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

Abstract

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.

Fatty acid capped, metal oxo clusters as smallest conceivable nanocrystal prototypes

“…This is in agreement with our earlier hypothesis that branching of the carboxylic acid at the alpha position is the deciding factor between monomer and dimer. 2 With increasing chain length, we also observe the growth of a peak at 1.5 Å, which we assign to C-C distances in the ligand chain.…”

“…Atomically precise clusters are valuable building blocks for material science. 1,2 [3][4][5][6][7] Clusters are used to build stimuli-responsive materials, 8 or hierarchical (porous) structures. 9,10 Clusters can be precursors or intermediates in nanocrystal synthesis.…”

“…7,[19][20][21] Apart from the typical Ti8, Zr6, and Hf6 oxo clusters used in MOFs, many discrete group 4 oxo clusters exist with different nuclearities. 2,22 Discrete group 4 oxo clusters are conceptually close to colloidal oxide nanocrystals and share some features with them. 2 For example, both have an inorganic core, usually capped by an organic ligand shell.…”

“…2,22 Discrete group 4 oxo clusters are conceptually close to colloidal oxide nanocrystals and share some features with them. 2 For example, both have an inorganic core, usually capped by an organic ligand shell. Discrete oxo clusters are usually synthesized with short and rigid ligands.…”

A diamantane-4,9-dicarboxylate based UiO-66 analogue: challenging larger hydrocarbon cage platforms

“…UiO-Zr-MOFs with the general formula of [Zr6O4(OH)4(L)6] are based on paradigmatic hexanuclear {Zr6(3-O)4(3-OH)4(RCOO)12} clusters 7,8 connected to 12 neighbors by dicarboxylate organic linkers (L) to form a fcu (fcc) network (Fm m max. symmetry).…”