Structural analysis of zirconium hydroxide nitrate monohydrates by X-ray powder diffraction

The crystal structures of alpha-Zr(OH)(2)(NO3)(2) . 1.65H(2)O and beta-Zr(OH)(2)(NO3)(2) . H2O were determined ab initio from laboratory X-ray powder diffraction data, The two zirconium hydroxide nitrates crystallize with triclinic unit cells (P (1) over bar) with the parameters: a=10.051(3)Angstrom, b=10.357(3)Angstrom, c=8.131(2)Angstrom, alpha=108.30(2)degrees, beta=112.02(2)degrees, gamma=79.75(3)degrees for the alpha phase, and a=9.180(3)Angstrom, b=10.465(4)Angstrom, c=8.076(2)Angstrom, alpha=109.58(3)degrees, beta=98.96(3)degrees, gamma=80.43(3)degrees for the beta phase, An interpretation of the Patterson functions led to the location of two independent Zr atoms for the alpha and beta forms, The light atom coordinates were determined from successive three-dimensional Fourier maps, The structure of alpha-Zr(OH)(2)(NO3)(2) . 1.65H(2)O is built from edge sharing ZrO8 trigonal dodecahedra, through double hydroxyl bridges, to form infinite neutral zigzag chains of chemical composition [Zr(OH)(4/2)(NO3)(2)](n), running along [011]. The 8-fold coordination of each Zr atom is completed by four oxygens from bidentate nitrate groups, They are involved in a complex hydrogen bonding network occurring between the chains via ''free'' water molecules, The loss of the weakly bonded water molecule leads to the beta form without collapse of the 1D framework of the precursor, In the beta variety, the 8-fold coordination is preserved for the two Zr atoms, However, the exact shapes of the polyhedra have not been precisely defined. (C) 1997 Academic Press.