Bismuth-Rich Intermetallic Rods with a Note of Zintl-Phase

Abstract

Black needle-shaped crystals of the bismuth-rich mixed halogenide Bi21Rh4Cl6I7 were obtained by slow cooling of a melt of Bi, RhI3 and BiCl3. Single-crystal X-ray diffraction revealed an orthorhombic structure that consists of infinite intermetallic rods (Figure presented.) Bi9Rh2]3+ and discrete anionic groups [BiII2Cl2I5]3− and [BiIIICl4I2]3−. The rods consist of Rh-centered [RhBi8] polyhedra that alternately share triangular and rectangular faces. Using traditional electron counting rules, the rod can be interpreted as a covalent polymer with Rh2 dumbbells bonded to molecular Bi2 and Bi5 units. However, a quantum-chemical bonding analysis shows that the bonds involving Rh atoms are largely diffuse, while two-center bonds dominate in the bismuth units. The below 240 K observed semiconducting behavior of Bi21Rh4Cl6I7 is consistent with a complete localization of the valence electrons. Above 240 K, the resistance along the needle axis is largely independent of temperature.