New Copper(II) Tetraazaannulene Complexes. Potential Building Blocks for Mixed Valence, Conducting, Molecular Crystals: Synthesis, Experimental and Theoretical Characterization

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 3dxy 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.