4,5-Dicarboxynaphthalene-1,8-dicarboxylic anhydride–1,10-phenanthroline (1/1)

In the crystal structure of the title 1:1 adduct, C12H8N2·C14H6O7, the carboxyl groups are involved in intermolecular O—H⋯O hydrogen bonds, which link the molecules into centrosymmetric dimers. These dimers are further linked by intermolecular O—H⋯N hydrogen bonds. C—H⋯O interactions also occur between the 1,10-phenanthroline (phen) and 4,5-dicarboxynaphthalene-1,8-dicarboxylic anhydride (H2NTC) molecules. In addition, the crystal structure exhibits π–π interactions of the phen⋯phen and H2NTC⋯H2NTC types with centroid–centroid distances of 3.579 (3) and 3.774 (3) Å, respectively.

The 1,10-phenanthroline (phen) has been widely used to build novel supramolecular architectures through aromatic π..π interactions (Che et al., 2006). We report herein on the crystal structure of the title compound (Fig. 1).
In the crystal packing ( Fig. 2), the carboxyl groups are involved in intermolecular O-H···O hydrogen bonds, which link the molecules into centrosymmetric dimers. These dimers are further linked by an intermolecular O-H···N hydrogen bond.

Experimental
The reagents, purchased from standard commercial sources and without further purification, were 1,4,5,8-naphthalenetetracarboxylic acid and 1,10-phenanthroline. A mixture of H 4 NTC (0.0304 g, 0.10 mmol), phen (0.018 g, 0.10 mmol) and water (10 mL) in a 25 mL Teflon-lined stainless steel autoclave was heated for 3 d at 433 K under autogenous pressure and cooled to room temperature. Yellow block crystals were obtained.

Refinement
All H atoms on C atoms were positioned geometrically and refined as riding atoms, with C-H = 0.93 Å and U iso = 1.2 U eq (C). The hydroxyl H atoms were located in a difference Fourier map, and were refined with suitable O-H distance restraint; U iso = 1.5 U eq (O). Fig. 1. The molecular structure of the title compound with the atom numbering scheme. Displacement ellipsoids are drawn at the 30% probability level. H atoms are presented as a small spheres of arbitrary radius.

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.