Bis(3-ammoniomethylpyridinium) cyclotetraphosphate

In the title compound, 2C6H10N2 2+·P4O12 4−, which involves a doubly protonated 3-ammoniomethylpyridinium cation and a cyclotetraphosphate anion, the cyclotetraphosphoric ring is arranged around an inversion center and the organic entity alternates with it, forming hybrid ribbons parallel to the b axis. The crystal structure is stabilized by a three-dimensional network of N—H⋯O and weaker C—H⋯O hydrogen bonds.


Experimental
Crystal data
Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: DN2541). Soumhi, E. H. & Jouini, T. (1996) Hybrid materials with organic and inorganic components continue to be a focus area in solid state chemistry and material sciences due to their potential applications in various fields, such as nonlinear optics (Aakeröy et al., 1989), heterogeneous catalysis (Centi, 1993), photochemical and photophysical process (Ozin, 1992), molecular sieves (Vaughan, 1993), ceramic precursors (Sankar et al., 1993) and other areas that include electronic materials (Teraski et al., 1987). In the present paper, the results of the x-ray structure analysis of a new organic cyclotetraphosphate, bis(3-ammoniomethylpyridinium) cyclotetraphosphate, are discussed with respect to the geometry and flexibility of the cyclotetraphosphate ring system and H-bonding interactions between the inorganic acceptor and the organic donor molecules.
The chemical composition of the title compound (I) includes two fundamental entities, the P 4 O 12 4ring and the organic cations (C 6 H 10 N 2 ) 2+ . The geometrical configuration of these entities is depicted in Figure 1, while the complete atomic arrangement is shown in Figure 2. This latter shows that the crystal structure of (C 6 H 10 N 2 ) 2 P 4 O 12 can be described by hybrid ribbons where the organic and inorganic species are alternated. These ribbons, extended in the b-direction, are also connected between them in the two other directions via H-bonds to develop a three-dimensional network. The P 4 O 12 rings are located around the inversion center (0, 0, 0) and are built up by only two independent PO 4 tetrahedra. The P-P-P angles are 84.43 (1) and 95.57 (1)° and show that the tetramembered phosphoric rings are distorted in comparison with the ideal value (90°). It should be noted that such deviations are commonly observed in cyclotetraphosphoric ring anions with low internal symmetry as (I) (Aloui et al., 2003;Hemissi et al., 2005). Nevertheless, this distortion is comparatively less important than that observed in the hexamembered P 6 O 18 rings (93.2 -145.5°) (Averbuch-Pouchot & Durif, 1991).
Consequently, P 4 O 12 is less flexible than the P 6 O 18 what could explain the pronounced distortion observed for the big rings compared with their smaller rings analogues. In spite of this distortion, the examination of the main geometrical feature of PO 4 tetrahedra (P-O distances and P-O-P angles) shows that they are in accordance with values generally observed in condensed phosphates (Durif, 1995).
One crystallographically independent organic group exists in the asymmetric unit. Inside this organic molecule, both nitrogen atoms are protonated and so it is formulated (C 6 H 10 N 2 ) 2+ . The examination of pyridinium ring shows that this unit is essentially planar with mean deviation of ±0.0036 Å from least-square plane defined by the six constituent atoms. The average C-N distances in pyridinium ring is 1.337 (2) Å and of the C-C bond lengths is 1.384 (2) Å. The latter value, being shorter than 1.39-1.41 Å, reported for non-substituent pyridine, may indicate some aromatic bond characters (Bak et al., 1959). The pyridinium ring is non coplanar with its methylamine substituent (-CH 2 -NH 3 ) which is evidenced by the torsion angle value of (C1-C2-C6-N2) equal to 96.29 (2)°. In addition to electrostatic and van der Waals interactions, the structure is further stabilized with a three-dimensional network of N-H···O and the weaker C-H···O hydrogen bonds (Table 1, Fig. 2)). In the hydrogen-bond scheme two main points should be noticed: (i) there is a bridging oxygen atom (O4) of the P 4 O 12 ring involved in hydrogen bond and so that is rarely observed in organic condensed phosphates. Indeed, it was only observed in (C 6 H 10 N 2 ) 2 P 4 O 12 .2H 2 O (Soumhi et al., 1996). (ii) Inside the structure, there are two strong hydrogen supplementary materials sup-2 bonds with N···O distances equal to 2.629 (2) and 2.708 (2) Å. The others are weaker within N(C)···O distances falling from 2.735 (2) to 3.381 (2) Å (Brown, 1976;Blessing, 1986).

Experimental
Crystals of the title compound were prepared by adding ethanolic solution (5 ml) of 3-aminopicolamine (11.04 mmol) dropwise to an aqueous solution of cyclotetraphosphoric acid (5.52 mmol, 20 ml). Good quality of colourless prisms were obtained after a slow evaporation during few days at ambient temperature. The cyclotetraphosphoric acid H 4 P 4 O 12 , was produced from Na 4 P 4 O 12 .4H 2 O, prepared according to the Ondik process (Ondik, 1964), through an ion-exchange resin in H-state (Amberlite IR 120).

Special details
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.
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 Rfactors(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.