Proton-conducting coordination polymers formed from bipyridine phosphonate ligands.

Area of Science:

• Materials Science
• Inorganic Chemistry
• Supramolecular Chemistry

Background:

• Phosphonate-based linkers are underexplored for proton-conductive coordination polymers.
• N-heteroaromatic phosphonate frameworks are a limited but promising class of materials.

Purpose of the Study:

• To synthesize and characterize new phosphonate-based coordination polymers using novel ligands.
• To investigate the proton conductivity and mechanisms of these new materials.

Main Methods:

• Synthesis of three new coordination polymers (ICR-25, ICR-26, ICR-27) using 4,4'-bipyridine-derived phosphonate ligands (H8BipyTP, H4BipyDP) and metal ions (Ca2+, Al3+, Mg2+).
• Structural characterization of the coordination polymers.
• Measurement of proton conductivity at varying relative humidity and temperature.
• Analysis of activation energies to determine proton transport mechanisms.

Main Results:

• ICR-25 and ICR-26 feature hydrophilic voids with water molecules, while ICR-27 is nonporous.
• ICR-25 possesses acidic -OH groups, and ICR-26 has uncoordinated N heteroatoms.
• Maximum proton conductivity of 2.0 × 10-4 S cm-1 was achieved by ICR-26 at 92% humidity and 306 K.
• Proton transport mechanisms identified as vehicle mechanism in ICR-25 and Grotthuss mechanism in ICR-26.

Conclusions:

• N-heteroaromatic phosphonate ligands are effective for constructing proton-conducting coordination polymers.
• The synthesized materials, particularly ICR-26, exhibit significant proton conductivity.
• This work opens new avenues for designing advanced proton-conductive materials based on phosphonate linkers.