Solid-state structural transformation doubly triggered by reaction temperature and time in 3D metal-organic frameworks: great enhancement of stability and gas adsorption

Abstract

In this work, we have demonstrated an unprecedented single-crystal-to-single-crystal (SCSC) transformation between two 3D metal-organic frameworks (MOFs). The centrosymmetric IFMC-68 ([(Zn₄O)₂(L)₃]·10H₂O·46DMA) transforms into a chiral IFMC-69 ([(Zn₄O)₂(L)₃H₂O]·H₂O·4DMA) doubly triggered by reaction temperature and time simultaneously in the presence or absence of solvent. To our knowledge, this is the first representative that the non-interpenetrated structure transforms into self-penetrated structure in MOFs. For the first time, we have studied the influence of reaction temperature and time on SCSC transformation, simultaneously, and get the transformation relationship among IFMC-68, IFMC-69 and the intermediate coming from the direct synthesis method and stepwise synthesis method at different temperatures and for different times. Meanwhile, we have achieved the conversion from an air-unstable to air-stable structure. Air-stable IFMC-69 exhibits the selective CO₂ uptake over N₂ and more excellent gas adsorption ability than IFMC-68. In addition, IFMC-69 shows an efficient capability in reversible adsorption of iodine. The electrical conductivity value (σ) of I₂@IFMC-69 is much higher than the pristine MOF and thus is promising for potential semiconductor materials in the future.