Scholarly article on topic 'Synthesis, spectroscopic investigation and antimicrobial activities of some transition metal complexes of a [(2-hydroxyacetophenone)-3-isatin]-bishydrazone'

Synthesis, spectroscopic investigation and antimicrobial activities of some transition metal complexes of a [(2-hydroxyacetophenone)-3-isatin]-bishydrazone Academic research paper on "Chemical sciences"

CC BY-NC-ND
0
0
Share paper
Academic journal
Arabian Journal of Chemistry
OECD Field of science
Keywords
{Bishydrazone / IR / EPR / "Antimicrobial activity" / "Corrosion inhibition"}

Abstract of research paper on Chemical sciences, author of scientific article — S.S. Swathy, R. Selwin Joseyphus, V.P. Nisha, N. Subhadrambika, K. Mohanan

Abstract A bishydrazone was obtained by the condensation of isatin monohydrazone with 2-hydroxyacetophenone, which formed a series of complexes with manganese(II), cobalt(II), nickel(II), copper(II) and zinc(II). The ligand and the metal complexes were characterized on the basis of elemental analysis, molar conductance, magnetic moment, IR, UV–Visible, mass, 1H NMR, EPR, and thermal analysis. Spectral studies revealed that the ligand acted as monobasic tridentate, coordinating to the metal ion through the deprotonated phenolate oxygen, azomethine nitrogen and carbonyl oxygen atom of the isatin moiety. The low molar conductance values indicate that all complexes are non-electrolytes. Based on the spectral results and magnetic susceptibility measurements, suitable geometry was proposed for each complex. The EPR spectral data indicated that metal–ligand bond had considerable covalent character. The ligand and its nickel(II) complex were subjected to XRD studies. Thermal decomposition study of nickel(II) complex was also carried out. In vitro biological screening effects of the compounds were tested against the bacteria and the fungal species by the agar disc diffusion method. A comparative study of the MIC values of the ligand and its complexes indicated that the copper(II) complex exhibited higher antimicrobial activity than the free ligand. The corrosion inhibitory activity of the ligand and its nickel(II) complex used in acid (H2SO4) media was also examined by weight loss measurements.

Academic research paper on topic "Synthesis, spectroscopic investigation and antimicrobial activities of some transition metal complexes of a [(2-hydroxyacetophenone)-3-isatin]-bishydrazone"

Arabian Journal of Chemistry (2012) xxx, xxx-xxx

King Saud University Arabian Journal of Chemistry

www.ksu.edu.sa www.sciencedirect.com

ORIGINAL ARTICLE

Synthesis, spectroscopic investigation and antimicrobial activities of some transition metal complexes of a [(2-hydroxyacetophenone)-3-isatin]-bishydrazone

S.S. Swathy a, R. Selwin Joseyphus b, V.P. Nisha a, N. Subhadrambika a, K. Mohanan a *

a Department of Chemistry, University of Kerala, Kariavattom Campus, Trivandrum 695 581, India b Department of Chemistry, St. John's College, Anchal, Kollam 691 306, Kerala, India

Received 14 February 2012; accepted 26 May 2012

KEYWORDS

Bishydrazone;

Antimicrobial activity; Corrosion inhibition

Abstract A bishydrazone was obtained by the condensation of isatin monohydrazone with 2-hydroxyacetophenone, which formed a series of complexes with manganese(II), cobalt(II), nickel(II), copper(II) and zinc(II). The ligand and the metal complexes were characterized on the basis of elemental analysis, molar conductance, magnetic moment, IR, UV-Visible, mass, 1H NMR, EPR, and thermal analysis. Spectral studies revealed that the ligand acted as monobasic tridentate, coordinating to the metal ion through the deprotonated phenolate oxygen, azomethine nitrogen and carbonyl oxygen atom of the isatin moiety. The low molar conductance values indicate that all complexes are non-electrolytes. Based on the spectral results and magnetic susceptibility measurements, suitable geometry was proposed for each complex. The EPR spectral data indicated that metal-ligand bond had considerable covalent character. The ligand and its nickel(II) complex were subjected to XRD studies. Thermal decomposition study of nickel(II) complex was also carried out. In vitro biological screening effects of the compounds were tested against the bacteria and the fungal species by the agar disc diffusion method. A comparative study of the MIC values of the ligand and its complexes indicated that the copper(II) complex exhibited higher antimicrobial activity than the free ligand. The corrosion inhibitory activity of the ligand and its nickel(II) complex used in acid (H2SO4) media was also examined by weight loss measurements.

© 2012 King Saud University. Production and hosting by Elsevier B.V. All rights reserved.

* Corresponding author. Tel.: +91 9447696794. E-mail addresses: rajendran.biju@gmail.com (S.S. Swathy), drkmohanan@rediffmail.com (K. Mohanan). Peer review under responsibility of King Saud University.

1878-5352 © 2012 King Saud University. Production and hosting by Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.arabjc.2012.05.004

1. Introduction

Hydrazones form an interesting class of chelating ligands which contain an azomethine group linked to a nitrogen atom and find extensive application in various fields (Mariar et al., 2004; Sridhar and Ramesh, 2001). The coordination behaviour of hydrazones depends on pH of the medium, nature of the substituent and position ofhydrazone group relative to other nucleus. Although metal complexes of monohydrazones derived from isatin have been extensively investigated, those formed from bishydrazones have received comparatively less attention so far (Sridhar et al., 2001; Murukan and Mohanan, 2007; Hassan, 1997). 2-Hydroxyacetophenone is a versatile chemical intermediate with significant commercial applications (Mohanan et al., 2008). The compounds containing isatin moiety possess interesting biological and pharmacological activities (Ercag et al., 2006; Pandeya et al., 1999; Sridhar et al. 2002). In this paper, we report the synthesis, structural characterization, thermal decomposition, antimicrobial and corrosion inhibitory activities of some transition metal complexes with the host of a bishydrazone derived from isatin monohydrazone and 2-hydroxyacetophenone viz. (L = [(2-hydroxyacetophenone)-3-isatin]-bishydrazone).

2. Experimental

2.1. Materials

was adjusted to ~7 using alcoholic ammonia solutions (buffer solution). The complex separated was filtered, washed with MeOH and then dried in vacuum.

2.3.2. Cobalt(II) complex

Cobalt(II) complex (M:L = 1:2) was synthesized according to the procedure similar to that followed for manganese(II) complex, except the refluxing time was about 4 h and the pH was maintained at The solid product was filtered off, washed several times with MeOH and dried in vacuum.

2.3.3. Nickel(II) complex

Nickel(II) complex (M:L = 1:1) was prepared by adopting the procedure for the preparation of cobalt(II) complex, except that the pH was maintained at ~6.5. On adding the nickel(II) chloride, the ligand solution turned to light brown colour. The reaction mixture was refluxed for 3 h. The product obtained was filtered, washed with MeOH and dried in vacuum.

2.3.4. Copper(II) complex

For the synthesis of copper(II) complex (M:L = 1:1) the above mentioned preparative method was followed, except that the refluxing time was about 2 h. The pH of the solution was maintained between 6.5 and 7.5. The reaction mixture was then reduced to half of its original volume and kept overnight. The complex separated out was filtered, washed with MeOH and dried in vacuum.

All chemicals used were of analytical grade. Isatin, hydrazine hydrate (99%) and 2-hydroxy acetophenone were obtained from Fluka and Sisco Chemicals.

2.2. Synthesis of ligand

2.2.1. Synthesis of monohydrazone

Isatin (1.47 g, 10 mmol) dissolved in MeOH (40 mL) and was added to a solution of hydrazine hydrate (0.5 mL, 10 mmol) dissolved in hot MeOH (10 mL). The resulting solution was re-fluxed for 3 h on a waterbath and the yellow coloured compound was separated out on cooling. It was filtered, dried in vacuum and further purified by recrystallization from methanol (m.p. 226 0C; yield ~95%).

2.2.2. Synthesis of bishydrazone

2-Hydroxyacetophenone (0.6 mL, 5 mmol) dissolved in MeOH (10 mL) was added to a solution of isatin monohydrazone (0.80 g, 5 mmol) in hot MeOH (70 mL). The resulting mixture was refluxed on a waterbath for 4 h. The volume of the solution was reduced to about 50 mL and allowed to cool at room temperature. The orange coloured compound separated out was filtered, washed with MeOH and dried in vacuum (m.p. 235 0C; yield ~83%).

2.3. Synthesis of metal complexes

2.3.1. Manganese(II) complex (M:L = 1:2) To a methanolic solution of ligand (0.28 g, 1 mmol) a solution of manganese(II) acetate (0.12 g, 0.5 mmol) in MeOH (10 mL) was added in small portions with constant stirring. The reaction mixture was then refluxed on a water bath for 5 h and then cooled to room temperature. The pH of the solution

2.3.5. Zinc(II) complex (M:L = 1:1)

A solution of zinc(II) chloride (0.14 g, 1 mmol) in metha-nol(15 mL), was added gradually in small amounts to a hot solution of ligand (0.28 g, 1 mmol) in MeOH (60 mL). The pH of the solution was maintained at ~7.5 and refluxed for about 6 h. The product obtained was filtered, washed with MeOH and dried in vacuum.

2.4. Physical measurements

Elemental analysis (C, H and N) was carried out using a Her-acus Carlo Erba 1108-CHN Analyzer. The metal contents in the complexes were analysed using an atomic absorption spectrometer (GBC Avanta). The electronic spectra were recorded on Hitachi 320 UV-Vis spectrometer in the range 200-900 nm. Infrared spectra of the ligand and the metal complexes were recorded on a Jasco FTIR-410 spectrometer using KBr pellets and far infrared in the 500-100 cm-1 region using CsI-discs on a polytech FIR 30 Fourier spectrometer. Proton NMR spectra of the ligand and its zinc(II) complex were recorded in DMSO-d6 on a JEOL GSX 400 NB 400 MHz FT-NMR spectrometer. FAB-mass spectra of the ligand and its nickel(II) complex were recorded on a JEOL SX102/DA-6000 mass spectrometer/data system using Argon/Xenon (6 kV, 10 mA) as the FAB gas. The accelerating voltage was 10 kV and the spectrum recorded at room temperature using m-nitrobenzoylalcohol as the matrix. Molar conductance measurements were conducted using 10~3 M solution of the complexes in DMSO at room temperature with a Systronics model 304 digital conductivity meter. Magnetic measurements of the metal complexes were performed on a Magway MSB Mk1 magnetic susceptibility balance. The EPR spectrum of the copper(II) complex was recorded using a Varian E-112 EPR spectrometer. The

thermogravimetric analysis of the nickel(II) complex was carried out using a thermobalance of the type Mettler Toledo System in dynamic air. The XRD patterns of the ligand and its nickel(II) complex were recorded on a Rigaku Dmax X-ray dif-fractometer using Cu Ka radiation (k = 1.5404 A).

2.5. In vitro antimicrobial activity

The in vitro antimicrobial activity of the ligand and its complexes were tested against the bacterial species, Staphylococcus aureus, Escherichia coli and Salmonella typhi, and the fungal species Rhizopus stolonifer and Candida albicans by agar disc diffusion method (Bauer et al., 1996). Streptomycin and Nys-tatin were used as standards for antibacterial and antifungal agents. The standard samples of antimicrobial activity are done at 100 ig/ml concentration in DMSO. The test organisms were grown on nutrient agar medium in petri plates. The antibacterial and antifungal activities of the ligand and its metal complexes were done at 50, 100 and 200 ig/ml concentration in DMSO solvent by the minimum inhibitory concentration (MIC) method. The discs were placed on the previously seeded plates and incubated at 37 0C. The diameter of inhibition zone around each disc was measured after 24 h for bacterial and 72 h for fungal species. Activity was determined by measuring the diameter of the zone showing complete inhibition (mm).

2.6. Corrosion

2.6.1. Corrosion weight loss determination

The pretreated coupons were weighed and suspended vertically for 15 days in 100 mL aerated, unstirred 1 M H2SO4 with and without the corrodent-inhibitor of different concentrations varying from 1 x 10-3 g to 5 x 10-3 g. The coupons were then removed and washed with 20% NaOH solution containing 200 g L-1 of zinc dust inorder to remove the corrosion products, dried in acetone and noted the weight loss. The percentage inhibitor efficiency was calculated according to the reported method (Negm and Zaki, 2008; Ouf et al., 2010).

2.6.2. Open circuit potential (OCP) measurements

The potential were measured for 15 days under open circuit condition as a function of time against a saturated calomel electrode. All mild steel coupons were prepared and immersed in the cell. The potential values were measured without any disturbance to the coupons. The electrolytes were kept under stagnant condition.

3. Results and discussion

3.1. Structure of the ligand

Condensation of istain monohydrazone with 2-hydroxyaceto-phenone occurred in 1:1 M ratio to form a bishydrazone, viz. [(2-hydroxyacetophenone)-3-isatin]-bishydrazone. Elemental analysis data and other details of the ligand are given in Table 1. The purity of the ligand was checked by TLC technique (silica gel). The electronic spectrum of the ligand show bands at 332 and 310 nm assignable to the n-p transitions of the ket-imine and aldimine moieties, respectively. Infrared spectrum of the ligand exhibit a broad band at 3357 cm-1, which can be attributed to the hydrogen bonded OH group of the acetophe-none moiety. A medium intensity band at 3156 cm-1 is due to the N-H vibrations of the indole ring and the strong band at 1687 cm-1 may be assigned to v(C=O) of isatin moiety. Vibrational characteristics of ketimine and aldimine group bands are observed at 1588 and 1551 cm-1, respectively. The bands observed at 1247 and 982 cm-1 corresponds to the phenolic (C-O) and (N-N) stretching vibrations, respectively (Nakam-oto, 1986). In agreement with the UV-Vis and IR spectral data, the *H NMR spectrum of the free ligand (Fig. 1) recorded in DMSO-d6 solution show a signal at 10.69 ppm, characteristic of intramolecular hydrogen bonded -OH proton (Mohanan and Murukan, 2005; Alyea and Malek, 1975). Signals appearing at 9.56 ppm can be attributed to the N-H proton of the indole ring. Aromatic proton signals are observed as multiplet in the range 6.84-7.37 ppm. The mass spectrum of the ligand (Fig. 2) shows the molecular ion peak at mjz 279 which is equivalent to the molecular formula of the ligand. The fragmentation peaks are observed at mjz 134, 159 and 186 corresponds to (C8H8NO), (C8H5N3O) and (C10H8N3O), respectively. The observed peaks are in good agreement with their empirical formula as obtained from elemental analysis data. On the basis of above spectral results, the structure as in Fig. 3 has been assigned for the ligand.

3.2. Structure of the metal complexes

The manganese(II) and cobalt(II) complexes were prepared by treating in 1:2 M ratio of metal salt and ligand, while the other complexes were prepared in 1:1 M ratio. Formation of the metal complexes can be represented by the following general equations.

Table 1 Analytical data and other details of ligand and its metal complexes.

Compound Molecular formula Yield (%) Elemental analysis

Found (Calcd.) (%)

Om (O-1 cm2 mol-1) ieff (BM)

C H N M

L Ci6Hi3N3O2 83 68.25 (68.82) 4.58 (4.66) 15.18 ((15.05) - - -

[MnL2] C32H24N6O4Mn 79 62.35 (62.84) 3.60 (3.92) 13.83 13.75) 9.12 (8.99) 5.7 5.85

[C0L2] C32H2.N6O.C0 87 62.75 (62.45) 3.7 (3.9) 13.76 (13.66) 9.38 (9.58) 9.4 4.80

[NiLCl] C16H12N3O2M 90 50.94 (51.6) 3.13 (3.22) 11.02 (11.28) 15.25 (15.77) 8.2 D

[CuLCl] C16H12N3O2CU 82 50.25 (50.92) 3.0 (3.2) 10.85 (11.14) 16.40 (16.85) 7.5 1.80

[ZnLCl] C16H12N3O2Zn 81 50.18 (50.68) 3.07 (3.17) 10.89 (11.08) 17.05 (17.25) 8.6 D

D - Diamagnetic.

14 13 12 11 10 9 8 7 6 5 4 3 Figure 1 The 1H NMR spectrum of the ligand.

Figure 2 Mass spectrum of the ligand.

N ^O O

Figure 3 The proposed structure of the ligand.

MX2 + L ! [MLX]+ HX;

where M = Cu(II), Ni(II), Zn(II) and X

MX2 + 2L ! [ML2]+ 2HX;

where M = Mn(II), Co(II); X = Cl-, CH3COO-, and L = [(2-hydroxyacetophenone)-3-isatin]-bishydrazone.

All complexes are non-hygroscopic solids insoluble in common organic solvents such as benzene, chloroform, carbon tetrachloride and toluene; but soluble in DMSO and DMF. Analytical data of the complexes presented in Table 1 are in good agreement with the theoretical values. The low molar conductance (Table 1) values of the metal complexes in DMSO indicate their non-electrolytic nature (Geary, 1971).

3.2.1. Infrared spectra

The IR spectral bands of the ligand and its metal complexes are given in Table 2 along with the tentative assignments. The internally hydrogen bonded -OH band disappear in the spectra of the metal complexes, indicating the deprotonation and formation of metal-oxygen bond. This is further supported by the shifting of phenolic v(C-O) towards higher frequency by ~40 cm-1, indicating the coordination of the phenolate oxygen to metal ion (Murukan et al., 2007; Keskio-glu et al., 2008). The v(C=N) vibration of the ligand occurs at 1551 cm-1, which is shifted to a lower frequency by about 2025 cm-1 in the complexes, indicating the involvement of the azomethine nitrogen in chelation with the metal ion. The band corresponding to v(C=O) at 1687 cm-1 is shifted to a lower frequency by about 30-40 cm-1, supporting the coordination of the carbonyl oxygen. However vibrational characteristics of the ring v(N-H) and v(C=N) of the ketimine moiety remain almost unaffected, indicating the non participation of these groups in coordination. The bands in the regions 540-550, 450-460, and 350-360 cm-1 are ascribed to v(M-O), v(M-N), and v(M-Cl) vibrations, respectively (Ferraro, 1971; Raju and Radhakrishnan, 2003). From the above observations, it can be concluded that the ligand binds to the metal ion in a tri-dentate fashion through the deprotonated phenolate oxygen,

Table 2 IR spectral bands of the ligand and its metal complexes (cm 1).

L [MnL2] [CoL2] [NiLCl] [CuLCl] [ZnLCl] Tentative assignments

3357 - - - - - Hydrogen bonded OH group

3156 3158 3154 3158 3156 3159 Indole ring NH

1687 1657 1658 1658 1657 1656 v(C=O) ring

1588 1586 1588 1587 1586 1588 v(C=N) ring

1551 1533 1529 1530 1527 1530 v(C=N) aldimine

1247 1285 1283 1282 1284 1285 v(C-O) phenolic

982 997 996 997 994 995 v(N-N)

- 461 457 453 456 457 v(M-N)

- 550 551 543 547 542 v(M-O)

- - - 355 357 356 v(M-Cl)

ppm 14 13 12 11 10 9 8 7 6 5 4 3 2 1 Figure 4 1H NMR spectrum of [ZnLCl] complex.

'I'M J*- 1*1—1

12 11 10 9 8 7 6 5 4 3 2 Figure 5 1H NMR spectrum of [NiLCl] complex.

M = Ni(II) and Cu(II)

Figure 6 Proposed structure of (1:1) metal complexes (a) tetrahedral geometry (b) square planar geometry.

M= Co(II) and Mn(II) Figure 7 Proposed structure of (1:2) metal complexes (octahedral).

aldimine nitrogen and the carbonyl oxygen of the isatin moiety.

3.2.2. Proton NMR and mass spectra

The spectra of zinc(II) and nickel(II) complexes recorded in DMSO-d6 are shown in Figs. 4 and 5. The signal at 10.69 ppm in the NMR spectrum of the ligand due to -OH proton, disappeared in the spectrum of both the complexes. This is a clear indication that the phenolate group is coordinated to the metal ion through the phenolate oxygen after deprotonation. On comparing the position of other proton signals in the complexes with those of the ligand signals, it can be concluded that these signals are in the expected region and shift only slightly due to the coordination of the ligand to the metal ion.

The mass spectrum of nickel(II) complex shows a molecular ion peak at mjz = 372.19, which corresponds to [NiC16H12N3 O2Cl] complex. Also it exhibited the significant peaks at mjz 337 and 278 corresponding to [NiC16H12N3O2] and

180016001400120010008006004002000

40 2 Theta

Figure 8 Powder XRD pattern of ligand.

(C16H12N3O2), due to the loss of chloride ion and demetalla-tion of the complex, respectively.

3.2.3. Electronic spectra and magnetic measurements

The electronic spectrum of manganese(II) complex show three peaks at 14,560, 16,400 and 20,000 cm-1, which are assigned to 6A1g fi 4T1g, 6A1g fi 4T2g and 6A1g fi 4Eg, 4A1g transitions, respectively. These data along with magnetic moment value indicate an octahedral geometry around the metal ion. The cobal-t(II) complex exhibits two low level energy bands at 10,760 and 17,600 cm-1, and a high level energy band at 20,500 cm-1 which can be assigned to 4T1g(F) fi 4T2g(F), 4T1g (F) fi4 A2g(F) and 4T1g(F) fi 4T2g(P) transitions, respectively, indicating a high-spin octahedral geometry. Cobalt(II) complex display a magnetic moment value of 4.80 BM, which correspond to highspin octahedral environment around the metal ion (Sathyanara-yana, 2001). The nickel(II) complex show three bands at 21,100, 18,240 and 13,700 cm-1, corresponding to 1A1g fi 1Eg, 1A1g fi 1A2g, and 1A1g fi 1B1g transitions, respectively. These observations and the diamagnetic nature indicate a square planar geometry for this complex (Amirnasr et al., 2006; Kaasjager et al., 2000; Nawar et al., 1990). The copper(II) complex exhibits a broad band centered at 13,660 cm-1 due to 2B1g fi 2A1g transition of a distorted square planar geometry. This observation together with the magnetic moment value of 1.80 BM, support a distorted square planar geometry for the copper(II) complex.

On the basis of the analytical data, molar conductance and diamagnetic nature, a tetrahedral geometry is presumed for the zinc(II) complex. It is reported that tetrahedral geometry is the most preferred structure for four coordinated zinc(II) complexes (Dudev and Lim, 2000). From the above spectral data, the structures as in Figs. 6a and b and 7 have been assigned for the metal complexes.

3.2.4. EPR spectrum

The EPR spectrum of the copper(II) complex has been studied in both solid state room temperature and liquid state nitrogen temperature in DMSO solution. At room temperature it shows an intense absorption band in the high field region and is isotro-pic due to the tumbling motion of the molecules. However, this complex at liquid nitrogen temperature show four well resolved peaks in low field region due to the coupling of the electron spin of the 63Cu nucleus (I = 3/2). The peaks are broad and have the

Table 3 X-ray diffraction data of ligand.

d (A) Observed (20) Calculated (20) Observed (Sin20) Calculated (Sin20) hkl

8.55837 10.32757 9.73037 0.008092 0.007913 011

7.08617 12.48098 12.17608 0.011804 0.011248 110

6.61728 13.36926 13.47934 0.013536 0.013773 101

5.71522 15.49145 15.40634 0.018147 0.017967 111

5.37974 16.46399 16.46116 0.02048 0.020494 102

4.12159 21.54258 21.42414 0.034893 0.034549 121

3.71011 23.96540 24.19917 0.043061 0.043937 201

3.63323 24.48029 24.33162 0.044903 0.044412 210

3.54497 25.09962 25.23564 0.047167 0.047719 113

3.33134 26.73808 27.15036 0.043411 0.055094 202

3.22107 27.67129 27.62343 0.05713 0.056993 213

3.17782 28.05561 28.18538 0.058696 0.059288 212

3.10574 28.72053 28.52983 0.061452 0.060712 221

2.84340 31.43576 31.50199 0.073315 0.073689 203

Table 4 X-ray diffraction data of [NiLCl] complex.

d (A) Observed (20) Calculated (20) Observed (Sin20) Calculated (Sin20) hkl

7.38414 11.97546 11.61971 0.010871 0.010247 110

5.54523 15.96938 15.46919 0.019276 0.018113 111

4.83777 18.3235 18.34401 0.025326 0.025408 200

4.50385 19.69506 19.88048 0.029221 0.029798 112

4.22749 20.99672 21.02052 0.033166 0.033274 210

3.80078 23.38556 23.48189 0.041320 0.041407 103

3.61505 24.60533 25.05360 0.045356 0.047044 220

3.38575 26.30063 26.72082 0.051708 0.053396 122

3.09887 28.78561 28.54213 0.061725 0.060767 221

2.94535 30.32103 38.30608 0.068327 0.068329 213

2.82156 31.68552 31.22965 0.074454 0.072452 222

2.62926 34.07098 34.18252 0.085743 0.086374 203

appearance of ill-resolved triplets. The triplet appearance of the peaks can be attributed to hyperfine splitting of the nitrogen atom (I = 1) of the ligand (Mac Donald et al., 1982). The liquid nitrogen temperature in DMSO solution of the complex possesses well-resolved gy and g? regions. The various spin Hamil-tonian parameters computed are gy = 2.237, g? = 2.064, Ay = 164 and A? = 50. Also the trend gy > g? > ge observed for this complex indicates the presence of unpaired electron in the dx2_yi orbital. The covalency parameter (a2) has been calculated using Kivelson and Nieman equation (Kivelson and Niemann, 1961). The a2 value (0.76) gives adequate support to the covalent character of the metal-ligand bond.

3.2.5. Powder XRD

The XRD pattern of the ligand (Fig. 8) shows 14 reflections between 2h ranging from 8° to 32° with maxima at 2h = 10.3275° corresponding to interplanar distance d = 8.5583 A. The XRD patterns of the ligand (Table 3) and the nickel(II) complex (Table 4) indicate their crystalline nature. A comparison of these values reveal good agreement between calculated and observed values of Sin2h and 2h. The ligand is successfully indexed to orthorhombic crystal system with the lattice constant parameters, a = 12.6263 A, b = 7.6789 A, c = 11.889 A and unit cell volume of 1152.7 A3 (Eye and Wait, 1960). The diffraction pattern of nickel(II) complex (Fig. 9) shows 12 reflections between 2h ranging from 10° to 35°. The maxima of 2h is observed at

160014001200-

0-|-.-1-.-,-.-1-.-1-.-,-.-r-

10 20 30 40 50 60 70 2 Theta

Figure 9 Powder XRD pattern of [NiLCl] complex.

11.9754°, with a d-spacing of 7.3841 A. The Sin2h and 2h values have been compared with the calculated ones for identifying the main peaks. The observed values fit well for nickel(II) complex with the lattice parameters, a = 12.3377 A, b = 9.6612 A, c = 8.6818 A corresponding to orthorhombic crystal system. The unit cell volume is calculated to be 1034.8 A3.

4.0-, 3.53.02.52.01.51.00.50.0-

1= .5? 'tu ä a)

0 100 200 300 400 500 600 700 Temperature (°C)

Figure 10 TGA profile of [NiLCl] complex.

3.2.6. Thermogravimetric analysis

The nickel(II) complex is subjected to thermogravimetric analysis in dynamic air in 50-800 0C temperature range, at a heating rate of 10 0C/min. The complex (Fig. 10) is stable up to 240 0C and exhibits a single stage decomposition pattern, as is evident from the DTG profile. The mass loss in the single stage decomposition is in the range of 240-390 0C with maximum peak at 335 oc, which can be attributed to the loss of li-gand moiety and its oxidative degradation to metal oxide, above 390 oc. The single stage decomposition of the metal complex usually occur when there is a high degree of electron delocalization along a conjugated system which leads to uniformity in bond strength (Andjelcovie et al., 2001).

3.2.7. Antimicrobial activity

The in vitro antimicrobial activity value of the compounds against the growth of micro-organisms is summarized in Table 5. Inhibition is found to increase with increase in concentration of metal complex. The results show that the metal complexes exhibit higher activity against each class of organism. The activity is related to the nature and structure of the complexes. However, all the complexes show higher activity against E. coli as compared to S. typhi and S. aureus. Antibacterial activity can be ordered as [CuLCl] > [NiLCl] > [MnL2] > [ZnLCl] > [CoL2] > L. These complexes do not show strong concentration dependence of antimicrobial activity as compared to anti-fungal activities of the same complexes. The relation between chelation and toxicity is very complex, expected to be a function of steric, electronic and pharmakinetic factors along with mechanistic pathways. The antifungal activity is enhanced several times when the compound is coordinated with metal. The activity of these complexes and ligand follows the order; Cu(II) > Ni(II) > Co(II) > Mn(II) > Zn(II) > L. Comparison of activities shows that the copper complex is more active than the ligand against R. stolonifer. The MIC values of some compounds, show significant activity against selected bacterial and fungi species. The results indicate that, these compounds are active in inhibiting the growth of the bacterial and fungal species. A comparative study of the ligand and its complexes indicate that the metal complex exhibit higher antimicrobial activity than the free ligand. Such increased activity of the complexes can be explained on the basis of the Overtone concept and the Tweedy chelation theory (Thimmaiah et al., 1985; Kulkarni et al., 2009). According to the Overtone concept ofcell permeability, the lipid membrane surrounding the cell favours the passage of only lipid-soluble materials, due to which liposol-ubility is an important factor controlling the antimicrobial

Table 5 Antibacterial and antifungal results of the investigated compounds.

Compound Conc. (ig/ml) Diameter of zones showing complete inhibition of growth (mm)

E. coli S. typhi S. aureus R. sstolonifer C. albicans

L 50 5 4 4 3 2

100 7 6 6 3 3

200 9 7 5 5 4

[MnL2] 50 13 12 10 5 4

100 17 15 14 6 5

200 19 18 17 8 7

[CoL2] 50 11 9 8 7 6

100 13 11 9 9 8

200 16 14 13 10 9

[NiLCl] 50 16 12 11 8 7

100 20 17 16 10 9

200 23 22 21 12 10

[CuLCl] 50 18 16 15 9 8

100 23 20 18 11 9

200 30 28 27 13 11

[ZnLCl] 50 12 11 10 3 2

100 15 14 12 5 4

200 17 16 15 7 6

Streptomycina 100 30 31 32 - -

Nystatina 100 - - - 35 33

Antibacterial activity: >15 mm, significant; 10-14 mm, moderate activity; <10, weak activity. Antifungal activity: >10 mm, significant activity; 9-7 mm, moderate activity; <7, weak activity. a Standards.

— 65

0.001 0.002 0.003 0.004

Concentration (Mole)

Figure 11 The effect of concentration on corrosion inhibition efficiency of the ligand and its [NiLCl] complex.

_ -0.6 UJ

SJ -0.7 >

£ -0.9

—■— 1x 10-3

—•— 2x 10-3

—A— 3x 10-3

—▼— Blank

10 12 14 16 18

Figure 12 Trend of open circuit potential decay for mild steel immersed in blank and inhibitor solutions.

activity. On chelation, the polarity of the metal ion will be reduced to a greater extent due to the overlap of the ligand orbital and partial sharing of the positive charge of the metal ion with donor groups. Furthermore, the mode of action of the compound may involve formation of a hydrogen bond through the azomethine group with the active centre of cell constituents, resulting in interference with normal cell processes.

3.2.8. Corrosion inhibition efficiency

The effect of concentration on the inhibition efficiency of the ligand and its nickel(II) complex are shown in Fig. 11. Corrosion inhibition is attributed to the adsorption of inhibitors on mild steel. The weight loss of mild steel immersed in 1 M H2SO4 for 15 days with and without the corrodent-inhibitor of varying concentration from 1 x 10—3 g to 5 x 10—3 g is measured and compared. Apart from this, the ligand is found to possess more inhibitory action than the metal complex. The inhibition efficiency increases with increase in concentration of the additives. The lone pair of electrons of nitrogen and oxygen atoms along with the delocalized p-electron can be the reason for higher inhibition efficiency (Sanyal and Kumar, 2010). These factors play the vital role in the adsorption of the inhibitor and the formation of coordinate bond with metal. The adsorption of inhibitor on the mild steel surface can occur either directly by the interactions between the p-electrons of the inhibitor and the vacant d-orbitals of metal surface atoms. The adsorption of inhibitor on mild steel may also be due to the interaction of nitrogen and oxygen with the surface atoms of metal. As inhibitor concentration increases, it covers more and more surface area and results in the reduction of corrosion rate (Hameed et al., 2012). It has been observed that Fig. 12 shows the trend of OCP decay with and without the corrodent inhibitor (Table 6) of varying concentration from 1 x 10—3 g to 5 x 10—3 g for 15 days. The OCP decay of a mild steel coupon kept in a blank cell i.e. without inhibitor (1 M H2SO4) is also given in Fig. 12 to understand the extent of OCP deviation due to the presence of the inhibitor. In the case of blank solution the initial OCP value instantly changes to a negative value as high as —0.925 mV which shows severe corrosion attack. However the addition of different concentration of the ligand and complex to the solution is able to bring the potential values towards positive region. This is due to the ability of the ligand-complex solution to form a passive film on the surface of mild steel coupons. Extend of film formation is more prominent in the ligand when compared to the complexes because the ligand is more chemical adsorptive than complexes. It can be explained on the basis of the effect of chemical structure. In this respect, the isatin ring, benzene ring, N-H, C=N and C=O of bishydrazone can form a big p bond accordingly, not only the p of benzene, C=O enter unoccupied orbital of iron, but also the p* orbital can accept the electron of d orbital of iron to form back bonds. These back bonds produce more than one centre of chemical adsorption on the mild steel surfaces (Hameed, 2011). In the case of metal complexes the chemical adsorption is less because the ligand shares its lone pair to the metal ion that will reduce the effective adsorption of mild steel surface.

Table 6 Variation of open circuit potential decay for mild steel immersed in blank and inhibitor solutions.

No. of days Potential blank (mV) Potential (mV) of ligand in various conc. Potential (mV) of complex in various conc.

1 • 10-3 (g) 3 x 10-3 (g) 5 x 10-3(g) 1 • 10-3 (g) 3 x 10-3 (g) 5 x 10-3 (g)

3 -0.496 -0.562 -0.551 -0.546 -0.689 -0.682 -0.677

6 -0.545 -0.553 -0.545 -0.539 -0.678 -0.673 -0.667

9 -0.623 -0.541 -0.534 -0.531 -0.652 -0.648 -0.639

12 -0.715 -0.536 -0.525 -0.521 -0.639 -0.633 -0.627

15 -0.880 -0.522 -0.519 -0.514 -0.620 -0.614 -0.608

18 -0.925 -0.513 -0.509 -0.506 -0.590 -0.582 -0.575

4. Conclusion

The bishydrazone derived from isatin monohydrazone and 2-hydroxyacetophenone acts as monobasic tridentate. On the basis of all the spectral data, it is observed that manganese(II) and cobalt(II) complexes possess an octahedral geometry, nickel(II) complex exhibit square planar geometry, copper(II) complex possess a distorted square planar geometry whereas zinc(II) complex possess a tetrahedral geometry. The XRD studies show that both the ligand and nickel(II) complex possess crystalline nature with orthorhombic crystal lattice. In view of biocidal activity observations of hydrazone derivatives, there is an enhancement in the antimicrobial activity of the complexes when compared to that of ligand. A comparative study of the MIC values of the ligand and its complexes indicate that the copper(II) complex exhibit higher antibacterial/ antifungal activity than the other compounds. Corrosion inhibition efficiency of the ligand and its nickel(II) complex reveal that the ligand possess greater activity than the metal complex.

Acknowledgements

We express our sincere thanks to Professor and Head, Department of Chemistry, University of Kerala, Kariavattom Campus, Trivandrum, for providing us with necessary facilities for carrying out this work successfully. Instrumental facilities provided by SAIF Cochin, IIT Bombay, CDRI Lucknow and NIIST Trivandrum are gratefully acknowledged.

References

Alyea, E.C., Malek, A., 1975. Synthesis and characterization of some dibasic tridentate Schiff base ligands. Can. J. Chem. 53, 939-941. Amirnasr, M., Schenk, K.J., Meghdadi, S., Morshedi, M., 2006. Synthesis, characterization and X-ray crystal structures of [Ni(Me-sal)2dpt] and [Ni(Me-sal)dpt]Cl. Polyhedron 25, 671-677. Andjelcovie, K., Sumar, M., Ivanovic-Burmazovic, I., 2001. Thermal analysis in structural characterization of hydrazone ligands and their complexes. J. Therm. Anal. Cal. 66, 759-778. Bauer, A.W., Kirby, W.M.M., Sherries, J.C., Turck, M., 1966. Antibiotic susceptibility testing by standard single disc diffusion method. Am. J. Clin. Pathol. 45, 493-496. Dudev, T., Lim, C., 2000. Tetrahedral vs. octahedral zinc complexes with ligands of biological interest: a DFT/CDM study. J. Am. Chem. Soc. 122, 11146-11153. Ercag, A., Yildirim, S.O., Akkurt, M., Ozgar, M.U., Heinemann, F.W., 2006. Novel isatin-Schiff base Cu(II) and Ni(II) complexes. X-ray crystal structure of bis[3-(4-hexylphenylimino)-1H-indol-2(3H)-one]-dichlorocopper(II) complex. Chin. Chem. Lett. 17, 243-246. Eye, R.W.M.D., Wait, E., 1960. X-ray Powder Photography in

Inorganic Chemistry. Butterworths, London. Ferraro, J.R., 1971. Low Frequency Vibrations of Inorganic and

Coordination Compounds. Plenum Press, New York. Geary, W.J., 1971. The use of conductivity measurements in organic solvents for the characterization of coordination compounds. Coord. Chem. Rev. 7, 81-122. Hameed, R.S.A.E., 2011. Aminolysis of polyethylene terephthalate waste as corrosion inhibitor for carbon steel in HCl corrosive medium. Adv. Appl. Sci. Res. 2, 483-499. Hameed, R.S.A.E., Shafey, H.I.A., Magd, A.S.A., Shehata, H.A., 2012. Pyrazole derivatives as corrosion inhibitor for C-steel in hydrochloric acid medium. J. Mater. Environ. Sci. 3, 294-305.

Hassan, A.M.A., 1997. Synthesis and characterization of Ni(II), Cr(III), Co(II), Cu(II), Zn(II) and Cd(II) complexes with isatin-isonicotinoyl hydrazone. Indian J. Chem. 36A, 241-245.

Kaasjager, V.E., Puglisi, L., Bouwman, E., Driessen, W.L., Reedijk, J., 2000. Synthesis, characterization and crystal structures of nickel complexes with dissymmetric tetradentate ligands containing a mixed-donor sphere. Inorg. Chim. Acta 310, 183190.

Keskioglu, E., Gunduzalp, A.B., Cete, S., Hamurcu, F., Erk, B., 2008. Cr(III), Fe(III) and Co(III) complexes of tetradentate (ONNO) Schiff base ligands: synthesis, characterization, properties and biological activity. Spectrochim. Acta A 70, 634-640.

Kivelson, D., Niemann, R., 1961. ESR studies on the bonding in copper complexes. J. Chem. Phys. 35, 149-155.

Kulkarni, A.D., Patil, S.A., Badami, P.S., 2009. Electrochemical properties of some transition metal complexes: synthesis, characterization and In-vitro antimicrobial studies of Co(II), Ni(II), Cu(II), Mn(II) and Fe(III) complexes. Int. J. Electrochem. Sci. 4, 717-729.

Mac Donald, L.G., Brown, D.H., Smith, W.E., 1982. The electron spin resonance of Cu(II) Schiff base complexes containing amino acids as part of the ligand. Inorg. Chim. Acta 63, 213-216.

Mariar, C.R., Belicchi, F.M., Franco, B., Corrado, P., Giorgio, P., Silvana, P., Monica, S., 2004. Synthesis, characterization and biological activity of Ni(II), Cu(II) and Zn(II) complexes of isatin hydrazones. J. Inorg. Biochem. 98, 313-321.

Mohanan, K., Murukan, B., 2005. Complexes of Mn(II), Fe(II), Co(II), Ni(II), Cu(II) and Zn(II) with a bishydrazone. Synth. React. Inorg. Met. Org. Chem. 35, 837-844.

Mohanan, K., Thankamony, M., Kumari, B.S., 2008. Synthesis, spectroscopic characterization, and thermal decomposition kinetics of some lanthanide(III) nitrate complexes of 2-(N-o-hydroxyace-tophenone)amino-3-carboxyethyl 4,5,6,7-tetrahydrobenzo[b]thio-phene. J. Rare Earths 26, 463-470.

Murukan, B., Mohanan, K., 2007. Synthesis, characterization and antibacterial properties of some trivalent metal complexes with [(2-hydroxy-1-naphthaldehyde)-3-isatin]-bishydrazone. J. Enzyme Inhib. Med. Chem. 22, 65-70.

Murukan, B., Kumari, B.S., Mohanan, K., 2007. Synthesis, spectral, electrochemical and antibacterial studies of Cu(II) complexes with isatin derived bishydrazone and different co-ligands. J. Coord. Chem. 60, 1607-1617.

Nakamoto, K., 1986. Infrared and Raman Spectra of Inorganic and Coordination Compounds. Wiley Interscience, New York.

Nawar, N., Khattab, M.A., Hosny, N.M., 1990. Some metal(II) complexes of o-aminoacetophenone benzoylhydrazone (Aabh): their preparation, characterization and antimicrobial activity. Synth. React. Inorg. Met. Org. Chem. 29, 1365-1384.

Negm, N.A., Zaki, M.F., 2008. Corrosion inhibition efficiency of nonionic Schiff base amphiphiles of p-aminobenzoic acid for aluminum in 4N HCL. Colloids Surf. Physicochem. Eng. Aspects 322, 97-102.

Ouf, A.E.F.M., Ali, M.S., Soliman, M.S., Defrawy, A.M.E., Mostafa, S.I., 2010. Synthesis and characterization of new transition metal complexes of Schiff base derived from 2-aminopyrimidine and 2,4-dihydroxybenzaldehyde and its applications in corrosion inhibition. J. Korean Chem. Soc. 54, 402.

Pandeya, S.N., Sriram, D., Nath, G., De Clercq, E., 1999. Synthesis, antibacterial, antifungal and anti-HIV evaluation of Schiff and Mannich bases of isatin derivatives with 3-amino-2-methylmercapto quinazolin-4(3H)-one. Pharm. Acta Helv. 74, 11-17.

Raju, K.C., Radhakrishnan, P.K., 2003. Complexes of Cu(II) with 2,3-dimethyl- 4-formyl-(benzhydrazide)-1-phenyl-3-pyrazolin-5-one. Synth. React. Inorg. Met. Org. Chem. 333, 1307-1318.

Sanyal, S., Kumar, A., 2010. Inhibitive effect of some Schiff base ligands for corrosion of mild steel in acidic media. J. Indian Chem. Soc. 87, 189-194.

Sathyanarayana, D.N., 2001. Electronic Absorption Spectroscopy and Related Techniques. University Press (India) Limited, Hyderabad, India.

Sridhar, S.K., Ramesh, A., 2001. Synthesis and pharmacological activities of hydrazones, Schiff and Mannich bases of isatin derivatives. Biol. Pharm. Bull. 24, 1149-1152.

Sridhar, S.K., Saravanan, M., Ramesh, A., 2001. Synthesis and antibacterial screening of hydrazones, Schiff and Mannich bases of isatin derivatives. Eur. J. Med. Chem. 36, 615-625.

Sridhar, S.K., Pandeya, S.N., Stables, J.P., Ramesh, A., 2002. Anticonvulsant activity of hydrazones, Schiff and Mannich bases of isatin derivatives. Eur. J. Pharm. 16, 129-132. Thimmaiah, K.N., Lloyd, W.D., Chandrappa, G.T., 1985. Stereochemistry and fungitoxicity of complexes of p-anisaldehydethiose-micarbazone with Mn(II), Fe(II), Co(II) and Ni(II). Inorg. Chim. Acta 106, 81-83.