dl-Tyrosinium chloride dihydrate

In the title compound, C9H12NO3 +·Cl−·2H2O, the cation has a protonated amino group resulting from proton transfer from chloridric acid. The structure displays double layers parallel to the [010] direction held together by N—H⋯O, N—H⋯Cl, O—H⋯O and O—H⋯Cl hydrogen bonds. These layers are stacked along the c axis at b = 1/2; within each layer, the tyrosinium cations are arranged in an alternating head-to-tail sequence, forming inversion dimers [R 2 2(10) motif]. The water molecules allow for the construction of a three-dimensional hydrogen-bonded network formed by centrosymmetric R 6 6(28) and R 8 8(34) motifs.

In the title compound, C 9 H 12 NO 3 + ÁCl À Á2H 2 O, the cation has a protonated amino group resulting from proton transfer from chloridric acid. The structure displays double layers parallel to the [010] direction held together by N-HÁ Á ÁO, N-HÁ Á ÁCl, O-HÁ Á ÁO and O-HÁ Á ÁCl hydrogen bonds. These layers are stacked along the c axis at b = 1 2 ; within each layer, the tyrosinium cations are arranged in an alternating head-to-tail sequence, forming inversion dimers [R 2 2 (10) motif]. The water molecules allow for the construction of a three-dimensional hydrogen-bonded network formed by centrosymmetric R 6 6 (28) and R 8 8 (34) motifs.
Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: NK2187). We report the crystal structure of DL-tyrosinium chloride dihydrate (I), as part of our research with organic salts of amino acids (Zeghouan et al., 2012;Guenifa et al., 2009).
The asymmetric unit of (I) contains a tyrosinium cation, chloride anion and two water molecules (Fig.1). As expected, tyrosine form protonated units in (I) with the transfer of an H atom from chloridric acid. A similar situation is observed in bis(L-tyrosinium) sulfate monohydrate, (Sridhar et al., 2002).

N-H···Cl, O-H···O and O-H···Cl hydrogen bonds
The water molecules, which plays a dual role as both donor and acceptor in hydrogen bonding interactions, generating the centrosymmetric hydrogen-bonded (R 2 4 (8) motif) via O2w-H21w···O1w (i) and O2w-H22w···O1w (vi) (Fig. 3), and are involved in two centred hydrogen bonding with the cations to produce a centrosymmetric R 6 6 (28) and R 8 8 (34) motifs, thus completing the three-dimensional hydrogen-bonded network. The structures of many amino acids with non-polar side chains have the arrangement of a double layers of carboxyl and amino groups held together by hydrogen bonds (Torii & Iitaka, 1973;Harding & Long, 1968).
The molecule packing of (I), consists of double layers stacked along the c axis, at b = 1/2, where in each layer the tyrosinium cations are arranged with alternating head-to-tail sequence.

Experimental
The compound was obtained as colourless crystals with melting points of 370°, after few days, by slow evaporation from an aqueous solution of tyrosine and chloridric acid in stoechiometric ratio of 1:1.

Refinement
The methine, methylene, and aromatic H atoms were placed at calculated positions respectively with C-H fixed at 0.98 Å (AFIX 13), 0.97 Å (AFIX 23), and C-H = 0.93 Å (Afix 43). All H atom attached to N or O were initially located by difference maps with restraint of the N-H bond length to 0.90 (2) Å (DFIX), and U fixed to be 1.2 times that of the N1; and O-H bond length to 0.85 (2) Å (DFIX) for hydroxyl group and 0.85 (1) Å (DFIX) for water molecule with H···H = 1.39 (2) and U fixed to be 1.5 times that of the o1, O2, o1w and o2w.

Figure 1
The asymmetric unit of (I) (Fig.1)   Special details Geometry. Bond distances, angles etc. have been calculated using the rounded fractional coordinates. All su's are estimated from the variances of the (full) variance-covariance matrix. The cell e.s.d.'s are taken into account in the estimation of distances, angles and torsion angles 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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq Cl1 0.26233 (