Po(IV) Hydration: A Quantum Chemical Study

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• 作者：Regla Ayala ; Jose Manuel Martinez ; Rafael R. Pappalardo ; A. Muñ ; oz-Paez ; Enrique Sanchez Marcos
• 刊名：Journal of Physical Chemistry B
• 出版年：2008
• 出版时间：May 1, 2008
• 年：2008
• 卷：112
• 期：17
• 页码：5416 - 5422
• 全文大小：230K
• 年卷期：v.112,no.17(May 1, 2008)
• ISSN：1520-5207

文摘

This work presents a theoretical study on the hydration of Po(IV) in solution. Three points have beenaddressed: (i) the level of calculation needed to properly describe the system under study, (ii) the hydrationnumber of Po(IV), and (iii) the nature of the polonium-water bonding. The condensed medium effects havebeen included by means of a continuum solvation model, thus different [Po(H₂O)_n]⁴⁺ hydrates were embeddedin a cavity surrounded by a polarizable dielectric medium. Among the quantum-mechanical calculation levelshere considered, the MPW1PW91 functional was shown to be the most suitable, allowing a proper descriptionof the Po-H₂O interactions at affordable cost. The hydration number of Po(IV) was found to be between 8and 9. This value is ruled by a dynamic equilibrium involving the octa- and ennea-hydrates, although the7-fold coordination cannot be completely excluded. The hydration free energy of Po(IV) is estimated to bearound -1480 kcal/mol. The Po-H₂O bonding is dominated by strong electrostatic contributions although asmall covalent contribution is responsible for the peculiar arrangement adopted by the smaller hydrates (n ges/entities/le.gif">5). A natural bond order (NBO) analysis of the hydrate wave functions shows that the covalent bond involvesthe empty 6p orbitals of the polonium ion and one lone pair on the oxygen atom of the water molecule. Aparallel investigation to the hydrate study, where the polonium ion was replaced by a tetravalent point chargeplus a repulsion potential, was carried out. These results allowed a detailed examination of the electrostaticand nonelectrostatic contributions to the polonium hydrate formation.