Crystal structure of 2-(aza­niumylmeth­yl)pyridinium bis­(hydrogen squarate)

The asymmetric unit of the title compound, C6H10N22+·2C4HO4−, comprises two hydrogen squarate (Hsq−; systematic name: 2-hy­droxy-3,4-dioxo­cyclo­butano­late) anions and a 2-(aza­niumylmeth­yl)pyridinium dication. The squaric acid mol­ecules each donate an H atom to the N atoms of the pyridine ring and the amino­methyl units of a 2-(amino­meth­yl)pyridine mol­ecule, forming the 1:2 salt. The Hsq− anions are linked by strong O—H⋯O hydrogen bonds and an N—H⋯O hydrogen bond links the 2-(aza­niumylmeth­yl)pyridinium cation to one of the squaric acid anions. The crystal structure features additional N—H⋯O and O—H⋯O hydrogen bonds, π–π stacking and unusual weak C—O⋯π(ring) inter­actions.