Dicyclohexylammonium thiocyanate: monoclinic polymorph

The title salt, C12H24N+·NCS−, represents a monoclinic polymorph of the previously reported orthorhombic form [Khawar Rauf et al. (2008 ▶). Acta Cryst. E64, o366]. Two independent formula units comprise the asymmetric unit with the major difference in their molecular structures relating to the relative dispositions of the cyclohexyl rings [dihedral angles = 79.88 (6) and 67.72 (5)°]. Further, the independent anions form distinctive patterns of hydrogen-bonding interactions, i.e. 2 × N—H⋯N versus N—H⋯N and N—H⋯S. The resulting supramolecular architecture is a supramolecular chain along the c axis based on a square-wave topology.

The title salt, C 12 H 24 N + ÁNCS À , represents a monoclinic polymorph of the previously reported orthorhombic form [Khawar Rauf et al. (2008). Acta Cryst. E64, o366]. Two independent formula units comprise the asymmetric unit with the major difference in their molecular structures relating to the relative dispositions of the cyclohexyl rings [dihedral angles = 79.88 (6) and 67.72 (5) ]. Further, the independent anions form distinctive patterns of hydrogen-bonding interactions, i.e. 2 Â N-HÁ Á ÁN versus N-HÁ Á ÁN and N-HÁ Á ÁS. The resulting supramolecular architecture is a supramolecular chain along the c axis based on a square-wave topology.

Comment
The crystal structure of the title salt (I) represents a monoclinic form of the previously reported (at 123 K) orthorhombic form (Khawar Rauf et al., 2008). In the latter, one formula unit comprises the asymmetric unit whereas two independent formula units comprise the asymmetric unit in (I), Fig. 1. The differences in the structure of (I) relate to a minor variation in the orientation of the cyclohexyl groups, Fig. 2, and in the nature of the intermolecular interactions they form, see below.
In terms of molecular structure, each cyclohexyl ring has a chair conformation and the r.m.s. differences for the cations are 0.0026 Å for distances and 0.530° for angles (Spek, 2009). The different orientations are probably best described by the dihedral angles formed between the least-squares planes through the pairs of rings, i.e. 79.88 (6) and 67.72 (5)°, for the N1-and N2-cations, respectively.
In terms of crystal packing, the N1-cation forms N-H···N hydrogen bonds exclusively whereas the N2-cation forms a N-H···N and a N-H···S hydrogen bond, Table 1. The result of the hydrogen bonding is the formation of a supramolecular chain with a square-wave topology along the c axis. The N1-cation bridges two N2-cations via N-H···N hydrogen bonds and the N2-cation bridges two N1-cations via the N and S atoms, Fig. 3. Chains assemble into layers in the ac plane which stack along the b axis, Fig. 4. In the orthorhombic polymorph, the thiocyanate anion bridges two cations via the N and S atoms to form a supramolecular chain.

Experimental
The title compound was obtained as an unexpected product from a reaction mixture containing dicyclohexylamine, isopthaloyl dichloride and potassium thiocyanate in acetone under reflux conditions. Crystals were grown from a solution of the compound in ethylacetate / petroleum ether (1:3).

Refinement
The H-atoms were placed in calculated positions (C-H 0.99 to 1.00 Å) and were included in the refinement in the riding model approximation, with U iso (H) set to 1.2U equiv (C). The ammonium-H atoms were refined without restraint.    as those based on F, and R-factors based on ALL data will be even larger.