Journal of the American Chemical Society, Vol.132, No.10, 3533-3542, 2010
A Rare Example of a Krypton Difluoride Coordination Compound: [BrOF2][AsF6]center dot 2KrF(2)
The synthesis of [BrOF2][AsF6]center dot 2KrF(2), its structural characterization, and bonding are described in this study. Although several KrF2 adducts with transition metal centers have been previously reported, none have been crystallographically characterized. The solid-state Raman spectrum of [BrOF2][AsF6]center dot 2KrF(2) has been assigned with the aid of quantum-chemical calculations. The low-temperature (-173 degrees C) X-ray crystal structure of [BrOF2][AsF6]center dot 2KrF(2) consists of isolated molecular units and represents an example of KrF2 coordinated to a main-group atom. The coordination geometry around the BrOF2+ cation renders the free valence electron lone pair more compact than in free BrOF2+. The KrF2 ligands are coordinated trans to the fluorine atoms of BrOF2+ with the AsF6-anion coordinated trans to oxygen. The quantum theory of atoms in molecules (QTAIM) and electron localization function (ELF) analyses have been carried out in order to define the nature of the bonding in the complex. A significant amount of charge (0.25 e) is transferred to BrOF2+ from the two KrF2 ligands (0.10 e each) and from the AsF6- anion (0.05 e). Significant polarization also occurs within the KrF2 ligands, which enhances the anionic characters of the fluorine bridges. The interaction energy is mostly governed by the electrostatic interaction of the positively charged bromine atom with the surrounding fluorine atoms.