Best Stephen P, Wang Feng, Islam M Tauhidul, Islam Shawkat, Appadoo Dominique, Trevorah Ryan M, Chantler Christopher T
School of Chemistry, University of Melbourne, Parkville, Victoria, 3010, Australia.
Department of Chemistry and Biotechnology, Swinburne University of Technology, Hawthorn, Melbourne, Victoria, 3122, Australia.
Chemistry. 2016 Dec 12;22(50):18019-18026. doi: 10.1002/chem.201603823. Epub 2016 Nov 11.
Molecular distortion of dynamic molecules gives a clear signature in the vibrational spectra, which can be modeled to give estimates of the energy barrier and the sensitivity of the frequencies of the vibrational modes to the reaction coordinate. The reaction coordinate method (RCM) utilizes ab initio-calculated spectra of the molecule in its ground and transition states together with their relative energies to predict the temperature dependence of the vibrational spectra. DFT-calculated spectra of the eclipsed (D ) and staggered (D ) forms of ferrocene (Fc), and its deuterated analogue, within RCM explain the IR spectra of Fc in gas (350 K), solution (300 K), solid solution (7-300 K), and solid (7-300 K) states. In each case the D rotamer is lowest in energy but with the barrier to interconversion between rotamers higher for solution-phase samples (ca. 6 kJ mol ) than for the gas-phase species (1-3 kJ mol ). The generality of the approach is demonstrated with application to tricarbonyl(η -norbornadiene)iron(0), Fe(NBD)(CO) . The temperature-dependent coalescence of the ν(CO) bands of Fe(NBD)(CO) is well explained by the RCM without recourse to NMR-like rapid exchange. The RCM establishes a clear link between the calculated ground and transition states of dynamic molecules and the temperature-dependence of their vibrational spectra.
动态分子的分子畸变在振动光谱中给出清晰的特征，可对其进行建模以估计能垒以及振动模式频率对反应坐标的敏感度。反应坐标方法（RCM）利用分子基态和过渡态的从头算光谱及其相对能量来预测振动光谱的温度依赖性。在RCM内对二茂铁（Fc）及其氘代类似物的重叠（D）和交错（D）形式进行密度泛函理论计算的光谱，解释了Fc在气体（350 K）、溶液（300 K）、固溶体（7 - 300 K）和固体（7 - 300 K）状态下的红外光谱。在每种情况下，D旋转异构体能量最低，但溶液相样品中旋转异构体之间相互转化的能垒（约6 kJ·mol）高于气相物种（1 - 3 kJ·mol）。通过将该方法应用于三羰基（η - 降冰片二烯）铁（0），即Fe（NBD）（CO），证明了该方法的通用性。Fe（NBD）（CO）的ν（CO）带的温度依赖性合并现象在RCM中得到了很好的解释，而无需借助类似核磁共振的快速交换。RCM在动态分子的计算基态和过渡态与其振动光谱的温度依赖性之间建立了明确的联系。
