Density Functional Theory Studies on the Structures and Water-Exchange Reactions of Aqueous Al(III)–Oxalate Complexes

Abstract

The structures and water-exchange reactions of aqueous aluminum-oxalate complexes are investigated using density functional theory. The present work includes (1) The structures of Al(C(2)O(4))(H(2)O)(4)(+) and Al(C(2)O(4))(2)(H(2)O)(2)(-) were optimized at the level of B3LYP/6-311+G(d,p). The geometries obtained suggest that the Al-OH(2) bond lengths trans to C(2)O(4)(2-) ligand in Al(C(2)O(4))(H(2)O)(4)(+) are much longer than the Al-OH(2) bond lengths cis to C(2)O(4)(2-). For Al(C(2)O(4))(2)(H(2)O)(2)(-), the close energies between cis and trans isomers imply the coexistence in aqueous solution. The (27)Al NMR and (13)C NMR chemical shifts computed with the consideration of sufficient solvent effect using HF GIAO method and 6-311+G(d,p) basis set are in agreement with the experimental values available, indicating the appropriateness of the applied models; (2) The water-exchange reactions of Al(III)-oxalate complexes were simulated at the same computational level. The results show that water exchange proceeds via dissociative pathway and the activation energy barriers are sensitive to the solvent effect. The energy barriers obtained indicate that the coordinated H(2)O cis to C(2)O(4)(2-) in Al(C(2)O(4))(H(2)O)(4)(+) is more labile than trans H(2)O. The water-exchange rate constants (k(ex)) of trans- and cis-Al(C(2)O(4))(2)(H(2)O)(2)(-) were estimated by four methods and their respective characteristics were explored; (3) The significance of the study on the aqueous aluminum-oxalate complexes to environmental chemistry is discussed. The influences of ubiquitous organic ligands in environment on aluminum chemistry behavior can be elucidated by extending this study to a series of Al(III)-organic system.

Identification of Al13 on the Colloid Surface Using Surface-Enhanced Raman Spectroscopy

“…It is known that the vibrational modes are related to the species and structures. 49 The characteristic Raman signals of Al 13 can be assigned to the vibration of bonds related to the Al 13 molecule structure. The molecule of Al 13 ions is considered to be symmetrical, assuming that the Al 13 group is free with Cl − .…”

DFT Studies on the Water-Assisted Synergistic Proton Dissociation Mechanism for the Spontaneous Hydrolysis Reaction of Al3+ in Aqueous Solution

“…If the DFT-CM method is used to model the kinetic dissociation reactions of the two kinds of hydroxyl protons, it would be possible to identify their lifetimes reasonably. In future applications, the DFT-CM method can be extended to study the micromorphology and elementary reaction kinetics of Al and other metal ion species in heterogeneous or nonaqueous environments, such as mineral or material surfaces, aerosols, flocs, and sediments, as well as the biological organisms, to explore the problems that are difficult to solve with traditional experimental methods. − …”

Density Functional Theory Studies on the Real and Apparent Water-Exchange Reaction Kinetics of Al3+ in Aqueous Solution

“…Moreover, aluminum is one of the most environmentally friendly metals on the planet, and used aluminum can be effectively recycled. The solvent exchange between the first and second hydration shells of the aluminum ion (Al 3+ ) controls its reactivity in aqueous solution, and it is the elementary reaction step in the transformation and transport of Al species in natural water. − Hugi-Cleary et al and Phillips et al . have measured the rate constant k ex 298 (1.29 ± 0.04 and 2.02 ± 0.38 s –1 ) for the water-exchange reaction of Al­(H 2 O) 6 3+ in aqueous solution by variable 17 O nuclear magnetic resonance (NMR) analysis and assigned a dissociative interchange ( I d ) mechanism based on the activation volume of +5.7 ± 0.2 cm 3 /mol .…”