Chemical preparation and crystal structure are reported for a new barium cesium cyclotriphosphate dihyd rate BaCsP3O9.2H2O. This salt crystallizes in the monoclinic system, space group P21/n a=7.6992(2) Å b=12.3237(3) Å c=11.8023(3) Å, β= 101.181° (3). The crystal structure was refined down to R1=0.0401, R2=0.0378 for 2213 unique reflections with I>2σ (I). The BaCsP3O9.2H2O structure can be described as; the phosphoric ring anions are interconnected by BaO8 dodecahedra. The two oxygen of the water molecules in the present arrangement participate in the coordination spheres of the associated barium and cesium cations. The ther mogravimetric analysis shows that the removal of these two water molecules occurs in two stages between 105 and 600°C. The vibrational study by IR absorption spectroscopy of the title compound reveals the presence of three bands and confirm the existence of non-equivalent positions of water molecules in the structure.
