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  • Title: Strong asymmetric hydrogen bonding in 2-(oxamoylamino)ethylammonium oxamate-oxamic acid (1/1).
    Author: Martinez Belmonte M, Price DJ.
    Journal: Acta Crystallogr C; 2010 Mar; 66(Pt 3):o147-50. PubMed ID: 20203413.
    Abstract:
    The title compound, C(4)H(10)N(3)O(2)(+) x C(2)H(2)NO(3)(-) x C(2)H(3)NO(3), 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) A] 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.
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