Study of six coordinated cobalt(III) oxophlorin with different axial ligands: Optimization of geometry and determining of energy and electronic configuration at various spin states by employing of B3LYP, BV86P and M06-2X methods

Abstract

The six coordinated Co^IIIoxophlorin have been studied with imidazole, pyridine and t-butylcyanide as axial ligands using B3LYP, BV86P and MO6-2X methods. Conversion between two isomers [(L)₂Co^III(PO)]${}^{†}$ and [(L)₂Co^III(PO)]${}^{\left|\right|}$ can be occurred at various spin multiplicities, namely singlet, triplet and quintet states. L is employed to show axial ligand namely, imidazole or pyridine. London forces have a basic role in the stability of the mentioned complexes due to non-specific solvent effects. The latter fact has been obtained using the PCM model. Also, it is specified that minimum geometries have not been obtained for some parallel or perpendicular six-coordinated complexes with special axial ligands at a finite spin state. The B3LYP method indicates that one and three $\alpha$-electron can be found on the Co atom in every optimized complex at triplet and quintet spin states, respectively. Also, another $\alpha$-electron is placed on the ring of oxophlorin. This fact is obtained for different isomers of [(IM₂(Co^III(PO)] and [(Py)₂Co^III(PO)] at triplet and quintet spin states, while these complexes are optimized using B3LYP. Besides, results obtained from B3LYP show that the most stable state for six coordinated Co^IIIoxophlorin with any axial ligand is the singlet state. Based on crystal field theory and molecular orbital theory, electron configuration and hybridization of cobalt in [(IM)₂Co^III(PO)] at singlet state can be written as t₂g⁶ eg⁰ and sp³d², respectively. Former electronic configuration indicates a strong field with low spin for d orbitals of cobalt, and latter hybridization is expected for a metal with a coordination number of 6 in a complex with O_h symmetry. The results obtained are completely satisfied by NBO analysis.