A Proton Magnetic Resonance Study of Cobalt(III) Complexes Containing 1,10-Phenanthroline and Ethylenediamine

The proton magnetic resonance (PMR) spectra of the phenanthroline ligand in [Co(phen)3]Cl3, [Co(phen)2-(en)]Cl3 (new complex) and [Co(phen)(en)2]Cl3 were measured in deuterium oxide and analyzed as ABX systems. Significant up-field shifts of signals were observed only for the protons 2 and 9 of [Co(phen)3]3+ and the proton 2 of [Co(phen)2(en)]3+, not for the proton 9 of [Co(phen)2(en)]3+ nor the protons 2 and 9 of [Co(phen)(en)2]3+. The up-field shift was considered to be due to the effect of the ring current of the other phenanthroline ligands, since the protons 2 and 9 of [Co(phen)3]3+ and the proton 2 of [Co(phen)2(en)]3+ lies very close and to above the neighboring aromatic ligand.