Abstract
The asymmetric unit of the title salt, C14H16N4O2 (2+)·2C9H5O6 (-), comprises half a dication, being located about a centre of inversion, and one anion, in a general position. The central C4N2O2 group of atoms in the dication are almost planar (r.m.s. deviation = 0.009 Å), and the carbonyl groups lie in an anti disposition to enable the formation of intra-molecular amide-N-H⋯O(carbon-yl) hydrogen bonds. To a first approximation, the pyridinium and amide N atoms lie to the same side of the mol-ecule [Npy-C-C-Namide torsion angle = 34.8 (2)°], and the anti pyridinium rings are approximately perpendicular to the central part of the mol-ecule [dihedral angle = 68.21 (8)°]. In the anion, one carboxyl-ate group is almost coplanar with the ring to which it is connected [Cben-Cben-Cq-O torsion angle = 2.0 (3)°], whereas the other carboxyl-ate and carb-oxy-lic acid groups are twisted out of the plane [torsion angles = 16.4 (3) and 15.3 (3)°, respectively]. In the crystal, anions assemble into layers parallel to (10-4) via hy-droxy-O-H⋯O(carbon-yl) and charge-assisted hy-droxy-O-H⋯O(carboxyl-ate) hydrogen bonds. The dications are linked into supra-molecular tapes by amide-N-H⋯O(amide) hydrogen bonds, and thread through the voids in the anionic layers, being connected by charge-assisted pyridinium-N-O(carboxyl-ate) hydrogen bonds, so that a three-dimensional architecture ensues. An analysis of the Hirshfeld surface points to the importance of O-H⋯O hydrogen bonding in the crystal structure.
Highlights
The asymmetric unit of the title salt, C14H16N4O22+Á2C9H5O6À, comprises half a dication, being located about a centre of inversion, and one anion, in a general position
The central C4N2O2 group of atoms in the dication are almost planar (r.m.s. deviation = 0.009 A ), and the carbonyl groups lie in an anti disposition to enable the formation of intramolecular amide-N—HÁ Á ÁO(carbonyl) hydrogen bonds
The pyridinium and amide N atoms lie to the same side of the molecule [Npy—C—C—Namide torsion angle = 34.8 (2)], and the anti pyridinium rings are approximately perpendicular to the central part of the molecule [dihedral angle = 68.21 (8)]
Summary
The n = 3 and 4 molecules have attracted interest from the crystal engineering community in terms of their ability to form co-crystals with iodocontaining species leading to aggregates featuring NÁ Á ÁI halogen bonding (Goroff et al, 2005; Jin et al, 2013) as well as carboxylic acids (Nguyen et al, 2001) It is the latter that has formed the focus of our interest in co-crystallization experiments of these molecules which has led to the characterization of both co-crystals (Arman, Kaulgud et al, 2012; Arman, Miller et al, 2012) and salts (Arman et al, 2013). The C—N—C angle in the pyridyl ring has expanded by over 3 cf that found in the only neutral form of N,N0-bis(pyridin-2-ylmethyl)ethanediamide characterized crystallographically in an all-organic molecule, i.e. in a 1:2 cocrystal with 2-aminobenzoic acid (Arman, Miller et al, 2012), Table 1. All groups are twisted out of the leastsquares plane through the benzene ring but, in the second anion, the carboxylate group is effectively co-planar with the
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