An Electronic Structural Analysis of O2-Binding Dicopper Complex: Insights from Spin Magnetism and Molecular Orbitals

We investigated the geometry and electronic structure of the oxygen-bridged dicopper complex [CuII2(NH3)4O2]2+ and discussed how different DFT methods and basis sets, including dispersion corrections and dielectric media, affect the predicted structure and spin state. Our results showed that pure functionals yielded the closed-shell singlet character, whereas hybrid functionals presented a partial diradical character that coincided with increased spin contamination. Incorporating a polarizable continuum model further enhanced the diradical character and more closely reproduced the measured Cu–Cu distance with a bent Cu2O2 core. Analysis of the molecular orbitals and computed absorption spectra revealed how orbitals produce the key transition from ligand-to-metal charge transfer. These findings underscore how environmental effects influence the description of Cu2O2 chemistry.