A second monoclinic polymorph of ethyl-enediammonium bis-(hydrogen squarate) monohydrate.

International audienceThe title compound, C(2)H(10)N(2) (2+)*2HC(4)O(4) (-)*H(2)O, a new polymorph of ethyl-enediammonium bis-(hydrogen squarate) monohydrate, was synthesized by slow evaporation of an acid solution. The asymetric unit contains two hydrogen squarate anions, two half-mol-ecules of protonated ethyl-enediamine arranged around a twofold axis and one water mol-ecule. 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 mol-ecules 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]