Tuning Metal–Organic Framework (MOF) Topology by Regulating Ligand and Secondary Building Unit (SBU) Geometry: Structures Built on 8-Connected M₆ (M = Zr, Y) Clusters and a Flexible Tetracarboxylate for Propane-Selective Propane/Propylene Separation

Abstract

Topology evolution originating from variations of linker and SBU (Secondary Building Unit) geometries could largely enrich the chemistry of metal−organic frameworks (MOFs). Here we report the synthesis and characterization of three MOF structures built on the same organic linker, N,N,N′,N′-Tetrakis(4-carboxyphenyl)-1,4-phenylenediamine (tcppda) and similar 8-connected M 6 (M = Zr or Y) clusters. The three compounds, HIAM-402, HIAM-403, and HIAM-311, feature 4,8-connected sqc, scu, and flu topology, respectively. Detailed structural analysis revealed that different geometries of the inorganic M 6 SBUs as well as the organic linker have led to the formation of distinct MOF nets. In particular, HIAM-402 features exceptional framework stability and high porosity and acts as a propane-selective adsorbent for the discrimination of propane and propylene. Its balanced adsorption selectivity (S propane/propylene = 1.43) and capacity (Q propane = 133.3 cm 3 /g, 298 K and 1 bar) endow it with the capability of separating propane and propylene mixtures and one-step production of highly pure propylene (purity >99.9%), as validated by column breakthrough measurements, with the presence of moisture or propyne. Ab initio calculations further confirm that the propane-selective behavior of HIAM-402 is a result of its higher binding energy toward propane compared to that of propylene.

Interpenetrating 3D Covalent Organic Framework for Selective Stilbene Photoisomerization and Photocyclization

“…In general, the 1,4-bis­(diphenylamino)­benzene (DAB) unit can adopt two configurations: one is square with C 2 h symmetry, and the other is tetrahedral with D 2 d symmetry (Figure S1). Both configurations of DAB have been seen in single-crystal X-ray structures of metal–organic frameworks assembled from the tetracarboxylate linkers containing the DAB unit. , The structure of TPDT-COF was modeled as a sevenfold diamond ( dia ) topology based on the geometrical connectivity of the two individual units. The experimental PXRD pattern showed good agreement with the calculated one based on the structural model (Figure b).…”

Microporous metal–organic frameworks for the purification of propylene

“…7a), which is built on an 8-connected hexanuclear Zr 6 cluster and tetrakis(4-carboxyphenyl)-1,4-phenylenediamine and features an sqc topology. 34 HIAM-402 possesses a highly robust framework as well as high porosity and exhibits selective adsorption of propane over propylene. Single-component adsorption isotherms revealed that propane is notably favored at low pressure compared to propylene although the saturation uptakes at 1 bar are similar for the two gases (Fig.…”

“…(b) Single-component adsorption-desorption isotherms of propane/propylene adsorption isotherms at 298 K. (c) Dynamic breakthrough curves of HIAM-402 for propane/propylene at 298 K and 1 bar. Optimized configuration of adsorbed propylene (d) and propane (e) in the channel of HIAM-402 by ab initio calculations.Reproduced with permission 34. Copyright 2022, American Chemical Society.…”

Metal‐Organic Frameworks for C6 Alkane Separation

“…[13,14] Metal-organic frameworks (MOFs) as a newer family of porous adsorbents are particularly desirable in addressing industrially challenging separations of hydrocarbons because of their diverse structural modularity, exceptional porosity, highly tunable pore size, pore shape, and surface functionality. [15][16][17][18] These unique features of MOFs have led to their excellent performance for the separation of physically and chemically similar mixtures including olefin/ paraffin, [19][20][21][22][23] alkyne/olefin, [24,25] carbon dioxide/ acetylene, [26][27][28] and alkane isomers. [29,30] In particular, the successful practice of reticular chemistry has enabled the precise control of pore structures of MOFs, affording adsorbents with desired discrimination capability toward C6 alkane isomers with different degrees of branching (Table 1).…”