The Crystallization of Extended Niobium-Cluster Framework Compounds: A Novel Approach Using Ionic Liquids

A new class of framework compounds with niobium mixed halide/pseudohalide cluster units and Cu-I ions is explored. The title duster compound [BMIm](2)[Nb6Cl12-(NCS)(6){Cu(CH3CN)}(2)]center dot 2CH(3)CN (1) and its one-electron oxidized analogue [BMIm](2)[Nb6Cl12(NCS)(6){Cu(CH3CN)}(2)] (2) are built up of [Nb6Cl12(NCS)(6)(a)](n-) units, with n = 3 or 4, and Cu-I complex cations. Thiophilic interactions between the Cu-I atoms and the S atoms of the isothiocyanato ligands, which are N-bonded to the cluster unit, lead to new extended three-dimensional cluster networks. The synthesis of compounds 1 and 2 is described, and their characterization by single-crystal and powder X-ray diffraction, IR spectroscopy, and elemental analyses. Both compounds crystallize monoclinic space group P2(1)/n with Z = 2; 1: a = 12.3431(3) angstrom, b = 12.9544(3) angstrom, c = 19.3934(5) angstrom, beta = 91.944(1)degrees, and V = 3099.2(2) angstrom(3); 2: a = 8.8591(4) angstrom, b = 13.9346(5) angstrom, c = 19.4040(8) angstrom, beta = 90.568(2)degrees, and V = 2395.3(2) angstrom(3). The use of the viscous ionic liquid [BMIm] [PF6] as crystallization medium and as cation source is the key feature to obtain the title cluster framework compounds in single-crystalline quality.