Constructing High-Generation Sierpiński Triangles by Molecular Puzzling

Three generations of metalated trigonal supramolecular architectures, so-called metallo-triangles, were assembled from terpyridine (tpy) complexes. The first generation (G1) metallo-triangles were directly obtained by reacting a bis(terpyridinyl) ligand with a 60° bite angle and Zn^II ions. The direct self-assembly of G2 and G3 triangles by mixing organic ligands and Zn^II , however, only generated a mixture of G1 and G2, as well as a trace amount of insoluble polymer-like precipitate. Therefore, a modular strategy based on the connectivity of ⟨tpy-Ru²⁺ -tpy⟩ was employed to construct two metallo-organic ligands for the assembly of G2 and G3 Sierpiński triangles. The metallo-organic ligands L^A and L^B with multiple free terpyridines were obtained through Suzuki cross-coupling of the Ru^II complexes, and then assembled with Zn^II or Cd^II to obtain high-generation metallo-triangular architectures in nearly quantitative yield. The G1-G3 architectures were characterized by NOESY and DOSY NMR spectroscopy, ESI-MS, TWIM-MS, and transmission electron microscopy.