An inorganic helix [Mn(IPG)(MeOH)](n)[PF6](n): Structural and magnetic properties of a syn-anti carboxylate-bridged manganese(II) chain involving a tetradentate ligand

Article abstract of DOI:10.1002/(SICI)1099-0682(199912)1999:12<2201::AID-EJIC2201>3.0.CO;2-K

The crystal structure of an infinite inorganic chain consisting of Mn(II) and an N-centered tripodal ligand N,N-(2-pyridylmethyl)[(1- methylimidazol-2-yl)-methyl]glycinate is presented. It exhibits a chiral helical structure with a pitch of two monomeric units (each monomeric unit containing one Mn atom). Each manganese is connected to its neighbor through a carboxylate bridge in a syn-antigeometry. Around each manganese center, two carboxylates bind in a cis geometry. This peculiar bridging geometry (syn- anti cis) provides a broken-line chain, running in a zig-zag manner along the b axis of the P2₁ space group. The magnetic properties have been investigated. They show a pseudo-2D magnetic structure, with one major pathway along the chain and an inter-chain minor one. The intrachain coupling is a weak antiferromagnetic interaction (J/k = -0.25). This low value is entirely consistent with the geometry of the bridge. The interchain coupling is a weaker antiferromagnetic coupling (J'/k = -0.11) and could be mediated through π-π interactions between pyridine and imidazole from two adjacent helixes.

Full text of DOI:10.1002/(SICI)1099-0682(199912)1999:12<2201::AID-EJIC2201>3.0.CO;2-K

FULL PAPER
[
‡]
An Inorganic Helix [Mn(IPG)(MeOH)] [PF6] : Structural and Magnetic
n
n
Properties of a syn-anti Carboxylate-Bridged Manganese(II) Chain Involving
a Tetradentate Ligand
[
a]
[a]
[b]
Clotilde Policar,* Fran c¸ ois Lambert, Mich e` le Cesario,
and Ir e` ne Morgenstern-Badarau[
a]
Keywords: Carboxylate syn-anti / N-centered tripodal ligand / Manganese / Imidazole / Helico ¨ı dal inorganic chiral
chain / Magnetism / π-π interaction
The crystal structure of an infinite inorganic chain consisting
of Mn and an N-centered tripodal ligand N,N-(2-
pyridylmethyl)[(1-methylimidazol-2-yl)-methyl]glycinate is
presented. It exhibits a chiral helical structure with a pitch of
two monomeric units (each monomeric unit containing one
1
along the b axis of the P2 space group. The magnetic
II
properties have been investigated. They show a pseudo-2D
magnetic structure, with one major pathway along the chain
and an inter-chain minor one. The intrachain coupling is a
weak antiferromagnetic interaction (J/k = –0.25). This low
Mn atom). Each manganese is connected to its neighbor value is entirely consistent with the geometry of the bridge.
through a carboxylate bridge in a syn-anti geometry. Around
each manganese center, two carboxylates bind in a cis
The interchain coupling is a weaker antiferromagnetic
coupling (JЈ/k = –0.11) and could be mediated through π-π
geometry. This peculiar bridging geometry (syn-anti cis) interactions between pyridine and imidazole from two
provides a broken-line chain, running in a zig-zag manner
adjacent helixes.
Introduction
the results of structural and magnetic susceptibility studies
on these Mn chains are described.
II
Carboxylate ligands play an important role in coordi-
nation chemistry. They are known to adopt binding modes
as diverse as terminal monodentate, chelating to one metal Results
center and bridging bidentate in a syn-syn, syn-anti or anti-
Synthesis
anti configuration to two metal centers. The syn-anti bridge
appears to be a rather uncommon binding mode.[
1][2]
In
Ligand Synthesis Ϫ A given tripod can be synthesized by
several different methods depending on the order chosen
for the introduction of the different moieties. Several stra-
tegies were investigated and we report here the higher yield
one. In the synthesis of a nitrogen-centered tripod, the
yield-limiting step is usually the tertiarization of the amine.
Here, the first step is an N-alkylation of a primary amine
to give a secondary amine which is easily purified by distil-
lation. This compound then reacts quantitatively with an
aldehyde by reductive amination. The overall yield is 70%
the past fifteen years, there has been a flow of interest in
carboxylate complexes as models for metalloproteins. The
carboxylate can be incorporated as an external ligand, usu-
ally as an acetate. However, in the metallic cores of metallo-
proteins, the carboxylato ligand is provided by the side
chain of an aspartate or a glutamate making polydentate
chelating ligands bearing a carboxylate and some other do-
nor biologically relevant.[
2][3]
We have prepared several ni-
trogen-centered tripodal ligands with three appended moi-
ties, one being a carboxylate. Mononuclear iron complexes
have previously been obtained and described with a monod-
entate carboxylate. They have been studied as models for
(
see Scheme 1). If the first two steps are switched, the over-
all yield drops to 35% due to the poor yield of the last step
less than 40%).
(
[
4][5]
nonheme enzymes.
gands,
Surprisingly, with one of these li-
N,N-(2-pyridylmethyl)[(1-methylimidazol-2-yl)-
methyl)]glycinate (IPG)[ (2), Mn forms infinite chains
6]
II
through carboxylato-bridges in a syn-anti geometry. Here,
[
[
°]
IPG: N,N-(2-pyridylmethyl)[(1-methylimidazol-2-yl)-methyl)]-
glycinate
a]
Laboratoire de Chimie Bio-organique et Bio-inorganique, ERS
1
824,
B aˆ timent 420, Universit e´ Paris XI, F-91405 Orsay Cedex,
France
Fax: (internat.) ϩ 33-169/157231
E-mail: cpolicar@icmo.u-psud.fr
Laboratoire de Cristallochimie, Institut de Chimie des Substan-
ces Naturelles du CNRS,
Scheme 1. IPGK (2K) synthesis
[
b]
Complex Preparation Ϫ To prevent pollution by partic-
II
F-91198, Gif-sur-Yvette, France
ules of MnO in the course of the preparation of the Mn
2
Eur. J. Inorg. Chem. 1999, 2201Ϫ2207

WILEY-VCH Verlag GmbH, D-69451 Weinheim, 1999
1434Ϫ1948/99/1212Ϫ2201 $ 17.50ϩ.50/0
2201

C. Policar, F. Lambert, M Cesario, I. Morgenstern-Badarau
FULL PAPER
complex, the ligand was used as a mixture of the potassium Table 1. Crystallographic data for 3
salt and the free acid (2K/2H mixture) with a pH controlled
Formula
14 19 6 4 3
C H F MnN O P
ratio (see Experimental Section). Crystals suitable for an X-
ray diffraction study were grown from a methanol solution.
Formula weight
Temperature [K]
491.24
293(2)
˚
Wavelength [A]
0.71073
crystal system
space group
monoclinic
P2
1
Description of the Structure
˚
a [A]
8.417(4)
9.626(5)
12.391(6)
90
˚
b [A]
˚
c [A]
An X-ray diffraction study was carried out on complex
α [°]
β [°]
3
. Experimental details are reported in the Experimental
92.61(5)
90
Section (Table 1). The crystal structure has been found to γ [°]
˚
3
II
V [A ]
1002.9(9)
2
consist of a polymeric sequence of Mn cations, bridged by
Z
syn-anti carboxylato groups. The charge of the
Ϫ3
d
calc [g.cm
]
1.627
0.815
II
ϩ
Ϫ
abs. coeff. [mmϪ1]
crystal size [mm]
collected reflections
[
{Mn IPG(MeOH)} ] chain is balanced by n (PF6
)
n
0.200 ϫ 0.150 ϫ 0.070
568
anions. The polymeric chain extends along the b axis of
the P2 chiral space group. An ORTEP representation of a independent reflections
531 [R(int) ϭ 0.0264]
531/43/149
1
data/restraints/para
succession of three monomeric units is shown in Figure 1.
The three units are labeled 0 for the central one, corre-
sponding to the crystallographic unit [x, y, z], Ϫ1 and ϩ1 R indices [all data]
2
goodness-of-fit on F
1.068
[a]
Final R indices [I > 2σ(I)]
R1 ϭ 0.0545,wR2 ϭ 0.1361
R1 ϭ 0.0587,wR2 ϭ 0.1425
Ϫ0.313 and 0.319
min and ∆ρmax [e.AϪ3]
˚
∆ρ
for the two adjacent ones along the chain, with the sym-
metry transformations [Ϫx, Ϫ0.5 ϩ y, 1 Ϫ z] and [Ϫx, 0.5
ϩ y, 1 Ϫ z] respectively. Selected bond lengths and angles
are presented in Table 2.
[
a]
2
2
2
Weighting scheme: w ϭ 1/[s (F
o
) ϩ (0.0776P) ϩ 8.47P] where
2
2
P ϭ (F
o c
ϩ 2F )/3.
II
Mn is hexacoordinated with a pseudo-octahedral en-
˚
vironment. Four of the donors are provided by the ligand is hexacoordinated. The MnϪN1A distance [2.13(2) A] is
2
, through the imidazole nitrogen N1A, the pyridine nitro- significantly shorter than the MnϪN1B distance [2.23(2)
˚
gen N1B, the tripodal nitrogen N and one carboxylato oxy- A], suggesting a stronger bond with the imidazole ligand.
gen O2. The fifth donor is provided by the carboxylato oxy- Such small MnϪNimidazole distances were reported to be
gen O1 from the carboxylato of unit (Ϫ1). The final coordi- characteristic of bridged structures.[ Imidazole and pyri-
nation site is filled by a molecule of methanol. The dine are in the trans positions with regard to Mn and the
7]
˚
MnϪNtripodal distance [2.35(3) A] is longer than the other two aromatic rings are parallel to each other [Φ ϭ 5(1)°].
MnϪN bonds, but shorter than the corresponding sum of The Mn atom and the three oxygens O1, O2Ј and O3 (see
˚
the van der Waals radii (2.82 A), indicating that the metal Figure 1) (carboxylate and methanol) are coplanar (mean
Figure 1. ORTEP drawing of complex 3 cationic chain with three adjacent monomeric units of the polymer; hydrogen atoms have been
omitted for clarity
2202
Eur. J. Inorg. Chem. 1999, 2201Ϫ2207

Structural and Magnetic Properties of a syn-anti Carboxylate-Bridged Manganese(II) Chain
FULL PAPER
˚
Table 2. Selected bond lengths [A] and angles [°] for 3
MnϪN(1A)
MnϪO(1)
MnϪO(2)
MnϪN(1B)
MnϪO(3)
MnϪN
2.13(2)
2.13(2)
2.18(2)
2.23(2)
2.26(2)
2.36(2)
O(1)ϪMnϪN(1B)
O(2)ϪMnϪN(1B)
N(1A)ϪMnϪO(3)
O(1)ϪMnϪO(3)
O(2)ϪMnϪO(3)
N(1B)ϪMnϪO(3)
N(1A)ϪMnϪN
98.2(6)
84.7(6)
88.4(7)
92.5(6)
171.8(5)
87.2(6)
75.7(6)
162.4(6)
75.5(6)
74.0(6)
102.7(6)
N(1A)ϪMnϪO(1)
N(1A)ϪMnϪO(2)
O(1)ϪMnϪO(2)
114.1(6) O(1)ϪMnϪN
98.8(7)
88.3(6)
O(2)ϪMnϪN
N(1B)ϪMnϪN
N(1A)ϪMnϪN(1B)
147.5(6) O(3)ϪMnϪN
˚
displacement 0.006 A), the tripodal nitrogen N being lo-
˚
cated at 0.34(2) A from this mean plane.
The carboxylates bridge two mononuclear units with a
syn-anti pattern, forming an infinite chain. The manganese
from unit 0 is slightly closer to the carboxylato oxygen O1
belonging to a ligand from the adjacent unit (Ϫ1) than to
Figure 2. View of the helico ¨ı dal organisation with space filling re-
presentation
˚
˚
O2 [see Figure 1; 2.13(2) A (MnϪO1) versus 2.18(2) A
MnϪO2)]. O1 interacts with the manganese through its
(
syn lone pair and O2 through its anti lone pair. All dis-
tances and angles (see Table 2) are consistent with those
previously found in manganese syn-anti µ-carboxylato sys-
[
8Ϫ16]
tems.
Although the H-atom of the coordinated meth-
anol could not be located on difference Fourier-syntheses,
it seems clear that a strong internal hydrogen bond occurs
between the acceptor oxygen O2 of the carboxylate group
and the oxygen donor of the methanol of the adjacent unit
˚
ϩ1 [see Figure 1; d(O2ϪO3Љ) ϭ 2.63(2) A]. This hydrogen
bond involves the syn lone pair of O2.
The two oxygens O1 and O2 are in a cis conformation
with regard to Mn, with a (O1ϪMnϪO2) angle of 88.3(6)°.
The chain develops in a zig-zag manner, with an
(
MnϪ1ϪMn ϪMnϩ1) angle of 125.3° and a nonplanar
0
MnϪOϪCϪOϪMn pattern. From unit Ϫ1 to unit 0, the
plane of the two aromatic rings is tipped over by 64° (see
Figure 2). The third unit along the chain can be deduced
˚
from the first one by translation (10.84 A). The structure
can be described as a chiral helix-like chain running parallel
to the b axis and with a pitch of two complexes (see Figure
˚
2
). The MnϪMn distance is 5.42 A and is in the typical
range which has previously been described for such syn-anti
II
˚
[9Ϫ16]
bridges between Mn [5.2Ϫ5.8 A].
The spatial arrangement of the complex 3 is displayed in
Figure 3. The packing diagram reveals a layer organisation
with entangled parallel helixes. A pyridine moiety from one
helix is parallel to an imidazole from the next, with a small
˚
interplanar distance (3.8 A). The closest distance between
˚
two Mn from two adjacent helixes is 8.42 A.
Figure 3. ORTEP packing diagram; the disorder of the anionic
units has been omitted for clarity
Magnetic Properties
ters in 3. The magnetic properties of such a chain can be
explained by the Heisenberg linear-chain model. The Ham-
iltonian used here is:
The results of susceptibility measurements are shown in
Figure 4. At very low temperature, the experimental suscep-
tibility is smaller than that predicted by a Curie law for S ϭ
5
/2 and g ϭ 2 (see inset, dash line). This indicates some
small antiferromagnetic coupling between two metallic cen-
Eur. J. Inorg. Chem. 1999, 2201Ϫ2207
2203

C. Policar, F. Lambert, M Cesario, I. Morgenstern-Badarau
FULL PAPER
where the summation is all along the chain and J is the Discussion
exchange coupling between two adjacent paramagnetic cen-
ters. An analytical law has been derived by Fisher for infi-
A syn-anti bridging configuration is rare by comparison
nite chains and large spins.[
17][18]
For an infinite S ϭ 5/2 with a syn-syn configuration. The former is made easier
[2]
chain, the expression of the chain molar magnetic suscepti- by steric congestion[
25][26]
and is more frequently found
[
19Ϫ21]
[27Ϫ30]
bility χ is:
when the carboxylate is part of a polydentate ligand
c
[
13,15,16,25]
or a substituted acetate,
including amino ac-
ids.[
14][31]
It has been reported for discrete complexes,
[15]
[9Ϫ14,16,31]
polymeric chains and networks with manganese.
The main structural feature of compound 3 is the chiral
helix-like structure with a nonlinear bridging network. This
is due both to the syn-anti bridging mode of the carboxylato
ligand and to the cis position of the two oxygens O1 and
O2 in the octahedron around Mn. IR spectroscopic data
are consistent with a bridging carboxylate and not a unid-
Fitting the data to that expression provided an estimate
of J (J/k ϭ Ϫ0.27). However, the g value thus obtained was
II
too small for a Mn high spin complex (g ϭ 1.946, with an
Ϫ4
agreement factor for the fitting R ϭ 1.51 ϫ 10 ). The fit-
entate one: the small value of ∆ν ϭ (νasCO) Ϫ (ν ) ϭ
sCO
ting was improved by taking into account interchain inter-
Ϫ1
[1]
actions via a mean-field.[
18][22]
131cm is characteristic of a bridging carboxylate. An-
other important feature is the layer organisation. In the
crystal packing, the chains are stacked by π-interactions
The expression used to fit
the data was:
˚
with an interplanar spacing of 3.8 A between the pyridine
from one helix and the imidazole from the next.
Very little is known about the magnetic properties of such
carboxylato syn-anti manganese chains. On the contrary,
the magnetic properties of manganese chains involving hal-
where JЈ is the interchain-exchange coupling and z the num- ogen bridges have been extensively described and are classi-
ber of nearest neighbors. The best fit of Equation 2 in the cal examples of linear chain compounds (see Table
temperature range 2Ϫ300 K was found for J/k ϭ Ϫ0.25 3).[
19Ϫ21,32]
The carboxylato syn-anti bridge has received
Ϫ1
Ϫ1
(
Ϫ0.17 cm ), zJЈ/k ϭ Ϫ0.11 (Ϫ0.078 cm ) and g ϭ 1.970 some attention because it allows a large variety of structural
with an agreement factor R ϭ 2.17 ϫ 10 . All three par- and magnetic features.
Ϫ5
[23,29,33]
Without being exhaustive, the
ameters were allowed to vary during the fitting process. As magnetic behavior has been studied for syn-anti carboxylato
can be seen in Figure 4, the experimental points and theor- bridges in chain structures involving homonu-
etical curve are superimposed in all the temperature range. clear[
23,28,29,33Ϫ35]
II
[36]
II
II
Cu , heterodinuclear Mn and Cu or
The J and JЈ values obtained are very small and thus the in discrete complexes[ (Fe ). The magnetic properties
27]
III
precision on their absolute value must be rather low. More- have also been studied for a 2D-polymer with a syn-anti
[
16]
II
over the ratio zJЈ/J ϭ 0.4 is at the high limit for the mean- carboxylato network
between Mn , and on a discrete
This increases the uncertainty Mn homodimer involving a mono syn-anti carboxylato
field model to be valid.[
22Ϫ24]
II
[
15]
on JЈ although the order of magnitude both for J and JЈ is bridge (see Table 3).
still meaningful.
The intrachain coupling constant in compound 3 is at
least one order of magnitude smaller than that reported for
II
halogenated Mn chains (see Table 3). The exchange coup-
ling through the carboxylato moiety is highly dependent on
the conformation of the bridge between the metal centers
that are interacting.[
18,34,37]
A syn-syn pattern provides small
metalϪmetal distances and a good overlap of magnetic or-
bitals. It induces high antiferromagnetic coupling, as has
previously been reported in Cu (CH COO)4·2H2O where
2
3
the four acetates are in a syn-syn configuration with J ϭ
Ϫ1 [38][39]
Ϫ150 cm
.
Syn-anti carboxylato bridges induce
much smaller J values because of the expanded metallic
core and a mismatch in the orientation of magnetic or-
bitals.[
23,29,34,36]
For compound 3, the MnϪMn intrachain
˚
distance is 5.42 A, which is rather large. Moreover, the
bridging network displays a “zig-zag” structure (see de-
scription of the structure). To the best of our knowledge,
Figure 4. Experimental and calculated temperature dependences of there are considerably fewer examples involving two car-
χT; for clarity only 50% of the experimental points are shown; the
boxylato syn-anti ligands in a cis position than in a trans
dashed line was generated with a Curie law for S ϭ 5/2 and g ϭ 2
position. The four closest structures, studied from a mag-
(
see text); the solid line is the best fit obtained including the mean-
netic point of view, found in the literature are: (a)[ and
29]
field correction (see text for parameters)
2204
Eur. J. Inorg. Chem. 1999, 2201Ϫ2207

Structural and Magnetic Properties of a syn-anti Carboxylate-Bridged Manganese(II) Chain
FULL PAPER
II
Table 3. Antiferromagnetic couplings for several Mn compounds (including chains, one 2D-polymer and one dimer) and related
MnϪMn distances
Compound
MnϪMn distance[c] [ A˚ ]
Bridge
J [K]
ref.
[
[
[
20]
32]
19]
[
(CH
CsMnBr
CsMnCl
Mn[(5-NO
3
)
4
N]MnCl
3
3
3.25
3.26
4.73
5.92
5.40
5.67
5.42
Chloro
Ϫ6.3
Bromo
Ϫ9.5
3
Chloro
Ϫ3
-salimH)MeOH(µ-HCO
2
(H O)
2
2
)][a]
)][ClO
Carboxylato anti-anti
Carboxylato syn-anti
Carboxylato syn-anti
Carboxylato syn-anti
Ϫ0.36
Ϫ0.3 to Ϫ0.4
Ϫ0.27
Ϫ0.25
[7]
2
[
b]
[16]
Mn[(MCPA)
(H
2
O)
2
2 n
]
[
15]
Mn[(bipy)
2
(Me
2
N CH
2
CO
2
4 2
]·2H O
3
this work
[
a]
-NO
2
-salimH ϭ 4-(2-[(5-nitrosalicylidene)amino)ethyl]imidazole. Ϫ [b] MCPA ϭ 2-methyl-4-chlorophenoxyacetic acid. Ϫ [c] For chains,
5
intrachain distance; for polymer, closest distance.
b)[
cluster
40][41]
two copper(II) chains, (c) a copper tetranuclear Conclusions
28]
(
[
and (d) a copper(II) ladder-like chain of dimer
[35]
In this article, we have reported the structure and mag-
netic study of a polymeric Mn compound involving car-
units with a di-µ-carboxylato.
Both (a) and (b) show a
II
helix-like structure that bears a great number of structural
similarities with compound 3 with a ferromagnetic coupling
J/k ϭ 2.4 and J/k ϭ 4.0, respectively. Compound (c) also
displays a ferromagnetic coupling J/k ϭ 3.8. In compound
d), a very small antiferromagnetic coupling was estimated
at Ϫ0.7 K.
boxylato syn-anti cis bridges. The compound described here
is of interest for several reasons. First, it involves a car-
boxylato bridge that is part of a polydentate ligand and not
a separate acetate. This carboxylate has been shown to be
(
II
coordinated to the Mn centers in a syn-anti mode, afford-
ing a chiral helix-like polymeric structure. It also displays a
pseudo-2D magnetic structure with a weak exchange inter-
action through intrachain syn-anti cis carboxylato bridges
and a weaker interaction through interchain π-interactions.
Finally, it presents a potentially open-shell. The ligand 2 is
tetradentate. In the solid state, the coordination sphere of
The importance of the syn-anti conformation on the mag-
nitude of J has previously been stressed for copper(II) com-
[
28Ϫ30]
pounds.
It can also be illustrated for compound 3 by
some relevant comparisons. First, two structures with syn-
II
anti carboxylato bridges between Mn have previously been
reported and studied from a magnetic point of view: (e) a
II
[
16]
each Mn center of compound 3 is completed by a mol-
2
D-polymer
containing a syn-anti carboxylato lozenge-
II
II
ecule of methanol and an oxygen atom (O1) from a car-
boxylato group from a neighboring molecule of 2. Com-
pound 3 is soluble in several solvents, indicating a dis-
rupture of the polymeric structure. This probably occurs by
the replacement of O1 by a further solvent molecule,[
shaped network between Mn and (f) a discrete Mn dimer
involving a mono syn-anti carboxylato bridge.
MnϪMn distance is 5.40 A and an antiferromagnetic coup-
ling J/k of Ϫ0.3 to Ϫ0.4 was estimated. In (f), the intermet-
allic distance is 5.67 A with an antiferromagnetic coupling
[15]
In (e), the
˚
7][44]
˚
II
thus keeping the usual octahedral environment of Mn
J/k ϭ Ϫ0.27. These exchange coupling constants are of the
complexes. In solution, this compound thus bears two labile
coordination sites available for substrate binding. Its reac-
tivity towards superoxide is now under investigation.
same order and are very close to that obtained for com-
pound 3.
chain with a dipodal N-centered ligand bearing one imidaz-
[
42]
Another comparison can be made with a MnII
ole and one phenolate involving a formate bridge in a anti-
[7]
anti cis binding mode (see Table 3). The MnϪMn dis-
tance along the chain is 5.92 A and J/k ϭ Ϫ0.36. Despite
˚
Experimental Section
a larger distance, the antiferromagnetic coupling is greater General: IR spectra (KBr) were recorded on a Bruker IFS 66 FT-
than in compounds 3 and (f).[ Presumably this is related IR spectrometer. H NMR spectra were recorded on Brüker AM
43]
1
to the anti-anti pattern inducing better orbital overlap.[
The geometric characteristics of 3 (syn-anti carboxylato
bridges, “zig-zag” structure with nonplanar MnϪOϪCϪ-
OϪMn pattern) account for the very low value determined
for the intrachain coupling constant (J/k ϭ Ϫ0.25).
The value of the ratio zJЈ/J ϭ 0.4 suggests a pseudo-2D
magnetic structure. The shortest MnϪMn interchain dis-
tance is 8.42 A, each Mn having two closest neighbors (z ϭ
30]
200 and AM 250 spectrometers. X-band electron paramagnetic res-
onance (EPR) was recorded on a Bruker ER 200E spectrometer.
Variable temperature magnetization measurements were collected
on ground crystals with a Quantum Design SQUID magnetometer
at a magnetic field of 1 T within the temperature range 300Ϫ2 K.
Data were corrected for diamagnetism of the ligand estimated to
Ϫ4
3
Ϫ1
[48]
Ϫ2.431500 ϫ 10 cm ·mol from PascalЈs constant. Chemical
reagents were purchased either from Aldrich or Acros and used
without further purification.
˚
2
). Two adjacent helixes seem to be connected through π-π
interactions between a pyridine moiety and the imidazole Synthesis and Characterization
group (see Figure 3). Despite the large MnϪMn interchain
distance (8.42 A), a π-π interaction provides an effective omethylpyridine (18.38 g) in 100 mL of anhydrous THF at 0°C,
N-(2-pyridylmethyl)aminoethyl acetate (1): To a solution of 2-amin-
˚
pathway for interchain exchange interaction.
ethylbromoacetate (14.19 g) in 100 mL of anhydrous THF was ad-
2205
Eur. J. Inorg. Chem. 1999, 2201Ϫ2207

C. Policar, F. Lambert, M Cesario, I. Morgenstern-Badarau
FULL PAPER
ded dropwise. The reaction mixture was left for 30 min. at 0°C and
culated and included in the refinement at their ideal positions
˚
˚
then allowed to warm to room temperature. After 15 h, the solution (CϪHar ϭ 0.93A, CϪHMe ϭ 0.96A) with an isotropic thermal par-
was filtered and the filtrate evaporated to dryness. The residual oil ameter of 1.2 for the bonded atoms. Only the manganese atom was
was distilled under reduced pressure (0.4 Torr, 100°C), to give a refined anisotropically to limit the number of parameters versus
1
colorless liquid. Yield: 75%. Ϫ H NMR (CDCl
H, CH ), 2.81 (s, 1 H, NH), 3.48 (s, 2 H, NϪCH
s, 2 H, pyϪCH ϪN), 4.20 (q, 2 H, OϪCH ), 7.17 (t, 1 H, Hpy),
.33 (d, 1 H, Hpy), 7.64 (t, 1 H, Hpy), 8.56 (d, 1 H, Hpy).
3
): δ ؍ 1.28 (t, 3
the number of data.
3
2
ϪCOOEt), 3.96
The asymmetric unit consists of one monomeric complex cation
and one counteranion (PF ). The latter shows disorder; two differ-
6
ent sites were found on a difference Fourier-syntheses. A better
convergence was obtained with an occupancy factor of 50% and
(
7
2
2
Potassium
N,N-[2-pyridylmethyl)(1-methylimidazol-2-yl)-methyl]-
glycinate (2K): A solution of 1 (3.88 g) and N-methyl-2-imidazol- refinement was pursued with restraints. A selection of bond lengths
[
45]
carboxaldehyde
over (Pd/C, 10%) for 24 h. After filtration and evaporation to dry-
ness, 2K was obtained by hydrolysis at room temperature in H O/
EtOH (3:1) with K CO (2.2 equiv.) for 48 h. Residual potassium
(2.2 g) in MeOH (100 mL) was hydrogenated
and angles is presented in Table 2 and the crystallographic number
scheme is presented in Figure 1 which shows three adjacent units
along the axis b.
2
2
3
Crystallographic data (excluding structure factors) for the structure
included in this paper have been deposited with the Cambridge
Crystallographic Data Centre as supplementary publication
no. CCDC-125980. Copies of the data can be obtained free of
charge on application to CCDC, 12 Union Road, Cambridge
CB2 1EZ, UK [Fax: (internat.) ϩ 44-1223/336-033; E-mail:
deposit@ccdc.cam.ac.uk].
salts were partially removed by extracting the carboxylate 2K with
anhydrous MeOH. Compound 2K was recrystallized from MeOH/
EtOEt. Yield: 95%. Ϫ 1H NMR (CD
OD): δ ؍ 2.95 (s, 2 H,
), 3.52 and 3.57 (2s, 2 ϫ 2 H,
ϪIm), 6.54 and 6.64 (2s, 2 ϫ 1 H, HIm),
3
NϪCH
NϪCH
2
COOK), 3.30 (s, 3 H, CH
Ϫpy and NϪCH
.03 (t, 1 H, Hpy), 7.14 (d, 1 H, Hpy), 7.52 (t, 1 H, Hpy), 8.15 (d, 1
H, Hpy). Ϫ IR (KBr): ν˜ ϭ 1591 (νasCO), 1396 (νsCO), 771
(νpyr. deform.), 742 (νimid. deform.) cm (strong bands only).
3
2
2
7
Ϫ1
n 6 n
Mn(IPG)(MeOH)] (PF )
(3): The pH of a 2 ϫ 10Ϫ3  solution
[
Acknowledgments
of 2K in water was adjusted by HCl addition in the 8Ϫ8.5 range.
After evaporation, the solid was dried under reduced pressure for
We thank Dr. E. Rivi e` re for his contribution to magnetic measure-
ments and Pr T. Mallah for useful discussions.
one night in the presence of P
tion of the ligand in anhydrous methanol. Typically, chain crystals
were obtained as followed. MnBr (330 mg) in deoxygenated
2 5
O and KCl was removed by extrac-
2
[
1]
G. B. Deacon, R. J. Phillips, Coord. Chem. Rev. 1980, 227Ϫ250.
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hours at 40°C. Then, after cooling, a deoxygenated solution of
[2]
1
5, 417Ϫ430.
[3]
Y. Akhriff, J. Server-Carrio, A. Sancho, J. Garcia-Lozano, E.
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NH
The solution was allowed to stand for a week during which time
crystals were formed. Yield: 50%. Ϫ C14 MnN P (491.2):
4 6
PF (3 equivalents) in MeOH (40 mL) was added dropwise.
1
174Ϫ1185.
[4]
M. C. Rodriguez, C. Policar, I. Morgenstern-Badarau, unpub-
lished results.
H
19
F
6
4 3
O
[
[
5]
6]
calcd C 34.2, H 3.9, N 11.4, P 6.3, Mn 11.2; found C 33.9, H 3.8,
M. C. Rodriguez, I. Morgenstern-Badarau, M. C e´ sario, J. Gu-
ilhem, B. Keita, L. Nadjo, Inorg. Chem. 1996,
In the IPG abbreviation, I stands for imidazole, P for pyridine
and G for glycinate.
N 11.3, P 5.9, Mn 10.6. Ϫ IR (KBr): ν˜ ϭ 1606 (sh), 1571 (νasCO),
Ϫ1
1
440 (νsCO), 770 (νpyr. deform.) 755 (νimid. deform.) cm (strong bands
only). Ϫ The EPR spectrum was recorded on ground crystals at
room temperature and 100 K. It shows a broad signal centered at
g ϭ 1.98, with no resolved hyperfine structure.
[7]
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[
[
8]
9]
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1
312Ϫ1316.
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[
[
12]
13]
Several crystals were tested for their suitability for X-ray diffraction
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0.2 ϫ 0.15 ϫ 0.07 mm was mounted on an EnrafϪNonius Cad 4
diffractometer with graphite monochromated Mo-K
α
radiation
[16]
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˚
[λ ϭ 0.7107A]. The unit cell dimensions were refined from setting
angles of 25 reflections [5.2 < Θ <11.6°]. Structure determination
and refinement data are reported in Table 1. Data collection was
performed at room temperature with ΘϪ2Θ scan technique mode,
in the 2Θ range from 4 to 32°. Three standard reflections were
measured every hour, to monitor instrument and crystal stability.
A 28% decay was observed. A total of 568 reflections was collected
7
655Ϫ7660.
[
[
[
17]
18]
19]
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6
43Ϫ648.
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Lorentz and polarization factors but not for absorption factors.
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[
46]
2
SHELXS86)
and refined on F for all reflections by least-
[25]
squares method using SHELXL-93.[ Hydrogen atoms were cal-
47]
2206
Eur. J. Inorg. Chem. 1999, 2201Ϫ2207

Structural and Magnetic Properties of a syn-anti Carboxylate-Bridged Manganese(II) Chain
FULL PAPER
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[I99254]
Eur. J. Inorg. Chem. 1999, 2201Ϫ2207
2207