Mixed Ligand Complexes of Al(III) with Chelating Organic Acids and Ethylenediamine

Mixed ligand complexes of Al(III) with o-Nitrophenol, 1-Nitroso-2-naphthol, 2,4-Dinitrophenol, 8-Hydroxyquinoline, 2,4,6-Trinitrophenol or o-Nitrobenzoic acid and Ethylenediamine were prepared and studied by elemental analyses, conductometric measurements, FTIR and UV-Vis measurements. These studies indicates the coordination of aluminium metal with o-Nitrophenol, 1-Nitroso-2-naphthol, 2,4-Dinitrophenol, 8-Hydroxyquinoline, 2,4,6-Trinitrophenol or o-Nitrobenzoic acid through oxygen or/and nitrogen atom and with Ethylenediamine through nitrogen atom.


INTRODUCTION
Analyses of complexes with varied ligand are of significance as more than one ligand is associated with the metal ion in the complex [1][2][3] . The presence of different type of ligand enhances the properties of the complex [4][5][6][7][8][9][10] . Ethylenediamine is an important bidentate ligand with two donor atoms which can construct a chelating ring with the metal. Ethylenediamine can form complexes with different metal ions with distinct bonding determined by the reaction conditions and the properties of the metal ion. Kriza et al have used azomethines and isopropoxides as ligands for the synthesis of mixed ligand complexes and has proposed monomeric structure for these complexes 11 . The adaptable chelating capacity of Ethylenediamine with several metals is distinctly been established 12,13 . Studies on mixed ligand complexes have been reported by several authors 14-16 . In this paper we describe the preparation and spectral properties of new Al(III) complexes with varied ligand derived from o-Nitrophenol, 1-Nitroso-2-naphthol, 2,4-Dinitrophenol, 8-Hydroxyquinoline, 2,4,6-Trinitrophenol or o-Nitrobenzoic acid and Ethylenediamine.

Preparation of Al(III) complexes
0.01 mol of aluminum basic acetate was dissolved in absolute alcohol to form a suspension. 0.02 mol of o-Nitrophenol or 1-Nitroso-2-naphthol or 2,4-Dinitrophenol or 8-Hydroxyquinoline or 2,4,6-Trinitrophenol or o-Nitrobenzoic acid was then mixed with constant stirring and further 0.01 mol of Ethylenediamine was added. The mixture was refluxed with magnetic stirrer for 1½ h at 80°C. It was then cooled to obtain a characteristic coloured complex. The complex was filtered and the collected precipitate was further washed with absolute alcohol. It was then dried in an electric oven at 100°C. The complex was preserved in desiccator over fused CaCl 2 .

RESULTS AND DISCUSSION
Mixed ligand complexes of Al(III) in solid state with varied colours were obtained. They are soluble in polar solvents viz. ethanol, DMF, methanol, etc; and insoluble in non-polar solvents viz. toluene, benzene, ether, etc. Higher decomposition temperature of the complexes than the ligand indicates higher stability of the complexes Table 1. The complexes when stored under dry conditions were found to be stable. Elemental analyses for hydrogen, carbon and nitrogen Table 2 were performed on Heraeus B6450 CHN elemental analyzer.

Molar conductance
All the mixed ligand complexes were measured for their molar conductance in DMF at 23°C on Systronics digital direct conductivity meter-306 at a concentration of 10 -3 M. A value of 32.2-43.5 ohm -1 cm 2 mol -1 appears characteristic of 1:1 electrolyte and indicates ionic nature of the complexes 17 Table 1.

Infrared Spectra
Infrared spectrum in the range 4000-400 cm -1 in KBr phase was recorded for Ethylenediamine and its various mixed ligand Aluminium(III) complexes. JASCO model-5300 FTIR instrument was employed for recording the Infrared absorption bands. The selected absorption bands are listed in Table 3.
For the ligand Ethylenediamine, the peaks at 3377 and 3316 cm -1 reflects stretching mode of N-H; N-H (asymm. def.) mode occurs at 1600 cm -1 ; N-H (symm. def.) mode at 1100 cm -1 and peak at 810 cm -1 for rocking mode of NH 2 are also observed. For the mixed ligand complexes, one N-H vibration band appears as broad peak except for C 16

UV-Visible spectra
UV-Visible spectra were taken using paraffin solvent on Perkin-Elmer-Lambda-15 UV-Vis instrument. Table 4 lists the position of UV-Vis spectral bands for the mixed ligand complexes of Al(III). UV-Visible absorption peaks for the mixed ligand complexes of Al(III) with Ethylenediamine are found at 240 nm and 248 nm which indicate p-p* transitions in these complexes 19 whereas bands in the range 328-390 nm are due to charge transfer spectra Table 4. There is a shift in the spots of p-p* transitions on complexation; the spots of charge transfer transitions also shows a shift. The shifting occurs on account of p-interactions between the ligand and metal orbitals. The elemental analyses, molar conductance measurements, infrared spectrum and UV-Visible spectrum suggest a probable structure for C 16 H 19 N 4 O 8 Al which is shown in Figure 1. Similarly, the structure for the other prepared mixed ligand complexes of Al(III) may also be suggested.