4,4′-Bipyridine–2-(carboxymethylsulfanyl)pyridine-3-carboxylic acid (1/1)

In the title co-crystal, C10H8N2·C8H7NO4S, the formate group is coplanar with the pyridyl ring of the acid [dihedral angle = 6.2 (7)°], while the carboxymethylsulfanyl group makes a C—S—C—C torsion angle of 70.2 (1)° with the pyridine ring. The dihedral angle between the pyridyl rings of the 4,4′-bipyridine molecule is 27.4 (1)°. The acid and the 4,4′-bipyridine molecules are involved in hydrogen bonding via carboxylic O and pyridyl N atoms. The structure is further consolidated by intermolecular C—H⋯O hydrogen bonds, generating a three-dimensional network.


Experimental
Crystal data
Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: PV2357).
The title compound is composed of 2-(carboxymethylsulfanyl)pyridine-3-carboxylic acid (C 8 H 7 NO 4 S) and 4,4'-bipyridine (C 10 H 8 N 2 ) ( Fig. 1). In the acid moiety, the formate group is coplanar with the pyridyl ring, while the carboxymethylsulfanyl group is almost vartical to the plane formed by the pyridine ring atoms with torsion angle, C1-S1-C7-C8, 70.2 (1)°. The dihedral angle between the pyridyl rings of the 4,4'-bipyridine molecule is 27.4 (1)°. The acid and the 4,4'bipyridine molecules are involved in hydrogen bonding via carboxylic O and pyridyl N atoms. The structure is further consolidated by intermolecular hydrogen bonds of type C-H···O ( Fig. 2 and Tab. 1).
Experimental 2-(Carboxymethylsulfanyl)pyridine-3-carboxylic acid was prepared according to the literature method (Wang et al., 2010). A mixture of CoCl 2 .6H 2 O (0.2379 g, 1.0 mmol), 4,4'-bipyridine (0.0468 g, 0.3 mmol) and 2-(carboxymethylsulfanyl)pyridine-3-carboxylic acid (0.2134 g, 1.0 mmol) was dissolved in 10.0 ml of distilled water and 3.0 ml ethanol at 328 K. The resulting solution was stirred and refluxed under basic condition for 2 h, the mixture was cooled to room temperature and filtered. Single crystals suitable for X-ray diffraction were obtained from the mother liquor by slow evaporation at room temperature for several days.

Refinement
The carbon-bound H-atoms were positioned geometrically and included in the refinement using a riding model with C-H = 0.93 and 0.97 Å for aryl and methylene H-atoms and U iso (H) = 1.2U eq (C). The oxygen-bound H-atoms was located in a difference Fourier map and refined with the O-H distance restrained to 0.85 (2) Å and U iso (H) = 1.2U eq (O).   as those based on F, and R-factors based on ALL data will be even larger.