Designable Aluminum Molecular Rings: Ring Expansion and Ligand Functionalization

Presented herein are the Al^III molecular ring architectures from 8‐ring to 16‐ring. Although there are numerous reported cyclic coordination compounds based on transition metals, gallium, or lanthanides, the Al versions are less developed due to the fast hydrolysis nature of Al³⁺ ion. With the assistant of monohydric alcohols, a series of atomic precisely Al molecular rings based on benzoates are synthesized. The ring expansion of these Al‐rings from 8‐ring to 16‐ring is related to the monohydric alcohol structure‐directing agents. Moreover, the organic ligands on the Al‐rings can be modified by using various benzoate derivatives, which lead to tunable surface properties of the Al‐rings from hydrophilicity to ultra‐hydrophobicity. Importantly, 4‐aminobenzoic acid bridged 16‐ring is soluble in organic solvents and exhibits high solution stability revealed by mass spectroscopy. Ligand substitution also can be performed between these Al‐rings, which reveal controllable ligand functionalization of these Al‐rings.