Crystal structure of the 1:2 adduct of bis(piperidinium) sulfate and 1,3-dimethylthiourea

The packing is centred on bis(piperidinium) sulfate ribbons parallel to the c axis; the cations are hydrogen bonded to the sulfate by N—H⋯O and C—H⋯O interactions. The 1,3-dimethylurea molecules are also hydrogen bonded to sulfate O atoms, and project outwards from the ribbon parallel to the b axis.


Chemical context
We are interested in the structures of adducts of urea and thiourea, and simple derivatives of these compounds, with neutral molecules. We have published two reports on adducts of dioxane and morpholine with various methylthioureas (Jones et al., 2013;Taouss & Jones, 2016). In the course of our current investigations, we attempted to obtain adducts of methylthioureas with piperidine, although monoamines are not good adduct partners for ureas and thioureas. Indeed, no simple adducts were obtained. In one case, however, we overlayered a solution of 1,3-dimethylthiourea (1,3-DMT) in piperidine with diethyl ether and obtained colourless crystals, the structure of which is reported here.

Structural commentary
The crystals proved to be a 1:2 adduct of bis(piperidinium) sulfate and 1,3-DMT (Fig. 1), with the sulfate anion presumably generated by partial hydrolysis and/or decomposition of the 1,3-DMT under the influence of peroxides in the ether. The C S bonds of both 1,3-DMT molecules lie along twofold axes. The sulfate sulfur atom also lies on a twofold axis. The piperidine lies on a general position. Molecular dimensions may be regarded as normal. Both 1,3-DMT molecules are essentially planar (r.m.s. deviation of non-H atoms: 0.004 and 0.010 Å ). Both NH functions of each 1,3-DMT are trans to the C S double bond across the respective C-N bond (associated with the hydrogen-bonding pattern, see below), so that the methyl groups are cis, with C methyl -N-C S torsion angles are close to zero [C11-N1-C1-S1 = 0.9 (2) and S2-C2-N2-C21 = À2.05 (17) ]. Free 1,3-DMT crystallizes with four independent molecules, each of which has one NH group cis and one trans to C S, but the structure is severely disordered (Jones et al., 2013).

Supramolecular features
The packing is based on bis(piperidinium) sulfate ribbons parallel to the c axis in the region x, y ' 1/2 ( Fig. 2) and also at x, y ' 0, etc.; the cations are hydrogen bonded to the sulfate by N-HÁ Á ÁO interactions, as expected, but also by a short interaction C15-H15AÁ Á ÁO2 (Table 1). Each pair of successive sulfate ions in the ribbon is bridged by two piperidinium cations. The 1,3-DMT molecules are also hydrogen bonded to sulfate oxygens (Figs. 1 and 3); each 1,3-DMT bridges two oxygens of the same anion and projects outwards from the ribbons parallel to the b axis. In the presence of the sulfate oxygen atoms as strong hydrogen-bond acceptors, the 1,3-DMT sulfur atoms do not accept any classical hydrogen bonds.

Figure 3
Packing diagram of the title compound: attachment of the thiourea molecules to the bis(piperidinium) sulfate chain, viewed perpendicular to the bc plane. Dashed lines represent hydrogen bonds. Methylene hydrogen atoms are omitted for clarity.

Figure 1
The structure of the title compound in the crystal. Only the asymmetric unit is labelled. Displacement ellipsoids represent 50% probability levels.
The dashed lines represent hydrogen bonds.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. The asymmetric unit was chosen such that the occupied twofold axis is 1 2 , y, 1 4 . The NH hydrogen atoms were refined freely. The H atoms of the methyl groups were identified in a difference synthesis, idealized and refined as rigid groups allowed to rotate but not tip (C-H 0.98 Å , H-C-H 109.5 ). Methylene H atoms were included using a riding model starting from calculated positions (C-H 0.99 Å ).   (Agilent, 2014); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: XP (Sheldrick, 2008); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008).

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 > 2sigma(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.