Theoretical study of inner and outer mononuclear complexes of Co(II), Ni(II), and Cu(II) with a compartmental hexadentate Schiff base derived from 3-formylsalicylic acid

Density functional theory (B3LYP/6-31G(d)) has been applied for optimization and calculation of the vibrational spectra of the compartmental hexadentate Schiff base derived from 3-formylsalicylic acid and 4,5-dichloro-1,2-phenylenediamine and 12 of its mononuclear complexes with Co(II), Ni(II), and Cu(II). Six of these complexes have the metal ion occupying the inner, N₂O₂, or the outer, O₂O₂, coordination sites in square planar geometry. The other six complexes possess octahedral geometry, occupying the inner or the outer coordination sites coordinating, additionally, to two waters. Significant changes in the ligand geometry have been observed in all complexes to permit efficient complexation with the metal. Assignments of the infrared bands are proposed based on calculations. Vibrational frequencies that are important for assignment and confirmation of the coordination sites are reported. Comparison of the total energies of the complexes reveals that inner complexes are more stable than corresponding outer complexes. Selectivity of metal ions to the coordination sites is also discussed.