Gao Yuan, Zhang Yang, Han Zhe, Wang Chunhui, Zhang Lei, Qiu Jie
School of Energy and Power Engineering, Xi'an Jiaotong University, Xi'an, China.
Engineering Laboratory of Advanced Energy Materials, Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences, Ningbo, China.
Front Chem. 2024 Dec 2;12:1507834. doi: 10.3389/fchem.2024.1507834. eCollection 2024.
Studies on cerium oxo clusters (CeOCs) are not only significant for understanding the redox and hydrolysis behaviors of Ce(III/IV) ions but also crucial for the rational synthesis of novel clusters and nanoceria with specific Ce(III)/Ce(IV) ratios. Here, two sets of reactions were conducted using cerium nitrate and HO-oxidized cerium nitrate, resulting in the formation of two distinct mixed-valent CeOCs [Ce Ce O(OH)(PhCO)(DMF)] (Ce) and [Ce Ce O(OH)(PhCO)(DMF)] (Ce). These two clusters exhibit different structures and Ce(III)/Ce(IV) ratios, demonstrating the critical role of cerium oxidation states and the occurrence of redox reactions in cluster formation. Ce is the first tetradecanuclear CeOC with a novel structure, whereas Ce differed in its Ce(III)/Ce(IV) ratio, protonation levels of O atoms, and ligands from previously reported 24-nuclear CeOCs. Furthermore, various techniques were employed to investigate the formation process of these two clusters. X-ray photoelectron spectra (XPS) revealed that the white precipitates formed during the preparation of Ce contain Ce(III) ions, while the reddish-brown precipitates formed during the preparation of Ce contain a mixture of Ce(III) and Ce(IV) ions. These two precipitations were individually dissolved in N,N-Dimethylformamide (DMF). The evolution of solution color and ultraviolet-visible (UV-Vis) spectra over time revealed the gradual oxidation of partial Ce(III) ions by oxygen in the solution of the white precipitation. As Ce(IV) ions increased in this solution, time-resolved small angle X-ray scattering (SAXS) data demonstrated the self-assembly of the Ce clusters after 4 days. In contrast, SAXS data and UV-Vis spectra revealed the rapid assembly of Ce clusters within 2 h due to the initial coexistence of Ce(IV) and Ce(III) ions in the DMF solution of the reddish-brown precipitation. The continued reduction of partial Ce(IV) ions in this solution does not affect Ce clusters' formation and stability. Our studies expand the family of CeOCs and enhance our understanding of the effects of cerium's oxidation states on cluster formation.
对铈氧簇（CeOCs）的研究不仅对于理解Ce(III/IV)离子的氧化还原和水解行为具有重要意义，而且对于合理合成具有特定Ce(III)/Ce(IV)比例的新型簇和纳米氧化铈至关重要。在此，使用硝酸铈和羟基氧化硝酸铈进行了两组反应，生成了两种不同的混合价CeOCs [Ce₁₄Ce₂O(OH)(PhCO)(DMF)]（Ce₁）和[Ce₂₄Ce₂O(OH)(PhCO)(DMF)]（Ce₂）。这两个簇具有不同的结构和Ce(III)/Ce(IV)比例，表明铈氧化态在簇形成过程中的关键作用以及氧化还原反应的发生。Ce₁是第一个具有新颖结构的十四核CeOC，而Ce₂在其Ce(III)/Ce(IV)比例、O原子的质子化水平以及配体方面与先前报道的二十四核CeOCs不同。此外，采用了各种技术来研究这两个簇的形成过程。X射线光电子能谱（XPS）显示，在制备Ce₁过程中形成的白色沉淀含有Ce(III)离子，而在制备Ce₂过程中形成的红棕色沉淀含有Ce(III)和Ce(IV)离子的混合物。将这两种沉淀分别溶解在N,N-二甲基甲酰胺（DMF）中。随着时间的推移，溶液颜色和紫外可见（UV-Vis）光谱的变化表明，白色沉淀溶液中的部分Ce(III)离子被溶液中的氧气逐渐氧化。随着该溶液中Ce(IV)离子的增加，时间分辨小角X射线散射（SAXS）数据表明Ce₁簇在4天后发生了自组装。相比之下，SAXS数据和UV-Vis光谱显示，由于红棕色沉淀的DMF溶液中最初同时存在Ce(IV)和Ce(III)离子，Ce₂簇在2小时内迅速组装。该溶液中部分Ce(IV)离子的持续还原并不影响Ce₂簇的形成和稳定性。我们的研究扩展了CeOCs家族，并增强了我们对铈氧化态对簇形成影响的理解。
