A second monoclinic polymorph of ethyl­enediammonium bis­(hydrogen squarate) monohydrate

The title compound, C(2)H(10)N(2) (2+)·2HC(4)O(4) (−)·H(2)O, a new polymorph of ethyl­enediammonium bis­(hydrogen squarate) monohydrate, was synthesized by slow evaporation of an acid solution. The asymetric unit contains two hydrogen squarate anions, two half-mol­ecules of protonated ethyl­enediamine arranged around a twofold axis and one water mol­ecule. In the crystal, N—H⋯O and O—H⋯O hydrogen bonds between the hydrogen squarate anions, protonated N atoms from the amine group and water mol­ecules lead to a three-dimensional framework. In particular, the cohesion between the squarate groups is ensured by very short intermolecular hydrogen bonds bonds. The title compound crystallized together with the previously reported polymorph [Mathew et al. (2002 ▶). J. Mol. Struct. 641, 263–279].