Chemical preparation, crystal structure, thermal behavior and IR studies of barium thallium cyclotriphosphate dihydrate Original Research Article

Chemical preparation, crystal structure, thermal behavior and IR studies are given for a new barium thallium cyclotriphosphate dihydrate, BaTlP3O9·2H2O. This compound is monoclinic P21/n with the following unit-cell dimensions: a=7.546(3) Å, b=12.105(4) Å, c=11.649(4) Å, β=100.34(3)° and Z=4. Its crystal structure has been determined by X-ray diffraction and refined down to R=0.040, using 1652 independent reflections. BaTlP3O9·2H2O is isotypic to BaNH4P3O9·2H2O. The thermal behavior of this new salt was studied, between 25 and 600 °C, by infrared spectroscopy, X-ray diffraction and thermal analyses TGA and DTA. BaTlP3O9·2H2O leads, between 300 and 500 °C, to the corresponding anhydrous phase, BaTlP3O9. This new phase which is isotypic to BaNaP3O9 was characterized by X-ray powder diffraction. It is stable up to its melting point at 560 °C. The IR spectrum of BaTlP3O9·2H2O was examined and interpreted in the domain of the valence frequencies of the cycles, in the light of its proposed crystalline structure, on the basis of our results of the 30 calculated fundamental IR frequencies and of the successive isotopic substitutions of the equivalent atoms (3P, 3Oi, 6Oe of the ring P3Oi3Oe6) for the ring P3O93− with high symmetry D3h.