Structure, Properties, and Reactivity of Polyoxocationic Zirconium and Hafnium Clusters: A Computational Investigation

Abstract

Tetravalent zirconium and hafnium molecular metal oxides clusters are key building blocks of many metal−organic frameworks; however, the chemical space to form all possible MOF nodes is vast, containing many potential new clusters. Our computational study provides a complete picture of the structure, properties, and reactivity of two tetrameric zirconium and hafnium [M 4 (μ 2 -η 2 :η 2 -O 2 ) x (μ 2 -OH) 8−2x (H 2 O) 16 ] 8+ polycationic clusters. The electronic structure of the studied species has characteristic polyoxometalate oxygen-based and metal-based bands in the valence region. The energetics for the evolution of pure metal clusters into mixed-metal clusters revealed that only the incorporation of zirconium into hafnium clusters is thermodynamically favorable. We confirmed that the incorporation of up to four peroxide ligands is thermodynamically favorable; however, the experimental absence of rich peroxide species with three or more peroxides is attributed to their thermal degradation. The mechanism for peroxide incorporation involves the partial dissociation of the cluster rather than complete dissociation.

Pertechnetate/perrhenate‐capped Zr/Hf‐Dihydroxide Dimers: Elucidating Zr−TcO4 Co‐Mobility in the Nuclear Fuel Cycle

“…[21b] . This dimer was recently predicted by computation to be the first step of Zr/Hf-hydrolysis, [27] but not observed in an isolated and soluble form, prior to this current study. The Zr/Hfdimers (Figure 1F) were synthesized two ways; 1) By dissolving corresponding Zr/Hf oxyhydroxide in perrhenic/pertechnic acid, or 2) By co-dissolving the corresponding oxychloride salt (Zr 4 / Hf 4 ) with perrhenic/pertechnic acid, followed by slow evaporation to yield crystals (see SI for more details).…”