High‐Frequency Fe–H Vibrations in a Bridging Hydride Complex Characterized by NRVS and DFT

Abstract

High-spin iron species with bridging hydrides have been detected in species trapped during nitrogenase catalysis, but there are few general methods of evaluating Fe-H bonds in high-spin multinuclear iron systems. An Fe nuclear resonance vibrational spectroscopy (NRVS) study on an Fe(μ-H) Fe model complex reveals Fe-H stretching vibrations for bridging hydrides at frequencies greater than 1200 cm . These isotope-sensitive vibrational bands are not evident in infrared (IR) spectra, showing the power of NRVS for identifying hydrides in this high-spin iron system. Complementary density functional theory (DFT) calculations elucidate the normal modes of the rhomboidal iron hydride core.

Computational Investigations of the Chemical Mechanism of the Enzyme Nitrogenase

“…This paper also collected and compared Fe−H frequencies measured for simpler model coordination complexes. Fe−H vibrational modes for relevant model compounds have been reported …”

Vibrational characterization of a diiron bridging hydride complex – a model for hydrogen catalysis

“…From previous NRVS work on Fe-H/D À complexes, 11,31,32 as well as guidance from the conventional vibrational spectroscopy literature, 33 we expect observation of the Fe-H stretching modes at vibrational energies above 1100 cm À1 . There are hints of such features at 1165 cm À1 and 1403 cm À1 , but the signal-tonoise is not convincing.…”

“…At higher energies, a band at 745 cm À1 is particularly signicantit represents an Fe-H-Fe wagging mode. This assignment is based on comparison with results for similar Fe-mH À -Fe synthetic complexes and their computational models, 31,32 as well as Ni-mH À -Fe models and the Ni-R state of [NiFe] hydrogenase. 11 The signicant weakening at this position in the mDSD spectrum supports this assignment; residual Fig.…”

Thermodynamic and Kinetic Considerations Regarding the Prospects for a Dual-Purpose Hydrogen Extraction and Separation Membrane

“…A typical metal-hydride vibration of ca. 1400 cm −1 is assumed here [40]. Since these frequency factors have a much weaker influence on the kinetics of the system than the energy barriers, plausible deviations from these values for the vibrational frequencies are unlikely to have a meaningful impact on the conclusions presented here.…”