An lcy-topology amino acid MOF as eco-friendly catalyst for cyclic carbonate synthesis from CO2: Structure-DFT corroborated study

Abstract

The concept of bio-metal-organic framework (bio-MOF) catalysts for CO₂ transformation was devised using L-glutamic acid as the natural surrogate for synthetic ligands, and demonstrated their catalytic efficacy for the first time, in the cycloaddition of CO₂ with epoxides, supplemented with the structure–DFT correlation. The water stable amino acid bio-MOF, zinc-glutamate-MOF (ZnGlu), with a rare 3D topology (3³·5⁹·6³)-lcy was synthesized as single crystals and bulk, through an ecofriendly protocol in aqueous medium, from zinc and the proteinogenic amino acid, L-glutamic acid. Amino acid MOFs (AA-MOFs), owing to their economic and environmental factors, are expected to be the future of MOF chemistry at industrial levels. The ZnGlu catalyst with open metal sites was successfully demonstrated as the first bio-MOF catalyst for cyclic carbonate synthesis from CO₂ and epoxides, and its efficiency was compared with those of prominent synthetic MOFs reported so far in the process. The as-synthesized catalyst operated even under moist conditions, was thermally and chemically stable; heterogeneous, easily separable (due to its high selectivity, absence of synthesis solvents, and easy catalyst recovery by filtration) and was recycled up to four times. Mechanistic aspects, possible intermediates, transition states and pathways were portrayed using a combination of the experimental inferences, previous reports and ab initio quantum mechanical calculations (DFT techniques) by its correlation with the single crystal XRD structure and topology.