کد مقاله کد نشریه سال انتشار مقاله انگلیسی نسخه تمام متن
1814095 1025644 2008 5 صفحه PDF دانلود رایگان
عنوان انگلیسی مقاله ISI
An ionic force-field study of monomers, dimers and higher polymers in pentafluoride vapors
موضوعات مرتبط
مهندسی و علوم پایه فیزیک و نجوم فیزیک ماده چگال
پیش نمایش صفحه اول مقاله
An ionic force-field study of monomers, dimers and higher polymers in pentafluoride vapors
چکیده انگلیسی

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 D3h trigonal bipyramid 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.

ناشر
Database: Elsevier - ScienceDirect (ساینس دایرکت)
Journal: Physica B: Condensed Matter - Volume 403, Issue 17, 1 August 2008, Pages 2797–2801
نویسندگان
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