5. Thermal analysis

All the Raman spectra available in the literature of compounds with the P3O9

their appearance in any IR spectrum indicates a symmetry lower than C3h.

and NiNa4(P3O9)2.6H2O [15] are characterized by three intense bands situated between 1153

(Table 6). Indeed, the theory predicts on the whole four bands with A'<sup>1</sup> modes for the P3O9 ring with D3h symmetry which are situated, according to our results, at 1169 cm<sup>1</sup> for νs P-Oe, 671 cm<sup>1</sup> for δs P-Oi, 559 cm<sup>1</sup> for δsPOiP, and 302 cm<sup>1</sup> for δs PO2. These four frequencies are predicted to be characteristic in any Raman spectrum of a cyclotriphosphate (with cycle of symmetry, C3, C2, Cs, or C1). These four IR fundamental frequencies have a null calculated intensity and are non-observable for D3h or C3h symmetries, and

C3h symmetry, in LnP3O9.3H2O [11] and MIIMI

and 1180, 640–680, and 297–313 cm<sup>1</sup>

13], MII

106 Chalcogen Chemistry

of Cs symmetry in NiRb4(P3O9)2.6H2O [17, 18], ZnM<sup>I</sup>

K4(P3O9)2.7H2O (MII = Ni,Co), C1 in MII

Table 7. Attribution of the observed valence IR frequencies (cm<sup>1</sup>

<sup>3</sup> cycle of

P3O9 with benitoite structure 4, and cycle

(NH4)4(P3O9)2.4H2O (MII = Cu, Co, Ni) [14],

, which confirm the results of our calculations

) of the P3O9 ring (C1) in BaCsP3O9.2H2O.

4(P3O9)2.6H2O (M<sup>I</sup> = K, Rb) [12,

The curve corresponding to the TG analyses in an air atmosphere and at a heating rate of 10C. min<sup>1</sup> of BaCsP3O9.2H2O is given in Figure 5. The dehydration of the barium cyclotriphosphate and of cesium dihydrate BaCsP3O9.2H2O is carried out in two steps in two temperature ranges from 105 to 180C and from 180 to 580C (Figure 5). In the thermogravimetric (TG) curve, the first step between 95 and 180C corresponds to the elimination of 1.14 water molecules; the second step from 180 to 580C is due to the removal of 0.86 water molecules.

Figure 5. TG curves of BaCsP3O9.2H2O at rising temperature (10C min<sup>1</sup> ).
