STRUCTURE OF A NOVEL LAYERED ZIRCONIUM DIPHOSPHONATE COMPOUND - ZR-2(O3PCH2CH2-VIOLOGEN-CH2CH2PO3)F-6.2H2O

We report the structure of a crystalline zirconium bisphosphonate compound, solved ab initio from X-ray powder diffraction data and refined by the Rietveld method. The structure of this material is unlike any other reported tetravalent metal phosphonate. The formula of this crystalline compound is Zr-2(O3PCH2CH2-viologen-CH2CH2PO3)F6-nCln.2H(2)O (n less than or equal to 2.5), which was confirmed by electron probe microanalysis of single (5-30 mu m) crystals. This compound crystallizes in the space group P2(1)/c, a = 6.6679(2) Angstrom, b = 12.5871(3) Angstrom, c = 13.5837(3) Angstrom, beta = 101.739(3)degrees, Z = 2. The structure is composed of layers stacked perpendicular to the b direction. The individual lamellae consist of double chains of ZrF3O3 octahedra, bridged by phosphono-viologen groups. In this structure the zirconium centers are formally negatively charged and stack above and below the viologen groups of an adjacent layer. Elemental analyses of the title compound prepared under different conditions as well as a mixed phosphate/phosphonate [Zr(O3POH)(O3PCH2CH2(bipyridinium)CH2CH2PO3)(0.5-) Cl] suggest that minimization of the electrostatic repulsion of adjacent viologen groups is important in determining the structures of these materials.