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 H2bipy(2+) cations and acetylenedicarboxylate (ADC(2-)) anions are linked through a typical supramolecular synthon, i.e. R2(2)(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 via π-π interactions between the H2bipy(2+) 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.