Terpyridine-based metallo-organic cages and supramolecular gelation by coordination-driven self-assembly and host–guest interaction

Abstract

Host–guest complexation based on terpyridine (tpy) three-dimensional (3D) metallo-cages has received less attention due to the complicated structure and solubility issues. Herein, a three-armed metallo-organic ligand (L) was synthesized via three 120°-bent bis-tpy groups as a rigid tetrakis-tpy core, which possesses one benzo-21-crown-7 (B21C7) for further host–guest interaction. The metallo-organic cages [M₃L₂] with molecular weights up to 13 000 Da and giant cavities were prepared in near-quantitative yield by self-assembly of L with metal ions, such as Zn²⁺ and Fe²⁺. The 3D metallo-supramolecules were characterized and their formation was supported by NMR, DOSY, ESI-MS and TEM. Hosts [M₃L₂] were threaded through a difunctional alkylammonium salt by host–guest interactions to polymerize, and subsequently generate novel metallo-gels between [Zn₃L₂] and bis-ammonium salt (N²).