Ti2Rh6B – a new boride with a double perovskite-like structure containing octahedral Rh6 clusters

Abstract

Abstract Single crystals of Ti2Rh6B were synthesized by arc-melting the elements in a water-cooled copper crucible under an argon atmosphere. The new silver-like compound with metallic luster crystallizes in space group Fm-3m (no. 225) with a = 7.8191(5) Å, V = 478.05(5) Å3, and Z = 4. The refinement converged to R 1 = 0.0169 and wR 2 = 0.0486 for all 96 unique reflections and 7 parameters. The structure can be described as a defect double perovskite, A2BB'O6, where the A site is occupied by titanium, the B site by boron, the O site by rhodium but the B' site is vacant leading to the formation of perfectly octahedral Rh6 clusters and BRh6 units. Rh—B, Rh—Ti, and Rh—Rh interactions are observed. According to density-functional (LMTO) electronic structure calculations, the strongest bonding occurs for the Rh—B contacts, and the Rh—Rh bonding within the clusters is more than two times stronger than in the BRh6 units.