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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Ab Initio Study of the Hydrolysis Reactions of Neutral and Anionic Mg - Pyrophosphate Complexes in the Gas Phase
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Ab Initio Study of the Hydrolysis Reactions of Neutral and Anionic Mg - Pyrophosphate Complexes in the Gas Phase

机译：中性和阴离子Mg-焦磷酸配合物在气相中水解反应的从头算研究。

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摘要

Ab initio calculations were performed to study the stability of various anhydrous and monohydrated complexes of Mg~(2+) with pyrophosphates and orthophosphates at the self-consistent-field (SCF) and second-order perturbation (MP2) levels of the theory, using a 6 - 31 + G~(**) basis set with diffuse and polarization functions. New equilibrium geometries were found for the anhydrous Mg - pyrophosphate complexes, that modify previous estimates of the isomerization energies. It is found that the interaction with the water molecule stabilizes the pyrophosphates with respect to the metaphosphate-containing complexes, thus modifying the reaction energies to such an extent that the isomerization results are endothermic and nonspontaneous for the dianionic complex. However, the hydrolysis reactions are all exothermic and spontaneous. Moreover, it is found that the water molecule readily breaks upon interacting with the dianionic complex, producing a hydroxide anion: H_2O + [Mg centre dot P_2O_7]~(2-) -> [HO centre dot Mg centre dot HP_2O_7]~(2-), and the resulting dianionic complex is much more stable than the isomer with a metaphosphate. It is shown that this result is consistent with both an associative and a dissociative mechanism for the hydrolysis. Finally, the estimate of free energies of solvation by means of the polarizable continuum model (PCM) yield values for the free energies of hydrolysis that are close to the experimental data.
机译：进行了从头算的计算，研究了Mg〜（2+）与焦磷酸盐和正磷酸盐在该理论的自洽场（SCF）和二阶扰动（MP2）水平下的各种无水和一水合物的稳定性。具有扩散和极化功能的6-31 + G〜（**）基集。发现了无水Mg-焦磷酸盐配合物的新平衡几何形状，该几何形状修改了以前对异构化能的估计。发现与水分子的相互作用使焦磷酸盐相对于含偏磷酸盐的配合物稳定，从而将反应能量改性到一定程度，使得异构化结果对于双阴离子配合物而言是吸热的且非自发的。但是，水解反应都是放热的和自发的。此外，发现水分子在与二价阴离子络合物相互作用时容易破裂，产生氢氧根阴离子：H_2O + [Mg中心点P_2O_7]〜（2-）-> [HO中心点Mg中心点HP_2O_7]〜（2 -），并且所得的双阴离子络合物比具有偏磷酸盐的异构体稳定得多。结果表明，该结果与水解的缔合和解离机理都一致。最后，借助可极化连续体模型（PCM）估计的溶剂化自由能产生的水解自由能值接近实验数据。

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