Wydział Chemii

Katarzyna A. Ślepokura

Paulina Kurowska

Daria Budzikur-Maciąg

Vasyl Kinzhybalo

2025

Acta Crystallographica Section B: Structural Science, Crystal Engineering and Materials

81

407-417

10.1107/s2052520625004408

Naukowa

Angielski

Artykuł

The ferroelectric di­ammonium hypodiphosphate, (NH₄)₂(H₂P₂O₆) (3), is the only known so far ammonium salt of hypodi­phospho­ric acid, H₄P₂O₆. A series of seven new ammonium salts is reported: triclinic (P1) (1) and monoclinic (C2/c) (2) polymorphs of mono­ammonium (NH₄)(H₃P₂O₆), isostructural (NH₄)₅(H₂P₂O₆)(HP₂O₆)·H₂O (4) and (NH₄)₃(HP₂O₆) (5), and tetra­ammonium (NH₄)₄(P₂O₆) (6), (NH₄)₄(P₂O₆)·H₂O (7) and (NH₄)₄(P₂O₆)·2H₂O (8). Mono­ammonium hypodiphosphates 1 and 2 crystallize in perovskite-type structures. Form 1 undergoes an order–disorder phase transition related to the dynamics of ammonium cations, the unit-cell doubling and no change in space group type. Dehydration–decomposition of 4 leads to the equimolar mixture of 3 and 5, whereas dehydration of dihydrate 8 proceeds in two steps, resulting in the formation of monohydrate 7 and then anhydrate 6. Compound 7 undergoes a reversible phase transition (P2₁/c ↔ C2/c) concerned with the reorganization of the hydrogen-bond network. Thermal analysis (DSC and TG-DTA) and variable-temperature microsample powder X-ray diffraction were used to analyse the phase transitions, dehydration and decomposition processes.

crystal structure, ammonium salts, hypodi­phospho­ric acid, phase transition, dehydration, decomposition, powder X-ray diffraction, thermal analysis, metal-free perovskite

http://dx.doi.org/10.1107/s2052520625004408