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Some new metal(II) complexes based on bis-Schiff base ligand derived from 2-acetylethiophine and 2,6-diaminopyridine: Syntheses, structural investigation, thermal, fluorescence and catalytic activity studies
Accepted Manuscript Some new metal(II) complexes based on bis-Schiff base ligand derived from 2acetylethiophine and 2,6-diaminopyridine: Syntheses, structural investigation, thermal, fluorescence and catalytic activity studies Manara A. Ayoub, Eman H. Abd-Elnasser, Mona A. Ahmed, Mariam G. Rizk PII:
S0022-2860(18)30283-7
DOI:
10.1016/j.molstruc.2018.03.006
Reference:
MOLSTR 24945
To appear in:
Journal of Molecular Structure
Received Date: 26 October 2017 Revised Date:
1 March 2018
Accepted Date: 2 March 2018
Please cite this article as: M.A. Ayoub, E.H. Abd-Elnasser, M.A. Ahmed, M.G. Rizk, Some new metal(II) complexes based on bis-Schiff base ligand derived from 2-acetylethiophine and 2,6-diaminopyridine: Syntheses, structural investigation, thermal, fluorescence and catalytic activity studies, Journal of Molecular Structure (2018), doi: 10.1016/j.molstruc.2018.03.006. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT
Some New Metal(II) Complexes Based On Bis-Schiff Base Ligand Derived From 2-acetylethiophine and 2,6-diaminopyridine: Syntheses, Structural Investigation, Thermal, Fluorescence and Catalytic Activity Studies
a
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Manara A. Ayouba,b *, Eman H. Abd-Elnasserb, Mona A. Ahmedb and Mariam G. Rizkb
* Chemistry Department, Faculty of Science, Taibah University, Al Madinah Al Munawarah, 41411, Saudi Arabia.
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Chemistry Department, Faculty of Women for Arts, Science and Education, Ain-Shams University, Cairo, 11757, Egypt
Corresponding Author: E-mail: [email protected]
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Tel: +2.02.01006496983
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Graphical Abstract
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Effect of pH and solvent on novel bis Schiff base ligand L
ACCEPTED MANUSCRIPT Some New Metal(II) Complexes Based On Bis-Schiff Base Ligand Derived From 2-acetylethiophine and 2,6-diaminopyridine: Syntheses, Structural Investigation, Thermal, Fluorescence and Catalytic Activity Studies Manara A. Ayouba,b*, Eman H. Abd-Elnasserb, Mona A. Ahmedb and Mariam G. Rizkb a
* Chemistry Department, Faculty of Science, Taibah University, Al Madinah Al Munawarah, 41411, Saudi Arabia.
b
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Chemistry Department, Faculty of Women for Arts, Science and Education, Ain-Shams University, Cairo, 11757, Egypt
ABSTRACT
A novel Schiff base ligand N, N`-bis (1-(thiophen-2-yl) ethylidene) pyridine-2, 6-diamine has
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been prepared by the condensation of 2,6-diaminopyridine and 2- acetylthiophene in ethanol in the molar ratio of 1:2. The Study by analytical and spectroscopic techniques indicated that
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the complexes have composition with the general formulae: [MLX2]· nH2O, where (M = Mn, Co, Ni, and Cu; X = Cl; n=4, 6, 6, 2), respectively. All the metal (II) complexes have been characterized with elemental analysis, FT−IR, Mass, 1H NMR, UV−Vis, magnetic moment, thermal analysis (TG and DTG) techniques, molar conductance and fluorescence spectra. Non electrolyte of complexes using DMF as a solvent is due to their low molar conductance. From FTIR spectral data, the coordination between the central metal ion with azomethine
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nitrogen and sulphur of acetylthiophene ring are confirmed. An octahedral geometry of all metal(II) complexes is investigated from electronic and magnetic data. The kinetic analysis of the thermogravimetric data was performed by using the Coats-Redfern equation. The
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fluorescence properties of theses complexes in DMSO, DMF, and CH3CN were studied. The effect of pH influencing the fluorescence intensity is discussed. The catalytic activities of metal(II) complexes were studied using H2O2 solution.
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Keywords Transition metal complexes of bis-Schiff base Spectroscopic analysis Thermogravimetric studies Fluorescence spectra Catalytic activity *Corresponding Author: Manara Ahmed Ayoub, E-mail: [email protected] Tel no: +2.02.01006496983
ACCEPTED MANUSCRIPT 1. Introduction All Schiff base complexes have been derived from heterocyclic compounds which belong to bioinorganic chemistry [1-3]. They have an important role in the development of modern coordination chemistry, and they are a major point in the development of inorganic
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biochemistry [4]. The presence of exocyclic nitrogen and sulphur atoms in the structure of Schiff bases provide a variety of coordination sites to link directly with the transition metal ions [5-6]. Different heterocyclic compounds such as pyridine are good ligands due to the presence of ring nitrogen atoms with a localized pair of electrons. So that, the application
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potential has led to formation a series of novel Schiff base compounds with a wide range of stability, reactivity, biological, chemical and physical properties [7-10]. For pyridine derivative ligands stabilize many different metals in various oxidation states, which are useful
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in clinical, biological, industrial and analytical applications. Moreover their great roles in organic synthesis and catalysis [11, 12]. Different derivatives of pyridine ligands were chosen as suitable building blocks for complexation reaction with various transition metal ions, they can be considered as soft Lewis acids. These compounds are flexible about the central C=N bond. Each ligand contains five potential sites for coordination to metal ions [13].
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Furthermore, a great interest of heterocyclic compounds contains transition metal complexes due to their ability to absorb visible light and act as electron sources that uses in photosensitizers applications [14-18]. The decomposition of hydrogen peroxide is used as standard reaction to determine the catalytic activity of metal oxide and metal complexes [19].
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In this work, we have reported the syntheses and characterization of a novel Schiff base derived from condensation of 2-acetylthiophene with to 2,6-aminopyridine, and its complexes
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with Mn(II), Co(II), Ni(II) and Cu(II). The synthesized Schiff base complexes have been characterized by elemental analyses, IR, MS, 1H NMR, UV−Vis, magnetic moment, TGA, molar conductance and fluorescence spectra studies. Schematic representation for the syntheses of Schiff base ligand N, N`[2-acetylthiophene]-2,6 diaminopyridineimine (L) and its complexes (Scheme 1).
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ACCEPTED MANUSCRIPT 2. Experimental
2.1. Materials and reagents All chemicals were purchased from commercial sources and used as received. The
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chemical used with high purity. They include 2,6-diaminopyridine (Aldrich), 2acetylthiophene (Merck), manganese(II) chloride tetrahydrate, cobalt(II) and nickel(II) chloride hexahydrate and copper(II) chloride dehydrate. Organic solvents used are absolute ethanol, methanol, diethyl ether, dimethylformamide (DMF), dimethylsulfoxide (DMSO),
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acetonitrile (CH3CN) and 1,2-dichloromethane as pure grade materials.
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2.2. Physical measurements
Microanalysis of (CHNS) was performed on a Perkin Elmer 2400 elemental analyzer. FTIR measurements (KBr discs) were recorded with a Shimadzu 8000 FTIR spectrometer at the central laboratory, Ain Shams University, Egypt. The FTIR spectra (600 – 200 cm-1) of the compounds were recorded as CsI discs using (Nexus 670) FTIR spectrophotometer,
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Nicolet (U.S.A) at the National Research Center, Gize, Egypt. 1H NMR measurements were recorded with a Varian-mercury 300 MHz spectrometer at the Microanalytical Center, Cairo University, Giza, Egypt. Samples were dissolved in DMSO-d6 using tetramethylsilane as an internal standard. Mass spectroscopy measurements of the solid ligands and complexes were
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recorded using a JEOL JMS-AX500 spectrometer at the National Research Center, Giza, Egypt. Magnetic susceptibility measurements were carried out by employing the Gouy
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method at room temperature using a magnetic susceptibility balance, Sherwood Scientific, Cambridge Science Park, Cambridge England. Thermogravimetric analysis (TG and DTG) were carried out under N2 atmosphere with a heating rate of 10°C/min using a Shimadzu TG-50H thermal analyzer at the Microanalytical Center, Cairo University, Giza, Egypt. All conductivity measurements were performed in DMF (1×10-3 M) at 25°C, using WAP, GMP 50 conductivity meter. UV-Vis spectra were obtained with a Shimadzu UV 1800 spectrophotometer in the range (200 − 800 nm) at the Micro analytical Center, Cairo University, Giza, Egypt. The photo luminescent properties of all complexes were performed on a Jenway 6270 fluorimeter, at the central laboratory, Ain Shams University, Egypt. All
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ACCEPTED MANUSCRIPT melting points were measured using an ordinary MEL-TEMP II Laboratory device (U.S.A), melting point apparatus. 2.3. Synthesis of N, N`-bis(1-(thiophen-2-yl)ethylidene)pyridine-2,6-diamine Schiff base L. The proposed ligand was synthesized by slow addition of 2-acetylthiophene (1.09 ml, 10
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mmole) in 50 ml ethanol to 2,6-diaminopyridine (1.09 g, 10 mmole) in 50 ml ethanol. The reaction mixture was refluxed for 4 hrs by using ultrasonic radiation. The yellow product was obtained by filtration, purified by crystallization from hot ethanol and washed with ethanol then diethylether. The ligand obtained was soluble in 1,2-dichloromethane, chloroform,
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dimethylformamide (DMF), dimethylsulfoxide (DMSO), and partially soluble in acetone, methanol and acetonitrile (CH3CN). The yield was (1.763g, 75%), m.p. (216−218°C). FT−IR
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(ν, cm‐1): 1631v.s, (νC=N, azomethine); 1457 v.s, (νC=C, Ar.); 781s, (νC‐S, thiophene). Calcd. for C17H15N3S2; C, 62.77; H, 4.62; N, 12.92; S, 19.69, Found: C, 62.77; H, 4.40; N, 12.80; S, 19.70 %. MS (EI, m/z (%)): 325(M+, 2). 1H NMR (300 MHz, DMSO-d6, δ, ppm): 3.311 (s, 6H, CH3), 5.280–7.028 (m, 3H, Py-H) and (m, 6H, thiophene protons).
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2.4. Synthesis of Schiff base metal(II) complexes 2.4.1. Reaction of MnCl2.4H2O with L.
A pink solution of MnCl2.4H2O (0.523 g, 1mmole) in ethanol (50ml) was added drop
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wise with continuously stirring to a solution of ligand L (0.325 g, 1 mmole) in ethanol (50ml). The solution was refluxed for 2 hrs, dark green precipitate was formed and washed
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with small amounts of ethanol then diethylether. The product obtained was insoluble in acetone and methanol but soluble in 1,2-dichloromethane, dimethylformamide (DMF) and dimethylsulfoxide (DMSO). The yield was 0.619 g (73%), m.p. (342−344°C). FT-IR (ν, cm‐1): 3400 br.s, (νOH, hydrated water); 1644v.s, (νC=N, azomethine); 1456 s, (νC=C, Ar.); 799 m, (νC‐S, thiophene); 567w, (νM-N); 469w, (νM-S); 350w, (νM-Cl). Calcd. for C17H23N3O4S2Cl2Mn; C, 39.09; H, 4.41; N, 8.05; S, 12.26, Found: C, 39.00; H, 4.29; N, 8.02; S, 12.21%.
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ACCEPTED MANUSCRIPT 2.4.2. Reaction of CoCl2.6H2O with L. A red solution of CoCl2.6H2O (0.563 g, 1 mmole) in ethanol (50 ml) was added drop wise with continuously stirring to a solution of ligand L (0.325 g, 1 mmole) in ethanol
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(50 ml). The solution was refluxed for 2 hrs, a red precipitate was formed and washed with small amounts of ethanol then diethylether. The product obtained was insoluble in acetone and methanol but soluble in 1,2-dichloromethane, dimethylformamide (DMF) and acetonitrile (CH3CN). The yield was 0.802 g (82%), m.p. (335−337°C). FT-IR (ν, cm‐1):
(νC‐S,
thiophene);
567w,
(νM-N);
486w,
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3348 br.w, (νOH, lattice water); 1640v.s, (νC=N, azomethine); 1493m, (νC=C, Ar.); 766 m, (νM-S);
342,
(νM-Cl).
Calcd.
for
S, 11.36 %.
2.4.3. Reaction of NiCl2.6H2O with L.
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C17H27N3O6S2Cl2Co; C, 36.31; H, 4.81; N, 7.47; S, 11.39, Found: C, 36.25; H, 4.82; N, 7.45;
A green solution of NiCl2.6H2O (0.563 g, 1 mmole) in ethanol (50ml) was added drop
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wise with continuously stirring to a solution of ligand L (0.325 g, 1 mmole) in ethanol (50ml). The solution was refluxed for 2hrs, a pale green precipitate was formed and washed with small amounts of ethanol then diethylether. The product obtained was insoluble in methanol but soluble in 1,2-dichloromethane and dimethylformamide (DMF) .The yield was
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0.622 g (70%), m.p. (319−320°C). FT-IR (ν, cm‐1): 3336 br.s (νOH, lattice water); 1653v.s, (νC=N, azomethine); 1464w, (νC=C, Ar.); 784w, (νC‐S, thiophene); 569w, (νM-N); 444w,
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(νM-S); 339, (νM-Cl). Calcd. for C17H27N3O6S2Cl2Ni; C, 36.32; H, 4.81; N, 7.48; S, 11.39, Found: C, 36.24; H, 4.90; N, 7.52; S, 11.36 %. 1H NMR (300 MHz, DMSO-d6, δ, ppm): 3.392 (s, 6H, CH3), 5.795–7.359 (m, 3H, Py-H) and (m, 6H, thiophene protons).
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ACCEPTED MANUSCRIPT 2.4.4. Reaction of CuCl2.2H2O with L. A green solution of CuCl2.2H2O (0.496 g, 1 mmole) in ethanol (50ml) was added drop wise with continuously stirring to a solution of ligand L (0.325 g, 1 mmole) in ethanol
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(50ml). The solution was refluxed for 2 hrs, a yellowish green precipitate was formed and washed with small amounts of ethanol then diethylether. The product obtained was insoluble in acetone but soluble in 1,2-dichloromethane and dimethylformamide (DMF). The yield was 0.657 g (80%), m.p. (309−310°C). FT-IR (ν, cm‐1): 3310 br.w (νOH, lattice water); 1618v.s,
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(νC=N, azomethine); 1424m, (νC=C, Ar.); 770w, (νC‐S, thiophene); 586w, (νM-N); 409w, (νM-S); 321, (νM-Cl). Calcd. for C17H19N3O2S2Cl2Cu; C, 41.25; H, 3.84; N, 8.49; S, 12.94,
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Found: C, 41.18; H, 3.91; N, 8.47; S, 12.93 %.
2.5. The fluorescence spectra of Schiff base L and its metal(II) complexes The fluorescence spectra of the Schiff base L and its metal(II) complexes measured in different solvents, dimethylformamide (DMF), dimethylsulfoxide (DMSO) and acetonitrile
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(CH3CN), at different pH values (2.2−9.4), were recorded at room temperature.
2.6. Catalytic activity of Schiff base Ligand L and its metal(II) complexes
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The catalytic activity of the complexes has been estimated by recording the rate of decomposition of hydrogen peroxide. The weight of metal complex 0.001 g was mixed with
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2 mL of H2O2 (0.4 %), diluted to 50 mL distilled water and shaking for 10 minutes. After 10 minutes, 5 mL aliquot from the reaction mixture was mixed with 10−15 mL H2SO4 (2.0 N) and then titrated against 0.02 M KMnO4. The decomposition of hydrogen peroxide was recorded each 5 min; from 0 to 1 hr. Study the effect of H2O2 concentration (0.8 and 1.2 %) with constant weight of metal complexes. Also study the effect of different weight of metal complexes with constant concentration of H2O2 (0.4 %).
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ACCEPTED MANUSCRIPT 3. Results and discussion The analytical & physical data of the Schiff base ligand L and its metal(II) complexes are presented in Table 1. 3.1. FTIR studies of the Schiff base ligand, L and its metal (II) complexes
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The FTIR spectrum of the Schiff base ligand, L exhibited a strong band at 1631 cm-1 assigned to ν(C=N) (azomethine) which indicates the formation of the Schiff base product. The spectrum exhibits bands at 1598 cm-1, 1575 cm-1 and 1457 cm-1, assigned to the ring stretching vibrations of the pyridine ring and also the bands at 722 cm-1 and 591 cm-1 which
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may be assigned to γ and δ (py-ring) in plane and out of plane deformation vibrations, respectively. A very strong band appears at 781 cm-1 which is assigned to νC-S
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acetylthiophene ring. The spectrum showed two bands which can be attributed to asymmetric and symmetric vibrations of νC-H aliphatic of methyl group at 2922 and 2852 cm-1. The vibrational frequency at 3064 cm-1 is assigned to ν(C-H) aromatic of pyridine and thiophene ring. The bands were observed in the region (1424−1493 cm-1) related to ν(C=C) stretching vibrations of 2-acetylthiophene and 2,6-diaminopyridine rings [20]. Upon comparison, the FTIR spectrum of free ligand displayed a strong band at 1631 cm-1 which is characteristic of
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ν(C=N) azomethine. The FTIR spectra of all complexes, displayed ν(C=N) bands in the region (1618−1653 cm-1). These bands are shifted to higher or lower energy regions compared to the free ligand L indicates that C=N of the ligand coordinates to the metal ions through nitrogen.
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The strong to very weak bands due to ν(C-S) stretching vibration of acetylthiophene ring exhibited at 781 cm-1 in the free Schiff base ligand, L. This band shifted to 779, 766, 784 and 770 cm-1 in Mn(II), Co(II), Ni(II) and Cu(II) complexes. These shifts refer to the coordination
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through acetylthiophene ring sulfur. The new bands appear at low frequency regions (567−588 cm-1), (409−469 cm-1) and (321−350 cm-1) are corresponding to ν(M-N), ν(M-S) and ν(M-Cl) vibrations. The bands corresponding to ν(OH) at (3310−3400 cm-1) showed that the metal complexes include hydrated water molecules which is coincided with the results of elemental and thermal analysis [21].
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ACCEPTED MANUSCRIPT 3.2. Mass spectral studies
The mass spectrum of ligand, L Fig. S1, which confirm the proposed formula of ligand by displaying a peak at 325 m/z due to molecular ion (parent peak), peak at 326 m/z due to
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(M+1) and base peak at 109 m/z. The series of peaks at 325, 310, 295, 268, 241,212, 201, 187, 160, 125, 118, 109, 83, 77, 51m/z may due to fragments [C17H15N3S2]+, [C16H12N3S2]+, [C15H9N3S2]+, [C13H7N3S2]+, [C13H12N3S]+, [C11H6N3S]+, [C11H10N2S]+, [C10H7N2S]+, [C8H5N2S]+, [C6H6NS]+, [C7H6N2]+, [C5H3NS]+, [C4H3S]+, [C5H3N]+ and [C4H3]+. The mass
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fragmentation pathway of the ligand, L is shown in Scheme S1 in the supplementary file.
The mass spectrum of [Co(C17H15N3S2)Cl2]·6H2O shows molecular ion peaks at 561.67
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m/z which is in accordance with the proposed formula of the complex Fig. S2, The other peaks at 454.68, 382.68, 325.57, 299.40, 258.37, 212.38, 186.31, 166.32, 160.32, 109.16, 83.21, 77.16, 57.18, 51.14 m/z may be due to the fragments [Co(C17H15N3S2)Cl2]+, [Co(C17H15N3S2)]+, [(C17H15N3S2)]+, [Co(C13H12N3S)]+, [Co(C11H10N2S)]+, [C11H6N3S]+, [C10H7N2S]+, [Co(C5H3NS)]+, [C8H4N2S]+, [C5H3NS]+, [C4H3S]+, [C4HN2]+, [Co]+ and
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[C3HN]+. The base peak at 109.16 m/z. The mass fragmentation pathway of [Co(C17H15N3S2)Cl2]·6H2O is shown in Scheme S2 in the supplementary file. 3.3. 1H NMR spectral studies
H NMR spectrum of the ligand L, in DMSO-d6, (Fig. 1) displayed singlet signal at 3.311
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ppm which is attributed to methyl protons of ligand L. The signals in the region (5.280−7.028
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ppm) are assigned to aromatic protons of acetyl thiophene and pyridyl ring.
The 1H NMR spectrum of [Ni(L)Cl2]· 6H2O complex, in DMSO-d6 is shown in Fig. 2. The spectrum of Ni(II) complex showed a singlet signal at 3.392 ppm which has been assigned to methyl protons and shifted to downfield. The signals in the region (5.795−7.359 ppm) were assigned to aromatic protons of pyridine and acetylthiophene ring and shifted downfield due to increased conjugation or coordination.
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ACCEPTED MANUSCRIPT 3.4. Electronic spectra, magnetic and molar conductance. The electronic spectrum of the ligand L under study in DMF solution was characterized mainly by two absorption bands, (Table S1). The first one appeared at 270 nm which can be assigned to (π−π*) transition of pyridyl, thiophene ring and azomethine group, this band
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shifted to longer wavelength (bathochromic shift) in the spectra of the Mn(II), Co(II), Ni(II) and Cu(II) complexes at 278nm, 277nm, 275nm and 282nm respectively. The second transition appeared at 308 nm assigned to the (n−π*) transition of the lone pair of the nitrogen in azomethine group and sulfur in thiophene ring, this band shifted to longer wavelength
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(bathochromic shift) in the spectra of the Mn(II), Co(II) and Cu(II) complexes at 312nm, 316nm and 323nm respectively but in case of Ni(II) complex has been shifted to shorter wavelength (hypsochromic shift) at 304nm. The Mn(II), Co(II), Ni(II) and Cu(II) complexes
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showed an additional absorption bands at 411nm, 417nm, 434nm and 432nm respectively which could be due to charge transfer transitions. The bands in the visible region, in the range (573− −750 nm) can be attributed to d-d transitions [22].
The Mn(II) complex displayed three absorption bands at 573, 635 and 706 nm assignable
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to 4T1g→6A1g, 4T2g(G)→6A1g and 4T1g (D)→6A1g transitions, respectively and metal to ligand (MLCT), transitions also occur at 411 nm indicating an octahedral geometry [23]. The observed µ eff value is 5.81 B.M. i.e. close to the spin only value manganese (II) in octahedral
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environmental [24].
The electronic spectrum of the Co(II) complex displayed three bands, two of them 720
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and 578 nm. These are assigned to the transition 4T1g(F)→4T2g(F) and 4T1g(F)→4A2g(F) respectively, suggesting an octahedral geometry around Co(II) ion. The third one at 417 nm points out to charge transfer band. The observed µ eff value is 4.75 B.M., which is indicative of an octahedral structure [25] The Ni(II) complex displayed three bands at 750, 685 and 582 nm were assigned to 3
A2g(F)→3T2g(F),
3
A2g(F)→3T1g(F) and
3
A2g(F)→3T1g(P) transitions, respectively. The
spectrum showed also band at 434nm which may attribute to ligand to metal charge transfer [26]. The magnetic moment of Ni(II) complex is 3.87 B.M. which is in the normal range observed for an octahedral Ni(II) complexes [27].
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ACCEPTED MANUSCRIPT The Cu(II) complex displayed one band at 578 nm which is assignable to 2Eg→2T2g transition and may support the six coordinated geometry[28]. The observed µ eff value is 1.91 B.M. The observed molar conductance of the complexes dissolved in DMF at 10-3 M were
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obtained in the range 14.15−20.70 ohm-1 cm-2 mol-1, (Table S1). These low values indicated that all these complexes are non-electrolytic nature with no counter ions.
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3.5. Thermal studies
The thermogram analysis (TGA/DTA) of the complexes is useful to prove the following:
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(i) presence of water molecule inside or outside the coordination sphere (ii) decomposition temperature and (iii) thermal stability of the compounds. The TGA curves of the metal complexes is shown in Fig. 3 and listed in Table 2.
The thermogravimetric analysis of [Mn(L)Cl2]·4H2O
involves four decomposition
steps. The first step from (44−113°C) showed removal of one lattice water with an estimated
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mass loss of 4.277(Calc., 3.449 %). The second step from (113−205°C) showed removal of two lattice water with an estimated mass loss of 6.587 (Calc., 7.144%). The third step from (206−426°C) showed removal of 1/2Cl2, 2CH3 and H2O with an estimated mass loss of 17.930 (Calc., 17.845 %). The last step from (427−1000°C) attributed to loss of 2SH, 2C=N,
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2H2 and 1/2Cl2 with an estimated mass loss of 41.112 (Calc., 40.973%). The overall weight
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loss of the decomposition steps is found to be 69.906 (Calc. 69.411).
The thermogravimetric analysis of [Co(L)Cl2]·6H2O involves three decomposition steps. The first step from (47−204°C) showed removal of two lattice water with an estimated mass loss of 7.113 (Calc., 6.407%). The second step from (204−281°C) showed removal of one lattice water with an estimated mass loss of 3.575 (Calc., 3.423%). The last step from (282−1000°C) attributed to loss of 3H2O, 2SH, 2C=N, CH3 and Cl2 with an estimated mass loss of 50.705 (Calc., 50.601%). The overall weight loss of the decomposition steps is found to be 61.393 (Calc. 60.431).
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ACCEPTED MANUSCRIPT The thermogravimetric analysis of [Ni(L)Cl2]·6H2O involves three decomposition steps. The first step from (43−346°C) showed partial dehydration of 4.5 mole of lattice water with an estimated mass loss of 14.768 (Calc., 14.421%). The second step from (346−533°C) showed removal of 1.5 mole of lattice water, Cl2, CH3 and 1/2C2 with an estimated mass loss of 25.271 (Calc., 25.795 %). The last step from (533−1000°C) attributed to loss of C4H3S,
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C5H3N and C=N with an estimated mass loss of 52.222 (Calc., 52.425 %). The overall weight loss of the decomposition steps is found to be 92.261 (Calc. 92.641).
The thermogravimetric analysis of [Cu(L)Cl2]·2H2O involves three decomposition steps.
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The first step from (44−144°C) showed removal of two lattice water with an estimated mass loss of 7.371(Calc., 7.280%). The second step from (145−310°C) showed removal of Cl2 and 1/2C2 with an estimated mass loss of 16.879 (Calc., 16.575 %). The last step from
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(311−1000°C) attributed to loss of 2C=N, 2CH3, C4H3S and 1/2C2 with an estimated mass loss of 45.971 (Calc., 45.752 %). The overall weight of the decomposition steps is found to be 70.221 (Calc. 69.607).
S0022-2860(18)30283-7
DOI:
10.1016/j.molstruc.2018.03.006
Reference:
MOLSTR 24945
To appear in:
Journal of Molecular Structure
Received Date: 26 October 2017 Revised Date:
1 March 2018
Accepted Date: 2 March 2018
Please cite this article as: M.A. Ayoub, E.H. Abd-Elnasser, M.A. Ahmed, M.G. Rizk, Some new metal(II) complexes based on bis-Schiff base ligand derived from 2-acetylethiophine and 2,6-diaminopyridine: Syntheses, structural investigation, thermal, fluorescence and catalytic activity studies, Journal of Molecular Structure (2018), doi: 10.1016/j.molstruc.2018.03.006. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT
Some New Metal(II) Complexes Based On Bis-Schiff Base Ligand Derived From 2-acetylethiophine and 2,6-diaminopyridine: Syntheses, Structural Investigation, Thermal, Fluorescence and Catalytic Activity Studies
a
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Manara A. Ayouba,b *, Eman H. Abd-Elnasserb, Mona A. Ahmedb and Mariam G. Rizkb
* Chemistry Department, Faculty of Science, Taibah University, Al Madinah Al Munawarah, 41411, Saudi Arabia.
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*
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Chemistry Department, Faculty of Women for Arts, Science and Education, Ain-Shams University, Cairo, 11757, Egypt
Corresponding Author: E-mail: [email protected]
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Tel: +2.02.01006496983
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Graphical Abstract
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Effect of pH and solvent on novel bis Schiff base ligand L
ACCEPTED MANUSCRIPT Some New Metal(II) Complexes Based On Bis-Schiff Base Ligand Derived From 2-acetylethiophine and 2,6-diaminopyridine: Syntheses, Structural Investigation, Thermal, Fluorescence and Catalytic Activity Studies Manara A. Ayouba,b*, Eman H. Abd-Elnasserb, Mona A. Ahmedb and Mariam G. Rizkb a
* Chemistry Department, Faculty of Science, Taibah University, Al Madinah Al Munawarah, 41411, Saudi Arabia.
b
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Chemistry Department, Faculty of Women for Arts, Science and Education, Ain-Shams University, Cairo, 11757, Egypt
ABSTRACT
A novel Schiff base ligand N, N`-bis (1-(thiophen-2-yl) ethylidene) pyridine-2, 6-diamine has
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been prepared by the condensation of 2,6-diaminopyridine and 2- acetylthiophene in ethanol in the molar ratio of 1:2. The Study by analytical and spectroscopic techniques indicated that
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the complexes have composition with the general formulae: [MLX2]· nH2O, where (M = Mn, Co, Ni, and Cu; X = Cl; n=4, 6, 6, 2), respectively. All the metal (II) complexes have been characterized with elemental analysis, FT−IR, Mass, 1H NMR, UV−Vis, magnetic moment, thermal analysis (TG and DTG) techniques, molar conductance and fluorescence spectra. Non electrolyte of complexes using DMF as a solvent is due to their low molar conductance. From FTIR spectral data, the coordination between the central metal ion with azomethine
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nitrogen and sulphur of acetylthiophene ring are confirmed. An octahedral geometry of all metal(II) complexes is investigated from electronic and magnetic data. The kinetic analysis of the thermogravimetric data was performed by using the Coats-Redfern equation. The
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fluorescence properties of theses complexes in DMSO, DMF, and CH3CN were studied. The effect of pH influencing the fluorescence intensity is discussed. The catalytic activities of metal(II) complexes were studied using H2O2 solution.
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Keywords Transition metal complexes of bis-Schiff base Spectroscopic analysis Thermogravimetric studies Fluorescence spectra Catalytic activity *Corresponding Author: Manara Ahmed Ayoub, E-mail: [email protected] Tel no: +2.02.01006496983
ACCEPTED MANUSCRIPT 1. Introduction All Schiff base complexes have been derived from heterocyclic compounds which belong to bioinorganic chemistry [1-3]. They have an important role in the development of modern coordination chemistry, and they are a major point in the development of inorganic
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biochemistry [4]. The presence of exocyclic nitrogen and sulphur atoms in the structure of Schiff bases provide a variety of coordination sites to link directly with the transition metal ions [5-6]. Different heterocyclic compounds such as pyridine are good ligands due to the presence of ring nitrogen atoms with a localized pair of electrons. So that, the application
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potential has led to formation a series of novel Schiff base compounds with a wide range of stability, reactivity, biological, chemical and physical properties [7-10]. For pyridine derivative ligands stabilize many different metals in various oxidation states, which are useful
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in clinical, biological, industrial and analytical applications. Moreover their great roles in organic synthesis and catalysis [11, 12]. Different derivatives of pyridine ligands were chosen as suitable building blocks for complexation reaction with various transition metal ions, they can be considered as soft Lewis acids. These compounds are flexible about the central C=N bond. Each ligand contains five potential sites for coordination to metal ions [13].
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Furthermore, a great interest of heterocyclic compounds contains transition metal complexes due to their ability to absorb visible light and act as electron sources that uses in photosensitizers applications [14-18]. The decomposition of hydrogen peroxide is used as standard reaction to determine the catalytic activity of metal oxide and metal complexes [19].
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In this work, we have reported the syntheses and characterization of a novel Schiff base derived from condensation of 2-acetylthiophene with to 2,6-aminopyridine, and its complexes
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with Mn(II), Co(II), Ni(II) and Cu(II). The synthesized Schiff base complexes have been characterized by elemental analyses, IR, MS, 1H NMR, UV−Vis, magnetic moment, TGA, molar conductance and fluorescence spectra studies. Schematic representation for the syntheses of Schiff base ligand N, N`[2-acetylthiophene]-2,6 diaminopyridineimine (L) and its complexes (Scheme 1).
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ACCEPTED MANUSCRIPT 2. Experimental
2.1. Materials and reagents All chemicals were purchased from commercial sources and used as received. The
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chemical used with high purity. They include 2,6-diaminopyridine (Aldrich), 2acetylthiophene (Merck), manganese(II) chloride tetrahydrate, cobalt(II) and nickel(II) chloride hexahydrate and copper(II) chloride dehydrate. Organic solvents used are absolute ethanol, methanol, diethyl ether, dimethylformamide (DMF), dimethylsulfoxide (DMSO),
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acetonitrile (CH3CN) and 1,2-dichloromethane as pure grade materials.
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2.2. Physical measurements
Microanalysis of (CHNS) was performed on a Perkin Elmer 2400 elemental analyzer. FTIR measurements (KBr discs) were recorded with a Shimadzu 8000 FTIR spectrometer at the central laboratory, Ain Shams University, Egypt. The FTIR spectra (600 – 200 cm-1) of the compounds were recorded as CsI discs using (Nexus 670) FTIR spectrophotometer,
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Nicolet (U.S.A) at the National Research Center, Gize, Egypt. 1H NMR measurements were recorded with a Varian-mercury 300 MHz spectrometer at the Microanalytical Center, Cairo University, Giza, Egypt. Samples were dissolved in DMSO-d6 using tetramethylsilane as an internal standard. Mass spectroscopy measurements of the solid ligands and complexes were
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recorded using a JEOL JMS-AX500 spectrometer at the National Research Center, Giza, Egypt. Magnetic susceptibility measurements were carried out by employing the Gouy
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method at room temperature using a magnetic susceptibility balance, Sherwood Scientific, Cambridge Science Park, Cambridge England. Thermogravimetric analysis (TG and DTG) were carried out under N2 atmosphere with a heating rate of 10°C/min using a Shimadzu TG-50H thermal analyzer at the Microanalytical Center, Cairo University, Giza, Egypt. All conductivity measurements were performed in DMF (1×10-3 M) at 25°C, using WAP, GMP 50 conductivity meter. UV-Vis spectra were obtained with a Shimadzu UV 1800 spectrophotometer in the range (200 − 800 nm) at the Micro analytical Center, Cairo University, Giza, Egypt. The photo luminescent properties of all complexes were performed on a Jenway 6270 fluorimeter, at the central laboratory, Ain Shams University, Egypt. All
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ACCEPTED MANUSCRIPT melting points were measured using an ordinary MEL-TEMP II Laboratory device (U.S.A), melting point apparatus. 2.3. Synthesis of N, N`-bis(1-(thiophen-2-yl)ethylidene)pyridine-2,6-diamine Schiff base L. The proposed ligand was synthesized by slow addition of 2-acetylthiophene (1.09 ml, 10
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mmole) in 50 ml ethanol to 2,6-diaminopyridine (1.09 g, 10 mmole) in 50 ml ethanol. The reaction mixture was refluxed for 4 hrs by using ultrasonic radiation. The yellow product was obtained by filtration, purified by crystallization from hot ethanol and washed with ethanol then diethylether. The ligand obtained was soluble in 1,2-dichloromethane, chloroform,
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dimethylformamide (DMF), dimethylsulfoxide (DMSO), and partially soluble in acetone, methanol and acetonitrile (CH3CN). The yield was (1.763g, 75%), m.p. (216−218°C). FT−IR
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(ν, cm‐1): 1631v.s, (νC=N, azomethine); 1457 v.s, (νC=C, Ar.); 781s, (νC‐S, thiophene). Calcd. for C17H15N3S2; C, 62.77; H, 4.62; N, 12.92; S, 19.69, Found: C, 62.77; H, 4.40; N, 12.80; S, 19.70 %. MS (EI, m/z (%)): 325(M+, 2). 1H NMR (300 MHz, DMSO-d6, δ, ppm): 3.311 (s, 6H, CH3), 5.280–7.028 (m, 3H, Py-H) and (m, 6H, thiophene protons).
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2.4. Synthesis of Schiff base metal(II) complexes 2.4.1. Reaction of MnCl2.4H2O with L.
A pink solution of MnCl2.4H2O (0.523 g, 1mmole) in ethanol (50ml) was added drop
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wise with continuously stirring to a solution of ligand L (0.325 g, 1 mmole) in ethanol (50ml). The solution was refluxed for 2 hrs, dark green precipitate was formed and washed
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with small amounts of ethanol then diethylether. The product obtained was insoluble in acetone and methanol but soluble in 1,2-dichloromethane, dimethylformamide (DMF) and dimethylsulfoxide (DMSO). The yield was 0.619 g (73%), m.p. (342−344°C). FT-IR (ν, cm‐1): 3400 br.s, (νOH, hydrated water); 1644v.s, (νC=N, azomethine); 1456 s, (νC=C, Ar.); 799 m, (νC‐S, thiophene); 567w, (νM-N); 469w, (νM-S); 350w, (νM-Cl). Calcd. for C17H23N3O4S2Cl2Mn; C, 39.09; H, 4.41; N, 8.05; S, 12.26, Found: C, 39.00; H, 4.29; N, 8.02; S, 12.21%.
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ACCEPTED MANUSCRIPT 2.4.2. Reaction of CoCl2.6H2O with L. A red solution of CoCl2.6H2O (0.563 g, 1 mmole) in ethanol (50 ml) was added drop wise with continuously stirring to a solution of ligand L (0.325 g, 1 mmole) in ethanol
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(50 ml). The solution was refluxed for 2 hrs, a red precipitate was formed and washed with small amounts of ethanol then diethylether. The product obtained was insoluble in acetone and methanol but soluble in 1,2-dichloromethane, dimethylformamide (DMF) and acetonitrile (CH3CN). The yield was 0.802 g (82%), m.p. (335−337°C). FT-IR (ν, cm‐1):
(νC‐S,
thiophene);
567w,
(νM-N);
486w,
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3348 br.w, (νOH, lattice water); 1640v.s, (νC=N, azomethine); 1493m, (νC=C, Ar.); 766 m, (νM-S);
342,
(νM-Cl).
Calcd.
for
S, 11.36 %.
2.4.3. Reaction of NiCl2.6H2O with L.
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C17H27N3O6S2Cl2Co; C, 36.31; H, 4.81; N, 7.47; S, 11.39, Found: C, 36.25; H, 4.82; N, 7.45;
A green solution of NiCl2.6H2O (0.563 g, 1 mmole) in ethanol (50ml) was added drop
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wise with continuously stirring to a solution of ligand L (0.325 g, 1 mmole) in ethanol (50ml). The solution was refluxed for 2hrs, a pale green precipitate was formed and washed with small amounts of ethanol then diethylether. The product obtained was insoluble in methanol but soluble in 1,2-dichloromethane and dimethylformamide (DMF) .The yield was
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0.622 g (70%), m.p. (319−320°C). FT-IR (ν, cm‐1): 3336 br.s (νOH, lattice water); 1653v.s, (νC=N, azomethine); 1464w, (νC=C, Ar.); 784w, (νC‐S, thiophene); 569w, (νM-N); 444w,
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(νM-S); 339, (νM-Cl). Calcd. for C17H27N3O6S2Cl2Ni; C, 36.32; H, 4.81; N, 7.48; S, 11.39, Found: C, 36.24; H, 4.90; N, 7.52; S, 11.36 %. 1H NMR (300 MHz, DMSO-d6, δ, ppm): 3.392 (s, 6H, CH3), 5.795–7.359 (m, 3H, Py-H) and (m, 6H, thiophene protons).
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ACCEPTED MANUSCRIPT 2.4.4. Reaction of CuCl2.2H2O with L. A green solution of CuCl2.2H2O (0.496 g, 1 mmole) in ethanol (50ml) was added drop wise with continuously stirring to a solution of ligand L (0.325 g, 1 mmole) in ethanol
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(50ml). The solution was refluxed for 2 hrs, a yellowish green precipitate was formed and washed with small amounts of ethanol then diethylether. The product obtained was insoluble in acetone but soluble in 1,2-dichloromethane and dimethylformamide (DMF). The yield was 0.657 g (80%), m.p. (309−310°C). FT-IR (ν, cm‐1): 3310 br.w (νOH, lattice water); 1618v.s,
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(νC=N, azomethine); 1424m, (νC=C, Ar.); 770w, (νC‐S, thiophene); 586w, (νM-N); 409w, (νM-S); 321, (νM-Cl). Calcd. for C17H19N3O2S2Cl2Cu; C, 41.25; H, 3.84; N, 8.49; S, 12.94,
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Found: C, 41.18; H, 3.91; N, 8.47; S, 12.93 %.
2.5. The fluorescence spectra of Schiff base L and its metal(II) complexes The fluorescence spectra of the Schiff base L and its metal(II) complexes measured in different solvents, dimethylformamide (DMF), dimethylsulfoxide (DMSO) and acetonitrile
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(CH3CN), at different pH values (2.2−9.4), were recorded at room temperature.
2.6. Catalytic activity of Schiff base Ligand L and its metal(II) complexes
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The catalytic activity of the complexes has been estimated by recording the rate of decomposition of hydrogen peroxide. The weight of metal complex 0.001 g was mixed with
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2 mL of H2O2 (0.4 %), diluted to 50 mL distilled water and shaking for 10 minutes. After 10 minutes, 5 mL aliquot from the reaction mixture was mixed with 10−15 mL H2SO4 (2.0 N) and then titrated against 0.02 M KMnO4. The decomposition of hydrogen peroxide was recorded each 5 min; from 0 to 1 hr. Study the effect of H2O2 concentration (0.8 and 1.2 %) with constant weight of metal complexes. Also study the effect of different weight of metal complexes with constant concentration of H2O2 (0.4 %).
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ACCEPTED MANUSCRIPT 3. Results and discussion The analytical & physical data of the Schiff base ligand L and its metal(II) complexes are presented in Table 1. 3.1. FTIR studies of the Schiff base ligand, L and its metal (II) complexes
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The FTIR spectrum of the Schiff base ligand, L exhibited a strong band at 1631 cm-1 assigned to ν(C=N) (azomethine) which indicates the formation of the Schiff base product. The spectrum exhibits bands at 1598 cm-1, 1575 cm-1 and 1457 cm-1, assigned to the ring stretching vibrations of the pyridine ring and also the bands at 722 cm-1 and 591 cm-1 which
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may be assigned to γ and δ (py-ring) in plane and out of plane deformation vibrations, respectively. A very strong band appears at 781 cm-1 which is assigned to νC-S
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acetylthiophene ring. The spectrum showed two bands which can be attributed to asymmetric and symmetric vibrations of νC-H aliphatic of methyl group at 2922 and 2852 cm-1. The vibrational frequency at 3064 cm-1 is assigned to ν(C-H) aromatic of pyridine and thiophene ring. The bands were observed in the region (1424−1493 cm-1) related to ν(C=C) stretching vibrations of 2-acetylthiophene and 2,6-diaminopyridine rings [20]. Upon comparison, the FTIR spectrum of free ligand displayed a strong band at 1631 cm-1 which is characteristic of
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ν(C=N) azomethine. The FTIR spectra of all complexes, displayed ν(C=N) bands in the region (1618−1653 cm-1). These bands are shifted to higher or lower energy regions compared to the free ligand L indicates that C=N of the ligand coordinates to the metal ions through nitrogen.
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The strong to very weak bands due to ν(C-S) stretching vibration of acetylthiophene ring exhibited at 781 cm-1 in the free Schiff base ligand, L. This band shifted to 779, 766, 784 and 770 cm-1 in Mn(II), Co(II), Ni(II) and Cu(II) complexes. These shifts refer to the coordination
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through acetylthiophene ring sulfur. The new bands appear at low frequency regions (567−588 cm-1), (409−469 cm-1) and (321−350 cm-1) are corresponding to ν(M-N), ν(M-S) and ν(M-Cl) vibrations. The bands corresponding to ν(OH) at (3310−3400 cm-1) showed that the metal complexes include hydrated water molecules which is coincided with the results of elemental and thermal analysis [21].
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ACCEPTED MANUSCRIPT 3.2. Mass spectral studies
The mass spectrum of ligand, L Fig. S1, which confirm the proposed formula of ligand by displaying a peak at 325 m/z due to molecular ion (parent peak), peak at 326 m/z due to
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(M+1) and base peak at 109 m/z. The series of peaks at 325, 310, 295, 268, 241,212, 201, 187, 160, 125, 118, 109, 83, 77, 51m/z may due to fragments [C17H15N3S2]+, [C16H12N3S2]+, [C15H9N3S2]+, [C13H7N3S2]+, [C13H12N3S]+, [C11H6N3S]+, [C11H10N2S]+, [C10H7N2S]+, [C8H5N2S]+, [C6H6NS]+, [C7H6N2]+, [C5H3NS]+, [C4H3S]+, [C5H3N]+ and [C4H3]+. The mass
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fragmentation pathway of the ligand, L is shown in Scheme S1 in the supplementary file.
The mass spectrum of [Co(C17H15N3S2)Cl2]·6H2O shows molecular ion peaks at 561.67
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m/z which is in accordance with the proposed formula of the complex Fig. S2, The other peaks at 454.68, 382.68, 325.57, 299.40, 258.37, 212.38, 186.31, 166.32, 160.32, 109.16, 83.21, 77.16, 57.18, 51.14 m/z may be due to the fragments [Co(C17H15N3S2)Cl2]+, [Co(C17H15N3S2)]+, [(C17H15N3S2)]+, [Co(C13H12N3S)]+, [Co(C11H10N2S)]+, [C11H6N3S]+, [C10H7N2S]+, [Co(C5H3NS)]+, [C8H4N2S]+, [C5H3NS]+, [C4H3S]+, [C4HN2]+, [Co]+ and
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[C3HN]+. The base peak at 109.16 m/z. The mass fragmentation pathway of [Co(C17H15N3S2)Cl2]·6H2O is shown in Scheme S2 in the supplementary file. 3.3. 1H NMR spectral studies
H NMR spectrum of the ligand L, in DMSO-d6, (Fig. 1) displayed singlet signal at 3.311
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ppm which is attributed to methyl protons of ligand L. The signals in the region (5.280−7.028
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ppm) are assigned to aromatic protons of acetyl thiophene and pyridyl ring.
The 1H NMR spectrum of [Ni(L)Cl2]· 6H2O complex, in DMSO-d6 is shown in Fig. 2. The spectrum of Ni(II) complex showed a singlet signal at 3.392 ppm which has been assigned to methyl protons and shifted to downfield. The signals in the region (5.795−7.359 ppm) were assigned to aromatic protons of pyridine and acetylthiophene ring and shifted downfield due to increased conjugation or coordination.
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ACCEPTED MANUSCRIPT 3.4. Electronic spectra, magnetic and molar conductance. The electronic spectrum of the ligand L under study in DMF solution was characterized mainly by two absorption bands, (Table S1). The first one appeared at 270 nm which can be assigned to (π−π*) transition of pyridyl, thiophene ring and azomethine group, this band
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shifted to longer wavelength (bathochromic shift) in the spectra of the Mn(II), Co(II), Ni(II) and Cu(II) complexes at 278nm, 277nm, 275nm and 282nm respectively. The second transition appeared at 308 nm assigned to the (n−π*) transition of the lone pair of the nitrogen in azomethine group and sulfur in thiophene ring, this band shifted to longer wavelength
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(bathochromic shift) in the spectra of the Mn(II), Co(II) and Cu(II) complexes at 312nm, 316nm and 323nm respectively but in case of Ni(II) complex has been shifted to shorter wavelength (hypsochromic shift) at 304nm. The Mn(II), Co(II), Ni(II) and Cu(II) complexes
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showed an additional absorption bands at 411nm, 417nm, 434nm and 432nm respectively which could be due to charge transfer transitions. The bands in the visible region, in the range (573− −750 nm) can be attributed to d-d transitions [22].
The Mn(II) complex displayed three absorption bands at 573, 635 and 706 nm assignable
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to 4T1g→6A1g, 4T2g(G)→6A1g and 4T1g (D)→6A1g transitions, respectively and metal to ligand (MLCT), transitions also occur at 411 nm indicating an octahedral geometry [23]. The observed µ eff value is 5.81 B.M. i.e. close to the spin only value manganese (II) in octahedral
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environmental [24].
The electronic spectrum of the Co(II) complex displayed three bands, two of them 720
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and 578 nm. These are assigned to the transition 4T1g(F)→4T2g(F) and 4T1g(F)→4A2g(F) respectively, suggesting an octahedral geometry around Co(II) ion. The third one at 417 nm points out to charge transfer band. The observed µ eff value is 4.75 B.M., which is indicative of an octahedral structure [25] The Ni(II) complex displayed three bands at 750, 685 and 582 nm were assigned to 3
A2g(F)→3T2g(F),
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A2g(F)→3T1g(F) and
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A2g(F)→3T1g(P) transitions, respectively. The
spectrum showed also band at 434nm which may attribute to ligand to metal charge transfer [26]. The magnetic moment of Ni(II) complex is 3.87 B.M. which is in the normal range observed for an octahedral Ni(II) complexes [27].
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ACCEPTED MANUSCRIPT The Cu(II) complex displayed one band at 578 nm which is assignable to 2Eg→2T2g transition and may support the six coordinated geometry[28]. The observed µ eff value is 1.91 B.M. The observed molar conductance of the complexes dissolved in DMF at 10-3 M were
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obtained in the range 14.15−20.70 ohm-1 cm-2 mol-1, (Table S1). These low values indicated that all these complexes are non-electrolytic nature with no counter ions.
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3.5. Thermal studies
The thermogram analysis (TGA/DTA) of the complexes is useful to prove the following:
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(i) presence of water molecule inside or outside the coordination sphere (ii) decomposition temperature and (iii) thermal stability of the compounds. The TGA curves of the metal complexes is shown in Fig. 3 and listed in Table 2.
The thermogravimetric analysis of [Mn(L)Cl2]·4H2O
involves four decomposition
steps. The first step from (44−113°C) showed removal of one lattice water with an estimated
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mass loss of 4.277(Calc., 3.449 %). The second step from (113−205°C) showed removal of two lattice water with an estimated mass loss of 6.587 (Calc., 7.144%). The third step from (206−426°C) showed removal of 1/2Cl2, 2CH3 and H2O with an estimated mass loss of 17.930 (Calc., 17.845 %). The last step from (427−1000°C) attributed to loss of 2SH, 2C=N,
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2H2 and 1/2Cl2 with an estimated mass loss of 41.112 (Calc., 40.973%). The overall weight
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loss of the decomposition steps is found to be 69.906 (Calc. 69.411).
The thermogravimetric analysis of [Co(L)Cl2]·6H2O involves three decomposition steps. The first step from (47−204°C) showed removal of two lattice water with an estimated mass loss of 7.113 (Calc., 6.407%). The second step from (204−281°C) showed removal of one lattice water with an estimated mass loss of 3.575 (Calc., 3.423%). The last step from (282−1000°C) attributed to loss of 3H2O, 2SH, 2C=N, CH3 and Cl2 with an estimated mass loss of 50.705 (Calc., 50.601%). The overall weight loss of the decomposition steps is found to be 61.393 (Calc. 60.431).
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ACCEPTED MANUSCRIPT The thermogravimetric analysis of [Ni(L)Cl2]·6H2O involves three decomposition steps. The first step from (43−346°C) showed partial dehydration of 4.5 mole of lattice water with an estimated mass loss of 14.768 (Calc., 14.421%). The second step from (346−533°C) showed removal of 1.5 mole of lattice water, Cl2, CH3 and 1/2C2 with an estimated mass loss of 25.271 (Calc., 25.795 %). The last step from (533−1000°C) attributed to loss of C4H3S,
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C5H3N and C=N with an estimated mass loss of 52.222 (Calc., 52.425 %). The overall weight loss of the decomposition steps is found to be 92.261 (Calc. 92.641).
The thermogravimetric analysis of [Cu(L)Cl2]·2H2O involves three decomposition steps.
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The first step from (44−144°C) showed removal of two lattice water with an estimated mass loss of 7.371(Calc., 7.280%). The second step from (145−310°C) showed removal of Cl2 and 1/2C2 with an estimated mass loss of 16.879 (Calc., 16.575 %). The last step from
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(311−1000°C) attributed to loss of 2C=N, 2CH3, C4H3S and 1/2C2 with an estimated mass loss of 45.971 (Calc., 45.752 %). The overall weight of the decomposition steps is found to be 70.221 (Calc. 69.607).