Iono/urothermal synthesis of strontium-MOFs

The iono- and urothermal methods, both involving solvents based on e-urea (2-imidazolidinone), 1:2 choline chloride:e-urea deep eutectic solvent and e-urea hemihydrate respectively, have been explored as synthetic approaches for the preparation of strontium-based metal-organic frameworks (Sr-MOFs). Using these media and seven different di-carboxylic acid ligands, a series of ten Sr-MOFs has been obtained and characterized by X-ray diffraction as well as by thermogravimetric and elemental analyses, infra-red spectroscopy and their optical properties have been investigated. While both preparation methods led to the same unique crystalline phase in some instances, different architectures were obtained for the majority of the ligands explored herein, depending on the synthetic approach employed. This highlights the key role of choline chloride in the ionothermal method and of water in the urothermal strategy, that can act as ligands/templates and thereby impact the formation of intermediate phases and the stability of the materials.