Two mixed-valent cerium oxo clusters: synthesis, structure, and self-assembly.

Area of Science:

• Inorganic Chemistry
• Materials Science
• Nanotechnology

Background:

• Cerium oxo clusters (CeOCs) are vital for understanding cerium ion redox and hydrolysis behaviors.
• Controlling the Ce(III)/Ce(IV) ratio in CeOCs and nanoceria is crucial for synthesizing materials with specific properties.

Purpose of the Study:

• To synthesize and characterize novel mixed-valent cerium oxo clusters (CeOCs).
• To investigate the influence of cerium oxidation states on the formation and self-assembly dynamics of CeOCs.
• To explore the structural diversity and formation mechanisms of CeOCs.

Main Methods:

• Synthesis of CeOCs using cerium nitrate and hydrogen peroxide-oxidized cerium nitrate.
• Characterization using X-ray photoelectron spectroscopy (XPS) to determine Ce(III)/Ce(IV) ratios.
• In-situ monitoring of cluster formation and assembly using ultraviolet-visible (UV-Vis) spectroscopy and time-resolved small-angle X-ray scattering (SAXS).

Main Results:

• Two distinct mixed-valent CeOCs, [Ce14III Ce10IV O14(OH)2(PhCO2)22(DMF)6] (Ce14) and [Ce2II22IV O28(OH)8(PhCO2)30(DMF)4] (Ce24C), were synthesized.
• Ce14 represents a novel tetradecanuclear CeOC structure, while Ce24C exhibits a unique Ce(III)/Ce(IV) ratio and ligandation compared to known 24-nuclear clusters.
• The study revealed different self-assembly pathways: Ce14 clusters self-assembled over 4 days, influenced by gradual Ce(III) oxidation, while Ce24C clusters assembled rapidly within 2 hours due to initial Ce(III)/Ce(IV) coexistence.

Conclusions:

• The synthesis of Ce14 and Ce24C expands the known family of CeOCs.
• Cerium oxidation states and redox reactions play a critical role in determining the structure and formation pathways of CeOCs.
• Understanding these formation dynamics provides insights for the rational design of novel CeOCs and ceria-based nanomaterials.