| 摘要: | 本論文利用高溫高壓水熱法在550℃、1400bar的狀態下，合成出三個鈾矽酸鹽化合物Na3K3[(UO2)3(Si2O7)2]·2H2O (A1)、Na3Rb3[(UO2)3(Si2O7)2](A2)和Na6Rb4[(UO2)4Si12O33] (B1)。藉由單晶X光繞射方法鑑定出化合物的晶體結構，並以粉末X光繞射分析儀確定樣品純度供後續分析，再以全反射式X光螢光光譜儀、光致發光光譜、熱重分析及固態核磁共振儀等儀器進行定性與定量分析。
A1與A2為純六價鈾矽酸鹽的等結構化合物，結構中的矽酸鹽形成一個[Si2O7]的Sorosilicate並且和UO6利用共角的方式形成二維層狀結構，Na+坐落在層內的八員環孔道，夾層間填入K+、H2O和Rb+，可依據valence-matching principle 來解釋A2在夾層中缺少的水分子。並將A1與文獻中結構相似的五六混價鈾矽酸鹽[Na9F2][(UVO2)(UVIO2)2(Si2O7)2]做討論。
B1為一新穎的六價鈾矽酸鹽，結構中矽氧四面體以共角方式連接形成一含有八員環孔道的unbrached dreire fourfold chain，其結構分子式可表示成{uB,41}[3Si12O33]，並與UO6利用共角的方式形成三維骨架結構。依據SiO4的配位環境分類，B1同時包含三種矽氧配位環境Q2、Q3及Q4。
;Three new uranyl silicates, Na3K3[(UO2)3(Si2O7)2]·2H2O (A1), Na3Rb3[(UO2)3(Si2O7)2] (A2), and Na6Rb4[(UO2)4Si12O33] (B1), have been synthesized by high-temperature, high-pressure hydrothermal reactions at 550 oC and 1440 bar. The crystal structures were determined by single-crystal X-ray diffraction. The purity of each compound was confirmed by powder X-ray diffraction. These compounds were further characterized by TXRF, PL, TGA and solid state NMR spectroscopy.
A1 and A2 are isostructural and contain layers of uranyl disilicate.The smaller cation, Na+, is located in the intralayer channels, whereas the larger cations, K+ and Rb+, and water molecule are located in the interlayer region.The absence of lattice water in A2 can be understood according to the valence-matching principle. The structure is related to that of a previously reported mixed-valence uranium(V,VI) silicate,[Na9F2][(UVO2)(UVIO2)2(Si2O7)2].
B1 adopts a three-dimensional framework structure and contains a unique unbrancheddreier fourfold chain with the structural formula {uB,41}[3Si12O33]. The measurement results from 29Si MAS NMR are consistent with the presence of Q2, Q3, and Q4 Si in the structure. |
