Theoretical study of specific solvent effects on the optical and magnetic properties of copper(II) acetylacetonate

Specific and basicity solvent effects on the visible near-infrared electronic transitions and the electron paramagnetic resonance (EPR) parameters of the copper(II) acetylacetonate complex, Cu(acac)₂, have been investigated at the density functional theory level. The computed absorption transitions as well as the EPR parameters show a strong dependence on the direct coordination environment around the Cu(II) complex. High solvatocromic shifts are observed for 3d-3d transitions, with the highest effect observed for the dz²→d_xy transition, which is red-shifted by 6000 cm^-1 and 9000 cm^-1 in water and pyridine solvent models, respectively. Compared to the electronic g-tensors, the hyperfine coupling constants of the Cu(acac)₂ complex show a more pronounced dependence on the effect of base strength of solvent. Overall, the present methodology satisfactorily models the solvent effect on the optical and magnetic properties of the Cu(acac)₂ complex, and theory and experiment agree sufficiently well to warrant the use of the computed optical and EPR parameters to elucidate the coordination environment of the Cu(II) systems in basic solutions.