Benchmark Acetylene Binding Affinity and Separation through Induced Fit in a Flexible Hybrid Ultramicroporous Material

Structural changes at the active site of an enzyme induced by binding to a substrate molecule can result in enhanced activity in biological systems. Herein, we report that the new hybrid ultramicroporous material sql-SIFSIX-bpe-Zn exhibits an induced fit binding mechanism when exposed to acetylene, C2H2. The resulting phase change affords exceptionally strong C2H2 binding that in turn enables highly selective C2H2/C2H4 and C2H2/CO2 separation demonstrated by dynamic breakthrough experiments. sql-SIFSIX-bpe-Zn was observed to exhibit at least four phases: as-synthesised (α); activated (β); and C2H2 induced phases (β′ and γ). sql-SIFSIX-bpe-Zn-β exhibited strong affinity for C2H2 at ambient conditions as demonstrated by benchmark isosteric heat of adsorption (Qst) of 67.5 kJ mol−1 validated through in situ pressure gradient differential scanning calorimetry (PG-DSC). Further, in situ characterisation and DFT calculations provide insight into the mechanism of the C2H2 induced fit transformation, binding positions and the nature of host-guest and guest-guest interactions.