Synthesis and Structural Characterization of Schiff Base Ligand and their Metal Complexes

In the present work, the synthesis and structural characterization of a 2-phenyl3(benzamido propyl) quinazoline (3H) -4one semicarbazone/ thiosemicarbazone hydrochloride and its metal complexes have been reported. All the synthesized compounds were characterized by using various physico-chemical techniques such as Infrared spectra, electronic spectra, molar conductivity and magnetic susceptibility measurements. The ligand and metal ions reacted to form in the 2:1 ratio as found from the elemental analyses and general stiochiometry was determined, [M(PBPQS)2X2] and [M(PBPQT)2X2]; where M = Co(II), Ni(II) and Cu(II); PBPQS = 2-phenyl3 (benzamido propyl) quinazoline (3H) -4one semicarbazone and PBPQT = 2phenyl3 (benzamido propyl) quinazoline (3H) -4one thiosemicarbazone. On the basis of analytical data, a proposed structure for the Cu(II) complexes are distorted octahedral and those for Co(II) and Ni(II) complexes are octahedral. Ligands PBPQS/ PBPQT have been proposed to act in a bidentate manner co-ordinating to the metal ions though azomethine nitrogen and oxygen/ sulphur atom of either semicarbazone/ thiosemicarbazone moiety. The remaining co-ordination sites are occupied by negative ions such as Cl-, Br-, Ior NO3 -. The ligands and its metal complexes were tested for their possible antimicrobial potentials.


INTROdUCTION
In recent years, [1][2][3][4][5][6][7][8][9][10] there has been considerable interest in the chemistry of transition metal of schiff base.This is due to the fact that schiff base transition metal complexes are one of the most adaptable and thoroughly studied systems.The Schiff base complexes have applicable in clinical and analytical fields.They are used as model molecule for biological oxygen carrier systems.Schiff bases metal complexes also exhibit several biocidal potential such as antifungal, anti-cancer, herbicidal and antibacterial.Because of their ease in preparation and versatile properties, herein; the syntheses, structural features, spectroscopic characterization of metal complexes of Co(II), Ni(II), Cu(II) with Schiff bases, 2-Phenyl 3(benzamido propyl) quinazoline (3H)-4-one semicarbozone and 2-phenyl-3(benzamido propyl) quinazoline (3H)-4-one thiosemicarbozone are reported.

ExpERIMENTAL physical Measurement
All the chemicals and solvents were of reagent grade and were used without further purification.
The ligand and metal complexes were analysed using standard procedure.Analytical data were collected on Perkin-Elmer-2400 CHNO/S elemental analyzer.Infrared spectra were recorded on Parkin-Elmer spectrometer model-577 using KBr disc.Electronic spectra was measured on Cary-2390 spectrophotometer.Molar conductance was using a Systronics conductivity meter model 303 using Ca 10 -3 M solutions in DMF.Magnetic susceptibility of the samples were made on Guoy balance using mercury tetraisothiocynato cobaltate as a calibrant.

preparation of the complexes
The compounds of Co(II), Ni(II) and Cu(II) have been formed by reacting an ethanolic solutions of metal halides/nitrates with ethanolic solutions of the ligand PBPQS/PBPQT in molar ratio 1:2.The resulting reaction mixtures were heated on water bath for 2-3 hours.The solid coloured complexes which separated out on cooling were filtered, washed with ethanol, dried and recrystallised with tetrahydrofuran; yield in all cases 65-70%.

Infrared Spectral Studies
The IR data of the spectra of the ligand PBPQS/PBPQT and its Co(II), Ni(II) and Cu(II) complexes are listed in Table-1.The characteristic IR band for the free ligands, when compared with those of their complexes provide meaningful information regarding the bonding sites of the ligand.
Semicarbazine/ thiosemicarbazone ligands can coordinate as bidentate ligands, in most cases through the azomethine nitrogen and oxygen/sulphur atom of either semicarbazone/ thiosemicarbazone.In the free ligands PBPQS/PBPQT the n C=N bands appear in the region of 1645-1635cm -1 .In all the complexes, the n C=N band is shifted to lower frequency in the range.1620-1605 cm -1 , indicating coordination of the Schiff bases through the azomethine nitrogen atom 11 .This is further supported by the appearance of a far IR band in the range 420-390 cm -1 in the complexes which may be assigned 12 to n M-N .
The IR spectrum of the ligand PBPQS exhibit strong and broad band at 1720 cm -1 assigned 11 to n C=O .This band undergoes red shift after complexation proposes co-ordination through carbonyl oxygen atom of semicarbozone moiety.It is further supported by the appearance of a new band in far IR region at 520-505cm -1 assigned 12 to n M-O .
The spectrum of the ligand PBPQT shows a sharp and strong band at 820 cm -1 assigned 11 to n C=S .In the spectra of the complexes this band shows red shift proposes coordination through thione sulphur.This is further supported by the appearance of a far IR band in the region at 480-455 cm -1 , assigned 12 to n M-S .
The co-ordination through halogen atom is confirmed by the appearance of a band in the far IR region at 315-255 cm -1 assigned 12 to n M-X (X= Cl -, Br -, I -).The evidence of metal halogen linkage is further confirmed on the basis of low value of molar conductance measurements of complexes in the range 4.7-11.2ohm -1 cm 2 mol -1 (Table-1).Nitrate  complexes show characteristic medium intensity bands at 1260 and 1100 cm -1 with a separation of 160 cm -1 due to monodentate linkage of nitrate group.Combination bands at 1660 and 1640 cm -1 with a separation of 20 cm -1 confirming the monodentate behavior of the nitrate group.
On the basis of above discussion on IR spectral data it is proposed that the ligand PBPQS/ PBPQT acts in a neutral bidentate manner.The remaining coordination positions of metal ions are satisfied by negative ions, such as Cl -, Br -, I -and NO 3 -.