Multivariate Sulfate-Pillared Metal Azolate Frameworks with Tunable Flexibility for CO₂ Capture from C2 Hydrocarbons

A series of sulfate-pillared metal azolate frameworks (MAFs) were synthesized via a multivariate (MTV) strategy to systematically tune framework flexibility and gas separation performance. The monotonic sulfate-pillared MAF, Zn₂(daTz)₂SO₄ (where daTz = 3,5-diamino-1,2,4-triazolate), exhibits pronounced structural dynamics upon adaptive guest inclusions, driven by triazolate linker rotation and reversible Zn─O bonds rearrangement, enabling dynamic pore modulation for efficient CO₂, C₂H₄, and C₂H₆ uptakes. Incorporation of an asymmetric, non-amino linker effectively suppresses framework flexibility by reducing intraframework hydrogen bonding, resulting in a locked structure with enhanced selectivity for CO₂ over light hydrocarbons. Gas adsorption and breakthrough experiments demonstrate that the MTV approach enabled structural control, leading to exceptional CO₂/C₂H₆ and CO₂/C₂H₄ separation performance. Notably, Zn₂(mTz)_0.74(daTz)_1.26SO₄ (where mTz = 3-methyl-1,2,4-triazolate) achieves 17-fold enhancement in ethylene purification. Comprehensive structural analyses and interaction energy calculations reveal the molecular basis of flexibility regulation, offering valuable insights for designing next-generation porous materials for selective gas separation.