Density Functional Theory Investigation of EPR Parameters for Tetragonal Cu(II) Model Complexes with Oxygen Ligands

Density functional theory (DFT) calculations of the electron paramagnetic resonance (EPR) parameters for a series of tetragonal Cu(II) model complexes were conducted. Model complexes containing four oxygen atoms directly coordinated to a Cu(II) metal center were chosen because of their importance in the Peisach−Blumberg truth tables and their frequent use in the interpretation of EPR spectra of Cu(II) proteins and copper-containing catalysts. Molecular g- and copper A-tensors were calculated using the BP86 and B3LYP density functionals. The DFT calculations reproduce the experimentally observed trends in the parallel components of the A- and g-tensors. Important insight into the structural basis for the empirical trends in g ∥ and A ∥ was obtained from the DFT calculations. Notably, g ∥ systematically increases and A ∥ systematically decreases with increasing Cu−O equatorial bond length. These results have been used to provide structural insight into copper EPR data for copper-exchanged zeolites.