Experimental X-ray and DFT Structural Analyses of M 12 L 8 Poly-[ n ]-catenanes Using exo-Tridentate Ligands.

Despite their potential applications in host-guest chemistry, there are only five reported structures of poly-[ n ]-catenanes self-assembled by elusive M 12 L 8 icosahedral nanocages. This small number of structures of M 12 L 8 poly-[ n ]-catenanes is because self-assembly of large metal-organic cages (MOCs) with large windows allowing catenation by means of mechanical bonds is very challenging. Structural reports of M 12 L 8 poly-[ n ]-catenanes are needed to increase our knowledge about the self-assembly and genesis of such materials. Poly-[ n ]-catenane ( 1· p -CT ) self-assembly of interlocked M 12 L 8 icosahedral cages ( M = Zn(II) and L = 2,4,6-tris-(4-pyridyl)benzene ( TPB )) including a new aromatic guest ( p -chlorotoluene ( p -CT )) is reported by single-crystal XRD. Despite the huge internal M 12 L 8 voids (> 2500 Å 3 ), p -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 TPB ligand, and various aromatic guests (i.e., o -dichlorobenzene ( o -DCB ), p -chloroanisole ( p -CA ), and nitrobenzene ( NBz )) included (ordered) within the M 12 L 8 cages were determined by single-crystal XRD. The computed maps of electrostatic potential ( MEPs ) 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 M 12 L 8 poly-[ n ]-catenanes, the reported combined experimental/DFT structural analyses approach can be exploited to use isostructural M 12 L 8 poly-[ n ]-catenanes as hosts for molecular separation and could find applications in the crystalline sponge method developed by Fujita and co-workers. We also demonstrate, exploiting the instant synthesis method, in solution (i.e., o -DCB ), and in the solid-state by neat grinding (i.e., without solvent), that the isostructural M 12 L 8 poly-[ n ]-catenane self-assembled with 2,4,6-tris-(4-pyridyl)pyridine ( TPP ) ligand and ZnX 2 (where X = Cl, Br, and I) can be kinetically 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 ( TPP vs TPB ), the kinetic control gives the poly-[ n ]-catenanes selectively. The dynamic behavior of the TPP amorphous phases upon the uptake of aromatic guest molecules can be used in molecular separation applications like benzene derivatives.