untitled European Journal of Chemistry 8 (1) (2017) 85‐95 European Journal of Chemistry ISSN 2153‐2249 (Print) / ISSN 2153‐2257 (Online)  2017 Atlanta Publishing House LLC ‐ All rights reserved ‐ Printed in the USA http://dx.doi.org/10.5155/eurjchem.8.1.85-95.1513 European Journal of Chemistry Journal webpage: www.eurjchem.com Synthesis, physicochemical, thermal, fluorescence and catalytic activity studies of novel Mn(II), Co(II), Ni(II) and Cu(II) complexes with tridentate (ONS) Schiff base ligand Manara Ahmed Ayoub *, Eman Hamed Abd‐Elnasser, Mona Abdel‐Aziz Ahmed and Marium Girgis Rizk Chemistry Department, Faculty of Women for Arts, Science and Education, Ain‐Shams University, Cairo, 11757, Egypt * Corresponding author at: Chemistry Department, Faculty of Women for Arts, Science and Education, Ain‐Shams University, Cairo, 11757, Egypt. Tel.: +2.02.01006496983. Fax: +2.02.24157804. E‐mail address: manara_2005@yahoo.com (M.A. Ayoub). ARTICLE INFORMATION ABSTRACT DOI: 10.5155/eurjchem.8.1.85-95.1513 Received: 02 December 2016 Received in revised form: 17 January 2017 Accepted: 21 January 2017 Published online: 31 March 2017 Printed: 31 March 2017   Syntheses and physicochemical studies of Mn(II), Co(II), Ni(II) and Cu(II) complexes with tridentate Schiff base ligand (E)‐2‐((1‐(thiophen‐2‐yl)ethylidene)amino)phenol (HL) (ATS) were characterized by elemental analysis, FT‐IR, Mass, 1H NMR, UV‐Vis, magnetic moment, thermal analysis (TG and DTG) techniques, molar conductance and fluorescence spectra. The IR spectra showed that complexes were coordinated in metal ions via the imine N, O and S atoms. Magnetic and UV‐Vis spectra, indicated that the geometrical structure of Mn(II), Co(II) and Ni(II) complexes are an octahedral while Cu(II) is a tetrahedral. The kinetic thermodynamic parameters such as E*, H*, S* and G* were determined for each thermal degradation stage of TG curves of the metal(II) complexes using Coat‐Redfern method. Fluorescence studies indicated that the Schiff base ligand HL (ATS), and its metal(II) complexes can serve as potential photoactive materials as indicated from their characteristic fluorescence properties and study the effect of solvent and pH on it. The catalytic activities of metal(II) complexes were studied using H2O2 solution. KEYWORDS ONS donor sites Catalytic activity Thermal analysis Schiff base ligand Metals complexes Fluorescence spectra 2‐((1‐(Thiophen‐2‐yl)ethylidene)amino)phenol Cite this: Eur. J. Chem. 2017, 8(1), 85‐95 1. Introduction Schiff bases have often been used as chelating ligands in coordination chemistry. It is well known that N and S atoms play a key role in the coordination of metals at the active sites of numerous metallobio molecules [1]. Schiff base metal complexes have been widely studied because they have industrial, antifungal, antibacterial, anticancer, anti‐oxidative activity, antibiotics, anti‐corrosion and catalysis applications [2‐4]. The Schiff base metal complexes are also very useful model systems in chelate chemistry. The metal ion in such complexes can be coordinated by the imine nitrogen atom and also by the other active centers present in the molecule. This can lead to many interesting catalytic and potential properties [5‐7]. Schiff base compounds often have the property of luminescence, especially, when their complexes have structure of rigidity plane and rich conjugation [8,9]. Many of tridentate Schiff base ligand showed enhanced fluorescence. Moreover, luminescent compounds of Schiff base ligand and its transition metal complexes are attracting much current research interest because of their application including emitting materials for organic light, light materials for photo fluorescent sensors for organic or inorganic analytes [10‐12]. The decomposition of hydrogen peroxide has been used as a model reaction for investigation of the catalytic activity of various transition metal complexes [13]. The present study describes the chelation behaviors of Schiff base derived from the condensation of 2‐acetylthio‐ phene with to 2‐aminophenol towards Mn(II), Co(II), Ni(II) and Cu(II) in molar ratio (1:1) (Ligand: Metal ion). The metal complexes were characterized by elemental analyses, IR, 1H NMR, MS, UV‐Vis, TGA, magnetic moment, molar conductance and fluorescence spectra. 2. Experimental 2.1. Materials and reagents All chemicals were reagent grade quality purchased from commercial sources and used as received. The chemicals used are of the highest purity available. 86 Ayoub et al. / European Journal of Chemistry 8 (1) (2017) 85‐95 Scheme 1 They include 2‐aminophenol (Aldrich), 2‐acetylthiophene (Merck), cobalt(II) and nickel(II) chloride hexahydrate and cupper(II) chloride dehydrate and manganese(II) chloride tetrahydrate, organic solvents used are absolute ethanol, methanol, diethyl ether, dimethylformamide (DMF), dimethyl sulfoxide (DMSO), acetonitrile (CH3CN) and 1,2‐dichloro methane as pure grade materials. 2.2. Physical measurements Elemental analysis (CHNS) was performed on a Perkin Elmer 2400 elemental analyzer. FT‐IR measurements (KBr pellets) were carried out on a Shimadzu 8000 FT‐IR spectrometer at the central laboratory, Ain Shams University, Egypt. 1H NMR measurements were performed on a Varian‐ mercury 300 MHz spectrometer at the Microanalytical Center, Cairo University, Giza, Egypt. Samples were dissolved in DMSO‐d6 with TMS as internal reference. Mass spectroscopy measurements of the solid ligands and complexes were carried out on a JEOL JMS‐AX500 spectrometer at the National Research Center, Giza, Egypt, magnetic measurements of the complexes were measured by the Gouy method at room tem‐ perature 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 DT‐50 thermal analyzer at the Microanalytical Center, Cairo University, Giza, Egypt. All conductivity measure‐ ments were performed in DMF (110‐3 M) at 25 °C, by using WAP, GMP 50 conductivity meter. Ultraviolet spectra were recorded using 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 studied using a Jenway 6270 fluorimeter, the central laboratory, Ain Shams University, Egypt. All melting points were measured using an ordinary MEL‐TEMP II Laboratory device (U.S.A), melting point apparatus. 2.3. Synthesis of the tridentate Schiff base ligand (E)‐2‐((1‐ (thiophen‐2‐yl)ethylidene)amino)phenol Schiff base (HL) The ligand was synthesized by slow addition of 2‐ acetylthiophene (1.09 mL, 10 mmole) in 50 mL ethanol to 2‐ aminophenol (1.09 g, 10 mmole) in 50 mL ethanol. The reaction mixture was heated to reflux for 4 hrs. The dark brown product obtained after cooling was filtered off and washed with different amounts of 1,2‐dichloromethane then diethyl ether, fine crystals were obtained by recrystallization from hot ethanol. The reaction for the formation of HL is illustrated in Scheme 1. Yield: 1.645 g, 70%. M.p.: 157‐159 °C. FT‐IR (KBr, , cm‐1): 3304 (νOH, phenolic), 3054 (C‐H, Ar.), 2958, 2851 (C‐H asym.&sym., aliph.), 1602 (νC=N, azomethine), 1141 (νC‐O, phenolic), 1467 (m) (C=C, Ar.), 743 (C‐S, thiophe nolic). MS (EI, m/z (%)): 217.10 (M+, 73.03). 1H NMR (300 MHz, DMSO‐d6, δ, ppm): 3.172 (s, 3H, CH3), 6.358‐6.986 (m, 4H, Ar‐H), 7.365‐7.722 (m, 3H, thiophene protons), 8.879 (s, 1H, OH). Anal. calcd. for C12H11NSO: C, 66.33; H, 5.10; N, 6.45; S, 14.75. Found: C, 66.40; H, 4.87; N, 6.60; S, 14.60%. 2.4. Synthesis of Schiff base metal complexes A solution of metal salts (1 mmole) in ethanol (50 mL) was added gradually with constant stirring to a solution of ligand HL (1 mmole) in ethanol (50 mL). The solution was refluxed for 2 hrs. On cooling the colored product was precipitated out. It was filtered, and then washed with cold ethanol and diethyl ether. 2.5. The fluorescence spectra of the Schiff bases HL and its metal(II) complexes The fluorescence spectra of the Schiff bases HL1 and the metal(II) complexes measured in different solvents, dimethyl formamide (DMF), dimethylsulfoxide (DMSO) and acetonitrile (CH3CN), in different pH range (2.2‐9.4), were recorded at room temperature. 2.6. Catalytic activity of Schiff base ligand HL and its metal(II) complexes The catalytic activity of the complexes has been evaluated by recording the rate of decomposition of hydrogen peroxide. The weight of metal complex 0.001 g was mixed with 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 extent of hydrogen peroxide decomposes at different time (each 5 min; from 0 to 1 hr) were recorded. Repeating with (0.8 and 1.2 %) H2O2 with constant weight of metal complexes. A different weight of metal complexes were taken with constant concentration of H2O2 (0.4 %). 3. Results and discussion The analytical and physical data of the Schiff base ligand HL and their metal(II) complexes are listed in Table 1. 3.1. IR spectra of the Schiff base ligands and their metal (II) complexes The IR spectra of the complexes are compared with those of the free ligand in order to determine the coordination sites that may be involved in chelation, shown in Figure 1 and the assignments are listed in Table 2. Upon comparison, it was determined that the (OH) stretching vibration which is found in the free ligand at 3375 cm‐1 disappeared in the spectra of complex, indicating the participation of OH group in chelate formation. All complexes showed a broad band in the range (3320‐3407 cm‐1) assigned to (OH) of the coordinated or hydrated water molecules associated with the complexes which were confirmed by elemental and thermal analysis. But the participation of the OH group in the complexes were evident from the shift in position of the (OH) in plane deformation vibration from 1267 cm‐1 in the spectrum of the free ligand to (1260‐1278 cm‐1) range in the spectra of the complexes. Ayoub et al. / European Journal of Chemistry 8 (1) (2017) 85‐95 87 Table 1. Physical and analytical data of the Schiff base, ligand HL and its metal(II) complexes. Ligand/complex Molecular formula Yield (%) Color M.p. (°C) Elemental analyses, Found (Calcd.), (%) C H N S HL C12H11NOS 70 Dark brown 157‐159 66.40 (66.33) 4.87 (5.10) 6.60 (6.45) 14.60 (14.75) [Mn(HL)(Cl2)(H2O)].3H2O C12H19NO5SCl2Mn 75 Yellow 309‐310 34.68 (34.71) 4.62 (4.61) 3.40 (3.37) 7.71 (7.72) [Co(HL)(Cl2)(H2O)].5H2O C12H23NO7SCl2Co 85 Red 315‐316 31.64 (31.66) 5.23 (5.09) 3.06 (3.08) 7.03 (7.04) [Ni(HL)(H2O)2Cl]Cl.4H2O C12H23NO7SCl2Ni 73 Pale brown 322‐324 31.66 (31.68) 5.06 (5.10) 3.08 (3.08) 7.03 (7.05) [Cu(HL)(H2O)]Cl2.H2O C12H15NO3SCl2Cu 76 Yellowish brown 320‐322 37.17 (37.17) 3.86 (3.90) 3.60 (3.61) 8.25 (8.27) Table 2. Characteristic infrared frequencies (cm‐1) of the Schiff base ligand HL and its metal(II) complexes *. Ligand/Complex OH, H2O C=N C=C, Arom. C‐O C‐S M‐N M‐O M‐S M‐Cl HL 3375 (v.s) 1602 (s) 1467 (s) 1141 (m) 743 (v.s) ‐ ‐ ‐ ‐ [Mn(HL)(Cl2)(H2O)].3H2O 3407 (v.s) 1601 (v.s) 1496 (w) 1148 (w) 757 (m) 583 (m) 470 (v.w) 416 (v.w) 410 (w) [Co(HL)(Cl2)(H2O)].5H2O 3383 (v.s) 1591 (v.s) 1461 (w) 1175 (w) 755 (m) 584 (m) 490 (v.w) 420 (v.w) 418 (w) [Ni(HL)(H2O)2Cl]Cl.4H2O 3382 (v.s) 1604 (s) 1462 (s) 1191 (w) 750 (s) 585 (w) 442 (w) 415 (v.w) 412 (w) [Cu(HL)(H2O)]Cl2.H2O 3320 (m) 1590 (v.s) 1486 (w) 1147 (w) 760 (m) 582 (w) 450 (w) 414 (w) 409 (v.w) * s, strong; m, medium; br, broad; w, weak. Additionally the IR spectrum of the ligand HL exhibits medium band at 1141 cm‐1 which may be referred to (C‐O) (phenolic) and shifted toward higher frequency in the metal complexes. This shift confirms the participation of the phenolic oxygen in coordination to the metal cation. The IR spectra of the free ligand showed a strong band at 1602 cm‐1 which is characteristic of the azomethine group. Coordination of the Schiff base to the metal ion through the nitrogen atom is expected to reduce the electron density and so the azomethine frequency shows a decrease in the stretching frequency for the complexes 1, 2, 4, increase in stretching frequency in complex 3, and being shifted to around (1590‐1604 cm‐1), which indicates the coordination of the azomethine nitrogen [14]. The strong to medium bands due to (C‐S) stretching vibration of acetyl thiophene ring appeared at 743 cm‐1 in the free Schiff base ligand [15,16]. These bands are shifted to 757, 755, 750 and 760 cm‐1 in Mn(II), Co(II), Ni(II) and Cu(II) metal comp‐ lexes. These shifts refer to the coordination through acetyl thiophene ring sulfur. The various absorption bands in the region (1461‐1496 cm‐1) may be assigned due to (C=C) aromatic stretching vibrations of 2‐acetylthiophene and 2‐ aminophenol. Conclusive evidence of the banding is also shown by observation that new bands in the spectra of all metal complexes appear in low frequency regions (582‐585, 442‐490, 414‐420 and 409‐418 cm‐1) characteristic to M‐N, M‐ O, M‐S and M‐Cl. Finally the results of IR spectra of complexes with ligand HL showed that the ligand behave as monobasic ONS tridentate, bonding to the metal(II) ion through phenolic oxygen, azomethine nitrogen and acetylthiophene ring sulfur. 3.2. Mass spectra Mass spectrometry has been successfully used to confirm the molecular ion peaks of HL Schiff base and investigate the fragment species. The fragment pattern of mass spectrum gives an impression for the successive degradation of the target compound with the series of peaks corresponding to various fragments. Also, the peaks intensity gives an idea about the stability of fragments especially with the base peak. The recorded mass spectrum of HL Schiff base ligand confirms the proposed formula of ligand by showing a peak at 217.10 m/z due to molecular ion (parent peak) and peak at 218 m/z due to (M+1). The series of peaks 57 (100%), 69 (65.17%), 76 (12.36%), 82 (12.36%), 94 (60.67%), 107 (76.40%), 134 (61.80%), 175 (64.04%), 187 (60.67%) and 202 (65.17%) m/z may correspond to various fragments and their intensity gives an idea of the stability. The mass fragmentation pattern of HL Schiff base ligand is depicted in Scheme 2. The mass spectrum of Ni(II) complex [Ni(HL1)(H2O)2Cl]Cl. 4H2O confirms the proposed formula of the complex by showing a peak at 456 m/z due to M+1 and base peak at 353 m/z. The series of peaks at 59(21%), 75(15%), 91(32%), 138 (65%), 151 (38%), 153 (41%), 163 (58%), 167 (67%), 175 (65%), 177 (71%), 183 (22%), 191(54%), 276 (16%), 349 (29%) and 353(100%) m/z may correspond to various fragments and their intensities which give an idea of their stability Scheme 3. 3.3. 1H NMR spectral studies 1H NMR spectrum of the Schiff base ligand, HL was recorded in DMSO‐d6 solution using tetramethylsilane (TMS) as internal standard. The signal at δ 3.172 ppm is assigned to methyl proton. The signals in the range (δ 6.358‐7.722 ppm) are assigned to aromatic protons of phenolic and acetyl thiophene ring. The signal at δ 8.879 ppm is assigned to OH proton. The spectrum of [Ni(HL)(H2O)2Cl]Cl. 4H2O complex showed a singlet signal at δ 3.297 ppm, which has been assigned to methyl protons and shifted to downfield. The signals in the range (δ 6.213‐7.679 ppm) were assigned to aromatic protons of phenolic and acetyl thiophene ring sulfur and shifted to upper‐field due to increased conjugation on coordination. The signal due to OH proton is shifted downfield at δ 9.125 ppm, indicating that OH group is involved in chelation. 3.4. Electronic spectra, magnetic and molar conductance. The electronic spectrum of the free ligand HL solution in DMF were characterized mainly by two absorption bands. The first absorption band appeared at 266 nm, was assigned to π‐ π* electronic transitions of phenolic, thiophene ring and azomethine group. The second band appeared at 416 nm was assigned to n‐π* transition of the lone pair of oxygen in phenolic, nitrogen in azomethine and sulfur in thiophene ring. In metal complexes, these transitions were found to be shifted to lower or higher energy region compared to the free ligands transition suggesting the coordination of oxygen, nitrogen and sulfur atoms of the ligand to metal (II) ions. The complexes showed additional absorption bands in the range 434‐437 nm which could be due to charge transfer transitions and the other types of bands in the visible region in the range 502‐762 nm can be attributed to d‐d transition [17]. Spectral data Table 3, includes electronic spectral studies magnetic moments and molar conductance of Schiff base HL1 and their metal(II) complexes. 88 Ayoub et al. / European Journal of Chemistry 8 (1) (2017) 85‐95 Figure 1. Infrared spectra of (A) the Schiff base ligand, HL; (B) [Mn(HL)(Cl)2(H2O)].3H2O; (C) [Co(HL)(Cl)2(H2O)].5H2O; (D)[Ni(HL)(H2O)2Cl] Cl.4H2O and (E) [Cu(HL)(H2O)]Cl2.H2O. The Mn(II) complex showed three absorption bands at 714 nm expected for 4T1g(s)→6A1g, at 610 nm corresponding to 4T2g(G) →6A1g and a broad band at 502 nm may be due to 4T1g(D) →6A1g, and metal to ligand, (MLCT) transitions also occur at 437 nm suggesting an octahedral geometry [18]. The magnetic moment of the Mn(II) complex found to be 5.86 B.M, falls within the range expected for an octahedral geometry. The electronic spectrum of cobalt (II) complex displays bands at 762, 690 and 503 nm these bands may be assigned to the following transitions 4T1g(F)→4T2g(F) 1, 4T1g(F)→4A2g(F) 2 and 4T1g(F)→4T1g(P) 3, respectively. Suggest an octahedral geometry of Co(II) complex. The magnetic moment of Co(II) complex is found to be 5.82 B.M. Falls within the range expected for octahedral geometry [19]. The electronic spectrum of the Ni(II) complex showed three bands at 729, 682 and 508 nm were assigned to 3A2g(F) →3T2g(F), 3A2g(F) →3T1g(F) and 3A2g(F) →3T1g(P) transitions respectively and metal to ligand charge transfer (MLCT) transition also occur at 434 nm, indicating an octahedral geometry around Ni(II) ion. The magnetic moment of Ni(II) complex is 4.31 B.M an additional evidence for an octahedral complex. Ayoub et al. / European Journal of Chemistry 8 (1) (2017) 85‐95 89 N OH S -e 217.29 m/z 217.29(217.10 m/z; 73.03%) -C4H3S N OH 134.16(134.10 m/z; 61.80%) -C N -CH3 201.99(202.10 m/z; 65.17%) -C2H2 175.95(175.10 m/z; 64.04%) -CHS C-N C OH 92.84(94.00 m/z; 60.67%) 75.83(76 m/z; 12.36%) -CHO 188.27(187.10 m/z; 60.67%) -CH3 175.25(175.10 m/z; 64.04%) 109.15(107.00 m/z; 76.40%) 83.13(82.00 m/z; 12.36%) 70.11(69.00 m/z; 65.17%) S 57.09(57 m/z;100% ) SS Base Peak N S N S N S OH2 N S -CH3 -C4H3 -C N -CH -CH -CH3 OH 93.10(94.00m/z; 60.67%) -OH 76.09(76 m/z; 12.36%) N OH S N OH S -OH Calculated (Found; Intensity %) Scheme 2 The electronic spectrum of Cu(II) complex showed band at 729 nm which can be assigned to 2T2g→2Eg transition within tetrahedral structure. Also, the spectrum of Cu(II) complex showed band at 435 nm which is assigned to (M→L, CT transition). The magnetic moment of Cu(II) complex was found to be 1.73 B.M, which is close to spin only value. Molar conductance of the metal(II) complexes are measured in DMF at a concentration of 10‐3 M. The observed conductance value for Ni(II) complex is 83 ohm‐1cm2mol‐1, indicates that this complex is (1:1) electrolyte whereas the observed conductance values for Mn(II) and Co(II) complexes are 39.50 and 14.75 ohm‐1cm2mol‐1 which indicates that these complexes are non‐electrolytes. But the observed conductance value of Cu(II) complex is 180 ohm‐1cm2mol‐1 indicates that this complex is (1:2) electrolyte. 3.5. Thermal studies Thermogravimetric (TGA) is a technique in which the change in the weight of a substance is recorded as a function of temperature or time. The TGA curves of the metal complexes is shown in Figure 2 and listed in Table 4. 90 Ayoub et al. / European Journal of Chemistry 8 (1) (2017) 85‐95 454.98m/z -e 454.98m/z -4H2O -Cl 347.48(349m/z; 29%) -2H2O -Cl 275.98(276m/z; 16%) -C4H3S 192.85(191 m/z; 54%) 150.69(151 m/z; 38%) -C6H4 HO Ni 74.69(75 m/z; 15%) -OH 182.87(183 m/z; 22%) 154.87(153 m/z; 41%) -C4NH2 90.87(91 m/z; 32%) 354.84 (353 m/z; 100) Base Peak -6H2O -2Cl 176.84(175m/z; 65%) Ni 58.84(59 m/z; 21%) H3C C N- N OH H3C S Ni OH2 OH2 Cl Cl. 4H2ON OH H3C S Ni OH2 OH2 Cl Cl. 4H2O N OH H3C S Ni OH2 OH2 Cl N OH H3C S Ni N OH H3C Ni OH Ni N H3C S Ni S Ni N H3C Ni OH2 O Cl Cl. 4H2O N H3C Ni -C4H3S 177.82(177 m/z; 71%) N OH Ni C N -C6H4 167.87(167 m/z; 67%) N S Ni -CH N S Ni -CH3 -CH3 -CH 163.84(163m/z; 54%) N H3C Ni 137.84(138m/z;65%) N H3C Ni -C2H2 -C3H2 -OH Calculated (Found; Intensity %) Scheme 3 The thermogravimetric analysis of [Co(HL)(Cl2)(H2O)]. 5H2O involves three decomposition steps. The first step from 29‐103 °C showed removal of the four lattice water with an estimated mass loss of 15.923 (Calc., 15.834%). The second step from 103‐309 °C showed loss of one lattice water then coordinated water and removal of 1/2Cl2 with an estimated mass loss of 19.139 (Calc., 18.660 %). The last step from 309‐ 1000 °C corresponds to the loss of loss of HCl, C2H2, C3H4, HCN and H2 with an estimated mass loss of 42.379 (Calc., 42.423 %). The total mass loss of the decomposition steps is found to be 76.441 (Calc., 76.917%). The thermogravimetric analysis of [Ni(HL)(H2O)2Cl]Cl. 4H2O involves five decomposition steps. The first step from 36‐103 °C showed removal of the three lattice water with an estimated mass loss of 12.395 (Calc., 11.882 %). Ayoub et al. / European Journal of Chemistry 8 (1) (2017) 85‐95 91 Table 3. Electronic Spectral data (nm) and magnetic moments of Schiff base HL and their metal(II) complexes. Compound    (nm) n   (nm) Charge transfer (nm) d –d Transition (nm) Magnetic moment (B.M.) Molar conductance ‐1mol‐1cm‐1 HL 266 416 ‐ ‐ ‐ ‐ [Mn(HL)(Cl2)(H2O)].3H2O 273 418 437 502, 610,714 5.86 39.50 [Co(HL)(Cl2)(H2O)].5H2O 277 412 436 503, 690,762 5.82 14.75 [Ni(HL)(H2O)2Cl]Cl.4H2O 275 414 434 508, 682,729 4.31 83 [Cu(HL)(H2O)]Cl2.H2O 262 415 435 729 1.73 180 Table 4. Thermoanalytical results (TGA, DTG) of Co(II), Cu(II)and Ni(II) metal complexes with HL. Complex Steps Temperature range (°C) DTG Peak TG weight loss, % Assignment Calcd. Found [Co(HL)(Cl)2(H2O)].5H2O 1st 29‐103 64 15.834 15.923 Loss of four lattice water 2nd 103‐309 219 18.660 19.139 Loss of 2H2O, 1/2Cl2 3rd 309‐1000 467 42.423 42.379 Loss of HCl, C2H2, C3H4, HCN, H2 [Ni(HL)(H2O)2Cl]Cl.4H2O 1st 36‐103 72 11.882 12.395 Loss of three lattice water. 2nd 103‐203 161 13.349 12.669 Loss of H2O, 1/2Cl2 3rd 203‐296 252 10.206 9.790 Loss of 1/2Cl2 4th 296‐445 315 8.348 7.463 Loss of C2H2. 5th 446‐1000 563 36.413 37.049 Loss of 2H2O, COH, C=N, CH [Cu(HL)(H2O)]Cl2.H2O 1st 37‐133 75 4.647 5.184 Loss of one lattice water 2nd 133‐244 204 10.407 10.956 Loss of HCl, H2 3rd 244‐513 439 31.857 31.708 Loss of 1/2Cl2 , H2O, C3H3, OH 4th 513‐1000 622 36.818 36.487 Loss of C=N, CH, C‐S Figure 2. TGA/DTG curves of (A) [Co(HL)(Cl)2(H2O)].5H2O; (B) Ni(HL) (H2O)2Cl]Cl.4H2O and (C) [Cu(HL)(H2O)]Cl2.H2O. The second step from 103‐203 °C showed removal of one lattice water and 1/2Cl2 with an estimated mass loss of 12.669 (Calc., 13.349%). The third step from 203‐296 °C corresponds to the loss of 1/2Cl2 with an estimated mass loss of 9.790 (Calc., 10.206%). The fourth step from 296‐445 °C corresponds to the loss of C2H2 with an estimated mass loss of 7.463 (Calc., 8.348%). The last step from 445‐1000 °C corresponds to the loss of two coordinated water molecules, COH, C=N, C‐H with an estimated mass loss of 37.049 (Calc., 36.412%). The total mass loss of the decomposition steps is found to be 79.366 (Calc., 80.198%). The thermogravimetric analysis of [Cu(HL)(H2O)]Cl2. H2O involves four decomposition steps. The first step from 37‐133 °C showed removal of the one lattice water with an estimated mass loss of 5.184 (Calc., 4.647%). The second step from 133‐ 244 °C showed removal of HCl and H2 with an estimated mass loss of 10.956 (Calc., 10.407%). The third step from 244‐513 °C corresponds to the loss of 1/2Cl2, one coordinated water molecule, C3H3 and OH with an estimated mass loss of 31.708 (Calc., 31.857%). The last step from 513‐1000 °C corresponds to the loss of C=N, CH and C‐S with an estimated mass loss of 36.487 (Calc., 36.818 %). The total mass loss of the decomposition steps is found to be 84.335 (Calc., 83.729 %). 3.6. Kinetic data The kinetic and thermodynamic activation parameters of decomposition processes of complexes namely activation energy (∆E*), enthalpy of activation (∆H*), entropy (∆S*) and Gibbs free energy change of the decomposition (∆G*) were evaluated graphically by employing the Coats‐Redfern relation [20]. Log [logWf (Wf  W)T2] = LogARq(12RT)] 2.303RT (1) where E*, R, A and θ are the heat of activation, the universal gas constant, pre‐exponential factor and rate of heating respectively, Wf is the mass loss at the completion of the decomposition reaction, W is the mass loss up to temperature T. Since 1‐2RT/E* ~ 1, the plot of the left hand side of equation (1) against 1/T would give a straight line. The other kinetic parameters; the entropy of activation (∆S*), enthalpy of activation (∆H*) and the free energy change of activation (∆G*) were calculated using the following equations: S = 2.303(log (AhKT))R (2) H = E ‐ RT (3) 92 Ayoub et al. / European Journal of Chemistry 8 (1) (2017) 85‐95 Table 5. The kinetic and thermodynamic data of the thermal decompositions of complexes. Complex Stage Mid Temp. (°K) ∆E* (KJ/mol) ∆A (S‐1) ∆S* (KJ/mol K) ∆H* (KJ/mol) ∆G* (KJ mol) [Co(HL)(Cl)2(H2O)].5H2O 1st 302 ‐ 375 213.55 4.3810‐1 ‐180.59 2.01 31.151 2nd 376 ‐ 582 237.29 2.8410‐2 ‐234.04 2.18 75.172 3rd 584 ‐ 1273 384.11 1.2010‐2 ‐268.58 3.73 96.213 [Ni(HL)(H2O)2Cl]Cl.4H2O 1st 309 ‐ 376 377.81 3.28102 ‐126.48 4.73 45.273 2nd 376 ‐ 569 847.05 1.1310‐6 ‐353.71 7.13 64.216 3rd 569 ‐ 1273 945.27 8.5210‐5 ‐378.17 9.84 84.729 [Cu(HL)(H2O)]Cl2.H2O 1st 310 ‐ 406 133.84 1.110‐6 ‐76.676 0.87 17.154 2nd 406 ‐ 517 263.57 2.2210‐1 ‐152.197 0.91 22.712 3rd 517‐ 606 369.32 1.3310‐1 ‐207.765 0.99 77.465 4th 606 ‐ 1273 429.54 8.97108 ‐287.799 1.26 95.928 Table 6. Fluorescence data of the Schiff base ligand HL and its transition metal (II) complexes. λemission (nm) λexcitation (nm) Name of compound 604 432 HL 555 434[Mn(HL)(Cl)2(H2O)].3H2O 560 436[Co(HL)Cl2(H2O)].5H2O 555 434[Ni(HL)Cl(H2O)2]Cl.4H2O 521 430[Cu(HL)(H2O)]Cl2.H2O Figure 3. Emission spectra of: ( ) Ligand (HL); ( ) [Mn(HL)(Cl)2(H2O)].3H2O; ( ) [Co(HL)Cl2(H2O)].5H2O; ( ) [Ni(HL)(H2O)2Cl]Cl.4H2O; and ( ) [Cu(HL)(H2O)2]Cl2.H2O. G = H ‐ TS (4) where, (k) and (h) are the Boltzman and Planck constants, respectively. The kinetic parameters are listed in Table 5. From the obtained results, it is apparent that ∆G* values of the complexes acquire highly positive magnitudes. The high value of the energy of activation of the complexes revealed the high stability of the investigated complexes due to their covalent character [21]. The negative values of ∆S* for the degradation process indicates that more ordered activated complex than the reactants and the decomposition reaction is slow [22]. The positive values of ∆H* mean that the decomposition process are endothermic. 3.7. Fluorescence spectral studies The fluorescence properties of the Schiff base ligand HL and its metal(II) complexes measured in DMSO were recorded at room temperature Figure 3. The excitation spectra of the ligand showed a maximum emission peak at 604 nm when excited at 432 nm. Generally, Schiff base systems exhibits fluorescence due to intra‐ligand π‐π* transitions. The fluores‐ cent data are summarized in Table 6. The excitation spectrum of Mn(II), Co(II), Cu(II) and Ni(II) complexes exhibited weak fluorescence emission bands in the range 521‐560 nm when excited at 430‐436 nm range. Significant difference in the position of maximum emission of Schiff base and each metal(II) complexes which is due to the coordination of the metal(II) ion to the ligand. Quenching of fluorescence through complexation is much interesting as it opens up the opportunity for photochemical applications of these complexes [23‐25]. 3.7.1. Effect of solvent and pH The influence of the solvent on Schiff base ligand HL and its metal(II) complexes were studied. The results showed that the optimal solvent for Schiff base ligand HL, Mn(II) and Co(II) complexes were DMF at λemi = 432, 434 and 436 nm, while the optimal solvent for Cu(II) complex was CH3CN λemi = 430 nm, as shown in Figure 4. The effect pH on the fluorescence intensity of Schiff base ligand HL and its metal(II) complexes were investigated between the pH range of 2.0‐10.0. The influence of pH on Schiff base ligand HL, Mn(II), Co(II) and Cu(II) complex were investigated in both acidic and alkaline media by the addition of dilute HCl and NH4OH. The optimum signals were recorded in strongly alkaline conditions. The highest intensity of Schiff base ligand HL1, Mn(II), Co(II) and Cu(II) complexes at 604, 555, 560 and 521 nm were obtained at pH = 9.4, as shown in Figure 4. 3.8. Catalytic Activity 3.8.1. Influence of hydrogen peroxide concentration on the rate of decomposition of Schiff base HL complexes A definite amount of catalyst (1 mg) was subjected to decomposition reaction by varying the concentration of H2O2 (0.4 % to 1.2 %). Ayoub et al. / European Journal of Chemistry 8 (1) (2017) 85‐95 93 Table 7. Influence of H2O2 concentration on the rate of decomposition in Schiff base HL complexes. Amount of catalyst (1 mg) Rate constant 103 K/min Concentration of H2O2 Mn(II) Co(II) Ni(II) Cu(II) 0.4% 25.356 31.321 25.333 33.439 0.8% 32.012 35.167 36.341 39.852 1.2% 39.151 44.356 52.462 45.369 (A) (B) (C) (D) Figure 4. Effect of solvent and pH on (A) Schiff base ligand HL; (B) [Mn(HL)(Cl)2(H2O)].3H2O; (C) [Co(HL)(Cl)2(H2O)].5H2O and (D) [Cu(HL)(H2O)]Cl2.H2O. The result for different complexes is given in Table 7 and Figure 5. The rate of reaction is found to increase with increase in concentration of H2O2 in all complexes. In case of concentration of H2O2 (0.4 and 0.8%) the Cu(II) complex is the most active, while in case of concentration (1.2%) the Ni(II) complex is the most active one. 3.8.2. The Influence of varying amount of catalyst in the Schiff base HL complexes The effect of varying amount of the catalyst on the decomposition reaction shows first order dependence. For a definite concentration of H2O2 (0.4%), varying amounts of catalyst (1 and 3 mg) are subjected to decomposition reaction. 94 Ayoub et al. / European Journal of Chemistry 8 (1) (2017) 85‐95 Table 8. The effect of different amounts of catalyst on the decomposition reaction for definite concentration of H2O2. Concentration of H2O2 (0.4%) Rate constant 103 K/min Amount of catalyst (mg) Mn(II) Co(II) Ni(II) Cu(II) 1 25.356 31.321 25.333 33.439 3 111.925 33.669 50.367 53.107 Figure 5. Kinetics of decomposition of hydrogen peroxide concentration (A) 0.4%, wt of catalyst 1 mg; (B) 0.4%, wt of catalyst 3 mg; (C) 0.8%, weight of catalyst 1 mg; (D) 1.2%, weight of catalyst 1mg catalyzed by [Mn(HL)(Cl)2(H2O)].3H2O, [Co(HL)(Cl)2(H2O)].5H2O, [Ni(HL)(H2O)2Cl]Cl.4H2O and [Cu(HL)(H2O)]Cl2.H2O complexes. Scheme 4 The rate of the reaction increased with increasing the amount of catalyst. The values are given in Table 8 and Figure 5. Here in case of 1 mg of catalyst, the Cu(II) complex is found to be the most active but in case of 3 mg of catalyst Mn(II) is the most active one. 4. Conclusion The Schiff base HL ligand and its metal complexes of Mn(II), Co(II) and Ni(II) have been structurally characterized. The spectral data shows that the Schiff base HL ligand acts as tridentate coordinating through phenolic oxygen, azomethine nitrogen and acetylthiophene sulfur. 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