Ab initio structure determination of Zr(OH)₂SO₄.3H₂O using the conventional monochromatic X-ray powder diffraction

The structure of Zr(OH)₂SO₄.3H₂O has been determined ab initio by conventional powder diffractometry using monochromatic X-rays. The pattern was indexed using the successive-dichotomy method yielding cell dimensions a = 8.3645 (4), b = 15.1694 (9), c = 5.4427 (3) Å, and β = 103.145 (5)°. The space group is P2₁/c with Z = 2. 519 integrated intensities were extracted by whole-pattern fitting and these were used to calculate the heavy-atom positions by the Patterson method. Successive Fourier syntheses located the nine O atoms. Rietveld refinement was carried out over an angular range of 15 to 135°(2θ) and this converged with R_F = 0.030, R_B = 0.066, R_p = 0.085 and R_wp = 0.109. The structure consists of zigzag chains in the direction of [001] formed by edge-sharing eightfold-coordinated zirconium polyhedra in the shape of a bicapped trigonal prism. Sulfate tetrahedra bridge within chains whilst a network of hydrogen bonding stabilizes interchain interactions to form `corrugated sheets' parallel to the (100) plane; between these sheets lie `free' water molecules that do not take part in the polyhedra but do play a major role in the hydrogen-bonding network. The ICDD Powder Diffraction File No. is 44–1493.