Unusual parallel entanglement of metal-organic 2D frameworks with coexistence of polyrotaxane, polycatenane and interdigitation

Three novel luminescent metal-organic frameworks [Zn(1,2-BBOMB)(4,4'-bipy)(1/2)](n) (1), [Zn-2(1,3-BBOMB)(2)(4,4'-bipy)](n) (2) and [Zn-4(1,2-BBOMB)(4)(bpp)(2)](n) (3) have been synthesized by combining the conformationally flexible V-shaped long multicarboxylate ligands and the rigid 4,4'-bipy or flexible bpp ligands with zinc ions under hydrothermal conditions. It is worth mentioning that the layers observed in the three compounds can be reduced to the same 6-connected topological net with (2(2).4(8).6(5)) symbol. These complexes display a structural evolution from a two-dimensional (2D) polyrotaxane and polycatenane framework to a three-dimensional (3D) architecture with coexistence of polyrotaxane, polycatenane and interdigitation. The three species contain loops and rods that are interlaced in a highly rare parallel fashion, but with twofold (2D -> 2D), triply (2D -> 2D) and triply (2D -> 3D) entangled features in complexes 1, 2 and 3, respectively. Furthermore, the rotaxane-like interactions between the loops and the rods exhibit a progressive change from one loop interacting with a single rod, to one loop interacting with two identical rods, to finally one loop interacting with two conformationally different rods in complexes 1, 2 and 3, respectively. Photoluminescence studies revealed that these complexes are potential violet, blue and green luminescent materials. The thermal stabilities of these complexes were also discussed.