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(parallel to) and A(parallel to) was obtained from the DFT calculations. Notably, g(parallel to) systematically increases and A(parallel to) 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.