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 ClO , BPh , PF and BF (X) were studied. The IR, electronic absorption spectra and 4 4 6 4 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 CuO N 2 2 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. INTRODUCTION electronic spectra according to the strength of Heteroloptic chelated complexes of copper (II) having This behavior in the heteroleptic chelated copper (II) the general formula [Cu(NN)(OO)] are reported to have complexes has received more interest because they may + potentially useful solvatochromism properties [1-3]. In the be used as a Lewis acid-base color indicator [2, 6] and above formula, (NN) stands for a diamine ligand and its also utilize to develop optical sensor materials to monitor derivatives, (OO) represents for acetylacetonate anion. pollutant levels in the environment [7, 8]. In this regard The phenomenon of solvatochromism which refers to extensive studies have been concentrated on the changes in electronic absorption spectra with solvent heteroleptic chelated complexes of copper (II) with acac is one of the important topics in solution chemistry. and diamine derivatives (acac, stands for acetylacetonate The origin of solvatochromism occurrence in metal ion) [9-15]. complexes are classified into two general types [4, 5]; in Recently, we prepared a series of heteroleptic chelate the first type, metal complexes in solution are interacted copper (II) complexes that are soluble almost in a large by solvent molecules in a direct fashion due to direct number of solvents and show solvatochromic property. attachment of the solvent molecules onto metal center and Our study demonstrated that the ClO counter-ion is in the second type, by indirect interactions between bound weakly above and below of the chelate plane in solvent molecules and ligands. Among the former whose solution, the perchlorate ions are driven out by color changes are due to those of d–d transitions, solvent molecules leading to their solvatochromism. copper(II) complexes with a strong John–Teller effect can In continuation of our study we wish to report the be anticipated to show simple and regular changes in their syntheses and the solvatochromic behavior of some of interactions with solvent molecules at the axial sites. 4