COMPLEXATION BETWEEN TUNGSTEN(VI) AND CITRATE - THE CRYSTAL AND MOLECULAR-STRUCTURE OF A DINUCLEAR COMPLEX, NA6[W2O5(CIT)2].10H2O

The crystals of the title compound are monoclinic, space group P2(1)/c with a = 9.014(l), b = 9.8668(5) c = 17.5000(3) angstrom, beta = 91.50(1)-degrees, V = 1556(1) angstrom3. The structure was determined by Patterson methods and refined by least squares to R = 0.038 for 3829 observed reflections and 224 parameters. There are two tungsten dimers in the unit cell, each formed by a bridging oxygen lying on a center of symmetry. Each tungsten has five more coordination sites; two occupied by terminal oxygens and the remaining three by citrate oxygens. Waters of crystallization are distributed throughout the cell and together with various of the anion oxygens, make the sodium cations either five-or six-coordinate.