Thermal behavior of zinc phenylphosphonate and structure determination of γ-Zn2P2O7 from X-ray powder diffraction data

The thermal behavior of zinc phenylphosphonate has been studied by temperature-dependent,X-ray powder diffraction and thermo-gravimetry in the temperature range 19-600 degrees C. The different phases occurring during the decomposition have been identified, i.e., the anhydrous phase and the three successive polymorphic varieties of Zn2P2O7. The first one is amorphous, delta-Zn2P2O7 is poorly crystalline, and gamma-Zn2P2O7 is a metastable phase. The last transforms into the beta variety at higher temperature. The crystal structure of gamma-Zn2P2O7 has been solved ab initio from powder diffraction data collected with conventional monochromatic Xrays. The symmetry is orthorhombic with the cell dimensions a 4.9504(5) Angstrom, b = 13.335(2) Angstrom, c = 16.482(3) Angstrom, space group Pbcm, Z = 8. The structure consists of infinite corrugated chains of ZnO5 trigonal bipyramids, running along [001]. These chains are linked together by P2O7 groups in the two other directions. The P2O74- anions display low angles and an eclipsed conformation, contrary to the alpha and beta phases, (C) 1998 Academic Press.