Spectroscopic studies on chromotropic mixed-ligand copper(II) complexes containing o-hydroxy benzoyl derivatives and dinitrogen bases.

Synthesis of chromotropic copper(II) mixed ligand complexes of o-hydroxy benzoyl derivatives (L1) and dinitrogen bases (L2), general formula Cun(L1)(L2)nXn; where n=1 or 2, L1=4,6-diacetyl-resorcinol (H2DACR), o-hydroxy benzaldhyde (HOHBZ) or o-hydroxy acetophenone (HOHAP), L2=N,N,N',N'-tetramethylethylenediamine (Me4en), 1,10-phenanthroline (phen) or bipyridine (bipy) and X=ClO4-, NO3- or Br- have been reported. Spectral, magnetic and molar conductance measurements as well as analytical data of these complexes show either mononuclear structure for OHBZ and OHAP or binuclear structure for DACR complexes. The IR stretching vibration frequencies of Cu-N and Cu-O are linearly correlated with the d-d absorption frequencies. The d-d absorption bands of Me4en-complexes in weak donor solvents suggest square-planar, distorted octahedral and distorted trigonal bipyramid geometries for the perchlorate, nitrate and bromide complexes, respectively. However, an octahedral structure is identified for the complexes in strong donor solvents. Perchlorate complexes show a remarkable color change from violet to green as the donor ability of the axial ligand increases, whereas bromide complexes are mainly affected by the Lewis acidity of the axial ligand. Specific and non-specific interactions of solvent molecules with the complexes are investigated using the unified solvation model. Calculations of the electronic transition probability (f) of the d-d band along with molecular orbital calculations of ligands have been carried out and correlated with the experimental data.