Giant 7-Fold Symmetric Eu28Ti14 Molecular Wheels

The atomically precise assembly of high-nuclearity lanthanide-titanium clusters remains challenging because of the distinct hydrolysis behaviors and coordination preferences of Ln3+ and Ti4+ ions. Herein, a dual-ligand coassembly strategy under solvothermal conditions affords two giant Ln-Ti heterometallic molecular wheels, Eu28Ti14(μ3-O)14(L)42(HL)14(Im)14(HOiPr)14(H2O)14 (Eu28Ti14-Im) and Eu28Ti14(μ3-O)14(L)42(HL)14(Bim)14(HOiPr)14(H2O)14 (Eu28Ti14-Bim; H2L = 5-chlorosalicylic acid; HIm = 1H-imidazole-2-carboxylic acid; HBim = 1H-benzimidazole-2-carboxylic acid; HOiPr = isopropanol). With 42 metal ions, they represent the highest-nuclearity Ln-Ti complexes reported to date. Both complexes feature rare molecular-level 7-fold symmetry generated by the alternating arrangement of chiral [Eu2Ti(μ3-O)]8+ subunits. Notably, Eu28Ti14-Bim acts as a photocatalyst for light-driven CO2 reduction in water without adding photosensitizers or sacrificial agents, producing CO and O2 simultaneously. In situ FT-IR spectroscopy and DFT calculations reveal that the Eu and Ti sites operate complementary catalytic centers, with Eu promoting water oxidation and Ti driving CO2 reduction, thereby establishing a dual-site synergistic mechanism. This work expands the structural chemistry of giant lanthanide-titanium molecular wheels and highlights their potential in solar-to-chemical conversion.