HIGH-RESOLUTION NMR ANALYSIS OF COBALT(III) COMPLEXES WITH 1,8-DIAMINO-3,6-DITHIAOCTANE

This article summarizes NMR data obtained for cobalt(III) complexes de rived from linear and tripodal tetradentate or pentadentate ligands co ntaining nitrogen and/or sulfur donor atoms, and not complexes of larg e Schiff-base macrocycles, porphyrins or corrins. The review is supple mented with recent NMR work on complexes that had their origin in the laboratories of Professor Busch at a time when the use of NMR spectros copy as an inorganic structural tool was in its infancy. The more rece nt capabilities and uses of nuclear magnetic resonance spectroscopy fo r assisting in metal complex structure assignments and isomeric identi fication 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 technique s. The spectra acquired using conventional pulse sequences include pro ton, carbon, DEFT, COSY and heteronuclear correlation. [Co(eee)(NO2)(2 )]Cl and [Co(eee)Cl-2]Cl both give rise to carbon-13 spectra which con tain only three signals and H-1-proton spectra which contain a highly pronounced A(2)B(2) pattern. This data is supportive of the,symmetrica l cis geometry. Assignments in the proton spectra were assisted by the use of the COSY experiment. Carbon-13 signals were assigned by hetero nuclear chemical shift spectroscopy. The DEFT spectra confirmed all ca rbon signals arise from methylene carbons. The study highlights the po wer of H-1 and C-13 NMR spectroscopic techniques for the structural ch aracterization of inorganic complexes. (C) 1998 Elsevier Science S.A. All rights reserved.