Nano Sized Schiff Base Complexes with Mn(II) - Canadian Chemical

Canadian Chemical Transactions Ca

ISSN 2291-6458 (Print), ISSN 2291-6466 (Online) Year 2014 | Volume 2 | Issue 2 | Page 108-121

Research Article

DOI:10.13179/canchemtrans.2014.02.02.0077

Nano Sized Schiff Base Complexes with Mn(II), Co(II), Cu(II), Ni(II) and Zn(II) Metals : Synthesis, Spectroscopic and Medicinal Studies Omar B. Ibrahim1, Mahmoud A. Mohamed1 and Moamen S. Refat1,2* 1

Department of Chemistry, Faculty of Science, Taif University, 888 Taif, Saudi Arabia Department of Chemistry, Faculty of Science, Port Said University, Port Said, Egypt

2

Corresponding Author, E-mail: [email protected] Received: December 17, 2013 Revised: January 6, 2014 Accepted: January 9, 2014 Published: January 12, 2014

Abstract: Metal chelates, [M(HL)2(H2O)2]X2 (where M= Mn(II), Co(II), Cu(II), Ni(II) or Zn(II), X= NO3–or Cl– and HL= Schiff base moiety), have been prepared and characterized by elemental analysis, magnetic and spectroscopic measurements (infrared, X-ray powder diffraction and scanning electron microscopy). Elemental analysis of the metal complexes was suggested that the stoichiometry is 1:2 (metal-ligand). Infrared spectra of the complexes agree with the coordination to the central metal atom through the nitrogen of the 2-chlorophenyl hydrazine (–Ph–NH-) group and the sulfur atom of the thiophene ring. The electronic spectra suggest a distorted octahedral geometry for all Schiff base complexes. The Schiff base and its metal chelates have been screened for their in vitro antibacterial activity against four bacteria, gram-positive (Staphylococcus aureus) and gram-negative (Escherichia coli) and two strains of fungus (Aspergillus flavus and Candida albicans). The metal chelates were shown to possess more antibacterial activity than the free Schiff-base chelate. Keywords: Spectroscopic, Transition Metal Complexes, Schiff Base

1. INTRODUCTION Schiff base ligands are considered “privileged ligands” because they are easily prepared by the condensation between aldehydes and imines. Stereogenic centers or other elements of chirality (planes, axes) can be introduced in the synthetic design. Schiff base ligands are able to coordinate with many different metals [1], and to stabilize them in various oxidation states. The Schiff base complexes have been used in catalytic reactions [2] and as models for biological systems [3]. Chiral Schiff bases derived from the condensation of salicylaldehydes with 2-amino alcohols have found widespread use as ligands in asymmetric synthesis. These compounds act as tridentate ONO ligands, and a great number of metallic complexes derived from them have been described in the literature [4]. Depending upon the nature of the metal centre, these chiral complexes are able to promote a variety of enantioselective transformations. It has been reported that the structure of the substituent bonded to the imino nitrogen affects the coordination geometry of the complex [5]. During the past two decades, considerable attention has been paid to the chemistry of the metal complexes of Schiff bases containing nitrogen and other donors [6].

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This may be attributed to their stability, biological activity [7] and potential applications in many fields such as oxidation catalysis, electrochemistry [8]. The complexes make these compounds effective and stereospecific catalysts for oxidation, reduction and hydrolysis and they show biological activity, and other transformations of organic and inorganic chemistry [9]. Nickel(II) Schiff base complexes containing sulfur donors have received considerable attention due to the identification of a sulfur rich coordination environment in biological nickel centers, such as the active sites of certain ureases, methyl-S-coenzyme-M-methyl reductase and hydrogenases [10]. The zinc(II) ion is known to have a high affinity towards nitrogen and sulfur donor ligands. Dowling and Perkin investigated Zn(II) complexes with mixed N, O and S coordination to understand the reactivity of the pseudo-tetrahedral zinc center in proteins [11]. The transition metals zinc and copper are some of the most frequently occurring elements integrated into essential biochemical pathways. There are a number of biologically important molecules showing the catalytic activity [12] or molecules involved in transfer processes, like oxygen transfer, and incorporating transition metals into their active sites. In contrast to zinc(II), the copper(II) ions are redox active and play a crucial role in catalytic sites of oxidoreductases. The cyclic redox process enables these ions to act as pro- or anti-oxidants. The published opinions on the structure and pro- or anti-oxidant activity relationships are, however, quite inconsistent [13]. We report herein the results of our studies on the metal complexes of a Schiff base derived from 2-thiophenecarboxaldehyde and 2-chlorophenyl hydrazine. Tentative structures have been proposed on the basis of analytical, spectral, magnetic, and conductance data. In order to establish a modern technique to prepare some of nanometric oxide using Schiff base compounds and collected the biological role of metals, this prepared Schiff base and its metal chelates have been screened for biological activity against some kind of bacterial (G+ and G–) and fungi. That synthesis of metal oxide nanoparticle has received considerable attention with their potential applications in various fields. Several varieties of nanoparticles with biomedical relevance are available including, polymeric nanoparticles, metal nanoparticles, liposomes, micelles, quantum dots, dendrimers, and nano-assemblies.

2. EXPERIMENTAL 2.1. Chemicals Reagent grade 2-thiophenecarboxaldehyde, 2-chlorophenyl hydrazine, and transition metal salts (manganese(II) chloride tetrahydrate, cobalt(II) nitrate hexahydrate, nickel(II) chloride hexahydrate, zinc(II) nitrate hexahydrate and copper(II) chloride dihydrate) were received from BDH and Aldrich Companies, and other chemicals and solvents were purchased and used as received. 2.2. Synthesis of Schiff base (HL) The Schiff base (HL, Fig. 1) was been prepared according to the previous procedure [14, 15]: An ethanolic solution of 2-thiophenecarboxaldehyde (1 mmol, 25 mL) was added to an ethanolic solution of 2-chlorophenyl hydrazine (1 mmol, 25 mL) and refluxed for 2 hour in a water bath. After concentration of the solution, the precipitate was separated, filtered, washed with ethanol, and dried over anhydrous calcium chloride under vacuum. Anal.: Calcd. For HL: C, 55.81; H, 3.83; N, 11.83; S, 13.55. Found: C, 55.24; H, 3.90; N, 11.50; S, 13.24. The calculated mass spectrum: m/e: 236.72 (100.0%), 240 (1.5%). 2.3. Synthesis of the [M(HL)2(H2O)2]X2 Schiff base complexes A mixture of HL (2 mmol, 50 mL) in ethanol was added to an aqueous solution of manganese(II) chloride tetrahydrate, nickel(II) chloride hexahydrate, cobalt(II) nitrate hexahydrate, zinc(II) nitrate hexahydrate or copper(II) chloride dihydrate (1 mmol, 10 mL). The mixture of reaction was refluxed for 2 hours and then excess solvent was distilled. The precipitated compounds that separated were filtered,


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washed with ethanol, and dried over CaCl2 in vacuum. Anal.: Calcd. For [Mn(HL)2(H2O)2]Cl2: C,41.72; H, 3.18; N, 8.85; S, 10.13; Mn, 8.67. Found: C, 41.66; H, 3.15; N, 8.83; S, 10.09; Mn, 8.62. Anal.: Calcd. For [Co(HL)2(H2O)2](NO3)2: C, 40.01; H, 3.64; N, 11.66; S, 8.90; Co, 8.18. Found: C, 39.87; H, 3.61; N, 11.53; S, 8.78; Co, 8.09. Anal.: Calcd. For [Cu(HL)2(H2O)2]Cl2: C, 42.90; H, 3.90; N, 8.34; S, 9.54; Cu, 9.46. Found: C, 42.76; H, 3.74; N, 8.28; S, 9.49; Cu, 9.39. Anal.: Calcd. For [Zn(HL)2(H2O)2](NO3)2: C, 37.92; H, 2.89; N, 12.06; S, 9.20; Zn, 9.38. Found: C, 37.88; H, 2.81; N, 12.00; S, 9.14; Zn, 9.32. Anal.: Calcd. For [Ni(HL)2(H2O)2]Cl2: C, 41.48; H, 3.16; N, 8.79; S, 10.07; Ni, 9.21. Found: C, 41.31; H, 3.11; N, 8.70; S, 9.93; Ni, 9.10.

Figure 1. Structure of Schiff base N-(2-Chloro-phenyl)-N'-thiophen-2-ylmethylene-hydrazine (HL) 2.4. Measurements The elemental analyses of carbon, hydrogen, nitrogen and sulfur contents were performed using a Perkin Elmer CHNS 2400 (USA). The molar conductivities of freshly prepared 1.0×10 -3 mol/cm3 dimethylsulfoxide (DMSO) solutions were measured for the dissolved HL Schiff base Mn(II), Ni(II), Co(II), Zn(II) and Cu(II) complexes using Jenway 4010 conductivity meter. The electronic absorption spectra of HL Schiff base complexes were recorded in DMSO solvent within 900-200 nm range using a UV2 Unicam UV/Vis Spectrophotometer fitted with a quartz cell of 1.0 cm path length. The infrared spectra with KBr discs were recorded on a Bruker FT-IR Spectrophotometer (4000–400 cm-1), while Raman laser spectra of samples were measured on the Bruker FT-Raman with laser 50 mW. Magnetic data were calculated using Magnetic Susceptibility Balance, Sherwood Scientific, Cambridge Science Park Cambridge, England, at Temp 25oC. Scanning electron microscopy (SEM) images were taken in Quanta FEG 250 equipment. The X-ray diffraction patterns for the MnII, NiII, CuII, CoII and ZnII Schiff base complexes were recorded on X 'Pert PRO PAN-analytical X-ray powder diffraction, target copper with secondary monochromate. The 1H-NMR spectra were recorded on Varian Mercury VX-300 NMR spectrometer. 1H spectra were run at 300 MHz spectra in deuterated dimethylsulphoxide (DMSO-d6). Chemical shifts are quoted in δ and were related to that of the solvents. 2.5 Antibacterial and antifungal evaluation Antimicrobial activity of the tested samples was determined using a modified Kirby-Bauer disc diffusion method [16]. Briefly, 100 μl of the tested bacteria/fungi were grown in 10 mL of fresh media until they reached a count of approximately108 cells/mL for bacteria or 105 cells/mL for fungi [17]. 100


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μl of microbial suspension was spread onto agar plates corresponding to the broth in which they were maintained. Isolated colonies of each organism that might be playing a pathogenic role should be selected from primary agar plates and tested for susceptibility by disc diffusion method [18, 19]. Of the many media available, National Committee for Clinical Laboratory Standards (NCCLS) recommends MuellerHinton agar due to: it results in good batch-to-batch reproducibility. Disc diffusion method for filamentous fungi tested by using approved standard method (M38-A) developed by the NCCLS [20] for evaluating the susceptibility of filamentous fungi to antifungal agents. Disc diffusion method for yeast developed standard method (M44-P) by the NCCLS [21]. Plates inoculated with filamentous fungi as Aspergillus Flavus at 25 oC for 48 hours; Gram (+) bacteria as Staphylococcus Aureus, Gram (-) bacteria as Escherichia Coli they were incubated at 35-37 oC for 24-48 hours and yeast as Candida Albicans incubated at 30 oC for 24-48 hours and, then the diameters of the inhabitation zones were measured in millimeters [16]. Standard discs of Tetracycline (Antibacterial agent), Amphotericin B (Antifungal agent) served as positive controls for antimicrobial activity but filter disc impregnated with 10 μl of solvent (distilled water and DMSO) were used as a negative control. The agar used is Meuller-Hinton agar that is rigorously tested for composition and pH. Further the depth of the agar in the plate is a factor to be considered in the disc diffusion method. This method is well documented and standard zones of inhabitation have been determined for susceptible values. Blank paper disks (Schleicher & Schuell, Spain) with a diameter of 8.0 mm were impregnated 10 μl of tested concentration of the stock solutions. When a filter paper disc impregnated with a tested chemical is placed on agar the chemical will diffuse from the disc into the agar. This diffusion will place the chemical in the agar only around the disc. The solubility of the chemical and its molecular size will determine the size of the area of chemical infiltration around the disc. If an organism is placed on the agar it will not grow in the area around the disc if it is susceptible to the chemical. This area of no growth around the disc is known as a "Zone of inhibition" or "Clear zone". For the disc diffusion, the zone diameters were measured with slipping calipers of the National for Clinical Laboratory Standers [18]. Agar-based methods such as disk diffusion test can be good alternatives because they are simpler and faster than broth methods [22, 23]. 3. RESULTS AND DISCUSSIONS 3.1 Physical measurements data Mn(II), Ni(II), Co(II), Cu(II) and Zn(II) Schiff base HL complexes were synthesized in powder form with high melting points (Table 1). They are not soluble in ethanol, diethyl ester, or chloroform, but are partially soluble in DMSO and DMF. The molar conductance of the Mn(II), Ni(II), Co(II), Cu(II) and Zn(II) Schiff base complexes in DMSO are 138, 105, 98, 121 and 127μs indicating there are electrolytic nature, these meaning that anions occurred out of the coordination sphere. Table 1. Analytical and physical data for HL Schiff base complexes Compounds [Mn(HL)2(H2O)2]Cl2 [Co(HL)2(H2O)2] (NO3)2 [Cu(HL)2(H2O)2]Cl2 [Ni(HL)2(H2O)2]Cl2 [Zn(HL)2].(NO3)2


Mp (oC) >250 >250 >250 >250 >250

Color brown Dark brown brown brown Light brown

M (–1cm2mol–1) 138 98 121 105 127

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3.2. Infrared and Raman spectra Main characteristic infrared absorption bands of HL and its Mn(II), Ni(II), Co(II), Cu(II) and Zn(II) complexes, along with their assignments, are presented in Table 2. N-H, C=N and C=C vibration motions The infrared spectrum of the HL ligand (Fig. 2) exhibits a band at 1595 cm−1 assignable to ν(C=N) of the azomethine group and an intense bands at (1492, 1452 and 1407) cm−1 corresponding to the C=C stretching of the benzene and thiophene rings. The comparison of the positions of these bands with those observed in the infrared spectra of its Mn(II), Ni(II), Co(II), Cu(II) and Zn(II) complexes indicated that the band at 1595 cm−1 did not show a marked shift, this discussed that azomethine group unshared in the complexation toward Mn(II), Ni(II), Co(II), Cu(II) and Zn(II) ions, while that bands at 3328 and 3306 cm−1 which assigned to stretching vibration motions –NH of phenyl hydrazine moiety is a mild decreasing in an intensity or absence. This fact suggests the coordination of HL through the nitrogen Ph–NH of phenylhydrazine. Proof of coordination to the N atom is provided by the occurrence of the new absorption bands at ~ 440 cm−1 in the IR spectra of all HL complexes. C-S-C and C-S vibration motions The observed medium intensity band at 912 cm−1 in the free HL ligand, which is ascribed to δ(CSC) of thiophene ring vibration [15], shifted to lower values for the five HL complexes, suggesting the involvement of the sulfur atom in the bonding with the metal’s ions. The band assigned to the stretching of ν(C−S) is similarly shifted to lower frequencies. This also confirms that the sulfur atom is taking part in the complex formation [15]. On the other hand, the Raman laser spectra of HL, [M(HL)2(H2O)2]X2 (where M= Mn(II), Co(II), Cu(II), Ni(II) or Zn(II); X= (NO3–or Cl–) Schiff base complex (Fig. 3) has a sharp broadening with distorted in the stretching vibration bands, this can be discussed under the knowledge that Raman analysis of fluorescent materials and compounds is a challenging task experimentally due to the overlap of fluorescence which, even when very weak, can overwhelm the inherently weak Raman scattering signal [24, 25]. It is tentatively suggested that the Schiff base HL ligand coordinates through the nitrogen of the phenyl hydrazine moiety and the sulfur of the thiophene ring, forming a stable chelating structure. According to the above discussion, distorted octahedral structures for [M(HL)2(H2O)2]X2 (where M= Mn(II), Co(II), Cu(II), Ni(II) or Zn(II); X= (NO3–or Cl–) complexes are drawn in Fig. 4. Table 2. Infrared characteristic bands frequencies (cm−1) of the HL ligand complexes Compounds

ν(C=N)

ν(C=C) phenyl + thiophene

δ(CSC)

ν(C−S)

ν(M−N)

HL [Mn(HL)2(H2O)2]Cl2 [Co(HL)2(H2O)2] (NO3)2

1595 1588 1585

1492, 1452, 1407 1501, 1447, 1405 1506, 1448, 1384

912 850 840

710 699 669

--442 438

[Cu(HL)2(H2O)2]Cl2

1597

1527, 1457, 1399

894

667

444

[Ni(HL)2(H2O)2]Cl2

1588

1520, 1499, 1447

851

699

442

[Zn(HL)2].(NO3)2

1596

1500, 1453, 1390

826

687

442


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Canadian Chemical Transactions


A

B

C

D

E

F

Ca

4000 3500 3000 2500 2000 1500 1000 500 Wavenumbers [nm]

Figure 2. Infrared spectra of (A): HL Schiff base, (B): [Mn(HL)2(H2O)2]Cl2, (C): [Co(HL)2(H2O)2](NO3)2, (D): [Cu(HL)2(H2O)2]Cl2, (E): [Ni(HL)2(H2O)2]Cl2 and (F): [Zn(HL)2(H2O)2](NO3)2 complexes

L

0.6 0.3

J

0.0 0.16 0.08 0.00

H

0.12 0.06

B

D

F

0.00 0.16 0.08 0.00 0.12 0.06 0.00 0.4 0.2 0.0 4000

3000

2000

1000

0

-1

Wavenumbers [cm ]

Figure 3. Raman spectra of (A): HL Schiff base, (B): [Mn(HL)2(H2O)2]Cl2, (C): [Co(HL)2(H2O)2] (NO3)2, (D): [Cu(HL)2(H2O)2]Cl2, (E): [Ni(HL)2(H2O)2]Cl2 and (F): [Zn(HL)2(H2O)2](NO3)2 complexes


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Ca

HC

N

H2O

CH

S

S Co

OH2

HC

N

N

H2O

HN

NH

S

S Mn

Cl

N

HN

NH

Cl

OH2

CH

Cl

Cl

.2NO3

HC

N

S

S H2O NH

Ni

OH2

.Cl2

CH

HC

N

N

H2O

HN

Cl

NH

Cl

.Cl2

N

OH2

N

HN

.Cl2

S

S H2O NH

Cl

Cu

CH

Cl

Cl

HC

S

S

Zn

OH2

CH

N

HN Cl

.2NO3

Figure 4. Proposed structures of [M(HL)2(H2O)2]X2 (where M= Mn(II), Co(II), Cu(II), Ni(II) or Zn(II); X= (NO3–or Cl–) Schiff base complex 3.3. Electronic spectra Upon the electronic spectrum of the HL Schiff base ligand, the two essential absorption bands were observed at 310 nm, (360 and 550) nm and assigned to the transitions n → π*, π → π*, respectively (Fig. 5). These transitions were existed also in the spectra of the complexes, but they shifted to different lower intensities, confirming the coordination of the ligand to the metal ions. In UV-Vis. spectra, the weak band should be at 400-500 nm are due to charge-transfer (ct) band in the complexes, which is absence in the HL. However, the weak broad band at 500-700 nm is due to different d-d transitions of the


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Ca

metal ions as mentioned. Information concerning the geometry of these compounds was obtained from the electronic spectra and from magnetic moment values. The electronic spectrum of the Mn(II) complex shows four medium intensity bands assigned to 6A1g → 4T1g(G), 6A1g → 4T2g(G), and 6A1g → 4Eg(G), 4 A1g(G), respectively, for a Mn(II) ion in an distorted octahedral field [26]. The electronic spectrum of octahedral CoII complex has three types of transitions due to 4T1g(F) → 4A2g(F), and 4T1g(F) → 4T2g(P) [26]. The diffuse reflectance spectrum of copper(II) complex is expected to show two allowed transitions namely 2B1g → 2Eg and 2B1g → 2B2g. These bands suggested distorted octahedral geometry around Cu(II) [26]. The electronic spectrum of the [Ni(HL)2(H2O)2].Cl2 complex could be assigned to octahedral geometry. The solid reflectance spectrum of the NiII complex showed two identified bands at 16722 and 22727 cm–1, assigned to the transitions 3A2g(F) → 3T1g(F) and, 3A2g(F) →3T1g(P) respectively [27]. 3.4. Magnetic measurements The magnetic susceptibility measurements thus help to predict the possible geometry of the metal complexes. In paramagnetic Mn(II), Ni(II), Co(II) and Cu(II) complexes, often the magnetic moment (µeff) gives the spin only value (µs.o.= (n(n+2))½ B.M.) corresponding to the number of unpaired electron. The variation from the spin only value is attributed to the orbital contribution and it varies with the nature of coordination and consequent delocalization. The octahedral geometry of Co(II) complex has a magnetic moments, number of unpaired electrons, corresponding to configuration and expected value as 5.32 BM, 4, d6 and 5.39 [26]. The magnetic moment, configurations, stereochemistry, hybrid orbitals, number of unpaired electrons and expected magnetic values of Cu(II) and Mn(II) HL Schiff base complexes are (1.94 B.M., d9, octahedral, sp3d2,1, 1.96 B.M.) and (5.97 B.M., d5, octahedral, sp3d2, 5, 6.00 B.M.), respectively. Thus the value of magnetic moment of a complex would give valuable insights into its constitution and structure. The magnetic susceptibility measurements obtained at room temperature for Ni(II) complex can be summarized with magnetic moment, configurations, stereochemistry, hybrid orbitals, number of unpaired electrons, spin-only and expected magnetic values at 3.30 B.M., d8, octahedral, sp3d2, n= 2, 2.83 B.M. and 3.32 B.M. The magnetic moment lies within the region expected for octahedral complexes.

2.4

2.0

Abs.

1.6

1.2

HL Mn(II) Co(II) Ni(II) Zn(II) Cu(II)

0.8

0.4

0.0 300

400

500

600

700

800

900

1000

Wavelength [nm]

Figure 5. Electronic spectra of [M(HL)2(H2O)2]X2 (where M= Mn(II), Co(II), Cu(II), Ni(II) or Zn(II); X= (NO3–or Cl–) Schiff base complex


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Ca

A

B

C

D

E

C

Fig 6. SEM image of synthesized (A):MnO, (B):CoO, (C):CuO, (D):NiO and (E):ZnO nanoparticles using [Mn(HL)2(H2O)2]Cl2, [Co(HL)2(H2O)2](NO3)2, [Cu(HL)2(H2O)2]Cl2, [Ni(HL)2(H2O)2]Cl2 and [Zn(HL)2(H2O)2](NO3)2 Schiff base complexes precursors at 600 °C. 1200 1000 800 600 400 200 0 2000 1500 B

1000 500

A

0 600 500 400 300 200 100 0 10

20

30

40

50

60



Figure 7. XRD patterns of (A): ZnO, (B): NiO and (C): CoO nanoparticles


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Table 3. Antimicrobial activity data of PTMH and its Mn(II), Co(II) and Cu(II) complexes Inhibition zone diameter (mm / mg sample) Sample

Standard

Control: DMSO

Escherichia coli (G-)

Staphylococcus aureus (G+)

Aspergillus flavus (Fungus)

Candida albicans (Fungus)

0.0

0.0

0.0

0.0

32

30

--

--

--

--

18

19

HL

11

11

10

12

Co(II) Cu(II) Zn(II) Mn(II) Ni(II)

16 13 14 9 7

13 13 15 11 13

0.0 12 0.0 0.0 0.0

12 10 10 10 10

Tetracycline Antibacterial agent Amphotericin B Antifungal agent

3.5. 1H NMR Spectra The 1H-NMR spectra of the HL Schiff base ligand and zinc(II) complex shows multiplet signals at 6.522-7.731 ppm, corresponding to the aromatic ring protons of the phenyl and thiophene moieties [27]. The singlet at 9.894 ppm was attributed to the proton of the azomethine group [28]. The signal of the –NH proton in the phenylhydrazine moiety was observed at 8.479 ppm. In comparison between the 1HNMR data of HL and its [Zn(HL)2(H2O)2](NO3)2, complex the mode of coordination in between the ligand and metal ions was clarified. Through the discussion of 1H-NMRspectrum of Zn(II) complex, we find that the signal specialized to –NH proton of phenylhydrazine moiety shifted to lower ppm with noticeable decreasing in the intensity. The appearance of new strong intense peak at 3.321 ppm can be assigned to the H-proton of H2O, which attached to the Zn(II) metal to complete the six coordination sphere. 3.6. SEM and XDR Spectra The Mn(II), Co(II), Cu(II), Ni(II) and Zn(II) oxides nanoparticles were synthesized at 600 oC using [M(HL)2(H2O)2]X2 (where M= Mn(II), Co(II), Cu(II), Ni(II) or Zn(II); X= (NO3–or Cl–) Schiff base complexes as precursors and their properties studied with the help of a scanning electron microscope (SEM) and X-ray diffraction. Figs. 6 and 7 show the SEM image of the synthesized MnO, CoO, CuO, NiO and ZnO nano-particles, with an image magnification. The assembly was attached to a computer running a program to analyze the mean size of the particles in the samples. It should be noted that the particle diameter is always overestimated due to the distortion of SEM images [29]. Figure 7 demonstrates the XRD patterns of the synthesized MnO, CoO, CuO, NiO and ZnO nanoparticles. The Xray diffraction data were recorded by using Cu Kα radiation (1.5406 Angstrom). The intensity data were collected over a 2θ range of 4–60°. The average grain size of the samples was estimated with the help of


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Ca

S.aureus E.coli Ni Mn

Sample

Zn Cu Co HL Amphotericin B Tetracycline DMSO 0

5

10

15

20

25

30

Inhibition zone diameter (mm / mg sample)

C.albicans A.flavus Ni Mn

Sample

Zn Cu Co HL Amphotericin B Tetracycline DMSO 0

2

4

6

8

10

12

14

16

18

20

Inhibition zone diameter (mm / mg sample)

Figure 8. Antimicrobial activity of HL Schiff base ligand and Mn(II), Co(II), Cu(II), Ni(II) and Zn(II) Schiff base complexes

the Scherrer equation, using the diffraction intensity peak. X-ray diffraction studies confirmed that the synthesized materials were MnO, CoO, CuO, NiO and ZnO, that all the diffraction peaks agreed with the reported standard data; no characteristic peaks were observed other than oxide, MO. The mean grain size (D) of the particles was determined from the XRD line broadening measurement using the Scherrer Equation (1): D = 0.89λ/(βCosθ) (1)


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Where λ is the wavelength (Cu Kα), β is the full width at the half- maximum (FWHM) of the MnO, CoO, CuO, NiO and ZnO line and θ is the diffraction angle. A definite line broadening of the diffraction peaks is an indication that the synthesized materials are in the nanometer range. The lattice parameters calculated were also in agreement with the reported values. The reaction temperature greatly influences the particle morphology of as-prepared MnO, CoO, CuO, NiO and ZnO powders. The results of nanoparticle size measurement of samples by XRD and SEM indicate that the size of the MnO, CoO, CuO, NiO and ZnO nanoparticles was about 150-300 nm. 3.7. Biological studies The antibacterial activity of the Schiff base and its Mn(II), Co(II), Ni(II), Zn(II) and Cu(II) complexes against gram-positive (Staphylococcus aureus) and gram-negative (Escherichia coli) and two strains of fungus (Aspergillus flavus and Candida albicans) were studied. The antibacterial and antifungal results are shown in Table 3 and Fig. 8. All the Schiff base complexes individually exhibited varying degrees of inhibitory effect on the growth of the tested bacterial species. Table 3 shows that the activity of the Schiff base complexes became more pronounced when coordinated with the metal ions. The biological activity of the complexes follow the order: Antibacterial effect: Co(II)>Zn(II) >Cu(II) >Ni(II)>Mn(II) and Antifungal effect: Cu(II)>Co(II)>Zn=Mn=Ni. 4. CONCLUSIONS In this paper we reported the synthesis, isolation of solid products, and spectroscopic characterization of a new bidentate Schiff base derived from 2-thiophenecarboxaldehyde, 2-chlorophenyl hydrazine, its complexes with Mn(II), Co(II), Cu(II), Ni(II) and Zn(II). It is tentatively proposed that the Schiff base ligand coordinates through the nitrogen of the 2-chlorophenyl hydrazine moiety and the sulfur of the thiophene ring, forming a stable chelate ring structures. Based on the above interpretations, distorted octahedral structures for all complexes are proposed with general formula [M(HL)2(H2O)2]X2 (where M= Mn(II), Co(II), Cu(II), Ni(II) or Zn(II); X= (NO3–or Cl–). The synthesized metal complexes, in comparison to the free Schiff base ligand, were screened for their antibacterial activity against some kinds of bacteria and fungi species. The antimicrobial activities of the complexes follow the order: Antibacterial effect: Co(II)>Zn(II) >Cu(II) >Ni(II)>Mn(II) and Antifungal effect: Cu(II)>Co(II)>Zn=Mn=Ni. REFERENCES AND NOTES

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[4]

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