UV-vis and H-1-NMR spectroscopy were applied to study axial coordination of imidazole (L1) and nitrogen monoxide (L2) with Co-II-porphyrins ((CoP)-P-II) containing halogen substituents in the pyrrole and meso-phenyl positions of the macrocycle. The number and positions of bromine and chlorine atoms cause considerable deformation of the tetrapyrrole macrocycle. Cyclic voltammetry was used to determine the oxidation potentials of Co-II/Co-III (E-ox(1)) in the compounds. Both mono-axial complexes (Co-II(L)) and diaxial complexes ((CoP)-P-III(L)(2)) or (CoP)-P-II-pi cation radicals could be the products of (CoP)-P-II interaction with L1 and L2, depending on the porphyrinate structure. The interconnection between halogen substitution in the porphyrin macrocycle and its ability to reversibly bind NO was established. The photochemical activity of the synthesized complexes in the presence of active oxygen forming (tert-butylperoxide) was investigated. The results extend our understanding of the valence state of cobalt cations in porphyrin molecules depending on the macrocycle structure and surrounding conditions (solvent, temperature, organic and inorganic impurities), and demonstrate the possibility of reversible binding of both the NO molecules and various imidazole-containing biomolecules and drug compounds based on them.
