ORIENTATION OF THE IMIDAZOLE TYPE LIGANDS IN COPPER-COMPLEXES STUDIEDBY ESEEM

Effects of nitrogen quadrupole coupling tensors on ESEEM spectra are d iscussed. 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 calcula tions for angle-selected nitrogen ESEEM spectra of copper complexes in the disordered state show that the double quantum transition line cha nges its intensity with the resonance magnetic field set position in t he EPR spectrum. These model calculations also show that estimation of the orientation of the imidazole type ligands with respect to the g p rincipal axes may be easily made without any tedious processes of comp uter simulation of the whole ESEEM spectral pattern. The usefulness of the method is experimentally shown by applying it to the structural s tudies of the copper complexes of 2-(2'-pyridyl)imidazole and 2-(2'-py ridyl)benzimidazole and their six coordinated complexes with nitrogene ous bases.