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

Introduction

The schiff base transition metal complexes have invited the attention of Inorganic Chemists because of vast application in pharmaceutical and industrial fields.^(1-5)Due to their simple synthesis and versatility Schiff  complexes continue to remain important and a popular area of research as such complexes persistently play a verysignificant role in understanding the various aspect of coordination chemistry of transition metals. ^(6-10) The schiffbase of triazole derivatives have been found pharmaceutically active.^{( 11-13)} The pharmaceutical activity of these schiffbase have been found to get enhanced on complexation with metal ions.¹⁴ The literature reveals that schiffbase complexes of 4- (2/,4/-diaminobenzaldimino)-3,5-dimercapto-1,2,4-triazole has not been taken care of. Therefore, in continuation of our previous work,¹⁵ in the present paper we report the synthesis and characterization of Mn(II), Cu(II) and Zn(II) complexes with Schiff  base, 4- (2/,4/-diamino -benzaldimino)-3,5-dimercapto-1,2,4-triazole.

Material and Method

All the reagents used in the present work were of Anal. R grade and were used as received. Thiocarbo –hydrazide, carbon disulphide, α- picoline, pyridine, ethanol, 2,4- diaminobenzaldehyde were procured from Merck (India) and metal salts of Mn(II), Cu(II) and Zn(II) procured from Lova Chemic (India ). For the preparation of the ligand at first the pyridinium salt of 4- amino-3,5-dimercapto-1,2,4-triazole was prepared by refluxing the mixture of thiocarbohydrazide and carbon disulphide in pyridine on oil bath for one hour. Thereafter, 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 2 drops concⁿ sulphuric acid for one hour to get yellow crystals of schiff base, i.e., 4- (2/,4/-diaminobenzaldimino)-3,5-dimercapto-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 α- picoline. 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 II elemental analyzer. IR spectra of ligand as well as complexes were recorded on Perkin- Elmer FTIR spectrophotomet- er (spectrum II) using KBr pellet. The magnetic moment of complexes were determined by Gouy balance method at room temperature. Determination of molar the conductivity of complexes with 10^-3 solution in DSMO was done usingElico direct reading Conductivity meter. The electronic spectra of complexes were recorded on Perkin- Elmer Lamda 950 spectrophotometer. Results are given in Table I

Table: 1

Compound	%M Calc (Found)	%C Calc (Found)	%H Calc (Found)	%N Calc (Found)	%S Calc (Found)	µeff (B.M.)	Conductivity moh cm-1 mole-1
LH	— (–)	42.857 (42.902)	3.968 (4.051)	27.778 (27.805)	25.397 (25.401)
[MnL2(α-pico)2]	7.375 (7.405)	48.326 (48.352)	4.564 (4.581)	22.552 (22.538)	17.183 (17.201)	5.96	16.20
[CuL2(α-pico)2]	8.432 (8.425)	47.775 (47.485)	4.512 (4.506)	22.295 (22.307)	16.986 (16.978)	2012	15.48
[ZnL2(α-pico)2]	8.654 (8.634)	47.659 (47.672)	4.501 (4.488)	22.241 (22.245)	16.945 (17.013)	—	14.00

LH = 4- (2/,4/-diaminobenzaldimino)-3,5-dimercapto-1,2,4-triazole α-pico=α- Picoline, Calc = Calculated

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 [ML₂(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 NH₂ group to the metal ions. The band at 30 10cm^-1 is assigned to ν_CH aromatic group while the band at 2950 cm^-1 is fairly assigned to ν_CH of azomethine group.^19-21 The strong band at 2560 cm^-1 is assigned 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 The other 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 mercaptosulphur 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 appears at 755 cm^-1 in the spectra of complexes which shows the presence of coordination of α-picolinein complexes.^24-28

The magnetic moment of Mn (II) complex is determined to be 5.96 B.M. which corresponds to 5 unpaired electrons. It shows that Mn (II) complex is paramagnetic and it is high spin complex. ^29-32Mn(II) complex displays three bands in its electronic spectra which may be assigned to spin forbidden transition as below :- 19500 cm^-1 (ν₁)=⁶A_1g→⁴T_1g(⁴G), 23480 Cm^-1 (ν₂)= ⁶A_1g→⁴T_2g(⁴G) and 19500 cm^-1(ν₃)= ⁶A_1g→⁴E_g(⁴D). 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

B=844.15 cm,^-1D_q= 1063.63 cm.^-1 So B₀=0.137, as according to Orgel the energy of ⁴G lies above ⁶A_1g by 17B +5C. So 17B +5C = ν_3. From this the value of C is calculated to be 3029.89 cm.^-1 Hence,

which is very close to theoretical value

(3.8) for Mn (II) complexes. The values of various crystal field parameters are in good agreement with the reported value for octahedral complexes of Mn (II).^28,33-34

The magnetic moment of Cu (II) complex is found to be 2.12 B.M. at room temperature which shows it is magnetically dilute octahedral complex.^35-38The electronic spectra of Cu (II) complex exhibit a broad band at 20350 cm^-1 due to ²E_g→²T_2g spin allowed transition. The broadness of band clearly indicates the further splitting of both ²E_gand ²T_2g due to departurate of symmetry from O_h to D_4h symmetry. However, the value is in good agreement with the reported value of distorted O_h complexes of Cu (II).^5,39-43

Zn (II) complex is diamagnetic which is in accordance with its d¹⁰ configuration. Hence it doesn’t display any band in electronic spectra. However, on the basis of elemental analysis and molar conductivity O_hstructure is assigned to Zn (II) complex

The tentative structure of complexes may be given below:-

Scheme 1 Click here to View scheme

 

Acknowledgement

One of the authors Mr. Bishwanath Kumar is thankful to the Principal, M.G. College, Gaya for carrying out research work in its P.G. Department laboratory.

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