1D CoII and NiII chiral polymers that exhibit ferromagnetic interactions

Article abstract of DOI:10.1002/ejic.201100534

Four transition-metal coordination compounds with d- and L-mandelic acid (Hmand) were synthesized and structurally and magnetically characterized. The structure, refined as {M^II(L/D-mand)(4-MePy)₃} _n·n(ClO₄) (M

Full text of DOI:10.1002/ejic.201100534

FULL PAPER
DOI: 10.1002/ejic.201100534
1D CoII and NiII Chiral Polymers That Exhibit Ferromagnetic Interactions
Ghenadie Novitchi,[a,b] Guillaume Pilet,[a] and Dominique Luneau*[a]
Keywords: Crystal engineering / Chain structures / Cobalt / Nickel / Carboxylate ligands
Four transition-metal coordination compounds with D- and
mandelic acid (Hmand) were synthesized and structurally
L
-
is chiral and completed by three 4Me–Py ligands. Magnetic
studies reveal the presence of a ferromagnetic interaction be-
tween the NiII centers [J = 0.64(5)–0.54(7) cm–1 and zero-field
splitting (ZFS) = –1.38(1)/–1.05(2) cm–1]. In the case of the
CoII-based polymer, ferromagnetic but negligible interaction
is suspected.
and magnetically characterized. The structure, refined as
{MII( -mand)(4-MePy)3}n·n(ClO4) (M = CoII and NiII; 4-
L/D
MePy = 4-methylpyridine), reveals a chiral 1D polymer that
consists of a chain complex built by the monocarboxylate li-
gand. The coordination sphere of the paramagnetic center
With these ideas in mind, we focused our attention on
the possibility of developing new chiral coordination poly-
mers that involve bivalent ions. Mandelic acid, Hmand, was
selected because it possesses different coordination
modes[24–35] (see Scheme 1) and is a good candidate to
elaborate new enantiopure 1D coordination polymers.
Meanwhile, the introduction of a second type of an in-
Introduction
Crystal engineering of structures that possess various
network topologies attracts much attention due to their po-
tential applications in many important fields such as cataly-
sis, hydrogen storage, metal–organic frameworks, electrical
conductivity, and molecular magnets.[1–11] Among these, co-
ordination polymers are an important class of engineered
structures. In this case, the strategies for the synthesis of
one-dimensional (1D), two-dimensional (2D), or three-di-
mensional (3D) frameworks often take advantage not only
of coordination bonding but also of other directional inter-
actions such as versatile hydrogen-bonding,[12,13] π–π-stack-
ing,[13,14] and electrostatic interactions.[15–17]
–
termetal center bridge such as azide, N3 , as the magnetic
relay between chiral chains was considered to favor the for-
mation of 2D chiral complexes with original magnetic be-
havior.
To obtain polymeric structures, a large variety of ligands
have been used. By contrast, chiral ligands remain underex-
plored, particularly in the design and preparation of an
acentric arrangement. In the field of molecular magnetic
materials, asymmetric ligands may be used to induce an
asymmetric environment of paramagnetic centers and/or a
non-centrosymmetric repartition of paramagnetic centers
along the polymers and also in crystal packing. Such non-
centrosymmetric repartition of the spin carriers can greatly
affect the bulk magnetic properties of the material as has
been shown in some 1D coordination systems of metal with
chiral nitroxide radical.[18–21] This might even give rise to
new phenomena such as magnetochiral dichroism (MCD)
and chiral wave propagation. In that context, high MCD
has been recently observed in chiral CrIII compounds.[22,23]
Scheme 1. Reported coordination modes for mandelic acid: A,[24,25]
B,[26] C,[25,27,28] D,[29–31] E,[32–34] and F.[35]
[a] Université Claude Bernard Lyon 1,
Laboratoire des Multimatériaux et Interfaces (UMR 5615),
Domaine Scientifique de La Doua,
69622 Villeurbanne Cedex, France
E-mail: luneau@univ-lyon1.fr
[b] Institute of Chemistry, Academy of Sciences of Moldova,
Academiei str. 3., 2028 Chisinau, Moldova
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.201100534.
In this paper, we report the result of a synthetic pro-
cedure with different metal ions (MnII, CoII, NiII, and
CuII). With NiII and CoII, new 1D enantiopure polymers
were crystallized as: {MII(l-mand)(4-MePy)3}n·n(ClO4) [M
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G. Novitchi, G. Pilet, D. Luneau
FULL PAPER
= Co: IL(Co); M = Ni: IL(Ni); 4-MePy = 4-methylpyridine] Complexes Based on Nickel(II) Ion
and {MII(d-mand)(4-MePy)3}n·n(ClO4) [M = Co: ID(Co);
With the same procedure, it was possible to isolate two
M = Ni: ID(Ni)]. Their crystal structures and the results of
circular dichroism and magnetic studies are reported here.
Optical studies showed that we obtained the sole enantio-
pure compounds for all. Additionally, magnetic studies re-
vealed ferromagnetic interactions between metal centers.
1D chiral nickel(II) polymers: {NiII(l-mand)(4-MePy)3}n·
n(ClO4) [IL(Ni)] and {NiII(d-mand)(4-MePy)3}n·n(ClO4)
[ID(Ni)], starting from l- or d-Hmand ligands, respectively.
Complexes Based on Cobalt(II) Ion
The same procedure under normal atmospheric aerobic
conditions gave a black compound. According to single-
crystal X-ray measurements, the compound corresponds to
the following refined formula: mer-[CoIII(4-MePy)3(N3)]
(II) with the cobalt ion in a +3 oxidation state and no man-
delic ligand (see the Supporting Information for more de-
tails). This is in agreement with the observation that the
l/d-mand ligand has a preference for metal ions in a +2
oxidation state that adopt an octahedral geometry. The
presence of azide ion, which is a strong crystal-field ligand,
together with aerobic oxidative conditions definitely fa-
vored the formation of mer-[CoIII(4-MePy)3(N3)] (II). The
CoIII ion has a slightly distorted octahedral CoN6 environ-
ment formed by coordination of three neutral 4-MePy li-
gands [Co–N 1.975(2), 1.983(2), 1.966(2) Å] and three azide
anions [Co–N 1.953(2), 1.961(2), 1.940(2) Å]. The three az-
ide anions totally compensate the triple positive charge of
the CoIII ion. By following the same procedure, but under
an inert (N2) atmosphere, it has been effectively possible to
isolate the two 1D chiral cobalt(II) compounds as for NiII,
{CoII(l-mand)(4-MePy)3}n·n(ClO4) [IL(Co)] and {CoII(d-
mand)(4-MePy)3}n·n(ClO4) [ID(Co)].
Results and Discussion
Chiral mandelic acid (l/d-Hmand) was introduced to
elaborate magnetic chiral 1D polymer complexes. It has
been already reported in the literature that the asymmetry
of ligands can induce an asymmetry in the environment of
the paramagnetic centers and/or a non-centrosymmetric re-
partition of the paramagnetic centers along the polymers
and within the crystal packing.[36–38] Azide salt was then
used with a view to connecting these chains in 2D chiral
–
polymers because the N3 bridge is known to be a good
magnetic bridge between metal centers.
Addition of an excess amount of 4-MePy to a solution of
chiral mandelic acid (l/d-Hmand) in methanol mixed with
M(ClO4)2·6H2O (MII = Cu, Mn, Co, and Ni) and NaN3 in
an equimolar ratio gave different compounds depending on
the metal ion. In the case of NiII and CoII, it was possible
to isolate the two 1D chiral compounds {MII(l-mand)(4-
MePy)3}n·n(ClO4) and {MII(d-mand)(4-MePy)3}n·n(ClO4)
(M = NiII or CoII) starting from either l- or d-Hmand li-
gands.
The role of azide is not thoroughly understood but it is
indispensable for the synthesis of the 1D IL(Ni), IL(Co),
ID(Ni), and ID(Co) compounds. The general chemical pro-
cesses with chiral mandelic acid are illustrated in Scheme 2.
Complexes Based on Copper(II) Ion
With this synthetic procedure, it was impossible to isolate
any complex that contained the mandelic ligand. Under all
conditions, we obtained a blue viscous oil to give in the end
a blue homogeneous film. From this we isolated a few crys-
tals of a binuclear complex and some crystals of a mononu-
clear complex with the following refined formula obtained
by single-crystal X-ray diffraction: [Cu2(μ-N3)(4-MePy)8-
(H2O)2](ClO4)3(4-MePy)4 (III) and [Cu(4-MePy)4(ClO4)2]
(IV) (see the Supporting Information). As can be seen, both
contain no mandelic acid.
Complexes Based on Manganese(II) Ion
Under the same conditions, a white crystalline com-
pound was formed. According to elemental analyses and
IR spectra, it corresponds to manganese(II) dimandelates
{[MnII(l-mand)2] (V); see the Supporting Information} that
have already been reported.[29–31] This result is probably due
to the best affinity of MnII ions for the oxygen environment
instead of nitrogen.[39] Changing the reacting salt from
MnII(ClO4)2·6H2O to MnIII(Ac)3·3H2O in the presence of
4-MePy also leads to the same [MnII(l-mand)2] final prod-
uct.
Scheme 2. Chemical transformation in the M2+/NaN3/mandelic
acid system.
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1D CoII and NiII Chiral Polymers
Our study focuses on nickel- and cobalt-based chiral 1D thereby confirming the existence of the opposite enantio-
polymers with l/d-Hmand acid. IR, single-crystal X-ray dif- meric structures.
fraction, circular dichroism, and magnetic properties analy-
In all cases (IL, ID), the metallic ion (Ni or Co) is located
ses were performed to thoroughly characterize the stereo- in an N3O3 slightly distorted octahedral environment. M–
chemical conformation of the four enantiopure compounds O/N bond lengths range from 2.056 to 2.204 Å (M = Co)
IL(Ni), IL(Co), ID(Ni), and ID(Co). Details about the non- and from 2.041 to 2.146 Å (M = Ni) and are in good agree-
chiral complexes II, III, and IV in Scheme 2 have been ment with those reported previously in the literature.[24–35]
listed in the Supporting Information.
It is worth noting that the octahedron in both metal cases
The IR absorption spectra of IL and ID complexes pro- is quite regular due to uniform bond lengths and O–M–O
vide strong evidence for the coordination modes of the bond angles (Tables 1 and 2).
carboxylate groups of the α-hydroxycarboxylate ligand
(l/d-Hmand). The Δν difference between the asymmetric
and symmetric stretching frequencies [Δν = νas(COO–),
–νs(COO–)] for the carboxylate ligand is characteristic of
a bidentate bridging coordination mode of the carboxylic
groups.[40] For example, in the case of the IL(Ni) IR spec-
trum, medium intensive bands were found at 1615 cm–1,
which are related to νas(COO–), and at 1422 cm–1, which are
attributed to νs(COO–) stretching vibrations. The difference
between these two frequencies is equal to 193 cm–1 and is
characteristic of a bidentate bridging coordination. A
strong peak at 1079 cm–1 in the IR spectrum of IL(Ni) indi-
cates the presence of perchlorate anions. Signals [ν(CH)Py
= 3065; ν(CN) = 1592; γ(CH)Py = 620 cm–1] for coordinated
pyridine rings and for valent oscillations of the ν(OH)
group in the range of 3615–2812 cm–1 are also present. The
latter are large, thus indicating that these –OH groups are
most probably involved in strong hydrogen bonds.
Table 1. Important bond lengths [Å] for the IL, ID complexes.
IL(Co)
ID(Co)
IL(Ni)
ID(Ni)
M = Ni
M = Co
M1–O1
M1–O3
M1–O5
M1–N21
M1–N31
M1–N41
2.063(2)
2.113(2)
2.146(2)
2.159(2)
2.099(3)
2.204(3)
2.056(2)
2.109(2)
2.146(2)
2.155(3)
2.099(3)
2.204(2)
2.041(2)
2.074(2)
2.096(2)
2.112(2)
2.057(2)
2.146(2)
2.043(2)
2.075(3)
2.093(3)
2.113(3)
2.055(3)
2.139(3)
Table 2. Important bond angles [°] for the IL, ID complexes.
IL(Co)
ID(Co)
M = Co
IL(Ni)
ID(Ni)
M = Ni
O1–M1–O3
O1–M1–O5
O3–M1–O5
O1–M1–N21 90.4(1)
O3–M1–N21 93.51(9)
165.86(8) 165.74(8)
169.25(6) 169.4(1)
91.49(9)
75.01(9)
91.63(9)
74.81(9)
90.3(1)
93.77(9)
88.8(1)
96.76(9)
96.8(1)
93.20(8)
76.65(8)
89.74(8)
93.46(7)
88.43(8)
93.93(7)
96.34(9)
93.2(1)
76.7(1)
89.7(1)
93.4(1)
88.4(1)
93.9(1)
96.3(1)
The two compounds derived from l-mandelic acid
[IL(Ni), IL(Co)] are isostructural and exhibit a 1D poly-
meric structure. The crystallographic independent entity is O5–M1–N21 88.9(1)
present in Figure 1 (left side). The refined Flack parameter
O1–M1–N31 96.67(9)
O3–M1–N31 96.8(1)
is equal to –0.02(1) and 0.02(2) for IL(Ni), IL(Co), respec-
O5–M1–N31 171.84(9) 171.60(8)
172.69(7) 172.7(1)
tively, according to the rules defined in the corresponding
part of the Experimental Section. As expected, ID(Ni) and
ID(Co) structures are the mirror image of IL(Ni) and
IL(Co), respectively. In those cases, the Flack parameters
are equal to 1.00(2) for IL(Ni) and 0.98(2) for IL(Co),
N21–M1–N31 91.2(1)
O1–M1–N41 90.85(9)
O3–M1–N41 85.26(9)
O5–M1–N41 90.8(1)
N21–M1–N41 178.8(1)
N31–M1–N41 88.9(1)
91.3(1)
90.84(9)
85.07(9)
91.0(1)
178.8(1)
88.8(1)
89.96(9)
91.21(8)
85.58(7)
91.35(8)
89.9(1)
91.2(1)
85.7(1)
91.4(1)
179.03(8) 179.1(1)
90.14(8) 90.2(1)
The square base of the metal octahedral environment is
composed of one nitrogen atom of one methylpyridine
(N31) and three oxygen atoms. Two of them belong to one
mand– ligand [one (O5) of the hydroxy group and the sec-
ond one (O3) of the carboxylate entity]. The third oxygen
atom (O1) comes from a second mand– ligand. This latter
is also connected to a neighboring metal ion to form a poly-
meric structure (Figure 2). The two apical positions in the
octahedral environment are occupied by two nitrogen atoms
(N41, N21) from 4-MePy molecules. The H51 hydroxo pro-
ton forms a strong intermolecular bond with the oxygen
atom (O3) of the carboxylate group along the chain,
thereby stabilizing the coordination environments of MII.
Similarly (see Scheme 1D), the coordination mode of the
mand– ligand has already been reported for related com-
pounds.[29–31] The charge of the polymetallic chain is com-
pensated by extra-sphere perchlorate ions and no solvent
molecule is present in the crystal packing.
Figure 1. Structure of complexes IL and ID. Hydrogen atoms have
been removed for clarity.
Eur. J. Inorg. Chem. 2011, 4869–4877
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However, this study clearly indicates that the two cobalt-
based enantiomers exhibit similar but opposite signals, thus
demonstrating the homochiral nature of their structure.
Figure 3. CD spectra of IL(Co) and ID(Co) in KBr.
The temperature dependence of the magnetic suscep-
tibility of complexes IL(Ni), IL(Co), ID(Ni), and ID(Co) has
been measured in the temperature range of 2–300 K under
a magnetic field of 0.1 T, as shown in Figure 4 (see also
Figure S6 in the Supporting Information). For nickel(II)-
based compounds [IL(Ni) and ID(Ni)], the χT product per
Figure 2. Polymeric chain IL and ID along the c axis of the unit
cell. Hydrogen atoms have been removed for clarity.
Chirality in bulk crystals was proven in absorption mode NiII atom at room temperature is equal to 1.21 and
by circular dichroism (CD) spectroscopy in KBr pellets 1.20 cm3 Kmol–1, respectively. As generally observed for
(Figure 3). In the case of cobalt-based chiral polymers, a nickel(II) complexes, these values are larger than the spin-
significant dichroism signature is observed in the 450– only value of 1.0 cm3 Kmol–1 for uncoupled NiII with S =
629 nm region, which corresponds to the 4T1g(F) Ǟ 4T1g(P) 1 and g = 2.00. A gradual increase in χT is observed on
(ν3) transition of Co2+ ions located in an octahedral envi- cooling to reach values equal to 1.40 and 1.38 cm3 Kmol–1,
ronment.[31,41–43] The deviation from a symmetric shape of respectively, at 5 K. This behavior is characteristic of ferro-
opposite signals in CD spectra between IL(Co) and ID(Co) magnetic interactions for complexes IL(Ni) and ID(Ni). Be-
is likely to be related to uncertainties in the background low 5 K, in both cases, the χT product decreases to
correction because the latter is very sensitive to small differ- 1.14 cm3 Kmol–1 at 2 K, thus suggesting the presence of
ences in the thickness and transparency of KBr pellets. Un- intermolecular interactions or the effect of zero-field split-
fortunately, the presence of perchlorate ions in these com- ting (ZFS) that is characteristic of octahedral NiII ion with
3
pounds does not allow one to apply the strong pressure that S = 1 in T2g configuration.[44] The magnetic susceptibility
is indispensable to fabricating KBr pellets of good quality. obeys the Curie–Weiss law with positive Weiss constants θ
Figure 4. χT and χ versus T plots data for ID(Ni) (left) and χT, χ, and χ–1 versus T plots for IL(Co) (right) per MII atom. The solid lines
correspond to the best fit with models and parameters indicated in the text.
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1D CoII and NiII Chiral Polymers
= 0.5(1) K [1.25(2) for ID(Ni)] and Curie constant C = The small ferromagnetic interactions, +1.71 and +1.49 cm–1
1.19 cm3 Kmol–1 [1.20(2) for ID(Ni)]. This confirms the obtained for IL(Ni) and ID(Ni), respectively, correspond to
presence of ferromagnetic interactions in these complexes. the magnetic interaction between NiII cations located in an
The Curie constant gives a factor g = 2.18 calculated with octahedral environment.
Ng2β2
The second model, Model 2, is based on the equation
that has been developed by Monfort et al. for alternate fer-
romagnetic S = 1 chains.[52] This model uses the isotropic
Hamiltonian:
C =
S(S + 1) in which S = 1.
3k
Different models (1–4) have been tested to estimate the
strength of the magnetic interaction in the S = 1 ferromag-
netic nickel-based chain and to estimate the zero-field split-
ting contribution.
The first tested model, Model 1, has been developed by
Fisher[45] assuming Heisenberg interactions between spins
within the chain with well-known Fisher formula:
in which J1 = J2 = J and was also used for the characteriza-
tion of NiII ferromagnetic chains:[46,52,53]
in which A = 0.14709, B = –0.788967, C = 0.866426, D =
J
This model has been predominantly used for isotropic S
0.096573, E = –0.624929, and x =
. As for Model 1,
= 5/2 systems (see, for example, the literature[46,47]) but also
kT
to characterize NiII chains with antiferromagnetic[48–50] or interchain magnetic interactions (zJЈ) and paramagnetic im-
ferromagnetic[51] exchange interactions. The magnetic be- purities (ρ) were included.
haviors of IL(Ni) and ID(Ni) compounds have been fitted
The best fit of the experimental data (2–300 K, Table 4,
using this model and by taking into account an intermo- Figure S6 in the Supporting Information) gave for the inter-
lecular interaction term (zJЈ) and an impurities contri- action (J) +1.67(9) and +1.39(4) cm–1 for IL(Ni) and ID(Ni),
bution (ρ). The best fits are presented in the Supporting respectively, which confirms the ferromagnetic interactions
Information, and resulting parameters are given in Table 3. along the chain.
Table 3. Best parameters obtained from magnetic-susceptibility data fitting.
Model 1[43]
ID(Ni)
Model 2[50]
ID(Ni)
Model 3[52]
ID(Ni)
Model 4[56]
IL(Ni)
IL(Ni)
IL(Ni)
IL(Ni)
ID(Ni)
J [cm–1]
D [cm–1]
g
1.71(6)
1.49(2)
1.67(9)
1.39(4)
2.3(1)
1.98(5)
0.64(5)
–1.38(1)
2.165(3)
–0.3(4)
–
0.54(7)
–1.05(2)
2.190(4)
–0.4(5)
–
2.145(5)
–0.77(2)
1.3(3)
2.187(2)
–0.78(1)
0.3(1)
2.132(6)
–0.64(2)
1.7(4)
2.178(4)
–0.65(1)
0.5(2)
2.135(6)
–0.65(2)
1.7(3)
2.180(3)
–0.66(1)
0.5(2)
zJ [cm–1]
ρ [%]
Table 4. Single-crystal X-ray data collection details and refinement results.
IL(Co)
ID(Co)
IL(Ni)
ID(Ni)
Empirical formula
Mr [gmol–1]
Crystal system
Space group
a [Å]
C26H28ClCoN3O7
588.9
C26H28ClCoN3O7
588.9
C26H28ClNiN3O7
588.7
C26H28ClNiN3O7
588.7
orthorhombic
P212121
9.7822(2)
12.5962(3)
22.6256(4)
2787.9(1)
4
orthorhombic
P212121
9.7495(2)
12.6069(3)
22.5939(5)
2777.0(3)
4
orthorhombic
P212121
9.6643(7)
12.7173(7)
22.375(1)
2750.0(4)
4
orthorhombic
P212121
9.6741(5)
12.6754(7)
22.3954(9)
2746.2(3)
4
b [Å]
c [Å]
V [Å3]
Z
T [K]
293
1.403
0.759
293
1.408
0.762
293
1.422
0.851
293
1.424
0.852
D [gcm–3]
μ [mm–1]
F(000)
Independent reflections
Rint
1220
3709
0.035
1220
3614
0.033
1224
6466
0.045
1224
3551
0.044
R(F)/Rw(F)
S
Reflections
Parameters
Δρmax/Δρmin [eÅ–3]
Absorption correction
Flack parameter
0.0309/0.0336
1.13
3801
0.0309/0.0342
1.13
3685
0.0347/0.0348
0.99
5286
0.0316/0.0340
1.13
3327
344
344
344
344
0.28/–0.21
multiscan
0.02(2)
0.33/–0.21
multiscan
0.98(2)
0.29/–0.34
analytical
–0.02(1)
0.31/–0.23
multiscan
1.00(2)
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The third model, Model 3, is a recent approach that has with g = 2.00 and suggests the presence of an important
been developed by M. Drillon on the basis of a noncritical spin–orbital contribution that is characteristic of octahedral
scaling model to describe the behavior of low-dimensional high-spin CoII. A gradual decrease in χT is observed with
magnetic systems.[54] This model was previously used to temperature; χT reaches values of 1.85 and
characterize CuII and NiII chains[55–57] by using the analyti- 1.78 cm3 Kmol–1 at 8 K and slowly goes up in the 8–2 K
cal expression:
temperature region (Figure 3). The magnetic behavior of
ID(Co) is similar to IL(Co) (in limit-of-error experiments)
and is dominated by a strong spin–orbital contribution
characteristic of octahedral CoII. It is worth noting here
that it seems to validate the potential presence of small fer-
romagnetic interactions along the chain. Similar small fer-
romagnetic interactions between octahedral CoII centers
through a bridged carboxylic group have been recently re-
ported in the literature.[31,43,55] To get an estimated value
for exchange interactions, a simple model that involves the
spin–orbit coupling and the exponential low-temperature
divergence of the susceptibility [χTϰexp(+J/2kT)] of an
Ising chain of anisotropic magnetic centers can be
used.[31,55,60,61] Two contributions are included in the equa-
tion:
Using this model, good agreements between the experi-
mental data and the simulated one have been obtained for
both nickel [IL(Ni) and ID(Ni)] chains, thereby confirming
the ferromagnetic interactions along the chain (see Table 3
and Figure S6 in the Supporting Information).
The last model tested to discuss the magnetic behavior
of our chiral 1D polymers, Model 4, has been proposed by
Neef for the characterization of an S = 1 ferromagnetic
chain with ZFS and is based on the Hamiltonian:[53,58,59]
in which J is the constant of magnetic interaction along the
chain, and D is the single-ion zero-field splitting factor of
NiII. The fitted parameters of the equation for the ferro-
magnetic NiII chain by Neef model are the following:
in which A1 + A2 is equal to the Curie constant, and the
A1 + A2
limiting Curie–Weiss equation χ =
was applied to
T – θ
constrain the fitting procedure. E1 and E2 are the activation
energies that correspond to the spin–orbit coupling and to
the ferromagnetic exchange interaction, respectively.
The three sets of experimental data (χ, χT, χ–1) for IL(Co)
and ID(Co) have been simultaneously fitted by using a non-
linear least-squares method.
J
D
in which x =
, y =
, F1 = 0.6666 + 1.7778x +
kT
kTЈ
1.4815x2 – 1.5802x3 – 2.1399x4 + 5.3728x5, F2 = –2 +
3.5555xy
+
6.2222x2y
+
1.9753x3y
–
6.2222x4y
–
–
0.43018x5y + 1.9259x2y2 + 5.9918x3y2 + 3.5084x4y2
The best fit was obtained for parameters IL(Co)
0.39506xy3 – 0.872243x2y3 + 0.55748x3y3 + 0.032922xy4 –
0.31358x2y4 + 0.04609xy5. Using the above expression, the
best fit of the magnetic-susceptibility behavior (2–300 K) is
obtained with the following parameters J = 0.64(5) cm–1, g
= 2.165(3), D = –1.38(1) cm–1 for IL(Ni) and J = 0.54(7)
cm–1, g = 2.190(4), D = –1.05(2) cm–1 for ID(Ni).
A1
= = =
2.01(4) cm3 Kmol–1, E1 56(2) cm–1, A2
1.88(4) cm3 Kmol–1, E2 = 0.02(7) cm–1, θ = –1.322(6) K,
and ID(Co) A1 = 1.97(4) cm3 Kmol–1, E1 = 52(2) cm–1, A2
= 1.82(4) cm3 Kmol–1, E2 = 0.02(7) cm–1, θ = –1.264(6) K.
The obtained parameters A1 and A2 are in good agreement
with those previously reported for CoII carboxylates, and
the sum of A1 and A2 represent the Curie constant.[62] The
E1 parameters are consistent with those reported in the lit-
erature (E1/k in the range of 50–100 K) and reflect the
spin–orbital coupling and distortion in octahedral
CoII.[31,43,55,63,64] The E2 parameter reflects the very small
ferromagnetic interaction (0.02 cm–1) within the Ising chain
approximation.
The obtained g value is in good agreement with what was
obtained in the case of Curie constants, and the J value that
corresponds to the ferromagnetic interaction is moderately
lower but still comparable to those from models presented
above. Magnetization curves per Ni atoms show deviation
from Brillouin behavior, and this phenomenon could be due
to ZFS or small ferromagnetic interactions along the chain.
Ac-susceptibility measurements were carried out for both
IL(Ni) and ID(Ni); however, there was no increase in the
out-of-phase χЈ signal down to 2 K and up to 1400 Hz. The
non-appearance of a χЈЈ signal for IL(Ni) and ID(Ni) sug-
gests the absence of long-range ordering process at mea-
sured temperatures (2–26 K).
Magnetization curves for compounds IL(Co) and ID(Co)
with saturation values of 2.31 M.B. and 2.35 M.B. at 5 T
are consistent with the values expected for a noninteracted
mononuclear CoII compound.[65–69]
In the case of the isostructural cobalt(II) compounds, the
decay of χT upon cooling is shown in Figure 4 (see also
Figure S7 in the Supporting Information). The χT product
Conclusion
Four new isomorphic coordination polymers have been
per CoII at room temperature is 3.43 and 3.37 cm3 Kmol–1 synthesized and fully characterized. Within the chains, di-
for IL(Co) and ID(Co), respectively. The value of χT is valent metal ions, CoII or NiII, are linked by a chiral mand-
larger than the spin-only 1.87 cm3 Kmol–1 for the S = 3/2 elic acid (d or l). X-ray analyses show non-centrosymmet-
4874
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Eur. J. Inorg. Chem. 2011, 4869–4877

1D CoII and NiII Chiral Polymers
2 K between 0 and 5 T. All data were corrected for the contribution
of the sample holder and diamagnetism of the samples estimated
with Pascal’s constants.[64,70] The analysis of magnetic data was car-
ried out by simulation of χT(T) and χ(T) thermal dependences in-
cluding impurities contribution (ρ) and intermolecular interactions
(zJЈ) according to the following expression:
ric (orthorhombic, P212121) structural organizations with
refined Flack parameters close to 0 or 1 for the l or d
isomer, respectively. The chirality of bulk materials was also
proven by circular dichroism spectroscopy in the solid state.
Magnetic studies on NiII and CoII compounds reveal that
the carboxylate bridge transmits ferromagnetic coupling
along the chains. Ferromagnetic coupling in the chiral NiII-
based polymer are similar in the two optical isomers
[0.64(5)/0.54(7) cm–1] with similar ZFS parameters
[–1.38(1)/–1.05(2) cm–1]. In the case of the CoII-based poly-
mer, negligible ferromagnetic interaction is suspected.
The theoretical magnetic susceptibility of χT(T) and χ(T) has been
obtained by models exposed further in the text. Minimization was
carried out with an adapted version of Visualiseur–Optimiseur for
Matlab[71,72] using nonlinear least-squares by the Lavenberg–Mar-
quard[73] algorithm.
Experimental Section
X-ray Analysis: It was possible to determine by single-crystal X-ray
diffraction the structure of four original 1D polymer metal com-
plexes. CCDC-824526 [for IL(Co)], -824527 [for ID(Co)], -824528
[for IL(Ni)], -824529 [for ID(Ni)], -824530 (for III), -824531 (for IV),
and -824532 (for II) 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.
General: All starting materials and solvents were purchased from
Aldrich and were used without further purification. IR spectra
were recorded with a GX system 2000 Perkin–Elmer spectropho-
tometer and samples were run as KBr pellets.
The circular dichroism (CD) spectra were recorded with a Chiras-
can spectropolarimeter using Chirascan software (Applied Bio-
physics Ltd., Leatherhead, UK) in KBr pellets.
Synthesis of IL(Ni): A mixture of Ni(ClO4)2·6H2O (2 mmol, 0.74 g),
l-mandelic acid (2 mmol, 0.30 g), and sodium azide (2 mmol
0.13 g) in methanol (80 mL) was stirred for 10 min at room tem-
perature. Then 4-MePy (2 mL) was added. In the following days,
slow evaporation of the solution at room temperature yielded blue
crystals of IL(Ni); yield 56% based on Ni. C26H28ClN3NiO7
(588.7): calcd. C 53.05, H 4.79, N 7.14; found C 52.85, H 4.91, N
7.10.
Diffraction data sets were collected with a Gemini Oxford dif-
fractometer equipped with a CCD camera and by using the related
software.[74] A semiempirical absorption correction (multiscan) has
been applied to all the data sets.[75] All the structures were solved by
direct methods using the SIR97 program[76] combined with Fourier
difference syntheses and refined against F using the CRYSTALS
program.[77] In each structure, all atomic displacements for non-
hydrogen atoms were refined with an anisotropic model. Hydrogen
atoms have been placed by Fourier. Differences account for the
hybridization of the supporting atoms and for the possible presence
of hydrogen bonds in the case of donor atoms.
The synthesis of ID(Ni) was identical to that of IL(Ni); yield 51%
based on Ni. C26H28ClN3NiO7 (588.7): calcd. C 53.05, H 4.79, N
7.14; found C 52.79, H 4.93, N 7.09.
Synthesis of IL(Co) and ID(Co): A procedure similar to IL(Ni) was
followed to prepare cobalt(II) compounds except Ni(ClO4)2·6H2O
was replaced by Co(ClO4)2·6H2O (2 mmol, 0.75 g). The final prod-
uct was contaminated by crystals of mononuclear compound mer-
[CoIII(4-MePy)3(N3)] (II), which were separated off and charac-
terized by single-crystal X-ray analysis. To obtain pure samples of
IL(Co) and ID(Co), the synthesis were performed in a similar man-
ner but under an inert atmosphere (N2) to prevent oxidation pro-
cess of CoII. In the following days, slow evaporation of the solution
at room temperature yielded reddish crystals of IL(Co); yield 43%
based on Co. C26H28ClCoN3O7 (588.9): calcd. C 53.03, H 4.79, N
7.14; found C 52.95, H 4.89, N 7.08. ID(Co): Yield 45% based on
Co. C26H28ClCoN3O7 (588.9): calcd. C 53.03, H 4.79, N 7.14;
found C 52.91, H 4.83, N 7.11.
All hydrogen atoms have been refined using a riding mode. The
structures have been solved and refined using a non-centrosymmet-
ric space group (orthorhombic, P212121). The Flack parameter[78]
has been refined for all structures by keeping the same atom-posi-
tion structural model and is then equal either to 0 or 1. This pre-
conception has been chosen to clearly demonstrate the obtaining
of pure opposite enantiomeric complexes for cobalt(II) and nicke-
l(II). X-ray crystallographic data and refinement details for com-
pounds named IL(Co), ID(Co), IL(Ni), and ID(Ni) are summarized
in Table 4. Important bond lengths and angles are presented in
Table 1 and Table 2, respectively.
Supporting Information (see footnote on the first page of this arti-
cle): X-ray data collection details and plots of the structures of
compounds II, III, IV. Fit of magnetic susceptibilities for IL(Ni)
and ID(Ni) using models 1–4, magnetization plots for investigated
compounds, and IR spectra.
A similar synthetic procedure was used with the MnII and CuII
perchlorate salts. According to the elemental analysis, IR spectra,
and powder X-ray analyses, the resulting compounds correspond
to those characterized and reported previously.[29–31]
Acknowledgments
In the case of synthesis with CuII salts, we obtained the oil with a
two type of crystals (III and IV), which were sorted out manually
for IR and single-crystal X-ray analyses. According to X-ray analy-
ses, the compositions corresponded to [Cu2(μ-N3)(4-MePy)8-
(H2O)2](ClO4)3(4-MePy)4 (III) and [Cu(4-MePy)4(ClO4)2] (IV).
G. N. thanks the Marie Curie Actions (FP7-People-IIF) for finan-
cial support.
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Received: May 25, 2011
Published Online: September 14, 2011
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