Crystal structures of 1,4-di-aza-bicyclo-[2.2.2]octan-1-ium 4-nitro-benzoate dihydrate and 1,4-di-aza-bicyclo-[2.2.2]octane-1,4-diium bis-(4-nitro-benzoate): the influence of solvent upon the stoichiometry of the formed salt.

The 1:1 co-crystallization of 1,4-di-aza-bicyclo-[2.2.2]octane (DABCO) with 4-nitro-benzoic acid in ethanol-water (3/1) gave the salt dihydrate C6H13N2 (+)·C7H4NO4 (-)·2H2O, (1), whereas from methanol, the salt C6H14N2 (2+)·2C7H4NO4 (-), (2), was isolated. In (1), the cation and anion are linked by a strong N-H⋯O hydrogen bond, and the carboxyl-ate anion is close to planar [dihedral angle between terminal residues = 6.83 (9)°]. In (2), a three-ion aggregate is assembled by two N-H⋯O hydrogen bonds, and the carboxyl-ate anions are again close to planar [dihedral angles between terminal residues = 1.7 (3) and 5.9 (3)°]. Through the inter-vention of solvent water mol-ecules, which self-assemble into helical supra-molecular chains along the b axis, the three-dimensional architecture in (1) is stabilized by water-DABCO O-H⋯N and water-carboxyl-ate O-H⋯O hydrogen bonds, with additional stability afforded by C-H⋯O inter-actions. The global crystal structure comprises alternating layers of water mol-ecules and ion pairs stacked along the c axis. In the crystal of (2), the three-ion aggregates are assembled into a three-dimensional architecture by a large number of methyl-ene-carboxyl-ate/nitro C-H⋯O inter-actions as well as π-π contacts between inversion-related benzene rings [inter-centroid distances = 3.5644 (16) and 3.6527 (16) Å]. The cations and anions assemble into alternating layers along the c axis.

N-(4-Chloro-phen-yl)-3-nitro-pyridin-2-amine.

In the title compound, C(11)H(8)ClN(3)O(2), the presence of intra-molecular N-H⋯O and C-H⋯N inter-actions help to establish an almost planar mol-ecule [dihedral angle between the pyridine and benzene rings = 9.89 (8)° and r.m.s. deviation for all 17 non-H atoms = 0.120 Å]. Supra-molecular tapes feature in the crystal packing whereby dimeric aggregates sustained by pairs of C-H⋯O inter-actions are connected by π-π inter-actions occurring between translationally related pyridine rings and between translationally related benzene rings along the b axis [centroid-centroid distance = length of b axis = 3.8032 (4) Å].