The V V and V IV oxosulfato complexes formed in V 2 O 5 -M 2 S 2 O 7 -M 2 SO 4 (M ) K, Cs) melts under SO 2 (g) or O 2 (g) atmosphere have been studied by electronic absorption (VIS/NIR) and Raman spectroscopy at 450 °C. VIS/NIR spectra have been obtained at 450 °C for V 2 O 5 -K 2 S 2 O 7 molten mixtures in SO 2 atmosphere (P SO 2 ) 0-1.2 atm). The data are in agreement with the V V T V IV equilibrium: (VO) 2 O(SO 4 ) 4 4-(l) + SO 2 (g) T 2VO(SO 4 ) 2 2-(l) + SO 3 (g). SO 2 does not coordinate to the V V complex but starts significantly to coordinate to V IV for P SO 2 > 0.4 atm according to VO(SO 4 ) 2 2-(l) + SO 2 (g) T VO(SO 4 ) 2 SO 2 2-(l). The Raman spectral features and the exploitation of the relative Raman intensities indicate that the (VO) 2 O(SO 4 ) 4 4dimeric complex unit, possessing a V-O-V bridge, is formed in the V 2 O 5 -M 2 S 2 O 7 binary mixtures. The spectral changes occurring upon interaction of the binary V 2 O 5 -K 2 S 2 O 7 mixtures with SO 2 or addition of M 2 SO 4 to the binary V 2 O 5 -M 2 S 2 O 7 mixtures indicate a cleavage of the V-O-V bridge and formation of the V IV O(SO 4 ) 2 2or V V O 2 (SO 4 ) 2 3monomeric complex units, respectively. The most characteristic bands due to the various complexes in the melts have been assigned. The spectral data are discussed in terms of possible structures. For the first time, high-temperature vibrational spectroscopy has been used to study the structural and vibrational properties of V 2 O 5 -K 2 S 2 O 7 and V 2 O 5 -K 2 S 2 O 7 -K 2 SO 4 melts. The results are valuable for the mechanistic understanding of SO 2 oxidation at the molecular level.

Glassy, supercooled, and molten ZnCl2 and ZnBr2 have been studied by Raman spectroscopy over the broad temperature range −196 to 800 °C in an effort to follow in detail the structural changes caused by temperature variation. A systematic study has also been undertaken for the corresponding crystalline polymorphs showing that each material exists in only one crystalline phase if water traces are not present. The reduced isotropic and anisotropic Raman spectra of the ZnCl2 and ZnBr2 glasses and melts are isomorphous. Unusually drastic changes of the relative intensities of particular bands occur with temperature in the reduced isotropic spectra. A comparison between the spectral features of crystals, glasses, and melts has revealed that the network structure of the glasses and melts consists of ZnX4/2 (X=Br,Cl) tetrahedra bound to each other by apex- and edge-bridged halides. The substructure of the glass/melt is formed by mixing a variety of tetrahedra participating in “open,” “cluster,” and “chain” networks which are bound to each other by bridged halides. The boundaries of the substructure involve neutral or charged terminal halide bonds with zinc of an average threefold coordination. Temperature rise breaks up the substructure to smaller fragments, increases the number of terminal bonds, and rearranges the apex- and edge-bridging networks. The good glass-forming ability of the ZnX2 melts is attributed to the existence and mixing of the three topologically different networks within the substructure. Our data of ZnCl2 are in qualitative agreement with molecular dynamics simulations as regards the frequency distribution of vibrational modes. However, simulations are not able to correctly predict polarization properties in the glass and the melt. The low-frequency Raman spectra reveal the presence of the Boson peak in both glasses, which interestingly persists, well resolved, also into the normal liquid state above the melting point. The spectra in the region of the Boson peak are also discussed in the framework of relevant theoretical models and empirical correlations.

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