Synthesis and characterization of semicarbazide and thiosemicarbazide ligand based metal complexes

ABSTRACT

Four new series of Schiff bases derived from semicarbazones and thiosemicarbazones were synthesized by the reaction 0f2-acetyi thiophene and thiophene-2-aldehyde in ethanol. Metal complexes of these Schiff bases has also been derived with Cu(II), Pb(II), Zn(II), Co(II), Ni(II) and Mg(II) metai salts. Such compounds and metai complexes were characterized by different physic- chemical techniques like melting point, elemental analysis, muitinuciear NMR (¹ Ķ¹³ c') and IR studies. All the complexes were found to have good agreement with the analytical data received. The possible geometries of the complexes were assigned on the basis of electronic and infrared spectral studies.

Keywords: Schiff bases; Semicarbazones; Thiosemicarbazones; metal complexes, IR,¹ H NMR.

1. INTRODUCTION

Schiff bases are condensation products of primary amines with carbonyl compounds and they were first reported by Schiff in 1864¹. The common structural feature of these compounds is the azomethine group with a general formula RHC=N-R¹, where R and R¹ are alkyl, aryl, cyclo alkyl or heterocyclic groups. Several studies showed that the presence of a lone pair of electrons in a sp2 hybridized orbital of nitrogen atom of the azomethine group is of considerable chemical and biological importance [2-9]. Because of the relative ease of preparation, synthetic route and the special property of C=N bond, Schiff bases are generally excellent chelating agents, [7-13] with N-0 and N-S donor ligands so as to form ring structure with metal ion, which can serve as models for biologically important species.

Schiff bases derived have a wide variety of applications in many fields, such as biological, inorganic, coordination and analytical chemistry. These compounds are further used as ionophore in membrane in ion selective electrodes study [14-16]. A large number of different Schiff base ligands have been used as cation carriers in potentiometric sensors as they have shown excellent selectivity, sensitivity and stability for specific metal ions such as Ag(II], Co(II], Cu(II], Al(III), Hg(II], Ni(II], Zn (II] and Pb(II] [17-22].

Metal complexes of thiosemicarbazones with transition metals have received attention because of their biological and electrochemical activity including antitumor, antibacterial, fungicidal and anticarcinogenic properties, [23-28] including as ion selective electrode as well²⁹. Thiosemicarbazones usually act as chelating ligands with transition metal ions, bonding through the s and N atoms [30-32]. The high affinity for the chelation of the Schiff bases towards the transition metal ions is utilized in preparing their solid complexes³³.

This paper presents a series of new Schiff bases with the synthesis and spectroscopic characterization of their metal complexes [34-36] with ligands 2-acetyl thiophene thiosemicarbazone (LL1], thiophene-2- aldehyde thiosemicarbazone (LL2], 2-acetyl thiophene semicarbazone (LL3], thiophene-2-aldehyde semicarbazone (LL4] (Schemes 2.1 & 2.2].

2. MATERIALS AND METHODS

All the chemicals used were of analytical grade (AR] and of the highest purity. They included 2-acetyl

thiophene (CDH], thiophene-2-aldehyde (CDH], thiosemicarbazide (CDH] and semicarbazide (CDH], Metal salts were purchased from E. Merck and were used as received.

2.1 Preparation of ligands

All the ligands were prepared by the methods reported earlier³⁷ by the coupling reactions.

2.1.1 Synthesis of 2-acetyl thiophene thiosemicarbazone Schiff Base (LL1 )

1.26 g of 2-acetyl thiophene(0.01mmol] was mixed with equivalent amount of thiosemicarbazide in hot ethanolic solutions (20 mL] with few drops of acetic acid were mixed with constant stirring .The mixture was refluxed for 2 h and the solid product formed was separated out by filtration, washed several times with 50% ethanol and then dried.

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Scheme 1: Synthesis of ligand (LL1)

2.1.2 Synthesis of thiophene-2-aldehyde

thiosemicarbazone Schiff Base (LL2)

1.12 g of thiophene-2-aldehyde (O.Olmmol] was mixed with equivalent amount of thiosemicarbazide in hot ethanolic solutions (20 mL] with few drops of acetic acid were mixed with constant stirring .The mixture was refluxed for 2 h and the solid product formed was separated out by filtration, washed several times with 50% ethanol and then dried.

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Scheme 2: Synthesis of ligand (LL2)

2.1.3 Synthesis of 2-acetyl thiophene semicarbazone Schiff Base (LL3)

1.26 g of 2-acetyl thiophene (O.Olmmol] was mixed with equivalent amount of semicarbazide in hot ethanolic solutions (20 mL] with equivalent amount of sodium acetate were mixed with constant stirring .The mixture was refluxed for 2 h and the solid product formed was separated out by filtration, washed several times with 50% ethanol and then dried.

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Scheme 3: Synthesis of ligand (LL3)

2.1.4 Synthesis of thiophene-2-aldehyde semicarbazone Schiff Base (LL4)

1.12 g of thiophene-2-aldehyde (O.Olmmol] was mixed with equivalent amount of semicarbazide in hot ethanolic solutions (20 mL] with equivalent amount of sodium acetate were mixed with constant stirring .The mixture was refluxed for 2 h and the solid product formed was separated out by filtration, washed several times with 50% ethanol and then dried.

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Scheme 4: Synthesis of ligand (LL4)

2.2 Preparation of complexes

2.2.1 Synthesis of metal complexes of Schiff base iminės [M(LL)2]C12

A general method has been adopted for the synthesis of metal complexes. Hot aqueous ethanolic solution (20 mL 1:1 v/v] of ligands (0.02m mol] and a hot aqueous solution (20 mL] of the hydrated metal salts (0.01m mol] were mixed with constant stirring. The mixture was refluxed for about 6 hrs. On cooling a precipitate was separated out. The same was filtered, washed with 50% ethanol and dried. The complexes were recrystallized.

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Scheme 5: Synthesis of metal complexes [M(LL)2]C12

2.2 Physical measurements

The C, H, N and s were analyzed on a Vario Micro Cube elemental analyzer, Model Vario-III.¹ H and¹³ c NMR spectra were recorded on a Bruker, Model DPX-300 NMR spectrophotometer using DMSO as solvent. Chemical shift are given in ppm relative to tetra methylsilane. The IR spectra were recorded as KBr pellets on a Perkin Elmer FT-IR spectrophotometer, Model No. BX-2

3. RESULTS AND DISCUSSION

The Schiff bases 2-acetyl thiophene thiosemicarbazone (LL1], thiophene-2-aldehyde thiosemicarbazone (LL2] and their metal complexes were subjected to elemental analyses. The results of elemental analyses (C, H, N, S] with molecular formula and melting points are presented in Table (1]. The results obtained are in good agreement with those calculated for the molecular formula and the melting points are sharp, indicating the purity of the compounds prepared. The structures of the ligand and metal complexes are also confirmed by IR,¹³ c and¹ H NMR spectra, which are discussed below:

3.1. Infrared spectra of the ligands

IR spectra in the region 4000 - 400 cm¹ ־ have been recorded for the ligand and its complexes and the assignments of the observed frequencies have been made to specific group vibrations by comparison with the spectra of related complexes. Infrared spectra of the ligands showed a strong band in the region ~1597 and 1535 cm¹ ־ was assigned to the symmetric or asymmetric [v(C=N]] vibrations of the azomethine group ³⁸. The strong band observed at 1294 cm¹ ־ & 838 cm¹ ־ in the spectrum was due to the v(C=S] & 5(C=S] ³⁹. The bands observed at 3407 cm¹ ־ and 3146 cm¹ ־ were assigned to v(NH2] and v(N-H] vibrations respectively. This further indicates that the ligand remained in the thione form.

The diagnostic IR spectral bands of the complexes (Fig. 5] are presented in Table (2], together with their tentative assignments. On complex formation the position of these bands shifted toward higher or lower side, indicating its involvement in coordination with metal ion. The v(C=S] stretching frequency was lowered in the spectra of the complexes, indicating the involvement of the thioketo sulphur in the coordination. These findings are further supported by the appearance of new bands at 470-528 cm¹ ־ and 410­439 cm¹ ־, which are assigned to v(M-N] and v(M-S] vibrations, respectively.

Therefore, it can be concluded that ligands (LL1 & LL2] binds to the metal ions through azomethine N and the thioketo s atoms which shows that the thiosemicarbazones act as bidentate chelating agent⁴⁰.

3.2. NMR Spectroscopy

The NMR spectra of the metal complexes are examined by comparing with those of the parant Schiff bases. The NMR spectra of the complex shows the absence of the signals due to (-NH-] in¹ H NMR and (C=S] in¹³ c NMR spectrum which were observed in the free ligand indicating the thiolization of (C=S] followed by deprotonation and complexation with metal ion. It was also found that a new signal was observed after complexation with metal ion [41-43].

3.2.1.1 H NMR

¹ H NMR spectra were recorded in DMSO solution, using TMS as internal standard for the synthesized compounds. The NMR spectra of the Schiff bases with the chemical shifts of the different types of protons are listed in Table (3]. The resonance of protons has been assigned on the basis of their integration and multiplicity pattern. The¹ H NMR spectra of the Schiff bases in DMSO exhibits signals at 10.28, 10.35 and 11.33 ppm attributed to -CH=N- protons. The multisignals within the range of 6.91- 7.58 ppm are assigned to the aromatic protons of the rings. The singlet peaks at 3.39, 2.92, 3.0 and 3.42 ppm are due to the -N=NH- group of Schiff bases synthesised. The peaks at 8.3, 8.14, 9.13 and 8.05 ppm are due to the - NH2 protons⁴³. The shifting of azomethine peaks in the observed spectra indicates the formation of Schiff bases.

Table 1: Physical and elemental analysis of ligands and their metal complexes.

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Table 2: IR spectral data [cm[1]־) of ligands (LL1, LL2] and their metal complexes.

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3.2.2.13 c NMR

The ¹³ c NMR spectra provided further support for the structural interpretation of Schiff bases, ¹³ c NMR spectral data of Schiff bases with peak assignment have been listed in Table (4]. The presence of number of signals found in ¹³ c NMR spectra corresponding to different types of nonequivalent carbon atoms present in the compounds corresponds. The signals were assigned by comparing with the literature values ⁴². The Schiff base ligand shows the signal at 521.42 ppm due to carbon atoms of methyl groups. On complexation no change has been observed. The spectra of the Schiff base ligand exhibits a strong band at δ 179.2 ppm due to c=s group. On complex formation the position of this band undergoes upfield shift to 5171.9 - 172.5 ppm. This indicates that sulphur is involved in coordination. The ¹³ c NMR spectral data of the Schiff bases are in accordence with the proposed structures.

Table 3: 1H NMR data (δ ppm) of compounds with peak assignment.

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Table 4: 13C NMR data (δ ppm) of compounds with peak assignment.

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Figure 1: Infra-Red spectrum of ligand (LL1)

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Figure 2: Infra-Red spectrum of ligand (LL2)

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Figure 3: 1H NMR spectrum of ligand (LL1) and (LL2)

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Figure 4: 13C NMR spectrum of ligand (LL1) and (LL2)

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Figure 5: 13C NMR spectrum of ligand (LL3) and (LL4)

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4. CONCLUSION

Schiff bases and their metal complexes of 2-acetyl thiophene and thiophene-2- aldehyde with thiosemicarbazide and semicarbazide were synthesized and characterized by analytical and spectral techniques. Analytical spectra shows the complexation of these Schiff bases with metal ions such as Pb² +, Cu² +, Zn² +, Ni² + and Co² + etc.

5. Acknowledgements

The authors are thankful to the University Grant Commission, New Delhi, for financial assistance in the form of RGNF and the Director, MAIT, New Delhi, for providing research facilities. The authors thank the US1C, Delhi University, for their help in carrying out c, H, N and s elemental analysis, FT-1R spectral analysis and Chemistry Department, IIT Delhi, for providing¹ H and¹³ c NMR spectroscopy facilities.

6. REFERENCES

1. Cimerman z, Miljanic s and Galie N (2000). Schiff Bases Derived from Aminopyridines as Spectrofluorimetric Analytical Reagents. Croatica Chemica Act. 73 (1), 81- 95

2. Muhammad AA, Mahmood к (2011). International Conference on Chemistry and Chemical Process (IPCBEE) voi.10

3. Singh p, Goel RL and Singh BP (1975). 8-acetyl-7-hydroxy-4- methyl coumarin as a gravimetric reagent for Cu² ł and Fe³ ł.y. Indian Chem. Soc. 52, 958-959

4. Репу BF, Beezer AE, Miles RJ et. al. (1988). Evaluation of microcalorimetry as a drug bioactivity screening procedure, application to a series of novel Schiff base compounds. Microbois. 45,181

5. Kabak M, Elmalı A, and Elerman Y (1999). Keto-enol tautomerism, conformations and structure of lV-(2-hydroxy- 5-methylphenyl), 2-hydroxybenzaldehydeimine. ]. Mol. Struct. 477,151-158

6. Patel PR, Thaker ВТ and Žele s (1999). Preparation and characterization of some lanthanide complexes involving a heterocyclic ß - diketone. Indian]. Chem. 38 A, 563-567

7. Valcarcel M, Laque de Castro MD (1994). Flow-Throgh Biochemical Sensors. Elsevier, Amsterdam.

8. Spichiger-Keller и (1998). Chemical Sesors and Biosensors for Medical and Biological ApplicationsWiley-VCH, Weinheim.

9. Lawrence JF, Frei RW (1976). Chemical Derivatization in Chromatography. ]. Chromatogr. Libr. Vol. 7, Elsevier, Amsterdam.

10. Patai s, Ed., (1970). The Chemistry of the Carbon-Nitrogen Double Bond./. Wiley & Sons, London.

11. Jungreis E, Thabet ss (1969). Analytical Applications of Schiff bases. Marcell Dekker, New York.

12. Metzler CM, Cahill A and Metzler DE, (1980).Equilibriums and absorption spectra of Schiff bases. /. Am. Chem. Soc. 102, 6075-6082

13. Dudek GO, Dudek EP (1965). Spectroscopic study of keto- enol tautomerization in phenol derivatives. Chem. Commun.464-466

14. Mashhadizadeh MH, Talleri EP and Sheikhshoaie I, (2007). A novel Mn² ł PVC membrane electrode based on a recently synthesized Schiff base. Talanta 72,1088-1092

15. Gupta VK, Jain AK and Maheshwari G, (2007). Manganese (II) selective PVC based membrane sensor using a Schiff base. Talanta 72, 49-53

16. Afkhamia A, Felehgaria FS, Madrakian T et. Al. (2013). Fabrication and application of a new modified electrochemical sensor using nano-silica and a newly synthesized Schiff base for simultaneous determination of Cd² ł, Cu² ł and Hg² ł ions in water and some foodstuff samples. Analytica Chimica Acta 771, 21-30

17. Abbaspour A, Esmaeilbeig AR, Jarrahpour AA et. al. (2002). Aluminium (Ill)-selective electrode based on a newly synthesized tetradentate Schiff base. Talanta 58, 397-403

18. Mahajan RK, Kauri and Kumar M, (2003). Silver ion-selective electrodes employing Schiff base p-terf-butyl calix⁴ arene derivatives as neutral carriers. Sens. Actuators B-91, 26-31

19. Ganjali MR, Golmohammadi M, Yousefi M et. al. (2003). Novel PVC-Based Copper (II) Membrane Sensor Based 0n2-(l,-(4'- (l"-Hydroxy-2"-naphthyl)-methyleneamino) butyliminomethyl)-l-naphthol. Anal. Sci. 19, 223

20. Jain AK, Gupta VK, Ganeshpure PA et. al. (2005). Ni (II)- selective ion sensors of salen type Schiff base chelates. Anal. Chim. Acto 553,177-184

21. Jeong T, Lee HK, Jeong DC et. al. (2005).A lead (Il)-selective PVC membrane based on a Schiff base complex of N,N'- bis(salicylidene)-2,6-pyridinediamine.ra/a!!to 65, 543-548

22. Gupta VK, Singh AK, Mehtab s et. al. (2006). A cobalt (II)- selective PVC membrane based on a Schiff base complex ofiV,iV'-bis(salicylidene)-3,4-diaminotoluene. Anal. Chem. Acta 566, 5-10

23. Scovili JP, Klayman DL and Franchino CF, (1982). 2- Acetylpyridine thiosemicarbazones. 4. Complexes with transition metals as antimalarial and antileukemic agents. /. Med. Chem. 25,1261-1264

24. Karon M, Benedict WF (1972).Chromatid Breakage: Differential Effect of Inhibitors of DNA Synthesis during G2 Phase. Science 178, 62

25. Dhunwad SD, Gudasi KB and Goudar TR, (1994). Synthesis and structural characterization of biologically active metal complexes of ΝΛ l-(N-morpholinoacetyl)-N/' 4-phenyl thiosemicarbazide and 3, 4-methylenedioxybenzaldehyde thiosemicarbazone with oxovanadium (IV), chromium (III), manganese (II), iron (III), cobalt (II), nickel (II), copper (II), cadmium (II), uranium (VI), thorium (IV) and silicon (IV) Ind. ]. Chem. ЗЗА, 320

26. West DX, Dietrich SL, Thientanavanich I et. al. (1994).Copper (II) complexes of 6-methyl-2-formylpyridine⁴ N-substituted thiosemicarbazones. Transition Met. Chem. 19,195-200

27. Wang M, Wang LF, Li YZ et. al. (2001). Antitumour activity of transition metal complexes with the thiosemicarbazone derived from 3-acetylumbelliferone. Transition Met Chem.26, 307-310

28. West DX, Liberta AE, Padhye SB et. al. (1993). Thiosemicarbazone complexes of copper (II): structural and biological studies. Coord. Chem. Rev. 123, 49-71

29. Chandra s, Sharma K, Kumar A et. al. (2010). Си (II) selective PVC membrane electrode based on zinc complex of Acetophenonethiosemicarbazone (ZATSC) as an ionophore. Der Pharma Chemica 2(6), 256-266

30. Saiz PC, Tojal JG, Mendia A et. al. (2003). Coordination Modes in a Tridentate NNS (Thiosemicarbazonato) copper(II) System Containing Oxygen-Donor Coligands - Structures of [{Cu(L)(X)}2] (X = Formato, Propionato, Nitrito) (pages 518­527). Eur.]. inorg. Chem. 518

31. Mohan M, Agarwal A and Jha NK (1988). Synthesis, characterization, and antitumor properties of some metal complexes of 2,6-diacetylpyridine bis(N⁴ -azacyclic thiosemicarbazones)./ Inorg. Biochem. 34, 41

32. Tang HN, Wang LF and Yang RD (2003). Synthesis, characterization and antibacterial activities of manganese(II), cobalt(II), nickel(II), copper(II) and zinc(II) complexes with soluble Vitamin K3thiosemicarbazone. Transition Met. Chem.28, 395-398

33. Mohamed GG, Omar MM and Hindy AM (2006). Metal complexes of Schiff basess, preparation, charac-terization and biological activity. Turk] Chem. 30, 361-382

34. Sawodny w, Riederer M (1977). Addition Compounds with Polymeric Chromium (Il)-Schiff Base Complexes (pages 859­860). Angew. Chem. Int. Edn. Engl. 16, 859-860

35. Tayım HA, SalamehAS (1983). Reactions of 2-thiazolin-2- ylthiophene with some metal ions. Polyhedron 2,1091-1094

36. Zhou S, Xie F and Ni s, (2001). Huaxue Shiji 23, 261-262

37. Sen AK, Singh G, Singh K et. ai. (1977). Indian ]. Chem. 36A, 891

38. Bindu p, Kurup MRP (1997).E.s.r. and electrochemical studies of four- and five-coordinate copper(II) complexes containing mixed ligands. Transition Met. Chem.22, 578-582

39. s Chandra, Tyagi VP and Raizada s (2003). Synthesis, Epr, Electronic and Magnetic Studies on Cobalt (II) Complexes of a Semicarbazone and Thiosemicarbazone. Synth. React. Inorg. Met.-Org. Chem. 33,147

40. Nand KS, Saty BS, Anurag s et. al. (2001). Spectral, magnetic and biological studies of l,4-dibenzoyl-3- thiosemicarbazide complexes with some first row transition metal ions. Proc. ind. Acad. Sci. 113, 4, 257-273

41. Clark c, Andrew R, Dilworth JR et. al. (2004). Pyridylthiosemicarbazide complexes of rhenium with potential radiopharmaceuticalapplications. Dalton Trans. 2402-2403

42. Kumer NRS, Metaji I and Patil КС, (1991).structure of bis(thiocyanato-iV)bis(thiosemicarbazide-iV¹,S)nickel(II): a redetermination. Acta. Cryst. C47 2052-2054

43. Talwar s, Usha, Chandra Set. al. (1991). Synthesis and Structural Studies on Manganese (II) Complexes of some N-0 and N-S Donor Ligands.Şynf/!. React. Inorg. Met.-Org. Chem.2i, 131