ESR Bonding parameter studies of single and mixed ligand complexes of copper(II)

ESR and optical absorption studies are described for a number of copper(II) single and mixed ligand complexes formed with substituted salicylic acids and acetylacetone. ESR spectra of all these complexes give well-resolved spectra in DMF both at room and liquid nitrogen temperatures. The molecular orbital coefficients are estimated assuming an axial symmetry. A partial covalency is observed in all the single ligand complexes while the in-planeπ-bonding is as strong as theσ-bonding in all the mixed ligand complexes. No regular trend is observed in the value ofχ (which is proportional to hyperfine constants) with the change in the overall electron withdrawing capacity of the substituent on salicylic acid, either in single ligand or in mixed ligand complexes. However, theχ values for all the complexes (except in the case of bis(acetylsalicylato)copper(II) and (acetylacetonato)-(3,5-dinitrosalicylato)copper(II)) are in agreement with the computed value ofχ = −3.61 for single crystals of copper-acetylacetonate possessing the same environment of four oxygens around copper(II).