期刊
MINERALS
卷 11, 期 11, 页码 -出版社
MDPI
DOI: 10.3390/min11111156
关键词
lead; oxoarsenates; solid state synthesis; hydrothermal synthesis; crystal chemistry; apatite structure type; belovite structure type; crystal structure comparison
Single crystals of lead(II) oxoarsenates(V) were successfully grown and their crystal structures were compared through X-ray diffraction. It was also found that NaPb4(AsO4)(3) is the first lacunar apatite comprising only tetrahedral anions and adopting the belovite structure type.
Single-crystals of lead(II) oxoarsenates(V) were grown from the melt (Pb2As2O7), from solution (Pb(H2AsO4)(2) and Pb-5(AsO4)(3)OH), and under hydrothermal conditions (NaPb4(AsO4)(3)). Crystal structure refinements from single-crystal X-ray diffraction data revealed isotypism for both Pb2As2O7 and Pb(H2AsO4)(2) with the corresponding barium and phosphate phases. A quantitative comparison of the crystal structures showed a high similarity for the isotypic M2X2O7 structures (M = Pb, Ba; X = As, P), whereas for the M(H2XO4)(2) structures only the pair Pb(H2AsO4)(2) and Pb(H2PO4)(2) is similar, but not Ba(H2AsO4)(2). Pb-5(AsO4)(3)OH adopts the apatite structure type in space group P6(3)/m, with the hydroxyl group disordered around Wyckoff position 2 b (0, 0, 0) in the channels of the structure. NaPb4(AsO4)(3) represents a lacunar apatite with two of the three metal positions occupationally disordered by Pb and Na. In contrast to a previous X-ray powder study of NaPb4(AsO4)(3) that reported an apatite-type structure in space group P6(3)/m, the current single-crystal data clearly revealed a symmetry reduction to space group P3 over bar . Hence, NaPb4(AsO4)(3) is the first lacunar apatite that comprises only tetrahedral anions and adopts the belovite structure type.
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