Absolute configurations of 1,10-phenanthroline and 2,2'-bipyridine metal complexes

The nonempirical circular dichroism method for determining the distribution of chelate rings in dissymmetric metal complexes, which is based on long-axis-polarized π → π ligand transitions, is reviewed and applied to some cobalt(III), chromium (III), and nickel (II) 1,10-phenanthroline and 2,2′-bipyridine complexes. It is found that the relative energies of the split components of these transitions for the bis and tris complexes are dependent on the metal ion and cannot be determined by the simple dipole-dipole interaction theory. However, the sign of the splitting was determined experimentally by comparing the centers of gravity Of the absorption bands for the bis and tris complexes with those of the equivalent mono complexes. The absolute configurations determined in this way are compared with those from the empirical method based on the d-d transitions and are found to be in good agreement.