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Reinterpretation of Dynamic Vibrational Spectroscopy to Determine the Molecular Structure and Dynamics of Ferrocene

机译:重新解释动态振动光谱法以确定二茂铁的分子结构和动力学

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摘要

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-5h) and staggered (D-5d) 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-5h rotamer is lowest in energy but with the barrier to interconversion between rotamers higher for solution-phase samples (ca. 6 kJ mol(-1)) than for the gas-phase species (1-3 kJ mol(-1)). The generality of the approach is demonstrated with application to tricarbonyl(eta(4)-norbornadiene)iron(0), Fe(NBD)(CO)(3). The temperature-dependent coalescence of the nu(CO) bands of Fe(NBD)(CO)(3) 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.
机译:动态分子的分子畸变在振动光谱中给出了清晰的特征,可以对其进行建模以给出能垒的估计以及振动模式频率对反应坐标的敏感性。反应坐标法(RCM)利用分子从头算得出的分子在其基态和过渡态的光谱以及它们的相对能量来预测振动光谱的温度依赖性。 DFT计算的偏二茂铁(Fc)(D-5h)和交错形式(D-5d)及其氘代类似物在RCM中的光谱解释了气体(350 K),溶液(300 K)中Fc的IR光谱),固溶(7-300 K)和固态(7-300 K)状态。在每种情况下,D-5h旋转异构体的能量最低,但对于固溶相样品(约6 kJ mol(-1)),旋转异构体之间的相互转换障碍要比气相物种(1-3 kJ mol)高(-1))。该方法的普遍性已证明适用于三羰基(η(4)-降冰片二烯)铁(0),Fe(NBD)(CO)(3)。 Fe(NBD)(CO)(3)的nu(CO)谱带的温度依赖性聚结由RCM很好地解释,而无需求助于类似NMR的快速交换。 RCM在计算的动态分子的基态和跃迁状态与它们的振动光谱的温度依赖性之间建立了明确的联系。

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