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Synthesis, Electrochemical and Synthesis, Electrochemical and Spectroscopic Characterization of Spectroscopic Characterization of
Diruthenium Complexes with Diruthenium Complexes with Mixed Anionic Bridging LigandsMixed Anionic Bridging Ligands
Rachel Garcia
SACNAS National Conference
Friday, October 27, 2006
Department of Chemistry
University of Houston
2
RuRu22 complex components complex components
RuRu22(O(O22CCHCCH33))44ClCl
Anionic bridging ligands Anionic bridging ligands surround the Rusurround the Ru22
5+5+ core which core which
also can be replaced by other also can be replaced by other bridging ligandsbridging ligands
Ru2 core in a 5+ oxidation state; are redox active
Contains an axial ligand which can be replaced by other ligands
i.e. communicating linkers
3
Previous StudiesPrevious Studies
Overall Process: Substitution Reaction:Overall Process: Substitution Reaction:
RuRu22(O(O22CCHCCH33))44Cl + 4 HCl + 4 HFapFap Ru Ru22(Fap)(Fap)44Cl + 4 Cl + 4 CHCH33COCO22HH
(3,1) conformation: Ru2(Fap)4Cl
ORTEP from Bear et al. Inorg. Chem. 2001, 40, 2282-2286
2-fluoroanilino pyridinate
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ObjectiveObjective
How do the electrochemical and spectroelectrochemical properties How do the electrochemical and spectroelectrochemical properties change as you increasingly replace one acetate by Fap?change as you increasingly replace one acetate by Fap?
IntermediatesIntermediates
a) Ru2(O2CCH3)3(Fap)Cl b) Ru2(O2CCH3)2(Fap)2Cl c)Ru2(O2CCH3)(Fap)3Cl
5
ApplicationApplication
Cotton and Murillo et. al. J Am. Chem. Soc. 2003, 125, 10327-10334
Precursors to supermolecular structures :Precursors to supermolecular structures :
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In MeOH, observe stepwise exchange:In MeOH, observe stepwise exchange:
SynthesisSynthesis
80° C
+
Reaction stopped at 4 hrs.
Ru2(CH3CO2)4Cl Fap ligand RuRu22(ac)(ac)22(Fap)(Fap)22ClCl
RuRu22(ac)(Fap)(ac)(Fap)33ClCl
RuRu22(ac)(ac)33(Fap)Cl(Fap)Cl
RuRu22(Fap)(Fap)44ClCl
Monitored reaction by TLC
time
3 equivalents of HFap
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PurificationPurification
FiltrationFiltration- Remove - Remove excess unreacted excess unreacted Ruthenium acetateRuthenium acetate
http://www.cdch.de/demos/laborglas/filtration.htm
SublimationSublimation- - Remove excess Remove excess unreacted bridging unreacted bridging ligandligand
ColumnColumn ChromatographyChromatography- - Separate and isolate Separate and isolate the products formedthe products formed
http://cwx.prenhall.com/horton/medialib/media_portfolio/text_images/FG03_11.JPG
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Electrochemistry of RuElectrochemistry of Ru22(Fap)(Fap)44Cl in Cl in
CHCH22ClCl22
oxidationoxidation reductionreduction
HOMO-LUMO = ∆│RedHOMO-LUMO = ∆│Red11-Ox-Ox11││
∆│ ∆│RedRed11-Ox-Ox11││
ORTEP from Bear et al. Inorg. Chem. 2001, 40, 2282-2286
01.6 -2.0Potential Potential
( V vs. SCE)( V vs. SCE)
I,II and III are all 1 electron transfers I,II and III are all 1 electron transfers
RuRu225+5+/Ru/Ru22
6+6+RuRu226+6+/Ru/Ru22
7+7+ RuRu225+5+/Ru/Ru22
4+4+
Cu
rren
tC
urr
ent
Ru2(Fap)4Cl
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Redox behaviorRedox behavior
RuRu22(ac)(ac)33(Fap)Cl(Fap)Cl
In this study we examined the electrochemistry of the mixed ligand series where
PhCN was the solvent :
RuRu22(ac)(Fap)(ac)(Fap)33ClCl
RuRu22(ac)(ac)22(Fap)(Fap)22ClCl
CompoundRu2
5+/6+Ru2
5+/4+
Ru24+/3+
0
Volts vs SCE
1.11
0.75
1.24
0.56 -0.63
-1.48
-0.57
-1.58
-0.43
-1.63Ru2
5+/6+Ru2
5+/4+
Ru24+/3+
0
Volts vs SCE
1.11
0.75
1.24
0.56 -0.63
-1.48
-0.57
-1.58
-0.43
-1.63
1.54 V
1.32 V
1.19 V
1.8 -1.7
Due to the increase of electron density around Due to the increase of electron density around the diruthenium corethe diruthenium core
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1st Half Wave Reduction Potential vs. Hammet Constant
y = -1.8x - 0.36
R2 = 0.9918
-0.9
-0.8
-0.7
-0.6
-0.5
-0.4
-0.3
-0.2
-0.1
0
0 0.05 0.1 0.15 0.2 0.25 0.3
Hammet Constant
Red
uct
ion
Po
ten
tial
(V
)
1st Half Wave Oxidation vs. Hammet Constant
y = -3.4667x + 1.265
R2 = 0.9918
0
0.2
0.4
0.6
0.8
1
1.2
0 0.05 0.1 0.15 0.2 0.25 0.3
Hammet Constant
Oxi
dat
ion
po
ten
tial (
V)
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UV-visible SpectroscopyUV-visible Spectroscopy
There is a red shift of the lower energy band as you increase the amount of Faps surrounding the
core
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Wavenumber of Ru25+ vs. Hammet Constant
y = -10587x + 15753
R2 = 0.9979
13000
13500
14000
14500
15000
15500
0 0.05 0.1 0.15 0.2 0.25 0.3
Hammet
Wav
enu
mb
er (
cm-1
)
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UV-visible SpectroelectrochemistryUV-visible Spectroelectrochemistry
Apply a potential to the solutionApply a potential to the solution
WE
CE
RE
N2
b
a
-0.68
-1.03
-0.80 V
0.00
0.20
0.40
0.60
0.80
1.00
1.20
300 350 400 450 500 550 600 650 700
Ab
sorb
ance
(AU
)
Wavelength (nm)A
3. Record the spectra as a function of time.
UV-visible lightthrough the thin-layer cell
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461 nm661 nm
590 nm424 nm
810 nm
437 nm690 nm
473 nm
Kadish et al. (2003). Inorg Chem 42: 8309-8319.
Ru25+ 6+Ru2
5+ 4+CompoundCompound
RuRu22(ac)(ac)22(Fap)(Fap)22ClCl
RuRu22(ac)(Fap)(ac)(Fap)33ClCl
RuRu22(ac)(ac)33(Fap)Cl(Fap)Cl
RuRu22(Fap)(Fap)44ClClRuRu22(ac)(ac)22(Fap)(Fap)22ClCl
RuRu22(ac)(Fap)(ac)(Fap)33ClCl
RuRu22(ac)(ac)33(Fap)Cl(Fap)Cl
RuRu22(Fap)(Fap)44ClCl
RuRu22(ac)(ac)22(Fap)(Fap)22ClCl
RuRu22(ac)(Fap)(ac)(Fap)33ClCl
RuRu22(ac)(ac)33(Fap)Cl(Fap)Cl
RuRu22(Fap)(Fap)44ClCl
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SummarySummary
The mixed ligand series, Ru2(ac)x(Fap)y where x+y = 4, were synthesized
Electrochemical studies reveal a negative shift for the 1st reduction and 1st oxidation, which can be explained by the increase of electron density around the diruthenium core as you replace the ac by Fap.
Linear relationships have been established between the number Fap ligands (the Hammet constant of fluorine) bound to the diruthenium core and the redox processes, Ru2
5+/4+ and Ru25+/6+.
With only 2 Fap’s bound to the core, spectral changes of the reduced and oxidized forms of a complex are similar to a complex with 4 Fap/s around the dimetal core.
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AcknowledgementsAcknowledgements
Dr. Kadish, my thesis advisor- for all of his help Dr. Kadish, my thesis advisor- for all of his help and support academically and financiallyand support academically and financially
Dr. “V” (Van Caemelbecke) from Houston Baptist Dr. “V” (Van Caemelbecke) from Houston Baptist University- for his great academic advice and helpUniversity- for his great academic advice and help
Dr. Chan, UH director of AGEP- financial plus Dr. Chan, UH director of AGEP- financial plus personal support and an opportunity to be here at personal support and an opportunity to be here at SACNAS SACNAS