The synthesis, structures and characterisation of new mixed-ligand manganese and iron complexes with tripodal, tetradentate ligands

Article abstract of DOI:10.1002/ejic.200701280

The preparation of new manganese and iron complexes with the general formula [M(tripod)(anion)] is described, where M = Fe^III or Mn ^III, tripod is a dianionic tetradentate tripodal ligand and the anion is a chelating β-diketonate, 8-oxyquinoline or acetate. The synthesis of this type of complexes was found to be straightforward, which allows for the preparation of a large variety of such coordination compounds. The complexes are characterised by X-ray crystallography, infrared spectroscopy, UV/Vis spectroscopy, cyclic voltammetry and elemental analysis. A correlation between the ligand sets and the electron density at the metal centre in the complexes is proposed, based on the UV/Vis data and the CV measurements. The tripodal ligands are significant π-donor ligands, and electron-withdrawing or electron-donating substituents on the phenolate arms were found to have a large influence on both the position of the d-d transitions in the UV/Vis spectra and the peak potentials in the CV measurements. The secondary β-diketonate or acetate ligand does not have such a large effect on the electron density of the metal centre. Wiley-VCH Verlag GmbH & Co. KGaA, 2008.

Full text of DOI:10.1002/ejic.200701280

FULL PAPER
DOI: 10.1002/ejic.200701280
The Synthesis, Structures and Characterisation of New Mixed-Ligand
Manganese and Iron Complexes with Tripodal, Tetradentate Ligands
Remy van Gorkum,[a] Joris Berding,[a] Allison M. Mills,[b] Huub Kooijman,[b]
Duncan M. Tooke,[b] Anthony L. Spek,[b] Ilpo Mutikainen,[c] Urho Turpeinen,[c]
Jan Reedijk,[a] and Elisabeth Bouwman*[a]
Keywords: Tripodal ligands / Iron / Manganese
The preparation of new manganese and iron complexes with
the general formula [M(tripod)(anion)] is described, where M
= FeIII or MnIII, “tripod” is a dianionic tetradentate tripodal
ligand and the anion is a chelating β-diketonate, 8-oxyquino-
line or acetate. The synthesis of this type of complexes was
found to be straightforward, which allows for the preparation
proposed, based on the UV/Vis data and the CV measure-
ments. The tripodal ligands are significant π-donor ligands,
and electron-withdrawing or electron-donating substituents
on the phenolate arms were found to have a large influence
on both the position of the d–d transitions in the UV/Vis spec-
tra and the peak potentials in the CV measurements. The
of a large variety of such coordination compounds. The com- “secondary” β-diketonate or acetate ligand does not have
plexes are characterised by X-ray crystallography, infrared
spectroscopy, UV/Vis spectroscopy, cyclic voltammetry and
elemental analysis. A correlation between the ligand sets and
the electron density at the metal centre in the complexes is
such a large effect on the electron density of the metal centre.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2008)
site could thus very well be good catalytic driers for alkyd
paints, especially if they are also able to catalytically decom-
pose hydroperoxides. The aim of our research is to find new,
metal complex based driers for alkyd paints, not containing
cobalt.[13–15] The use of cobalt compounds in paints is a
topic of concern, due to the toxicity and suspected carcino-
genity of cobalt.[16–19] The active site of the lipoxygenase
enzyme has been modelled by iron complexes using tripodal
ligands with exclusively nitrogen donor atoms.[20–23]
The general motivation for using tripodal ligands in the
development of paint-drying catalysts is that such large,
tetradentate ligands usually form very stable complexes
with manganese and iron. The structure of the formed com-
plexes is thus expected to be “robust” and not easily de-
stroyed under oxidising conditions. This last point is espe-
cially important, since the complexes that are made with
these ligands have to function as radical autoxidation cata-
lysts and are thus subject to extremely oxidising conditions.
An additional benefit of the used ligand type is that the
synthesis of the ligands is straightforward and variations on
the ligand structure are easily made. The tripodal ligands
that have been prepared all have one or two (substituted)
phenol groups. Consequently, these ligands can coordinate
as mono- or dianions. β-Diketonates were chosen as the
“secondary” ligand, because good autoxidation results were
obtained with simple, homoleptic manganese β-diketonate
complexes.[13,24]
Introduction
Tripodal ligands have been used abundantly in the syn-
thesis of metal complexes as model systems for the active
site of various enzymes. Chelating ligands in which one or
more of the “arms” consist of phenol groups have been
used extensively for the preparation of copper complexes
that model the active site of the enzyme galactose ox-
idase,[1–5] and also in the synthesis of iron and manganese
complexes to model the active sites of various dioxygenase
and phosphatase enzymes.[6–11] Lipoxygenases are non-
heme, non-sulfur iron or manganese dioxygenases that act
on lipid substrates containing one or more (Z,Z)-1,4-pen-
tadiene moieties.[12] Common polyunsaturated fatty acids,
such as linoleic, linolenic and arachidonic acids are the nat-
ural substrates for these enzymes, which are widely distrib-
uted among plants and animals. The primary reaction
products are hydroperoxides of conjugated (E,Z)-dienes,
which is why model complexes for the lipoxygenase active
[a] Leiden Institute of Chemistry, Gorlaeus Laboratories, Leiden
University,
P. O. Box 9502, 2300 RA Leiden, The Netherlands
Fax: +31-71-5274451
E-mail: bouwman@chem.leidenuniv.nl
[b] Bijvoet Center for Biomolecular Research, Crystal and Struc-
tural Chemistry, Utrecht University,
The Netherlands
[c] Laboratory of Inorganic Chemistry, Department of Chemistry,
University of Helsinki,
P. O. Box 55, (A.I.Virtasen aukio 1), 00014 Helsinki, Finland
Supporting information for this article is available on the
WWW under http://www.eurjic.org/ or from the author.
The complexes that are presented in this manuscript are
manganese(III) or iron(III) coordination compounds with
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E. Bouwman et al.
FULL PAPER
one dianionic tripodal ligand (Scheme 1) and one β-dike-
tonate ligand; some complexes have been prepared contain-
ing an anionic ligand such as 8-oxyquinoline or acetate in-
stead of the β-diketonate. The resulting complexes are non-
charged, which is expected to increase their solubility in
apolar solvents. For potential paint driers a good solubility
in the apolar paint medium is considered to be one of the
most crucial properties.[25]
Scheme 2. Overview of the synthesized complexes.
Scheme 1. Tripodal ligands used in this study.
The general method used to prepare these complexes was
to react a [M(β-diketonate)3] complex with the tripodal li-
gand in an appropriate solvent (typically CH2Cl2 or CHCl3)
with the addition of triethylamine. Alternatively, complex
4, [MnIII(pppy)(dpm)], could also be prepared by addition
of 1 equiv. of Hdpm and 1 equiv. of H2pppy to the manga-
nese salt [MnII(H2O)6](ClO4)2 in CH2Cl2 solution in the
Results and Discussion
Two strategies are commonly used to prepare tripodal
ligands based on a tertiary amine: By nucleophilic substitu-
tion of a chloro(bromo)alkyl group with a primary or sec-
ondary amine or through reductive amination, i.e. reaction
of an aldehyde with an appropriate amine, followed by re-
duction of the formed Schiff-base compound. The ligands
H2pppy and H2dnpppy have been prepared using the re-
ductive amination. The ligand H2pppy was obtained in
27% yield according to the reported method.[26] The ligand
H2dnpppy has been reported coordinated as a ligand in
copper and iron complexes,[27,28] but not as purified and
isolated molecule. Although H2dnpppy was obtained in
high purity, the overall yield was quite low, being only 14%.
The ligand H2tbpppy was prepared in one step using the
Mannich reaction; 2-aminomethylpyridine was treated with
2,4-di-tert-butylphenol and paraformaldehyde in refluxing
ethanol. Both the ligand and the used reaction method have
been reported in literature.[2] The literature method was fol-
lowed with the differences that the quantity of the reagents
was doubled, as was the reagent concentration in the reac-
tion mixture and the reaction time. This resulted in a higher
yield of 71%, vs. 56% reported in literature.
presence of 2 equiv. of triethylamine. Complex 5, [MnIII
-
(pppy)(quin)], was also prepared using the latter method.
Complex 9, [MnIII(tbpppy)(OAc)], was prepared according
to the general method employed for β-diketonate contain-
ing complexes but using manganese(III) acetate as a start-
ing compound.
The yields vary greatly (10–90%), but no attempts have
been undertaken to optimise the yield for each individual
complex. Since only a very small amount of complex is nec-
essary to examine its autoxidation activity,[14,29] obtaining
pure compounds was given higher priority than maximising
the yields.
Description of the Structures
Single crystals were obtained for the complexes 1–5 and
9, and their structures have been determined. The molecular
structures of the complexes 1–5 and 9 are depicted in Fig-
ure 1. A selection of bond lengths and angles is given in
Table 1 and Table 2.
The asymmetric units of 1 and 4 contain two indepen-
dent molecules. Although some bond lengths and angles
vary slightly for the two complexes in the asymmetric unit,
only the data for one of the independent molecules are
given in Table 1. For the three related complexes 1, 3 and 4
Complex Synthesis
The obtained complexes have the general formula [M(tri- the bond lengths are rather similar. The manganese(III) ion
pod)(anion)], in which M is FeIII or MnIII, “tripod” is one has a somewhat distorted octahedral coordination environ-
of the dianionic ligands pppy, dnpppy, or tbpppy and ment. The equatorial plane is composed of the two phenol-
“anion” is a bidentate monoanionic ligand such as 8- ate oxygen atoms of the tripodal ligand, the tertiary amine
oxyquinoline (quin), acetate (OAc), or one of the β-diketon- nitrogen and one of the β-diketonate oxygen donors. The
ates 2,4-pentanedionate (acac), 1,3-diphenylpropane-1,3-di- axial positions are occupied by the other β-diketonate oxy-
onate (dbm) and 2,2,6,6-tetramethyl-3,5-heptanedionate gen atom and the pyridyl nitrogen atom. The larger axial
(dpm). An overview of the synthesised complexes is given bond lengths, Mn1–N31 and Mn1–O46 are consistent with
in Scheme 2.
a Jahn–Teller distortion, as is expected for a high-spin octa-
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Eur. J. Inorg. Chem. 2008, 1487–1496

Mn and Fe Complexes with Tripodal, Tetradentate Ligands
Figure 1. Projections of the molecular structures of [Mn(pppy)(acac)] (1); [Fe(pppy)(acac)] (2); [Mn(pppy)(dbm)] (3); [Mn(pppy)(dpm)]
(4); [Mn(pppy)(quin)] (5); [Mn(tbpppy)(OAc)] (9). Hydrogen atoms have been omitted for clarity.
Table 1. Selected bond lengths [Å] and angles [°] for 1, 3 and 4.
O(phenolato) distances the two six-membered chelate rings
containing manganese, a phenolate oxygen atom and the
tertiary amine nitrogen atom are significantly puckered.
The difference in molecular structure for each of the com-
pounds 1, 3 or 4 is obviously related to the different β-
diketonate ligand that is coordinated in each of the com-
plexes. In all three complexes the β-diketonate ligand is co-
ordinated asymmetrically, with the longest Mn–O distance
trans to the pyridine nitrogen in the axial position. The
asymmetry is more pronounced in complexes 3 and 4. The
least-squares plane defined by the atoms of the acac ligand
in 1 makes an acute angle of 21.60° with the plane defined
by Mn1–O46–O47. Such a slight folding of the chelate ring
is frequently observed for β-diketonate ligands and is com-
monly attributed to packing effects in the crystal lattice.[31]
Similarly, the dpm ligand in 4 is folded over the O46–O47
axis, with a folding angle that is notably larger than for acac
in 1, being 31.2(2)°. This observation is in agreement with
the assumption that the folding is a consequence of the
crystal packing, since the dpm ligand is considerably more
bulky than the acac ligand. The dbm ligand in complex 3
is also slightly folded, but the folding angle is the smallest
of the three complexes, being only 7.99(6)°.
1
3
4
Mn1–N1
Mn1–N31
Mn1–O17
Mn1–O27
2.1631(15) 2.1425(11) 2.104(5)
2.2281(17) 2.2205(11) 2.231(5)
1.8894(13) 1.8703(10) 1.870(4)
1.8672(13) 1.8739(10) 1.873(4)
Mn1–O46
Mn1–O47
2.0843(14) 2.1145(9)
2.0230(13) 1.9854(11) 1.969(4)
2.112(4)
N1–Mn1–N31
O17–Mn1–O27
O17–Mn1–O46
O17–Mn1–O47
O17–Mn1–N1
O17–Mn1–N31
O27–Mn1–O46
O27–Mn1–O47
O27–Mn1–N1
O27–Mn1–N31
O46–Mn1–O47
O46–Mn1–N1
O46–Mn1–N31
O47–Mn1–N1
O47–Mn1–N31
78.11(6)
177.52(6)
91.14(6)
91.47(5)
91.85(6)
91.30(6)
90.46(6)
90.48(5)
86.08(6)
86.93(6)
88.25(6)
96.26(6)
173.94(6)
174.34(6)
97.23(6)
78.46(4)
175.00(4)
89.86(4)
87.83(4)
93.26(4)
86.38(4)
93.76(5)
88.89(4)
90.04(4)
90.60(5)
87.46(4)
92.28(4)
169.77(4)
178.88(4)
101.88(4)
7.99(6)
79.38(19)
177.70(17)
87.22(17)
88.73(18)
92.12(18)
86.90(17)
94.02(17)
89.40(18)
89.67(18)
92.02(17)
87.10(17)
96.06(18)
172.41(19)
176.77(17)
97.56(18)
31.2(2)
folding angle over O46–O47 21.60(9)
hedral d4 metal ion. The Mn1–O(phenolato) distances fall
within the range reported for related MnIII–O(phenolato)
Complex 2 is an iron(III) complex that has the same li-
gand set as complex 1. In contrast to complex 1, the two
distances.[30] To accommodate the relatively short MnIII
–
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E. Bouwman et al.
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Table 2. Selected bond lengths [Å] and angles [°] for the complexes 2, 5 and 9.
2
5
9
Fe1–N2
Fe1–N31
Fe1–O17
Fe1–O27
Fe1–O46
Fe1–O47
2.1972(15)
2.181(2)
1.9047(16)
1.9299(15)
2.0948(15)
1.9924(15)
77.17(7)
100.18(7)
91.66(6)
100.18(6)
88.83(7)
165.08(7)
168.15(7)
92.13(6)
92.48(6)
85.77(7)
Mn1–N101
Mn1–N131
Mn1–O117
Mn1–O127
Mn1–O201
Mn1–N201
N101–Mn1–N131
O117–Mn1–O127
O117–Mn1–O201
O117–Mn1–N201
O117–Mn1–N101
O117–Mn1–N131
O127–Mn1–O201
O127–Mn1–N201
O127–Mn1–N101
O127–Mn1–N131
O201–Mn1–N201
O201–Mn1–N101
O201–Mn1–N131
N201–Mn1–N101
N201–Mn1–N131
2.237(3)
2.110(3)
1.8794(19)
1.896(2)
1.9133(19)
2.236(3)
78.28(12)
91.33(9)
175.46(13)
97.50(11)
90.35(10)
89.56(9)
Mn1–N18
Mn1–N31
Mn1–O10
Mn1O20
Mn1–O2
Mn1–O1
2.095(4)
2.223(4)
1.844(4)
1.867(4)
2.351(4)
1.998(4)
N2–Fe1–N31
O17–Fe1–O27
O17–Fe1–O46
O17–Fe1–O47
O17–Fe1–N2
O17–Fe1–N31
O27–Fe1–O46
O27–Fe1–O47
O27–Fe1–N2
O27–Fe1–N31
O46–Fe1–O47
O46–Fe1–N2
O46–Fe1–N31
O47–Fe1–N2
O47–Fe1–N31
folding angle over O46–O47
N18–Mn1–N31 78.93(15)
O10–Mn1–O20
O10–Mn1–O2
O10–Mn1–O1
O10–Mn1–N18 91.82(18)
O10–Mn1–N31 96.06(17)
O20–Mn1–O2
O20–Mn1–O1
O20–Mn1–N18 92.43(18)
O20–Mn1–N31 89.96(17)
O2–Mn1–O1
O2–Mn1–N18
O2–Mn1–N31
O1–Mn1–N18
O1–Mn1–N31
173.20(14)
86.19(16)
87.09(15)
92.28(9)
87.46(16)
87.62(15)
96.44(11)
91.89(11)
170.14(13)
79.37(10)
92.27(10)
87.35(9)
86.25(6)
87.20(6)
82.61(7)
169.00(6)
93.22(7)
59.69(15)
108.00(15)
172.70(16)
167.68(16)
113.39(16)
168.39(9)
93.18(12)
10.25(10)
phenolato oxygen atoms are now coordinated in cis posi-
Compound [Mn(tbpppy)(OAc)] (9) is different from all
tions. In complex 1, the phenolato arms are more or less the complexes discussed so far, given that the complex has
“forced” to occupy trans positions to allow for a Jahn– a pppy ligand with bulky tert-butyl substituents on the phe-
Teller distortion. Because the d5 high-spin iron(III) ion is nolate groups. Furthermore, it has a bidentate acetate li-
not prone to the Jahn–Teller effect, the phenolato arms can gand as the second anionic ligand, binding in a significantly
occupy cis positions, thus allowing for a less distorted octa- asymmetric fashion. The Mn1–O2 bond is rather long due
hedron. A similar arrangement of cis-phenolate groups has to the Jahn–Teller distortion and the small bite-angle of the
been reported for an iron(III) complex of an analogous acetate ligand, however, since the N31–Mn1–O2 bond angle
tripodal ligand with a tetrahydrofuran group instead of the is 172.70(16)°, the O2 acetate oxygen is reasonably well
pyridine group.[32] The Fe1–O(phenolato) distances are con- aligned with the octahedral z-axis. The O1 acetate oxygen
current with published values.[28] The Fe1–N31(pyridine) forms a regular Mn1–O1OAc bond of 1.998(4) Å but has a
and Fe1–N2(amine) bond lengths are typical for FeIII–N N18–Mn1–O1 bond angle of 167.68(18)°. The tbpppy li-
bonds.[28] The acac ligand in complex 2 is bound asymmet- gand binding distances are in the same range as for the
rically, with the Fe1–O47 distance shorter than the Fe1– manganese pppy complexes. The tert-butyl substituents on
O46 distance. The folding out of the chelate plane for the the pppy ligand thus do not seem to have a significant influ-
acac ligand is less than in complex 1, being 10.25(10)°.
The asymmetric unit of complex 5 contains one complex
molecule and one molecule of dichloromethane. The
oxyquinoline ligand in the compound [MnIII(pppy)(quin)]
(5) allows for the pppy ligand to adopt cis positions for the
phenolate arms. The Jahn–Teller axis is now located along
the bonds Mn1–N201 and Mn1–N101. The Jahn–Teller dis-
tortion is clearly visible in complex 5, since the Mn–N-
(amine) distance is notably larger than those in the com-
plexes 1, 3 and 4. Also, the Mn–N(py) distance is shorter
in complex 5 than in each of the complexes 1, 3 and 4,
because in complex 5 the pyridyl arm is not in an axial
ence on the coordination geometry of complex 9. A similar
structure has been reported for copper: [CuII(Htbpppy)-
(OAc)].[2] In this copper complex one of the two phenolate
oxygen atoms is not deprotonated (but still coordinated)
and the copper ion has a square-pyramidal coordination
geometry with the acetate anion coordinated as a mono-
dentate ligand.
Electronic Absorption Spectroscopy
The electronic absorption spectra for the manganese(III)
position. The equatorial plane of the coordination octahe- complexes have been recorded in CH2Cl2 solution; the data
dron consists of the pyridine nitrogen, the two cis phenolate are collected in Table S1. The electronic spectrum of 1 as a
oxygen atoms and the quinolinato oxygen atom. In contrast typical example is given in Figure S1. The free-ion ground
5
with the folding observed for β-diketonate ligands, the man- term for high-spin d4 manganese(III) is D. In an octahe-
ganese ion lies in the chelate plane of the 8-oxyquinoline dral ligand field this term is split in 5T2g and 5Eg, and there
5
ligand.
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would be one spin-allowed transition: T2g ǟ 5Eg.[33] How-
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Mn and Fe Complexes with Tripodal, Tetradentate Ligands
ever, since the complexes are all axially elongated due to ferent from the values observed for the complexes with the
5
5
the Jahn–Teller effect, the Eg term is further split in B1g pppy ligand.
5
5
5
5
and A1g and the T2g term in B2g and Eg. Three spin-
The electronic absorption spectra of the two iron com-
allowed transitions would now theoretically be possible: plexes 2 and 7 have also been recorded (see the electronic
5A1g ǟ 5B1g, 5B2g ǟ 5B1g and 5Eg ǟ 5B1g. Only one d–d spectra of 2 and 7 in Figure S2). As is expected, no absorp-
transition could be observed for all the measured complexes tions due to d–d transitions are observed for the iron com-
in the range 625–720 nm, tentatively attributed to plexes, since these are spin-forbidden for the high-spin d5
5B2g ǟ 5B1g.[33,34] Since this transition has an energy equal FeIII ion and therefore extremely weak. As for the manga-
to 10 Dq,[34] the ligand-field splitting of the d-orbitals is nese complexes, two absorptions are attributed to L Ǟ M
thus directly assessable for each of the manganese com- charge transfer transitions.[7,28,39,40] The absorption around
plexes. The obtained values for 10 Dq are in good agree- 280 nm could be due to the π3–π4 transition of the acac
ment with reported values for related manganese(III) com- ligand (as it was assigned in the manganese complexes).
plexes.[34] Two absorptions between 350–520 nm are as- However, the same absorption was reported for a similar
signed as L Ǟ M charge-transfer transitions from a pπ or- iron(III) complex with a bis(phenolate) ligand without a β-
bital on a phenolate oxygen to the partially-filled dπ orbit- diketonate ligand;[39] and could thus also be due to a tripo-
als on the manganese ion, in analogy with assignments dal ligand π–π* absorption. The transitions for complex 7
made for other MnIII complexes with phenolate li- with the tert-butyl-substituted pppy ligand are shifted to
gands.[30,35] The assignment is tentative for complex 5, since lower energy, as is expected and also observed for the man-
the oxyquinoline ligand also has a π–π* transition in this ganese complexes with the tbpppy ligand. Furthermore, all
region.[36] An absorption around 320 nm in complexes with the absorptions for complex 7 have a lower extinction coef-
a β-diketonate ligand is assigned to a M ǞL transition ficient than for complex 2.
from the metal dxz or dyz orbital to the β-diketonate π4
orbital (see LCAO-MO calculations for the π-energy levels
of metal β-diketonates by Barnum),[37,38] in agreement with
Cyclic Voltammetry
the assignment for [MnIII(acac)3]. The observation of this
transition supports the assumption that the β-diketonate li-
The cyclic voltammograms (CVs) of all complexes with
gands do not dissociate in CH2Cl2 solution. In the com- an unsubstituted pppy ligand (complexes 1–5) are depicted
plexes 3 and 10 this absorption is obscured by very intense in Figure 2. The peak potentials and E1/2 values calculated
π–π* charge-transfer transitions, due to the phenyl rings of from each of those CV measurements are listed in Table 3,
the dbm ligand for 3 and the nitro groups on the dnpppy as are the peak potentials obtained from the CVs of com-
ligand for 10.[7,39] All manganese complexes show an ab- plex 10 (shown in Figure S3). All these complexes show
sorption at around 230–260 nm, which is attributed to a comparable CVs: a (pseudo) reversible couple at positive
π–π* transition originating from the (substituted) pppy potential (1ox and 1red, termed “couple 1”) and two peaks
ligand.
at negative potential (2red and 3ox). The iron complex 2 dif-
The average value of 10 Dq for each of the manganese fers from the Mn complexes; it displays a reversible couple
complexes with a pppy-type tripodal ligand is: 14000 cm–1 at negative potential and shows an irreversible oxidation at
(tbpppy) Ͻ 15400 cm–1 (pppy) Ͻ 16000 cm–1 (dnpppy). positive potential. For each of the complexes 1–5 it was
Substitution of the phenolate rings with electron-donating observed that if the potential is scanned beyond +1.5 V, an
tert-butyl groups thus results in smaller ligand-field split- additional irreversible oxidation peak can be detected, but
ting, while substitution of the phenolate rings with electron- then no reduction peaks occur over the entire potential
withdrawing nitro groups results in larger ligand-field split- range on the return scan, indicating decomposition of the
ting relative to the unsubstituted pppy ligand. It is thus complex at the electrode. The CVs. of the complexes with
clear that the tripodal ligands are predominantly π-donor tert-butyl-substituted pppy ligand (6–9) are provided in Fig-
ligands. The relative order for the values of 10 Dq would ure S4; the peak potentials derived from these CVs. are
likely be reversed if σ-type donation of the phenolate oxy- listed in Table S2. Compounds 6 and 8 have very similar
gens would play a more important role.
CVs. when scanned up to 1.2 V, with one broad oxidation
Another interesting observation is that the ligand-field peak (1ox) and two reduction peaks (1red and 4red) at posi-
splitting of the manganese(III) ion is mainly influenced by tive potential. Only very small oxidation and reduction
the tripodal ligand and hardly by the “secondary” ligand. peaks are visible at negative potentials.
This is clear from the values for 10 Dq for complexes with
The effect of substituting the tripodal ligand with elec-
the same tripodal ligand, but with different “secondary” tron-donating or -withdrawing groups on the redox poten-
ligands, for example the complexes 1, 3 and 4 which all have tials of the manganese complexes is clearly discernible: the
a different β-diketonate ligand but the same pppy ligand. peak potential designated as 1ox shifts from 0.98 V to
These three complexes have very similar values for 10 Dq 0.74 V to 0.67 V for complex 10 (dnpppy), 1 (pppy) and 6
(15400 cm–1 on average). The same observation can be (tbpppy), respectively. The position of redox couple 1 (com-
made for the complexes with a tbpppy ligand (6, 9 and 8), plexes 1–5, and 10) thus evidently depends on the electron
which also all have nearly identical values for 10 Dq density on the metal centre and is therefore attributed to
(14000 cm–1 on average), but these values are clearly dif- the metal-centred redox couple MnIII/MnIV. The peaks at
Eur. J. Inorg. Chem. 2008, 1487–1496
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1491

E. Bouwman et al.
FULL PAPER
negative potential are also attributed to metal-centered pro-
cesses, and are assigned as the reduction to MnII (2red) and
the re-oxidation to MnIII (3ox), in analogy with the assign-
ment for [MnIII(acac)3].[13] The manganese complexes with
a pppy ligand all show very similar CVs, regardless of the
used “secondary” β-diketonate or oxyquinoline ligand.
Only a small effect is visible for the complexes with the
more electron-donating secondary ligands dpm (4) and
quin (5): the peak potentials are shifted to slightly lower
values relative to the potentials for complex 1. The ligand
field data also showed this trend; the secondary ligands
have little influence on the ligand-field splitting of the metal
ion. Relative to [Mn(acac)3],[13] the position of the MnIII
/
MnIV couples for [Mn(pppy)(acac)] have shifted by 0.39 V
to a lower potential. The higher oxidation state MnIV is
thus greatly stabilised in the pppy complexes, due to the
very good donor capacity of the tripodal ligand. Conse-
quently, reduction to MnII is quite difficult for all the Mn
complexes with a pppy ligand and especially with the do-
nating tbpppy ligand.
A MnIII reduction peak is hardly visible for complexes 6
and 8. The appearance of “couple 1”, the reversible couple
at positive potential that all manganese complexes with the
pppy ligand have, is not apparent for the complexes with a
tbpppy ligand. The tbpppy ligand is more easily oxidised
than the pppy ligand,[8,41] and for complexes 6 and 8 the
peak potentials 1ox, 1red and 4red might not be solely metal-
centred. The direct oxidation/reduction potentials of the
4,6-di-tert-butylphenolate arms of the tbpppy ligand are as-
signed to couples 2 and 3.[41,42] Complex 8 also shows two
oxidation potentials at higher potentials, but these are
irreversible and cause the deposition of insoluble oxidation
products on the working electrode. An assignment other
than purely manganese-based for the redox processes of 6
and 8 can be that the complex is first oxidised to MnIV and
then one of the coordinated phenolate ligands is at least
partially oxidised to a phenoxy radical by MnIV. Schmitt
and co-workers have reported such a sequence of events for
a MnIII complex with a ligand containing three phenolate
groups.[43] In the case of compound 6, the resulting species
[MnIII(tbpppy·)(acac)] is reduced back to the starting com-
pound at the peak potential 4red, as shown in Scheme 3.
The tiny shoulder 1red becomes more prominent upon in-
crease of the scan rate. This small shoulder can be attrib-
uted to the direct electrochemical reduction of the MnIV
species that is initially formed by the oxidation 1ox
Figure 2. Cyclic voltammograms of the complexes 1–5 with pppy.
Scan rate for each of the CVs was 200 mV/s.
Table 3. Peak potentials E (in V vs. Ag/AgCl) of complexes 1–5 and 10 as determined from cyclic voltammetry.[a]
MIII/MIV
1ox
MIII/MII
2red
Compound
1red
1E1/2
3ox
[MnIII(pppy)(acac)] (1)
[MnIII(pppy)(dbm)] (3)
[MnIII(pppy)(dpm)] (4)
[MnIII(pppy)(quin)] (5)
[FeIII(pppy)(acac)] (2)
[MnIII(dnpppy)(acac)] (10)
0.74
0.77
0.64
0.59
0.94
0.98
0.48
0.51
0.46
0.47
–
0.61
0.64
0.55
0.53
–
–1.08
–0.99
–1.12
–0.84
–1.08
–0.38
0
–0.07
–0.18
–0.20
–0.87
0.166
0.8
0.89
[a] CV on 1 m solutions of the complex in CH2Cl2 under argon, Electrolyte 0.1  [N(butyl)4]PF6, Pt working electrode and Ag/AgCl
reference electrode, E1/2 = (Eox + Ered)/2. See Figure 2.
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Eur. J. Inorg. Chem. 2008, 1487–1496

Mn and Fe Complexes with Tripodal, Tetradentate Ligands
(Scheme 3). The assumed radical species [MnIII(tbpppy·)(β- cant π-donor ligands, and electron-withdrawing or electron-
diketonate)] is likely to be more stable, due to delocalisation donating substituents on the phenolate arms were found
of the radical over both phenolate arms and perhaps even to have a large influence on both the position of the d–d
over the β-diketonate ligand.
transitions in the UV/Vis spectra and the peak potentials
in the CV measurements. The “secondary” β-diketonate or
acetate ligand does not have such a large effect on the elec-
tron density of the metal centre. Complexes with the same
tripodal ligand but different β-diketonate ligands (for exam-
ple 1, 3–5) were found to have very similar cyclic voltammo-
grams and a comparable energy for the observed d–d transi-
tion.
Especially the complexes of the tert-butyl-substituted li-
gand have excellent solubility in apolar solvent, necessary
for their possible application in alkyd paint drying. The ac-
tivity of the complexes in the autoxidation of ethyl linoleate
and the proposed mechanism of the oxidation reactions are
reported elsewhere.[29]
Scheme 3. Assignment of the peak potentials 1ox, 1red, and 4red in
the CVs of complexes 6 and 8. See text for explanation.
Complex 9 does not show any reversible redox couple.
Apparently, the secondary ligand does have an influence on
stabilising higher oxidation states and the acetate ligand
might just not be electron-donating enough. The peak po-
tentials 1ox, 2ox and 3ox are tentatively attributable to oxi-
dation to MnIV and oxidations of the tbpppy ligand, but
assigning the peak potentials is not unambiguous. The
peaks 4red and 5ox are due to reduction to MnII and then
oxidation of a MnII species.
The lower donor capacity of the ligand dnpppy results
in a metal centre which is much easier to reduce, as the peak
potential 2red has shifted to a considerable more positive
potential relative to the value for complex 1 (see Table 3).
Consequently, redox couple 1 has shifted to a significantly
more positive E1/2 value.
The peak potentials of the iron complexes 2 (Figure 2)
and 7 are influenced by the tripodal ligand, just as observed
for the manganese complexes. The iron complex with a
pppy ligand (2) does not show a reversible oxidation at pos-
itive potential, probably because the FeIV state is less easily
attained than the MnIV state. The oxidation peak 1ox can
thus be attributed to the irreversible oxidation to FeIV or to
a ligand based oxidation. The couple 2ox,red can probably
be attributed to the FeII/FeIII redox couple. The iron com-
plex with the tbpppy ligand (7) does show an oxidation and
a reduction at positive potential (2ox = 1.01 V, 2red = 0.72 V)
which is tentatively assigned to the oxidation an reduction
of one of the phenolate arms of the tbpppy ligand.[42] The
shoulder on the peak 2ox, 1ox, might be due to either oxi-
dation to FeIV or ligand oxidation.
Experimental Section
General: Salicylaldehyde, 2-(aminomethyl)pyridine, 2-hydroxy-5-ni-
trobenzaldehyde, 2,4-di-tert-butylphenol, paraformaldehyde, 2,4-
pentanedione, 1,3-diphenylpropane-1,3-dione and 2,2,6,6-tetra-
methyl-3,5-heptanedione were purchased from Fisher Scientific
and used as received. The complexes [MnIII(acac)3],[44] [FeIII
-
(acac)3],[45] [MnIII(dpm)3],[46] and [MnIII(dbm)3],[47] were prepared
according to literature procedures.
1
Physical Measurements: H NMR measurements were carried out
with a 200 MHz Jeol FX-200 spectrometer equipped with a Tecmag
data station. Infrared spectroscopy was done with a Perkin–Elmer
1000 FT-IR spectrophotometer, with a diamond ATR device. UV/
Vis spectra were recorded with a Varian Cary 50 spectrophotometer
and elemental analyses on C, H and N were performed with a
Perkin–Elmer series II CHNS/O Analyzer 2400. Cyclic voltamme-
try measurements were performed on CH2Cl2 solutions with an
Autolab PGSTAT 10 potentiostat using an Ag/AgCl reference elec-
trode, a Pt working electrode and a Pt counter electrode with 0.1 
tetrabutylammonium hexafluorophosphate as an electrolyte. Ferro-
cene was measured as a reference under the exact same conditions
as the complexes; E1/2 = 0.45 V vs. Ag/AgCl.
Ligand Synthesis: 2-[(2-Hydroxybenzyl)aminomethyl]pyridine.[26]
This compound was obtained as a light yellow needles in 67% yield
(2.86 g) after column purification, following a literature procedure.
In a different batch, the crude product was obtained as a yellow
oil (the column purification was omitted) in 80% yield (8.53 g).
This oil is sufficiently pure for further reactions. 1H NMR (CDCl3):
(yellow needles): δ = 8.58 (m, 1 H, py), 7.67 (dt, 1 H, py), 7.19 (m,
2 H, py), 7.25–6.78 (m, 4 H, aryl), 4.02 (s, 2 H, N-CH2-phenol),
Conclusions
3.93 (s, 2 H, N-CH -py) ppm. IR (neat): ν = 3265, 2948, 2916,
˜
2
2860, 1593, 1568, 1481, 1464, 1456, 1428, 1354, 1320, 1279, 1278,
1258, 1218, 1187, 1149, 1108, 1088, 1069, 1045, 1038, 984, 979,
968, 923, 863, 845, 810, 794, 746, 624, 564, 543, 508, 472, 460, 438,
404 cm–1.
Several new mononuclear manganese and iron complexes
of dianionic tripodal ligands have been prepared. Variation
of the complexes, employing various ligand combinations
show interesting variations in properties, which are useful
in the study of a structure–activity relationship in oxidation
catalysis.
A clear correlation between the ligand sets and the elec-
tron density of the metal centre in the complexes could be
made, as was shown by the UV/Vis data and corroborated
2-[Bis(2-hydroxybenzyl)aminomethyl]pyridine (H2pppy):[26] This
compound was synthesised according to literature, and was ob-
tained as a white powder in 27% yield (1.75 g). 1H NMR (CDCl3):
δ = 8.67 (d, 1 H, py), 7.73 (dt, 1 H, py), 7.30 (m, 1 H, py), 7.23–
7.13 (m, 3 H, aryl and py), 7.09 (dd, 2 H, aryl), 6.90–6.76 (m, 4 H,
aryl), 3.92 (s, 2 H, CH2-Py), 3.85 (s, 4 H, CH2-phenol) ppm. IR
by the CV measurements. The tripodal ligands are signifi- (neat): ν = 3014, 2924, 2825, 1585, 1490, 1431, 1379, 1281, 1250,
˜
Eur. J. Inorg. Chem. 2008, 1487–1496
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1493

E. Bouwman et al.
FULL PAPER
1188, 1149, 1090, 1040, 1004, 977, 956, 934, 868, 852, 807, 746,
630, 478 cm–1.
and 0.5 mmol (0.160 g) H2pppy. The brown powder that was ini-
tially obtained contained Hdbm as an impurity and needed to be
recrystallised twice from CH2Cl2/n-hexane to obtain pure com-
pound 3. The yield of the recrystallised brown powder was 120 mg
(40%). C35H29MnN2O4 (596.56): calcd. C 70.47, H 4.90, N 4.70;
2-[Bis(2-hydroxy-5-nitrobenzyl)aminomethyl]pyridine (H2dnpppy):
The intermediate compound 2-[(2-hydroxy-5-nitrobenzyl)amino-
methyl]pyridine was prepared according to the literature method[26]
and the obtained yellow powder was used without further purifica-
tion for the synthesis of H2dnpppy. H2dnpppy was prepared ac-
cording to the method for H2pppy, but column purification of the
final product proved to be unnecessary: washing the crude yellow
powder with CHCl3 resulted in the pure ligand in 14% (0.45 g)
yield. 1H NMR ([D6]acetone): δ = 8.68 (d, 1 H, OH), 8.17 (d, 2 H,
aryl), 8.08 (d, 2 H, aryl), 8.01 (d, 1 H, py), 7.93 (t, 1 H, aryl), 7.46
(t, 2 H, py), 6.93 [d, 2 H, ar (ortho to OH)], 4.13 (s, 2 H, py-CH2),
found C 69.21, H 4.92, N 4.85. IR (neat): ν ≈ 3050 (arom. C-H),
˜
1592, 1550, 1513, 1476, 1449, 1379, 1334, 1292, 1274, 1224, 1180,
1162, 1070, 1056, 1019, 1000, 965, 938, 927, 887, 876, 850, 808,
778, 750, 736, 724, 695, 680, 639, 618, 610, 566, 530, 489, 476, 422,
389, 343, 324 .
[MnIII(pppy)(dpm)] (4): This complex has been prepared following
two different methods:
A: According to the general method, starting from 0.5 mmol
(0.302 g) [MnIII(dpm)3] and 0.5 mmol (0.160 g) H2pppy, no triethyl-
amine was added in this synthesis. Black crystalline material was
obtained from the acetone solution, after addition of H2O. Another
batch of crystalline material was obtained from this solution after
standing overnight at +4 °C. Total yield 92 mg (33%). Single crys-
tals suitable for X-ray diffraction were obtained from letting an
acetone/H2O solution of the complex stand at +4 °C.
4.07 (s, 4 H, ar-CH ) ppm. IR (neat): ν = 3100 (vb, OH), 2548 (vb),
˜
2
1621, 1600, 1586, 1521, 1505, 1486, 1465, 1433, 1393, 1332, 1295,
1260, 1243, 1216, 1178, 1152, 1093, 1048, 1012, 977, 940, 908, 867,
840, 824, 750, 737, 724, 667, 654, 636, 620, 557, 524, 495, 477, 452,
412, 367, 337 cm–1.
2-[Bis(2-hydroxy-3,5-di-tert-butylbenzyl)aminomethyl]pyridine
(H2tbpppy):[2] This ligand has been prepared according to a litera-
ture procedure, however, doubling the concentration of the rea-
gents, the quantity of the reagents and the reaction time resulted
in a higher yield than previously reported. A white powder was
B: To a solution of 0.5 mmol (0.160 g) H2pppy and 1 mmol
(140 µL) triethylamine in 20 mL of MeOH was added a solution of
[MnII(H2O)6](ClO4)2 in 10 mL of MeOH, while stirring. Caution!
Perchlorate complexes are hazardous and potentially explosive! The
resulting reaction mixture immediately turned brown. After 10 min
of stirring, a solution of 0.5 mmol (92 mg) Hdpm and 0.5 mmol
(70 µL) triethylamine in 10 mL of MeOH was added. Stirring was
continued for 1 h. Then, the reaction mixture was concentrated on
a rotary evaporator to approximately 15 mL. While stirring the
concentrated solution, water was slowly added until a brown pow-
der precipitated. The water/MeOH mixture was left stirring for an
additional 10 min, and the brown powder was collected by fil-
tration. The powder was dried in vacuo over P2O5 for 48 h. This
was the desired product in 74% (0.2 g) yield. C31H37MnN2O4
(556.58): calcd. C 66.90, H 6.70, N 5.03; found C 66.79, H 6.72, N
1
obtained in 71% (7.73 g) yield. H NMR: δ = 10.51 (s, 2 H, OH),
8.69 (d, 1 H, py), 7.21 (d, 2 H, aryl), 7.14 (d, 1 H, py), 6.94 (d, 2
H, aryl), 3.84 (s, 2 H, py-CH2), 3.78 (m, 4 H, Ar-CH2), 1.60 [m,
18 H, (CH ) C], 1.24 [m, 18 H, (CH ) C] ppm. IR (neat): ν = 3100
˜
3 3
3 3
(OH) 2952 (CHalif), 2867, 1598, 1571, 1482, 1435, 1418, 1362,
12.94, 1231, 1204, 1164, 1122, 1093, 1050, 1004, 976, 941, 876, 863,
822, 800, 760, 732, 686, 668, 648 cm–1.
Complex Synthesis: The preparation of the complex [MnIII(pppy)-
(acac)] is given as an example for the general method used to obtain
complexes of the type [M(tripod)(β-diketonate)].
[MnIII(pppy)(acac)] (1): No special precautions were taken to purify
solvents and the reaction was performed in air. 1 mmol (0.352 g)
of [Mn(acac)3] was dissolved in 20 mL of CH2Cl2 in an erlenmeyer
flask. 1 mmol (0.320 g) of H2pppy was dissolved in 20 mL of
CH2Cl2 in another Erlenmeyer flask, with the addition of 2 equiv.
(273 µL) of triethylamine. Then, the ligand solution was added to
the [Mn(acac)3] solution while stirring. The color of the [Mn-
(acac)3] solution changed slightly from brown to brown/red. The
reaction mixture was left stirring at room temperature, typically for
18 h. Then the solvent was evaporated and the residue was taken
up in 20 mL of acetone. Addition of an equal volume of H2O pre-
cipitated the complex as a brown powder, which was dried in vacuo
over P2O5. Yield 45 mg (10%). Black single crystals were obtained
by solvent diffusion of n-hexane into a solution of the complex in
CH2Cl2. C25H25MnN2O4 (472.42): calcd. C 63.56, H 5.33, N 5.93;
4.95. IR (neat): ν = 2962, 1597, 1569, 1528, 1498, 1477, 1451, 1384,
˜
1356, 1298, 1265, 1225, 1180, 1134, 1110, 1018, 964, 874, 790, 754,
737, 643, 628, 528, 492, 475, 460, 418, 390 cm–1.
[MnIII(pppy)(quin)] (5): This complex was prepared according to
method B for complex 4. Yield 56% (145 mg). Single crystals (fine
brown needles) suitable for X-ray diffraction were obtained by let-
ting a solution of the compound in CH2Cl2/n-hexane (1:1) stand at
–20 °C. C29H24MnN3O3·(CH2Cl2)0.3 (542.94): calcd. C 64.82, H
4.57, N 7.74; found C 64.99, H 4.55, N 7.84. IR (neat): ν = 3044,
˜
2836, 1613, 1593, 1572, 1496, 1464, 1448, 1440, 1386, 1373, 1322,
1291, 1266, 1230, 1190, 1160, 1106, 1059, 1037, 992, 967, 932, 882,
825, 804, 792, 752, 723, 696, 647, 631, 599, 527, 485, 424, 396 cm–1.
[MnIII(tbpppy)(acac)] (6): This complex was prepared according to
the general method. A brown powder was obtained. The yield was
60% (240 mg). C41H57MnN2O4·2H2O (732.88): calcd. C 67.19, H
found C 62.96, H 5.40, N 5.99. IR (neat): ν = 3065, 1654, 1591,
˜
1540, 1516, 1476, 1448, 1424, 1373, 1346, 1268, 1226, 1194, 1148,
1112, 1096, 1048, 1019, 967, 922, 887, 874, 804, 766, 749, 730, 716,
665, 648, 628, 610, 564, 524, 492, 478, 428, 405, 380, 316 cm–1.
8.39, N 3.82; found C 67.78, H 8.39, N 3.86. IR (neat): ν = 2953
˜
[FeIII(pppy)(acac)] (2): This complex was synthesised according to
the general method. Yield 60 mg (13%) of a red/brown powder.
Single crystals were obtained by solvent diffusion of hexane into a
solution of the complex in CH2Cl2. C25H25FeN2O4 (473.33): calcd.
C 63.44, H 5.32, N 5.92; found C 62.39, H 5.40, N 5.98. IR (neat):
(CHalif), 1654, 1590, 1516, 1472, 1440, 1414, 1386, 1361, 1304,
1256, 1238, 1203, 1168, 1130, 1094, 1050, 1016, 976, 914, 875, 837,
668, 645, 611, 568, 499, 451, 420, 401 cm–1.
[FeIII(tbpppy)(acac)] (7): This complex was synthesised following
the general procedure, using [Fe(acac)3] and H2tbpppy. The yield
was 16% (55 mg) of a purple powder. C41H57FeN2O4 (697.76):
calcd. C 70.58, H 8.23, N 4.01; found C 69.99, H 8.85, N 4.00. IR
ν = 3067, 2915, 1592, 1576, 1558, 1516, 1476, 1456, 1445, 1418,
˜
1374, 1283, 1266, 1193, 1155, 1112, 1088, 1038, 1022, 968, 928,
884, 841, 792, 752, 731, 647, 633, 606, 550, 511, 479, 427 cm–1.
(neat): ν = 2951 (CHalif), 1654, 1590, 1522, 1481, 1436, 1415, 1386,
˜
MnIII(pppy)(dbm)] (3): This complex was prepared according to the
1361, 1295, 1269, 1232, 1202, 1166, 1129, 1051, 1008, 974, 930,
general method, starting with 0.5 mmol (0.362 g) [MnIII(dbm)3]
877, 861, 836, 800, 754, 666, 648, 608, 545, 506, 478, 432, 400 cm–1.
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Mn and Fe Complexes with Tripodal, Tetradentate Ligands
Table 4. Crystallographic data and details of the structure determinations for complexes 1–5 and 9.
1
2
3
4
5
9
Formula
Fw
Space group
T [K]
a [Å]
b [Å]
c [Å]
α [°]
β [°]
C25H25MnN2O4
472.4
P21/c
C25H25FeN2O4
473.3
C2/c
C35H29MnN2O4
596.5
P212121
150
13.8331(10)
13.8434(10)
14.6932(10)
90
90
90
2813.7(3)
1.4082(2)
4
C31H37MnN2O4
556.6
P1
C29H24MnN3O3·CH2Cl2 C38H53MnN2O4
602.4
656.8
¯
P21/c
P21/c
150
150
150
150
173
8.0774(1)
29.1222(3)
20.0292(2)
90
106.4840(10)
90
4517.85(9)
1.389
8
22.4132(5)
6.9219(1)
30.6673(6)
90
109.6502(8)
90
4480.71(15)
1.403
8
12.151(11)
14.049(18)
17.291(7)
85.79(7)
86.16(6)
77.09(10)
2866(5)
1.290(2)
4
14.8062(10)
12.4055(10)
20.5767(10)
90
16.035(4)
13.233(5)
18.957(3)
90
133.708(3)
90
111.09(2)
90
γ [°]
V [Å3]
Dcalcd. [gcm–3
Z
2732.1(3)
1.4645(2)
4
3753.1(19)
1.1623(6)
4
]
Crystal size [mm]
2θmax [°]
0.15ϫ0.21ϫ0.36 0.06ϫ0.15ϫ0.54 0.20ϫ0.20ϫ0.25 0.05ϫ0.06ϫ0.51 0.03ϫ0.10ϫ0.24
0.06ϫ0.17ϫ0.20
50.5
55
55
55
45
55
Unique data
10249
0.0377
0.0928
0.060
5020
6455
7468
6239
6717
R[a]
0.0384
0.0849
0.050
0.0231
0.0597
0.046
0.0597
0.1257
0.104
0.0494
0.1244
0.078
0.0819
0.1806
0.199
[b]
wR2
R(int.)
∆ρmin,∆ρmax [eÅ–3] –0.32, 0.31
–0.36, 0.33
–0.29, 0.19
–0.39, 0.44
–0.80, 0.89
–0.36, 0.92
[a] R = Σ(||Fo| – |Fc||)/Σ|Fo|. [b] wR2 = {Σ[w(Fo – Fc ) ]/Σ[w(Fo2)2]}1/2
.
2
2 2
[MnIII(tbpppy)(dpm)] (8): This complex was prepared according to
calculated positions and were refined riding on their parent atoms.
the general method, starting from 0.5 mmol (0.30 g) [Mn(dpm)3] Structure 4 contains small solvent accessible voids of 37 and 70 Å3.
and 0.5 mmol (0.272 g) H2tbpppy, with CHCl3 as a solvent and a
reaction time of 48 h. A black/brown micro-crystalline powder was
obtained in 90% (0.35 g) yield. C47H69MnN2O4 (781.01): calcd. C
The contribution of the disordered solvent of crystallization in the
voids was taken into account in the structure factor calculation
with the PLATON/SQUEEZE routine. Geometric calculations and
molecular graphics were performed with the PLATON package.[48]
72.28, H 8.90, N 3.59; found C 71.21, H 9.35, N 3.49. IR (neat): ν
˜
= 2951, 1589, 1570, 1526, 1496, 1471, 1437, 1400, 1386, 1360, 1306,
1279, 1240, 1220, 1202, 1167, 1130, 1087, 1047, 1016, 976, 932,
914, 869, 840, 808, 788, 775, 761, 752, 644, 613, 568, 558, 529, 499,
475, 452, 397, 368 cm–1.
[MnIII(tbpppy)(OAc)] (9): 0.20 g (0.37 mmol) H2tbpppy, together
with 74 mg (0.73 mmol) triethylamine, was dissolved in 15 mL
CH2Cl2 and added to 0.09 g (0.37 mmol) [Mn(OAc)3]·2H2O, dis-
solved in 5 mL CH2Cl2. After 24 h of stirring a precipitate could
be collected by filtration. A purple powder was obtained in 26%
(63 mg) yield. Single crystals were obtained by solvent diffusion of
hexane into a solution of the complex in CH2Cl2. C38H53MnN2O4
(656.78): calcd. C 69.49, H 8.13, N 4.27; found C 68.98, H 8.39, N
CCDC-651099 (for 1), -651100 (for 2), -651101 (for 3), -651102 (for
4), -651103 (for 5) and -651578 (for 9) contain 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.
Supporting Information (see also the footnote on the first page of
this article): Electronic spectra and data, cyclic voltammograms
and electrochemical data.
Acknowledgments
4.29. IR (neat): ν = 2950, 1604, 1578, 1478, 1439, 1413, 1390, 1362,
˜
This work was carried out as part of the SENTER/Innovation Ori-
ented Research Program on Heavy Metals (IOP), sponsored by the
Dutch Ministry of Economic Affairs (project no. IZW99241c). The
crystallography was supported by the Nederlandse Organisatie
voor Wetenschappelijk Onderzoek, Chemische Wetenschappen
(NWO-CW) (A. L. S., A. M. M., D. M. T.).
1332, 1309, 1276, 1239, 1204, 1169, 1129, 1080, 1048, 1015, 975,
914, 877, 840, 808, 778, 762, 752, 729, 695, 668, 656, 643, 614, 575,
559, 500, 454, 402, 352 cm–1.
[MnIII(dnpppy)(acac)] (10): This compound was prepared according
to the general procedure. A greenish brown powder was obtained,
yield 29% (81 mg). C25H23MnN4O8 (562.41): calcd. C 53.39, H
4.12, N 9.96; found C 52.62, H 4.10, N 10.09. IR (neat): ν = 1600,
˜
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Received: November 29, 2007
Published Online: January 29, 2008
1496
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