Li Yong-Xia, Bai Li-Xia, Guo Jin-Chang
Department of Chemistry, Xinzhou Teachers University, Xinzhou 034000, China.
Nanocluster Laboratory Institute, Molecular Science Shanxi University, Taiyuan 030006, China.
Molecules. 2023 Jul 22;28(14):5583. doi: 10.3390/molecules28145583.
As one of the important probes of chemical bonding, planar tetracoordinate carbon (ptC) compounds have been receiving much attention. Compared with ptC clusters, the heavier planar tetracoordinate silicon, germanium, tin, lead (ptSi/Ge/Sn/Pb) systems are scarcer and more exotic. The 18-valence-electron (ve)-counting is one important guide, though not the only rule, for the design of planar tetra-, penta-coordinate carbon and silicon clusters. The 18ve ptSi/Ge system is very scarce and needs to be expanded. Based on the isoelectronic principle and bonding similarity between the Al atom and the BeH unit, inspired by the previously reported ptSi global minimum (GM) SiAl, a series of ternary 18 ve XBe4H5 (X = Si, Ge, Sn, Pb) clusters were predicted with the ptSi/Ge/Sn/Pb centers. Extensive density functional theory (DFT) global minimum searches and high-level CCSD(T) calculations performed herein indicated that these ptSi/Ge/Sn/Pb XBeH (X = Si, Ge, Sn, Pb) clusters were all true GMs on their potential energy surfaces. These GMs of XBeH (X = Si, Ge, Sn, Pb) species possessed the beautiful fan-shaped structures: XBe unit can be stabilized by three peripheries bridging H and two terminal H atoms. It should be noted that XBeH (X = Si, Ge, Sn, Pb) were the first ternary 18 ve ptSi/Ge/Sn/Pb species. The natural bond orbital (NBO), canonical molecular orbitals (CMOs) and adaptive natural densitpartitioning (AdNDP) analyses indicated that 18ve are ideal for these ptX clusters: delocalized one π and three σ bonds for the XBe core, three Be-H-Be 3c-2e and two Be-H σ bonds for the periphery. Additionally, 2π plus 6σ double aromaticity was found to be crucial for the stability of the ptX XBeH (X = Si, Ge, Sn, Pb) clusters. The simulated photoelectron spectra of XBeH (X = Si, Ge, Sn, Pb) clusters will provide theoretical basis for further experimental characterization.
作为化学键的重要探针之一，平面四配位碳（ptC）化合物一直备受关注。与ptC簇相比，较重的平面四配位硅、锗、锡、铅（ptSi/Ge/Sn/Pb）体系更为稀少且更具特殊性。18价电子计数是设计平面四配位、五配位碳和硅簇的一个重要指导原则，尽管不是唯一规则。18价电子的ptSi/Ge体系非常稀少，需要加以拓展。基于等电子原理以及Al原子与BeH单元之间的键合相似性，受先前报道的ptSi全局最小值（GM）SiAl的启发，预测了一系列具有ptSi/Ge/Sn/Pb中心的三元18价电子XBe4H5（X = Si、Ge、Sn、Pb）簇。本文进行的广泛密度泛函理论（DFT）全局最小值搜索和高水平CCSD(T)计算表明，这些ptSi/Ge/Sn/Pb XBeH（X = Si、Ge、Sn、Pb）簇在其势能面上均为真正的全局最小值。这些XBeH（X = Si、Ge、Sn、Pb）物种的全局最小值具有美丽的扇形结构：XBe单元可通过三个外围桥连H原子和两个末端H原子得以稳定。应当指出的是，XBeH（X = Si、Ge、Sn、Pb）是首批三元18价电子的ptSi/Ge/Sn/Pb物种。自然键轨道（NBO）、正则分子轨道（CMO）和自适应自然密度划分（AdNDP）分析表明，18价电子对这些ptX簇是理想的：XBe核心有一个离域π键和三个σ键，外围有三个Be-H-Be 3c-2e键和两个Be-H σ键。此外，发现2π加6σ双芳香性对ptX XBeH（X = Si、Ge、Sn、Pb）簇的稳定性至关重要。XBeH（X = Si、Ge、Sn、Pb）簇的模拟光电子能谱将为进一步的实验表征提供理论依据。
