Crystal structures of morpholinium hydrogen bromanilate at 130, 145 and 180 K

Crystal structures of morpholinium hydrogen bromanilate have been determined at 130, 145 and 180 K. The asymmetric unit comprises one morpholinium cation and two halves of crystallographically independent bromanilate monoanions. The conformations of the two independent bromanilate anions are different from each other with respect to the O—H orientation. The two different anions are linked alternately into a chain though a short O—H⋯O hydrogen bond, in which the H atom is disordered over two positions.

, were determined at three temperatures, viz. 130, 145 and 180 K. The asymmetric unit comprises one morpholinium cation and two halves of crystallographically independent bromanilate monoanions, which are located on inversion centres. The conformations of the two independent bromanilate anions are different from each other with respect to the O-H orientation. In the crystal, the two different anions are linked alternately into a chain along [211] through a short O-HÁ Á ÁO hydrogen bond, in which the H atom is disordered over two positions. The refined site-occupancy ratios, which are almost constant in the temperature range studied, are 0.49 (3) (3), respectively, at 130, 145 and 180 K, and no significant difference in the molecular geometry and the molecular packing is observed at the three temperatures. The morpholinium cation links adjacent chains of anions via N-HÁ Á ÁO hydrogen bonds, forming a sheet structure parallel to (111).

Chemical context
Anilic acid (2,5-dihydroxy-1,4-benzoquinone) derivatives, such as chloranilic acid (2,5-dichloro-3,6-dihydroxy-1,4benzoqinone) and bromanilic acid (2,5-dibromo-3,6-dihydroxy-1,4-benzoqinone), appear particularly attractive as a versatile template for generating hydrogen-bonded selfassemblies with various organic bases (Zaman et al., 2001;Molčanov & Kojić-Prodić, 2010;Gotoh & Ishida, 2011;Thomas et al., 2013) and also as a model compound for investigating proton dynamics in hydrogen-bond systems (Ikeda et al., 2005;Seliger et al., 2009). Furthermore, salts and co-crystals of anilic acids with organic bases have attracted much interest with respect to organic ferroelectrics (Horiuchi et al., 2008(Horiuchi et al., , 2009(Horiuchi et al., , 2013. In our previous study, we reported the crystal structure of morpholinium hydrogen chloranilate, C 4 H 10 NO + ÁC 6 HCl 2 O 4 À , in which a short O-HÁ Á ÁO hydrogen bond is formed between the chloranilate ions and the H atom in the hydrogen bond is disordered over two sites (Ishida & Kashino, 1999). The measurements of 35 Cl NQR (nuclear quadrupole resonance) for the compound in the temperature range 4-300 K showed an anomalous temperature dependence of the NQR frequencies, which cannot be explained by the conventional Bayer-type lattice motion: one of the two frequencies exhibits an anomalous increase with increasing temperature from 4.2 K while the other frequency shows a rather fast decrease with temperature. The anomalous behavior was ascribed to a drastic temperature variation of the disordered O-HÁ Á ÁO ISSN 2056-9890 hydrogen bond, as revealed by multi-temperature X-ray diffraction (Tobu et al., 2012). In the present study, we have undertaken the structural determination of morpholinium hydrogen bromanilate, C 4 H 10 NO + ÁC 6 HBr 2 O 4 À , to extend the study of hydrogen-bonding in the amine-halohydroxybenzoquinone system.

Structural commentary
The title compound is isomorphous with morpholinium hydrogen chloranilate in the space group P1 (Ishida & Kashino, 1999;Tobu et al., 2012) and has a quite similar molecular packing to the chloranilate. The asymmetric unit of the title compound comprises one morpholinium cation and two halves of crystallographically independent bromanilate monoanions, which are each located on an inversion centre (Fig. 1). The conformations of two bromanilate anions are different from each other with respect to the O-H orientation as shown schematically in Fig. 2.

Database survey
Although a search of the Cambridge Structural Database (Version 5.36, last update February 2015; Groom & Allen, 2014) for organic salts and co-crystals with bromanilic acid gave 31 hits, no crystal structure including the A form ( Fig. 2) was found.

Synthesis and crystallization
Single crystals of the title compound suitable for X-ray diffraction were prepared by slow evaporation from an acetonitrile solution (200 ml) of bromanilic acid (200 mg) with morpholine (60 mg) at room temperature.

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. Reflections were merged by SHELXL according to the crystal class for the calculation of statistics and refinement.