4-[Bis(4-fluorophenyl)methyl]piperazin-1-ium 2-(2-phenylethyl)benzoate

The asymmetric unit of the title salt, C17H19F2N2 +.C15H13O2 −, derived from a 1,4-diazacyclohexane derivative and a carboxylic acid, contains two formula units. The cation is protonated at the secondary amine functionality. The six-membered heterocycles adopt chair conformations. The fluorophenyl rings in the two cations make dihedral angles of 77.21 (19) and 78.8 (2)° while the aromatic rings in the anions enclose angles of 69.5 (2) and 69.9 (2)°. In the crystal, classical N—H⋯O hydrogen bonds as well as C—H⋯F and C—H⋯O contacts connect the entities into layers parallel to ac.

In both cations present in the asymmetric unit protonation occurred on the secondary amine functionality. According to a conformational analysis (Cremer & Pople, 1975), both diazacyclohexane moieties adopt a 4 C 1 chair conformation.
In the crystal, classical hydrogen bonds as well as C-H···F contacts and C-H···O contacts whose range falls by more than 0.1 Å below the sum of van-der-Waals radii of the atoms participating are observed. The classical hydrogen bonds are apparent between the protonated amine functionality and both oxygen atoms of the carboxylic acid and give rise to the formation of cyclic patterns involving both symmetry-independent cations and anions of the asymmetric unit. While the C-H···F contacts exclusively involve hydrogen atoms in ortho-position to the fluorine atoms on the para-fluorophenyl moieties and connect only one of the cations with its symmetry-generated equivalents, the C-H···O contacts appear between hydrogen atoms of the methylene groups in the carboxylates and "dimerize" the two independent anions present in the asymmetric unit. In terms of graph-set analysis (Etter et al., 1990;Bernstein et al., 1995), the descriptor for the classical hydrogen bonds is DDDD on the unitary level while a R 4 4 (12) descriptor on the quartenary level emphasizes the presence of the cyclic patterns illustrated in Figure 2. For the C-H···F contacts, a C 1 1 (10)C 1 1 (10) descriptor on the unitary level shows the presence of two homodromic chains as depicted in Figure 3 while a R 2 2 (12) descriptor on the binary level is indicative for the cyclization of the two anions present in the asymmetric unit on grounds of C-H···O contacts (Fig. 4). In total, the entities of the title compound are connected to planes parallel to ac. The shortest intercentroid distance between two centers of gravity was found at 4.615 (3) Å.
The packing of the title compound in the crystal is shown in Figure 5. was also dissolved in 10 ml of methanol. Both the solutions were mixed and stirred in a beaker at 333 K for 60 minutes.
The mixture was kept aside for a day at room temperature. The salt formed was filtered & dried in vaccum desiccator over phosphorous pentoxide. X-ray quality crystals of the title compound were obtained from ethanol by slow evaporation.

Refinement
Carbon-bound H atoms were placed in calculated positions (C-H 0.95 Å for aromatic carbon atoms, C-H 0.99 Å for methylene groups and C-H 1.00 Å for methine groups) and were included in the refinement in the riding model approximation, with U(H) set to 1.2U eq (C). All nitrogen-bound H atoms were located on a difference Fourier map and refined freely. A search for higher or missed symmetry by means of PLATON (Spek, 2009) revealed the presence of a local center of symmetry which is not compatible with the reported space-group symmetry nor with another space group. Fig. 1. The molecular structure of the title compound, with atom labels and anisotropic displacement ellipsoids (drawn at 50% probability level).