4-Cyanopyridinium dihydrogen phosphate–isonicotinonitrile–phosphoric acid (1/1/1)

The asymmetric unit of the title compound, C6H5N2 +·H2PO4 −·C6H4N2·H3PO4, contains one 4-cyanopyridinium cation, one H2PO4 − anion, one independent isonicotinonitrile molecule and one independent H3PO4 molecule. The dihedral angle between the mean planes of the separate protonated and unprotonated pyridine rings is 9.93 (8)°. In the crystal, N—H⋯O and O—H⋯N hydrogen bonds and weak C—H⋯O and C—H⋯N intermolecular interactions connect the organic molecules into a two-dimensional network parallel to the ac plane. O—H⋯O hydrogen-bonding interactions involving the H2PO4 − anions and H3PO4 molecules provide additional support from the inorganic groups Weak π–π stacking interactions between the pyridine rings of neighbouring organic molecules [centroid–centroid distances = 3.711 (4) and 3.784 (2) Å] further link the layers into a three-dimensional network.


Ying-Chun Wang Comment
Simple organic salts containing strong intrermolecular H-bonds have attracted attention as materials which display ferroelectric-paraelectric phase transitions Huang, et al. 1999;Zhang, et al. 2001). In an effort to obtain phase transition crystals of organic salts, various organic molecules have been studied with a series of new crystal materials (Wang et al., 2002;Xue, et al. 2002;Ye et al., 2008). Herewith, we present the synthesis and crystal structure of the title compound, C 6 H 5 N 2 + .H 2 PO 4 -.C 6 H 4 N 2 .H 3 PO 4 ,(I).
The asymmetric unit of (I) is comprised of one 4-cyanopyridinium cation, one H 2 PO 4anion, one independent isonicotinonitrile molecule and one independent H 3 PO 4 molecule (Fig. 1). The two separate pyridine rings in the asymmetric unit are almost planar with the largest deviation from the least-squares plane being 0.001 (1) Å and 0.003 (1) Å, respectively. The dihedral angle between the mean planes of the two separate pyridine rings is 9.93 (8)°. Bond lengths and angles in each of these units are in normal ranges.

Experimental
Isonicotinonitrile (10 mmol and stirred at 60°C for 2 h. The precipitate was then filtrated. Colourless crystals suitable for X-ray diffraction were obtained by slow evaporation of the solution.

Refinement
H2, H3, H4, H6 and H8 were refined freely. In the last stages of the refinement these atoms were restrained with N3-H3 = 0.90 (2)Å and O2-H2, O4-H4, O6-H6, O8-H8 all = 0.82 (2)Å with U iso (H) = 1.2U eq (N) and U iso (H)=1.5U eq (O). All the remaining H atoms attached to C atoms were placed in calculated positions and then refined using the riding model with C-H lengths of 0.95 Å (CH). The isotropic displcement parameers for these atoms were set to 1.2 (CH) times U eq of the parent atom.

Computing details
Data collection: CrystalClear (Rigaku, 2005); cell refinement: CrystalClear (Rigaku, 2005); data reduction: CrystalClear (Rigaku, 2005); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure:      where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.001 Δρ max = 0.34 e Å −3 Δρ min = −0.40 e Å −3 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 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.