Density functional theory calculations of the EPR parameters for transition metal complexes

Density functional theory calculations of EPR parameters, such as electronic g tensors and metal hyperfine interaction (A) tensors, have been completed for a sense of transition metal complexes. The g tensors were calculated using the zeroth-order regular approximation (ZORA) for relativistic effects as incorporated into the Amsterdam Density Functional (ADF) program. The A tensors were calculated using relativistic and nonrelativistic methods as implemented in ADF and Gaussian98 programs, respectively.;These methods were used to calculate the EPR parameters for Cu 2+ and VO2+ complexes. The accuracy of the methods was assessed and the results of the relativistic and nonrelativistic methods were compared. The best overall agreement for VO2+ with experimental A values was obtained with the nonrelativistic method using the half and half hybrid functionals, such as BHPW91, BHP86, and BHLYP. Density functional theory (DFT) calculations of EPR hyperfine and quadrupole coupling constants for it model complex, [VO(imid)(H2O)4]2+, were used to elucidate the orientation dependence of the vanadium and nitrogen hyperfine coupling constants for an equatorially coordinated imidazole ligand. Density functional theory (DFT) calculations of nitrogen hyperfine and quadrupole coupling constants were conducted for a series of oxovanadium complexes with axial and equatorial nitrogen ligands. Very good quantitative agreement was obtained between the calculated and experimental coupling constants using the scalar-relativistic spin-unrestricted open shell Kohn Sham (SR UKS) method.;DFT calculations of the A tensor for Cu2+ complexes indicate that the inclusion of spin orbit coupling effects was essential for accurate calculations.