1. 11
Synthesis, Electrochemical andSynthesis, Electrochemical and
Spectroscopic Characterization ofSpectroscopic Characterization of
Diruthenium Complexes withDiruthenium 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. 2
RuRu22 complex componentscomplex components
RuRu22(O(O22CCHCCH33))44ClCl
Anionic bridging ligandsAnionic bridging ligands
surround the Rusurround the Ru22
5+5+
core whichcore which
also can be replaced by otheralso 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
4. 4
ObjectiveObjective
How do the electrochemical and spectroelectrochemical propertiesHow 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. 5
ApplicationApplication
Cotton and Murillo et. al. J Am. Chem. Soc. 2003, 125, 10327-10334
Precursors to supermolecular structures :Precursors to supermolecular structures :
6. 6
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
7. 7
PurificationPurification
FiltrationFiltration- Remove- Remove
excess unreactedexcess unreacted
Ruthenium acetateRuthenium acetate
http://www.cdch.de/demos/laborglas/filtration.htm
SublimationSublimation--
Remove excessRemove excess
unreacted bridgingunreacted bridging
ligandligand
ColumnColumn
ChromatographyChromatography--
Separate and isolateSeparate and isolate
the products formedthe products formed
http://cwx.prenhall.com/horton/medialib/me
dia_portfolio/text_images/FG03_11.JPG
8. 8
Electrochemistry of RuElectrochemistry of Ru22(Fap)(Fap)44Cl inCl 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 -2.0
PotentialPotential
( V vs. SCE)( V vs. SCE)
I,II and III are all 1 electron transfersI,II and III are all 1 electron transfers
RuRu22
5+5+
/Ru/Ru22
6+6+
RuRu22
6+6+
/Ru/Ru22
7+7+
RuRu22
5+5+
/Ru/Ru22
4+4+
CurrentCurrent
Ru2(Fap)4Cl
9. 9
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
Compound
Ru2
5+/6+
Ru2
5+/4+
Ru2
4+/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
Ru2
5+/6+
Ru2
5+/4+
Ru2
4+/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 aroundDue to the increase of electron density around
the diruthenium corethe diruthenium core
12. 12
Wavenumber of Ru2
5+
vs. Hammet Constant
y = -10587x + 15753
R
2
= 0.9979
13000
13500
14000
14500
15000
15500
0 0.05 0.1 0.15 0.2 0.25 0.3
Hammet
Wavenumber(cm-1
)
13. 13
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
Absorbance(AU)
Wavelength (nm)A
3. Record the spectra as a function of time.
UV-visible light
through the thin-layer cell
15. 15
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 Ru2
5+/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.
16. 16
AcknowledgementsAcknowledgements
Dr. Kadish, my thesis advisor- for all of his helpDr. Kadish, my thesis advisor- for all of his help
and support academically and financiallyand support academically and financially
Dr. “V” (Van Caemelbecke) from Houston BaptistDr. “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 plusDr. Chan, UH director of AGEP- financial plus
personal support and an opportunity to be here atpersonal support and an opportunity to be here at
SACNASSACNAS
Editor's Notes
Good afternoon today I will be talking about the synthesis and characterization of diruthenium complexes which have mixed bridging ligands
First I will go over some components of a diruthenium complex. This compound is called ruthenium acetate, which was one of the pioneering diruthenium molecule that many scientists including Dr. Cotton from A and M university have characterized. It’s chemistry is well known and is frequently used for comparison to novel diruthenium compounds. First we have the diruthenium core, where the rutheniums are bound together, and this core as a whole has a 5+ oxidation state. This core is redox active, meaning that the oxidation state can vary from a +3 to +7 to date, using chemical and electrochemical means.
Previously in our lab in 2001, a diruthenium compound was made and its synthesis is shown here. We started off with ruthenium acetate and added another type of anionic bridging ligand called fluoroanilino pyridintae, or fap for short. The ligand binds to the compound via the nitrogen's located here, this is what the x-ray crystallography data of the new compound looks like, and since the ligand is anionic, the diruthenium core still has a 5+ oxidation state in the neutral form. This paper also studied the elecrochemical and spectroscopic prperties of this compound.
My objective was to synthesize compounds that contain a mixed ligand set of acetate and fap bridging ligands as shown here and study the electrochemical and spectroscopic properties of this series. A more systematic approach is answer the question.
As you can see, this reaction produces 4 primary products. My target product is the blue compound, with 2 acetate and 2 fap ligands attatched. A technique called Thin layer chromatography was used periodically throughout the reaction to check the amount of blue product was formed, If you let it react too long, you will start to convert to the other products, as the acetate ligands start to be replaced by more fap ligands. So the average Reflux time was approx 4 hrs
Then we go to the purification phase to extract on the blue product out from everything else. First we do what is called filtration, we simply filter out the solution using filter paper and acetone to rinse out the flask. The What remains on the filter paper is excess ruthenium acetate Next we do sublimation on the filtrate we collected from filtration. This removes the excess unreacted ligand and it is deposited on the sides. Finally we do column chromatography, which is like the thin layer chromatography, where we separate out the different colored products.
Now that the compound have been made their electrochemical properties can be characterize. First I will explain a little about electrochemistry of the previous made compound, ru2fap4cl and use this data for comparison. Here is a cyclic voltammogram of the compound in dichloromethane. This technique generally displays a change in current as a potential is applied to the solution. In the literature as well as analyzing the voltammogram, the number of electrons transferred is one for each process. It is also cited that the redox of this compound involves the diruthenium core, so when reduced, the oxidation state of the core is now 4+, when oxidized, the compound oxidized to 6+, and the 6+ can be further reduced to 7+.
I investigated the cyclic voltammetry in PhCN, of all 3 compounds as shown here. The potenetial differenced for the first oxidation and first reduction are shown in red, and as you can see the value decreases as the number of faps around the diruthenium core increases. Also there is another trend you can see, and that is the E1/2 values of the 1 st oxidation state shift negitavely, from 1.11 volts to 0.56. The same trend is observed for the 1 st reduction, in which the potnential becomes more negative, from -0.43 to -0.63. So in general, the more faps there are around the core the easier it is to lose electrons, and the harder to accept electrons, and this is attributed to the increase of electron density around the core, so it is harder for more electrons to be added to that area. It has been cited that the dependance of the potential values on the electronic effect of the fap can be quantified by the linear-square fit of the data
So the change to the potneital is equal to the sum of the substituent constants sum of (p)(sigma), p is the reactivity constant and sigma is the electronic effect of the bridging ligand. Here is the plot of the oxidation potential vs the hammet comstnat of the substituent: where you can see has a r2 value of .99, suggesting a linear relationship.
Here is the uv-visible spectra of the mixed ligand complexes as well as the fully substitued compound, and ruthenium acetate. You can see that the lower energy band, assigned to have this electronic transisiton shifts to lower energy as you add more faps to the core.
If you plot the wavenumber that corresponds to the low energy band vs the substituent constant of fap, there is also a linear relationship.
Uv visible spectroelectrochemistry is a techinique in which you monitor the absorption spectra as you apply a potential to the solution. 1 st , you apply the potential past the redox process you want to examine, which should therefore generate the reduced species, for example in the solution by the working electrode. Then light is passed trough the cell to record the spectra of the newly reduced species. Then you can observe the spectral changes going from the neutral to the reduced species for example.
