A VSEPR-inspired force field for determining molecular properties of PF 5
A VSEPR-inspired force field for determining molecular properties of PF 5
复制标题
用于确定 PF 5 分子特性的受 VSEPR 启发的力场
DOI：
10.1080/00268976.2018.1543907
复制
发表时间：
2018
影响因子：
1.7
通讯作者：
Stanton, John F.
中科院分区：
文献类型：
--
作者：
McCaslin, Laura M.;Stanton, John F.
价壳层电子对排斥（VSEPR）理论通常在化学入门课程中教授，它为理解XY型分子的分子结构提供了基础，其中X是一个被my配体包围的中心原子。虽然VSEPR通常被认为只是一个定性理论，但Bartell和同事构建了一个半定量模型电位，通过引入球上点（POS）电位来解决VSEPR的物理基础，这样所有的X-Y键都是固定长度的，所有的原子都相互排斥。四十多年前，与半经验和相当原始的方法计算的值相比，这个简单的模型被证明在再现各种二元羟基化合物的相对二次和三次弯曲力常数方面是有效的。这里展示的工作努力超越Bartell及其同事在早期调查中使用的模型。具体来说，任何具有固定半径的POS模型都明显省略了拉伸力常数，并且通过将所有X-Y键视为简单的（等效的）莫尔斯振荡器（Morse oscillator），在这里（基本地）包含了拉伸力常数。利用莫尔斯势在参数化过程中增加的自由度，对得到的模型进行了研究。本文研究了这个简单的力学模型在多大程度上可以再现PFis的二次和三次力场，以及它如何解决一个更困难的问题——（Berry）伪旋转过程中中间体的能量学和过渡态性质，该过程在这个原型分子中交换轴向和赤道氟。五参数Morse-POS模型在描述二次和三次力场以及伪旋转过程方面表现得相当好，考虑到模型的幼稚性，这是一个相当令人印象深刻的壮举。
Valence Shell Electron Pair Repulsion (VSEPR) theory, commonly taught in introductory chemistry courses, provides a basis for understanding the molecular structures of molecules of the type XY, where X is a central atom surrounded bymY ligands. While VSEPR is generally thought of only as a qualitative theory, Bartell and coworkers constructed a semi-quantitative model potential to address the physical underpinnings of VSEPR by introducing a points-on-a-sphere (POS) potential such that all X-Y bonds are of fixed length and all atoms Yrepel each other. More than forty years ago, this simple model was shown to be effective in reproducing relative quadratic and cubic bending force constants for a variety of binary XYcompounds when compared to values computed with semi-empirical and fairly primitivemethods. The work presented here endeavours to go beyond the model used in the early investigations by Bartell and coworkers. Specifically, stretching force constants are clearly omitted from any POS model with a fixed radius, and are (primitively) included here by treating all X-Y bonds as simple (and equivalent) Morse oscillators. With the additional degrees of freedom in the parametrization that come from the Morse potential, the resulting model was investigated. The degree to which this simple mechanical model can reproduce quadratic and cubic force fields for PFis studied here, as well as how it works for a more difficult problem – the energetics and transition state properties for the intermediate in the (Berry) pseudorotation process that interchanges axial and equatorial fluorines in this prototype molecule. The five parameter Morse-POS model is shown to be do quite well in describing the quadratic and cubic force fields, as well as the pseudorotation process, a fairly impressive feat given the naivete of the model.