Construction And Study Of Host-Guest Chemistry Of Ce-based Metal-organic Cages

The design and assembly of metal-organic cages with well-defined shape and size has achieved always been challenges and targets for chemists, owing to their broad utility in wide-ranging applications from chemistry to medicinal and academic arenas. The lanthanide ions exhibiting low stereochemical preferences and high coordination numbers are seldom used to construct the molecular capsules, despite that such molecular cages have the potential to exhibit interesting such as luminescence properties. In another hand, H-bonding is the main mode in saccharide-protein interactions, but the design of ligands with host-guest binding sites in metal-organic cages is still a change. On the basis of this context, this paper contains the following aspects of contents:1. By incorporating-NOO-tridentate chelators into the rationally designed ligands with C2 or C2V symmetries, Ce-SABB and Ce-TBMS were synthesized with Ce3+ via self-assembly. Single crystal X-ray structural analysis reveals the formation of tetranuclear cerium rectangle of Ce-SABB. Two ligands bridge two metal centers in a helical fashion to form the two short edges of the rectangle and are further connected through two SABB. The neutral Ce-TBMS molecule comprised eight cerium ions and six TBMS ligands in a cubic-like cage. Eight Cerium centers sited at the eight corners of the cage, and each is nine coordinated by three tridentate chelating groups that from difference ligands. Four of the six ligands were parallel to each other with the methylene group bend inside the cage, and other two of the six ligands which bend outside the cube positioned in the direction perpendicularly to that of the four ligands positioned. Accordingly the cube-like cage exhibited pseudo-54 symmetry. Through limiting the number and orientation of the ligands coordinating to the lanthanide centers, such an approach is validated to be powerful in assembling highly ordered lanthanide architectures.2. By the similar strategy ce-based werner type tetrahedrons Ce-NDCS and Ce-BDCN were achieved for the size-selective sensing of saccharides. The tetrahedrons comprised of four metal centers that each coordinated to three tridentate chelating groups. Each ligand positioned on one of the six edges of the tetrahedron defined by four metal ions and bridged two metal centers. The luminescence titration of Ce-NDCS upon the addition of hexoses showed that the affinities of Ce-NDCS for hexoses were larger than those for the smaller size monosaccharides and bigger size disaccharides, and upon the addition of saccharides showed that the affinities of Ce-BDCN for disaccharides were larger than those for the smaller size monosaccharides. Amide groups act as the multiple hydrogen bonding triggers and binding-signalling transductor.3. A series of cerium-based triple-stranded helicates were achieved the similar strategy. The self-assembly of the interlocked [Ce-DCSS]2 demonstrates that a novel 3D-[2]catenanes motif is accessible for chemical systems. It is formed by symmetrical 3D metallosupramolecular assemblies where the ligands do not show any extensive interaction between them. Little changes at the end groups or the angle between the arms of ligands will case larger stereo-hindrance effect or smaller inner volume, and no interlocking between the cages. The helicate Ce-DCDS with smaller inner volume acting as 3D cavities which show binding towards Al3+ with a significant luminescence enhancement.