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 compositi on [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 str ucture 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 te trahedrally 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 dis tances in [HgBr4](2-) anion are 2.614(2) Angstrom in 1 and 2.622(2) An gstrom in 2. The crystal packing patterns of the isostructural cluster s 1 and 2 involve the three-dimensional hydrogen bond network; the cry stal line water molecules act as donors of hydrogen to the bromine ato ms of the cluster and [HgBr4](2-) units, whereas the coordinated water molecules form hydrogen bonds to the crystalline water molecules. [Nb 6Br12(H2O)(6)][HgBr4] . 12 H2O is diamagnetic and semiconducting with the activation energy, E-a = 0.20 eV.