Characterizing slight structural disorder in solids by combined solid-state NMR and first principles calculations.
Characterizing slight structural disorder in solids by combined solid-state NMR and first principles calculations.
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DOI：
10.1021/jp810138y
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发表时间：
2009-02
期刊：
影响因子：
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通讯作者：
Sylvian Cadars;A. Lesage;C. Pickard;P. Sautet;L. Emsley
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文献类型：
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作者：
Sylvian Cadars;A. Lesage;C. Pickard;P. Sautet;L. Emsley
提出了一种结合高分辨率二维核磁共振（NMR）和第一性原理计算的局部无序结构解释的一般方法。我们发现，小的化学位移变化的顺序ppm可以解释在详细的结构方面与先进的密度泛函理论方法。专注于一个模型系统的bisphosphinoamine，我们证明了小振幅的障碍的存在和空间范围可以探测使用定量统计分析的二维NMR线的形状通过空间相关实验收集使用可变的混合时间。我们展示了如何从第一原理计算的低能量振动模式可以方便地使用，而不是作为一个原因的混乱，而是，产生一个基本的物理上合理的本地扭曲来描述候选人的静态分布的本地几何形状。计算的（31）P NMR各向同性化学位移，然后第一次用于模拟与这些扭曲，这允许他们的评价作为一个潜在的来源的障碍，通过比较实验的2D交叉峰之间的磷网站的二维相关线形。这种新型的结构约束允许识别键合几何形状的变化，最有可能有助于局部结构紊乱。因此，我们确定至少一种类型的结构变形，这是兼容的实验2D NMR数据，也是在数量级的“热椭球”与原子位置的X射线衍射结构的不确定性。
A general approach for structural interpretation of local disorder in partially ordered solids is proposed, combining high-resolution two-dimensional (2D) nuclear magnetic resonance (NMR) and first principles calculations. We show that small chemical shift variations of the order of a ppm can be interpreted in detailed structural terms with advanced density functional theory methods. Focusing on a model system of bisphosphinoamine, we demonstrate that the existence and the spatial range of small amplitude disorder can be probed using quantitative statistical analyses of 2D NMR line shapes obtained from through-space correlation experiments collected using variable mixing times. We show how low-energy vibration modes calculated from first principles can be conveniently used not as a cause of disorder but, instead, to generate a basis set of physically plausible local distortions to describe candidate static distributions of local geometries. Calculations of (31)P NMR isotropic chemical shifts are then used for the first time to simulate 2D correlation lineshapes associated with these distortions, which permit their evaluation as a potential source of disorder by comparison to experimental 2D cross-peaks between phosphorus sites. This new type of structural constraints allows the identification of changes in the bonding geometry that most likely contribute to the local structural disorder. We thus identify at least one type of structural deformation that is compatible with the experimental 2D NMR data and is also within the order of magnitude of the "thermal ellipsoids" associated with the uncertainties on the atomic positions of the X-ray diffraction structure.