Synthesis and Spectral Studies on Heteroleptic Chelated Copper (II) Complexes of Diamine and Acetylacetonate

The infrared and electronic absorption spectra of a series of new heteroleptic chelated copper (II) complexes [Cu(diamine)(acac)]X that encompass N,N′-1,6-bis(2-bromophenyl)-2,5-diazahexane (diamine), acetylacetonate (acac) and ClO4-, BPh4-, PF6- and BF4-(X) were studied. The IR, electronic absorption spectra and the molar conductivity of the newly prepared complexes were presented and discussed. The molar conductivity in dichloromethane reveals a predominance of electrostatic interactions between [Cu(diamine)(acac)]+ entity and anions, X- that counterbalance the positive charge. The resulting complexes with local symmetry of CuO2N2 attain a square-coplanar structure and exhibit the tendency for axial ligation, which is enhanced when an electron-attracting substituent is attached to the phenyl ring of diamine moiety. The tendency for axial ligation is particularly fulfilled when suitable nucleophiles (solvents) with different donor abilities exist, leading to solvatochromism. The solute-solvent interactions are revealed by shifts in the ligand field absorption spectra that are enhanced as the donor power of the solvent increases. Linear dependence of the ligand field absorption maximum on solvent donor number is generally observed.