NMR in paramagnetic complexes of radicals with organic ligands. II. Method of identification of electronic structure of complexes — Theory

A method of identification of the electronic structure of stable nitroxide radical complexes with organic ligands is developed. The idea of this approach is that the concentration dependences of the paramagnetic shifts and line widths of the NMR spectra of two ligands in solution depend on whether these ligands form complexes with the same radical orbital or with different orbitals. In the latter case the complexation of one ligand should not influence the paramagnetic shift and line broadening of another ligand molecule present in the solution. In contrast, in the former case such influence should exist since both ligands are in competition. On this basis different schemes of complexation are considered and theoretical expressions for paramagnetic shifts and line widths are derived that show what kind of experimental data is required to identify the structure of the complex. The theory developed can be generalized to other paramagnetic complexes of radicals, ions and molecules.