Quantum Chemical Studies of Mononuclear Zinc Species of Hydration and Hydrolysis

Abstract

Optimal geometries, charge distributions, bond analysis, changes of Gibbs free energy, entropies and enthalpies of hydration, and hydrolysis reactions for mononuclear species of Zn 2+ including hydrated and hydrolysis complexes were investigated using quantum chemical calculations in the gas phase. Optimized geometrical structures showed that the stable hydrated and hydrolysis zinc species without outer-sphere water molecules . Results of NPA (Natural Population Analysis) indicated that the charge on the Zn atom of the hydrated ions decreased but the charge on the zinc atom of the hydrolysis species increased with the increase of inner-sphere water molecules. NBO (Natural Bond Orbital) analyses demonstrated that hydrated and hydrolysis species of zinc were mainly electrostatic bonding compounds. Calculations of reaction energies indicated that inner-sphere water molecules became more unfavorable as the hydrolysis increased. Stepwise hydrolysis equilibrium constants decreased successively and the order remained unchanged when the inner-sphere dehydration occurred.

Influence of pH on Initial Concentration Effect of Arsenate Adsorption on TiO2 Surfaces: Thermodynamic, DFT, and EXAFS Interpretations

“…To eliminate boundary effect and reduce charge of the clusters, the hanging bonds of O atoms were saturated with H atoms. 5,15,16 Geometries were predicted using 6-31+G(d) basis set for O, H, 6-311+G(d) basis set for As, and LANL2DZ relativistic effective core potential (RECP) basis set for Ti atoms. 14,15 It was reported that the surface of anatase TiO 2 particle predominantly consisted of (101), (100), and (001) crystal plane, 17,18 and the exposition of crystal plane depended on the synthetic technique.…”

EXAFS studies on adsorption irreversibility of Zn(II) on TiO2: Temperature dependence

“…It has been reported that the most common coordination geometries of hydrous Zn(II) are octahedron (i.e., Zn(H 2 O) 2+ 6 ) with a Zn-O bond length of 2.07-2.18 Å and tetrahedron (i.e., ZnO(s), Zn(OH) 2− 4 ) with a Zn-O bond length of 1.92-1.99 Å [45]. Zhu and Pan [46] reported that in acidic solutions (pH 6.9) Zn 2+ (aq) is present in the form of octahedron with an average Zn-O bond length of 2.08 Å. As shown in Table 3, the average Zn-O bond length of the three samples is 1.98 ± 0.01 Å, and the average coordination number is 4.3 ± 0.02 Å.…”

Coordination Structure of Adsorbed Zn(II) at Water−TiO2Interfaces

“…This difference between experimental and theoretical values has been attributed to the theoretical underestimation of solvent effect from outer-sphere water molecules. 39 However, we expect that this artifact does not affect the relative stability of the adsorption modes and their coordination properties.…”