Aqua Complexes of Rare Earth Metals (Ce3+, Eu3+, Gd3+, and Yb3+) with closo-Dodecaborate Anion: Synthesis, Structure, and Properties

Aqua complexes [M(H2O)8]2[B12H12]3·15H2O (M = Eu3+, Gd3+, Yb3+) and [Ce(H2O)9]2[B12H12]3·15H2O stabilized by the closo-dodecaborate anion have been synthesized by neutralization of an (H3O)2[B12H12] solution with rare earth (RE) oxides M2O3 (M = Eu3+, Gd3+, Yb3+) and CeO2. The structures of [Eu(H2O)8]2[B12H12]3·15H2O and [Ce(H2O)9]2[B12H12]3·15H2O have been determined by single-crystal X-ray diffraction analysis. It has been demonstrated that the reaction in the СеО2/(H3O)2[B12H12] system is accompanied by the redox transformation Ce4+ → Ce3+, while for the M2O3 (M = Eu3+, Gd3+, Yb3+)/(H3O)2[B12H12] systems, the oxidation state of the corresponding RE cation remains unchanged. Studying the luminescent properties of [Ce(H2O)9]2[B12H12]3·15H2O has shown that this compound emits in the near ultraviolet region with an emission maximum at 370 nm.