The role of electronic delocalization over the chelate ring in stabilizing complexes of 2,2′-bipyridyl

Abstract

The ligand-field spectra of [ML₃] complexes have been recorded [M = Co^II, Co^III, or Ni^II; L = 2.2′-bipyridyl (bipy), 2-aminomethylpyridine (amp), and ethylenediamine (en)]. The positions of the bands in the spectra of the 2 amp complexes are the means of the positions of the same bands in the analogous bipy and en complexes, suggesting that electronic delocalization over the chelate ring is not of importance in producing the high position of bipy in the spectrochemical series. A model of the chelate effect is used to support this finding. The significance of the crossover of the ³T_2g and ¹E_g energy levels in the nickel(II) complexes is discussed in relation to the problem of assigning the ³A_2g→³T_2g and ³A_2g→¹E_g transitions.