Entity

Time filter

Source Type


Qian Z.,State Key Laboratory of Coordination Chemistry of China | Qian Z.,Zhejiang Normal University | Feng H.,State Key Laboratory of Coordination Chemistry of China | Feng H.,Zhejiang Normal University | And 4 more authors.
Geochimica et Cosmochimica Acta | Year: 2010

In this paper, the structure of the Al30O8(OH)56(H2O)26 18+(Al30) polyoxocation in aqueous solution is investigated, including an exploration of its water-exchange reaction using a supramolecular model. Thirty-one solvent water molecules were explicitly included in the supramolecular model to approximate the influence of the solvent. The calculated results indicated that both the gas-phase and the supramolecular models could correctly reproduce the structure of the Al30 polyoxocation, but the supramolecular model described the structure more accurately. Using the supramolecular model, we calculated the 27Al NMR chemical shifts of various aluminum atoms using HF and GIAO methods, and they compared well to the chemical shifts determined experimentally. The water-exchange reaction of the Al30 polyoxocation could not be simulated with the gas phase model because of a proton-transfer reaction that is induced by the highly positive charge of the Al30 polyoxocation. However, the inclusion of an explicit second solvation sphere lowered the acidity of the coordinated water molecules and allowed simulation of the water exchange reaction. © 2009 Elsevier Ltd. All rights reserved. Source


Yang W.,State Key Laboratory of Coordination Chemistry of China | Qian Z.,State Key Laboratory of Coordination Chemistry of China | Lu B.,State Key Laboratory of Coordination Chemistry of China | Zhang J.,State Key Laboratory of Coordination Chemistry of China | Bi S.,State Key Laboratory of Coordination Chemistry of China
Geochimica et Cosmochimica Acta | Year: 2010

The formation mechanism of Al30O8(OH)56(H2O)26 18+ (Al30) has been investigated by the density functional theory based on the supermolecule model and kinetic analysis on the 27Al nuclear magnetic resonance (NMR) experimental results in monitoring Al30 synthesis process. The theoretical chemistry calculations on the four possible schemes show that δ-Na-Al13 is the reasonable intermediate followed by the substitution of Na with Al to form δ-Al14, and Na+ plays an important role in stabilizing the intermediate (δ-Na-Al13) in the transformation. The kinetic analysis on the 27Al NMR experimental data indicates that ε-Al13 decomposes and isomerizes in the formation of Al30, while Al monomers facilitate the decomposition of ε-Al13 and so the isomerization of ε-isomers to δ-isomers effectively. The favorable formation mechanism of Al30 includes three steps: (1) ε-Al13 decomposes and rearranges into the isomer δ-Al13; (2) Na+ reacts with δ-Al13 to stabilize the intermediate δ-Na-Al13, followed by Al monomers replacing Na to form δ-Al14; (3) δ-Al14 reacts with the Al monomers in the solution to finally form Al30. Both Al monomers and Na+ are important in the transformation. Al monomers are the basic building units and helpful to the isomerization while Na+ can well stabilize the isomer δ-Al13 to yield intermediate δ-Na-Al13. The results also show that other isomers of ε-Al13 (β-Al13 and α-Al13) form in the formation of Al30, and their calculated 27Al NMR tetrahedral resonance shifts are consistent with the experimental 27Al NMR tetrahedral signals in the preparation process of Al30. © 2009 Elsevier Ltd. All rights reserved. Source

Discover hidden collaborations