Dicyclohexylammonium 2-methoxybenzoate

The asymmetric unit of the title compound, C12H24N+·C8H7O3 −, contains one dicyclohexylammonium cation and one 2-methoxybenzoate anion. Two cations and two anions are linked together to form a four-ion cluster through a set of N—H⋯O hydrogen bonds. Weak C—H⋯O hydrogen bonds connect the clusters into chains that are stacked along the crystallographic c axis.

, contains one dicyclohexylammonium cation and one 2-methoxybenzoate anion. Two cations and two anions are linked together to form a four-ion cluster through a set of N-HÁ Á ÁO hydrogen bonds. Weak C-HÁ Á ÁO hydrogen bonds connect the clusters into chains that are stacked along the crystallographic c axis.
Financial support by the Ministry of Science, Education and Sport of the Republic of Croatia is gratefully acknowledged (grant Nos. 098-0982914-2935 and 119-1193079-1084).

Comment
The title compound was synthesized as a model for the purposes of a workshop on parallel synthesis and combinatorial chemistry. The compound was selected because of its resemblance to dicyclohexylammonium salts of substituted cinnamic acids, that are widely known as gelators of organic fluids (Ballabh et al., 2005;Trivedi et al., 2005, Trivedi et al., 2004. The molecular structure of the title compound is shown in Fig. 1. The asymmetric unit consist of a dicyclohexylammonium cation and a 2-methoxybenzoate anion. The carboxylate group of the anion is twisted with respect to the parent benzene ring by 65.1 (2)°. All bond lengths fall within normal ranges (Allen et al., 1987). Two cations and two anions self-assemble into a tetrameric structural unit by two hydrogen bonds; N1-H2···O1 and N1-H1···O2 i (Fig. 2 Weak C20-H20···O1 ii hydrogen bonds (Fig. 3, Table 1) link these tetrameric units into chains that are stacked together in a zipper-like manner, so as to produce narrow channels between them (Fig. 4a). The appearance of the channels is consistent with the relatively low calculated density of the title compound (1.14 g cm -3 ).
The zipper-like stacking is achieved by the interdigitation of protruding benzene groups in each chain ( Fig. 4 b), thus maximizing the intermolecular contacts.

Experimental
A solution of dicyclohexylamine (363 mg, 2.00 mmol) in toluene (5 ml) was added with stirring to a solution of 2-methoxybenzoic acid (304 mg, 2.00 mmol) in toluene (5 ml). The resulting solution was allowed to stand in an open beaker for several days until crystals of the title compound formed by slow solvent evaporation. The crystals were suitable for single-crystal X-ray diffraction. The compound was also analyzed by thermal methods (TG and DSC). Thermal analyses were performed on METTLER thermal analysis modules DSC823 e and TGA/SDTA851 e . The calorimetric thermogram exhibited one endothermic signal that was sharp and well defined, corresponding to the melting point of the compound. The onset temperature of the signal is T f = 416 K with enthalpy of fusion, ΔH fus = 37,9 kJ mol -1 . Degradation of the sample begins above 524 K.

Refinement
Carbon-bound H atoms were placed in calculated positions and included in the refinement using the riding-model approximation, with C-H distances of 0.93 Å for phenyl, 0.97 Å for methylene, 0.98 Å for methine and 0.96 Å for methyl groups, and with U iso (H) = 1.2U eq (C) or 1.2U eq (C methyl ). A rotating group model was used for the methyl groups. The hydrogen atoms of the amine group were located in the final Fourier difference map and their coordinates were blocked during the refinement process. Fig. 1. The molecular structure of the title compound, showing the atomic numbering scheme. Displacement ellipsoids are drawn at the 30% probability level and H atoms are shown as small spheres of arbitrary radius.