Bis[2,2′-(2-aminoethylimino)di(ethylammonium)] di-μ-sulfido-bis[disulfidostannate(IV)]

The asymmetric unit of the title compound, (C6H20N4)2[Sn2S6], comprises half of a [Sn2S6]4− anion and a diprotonated tris(2-aminoethyl)amine cation. The anion lies on an inversion center, while the atoms of the cation occupy general positions. An intramolecular N—H⋯N hydrogen bond is observed in the cation. In the crystal, strong N—H⋯S hydrogen bonding between the terminal sulfur atoms of the anion and the protonated amine N atoms of the cations result in a three-dimensional network.

The asymmetric unit of the title compound, (C 6 H 20 N 4 ) 2 [Sn 2 S 6 ], comprises half of a [Sn 2 S 6 ] 4À anion and a diprotonated tris(2-aminoethyl)amine cation. The anion lies on an inversion center, while the atoms of the cation occupy general positions. An intramolecular N-HÁ Á ÁN hydrogen bond is observed in the cation. In the crystal, strong N-HÁ Á ÁS hydrogen bonding between the terminal sulfur atoms of the anion and the protonated amine N atoms of the cations result in a three-dimensional network.

Comment
While solvothermal syntheses have produced an assortment of anionic thiostannate building blocks, the [Sn 2 S 6 ] 4moiety has been one of the most common (Zhou et al., 2009). It has also been shown that under certain conditions [Sn 2 S 6 ] 4anions can be converted to forms such as [Sn 3 S 7 ] 2and [Sn 4 S 9 ] -, forming two-dimensional layered anionic networks (Jiang et al., 1998a,b). In 2003, solvothermal experiments aimed at preparing [Co(tren) 2 ][Sn 2 S 6 ] using the chelating ligand tris(2aminoethyl)amine (C 6 H 18 N 4 , tren), resulted in the isolation and characterization of (H 2 tren) 2 [Sn 2 S 6 ] . 2H 2 O (Näther et al., 2003) as a side product. We have now shown that the anhydrous version of this compound, (I) can be accessed when the reaction is carried out in anhydrous conditions and without any transition metal present. In the title compound, (H 2 tren) 2 [Sn 2 S 6 ], ( Fig. 1), the terminal Sn-S bonds, at 2.3307 (4) and 2.3447 (5) Å, are shorter than the Sn-S bond of 2.4565 (6) Å formed with the bridging sulfur. The interior S-Sn-S angle of 92.78 (2)° is tighter than those involving terminal sulfurs, where these angles range from 108.22 (2) to 120.55 (2)°. Collectively, the geometric parameters of the [Sn 2 S 6 ] 4anion are in reasonable accordance with similar structures (Näther et al., 2003;Behrens et al., 2003). In the (H 2 tren) 2+ cation, the C-N bond lengths for the two protonated pendant amines are slightly longer, at 1.490 (3) and 1.473 (3) Å, than the 1.446 (5) Å C-N bond for the neutral arm. The most distinct structural difference between the anhydrous structure and the previously reported hydrated form (Näther et al., 2003) is the positioning of the NH 2 pedant amine. In the hydrated structure, it is aligned to facilitate a H-bonding interaction (H···N-H of 2.08 Å) with an NH 3 + amine on a neighboring cation. In the anhydrous structure, the hydrogen bonding interaction (N9-H9C···N10, 2.10 Å) is formed within the same ligand, Fig. 2.
Strong hydrogen bonding between the terminal sulfur atoms on the anion and the protonated amine centers on the cation Table 2) results in a three-dimensional network, Fig. 3.

Experimental
The title compound was prepared by solvothermal synthesis, using conditions comparable to Näther et al. (2003). 5.0 ml of tris-2-aminoethylamine (tren) was mixed with 1.00 mmol Sn and 3.0 mmol S in a 23 ml Parr (R) ; acid digestion apparatus. The mixture was heated to 423 K over 5 h and maintained at that temperature for 144 h. It was cooled to 363 K at 2 K/h, then cooled to 313 K at 6 K/h. The clear, colorless crystals were washed with hexane and recovered by vacuum filtration.
This protocol produced large crystals, often several mm on the longest axis, and in one instance measuring over 20 mm.

Refinement
All H atoms except for those on N(10) were placed at calculated positions (C-H at 0.97 Å, N-H at 0.87 Å) and refined as riding atoms with U iso (H) = 1.2U eq (C) and U iso (H) = 1.5U eq (N). The two H atoms on N(10) were identified from the difference Fourier map and refined as a rigid group with U iso (H) = 1.5U eq (N).  Fig. 1. The structure of (C 6 H 20 N 4 ) 2 [Sn 2 S 6 ].The thermal ellipsoids have been drawn at the 50% probability level. Symmetry code: (i) = -x, -y + 1, -z + 1.  Table 2. Fig. 3. View down the a axis illustrating the three-dimensional hydrogen bonding network.

Bis[2,2'-(2-aminoethylimino)di(ethylammonium)] di-µ-sulfido-bis[disulfidostannate(IV)]
Crystal data (C 6  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.