[论文解读] Dominance of eclipsed ferrocene conformer in solutions revealed by the IR fingerprint spectral splitting

Narges Mohammadi, Feng Wang+3 more|arXiv (Cornell University)|Jun 4, 2013

Ferrocene Chemistry and Applications参考文献 29被引用 4

一句话总结

本研究结合高分辨率傅里叶变换红外光谱（FTIR）与DFT计算（B3LYP/6-31G(d)），证明在溶液中，全重叠构象的二茂铁占主导地位，其证据为在480–500 cm⁻¹的指纹区出现一致的15 cm⁻¹红外光谱分裂。溶剂效应微弱，SMD隐式溶剂模型在未校正振动频率的情况下，能产生最准确的红外光谱。

ABSTRACT

A combined high-resolution Fourier transform infrared (FTIR) spectra of ferrocene (Fc) and density functional theory (DFT) based quantum mechanical calculations confirmed the dominance of the eclipsed Fc conformer in the fingerprint region of 400-500 cm-1. The IR spectra of Fc were measured in solutions with a number of non-polar solvents such as acetonitrile, dichloromethane, tetrahydrofuran and dioxane. The measurements agree well with the earlier IR spectra of Lippincott and Nelson (1958) as well as the most recent IR spectral measurement in dichloromethane solution of Duhovic and Diaconescu (2013). All experimental measurements in the solutions unambiguously exhibit an IR spectral splitting of ca. 15 cm-1 in the 480-500 cm-1 region. The DFT based B3LYP/m6-31G(d) quantum mechanical calculations using implicit solvent models in this study indicates that only the ground electronic state of the eclipsed (D5h) Fc splits in the IR fingerprint region of ca. 500 cm-1. The IR spectral splitting characterises the centre Fe metal related vibrations of the eclipsed Fc, in agreement with our previous finding in gas phase [Mohammadi et al, 2012]. The present study further suggests that the effects of solvents on the IR spectra of Fc in this region are small and the solvent model effects are also small but the solute molecular density (SMD) model seems to produce the most accurate IR spectrum in the region of 400-600 cm-1 of Fc without scaling the calculated results.

研究动机与目标

• 利用高分辨率红外光谱确定二茂铁在溶液中的主要构象。
• 研究非极性溶剂对二茂铁指纹区红外光谱的影响。
• 验证DFT计算中隐式溶剂模型在预测二茂铁红外光谱方面的准确性。
• 确定400–500 cm⁻¹区域观察到的红外光谱分裂的振动起源。

提出的方法

• 在乙腈、二氯甲烷、四氢呋喃和二氧六环中对二茂铁进行高分辨率傅里叶变换红外（FTIR）光谱测定。
• 采用B3LYP泛函和6-31G(d)基组进行密度泛函理论（DFT）计算。
• 应用隐式溶剂模型（SMD）模拟溶剂对红外光谱的影响。
• 将计算得到的红外光谱与实验数据在400–600 cm⁻¹区域进行比较。
• 分析480–500 cm⁻¹区域的光谱分裂，以确定其对应于全重叠构象的振动模式。
• 评估SMD模型在未校正振动频率情况下的准确性。

实验结果

研究问题

• RQ1 在溶液中，哪种二茂铁构象占主导地位：全重叠构象还是交错构象？
• RQ2 480–500 cm⁻¹区域观察到的15 cm⁻¹红外光谱分裂是由什么引起的？
• RQ3 不同非极性溶剂如何影响二茂铁在指纹区的红外光谱？
• RQ4 哪种DFT溶剂模型最能再现二茂铁的实验红外光谱？
• RQ5 400–500 cm⁻¹区域的振动模式是否主要与全重叠构象中的铁中心相关？

主要发现

• 所有测试的非极性溶剂中，实验FTIR光谱在480–500 cm⁻¹区域均表现出一致的15 cm⁻¹分裂。
• DFT计算证实，仅全重叠（D5h）构象表现出该光谱分裂，其归因于铁中心的振动。
• SMD隐式溶剂模型在未校正频率的情况下产生最准确的红外光谱，优于其他溶剂模型。
• 在400–600 cm⁻¹区域，溶剂效应对红外光谱的影响微弱，表明光谱特征是全重叠构象的本征性质。
• 观察到的光谱分裂与先前气相研究结果一致，证实全重叠构象在溶液中具有稳定性。
• 实验与理论结果的高度一致支持了全重叠构象在多种溶剂中均占主导地位。