Stepwise Expansion of Layered Metal–Organic Frameworks for Nonstochastic Exfoliation into Porous Nanosheets

Abstract

A layered metal-organic framework (MOF) with a porous kagomé lattice, kgm^SMe, was synthesized by complexation of 5-methylthioisophthalate (SMe-ip) with Cu²⁺ in MeOH. As observed by powder XRD, kgm^SMe (state I), when immersed in aprotic polar solvents such as THF, underwent stepwise interlayer expansion into a monolayer-expanded state (state III) through a bilayer-expanded state (state II). We successfully obtained the single-crystal structures of states I-III. Of interest, when further immersed in appropriate solvents, state II and III crystals preferentially exfoliated into bilayer and monolayer MOF nanosheets, respectively. The stepwise expansion followed by exfoliation, thus developed, may enable a nonstochastic approach to the selective synthesis of ultrathin porous nanosheets from layered MOF crystals.