Dichloromaleic anhydride

Although molecules of the title compound, 3,4-dichloro-2,5-dihydrofuran-2,5 -dione (dichloromaleic anhydride, C4Cl2O3), (I), possess approximate non-cr ystallographic C-2 nu symmetry, the two chlorine substituents deviate from the ring plane. Their deviations are in the same direction, but with values of 0.0356 (17) and 0.0167 (17) Angstrom, they differ significantly in magn itude. The closest intermolecular contact is of 2.888 (2) Angstrom between a carbonyl O atom and the C atom of a carbonyl group, with the O ... C dire ction orthogonal to the C=O bond [O5 ... C2(i)=O2(i) 93.6 (2)degrees; symme try code: (i) 3/2 - x, -1/2 + y, z]. These contacts form infinite chains of molecules running parallel to the crystallographic b direction.