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Jens Uhlig. Portrait.

Jens Uhlig

Senior lecturer

Jens Uhlig. Portrait.

Quantifying the Steric Effect on Metal-Ligand Bonding in Fe Carbene Photosensitizers with Fe 2p3d Resonant Inelastic X-ray Scattering

Author

  • Kristjan Kunnus
  • Meiyuan Guo
  • Elisa Biasin
  • Christopher B. Larsen
  • Charles J. Titus
  • Sang Jun Lee
  • Dennis Nordlund
  • Amy A. Cordones
  • Jens Uhlig
  • Kelly J. Gaffney

Summary, in English

Understanding the electronic structure and chemical bonding of transition metal complexes is important for improving the function of molecular photosensitizers and catalysts. We have utilized X-ray absorption spectroscopy (XAS) and resonant inelastic X-ray scattering (RIXS) at the Fe L3 edge to investigate the electronic structure of two Fe N-heterocyclic carbene complexes with similar chemical structures but different steric effects and contrasting excited-state dynamics: [Fe(bmip)2]2+ and [Fe(btbip)2]2+, bmip = 2,6-bis(3-methyl-imidazole-1-ylidine)pyridine and btbip = 2,6-bis(3-tert-butyl-imidazole-1-ylidene)pyridine. In combination with charge transfer multiplet and ab initio calculations, we quantified how changes in Fe-carbene bond length due to steric effects modify the metal-ligand bonding, including σ/πdonation and πback-donation. We find that σ donation is significantly stronger in [Fe(bmip)2]2+, whereas the πback-donation is similar in both complexes. The resulting stronger ligand field and nephelauxetic effect in [Fe(bmip)2]2+ lead to approximately 1 eV destabilization of the quintet metal-centered 5T2g excited state compared to [Fe(btbip)2]2+, providing an explanation for the absence of a photoinduced 5T2g population and a longer metal-to-ligand charge-transfer excited-state lifetime in [Fe(bmip)2]2+. This work demonstrates how combined modeling of XAS and RIXS spectra can be utilized to understand the electronic structure of transition metal complexes governed by correlated electrons and donation/back-donation interactions.

Department/s

  • Chemical Physics
  • NanoLund: Centre for Nanoscience

Publishing year

2022

Language

English

Pages

1961-1972

Publication/Series

Inorganic Chemistry

Volume

61

Issue

4

Document type

Journal article

Publisher

The American Chemical Society (ACS)

Topic

  • Physical Chemistry (including Surface- and Colloid Chemistry)
  • Atom and Molecular Physics and Optics

Status

Published

ISBN/ISSN/Other

  • ISSN: 0020-1669