Crystal structure of propane-1,3-diaminium squarate dihydrate

Propane-1,3-diaminium squarate dihydrate, C₃H₁₂N₂ ²⁺·C₄O₄ ^2-·2H₂O, results from the proton-transfer reaction of propane-1,3-di-amine with squaric acid and subsequent crystallization from aqueous medium. The title compound crystallizes in the tetra-gonal crystal system (space group <i>P</i>4<i>bm</i>) with <i>Z</i> = 2. The squarate dianion belongs to the point group <i>D</i> _4<i>h</i> and contains a crystallographic fourfold axis. The propane-1,3-diaminium dication exhibits a <i>C</i> _2<i>v</i> -symmetric all-<i>anti</i> conformation and resides on a special position with <i>mm</i>2 site symmetry. The orientation of the propane-1,3-diaminium ions makes the crystal structure polar in the <i>c-</i>axis direction. The solid-state supra-molecular structure features a triperiodic network of strong hydrogen bonds of the N-H⋯O and O-H⋯O types.