Structural studies of trimeric pyridinium carboxylate carboxylic acid cocrystals

[2-Hydroxy-1,1-bis(hydroxymethyl)ethyl]bis(2-hydroxyethyl)ammonium 4-nitrobenzoate monohydrate

“…Comment 4-Nitrobenzoic acid can easily lose its acidic H atom and form complexes with other compounds through hydrogen bonding. Complexes of 4-nitrobenzoic acid (forming dimers through hydrogen bonding; Tonogaki et al, 1993), pyridinium 4nitrobenzoate 4-nitrobenzoic acid (Carrow & Wheeler, 1998), tris(2-benzimidazylmethyl) ammonium 4-nitrobenzoate (Ji et al, 2000), 4-nitrobenzoic acid-3-amino-1,2,4-triazole (Byriel et al, 1992) and 4-nitrobenzoic acid-4-nitropyridine N-oxide (Moreno-Fuquen et al, 2000) have already been reported. In these complexes, the hydrogen bonds play an important role in both building and stabilizing the structure.…”

Cocrystallisation of succinic and fumaric acids with lutidines: a systematic study

“…A previous study 17 suggests that this inclusion of a second carboxylic acid-containing molecule in the structures of simple carboxylate salts occurs to stabilize the carboxylate anion (in the absence of other hydrogen bond donors), rather than as a result of crystal packing forces exclusively. Another study of the average hydrogen bonding frequency to O and N atoms of functional groups in the CSD has been described elsewhere.…”

The authors' reply

“…For example, polycyclic aromatic hydrocarbons (PAHs) can take four distinctly defined molecular packing structures: herringbone, sandwich‐herringbone, γ, and β structures, according to the relative orientation of molecular planes in the crystal 4. In addition, the packing structures of polar compounds can be further complicated because of the existence of functional groups capable of complexation 5. Second, the surface of graphite is highly polarized; the basal plane of graphite in the vicinity of the edges is electron‐rich, while the regions in the center of the graphitic surface are typically electron‐depleted 3.…”

“…However, the surfaces of the pure compounds considered herein do not necessarily possess this property. Third, given the basal plane structure of nonporous graphite, the planar molecules of aromatic adsorbates most likely take the face‐to‐face configuration when adsorbed to graphite, whereas adsorbate molecules in their solid state might not necessarily take such configuration 4, 5. Such a configuration variation could result in considerable difference in entropy change during the solvation process, because water cavities of different sizes and shapes would form around the adsorbate molecules on the graphite surface and those on the pure solid of the adsorbate.…”