NaI-Mediated Defluorination: A Mild Route to Reduced Ruddlesden-Popper Oxyfluorides Demonstrated on La2CoO3F3 as
Jonas Jacobs1, Tommi Aalto2, Yorik Puffaldt2
1Faculty of Natural Sciences II, Institute of Chemistry, Inorganic Chemistry, Martin Luther University Halle-Wittenberg, Kurt-Mothes-Straße 2, 06120 Halle, Germany.
Journal of the American Chemical Society
|May 25, 2026
Summary
Sodium iodide (NaI) enables mild, low-temperature defluorination of Ruddlesden-Popper oxyfluorides. This process creates new Co(II) phases like La2CoO3F2, inaccessible by other methods.
Area of Science:
- Materials Science
- Solid-State Chemistry
- Inorganic Chemistry
Background:
- Ruddlesden-Popper (RP) oxyfluorides are advanced materials with tunable properties.
- Synthesizing specific RP oxyfluoride phases, especially those with reduced metal oxidation states, remains challenging.
- Conventional methods for modifying oxyfluorides often require harsh conditions or lead to undesired side reactions.
Purpose of the Study:
- To introduce a novel, mild method for topochemical defluorination of RP oxyfluorides.
- To synthesize and characterize previously inaccessible oxyfluoride phases, specifically La2CoO3F2.
- To demonstrate the utility of sodium iodide (NaI) as a defluorination reagent.
Main Methods:
- Topochemical fluorination of La2CoO4 using poly(vinylidene fluoride) (PVDF) or polytetrafluoroethylene (PTFE).
- Low-temperature defluorination of the fluorinated intermediate using NaI.
- In situ X-ray diffraction (XRD) for monitoring reaction progress and structural changes.
- X-ray and neutron powder diffraction for crystal structure determination.
- Magnetization measurements to assess changes in cobalt oxidation state and spin state.
Main Results:
- La2CoO4 was successfully fluorinated to La2CoO3F3 via four crystalline intermediates.
- NaI-mediated defluorination yielded La2CoO3F2, a phase not obtainable through direct fluorination.
- The crystal structures of La2CoO3F3 (monoclinic, P21/c) and La2CoO3F2 (orthorhombic, Cccm) were determined.
- Magnetization studies confirmed the reduction of cobalt oxidation state during defluorination.
Conclusions:
- Sequential topochemical fluorination and NaI-mediated defluorination offer a mild route to metastable RP oxyfluorides.
- This method provides access to anion-ordered phases like La2CoO3F2, which are difficult to synthesize otherwise.
- NaI is an effective and selective defluorination reagent, avoiding cation reduction and anion substitution.
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