Ethylenediaminium hemioxalate thiocyanate

In the title compound, C2H10N2 2+·0.5(C2O4)2−·NCS−, the ethylenediaminium dication adopts a (+)-synclinal conformation with an N—C—C—N torsion angle of 62.64 (15)°. The oxalate dianion lies across an inversion centre. In the crystal structure, the ions are linked through N—H⋯N, N—H⋯O and C—H⋯S hydrogen bonds, leading to the formation of a three-dimensional network.


Comment
Aqueous solution of ethylenediamine and oxalic acid regardless of their stiochiometric ratio was reported to give ethylenediammonium bis(monohydrogen oxalate) monohydrate (II) (Barnes et al., 1998). However, the same reaction but in the presence of ammonium thiocyanate was found to give an ethylenediammonium hemioxalate thiocynate, the title compound, (I, Fig.1), indicating that the oxalic acid has been completely deprotonated.
The centrosymmetric oxalate anion is planar as commonly observed in many oxalate salts (Tang et al., 2009;Seidel et al., 2008).  (Tang et al., 2009). The ethylenediaminium ion in this salt is not planar but twisted with a N3-C3-C4-N2 torsion angle of 62.64 (15)°. In compound (II), and ethylenediammonium pyridine-2,5-dicarboxylate dihydrate (IV) (Smith et al., 2006), the ethylenediammonium cation is centrosymmetric and has an extended conformation with a N-C-C-N torsion angle of 180°. The thiocyanate anion is linear. The bond lengths and angles are in normal ranges (Allen et al., 1987) and comparable with those in (II), (III) and (IV).
In the crystal structure, the molecules are linked by N-H···N, N-H···O and C-H···S hydrogen bonds (Table 1) forming a three-dimemsional network (Fig. 2).

Refinement
After their location in a difference map, the methylene and ammonium H-atoms were positioned geometrically [N-H = 0.89 Å and C-H = 0.97 Å] and allowed to ride on the parent atoms, with U iso (H) = 1.2U eq (C,N). A rotating group model was used for the ammonium group. Fig. 1. The asymmetric unit of the title compound. Displacement ellipsoids are drawn at the 50% probability level. Unlabelled atoms in the dianion are related to other labelled atoms in it by the symmetry operation (1 -x, -y, 1 -z).

Special details
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.
Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating Rfactors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.