Optical Configurations of Complexes of Amino-acids with Cobalt(III)

Abstract

COMPLEXES of cobalt(III) with α-amino-acids have recently attracted much attention. Perhaps most interest has been focused^1,2 on the interplay of the asymmetry of L-amino-acids with that of cobalt in an asymmetric octahedral site. For investigations of this type, a knowledge of the absolute configuration about the cobalt ion is required, and here an empirical rule has proved useful. This states³ that any complex of cobalt (III) which contains two or three five-membered chelate rings and has a dominantly positive Cotton effect for the longer wavelength d–d absorption band has the D-configuration. There are two apparent exceptions to this rule, and it is the purpose of the present note to remove this contradiction.