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 urn:x-wiley:00442313:media:zaac202300124:zaac202300124-math-0001 Bi9Rh23+ and discrete anionic groups BiII2Cl2I53− and BiIIICl4I23−. 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.
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