Synthesis, characterization, and biological activity of coordination polymers derived from pyromellitic dianhydride

A new ligand, 2,5-bis(furan-2-ylmethylcarbamoyl)terephthalic acid (BFMTA), was synthesized using 1,2,4,5- benzenetetracarboxylic dianhydride (pyromellitic dianhydride-PMDA) with furan-2-ylmethanamine (2-furfurylamine). New coordination polymers of the ligand (BFMTA) were also prepared using transition metal ions Mn(II), Fe(II), Co(II), Ni(II), Cu(II), and Zn(II) metal salts. The coordination polymers and ligand were characterized by physicochemical characteristics, magnetic susceptibilities, spectroscopic investigations, and thermogravimetry.

⃝ T¨UB˙ITAK

doi:10.3906/kim-1206-22

h t t p : / / j o u r n a l s t u b i t a k g o v t r / c h e m /

Research Article

Synthesis, characterization, and biological activity of coordination polymers

derived from pyromellitic dianhydride

Yogesh Shantilal PATEL,1 Ritu Bharat DIXIT,2 Hasmukh Shanubhai PATEL1, ∗

1

Department of Chemistry, Sardar Patel University, Vallabh Vidyanagar, Gujarat, India 2

Ashok & Rita Patel Institute of Integrated Studies and Research in Biotechnology and Allied Sciences,

New Vallabh Vidyanagar, Gujarat, India

Received: 12.06.2012 • Accepted: 11.06.2013 • Published Online: 04.11.2013 • Printed: 29.11.2013 Abstract: A new ligand, 2,5-bis(furan-2-ylmethylcarbamoyl)terephthalic acid (BFMTA), was synthesized using

1,2,4,5-benzenetetracarboxylic dianhydride (pyromellitic dianhydride-PMDA) with furan-2-ylmethanamine (2-furfurylamine) New coordination polymers of the ligand (BFMTA) were also prepared using transition metal ions Mn(II), Fe(II), Co(II), Ni(II), Cu(II), and Zn(II) metal salts The coordination polymers and ligand were characterized by physico-chemical characteristics, magnetic susceptibilities, spectroscopic investigations, and thermogravimetry Antimicrobial activity was tested using the agar-plate method against various strains of bacteria and spores of fungi The results showed significantly higher antimicrobial activity of coordination polymers compared to the ligand

Key words: Coordination polymer, spectral studies, thermogravimetric analysis (TGA), biological activity

1 Introduction

The metal–organic framework (MOF) architecture has witnessed a tremendous growth because of its intriguing structures and potential properties Much research is being devoted to the preparation of a polymeric chain

by the formation of metallic chelates Some success has been achieved in the preparation of coordination polymers from bi-functional ligands MOFs derived from bisamic acid have received less attention, apart from bisamic acid based on maleic anhydride,1 and amic acid based on phthalic anhydride.2−4 More particularly,

multicarboxylate material shows good building blocks in the design of MOFs with desired topologies owing to their rich coordination modes Therefore, the dianhydride of 1,2,4,5-benzenetetracarboxylic acid (pyromellitic dianhydride) has been selected for further work It is also used extensively as an important monomer in the preparation of a variety of polymers Moreover, it is useful in the preparation of high performance coatings that have been widely employed in many fields because of its excellent thermal and oxidative stability and excellent mechanical properties.5−7 This may offer the compound both metal gripping potentiality and good biological

efficacy due to anhydride moiety The MOF based on bisamic acid of pyromellitic dianhydride has not attracted any attention Hence, the initial work in this direction has been reported by us recently.8,9 This prompted us

to extend our work by using other auxiliary ligands such as 2,5-bis(furan-2-ylmethylcarbamoyl)terephthalicacid (BFMTA) Considering the special biological activity along with its properties, we have focused our work on this ligand by complexation using Mn(II), Fe(II), Co(II), Ni(II), Cu(II), and Zn(II) metal ions

∗Correspondence: drhspatel786@yahoo.com

2 Experimental

All common reagents and solvents used were of analytical grade Alumina supported pre-coated silica gel 60 F254 thin layer chromatography (TLC) plates were purchased from E Merck (India) Limited, Mumbai, and were used to check the purity of compounds and to study the progress of the reaction, whereby TLC plates were illuminated under ultraviolet light (254 nm), evaluated in I2 vapors, and visualized by spraying with Draggendorff’s reagent Infrared spectra (FT-IR) were obtained from KBr pellets in the range of 4000–400

cm−1 with a PerkinElmer spectrum GX spectrophotometer (FT-IR). 1H NMR and 13C NMR spectra were

acquired at 400 MHz on a Bruker NMR spectrometer using DMSO- d6 (residual peak at δ ∼2.5 or ∼39.5

ppm, 300 K) as a solvent as well as TMS an internal reference standard Microanalytical (C, N, H) data were obtained using a PerkinElmer 2400 CHN elemental analyzer The solid diffuse electronic spectra were recorded on a Beckman DK-2A spectrophotometer with a solid reflectance attachment MgO was employed

as a reference Magnetic moments10 were determined by the Gouy method with mercury tetrathiocyaneto cobaltate(II), with [HgCo(NCS)4] as calibrant (Xg = 1644 × 10 −6 cgs units at 20 ◦C), by Citizen balance

(at room temperature) Molar susceptibilities were corrected using Pascal’s constant.11 The thermogravimetric analysis studies were carried out with a PerkinElmer thermogravimetry analyzer at a heating rate of 10 ◦C

min−1 in the temperature range 50–700◦C under nitrogen The metal content of the coordination polymers was

determined by decomposing a weighed amount of each coordination polymer with HClO4, H2SO4, and HNO3 (1:1.5:2.5) mixture followed by standard EDTA titration.12 The number-average molecular weight ( Mn) of coordination polymers was determined by nonaqueous conductometric titration It was carried out in pyridine solution against standard sodium methoxide in pyridine solution as titrant The number-average molecular weight of each sample was calculated as reported in the literature13 and the results are shown in Table 1 The melting point was determined by the standard open capillary method

Table 1 Physicochemical parameters of the ligand and its coordination polymers.

Empirical formula of Empirical

a Elemental analysis calc (found %) µef f

M n DP

BFMTA

[Mn(BFMTA)H 2 O) 2 ]n

[Fe(BFMTA)(H 2 O) 2 ]n

[Co(BFMTA)(H 2 O) 2 ]n

[Ni(BFMTA)(H 2 O) 2 ]n

[Cu(BFMTA)(H 2 O) 2 ]n

[Zn(BFMTA)(H 2 O) 2 ]n

a The melting points were checked by standard open capillary method and are uncorrected, µ ef f B.M.: Magnetic moment

M n Number average molecular weights, DP: Degree of polymerization, D: Diamagnetic

2.1 Preparation of 2,5-bis(furan-2-ylmethylcarbamoyl)terephthalicacid (BFMTA)

Adding dropwise a solution of furan-2-ylmethanamine (19.43 g, 0.2 mol) to a stirred solution of pyromellitic dianhydride (21.813 g, 0.1 mol) and keeping the temperature of the medium close to 0–5 ◦C for 1 h (Scheme),

the solution obtained was poured into ice water in which the reaction product precipitated The final white precipitates were filtered, washed, and purified by column chromatography Yield was 65%; M Wt 412.35 g; Decomposition temp.: 250–260 ◦C (uncorrected); Elemental Analysis Calculated for C

20H16N2O8: C 58.25,

H 3.91, N 6.79% Found: C 57.87, H 3.75, N 6.58%; 1H NMR (DMSO- d6, δ ppm): 10.93 (s, 2H, -COOH), 8.90 (t, J = 5.2 Hz, 2H, -NH-CO-), 8.12 (s, 2H, Ar.H), 7.49–7.93 (m, 6H, Ar.H), 4.32 (d, J = 5.2 Hz, 4H, -CH2-);

DEPT-135 (DMSO- d6, δ ppm): 42.24, 117.78, 119.24, 123.46, 126.10, 129.33; EI MS m/z: 413.23 [M + H]+

metal ion

n 0-5 °C

Co-ordination polymers M=Mn(II),Fe(II),Co(II),Ni(II),Cu(II),Zn(II)

O O

O

O

O OH

O HO NH O

O

O

furan-2-yl methanamine

pyromellitic dianhydride

NH

O O

O

M

O

H2O

H2O NH

O O

O M

O

H2O

H2O

2,5-bis((furan-2-ylmethyl)carbamoyl)terephthalic acid

(BFMTA)

Scheme Synthetic route for the coordination polymers.

2.2 Preparation of coordination polymers

All the coordination polymers were synthesized by using equimolar amounts of ligand and metal salt A warm and clear solution of BFMTA (4.1235 g, 0.01 mol) in dimethylsulfoxide was neutralized by adding dropwise 0.1 M sodium hydroxide solution When a pasty mass was observed, it was diluted with water to make the solution clear To the above solution was added a solution of copper acetate (1.997 g, 0.01 mol) with constant stirring and the pH of the reaction mixture was adjusted to 4–5 The BFMTA-Cu2+ coordination polymer thus separated out in the form of a suspension was digested on a water bath for 1 h, filtered, washed, and dried in air at room temperature The BFMTA-Cu2+ polymer is insoluble in common organic solvents like methanol,

ethanol, chloroform, acetone, and benzene A similar procedure was followed to prepare other coordination polymers such as BFMTA-Mn2+, BFMTA-Fe2+, BFMTA-Co2+, BFMTA-Ni2+, and BFMTA-Zn2+ by using their respective salts and maintaining pH accordingly The synthetic route is shown in the Scheme

3 Results and discussion

3.1 Characterization of 2,5-bis(furan-2-ylmethylcarbamoyl)terephthalicacid (BFMTA)

To the best of our knowledge, BFMTA has not been reported previously The characterization of the reaction product provided the first unambiguous proof of the successful synthesis of BFMTA The FTIR spectrum of BFMTA showed the most relevant peaks of the furan ring and 1,2,4,5-tetra substituted benzene ring, other than typical absorptions arising from the band at 3528 cm−1 and 1711 cm−1 for carboxylic acid and 3254

cm−1 and 1680 cm−1 for the O = C-NH group.14 In the 1H NMR spectroscopy (Figure 1), the signals in the range of 7.49–7.93 ppm were ascribed to the protons of the aromatic rings The singlet at 10.93 ppm was ascribed to the protons of the carboxylic -OH group and the triplet at 8.90 ppm was attributed to the -NH proton of the amide group, which was further confirmed by DEPT-135 values In the DEPT-135 spectrum

of BFMTA (Figure 2), the inverted peak at 42.24 ppm indicated a methylene bridge between the amide and furan ring The peaks at 126.10 ppm and 129.33 ppm indicated the carbonyl carbon of amide and carboxylic functionality Peaks of substituted carbon of aromatic rings were not observed while the peaks of unsubstituted aromatic carbon were observed at 117.78, 119.24, and 123.46 in the DEPT-135 spectra The monomer BFMTA started to lose weight because of thermal degradation The thermogram of the product BFMTA (Figure 3) indicated that the degradation occurred into 2 steps The first stage of degradation, from 180 to 300 ◦C,

might be attributed to decarboxylation of the product BFMTA The value of wt loss 20.91% is consistent with the theoretical value 21.34% The second major stage, at about 300 to 700 ◦C, was attributed to the

monomer decomposition/pyrolysis The 3% to 4% char residue remained at 700 ◦C The expected structure

was thus clearly verified by the spectroscopic and thermal analysis, which indicated moreover the absence of any detectable impurity, particularly of the 2 reagents used to prepare BFMTA

3.2 Characterization of coordination polymers

Elemental analysis (Table 1) of the coordination polymers is in good agreement with the proposed structures All the coordination polymers exhibited 1:1 metal to ligand stoichiometry The structures of the coordination polymers are consistent with the FTIR, electronic spectra, and TGA The geometry of the central metal ion was confirmed by electronic spectra and magnetic susceptibility measurements The degrees of polymerization (DP) for all the coordination polymers are in the range of 5 to 6 All the data provide good evidence that the chelates are polymeric in nature The suggested structure of the coordination polymers is shown in the Scheme

A comparison of the IR spectra (Table 2) of the ligand and its metal (II) coordinated polymers showed some significant characteristic differences Considerable differences to be expected were the band at about 3530

cm−1 for carboxylic acid in ligand that was virtually absent from the spectra of polymers and the presence of a

more broadened band in the region near 3000 cm−1 for the coordinated polymers As the oxygen atom of the OH

group of the ligand forms a coordination bond with the metal ions, the broadening of this band may be attributed

to the presence of coordinated water molecules.15 The asymmetric and symmetric stretching frequencies of the carboxylate ion in the polymers were shifted to lower frequencies The C–O also registered a significant shift

to lower frequency, indicating the participation of metal through carboxylate oxygen.16 Vibrational bands for

O = C–NH (amide carbonyl linkage) shifted to lower frequencies, indicating the coordination of amide nitrogen

Figure 1 NMR of 2,5-bis(furan-2-ylmethylcarbamoyl)terephthalic acid (BFMTA).

Figure 2 DEPT of 2,5-bis(furan-2-ylmethylcarbamoyl)terephthalic acid (BFMTA).

to metal ion, and this can be explained by the donation of electrons from nitrogen to metal atom.17The presence

of a sharp band in the region of 525–535 cm−1 can be assigned to ν (M-N),18 which indicated the involvement

of nitrogen in coordination A medium intensity band for ν (M-O)19 was observed at 625–640 cm−1 due to

M-O coordination These features confirmed the proposed structure of coordination polymers

6A

4T

]n

6A

4T

6A

4A

]n

5T

3E

5T

3T

4T

4T

]n

4T

4A

4T

4T

3A

3T

]n

3A

3T

3A

3T

]n

2T

2E

]n

The information regarding geometry of the coordination polymers was obtained from their electronic spectral data and magnetic moment values The diffuse electronic spectrum of the [Cu(BFMTA)(H2O)2]n

shows 2 broad bands around 15,922 cm−1 and 22,757 cm−1 due to the 2T2g →2Eg transition; the second may be due to charge transfer This suggests a distorted octahedral structure for the [Cu(BFMTA)(H2O)2]n

polymer The [Ni(BFMTA)(H2O)2]n coordination polymer shows 2 absorption bands at 15,584 cm−1, 22,978

cm−1, and 9891 cm−1 due to 3A2g →3T1g(F), 3A2g →3T1g(P), and 3A2g →3T2g respectively The [Co(BFMTA)(H2O)2]n polymer shows 2 absorption bands at 22,941 cm−1, 15,520 cm−1, and 9830 cm−1

corresponding to 4T1g(F)→4T1g(P), 4T1g(F)→4A2g(F), and 4T1g(F)→4T2g(F) transitions, respectively, indicating an octahedral configuration for the [Ni(BFMTA)(H2O)2]n and [Co(BFMTA)(H2O)2]n polymers.20 The spectrum of [Fe(BFMTA) (H2O)2]n shows bands at 36,022 cm−1 and 19,038 cm−1 assigned to the

transitions 5T2g(F)→3T1g and 5T2g(F)→3Eg, suggesting an octahedral configuration The spectrum of [Mn(BFMTA)(H2O)2]n shows weak bands at 16,486 cm−1, 17,710 cm−1, and 23,179 cm−1 assigned to

the transitions 6A1g →4T1g(4G), 6A1g →4T2g(4G), and 6A1g →4A1g,4Eg respectively, suggesting an octahedral structure for the [Mn(BFMTA)(H2O)2]n polymer.21 The spectrum of the [Zn(BFMTA)(H2O)2]n polymer is not well interpreted, but its µ ef f value shows that it is diamagnetic as expected Magnetic moments

µ ef f of coordination polymers reveal that all the polymers except Zn(II) metal ion polymer are paramagnetic while Zn(II) metal ion polymer is diamagnetic

The thermal behavior was investigated by PerkinElmer TGA analyzer at a heating rate of 10 ◦C min−1

in the temperature range 50–700 ◦C under nitrogen, which provides much information about the coordination

compounds In all the coordination polymers, decomposition occurred in 2 steps (Figure 3) The first step, between 100 and 200 ◦C, might be attributed to mass loss corresponding to water molecules The weight loss

indicated that 2 water molecules were coordinated to the metal ion The second step, between 200 and 700

◦C with the inflation at 350 ◦C, exhibits a mass loss corresponding to decomposition of metal from the ligand

part in the polymer The weight loss observed in the range of 11%–13% is consistent with metal degradation The major weight loss of the coordination polymers was noticeable beyond 400 ◦C The rate of degradation

became maximal at a temperature between 400 and 600 ◦C This might be due to accelerating by metal oxide

that formed in situ Each polymer lost about 80% of its weight when heated up to 700 ◦C On the basis of

the relative decomposition (% weight loss) and the nature of thermogram, the coordination polymers might be

arranged in order of their increasing stability as follows: Cu < Fe < Ni < Co < Zn < Mn.

3.3 Biological activity

Antibacterial activity of BFMTA and its coordination polymers (Table 3) was tested against gram-positive

bacteria (Bacillus subtilis and Staphylococcus aureus) and gram-negative bacteria (E coli and Salmonella

typhi ) at a concentration of 50 µ g/mL by agar cup plate method A DMSO system was used as control in this

method The area of inhibition was measured in millimeters The fungicidal activity of all the compounds was

studied at 1000 ppm concentration in vitro The plant pathogenic organisms used were Penicillium expansum,

Botrydepladia thiobromine, Nigrospora sp., and Trichothesium sp The antifungal activity of BFMTA and its

coordination polymers was measured on each of these plant pathogenic strains on a potato dextrose agar (PDA) medium Such a PDA medium contains potato 200 g, dextrose 20 g, agar 20 g, and water 1 L Five-day-old cultures were used The compounds to be tested were suspended (1000 ppm) in a PDA medium and autoclaved

at 120 ◦C for 15 min at 15 atm pressure These media were poured into sterile petri plates and the organisms

were inoculated after cooling the petri plates The percentage inhibition for fungi was calculated after 5 days using the formula given below:

Percentage of inhibition = 100 (X – Y) / X where X = area of colony in control plate

Y = area of colony in test plate

0

10

20

30

40

50

60

70

80

90

100

110

Temperature

BFMTA [Mn(BFMTA)H2O)2]n [Fe(BFMTA)H2O)2]n [Co(BFMTA)(H2O)2]n [Ni(BFMTA)(H2O)2]n [Cu(BFMTA)(H2O)2]n [Zn(BFMTA)(H2O)2]n

Figure 3 Thermogram of BFMTA and its coordination polymers.

Table 3 Antibacterial and antifungal activity of the ligand and its polymers.

Compound

Antibacterial activity Antifungal activity Zone of inhibition Zone of inhibition Gram +ve Gram –ve

BS: Bacillus subtilis, SA: Staphylococcus aureus, ST: Salmonella typhi, EC: Escherichia coli,

PE: Penicillium expansum, BT: Botrydepladia thiobromine, NS: Nigrospora sp., TS : Trichothesium sp

The levels of antibacterial and antifungal activity were compared with those of the standard drug ciprofloxacin As compared to ciprofloxacin, the compounds were less active The ligand was found biologically active, and its polychelates showed significantly enhanced biological activity compared to the ligand Among the coordination polymers, Fe(II) and Cu(II) coordination polymers showed better activity against all gram-positive and gram-negative bacteria They also showed better activity against the plant pathogenic strain This might be due to the additive biological effect of parent molecule and/or the metal chelating properties of Fe(II) and Cu(II)

4 Conclusions

A new ligand and its coordination polymers were prepared in good amount of yield and were duly characterized

In the coordination polymers the ligand coordinates with 1 central metal atom at 4 coordination sites along with 2 water molecules The structures of the ligand and its coordination polymers are consistent with the elemental, spectral, and thermal analyses The geometry of the central metal ion was confirmed by electronic spectra and magnetic susceptibility measurements All the data provide good evidence that the chelates are polymeric in nature These polymers do not melt up to 400 ◦C The polymers have moderate thermal stability

and show good biological activity

Acknowledgments

One of the authors, Yogesh S Patel, is greatly thankful to the UGC for sanctioning his Teacher Fellowship under the scheme of the Faculty Improvement Programme for the research work

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