Orientation of the imidazole type ligands in copper complexes studied by ESEEM

Effects of nitrogen quadrupole coupling tensors on ESEEM spectra are discussed. It is shown from theoretical considerations that the spectra, especially the double quantum transition line, are strongly affected by changes of tensor orientation in the magnetic field. Model calculations for angle-selected nitrogen ESEEM spectra of copper complexes in the disordered state show that the double quantum transition line changes its intensity with the resonance magnetic field set position in the EPR spectrum. These model calculations also show that estimation of the orientation of the imidazole type ligands with respect to the g principal axes may be easily made without any tedious processes of computer simulation of the whole ESEEM spectral pattern. The usefulness of the method is experimentally shown by applying it to the structural studies of the copper complexes of 2-(2′-pyridyl)imidazole and 2(2′-pyridyl) benzimidazole and their six coordinated complexes with nitrogeneous bases.