Crystal structure of hexaaquanickel(II) bis{5-bromo-7-[(2-hydroxyethyl)amino]-1-methyl-6-oxidoquinolin-1-ium-3-sulfonate} monohydrate

The packing of the title compound is built up by columns of π–π stacking quinoline derivatives running along the c axis, which are interconnected by [Ni(H2O)6]2+ complex cations through hydrogen bonding.


Chemical context
Among heterocyclic rings, the quinoline ring system is of great importance due to its therapeutic and biological activities. Many new quinoline derivatives have been synthesized and used as new potential agents to treat HIV (Cecchetti et al., 2000;Tabarrini et al., 2008) and malaria (Nayyar et al., 2006) or to inhibit human tumor cell growth (Rashad et al., 2010). Recently, a simple aminoquinoline derivative has been used in colorimetric sensors for pH (Wang et al., 2014). In addition, complexes of quinoline compounds with transition metals are also known to exhibit a wide variety of structures and possess profound biochemical activities which allow them to act as antimicrobial, anti-Alzheimer's (Deraeve et al., 2008) or antitumoral agents (Yan et al., 2012;Kitanovic et al., 2014). Some complexes of polysubstituted quinoline compounds have also been used in dye-sensitized solar cells or in efficient organic heterojunction solar cells .
The new quinoline derivative (6-hydroxy-3-sulfoquinolin-7yloxy)acetic acid (Q) was synthesized from eugenol and its antibacterial activities have been reported (Dinh et al., 2012). From Q, a series of polysubstituted quinoline compounds has ISSN 2056-9890 been synthesized, including 5-bromo-6-hydroxy-7-[(2-hydroxyethyl)amino]-1-methyl-3-sulfoquinoline (QAO). As polysubstituted quinoline rings are known to coordinate to metal ions, the reaction between QAO and NiCl 2 was studied. The reaction product could not be characterized unambiguously by IR or 1 H NMR spectroscopy. Although the obtained spectroscopic data are different from those of free QAO, indicating the presence of a deprotonated hydroxyl group, no conclusion about complex formation was possible and further investigation by X-ray diffraction was necessary.
A solution containing NiCl 2 Á6H 2 O (262 mg, 1.1 mmol) in 10 mL water was added dropwise to 15 mL aqueous solution of QAO (754 mg, 2 mmol) and NH 3 (pH ' 6-7). The obtained solution was stirred and refluxed at 313-323 K for three h. The brown precipitate was collected by filtration, washed consecutively with ethanol and dried in vacuo. The obtained crystals were soluble in water and DMSO, but insoluble in ethanol, acetone and chloroform. The yield was 60%. Single crystals suitable for X-ray investigation were obtained by slow evaporation from a ethanol-water (1:2 v/v) solution at room temperature.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. H atoms for N18, O21, O23, O24, O25 and O26 were located in difference Fourier maps. The coordinates of H21 and H26 were refined freely, while the other H atoms were refined as riding. All C-bound H atoms were placed at idealized positions and refined as riding, with C-H distances of 0.95 (aromatic), 0.99 (methylene) and 0.98 Å (methyl). For most H atoms, U iso (H) values were assigned as 1.5U eq of the parent atoms (1.2U eq for H2, H4, H10, H18, H19A/B and H20A/B).

Figure 4
Partial packing diagram of the title compound viewed along the a axis, showing the X-HÁ Á ÁO hydrogen bonds (red dotted lines, see Table 1 for details) and C-HÁ Á ÁBr interactions (brown dotted lines). SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL2014 (Sheldrick, 2015); molecular graphics: OLEX2 (Dolomanov et al., 2009); software used to prepare material for publication: OLEX2 (Dolomanov et al., 2009). 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.