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首页> 外文期刊>Zeitschrift fur Anorganische und Allgemeine Chemie >Structures and bonding situation of the allyl systems and cyclic isomers [H_2E-E(H)-EH_2]~-,?,+ (E = C, Si, Ge, Sn)
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Structures and bonding situation of the allyl systems and cyclic isomers [H_2E-E(H)-EH_2]~-,?,+ (E = C, Si, Ge, Sn)

机译：烯丙基体系和环状异构体[H_2E-E（H）-EH_2]〜-，？，+（E = C，Si，Ge，Sn）的结构和键合情况

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摘要

Quantum chemical calculations using DFT and ab initio methods were carried out on the structures of the title compounds. The nature of the bonding was investigated with an energy decomposition analysis. The calculations predict that the planar C2v allyl structures of the neutral and charged heavier group-14 homologues [H_2E-E(H)-EH_2] -,?,+ (E = Si - Sn) are no minima on the potential energy surface. Energy minima for allyl-type structures of the latter systems possess Cs symmetry and pyramidal EH_2 groups. The energetically lowest lying form of [H_2E-E(H)-EH_2]-,?,+ (E = Si - Sn) has a cyclic structure for the neutral molecules and the anion and a quasi-cyclic equilibrium arrangement for the cations. In contrast, the cyclic isomers of the carbon molecules [H_2C-C(H)-CH_2] -,?,+are significantly higher in energy than the allyl structures. Energy decomposition analyses show that the lower stability of the planar C_2v allyl structures of [H_2E-E(H)-EH_2]-,?,+ (E = Si - Sn) does not come from weak π conjugation. The relative contribution of π conjugation in the latter species is even higher than in the allyl system of carbon. The cyclic form of [H_2E-E(H)-EH_2]-,?,+ (E = Si - Sn) is lower in energy than the allyl form, because the σ bonding in the former structures is much stronger than in the latter. This overcompensates the higher Pauli repulsion in the cyclic form. In the carbon systems, the Pauli repulsion of the cyclic structures is very strong, because the bonds are much shorter than in the heavier homologues. Consequently, the stronger Pauli repulsion in the cyclic isomers is not compensated by the stronger attraction compared with the allyl system.
机译：使用DFT和从头算方法对标题化合物的结构进行了量子化学计算。通过能量分解分析研究了键合的性质。该计算预测中性和带电的较重的第14组同系物[H_2E-E（H）-EH_2]-，？，+（E = Si-Sn）的平面C2v烯丙基结构在势能面上没有极小值。后一系统的烯丙基型结构的能量最小值具有Cs对称性和锥体EH_2基团。能量最低的[H_2E-E（H）-EH_2]-，α，+（E = Si-Sn）形式对中性分子和阴离子具有环状结构，对阳离子具有准循环平衡排列。相反，碳分子[H_2C-C（H）-CH_2]-，α，+的环状异构体在能量上显着高于烯丙基结构。能量分解分析表明，[H_2E-E（H）-EH_2]-，α，+（E = Si-Sn）的平面C_2v烯丙基结构的较低稳定性并非来自弱π共轭。后一种物种中π共轭的相对贡献甚至比碳的烯丙基体系中更高。 [H_2E-E（H）-EH_2]-，？，+（E = Si-Sn）的环状形式的能量低于烯丙基形式，因为前者结构中的σ键比后者强得多。这以循环形式过度补偿了较高的保利排斥力。在碳体系中，环状结构的保利排斥力非常强，因为这些键比重的同系物短得多。因此，与烯丙基体系相比，环状异构体中更强的保利斥力没有被较强的吸引力所补偿。

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