An Fe(II)-Based Hexagon-Fused Wheel Constructed via Post-Synthetic Transmetalation

Fe(II)-based supramolecules have attracted considerable interest in catalysis, environmental science, and biomedicine due to their low toxicity, low cost, and versatile oxidation states. However, the strong coordination affinity of Fe(II) often compromises the reversibility of self-assembly, and conventional one-pot synthesis─hindered by intricate ligand design and kinetic traps─hampers the direct formation of desired Fe(II)-based topological architectures. To overcome these limitations, a postsynthetic transmetalation strategy was employed: a Zn(II)-based hexagon-fused wheel was first assembled from a Ru(II)-centered metallo-ligand LA and a multitopic terpyridine ligand LB, followed by complete Zn(II)-to-Fe(II) exchange to afford the target discrete Fe(II) complex (diameter 14.2 nm, molecular weight ∼ 47,690 Da). This work demonstrates a supramolecule-to-supramolecule metal exchange within a large discrete architecture. The structure was characterized by UV-vis spectroscopy, NMR, and mass spectrometry. Therefore, this transmetalation strategy presents an alternative platform that overcomes the reversibility constraint in Fe(II) coordination. It facilitates the creation of novel functional complexes beyond the scope of direct synthesis, promoting the development of structurally sophisticated and functional Fe-based supramolecules.