Experimental X-ray and DFT Structural Analyses of ML Poly-[]-catenanes Using exo-Tridentate Ligands.

Despite their potential applications in host-guest chemistry, there are only five reported structures of poly-[]-catenanes self-assembled by elusive icosahedral nanocages. This small number of structures of poly-[]-catenanes is because self-assembly of large metal-organic cages (MOCs) with large windows allowing catenation by means of is very challenging. Structural reports of poly-[]-catenanes are needed to increase our knowledge about the self-assembly and genesis of such materials. Poly-[]-catenane () self-assembly of interlocked icosahedral cages ( = Zn(II) and L = 2,4,6-tris-(4-pyridyl)benzene ()) including a new aromatic guest (-chlorotoluene ()) is reported by single-crystal XRD. Despite the huge internal voids (> 2500 Å), -CT is ordered, allowing a clear visualization of the relative host-guest positions. DFT calculations have been used to compute the electrostatic potential of the ligand, and various aromatic guests (i.e., -dichlorobenzene (), -chloroanisole (), and nitrobenzene ()) included (ordered) within the cages were determined by single-crystal XRD. The computed maps of electrostatic potential () allow for the rationalization of the guest's inclusion seen in the 3D X-ray structures. Although more crystallographic X-ray structures and DFT analysis are needed to gain insights of guest inclusion in the large voids of poly-[]-catenanes, the reported combined experimental/DFT structural analyses approach can be exploited to use isostructural poly-[]-catenanes as hosts for molecular separation and could find applications in the method developed by Fujita and co-workers. We also demonstrate, exploiting the method, in solution (i.e., ), and in the solid-state by (i.e., without solvent), that the isostructural poly-[]-catenane self-assembled with 2,4,6-tris-(4-pyridyl)pyridine () ligand and ZnX (where X = Cl, Br, and I) can be synthesized as crystalline (yields ≈ 60%) and amorphous phases (yields ≈ 70%) in short time and large quantities. Despite the change in the aromatic nature at the center of the rigid exo-tridentate pyridine-based ligand ( vs ), the gives the poly-[]-catenanes selectively. The dynamic behavior of the amorphous phases upon the uptake of aromatic guest molecules can be used in molecular separation applications like benzene derivatives.