标题： 从球体到圆锥体：三价金属离子纳米团簇中圆锥区域的结构不稳定性和酸性 显示英文标题

标题： From Spheres to Cones: Structural Instabilities and Acidity at Conical Regions in Trivalent Metal Ion Nano-clusters

摘要： 亚纳米级的水簇含有单个三价金属阳离子，可能会表现出电荷引起的结构不稳定。 在这里，我们提供了计算证据，表明含有单个\ce{Fe^{3+}}、\ce{Lu^{3+}}或\ce{La^{3+}}离子的簇由于这种不稳定性而经历连续的几何变化。 这些簇在势能景观上动态演化，采用三角形、伸长的两点、单点以及更球形的构型，通常带有明显的锥形表面凸起。 这种不稳定性表现与在包含大离子的介观和微观液滴中观察到的不同，在这些液滴中形成稳定的“星状”结构，其特征是特定数量的锥形凸起，该数量随液滴大小而变化。 在本研究中，我们发现围绕金属离子的\ce{H2O}分子的取向不仅受三价离子电场的影响，还受局部锥形凸起的影响。 为了进一步研究锥形凸起中的局部酸性，我们采用了一个代理模型系统，该系统由一个含有三个\ce{H3O+}离子的水纳米簇组成，并使用从头算分子动力学进行模拟。 在簇的锥形区域中，质子在多个水分子之间扩散，这与在簇致密体中观察到的更局部的质子离域现象形成对比。 这些发现表明，局部几何结构可以显著调节高度带电纳米簇中的酸性，这对于理解电喷雾电离质谱等技术中的电荷转移和电离机制具有潜在意义，并可补充来自红外光谱数据的解释。 显示英文摘要

摘要： Sub-nanometer aqueous clusters containing a single trivalent metal cation can exhibit charge-induced structural instabilities. Here, we present computational evidence that clusters containing a single \ce{Fe^{3+}}, \ce{Lu^{3+}}, or \ce{La^{3+}} ion undergo continuous geometric transformations as a consequence of this instability. These clusters dynamically evolve across their potential energy landscape, adopting triangular, elongated two-point, single-point, and more spherical configurations often with distinct conical surface protrusions. The manifestation of this instability differs from that observed in mesoscopic and microscopic droplets containing macroions, where stable ``star-like'' structures form, characterized by a specific number of conical protrusions that varies with the droplet size. In the present study, we find that the orientation of the \ce{H2O} molecules surrounding the metal ion is influenced not only by the electric field of the trivalent ion but also by the local conical protrusions. To further investigate the local acidity in the conical protrusions, we employ a proxy model system consisting of an aqueous nano-cluster containing three \ce{H3O+} ions, simulated using ab initio molecular dynamics. Within the conical regions of the cluster, protons exhibit diffusion across several water molecules, in contrast to the more localized proton delocalization observed in the compact body of the cluster. These findings suggest that local geometry can significantly modulate acidity in highly charged nano-clusters, with potential implications for understanding charge-transfer and ionization mechanisms in techniques such as electrospray ionization mass spectrometry and complement interpretations from infrared spectroscopic data.