Circular dichroism spectra of amino acid complexes. II. Chelated amino acid complexes with the CoN₅O chromophore

Abstract

The circular dichroism spectra of a series of optically active (α-aminocarboxylato)tetraamminecobalt(111) complexes have been measured in aqueous solution, and in the presence of salts of polarizable anions. The observed spectra in the visible region have been analysed to determine the signs of the Cotton effects of the three components of the ¹A_1g ↔ ¹T_1g cobalt(111) transition. For L-amino acids, the transition with A_2g(D_4h) parentage is negative, and the two transitions with E_g(D_4h) parentage have opposite signs. Published circular dichroism spectra of complexes of the type [Co(en)₂(L-am)]²⁺ were similarly interpreted in terms of a perturbed tetragonal chromophore, and it was shown that the vicinal effect of the L-amino acids imposed the same signs onto the component transitions as for the tetraammines and for a similar series of pentaamminecobalt(111) complexes.