Gervais Christel, Bonhomme-Coury Laure, Mauri Francesco, Babonneau Florence, Bonhomme Christian
Laboratoire de Chimie de la Matière Condensée de Paris, UMR CNRS 7574, Université Pierre et Marie Curie, Collège de France, Paris, France.
Phys Chem Chem Phys. 2009 Aug 28;11(32):6953-61. doi: 10.1039/b907450c. Epub 2009 Jun 26.
Octameric silsesquioxanes (RSiO(1.5))(8) are versatile and interesting nano building blocks, suitable for the synthesis of nanocomposites with controlled porosity. In this paper, we revisit the (29)Si and (13)C solid state NMR spectroscopy for this class of materials, by using GIPAW (gauge including projected augmented wave) first principles calculations [Pickard & Mauri, Phys. Rev. B, 2001, 63, 245101]. Full tensorial data, including the chemical shift anisotropies (CSA) and the absolute orientation of the corresponding principal axes systems (PAS), were calculated. Subsequent averaging of the calculated tensors (due to fast reorientation of the R groups around the Si-C bonds) allowed for the interpretation of the strong reduction of CSA and dipolar couplings for these derivatives. Good agreement was observed between the averaged calculated data and the experimental parameters. Interesting questions related to the interplay between X-ray crystallography and solid state NMR are raised and will be emphasized.
八聚倍半硅氧烷（RSiO(1.5)）(8) 是用途广泛且有趣的纳米结构单元，适用于合成具有可控孔隙率的纳米复合材料。在本文中，我们通过使用GIPAW（含投影增强波的规范）第一性原理计算 [皮卡德和毛里，《物理评论B》，2001年，63卷，245101页]，重新审视了这类材料的（29）Si和（13）C固态核磁共振光谱。计算了完整的张量数据，包括化学位移各向异性（CSA）以及相应主轴系统（PAS）的绝对取向。随后对计算出的张量进行平均（由于R基团围绕Si-C键的快速重排），从而能够解释这些衍生物的CSA和偶极耦合的显著降低。计算出的平均数据与实验参数之间观察到了良好的一致性。提出并将着重强调与X射线晶体学和固态核磁共振之间相互作用相关的有趣问题。
