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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Cooperativity in Al~(3+) hydrolysis reactions from density functional theory calculations
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Cooperativity in Al~(3+) hydrolysis reactions from density functional theory calculations

机译：基于密度泛函理论计算的Al〜（3+）水解反应的协同性

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摘要

Aqua/hydroxo mononuclear Al~(3+) species in aqueous solution are investigated using density functional theory (DFT B3LYP/6-311++G(d,p)) and the polarized continuum model (PCM). Optimized gas-phase geometries have been obtained for the species Al(OH)_n(H_2O)_m(3-n) ~+ in which n = 0, 1, 2, 3, or 4 while (n + m) = 4, 5, or 6. For Al(OH)_2(H_2O)_4~(1+) the cis and trans geometries were considered. The structures were analyzed in terms of water and hydroxide M-O and O-H distances, which are shown to be strongly modulated by water hydrolysis. The atomic charges were computed and the electronic structure of these complexes is discussed. The conversion from one aqua-/hydroxo- species to another follows independent hydrolysis and dehydration reactions for which the aqueous Gibbs free energies have been estimated by means of constructing thermodynamic cycles. Results clearly demonstrate that the dehydration reaction is increasingly favorable as hydrolysis proceeds. Similarly, as the complex coordination number decreases the hydrolysis reaction proceeds increasingly more favorably. The aqueous Gibbs free energy of each species, relative to Al(H _2O)_6~(3+), has been determined by combining the appropriate Gibbs free energies of the hydrolysis and dehydration reactions demonstrating that the additive effect is quite complex showing a gradual transition from preferring the 6-coordination to 5-coordination to 4-coordination as a function of ligand hydrolysis, in agreement with published experimental and theoretical work. We have also computed the equilibrium constants of each of the above reactions and, using [H~+] as a parameter, estimated the mole fraction of each species as a function of pH. This offers a clear demonstration that the qualitative hydrolysis behavior, e.g., cooperativity, of aqueous Al~(3+) species is obtained at the B3LYP/IEF-PCM level of theory.
机译：利用密度泛函理论（DFTB3LYP / 6-311 ++ G（d，p））和极化连续模型（PCM）研究了水溶液中的水/羟基单核Al〜（3+）物种。已获得Al（OH）_n（H_2O）_m（3-n）〜+的最佳气相几何结构，其中n = 0、1、2、3或4而（n + m）= 4， 5或6。对于Al（OH）_2（H_2O）_4〜（1+），考虑了顺式和反式几何形状。根据水和氢氧化物的M-O和O-H距离对结构进行了分析，这些距离显示被水水解强烈调节。计算了原子电荷并讨论了这些配合物的电子结构。从一种水/氢氧根向另一种水/氢氧根的转化遵循独立的水解和脱水反应，为此已经通过构建热力学循环估算了吉布斯水溶液的自由能。结果清楚地表明，随着水解的进行，脱水反应越来越有利。类似地，随着复杂配位数的降低，水解反应越来越有利地进行。相对于Al（H _2O）_6〜（3+），每种物质的含水吉布斯自由能是通过组合适当的水解和脱水反应的吉布斯自由能确定的，表明加性效应非常复杂，显示出逐渐的与公开的实验和理论工作相一致，从6配位到5配位向4配位的转变是配体水解的函数。我们还计算了上述每个反应的平衡常数，并使用[H〜+]作为参数，估算了每种物质的摩尔分数随pH的变化。这清楚地证明了在理论上的B3LYP / IEF-PCM水平上获得了水性Al〜（3+）物种的定性水解行为，例如协同作用。

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