Doerr Markus, Marian Christel M
Institut für Theoretische Chemie und Computerchemie, Heinrich-Heine-Universität Düsseldorf, Universitätsstr. 1, 40225 Düsseldorf, Germany.
Solid State Nucl Magn Reson. 2006 Jul;30(1):16-28. doi: 10.1016/j.ssnmr.2005.12.003. Epub 2006 Jan 26.
Nuclear magnetic resonance (NMR) chemical shifts in solids may be calculated by ab initio methods approximating the solid state by molecular clusters. We employed this technique to obtain estimates of (15)N chemical shifts in NB(2)Si and NBSi(2) environments in the solid state. Such nitrogen environments are found in amorphous (Si/B/N-)ceramics which exhibit very interesting features such as high thermal and mechanical stability. We based our calculations on cutouts of hypothetical Si(3)B(3)N(7) crystals suggested by Kroll and Hoffmann [Silicon boron nitrides: hypothetical polymorphs of Si(3)B(3)N(7), Angew. Chem. Int. Ed. 37 (1998) 2527]. Taking the systematic errors of our calculations into account we expect the chemical shifts in NBSi(2) environments around -293+/-5ppm. Chemical shifts in NB(2)Si environments are expected at -272+/-6ppm. The range of the calculated chemical shifts in NBSi(2) environments coincides with experimental chemical shifts in molecular compounds. Experimental chemical shifts of NB(2)Si nitrogen in molecules appear at lower field than our calculated chemical shifts in the solid state.
固体中的核磁共振（NMR）化学位移可通过从头算方法来计算，该方法通过分子簇来近似固态。我们采用此技术来获得固态下NB₂Si和NBSi₂环境中¹⁵N化学位移的估计值。在非晶态（Si/B/N -）陶瓷中发现了此类氮环境，这些陶瓷具有非常有趣的特性，如高热稳定性和机械稳定性。我们的计算基于Kroll和Hoffmann提出的假设Si₃B₃N₇晶体的片段[氮化硅硼：Si₃B₃N₇的假设多晶型物，《德国应用化学》国际版37 (1998) 2527]。考虑到我们计算的系统误差，我们预计NBSi₂环境中的化学位移约为 - 293±5 ppm。预计NB₂Si环境中的化学位移为 - 272±6 ppm。NBSi₂环境中计算出的化学位移范围与分子化合物中的实验化学位移一致。分子中NB₂Si氮的实验化学位移出现在比我们计算的固态化学位移更低的场强处。
