SPECTROSCOPIC STUDIES ON COPPER(II) COMPLEXES OF CHIRAL CYCLENS - [CUN4CL] CHROMOPHORES VARYING FROM SQUARE PYRAMIDAL TO TRIGONAL BIPYRAMIDAL STEREOCHEMISTRY

A series of five copper(II) complexes with four geometrically isomeric ligands of 1,4,7,10-tetrabenzyl-2,5,8,11-tetraethyl-1,4,7,10-tetraazacyclododecan and with (2R,5R,8R,11R)-2,5,8,11-tetraethyl-1,4,7,10-tetraazacyclododecane has been investigated by means of ESR, CD and MCD in solution. X-ray studies reported separately had shown that the [CuN4Cl] chromophores were distorted to varying extents from square pyramidal to trigonal bipyramidal geometry. The stability and rigidity of the molecular structure have enabled us to carry out a complementary study of the crystalline state and solution chemistry. The ground state Kramers doublets varied from 3d(x2-y2) to 3d(z2) type with increasing distortion around the copper ion. The orbital sequence of the 3d(1) positive hole, d(x2-y2)<d(z2)<d(yz,xz)<d(xy), has been obtained for the C-4v complexes. The 3d(xy) orbital is also the highest in energy for the complex with the 3d(z2) type ground state doublet. This complex exhibited superhyperfine splitting in the g, region due to the chlorine nucleus, which implies the principal z axis of the g tenser is along the Cu-Cl bond. The sign of the copper hyperfine tensors was determined by means of Swalen's treatment. The changing values of the orbital coefficients decreasing for the 3d(x2-y2) and increasing for the 3d(z2), 3d(xz) and 3d(yz) in the ground state doublets have been attributed to concomitant elongation of the in-plane Cu-N bond and reduction of the out-of-plane Cu-Cl bond length with the increasing distortion around the copper ions.