

Very few are known, all may be seen as derived from FKr+. All are thermodynamically unstable and energetic fluorinating agents. Listed are Fluorohydrocyanokrypton hexafluoroarsenate, 0367 Fluorokrypton hexafluoroarsenate, 0096 Krypton difluoride, 4313 See also xenon compounds... 

Hydrogen bromide, 0247 Hydrogen chloride, 3993 Hydrogen fluoride, 4294 Krypton difluoride, 4313... 

Krypton difluoride, 4313 Potassium hexaoxoxenonate-xenon trioxide, 4674 Tetrafluoroammonium hexafluoroxenate, 4386 Xenon difluoride dioxide, 4322 Xenon difluoride oxide, 4319 Xenon difluoride, 4332 Xenon hexafluoride, 4377 Xenon tetrafluoride, 4353 Xenon tetrafluoride oxide, 4346 Xenon tetraoxide, 4863 Xenon trioxide, 4857 Xenon(II) fluoride methanesulfonate, 0443 Xenon(II) fluoride perchlorate, 3977 Xenon(II) fluoride trifluoroacetate, 0634 Xenon(II) fluoride trifluoromethanesulfonate, 0356 Xenon(IV) hydroxide, 4533 Xenon(II) pentafluoroorthoselenate, 4382 Xenon(II) pentafluoroorthotellurate, 4383 Xenon(II) perchlorate, 4110 See Other NON-METAL HALIDES, NON-METAL OXIDES... 

Krypton is a rather dense, tasteless, colorless, odorless gas. Its critical temperature is between that of oxygen and carbon dioxide. It is extracted during fractional distillation of liquid oxygen at a temperature of about -63.8°C. At one time it was thought that krypton, as well as the other noble gases, were completely inert. However, in 1967 scientists were able to combine fluorine with krypton at low temperatures to form the compound krypton difluoride (KrFj). In this case krypton has a valence of 2. 

Krypton is an inert gas element. Its closed-shell, stable octet electron configuration allows zero reactivity with practically any substance. Only a few types of compounds, complexes, and clathrates have been synthesized, mostly with fluorine, the most electronegative element. The most notable is krypton difluoride, KrF2 [13773-81-4], which also forms complex salts such as Kr2F3+AsFe [52721-23-0] and KrF+PtFF [52707-25-2]. These compounds are unstable at ambient conditions. Krypton also forms clathrates with phenol and hydroquinone. Such interstitial substances are thermodynamicahy unstable and have irregular stoichiometric compositions (See Argon clathrates). 

Krypton difluoride is used as a powerful oxidizing agent to oxidize halogen fluorides and gold. 

Krypton difluoride forms complexes with fluorides of many metals, such as arsenic, antimony, tantalum, niobium, gold, and platinum. 

Krypton difluoride decomposes into its elements at ambient temperatures. 

Elemental composition Kr 68.80%, F 31.20%. Krypton difluoride may be analyzed by GC/MS under cryogenic conditions following its decomposition into its gaseous elements. 

See Krypton difluoride Arsenic pentafluoride See other NON-METAL HALIDES... 

---