High temperature Raman spectroscopy is used for the first time for establishing the structural and vibrational properties of VV complexes in V2O5- Cs2S2O7 (0≤ XV2O5 0≤ 0.24) and V2O5- Cs2S2O7- Cs2SO4 (0≤ XV2O5 0≤ 0.25) molten salt mixtures at 450°C under static equilibrium conditions. Based on Raman band intensity correlations and band assignments it is found that the VV complex present in V2O5- Cs2S2O7 molten mixtures has a dimeric (VO)2O(SO4)4 4-configuration containing a V-O-V bridge. Addition of Cs2SO4 in V2O5- Cs2S2O7 mixtures results in the reaction of the VV dimer with sulfate ions and the spectral data obtained are accounted for by the following reaction scheme: (VO)2O(SO4)4 4-+2SO4 2-→ 2VO2(SO4)2 3-+ S2O7 2-. The results are of value for the progress on the mechanistic understanding of the SO2 oxidation at the molecular level.