On the Question of Site-Selective Ligand Exchange in Carboxylate-Substituted Metal Oxo Clusters

Nonaqueous Chemistry of Group 4 Oxo Clusters and Colloidal Metal Oxide Nanocrystals

We review the nonaqueous precursor chemistry of the group 4 metals to gain insight into the formation of their oxo clusters and colloidal oxide nanocrystals. We first describe the properties and structures of titanium, zirconium, and hafnium oxides. Second, we introduce the different precursors that are used in the synthesis of oxo clusters and oxide nanocrystals. We review the structures of group 4 metal halides and alkoxides and their reactivity toward alcohols, carboxylic acids, etc. Third, we discuss fully condensed and atomically precise metal oxo clusters that could serve as nanocrystal models. By comparing the reaction conditions and reagents, we provide insight into the relationship between the cluster structure and the nature of the carboxylate capping ligands. We also briefly discuss the use of oxo clusters. Finally, we review the nonaqueous synthesis of group 4 oxide nanocrystals, including both surfactant-free and surfactant-assisted syntheses. We focus on their precursor chemistry and surface chemistry. By putting these results together, we connect the dots and obtain more insight into the fascinating chemistry of the group 4 metals. At the same time, we also identify gaps in our knowledge and thus areas for future research.

Expansion of Zirconium Oxide Clusters by 3d/4f Ions

Two series of charge-neutral coordination clusters featuring quasi-isostructural metal oxide cores, isolated as [Zr₆Fe₂Ln₂O₈(ib)₁₄(bda)₂(NO₃)₂]·xMeCN (Ln = La (1), Ce (2), Pr (3), and Nd (4); ib^- = isobutyrate; H₂bda = N-butyldiethanolamine) and [Zr₆Fe₂Ln₂O₈(ib)₁₄(mda)₂(NO₃)₂]·xMeCN (Ln = La (5), Ce (6), Pr (7), and Nd (8); H₂mda = N-methyldiethanolamine), were obtained via one-pot reactions of [Fe₃O(ib)₆(H₂O)₃]NO₃ as a critical precursor, Ln(NO₃)₃·6H₂O (Ln = La, Ce, Pr, and Nd), the respective aminoalcohol, and [Zr₆O₄(OH)₄(ib)₁₂(H₂O)]·3Hib in an acetonitrile solution. The coordination clusters in 1-8 feature {Zr₆O₈} cores that are structurally expanded by two 4f (Ln³⁺) and two 3d (Fe³⁺) metal ions, each individually coordinated to one of the eight oxide centers of {Zr₆O₈}, producing a metal skeleton where the 3d/4f positions cap four of the triangular faces of the central Zr₆ octahedron. The coordination clusters differ in the chosen aminoalcohol coligands, N-butyldiethanolamine or N-methyldiethanolamine, which lead to a different isobutyrate coordination pattern in the two series, while the {Fe₂Ln₂Zr₆O₈} core structure remains virtually unaffected. All eight coordination clusters are obtained in moderate to good yields of 29-66% after only several days. Complexes 1-8 are stable against air and moisture; they are also surprisingly thermally stable up to 280 °C in air and in nitrogen atmosphere, and they represent the first reported examples of 3d/4f-functionalized zirconium oxide clusters.

Incorporation of an intact dimeric Zr12 oxo cluster from a molecular precursor in a new zirconium metal–organic framework

A dimeric Zr₁₂ oxo cluster was used as new molecular building block in construction of metal–organic frameworks utilizing the precursor approach.