Fluorine-functionalized metal–organic frameworks and porous coordination polymers

Abstract

Fluorine, the element with the highest electronegativity and low electric polarizability, can produce a variety of characteristics, including specific adsorption sites for molecules as well as flexibility to the host materials. In this review, we will introduce fluorine-functionalized metal-organic frameworks/porous coordination polymers that show unique and unprecedented structures, structural transformations, and gas and vapor adsorption/separation properties derived from the fluorine characteristics. NPG Asia Materials (2017) 9, e433; doi:10.1038/am.2017.165; published online 29 September 2017 INTRODUCTIONDuring the last two decades, metal-organic frameworks (MOFs)/ porous coordination polymers (PCPs) composed of metal ions and organic bridging ligands as main building units and, in some cases, inorganic ligands, have been investigated extensively because of their versatile structural diversity, high structural controllability (pore size, shape, dimension, flexibility and surface environment), high crystallinity, and their potential porous properties/functionalities in a variety of research fields such as storage and separation, catalysis, drug delivery and sensing ability. 1-3 The porous properties of MOFs/PCPs can be finely tailored by not only chemical modification of organic ligands and judicious choice of components but also a variety of techniques such as solid solution formation, defect engineering, core-shell structure, crystal morphology and size control, and so on. For example, the appropriate combination of organic bridging ligands provided the Zn(II) MOF, [Zn 4 O(bte) 4/3 (bpdc)] (bte = 4,4′,4′′-[benzene-1,3,5-triyl-tris (ethyne-2,1-diyl)]tribenzoate, bpdc = biphenyl-4,4′-dicarboxylate), with ultra-high Brunauer-Emmett-Teller and Langmuir specific surface areas close to 6000 and 10 000 m 2 g − 1 , respectively. 4 Unlike porous inorganic zeolites and porous carbon materials, MOFs often give flexible structures. As coordination bonds, hydrogen bonds and van der Waals interactions that are used to assemble each component are weaker (bonding energies are 10~200 kJ mol − 1 ) than covalent and ionic bonds (200~1000 kJ mol − 1 ), reversible rotation, bending and breaking of these weaker bonds easily occurs, resulting in structural changes. One representative of flexible MOFs is [Cr(OH)(1,4-bdc)] (MIL-53(Cr), 1,4-bdc = 1,4-benzenedicarboxylate), in which local reorientation of the coordination bond triggered by guest adsorption/ desorption induced the structural transformation between narrow pore and large pore forms. 5 In addition, many MOFs show high crystallinity as with porous inorganic zeolites, which is advantageous for understanding deeply the structure-property relationship using single-crystal and powder X-ray diffraction techniques. For example, the unprecedented highly selective CO sorption from a CO/N 2 mixture, which is

Self‐Assembled, Fluorine‐Rich Porous Organic Polymers: A Class of Mechanically Stiff and Hydrophobic Materials

“…Fluorinated porous networks such as fluorinated MOFs have been recognised in the recent literature to exhibit excellent water repellence alongside affinity toward hydrocarbon vapours such as benzene . As evidence of the fluorine‐dense nature, water‐vapour sorption isotherm experiments with the FPOPs showed negligible uptake, even under saturation vapour pressure of water (3.17 kPa at 298 K), whereas hydrophobic oil‐constituent hydrocarbon benzene showed slow opening‐assisted high saturation uptake profiles (Figures a and b).…”

A biomimetic design for a sialylated, glycan-specific smart polymer

“…In addition, developing glycan-sensitive materials capable of recognizing and responding to the addition or absence of a single monosaccharide in a glycan, such as those of blood-type-sensitive materials taking individual differences into account, is highly desirable and will help scientists better understand the mysterious world of glycans. Furthermore, emerging mesoporous materials, such as metal organic frameworks 46 and covalent organic frameworks, 47 integrated with smart polymer designs could remarkably increase the specificity and separation efficiency of the composite materials for the target glycans, which would facilitate a variety of exciting applications in the fields of bio-sensing and bio-separation.…”

Metal–organic framework-based nanomaterials for adsorption and photocatalytic degradation of gaseous pollutants: recent progress and challenges

“…Moreover, using strong-field ligands such as an azolate-terminated organic ligand to build MOFs, and pre-or post-synthetic incorporation of alkane or fluoroalkane in the organic linker is also reported for tuning the hydrophilic/hydrophobic properties of MOFs against water vapor and introducing new binding sites for gaseous pollutant adsorption, leading to the improved adsorption performance of modified MOFs. 83,[131][132][133] 3.3 Post-modification via incorporating ionic elements, polyoxometalates (POMs) and other functional materials within MOFs…”