Xe3OF3 +, a Precursor to a Noble-Gas Nitrate; Syntheses and Structural Characterizations of FXeONO2, XeF2·HNO3, and XeF2·N2O4

Xenon fluoride nitrate has been synthesized by reaction of NO(2)F with [FXeOXeFXeF][AsF(6)] at -50 °C. It was characterized in SO(2)ClF and CH(3)CN solutions by low-temperature (14)N, (19)F, and (129)Xe NMR spectroscopy and in the solid state by low-temperature Raman spectroscopy (-160 °C) and single-crystal X-ray diffraction (-173 °C). The reactions were carried out using natural abundance and (18)O-enriched [FXeOXeFXeF][AsF(6)] and (15)NO(2)F to aid in the vibrational assignments of FXeONO(2) and to establish the likely reaction pathway. Raman spectroscopy showed that FXe(16)ON((16)O(18)O) was formed, along with XeF(2) and [NO(2)][AsF(6)], when an excess of N(16)O(2)F reacted with [FXe(18)OXeFXeF][AsF(6)]. A reaction mechanism consistent with these findings is discussed. The crystal structure consists of well-separated FXeONO(2) molecules which display no significant intermolecular interactions, providing geometric parameters that are in good agreement with the gas-phase values determined from quantum-chemical calculations. Decomposition of solid FXeONO(2) is proposed to occur by three reaction pathways to give XeF(2), Xe, O(2), N(2)O(5), N(2)O(4), and NO(2)F. Attempts to synthesize FXeONO(2) and Xe(ONO(2))(2) by reaction of XeF(2) with HNO(3) in SO(2)ClF solution below -30 °C led to XeF(2)·HNO(3). The structure of XeF(2)·HNO(3) includes a hydrogen bond between HNO(3) and a fluorine atom of XeF(2), as well as an interaction between the xenon atom and an oxygen atom of HNO(3), leading to a crystal lattice comprised of layered sheets. A molecular addition compound between XeF(2) and N(2)O(4) crystallized from liquid N(2)O(4) below 0 °C. The crystal structure of XeF(2)·N(2)O(4) displayed weak interactions between the xenon atom of XeF(2) and the oxygen atoms of N(2)O(4). Quantum-chemical calculations have been used to assign the vibrational spectra of FXeONO(2), XeF(2)·HNO(3), and XeF(2)·N(2)O(4) and to better understand the nature of the interactions of HNO(3) and N(2)O(4) with XeF(2). The synthesis of [XeONO(2)][AsF(6)] was attempted by the reaction of FXeONO(2) with excess liquid AsF(5) between -78 and -50 °C, but resulted in slow formation of [NO(2)][AsF(6)], Xe, and O(2). Thermodynamic calculations show that the pathways to [XeONO(2)][AsF(6)] formation and decomposition are exothermic and spontaneous under standard conditions and at -78 °C.