Relative stability of the cis and trans isomers of octahedral cobalt(iii) complexes of the type [Co(N2O2)X2] with tetradentate salen type Schiff bases: a combined theoretical and experimental study

Abstract

Octahedral cobalt(III) complexes of the type [Co(N₂O₂)X₂] with N₂O₂ donor tetradentate salen type Schiff bases may form cis and trans isomers. DFT calculations are used to explore and analyze in detail a series of octahedral cobalt(III) complexes. The cis isomers are found to be more stable in most cases. One such complex, [Co^IIIL^a(N₃)(DMSO)] {H₂L^a = N,N-bis(3,5-dichlorosalicylidene)2,2-dimethyl-1,3-propanediamine}, is synthesized and its structure is confirmed by single crystal X-ray diffraction analysis. As predicted from the theoretical calculations, this structure corresponds to a cis isomer. A Cl⋯Cl close contact exists in the solid-state structure of the synthesized complex and the nature of the interaction is analyzed using theoretical computations. Bader's theory of atoms in molecules (AIM) approach is applied to calculate the Cl⋯Cl interaction energy in the crystal via the electron density features at the Cl⋯Cl bond critical point. The value of the total energy density which is the sum of the kinetic and potential energy densities at the bond critical point (BCP) of a Cl⋯Cl close contact is 3.99 kJ mol⁻¹ Bohr⁻³.