Synthesis, characterization and properties of oxo-bridged diruthenium(III) complexes with thiocyanato and cyanato ligands

Abstract

The oxo-bridged diruthenium(III) complexes with thiocyanato and cyanato ligands, trans(μ-O,L)-[Ru2(μ-O)(μ-CH3COO)2(bpy)2(L)2] (bpy=2,2′-bipyridine; L=SCN− (1); OCN− (2)), have been synthesized, characterized, and their properties studied. X-ray single crystallography revealed that the thiocyanato ligands of 1 are N-bonded to the Ru centers at the trans sites to the oxo-bridge. The OCN− ligand in 2 is also N-bonded based on the infrared spectroscopy. The cyclic voltammograms of 1 and 2 in dimethyl sulfoxide (DMSO) solutions of 0.1M (n-Bu)4NPF6 showed two redox couples at around −0.5V and +0.5Vvs Ag/AgCl, which were assigned to the processes Ru2III,III/Ru2III,II and Ru2IV,III/Ru2III,III, respectively. The electronic absorption spectra of 1 and 2 in CH3CN solutions showed strong absorption bands at 625 and 637nm, respectively. The bands showed a remarkable blueshift in H2O to 578 and 581nm as a consequence of the solvent interactions at the free end of the thiocyanato and cyanato ligands, respectively. The theoretical calculations of both 1 and 2 and also their coordination isomers (N-bonded and S-bonded for the thiocyanate complex, and N-bonded and O-bonded for the cyanate complex) revealed that the N-bonded isomers are energetically more stable. Both the SCN− and OCN− ligands are primarily good σ donors to the Ru2O core. The contributions of SCN− to the dπ(Ru)–pπ(μ-O) conjugated system are particularly significant (>20%). The strong visible absorption bands of both 1 and 2 were attributed to mainly the metal-to-metal charge transfer (MMCT) transitions with some contributions from the ligand (SCN−, OCN−)-to-ligand (μ-O) charge transfer (LLCT).