Synthesis, X-ray crystal structure and DFT studies of two octahedral Cobalt(II) complexes with N,N,N-tridentate triazine-type ligands

Two new Co(II) complexes, [CoL2]X2∙2H2O, with N,N,N-tridentate triazine type ligand (L) and X = Cl− (1) or NO3− (2) are synthesized and characterized using elemental analysis, FTIR spectra, and single-crystal X-ray diffraction. Complexes 1 and 2 are crystallized in the centrosymmetric space groups P-1 and C2/c, respectively. The Co atoms are surrounded by two neutral tridentate ligands coordinated via nitrogen atoms, thus forming a distorted octahedral coordination sphere. Hirshfeld topology analyses of the molecular packing revealed that the polar Cl⋯H, O⋯H and N⋯H contacts are the most important intermolecular interactions while the nonpolar C⋯H and C⋯C (π–π stacking) contacts are weak and insignificant, respectively. DFT calculations indicated that the high-spin state is energetically more favored than the low-spin case. The Co(II) center transfers its spin density to the ligand donor atoms via the spin delocalization mechanism. Based on the atoms in molecules (AIM) results, all Co–N interactions have a predominant covalent character. The strength of the Co–N interactions decreases in the order Co–N(hydrazone) > Co–N(triazine) > Co–N(amine). The metal anti-bonding natural orbitals involved in the Co–N interactions have high and s-orbital characters. Both complexes showed good thermal stability up to 276°C and 250°C for complexes 1 and 2, respectively