Observation of magnetic behavior with two broad maxima of magnetic susceptibility in [Ni(mnt)2]- complexes

Article abstract of DOI:10.1016/j.molstruc.2010.01.022

Three complexes of [Ni(mnt)₂]^- (mnt^2- = maleonitriledithiolate) with benzylpyridinium derivatives, 1-(2′,6′-dichlorobenzyl)-4-aminopyridinium (abbr. Cl₂BzNH₂Py⁺) and 1-(2′,6′-dichlorobenzyl)quinolinium (abbr. Cl₂BzQl⁺), have been characterized structurally and magnetically. The [Cl₂BzNH₂Py][Ni(mnt)₂] solution in MeCN was slowly evaporated to give the crystals of 2, whilst its solution in i-PrOH/MeCN yields 2·0.5i-PrOH. The [Ni(mnt)₂]^- anions are arranged in the mixed stacks of anions and cations in 2, and the segregated stacks of anions and cations in 2·0.5i-PrOH and 4. Even though three complexes exhibit different stacking pattern of magnetic anions, their temperature dependences of magnetic susceptibilities in 2-300 K range show a common feature, namely, two broad maxima of magnetic susceptibility. Powder X-ray examination for three complexes excluded that the impurity causes such complicated magnetic behaviors. Combined with the single crystal structure analyses, the double broad maxima of magnetic susceptibility is probably attributed to anisotropic magnetic exchange interactions between magnetic anions.

Full text of DOI:10.1016/j.molstruc.2010.01.022

Journal of Molecular Structure 968 (2010) 67–75
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Observation of magnetic behavior with two broad maxima of magnetic
susceptibility in [Ni(mnt)2]ꢀ complexes
a
b,
Fang Xuan a, Zheng-Fang Tian a, Xiao-Ming Ren a,b, , Hai-Bao Duan , Qing-Jin Meng
*
*
a College of Science, Nanjing University of Technology, Nanjing 210009, PR China
b State Key Laboratory and Coordination Chemistry Institute, Nanjing University, Nanjing 210023, PR China
a r t i c l e i n f o
a b s t r a c t
Three complexes of [Ni(mnt)2]ꢀ (mnt2ꢀ = maleonitriledithiolate) with benzylpyridinium derivatives, 1-
(20,60-dichlorobenzyl)-4-aminopyridinium (abbr. Cl2BzNH2Py+) and 1-(20,60-dichlorobenzyl)quinolinium
(abbr. Cl2BzQl+), have been characterized structurally and magnetically. The [Cl2BzNH2Py][Ni(mnt)2]
solution in MeCN was slowly evaporated to give the crystals of 2, whilst its solution in i-PrOH/MeCN
yields 2ꢁ0.5i-PrOH. The [Ni(mnt)2]ꢀ anions are arranged in the mixed stacks of anions and cations in 2,
and the segregated stacks of anions and cations in 2ꢁ0.5i-PrOH and 4. Even though three complexes exhi-
bit different stacking pattern of magnetic anions, their temperature dependences of magnetic susceptibil-
ities in 2–300 K range show a common feature, namely, two broad maxima of magnetic susceptibility.
Powder X-ray examination for three complexes excluded that the impurity causes such complicated
magnetic behaviors. Combined with the single crystal structure analyses, the double broad maxima
of magnetic susceptibility is probably attributed to anisotropic magnetic exchange interactions between
magnetic anions.
Article history:
Received 12 December 2009
Accepted 12 January 2010
Available online 20 January 2010
Keywords:
Bis(maleonitriledithiolato)nickelate
monoanion
Crystal structure
Double broad maxima of magnetic
susceptibility
Ó 2010 Elsevier B.V. All rights reserved.
1. Introduction
feature of the first-order transition, is observed in the heat capacity
measurements [14,24]. (2) In other cases, no structural phase tran-
One dimensional (1D) S = 1/2 quantum spin system offers a
wide range of ground states, for example, Peierls and spin-Peierls
transition [1–3], charge density wave (CDW) [4–6], spin density
wave (SDW) [5,7] and charge ordering [8,9] due to the inherent
instability of 1D electron gas [10]. Such spin systems are of inter-
est, because of the importance for understanding the mechanism
of high-Tc superconductivity [11]. Furthermore, the relatively sim-
ple 1D quantum spin systems that are accessible by ab initio the-
ory might help towards the understanding of fundamental
quantum–mechanical properties of solids [3].
In previous studies, we have built up a series of 1D spin-Peierls-
like quantum magnetic chain systems from the magnetic
[Ni(mnt)2]ꢀ (mnt2ꢀ = maleonitriledithiolate) anion and the ben-
zylpyridinium derivative counter cation [12–23]. Their magnetic
transitions exhibit the following diversity features in these fami-
lies: (1) in some cases, the magnetic chain is uniform above the
transition temperature and dimerization below the transition tem-
perature, this nature is similar to the spin-Peierls transition. How-
ever, a sharp k-shaped thermal anomaly, a typical thermodynamic
sition as well as no sizable enthalpy change is associated with the
magnetic transition, which exhibits the thermodynamic character
of the second-order phase transition [16]. (3) From high- to low-
temperature phases, a lattice compression is observed for the most
1D complexes, whereas a lattice expansion for one example [25].
(4) For the case of the cell volume shrinking in the low-tempera-
ture phase, applied pressure strongly promotes the transition
[26]; it is interesting that the cell volume increasing in the low-
temperature phase is opening a new issue, which is whether the
transition temperature Tc does or not decrease with applied pres-
sure [25].
On the other hand, it has been found that the packing structure
for the series of complex of [Ni(mnt)2]ꢀ with benzylpyridinium
derivative cation is highly sensitive to a balance of all the intermo-
lecular non-covalent interactions present in the crystal, and the
competition and cooperation between them lead to less straight-
forward to establish how they will collectively direct the crystal
packing. For example, when strong intermolecular H-bonding
interactions are present between the anions and the benzylpyridi-
nium derivative cations, the magnetic anions do not form a uni-
form chain but a tetrameric chain [27].
* Corresponding authors. Address: College of Science, Nanjing University of
Technology, Nanjing 210009, PR China. Tel.: +86 25 83587820; fax: +86 25
83587438 (X.-M. Ren).
In order to get deeper understandings of how the existence of
more than one type of non-covalent interaction will collectively
direct the crystal packing as well as the relationship between the
E-mail address: xmren@njut.edu.cn (X.-M. Ren).
0022-2860/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2010.01.022

68
F. Xuan et al. / Journal of Molecular Structure 968 (2010) 67–75
stacking pattern of magnetic anion and magnetic behaviors, it is
necessary to systematically investigate the crystal structures and
magnetic properties for the new members in the series of com-
plexes of [Ni(mnt)2]ꢀ with benzylpyridinium derivative cations.
This work reports the crystal structures and magnetic properties
for three new members in this family, which possess a common
magnetic nature with two broad maxima of magnetic
susceptibility.
2.2. Preparations of complexes
2.2.1. [Cl2BzNH2Py]2[Ni(mnt)2] (1)
Na2mnt (456 mg, 2.5 mmol) and NiCl2ꢁ6H2O (297 mg,
1.25 mmol) were mixed under stirring in water (30 mL) at room
temperature. Subsequently, a solution of [Cl2BzNH2Py]Br (834
mg, 2.5 mmol) in water (15 mL) was added to the mixture, the
2. Experimental
2.1. General materials and techniques
All chemicals and solvents were of reagent grade and used
without further purification. 1-(20,60-dichlorobenzyl)-4-aminopy-
ridinium (abbr. [Cl2BzNH2Py]Br), 1-(20,60-dichlorobenzyl)quinolini-
um (abbr. [Cl2BzQl]Br) were prepared following the literature
methods [28]. Disodium maleonitriledithiolate (Na2mnt) was syn-
thesized according to a published procedure [29]. Elemental anal-
yses for C, H and N were run on a Model 240 Perkin–Elmer
instrument. IR spectra were recorded on an IF66V FT-IR (4000–
400 cmꢀ1) spectrophotometer with KBr pellets. Magnetic suscepti-
bility measurements for polycrystalline samples were carried out
with a Quantum Design MPMSXL superconducting quantum inter-
ference device (SQUID) magnetometer (under 1.0 T for 2, 4 and 0.1
T for 2ꢁ0.5i-PrOH in the temperature range 2–300 K), and the dia-
magnetism correction were performed by Pascal’s constants [30].
The thermogravimetric (TG) analysis was investigated on a stan-
dard TGA analyzer under nitrogen flow at a heating rate of 10 °C/
min for all measurements.
Fig. 1. ORTEP view with non-H atomic numbering for 1ꢁ2MeCN at 30% probability
thermal ellipsoids (H-atoms and the solvent MeCN molecule are omitted for
clarity).
Table 1
Crystal and structural refinement data of 1ꢁ2MeCN, 2, 2ꢁ0.5i-PrOH, 3 and 4.
Compound
1ꢁ2MeCN
2
2ꢁ0.5i-PrOH
3
4
Chemical formula
Formula weight
Temperature (K)
Wavelength (Å)
Crystal system
Space group
a (Å)
C36H28Cl4N10NiS4
929.45
293(2)
0.71070
Triclinic
C20H11Cl2N6NiS4
593.22
296(2)
0.71073
Triclinic
C21.5H14Cl2N6NiO0.5S4
619.24
298(2)
0.71073
Monoclinic
C2/c
37.247(10)
6.9376(18)
23.014(7)
90.00
120.259(9)
90.00
5137(3)/8
1.601
1.318
2576
C40H24Cl4N6NiS4
917.42
293(2)
0.71070
Triclinic
C24H12Cl2N5NiS4
628.26
293(2)
0.71073
Monoclinic
P21/c
7.729(7)
15.445(15)
22.28(2)
90.00
99.666(18)
90.00
2622(4)/4
1.592
1.287
1268
ꢀ
ꢀ
ꢀ
P1
P1
P1
9.420(2)
9.679(2)
111.746(3)
86.001(13)
89.806(13)
74.442(10)
1029.1(4)/1
1.500
8.2590(10)
11.6313(14)
13.889(2)
114.7210(10)
93.708(2)
99.488(2)
1182.0(3) /1
1.667
8.4417(11)
9.0060(15)
14.308(3)
87.645(17)
83.124(16)
66.226(13)
988.3(3)/1
1.541
b (Å)
c (Å)
a
(°)
b (°)
c
(°)
V (Å3)/Z
Density (g cmꢀ3
)
Abs. coeff. (mmꢀ1
F(0 0 0)
)
0.975
474
1.423
598
1.012
466
Data collect h
range
3.13–25.34
1.63–25.50
2.32–25.50
3.02–25.35
1.61–25.50
Index range
ꢀ11 ꢂ h ꢂ 11,
ꢀ11 ꢂ k ꢂ 11,
ꢀ1 ꢂ l ꢂ 14
9790
ꢀ9 ꢂ h ꢂ 9,
ꢀ14 ꢂ k ꢂ 12,
ꢀ16 ꢂ l ꢂ 16
8696
ꢀ41 ꢂ h ꢂ 44,
ꢀ8 ꢂ k ꢂ 8,
ꢀ27 ꢂ l ꢂ 22
12575
ꢀ10 ꢂ h ꢂ 10,
ꢀ10 ꢂ k ꢂ 10,
ꢀ17 ꢂ l ꢂ 17
9658
ꢀ16 ꢂ h ꢂ 16,
ꢀ8 ꢂ k ꢂ 6,
ꢀ18 ꢂ l ꢂ 22
13784
Reflns. collected
Independent
reflns.
3730
4324
4735
3624
4874
Rint
0.0548
0.0279
0.0962
0.0285
0.1772
Refinement
method on F2
Data/restraints/
parameters
Full-matrix least-squares
3767/0/252
4324/0/298
4735/0/326
3624/0/250
4874/0/325
Goodness-of-fit on
1.082
1.034
1.064
1.095
0.637
F2
Final R indices
[I > 2d(I)]
R1 = 0.0406, wR2 = 0.0951
R1 = 0.0351, wR2 = 0.0864
R1 = 0.0501, wR2 = 0.1270
R1 = 0.0450, wR2 = 0.0944
R1 = 0.0459, wR2 = 0.0726
R indices (all data)
R1 = 0.0477, wR2 = 0.0999
0.341 and ꢀ0.262
R1 = 0.0564, wR2 = 0.1053
0.379 and ꢀ0.417
R1 = 0.0639, wR2 = 0.1348
0.593and ꢀ0.454
R1 = 0.0556, wR2 = 0.0997
0.433and ꢀ0.511
R1 = 0.2067, wR2 = 0.0942
0.268 and ꢀ0.296
Residual (e Åꢀ3
)
P
P
P
P
R1
=
(||Fo| ꢀ |Fc||)/ |Fo|, wR2 = [ w(|Fo|2 ꢀ |Fc|2)2/ w(|Fo|2)2]1/2
.

F. Xuan et al. / Journal of Molecular Structure 968 (2010) 67–75
69
Table 2
red precipitate immediately formed was filtered off, and washed
Selected bond angles (°) and bond lengths (Å) for 1ꢁ2MeCN, 2, 2ꢁ0.5i-PrOH, 3, 4.
with water. The crude product was recrystallized in MeCN
(20 mL) to give red crystals. Yield: ꢃ76%. Anal. Calc. for
C32H22Cl4N8S4Ni: C, 45.36; H, 2.62; N, 13.22%. Found: C, 45.44; H,
2.35; N, 13.31%. IR spectrum (cmꢀ1): 3385s, 3316s and 3320s
1ꢁ2MeCN
Ni(1)–S(1)
Ni(1)–S(2)
2.1721(8)
2.1751(7)
S(1)–Ni(1)–S(2)
S(1)–Ni(1)–S(2A)
92.18(3)
87.82(3)
Symmetric code: A = ꢀx, ꢀy + 1, ꢀz + 1
2
(
(
mN–H of –NH2); 3061s (mC–H of benzene and pyridine ring); 1649s
mC@N of pyridine and mC@C of benzene); 2198s (mC„N of mnt2ꢀ
Ni(1)–S(1)
Ni(1)–S(3)
S(1)–Ni(1)–S(2)
S(2)–Ni(1)–S(4)
2.1412(10)
2.1440(10)
92.26(4)
Ni(1)–S(2)
Ni(1)–S(4)
S(1)–Ni(1)–S(3)
S(3)–Ni(1)–S(4)
2.1418(9)
2.1533(10)
86.95(4)
ligands) and 1484s (mC@C of mnt2ꢀ ligands).
88.15(4)
92.69(4)
2.2.2. [Cl2BzNH2Py][Ni(mnt)2] (2)
2ꢁ0.5i-PrOH
A solution of I2 (150 mg, 0.59 mmol) in MeCN (10 mL) was
slowly added into 1 (848 mg, 1.0 mmol) in MeCN (20 mL) and
the mixture was stirred. The produced dark microcrystals
(498 mg) were filtered off, washed with MeOH and Et2O sequen-
Ni(1)–S(1)
2.1456(13)
2.1313(14)
92.84(5)
Ni(1)–S(2)
Ni(1)–S(4)
S(1)–Ni(1)–S(4)
S(3)–Ni(1)–S(4)
2.1436(14)
2.1487(13)
88.55(5)
Ni(1)–S(3)
S(1)–Ni(1)–S(2)
S(2)–Ni(1)–S(3)
86.19(5)
92.45(5)
Symmetric code: A = ꢀx, y, ꢀz + 3/2
3
tially and dried in
a
vacuum. Yield: ꢃ59%. Anal. Calc. for
C20H11Cl2N6S4Ni: C, 40.49; H, 1.87; N, 14.17%. Found: C, 40.56; H,
1.84; N, 14.44%. IR spectrum (cmꢀ1): 3401s, 3342s and 3232s
Ni(1)–S(1)
S(1)–Ni(1)–S(2)
2.1807(9)
92.31(3)
Ni(1)–S(2)
S(1A)–Ni(1)–S(2)
2.1683(8)
87.69(3)
(mN–H of –NH2); 3016s (mC–H of benzene and pyridine ring);
2975w, and 2925w (mC–H of –CH2–); 1658s and 1641s (mC@N of pyr-
Symmetric code: A = ꢀx, ꢀy + 1, ꢀz + 1
4
idine ring and mC@C benzene ring); 2208s (mC„N of mnt2ꢀ ligands)
and 1436s (mC@C of mnt2ꢀ ligands).
Ni(1)–S(1)
Ni(1)–S(3)
S(1)–Ni(1)–S(2)
S(2)–Ni(1)–S(4)
2.146(3)
2.152(3)
92.13(8)
87.84(8)
Ni(1)–S(2)
Ni(1)–S(4)
S(1)–Ni(1)–S(3)
S(3)–Ni(1)–S(4)
2.148(3)
2.146(3)
87.81(8)
92.22(8)
2.2.3. 2ꢁ0.5i-PrOH
The crude product of 2 was recrystallized in i-PrOH/MeCN to
give 2ꢁ0.5i-PrOH. Anal. Calc. for C21.5H14Cl2N6O0.5S4Ni: C, 41.53;
H, 2.22; N, 13.21%. Found: C, 41.43; H, 2.29; N, 13.70%. IR spectrum
pyridine ring and mC@C benzene ring); 2205s (mC„N of mnt2ꢀ
ligands) and 1435s ( C–H of i-PrOH)
C@C of mnt2ꢀ ligands); 2069w (
and 1119w (mC–O of i-PrOH).
(cmꢀ1): 3423sh, 3346w, and 3236w (
m
N–H of –NH2); 3016s ( C–H of
m
m
m
benzene and pyridine ring); 2925w (
m
C–H of –CH2–); 1655s (mC@N of
Fig. 2. Two adjacent cations form a dimer via Clꢁꢁꢁ
p interactions and the anions bridge the neighboring cationic dimers into a supramolecular chain through CNꢁꢁꢁH2N H-
ꢀ
bonding interactions along ½211ꢄ direction (with the H-bonding geometric parameters of \N4A–H4BAꢁꢁꢁN2 = 175.7°, N4AꢁꢁꢁN2 = 3.012 Å and symmetric code A = 1 + x, y, z) in
the crystal of 1ꢁ2MeCN.

70
F. Xuan et al. / Journal of Molecular Structure 968 (2010) 67–75
Fig. 3. ORTEP views with non-H atomic numbering for (a) 2 and (b) 2ꢁ0.5i-PrOH at 30% probability thermal ellipsoids (H-atoms are omitted for clarity).
Fig. 4. (a) Packing diagram of 2 and (b) the side view for a mixed stack of anions and cations along a-axis.

F. Xuan et al. / Journal of Molecular Structure 968 (2010) 67–75
71
2.2.4. [Cl2BzQl]2[Ni(mnt)2] (3)
0.71070 Å) on a CCD area detector (Bruker-SMART). Structures
were solved by the direct method and refined by the full-matrix
least-squares procedure on F2 using SHELXL-97 program [31]. All
non-hydrogen atoms were refined anisotropically. For 1ꢁ2MeCN,
2, 3 and 4, the hydrogen atoms were introduced at calculated posi-
tions; whereas for 2ꢁ0.5i-PrOH, the solvent i-PrOH molecule is dis-
ordered, and the C-atoms for two –CH3 groups (C22 and C23) lie on
the twofold axes, respectively. As a result, the occupied factors of
C21 as well as O1 in i-PrOH molecule were kept fixed as 0.5 for
each of two sites and the H atoms of the disordered solvent mole-
cule have been omitted during refinement. The crystallographic
data and structure refinements are summarized in Table 1.
A similar procedure as 1 was employed to produce the crystals
of 3. Cl2BzNH2Py+ was replaced by Cl2BzQl+. Yield: ꢃ85%. Anal.
Calc. for C40H24Cl4N6S4Ni: C, 52.37; H, 2.64; N, 9.16%. Found: C,
52.66; H, 2.25; N, 9.53%. IR spectrum (cmꢀ1): 3057s (mC–H of ben-
zene and pyridine ring); 2993w (mC–H of –CH2–); 1626s (mC@N, mC@C
of quinoline ring and of benzene ring); 2219w, 2199s (mC„N of
mnt2ꢀ ligands) and 1429s (mC@C of mnt2ꢀ ligands).
2.2.5. [Cl2BzQl][Ni(mnt)2] (4)
A method similar to that used for 2 was utilized to prepare 4.
Yield: ꢃ81%. Anal. Calc. for C24H12Cl2N5S4Ni: C, 45.88; H, 1.93; N,
11.15%. Found: C, 45.74; H, 1.82; N, 11.10%. IR spectrum (cmꢀ1):
3010s (
1595s (
of mnt2ꢀ ligands) and 1439s (
The single crystals of 2 and 4 suitable for X-ray crystallographic
analysis were obtained by slow evaporation of the MeCN solution
of the corresponding complexes.
m
m
C–H of benzene and pyridine ring); 2925w (
C@N of quinoline ring and C@C benzene ring); 2207s (mC„N
C@C of mnt2ꢀ ligands).
mC–H of –CH2–);
3. Result and discussion
m
m
3.1. Crystal structures
ꢀ
1ꢁ2MeCN crystallizes in triclinic space group P1, and an asym-
metric unit consists of half centrosymmetric [Ni(mnt)2]2ꢀ and
one Cl2BzNH2Py+ together with one MeCN molecule. In the planar
anion moiety, the Ni-atom occupies at an inversion center (as
shown in Fig. 1), and the Ni–S distances as well as the S–Ni–S bite
angle are normal (see Table 2), which are comparable to the re-
ported [Ni(mnt)2]2ꢀ complexes [32]. In the Cl2BzNH2Py+ moiety,
2.3. X-ray crystallography
The diffraction data for 1ꢁ2MeCN, 2, 2ꢁ0.5i-PrOH, 3 and 4 were
collected at 293 K with graphite-monochromated Mo K
a (k =
Fig. 5. (a) Packing diagram of 2ꢁ0.5i-PrOH projected along b-axis and (b) the side view for an anionic stack.

72
F. Xuan et al. / Journal of Molecular Structure 968 (2010) 67–75
Fig. 6. (a) ORTEP view with non-H atomic numbering for 3 at 30% probability thermal ellipsoids (H-atoms are omitted for clarity); (b) and (c)
anions and cations.
pꢁꢁꢁp interaction between the

F. Xuan et al. / Journal of Molecular Structure 968 (2010) 67–75
73
the phenyl and pyridyl rings twisted with respect to the reference
plane of C(phenyl)–C(H2)–N(pyridine), have a dihedral angle of
114.03°.
supramolecular chain; and the adjacent chains are held together
via van der Waals forces.
Complexes 2 and 2ꢁ0.5i-PrOH are pseudo-polymorphs, and their
One of the fascinating structural features is the existence of
ORTEP views are displayed in Fig. 3. The crystal of 2 belongs to tri-
interaction between two neighboring Cl2BzNH2Py+ cations.
clinic system with space group P1, its asymmetric unit contains
ꢀ
Clꢁꢁꢁ
As illustrated in Fig. 2, the Cl-atoms are nearly orientated to the
neighboring pyridyl ring with Clꢁꢁꢁ (centroid) distance of 3.368 Å
(centroid) distances range
p
one [Ni(mnt)2]ꢀ and one Cl2BzNH2Py+; the crystal of 2ꢁ0.5i-PrOH
belongs to monoclinic system with space group C2/c, and an asym-
metric unit consists of one [Ni(mnt)2]ꢀ and one Cl2BzNH2Py+ cation
together with one half of disordered i-PrOH molecule. The
[Ni(mnt)2]ꢀ monoanions in both 2 and 2ꢁ0.5i-PrOH possess roughly
planar geometry, the bond lengths and angles are in good agree-
ment with various reported [Ni(mnt)2]ꢀ complexes [12–23]. In
comparison of 2 and 2ꢁ0.5i-PrOH, the main differences of the crys-
tal structures are involved with the molecular conformations of the
Cl2BzNH2Py+ cations as well as the arrangement manners of anions
and cations. The dihedral angles between phenyl/pyridyl and the
reference plane of C(phenyl)–C(H2)–N(pyridine) as well as be-
tween phenyl and pyridyl are 77.93°/56.49° and 77.37° in 2 versus
81.8°/70.68° and 68.66° in 2ꢁ0.5i-PrOH. As demonstrated in Fig. 4a,
the anions and cations form the mixed stacks along a-axis in 2;
within a mixed stack (Fig. 4b) the neighboring anions overlap in
p
(this distance falls in the reported Clꢁꢁꢁ
p
from 3.466 to 3.697 Å [33]) as well as the interatomic separations
of 3.519, 3.432 Å for Cl1–C5A, Cl1–C6A (which are shorter than the
sums of the van der Waals radii [34]; symmetric code A = ꢀx, ꢀy,
ꢀz), respectively. As a result, there probably exists lone-pairꢁꢁꢁ
p
interactions between the Cl-atoms and the electron-deficient
pyridinium rings. Although the Clꢁꢁꢁ
p
(lone-pairꢁꢁꢁ
p
) interactions
have been observed between the electron-deficient triazine ring
and the Cl-atom or Clꢀ ion [33,35,36], notably, thorough CSD
search indicated that the reported Clꢁꢁꢁ
p interaction examples are
interactions, there were important
really rare. Besides the Clꢁꢁꢁ
p
H-bonding interactions as well. The strong H-bonding interactions
between CN groups of mnt2ꢀ ligands and NH2 groups on the pyri-
dyl rings connect the anions and the cationic dimers to form a
Fig. 7. (a) ORTEP view with non-H atomic numbering at 30% probability thermal ellipsoids (H-atoms are omitted for clarity) (b) packing diagram for 4 which shows
segregated anion and cation stacks.

74
F. Xuan et al. / Journal of Molecular Structure 968 (2010) 67–75
a fashion of highly longitudinal offset with two kinds of NiꢁꢁꢁNi dis-
tances, 4.315 and 6.707 Å. The pyridyl rings of the adjacent cations
eclipse the molecular plane of one mnt2ꢀ ligand with a dihedral an-
gle of 8.93° between pyridyl and the mean molecular plane of
mnt2ꢀ ligand. For 2ꢁ0.5i-PrOH, the anions are stacked in column
along b-axis; the cations and the lattice solvent molecules fill in
the spaces between the neighboring anionic columns (Fig. 5a).
Within an anionic column, the neighboring anions are stacked in
a fashion of slightly longitudinal and transverse offset (Fig. 5b),
which is distinct from 2, with the alternative NiꢁꢁꢁNi distances of
4.374 and 4.795 Å.
ꢀ
The crystal of 3 belongs to triclinic system with space group P1,
its asymmetric unit is displayed in Fig. 6a. Similarly to the crystal
of 1, the planar [Ni(mnt)2]2ꢀ dianion is centrosymmetric, and the
bond distances and angles are normal (see Table 2). In the Cl2BzQl+
moiety, the mean molecular plane of dichlorophenyl twists heavily
with respect to the reference plane of C(phenyl)–C(H2)–N(pyri-
dine) with a dihedral angle of 51.52° due to the steric hindrance
between the fused phenyl ring of the quinoline moiety and the
Cl-atom of dichlorophenyl. The intriguingly structural feature of
the crystal of 3 is the existence of strong
pꢁꢁꢁp stacking interaction
between the quinoline ring of the cation and the electron delocal-
ized mnt2ꢀ ligand (Fig. 6b), the dihedral angle between the quino-
line ring and the mean molecular plane of mnt2ꢀ ligand is 2.52°
and the shorter interatomic distance, 3.374 Å of C1ꢁꢁꢁC11A (sym-
metric code A = ꢀ1 + x, y, z), is less than the sums of the van der
Waals radii [34], which is clear to exist ClꢁꢁꢁCl interaction [37].
The crystal of 4 crystallizes in monoclinic space group P21/c, and
its ORTEP view is shown in Fig. 7a. The anions and cations form the
segregated stacks along a-axis, and both anionic and cationic
stacks are irregular (Fig. 7b). Within an anionic stack, the adjacent
co-facial [Ni(mnt)2]ꢀ anions slip along the longer molecular axis
and the NiꢁꢁꢁNi distances between the nearest neighboring anions
alternate as 3.883 and 4.296 Å. Within a cationic stack, the neigh-
boring Cl2BzQl+ cations are related by an inversion center to adapt
anti-parallel arrangement, which lead to two quinoline rings are
parallel to each other with a dihedral angle of 0°. The interatomic
0
contact of two adjacent Cl-atoms is 3.433 ÅA, which is 0obviously
shorter than the sums of the van der Waals radii (3.50 ÅA) [34]. As
a result, there probably exists ClꢁꢁꢁCl interaction.
3.2. Magnetic properties
The temperature dependences of the magnetic susceptibilities
for 2, 2ꢁ0.5i-PrOH and 4 are displayed in Fig. 8. Three complexes
show common features in the plots of vm versus T as below: (1)
the
v
mT values at 300 K (0.188, 0.147 and 0.238 emu K molꢀ1 for
2, 2ꢁ0.5i-PrOH and 4, respectively) are much lower than
0.375 emu K molꢀ1 which is the spin-only value for a S = 1/2 iso-
lated spin system; (2) two broad maxima of magnetic susceptibil-
ity are observed, the first maximum in high-temperature region
are beyond 300 K and the second maximum in low-temperature
region is around 90, 75 and 13 K for 2, 2ꢁ0.5i-PrOH and 4, respec-
tively; (3) a Curie-type paramagnetic tail appears at lower temper-
ature range due to magnetic impurities.
The broad maximum of magnetic susceptibility is the character
of a short-range antiferromagnetic (AFM) interaction [38], and this
means that the interactions are dominated by AFM exchange cou-
pling in three complexes which is in agreement with the fact that
Fig. 8. Functions of molar magnetic susceptibility as temperature for (a) 2 (b)
2ꢁ0.5i-PrOH and (c) 4, respectively.
tence of different magnetic sublattices and each sublattice can
exhibit its own maximum of magnetic susceptibility [39]; (2) the
anisotropic magnetic exchange interaction [40] and (3) a frustra-
tion spin system [41]. The crystal structure analyses disclosed that
the arrangement manner of magnetic [Ni(mnt)2]ꢀ anions in three
complexes do not belong to any frustrated spin system; on the
other hand, there is only one kind of [Ni(mnt)2]ꢀ stack owing to
the only crystallographically independent [Ni(mnt)2]ꢀ anion is
present in an asymmetric unit of the crystals. As a consequence,
the possibility of the spin frustration or the presence of different
magnetic sublattices leading to two broad maxima of magnetic
susceptibility could be excluded. From the above analyses, the
their vmT values decrease with lowering temperature (see Fig. S7).
To understand the reasons what cause two broad maxima of mag-
netic susceptibility, the powder X-ray diffraction examination
were performed for three complexes and the results excluded that
the impurity cause such complicated magnetic behaviors (Fig. S6).
Therefore, the origin of the double maxima of magnetic suscepti-
bility could be related to other possibilities, such as (1) the exis-

F. Xuan et al. / Journal of Molecular Structure 968 (2010) 67–75
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In summary, three complexes of [Ni(mnt)2]ꢀ with benzylpyrid-
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and were gained from different crystallization approaches. The
[Ni(mnt)2]ꢀ anions are arranged in the mixed stacks of anions
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Crystallographic data (excluding structure factors) for
1ꢁ2MeCN, 2, 2ꢁ0.5i-PrOH, 3 and 4 at 293 have been deposited at
the Cambridge Crystallographic Data Centre as supplementary
publication Nos. CCDC 740903–740907. Copies of the data can be
obtained free of charge via www.ccdc.cam.ac.uk/conts/retriev-
ing.html or by application to The Director, CCDC, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: (+44) 1223 336 033;
deposit@ccdc.cam.ac.uk.
Acknowledgments
We thank Jiangsu Science and Technology Department and the
National Nature Science Foundation of China for financial support
(BK2007184, 20871068, 20771056 and 20490218).
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