APSe6 (A = K, Rb, and Cs): Polymeric selenophosphates with reversible phase-change properties

Area of Science:

• Solid-state chemistry
• Inorganic materials science
• Crystallography

Background:

• Ternary alkali selenophosphates are an emerging class of materials with potential applications.
• Understanding their crystal structures and phase transitions is crucial for material design.

Purpose of the Study:

• To synthesize and characterize new ternary alkali selenophosphates: KPSe6, RbPSe6, and CsPSe6.
• To investigate the crystal structures and phase transition behaviors of these compounds.

Main Methods:

• Single-crystal X-ray diffraction was used to determine the crystal structures.
• Differential thermal analysis (DTA) or similar techniques were employed to study the glass-crystal transition.
• Phosphorus-31 Nuclear Magnetic Resonance (31P NMR) spectroscopy was utilized to probe structural changes during crystallization.

Main Results:

• KPSe6 and RbPSe6 crystallize in the polar orthorhombic space group Pca2(1).
• CsPSe6 crystallizes in the monoclinic space group P2/n.
• All compounds contain infinite one-dimensional chains of [PSe6] units, featuring bridging Se4(2-) ligands.
• A reversible glass-crystal transition was observed for these selenophosphates.

Conclusions:

• The synthesis and structural elucidation of KPSe6, RbPSe6, and CsPSe6 expand the family of ternary alkali selenophosphates.
• The observed glass-crystal transition suggests potential for these materials in applications requiring tunable properties.
• 31P NMR data indicate a strong correlation between the crystallization process and the formation of the characteristic infinite [PSe6] chains.