19F-NMR solid state investigations of monovalent alkali metal fluorides and tetra-alkylammonium fluorides
19F-NMR solid state investigations of monovalent alkali metal fluorides and tetra-alkylammonium fluorides
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DOI：
10.1016/s0022-1139(02)00062-3
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发表时间：
2002-06-28
影响因子：
1.9
通讯作者：
Kemnitz, E
中科院分区：
文献类型：
--
作者：
Gross, U;Rüdiger, S;Kemnitz, E
在严格无水条件下测量碱金属氟化物和单价四烷基铵氟化物的F-19-NMR化学位移。为了减少宽共振信号的线宽，使用了32 kHz旋转频率的传统和超快MAS以及CRAMPS（组合旋转和多脉冲光谱）技术。用MAS平均了氟原子间的强均质偶极相互作用，给出了（CH_3）（4）N+ F ~-谱线宽度与样品旋转频率的关系。所得数据与CRAMPS结果进行了比较。在屏蔽的立方碱金属氟化物中的列从LiF到CsF的氟核的广泛分布的阳离子-阴离子极化效应方面进行了讨论，创建一个部分共价键。实验化学位移值与Allred-Rochow电负性和碱金属氟化物晶体中离子的极化率相关。两者的线性拟合给出了优于0.96的R值。从后者，外推在-293 ppm的“游离F-离子”的化学位移，称为CCl 3F。(C)2002 Elsevier Science B. V.保留所有权利。
The F-19-NMR chemical shifts of the alkali metal fluorides and of monovalent tetra-alkylammonium fluorides were measured under strictly anhydrous conditions. For reducing the line widths of the broad resonance signals, conventional and ultrafast MAS at 32 kHz rotational frequency as well as CRAMPS (combined rotation and multiple-pulse spectroscopy) techniques were used. Averaging the strong homonuclear dipolar interactions of fluorine by MAS, the dependence of line width on the frequency of sample rotation is given for (CH3)(4)N+ F-. The data obtained are compared with CRAMPS results. The broad distribution in shielding of the fluorine nucleus in the cubic alkali fluorides in the column from LiF to CsF is discussed in terms of cation-anion polarization effects, creating a partial covalent bond. The experimental chemical shift values were correlated with the Allred-Rochow electronegativities and with the polarizabilities of ions in the alkali fluoride crystals. The linear fit of both gave R-values better than 0.96. From the latter, a chemical shift of the "free F-ion" at -293 ppm, referred to CCl3F, was extrapolated. (C) 2002 Elsevier Science B.V. All rights reserved.