F NMR Line Assignments

Bureau et al. [70] proposed a semi-empirical superposition model the is consid- 

SisoiC(,Ff, = —127.1 — S cTi with cti = exp -afd - iio)] do is taken as equal to the F-M distance in the related basic fluoride (MFn) yi,o determines the order of magnitude of the cationic paramagnetic contribution to the shielding and was deduced from measurements in the related basic fluoride. ai describes the behaviour of the paramagnetic contribution with the F-M distance. This model was satisfactorily tested on fluorides of increasing complexity [70]. 

Ab initio calculations of have also been carried out, using gauge-independent 

One way to overcome the limitation of the cluster method is to take into account the crystal periodicity in the chemical shift computation through the use of software that includes the periodic boundary conditions [122]. 

For p-BaAlFs and Ba3Al2Fi2, line assignments obtained from F DQ-SQ MAS correlation experiments [57] question those established from these calculations [1]. This 

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