NMR spectroscopic studies of ligand exchange in paramagnetic complexes of Co and Ni hydrometallatranes

Paramagnetic complexes of hydrometallatranes with Co 2+ and Ni 2+ were studied by high-resolution 1 H and 13 C NMR spectroscopy. The paramagnetic shifts of the signals in the 1 H NMR spectra by ∼100 ppm downfield with respect to their position in the spectra of uncoordinated ligands were observed. A similar upfield shift by ∼400 ppm was observed in the 13 C NMR spectra. Analysis showed that paramagnetic shifts are caused by the contact hyperfine or electron-nucleus interactions between the unpaired electrons and the resonating nuclei of the ligand molecules. It was found that the preferred tridentate N,O,O-state of the ligand (triethanolamine) in aqueous solutions is accompanied by the intraligand exchange, in which two out of three oxygen centers compete for coordination. Triethanolamine was found to undergo substitution with 1-methylimidazole under mild conditions with the formation of complexes of the composition M(MIm) 4 X 2 (M = Co, Ni; X = Cl, AcO). This causes a paramagnetic shift of the signals in the 13 C NMR spectra as a result of the hyperfine interaction of the MIm nuclei with the unpaired spins of the coordinating ion.