4-(4-Pyridyl)pyridinium perchlorate methanol solvate

In the cation of the title hydrated molecular salt, C10H9N2 +·ClO4 −·CH3OH, the dihedral angle formed by the pyridine rings is 28.82 (15)°. The crystal structure is stabilized by intermolecular N—H⋯O and O—H⋯N hydrogen bonds and π–π stacking interactions, with centroid-to-centroid distances of 3.5913 (7) and 3.6526 (7) Å. Three O atoms of the perchlorate anion are disordered over two positions with refined occupancy factors of 0.649 (7):0.351 (7).

The asymmetric unit of the title compound ( Fig. 1) consists of one 4,4'-bipyridin-1-ium cation, one ClO 4 anion and one methanol molecule. In the cation, the pyridine rings are tilted by 28.82 (15)°. The crystal structure is stabilized by intermolecular N-H···O and O-H···N hydrogen bonds (Table 1) and π-π stacking interactions involving the unprotonated pyridine rings, with centroid-to-centroid distances of 3.5913 (7) and 3.6526 (7) Å. The hydrogen bonds result in the formation of chains along the c axis (Fig. 2).
Experimental 4,4'-Bipyridine (10 mmol) and 10% aqueous HClO 4 in a molar ratio of 1:1 were mixed and dissolved in methanol. The mixture was heated to 323 K until a clear solution formed. The reaction mixture was cooled slowly to room temperature, crystals of the title compound suitable for X-ray analysis were obtained, collected and washed with dilute aqueous HClO 4 .

Refinement
All H atoms were placed in calculated positions, with C-H = 0.93 Å, O-H = 0.85 Å and N-H = 0.86 Å, and refined using a riding model, with U iso (H) = 1.2U eq (C, N) or 1.5U eq (O). The O2, O3 and O4 oxygen atoms of the perchlorate anion are disordered over two positions with refined occupancy factors of 0.649 (7):0.351 (7). Within the anion, the geometry of the Cl-O bonds was restrained to be similar by the SAME instruction, and the displacement ellipsoids were restrained to be nearly isotropic by the ISOR instruction.
Figures Fig. 1. The asymmetric unit of the title compound with atom labels. Displacement ellipsoids were drawn at the 30% probability level.

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.