Short N⋯O hydrogen bonds in the 1:1 adduct of 4,4′‐bipyridyl and oxalic acid

Oxalic acid, C 2 O 4 H 2 , and 4,4′‐bipyridyl, C 10 H 8 N 2 , crystallize in a 1:1 ratio. The asymmetric unit consists of one oxalic acid (OXA) molecule and one 4,4'bipyridyl (BPY) molecule in general positions, together with one half‐OXA molecule and one half‐BPY molecule; the latter two molecules are centrosymmetric. The molecules are linked in two parallel independent chains by strong O—H⋯N hydrogen bonds. In one chain there is one independent O—H⋯N hydrogen bond [N⋯O = 2.557 (3) Å] and the molecules lie on centres of symmetry and are therefore constrained to have planar central portions. The second chain contains two independent O—H⋯N hydrogen bonds [O⋯N = 2.549 (3) and 2.581 (3) Å] and both molecules are twisted about their central bonds.