CORRELATION OF X-RAY CRYSTALLOGRAPHIC DATA AND SPECTROSCOPIC PROPERTIES OF DIVALENT METAL-COMPLEXES OF OCTAETHYLPORPHYRIN

The infrared and visible spectra of divalent metal complexes of OEP were obtained. The variations in precise absorbances for five metal-sensitive infrared bands at ca. 3050, 1230, 990, 920, and 750 cm-1 are examined as a function of macrocyclic conformation and metal-pyrrolic nitrogen (M-N(p)) bond distances. The exact positions of the bands at ca. 920, 990, 1230, and 3050 cm-1 are dependent on the M-N(p) bond distances. Additionally, the bands at 920, 990, and 1230 cm-1 are dependent on the size of the lowest unoccupied p(z) orbital. The 1230- and 3050-cm-1 bands are sensitive to the macrocyclic conformation. In the visible region the variations in lambda(max) of the alpha and beta bands are also examined as a function of M-N(p) bond distance. These appear to be a function of the M-N(p) bond distance and size of the lowest unoccupied p(z) orbital. These findings are discussed in terms of stabilization of the a2u orbital on the porphyrin ligand. Implications for porphyrin reactivity are considered.