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Novel Porous Polycatenated Iodo-Cadmium Coordination Polymer for Iodine Sorption and Electrical Conductivity Measurement Kaushik Naskar, Arka Dey, Suvendu Maity, Manas K. Bhunia, Partha Pratim Ray, and Chittaranjan Sinha Cryst. Growth Des., Just Accepted Manuscript • DOI: 10.1021/acs.cgd.8b01806 • Publication Date (Web): 20 Feb 2019 Downloaded from http://pubs.acs.org on February 23, 2019
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Novel Porous Polycatenated Iodo-Cadmium Coordination Polymer for Iodine Sorption and Electrical Conductivity Measurement Kaushik Naskar,a, ‡ Arka Dey,b,d ‡ Suvendu Maity,a, ‡Manas K. Bhunia,c, ‡ Partha Pratim Ray*,b, ‡ and Chittaranjan Sinha*,a, ‡ aDepartment
of Chemistry, Jadavpur University, Kolkata–700032, India.
bDepartment
of Physics, Jadavpur University, Kolkata– 700032, India.
cDepartment
of Chemistry, Central University of Tamil Nadu, Thiruvarur–610005, India.
dDepartment
of Condensed Matter Physics and Material Sciences, S. N. Bose National Centre for
Basic Sciences, Block JD, Sec. III, Salt Lake, Kolkata 700106, India.
ABSTRACT. The porous materials are efficient storage and exchange system of small molecules and ions. Some of the porous materials may be used as efficient storage system of iodine. Herein, a honeycomb (hcb) type 2D+2D, parallel polycatenated Porous Polycatenated Coordination Polymer (PPCP) {[Cd2I2(BDC)2(INH)2].(2DMF)(H2O)}n, 1 (INH, Isoniazid; H2BDC, terephthalic acid) is characterized which reversibly uptakes I2 from organic medium (more than 98%). The single crystal X-ray structure determination reveals the CdIN2O3 distorted octahedral geometry and the micro-porous channel (~ 1.7 nm) is generated by polycatenation
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along with the supramolecular interaction. On thermal treatment at 120 C the polymer, 1, loses solvents while the crystalinity is reserved. The solvent-free activated state of the coordination polymer, [Cd2I2(BDC)2(INH)2]n, 1′, adsorbs N2 and the adsorption-desorption analysis has displayed the increase in porosity to mesoporous range (~ 14.7 nm) with very high specific BET surface area which may be due to the rise in interparticle void space. Iodine (I2) sorption studies of mesoporous architecture of 1′ is examined and shows high I2 removal efficiency (98.9%) which is revealed from the reversible iodine uptake kinetics study. Typically, uptake of three moles of I2 per unit cell associated with color change from colorless to brown is discernible from thermal analysis. Interestingly, the iodine-loaded polymer (I2@1′) shows ∼1.5 times enhancement in electrical conductivity compared to 1′ only. The optical band gap obtained from DFT calculation and the experimental values are 1, 3.48 eV (DFT), 3.70 eV (experimental) and I2@1′, 3.19 eV (DFT), 3.50 eV (experimental). The lowering of band gap after I2 sorption is presumably due to the interaction of I2 with Cd–I (Cd-I---I–I) in hcb core which has been as evidenced from Raman Spectra analysis.
Introduction Isoniazid1 (INH) has two donor sites, pyridyl-N and hydrazide-O, N-chelator, and becomes an excellent bridging ligand to form a coordination polymer.2,3 Porous Coordination Polymers (PCPs)4 owing to the high surface area and variable pore architecture are valuable material in sorption and separation of gases,5–8 catalysis,8,9 fluorosensors,10 and drug delivery.11,12 The electrical conductivity of the coordination polymers13-15 are developing recently. To improve the electrical conductivity16,17 various modifications have been mooted in the design of PCPs and some of these are the use of high H+ conducting organic ligands, inclusion of the protic guests
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into the micro-channels, through the engineering of hetero-domain crystal systems, use of redox non-innocent cations/anions, binding with conformationally stable organic linkers who have very high tolerance to external stimuli preferably magnetic and optical, encapsulation of iodine18-21 (I2, I3-) etc. Iodine, an important trace element to human health,22 marine environments and in organic synthesis as a catalyst,23 has recently been focused in public issues because of the growth of the nuclear industry.24 The extensive implementation of nuclear power (very high energy density, ~500 million times higher than gasoline by volume) vast quantity of iodine radioisotopes are released in the environment and radioactive-I2 (123,
125, 129, 131I)
has severe health risk to
mammalians.24 Among various types of capturing systems like zeolites,25 chalcogels,26 microporous polymers,27 porous aromatic frameworks,28,29 covalent or hydrogen-bonded organic frameworks;30 and silver exchanged zeolites31 were found to be very promising materials as solid adsorbents for I2 capture. It is important to design selective MOF comprising an appropriate active site which may absorb iodine effectively.18-21 It is demonstrated that polar cavity with electron donating groups, for example, –OH and –NH2, normally improve iodine sorption efficiency which leads to increase electrical conductivity.18 The metaliodide (MI) coordination bond(s) in the PCPs may enhance I2 capturing capacity via M–I---I2 binding, thus increasing the sorption amount for iodine. The releasing processes of iodine from the porous materials are also vital for use of iodine as medicine. Iodine and its radionuclides have been vastly used as I123 (t1/2 = 13 h) in imaging thyroid glands,32 I131 (t1/2 = 8 days) against cancer treatment,33 I125 (t1/2 = 59 days) as a -emitting tag for proteins,34, I129 (t1/2 = 15.7 million years) used for monitoring long living environmental contaminants, etc. So, capturing, storing and releasing of iodine35,36 by using PCPs are the growing field of attention and has also been focused on.
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In this work, we have synthesized a honeycomb (hcb) type porous Cd(II)-based 2D+2D structure, parallel polycatenated PCP with isoniazid (INH) and terephthalic acid (H2BDC) as pillar forming ligands, {[Cd2I2(BDC)2(INH)2].(2DMF)(H2O)}n, 1. The structural analysis shows polycatenation with a microporous channel (~ 1.7 nm). Upon thermal treatment, the Complex 1 has been transformed to a robust solvent-free activated state, [Cd2I2(BDC)2(INH)2]n, 1 ′ , and nitrogen adsorption-desorption analysis has displayed mesoporous channel (~ 14.7 nm) with a very high specific-BET surface area. The nitrogen adsorption/desorption analysis of the activated polymer (1ʹ) showed high BET-specific surface area with type-IV isotherm partaking steep uptake of N2 at low pressure, indicating typically of mesoporous nature, whereas initial uptake implies microporosity. The nature of porosity presumably originates from the inter-particle voids since the unit cell parameters are typically within the range of 2 nm. The compound is used to sorb iodine. The ease of reversible iodine sorption and desorption with the change from nonpolar to polar solvent has paramount importance for the application of this PCP. The I2–adsorbed PCP i.e. I2@1′ has intriguingly shown 1.5 times enhanced electrical conductivity. In conjunction with the experiments, the quantum mechanical calculations (DFT and TD DFT) have been performed both for 1ʹ, 3.48 eV and I2@1′, 3.19 eV to get insight into the band gap and band positions and to the origin of electrical conductivity.
Experimental Section Materials and Physical Methods Isoniazid, (INH), Terephthalic acid (H2BDC), and CdI2 were purchased from Sigma–Aldrich Chemical Co. Inc. and were used as received. All other chemicals and solvents were of reagent grade and purchased from Merck and used without further purification. Micro-analytical data (C,
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H, N) were collected on Perkin-Elmer 2400 CHNS/O elemental analyzer. Spectroscopic data were obtained using the following instruments: IR spectra (KBr disk, 4000–400 cm−1) from a Perkin Elmer RX–1 FTIR spectrophotometer. Thermo gravimetric analyses (TGA) were performed under a nitrogen atmosphere with a heating rate of 10°C/min using a Pyris Diamond TG/DTA instrument in the range of 30-600°C. X-ray powder diffraction was performed using a Bruker D8 ADVANCE X-ray diffractometer. Nitrogen adsorption-desorption isotherms were obtained using a Micromeritics ASAP 2420 surface area analyzer at liquid nitrogen temperature (-196ºC). Prior to gas adsorption, sample was pre-treated with dry methanol for every 6 h for two days, every time freshly dried solvent was used to remove the guests form the PCP and then it was degassed at 120°C for 4 h, where the sample was activated due to generation of the porosity. Raman spectra was carried out by using Triple Raman spectrometer (Model: T64000, J-Y Horiba) with a 532 nm laser and an 1800 grooves/ mm grating. Morphology and EDS analyses of Compound 1′ and I2@1′ were carried out via field emission scanning electron microscopy (FESEM) (JEOL, JSM-6700F). Synthesis of {[Cd2I2(BDC)2(INH)2].(2DMF)(H2O)}n, 1 To methanol solution (10 ml) of INH (isoniazid) (0.137 g, 1 mmol) was carefully layered by the help of DMF solvent over the aqueous solution of (10 ml) of CdI2 (0.366 g, 1 mmol). Terephthalic acid (H2BDC) (0.166 g, 1 mmol) in ethanol (10 ml) was neutralized with Et3N solution (0.212 g, 2 mmol) and was injected cautiously over the isoniazid solution followed by DMF solvent to make an undisturbed layer. It was then allowed to diffuse for a week. The colorless needle-shaped crystals were deposited on the glass wall. The crystals were separated mechanically under a microscope and washed with methanol and water (1:1) mixture, and dried. The yield of {[Cd2I2(BDC)2(INH)2].(2DMF)(H2O)}n, 1 was 72 % (0.039 g). Elemental analysis
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calculated for (C26H34Cd2I2N8O9)n (1): C, 28.88; H, 3.17; N, 10.36,Found: C, 28.82; H,3.11; N, 10.26 %, IR (KBr pellet, cm-1): 1663, νas(COO−); 1380, νs(COO−).(ESI†, Figure S1) X-ray Crystallography Crystal data and experimental details for data collection and structure refinement are reported in Table S1. The crystal structure of 1 was determined by X-ray diffraction methods. Suitable single crystal of 1 having an appropriate dimension (0.412×0.085×0.012 mm) was used for data collection via Bruker SMART APEX II diffractometer, having graphite-monochromated Mo-Kα radiation (λ, 0.71073 Å). The unit cell parameters and crystal-orientation matrices were determined by least-squares refinement of all reflections within hkl range –22
