3-Aminopyridinium 4-hydroxy-3-iodonaphthalene-1-sulfonate dihydrate

In the hydrated title salt, C5H7N2 +·C10H6IO4S−·2H2O, the component species are linked by O—H⋯O and N—H⋯O hydrogen bonds, forming an infinite three-dimensional framework.

In the hydrated title salt, C 5 H 7 N 2 + ÁC 10 H 6 IO 4 S À Á2H 2 O, the component species are linked by O-HÁ Á ÁO and N-HÁ Á ÁO hydrogen bonds, forming an infinite three-dimensional framework.
Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: HB2719).

Comment
This work continues our previous synthetic and structural studies of the hydrogen bonding interactions between various organic acids and substituted pyridines (Li, 2007).

Experimental
A 5-ml ethanol solution of 3-aminopyridine (1.0 mmol, 0.094 g) was added to a 20-ml hot aqueous solution of 8-hydroxy-7-iodo-5-quinolinesulfonic acid (1.0 mmol, 0.351 g) and the mixture was stirred for 20 minutes at 373 K. Then the solution was filtered, and the filtrate was kept at the room temperature. After two weeks, yellow blocks of (I) were obtained.

Refinement
The N-and O-bonded H atoms bonded were located in a difference synthesis and refined isotropically with N-H = 0.89 (1), O-H = 0.85 (1) and H···H = 1.34 (1) Å, respectively. All the remaining H atoms were placed in calculated positions, with C-H = 0.93Å and were refined as riding with U iso = 1.2U eq (C). This refinement scheme results in a short intramolecular H4···H6 contact of 1.71Å, although H4 participates in a plausible intermolecular hydrogen bond: thus the location of H4 should be regarded as less certain. Other placement schemes for H4 appear to lead to disordered hydrogen bond arrangements. Fig. 1. The molecular structure of (I). Displacement ellipsoids for the non-H atoms are drawn at the 50% probability level. Hydrogen bonds are shown as dashed lines.  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.