4,4′-Bipyridinium bis(perchlorate)–4-aminobenzoic acid–4,4′-bipyridine–water (1/4/2/2)

In the structure of the title compound, C10H10N2 2+·2ClO4 −·4C7H7NO2·2C10H8N2·2H2O, the 4,4′-bipyridinium cation has a crystallographically imposed centre of symmetry. The cation is linked by N—H⋯N hydrogen bonds to adjacent 4,4′-bipyridine molecules, which in turn interact via O—H⋯N hydrogen bonds with 4-aminobenzoic acid molecules, forming chains running parallel to [30]. The chains are further connected into a three-dimensional network by N—H⋯O and O—H⋯O hydrogen-bonding interactions involving the perchlorate anion, the water molecules and the 4-aminobenzoic acid molecules. In addition, π–π stacking interactions with centroid–centroid distances ranging from 3.663 (6) to 3.695 (6) Å are present. The O atoms of the perchlorate anion are disordered over two sets of positions, with refined site occupancies of 0.724 (9) and 0.276 (9).

In the structure of the title compound, C 10 H 10 N 2 2+ Á2ClO 4 À Á-4C 7 H 7 NO 2 Á2C 10 H 8 N 2 Á2H 2 O, the 4,4 0 -bipyridinium cation has a crystallographically imposed centre of symmetry. The cation is linked by N-HÁ Á ÁN hydrogen bonds to adjacent 4,4 0bipyridine molecules, which in turn interact via O-HÁ Á ÁN hydrogen bonds with 4-aminobenzoic acid molecules, forming chains running parallel to [302]. The chains are further connected into a three-dimensional network by N-HÁ Á ÁO and O-HÁ Á ÁO hydrogen-bonding interactions involving the perchlorate anion, the water molecules and the 4-aminobenzoic acid molecules. In addition,stacking interactions with centroid-centroid distances ranging from 3.663 (6) to 3.695 (6) Å are present. The O atoms of the perchlorate anion are disordered over two sets of positions, with refined site occupancies of 0.724 (9) and 0.276 (9).

Related literature
For details of the hydrogen-bonding networks formed by 4aminobenzoic acid and 4,4-bipyridine, see: Clemente & Marzotto (2004); Hu et al. (2003); Yang et al. (2004).  Table 1 Hydrogen-bond geometry (Å , ). Hydrogen-bonding interactions between ligands are specific and directional. In this sense, 4-aminobenzoic acid and 4,4bipyridine are the excellent candidates for the construction of three-dimensional network motifs, as they form regular hydrogen bonds functioning as both hydrogen-bond donors and acceptors (Clemente & Marzotto, 2004;Hu et al., 2003;Yang et al., 2004). Recently, we obtained the title compound under hydrothermal conditions and report its crystal structure herein.

S3. Refinement
The disordered perchlorate ion was refined into two sites with refined occupancies of 0.724 (9) and 0.276 (9). The Cl···O and O···O distances were restrained to be 1.44 (1) and 2.35 (1) Å, respectively. Water H atoms were located in a The molecular structure showing the atomic-numbering scheme. Displacement ellipsoids drawn at the 30% probability level. Symmetry codes:

Figure 2
Packing diagram of the title compound viewed along the a axis. Hydrogen bonds are shown as dashed lines.

4,4′-Bipyridinium bis(perchlorate)-4-aminobenzoic acid-4,4′-bipyridine-water (1/4/2/2)
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 > 2sigma(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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq Occ.