A Water Stable U(IV) Complex Based on a Macrocyclic Ligand Displaying NIR Emission
Elsa Jourdain1, Mehdi Arab2, Carlos Platas-Iglesias3
1Equipe de synthèse pour l'analyse, IPHC UMR 7178, CNRS, Université de Strasbourg, ECPM, 25 rue becquerel, 67087, Strasbourg, France.
Chemistry (Weinheim an Der Bergstrasse, Germany)
|July 24, 2025
Summary
Researchers created a water-stable Uranium(IV) complex using a macrocyclic ligand. This novel complex exhibits unique near-infrared (NIR) emission and remains stable across a wide pH range.
Area of Science:
- Coordination Chemistry
- Lanthanide and Actinide Chemistry
- Materials Science
Background:
- Uranium(IV) complexes are challenging to stabilize in solution due to hydrolysis.
- Macrocyclic ligands offer potential for enhanced stability and unique photophysical properties.
- Functionalized macrocycles can tune the coordination environment and reactivity of metal ions.
Purpose of the Study:
- To synthesize and characterize a water-stable Uranium(IV) complex using a phosphonated pyridyl-functionalized macrocycle.
- To investigate the photophysical properties, specifically UV-Vis-NIR emission, of the Uranium(IV) complex.
- To assess the hydrolytic stability of the Uranium(IV) complex across a broad pH range.
Main Methods:
- Complexation of U(IV) with a 1,4,7-triazacyclonane (tacn) macrocycle bearing phosphonated pyridyl arms.
- Monitoring complexation using UV-Vis-NIR absorption spectroscopy.
- Characterization via 1H, 13C, 31P-NMR spectroscopy and mass spectrometry.
- Computational analysis using Density Functional Theory (DFT) modeling.
- Emission spectroscopy to observe UV-visible and NIR bands.
Main Results:
- A water-stable and soluble [U(IV)L] complex was successfully synthesized.
- DFT modeling confirmed U(IV) encapsulation within the nonadentate ligand cavity.
- First-time observation of a broad NIR emission band at 1080 nm for a U(IV) complex.
- UV-visible emission was also observed upon electronic excitation.
- The complex demonstrated hydrolytic stability in aqueous solutions from pH 1.6 to 10 under aerobic conditions for several weeks.
Conclusions:
- The phosphonated pyridyl-functionalized macrocycle effectively chelates U(IV), affording unprecedented stability.
- The [U(IV)L] complex exhibits unique photoluminescent properties, including NIR emission.
- This work provides a foundation for developing stable U(IV) materials with tailored optical properties.
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