Bis[2-(ethoxycarbonylamino)ethanaminium] hexabromidostannate

In the title salt, (C5H13N2O2)2[SnBr6], the Sn atom (site symmetry ) exists in a slightly distorted octahedral geometry. The cation is non-planar as the terminal CH2NH3 + residue lies below the plane defined by the remaining non-H atoms. In the crystal, cations associate via N—H⋯O hydrogen bonds involving the ammonium and carbonyl residues, forming a 14-membered {⋯HNC2NCO}2 synthon. The cations and anions are arranged in alternating layers arranged along the a-axis direction, the major association between them being N—H⋯Br contacts.

In the title salt, (C 5 H 13 N 2 O 2 ) 2 [SnBr 6 ], the Sn atom (site symmetry 1) exists in a slightly distorted octahedral geometry. The cation is non-planar as the terminal CH 2 NH 3 + residue lies below the plane defined by the remaining non-H atoms. In the crystal, cations associate via N-HÁ Á ÁO hydrogen bonds involving the ammonium and carbonyl residues, forming a 14-membered {Á Á ÁHNC 2 NCO} 2 synthon. The cations and anions are arranged in alternating layers arranged along the a-axis direction, the major association between them being N-HÁ Á ÁBr contacts.
The use of the EPSRC X-ray crystallographic service at the University of Southampton, England and the valuable assistance of the staff there is gratefully acknowledged. JLW acknowledges support from FAPEMIG (Brazil).  (Wilson & Nowick, 1998) and acids, e.g., ring opening of 1-methyl-3-3-hydroxyphenyl-2-imidaxolidone by concentrated HCl to give MeNHCH 2 CH 2 NHC 6 H 4 OH-m (Duschinsky, 1950). With reduced acidity, co-crystallization can occur instead as shown by the isolation of a 1:1 adduct of 2-imidazolidone and 5-nitrosalicylic acid (Smith et al., 1998). The free base of 2 has been reported from the reaction of H 2 NCH 2 CH 2 NH 2 with EtO 2 CO(MeO)CCH 2 (Kita et al., 1980). The structure of (I) comprises ethyl (2-ammonioethyl)carbamate cations and SnBr 6 dianions in the ratio 2:1; the Sn atom is located on a crystallographic centre of inversion so that the asymmetric unit is defined by one cation and half an anion, Fig. 1. The cation is not planar. While the RMS deviation of the O1, O2, N1 and C1-C4 atoms is 0.019 Å, the C5 atom lies 1.410 (5) Å out of this plane; the C3/N1/C4/C5 torsion angle of 96.4 (4)°. In the anion, the Sn-Br2 bond distance of 2.5820 (4) Å is significantly shorter than the Sn-Br1 and Sn-Br3 bond distances of 2.6075 (4) and 2.6053 (4) Å, respectively, an observation rationalized in terms of the pattern of intermolecular interactions,see below. The carbonyl-O1 atom forms a hydrogen bond with an ammonium-H atom to form a dimeric aggregate, Table 1 and Fig. 2. The resulting 14-membered {···HNC 2 NCO} 2 synthon has twofold symmetry. The remaining acidic H atoms form contacts to the Br1 and Br3 atoms, Table 1, explaining the variation of the Sn-Br bond distances, whereby the Br2 atom not engaged in a significant intermolecular contact forms the shorter of the Sn-Br bonds. Globally, the crystal packing comprises alternating layers of cations and anions stacking along the a direction.

S3. Refinement
All H atoms were located from a difference map but, were geometrically placed (C-H = 0.98-0.99 Å, and N-H = 0.88-0.91 Å) and refined as riding with U iso (H) = 1.2-1.5U eq (C, N). The maximum and minimum residual electron density peaks of 0.85 and 1.26 e Å -3 , respectively, were located 1.81 Å and 0.82 Å from the S1 and Sn atoms, respectively.

Figure 3
Unit-cell contents for (I) viewed in projection down the c axis. The N-H···O hydrogen bonds (orange dashed lines) and N-H···Br contacts (blue dashed lines) indicate the mode of asscoiated between the components of the crystal structure.

Figure 4
The formation of the title compound.

Bis[2-(ethoxycarbonylamino)ethanaminium] hexabromidostannate
Crystal data (C 5  where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.001 Δρ max = 0.87 e Å −3 Δρ min = −1.35 e Å −3 Special details Geometry. All s.u.'s (except the s.u. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell s.u.'s are taken into account individually in the estimation of s.u.'s in distances, angles and torsion angles; correlations between s.u.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell s.u.'s is used for estimating s.u.'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 > 2σ(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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq