Spectroelectrochemical studies and excited-state resonance-Raman spectroscopy of some mononuclear rhenium(I) polypyridyl bridging ligand complexes. Crystal structure determination of tricarbonylchloro[2,3-di(2-pyridyl)quinoxaline]rhenium(I)

A number of mononuclear rhenium(I) complexes have been prepared and their physical properties and excited-state and spectroelectrochemical resonance-Raman spectra studied. These compounds have the general formula [Re(CO)(3)Cl(L)]. where L can be 2,3-di(2-pyridyl)quinoxaline (dpq), 2-(2-pyridyl)quinoxaline (pq) or 5-methyl-2,3-di(2-pyridyl)quinoxaline (mdpq). The structure of [Re(CO)Cl(dpq)] was determined by single-crystal X-ray diffraction. The NMR data for complexes with dpq and mdpq suggest the unbound pyridyl is shielding protons on the bound pyridyl moiety. The resonance-Raman spectra of the reduced complexes show some polarisation of electron density towards the bound pyridyl ring. The excited states have very similar spectral features to those of the reduced complexes. This suggests that electrochemically prepared redox states model the metal-to-ligand charge-transfer state well, for these systems.