SYNTHESIS OPTIMIZATION AND CRYSTAL-STRUCTURES OF LAYERED METAL(IV) HYDROGEN PHOSPHATES, ALPHA-M(HPO4)2-CENTER-DOT-H2O (M=TI,SN,PB)

The syntheses of three layered metal(IV) hydrogen phosphates with formula alpha-M(HPO4)(2).H2O (M = Ti, Sn, Pb) have been optimized to yield single phases of highly crystalline materials. The crystal structures of these compounds have been studied using X-ray powder diffraction data by the Rietveld method. These three hydrogen phosphates are isomorphous and belong to the alpha-Zr(HPO4)(2).H2O structure type. The unit cell parameters are as follows: M = Ti, a = 8.6403(2) Angstrom, b = 5.0093(1) Angstrom, c = 15.5097(4) Angstrom, beta = 101.324(2)degrees, space group P2(1)/n; M = Sn, a = 8.6115(3) Angstrom, b = 4.9643(5) Angstrom, c = 15.861(2) Angstrom, beta = 100.003(1)degrees, space group C2/c; M = Pb, a = 8.6238(4) Angstrom, b = 4.9870(2) Angstrom, c = 16.1250(6) Angstrom, beta = 100.615(3)degrees, space group P2(1)/n. The agreement factors obtained by Rietveld refinements, R(WP), ranged between 12.5 and 9%. Although the prototype of this series is alpha-ZrP, here we report that the volume of the unit cell of this compound is markedly larger than the volumes of the other studied members of the series. This is due to the presence of less corrugated layers in alpha-ZrP. IR and thermal studies of M(HPO4)(2).H2O (M = Ti, Sn, Zr, Pb) indicate the existence of a trend in the strength of the H-bonds that retain the hydration water in the interlayer region.