SPIN-DELOCALIZATION MECHANISMS IN SOME PARAMAGNETIC TRIS-2,2'-BIPYRIDINE COMPLEXES OF NICKEL(2)

The proton nmr contact shifts of Ni(bipy)32+ (bipy = 2,2′-bipyridine) and some substituted bipyridyl complexes are reported, and the mechansims of unpaired electron spin delocalization in these complexes are discussed. It is found that both σ- and π-delocalization mechanisms are important. The shifts can be interpreted quantitatively by comparing the experimental contact shifts with those predicted from extended Hückel molecular orbital calculations. These results and the change in direction of the shifts on substituting CH3 for H at various ring positions are employed to indicate which ligand MO´s are most extensively mixed with the metal ion in the MO´s containing unpaired electrons. © 1968, American Chemical Society. All rights reserved.