Spectroscopic studies of inorganic fluoro-complexes. Part II. 19F nuclear magnetic resonance studies of tin(IV) fluoro-complexes

Abstract

Approximately 100 anions of the general type SnF_6–nX_n^2– have been characterised in solution by ¹⁹F n.m.r. spectroscopy, where X is one of a wide range of unidentate ligands or half a bidentate ligand. Complexes containing two different groups X, and mononegative anions containing a neutral ligand, have also been studied. cis/trans ratios have been obtained for many of the geometrical isomers. ¹⁹F chemical shifts and tin–fluorine and fluorine–fluorine coupling constants are reported. The ¹⁹F chemical shifts δ(relative to the SnF₆^2– ion) of a fluorine atom in these complexes are given, to a good approximation, by δ=pC+qT, where C and T are constants characteristic of the ligand X, and p and q are the number of substituents cis and trans to the fluorine atom respectively. It is suggested that the effect of ligands in cis-positions is largely due to intramolecular van der Waals interactions. Approximate equilibrium constants have been obtained for the displacement of fluoride ion from SnF₆^2– by chloride, bromide, and hydroxide ions, and by water.