Synthesis, structure and characterisation of a new trinuclear di-μ-phenolato-μ-carboxylato MnIIIMnIIMn III complex with a bulky pentadentate ligand: Chemical access to mononuclear MnIV-OH entities

Article abstract of DOI:10.1002/ejic.200500501

A new trinuclear Mn^IIIMn^IIMn^III complex has been isolated and X-ray characterised, namely [(py-salpn)Mn ^III(μ-OAc)-Mn^II(μ-OAc)Mn^III(py-salpn)] ²⁺ (1), where H₂py-salpn is the new bulky [N ₃O₂] ligand derived from the H₂salpn Schiff base by the addition of one pyridine arm and the reduction of the imine function. The crystal structure reveals that the complex has a strictly 180° Mn^III...Mn^II...Mn^III angle, the Mn^II ion being located at an inversion centre. The complex is valence-trapped, with the terminal Mn^III ions showing a Jahn-Teller elongation along the pyridine-Mn^III-acetate axis. The Mn ^II...Mn^III separation is 3.1224(13) A. The EPR spectra recorded on solid and frozen solutions are consistent with an Mn ^IIIMn^IIMn^III species. The electrochemical response of complex 1 in acetonitrile solution exhibits two, one-electron reduction waves at E_1/2 = 0.140 and -0.075 V vs. SCE. Phenolato and acetato→Mn^III ligand-to-metal charge-transfer transitions are detected by UV/Visible spectroscopy at 359 and 587 nm, respectively. Chemical oxidation of an acetonitrile solution with tert-butyl hydroperoxide leads to mononuclear Mn^IV-hydroxo species, as evidenced by UV/Visible and EPR spectroscopy as well as ESI mass spectrometry. Wiley-VCH Verlag GmbH & Co. KGaA, 2005.

Full text of DOI:10.1002/ejic.200500501

FULL PAPER
DOI: 10.1002/ejic.200500501
Synthesis, Structure and Characterisation of a New Trinuclear Di-μ-phenolato-
μ-carboxylato MnIIIMnIIMnIII Complex with a Bulky Pentadentate Ligand:
Chemical Access to Mononuclear MnIV–OH Entities
Christelle Hureau,*[a,b] Elodie Anxolabéhère-Mallart,*[a] Geneviève Blondin,[a]
Eric Rivière,[a] and Martine Nierlich[c]
Keywords: EPR spectroscopy / Manganese / Mass spectrometry / N,O ligands / Oxidation
A new trinuclear MnIIIMnIIMnIII complex has been isolated
and X-ray characterised, namely [(py-salpn)MnIII(μ-OAc)-
MnII(μ-OAc)MnIII(py-salpn)]2+ (1), where H2py-salpn is the
new bulky [N3O2] ligand derived from the H2salpn Schiff
base by the addition of one pyridine arm and the reduction
of the imine function. The crystal structure reveals that the
complex has a strictly 180° MnIII···MnII···MnIII angle, the MnII
ion being located at an inversion centre. The complex is val-
ence-trapped, with the terminal MnIII ions showing a Jahn–
Teller elongation along the pyridine–MnIII–acetate axis. The
MnIIIMnIIMnIII species. The electrochemical response of
complex 1 in acetonitrile solution exhibits two, one-electron
reduction waves at E1/2 = 0.140 and –0.075 V vs. SCE.
Phenolato and acetatoǞMnIII ligand-to-metal charge-trans-
fer transitions are detected by UV/Visible spectroscopy at
359 and 587 nm, respectively. Chemical oxidation of an ace-
tonitrile solution with tert-butyl hydroperoxide leads to mo-
nonuclear MnIV–hydroxo species, as evidenced by UV/Vis-
ible and EPR spectroscopy as well as ESI mass spectrometry.
MnII···MnIII separation is 3.1224(13) Å. The EPR spectra re- (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
corded on solid and frozen solutions are consistent with an
Germany, 2005)
rium Thermosynechococcus elongatus have appeared in the
literature, one at 3.5 Å[11] and the other at 3.2 Å resolu-
tion.[12] The structure of the Mn cluster, however, is still a
matter of debate. Nevertheless, the resolution level allows
the authors to propose two models of the OEC that agree
in terms of having two moieties: a small one containing one
cation and a larger one containing three or more cations.
Zouni et al. describe the OEC cluster as containing only
four metal ions, whereas Ferreira et al. describe the oxo-
manganese entity as a “3+1” tetranuclear manganese com-
plex. More precisely, in the latter case three manganese ions
together with one calcium ion are arranged in a tetrahedral
geometry at four corners of a distorted cube, the other four
corners being occupied by bridging oxo ions. The fourth
manganese ion is linked to the Mn–Ca–oxo cube by a
unique oxo bridge. Two amino acid residues are involved in
the coordination of the fourth manganese ion, namely
Asp170 and Glu333, and Asp61 is coordinated through a
water molecule. Lastly, one exogenous labile hydrogencar-
Introduction
The development of bioinorganic manganese chemistry
has been stimulated by the involvement of manganese ions
in many biological systems,[1,2] such as superoxide dismu-
tase,[3] catalase[4] and photosystem II of green plants.[5–8] In
this last intricate machinery, an oxomanganese entity is the
key element of the oxygen evolving complex (OEC), which
performs the light-induced oxidation of water into di-
oxygen. This reaction requires the photogeneration of four
oxidative equivalents and their storage by the OEC. These
two processes are accomplished during the first four steps
of the Kok cycle,[9,10] (S0ǞS1, S1ǞS2, S2ǞS3 and S3ǞS4)
where Si (i = 0–4) denote the five oxidation states of the
OEC, dioxygen being released during the last step (S4ǞS0).
High-valent oxidation states are thus reached by the man-
ganese ions in the S4 state. Recently, two X-ray structures
obtained for the photosystem II (PSII) of the cyanobacte-
[a] Laboratoire de Chimie Inorganique, UMR 8613, LCR-CEA
no. 33V, Institut de Chimie Moléculaire et des Matériaux d’Or- bonate ligand is proposed to interact with the fourth man-
say, Université Paris Sud,
ganese and the calcium ions. Due to its peculiar location
91405 Orsay Cedex, France
and to the presence in its surroundings of labile positions
along with the tightly bound Ca2+, this fourth manganese
ion is anticipated to ensure a special role in the water oxi-
dation process. In particular, the present structure supports
recent hypotheses in which one of the four manganese ions
binds a water molecule, thus producing a highly reactive
intermediate. This electrophilic species is then predisposed
E-mail: eanxolab@icmo.u-psud.fr
[b] Current address: Service de Bioénergétique, CNRS URA 2096,
Département de Biologie Joliot Curie, CEA Saclay, Bât 532,
91191 Gif-sur-Yvette, France
E-mail: hureau@ozias.saclay.cea.fr
[c] CEA Saclay, DRECAM/SCM Bât 125,
91191 Gif-sur-Yvette, France
Supporting information for this article is available on the
WWW under http://www.eurjic.org or from the author.
4808
© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2005, 4808–4817

A Chemical Access to Mononuclear MnIV–OH Entities
FULL PAPER
to be attacked by the second water molecule bound to the of mononuclear MnIV species that are identified as MnIV–
calcium ion to form the O–O bond.[13]
OH complexes by mass spectrometry measurements.
The water oxidation mechanisms proposed by Siegbahn
et al.[14–16] and Brudvig et al.[17] all rely on a tightly bound
Ca2+ ion located close to a manganese ion. Indeed, it is
proposed that during the Kok cycle only one of the Mn
ions binds a water substrate molecule and, before dioxygen
formation, produces either a highly reactive electrophilic in-
termediate or an MnIV–oxyl radical. A MnV centre has also
been advocated by Pecoraro et al.[18] In these assumptions,
the reactive manganese ion would be the fourth manganese
ion of the “3+1” tetranuclear complex.
The large number of papers found in the literature attests
that high-valent manganese compounds have been devel-
oped as selective organic oxidation catalysts,[19–25] and
tested in bleaching processes.[26–28] Consequently, generat-
ing high-valent and/or Mn–oxo complexes is a relevant
challenge for inorganic chemists, both for OEC modelling
and for the development of oxidation catalysts.
Results and Discussion
The reaction of H2py-salpn with MnIII(OAc)3·2H2O in
ethanol solution leads to the formation of the cation [(py-
salpn)MnIII(μ-OAc)MnII(μ-OAc)MnIII(py-salpn)]2+
(1),
which was precipitated by addition of two equivalents of
sodium tetraphenylborate. It is worth noting that the pres-
ence of MnII in the complex is not unexpected considering
that the MnIII(OAc)3·2H2O starting material contains MnII
species, even after recrystallisation.
Crystal Structure of [(py-salpn)MnIII(μ-OAc)MnII(μ-OAc)-
MnIII(py-salpn)]2+ (1)
The structure of complex 1 is presented in Figure 1 and
principal bond lengths and angles are listed in Table 1. The
cation consists of three manganese ions, two (py-salpn)2–
Among the numerous manganese compounds synthe-
sised, complexes containing Schiff-base ligands, like
H2salen or H2salpn,[29] or their derivatives, have been inten-
sively studied as much for their biological relevance[30–33] as
for their catalytic activity.[25,28,34–38] Indeed, these com-
plexes possess the ability to form high-valent Mn–oxo spe-
cies,[39,40] the sixth position being occupied by various li-
gands.[41,42] In particular, the use of pyridine as the sixth
ligand has been proposed to assist the formation of MnV–
oxo species from the [(salen)MnIII +
butyl hydroperoxide as the oxidant.[25]
] complex, using tert-
Taking into account these different elements, we designed
a new bulky pentadentate ligand, derived from reduced
H2salpn by the addition of one pyridine arm and denoted
H2py-salpn (see Scheme 1). In the present work, we de-
scribe the synthesis and the crystal structure of the new
trinuclear manganese complex [(py-salpn)MnIII(μ-OAc)-
MnII(μ-OAc)MnIII(py-salpn)](BPh4)2 [1(BPh4)2]. The mag-
netic and EPR properties of 1(BPh4)2 have been investi-
gated on crystalline product. Characterisations of complex
1(BPh4)2 upon dissolution in acetonitrile have been per-
formed by EPR and UV/Visible spectroscopy, as well as
cyclic voltammetry and mass spectrometry. We also de-
scribe the reactivity of 1 upon addition of tert-butyl hydro-
peroxide, where EPR spectroscopy suggests the formation
Figure 1. ORTEP view of the cation of 1, with 10% thermal ellip-
soids, showing the atom labelling scheme.
Table 1. Selected bond lengths [Å] and angles [°] for 1.[a]
Mn1–O1
Mn1–O2
Mn1–O3
Mn2–O1
Mn2–O2
O1–Mn1–O1Ј 180.0
O2–Mn1–O2Ј 180.0
2.158(3)
2.191(3)
2.155(4)
1.940(3)
1.924(4)
Mn2–O4
Mn2–N1
Mn2–N2
Mn2–N3
2.099(3)
2.059(5)
2.141(4)
2.234(4)
Mn1···Mn2
O2–Mn2–N1
O2–Mn2–O4
O2–Mn2–N2
O2–Mn2–N3
O4–Mn2–N1
O4–Mn2–N2
O4–Mn2–N3
N1–Mn2–N2
N1–Mn2–N3
N2–Mn2–N3Ј
3.1224(13)
175.86(14)
91.60(14)
92.67(18)
86.87(16)
88.39(16)
91.26(14)
169.62(13)
91.47(19)
93.89(18)
78.57(15)
O3–Mn1–O3Ј 180.0
O1–Mn1–O2 72.85(12)
O1–Mn1–O3 86.70(14)
O2–Mn1–O3 86.03(13)
O1–Mn2–N1 91.98(16)
O1–Mn2–O2 83.89(14)
O1–Mn2–O4 93.90(13)
O1–Mn2–N2 173.87(17)
O1–Mn2–N3 96.14(14)
Mn2···Mn1···Mn2Ј 180.0
[a] Symmetry transformation used to generate equivalent atoms:
–x, –y, –z + 1.
Scheme 1. H2salpn, H2py-salpn and H2py-salpnimine
.
Eur. J. Inorg. Chem. 2005, 4808–4817
© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
4809

C. Hureau, E. Anxolabéhère-Mallart, G. Blondin, E. Rivière, M. Nierlich
FULL PAPER
ligands and two bridging acetate ions. The Mn1 ion is lo- with the μ-alkoxo-bis-μ-carboxylato-MnIIMnIII core com-
cated at the inversion centre of the cation in a quasi-regular plexes that are usually found to be weakly antiferromag-
octahedral geometry. The Mn1 and Mn2 (or Mn2Ј) ions netically coupled, with JMnIIMnIII lying between –8 and
are held together by two bridging phenolato arms from one –14.2 cm–1, using the expression –JSMnII·SMnIII for the ex-
(py-salpn)2– ligand and by one bridging acetate ion. Mn1 is change Hamiltonian within a pair.[47–49] A weak exchange
coordinated by the four phenolic bridging oxygen atoms interaction, either antiferromagnetic or ferromagnetic, has
from the two (py-salpn)2– ligands that indeed form a plane been observed in analogous MnIIIMnIIMnIII trinuclear sys-
and, quasi-perpendicularly to it, by two oxygen atoms from tems where the MnIII and the MnII ions are connected by
the two acetate bridging ligands. Mn2 and Mn2Ј are coordi- one phenolato, one alkoxo and one carboxylato bridge.[44]
nated by the three nitrogen atoms and the two bridging phe- The magnitude of the exchange interaction is indeed con-
nolato arms of the (py-salpn)2– ligand and by one oxygen trolled by the presence of two alkoxo or phenoxo bridges.
atom from the acetate bridging ligand. The phenolato arms Such doubly bridged MnIIMnIII core units present J values
are in a cis position, as are two amine nitrogen atoms, ranging from –3.4 to 13.2 cm–1.[31,54–56]
whereas the pyridine nitrogen atom and the oxygen atom
The X-band EPR spectrum was recorded at 10 K using
of the acetate ion are in a trans position. The metal–ligand the conventional perpendicular mode on a powder sample
distances reported in Table 1 reveal that 1 is a valence- of complex 1(BPh4)2·3CH3CN and is presented in Fig-
trapped MnIIIMnIIMnIII complex, with the terminal MnIII ure S1 (trace a). An intense and broad line is observed at
ions exhibiting a Jahn–Teller elongation along the acetate– 335 mT (geff = 2). Two weaker lines are also detected at 145
Mn–pyridine (O4–Mn2–N3) direction. The bridging acetate and 558 mT, which are strongly indicative of weak interac-
ions are in the usual syn-syn coordination mode, as reported tions between the Mn ions within complex 1. In the absence
for analogous trinuclear manganese complexes.[43] The dis- of an interaction between the metal ions, the EPR signal
tance between the MnII and the MnIII ions in 1 is would originate solely from the MnII site as the Jahn–Teller-
3.1224(13) Å, which is slightly shorter than that reported in elongated MnIII centres exhibit a strong zero-field splitting
similar core units (3.137–3.173 Å).[44] It is, however, signifi- effect that prevents the detection of any EPR signal at
cantly shorter than in μ-alkoxo-bis-μ-carboxylato-bridged 9 GHz. In addition, the regular environment of the MnII
MnIIIMnIIMnIII
trinuclear
complexes
(3.419– ion should induce a small zero-field splitting effect. Conse-
3.551 Å).[45–49] The presence of two phenolato bridges in 1 quently, a broad line at geff = 2 is expected. The dipolar and
is the origin of this shortening of the distance. Crystal data isotropic exchange interactions between the central MnII
also reveal that the secondary amine function is not oxi- site and the two terminal MnIII ions split this signal quasi-
dised during the metallation [N1–C7 = 1.501(7) Å], as could symmetrically and new lines appear at both lower and
be anticipated from reported syntheses of similar com- higher fields. This was checked by calculating powder X-
plexes.[50]
band EPR spectra for a fictitious system containing two
terminal S = 1 and one central S = 1/2 sites. The profile is,
however, strongly dependent on the relative orientation of
the terminal zero-field splitting tensors towards that of the
dipolar tensors and on the nature − ferro- or antiferromag-
IR, Magnetic and EPR Properties of 1(BPh4)2
The IR spectrum of 1(BPh4)2 presents significant absorp- netic − of the exchange interaction (see Figure S2 in the
tion bands at 1602, 1559, 1424, 760, 734 and 708 cm–1. The Supporting Information). Due to the important spin values
three bands detected below 800 cm–1 are assigned to the of the manganese ions and to the number of parameters,
tetraphenylborate counterions, whereas the two broad no simulation was attempted on the real system.
bands detected at 1559 and 1424 cm–1 are attributed to the
bridging acetate ions.[51,52] The difference of 135 cm–1 calcu-
Characterisation of 1(BPh4)2 upon Dissolution in
lated between the symmetrical and the unsymmetrical C=O
Acetonitrile
vibration bands is in agreement with the syn-syn bridging
coordination mode of the acetate ions.[51] The C=N vi-
The X-band EPR spectra of millimolar dichloromethane
bration band of the pyridine function is detected at and acetonitrile solutions of complex 1 at 10 K are pre-
1602 cm–1. Lastly, the absence of a broad absorption band sented in Figure S1 (see Supporting Information; traces b
near 1630 cm–1 confirms the absence of the imine function and c, respectively). The EPR signatures of complex 1 upon
in 1.[53]
dissolution are close to that recorded for a powder sample.
The product of the molar magnetic susceptibility, χM, In acetonitrile solvent, however, an additional six-line signal
and the temperature, T, recorded on a powder sample of is detected at geff = 2, which is attributed to solvated MnII.
1(BPh4)2·3CH3CN is approximately constant between 50 This contribution has been quantified (See Experimental
and 300 K. The χMT product lies between 10.31 and Section for details) and accounts for less than 5% of the
10.37 cm3 mol–1 K. This is close to the theoretical value of total Mn-based species. This experiment shows that the tri-
10.375 cm3 mol–1 K expected for two SMnIII = 2 and one nuclear structure of complex 1 is essentially maintained
SMnII = 5/2 uncoupled spins with g-factor values fixed to upon dissolution in acetonitrile.
2. The observed temperature dependence indicates that the
The UV/Visible spectrum of complex 1 in acetonitrile is
manganese ions are very weakly coupled. This contrasts reproduced in Figure 2 (dashed line-left scale). Two major
4810
www.eurjic.org
© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2005, 4808–4817

A Chemical Access to Mononuclear MnIV–OH Entities
FULL PAPER
bands are detected at 587 and 359 nm, with extinction coef- dation of complex 1, leading to the formation of [(py-salpn)-
ficient values (ε) of 3.1 and 8.9×103 m–1 cm–1, respectively, Mn(μ-OAc)Mn(μ-OAc)Mn(py-salpn)]3+
which further
,
with a shoulder at 450 nm (ε = 4.0×103 m–1 cm–1). The band evolves chemically. Unfortunately, the interaction of the
at 587 nm is attributed to a phenolatoǞMnIII ligand-to- oxidised tetraphenylborate ion generated at the electrode
metal charge transfer (LMCT) transition,[50,53,57,58] whereas surface with complex 1 and/or with the [(py-salpn)Mn(μ-
the other two transitions may originate from either phenol- OAc)Mn(μ-OAc)Mn(py-salpn)]3+ species renders the pro-
atoǞMnIII or acetatoǞMnIII LMCT transitions.[59] The cess difficult to analyse.
large ε values of the LMCT transitions prevent the observa-
tion of the MnIII d–d transitions, which are theoretically
expected with lower ε values.[60,61]
Figure 3. Cyclic voltammograms of 1(BPh4)2 (10–3 m in acetonitrile
with 0.1 m of tetrabutylammonium perchlorate). T = 20 °C and
scan rate = 100 mVs–1.
Figure 2. UV/Visible spectra of complex 1(BPh4)2 (10–3 m in aceto-
nitrile, dashed line) and immediately after the addition of 20 equiv-
alents of tBuOOH (solid line). T = 20 °C, l = 1 mm.
Chemical Oxidation
The cyclic voltammogram recorded under argon on a
The chemical oxidation of complex 1 was performed on
millimolar solution of complex 1 in acetonitrile in the pres-
a millimolar acetonitrile solution with tert-butyl hydroper-
ence of 0.1 m tetrabutylammonium perchlorate is presented
oxide (tBuOOH) as the oxidant. The oxidant was added in
in Figure 3. Two quasi-reversible waves of equal intensity
large excess (20 equivalents). Upon addition, the solution
are detected when scanning towards cathodic potentials at
turned from dark green to black. We will show in the next
E1/2 = 0.140 (ΔEP = 80 mV) and –0.075 V vs. SCE (ΔEP
= 80 mV), respectively.[62] When scanning towards anodic
potentials, an intense irreversible wave is observed at EP =
0.88 V vs. SCE that remains irreversible when reversing the
scan at 1.0 V vs. SCE. A second, weaker-intensity, irrevers-
ible wave is detected at EP = 1.16 V vs. SCE. The two re-
duction waves are attributed to two successive one-electron
reductions of complex 1, leading firstly to [(py-salpn)-
MnIII(μ-OAc)MnII(μ-OAc)MnII(py-salpn)]+ and then to
[(py-salpn)MnII(μ-OAc)MnII(μ-OAc)MnII(py-salpn)]. The
MnIII/MnII reduction process presents low potential values,
as it is to be expected considering the anionic environment
of the MnIII centre. These values are close to those reported
for other diphenolato-coordinated MnIII complexes.[63] The
detection of two single-electron MnIII/MnII processes pres-
enting E1/2 potentials that differs by 225 mV (ΔE1/2) is in-
dicative of a weak electrostatic interaction between the two
Figure 4. EPR spectra of complex 1(BPh4)2 (10–3 m in acetonitrile,
grey line) and immediately after the addition of 20 equivalents of
tBuOOH (black line). Recording conditions: 0.5 mT modulation
amplitude, 100 kHz modulation frequency, T = 100 K, 2.0 mW mi-
crowave power, ν = 9.39 GHz. The tBuO·– radical signal has been
MnIII ions. The low ΔE1/2 value is related to the long dis-
tance between the two MnIII ions (6.24 Å).[64] The first an-
odic process detected is attributed to the oxidation of the
tetraphenylborate counterion of complex 1,[65] and the sec-
ond irreversible anodic process may be attributed to the oxi- removed off the black trace.
Eur. J. Inorg. Chem. 2005, 4808–4817
© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
4811

C. Hureau, E. Anxolabéhère-Mallart, G. Blondin, E. Rivière, M. Nierlich
FULL PAPER
section that the chemical oxidation of complex 1 leads to gion and presents a strong absorbance in the UV domain.
the formation of high-valent Mn species (1ox). The 1ox spe- Shoulders are observed at 463 and 685 nm. These observa-
cies were characterised by UV/Visible and EPR spec- tions are reminiscent of previous observations for hydroxyl-
troscopy and ESI mass spectrometry.
rich[66] or for carboxylato[67] mononuclear MnIV Schiff-base
The UV/Visible spectrum of 1ox, shown in Figure 2 (so- complexes. The intense absorption band in the UV region
lid line, right scale), is mainly featureless in the visible re- may therefore be attributed to a phenolatoǞMnIV or to a
Figure 5. Electrospray mass spectrum of complex 1 (10–4 m in acetonitrile) recorded for the starting solution (top) and after addition of
20 equivalents of tBuOOH (bottom).
4812
www.eurjic.org
© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2005, 4808–4817

A Chemical Access to Mononuclear MnIV–OH Entities
FULL PAPER
hydroxoǞMnIV LMCT transition. The shoulders observed near geff = 1.5 suggest that the present MnIV species exhibits
in the visible region can be attributed to a poorly resolved a strong ZFS effect. The divergence from a geff value of
phenolatoǞMnIV MLCT[50,53,57] or to MnIV d–d transi- around 4 originates from the rhombicity of the ZFS. Ac-
tions, the strong intensity of which originates from the tail cording to the diagram showing the evolution of the geff
of the absorption in the UV region.
values for the two Kramer doublets as a function of E/D,[77]
The X-band EPR spectrum of 1ox at 100 K, recorded in one can see that the line positions at geff = 4.9, 3.0, 1.5 and
the perpendicular detection mode, is presented in Figure 4 1.17 can be well reproduced with E/D = 0.17. These first
(black line). An intense g = 2 signal corresponding to an two characterisations suggest that 1ox is a mononuclear
organic radical has been removed for clarity. The EPR sig- MnIV species.
nature of complex 1 recorded under the same conditions is
In order to identify the MnIV species formed, ESI/MS
also reproduced (grey line in Figure 4). The signal of com- experiments were performed. The mass spectra of com-
plex 1 differs slightly from trace c of Figure S2, with the plexes 1 and 1ox are presented in Figure 5. The mass spec-
low-field transitions being undetectable at this recording trum of complex 1 exhibits a major molecular peak at m/z
temperature. Four new transitions appear at geff = 4.9, 3.0, = 430 amu and three other peaks at m/z = 322, 324 and
1.5 and 1.17 after the addition of the oxidant.[68] These res- 365 amu.[78] The first peak is attributed to the mononuclear
onances are broad and show no evidence for 55Mn hyper- MnIII entity {[(py-salpn)Mn]}+, and the peaks at 322 and
fine coupling. The EPR signature of 1ox is indicative of an 324 amu correspond to MnII species, namely {[(L1imine)-
S = 3/2 MnIV ion. The complexity of the EPR spectrum of Mn]}+ and {[(L1)Mn]}+, where L1 stands for the (py-
a d3 species depends on the magnitude of the zero-field salpn)2– ligand after the loss of one phenolato arm and
splitting (ZFS) compared to the applied microwave fre- L1imine for L1 with a reduced secondary amine function (see
quency. In axial symmetry (E/D = 0), two limiting cases can Figure 5). The peak at m/z = 365 amu can be attributed to
be discussed depending on the relative magnitude of |2D| the adduct {[(L1)Mn]CH3CN}+, even though such solvated
vs. hν, where D is the axial ZFS parameter. At X-band (hν species are rarely detected under the present recording con-
= 0.3 cm–1), and when |2D| ϾϾ hν, the ZFS effect domi- ditions. After addition of tBuOOH, the peak at m/z =
nates the Zeeman effect, and a strong transition is expected 430 amu disappears and the peak at 322 amu increases in
at low field (geff Ϸ 4) with a weak component at around intensity together with the apparition of three new peaks at
geff = 2. This behaviour has been observed for numerous m/z = 428, 445 and 447 amu. The peak at 428 amu corre-
MnIV centres with anionic chelating ligands, such as hy- sponds to the MnIII species {[(py-salpnimine)Mn]}+, where
droxo, phenolato, carboxylato or anilido.[57,66,67,69–74] When subscript imine means that the secondary amine function
|2D| ϽϽ hν, the Zeeman effect dominates the ZFS effect has been oxidised to an imine (Scheme 1). The peaks at 445
and the signal is centred at geff Ϸ 2, with weaker lines at and 447 are attributed to the mononuclear hydroxo MnIV
both the low- and high-field edges. This behaviour has been entities {[(py-salpnimine)Mn(OH)]}+ and {[(py-salpn)-
reported for rare MnIV–tetraphenolato,[72] MnIV–thiohyd- Mn(OH)]}+, respectively. It is worth noting that the forma-
roxamato,[75] and MnIV–thiocarbamato[76] complexes. The tion of the imine function may be due to the use of the
strong absorption detected at geff = 4.9 and the weaker one oxidant tBuOOH. Species 1ox is subsequently attributed to
Scheme 2. Proposed mechanism for the formation of the MnIV–OH species.
Eur. J. Inorg. Chem. 2005, 4808–4817
© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
4813

C. Hureau, E. Anxolabéhère-Mallart, G. Blondin, E. Rivière, M. Nierlich
the Service de Microanalyse of the CNRS (Gif sur Yvette, France)
FULL PAPER
the mixture of the two MnIV monocations {[(py-salpnimine)-
Mn(OH)]}+ and {[(py-salpn)Mn(OH)]}+.
for carbon, nitrogen and hydrogen and by the Service Central
d’Analyse of CNRS (Vernaison, France) for manganese and chlo-
ride. Infrared spectra were recorded as KBr pellets in the range of
4000 to 200 cm–1 with a Perkin–Elmer Spectrum 1000 spectropho-
Lastly, according to the EPR spectra, we can propose
that the central MnII ion is oxidised into an EPR-silent
MnIII species, the UV/Visible signature of which may be
masked by the tail of the UV absorbance of complexes 1ox.
1
tometer. H NMR spectra were recorded withg a Bruker AM-250
(250 MHz) spectrometer. Electrospray ionisation mass spectra were
recorded with a Finnigan Mat95S in a BE configuration at low
resolution on millimolar acetonitrile solutions.
Formation of the MnIV–hydroxo Entities
A mechanism for the formation of the MnIV–hydroxo
species 1ox is tentatively proposed in Scheme 2. For clarity,
only the terminal MnIII ions of complex 1 are considered.
We propose that after the coordination of the tBuOOH oxi-
dant to the MnIII centre, the homolytic breakage of the O–
O bond[79] would lead to the release of the radical tBuO·–
and to the formation of the MnIV–OH complex.
We should mention that it is also plausible that the ace-
tate ion, which is a particularly strong base in acetonitrile
(pKa = 22)[80] would be able to deprotonate the hydroxo
ion coordinated to the MnIV ion, thus forming a MnIV–oxo
species. The EPR and UV/Visible spectra do not allow us
Caution: Perchlorate salts of metal complexes with organic ligands
are potentially explosive. Only small quantities of these compounds
should be prepared and they should be handled behind suitable protec-
tive shields.
Synthesis of H2py-salpn: The two-step synthesis of the ligand H2py-
salpn from the reduced H2salpn is shown in Scheme 3. The reduced
H2salpn ligand 2.86 g, (10 mmol), prepared according to a pre-
viously reported synthesis,[57] was dissolved in 100 mL of methanol
and 2-pyridinecarboxaldehyde (1 mL, 10 mmol) was added with
stirring. The white precipitate that appeared was filtered and
washed with methanol, and then redissolved in methanol by ad-
dition of two equivalents of trifluoroacetic acid. Two equivalents
of sodium cyanoborohydride were added and the solution and was
to discriminate an oxo from a hydroxo MnIV species. The stirred for 12 h. Methanol was eliminated and 150 mL of water was
added. The aqueous solution was extracted three times with 50 mL
of dichloromethane. After removal of the solvent, H2py-salpn was
obtained as a yellow oil. Yield: 62% (2.3 g). H NMR (250 MHz,
detection in of peaks at 445 and 447 amu in the ESI mass
spectrum may then be explained by the formation of a pro-
ton adduct of the neutral MnIV–oxo entities, leading to
{[(py-salpnimine)Mn(O)]H}+ and {[(py-salpn)Mn(O)]H}+. It
is also worth noting that the presence of the oxidised ligand
may be due to the formation of MnIV species or to the
tBuOOH itself.
1
CDCl3): δ = 8.29 (d, J = 4.6 Hz, 1 H, H-Py), 7.62–7.55 (m, 2 H,
H-Ar), 7.18–7.05 (m, 3 H, H-Ar), 7.00–6.93 (m, 2 H, H-Ar), 6.86
(d, 1 H, H-PhOH), 6.79 (d, 1 H, H-PhOH), 6.72–6.65 (m, 2 H, H-
Ar), 3.91 (s, 2 H, RN-CH2-PhOH), 3.77 (s, 2 H, RN-CH2-Py), 3.54
(s, 2 H, HN-CH2-PhOH), 2.65 (t, J = 5.8 Hz, 2 H, HN-CH2-CH2),
2.55 (t, J = 5.8 Hz, 2 H, RN-CH2-CH2), 1.78 (q, J = 5.8 Hz, 2 H,
CH2-CH2-CH2) ppm. 13C NMR (62.9 MHz, CDCl3) 157.5, 157.3,
156.6, 148.7, 137.3, 130.5, 129.8, 129.5, 129.3, 123.4, 122.9, 122.5,
120.0, 119.2, 119.1, 116.6, 58.2, 56.7, 52.2, 51.0, 47.6, 24.4 ppm.
Concluding Remarks
A new trinuclear MnIIIMnIIMnIII complex 1 containing
IR: ν = 1674 cm–1 (s), 1613 (m), 1595 (s), 1489 (m), 1460 (s), 1436
a bulky [N3O2] ligand derived from the H2salpn Schiff-base
˜
ligand by the addition of one pyridine arm has been iso- (m), 1383 (m), 1265 (s), 1201 (m), 1134 (m), 1104 (w), 737 (s). ESI-
MS: m/z (%) = 378.2 (45) [M + H]+, 272.2 (100) [M – CH2PhOH
lated and X-ray characterised. This complex has been fully
characterised by magnetic studies, UV/Visible, IR and EPR
+ H]+, 166.1 (60) [M – 2CH2PhOH + H]+.
spectroscopy, cyclic voltammetry and ESI mass spectrome-
try. The chemical oxidation of the trinuclear complex 1 by
tBuOOH leads to the formation of MnIV entities, which are
UV/Visible and EPR characterised and identified by mass
spectrometry as mononuclear MnIV–OH species.
From the recent crystallographic data obtained for the
Synechococcus elongatus PSII, a “3+1” structure has been
proposed for the OEC. Some water oxidation mechanisms
consistent with this recent structure favour the role of a
unique highly reactive Mn ion. In this context, the synthesis
and the complete characterisation of trinuclear species as
well as high-valence mononuclear Mn entities remains
highly relevant for the spectroscopic OEC modelling. In the
near future, it will be interesting to substitute the central
MnII ion in complex 1 by a calcium ion as such a putative
complex should present some OEC relevant Mn–Ca–car-
boxylate interactions.
Scheme 3. Synthetic route from reduced H2salpn to H2py-salpn.
Experimental Section
General Remarks: Reagents and solvents were purchased commer-
Synthesis of [(py-salpn)MnIII(μ-OAc)MnII(μ-OAc)MnIII(py-salpn)]-
(BPh4)2·2CH3CN·0.5H2O [1(BPh4)2·2CH3CN·0.5H2O]: Mn(OAc)3·
2H2O (268 mg, 1.0 mmol) was added to a 5 mL ethanol solution
cially and used as received. Elemental Analysis was performed by
4814
www.eurjic.org
© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2005, 4808–4817

A Chemical Access to Mononuclear MnIV–OH Entities
FULL PAPER
of H2py-salpn (377 mg, 1.0 mmol). The solution turned from pur-
ple to dark green. Addition of an excess (1.5 mmol) of sodium tet-
raphenylborate led to the precipitation of a dark green powder,
which was collected by filtration and washed carefully with ethanol.
SHELXTL.[83] All calculations were performed on a Silicon Graph-
ics R10000 workstation.
CCDC-233590 contains the supplementary crystallographic data
for this paper. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif.
Yield:
68%
(239 mg).
C
102H103B2N8O8.5Mn3
[1(BPh4)2·
2CH3CN·0.5H2O] (1761): calcd. C 69.5, H 5.9, N 6.3, B 1.2, Mn
9.3; found C 69.3, H 5.7, B 1.2, Mn 9.4, N 6.2. IR: ν = 3439 cm–1
˜
(m), 3176 (m), 3054 (m), 1602 (m), 1558 (s), 1483 (s), 1458 (m),
1444 (m), 1425 (s), 1345 (w), 1249 (s), 1204 (w), 1113 (w), 1006 (w),
791 (w), 760 (m), 734 (m), 708 (m), 655 (w), 612 (m), 573 (w). The
powder was then redissolved in acetonitrile and the solution was
filtered and placed in an atmosphere of diethyl ether. Crystals of
1(BPh4)2·3CH3CN suitable for X-ray crystallographic study were
obtained, collected by filtration, washed with diethyl ether and
dried in air.
Magnetic Susceptibility Measurements: Magnetic susceptibility data
were recorded on a MPMS5 magnetometer (Quantum Design
Inc.). The calibration was made at 298 K using a palladium refer-
ence sample furnished by Quantum Design Inc. The data were col-
lected over a temperature range of 50–300 K at a magnetic field of
5000 Oe and were corrected for diamagnetism.
EPR Spectroscopy: EPR spectra were recorded with a Bruker
ELEXSYS 500 spectrometer at X-band. For low-temperature stud-
ies, an Oxford Instruments continuous flow liquid helium cryostat
and a temperature control system were used. The quantity of free
MnII was estimated by comparison with spectra of Mn(ClO4)2·
6H2O dissolved in acetonitrile to various concentrations.
Crystallographic Data Collection and Refinement of the Structure of
1(BPh4)2·3CH3CN: The crystal data of 1(BPh4)2·3CH3CN and the
parameters of data collection are summarised in Table 2. Crystal
data for 1(BPh4)2·3CH3CN were collected on a Nonius Kappa-
CCD area detector diffractometer using graphite-monochromated
Mo-Kα radiation. The lattice parameters were determined from ten
images recorded with 2° φ-scans and later refined on all data. The
data were recorded at 123 K. A 180° φ-range was scanned with 2°
steps with a crystal-to-detector distance fixed at 30 mm. Data were
corrected for Lorentz polarisation. The structures were solved by
direct methods with SHELXS-86[81] and refined by full-matrix le-
ast-squares on F2 with anisotropic thermal parameters for all non-
H atoms with SHELXTL-93.[82] H atoms (unless H of CH3CN
solvent molecule) were introduced at calculated positions as riding
atoms with an isotropic displacement parameter equal to 1.2 (CH,
and CH2) or 1.5 (CH3) times that of the parent atom. The CH3CN
solvent molecules were found disordered over two positions with
0.5 occupancy factors. The molecular plots were drawn with
Cyclic Voltammetry: Cyclic voltammetry measurements were re-
corded with an EGG PAR potentiostat (M273 model). The counter
electrode was an Au wire, the working electrode a glassy carbon
disk, which was carefully polished before each voltammogram with
a 1-μm diamond paste, sonicated in an ethanol bath and then
washed carefully with ethanol. The reference electrode was an Ag/
AgClO4 electrode (0.530 V vs. NHE electrode), isolated in a fritted
bridge. The solvent used was distilled acetonitrile and tetrabu-
tylammonium perchlorate was added to obtain a 0.1 m supporting
electrolyte.
UV/Visible Spectroscopy: UV/Visible spectra were recorded with a
Cary 300 Bio spectrophotometer at 20 °C with 0.1-cm quartz cu-
vettes.
Supporting Information (see footnote on the first page of this arti-
cle): The X-band 10 K EPR spectra of millimolar dichloromethane
and acetonitrile solutions of complex 1 are presented in Figure S1
(traces b and c, respectively). Theoretical powder X-band EPR
Table 2. Details of structure determination, refinement and experi-
mental parameters for 1(BPh4)2·3CH3CN.
Empirical formula
C104H103B2Mn3N9O8
1793.39
123(2)
spectra calculated for a trinuclear system with two terminal St1
St2 = 1 and one central Sc = 1/2 spins (ν = 9.39 GHz, T = 10 K) is
given in Figure S2.
=
Formula mass [gmol–1]
Temperature [K]
Wavelength [Å]
0.71073
Crystal system
Space group
triclinic
P1
¯
Acknowledgments
a [Å]
11.573(2)
b [Å]
c [Å]
α [°]
β [°]
14.073(3)
15.889(3)
71.26(3)
85.08(3)
72.05(3)
2331.0(9)
1
We are grateful to Félix Perez for mass spectrometry measurements,
to Guillaume Blain for EPR technical assistance, and to Dr. Alain
Boussac (Service de Bioénergétique, URA CNRS 2096, CEA Sa-
clay, Gif-sur-Yvette, France) for EPR facilities. Laurent Sabater is
acknowledged for NMR technical assistance. We thank Prof. Jean-
Jacques Girerd and Prof. Vincent L. Pecoraro for stimulating dis-
cussions. The Conseil Régional de l’Ile de France is acknowledged
for its contribution to the acquisition of the Bruker ELEXSYS X-
band EPR spectrometer. The COST D21 European action and the
LRC-CEA project are acknowledged for their financial support.
γ [°]
Volume [Å3]
Z
Density (calculated) [gcm–3]
Absorption coefficient [mm–1]
Crystal size [mm]
θ range for data collection [°]
Index ranges
1.278
0.462
0.15×0.10×0.10
2.47 to 24.70
0 Յ h Յ 13, –15 Յ k Յ 16,
–18 Յ l Յ 18
14334
7285 [R(int) = 0.0530]
4705
Reflections collected
Independent reflections/R(int)
Data
[1] E. J. Larson, V. L. Pecoraro, in Manganese Redox Enzymes
(Ed.: V. L. Pecoraro), VCH Publishers, Inc., New York, 1992,
pp. 1–28.
[2] J. D. Crowley, D. A. Traynor, D. C. Weatherburn, in Metal Ions
in Biological Processes (Eds.: A. Sigel, H. Sigel), Marcel
Dekker, Basel, Switzerland, 2000, pp. 209–278.
[3] R. H. Holm, P. Kennepohl, E. I. Solomon, Chem. Rev. 1996,
96, 2239–2314.
Parameters
601
0.913
Goodness-of-fit on F2
Final R indices [I Ͼ 2σ(I)]
R indices (all data)
Largest diff. peak/hole [eÅ–3]
R1 = 0.0704, wR2 = 0.1893
R1 = 0.1131, wR2 = 0.2265
0.631/–0.433
Eur. J. Inorg. Chem. 2005, 4808–4817
© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
4815

C. Hureau, E. Anxolabéhère-Mallart, G. Blondin, E. Rivière, M. Nierlich
FULL PAPER
[4]
[37] T. J. Collins, R. D. Powell, C. Slebodnick, E. S. Uffelman, J.
Am. Chem. Soc. 1990, 112, 899–901.
V. V. Barynin, M. M. Whittaker, S. V. Antonyuk, V. S. Lamzin,
P. M. Harrison, P. J. Artymiuk, J. W. Whittaker, Structure 2001,
9, 725–738.
V. K. Yachandra, K. Sauer, M. P. Klein, Chem. Rev. 1996, 96,
2927–2950.
A. W. Rutherford, P. Faller, Trends Biochem. Sci. 2001, 26, 341–
344.
V. K. Yachandra, Philos. Trans. R. Soc. London, Ser. B 2002,
357, 1347–1358.
[38] T. J. Collins, S. W. Gordon-Wylie, J. Am. Chem. Soc. 1989, 111,
[5]
[6]
[7]
4511–4513.
[39] D. Feichtinger, D. A. Plattner, Chem. Eur. J. 2001, 7, 591–599.
[40] D. Feichtinger, D. A. Plattner, Angew. Chem. Int. Ed. Engl.
1997, 36, 1718–1719.
[41] J. El-Bahraoui, O. Wiest, D. Feichtinger, D. A. Plattner, Angew.
Chem. Int. Ed. 2001, 40, 2073–2076.
[42] D. Feichtinger, D. A. Plattner, J. Chem. Soc., Perkin Trans. 2
2000, 1023–1028.
[43] M. Hirotsu, M. Kojima, W. Mori, Y. Yoshikawa, Bull. Chem.
Soc. Jpn. 1998, 71, 2873–2884.
[44] M. Hirotsu, M. Kojima, Y. Yoshikawa, Bull. Chem. Soc. Jpn.
1997, 70, 649–657.
[45] X. Li, D. P. Kessissoglou, M. L. Kirk, C. J. Bender, V. L. Pecor-
aro, Inorg. Chem. 1988, 27, 1–3.
[46] D. P. Kessissoglou, M. L. Kirk, C. A. Bender, M. S. Lah, V. L.
Pecoraro, J. Chem. Soc., Chem. Commun. 1989, 84–86.
[47] D. P. Kessissoglou, M. L. Kirk, M. S. Lah, X. Li, C. Raptopou-
lou, W. E. Hatfield, V. L. Pecoraro, Inorg. Chem. 1992, 31,
5424–5432.
[48] V. Tangoulis, D. A. Malamatari, K. Soulti, V. Stergiou, C. P.
Raptopoulou, A. Terzis, T. A. Kabanos, D. P. Kessissoglou, In-
org. Chem. 1996, 35, 4974–4983.
[49] V. Tangoulis, D. A. Malamatari, G. A. Spyroulias, C. P. Rapto-
poulou, A. Terzis, D. P. Kessissoglou, Inorg. Chem. 2000, 39,
2621–2630.
[50] C. Hureau, L. Sabater, E. Anxolabéhère-Mallart, M. Nierlich,
M.-F. Charlot, F. Gonnet, E. Rivière, G. Blondin, Chem. Eur.
J. 2004, 10, 1998–2010.
[51] S. Pal, J. W. Gohdes, W. C. A. Wilisch, W. H. Armstrong, Inorg.
Chem. 1992, 31, 713–716.
[52] K. Wieghardt, U. Bossek, L. Zsolnai, G. Huttner, G. Blondin,
J.-J. Girerd, F. Babonneau, J. Chem. Soc., Chem. Commun.
1987, 651–653.
[53] O. Horner, E. Anxolabéhère-Mallart, M.-F. Charlot, L. Tchert-
anov, J. Guilhem, T. A. Mattioli, A. Boussac, J.-J. Girerd, Inorg.
Chem. 1999, 38, 1222–1232.
[54] J. Yoo, A. Yamaguchi, M. Nakano, J. Krzystek, W. E. Streib,
L.-C. Brunel, H. Ishimoto, G. Christou, D. N. Hendrickson,
Inorg. Chem. 2001, 40, 4604–4616.
[8]
[9]
A. W. Rutherford, A. Boussac, Science 2004, 303, 1782–1784.
P. Joliot, G. Barbieri, R. Chabaud, Photochem. Photobiol. 1969,
10, 309–329.
B. Kok, B. Forbush, M. McGloin, Photochem. Photobiol. 1970,
11, 457–475.
K. N. Ferreira, T. M. Iverson, K. Maghlaoui, J. Barber, S.
Iwata, Science 2004, 303, 1831–1838.
J. Biesiadka, B. Loll, J. Kern, K.-D. Irrgang, A. Zouni, Phys.
Chem. Chem. Phys. 2004, 6, 4733–4736.
J. P. McEvoy, G. W. Brudvig, Phys. Chem. Chem. Phys. 2004,
6, 4754–4763.
P. E. M. Siegbahn, R. H. Crabtree, J. Am. Chem. Soc. 1999,
121, 117–127.
P. E. M. Siegbahn, Inorg. Chem. 2000, 39, 2923–2935.
P. E. M. Siegbahn, Curr. Opin. Chem. Biol. 2002, 6, 227–235.
J. S. Vrettos, J. Limburg, G. W. Brudvig, Biochim. Biophys. Acta
2001, 1503, 229–245.
V. L. Pecoraro, M. J. Baldwin, M. T. Caudle, W.-Y. Hsieh,
N. A. Law, Pure Appl. Chem. 1998, 70, 925–929.
E. M. McGarrigle, D. G. Gilheany, Chem. Rev. 2005, 105,
1563–1602.
V. C. Quee-Smith, L. DelPizzo, S. H. Jureller, J. L. Kerschner,
R. Hage, Inorg. Chem. 1996, 35, 6461–6465.
D. De Vos, T. Bein, Chem. Commun. 1996, 917–918.
A. Berkessel, C. A. Sklorz, Tetrahedron Lett. 1999, 40, 7965–
7968.
J. Brinksma, L. Schmieder, G. Van Vliet, R. Boaron, R. Hage,
D. E. De Vos, P. L. Alsters, B. L. Feringa, Tetrahedron Lett.
2002, 43, 2619–2622.
C. Zondervan, R. Hage, B. L. Feringa, Chem. Commun. 1997,
419–420.
K. Srinivasan, P. Michaud, J. K. Kochi, J. Am. Chem. Soc.
1986, 108, 2309–2320.
R. Hage, J. E. Iburg, J. Kerschner, J. H. Koek, E. L. M. Lem-
pers, R. J. Martens, U. S. Racherla, S. W. Russell, T. Swarthoff,
M. R. P. van Vliet, J. B. Warnaar, L. van der Wolf, B. Krijnen,
Nature 1994, 369, 637–639.
[10]
[11]
[12]
[13]
[14]
[15]
[16]
[17]
[18]
[19]
[20]
[21]
[22]
[23]
[24]
[25]
[26]
[55] A. Yoshino, T. Miyagi, E. Asato, M. Mikuriya, Y. Sakata, K.-
i. Sugiura, K. Iwasaki, S. Hino, Chem. Commun. 2000, 1475–
1476.
[56]
H. Diril, H.-R. Chang, X. Zhang, S. K. Larsen, J. A. Potenza,
C. G. Pierpont, H. J. Schugar, S. S. Isied, D. N. Hendrickson,
J. Am. Chem. Soc. 1987, 109, 6207–6208.
[27]
[28]
[29]
T. Tzedakis, Y. Benzada, M. Comtat, Ind. Eng. Chem. Res.
2001, 40, 3435–3444.
[57]
A. Neves, S. M. D. Erthal, I. Vencato, A. S. Ceccato, Y. P. Mas-
carenhas, O. R. Nascimento, M. Hörner, A. A. Batista, Inorg.
Chem. 1992, 31, 4749–4755.
W. Zhang, J. L. Loebach, S. R. Wilson, E. N. Jacobsen, J. Am.
Chem. Soc. 1990, 112, 2801–2803.
H2salen = N,NЈ-bis(salicylidene)ethane-1,2-diamine, H2salpn =
N,NЈ-bis(salicylidene)propane-1,3-diamine, H2py-salpn = N-(2-
pyridylmethyl)-N,NЈ-bis(2-hydroxybenzyl)propane-1,3-diamine.
A. J. Wu, J. E. Penner-Hahn, V. L. Pecoraro, Chem. Rev. 2004,
104, 903–938.
A. Gelasco, M. L. Kirk, J. W. Kampf, V. L. Pecoraro, Inorg.
Chem. 1997, 36, 1829–1837.
M. J. Baldwin, V. L. Pecoraro, J. Am. Chem. Soc. 1996, 118,
11325–11326.
N. Aurangzeb, C. E. Hulme, C. A. McAuliffe, R. G. Pritchard,
M. Watkinson, M. R. Bermejo, A. Garcia-Deibe, M. Rey, J.
Sanmartin, A. Sousa, J. Chem. Soc., Chem. Commun. 1994,
1153–1155.
A. Gelasco, S. Bensiek, V. L. Pecoraro, Inorg. Chem. 1998, 28,
3301–3309.
F. M. MacDonnell, N. L. P. Flacker, C. Stern, T. V. O’Hallo-
ran, J. Am. Chem. Soc. 1994, 116, 7431–7432.
E. J. Larson, V. L. Pecoraro, J. Am. Chem. Soc. 1991, 113,
7809–7810.
[58]
[59]
[60]
J. A. Bonadies, M. J. Maroney, V. L. Pecoraro, Inorg. Chem.
1989, 28, 2044–2051.
C. Hureau, E. Anxolabéhère-Mallart, M. Nierlich, F. Gonnet,
E. Rivière, G. Blondin, Eur. J. Inorg. Chem. 2002, 2710–2719.
T. S. Davis, J. P. Fackler, M. J. Weeks, Inorg. Chem. 1968, 7,
1994–2002.
[30]
[31]
[32]
[33]
[61]
[62]
R. Dingle, Acta Chem. Scand. 1966, 20, 33–44.
E1/2 is defined as (EP + EPc)/2 and ΔEP = |EP – EPc|, where
a
a
EPa (EPc) is defined as the potential of the maximum of current
intensity when scanning toward anodic (cathodic) potentials.
See ref. and references cited therein.
J.-J. Girerd, E. Anxolabéhère-Mallart, in Spectroscopic Meth-
ods in Bioinorganic Chemistry, Vol. 14 (Eds.: E. I. Solomon,
K. O. Hodgson), American Chemical Society, Washington DC,
1998, pp. 262–271.
[57]
[63]
[64]
[34]
[35]
[36]
[65]
[66]
P. K. Pal, S. Chowdhury, M. G. B. Drew, D. Datta, New J.
Chem. 2002, 26, 367–371.
D. P. Kessissoglou, X. Li, W. M. Butler, V. L. Pecoraro, Inorg.
Chem. 1987, 26, 2487–2492 and references cited therein.
4816
www.eurjic.org
© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2005, 4808–4817

A Chemical Access to Mononuclear MnIV–OH Entities
FULL PAPER
[67] S. K. Chandra, P. Basu, D. Ray, S. Pal, A. Chakravorty, Inorg.
Chem. 1990, 29, 2423–2428.
[68] In addition, a multiline signal of small intensity is detected be-
tween 300 and 380 mT. This signal is attributed to the presence
of a small quantity of solvated MnII in solution.
[69] D. T. Richens, D. T. Sawyer, J. Am. Chem. Soc. 1979, 101,
3681–3683.
[77] B. H. Huynh, T. A. Kent, in Advances in Mössbauer Spec-
troscopy. Applications to Physics, Chemistry and Biology (Eds.:
B. V. Thosar, P. K. Iyengar, J. K. Srivastava, S. C. Bhargava),
Elsevier Science Publishers B. V., Amsterdam, 1983, pp. 490–
560.
[78] Detection of the molecular peak of the trinuclear complex 1
was always thwarted, whatever the experimental conditions.
[79] M. T. Caudle, P. J. Riggs-Gelasco, A. K. Gelasco, J. E. Penner-
Hahn, V. L. Pecoraro, Inorg. Chem. 1996, 35, 3577–3584.
[80] K. Izutsu, Acid-Base Dissociation Constants in Dipolar Aprotic
Solvents, Vol. 35, Blackwell Scientific Publications, Brookline
Village, M. A., 1990.
[81] G. M. Sheldrick, Acta Crystallogr., Sect. A 1990, 46, 467.
[82] G. M. Sheldrick, SHELXTL: Program for the Refinement of
Crystal Structures, University of Göttingen, Germany, 1993.
[83] G. M. Sheldrick, SHELXTL, Version 5.1, University of
Göttingen, Germany, 1999, distributed by Bruker AXS, Madi-
son, WI, USA.
[70] S. M. Saadeh, M. S. Lah, V. L. Pecoraro, Inorg. Chem. 1991,
30, 8–15.
[71] O. Schlager, K. Wieghardt, B. Nuber, Inorg. Chem. 1995, 34,
6456–6462.
[72] T. M. Rajendiran, J. W. Kampf, V. L. Pecoraro, Inorg. Chim.
Acta 2002, 339, 497–502.
[73] T. K. Paine, T. Weyhermüller, E. Bothe, K. Wieghardt, P.
Chaudhuri, Dalton Trans. 2003, 3136–3144.
[74] W. Adam, C. Mock-Knoblauch, C. R. Saha-Möller, M. Herd-
erich, J. Am. Chem. Soc. 2000, 122, 9685–9691.
[75] S. Pal, P. Ghosh, A. Chakravorty, Inorg. Chem. 1985, 24, 3704–
3706.
Received: June 3, 2005
[76] K. L. Brown, R. M. Golding, P. C. Healy, J. K. Jessop, W. C.
Tennant, Aust. J. Chem. 1974, 27, 2075–2081.
Published Online: October 20, 2005
Eur. J. Inorg. Chem. 2005, 4808–4817
© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
4817