Matrix-isolated Al2OF62- ion in molten and solid LiF/NaF/KF

A Raman spectrum consistent with that expected from an Al2OF62- ion was obs erved when Na2O was dissolved in a eutectic LiF/NaF/KF (FLINAK) melt at 500 degreesC, which contained a low concentration of either AlF3 or Na3AlF6. F urthermore, it was possible to trap the Al2OF62- ion in the frozen solid an d to measure its Raman and IR spectra at 25 degreesC. A number of bands hav e been detected; among those, the two most characteristic bands of the Al2O F62- ion at 494 (polarized) and 265 cm(-1) in the FLINAK melt at 500 degree sC, and those at 509 and 268 (Raman) and similar to 780 to similar to 900 ( IR) cm(-1) for the compound matrix isolated in solid FLINAK at 25 degreesC. In the absence of added oxide, the dissolved aluminum fluoride was in the form of the octahedral AlF63- ion, which has characteristic Raman bands at 542 and 325 cm(-1) in the FLINAK melt at 500 degreesC. Whereas alumina, Al2 O3, was found to be essentially insoluble in FLINAK melts, it was possible to dissolve sufficient amounts: of Na2O to convert most of the AlF63- to th e oxyfluoroaluminate, Al2OF62-. These solutions appeared to be metastable w ith respect to formation of insoluble alumina at higher temperatures. The p resent results can be compared to previous measurements on alumina dissolve d in pure molten cryolite at much higher temperatures, where alumina solubi lity is low and broad bands due to oxide species ate difficult to detect du e to overlap with bands from AlF63- and AlF4-.