NMR Spectra Transformed by Electron-Nuclear Coupling as Indicator of Structural Peculiarities of Magnetically Active Molecular Systems.

The peculiarities of nuclear spin relaxation in the paramagnetic systems have been analyzed taking into account the exchange processes. The analysis is based on the modified Solomon-Bloembergen equations. In this line, the conditions of detecting of the NMR signals of samples are discussed depending on resonance frequency of the NMR spectrometer and characteristic relaxation time. On this basis, (1)H NMR spectra of cobalt semiquinolate complex have been analyzed. It has been shown that the satellite signals observed in the spectrum are caused by hyperfine coupling of the tert-butyl group protons with α and ß states (localized on pz orbital of the aromatic carbon) of unpaired electron spin. The relaxation process of the resonance protons is controlled by paramagnetic dipole-dipole coupling. The contact hyperfine coupling does not contribute to the paramagnetic broadening. A mechanism involving paramagnetic molecular structures, which are responsible for intramolecular exchange processes in the cobalt semiquinolate complex, is given.

The study of structure and dynamics of molecules: NMR spectra transformed by superfine coupling.

In the present paper, the peculiarities of NMR phenomenon in paramagnetic systems are reported. Specifics of detection of high-resolution NMR spectra transformed by superfine interaction are discussed. Concrete examples illustrate the modern possibilities of NMR application for the study of structure and dynamics of the molecular (multielectron) systems.

Changes in the NMR characteristics of 3,6-di-tert-butylquinone on formation of paramagnetic complexes.

High-resolution NMR spectra of 3,6-di-tert-butylquinone were recorded and analyzed for the first time in a wide range of temperatures. The spectra were transformed by paramagnetic additives of cobalt, nickel, and copper complexes synthesized on the basis of metal semiquinolates. Chloroform, dimethylsulfoxide, toluene, and acetone were used as solvents. It was shown that the spectra changed by paramagnetic additives can contain valuable information on the nature of a superfine interaction in paramagnetic complexes and on peculiarities of intramolecular dynamics inherent in these compounds.

Peculiarities of intramolecular exchange and valence tautomerism in metal semiquinolates determined by high-resolution NMR spectroscopy.

The (1)H NMR spectra of semiquinalate cobalt complex have been analyzed in a wide range of temperatures. It has been established that the intramolecular exchange requires the obligatory presence of a paramagnetic structure containing non-compensated electron spin localized on the carbon atom of the ligand aromatic ring, the cobalt atom being trivalent. The presence of such a structure leads to the appearance of satellite signals in the NMR spectra because of the superfine interactions.