Novel Porous Polycatenated Iodo–Cadmium Coordination Polymer for Iodine Sorption and Electrical Conductivity Measurement

Abstract

The porous materials are efficient storage and exchange systems of small molecules and ions. Some of the porous materials may be used as an efficient storage system of iodine. Herein, a honeycomb (hcb)-type 2D+2D (2D = two-dimensional), parallel polycatenated Porous Polycatenated Coordination Polymer (PPCP) {[Cd2I2(BDC)2(INH)2]·(2DMF)(H2O)}n, 1 (INH, isoniazid; H2BDC, terephthalic acid; DMF, dimethylformamide) is characterized that reversibly uptakes I2 from organic medium (more than 98%). The single-crystal X-ray structure determination reveals the CdIN2O3 distorted octahedral geometry, and the microporous channel (∼1.7 nm) is generated by polycatenation 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 displayed the increase in porosity to mesoporous range (∼14.7 nm) with very high specific Brunauer–Emmett–Teller surface area, which may be due to the rise in interparticle void space. Iodine (I2) sorption studies of mesoporous architecture of 1′ show 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 density functional theory (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 was evidenced from Raman spectra analysis.