Niobium thiobromide, Nb3SBr7, with triangle Nb-3 cluster: Structure and bondingстатья
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Аннотация:The reaction of Nb, S, and Br-2 in a sealed quartz ampoule at 550 degrees C yielded Nb3SBr7. The structure of Nb3SBr7 determined by the single-crystal X-ray diffraction method (P3m1, a = 7.1012(6) Angstrom, c = 6.3040(9) Angstrom, V = 275.30(9) Angstrom(3), Z = 1, d(calc) = 5.248(2) g/cm(3), R = 0.0395, R(w) = 0.0392) consists of one-layer packing of {[Nb3SBr3]Br6/2Br3/3}(2) infinity layers. The molecular orbitals of the model anions [Nb3Br13](5-) and [Nb3SBr12](5-), Which involve the triangle Nb, cluster with the nearest ligand environment in the structures of Nb3Br8 and Nb3SBr7, respectively, were calculated by applying the extended Huckel method. The HOMO in [Nb3Br13](5-) has slightly metal-metal bonding character which is consistent with an Nb-Nb bond length increase from 2.88 Angstrom in a seven-electron Nb3Br8 to 2.896(1) Angstrom in a six-electron Nb3SBr7. The bonding schemes are in accordance with magnetic properties of Nb3Br8, which is paramagnetic, and Nb3SBr7, which is diamagnetic. (C) 1995 Academic Press, Inc.