Nuclear magnetic resonance studies of the difluoride ion. Part 2.—Difluorides of the alkali metals and alkaline earths

The 1H and 19F magnetic resonance spectra of the difluoride salts of the alkali metals, of thallium and the double fluorides of strontium and barium have been examined by pulsed methods, and the free induction decays compared with those calculated for a 3-spin, dipole–dipole broadened system. In the case of the sodium, potassium, rubidium and caesium salts, the best fit between theory and experiment is obtained for a centred difluoride ion (to within ±0.04 A in most cases) although the technique does not distinguish between a single potential energy minimum and a symmetric double one with fast transfer, except that in the latter case the two minima must be <0.18 A apart. In the case of the lithium and thallium salts and the strontium and barium double fluorides, an accurate configuration cannot be assigned, except that any displacement of the proton from centring is unlikely to exceed 0.06 A.