High-pressure synthesis and crystal structure of the samarium meta-oxoborate γ-Sm(BO2)3

γ-Sm(BO2)3 was obtained via a high-pressure/high-temperature approach in a multi-anvil apparatus at 10 GPa and 1673 K. It crystallizes in the orthorhombic space group Pca21 (no. 29) with the lattice parameters a = 18.3088(8), b = 4.4181(2), and c = 4.2551(2) Å. The compound was analysed by means of X-ray diffraction and vibrational spectroscopy. The structure is isotypic to that of the already known meta-oxoborates γ-RE(BO2)3 (RE = La−Nd) and built up of a highly condensed borate framework containing three-, four-, six-, and ten-membered rings. Next to neodymium, samarium represents the second rare earth element that forms the α-, β-, and γ-modification of the four known rare earth meta-oxoborate structure types.