Phase formation of hexarhenium thiobromide clusters Re6S4+nBr10-2n (n = 0–4) and synthetic technique for the preparation of pure compounds

Abstract

A detailed study of the Re–S–Br system in the temperature range (650 – 1150 °C) of the formation of hexarhenium thiobromides with the general formula Re6S4+nBr10–2n, has revealed the features of phase formation and the factors influencing the production of pure phases. It was found that in reactions with a given stoichiometry 6Re + nS, a mixture of products is usually formed, namely a compound based on a cluster core with the targeted Re/S stoichiometry Re6Sn, an admixture compound with Re6Sn+1 core, and a soluble by-product (3–5% of the total mass), consisting of rhenium bromides and thiobromides. It was found that the composition of the by-product (Re/S ratio) has a significant effect on the fraction of the admixture compound with higher sulfur content. The slow cooling rate of the reaction mixture, leads to the obtaining of a pure target compound with the {Re6SnBr8–n} cluster core. In the course of the study of the Re–S–Br system, the crystal structure of Re6S7Br4 was solved (space group R–3c, a = 9.5804(2) Å, c = 31.0676(10) Å, V = 2469.48(13) Å3, Z = 6). The study of the thermal behavior showed that the stability of Re6S4+nBr10–2n increases with increasing sulfur content in the cluster core. XPRD data showed that the decomposition of octahedral cluster thiobromides leads to the formation of sulfur-rich phases. This process is accompanied by the release of elemental bromine, metallic rhenium and the formation of soluble by-products with the overall composition “Re2SBrx".