INTRODUCTION:

Schiff base complexes of transition metals have been of interest in coordination chemistry for many years due to their ease of synthesis and wide applications^1-2. The design and synthesis of macrocyclic Schiff base complexes are currently attracting considerable attention since they can be used as supra molecular devices and sensors³ and contrast agents in magnetic resonance imaging^4-6. DFMPM is prepared from cardanol using formalaldehyde, epichlorohydrin and sodium periodate in three stages. DFMPM formed 2+2 macrocylic Schiff base ligand with ethylenediamine. The formation of Schiff base intermediates in reactions of biological importance is well documented. The present investigation involves the synthesis and characterization of the Schiff base complexes of Zr(IV) and Th(IV) with the (2+2) macrocyclic Schiff base ligand. The results indicate that both Zr(IV) and Th(IV) complexes are octacoordinated having moderate antibacterial activity.

MATERIAL AND METHODS:

Cardanol was obtained from M/S. Satya Cashew, Chennai India, formaldehyde (37 % solution), hydrochloric acid, epichlorohydrin, ethylenediamine, sodiumhydroxide and other chemicals used were of GR/AR grade quality obtained from Merck chemicals. All the solvent used was purified by standard methods⁷.

The micro analytical data (C, H, N) were collected using Perkin Elmer 2400 instrument. The metal ion intakes were estimated by standard methods⁸. IR spectra were obtained using PE IR spectrum instrument Model: System 2000. ¹H NMR spectra were obtained using AMX-300MHz, FT NMR spectrometer.

Synthesis of Schiff base ligand :

Cardanol is the starting material for the synthesis of ligand. The synthesis involved the following stages (i) cardanol is converted into bis (3-pentadecenylphenol) methane (BPPM) by heating cardanol and formaldehyde in the molar ratio 2:1^9-11. (ii) BPPM into DFMPM on treatment with epichlorohydrin followed by the action of sodium periodate^12-17 (scheme 1). (iii) DFMPM formed (2+2) macrocylic Schiff base ligand with ethylenediamine^18-20. Equimolar ethanolic solutions of DFMPM and ethylenediamine were mixed and refluxed for about an hour and the reaction product is poured in ice, (2+2) macrocylic Schiff base ligand was obtained. The precipitated yellow compound was filtered, washed with water and dried over anhydrous calcium chloride. The crude sample was recrystalised from 50% absolute alcohol. Yield = 58% Molecular formula (C₉₄H₁₅₆N₄O₄). The probable structure of the ligand is given in Fig. 1.

Synthesis of Zr(IV) and Th(IV) Schiff base complexes :

The solution of Zirconium (IV) nitrate, and Thorium (IV) nitrate in ethanol was added drop wise to the ethanolic solution of Schiff base ligand in the molar ratio 1:1 and refluxed to about twelve hours at 80ºC ²¹. The resulting product was collected by filtration, washed with ethanol, diethyl ether and hot water, and finally dried under vacuum at 90 ⁰C. Yield = 57-58%.

Estimation of metal ion intake:

The filtrates obtained in the above methods were collected. The collections were used for the estimation of the transition metal ions used for complexation by using standard methods⁸.

RESULTS AND DISCUSSION:

The metal complexes of Zr(IV) and Th(IV) coloured solids, stable towards air and have high melting points (above 250 ⁰C). The complexes are insoluble in water and common organic solvents but are soluble in DMF, CDCl₃ and DMSO. Analytical data suggest that the metal to ligand ratio in all the complexes to be 1:1 (Table 1). Conductivities of solutions of the complexes in DMF are shown in Table 1. All the complexes are non-electrolytes because their conductivity values were in the range 18-25 ohm^-1 cm² mol¹. However, the conductivity value is higher than expected for non-electrolytes probably due to partial solvolysis of the complexes in DMF medium.

IR Spectra :

The characteristic FT IR absorption around 3300 cm^-1 (hydroxyl group, broad band), 3000 cm^-1 (aromatic C-H_str, weak) 1500 cm^-1 (phenyl ring) and 1475 cm^-1 (-CH₂-bending). The two strong bands around 1230 cm^-1 and 1010 cm^-1 are characteristic of C-O stretching in phenol and alcohol groups respectively were due to the formation of BPPM. Molecular formula, C₄₃H₆₈O₂. Molecular weight is _•614. Yield = 43 %.

In the FT IR spectrum of DFMPM the absorption at 1706 cm-1 is the characteristics of the aldehyde group. The strong band at 1067cm^-1 and 1595 cm^-1 are due to ether linkage and non-conjugated C = C bond respectively. The absence of absorption around 3300 cm^-1 showed the absence of –OH group in DFMPM. All other absorptions were found almost the same region indicated the presence of all other groups except-OH group in DFMPM. Molecular formula, C₄₇H₇₂O₄. Molecular weight is _• 700. Yield = 46 %.

Selected IR spectral bands for the ligand and its complexes are given in Table 2. The IR spectrum of the free ligand is characterized mainly by the strong bands at 2851.2 cm^-1, 2919.8 cm^-1 and 1642 cm^-1 which are attributed the stretching frequencies of -OC, -CH and- C = N (azomethine) respectively¹⁹. The IR Spectrum of the free ligand was compared with the spectra of metal complexes. The characteristic absorption bands 3420-3441 cm^-1 range were attributed to -OH group of the coordinated water or lattice water²². The absorption bands in the range 2853 – 2853.6 cm^-1, 2926.4-2927 cm^-1 and 1612–1632 cm^-1 were assigned to -OC, -CH and -C = N respectively²³. The imine peak in the metal complexes showed change in shifts compared to the ligand indicating coordination of the imine nitrogen atom to the metal ion due to coordination. On the other hand, in the IR spectra of complexes new absorption bands at 454-510 cm^-1 and 432-462 cm^-1 were observed, which indicated the M-N and M-O bonds respectively²⁴. The absence of M-O absorption in Th (IV) complex indicated the absence of coordinated water with the central Th (IV) ion²⁵(Fig 2 and 3).

Table 1 Physical characteristics and analytical data of the complexes

Compound	Yield %	Colour	Molecular formula	Molecular weight	Melting point ^oC	Elemental analysis, found (calcd) %			Molar conductance Ohm^-1 cm² mol^-1	Metal ion intake meq/g
Compound	Yield %	Colour	Molecular formula	Molecular weight	Melting point ^oC	C	H	N	Molar conductance Ohm^-1 cm² mol^-1	Metal ion intake meq/g
Ligand (L) (C₉₄H₁₅₆N₄O₄)	60	Brown	C₉₄H₁₅₆N₄O₄	1404	217	80.12 (80.34)	10.99 (11.11)	4.01 (3.98)		
[ZrL(NO₃)₄]2H₂O	58	Light brown	C₉₄H₁₆₀N₈O₁₈Zr	1779	> 250	63.39 (63.36)	8.99 (9.10)	6.29 (6.32)	25	1.0200
[ThL(NO₃)₄]2H₂O	57	Grey	C₉₄H₁₆₀N₈O₁₈Th	1920	> 250	58.74 (59.12)	8.33 (8.38)	5.83 (6.01)	18	1.5997

Table 2 Selected FT IR frequencies (cm^-1) and UV-visible spectral data (nm) of the ligand and complexes

Ligand/ Complex	n_O-H ^(H2O)	n_O-C	n_C-H	n_C=N	n_M-N	n_M-O	l_{max (nm)}
C₉₄H₁₅₆N₄O₄ (L)	-	2851.2	2919.8	1642	-	-	276	360	385
[ZrL(NO₃)₄]2H₂O	3420	2853.6	2926.4	1612	454.4	462	360	350	375
[ThL(NO₃)₄]2H₂O	3441.3	2853	2927	1632	510	-	355	360	380

¹H NMR Spectra :

The NMR spectrum of Schiff base ligand exhibited a multiplet signal at d 7.142 – 7.66 ppm is due to substituted aromatic ring protons. The singlet at d 8.8 ppm is due to the proton of H - C = N. A signal at d 1.3938 ppm, d 2.35 ppm and d 3.78 ppm were due to -CH₂ – protons. The multiplet at d 6.17 – 6.7 ppm and d 3.36 – 3.78 ppm were due to the olifinic protons of the side chain and – CH2-group of the ligand respectively²⁶.

UV – Visible Spectra :

The UV – visible spectra are often very helpful in the evaluation of results furnished by other methods of structural investigation. The ligand showed a broad band at 360 nm which is assigned to p- p* transition of the C = N chromophore²⁷. On complexation this bond was shifted to lower wavelength suggesting the coordination of imine nitrogen with central metal ion. The UV absorption spectra of the Zr(IV) and Th (IV) exihibit only one extra highly intensive band in the region on 350 nm – 380 nm which may be due to charge transfer band besides ligand bands. However UV – visible spectra could not provide structural details of these complexes^28-29.Zr (IV) has the coordination number of 4,6,7 and 8. Earlier research is indicated the coordination number of Th (IV) is also 6, 8 or 10. The Zr (IV) and Th (IV) formed 1:1 complexes. Hence the complexes of Zr (IV) and Th(IV) are believed to have the coordination number of 8. The –NO₃ group is present in the coordination sphere because conductance data showed the complexes are non-electrolytes and the NO₃groups were coordinated with the central Zr(IV) or Th(IV) ion. The appearance of additional band at the region 1354.5 cm^-1 and 1054 cm^-1 corresponding to the coordinating nitrate ion²⁹. On the basis of foregoing observation the probable structure of Zr(IV) and Th (IV) complexes may be presented as follows³⁰ (Fig.4). Earlier researchers also reported the octacoordination of Zr(IV) and Th (IV) Schiff base complexes^31-33

Metal ion intake:

The complexation behaviour of cardanol based Schiff base was affected by structural parameters³⁴.This study indicated that the metal ion intake decreased from Th(IV)>Zr(IV) at their natural pH (Table 1). This order can be explained by Pearson's proposal^35-37, hard acids prefer to combine with hard base and soft acids prefer to combine with soft base. Nature of the ligand and the chelate effect were the factors involved in complexation. Hence the ligand has been used as metal ion acceptor in the environmental chemistry and technological interest²¹. It can be also used for the removel of Zr(IV) and Th(IV) from waters.

Antibacterial activity:

Antibacterial activities of the ligand, complexes and standard drugs were screened by agar cup method in DMF solvent at a concentration of 1mg/mL and were checked against gram positive bacteria B. subtilis and S.aureus are and gram negative bacteria E.coli and S.typhi using ampicillin and tetracycline as standards. The results of antibacterial study are given in Table 3. In this method, a well was made on the agar medium, inoculated with microorganisms. The well was filled with the test solution using a micropipette and the plate was incubated at room temperature for two days. During this period the test solution was diffused and growth of microorganisms was affected. The antibacterial activity was estimated based on the size of inhibition zone in the cups³⁸. Under identical conditions the Table 3 shows that the Schiff base complex of Zr (IV) shows less antibacterial activity and Th (IV) shows moderate antibacterial activity against these bacteria.

Table 3 Antibacterial activity data of ligand and complexes.

Ligand/ Complex	*B. subtilis*	*S. aerus*	*E-coli*	*S.typhi*
C₉₄H₁₅₆N₄O₄ (L)	+	+	+	+
[ZrL(NO₃)₄]2H₂O	++	++	++	++
[ThL(NO₃)₄]2H₂O	+++	+++	+++	+++

1-5 mm (++) = less active 6-10 mm (+++) = Moderately active

CONCLUSION:

Schiff base complexes of Zr(IV) and Th(IV) were synthesised from cardanol using ethylenediamine were clearly described and characterized on the basis of analytical and spectral data. Metal ion intake explained that the ligand could be effectively used for extraction of metal ion from waters. Antibacterial study showed that the complex of Th(IV) have moderate antibacterial activity than Zr(IV).

ACKNOWLEDGEMENT:

One of the authors (ISR) is grateful to the UGC, New Delhi and Management of N.M. Christian College, Marthandam-629165, K.K. District, Tamil Nadu, India for selecting under FDP Programme.

REFERENCES:

1. Schiff H and Holm RH. Prog Inorg Chem 7; 1996: 85.

2. Di Bella S. Chem Soc Rev. 30; 2001: 355.

3. Oude Wolbers MP, Van Veggel FCJM, Snellick-Ru BHM, Hofstraat JW, Guerts FAJ and Reinhoudt DNJ.J Am Chem Soc. 119; 1997: 138.

4. Geze C, Mouro C, Hindre F, Leplouzennec M, Moinet C, Rolland R, Alderighi L, Vacca A and Simmonneaux G. Bull Chem Soc Chim Fr. 133; 1996: 267.

5. Choppin GR and Schaab KM. Inorg. Chim. Acta. 252; 1996: 299.

6. Sessler JL, Moody TD, Hemmi GW, Lyneh V, Young SW and Miller RA. J Am Chem Soc. 115; 1993: 10368.

7. Nair MS and David ST. Ind J Chem Soc. 78; 2001: 308.

8. Vogel AI, A text book of Quantitative Inorganic Analysis Including Elementary Intrumental Analysis, Longman, London. 1978.

9. Devil A, Kumar C and Srivastava D. In Proceedings of the 14^th National Symposium on Thermal Analysis. Baroda. 222; 2004.

10. Devi A and Srivastava D. J Applied Polymer Science. 102; 2006: 2730.

11. Yadav Y and Srivastava D. Materials Chemistry and Physics. 102; 2007: 74.

12. Hermansen Ralph D and Lau Steren E. US Patent. 5575956; 2004

13. Tan TTM and Polymer J, Mater. 13; 1996: 195.

14. Ghatge ND and Patil DR. Ind J Tech. 17(2); 1979: 52.

15. Nagarkatti and Asheley. Tetrahedron Lett. 1973: 4599.

16. Maerker G and Elizabeth T. US Patent. 3405; 1968: 149.

17. Telvekav VN, Patel DJ and Mishra SJ. Syn. Comm. 39(2); 2008: 311.

18. Rama Krishna Reddy K and Mahendra KN. Molbank M. 2006: 516.

19. Lakshmi B, Shivananda KN, Prakash GA, Rama KRK and Mahendra KN. Bull Korean Chem Soc. 32(5); 2011: 1613.

20. Borisova NE, Reshetora M.D and Ustynyuk YA, Chemical Reviews. 107; 2007: 46.

21. Tuncel M and Serin S. Transition Metal Chemistry. 31; 2006: 805.

22. Nanjundan S, Selvamalar CSJ and Jayakumar R. Eur Polym J. 40; 2004: 2313.

23. Raman N, Ravichandran S and Thangaraj C. J Chem Sci. 116(4); 2004: 215.

24. Tuncel M, Ozbulbul A and Serin S, Reactive and functional Polymers. 68; 2008: 292.

25. Rajendran G, Amritha CS, Anto RJ and Cheriyan VT. J Serb Chem Soc. 75(6); 2010: 749.

26. Sharma RC, Giri PP and Kumar D, J. Indian Chem. Soc. 88; 2011: 421.

27. Selwin Joseyphus R, Justin Dhanaraj C and Sivasankaran Nair M. Transition Metal Chemistry. 31; 2006: 699.

28. Mohapatra RK and Chandran Dash D. J Korean Chem Soc. 54(4); 2010: 395.

29. Dash DC, Mahapatra A, Mohapatra RK, Gosh S and Naik P. Ind J Chem. 47A; 2008: 1009.

30. Agarwal RK, Garg R and Sindhu SK. Bull Chem Soc. Ethiop. 19(2); 2005: 185.

31. Day VW and Fay RC. J Amer Chem Soc. 97; 1975: 5136.

32. Muller EG, Day VW and Fay RC. J Amer Chem. Soc. 98; 1976: 2165.

33. Peterson EJ, Van Dreele RB and Brown IM. Inorg. Chem. 15; 1976: 309.

34. Pillai VNR and Mathew B. Indian J Technol. 31; 1993: 302.

35. Pearson RG. Coord. Chem. Rev. 100; 1990: 403.

36. San Miguel V, Fernando, Catalina A and Peinado C. European Polymer Journal. 44; 2008: 1368.

37. Bera P and Nitis Chandra Sahab. J Indian Chem. Soc. 87; 2010: 919.

38. Mukherjee PK, Saha K, Giri SM, Pal M and Saha BP. Indian. J Microbiol. 35; 1995: 327.

Received on 30.09.2011 Modified on 16.10.2011

Asian J. Research Chem. 4(11): Nov., 2011; Page 1765-1768