**3. Structure description**

Crystal data and details of structure refinement are summarized in **Table 1**. Molecular graphics were performed employing Diamond [14]. The chemical composition of [C17H22N2]3[P6O18][H2O]8 includes three entities, one phosphoric ring, eight water molecules and three crystallographically distinct organic cations. An ORTEP view of the geometrical configuration of these entities is depicted in **Figure 1**, while


#### **Table 1.**

*The crystal data and experimental parameters used for the intensity data collection. Procedure and final results of the structure determination.*

*Crystal Structure of [C17H22N2]3[P6O18][H2O]8 DOI: http://dx.doi.org/10.5772/intechopen.108160*

#### **Figure 1.**

*ORTEP Plot of phosphoric ring and independent organic cations of [C17H22N2]3[P6O18][H2O]8 with numbering scheme. Thermal ellipsoids are drawn at 40% of probability. The water molecules are omitted for figure clarity.*

#### **Figure 2.**

*Projection of the structure of [C17H22N2]3[P6O18][H2O]8, along the b axis, The phosphoric anions are given in tetrahedral representation. Hydrogen bonds are shown as dashed lines.*

**Figure 2** exhibits the complete atomic arrangement. The packing of the title compound consists of hybrid layers where the organic and inorganic species are alternated. Theses layers, extended perpendicularly to the b-axis, are also connected by H-bonds in the two other directions assuring the cohesion of the lattice.

A chair conformation for the P6O18 ring anion was adopted (**Figure 3**-**a**). This phosphoric ring includes six independent PO4 tetrahedra. The values of the P∙O∙P, O∙P∙O angles and the P∙O and O∙O distances, are listed in **Table 2**. The P∙O bond lengths vary between 1.457 and 1.612 Å with an average value of 1.534 Å. The variation of the environment around the oxygen atoms can explains this divergence. Despite this diversity in P∙O distances, each tetrahedron in the P6O18 anion can be represented by typical O atoms arrangement with phosphorus atom moved of 0.117, 0.134, 0.138, 0.134, 0.147, 0.147 Å from the centre (**Table 3**, **Figure 3**-**a**). In addition, the distortion indices (DI) [15]: DI(PO) = 0.039, DI(OPO) = 0.038 and DI(OO) = 0.014 show an above distortion of the O-O bond lengths compared to P-O and O-P-O ones as illustrated in **Table 3**.

**Figure 3.** *Chair conformation of the inorganic and organic rings.*

### *Crystal Structure of [C17H22N2]3[P6O18][H2O]8 DOI: http://dx.doi.org/10.5772/intechopen.108160*


**Table 2.** *Main interatomic distances (Å) and bond angles (°) in [C17H22N2]3[P6O18][H2O]8.*


#### **Table 3.**

*Interatomic PO and OO distances (Å), OPO angles (°), tetrahedral distortion indexes ID(PO), ID(OPO) and ID(OO) of the cyclohexaphosphate in [C17H22N2]3[P6O18][H2O]8. The last column corresponds to the shift parameter.*


#### **Table 4.**

*Hydrogen-bond geometry (Å, °) in [C17H22N2]3[P6O18][H2O]8.*

The P-O-P angle values match well with those noticed in others cyclohexaphoshates [16, 17]. But the P1-O6-P6 angle of 140.09°, diverge from the value generally observed in such anions. This angle induces a longer P–P distance (2.982°).

#### *Crystal Structure of [C17H22N2]3[P6O18][H2O]8 DOI: http://dx.doi.org/10.5772/intechopen.108160*

It should be signaled that these values display the greatest discrepancy measured until now. The P–P–P angles ranging from 103.08 to 114.21° which averages are 107.62°, show large deviations from the ideal value (120°). In spite of this variance, the distortion is more important if compared with that observed in [C9H14N]4[H3O]2[P6O18] [18] with the same space C2\c group in which the average of the P–P–P angle is 101.0°.

In the crystal structure there are three independent 1-(diphenylmethyl)piperazinium cations that are associated with phosphoric entities through electrostatic interactions and hydrogen bonds involving hydrogen atoms of NH and NH2. Each six-membered piperazinedium ring adopts a chair conformation (**Figure 3**-**b**). In all hydrogen bonds, the nitrogen atoms are donors, whereas the oxygen from the P6O18 6− acts as acceptor atoms (**Table 4**), with N…O separations ranging from 2.6354 to 2.9864 Å. The (N-C, C-C) bond lengths and bond angles (N-C-C, C-C-C) ranging from 1.346(9) to 1.528(4) Å and from 108.4(3) to 124.6(4) ° (**Table 5**) are comparable with those observed in other organic phosphates [19].



*Crystal Structure of [C17H22N2]3[P6O18][H2O]8 DOI: http://dx.doi.org/10.5772/intechopen.108160*


**Table 5.**

*Selected bond lengths (Å) and bond angles (°) in the organic groups of [C17H22N2]3[P6O18][H2O]8.*

It must be noted that: Firstly, all water molecules are not involved in the inorganic layers which may explain their high thermal factors. Such thermal factor values were observed too in others similar structures [20, 21]. Secondly and except O(1 W) and O(2 W), the others water molecules have a static disorder, being split into two fragments with an occupancy rates of 0.5.

## **4. Conclusion**

Along this work, a new [C17H22N2]3[P6O18][H2O]8 organic cyclohexaphosphate has been successfully synthesized and grown by solution growth method at ambient temperature. According to the X-ray structural results, the crystal structure is governed by hydrogen bonding and intermolecular interactions, resulting infinite inorganic and organic layers. This analysis indicated that the PO4 tetrahedra possessed a slightly distorted geometry. The P1-O6-P6 angle of 140.09°, depart significantly from the value generally observed in such anions and The P–P–P angles ranging from 103.08 to 114.21° which averages are 107.62°, show large deviations from the ideal value (120°). The title compound was further characterized by FT-IR NMR spectroscopy and DFT calculation.
