Zr2Ir6B with an eightfold superstructure of the cubic perovskite-like boride ZrIr3B0.5: Synthesis, crystal structure and bonding analysis

Single phase powder samples and single crystals of Zr2Ir6B 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 ZrIr3Bx phase. The new phase, which has a metallic luster, crystallizes in space group View the MathML sourceFm3¯m (no. 225) with the lattice parameters a=7.9903(4) Å, V=510.14(4) Å3. Its crystal structure was refined on the basis of powder as well as single crystal data. The single crystal refinement converged to R1=0.0239 and wR2=0.0624 for all 88 unique reflections and 6 parameters. Zr2Ir6B is isotypic to Ti2Rh6B and its structure can be described as a defect double perovskite, A2BB′O6, 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 Ir6 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 BIr6 octahedra.