Abstract
Because of the diverse nature of this thesis, each of the six chapters are briey described
individually.
Chapter 1 details the synthesis and characterisation of a rare example of a ferromagnetically
coupled chromium(III) dimer (Ph4P)4[(SCN)4Cr(OH)2Cr(NCS)4] 2 NCCH3.
The compound has been characterised by EPR and the powder spectra successfully
simulated using two generic multiplet Hamiltonians, one for S = 2 and one for S = 3.
The exchange coupling in chromium diols are investigated with a Broken Symmetry
DFT model, which is able to accurately predict the exchange coupling constant J from
weakly to strongly coupled systems. This represents a quantitative improvement over
the established GHP model based on AOM arguments, and the qualitative interpretation
of said model is corroborated by in silica magnetostructural correlation studies.
Chapter 2 details a single crystal EPR study on dinuclear chromium(III) compounds.
(Ph4P)4[(SCN)4Cr(OH)2Cr(NCS)4] 2 NCCH3 is investigated again as a ’proof of concept’
that it is possible to accurately simulate the single crystal spectra of a low-symmetry
system (monoclinic) where two orientations of the molecules are present in the
unit cell. There are commonly two ways to describe coupled dinuclear systems with
spin-Hamiltonians; the so called ’dimer model’ and the ’generic multiplet’ model. The
strengths and weaknesses of these models are highlighted by measurements on highly
symmetrical dinuclear chromium(III) compounds and the exceptional data quality of
single crystal multi frequency EPR is used to make a new model which is more physically
accurate and which better describes the observed experimental behaviour. This
has implications not just for the investigated chromium systems, but for exchange coupled systems in general.
Chapter 3 details the serendipitous synthesis of the nitrido-bridged [Rh(en)3]2-
[(CN)5MnNMn(CN)5]. The complex anion have previously been studied in the form of
the mixed Rb4Na2-salt. In this earlier study, the nitrido-bridge was found to be asymmetrical
with the axial ligands in an eclipsed formation. The complex was described as
a mixed valence MnII/MnV system. This is not the case for the present system where the
bridge is symmetrical, slightly bent and the axial ligands are in a staggered conformation. XANES measurements along with DFT calculations suggest that the Rb4Na2-salt is indeed best described as MnII/MnV whereas the [Rh(en)3]2-salt is best described as Mn3.5/Mn3.5. This means that the [(CN)5MnNMn(CN)5]6􀀀 ion displays crystal packing induced oxidation state isomerism, a rare phenomenon.
Chapter 4 details the synthesis and characterisation of group 9 dithiolene complexes
with focus on the hitherto unknown homoleptic iridium dithiolene complexes. When
the complexes [M(mnt)3]3􀀀, M = Rh and Co are chemically oxidized, they decompose
to yield dinuclear complexes with the metal still in oxidation state III. This is not the
case for the corresponding Ir complex which can be oxidized and the oxidation product
[Ir(mnt)3]2􀀀 isolated. The systems are characterised by numerous techniques including
Ir and S XAS, X-ray crystallography and DFT and ab initio calculations.
Chapter 5 details the synthesis of unexpected hexacoordinated silver(I) complexes
with halide ligands, [(CH3CN)3IrX3AgX3Ir(NCCH3)3]+ with X = Cl and Br. The extreme
kinetic robustness of the Ir(III) centers prevents chloride abstraction by Ag(I)
and the unusual complexes are formed instead. A ligand eld and ab initio study of the
ligand complexes [IrX3(NCCH3)3] is performed and compared to the silver complexes
and it is found that the coordination of Ag(I) has no perceivable eect on the Ir ligand
eld.
Chapter 6 details the synthesis of new terminal ruthenium carbide complexes by
ligand substitution on the Ru center. This approach to new, rationally tuned carbide
complexes is virtually unexplored. The reaction of the known carbide complex
[RuC(Cl)2(PCy3)2] with cyanide aords the cyanide analogue [RuC(CN)2(PCy3)2]. The
reaction kinetics are studied with NMR. It is also possible to exchange only one of the
chloride ligands, with the intermediate [RuC(Cl)(NCCH3)(PCy3)2]+ and this control
of the ligand environment opens up the possibility of for instance incorporating the
carbide functionality into other systems.
Several chapters and papers include X-ray spectroscopy measurements and a very
brief introduction to the techniques is given in Appendix A. Throughout the thesis
computational studies of various kinds have been used to help the elucidation of experimental observations and a brief study on the computation of ligand eld transitions
in transition metal complexes is given in Appendix B.
individually.
Chapter 1 details the synthesis and characterisation of a rare example of a ferromagnetically
coupled chromium(III) dimer (Ph4P)4[(SCN)4Cr(OH)2Cr(NCS)4] 2 NCCH3.
The compound has been characterised by EPR and the powder spectra successfully
simulated using two generic multiplet Hamiltonians, one for S = 2 and one for S = 3.
The exchange coupling in chromium diols are investigated with a Broken Symmetry
DFT model, which is able to accurately predict the exchange coupling constant J from
weakly to strongly coupled systems. This represents a quantitative improvement over
the established GHP model based on AOM arguments, and the qualitative interpretation
of said model is corroborated by in silica magnetostructural correlation studies.
Chapter 2 details a single crystal EPR study on dinuclear chromium(III) compounds.
(Ph4P)4[(SCN)4Cr(OH)2Cr(NCS)4] 2 NCCH3 is investigated again as a ’proof of concept’
that it is possible to accurately simulate the single crystal spectra of a low-symmetry
system (monoclinic) where two orientations of the molecules are present in the
unit cell. There are commonly two ways to describe coupled dinuclear systems with
spin-Hamiltonians; the so called ’dimer model’ and the ’generic multiplet’ model. The
strengths and weaknesses of these models are highlighted by measurements on highly
symmetrical dinuclear chromium(III) compounds and the exceptional data quality of
single crystal multi frequency EPR is used to make a new model which is more physically
accurate and which better describes the observed experimental behaviour. This
has implications not just for the investigated chromium systems, but for exchange coupled systems in general.
Chapter 3 details the serendipitous synthesis of the nitrido-bridged [Rh(en)3]2-
[(CN)5MnNMn(CN)5]. The complex anion have previously been studied in the form of
the mixed Rb4Na2-salt. In this earlier study, the nitrido-bridge was found to be asymmetrical
with the axial ligands in an eclipsed formation. The complex was described as
a mixed valence MnII/MnV system. This is not the case for the present system where the
bridge is symmetrical, slightly bent and the axial ligands are in a staggered conformation. XANES measurements along with DFT calculations suggest that the Rb4Na2-salt is indeed best described as MnII/MnV whereas the [Rh(en)3]2-salt is best described as Mn3.5/Mn3.5. This means that the [(CN)5MnNMn(CN)5]6􀀀 ion displays crystal packing induced oxidation state isomerism, a rare phenomenon.
Chapter 4 details the synthesis and characterisation of group 9 dithiolene complexes
with focus on the hitherto unknown homoleptic iridium dithiolene complexes. When
the complexes [M(mnt)3]3􀀀, M = Rh and Co are chemically oxidized, they decompose
to yield dinuclear complexes with the metal still in oxidation state III. This is not the
case for the corresponding Ir complex which can be oxidized and the oxidation product
[Ir(mnt)3]2􀀀 isolated. The systems are characterised by numerous techniques including
Ir and S XAS, X-ray crystallography and DFT and ab initio calculations.
Chapter 5 details the synthesis of unexpected hexacoordinated silver(I) complexes
with halide ligands, [(CH3CN)3IrX3AgX3Ir(NCCH3)3]+ with X = Cl and Br. The extreme
kinetic robustness of the Ir(III) centers prevents chloride abstraction by Ag(I)
and the unusual complexes are formed instead. A ligand eld and ab initio study of the
ligand complexes [IrX3(NCCH3)3] is performed and compared to the silver complexes
and it is found that the coordination of Ag(I) has no perceivable eect on the Ir ligand
eld.
Chapter 6 details the synthesis of new terminal ruthenium carbide complexes by
ligand substitution on the Ru center. This approach to new, rationally tuned carbide
complexes is virtually unexplored. The reaction of the known carbide complex
[RuC(Cl)2(PCy3)2] with cyanide aords the cyanide analogue [RuC(CN)2(PCy3)2]. The
reaction kinetics are studied with NMR. It is also possible to exchange only one of the
chloride ligands, with the intermediate [RuC(Cl)(NCCH3)(PCy3)2]+ and this control
of the ligand environment opens up the possibility of for instance incorporating the
carbide functionality into other systems.
Several chapters and papers include X-ray spectroscopy measurements and a very
brief introduction to the techniques is given in Appendix A. Throughout the thesis
computational studies of various kinds have been used to help the elucidation of experimental observations and a brief study on the computation of ligand eld transitions
in transition metal complexes is given in Appendix B.
| Original language | English |
|---|
| Publisher | Department of Chemistry, Faculty of Science, University of Copenhagen |
|---|---|
| Number of pages | 367 |
| Publication status | Published - 2015 |