Ce₂B₈O₁₅: High-pressure synthesis and crystal structure determination of a rare-earth polyborate exhibiting a new “Fundamental Building Block”

Abstract

The new cerium polyborate Ce₂B₈O₁₅ was synthesized under high-pressure/high-temperature conditions of 6 GPa and 1050 ºC in a Walker-type multianvil apparatus. The single-crystal structure determination revealed that the new compound crystallizes in the space group P2/c with the lattice parameters a = 916.6(2), b = 421.0(1), c = 1248.9(3) pm, β = 116.7(1)º, V = 0.4303(2) nm³, R1 = 0.0356, and wR2 = 0.0504. The crystal structure of Ce₂B₈O₁₅ exhibits a new fundamental building block (FBB) in borate chemistry that consists of four BO₄ tetrahedra and can be written as 4□: [Φ] 〈3□〉|□|. These FBB are interconnected via common corners, forming a complex threedimensional network that contains the Ce³⁺ cations. Ce₂B₈O₁₅ represents the most boron rich rare-earth borate synthesized under high-pressure/high-temperature conditions so far. We report about the synthetic conditions, structural details, thermal behaviour, and the IR/Raman spectra of Ce₂B₈O₁₅.