Peculiar magnetic transition behaviour around 208 K in one-dimensional nickel(III) chain complex [1-(4′-vinylbenzyl)pyridinium][Ni(mnt) 2] (mnt2- = maleonitriledithiolate)

Article abstract of DOI:10.1246/cl.2005.680

A new ion-pair complex, [VBzPy][Ni(mnt)₂], where [VBzPy] ⁺ = 1-(4′-vinylbenzyl)pyridinium and mnt^2- = maleonitriledithiolate, has been synthesized. The cations and anions stack into completely separated columns and Ni(III)

Full text of DOI:10.1246/cl.2005.680

680
Chemistry Letters Vol.34, No.5 (2005)
Peculiar Magnetic Transition Behaviour Around 208 K in One-dimensional Nickel(III) Chain
Complex [1-(40-Vinylbenzyl)pyridinium][Ni(mnt)2] (mnt2ꢀ = Maleonitriledithiolate)
Dongbin Dang, Chunlin Ni, Yan Bai, Zhengfang Tian, Zhaoping Ni, Lili Wen, Qingjin Meng,ꢀ and Song Gaoy
Coordination Chemistry Institute, State Key Laboratory of Coordination Chemistry, Nanjing University, Nanjing, 210093, P. R. China
yState Key Laboratory of Rare Earth Materials Chemistry and Applications, Peking University, Beijing, 100871, P. R. China
(Received January 24, 2005; CL-050107)
A
new ion-pair complex, [VBzPy][Ni(mnt)2], where
[VBzPy]þ = 1-(40-vinylbenzyl)pyridinium and mnt2ꢁ = maleo-
nitriledithiolate, has been synthesized. The cations and anions
stack into completely separated columns and Ni(III) ions form
a uniformly spaced one-dimensional (1-D) zigzag chain within
a [Ni(mnt)2]ꢁ column in solid state. Magnetic susceptibility
and DSC measurements revealed that there exists a first-order
phase transition at approximately 208 K.
Transition-metal complexes of maleonitriledithiolate (mnt)
have drawn great attention in the field of chemistry and physics
because of their specific electrical, magnetic, and optical proper-
ties.1–4 Recently, we have reported a series of complexes formed
by [M(mnt)2]ꢁ and benzylpyridinium derivatives.5,6 One of in-
teresting features of them is that the constituent planar anions
[Ni(mnt)2]ꢁ form completely segregated stacking column and
further result in an uniform or alternately spaced 1-D magnetic
chain of spin S = 1/2 through the intermolecular dz2 or ꢀ orbital
interactions. In addition, the stacking structure of these com-
plexes can be tuned by systemically varying of the substituents
on aryl ring of the cations, and further lead to versatile magnetic
exchange properties. To extend our research and understand
these novel magnetic properties, we should investigate the rela-
tionship between the magnetic interactions and the stacking pat-
tern of anions and cations systematically. Herein, we report a
new ion-pair complex [1-(40-vinylbenzyl)pyridinium][Ni(mnt)2]
(1) showing a peculiar transition around 208 K. To our best
knowledge, the transition temperature higher than 200 K is very
rare in the [M(mnt)2]ꢁ complexes.
Figure 1. Structure of the anions and cations of the complex
viewed along the c axis.
(a)
(b)
[VBzPy]2[Ni(mnt)2] was prepared by the direct combina-
.
tion of 1:2:2 mol equiv. of NiCl2 6H2O, Na2mnt and [VBzPy]Br
Figure 2. (a) one-dimensional (1-D) zigzag chain of Ni(III)
ions. (b) ꢀ–ꢀ interactions between vinyl groups and benzene
rings.
in H2O. Oxidation of [VBzPy]2[Ni(mnt)2] with I2 in MeCN fur-
nished complex 1 in 78% yield. Single crystals suitable for X-ray
structure analyses were obtained by evaporating the MeCN solu-
tion of 1.
illustrated in Figure 2, within a column of [VBzPy]þ, the neigh-
boring benzene rings are almost parallel to each other with the
dihedral angle of 6.0ꢂ. The distance of the center of the disor-
dered vinyl group and the center of the neighboring benzene ring
Complex 1 crystallizes in the monoclinic space group P21=c
at room temperature.7 The coordination geometry of the nickel
atom in the [Ni(mnt)2]ꢁ exhibits square planar with four sulfur
atoms. The average S–Ni–S bond angle within the five-mem-
bered ring is 92.29(8)ꢂ. The average Ni–S bond distance is
2.141(2) A, which is in agreement with those found in other
mnt complexes.5,6 In the cation, the terminal methylene of vinyl
ꢀ
group is disordered between two positions about 1.63 A apart,
and one of which is modeled at 50% occupancy. The benzene
ring and pyridine ring are twisted to the reference plane defined
by N5–C14–C15 with the dihedral angles 93.2ꢂ for benzene ring
and 85.7ꢂ for pyridine ring, respectively. As might be anticipat-
ed, in complex 1, anions and cations form completely segregated
stacking column along the direction of c axis (Figure 1). As
ꢀ
is 3.76 A. Obviously, the cations form 1-D chain through ꢀ–ꢀ
interactions between vinyl groups and benzene rings; Within
an anion column, Ni(III) ions form a uniformly spaced 1-D zig-
zag chain and the nearest NiꢃꢃꢃNi, NiꢃꢃꢃS, and SꢃꢃꢃS distances are
ꢀ
ꢀ
3.86, 3.65, 3.72 A, respectively. The closest NiꢃꢃꢃNi separation
ꢀ
between anion chains is 11.95 A, which is significantly longer
than that within a chain. Therefore, from viewpoint of crystal
structure, the [Ni(mnt)2]ꢁ anion column can be considered as
1-D magnetic chain.
The variable-temperature magnetic properties of 1 have
been investigated at 2 kOe in the temperature range 2–300 K
Copyright Ó 2005 The Chemical Society of Japan

Chemistry Letters Vol.34, No.5 (2005)
681
(Figure 3). The overall magnetic behavior of 1 corresponds to an
antiferromagnetic system. The value of ꢁmT at 300 K is
Where ꢂ is a constant value corresponding to the dispersion
of excitation energy, ꢃ is the magnitude of the spin gap, ꢁ0 is the
constant term caused by the core diamagnetism and the possible
Van Vleck paramagnetism, and other symbols have their usual
meaning.6,8 The best fit curve in the temperature range 2–200
K is displayed in Figure 3, and the corresponding parameters
0.308 emuꢃKꢃmolꢁ1
, significantly less than the value of
0.375 emuꢃKꢃmolꢁ1 expected for one spin-only Ni(III) ion with
S = 1/2 per formula unit. With decreasing temperature, the
ꢁmT value first decreases slightly till reaching 0.243 emuꢃKꢃ
molꢁ1 at 208 K. Then ꢁmT drops more sharply below this tem-
perature. On increase of the temperature back to the original
temperature, the same curve is obtained, and no hysteresis is de-
tected. Obviously, 1 undergoes a phase transition at approxi-
mately 208 K. To obtain more information about this transition,
DSC measurements of 1 were performed in the temperature
range of 170–240 K at a warming rate of 20 Kꢃminꢁ1. There is
an abrupt endothermic peak in the DSC trace, which indicates
the phase transition is of first order. The endothermic enthalpy
change (ꢁH) is 559.4 Jꢃmolꢁ1. The phase transition temperature
observed from DSC trace is 208.1 K, in agreement with the value
measured from magnetic susceptibility measurements.
are given as following: ꢂ ¼ 114 emuꢃKꢃmolꢁ1
,
ꢃ=kB ¼
P
2
1337 K, C ¼ 5:7 ꢄ 10ꢁ4 emuꢃKꢃmolꢁ1, R ¼ ðꢁmobs ꢁ ꢁcmalcÞ =
P
2
ðꢁombsÞ ¼ 5:38 ꢄ 10ꢁ11. The value of the parameter, 2ꢃ=
kBTc (Tc is the transition temperature 208 K), is 14.18 and more
removed from the ideal value of 3.53 derived using the BCS for-
mula in a weak coupling regime. This exceptionally large value
means that the short-range magnetic correlations within the
chain are not fully developed and intrinsic magnetoelastic insta-
bility of a 1-D system cannot be considered as a driving force for
the transition; namely, the transition is not a conventional spin–
Peierls transition.6 The phase transition results from cooperative
interactions of ꢀ–ꢀ stacking interactions between the adjacent
cations, NiꢃꢃꢃS bonding, interplane repulsion of anions,9 spin–
spin coupled interaction between nearest neighbor anions,10
and spin lattice interactions.11,12
In the low-temperature phase, 1 exhibits the characteristics
of a spin gap system, so the magnetic susceptibility may be
estimated by the eq 1:
ꢀ
ꢁ
ꢂ
ꢃ
C
T
The authors acknowledge the National Natural Science
Foundation (No. 20171022, No. 20490218) and The Center of
Analysis and Determining of Nanjing University.
ꢁm
¼
exp ꢁ
þ
þ ꢁ0
ð1Þ
T
kBT
0.0014
0.0012
0.0010
0.0008
0.0006
0.0004
0.0002
0.0000
0.35
0.30
0.25
0.20
0.15
0.10
References and Notes
1
2
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χ
0.05
3
4
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0.00
0
50
100
150
200
250
300
T / K
χ
5
6
7
a) X. M. Ren, Y. C. Chen, C. He, and S. Gao, J. Chem. Soc.,
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0
50
100
150
T / K
200
250
300
Figure 3. The plot of ꢁm vs T for 1. The solid line represents
the best fit; inset: ꢁmT vs T for 1.
a) X. M. Ren, Q. J. Meng, Y. Song, C. S. Lu, C. J. Hu, and X. Y.
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12
11
T = 208.1 K
c
∆H = 559.4 J mol −1
Crystallographic data of 1 are: C22H14N5NiS4, monoclinic,
P21=c, fw 535.33, a ¼ 12.168(3), b ¼ 27:046(7), c ¼ 7:354(2)
10
ꢂ
ꢀ
ꢀ 3
A, ꢄ ¼ 103:00(1) , V ¼ 2358:1(11) A , Z ¼ 4, Dcalcd ¼ 1:508
g cmꢁ3
,
T ¼ 293 K, R ¼ 0:076 [I > 2ꢅðIÞ], and 4066
9
8
7
6
independent reflections. Deposited in No. CCDC-260369.
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170
180
190
200
210
220
230
240
T / K
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Soc., 125, 4984 (2003).
Figure 4. DSC plot for 1 showing the phase transition at
208.1 K.
Published on the web (Advance View) April 9, 2005; DOI 10.1246/cl.2005.680