Department of Physics, Virginia Commonwealth University, Richmond, Virginia 23284, United States.
J Am Chem Soc. 2012 Dec 19;134(50):20507-12. doi: 10.1021/ja309473s. Epub 2012 Dec 5.
The quantum states in metal clusters are bunched into electronic shells as in atoms. Ligands including halogens or thiols modify the electronic structure through bonding, resulting in stable clusters with filled electronic shells that are resistant to oxygen etching. We demonstrate that the stabilization afforded by ligands is partially confounded because the ligands perturb the charge density of the metallic core, inducing Lewis acid-base sites that make the cluster reactive in a protic environment. We demonstrate the importance of induced active sites by studying the reactivity of methanol with two classes of iodine-passivated aluminum cluster anions: Al(13)I(x)(-), which has a closed geometric shell, and Al(14)I(y)(-), which has an adatom-decorated core. Two adjacent ligands on the closed geometric shell of Al(13)(-) activate the cluster, while in Al(14)I(3)(-) the I induces an active site on the adatom, making the cluster reactive, explaining ligand-protected clusters' preference for closed geometric shells.
金属团簇中的量子态像原子一样聚集在电子壳层中。配体（包括卤素或硫醇）通过成键来改变电子结构，从而形成具有满壳层电子的稳定团簇，这些团簇不易被氧刻蚀。我们证明，配体提供的稳定性部分受到干扰，因为配体扰动了金属核的电荷密度，诱导出路易斯酸碱位点，使团簇在质子环境中具有反应性。我们通过研究甲醇与两类碘钝化的铝团簇阴离子的反应性来证明诱导活性位点的重要性：具有封闭几何壳层的 Al(13)I(x)(-)和具有原子修饰核的 Al(14)I(y)(-)。封闭几何壳层上的两个相邻配体激活了团簇，而在 Al(14)I(3)(-)中，I 在原子上诱导出活性位点，使团簇具有反应性，这解释了配体保护的团簇对封闭几何壳层的偏好。
