Correlations between spectroscopic, electrochemical, and kinetic properties of cyano-bridged binuclear complexes. Analyses of temperature, pressure, and solvent effects

Several asymmetric cyano-bridged mixed-valence binuclear complexes were stu died using electrochemical (square wave and cyclic voltammetry), spectrosco pic (UV-vis-NIR absorption and H-1 NMR), and kinetic (stopped-flow) techniq ues, with special attention to the correlations between thermodynamic and o ptical charge-transfer characteristics determined through the variation of temperature and pressure. The CN-bridged isomers for representative EDTA-li gated complexes, viz,, [(EDTA)Ru-III(mu-CN)M(CN)(x)](5-) (M = Fe-II, x = 5; M = Mo-IV, x = 7), were synthesized and characterized and shown to exhibit essentially different electrothermodynamic and optical charge-transfer par ameters compared to "normal" isomers. The binuclear complex-formation kinet ics, spectroscopic and preliminary H-1 NMR data indicate that at least two EDTA ligand conformer states are formed in the course of the dimerization p rocess studied. Using the difference DO-D stretching overtone spectroscopy of heavy water acting as solvent, it was shown that the change in hydrogen- bonding order of specifically solvating water molecules present in the firs t solvation shells around the redox centers may be largely responsible fur the observed dramatic changes in electrothermodynamical and optical charact eristics upon the variation of the nature of the ligands and their conforme r (EDTA) or bridging-isomer (mu-CN) states.