A rare positively charged nicotinic acid di-sulfide: 2,2'-di-thio-dinicotinic acid hydro-chloride monohydrate.

The title compound {systematic name: 3-carb-oxy-2-[2-(3-carb-oxy-pyridin-2-yl)disulfan-1-yl)]pyridin-1-ium chloride monohydrate}, C(12)H(9)N(2)O(4)S(2)(+)·Cl(-)·H(2)O, crystallizes in the triclinic space group P . A pair of 2-mercaptonicotinic acid moieties is connected by a 2,2'-di-sulfide bond with a dihedral angle of 78.79†(3)°. One of the N atom is protonated, as are both carboxyl-ate groups, resulting in an overall +1 charge on the dimer. The structure comprises a zigzagging layer of the dimerized di-thio-dinicotinic acid rings, with charge-balancing chloride ions and water mol-ecules between the layers. Hydrogen bonding between the chloride and water sites with the dimer appears to hold the structure together. Nearest neighbor nicotinic acid rings are offset when viewed down the a axis, suggesting no added stability from ring stacking. The asymmetric unit corresponds to the empirical formula of the compound, and it packs with two formula units per unit cell.