Co-crystal screening of disubstituted adamantane molecules with N-heterocyclic moieties for hydrogen-bonded arrays

Abstract

Four disubstituted adamantane-based molecules containing N-heterocyclic moieties were designed and synthesized as hydrogen bond acceptors for the preparation of co-crystals with hydrogen bond donors. Co-crystal screening of the four adamantane-based molecules with terephthalic acid was firstly attempted in mixed solvents. Only the compound with methylimidazole moieties (1) afforded the co-crystals in 1:1 ratio, whereas the others gave individual crystals. X-ray crystallographic analysis demonstrated that the hydrogen bonds between the imidazole and the carboxylic acid moieties of both components provided infinite one-dimensional chains that were assembled into network structures through CH···O interactions. When isophthalic acid or resorcinol was employed as the partner, the co-crystals were similarly generated by intermolecular non-covalent interactions. The selective co-crystal formation of 1 is mainly attributed to the increase of strength of the hydrogen-bonding acceptor on the nitrogen atoms of the N-heterocyclic moieties and the stabilization of the hydrogen-bonded complexes due to the electron-donating ability and the steric effect of the methyl groups.