Solvatochromic mixed-chelate copper(II) complexes, [Cu(Cl-acac)(diamine)]X (where Cl-acac = 3-chloroacetylacetonate ion, diamine = N,N0-dimethyl,N0-benzyl-1,2-iaminoethane and X = B(Ph)4 , PF6, BF4and ClO4), have been prepared. The complexes were characterized on the basis of elemental analysis, molar conductance, UV–Vis and IR spectroscopies. Single crystals of [Cu(Cl-acac)(diamine)(H2O)]PF6, complex 2, were also characterized by X-ray diffraction. The influence of the solvent polarity and counter ions on the mmax values of the d–d bands of the complexes have been investigated by means of visible spectroscopy. All the complexes demonstrated negative solvatochromism. A multi-parametric equation has been utilized to explain the solvent effect on the d–d transition of the complexes using SPSS/PC software.The stepwise multiple linear regression (SMLR) method demonstrated that the donor power of the solvent plays the most important role in the solvatochromism of the compounds. The relative donor power of the anions X was determined by visible spectra in the solvent dichloromethane.
