Ab initio calculation and NMR spin-echo measurement of F-19 chemical shielding in the alkali-metal fluorides

Experimental values of F-19 chemical shielding in the series of anhydrous alkali-metal fluorides LiF to CsF are reported. An NMR spin-echo technique is used for the measurements and the results are shown to compare favourably with others, in particular those determined by magic-angle spinning (MAS) techniques, reported in the literature. Ab initio methods of calculating F-19 chemical shielding in these primarily ionic materials are then discussed in terms of simplified model systems. For all the alkalimetal fluorides, values of absolute F-19 chemical shielding are calculated which are significantly less than the free fluoride ion value. In the specific cases of LiF and NaF reasonable agreement between ab initio calculation and experiment is achieved.