3-[(Benzo-1,3-dioxol-5-yl)amino]-4-meth­oxy­cyclo­but-3-ene-1,2-dione: polymorphism and twinning of a precursor to an anti­mycobacterial squaramide

3-[(Benzo-1,3-dioxol-5-yl)amino]-4-meth­oxy­cyclo­but-3-ene-1,2-dione forms concomitant polymorphs, namely, block-shaped crystals of a monoclinic form I (space group P 2 1 / c , Z = 8, Z ′ = 2) and needle-shaped crystals of a triclinic form II (space group P , Z = 4, Z ′ = 2), the latter of which exhibits twinning by pseudomerohedry. The title compound, 3-[(benzo-1,3-dioxol-5-yl)amino]-4-meth­oxy­cyclo­but-3-ene-1,2-dione, C 12 H 9 NO 5 ( 3 ), is a precursor to an anti­mycobacterial squaramide. Block-shaped crystals of a monoclinic form ( 3 -I, space group P 2 1 / c , Z = 8, Z ′ = 2) and needle-shaped crystals of a triclinic form ( 3 -II, space group P -1, Z = 4, Z ′ = 2) were found to crystallize concomitantly. In both crystal forms, R 2 2 (10) dimers assemble through N—H⋯O=C hydrogen bonds. These dimers are formed from crystallographically unique mol­ecules in 3 -I, but exhibit crystallographic C i symmetry in 3 -II. Twinning by pseudomerohedry was encountered in the crystals of 3 -II. The conformations of 3 in the solid forms 3 -I and 3 -II are different from one another but are similar for the unique mol­ecules in each polymorph. Density functional theory (DFT) calculations on the free mol­ecule of 3 indicate that a nearly planar conformation is preferred.