CIRCULAR DICHROISM OF SQUARE-PLANAR, TETRADENTATE SCHIFF BASE CHELATES OF COPPER(2)

The circular dichroism (CD) and electronic absorption spectra of a series of nine copper(II) complexes with tetradentate Schiff bases derived from (R)-(-)-propane-l,2-diamine and (RR)-(-)-cyclohexane-l,2-diamine have been measured in chloroform and in pyridine. The signs of the Cotton effects of d-d and ligand transitions for this series of complexes can be correlated with the absolute configuration of a proposed flattened tetrahedral array of donor atoms about the copper ion. This configuration is produced stereospecifically by the conformational preference of the central (gauche) chelate ring which results from the steric requirements of the ligands. The circular dichroism spectra of these complexes reveal more detailed band splittings in the d-d transition region than do the corresponding electronic spectra. By comparison of these CD bands with published polarized crystal spectra, tentative assignments of the metal ion transitions are proposed. Solvent effects, when they are not precluded by steric interactions, assist in the assignment of the metal ion transitions. © 1969, American Chemical Society. All rights reserved.