Abstract

Noble-gas reactivity was discovered in 1962 when Neil Bartlett showed that xenon gas was oxidized by PtF₆ to XePtF₆. Pursuant to his discovery, numerous xenon and krypton compounds were synthesized in macroscopic quantities. Among the noble-gas elements, xenon has the most extensive chemistry, and can possess formal oxidation states of 0, +½, +2, +4, +6 and +8 in its compounds by forming fluorides, oxides and oxide fluorides as well as derivatives in which xenon is bonded to polyatomic groups through oxygen, nitrogen and carbon. In addition, several compounds containing Xe-Au bonds and one compound containing an Xe-Xe bond are known. Other xenon-element bonds are known in the gas phase or in low-temperature matrices, which provide examples of Xe-H, Xe-Si, Xe-S, Xe-X (X = Cl, Br, I) and Xe-U bonds. Krypton chemistry is more limited. Only compounds with krypton in the +2 oxidation state are known, namely, KrF₂, salts of the KrF⁺ and Kr₂F₃⁺ cations, by analogy with xenon, Kr(OTeF₅)₂ and several species containing Kr-N bonds. Several gas-phase and matrix-isolated species in which krypton is bonded to carbon, hydrogen and halides other than fluorine are also known. Radon is believed to form RnF₂ and RnF⁺ by analogy with krypton and xenon. The only argon species that are known are the ArF⁺ cation, which has been observed in the gas phase, and HArF, which has been stabilized in a low-temperature argon matrix. To date, no argon, neon or helium compounds have been isolated in macroscopic amounts. Noble-gas compounds have been utilized as oxidizers and oxidative fluorinating agents in chemical syntheses.