Quantum Chemical Simulation of Hexa-, Penta-, and Tetracoordination Modes in Stereoisomers of the Co(II) and Ni(II) Bis(ligand) Complexes Based on (N,O,S(Se))-Tridentate Azomethines

Abstract

The molecular structures and relative energies of hexa-, penta-, and tetracoordinated stereoisomers of the Co(II) and Ni(II) bis(ligand) complexes based on (N,O,Y)-tridentate azomethines with the phenyl thio(seleno) ether substituent at the azomethine nitrogen atom (coordination modes of the competing stereoisomers MN₂O₂Y₂, MN₂O₂Y, or MN₂O₂ (Y = S, Se)) are calculated using the density functional theory. Hexacoordination is predominant in the Co(II) and Ni(II) complexes (combined with tetracoordination for the Co(II) complexes), unlike pentacoordination prevailing in similar Co(II) and Ni(II) complexes based on azomethines with thio(seleno)benzimidazole fragments (with Y atoms in the thione form). The quantum chemical simulation is performed for possible stereoisomerization reactions in the CoL₂ complexes to take into account the role of interconfiguration transitions in the competition of the hexa-, penta-, and tetracoordinated stereoisomers.