MacDiarmid Institute for Advanced Materials and Nanotechnology, Industrial Research Ltd., Lower Hutt 5040, New Zealand.
Phys Chem Chem Phys. 2011 Dec 21;13(47):21109-15. doi: 10.1039/c1cp22190f. Epub 2011 Oct 20.
Motivated by recent developments in the field of so-called "superatom complexes", as well as by the challenge posed to theory in understanding the many polymorphs of gallium, we analyse the electronic structure of several previously synthesised ligand-protected gallium clusters and their model derivatives using density functional theory. The calculated electron charge densities within the respective gallium cores are shown to be consistent with the jellium superatom model, exhibiting well-defined global spherical shells and wide HOMO-LUMO gaps--indicating enhanced chemical stability. It is demonstrated that the HOMO-LUMO gaps are widened due to the presence of covalent gallium-ligand bonds and a closed electron shell (i.e. electron "magic" number). The tendency of retaining a filled electron shell is shown to be particularly apparent in two closely-related clusters, with one derived from the other simply via substituting a doubly negative charge by a single protective moiety containing a lone electron pair. This analysis verifies that spherical electron shells can influence the chemical stability of ligand-protected gallium clusters, and also demonstrates the significant stabilising effects of metal-ligand interactions-something that is poorly accounted for in the current superatom model.
受最近所谓“超原子配合物”领域的发展以及理论在理解镓的多种多晶型方面所面临的挑战的启发，我们使用密度泛函理论分析了几种先前合成的配体保护镓簇及其模型衍生物的电子结构。计算得出的各镓核内的电子电荷密度与类金属超原子模型一致，表现出明确的全局球形壳层和较宽的 HOMO-LUMO 能隙——表明增强了化学稳定性。结果表明，由于存在共价镓-配体键和闭合的电子壳层（即电子“幻数”），HOMO-LUMO 能隙变宽。通过用仅含有一个孤对电子的单个保护基团代替双负电荷，从另一个类似物中简单地衍生出两个密切相关的簇，表明保留填满的电子壳层的趋势尤其明显。该分析验证了球形电子壳层可以影响配体保护镓簇的化学稳定性，并且还表明金属-配体相互作用具有显著的稳定化效应——这在当前的超原子模型中考虑不足。
