Amino Acid Residues Determine the Response of Flexible Metal–Organic Frameworks to Guests

Flexible
metal–organic frameworks (MOFs) undergo structural
transformations in response to physical and chemical stimuli. This
is hard to control because of feedback between guest uptake and host
structure change. We report a family of flexible MOFs based on derivatized
amino acid linkers. Their porosity consists of a one-dimensional channel
connected to three peripheral pockets. This network structure amplifies
small local changes in linker conformation, which are strongly coupled
to the guest packing in and the shape of the peripheral pockets, to
afford large changes in the global pore geometry that can, for example,
segment the pore into four isolated components. The synergy among
pore volume, guest packing, and linker conformation that characterizes
this family of structures can be determined by the amino acid side
chain, because it is repositioned by linker torsion. The resulting
control optimizes noncovalent interactions to differentiate the uptake
and structure response of host–guest pairs with similar chemistries.