Research Department, Naval Surface Warfare Center, Indian Head, Maryland 20640, USA.
J Phys Chem A. 2011 Dec 8;115(48):14100-9. doi: 10.1021/jp207292t. Epub 2011 Nov 11.
We present quantum chemistry simulations of aluminum clusters surrounded by a surface layer of cyclopentadiene-type ligands to evaluate the potential of such complexes as novel fuels or energetic materials. Density functional theory simulations are used to examine the aluminum-ligand bonding and its variation as the size of the aluminum cluster increases. The organometallic bond at the surface layer arises mainly from ligand charge donation into the Al p orbitals balanced with repulsive polarization effects. Functionalization of the ligand and changes in Al cluster size are found to alter the relative balance of these effects, but the surface organometallic bond generally remains stronger than Al-Al bonds elsewhere in the cluster. In large clusters, such as the experimentally observed Al(50)Cp(12), this suggests that unimolecular thermal decomposition likely proceeds through loss of surface AlCp units, exposing the strained interior aluminum core. The calculated heats of combustion per unit volume for these systems are high, approaching 60% that of pure aluminum. We discuss the possibility of using organometallic aluminum clusters as a means of achieving rapid combustion in propellants and fuels.
我们展示了受环戊二烯型配体表面层包围的铝团簇的量子化学模拟，以评估此类配合物作为新型燃料或含能材料的潜力。密度泛函理论模拟用于研究铝-配体键及其随铝团簇尺寸增加的变化。表面层的金属有机键主要来自配体电荷向 Al p 轨道的贡献，与排斥极化效应平衡。配体的功能化和 Al 团簇尺寸的变化被发现改变了这些效应的相对平衡，但表面金属有机键通常比团簇中其他地方的 Al-Al 键更强。在大团簇中，例如实验观察到的 Al(50)Cp(12)，这表明单分子热分解可能通过表面 AlCp单元的损失而发生，暴露出应变的内部铝核。这些体系的单位体积燃烧热很高，接近纯铝的 60%。我们讨论了将金属有机铝团簇用作在推进剂和燃料中实现快速燃烧的一种手段的可能性。
