In order to study structure-activity relationships, a series of mono-, di- and trioxy­genated xanthones has been synthesized and the structures of methyl 2-(3,4-di­methoxy­phenoxy)­benzoate, C₁₆H₁₆O₅, 2-(3,4-di­methoxy­phenoxy)­benzoic acid, C₁₅H₁₄O₅, 1,2-di­methoxy-9H-xanthen-9-one, C₁₅H₁₂O₄, and 1,2,8-tri­methoxy-9H-xanthen-9-one, C₁₆H₁₄O₅, have been determined. The first two compounds both assume skew conformations, the dihedral angles between the two phenyl rings being 80.04 (8) and 83.0 (1)°, respectively. The latter two compounds are essentially planar and their methoxy substituents assume orientations consistent with minimum steric interactions.

The xanthone skeleton of the title compound, C₁₃H₈O₄·3H₂O, exhibits a planar conformation, with the hydr­oxy H atoms lying in the plane. In the crystal structure, the mol­ecules are packed into columns with their planar skeletons parallel to one another.

In the title compound, C₁₉H₁₀ClNO₄, the dihedral angle between the naphtho­quinone and coumarin rings is 48.99 (6)°. In the crystal, mol­ecules are linked by strong N—HO hydrogen bonds into chains with graph-set motif C(6) along [101]. The packing also features π–π stacking inter­actions between naphtho­quinone and coumarin rings [centroid-to-centroid distances = 3.7679 (12) and 3.6180 (13) Å].