(E)-2-[2-(4-Carboxyphenyl)ethenyl]-8-hydroxyquinolin-1-ium chloride ethanol monosolvate

In the title compound, C18H14NO3 +·Cl−·CH3CH2OH, the dihedral angle formed by the mean planes of the quinolinium and benzene rings is 3.4 (1)°, while the carboxy substituent is tilted at an angle of 4.8 (1)° with respect to the benzene ring. There is a short N—H⋯O contact in the cation. In the crystal, due to the planar molecular geometry, two-dimensional aggregates are formed parallel to (221) via C—H⋯O, C—H⋯Cl, O—H⋯Cl and N—H⋯Cl hydrogen bonds. Interlayer association is accomplished by O—Hethanol⋯Cl and O—H⋯Oethanol hydrogen bonds and π–π stacking interactions [centroid–centroid distances vary from 3.6477 (12) to 3.8381 (11) Å]. A supramolecular three-dimensional architecture results from a stacked arrangement of layers comprising the ionic and hydrogen-bonded components.

In the title compound, C 18 H 14 NO 3 + ÁCl À ÁCH 3 CH 2 OH, the dihedral angle formed by the mean planes of the quinolinium and benzene rings is 3.4 (1) , while the carboxy substituent is tilted at an angle of 4.8 (1) with respect to the benzene ring. There is a short N-HÁ Á ÁO contact in the cation. In the crystal, due to the planar molecular geometry, two-dimensional aggregates are formed parallel to (221) via C-HÁ Á ÁO, C-HÁ Á ÁCl, O-HÁ Á ÁCl and N-HÁ Á ÁCl hydrogen bonds. Interlayer association is accomplished by O-H ethanol Á Á ÁCl and O-HÁ Á ÁO ethanol hydrogen bonds andstacking interactions [centroid-centroid distances vary from 3.6477 (12) to 3.8381 (11) Å ]. A supramolecular three-dimensional architecture results from a stacked arrangement of layers comprising the ionic and hydrogen-bonded components.

Comment
Bifunctional organic ligands have proven very efficient building units in the construction of metal-organic frameworks (MOFs) (MacGillivray, 2010). In particular, one may expect new MOF-architectures from ligands comprising two different coordination sites (Noro et al., 2010). Due to the well known complexation properties of quinolin-8-ol (Albrecht et al., 2008;Weber & Vögtle, 1975) and taking into account the commonly noted coordination behaviour of carboxylic acid groups to various metal ions (Kitagawa et al., 2004;Böhle et al., 2011), corresponding ligands featuring both these structural elements are rated high in this connection. Preparation of a respective hetero bifunctional ligand led to the formation of the title compound. This was isolated as crystals which were found to be a hydrochloride salt containing included ethanol.
In the structure of the title compound ( Fig. 1), the principal molecule has an E configuration with reference to the ethenyl bond, C10═C11. The overall geometry of this molecule shows approximate planarity with the largest atomic distance from the mean plane of the quinolinium moiety (N1/C1-C9) being -0.018 (1) Å for C8 and 0.011 (2) Å for C9, whereas the phenyl ring (C12-C17 ) is perfectly planar. The dihedral angle between the mean planes of these aromatic building blocks is 3.4 (1) °, while the carboxy substituent (C18/O2/O3) is inclined at an angle of 4.8 (4) ° referring to the phenyl ring. The bond distances within the quinolinium moiety are within expected values (Tan, 2007;Zinczuk et al., 2008).

Experimental
The title compound was synthesized via Knoevenagel type condensation (Yuan et al., 2012) using 8-hydroxyquinaldine (320 mg, 2.0 mmol) and 4-formylbenzoic acid (1.20 g, 8.0 mmol) in acetic anhydride (100 ml). The mixture was stirred for 30 h under reflux. After removal of the solvent, the residue was dissolved in 100 ml of pyridine/water (v/v = 4:1) and heated at 373 K for 1 h. Evaporation of the solvent under vacuum and purification of the crude product by recrystallization from ethanol and treatment with hydrochloric acid (37%) yielded 370 mg (63%) of the title compound as brown crystals. The E configuration of the compound was confirmed by 1 H NMR analysis (ethenylene protons); M. p. = 514 K.; MS (ESI) m/z: found 292.0 [M+H]+; calc. for C 18 H 18 NO 3 291.09. Spectroscopic data, including IR and 1 H and 13 C NMR, for the title compound are available in the archived CIF.

Figure 1
A view of the molecular structure of the title compound, with atom labelling. Displacement ellipsoids are drawn at the 50% probability level. Hydrogen bonds are shown as dashed lines (see Table 1 for details).  A partial view of the crystal packing of the title compound. Hydrogen bonds are shown as dashed lines within the layer motif (see Table 1 for details).  110.9, 117.4, 120.9, 126.9, 127.1, 127.7, 129.2, 129.8, 130.1, 130.4, 133.1, 136.4, 140.6, 152.8, 152.9, 167.0. 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.