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 (H(2)bipy) acetylenedicarboxylate, C10H12N22+center dot C4O(4)(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 (H(2)bipy)[Cu(ox)(2)] (ox is oxalate), (2), (H(2)bipy)[NaH(ox)(2)], (3), and (H(2)bipy)[H-2(ox)(2)], (4). Compound (1) has a one-dimensional structure, in which H(2)bipy(2+) cations and acetylenedicarboxylate (ADC(2-)) anions are linked through a typical supramolecular synthon, i.e. R-2(2)(7), and form linear '-cation-anion-' ribbons. Through an array of nonclassical CH center dot center dot center dot O hydrogen bonds, adjacent ribbons interact to give two-dimensional sheets. These sheets stack to form a layered structure via pi-pi interactions between the H(2)bipy(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 center dot center dot center dot O hydrogen bonds, C-H center dot center dot center dot O contacts and pi-pi interactions.