In summary, the above observations allow us to assign the signal in the range of -118 to -125 ppm to the shielding contribution of cations (Zn 2+ and H + ) in the outer shell of F -. The shift of the signal reflects the conversion of free solvated F -, SSIPs and 2SSIPs. The second signal at ~-130 ppm is assigned to the formation of Zn 2+ -F -CIPs. M 2+ -F -ion pairing in the solutions prepared by different paths. Based on the discussion above, the fraction distribution of Zn 2+ /Cd 2+ -F -CIPs in the solutions prepared by both paths as a function of salinity, as well as the Zn 2+ //F -//Na + //ClO4 - solutions with 0.04 mol•kg -1 ZnF2 prepared by paths 1 and 2 along with aging time is shown in Fig. (Tables and). It could be seen that the solvated F -predominates in both series of solutions (~98%), whereas the F -of less than 2% forms the CIPs. Even so, the content of CIPs exhibits a distinguishable difference in both series of solutions and this difference increases as the MF2 concentration increases. As shown in Fig. , the difference is up to 1% as the MF2 concentration is 0.18 mol•kg -1 . These results suggest that the formation of M 2+ -F -CIPs is concentration dependence, which is favored in relatively high fluoride molality environment. In relatively high or low concentration, i.e., ≤ 0.03 mol•kg -1 or ≥ 0.1 mol•kg -1 for Zn 2+ solutions (Figs. and) and ≤ 0.01 mol•kg -1 or ≥ 0.1 mol•kg -1 for Cd 2+ solutions (Fig. ), the NMR chemical signal is consistent of path 1 and path 2, which is only SIPs in relatively dilute solution, but SIPs and CIPs co-exist in another case. The discrepancy occurs in the middle-level concentration, i.e., between 0.03 and 0.1 mol•kg -1 for Zn 2+ solutions (Figs. 1, S1 and S2) and between 0.01 and 0.1 mol•kg -1 for Cd 2+ solutions (Fig. ).