Topologically guided exfoliation of 3D metal-organic frameworks into nanosheets

Abstract

Herein a general concept for screening 3D metal-organic frameworks (MOFs) for 2D nanosheets design is presented. Active coordination centers and terminal ligands of 3D-to-2D MOF nanosheets can result in self-assembly of multilayer structures. In comparison to 2D MOFs, 3D frameworks can provide nanosheets with better adhesion, strength, adsorptive capacity and catalytic activity. They are also promising in semiconductors, sensorics, and drug delivery systems. However, less than a dozen of 3D-to-2D MOF nanosheets have been produced to date. Therefore, we applied topological tools of ToposPro and Cambridge Structural Database for screening 3D MOFs as sources of new 2D nanosheets. Cluster representation uncovered the potential existence of 2D nanosheets as subnets of 3D networks in 3032 structures. Furthermore, parameters of building units, net topologies, and accessible channels were analyzed. The concept was proved by synthesis and successful exfoliation of new compound [Zn4(THIP)(HCO2)3(H2O)4]∙DMF (1), which was assembled from 4,5,6-trihydroxyisophtalic acid (H5THIP) as intralayer linker, formate anions as both intralayer linker and interlayer pillar, and Zn(II) as coordination center. In the compound, H5THIP shows complete deprotonation that is unique for hydroxyisophthalate ligands. The crystalline phase of the compound was studied by SCXRD, PXRD, FTIR, and TGA measurements. Nanosheets of height 0.1–90 nm and lateral sizes above 400 nm were produced by sonication of crystals in ethanol. The exfoliation was proved by SEM with EDS, PXRD, AFM, TEM, and BET surface measurements.