Research Journal of Chemical Sciences ______________________________________________ ISSN 2231-606X Vol. 3(11), 36-46, November (2013) Res. J. Chem. Sci. International Science Congress Association 36 Synthesis, Spectral and Thermal degradation Kinetics studies of Benzimidazole substituted Metal phthalocyanine through oxadiazole Bridge (M=Co,Ni,Cu)Tantry Rajesh N., Jathi Keshavayya*, Harish M.N.K., Angadi Shoukat Ali R, and Chinnagiri Keerthi Kumar T. Dept. of Studies and Research in Chemistry, Kuvempu University, Janna Sahyadri, Shankaragatta-577451, Shimoga District, Karnataka, INDIAAvailable online at: www.isca.in, www.isca.me Received 12th August 2013, revised 26th October 2013, accepted 17th November 2013Abstract In this study, new type of benzimidazole substituted metal Phthalocyanine complexes connected by oxadiazole bridge were prepared by the acid catalysed melt condensation of hydrazides with tetracarboxy metal Phthalocyanine in the presence of PPA. Which in turn, tetracarboxy metal Phthalocyanines and 2-(2-substituted-1H-benzimidazol-1-yl)acetohydrazide were synthesized by suitable modification of reported procedure. Novel dark green coloured 1,8,15,22-Tetra-[1-(1,3,4-oxadiazol-2-ylmethyl)-1H-benzimidazole] M(II) Phthalocyanine (M=Co,Cu,Ni) were characterized by elemental analysis, UV-Vis and IR-Spectroscopic techniques. Thermal stability of newly synthesized phthalocyanine complexes were investigated by means of thermogravimetric analysis (TGA). On basis of the TGA data, the kinetic and thermodynamic parameters such as activation energy (Ea),order of reaction (n), entropy change (S), free energy (G), enthalpy (H) and frequency factor (A) were calculated using Broido’s method. Keywords: Phthalocyanines, 1, 3, 4—Oxadiazole, Benzimidazole, electronic, IR, PPA, TGA. Introduction Phthalocyaninesare synthetic macromolecules having structural similarities with natural pigments of life, the porphyrins, such as chlorophyll and haemoglobin. After the accidental discovery in 1928, phthalocyanines showed its commercial importance as colorants next to pervasiveazo dyes. Phthalocyanine ligand has a heteroaromatic system and readily forms complexes with many group and transitions metals. The azo-nitrogen and peripheralfixed benzene rings impart chemical and thermal stability to the ligand1-4. Phthalocyanines have been used as materials for numerous technological applications, such as photovoltaic solar cells, electrophotography, molecular electronics, Langmuir–Blodgett films, electrochromism in display devices, gassensors, liquid crystals, nonlinear optics and medical applications5-13. Recently, many research articles published on synthesis of substituted metal phthalocyanine, because their properties can be extensively modified by varying the metal and peripheral substituents14-17. Heterocyclic compounds having widespread application both in medicinal and material science18-21. Among various heterocycles, 1,3,4-oxadiazole derivatives are planner, electron deficient and having high charge carrying mobility. These attractive properties of 1,3,4-oxadiazole derivatives utilised in photo-electronic devices, organic light emitting devices and organic electronics22-25. Earlier reports showed introduction of aryl-1,3,4-oxadiazole subunits onto the peripheral positions of Pc, resulted in increased solubility and semiconducting properties26-28. Therefore, in this contribution, we attached the Benzimidazole-1,3,4-oxadiazole moieties onto electron-rich Pc, which wouldendow the synthesized symmetricaltetra-[1-(1,3,4-oxadiazol-2-ylmethyl)-1benzimidazole] M(II) Phthalocyanine (4a-c)with new properties and better performances of thedevices fabricated with it. Synthesised compounds characterised by elemental analysis, FT-IR, solid-state UV-Visspectroscopy, along with X-ray diffraction (XRD). Optical and thermal stability were evaluated by using UV-Visible and thermal analyses respectively. Material and MethodsMaterials: 1,2,4-Benzene tricarboxylic anhydride and Benzimidazole were purchased from Aldrich and other chemicals were obtained from Merck (India), Spectrochem and used without purification. All solvents used were dried and purified before use. Tetracarboxymetalphthalocyanine (3 a-c)andbenzimidazol-1-yl acetohydrazide were prepared according to the described procedure with suitable modifications29-30Synthesis of benzimidazol-1-yl acetate(1): Ethylchloroacetate (0.07mol) was added to a solution of dry acetone (25ml) containing 1H-benzimidazole (0.006 mol). Reaction mixture was refluxed for 10-12 h after adding anhydrous KCO(0.024 mol). After completion of reaction acetone was removed distillation and residue was recrystallized from ethanol. The purity of the compound was evaluated by thin layer chromatography. Yield 70%, mp 178–180C (Found: C, 64.67; H, 5.91; N, 13.70. Calcd. for C1112: C, 64.69; H, 5.92; N, 13.72%). [IR (KBr) max/cm-1]: 1632 (–C=N), 1150 (–C–N), Research Journal of Chemical Sciences ___________________________________________________________ ISSN 2231-606XVol. 3(11), 36-46, November (2013) Res. J. Chem. Sci. International Science Congress Association 37 1745 (–C=O ester), 1460 (–N–CH)cm-1H NMR (CDCl) ppm: 3.70 (s, 2H, –N–CH), 4.21(q, 2H, –COOCHCH), 1.32 (t, 3H, –COOCHCH), 8.50 (s, 1H,–N=CH), 7.72–7.90 (m, 4H, Ar–H); EI-MS: 205 (M +1). Synthesis of benzimidazol-1-yl acetohydrazide (2): To a solution of compound 1 (0.003 mol) dissolved in dry methanol (25ml), 99% hydrazine hydrate (0.02 mol) was added and the mixture was refluxed for 4-5h. Solid obtained after cooling reaction mixture was filtered and washed with small quantity of cold methanol to give the compound 2.The purity of the compound was evaluated by thin layer chromatography. Yield 70%, mp 200–202C (Found: C, 56.82; H, 5.29; N, 29.43. Calcd for C10O: C, 56.83; H, 5.30; N, 29.46%). [IR (KBr) max/cm-1]: 1645 (–C=N), 1122 (–C–N), 1680 (–C=O amide), 1461 (–N–CH)cm-1; H NMR (CDCl) ppm: 3.62 (s, 2H, –N–CH), 8.40 (s, 1H, –N=CH), 8.10 (m, 3H, –CONHNH), 7.60–8.00 (m, 4H, Ar–H); EI-MS: 191 (M +1). Synthesis of 1,3,4-oxadiazol-2-ylmethyl-1-benzimidazole substituted M (II) Phthalocyanine (4a-c): Tetracarboxymetal phthalocyanine (3a-c) (0.0128 mol) and benzimidazol-1-yl-hydrazide (7) (0.0027 mol, 0.5g.) were stirred into preheated PPA (100 g) containing 10 g P5 at 100C in a three necked round bottom flask containing mechanical stirrer, condenser and thermometer for 1h and then maintained at 150C for 20h under nitrogen atmosphere. The reaction mixture was allowed to cool to 100C and quenched with ice cold water and filtered. The product obtained was repeatedly treated with 0.1N sodium hydroxide solution followed by water, hot acetic acid, 10% sodium bicarbonate solution, water, and acetone to get 4a-c. 1,8,15,22-Tetra-[1-(1,3,4-oxadiazol-2-ylmethyl)-1benzimidazole] Ni(II)Phthalocyanine (4a): Yield 60%, (Found: C, 62.0; H, 2.81; N, 24.5. Calcd for C724024NiO: C, 63.40; H, 2.96; N, 24.65%).[IR (KBr) max/cm-1]: 1665 (–C=N), 1160 (–C–N), 1468 (–N–CH), 1530(–C-O), 1090, 930, 834, 725 (Pc skeleton vibration); UV-Vis (solid state) max/nm 359.5, 435, 608, 740.0. 1,8,15,22-Tetra-[1-(1,3,4-oxadiazol-2-ylmethyl)-1benzimidazole] Co(II)Phthalocyanine (4b): Yield 65%, (Found: C, 63.0; H, 2.89; N, 24.4. Calcd for C724024NiO: C, 63.40; H, 2.96; N, 24.65%). [IR (KBr)max/cm-1]: 1670 (–C=N), 1138 (–C–N), 1470(–N–CH), 1536(–C-O), 1092, 935, 830, 721 (Pc skeleton vibration); UV-Vis (Solid state) max/nm 345.8, 433.8, 615, 710.2. 1,8,15,22-Tetra-[1-(1,3,4-oxadiazol-2-ylmethyl)-1benzimidazole] Cu(II)Phthalocyanine (4c): Yield 75%, (Found: C, 62.8; H, 3.01; N, 23.9. Calcd for C724024NiO: C, 63.40; H, 2.96; N, 24.65%). [IR (KBr)max/cm-1]: 1675 (–C=N), 1155 (–C–N), 1475(–N–CH), 1532(–C-O), 1085, 935, 830, 728 (Pc skeleton vibration); UV-Vis (Solid state) max/nm 351.4, 482.05, 590.3, 780. ClCHCOOEtCORefluxCHCOOC CHCONHNH NHNH.HMethnolReflux Scheme-1 Synthesis of benzimidazol-1-yl acetohydrazide(2) Table-1 Elemental analysis, yield and solubility data of compounds 1,2,3a-c,4a-c Compound Emperical Formula M.wt g/mol Colour Yield (%) Content(Calculated)found solubility % C % H % N 1 C1112 204.22 White 72 (64.69) 64.82 (5.92) 6.20 (13.72) 13.32 Acetone 2 C10O 190.20 White 60 (56.83) 57.02 (5.30) 5.92 (29.46) 29.12 Chlorofom 3a C3616NiO 747.25 Green 65 (57.86) 58.13 (2.16) 2.03 (15.00) 15.11 DMF 3b C3616CoO 747.49 Bluishgreen 75 (57.84) 58.32 (2.16) 2.47 (14.99) 14.62 DMSO 3c C3616CuO 752.10 Violet blue 70 (57.49) 58.03 (2.14) 2.63 (14.90) 13.43 DMSO 4a C724024NiO 1363.93 Bottle green 55 (63.40) 63.92 (2.96) 3.24 (24.65) 24.13 Insoluble 4b C724024CoO 1364.17 Bottle green 60 (63.39) 64.02 (2.96) 3.41 (24.64) 24.12 Insoluble 4c C724024CuO 1368.79 Bottle green 65 (63.18) 63.73 (2.95) 3.01 (24.56) 24.33 Insoluble Research Journal of Chemical Sciences ___________________________________________________________ ISSN 2231-606XVol. 3(11), 36-46, November (2013) Res. J. Chem. Sci. International Science Congress Association 38 CHCONHNH M OHOH Tetracarboxy metal phthalocyanine3 a - cPPA, P150C, 20 hrs Ni 4 a - cM = 4a = NiM = 4b = CoM = 4c = CuScheme-2 Synthetic route for preparation of 1,3,4-oxadiazol-2-ylmethyl-1-benzimidazole substituted M (II) Phthalocyanine(4a-c) Analyses: Elemental analyses (C, H, and N) were performed using a Thermo finnigan, FLASHEA 1112 elemental analyzer. H NMR Varian 200 MHz spectrometer using DMSO as solvent, chemical shift are given in ppm relative totetramethylsilane (TMS). Electron impact mass spectra were recorded on a Jeol, JMS, DX-303 mass spectrometer. Solid state electronic absorption spectra were recorded on USB 4000 Ocean Optics UV-Visible spectrophotometer in the range 200–800 nm. IR spectra (4000–400 cm-1) were recorded as KBr pellets on Bruker FT-IR Spectrophotometer. Thermogravimetric analysis (TG/DTG) was carried out in the temperature range from 25 to 600C in air atmosphere using Shimadzu TGA 50H thermal analyser, at heating rate of 10C/min. Results and Discussion Bottle green coloured 2,9,16,23–tetra (1,3,4-oxadiazol-2-ylmethyl-1-benzimidazole) metal (II) Phthalocyanine (4a-c) were obtained in good yield and purity by melt condensation of compound 3a-c with hydrazide (2) using PPA as condensing agent. The elemental analyses for carbon, hydrogen and nitrogen and gravimetric methods for metals are in good agreement with thecalculated values and consistent with the proposed structure, table-1. IR absorption spectra: The entire complexes showed broad peak observed in the range 3436-3493 cm-1is assigned to the hydrogen bonding formed between the nitrogen atoms of the phthalocyanine macromolecule and H-atom of moisture observed on the KBr pellets during palletisation31. The very weak signal observed in the range2344-2360 cm-1is due to C-H stretching at the periphery of the phthalocyanine moiety. In comparison with FT-IR spectra of tetracarboxy metal phthalocyanine (3a-c) characteristic C=O peak at 1697 cm-1of –COOH group has disappeared in compounds 4a-c, along with these changes new characteristic bands at region 1603–1614 and 1528–1530 assigned for C=N and C-O of oxadiazole, coupled with C=N and C=C in plane skeletal vibrations of the Pc core. Peaks observed at 1672 cm-1, 1155 cm-1 and 1473 cm-1were assigned to the characteristic stretching vibrations of –C–N, –C=N and –N–CH2 respectively for benzimidazole ring at the periphery of Pc core. All the remaining bands observed in the range 1201-1284, 1041-1180, and 596-875 cm-1 can be Research Journal of Chemical Sciences ___________________________________________________________ ISSN 2231-606XVol. 3(11), 36-46, November (2013) Res. J. Chem. Sci. International Science Congress Association 39 assignedto various characteristic skeletal vibrations of the phthalocyanines. UV-Visible spectral studies: Optical study of compounds 4a-c films was carried in the range 200-800 nm for the films deposited at room temperature. Solid state UV-Visible Absorption spectra are obtained directly from the spectrometer, absorption maxima were recorded in table-2, figure-1. The value of absorption coefficient () was calculated for all the films which provides valuable information about the inter band transition and hence the energy band structure of the materials. Band gap of the synthesised compounds were tabulated in table-3. Table-2 Solid-state electronic absorption data of 4a-c Compound Peaks max (nm) 4a 359.5, 435, 608, 740.0 4b 345.8, 433.8, 615, 710.2 4c 351.4, 482.05, 590.3, 780 Table-3 Optical band gap data for compound 4a-c Compound Peaks max(nm) Band Gap(eV) 4a 608.0 1.974 740.0 1.461 4b 615.0 1.974 710 1.444 4c 590 1.974 780 1.446 Thermodynamic and Kinetic studies: Thermogravimetric analysis results of title compounds were presented in table-4, figure-2. Thermogram shows decomposition of the complexes occurs in three distinct stepsand char residue isfound to be in the range of 7–5% corresponding to their metaloxides. At 110-120C initial weight loss of 1–2% was observed for all the complexes corresponding to the loss of free moisture. All the complexes shown a weight loss of 20–22% in the temperature range of 160–300C which corresponds to the loss of benzimidazole moiety of the macromolecule. Decomposition of oxadiazole bridge will not be distinct in all the complexes, it is varying from 15-35% at temperature range 260-400C. Gradual and major decomposition of 40-45% observed in temperature range of 400–580C corresponding to the oxidative degradation of phthalocyanine moiety. The observed thermal stabilities of metal complexes in air was inthe order of 4b�4c�4a.Degradation mechanism, kinetic and thermodynamic parameters of the synthesised complexes have been evaluated by Broido’s graphical method for straight line decompsotion portion of the thermodynamic analytical curve32. Energy of activation (E) were calculated by the slope of ln (ln1/y) versus 1/T, where yis the fraction of the complex undecomposed. Since plots of ln (a/a-x) versus time, gives straight line for all the three stage degradation steps, this indicate degradation follows first order kinetics, where a is the initial weight of sample taken and (a-x) is the weight of sample left after time t, The thermodynamic properties like change in enthalpy (H), entropy(S), free energy (G) and frequency factor (A) are calculated using the standard equations as explained elsewhere and data presented in table-5, figure- 3 to 8. Figure-1 Solid state UV-Visible spectra for compounds 4a-c Research Journal of Chemical Sciences ___________________________________________________________ ISSN 2231-606XVol. 3(11), 36-46, November (2013) Res. J. Chem. Sci. International Science Congress Association 40 Table-4 TGA Data of the complexesCompound Decomposition Temp C Mass Loss Probable mode of decomposition and fragment lost % found % calculated 4a 166-259 35 34 4 Benzimidazole group 262-349 13 23 4 oxadiazole group 355-559 42 40 Pc moeity 4b 156-257 22 34 4 Benzimidazole group 258-400 35 23 4 oxadiazole group 410-536 34 40 Pc moeity 4c 180-280 23 34 4 Benzimidazole group 290-340 37 23 4 oxadiazole group 350-545 35 40 Pc moeity 010020030040050060020406080100 % weight lossTemp(C) 4a 4b 4cFigure-2 TGA pattern of compound 4a-c 1.81.92.02.12.22.32.4-5.0-4.5-4.0-3.5-3.0-2.5-2.0-1.5-1.0-0.5 Ln(-Lny)1000/T K 4a 4b 4cFigure-3 Plots of ln(ln 1/y) vs. 1000/T K plots for the first step decomposition of compound 4a-c, using Broido method Research Journal of Chemical Sciences ___________________________________________________________ ISSN 2231-606XVol. 3(11), 36-46, November (2013) Res. J. Chem. Sci. International Science Congress Association 41 1.451.501.551.601.651.701.751.801.85-1.2-1.1-1.0-0.9-0.8-0.7-0.6-0.5-0.4-0.3-0.2-0.10.00.10.2 Ln (-Lny)1000/T K 4a 4b 4cFigure-4 Plots of ln(ln 1/y) vs. 1000/T K plots for the second step decomposition of compound 4a-c, using Broido method 1.151.201.251.301.351.401.451.501.551.60-0.50.00.51.01.52.0 Ln (-Ln y)1000/T K 4a 4b 4cFigure-5 Plots of ln(ln 1/y) vs. 1000/T K plots for the third step decomposition of compound 4a-c, using Broido method Research Journal of Chemical Sciences ___________________________________________________________ ISSN 2231-606XVol. 3(11), 36-46, November (2013) Res. J. Chem. Sci. International Science Congress Association 42 12141618202224-0.2-0.10.00.10.20.30.4 Ln (a/a-x)Time (in min) 4a 4b 4cFigure-6 Plots of log(a/a-x) vs time for the first step decomposition of compound 4a-c 262830323436380.10.20.30.40.50.60.70.80.91.0 Ln (a/a-x)Time (in min) 4a 4b 4cFigure-7 Plots of log(a/a-x) vs time for the second step decomposition of compound 4a-c Research Journal of Chemical Sciences ___________________________________________________________ ISSN 2231-606XVol. 3(11), 36-46, November (2013) Res. J. Chem. Sci. International Science Congress Association 43 35404550550.51.01.52.02.53.0 Ln (a/a-x)Time (in min) 4a 4b 4cFigure-8 Plots of log(a/a-x) vs time for the third step decomposition of compound 4a-cTable-5 Kinetic and thermodynamic parametersCompoundDecomposition range(in k) a (kJ mol-1 H (kJ mol-1 S ( J K-1 G (kJ mol-1 A (s-1 4a423-523 64.12 68.06 -275.52 130.518 2.43X10-19 553-633 15.36 20.29 -279.06 165.6512 4.66X10-19 653-835 33.53 39.72 -272.19 202.6549 2.56X10-19 4b419-503 46.71 50.55 -278.21 128.4288 3.27X10-19 573-683 36.27 41.50 -273.05 171.6493 2.40X10-19 693-803 59.50 65.72 -268.22 200.8222 1.60X10-19 4c443-548 68.22 72.35 -281.33 139.64 5.12X10-19 565-623 19.00 23.94 -282.17 167.8647 6.79X10-19 667-801 40.64 46.74 -270.07 198.2978 1.96X10-19 XRD Studies: Degree of crystallinity of synthesised compounds was studied qualitatively using X-ray diffraction studies. The powder X-ray diffraction pattern of synthesizedmetal (II) phthalocyanines are obtained using Cu- K radiation (= 1.542 A\r) taken through a range of 2 angles 6-70. The X-ray diffraction pattern showed in figure-9 and summarized data presented in table-6, clearly indicating the crystal line nature of the samples. Spectrum shows sharp peaks at lower angles with maximum intensity and broad peaks with minimum intensity in higher angles. The observed patterns of title complex showed broadening of the peaks with diffused intensity in comparison with unsubstituted parent phthalocyanines. The broadening may be due to the presence of substituents and which seems to play an important role in the stacking of the metal phthalocyanine derivatives. Quantitiessuch as 2 angles, intra planar spacing (d), crystallitesize were calculated using standard equation’s33. Research Journal of Chemical Sciences ___________________________________________________________ ISSN 2231-606XVol. 3(11), 36-46, November (2013) Res. J. Chem. Sci. International Science Congress Association 44 Table-6 Powdered XRD data for complexes 4a-cSl.No. Complex compound (Code name) 2 qq(degress) Lattice spacing (d) (A) Relative Intensity crystallite size 1. 4 a 12.5419 17 18.68 20.2785 22.3044 26.6 41.4 7.0579 5.21575 4.75029 4.37929 3.9859 3.35118 2.18102 22.0 36.4 80.6 28.0 30.2 100 15.1 584 nm 2. 4 b 12.9 17.2488 18.96 21.8865 26.6745 33.4655 44.6 6.86277 5.14107 4.68076 4.06105 3.34199 2.67772 2.03169 15.3 73.2 38.5 33.7 100 13.0 12.2 492 nm 3. 4 c 15.4145 18.96 22.3014 24.02 27.28 31.9065 56.86 5.74847 4.68076 3.98643 3.70496 3.26917 2.80491 1.61933 60.1 35.4 52.0 100 85.7 22.4 8.6 512 nm 101520253035404550556065707580 Intensity (Arbitrary unit)2 4 a 4 b 4 cFigure-9 Powder XRD patterns for compounds 4a-c Research Journal of Chemical Sciences ___________________________________________________________ ISSN 2231-606XVol. 3(11), 36-46, November (2013) Res. J. Chem. Sci. International Science Congress Association 45 Conclusion Here we are reporting convenient and cast effective methodology for the synthesis of heterocyclic substituted metal phthalocyanine. Synthesised compounds showed decreased band gap and greater thermal stability in comparison with theearlier oxadiazole substituted metal phthalocyanine. Synthesised compounds may be useful for optical sensor and charge-carrier semiconducting materials with high chemical and thermalstabilities. Acknowledgement The authors thank to Dr. Fasiulla, ‘Manipal Institute of technology’ for providing (TGA) thermogravimetric analytical data. References 1.Dent C.E., linstead R.P. and Lowe A.R., Phthalocyanines, Part VI, The structure of the phthalocyanines, J. Am.Chem.Soc, , 1033-1039 (1934)2.Myers J.F., Rayner Canham G.W. and Lever A.B.P., Higher oxidation level phthalocyanine complexes of chromium, iron, cobalt and zinc. Phthalocyanine radical species, Inorg. 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