Hierarchical packing of racemic metallosupra­molecular cages with Ni(II)-based triple-stranded helicate building blocks

Three novel hierarchical Ni-based metallosupramolecular cages were constructed from nickel ions, pyridine di­carboxyl­ates and isophthalate derivative ligands (the substituents on C5 of isophthalate are methyl, tert-butyl and bromo groups). In every cage, two multinuclear nickel clusters, assembled from four nickel atoms and three pyridine di­carboxyl­ate ligands, are interlinked by three isophthalate-derivative ligands to form a nickel-based triple-stranded helicate (TSH), which then becomes the supramolecular building block for the fabrication of a metallocage. Six homochiral TSH supramolecular building blocks, either left (M)-handed or right (P)-handed, are connected by four linking nickel atoms to generate M (6) and P (6) discrete racemic cage molecules (M (6) – cage with six M-TSHs; P (6) – cage with six P-TSHs). The crystal packing of the racemic cages was characterized by single-crystal X-ray diffraction. An additional cobalt-based molecular cage with 5-methyl­isophthalate bridging ligands was synthesized for host–guest interaction studies. The methyl groups in Co- and Ni-TSH can act as guest units to be accommodated in the cone-shaped metal clusters (host) of an adjacent cage.