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Solid-State NMR Spectroscopic Study of Coordination Compounds of XeF2 with Metal Cations and the Crystal Structure of [Ba(XeF2)5][AsF6]2

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posted on 23.07.2007, 00:00 by Michael Gerken, Paul Hazendonk, Adriana Iuga, Jared Nieboer, Melita Tramšek, Evgeny Goreshnik, Boris Žemva, Shaohui Zheng, Jochen Autschbach
The coordination compounds [Mg(XeF2)2][AsF6]2, [Mg(XeF2)4][AsF6]2, [Ca(XeF2)2.5][AsF6]2, [Ba(XeF2)3][AsF6]2, and [Ba(XeF2)5][AsF6]2 were characterized by solid-state 19F and 129Xe magic-angle spinning NMR spectroscopy. The 19F and 129Xe NMR data of [Mg(XeF2)2][AsF6]2, [Mg(XeF2)4][AsF6]2, and [Ca(XeF2)2.5][AsF6]2 were correlated with the previously determined crystal structures. The isotropic 19F chemical shifts and 1J(129Xe−19F) coupling constants were used to distinguish the terminal and bridging coordination modes of XeF2. Chemical-shift and coupling-constant calculations for [Mg(XeF2)4][AsF6]2 confirmed the assignment of terminal and bridging chemical-shift and coupling-constant ranges. The NMR spectroscopic data of [Ba(XeF2)3][AsF6]2 and [Ba(XeF2)5][AsF6]2 indicate the absence of any terminal XeF2 ligands, which was verified for [Ba(XeF2)5][AsF6]2 by its X-ray crystal structure. The adduct [Ba(XeF2)5][AsF6]2 crystallizes in the space group Fmmm, with a = 11.6604(14) Å, b = 13.658(2) Å, c = 13.7802(17) Å, V = 2194.5(5) Å3 at −73 °C, Z = 4, and R = 0.0350 and contains two crystallographically independent bridging XeF2 molecules and one nonligating XeF2 molecule. The AsF6- anions in [Mg(XeF2)4][AsF6]2, [Ca(XeF2)2.5][AsF6]2, [Ba(XeF2)3][AsF6]2, and [Ba(XeF2)5][AsF6]2 were shown to be fluxional with the fluorines-on-arsenic being equivalent on the NMR time scale, emulating perfectly octahedral anion symmetry.