The d-electron optical activity of the trisdiamine complexes of cobalt (111) , whether randomly oriented or with a fixed orientation in a single crystal, is quantitatively rationalised by a model in which the transient-induced electric dipole moments in the ligand groups are correlated collinear to the magnetic dipole moment of the metal-ion transition by the leading electric multipole moment of that transition, a hexadecapole.IN octahedral and other centrosymmetric transition metal complexes the intensity mechanism for d-electron transitions discussed in the preceding communication1 is forbidden, although the corresponding vibronic mechanism, dependent upon the ungerade nuclear modes, remains operative. On reducing the symmetry of a 6-co-ordinate complex from 0, to 0 the mechanism becomes allowed, but not for the quadrupolar d-electron transitions which are the effective excitations in the complexes belonging to the isomorphous T , group. For a complex of 0 symmetry only the charge distribution of the hexadecapolar d-electron transitions constructively correlate transient induced electric dipole moments in the ligands (Figure). In contrast to the T, case, the xy(x2 -y"), yz(y2 -z2), and x z ( Px z ) components of a hexadecapole transform under the same row of the T , representation in 0 as, respectively, the z, x , and y component of an electric and a magnetic dipole moment. The d-electron transitions I A o) + I A&) with an electric hexadecapole moment , H o , are generally magnetic-dipole allowed, the moment I ma0 I being2 e.g., 22/2 Bohr magneton for each of the three components of the 'A1, -+ ,TI, transition of [ C O ( N H ~) ~] ~+ a t 21 kK.t I n non-centrosymmetric f 1kK = lo3 cm-1.