4. Vibrational study

The vibration modes of the phosphate anions usually occur in the 1400–650 cm<sup>1</sup> area. The two IR bands observed at 1384 and 1286 cm<sup>1</sup> can be attributed to the νas (PO2) stretching vibration (Table 5). The shouldered band at 1157 cm<sup>1</sup> and the doublet observed at 1100 and

δ HOH

δ OPO

) Vibration

3449 ν OH

1384 νas OPO

1157 ν<sup>s</sup> OPO

983 νas POP 767 ν<sup>s</sup> POP

637 + 519 r OPO

) of IR absorption bands for BaCsP2O9.2H2O.

Figure 4. FTIR spectrum of BaCsP3O9.2H2O crystal.

ν (cm<sup>1</sup>

104 Chalcogen Chemistry

1637

1637

1286

1100

747 685

Table 5. Frequencies (cm<sup>1</sup>

The percentage of participation of each group was determined (Table 6). The geometrical parameters of the P3O9 3-ring with D3h symmetry, optimized by the MNDO [10] programs, are comparable with those obtained, by X-ray diffraction for the compounds with known structures.


Table 6. IR frequencies and displacements (Δν in cm<sup>1</sup> ) calculated for the P3O9 (D3h symmetry). All the Raman spectra available in the literature of compounds with the P3O9 <sup>3</sup> cycle of C3h symmetry, in LnP3O9.3H2O [11] and MIIMI P3O9 with benitoite structure 4, and cycle of Cs symmetry in NiRb4(P3O9)2.6H2O [17, 18], ZnM<sup>I</sup> 4(P3O9)2.6H2O (M<sup>I</sup> = K, Rb) [12, 13], MIIK4(P3O9)2.7H2O (MII = Ni,Co), C1 in MII(NH4)4(P3O9)2.4H2O (MII = Cu, Co, Ni) [14], and NiNa4(P3O9)2.6H2O [15] are characterized by three intense bands situated between 1153 and 1180, 640–680, and 297–313 cm<sup>1</sup> , which confirm the results of our calculations (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 their appearance in any IR spectrum indicates a symmetry lower than C3h.

This allowed us an attribution of the 30 fundamental frequencies of the cycle D3h on valid theoretical bases including 12 valence vibration frequencies and 18 bending vibration frequencies. The correlation between the D3h group and the site group C1 shows that the simple normal modes (A'1, A'2, A"1, and A"2), of the D3h group, are resolved each into the mode A of the C1 group and the doubly degenerate E' and E" modes are resolved into two modes and are active in IR and Raman. The factor group analysis predicts for four cycles of the unit cells of BaCsP3O9.2H2O (C2h), respectively, 24 and 36 valence vibration bands active in IR. But, we observe in the IR spectra of BaCsP3O9.2H2O (C2h) only six or seven bands and one inflection (Figure 4). It seems that the vibrational couplings between the P3O9 cycles of the unit cell are absent or very weak; thus, we will be able to interpret the IR spectrum, in the range 1400–

, of BaCsP3O9.2H2O according to the vibrations of an isolated cycle with local sym-

, of the P3O9 ring, with D3h symmetry of BaCsP3O9.2H2O.

Vibrational Study and Crystal Structure of Barium Cesium Cyclotriphosphate Dihydrate

http://dx.doi.org/10.5772/intechopen.81118

107

).

metry C1. The values of the calculated frequencies, for the D3h symmetry, are close to those observed for BaCsP3O9.2H2O (Table 6). Table 7 gives the attribution of the observed valence

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.

650 cm<sup>1</sup>

frequencies, 1400–650 cm<sup>1</sup>

5. Thermal analysis

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


This allowed us an attribution of the 30 fundamental frequencies of the cycle D3h on valid theoretical bases including 12 valence vibration frequencies and 18 bending vibration frequencies. The correlation between the D3h group and the site group C1 shows that the simple normal modes (A'1, A'2, A"1, and A"2), of the D3h group, are resolved each into the mode A of the C1 group and the doubly degenerate E' and E" modes are resolved into two modes and are active in IR and Raman. The factor group analysis predicts for four cycles of the unit cells of BaCsP3O9.2H2O (C2h), respectively, 24 and 36 valence vibration bands active in IR. But, we observe in the IR spectra of BaCsP3O9.2H2O (C2h) only six or seven bands and one inflection (Figure 4). It seems that the vibrational couplings between the P3O9 cycles of the unit cell are absent or very weak; thus, we will be able to interpret the IR spectrum, in the range 1400– 650 cm<sup>1</sup> , of BaCsP3O9.2H2O according to the vibrations of an isolated cycle with local symmetry C1. The values of the calculated frequencies, for the D3h symmetry, are close to those observed for BaCsP3O9.2H2O (Table 6). Table 7 gives the attribution of the observed valence frequencies, 1400–650 cm<sup>1</sup> , of the P3O9 ring, with D3h symmetry of BaCsP3O9.2H2O.
