Structural Landscape and Proton Conduction of Lanthanide 5-(Dihydroxyphosphoryl)isophthalates

Area of Science:

• Materials Science
• Inorganic Chemistry
• Solid-State Chemistry

Background:

• Metal phosphonate-carboxylate compounds are explored for proton conduction.
• Lanthanide-based compounds derived from 5-(dihydroxyphosphoryl)isophthalic acid (PiPhtA) are investigated.

Purpose of the Study:

• To investigate the structural, thermal, and proton conduction properties of three groups of lanthanide-based compounds.
• To evaluate the effect of ammonia vapor exposure on proton conductivity.

Main Methods:

• Crystal structures were solved using ab initio X-ray powder diffraction.
• Proton conductivity was measured using impedance spectroscopy.
• Compounds were exposed to ammonia vapors (14% and 28% aqueous solutions).

Main Results:

• Three-dimensional frameworks were observed in Ln-I and Ln-II groups, while Ln-III exhibited a layered structure.
• Initial proton conductivity followed a vehicle-type mechanism, enhanced by water.
• Ammonia and water adsorption significantly increased proton conductivity via a Grotthuss-type mechanism.
• Postsynthetic modification of group II compounds led to a conductivity increase from ~5 × 10^-6 to ~10^-4 S·cm^-1.
• The NH₃(28%)-exposed Yb-III compound reached ~5 × 10^-3 S·cm^-1 conductivity.

Conclusions:

• Lanthanide phosphonate-carboxylate compounds exhibit tunable proton conductivity.
• Ammonia exposure induces structural changes and enhances proton conduction through Grotthuss-type mechanisms.
• These materials show potential for applications requiring efficient proton transport.