Synthesis, crystal structure and magnetic characterization of two new ion-pair complexes containing bis(maleonitriledithiolate)nickelate anion and substituted benzylpyridinium cation

Article abstract of DOI:10.1016/j.ica.2009.04.021

Two new ion-pair complexes, [FBrBzPyN(CH₃)₂]₂[Ni(mnt)₂] (1) and [FBrBzPyN(CH₃)₂][Ni(mnt)₂] (2) (mnt^2- = maleonitriledithiolate, [FBrBzPyN(CH₃)₂]⁺ = [1-(4′-fluoro-2′-bromobenzyl)-4-dimethylaminopyridinium]) have been prepared and characterized by elemental analyses, UV, IR, single crystal X-ray diffraction and magnetic susceptibility. The cations (D) and the anions (A) in 1 stack into a 1D alternating column (i.e., of type ?DDADDADD?) via short S?Br, N?F, C?N interactions, and C-H?Br hydrogen bonds. The cation-cation π?π stacking interactions within the columns give further rise to a 2D network structure. Compound 2 forms a 3D structure in which the Ni(III) ions stack into a uniform 1D zigzag magnetic chain through Ni?S, Ni?Ni, or π?π interactions with a Ni?Ni distance of 4.024 A?. Magnetic susceptibility measurements in the temperature range 2-300 K show that 1 is expected to be diamagnetic, and 2 exhibits an interesting spin-gap transition (Δ/k_b = 460.6 K) around 155 K.

Full text of DOI:10.1016/j.ica.2009.04.021

Inorganica Chimica Acta 362 (2009) 3657–3662
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Inorganica Chimica Acta
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Synthesis, crystal structure and magnetic characterization of two new ion-pair
complexes containing bis(maleonitriledithiolate)nickelate anion and substituted
benzylpyridinium cation
Hong-Rong Zuo a, Li-Xia Wu a, Qian Huang a, Xing Chen a, Jia-Rong Zhou a, Le-Min Yang a, Chun-Lin Ni a,
,
*
Xue-Lei Hu b
a Department of Applied Chemistry, Centre of Inorganic Functional Materials, College of Science, South China Agricultural University, Wushan, Tianhe District, Guangzhou,
Guangdong 510642, PR China
b School of Chemical Engineering and Pharmacy, Wuhan Institute of Technology, 430073 Wuhan, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Two new ion-pair complexes, [FBrBzPyN(CH3)2]2[Ni(mnt)2] (1) and [FBrBzPyN(CH3)2][Ni(mnt)2] (2)
(mnt2ꢀ = maleonitriledithiolate, [FBrBzPyN(CH3)2]+ = [1-(40-fluoro-20-bromobenzyl)-4-dimethylamino-
pyridinium]) have been prepared and characterized by elemental analyses, UV, IR, single crystal X-ray
diffraction and magnetic susceptibility. The cations (D) and the anions (A) in 1 stack into a 1D alternating
column (i.e., of type ꢁ ꢁ ꢁDDADDADDꢁ ꢁ ꢁ) via short Sꢁ ꢁ ꢁBr, Nꢁ ꢁ ꢁF, Cꢁ ꢁ ꢁN interactions, and C–Hꢁ ꢁ ꢁBr hydrogen
Received 2 December 2008
Received in revised form 4 April 2009
Accepted 17 April 2009
Available online 3 May 2009
bonds. The cation–cation
p p stacking interactions within the columns give further rise to a 2D network
ꢁ ꢁ ꢁ
Keywords:
structure. Compound 2 forms a 3D structure in which the Ni(III) ions stack into a uniform 1D zigzag mag-
netic chain through Niꢁ ꢁ ꢁS, Niꢁ ꢁ ꢁNi, or ꢁ ꢁ ꢁ interactions with a Niꢁ ꢁ ꢁNi distance of 4.024 Å. Magnetic sus-
ceptibility measurements in the temperature range 2–300 K show that 1 is expected to be diamagnetic,
and 2 exhibits an interesting spin-gap transition ( /kb = 460.6 K) around 155 K.
Ó 2009 Elsevier B.V. All rights reserved.
Substituted 4-dimethylaminopyridinium
Bis(maleonitriledithiolate)nickelate
Crystal structure
Magnetic properties
Spin-gap transition
p
p
D
1. Introduction
tions. It is interesting that these ion-pair complexes exhibit an
unusual spin gap transition around 140 K, 200 K, and 55 K, respec-
tively. With a view to extending our research work and investigat-
ing the effect of substituted groups in the phenyl ring of the cation
on the structure and magnetic properties, two new ion-pair com-
plexes, [FBrBzPyN(CH3)2]2[Ni(mnt)2](1) and [FBrBzPyN(CH3)2]
[Ni(mnt)2](2), were designed and prepared to gain more insight
into the magneto-structural relationship. The experimental results
have shown that 1 and 2 form a 2D and 3D structure, respectively.
The Ni(III) ions of 2 form a uniform 1D zigzag magnetic chain with-
in a [Ni(mnt)2]ꢀ column and the magnetic behavior is in agreement
with a spin gap feature.
The syntheses and properties of numerous molecular magnets
that possess spin bistability have received attention in recent years
due to their potential applications in molecular switch, data stor-
age and displays [1–4]. In this regard, the spin molecular system
based on [M(mnt)2]ꢀ (M = Ni, Pd, or Pt ions, mnt2ꢀ = maleonitrile-
dithiolate) anions are very attractive in that it posses a planar con-
figuration with an extended electronic structure and the magnetic
coupling is highly sensitive to the interactions contacts and the
overlap patterns of [M(mnt)2]ꢀ anions [5–10]. As a part of our
continuing efforts to find more suitable counter ions to tune the
crystal stacking structure of [M(mnt)2]ꢀ anions with a view to
obtaining ideal magnetic materials displaying a spin gap transition
[11–13]. In this direction, we have recently utilized substituted 4-
dimethylaminopyridinium as countercations to obtain three new
2. Experimental
2.1. General materials
ion-pair
complexes,
[BiClBzPyN(CH3)2][Ni(mnt)2]
[14],
All regents used in the syntheses were of analytical grade. 1-(40-
[BrFBzPyN(CH3)2][Ni(mnt)2] [15] and [FClBzPyN(CH3)2][Ni(mnt)2]
[16], in which the [Ni(mnt)2]ꢀ anions and the cations stack into
well-segregated columns and the Ni(III) ions form a 1D zigzag
fluoro-20-bromobenzyl)-4-dimethylaminopyridinium
bromide
maleonitriledithiolate
([FBrBzPyN(CH3)2]Br)
and
disodium
chain through intermolecular Niꢁ ꢁ ꢁS, Sꢁ ꢁ ꢁS, Niꢁ ꢁ ꢁNi, or
pꢁ ꢁ ꢁp interac-
(Na2mnt) were synthesized following the literature procedures
[17,18]. Elemental analyses were run on a Model 240 Perkin-Elmer
CHN instrument. IR spectra were recorded on a Nicolet Avatar 360
FT–IR (4000–400 cmꢀ1 region) spectrophotometer in KBr pellets.
* Corresponding author. Tel.: +86 20 85282568; fax: +86 20 85282366.
E-mail address: niclchem@scau.edu.cn (C.-L. Ni).
0020-1693/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2009.04.021

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H.-R. Zuo et al. / Inorganica Chimica Acta 362 (2009) 3657–3662
Table 1
Electronic spectra were recorded on a SHIMADZU UV-2550 spec-
trophotometer. All solution concentrations were ca. 10ꢀ5 mol dmꢀ3
in CH3CN. Magnetic susceptibility measurements were carried out
in the temperature range 2–300 K using a Quantum Design MPMS-
XL superconducting quantum interference device (SQUID)
magnetometer.
Crystallographic data for 1 and 2.
Compound
1
2
Empirical formula
Formula weight
Temperature/K
Crystal system
Space group
C36H30Br2F2N8NiS4
959.45
C22H15BrFN6NiS4
649.26
291(2)
291(2)
Triclinic
P1
Monoclinic
P21/c
ꢀ
2.2. Synthesis of [FBrBzPyN(CH3)2]2[Ni(mnt)2])(1)
Unit cell dimensions
a/Å
b/Å
c/Å
8.593(4)
9.221(4)
7.0584(9)
17.869(2)
21.021(3)
90
92.063(2)
90
2649.6(6)
4
1.628
To a solution of Na2mnt (360 mg, 2 mmol) in water (20 cm3), a
solution of NiCl2ꢁ6H2O (238 mg, 1 mmol) in 10 cm3 water was then
added dropwise with vigorous stirring at room temperature. A
solution of [FBrBzPyN(CH3)2]Br (790 mg, 2 mmol) in 20 cm3 MeOH
was slowly added to the red solution above. The product was fil-
tered, washed by water, dried under vacuum and recrystallized
with acetone–MeOH to give red solid 817 mg, yield 85%. Elemental
Anal. Calc. for C36H30Br2F2N8NiS4: C, 45.06; H, 3.15; N, 11.68.
Found: C, 45.01; H, 3.23; N, 11.62%. IR (KBr, cmꢀ1): 3067(m),
2919(w), 2853(w), 2213(s), 2195(s), 1647(s), 1596(m), 1572(s),
1485(vs), 1451(m), 1227(s), 1163(s), 1148(s), 1107(m), 1035(s),
824(m), 807(m), 783(s), 737(m), 586(s), 538(s), 509(s).
13.507(6)
77.932(5)
86.618(6)
72.054(5)
995.7(8)
a
/°
b/°
c
/°
V/Å3
Z
1
Density (calculated), mg/m3
1.600
2.751
482
Mu(Mo K
a)/mm
2.586
1300
F(0 0 0)
Crystal size/mm3
0.12 ꢂ 0.18 ꢂ 0.25
0.11 ꢂ 0.13 ꢂ 0.25
1.9, 25.0
18650
4664 (0.031)
18650/4664/318
1.017
hmin, hmax (°)
2.4, 25.0
Reflection collected
Independent reflections (Rint
Data/restrains/parameters
Goodness of fit on F2
6984
)
3450 (0.025)
6984/3450/243
1.046
Final R indices [I > 2
r
(I)]
R1 = 0.0493,
wR2 = 0.1371
R1 = 0.0603,
wR2 = 0.1472
0.94 and ꢀ1.25
R1 = 0.0510,
wR2 = 0.1862
R1 = 0.0697,
wR2 = 0.1982
0.73 and ꢀ0.60
2.3. Synthesis of [FBrBzPyN(CH3)2][Ni(mnt)2])(2)
Final R indices (all data)
An acetone solution (10 cm3) of I2 (120 mg, 0.47 mmol) was
slowly added to
a 1 (721 mg,
acetone solution (20 cm3) of
Largest difference peak and hole
(e Åꢀ3
0.75 mmol) and the mixture was stirred for 12 h. MeOH (60 cm3)
was then added, and the mixture allowed to stand overnight,
390 mg of black micro-crystals formed were filtered off, washed
with MeOH and dried in vacuum. Yield: 80%. Anal. Calc. for
C22H15BrFN6NiS4: C, 40.70; H, 2.33; N, 12.94. Found: C, 40.66; H,
2.38; N, 12.91%. IR (KBr, cmꢀ1): 3030(w), 2919(m), 2846(m),
2362(m), 2208(s), 1655(s), 1577(m), 1487(s), 1396(s), 1299(m),
1220(s), 1098(m), 987(m), 937(w), 876(s), 811(m), 533(m).
Single crystals suitable for X-ray structure analyses were ob-
tained by evaporation of the solvents from MeCN/i-PrOH
(v:v = 1:2) solutions of 1 and 2.
)
R1
=
R
(||Fo|ꢀ|Fc||)/
R
|Fo|, wR2 = [
R
w(|Fo|2ꢀ|Fc|2)2/
R .
w(|Fo|2)2]1/2
Table 2
Selected bond parameters and intermolecular contacts for 1 and 2.
Compound 1
Ni(1)–S(1)
Ni(1)–S(2)
2.1795(15)
2.1746(16)
S(1)–Ni(1)–S(2)
91.98(4)
Compound 2
Ni(1)–S(1)
Ni(1)–S(2)
Ni(1)–S(3)
Ni(1)–S(4)
2.1450(16)
2.1502(19)
2.1484(16)
2.1434(19)
S(1)–Ni(1)–S(2)
S(1)–Ni(1)–S(4)
S(2)–Ni(1)–S(3)
S(3)–Ni(1)–S(4)
92.06(7)
87.82(7)
87.82(6)
92.33(7)
2.4. Determination of crystal structure
X-ray diffraction experiments were performed with a Bruker
SMART CCD area detector diffractometer using graphite mono-
chromated Mo Ka radiation (k = 0.71073 Å) in
x
and / scans mode.
agreement with those of other molecular solids based on
[Ni(mnt)2]2ꢀ anion and substituted pyridinium [22,23]. In the
[FBrBzPyN(CH3)2]+ cation, the phenyl and pyridine rings are
twisted with respect to the C(10)–C(11)–N(3) plane, having the
dihedral angle of 96.6° for the former and 64.5° for the latter.
The dihedral angle of the phenyl and pyridine ring is 77.1°. As
shown in Fig. 1b, the cations (D) and the anions (A) in 1 stack into
a 1D alternating column (i.e., of type ꢁ ꢁ ꢁDDADDADDꢁ ꢁ ꢁ) via short
S(2)ꢁ ꢁ ꢁBr(1)(3.681 Å), N(2)ꢁ ꢁ ꢁF(1)(3.651 Å), C(14)ꢁ ꢁ ꢁN(3)(3.769 Å)
interactions, and C(18)–H(18)ꢁ ꢁ ꢁBr(1i) (symmetry code: i = ꢀx + 1,
ꢀy + 1, ꢀz + 1) H-bonding interaction with a C(18)ꢁ ꢁ ꢁBr(1i) distance
A semi empirical absorption correction was carried out using SAD-
ABS [19]. Data collection, cell refinement and data reduction were
done with the SMART and SAINT programs [20]. The structures
were solved by direct method using SHELXS 2000 and refined on
F2 by full-matrix least-squares methods (SHELXL2000) [21]. All
the non-hydrogen atoms were easily found from Fourier maps
and 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. The details of data collection,
refinement and crystallographic data are summarized in Table 1.
Selected bond distances and angles are given in Table 2.
of 3.643 Å. The cation–cation
pꢁ ꢁ ꢁp stacking interactions (the dis-
tance between the phenyl rings is 3.552 Å, Fig. 2a) within the
above column give further rise to a 2D network structure (Fig. 2b).
The crystal system is changed from triclinic to monoclinic when
the Ni(II) ion of 1 is oxidized into Ni(III) ion. An asymmetric unit in
3. Results and discussion
a
cell of 2
comprises an pair of [Ni(mnt)2]ꢀ anions and
[FBrBzPyN(CH3)2]+ cation as shown in Fig. 3a. The selected bond
lengths and bond angles are listed in Table 2. The average Ni–S
bond distance of 2.147 Å is significantly shorter than that
(2.177 Å) of 1. The coordination geometry of anion and the confor-
mation of cation in 2 are essentially identical to those described
above for 1, and while both anions and cations form segregated
3.1. Descriptions of structures
The structure of 1 composed of a cation and a half anion in an
asymmetric unit is shown in Fig. 1a, and the anion lies on a centre
of inversion. The NiS4 core exists in the square planar coordination
geometry. The bond lengths and angles within the anion are in fair

H.-R. Zuo et al. / Inorganica Chimica Acta 362 (2009) 3657–3662
3659
a
b
Fig. 1. (a) ORTEP plot (30% probability ellipsoids) showing the molecule structure of 1. (b) The cations (D) and the anions (A) in 1 stacking into a 1D alternating column (i.e., of
type ꢁ ꢁ ꢁDDADDADDꢁ ꢁ ꢁ).
a
b
Fig. 2. (a) The 1D column of the cations through C–Hꢁ ꢁ ꢁBr and pꢁ ꢁ ꢁp interaction between the cations of 1. (b) The 2D network structure for 1.

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H.-R. Zuo et al. / Inorganica Chimica Acta 362 (2009) 3657–3662
stacks whose directions do parallel to a-axis as shown in Fig. 3b.
The most interesting fact is that the four columns of cations create
cubic-like large channel in which the [Ni(mnt)2]ꢀ columns are lo-
cated (Fig. 3b). The Ni(III) ions form an uniform chain through
intermolecular Niꢁ ꢁ ꢁS, Sꢁ ꢁ ꢁS, or Niꢁ ꢁ ꢁNi interactions with Niꢁ ꢁ ꢁNi
distance being 4.024 Å (Fig. 4a). The Ni-ring overlapping mode
(Fig. 4b) was found in the pack of [Ni(mnt)2]ꢀ anions. In the
[FBrBzPyN(CH3)2]+ cation, the dihedral angles between aromatic
ring and the C(14)–C(15)–N(5) plane are 7.8° for the phenyl ring
and 86.7° for the pyridine ring. The dihedral angle between the
phenyl and pyridine rings is 83.2°. These values are significantly
tances are 3.457 Å and 3.285 Å, respectively. These weak cation–
cation, anion–anion, and anion–cation interactions in the crystal
of 2 generate a 3D network structure (Fig. 3b), and play an impor-
tant role in the magnetic coupling.
By comparing the structures of 1 and 2, we conclude that the
NiIII ion of the anion favors separated columnar molecular stacks
of anions and cations of the crystal when the cation is identical
in the two molecular solids. In addition, some short such as Sꢁ ꢁ ꢁBr,
Nꢁ ꢁ ꢁF, Cꢁ ꢁ ꢁN interactions, C–Hꢁ ꢁ ꢁN, C–Hꢁ ꢁ ꢁBr hydrogen bonds, and
p p stacking interactions play an important role in the stacking
ꢁ ꢁ ꢁ
and magnetic coupling in the crystal.
different from those of 1. The
p p stacking interactions between
ꢁ ꢁ ꢁ
the phenyl rings of the neighboring cations with the distance of
3.425 Å give a cations column (Fig. 4c); Besides, two weak H-bond-
ing interactions such as C(10)–H(10)ꢁ ꢁ ꢁN(3iii), and C(15)–
H(15)ꢁ ꢁ ꢁN(4iii) (symmetry code: iii = ꢀx, yꢀ1, z) are found between
the anion and the cation, and the C(10)ꢁ ꢁ ꢁN(3), C(15)ꢁ ꢁ ꢁN(4) dis-
3.2. Infrared spectra and UV–Vis spectra
The infrared spectra of 1 and 2 are very much consistent with
the structural data presented above. The bands at 3067, 2919,
2853 cmꢀ1 for 1 and 3060, 2919, 2846 cmꢀ1 for 2 are due to the
a
b
Fig. 3. (a) ORTEP plot (30% probability ellipsoids) showing the molecule structure of 2. (b) The packing diagram for 2 as viewed along the a-axis.

H.-R. Zuo et al. / Inorganica Chimica Acta 362 (2009) 3657–3662
3661
a
b
c
Fig. 4. (a) The Ni(III) ions of [Ni(mnt)2]ꢀ anions form a 1D zigzag uniform magnetic chain by intermolecular Niꢁ ꢁ ꢁS, Niꢁ ꢁ ꢁNi, or
pꢁ ꢁ ꢁp
interactions of 2. (b) Mode of overlapping
of the [Ni(mnt)2]ꢀ anions of 2. (c) The column of cations via
pꢁ ꢁ ꢁp stacking interactions between the phenyl rings for 2.
stretching vibration frequencies of C–H in the aromatic rings and
the methylene. The CN stretching bands lie at 2213, 2195 cmꢀ1
for 1 and 2208 cmꢀ1 for 2, respectively, which shows the nickel
of 2 is Ni(I) [24]. The bands at 1647, 1596, and 1572 cmꢀ1 for 1,
and 1655, 1577, and 1487 cmꢀ1 for 2, are attributable to the
C@N and C@C stretching bands for the phenyl and pyridine rings.
The UV–Vis absorption spectra of 1 and 2 in CH3CN solvent in
the region of 200–900 nm are attributed to the anionic portions
of these compounds. The characteristic bands of 1 at 878, 472.0,
L* ? L bands of 2 are at 864, 474, 376, and 272 nm, respectively,
which are similar to these of [Bu4N][Ni(mnt)2] [25].
3.3. Magnetic properties and analyses
The magnetic susceptibility data of 2 measured under an ap-
plied field of 2000 Oe in the 2–300 K temperature range is shown
in Fig. 5, where vm is the magnetic susceptibility per nickel atom
corrected by the diamagnetic contribution. The overall magnetic
behavior of 2 corresponds to a paramagnetic system with an anti-
379, and 272 nm, are assigned as d ? d, M ? L, L(
L( ) ? M, respectively, which is basically similar to those observa-
tions in [Bu4N]2[Ni(mnt)2] [25]. The d ? d, M ? L, L( ) ? M, and
p) ? M, and
r
ferromagnetic coupling interaction. The
vmT value at 300 K is only
p
0.260 emu K molꢀ1 which is significantly lower than the spin-only

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H.-R. Zuo et al. / Inorganica Chimica Acta 362 (2009) 3657–3662
network structure, respectively. The Ni(III) ions for 2 form a uni-
1.0
0.8
0.6
0.4
0.2
0.0
form 1D zigzag magnetic chain through Niꢁ ꢁ ꢁS, Niꢁ ꢁ ꢁNi, or
p p
ꢁ ꢁ ꢁ
interactions with Niꢁ ꢁ ꢁNi distance of 4.024 Å. Magnetic susceptibil-
ity measurements in the temperature range 2–300 K show that 1 is
expected to be diamagnetic, and 2 exhibits an interesting spin-gap
transition (D/kb = 460.6 K) around 155 K.
2.0
1.5
1.0
0.5
0.0
T = 154.6 K
5. Supplementary material
CCDC 711693 and 711694 contain the supplementary crystallo-
graphic data for this paper. These data can be obtained free of
charge from the Cambridge Crystallographic Data Center, via
http://www.ccdc.cam.ac.uk/data_request/cif.
0
60 120 180 240 300
T (K)
Acknowledgements
50
0
100
150
T (K)
200
250
300
The authors thank the Science and Technology Project (No.
2008B080701011) from Guangdong Science and Technology
Department and the President’s Science Foundation of South China
Agricultural University (No. 2008X015) for financial support of this
work.
Fig. 5. Plot of
vm vs. T for 2 (inset: the plot d(vmT)/dT vs. T) (the red solid lines are
reproduced from the theoretic calculations and detailed fitting procedure described
in the text). (For interpretation of the references to colour in this figure legend, the
reader is referred to the web version of this article.)
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vm-T curves are obtained without hysteresis that
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v
mT)/dT derivative, that is, ꢃ155 K for 1 (inset of
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vm
¼
a
expðꢀ
D
=kbTÞ=T þ C=T þ v0
ð1Þ
where
energy,
a is a constant corresponding to the dispersion of excitation
D
is the magnitude of the spin gap, kb is the Boltzmann con-
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possible Van Vleck paramagnetism. As observed in Fig. 5 (the red
solid line), Eq. (1) provides a good fit of experimental data within
the range of 2.0–155 K for
2 with a = 1.99, D/kb = 460.6 K,
v
0 = 3.0 ꢂ 10ꢀ5 emu molꢀ1
,
C = 2.0 ꢂ 10ꢀ5 emu K molꢀ1
,
and
R = 1.1 ꢂ 10ꢀ6 (R is defined as
R
(vmꢀ
vmobsd)2/(vmobsd)2). The
calcd
value of the parameter 2D/kbTc (Tc is the transition temperature)
is estimated to be 5.96 for 1, which is larger than the ideal value
of 3.53 derived from the BCS formula in a weak coupling regime.
The magnetic coupling between [Ni(mnt)2]ꢀ anions is very sensitive
to the overlap fashion of neighboring [Ni(mnt)2]ꢀ anions and inter-
molecular contacts [5,31]. On the temperature is lowered, the non-
uniform compression of the magnetic chain and slippage of the
[Ni(mnt)2]ꢀ stack due to the anisotropic contraction of the crystal
result in the magnetic exchange constant changing and trigger a
spin-gap transition [32].
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408.
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127 (2005) 14330.
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(2006) 1988.
4. Conclusion
In summary, two new ion-pair complexes, [FBrBzPyN(CH3)2]2
[Ni(mnt)2] (1) and [FBrBzPyN(CH3)2][Ni(mnt)2] (2) has been pre-
pared and characterized by single crystal X-ray diffraction and
magnetic measurements. Compounds 1 and 2 form a 2D and 3D