William W. Wilson

Lewis acid behavior of xenon (II) cations and the synthesis and characterization of fluoro- and oxofluoro-xenon anions at the limits of coordination.

Abstract By taking advantage of the Lewis acid properties of the XeF+ and KrF+ cations, it has been possible to prepare a diverse range of noble-gas adduct cations; Fue5f8Xeue5f8L+, Fue5f8Krue5f8Nue5fcCH+ and Fue5f8Krue5f8Nue5fcCRF+ (L ue5fb HCue5fcN, RCue5fcN, RFCue5fcN, C5F5N, sue5f8C3F3N3). The adduct salts have stabilities which range from explosive at −60 °C for Fue5f8Krue5f8Nue5fcCH+AsF6− (the first example of a Krue5f8N bond), to stable at room temperature for sue5f8C3F3N2Nue5f8Xeue5f8F+AsF6− and have been characterized by multi-NMR spectroscopy and Raman spectroscopy. We have recently extended this work to the related noble-gas cations XeOTeF5+ and XeOSeF5+, to yield the first examples of Oue5f8Xeue5f8N linkages, and to the inorganic base F3Sue5fcN. The adduct cation Fue5f8Xeue5f8Nue5fcSF3+ undergoes successive additions of HF to the Nue5fcS bond in anhydrous HF to give the adduct cations Fue5f8Xeue5f8N(H)ue5fbSF4+ and Fue5f8Xeue5f8N(H2)ue5f8SF5+. The Fue5f8Xeue5f8N(H2)ue5f8TeF5+ cation has also been synthesized. The study of fluoro-anions having coordination numbers higher than six and, in particular, those involving at the same time free valence electron pairs, have recently received considerable interest. To a large extent, these studies have been greatly facilitated by the realization that anhydrous N(CH3)4+F− is an excellent reagent for the preparation of novel, high-oxidation state complex fluoride or oxofluoride anions. We have recently synthesized (CH3)4N+XeF5− by the reaction of stoichiometric amounts of XeF4 and N(CH3)4+F− in dry CH3CN. The salt was fully characterized by Raman spectroscopy, 19F and 129Xe NMR spectroscopy and X-ray crystallography. The XeF5− anion has a pentagonal planar (D5h) structure with five equivalent fluorines and is of considreable significance as it represents the first example of an AX5E2 (E = valence electron lone pair) system. The syntheses and structural characterization of other high-coordination number hypervalent fluoro- and oxofluoro- anions of xenon will also be discussed, i.e., XeF5O−, XeF7−, XeOF3−, XeO2F3−.