Molecular Structure of the Monohydrate Hydrochloride Salt of the Antimalarial Drug Chloroquine

We report the crystallization and single-crystal X-ray analysis of the monohydrate hy-drochloride salt of chloroquine, designed CQCl·H2O, an antimalarial drug (CQ) with the formula C₁₈H₂₆ClN₃. The crystal structure reveals a well-defined supramolecular architecture stabilized by an extensive hydrogen-bonding network involving CQH⁺ cations, chloride anions, and water molecules. Notably, this study provides the first crystallographic characterization of a monoprotonated chloroquine salt. Additionally, our findings demonstrate the feasibility of isolating pseudo-polymorphic forms of a commercially available CQ salt via heterogeneous crystallization.