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), [Zn2(1,3-BBOMB)2(4,4′-bipy)]n (2) and [Zn4(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 (22·48·65) 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.