Brooker M H, Berg R W, von Barner J H, Bjerrum N J
Department of Chemistry, Memorial University of Newfoundland, St. John's, Newfoundland, Canada A1B 3X7.
Inorg Chem. 2000;39(16):3682-9. doi: 10.1021/ic000260h.
Raman spectra have been obtained for matrix-isolated AlF6(3-) in an LiF/NaF/KF (FLINAK) eutectic mixture. Three Raman bands characteristic of the hexafluoroaluminate ion were identified in the solids formed from FLINAK melts which contained small amounts (5-11 mol%) of either AlF3 or Na3AlF6. The three allowed Raman-active bands of the matrix-isolated octahedral complex ion, nu 1(A1g), nu 2(Eg), and nu 5(F2g), were observed at 560.5, 380, and 325 cm-1, respectively, for the solid sample at 25 degrees C. Wavenumbers and relative intensities were similar to those of Na3AlF6 (cryolite), K3AlF6, and K2NaAlF6 (elpasolite) and other crystals known to contain discrete, octahedral AlF6(3-) ions. Peak positions, half-widths, and relative intensities for the bands were measured for samples at temperatures different from room temperature through the melting transition and into the molten state. The transition from high-temperature solid to molten salt at about 455 degrees C occurred gradually without perceptible change in the peak positions, half-widths, or relative intensities. For a sample in molten FLINAK at 455 degrees C, the nu 1(A1g), nu 2(Eg), and nu 5(F2g) modes of the AlF6(3-) ion were observed at 542, 365, and 324 cm-1, respectively. Raman depolarization experiments were consistent with these assignments, and the low value of the depolarization ratio of the nu 1(A1g) mode at 542 cm-1 indicated that the sample was molten above 455 degrees C. Differential thermal analysis also indicated that the FLINAK samples melted at about 455 degrees C. Raman measurements were performed for samples at temperatures from 25 to 600 degrees C in a silver dish, on a hot stage, in an argon-filled atmosphere, under a microscope. Additional Raman experiments were performed on samples at temperatures from 25 to 750 degrees C in a conventional graphite windowless cell, in an argon-filled quartz tube, in a standard furnace. Over the concentration range 4.8-11 mol% AlF3 (CR 23-8.0) in FLINAK, only bands due to the AlF6(3-) ion were detected. There was no evidence to support the presence of other aluminum complexes in these melts.
已获得在LiF/NaF/KF（FLINAK）共晶混合物中基质隔离的AlF6(3-)的拉曼光谱。在由含有少量（5-11摩尔%）AlF3或Na3AlF6的FLINAK熔体形成的固体中，鉴定出了六氟铝酸根离子的三个特征拉曼谱带。对于25℃的固体样品，基质隔离的八面体络合离子的三个允许的拉曼活性谱带，即ν1(A1g)、ν2(Eg)和ν5(F2g)，分别在560.5、380和325 cm-1处观察到。波数和相对强度与Na3AlF6（冰晶石）、K3AlF6和K2NaAlF6（钾冰晶石）以及其他已知含有离散八面体AlF6(3-)离子的晶体相似。通过熔化转变直至熔融状态，在不同于室温的温度下对样品测量了谱带的峰位置、半高宽和相对强度。在约455℃时从高温固体到熔盐的转变逐渐发生，峰位置、半高宽或相对强度没有明显变化。对于455℃下FLINAK熔体中的样品，AlF6(3-)离子的ν1(A1g)、ν2(Eg)和ν5(F2g)模式分别在542、365和324 cm-1处观察到。拉曼去偏振实验与这些归属一致，并且在542 cm-1处ν1(A1g)模式的去偏振比的低值表明样品在455℃以上是熔融的。差示热分析也表明FLINAK样品在约455℃熔化。在银盘中、热台上、充氩气氛下、显微镜下对25至600℃温度范围内的样品进行了拉曼测量。在传统的无石墨窗池中、充氩石英管中、标准炉中对25至750℃温度范围内的样品进行了额外的拉曼实验。在FLINAK中AlF3浓度范围为4.8-11摩尔%（CR 23-8.0）时，仅检测到归因于AlF6(3-)离子的谱带。没有证据支持这些熔体中存在其他铝络合物。
