Rational Construction of Breathing Metal–Organic Frameworks through Synergy of a Stretchy Ligand and Highly Variable π–π Interaction

The synergy of a
stretchy ligand and highly variable π–π
interaction has been proposed as a rational strategy for the construction
of breathing metal–organic frameworks (MOFs). Based on this
strategy, a breathing MOF, {[Cd2(AzDC)2(TPT)2]­(DMF)3}n, was successfully
constructed with stretchy 4,4′-diazene-1,2-diyldibenzoate acid
(H2AzDC) and 2,4,6-tris­(4-pyridyl)­triazine (TPT) as a source
of the π–π interaction. The MOF features structure
transformation upon stimulation with solvent guests and varied temperatures,
which is straightforwardly characterized by single-crystal structures.
Moreover, the solvent-free framework shows breathing behaviors in
response to light hydrocarbon (C2H4, C2H6, C3H6, and C3H8) sorption, which was verified by stepwise sorption isotherms
and in situ powder X-ray diffraction. Additional
investigation of the sorption selectivity of C3/C2 systems indicated
that the selectivity can be regulated by the modulation of the dynamic
breathing behaviors, which can be used for the selective separation
of C3/C2 light hydrocarbons.