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Issue 47, 2020
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The effect of N-heterocyclic carbene units on the absorption spectra of Fe(ii) complexes: a challenge for theory

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Abstract

The absorption spectra of five Fe(II) homoleptic and heteroleptic complexes containing strong sigma-donating N-heterocyclic carbene (NHC) and polypyridyl ligands have been theoretically characterized using a tuned range-separation functional. From a benchmark comparison of the obtained results against other functionals and a multiconfigurational reference, it is concluded that none of the methods is completely satisfactory to describe the absorption spectra. As a compromise using 20% exact exchange, the electronic excited states underlying the absorption spectra are analyzed. The low-lying energy band of all the compounds shows predominant metal-to-ligand charge transfer (MLCT) character while the triplet excited states have metal-centered (MC) nature, which becomes more pronounced with increasing the number of NHC-donor groups. Excited MC states with partial charge transfer to the NHC-donor groups are higher in energy than comparable states without these contributions. The presence of the low-lying MC states prevents the formation of long-lived MLCT states.

Graphical abstract: The effect of N-heterocyclic carbene units on the absorption spectra of Fe(ii) complexes: a challenge for theory

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Article information


Submitted
09 Sep 2020
Accepted
20 Nov 2020
First published
20 Nov 2020

Phys. Chem. Chem. Phys., 2020,22, 27605-27616
Article type
Paper

The effect of N-heterocyclic carbene units on the absorption spectra of Fe(II) complexes: a challenge for theory

O. S. Bokareva, O. Baig, M. J. Al-Marri, O. Kühn and L. González, Phys. Chem. Chem. Phys., 2020, 22, 27605
DOI: 10.1039/D0CP04781C

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