Ab initio structure determination of new mixed zirconium hydroxide nitrates ZrM(OH)(2)(NO3)(3) (M = K, Rb) from X-ray powder diffraction data

Two new mixed zirconium hydroxide nitrates ZrM(OH)(2)(NO3)(3) (M = K, Rb) h ave been synthesized through a wet chemical process. The two crystal struct ures have been solved ab initio from powder diffraction data collected with conventional monochromatic X-rays, ZrK(OH)(2)(NO3)(3) crystallizes with a monoclinic symmetry [a = 16.569(3) Angstrom, b = 5.791(1) Angstrom, c = 9.8 13(2) Angstrom, beta = 90.17(2)degrees, P2(1)/n, Z = 4] and ZrRb(OH)(2)(NO3 )(3) with an orthorhombic symmetry [a 10.126(3) Angstrom, b = 16.492(3) Ang strom, c = 5.855(2) Angstrom, Pbcn, Z = 4], The heavy atoms have been locat ed from an interpretation of Patterson functions. The coordinates of the re maining light atoms have been determined from successive three-dimensional Fourier maps. The final Rietveld refinement indicators were R-F = 0.042, R- p = 0.077 (M = K) and R-F = 0.064, R-p = 0.115 (M = Rb), Like the structure s of alpha-Zr(OH)(2)(NO3)(2). 1.65H(2)O and beta-Zr(OH)(2)(NO3)(2). H2O, th e structures of the mixed basic zirconium nitrates are built from edge-shar ing ZrO8 polyhedra to form infinite neutral zigzag chains of chemical compo sition [Zr(OH)(4/2)(NO3)(2)](n). The main difference with respect to the hy drated phases is the nature of the cohesion in the structures based on ioni c contacts involving intercalated K+ or Rb+ and NO; species in the mixed co mpounds and on a complex hydrogen-bonding network in the hydrated phases. T he crystal chemistry of the zirconium hydroxide nitrates is discussed and t hree structure types are identified. (C) 2000 Academic Press.