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

Journal Article · Mon Nov 12 04:00:00 EST 2007 · Inorganic Chemistry, 46(23):10016-10021

DOI:https://doi.org/10.1021/ic701313h· OSTI ID:921230

Dixon, David A; Wang, Tsang-Hsiu; Grant, Daniel J; Peterson, Kirk A; Christe, Karl O; Schrobilgen, Gary J

The research described in this product was performed in part in the Environmental Molecular Sciences Laboratory, a national scientific user facility sponsored by the Department of Energy's Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory. 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-consistent basis sets for krypton. To achieve near chemical accuracy (±1 kcal/mol), three corrections were added to the complete basis set binding energies based on frozen core coupled-cluster theory energies: a correction for corevalence 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 the heat of formation of KrF₂ is in excellent agreement with the experimental value. Contrary to the analogous xenon fluorides, KrF₂, KrF₄, and KrF₆ are predicted to be thermodynamically unstable with respect to loss of F₂. An analysis of the energetics of KrF₄ and KrF₆ with respect to fluorine atom loss together with calculations of the transition states for the intramolecular loss of F₂ show that fluorine atom loss is the limiting factor determining the kinetic stabilities of these molecules. Whereas KrF₄ possesses a marginal energy barrier of 10 kcal/mol toward fluorine atom loss and might be stable at moderately low temperatures, the corresponding barrier in KrF₆ is only 0.9 kcal/mol, suggesting that it could exist only at very low temperatures. Although the simultaneous reactions of either two or four fluorine atoms with KrF₂ to give KrF₄ or KrF₆, respectively, are exothermic, they do not represent feasible synthetic approaches because the attack of the fluorine ligands of KrF₂ by the fluorine atoms, resulting in F₂ abstraction, is thermodynamically favored over oxidative fluorination of the krypton central atom. Therefore, KrF₆ could exist only at very low temperatures, and even the preparation of KrF₄ will be extremely difficult.

• Research Organization: Pacific Northwest National Laboratory (PNNL), Richland, WA (US), Environmental Molecular Sciences Laboratory (EMSL)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC05-76RL01830
• OSTI ID: 921230
• Journal Information: Inorganic Chemistry, 46(23):10016-10021, Journal Name: Inorganic Chemistry, 46(23):10016-10021 Journal Issue: 23 Vol. 46; ISSN 0020-1669; ISSN INOCAJ
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
ELECTRONIC STRUCTURE
Environmental Molecular Sciences Laboratory
FORMATION HEAT
KRYPTON FLUORIDES
STABILITY
THERMODYNAMICS