Turning Flexibility into Rigidity: Stepwise Locking of Interpenetrating Networks in a MOF Crystal through Click Reaction

Abstract

Post-synthetic modifications of metal–organic frameworks (MOFs) enable synthesis of materials with enhanced performance characteristics or those inaccessible by direct synthetic routes. In this work, for the first time, we utilize inverse-electron demand Diels–Alder (iEDDA) modification to control the structural flexibility and porosity of an open framework material. We selected a series of dienophiles with increasing bulkiness including ethyl vinyl ether (eve), cyclohexene (chx), norbornene (nor), and 5-norbornene-2-methanol (noh) to modify a tetrazine-based linker (3,6-dipyridyl-1,2,4,5-tetrazine, dpt) incorporated in a unique doubly interpenetrated 3D hybrid MOF–HOF porous material (HOF, hydrogen-bonded organic framework), {[Cd2(coh)2(dpt)2]·guests} n (JUK-20). Each subnetwork in JUK-20 is built of 2D coordination layers stacked by strong complementary CO···H–N hydrogen bonds between carbohydrazide dibenzoate linkers (coh). By using the [4 + 2] click reactions of JUK-20, which proceed in a prominent single-crystal-to-single-crystal manner, we obtained a series of JUK-20-dienophile MOFs. The modifications lead to a stepwise decrease in structural flexibility of the JUK-20 platform until the highest rigidity and stability is reached for JUK-20-noh. Consequently, the adsorption capacity in the JUK-20-dienophile series increases, as revealed collectively by single-crystal X-ray diffraction, physisorption isotherms (N2, CO2, and MeOH), and grand canonical Monte Carlo simulations. Our work demonstrates that post-synthetic iEDDA modification is a versatile and efficient tool for systematic functionalization of open framework materials under mild conditions.

Exploration of Hierarchical Metal–Organic Framework as Ultralight, High-Strength Mechanical Metamaterials

“…According to previous studies, ,, the flexibility of MOF was originated from rotation and translation of nodes and linkers upon deformation. However, upon a large dose of electron beam irradiation inside the TEM, the hingelike connections between linkers and clusters were changed from a “flexible” to a “locked” mode, , and their mechanical behaviors transformed from a flexible “spring” mode to a rigid “truss” mode when supporting the whole octahedron structures. Such transition impaired the self-coordination ability of the frameworks ,, but made them stronger and stiffer upon deformation.…”

Tetrazine Linkers as Plug‐and‐Play Tags for General Metal‐Organic Framework Functionalization and C60 Conjugation

“…The alternative integration of dienes to the MOF structure would be arguably more adequate for all‐purpose ligation chemistry but the number of candidates remains still very limited. [ 14 , 15 , 16 ] We recently reported the synthesis of UiO‐68‐TZDC crystals by reticulation of 4,4′‐(1,2,4,5‐tetrazine‐3,6‐diyl)dibenzoic acid (H 2 tzdc) diene linkers into a mesoporous framework. [17] Here we present this tetrazine MOF as an ideal platform towards the generalization of iEDDA PSM chemistry for one‐step functionalization with a broad scope of alkene/alkyne dienophiles to generate multiple pore environments with diverse chemical functionalities (Figure 1 a).…”

CCIQS-1: A Dynamic Metal–Organic Framework with Selective Guest-Triggered Porosity Switching

“…28−30 In this regard, Matoga and co-workers have demonstrated that the covalent post-synthetic modification of MOFs not only can be used for introducing desired functionalities into the pore framework but also it represents a versatile and efficient tool for finely tuning the structural flexibility and porosity of interpenetrated structures. 31 Herein, we present a new guest-responsive flexible MOF CCIQS-1 (from Centro Conjunto de Investigacioń en Qui ́mica Sustentable UAEM-UNAM) consisting of three interpenetrated honeycomb networks featuring a reversible guest-dependent porosity change via a crystal-to-crystal transformation and adaptability of the networks to the size and polarity of guest molecules. A combination of the breathing effect and subnetwork displacement is responsible for these transformations.…”

“…The soft properties of porous materials and their tunable host–guest and guest–guest interactions provide opportunities for their application in the selective separation of complex mixtures through a molecular recognition mechanism. − In this regard, Matoga and co-workers have demonstrated that the covalent post-synthetic modification of MOFs not only can be used for introducing desired functionalities into the pore framework but also it represents a versatile and efficient tool for finely tuning the structural flexibility and porosity of interpenetrated structures …”