Carbonyl-carbonyl, carbonyl-π 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 P2(1)/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)degrees for ( I), and by 9.07 (8) and 18.96 (18)degrees for (II), owing to their involvement in intermolecular interactions. In both compounds, layers of centrosymmetric hydrogen- bonded dimers are developed in the [5222] plane through C-(HO)-O-... interactions, involving both carbonyl groups as acceptors. Two families of dimers stack through C=(OC)-C-...=O, C=O-...pi and C - (XC)-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.