9-Methoxy-9-(2-methoxyphenyl)-9H-xanthene

In the title compound, C21H18O3, the xanthene system and the methoxyphenyl ring are practically orthogonal with a dihedral angle between their mean planes of 89.27 (3)°. The methoxy group attached to the phenyl ring makes a C—O—C—C torsion angle of 11.56 (18)°. In the crystal, molecules are linked by C—H⋯O interactions into chains along [010]. Weak C—H⋯π interactions also occur.

In the title compound, C 21 H 18 O 3 , the xanthene system and the methoxyphenyl ring are practically orthogonal with a dihedral angle between their mean planes of 89.27 (3) . The methoxy group attached to the phenyl ring makes a C-O-C-C torsion angle of 11.56 (18) . In the crystal, molecules are linked by C-HÁ Á ÁO interactions into chains along [010]. Weak C-HÁ Á Á interactions also occur.
Cg is the centroid of the C14-C19 ring.
Xanthenol compounds have been used extensively in host-guest chemistry as versatile hosts for the inclusion of small organic guests (Jacobs et al., 2005), solvent free reactions (Jacobs et al., 2009) and guest exchange experiments (Jacobs et al., 2007). This class of compounds conforms to Weber's rules (Weber, 1991) for efficient hosts in that they are bulky and contain functionalities that can participate in hydrogen bonding. Charge delocalization into the adjacent aromatic rings of the xanthene moiety can stabilize a cationic centre at C13 (Fig. 1), facilitating nucleophilic attack. The loss of the hydroxyl group yields a compound without a strong hydrogen bond donor.
The packing diagram down [010] is shown in Fig. 3. The xanthene ring and the methoxyphenyl moiety are practically orthogonal with a dihedral angle between the least squares planes of 89.27 (3)°. The methoxy moiety attached to the phenyl ring deviates from the C14-C19 plane with a resultant C20-O3-C15-C16 torsion angle of 11.56 (18)°.

Refinement
The aromatic and methyl hydrogen atoms were geometrically constrained, with C-H distances fixed at 0.95 Å and 0.98 Å respectively. For the aromatic H atoms U iso (H) = 1.2U eq (C aryl ) and for the methyl H atoms U iso (H) = 1.5U eq (C methyl ).

Special details
Experimental. Absorption corrections were made using the program SADABS (Sheldrick, 1996) 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.