l-Leucinium fluoride monohydrate

The asymmetric unit of the title hydrated salt, C6H14NO2 +·F−·H2O, contains a discrete cation with a protonated amino group, a halide anion and one water molecule. The crystal structure is composed of double layers parallel to (010) held together by N—H⋯O, N—H⋯F, O—H⋯F and C—H⋯F hydrogen bonds, forming a two-dimensional network, and stacked along the c axis, viz. hydrophilic layers at z = 0 and 1/2 and hydrophobic layers at z = 1/3 and 2/3.

The asymmetric unit of the title hydrated salt, C 6 H 14 NO 2 + Á-F À ÁH 2 O, contains a discrete cation with a protonated amino group, a halide anion and one water molecule. The crystal structure is composed of double layers parallel to (010) held together by N-HÁ Á ÁO, N-HÁ Á ÁF, O-HÁ Á ÁF and C-HÁ Á ÁF hydrogen bonds, forming a two-dimensional network, and stacked along the c axis, viz. hydrophilic layers at z = 0 and 1/2 and hydrophobic layers at z = 1/3 and 2/3.
Technical support (X-ray measurements at SCDRX) from Université Henry Poincaré, Nancy 1, France, is gratefully acknowledged. Leucine is one of the most important amino acids, essential for the growth and maintenance of living organisms. Simple carboxylic acids, which are believed to have existed in the prebiotic earth (Miller & Orgel, 1974;Kvenvolden et al., 1971), form crystalline complexes with amino acids. The present paper is a part of our research with organic salts of amino acids (Guenifa et al., 2009;Moussa Slimane et al., 2009).
The asymmetric unit of the title compound contains a leucinium cation, fluoride anion and one water molecule ( Fig. 1).
As expected, leucine form the protonated unit with the transfer of an H atom from the inorganic acid. The similar situation is observed in L-leucinium oxalate (Rajagopal et al., 2003) and L-leucinium perchlorate (Janczak & Perpétuo, 2007).
In the supramolecular structure of the title compound, the ions are connected into a two-dimensional hydrogen-bonded network via N-H···O, N-H···F, O-H···F and C-H···F hydrogen bonds (Table 1). The leucinium cations are interlinked by two intermolecular N-H···F and O-H···F hydrogen bonds to form a double layers [C 1 2 (7) motif] (Bernstein et al.,, 1995), (Fig. 2), resulting in an overall one-dimensional hydrogen-bonded network.
In the title compound, the water molecules and floride anions bridges in two-dimensional hydrogen bonded network, forming a non centrosymmetric hydrogen-bonded R 3 5 (13) and R 3 5 (10) motifs, which run into zigzag parallel to the [010] direction (Fig. 3).
The molecular packing of the title compound consists of double layers is stacked along the c axis, viz. hydrophilic layers at z = 0 and 1/2 and hydrophobic layers at z = 1/3 and 2/3. The hydrophilic layers include the head of the leucinium residue (ammonium and carboxylic groups), floride anion and water molecule.

Experimental
The experiment consists of heating an equimolar solution of leucine and hydrofluoric acid acid until the reaction is complete. Colourless crystal with melting points of 618 K were obtained by evaporation of the solution at room temperature over the course of a few days.

Refinement
The H atoms attached to C atoms were placed at calculated positions with C-H fixed at 0.93 -0.98 Å The H atoms attached to N and O were initially located from difference maps and refined with distance restraint for the N-H bond length 0.90 (2) Å and O-H bond length 0.85 (2) Å. The U iso (H) were set to 1.5U eq (C, O) for methyl and amino groups and to 1.2U eq (C, N) for the rest atoms.

Special details
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.