Synthesis, Characterization and Antimicrobial Activity of Metal Chelates of 5-[4-Chloro phenyl(1, 3, 4)thiadiazol-2-ylamino methylene]-8-hydroxy quinoline

: 5-Chloromethyl-8-quinolinol was condensed stoichiometrically with 5-(4-chlorophenyl)-(1,3,4) thiadiazol-2-ylamine in the presence of sodium bicarbonate. The resulting 5-[4-chlorophenyl-(1,3,4)thiadiazol-2-ylamino methylene]-8-quinolinol (CTAQ) was characterized by elemental analysis and spectral studies. The transition metal chelates viz . Cu 2+ , Ni 2+ , Co 3+ , Mn 2+ and Zn 2+ of CTAQ were prepared and characterized by metal-ligand (M:L) ratio, IR and reflectance spectroscopies and magnetic properties. The antifungal activity of CTAQ and its metal chelates was screened against various fungi. The results show that all these samples are good antifungal agents.


Synthesis of metal chelates of CTAQ
The metal chelates of CTAQ with Cu 2+ , Co 2+ , Zn 2+ , Mn 2+ and Ni 2+ metal ions were prepared in two steps. All the metal chelates were prepared in an identical procedure. The details are given as follows.

Preparation of CTAQ solution
CTAQ (0.05 mol) was taken in 500 mL beaker and formic acid (85% v/v) was added up to slurry formation. To this slurry, water was added till the complete dissolution of CTAQ. It was diluted to 100 mL.

Synthesis of CTAQ-metal-chelates
In a solution of metal acetate (0.005 mol) in acetone: water (50:50 v/v) mixture (40 mL) 20 mL of above mentioned CTAQ solution (i.e. containing 0.01 M CTAQ) was added with vigorous stirring at room temperature. The appropriate pH was adjusted by addition of sodium acetate for complete precipitation of metal chelate. The precipitates were digested on a boiling water bath. The precipitates of chelate were filtered off, washed by water and air dried.

Measurements
The elemental contents were determined by Thermo Finigen Flash1101 EA (Itally), the metals were determined volumetrically by Vogel's method 18 . To 100 mg chelate sample, each 1 mL of HCl, H 2 SO 4 and HClO 4 were added and then 1 g of NaClO 4 was added. The mixture was evaporated to dryness and the resulting salt was dissolved in double distilled water and diluted to the mark. From this solution the metal content was determined by titration with standard EDTA solution. Infrared spectra of the synthesized compounds were recorded on Nicolet760 FT-IR spectrometer. NMR spectrum of CTAQ was recorded on 400 MHz NMR spectrophotometer. Magnetic susceptibility measurement of the synthesized complexes was carried out on Gouy Balance at room temperature. Mercury tetrathiocynatocobalate(II) Hg[Co(NCS) 4 ] was used as a calibrant. The electronic spectra of complexes in solid were recorded on at room temperature. MgO was used as reference. Antifungal activity of all the samples was monitored against various fungi, following the method reported in literature 19 .
The broad band due to -OH group appeared at 3800-2700 cm -1 . In this band the inflections are observed at 2950, 2920 and 2850 cm -1 .While the latter two might be attributed to asymmetric and symmetric vibration of CH 2 of CMQ. The NMR spectrum of CTAQ in DMSO indicates that the singlet of 2 H at 2.6 δ ppm of N-CH 2 -Ar group. While the singlet at 3.8 δ ppm due to -OH group. The aromatic protons are appeared in multiplicity at 7.2 δ. The vigorous oxidations of CTAQ yield 8-hydroxy quinoline-5carboxylic acid. The melting point 20 is 230°C. Thus the structure of CTAQ is confirmed as shown in Scheme 1.
The metal and C,H,N contents of metal chelates of CTAQ Table 1 are also consistent with the predicted structure. The results show that the metal: ligand (M:L) ratio for all divalent metal chelate is 1:2.
The infrared spectra of all the chelates are identical and suggest the formation of all the metalocyclic compound by the absence of band characteristic of free -OH group of parent CTAQ. The other bands are almost at their respectable positions as appeared in the spectrum of parent-CTAQ ligand. However, the band due to (M-O) band could not be detected as it may appear below the range of instrument used. The important IR spectral data are shown in Table 2.
Magnetic moments of metal chelates are given in Table 2. The diffuse electronic spectrum of Cu 2+ chelates shows two broad bands 15780 and 23156 cm -1 . The first band may be due to a 2 B 1g → 1 A 1g transition, while the second band may be due to charge transfer. The first band shows structures suggesting a distorted octahedral structure for the Cu 2+ metal chelates 21,22 . The higher value of the magnetic moment of the Cu 2+ chelate supports the same. The Co 2+ metal chelate gives rise to two absorption bands at 22625 and 15166 cm -1 , which can be assigned 4 T 1g → 2 T 2g , 4 T 1g → 4 T 1g (P)transitions, respectively. These absorption bands and the µeff value indicate an octahedral configuration of the Co 2+ metal chelate 23,24 . The spectrum of Mn 2+ polymeric chelate comprised two bands at 18241 cm-1 and 23720 cm-1 . The latter does not have a very long tail. These bands may be assigned to 6 A 1g → 4 T 2g(G) and 6 A 1g → 4 A 2g(G) transitions, respectively. The high intensity of the bands suggests that they may have some charge transfer character. The magnetic moment is found to be lower than normal range. In the absence of low temperature measuremet of magnetic moment it is difficult to attach any significance to this. As the spectrum of the metal chelate of Ni 2+ show two distinct bands at 22487 and 15280 cm -1 are assigned as 3 A 2g (F)→ 3 T 1g (F) and 3 A 2g (F)→ 3 T 1g (F) transition, respectively suggested the octahedral environment for Ni 2+ ion. The observed µeff values in the range 3.01-3.2 B.M are consistent with the above moiety 25, 26 .
The examination of antifungal activity of CTAQ ligand and its all chelates Table 3 reveals that the ligand is moderately toxic against fungi, while all the chelates are more toxic than ligand. Among all the chelates the Cu 2+ chelate is more toxic against fungi.