Self-Assembled Metal-Organic Cages and their Host-Guest studies

Abstract

Metal-organic cages are a class of materials that are emerging as potential candidates for their excellent host-guest binding abilities. These are essentially metal-based assemblies and have metal-organic (MOPs) frameworks and have inbuilt well-defined cavities with engineerable pores dimensions that make them so distinct. These well-built cavities for example in the case of palladium derived cages have been used as the catalyst for enantio-selectivity. The applications of metal-organic cages however are hindered due to their poor stability due to complex aqueous solution dynamics and short-lived and unstable intermediates during their preparation. The work done in this project highlights the synthesis of ligands with the purpose of improving the synthesis of cages in the solution state. The approach is based on hetero atom ligands containing phosphorus-nitrogen bonds due to their ease of bond formation and these form chemically stable bonds. Amongst various phosphorus nitrogen-based compounds the Amido and imido P(V) compounds, analogues to phosphorus oxo-groups, are very interesting molecules to work with, in the development of metal-organic cages. The stout P- N bonds are capable of forming ligands used for the synthesis metal complexes. In my lab, amino P(V) backbones are employed as an attractive platforms for the synthesis of multipurpose ligands. In polar solvents, soft transition metal ions such as Pd(II) are employed for the development of P(V) bound poly imido species. In addition, we have also attempted to explore Zirconium carboxylate Cages, which to our knowledge has not been studied with respect to host-guest studies. These studies revealed that one of the cages, Zr-Nap cage, exhibits selective binding p-Xylene over its other ortho- and meta-isomers as indicated by mass spectral analysis and host-guest binding constants obtained from UV-VIS titrations.