Identifying the Gate-Opening Mechanism in the Flexible Metal–Organic Framework UTSA-300

Abstract

Atomic-level understanding of the gate-opening phenomenon in flexible porous materials is an important step toward learning how to control, design, and engineer them for applications such as the separation of gases from complex mixtures. Here, we report such mechanistic insight through an in-depth study of the pressure-induced gate-opening phenomenon in our earlier reported metal–organic framework (MOF) Zn­(dps)2(SiF6) (dps = 4,4′-dipyridylsulfide), also called UTSA-300, using isotherm and calorimetry measurements, in situ infrared spectroscopy, and ab initio simulations. UTSA-300 is shown to selectively adsorb acetylene (C2H2) over ethylene (C2H4) and ethane (C2H6) and undergoes an abrupt gate-opening phenomenon, making this framework a highly selective gas separator of this complex mixture. The selective adsorption is confirmed by pressure-dependent in situ infrared spectroscopy, which, for the first time, shows the presence of multiple C2H2 species with varying strengths of bonding. A rare energetic feature at the gate-opening condition of the flexible MOF is observed in our differential heat energies, directly measured by calorimetry, showcasing the importance of this tool in adsorption property exploration of flexible frameworks and offering an energetic benchmark for further energy-based fundamental studies. Based on the agreement of this feature with ab initio-based adsorption energies of C2H2 in the closed-pore structure UTSA-300a (“a” refers to the activated form), this feature is assigned to the weakening of the H-bond C–H···F formed between C2H2 and fluorine of the MOF. Our analysis identifies the weakening of this H-bond, the expansion of the closed-pore MOF upon successive C2H2 coadsorption until its volume is close to that of the open-pore MOF, and the spontaneous gate opening to energetically favor C2H2 adsorption in the open-pore structure as crucial steps in the gate-opening mechanism in this system.

Luminescent Porous Organic Crystals for Adsorptive Separation of Toluene and Methylcyclohexane

“…Consequently, the effective adsorption of Mcy by X-HOF-5a is hindered. On the contrary, while Tol molecules are absorbed on the surface of X-HOF-5a, they can readily diffuse into the crystal through 1D voids because strong intermolecular weak interactions may induce opening of these small holes and subsequently trigger a phase transformation from X-HOF-5a to X-HOF-5. − However, due to the sluggish nature of the crystal phase transition, it necessitates several hours for X-HOF-5a to achieve saturation upon adsorbing Tol. Subsequently, X-HOF-5a is anticipated to serve as an efficacious adsorptive separation material for the excellent separation of Tol and Mcy.…”

Optimizing the pore space of a robust nickel–organic framework for efficient C2H2/C2H4 separation

“…[12][13][14][15][16][17][18] Recently, MOFs have attracted increasing attention for their potential applications in C 2 hydrocarbon separation (C 2 H 2 /C 2 H 4 , C 2 H 4 /C 2 H 6 , and C 2 H 2 /C 2 H 6 , etc.). [19][20][21][22][23][24][25] To improve the separation performance of MOFs, several strategies have been proposed, including pore size customization, pore surface functionalization, open metal sites (OMSs), etc. Since the first porous MOF (M′MOF) for C 2 H 2 /C 2 H 4 separation was reported in 2011, researchers have taken considerable effort to implement some porous MOFs to achieve their efficient separation.…”

“…). 19–25 To improve the separation performance of MOFs, several strategies have been proposed, including pore size customization, pore surface functionalization, open metal sites (OMSs), etc. Since the first porous MOF (M′MOF) for C 2 H 2 /C 2 H 4 separation was reported in 2011, researchers have taken considerable effort to implement some porous MOFs to achieve their efficient separation.…”

Desolvation-Degree-Induced Structural Dynamics in a Rigid Cerium–Organic Framework Exhibiting Tandem Purification of Ethylene from Acetylene and Ethane

“…Emerging as a new class of porous materials, metal–organic frameworks (MOFs) have witnessed great success in the last two decades toward gas storage, separation, catalysis, etc. − Remarkably, reticular chemistry , of MOFs has played important roles in the binary separation of C 2 H 2 /C 2 H 4 and C 2 H 4 /C 2 H 6 by virtue of isoreticular and/or isostructural extension/contraction/expansion/functionalization approaches. − Very recently, a few groups have even reported that a single MOF material is capable of simultaneous removal of both C 2 H 2 and C 2 H 6 from a ternary mixture of C 2 H 2 /C 2 H 4 /C 2 H 6 to enable C 2 H 4 purification by a single-step process. − Additionally, Zaworotko and Chen et al employed the synergistic sorbent separation technique to pack three task-specific MOFs in a fixed-bed column to empower high-purity C 2 H 4 production from the aforementioned ternary mixture …”