The influence of distortion in the porphine ring on the electronic structure of the central metal ion was studied by means of the ESR spectra of copper(II) chlorophylls (CuChls). A linear correlation between ESR parameters, i.e. g and A values, indicated that the electronic structure of the central copper(II) ion in CuChls is different from that in compounds having the regular porphine skeleton. The weakened CuN bond in CuChls was evidenced by a decrease in the bonding coefficient α2. These observations on the ESR parameters of CuChls were explained by a partially saturated and distorted macrocyclic structure.
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