The target complexes, bis{(E,E)-3,5-bis[4-(diethylamino)benzylidene]-4-oxopiperidinium} butanedioate, 2C27H36N3O(+)·C4H4O4(2-), (II), and bis{(E,E)-3,5-bis[4-(diethylamino)benzylidene]-4-oxopiperidinium} decanedioate, 2C27H36N3O(+)·C10H16O4(2-), (III), were obtained by solvent-mediated crystallization of the active pharmaceutical ingredient (API) (E,E)-3,5-bis[4-(diethylamino)benzylidene]-4-piperidone and pharmaceutically acceptable dicarboxylic (succinic and sebacic) acids from ethanol solution. They have been characterized by melting point, IR spectroscopy and single-crystal X-ray diffraction. For the sake of comparison, the structure of the starting API, (E,E)-3,5-bis[4-(diethylamino)benzylidene]-4-piperidone methanol monosolvate, C27H35N3O·CH4O, (I), has also been studied. Compounds (II) and (III) represent salts containing H-shaped centrosymmetric hydrogen-bonded synthons, which are built from two parallel piperidinium cations and a bridging dicarboxylate dianion. In both (II) and (III), the dicarboxylate dianion resides on an inversion centre. The two cations and dianion within the H-shaped synthon are linked by two strong intermolecular N(+)-H···(-)OOC hydrogen bonds. The crystal structure of (II) includes two crystallographically independent formula units, A and B. The cation geometries of units A and B are different. The main N-C6H4-C=C-C(=O)-C=C-C6H4-N backbone of cation A has a C-shaped conformation, while that of cation B adopts an S-shaped conformation. The same main backbone of the cation in (III) is practically planar. In the crystal structures of both (II) and (III), intermolecular N(+)-H···O=C hydrogen bonds between different H-shaped synthons further consolidate the crystal packing, forming columns in the [100] and [101] directions, respectively. Salts (II) and (III) possess increased aqueous solubility compared with the original API and thus enhance the bioavailability of the API.