Coordination Polymers based on Terephthaloyl bis(isonicotinoylhydrazone): Synthesis, Structural Characterization and Thermal Analysis

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ScienceDirect Materials Today: Proceedings 15 (2019) 481–489

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ICMAM-2018

Coordination Polymers based on Terephthaloyl bis(isonicotinoylhydrazone): Synthesis, Structural Characterization and Thermal Analysis Mahejabeen Azizul Haque* and L. J. Paliwal Post Graduate Teaching Department of Chemistry, Rashtrasant Tukadoji Maharaj Nagpur University, Nagpur- 440 033, Maharashtra, India.

Abstract A new terephthaloyl bis(isonicotinoylhydrazone) (TPBI) bis-ligand has been synthesized by reacting isoniazid with terephthaloyl chloride. The chelating bis-ligand has been characterized using elemental analyses, ESI mass spectra, FTIR, 1H and 13C NMR spectroscopic techniques. The new Cu(II) and Zn(II) coordination polymers were prepared from terephthaloyl bis(isonicotinoylhydrazone) (TPBI) bis-ligand and characterized using elemental analyses, FTIR, UV-Visible spectra, magnetic moment values, XRD, SEM and thermogravimetric analyses. The results indicated formation of 1:2 metal chelates. The FTIR spectral data suggest that the synthesized TPBI ligand is an octadentate chelating ligand. On account of the analytical data, Cu(II) polychelate has an octahedral geometry whereas Zn(II) polychelate has tetrahedral geometry. The thermal degradation behaviour of the synthesized bis-ligand and the coordination polymers has been investigated by applying TG/DTA techniques.

© 2019 Elsevier Ltd. All rights reserved. Selection and Peer-review under responsibility of INTERNATIONAL CONFERENCE ON MULTIFUNCTIONAL ADVANCED MATERIALS (ICMAM-2018).

Keywords: Coordination polymer; Isoniazid; Bis-ligand; FTIR; Thermal analysis

*Email address: [email protected]

2214-7853 © 2019 Elsevier Ltd. All rights reserved. Selection and Peer-review under responsibility of INTERNATIONAL CONFERENCE ON MULTIFUNCTIONAL ADVANCED MATERIALS (ICMAM-2018).

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1.0 Introduction Coordination polymers are related to several fields such as organic and inorganic chemistry, materials science, electrical, and pharmacology, and find many potential applications [1]. This interdisciplinary nature has led tremendous increase in study of coordination polymers in the past few decades [2-4].Coordination polymers have wide range of potential applications [4-10]. Transition metals have been known to display properties of both geometric and electronic nature and since their chemistry is well documented, they can be expediently applied to incorporation into coordination polymers. Consequently, the coordination polymers of transition metals are studied more than any other type of metal-organic polymers [11-12]. Coordination polymers to which present work is concerned are chelate polymers [13-14]. The chelate polymers are found to be extremely thermally stable as compared to ordinary complex and ligand. The thermal stability of coordination polymers usually depend on chelating ligand because the stability is enhanced with increase in aliphatic chain in the molecule [15-18]. Many multifunctional ligands have been extensively investigated for synthesis of chelate polymers owing to their versatile coordination modes. Isoniazid (Isonicotinic acid hydrazide, INH) is a potent and selective therapeutic prodrug agent used to cure infections by Mycobacterium tuberculosis H37Rv [19]. Moreover, hydrazine and hydrazone derivatives of isoniazid have shown to possess potential pharmacological applications [20]. The various metal compounds of hydrazones have attracted special attention due to their physicochemical characteristics and probable applications in various disciplines [21-22]. In view of the above applications, the present work reports the synthesis and systematic study of structural, physicochemical and thermal properties of newly synthesized terephthaloyl bis(isonicotinoylhydrazone) (TPBI) bisligand and its polychelates. 2.0 Experimental 2.1 Materials and instruments The chemicals and solvents used were of analar grade and used as such without purification. Isoniazid used was from Sd fine chem. Ltd. (India). Elemental studies were performed on Elementar Vario EL III, CHN elemental analyzer. 1H and 13C NMR spectra were obtained using a Bruker-Avance-II (400 MHz) spectrophotometer and DMSO-d6 used as a solvent. EI-MS spectrum was recorded on LCQ ion trap mass spectrometer with an EI source (Thermo Fisher, San Jose, CA, USA). Magnetic moment values were calculated on a standard Gouy balance and Hg[Co(SCN)4] was used as calibrant. The electronic spectra were scanned on a Varian, Cary 5000 spectrophotometer. TG/DTG/DTA data were obtained on a Perkin Elmer, Diamond TG/DTA instrument at 10 °C min-1 heating rate from ambient temperature to 1000 °C. 2.2 Synthesis of ligand (TPBI) The terephthaloyl dichloride was synthesized as reported in the literature [23]. Terephthaloyl dichloride (0.01 m) was reacted with isoniazid (0.02 m) in 50 mL acetone and 3 mL pyridine with constant stirring in cold condition. The precipitation occurred as soon as the two reactants were mixed. The resulting mixture was refluxed on water bath at 60-70 °C for about 5 h in presence of a guard tube of fused CaCl2 fitted to condenser and later allowed to cool at room temperature. Moreover, the reaction was monitored at regular intervals by thin layer chromatography. The reaction mixture was slowly added into ice cold water with gradual stirring as a result of which the off-white precipitate was formed. The obtained precipitate was later filtered, washed with aqueous sodium bicarbonate solution to remove unreacted reactants and the acid which may have formed owing to reaction of excess acid chloride with water, and finally dried. The final product was purified by recrystallization using ethanol-DMF solvent. Yield: 79.59 %, m.p.: >280 °C. The reaction involved in the synthesis of terephthaloyl bis(isonicotinoylhydrazone) (TPBI) ligand shown by scheme 1 is as follows:

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N

H N

2 O Isoniazid

N H

N

O

O

Terephthaloyl chloride -2 HCl

O

Cl

Cl NH2

483

Reflux in acetone+ Py H N

H N O

O

O N H

N

Terephthaloyl bis-isoniazid (TPBI) Scheme 1 - Synthesis of Terephthaloyl bis(isonicotinoylhydrazone) (TPBI)

2.3 Synthesis of coordination polymers The polychelates of terephthaloyl bis(isonicotinoylhydrazone) (TPBI) bis-ligand with Cu(II) and Zn(II) transition metal ions were synthesized by mixing hot solutions of metal acetates (0.02 m) and TPBI bis-ligand (0.01 m) in least quantity of hot dimethylformamide (25 ml) with gradual stirring (Scheme 2). The resultant reaction mixture was digested in an oil bath at 130-140 °C. The polychelates of Cu(II) appeared in 3-5 h of digestion while Zn(II) polychelates required 12 to 14 h. The resulting product was filtered, washed with hot DMF, followed by alcohol and later with acetone and finally dried in vacuum desiccator over silica gel blue as desiccant. The scheme for the synthesis of the polychelates of TPBI ligand is as follows:

2 [M(CH3COO)2] TPBI

DMF Reflux, 3-5 h

{[M2(TPBI)(H2O)x] yH2O}n 2 CH3COOH

Scheme 2 - Synthesis of the coordination polymer

3.0 Results and discussion Both the synthesized polychelates are stable and found to be insoluble in common organic solvents. The elemental analyses confirm 2:1 (metal: ligand) ratio for both the polychelates. The physicochemical properties of the bisligand (TPBI) and its polychelates are given in Table 1. 3.1 1H NMR and 13C NMR Spectra The 1H NMR spectrum of TPBI bis-ligand in DMSO-d6 exhibits signals at 10.87, 8.79, 8.01, and 7.92 δ (ppm). A multiplet observed at δ 10.87 (ppm) may be assigned to four –NH protons attached to the carbonyl (C=O) group. Two doublets (J = 5.48 Hz) observed at δ 8.79 and 7.92 (ppm) may be attributed to the =CH- protons of the two pyridine rings. A multiplet observed at δ 8.01 (ppm) corresponds to four protons of the aromatic ring. The 13C NMR spectrum of TPBI bis-ligand shows characteristic peaks at 134.32, 129, and 127.5 ppm assigned to carbons of the aromatic ring, while peaks at 149.67, 139.75, and 121.47 ppm may be due to carbon atoms of the pyridine ring. The peaks at 165.00 and 166.65 ppm may be assigned to carbonyl (C=O) carbons attached to aromatc ring and pyridine ring, respectively.

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M.A. Haque and L.J. Paliwal / Materials Today: Proceedings 15 (2019) 481–489 Table 1 - Analytical data and colour of the bis-ligand (TPBI) and its coordination polymers Formula weight (g) 404.42

Compound

Empirical formula

TPBI

C20H16N6O4

{[Cu2(TPBI)(H2O)4]}n

C20H20Cu2N6O8

{[Zn2(TPBI)].2H2O}n

C20H16Zn2N6O6

Color

Elemental analysis (%) Exp. (Calcd.)

Off white

M -

C 59.18 (59.39)

H 3.84 (3.99)

N 20.81 (20.78)

597.10

Dark green

19.99 (21.22)

39.84 (40.06)

3.13 (3.34)

13.13 (14.02)

510.76

Yellow

23.10 (23.07)

42.00 (42.35)

2.71 (2.82)

14.93 (14.82)

3.2 Mass spectrum The ESI mass spectrum of TPBI ligand depicts [M+Na] peak at m/z 427 amu due to formation of sodium adduct which is in good agreement with the calculated molecular weight 404.42, thus confirming formation of the compound. 3.3 IR spectra The information regarding the coordination modes in Cu(II) and Zn(II) polymers is attained by comparing IR frequencies of free TPBI ligand and its metal coordination polymers. The IR frequencies of some of the significant bands of the free TPBI ligand and their polychelates are compiled in Table 2. Table 2 - IR spectral data of TPBI ligand and its coordination polymers C=N (py)

C=NN=C

Compound

N-H

-OH

C=O

TPBI {[Cu2(TPBI)(H2O)4]}n

3293

3163

1676

1574

-

-

-

1522

{[Zn2(TPBI)].2H2O}n

-

-

-

1557

1620

M-O

M-N

ν(H2O)

δ(H2O)

ρr(H2O)

C-O

C-N

1639

1180

1320

-

-

-

-

-

1607

1216

-

621

486

3053

1388

835

1219

-

664

612

3399

1393

-

IR spectrum of TPBI bis-ligand depicts characteristic band at 3293 1676 cm-1 assigned to stretching vibrations of – NH- group. The bands observed at 3052 cm-1 correspond to stretching vibrations of C-H of aromatic ring. The ligand also shows IR absorption bands at 1676 cm-1 due to >C=O group, 1574 cm-1 due to C=N(py) group and 1323 cm-1 due to C-N group. Moreover, a moderate absorption band observed at 3163 cm-1 is assigned to hydrogenbonded enolic –OH stretching vibrations, indicating the possibility of existence of keto-enol tautomeric forms of TPBI ligand (Fig. 1). However, this band disappears in the spectra of both the coordination polymers indicating deprotonation of enolic –OH groups of the ligand on ligation with metal in coordination polymers. Moreover, a peak at 1180 cm-1 owing to C-O stretching is found to appear at higher frequency region (1216-1219 cm-1) signifying the replacement of proton from enolic –OH group of bis-ligand leading to formation of M-O bond on chelation. The complete disappearance of C=O stretching band is also an indication of coordination of metal through the oxygen atom of the ligand. Further, a strong absorption band at 1639 cm-1 in the ligand due to presence of exocyclic C=N-N=C group is reduced to 1607-1620 cm-1 in both the coordination polymers indicating wider delocalisation of electronic charge in chelate ring. Moreover, coordination nitrogen atom of of exocyclic C=N-N=C group to metal leads to shift on the lower side. The new medium to weak bands in the range 621-664 cm-1 and 486-612 cm-1 may be attributed to M-O and MN vibration frequencies, respectively. Generally, water of hydration absorbs at 3300-3450 cm-1. The IR spectrum of Cu(II) coordination polymer depicts absorption bands at 3053, 1388, and 835 cm-1 attributed to –OH stretching, bending, and rocking vibrations, respectively [14-16] confirming existence of water of coordination. Thus, Cu(II) polychelate has six coordinated octahedral structure. However, Zn(II) coordination polymer may have tetrahedral geometry which is suggested on the basis of absence of rocking vibrations of water of coordination in IR spectra.

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From the above findings, it is clear that the ligand binds with central metal ion in the polychelates through the oxygen of carbonyl group and nitrogen of exocyclic C=N-N=C group of TPBI bis-ligand. The 5-membered chelate ring formed as a result of chelation of oxygen and nitrogen atoms with central metal ion is found to be stable. Each polychelate possesses such four 5-membered rings per repeat unit leading to an extra stability to these coordination polymers [15-17, 24]. Thus, examination of IR spectral data indicates that the ligand acts as an octadentate chelating ligand in both the polymers.

O N

N H

H N

H N O

I

N

N H

OH N

N

N

N OH

IV

O

II

N

N

N H

Fig. 1 - Keto-enol tautomeric forms of TPBI ligand

3.4 Electronic spectra and magnetic moments

Fig. 2 - Structure of coordination polymers

OH N N

O

O

O

N

OH

H N

H N

N

OH

OH N

O

O

N

N OH

III

OH

N H

N

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The electronic spectrum of Cu(II) coordination polymer shows three bands at ~14260, ~12420 and ~11114 cm-1. A band at ~14260 cm-1 suggests distorted octahedral geometry. These three absorption bands may be assigned to transitions viz. 2B1g → 2Eg, 2B1g → 2B2g and 2B1g → 2A1g respectively, which are in agreement with distorted octahedral geometry of Cu(II) polychelate. The obtained magnetic moment value, 1.95 B.M., is somewhat higher than the spin-only value, which is an additional evidence of distortion from usual octahedral geometry [13-17]. The Zn(II) polychelate is found to be diamagnetic in nature and has a tetrahedral structure. Therefore, from these findings, following structures may be anticipated for the polychelates (Fig. 2). 3.5 Morphology of coordination polymer Powder X-ray Diffraction (PXRD) technique can be effectively applied to explain the crystalline or amorphous nature of materials. The X-ray diffractograms of Cu(II) and Zn(II) polychelates (Fig. 3) showed some broad and less intense peaks confirming the amorphous nature of the two polymers. Amorphous materials fail to show any significant peak in diffraction pattern due to lack of periodic array with long-range order. The SEM micrograph of Cu-TPBI polymer (Fig. 4) depicts stratified arrangement of micro-structures of the polymer. While, that of Zn-TPBI polychelate (Fig. 4) shows striking coral shaped clusters with occasional cavities.

Fig. 3 - Powder XRD of Cu-TPBI and Zn-TPBI coordination polymers

Fig. 4 - SEM Micrographs of Cu-TPBI and Zn-TPBI Coordination Polymers

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3.6 Thermal analysis The thermal decomposition behaviour and stability of the polychelates were determined with the aid of TG/DTG/DTA studies performed at a heating rate of 10 ºC min-1 from ambient temperature to 1000 ºC. The thermograms of TPBI bis-ligand and its coordination polymers are depicted in Fig. 5-7 and thermoanalytical data are tabulated in Table 3. The kinetic and thermodynamic parameters were calculated graphically with the help of Coats-Redfern (CR) method [25]. Table 3 - Thermoanalytical data of the coordination polymers of TPBI ligand Polymers {[Cu2(TPBI)(H2O)4]}n

{[Zn2(TPBI)].2H2O}n

TG range (ºC) 40-270 270-380 380-825 39-150 150-430 430-520 520-825

DTGmax (ºC) 364 80 408 487 -

Th (ºC) 374

493

Mass loss (%) obs. (calc.) 12.09 (12.01) 39.11 6.26 (6.32) 26.58 22.55 -

Assignment Loss of four coordinated water molecules Removal of 58.58 % ligand Removal of total ligand leaving CuO residue Loss of two lattice water molecules Removal of 37.66 % ligand Removal of 31.95 % ligand Removal of total ligand leaving ZnO residue

The thermal analyses suggest that TPBI ligand degrades in two consecutive steps (Fig. 5) while the polychelates decompose in three to four steps. The DTG thermogram of ligand shows peaks at 260 and 362 ºC which are assigned to loss of solvent trapped during crystallization and decomposition of ligand respectively. The half decomposition temperature of TPBI ligand is found to be 355 ºC.

Fig. 5 - TG/DTG curves of TPBI ligand

The thermal decomposition of Cu-TPBI polychelate (Fig. 6) occurs in three steps between 40-825 ºC. The first decomposition stage is obtained between 40-270 ºC, with loss of 12.09 % mass which corresponds to removal of four molecules of water of coordination. The second step between 270-380 ºC with DTG peak at 364 ºC indicates removal of 58.58 % part of the ligand with 39.11 % mass loss. The decomposition of organic ligand occurs in last step between 380-825 ºC leading to formation of CuO as the final residue which corresponds to 17.50 %. Whereas, the TG curve of Zn-TPBI coordination polymer (Fig. 7) depicts four thermal decomposition steps from 38-825 ºC. The step observed between 38-150 ºC involves removal of two lattice water molecules as 6.26 % mass loss. This step gives a DTG peak at 80 ºC. The second decomposition step obtained between 150-430 ºC, due to removal of 26.58 % corresponds to elimination of 37.66 % of the ligand. This step gives a DTG peak at 408 ºC. The organic ligand further decomposes slowly in last two successive steps in temperature ranges 430-520 ºC and 520-825 ºC, giving a DTG peak at 487 ºC, leaving behind ZnO as residue. Thus, on the basis of thermoanalytical data, the polychelates are thermally more stable.

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Fig. 6 - TG/DTG curves of Cu-TPBI Polymer

Fig. 7 - TG/DTG curves of Zn-TPBI Polymer

The kinetic data (Table 4) shows that both the polychelates have negative entropy (∆S*) which demonstrates that the polymers are more ordered than reactants [26-27]. The non-spontaneous nature of thermal decomposition stages can be suggested on the basis of high positive values of ∆G*. While the second and higher stages of thermal decomposition stages show higher activation energy values indicative of slow decomposition water of coordination and ligand parts in polychelates, respectively. The higher thermal stability of the polychelates can be confirmed on the basis of fairly greater values of activation. Table 4 - Evaluation of Kinetic parameters of the coordination polymers of TPBI by Coats & Redfern (CR) method Polymers {[Cu2(TPBI)(H2O)4]}n

{[Zn2(TPBI ].2H2O}n

Ea *(kJmol-1) 51.29 65.36 11.93 29.23 34.27 43.46 140.45

n 1.5 1.5 1.9 1.5 1.5 1.5 1.5

A (s-1) 5

1.08 x 10 1.25 x 106 8.27 x 10 6.03 x 103 6.22 x 102 3.10 x 103 6.13 x 107

r2

∆S* (JK-1mol-1)

0.994 0.997 0.997 0.997 0.998 0.998 0.992

-153.25 -134.49 -215.15 -173.94 -198.29 -185.86 -106.64

∆H *(kJmol-1) 46.94 60.06 62.11 26.30 28.61 37.15 131.35

∆G* (kJmol-1) 127.09 145.73 154.23 87.69 163.64 178.39 248.02

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4.0 Conclusions The synthesis of a new octadentate bis-ligand (TPBI) and its coordination polymers have been successfully demonstrated. The elemental examination, mass spectrum, FTIR, 1H and 13C NMR studies confirm the formation and structure of TPBI bis-ligand. Two new Cu(II) and Zn(II) polychelates have been prepared and their structures have been assigned with the help of elemental studies, FTIR, UV-Visible spectra, magnetic moment values, XRD, SEM and thermal studies . The octadentate chelating nature of the TPBI bis-ligand, 2:1 (metal–ligand) ratio and high thermal stability imply their polymeric character. On account of the analytical data, Cu(II) polychelate has an octahedral geometry whereas Zn(II) polychelate has tetrahedral geometry. The thermal degradation behaviour of the TPBI bis-ligand and its polychelates has been investigated by applying TG/DTA techniques. Acknowledgements The authors are grateful to the Head, Department of Chemistry, PGTD, Rashtrasant Tukadoji Maharaj Nagpur University, Nagpur, Maharashtra, India, for the laboratory facilities. The authors are gratified to SAIF Chandigarh, Punjab University for spectroscopic data and STIC, Cochin, Kerala for thermoanalytical data. The authors also thank Post Graduate teaching Department of Physics, R.T.M. Nagpur University, Nagpur, for XRD and SEM analyses facilities. References 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27.

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