Delamination and Photochemical Modification of a Novel Two‐Dimensional Zr‐Based Metal–Organic Frameworks

Abstract

In this contribution we present a novel two-dimensional Zr-based metal-organic framework (MOF) which offers the possibility for delamination and post-synthetic photochemical modification at the linker molecule derived from benzophenone-4,4'-dicarboxylic acid (H bzpdc). The new Zr-bzpdc-MOF crystallizes in the orthorhombic system as crystals with rhombic shape. The structure was determined from single-crystal diffraction data. The MOF is stable up to 300 °C in air and exhibits a moderate BET surface area of 650 m g . The material can be obtained as thin sheets of a few nanometer thickness. Single crystals were modified post-synthetically, exploiting the intrinsic reactivity of the benzophenone group with C-H bond containing molecules. In this way, the surface properties of the MOF crystals (e.g., dispersibility in different solvents) can be changed drastically. Delamination and adaptation of the surface chemistry open up novel ways for shaping MOFs, for example, for the incorporation into polymer composites, and pave the way for various applications.

Inside/Outside: Post‐Synthetic Modification of the Zr‐Benzophenonedicarboxylate Metal–Organic Framework

“…The Zr‐ bzpdc ‐MOF possesses high chemical and good thermal stability, basic prerequisites for successful post‐synthetic reactions. According to its crystal structure, all benzophenone moieties present throughout the framework are accessible via the pore system; in addition, the rhombic‐shaped crystals present benzophenone groups on their predominant basal surfaces . The Zr‐ bzpdc ‐MOF exhibits moderate permanent porosity consisting of corrugated channels with a minimum free pore diameter of 6.5 Å (visualized in the Supporting Information, Section 1.3, Figure S13).…”

“…Although judging from their largest dimension (diameter of the methylene chain of the alcohols: 4.8 Å), all alcohol molecules should be able to enter the pore system of the Zr‐ bzpdc ‐MOF (minimum free pore diameter: 6.5 Å), the corrugated channel structure could strongly impede the diffusion of longer‐chain alcohols (C 5 to C 8 ) into the interior of the crystal whereas small‐chain alcohols (C 1 to C 4 ) can diffuse through the whole pore system (although the diffusion of butanol takes considerable time, see above). Another possibly important aspect is that with the chain length of the alcohols, their hydrophobic character increases, which could lead to a decreased diffusion into the pore structure of the rather hydrophilic Zr‐ bzpdc ‐MOF . Therefore, we furthermore tested the PSM reaction with more hydrophobic alkanes, starting with butane and increasing the chain length up to octane.…”

“…Retrospectively, it is of interest to note the differences between the products of the PSM obtained after irradiation in PEG and decane which we had described in our original paper on the Zr‐ bzpdc ‐MOF . According to PXRD, the reactions only occurred at the outer surface.…”

“…Upon excitation by irradiation with UV light, the ketyl radicals formed react with practically any C−H bond of an organic molecule according to the reaction mechanism schematically shown in Scheme . We have employed the linker molecule benzophenone‐4,4′‐dicarboxylic acid (H 2 bzpdc ) to synthesize the Zr‐based metal–organic framework Zr‐ bzpdc ‐MOF . The synthesis made use of the modulation method and lead to a compound with formula Zr 6 O 4 (OH) 6 (HCO 2 ) 2 ( bzpdc ) 4 .…”

“…Its high chemical and thermal stability make it highly suitable for PSM reactions. In a preliminary study, we have converted this MOF in photochemical PSM reactions with decane and PEG and have observed drastically different wetting properties of the products . Furthermore, we have initiated photochemical grafting‐from polymerisation reactions of EDOT (3,4‐ethylenedioxythiophene) to yield nanoporous electrically conducting MOF‐PEDOT composites .…”