Studying the coordination geometry of 3d transition-metal ions in complexes of crown-substituted porphyrins by EXAFS spectroscopy with allowance for multiple scattering

Abstract

The structure of a series of complexes of 3d metals (Co, Ni, and Cu) with substituted porphyrins is studied by X-ray EXAFS spectroscopy. Together with complexes based on tetraphenylporphyrin and octaethylporphyrin with known crystalline structures, new complexes of asymmetrically substituted tetraphenylporphyrin, 5-(4-(((4′-hydroxy-benzo-15-crown-5)-5′-yl)diazo)phenyl)-10,15,20-triphenylporphyrin, are studied. Based on an analysis of experimental spectra with allowance for the contributions of multiple scattering, the coordination parameters of metal atoms at the center of the porphyrin ring are determined: the bond distances and valence angles between them for the first four coordination spheres around metal atoms. The EXAFS spectra are shown to be sensitive to the angular parameters. Differences in the geometric parameters in the series of studied metal-porphyrin complexes are analyzed.