Chemical preparation, thermal behavior and crystal structure of ammonium barium cyclotriphosphate dihydrate

Ammonium and barium cyclotriphosphate mo-nohydrate, BaNH4P3O9·1H2O, was prepared for the first time by using Boulle’s process [1] by Durif et al. [2] who reported a complete description of the atomic arrangement. BaNH4P3O9·1H2O is monoclinic P21/n with the following unit-cell dimensions: a=11.70(1)A, b=12.12(1)A, c=7.559(5)A, β=101.05(5) and Z=4. There-fore, some discrepancies appear in the literature and stimulated further investigation of this compound to conclude concerning hydration level and structure. The thermal behavior of BaNH4P3O9·nH2O [3] showed that this cyclotriphosphate is a dihydrate and up to now no other hydrate has been described for this salt. So, the present study reports the chemical preparation, thermal behavior and crystal structure of BaNH4P3O9·2H2O, the first cyclotriphosphate of mixed ammonium-bivalent cations MII with a new general formula MIINH4P3O9·nH2O. Dehydration and decomposition of such cyclotriphosphates lead generally to long-chain polyphosphates, [MII(PO3)2]∞ which can be used as corrosion inhibitors [4]. The title compound has been studied through the following techniques: X-ray diffraction, IR spectrometry and thermal analyses TGA-DTA coupled.