Unusual magnetic property associated with a structural phase transition within a new ion-pair complex

Article abstract of DOI:10.1016/j.inoche.2004.07.011

A novel ion-pair complex, [BrbzPyNH₂][Ni(mnt)₂], where [BrbzPyNH₂]⁺ = 1-(4′-bromobenzyl)-4- aminopyridinium and mnt^2- = maleonitriledithiolate, forms a completely segregated uniform stacking column with the Ni?Ni distance 3.952 ? and undergoes a magnetic phase transition from paramagnetism in the high-temperature (HT) phase to diamagnetism in the low-temperature (LT) phase at around 105 K.

Full text of DOI:10.1016/j.inoche.2004.07.011

Inorganic Chemistry Communications 7 (2004) 1034–1036
www.elsevier.com/locate/inoche
Unusual magnetic property associated with a structural
phase transition within a new ion-pair complex
a
a
b
a
Chun-Lin Ni a,1, Dong-Bin Dang , Yi-Zhi Li , Zuan-Ru Yuan , Zhao-Ping Ni ,
a
Zheng-Fang Tian , Qing-Jin Meng
a,
*
a
State Key Laboratory of Coordination Chemistry, Coordination Chemistry Institute, Nanjing University, Hankou Road 22, Nanjing 210093, PR China
b
The Center of Analysis and Determination, Nanjing University, Nanjing 210093, PR China
Received 20 May 2004; accepted 19 July 2004
Available online 12 August 2004
Abstract
novel ion-pair complex, [BrbzPyNH2][Ni(mnt)2], where [BrbzPyNH2]+ = 1-(40-bromobenzyl)-4-aminopyridinium and
A
mnt2ꢀ = maleonitriledithiolate, forms a completely segregated uniform stacking column with the Niꢁ ꢁ ꢁNi distance 3.952 A and
undergoes a magnetic phase transition from paramagnetism in the high-temperature (HT) phase to diamagnetism in the low-tem-
perature (LT) phase at around 105 K.
˚
ꢀ 2004 Elsevier B.V. All rights reserved.
Keywords: 1-(40-bromobenzyl)-4-aminopyridinium; Bis(maleonitriledithiolate)nickelate(III) complex; X-ray structure; Magnetic phase transition
1D molecular-based materials are currently of exten-
sive interest owing to their multifarious physical proper-
ties such as spin-Peierls transition, valence-ordering,
spin-charge separation states, charge-density-wave
states and spin-density-wave states [1].
search with [M(mnt)2]ꢀ complexes is to find more suita-
ble multifunctional organic cations to tune the crystal
stacking structure of [M(mnt)2] anion, and 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 magnets [1-(40-bromobenzyl)-4-aminopy-
ridinium][Ni(mnt)2] (1) which exhibits a switching from
paramagnetism to diamagnetism at around 105 K. To
the best of our knowledge, the uniformly spaced 1D
Ni(III) chain exhibiting magnetic switching is very rare
The study on Ni(mnt)2 complexes as building blocks
for new molecular magnets has attracted much attention
because they show novel magnetic properties [2]. Espe-
cially, the discovering in 1996 of the ferromagnetic com-
plex containing NiðmntÞꢀ ion, NH4 Æ Ni(mnt)2 Æ H2O,
2
strongly stimulated this field [3]. Recently, in the course
of our project to design 1D molecular-based magnets,
for the MðmntÞꢀ complexes.
2
we have developed
a
new class of complexes
[1-(40-bromobenzyl)-4-aminopyridinium]2[Ni(mnt)2]
was prepared by the direct combination of 1:2:2 mol-
equivalent of NiCl2 Æ 6H2O, Na2mnt and 1-(40-brom-
obenzyl)-4-aminopyridinium)pyridinium bromide in
water by a similar mothod described in the literature
[5]. The resulting red precipitate product (1.0 mmol)
was solved in 20 ml MeCN, then a MeCN solution (10
ml) of I2 (0.59 mmol) was slowly added, the mixture
was stirred for 1 h, and then 100 ml i-PrOH was added.
[RbzPy]+[M(mnt)2]ꢀ ([RbzPy]+ = benzylpyridinium deri-
vative), and found that these ion-pair complexes exhibit
versatile magnetic properties [4]: Our continuing re-
*
Corresponding author. Tel.: +86 25 83597266; fax: +86 25
83314502.
E-mail addresses: ctgunicl@163.com (C.-L. Ni), mengqj@netra.
nju.edu.cn (Q.-J. Meng).
1
Tel.: +86 25 83685302.
1387-7003/$ - see front matter ꢀ 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.inoche.2004.07.011

C.-L. Ni et al. / Inorganic Chemistry Communications 7 (2004) 1034–1036
1035
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 Niꢁ ꢁ ꢁNi
˚
distance is 3.952 A, the nearest Sꢁ ꢁ ꢁS and Niꢁ ꢁ ꢁS con-
˚
tacts have 3.773 and 3.712 A, respectively. Therefore,
the Ni(III) ions within a [Ni(mnt)2]ꢀ anionic column
form a 1D-uniformly spaced chain via intermolecular
Niꢁ ꢁ ꢁS, Sꢁ ꢁ ꢁS, Niꢁ ꢁ ꢁNi or pꢁ ꢁ ꢁp interactions. Within a
column of [BrbzPyNH2]+ cation, the adjacent cations
stack into chair-type conformation and form 1D chains
via p–p interactions between Br atom and benzene rings.
The closest Niꢁ ꢁ ꢁNi separation between anion chains is
˚
13.532 A, which is significantly longer than that of
˚
Niꢁ ꢁ ꢁNi separation within a chain (3.952 A). From the
point of view of the structure, 1 is an ideal 1D magnetic
chain system.
Fig. 1. ORTEP plot (30% probability ellipsoids) showing the molecule
˚
structure of complex 1. Selected bond distances (A) and angles (ꢁ):
Ni(1)–S(1) 2.1455(12), Ni(1)–S(2) 2.1351(12), Ni(1)–S(3) 2.1396(12),
Ni(1)–S(4) 2.1402(12), S(1)–Ni(1)–S(2) 92.47(5), S(1)–Ni(1)–S(4)
89.23(5), S(3)–Ni(1)–S(4) 92.23(5), S(2)–Ni(1)–S(3) 86.02(5).
The plot of vmT versus T for the complex is shown in
Fig. 3 with vm being the magnetic susceptibility per nick-
el atom corrected by the diamagnetic contribution. For
the complex 1, the overall magnetic behavior corre-
sponds to an antiferromagnetically coupled system.
The value of vmT at 300 K is 0.135 emu K molꢀ1, a va-
lue which is significantly lower than the expected for
magnetically isolated Ni(III) ion(0.375 emu K molꢀ1).
Upon cooling down of the sample, vmT smoothly in-
creases and reaches a value of 0.268 emu K molꢀ1 at
130 K. This behavior is indicative of weak ferromagnetic
coupling between Ni(III) ions in the 1D magnetic chain.
It is interesting that the complex 1 exhibits a switching
from paramagnetic to diamagnetic around 105 K which
may be estimated from the d(vmT)/dT vs. T plot (the in-
set of Fig. 3). The magnetic susceptibility abrupt de-
crease at 105 K is associated with the pack structure
changing of 1 from uniform spin clusters to dimmers be-
tween neighboring spin carries, which is often found in
the similar systems [4b,4e,4f]. The feature that the value
of vmT at room temperature is significantly lower than
After the mixture was allowed to stand overnight, 510 mg
dark microcrystals produced were filtered off, washed
with i-PrOH and Et2O and dried in a vacuum [6].
An ORTEP drawing of 1 with non-hydrogen atomic
labeling in an asymmetric unit is shown in Fig. 1 [7]. The
Ni (III) ion in the [Ni(mnt)2]ꢀ anion is coordinated by
four sulfur atoms of two mnt2ꢀ ligands, and exhibits
square planar coordination geometry. The average S–
Ni–S bond angle within the five-membered ring is
˚
90.0ꢁ, and the average Ni–S bond distance is 2.14 A,
these values are in agreement with those of found in
other [Ni(mnt)2]ꢀ complexes [8]. In the [BrbzPyNH2]+
moiety, the dihedral angles of the C(14)–C(15)–N(5) ref-
erence plane are 100.4ꢁ for benzene ring, 83.7ꢁ for pyri-
dine ring, respectively.
0.30
0.25
0.20
0.15
0.10
0.05
0.00
0.06
0.05
0.04
0.03
0.02
0.01
0.00
Peak temperature = 105K
0
50
100
150
200
T(K)
0
50
100
150
200
250
300
T(K)
Fig. 2. The packing diagram of a unit cell for complex 1 as viewed
along c-axis.
Fig. 3. The plot of vmT versus T for complex 1 (inset: d(vmT)/dT
versus T).

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C.-L. Ni et al. / Inorganic Chemistry Communications 7 (2004) 1034–1036
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16
14
12
10
8
Acknowledgements
We thank financial support from the National Natu-
ral Science Foundation (No. 20171022). The Center of
Analysis and Determination of Nanjing University are
acknowledged.
Tpeak = 111.3 K
delta H = 401.7 J/mol
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form completely segregated uniform stacking columns
ꢀ
˚
with the Niꢁ ꢁ ꢁNi distance 3.952 A in the NiðmntÞ stack-
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pꢁ ꢁ ꢁp interactions. The measurement of the temperature
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3381.7s, 1650.9vs, 2205.2s, 1453.9s.
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˚
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˚
˚
˚
a = 11.988(3) A, b = 26.662(6) A, c = 7.560(2) A, a = 102.43(4)ꢁ,
3
3
˚
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0.1048, respectively. The structure was solved by the direct method
and refined by the full-matrix least-squares against F2 using a
SHELXTL software package.
Supplementary material
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from the Cambridge Crystallographic Data Centre,
CCDC No. 238997. 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://
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