π-Hole aerogen bonding interactions

In this manuscript we combine high level ab initio calculations (RI-MP2/aug-cc-pVTZ) and the analysis of several crystal structures to demonstrate the existence of π-hole aerogen bonding interactions in Xe(iv) compounds. The ability of XeF4 and Xe(OMe)4 to interact with electron rich molecules is rationalized using several computational tools, including molecular electrostatic potential surfaces, energetic and geometric features of the complexes and "atoms in molecules" (AIM) and Natural Bond Orbital (NBO) analyses. We have found support for the π-hole interaction involving the xenon atom from the solid state architecture of several X-ray structures retrieved from the crystal structural depot. Particularly, π-hole aerogen bonding interactions are quite common in the solid state of Xe(IV) compounds.

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.

XeOF2, F2OXeN identical with CCH3, and XeOF2.nHF: rare examples of Xe(IV) oxide fluorides

The syntheses of XeOF2, F2OXeNCCH3, and XeOF2.nHF and their structural characterizations are described in this study. All three compounds are explosive at temperatures approaching 0 degrees C. Although XeOF2 had been previously reported, it had not been isolated as a pure compound. Xenon oxide difluoride has now been characterized in CH3CN solution by 19F, 17O, and 129Xe NMR spectroscopy. The solid-state Raman spectra of XeOF2, F2OXeNCCH3, and XeOF2.nHF have been assigned with the aid of 16O/18O and 1H/2H enrichment studies and electronic structure calculations. In the solid state, the structure of XeOF2 is a weakly associated, planar monomer, ruling out previous speculation that it may possess a polymeric chain structure. The geometry of XeOF2 is consistent with a trigonal bipyramidal, AX2YE2, VSEPR arrangement that gives rise to a T-shaped geometry in which the two free valence electron lone pairs and Xe-O bond domain occupy the trigonal plane and the Xe-F bond domains are trans to one another and perpendicular to the trigonal plane. Quantum mechanical calculations and the Raman spectra of XeOF2.nHF indicate that the structure likely contains a single HF molecule that is H-bonded to oxygen and also weakly F-coordinated to xenon. The low-temperature (-173 degrees C) X-ray crystal structure of F2OXeNCCH3 reveals a long Xe-N bond trans to the Xe-O bond and a geometrical arrangement about xenon in which the atoms directly bonded to xenon are coplanar and CH3CN acts as a fourth ligand in the equatorial plane. The two fluorine atoms are displaced away from the oxygen atom toward the Xe-N bond. The structure contains two sets of crystallographically distinct F2OXeNCCH3 molecules in which the bent Xe-N-C moiety lies either in or out of the XeOF2 plane. The geometry about xenon is consistent with an AX2YZE2 VSEPR arrangement of bond pairs and electron lone pairs and represents a rare example of a Xe(IV)-N bond.