High-resolution NMR analysis of cobalt(III) complexes with 1,8-diamino-3,6-dithiaoctane

Abstract

This article summarizes NMR data obtained for cobalt(III) complexes derived from linear and tripodal tetradentate or pentadentate ligands containing nitrogen and/or sulfur donor atoms, and not complexes of large Schiff-base macrocycles, porphyrins or corrins. The review is supplemented with recent NMR work on complexes that had their origin in the laboratories of Professor Busch at a time when the use of NMR spectroscopy as an inorganic structural tool was in its infancy. The more recent capabilities and uses of nuclear magnetic resonance spectroscopy for assisting in metal complex structure assignments and isomeric identification are illustrated by the following work. Cobalt(III) complexes containing the quadridentate ligand 1,8-diamino-3,6-dithiaoctane (eee) were examined by high resolution one and two-dimensional NMR techniques. The spectra acquired using conventional pulse sequences include proton, carbon, DEPT, COSY and heteronuclear correlation. [Co(eee)(NO 2) 2]Cl and [Co(eee)Cl 2]Cl both give rise to carbon-13 spectra which contain only three signals and 1H-proton spectra which contain a highly pronounced A 2B 2 pattern. This data is supportive of the symmetrical cis geometry. Assignments in the proton spectra were assisted by the use of the COSY experiment. Carbon-13 signals were assigned by heteronuclear chemical shift spectroscopy. The DEPT spectra confirmed all carbon signals arise from methylene carbons. The study highlights the power of 1H and 13C NMR spectroscopic techniques for the structural characterization of inorganic complexes.