Hydrogen bonding and π-π Inter-actions in 1-benzofuran-2,3- dicarboxylic acid and its 1:1 cocrystals with pyridine, phenazine and 1,4-phenyl-enediamine

The structure of 1-benzofuran-2,3-dicarboxylic acid (BFDC), C ₁₀H₆O₅, (I), exhibits an intra-molecular hydrogen bond between one -COOH group and the other, while the second carboxyl function is involved in intermolecular hydrogen bonding to neighbouring species. The latter results in the formation of flat one-dimensional hydrogen-bonded chains in the crystal structure, which are π-π stacked along the normal to the plane of the mol-ecular framework, forming a layered structure. 1:1 Cocrystallization of BFDC with pyridine, phenazine and 1,4-phenyl-enediamine is associated with H-atom transfer from BFDC to the base and charge-assisted hydrogen bonding between the BFDC^- monoanion and the corresponding ammonium species, while preserving, in all cases, the intra-molecular hydrogen bond between the carboxyl and carboxyl-ate functions. The pyridinium 2-carboxyl-ato-1-benzofuran-3-carboxylic acid, C₅H₆N ⁺·C₁₀H₅O₅^-, (II), and phenazinium 3-carboxyl-ato-1-benzofuran-2-carboxylic acid, C ₁₂H₉N₂⁺·C₁₀H ₅O₅^-, (III), adducts form discrete hydrogen-bonded ion-pair entities. In the corresponding crystal structures, the two components are arranged in either segregated or mixed π-π stacks, respectively. On the other hand, the structure of 4-amino-anilinium 2-carboxyl-ato-1-benzofuran-3-carboxylic acid, C₆H₉N ₂⁺·C₁₀H₅O₅ ^-, (IV), exhibits an intermolecular hydrogen-bonding network with three-dimensional connectivity. Moreover, this fourth structure exhibits induction of supra-molecular chirality by the extended hydrogen bonding, leading to a helical arrangement of the inter-acting moieties around 21 screw axes. The significance of this study is that it presents the first crystallographic characterization of pure BFDC, and manifestation of its cocrystallization with a variety of weakly basic amine mol-ecules. It confirms the tendency of BFDC to preserve its intra-molecular hydrogen bond and to prefer a monoanionic form in supra-molecular association with other components. The aromaticity of the flat benzofuran residue plays an important role in directing either homo- or heteromolecular π-π stacking in the first three structures, while the occurrence of a chiral architecture directed by multiple hydrogen bonding is the dominant feature in the fourth.