Heats of Formation of Krypton Fluorides and Stability Predictions for KrF4 and KrF6 from High Level Electronic Structure Calculations

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• 作者：David A. Dixon ; Tsang-Hsiu Wang ; Daniel J. Grant ; Kirk A. Peterson ; Karl O. Christe ; Gary J. Schrobilgen
• 刊名：Inorganic Chemistry
• 出版年：2007
• 出版时间：November 12, 2007
• 年：2007
• 卷：46
• 期：23
• 页码：10016 - 10021
• 全文大小：60K
• 年卷期：v.46,no.23(November 12, 2007)
• ISSN：1520-510X

文摘

Atomization energies at 0 K and heats of formation at 0 and 298 K are predicted for KrF⁺, KrF^-, KrF₂, KrF₃⁺, KrF₄,KrF₅⁺, and KrF₆ from coupled-cluster theory (CCSD(T)) calculations with effective core potential correlation-consistentbasis sets for krypton. To achieve near chemical accuracy (±1 kcal/mol), three corrections were added to thecomplete basis set binding energies based on frozen core coupled-cluster theory energies: a correction for core-valence effects, a correction for scalar relativistic effects, and a correction for first-order atomic spin-orbit effects.Vibrational zero point energies were computed at the coupled-cluster level of theory. The calculated value for theheat of formation of KrF₂ is in excellent agreement with the experimental value. Contrary to the analogous xenonfluorides, KrF₂, KrF₄, and KrF₆ are predicted to be thermodynamically unstable with respect to loss of F₂. Ananalysis of the energetics of KrF₄ and KrF₆ with respect to fluorine atom loss together with calculations of thetransition states for the intramolecular loss of F₂ show that fluorine atom loss is the limiting factor determining thekinetic stabilities of these molecules. Whereas KrF₄ possesses a marginal energy barrier of 10 kcal/mol towardfluorine atom loss and might be stable at moderately low temperatures, the corresponding barrier in KrF₆ is only0.9 kcal/mol, suggesting that it could exist only at very low temperatures. Although the simultaneous reactions ofeither two or four fluorine atoms with KrF₂ to give KrF₄ or KrF₆, respectively, are exothermic, they do not representfeasible synthetic approaches because the attack of the fluorine ligands of KrF₂ by the fluorine atoms, resulting inF₂ abstraction, is thermodynamically favored over oxidative fluorination of the krypton central atom. Therefore, KrF₆could exist only at very low temperatures, and even the preparation of KrF₄ will be extremely difficult.