SPECTROELECTROCHEMICAL STUDIES AND EXCITED-STATE RESONANCE-RAMAN SPECTROSCOPY OF SOME MONONUCLEAR RHENIUM(I) POLYPYRIDYL BRIDGING LIGAND COMPLEXES - CRYSTAL-STRUCTURE DETERMINATION OF ONYLCHLORO[2,3-DI(2-PYRIDYL)QUINOXALINE]RHENIUM(I)

A number of mononuclear rhenium(I) complexes have been prepared and th eir physical properties and excited-state and spectroelectrochemical r esonance-Raman spectra studied. These compounds have the general formu la [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)quinoxali ne (mdpq). The structure of [Re(CO)Cl(dpq)] was determined by single-c rystal 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 som e polarisation of electron density towards the bound pyridyl ring. The excited states have very similar spectral features to those of the re duced complexes. This suggests that electrochemically prepared redox s tates model the metal-to-ligand charge-transfer state well, for these systems.