Synthesis, characterization and solvatochromism studies of two new mixed-chelate copper(II) complexes containing β-ketoamine and diamine ligands

Abstract

Two mixed-chelate copper(II) complexes that encompass N,N,N′,N′-tetramethylethylenediamine (tmen) and a β-ketoamine derivative were prepared. The elemental analysis, spectroscopic, conductance measurements and X-ray structural analysis of the newly prepared complexes are presented and discussed. The molar conductivity values in various solvents reveal the predominance of electrostatic interactions between the [Cu(tmen)(β-ketoamine)(H2O)]+ entity and the NO3− anion that counterbalances the positive charge. The resulting complexes, with a local symmetry of CuO2N3, attain nearly square-pyramidal structures and display an affinity for axial ligation. The tendency for the axial ligation is particularly fulfilled when suitable nucleophiles (solvents) with different donor abilities exist, leading to solvatochromism. The solute–solvent interactions are revealed by shifts in the ligand field absorption spectra, which are enhanced as the donor power of the solvent increases. A multi-parametric equation has been utilized to explain the solvent effect on the d–d transitions of the complexes using SPSS/PC software. To explore the mechanism of the interaction between the solvent molecules and the complexes, different solvent parameters such as DN (donor number), AN (acceptor number), α (hydrogen bonding ability), ET30 (Dimorth and Richardt’s), π∗ (polarity/polarizability parameter) and β (electron pair donating ability) using the multiple linear regression (MLR) method were employed. The results demonstrated that the donor power of the solvent plays the most important role in the solvatochromism of the compounds. A linear dependence of the ligand field absorption maximum on the solvent donor number is generally observed.