A new series of cobalt, nickel, copper, and zinc complexes of bidentate Schiff base derived from the condensation of 5-bromothiophene-2-carboxaldehyde with 4-amino-3-mercapto-6-methyl-5-oxo-[1,2,4]triazine were synthesized. Physical (magnetic measurements, molar conductance, TG), spectral (UV-Vis, IR, 1HNMR, fluorescence, ESR), and analytical data have established the structures of synthesized Schiff base and its metal complexes. The presence of coordinated water in metal complexes was confirmed by IR and TG studies. The Schiff base exhibits a strong fluorescence emission, contrast to this partial fluorescence quenching phenomena is observed in its metal complexes. A square planar geometry for Cu(II) and octahedral geometry for Co(II), Ni(II) and Zn(II) complexes have been proposed. The Schiff base and its metal complexes have been screened for antibacterial (
Triazine chemistry has attracted attention due to the utility of melamine derivatives as starting material for a variety of polymers [
Encouraged by above-mentioned finding, we found it is to investigate the thermal, spectral, fluorescence, and antimicrobial studies of cobalt, nickel, copper, and zinc complexes derived from 4-[(5-bromo-thiophen-2-ylmethylene)-amino]-3-mercapto-6-methyl-5-oxo
All the chemicals used in the present study were of analytical grade and used without further purification. 4-Amino-3-mercapto-6-methyl-5-oxo-1,2,4-triazine [
A solution of 4-amino-3-mercapto-6-methyl-5-oxo-1,2,4-triazine (2.12 g, 13.5 mmol) in ethanol (40 mL) was treated with 5-bromothiophene-2-carboxaldehyde (2.69 g, 13.5 mmol). The reaction mixture was refluxed for 7 h and kept overnight at room temperature. The bluish white-colored solid crude so obtained was filtered off and washed with cold ethanol, dried, and recrystallized in ethanol.
Bluish white; yield (76%); m.p. 234–236°C; anal. calcd. for C9H7BrN4OS2: C, 32.64; H, 2.13; N, 16.92; found: C, 32.42; H, 2.08; N, 16.92%.
The solid complexes were prepared by mixing hot ethanolic solutions of the Co(L)OAc·3H2O: anal. calcd. for C11H15BrCoN4O6S2: C, 26.31; H, 3.01; N, 11.16; Co, 11.73; found: C, 26.13; H, 2.85; N, 11.12; Co, 11.30%. Ni(L)OAc·3H2O: anal. calcd. for C11H15BrN4NiO6S2: C, 26.32; H, 3.01; N, 11.16; Ni, 11.69; found: C, 26.10; H, 3.00; N, 11.03; Ni, 11.22%. Cu(L)OAc·H2O: anal. calcd. for C11H11BrCuN4O4S2: C, 28.06; H, 2.35; N, 11.90; Cu, 13.50; found: C, 28.00; H, 2.15; N, 11.82; Cu, 13.10%. Zn(L)OAc·3H2O: anal. calcd. for C11H15BrN4O6S2Zn: C, 25.97; H, 2.97; N, 11.01; Zn, 12.85; found: C, 25.65; H, 2.97; N, 11.01; Zn, 12.87%.
The aqueous ethanolic solutions of acetates of Co(II) (0.17 g, 0.68 mmol), Ni(II) (0.17 g, 0.68 mmol), Cu(II) (0.14 g, 0.68 mmol), and Zn(II) (0.15 g, 0.68 mmol) were treated with the hot ethanolic solutions of the HL (0.45 g, 1.3 mmol). The products formed were filtered and purified by washing thoroughly with warm water, with aqueous ethanol to remove unreacted metal acetates or ligands, and finally with acetone and dried. Co(L)2·2H2O: anal. calcd. for C18H16Br2CoN8O4S4: C, 28.62; H, 2.13; N, 14.83; Co, 7.80; found: C, 28.18; H, 2.01; N, 14.83; Co, 7.53%. Ni(L)2·2H2O: anal. calcd. for C18H16Br2N8NiO4S4: C, 28.63; H, 2.14; N, 14.84; Ni, 7.77; found: C, 28.63; H, 2.12; N, 14.80; Ni, 7.72%. Cu(L)2: anal. calcd. for C18H12Br2CuN8O2S4: C, 29.86; H, 1.67; N, 15.48; Cu, 8.78; found: C, 29.85; H, 1.65; N, 15.80; Cu, 8.38%. Zn(L)2·2H2O: anal. calcd. for C18H16Br2N8O4S4Zn: C, 28.38; H, 2.12; N, 14.71; Zn, 8.58; found: C, 28.37; H, 2.10; N, 14.53; Zn, 8.23%.
The elemental analyses (C, H, and N) were carried out at SAIF, Punjab University, Chandigarh, by using Perkin-Elmer 2400 Elemental Analyzer. The metal contents were determined gravimetrically by a literature procedure [
The newly synthesized Schiff base (HL) and its metal complexes were screened
The newly synthesized Schiff base (HL) and its metal complexes were screened
MIC is the lowest concentration of an antimicrobial compound that will inhibit the visible growth of a microorganism after overnight incubation.MIC of the various compounds against bacterial strains was tested through a modified agar well-diffusion method [
The synthesis of Schiff base (HL) is schematically represented in Figure
Scheme for the synthesis of Schiff base.
The comparative analysis of the IR spectra of the complexes and of the free ligand (Table
IR spectral data of the ligand and its metal complexes.
Compound |
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HL | 1690 | 1599 | — | 2476 | — | — | — | — |
Co(L)(OAc)·3H2O | 1685 | 1582 | 748 | — | 1744 | 3310 | 376 | 498 |
Co(L)2·2H2O | 1688 | 1575 | 750 | — | — | 3318 | 378 | 493 |
Ni(L)(OAc)·3H2O | 1686 | 1587 | 756 | — | 1744 | 3298 | 382 | 488 |
Ni(L)2·2H2O | 1686 | 1589 | 756 | — | — | 3298 | 381 | 488 |
Cu(L)(OAc)·H2O | 1687 | 1582 | 748 | — | 1745 | 3307 | 371 | 490 |
Cu(L)2 | 1686 | 1583 | 752 | — | — | — | 373 | 495 |
Zn(L)(OAc)·3H2O | 1689 | 1580 | 737 | — | 1743 | 3313 | 372 | 492 |
Zn(L)2·2H2O | 1690 | 1582 | 733 | — | — | 3315 | 373 | 490 |
In the 1H-NMR spectra (Table
1H NMR spectral data of Schiff base and Zn(II) metal complexes.
Compound | 1H NMR (ppm) |
---|---|
HL [C9H7BrN4OS2] | CDCl3, 2.35 (s, 3H, –CH3), 7.16 (d, 1H, Ar–H), 7.33 (d, 1H, Ar–H), 8.52 (s, 1H, –N=CH–), 10.30 (s, 1H, –SH) |
Zn(L)(OAc)·3H2O [C11H15BrN4O6S2Zn] | DMSO d6, 2.18 (s, 3H, –CH3), 7.22 (d, 1H, Ar–H), 7.38 (d, 1H, Ar–H), 8.80 (s, 1H, –N=CH–), 1.85 (s, 3H, CH3COO) |
Zn(L)2·2H2O [C18H16Br2N8O4S4Zn] | DMSO d6, 2.20 (s, 6H, –CH3), 7.38 (d, 2H, Ar–H), 7.59 (d, 2H, Ar–H), 8.73 (s, 2H, –N=CH–) |
In order to obtain further structural information, the electronic spectra and magnetic moments of the complexes have been measured (Table
Electronic spectra, magnetic data, and ligand field parameters of metal complexes.
Compound | Transitions (cm-1) | Dq cm-1 |
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Co(L)(OAc)·3H2O | 12004 | 25348* | 22779 | 1334.4 | 807.6 | 2.11 | 0.831 | 16.9 | 4.13 |
Co(L)2·2H2O | 11560 | 24431* | 22258 | 1287.1 | 800.6 | 2.11 | 0.824 | 17.6 | 4.20 |
Ni(L)(OAc)·3H2O | 11261 | 16200 | 26115 | 1126.1 | 568.8 | 1.43 | 0.546 | 45.4 | 3.78 |
Ni(L)2·2H2O | 11376 | 16345 | 26238 | 1137.6 | 563.6 | 1.43 | 0.541 | 45.9 | 3.76 |
Cu(L)(OAc)·H2O | 20123 | — | — | — | — | — | 1.75 | ||
Cu(L)2 | 19998 | — | — | — | — | — | 1.75 |
*Calculated value.
The Ni(II) complexes reported herein are found to have room temperature magnetic moment values 3.78 and 3.76 BM, corresponding to two unpaired electrons. The electronic spectra of Ni(II) complexes display three absorption bands in the range 11261–11376, 16200–16345, and 26115–26238 cm−1. These bands may be assigned to three spin allowed transitions
The photoluminescence emission spectra of the Schiff base (HL) and its 1 : 2 metal complexes are recorded in DMF at room temperature (Figure
Fluorescence emission spectra of Schiff base and its metal complexes.
ESR spectra (Figure
X-band ESR spectra of Cu(L)(OAc)·H2O.
Thermal studies of Zn(L)2·2H2O and Ni(L)2·2H2O (Figure
Thermogravimetric curves of Zn(L)2·2H2O and Ni(L)2·2H2O.
TGA studies of Ni(L)2·2H2O indicated first weight loss (4.3%) in the range of 50–235°C, attributed to the loss of two water molecules (calcd. 4.8%). The second weight loss of 49.9% (calcd. 50.0%) from 235–300°C corresponds to loss of organic moiety (C10H6Br2N2S2). In the last step of decomposition triazine moiety comes out in the range 300–800°C with mass loss of 37.1% (Calcd. 37.5%). The final residual weight is 9.1% (calcd. 9.8%) corresponding to NiO.
The ligand (HL), metal complexes, standard drugs, and DMSO solvent were screened separately for their antibacterial activity against Gram-positive (
Antibacterial activity of synthesized compounds through agar well diffusion method.
Compound | Diameter of growth of inhibition zone (mm)a | |||
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HL | 16.3 | 18.3 |
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Co(L)(OAc)·3H2O | 18.3 | 18.3 |
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Co(L)2·2H2O | 16.3 | 19.6 |
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Ni(L)(OAc)·3H2O | 17.3 | 18.0 |
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Ni(L)2·2H2O | 17.3 | 19.6 |
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Cu(L)(OAc)·H2O | 16.3 | 18.3 |
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Cu(L)2 | 20.6 | 22.6 |
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Zn(L)(OAc)·3H2O | 19.3 | 21.3 |
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Zn(L)2·2H2O | 17.3 | 19.6 |
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Ciprofloxacin | 26.6 | 24.0 | 25.0 | 22.0 |
—No activity.
aValues, including diameter of the well (8 mm), are means of three replicates.
Minimum inhibitory concentration (MIC) (
Compound |
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HL | 128 | 64 |
Co(L)(OAc)·3H2O | 128 | 64 |
Co(L)2·2H2O | 128 | 64 |
Ni(L)(OAc)·3H2O | 128 | 64 |
Ni(L)2·2H2O | 128 | 64 |
Cu(L)(OAc)·H2O | 128 | 64 |
Cu(L)2 | 64 | 32 |
Zn(L)(OAc)·3H2O | 64 | 32 |
Zn(L)2·2H2O | 128 | 64 |
Ciprofloxacin | 6.25 | 6.25 |
Antifungal activity of Schiff base and metal complexes.
Compound | Mycelial growth inhibition (%) | |
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HL | 45.2 | 46.6 |
Co(L)(OAc)·3H2O | 47.7 | 51.1 |
Co(L)2·2H2O | 48.8 | 52.2 |
Ni(L)(OAc)·3H2O | 45.5 | 48.8 |
Ni(L)2·2H2O | 43.3 | 46.6 |
Cu(L)(OAc)·H2O | 45.5 | 48.8 |
Cu(L)2 | 58.8 | 63.3 |
Zn(L)(OAc)·3H2O | 56.6 | 61.1 |
Zn(L)2·2H2O | 51.1 | 56.6 |
Fluconazole | 81.1 | 77.7 |
Tested chemical compounds showed zone of inhibition ranging between 16 mm and 22 mm against the Gram-positive bacteria. On the basis of zone of inhibition produced against the test bacterium, Cu(L)2 was found to be most effective against
The present work describes the synthesis of cobalt, nickel, copper, and zinc complexes of bidentate Schiff base derived from the condensation reaction of 5-bromothiophene-2-carboxaldehyde with 4-amino-3-mercapto-6-methyl-5-oxo
Proposed structures of metal complexes.
The Kumar is highly thankful to the University Grant Commission, New Delhi for the providing, Senior Research Fellowship (SRF) and the Department of Chemistry, Kurukshetra University, Kurukshetra, for providing facilities to carry out this research work.