Unique Proton Dynamics in an Efficient MOF-Based Proton Conductor.

Area of Science:

• Materials Science
• Chemistry
• Solid-State Chemistry

Background:

• Metal-organic frameworks (MOFs) are emerging as promising proton conductive materials.
• Direct observation of proton transfer mechanisms in crystalline materials remains a significant challenge.
• Understanding proton dynamics is crucial for developing advanced proton conductors.

Purpose of the Study:

• To synthesize and characterize a novel proton-conducting MOF.
• To investigate the proton transfer mechanism within the MOF structure.
• To evaluate the anhydrous and water-assisted proton conductivity of the material.

Main Methods:

• Solvothermal synthesis of the (Me2NH2)[Eu(L)] MOF.
• Anisotropic conductivity measurements on single crystals and pellets.
• In situ variable-temperature characterization: PXRD, SCXRD, DRIFTS, and photoluminescence.
• Control experiments to confirm proton dynamics.

Main Results:

• The synthesized MOF, (Me2NH2)[Eu(L)], exhibits a layered structure with proton-conducting N-H···O hydrogen-bonded chains.
• Single-crystal anhydrous conductivity of 1.25 × 10⁻³ S·cm⁻¹ at 150 °C was achieved.
• Water-assisted proton conductivity reached 3.76 × 10⁻³ S·cm⁻¹ at 100 °C and 98% RH.
• Direct observation of proton vibration and transfer within the N-H···O chains.
• A rare single-crystal to single-crystal (SCSC) transformation involving proton transfer was identified.

Conclusions:

• The (Me2NH2)[Eu(L)] MOF demonstrates efficient proton conductivity through well-defined hydrogen-bonded chains.
• The study provides direct evidence of proton dynamics in crystalline materials.
• The observed SCSC transformation offers insights into structural flexibility and proton transfer pathways in MOFs.