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ACTA CRYSTALLOGRAPHICA SECTION C-STRUCTURAL CHEMISTRY, vol.59, 2003 (SCI-Expanded)
The crystal structure determination of the dinicotinamidium squarate salt, 2C(6)H(7)N(2)O(+).C4O42-, is reported, with the squarate dianion residing on an inversion centre and the unique cation in a general position. Salt formation occurs by donation of two H atoms from squaric acid to the nicotinamide base. The crystal packing is derived from three types of hydrogen bonding. The primary hydrogen bond involves a squarate anion O atom and an H atom of the protonated pyridine group of the nicotinamide, with an N...O distance of 2.5760 (13) Angstrom. The second hydrogen bond involves a second anion O atom and an amide H atom, with an N...O distance of 2.8374 (14) Angstrom. Thirdly, an intermolecular interaction between two coplanar nicotinamide moieties occurs between an amide O atom and a symmetry-related amide H atom, with an N1...O3 distance of 2.8911 (15) Angstrom. These hydrogen bonds are also responsible for the planarity of the nicotinamide moiety in the salt.