Pyridinium nitrate at 290 K

The crystal structure of pyridinium nitrate, (I), as determined by Serewicz et al. (1965), implied the existence of a strong hydrogen bond between the pyridinium and nitrate ions, but the precision of the data (measured at room temperature by the Weissenberg method) was insuf®cient to locate H atoms directly. We have redetermined this structure at two temperatures in the course of screening for materials suitable for neutron-diffraction and charge-density studies of hydrogen bonds. The 290 K structure (Fig. 1 and Table 1) is reported here. The results reported by Serewicz et al. (1965) are essentially con®rmed, though the unit cell is slightly larger than reported previously (without s.u. values): a = 3.905, b = 12.286, c = 13.470 AÊ , = 90.5 and V = 646 AÊ .


Comment
The crystal structure of pyridinium nitrate, (I), as determined by Serewicz et al. (1965), implied the existence of a strong hydrogen bond between the pyridinium and nitrate ions, but the precision of the data (measured at room temperature by the Weissenberg method) was insuf®cient to locate H atoms directly. We have redetermined this structure at two temperatures in the course of screening for materials suitable for neutron-diffraction and charge-density studies of hydrogen bonds. The 290 K structure ( Fig. 1 and Table 1) is reported here. The results reported by Serewicz et al. (1965) are essentially con®rmed, though the unit cell is slightly larger than reported previously (without s.u. values): a = 3.905, b = 12.286, c = 13.470 A Ê , = 90.5 and V = 646 A Ê 3 .
For the low-temperature results and the general discussion, see Batsanov (2004).

Experimental
The crystals of (I) were grown by slow evaporation, at room temperature, of an aqueous solution of equimolar amounts of pyridine and nitric acid.

Figure 1
The molecular structure of (I) at 290 K. Displacement ellipsoids are drawn at the 50% probability level. The dashed and dotted lines indicate strong and weak hydrogen bonds, respectively.

Special details
Experimental. The data collection nominally covered full sphere of reciprocal space, by a combination of 4 sets of ω scans, each set at different φ and/or 2θ angles and each scan (15 s exposure) covering 0.3° in ω. Crystal to detector distance 4.95 cm. Crystal decay was monitored by repeating the first 50 frames at the end of the data collection and comparing the intensities of 31 duplicate reflections.

sup-2
Acta Cryst. (2004). E60, o2424-o2425 Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s 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. H(1) atom (Nbonded) was refined in isotropic approximation (All H-atom parameters refined), other H atoms treated as riding (Hatom parameters constrained).