Measurement of heteronuclear bond distances in polycrystalline solids by solid-state NMR techniques
Measurement of heteronuclear bond distances in polycrystalline solids by solid-state NMR techniques
复制标题
通过固态核磁共振技术测量多晶固体中的异核键距
DOI：
10.1021/ja00248a006
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发表时间：
1987
影响因子：
15
通讯作者：
R. Griffin
中科院分区：
文献类型：
--
作者：
James E. Roberts;G. Harbison;M. Munowitz;J. Herzfeld;R. Griffin
高分辨率偶极/化学位移NMR实验固体的严格审查和用于测量15 N-* H键的距离在一系列的化合物，其中许多也已研究了中子衍射。结果表明，当仔细记录时，注意所描述的实验步骤，二维偶极/化学位移谱可以产生精确到0.005 μ m以内的键距，偶极和化学位移张量的相互取向精确到3 μ m以内。将NMR距离与中子衍射实验的类似数据进行比较，结果显示NMR距离均匀地长约0.035 μ m，这一结果与15 N-'H偶极相互作用的振动平均一致。总的来说，这里描述的实验数据和程序首次证明，高分辨率偶极/化学位移NMR实验是一种可行的方法，用于定位质子在多晶或非晶固体。在此之前，只有单晶中子衍射技术才有可能进行这样的测定。在几乎所有为自旋f 2系统设计的固态NMR实验中，原子核产生的磁偶极场都占有重要地位，它们既为高分辨率光谱学带来了障碍，也带来了机会。一方面，由于样品中存在相对较强的各向异性磁场而导致的共振频率的扩展不可避免地扩大了，有时甚至模糊了样品中所有原子核的响应;另一方面，在存在这种局部场的情况下获得的光谱富含分子结构的细节，
High resolution dipolar/chemical shift NMR experiments for solids are critically reviewed and used to measure l5N-* H bond distances in a series of compounds, many of which have also been studied by neutron diffraction. The results demonstrate that when recorded carefully, with attention paid to the experimental procedures described, two-dimensional dipolar/chemical shift spectra can yield bond distances accurate to within 0.005 Á and mutual orientations of dipolar and chemical shift tensors accurateto within 3. A comparison of the NMR distances with similar data from neutron diffraction experiments shows the NMR distances to be uniformly~ 0.035 Á longer, a result that is consistent with some vibrational averaging of the 15N-'H dipolar interaction. Collectively, the experimental data and procedures described here demonstrate for the first time that high resolution dipolar/chemical shift NMR experiments are a viable method for locating protons in polycrystalline or amorphous solids. Previously, such determinations have been possible only with single crystal neutron diffraction techniques.Magnetic dipolar fields produced by nuclei figure prominently in almost all solid-state NMR experiments designed for spin f 2 systems, where they create both obstacles and opportunities for high-resolution spectroscopy. On the one hand, the spread of resonant frequencies that results from theexistence of relatively strong anisotropic magnetic fields in the sample inevitably broadens, and sometimes obscures, the response of all the nuclei within; on the other hand, a spectrum obtained in the presence of such a local field is rich with details of molecular structure,