Acta Cryst. (2007). E63, o1240-o1242  [ doi:10.1107/S1600536807005156 ]

Short NO hydrogen bonds in the 1:1 adduct of 4,4'-bipyridyl and oxalic acid

J. A. Cowan, J. A. K. Howard, H. Puschmann and I. D. Williams

Abstract: Oxalic acid, C₂O₄H₂, and 4,4'-bipyridyl, C₁₀H₈N₂, 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-HN hydrogen bonds. In one chain there is one independent O-HN hydrogen bond [NO = 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-HN hydrogen bonds [ON = 2.549 (3) and 2.581 (3) Å] and both molecules are twisted about their central bonds.

Online 9 February 2007

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