EHDTA: a green approach to efficient Ln³⁺-chelators

The rich coordination chemistry of lanthanoid ions (Ln³⁺) is currently exploited in a vast and continuously expanding array of applications. Chelating agents are central in the development of Ln³⁺-complexes and in tuning their physical and chemical properties. Most chelators for Ln³⁺-complexation are derived from the macrocyclic DOTA or from linear DTPA platforms, both of which arise from fossil-based starting materials. Herein, we report a green and efficient approach to a chelating agent (EHDTA), derived from cheap and largely available furfurylamine. The oxygenated heterocycle of the latter is converted to a stereochemically defined and rigid heptadentate chelator, which shows good affinity towards Ln³⁺ ions. A combination of NMR, relaxometric, potentiometric and spectrophotometric techniques allows us to shed light on the interesting coordination chemistry of Ln³⁺-EHDTA complexes, unveiling a promising ligand for the chelation of this important family of metal ions.