Acta Chimica Sinica ›› 2013, Vol. 71 ›› Issue (9): 1307-1312.

Article

### Pb(II)水合结构的密度泛函及分子动力学研究

1. a 中国海洋大学海洋化学理论与工程技术教育部重点实验室 青岛 266100;
b 青岛农业大学化学与药学院 青岛 266109
• 投稿日期:2013-04-04 发布日期:2013-04-10
• 通讯作者: 王娟,E-mail:juaner80@163.com;夏树伟,E-mail:shuweixia@ouc.edu.cn E-mail:juaner80@163.com;shuweixia@ouc.edu.cn
• 基金资助:

项目受国家自然科学基金(No. 20677053)资助.

### Hydration Structure of Pb(II) from Density Functional Theory Studies and First-Principles Molecular Dynamics

Wang Juana,b, Xia Shuweia, Yu Liangmina

1. a Education Ministry Key Laboratory of Marine Chemistry Theory and Technology, Ministry of Education Ocean University of China, Qingdao 266100;
b College of Chemistry and Pharmacy, Qingdao Agricultural University, Qingdao 266109
• Received:2013-04-04 Published:2013-04-10
• Supported by:

Project supported by the National Natural Science Foundation of China (No. 20677053).

Experimental investigation of the hydration structure of Pb(II) has been poorly documented, and the bonding mechanism is not clear. Geometries of Pb(H2O)1~92+ were optimized using the Perdew-Burke-Ernzerhof generalized gradient approximation (PBE-GGA) of density functional theory with CASTEP code under the periodic boundary conditions. The interaction between nuclei and electrons was approximated with Vanderbilt ultrasoft pseudopotential. First-principles molecular dynamics (MD) study of Pb(H2O)52+ in an aqueous medium was carried out in order to gain insight into solvation behavior of Pb(II), where the density of water in solution was 1.0×103 kg/m3. The MD simulation was performed in the NVT ensemble at 298 K, with a time step of 1.0 fs and simulation time of 8.0 ps. Then the Mulliken charge population, partial density of states (PDOS) and charge density difference of hydrated Pb(II) complex were analyzed. Determination of bond length, binding energy and Mulliken charge population of equilibrium geometries of Pb(H2O)1~92+ indicated that the primary hydration numbers of 6, 7 and 8 were all possible, and the geometry of Pb(H2O)62+ was found to be the transition state between the holodirected and the hemidirected. According to the relaxation of Pb(H2O)52+ in aqueous solution, there was always water exchange between the primary and secondary hydration shells of Pb(II). Based on the equilibrium structural parameters of Pb(H2O)1~92+, relaxation of Pb(H2O)52+ in aqueous solution and the experimental extended X-ray absorption fine structure (EXAFS) results, the most probable coordination number of the first hydration shell of aqueous Pb(II) was 6 of a complex with approximately hemi-directed structure. Bonds of Pb—O in Pb(H2O)62+ exhibit strong ionicity with few covalent character. The distortion of Pb(H2O)62+ in structure does not originate from a 6s-6p hybridization on the heavy metal as the Pb 6s and 6p states are energetically too far apart to mix directly. It is the coupling of Pb6p6d with the antibonding Pb6s-O2p state that gives rise to the net asymmetry in the electron density on Pb, which results in the distorted structure of Pb(H2O)62+.