An angular overlap model analysis was performed on the electronic spec
trum of [Cr(D-pen)(2)](-) and [Cr(D-pen)(L-pen)](-) (H(2)pen = penicil
lamine), in both of which penicillamine acts as a tridentate ligand. T
he D-penicillamine complex has the trans-S, cis-N, cis-O configuration
, while the DL-penicillamine complex has the cis-S, cis-N, cis-O confi
guration. The carboxylate group is a strong pi-donor and the deprotona
ted sulphydryl a moderate pi-donor.