Zr 2Ir 6B with an eightfold superstructure of the cubic perovskite-like boride ZrIr 3B 0.5: Synthesis, crystal structure and bonding analysis

Abstract

Single phase powder samples and single crystals of Zr 2Ir 6B were successfully synthesized by arc-melting the elements in a water-cooled copper crucible under an argon atmosphere. Superstructure reflections were observed both on powder and on single crystal diffraction data, leading to an eightfold superstructure of ZrIr 3B x phase. The new phase, which has a metallic luster, crystallizes in space group Fm 3 ¯ m (no. 225) with the lattice parameters a=7.9903(4) Å, V=510.14(4) Å 3. Its crystal structure was refined on the basis of powder as well as single crystal data. The single crystal refinement converged to R 1=0.0239 and w R 2=0.0624 for all 88 unique reflections and 6 parameters. Zr 2Ir 6B is isotypic to Ti 2Rh 6B and its structure can be described as a defect double perovskite, A 2 BB′ O 6, where the A site is occupied by zirconium, the B site by boron, the O site by iridium but the B′ site is vacant, leading to the formation of empty and boron-filled octahedral Ir 6 clusters. According to the result of tight-binding electronic structure calculations, Ir–B and Ir–Zr interactions are mainly responsible for the structural stability of the phase. According to COHP bonding analysis, the strongest bonding occurs for the Ir–B contacts, and the Ir–Ir bonding within the empty clusters is two times stronger than that in the BIr 6 octahedra.