Dinuclear Manganese Complexes Artificial Photosynthesis for

Dinuclear Manganese Complexes
for
Artificial Photosynthesis
Synthesis and Properties
Magnus Anderlund
Department of Organic Chemistry
Stockholm University
2005
Doctoral Dissertation 2005
Department of Organic Chemistry
Arrhenius Laboratory
Stockholm University
Sweden
Abstract
This thesis deals with the synthesis and characterisation of a series of
dinuclear manganese complexes. Their ability to donate electrons to photogenerated ruthenium(III) has been investigated in flash photolysis
experiments followed by EPR-spectroscopy. These experiment shows several
consecutive one-electron transfer steps from the manganese moiety to
ruthenium(III), that mimics the electron transfer from the oxygen evolving
centre in photosystem II.
The redox properties of these complexes have been investigated with
electro chemical methods and the structure of the complexes has been
investigated with different X-ray techniques. Structural aspects and the effect
of water on the redox properties have been shown.
One of the manganese complexes has been covalently linked in a triad
donor-photosensitizer-acceptor (D–P–A) system. The kinetics of this triad has
been investigated in detail after photo excitation with both optical and EPR
spectroscopy. The formed charge separated state (D––P–A+) showed an
unusual long lifetime for triad based on ruthenium photosensitizers.
The thesis also includes a study of manganese-salen epoxidation
reactions that we believe can give an insight in the oxygen transfer mechanism
in the water oxidising complex in photosystem II.
© Magnus Anderlund
ISBN 91-7155-018-6 pp 1-49
Intellecta Docusys AB, Göteborg
2
“ Äntligen ”
Gert Fylking
3
Table of Contents
Abstract ........................................................................................................................... 2
Table of Contents ........................................................................................................... 4
List of Publications ........................................................................................................ 5
List of Abbreviations ..................................................................................................... 6
1. Introduction................................................................................................................ 7
1.1 Basic Mechanism of Photosynthesis ................................................................. 7
1.2 Water oxidation in PS II...................................................................................... 8
1.3 Water oxidation catalysts ................................................................................... 9
1.4 Artificial Photosynthesis................................................................................... 10
2. Synthesis of Manganese Complexes ..................................................................... 11
2.1 Synthesis of ligands........................................................................................... 11
2.2 Synthesis of manganese complexes ................................................................ 14
2.2.1 Synthesis of 18............................................................................................. 14
2.2.2 Synthesis of 19............................................................................................. 14
2.2.3 Synthesis of 20............................................................................................. 15
2.2.4 Synthesis of 21............................................................................................. 16
2.2.5 Synthesis of 23............................................................................................. 16
3. Electrochemistry ...................................................................................................... 19
3.1 The effect of water ............................................................................................. 19
4. Light Induced Oxidations....................................................................................... 21
4.1 EPR-spectroscopy .............................................................................................. 21
4.2 Flash photolysis of 18........................................................................................ 23
4.3 Flash photolysis of 20........................................................................................ 24
4.4 Flash photolysis of 19........................................................................................ 25
4.5 Observations from photolysis experiments of 18, 19 and 20....................... 26
4.6 Flash photolysis of 23........................................................................................ 28
5. X-ray Structures ....................................................................................................... 31
5.1 Crystal structure of 19....................................................................................... 31
5.2 Crystal Structure of 20 ...................................................................................... 32
5.3 Crystal structure of 21....................................................................................... 33
5.4 Manganese ligand spheres in 19...................................................................... 34
5.5 X-ray absorption spectroscopy ........................................................................ 36
6. Oxygen transfer reaction ........................................................................................ 37
7. Concluding Remarks............................................................................................... 39
8. Supplementary Information................................................................................... 41
8.1 Synthesis of 20.................................................................................................... 41
8.2 Chrystal structure determination of 20 .......................................................... 41
References ..................................................................................................................... 45
Acknowledgements..................................................................................................... 49
4
List of Publications
I
Light-indused multistep oxidation of dinuclear manganese complexes for artificial
photosynthesis
Huang, P.; Högblom, J.; Anderlund, M.F.; Sun, L.; Magnuson, A.; Styring, S.
Journal of Inorganic Biochemistry, 2004, 98, 733-745
Reprint was made with the kind permission of the publisher.
II
Synthesis, Structure and Redox Chemistry of a Dinuclear Manganese Complex
with a Novel Unsymmetric N5O2 Ligand
Anderlund, M.F.; Högblom, J.; Shi, W.; Huang, P.; Eriksson, L.; Weihe, H.; Styring, S.;
Åkermark, B.; Magnuson, A.
Manuscript
III
Light Induced Manganese Oxidation and Long-lived Charge Separation in a
Mn2II,II-RuII-acceptor Triad
Borgström, M.; Shaikh, N.; Johansson, O.; Anderlund, M.F.; Styring, S.; Åkermark, B.;
Magnuson, A.; Hammarström, L.
Manuscript
IV
Bridging-mode changes in response to manganese oxidation in two binuclear
manganese complexes – implications for photosynthetic water-oxidation
Magnuson, A.; Liebisch, P.; Haumann, M.; Högblom, J.; Anderlund M.F.; Lomoth, R.;
Meyer-Klaucke, W.; Dau, H.
Submitted
V
A New, Dinuclear High Spin Manganese(III) Complex with Bridging Phenoxy
and Methoxy Groups. Structure and Magnetic Properties
Anderlund, M.F.; Zheng, J.; Ghiladi, M.; Kritikos, M.; Rivière, E.; Sun, L.; Girerd, J.J.;
Åkermark, B.
Submitted
VI
The Effect of Phenolates in the Mn(salen)-Catalyzed Epoxidation Reaction
Linde, C.; Anderlund, M.F.; Åkermark, B.
Submitted
Paper not included in this thesis:
Reverse-flow operation for application of imperfectly immobilized catalysts.
Hung, K.G.W.; Papadias, D.; Björnbom, P.; Anderlund, M.; Åkermark, B.
AIChE Journal, 2003, 49(1), 151-167
5
List of Abbreviations
A
ATP
bpmp
bpy
CV
D
EPR
EXAFS
LHC II
MeCN
NADP+
NADPH
NDI
OAc
OEC
P
P680
P700
pheo
PS I
PS II
terpy
TFA
WOC
XANES
6
electron acceptor
adenosine triphosphate
2,6-bis((N,N-di(pyridylmethyl)amino)methyl)-4-methylphenol
2,2’-bipyridine
cyclic voltammetry
electron donor
electron paramagnetic resonance
extended X-ray absorption fine-structure
light harvesting complex II
acetonitrile
niccotinamide adenine dinucleotide phosphate
niccotinamide adenine dinucleotide phosphate, reduced form
naphthalene diimide
acetate
oxygen evolving centre
photosensitizer
reaction centre of photosystem II
reaction centre of photosystem I
pheophytin
photosystem I
photosystem II
2,2’:6’,2’’-terpyridine
trifluoroacetic acid
water oxidation complex
X-ray absorption near-edge spectroscopy
1. Introduction
The never ending demand of energy in combination with environmental
issues has made mankind aware of the future need for renewable energy
sources. It is especially society’s demand for transportation that will cause
problems due to the limited resources of fossil fuel. Our society therefore needs
to find new (or not utilized) energy sources. In the search for renewable energy,
solar energy has emerged as a possible sustainable energy source.
Nature has created a process which is capable of harvesting the solar
energy that reaches our planet and use it to sustain life. This process is called
photosynthesis and the chemical reactions within it are probably the most
important reactions taking place on earth 1. It is the photosynthesis in
cyanobacteria, certain algae and higher plants that produce the oxygen we
breathe, most of our food and much of our raw materials. If mankind could
understand and mimic the basic principles of photosynthesis, an endless and
non-polluting energy source would become accessible.
1.1 Basic Mechanism of Photosynthesis
The protein complexes of the photosynthetic machinery are located in the
thylakoid membrane of the chloroplasts. This machinery includes light
harvesting proteins, reaction centers, electron transport chains and ATP
synthase (ATP = adenosine triphosphate). The initial step in photosynthesis is
the absorption of light by the light harvesting complex II (LHC II). LHC II
consists of an antenna system that absorbs light and transfer the energy to the
reaction centre (P680) of photosystem II (PS II). The exited P680 reduces a
nearby pheophytin (pheo) to form a primary charge separation 2 (eq 1.1).
hν
P680 pheo ⎯⎯
⎯→
P680+ pheo–
(1.1)
The negative charge is transferred through an ingenious chain of electron
acceptors via the cytochrome bf complex to photosystem I (PS I). In PS I another
reaction centre (P700) is responsible for providing the reducing power for the
conversion of NADP+ to NADPH.
7
The P680+ formed in the primary charge separation extracts an electron
from a nearby tyrosine in the D1 protein. This tyrosyl radical abstracts an
electron from the oxygen evolving complex (OEC), also called the water
oxidizing centre (WOC). The OEC serves as a charge accumulator that enables
water oxidation with release of O2 without creating strongly oxidizing
intermediates that could harm the organism.
The electron transfer chain releases protons into the thylakoid lumen from
PSII and cytochrome bf. This generates a proton gradient that is used to
produce ATP in the ATP synthase. The NADPH and ATP produced in
photosynthesis are used by the organism to convert CO2 to carbohydrates.
1.2 Water oxidation in PS II
3
As mentioned above excitation of P680 drives the fourfold stepwise
oxidation of the OEC. It was the work of Joliot 4 and Kok 5 that developed the
basic principles for the function of the oxygen evolving complex (OEC),
visualised in the Kok cycle, Scheme 1.1.
Scheme 1.1 Kok cycle
S0
hv
S1
hv
O2 + 4H +
S2
hv
S3
hv
[S4]
2H2O
The five different oxidation states are assigned as S0–S4 where S4 is a shortlived intermediate state were oxygen is released and water binds to the
complex to reform the S0 state. As the Kok cycle indicates, protons are released 6
from OEC and probably done so in a 1:0:1:2 (S0–S1–S2–S3–S0) pattern. This is
consistent with an observed charge accumulation in the S1–S2 transition 7.
8
The actual structure of the OEC has been debated during many years,
mostly based on spectroscopic and X-ray diffraction signatures 8. With a recent
X-ray crystal structure with a resolution of 3.5 Å 9 more details of the structure
have started to emerge. The crystal structure showed a Mn3Ca-cubane with a
forth manganese attached to the cubane, perhaps via an oxo-bridge. Structural
features derived from EXAFS data are in agreement with this crystal structure.
However, it is now clear that the very high X-ray fluxes in this X-ray diffraction
experiment reduced the high valence manganese to manganese(II) and thereby
distorted the structure 10. Future refinement of the X-ray techniques will
hopefully improve the understanding of the structure that will help to elucidate
the water oxidation mechanism in PSII.
1.3 Water oxidation catalysts
An enormous amount of manganese complexes have been synthesised to
provide structural and mechanistic insight in the oxygen evolution from OEC in
PS II 3b,11. Unfortunately, the vast majority of these complexes do not oxidise
water but there are a few manganese and ruthenium complexes that in
homogeneous solutions are capable to do that 12. Meyer et al. 13 have reported a
ruthenium dinuclear complex, [(bpy)2(H2O)RuIIIORuIII(H2O)(bpy)2]4+ that
catalyses the oxidation of water by CeIV. The manganese analogue,
[(bpy)2MnIII(µ-O)2MnIII(bpy)2]3+
14
oxidises water in aqueous suspensions but
not in solution. Manganese complexes of Schiff bases 15 and a covalently linked
porphyrin dimer 16 have been reported to oxidise water in homogeneous
solution. Recently, Yagi and Narita showed that the complex
[(terpy)(H2O)MnIIIOMnIII(H2O)(terpy)]3+ catalysed water oxidation, with CeIV as
oxidant, when it was adsorbed onto kaolin clay 17. They also showed that in
solution the complex did not evolve oxygen and thereby they challenged earlier
results from Limburg et al. 18 who claimed that the complex did oxidise water
and evolve O2 when treated with NaClO or KHSO5. Limburg et al. claimed that
the oxygen atoms in O2 came from water and not the oxidants.
9
1.4 Artificial Photosynthesis
The dream of artificial photosystem is to create a supramolecular system
mimicking the photosynthesis in nature 12,19. This system needs a
photosensitizer (P), to harvest the light, coupled to an electron donor (D) and
acceptor (A) that can create a long lived charge separated state (D––P–A+).
This charge separation should facilitate the oxidation of water to give oxygen
and some energy rich substance (Figure 1.1).
hv
e
O2
D
H 2O
e
P
H2
A
2H
Figure 1.1 Principle of an artificial system that consist of a
photosensitizer (P), electron acceptor (A) and donor (D).
10
2. Synthesis of Manganese Complexes
The synthesis part of this thesis describes five dinuclear manganese
complexes 18-21 and 23. The complexes are all based on the same principle, that
manganese is held by chelating ligands attached to a bridging central phenol 20.
2.1 Synthesis of ligands
As shown in Scheme 2.1, 4-methylphenol 1 was formylated to bisaldehyde 2. Reduction followed by chlorination gave 4 which were further used
as central building block for the synthesis of the ligands in paper I, IV and V.
Scheme 2.1
N
N
N
N
NaBH4
SOCl2
TFA
OH
O
1
OH O
OH OH
2
OH
Cl
3
OH
Cl
4
As chelating “arms”, secondary amines 5, 6 and 7 were used to prepare ligand
8, 9 and 10, respectively, by reaction with the phenol 4 (Scheme 2.2 and 2.3).
Scheme 2.2
N
H
N
N
5
N
Cl
OH
4
Cl
N
N
OH
N
N
N
8
11
Scheme 2.3
H
N
N
6
OH
N
OH
N
OH
HO
N
N
9
Cl
OH
Cl
H
N
4
N
7
OH
N
OH
N
OH
HO
N
N
10
The amines were synthesised via imine condensation between 2-aminomethyl
pyridine 11 and suitable aldehydes 12, 13, 14, followed by reduction.
Scheme 2.4
11
1)
O
N
NH2
N
2) NaBH4
N
11
1)
O
NH2
N
H
N
2) NaBH4
OH
6
11
1)
O
12
N
OH
13
14
N
5
12
OH
H
N
N
NH2
H
N
2) NaBH4
OH
7
N
Since partial reduction of the bis-aldehyde 2 failed (not reported), the
unsymmetrical phenol 15 was obtained by partial oxidation of the benzylic
alcohols in 3 by manganese dioxide 21. Chlorination of the benzylic alcohol in 15
followed by reaction with 7 gave 16. Reduction of the carbonyl in 16 followed
by chlorination and reaction with 5 gave the unsymmetrical ligand 17.
Scheme 2.5
1) SOCl2
2)
MnO2
H
N
OH OH OH
O
3
N
OH
OH OH
7
15
1) NaBH4
2) SOCl2
O
OH
N
3)
OH
N
N
16
H
N
N
N
N
OH
N
OH
5
N
N
17
13
2.2 Synthesis of manganese complexes
2.2.1 Synthesis of 18
Complex 18 was synthesised by reaction of 8 with manganese(II) acetate 22.
It was isolated as a crystalline dinuclear Mn2II,II perchlorate salt with two µacetates (Scheme 2.6). Care had to be taken to exclude air, otherwise an oxidized
impurity of a mixed Mn2II,III complex could be detected by EPR spectroscopy
(EPR = electron paramagnetic resonance). The X-ray structure for this complex
was published during this work by Blondin et al. 23.
Scheme 2.6
+
N
N
OH
N
N
N
8
N
Mn(OAc)2
N
N
Mn
MeOH
N
N
O
N
Mn
O O OO
N
18
2.2.2 Synthesis of 19
Complex 19 was obtained by reaction of 17 with manganese(III) acetate
(Scheme 2.7). The Mn2II,III complex, as perchlorate salt, was crystallised from the
reaction solution (No neutral Mn2III,III complex has been isolated). Recrystallisation
gave dark brown-red single crystals suitable for X-ray diffraction.
The reduction of MnIII to MnII occurs possibly by oxidation of solvent
(ethanol) or by disproportionation of MnIII to MnO2 and MnII in the presence of
water 24. Although no MnO2 has been detected it can not be ruled out that
colloidal MnO2 is formed in the reaction. This means that some water should be
present during the synthesis of 19 to facilitate the manganese reduction.
14
Scheme 2.7
+
N
N
N
N
Mn(OAc)3
OH N
HO
N
EtOH
N
Mn
N
N
O
OO OO
17
O
Mn
N
19
2.2.3 Synthesis of 20
As above, 10 was reacted with manganese(III) acetate to give 20. It was
isolated as a Mn2III,III complex both as perchlorate (Chapter 8.1) and
hexafluorophospate salt 25 both with two µ-acetates (Scheme 2.8). The
perchlorate was micro-crystalline, slowly precipitating out, while the
hexafluorophospate precipitated very rapidly, often containing an impurity of a
Mn2II,III complex. The perchlorate salt of 20 was recrystallised and the X-ray
structure was determined, see below (Chapter 5.1 and 8.2).
Scheme 2.8
+
N
Mn(OAc)3
OH N
OH
HO
N
N
10
N
O
Mn
EtOH
N
N
O
O
Mn
O O O O
N
20
15
2.2.4 Synthesis of 21
Ligand 9 was reacted with manganese(II) perchlorate in the presence of
triethylamine to facilitate the deprotonation of the ligand. The complex was
isolated as perchlorate salt with a µ-methoxy, methoxy and methanol (Scheme
2.9). Recrystallisation gave dark black-green single crystals suitable for X-ray.
Scheme 2.9
+
N
OH N
N
N
OH
Mn(ClO4)2
HO
9
N
O
Mn
MeOH
N
N
O
O
O
Mn
O
OH
N
21
Although 21 is a Mn2III,III complex it is interesting to note that oxidation of
manganese(II) is the only way the complex could be isolated. Complexation with
manganese(III) salts as with 19, failed. With manganese(III) acetate a mixture of
Mn2II,III and Mn2III,III with µ-acetates was obtained (unpublished results).
2.2.5 Synthesis of 23
The synthesis of the precursor 22 has been described earlier 26 and is not
within the scope of this thesis. When preparing [Ru(bpy)3]2+-complexes with
differently substituted bipyridines, mixtures of geometrical isomers are
obtained. In 23 that contains two naphthalene diimide acceptors and one Mn2II,II
donor, four geometrical isomers are possible and it is assumed that a statistical
mixture of these was isolated.
The precursor 22 was reacted with manganese(II) acetate to give 23
(Scheme 2.10). Care was taken to exclude air to prevent unwanted oxidation of
the manganese, and the reaction was performed in the dark to prevent photoinduced reaction. The complex was isolated as hexafluorophospate salt and not
perchlorate salt as the related dinuclear manganese complex 18.
16
Scheme 2.10
O
2+
O
C8H17
C8H17
O
O
O
O
O
O
N
N
N
Ru
N
N
N
Mn(OAc)2
HN
O
EtOH/MeCN
EtO2C
N
N
OH
N
N
N
N
22
O
3+
O
C8H17
C8H17
O
O
O
O
O
O
N
N
N
Ru
N
N
N
HN
O
EtO2C
N
N
Mn
N
N
O
N
Mn
O O OO
N
23
17
18
3. Electrochemistry
The redox potentials in dry acetonitrile for 18, 19 and 20 are presented in
Table 3.1. The trend is quite clear; the redox potential is lowered with increased
negative ligand charge which can balance the higher positive charge at the
metal centre. For 18, the two oxidations at ∆E1/2= 0.12 and 0.68 V are chemically
reversible and confirmed as metal centred, while the third oxidation at Epa =
1.75 is non reversible. In 19 the reduction and first oxidation at ∆E1/2= – 0.53 and
0.38 V respectively are metal-centred and chemically reversible. The second
oxidation at ∆E1/2= ~0.75 V is not reversible at normal cyclic voltammogram
(CV) time-scales (v= 0.100 Vs–1) but quasi-reversible at higher scan rates.
In 20 there are two quasi-reversible reductions at ∆E1/2= –0.34 and –0.70 V
and two almost merged non-reversible oxidations, the first at ∆E1/2 = 0.58 V, the
second at ∆E1/2= 0.85 V. The second oxidation wave leads to degradation of the
material in bulk electrolysis.
Table 3.1a Cyclic voltammetry data obtained in dry acetonitrile.
Complex
a
b
∆E1/2 (V) vs Fc+/0
Mn2II,III / Mn2II,II
Mn2III,III / Mn2II,III
Mn2III,IV / Mn2III,III
18
0.12
0.68
1.75 b
19
– 0.53
0.38
0.75 b
20
– 0.70
– 0.34
0.58
All redox potentials are relative to the ferrocenium/ferrocene couple (Fc+/0)
Epa value; The ∆E1/2 value not determined due to irreversibility of this oxidation.
3.1 The effect of water
When water is added in the electrochemical measurements of 18 the most
pronounced effect is a shift to lower potential for the third oxidation wave to
~1.15 V in 1% water and ~0.95 V in 10 % water. The potential and chemically
reversibility of the first process is nearly unaffected by the presence of water
(v:v ≤10%). The second oxidation wave becomes broader and chemically
irreversible when water is added.
19
For 19 the first oxidation wave is unaffected by the presence of 1% water.
This means that the Mn2II,III starting material and the Mn2III,III state is stable to
water under those conditions. For the second oxidation some increase in anodic
current is observed which might indicate a subsequent oxidation of the
products of the second oxidation process. In 10% water, the Mn2II,III complex
probably reacts with water and a depletion of the first oxidation wave at 0.4 V
could be observed. On further oxidation two new anodic waves arise at 0.6 V
and 0.9 V. These two waves originate most probably from successive oxidation
of the product from Mn2III,III that reacted with water after the first oxidation
wave. On the reverse scan two cathodic peaks at –0.1 V and 0.5 V are observed
which, most likely, are the reduction of the products formed in the oxidation
processes at 0.6 V and 0.9V, respectively. The redox behaviour of 20 has not yet
been studied in the presence of water.
20
4. Light Induced Oxidations
It has been demonstrated that flash photolysis, using [Ru(bpy)3]2+ as
photosensitizer and a sacrificial electron acceptor, for example CoIII(NH3)5Cl,
produces [Ru(bpy)3]3+, a versatile one electron oxidant 19. One of the advantages
of photo-oxidation in this manner over the use of chemically produced
[Ru(bpy)3]3+ is the uniform distribution of the oxidant throughout the sample.
This eliminates mixing problems with high local concentration of the oxidant.
By applying more flashes to the sample, it is possible to follow the lightinduced oxidation of, for example a manganese complex, with a suitable
spectroscopic method. The overall redox reaction in such a system is
schematically shown below (eq. 4.1 and 4.2).
[Ru(bpy)3]2+ + CoIII
hv
⎯
⎯→
[Ru(bpy)3]3+ + CoII
(4.1)
[Ru(bpy)3]3+ + Mn2RED
⎯
⎯→
[Ru(bpy)3]2+ + Mn2OX
(4.2)
4.1 EPR-spectroscopy
The flash photolysis oxidations discussed here have been followed by Xband EPR spectroscopy. The distinct features of the EPR signals from different
manganese species are shown in Figure 4.1 a-d.
Monomeric MnII has an electronic spin of S = 1/2 that couples to the
manganese nuclear spin of I = 5/2 and is observed as a distinct six-line signal
around g = 2 in EPR-spectroscopy (Figure 4.1a). Dinuclear Mn2II,II complexes have
integer total spin, with a ground state (S=0) at 4 K (no EPR-signal), but often
display EPR visible, excited states (S≠0), at temperatures above ~7 K 27 (Figure
4.1b). Mixed valence Mn2II,III complexes display characteristic EPR signals in the g
= 2 region at 4 K (fig 4.1c), arising from the S=1/2 electronic ground state that
couples to both manganese nuclei. At elevated temperatures, the first and second
exited states become populated and give rise to other detectable features
28
.
21
Mn2III,III complexes have an integer spin system. They might produce EPR active
exited states at higher temperatures, but so far no one has reported such a
feature. The mixed valence Mn2III,IV display, as Mn2II,III, strong EPR signals in the
g = 2 region at cryogenic temperatures, arising from the S=1/2 ground state
(Figure 4.1d) but the Mn2III,IV signal is significantly narrower than the Mn2II,III
signal 29. Taken together all these features allow identification and quantification
of mixtures of manganese complexes at different oxidation states.
a)
b)
c)
*
100
d)
200
300
400
500
Magnetic Field (mT)
Figure 4.1 Typical X-band EPR-spectra: a) monomeric MnII, b) dinuclear
Mn2II,II, c) dinuclear Mn2II,III, d) dinuclear Mn2III,IV , * indicate
removed feature from a reduced electron acceptor (CoII).
Spectra a), b) and c) are from compound 19 in different
oxidation states while spectrum a) originates from MnIICl2.
22
4.2 Flash photolysis of 18
Earlier investigations demonstrated oxidation of 18 to a Mn2III,IV state
using photo generated [Ru(bpy)3]3+ as oxidant 30. This experiment failed to
detect the Mn2II,III intermediate, but it was proposed that tree consecutive oneelectron reactions occurred to give the Mn2III,IV state. This experiment was
performed in water solution with 10 % acetonitrile and later results show that
under these conditions acetate is no longer coordinated to the complex 31. One
plausible reason why Mn2II,III was not detected might be that the driving force
for the oxidation of Mn2II,II to Mn2II,III is lower than for oxidation of Mn2II,III to
Mn2III,III. This would prevent accumulation of Mn2II,III and explain the absence of
spectral evidence for that oxidation state in the experiment.
In paper I the experiment was repeated in acetate buffer. Here the
formation and disappearance of both Mn2II,III and Mn2III,IV could be followed
(Figure 4.2). This result demonstrates the stepwise one-electron oxidation of the
manganese complexes even though the Mn2II,III intermediate never reaches a high
concentration. In this case the acetates may suppress the exchange of coordinated
acetate for water and change the driving force for the two mentioned oxidations.
Figure 4.2 The result of photo induced oxidation of 18 with
[Ru(bpy)3]2+ and CoIII(NH3)5Cl in acetonitrile:water =
1:9. Flash number dependent decrease of Mn2II,II (-•-)
and formation of Mn2II,III (-○-) and Mn2III,IV (-∆-).
Figure from paper I.
23
4.3 Flash photolysis of 20
Oxidation with photogenerated [Ru(bpy)3]3+ of 20 starting from Mn2III,III,
resulted in the formation of Mn2III,IV (Figure 4.3a). On further oxidation a
decrease in the Mn2III,IV EPR signal was observed until it completely disappears.
The absence of new EPR features and the lack of precipitation of MnO2
indicated that an EPR silent manganese species was reached. This oxidation
product may be a strongly coupled Mn2IV,IV with an integer spin (EPR silent) or
a ligand based radical, strongly coupled to the Mn2III,IV dimer.
On further oxidation with more flashes a radical signal overlaying a weak
six-line signal appeared in the composite EPR spectra (Figure 4.3a 750 fl). The
six-line signal had similarities to a “typical” monomeric MnII signal while the
radical had features of a deprotonated phenolic radical (high g-value = 2.0046)
with unusually enhanced magnetic relaxation properties. This enhanced
relaxation is usually seen when the radical has a strong magnetic interaction
with metals, as in the case of the Tyrosine-Z radical in PS II which is situated ca
7 Å from the CaMn4-cluster 32.
a)
b)
0 fl
0.16
50 fl
350 fl
0.12
(mM)
150 fl
0.08
750 fl
0.04
2500
3000
3500
Magnetic Field (mT)
4000
4500
0
200
400
600
800
Flash number
Figure 4.3 The result of photo induced oxidation of 20 with [Ru(bpy)3]2+ and
CoIII(NH3)5Cl in acetonitrile:water = 1:1. a) Selected EPR spectra after
the sample had been exposed to 0, 50, 150, 350 and 750 flashes. b) Flash
number dependent formation and disappearance of Mn2III,IV (-•-).
Figure from paper I.
24
4.4 Flash photolysis of 19
Oxidation by flash photolysis of the dinuclear Mn2II,III complex 19, resulted
in a rapid decrease of the Mn2II,III EPR-signal. A new signature from a strongly
coupled Mn2III,IV species started to appear after a short lag phase (Figure 4.4).
The observation of a lag phase indicates that a Mn2III,III species was probably
formed as an intermediate. On further oxidation the Mn2III,IV signal peaks, and
subsequently starts to decrease. Also in this case, the disappearing EPR
spectrum was not immediately replaced by any other paramagnetic species.
The most likely explanation is that the Mn2III,IV complexes were further oxidized
to an EPR inactive form. This oxidation product may be a strongly coupled
Mn2IV,IV or a ligand based radical, strongly coupled to the Mn2III,IV dimer.
As for 20, even further oxidation led to the formation of a monomeric MnII
signal and a phenolic radical with unusual, enhanced relaxation behaviour.
0.5
0.4
0.3
(mM)
(mM)
0.4
0.2
0.1
0.3
0.0
0.2
0
10 20 30 40 50
Flash number
0.1
0.0
0
50
100
150
Flash number
200
250
Figure 4.4 The result of photo induced oxidation of 19 with
[Ru(bpy)3]2+ and CoIII(NH3)5Cl in acetonitrile:water = 1:1.
Flash number dependent decrease of Mn2II,III (-○-) and
formation of Mn2III,IV (-•-). Figure from paper II
25
4.5 Observations from photolysis experiments of 18, 19 and 20
At a first glance it can be hard to see how an oxidation of a complex in the
Mn2III,IV state could result in formation of a monomeric MnII. It is easier to
understand degradation of the complex to colloidal MnO2. One possibly way to
get degradation and reduction to MnII should be if the ligand was easily oxidised.
High valence manganese could in that case oxidise the ligand and thereby get
reduced to MnII. Another candidate to be oxidised is water which would indicate
that the complexes work as a non catalytic water oxidizing agent.
When the amount of flashes needed for oxidising 18, 19 and 20 is taken
under consideration interesting observations can be made. For example, 18
needs about 40 flashes to reach beyond Mn2III,IV (Figure 4.2), a four electron
oxidation while 19 needs 300 flashes for three electron oxidation (Figure 4.4)
and 20 needs about 600 flashes for a two electron oxidation (Figure 4.3b). From
our quantification it is clear that a substantial amount of 18 is oxidised to high
valence and the difference can not be explained by low yields in the flash
photolysis. There are at least two mechanisms that could explain this.
First reductive quenching of photo exited [Ru(bpy)3]2+ were the electron
transfer goes backwards and reduces the manganese complex instead of the
sacrificial acceptor to form [Ru(bpy)3]3+. However, when redox behaviour of the
complexes is considered, it is unlikely that reductive quenching can explain
why such large amount of flashes is needed to oxidise 19 and 20. The increased
negative charge in the ligand of 19 and 20 lowers the potential for oxidation of
the complex. This means that reduction of Mn2III,IV should be easier in 18, less
stabilized, and photo oxidation of 18 should undergo more efficient reductive
quenching than 19 and 20. In that case, the photo oxidation would need more
flashes for 18 than 19 and 20, and that is not the case. This suggests that the
reductive quenching is not a plausible explanation of the observed behaviour.
The second mechanism that might explain the different flash behaviour
involves energy transfer from photo exited [Ru(bpy)3]2+ to the manganese
complexes which would not generate any oxidation. This is a more likely
mechanism, as the UV-Vis spectra of the complexes 18, 19 and 20 respectively
shows different overlaps in the absorption in the Mn2III,III state on the
[Ru(bpy)3]2+ absorption (fig 4.5). The overlap integrals are (J/10–14 M–1cm3): 1.18
(18), 1.50 (19) and 2.22 (20). When assuming a distance of 10Å, the rate constants
26
of Förster energy transfer are (kF/108s–1): 1.3, 1.6, 2.4 respectively 33. If similar
relative rates for energy transfer are assumed for the Mn2III,IV states and
different experimental condition (concentration etc) are considered, energy
transfer might explain some of the observed differences in the amount of
flashes needed for the light induced oxidation of 18, 19 and 20.
5
0.5
4
0.4
8
3
2
0.3
4
0.2
Inorm x1000
ε / 104 M−1cm−1
ε / 104 M−1cm−1
6
2
1
0.1
0
0.0
200
250
300
λ / nm
350
400
600
800
0
1000
λ / nm
Figure 4.5 Absorption spectra of the Mn2III,III states of 18 (-·-), 19 (---) and 20 (—)
and normalized emission spectrum of [Ru(bpy)3]2+ in acetonitrile 33.
27
4.6 Flash photolysis of 23
In order to study the interaction between the manganese moiety and the
ruthenium photosensitizer in more detail, systems where a manganese electron
donor and an electron acceptor were covalent linked to the ruthenium
photosensitizer. A previous study 26 of the triad bpmp–RuII–NDI 22 (bpmp =
2,6-bis((N,N-di(pyridylmethyl)amino)methyl)-4-methylphenol) showed that
both the phenol and the tertiary amine in bpmp could act as electron donors.
Another study 22 of the compound without the covalent linked NDI acceptor
(naphthalene diimide), Mn2II,II–RuII(bpy)3 24 (Scheme 4.1), performed with
external acceptors showed a fast (~110 ns for the main component) electron
transfer from the manganese moiety to photo-oxidised ruthenium. This electron
transfer was limited by diffusion of the external electron acceptor. In paper III
the photo-induced electron transfer in Mn2II,II–RuII–NDI, 23 was studied by time
resolved optical and EPR spectroscopy, following laser flash excitation.
Scheme 4.1
3+
N
N
N
Ru
N
N
N
HN
O
EtO2C
N
N
Mn
N
N
O
Mn
O O OO
24
28
N
N
Transient absorption spectroscopy of 23 at room temperature showed that
photoexcitation of the photosensitizer, RuII(bpy)3-moity, lead to formation of a
NDI-radical. The recovery of the ground state of the photosensitizer followed
the same kinetics as the formation of the radical. The fact that no long-lived
RuIII was observed suggested that a fast (τ <30 ns) secondary electron transfer
step followed the reduction of NDI. In accordance with EPR spectroscopy, this
electron transfer was proposed to come from the Mn2II,II moiety that was
oxidised to a Mn2II,III state. The optical absorption of the manganese redox states
was too small to be observed in the transient absorption experiment, although
the following photoinduced reaction sequence was proposed (eq. 4.3):
Mn2II,II–RuII–NDI
hν
⎯⎯
⎯→
Mn2II,III–RuII–NDI•–
(4.3)
The lifetime of the charge-separated state at 298 K could be well fitted with
three exponents: τ1 = 15 µs (A1 = 0.5), τ2 = 200 µs (A2 = 0.25) and τ3 = 2.3 ms (A3
= 0.25). The average lifetime was very long, at least in the order of two
magnitudes longer than previously reported triads based on RuII(bpy)3 34.
At 140 K the recombination was even slower with τ1 = 100 ms (A1 = 0.45),
τ2 = 500 ms (A2 = 0.55) that was in good agreement with the lifetimes obtained
by EPR spectroscopy. In addition to these processes, another component on the
minute time-scale was observed in the EPR experiment that was not visible in
the optical measurement. One possible explanation of this very long lifetime
could be formation of aggregates involving π-stacking of the NDI-moieties. This
could permit inter-molecular electron transfer and stabilisation of the NDIradical making the charge recombination a bimolecular “slow” process.
The quantum yields of the fully charged separated states at 298 and 140 K
for the triad 23 were calculated to ΦCS ~20% and ΦCS ~ 40% respectively.
29
30
5. X-ray Structures
5.1 Crystal structure of 19
The crystal structure of 19 (Figure 5.1) which is a monovalent cation, with
perchlorate as counter-ion (not shown) has been determined by single crystal Xray diffraction. The anisotropic displacement parameters of the oxygens in
perchlorate are heavily anisotropic, in agreement with a weakly coordinated
perchlorate ion. The unusually low calculated density is 0.950 g cm–1 and can be
explained by non-ordered solvent molecules that are present in the structure.
N2
N3
N41
Mn2
O51 O1B
O31
O1A
N21
Mn1
O2A
N11
O2B
Figure 5.1 Crystal structure of 19, ORTEP view with 50% probability ellipsoids
of the Mn-atoms and the rest of the atoms being isotropic. Hydrogen
omitted for clarity. Figure drawn by Diamond 35.
The data show that the two manganese ions are bridged by the central
phenolate oxygen and two bidental acetate groups. The coordination of Mn(1)
is completed by the two pyridyl nitrogen and one amine nitrogen of one branch
of the ligand, resulting in a N3O3 ligand sphere. In the other branch, the oxygen
atom from the tert-butyl substituted phenolate coordinates Mn(2) in a trans
position to the bridging phenolate group. The N2O4 coordination sphere of
Mn(2) is completed by the pyridyl and amine nitrogens. The Mn–Mn distance is
31
3.498 Å, and the Mn(1)–O–Mn(2) angle is 116.95º. This is similar to and in the
range of other Mn2II,III complexes 28b,36. A close-up view of the local environment
of the manganese coordination sphere is shown in figure 5.4a.
Bond valence calculations 37 gave the valence 2.1 for Mn(1) and 3.2 for
Mn(2) which thereby can be identified as the MnII and MnIII respectively. In
conclusion, the chrystal structure suggests that the terminal phenoxyl in one
branch of the ligand favors coordination of MnIII over MnII.
5.2 Crystal Structure of 20
As fore 19, the crystal structure of 20 is a monovalent cation,
counterbalanced with a perchlorate ion in the crystal structure (figure 5.2). The
anisotropic displacement parameters of the oxygen’s in the perchlorate are
heavily anisotropic completely in agreement with a weakly coordinated
perchlorate ion. The calculated density of the crystal is rather low (1.226 g cm–1)
as there are non-ordered solvent molecules present in the structure.
N2
N5
O1
O7
N4
Mn2
O2
N6
O3
O4
Mn1
O6
O5
Figure 5.2 Crystal structure of 21, ORTEP view with 50% probability ellipsoids
of the Mn-atoms and the rest of the atoms being isotropic. Hydrogen
omitted for clarity. Figure drawn by Diamond 35.
Bond valence calculations 37 gave the valence 3.4 for Mn(1) and 3.5 for
Mn(2), thus both manganese ions could be identified as MnIII. Both manganese
nuclei have an octahedrally N2O4 coordination sphere connected to each other
32
via a common corner (O(1)). The two octahedra are further connected via the
two acetate groups. A close-up view of the local environment of the manganese
coordination sphere is shown in figure 5.4b. Selected crystal data, bond lengths
and angles are presented in Table 8.1 and 8.2 .
5.3 Crystal structure of 21
Both manganese ions in the dinuclear complex exhibit a highly irregular
N2O4 coordination sphere. The coordination environment around each metal
centre shows that Mn(1) is coordinated by two amine nitrogens, two phenolate
oxygens and two methoxide oxygens whereas Mn(2) is coordinated by two
amine nitrogens, two phenolate oxygens, one methoxide oxygen and one
methanolic oxygen. One interesting structural feature is the hydrogen bond
between methanol (O(6)) and the phenolic oxygen (O(4)) (not shown).
Bridging angles Mn(1)–O(1)–Mn(2), phenolate and Mn(1)–O(2)–Mn(2),
methoxide are 104.7° and 97.5°, respectively. The Mn–Mn distance of 3.122 Å is
in accordance with other trivalent Mn2(µ-OR)2 complexes 3b,38. Calculated bond
valence sums, 3.08 and 3.11, respectively, for Mn(1) and Mn(2) are in agreement
with the stipulated trivalent oxidation states of the manganese. The atomic
parameters where taken from the work of O´Keeffe and Brese 39.
N1
O1
Mn1
O4
N2
O6
N3
Mn2
O3
N4
O2
O5
Figure 5.3 Crystal structure of 22, ORTEP view with 50% probability ellipsoids
of the Mn-atoms and the rest of the atoms being isotropic. Hydrogen
omitted for clarity. Figure drawn by Diamond 35.
33
5.4 Manganese ligand spheres in 19
A comparison between the manganese ligand spheres in the crystal structure
of 19 with corresponding manganese in 20 and Mn2II,III(bpmp)(OAc)2(ClO4)2 25
28
reveals striking similarities. The MnII in 19 has the same ligand sphere as the
MnII in 25 (N3O3 coordination) while the MnIII has the same ligand sphere as
one of the manganese in 20 (N2O4 coordination). Bond lengths and angels for
respective manganese in 19 (Mn(1) = MnII and Mn(2) = MnIII) and for the
corresponding data from the structures of 20 and 25 are listed in Table 5.1. The
bond distances around MnIII in 19 are shorter in general than corresponding
bonds in 20 while around the MnII there are both shorter and longer bonds
compared to 25. One interesting observation is the compression of three, out of
four distances between manganese and oxygen in the bridging acetates. There
are also a slight decrease in the distances between the manganese and the
bridging phenol for both Mn(1) and Mn(2).
N2
N41
O31
N21
Mn2
Mn1
N3
O1A
O2A
N11
O51
O2B
O1B
N5
N2
O1
O7
Mn2
N4
N6
O3
Mn1
O2
O6
O4
O5
Figure 5.4 View of the coordination polyhedra around
both manganese atoms in: a) 19 b) 20. Figure
drawn by Diamond 35.
34
Table 5.1 Selected bond lengths (Å) and angels (˚) for the manganese
ligand sphere in 19 (Mn(1) = MnII and Mn(2) = MnIII) compared
with representative value for the manganese ligand spheres in
20 (Table 8.2) and 25 28b.
Bond
Mn(1) – O(31)
Mn(1) – N(11)
Mn(1) – O(2)A
Mn(1) – N(21)
Mn(1) – O(2)B
Mn(1) – N(2)
O(31)–Mn(1)–N(11)
O(2)B–Mn(1)–N(2)
O(2)A–Mn(1)–N(21)
Mn(2) – O(31)
Mn(2) – O(51)
Mn(2) – O(1)A
Mn(2) – N(3)
Mn(2) – O(1)B
Mn(2) – N(41)
O(51)–Mn(2)–O(31)
O(1)A–Mn(2)–N(3)
O(1B)–Mn(2)–N(41)
19
20
25
Difference
(%)
2.179
2.256
2.127
2.281
2.090
2.318
2.193 (4)
2.210 (6)
2.166 (4)
2.271 (6)
2.066 (6)
2.324 (5)
–0.6
2.0
–1.8
0.4
1.1
–0.3
156.78 (19)
164.6 (2)
169.2 (2)
156.4 (2)
166.2 (2)
169.7 (2)
0.2
–1.0
–0.3
1.922 (4)
1.820 (4)
1.972 (4)
2.114 (4)
2.154 (5)
2.266 (6)
1.946 (11)
1.856 (12)
2.065 (13)
2.105 (14)
2.226 (12)
2.306 (14)
–1.3
–2.0
–4.7
0.4
–3.3
–1.7
177.1 (2)
169.45 (18)
169.02 (19)
175.5 (5)
170.4 (5)
172.5(5)
0.9
–0.6
–2.1
35
5.5 X-ray absorption spectroscopy
In paper IV, 18 and 20 have been investigated in different oxidation states in
solution by X-ray absorption near-edge spectroscopy (XANES) and extended Xray absorption fine-structure (EXAFS). In XANES the positions of the X-ray Kedge spectra reflect the manganese oxidation state and EXAFS provide insight in
structural changes of 18 and 20 that are associated with oxidation-state changes.
The magnitude of the edge shift observed in XANES for the samples in
different oxidation states agrees with the anticipated values for one electron
oxidations. The purity of these samples, with respect to oxidation state and
integrity of the complex clearly exceeds 80% for both 18 and 20. The XANES
spectra are compatible with the following oxidation states: Mn2II,II, Mn2II,III and
Mn2III,III in 18 and Mn2II,III, Mn2III,III and Mn2III,IV in 20.
The EXAFS analysis indicates minor differences in the Mn–Mn distance
between the Mn2II,II and the Mn2II,III states in 18 and the Mn2II,III and Mn2III,III
states in 20, in contrast to a decrease in the Mn–Mn distance by more than 0.5 Å
upon formation of the Mn2III,III state in 18 and the Mn2III,IV state in 20. These
findings are in agreement with the assumption that in both complexes the first
oxidizing transition is not related to major structural changes, whereas the
second oxidation is associated with a modification of the bridging mode
between the manganese ions in combination with oxidation state changes.
36
6. Oxygen transfer reaction
Irrespective of the mechanism for water oxidation in PS II, one thing is
clear: an oxygen–oxygen bond has to be formed! One way of looking at this is to
see the bond-formation as an oxygen transfer reaction were the oxygen from
one water molecule is transferred to the oxygen of another. To investigate the
mechanism of oxygen transfer from manganese oxo complexes we have turned
to manganese-salen catalysts that are known to transfer oxygen atoms from
terminal oxidants to olefins 40.
It was Kochi and co-workers
41
that developed manganese-salen
complexes for epoxidations but it was Jacobsen 42 and Katsuki 43 who in parallel
developed the asymmetric epoxidation reaction with chiral manganese-salen
complexes. As with the mechanism of water oxidation in PS II, there has been
an ongoing debate on the mechanism of this epoxidation reaction. It has been
shown that the reaction takes place through a radical mechanism under some
conditions but not under others 40d-e.
Since the manganese complexes which we have been investigated, contain
phenolic ligands, it seemed important to try to study the behaviour of
manganese-salen complex in oxygen transfer reactions in the presence of
phenolates. In paper VI it is demonstrated that one-electron reduction by
phenolates of the presumed manganese(V)-oxo to a manganese(IV)-oxo
intermediate facilitates a radical mechanism were the cis-alkene gives
dominantly the trans-epoxide.
37
38
7. Concluding Remarks
This thesis describes the synthesis and characterisation of several dinuclear
manganese complexes. These have been used as electron donor models in
reactions mimicking photo-induced oxidation of the oxygen evolving complex in
photosystem II. Flash induced oxidation, with ruthenium(II) as photosenzitiser
and cobalt(III) as external acceptor, followed by EPR spectroscopy showed
stepwise one electron oxidation from a Mn2II,II state to, at least, a Mn2III,IV state for
this series of complexes. The redox behaviour was determined with
electrochemical methods in acetonitrile. A shift to lower potential was observed
for the high valence oxidations when some water was added.
One of the manganese complexes was covalent linked in a triad containing
ruthenium(II) trisbipyridine as photosenzitiser and naphthalene diimide as
electron acceptor. This triad was made to study the kinetics of electron transfer
in the formation and recombination of the charge separated state. The formed
charge separated state had a lifetime of two magnitude longer than previously
reported triads based on ruthenium(II) trisbipyridyl moiety as photosenzitiser.
For three of the manganese complexes, structure was determined with Xray diffraction and two of the structures showed similarities in the ligand
sphere for the manganese ions.
39
40
8. Supplementary Information
8.1 Synthesis of 20
Mn2(10)(µ-OAc)2·ClO4, 20. To an ethanol solution (3 ml) of 10 (154.6 mg,
0.20 mmol), MnIII(AcO)3·(H2O)2 (143.8 mg, 0.54 mmol) was added in one
portion. The dark red-brown solution was heated to 50 ˚C under argon for 20
min. A solution of NaClO4·H2O (93.4 mg, 0.66 mmol) in 1 ml ethanol was
added and the reaction solution was slowly cooled to room temperature
where after it was stored in the freezer for 48 h. The dark red-brown
microcrystalline solid was filtered of and washed with cooled ethanol and
diethyl ether. The solid was re-crystallized from ethanol to give 180.3 mg dark
red-brown crystals (yield 82.5 %).
8.2 Chrystal structure determination 44 of 20
Single crystal X-ray diffraction patterns were recorded with a Stoe IPDS
diffractometer on a rotating anode Mo-radiation source (λ= 0.71073Å) with φscans of 1° width. Total rotation range was 200°. The sample-detector distance
was 100 mm and with the diameter of the image plate being 180 mm this gave
max 2θ ≈ 40°. Measuring further out in 2θ proved to give very little extra,
significant data. The crystals were mounted and measured inside sealed glass
capillaries with mother liquor surrounding the crystals. Attempts to measure
crystals simply glued to a glass pin was unsuccessful as the ceased to diffract
after a few minutes. Indexing, cell refinements and integration of reflection
intensities were performed with the STOE IPDS software
45
. Numerical
46
absorption correction was performed with the program X-RED using multiple
measurements of symmetry equivalent reflections and verifying the crystal shape
with program X-shape
47
. The structure was solved by direct methods using
SHELXS97 48 giving electron density maps where most of the non-hydrogen
atoms could be resolved. The rest of the non-hydrogen atoms were located from
difference electron density maps and the structure model was refined with full
matrix least square calculations on F2 using the program SHELXL97-2 49. The
manganese atoms and the atoms of the perchlorate ion were refined with
anisotropic displacement parameters and all the other atoms was refined with
41
isotropic displacement parameters due to lack of significant reflections. The
hydrogen’s, were placed at geometrically calculated positions and let to ride on
the atoms they were bonded to, were given isotropic displacement parameters
calculated as ξ⋅Ueq. for the non-hydrogen atoms with ξ = 1.5 for methyl
hydrogen’s (-CH3) and ξ=1.2 for methylene (-CH2-) and aromatic hydrogen’s.
Selected crystal data are given in Table 8.1 and selected bond lengths and
angles in Table 8.2. Note that only 19.7% of the reflections were fulfilling the
significance criterion I>2σ(I) thus the residual values calculated from all reflection
are considerably larger than those calculated from the significant reflections.
Table 8.1 Selected crystal data for 20
Empirical formula
Fw
Crystal system
Space group
a, Å
b, Å
c, Å
α, °
β, °
γ, °
V, Å3
Z
ρcalc, g cm-3
Temperature, K
µ (MoKα), (mm-1)
N(meas),
N(uniq),
R(int)
N(obs),
N(par),
S
(GoF)
R1, wR2 both with
(I > 2σ(I))
R1, wR2 (all data)
∆ρmin, ∆ρmax (e/Å3)
42
C55H71ClMn2N4N18
1109.49
Triclinic
P –1
11.200(3)
15.822(5)
18.622(6)
110.67(4)
99.25(3)
95.37(3)
3006.6(15)
2
1.226(1)
293(2)
0.518
11771, 5399, 0.3564
1064, 328, 0.644
0.0958, 0.2925
0.3287, 0.1985
-0.526, 0.387
Table 8.2 Selected bond lengths (Å) and angles (°) for 20. The distances
and angles describe the coordination polyhedrons around each
manganese ions and the orientation of the two polyhedrons
with respect to each other.
Mn1…Mn2
3.528(15)
Mn1-O1-Mn2
120.9(2)
Mn1 – O6
Mn1 – O1
Mn1 – O2
Mn1 – N4
Mn1 – O5
Mn1 – N2
1.856(12)
1.946(11)
2.065(13)
2.105(14)
2.226(12)
2.306(14)
Mn2 - O7
Mn2 - O3
Mn2 - O4
Mn2 - O1
Mn2 - N6
Mn2 - N5
1.860(10)
1.971(11)
2.019(12)
2.108(12)
2.197(15)
2.204(12)
O6 Mn1 O1
O6 Mn1 O2
O1 Mn1 O2
O6 Mn1 N4
O1 Mn1 N4
O2 Mn1 N4
O6 Mn1 O5
O1 Mn1 O5
O2 Mn1 O5
N4 Mn1 O5
O6 Mn1 N2
O1 Mn1 N2
O2 Mn1 N2
N4 Mn1 N2
O5 Mn1 N2
175.5(5)
89.1(5)
90.5(5)
88.2(5)
92.9(5)
170.4(5)
89.1(5)
86.5(4)
94.2(5)
95.0(5)
95.0(5)
89.5(5)
92.2(5)
78.8(5)
172.5(5)
O7 Mn2 O3
O7 Mn2 O4
O3 Mn2 O4
O7 Mn2 O1
O3 Mn2 O1
O4 Mn2 O1
O7 Mn2 N6
O3 Mn2 N6
O4 Mn2 N6
O1 Mn2 N6
O7 Mn2 N5
O3 Mn2 N5
O4 Mn2 N5
O1 Mn2 N5
N6 Mn2 N5
177.4(5)
93.4(5)
89.3(5)
91.9(5)
87.8(5)
97.4(5)
97.8(5)
82.0(5)
93.6(5)
164.9(5)
88.1(5)
89.3(5)
171.1(5)
91.3(5)
77.5(5)
43
44
References
1
Lehninger, A.L.; Nelson, D.L., Cox, M.M., in Principles of Biochemistry, Worth
Publisher, Inc., 2nd Ed., 1993, p. 571
2
a) Diner, B.A.; Rappaport, F., Annu. Rev. Plant. Biol., 2002, 53, 551-580, b) Barber, J.
Q. Rev. Biophys. 2003, 36, 71-89, c) Wydrzynski, T.; Satoh, K., in Advances in
Photosynthesis and espiration (Series Ed. Govindjee); Photosynthesis II: The WaterPlastoquinone Oxido-Reductase in Photosynthesis, Kluwer Academic Publisher.
Dordrecht, Netherland, 2005
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Acknowledgements
There are some persons I would like to thank:
First of all I would like to thank my supervisor Björn Åkermark for recruiting
me as a graduate student and for all encouragement and support you have
given me during all these years.
I am also grateful to Licheng Sun and Björn Åkermark for introducing me in the
wonderful world of manganese chemistry and artificial photosynthesis.
I would like to thank all present and past members of the BÅ group and all
people at the Department of Organic Chemistry for a wonderful time.
Prof. Jan-Erling Bäckvall for his kind interest in our work.
Per Unger for good advices.
All present and past friends and co-workers in the Swedish Consortium for
Artificial Photosynthesis.
All the people that have been involved in the papers that this thesis is based on.
All the people involved in SELCHEM, especially Tord Svedberg, Krister
Lundmark, Veronica Profir and Ann-Britt Fransson.
Joakim, Ann, Ping and Stenbjörn for all our discussions during the years.
Financial support from the Swedish Foundation for Strategic Research (SSF)
and the Swedish Energy Agency is gratefully acknowledged.
All my wonderful friends from Kårspexet and Pilsnerlistan. Speciellt Gunilla,
Anna C, Pär och Johan. Vad vore livet utan er!
Burt och Magnus på Sunkit.
Kristoffer, Samuel, Henrik, Johan S., Stefan, Nicholas och Micke, vissa vänner
bara finns! Tack
Mor och Far
Syster
49