Green synthesis of coordination polymers using supercritical carbon dioxide

Resumen

Recently, the research in coordination polymers (CPs) and porous metal-organic frameworks (MOFs) has raised a large interest, since these materials are considered potential candidates for numerous applications, including drug delivery, catalysis, gas separation and storage. Generally, these materials are synthetized using toxic organic solvents and high temperatures. Therefore, the development of sustainable synthetic approaches becomes necessary to speed up the industrial expansion of these products. The main aim of this work is to synthetize CPs using a green technology based on supercritical carbon dioxide (scCO2) solvent. To date, the use of scCO2 in the field of CPs and MOFs has been mainly limited to the post-synthetic activation or cleaning steps. The use of scCO2 can go further, including the synthesis of these materials. Hence, the main objective of this work is to demonstrate this possibility, stablishing a synthetic protocol. In order to achieve the main aim, a new methodology has been developed to explore the synthesis of new single and mixed-metal CPs with different dimensionalities. CPs have been obtained by reacting a metallic complex and an organic linker in scCO2. Fluorinated organometallic complexes (i.e., hexafluoroacetylacetonate) and N-donor organic linkers have been selected taking into account their significant solubility in scCO2. Alternatives for systems involving metal complexes with low solubility have been also developed, based on the use of ancillary ligands for the metal. Linear bipyridyl and trigonal polypyridyl connectors have also been used. The growing interest in the synthesis of these CPs based on N-donor organic linkers is related to their core’s planar geometry, ideally suited to generate highly symmetrical structures. Most importantly, the green character of the synthesis allows to consider its use for the synthesis of biocompatible materials. Therefore, as a proof of concept the use of bio-linkers, e.g., curcumin and ferulic acid, for 2D and 3D bioMOFs synthesis has been explored. In short, along the different Chapters the viability of the easy, fast and eco-friendly synthesis of CPs and MOFs using scCO2 has been demonstrated. Using diverse metal nodes and linkers, 17 new CPs have been crystallized in this solvent, most of them elucidated crystallographically. The way in which synthetic obstacles in scCO2, such as low solubility of reagents or fast precipitation of kinetic phases are overcome, has been described along the different Chapters. Applications in gas adsorption, magnetism and drug delivery have also been presented.