Synthesis, spectroscopic properties and structural characterization of sodium potassium citrato oxotungstate(VI) dimer

The sodium-potassium citrate oxotungstate(VI) dimer, Na4K2[W2O5-(cit)(2)]. 11H(2)O (H(4)cit = citric acid) was obtained by the reaction of sodium tung state (VI) and excess potassium citrate monobasic (KH(3)cit) in neutral sol ution. The crystal data for the title compound: monoclinic, C12H30K2Na4W2O3 0, M-r = 1192. 21, space group P2(1)/n, a = 17.427(4), b = 10.022(2), c = 1 8.631(3) Angstrom, beta = 92.62(1)degrees, V = 3252 (2) Angstrom(3), Z = 4, D-c = 2.435 g/cm(3), mu(MoK alpha) = 76.38 cm(-1), F (000) = 2288. The str ucture was refined to R = 0.0434 for 6327 independent observed reflections with I>3 sigma(I). The complex anion contains a quasi-centrosymmetric (O2W) O-b(WO2) core with a bent bridging oxo group [W-O-b-W 175. 0(4)degrees]. Ea ch citrate as tridentate ligand coordinates to a tungsten atom through the alkoxy, alpha-carboxyl, and one beta-carboxyl group, while the other P-carb oxyl group remains uncoordinated. Principal dimensions are: W-O-b 1. 883(6) Angstrom, (W = O-t)av 1.715(6) Angstrom, W-O (alkoxy) 1.959 (6) Angstrom, W-O (alpha-carboxy) 2. 176(6) Angstrom and W-O (beta-carboxy) 2. 231(6) Ang strom. The tungsten atom is located in a distorted-octahedron environment.