Anion-π-Directed Self-Assembly between Di- and Trisulfonates and a Rigid Molecular Cage with Three Electron-Deficient V-Clefts.

Anion-π-directed self-assembly between a series of di- and trisulfonate anions and a rigid molecular cage 1 was presented. The self-assembly study was established on a combination of X-ray crystallography, NMR, mass spectrometry (MS), and scanning electron microscopy (SEM) techniques. As revealed in the crystal structures, the cage provided two V-shaped electron-deficient clefts to accommodate sulfonate groups through anion-π interactions. Depending on their structure, the series of anions showed different intermolecular interaction details with the cage and led to the formation of diverse self-assembly motifs. For 1,2-ethanedisulfonate (EDS2-), 1,3-propanedisulfonate (PDS2-), and 1,4-butanedisulfonate (BDS2-), very similar and uniform 2D ladder-like self-assemblies were formed. For 1,6-hexanedisulfonate (HDS2-) with a longer alkyl chain, a helical chain assembly was formed, while 1,3,5-tris(4-sulfophenyl)benzene (TSPB3-) led to a 3D frame structure. In solution, NMR titrations suggested that the cage can complex these anions, with association constants falling in range of 5-114 M-1. NMR spectra recorded at variable concentrations and temperatures and electrospray ionization MS further confirmed self-assembly formation. The morphologies of the diverse self-assemblies formed between the cage and sulfonates were revealed by SEM. This study, hence, provides evidence that anion-π interactions can play decisive roles in self-assembly.