Synthesis, spectroscopic and electrochemical characterization of copper(I) complexes with functionalized pyrazino[2,3-f]-1,10-phenanthroline

Abstract

The present work reports the synthesis and spectroscopic and electrochemical characterization of homoleptic copper(l) complexes with substituted pirazino [2,3-f]-1,10-phenanthroline, RpplR', (R = H, Me, COOH or COOMe, and R' = H, Me) as ligand. The ligand ppl works as an acceptor of electronic density, which is delocalized mainly in the quinoxaline part of its structure. The UV-Vis spectra show that all the complexes display bands in the range 400-650 nm, which are MLCT in character. The lambda(max) and extinction coefficients of the MLCT band at 450 nm. and the LC band do not change significatively when varying the R substituent. Nevertheless, the intensity of the shoulder around 500 nm does change; this absorption has been related to either a static or dynamic flattening distortion of the complex D-2d -> D-2 symmetry. The cyclic voltammetry of the complexes shows irreversible redox processes with E-p values that do not follow the tendency expected from the donor/acceptor character of the substituents on the ligand. All the complexes studied showed no emission both in acetonitrile and dichloromethane as solvent at room temperature and under argon atmosphere. All the results are discussed in relation to the proposed flattened distortion of the ground state, as well as in relation to the donor/acceptor character of the substituents on the ligand, the steric effects on the symmetry of the metal center and the excited state distortion.