A High-Pressure Praseodymium Fluoride Borate Linking Multiple Structural Features of Apatite-Type Compounds.

Author(s) Glätzle, M.; Pitscheider, A.; Oeckler, O.; Wurst, K.; Huppertz, H.
Journal Chemistry
Date Published 2019 Feb 01

Pr (BO ) (BO ) (F,OH) O (x≈1.6), a boron-containing fluoride-oxoapatite-like compound, was obtained by the application of high-pressure/high-temperature synthesis. It exhibits a superstructure of the apatite type with a tripled c lattice parameter (space group P6 /m) and shows complex anion disorder along the 6 screw axis and occupation of distorted octahedra, as well as almost trigonal planar sites, by oxygen and fluorine atoms. Furthermore, a distinct BO /(BO +F) group disorder is found; 46 % of the sites being occupied by BO groups and 54 % by BO groups, with a fluoride ion located near the missing oxygen atom. The rare earth cations in the 4f sites exhibit a specific distorted tricapped trigonal prismatic coordination with a mean metaprism twist angle of 21.3°. The crystal structure of Pr (BO ) (BO ) (F,OH) O (x≈1.6) shows much "flexibility" resulting in split and off-site positions of all other rare earth cations. The title compound therefore combines many structural features of apatite-like compounds, for example biologically highly-important carbonated apatites, shedding more light onto the complex structural chemistry of apatites.

DOI 10.1002/chem.201805092
ISSN 1521-3765
Citation Chemistry. 2019;25(7):17671772.

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