By their effectiveness in inducing pronounced asymmetry within the -POS2group.Cu2f and Zn2+ are shown to form inner sphere complexes with these ligands. In complexes of alkaline earth ions and of the 3d-metal ions Mn2+, Co2+ and Ni2+, the ligand absorptions are only slightly perturbed. This is taken as evidence for the predominance of outer sphere structures in solutions of these complexes.