Structural phase transitions, dehydration and decomposition of ammonium hypodiphosphates.

Area of Science:

• Solid-state chemistry
• Crystallography
• Materials science

Background:

• Diammonium hypodiphosphate, (NH4)2(H2P2O6) (3), is the sole known ammonium salt of hypodiphosphoric acid.
• Understanding ammonium hypodiphosphates is crucial for exploring novel materials with potential ferroelectric properties.

Purpose of the Study:

• To synthesize and characterize a series of new ammonium hypodiphosphate salts.
• To investigate the structural, phase transition, dehydration, and decomposition behaviors of these novel compounds.

Main Methods:

• Single-crystal X-ray diffraction for structural determination of seven new ammonium hypodiphosphates.
• Differential scanning calorimetry (DSC) and thermogravimetric-differential thermal analysis (TG-DTA) for thermal analysis.
• Variable-temperature microsample powder X-ray diffraction for studying phase transitions.

Main Results:

• Synthesis and structural characterization of seven new ammonium hypodiphosphates, including polymorphs and hydrates.
• Monammonium hypodiphosphates (1 and 2) crystallize in perovskite-type structures with phase transitions.
• Dehydration and decomposition pathways were elucidated for several compounds, leading to different salt formations.

Conclusions:

• The study expands the known family of ammonium hypodiphosphates, revealing diverse structural motifs and properties.
• The identified phase transitions and thermal behaviors provide insights into the stability and reactivity of these salts.
• These findings contribute to the fundamental understanding of ammonium hypodiphosphate chemistry and their potential applications.