Corminboeuf Clémence, Wodrich Matthew D, King R Bruce, von Ragué Schleyer Paul
Department of Chemistry, Center for Computational Chemistry, University of Georgia, Athens, Georgia 30602, USA.
Dalton Trans. 2008 Apr 7(13):1745-51. doi: 10.1039/b716323a. Epub 2008 Feb 29.
The symmetry constrained geometries of the eight- and nine-vertex polyhedral boranes and haloboranes BnXnz (n = 8 and 9; X = H, F and Cl; z = -2, -1 and 0) were optimized at the B3LYP/6-311+G(d) level and their nucleus-independent chemical shifts (NICS) were calculated using the GIAO method with Kohn-Sham orbitals. Substitution of halogens on borane cages was found to significantly impact not only the geometric but also magnetic properties. Multiple fluorine substituents cause a deviation from the Wade-Mingos skeletal electron rules in B8F8(2-), resulting in a distortion from the expected D2d bisdisphenoid to a C2v nido type bicapped trigonal prism. However, all of the nine-vertex cages B9X9z retain the D3h tricapped trigonal prismatic structure of B9H9(2-). The presence of halogen substituents was found to enhance the three-dimensional diatropic ring currents within the dianionic borane cages B8X8(2-) and B9X9(2-). For the neutral structures the NICS values indicate BnFn to be aromatic, BnCln to be essentially non-aromatic, and BnHn to be antiaromatic (n = 8, 9).
在B3LYP/6-311+G(d)水平下优化了八顶点和九顶点多面体硼烷及卤硼烷BnXnz（n = 8和9；X = H、F和Cl；z = -2、-1和0）的对称约束几何结构，并使用含时密度泛函理论（GIAO）方法结合Kohn-Sham轨道计算了它们的核独立化学位移（NICS）。研究发现，硼烷笼上卤素的取代不仅对几何性质有显著影响，对磁性性质也有显著影响。多个氟取代基导致B8F8(2-)偏离Wade-Mingos骨架电子规则，使其从预期的D2d双蝶形畸变到C2v巢型双帽三棱柱。然而，所有九顶点笼B9X9z都保留了B9H9(2-)的D3h三帽三棱柱结构。研究发现，卤素取代基的存在增强了双阴离子硼烷笼B8X8(2-)和B9X9(2-)内的三维抗磁环流。对于中性结构，NICS值表明BnFn具有芳香性，BnCln基本不具有芳香性，BnHn具有反芳香性（n = 8, 9）。
