RE4B4O11F2 (RE = Pr, Nd): Two New Rare-earth Fluoride Borates Isotypic to Gd4B4O11F2

Dedicated to Professor Heinrich Nöth on the occasion of his 85th birthday The rare-earth fluoride borates RE4B4O11F2 (RE = Pr, Nd) were obtained in a Walkertype multianvil device from the corresponding rare-earth oxides and fluorides, and boron oxide. Pr4B4O11F2 was obtained under high-pressure/high-temperature conditions of 8.5 GPa/1150 ◦C, and Nd4B4O11F2 at 8 GPa and 1300 ◦C. The single-crystal structure determinations revealed that both compounds are isotypic to RE4B4O11F2 (RE = Eu, Gd, Dy), crystallizing in the space group C2/c (Z = 4) with the parameters a = 1397.3(3), b = 472.78(9), c = 1400.2(3) pm, β = 91.1(1)◦, V = 0.9248(3) nm3, R1 = 0.0444, and wR2 = 0.0539 (all data) for Pr4B4O11F2, and a = 1389.1(3), b = 471.2(1), c = 1394.4(3) pm, β = 91.1(1)◦, V = 0.9125(3) nm3, R1 = 0.0286, and wR2 = 0.0601 (all data) for Nd4B4O11F2. The structure type of Gd4B4O11F2 contains BO4 tetrahedra as well as BO3 groups connected via common corners. Here, we report about the crystallographic characterization of both compounds in comparison to the isotypic phases and discuss their IR spectra.