National Technical Reports Library

The National Technical Information Service acquires, indexes, abstracts, and archives the largest collection of U.S. government-sponsored technical reports in existence. The NTRL offers online, free and open access to these authenticated government technical reports. Technical reports and documents in its repository may be available online for free either from the issuing federal agency, the U.S. Government Publishing Office’s Federal Digital System website, or through search engines.

Details

Problem of Heptacoordination: Vibrational Spectra, Structure, and Fluxionality of Iodine Heptafluoride. (Reannouncement with New Availability Information).

ADA266768

Publication Date	1993
Personal Author	Christe, K. O.; Curtis, E. C.; Dixon, D. A.
Page Count	8
Abstract	Iodine heptafluoride, the most studied prototype of a heptacoordinated molecule, had presented many mysteries concerning its spectroscopic and structural properties. It is shown by ab initio calculations and a reexamination of the vibrational spectra and their normal coordinate analysis that most of the previously implied abnormalities were due to incorrect assignments. All the available structural data for IF7 are consistent with a highly fluxional, dynamically distorted pentagonal-bipyramidal molecule possessing D sub 5h symmetry in the ground state. The fluxionality of IF7, can be attributed to (1) a rapid dynamic puckering of the highly congested pentagonal equatorial plane involving a very low frequency, large amplitude puckering mode which induces a small axial bend and (2) a much slower intramolecular exchange of the axial and equatorial fluorines resulting in their equivalence on the NMR time scale. The high degree of ligand congestion in the equatorial plane of the pentagonal bipyramid, combined with a semi-ionic, 6-center 10-electron bonding scheme, results in the equatorial I-F bonds being significantly longer than the axial ones and the equatorial in-plane deformation force constants being much larger than the out-of-plane ones. It is shown that the VSEPR model of repelling points on a sphere cannot account for either the pentagonal-bipyramidal structure of heptacoordinated molecules or the planarity of their equatorial fluorine belts. These features can be explained, however, by a bonding scheme involving a planar, delocalized p sub xy hybrid on the central atom for the formation of five equatorial, semi-ionic, 6-center 10-electron bonds and an sp sub z, hybrid for the formation of two mainly covalent axial bonds.
Keywords	Chemical bonds Iodine Ligands Molecular structure Inorganic compounds Valence Fluorine Ground state Models Vibrational spectra Reprints Fluorides Iodine heptafluoride Heptacoordination Valence Shell Electron Pair Repulsion Theory
Source Agency	Army Non Paid Reprints
NTIS Subject Category	99F - Physical & Theoretical Chemistry 99D - Basic & Synthetic Chemistry
Corporate Authors	Rockwell International, Canoga Park, CA.; Army Research Office, Research Triangle Park, NC.
Document Type	Journal Article
NTIS Issue Number	199607
Contract Number	DAAL03-91-C-0025

Problem of Heptacoordination: Vibrational Spectra, Structure, and Fluxionality of Iodine Heptafluoride. (Reannouncement with New Availability Information).

Problem of Heptacoordination: Vibrational Spectra, Structure, and Fluxionality of Iodine Heptafluoride. (Reannouncement with New Availability Information).
ADA266768

Publication Date	1993
Personal Author	Christe, K. O.; Curtis, E. C.; Dixon, D. A.
Page Count	8
Abstract	Iodine heptafluoride, the most studied prototype of a heptacoordinated molecule, had presented many mysteries concerning its spectroscopic and structural properties. It is shown by ab initio calculations and a reexamination of the vibrational spectra and their normal coordinate analysis that most of the previously implied abnormalities were due to incorrect assignments. All the available structural data for IF7 are consistent with a highly fluxional, dynamically distorted pentagonal-bipyramidal molecule possessing D sub 5h symmetry in the ground state. The fluxionality of IF7, can be attributed to (1) a rapid dynamic puckering of the highly congested pentagonal equatorial plane involving a very low frequency, large amplitude puckering mode which induces a small axial bend and (2) a much slower intramolecular exchange of the axial and equatorial fluorines resulting in their equivalence on the NMR time scale. The high degree of ligand congestion in the equatorial plane of the pentagonal bipyramid, combined with a semi-ionic, 6-center 10-electron bonding scheme, results in the equatorial I-F bonds being significantly longer than the axial ones and the equatorial in-plane deformation force constants being much larger than the out-of-plane ones. It is shown that the VSEPR model of repelling points on a sphere cannot account for either the pentagonal-bipyramidal structure of heptacoordinated molecules or the planarity of their equatorial fluorine belts. These features can be explained, however, by a bonding scheme involving a planar, delocalized p sub xy hybrid on the central atom for the formation of five equatorial, semi-ionic, 6-center 10-electron bonds and an sp sub z, hybrid for the formation of two mainly covalent axial bonds.
Keywords	Chemical bonds Iodine Ligands Molecular structure Inorganic compounds Valence Fluorine Ground state Models Vibrational spectra Reprints Fluorides Iodine heptafluoride Heptacoordination Valence Shell Electron Pair Repulsion Theory
Source Agency	Army Non Paid Reprints
NTIS Subject Category	99F - Physical & Theoretical Chemistry 99D - Basic & Synthetic Chemistry
Corporate Authors	Rockwell International, Canoga Park, CA.; Army Research Office, Research Triangle Park, NC.
Document Type	Journal Article
NTIS Issue Number	199607
Contract Number	DAAL03-91-C-0025