Hydrogen bonding, π–π stacking and van der Waals forces-dominated layered regions in the crystal structure of 4-amino­pyridinium hydrogen (9-phosphono­non­yl)phospho­nate

The asymmetric unit of the title mol­ecular salt, [C(5)H(7)N(2) (+)][(HO)(2)OP(CH(2))(9)PO(2)(OH)(−)], consists of one 4-amino­pyridinium cation and one hydrogen (9-phos­phono­non­yl)phospho­nate anion, both in general positions. As expected, the 4-amino­pyridinium moieties are protonated exclusively at their endocyclic nitro­gen atom due to a mesomeric stabilization by the imine form which would not be given in the corresponding double-protonated dicationic species. In the crystal, the phosphonyl (–PO(3)H(2)) and hydrogen phospho­nate (–PO(3)H) groups of the anions form two-dimensional O—H⋯O hydrogen-bonded networks in the ab plane built from 24-membered hydrogen-bonded ring motifs with the graph-set descriptor R (6) (6)(24). These networks are pairwise linked by the anions’ alkyl­ene chains. The 4-amino­pyridinium cations are stacked in parallel displaced face-to-face arrangements and connect neighboring anionic substructures via medium–strong charge-supported N—H⋯O hydrogen bonds along the c axis. The resulting three-dimensional hydrogen-bonded network shows clearly separated hydro­philic and hydro­phobic structural domains.