Hydrogen Bonds Defined Pore Windows Enable Sieving\nSeparation of Propylene from Propane in an Ultramicroporous Metal–Organic\nFramework

Tailoring\na MOF with suitable pore windows for the sieving C<sub>3</sub>H<sub>6</sub>/C<sub>3</sub>H<sub>8</sub> separation is attractive\nbut challenging, where controlling the local framework flexibility\nby introducing functionality provides a solution. In this work, four\nisoreticular ultramicroporous Zn–triazolate–dicarboxylate\nframeworks, <b>Zn-ATZ-IP(R)</b> (R = −F, −OH,\n−NH<sub>2</sub>, and −CH<sub>3</sub>) (HATZ = 3-amino-1,2,4-triazole;\nH<sub>2</sub>IP-R = R group functionalized isophthalic acid) with\nvariable pore apertures, were targeted as platforms to study the effect\nof functional groups on their separation performance. Single-component\nadsorption isotherms uncovered the potential of <b>Zn-ATZ-IP(OH)-a</b> with hydroxyl groups as a sieving adsorbent. Single X-ray diffraction\n(SXRD) measurements revealed that strong intraframework hydrogen bonds\nhinder the free torsion of ATZ<sup>–</sup> ligand in <b>Zn-ATZ-IP(OH)-a</b>, defining rigid pore windows that admit C<sub>3</sub>H<sub>6</sub> while exclude C<sub>3</sub>H<sub>8</sub>, whereas\nother groups give adaptive larger pores that allow both C<sub>3</sub>H<sub>6</sub> and C<sub>3</sub>H<sub>8</sub> in. Further, <i>in situ</i> XRD measurements suggested that temperature alters\nthe strength of hydrogen bonds, making <b>Zn-ATZ-IP(OH)-a</b> ideal for room-temperature sieving of C<sub>3</sub>H<sub>6</sub>/C<sub>3</sub>H<sub>8</sub>. This work highlights the superiority\nof customizing sieving pores sustained by hydrogen bonds, which advances\nthe rational design of smart adsorbents for energy-efficient light\nhydrocarbon separations.