Directed Intermolecular Association by Complementary Molecular Edges in 6-Methoxycoumarin

The design of complementary hydrogen bonding interactions between molecules is often used in crystal engineering and other molecular recognition research. Herein we report the ability of complementary molecular edges in 6-methoxycoumarin (1) to form CH···O interactions and thereby direct intermolecular association of this compound. Cocrystallization experiments between 2-methoxynaphthalene (2) and coumarin (3) yield a powdery eutectic at a 1:1 stoichiometry but provide no indication of whether similar intermolecular edge interactions between 2 and 3 are stable in solution. The lack of net secondary interactions in the intermolecular association of 1 does not prevent edge-directed association between CH···O groups. Indeed, fumaric acid monoethyl ester (4) associates through edge-directed CH···O interactions in the solid-state with seemingly unfavorable secondary interactions. The use of complementary edges capable of associating through CH···O interactions may serve as useful molecular recognition elements by themselves or within the context of other predictable intermolecular forces.