Aqueous Isolation of 17-Nuclear Zr/Hf Oxide Clusters during the Hydrothermal Synthesis of ZrO2 /HfO2.

Novel 17-nuclear Zr/Hf oxide clusters ({Zr17 } and {Hf17 }) are isolated from aqueous systems. In the clusters, Zr/Hf ions are connected through μ3 -O, μ3 -OH, and μ2 -OH linkages into a pinwheel core which is wrapped with SO4 2- , HCOO- , and aqua ligands. Octahedral hexanuclear Zr/Hf oxide clusters ({Zr6 }oct and {Hf6 }oct ) are also isolated from the same hydrothermal system by decreasing the synthesis temperature. Structures, synthetic conditions, vibrational spectra, and ionic conductivity of the clusters are studied. Structural studies and synthesis inspection suggest that formation of {Zr6 }oct and {Zr17 } involves assembly of the same transferable building blocks, but the condensation degree and thermodynamic stability of the products increase with hydrothermal temperature. The role of {Zr6 }oct and {Zr17 } in the formation of ZrO2 nanocrystals are then discussed in the scenario of nonclassical nucleation theory. In addition, the Zr oxide clusters exhibit ionic conductivity owing to the mobility of protons. This study not only adds new members to the Zr/Hf oxide cluster family, but also establishes a connection from Zr4+ ions to ZrO2 in the hydrothermal preparation of zirconium oxide nanomaterials.