USING TWO DIMENSIONAL NMR TECHNIQUES TO ASSIGN PROTON AND CARBON SPECTRA FOR COBALT(III) COMPLEXES DERIVED FROM LINEAR QUINQUEDENTATE LIGANDS CONTAINING NITROGEN AND SULFUR DONOR ATOMS

Abstract

High resolution NMR spectroscopy was used to study the structure of a cobalt(III) complex derived from the linear quinquedentate ligand, 7-methyl-4, 10-dithia-l, 7, 13-tria-zatridecane, NH₂-CH₂CH₂-S-CH₂CH₂-N(CH₃)-CH₂CH₂-S-CH₂CH₂-NH₂. The flexibility of this ligand allows it theoretically to form four distinct structural isomers with metal ions. The one dimensional proton spectrum exhibited by [Co(NSNSN)Cl]Cl₂, is complicated and does not provide structural insight. A combined utilization of proton, carbon, DEPT, COSY, NOESY and HETCOR spectra was employed to establish geometric structure type, make individual proton assignments, identify proton-proton connectivities that result from scalar coupling, and distinguish interactions occurring as a result of through-space interactions. Information about the five-membered chelate ring orientations was also obtained. Two groups of signals were shown to correlate with each carbon signal, exhibiting a definite nonequivalence between geminal protons. Geminal protons were found to have coupling constants of 14 Hz. In contrast, the vicinal protons were found to have coupling constants of 5-7 Hz.