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 4,40-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. 4,40-bipyridinium 2,5-dicarboxybenzene-1,4-dicarboxylate 1.8hydrate, C10H12N2 2+ C10H4O8 1.8H2O, (I), in the space group P1, with both BTA and BPY lying on inversion centres. BTA and BPY crystallize in a 2:1 ratio, viz. 4,40-bipyridinium bis(2,4,5-tricarboxybenzoate), C10H12N2 2+ 2C10H5O8, (II), in the space group Cc. The crystal structure of the 1:1 cocrystal contains one short NÐH O hydrogen bond [N O = 2.6047 (19) AÊ ] and one intramolecular OÐH O hydrogen bond [O O = 2.423 (3) AÊ ]. The crystal structure of the 2:1 cocrystal contains two NÐH O hydrogen bonds [N O = 2.639 (3) and 2.674 (2) AÊ ], and two intramolecular [O O = 2.404 (3) and 2.420 (3) AÊ ] and four strong intermolecular OÐ H O hydrogen bonds [O O = 2.613 (3), 2.718 (3), 2.628 (3) and 2.739 (3) AÊ ].