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

作者：Wang Juan^*; Xia Shuwei; Yu Liangmin

来源：Acta Chimica Sinica, 2013, 71(9): 1307-1312.

DOI：10.6023/A13040368

• Pb(II)
• hydration structure
• density functional theory
• first-principles molecular dynamics
• density of states

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 similar to 9)(2+) 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)(5)(2+) 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 1.0x10(3) kg/m(3). 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 similar to 9)(2+) indicated that the primary hydration numbers of 6, 7 and 8 were all possible, and the geometry of Pb(H2O)(6)(2+) was found to be the transition state between the holodirected and the hemidirected. According to the relaxation of 2 Pb(H2O)(5)(2+) 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 similar to 9)(2+) , relaxation of Pb(H2O)(5+) 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)(6)(2+) exhibit strong ionicity with few covalent character. The distortion of Pb(H2O)(6)(2+) 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)(6)(2+).

• 出版日期2013-9-15
• 单位中国海洋大学