Alnemrat Sufian, Hooper Joseph P
Department of Physics, Naval Postgraduate School, Monterey, California 93943, USA.
J Chem Phys. 2014 Mar 14;140(10):104313. doi: 10.1063/1.4867467.
We report Car-Parrinello molecular dynamics simulations of the oxidation of ligand-protected aluminum clusters that form a prototypical cluster-assembled material. These clusters contain a small aluminum core surrounded by a monolayer of organic ligand. The aromatic cyclopentadienyl ligands form a strong bond with surface Al atoms, giving rise to an organometallic cluster that crystallizes into a low-symmetry solid and is briefly stable in air before oxidizing. Our calculations of isolated aluminum/cyclopentadienyl clusters reacting with oxygen show minimal reaction between the ligand and O2 molecules at simulation temperatures of 500 and 1000 K. In all cases, the reaction pathway involves O2 diffusing through the ligand barrier, splitting into atomic oxygen upon contact with the aluminum, and forming an oxide cluster with aluminum/ligand bonds still largely intact. Loss of individual aluminum-ligand units, as expected from unimolecular decomposition calculations, is not observed except following significant oxidation. These calculations highlight the role of the ligand in providing a steric barrier against oxidizers and in maintaining the large aluminum surface area of the solid-state cluster material.
我们报告了对形成典型团簇组装材料的配体保护铝团簇氧化过程的卡-帕里尼罗分子动力学模拟。这些团簇包含一个被单层有机配体包围的小铝核。芳香族环戊二烯基配体与表面铝原子形成强键，产生一种有机金属团簇，该团簇结晶为低对称性固体，在空气中短暂稳定后再氧化。我们对孤立的铝/环戊二烯基团簇与氧气反应的计算表明，在500和1000 K的模拟温度下，配体与O₂分子之间的反应极小。在所有情况下，反应途径都涉及O₂扩散穿过配体屏障，与铝接触时分解为原子氧，并形成铝/配体键基本保持完整的氧化物团簇。除了显著氧化后，未观察到单分子分解计算预期的单个铝-配体单元的损失。这些计算突出了配体在提供对抗氧化剂的空间位垒以及维持固态团簇材料的大铝表面积方面的作用。
