Carbonyl-carbonyl, carbon-yl-π and carbon-yl-halogen dipolar inter-actions as the directing motifs of the supra-molecular structure of ethyl 6-chloro-2-oxo-2H-chromene-3-carboxyl-ate and ethyl 6-bromo-2-oxo-2H-chromene-3- carboxyl-ate

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-carb-oxy 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 inter-molecular inter-actions. In both compounds, layers of centrosymmetric hydrogen-bonded dimers are developed in the [ 22] plane through C - H⋯O inter-actions, involving both carbonyl groups as acceptors. Two families of dimers stack through C=O⋯C=O, C=O⋯π and C - X⋯C=O (X = Cl and Br) dipolar inter-actions, as well as a C - H⋯π inter-action, developing the three-dimensional structure along the c axis.