F5SN(H)Xe+;: a rare example of xenon bonded to Sp3-hybridized nitrogen;: Synthesis and structural characterization of [F5SN(H)Xe][AsF6]

The salt [F5SN(H)Xe][AsF6] has been synthesized by the reaction of [F5SNH3][AsF6] with XeF2 in anhydrous HF (aHF) and BrF5 solvents and by solvolysis of [F3S equivalent to NXeF][AsF6] in aHF. Both F5SN(H)Xe+ and F5SNH3+ have been characterized by Xe-129, F-19, and H-1 NMR spectroscopy in aHF (-20 degrees C) and BrF5 (supercooled to -70 degrees C). The yellow [F5SN(H)Xe][AsF6] salt was crystallized from aHF at -20 degrees C and characterized by Raman spectroscopy at -45 degrees C and by single-crystal X-ray diffraction at -173 degrees C. The Xe-N bond length. (2,069(4) angstrom) of the F5SN(H)Xe+ cation is among the shortest Xe-N bonds presently known. The cation interacts with the AsF6- anion by means of a Xe --- F-As bridge in which the Xe --- F distance (2.634(3) angstrom) is significantly. less than the sum of the Xe and F van der Waals radii (3.63 angstrom) and the AsF6- anion is significantly distorted from Oh symmetry. The F-19 and Xe-129 NMR spectra established that the [F5SN(H)Xe][AsF6] ion pair is dissociated in aHF and BrF5 solvents. The F5SN(H)Xe+ cation decomposes by HF solvolysis to F5SNH3+ and XeF2, followed by solvolysis of F5SNH3+ to SF6 and NH4+center dot angstrom minor decomposition channel leads to small quantities of F5SNF2. The colorless salt, [F5SNH3][AsF6], was synthesized by the HF solvolysis of F3S equivalent to NAsF5 and was crystallized from aHF at -35 degrees C. The salt was characterized by Raman spectroscopy at -160 degrees C, and its unit cell parameters were determined by low-temperature X-ray diffraction. Electronic structure calculations using MP2 and DFT methods were used to calculate the gas-phase geometries, charges, bond orders, and valencies as well as the vibrational frequencies of F5SNH3+ and F5SN(H)Xe+ and to aid in the assignment of their experimental vibrational frequencies. In addition to F5TeN(H)Xe+, the F5SN(H)Xe+ cation provides the only other example of xenon bonded to an Sp(3)-hybridized nitrogen center that has been synthesized and structurally characterized. These cations represent the strongest Xe-N bonds that are presently known.