Resonance Raman spectroscopic detection of steric-induced distortions of axial ligand binding for dioxygen adducts of superstructured cobalt-porphyrin complexes

Article abstract of DOI:10.1021/ja00024a011

Resonance Raman studies are carried out for the O₂ adducts of superstructured "jellyfish" cobalt-porphyrin complexes with several trans-axial ligands, namely, pyridine, 3,5-lutidine, and imidazole as well as several of their deuteriated analogues. Two superstructured, bis-strapped porphyrins, having either short (9 carbon atoms) or long (12 carbon atoms) strap lengths, are employed along with sterically relaxed (non-strapped) porphyrins. It is found that the short-strap derivative induces distortion of the bound ligands while the long-strap analogue permits normal, unencumbered binding. While the distortion of the trans-axial ligand does not significantly affect the Co-O₂ linkage, as judged by the constancy of the inherent frequency of ν(O-O), significant shifts of the ligand internal modes give rise to substantially altered spectra as a result of variations in the strength of vibrational coupling of the ν(O-O) with internal modes of the trans-axial ligand.