Resonance Raman Spectra of Dioxygen Adducts of Cobalt Porphyrin-Imidazole Complexes. Remarkable Spectroscopic Consequences of Hydrogen Bonding of the Coordinated Imidazole and the Lack of an Effect on the Cobalt-Oxygen Linkage

Article abstract of DOI:10.1021/ja00200a024

Resonance Raman (RR) spectroscopic studies of O2 adducts of the imidazole complexes of a highly protected cobalt-porphyrin are reported.Strategic isotopic labeling studies, employing dioxygen isotopomers and selectively deuteriated imidazole analogues, are used to document and interpret the complicated spectral patterns that emerge as a result of complex vibrational coupling of ν(O-O) with internal modes of the trans-coordinated imidazole ligand.In addition, the observed spectral patterns are shown to be dependent upon temperature, imidazole concentration, and theaddition of a hydrogen-bond acceptor.These results indicate that hydrogen bonding of the ligated imidazole to other solution components does not lead to differences in the inherent frequency of ν(O-O) but does result in dramatic alterations of the observed spectral patterns as a consequence of diferences in vibrational coupling parameters.The implications of these studies for the interpretation of RR spectra of O2 adducts of cobalt-substituted hemeproteins are discused.