High-Frequency Fe–H and Fe–H2 Modes in a trans-Fe(η2‑H2)(H) Complex: A Speed Record for Nuclear Resonance Vibrational Spectroscopy

Nuclear resonance vibrational spectroscopy (NRVS) and density functional
theory (DFT) are complementary tools for studying the vibrational
and geometric structures of specific isotopically labeled molecular
systems. Here we apply NRVS and DFT to characterize the trans-[57Fe­(η2-H2)­(H)­(dppe)2]­[BPh4] [dppe = 1,2-bis­(diphenylphosphino)­ethane]
complex. Heretofore, most NRVS observations have centered on the spectral
region below 1000 cm–1, where the 57Fe
signal is strongest. In this work, we show that state-of-the-art synchrotron
facilities can extend the observable region to 2000 cm–1 and likely beyond, in measurements that require less than 1 day.
The 57Fe–H stretch was revealed at 1915 cm–1, along with the asymmetric 57Fe–H2 stretch
at 1774 cm–1. For a small fraction of the H2-dissociated product, the 57Fe–H stretch
was detected at 1956 cm–1. The unique sensitivity
to 57Fe motion and the isolated nature of the Fe–H/H2 stretching modes enabled NRVS to quantitatively analyze the
sample composition.

核共振振动光谱学（Nuclear Resonance Vibrational Spectroscopy，简称NRVS）与密度泛函理论（Density Functional Theory，简称DFT）作为研究特定同位素标记分子系统振动和几何结构的互补工具。本研究中，我们运用NRVS与DFT对trans-[57Fe(η2-H2)(H)(dppe)2][BPh4]（其中dppe表示1,2-双(二苯基膦基)乙烷）复合物进行了表征。迄今为止，NRVS的观测主要集中在低于1000 cm–1的频谱区域，该区域的57Fe信号最为显著。在本研究中，我们揭示了先进同步辐射设施可将可观测区域扩展至2000 cm–1及以上，且测量时间少于1天。在1915 cm–1处揭示了57Fe–H伸缩振动，以及位于1774 cm–1处的非对称57Fe–H2伸缩振动。对于一小部分H2解离产物，57Fe–H伸缩振动在1956 cm–1处被检测到。NRVS对57Fe运动的独特敏感性以及Fe–H/H2伸缩模式的孤立特性使其能够定量分析样品组成。