Vibrational-electronic interaction in the infrared circular dichroism spectra of transition-metal complexes

The circular dichroism spectra of the quasi-tetrahedral complexes of transition-metal ions with (?)-spartein, M(l-sp)Cl₂], over the C-H stretching vibration range, show an optical activity which is weak in the Zn(II) case, but enhanced in the Co(II) and Ni(II) analogues through the coupling of the sharp vibrational transition with underlying broad d-d electronic excitation.