Complicated magnetic behavior in one-dimensional nickel(III) chain complex [1-(4′-cyanobenzyl)pyridinium] [Ni(mnt)2] (mnt2 = maleonitriledithiolate)

Article abstract of DOI:10.1016/S0009-2614(02)01953-X

A new ion-pair complex [1-(4′-cyanobenzyl)pyridinium] [Ni(mnt)₂] (1), in which mnt^2- = maleonitriledithiolate, have been fabricated and its X-ray single crystal structural analyses at 293, 180 and 140 K shown that the [Ni(mnt)₂]^- anions and [CNBzPy]⁺ cations form a well-separated stacking column along c-axis direction, within which [Ni(mnt)₂]^- anions are uniformly spaced to give a one-dimensional (1-D) chain structure. Bulk magnetic properties of this complex have been investigated in the temperature range of 2-400 K and shown there exists spin kink at ～ 190 K. In low temperature region, weak ferromagnetic behavior occurs in 1.

Full text of DOI:10.1016/S0009-2614(02)01953-X

Chemical Physics Letters 369 (2003) 41–48
www.elsevier.com/locate/cplett
Complicated magnetic behavior in one-dimensional
nickel(III) chain complex [1-(40-cyanobenzyl)pyridinium]
½NiðmntÞ Š ðmnt2À ¼ maleonitriledithiolate)
2
Jingli Xie , Xiaoming Ren a,b, Cheng He , You Song , Qingjin Meng
,
a
a
a
a,
*
R.K. Kremer c,1, Yuangen Yao
d
a
State Key Laboratory of Coordination Chemistry, Coordination Chemistry Institute,
Nanjing University, 22 Hankou Rd., 210093 Nanjing, PR China
b
Department of Electronic Science and Engineering, Nanjing University, 210093 Nanjing, PR China
c
Max-Planck-Institut f€ur Festk€orperforschung, Heisenbergstrasse 1, Postfach 800665, D-70569 Stuttgart, Germany
State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, 350002 Fuzhou, PR China
d
Received 25 August 2002; in final form 30 November 2002
Abstract
A new ion-pair complex [1-(40-cyanobenzyl)pyridinium] ½NiðmntÞ Š (1), in which mnt2À ¼ maleonitriledithiolate, have
2
À
À
been fabricated and its X-ray single crystal structural analyses at 293, 180 and 140 K shown that the ½NiðmntÞ Š anions
2
þ
and ½CNBzPyŠ cations form a well-separated stacking column along c-axis direction, within which ½NiðmntÞ Š anions
2
are uniformly spaced to give a one-dimensional (1-D) chain structure. Bulk magnetic properties of this complex have
been investigated in the temperature range of 2–400 K and shown there exists spin kink at ꢀ190 K. In low temperature
region, weak ferromagnetic behavior occurs in 1.
Ó 2003 Elsevier Science B.V. All rights reserved.
1. Introduction
state, furthermore, have prominent affection on
molecular interaction and resultant magnetic di-
versity [3–9]. Recently, we fabricated and struc-
Square-planar MðdithioleneÞ complexes have
2
þ
À
attracted extensive interests in the areas of con-
ducting and magnetic materials, dyes, non-linear
optics, catalysis [1,2]. In this series of complex,
previous works shown that different counterions
could induce versatile stacking modes in the solid
tural characterized a series of ½BzPyŠ ½MðmntÞ Š
2
þ
(M ¼ Ni or Pt) complexes, where ½BzPyŠ denoted
benzylpyridinium derivative, and found that there
are markedly different magnetic exchange proper-
ties although these complexes have extremely
similar molecular and stack structures [10–14]. In
order to further understand the magnetic coupling
mechanism, we have systematic investigated the
relationship between stack structure and magnetic
* Corresponding author. Fax: +86-25-3314502.
E-mail address: njujlxie@yahoo.com (Q. Meng).
1
Also corresponding author.
0009-2614/03/$ - see front matter Ó 2003 Elsevier Science B.V. All rights reserved.
doi:10.1016/S0009-2614(02)01953-X

42
J. Xie et al. / Chemical Physics Letters 369 (2003) 41–48
was carried out on warming (rate of 20 K minÀ1
)
in the temperature range of )180 to 120 °C (93–
393 K).
Scheme 1.
3. Results and discussion
properties for this series of complexes. Herein we
report the synthesis and crystal structure of an ion-
pair complex (Scheme 1), [1-(40-cyanobenzyl)py-
3.1. Crystal structure of 1 in high-temperature phase
(293 K)
ridinium]½NiðmntÞ Š, with a well-discreted stacking
½CNBzPyŠ½NiðmntÞ Š (1) crystallizes in the
2
2
column. Its complicated magnetic properties show
a spin kink around 190 K and following this
transition, weak ferromagnetic behavior occurs in
this complex in low temperature region.
monoclinic space group P21=c at room temperature
and crystallographic details are summarized in
Table 1. Selected bond lengths and bond angles are
À
listed in Table 2. For the ½NiðmntÞ Š anion, the
2
Ni(III) ion is co-ordinated to four sulfur atoms of
two mnt2À ligands, and exhibits square-planar co-
ordination geometry. The five-membered nickel-
2. Experimental
containing rings are slightly puckered, as have been
found with other ½MðmntÞ Š structures [17]. The
nÀ
½1-ð40-cyanobenzylÞpyridiniumŠ ½NiðmntÞ Š was
2
2
2
prepared by the direct combination of 1:2:2 mol
equiv of NiCl2 ꢁ 6H2O, Na2mnt and 1-(40-cyanob-
enzyl)pyridinium bromide in water. The resulting
red precipitate product was obtained by filtration
average S–Ni–S bond angle within the five-mem-
bered ring is 92.6°, and the average Ni–S bond
distance is 2.15 A, these values are in agree-
ꢀ
À
ment with that of ½NiðmntÞ Š complexes reported
2
and dried. ½1-ð40-cyanobenzylÞpyridiniumŠ ½Ni
2À
[10–14]. The CNgroups of mnt
ligand are bent
2
ðmntÞ Š (729.5 mg, 1.0 mmol) was solved in 20 cm3
away from the coordinating plane defined by Ni
atom and four sulfur atoms. The deviations of four
terminal Natoms from the plane are )0.0385,
2
MeCN, then a MeCN solution (10 cm3) of I2 (150
mg, 0.59 mmol) was slowly added and the mixture
was stirred for 2 h. The resulting dark precipitates
0
ꢀ
0.0215, 0.2143, 0.0921 A, respectively. In the 1-(4 -
cyanobenzyl)pyridinium cation, the dihedral angles
of the C(15)–C(14)–N(5) reference plane are 80.1°
for phenyl ring, 80.6° for pyridine ring, respectively.
The most notable structural feature of 1 is that
the anion and cation possess the stacking structure
with well-separated column along the direction of
were recrystallized from MeCNto give pure
1
[15,16]. Yield 433 mg, 81%. Anal. Calc. for
C21H11N6NiS4: C, 47.2%; H, 2.08%; N, 15.7%.
Found: C, 47.0%; H, 2.09%; N, 15.8%. Infrared
spectrum ðcmÀ1Þ: m(CN), 2207.6 vs, m(C@C) of
mnt2À 1446.7 m. Elemental analyses were per-
formed with a Perkin-Elmer 240 analytical in-
strument. IR spectra were recorded on a Fourier
Transform Infrared Spectrometer (170SX) (KBr
pellet). Magnetic susceptibility data on powder-
sample were collected over the temperature range
of 2–400 K using a Quantum Design MPMS-5S
superconducting quantum interference device
(SQUID) magnetometer, and diamagnetic correc-
tions were made estimating experimentally using
Na2mnt, 1-(40-cyanobenzyl)pyridinium bromide,
NaBr. DSC experiment was performed on a Per-
kin-Elmer calorimeter. Thermal analysis of poly-
crystalline samples placed in an aluminum crucible
c-axis (Fig. 1a). Within an anion column, the
½NiðmntÞ Š anions form a 1-D uniformly spaced
À
2
chain, and the slipped zig-zag configuration of
½NiðmntÞ Š anions are displayed in Fig. 1b. The
À
2
nearest S ꢁ ꢁ ꢁ S, S ꢁ ꢁ ꢁ Ni and Ni ꢁ ꢁ ꢁ Ni distances arÀe
ꢀ
of 3.85, 3.65 and 4.54 A within the ½NiðmntÞ Š
2
anion chain, respectively. Obviously, there exist
intermolecÀular interactions between neighboring
½NiðmntÞ Š anions within an anionic chain due to
2
the shorter intermolecular separations. While the
closest Ni ꢁ ꢁ ꢁ Ni separation between anionic chains
ꢀ
is 8.08 A, which is significantly longer than the
distance of Ni ꢁ ꢁ ꢁ Ni separation within a chain.

J. Xie et al. / Chemical Physics Letters 369 (2003) 41–48
43
Table 1
Crystal data and structure refinement for 1
1
1
1
Temperature
293(2) K
C21H11N6NiS4
534.31
180(2) K
C21H11N6NiS4
534.31
140(2) K
C21H11N6NiS4
534.31
Empirical formula
Formula weight
Wavelength
ꢀ
0.71073 A
ꢀ
0.71073 A
ꢀ
0.71073 A
Crystal system
Space group
Unit cell dimensions
Monoclinic
P21=c
Monoclinic
P21=c
Monoclinic
P21=c
ꢀ
a (A)
15.197 (3)
17.796(4)
15.0630(3)
17.7252(4)
8.5663(2)
15.0218(3)
17.6926(3)
8.54580(10)
90
ꢀ
b (A)
ꢀ
c (A)
8.6089(17)
90
95.15(3)
a (°)
b (°)
c (°)
90
94.6499(10)
90
94.5089(8)
90
90
ꢀ3
Volume (A ), Z
2318.9(8), 4
1.530 g/cm3
1.219 mmÀ1
1084
2279.63(9), 4
1.557 g/cm3
1.239 mmÀ1
1084
2264.23(6), 4
1.567 g/cm3
1.248 mmÀ1
1084
Density (calculated)
Absorption coefficient
F(0 0 0)
Crystal size (mm3)
h range for data collection
Limiting indices
0:15 ꢂ 0:10 ꢂ 0:10
3.48–27.49°
À19 6 h 6 19
À23 6 k 6 23
À11 6 l 6 11
33282
0:15 ꢂ 0:10 ꢂ 0:10
3.51–27.48°
À19 6 h 6 19
À22 6 k 6 22
À11 6 l 6 11
36213
0:15 ꢂ 0:10 ꢂ 0:10
3.52–27.48°
À19 6 h 6 19
À22 6 k 6 22
À11 6 l 6 11
37792
Reflections collected
Independent reflections
5303
ðRint ¼ 0:0427Þ
Empirical
5099
5130
ðRint ¼ 0:0928Þ
Empirical
0.884 and 0.830
ðRint ¼ 0:0503Þ
Empirical
0.883 and 0.830
Absorption correction
Max. and min. transmission
Refinement method
0.886 and 0.833
Full-matrix least-squares
on F 2
Data/restraints/parameters
Goodness-of-fit on F 2
5303/0/289
1.024
5099/0/289
1.008
5130/0/289
1.031
Final R indices ½I > 2rðIފ
R1 ¼ 0:0332
wR2 ¼ 0:0733
R1 ¼ 0:0582
wR2 ¼ 0:0835
0.253 and )0.342
R1 ¼ 0:0386
wR2 ¼ 0:0693
R1 ¼ 0:1012
wR2 ¼ 0:0823
0.317 and )0.398
R1 ¼ 0:0283
wR2 ¼ 0:0594
R1 ¼ 0:0511
wR2 ¼ 0:0652
0.269 and )0.298
R indices (all data)
ꢀÀ3
Largest diff. Peak and hole (e A
)
Therefore, the magnetic interaction between two
anionic columns separated by a sizable diamag-
netic cationic column is generally weak, and 1 is a
1-D magnetic chain system from the viewpoint of
the structure analysis.
creasing temperature change to a much less extent,
i.e., the cell parameters of a, b, c, b and V decrease
ꢀ
ꢀ
ꢀ
ꢀ3
0.134 A, 0.071 A, 0.043 A, 0.50°, 39.3 A at 180 K,
ꢀ
ꢀ
ꢀ
ꢀ3
and 0.175 A, 0.103 A, 0.063 A, 0.64°, 54.7 A at
140 K, respectively. The corresponding bond
lengths and bond angles in 1 at 180 and 140 K are
in agreement well with the values at room tem-
perature, the separations between adjacent mole-
cules gradually decreases as the temperature
decreasing, and see also in Table 2. Complex 1
preserve the stacking structure with well-separated
column alÀong the direction of c-axis and the
3.2. Crystal structures of 1 in low-temperature
phase (180 and 140 K)
The molecular structures of 1 in low-tempera-
ture phase (180 and 140 K) are crystallographically
indistinguishable with that in high-temperature
phase (Table 1). The lattice contraction with de-
½NiðmntÞ Š anions also form a 1-D uniformly
2

44
J. Xie et al. / Chemical Physics Letters 369 (2003) 41–48
Table 2
Selected bond parameters and intermolecular contacts for 1
1 (293 K)
1 (180 K)
1 (140 K)
ꢀ
Bond distances (A)
Ni(1)–S(1)
Ni(1)–S(2)
2.1388(7)
2.1495(7)
2.1493(7)
2.1471(7)
2.1517(7)
2.1394(7)
2.1498(7)
2.1508(7)
2.1506(5)
2.1490(5)
2.1413(5)
2.1517(5)
Ni(1)–S(3)
Ni(1)–S(4)
Bond angles (°)
S(1)–Ni(1)–S(2)
S(1)–Ni(1)–S(3)
S(3)–Ni(1)–S(4)
S(2)–Ni(1)–S(4)
92.50(3)
87.10(3)
92.69(3)
87.73(3)
92.63(3)
87.73(3)
92.72(3)
86.97(3)
92.771(18)
86.874(18)
92.651(18)
87.753(19)
ꢀ
Intrachain distances (A)
Niꢁ ꢁ ꢁNi
4.539
3.652
3.845
4.517
3.629
3.804
4.506
3.619
3.789
Niꢁ ꢁ ꢁS
Sꢁ ꢁ ꢁS
(the nearest separation)
ꢀ
Interchain distances (A)
Niꢁ ꢁ ꢁNi
8.080
8.045
8.029
(the nearest separation)
À
Fig. 1. (a) The packing diagram of a unit cell for 1. (b) 1-D ½NiðmntÞ Š anion chain with equal Ni ꢁ ꢁ ꢁ Ni distant viewing along the
2
c-axis.

J. Xie et al. / Chemical Physics Letters 369 (2003) 41–48
45
Fig. 2. Variable temperature X-ray powder patterns in the temperature range 113–278 K exhibit no change for complex 1.
spaced chÀain at 180 and 140 K. Within the
results are in agreement with that of the variable-
temperature X-ray powder diffraction measured in
the temperature ranges 113–278 K (Fig. 2).
½NiðmntÞ Š chain, the nearest S ꢁ ꢁ ꢁ S, S ꢁ ꢁ ꢁ N i and
2
ꢀ
ꢀ
Ni ꢁ ꢁ ꢁ Ni distances are of 3.80 A at 180 K (3.79 A
ꢀ
ꢀ
at 140 K), 3.63 A at 180 K (3.62 A at 140 K) and
ꢀ
4.52 A at 180 K (4.51 A at 140 K), respectively.
ꢀ
3.3. Magnetic properties
The corresponding closest Ni ꢁ ꢁ ꢁ Ni separation
ꢀ
ꢀ
between anion chains is 8.05 A at 180 K (8.03 A at
140 K). In a word, there are not notable changes
for the molecular and stacking structures of 1 be-
tween high- and low-temperature phases, and the
Magnetic susceptibilities of a polycrystalline
sample of complex 1 were measured at a field of 1
T in the temperature range from 400 to 2 K, the vm
versus T plot is displayed in Fig. 3. At 400 K, the
Fig. 3. The plot of vm of 1 measured at 10 kOe field (the solid line represents the best fit at high- and low-temperature range). Inset:
derivative dðvmÞ=dT versus T.

46
J. Xie et al. / Chemical Physics Letters 369 (2003) 41–48
to magnetic impurity. Cycling the applied field
between +10 and )10 kOe at 2 K generates a
hysteresis loop as shown in Fig. 4, as expected for
a material exhibiting weak ferromagnetic behav-
ior. The weak ferromagnetism of 1 at low tem-
perature may be due to a consequence of canted
spin antiferromagnetism. Spin canting arises
through
a
Dzyaloshinsky–Moriya interaction
[18–20], which minimizes the coupling energy
when two spins are perpendicular to one another.
Moreover, the assumption is supported by the fact
which shown in the inset of Fig. 4 that the highest
magnetization of 10.56 emu G molÀ1 (at 2 K and
50 kOe) is significantly smaller than the theoretical
saturation value of 5585 emu G molÀ1 [18].
Fig. 4. Hysteresis loop exhibited for 1 at 2 K. The inset shows
the M–H curve.
The magnetic susceptibility anomaly around
190 K is very interesting, the variable-temperature
crystallographic structural analyses of both single
crystal and powder shown that there is not distinct
structural change between the high- and low-tem-
perature phases, which means this phase transition
is only magnetic but not structural transition
character. To obtain more information about the
thermodynamic properties of the phase transition,
DSC measurements of 1 were performed in the
temperature range of 93 to 393 K. There are no
any obvious exothermic or endothermic phenom-
ena except base-line shift of the DSC curve (Fig.
5). So the phase transition observed ꢀ190 K is
expected to be a second-order phase transition
[21,22]. The phase transition observed is phe-
nomenally similar to spin–Peierls transition, which
value of the effective moment leff equals to 1.023
lB, which is significantly less than the spin-only
value of 1.732 lB expected for a non-interaction
Ni(III) ion with S ¼ 1/2, indicating that there
exists antiferromagnetic exchange interactions be-
tween neighbor Ni(III) ions. As the temperature
decreases, the value of vm gradually decreases,
and a prominent kink is observed around 190 K,
which may be estimated from the extreme of
dðvmÞ=dT versus T plot (inset of Fig. 3). Here-
after, the value of vm decreases more sharply and
reaches a minimum (1:04 ꢂ 10À4 emu molÀ1) at
ꢀ60 K. Below 60 K, upturn in vm values is ob-
served at lower temperature as T approaches to
0 K and do not simply attributed to Currie-tail due
Fig. 5. Differential scanning calorimetry of 1 showing base-line shift.

J. Xie et al. / Chemical Physics Letters 369 (2003) 41–48
47
occurs below a critical temperature ðTspÞ in uni-
form Heisenberg spin chain system with S ¼ 1=2
due to spin–lattice interaction, is a thermodynamic
second-order transition. Additionally, 1 meet two
conditions required for spin–Peierls transition.
Firstly, 1 is a 1-D antiferromagnetic chain system.
Secondly, the structure of 1 is flexible, in the sense
that the dimerization should not require too large
an energy. Experimentally, there are a knee in plot
of vm À T at Tsp and rather abrupt fall of vm below
Tsp, which is one feature of the spin–Peierls tran-
sition [23].
susceptibility may be fitted by vm ¼ ½að1 À PÞ exp
ðÀD=kBT ފ= T þ PNg2lB2 =4kBT þ v0, where a is a
constant value corresponding to the dispersion of
excitation energy, D is the magnitude of spin gap, P
is the uncoupling impurities content, v0 is the
constant term caused by diamagnetism of core
electron shell and Van Vleck paramagnetism and
other signs have their usual meaning. The best fit
curve is shown in Fig. 3, and the corresponding
parameters are given as following: g ¼ 2:079 which
is near the value measured by EPR, P ¼ 2:8 ꢂ 10À4
,
a ¼ 0:48, D=kB ¼ 614:2 K, v0 ¼ 1:1 ꢂ 10À4 emu
The experimental data in high-temperature
phase for 1 are analyzed with the general expres-
sion [24]:
molÀ1 and agreement factor R ¼ 6:67 ꢂ 10À8
P
P
2
2
[R ¼ ðvombs À vcmalcÞ = ðvombsÞ Š. The obtained va-
lue of the parameter, 2D=kBTsp (Tsp is the transition
temperature of 190 K), is 6.47 and significantly
larger than the ideal value of 3.53 derived from the
BCS formula in a weak coupling regime. These
results mean that the short-range magnetic corre-
lations within the chain are not fully developed and
intrinsic magnetoelastic instability of a 1-D system
cannot be considered as a driving force for the
transition, namely, the transition is not a pure
spin–Peierls transition but an exotic one [13].
vðTÞ ¼ v0 þ vCWðT Þ þ vspinðTÞ;
v0 ¼ vcore þ vVV
;
Cimp
vCWðTÞ ¼
;
T À h
Ng2l2
ꢀ
ꢁ
kBT
J
vspinðTÞ ¼
v
;
B ꢁꢃ
J
where v0 is the sum of a temperature independent
and isotropic orbital diamagnetic core contribution
4. Conclusion and outlook
and
independent orbital paramagnetic Van Vleck con-
a
usually anisotropic and temperature
In this contribution, an ion-pair complex [1-(40-
cyanobenzyl)pyridinium] ½NiðmntÞ Š, in which
2
ꢁꢃ
tribution, v is the reduced spin susceptibility.
mnt2À ¼ maleonitriledithiolate, have been fabri-
cated and its single crystal X-ray structural anal-
yses at 293, 180 and 140 K show that the molecular
Because the magnetic coupling interactions in
this series of compounds are sensitive to the
intermolecular contacts, that is, J is dependent on
temperature, so the relationship between J and
temperature, J ¼ J0ð1 þ a1T þ a2T2Þ, is assumed
[24]. The best fit parameters are attained as follows
using a magnetic susceptibility simulation program
edited by R.K. Kremer et al. [25]: J0=kB ¼ 295:6 K,
Cimp ¼ 1:34 ꢂ 10À3 emu K molÀ1, h ¼ À2:48 K,
v0 ¼ 4:68 ꢂ 10À4 emu molÀ1, zJ=kB ¼ À5:5 ꢂ 10À2
and stacking structures have not notable change,
À
and ½NiðmntÞ Š anions are uniformly spaced
2
along crystallographic c-axis direction. Its tem-
perature dependence magnetic susceptibilities
shown there exists a phase transition ꢀ190 K, but
both DSC and variable-temperature X-ray powder
diffraction measurements further reveal no struc-
tural transition. Although this transition is phe-
nomenally similar to spin–Peierls transition, the
magnetic data analysis in low-temperature phase
and weak ferromagnetic behavior at ꢀ2 K indicate
this transition is not a pure spin–Peierls transition
but an exotic one. Therefore lots of investiga-
tions should continue in order to understand the
complex magnetic behavior of 1, the intensive
K, a1 ¼ 2:48 ꢂ 10À3 KÀ1, a2 ¼ À8:9 ꢂ 10À6 KÀ2
,
and g factor of 2.06 was fixed, which is the average
value of EPR measurement.
Below the transition temperature, the magnetic
susceptibility of 1 gradually decreases with de-
creasing temperature to indicate the magnetic
susceptibility being activated [26], so the magnetic

48
J. Xie et al. / Chemical Physics Letters 369 (2003) 41–48
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UK, Fax: +44-1223-336-033; e-mail: deposit@
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Acknowledgements
The authors give many thanks to B. Eva for
magnetic susceptibility measurements, R. Willi for
variable-temperature X-ray powder diffraction
measurements, and we express our gratitude to Dr.
A. Das for helpful discussion. The authors also
acknowledge the National Natural Science Foun-
dation (No. 2017022, No. 29831010), Jiangsu Sci-
ence and Technology Department and The Center
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