Dinuclear Manganese(III,III) Complex with Three Phenolate Ligands
FULL PAPER
Electrochemistry: Cyclic voltammetry, differential pulse voltamme-
try, and controlled potential electrolysis were performed with an centration of Mn2
Autolab potentiostat and a GPES electrochemical interface in a 3-
reduction was monitored coulometrically providing the exact con-
II,III
after electrolysis.
[Mn2III,IV(µ-O)2(bpy)4]3ϩ was utilized as the standard for quanti-
electrode cell with the counter electrode separated from the bulk
by a fritted disk. The working electrode was a glassy carbon disc
(diameter 3 mm) for voltammetry or a platinum grid cylinder
(15 mm ϫ 15 mm diameter) for bulk electrolysis, respectively. The
reference electrode was a nonaqueous Ag/Agϩ electrode (10 m
AgNO3 in acetonitrile) of double-junction design. The reference
electrode has a potential of Ϫ0.08 V vs. the ferrocene/ferrocenium
couple in acetonitrile as an external standard. All potentials re-
ported here are vs. the saturated calomel electrode (SCE) and have
been converted by adding 0.30 V to the potentials measured vs.
the Ag/Agϩ electrode according to E1/2 ϭ 0.38 V vs. SCE for the
ferrocene/ferrocenium couple.[26]
III,IV
fication of the Mn2
complex formed after one-electron oxida-
tion of 4. The precise concentration of the [Mn2III,IV(µ-O)2(bpy)4]3ϩ
standard was determined spectrophotometrically at 684 nm.[27]
MnII acetate (purity Ͼ 99.9%) in 10% water/90% acetonitrile was
used as standard for quantification of monomeric MnII species
formed, e.g. after two-electron reduction. MnII acetate was used
as purchased.
Magnetic Susceptibility Measurements: Magnetic susceptibility
measurements were performed on an MPMS5 magnetometer
(Quantum Design Inc.) over a temperature range of 2Ϫ300 K and
at a magnetic field of 1.0 T. A palladium reference (Quantum De-
sign Inc.) was used for callibration at 298 K. Data were corrected
for diamagnetism and the χT vs. T plot was fitted according to the
procedure described in ref.[28]
Electrolyte solutions were prepared from dry acetonitrile (Merck,
˚
spectroscopy grade, dried with MS 3 A) with 0.1 tetrabutylam-
monium hexafluorophosphate (Fluka, electrochemical grade, dried
at 373 K) as supporting electrolyte. The glassware used was oven
dried, assembled and flushed with argon while hot. Before all meas-
urements, the solutions were deoxygenated by bubbling solvent sat-
urated argon through the stirred solutions for 10 minutes. Whilst
measuring the samples were kept under an argon atmosphere.
Acknowledgments
`
´
Eric Riviere (Universite Paris-Sud, Orsay) is gratefully acknow-
ledged for performing and analyzing the magnetic susceptibility
measurements. This work was supported by the Knut and Alice
Wallenberg Foundation, the Swedish National Energy Administra-
tion, the Swedish Research Council, and DESS.
The electrochemical preparation of EPR samples was performed
by bulk electrolysis of 1 mm (3 mL) solutions at controlled poten-
tials. The electrolysis was followed by amperometry and coulo-
metry. After electrolysis, samples of 250 µL were taken with an
argon filled syringe via a septum from the electrolysis vessel and
transferred to argon flushed EPR tubes. The samples were immedi-
ately frozen and kept in liquid nitrogen.
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bpmp
phenol.
[1]
[1b]
UV/Vis Spectroelectrochemistry: Spectroelectrochemical measure-
ments were made in an OTTLE-type quartz cell with an optical
path length of 1 mm. A platinum grid of size 10 ϫ 30 mm2 and 400
meshes per cm2 was used as working electrode. The counter and
reference electrodes were of the same type as described for electro-
chemistry. Solvent saturated argon was bubbled through samples
for 15 min, and they were then transferred to the argon flushed cell
with an argon stream. The spectra were recorded on an UV/Vis
diode array spectrophotometer (Hewlett Packard 8435).
[1c]
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˚
[2b]
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See ref.[1c]
ϭ 2,6-bis[bis(2-pyridylmethyl)amino]methyl-4-methyl-
[2c]
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´
L. Sun, M. K. Raymond, A. Magnuson, D. LeGourrierec,
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´
˚
IR Spectroscopy: IR spectra were recorded on a FT-IR spectro-
meter (Bruker IFS 66v/S) with the sample as a KBr pellet.
˚
G. Stenhagen, L. Hammarström, S. Styring, B. Akermark, J.
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´
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EPR Spectroscopy: All EPR spectra were recorded on a Bruker
E580-ELEXSYS spectrometer equipped with an Oxford 900 liquid
helium cryostat and an ITC 503 temperature controller. An
ER4116DM dual mode X-band resonator of rectangular type
(TE102 for perpendicular and TE012 for parallel mode) was used for
all measurements. Data analysis was carried out with either the X-
Epr or X-Winpro software packages.
˚
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Quantification of 4 in different oxidation states was carried out by
double integration of the perpendicular EPR mode signal studied
within the selected spectral region. The signal intensity was then
converted into spin concentration by comparison with the signal
intensity in a standard sample in the same oxidation state with
known concentration. All EPR spectra used for the evaluation of
the different concentrations were recorded using nonsaturating mi-
crowave power.
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The amount of Mn2II,III found in the preparation of 4 was obtained
[9] [9a]
by comparison with the signal in the g ϭ 2 region recorded after
II,III
[9b]
exhaustive one electron reduction of 4 to the Mn2
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state. The
M. Suzuki, M. Miku-
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