High-Frequency Fe-H and Fe-H Modes in a -Fe(η-H)(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 -[Fe(η-H)(H)(dppe)][BPh] [dppe = 1,2-bis(diphenylphosphino)ethane] complex. Heretofore, most NRVS observations have centered on the spectral region below 1000 cm, where the Fe signal is strongest. In this work, we show that state-of-the-art synchrotron facilities can extend the observable region to 2000 cm and likely beyond, in measurements that require less than 1 day. The Fe-H stretch was revealed at 1915 cm, along with the asymmetric Fe-H stretch at 1774 cm. For a small fraction of the H-dissociated product, the Fe-H stretch was detected at 1956 cm. The unique sensitivity to Fe motion and the isolated nature of the Fe-H/H stretching modes enabled NRVS to quantitatively analyze the sample composition.