Synthesis and characterization of 1,2-bis(2-(5-bromo-2-hydroxybenzilidenamino)-4-chlorophenoxy)ethane and its metal complexes: An experimental, theoretical, electrochemical, antioxidant and antibacterial study

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 118 (2014) 632–642

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Synthesis and characterization of 1,2-bis(2-(5-bromo-2-hydroxybenzilidenamino)-4-chlorophenoxy)ethane and its metal complexes: An experimental, theoretical, electrochemical, antioxidant and antibacterial study Salih Ilhan a,⇑, Haci Baykara a,d,⇑, Abdussamet Oztomsuk a, Veysi Okumus b, Abdulkadir Levent c, M. Salih Seyitoglu a, Sadin Ozdemir b a

Faculty of Art and Science, Chemistry Department, Siirt University, Siirt, Turkey Faculty of Art and Science, Biology Department, Siirt University, Siirt, Turkey c Batman University, Health Services Vocational College, 72100 Batman, Turkey d Escuela Superior Politécnica del Litoral, ESPOL, CIDNA, Km 30.5 Via Perimetral, Guayaquil, Ecuador b

h i g h l i g h t s

g r a p h i c a l a b s t r a c t

 The1,2-bis(2-(5-bromo-2-

hydroxybenzilidenamino)-4chlorophenoxy)ethane synthesized.  New Cu(II) Ni(II), Co(II), Fe(III) V(III) and Zn(II) complexes synthesized.  The structures of metal complexes were characterized by different analysis.  In addition, antioxidant, theoretical NMR and cyclic voltammetry studies done.

a r t i c l e

i n f o

Article history: Received 14 May 2013 Received in revised form 8 July 2013 Accepted 15 August 2013 Available online 7 September 2013 Keywords: Schiff base complexes Cyclic voltammetry Antioxidant Gaussian DFT HF

a b s t r a c t A new Schiff base ligand was synthesized by reaction of 5-bromosalicylaldehyde with 1,2-bis(4-chloro-2aminophenoxy)ethane. Then the Schiff base complexes were synthesized by the reaction of metal salts and the novel Schiff base. The molar conductivity properties of the complexes were studied and found out that the complexes are nonelectrolytes. The structures of the ligand and its metal complexes were characterized by elemental analysis, FT-IR, UV–VIS, magnetic susceptibility measurements, molar conductivity measurements, and thermal gravimetric analysis. In addition antioxidant, theoretical NMR studies and cyclic voltammetry of the complexes were done. Two methods namely metal chelating activity and diphenylpicrylhydrazyl (DPPH) radical scavenging method were used to determine the antioxidant activity, and antibacterial properties of the compounds were also studied. Ó 2013 Elsevier B.V. All rights reserved.

Introduction

⇑ Corresponding authors. Address: Faculty of Art and Science, Chemistry Department, Siirt University, Siirt, Turkey (H. Baykara). Tel.: +90 (506) 611 55 48; fax: +90 (484) 223 20 86. E-mail address: [email protected] (S. Ilhan). 1386-1425/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.saa.2013.08.069

Schiff bases and their metal complexes play a key role in understanding the coordination chemistry of transition metals [1,2]. A large number of reports are available on the chemistry and the biological activities of transition metal complexes containing O, N and

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S, N donor atoms [3,4]. The transition metal Schiff base complexes have biological activities, antibacterial, antifungal, antioxidant and many industrial applications [5–9]. Transition metal complexes with tetradentate Schiff-base ligands have been extensively investigated as catalysts for a number of organic redox reactions and electrochemical reduction processes [10–12]. Cyclic voltammetry has been a useful technique to investigate the mechanisms of catalysis by Schiff-base metal complexes as well as to study the structure–reactivity relationship in the compounds [13–15]. The molecular parameters: Gaussian, theoretical NMR studies, total energy, heat of bonding energy, isolated energy, electronic energy, heat of formation, dipole moment, HOMO and LUMO of the ligand and complexes have been studied recently [16–21]. In the present work, we have synthesized a new Schiff base ligand by the reaction of 5-bromosalicylaldehyde and 1,2-bis (4-chloro-2-aminophenoxy)ethane. The corresponding Schiff base complexes were synthesized by the reactions of metal salts and the Schiff base. Spectral analyses, cyclic voltammetry, antioxidant studies and magnetic properties of the new compounds were studied in details. A theoretical NMR study was also successfully carried out as a supportive characterization study with linear regression analysis.

with the solvent/supporting electrolyte mixture. Before starting each experiment, the glassy carbon electrode was polished manually with alumina (U: 0.01 lm). Cyclic voltammetric (CV) experiments were recorded at room temperature in extra pure dimethyl formamide (DMF), and ionic strength was maintained at 0.1 mol L1 with electrochemical grade tetrabutylammonium perchlorate (TBAP) as the supporting electrolyte. Solutions were deoxygenated by a stream of high purity nitrogen for 15 min prior to the experiments, and during the experiments nitrogen flow was maintained over the solution. Gaussian computations were carried out using a PC having 4G RAM.

Synthesis of Schiff base 5-Bromosalicylaldehyde (40 mmol) in ethanol (40 mL) was added dropwise to a stirred solution of 1,2-bis(4-chloro-2-aminophenoxy)ethane (20 mmol) in ethanol (60 mL). After the addition was completed, the stirring was continued for 2 h, and then precipitate was filtered, washed with ethanol and dried in the vacuum oven at 35 °C under the low pressure for 24 h (Fig. 3). Synthesis of Schiff base complexes

Experimental The 1,2-bis(4-chloro-2-aminophenoxy)ethane used in the synthesis were prepared from 4-chloro-2-nitrophenol, 1,2-dibromoetane and K2CO3 as shown in Figs. 1 and 2 [22,23]. All the chemicals and solvents were of analytical grade and used as received. Elemental analysis was carried out on a LECO CHNS model 932 elemental analyzer. IR spectra were recorded on a PERKIN ELMER SPECTRUM 100 FTIR spectrometer on a universal ATR accessory, with a wavenumber range of 4000–650 cm1. Electronic spectral studies were conducted on a PERKIN ELMER LAMBDA 750 model UV Visible spectrophotometer in the wavelength 200– 900 nm. Molar conductivities were measured with a WTW LF model 330 conductivity meter using prepared solution (103 M) of the complexes in DMF solvent. 1H and 13C NMR spectra were recorded using a BRUKER AVANCE DPX-400 NMR spectrometer. Magnetic Susceptibilities were determined on a Sherwood Scientific Magnetic Susceptibility Balance (Model MK1) at room temperature (20 °C) using Hg[Co(SCN)4] as a standard; diamagnetic corrections were calculated from Pascal’s constants [24]. Thermal gravimetric analyses were determined on an EXSTAR S II TG/DTA 6300 Model. Electrochemical experiments were performed with an Autolab PGSTAT 128N potentiostat, (The Netherlands) using a three electrode system, glassy carbon working electrode (U: 3 mm, BAS), platinum wire as auxiliary electrode and Ag/AgCl (NaCl 3 M, Model RE-1, BAS, USA) as reference electrode. The reference electrode was separated from the bulk solution by a fritted-glass bridge filled

Cl

A solution of metal salt in DMF (40 mL) was mixed with the Schiff base ligand (2 mmol) in DMF (60 mL) at a molar ratio 1:1. The contents were refluxed in 100 mL of DMF on an oil-bath for 3 h. The product was separated by filtration, washed with ethanol and dried in vacuum oven at room temperature for 24 h. All the complexes were almost insoluble in common organic solvents such as ethanol, methanol, benzene, acetone, nitrobenzene, dichloromethane and chloroform. However, they were fairly soluble in polar organic solvents such as dimethyl sulfoxide and dimethyl formamide. A representative reaction scheme for the reaction between metal salts and ligand can be seen on Fig. 4.

O H 2C

NH2

O

O

+

Br(CH2CH2)Br

OH

H 2C

H

2

H 2C

OH

NH2

-H2O

NO2 O

O 2N

Cl

O CH2 CH2

Fig. 1. Synthesis of the 1,2-bis(4-chloro-2-nitrophenoxy)ethane.

Cl

NO2

O2N

Cl +

O

O CH2 CH2

Cl N2H4.H2O

NH2

H2N

Pd/C Absolute Ethanol

N

OH

O

N

OH

Cl Br Fig. 3. Synthesis of the ligand (L).

-KBr, -CO2, -H2O

O

H 2C

Cl

Cl K2CO3

Br +

NO2 +

Cl Br

Cl

O

O CH2 CH2

Fig. 2. Synthesis of the 1,2-bis(4-chloro-2-aminophenoxy)ethane (L).

Cl

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Characterization of Schiff base (L) Molecular Weight: 679. M.P: 240–242 °C. Color: Yellow. Yield: 12 g (88.4%). Anal Calcd. for C28H20N2O4Cl2Br2: C, 49.48, H, 2.94, N, 4.12. Found: C, 49.64, H, 3.09, N, 4.87. IR (cm1): 3066 m(ArACH), 2955, 2891 m(Alf.ACH), 1617 m(C@N), 1494, 1472 m(ArAC@C), 1285, 1255 m(ArAO), 1177, 1160 m(RAO). UV–vis: k1 = 291 nm(e = 3000), k2 = 366(e = 4000) nm. 13C NMR (ppm, in DMSO-d6): OCH2: 64.26, OHAC: 161.23, HC@N: 158.17, (ArAC): 111.04, 119.41, 121.06, 132.04, 135.98. 1H NMR (ppm, in DMSOd6): d = 4.43 (s, OCH2), d = 6.64–7.95 (ArAH), d = 8.95 (HC@N), d = 13.37 (OH). Characterization of CuL Molecular Weight: 741. M.P: 141 °C decompose. Color: Pale green. Yield: 1.28 g (86.3%). Anal Calcd. for CuC28H18N2O8Cl2Br2: C, 45.34, H, 2.42, N, 3.77. Found: C, 45.58, H, 2.61, N, 3.77. Selected IR data (KBr, m cm1): 3060 m(ArACH), 2926, 2871 m(Alf.ACH), 1607 m(C@N), 1486, 1451 m(ArAC@C), 1282, 1240 m(ArAO), 1162, 1128 m(RAO). UV–vis: k1 = 259 nm(e = 4200), k2 = 267 nm(e = 2200), k3 = 396 nm(e = 1400). leff = 1.78 B.M. (Bohr Magneton). Characterization of NiL Molecular Weight: 736. M.P: 217–219 °C decompose. Color: Pale yellow. Yield: 1.30 g (88.3%). Anal Calcd. for NiC28H18N2O8Cl2Br2: C, 45.65, H, 2.44, N, 3.80. Found: C, 45.55, H, 2.65, N, 4.03. Selected IR data (KBr, m cm1): 3063 m(ArACH), 2923, 2874 m(Alf.ACH), 1607 m(C@N), 1486, 1450 m(ArAC@C), 1311, 1240 m(ArAO), 1161, 1128 m(RAO). UV–vis (kmax, nm) in DMF: k1 = 257 nm(e = 32,000), k2 = 437 nm(e = 2500). leff = 2.85 B.M. Characterization of CoL Molecular Weight: 737. M.P: 219–221 °C. Color: Brown. Yield: 1.20 g (81.5%). Anal Calcd. for CoC28H18N2O8Cl2Br2: C, 45.59, H, 2.44, N, 3.80. Found: C, 45.29, H, 2.84, N, 4.06. Selected IR data (KBr, m cm1): 3062 m(ArACH), 2926, 2870 m(Alf.ACH), 1607 m(C@N), 1488, 1450 m(ArAC@C), 1262, 1252 m(ArAO), 1162, 1128 m(RAO). UV–vis (kmax, nm) in DMF: k1 = 257 nm(e = 29,600), k2 = 258 nm(e = 27,000), k3 = 285 nm(e = 3300) k4 = 364 nm(e = 3200). leff = 3.57 B.M. Characterization of ZnL Molecular Weight: 742. M.P: 233–235 °C. Color: Light Yellow. Yield: 1.28 g (86.2%). Anal Calcd. for ZnC28H18N2O8Cl2Br2: C, 45.28, H, 2.42, N, 3.77. Found: C, 46.50, H, 2.88, N, 3.65. Selected

IR data (KBr, m cm1): 3059 m(ArACH), 2930, 2871 m(Alf.ACH), 1608 m(C@N), 1484, 1452 m(ArAC@C), 1289, 1252 m(ArAO), 1160, 1132 m(RAO). 1H NMR (ppm, in DMSO-d6): d = 4.18 (OCH2), d = 6.3–9.0 (ArAH), d = 11.14 (HC@N). UV–vis (kmax, nm) in DMF: k1 = 257 nm(e = 28300), k2 = 291 nm(e = 3800), k3 = 366 nm(e = 3200), k4 = 431 nm(e = 1800leff = Diamagnetic.

Characterization of MnL Molecular Weight: 732. M.P: 215 °C decompose. Color: light brown. Yield: 0.84 g (57.3%). Anal Calcd. for MnC28H18N2O8Cl2Br2: C, 45.90, H, 2.46, N, 3.82. Found: C, 45.79, H, 2.85, N, 4.00. Selected IR data (KBr, m cm1): 3060 m(ArACH), 2958, 2888 m(Alf.ACH), 1615 m(C@N), 1493, 1473 m(ArAC@C), 1286, 1254 m(ArAO), 1173, 1134 m(RAO). UV–vis (kmax, nm) in DMF: k1 = 258 nm(e = 28,000), k2 = 270 nm(e = 3000), k3 = 360 nm(e = 2800). leff = 5.47 B.M.

Characterization of TiLCl Molecular Weight: 760. M.P: 185–186 °C. Color: brown. Yield: 0.99 g (65.2%). Anal Calcd. for TiC28H18N2O8Cl3Br2: C, 44.21, H, 2.36, N, 3.68. Found: C, 44.97, H, 2.43, N, 3.62. Selected IR data (KBr, m cm1): 3066 m(ArACH), 2926, 2871 m(Alf.ACH), 1614 m(C@N), 1495, 1472 m(ArAC@C), 1256, 1208 m(ArAO), 1177, 1132 m(RAO). UV–vis (kmax, nm) in DMF: k1 = 262 nm(e = 3800), k2 = 259 nm(e = 3400), k3 = 366 nm(e = 2100). leff = 1.87 B.M.

Characterization of VLCl Molecular Weight: 763. M.P: 206–207 °C. Color: Green. Yield: 1.16 g (76.3%). Anal Calcd. for VC28H18N2O8Cl3Br2: C, 44.03, H, 2.36, N, 3.67. Found: C, 44.30, H, 2.57, N, 3.91. Selected IR data (KBr, m cm1): 3065 m(ArACH), 2952, 2885m(Alf.ACH), 1612 m(C@N), 1495, 1474 m(ArAC@C), 1283, 1256 m(ArAO), 1179, 1130 m(RAO). UV–vis (kmax, nm) in DMF: k1 = 290 nm(e = 3500), k2 = 360 nm(e = 3600). leff = 3.69 B.M.

Characterization of FeLNO3 Molecular Weight: 795. M.P: 154 °C decompose. Color: Dark brown. Yield: 0.99 g (62.3%). Anal Calcd. for VC28H18N2O8Cl3Br2: C, 42.26, H, 2.26, N, 3.52. Found: C, 43.07, H, 2.61, N, 3.77. Selected IR data (KBr, m cm1): 3060 m(ArACH), 2953, 2886 m(Alf.ACH), 1736,1611, m(C@N), 1453, 1474 m(ArAC@C), 1296, 1203 m(ArAO), 1173, 1128 m(RAO). UV–vis (kmax, nm) in DMF: k1 = 261 nm(e = 1200). leff = 4.55 B.M. Cl Br

Cl Br

H2C

O

N

OH

H2C +

M(Salt)x.nH 20

H2C O

N

OH

Cl Br M= Cu, Ni, Co, Zn, Mn, Ti, V, Fe x= 2-3

O

Cl Br

N

O M

X

H2C

H2C

O

N

O

N

or

O M

Cl

H2C O

N

O

Cl Br M= Zn(II), Cu(II), Co(II), Ni(II), X=M= Fe(III), X= -NO 3

Cl Br M= (Ti(III) and V(III)

Fig. 4. Reaction scheme of the complex formation reaction between metal salts and ligand (L).

O

S. Ilhan et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 118 (2014) 632–642

Electrochemical analysis The electrochemical properties of the present compounds were investigated by CV and on a glassy carbon electrode in DMF containing 0.1 M TBAP, in the concentration of 1  103 M vs. Ag/AgCl (see Table 4). The electrochemical data upon the peak potentials have been reported in Table 4. In the cathodic direction from +1.0 V to 2.3 V at scan rate of 100 mV s1, the CV of L is characterized by three cathodic waves (Ic, IIc and IIIc at about 0.28, 1.76 and 1.97 V, respectively) and one wave was observed (Ia at about +0.65 V) as depicted by cyclic voltammograms given in Fig. 9 A. These peaks are irreversible. At higher scan rates (>400 mV s1) the Ia oxidation wave not observed (Fig. 10A), whereas the specifics of the reduction peaks in the cathodic direction with increasing scan rate increased and was shifted to more negative potentials. DPPH radical scavenging activity Free radical scavenging activity of the test samples ligand (L), Cu(II), Ni(II), Co(II), Zn(II), Mn(II), Ti(III), V(III) and Fe(III) complexes were carried out by the DPPH assay method. The stock solution (1 mg/mL) was diluted to final concentrations of 5, 10, 25, 50 and 100 mg/L in methanol. DPPH methanol solution (1.6 mL) was added to 0.4 mL different concentrations of compounds solutions and allowed to incubated at room temperature in the dark for 30 min. After incubation the decrease in absorbance values of DPPH were measured at 517 nm. The DPPH scavenging activity was calculated according to following equation:

Scavenging activityð%control Þ ¼ ðAcontrol  Asample Þ=Acontrol  100: where Acontrol is the absorbance of the control reaction (containing all reagents except for the compounds and its complexes), and Asample is the absorbance of the test compound. Tests were repeated tree times. Ascorbic acid and Trolox were used as positive control. Metal-chelating activity The metal chelation activity by ligand and its metal complexes was experimented by Dinis method [25]. The stock solution (1 mg/ mL) was diluted to final concentrations of 5, 10, 25, 50 and 100 mg/ L in methanol. Briefly, 2 mM FeCl2 (50 lL) was added to 0.5 mL of different concentrations of the ligand and its compexes compounds in methanol. The reaction was initiated by addition of ferrozine solution (5 mM, 0.1 mL). The mixture was vigorously shaken and left to stand at room temperature. After 10 min incubation, the absorbance of the solution was measured at 562 nm. EDTA was used as positive control. The chelating activity was calculated by using the formula given;

Ferrous ion-chelating activityð%Þ ¼ ðAcontrol  Asample Þ=Acontrol  100; where Acontrol is the absorbance of the control reaction, and Asample represents the absorbance obtained in the presence of EDTA. The inhibition percentage of the ferrozine–Fe2+ complex formation was calculated. Antimicrobial activity Escherichia coli (ATCC 10536), Staphylococcus aureus (ATCC 6538), Micrococcus luteus (ATCC 9341), Enterococcus hirae (ATCC 10541), Pseudomonas aeruginosa (ATCC 9027), Legionella pneumophila subsp. pneumophiia (ATCC 33152) and Bacillus subtilis (ATCC 6051) were used as test microorganisms. In this study, disc

635

diffusion method was used for determination antibacterial activity of compounds and its metal complexes [26]. Results and discussion Schiff base and metal complexes In this work, a new Schiff base ligand 1,2-bis(2-(5-bromo-2hydroxybenzilidenamino)-4-chlorophenoxy), was synthesized by the reaction of 5-bromosalicylaldehyde and 1,2-bis(4-chloro-2aminophenoxy)ethane in ethanol and, purified by recrystallization from DMF. Then, the Schiff base was reacted with metal salts to obtain corresponding metal complexes. The products were washed with ethanol, filtrated and dried in the vacuum oven at 30 °C room temprature under the low pressure. The ligand and its metal complexes were characterized by elemental analysis, IR, UV–vis, TGADTA, 1H NMR and 13C NMR, conductivity measurements, cyclic voltammetry and magnetic susceptibility. In addition, a theoretical calculation study for the ligand was carried out to determine optimized spatial structure and theoretical proton NMR properties. Furthermore, a regression analysis was also carried out between experimental 1H NMR shifts and theoretical 1H NMR shifts to analyze the compatibility between both values. Electrochemical analysis were studied and given related section. Since the crystals were not suitable for X-ray structural determination. The compounds were not soluble in most common solvents such as water, methanol, ethanol, ethyl acetate and acetonitrile but they were fairly soluble in N,N-dimethylformamide (DMF) and dimethyl sulfoxide (DMSO). FTIR spectra Some IR bands and peaks assigned to stretching and bending vibrations for the ligand and its complexes can be seen in Table 1. Because of strong intramolecular hydrogen bonding OAH stretching peak (band) was not observed in the IR spectra of the ligand. The Same situations were observed at the same frequency in the IR spectra of salicylideneanilines [22,27]. OAH stretching peak (band) was not observed in the IR spectra of the complexes. The band at 1285 cm1 in the IR spectrum of the ligand is assigned to the phenolic CAO stretching vibration. This band is found in the region 1300–1250 cm1 in the spectra of the metal complexes. These changes suggest that hydroxyl groups of the Schiff base has taken part in complex formation [28]. The new band was observed around 1617 cm1 assigned to azomethine m(C@N) group in the ligand structure. This peak proofs the formation of the ligand besides that disappearing of the peaks at 1735 cm1 (AC@O group in the structure of aldehyde) and 3420 cm1 (ANH2 amino groups in the structure of amine) is another strong proof for the formation of the ligand [15,29,30]. The strong band within the range at ca. 1605–1620 cm1 in the spectra of all the complexes can be attributed to stretching vibrations of imine t(AC@N) group [30,31]. The IR spectra of the complexes compared with those of the ligand indicate that the C@N band 1617 cm1 is shifted to lower values for complexes. These shifted IR values indicate that there is a coordination of the azomethine nitrogen to metal [32]. In the spectra of all of the complexes are dominated by bands at 2950–2850 cm1 due to m(Alph.ACAH) groups and 3100–3050 cm1 m(Ar.ACAH) stretching vibrations [33]. Electronic spectra Electronic absorption spectral data of the complexes in dimethylformamide (DMF) at room temperature that are presented in experimental section. The electronic spectra of the complexes in

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Table 1 Physical characterization, analytical, molar conductance and spectral data of the complexes. Compound

Yield mass (%)

Color

Melting point (°C)

Formula weight

(calctd) Found %C

%H

%N

m(C@N) (cm1)

leff (BM)

Ligand (L)

12 g (88.4) 1.28 (86.3) 1.30 (88.3) 1.20 (81.5) 1.28 (76.2) 0.84 (57.3) 0.99 (65.2) 1.16 (76.3) 0.99 (76.3)

Yellow

240–242

679 741

1607 m

1.82

1607 m

2.85

219–221

737

1607 m

3.57

Light Yellow Light Brown Brown

233–235

742

1608 m

–

215 Decom. 185–186

732

1615 m

5.47

1614 m

1.87

Green

206–207

763

1612 m

3.69

Dark Brown

154 Decom.

795

(4.12) 4.87 (3.77) 3.77 (3.80) 4.03 (3.80) 4.06 (3.77) 3.65 (3.82) 4.00 (3.68) 3.62 (3.67) 3.91 (3.52) 3.77

–

141 Decom. 217–219

(2.94) 3.07 (2.42) 2.61 (2.44) 2.65 (2.44) 2.84 (2.42) 2.88 (2.46) 2.85 (2.36) 2.43 (2.36) 2.57 (2.26) 2.61

1617 m

Pale Green Pale Yellow Brown

(49.98) 49.64 (45.34) 45.58 (45.65) 45.55 (45.59) 45.29 (45.28) 46.50 (45.90) 45.79 (44.21) 44.97 (44.03) 44.30 (42.26) 43.07

1611 m

4.55

[CuL] [NiL] [CoL] [ZnL] [MnL] [TiLCl] [VLCl] [FeLNO3]

736

760

m : Medium.

DMF show few bands in the UV–visible region. The absorption bands below 300 nm are practically identical and can be assigned to p ? p* transitions in the benzene ring and azomethine (AC@N) groups. The absorption bands observed between 300 and 400 nm range are due to the n ? p* transitions of imine groups [13]. The n ? p* and p ? p* transitions of the ligand shifted higher wavelengths in UV–Vis spectra of the complexes. These bands are very strong and d–d transitions are too weak, so d–d transitions could not be seen [34].

Magnetic measurements and molar conductivity The magnetic moment measurements of the compounds were carried out at 25 °C using a magnetic susceptibility balance. Magnetic susceptibility measurements provide data to characterize the structure of the complexes. The magnetic moments of the complexes were given in the experimental section of complexes. This technique gives the information whether Ni(II) complexes are tetrahedral or square planar. The complexes are non-electrolytes as shown by their molar conductivities (KM) in DMF (dimethyl formamide) at 103 M, which are in the range of 5–10 X1 cm2 mol1 [22,27,32].

1

H NMR and

13

C NMR

The 1H NMR and 13C NMR spectra of the ligand and its diamagnetic complexes were recorded in DMSO-d6 and reported along with possible assignments in the experimental section. Comparison of chemical shifts of the ligand with those of the complexes show that the signal due to phenolic proton of the ligand was absent in NMR spectra of the complexes, suggesting coordination after deprotonation. The azomethine proton (ACH@NA) undergoes a significant shift, indicating coordination of the azomethine nitrogen. More detailed information about the structure of the ligand was provided by 13C NMR spectra. All the carbon atoms, heteroatomic and aromatic groups were found in their expected regions [35]. In the spectra of diamagnetic complexes, these signals shifted downfield due to the increased conjugation and coordination to the metal ions. The number of protons and carbons calculated from the integration curves agreed with those obtained from the values of the CHN elemental analysis [36].

TGA studies The thermal stability of the ligand and its complexes was investigated by thermo gravimetric analysis. The thermo gravimetric analysis (TGA) (Table 2) curves were obtained at a heating rate of 10 °C/min in a nitrogen atmosphere over a temperature range of 50–900 °C. The ligand was stable up to 290 °C and its decomposition started at this temperature. The ligand underwent decomposition in one stage (290–492 °C). The DTG peak of this weight loss is 321 °C and it can be attributed to loss of C12H6Br2. The Cu(II) was stable up to 301 °C and its decomposition started at this temperature. The complexes underwent decomposition in one stage (301–500 °C). The one stage (301–500 °C) with DTG peak at 329 °C corresponds to loss of C12H6Br2. The Ni(II) was stable up to 252 °C and its decomposition started at this temperature. The complexes underwent decomposition in two stages (252–490 °C). The first (252–405 °C) with DTG peak at 328 °C corresponds to loss of C12H6Br2. The second stage (416– 490 °C) with DTG peak at 449 °C corresponds to loss of CH2CH2. The Co(II) was stable up to 290 °C and its decomposition started at this temperature. The complexes underwent decomposition in one stage (290–350 °C). The one stage (290–350 °C) with DTG peak at 322 °C corresponds to loss of C12H6Br2. The Zn(II) was stable up to 267 °C and its decomposition started at this temperature. The complexes underwent decomposition in one stage (267–410 °C). The one stage with DTG peak at 346 °C corresponds to loss of C12H6Br2 and OCH2CH2O. The Mn(II) was stable up to 250 °C and its decomposition started at this temperature. The complexes underwent decomposition in one stage (250–390 °C). The one stage with DTG peak at 316 °C corresponds to loss of C12H6Br2 and OCH2CH2O. The Ti(III) was stable up to 205 °C and its decomposition started at this temperature. The complexes underwent decomposition in three stages (205–648 °C). The first (205–305 °C) with DTG peak at 277 °C corresponds to loss of Cl. The second stage (340– 430 °C) with DTG peak at 385 °C corresponds to loss of C12H6Br2. The third stage (450–648 °C) with DTG peak at 535 °C corresponds to loss of OCH2CH2O. The V(III) was stable up to 230 °C and its decomposition started at this temperature. The complexes underwent decomposition in three stages (230–557 °C). The first stage (230–390 °C) with DTG peak at 280 °C corresponds to loss of C12H6Br2. The second stage (430–557 °C) with DTG peak at 535 °C corresponds to loss of OCH2CH2O.

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S. Ilhan et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 118 (2014) 632–642 Table 2 TGA data of the complexes. Compounds

First step, °C (DTG °C) Weight loss%, Calculated (found) Decomposition group

Ligand (L)

290–492 (321) 45.6 (44.5) C12H6Br2 301–500 (329) 41.8 (40.2) C12H6Br2 252–405 (328) 42.1 (41.2) C12H6Br2 290–350 (322) 42.1 (41.2) C12H6Br2 267–410 (346) 49.9 (49.1) C12H6Br2 and OCH2CH2O 250–390 (316) 46.5 (48.1) C12H6Br2 and OCH2CH2O 205–305 (277) 4.7 (5.2) Cl 230–390 (280) 4.7 (5.2) Cl 200–400 (255) 46.8 (45.2) C12H6Br2

[CuL]

[NiL]

[CoL]

[ZnL]

[MnL]

[TiLCl]

[VLCl]

[FeLNO3]

The Fe(III) was stable up to 200 °C and its decomposition started at this temperature. The complexes underwent decomposition in one stage (200–400 °C). The one stage (200-400 °C) with DTG peak at 255 °C corresponds to loss of C12H6Br2. The weight losses for Cu(II), Ni(II), Co(II), Zn(II), Mn(II), Ti(III), V(III) and Fe(III) complexes were found to be approximately the same, when expressed as the percentages calculated stoichiometrically from their chemical formulas given in Table 2. Single crystals of the complexes could not be isolated from any solutions, thus no definitive structure could be described.

Second Step, °C(DTG °C) Weight loss%, Calculated (found) Decomposition group

Third step, °C (DTG °C) Weight loss%, Calculated (found) Decomposition group

416–490 (449) 45.9 (45.3) CH2CH2

340–430 (385) 45.5 (44.3) C12H6Br2 430–557 (535) 45.3 (46.8) C12H6Br2

450–648 (535) 53.4 (53.8) OCH2CH2O

However, the analytical, spectroscopic and magnetic data enable us to propose the possible structures. Theoretical studies Theoretical NMR calculations were carried out by performing Gaussian 09 program and for the visualization all of the input and output files, GaussView 5.0.9 program was used [37–39]. 1,2-Bis(2-(5-bromo-2-hydroxybenzilidenamino)-4-chlorophenoxy)ethane (L) was optimized (Fig. 5) with restricted Becke-3–

Fig. 5. Optimized 3D structure of 1,2-Bis(2-(5-bromo-2-hydroxybenzilidenamino)-4-chlorophenoxy)ethane (L).

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Table 3 Regression analysis data of the theoretical and experimental NMR shifts. Code

Compared methods 1

a

b

R

Standard error

L

Experimental and HF/6/31G(p)- H NMR

0.9179

2.0611

0.6375

2.1520

L

Experimental and B3LYP/6-311G(2d,p)-1H NMR

0.9179

2.7178

0.6375

2.1520

L (58 numbered proton was neglected)

Experimental and HF/6/31G(p)-1H NMR

1.2631

-0.6595

0.9301

0.9419

L (58 numbered proton was neglected)

Experimental and B3LYP/6-311G(2d,p)-1H NMR

1.2631

0.2442

0.9301

0.9419

Table 4 Voltammetric results in 100 mV s1 vs. Ag/AgCl. Ec: cathodic, Ea: anodic. Compound

Ec (V)

Ea (V)

L CuL NiL CoL

Ic: 0.28, IIc: 1.76, IIIc: 1.97 Ic: 1.10 Ic: 0.42, IIc: 1.98 Ic: 1.78, IIc: 2.00

Ia: +0.65 Ia: 0.92, IIa: 0.22 Ia:1.87, IIa: +0.15, IIIa: +0.57 Ia: +0.11, IIa: +0.67, IIIa: +0.79

Lee–Yang–Parr (RB3LYP) level of Density Functional Theory (DFT) method, using the 6-311G basis set. Both Hatree–Fock (HF) and DFT methods were used for theoretical calculations [37–39]. Theoretical NMR calculation was realized by using the Gauge-Independent Atomic Orbital (GIAO) method at gas phase [37–43]. In this calculation tetramethylsilane’s proton NMR shifts were used as reference for the theoretical NMR calculation of the ligand. Additionally, a regression analysis was also carried out to determine the correlation between theoretical and experimental 1H NMR shifts (Table 3). According to the regression analysis there is a good conformity between theoretical and experimental NMR shifts but, as can be seen in Fig. 6, there is a big difference between both NMR values. Those NMR shifts can be assigned to the theoretical and experimental NMR shifts of ligand’s hydroxyl groups. Linear regression analysis was carried out according to the following equation: 1

R = 0.6375, SE = 2.1520. Then, 58 numbered OH group’s proton NMR shift was neglected (Figs. 7 and 8 and Table 3) and regression analysis was carried out again. In this case, comparisons of experimental proton NMR shifts to HF/6-31G and B3LYP/6-311G methods a, b, R and SE values were found respectively, 1.2631, 0.6595, 0.9301, 0.9419; 1.2631, 0.2442, 0.9301, 0.9419. This regression analysis shows that if OH group’s proton NMR shift is neglected, a better adjustment between experimental and theoretical NMR shifts is reached and more accurate a, b, R and SE values are found (Table 3). The difference between experimental and theoretical NMR shifts is owing to the acidic properties of phenolic protons and, execution of the theoretical calculations at gas phase

1

dExperimentalH NMR ¼ a:dTheoreticalH NMR þ b: Even though it was determined that there is a good adjustment (Fig. 6) between experimental and theoretical values but, regression analysis results are not good enough (Table 3). As can be seen in Table 3, comparison of experimental-1H NMR values to HF/6-31G and B3LYP/6-311G 1H NMR values respectively a, b, correlation coefficient (R) and standard error (SE) were found as; a = 0.9179, b = 2.0611, R = 0.6375, SE = 2.152; a = 0.9179, b = 2.7178,

16

Fig. 7. The plot of experimental 1H NMR and theoretical (HF/6-31G) 1H NMR values (by the neglecting of 58 numbered proton).

(B3LYP/6-311G (2d,p)) 1H NMR-Experimental 1H NMR (HF/6-21G(d))-1H NMR-Experimental 1H NMR

Experimental 1H NMR(ppm)

14 12 10 8 6 4 2 2

4

6

8

10

12

1

Theoretical (HF/6-21G(d) ve B3LYP(6-311G(2d,p) H NMR(ppm) Fig. 6. The plot of experimental and theoretical 1H NMR values.

Fig. 8. The plot of experimental 1H NMR and theoretical (B3LYP/6-311G) 1H NMR values (by the neglecting of 58 numbered proton).

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Fig. 9. Cyclic voltammograms of 1  103 mol L1 compound solutions in DMF at glassy carbon electrode; A:L, B:CuL, C:NiL, D:CoL in v: 100 mV s1.

[40–43]. So, all of the results comply with previously published articles and literature [40–43]. Cyclic voltammetry of the complexes The electrochemical behavior of the CuL compex is presented in Fig. 9B. In the CV measurements upon scanning cathodically at the negative potential side (from +1.0 to 2.3 V at 100 mV s1), the CV of CuL is characterized by one cathodic peak (Ic at about 1.10 V) and two anodic waves (Ia and IIa at about 0.92 and 0.22 V). DEp for Ia/Ic from this redox couple was also found to be 200 mV. It indicates a quasi-reversible electron transfer in the electrode reaction. We should bear in mind that [43–46] after occurring the oneelectron reduction process corresponding to [CuIIL]/[CuIL], part of [CuIL2] species are chemically decomposed to copper metal (reaction 1). Therefore, it may be assumed that the corresponding anodic waves (Ia–IIa) are associated with the reoxidation of electrodeposited copper metal to free Cu+ and Cu2+ according to the reaction 2:

½CuII L $ Cuþ2 þ L þ e $ Cuþ þ L

ð1Þ

Cuþ $ Cuþ2 þ e

ð2Þ

At higher scan rates (P200 mV s1) a new reduction wave occurred from Ic reduction peak than in the negative region (Fig. 10B). When increasing scan rate, the anodic peak IIa turned into a flat waveform. The voltammograms of NiL complex investigated in the same experimental conditions (from +1.0 V to 2.3 V at 100 mV s1 in Fig. 9C), two waves (Ic and IIc at about 0.42 and 1.98 V, respectively) and three anodic waves (Ia, IIa and IIIa at about 1.87, +0.15 and +0.57 V, respectively). In the potential range of 2.3 V to +1.0 V at scan rate of 100 mV s1, on the cathodic side, the CV of CoL complex (Fig. 9D) shows two cathodic peaks (Ic and IIc at about 1.78 and 2.00 V, respectively) and three anodic peaks ((Ia, IIa and IIIa at about +0.11, +0.67 and +0.79 V, respectively). At higher scan rates (P200 mV s1), Ia peak turned into a broad oxidation peak and IIa peak was not observed (Fig. 10D). From the CVs (Fig. 10), it was found that the initial oxidation peak current of L, CuL, NiL and CoL gradually increased and a negative shift in the peak potential existed with increasing scan rate. From the results obtained between 50 and 1000 mV s1, a plot of logarithm of peak current significantly correlated with the logarithm of scan rate for all L, CuL, NiL and CoL with slopes between 0.43, 0,51, 0.49 and 0.53, respectively (correlation coefficient between 0.981, 0.957, 0.991 and 0.949) (Table 4). These findings

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Fig. 10. Cyclic voltammograms of 1  103 mol L1 compound solutions at different scan rates; A: L, B: CuL, C: NiL, D: CoL.

showed that the redox processes were predominantly diffusion controlled in the whole scan rate range studied [43–46]. Antioxidant studies DPPH scavenging activity It is well known that free radicals are major factor in biological damages in living organisms [47]. The DPPH radical-scavenging

Fig. 11. Radical-scavenging activity on DPPH radicals (%) of the compounds.

process is a widely used to determine the ability of various extracts and compounds to scavenge free radicals generated from DPPH reagent. Fig. 11 shows DPPH radical-scavenging activities percent of the samples. The samples showed dose-dependent DPPH radicalscavenging activities. Ligand (L), Cu(II), Ni(II), Co(II), Zn(II), Mn(II), Ti(III), and Fe(III) complexes exhibited weak DPPH scavenging activity. The maximum DPPH scavenging activity of about 59.1% was observed with V(III) at concentration of 100 mg/L. The experimental results of this study showed in agreement with the previous reports of Agirtas et al. [48,49]. Metal chelating activity The prooxidant metal chelation is one of the most important mechanisms of secondary antioxidants’ action. Chelation of metals by certain compounds decreases their prooxidant effect by reducing their redox potentials and stabilizing the oxidized form of the metal [50]. Effects of the ligand and its metal complexes on metal chelating activity are presented in Fig. 12. The chelating ability of the test samples and EDTA is concentration-dependent. The chelating activity order of the compounds from maximum to minimum was found to be ligand (L) > Zn(II) > Mn(II) > Ti(III) > Ni(II) > Co(II) > V(III) > Cu(II) > Fe(III) at a concentration of 100 mg/L.

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641

capped octahedron in which a seventh ligand has been added to triangular face around the central metal ions [51,12,52–55]. Theoretical calculations and regression analyses show that experimental and theoretical 1H NMR values are compatible so, it means that suggested structure for the ligand (L) is correct and it is a proof for the successfully synthesizing of the new di-mine ligand (L) [40– 43,50]. The reduction–oxidation properties of the ligand and its complexes were studied in details and found that redox processes were predominantly diffusion controlled in the whole scan rate range studied [43–46]. The maximum DPPH scavenging activity of about 59.1% was observed with V(III) complex. Antibacterial results compared to standard medicines have indicated that some of studied compounds were active but, their activities were lesser than the standard medicines.

Fig. 12. Chelating effect of compounds on ferrous ion.

Acknowledgements Cl Br

Cl Br

This study was supported by Scientific Research Projects Unit of _ Siirt University (Project code: BAP-2011-SIÜFED-YL1), (Turkey).

H2C

O

O

N M

H2C

O

X

H2C

O

N M

H2C O

N

O

O

N

Appendix A. Supplementary material

Cl O

Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.saa.2013.08.069. References

Cl Br M= Zn(II), Cu(II), Co(II), Ni(II), X=M= Fe(III), X= -NO3

Cl Br M= (Ti(III) and V(III)

Fig. 13. Suggested structures of the complexes.

Ligand (L), Cu(II) and Mn(II) showed high metal chelating activity. The metal chelating activities were 97.9%, 97.5% and 96.2% for Ligand (L), Cu(II) and Mn(II), respectively at 100 mg/L. From that point of view, after toxicological test systems, ligand (L), Cu(II) and Mn(III) can be used as a standard material for chelating agent like EDTA. Antibacterial activity In this research paper, the antibacterial activities of the samples were studied by the disk diffusion method at concentration of 500 mg/L against different bacteria. The Schiff base derived from 5-bromosalicylaldehyde with 1,2-bis(4-chloro-2-aminophenoxy)ethane and its all metal complexes showed weak antibacterial activities against E. coli, while Ligand (L), Cu(II), Ni(II), Co(II), Zn(II), Ti(III), V(III) and Fe(III) complexes showed weak antibacterial activities against B. subtilis except Mn(II). On the other hand, Ni(II) complex exhibited strong antibacterial activity against M. luteus, Zn(II) and Mn(II) showed weak antibacterial activities against M. luteus. The ligand and its all metal complexes did not exhibit antibacterial activities against P. aeruginosa. The results compared to standard medicines have indicated that some of studied compounds were active but, their activities were lesser than the standard medicine. Conclusion A novel Schiff base and its eight complexes were prepared and characterized. General structures of the complexes are shown both Figs. 4 and 13. The Ni(II), Co(II), Zn(II) and Mn(II) complexes show probability tetrahedral geometry, Cu(II) complex probability show square planar geometry, Fe(III) complex probability show square pyramid geometry, V(III) and Ti(III) complexes probability show a

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