Interpenetration Control in Thorium Metal–Organic Frameworks: Structural Complexity toward Iodine Adsorption

Abstract

The rational design and synthesis of metal−organic frameworks with wellcontrolled interpenetration have been active research areas of inquiry, particularly for porosityrelated applications. Herein, we extend the use of the ligand steric modulation strategy to initiate the first study of the interpenetration control of thorium-based MOFs. The approximate "hardness" of the Th 4+ cation, which was conjugated with aromatic substitutions and delicately modified synthetic conditions, allows for the crystallization of single crystals of seven new Th-MOFs with five distinct topologies. Solvothermal reactions of Th(NO 3 ) 4 with the triphenyl H 2 TPDC ligand under variable conditions exclusively gave rise to an interpenetrated Th-MOF with a hex topology, namely Th-SINAP-16. Modifications of the ligand sterics with two pendant methyl groups to 2′,5′-Me 2 TPDC 2− and 2,2″-Me 2 TPDC 2− afforded two noninterpenetrated UiO-68-type Th-MOFs (Th-SINAP-17 and Th-SINAP-20, respectively) with record-high pore volumes (74.8% and 75.3%, respectively) among all the thorium MOFs. Moreover, another four Th-MOFs Th-SINAP-n (n = 18, 19, 21, and 22) with three different topologies were obtained by a simple synthetic modulation. Notably, Th-SINAP-16 and Th-SINAP-21 represent the second rare examples of interpenetrated Th-MOFs reported to date. These findings revealed the unprecedented structural complexity and synthetic accessibility of Th-MOFs among all tetravalent metal containing MOFs. Such features make Th-MOFs as an ideal platform to elucidate the structure−property relationship for various applications, e.g. iodine adsorption.

Recent advances in pillar‐layered metal‐organic frameworks with interpenetrated and non‐interpenetrated topologies as supercapacitor electrodes

“…Except for altering the pillar ligand, changing the metalredox sites of Co(II) to Ni(II), Mn(II), or Fe(II) center was also documented subsequently. [66] For example, through the introduction of the ultralong pillar ligand and documenting Ni centers, two isostructural topological structures with the symbol of 4 22 • 5 4 • 6 2 were generated (Figure 6a). Due to the flexible coordination mode of long-chain pillars, two types of left-and right-handed helical channels with a mean diameter of 1.1 nm result in large void space in 3D networks.…”

“…[20] To date, 4/5/6/18-and the ultrahigh 54-fold interpenetrating MOFs architecting from 2D layers have been constructed. [21] These above-mentioned synthetic experiences indicate that the preparation of interpenetrating or non-interpenetrating MOFs is still challenged by a large number of factors: i) Long or ultra-long organic building units tend to construct high pore volume inside, which makes the interior pores easier to be interpenetrated to form entangled structures; [22] and ii) The selfassembly process of interpenetrating MOFs is directly related to the experimental environment including temperature, solvent properties, concentration, pH, modifiers, time, light and pressure. All reported results suggest that low temperature and more dilute reaction solutions benefit to generate non-interpenetrating pillar-layered MOFs with larger pores.…”

Unveiling the Unique Roles of Metal Coordination and Modulator in the Polymorphism Control of Metal‐Organic Frameworks

“…The solvent-accessible volume of Th-SINAP-23 was calculated to be 75.9 %, which sets a new record for TOFs reported to date. [6] Subjecting Th(NO 3 ) 4 • 6H 2 O and H 2 MeTPDC to solvothermal synthesis in DMF accompanied with HCl as a modulator gives rise to hexagonal crystals of Th-SINAP-24, which crystallizes in the trigonal space group P-3. One of the most intriguing structural features is the threefold interpenetrated framework (Figure 1b).…”

“…The interpenetration of three networks significantly reduces the solvent-accessible volume (15.5 %) of Th-SINAP-24, compared to that of 59.5 % of a twofold interpenetrated Th-SINAP-16. [6] In a synthesis using Th(NO 3 ) 4 • 6H 2 O, H 2 MeTPDC, and HCl with addition of DMF/water, colorless needle crystals of Th-SINAP-25 were co-crystalized with Th-SINAP-24. Th-SINAP-25 crystallizes in the orthorhombic space group Imma with its symmetric unit consisting of 1/4 Th 6 (μ 3 -OH) 4 (μ 3 -O) 4 hexamers, one MeTPDC 2À anion, two 1/2 coordinated H 2 O molecules, two 1/4 nitrate anions, and one 1/2 formate groups.…”

“…Modifying either one introduces additional variable beside structural variation, which together result in the synergistic effect undesirable for obtaining mechanistic insights. [6] Modulated synthesis, which incorporates monotopic acid into solvothermal syntheses, has been considered as an effective approach to control the particle size, enhance the crystallinity, and create the missing-linker defects. [7] Furthermore, modulators can potentially trigger the polymorphism of MOFs by pre-organizing metal nodes or by influencing the kinetics of self-assembly.…”