Fleischer Holger, McKean Donald C, Torto Ivy
Institut für Anorganische Chemie und Analytische Chemie, Johannes Gutenberg Universität, Germany.
Spectrochim Acta A Mol Biomol Spectrosc. 2002 Mar 15;58(5):911-25. doi: 10.1016/s1386-1425(01)00566-2.
Quantum-chemical calculations at HF, MP2 and B3LYP levels with 6-31G* and 6-311G** basis sets are reported for disilylamine, NH(SiH3)2. The equilibrium structure is found to vary with both level and basis set, all but one of the structures exhibiting a small lack of planarity of the HNSi2 system. The barrier to inversion, however, is found to be very low, at most 38 cm(-1). Vibration frequencies and intensities are calculated. The frequencies are scaled, where possible, either using updated infrared data or with the aid of factors transferred from N(CH3)(SiH3)2. Unobserved frequencies due to the v(s)NSi2, deltaNSi2 and delta(perpendicular)NH modes are predicted near 610, 210 and 360 cm(-1), respectively. The lower silyl torsion lies below 40 cm(-1). The appearance of a single broad vSiH band in gas-phase samples of both NH(SiH3)2 and NH(SiH3)(SiD3) is suggestive of signal averaging due to internal rotation. The frequencies v(is)SiH, infrared intensities and Raman scattering activities of the bands due to an isolated SiH bond in an otherwise deuterated species are calculated and correlated with the torsional angle of this bond and with the Mulliken charge on the hydrogen atom. The strength of the bond is a minimum, and the infrared intensity and Raman scattering activity are maxima, when the bond direction is roughly orthogonal to the skeletal plane. A major part of the frequency and intensity variations is attributed to n(p)(N)-sigma*(Si-H)) hyperconjugation which, NBO calculations show, reaches a maximum for this conformation. However, systematic smaller variations are found for SiH bonds lying in the skeletal plane, which reflect the proximity of the other silyl group and only partly correlate with Mulliken charge. vSiH-vSiH interaction force constants, f', are calculated for pairs of SiH bonds in different silyl groups and compared with the corresponding dipole-dipole potential energy, the latter calculated using a classical treatment of the interaction between point dipoles arising from delta mu/delta r for the SiH bonds involved. The gradient of the correlation is very close to that expected from the theory, but a negative intercept indicates the presence of additional factors.
本文报道了采用6-31G和6-311G**基组在HF、MP2和B3LYP水平上对二硅胺NH(SiH₃)₂进行的量子化学计算。发现平衡结构随计算水平和基组的变化而变化，除一种结构外，所有结构的HNSi₂体系均表现出轻微的非平面性。然而，发现反转势垒非常低，最高为38 cm⁻¹。计算了振动频率和强度。在可能的情况下，使用更新的红外数据或借助从N(CH₃)(SiH₃)₂转移的因子对频率进行缩放。预测了由于v(s)NSi₂、δNSi₂和δ(垂直)NH模式导致的未观察到的频率分别在610、210和360 cm⁻¹附近。较低的硅烷基扭转低于40 cm⁻¹。在NH(SiH₃)₂和NH(SiH₃)(SiD₃)的气相样品中出现单一宽的vSiH带，表明由于内旋转导致信号平均。计算了在其他位置为氘代的物种中孤立SiH键的v(is)SiH频率、红外强度和拉曼散射活性，并将其与该键的扭转角以及氢原子上的穆利肯电荷相关联。当键方向大致垂直于骨架平面时，键强度最小，红外强度和拉曼散射活性最大。频率和强度变化的主要部分归因于n(p)(N)-σ(Si-H)超共轭，NBO计算表明，这种构象下超共轭达到最大值。然而，对于位于骨架平面内的SiH键，发现了系统的较小变化，这反映了另一个硅烷基的接近程度，并且仅部分与穆利肯电荷相关。计算了不同硅烷基中SiH键对的vSiH-vSiH相互作用力常数f'，并与相应的偶极-偶极势能进行比较，后者使用对所涉及的SiH键的δμ/δr产生的点偶极之间的相互作用的经典处理方法计算。相关性的梯度非常接近理论预期，但负截距表明存在其他因素。
