Exploring the mechanism of in situ formation of oxalic acid for producing mixed fumarato-oxalato lanthanide (Eu, Tb and Gd) frameworks

Mixed fumarato-oxalato ligands lanthanide metal-organic frameworks (MOFs) [Ln2(fum)2(ox)(H2O)4]⋅4H2O (Ln = Eu, Gd, and Tb) were obtained from hydrothermal treatment of aqueous acid solutions of trivalent lanthanide ions and fumaric acid with nitrate or sodium hypochlorite as oxidants. The crystal structure for [Gd2(fum)2(ox)(H2O)4]⋅4H2O was determined. Other oxidants (H2O2 and NaSO4) or conditions (NaOCl at room temperature and atmospheric pressure) yielded other MOFs or products. Oxalic acid was formed in situ and mechanisms based on the hydration of fumaric acid mediated by Ln3+ followed by oxidation and decarboxylation steps were proposed. The mechanisms were able explain the dual role of Ln3+ ions and the nature of the oxidant in forming the frameworks.

Hydrothermal synthesis of mixed ligands [Ln2(fum)2(ox)(H2O)4]⋅4H2O (Ln = Eu, Gd, and Tb) MOFs. The in situ mechanisms for oxalic acid formation are proposed and show the dual roles of Ln3+ and relevance of choosing adequate oxidant.Figure optionsDownload as PowerPoint slideHighlights
► First mechanistic study of in situ oxalate formation from fumaric acid.
► Formation of mixed ligand fumarato-oxalato lanthanide MOFs.
► Hydrothermal synthesis of lanthanide based coordination polymers.