Controlled synthesis and luminescence properties of trans-[Re _6S_8(CN)_4(OH)_(2-n)(H)_2O)_n]_(n-4) octahedral rhenium(III) cluster units (n = 0, 1 or 2)

摘要

This work is devoted to the preparation of trans-[Re_6S _8(CN)_4(OH)(H_2O)]~(3-) and trans-[Re_6S_8(CN)_4(H_2O) _2]~(2-) cluster complexes starting from trans-[Re _6S_8(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-[Re_6S_8(CN) _4(OH)_2]~(4-), aquahydroxo trans-[Re ~6S~8(CN)_4(OH)(H_2O)]~(3-) and the diaqua trans-[Re_6S_8(CN)_4(H _2O)_2]~(2-) complexes, respectively. The stepwise acid dissociation constants of trans-[Re_6S_8(CN) _4(H_2O)_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: (Bu _4N)_4[Re_6S_8(CN)_4(OH) _2]·Bu_4NOH (1), (Ph_4P) 3[Re_6S_8(CN)_4(OH)(H _2O)]·3.5H_2O (2), (Bu_4N) 3[Re_6S_8(CN)_4(OH)(H _2O)]·2H_2O (3), (Bu_4N) _2K[Re_6S_8(CN)_4(OH)(H _2O)]·6H_2O (4) and (Bu_4N) _2[Re_6S_8(CN)_4(H_2O) _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 H_2O ligands in the trans-positions of the complex [Re_6S_8(CN)_4(OH)(H_2O)] ~(3-) leads to the formation of H_3O2- intercluster bridging groups through strong hydrogen bonding. The trans disposition of the H _3O2- groups around Re_6 enables the formation of polymeric linear chains of cluster complexes.