Picolinamidium squarate and di-p-toluidinium squarate dihydrate

The crystal structure determinations of picolinamidium squarate, C₆H₇N₂O⁺·C₄O₄⁻, (I), and di-p-toluidinium squarate dihydrate, 2C₇H₁₀N⁺·C₄O₄²⁻·2H₂O, (II), are reported. While salt formation occurs by donation of one H atom from squaric acid to the picolin­amide mol­ecule in (I), in compound (II), each squaric acid mol­ecule donates one H atom to the p-toluidine N atom of two trans p-toluidine molecules. In (I), the pyridine ring is coplanar with the squarate monoanion through imposed crystallographic mirror symmetry; in (II), the dihedral angle between the p-toluidine moiety and the squarate dianion is 70.71 (1)°. In (I), a three-dimensional structure is formed via van der Waals interactions between parallel planes of mol­ecules, with hydrogen-bond interactions (N—H⋯O and O—H⋯O) acting within the planes; hydrogen bonds form a three-dimensional network in (II).