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How Rigidity and Conjugation of Bidentate Ligands Affect the Geometry and Photophysics of Iron N-Heterocyclic Complexes : A Comparative Study

Prakash, Om LU ; Chábera, Pavel LU ; Kaul, Nidhi ; Hlynsson, Valtýr F. LU ; Rosemann, Nils W. LU ; Losada, Iria Bolaño LU ; Hoang Hai, Yen Tran LU ; Huang, Ping ; Bendix, Jesper and Ericsson, Tore , et al. (2024) In Inorganic Chemistry 63(10). p.4461-4473
Abstract

Two iron complexes featuring the bidentate, nonconjugated N-heterocyclic carbene (NHC) 1,1′-methylenebis(3-methylimidazol-2-ylidene) (mbmi) ligand, where the two NHC moieties are separated by a methylene bridge, have been synthesized to exploit the combined influence of geometric and electronic effects on the ground- and excited-state properties of homoleptic FeIII-hexa-NHC [Fe(mbmi)3](PF6)3 and heteroleptic FeII-tetra-NHC [Fe(mbmi)2(bpy)](PF6)2 (bpy = 2,2′-bipyridine) complexes. They are compared to the reported FeIII-hexa-NHC [Fe(btz)3](PF6)3 and FeII-tetra-NHC... (More)

Two iron complexes featuring the bidentate, nonconjugated N-heterocyclic carbene (NHC) 1,1′-methylenebis(3-methylimidazol-2-ylidene) (mbmi) ligand, where the two NHC moieties are separated by a methylene bridge, have been synthesized to exploit the combined influence of geometric and electronic effects on the ground- and excited-state properties of homoleptic FeIII-hexa-NHC [Fe(mbmi)3](PF6)3 and heteroleptic FeII-tetra-NHC [Fe(mbmi)2(bpy)](PF6)2 (bpy = 2,2′-bipyridine) complexes. They are compared to the reported FeIII-hexa-NHC [Fe(btz)3](PF6)3 and FeII-tetra-NHC [Fe(btz)2(bpy)](PF6)2 complexes containing the conjugated, bidentate mesoionic NHC ligand 3,3′-dimethyl-1,1′-bis(p-tolyl)-4,4′-bis(1,2,3-triazol-5-ylidene) (btz). The observed geometries of [Fe(mbmi)3](PF6)3 and [Fe(mbmi)2(bpy)](PF6)2 are evaluated through L-Fe-L bond angles and ligand planarity and compared to those of [Fe(btz)3](PF6)3 and [Fe(btz)2(bpy)](PF6)2. The FeII/FeIII redox couples of [Fe(mbmi)3](PF6)3 (−0.38 V) and [Fe(mbmi)2(bpy)](PF6)2 (−0.057 V, both vs Fc+/0) are less reducing than [Fe(btz)3](PF6)3 and [Fe(btz)2(bpy)](PF6)2. The two complexes show intense absorption bands in the visible region: [Fe(mbmi)3](PF6)3 at 502 nm (ligand-to-metal charge transfer, 2LMCT) and [Fe(mbmi)2(bpy)](PF6)2 at 410 and 616 nm (metal-to-ligand charge transfer, 3MLCT). Lifetimes of 57.3 ps (2LMCT) for [Fe(mbmi)3](PF6)3 and 7.6 ps (3MLCT) for [Fe(mbmi)2(bpy)](PF6)2 were probed and are somewhat shorter than those for [Fe(btz)3](PF6)3 and [Fe(btz)2(bpy)](PF6)2. [Fe(mbmi)3](PF6)3 exhibits photoluminescence at 686 nm (2LMCT) in acetonitrile at room temperature with a quantum yield of (1.2 ± 0.1) × 10-4, compared to (3 ± 0.5)

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organization
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type
Contribution to journal
publication status
published
subject
in
Inorganic Chemistry
volume
63
issue
10
pages
13 pages
publisher
The American Chemical Society (ACS)
external identifiers
  • pmid:38421802
  • scopus:85186388161
ISSN
0020-1669
DOI
10.1021/acs.inorgchem.3c03972
language
English
LU publication?
yes
id
b46c296e-bd62-4d8e-9794-d4a07c35d0c0
date added to LUP
2024-03-19 14:01:46
date last changed
2024-04-16 12:33:30
@article{b46c296e-bd62-4d8e-9794-d4a07c35d0c0,
  abstract     = {{<p>Two iron complexes featuring the bidentate, nonconjugated N-heterocyclic carbene (NHC) 1,1′-methylenebis(3-methylimidazol-2-ylidene) (mbmi) ligand, where the two NHC moieties are separated by a methylene bridge, have been synthesized to exploit the combined influence of geometric and electronic effects on the ground- and excited-state properties of homoleptic Fe<sup>III</sup>-hexa-NHC [Fe(mbmi)<sub>3</sub>](PF<sub>6</sub>)<sub>3</sub> and heteroleptic Fe<sup>II</sup>-tetra-NHC [Fe(mbmi)<sub>2</sub>(bpy)](PF<sub>6</sub>)<sub>2</sub> (bpy = 2,2′-bipyridine) complexes. They are compared to the reported Fe<sup>III</sup>-hexa-NHC [Fe(btz)<sub>3</sub>](PF<sub>6</sub>)<sub>3</sub> and Fe<sup>II</sup>-tetra-NHC [Fe(btz)<sub>2</sub>(bpy)](PF<sub>6</sub>)<sub>2</sub> complexes containing the conjugated, bidentate mesoionic NHC ligand 3,3′-dimethyl-1,1′-bis(p-tolyl)-4,4′-bis(1,2,3-triazol-5-ylidene) (btz). The observed geometries of [Fe(mbmi)<sub>3</sub>](PF<sub>6</sub>)<sub>3</sub> and [Fe(mbmi)<sub>2</sub>(bpy)](PF<sub>6</sub>)<sub>2</sub> are evaluated through L-Fe-L bond angles and ligand planarity and compared to those of [Fe(btz)<sub>3</sub>](PF<sub>6</sub>)<sub>3</sub> and [Fe(btz)<sub>2</sub>(bpy)](PF<sub>6</sub>)<sub>2</sub>. The Fe<sup>II</sup>/Fe<sup>III</sup> redox couples of [Fe(mbmi)<sub>3</sub>](PF<sub>6</sub>)<sub>3</sub> (−0.38 V) and [Fe(mbmi)<sub>2</sub>(bpy)](PF<sub>6</sub>)<sub>2</sub> (−0.057 V, both vs Fc<sup>+/0</sup>) are less reducing than [Fe(btz)<sub>3</sub>](PF<sub>6</sub>)<sub>3</sub> and [Fe(btz)<sub>2</sub>(bpy)](PF<sub>6</sub>)<sub>2</sub>. The two complexes show intense absorption bands in the visible region: [Fe(mbmi)<sub>3</sub>](PF<sub>6</sub>)<sub>3</sub> at 502 nm (ligand-to-metal charge transfer, <sup>2</sup>LMCT) and [Fe(mbmi)<sub>2</sub>(bpy)](PF<sub>6</sub>)<sub>2</sub> at 410 and 616 nm (metal-to-ligand charge transfer, <sup>3</sup>MLCT). Lifetimes of 57.3 ps (<sup>2</sup>LMCT) for [Fe(mbmi)<sub>3</sub>](PF<sub>6</sub>)<sub>3</sub> and 7.6 ps (<sup>3</sup>MLCT) for [Fe(mbmi)<sub>2</sub>(bpy)](PF<sub>6</sub>)<sub>2</sub> were probed and are somewhat shorter than those for [Fe(btz)<sub>3</sub>](PF<sub>6</sub>)<sub>3</sub> and [Fe(btz)<sub>2</sub>(bpy)](PF<sub>6</sub>)<sub>2</sub>. [Fe(mbmi)<sub>3</sub>](PF<sub>6</sub>)<sub>3</sub> exhibits photoluminescence at 686 nm (<sup>2</sup>LMCT) in acetonitrile at room temperature with a quantum yield of (1.2 ± 0.1) × 10<sup>-4</sup>, compared to (3 ± 0.5)</p>}},
  author       = {{Prakash, Om and Chábera, Pavel and Kaul, Nidhi and Hlynsson, Valtýr F. and Rosemann, Nils W. and Losada, Iria Bolaño and Hoang Hai, Yen Tran and Huang, Ping and Bendix, Jesper and Ericsson, Tore and Häggström, Lennart and Gupta, Arvind Kumar and Strand, Daniel and Yartsev, Arkady and Lomoth, Reiner and Persson, Petter and Wärnmark, Kenneth}},
  issn         = {{0020-1669}},
  language     = {{eng}},
  number       = {{10}},
  pages        = {{4461--4473}},
  publisher    = {{The American Chemical Society (ACS)}},
  series       = {{Inorganic Chemistry}},
  title        = {{How Rigidity and Conjugation of Bidentate Ligands Affect the Geometry and Photophysics of Iron N-Heterocyclic Complexes : A Comparative Study}},
  url          = {{http://dx.doi.org/10.1021/acs.inorgchem.3c03972}},
  doi          = {{10.1021/acs.inorgchem.3c03972}},
  volume       = {{63}},
  year         = {{2024}},
}