4,4′-Bipyridine-1,1′-diium acetylenedicarboxylate: A new member of the (H₂bipy)[Cu(ox)₂] (bipy is 4,4′-bipyridine and ox is oxalate) family

4,4′-Bipyridine-1,1′-diium (H₂bipy) acetylenedicarboxylate, C₁₀H₁₂N₂ ²⁺·C₄O₄ ^2-, (1), is a new member of a family of related structures with similar unit-cell parameters. The structures in this family reported previously [Chen et al. (2012). CrystEngComm, 14, 6400-6403] are (H₂bipy)[Cu(ox)₂] (ox is oxalate), (2), (H₂bipy)[NaH(ox)₂], (3), and (H₂bipy)[H₂(ox)₂], (4). Compound (1) has a one-dimensional structure, in which H₂bipy²⁺ cations and acetylenedicarboxylate (ADC^2-) anions are linked through a typical supramolecular synthon, i.e. R₂²(7), and form linear '-cation-anion-' ribbons. Through an array of nonclassical C-HO hydrogen bonds, adjacent ribbons interact to give two-dimensional sheets. These sheets stack to form a layered structure via π-π interactions between the H₂bipy²⁺ cations of neighbouring layers. The supramolecular isostructurality of compounds (1)-(4) is ascribed to the synergistic effect of multiple interactions in these structures. The balanced strong and weak intermolecular interactions stabilizing this structure type include strong charge-assisted N-HO hydrogen bonds, C-HO contacts and π-π interactions.