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

Pr(5)(BO(4))(3−x)(BO(3))(x)(F,OH)(2.67)O(0.28) (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(3)/m) and shows complex anion disorder along the 6(3) screw axis and occupation of distorted octahedra, as well as almost trigonal planar sites, by oxygen and fluorine atoms. Furthermore, a distinct BO(4)/(BO(3)+F) group disorder is found; 46 % of the sites being occupied by BO(4) groups and 54 % by BO(3) 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(5)(BO(4))(3−x)(BO(3))(x)(F,OH)(2.67)O(0.28) (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.