Synthesis and Structural Characterization of Schiff Base Ligand and their Metal Complexes

Introduction

In recent years,^1-10 there has been considerable interest in the chemistry of transition metal of schiff base^16-18. This is due to the fact that schiff base transition metal complexes are one of the most adaptable and thoroughly studied systems. The Schiff base complexes have applicable in clinical and analytical fields. They are used as model molecule for biological oxygen carrier systems. Schiff bases metal complexes also exhibit several biocidal potential such as antifungal^28-32, anti-cancer, herbicidal and anti-bacterial. Because of their ease in preparation and versatile properties, herein; the syntheses, structural features, spectroscopic characterization of metal complexes of Co(II), Ni(II), Cu(II) with Schiff bases, 2-Phenyl 3(benzamido propyl) quinazoline (3H)-4-one semicarbozone and 2-phenyl-3(benzamido propyl) quinazoline (3H)-4-one thiosemicarbozone are reported.

Experimental

Physical Measurement

All the chemicals and solvents were of reagent grade and were used without further purification.

The ligand and metal complexes were analysed using standard procedure. Analytical data were collected on Perkin-Elmer-2400 CHNO/S elemental analyzer. Infrared spectra were recorded on Parkin-Elmer spectrometer model-577 using KBr disc. Electronic spectra was measured on Cary-2390 spectrophotometer. Molar conductance was using a Systronics conductivity meter model 303 using Ca   10^-3 M solutions in DMF. Magnetic susceptibility of the samples were made on Guoy balance using mercury tetraisothiocynato cobaltate as a calibrant.

Synthetic Procedure

Preparation of the bidentate Schiff base ligand PBPQS/PBPQT

The compound 2-phenyl-3-(benzamido propyl) quinazolin (3H)-4-one was synthesized by earlier reported method. Ethanolic solution 2-phenyl-3-(benzamido propyl) quinazolin(3H) 4-one was allowed to react with Semicarbazide/thiosemicarbazide hydrochloride dissolved in 10% ethanolic solution of Sodium acetate. The resulting mixture were heated on water bath for 3-4 hr with frequent stirring. After cooling the precipitate was collected, washed with tetrahydrofuran, treated with dilute sodium carbonate solution and filtered. The solid was washed with water and crystallised twice from ethanol to furnish 2-phenyl-3-benzamido propyl) quinazoline (3H) 4-one semicarbazone/ thiosemicarbazone as colourless compounds m.p. 262 ±1^OC for ligand PBPQS and 273 ±1⁰C for ligand PBPQT yield, 70%.

Preparation of the complexes

The compounds of Co(II), Ni(II) and Cu(II) have been formed by reacting an ethanolic solutions of metal halides/nitrates with ethanolic solutions of the ligand PBPQS/PBPQT in molar ratio 1:2. The resulting reaction mixtures were heated on water bath for 2-3 hrs. The solid coloured complexes which separated out on cooling were filtered, washed with ethanol, dried and recrystallised with tetrahydrofuran; yield in all cases 65-70%.

Results and Discussion

Infrared Spectral Studies

The IR data of the spectra of the ligand PBPQS/PBPQT and its Co(II), Ni(II) and Cu(II) complexes are listed in Table-1. The characteristic IR band for the free ligands, when compared with those of their complexes provide meaningful information regarding the bonding sites of the ligand.

Semicarbazine/ thiosemicarbazone ligands can coordinate as bidentate ligands, in most cases through the azomethine nitrogen and oxygen/sulphur atom of either semicarbazone/ thiosemicarbazone. In the free ligands PBPQS/PBPQT the v_C=N bands appear in the region of 1645-1635cm^-1. In all the complexes, the v_C=N band is shifted to lower frequency in the range. 1620-1605 cm^-1, indicating coordination of the Schiff bases through the azomethine nitrogen atom¹¹. This is further supported by the appearance of a far IR band in the range 420-390 cm^-1 in the complexes which may be assigned¹² to v_M-N.

The IR spectrum of the ligand PBPQS exhibit strong and broad band at 1720 cm^-1 assigned¹¹ to v_C=O. This band undergoes red shift after complexation proposes co-ordination through carbonyl oxygen atom of semicarbozone moiety. It is further supported by the appearance of a new band in far IR region at 520-505cm^-1 assigned¹² to v_M-O.

The spectrum of the ligand PBPQT shows a sharp and strong band at 820 cm^-1 assigned to v_C=S. In the spectra of the complexes this band shows red shift proposes coordination through thione sulphur. This is further supported by the appearance of a far IR band in the region at 480-455 cm^-1, assigned¹² to v_M-S.

Table 1: Analytical and Physical Data of the Ligand Pbpqs/ Pbpqt and its Metal Complexes

Compounds (Colour)	Molar Mass	% Analysis found (Calculated)				D.T.   oC	meff       (B.M.)	Wm  ohm-1 cm2 mol-1	lmax electronic cm-1
		M	C	N	H
PBPQS        Colourless	472		60.83 (61.01)	17.70 (17.79)	4.97 (5.08)
PBPQT      (Colourless)	488		58.87 (59.01)	17.12 (17.21)	4.86 (4.91)
[Co(PBPQS)2Cl2] Yellowish red	1073.93	5.37 (5.49)	53.41 (53.63)	15.58 (15.64)	4.40 (4.46)	236	5.06	6.7	13640, 19760
[Co(PBPQT)2Cl2] Yellowish red	1105.93	5.24 (5.32)	51.84 (52.08)	15.08 (15.19)	4.28 (4.34)	242	5.01	6.1	13470, 19280
[Co(PBPQS)2Br2] Reddish yellow	1162.748	4.93 (5.06)	49.38 (49.53)	14.33 (14.44)	4.08 (4.12)	227	4.89	6.9	12810, 19640
[Co(PBPQT)2Br2] Reddish yellow	1194.748	4.87 (4.93)	48.09 (48.21)	13.97 (14.06)	3.96 (4.01)	238	4.94	6.2	12930, 20100
[Co(PBPQS)2I2]   Deep yellow	1256.73	4.59 (4.68)	45.70 (45.83)	13.23 (13.36)	3.77 (3.81)	220	4.98	6.4	12960, 21200
[Co(PBPQT)2I2]   Deep yellow	1288.73	4.48 (4.57)	44.53 (44.69)	12.90 (13.03)	3.68 (3.72)	248	4.93	6.3	13010, 20740
[Co(PBPQS)2(NO3)2] Yellowish red	1126.93	5.14 (5.22)	50.98 (51.11)	144.78 (14.90)	4.20 (4.25)	214	5.12	6.8	13220, 20960
[Co(PBPQT)2(NO3)2] Yellowish red	1158.93	4.96 (5.08)	49.53 (49.70)	14.36 (14.49)	4.09 (4.14)	209	5.09	6.6	13270, 19730
[Ni(PBPQS)2Cl2] Brown	1073.71	5.33 (5.46)	53.40 (53.64)	15.56 (15.64)	4.43 (4.47)	253	3.11	4.7	10640, 15210, 24390
[Ni(PBPQT)2Cl2] Brown	1105.71	5.22 (5.30)	51.86 (52.09)	15.06 (15.19)	4.29 (4.34)	234	3.09	4.1	10560, 15340, 24580
[Ni(PBPQS)2Br2] Brown	1162.52	4.92 (5.05)	49.36 (49.54)	14.32 (14.45)	4.06 (4.12)	213	3.07	4.9	10580, 15240, 24600
[Ni(PBPQT)2Br2] Deep red	1194.52	4.85 (4.91)	48.06 (48.22)	13.96 (14.06)	3.95 (4.01)	238	3.04	4.89	10320, 15710, 24520
[Ni(PBPQS)2I2]    Deep yellow	1256.51	4.60 (4.68)	45.72 (45.85)	13.24 (13.37)	3.78 (3.82)	256	3.06	4.64	10430, 15460, 14380
[Ni(PBPQT)2I2]         Red	1288.51	4.49 (4.55)	44.54 (44.70)	12.91 (13.03)	3.67 (3.72)	248	3.12	5.10	10100, 15840, 24320
[Ni(PBPQS)2(NO3)2] Reddish brown	1126.71	5.14 (5.21)	51.01 (51.12)	14.77 (14.91)	4.02 (4.26)	270	3.17	5.2	10210, 15740, 24380
[Ni(PBPQT)2(NO3)2] Reddish brown	1158.71	4.94 (5.06)	49.54 (49.71)	14.37 (14.449)	4.10 (4.14)	261	3.15	5.6	10380, 15900, 24240
[Cu(PBPQS)2Cl2]   Blue	1078.54	5.80 (5.89)	53.22 (53.40)	15.49 (15.57)	4.39 (4.45)	280	1.89	11.2	12310, 17480
[Cu(PBPQT)2Cl2]    Blue	1110.54	5.63 (5.72)	51.72 (51.86)	18.51 (18.65)	4.26 (4.32)	276	1.98	10.8	12240, 17320
[Cu(PBPQS)2Br2]    Blue	1167.35	5.36 (5.44)	49.22 (49.34)	13.88 (14.00)	4.02 (4.11)	268	1.90	10.2	12140, 17540
[Cu(PBPQT)2Br2]  Blue	1199.35	5.20 (5.29)	47.83 (48.02)	13.84 (14.00)	6.61 (6.67)	255	1.92	11.3	12540, 17610
[Cu(PBPQS)2(NO3)2] Deep blue	1131.54	5.52 (5.61)	50.79 (50.90)	14.72 (14.84)	4.19 (4.24)	260	1.94	9.8	12620, 17520
[Cu(PBPQT)2(NO3)2] Deep blue	1163.54	5.37 (5.46)	49.33 (49.50)	14.32 (14.43)	4.07 (4.12)	268	1.93	9.4	12480, 17460

 

Table 2: Salient Features of IR Spectral Data for Ligand and its Metal Complexes

Compounds	nC=O	nC=N	nC=S	nM-O	nM-S	nM-N	nM-X
PBPQS	1720  s,b	1635 s,b
PBPQT		1645   s,b	820   s,b
[Co(PBPQS)2Cl2]	1690    m,b	1605   m,b		505       m		405     m	255      m
[Co(PBPQT)2Cl2]		1610   m,b	795   m,b		460    m	405    m	255    m
[Co(PBPQS)2Br2]	1695    m,b	1605      m,b		505 m,b		405    m	260    m
[Co(PBPQT)2Br2]		1610   m,b	790   m,b		455   m	405     m	260    m
[Co(PBPQS)2I2]	1690      m,b	1600  m,b		500 m,b		405    m	270     m
[Co(PBPQT)2I2]		1615  m,b	790  m,b		470   m	410    m	270   m
[Co(PBPQS)2(NO3)2]	1695  m,b	1600   m,b		515    m		415    m
[Co(PBPQT)2(NO3)2]		1620    m,b	790    m,b		470    m	415    m
[Ni(PBPQS)2Cl2]	1690   m,b	1600    m,b		515     m		3415    m	295    m
[Ni(PBPQT)2Cl2]		1620      m,b	795      m,b		475    m	415      m	295      m
[Ni(PBPQS)2Br2]	1690  m,b	1600    m,b		510    m		420    m	295    m
[Ni(PBPQT)2Br2]		1620   m,b	795     m,b		475    m	420    m	295     m
[Ni(PBPQS)2I2]	1690   m,b	1600    m,b		510     m		420    m	310    m
[Ni(PBPQT)2I2]		1605   m,b	790   m,b		475   m	420   m	315    m
[Ni(PBPQS)2(NO3)2]	1690  m,b	1605   m,b		515   m		410   m
[Ni(PBPQT)2(NO3)2]		1600   m,b	795    m,b		480   m	410   m
[Cu(PBPQS)2Cl2]	1690   m,b	1605    m,b		515   m		470    m	285    m
[Cu(PBPQT)2Cl2]		1600 m,b	795    m,b		480   m	470     m	290     m
[Cu(PBPQS)2Br2]	1690    m,b	1605   m,b		515     m		410      m	285     m
[Cu(PBPQT)2Br2]		1600  m,b	795     m,b		480     m	410    m	290   m
[Cu(PBPQS)2(NO3)2]	1690   m,b	1690    m,b		515    m		470     m
[Cu(PBPQT)2(NO3)2]		1600  m,b	795    m,b		480    m	410   m

 

Figure 1: [M(PBPQS)2]X2 and [M(PBPQT)2]X2 M = Co(II), Ni(II) and Cu(II) ;  X = Cl–,  Br– ,  I– and NO3– ; Y = Oxygen or Sulphur; R = Phenyl;  R’ = benzamido propyl   Click here to View figure

 

The co-ordination through halogen atom is confirmed by the appearance of a band in the far IR region at 315-255 cm^-1 assigned to n_M-X (X= Cl^–, Br^–, I^–). The evidence of metal halogen linkage is further confirmed on the basis of low value of molar conductance measurements of complexes in the range 4.7-11.2 ohm^-1 cm² mol^-1 (Table-1). Nitrate complexes show characteristic medium intensity bands at 1260 and 1100 cm^-1with a separation of 160 cm^-1 due to monodentate linkage of nitrate group. Combination bands at 1660 and 1640 cm^-1 with a separation of 20 cm^-1 confirming the monodentate behavior of the nitrate group.

On the basis of above discussion on IR spectral data it is proposed that the ligand PBPQS/PBPQT acts in a neutral bidentate manner. The remaining coordination positions of metal ions are satisfied by negative ions, such as Cl^–, Br^–, I^– and NO₃^–.

Electronic spectra and magnetic susceptibility of the complexes

The electronic spectra of all the complexes have been recorded in the region 10000-25000 cm^-1. The Co(II) complexes exhibit two bands in the regions at 13470-12870 cm^-1 and 21200-19280 cm^-1 assigned to the transitions; ⁴A_2g(F) ← ⁴T_1g(F) and ⁴T_1g(P) ← ⁴T_1g(F) respectively, proposing octahedral geometry for Co(II) complexes.

The octahedral geometry for Co(II) complexes are further supported by the high magnetic susceptibility in the range 4.89-5.12 BM. The Ni(II) complexes exhibit three spectral bands in the region, 10800-10100 cm^-1, 15900-15200 cm^-1 and 24600-24000 cm^-1 assigned to the transitions, ; ³T_2g(F)← ³A_2g(F), ⁴T_1g(F) ←³A_2g(F) and  ⁴T_1g(P) ←³A_2g(F) respectively, proposing octahedral geometry for Ni(II) complexes. The proposed geometry of Ni(II) complexes is further supported by the magnetic susceptibility value in the range 3.04-3.17 BM. The Cu(II) complexes exhibit two spectral bands in the regions, 12600-12100 cm^-1 and 17900-17300 cm^-1 assigned to the transitions, ²T_2g ← ²E_g and charge transfer band which proposing octahedral geometry for Cu(II) complexes. The magnetic value of Cu(II) complexes lies in the range 1.89-1.98 B.M.

Conductivity Measurement

Molar conductance of the complexes was measured in solvent dimethyl formamide. All the complexes have conductivity value in the range of 4.7-11.2 ohm^-1cm²mol^-1indicating their non-electrolyte behaviour.

Conclusion

Thus on the basis of above physico-chemical studies it is concluded that the ligand PBPQS/PBPQT acts in a neutral bidentate manner and coordination is proposed through azomethine nitrogen and through carbonyl oxygen atom or sulphur atom of semicarbazone/ thiosemicarbazone moiety. The remaining position of metal ion is satisfied by negative ions such as Cl^–, Br^–, I^– and No₃^–. The geometry of the Co(II), Ni(II) and Cu(II) are proposed to be octahedral in nature as shown in Fig.1.

References

1. Ragab, R. Amin; Asian J. Chem, 2000, 12, 394-354.
2. Prasad, N.B.L. and Hssain, K. Reddy; J. Indian Chem. Soc., 2004, 81, 794-796.
3. Mehta, B. H. and Shaikh, J.A.; J. Indian Chem. Soc., 2009, 26, 1-6.
4. Kumar, Brajesh; Sangal, S.K. and Kumar Arun; J. Indian Chem. Soc., 2009, 86, 514-517.
5. Ramachary, M.; Padmaja, N.; Ravinder, M. and Srihari, S.; Orient J. Chem., 2010, 26, 1159-1162.
6. Shakti, Shiva; Mishra, P.M.; Mishra, Satyendra Kumar and Jha, Ajay Kumar; Asian J. Chem, 2010, 22, 5013-5018.
7. Raghav, N.; Kaur, Ravider; Singh, Mamta;  Suman and Priyanka; Asian J. Chem., 2010, 22, 7097-7101.
8. Elyas, Mohammad and Siddiqui, Ashan Rasheed; Orient J. Chem., 2011, 27, 627-632.
9. Tyagi, Monika and Chandra Sulekh; J. Indian Chem. Soc., 2012, 89, 147-154.
10. Anitha P.; Manikanandan, R.; Vijayan, P.; Prakash, G.; Viswanathmurthi, P. and Butcher Ray Jay; J. Chem. Sci., 2015, 127, 597-608.
    CrossRef
11. Esmati, N.; Yousifi, M.; Shafiee, A. and Foroumadi, A.; Asian J. Chem, 2011, 23, 4011-4013.
12. Ali, Ahmed Mohammed Fakruddin and Moahammadyunis, V.; Orient J. Chem, 2014, 30, 111-117.

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