In Situ X-ray Diffraction Study of Cesium Exchange in Synthetic Umbite

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• 作者：Christopher S. Fewox ; Abraham Clearfield ; Aaron J. Celestian
• 刊名：Inorganic Chemistry
• 出版年：2011
• 出版时间：April 18, 2011
• 年：2011
• 卷：50
• 期：8
• 页码：3596-3604
• 全文大小：1069K
• 年卷期：v.50,no.8(April 18, 2011)
• ISSN：1520-510X

文摘

The exchange of Cs⁺ into Hb>1.22b>Kb>0.84b>ZrSib>3b>Ob>9b>路2.16Hb>2b>O (umbite-(HK)) was followed in situ using time-resolved X-ray diffraction at the National Synchrotron Light Source. The umbite framework (space group P2b>1b>/c with cell dimensions of a = 7.2814(3) 脜, b = 10.4201(4) 脜, c = 13.4529(7) 脜, and 尾 = 90.53(1)掳) consists of wollastonite-like silicate chains linked by isolated zirconia octahedra. Within umbite-(HK) there are two unique ion exchange sites in the tunnels running parallel to the a-axis. Exchange Site 1 is marked by 8 member-ring (MR) windows in the bc-plane and contains K⁺ cations. Exchange Site 2 is marked by a larger 8-MR channel parallel to [100], and contains Hb>2b>O molecules. The occupancy of the Cs⁺ cations through these channels was modeled by Rietveld structure refinements of the diffraction data and demonstrated that there is a two-step exchange process. The incoming Cs⁺ ions populated the larger 8-MR channel (Exchange Site 2) first and then migrated into the smaller 8-MR channel. During the exchange process a structural change occurs, transforming the exchanger from monoclinic P2b>1b>/c to orthorhombic P2b>1b>2b>1b>2b>1b>. This structural change occurs when Cs⁺ occupancy in the small cavity becomes greater than 0.50. The final in situ ion exchange diffraction pattern was refined to yield umbite-(CsK) with the molecular formula Hb>0.18b>Kb>0.45b>Csb>1.37b>ZrSib>3b>Ob>9b>路0.98Hb>2b>O and possessing an orthorhombic unit cell with dimensions a = 10.6668(8) 脜, b = 13.5821(11) 脜, c = 7.3946(6) 脜. Solid state ¹³³Cs MAS NMR showed there is only a slight difference between the two cavities electronically. Valence bond sums for the completely occupied Exchange Site 1 demonstrate that Cs鈭扥 bonds of up to 3.8 脜 contribute to the coordination of the Cs⁺ cation.