(R)-1-Phenyl-ethanaminium (S)-4-chloro-mandelate.

The absolute configuration of the title complex, C(8)H(12)N(+)·C(8)H(6)ClO(3) (-) or [R-C(6)H(5)C(H)CH(3)NH(3)][S-4-ClC(6)H(4)C(H)(OH)CO(2)], has been confirmed by the structure determination. In the crystal structure, inter-molecular O-H⋯O and N-H⋯O hydrogen bonds form a two-dimensional network perpendicular to the c axis.


Comment
In our previous work, phenylethylamine (PEA) has been proven to be an efficient resolving agent for resolution of racemic 4-chloromandelic acid. In order to further investigate the chiral recognition mechanism, the single-crystal structure of the corresponding more soluble salt, (R)-Phenylethylammonium (S)-4-chloromandelate, is reported here for comparison with that of the less soluble salt (R)-Phenylethylammonium (R)-4-chloromandelate (He et al., 2007).
The title complex consists of an ion pair; an amine cation and a carboxylate anion (see Fig. 1). The absolute stereochemistry of each ion has been confirmed by the structure determination [absolute structure parameter −0.03 (8); (Flack, 1983)].

All three H atoms of the -NH 3 group and the H atom of the O-H group act as hydrogen bond donors in intermolecular
O-H···O and N-H···O hydrogen bonds, forming a two-dimensional network perpendicular to the c axis. The hydrogen bond motif in the title compound is different to that observed in the room temperature structure of the R,R diastereomer (He et al., 2007).

Experimental
To a solution (S)-4-chloromandelate (2.0 g, 0.01 mol) in 10 ml 2-propanol, (1.3 mL, 0.01 mol), (R)-Phenylethylammonium, was added gradually. A white crystalline solid appeared. The crystals were collected and washed with 2-propanol twice to give the title compound (1.85 g), yield 56%. Single crystals were grown from a concentrated methanol solution of the title compound by slow evaporation at room temperature.

Refinement
All H atoms were positioned geometrically and constrained as riding atoms with; C-H = 1.00Å and U iso (H) = 1.2U eq (C) for methyne H atoms, C-H = 0.98Å and U iso (H) = 1.5U eq (C) for methyl H atoms, C-H = 0.95Å and U iso (H) = 1.2U eq (C) for aromatic H atoms, O-H = 0.84Å and U iso (H) = 1.5U eq (C) for hydroxyl H atoms and N-H = 0.91Å and U iso (H) = 1.5U eq (C) for amine H atoms. Fig. 1. The molecular structure of the title compound with 30% probability displacement ellipsoids and the atom labelling scheme.  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.