Reactions of hexanuclear niobium and tantalum halide clusters with mercury(II) halides .1. Synthesis and structures of the semiconducting compounds [M6Br12(H2O)(6)][HgBr4]center dot 12H(2)O, M=Nb, Ta

A method for the preparation of new solvated clusters of the composition [M6Br12(H2O)(6)][HgBr2X2] . 12H(2)O (M = Nb, Ta; X = Cl, Br, I) is given. The cubic crystals of [Nb6Br12(H2O)(6)][HgBr4] . 12 H2O 1 and [Ta6Br12(H2O)(6)][HgBr4] . 12 H2O 2 were characterized by the X-ray structure analysis: 1: cubic, space group Fd(3) over bar m, a = 21.0072(6) Angstrom, Z = 8, R = 0.051 (R-w = 0.066); 2: cubic, space group Fd(3) over bar m, a = 20.9698(1) Angstrom, Z = 8, R = 0.038 (R-w = 0.050). 1 and 2 contain octahedral cluster cation [M6Br12(H2O)(6)](2+) and tetrahedrally arranged [HgBr4](2-) an ion. The M-M bond distances are 2.949(1) Angstrom for 1 and 2.9000(8) Angstrom for 2. The Hg-Br bond distances in [HgBr4](2-) anion are 2.614(2) Angstrom in 1 and 2.622(2) Angstrom in 2. The crystal packing patterns of the isostructural clusters 1 and 2 involve the three-dimensional hydrogen bond network; the crystal line water molecules act as donors of hydrogen to the bromine atoms of the cluster and [HgBr4](2-) units, whereas the coordinated water molecules form hydrogen bonds to the crystalline water molecules. [Nb6Br12(H2O)(6)][HgBr4] . 12 H2O is diamagnetic and semiconducting with the activation energy, E-a = 0.20 eV.