(2-Pyridyl)[5-(2-pyridylcarbonyl)-2-pyridyl]methanone

In the centrosymmetric title compound, C17H11N3O2, the dihedral angle between the central and pendant pyridyl rings is 50.29 (9)°. In the crystal, molecules stack along the a axis by π–π interactions between the pyridine rings with centroid–centroid distances of 3.845 (2) Å. The N atom and one of the C atoms of the central ring are disordered by symmetry.

In the centrosymmetric title compound, C 17 H 11 N 3 O 2 , the dihedral angle between the central and pendant pyridyl rings is 50.29 (9) . In the crystal, molecules stack along the a axis by interactions between the pyridine rings with centroidcentroid distances of 3.845 (2) Å . The N atom and one of the C atoms of the central ring are disordered by symmetry.   Di-2-pyridylmethanone has attracted great interest in recent years as it can exist in various forms in stabilizing its metal complexes, including its neat ketone form, singly and doubly deprotonated gem-diol forms, as well as the monoanion of its hemiacetal form (Papaefstathiou et al., 2002;Dendrinou-Samara et al., 2003;Crowder et al., 2004). Therefore, homolog compounds such as 2,6-pyridinediylbis(2-pyridyl)methanone (Chen et al., 2005) and 2,6-pyridinediylbis(3-pyridyl)methanone (Wan et al., 2008) were also synthesized and characterized.

Related literature
In the present study, a new member of this family, namely 2,5-pyridinediylbis(2-pyridyl)methanone (C 17 H 11 N 3 O 2 ), is reported. X-ray diffraction analysis shows that the N2 and C9 atoms of the 2,5-pyridinediyl ring have an equal occupancy at the same site. Thus the molecule is centrosymmetric with two 2-pyridyl methanone groups bonding to the 2,5-pyridinediyl ring at the 2 and 5 positions, respectively. The 2-pyridyl and the center 2,5-pyridinediyl rings exhibit a dihedral angle of 50.29 (9)° ( Fig. 1). Along the a axis, the packing between the molecules is provided by weak un-covalent interaction only: /p-electron···/p-electron ring interaction. The distance between the centroids of the proximate pyridyl rings equals 3.845 (2) Å, as shown in Fig. 2.

Experimental
The preparation of the title compound followed the procedure previously developed for 2,6-pyridinediylbis(3pyridyl)methanone (Wan et al., 2008).The crude product was extracted with chloroform, and the combined organic extract was dried over anhydrous sodium sulfate and finally concentrated in vacuo to give a brown oil. Further purification by chromatography on silica gel (R f = 0.44, eluent: ether acetate/dichloromethane = 1:6, v/v), giving 2.96 g of light yellow powder of 2,5-pyridinediylbis(2-pyridyl)methanone in 41% yield; m.p. 108-110°C; The yellow crystals of the title compound having a average 0.40 × 0.30 × 0.20 mm dimension were obtained by slow evaporation from its solution of dichloromethane/N,Ndimethylformamide 1/1 (v/v).

Refinement
The hydrogen atoms were placed in idealized positions and allowed to ride on the relevant carbon atoms, with C-H = 0.93 Å and Uĩso~(H) = 1.2U~eq~(C). Fig. 1. The atom-numbering scheme of the title compound C 17 H 11 N 3 O 2 . Displacement ellipsoids are drawn at the 50% probability level and H atoms are shown as sticks of arbitrary radii. Symmetry code: i -x + 2, -y + 2, -z.

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 > 2σ(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.
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )