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

Kunnus, Kristjan ; Guo, Meiyuan LU ; Biasin, Elisa ; Larsen, Christopher B. ; Titus, Charles J. ; Lee, Sang Jun ; Nordlund, Dennis ; Cordones, Amy A. ; Uhlig, Jens LU and Gaffney, Kelly J. (2022) In Inorganic Chemistry 61(4). p.1961-1972
Abstract

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... (More)

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.

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author
; ; ; ; ; ; ; ; and
organization
publishing date
type
Contribution to journal
publication status
published
subject
in
Inorganic Chemistry
volume
61
issue
4
pages
1961 - 1972
publisher
The American Chemical Society (ACS)
external identifiers
  • pmid:35029978
  • scopus:85123838102
ISSN
0020-1669
DOI
10.1021/acs.inorgchem.1c03124
language
English
LU publication?
yes
additional info
Publisher Copyright: ©
id
73ee3fa5-e297-4be5-8b31-dd91a8db5e5d
date added to LUP
2022-02-16 16:01:47
date last changed
2024-05-02 06:51:20
@article{73ee3fa5-e297-4be5-8b31-dd91a8db5e5d,
  abstract     = {{<p>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. </p>}},
  author       = {{Kunnus, Kristjan and Guo, Meiyuan and Biasin, Elisa and Larsen, Christopher B. and Titus, Charles J. and Lee, Sang Jun and Nordlund, Dennis and Cordones, Amy A. and Uhlig, Jens and Gaffney, Kelly J.}},
  issn         = {{0020-1669}},
  language     = {{eng}},
  number       = {{4}},
  pages        = {{1961--1972}},
  publisher    = {{The American Chemical Society (ACS)}},
  series       = {{Inorganic Chemistry}},
  title        = {{Quantifying the Steric Effect on Metal-Ligand Bonding in Fe Carbene Photosensitizers with Fe 2p3d Resonant Inelastic X-ray Scattering}},
  url          = {{http://dx.doi.org/10.1021/acs.inorgchem.1c03124}},
  doi          = {{10.1021/acs.inorgchem.1c03124}},
  volume       = {{61}},
  year         = {{2022}},
}