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

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.