Structural variety and dehydration in 3-aminopyridine–hypodiphosphoric acid–water system†
Abstract
Organic–inorganic salts and ionic co-crystals of hypodiphosphoric acid (H4P2O6, PP) with 3-aminopyridine (3ap) have been synthesized and characterized by X-ray diffraction (single-crystal and micro-powder), thermogravimetry and Fourier-transform infrared spectroscopy. (3apH)2(H2P2O6)·0.5H4P2O6·H2O (1), (3apH)6(H2P2O6)(P2O6)·2H2O (3) and (3apH2)(H2P2O6) (5) were obtained in crystalline form in typical solution-crystallization processes, using the molar ratio of PP acid (water solution) : 3ap (solid) 1 : 1, 1 : 3 or 2 : 1, respectively. Compounds (3apH)4(H3P2O6)2(H2P2O6) (2) and (3apH)2(H2P2O6)·3ap (4) were formed during dehydration processes of (1) and (3), respectively, which took place as destructive transformations. Compound (2) was also obtained by crystallization from a molten salt. The removal of water results in rearrangement of the crystal architecture (both the hypodiphosphate substructure and the organic part), and formation of polar structure in (4).
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