Received 12 June 2013
The title hydrated salt, C6H6NO2+·C10H5O8-·H2O, was isolated from the 1:1 cocrystallization of benzene-1,2,4,5-tetracarboxylic acid and isonicotinic acid in ethanol solution. In the crystal, the cation is close to planar [r.m.s. deviation = 0.085 Å for the nine fitted atoms; the C-C-C-O(carbonyl) torsion angle = -8.7 (4)°], but twists are evident in the anion, with all but the carboxylic acid group diagonally opposite the carboxylate group being significantly twisted out of the plane of the benzene ring [C-C-C-O(carbonyl) torsion angles = -118.1 (2), -157.6 (2), 4.3 (3) and 77.3 (3)°]. In the crystal, the ions and water molecules are consolidated into a three-dimensional architecture by O-HO and N-HO hydrogen bonding along with C-HO interactions.
For background to pharmaceutical co-crystals, see: Almarsson & Zaworotko (2004). For related co-crystallization studies on 1,2,4,5-benzenetetracarboxylic acid, see: Arman & Tiekink (2013a,b). For the structure of isonicotinic acid, see: Takusagawa & Shimada (1976). For the structure of the analogous salt formed from nicotinic acid, see: Dos Santos et al. (2012). For the calculation of pKa values, see: Chemaxon (2009).
Data collection: CrystalClear (Molecular Structure Corporation & Rigaku, 2005); cell refinement: CrystalClear; data reduction: CrystalClear; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 for Windows (Farrugia, 2012) and DIAMOND (Brandenburg, 2006); software used to prepare material for publication: publCIF (Westrip, 2010).
Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: HB7093 ).
We gratefully thank the Ministry of Higher Education (Malaysia) for funding structural studies through the High-Impact Research scheme (UM.C/HIR-MOHE/SC/12).
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