Trinegative [Re6S7Br7]3− Anionic Cluster Unit Synthesized via Direct High-Temperature Route in the Quaternary System M–Re–S–Br (M=Alkaline) and Its Tetrahydrate Rb3[Re6S7Br7]·4H2O

A trivalent cluster unit has been synthesized by the solid-state route for the first time in the Rb–Re–S–Br system. The new rhombohedral compound Rb3Re6S7Br7 is built from octahedral Re6 clusters surrounded by two μ3-Si and six μ3-Li ligands in which Li acts as 16Br+56S. These Li ligands exhibit a rotational disorder. The stacking and environments in this structure are very comparable to those of the tetravalent cluster unit in Rb5Re6S8Br6, Br. Acetone solutions of Rb3Re6S7Br7, when evaporated in air, deposit crystals of the triclinic tetrahydrate Rb3Re6S7Br7·4H2O which is in thermodynamic equilibrium with the anhydrous salt.