4-aminopyridinium 2-(anthracen-9-yl)-3-oxo-3H-inden-1-olate monohydrate.

The title compound, 2C(5)H(7)N(2)(+)·2C(23)H(13)O(2)(-)·H(2)O, formed as a by-product in the attempted synthesis of a nonlinear optical candidate molecule, contains two independent 4-aminopyridinium cations and 2-(anthracen-9-yl)-3-oxo-3H-inden-1-olate anions with one solvent water molecule. This is the first reported structure containing these anions. The two anions are not planar, having different interplanar angles between the anthracenyl and inden-1-olate moieties of 59.07 (5) and 83.92 (5)°. The crystal packing, which involves strong classical hydrogen bonds and one C-H...π interaction, appears to account for both the nonplanarity and this difference.