Functional porous metal–organic frameworks (MOFs) have been explored for a number of potential applications in catalysis, chemical sensing, water capture, gas storage, and separation. MOFs are among the most promising candidates to address challenges facing our society related to energy and environment, but the successful implementation of functional porous MOF materials are contingent on their stability; therefore, the rational design of stable MOFs plays an important role towards the development of functional porous MOFs. In this Focus article, we summarize progress in the rational design and synthesis of stable MOFs with controllable pores and functionalities. The implementation of reticular chemistry allows for the rational top-down design of stable porous MOFs with targeted topological networks and pore structures from the pre-selected building blocks. We highlight the reticular synthesis and applications of stable MOFs: (1) MOFs based on high valent metal ions (e.g., Al³⁺, Cr³⁺, Fe³⁺, Ti⁴⁺ and Zr⁴⁺) and carboxylate ligands; (2) MOFs based on low valent metal ions (e.g., Ni²⁺, Cu²⁺, and Zn²⁺) and azolate linkers. We envision that the synthetic strategies, including modulated synthesis and post-synthetic modification, can potentially be extended to other more complex systems like metal-phosphonate framework materials.

The on–off switching of spin-crossover (SCO) and single-molecule magnetism (SMM) remains highly attractive, especially if it involves dynamic crystal-to-crystal transformation. Herein we report the first molecule, a mononuclear cobalt(II) complex, that exhibits on–off switching between SCO and SMM reversibly during crystal-to-crystal transformation. Subtle structural transformation triggered by a simple dehydration–rehydration process induces significant geometrical changes of the Co^II center and modification of the supramolecular interactions and switches its colour and magnetic properties (dark red/SCO-on/SMM-off ↔ orange/SCO-off/SMM-on). This work suggests that modification of the weak supramolecular interactions could be very effective in achieving switchable materials involving both SCO and SMM properties.

Numerous natural products and drugs contain flexible alkyl chains. The resulting conformational motion can create challenges in obtaining single crystals and thus determining their molecular structures by single-crystal X-ray diffraction (SCXRD)^{1,2,3,4,5,6,7,8,9,10,11}. Here we demonstrate that by using pillar[5]arene-incorporated metal–organic frameworks (MOFs) and taking advantage of pillar[5]arene−alkyl chain host−guest recognition^12,13,14,15, it is possible to reduce this motion and bring order to alkyl-chain-containing molecules as the result of docking within accessible pillar[5]arene units present in an overall MOF. This has allowed the single-crystal structures of 48 alkyl-chain-containing molecules, including 6 natural products, 2 approved drugs and 18 custom-made compounds collected from 16 research groups, to be determined using standard SCXRD instrumentation. The structures of alkyl-chain-containing molecules derived from crude reaction products can also be determined directly by SCXRD analyses without further purification. The simplicity, high efficiency and apparent generality of the present pillar[5]arene-incorporated MOF-based supramolecular docking approach suggest that it could emerge as a new tool for the analyses of natural products and drugs that might not be amenable to traditional SCXRD-based structure determination.

We report the design and synthesis of a 1D Dy(III) coordination polymer, comprised of sulfonate functionalised ligand 8-hydroxyquinoline-5-sulfonic acid (H₂SQ) and Dy³⁺ ions, with a hydrogen-bonded supramolecular 3D structure. Interestingly, the coordination compound can exhibit reversible structural transformation from a trihydrate (1·3H₂O) to a monohydrate (1·H₂O) phase during partial desorption/adsorption processes of water molecules in a single-crystal-to-single-crystal (SC–SC) fashion. Importantly, the field-induced slow magnetic relaxation behaviour and proton conduction performance were both switched during the dynamic structural transformation, giving rise to a proton conductive SIM of 1·3H₂O and a SIM-insulator of 1·H₂O. Variable temperature single-crystal structural analyses reveal that the non-coordinated water molecules play a vital role in the changes in primary coordination environments around the Dy³⁺ ions, and the global hydrogen-bonding networks, resulting in the modification of magnetic properties and proton transport pathways in 1·3H₂O and 1·H₂O, respectively. The previous results not only provide the first example of a Dy(III) sulfonate showing switched single-ion magnetism and proton conduction behaviour but also highlight a promising way to use water for dynamic control of magnetic and electrical properties.