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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Hydration of the Fluoride Anion: Structures and Absolute Hydration Free Energy from First-Principles Electronic Structure Calculations
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Hydration of the Fluoride Anion: Structures and Absolute Hydration Free Energy from First-Principles Electronic Structure Calculations

机译：氟化物阴离子的水合：第一性原理电子结构计算的结构和绝对水合自由能

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A series of first-principles electronic structure calculations have been performed to determine the most stable structures of F~-(H_2O)_n clusters (n = 4, 8, 12, and 16) and the hydration free energy of fluoride anion (F~-). The calculated results show that a new, tetrahedrally coordinated fluoride anion hydration structure F~-(H_2O)_4 cluster is lower in Gibbs free energy than the previously considered most stable structure of F~-(H_2O)_4. The first ab initio prediction of potential stable hydration structures for F~-(H_2O)_n clusters (n = 8, 12, and 16) are given. The energetic results show that the tetrahedrally coordinated fluoride anion hydration structure becomes more stable as compared to the other hydration structures with a pyramidal coordination, i.e., a surface ion cluster state, as the cluster size increases from n = 8 to n = 12 to n = 16. This suggests that, with increasing n, the fluoride anion will be internally solvated in large enough F~-(H_2O)_n clusters. These results provide insight into the transition from the hydration structure found in small gas-phase hydrated-anion clusters to the hydration structure observed in aqueous solution. The calculated results show that, for a given n, the bulk solvent effects can qualitatively change the relative thermodynamic stability of different possible isomers of F~-(H_2O)~n clusters and the most stable structure in solution is not necessarily the most stable structure in the gas phase. When n = 16, a pyramidally coordinated fluoride anion hydration structure is the most stable structure in the gas phase, whereas a tetrahedrally coordinated fluoride anion hydration structure has the lowest free energy in solution. The absolute hydration free energy of fluoride anion in aqueous solution, ΔG_(hyd)~(298)(F~-), is predicted to be -104.3 ± 0.7 kcal/mol by using a reliable computational protocol of first-principles solvation-included electronic structure calculations. The predicted ΔG_(hyd)~(298)(F~-) value of -104.3 ± 0.7 kcal/mol, together with our previously calculated ΔG_(hyd)~(298)(H~+) value of -262.4 kcal/mol determined by using the same computational protocol, gives ΔG_(hyd)~(298)(F~-) + ΔG_(hyd)~(298)(H~+) = -366.7 ± 0.7 kcal/mol in excellent agreement with the value of -366.5 kcal/mol derived from the available experimental data.
机译：已经进行了一系列的第一性原理电子计算，以确定F〜-（H_2O）_n团簇（n = 4、8、12和16）的最稳定结构以及氟离子的水合自由能（F〜 -）。计算结果表明，新的四面体配位的氟阴离子水合结构F〜-（H_2O）_4团簇的吉布斯自由能比以前认为最稳定的F〜-（H_2O）_4结构低。首先给出了F〜-（H_2O）_n团簇（n = 8、12和16）的潜在稳定水合结构的从头算预测。能量结果表明，随着簇尺寸从n = 8增加到n = 12至n，四面体配位的氟化物阴离子水合结构比其他具有金字塔配位的水合结构（即表面离子簇状态）更稳定。 =16。这表明，随着n的增加，氟阴离子将在内部形成足够大的F〜-（H_2O）_n簇。这些结果提供了从小型气相水合阴离子簇中发现的水合结构向水溶液中观察到的水合结构过渡的见解。计算结果表明，对于给定的n，本体溶剂效应可以定性地改变F〜-（H_2O）〜n团簇的各种可能异构体的相对热力学稳定性，溶液中最稳定的结构不一定是最稳定的结构。在气相中。当n = 16时，气相中金字塔状配位的氟阴离子水合结构是最稳定的结构，而四面体配位的氟阴离子水合结构在溶液中的自由能最低。通过使用包括第一原理溶剂化的可靠计算规程，预测氟离子在水溶液中的绝对水合自由能ΔG_（hyd）〜（298）（F〜-）为-104.3±0.7 kcal / mol电子结构计算。预测的ΔG_（hyd）〜（298）（F〜-）值为-104.3±0.7 kcal / mol，以及我们先前计算的ΔG_（hyd）〜（298）（H〜+）值为-262.4 kcal / mol使用相同的计算协议确定，得出ΔG_（hyd）〜（298）（F〜-）+ΔG_（hyd）〜（298）（H〜+）= -366.7±0.7 kcal / mol，与该值非常吻合-366.5 kcal / mol来自可得的实验数据。

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