Tuning the Atrazine Binding Sites in an Indium-Based Flexible Metal–Organic Framework

Constructing
flexible metal–organic frameworks (MOFs) with targeted properties
is of high interest given their demonstrated potential as smart materials
that undergo structural transformations in response to external stimuli.
Herein, we report a flexible and interpenetrated indium-based MOF, NU-50, comprising four-connected [In­(CO2)4]− nodes and tetracarboxylate pyrene-based ligands
assembled in the pts topology. The flexible framework
of NU-50 exhibits intricate structural transformations
upon exposure to external stimuli, namely, guest solvent molecules
and elevated temperatures. The high density of pyrene moieties throughout
the interpenetrated framework offers numerous sites for the adsorption
of highly conjugated guest molecules such as atrazine via π–π
interactions. As a result, NU-50 efficiently removes
atrazine from water, achieving a maximum atrazine uptake capacity
of 74 mg of atrazine per gram of NU-50. Molecular simulations
reveal that the dynamic behavior of NU-50 involves the
distortion of metal–ligand bonds, resulting in a narrow pore
structure that affords effective adsorption of atrazine molecules
in a sandwich-like geometry. Moreover, washing in acetone quickly
regenerates the sorbent.