Wacker Jennifer N, Ditter Alexander S, Cary Samantha K, Murray Aphra V, Bertke Jeffery A, Seidler Gerald T, Kozimor Stosh A, Knope Karah E
Department of Chemistry, Georgetown University, 37th and O Streets NW, Washington, D.C. 20057, United States.
Los Alamos National Laboratory (LANL), P.O. Box 1663, Los Alamos, New Mexico 87545, United States.
Inorg Chem. 2022 Jan 10;61(1):193-205. doi: 10.1021/acs.inorgchem.1c02705. Epub 2021 Dec 16.
A cerium-oxo nanocluster capped by chloride ligands, [CeCeO(OH)Cl(HO)] ( = 1-24), has been isolated from acidic chloride solutions by using potassium counterions. The crystal structure was elucidated using single crystal X-ray diffraction. At the center of the cluster is a {Ce} core that exhibits the same fluorite-type structure as bulk CeO, with eight-coordinate Ce sites bridged by tetrahedral oxo anions. The {Ce} is further surrounded by a peripheral shell of six tetranuclear {Ce} subunits that are located on each of the faces of the core to yield the {Ce} cluster. The surface of the cluster is capped by 51 bridging/terminal chloride ligands and 11 water molecules; the anionic cluster is charge balanced by potassium counterions that exist in the outer coordination sphere. While assignment of the Ce oxidation state by bond valence summation was ambiguous, Ce L-edge X-ray absorption, X-ray photoelectron, and UV-vis-NIR absorption results were consistent with a Ce/Ce cluster. Systematic changes in the XANES and UV-vis-NIR absorption spectra over time pointed to reactivity of the cluster upon exposure to air. These changes were examined using single crystal X-ray diffraction, and a clear single-crystal-to-single-crystal transformation was captured; an overall loss of surface-bound chlorides and water molecules as well as new μ-OH sites was observed on the cluster surface. This work provides a rare snapshot of metal oxide cluster reactivity. The results may hold implications for understanding the physical and chemical properties of ceria nanoparticles and provide insight into the behavior of other metal-oxo clusters of significant technological and environmental interest.
一种由氯离子配体封端的铈氧纳米簇合物[CeCeO(OH)Cl(HO)]（= 1 - 24），已通过使用钾抗衡离子从酸性氯化物溶液中分离出来。利用单晶X射线衍射解析了其晶体结构。在该簇合物的中心是一个{Ce}核，它呈现出与块状CeO相同的萤石型结构，八配位的Ce位点由四面体氧阴离子桥连。{Ce}核进一步被六个四核{Ce}亚基组成的外围壳层所包围，这些亚基位于核的每个面上，形成{Ce}簇合物。该簇合物的表面由51个桥连/端基氯化物配体和11个水分子封端；阴离子簇合物通过存在于外配位球中的钾抗衡离子实现电荷平衡。虽然通过键价求和法对Ce氧化态的归属不明确，但Ce L边X射线吸收、X射线光电子能谱以及紫外 - 可见 - 近红外吸收结果与Ce/Ce簇合物一致。随着时间推移，X射线吸收近边结构（XANES）和紫外 - 可见 - 近红外吸收光谱的系统变化表明该簇合物在暴露于空气时具有反应活性。使用单晶X射线衍射对这些变化进行了研究，并捕捉到了清晰的单晶到单晶的转变；在簇合物表面观察到表面结合的氯化物和水分子总体损失以及新的μ - OH位点。这项工作提供了金属氧化物簇合物反应活性的罕见快照。这些结果可能对理解二氧化铈纳米颗粒的物理和化学性质具有启示意义，并为洞察其他具有重大技术和环境意义的金属氧簇的行为提供思路。
