FAST, CLEAN, PILLARED: MECHANOCHEMICAL ROUTES TO INTERPENETRATED MOFS

The mechanochemical synthesis of pillared Metal-Organic Frameworks (MOFs) is a well-established and sustainable strategy for constructing porous crystalline architectures. And it is particularly advantageous for assembling frameworks made by poorly soluble ligands, where traditional solvothermal methods face significant limitations. In this study, we investigate the formation of interpenetrated MOFs based on carboxylate-linked 2D layers, pillared by a custom-designed bis-pyridinic bis-amidic ligand featuring a rigid, aromatic backbone. Due to its extremely low solubility—only dissolving in hot DMF—this ligand is ideally suited for mechanochemical synthesis. Among the synthesized materials, PUM198 (Parma University Material 198) stands out as a double-interpenetrated double-pillared MOF composed of terephthalate based 2D layers pillared by the bis-amidic ligand. Its mechanochemical analogue, PUM198-m can be synthetized within minutes using only microliter quantities of solvent. The structure of PUM198-m was resolved by 3D electron diffraction (3DED) directly from the mechanochemical powder. Due to the high-vacuum conditions during data collection, an evacuated form of the MOF was obtained. Using a combination of Rietveld and periodic DFT calculations, we were able to model and precisely locate DMF guest molecules within the freshly synthesized framework. While solvothermal conditions often lead to competition between homoleptic and heteroleptic framework formation, ball milling allows for a highly selective and rapid assembly of the heteroleptic pillared structure, and can open access to new MOFs with particular structural features.