An empirical model to calculate 19F isotropic chemical shifts in alkali-hexafluoroaluminates

As magic angle spinning solid-state NMR (MAS NMR) has become a powerful method in solid-state sciences, also models for the prediction of chemical shift values have become important topics in recent research. present study, an empirical model to describe the cationic contribution to the 19F isotropic chemical shift values in hexafluoroaluminates with isolated AlF6-octahedra is presented. Using the corresponding alkali cryolites MI3AlF6 (MI = Li-Cs) as the basis of the calculation, this model is able to provide mean δiso-values for the whole series of Al-elpasolites used here in order to test the model. The achieved results are compared to experimentally derived values and values calculated using the superposition model developed by Bureau et al. [B. Bureau, G. Silly, J.Y. Buzaré, J. Emery, Chem. Phys. 249 (1999) 89–104] to demonstrate the quality of this new approach. It is shown that a proper choice of the calculation basis leads to values very close to the experiment. s model can be extended to other systems with isolated AlF6-octahedra, it can be regarded as an additional possibility to the methods used so far.