Fowler Patrick W, Gray Benjamin R
Department of Chemistry, University of Sheffield, Sheffield S3 7HF, UK. p.w.fowler@ sheffield.ac.uk
Inorg Chem. 2007 Apr 2;46(7):2892-7. doi: 10.1021/ic062302t. Epub 2007 Mar 8.
The newly discovered atom-centered polygonal wheels B8(2-) and B9- are predicted to show ring currents characteristic of aromatic systems. Ipsocentric mapping of induced current density for both molecules attributes a pi diatropic current to the four electrons of the doubly degenerate pi HOMO and a sigma diatropic current to the four electrons of the doubly degenerate sigma HOMO, each orbital pair having an available transition to corresponding LUMO orbitals in which the angular node count increases by one. Thus, on the magnetic criterion, B8(2-) and B9- are each both pi- and sigma-aromatic as a consequence of the nodal properties of the frontier orbitals of the pi- and sigma-stacks.
新发现的以原子为中心的多边形轮状结构B8(2-)和B9-预计将表现出芳香体系特有的环电流。对这两种分子的感应电流密度进行的中心映射表明，双重简并π型最高占据分子轨道（HOMO）的四个电子具有π向心电流，双重简并σ型HOMO的四个电子具有σ向心电流，每对轨道都有向相应最低未占分子轨道（LUMO）的可用跃迁，其中角节点数增加一个。因此，根据磁性标准，由于π-和σ-堆叠前沿轨道的节点性质，B8(2-)和B9-各自既是π-芳香性又是σ-芳香性。
