Regiochemistry of topochemical reactions depends on the crystal packing and biasing the regiochemistry necessitates precise crystal engineering. The pristine crystals of monomer 1 upon topochemical azide-alkyne cycloaddition (TAAC) reaction give a 1 : 1 blend of 1,4- and 1,5-triazole-linked polymers due to the presence of two self-sorted reactive conformers in the crystal. We designed a binary isomorphous cocrystal of monomer 1 and a structurally similar dummy molecule 2 to limit the number of reactive conformers of 1 to one and thus to get one type of polymer. Equimolar solution of 1 and 2 in chloroform-acetone mixture gave two 1 : 1 cocrystals Co-I and Co-II. The Co-II, a chloroform adduct, on heating undergoes desolvation and polymorphic transition to Co-I. Co-I is isomorphic to 1 and 2 and possess self-sorted arrays of 1 and 2. Heating Co-I results in the TAAC polymerization giving 1,4-triazolyl-linked polymer of 1 selectively, showing the power of crystal engineering in regiocontrol.
Keywords: Cocrystal; Crystal Engineering; Polymer; Regioselectivity; Topochemical Reaction.
© 2022 Wiley-VCH GmbH.