Neutron diffraction studies of the 1 : 1 and 2 : 1 cocrystals of benzene-1,2,4,5-tetracarboxylic acid and 4,4 `-bipyridine

The 1:1 and 2:1 cocrystals of benzene-1,2,4,5-tetra­carboxylic acid (BTA) and 4,4′-bipyridine (BPY) have been studied using neutron diffraction at 215 and 20 K, respectively. BTA and BPY crystallize in a 1:1 ratio with 1.8 mol­ecules of water, viz. 4,4′-bipyridinium 2,5-dicarboxy­benzene-1,4-dicarboxyl­ate 1.8-hydrate, C10H12N22+·C10H4O82−·1.8H2O, (I), in the space group P\overline{1}, with both BTA and BPY lying on inversion centres. BTA and BPY crystallize in a 2:1 ratio, viz. 4,4′-bipyridinium bis­(2,4,5-tricarboxy­benzoate), C10H12N22+·2C10H5O8−, (II), in the space group Cc. The crystal structure of the 1:1 cocrystal contains one short N—H⋯O hydrogen bond [N⋯O = 2.6047 (19) A] and one intra­molecular O—H⋯O hydrogen bond [O⋯O = 2.423 (3) A]. The crystal structure of the 2:1 cocrystal contains two N—H⋯O hydrogen bonds [N⋯O = 2.639 (3) and 2.674 (2) A], and two intra­molecular [O⋯O = 2.404 (3) and 2.420 (3) A] and four strong inter­molecular O—H⋯O hydrogen bonds [O⋯O = 2.613 (3), 2.718 (3), 2.628 (3) and 2.739 (3) A].