Synthesis, Spectral and Biocidal Screening of Schiff Base Complexes of Co(II), Ni(II) and Cu(II) Containing Nitrogen and Sulphur Donor atoms

Introduction

Indole derivatives are the basic framework of biologically active compounds. The indole ring system is found to be present in a number of drug molecules and biologically active compounds^1-3. Indole derivative exhibits several biocidal activities such as chemotherapeutic importance. Indole derivatives possess various types of pharmacological properties^4–6 such as antifungal , antibacterial, antitumour and antitubercular activities. It is established from the literatures survey that biologically active compound when coordinated with suitable metal ion, its biological activity is enhanced⁷ many folds.

Schiff base complexes play a vital role in application in biocidal, clinical, analytical and pharmaceutical areas. Schiff bases are now attracting a new kind of chemotherapeutic activities by several workers^8-9. Keeping the above considerations in mind and in continuation of our earlier   work^10-16 in this field, we herein report the synthesis, charactrization and antifungal screening of Schiff base, 2 ethyl indole 3-carboxaldehyde thiosemicarbazone (EICT) and its complexes with Co(II), Ni(II) and Cu(II).

Experimental

All the chemicals used were of AnalR grade and used without further purification. Metals salts were purchased from E-Merck and used as received.

Synthesis of Ligand [Eict]

The hot ethanolic solution (20 ml) of 2 ethyl indole 3-carboxaldehyde (0.01 M) and thiosemicarbazide hydrochloride (0.01 M) dissolved in 10% ethanolic solution of sodium acetate were refluxed for 4 h. The resulting mixture was poured on crushed ice. The product obtained was filtered, washed with water, dried and recrystallized from ethanol. Yield-70%; m.p. 167±1^oC.

Preparation of the Complexes

Preparation of halide complexes

The complexes were prepared by respective metal halides (0.001 M) in ethanol with ligand 2 ethyl indole 3-carboxaldehyde thiosemicarbazone (EICT) (0.002 M) in molar ratio 1:2. The resulting reaction mixture was refluxed on a water bath for 2-3 h. The precipitated complexes were filtered, washed with aqueous ethanol and dried in electric oven. Yield 65-70%.

Preparation of nitrate complexes

The following general method was adopted for the preparation of nitrate complexes. Ethanolic solution of respective metal nitrate (0.001 M) is treated with ligand 2 ethyl indole 3-carboxaldehyde thiosemicarbazone (0.002 M) dissolved in ethanol. The resulting reaction mixture was heated on a water bath for 2-3 h. The precipitated complexes were filtered, washed several times with ethanol and then dried in electrc oven. Yield 70-75%.

Melting point was taken in open capillary tubes and is therefore uncorrected. Analytical data (C,H,N) were collected on Perkin Elmer-2400 CHNS/O elemental analyzer. Magnetic susceptibility of the samples were made on a Gouy balance using Hg[Co(NCS)₄] as a calibrant. IR spectra of the ligand and complexes were recorded on Perkin-Elmer-577 spectrophotometer in the range 4000-200 cm^‑1 using KBr disc. Molar conductance were recorded on Systronics conductivitymeter model 303 using DMF as a solvent. The electronic spectra were recorded on Cary 2390 spectrophotometer.

Results and Discussion

The IR spectrum shows a sharp and strong band at 3400 cm^-1 assignable^17,19 to n_N–H vibration. In spectra of all the complexes, this band without change in position and intensity, clearly indicates noninvolvement of nitrogen atom of either amino of imino group in coordination with metal ion. A broad and sharp band was obtained at 1470 cm^-1 in the ligand assignable^17,19,20 to n_C=N vibration. This band has been reduced by 20-30   cm^-1 in the complexes suggesting coordination of azomethine N with metal ion. The next IR band of the ligand shows a broad and strong band at 780 cm^-1 assignable^17,20,21 to n_C=S vibration. After complexation this band shows red shift with slightly reduced intensity. The shift of the band and change in intensity indicate coordination of thione sulphur with metal ion.

The conclusive evidence of bonding of ligand to metal ion through oxygen atom of nitrate group, nitrogen atom of azomethine group and sulphur atom of thiosemicarbazone moiety is indicated by the appearance of far ir bands due to   n_M–O^22,23 at 540-510 cm^-1, n_M–N^22,23 at 475-455 cm^­-1 and n_M–S^22,23 at 425-395 cm^-1 respectively. The evidence of metal halogen linkage is supported by the low molar conductance value of the complexes in the range 12.1-17.9 ohm^-1 cm² mol^-1 and appearance of a band in the far ir region at 325-265 cm^-1 assigned^22-23 to n_M–X (X=Cl^–,Br^–,I^–)

The next IR bands at 1635 and 1500 cm^-1 with a separation of 135 cm^‑1 suggest monocoordinated behaviour of nitrate group^24-26.

Electronic spectra and Magnetic susceptibility of the Complexes

The Co(II) complexes display three bands in the region, 10070-10160, 16930-17110 and 23540-23630 cm^-1, assigned to the transitions, ⁴T_2g (F) ¬ ⁴T_1g (F), ⁴A_2g (F) ¬ ⁴T_1g (F) and ⁴T_1g (P) ¬ ⁴T_1g (F) respectively, which indicate octahedral^27,28 geometry. The octahedral geometry of Co(II) complex is supported^29-31 by high m_eff value in the range 4.87-4.99 B.M. The Ni(II) complexes exhibit three bands in the region 11430-11540 cm^-1,  18300-18390 cm^-1 and 23170-23400 cm^-1 assigned to transitions ³T_2g (F) ¬ ³A_2g (F), ³T_1g (F) ¬ ³A_2g (F) and ³T_1g (P) ¬ ³A_2g (F) respectively, which indicate octahedral^28,32 geometry for all the Ni(II) complexes, which is further supported^29,30,33 by the m_eff value in the range 3.2-3.14 B.M. for all the Ni(II) complexes. The Cu(II) complexes display two ligand field bands in the region 16010-16220 cm^-1 and 22100-22260 cm^-1 assigned to the transitions ²T_2g ¬ ²E_g and charge transfer band respectively. The electronic spectra of all the Cu(II) complexes suggest octahedral^28,34 geometry around central metal ion. The magnetic moment value of Cu(II) complexes lie in the range 1.87-1.96 B.M.^29,30,35

Molar conductivity

Molar conductance data of the complexes were measured in the solvent DMF and the complexes were found to be nonelectrolytic³⁶ in nature. The molar conductance value of the complexes is in the range 12.1-17.9 ohm^-1 cm² mol^-1.

Antifungal activity

The ligand EICT and their complexes of Co(II), Ni(II) and Cu(II) have been screened for their antifungal activity against Aspergillus flavus and Aspergillus niger by disc plate method³⁷. On comparison with reference to fungicide, the complexes were found to move more effectively than free ligand due to chelation theory³⁸.

Conclusion

On the basis of above mentioned studies the complexes tentatively proposed an octahedral geometry as shown in Fig.1

Figure 1: [M(EICT)2X2]; M = Co(II) and Ni(II); X = Cl–, Br–, I– and NO3–;  M = Cu(II); X = Cl–, Br– and NO3–. Click here to View figure

 

Table 1: Analytical, Molar mass, Electronic spectra, Magnetic susceptibility, Decomposition temperature, Molar conductance measurement of ligand EICT and its Metal Complexes.

Compounds        (Colour)	Molar mass	Yield %	% Analysis found (calculated)				lmax electronic cm-1	meff B.M.	DT    oC	Wm ohm-1 cm2 mol-1
			M	C	N	H
EICT	263	70		54.63 (54.75)	21.18 (21.29)	5.62 (5.70)			167
[Co(EICT)2Cl2]       (Colourless)	655.93	65	8.91 (8.98)	43.83 (43.90)	17.01 (17.07)	4.50 (4.57)	10090, 16980, 23630	4.89	183	15.4
[Co(EICT)2Br2] (Chocolate brown)	744.94	68	7.87 (7.91)	38.60 (36 (67)	14.97 (15.03)	3.98 (4.02)	10070, 16960, 26580	4.94	181	17.6
[Co(EICT)2I2] (Brown)	838.73	64	6.97 (7.02)	34.26 (34.33)	13.30 (13.35)	3.52 (3.57)	10110, 16930, 23620	4.99	193	16.9
[Co(EICT)2(NO3)2] (Deep brown)	708.93	66	8.26 (8.31)	40.57 (40.62)	13.67 (13.71)	4.15 (4.23)	10100, 16930, 23620	4.90	184	14.1
[Ni(EICT)2Cl2] (Green)	655.71	68	8.90 (8.95)	13.05 (13.12)	17.01 (17.08)	4.45 (4.57)	11530, 18300, 13510	3.14	171	12.9
[Ni(EICT)2Br2] (Green)	744.52	63	7.80 (7.88)	38.60 (38.68)	14.94 (15.04)	3.93 (4.02)	11460, 18390, 28310	3.2	189	11.7
[Ni(EICT)2I2] (Green)	838.71	61	6.90 (6.99)	34.25 (34.33)	13.29 (13.35)	3.26 (3.37)	11430, 18340, 23220	3.6	183	12.1
[Ni(EICT)2(NO3)2] (Green)	708.71	67	8.21 (8.28)	40.57 (40.63)	15.73 (15.80)	4.15 (4.23)	11590, 18360, 23170	3.9	176	13.2
[Cu(EICT)2Cl2] (Blue)	660.54	69	9.55 (9.61)	43.52 (43.60)	16.85 (16.95)	4.49 (4.54)	16220, 22100	1.89	217	14.3
[Cu(EICT)2Br2] (Bluish green)	749.35	63	8.41 (8.47)	38.35 (38.43)	14.07 (14.14)	3.92 (4.00)	16340, 22110	1.93	210	17.9
[Cu(EICT)2(NO3)2] (Blue)	713.54	69	8.83 (8.90)	40.30 (40.36)	15.61 (15.69)	4.11 (4.20)	16060 22060	1.96	207	13.8

DT = Decomposition Temperature

Table 2: Ir Spectral Bands of Ligand Eict and its Metal Complexes of Co(Ii), Ni(Ii) And Cu(Ii)

Compounds	nN–H	nC = N	nC = S	nM–O	nM–N	nM–S	nM–X
EICT	3400 s,b	1470 s,b	780 s,b
[Co(EICT)2Cl2]	3400 s,b	1450 m,b	745 m,b		470 m		310 m
[Co(EICT)2Br2]	3400 s,b	1445 m,b	750 m,b		470 m	425 m	315 m
[Co(EICT)2I2]	3400 s,b	1440 m,b	755 m,b		470 m	435 m	315 m
[Co(EICT)2(NO3)2]	3400 s,b	1445 m,b	755 m,b	535 m	470 m	420 m
[Ni(EICT)2Cl2]	3400 s,b	1445 m,b	755 m,b		475 m	425 m	280 m
[Ni(EICT)2Br2]	3400 s,b	1440 m,b	750 m,b		475 m	415 m	275 m
[Ni(EICT)2I2]	3400 s,b	1445 m,b	750 m		470 m	405 m	265 m
[Ni(EICT)2(NO3)2]	3400 s,b	1445 m,b	750 m,b	520 m	470 m	410 m
[Cu(EICT)2Cl2]	3400 s,b	1445 m,b	750 m,b		460 m	400 m	280 m
[Cu(EICT)2Br2]	3400 s,b	1450 m,b	750 m,b		465 m	395 m	315 m
[Cu(EICT)2(NO3)2]	3400 s,b	1450 m,b	750 m,b	510 m	455 m	395 m

m = medium,   s = strong,   b = broad

Acknowledgement

B.K. Rai thanks University Grant Commission, for awarding Minor Research Project  [Grant No.PSB-001/08-09 dated 12 Dec-2008]. The authors are grateful to professor D.C. Baluni, Professor and Head Deptt. of Zoology , R.D.S. College, Muzaffarpur for his help in determination of antifungal effect of ligand and complexes.

References

1. Rai A., Sengupta S. K. and Pandey O. P., Indian J. Chem., 39A, 1198 (2000).
2. Kar D. M., Sahu S. K., Pradhan D., Dash G. K. and Misra P. K., J. Teaching Res. Chem., 10, 20 (2003)
3. Verma M., Nath S., Singh K. N. and James P. S., Acta Pharmaceutica, 54, 49 (2004).
4. Trivedi G. S. and Desai N. C., Indian J. Chem., 31B, 366 (1992).
5. Dunniyamurthy T, Kalra S. J. S. and Iqbal J., Tetrahedron Lett., 36, 8497 (1995).
6. Hitoshi T., Tamao N., Hideyaki A., Manabu and Takayuki M., Polyhedron, 16, 3787 (1997).
7. Parashar R. K. and Sharma R. C., J. Inor. Biochem., 28, 225 (1987).
8. Chui Y. K., Chjo K. H., Park S. M. and Daddaponani N., J. Electrochem. Soc., 142, 4107 (1995).
9. Katia B., Simon L., Anne R., Gerard C., Francoise D. and Bernard M., Inorg. Chem., 35, 387 (1996).
10. Rai B. K., Asian J. Chem., 22, 2761 (2010); Rai B. K. and Kumar Chandan, Asian J. Chem., 22, 5613 (2010); Rai B. K. and Singh Sateydeo, Asian J. Chem., 22, 5619 (2010); Rai B. K. and Sharma K. K., Asian J. Chem., 22, 5625 (2010)
11. Rai B. K., Kumar Hitesh, Sharma Minaxi and Rastogi V. K., J. Indian Chem, Soc, 87, 1241 (2010); Kishore K. R. and Rai B. K., Asian J. Chem., 22, 8055 (2010); Rai B. K. and Kumar Bimal, Asian J. Chem. 22, 8073 (2010); Rai B. K. and Singh S., Orient J. Chem, 26, 989 (2010); Rai B. K. and Kumar Chandan, Orient J. Chem, 26, 1019 (2010); Rai B. K.and Kumar, Orient J. Chem., 26, 1097 (2010).
12. Rai B. K. and Kumari Rachana, Asian J. Chem., 23, 4625 (2011).
13. Rai B. K., Sinha Puja, Vidyarthi S. N. and Singh Vineeta, Asian J. Chem., 23, 4629 (2011).
14. Rai B. K. and Kumar Bimal, Asian J. Chem., 23, 4635 (2011).
15. Rai B. K., Singh Vineeta, Vidyarthi S. N. and Sinha Puja, Asian J. Chem., 23, 4638 (2011).
16. Rai B. K. and Anand Puja, Orient J. Chem., 28, 525 (2012).
17. Kemp William, Organic Spectroscopy, Polgrave, Macmillan Press Ltd, New York, Silverstein R. M. and Webster F. X., Spectrometric Identification of Organic Compounds 6^th edn, John Wiley and Sons, 109, 2008, (2008).
18. Patil M. S. and Shah J. R., J. Indian Chem; Soc, 58, 944 (1981).
19. Maurya R. C., Patel P. and Rajput S., Synth. React. Inorg. Metal-Org. Chem., 33, 817 (2003).
20. Rao C. N., Chemical Application of IR Spectroscopy, Academic Press, New York, 260 (1963).
21. Agarwal R. K., Himanshu Agarwal and Indranil Chakraborti, Synth. React. Inorg. Met. Org. Chem., 25, 679 (1995).
22. Ferraro J. R., “Low Frequency Vibration of Inorganic and Co-ordination Compound“, Plenum Press, New York.
23. Goldstein M. and Unswarth D., Inorg. Chim, Acta, 4, 342 (1970).
24. Nakamoto K., Infrared Spectra of Inorganic and Coordination Compounds, John Wiley and Sons, New York (1976).
25. Addison C. C., Logan N., Wallwork S. C. and Barner D. C., Quart, Rev (1971).
26. Nyquist R. A., Putzig C. L., Leugers M. A., Infrared and Raman Spectral Atlas of Inorganic Compounds and Organic Salts, Academic Press, New York (1995).
27. Mane P. S., Shirodhar S. G., Arbad B. R.  and Chondekar T. K., Indian J. Chem, 40 A, 648 (2000).
28. Lever ABP, Inorganic Electronics Spectroscopy, Elsevier Amsterdam, 395 (1968); Jorgenson C. K., Acta Chem.; Scand, 19, 887 (1966). Allen J. R,  Brown D. H., Nutal R. H. and Sharp D.W. A.,  J. Inorg Nucl. Chem, 26, 1895 (1964).
29. Figgis B. N., Introduction to Ligand Field, Wiley Eastern Ltd., New Delhi, 279 (1976).
30. Carlin R. L. and Van Dryneveledt A. J., Magnetic Properties of Transition Metal Compounds, Springer Verlag, New York (1997).
31. Ballhauson C. J. and Gray H. B., Inorg. Chem., 1, 111 (1962).
32. Tahir A. K., Shivajnl H. S.  and Shoukat K., Indian J. Chem Sect, A. 39, 450 (2000).
33. Jetty V. K., Singh J., Shukla M., Rehman and Rastogi S. N., J. Indian Chem. Soc., 67, 987 (1990).
34. Mishra A. P., Khare M. and Gautam S. K., Synth. React. Inorg. Met. Org. chem; 32, 1485 (2002).
35. Singh N. K. and Agarwal N. K., Indian J. Chem. Sect. A., 37, 276 (1998).
36. Wolmsley J. A. and Tyree S. V., Inorg. Chem., 2, 312 (1963); Sathyanarayan D. N. and Patel C. C., Indian J. Chem., 5, 360 (1967).
37. Mukherjee P. K., Saha K., Giri S. N., Pal M. and Saha B. P.; Indian J. Microbiology, 35 (1995).
38. Nishant N., Ahmad S. and Ahmad R. T., J. Appl. Polym. Sci., 100, 928 (2006).

---

This work is licensed under a Creative Commons Attribution 4.0 International License.