Bis(3-azoniapentane-1,5-diaminium) cyclohexaphosphate dihydrate: a monoclinic polymorph

In the title hydrated molecular salt, 2C4H16N3 3+·P6O18 6−·2H2O, the complete cyclohexaphosphate anion is generated by crystallographic inversion symmetry. The six P atoms of the P6O18 6− anion form a chair conformation and the organic cation has a corrugated linear geometry. In the crystal, the cations and the anions are connected by N—H⋯O hydrogen bonds into slabs propagating in the ac plane. The water molecules link the slabs by accepting N—H⋯O links and forming O—H⋯O links. The triclinic polymorph was reported by Gharbi et al. [(1995). J. Solid State Chem. 114, 42–51].

In the title hydrated molecular salt, 2C 4 H 16 N 3 3+ ÁP 6 O 18 6À Á-2H 2 O, the complete cyclohexaphosphate anion is generated by crystallographic inversion symmetry. The six P atoms of the P 6 O 18 6À anion form a chair conformation and the organic cation has a corrugated linear geometry. In the crystal, the cations and the anions are connected by N-HÁ Á ÁO hydrogen bonds into slabs propagating in the ac plane. The water molecules link the slabs by accepting N-HÁ Á ÁO links and forming O-HÁ Á ÁO links. The triclinic polymorph was reported by Gharbi et al. [(1995). J. Solid State Chem. 114, 42-51].
The packing of (I) consists of hybrid layers where the organic and inorganic species are alternated. Theses layers, extended perpendicularly to the b axis, are also connected between them in the two other directions via H-bonds assuring the cohesion of the network. The P 6 O 18 rings are located around the inversion centers (0, 0, 0) and (1/2, 1/2, 1/2) and are built up by only three independent PO 4 tetrahedra. The P-P-P angles of 98.85 (1), 109.09 (1) and 138.42 (1)° show that the rings are significantly distorted from the ideal threefold symmetry. It should be noted that these large deviations are commonly observed in cyclohexaphosphates with a ring of low local symmetry (Khedhiri et al., 2003, Khedhiri et al., 2007, as in the title compound. Nevertheless, this distortion is comparatively less important than that observed in Cs 6 P 6 O 18 .6H 2 O, which shows the greatest distortion for the same angles, ranging between 93.2 and 145.5° (Averbuch- Pouchot and Durif, 1991). The great flexibility of the hexamembered P 6 O 18 rings can probably explain the pronounced distortion observed for the big rings compared with their smaller ring analogues. Examination of the main geometrical features of the three independent PO 4 tetrahedra (P-O and P-P distances as well as P-O-P or O-P-O angles) shows clearly that, in spite of the P-P-P angles deformation, they are in accordance with values generally observed in condensed phosphate anions.
In the organic entity, N-C and C-C distances and N-C-C and C-N-C angles, spreading within the respective ranges 1.477 (1) -1.512 (2) Å and 109 (1) -111.5 (9)°, are similar to those observed in others compounds (Kamoun et al., 1990;Bridi et al., 1989). All nitrogen atoms of the used amine are protonated and so it is formulated by [C 4 N 3 H 16 ] 3+ . Among the eight hydrogen atoms of this group, only one, H1B, establishes a hydrogen bond with a water molecule, the remaining ones are connected to the external oxygen atoms of three phosphoric rings to form an anionic entity of formula This study shows that (I) is a polymorph of the triclinic structure published elsewhere (Gharbi et al., 1995). Both phases have the same chemical formula and some structural analogeous but they present several differences in their crystal data,

Experimental
Single crystals of the title compound were prepared in two steps. In the first one, 50 ml of an aqueous solution of cyclohexaphosphoric acid was prepared by protonation of 4 g of Li 6 P 6 O 18 .6H 2 O, obtained by the Schülke process (Schülke et al., 1985), with an ion-exchange resin (Amberlite IR 120). In the second one, the frech acidic solution (20 ml, 2.6 mmol) was immediately neutralized with a solution of aza-3 pentanediyl-1,5 diamine (2.8 mmol in 10 ml of ehanol) under continuous stirring. Good quality of prismatic-shaped crystals were obtained after a slow evaporation during few days at ambient temperature

Figure 1
The structure of (I) with displacement ellipsoids are drawn at the 30% probability level. Hydrogen bonds are represented  Structure projection of (I) along the a axis. The H-atoms not involved in H-bonding are omitted. Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.