Substituent effect in the γ-position of acetylacetonate on the solvatochromic property of mixed-chelate copper(II) complexes consisting of diamine and acetylacetonate ligands

The infrared and electronic absorption spectra of a series of new mixed-chelate copper(II) complexes that encompass N,N-dibenzylethylenediamine (diamine) and 3-substituted derivatives of acetylacetone (x-acacH) were studied. The IR and electronic absorption spectra and the molar conductivity of the newly prepared complexes are presented and discussed. The molar conductivity in dichloromethane reveals a predominance of electrostatic interactions between [Cu(diamine)(x-acac)]+ entity and perchlorate anions that counterbalance the positive charge. The resulting complexes with local symmetry of CuO2N2 attains a square-coplanar structure and exhibits the tendency for axial ligation, which is enhanced when an electron-attracting substituent is attached to the γ-position of acetylacetonate moiety. The tendency for axial ligation is particularly fulfilled when suitable nucleophiles (solvents) with deferent donor abilities exist, leading to solvatochromism. The solute–solvent interactions are revealed by shifts in the ligand field absorption spectra that are enhanced as the donor power of the solvent increases. Linear dependence of the ligand field absorption maximum on solvent donor number is generally observed.