Meso-Helicates with Rigid Angular Tetradentate Ligand: Design, Molecular Structures, and Progress Towards Self-Assembly of Metal–Organic Nanotubes

The self-assembly of two novel metallosupramolecular complexes of the general formulas [L2M2(CH3CN)4]­[BF4]4 (M = Co, 1a; M = Ni, 1b), where L stands for the tetradentate ligand 3,5-bis­[4-(2,2′-dipyridylamino)­phenylacetylenyl]­toluene, is reported together with their molecular structures ascertained by single-crystal X-ray diffraction studies. Complexes 1a and 1b are isostructural and show the formation of dinuclear meso-helicates with the two octahedral metal centers displaying respectively Δ and Λ configurations. These meso-helicates display large nanocavities with metal---metal separation distance of >2 nm; furthermore, π–π-stacking occurs among individual units to form one-dimensional (1D) polymers which further autoassemble in another direction through π–π contacts among neighboring chains to generate a two-dimensional (2D) network with regular nanocavities. Our approach might be of interest to prepare metal–organic nanotubes via a bottom-up strategy depending on the assembling functional ligand and the geometry of molecular building block.