Supramolecular dual-synthon in cocrystals of 1-azaanthracene and naphthols: cooperation between hydrogen bonds and cation–π interactions

Abstract

Cocrystals of 1-azaanthracene and several naphthols were prepared by cocrystallization using the solvent evaporation and grinding methods. Their crystal structures were elucidated by X-ray crystallography and PXRD. While cocrystallization of 1-azaanthracene and 2-hydroxynaphtharene (2-HNP) in a 1 : 1 ratio afforded cocrystal (AA)·(2-HNP) (1), cocrystallization in a 2 : 1 ratio produced cocrystal (AA)₂(2-HNP) (2). When 2,6-dihydroxy- and 2,7-dihydroxynaphtharenes were used instead of 2-HNP, corresponding cocrystals 3 and 4 were obtained, respectively. The X-ray crystallographic analyses of 1 to 4 revealed that these cocrystals are composed of a common supramolecular dual-synthon assembled by hydrogen bonds and cation–π interactions, with AA molecules arranged in face-to-face and head-to-tail fashion. The observed supramolecular dual-synthon is thought to be the result of cooperation between hydrogen bonding and cation–π interactions. Interestingly, the hydroxy group of 2-HNP in cocrystal 2 exhibited significant disorder at the 2- and 6-positions of the naphthalene ring with a 50% probability, behaving as if it were 2,6-dihydroxynaphthalene having two OH groups. In fact, cocrystal (AA)₂(2-HNP) (2) was found to have nearly the same crystal structure as (AA)₂·(2,6-DHNP) (3). UV irradiation of cocrystals 1 to 4 gave antiHT dimer quantitatively, while irradiation of cocrystals 1′–4′, which were formed by grinding, afforded antiHT dimers along with antiHH dimers.