Reversible crystal-to-crystal transformation in nano-porous three-dimensional lead(ii) MOFs; study of solvent attendance on iodide adsorption affinity

Abstract

A reversible crystal to crystal transformation of a new porous 3D lead(II) coordination polymer with the ligand 2,5-bis(4-pyridyl)-3,4-diaza-2,4-hexadiene (4-bpdh), [Pb(4-bpdh)(NO₃)₂]_n (HMTI-2) to [Pb(4-bpdh)(NO₃)₂(H₂O)]_n (HMTI-1), by hydration and dehydration, has been observed. Powder X-ray diffraction experiments and IR analysis showed that the compounds obtained by hydration and dehydration have same crystalline lattice. Among the proposed methods for the removal of dyes and toxic materials such as iodine from contaminated water, removal by adsorption technologies is regarded as one of the competitive methods because of high efficiency, economic feasibility and simplicity of operation. In this work, we successfully loaded compounds HMTI-2 and HMTI-1 with I₂ by suspending them in a cyclohexane solution of I₂. The delivery of I₂ from compounds HMTI-2 and HMTI-1 in ethanol at room temperature was determined by UV-vis spectroscopy. Adsorption and desorption rate of iodide in HMTI-1 and HMTI-2 shows that present of H₂O molecules have effective role in increase of iodine adsorption in HMTI-1.