Carbon­yl-carbonyl, carbon­yl-[pi] and carbon­yl-halogen dipolar inter­actions as the directing motifs of the supra­molecular structure of ethyl 6-chloro-2-oxo-2H-chromene-3-carboxyl­ate and ethyl 6-bromo-2-oxo-2H-chromene-3-carboxyl­ate

The title compounds, C₁₂H₉ClO₄, (I), and C₁₂H₉BrO₄, (II), are isomorphous and crystallize in the monoclinic space group P2₁/c. Both compounds present an anti conformation between the 3-carb­oxy and the lactone carbonyl groups. Both carbonyl groups are out of the plane defined by the remaining chromene atoms, by 8.37 (6) and 17.57 (6)° for (I), and by 9.07 (8) and 18.96 (18)° for (II), owing to their involvement in inter­molecular inter­actions. In both compounds, layers of centrosymmetric hydrogen-bonded dimers are developed in the [ 22] plane through C-H...O inter­actions, involving both carbonyl groups as acceptors. Two families of dimers stack through C=O...C=O, C=O...[pi] and C-X...C=O (X = Cl and Br) dipolar inter­actions, as well as a C-H...[pi] inter­action, developing the three-dimensional structure along the c axis.