Design and Fabrication of Switchable Metal Organic Frameworks

Abstract

Metal organic frameworks (MOFs) are a versatile class of porous crystalline materials constructed from metal nodes and organic linkers. Postsynthetic modification (PSM) has emerged as an important late-stage approach to functionalizing MOFs. The introduction of the desired functional groups via PSM strategies requires chemical handles or tags within the MOFs‟ lattice though appropriate linker molecules during their synthesis. Click reactions offer dynamic covalent chemistries that result in changes of surface properties by allowing very fast and reversible reactions under mild condition. The present work demonstrates the synthesis of amine functionalized metal organic frameworks followed by the post synthetic modification via various strategies involving click chemistry. A thermally reversible Diels– Alder ligation between cyclopendienyl (Cp) groups functionalized MOFs (NH2-MIL-88B-Fe and ML-88B-Fe) and small molecules bearing maleimide groups was employed to fabricate MOFs with switchable chemical nature. The thermally induced Hetero Diels-Alder (HDA) reactions between cyclopendienyl (Cp) groups grafted on NH2-MIL-53-Al and dithioester based moieties were performed to prepare MOFs able to reprogrammable chemical nature. Maleimide group containing molecules of markedly different chemical nature were utilized to demonstrate the reversible switching of functionalities on furan groups containing MOF (NH2-UiO-66-Zr) presenting an unprecedented concept of a MOF that may be transformed to perform distinct functions simply by switching their chemical functionalities. The potential of thiol-ene click chemistry was utilized to postsynthetically modify MOF (IRMOF-3-Zn). The thiol–maleimide Michael addition approach allows the maleimide bearing frameworks to graft cysteine based biomolecules. All the results in the presented thesis were supported by scanning electron microscopy (SEM), Energy-dispersive X-ray spectroscopy (EDX), X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC) analysis.