Hydrothermal synthesis, single-crystal structure analysis, and solid-state NMR characterization of Zn-2(OH)(0.14(3))F-0.86(3)(PO4)

摘要

The zinc fluoro phosphate Zn2F(PO4) has been produced by hydrothermal synthesis employing hydrofluoric acid as a mineralizer in a H2O or D2O medium. A single-crystal X-ray synchrotron diffraction analysis of Zn2F(PO4) shows that the zinc fluoro phosphate is monoclinic, a = 9.690(l), b = 12.793(1), and c =11.972(1) Angstrom, beta = 108.265(1)degrees, space group P2(1)/c, No. 14, Z 16. Reflections hkl with k = 2n + 1 are weak but significant and the structure shows pseudosymmetry. Zn2F(PO4) has the wagnerite-type M2F(XO4) structure with four Zn atoms each coordinated to four 0 atoms and one F atom while four other Zn atoms are coordinated to four O atoms and two F atoms. A difference Fourier map, calculated from the single-crystal X-ray data, shows additional electron density close to the four fluorine atoms, indicating a possible partial substitution of F- by OH- ions. This is unambiguously confirmed by P-31-{H-1} cross-polarization magic-angle spinning (MAS) and by, H-1 H-2 MAS NMR spectroscopy. The narrow line width observed for the H-1 resonance and the unique set of H-2 quadrupole coupling parameters (obtained for the Zn2F(PO4) sample using D2O as medium) show that H-1/H-2 is present as OH(D) groups rather than as water of crystallization in the structure. Quantitative H-1 MAS NMR analysis shows that the composition of the sample is Zn-2(OH)(0.14(3))F-0.86(3)(PO4). The high-speed F-19 MAS NMR spectrum exhibits two resolved resonances with equal intensity, which are ascribed to an overlap of resonances from the four distinct fluorine sites in Zn-2(OH)(0.14(3))F-0.86(3)(PO4). (C) 2002 Elsevier Science (USA). [References: 37]