Electronic structure and spectra of cupric acetate mono-hydrate revisited

The electronic structure and spectra of cupric acetate mono-hydrate were investigated by measuring magnetic susceptibility from 2–300 K, temperature dependence of electronic spectra in EPA solutions and DFT calculations. A comparison of electronic spectra at 300 K and 77 K revealed four isosbestic points indicating the coexistence of the triplet and singlet bands. Calculations showed that the Cu 3dx2 − y2 orbitals are strongly bonded with the acetate groups and that there was no obvious direct overlap of Cu–Cu δ-type orbitals in the singlet ground state. The magnetic interaction energy J was estimated using the unrestricted MO calculation and HOMO–LUMO mixing method. The UKS HOMO indicated the importance of the super-exchange interaction via the acetate group. Assignments of electronic spectra are presented for the singlet and triplet bands by the TD-DFT method. Polarization characteristics are explained for the visible and near-UV electron transfer band between the two Cu ions proposed by Yamada et al. [S. Yamada, H. Nakamura, R. Tsuchida, Bull. Chem. Soc. Jpn. 30 (1957) 303].

Graphical abstractThe Cu2+ ions in cupric acetate mono-hydrate are bound by the acetate groups. The α-HOMO and β-HOMO are calculated by DFT method, which show spin-polarized ground state. The σ-orbital of acetate groups interact with the Cu 3dx2 − y2 orbitals and the spin-polarized acetate orbitals produce the super-exchange interaction between the Cu2+ ions. The orbitals of two of four acetate groups are shown for clear illustration.Figure optionsDownload full-size imageDownload as PowerPoint slide