N,N′-Bis(4-hydroxyphenyl)pyridine-2,6-dicarboxamide dimethylformamide monosolvate

The molecular structure of the pyridine derivative, C19H15N3O4·C3H7NO, shows almost planar geometry with dihedral angles of 6.9 (1) and 13.4 (1)° between the pyridine ring and the two benzene rings. This conformation is stabilized by two intramolecular N—H⋯N(pyridine) bonds. In the crystal, strong O—H⋯O(carboxamide) and N—H⋯O(hydroxyphenyl) hydrogen bonds link the molecules, forming a three-dimensional structure. The dimethylformamide solvent molecules are not involved in the hydrogen bonding. The structure shows pseudosymmetry, but refinement in the space group Pbcn leads to significantly worse results and a disordered dimethylformamide molecule.


Related literature
Data collection: SMART (Bruker, 2002); cell refinement: SAINT (Bruker, 2002); data reduction: SAINT; program(s) used to solve structure: SHELXTL (Sheldrick, 2008); program(s) used to refine structure: SHELXTL; molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL and local programs. monomer having inbuilt amide functionality. It enhances the solubility of resulting poly(amid-imide)s without deteriorating the inherent properties of the polymer.

Experimental
This preparation was carried out by using reagent grade quality chemicals without their further purification. In a 100 ml, three necked, round bottomed flask, equipped with a condenser, a nitrogen gas inlet tube, a thermometer and a magnetic stirrer, 0.02mole (2.18 g m) of 4-hydroxyaniline in 30 mL of dry tetrahydrofuran(THF) stirred at 273-278 K for 30 minutes and 0.01 mol (2.04 g m) of pyridine -2,6-dicarbonyl dichloride in 35 mL of THF was added dropwise by dropping funnel and stirring was continued for further 1 h under same conditions. The temperature of reaction mixture was then raised to 308-313 K and stirring was continued for 30 minutes. The flask content was cooled to room temperature, poured into water and let it for 24 h. Resulting purplish precipitates were filtered, washed with hot water and 5% NaOH solution. Finally, product was washed with hot water and methanol, dried under vacuum at 80°C. The crude product was recrystallized from tetrahydrofuran and dimethylformamide(4:1).

Refinement
Hydrogen atoms were clearly identified in difference syntheses, refined at idealized positions riding on the carbon, nitrogen or oxygen atoms with C-H 0.95-0.98, N-H 0.88, O-H 0.84 Å and with isotropic displacement parameters U iso (H) = 1.2U eq (C/N) or 1.5U eq (-CH 3 and -OH H atoms). All CH 3 and OH hydrogen atoms were allowed to rotate but not to tip.
The title compound crystallizes in the non-centrosymmetric space group Pca2 1 ; however, in the absence of significant anomalous scattering effects, the Flack parameter is essentially meaningless. Accordingly, Friedel pairs were merged.

Special details
Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s 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 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.