Crystal structure of 1,2,3,4-tetrahydroisoquinolin-2-ium (2S,3S)-3-carboxy-2,3-dihydroxypropanoate monohydrate

The crystal structure of 1,2,3,4-tetrahydroisoquinolin-2-ium (2S,3S)-3-carboxy-2,3- dihydroxypropanoate monohydrate (orthorhombic crystal system, space group P212121, Z = 4) features an intricate two-dimensional hydrogen-bond network.


Supramolecular features
The solid state supramolecular structure features an intricate network of N-H� � �O and O-H� � �O hydrogen bonds (Fig. 2).Table 1 lists the corresponding geometric parameters, which are within expected ranges (Thakuria et al., 2017).The hydrogen tartrate anions form hydrogen-bonded chains by translational symmetry in the b-axis direction through hydrogen bonding between the carboxy group and the carboxylate group of an adjacent molecule (O5-H5A� � �O1 iii ).In the a-axis direction, the hydrogen tartrate ions are connected along a 2 1 screw axis via two hydrogen bonds with the two hydroxy groups as donors and a hydroxy group (O3-H3� � �O4 ii ) and the carboxylate group (O4-H4� � �O2 ii ) of a neighbouring molecule as acceptors.These O-H� � �O hydrogen-bonding interactions that extend in the a-and b-axis directions result in diperiodic hydrogenbonded sheets parallel to (001).The protonated amino group of the tetrahydroisoquinolinium cation forms a bifurcated hydrogen bond to the carboxy groups of two adjacent hydrogen tartrate anions (N2-H2B� � �O5 and N2-H2B� � �O6 i ) and another hydrogen bond to the solvent water molecule (N2-H2A� � �O7).The water molecule in turn acts as a hydrogen-bond donor towards the carboxylate group Table 1 Hydrogen-bond geometry (A ˚, � ).

Figure 3
Space-filling representation of the crystal structure, viewed along the aaxis direction.Colour scheme: C, grey; H, white; N, blue; O, red.

Figure 1
The asymmetric unit of the title compound with displacement ellipsoids at the 50% probability level.Hydrogen atoms are presented by small spheres of arbitrary radius.Dashed lines illustrate hydrogen bonds.
(O7-HA� � �O2) and a hydroxy group (O7-HB� � �O3 iv ) of two hydrogen tartrate anions.The hydrocarbon parts of the tetrahydroisoquinolinium cations are oriented approximately perpendicular to the diperiodic hydrogen-bonded sheets formed by the hydrogen tartrate anions.The crystal packing in the third dimension is achieved by stacking in the c-axis direction with interlocking of the hydrocarbon tails through van der Waals packing (Fig. 3).This affords hydrophobic and hydrophilic regions in the crystal structure.

Synthesis and crystallization
Starting materials were obtained from commercial sources and used as received.A mixture of 1,2,3,4-tetrahydroisoquinoline (266 mg, 2 mmol) and excess (2S,3S)-tartaric acid (1.50 g, 10 mmol) in 60 mL of deionized water was stirred for four h at room temperature.Subsequently, the salt was isolated by filtration.Colourless crystals suitable for single-crystal X-ray diffraction were obtained from a water/methanol (3:1) solution of the salt, after the solvents were allowed to evaporate slowly at ambient conditions.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. Carbon-bound hydrogen atoms were placed in geometrically calculated positions and refined using the appropriate riding model with C-H aromatic = 0.95 A ˚, C-H methylene = 0.99 A ˚, C-H methine = 1.00A ˚and U iso (H) = 1.2 U eq (C).Nitrogen-and oxygen-bound hydrogen atoms were located in difference-Fourier maps and subsequently refined semi-freely with the N-H and the O-H distances restrained to target values of 0.88 (2) A ˚and 0.84 (2) A ˚, respectively.The absolute structure was inferred from the known absolute configuration of the starting material.

Special details
Geometry.All esds (except the esd in the dihedral angle between two l.s.planes) are estimated using the full covariance matrix.The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry.An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s.planes.
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )

Table 2
Experimental details.