Molecular Structure of Iodine Heptafluoride

Abstract

Electron diffraction photographs taken in 1951 are here reanalyzed. All measurements and intensity estimates had been made visually; in the computations, allowance is made for the relative phase change of the scattering amplitudes between the iodine and fluorine atoms. Within a spread of 0.06 A, the I—F distances are approximately equal; the average value is 1.825±0.015 A. The molecular symmetry is almost D_5h, in agreement with spectroscopic and crystal structure results. However, the electron diffraction patterns clearly indicate that the five fluorine atoms in the girdle are not coplanar and possibly are not equally spaced from the central iodine. The disorder reported in the crystalline state and the unusually broad NMR spectra of the liquid are readily accounted for by a sequential puckering about the polar axis and the possible out‐of‐phase extension from the axis of the girdle atoms. Revised values for the thermodynamic functions of the ideal gas are included.