Signal assignment. In the solutions with lowest Zn(Cd)F2 concentration (0.001 mol•kg -1 ), a single peak at ~-120 ppm (A) could be observed. This signal has been assigned to the solvated fluoride ion . As the Zn(Cd)F2 concentration increases, the peak gradually shifts upfield, indicating that the 19 F nucleus is shielded. Water molecules make F -less shielded , resulting in a downfield shift. Therefore, the shielding effect of 19 F nucleus in current solutions comes from the interference of cations. As shown in Fig. , when the ZnSO4 is gradually added to the ZnF2 solutions and the ZnF2 concentration is kept at 0.005 and 0.05 mol•kg -1 , respectively, the chemical shifts (A) of F -gradually shift upfield. Analogous case is also observed when the ZnSO4 is replaced by Zn(ClO4)2 (Fig. ). It should be noted that the F -shielded by Zn(ClO4)2 is stronger than that by ZnSO4 (Figs. and). This is because of the strong interaction between SO4 2-and Zn 2+ , weakening the shielding effect of Zn 2+ for seems not to disturb the F -. This is perhaps not surprising because the interaction between Na + and F -is very weak and only a small quantity of predominantly 2SSIPs (solvent-separated/shared ion pairs (SIP) with double solvent layer existing in the space between the ion partners of the pair) is formed, even in the close saturated NaF solution at room temperature . Meanwhile, the increase of NaClO4 concentration decreases the average number of Zn 2+ around F -, making Na + exhibit a deshielding effect. This might be the reason why the chemical shifts (A) of F -gradually shift downfield when the NaClO4 concentration increases (Fig. ).