2.1. Chemical preparation

Single crystals of BaCsP3O9.2H2O were prepared by slowly adding dilute cyclotriphosphoric acid, H3P3O9, to an aqueous solution of barium carbonate, BaCO3, and cesium carbonate, Cs2CO3, with a stoichiometric ratio of Ba-Cs = 1:1, according to the following chemical reaction:

H3P3O9 <sup>þ</sup> BaCO3 <sup>þ</sup> <sup>1</sup>=2Cs2CO3 !BaCsP3O9:2H2O <sup>þ</sup> <sup>3</sup>=2CO2

The solution was then slowly evaporated at room temperature for 45 days until single crystals of BaCsP3O9.2H2O were obtained. The cyclotriphosphoric acid, H3P3O9, used in this reaction was prepared from an aqueous solution of Na3P3O9 passed through an ion-exchange resin "Amberlite IR120" [3]. Na3P3O9 was obtained by thermal treatment of sodium dihydrogen monophosphate, NaH2PO4, at 530�C for 5 h in the air, according to the following chemical reaction [4]:

3NaH2PO4 ! Na3P3O9 <sup>þ</sup> 3H2O

#### 2.2. XRD, crystal data, intensity data collection, and structure

A single-crystal X-ray structure determination of BaCsP3O9.2H2O was performed by using an Oxford Xcalibur S diffractometer at 293 K.

The structure was solved by direct methods using SHELXS [5] implemented in the Olex2 program [6]. The refinement was then carried out with SHELXL by full-matrix least squares minimization and difference Fourier methods. All non-hydrogen atoms were refined with anisotropic displacement parameters. Hydrogen atoms were generated in idealized positions, riding on the carrier atoms, with isotropic thermal parameters.

The final R1 value is 0.0401 for 1782 reflections with I > 2σ (I), and full X-crystal data is presented in Table 1. The main geometrical features, bond distances, and angles are reported in Table 6.

3. Results and discussion

arrays delimiting large channels parallel to the c direction.

Compound 2

90

 90 V/Å<sup>3</sup> 1098.57(5)Å<sup>3</sup>

Z 4

101.18(3)

) 7.362

Color/shape Colorless/prism Temp (K) 293(2)K Theta range for collection 3.50/27.59 Reflections collected 9176 Independent reflections 2448 Data/restraints/parameters 2448/0/147 Goodness of fit on F<sup>2</sup> 1.113

) 3.284 g/cm<sup>3</sup>

Final R indices [I > 2σ(I)] R1 = 0.0285, wR2 = 0.0611 R indices (all data) R1 = 0.0329, wR2 = 0.0638

Largest difference peak/hole 0.78/1.40 Å<sup>3</sup>

Crystal size (mm) 0.3296 0.1602 0.0957 mm3

Empirical formula BaCs H4O11P3 Formula weight 543.20 g.mol<sup>1</sup> Crystal system/space group Monoclinic/P 21/n a/Å 7.6992(2) Å b/Å 12.3237(3) Å c/Å 11.8023(3) Å

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The final atomic positions and anisotropic thermal parameters for the non-hydrogen atoms in the BaCsP3O9.2H2O structure are given in Tables 2 and 3, respectively. A projection of the BaCsP3O9.2H2O atomic arrangement along the c axis is given in Figure 1. It shows that all the components of the atomic arrangements are located around the two axes in order to form

Table 1. Crystal data and experimental parameters for the X-ray intensity data collection for BaCsP3O9.2H2O.

3.1. Structural analysis

α/

β/

γ/

D calc (g/cm3

μ (mm<sup>1</sup>

#### 2.3. Fourier transform infrared spectroscopy (FTIR)

A Nicolet Magna IR 560 spectrometer (resolution 1 cm�<sup>1</sup> , 200 scans) and an OMNIC software were used to characterize the stretching and bending bands between 400 and 4000 cm�<sup>1</sup> .


Table 1. Crystal data and experimental parameters for the X-ray intensity data collection for BaCsP3O9.2H2O.

## 3. Results and discussion

#### 3.1. Structural analysis

c = 11.8023 (3) Å, and β = 101.181 (5)� with a brief report of the structural refinement based on single-crystal XRD data. In the present work, we report the chemical preparation, crystalline structure, thermogravimetric analysis, and infrared study of this crystal barium and cesium cyclotriphosphate dihydrate, BaCsP3O9.2H2O, in order to have maximum information about

Single crystals of BaCsP3O9.2H2O were prepared by slowly adding dilute cyclotriphosphoric acid, H3P3O9, to an aqueous solution of barium carbonate, BaCO3, and cesium carbonate, Cs2CO3, with a stoichiometric ratio of Ba-Cs = 1:1, according to the following chemical reaction:

H3P3O9 <sup>þ</sup> BaCO3 <sup>þ</sup> <sup>1</sup>=2Cs2CO3 !BaCsP3O9:2H2O <sup>þ</sup> <sup>3</sup>=2CO2

The solution was then slowly evaporated at room temperature for 45 days until single crystals of BaCsP3O9.2H2O were obtained. The cyclotriphosphoric acid, H3P3O9, used in this reaction was prepared from an aqueous solution of Na3P3O9 passed through an ion-exchange resin "Amberlite IR120" [3]. Na3P3O9 was obtained by thermal treatment of sodium dihydrogen monophosphate,

3NaH2PO4 ! Na3P3O9 <sup>þ</sup> 3H2O

A single-crystal X-ray structure determination of BaCsP3O9.2H2O was performed by using an

The structure was solved by direct methods using SHELXS [5] implemented in the Olex2 program [6]. The refinement was then carried out with SHELXL by full-matrix least squares minimization and difference Fourier methods. All non-hydrogen atoms were refined with anisotropic displacement parameters. Hydrogen atoms were generated in idealized positions,

The final R1 value is 0.0401 for 1782 reflections with I > 2σ (I), and full X-crystal data is presented in Table 1. The main geometrical features, bond distances, and angles are reported

were used to characterize the stretching and bending bands between 400 and 4000 cm�<sup>1</sup>

, 200 scans) and an OMNIC software

.

NaH2PO4, at 530�C for 5 h in the air, according to the following chemical reaction [4]:

2.2. XRD, crystal data, intensity data collection, and structure

riding on the carrier atoms, with isotropic thermal parameters.

2.3. Fourier transform infrared spectroscopy (FTIR)

A Nicolet Magna IR 560 spectrometer (resolution 1 cm�<sup>1</sup>

Oxford Xcalibur S diffractometer at 293 K.

in Table 6.

structure and reactivity of the solids.

2. Experimental parameters

2.1. Chemical preparation

98 Chalcogen Chemistry

The final atomic positions and anisotropic thermal parameters for the non-hydrogen atoms in the BaCsP3O9.2H2O structure are given in Tables 2 and 3, respectively. A projection of the BaCsP3O9.2H2O atomic arrangement along the c axis is given in Figure 1. It shows that all the components of the atomic arrangements are located around the two axes in order to form arrays delimiting large channels parallel to the c direction.


Atom U11(s) U22 U33 U23 U13 U12

) for BaCsP3O9.2H2O.

Figure 1. Projection along the c axis of the atomic arrangement in BaCsP3O9.2H2O.

i, internal; e, external; w, water.

Table 3. Anisotropic thermal parameters (Å<sup>2</sup>

Ba 0.01483(15) 0.01281(16) 0.01595(15) 0.00044(10) 0.00056(11) 0.00029(10) Cs 0.02411(18) 0.0258(2) 0.02600(18) 0.00406(13) 0.00715(14) 0.00042(13) P(1) 0.0146(6) 0.0132(6) 0.0122(5) 0.0016(4) 0.0015(5) 0.0020(5) P(2) 0.0150(6) 0.0130(6) 0.0134(5) 0.0004(5) 0.0016(5) 0.0028(5) P(3) 0.0171(6) 0.0193(7) 0.0171(6) 0.0062(5) 0.0015(5) 0.0022(5) O(1i) 0.0173(16) 0.0172(17) 0.0207(17) 0.0054(14) 0.0035(14) 0.0032(14) O(2i) 0.0195(17) 0.0166(17) 0.0113(15) 0.0007(13) 0.0023(13) 0.0071(14) O(3i) 0.0192(17) 0.0140(17) 0.0176(17) 0.0035(13) 0.0026(14) 0.0027(14) O(4e) 0.025(2) 0.027(2) 0.058(3) 0.0226(19) 0.0086(19) 0.0009(17) O(5e) 0.037(2) 0.037(2) 0.0201(18) 0.0038(16) 0.0079(17) 0.0101(18) O(6e) 0.0241(18) 0.0194(17) 0.0210(18) 0.0080(14) 0.0067(15) 0.0069(15) O(7e) 0.0173(17) 0.0245(19) 0.0247(18) 0.0051(15) 0.0031(15) 0.0064(14) O(8e) 0.0201(17) 0.0147(17) 0.0253(18) 0.0064(14) 0.0042(15) 0.0009(14) O(9e) 0.0177(17) 0.0185(18) 0.0255(18) 0.0026(14) 0.0050(15) 0.0004(14) O(10w) 0.0190(17) 0.027(2) 0.0236(18) 0.0012(15) 0.0043(15) 0.0010(15) O(11w) 0.030(2) 0.034(2) 0.028(2) 0.0008(17) 0.0009(18) 0.0001(18)

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Table 2. Final atomic coordinates and U-equivalent temperature factors for BaCsP3O9.2H2O.

#### 3.2. Barium and cesium arrangement in the structure

The barium atom, located on the twofold axis, is coordinated by two water molecules and six oxygen atoms (Figure 2), forming an almost regular dodecahedron. The Ba-O distances spread between 2.298(6) and 2.349(6) Å. Each BaO8 dodecahedron shares six oxygen atoms with two anionic rings belonging to two phosphoric layers, thus providing the cohesion between these layers (Figure 2). BaO8 dodecahedra do not share any edge or corner and form layers alternating with P3O9 ones. The shortest Ba-Ba distance is found to be 4.70731 Å (Table 4).

The cesium atom occupies a general position and is coordinated to 10 external oxygen atoms and one water molecule (Figure 3). The Cs-O distances spread between 3.0278(2) and 3.5982(9) Ǻ.

The water group, its environment, established by strong hydrogen bonds, is depicted in (Figure 3) as an ORTEP representation [7].

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i, internal; e, external; w, water.

3.2. Barium and cesium arrangement in the structure

i, internal; e, external; w, water.

100 Chalcogen Chemistry

(Figure 3) as an ORTEP representation [7].

The barium atom, located on the twofold axis, is coordinated by two water molecules and six oxygen atoms (Figure 2), forming an almost regular dodecahedron. The Ba-O distances spread between 2.298(6) and 2.349(6) Å. Each BaO8 dodecahedron shares six oxygen atoms with two anionic rings belonging to two phosphoric layers, thus providing the cohesion between these layers (Figure 2). BaO8 dodecahedra do not share any edge or corner and form layers alternat-

The cesium atom occupies a general position and is coordinated to 10 external oxygen atoms and one water molecule (Figure 3). The Cs-O distances spread between 3.0278(2) and 3.5982(9) Ǻ.

The water group, its environment, established by strong hydrogen bonds, is depicted in

ing with P3O9 ones. The shortest Ba-Ba distance is found to be 4.70731 Å (Table 4).

Table 2. Final atomic coordinates and U-equivalent temperature factors for BaCsP3O9.2H2O.

Atoms X Y Z Ueq Ba 0.24946(3) 0.06963(2) 0.37463(2) 0.01486(9) Cs 1.23531(4) 0.37670(3) 0.60501(3) 0.02500(10) P(1) 0.49653(15) 0.33939(9) 0.34729(10) 0.0135(2) P(2) 0.75498(15) 0.17362(10) 0.42595(10) 0.0140(2) P(3) 0.72984(16) 0.35936(10) 0.57392(11) 0.0185(3) O(1i) 0.8311(4) 0.2619(3) 0.5238(3) 0.0194(7) O(2i) 0.6424(4) 0.2510(2) 0.3278(2) 0.0159(7) O(3i) 0.6022(4) 0.4024(2) 0.4588(3) 0.0178(7) O(4e) 0.8606(5) 0.4456(3) 0.6136(4) 0.0393(10) O(5e) 0.6256(5) 0.3191(3) 0.6572(3) 0.0312(9) O(6e) 0.4740(4) 0.4168(2) 0.2497(3) 0.0212(7) O(7e) 0.9053(4) 0.1308(3) 0.3805(3) 0.0223(8) O(8e) 0.6306(4) 0.0994(3) 0.4691(3) 0.0201(7) O(9e) 0.3428(4) 0.2843(3) 0.3783(3) 0.0205(7) O(10w) 0.2195(4) 0.1274(3) 0.5953(3) 0.0233(8) O(11w) 0.5532(5) 0.0975(3) 0.7172(3) 0.0315(9) H(1) 0.5738 0.0941 0.7926 0.047 H(2) 0.5846 0.1617 0.6363 0.047 H(3) 0.1274 0.1017 0.6242 0.035 H(4) 0.3191 0.0980 0.6366 0.035

Table 3. Anisotropic thermal parameters (Å<sup>2</sup> ) for BaCsP3O9.2H2O.

Figure 1. Projection along the c axis of the atomic arrangement in BaCsP3O9.2H2O.

Figure 2. The coordination of the barium atom in BaCsP3O9.2H2O.

3.3. Characterization by infrared spectroscopy

Tetrahedron around P(1)

Tetrahedron around P(2)

Tetrahedron around P(3)

P(2)–P(1)–P(3) 60.2(1) P(1)–P(2)–P(3) 60.7(2) P(1)–P(3)–P(2) 59.1(6)

expected in the domain 1400–650 cm<sup>1</sup>

due to water molecules in the domain 4000–1600 cm<sup>1</sup>

Table 4. Main interatomic distances (A) and bond angles () in the P3O9 ring [8].

P3O9 cycles and water molecules and also of water vibration modes.

Crystals were ground in a mortar with dry KBr powder in a ratio of 2:200 and pelleted in a

P(1) O(2i) O(3i) O(6e) O(9e) O(2i) 1.6126(5) 100.5(9) 107.8(1) 109.7(7) O(3i) 2.4804(3) 1.6065(6) 106.9(7) 108.7(6) O(6e) 2.4983(3) 2.4803(1) 1.4795(3) 120.9(4) O(9e) 2.5254(9) 2.5046(5) 2.5662(1) 1.4708(8)

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P(2) O(1i) O(2i) P(2) O(1i) O(1i) 1.6120(2) 100.7(7) 107.4(8) 109.7(3) O(2i) 2.4853(7) 1.6164(2) 107.3(7) 108.6(1) O(7e) 2.4843(1) 2.4879(6) 1.4650(7) 120.7(8) O(8e) 2.5346(1) 2.5175(5) 2.5637(8) 1.4838(6)

P(3) (O1i) (O3i) (O4e) (O5e) O(1i) 1.6058(7) 101.4(4) 107.8(7) 111.2(4) O(3i) 2.4836(6) 1.6045(7) 107.4(7) 110.5(9) O(4e) 2.4914(1) 2.48390 1.4762(3) 117.3(4) O(5e) 2.5386(2) 2.5308(4) 2.5158(1) 1.4705(7)

The IR spectrum of BaCsP3O9.2H2O illustrated in Figure 4 reveals the presence of three bands

nonequivalent positions of water molecules in the BaCsP3O9.2H2O atomic arrangement: 3449 cm<sup>1</sup> attributed to O-H valence vibration, around 3270 cm<sup>1</sup> to hydrogen bonds and 1637 cm<sup>1</sup> to δHOH deformation. The valence vibration bands related to the P3O9 cycles are

. This confirms the existence of

, as well as possible bands due to interactions between

press (8\*103 kg, 30 s). Then, they were stored at 95C for 1 d to dry before use.

P(1)–P(2) 2.8773(2) P(2)–O(1i)–P(3) 129.4(1) P(1)–P(3) 2.9289(6) P(1)–O(2i)–P(3) 131.6(6) P(2)–P(3) 2.9081(6) P(1)–O(3i)–P(2) 125.8(9)

Figure 3. ORTEP representation of BaCsP3O9.2H2O (H-bonds are represented by dashed lines). Thermal ellipsoids are scaled to enclose 50% probability.


Table 4. Main interatomic distances (A) and bond angles () in the P3O9 ring [8].

#### 3.3. Characterization by infrared spectroscopy

Figure 2. The coordination of the barium atom in BaCsP3O9.2H2O.

102 Chalcogen Chemistry

scaled to enclose 50% probability.

Figure 3. ORTEP representation of BaCsP3O9.2H2O (H-bonds are represented by dashed lines). Thermal ellipsoids are

Crystals were ground in a mortar with dry KBr powder in a ratio of 2:200 and pelleted in a press (8\*103 kg, 30 s). Then, they were stored at 95C for 1 d to dry before use.

The IR spectrum of BaCsP3O9.2H2O illustrated in Figure 4 reveals the presence of three bands due to water molecules in the domain 4000–1600 cm<sup>1</sup> . This confirms the existence of nonequivalent positions of water molecules in the BaCsP3O9.2H2O atomic arrangement: 3449 cm<sup>1</sup> attributed to O-H valence vibration, around 3270 cm<sup>1</sup> to hydrogen bonds and 1637 cm<sup>1</sup> to δHOH deformation. The valence vibration bands related to the P3O9 cycles are expected in the domain 1400–650 cm<sup>1</sup> , as well as possible bands due to interactions between P3O9 cycles and water molecules and also of water vibration modes.

983 cm<sup>1</sup> can be assigned to νs(PO2) and νas(POP), respectively. The most characteristic feature of the P3O9 ring anions is the occurrence of a strong intensity band near 767 cm<sup>1</sup> in addition to 747 cm<sup>1</sup> due to the νs(POP) stretching vibration. The weak peak appearing at 685 cm<sup>1</sup> can be assigned to νs(POP) [9]. The broad bands observed at 519 cm<sup>1</sup> and the weak

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

, the spectrum of BaCsP3O9.2H2O (Figure 4) shows

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Vibrational Study and Crystal Structure of Barium Cesium Cyclotriphosphate Dihydrate

) calculated for the P3O9 (D3h symmetry).

peak at 637 cm<sup>1</sup> can be due to the deformation vibrations of the anionic group.

bending vibration band characteristic of phosphates with ring anions.

In the spectral domain 650–400 cm<sup>1</sup>

Table 6. IR frequencies and displacements (Δν in cm<sup>1</sup>

4. Vibrational study

structures.

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

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


Table 5. Frequencies (cm<sup>1</sup> ) of IR absorption bands for BaCsP2O9.2H2O. 983 cm<sup>1</sup> can be assigned to νs(PO2) and νas(POP), respectively. The most characteristic feature of the P3O9 ring anions is the occurrence of a strong intensity band near 767 cm<sup>1</sup> in addition to 747 cm<sup>1</sup> due to the νs(POP) stretching vibration. The weak peak appearing at 685 cm<sup>1</sup> can be assigned to νs(POP) [9]. The broad bands observed at 519 cm<sup>1</sup> and the weak peak at 637 cm<sup>1</sup> can be due to the deformation vibrations of the anionic group.

In the spectral domain 650–400 cm<sup>1</sup> , the spectrum of BaCsP3O9.2H2O (Figure 4) shows bending vibration band characteristic of phosphates with ring anions.
