Issue 9, 2023

Dynamic effects on ligand field from rapid hydride motion in an iron(ii) dimer with an S = 3 ground state


Hydride complexes are important in catalysis and in iron–sulfur enzymes like nitrogenase, but the impact of hydride mobility on local iron spin states has been underexplored. We describe studies of a dimeric diiron(II) hydride complex using X-ray and neutron crystallography, Mössbauer spectroscopy, magnetism, DFT, and ab initio calculations, which give insight into the dynamics and the electronic structure brought about by the hydrides. The two iron sites in the dimer have differing square-planar (intermediate-spin) and tetrahedral (high-spin) iron geometries, which are distinguished only by the hydride positions. These are strongly coupled to give an Stotal = 3 ground state with substantial magnetic anisotropy, and the merits of both localized and delocalized spin models are discussed. The dynamic nature of the sites is dependent on crystal packing, as shown by changes during a phase transformation that occurs near 160 K. The change in dynamics of the hydride motion leads to insight into its influence on the electronic structure. The accumulated data indicate that the two sites can trade geometries by rotating the hydrides, at a rate that is rapid above the phase transition temperature but slow below it. This small movement of the hydrides causes large changes in the ligand field because they are strong-field ligands. This suggests that hydrides could be useful in catalysis not only due to their reactivity, but also due to their ability to rapidly modulate the local electronic structure and spin states at metal sites.

Graphical abstract: Dynamic effects on ligand field from rapid hydride motion in an iron(ii) dimer with an S = 3 ground state

Supplementary files

Article information

Article type
Edge Article
21 Nov 2022
17 Jan 2023
First published
08 Feb 2023
This article is Open Access

All publication charges for this article have been paid for by the Royal Society of Chemistry
Creative Commons BY license

Chem. Sci., 2023,14, 2303-2312

Dynamic effects on ligand field from rapid hydride motion in an iron(II) dimer with an S = 3 ground state

S. F. McWilliams, B. Q. Mercado, K. C. MacLeod, M. S. Fataftah, M. Tarrago, X. Wang, E. Bill, S. Ye and P. L. Holland, Chem. Sci., 2023, 14, 2303 DOI: 10.1039/D2SC06412J

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