Synthesis, crystal structure and magnetic property of a new 1D molecular material [1-(4′-chlorobenzyl)-4-aminopyridinium](+) bis(maleonitriledithiolato)nickel(-)

Article abstract of DOI:10.1016/j.jssc.2004.11.002

A new ion-pair complex, [1-(4′-chlorobenzyl)-4-aminopyridinium](+) bis(maleonitrile-dithiolato)nickel(-),[ClbzPyNH₂][Ni(mnt) ₂] (1), has been prepared and characterized. X-ray single crystal structure conforms that the Ni(mnt)₂^- anions and [ClbzPyNH₂]⁺ cations of 1 form completely segregated uniform stacking columns with the Ni...Ni distance 3.944 A in the Ni(mnt)₂^- stacking column. The temperature dependence of the magnetic susceptibility reveals that 1 undergoes a magnetic transition, and exhibits ferromagnetic interaction in the high-temperature phase and spin gap system in the low-temperature phase.

Full text of DOI:10.1016/j.jssc.2004.11.002

ARTICLE IN PRESS
Journal of Solid State Chemistry 178 (2005) 100–105
www.elsevier.com/locate/jssc
Synthesis, crystal structure and magnetic property of a new1D
molecular material [1-(40-chlorobenzyl)–4-aminopyridinium](+)
bis(maleonitriledithiolato)nickel(–)
Chunlin Nia, Dongbin Danga, Yizhi Lia, Song Gaob, Zhaoping Nia, Zhengfang Tiana,
Ã
Qingjin Menga,
aState Key Laboratory of Coordination Chemistry, Department of Chemistry, Coordination Chemistry Institute, Nanjing University, Hankou Road,
Number 22, Nanjing city, Jiangsu province 210093, People’s Republic of China
bState Key Laboratory of Rare Earth Materials Chemistry and Applications, Peking University, 100 871 Beijing, People’s Republic of China
Received 23 May 2004; received in revised form 22 June 2004; accepted 1 November 2004
Abstract
A
newion-pair complex, [1-(4 0-chlorobenzyl)–4-aminopyridinium](+)bis(maleonitrile-dithiolato)nickel(À),[ClbzPyNH2]
[Ni(mnt)2] (1), has been prepared and characterized. X-ray single crystal structure conforms that the Ni(mnt)À2 anions and
[ClbzPyNH2]+ cations of 1 form completely segregated uniform stacking columns with the Ni?Ni distance 3.944 A in the Ni(mnt)2À
stacking column. The temperature dependence of the magnetic susceptibility reveals that 1 undergoes a magnetic transition, and
exhibits ferromagnetic interaction in the high-temperature phase and spin gap system in the low-temperature phase.
r 2004 Elsevier Inc. All rights reserved.
Keywords: 1-(40-Chlorobenzyl)–4-aminopyridinium; Bis(maleonitriledithiolate)nickelate(III) complex; X-ray structure; Ferromagnetic interaction;
Spin gap
1. Introduction
([RbzPy]+ ¼ benzylpyridinium derivative), and found
that these ion-pair complexes exhibit versatile magnetic
properties such as ferromagnetic ordering at low
temperature [13], magnetic transition from ferromagnetic
coupling to diamagnetism [14], meta-magnetism [15] and
spin-Peierls-like transitions [16–18]. In these ion-pair
complexes, the prominent structural feature is that the
Ni(mnt)À2 ions and [RbzPy]+ cations stack into well-
segregated columns in the solid state. In our continuing
research with [M(mnt)2]À complexes, we have focused on
the following two strategies. One is to find more suitable
multifunctional organic cations to tune the crystal
stacking structure of [M(mnt)2] anion with a view to
obtaining ideal molecular magnets. The second strategy
is to establish a relationship between the magnetic
interactions and the stacking pattern of anions or
cations. Herein, we report the crystal structure and
magnetic property of a novel 1D molecular material
[1-(40-chlorobenzyl)–4-aminopyridinium][Ni(mnt)2](1)
Transition metal complexes of 1,2-dithiolenes are
currently of extensive interest owing to their application
as potentially building blocks in molecular-based materi-
als showing magnetic, superconducting, and optical
properties
[1–3].
The
complexes
containing
[M(mnt)2]À(mnt2À ¼ maleonitriledithiolate, M ¼ Ni(III)
or Pt(III)) ions) have attracted much attention because
they shownovel magnetic properties [4–11]. Especially,
the discovery of the ferromagnetic complex containing
Ni(mnt)À2 ion, NH4?Ni(mnt)2?H2O, in 1996, strongly
stimulated the study on Ni(mnt)2 complexes as building
blocks for newmolecular magnets [12]. One of the
current interests in our laboratory has been developed
newclass
of
complexes
[RbzPy]
+[M(mnt)2]À
Ã
Corresponding author. Fax: +86 25 83314502.
E-mail address: njuchem1024@163.com (Q. Meng).
0022-4596/$ - see front matter r 2004 Elsevier Inc. All rights reserved.
doi:10.1016/j.jssc.2004.11.002

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C. Ni et al. / Journal of Solid State Chemistry 178 (2005) 100–105
101
Table 1
Crystallographic data for 1
showing a magnetic transition at around 86.5 K. To the
best of our knowledge, the uniformly spaced 1D chain
exhibiting magnetic transition is very rare for the
Ni(mnt)2 complexes.
Formula
M
C20H12ClN6NiS4
558.76
Crystal system
Space group
a (A)
Monoclinic
P21/c
12.000(2)
26.544(3)
7.504(1)
2. Experimental
b (A)
c (A)
2.1. Materials and methods
b (1)
102.10(2)
2337.2(5)
4
V (A3)
Z
All chemicals and solvents were of reagent grade and
were used without further purification. 1-(40-chloroben-
zyl)–4-aminopyridinium bromide and disodium maleo-
nitriledithiolate (Na2mnt) were synthesized following
the published procedures [19,20]. [1-(40-chlorobenzyl)–4-
aminopyridinium]2[Ni(mnt)2] was prepared by the direct
combination of 1:2:2 mol equivalent of NiCl2 Á 6H2O,
Na2mnt and 1-(40-chlorobenzyl)–4-aminopyridinium
bromide in water by a similar method described in the
literature [20]. Elemental analyses were run on a Model
240 Perkin-Elmer CHN instrument. IR spectra were
recorded on an IF66 V FT-IR (400–4000 cmÀ1 region)
spectrophotometer in KBr pellets. Magnetic suscept-
ibility data on crushed single crystals of 1 were collected
over the temperature range 2–300 K using a Quantum
Design MPMS-5S super-conducting quantum interfer-
ence device (SQUID) magnetometer, and the experi-
mental data were corrected for diamagnetism of the
constituent atoms estimated from Pascal’s constants.
Dc (g/cm3)
F(0 0 0)
1.588
1132
1.016
Goodness-of-fit on F2
R1,wR2[I42s(I)]a
(all data)
0.0550, 0.1008
0.1037, 0.1129
0.984, À0.920
(Dr)max, (Dr)min (eAÀ3
)
aR1 ¼ S||Fo|À|Fc||/S|Fo|, wR2 ¼ [Sw(F2o–Fc2)2/Sw(Fo2)2]1/2
.
Table 2
Selected bond parameters and intermolecular contacts for 1
˚
Bond distances (A)
Ni(1)–S(1)
Ni(1)–S(2)
2.1352(12)
2.1501(13)
2.1457(12
2.1330(12)
Ni(1)–S(3)
Ni(1)–S(4)
Bond angles (1)
S(1)–Ni(1)–S(2)
S(1)–Ni(1)–S(4)
S(3)–Ni(1)–S(4)
S(2)–Ni(1)–S(3)
92.40(5)
86.53(5)
92.00(5)
89.02(5)
˚
Intrachain distances (A)
Ni?Ni (nearest separation)
Ni?S
2.2. Synthesis of [1-(40-chlorobenzyl)– 4-
aminopyridinium][Ni(mnt)2]
3.944
3.680
3.767
S?S
Interchain distances (A)
[1-(40-Chlorobenzyl)–4-amino pyridinium]2[Ni(mnt)2]
(778 mg, 1.0 mmol) was solved in 20 cm3 MeCN, then a
MeCN solution (10 cm3) of I2 (150 mg, 0.59 mmol) was
slowly added, the mixture was stirred for 1 h, and then
50 cm3 i-PrOH was added. After the mixture was
allowed to stand overnight, 546 mg dark microcrystals
produced were filtered off, washed with i-PrOH and
Et2O and dried in a vacuum. Yield: 86%. Found (calcd.)
for C20H12ClN6NiS4: C, 42.72 (42.99); H, 2.25 (2.16); N,
14.85 (15.04)%. IR (cmÀ1): 3381.3 m, 1651.2 s, 2205.7 s,
and 1453.3 s.
˚
Ni?Ni (nearest separation)
13.530
and observed reflections [I42sðIÞ] are 12497, 4581, and
2955 (Rint ¼ 0:038). The structure was solved by direct
method by using SHELXS 97 and refined on F2 by full-
matrix least-squares methods. All the non-hydrogen
atoms were refined anisotropically. Hydrogen atoms
were constrained to ride on the respective carbon atoms
with an isotropic displacement parameter equal to 1.2
times the equivalent isotropic displacement parameter of
their parent atom. Crystal data are summarized in Table
1. Selected bond lengths, bond angles and some short
stacking contacts are listed in Table 2.
2.3. X-ray structure determination
Single crystals suitable for X-ray structure analyses
were obtained by evaporating solution of 1 in mixtures
of MeCN and i-PrOH (1:1v/v). A single crystal with
dimension 0.3 Â 0.2 Â 0.2 mm3 for 1 was used for
structural determination at 293 K on a Siemens SMART
CCD area detector equipped with graphite-monochro-
mated MoKa radiation. All computations were carried
out via a PC-586 computer using the SHELXTL-PC
program package [21]. Number of measured, unique,
3. Results and discussion
3.1. Crystal structures
[ClbzPyNH2][Ni(mnt)2](1) crystallizes in the mono-
clinic space group P21=c at room temperature. An

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102
ORTEP drawing of 1 with non-hydrogen atomic
labeling in an asymmetric unit is shown in Fig. 1. The
Ni(III) ion in the [Ni(mnt)2]À anion is coordinated by
four sulfur atoms of two mnt2À ligands, and exhibits
square planar coordination geometry. The average
S–Ni–S bond angle within the five-membered ring is
90.01, and the average Ni–S bond distance is 2.15 A;
these values are in agreement with those found in other
[Ni(mnt)2]À complexes [22]. In the [ClbzPyNH2]+moi-
ety, the dihedral angles of the C(14)–C(15)–N(5)
reference plane are 103.11 for benzene ring, and 96.51
for pyridine ring.
The most notable structural feature of 1 is that
the anions and cations posses the stacking pattern with
well-separated column along the direction of c-axis
(Fig. 2). Within an anion column, the nearest
Ni?Ni distance is 3.944 A, the nearest S?S and
Ni?S contacts have 3.767 and 3.68 A, respectively.
Therefore, the Ni(III) ions within a [Ni(mnt)2]À anionic
3.2. Magnetic properties
The temperature dependence of the magnetic suscept-
ibility for 1 was measured under an applied field of
1000 Oe in temperature range 2–300 K. The plots of wm
versus T and wmT versus T for these complexes are
shown in Figs. 2, 5 and 6 with wm is the magnetic
susceptibility per nickel atom corrected by the diamag-
netic contribution. For the complex 1, the overall
magnetic behavior corresponds to an antiferromagneti-
cally coupled system. On increasing the temperature
back to the original temperature, the same wmT curve is
obtained without hysteresis effect being detected.
The value of wmT at 300 K is 0.299 cm3 K molÀ1, a
value which is somewhat lower than the expected for
magnetically isolated Ni(III) ion (0.375 cm3 K molÀ1).
Upon cooling down the sample, wmT smoothly increases
and reaches a value of 0.447 cm3 K molÀ1 at 100 K. This
behavior is indicative of weak ferromagnetic coupling
between Ni(III) ions in the 1D magnetic chain. The
high-temperature region (T495 K) can be well fitted by
the equation wm ¼ C=ðT À yÞ þ TIP with the fitting
parameters being C ¼ 0:421 cm3 K molÀ1; y ¼ 2:70 K;
and TIP ¼ 5:0 Â 10À4 cm3 molÀ1 (Fig. 6).
column form
a 1D uniformly spaced chain via
intermolecular Ni?S, S?S, Ni?Ni or p?p interac-
tions (Fig. 3). Within a column of [ClbzPyNH2]+
cations, the adjacent cations stack into chair-type
conformation (Fig. 4) and form 1D chains via p–p
interactions between Cl atom and benzene rings. Similar
phenomena have been found in halogen-benzene deri-
vatives in solid state [23–25]. The closest Ni?Ni
separation between anion chains is 13.530 A, which is
significantly longer than that of Ni?Ni separation
within a chain (3.944 A). Therefore, 1 is an ideal 1D
magnetic chain system from the point of viewof the
structure.
As the sample 1 was continuously cooled, the wmT
value first slightly decreases; around 95 K, the abrupt
drops of the value of wmT from 0.444 to
0.094 cm3 K molÀ1 within 9.5 K indicates that 1 exhibits
the characteristics of a spin gap system. The transition
temperature, 86.5 K, may be estimated from the
dðwmTÞ=dT versus T plot (the inset of Fig. 5). The
magnetic susceptibility of 1 may be estimated by the
Fig. 1. ORTEP plot (30% probability ellipsoids) showing the molecule structure of complex 1.

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103
Fig. 2. The packing diagram of a unit cell for complex 1 as viewed along c-axis.
Fig. 3. Side viewof the anions stack of complex 1 showing the uniform space linear-chain of [Ni(mnt)2]À.
formula wm ¼ ½a expðÀD=kBTÞꢀ=T þ C=T þ w0; where a
is a constant value corresponding to the dispersion of
excitation energy, D is the magnitude of the spin gap, w0
contributes from the core diamagnetism and the possible
Van Vleck paramagnetism, and the other symbols have
their usual meaning [26]. The best fit curve (2–86.5 K)
for 1 are shown in Fig. 6, and the corresponding
parameters are given as follows: a ¼ 7:55; D=kB ¼
398:70;
w0 ¼ À1:5 Â 10À4 cm3 molÀ1
;
C ¼ 1:69 Â
10À3 cm3 K molÀ1; and R ¼ 1:8 Â 10À9 (R is defined as
2
2
SðwmcaÀlcdwombsdÞ =ðwombsdÞ Þ: The values of the parameter
2D=kBTc (Tc is the transition temperature) are estimated
to be 9.22 for 1 on the basis of the above results, which is
higher than the ideal value of 3.53 derived from the BCS

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104
Fig. 4. Side viewof the cations stack of complex 1
formula in a weak coupling regime. This result thus
means that the short-range magnetic correlations within
a chain are not fully developed and intrinsic magneto
elastic instability of a 1D system cannot be considered as
a driving force for this transition; namely, the transition
is not a pure spin-Peierls transition [18]. The origins of
the phase transition for 1 are attributed to cooperative
interactions of Ni?S bonding, inter-plane repulsion of
the [Ni(mnt)2]À anions [27], p?p stacking interactions
between of adjacent cations, spin–lattice interaction [28]
and spin–spin coupled interaction between nearest-
neighbor anions [29].
This work describes the synthesis, crystal struc-
ture and magnetism of a newion-pair complex contain-
ing Ni(mnt)À2 anion. The X-ray structural characteriza-
tion shows Ni(mnt)À2 anions of the complex form
completely segregated uniform stacking columns with
the Ni?Ni distance 3.944 A in the Ni(mnt)À2 stacking
column by intermolecular Ni?S, S?S, Ni?Ni or
p?p interactions. The measurement of the temperature
dependence of the magnetic susceptibility reveals that
the title complex undergoes a magnetic transition,
and exists ferromagnetic interaction in the high-
temperature phase and spin gap system in the low-
temperature phase.
Fig. 5. The plot of wmT versus T for complex 1 (inset: dðwmTÞ=dT
versus T).
4. Supplementary materials
Supplementary crystallographic data are available
from the Cambridge Crystallographic Data Center,
CCDC No. 239015. Copies of this information may be
obtained free of charge from The Director, CCDC, 12
Union Road, Cambridge, CB2 1EZ, UK (fax:
+44 1223 336033; deposit@ccdc.cam.ac.uk or www:
http://www.ccdc.cam.ac.uk).
Fig. 6. Plot of wm versus T for 1. The solid line are reproduced from
the theoretic calculations and detailed fitting procedure described in
the text.

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Acknowledgments
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We thank financial support from the National
Natural Science Foundation (No. 20171022, No.
20490210). The Center of Analysis and Determination
of Nanjing University are acknowledged.
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