TELLURIUM POLYCATIONS STABILIZED BY HALOGENOBISMUTATES - SYNTHESES AND CRYSTAL-STRUCTURES OF TE-4[BI6CL20] AND TE-4[BI2BR8]

The reaction of Te, TeX4 and BiX3 [X = Cl, Br] in sealed, evacuated gl ass ampoules in the temperature range 170 --> 100 degrees C yields a v ariety of compounds composed of tellurium polycations and halobismutat e anions. Two of these have been identified by crystal structure analy ses as Te-4[Bi6Cl20] (triclinic, <P(1)over bar>, a = 738.8(2), b = 875 .1(2), c = 1389.1(6) pm, a = 87.89(2), beta = 82.87(4), gamma = 87.89( 2)degrees, Z = 1) and Te-4[Bi2Br8] (triclinic, <P(1)over bar>, a = 726 .0(4), b = 773.7(4), c = 901.8(5) pm, alpha = 92.95(2), beta = 102.23( 2), gamma = 92.87(2)degrees, Z = 1). Both compounds were obtained as b lack crystals with a violet lustre and contain square-planar Te-4(2+) cations. Te-4[Bi6Cl20] contains a two-dimensional polymeric anion [Bi6 Cl20](2-) made up of corner-and edge-sharing BiCl6 octahedra with atta ched BiCl3 groups. The Bi-Cl distances vary over a very wide range fro m 245 to 334 pm. Te-4[Bi2Br8] consists of a one-dimensional chain [BiB r2Br4/2-](n) of cis-edge-connected BiBr6 octahedra with Bi-Br distance s ranging from 264 to 318 pm.