Guest-Controlled Incommensurate Modulation in a Meta-Rigid Metal–Organic Framework Material

Structural
transitions of host systems in response to guest binding
dominate many chemical processes. We report an unprecedented type
of structural flexibility within a meta-rigid material, MFM-520, which
exhibits a reversible periodic-to-aperiodic structural transition
resulting from a drastic distortion of a [ZnO4N] node controlled
by the specific host–guest interactions. The aperiodic crystal
structure of MFM-520 has no three-dimensional (3D) lattice periodicity
but shows translational symmetry in higher-dimensional (3 + 2)­D space.
We have directly visualized the aperiodic state which is induced by
incommensurate modulation of the periodic framework of MFM-520·H2O upon dehydration to give MFM-520. Filling MFM-520 with CO2 and SO2 reveals that, while CO2 has
a minimal structural influence, SO2 can further modulate
the structure incommensurately. MFM-520 shows exceptional selectivity
for SO2 under flue-gas desulfurization conditions, and
the facile release of captured SO2 from MFM-520 enabled
the conversion to valuable sulfonamide products. MFM-520 can thus
be used as a highly efficient capture and delivery system for SO2.