Dimethyl 6,6′-dicyano-2,2′-bipyridine-3,3′-dicarboxylate

In the title compound, C16H10N4O4, the two pyridine rings are twisted by 44.41 (2)° and the ester groups form dihedral angles of 48.77 (4) and 45.75 (2)° with the corresponding pyridine rings. The crystal structure is stabilized by intermolecular C—H⋯O hydrogen bonds and π–π stacking interactions between the pyridine rings [centroid-to-centroid distance 3.797 (2) Å].

In the title compound, C 16 H 10 N 4 O 4 , the two pyridine rings are twisted by 44.41 (2) and the ester groups form dihedral angles of 48.77 (4) and 45.75 (2) with the corresponding pyridine rings. The crystal structure is stabilized by intermolecular C-HÁ Á ÁO hydrogen bonds andstacking interactions between the pyridine rings [centroid-to-centroid distance 3.797 (2) Å ].
Symmetry code: (i) Àx þ 1; Ày þ 1; Àz þ 1. Dimethyl 6,6'-dicyano-2,2'-bipyridine-3,3'-dicarboxylate X. He, G.-R. Qu, D. Deng and B. Ji Comment Binicotinic acid and its derivatives have been proved to be a kind of multifunctional and flexible ligand in the construction of complexes possessing novel and interesting topological structures. Our interest in these compounds has led us to prepare the title compound. First, we synthesized dimethyl 2,2'-bipyridine-3,3'-dicarboxylate 1,1'-dioxide according to the reported method (Tichy et al. 1995). Second, the incorporation of cyano group onto 6 and 6' positions of the above compound could be readily performed when adopting the literature methods (Glaup et al. 2005;Heirtzler 1999). In this contribution, we report the synthesis and crystal structure of the title compound.
The asymmetric unit of the title compound contains one molecule ( Fig. 1.). In the crystal structure, the most striking feature of the title compound is the interesting arrangement of the title molecules, which are linked into centrosymmetric dimers by formation of intermolecular C-H···O hydrogen bonds, in which C4-H4A is a donor and O4 is an acceptor (Table 1, Fig. 2). Short π···π contacts between two pyridine rings with centroid-centroid distance of 3.797 (2) Å are observed in the structure.
After stirring overnight at room temperature, 10% aq Na 2 CO 3 was carefully added to the chilled reaction mixture and it was concentrated at 200 mbar to complete crude product precipitation. This was collected by filtration, washed with water and dried. Purification by silica gel chromatography using 100 ~200 mesh ZCX II eluted by hexane-ethyl acetate (3:1, v/v) gave the yellow solid. The crystalline compound was obtained by slow evaporation of CH 2 Cl 2 solution containing the title compound.
supplementary materials sup-2 Figures Fig. 1. View of the title molecule with the atom numbering scheme and 30% probability displacement ellipsoids for non-hydrogen atoms. Hydrogen atoms are omitted for clarity.

Special details
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.
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 > 2sigma(F 2 ) is used only for calculating R-factors(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.