- Email: [email protected]
Synthesis, structural and biochemical activity studies of a new hexadentate Schiff base ligand and its Cu(II), Ni(II), and Co(II) complexes
Journal of Molecular Structure 1099 (2015) 189e196
Contents lists available at ScienceDirect
Journal of Molecular Structure journal homepage: http://www.elsevier.com/locate/molstruc
Synthesis, structural and biochemical activity studies of a new hexadentate Schiff base ligand and its Cu(II), Ni(II), and Co(II) complexes Pinar Ekmekcioglu a, Nevin Karabocek a, *, Serdar Karabocek a, Mustafa Emirik b a b
Department of Chemistry, Karadeniz Technical University, Trabzon, Turkey an University, Rize, Turkey Department of Chemistry, Recep Tayyip Erdog
a r t i c l e i n f o
a b s t r a c t
Article history: Received 19 March 2015 Received in revised form 14 June 2015 Accepted 15 June 2015 Available online 20 June 2015
A new Schiff base ligand (H2L) and its metal complexes have been prepared and characterized by elemental analysis, magnetic moment and spectral studies. The comparative in-vitro antimicrobial activities against various pathogens with reference to known antibiotics activity under the standard control of different concentrations revealed that the metal complexes (6e8) showed enhanced antimicrobial activities in general as compared to free ligand. As an exception, the free ligand showed better activity against Trichoderma. The antifungal activity experiments were performed in triplicate. The order of biochemical activity for metal complexes were observed as in the following. CuL > CoL > NiL, which is exactly same as the order of stability constants of these complexes. Additionally, we performed DFT and TD-DFT calculation for free ligand and Cu(II) complex to support the experimental data. The geometries of the Cu(II) complex have been optimized using the B3LYP level of theory. The theoretical calculations confirm that the copper (II) center exhibits a distorted square pyramidal geometry which is favored by experimental results. © 2015 Elsevier B.V. All rights reserved.
Keywords: Hexadentate Schiff base Biological activity Copper (II) complex
1. Introduction Polydentate Schiff base ligands are well-studied area of research in coordination chemistry due to having remarkable biological activities and capable of forming very stable complexes with transition metals. These ligands have preparative accessibilities, structural variety, different coordination numbers and crystalline architectures [1,2]. Recent research indicates that the antibacterial activities of the coordinated metal complexes were increased according to Schiff bases [3]. The Schiff bases and their metal complexes play a key role in the coordination chemistry [4e6]. Schiff base metal complexes have interested for their noteworthy contributions in magnetism, material science [7] and catalysis such as carboxylation, reduction, oxidation, epoxidation, and hydrolysis reactions [8]. Schiff bases have been prepared by the reaction of primary amines and carbonyl compounds [9] and widely used chelating agents for the synthesize transition metal complexes. Their copper (II), nickel (II), and cobalt (II) complexes with pseudo
* Corresponding author. E-mail address: [email protected] (N. Karabocek). http://dx.doi.org/10.1016/j.molstruc.2015.06.051 0022-2860/© 2015 Elsevier B.V. All rights reserved.
halides are well known for preparative accessibilities, exhibiting the flexibility of the coordination center [10]. In this work, a new Schiff base ligand and its copper (II), nickel (II), and cobalt (II) complexes have been synthesized. The complex structures have been characterized by magnetic, physical, elementary analyses and spectral methods. The free ligand and its metal complexes were evaluated for antimicrobial activity against S. aureus, Escherichia coli, A. Niger and Trichoderma. The free ligand (H2L) activity increases against Trichoderma. DFT and TD-DFT calculations were also performed to support the experimental results. 2. Experimental 2.1. Materials and spectral measurements 2,20 -[1,2-phenylenebis(methyleneoxy)]dibenzaldehyde(3) have been prepared according to reference [11]. C, H and N content analysis were carried out a Carlo Erba 1106 elemental analyzer (Milan, Italy). Metal complex structures were degraded with concentrated nitric acid, then solutions were neutralized with aqueous ammonia solution and the metal ions titrated with EDTA [12]. Mass spectra (ESI) were carried out on Micro mass Quattroo
190
P. Ekmekcioglu et al. / Journal of Molecular Structure 1099 (2015) 189e196
LC-MS/MS spectrophotometer (Manchester, United Kingdom). 1H NMR and 13C- NMR spectra were recorded on an Agilent 400eNMR DD2 MHz spectrometer in the CDCl3 solvent. IR and UVeVis spectra were carried out on Perkin Elmer FT-IR Spectrometer (KBr disk, 4000e400 cm1) and on a Perkin Elmer Lambda 25 UV/VIS Spectrometer (USA), respectively. Magnetic susceptibilities were carried on a PAR model 155 vibrating in room temperature. All chemicals were obtained from local suppliers and used as received purity. The test microorganisms; E. coli RSKK 340, S. aureus RSKK 96090, A. niger Z10, T. harzianum, (Rifai) were obtained from the Refik Saydam National Public Health Agency. 2.2. Synthesis of 2,20 -{1,2-phenylenebis[methyleneoxy-2,1phenylene(Z)methylylidene-nitrilo]}dibenzenethiol, (H4L), (5) A solution of dialdehyde (3) (1.73 g, 5 mmol) and 2aminothiophenol (1.25 g, 10 mmol) were refluxed for 10 h in EtOH (25 mL). This solution was then poured in to water (50 mL) and the solid product filtered off. The crude product was crystallized from ethanol with decolorizing charcoal. The compound (5), M.P. 107 C, was isolated in 60% yield; IR (KBr disc.)/cm1 1594 y(C]N), and 1228 y(CeO) and 2600 y(SeH); 1H NMR (CDCl3)/ ppm d: 7.5e8 (d, 2H, N]CeH), 7.0e7.8 (m, 20H, aryl-H), 5.4 (s, 4H, eOCH2), 4.3 (b s., 2H, Aryl-SH), 1.6 (b s., water in CDCl3). MS(ESI): m/ z ¼ 579 [H2L.H2O]þ Elemental Anal. Calcd. (%): C, 70.5; H, 5.2; Found: C, 70.4; H, 5.1 for C34H28N2O2S2. 2.3. Synthesis of copper(II), nickel(II) and cobalt(II) complexes (6e8) Metal complexes (6e8) have been prepared by the same method. A solution (25 mL) of ligand (0.6 g, 1 mmol) was added dropwise to an ethanolic solution (10 mL) of M(ClO4)2.6H2O (1 mmol). The mixture was heated at 60 C under reflux with stirring for 4 h. Then, hot water was added dropwise to the mixture and the solution was left to crystallize at room temperature. The products were filtered off, washed with H2O, and dried over P2O5. C34H26CuN2O2S2, (6): elemental Anal. Calcd. (%): C, 62.0; H, 4.6; Cu, 9.6; Found: C, 62.0; H, 4.5; Cu, 9.5. MS (ESI): m/z ¼ 657.9 [CuL.2H2O]þ. Yield, a grey solid: 0.5 g (70%). C34H26NiN2O2S2, (7): elemental Anal. Calcd. (%): C, 65.9; H, 4.2; Ni, 9.5; Found: C, 66.0; H, 4.1; Ni, 9.4. MS (ESI): m/z ¼ 617.14 [NiL]þ, yield, a brown solid: 0.4 g (64%). C34H26CoN2O2S2, (8): elemental Anal. Calcd. (%): C, 66.0; H, 4.2; Co, 9.5; Found: C, 66.1; H, 4.1; Co, 9.4. MS (ESI): m/z ¼ 618 [CoL]þ, a dark grey solid: 0.4 g (70%). 2.4. Antimicrobial activity The antimicrobial activity tests were carried out according to reference [13] by paper disc method. The experimental results were compared with ciprofloxin. By the mycelia dry weight (MDW) method, the Schiff base ligand and its metal complexes, metal salts, and the control (DMSO) were screened for antifungal activity against the fungi A. niger and Trichoderma at 0.5 and 1 mgL1 [14]. The antifungal activity tests were carried out according to reference [15]. The percentage error was found to be ±0.01. The obtained results indicate that the ligand and its metal complexes arrested the growth of fungi. The results of the antimicrobial and antifungal activity were given in the Table 4. 2.5. Computational methods The geometrical optimizations have been performed with the DFT/B3LYP [16,17] level of theory without any symmetry constrain
using the GAUSSIAN 03 software package [18]. For C, H, N and O atoms, the 6e311 þ G(2d,p) basis set was employed, while for Cu the LANL2TZ(f) basis set obtained from the EMSL Basis Set Library with an effective core potential was assigned [19,20]. The calculations of vibrational frequency were performed to ensure that the optimized geometries at the local minima with the positive Eigen values. MEP mapped surface and the frontier orbital schemes were obtained by the same method. Vertical electronic excitations based on optimized geometries were carried out according to reference [21,22]. The lowest 150 singletesinglet transitions of Cu (II) complex were calculated with the computer. GaussSum [23] was used to obtain the fractional contributions of the various fragment to each molecular orbital. GaussView 5.0 was used to visualize the results of computations [24]. 3. Results and discussion The ligand was synthesized in EtOH by reaction dialdehyde (3) (1.73 g, 5 mmol) and 2-aminothiophenol (1.25 g, 10 mmol) (Scheme 1). The Schiff base was characterized by elemental analysis, 1H NMR, 13C NMR, IR, and mass spectral data. The Cu (II), Ni (II), and Co (II) complexes have been obtained and characterized by elemental analysis, magnetic moment, UVeVis, and mass spectral data. The N2S2O2 units of Schiff base ligand (H2L) are available for the complexation with Cu (II), Ni (II), and Co (II) metal ions. 3.1. NMR spectra In the 1H NMR spectrum of Schiff base ligand, the following signals were observed in CDCl3: doublet signals at d ¼ 8e7.5 ppm were attributed to tautomeric hydrogen of eC]NH group (d, 2H). The signals of Aryl-H were seen at d ¼ 7.0e7.8 (m, 20H) ppm. The signal of eCH2-O- was observed at 5.4 (s, 4H) ppm. The signal of Aryl-SH was observed at 4.3(b. s, 2H) ppm [25]. Signal of water in CDCl3 was observes at 1.6 ppm [26]. Integrated data are consistent with the molecular formula of the ligand. The seventeen resonance signals were observed in the 13C NMR spectra of the Schiff base ligand (H2L), which were also consistent with the formula for H2L (Fig. 1). 3.2. Mass spectra The mass spectra of the ligand and its metal complexes were recorded in acetonitrile solution. The mass spectra (ESI-MS) exhibited the molecular ion at m/z ¼ 579 [H2L.H2O]þ for the free Schiff base ligand, which indicated formation of ligand. The molecular ion peaks appeared (m/z, ESI) at 657.9 [CuL.2H2O]þ at 617.14 [NiL]þ and at 618.45 [CoL]þ for the CuL, NiL, and CoL, respectively. The mass spectra confirmed the formation of the ligand and its metal complexes given molecular structure in Fig. 2. 3.3. IR spectra Characteristic IR bands were given in Table 1. The band at 2600 cm1 and the strong band at 1594 cm1 might be assigned to n(SeH) and n(C¼ N) vibration of the ligand, respectively [27]. In the metal (II) complexes, n(C]N) vibrations were shifted to lower frequency field (z10 cm1), and n(SeH) vibrations could not be observed, after the complex formations [28]. In the IR spectra of metal complexes, the peaks appearing between 430 and 480 cm1 are attributed to n(MN) [28,29]. The changes in the n(C]N) vibration bands and the disappearing of vibration band of n(SeH) support the concept of coordination of the ligand through the Schiff base donor atoms.
P. Ekmekcioglu et al. / Journal of Molecular Structure 1099 (2015) 189e196
Scheme 1. Preparation of the hexadentate Schiff base ligand, (H2L).
Fig. 1.
13
C-NMR spectrum of the Schiff base Ligand (H2L).
191
192
P. Ekmekcioglu et al. / Journal of Molecular Structure 1099 (2015) 189e196
14184, and 31746 cm1 were assignable to T1g(F) / 4T2g(P),4T1g(F) / 4T1g(P), and 4T1g(F) / 4A2g(P) transitions, respectively. These bands and measured magnetic moment (3.7 BM) support the octahedral Co(II) complex [28,32e34]. Furthermore, ded transition bands were observed as weak signals in all complexes. The calculated values of the ligand field splitting energy (10 Dq), Racah inter electronic repulsion parameter (B), covalent factor (b), ratio v2/v1, and ligand field stabilization energy (LFSE) were given in Table 3. The obtained data support the proposed geometry of the Cu (II), Ni(II), and Co(II) complexes [34]. 4
N
O
S
M O
S N
3.5. Antimicrobial activity
M = Cu(II), Ni(II), Co(II) Fig. 2. Proposed structures for the copper(II), nickel(II) and cobalt(II) complexes.
3.4. Magnetic properties and electronic absorption spectra The electronic spectra of the Cu (II), Ni (II), and Co (II) complexes were recorded in DMSO. The spectral data were given in Table 2. In the UV spectra of the Cu (II) complex two bands were seen at 13192 and 30770 cm1, owing to a 2Eg / 2T2g transition and charge transfer. The magnetic moment of the Cu(II) complex is 1.85 B M. which agrees with the known values for Cu(II) complexes in octahedral geometry [28,30]. Ni (II) complex displays bands at 11900, 14400, and 33000 cm1 assignable to a 3 3 3 3 A2g / T2g(F), A2g / T1g(F), and 3A2g / 3T1g(P), respectively. Magnetic moment has been obtained as 2.80 B M. which suggest octahedral geometry for Ni(II) complex [28,31]. In the electronic spectra of Co(II) complex, observed three bands at 12500 (740),
Table 1 Characteristic IR bands of the free ligand and its metal complexes (in cm1). Compound
n(H2O)
n(SeH)
n(C]O)
n(C]N)
n(CeO)
n(MN)
3 H2L CuL NiL CoL
e 3400 e e e
e 2600 e e e
1692 e e e e
e 1594 1579 1579 1579
1233 1228 1214 1214 1214
e e 455 430 480
The free ligand and its metal complexes were appraised for biochemical activity against S. Aureus, E. coli and fungi A. Niger, Trichoderma. The experimental results were given in Table 4. The free ligand and its metal complexes have been exhibited antibacterial activity against both strains according to these results. The metal complexes exhibit higher activity than the free ligand. Ciprofloxin were used as a standard in the antibacterial inhibitions. The free ligand and its metal complexes showed lower antimicrobial activity than the standard. The metal salts used for synthesis of metal complexes exhibit antimicrobial activities [35,36]. The activity of metal complexes can be explained on the basis of Overtones and Tweedy's concepts [37]. Antibacterial inhibition was directly proportionate to the concentration of reagent. The results showed that the Cu(II) complex exhibits higher activity against each class of organism. The structures of metal complexes are strictly related to the activity [38]. The higher activity of the Cu(II) complex may be caused to its higher stability constant. The free ligand and its metal complexes show more activity against gramenegative E. coli than against gram-positive S. Aureus. Antibacterial activity can be ordered as CuL > CoL > NiL, similar to earlier observations [28,39]. Antifungal activity results showed that all the metal complexes are more toxic than the ligand [40]. The antifungal activity was improved several times on being coordinated with metal. The metal complexes activity increases as the stability of the complex increases. The metal complex activities follow the order CuL > CoL > NiL, which is exactly same as the order of stability constants of these complexes. The experimental results shows that the Cu (II) complex is more active than the ligand against A. niger. However, the free form of the Schiff base ligand showed better activity against Trichoderma. Table 4 Antibacterial activities of (diameter inhibition zone in mm) and antifungal activity weight (mg) (% inhibition) of the ligand and metal complexes. Antibacterial activity (mg mL1)
Table 2 Physical data of the ligand and its metal complexes. a
Compound
Color
meff
H2L CuL NiL CoL
Yellow Grey Brown Dark-grey
e 1.85 2.8 3.7
a
E. coli 1
Yield
Sol.l
60 70 64 70
e 13.192, 30.770 11.900, 14.400, 33.000 12.500, 14.184, 31.746
a max
(cm
*)
Per metal atom at 297 K (B.M.). *UVeVis spectra were recorded in DMSO.
Conc. Control(DMSO) Ciprofloxin H2L CuL NiHL CoHL
0.5 0 40 10 20 12 15
1 0 45 12 25 15 20
Antifungal activity (mg mL1)
S. Aureus
A. niger
0.5 0 42 10 15 10 12
0.5 0 74 80(15) 50(30) 60(35) 65(30)
1 0 44 15 20 12 15
Trichoderma 1 0 72 60(10) 30(70) 20(75) 30(70)
0.5 0 65 50(25) 35(50) 35(55) 25(65)
1 0 60 40(50) 30(70) 25(60) 25(65)
Table 3 Ligand field parameter of the metal complexes. Complex
Ligand field splitting energy (Dq cm1)
Racah interelectronic repulsion parameter (B cm1)
Covalent factor (b)
b (%)
Ratio v2/v1
LFSE (kcal mol1)
CuL NiL CoL
13192 11.900 12500
96.06 1030 971
e 0.75 0.58
e 19.5 3.81
e 1.03 1.05
37.70 34.0 35.70
P. Ekmekcioglu et al. / Journal of Molecular Structure 1099 (2015) 189e196
193
Fig. 3. The optimized molecular geometries of (a) free ligand and (b) its Cu (II) complex, respectively. Hydrogen atoms were omitted for clarity.
Table 5 The coordination distances in (a) 5- coordinated (b) 6-coordinated (c) 6-coordinated Cu(II) complexes. Atoms
CueO14 CueO15 CueS62 CueS63 CueN40 CueN41
Distances (Å) (a)
(b)
(c)
3.324 2.338 2.311 2.346 2.176 2.287
2.491 2.483 2.416 2.416 2.032 2.032
2.493 2.367 2.341 2.345 2.150 2.231
3.6. Quantum chemical calculations
Fig. 4. MEP mapped surface of the ligand.
All calculations were performed using DFT/B3LYP method with 6e311 þ G(2d,p)) basis set for free ligand and the combination of 6e311 þ G(2d,p)) and LanL2TZ(f) basis sets for its Cu(II) complex. The molecular structures, orbital shapes (HOMO-LUMO) and molecular electrostatic potential (MEP) of the mentioned free ligand and its Cu(II) complex were plotted in GaussView 5 program. The optimized molecular structures of the free ligand and of its Cu (II) metal complex are given in Fig. 3(a) and (b), respectively.
Fig. 5. The molecular geometries of the most stable three Cu(II) metal complexes. (a) 5- coordinnated (b) 6-coordinated (c) 6-coordinated Cu (II) complexes.
194
P. Ekmekcioglu et al. / Journal of Molecular Structure 1099 (2015) 189e196
Table 6 Selected Bond Lengths (Å) and Angles ( ) for optimized Cu(II) Complex. CueO14 CueS62 CueN40 S62eCueS63 N41eCueN40 N41eCueO14 N41eCueO15 O14eCueN40 S62eCueO15 S63eCueO15 O15eCueN40
2.493 2.341 2.150 99.893 159.400 73.207 89.595 87.679 159.745 96.712 77.005
CueO15 CueS63 CueN41 O14eCueO15 N41eCueS63 N41eCueS62 O14eCueS63 O14eCueS62 S62eCueN40 S63eCueN40
2.367 2.345 2.231 72.160 84.798 103.339 155.123 96.439 86.039 111.968
Complexation behavior of the ligand was analyzed by molecular electrostatic potential (MEP). MEP mapped surface gives information about the interaction of the molecules. The red regions of MEP surface are interpreted as the negative side of the ligand while yellow regions show positive electrostatic potential. MEP mapped surface of the ligand is given in Fig. 4. The electron rich red regions between two sulfur atom and around oxygen and nitrogen are
theoretically potential active sides of the ligand to positively charged metals as expected. Thus, the coordination is expected to be formed on the red regions of Fig. 4 in the metal complex. Furthermore, DFT calculations were performed to determine the stable geometric structure of the Cu(II) complex. The most stable conformations, 5-coordinated and two 6-coordinated Cu (II) complexes were compared with regard to their SCF energies. The obtained results were given in Fig. 5. According to this results, hexadentate Cu (II) complex is more stable than the penta-dentate Cu (II) complex which is consistent with experimental results. Additionally, the distance of Cu (II) center to donor atoms are given in Table 5 for each conformation. As it seen clearly from the Table 5, the one of the oxygen atoms in (a) is far away to metal atom and the distance was calculated as 3.324 Å while 2.49 Å for 6-coordinated Cu(II) complexes. According to this results, six coordinated Cu(II) complex, Fig. 5 (c), is more stable. For the optimized structure of Cu(II) complex, The around of copper center consists as a distorted octahedral geometry in a N2O2S2 manner. Two ether oxygen atoms and two thiolate sulfur atoms occupy the equatorial positions of copper ions, the two
Fig. 6. The frontier molecule orbitals (FMOs) plot of the theoretically investigated compound. (I) FMOs for the ligand, (II) Alpha spin state FMOs for the Cu complex and (III) Beta spin state FMOs for the Cu complex.
P. Ekmekcioglu et al. / Journal of Molecular Structure 1099 (2015) 189e196
195
Fig. 7. The plot of calculated absorption spectra.
remaining positions in the distorted octahedral geometry are the axial positions which are occupied by two nitrogen atoms. The selected bond lengths and angles for optimized Cu(II) complex were given in Table 6. This situation seems to correspond with the reference [41]. 3.7. Electronic absorption and HOMO and LUMO analysis The outermost orbital filled by electrons called highest occupied molecular orbital (HOMO) and the first empty innermost orbital unfilled by electron called lowest unoccupied molecular orbital (LUMO) are the mainly responsible for chemical reactions. The HOMO is directly related to the ionization potential and behaves as an electron donor while the LUMO is directly related to the electron affinity and behaves as an electron acceptor. The energy gap formed between the HOMO-LUMO indicates the molecular chemical stability [42]. A large HOMOeLUMO gap indicates stable molecule with low chemical reactivity [43]. The energy gap between the HOMO-LUMO is important to determine the electrical transport properties of molecules [44]. By the complexation of the ligand with Cu(II), the HOMO-LUMO gap is decreasing from 0.13093 to 0.07383 Hartree. Thus, the Cu (II) complex of the ligand is less stable and more reactive than the free Schiff base form. 3D plots and energy values of the HOMO-LUMO are given in Fig. 6. The TD-DFT calculations have been performed to explain the electronic transitions of Cu (II) complex. The bands observed by experimentally at 325 nm originates mainly in the HOMO-5/ HOMO-6 to LUMO of alpha spin state transition, and can be interpreted as intra-ligand charge transfer (p / p*) according to the orbital characters (Fig. 7). Alpha HOMO-5, HOMO-6 and LUMO orbitals are mostly (80%) contributed by carbon atoms. The theoretically obtained these bands at 327.22, 302.83 and 329.36 nm as a broad band. Absorption bands observed by experimentally at 758 nm originates mainly in the HOMO-15/HOMO-16 to LUMO of beta spin state transition, and can be interpreted as ded transitions of Cu (II) ions according to the orbital characters. Beta HOMO-15,
HOMO-16 and LUMO orbitals are mostly (50%) contributed by Cu atom. This band obtained theoretically at 725.16 and 797.55 nm as a two intense bands. The TD-DFT calculations exhibit good quantitative agreement with the spectral position of the absorption bands of Cu (II) complex. Theoretically obtained absorption spectrum was given in Fig. 7. 4. Conclusion We have shown the synthesis and characterization of new hexadentate Schiff base and its copper (II), nickel(II), and cobalt(II) complexes in this study. Paramagnetic properties of whole metal complexes have been found. The ligand were complexed with metal atom ions in octahedral geometry [34]. The obtained experimental data were supported proposed structural features for the ligand and its metal complexes. Quantum chemical calculations were also supported the experimentally proposed structures. The ligand and its copper (II), nickel (II), and cobalt (II) complexes (6e8) were assessed for antimicrobial activity against one gram-positive bacterium (S.aureus), a gram negative bacterium (E. coli), and the fungi A. niger and Trichoderma. The free ligand and copper (II), nickel (II) and cobalt (II) complexes (6e8) were found to be antibacterial activity against both species. The metal complexes activity increases as the stability of the complex increases. The metal complex activities follow the order CuL > CoL > NiL. Comparison of activities shows that the Cu (II) complex is more active than the free base ligand against A. Niger. Furthermore, HOMOeLUMO calculations endorsed that Cu (II) complex is more reactive than the free ligand. The Schiff base ligand has a better antimicrobial activity against Trichoderma. Acknowledgments The authors are very grateful to Karadeniz Technical University Research Fund for providing financial support (project no. 8665). The numerical calculations reported in this paper were performed
196
P. Ekmekcioglu et al. / Journal of Molecular Structure 1099 (2015) 189e196
at TUBITAK ULAKBIM, High Performance and Grid Computing Center (TRUBA Resources). References [1] Y.C. Yongming, X. Dong, Y. Li, Z. Li, W. Chen, Eur. J. Med. Chem. 58 (2012) 323e331. [2] G.B. Bagihalli, P.G. Avaji, S.A. Patil, P.S. Badami, Eur. J. Med. Chem. 43 (2008) 2639e2649. [3] X.Y. Sun Synth, React. Inorg. Met. Org. Chem. 36 (2006) 621e625. [4] C. Celik, M. Tumer, S. Serin Synth, React. Inorg. Met. Org. Nano-Met. Chem. 32 (2002) 1839e1854. [5] N. Karabocek, S. Karabocek, F. Kormali Turk, J. Chem. 31 (2007) 271e277. [6] L. Lekha, K.K. Raja, G. Rajagopal, D. Easwaramoorthy, J. Organomet. Chem. 753 (2014) 72e80. [7] C.O.R. deBarbarin, N.A. Bailey, D.E. Fenton, Q.Y. He, J. Chem. Soc. Dalton Trans. 2 (1997) 161e166. [8] M.M.T. Khan, S.B. Halligudi, S. Shukla, Z.A. Shaikh, J. Mol. Catal. 57 (1990) 301e305. [9] U. Casellato, P. Vigato, M. Vidali Coord, Chem. Rev. 23 (1977) 31e117. [10] D. Bose, J. Banerjee, S.H. Rahaman, G. Mostafa, H.K. Fun, R.D. Bailey Walsh, M.J. Zaworotko, B.K. Ghosh, Polyhedron 23 (2004) 2045e2053. lu Chin, J. Poly. Sci. 30 (2012) 682e693. [11] I. Kaya, S. Çulhaog [12] H.E. Gottlieb, V. Kotlyar, A. Nudelman, J. Org. Chem. 62 (1997) 7512e7515. [13] E. Canpolat, A. Yazıci, M. Kaya, J. Coord. Chem. 60 (2007) 473e480. [14] N. Karabocek, M. Armutcu, S. Karabocek, H. Tanak, S. Isik, O. Baskan, Synth. React. Inorg. Met. Org. Nano-Met. Chem. 41 (2011) 1249e1256. [15] M.M. Mashaly, Z.H. Abd-Elwahab, A.A. Faheim, Synth. React. Inorg. Met. Org. Nano-Met. Chem. 34 (2004) 233e268. [16] G.L. Eichhorn, J.C. Bailar, J. Am. Chem. Soc. 75 (1953) 2905e2907. [17] A.B. P, Lever Inorganic Electronic Spectroscopy, Elsevier, Amsterdam, 1968, pp. 275e361. [18] F.A. Cotton, G. Wilkinson, Advanced Inorganic Chemistry, fifth ed., Wiley, New York, USA, 1988. [19] F. Firdaus, K. Fatma, A.U. Khan, M. Shakir, J. Serb. Chem. Soc. 74 (2009) 939e951. [20] M.S. Jana, A.K. Pramanik, T.K. Mondal, Polyhedron 76 (2014) 29e35. [21] E.K. Efthimiadou, G. Psomas, Y. Sankis, N. Katsaros, J. Inorg. Biochem. 101 (2007) 525e535. [22] A. El-Dissouky, O. Al-Fulaji, M.K. Awad, S. Rizk, J. Coord. Chem. 63 (2010) 330e345. [23] D. Thangadurai, K. Natarajan, Synth. React. Inorg. Met. Org. Nano-Met. Chem.
[24] [25] [26] [27] [28] [29] [30] [31] [32] [33] [34]
[35] [36] [37]
[38] [39] [40] [41] [42] [43] [44]
31 (2001) 549e567. N. Raman, S. Johnson Raja, A. Sakthivel, J. Coord. Chem. 62 (2009) 691e709. K.Z. Ismail, A.E. Dissouky, A.Z. Shehada, Polyhedron 16 (1997) 2909e2916. J.R. Anacona, F. Acosta, J. Coord. Chem. 59 (2006) 621e627. K. Fukui, Science 218 (1982) 747e754. M. Rizwan, S. Ali, S. Shahzadi, S.K. Sharma, K. Qanungo, M. Shahid, S. Mahmood, J. Coord. Chem. 67 (2014) 341e351. R.G. Pearson, P. Natl. Acad. Sci. (USA) 83 (1986) 8440e8441. M. Hesse, H. Meier, B. Zeeh, Spectroscopic Methods in Organic Chemistry, second ed, Thieme, Stuttgart, New York, 2007. A.I. Vogel, Textbook of Quantitative Inorganic Analysis, fourth ed, Longman, London, UK, 1978. A.S. Munde, A.N. Jagdale, S.M. Jadhav, T.K. Chondhekar, J. Kor. Chem. Soc. 53 (2009) 407e414. I. Ahmad, Z. Mehmood, F. Mohammed, J. Ethnopharmacol. 62 (1998) 183e193. G.L. Woods, B.A. Brown-Elliott, E.P. Desmond, G.S. Hall, L. Heifets, G.E. Pfyffer, J.C. Ridderhof, R.J. Wallace, N.C. Warren, F.G. Witebsky, Approved Standard, NCCLS document M24-A, 2003. A.D. Becke, Phys. Rev. A 38 (1988) 3098e3100. C. Lee, W. Yang, R.G. Parr, Phys. Rev. B 37 (1988) 785e789. M.J. Frisch, G.W. Trucks, H.B. Schlegel, G.E. Scuseria, M.A. Robb, J.R. Cheeseman, G. Scalmani, V. Barone, B. Mennucci, G.A. Petersson, H. Nakatsuji, M. Caricato, X. Li, H.P. Hratchian, A.F. Izmaylov, J. Bloino, G. Zheng, J.L. Sonnenberg, M. Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai, T. Vreven Jr., J.A. Montgomery, J.E. Peralta, F. Ogliaro, M.J. Bearpark, J. Heyd, E.N. Brothers, K.N. Kudin, V.N. Staroverov, R. Kobayashi, J. Normand, K. Raghavachari, A.P. Rendell, J.C. Burant, S.S. Iyengar, J. Tomasi, M. Cossi, N. Rega, N.J. Millam, M. Klene, J.E. Knox, J.B. Cross, V. Bakken, C. Adamo, J. Jaramillo, R. Gomperts, R.E. Stratmann, O. Yazyev, A.J. Austin, R. Cammi, C. Pomelli, J.W. Ochterski, R.L. Martin, K. Morokuma, V.G. Zakrzewski, G.A. Voth, P. Salvador, J.J. Dannenberg, S. Dapprich, A.D. Daniels, O. Farkas, J.B. Foresman, J.V. Ortiz, J. Cioslowski, D.J. Fox, Gaussian, Inc., Wallingford, CT, USA, 2009. P.J. Hay, W.R. Wadt, J. Chem. Phys. 82 (1985) 270e283. D. Feller, J. Comp. Chem. 17 (1996) 1571e1586. B. Burke, J. Werschnik, E.K.U. Gross, J. Chem. Phys. 123 (2005) 1e9. B.K. Koo, Bull. Korean Chem. Soc. 34 (2013) 3233e3238. V. Barone, M. Cossi, J. Phys. Chem. A 102 (1998) 1995e2001. N.M. O'Boyle, A.L. Tenderholt, K.M. Langner, J. Comp. Chem. 29 (2008) 839e845. R.K. Dennington, T. Millam, in: S.M. KS (Ed.), J. Semichem Inc, 2009.
Contents lists available at ScienceDirect
Journal of Molecular Structure journal homepage: http://www.elsevier.com/locate/molstruc
Synthesis, structural and biochemical activity studies of a new hexadentate Schiff base ligand and its Cu(II), Ni(II), and Co(II) complexes Pinar Ekmekcioglu a, Nevin Karabocek a, *, Serdar Karabocek a, Mustafa Emirik b a b
Department of Chemistry, Karadeniz Technical University, Trabzon, Turkey an University, Rize, Turkey Department of Chemistry, Recep Tayyip Erdog
a r t i c l e i n f o
a b s t r a c t
Article history: Received 19 March 2015 Received in revised form 14 June 2015 Accepted 15 June 2015 Available online 20 June 2015
A new Schiff base ligand (H2L) and its metal complexes have been prepared and characterized by elemental analysis, magnetic moment and spectral studies. The comparative in-vitro antimicrobial activities against various pathogens with reference to known antibiotics activity under the standard control of different concentrations revealed that the metal complexes (6e8) showed enhanced antimicrobial activities in general as compared to free ligand. As an exception, the free ligand showed better activity against Trichoderma. The antifungal activity experiments were performed in triplicate. The order of biochemical activity for metal complexes were observed as in the following. CuL > CoL > NiL, which is exactly same as the order of stability constants of these complexes. Additionally, we performed DFT and TD-DFT calculation for free ligand and Cu(II) complex to support the experimental data. The geometries of the Cu(II) complex have been optimized using the B3LYP level of theory. The theoretical calculations confirm that the copper (II) center exhibits a distorted square pyramidal geometry which is favored by experimental results. © 2015 Elsevier B.V. All rights reserved.
Keywords: Hexadentate Schiff base Biological activity Copper (II) complex
1. Introduction Polydentate Schiff base ligands are well-studied area of research in coordination chemistry due to having remarkable biological activities and capable of forming very stable complexes with transition metals. These ligands have preparative accessibilities, structural variety, different coordination numbers and crystalline architectures [1,2]. Recent research indicates that the antibacterial activities of the coordinated metal complexes were increased according to Schiff bases [3]. The Schiff bases and their metal complexes play a key role in the coordination chemistry [4e6]. Schiff base metal complexes have interested for their noteworthy contributions in magnetism, material science [7] and catalysis such as carboxylation, reduction, oxidation, epoxidation, and hydrolysis reactions [8]. Schiff bases have been prepared by the reaction of primary amines and carbonyl compounds [9] and widely used chelating agents for the synthesize transition metal complexes. Their copper (II), nickel (II), and cobalt (II) complexes with pseudo
* Corresponding author. E-mail address: [email protected] (N. Karabocek). http://dx.doi.org/10.1016/j.molstruc.2015.06.051 0022-2860/© 2015 Elsevier B.V. All rights reserved.
halides are well known for preparative accessibilities, exhibiting the flexibility of the coordination center [10]. In this work, a new Schiff base ligand and its copper (II), nickel (II), and cobalt (II) complexes have been synthesized. The complex structures have been characterized by magnetic, physical, elementary analyses and spectral methods. The free ligand and its metal complexes were evaluated for antimicrobial activity against S. aureus, Escherichia coli, A. Niger and Trichoderma. The free ligand (H2L) activity increases against Trichoderma. DFT and TD-DFT calculations were also performed to support the experimental results. 2. Experimental 2.1. Materials and spectral measurements 2,20 -[1,2-phenylenebis(methyleneoxy)]dibenzaldehyde(3) have been prepared according to reference [11]. C, H and N content analysis were carried out a Carlo Erba 1106 elemental analyzer (Milan, Italy). Metal complex structures were degraded with concentrated nitric acid, then solutions were neutralized with aqueous ammonia solution and the metal ions titrated with EDTA [12]. Mass spectra (ESI) were carried out on Micro mass Quattroo
190
P. Ekmekcioglu et al. / Journal of Molecular Structure 1099 (2015) 189e196
LC-MS/MS spectrophotometer (Manchester, United Kingdom). 1H NMR and 13C- NMR spectra were recorded on an Agilent 400eNMR DD2 MHz spectrometer in the CDCl3 solvent. IR and UVeVis spectra were carried out on Perkin Elmer FT-IR Spectrometer (KBr disk, 4000e400 cm1) and on a Perkin Elmer Lambda 25 UV/VIS Spectrometer (USA), respectively. Magnetic susceptibilities were carried on a PAR model 155 vibrating in room temperature. All chemicals were obtained from local suppliers and used as received purity. The test microorganisms; E. coli RSKK 340, S. aureus RSKK 96090, A. niger Z10, T. harzianum, (Rifai) were obtained from the Refik Saydam National Public Health Agency. 2.2. Synthesis of 2,20 -{1,2-phenylenebis[methyleneoxy-2,1phenylene(Z)methylylidene-nitrilo]}dibenzenethiol, (H4L), (5) A solution of dialdehyde (3) (1.73 g, 5 mmol) and 2aminothiophenol (1.25 g, 10 mmol) were refluxed for 10 h in EtOH (25 mL). This solution was then poured in to water (50 mL) and the solid product filtered off. The crude product was crystallized from ethanol with decolorizing charcoal. The compound (5), M.P. 107 C, was isolated in 60% yield; IR (KBr disc.)/cm1 1594 y(C]N), and 1228 y(CeO) and 2600 y(SeH); 1H NMR (CDCl3)/ ppm d: 7.5e8 (d, 2H, N]CeH), 7.0e7.8 (m, 20H, aryl-H), 5.4 (s, 4H, eOCH2), 4.3 (b s., 2H, Aryl-SH), 1.6 (b s., water in CDCl3). MS(ESI): m/ z ¼ 579 [H2L.H2O]þ Elemental Anal. Calcd. (%): C, 70.5; H, 5.2; Found: C, 70.4; H, 5.1 for C34H28N2O2S2. 2.3. Synthesis of copper(II), nickel(II) and cobalt(II) complexes (6e8) Metal complexes (6e8) have been prepared by the same method. A solution (25 mL) of ligand (0.6 g, 1 mmol) was added dropwise to an ethanolic solution (10 mL) of M(ClO4)2.6H2O (1 mmol). The mixture was heated at 60 C under reflux with stirring for 4 h. Then, hot water was added dropwise to the mixture and the solution was left to crystallize at room temperature. The products were filtered off, washed with H2O, and dried over P2O5. C34H26CuN2O2S2, (6): elemental Anal. Calcd. (%): C, 62.0; H, 4.6; Cu, 9.6; Found: C, 62.0; H, 4.5; Cu, 9.5. MS (ESI): m/z ¼ 657.9 [CuL.2H2O]þ. Yield, a grey solid: 0.5 g (70%). C34H26NiN2O2S2, (7): elemental Anal. Calcd. (%): C, 65.9; H, 4.2; Ni, 9.5; Found: C, 66.0; H, 4.1; Ni, 9.4. MS (ESI): m/z ¼ 617.14 [NiL]þ, yield, a brown solid: 0.4 g (64%). C34H26CoN2O2S2, (8): elemental Anal. Calcd. (%): C, 66.0; H, 4.2; Co, 9.5; Found: C, 66.1; H, 4.1; Co, 9.4. MS (ESI): m/z ¼ 618 [CoL]þ, a dark grey solid: 0.4 g (70%). 2.4. Antimicrobial activity The antimicrobial activity tests were carried out according to reference [13] by paper disc method. The experimental results were compared with ciprofloxin. By the mycelia dry weight (MDW) method, the Schiff base ligand and its metal complexes, metal salts, and the control (DMSO) were screened for antifungal activity against the fungi A. niger and Trichoderma at 0.5 and 1 mgL1 [14]. The antifungal activity tests were carried out according to reference [15]. The percentage error was found to be ±0.01. The obtained results indicate that the ligand and its metal complexes arrested the growth of fungi. The results of the antimicrobial and antifungal activity were given in the Table 4. 2.5. Computational methods The geometrical optimizations have been performed with the DFT/B3LYP [16,17] level of theory without any symmetry constrain
using the GAUSSIAN 03 software package [18]. For C, H, N and O atoms, the 6e311 þ G(2d,p) basis set was employed, while for Cu the LANL2TZ(f) basis set obtained from the EMSL Basis Set Library with an effective core potential was assigned [19,20]. The calculations of vibrational frequency were performed to ensure that the optimized geometries at the local minima with the positive Eigen values. MEP mapped surface and the frontier orbital schemes were obtained by the same method. Vertical electronic excitations based on optimized geometries were carried out according to reference [21,22]. The lowest 150 singletesinglet transitions of Cu (II) complex were calculated with the computer. GaussSum [23] was used to obtain the fractional contributions of the various fragment to each molecular orbital. GaussView 5.0 was used to visualize the results of computations [24]. 3. Results and discussion The ligand was synthesized in EtOH by reaction dialdehyde (3) (1.73 g, 5 mmol) and 2-aminothiophenol (1.25 g, 10 mmol) (Scheme 1). The Schiff base was characterized by elemental analysis, 1H NMR, 13C NMR, IR, and mass spectral data. The Cu (II), Ni (II), and Co (II) complexes have been obtained and characterized by elemental analysis, magnetic moment, UVeVis, and mass spectral data. The N2S2O2 units of Schiff base ligand (H2L) are available for the complexation with Cu (II), Ni (II), and Co (II) metal ions. 3.1. NMR spectra In the 1H NMR spectrum of Schiff base ligand, the following signals were observed in CDCl3: doublet signals at d ¼ 8e7.5 ppm were attributed to tautomeric hydrogen of eC]NH group (d, 2H). The signals of Aryl-H were seen at d ¼ 7.0e7.8 (m, 20H) ppm. The signal of eCH2-O- was observed at 5.4 (s, 4H) ppm. The signal of Aryl-SH was observed at 4.3(b. s, 2H) ppm [25]. Signal of water in CDCl3 was observes at 1.6 ppm [26]. Integrated data are consistent with the molecular formula of the ligand. The seventeen resonance signals were observed in the 13C NMR spectra of the Schiff base ligand (H2L), which were also consistent with the formula for H2L (Fig. 1). 3.2. Mass spectra The mass spectra of the ligand and its metal complexes were recorded in acetonitrile solution. The mass spectra (ESI-MS) exhibited the molecular ion at m/z ¼ 579 [H2L.H2O]þ for the free Schiff base ligand, which indicated formation of ligand. The molecular ion peaks appeared (m/z, ESI) at 657.9 [CuL.2H2O]þ at 617.14 [NiL]þ and at 618.45 [CoL]þ for the CuL, NiL, and CoL, respectively. The mass spectra confirmed the formation of the ligand and its metal complexes given molecular structure in Fig. 2. 3.3. IR spectra Characteristic IR bands were given in Table 1. The band at 2600 cm1 and the strong band at 1594 cm1 might be assigned to n(SeH) and n(C¼ N) vibration of the ligand, respectively [27]. In the metal (II) complexes, n(C]N) vibrations were shifted to lower frequency field (z10 cm1), and n(SeH) vibrations could not be observed, after the complex formations [28]. In the IR spectra of metal complexes, the peaks appearing between 430 and 480 cm1 are attributed to n(MN) [28,29]. The changes in the n(C]N) vibration bands and the disappearing of vibration band of n(SeH) support the concept of coordination of the ligand through the Schiff base donor atoms.
P. Ekmekcioglu et al. / Journal of Molecular Structure 1099 (2015) 189e196
Scheme 1. Preparation of the hexadentate Schiff base ligand, (H2L).
Fig. 1.
13
C-NMR spectrum of the Schiff base Ligand (H2L).
191
192
P. Ekmekcioglu et al. / Journal of Molecular Structure 1099 (2015) 189e196
14184, and 31746 cm1 were assignable to T1g(F) / 4T2g(P),4T1g(F) / 4T1g(P), and 4T1g(F) / 4A2g(P) transitions, respectively. These bands and measured magnetic moment (3.7 BM) support the octahedral Co(II) complex [28,32e34]. Furthermore, ded transition bands were observed as weak signals in all complexes. The calculated values of the ligand field splitting energy (10 Dq), Racah inter electronic repulsion parameter (B), covalent factor (b), ratio v2/v1, and ligand field stabilization energy (LFSE) were given in Table 3. The obtained data support the proposed geometry of the Cu (II), Ni(II), and Co(II) complexes [34]. 4
N
O
S
M O
S N
3.5. Antimicrobial activity
M = Cu(II), Ni(II), Co(II) Fig. 2. Proposed structures for the copper(II), nickel(II) and cobalt(II) complexes.
3.4. Magnetic properties and electronic absorption spectra The electronic spectra of the Cu (II), Ni (II), and Co (II) complexes were recorded in DMSO. The spectral data were given in Table 2. In the UV spectra of the Cu (II) complex two bands were seen at 13192 and 30770 cm1, owing to a 2Eg / 2T2g transition and charge transfer. The magnetic moment of the Cu(II) complex is 1.85 B M. which agrees with the known values for Cu(II) complexes in octahedral geometry [28,30]. Ni (II) complex displays bands at 11900, 14400, and 33000 cm1 assignable to a 3 3 3 3 A2g / T2g(F), A2g / T1g(F), and 3A2g / 3T1g(P), respectively. Magnetic moment has been obtained as 2.80 B M. which suggest octahedral geometry for Ni(II) complex [28,31]. In the electronic spectra of Co(II) complex, observed three bands at 12500 (740),
Table 1 Characteristic IR bands of the free ligand and its metal complexes (in cm1). Compound
n(H2O)
n(SeH)
n(C]O)
n(C]N)
n(CeO)
n(MN)
3 H2L CuL NiL CoL
e 3400 e e e
e 2600 e e e
1692 e e e e
e 1594 1579 1579 1579
1233 1228 1214 1214 1214
e e 455 430 480
The free ligand and its metal complexes were appraised for biochemical activity against S. Aureus, E. coli and fungi A. Niger, Trichoderma. The experimental results were given in Table 4. The free ligand and its metal complexes have been exhibited antibacterial activity against both strains according to these results. The metal complexes exhibit higher activity than the free ligand. Ciprofloxin were used as a standard in the antibacterial inhibitions. The free ligand and its metal complexes showed lower antimicrobial activity than the standard. The metal salts used for synthesis of metal complexes exhibit antimicrobial activities [35,36]. The activity of metal complexes can be explained on the basis of Overtones and Tweedy's concepts [37]. Antibacterial inhibition was directly proportionate to the concentration of reagent. The results showed that the Cu(II) complex exhibits higher activity against each class of organism. The structures of metal complexes are strictly related to the activity [38]. The higher activity of the Cu(II) complex may be caused to its higher stability constant. The free ligand and its metal complexes show more activity against gramenegative E. coli than against gram-positive S. Aureus. Antibacterial activity can be ordered as CuL > CoL > NiL, similar to earlier observations [28,39]. Antifungal activity results showed that all the metal complexes are more toxic than the ligand [40]. The antifungal activity was improved several times on being coordinated with metal. The metal complexes activity increases as the stability of the complex increases. The metal complex activities follow the order CuL > CoL > NiL, which is exactly same as the order of stability constants of these complexes. The experimental results shows that the Cu (II) complex is more active than the ligand against A. niger. However, the free form of the Schiff base ligand showed better activity against Trichoderma. Table 4 Antibacterial activities of (diameter inhibition zone in mm) and antifungal activity weight (mg) (% inhibition) of the ligand and metal complexes. Antibacterial activity (mg mL1)
Table 2 Physical data of the ligand and its metal complexes. a
Compound
Color
meff
H2L CuL NiL CoL
Yellow Grey Brown Dark-grey
e 1.85 2.8 3.7
a
E. coli 1
Yield
Sol.l
60 70 64 70
e 13.192, 30.770 11.900, 14.400, 33.000 12.500, 14.184, 31.746
a max
(cm
*)
Per metal atom at 297 K (B.M.). *UVeVis spectra were recorded in DMSO.
Conc. Control(DMSO) Ciprofloxin H2L CuL NiHL CoHL
0.5 0 40 10 20 12 15
1 0 45 12 25 15 20
Antifungal activity (mg mL1)
S. Aureus
A. niger
0.5 0 42 10 15 10 12
0.5 0 74 80(15) 50(30) 60(35) 65(30)
1 0 44 15 20 12 15
Trichoderma 1 0 72 60(10) 30(70) 20(75) 30(70)
0.5 0 65 50(25) 35(50) 35(55) 25(65)
1 0 60 40(50) 30(70) 25(60) 25(65)
Table 3 Ligand field parameter of the metal complexes. Complex
Ligand field splitting energy (Dq cm1)
Racah interelectronic repulsion parameter (B cm1)
Covalent factor (b)
b (%)
Ratio v2/v1
LFSE (kcal mol1)
CuL NiL CoL
13192 11.900 12500
96.06 1030 971
e 0.75 0.58
e 19.5 3.81
e 1.03 1.05
37.70 34.0 35.70
P. Ekmekcioglu et al. / Journal of Molecular Structure 1099 (2015) 189e196
193
Fig. 3. The optimized molecular geometries of (a) free ligand and (b) its Cu (II) complex, respectively. Hydrogen atoms were omitted for clarity.
Table 5 The coordination distances in (a) 5- coordinated (b) 6-coordinated (c) 6-coordinated Cu(II) complexes. Atoms
CueO14 CueO15 CueS62 CueS63 CueN40 CueN41
Distances (Å) (a)
(b)
(c)
3.324 2.338 2.311 2.346 2.176 2.287
2.491 2.483 2.416 2.416 2.032 2.032
2.493 2.367 2.341 2.345 2.150 2.231
3.6. Quantum chemical calculations
Fig. 4. MEP mapped surface of the ligand.
All calculations were performed using DFT/B3LYP method with 6e311 þ G(2d,p)) basis set for free ligand and the combination of 6e311 þ G(2d,p)) and LanL2TZ(f) basis sets for its Cu(II) complex. The molecular structures, orbital shapes (HOMO-LUMO) and molecular electrostatic potential (MEP) of the mentioned free ligand and its Cu(II) complex were plotted in GaussView 5 program. The optimized molecular structures of the free ligand and of its Cu (II) metal complex are given in Fig. 3(a) and (b), respectively.
Fig. 5. The molecular geometries of the most stable three Cu(II) metal complexes. (a) 5- coordinnated (b) 6-coordinated (c) 6-coordinated Cu (II) complexes.
194
P. Ekmekcioglu et al. / Journal of Molecular Structure 1099 (2015) 189e196
Table 6 Selected Bond Lengths (Å) and Angles ( ) for optimized Cu(II) Complex. CueO14 CueS62 CueN40 S62eCueS63 N41eCueN40 N41eCueO14 N41eCueO15 O14eCueN40 S62eCueO15 S63eCueO15 O15eCueN40
2.493 2.341 2.150 99.893 159.400 73.207 89.595 87.679 159.745 96.712 77.005
CueO15 CueS63 CueN41 O14eCueO15 N41eCueS63 N41eCueS62 O14eCueS63 O14eCueS62 S62eCueN40 S63eCueN40
2.367 2.345 2.231 72.160 84.798 103.339 155.123 96.439 86.039 111.968
Complexation behavior of the ligand was analyzed by molecular electrostatic potential (MEP). MEP mapped surface gives information about the interaction of the molecules. The red regions of MEP surface are interpreted as the negative side of the ligand while yellow regions show positive electrostatic potential. MEP mapped surface of the ligand is given in Fig. 4. The electron rich red regions between two sulfur atom and around oxygen and nitrogen are
theoretically potential active sides of the ligand to positively charged metals as expected. Thus, the coordination is expected to be formed on the red regions of Fig. 4 in the metal complex. Furthermore, DFT calculations were performed to determine the stable geometric structure of the Cu(II) complex. The most stable conformations, 5-coordinated and two 6-coordinated Cu (II) complexes were compared with regard to their SCF energies. The obtained results were given in Fig. 5. According to this results, hexadentate Cu (II) complex is more stable than the penta-dentate Cu (II) complex which is consistent with experimental results. Additionally, the distance of Cu (II) center to donor atoms are given in Table 5 for each conformation. As it seen clearly from the Table 5, the one of the oxygen atoms in (a) is far away to metal atom and the distance was calculated as 3.324 Å while 2.49 Å for 6-coordinated Cu(II) complexes. According to this results, six coordinated Cu(II) complex, Fig. 5 (c), is more stable. For the optimized structure of Cu(II) complex, The around of copper center consists as a distorted octahedral geometry in a N2O2S2 manner. Two ether oxygen atoms and two thiolate sulfur atoms occupy the equatorial positions of copper ions, the two
Fig. 6. The frontier molecule orbitals (FMOs) plot of the theoretically investigated compound. (I) FMOs for the ligand, (II) Alpha spin state FMOs for the Cu complex and (III) Beta spin state FMOs for the Cu complex.
P. Ekmekcioglu et al. / Journal of Molecular Structure 1099 (2015) 189e196
195
Fig. 7. The plot of calculated absorption spectra.
remaining positions in the distorted octahedral geometry are the axial positions which are occupied by two nitrogen atoms. The selected bond lengths and angles for optimized Cu(II) complex were given in Table 6. This situation seems to correspond with the reference [41]. 3.7. Electronic absorption and HOMO and LUMO analysis The outermost orbital filled by electrons called highest occupied molecular orbital (HOMO) and the first empty innermost orbital unfilled by electron called lowest unoccupied molecular orbital (LUMO) are the mainly responsible for chemical reactions. The HOMO is directly related to the ionization potential and behaves as an electron donor while the LUMO is directly related to the electron affinity and behaves as an electron acceptor. The energy gap formed between the HOMO-LUMO indicates the molecular chemical stability [42]. A large HOMOeLUMO gap indicates stable molecule with low chemical reactivity [43]. The energy gap between the HOMO-LUMO is important to determine the electrical transport properties of molecules [44]. By the complexation of the ligand with Cu(II), the HOMO-LUMO gap is decreasing from 0.13093 to 0.07383 Hartree. Thus, the Cu (II) complex of the ligand is less stable and more reactive than the free Schiff base form. 3D plots and energy values of the HOMO-LUMO are given in Fig. 6. The TD-DFT calculations have been performed to explain the electronic transitions of Cu (II) complex. The bands observed by experimentally at 325 nm originates mainly in the HOMO-5/ HOMO-6 to LUMO of alpha spin state transition, and can be interpreted as intra-ligand charge transfer (p / p*) according to the orbital characters (Fig. 7). Alpha HOMO-5, HOMO-6 and LUMO orbitals are mostly (80%) contributed by carbon atoms. The theoretically obtained these bands at 327.22, 302.83 and 329.36 nm as a broad band. Absorption bands observed by experimentally at 758 nm originates mainly in the HOMO-15/HOMO-16 to LUMO of beta spin state transition, and can be interpreted as ded transitions of Cu (II) ions according to the orbital characters. Beta HOMO-15,
HOMO-16 and LUMO orbitals are mostly (50%) contributed by Cu atom. This band obtained theoretically at 725.16 and 797.55 nm as a two intense bands. The TD-DFT calculations exhibit good quantitative agreement with the spectral position of the absorption bands of Cu (II) complex. Theoretically obtained absorption spectrum was given in Fig. 7. 4. Conclusion We have shown the synthesis and characterization of new hexadentate Schiff base and its copper (II), nickel(II), and cobalt(II) complexes in this study. Paramagnetic properties of whole metal complexes have been found. The ligand were complexed with metal atom ions in octahedral geometry [34]. The obtained experimental data were supported proposed structural features for the ligand and its metal complexes. Quantum chemical calculations were also supported the experimentally proposed structures. The ligand and its copper (II), nickel (II), and cobalt (II) complexes (6e8) were assessed for antimicrobial activity against one gram-positive bacterium (S.aureus), a gram negative bacterium (E. coli), and the fungi A. niger and Trichoderma. The free ligand and copper (II), nickel (II) and cobalt (II) complexes (6e8) were found to be antibacterial activity against both species. The metal complexes activity increases as the stability of the complex increases. The metal complex activities follow the order CuL > CoL > NiL. Comparison of activities shows that the Cu (II) complex is more active than the free base ligand against A. Niger. Furthermore, HOMOeLUMO calculations endorsed that Cu (II) complex is more reactive than the free ligand. The Schiff base ligand has a better antimicrobial activity against Trichoderma. Acknowledgments The authors are very grateful to Karadeniz Technical University Research Fund for providing financial support (project no. 8665). The numerical calculations reported in this paper were performed
196
P. Ekmekcioglu et al. / Journal of Molecular Structure 1099 (2015) 189e196
at TUBITAK ULAKBIM, High Performance and Grid Computing Center (TRUBA Resources). References [1] Y.C. Yongming, X. Dong, Y. Li, Z. Li, W. Chen, Eur. J. Med. Chem. 58 (2012) 323e331. [2] G.B. Bagihalli, P.G. Avaji, S.A. Patil, P.S. Badami, Eur. J. Med. Chem. 43 (2008) 2639e2649. [3] X.Y. Sun Synth, React. Inorg. Met. Org. Chem. 36 (2006) 621e625. [4] C. Celik, M. Tumer, S. Serin Synth, React. Inorg. Met. Org. Nano-Met. Chem. 32 (2002) 1839e1854. [5] N. Karabocek, S. Karabocek, F. Kormali Turk, J. Chem. 31 (2007) 271e277. [6] L. Lekha, K.K. Raja, G. Rajagopal, D. Easwaramoorthy, J. Organomet. Chem. 753 (2014) 72e80. [7] C.O.R. deBarbarin, N.A. Bailey, D.E. Fenton, Q.Y. He, J. Chem. Soc. Dalton Trans. 2 (1997) 161e166. [8] M.M.T. Khan, S.B. Halligudi, S. Shukla, Z.A. Shaikh, J. Mol. Catal. 57 (1990) 301e305. [9] U. Casellato, P. Vigato, M. Vidali Coord, Chem. Rev. 23 (1977) 31e117. [10] D. Bose, J. Banerjee, S.H. Rahaman, G. Mostafa, H.K. Fun, R.D. Bailey Walsh, M.J. Zaworotko, B.K. Ghosh, Polyhedron 23 (2004) 2045e2053. lu Chin, J. Poly. Sci. 30 (2012) 682e693. [11] I. Kaya, S. Çulhaog [12] H.E. Gottlieb, V. Kotlyar, A. Nudelman, J. Org. Chem. 62 (1997) 7512e7515. [13] E. Canpolat, A. Yazıci, M. Kaya, J. Coord. Chem. 60 (2007) 473e480. [14] N. Karabocek, M. Armutcu, S. Karabocek, H. Tanak, S. Isik, O. Baskan, Synth. React. Inorg. Met. Org. Nano-Met. Chem. 41 (2011) 1249e1256. [15] M.M. Mashaly, Z.H. Abd-Elwahab, A.A. Faheim, Synth. React. Inorg. Met. Org. Nano-Met. Chem. 34 (2004) 233e268. [16] G.L. Eichhorn, J.C. Bailar, J. Am. Chem. Soc. 75 (1953) 2905e2907. [17] A.B. P, Lever Inorganic Electronic Spectroscopy, Elsevier, Amsterdam, 1968, pp. 275e361. [18] F.A. Cotton, G. Wilkinson, Advanced Inorganic Chemistry, fifth ed., Wiley, New York, USA, 1988. [19] F. Firdaus, K. Fatma, A.U. Khan, M. Shakir, J. Serb. Chem. Soc. 74 (2009) 939e951. [20] M.S. Jana, A.K. Pramanik, T.K. Mondal, Polyhedron 76 (2014) 29e35. [21] E.K. Efthimiadou, G. Psomas, Y. Sankis, N. Katsaros, J. Inorg. Biochem. 101 (2007) 525e535. [22] A. El-Dissouky, O. Al-Fulaji, M.K. Awad, S. Rizk, J. Coord. Chem. 63 (2010) 330e345. [23] D. Thangadurai, K. Natarajan, Synth. React. Inorg. Met. Org. Nano-Met. Chem.
[24] [25] [26] [27] [28] [29] [30] [31] [32] [33] [34]
[35] [36] [37]
[38] [39] [40] [41] [42] [43] [44]
31 (2001) 549e567. N. Raman, S. Johnson Raja, A. Sakthivel, J. Coord. Chem. 62 (2009) 691e709. K.Z. Ismail, A.E. Dissouky, A.Z. Shehada, Polyhedron 16 (1997) 2909e2916. J.R. Anacona, F. Acosta, J. Coord. Chem. 59 (2006) 621e627. K. Fukui, Science 218 (1982) 747e754. M. Rizwan, S. Ali, S. Shahzadi, S.K. Sharma, K. Qanungo, M. Shahid, S. Mahmood, J. Coord. Chem. 67 (2014) 341e351. R.G. Pearson, P. Natl. Acad. Sci. (USA) 83 (1986) 8440e8441. M. Hesse, H. Meier, B. Zeeh, Spectroscopic Methods in Organic Chemistry, second ed, Thieme, Stuttgart, New York, 2007. A.I. Vogel, Textbook of Quantitative Inorganic Analysis, fourth ed, Longman, London, UK, 1978. A.S. Munde, A.N. Jagdale, S.M. Jadhav, T.K. Chondhekar, J. Kor. Chem. Soc. 53 (2009) 407e414. I. Ahmad, Z. Mehmood, F. Mohammed, J. Ethnopharmacol. 62 (1998) 183e193. G.L. Woods, B.A. Brown-Elliott, E.P. Desmond, G.S. Hall, L. Heifets, G.E. Pfyffer, J.C. Ridderhof, R.J. Wallace, N.C. Warren, F.G. Witebsky, Approved Standard, NCCLS document M24-A, 2003. A.D. Becke, Phys. Rev. A 38 (1988) 3098e3100. C. Lee, W. Yang, R.G. Parr, Phys. Rev. B 37 (1988) 785e789. M.J. Frisch, G.W. Trucks, H.B. Schlegel, G.E. Scuseria, M.A. Robb, J.R. Cheeseman, G. Scalmani, V. Barone, B. Mennucci, G.A. Petersson, H. Nakatsuji, M. Caricato, X. Li, H.P. Hratchian, A.F. Izmaylov, J. Bloino, G. Zheng, J.L. Sonnenberg, M. Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai, T. Vreven Jr., J.A. Montgomery, J.E. Peralta, F. Ogliaro, M.J. Bearpark, J. Heyd, E.N. Brothers, K.N. Kudin, V.N. Staroverov, R. Kobayashi, J. Normand, K. Raghavachari, A.P. Rendell, J.C. Burant, S.S. Iyengar, J. Tomasi, M. Cossi, N. Rega, N.J. Millam, M. Klene, J.E. Knox, J.B. Cross, V. Bakken, C. Adamo, J. Jaramillo, R. Gomperts, R.E. Stratmann, O. Yazyev, A.J. Austin, R. Cammi, C. Pomelli, J.W. Ochterski, R.L. Martin, K. Morokuma, V.G. Zakrzewski, G.A. Voth, P. Salvador, J.J. Dannenberg, S. Dapprich, A.D. Daniels, O. Farkas, J.B. Foresman, J.V. Ortiz, J. Cioslowski, D.J. Fox, Gaussian, Inc., Wallingford, CT, USA, 2009. P.J. Hay, W.R. Wadt, J. Chem. Phys. 82 (1985) 270e283. D. Feller, J. Comp. Chem. 17 (1996) 1571e1586. B. Burke, J. Werschnik, E.K.U. Gross, J. Chem. Phys. 123 (2005) 1e9. B.K. Koo, Bull. Korean Chem. Soc. 34 (2013) 3233e3238. V. Barone, M. Cossi, J. Phys. Chem. A 102 (1998) 1995e2001. N.M. O'Boyle, A.L. Tenderholt, K.M. Langner, J. Comp. Chem. 29 (2008) 839e845. R.K. Dennington, T. Millam, in: S.M. KS (Ed.), J. Semichem Inc, 2009.