Strong asymmetric hydrogen bonding in 2-(oxamoylamino)ethyl­ammonium oxamate–oxamic acid (1/1)

摘要

The title compound, C4H10N3O2 ⁺·C2H2NO3 ⁻·C2H3NO3, con­tains at least 11 distinct hydrogen-bond inter­actions showing a great variety of bond strengths. The shortest and strongest hydrogen bond [O⋯O = 2.5004 (12) Å] is found between the uncharged oxamic acid molecule and the oxamate mono­anion. The grouping formed by such a strong hydrogen bond can thus be considered as a hydrogen bis­(oxamate) monoanion. It lacks crystallographic symmetry and the two oxamate groups have different conformations, showing an asymmetric hydrogen-bond inter­action. Significantly, the asymmetry allows us to draw a direct comparison of site basicity for the two inequivalent carboxyl­ate O atoms in the planar oxamate anion. The constituent mol­ecular ions of (I) form ribbons, where all amide and carboxyl­ate groups are coplanar. Graph-set analysis of the hydrogen-bonded net­works reveals the R ² 2(10) and R ² 2(9) homodromic nets as important structure-directing motifs, which appear to be a common feature of many oxamate-containing compounds.