Bi12Rh3Br2: a subbromide from the oxidation of the intermetallic compound Bi4Rh

Bi12Rh3Br2 was synthesized from the elements using niobium bromides as auxi liaries to modify the partial pressures in the course of the reaction. The orthorhombic crystal structure (space group Fddd (no. 70); a = 717.12(3) pm , b = 1680.37(6) pm, c = 3187.1(1) pm) consists of a three-dimensional fram ework of [RhBi8] cubes and square antiprisms, which share common edges. Bro mide ions fill the chiral pores of the framework. The crystal structure of Bi12Rh3Br2 = (Bi4Rh)(3)Br-2 is closely related to that of the intermetallic compound alpha -Bi4Rh. The oxidation of Bi4Rh to Bi12Rh3Br2 is accompanied by an emptying of Bi-Bi and Bi-Rh antibonding states near the Fermi level, leading to a strengthening of bonding in the intermetallic part of the str ucture. Despite the partial oxidation the metallic conductivity is retained . (C) 2001 Editions scientifiques et medicales Elsevier SAS. All rights res erved.