DFT calculations of EPR parameters of transition metal complexes: Implications for catalysis

Transition metal and ligand hyperfine coupling constants for paramagnetic vanadium and copper model complexes have been calculated using DFT methods that are available in commercial software packages. Variations in EPR parameters with ligand identity and ligand orientation are two of the trends that have been investigated with DFT calculations. For example, the systematic variation of the vanadium hyperfine coupling constant with orientation for an imidazole ligand in a VO2+ complex has been observed experimentally and has also been reproduced by DFT calculations. Similarly, changes in the vanadium hyperfine coupling constant with ligand binding have been calculated using model complexes and DFT methods. DFT methods were also used to calculate ligand hyperfine coupling constants in transition metal systems. The variation of the proton hyperfine coupling constant with water ligand orientation was investigated for [VO(H2O)5]2+ and the results were used to interpret high resolution EPR data of VO2+-exchanged zeolites. Nitrogen hyperfine and quadrupole coupling constants for VO2+ model complexes were calculated and compared with experimental data. The computational results were used to enhance the interpretation of the EPR data for vanadium-exchanged zeolites which are promising catalytic materials. The implications of the DFT calculations of EPR parameters with respect to catalysis will be discussed.