Grubisic A, Li X, Stokes S T, Cordes J, Ganteför G F, Bowen K H, Kiran B, Jena P, Burgert R, Schnöckel H
Department of Chemistry and Materials Science, Johns Hopkins University, Baltimore, Maryland 21218, USA.
J Am Chem Soc. 2007 May 9;129(18):5969-75. doi: 10.1021/ja0700404. Epub 2007 Apr 17.
Anion photoelectron spectroscopy and density functional theory were employed to study aluminum hydride clusters, AlnHm- (4 <or= n <or= 8, 0 <or= m <or= 10). Photoelectron spectra revealed that Al4H4, Al4H6, and a family of species with general formula AlnHn+2 (5 <or= n <or= 8) have small adiabatic electron affinities and large HOMO-LUMO gaps (ranging from 0.5 to 1.9 eV) relative to those of their stoichiometric neighbors, implying their enhanced stabilities. Formulas reminiscent of boranes led us to investigate whether Wade's rules could be applied to alanes as well. DFT calculations showed that the AlnHn+2 (5 <or= n <or= 8) family adopts n-vertex polyhedral closo-structures with two extra hydrogen atoms occupying opposite bridging positions in agreement with the Wade's (n + 1) rule. These can be viewed as aluminum versions of hypothetical diprotonated closo-borane dianions (BnHn2- + 2H+). In addition, Al4H4 assumes a closo-tetrahedral geometry, while Al4H6 takes on a distorted tetrahedral (D2d) structure with two counter-positioned bridging hydrogen atoms and has the largest HOMO-LUMO gap (1.9 eV) of all the alanes we studied. All of these species can be understood in terms of underlying polyhedral skeletal electron pair theory (PSEPT) concepts. Although, the herein studied alanes do not have direct borane analogues, the ability to understand their structures in terms of the Wade-Mingos rules and the underlying PSEPT concepts suggests that they can be considered as borane analogues, thereby opening a new chapter in aluminum hydride chemistry.
采用阴离子光电子能谱和密度泛函理论研究氢化铝簇合物AlnHm-（4≤n≤8，0≤m≤10）。光电子能谱表明，相对于其化学计量比相邻的物种，Al4H4、Al4H6以及通式为AlnHn+2（5≤n≤8）的一系列物种具有较小的绝热电子亲和能和较大的HOMO-LUMO能隙（范围为0.5至1.9电子伏特），这意味着它们具有更高的稳定性。与硼烷相似的化学式促使我们研究韦德规则是否也能应用于铝烷。密度泛函理论计算表明，AlnHn+2（5≤n≤8）系列采用n顶点多面体闭合结构，有两个额外的氢原子占据相对的桥连位置，这与韦德的（n + 1）规则一致。这些可以看作是假设的双质子化闭合硼烷二价阴离子（BnHn2- + 2H+）的铝类似物。此外，Al4H4具有闭合四面体几何结构，而Al4H6具有扭曲的四面体（D2d）结构，有两个相对位置的桥连氢原子，并且在我们研究的所有铝烷中具有最大的HOMO-LUMO能隙（1.9电子伏特）。所有这些物种都可以根据基础的多面体骨架电子对理论（PSEPT）概念来理解。尽管本文研究的铝烷没有直接的硼烷类似物，但根据韦德-明戈斯规则和基础的PSEPT概念来理解它们的结构的能力表明，它们可以被视为硼烷类似物，从而为氢化铝化学开启了新的篇章。
