Electronic structure, chemical bonding, and oxidation numbers of first‐row transition metals in [MePIm₂] complexes and their cations

Abstract

ABSTRACT:The qualitative structures of the upper one-electron energy levels of imidazole-coordinated first-row transition metal porphyrin [MePIm 2 ] complexes established in the present study have shown that the second oxidation number of the first-row transition metals in the neutral complexes do not change in their cations and double cations. It was found that occupied orbitals of the density functional theory method obtained with B3LYP functional are not correctly ordered. Therefore, they cannot be used in investigations of the orbital structure of the upper molecular orbitals. A qualitative analysis of density functional theory method wave functions in terms of Mulliken and natural charges of atoms, together with an analysis of electrostatic potentials of the neutral [MePIm 2 ] complex, its single and double cations, demonstrates that the highest occupied orbitals of these complexes are mainly formed by atomic orbitals of the porphyrin ring atoms. Therefore, transition metal atoms are not active in chemical reactions with these complexes unless the 3d electrons of transition metal atoms are excited, for example by light. A mechanism of an electron transfer reaction that occurs between a heme cytochrome and Fe-oxide mineral surface is discussed in the light of the obtained results.