Crystal structure and Rietveld refinement using X-ray powder diffraction data of two potassium and ammonium-samarium condensed phosphates: KSmHP3O10 and NH4SmHP3O10

The structure of KSmHP3O10 has been determined by a single crystal X-ray an alysis and has been solved by using 3299 independent reflections with a fin al R value of 0.019. This condensed phosphate crystallizes in the triclinic space group P (1) over bar with unit cell parameters a = 6.956(2) Angstrom , b = 7.711(1) Angstrom, c = 8.570(2) Angstrom, alpha = 106.64(2)degrees, b eta = 106.63(2)degrees, gamma = 82.47(3)degrees, V = 421.4(2) Angstrom(3) a nd D-cal = 3.494 g cm(-3) for Z = 2. The structure of NH4SmHP3O10-ammonium samarium hydrogen triphosphate has been determined from conventional X-ray powder diffraction data using the Rietveld method, with the isostructural c ompounds KSmHP3O10 and NH4BiHP3O10 as starting model. The cell is triclinic (space group P (1) over bar Z = 2), with a = 6.9782(2) Angstrom, b = 7.757 8(2) Angstrom, c = 8.6230(3) Angstrom, alpha = 106.354(2)degrees, P = 105.9 61(2)degrees, gamma = 82.471(2)degrees, V = 429.93(7) Angstrom(3) and D-cal = 3.26 g cm(-3). Refinement of 83 parameters by the Rietveld method, using 2547 reflections, leads to cR(wp) = 0.152, cR(p) = 0.117 and R-B = 0.0437. The unit cell contains two P3O105- groups linked with OH ... O hydrogen bo nding along the c axis. The samarium atoms in a eightfold co-ordination bui ld infinite chains of edge-sharing SmO8 polyhedra running parallel to the a axis. The cations in this structure (K+ and NH4+) an located between chain s formed of (HP3O104-) to form two dimensional zig zag sheets. The two poly hedra (SmO8 and KO10 or (NH4)O-10) are connected by P3O105- to built a thre e dimensional network. (C) 2000 Elsevier Science Ltd. All rights reserved.