Redetermination of trans-cyclohexane-1,4-diammonium dichloride

A redetermination of the crystal structure of the title compound, C6H16N2 2+·2Cl−, was undertaken. All atomic coordinates including those of the H atoms were refined freely. The cation is located on a centre of symmetry. Important for the crystal structure are wavy hydrogen-bonded layers that are formed by ammonium groups and chloride anions, giving hydrogen-bonded rings.

A redetermination of the crystal structure of the title compound, C 6 H 16 N 2 2+ Á2Cl À , was undertaken. All atomic coordinates including those of the H atoms were refined freely. The cation is located on a centre of symmetry. Important for the crystal structure are wavy hydrogen-bonded layers that are formed by ammonium groups and chloride anions, giving hydrogen-bonded R 3 6 ð12Þ rings.
Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: GD2030).

Comment
The title compound was first crystallographically characterized by Dunitz and coworkers in 1966(Dunitz & Strickler,1965, 1966). This quality structure determination only lacks the fact that all hydrogen atom positions, especially those of the ammonium group, were introduced into the structure model on the basic of geometrically calculated positions, with the N-H and the C-H distances set to 1.1 Å. For X-ray data refinement of hydrogen atom positions significantly shorter values are commonly found. We now describe an improved structure model -the hydrogen atoms were reliably found and refined from quality X-ray data.
Using data with reflections up to 65°/2Θ a more stable refinement is possible and the standard uncertainies of the N-Hdistances are smaller.
The title structure consists of hydrogen bonded hydrophilic layers in the ac-plane. These wavy layers are built by an annulated ring-motif (R 3 6 (12); Etter, 1990) constructed by three chloride anions and three ammonium groups (Fig. 3). Each ammonium group donates three hydrogen bonds of only slightly different strength to neighbouring chloride anions (Tab. Fig. 1 + 2). The title compound is therefore isostructual but not isotypic to the cyclohexane-1,4-diammonium dibromide (Rademeyer, 2006).

2,
In terms of crystal engineering the structure of the title compound is dominated by the hydrogen bonded layers. The aliphatic cyclohexane-1,4-diyl fragments connect these layers. According to the positions of the ammonium groups in the hydrogen bonded network the cyclohexyl-fragments do not appear cloesly packed (Fig. 3).

Refinement
All hydrogen atom positions were obtained from difference fourier maps, all hydrogen atoms were refined freely and with an individual isotropic displacement parameter for each (H-X distance range: 0.88-1.01 A).
supplementary materials sup-2 Figures   Fig. 1. The structure of the title compound (displacement ellipsoids at the 40% probability level, H-atoms drawn with arbitrary radius)·Thin dashed lines show hydrogen bonds to neighbouring chloride anions. The atoms of the asymmetric unit are labeled.