Isomeric enrichment of 1,3-bis(aminomethyl)cyclohexane by sequential crystallization of its mono- and di-iodide salts

Commercial 1,3-bis(aminomethyl)cyclohexane (BAC), recently applied as dopant/stabilizer in functional perovskite materials, contains variable amounts of cis/trans isomers and requires purification, as only the cis form was found effective. Here we propose a simple purification strategy, based on sequential and selective crystallization steps of the iodide salts, with an improvement of the initial 3 : 1 to the final 13 : 1 cis : trans ratio. We also performed a rich study of the structural and energetic landscape of BAC mono and diiodides, evidencing, through solid-state transformations and subtle recrystallization processes, alternative reaction paths linking the different polymorphs. Finally, we ascertained that all prepared crystal phases contain vicariant trans-BAC molecules, hosted in the lattice of predominantly cis isomer-rich iodides, with no evidence of diastereoisomeric segregation.