Controlled synthesis and luminescence properties of trans-[Re6S8(CN)4(OH)2−n(H2O)n]n−4 octahedral rhenium(III) cluster units (n = 0, 1 or 2)

This work is devoted to the preparation of trans-[Re6S8(CN)4(OH)(H2O)]3− and trans-[Re6S8(CN)4(H2O)2]2− cluster complexes starting from trans-[Re6S8(CN)4(OH)2]4− and a study of their luminescence properties. The controlled separation of each species could be achieved by pH adjustment: pH > 10, 5.5 < pH < 9 and pH < 3.5 for the dihydroxo trans-[Re6S8(CN)4(OH)2]4−, aquahydroxo trans-[Re6S8(CN)4(OH)(H2O)]3− and the diaqua trans-[Re6S8(CN)4(H2O)2]2− complexes, respectively. The stepwise acid dissociation constants of trans-[Re6S8(CN)4(H2O)2]2− were determined to be pKa1 = 3.3 and pKa2 = 6.6. Five novel compounds built up from the title cluster units were isolated and characterized: (Bu4N)4[Re6S8(CN)4(OH)2]·Bu4NOH (1), (Ph4P)3[Re6S8(CN)4(OH)(H2O)]·3.5H2O (2), (Bu4N)3[Re6S8(CN)4(OH)(H2O)]·2H2O (3), (Bu4N)2K[Re6S8(CN)4(OH)(H2O)]·6H2O (4) and (Bu4N)2[Re6S8(CN)4(H2O)2] (5). Compounds 2, 3 and 4 were characterized by single-crystal X-ray diffraction analysis. For 2 and 3, it was found that the availability of the OH− and H2O ligands in the trans-positions of the complex [Re6S8(CN)4(OH)(H2O)]3− leads to the formation of H3O2- intercluster bridging groups through strong hydrogen bonding. The trans   disposition of the H3O2- groups around Re6 enables the formation of polymeric linear chains of cluster complexes.

The preparation and controlled separation of trans-[Re6S8(CN)4(OH)(H2O)]3– and trans-[Re6S8(CN)4(H2O)2]2– cluster units from trans-[Re6S8(CN)4(OH)2]4– was achieved by pH adjustment. Determination of acid–base constants, luminescence characteristics of aqueous solutions of the complexes, isolation and characterization of novel compounds based on these cluster anions are reported herein.Figure optionsDownload as PowerPoint slide