New copper(II)-tetraazaannulene complexes. Potential building blocks for mixed valence, conducting, molecular crystals: Synthesis, experimental and theoretical characterization

Abstract

Copper(II)-tetraaza[14]annulene complexes: Cu(dibenzo[b,i][1,4,8,11]tetraaza [14]annulene), Cu(dbTAA); Cu(dinaphtho[b,i][1,4,8,11] tetraaza[14]annulene), Cu(dnTAA) and Cu(diphenanthro[b,i][1,4,8,11]tetraaza[14]annulene), Cu(dpTAA) have been synthesized and studied by UV-vis spectroscopy, static magnetic susceptibility, ESR and cyclic voltammetry. UV-vis spectral evidence for Cu(dbTAA) and Cu(dnTAA) association was found in low donor ability solvents. The ground state electronic structure of Cu(dbTAA) has been investigated by very accurate SCF-LCAO calculations in the local-density approximation. According to the ESR and magnetic susceptibility data, the theoretical results indicate that the unpaired electron is shared in almost equal amounts by metal 3 d xy and ligand nitrogen orbitals. The optical transitions in the case of Cu(dbTAA) have been calculated by a ΔSCF procedure and compared with experimental spectra obtained in highly diluted solution. Cyclic voltammetry, UV-vis and theoretical calculations suggest that the dpTAA ligand both in the free state as well as in the complex strongly deviates from planarity.