Different metal-ion-induced dimeric self-assembling cavities based on thiacalix[4]benzocrown-4 isomers

Abstract

To construct the self-assembly of metal-ion-induced well-ordered architectures based on calixcrowns, isomeric thiacalix[4]benzocrowns-4 1 and 2 with rigid and small crown units were employed as the new scaffolds. They all show remarkable selectivity for Ag⁺ and their complexation ability towards Ag⁺ results in two novel dimeric aggregates of calixcrowns, which were first evidenced by ESI-MS, ¹H and DOSY-NMR spectra. Ultimately, X-ray diffraction experiments confirmed unambiguously the existence of the two metal-ion-induced dimers in lower rim/lower rim mode, and showed that dimerization of calixcrown 1 or 2 in the presence of Ag⁺ could form dimeric supramolecular cavity with a small inner room. Moreover, the positional isomerism of their crown units (o-benzocrown unit for ligand 1 and m-benzocrown unit for 2) led to a dramatic change in the configuration of the two dimeric cavities 1·Ag⁺ and 2·Ag⁺. For dimeric cavity 1·Ag⁺, two silver centers seamed two thiacalix[4]crown molecules together and resided at the edge of the dimeric self-assembling cavity; for dimeric cavity 2·Ag⁺, one Ag⁺ stitched two thiacalixcrowns together and was encapsulated in the center of the self-assembling cavity, while the other Ag⁺ is tied down to one end of the dimer. Consequently, as a result of the different construction of dimeric cavities 1·Ag⁺ and 2·Ag⁺ the extended structures of the complexes are also different. The neighbour self-assembling cavities 1·Ag⁺ are mutually oriented side-by-side and form a 1-D rectilineal polymeric chain. While, the neighbour self-assembling cavities 2·Ag⁺ arrange themselves in a typical head-to-tail fashion to form a zig-zag polymeric chain.