In the title mol­ecule, C17H14O4, the C atom of the carboxyl group deviates by 1.221 (3) A from the plane [maximum deviation = 0.0122(2) A] of the tricycic ring system. In the crystal structure, inter­molecular O—H⋯O hydrogen bonds link the mol­ecules into centrosymmetric dimers, and π–π inter­actions [centroid–centroid distances = 3.491 (3), 3.591 (3), 3.639 (3) and 3.735 (3) A] link these dimers into layers parallel to the ac plane. Weak inter­molecular C—H⋯O inter­actions further consolidate the crystal packing.

Additional excerpts

https://journals.iucr.org/e/issues/2010/08/00/cv2747/cv2747.pdf

2,3,4-Trichloro-6-(diethylamino)-9-oxo-9H-xanthene-1-carboxylic acid methanol solvate

Citations

Vadimezan: 2-(5,6-dimethyl-9-oxo-9H-xanthen-4-yl)acetic acid.