Spectroscopic and electrochemical properties of [Mn(phen)(CO)3(imidazole)](SO3CF3) complexes

Article abstract of DOI:10.1016/S0020-1693(99)00505-8

The spectroscopic and electrochemical properties of [Mn(phen)(CO)₃(L)]⁺ type complexes where L is an imidazole or an imidazole derivative containing a methyl, phenyl or NO₂ group, have been investigated. Introduction of the substituents to the σ-donor ligand has been found to produce significant changes in the electrochemical behaviour without significantly altering the fundamental electronic structure of the complexes. The oxidation potentials of the fac-[Mn(phen)(CO)₃L]⁺ and mer-[Mn-(phen)(CO)₃L]⁺ isomers are very different, allowing detailed electrochemical studies to be made. Cyclic voltammetry of both the fac and mer isomers provides a complete description of a cyclic process involving the following reactions. (C) 2000 Elsevier Science S.A.

Full text of DOI:10.1016/S0020-1693(99)00505-8

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Inorganica Chimica Acta 299 (2000) 231–237
Spectroscopic and electrochemical properties of
[Mn(phen)(CO)3(imidazole)](SO3CF3) complexes
Rose Maria Carlos a, Ivani Ap. Carlos b, Benedito S. Lima Neto a,
Miguel G. Neumann a,*
a Instituto de Qu´ımica de Sa˜o Carlos, Uni6ersidade de Sa˜o Paulo, Caixa Postal 780, 13560-970 Sa˜o Carlos, SP, Brazil
b Departamento de Qu´ımica, Uni6ersidade Federal de Sa˜o Carlos, Caixa Postal 676, 13565-905 Sa˜o Carlos, SP, Brazil
Received 11 March 1999; accepted 5 November 1999
Abstract
The spectroscopic and electrochemical properties of [Mn(phen)(CO)3(L)]+ type complexes where L is an imidazole or an
imidazole derivative containing a methyl, phenyl or NO2 group, have been investigated. Introduction of the substituents to the
s-donor ligand has been found to produce significant changes in the electrochemical behaviour without significantly altering the
fundamental electronic structure of the complexes. The oxidation potentials of the fac-[Mn(phen)(CO)3L]+ and mer-[Mn-
(phen)(CO)3L]+ isomers are very different, allowing detailed electrochemical studies to be made. Cyclic voltammetry of both the
fac and mer isomers provides a complete description of a cyclic process involving the following reactions.
© 2000 Elsevier Science S.A. All rights reserved.
Keywords: Electrochemistry; Manganese complexes; Phenanthroline complexes; Imidazole complexes; Carbonyl complexes
1. Introduction
‘spectator’ ligands X (halides) was investigated [1,4–
13], although alkyl complexes have also been studied
[3,6]. Therefore, as the ligand field strength of the
ligands should affect significantly the physical and
chemical properties of the complex it seems of interest
to extend the range of ligands investigated to those with
strong s donors properties.
Since imidazole ligands contain a number of possible
bridging sites, the spectroscopic and electrochemical
properties of a series of monometallic Mn(I) tricarbonyl
complexes containing CH3-, C6H5-, NO2-substituted
imidazole ligands were examined with the goal of ma-
nipulating the basicity of the imidazole ligand, and
consequently the p-acidity of the compound. The stud-
ies described illustrate how structural features can mod-
ify the bonding properties and the excited state
dynamics of the Mn(I) complexes. Understanding the
Mn(I) tricarbonyl complexes, containing bidentate
heterocyclic ligands have been a source of continuous
interest for several years [1–10]. One goal of these
studies has been the systematic investigation of com-
plexes with different ligand combinations in order to
establish both the generalities and discontinuities in the
excited state behaviour of homologous systems [1–8].
Whereas, most work has grown around N,N-chelating
pyridine bases [5] and related species like MnX(CO)3(a-
diimine) [1,3,5–8], only the influence of p-donating
* Corresponding author. Tel.: +55-16-273 9940; fax: +55-16-273
9952.
E-mail address: neumann@iqsc.sc.usp.br (M.G. Neumann)
0020-1693/00/$ - see front matter © 2000 Elsevier Science S.A. All rights reserved.
PII: S0020-1693(99)00505-8

232
R.M. Carlos et al. / Inorganica Chimica Acta 299 (2000) 231–237
consequences of such molecular perturbations is essen-
tial in the design of chemical systems for practical
applications.
2.2.3. [Mn(CO)3(phen)L](trif)
The following procedure, described for [Mn(CO)3-
(phen)(Im)](trif), is also representative of the synthesis
of the other substituted imidazole complexes (L: CH3-
Im, C6H5-Im, Metro-Im). Imidazole (0.044 g, 0.51
mmol) was added to
a
solution of Mn(trif)-
2. Experimental
(CO)3(phen) (0.15 g, 0.32 mmol) in CH2Cl2 (40 ml)
and the mixture was stirred for 24 h at room temper-
ature in the dark. The solution was concentrated to
ca. 10 ml, mixed with cold ethyl ether (5 ml), filtered
and vacuum dried. The product was recrystallized
from CH2Cl2/ethyl ether to give a bright yellow mi-
crocrystalline powder. Yield: 90%. The yield for
[Mn(CO)3(phen)(Metro-Im)](trif) is usually smaller
(ꢀ60%).
The elemental analyses of the final compounds
were consistent with the composition of the anhy-
drous complexes: [Mn(CO)3(phen)(Im)](trif). Calc.: C,
42.55; H, 2.24; N, 10.44. Found: C, 43.02; H, 2.18;
N, 10.64%. [Mn(CO)3(phen)(CH3-Im)](trif). Calc.: C,
43.65; H, 2.55; N, 10.18. Found: C, 45.60; H, 2.75;
N, 10.7%. [Mn(CO)3(phen)(Metro-Im)](trif). Calc.: C,
50.03; H, 2.92; N, 9.13. Found: C, 49.02; H, 2.61; N,
9.15%. [Mn(CO)3(phen)(C6H5-Im)](trif). Calc.: C,
41.08; H, 2.63; N, 10.95; S, 5.01. Found: C, 40.82; H,
2.62; N, 10.76; S, 4.90%.
2.1. Materials
Mn(CO)5Br was from Strem, 1,10-phenanthroline,
imidazole, 2-methyl-imidazole and 2-phenyl-imidazole
were from Aldrich and Metroimidazole (2-methyl-5-
nitroimidazole-1-ethanol) was from Sigma. Methylene
chloride, acetonitrile, methanol, ethanol, tetrahydro-
furan and acetone were HPLC grade. Tetrabutylam-
monium perchlorate (TBPA) from Eastman Kodak
used as supporting electrolyte for electrochemical ex-
periments was dried overnight under vacuum at 50°C
and stored under vacuum before use. The ligands
were phenanthroline (phen), trifluoromethanesulfonic
ion (trif), imidazole (Im), 2-methyl-imidazole (CH3-
Im), 2-phenyl-imidazole (C6H5-Im), and 2-methyl-5-ni-
troimidazole-1-ethanol (Metro-Im).
2.2. Syntheses
2.3. Instruments and procedures
All syntheses and preparations for electrochemical
experiments were carried out under purified N2 atmo-
sphere, using Schlenk techniques. The solutions were
carefully handled in the dark before the experiments
were performed.
Microanalyses (C,H,N) were performed on a Eager
200 elemental analyzer. Infrared spectra were ob-
tained on a Bomen MB spectrometer using KBr pel-
lets. UV–Vis spectra were obtained with a U2000
Hitachi spectrophotometer. 13C NMR spectra were
recorded on a Bruker DRX 400 spectrometer using
CD2Cl2 solutions.
2.2.1. MnBr(CO)3(phen)
The halo complex was prepared by reacting
Mn(CO)5Br (1.0 g, 3.65 mmol) with phenanthroline
(0.65 g, 3.60 mmol), as described by Riera and co-
workers [14] but using 40 ml CH2Cl2 (freshly distilled
and dried under P2O5) instead of benzene. The mix-
ture was left in the dark overnight at room tempera-
ture, after which the complex was precipitated by
addition of cold ethyl ether. Yield: 1.31 g (90%).
Cyclic voltammetry was performed using an EG&G
Princeton Applied Research Model 173 potentiostat/
galvanostat in conjunction with a three-electrode cell.
Voltammograms were obtained in CH2Cl2 (1 mM
TBPA) at 22°C in a light-protected voltammetric cell
with a platinum cylinder for both the working and
the auxiliary electrodes. A silver wire coated with sil-
ver chloride was used as reference electrode, con-
nected to the bulk of the solution by a Luggin
capillary filled with the same solvent and electrolyte.
The area of the working electrode was 0.30 cm2
as determined by the Cottrell equation using
K4[Fe(CN)6] in aqueous 1 mM KCl. The platinum
electrodes were prepared by carefully polishing with
0.3 mm alumina (in water suspension) followed by
cleaning with HNO3 1 mM, and rinsed with distilled
water. Solutions were deoxygenated with a stream of
N2 and maintained under a positive pressure of N2
during the measurements. The concentration of the
complexes was kept always at 1 mM. A 1.0 mM
2.2.2. Mn(trif)(CO)3(phen)
Ag(trif) (0.27 g, 1 mmol) was added to a solution
of MnBr(CO)3(phen) (0.30 g, 0.75 mmol) in 40 ml
CH2Cl2 (freshly distilled and dried under P2O5). The
mixture was stirred overnight at room temperature in
the dark. During this time a white precipitate was
formed. The reaction mixture was filtered and the re-
sulting solution was concentrated in vacuo to ca. 10
ml. Addition of cold ethyl ether (2 ml) with stirring
precipitated a dark yellow crystalline solid, that was
recrystallized from CH2Cl2/ethyl ether. Yield: 0.31 g
(90%)

R.M. Carlos et al. / Inorganica Chimica Acta 299 (2000) 231–237
233
ferrocene (Fc) solution in CH2Cl2 (0.1 mM TBPA) was
used as voltammetric reference redox couple.
3. Results and discussion
3.1. Preparation and characterization of
[Mn(CO)3(phen)(L)](trif)
The Mn complexes were prepared by the reaction of
a halo derivative with Ag(trif), which leads to the
precipitation of the silver halide and the formation of a
trifluoromethanesulfonate complex. The application of
this process was used as a general method for the
synthesis of the cationic organocomplexes. Owing to its
poor donor capacity [15] the triflate group in Mn-
(trif)(CO)3(phen) may readily be replaced by a variety
of substituted imidazole ligands even at room tempera-
ture. These ligand substitutions were monitored by the
changes in the UV–Vis spectra as a function of time.
The solid complexes are soluble in organic solvents,
slightly soluble in water and stable in air at room
temperature. In solution they are sensitive to light and
air.
Fig. 2. Absorption spectra of fac-[Mn(CO)3(phen)(L)](trif) complexes
in dichloromethane. (a) L=Br; (b) L=trif; (c) L=Im; (d) L=CH3-
Im; (e) L=C6H5-Im.
shifts of the imine carbon atoms are indicative of the
structure of the complexes and electronic distribution in
the imine structure. The equivalence of both phenan-
throline ligand halves as indicated by the presence of a
single set of lines in the spectra indicates that the phen
ligand is in the s,s-bidentate coordination mode and
that only the facial isomer is formed (Fig. 1).
3.2. 13C NMR spectra
The 13C NMR chemical shifts of the phenanthroline
and its complexes are listed in Table 1. The chemical
3.3. Infrared spectra
Table 1
The carbonyl bands of the complexes show a notice-
able frequency shift towards higher frequencies when
compared to the Mn(Br)(CO)3(phen) precursor (Table
1). This effect is expected from the increase of the
positive charge on the manganese ion that reduces the
d-electron back-bonding to the CO resulting in a larger
triple bond character of the coordinated carbonyls.
This pattern of three strong bands between 2050 and
1950 cm−1 is consistent with the facial arrangement
[16] of the three COs in the coordination sphere, con-
firming the structure derived from the NMR spectra.
13C NMR and infrared stretching frequencies (cm−1) for manganese
carbonyl complexes and phenanthroline
Compound
w(CO)
C (imine)
(ppm)
Phenanthroline (phen)
MnBr(CO)3(phen)
[Mn(CO)3(phen)(CH3-Im)](trif)
150.3
153.7
153.3
2020(vs); 1922(s)
2029(vs); 1942(s);
1916(s)
2037(vs); 1941;
1921(s)
[Mn(CO)3(phen)Im](trif)
[Mn(CF3SO3)(CO)3(phen)]
[Mn(CO)3(phen)(C6H5-Im)](trif)
[Mn(CO)3(phen)(Metro-Im)](trif) 2044(vs); 1949(s);
1929(s)
2037(vs); 1946(s);
1921(s)
2038(vs); 1932(s);
155.9
154.5
Table 2
Electronic absorption maxima for fac-[Mn(CO)3(phen)(L)]0/+ com-
plexes in dichloromethane solution, at 22°C
L
u, nm (m, M−1 cm−1
)
Br
CF3SO3
Im
382(3300); 422(3400); 267(34 000)
366(3700); 395(4000); 269(37 000)
376(4200); 266(35 000)
CH3-Im
C6H5-Im
Metro-Im
380(3700); 266(37 000)
384(3700); 266(33 000)
400(3800); 268(32 000)
Fig. 1. Structure of [Mn(CO)3(phen)(L)]+ complexes.

234
R.M. Carlos et al. / Inorganica Chimica Acta 299 (2000) 231–237
Table 3
Solvatochromism
[Mn(CO)3(phen)(L)](trif)
complexes, the position of the longer wavelength band
is shifted by 700–800 cm−1 when changing the solvents
(Table 3). In contrast, the shorter wavelength band is
solvent-independent. On the basis of the solvent and
ligand dependencies of those bands and their rather
large intensities, the lower energy absorption band is
assigned to a metal-to-ligand (Mn“phen) charge
transfer transition. The analogous [Re(CO)3(phen)-
(Im)]+ complex [19] also presents a MLCT transition
which corresponds to the lowest energy absorption.
This Re complex shows an intense absorption band
near the free ligand phenanthroline absorption which is
assigned to an intra-ligand (IL) transition. Therefore,
the corresponding band in [Mn(CO)3(phen)(L)]+ is also
assigned to an IL transition.
The first ligand field absorption band [20] for
[Mn(CO)6]+ occurs at 24 000 cm−1. Substitution of
three of the CO ligands by Im and two nitrogen donors
should substantially lower the average ligand field (LF)
strength and yield lower lying LF states for [Mn-
(CO)3(phen)(L)](trif). Therefore, the LF transitions are
expected to appear above 26 000 cm−1 based on the
[Mn(CO)6]+ spectra. However, this region is obscured
by the strong MLCT absorption. The MLCT band is
strongly solvatochromic, and the MLCT states are sta-
bilized in nonpolar solvents. On the other hand, the
energy of the LF states is generally solvent-independent
[21,22]. Therefore, using the information obtained from
the electronic spectra, the LF-MLCT energy gap in
CHCl3 can be estimated to be 650, 800, and 900 cm−1
larger than in CH3CN for L=H-Im, CH3-Im and
C6H5-Im, respectively.
These results show that replacement of the bromide
ligand by a strong s-donor ligand as imidazole, is an
effective way of altering the energy states of [Mn-
(CO)3(phen)(L)](trif) complexes. The imidazole groups
are merely s donors to Mn(I), whereas in Ru(III)
complexes they act as s+p donors [23]. Thus, in the
case of imidazole complex the lowest energy transitions
will be MLCT in character in contrast to XLCT/MLCT
for L=Br−. Due to the change in the XLCT/MLCT
character, the attraction between the metal and the
phenanthroline ligand increases, strengthening this
bond. As a consequence, the intensity of the visible
absorption increases and shifts to shorter wavelengths,
as shown in Fig. 2.
On the other hand, altering the substituents on the
imidazole ligand will affect the complex mainly by
destabilizing the eg orbitals (considering an Oh micro-
symmetry). However, the MLCT states arise from the
promotion of an electron from a t2g orbital, which is
only affected slightly by the imidazole ligand basicity.
For this reason, the energy of the intense MLCT band
(ꢀ104 M−1 cm−1) does not change significantly with
the substituents on the imidazole ring. This argument
of
the
absorption
bands
of
fac-
L
Solvent
CHCl3
THF
MeOH
CH3CN
umax, nm (m, M−1 cm−1
)
Im
378(3900); 266(32 000)
371(4000); 267(29 000)
369(3500); 266(27 000)
369(4000); 267(29 000)
CH3-Im
CHCl3
THF
MeOH
CH3CN
383(3400); 266(30 000)
376(3300); 266(29 000)
372(2800); 266(26 000)
372(3000); 266(29 000)
C6H5-Im
Metro-Im
CHCl3
THF
MeOH
CH3CN
387(3000); 267(30 000)
378(3500); 266(27 000)
376(2600); 266(27 000)
374(2800); 266(28 000)
CHCl3
THF
MeOH
CH3CN
400(2700); 266(25 000)
400(2800); 268(22 000)
400(2800); 266(23 000)
400(2600); 269(20 000)
3.4. Electronic absorption spectra
Absorption properties of the fac-[Mn(CO)3-
(phen)(L)]0/+ complexes in dichloromethane are shown
in Fig. 2. The absorption maxima and extinction coeffi-
cients in dichloromethane and various other solvents
are collected in Tables 2 and 3, respectively. Each of the
complexes shows absorption maxima in the range 370–
400 nm with molar extinction coefficients between 2000
and 4000 M−1 cm−1. In addition, all the complexes
present also an intense transition in the UV region
(mꢀ35 000 M−1 cm−1).
Fig. 2 clearly shows that the change of the ligand has
a strong influence on the positions and relative intensi-
ties of the absorption maxima of the Mn complexes.
When changing from bromide to the poor p-acceptor
triflate ligand, both absorption shoulders shift to higher
energies. At the same time the intensity of the first band
increases, and the intensity of the second one decreases.
For imidazole, the shifts are so large that both shoul-
ders merge into an unique absorption band at 370 nm.
The wavelength shift of the visible absorption band
for the complexes with imidazole derivatives compared
to that with unsubstituted imidazole was smaller than
expected from the range of the donor/acceptor sub-
stituents used on the imidazole ring [17,18]. Although
the methyl and phenyl groups do not produce large
shifts of the absorption maximum, the electronic spec-
trum of Metro-Im substituent is seen to be very differ-
ent from those of the other imidazole complexes,
presenting the band at 400 nm as a shoulder of the high
energy absorption.
The energies of the absorption bands in the visible
region were found to be solvent-dependent. For all

R.M. Carlos et al. / Inorganica Chimica Acta 299 (2000) 231–237
235
Table 4
3.5. Electrochemical studies
Oxidation and reduction potentials (in V) of fac-[Mn(CO)3-
(phen)(L)](trif) in dichloromethane a
The voltammetric data are summarized in Table 4.
The electrochemical behaviour observed for fac-
[Mn(CO)3(phen)(CH3-Im)]+ is representative of the
other substituted imidazole Mn(I) complexes studied.
Fig. 3a shows a cyclic voltammogram (scan rate 200
mV s−1) for a 1 mM solution of the fac-[Mn-
(CO)3(phen)(CH3-Im)](trif) complex over the range
0.2–1.8 V (vs. Fc+/Fc) in dichloromethane (TBPA 0.1
M). On the first positive-going potential scan an oxida-
tive response (electrode process I) is observed and the
corresponding reduction response (process I%) is seen on
the reverse scan. Second and subsequent scans, under
these conditions, show a small shift towards more
positive potentials for both the oxidation and reduction
responses. Whereas the current associated with the
oxidative response decreases with successive scans, the
ic current increases. Processes I and I% become time-in-
dependent after seven cycles, when Eox and Ered reach
values of +1.00 and +0.72 V versus Fc+/Fc, respec-
tively. These results suggest that interactions between
the complex and the solvent during the redox cycle
produce changes in the nature of the complex that are
more pronounced during the initial stages of the
voltammetric experiments. In tetrahydrofuran, a coor-
dinating solvent, although the oxidative response was
not very intense, the cyclic voltammetry showed reduc-
tion processes that are virtually unaltered even after
repeated cycles, supporting the above arguments. Cyclic
voltammetry was therefore carried out only in CH2Cl2,
where better defined and more informative electrochem-
istry was obtained.
L
Process
Eox
Ered
Im
I,I%
II,II%
+0.80
+0.26
+0.60
−0.12
CH3-Im
I,I%
II,II%
+0.92
+0.28
+0.52
−0.06
C6H5-Im
Metro-Im
I,I%
II,II%
+0.78
+0.18
+0.48
−0.42
I,I%
II,II%
+0.78
+0.58
+0.68
−0.22
a Potentials are vs. Fc/Fc+ couple in TBPA 0.1 mM, t=22°C,
conc. 1.0 mM, 6=200 mV s−1
also accounts for the values of the Mn(I/II) oxidation
potentials, which measures the easiness of the removal
of t2g electron, as discussed below.
Fig. 3b shows a cyclic voltammogram in dichloro-
methane (TBPA 0.1 M, scan rate 200 mV s−1) over a
wider potential range. A second reductive response at
0.08 V versus Fc+/Fc can be observed on the first scan
(process II%), with the corresponding reduction response
at 0.24 V (process II). Multiple scans resulted in super-
posable cyclic voltammograms, thereby showing the
marked stability of the Mn species involved in the
electrochemical cycle.
The reversible couple II, II% is not observed when the
potential is switched to the −0.6 to 0.4 V range,
proving that the electrode processes II and II% are
derived from a product formed in the first oxidation
step. Thus, the electrode processes I and I% can be
summarized as
fac-[Mn(CO)3(phen)(CH3-Im)]+
−e
−
ꢀꢀꢀꢁfac-[Mn(CO)3(phen)(CH3-Im)]2+
When fac-[Mn(CO)3(phen)(CH3-Im)]+ is oxidized at
the electrode surface it rapidly causes electrode pro-
cesses II and II% to happen in a cyclic way, even after
(1)
Fig. 3. Cyclic voltammograms of fac-[Mn(CO)3(phen)(CH3-Im)](trif)
in CH2Cl2 (TBPA 0.1 M) at a platinum electrode vs. Fc/Fc+; scan
rate 200 mV s−1. (a) range between 0.2 and 1.8 V; (b) range between
−0.2 and 1.8 V.

236
R.M. Carlos et al. / Inorganica Chimica Acta 299 (2000) 231–237
repeated scans, indicating that the oxidizable species is
never exhausted.
Acknowledgements
Extensive studies have been made on the electro-
chemical behaviour of many carbonyl complexes of
Mn(I), Cr(III), Mo(I) and W(I) transition metals [2,24–
28]. The fac–mer isomerization induced by oxidation
has already been observed for several complexes. In the
case of Mn(I) complexes [2,24–26], it was shown that
after chemical or electrochemical oxidation the 17-elec-
tron fac-compound isomerizes to the mer-configuration
which, in turn, is readily reduced to the 18-electron
mer-configuration. Using a series of similar Mo com-
plexes [27] it was demonstrated that the 18-electron
reduction product isomerizes back to the starting spe-
cies in a cyclic process.
R.M.C. thanks FAPESP for a Post-Doctoral Fellow-
ship (Proc. 97/10047-0). We thank Professor Nabil El
Murr (Universite´ de Nantes, France) for helpful
discussions.
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Based on those studies, it is suggested that at room
temperature fac-[Mn(CO)3(phen)(CH3-Im)]2+ isomer-
izes to the mer-[Mn(CO)3(phen)(CH3-Im)]2+ isomer,
which suffers the electrode processes II and II%
mer-[Mn(CO)3(phen)(CH3-Im)]2+
−
+e
ꢀꢀꢀꢁ mer-[Mn(CO)3(phen)(CH3-Im)]+
(2)
The generated mer-[Mn(CO)3(phen)(CH3-Im)]+ re-
verts back to fac-[Mn(CO)3(phen)(CH3-Im)]+ closing
the cycle.
Although all the components of the cyclic scheme
can be detected voltammetrically at the electrode sur-
face, attempts to isolate the mer-[Mn(CO)3(phen)(CH3-
Im)]+ intermediate by potential-controlled oxidation
have failed indicating that the fac-[Mn(CO)3(phen)-
(CH3-Im)+ isomer is electronically favoured. These
studies also show that the back reaction or isomeriza-
tion mer2+ “fac2+ is negligible.
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4. Conclusions
Synthesis of [Mn(phen)(CO)3(imidazole)]+ type com-
plexes was achieved with relatively high yields.
Modifying the ‘spectator’ ligand (from Br− to Im) is
a better way of changing the characteristics of the
transitions than substitution on the chromophore (imi-
dazole ligand). Not only the XLCT/MLCT character
can be modified, but the energy gap between MLCT
and LF states can be varied, affecting the electronic
absorption and electrochemical properties of the com-
plex as well as the properties of the lowest energy
excited state.
The fac-[Mn(CO)3(phen)L]+ isomer is the preferred
configuration for the complex of Mn(I), whereas after
electrochemical oxidation to Mn(II) the mer-isomer is
favoured. This gives place to an electrochemical cycle
involving
−
−
fac+−ꢀꢀeꢁ fac+2“mer+2 ꢀꢀꢁ mer+“fac+
+e

R.M. Carlos et al. / Inorganica Chimica Acta 299 (2000) 231–237
237
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