Microwave Preparation and Spectroscopic Investigation of Binuclear Schiff Base Metal Complexes Derived from 2 , 6-Diaminopyridine with Salicylaldehyde

The binuclear Schiff base complexes prepared by condensation 2,6-diaminopyridine and salicylaldehyde (LH) by using microwave and adding metal salts to ligand by same ratio. The Schiff base ligand was checked by infrared, electronic spectra and HNMR spectroscopy and prepared complexes characterized by molar conductivity, infrared, electronic spectra and susceptibility measurements. The values of molar conductivities reveal that the complexes are non-electrolytes, from obtained data of electronic spectra and magnetic moment, an octahedral geometry was suggested, coordinated to the metal ions in a manner with N donor sites of imine groups, and oxygen of phenolic OH group.


Introduction
The reactions of aldehyde or ketone with primarily amine in which carbonyl group is replaced by imine group is called Schiff bases, are widely used in organic synthesis [1].Schiff bases' importance increased due to a wide range of applications [2]: Exhibit antimicrobial activity, fungicidal activity [3], pharmacological applications [4].Salicylaldehyde is an important precursor to a variety of chelating agents [5].Schiff bases of salicylaldehyde are well known as the polydentate ligands, coordinating as a deprotonated or neutral forms.Schiff bases with Schiff bases and their metal complexes due to synthetic flexibility and sensitivity toward a variety of metal atom and there are many studies [6] which prove this situation [7] [8].Recently, synthesized Cu(II), Ni(II) and Co(II) complexes show the current interest of researchers in the field of coordination chemistry of these metal ions [9].Microwave is one of the modern green synthetic methodologies for Schiff bases [10] [11].

Materials and Methods
Higher grade reagents and solvents were commercially available (Fluka A.G., Merck, BDH) and used as received.Infrared spectra were recorded on a Nicolet 100 FTIR spectrophotometer in the 400 -4000 cm −1 range using KBr discs.NMR spectroscopy recorded by Av 300 instrument.Conductivity measurements were carried out on 10 −3 M solution of the complexes in DMF using conductivity meter Jenway PCM3 at an ambient temperature.The electronic spectra were recorded on a PgT92+ UV-visible spectrophotometer for 10 −3 M solutions of complexes in DMF as solvent at 25˚C using 1 cm quartz cell.Melting points were recorded on an Electrothermal 9300 apparatus.The magnetic susceptibility measurements were carried out at 25˚C on the solids by Gouy's method using Sherwood Scientific instrument.

Results and Discussion
The ligand was prepared by condensation of primary amine and aldehyde under microwave irradiated the complexes were prepared by direct addition of the ethanoic solution of the metals salts (Scheme 1).
The physical properties and analytical data for ligand and complexes are given in Table 1.The values of molar conductivities of the complexes in DMF (12 -26 ohm −1 •cm 2 •mol -1 ) indicate that all the prepared complexes are non-electrolytes [12].
Table 1.Analytical and some physical properties of the ligand and prepared complexes.

Infra-Red Spectroscopy
The most important of infrared frequencies of Schiff base and its Co(ΙΙ), Ni(II), Cu(II), Zn(ΙΙ), Cd(ΙΙ) complexes are recorded in Table 2.The spectrum of ligand showed the absence of C=O absorption band at 1850 -1650 cm −1 .And appearance of a new band at (1601) cm −1 due to azomethine spectra, suggest the formation of ligand [13] [14].The ligand spectra show a broad band at 3375 cm −1 due to stretching vibration of υ (O-H), as well as the C-N band at 1454 cm −1 , the band at 1601 cm −1 assign to υ (C=N ), and the υ (C-O) band at 1277 cm −1 [15].The prepared complexes exhibited very comparable IR features, suggesting that they are of similar structure [16].In the complexes the absorption band of stretching vibrations υ (O-H) disappeared which is assigned to the complexes formation [17].The complexes shown absorption bands (1608 -1613) cm −1 due to υ (C=N) shifted to higher frequency compared with ligand [18] [19].And absorption band of υ (C-N) shows a shifted to lower frequency assign to coordination [7].The bands in the region of (586 -421) cm -1 confirm the nature of the metal-ligand bonding [20].

Magnetic Properties
The cobalt complex exhibit magnetic moment value of 4.80 B.M. this value is greater than spin only due to orbital contribution suggesting octahedral geometry [26].The Ni(II) complex show magnetic moment value of 2.82 B.M. indicating an octahedral environment.The observed magnetic moment values for the Cu(II) complex are 1.84 suggesting a distorted octahedral geometry [27].
How to cite this paper: Mohammed, H.A. and Taha, N.I.(2017) Microwave Preparation and Spectroscopic Investigation of Binuclear Schiff Base Metal Complexes Derived from 2,6-Diaminopyridine with H. A. Mohammed, N. I. Taha DOI: 10.4236/ijoc.2017.74033413 International Journal of Organic Chemistry used as a ligand in coordination chemistry because its donor ability that deals

Table 3 .
Electronic spectral data of the complexes.