SYNTHESIS OF CIS-TETRABROMOBISPYRIDINEMOLYBDATES(III) AND THE CRYSTAL-STRUCTURE OF CIS-(NH4)[MOBR4PY2].1/3H2O (PY=PYRIDINE)

The reaction between (NH4)[MoBr5 . H2O] and pyridine in acetonitrile (CH3CN) at room temperature results in the mixture of cis- and trans-(pyH)[MoBr4py3] which can be separated on the basis of solubility. cis-M[MoBr4py2] . 1/3 H2O (M = NH4+, Rb+, Cs+), cis-(bipyH)[MoBr4py2] (bipy = 2,2'-bipyridil) and cis-(PPh4)[MoBr4py2], were prepared from cis(pyH)[MoBr4py2]. At the temperature of boiling acetonitrile irreversible cis to trans isomerisation takes place. Bromine oxydizes cis isomers at room temperature to trans-MoBr4py2. The compounds were characterised by chemical analysis, infrared, UV-VIS spectroscopy, conductivity measurements and powder diffraction. The crystal structure of cis-(NH4)[MoBrpy2] . 1/3 H2O has been determined: rhombohedral, R3c, (No. 161), a = 15.809(3) angstrom, alpha = 112.79(2)-degrees, Z = 6, D(C) = 2.29, D(O) = 2.27(3) g/cm3, V = 2 601(1) angstrom3, R1 = 0.046, R(W) = 0.068. Average Mo-Br and Mo-N(pyridine) distances within the anion are 2.58(2) and 2.20(2) angstrom. cis-Rb[MoBrpy2] . 1/3 H2O and cis-Cs[MoBr4PY2] . 1/3 H2O are isostructural with cis-(NH4)[MoBr4py2] . 1/3 H2O.