Synthesis and crystal structure of ammonium cis-dioxo dibenzilato tungstate(VI) dihydrate

A mononuclear tungsten-benzilate, (NH4)(2)[WO2(Ph2COCOO)(2)] 2H(2)O was obtained by the reaction of ammonium tungstate(VI) with excess benzilic acid in ethanol solution at pH 5similar to6. The title compound crystallizes in monoclinic system, space group P2(1)/n with a = 8.1078(5), b = 25.797(2), c = 13.6815(8) Angstrom, beta = 91.001(1)degrees, V = 2861.1(3) Angstrom(3), D-c = 1.719 g/cm(3), F(000) = 1472, C28H32N2O10W, M-r = 740.41, mu(MoKalpha) = 4.097 mm(-1) and Z = 4. The full-matrix least-squares refinement resulted in R = 0.033 and Rw = 0.068 for 3974 observed reflections with I >2sigma(1). The tungsten atom is six-coordinated by two cis-oxo groups and two bidentate benzilate ligands through deprotonated alpha-alkoxyl and alpha-carboxyl groups, forming a stable five-membered chelate ring. The compound has a distorted octahedral geometry, which is mainly attributable to the bulky ligand-ligand repulsions.