Tetratellurium bis[heptachlorodigallate(III)], Te4[Ga2Cl7]2

Abstract

Compounds containing main-group clusters, with focus on bismuth polycations, have been synthesized and characterized using X-ray diffraction and spectroscopic methods. Six new compounds have been isolated from synthesis in GaX3-arene media; Bi8[GaCl4]2, Bi8 [GaBr4]2, Sb8[GaCl4]2, Sb8[GaBr4]2, Te4[Ga2Cl7]2 and Te4[Ga2Br7]2. Sb2+ 8 is the first homopolyatomic antimony cation to be isolated. The cation forms a square antiprism, in correlation with Wade’s rules, and displays a significant difference in length between the inter-square and intra-square Sb–Sb distances. The geometries of the Sb2+ 8 cations in Sb8[GaCl4]2 and Sb8[GaBr4]2 are in excellent agreement; the average intra-square and intersquare Sb–Sb distances are 2.87 A and 2.97 A, respectively. A very strong Raman band attributed to Sb2+8 is found at 180 cm-1. The Bi2+8 (square antiprismatic) and Te2+4 (squareplanar) polycations are known from earlier compounds. The Bi–Bi distances in Bi8[GaCl4]2 (3.07–3.12 A) are in general agreement with previous structures, while the Bi–Bi distances of Bi8[GaBr4]2 (2.92–3.18 A) display a wider distrubution than previously observed. The Te–Te distances of the cations of Te4[Ga2Cl7]2 and Te4[Ga2Br7]2 are 2.66 and 2.67 A, respectively. Quantum chemical calculations on bismuth polycations show that all species predicted byWade’s rules are local minima on a potential energy surface. The cation–anion interactions have been considered for salts containing bismuth polycations and it has been confirmed that such interactions have a major influence on the polycation stability. The new compound Bi16I4 has been isolated from molten Bil3. The structure consists of polymerized Bi16I4 molecules forming infinite ribbons and is very similar to the structure of the known metal-rich bismuth iodides, Bi14I4 and Bi18I4. DFT calculations predict all three compounds to be metallic conductors, while Bi4I4 is a semiconductor.