l-Argininium ethyl sulfate

The title compound, C6H15N4O2 +·C2H5O4S−, exhibits nonlinear optical properties. An extensive hydrogen-bonding network [N⋯O = 2.786 (4)–3.196 (5) Å] links cations and anions into a three-dimensional structure.

The author expresses his thanks to Dr A. M. Petrosyan for providing the crystals and for valuable discussion of the results. This work was supported by US CRDF grant No. AE2-2533-YE-03.
Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: CV2443).

S1. Comment
In a search of analogs of the L-arginine phosphate (LAP) a large number of new materials [Monaco et al., 1987, Petrosyan et al., 2000 have been obtained by the interaction of L-arginine with various acids by choosing appropriate conditions. The crystals from the interaction of L-arginine with H 2 SO 4 could not be obtained due to extremely high solubility of reaction product (Petrosyan, 2005). Nevertheless, the conditions for obtaining the crystals of L-arginine salt with ethylsulforic acid were found (Petrosyan, 2005).
We present herein a structural study of the L-argininium ethylsulfate, C 6 H 15 N 4 O 2 + .C 2 H 5 O 4 S -, (I). A view of the asymmetric unit is shown in Fig. 1. The geometric parameters found in (I) are in a good agreement with the common accepted values. In the crystal, all eight active H atoms are involved in hydrogen bonding (Table 1), which link the kations and anions into three-dimensional structure.

S2. Experimental
The single crystals of (I) were obtained by slow evaporation of the aqueous solution of exchange reaction product described by Petrosyan (2005): L-Arg × HBF 4 + KC 2 H 5 SO 4 → L-Arg × HC 2 H 5 SO 4 + KBF 4 .

S3. Refinement
All H atoms were placed in geometrically calculated positions (C-H 0.96-0.98 Å, N-H 0.86-0.89 Å) and included in the refinement in a riding model approximation, with U iso (H)= 1.5U eq (of Me-and N + H 3 groups) and 1.2U eq (other carrier atoms). High values of U eq of some ethylsulforic anion atoms, except S, as compared to the other atoms of the structure, demonstrate potential thermal motion (rotation) of this group around the relatively heavy S atom.  A perspective view of the asymmetric unit of (I) showing the atomic numbering and displacement ellipsoids at the 50% probability level.

Special details
Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s 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 R-factors(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.