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.