SPECTROSCOPIC AND ELECTROCHEMICAL STUDIES OF RHENIUM(I) BIMETALLIC COMPLEXES WITH ASYMMETRIC POLYPYRIDYL BRIDGING LIGANDS

The synthesis and electrochemical and spectroscopic properties of a number of binuclear rhenium(I) ligand-bridged complexes are reported. The ligands are as follows: 2,3 -di(2-pyridyl)quinoxaline; 2,3-di(2-pyridyl)-6-methyl quinoxaline; 2,3-di(2-pyridyl)pyrido[2,3-b]pyrazine; 2,3-di(2-pyridyl)pyrido[3,3-b]pyrazine. Complexes with these ligands show different electrochemical and spectroscopic properties. The pyridopyrazine ring systems show longer wavelength MLCT transitions and are easier to reduce. However, spectroelectrochemical studies reveal that the reduction products for this series of complexes are spectroscopically similar. Raman measurements on the reduced species suggest that the redox orbital for the first reduction resides in an orbital that is localized at the dipyridyl section of each ligand. This is surprising in view of the fact that the larger ring system would be expected to localize the charge. It suggests that the rhenium centers modify the nature of the redox MO to a greater extent than the pyridopyrazine ring system.