Turning Flexibility into Rigidity: Stepwise Locking of Interpenetrating Networks in a MOF Crystal through Click Reaction
Damian Jędrzejowski, Marzena Pander, Wojciech Nitek, Wojciech Bury, Dariusz Matoga
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 5norbornene-2-methanol (noh) to modify a tetrazine-based linker (3,6-dipyridyl-1,2,4,5tetrazine, dpt) incorporated in a unique doubly interpenetrated 3D hybrid MOF-HOF porous material (HOF, hydrogen-bonded organic framework), {[Cd 2 (coh) 2 (dpt) 2 ] guests} n (JUK-20).Each subnetwork in JUK-20 is built of 2D coordination layers stacked by strong complementary CO 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 (N 2 , CO 2 , 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.