Neutral and ionic Co(II) Metal-Organic Frameworks with 2-Methylimidazole and Trimesate: Design and Evaluation for Molecule Encapsulation and Slow Release

Abstract

Two Co(II) mixed-ligand metal-organic frameworks (MOFs) based on 2-methylimidazole and trimesate were synthesised at room temperature. The structure and properties of the two MOFs, named mDESY-1 and mDESY-2, were verified by single crystal X-ray diffraction (SCXRD), powder X-ray diffraction (PXRD), SQUID magnetic susceptibility and N2 adsorption. The structural analysis indicates that mDESY-1 is a 3-D ionic framework with 2-methyl-1H-imidazol-3-ium counterions residing in its pores, while mDESY- 2 is a 2D neutral framework isostructural to ITH-1, with water as co-crystallising solvent. PXRD data demonstrated that mDESY-1 exhibit better crystallinity than mDESY-2. Magnetic measurements indicate that both MOFs are paramagnetic with a weak ferromagnetic transition above room temperature. Although both structures suggest the presence of voids, N2 adsorption data confirmed that these voids are not accessible in either MOF. Nevertheless, mDESY-1 was capable of encapsulating azobenzene during synthesis, which can be observed via SCXRD. The encapsulated molecules were then slowly released in ethanol, with a release of up-to 30mg of azobenzene per g of MOF in a period of 60 days.