Proton-Rich POM-Type K₁₂Mo₈O₂₀(HPO₄)₈(PO₄)Cl with Ion-Exchange Capabilities

Area of Science:

• Inorganic Chemistry
• Materials Science
• Solid-State Chemistry

Background:

• Molybdenum phosphates are known for diverse structures and properties.
• Proton-rich materials are of interest for ion exchange and catalytic applications.
• Polyoxometalates (POMs) offer tunable frameworks for functional materials.

Purpose of the Study:

• To synthesize and characterize a novel proton-rich POM-type molybdenum phosphate.
• To investigate the structural features, including hydrogen bonding and interlayer spacing.
• To explore the ion-exchange capabilities and potential applications in pollutant remediation.

Main Methods:

• Single-crystal X-ray diffraction for structural determination.
• Density Functional Theory (DFT) calculations to confirm hydrogen positions.
• Spectroscopic techniques (1H, 7Li, 31P MAS NMR, IR) and thermal analysis for characterization.

Main Results:

• Successful synthesis of K12Mo8O20(HPO4)8(PO4)Cl, crystallizing in a noncentrosymmetric tetragonal space group P-4.
• Identification of proton-rich [Mo4P4O26H4]4- layers with corrugated structure and significant interlayer spacing.
• Demonstration of susceptibility to ion exchange (e.g., Cs+, Ba2+, Zn2+, Pb2+, Cu2+, Ni2+) due to weak bonding and large spaces.

Conclusions:

• The synthesized compound exhibits a unique POM-type framework with potential for ion exchange.
• Its structure is well-suited for capturing various cations, including those found in pollutants and nuclear waste.
• The material's noncentrosymmetric nature is confirmed and indicated by a small second-harmonic generation signal.