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, C(10)H(12)N(2)(2+)center dot C(10)H(4)O(8)(2-)center dot 1.8H(2)O, (I), in the space group PT, 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), C(10)H(12)N(2)(2+)center dot 2C(10)H(5)O(8)(-), (II), in the space group Cc. The crystal structure of the 1:1 cocrystal contains one short N-H center dot center dot center dot O hydrogen bond [N center dot center dot center dot O = 2.6047 (19) angstrom] and one intramolecular O-H center dot center dot center dot O hydrogen bond [O center dot center dot center dot O = 2.423 (3) angstrom]. The crystal structure of the 2:1 cocrystal contains two N-H center dot center dot center dot O hydrogen bonds [N center dot center dot center dot O = 2.639 (3) and 2.674 (2) angstrom], and two intramolecular [O center dot center dot center dot O = 2.404 (3) and 2.420 (3) angstrom] and four strong intermolecular O H center dot center dot center dot O hydrogen bonds [O center dot center dot center dot O = 2.613 (3), 2.718 (3), 2.628 (3) and 2.739 (3) angstrom].