Propane-1,3-diyl bis(pyridine-3-carboxylate)

The title compound, C15H14N2O4, has a trans–gauche [O/C/C/C–O/C/C/C] (TG) conformation. The angle between the planes of aromatic rings is 76.4 (3)°. The crystal structure is stabilized by van der Waals interactions and C—H⋯O hydrogen bonds. The crystal used was a non-merohedral twin with a fractional contribution of the minor component of 0.443 (5).

We thank the Spanish Research Council (CSIC) for providing us with a free-of-charge licence for the CSD system. JV thanks the Universidad de Antofagasta for PhD fellowships.

Comment
In the past decade, crystalline nanoporous coordination polymers have been extensively studied for their potential applications in magnetism (Xiang et al., 2005), catalysis (Wu et al., 2005) and gas adsorption or separation (Matsuda et al., 2005).

Experimental
Nicotinic acid (15 g, 0.122 mol) was stirred in SOCl 2 (40 ml) in the presence of DMF (0.6 ml) at 60 °C for 12 h. Excess thionyl chloride was removed in vacuo. Dried propanediol (4.3 ml, 0.061 mol) was added. After the evolution of hydrogen chloride ended, the mixture was heated at 150 °C for 2 h. The mixture was dissolved in water, and NH 4 OH solution was added. After filtration, recrystallization in ethyl acetate gave colorless crystal. Yield 11.53 g (80 %). Analysis calculated for

Refinement
The crystal turned out to be a non-merohedral twin (twin law: -1 0 0/0 -0.476 -0.740/ 0 -1 0.478) with a fractional contribution of the minor component of 0.443 (5). H atoms were placed in idealized positions and treated as riding atoms with C-H distances in the range 0.95-0.99 Å and U iso (H) = 1.2U eq (C). The material was difficult to obtain in a suitable crystalline form. Fig. 1. A view of the molecular structure with the atom-numbering scheme. Displacemenent ellipsoids are drawn at the 50% probability level and H atoms are shown as small spheres of arbitrary radii.

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 > 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.