(S)-(−)-1-Phenylethanaminium hexanoate

A binary mixture of (S)-(−)-1-phenylethanamine and hexanoic acid was allowed to react to form the title salt, C8H12N+·C6H11O2 −. This crystal contains a 1:1 stoichiometric mixture of the acid- and amine-derived species and displays a chiral structure with N—H⋯O hydrogen-bonded chains propagating along the c-axis direction.

A binary mixture of (S)-(À)-1-phenylethanamine and hexanoic acid was allowed to react to form the title salt, C 8 H 12 N + ÁC 6 H 11 O 2 À . This crystal contains a 1:1 stoichiometric mixture of the acid-and amine-derived species and displays a chiral structure with N-HÁ Á ÁO hydrogen-bonded chains propagating along the c-axis direction.   Table 1 Hydrogen-bond geometry (Å , ).  The existence of stable acid:amine complexes formed from simple acid and amine reagents has been reported in the literature (Klokkenburg et al., 2007;Karlsson et al., 2000). Many examples adopt a 1:1 stoichiometry, although acid-rich complexes are not uncommon, with both 2:1 and 3:1 adducts observed in some cases (Sun et al., 2011;Kohler et al., 1981). Amine-rich complexes are thought to be inherently instable and thus unlikely to form (Paivarinta et al., 2000), although there is a report of a diamine complex formed between methylamine and dnsa (3,5-dinitrosalicyclic acid) due to deprotonation of the phenolic group in the acid (Smith et al., 2001;Smith et al., 2002).

Related literature
The stability of complexes such as the title compound derives from the reactive exchange of a proton giving cations and anions with a strong electrostatic attraction. These ions subsequently interact via strong hydrogen-bond formation; each ammonium ion in the s-(-)-α-methylbenzylammonium hexanoate example is able to form three hydrogen bonds (shown in This work focuses on the use of a chiral amine, s-(-)-α-methylbenzylamine.
Whilst spectroscopic studies identifying such acid:amine complexes are reasonably common, there still only a few examples of single-crystal X-ray data, as reported here. This may be attributed to the difficulty of growing suitable crystals as outlined in the experimental section.

Experimental
Hexanoic acid and s-(-)-methylbenzylamine, with purities of 99.5% and 99.8% respectively as determined by titration and GC, were purchased from Sigma Aldrich and used without further purification. The crystals were grown by pipetting a small volume (approximately 1 ml) of each into small vials and leaving within a larger vial along with a polypropylene nucleation surface under an inert atmosphere (to minimize amine reaction with atmospheric CO 2 (Sun et al., 2011)). After several weeks abundant crystal growth on the polypropylene surface was observed and a sample selected for X-ray characterization.
The experimental sample temperature 180 K represents a compromise of improved thermal factors but avoiding sample fracture.

Refinement
The absolute structure was assigned from the known configuration of the starting material. 1183 Friedel pairs were averaged for the refinement.
Hydrogen site location were inferred from neighbouring sites and H-atom parameters were constrained in the refinement.    where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.11 e Å −3 Δρ min = −0.14 e Å −3 Special details Experimental. multi-scan from symmetry-related measurements Sortav (Blessing, 1995) Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s 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 > σ(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.