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Abstract A highly water‐ and air‐stable Fe(II) complex with the quinol‐containing macrocyclic ligand H4qp4 reacts with H2O2to yield Fe(III) complexes with less highly chelating forms of the ligand that have either one or twopara‐quinones. The reaction increases theT1‐weighted relaxivity over four‐fold, enabling the complex to detect H2O2using clinical MRI technology. The iron‐containing sensor differs from its recently characterized manganese analog, which also detects H2O2, in that it is the oxidation of the metal center, rather than the ligand, that primarily enhances the relaxivity.
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Modeling the roles of rigidity and dopants in single-atom methane-to-methanol catalysts
Doped graphitic single-atom catalysts (SACs) with isolated iron sites have similarities to natural enzymes and molecular biomimetics that can convert methane to methanol via a radical rebound mechanism with high-valent Fe( iv )O intermediates. To understand the relationship of SACs to these homogeneous analogues, we use range-separated hybrid density functional theory (DFT) to compare the energetics and structure of the direct metal-coordinating environment in the presence of 2p ( i.e. , N or O) and 3p ( i.e. , P or S) dopants and with increasing finite graphene model flake size to mimic differences in local rigidity. While metal–ligand bond lengths in SACs are significantly shorter than those in transition-metal complexes, they remain longer than SAC mimic macrocyclic complexes. In SACs or the macrocyclic complexes, this compressed metal–ligand environment induces metal distortion out of the plane, especially when reactive species are bound to iron. As a result of this modified metal-coordination environment, we observe SACs to simultaneously favor the formation of the metal–oxo while also allowing for methanol release. This reactivity is different from what has been observed for large sets of square planar model homogeneous catalysts. Overall, our calculations recommend broader consideration of dopants ( e.g. , P or S) and processing conditions that allow for local distortion around the metal site in graphitic SACs.
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- PAR ID:
- 10318114
- Date Published:
- Journal Name:
- Journal of Materials Chemistry A
- ISSN:
- 2050-7488
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/D1TA08502F
