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.