Active control of molecular stacking types in a congeneric library of dihalogenated salicylideneaniline crystals and their solid solutions

Abstract

Intentional crystal packing modification is a crucial subject in crystal engineering to achieve functional modulation. In this study, we report a series of congeneric N-(4′-halosalicylidene)-4-haloanilines (4XY, where X and Y = C or B for Cl or Br substitution, respectively). 4BB afforded three polymorphic crystals in which, the isostructural layers were stacked differently, also called polytypes. The structural differences resulted from the different types of interhalogen contacts between the layers. 4CC-y, 4BC, and 4CB crystals were isostructural to one of the 4BB polytypes, reflecting the preferred type of interhalogen contacts depending on the halogen atoms involved. A similar polytypism was found for the 5′-substituted compounds 5XY. By changing the ratio of the 4XY compositions, we obtained a series of binary solid solutions that exhibited various stacking arrangements and melting points while retaining their fundamental molecular structures and properties. The present work serves as a successful example of controlling crystal structures by means of systematic change of constituent atoms in molecular crystals.