Methyl 7-methoxy-9-oxo-9H-xanthene-2-carboxylate

The crystal structure of the title compound, C16H12O5, is stabilized by C—H⋯O hydrogen bonds and C=O⋯π interactions; π–π interactions are also present. With respective average deviations from planarity of 0.003 (2) and 0.002 (1) Å, the xanthone and ester fragments are oriented at an angle of 2.8 (2)° with respect to each other. The mean planes of the xanthone skeleton lie either parallel to each other or are inclined at an angle of 85.5 (2)° in the crystal structure.

The crystal structure of the title compound, C 16 H 12 O 5 , is stabilized by C-HÁ Á ÁO hydrogen bonds and C OÁ Á Á interactions;interactions are also present. With respective average deviations from planarity of 0.003 (2) and 0.002 (1) Å , the xanthone and ester fragments are oriented at an angle of 2.8 (2) with respect to each other. The mean planes of the xanthone skeleton lie either parallel to each other or are inclined at an angle of 85.5 (2) in the crystal structure.

Comment
Xanthones represent a structurally diverse group of natural products with a broad range of biological activities. The unsubstituted xanthones have not been discovered in nature but its numerous derivatives have been isolated from representatives of higher plants, lichens, and lower fungi (Denisova-Dyatlova & Glyzin, 1982). Many naturally occurring xanthones as well as their synthetic derivatives described in numerous scientific publications exploit wide spectrum of biological activities: anti-allergic (Pfister et al., 1972), anti-inflammatory (Librowski et al., 2005), antitumor (Ito et al., 2003), antimicrobial (Fukai et al., 2005), cardiovascular (Chen et al., 1993), antimalarial (Gopalakrishnan et al., 1997) and antifungal activity (Ignatushchenko et al., 2000). The biological activity and the features responsible for the activity of xanthones largely depends on their structures. It is know that the 7-substituted xanthone-2-carboxylic acids and their esters show anti-allergic activity, which depends on the substituted groups (Pfister et al., 1980).
In the molecule of the title compound ( Fig. 1) the bond lengths and angles characterizing the geometry of the xanthone skeleton are typical for this group compounds (Evans et al., 2004;Shi et al., 2004;Macias et al., 2001).
With respective average deviations from planarity of 0.003 (2) and 0.002 (1) Å, the xanthone and ester fragment are oriented at 2.8 (2)° to each other. The methoxy group lies nearly in the mean plane of the xanthone skeleton; the dihedral angles between the mean planes xanthone skeleton and delineated by atoms C7/O19/C20 are equal 0.7 (2)°. The mean planes of the xanthone skeleton lie either parallel or are inclined at an angle of 85.5 (2)° in the lattice.
In the crystal structure, weak intermolecular C-H···O hydrogen bonds (Table 1, Fig. 2) link the molecules, forming layers. The central ring A and the lateral rings B and C are involved in multidirectional π-π interactions and link layers between themselves (Table 2, Fig. 3). The O16(carboxyl) atom is involved in weak C-O···π interactions directed toward the lateral aromatic ring (ring B) ( Table 3, Fig. 3).

Refinement
All H atoms were positioned geometrically and refined using a riding model, with C-H = 0.93 Å and U iso (H) = 1.2U eq (C) for aromatic, and with C-H = 0.96 Å and U iso (H) = 1.5U eq (C) for methyl groups. Fig. 1. The molecular structure of the title compound showing the atom-labeling scheme. Displacement ellipsoids are drawn at the 25% probability level and H atoms are shown as small spheres of arbitrary radius. CgA, CgB and CgC denote the ring centroids.  Methyl 7-methoxy-9-oxo-9H-xanthene-2-carboxylate  Symmetry code: (iii) 1 + x, y, z. CgA, CgB and CgC are the centroids of the C9/O10/C11-C14, C1-C4/C12/C11 and C5-C8/C13/C14 rings, respectively. The dihedral angle is that between the planes of the rings CgI and CgJ. The interplanar distance is the perpendicular distance of CgI from ring J. The offset is the perpendicular distance of ring I from ring J.