Synthesis and Characterization of Manganese , Copper and Zinc Complexes Derived from Schiff-Base Ligand

A Schiff base has been prepared by the condensation of 4amino -3,5-dimercapto, 1,2,4-triazole with 2,4-diaminobenzaldehyde. The ligand has been used for complexation with Mn(II), Cu(II) and Zn(II) metal ions. The complexes have been characterized by their elemental analysis, molar conductivity, magnetic susceptibility, IR spectra and electronic spectra. The very low value of molar conductivity of complexes shows their non-electrolytic nature. The comparison of IR spectra of complexes with that of free ligand reveals that the ligand is coordinated through azomethine nitrogen and deprotonated thiol sulphur forming five membered heterochelates. The magnetic moment values and electronic spectral bands clearly indicate the octahedral geometry around metal ions in complexes


MATERIAL AND METHOD
All the reagents used in the present work were of AnalR grade and were used as received.
Thiocarbohydrazide,carbon disulphide, α-picoline, pyridine,ethanol, 2,4-diaminobenzaldehyde were procured from Merck (India) and metal salts of Mn(ΙΙ), Cu(ΙΙ) and Zn(ΙΙ) procured from Lova Chemic (India For the preparation of the ligand at first the pyridinium salt of 4-amino-3,5-dimercapto-1,2,4triazole was prepared by refluxing the mixture of thiocarbohydrazide and carbon disulphide in pyridine on oil bath for one hour.There after, the pyridinium salt was treated with hydrochloric acid to get 4-amino-3,5-dimercapto-1,2,4-triazole.This amine was refluxed with 2.4-diaminobenzaldehyde in ethanol in the presence of 2 drops conc n sulphuric acid for one hour to get yellow crystals of Schiff base, i.e.,4-(2 / ,4 / -diaminobenzaldimino)-3,5dimercapto-1,2,4-triazole.This ligand was used for complexation with metal chloride in ethanolic medium by usual method of reflux by adding 2 ml of αpicoline.On cooling the reaction mixture the solid complex was separated out which was filtered and washed with alcohol.It was dried in desiccator over anhydrous calcium chloride.The C, H and N elemental analysis were carried out using Perkin Elmer 2400 ΙΙ elemental analyzer.IR spectra of ligand as well as complexes were recorded on Perkin-Elmer FTIR spectrophotometer (spectrum II) using KBr pellet.The magnetic moment of complexes were determined by Gouy balance method at room temperature.Determination of molar conductivity of complexes with 10 -3 M solution in DSMO was done using Elico direct reading conductivity meter.The electronic spectra of complexes were recorded on Perkin-Elmer Lamda 950 spectrophotometer.Results are given in Table .1

RESULT AND DISCUSSION
The molar conductivity values of complexes are indicative of their non electrolytic nature [16][17] .On the basis of elemental analysis and molar conductivity values, the complexes are formulated as[ML 2 (α-pico) 2 ], where L is the Schiff base ligand.IR spectra of complexes are very cumbersome and hence only important bands have been assigned and explained.The IR spectra of free ligand display two bands at 3013 and 2859 cm -1 which are assigned to ν asym NH2 and ν sym NH2 stretching vibration 18 .These two bands do not undergo any appreciable change in their frequencies in the spectra of complexes.It shows no coordination of NH 2 group to the metal ions.The band at 3010 cm -1 is assigned to ν CH aromatic group while the band at 2950 cm -1 is fairly assigned toν CH of azomethine group [19][20][21] .The strong band at 2560 cm -1 isassigned to ν SH stretching vibration of the ligand.In the spectra of complexes this band appears at lower frequency with highly decreased intensity.It shows that out of two SH group one has undergone deprotonation and coordination occur though deprotonated mercapto sulphur. 22 major change is found in the absorption frequency of azomethine group of the free ligand which absorbs at 1630 cm -1 in the spectrum of free ligand and shifts to lower frequencies by 30-40 cm -1 in the spectra of the complexes.It is indicative of coordination through azomethine nitrogen of ligand.The coordination through deprotonated mercapto sulphur and azomethine nitrogen is further confirmed by appearance of new bands at 510 and 370 cm -1 due to ν M-N and ν M-S stretching vibration respectively in complexes.The new band appearing at 755 cm -1 in the spectra of complexes shows the presence of coordinated α-picoline in complexes [24][25][26][27][28] .
The magnetic moment of Mn (ΙΙ) complex is determined to be 5.96 B.M. which corresponds to 5 unpaired electrons.It shows that Mn (ΙΙ) complex is paramagnetic and it is high spin complex [29][30][31][32] .Mn(ΙΙ) complex displays three bands in its electronic spectra which may be assigned to spin forbidden transition as below:-19500 cm -1 (ν 1 )= 6 A 1g → 4 T 1g ( 4 G), 23480 cm -1 (ν 2 )= 6 A 1g → 4 T 2g ( 4 G)and 19500 cm -1 (ν 3 )= 6 A 1g → 4 E g ( 4 D).As the transitions are spin forbidden and also Laporte forbidden the intensity is very very poor.Using Tanabe -Sugano diagram the various crystal field parameters have been calculated with values = 1.204,B=844.15cm -1 D q = 1063.63cm -1 So β=0.879 0.137, as according to Orgel the energy of 4 G lies above 6 A 1g by 17B +5C.So 17B +5C = ν 3. From this the value of C is calculated to be 3029.89cm. - Hence, = 3.589 which is very close to theoretical value (3.8) for Mn (ΙΙ) complexes.6][37][38] The electronic spectra of Cu (ΙΙ) complex exhibit a broad band at 20350 cm -1 due to 2 E g → 2 T 2g spin allowed transition.The broadness of band clearly indicates the further splitting of both 2 E g and 2 T 2g due to departurate of symmetry from O h to D 4h symmetry.[41][42][43] Zn (II) complex is diamagnetic which is in accordance with its d 10 configuration.Hence it doesn't display any band in electronic spectra.However, on the basis of elemental analysis and molar conductivity O h structure is assigned to Zn (II) complex.
The tentative structure of complexes may be given below:-