Epitaxial growth of high-nuclearity zirconium oxo clusters from Zr16 to Zr20 and subsequent ligand exchange

Synthesizing zirconium-oxo clusters (ZrOCs) with precisely defined “mother-daughter” architectures (large clusters containing smaller cluster units) is essential for gaining a profound understanding of their assembly mechanism and precisely controlling their properties. However, owing to considerable synthetic difficulties, achieving this goal remains a formidable challenge. Herein, we report the synthesis of two novel high-nuclearity ZrOCs, namely [Zr16(μ3-O/OH)24(μ2-OH)4(QE)4(PA)20] (Zr16; H2QE = 2,8-quinolinediol; HPA = propanoic acid) and [Zr20(μ3-O/OH)32(μ2-OH)4(QE)8(PA)20] (Zr20), via a facile solvent-induced synthetic strategy. Surprisingly, we found that Zr16 and Zr20 exhibit a “mother-daughter” relationship, where Zr16, as the “daughter”, is embedded within Zr20, the “mother”, with the PA ligands excluded. Moreover, Zr20 can react with benzoic acid (HBA) via post-synthetic reactions to yield another new cluster, [Zr20(μ3-O/OH)32(μ2-OH)4(QE)8(BA)20] (Zr20-BA), which retains the metal core and QE ligands of Zr20, with only the peripheral PA ligands replaced by BA ligands, highlighting the framework stability and flexibility of ligand shell of Zr20. Of note, Zr20 exhibited better thermal catalytic cycloaddition of CO2 and epoxides performance due to the rich Lewis acidity of Zr sites, achieving near-complete conversion of diverse epoxides. This work not only expands the structural landscape of high-nuclearity ZrOCs but also provides deeper insights into their underlying assembly mechanism.