Magnetic Circular Dichroism of Nickel(II) and Copper(II) Complexes with 1,4,8,11-Tetraazacyclotetradecane Derivatives

Abstract

Abstract The magnetic circular dichroism (MCD) spectra of nickel(II) and copper(II) complexes with 1,4,8,11-tetraazacyclotetradecane derivatives were measured. An anomalous MCD dispersion was observed in a (d, d*) band at 22000 cm−1 for the copper(II) complexes and at 22000–23000 cm−1 for the nickel(II) complexes. In the ultraviolet region, the nickel(II) complexes show a normal MCD dispersion in the 35500 cm−1 band which appears only for the ligands with >C=N- double bonds, while the copper(II) complexes show an anomalous dispersion in the 39000 cm−1 band which appears even if the ligand lacks >C=N- double bonds. The 35500 cm−1 band of the nickel(II) complexes is assigned to a “metal to ligand” charge-transfer transition leg→π* and the 39000 cm−1 band of the copper(II) complexes to a “ligand to metal” charge-transfer transition leu→2b1g. In the nickel(II) complex of a ligand with two isolated and two conjugated double bonds shows a normal MCD dispersion in the 25000 cm−1 band. The absorption band is assigned to a “metal to ligand conjugated double bonds” charge-transfer transition rather than a (d, d*) transition.