Host–Guest Recognition in the Crystalline State: Selective Inclusion of 1,4-Dibromobutane by Bromoethoxy-Functionalized Pillar[5]arenes

Abstract The guest encapsulation behavior and solid-state supramolecular assembly of four bromoethoxy-substituted pillar[5]arenes were investigated. These macrocycles selectively encapsulate 1,4-dibromobutane from equimolar mixtures of four α,ω-dibromoalkanes, forming 1:1 crystalline inclusion complexes. Single-crystal X-ray diffraction revealed that encapsulation is stabilized by C–H···π and C–H···O interactions within the macrocyclic cavity. The number and position of bromoethoxy groups significantly influence the supramolecular packing. While mono- and di-bromoethoxy-functionalized pillar[5]arenes exhibit only C–H···π and C–H···O interactions, the tetra- and hexa-bromoethoxy derivatives additionally display C–H···Br contacts, with the guest contributing to the assembly. Notably, the hexabromoethoxy-functionalized pillar[5]arene also exhibits Br···Br interactions, resulting in a distinct packing arrangement compared to the other systems.