Electron Diffraction Study of Rhenium Fluorides. I. Heavy-Atom Corrections and Structure of ReF6

Abstract

To date, no theoretical models for electron molecular scattering have been developed which bring calculated scattered intensities from heavy atoms into satisfactory agreement with experiment. Preparatory to an electron diffraction study of ReF₇, a molecule with an uncertain and possibly complex structure, an investigation of ReF₆ was undertaken. The simplicity of the hexafluoride's geometry ($O_h$ symmetry) allows an empirical characterization of the discrepancy between experimental and calculated intensities, a discrepancy which can be attributed chiefly to the behavior of ReF interference terms rather than to uncertainties in structural parameters. After a structure analysis of ReF₆, the observed difference signal ${\mathrm{(I}}^{\mathrm{obs}}{\mathrm{\hspace{0.17em}-\hspace{0.17em}I}}^{\mathrm{calc}})$ was used with appropriate scaling to modify ReF₇ intensities before structural parameters for the heptafluoride were refined. Parameters determined for ReF₆, e.g., $r_g(\mathrm{ReF}\text{)\hspace{0.17em}=\hspace{0.17em}1.832\hspace{0.17em}±\hspace{0.17em}0.004 Å}$ and $l_g(\mathrm{ReF}\text{)\hspace{0.17em}=\hspace{0.17em}0.044 Å}$ , are in excellent agreement with those reported from diffraction studies of other $\text{5d}$ transition‐metal hexafluorides. Results for ReF₇ are reported in Paper II.