Biocidal and Spectroscopic Study of the Co(II), Ni(II) and Cu(II) Complexes with Schiff Bases

introduction

The chemistry of Schiff base and their metal complexes have been extensively studied in recent years owing to their pharmacological properties^1-5. Schiff base ligands have been extensively investigated with respect to their numerous applications in organic synthesis as well as in pharmacology. Schiff base ligands have been sucessfully used in several catalytic asymmetric reactions^6-7. Schiff base metal complexes of nitrogen, oxygen and sulphur donar atoms are found to be effective catalysts for oxidation reactions^8-9. In particular, the selective oxidation of alcohol into carbonyl compounds by metal complexes are well documented in the literature^10-12. Schiff base complexes have served as a selective antimetastatic agent¹³, as anticancer drugs against^14-16 colorectal tumors. Recently, Schiff base transition metal complexes are reported by several workers.^17-21 Receiving impetus from the above observations and in continuation of our research programme^22-26 on complexes of Schiff base ligand, the present paper, illustrates the synthesis and structural investigation of Schiff base complexes of Co(II), Ni(II) and Cu(II) with 1-methyl-2-6-diethyl piperidone semicarbazone (MDES).

Experimental

All the chemicals used were BDH reagents. Melting points were determined in open capillaries and are uncorrected. The metal contents of all the complexes were analysed using standard procedure²⁷. The IR spectra of the ligand and complexes were recorded on Beckmann IR-20 spectrophotometer using KBr pellets. The electronic spectra of the complexes were recorded on a Cary 2390 Spectrophotometer. Magnetic moment was measured by Gouy balance using Hg[Co(NCS)₄]as a calibrant. The molar conductance were done on Toshniwal conductivity bridge using DMF as a solvent. Analytical data, colour, molar conductivity, electronic spectral data, magnetic susceptibility, decomposition temperature and molar mass are recorded in Table – 1 and salient features of IR spectra are recorded in Table – 2.

Table 1: Analytical, colour, molar mass, magnetic susceptibility, conductivity measurement and decomposition temperature of ligand MDES and its metal complexes

Compounds        (Colour)	Molar   mass	% Analysis found (calculated)				meff B.M.	lmax electronic cm-1	Wm ohm-1 cm2 mol-1	Decompo-sition Temp. oC
		M	C	N	H
MDES      (Colourless)	224		58.87 (58.92)	24.96 (25.00)	6.87 (6.92)
[Co(MDES)2Cl2]         (Yellowish red)	577.93	10.13 (10.19)	45.65 (45.68)	19.33 (19.40)	6.87 (6.92)	5.16	13600 19900	7.4	271
[Co(MDES)2Br2]      (Yellowish red)	666.74	8.75 (8.83)	39.55 (39.61)	16.75 (16.79)	5.90 (5.99)	5.11	13900 19300	7.8	280
[Co(MDES)2I2]        (Dark brown)	760.73	7.70 (7.74)	34.65 (34.70)	14.68 (14.72)	5.19 (5.25)	4.87	14300 20000	7.1	301
[Co(MDES)2(NO3)2] (Dark brown)	630.93	9.30 (9.34)	41.80 (41.84)	17.70 (17.75)	6.25 (6.33)	4.93	14000 19400	7.3	289
[Ni(MDES)2Cl2] (Light yellow)	577.71	10.10 (10.16)	45.62 (45.69)	19.31 (19.38)	6.86 (6.92)	3.04	11200 15080 24000	8.3	316
[Ni(MDES)2Br2] (Light yellow)	666.53	8.74 (8.80)	39.55 (39.60)	16.75 (16.80)	5.92 (6.00)	3.01	11900 15200 25100	8.1	312
[Ni(MDES)2I2]   (Yellowish brown)	760.51	7.65 (7.71)	34.67 (34.71)	14.65 (14.72)	5.18 (5.25)	3.12	11300 16400 23600	8.8	317
[Ni(MDES)2(NO3)2]  Brownish yellow)	630.71	9.24 (9.30)	41.79 (41.85)	17.67 (17.75)	6.30 (6.34)	3.09	11600 16600 25100	8.4	303
[Cu(MDES)2Cl2] (Blue)	582.54	10.82 (10.90)	45.25 (45.31)	19.15 (19.22)	6.80 (6.86)	1.87	11300 15400	8.7	269
[Cu(MDES)2Br2]  (Bliush green)	611.35	9.40 (9.46)	39.25 (39.31)	16.60 (16.68)	5.90 (5.95)	1.94	12100 15700	9.1	263
[Cu(MDES)2(NO3)2] (Deep blue)	635.54	9.91 (9.99)	41.47 (41.53)	17.57 (17.62)	7.15 (7.22)	1.96	12000 18500	8.2	27

 

Table 2: Key ir spectral bands of ligand MDES and its metal complexes

Compounds	nC = O	nC = N	nM – O	nM – N	nM – X
MDES	1665 s,b	1480 s,m
[Co(MDES)2Cl2]	1700 m,b	1455 m,b	505 m	400 m	305 m
[Co(MDES)2Br2]	1695 m,b	1460 m,b	510 m	420 m	280 m
[Co(MDES)2I2]	1690 m,b	1455 m,b	515 m	410 m	270 m
[Co(MDES)2(NO3)2]	1695 m,b	1450 m,b	510 m	415 m
[Ni(MDES)2Cl2]	1700 m,b	1460 m,b	500 m	400 m	325 m
[Ni(MDES)2Br2]	1695 m,b	1455 m,b	495 m	395 m	295 m
[Ni(MDES)2I2]	1690 m,b	1455 m,b	500 m	400 m	275 m
[Ni(MDES)2(NO3)2]	1695 m,b	1460 m,b	395 m	395 m
[Cu(MDES)2Cl2]	1695 m,b	1455 m,b	495 m	410 m	315 m
[Cu(MDES)2Br2]	1700 m,b	1450 m,b	500 m	420 m	285 m
[Cu(MDES)2(NO3)2]	1690 m,b	1455 m,b	495 m	415 m

m = medium,   s = strong,   b = broad

Preparation of the ligand

Ethanolic solution of 1-methyl-2 , 6 diethyl piperidone was treated with ethanolic solution of semicarbazide/thiosemicarbazide in 1:1 molar ratio. The resulting reaction mixture was heated on water bath for

Preparation of the ligand

Ethanolic solution of 1-methyl-2 , 6 diethyl piperidone was treated with ethanolic solution of semicarbazide/thiosemicarbazide in 1:1 molar ratio. The resulting reaction mixture was heated on water bath for 5-6 h, when polycrystalline colourless solid began to separate out after allowing the solution to stand overnight. It was filtered washed with ethanol and dried in an electric oven, yield 65-70%, mp 171±1⁰c.

Preparation of the complexes

The complexes of Co(II), Ni(II) and Cu(II) have been formed by reacting an ethanolic solution of corresponding metal halide/metal nitrate with ethanolic solution of ligand 1-methyl-2, 6 diethyl piperidone semicarbazone (MDES) in the molar ratio 1:2. The procedure carried out in each case was of similar nature with a slight variation of timing of reflux. The coloured complexes obtained in each case were cooled, filtered and washed with ethanol several times to remove any excess of the ligand. Finally, complexes were washed with anhydrous diethyl ether and dried in electric oven. Yield 65-70%.

Results and Discussion

The IR spectra of the ligands as well as complexes have been measured in the region 4000-200 Cm^-1. The IR spectra of the ligand shows strong band at 1480cm^-1 assignable^28-30 to the n_C=N.  In the spectra of the complexes, this band shows red shift with slightly reduced intensity. The  shift of the band and change in intensity suggest coordination of the azomethine nitrogen with metal ion. The linkage with azomethine N is further supported by the appearance of a far ir band in the region 420-400 cm^-1 in the complexes assigned^29-33 to n_M—N.  The next IR spectra of the ligand shows a sharp and strong band at 1665 cm^-1 assigned^29,34 to n_C=O.  In the spectra of the complexes this band also shows red shift appearing in the region at 1700cm^-1 indicating coordination through carbonyl oxygen of semicarbazone moiety. The coordination with carbonyl oxygen atom is further supported by the appearance of a band in the far ir region at 520-500 cm^-1 assigned ^{29,30,32,33,35} as n_M—O.  The coordination through metal halogen is indicated by the appearance of a band in the region 325-270 cm^-1 assigned^29,30,32,33. to n_M-X.  (Cl^–, Br^– or I^–). The evidence of metal halogen is further supported by the low value of molar conductance of the complexes in the range 2.3-5.8 ohm^-1, cm², mol^-1. The nitrate complexes exhibit two additional ir bands at 1580 cm^-1 and 1460 cm^-1 with a separation of 120 cm^-1 suggests monocoordinated behaviour of nitrate group^33,36.

On the basis of above ir spectral bands assignments, it is proposed that ligand MDES behaves as neutral bidentate manner and coordination takes place through azomethine nitrogen and carbonyl oxygen atom of semicarbazone moiety. The remaining coordination sites are occupied by anions such as Cl^–,  Br^–, I^– and NO₃^–.

The electronic spectral and magnetic susceptibility values tentatively proposes octahedral geometry of Cobalt(II), Nickel(II) and Copper(II) complexes

Molar conductivity

Molar conductance value of the complexes are measured in the solvent DMF and the complexes were found to be non electrolytic³⁷ in nature. The molar conductance value of the complexes are lies in the range 7.1-9.1 ohm^-1 cm² mol^-1.

Antimicrobial activity

Antimicrobial activity of the ligand MDES and their metal complexes of Co(II), Ni(II) and Cu(II) have been screened by disc plate method³⁸. On comparison with reference to antibiotic, the complexes were found to be more effective than ligand due to chelation theory³⁹.

Conclusion

Thus on the basis of above observations the complexes of Cobalt(II), Nickel(II) and Copper(II)  tentatively propose an octahedral geometry as shown in Fig.-1

Fig.1  [M(MDES)2X2]Click here to View figure

 

Acknowledgement

The authors are grateful to Dr. D. C. Baluni, Prof. and Head, Postgraduate Deptt. of Zoology, R.D.S. College, Muzaffarpur for his help in measurements of  antimicrobial screening of ligand and its complexes. The author [BKR] is grateful to UGC, New Delhi for financial assistance [Grant No.- PSB-001/08-09 dated 12 Dec-2008.

References

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