A fluorine magnetic resonance study of the solid addition compounds SF4•AsF5 and IF7•AsF5

Abstract

A broad-line fluorine magnetic resonance study of the solid addition compounds SF4•AsF5 and IF7•AsF5 shows that each has two types of chemically distinct fluorine in the ratios of 1:2 and 1:1, respectively. The fine structure and the second moments of the spectra are consistent with the ionic formulations SF3+AsF6− and IF6+AsF6−. Bond lengths in the iodine compound are discussed in relation to the observed second moment at liquid-nitrogen temperature and the calculated rigid-lattice second moment based on the detailed sodium-chloride-type crystal structure of Beaton. The chemical shifts of the fluorines in the three ionic species are measured relative to trifluoracetic acid and to HF. Reorientations of the ions in the solid state are discussed on the basis of the change in second moment with temperature for each compound. A very rough estimate of the anisotropy of chemical shift in IF6+AsF6− is made from the slope of the second moment vs. field-squared line at liquid-nitrogen temperature.