The heterospin cobalt complexes: peculiarities of high-resolution NMR spectra

The high-resolution H-1 and C-13 NMR spectra (CHCl3 solution) of sterically non-rigid heterospin complexes CoL2, CoL2-dipy, and CoL2-phen (where L is 4-(3',3',3'-trifluoro-2'-oxopropylidene)-2,2,5,5-tetramethyl-3-imidazoli-dine-1-oxyl) have been studied. The specific of the NMR phenomenon in paramagnetic systems is briefly analyzed. It is shown that the NMR spectra modified by hyperfine coupling can be successfully employed for investigation of the complexation processes. In accordance with the common protocols, the H-1 and C-13 NMR signals are assigned using the information on C-13-H-1 spin-spin coupling. In addition, the preliminarily recorded H-1 and C-13 NMR spectra of radical L are also used in the work. The temperature dependences of H-1 and C-13 paramagnetic shifts in the complexes under study have been obtained. A fundamental feature of these dependences is that they obey to the Curie law in a fairly wide temperature range (up to 100 degrees C). This observation can be used to control intramolecular processes of sterically nonrigid heterosystems in solutions.