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.