2,2′-Bipyridine–cyclopentane-1,2,3,4-tetracarboxylic acid (1/1)

The asymmetric unit of the title compound, C10H8N2·C9H10O8, contains a half-molecule of 2,2′-bipyridine and a half-molecule of 1,2,3,4-cyclopentanetetracarboxylic acid, both components being completed by crystallographic inversion symmetry. In the crystal, the molecules are assembled into chains extending along [010] by O—H⋯N hydrogen bonds; adjacent chains are linked by O—H⋯O hydrogen bonds into a three-dimensional network.

The asymmetric unit of the title compound, C 10 H 8 N 2 ÁC 9 H 10 O 8 , contains a half-molecule of 2,2 0 -bipyridine and a half-molecule of 1,2,3,4-cyclopentanetetracarboxylic acid, both components being completed by crystallographic inversion symmetry. In the crystal, the molecules are assembled into chains extending along [010] by O-HÁ Á ÁN hydrogen bonds; adjacent chains are linked by O-HÁ Á ÁO hydrogen bonds into a three-dimensional network.

Comment
In hydrogen-bonded adducts of simple di-, tri-and tetracarboxylic acids with tertiary diamines, the modes of hydrogenbonded chains are often determined by hard and soft types. Our investigation builds on the associative behavior of carboxyl and pyridine functions. In this contribution, we report the title compound with bipyridine-cyclopentanetetracarboxylic acid cocrystal.
Both bipyridine and cyclopentanetetracarboxylic acid molecules are generated via crystallographic 2-fold rotation axes ( Fig.   1), and C3 atoms are located at the Wyckoff 4c sites. The carboxylic groups of cyclopentanetetracarboxylic acid connect with the corresponding bipyridine molecules through O4-H4A···N1 ii hydrogen bonds generating a one-dimensional chain along [010] (Fig. 2). In this way, the adjacent one-dimensional chains are interconnected by O2-H2B···O3 i hydrogen bonds to give three-dimensional network parallel to (001) (Fig. 3).

Experimental
Under continuous stirring, a solution of 2,2'-bipyridine (0.1560 g, 1.00 mmol) in 10 ml CH 3 OH was added dropwise to an aqueous solution of 1,2,3,4-cyclopentanetetracarboxylic acid (0.1230 g, 0.50 mmol) in 10 ml H 2 O. The resulting mixture was further stirred for ca 30 min. After slow evaporation of the solution for one week at 35°C, colorless pillar sized crystals were obtained.

Refinement
H atoms bonded to C atoms were palced in geometrically calculated position and were refined using a riding model, with U iso (H) = 1.2 U eq (C). H atoms attached to O atoms were found in a difference Fourier synthesis and were refined using a riding model, with the O-H distances fixed as initially found and with U iso (H) values set at 1.2 Ueq(O).  2,2'-Bipyridine-cyclopentane-1,2,3,4-tetracarboxylic acid (1/1) Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating Rfactors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.