Structures of the BrF4(+) and IF4(+) Cations
Abstract
The large discrepancies between the calculated and observed structures for BrF4(+) and IF4(+) (J. Am. Chem. Soc. 2001, 123, 6338) prompted a redetermination of the crystal structures of BrF4(+)Sb2F11(-) (monoclinic, P2 sub 1/c, a = 5.2289(6) A, b = 14.510(2) A, c = 14.194(2) A, * = 90.280(1)(sup o), Z = 4) and IF4(+)SbF6(-) (orthorhombic, Ibca, a = 8.2702(9) A, b = 8.3115(9) A, c = 20.607(2) A, z = 8). It is shown that for BrF4(+), the large differences were mainly due to large errors in the original experimental data. For IF4(+)SbF6(-), the geometry previously reported for IF4(+) was reasonably close to that found in this study in spite of a very large R-factor of 0.15 and a refinement in an incorrect space group. The general agreement between the calculated and the redetermined geometries of BrF4(+) and IF4(+) is excellent, except for the preferential compression of one bond angle in each ion due to the influence of inter-ionic fluorine bridges. In BrF4(+), the fluorine bridges are equatorial and compress this angle. In IF4(+), the nature of the fluorine bridges depends on the counter ion, and either the axial (in IF4(+)SbF6(-) or the equatorial (in IF4(+)Sb2F11(-) bond angle is preferentially compressed. Therefore, the geometries of the free ions are best described by the theoretical calculations.
Document Details
- Document Type
- Technical Report
- Publication Date
- Aug 01, 2002
- Accession Number
- ADA406379
Entities
People
- Ashwani Vij
- Fook S. Tham
- Karl O. Christe
- Vandana Vij
- William W. Wilson
Organizations
- Air Force Research Laboratory