Like the Co 2+ //F -//Na + //SO4 2-solutions, the UV-Vis spectral features of Cu 2+ //F -//Na + //SO4 2-solutions prepared by path 1 with aging time of 5 days in 600-900 nm are very close to those of diluting the CuF2 solutions with identical concentration, while those prepared by path 2 are very close to those of CuSO4 solutions. However, the absorption bands of path 1 and 2 samples in 270-320 nm are almost overlapped and are close to those of CuSO4 solutions (Fig. ). This seems to be difficult to conclude what happens in these solutions due to the complexation complexity of Cu 2+ , SO4 2-and F -. Nevertheless, the UV-Vis spectra for 0.01 and 0.02 mol•kg -1 Cu 2+ path 2 samples exhibit a significant difference between with aging time of 6 hours and 5 days (Figs. and). By monitoring the 0.02 mol•kg -1 Cu 2+ path 2 sample, we found that its UV-Vis spectrum continually develops with aging time increasing and achieves stability within 24 hours (inset of Fig. ). This implies that the addition of F -to CuSO4 solution indeed exhibit the generally recognized as structural hysteresis, representing the delay of interaction between Cu 2+ and F -. It should be noted that such spectral time evolution is not observed in the Co 2+ solutions above, indicative of different representations of interaction hysteresis of M 2+ and F -.