A family of octahedral rhenium cluster complexes [Re6Q8(H2O)n(OH)6-n]n-4 (Q = S, Se; n=0-6):: Structural and pH-Dependent spectroscopic studies

The conversions of hexahydroxo rhenium cluster complexes [Re(6)Q(8)(OH)(6)](4-) (Q = S, Se) in aqueous solutions in a wide pH range were investigated by chemical methods and spectroscopic measurements. Dependences of the spectroscopic and excited-state properties of the solutions on pH have been studied in detail. It has been found that a pH decrease of aqueous solutions of the potassium salts K-4[Re(6)Q(8)(OH)(6)]center dot 8H(2)O (Q = S, Se) results in the formation of aquahydroxo and hexaaqua cluster complexes with the general formula [Re(6)Q(8)(H2O)(n)(OH)(6 - n)](n-4) that could be considered as a result of the protonation of the terminal OH- ligands in the hexahydroxo complexes. The compounds K-2[Re6S8(H2O)(2)(OH)(4)]center dot 2H(2)O (1), [Re6S8(H2O)(4)(OH)(2)]center dot 12H(2)O (2), [Re6S8(H2O)(6)][Re6S6Br8]center dot 10H(2)O (3), and [Re6Se8(H2O)(4)(OH)(2)] (4) have been isolated and characterized by X-ray single-crystal diffraction and elemental analyses and infrared (IR) spectroscopy. In crystal structures of the aquahydroxo complexes, the cluster units are connected to each other by an extensive system of very strong hydrogen bonds between terminal ligands.