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首页> 外文期刊>Physica, B. Condensed Matter >An ionic force-field study of monomers, dimers and higher polymers in pentafluoride vapors
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An ionic force-field study of monomers, dimers and higher polymers in pentafluoride vapors

机译：五氟化物蒸气中单体，二聚体和高级聚合物的离子力场研究

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Pentafluoride compounds such as NbF5 and TaF5 have been reported in the literature to admit various states of polymerization coexisting with monomers in their vapor phase, in relative concentrations that vary with temperature and pressure. We construct a microscopic interionic force-field model for the molecular monomer of these compounds (including VF5, SbF5 and MoF5 in addition to NbF5 and TaF5), the stable form of the monomer being in the shape of a D-3h trigonal hipyramid in all cases. The model emulates chemical bonds by allowing for electrical and short-range overlap polarizabilities of the fluorines, and is used to evaluate the structure and the stability of (MF5)(n) molecules with n running from 2 to 6. The dimer is formed by two distorted edge-sharing octahedral, while the trimer and the higher polymers can form rings of distorted corner-sharing octahedra. A chain-like configuration is also found for the trimer of NbF5, which consists of a seven-fold coordinated Nb bonded to two distorted octahedra via edge sharing. Comparison of calculated vibrational frequencies and bond lengths with experimental data is made whenever possible. We find that there is a small net gain of energy in the formation of a dimer, while otherwise the static energy of the n-mer is very close to that of n separated monomers. High sensitivity of the state of molecular aggregation to the thermodynamic conditions of the vapor is clearly indicated by our calculations. (C) 2008 Elsevier B.V. All rights reserved.
机译：在文献中已经报道了诸如NbF5和TaF5之类的五氟化物化合物，其在气相中与单体共存的各种聚合状态，其相对浓度随温度和压力而变化。我们为这些化合物的分子单体（除NbF5和TaF5之外还包括VF5，SbF5和MoF5）构建了一个微观的离子力场模型，该单体的稳定形式总体上为D-3h三角型金字塔形案件。该模型通过允许氟的电和短程重叠极化来模拟化学键，并用于评估n为2至6的（MF5）（n）分子的结构和稳定性。两个扭曲的边共享八面体，而三聚体和高级聚合物可以形成扭曲的边共享八面体的环。还发现NbF5的三聚体呈链状构型，其由通过边缘共享键合到两个扭曲的八面体的七倍配位Nb组成。尽可能将计算出的振动频率和键长与实验数据进行比较。我们发现，在形成二聚体时会有很小的净能量获取，而否则，n-mer的静态能量非常接近n个分离的单体的静态能量。我们的计算清楚地表明了分子聚集状态对蒸汽热力学条件的高度敏感性。 （C）2008 Elsevier B.V.保留所有权利。

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