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Designing Mn(I), Fe(II) and Mn(II) tris(diisocyanide) complexes

Hansen, Anette LU (2024) KEMR30 20241
Department of Chemistry
Abstract
First-row transition metal complexes are considered a more sustainable and cheaper alternative to ruthenium in photoredox-active complexes. However, the fast excited state relaxation of complexes based on first-row transition metals hinders direct replacement of Ru(II) with its 3d6 counterparts Mn(I) and Fe(II). Diisocyanide ligands have previously been used to achieve photostable 3d6 complexes while also improving MLCT lifetimes in Cr(0) and Mn(I) complexes. In the current project, the impact of ligand optimisation on the excited states of Mn(I) and Fe(II) complexes is studied through a new diisocyanide ligand with an electron deficient backbone. Steady-state and transient absorption spectroscopy, infrared spectroscopy and cyclic... (More)
First-row transition metal complexes are considered a more sustainable and cheaper alternative to ruthenium in photoredox-active complexes. However, the fast excited state relaxation of complexes based on first-row transition metals hinders direct replacement of Ru(II) with its 3d6 counterparts Mn(I) and Fe(II). Diisocyanide ligands have previously been used to achieve photostable 3d6 complexes while also improving MLCT lifetimes in Cr(0) and Mn(I) complexes. In the current project, the impact of ligand optimisation on the excited states of Mn(I) and Fe(II) complexes is studied through a new diisocyanide ligand with an electron deficient backbone. Steady-state and transient absorption spectroscopy, infrared spectroscopy and cyclic voltammetry indicate that the MLCT energy decreases as a result of LUMO stabilisation without impacting the excited state dynamics of the complexes. However, the new tris(diisocyanide) 3d6 complexes photodissociate under irradiation into their MLCT bands. Inspired by the promising properties of Fe(III)-carbene complexes, the LMCT transition in a 3d5 Mn(II) tris(diisocyanide) complex was also explored. Mn(II)-isocyanide complexes are known to be unstable in solution, which was also the key finding in this work. In summary, this project provides valuable insight into the design of first-row transition metal isocyanide complexes and their photostability. (Less)
Popular Abstract
Sunlight is a widely available and renewable source of energy. Therefore, there is a large interest in utilising sunlight in various processes including solar cells and photocatalysis. Transition metal complexes can absorb light, which gives them their oftentimes strong colours. Furthermore, the absorption of sunlight allows practical application of such complexes as photosensitisers in dye-sensitised solar cells and photocatalysis. Especially ruthenium complexes are known to be very well-performing for the aforementioned purposes but, unfortunately, ruthenium is a scarce metal on Earth. From both a sustainability and a cost point of view, it is therefore sensible to replace ruthenium with more abundant transition metals.
The transition... (More)
Sunlight is a widely available and renewable source of energy. Therefore, there is a large interest in utilising sunlight in various processes including solar cells and photocatalysis. Transition metal complexes can absorb light, which gives them their oftentimes strong colours. Furthermore, the absorption of sunlight allows practical application of such complexes as photosensitisers in dye-sensitised solar cells and photocatalysis. Especially ruthenium complexes are known to be very well-performing for the aforementioned purposes but, unfortunately, ruthenium is a scarce metal on Earth. From both a sustainability and a cost point of view, it is therefore sensible to replace ruthenium with more abundant transition metals.
The transition metal manganese is nearly one million times more abundant than ruthenium. In previous research, manganese-isocyanide complexes have shown potential as photosensitisers. My aim is to continue this exploration and try to optimise the properties of manganese-isocyanide complexes as photosensitisers. Iron is even more abundant than manganese, but iron-isocyanide complexes are less explored and understood. In this project, I also synthesised iron-isocyanide complexes and gained new insight about them.
The manganese and iron complexes I have synthesised are not terrific photosensitisers – in fact they fall apart when light is shone on them. Therefore, the new complexes have no practical applications as photosensitisers, but they have given valuable and fundamental knowledge about what considerations that should be made when designing more sustainable transition metal complexes in the future. (Less)
Please use this url to cite or link to this publication:
author
Hansen, Anette LU
supervisor
organization
alternative title
Towards more sustainable transition metal photosensitisers
course
KEMR30 20241
year
type
H2 - Master's Degree (Two Years)
subject
keywords
Fe(II), isocyanide, Mn(I), Mn(II), photosensitiser, photodissociation, chemical physics
language
English
id
9168591
date added to LUP
2024-06-27 08:37:01
date last changed
2024-06-27 08:37:01
@misc{9168591,
  abstract     = {{First-row transition metal complexes are considered a more sustainable and cheaper alternative to ruthenium in photoredox-active complexes. However, the fast excited state relaxation of complexes based on first-row transition metals hinders direct replacement of Ru(II) with its 3d6 counterparts Mn(I) and Fe(II). Diisocyanide ligands have previously been used to achieve photostable 3d6 complexes while also improving MLCT lifetimes in Cr(0) and Mn(I) complexes. In the current project, the impact of ligand optimisation on the excited states of Mn(I) and Fe(II) complexes is studied through a new diisocyanide ligand with an electron deficient backbone. Steady-state and transient absorption spectroscopy, infrared spectroscopy and cyclic voltammetry indicate that the MLCT energy decreases as a result of LUMO stabilisation without impacting the excited state dynamics of the complexes. However, the new tris(diisocyanide) 3d6 complexes photodissociate under irradiation into their MLCT bands. Inspired by the promising properties of Fe(III)-carbene complexes, the LMCT transition in a 3d5 Mn(II) tris(diisocyanide) complex was also explored. Mn(II)-isocyanide complexes are known to be unstable in solution, which was also the key finding in this work. In summary, this project provides valuable insight into the design of first-row transition metal isocyanide complexes and their photostability.}},
  author       = {{Hansen, Anette}},
  language     = {{eng}},
  note         = {{Student Paper}},
  title        = {{Designing Mn(I), Fe(II) and Mn(II) tris(diisocyanide) complexes}},
  year         = {{2024}},
}