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, C₁₀H₁₂N₂²⁺·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—H...O hydrogen bonds, adjacent ribbons interact to give two‐dimensional sheets. These sheets stack to form a layered structure viaπ–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—H...O hydrogen bonds, C—H...O contacts and π–π interactions.