Multiple intermolecular interactions in guest inclusion by acyclic host compounds

Abstract

Disubstituted adamantanes having nitrophenol moieties were examined for their ability to recognize ketone and ester molecules through multiple intermolecular interactions, with the hydroxyl and nitro groups serving as hydrogen bond donors and acceptors. Crystallization of 1,3-bis(2-hydroxy-5-nitrophenyl)adamantane (1) in acetone, 2-butanone, and methyl acetate afforded three inclusion crystals with 1 : 1 stoichiometry. X-ray crystallographic analysis revealed that the hydroxyl groups of 1 engaged in OH⋯O interactions with the guest oxygen atoms in all crystals. Moreover, the guest hydrogen atoms participated in CH⋯O interactions with the host nitro and hydroxyl groups at three, four, or five points. These findings suggest that the guest molecules were captured through interactions with multiple functional groups in a manner resembling that of guest inclusion in enzyme pockets. Crystallization of 1,3-bis(4-hydroxy-3-nitrophenyl)adamantane (2) and 1,3-bis(2-ethoxy-5-nitrophenyl)adamantane (3) in acetone resulted in the formation of guest-free crystals, with NO₂⋯NO₂ interactions being prominent in the crystal of 3.