DFT and TD-DFT studies on copper(II) complexes with tripodal tetramine ligands

Copper(II) complexes, containing aliphatic tripodal tetramine ligand, [Cu(trpn)(NH3)] 2+ (1), [Cu(tren)(NH3)] 2+ (2), [Cu(332)(NH3)] 2+ (3) and [Cu(322)(NH3)] 2+ (4) are optimized at B3LYP/ LANL2DZ and B3LYP/GEN levels of theory in gas phase (where (trpn), (tren), (332) and (322) are N(CH2CH2CH2NH2)3, N(CH2CH2NH2)3, N[(CH2CH2CH2NH2)2(CH2CH2NH2)] and N[(CH2CH2CH2NH2)(CH2CH2NH2)2], respectively). The optimization results show that the copper(II) center is trigonal bipyramidal for the studied complexes. Charge distributions on the donor and acceptor atoms are evaluated by natural population analysis. The charge distribution indicates that the ligands transfer their negative charges to copper(II) ions during formation of the complexes. Electronic excitation energies of copper(II) complexes are calculated with time dependent density functional theory in gas phase. It is found that the most intense bands at electronic spectra of complexes stem from dxz, dyz→dz or dx-y, dxy→dz transitions.