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

The synthesis and electrochemical and spectroscopic properties of a nu mber of binuclear rhenium(I) ligand-bridged complexes are reported. Th e ligands are as follows: 2,3 -di(2-pyridyl)quinoxaline; 2,3-di(2-pyri dyl)-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 pyridopyr azine ring systems show longer wavelength MLCT transitions and are eas ier 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 r edox orbital for the first reduction resides in an orbital that is loc alized at the dipyridyl section of each ligand. This is surprising in view of the fact that the larger ring system would be expected to loca lize the charge. It suggests that the rhenium centers modify the natur e of the redox MO to a greater extent than the pyridopyrazine ring sys tem.