DESARROLLO DEL PROYECTO
4.2 Métodos constructivos
4.2.2 Método a percusión.
The dicarboxylate salt isolations from the acids and recrystallizations were
done from water. The simple salts NaF, KF, LiF and CsF were purchased from
Aldrich, EM Science, JT Baker Chemical or Mallinckrodt and were used as received.
The dicarboxylic acids were purchased from Aldrich. The K4Fe(CN)6 salt was
purchased from Aldrich, and the K4RuII(CN)6 and K4Os(CN)6 salts were synthesized
by Angela Qin of this laboratory30 according to the methods outlined by Curtis31 and
used without further purification. The [RuII (NH3)5 py] (PF6)2 and [RuIII (NH3)5 3Fpy]
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Sodium Salts of the Dicarboxylic Acids
Approximately 1.0 g of a given dicarboxylic acid was weighed out and placed
in a 500 mL round-bottom flask. About 50-70 mL of distilled H2O was added
followed by 18 M NaOH solution dropwise (protective gear!) until most of the acid
dissolved. The solution pH was then adjusted to 6.5 by adding small amounts of HCl
or NaOH if necessary. The solution was then rotary-evaporated until dry (about 3~4
hours with a water bath temperature of 70-80C). An alternative method was to
precipitate the sodium salt product by adding a 5-fold volume excess of reagent-
grade acetone to the pH 6.5 solution followed by vacuum filtration of the sodium salt
precipitate.26
Recrystalization of the Disodiumdicarboxylate Salt
The crude disodium(dicarboxylate) salt was dissolved in a minimum amount
of 1:3 water/ethanol mixture with continuous stirring and heating. The hot salt
solution was filtered, and upon cooling purified crystals of the disodium salt were
isolated by filtration.
Synthesisof Pentaammineruthenium(II)pyridyine Perchlorate
(NH3)5RuIIpy(ClO4)2
Approximately 40-50 mg of [RuII(NH3)5(py)](Cl)2 was dissolved in a minimum
amount of H2O (~10 drops). To this, freezer-saturated NaClO4 or LiClO4 was added
(~10-15 drops) and the mixture was placed in a freezer for about 30 minutes in order
to optimize yield. The product was isolated by filtration and then washed with 3 mL
of 70:30 ether/ethanol solute ion (to remove trace water speed up the air- drying
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BY VACUUM!) for about 2-3 hours. These perchlorate salts were found to be stable
for at least three weeks if sealed properly and stored in a freezer.
Caution: All perchlorate salts of ruthenium (II) and (III) complexes are known to be explosive. No more than 30 mg of ANY ruthenium perchlorate should ever be isolated at one time. Great care must be taken in handling them. They should never be dried in a vacuum desiccator since extreme dryness increases explosion danger. They must be kept away from flammable organic solvents at all times during handling them. A Teflon-coated spatula or plastic spatula should be used to gently displace perchlorate precipitates from frits since this operation presents the greatest moment detonation danger (vigorous scraping with a metal spatula can be a source of detonation). They should be kept well-sealed from air and in the freezer once isolated so as to minimize decomposition.
Synthesis of Pentaammineruthenium(III)3-fluoropyridyine Perchlorate
(NH3)5RuIII3F(ClO4)3
Approximately 40-50 mg of [RuIII(NH3)5(3Fpy)](Cl)3 was dissolved in a
minimum amount of H20 (~10 drops). To this, freezer saturated NaClO4 or LiClO4
was added (10-15 drops) and then the mixture was placed in a freezer for about 30
minutes to increase the yield. The resulting pale-yellow product was isolated by
filtration and the solid in the frit was washed with 3 mL portions of 70:30
ether/ethanol solution to increase the drying efficiency. The product as then dried in
the frit by air-suction (NOT BY VACCUM DESICATOR) at least for about 2-3 hours.
Perchlorates salts stay stable for at least three weeks, if sealed properly and stored
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Caution: All perchlorate salts of ruthenium (II) and (III) complexes are known to be explosive. No more than 30 mg of ANY ruthenium perchlorate should ever be isolated at one time. Great care must be taken in handling them. They should never be dried in a vacuum desiccator since extreme dryness increases explosion danger. They must be kept away from flammable organic solvents at all times during handling them. A Teflon-coated spatula or plastic spatula should be used to gently displace perchlorate precipitates from frits since this operation presents the greatest moment detonation danger (vigorous scraping with a metal spatula can be a source of detonation). They should be kept well-sealed from air and in the freezer once isolated so as to minimize decomposition.
Purification of the (NH3)5RuIII3Fpy(ClO4)3
The purity of a given (NH3)5RuIIIL(ClO4)3 oxidant complex can be evaluated
by in-situ reduction to the Ru(II) form and spectrophotometric assay (as described in
Ch.2 on page 51) and by electrochemical analysis (DPP and CV) as described on
page 52 of Ch.2. The impure perchlorate compound was dissolved in a minimum
amount, 1-3 mL, of warm distilled water and filtered. To this filtrate, freezer-
saturated NaClO4 or LiClO4 was added (6 to 10 drops) and the flask was placed in
the freezer for 1-2 hours to obtain optimum yield. The recrystallized precipitate was
then filtered and dried by air suction for 2-3 hours (NOT BY VACUUM).
Caution: All perchlorate salts of ruthenium (II) and (III) complexes are known to be explosive. No more than 30 mg of ANY ruthenium perchlorate should ever be isolated at one time. Great care must be taken in handling them. They should never be dried in a vacuum desiccator since extreme dryness
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increases explosion danger. They must be kept away from flammable organic solvents at all times during handling them. A Teflon-coated spatula or plastic spatula should be used to gently displace perchlorate precipitates from frits since this operation presents the greatest moment detonation danger (vigorous scraping with a metal spatula can be a source of detonation). They should be kept well-sealed from air and in the freezer once isolated so as to minimize decomposition.
Once we have the pure compounds and after having the data compared with
the known values of λmax and ε we did the kinetics studies of salts effects for the
reaction 3.10. For this particular reactant pair where pyridine and 3-folouropydine
used as reactants the driving force was calculated from the E1/2 values (given in
Chapter Two Table 2.5) which was determined by using DPV (differential pulse
voltammetry) found to be 65.0 + 5 mV and this value is also given in Sista27,
Inagaki25 theses.
Running the Stopped-Flow Experiments
Stopped-flow kinetic spectroscopy was used to do all the kinetics work
described in this chapter. Operation of the stopped-flow apparatus and analysis of
the kinetic data are described in detail in Chapter 2 of this thesis. Once we have
synthesized the reactants for stopped-flow kinetic spectroscopy, the measured
reactant purity should be at least 90% of the highest purities attained previously.
This final purity check must be done by UV-Vis spectroscopy.
Making up the run solutions for salt studies is somewhat different than
making up the solutions for driving force kinetic studies as discussed in the previous
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final required GP at a particular ruthenium concentration. First, the range of reactant
RuII/RuIII concentrations were chosen to be 7.5×10-5 M, 1.0×10-4 M, 1.5×10-4 M,
2.0×10-4 M, and 2.5×10-4 M. The corresponding initial (prior to adding any other salt)
GP values at these concentrations were found using the following relation,
1/2 1/2
μ
1
μ
GP
(3.11)32where is the ionic strength of the solution as given by,
i i 2 iC Z 2 1 μ (3.12)7(zi is the charge of a particular ion and ci is the concentration of the ion). The resulting set of corresponding no-added salt or “initial” GP values in the mixed, reacting solutions (in the stopped-flow cell) are then 0.0253, 0.0291, 0.0354, 0.0407
and 0.0452, respectively.
From the initial, no-added salt GP values, the amount of the salt necessary
calculated based on the increment in ionic strength necessary to bring the total GP
(reactants + salt) up to the desired value. A stock solution of the salt to be added
was prepared by adding a measured amount of the salt solution to the solution
containing the ruthenium reactant in its +2 oxidation state. This was done because
some of the salts may act as slow reductants at high concentration and partially
reduce the Ru3+ oxidant to Ru2+ before the stopped-flow reaction has started. The
actual amount of salt to be added to the Ru2+ solution must be double that of what is
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together cuts the concentration to half (and the same is true, for the ruthenium
solutions).