Solution Studies of Self-Assembling Pnictogen Cages.

Secondary bonding interactions of p-block elements in materials chemistry have been largely utilized in areas such as anion binding, molecular recognition, crystal engineering, and supramolecular catalysis, because of their unique nature. This upcoming phenomenon has proven to be a useful tool for supramolecular chemistry, however, foundations of the phenomenon such as complete understanding of the secondary bonding interactions of the pnictogens, remain undeveloped. In this regard, the goal of this study is to develop pnictogen-centered cages that can form multiple pnictogen-bonds and ultimately, supramolecular structures via homomolecular self-assembly. A survey into the Cambridge Structural Database was performed to gain insight into these interactions. Crucial features of these interactions revealed the direct correlation between the binding energy of these interactions and the secondary bond distances based on the covalent radii of each element, allowing for the general categorization of secondary bonding interactions. This information identified essential design criteria for the synthesis of new pnictogen bonding forming molecules. Antimony alkoxide and thiolate cages were designed previously and revealed the formation of reverse bilayer vesicles in organic media. Of great interest is the ability of alternative pnictogen-centered cages to form similar supramolecular structures. Analogous moieties of arsenic(III) alkoxide and thiolate compounds were prepared to confirm the importance of our proposed design criteria to form predictable vesicles. These vesicles were used to partition organic media so that reactions could occur in and outside the vesicles. Studies of the effect of molecular features of pnictogen-centered cages, such as the tail length, and preparation method of allowed us to propose a model for influence of solvent and reverse bilayer parameters on the formation of vesicles. Investigating compounds with expanded molecular features of the established pnictogen-centered cages again confirmed the importance of our proposed design criteria to form predictable vesicles. While antimony(III) DTT-based cages revealed an alternative method for forming reverse bilayer vesicles and combining the advantages of the symmetric cages, a different set of antimony(III) alkoxide cages resulted in non-bilayer, oligomeric systems. However, these systems revealed an interesting relationship between their solid and solution states. To further investigate this relationship, the solution energetics for the self-recognition of these molecules were determined.