Halogen Interactions in Macrocyclic Thiacalix[4]arene Systems

The crystalline supramolecular assemblies of brominated thiacalix[4]­arene alkyl ethers were studied by single-crystal X-ray diffraction and computational analysis. Eight compounds were synthesized that exhibited linear alkyl groups of varying lengths projecting from the thiacalixarene lower rims (−CH₃: 4, −CH₂CH₃: 5, −(CH₂)₄CH₃) to –(CH₂)₉CH₃): 6–11) in order to study the intermolecular halogen interactions between the macrocycles. These crystals displayed remarkably different assemblies, which was rationalized as an effect of varying alkyl chain length on the stabilization afforded by the halogen interactions. The two compounds with the shortest alkyl chains, 4 and 5, assembled primarily through the influence of halogen−π interactions between distinct molecules. In contrast, the compounds with the longest chains, 8–11, assembled primarily through the influence of halogen–sulfur halogen bonding. Oddly, 6 and 7 did not follow this pattern in that they showed no major assembly motivated by halogen interactions. Finally, the supramolecular assemblies were found to be stabilized by additional intermolecular interactions, including hydrogen bonding, S-π, CH-π, and Br–H interactions.