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

A layered metal–organic framework (MOF) with a porous kagomé lattice, kgmSMe, was synthesized by complexation of 5-methylthioisophthalate (SMe-ip) with Cu2+ in MeOH. As observed by powder XRD, kgmSMe (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.