4,4′-Ethylenedipyridinium bis(3,4,5-trihydroxybenzoate) sesquihydrate

Abstract

The asymmetric unit of the title compound, C12H14N2 2+·2C7H5O5 −·1.5H2O, contains two 4,4′-ethyl­enedipyridinium cations, four gallate anions and three water mol­ecules. In the 4,4′-ethyl­enedipyridinium cations, the dihedral angles between the pyridinium rings are 4.3 (3) and 18.6 (3)°. Extensive classical N—H⋯O and O—H⋯O hydrogen bonding and weak C—H⋯O hydrogen bonding and C—H⋯π inter­actions are present in the crystal structure. π–π stacking is also observed, the centroid–centroid separations between the benzene and pyridine rings being 3.611 (3), 3.448 (3) and 3.536 (3) Å.

New Co-Crystals/Salts of Gallic Acid and Substituted Pyridines: An Effect of Ortho-Substituents on the Formation of an Acid–Pyridine Heterosynthon

“…Depending on the choice of the pyridine-containing compound, the neutral or ionic nature of the resulting two-component system of gallic acid mostly follows the pKa rule [55,[91][92][93][94] stating that a salt is formed if ∆pKa > 3 and a co-crystal, if ∆pKa < −1 (Table S6 of Supplementary Materials). The exceptions are the salt of 4,4 -ethylenedipyridin (DUTJEI), which is obtained with lattice water molecules [65] to affect the pKa values of the components [95], and of isoniazid (LODHIX and LODHOD), which is a superposition of a salt and a co-crystal not attained at the highest accessed temperature [64], as well as the previously reported co-crystal 1 [63] and its new solvatomorph 2. In these co-crystals, the appropriate hydroxylpyridine adopts its keto-form (Scheme S1 of Supplementary Materials) preferred in the crystal state [67,68], thereby precluding the proton transfer to the nitrogen atom and the formation of a predicted salt.…”

“…Some 'local' differences arise due to distinctive features of the pyridine-containing compounds, such as an extended aromatic system or an additional neutral pyridine fragment. Mirroring the co-crystals 1-3, the salts 4 and 5 feature the multi-point heterosynthons (Scheme 1, center and right) instead of the single-point heterosynthon (Scheme 1, left) found in all the (ordered) gallate salts of pyridine-containing compounds [60,[63][64][65]86] available in the Cambridge Structural Database (CCDC Version 2021.2.0) (Scheme 4), including the one of 3-hydroxypyridine (RefCode XUMKAU [63]). This difference, however, has only a minor effect on the contributions of interactions formed by the gallate anion (Figure S11 of SI).…”

“…Scheme 4. Salts of gallic acid and pyridine-containing compounds and their RefCodes [60,[63][64][65][66]86]. X-ray diffraction data for LODHIX and LODHOD are collected from the same salt at 100 K and at room temperature, respectively; LODHIX, LODHOD, EHUGOE, and DUTJEI also contain lattice water molecules.…”

“…As their aromatic fragments are not in-Scheme 4. Salts of gallic acid and pyridine-containing compounds and their RefCodes [60,[63][64][65][66]86].…”

“…The latter is further stabilized by a pyridine compound containing proton-donating groups in the ortho-positions to Co-crystallization of a carboxylic acid with a pyridine compound may produce either a co-crystal [53] built by neutral components or a salt featuring the proton transfer from acid to base [54,55], both useful in the pharmaceutical industry [56][57][58]. Although such twocomponent systems are widely studied in supramolecular chemistry [59], only a few reports exist on those formed by gallic acid, including co-crystals [41,[60][61][62][63] and salts [60,[63][64][65][66], and none of them contain an ortho-substituted pyridine except for 2-hydroxypyridine [63]. In an appropriate co-crystal, the latter exists as the preferred tautomer [67,68], pyridone-2 (Scheme S1 of supplemantary), that forms with gallic acid the typical two-point heterosynthon (Scheme 1, center) [63].…”