Structural Evolution of Iridium Oxide Cluster Anions IrnOm- (n = 5-8) with Sequential Oxidation: Binding Mode of O Atoms and Ir Framework
Structural Evolution of Iridium Oxide Cluster Anions IrnOm- (n = 5-8) with Sequential Oxidation: Binding Mode of O Atoms and Ir Framework
复制标题
氧化铱簇阴离子 IrnOm- (n = 5-8) 连续氧化的结构演化：O 原子与 Ir 骨架的结合模式
DOI：
10.1021/acs.jpcc.9b02935
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发表时间：
2019
期刊：
影响因子：
3.7
通讯作者：
T. Tsukuda
中科院分区：
文献类型：
--
作者：
R. Tomihara;K. Koyasu;T. Nagata;J. W. J. Wu;M. Nakano;K. Ohshimo;F. Misaizu;T. Tsukuda
通过离子迁移质谱（IMMS）和理论计算研究了氧化铱IrnOm–（n= 5-8，m= 0-14）小团簇阴离子的几何结构，以阐明O原子的结合模式和Ir骨架的基序随m的变化行为。 IMMS 确定的 forn= 5-7 的碰撞截面 (CCS) 显示随 m 单调增加，而那些 forn= 8 的碰撞截面突然下降约 10% atm= 11，否则随 m 逐渐增加。 Forn= 5，实验 CCS 值与各种结构异构体计算值之间的详细比较表明，Ir5Om– 中的 O 原子在整个 m= 1–8 中优先键合到 Ir5– 核心的末端位点：Ir5– 核心在 tom= 5 之前保留了紧凑的基序，但在形式 = 6–8 时显着扭曲。 Ir6O6 和 Ir7O7 的实验 CCS 值也可以通过 O 原子的顶部结合来解释，同时保留 Ir 框架的基序。 n = 8 的 CCS 值表明 O 原子顺序键合到立方 Ir8 骨架形式 = 1–6 和变形 Ir8 骨架形式 = 7–11 的末端位置。小 Ir 簇上 O 原子的这些顶部结合模式与其他过渡金属簇上桥位点 O 原子的 μ2 模式形成鲜明对比，并归因于非面心立方 (fcc) Ir 骨架。 Ir8Om–atm= 11 的 CCS 值突然下降与 Ir 框架中的键断裂有关，该断裂是由 O 原子的结合模式从顶部基序转变为 μ2 桥接基序引起的。这些结果表明，小 Ir 团簇通过利用吸附在非面心立方 Ir 团簇顶部位置的 O 原子的独特化学性质，表现出新颖的氧化催化作用。
Geometric structures of small cluster anions of iridium oxide IrnOm–(n= 5–8,m= 0–14) were investigated by ion mobility mass spectrometry (IMMS) and theoretical calculation to clarify the evolutional behavior of the binding modes of the O atoms and the motif of the Ir frameworks as a function ofm. The collision cross sections (CCSs) forn= 5–7 determined by IMMS showed a monotonic increase withm, whereas those forn= 8 dropped abruptly by ∼10% atm= 11, which otherwise gradually increased withm. Forn= 5, detailed comparison between the experimental CCS values and those calculated for various structural isomers revealed that the O atoms in Ir5Om–are preferentially bonded to terminal sites of the Ir5–cores throughoutm= 1–8: the Ir5–cores retained compact motifs up tom= 5 but distorted significantly form= 6–8. The experimental CCS values for Ir6O6–and Ir7O7–were also explained by on-top binding of O atoms while retaining the motifs of the Ir frameworks. The CCS values forn= 8 suggest that the O atoms are sequentially bonded to terminal sites of the cubic Ir8frameworks form= 1–6 and of the deformed Ir8frameworks form= 7–11. These on-top binding modes of the O atoms on small Ir clusters are in sharp contrast to the μ2mode of the O atoms at bridge sites on the clusters of other transition metals and are ascribed to non-face-centered cubic (fcc) Ir frameworks. The sudden drop in the CCS values of Ir8Om–atm= 11 was associated with bond breakage in the Ir framework induced by transition of the binding mode of O atoms from an on-top motif to a μ2bridging motif. These results suggest that the small Ir clusters exhibit novel oxidation catalysis by taking advantage of the unique chemical properties of O atoms adsorbed on the on-top sites on non-fcc Ir clusters.