Hexagonal Microparticles from Hierarchical Self-Organization of Chiral Trigonal Pd3L6 Macrotetracycles

Construction of structurally complex architectures using inherently chiral, asymmetric, or multi-heterotopic ligands is a major challenge in metallosupramolecular chemistry. Moreover, the hierarchical self-organization of such complexes is unique. Here, we introduce a water-soluble, facially amphiphilic, amphoteric, chiral, asymmetric, and hetero-tritopic ligand derived from natural bile acid, ursodeoxycholic acid. We show that via the supramolecular transmetalation reaction, using nitrates of Cu(II) or Fe(III), and subsequently Pd(II), a superchiral Pd3L6 complex can be obtained. Even though several possible constitutional isomers of Pd3L6 could be formed, because of the ligand asymmetry and relative flexibility of carbamate-pyridyl moieties attached to the steroid scaffold, only a single product with C3 rotational symmetry was obtained. Finally, we demonstrate that these amphiphilic complexes can self-organize into hexagonal microparticles in aqueous media. This finding may lead to the development of novel self-assembled metal-organic functional materials made of natural, abundant, and relatively inexpensive steroidal compounds.