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 Rb-3[Re6S7Br7]center dot 4H(2)O

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 Rb-R e-S-Br is built from octahedral Re, clusters surrounded by two mu(3)-S-i an d six mu(3)-L-i ligands in which L-i acts as Br-1(6) + S-5(6). These L-i li gands exhibit a rotational disorder. The stacking and environments in this structure are very comparable to those of the tetravalent cluster unit in R b5Re6S8Br6, Br. Acetone solutions of Rb3Re6S7Br7, when evaporated in air, d eposit crystals of the triclinic tetrahydrate Rb3Re6S7Br7. 4H(2)O which is in thermodynamic equilibrium with the anhydrous salt. (C) 1999 Academic Pre ss.