Bis(tridentate)cobalt(III) complexes with diethylenetriamine and 4-Methyldiethylenetriamine [2,2'-Methyliminodi(ethylamine)]: Assignment of geometric configurations by 1H and 13C N.M.R. spectroscopy

Abstract

The new complexes symmetrical-facial-[Co(medien)2]3+ and s-fac- [Co(dien)(medien)]3+ have been isolated. The 1H N.M.R. spectra of these complexes, the s-far, u-far and meridional isomers of [Co(dien)2]3+, and u-fac-[Co(daes)2]3+ show different splittings of the NH2 proton resonances [dien = diethylenetriamine, medien = 4- methyldiethylenetriamine or 2,2?-methyliminodi(ethyl-amine), daes = di(2-aminoethyl) sulphide or 2,2?-thiodi(ethylamine)]. These splittings depend on the geometries of the complexes (different numbers of stereochemically distinct NH2 groups), the particular chelated ligands (splittings due to coupling between the two protons on each NH2 may vary with chelate ring conformational mobility), and the counter-anions (different extents of ion- association through hydrogen bonding). Thus NH2 proton resonance signals may not always provide a reliable method for establishing molecular geometries. In contrast, the 13C N.M.R. spectra of all these complexes are completely diagnostic of the detailed geometries, and most of the resonances observed have been assigned to particular carbon atoms.