• 主题
高级搜索  >
历史搜索 清空历史
首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Structure, bonding, and energetic properties of nitrile-borane complexes: RCN-BH_3
【24h】

Structure, bonding, and energetic properties of nitrile-borane complexes: RCN-BH_3

机译：腈-硼烷配合物的结构，键合和能量性质：RCN-BH_3

获取原文
获取原文并翻译 | 示例
           
页面导航
  • 摘要
  • 著录项
  • 相似文献
  • 相关主题

摘要

The structural and energetic properties of CH_3CN-BH_3, HCN-BH_3, FCH_2CN-BH_3, and F_3CCN- BH_3 have been examined via density functional theory and post-Hartree-Fock calculations. The B-N distances in these systems are notably short, less than 1.6 ?, and the binding energies are substantial, about 20 kcal/mol. The properties of these systems do vary as a result of the nitrile substituent, but surprisingly, more electronegative substituents result in shorter B-N distances. For example, the B-N distance for F_3CCN- BH_3 is 1.576 ? via MP2/aug-cc-pVTZ, while that for CH _3CN-BH_3 is 1.584 ?. However, the binding energies vary as expected, from 17.4 kcal/mol in the case of F_3CCN-BH _3 to 22.6 kcal/mol for CH_3CN-BH_3 (via MP2/aug-cc-pVTZ). The extent of charge transfer and the degree of covalent character in the B-N bonds were explored by a natural bond orbital analysis, and the atoms in molecules formalism, respectively, and do provide some rationale for the substituent effects. Frequency calculations indicate that BH _3-localized vibrational modes do shift appreciably upon complex formation, especially the BH_3 asymmetric stretch. For CH _3CN-BH_3, experimental and calculated frequency shifts compare well for the asymmetric BH_3 bending mode, but the observed shift for the BH_3 asymmetric stretch, the most structurally sensitive mode, is about 40 cm~(-1) larger than the predictions. While this may suggest a very slight contraction of the B-N bond upon formation of solid CH_3CN-BH_3 (for which experimental data are available) the balance of evidence indicates that no significant medium effects occur in these complexes. We also discuss the distinct differences between these complexes and their BF_3 analogs. The underlying reasons for the markedly different structural properties are illustrated through an energy decomposition analysis applied to HCN-BH_3 and HCN-BF_3. These data indicate that less Pauli repulsion of the electrons on each respective subunit is the most significant factor that favors the overall stability of the BH_3 complex.
机译：CH_3CN-BH_3，HCN-BH_3，FCH_2CN-BH_3和F_3CCN-BH_3的结构和能量性质已通过密度泛函理论和Hartree-Fock后计算进行了检验。这些系统中的B-N距离特别短，小于1.6Ω，结合能很大，约为20kcal / mol。这些系统的性能确实由于腈取代基而变化，但是令人惊讶的是，更多的带负电的取代基导致更短的B-N距离。例如，F_3CCN-BH_3的B-N距离为1.576Ω。通过MP2 / aug-cc-pVTZ，而CH _3CN-BH_3则为1.584？。但是，结合能按预期变化，从F_3CCN-BH _3的17.4 kcal / mol到CH_3CN-BH_3的22.6 kcal / mol（通过MP2 / aug-cc-pVTZ）。通过自然键轨道分析以及分子中的原子形式，分别探索了B-N键中电荷转移的程度和共价特征的程度，这确实为取代基效应提供了一些理论依据。频率计算表明，BH _3-局部振动模态在复合物形成时会发生明显的偏移，尤其是BH_3的不对称拉伸。对于CH _3CN-BH_3，在非对称BH_3弯曲模式下，实验和计算的频移比较好，但是在BH_3非对称拉伸（结构上最敏感的模式）下观察到的频移比预测值大40 cm〜（-1）。尽管这可能表明在形成固体CH_3CN-BH_3时B-N键会​​非常轻微的收缩（可获得实验数据），但证据的平衡表明在这些配合物中没有发生明显的介质作用。我们还讨论了这些复合物与其BF_3类似物之间的明显区别。通过对HCN-BH_3和HCN-BF_3进行的能量分解分析，说明了结构特性明显不同的根本原因。这些数据表明，每个亚基上电子的保利排斥力越小，这是促进BH_3配合物整体稳定性的最重要因素。

著录项

相似文献

  • 外文文献
  • 中文文献
  • 专利
获取原文

客服邮箱：kefu@zhangqiaokeyan.com

京公网安备：11010802029741号 ICP备案号：京ICP备15016152号-6 六维联合信息科技 (北京) 有限公司©版权所有

  • 客服微信

  • 服务号