Experimental

R factor = 0.057; wR factor = 0.178; data-to-parameter ratio = 15.0. The title compound, C16H12O4, crystallizes with two half-molecules in the asymmetric unit, each of which is completed by a crystallographic inversion center. The two crystal-lographically independent molecules have almost the same geometry and are almost planar [maximum deviations = 0.018 (3) and 0.049 (3) Å]. They adopt a conformation in which the Cmethyl—O bonds are directed along the molecular short axis [C—C—O—C torsion angles of 179.6 (2) and 178.0 (2)]. In the crystal, the molecular packing is character-ized by a combination of a columnar stacking and a herringbone-like arrangement. The molecules form slipped -stacks along the b axis, in which there are two kinds of columns differing from each other in their slippage. The interplanar distances between neighboring molecules are 3.493 (3) for one column and 3.451 (2) A ̊ for the other. Related literature For a study of the effects of alkoxy substituents on the structures and solid-state photophysics of anthraquinones, see: Ohta, Hattori, Kusumoto, et al. (2012). For the synthesis, see: Keller & Rüchardt (1998). For a related structure, see: Ohta, Hattori, Kawase, et al. (2012)