Investigating reaction conditions for controlling the self-assembly of metal-seamed pyrogallol[4]arene nanocapsules

Abstract

[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT REQUEST OF AUTHOR.] Upon coordination to metal ions, C-alkylpyrogallol[4]arenes (PgCn, where n is the number of carbon atoms in the pendant alkyl chains), can be assembled into spherical metal-organic nanocapsules (MONCs). MONCs are generally arranged into two different structural types, hexamers and dimers, of which six or two PgCn units assemble into capsular structures by coordination to 24 or 8 metal ions, respectively. Co[II]-, Zn[II]-, and Mn[II]-coordinated MONCs have been synthesized under ambient conditions and structurally characterized. Under certain reaction conditions, some transition metal ions and other reagents seem to act as electron accepting or donating reagents, such that appropriate oxidation or reduction reactions may occur. These types of in-situ redox reactions lead to the formation of mixed-valence Mn[II]/Mn[III]- and Fe[II]/Fe[III]-seamed MONCs. The occurrence of such oxidation/reduction reactions appears to be promoted by certain factors such as resulting pH conditions, size of the coordinating ions/ligands, and oxidizing/reducing abilities of reagents used in each synthesis. In addition, studies have been carried out to incorporate some defects into the MONC outer framework by using mixed-macrocycles as the starting materials. Mixed-macrocycles are synthesized by fusing both resorcinol and pyrogallol into the same macrocycle, and the position of resorcinol units in the MONC usually appears as a hole or defect on the capsule surface. Incorporations of such defects give MONCs potential for, for example, selective filtering of small molecules into the capsule interior and magnetic and electronic applications by varying the electrostatic interaction between adjacent metal ions.