Theoretical and Computational Chemistry Laboratory, School of Chemistry, Bharathidasan University, Tiruchirappalli 620024, Tamil Nadu, India.
J Phys Chem A. 2013 Apr 25;117(16):3529-38. doi: 10.1021/jp401210c. Epub 2013 Apr 11.
Hypercoordination in silicon has long been reviewed. Dihalogenated perhalocyclohexasilane inverse sandwich complexes (ISCs) are the only group of hypercoordinate Si complexes with anion donors that contact six neutral silicon atoms; opening prospective applications in Si self-assembled nanostructures. Hypercoordinate bonds in 16 such ISCs were studied and their anion ring interactions have been understood with respect to halides. μ(6) mode of coordination was confirmed by the presence of 6 equivalent (3,-1) bond critical points through Bader's QTAIM perspective. The presence of Lewis acid sites above and below the flat Si rings were examined through a reduced density gradient (RDG) analysis, and the ability of halide anions (X' = F, Cl, Br, I) to hypercoordinate has been understood. Role of the ring halides (X) in tuning size and acidity of Lewis sites has been addressed. While the total interaction between the two anions and the ring is quantified through EDA, each SiX' hypercoordinate bond was identified as either purely ionic or transient through QTAIM computations. CDA shows that these complexes are of donor-acceptor type with significant back-donation. The analysis shows that BrF' and IF' were found to reach maximum covalency within the group. Hence in future, tuning these ISCs for construction of nanocrystalline Si structures for optoelectronic properties can essentially utilize the collective, weak yet hypercoordinate Si in these complexes.
硅的超配位早已被研究过。二卤代全卤代环己硅烷反夹心配合物（ISC）是唯一一组具有阴离子供体的超配位 Si 配合物，它与六个中性硅原子接触；为 Si 自组装纳米结构的应用开辟了前景。研究了 16 种此类 ISC 中的超配位键，并根据卤素了解了它们的阴离子环相互作用。Bader 的 QTAIM 观点通过存在 6 个等效的（3，-1）键临界点证实了 μ(6)配位模式。通过密度梯度（RDG）分析检查了在平坦 Si 环上方和下方存在的路易斯酸位，并了解了卤化物阴离子（X'=F、Cl、Br、I）的超配位能力。已经解决了环卤化物（X）在调节路易斯位点的大小和酸度方面的作用。虽然通过 EDA 量化了两个阴离子和环之间的总相互作用，但通过 QTAIM 计算将每个 SiX'超配位键识别为纯离子或瞬态。CDA 表明这些配合物是供体-受体型的，具有显著的回供电子作用。分析表明，BrF'和 IF'在该组中被发现达到最大共价性。因此，在未来，可以利用这些配合物中集体的、弱但超配位的 Si，对这些 ISC 进行调谐，以构建用于光电性能的纳米晶 Si 结构。
