Contact and dipolar NMR shifts in nickel and cobalt pyridine complexes

Abstract

Proton magnetic resonance data are presented for the paramagnetic complexes M(ligand) 4X 2 where MCo and Ni, ligand=pyridine and γ-picoline and XCl, Br, I, and NCS. The shifts exhibited by the nickel compounds can be interpreted in terms of a contact interaction involving the same electron spin delocalization mechanisms as found previously for other pyridine complexes. In the cases of the cobalt complexes, both contact and dipolar effects contribute to the observed shifts. However, the sign of the dipolar effect is found to depend upon the nature of X. The cloroform solvent resonances suffer large shifts in the cobalt systems attributable to a dipolar interaction.