Two new heterocyclic Schiff bases of 4-amino-5-mercapto-3-H/propyl-1,2,4-triazole and 5-nitrofurfuraldehyde [
Recently, for the rapid development of drug resistance, new antimicrobial agent should be designed and synthesized with chemical characteristics clearly different from those of existing ones. 1,2,4-triazoles and their fused heterocyclic derivatives have received considerable attention owing to their synthetic and effective biological importance such as analgesic [
Schiff bases represent an important class of compounds because they are utilized as starting materials in the synthesis of industrial products [
Keeping in view medicinal and industrial applications of triazoles and potential chemistry of transition metals; new heterocyclic Schiff bases of 4-amino-5-mercapto-3-H/propyl-1,2,4-triazole with 5-nitrofurfuraldehyde [
All starting precursor were of analytical grade. The reagents and solvents were purchased commercially and used without further purification unless otherwise noted. 4-Amino-5-mercapto-1,2,4-triazole (AMT) and 4-amino-5-mercapto-3-propyl-1,2,4-triazole (AMPT) were prepared by reported literature method [
4-Amino-5-mercapto-1,2,4-triazole (0.61 g, 5.06 mmol) dissolved in warm ethanol (20 mL) was added to an ethanol solution (30 mL) containing 5-nitrofurfuraldehyde (0.72 g, 5.06 mmol). The mixture was refluxed for 5 hrs. The reaction mixture was then cooled to room temperature and the yellow solid formed was filtered. It was then recrystallized from ethanol and dried. m.p. 168–170°C, (Found: C, 35.01; H, 2.11; N, 29.28%. Calcd. for C7H5N5O3S: C, 35.15; H, 2.11; N, 29.28%).
To a solution of 5-nitrofurfuraldehyde (0.52 g, 3.68 mmol) in ethanol (30 mL), 4-amino-5-mercapto-3-propyl-1,2,4-triazole (0.58 g, 3.68 mmol) in ethanol (20 mL) was added. The mixture was refluxed for 6 h. The reaction mixture was then cooled to room temperature and the reddish yellow solid formed was filtered. It was then recrystallized from ethanol and dried. m.p. 142–144°C, (Found: C, 42.70; H, 3.33; N, 24.33%. Calcd. for C10H11N5O3S: C, 42.70; H, 3.94; N, 24.90%).
The metal complexes were synthesized by reacting aqueous ethanolic solutions of acetates of Co(II) (0.14 g, 0.57 mmol), Ni(II) (0.14 g, 0.57 mmol), Cu(II) (0.11 g, 0.57 mmol), and Zn(II) (0.13 g, 0.57 mmol) with the hot ethanolic solutions of the HL1 (0.27 g, 1.14 mmol). The solid complexes formed were filtered off and washed several times with warm water, aqueous ethanol to remove unreacted metal acetates or ligands, and finally with acetone and vacuo dried. Co(L1)2·2H2O: (Found: C, 29.21; H, 2.01; N, 24.11; Co, 10.13% Calcd. for C14H12CoN10O8S2: C, 29.43; H, 2.12; N, 24.51; Co, 10.31%). Ni(L1)2·2H2O: (Found: C, 29.12; H, 2.02; N, 24.08; Ni, 10.11% Calcd. for C14H12N10NiO8S2: C, 29.44; H, 2.12; N, 24.52; Ni, 10.28%). Cu(L1)2: (Found: C, 31.00; H, 1.39; N, 25.88; Cu, 11.40% Calcd. for C14H8CuN10O6S2: C, 31.14; H, 1.49; N, 25.94; Cu, 11.77%). Zn(L1)2·2H2O: (Found: C, 28.96; H, 1.99; N, 24.20; Zn, 11.31% Calcd. for C14H12N10O8S2Zn: C, 29.10; H, 2.09; N, 24.24; Zn, 11.32%).
The metal acetates of Co(II) (0.17 g, 0.67 mmol), Ni(II) (0.17 g, 0.67 mmol), Cu(II) (0.13 g, 0.67 mmol), and Zn(II) (0.15 g, 0.67 mmol) in aqueous ethanol were treated with hot ethanolic solution of the HL2 (0.37 g, 1.34 mmol). The colored complexes formed were filtered off and washed several times with warm water, aqueous ethanol to remove unreacted metal acetates or ligands, and finally with acetone and vacuo dried. Co(L2)2·2H2O: (Found: C, 36.22; H, 3.47; N, 21.23; Co, 8.23% Calcd. for C20H24CoN10O7S2: C, 36.64; H, 3.69; N, 21.37; Co, 8.99%). Ni(L2)2·2H2O: (Found: C, 36.53; H, 3.51; N, 21.18; Ni, 8.53% Calcd. for C20H24N10NiO7S2: C, 36.66; H, 3.69; N, 21.37; Ni, 8.96%). Cu(L2)2: (Found: C, 38.15; H, 3.18; N, 22.13; Cu, 10.23% Calcd. for C20H20CuN10O6S2: C, 38.49; H, 3.23; N, 22.44; Cu, 10.18%). Zn(L2)2·2H2O: (Found: C, 36.06; H, 3.43; N, 21.15; Zn, 9.43% Calcd. for C20H24N10O7S2Zn: C, 36.29; H, 3.65; N, 21.16; Zn, 9.88%).
Elemental analyses (C, H, and N) were performed on Perkin-Elmer 2400 Elemental Analyzer available at SAIF, Punjab University, Chandigarh. The metal contents were determined gravimetrically by a literature procedure [
Two Gram-positive bacteria (
The antimicrobial activity of the newly synthesized compounds was assayed by using agar wells diffusion technique [
MIC of all the compounds was determined by the modified agar well diffusion method [
The scheme for the syntheses of Schiff bases is represented in Figure
Scheme for the syntheses of Schiff bases.
The 1H NMR spectral data of Schiff bases (
1H NMR and 13C NMR spectral data of Schiff bases and their metal complexes.
Compounds | 1H NMR (DMSO-d6) (ppm) | 13C NMR (DMSO-d6) (ppm) |
---|---|---|
HL1 |
7.55 (d, 1H, Ar–H), 7.84 (d, 1H, Ar–H), |
114.37, 120.34, 139.44, 146.98, 149.43, 152.12 (Aromatic), 163.34 (–N=CH–) |
Zn(L1)2·2H2O |
7.42 (d, 2H, Ar–H), 7.66 (d, 2H, Ar–H), 9.05 |
114.31, 121.02, 139.28, 146.76, 150.22, 152.38 (Aromatic), 171.18 (–N=CH–) |
HL2 |
0.93 (t, 3H, –CH3), 1.66 (m, 2H, –CH2–), 2.69 |
13.84 (–CH3), 19.21 (–CH2–), 26.69 (–CH2–), 114.32, 120.4, 148.28, 149.50, 151.97, 153.52 (Aromatic), 161.9 (–N=CH–) |
Zn(L2)2·2H2O |
0.80 (t, 6H, –CH3), 1.57 (m, 4H, –CH2–), 2.63 |
13.74 (–CH3), 19.63 (–CH2–), 26.79 (–CH2–), 114.22, 121.5, 148.75, 152.87, 153.50, 153.70 (Aromatic), 169.72 (–N=CH–) |
The 13C NMR spectral data of Schiff bases (
The bonding of the ligands to metal ions has been judged by careful comparison of the infrared spectra of the complexes with those of the free ligand (Table
Important IR spectral bands (cm−1) of Schiff bases and their metal complexes.
Compound |
|
|
|
|
|
|
---|---|---|---|---|---|---|
HL1 | 1622 | — | 2739 | — | — | — |
Co(L1)2·2H2O | 1613 | 733 | — | 3441 | 360 | 502 |
Ni(L1)2·2H2O | 1607 | 734 | — | 3356 | 347 | 512 |
Cu(L1)2 | 1612 | 715 | — | — | 351 | 497 |
Zn(L1)2·2H2O | 1610 | 717 | — | 3425 | 361 | 511 |
HL2 | 1625 | — | 2770 | — | — | — |
Co(L2)2·2H2O | 1613 | 735 | — | 3440 | 355 | 493 |
Ni(L2)2·2H2O | 1611 | 730 | — | 3410 | 347 | 490 |
Cu(L2)2 | 1609 | 710 | — | — | 362 | 503 |
Zn(L2)2·2H2O | 1606 | 718 | — | 3395 | 353 | 510 |
The electronic paramagnetic resonance spectra of Cu(L1)2 (Figure
X-Band ESR spectrum of Cu(L1)2.
The observed electronic transitions and calculated ligand field parameters of the metal complexes are listed in Table
Electronic spectral data (in DMF) and ligand field parameters of metal complexes.
Compound | Transitions (cm−1) |
|
|
|
|
|
|
||
---|---|---|---|---|---|---|---|---|---|
|
|
| |||||||
Co(L1)2·2H2O | 10599 | 22425* | 20809 | 1182.6 | 762.4 | 2.11 | 0.78 | 22 | 4.20 |
Co(L2)2·2H2O | 10913 | 23063* | 20998 | 1215.0 | 754.8 | 2.11 | 0.77 | 22 | 4.11 |
Ni(L1)2·2H2O | 9907 | 16226 | 24372 | 990.7 | 725.1 | 1.63 | 0.69 | 31 | 3.79 |
Ni(L2)2·2H2O | 9933 | 16283 | 23415 | 993.3 | 659.9 | 1.63 | 0.63 | 37 | 3.73 |
Cu(L1)2 | 17981 | — | — | — | — | — | 1.86 | ||
Cu(L2)2 | 18121 | — | — | — | — | — | 1.92 |
*Calculated value.
The Ni(II) complex reported herein are high spin with room temperature magnetic moment value ~3.75 BM, which is in the normal range observed for octahedral complexes. The electronic spectra of Ni(II) complexes displayed three bands in the regions 9907–9933 cm−1, 16226–16283 cm−1, and 23415–24372 cm−1, assigned to
The Band-fitting equations [
The copper complexes of
In order to investigate the effect of M(II) ions on the fluorescence of the ligands, the fluorescence spectra of ligands (
Fluorescence spectra of HL1 and its metal complexes.
Fluorescence spectra of HL2 and its metal complexes.
Thermogravimetric analyses of the complexes Ni(L1)2·2H2O and Cu(L1)2 are given in Table
Thermogravimetric data of Ni(L1)2·2H2O and Cu(L1)2 complexes.
Compound | Decomposition stages and assignment | Temp. (°C) | % Weight loss found (Calcd.) |
---|---|---|---|
Ni(L1)2·2H2O |
(1) Water molecules | 50–190 | 6.9 (6.3) |
(2) Organic moiety | 190–424 | 48.2 (48.6) | |
(3) Triazoles moiety | 424–750 | 34.5 (34.6) | |
| |||
Cu(L2)2 |
(1) Organic moiety | 50–245 | 46.9 (46.3) |
(2) Triazole moiety | 245–445 | 20.1 (20.9) | |
(3) Triazole moiety | 445–750 | 20.3 (20.9) |
Thermogravimetric Curves of Ni(L1)2·2H2O and Cu(L1)2 complexes.
The ligands (
Antimicrobial activity of the synthesized compounds.
Compound | Diameter of growth of inhibition zone (mm) | ||||
---|---|---|---|---|---|
|
|
|
|
|
|
HL1 | 17.3 | 19.6 | 15.2 | 12.7 | 15.2 |
Co(L1)2·2H2O | 17.4 | 16.5 | 16.3 | — | 19.5 |
Ni(L1)2·2H2O | 18.2 | 16.9 | 15.4 | — | 16.5 |
Cu(L1)2 | 17.2 | 18.4 | 17.6 | 21.2 | 19.5 |
Zn(L1)2·2H2O | 15.4 | 16.8 | 17.4 | 17.6 | 15.8 |
HL2 | 15.4 | 12.6 | 15.4 | 13.7 | 15.3 |
Co(L2)2·2H2O | — | 14.6 | 19.4 | 17.3 | 14.8 |
Ni(L2)2·2H2O | — | 14.8 | 16.2 | 17.3 | 17.9 |
Cu(L2)2 | — | — | 19.2 | 17.4 | 14.6 |
Zn(L2)2·2H2O | 15.4 | — | 13.3 | 12.4 | 15.7 |
Ciprofloxacin | 23.0 | 24.0 | 23.0 | 20.0 | nt |
—: Indicates no activity, nt: not tested.
Minimum inhibitory concentration (MIC) (
Compounds |
|
|
|
|
|
---|---|---|---|---|---|
NFMT | 300 | 200 | 400 | 800 | 200 |
Co(L1)2·2H2O | 300 | 100 | 200 | — | 100 |
Ni(L1)2·2H2O | 100 | 400 | 200 | — | 200 |
Cu(L1)2 | 200 | 200 | 200 | 500 | 200 |
Zn(L1)2·2H2O | 400 | 500 | 500 | 700 | 500 |
NFMPT | 500 | 800 | 300 | 500 | 700 |
Co(L2)2·2H2O | — | 800 | 500 | 700 | 700 |
Ni(L2)2·2H2O | — | 500 | 800 | 400 | 700 |
Cu(L2)2 | — | — | 100 | 600 | 500 |
Zn(L2)2·2H2O | 200 | — | 500 | 800 | 200 |
Ciprofloxacin | 5 | 5 | 5 | 5 | — |
—: Not tested.
The newly synthesized compounds showed zone of inhibition ranging from 12.6 mm to 19.6 mm against the Gram positive bacteria and 12.7 mm to 21.2 mm against Gram negative bacteria. On the basis of zone of inhibition produced against the test bacterium, it is observed that Cu(L1)2 shows antibacterial activity comparable to standard drug in case of
The overtone’s concept [
The synthesized Schiff bases act as bidentate ligands and coordinated to metal ion through azomethine nitrogen and sulphur of thiol group. The bonding of ligand to metal ion is confirmed by elemental analyses, spectral studies (UV-Vis, IR, 1H NMR, ESR, Fluorescence), TGA, and magnetic and conductance measurements. The spectral studies suggested octahedral geometry for the Co(II), Ni(II), and Zn(II) complexes and square planar for Cu(II) complexes (Figure
Structures of Metal Complexes.
Y. Kumar is highly thankful to University Grant Commission, New Delhi, for providing Senior Research Fellowship (SRF) and Department of Chemistry, Kurukshetra University Kurukshetra, for providing facilities to carry out this research work.