Hydrogen bonding and C-H⋯X interactions in two triclinic phases of 4-carboxyquinolinium chloride monohydrate

The title substance, C₁₀H₈NO₊²·Cl ^-·H₂O, crystallized in the centrosymmetric space group P1 in two phases, α and β, each with one organic cation, one Cl^- ion and one water molecule in the asymmetric unit. The principal structural difference in the two asymmetric units lies in the relative orientation of the water molecule. Three hydrogen bonds in the α phase have donor-acceptor distances (N⋯Cl or O⋯Cl) ranging from 3.052 (1) to 3.189 (2) Å, while one has an O⋯O distance of 2.603 (3) Å. Three hydrogen bonds in the β phase have donor-acceptor distances (N⋯Cl or O⋯Cl) ranging from 3.044 (2) to 3.206 (2) Å, while two have O⋯O distances of 2.586 (2) and 3.147 (3) Å. The H atoms in all these hydrogen bonds are ordered. Each of these phases has five leading C-H⋯X interactions, for which the H⋯X distances are less than, or at most slightly greater than, the corresponding van der Waals radius sums. Taken together, these hydrogen bonds and C-H⋯X interactions form a three-dimensional network of interactions in each phase. The dihedral angle between the best-fit quinoline core plane and the carboxyl group plane is 25.9 (1)° for the α phase and 20.0 (1)° for the β phase.