Effects of Organic Base Structure, Functional Substitution in the Macrocycle, and Environment on Axial Coordination of Manganese(III) Porphyrins

The axial coordination of base molecules and ions on metalloporphyrins is a relevant approach to the preparation of molecular and structured materials for optoelectronics, catalysis, and biomimetics. In this work, we present the results of a comparative analysis of the thermodynamics and spectroscopy of the axial coordination of pyridine (Py), imidazole (Im), 1-methylimidazole (MeIm), 4-(1H-imidazol-1-yl)benzaldehyde (ImC6H4CHO), and N-methyl-2-(1H-imidazol-1-yl)-phenyl-3,4-fullero[60]pyrrolidine (ImC60) on manganese(III) porphyrins with different sets of substituents in the macrocycle depending on the reaction medium, in order to further develop the theory and optimization of the axial coordination processes. The influence of these factors on the stoichiometry of complexation and the stability of the axial complexes obtained is determined. The picture of the influence of the chemical structure and, therefore, the basicity of the axial ligand is complicated by the manifestation of steric effects during complex formation, while chloroform and toluene, as media for the reaction, have a very different effect on the equilibrium constant in a series of studied bases added to (Cl)MnOEP.