Acidity of M(VI)O2(OH)2 for M = Group 6, 16, and U as Central Atoms

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• 作者：Rulin Feng ; Monica Vasiliu ; Kirk A. Peterson ; David A. Dixon
• 刊名：Journal of Physical Chemistry A
• 出版年：2017
• 出版时间：February 9, 2017
• 年：2017
• 卷：121
• 期：5
• 页码：1041-1050
• 全文大小：436K
• ISSN：1520-5215

文摘

Gas-phase acidities and aqueous solution pK_a’s are predicted for MO₂(OH)₂, where the center atom M is a main Group 6, 16, and U atom using the Feller–Peterson–Dixon approach based on coupled cluster CCSD(T) calculations with additional corrections. The gas-phase acidities of the MO₂(OH)₂ compounds are essentially the same for elements (M) of the same group, 304–310 kcal/mol at 298 K. All of the Group 6 compounds are 5–6 kcal/mol less acidic in the gas phase than H₂SO₄. The gas-phase acidity of UO₂(OH)₂ is calculated to be up to 338.0 kcal/mol, ∼10% less acidic in the gas phase than the other MO₂(OH)₂ acids. The most acidic molecule in aqueous solution is predicted to be H₂SO₄. Overall, for the Group 16 compounds, the pK_a’s increase going down the group, with H₂PoO₄ predicted to be slightly more acidic than nitric acid. H₂CrO₄ is the most acidic of the Group 6 transition metal compounds. The aqueous acidities of H₂MoO₄ and H₂WO₄ are comparable and about 3 pK_a units less acidic than H₂CrO₄ and comparable in acidity to HNO₃. H₂UO₄ is not acidic at all in aqueous solution with a pK_a near 20 pK_a units and is also not predicted to readily undergo hydrolysis reactions.