19F/29Si distance determinations in fluoride-containing octadecasil from solid-state NMR measurements
19F/29Si distance determinations in fluoride-containing octadecasil from solid-state NMR measurements
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DOI：
10.1021/ja9701873
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发表时间：
1997-12-17
影响因子：
15
通讯作者：
Grondey, H
中科院分区：
文献类型：
--
作者：
Fyfe, CA;Lewis, AR;Grondey, H
在目前的工作中，我们报告的结果CP，REDOR和TEDOR NMR实验进行定位的三维框架内的硅酸盐十八烷基的氟阴离子。通过测量这些实验中的F-19/Si-29偶极耦合，获得了精确的Si-F距离。D4 R单元中硅的REDOR和TEDOR数据的加权非线性最小二乘拟合给出D = 1150 +/-50 Hz的平均值，由此计算出Si-F原子间距离为2.69 +/-0.04埃。该距离与X射线测定的单晶结构中报道的2.63埃的值非常一致，并证实F-阴离子位于D4 R单元内。当考虑到在这些T-2位点中围绕Si核的多个当量氟阴离子的特定几何（四面体）排列时，对于不在D4 R中的硅的REDOR和TEDOR数据的计算和拟合给出= 120 +/- 20 Hz。与从衍射测量获得的值5.69埃相比，这产生5.7 +/-0.4埃的Si-F距离。在不同的情况下进行的最佳实验的选择和实验变量的结果的依赖性的影响因素进行了讨论。这些研究清楚地建立了F-19/Si-29 REDOR和TEDOR NMR实验的可行性和可靠性，以获得距离信息，该距离信息可用于确定含氟物质在这种骨架结构内的精确位置，或者在合适的情况下，在骨架结构本身未知的情况下，帮助确定骨架结构本身。
In the present work we report results from CP, REDOR, and TEDOR NMR experiments carried out to locate the fluoride anions within the three-dimensional framework of the silicate octadecasil. Accurate Si-F distances were obtained-through measurements of the F-19/Si-29 dipolar couplings from these experiments. Weighted, nonlinear least-squares fittings of the REDOR and TEDOR data for the silicons in the D4R units gave an average value of D = 1150 +/- 50 Hz from which the Si-F interatomic distance was calculated to be 2.69 +/- 0.04 Angstrom. This distance is in excellent agreement with the value of 2.63 Angstrom reported from the X-ray determined single crystal structure-and confirms that the F- anions are located inside the D4R units. Calculations and fittings of the REDOR and TEDOR data for the silicons not in the D4R gave = 120 +/- 20 Hz when the specific geometrical (tetrahedral) arrangement of the multiple equivalent fluoride anions surrounding the Si nuclei in these T-2 sites was taken into account. This yields a Si-F distance of 5.7 +/- 0.4 Angstrom, compared to the value 5.69 Angstrom obtained from the diffraction measurements. Factors influencing the selection of the optimum experiments to perform in different situations and the dependence of the results on experimental variables are discussed. These studies clearly establish the viability and reliability of F-19/Si-29 REDOR and TEDOR NMR experiments to obtain distance information which can be used to determine the precise location of fluorine-containing species within such framework structures or in suitable cases to assist in the determination of the framework structure itself where it is unknown.