A series of molecular rhenium sulfide clusters K-4[Re5S8Cl6] (1), K-4[Re6S8(OH)(6)], and [Re6S8(H2O)(6)]SO4 supported on silica gel catalyze ring-opening addition of thiols to epoxides to yield beta-hydroxy sulfides in a stream of hydrogen at temperatures ranging from 175 to 250 degrees C. The thermal activation mechanisms of 1 is studied. Powder X-ray diffraction analyses and Raman spectrometry reveal the retention of integrity of the octahedral cluster framework up to 500 degrees C. Thermogravimetry and elemental analyses of the silica gel-supported 1 show the loss of chlorido ligands, and evolution of hydrogen chloride is observed on activation. No coordinatively unsaturated metal site is observed by CO titration. Titration of the activated cluster shows the appearance of weak Bronsted acid sites with H-0 approximate to 1.8. The catalytically active site of the silica gel-supported 1 is a hydroxo ligand that is formed by reaction with silanol groups. (C) 2015 Elsevier B.V. All rights reserved.