Spectral assignments and NMR parameter-structure relationships in borates using high-resolution 11B NMR and density functional theory.
Spectral assignments and NMR parameter-structure relationships in borates using high-resolution 11B NMR and density functional theory.
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DOI：
10.1039/c3cp50772f
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发表时间：
2013-05
期刊：
影响因子：
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通讯作者：
O. Alderman;D. Iuga;A. Howes;K. J. Pike;D. Holland;R. Dupree
中科院分区：
文献类型：
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作者：
O. Alderman;D. Iuga;A. Howes;K. J. Pike;D. Holland;R. Dupree
采用双旋转、多量子魔角旋转和同位素稀释技术，在强磁场下获得了一系列多晶硼酸盐的高分辨固体（11）B NMR谱。在同位素稀释的样品中，DOR线宽可以小于0.2 ppm，从而可以获得各向同性化学位移、δiso和电场梯度的高度精确值。实验值被用来作为测试的密度泛函计算使用投影仪增强波的CASTEP和WIEN 2k。用CASTEP方法计算的δiso值与实验值符合得很好。偏差0.40 ppm。WIEN 2k计算的电场梯度大小CQ和不对称性η也与实验非常一致，r.m.s.偏差分别为0.038MHz和0.042。然而，尽管CASTEP给出了η（0.043）的类似偏差，但它高估了CQ约15%。将计算的电场梯度按0.842缩放后，CQ的偏差实际上与WIEN 2k计算的偏差相同。从实验和计算结果得出的光谱归属允许识别δiso和（a）对于三配位和四配位硼的平均B-O-B键角θ[结合上划线]之间的相关性，给出δiso（B（III））=（185.1 -θ[合并划线]）/3.42 ppm和δiso（B（IV））=（130.2 -θ[合并划线]）/5.31 ppm;（B）环位T（3）单位三角平面角偏差Stri，δiso（T（3）（ring））=（1.642 × 10（-2）-Stri）/（8.339 × 10（-4））ppm。
High-resolution, solid-state (11)B NMR spectra have been obtained at high magnetic fields for a range of polycrystalline borates using double-rotation (DOR), multiple-quantum magic angle spinning and isotopic dilution. DOR linewidths can be less than 0.2 ppm in isotopically diluted samples, allowing highly accurate values for the isotropic chemical shift, δiso, and electric field gradient to be obtained. The experimental values are used as a test of density functional calculations using both projector augmented wave based CASTEP and WIEN2k. The CASTEP calculations of δiso are generally in very good agreement with experiment, having r.m.s. deviation 0.40 ppm. WIEN2k calculations of electric field gradient magnitude, CQ, and asymmetry, η, are also in excellent agreement with experiment, with r.m.s. deviations 0.038 MHz and 0.042 respectively. However, whilst CASTEP gives a similar deviation for η (0.043) it overestimates CQ by ∼15%. After scaling of the calculated electric field gradient by 0.842 the deviation in CQ is practically identical to that of the WIEN2k calculations. The spectral assignments that follow from the experimental and computational results allow identification of correlations between δiso and (a) the average B-O-B bond angle, θ[combining overline], for both three and four coordinated boron, giving δiso(B(III)) = (185.1 -θ[combining overline])/3.42 ppm and δiso(B(IV)) = (130.2 -θ[combining overline])/5.31 ppm; and (b) the ring-site T(3) unit trigonal planar angular deviation, Stri, giving δiso(T(3)(ring)) = (1.642 × 10(-2)-Stri)/(8.339 × 10(-4)) ppm.