Ligand displacement for fixing manganese: Relevance to cellular metal ion transport and synthesis of polymeric coordination complexes

Article abstract of DOI:10.1039/c2dt32547k

A dinuclear manganese(iii) complex (1) of an N-(carboxymethyl)-N-[3,5- bis(α,α-dimethylbenzyl-2-hydroxybenzyl)]glycine (HDA) ligand (L) binds a manganese(ii) species through displacement of its solvating ligands by appropriately dispositioned carbonyl groups of a dinuclear complex {[Mn ₂(L)₂(OH)(OCH₃)][Mn(H₂O) ₃(CH₃OH)₃], 2, triclinic P1, a = 13.172(3) A?, b = 15.897(3) A?, c = 19.059(4) A?, V = 3461.9(13) A?³} leading to a trinuclear complex {3, monoclinic P21/n, a = 11.7606(8) A?, b = 21.3505(8) A?, c = 26.7827(17) A?, V = 6722.7(7) A?³} with cyclization of two of the carboxy groups through the doubly-carboxy group coordinated Mn²⁺ ion. The reaction is discussed in terms of its significance as an illustration of how Mn ²⁺ ions might be sequestered in biological systems. A similar solvato-ligand displacement reaction was used to synthesise coordination polymers of an HDA iron(iii) complex involving polymerization through a bridging carboxylato group. Several isostructural polymers (5-7; for 5: orthorhombic Pbca, a = 9.411(5) A?, b = 16.390(8) A?, c = 37.968(19) A?, V = 5856(5) A?³) with different coordinated alcohols could be prepared indicating the potential synthetic uses of this method.

Full text of DOI:10.1039/c2dt32547k

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PAPER
Ligand displacement for fixing manganese: relevance
to cellular metal ion transport and synthesis of
polymeric coordination complexes†
Cite this: Dalton Trans., 2013, 42, 2779
Noelia M. Sanchez-Ballester,a Lok Kumar Shrestha,a Mark R. J. Elsegood,b
Wolfgang Schmitt,c Katsuhiko Ariga,a,d Christopher E. Anson,e Jonathan P. Hill*a,d
and Annie K. Powell*e,f
A dinuclear manganese(III) complex (1) of an N-(carboxymethyl)-N-[3,5-bis(α,α-dimethylbenzyl-2-hydroxy-
benzyl)]glycine (HDA) ligand (L) binds a manganese(II) species through displacement of its solvating
ligands by appropriately dispositioned carbonyl groups of a dinuclear complex {[Mn2(L)2(OH)(OCH3)][Mn-
3
ˉ
(H2O)3(CH3OH)3], 2, triclinic P1, a = 13.172(3) Å, b = 15.897(3) Å, c = 19.059(4) Å, V = 3461.9(13) Å }
leading to a trinuclear complex {3, monoclinic P21/n, a = 11.7606(8) Å, b = 21.3505(8) Å, c = 26.7827(17)
Å, V = 6722.7(7) Å3} with cyclization of two of the carboxy groups through the doubly-carboxy group
coordinated Mn2+ ion. The reaction is discussed in terms of its significance as an illustration of how Mn2+
ions might be sequestered in biological systems. A similar solvato-ligand displacement reaction was used
to synthesise coordination polymers of an HDA iron(III) complex involving polymerization through a brid-
ging carboxylato group. Several isostructural polymers (5–7; for 5: orthorhombic Pbca, a = 9.411(5) Å, b =
16.390(8) Å, c = 37.968(19) Å, V = 5856(5) Å3) with different coordinated alcohols could be prepared
indicating the potential synthetic uses of this method.
Received 24th October 2012,
Accepted 28th November 2012
DOI: 10.1039/c2dt32547k
www.rsc.org/dalton
one of the critical elements involved in life processes due to its
variability both of oxidation state and coordinative form.5 It is
Introduction
Coordination complexes of manganese with organic ligands particularly notable for its presence (as an oligonuclear
have attracted attention as potential materials for catalysis1 cluster) at the water splitting core of Photosystem II (PSII) in
and molecular magnetics.2 For the latter, many oligonuclear photosynthetic bacteria.6 Apart from that role, manganese
complexes have been prepared that not only present unique cations are present at the active sites of many important
structural motifs but also possess properties illustrating their enzymes including superoxide dismutase7 and catalase.8 Co-
importance as magnetic materials.3 Moreover, mixed metal oligo- incidentally, manganese is also involved in mechanisms of bac-
nuclear complexes of manganese with other cations such as terial pathogenicity9 and in human disease states such as
those of the lanthanides have been investigated due to their Parkinsonism and other brain disorders.10 Because of these
significant and novel properties.4 Additionally, manganese is matters and also due to its ubiquity in biological systems,
questions arise as to how it is fixed and transported in cellular
media. Investigations of manganese transport have included
aWPI-Centre for Materials Nanoarchitectonics, National Institute of Materials
X-ray crystal structural studies11 to reveal, in depth, the fate of
Science (NIMS), Namiki 1-1, Tsukuba, Ibaraki 305-0044, Japan.
manganese in cells including its supply to important active
sites like PSII.12 High resolution X-ray studies have revealed
that the chemical nature of the interactions between proteins
and manganese ions is largely through coordination by carboxy-
late and imidazole side chains of, for instance, glutamate (or
aspartate) and histidine amino acid residues.13 In low valent
complexes, two Mn2+ ions may be bridged in 1,3 fashion by
carboxylate groups while enzymes containing manganese in
higher oxidation states sometimes contain electronegative
bridging groups such as oxide or hydroxide.14 However, there
is little information regarding how manganese cations are
E-mail: Jonathan.Hill@nims.go.jp; Tel: +81-29-860-4399
bChemistry Department, Loughborough University, Loughborough, Leicestershire,
United Kingdom
cDepartment of Chemistry, Trinity College Dublin, Dublin 2, Ireland
dJST-CREST, Namiki 1-1, Tsukuba, Japan
eAnorgansiche II, University of Karlsruhe, Engesserstr. 15, Karlsruhe, D-76128
Germany. E-mail: annie.powell@kit.edu; Tel: +49-721-608-42135
fInstitute for Nanotechnology, Karlsruhe Institute of Technology, Hermann-von-
Helmholtz-Platz 1, Eggenstein-Leopoldshafen, Germany
†Electronic supplementary information (ESI) available: CIFs for compounds 2, 3,
5–7; additional figures of compounds 6 and 7. CCDC 893592, 893593, 893594,
893595, 906345. For ESI and crystallographic data in CIF or other electronic
format see DOI: 10.1039/c2dt32547k
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bridging hydroxide is confirmed by a hydrogen-bonded water
molecule in its vicinity. Dinuclear complexes of manganese
with various ligands are known,21,22 but in the case of 1 two
peripheral carbonyl groups of the complex are oriented such
that they can interact with a further species, here a solvated
Mn(II) cation. The nature of the interaction depends on solu-
tion conditions and in the presence of base a complex system
of hydrogen bonds (H-bonds) fixes a meridionally structured
[Mn(H2O)3(CH3OH)3]2+ in the proximity of the two aforemen-
tioned peripheral carbonyl groups. Fig. 1a shows the X-ray
crystal structure of this trinuclear complex (2) and reveals
H-bonds between each of two carboxylate groups of 1 and one of
the aquo ligands of mer-[Mn(H2O)3(CH3OH)3]2+. Additional
H-bonds between other solvato ligands of mer-[Mn(H2O)3-
(CH3OH)3]2+, proximal methanol and the other oxygen
atoms of the same carboxylate groups stabilize this complex. If
no base is added during the reaction between L and manga-
nese(II) acetate tetrahydrate then complex 3 (Fig. 1b) is
obtained where two ligating solvent molecules of the pre-
viously H-bonded solvated Mn2+ atom have been displaced by
the appropriately dispositioned carbonyl groups of complex 1.
In biological systems, manganese ions (probably [Mn-
(H2O)6]2+) must at some point be free from interaction with
protein and we propose that a process of ligand displacement
similar to that apparent here from 2 to 3, leading to fixing of
Mn2+ by appropriately oriented carbonyl groups, may be analo-
gous with processes occurring where manganese is initially
sequestered. The ‘fixed’ manganese atom remains in its +2 oxi-
dation state in both 2 and 3 and this is also consistent with
biological systems where manganese is known to be trans-
ported in a divalent state. Once sequestered, Mn2+ is trans-
ferred in vivo by inter-protein interactions13,15,23 although this
would not preclude transport processes again involving small
ligands such as aquo. Variable binding activity by carboxylate
groups in enzymes has been noted in vitro by Lippard and
coworkers.16a
Scheme 1 The ligand N-[3,5-bis(α,α-dimethylbenzyl-2-hydroxybenzyl)] imino-
diacetic acid (L) (left) and the dinuclear manganese complex [(μ2-OH)(μ2-OCH3)-
L2Mn2]2− (right) described here (α,α-dimethylbenzyl groups removed for clarity).
initially fixed in the Mn2+ state (manganese and other tran-
sition metal cations are known to be transported in cells in
divalent form15) although modes of binding in enzymes have
been investigated.16
In this work we present X-ray structural studies of manga-
nese complexes in which solvated Mn2+ ions are observed to
have undergone ligand displacement reactions during the
process of forming a trinuclear manganese complex from a
dinuclear precursor. We also present structures of linear poly-
nuclear coordination complexes of iron(III) prepared using a
selective ligand displacement protocol deduced from the for-
mation of the Mn3 complex.
Ligands containing (2-hydroxyphenylmethyl)-iminodiacetic
acid have been known for over sixty years17 and they have been
used extensively in preparation of coordination complexes
especially with transition metal ions. Complexes prepared
from these and similar ligands have been proposed as models
of enzyme reaction centers.18 We have previously investigated
the structure-directing effects of iminodiacetic acid substituted
phenols and characterised the supramolecular structures and
properties of the resulting complexes (Scheme 1).19 By varying
the substituent structure of the phenol ligand, it has proved
possible to vary the structures of the resulting complexes
leading to several significant phenomena including cation–π
binding of potassium counterions19a and formation of porous
coordination complexes (i.e. MOFs).19b The cation–π effect was
observed using a (2-hydroxyphenylmethyl)-iminodiacetic acid
(HDA) ligand substituted with α,α-dimethylbenzyl groups.19a
The structure of this ligand (L) is shown in Scheme 1 together
with chemical structures of the basic dinuclear manganese
complex (1) used here. In this work, the substituent α,α-di-
methylbenzyl groups served to improve the solubility of L.
2 is isolated from reactions containing hydroxide while 3
forms under slightly acidic conditions. Our proposed mechan-
ism (Fig. 1c) for the formation of 2 from 3 thus includes repla-
cement of aquo by carbonyl oxygen atoms as ligands which
should be favoured under acidic conditions since protonation
of water promotes its ability to act as a leaving group. Sub-
sequent displacement of an alcoholato ligand is favoured by
its proximity to the adjacent carbonyl group.
The dinuclear units in 2 and 3 have very similar forms and
bond lengths about the two manganese atoms. The Jahn–
Teller axis occurs in both cases between the coordinating car-
boxylate groups of the ligand (for bond lengths and angles see
Results and discussion
Fig. 1 caption) and is roughly perpendicular to the plane of
21
Complex
1
contains the [(μ2-OH)(μ2-OCH3)L2Mn2]2− unit, the bridging hydroxo/alkoxo as is typical for Mn3+
.
The Mn–
2
which contains trivalent manganese stabilized by the electro- Mn distances in 2 and 3 are 2.9832(18) Å and 2.9661(12) Å,
negative ligand set including phenoxide and hydroxide/meth- respectively. In 2, the mer-[Mn(H2O)3(CH3OH)3]2+ moiety is
oxide.20 In this work, we could not obtain crystals of the only slightly distorted as expected (which is typical for unsym-
dinuclear unit alone but we presume its existence in solution metrically substituted hexasolvatomanganese(II) complexes)
together with the solvated Mn2+, which either cocrystallizes and all the solvato groups are involved in a hydrogen bonding
giving 2 or reacts with 1 leading to 3. The presence of the network. In 3, one aquo and one alcoholato ligand have been
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Fig. 1 (a) X-ray crystal structure of 2 showing the dinuclear unit interacting with mer-[Mn(H2O)3(CH3OH)3]2+ through a hydrogen bonding manifold involving two
additional molecules of methanol. Edge-on view is shown at the right. (b) X-ray crystal structure of 3 where the manganese atom remote from the dinuclear
complex has been ‘fixed’ through carbonyl oxygen atom coordinate bonds. Edge-on view is shown at the right. (c) Proposed mechanism for transformation from 2
to 3 involving solvato ligand displacement from the incoming manganese atom (α,α-dimethylbenzyl groups removed throughout for clarity). Important bond
lengths (Å) and angles (°): 2: Mn1–N1 2.137(7), Mn1–O1 1.927(5), Mn1–O2 1.952(5), Mn1–O3 1.862(5), Mn1–O4 2.155(5), Mn1–O6 2.187(5), Mn2–N2 2.113(6),
Mn2–O1 1.919(5), Mn2–O2 1.944(6), Mn2–O8 1.853(5), Mn2–O9 2.170(5), Mn2–O11 2.195(5), Mn3–O13 2.178(6), Mn3–O14 2.113(7), Mn3–O15 2.133(6), Mn3–
O16 2.178(7), Mn3–O17 2.159(7), Mn3–O18 2.253(6), Mn1–O1–Mn2 101.7(2), Mn1–O2–Mn2 99.9(2); 3: Mn1–N1 2.125(5), Mn1–O1 1.930(4), Mn1–O2 1.944(5),
Mn1–O3 2.207(4), Mn1–O5 2.190(4), Mn1–O7 1.841(4), Mn2–N2 2.145(5), Mn2–O1 1.938(4), Mn2–O2 1.941(4), Mn2–O8 2.232(4), Mn2–O10 2.148(4), Mn2–O12
1.860(4), Mn3–O4 2.107(5), Mn3–O9 2.163(5), Mn3–O13 2.145(5), Mn3–O14 2.230(5), Mn3–O15 2.213(4), Mn3–O16 2.228(5), Mn1–O1–Mn2 100.16(18), Mn1–
O2–Mn2 99.55(19), O4–Mn3–O9 93.14(18).
replaced in a cis configuration by carbonyl oxygen atoms C–H⋯pi interactions and there is obviously amphiphilic segre-
of the 1 moiety. The two remaining aquo ligands lie trans gation within the structure with hydrophobic α,α-dimethylben-
to the coordinating carbonyl groups with the two methanolato zyl groups contained in layers.
ligands occupying sites above and below the carbonyl/
Having observed the potential solvent/ligand displacement
water coordination plane with one of them undergoing reaction we considered that this process might be applied in a
an intramolecular H-bond with a carboxylate oxygen atom synthetic sense for preparation of coordination complexes of
of the dinuclear unit (for bond lengths and angles see Fig. 1 predictable structure or form if selective displacement analo-
caption).
gous with the 1 system could be achieved. In previous work,19d
The long range structures of complexes 2 and 3 are strongly one of us prepared the complex 4 which is a mononuclear
influenced by hydrogen bonding involving basic ligands of the complex of iron(III) with L containing coordinated solvent
Mn2+ cation, solvent molecules and carboxyl groups of the (water and methanol). This complex also provides the opportu-
HDA ligand. The bridging hydroxyl group of the dinuclear unit nity for determining whether there is any selectivity in the labi-
is also involved. Essentially, in both 2 and 3, dinuclear units of lity of the coordinated solvent. Under conditions that lead to
1 are respectively linearly polymerized through H-bonding crystallisation of a product we found that water is selectively
between the carboxyl groups of the HDA and ligands and the displaced yielding a coordination polymer 5 (see Fig. 3a,b)
ligands of the Mn2+ cation (see Fig. 2). Linear polymeric units through the expected displacement of coordinated solvent by a
are then joined through further H-bonding interactions. In 2, peripheral carbonyl group in a neighbouring mononuclear
this involves mutual H-bonds between carboxyl groups and unit. Similarly to the case of 2, acidic conditions lead to the
solvato groups of the Mn2+ cation but additionally includes displacement of aquo selectively over alcoholato ligands sup-
bridging between polymeric strands through hydroxo bridges porting our mechanism (Fig. 1c) involving initial displacement
mediated by solvent water molecules. For 3, it appears that of aquo from 2. Other alcohols including 1-propanol (6) and
only mutual H-bonding between the bridging hydroxo groups ethylene glycol (7) behave consistently leading to isostructural
of the dinuclear units is required. These interactions are sum- complexes (see Table 1). In the ethylene glycol complex there
marized in Fig. 2. Apart from H-bonding there also exist is an additional weak O–H⋯π interaction between the non-
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Fig. 2 Hydrogen bonding in 2 and 3. (a) Structure of 2 showing its extensive hydrogen bond network forming a linear H-bond polymer. (b) Structure of 3 also
revealing extensive hydrogen bonding forming linear chains of the complex. (c) H-bonds between linear chains involve the hydroxo bridge group and solvent water
molecules. (d) In 3, mutual H-bonding between chains occurs between hydroxo bridges and carbonyl oxygen atoms in adjacent chains (α,α-dimethylbenzyl groups
removed throughout for clarity). Important H-bond lengths (Å) (and angles in degrees): 2: O13–H13a⋯O4 2.718(8) (159(7)), O13–H13a⋯O9 2.784(7) (166(7)),
O14–H14a⋯O5 2.685(9) (174(10)), O18–H18a⋯O10 2.627(8) (119.1), O16–H16⋯O19 2.698(9) (171(9)), O15–H15a⋯O7 2.709(8) (167(8)), O15–H15b⋯O12
2.693(8) (164(8)), O17–H17⋯O21 2.605(9) (177(10)), O14–H14b⋯O10 2.710(9) (174(11)), O2–H2⋯O20 2.722(8) (154(8)), O20–H20B⋯O12 2.727(9) (106(7)). 3:
O16–H16⋯O3 3.0533(7) (113(11)), O15–H15⋯O6 2.589(6) (163(6)), O13–H131⋯O5 2.780(6) (173(8)), O13–H132⋯O71 2.684(8) (155(7)), O71–H71⋯O10
2.834(7) (163.3), O2–H2⋯O11 2.710(6) (164(6)).
Fig. 3 Polymerization by selective displacement of coordination solvent in the mononuclear Fe3+ complex of L. (a) Schematic of monomer (4) and the resulting
polymer (5). (b) Corresponding X-ray crystal structures of compounds shown in (a). Packing of the coordination polymer chains viewed along (c) the a-axis, (d) the
b-axis. Important bond lengths and distances (Å): Fe1–N1 2.187(7), Fe1–O2 2.015(6), Fe1–O3 2.034(6), Fe1–O4 1.938(6), Fe1–O5 2.033(6), Fe1–Fe1A 5.840(3).
2782 | Dalton Trans., 2013, 42, 2779–2785
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Table 1 X-ray crystallographic data and structure refinements for compounds 2, 3, 5–7
2
3
5
6
7
Formula
Mr
Diffractometer
Crystal system
Space group
T [K]
C
64H92Mn3N2O21
C126H157Mn6N4O38
2665.21
Stoe IPDS
Monoclinic
P21/n
C31H36FeNO7
590.46
Bruker Apex
Orthorhombic
Pbca
C32H38FeNO7
606.50
Bruker Apex
Orthorhombic
Pbca
C31H37FeNO8
607.47
Bruker Apex
Orthorhombic
Pbca
1390.22
Bruker Apex II
Triclinic
ˉ
P1
150
200
150
150
296
a [Å]
b [Å]
c [Å]
α [°]
13.172(3)
15.897(3)
19.059(4)
70.363(4)
83.939(4)
67.134(3)
3461.9(13)
2
11.7606(8)
21.3505(8)
26.7827(17)
90
91.494(8)
90
6722.7(7)
4
1.317
9.411(5)
16.390(8)
37.968(19)
90
90
90
5856(5)
8
1.339
0.71073
0.562
2488
9.556(2)
16.496(4)
38.041(9)
90
90
90
5997(2)
8
1.344
0.71073
0.551
2568
9.467(10)
16.4024(17)
37.998(4)
90
90
90
5900.4(11)
8
1.368
0.71073
0.563
2560
β [°]
γ [°]
V [Å3]
Z
ρcalcd [g cm−3
λ [Å]
]
1.334
0.71073
0.611
0.71073
0.624
2790
μ [mm−1
F (000)
]
1466
Reflections collected
Unique data
Rint
Data with [I > 2σ(I)]
Parameters/restraints
S on F2 (all data)
wR2 (all data)
31 865
10 045
0.1734
4622
865/197
0.982
0.2054
0.0744
+0.961/−0.689
39 608
9629
0.0968
4888
800/17
1.011
0.1224
0.0567
43 338
6102
0.1358
3625
374/0
1.007
0.1454
0.0659
+0.777/−0.313
43 888
6245
0.0370
5318
387/0
1.106
0.1078
0.0466
+0.506/−0.256
32 741
6245
0.0636
4108
383/0
1.036
0.1281
0.0510
+0.467/−0.689
R1 (I > 2σ(I))
Largest residuals [e Å−3
]
+0.927/−0.087
coordinated hydroxyl group of ethylene glycol and a phenyl glycine was prepared following a previously reported literature
ring in an adjacent chain.
method.19a Elemental analyses were performed by the elemental
analysis service of the University of Tsukuba.
Conclusions
X-ray crystallographic data collection and structure refinement
Diffraction data for 2, 3 and 5, 6 and 7 were collected using
either Bruker Apex CCD diffractometers or a Stoe IPDS with
sealed tube sources. For 2 and 3 data above 2θ = ∼46.8° were
removed due to the weakness of the high angle peaks. Narrow-
frame exposures were employed. Cell parameters were refined
from all strong reflections in each data set. Intensities were
corrected semi-empirically for absorption, based on symmetry-
equivalent and repeated reflections. Structure solution was
carried out by direct methods and full-matrix refinement
against F2 (all data) using the SHELXTL package.24 All non-
hydrogen atoms were refined anisotropically. Water hydrogen
atoms were located in the difference Fourier map and the co-
ordinates allowed to freely refine, while the remaining hydrogen
coordinates were constrained using a riding model with Ueq
set to 1.2Ueq of the carrier atom (1.5Ueq for methyl hydrogen).
Crystallographic data (excluding structure factors) for the
structures in this paper have been deposited with the Cam-
bridge Crystallographic Data Centre as supplementary publi-
cation nos. CCDC 893592 (2), 893593 (3), 893594 (5) and
893595 (6) 906345 (7).
In conclusion, we have shown a potential model for initial fix-
ation of Mn2+ in biological systems by using a molecule (co-
incidentally a coordination complex) with carbonyl groups in the
proper orientation to cause solvent displacement from solvated
Mn2+. Further, we have demonstrated that the ligand displace-
ment by carboxylate carbonyl groups can be used to form
stable polymeric coordination complexes. We are currently
testing the reversibility of manganese fixation for 1 in order to
better understand the process with respect to any therapeutic
properties these and similar complexes might have. It may be
also possible to generate polymeric coordination structures
based on 2a with higher dimensionalities such as in 2D (e.g.
on surfaces) or in 3D (e.g. to form porous networks or MOFs) if
appropriately structured ligands are prepared. We will report
on those aspects of this system in due course.
Experimental section
General
All chemicals were obtained from Tokyo Kasei Chemical Co. or
2: Manganese(II) acetate tetrahydrate (0.115 g, 0.5 mmol)
Wako Chemical Co. and were used as received. FTIR spectra and L (0.112 g, 0.2 mmol) were dissolved in methanol (20 mL)
were measured using a Nicolet NEXUS 670 FT-IR spectropho- and aqueous KOH (2 M; 3 mL) was slowly added to the stirred
tometer from samples prepared as KBr pellets. The ligand L reaction mixture. Slow evaporation of the solution yielded
N-(carboxymethyl)-N-[3,5-bis(α,α-dimethylbenzyl-2-hydroxybenzyl)]- green-grey crystals of 2 after 1 week. Yield: 61% based on
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ligand. IR data (KBr): ν = 3403 [br, OH (str)], 2965 (w), 2954
(w), 2945 (s) [all C–H (str)], 1602 [m, CvO (str)], 1493 (s), 1465
(m), 1445 (s), 1412 (w), 1312 (s), 1234 (s), 1201 (m), 1157 (m),
978 (w), 921 (m), 867 (w) cm−1. Elemental analyses: expected
for C64H92Mn3N2O21: %C 55.27, %H 6.67, %N 2.02, found %C
55.69, %H 6.53, %N 2.06.
3: A solution of L (0.120 g, 0.25 mmol) in ethanol (10 mL)
was added to a solution of manganese(II) acetate tetrahydrate
(0.095 g, 0.4 mmol) in a mixture of ethanol (10 mL) and water
(2 mL). Green crystals of 3 were grown upon slow evaporation
of the solvent. Yield: 37% based on ligand. IR data (KBr): ν =
3394 [br, OH (str)], 2950 (w), 2882 (w) [all C–H (str)], 1650 [m,
CvO (str)], 1528 (s), 1463 (m), 1414 (m), 1402 (w), 1386 (w),
1314 (w), 1206 (w), 1086 (w), 1042 (w), 883 (w) cm−1. Elemental
analyses: expected for C63H76Mn3N2O19: %C 56.87, %H 5.76,
%N 2.11, found %C 57.35, %H 5.59, %N 2.16.
5: L (0.107 g, 0.2 mmol) and iron(III) chloride hexahydrate
(0.100 g, 0.4 mmol) were together dissolved in ethanol (10 mL)
yielding a solution of 4.19d Acetic acid (2 mL) and water
(10 mL) were added and the solution left to stand for 2 days
whereupon blue crystals of the complex 5 formed. Yield: 80%
based on ligand. IR data (KBr): ν = 3422 [br, OH (str)], 2973
(w), 2957 (w), 2926 (s), 2852 (w) [all C–H (str)], 1656 [m, CvO
(str)], 1578 [m, CvO (str)], 1521 (s), 1507 (s), 1492 (s), 1464 (w),
1443 (s), 1382 (w), 1304 (w), 1027 (m), 940 (w), 907 (m), 829 (w)
cm−1. Elemental analyses: expected for C31H36FeNO7: %C
63.03, %H 6.15, %N 2.37, found %C 63.30, %H 5.93, %N 2.42.
If 1-propanol or ethylene glycol were used instead of ethanol, 6
or 7 were respectively obtained.
2 (a) W. Schmitt, M. Murugesu, J. C. Goodwin, J. P. Hill,
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Acknowledgements
This research was partly supported by the World Premier Inter-
national Research Center Initiative on Materials Nanoarchitec-
tonics from MEXT, Japan, and by the Core Research for
Evolutional Science and Technology (CREST) program of JST,
Japan. N. M. S.-B. thanks the Japan Society for the Promotion
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