Xenon difluoride

Xenon difluoride is a powerful fluorinating agent with the chemical formula XeF2, and one of the most stable xenon compounds. Like most covalent inorganic fluorides it is moisture-sensitive. It decomposes on contact with water vapor, but is otherwise stable in storage. Xenon difluoride is a dense, colourless crystalline solid. It has a nauseating odour and low vapor pressure. Xenon difluoride is a linear molecule with an Xe–F bond length of 197.73pm in the vapor stage, and 200 pm in the solid phase. The packing arrangement in solid XeF2 shows that the fluorine atoms of neighbouring molecules avoid the equatorial region of each XeF2 molecule. This agrees with the prediction of VSEPR theory, which predicts that there are 3 pairs of non-bonding electrons around the equatorial region of the xenon atom. At high pressures, novel, non-molecular forms of xenon difluoride can be obtained. Under a pressure of ~50 GPa, XeF2 transforms into a semiconductor consisting of XeF4 units linked in a two-dimensional structure, like graphite. At even higher pressures, above 70 GPa, it becomes metallic, forming a three-dimensional structure containing XeF8 units. However, a recent theoretical study has cast doubt on these experimental results. The Xe–F bonds are weak. XeF2 has a total bond energy of , with first and second bond energies of and , respectively. However, XeF2 is much more robust than KrF2, which has a total bond energy of only . Synthesis proceeds by the simple reaction: Xe + F2 → XeF2 The reaction needs heat, irradiation, or an electrical discharge. The product is a solid. It is purified by fractional distillation or selective condensation using a vacuum line. The first published report of XeF2 was in October 1962 by Chernick, et al. However, though published later, XeF2 was probably first created by Rudolf Hoppe at the University of Münster, Germany, in early 1962, by reacting fluorine and xenon gas mixtures in an electrical discharge.