AB-INITIO CRYSTAL-STRUCTURE DETERMINATION OF VO(H2PO2)2.H2O FROM X-RAY AND NEUTRON POWDER DIFFRACTION DATA - A MONODIMENSIONAL VANADIUM(IV)HYPOPHOSPHITE

The oxovanadium(IV) bis(hypophosphite) hydrate structure is determined ab initio from X-ray and neutron powder diffraction data and refined by using the Rietveld method. Samples may present quite different cell parameters, according to the synthesis conditions, although they are described using the same space group (C2/c; Z = 4) and basically the s ame structure. Extreme cell parameters values at 25-degrees-C: a = 12. 046(3) angstrom, b = 8.147(1) angstrom, c = 7.548(2) angstrom, beta = 121.83(2)degrees; a = 12.262 (8) angstrom, b = 8.069(2) angstrom, c = 7.702(5) angstrom, beta = 123.34(5)degrees. The structure consists of VO6 octahedra linked throught bis(mu-hypophosphite-O,O') bridges, givi ng rise to isolated chains running along the [101BAR] direction. The o nly connection between chains is due to hydrogen bonding involving the coordinated water molecule and one oxygen atom of the H2PO2 group. It is suggested that differences among samples are related to additional uncoordinated water molecules randomly inserted between chains (not l ocated). Thermal, IR spectroscopy, and magnetic studies have been perf ormed. X-ray induced amorphization has been followed by powder diffrac tion and IR spectroscopy.