Structure And Characterization Of A Novel Heteropolyoxoanion [{Na-2 (H2o)(3)}Ni (H2o)Voas4w40o140](21-)

A novel large polyoxometalate (NH4)(21)[{Na-2(H2O)(3)}Ni(H2O)VOAs4W40O140] . 53H(2)O was synthesized by the reaction of Na-27[ NaAs4W40O140] . 60H(2)O with NiCl2 . 6H(2)O, NaVO3 . 4H(2)O and NH4Cl in pH = 4. 5 aqueous solution. Its structure was determined by single crystal X-ray diffraction. Crystal data for the titled compound are: orthogonal system, Pmmn space group, a = 2.3305(14) nm, b = 2.9467(19) nm, c = 1.2671(16) nm, V = 8.701 (9) nm(3), Z = 2, D-c = 4. 378 g/cm(3), p = 27.372 mm(-1), R-1 = 0.0596, wR(2) = 0.1056 [I > 2sigma(I)]. The opposite two of four S2 sites of the big cyclic ligand [As4W40O140](28-) are disorderly occupied by one V5+ and one Ni2+ with the probability that each transition metal ion occupies the same S2 site being 50%, and the other two S2 sites are occupied by two Na+ which are bridged by a water molecule. IR spectra, TG and magnetic properties of the compound were also discussed.