The Effect of Axial Pyridine Ligands on the Charge Transfer Bands of trans-Bis(dimethylglyoximato)Cobalt(III) and -Iron(II) Complexes

Abstract

Abstract The electronic absorption spectra of [CoIII(dmgH)2B2]+ and [FeII(dmgH)2B2] (dmgH=dimethylglyoximate monoanion and B=pyridine derivatives) are inspected with respect to the effect of the axial pyridine ligands on the charge-transfer bands of the complexes. The characteristic bands observed in the 275–305 mμ region for the Co(III) complexes and in the 485–555 mμ region for the Fe(II) complexes, which have been assigned to a metal→oxime charge-transfer band, are shifted to shorter wavelengths with a decrease in the basicity of the pyridine derivatives. The results have been discussed by taking into account the π-interaction of the dπ(dxz, dyz) orbital of the central metal ion with the empty π-orbitals of both the dimethylglyoximate and the pyridine derivatives. It is suggested that the π-interaction is stronger in the Fe(II) complexes than in the Co(III) complexes, while the σ-bond is stronger in the latter. The infrared spectral evidence that the C=N stretching frequency is dependent on the axial pyridine derivatives, and that it is observed at a lower frequency in the Fe(II) than in the Co(III) complexes, is consistent with the above results.