Propane-1,3-diyl bis(pyridine-4-carboxylate)

The title compound. C15H14N2O4, (I), has a gauche–gauche (O/C/C/C—O/C/C/C or GG) conformation and is a positional isomer of propane-1,3-diyl bis(pyridine-3-carboxylate), (II). The molecule of (I) lies on a twofold rotation axis, which passes through the central C atom of the aliphatic chain, giving one half-molecule per asymmetric unit. There is excellent agreement of the geometric parameters of (I) and (II). The most obvious differences between them are the O/C/C/C—O/C/C/C torsion angles [56.6 (2)° in (I) and 174.0 (3)/70.2 (3)° in (II) for GG and TG conformations, respectively] and the dihedral angle between the planes of the aromatic rings [80.3 (10)° in (I) and 76.5 (3)° in (II)]. The crystal structure is stabilized by weak C—H⋯ N and C—H⋯ O hydrogen bonding.

The title compound. C 15 H 14 N 2 O 4 , (I), has a gauche-gauche (O/C/C/C-O/C/C/C or GG) conformation and is a positional isomer of propane-1,3-diyl bis(pyridine-3-carboxylate), (II). The molecule of (I) lies on a twofold rotation axis, which passes through the central C atom of the aliphatic chain, giving one half-molecule per asymmetric unit. There is excellent agreement of the geometric parameters of (I) and (II). The most obvious differences between them are the O/C/C/C-O/ C/C/C torsion angles [56.6 (2) in (I) and 174.0 (3)/70.2 (3) in (II) for GG and TG conformations, respectively] and the dihedral angle between the planes of the aromatic rings [80.3 (10) in (I) and 76.5 (3) in (II)]. The crystal structure is stabilized by weak C-HÁ Á Á N and C-HÁ Á Á O hydrogen bonding.
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.
Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: FL2297).   Fig. 2). The title compound can be used as a nucleophilic tecton in self-assembly reactions with metal centres of varying lability.

Experimental
Isonicotinic 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 1,3-Propanediol (4.9 ml, 0.061 mol) was added. After the evolution of hydrogen chloride ended, the mixture was heated at 110°C for 2 h. The mixture was then dissolved in water, and NH 4 OH was added. After filtration, recrystallization in ethyl acetate gave colorless crystals suitable for X-ray analysis. Yield 8.23 g(24%). Analysis

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.