Syntheses and X-ray powder structures of two zinc propylenebis(phosphonates)

The crystal structures of two new zinc compounds of propylenebis(phosphonic acid) were determined ab initio from their powder diffraction data. These compounds were prepared by the reaction of zinc chloride with the phosphonic acid at different pH conditions. The compound, Zn(HO3PC3H6PO3H) (1), crystallizes in the monoclinic space group P2(1)/n with a = 18.167(3) Angstrom, b = 5.085(1) Angstrom, c = 8.658(1) Angstrom, beta = 93.630(2)degrees and Z = 4. The other compound, Zn-3[(HO3PC3H6PO3)(2)]. 2H(2)O (2), also crystallizes in the monoclinic symmetry but with space group C2/c. Crystal data: a = 20.5853(4) Angstrom, b = 5.0472(1) Angstrom, c = 18.0140(4) Angstrom, b = 97.226(1)degrees, Z = 4. The intensities of the structure factors were extracted from the powder patterns using the Le Bail method and were used for structure solution by direct methods. The structures were then completed by Fourier methods and refined by Rietveld methods. In structure 1, the metal atoms are tetrahedrally coordinated by four oxygen atoms, two each from two independent phosphonates. The remaining oxygen atom of both phosphonate groups is protonated and is involved only in hydrogen bonding. The metal phosphonate interactions lead to double chains that are linked to each other through the organic linkages, leading to two-dimensional slabs or sheets. These slabs are connected through hydrogen bonds, thus forming a loosely held three-dimensional metal phosphonate network. In the case of compound 2, only one of the phosphonate groups is protonated, while the other is completely deprotonated. In this structure, there are two independent metal atoms that are tetrahedrally coordinated. One is coordinated completely by phosphonate oxygen atoms, while the coordination of the other zinc atom is by two phosphonate oxygens and two water oxygen atoms. The structure is interesting in that it consists of large one-dimensional pores whose dimensions are determined by the length of the organic moiety. Thus, this structure provides a starting point for a broad exploration of a new class of metal phosphonate porous materials with varied pore sizes.