Hydrogen Bonds Defined Pore Windows Enable Sieving Separation of Propylene from Propane in an Ultramicroporous Metal–Organic Framework

Abstract

Tailoring a MOF with suitable pore windows for the sieving C₃H₆/C₃H₈ separation is attractive but challenging, where controlling the local framework flexibility by introducing functionality provides a solution. In this work, four isoreticular ultramicroporous Zn–triazolate–dicarboxylate frameworks, Zn-ATZ-IP(R) (R = −F, −OH, −NH₂, and −CH₃) (HATZ = 3-amino-1,2,4-triazole; H₂IP-R = R group functionalized isophthalic acid) with variable pore apertures, were targeted as platforms to study the effect of functional groups on their separation performance. Single-component adsorption isotherms uncovered the potential of Zn-ATZ-IP(OH)-a with hydroxyl groups as a sieving adsorbent. Single X-ray diffraction (SXRD) measurements revealed that strong intraframework hydrogen bonds hinder the free torsion of ATZ^– ligand in Zn-ATZ-IP(OH)-a, defining rigid pore windows that admit C₃H₆ while exclude C₃H₈, whereas other groups give adaptive larger pores that allow both C₃H₆ and C₃H₈ in. Further, in situ XRD measurements suggested that temperature alters the strength of hydrogen bonds, making Zn-ATZ-IP(OH)-a ideal for room-temperature sieving of C₃H₆/C₃H₈. This work highlights the superiority of customizing sieving pores sustained by hydrogen bonds, which advances the rational design of smart adsorbents for energy-efficient light hydrocarbon separations.