The electronic spectra, optical rotatory power and absolute configuration of metal complexes the dextro-tris (ethylenediamine)cobalt (III) ion

Abstract

The circular dichroism, optical rotatory dispersion and electronic absorption spectrum of the d-Co(en)3 3+ ion have been measured in solution and in the hexagonal uniaxial crystal, 2[d-Co(en)3Cl3]. NaCl. 6H2O, of known structure. The derived rotational and dipole strengths give a magnetic moment of the order required theoretically (4 Bohr magneton) for the 1 Ea transition. The ionic crystal field model is found to account for neither the sign nor the magnitude of the observed rotational strength, and a new model is proposed in which the metal ion transitions acquire a rotational strength by mixing with ligand transitions having electric moments directed perpendicular to the planes of the chelate rings. A new experimental criterion is advanced for the absolute configuration of dihedral d 3 and d 6 transition metal complexes, relating the chirality of the enantiomers giving an Ea transition with a positive rotational strength to that of the d-Co(en)3 3+ ion.