3D network structure and spin gap behavior in two new molecular magnets based on bis(maleonitriledithiolato)nickelate monoanion

Article abstract of DOI:10.1016/j.ica.2008.11.005

Two new molecular magnets, based on [Ni(mnt)₂]^- monoanion, [DiBrBzPy][Ni(mnt)₂] (1) and [DiBrBzIQl][Ni(mnt)₂] (2) ([DiBrBzPy]⁺ = 1-(3′,5′-dibromobenzyl)pyridinium, [DiBrBzIQl]⁺ = 1-(3′,5′-dibromobenzyl)isoquinolinium and mnt^2- = maleonitriledithiolate), were prepared and characterized by elemental analyses, IR, ESI-MS spectra, single crystal X-ray diffraction and magnetic measurements. The [Ni(mnt)₂] anions and the cations of 1 and 2 are alternately stacked and form 1D column via π?π stacking interactions between the [Ni(mnt)₂] anions and the neighboring cations. Some weak Ni?N, C?N interactions and C{single bond}H?Br, C{single bond}H?N hydrogen bonds between the adjacent columns further generate a 3D network structure. Magnetic susceptibility measurements show that both 1 and 2 exhibit the typical magnetic behavior of a spin gap system with an energy gap of 1151.9 K for 1 and 73.9 K for 2.

Full text of DOI:10.1016/j.ica.2008.11.005

Inorganica Chimica Acta 362 (2009) 2461–2466
Contents lists available at ScienceDirect
Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
3D network structure and spin gap behavior in two new molecular magnets
based on bis(maleonitriledithiolato)nickelate monoanion
a
a,
b
Qian Huang a, Jin-fang Liu a, Hong-rong Zuo a, Jia-rong Zhou a, , Yong Hou , Chun-lin Ni , Qing-jin Meng
*
*
a Department of Applied Chemistry, College of Science, Centre of Inorganic Functional Materials, South China Agricultural University, 510642 Guangzhou, PR China
b State Key Laboratory of Coordination Chemistry, Coordination Chemistry Institute, Nanjing University, 210093 Nanjing, PR China
a r t i c l e i n f o
a b s t r a c t
Two new molecular magnets, based on [Ni(mnt)2]ꢀ monoanion, [DiBrBzPy][Ni(mnt)2] (1) and [DiB-
rBzIQl][Ni(mnt)2] (2) ([DiBrBzPy]+ = 1-(30,50-dibromobenzyl)pyridinium, [DiBrBzIQl]+ = 1-(30,50-dibro-
mobenzyl)isoquinolinium and mnt2ꢀ = maleonitriledithiolate), were prepared and characterized by
elemental analyses, IR, ESI-MS spectra, single crystal X-ray diffraction and magnetic measurements.
Article history:
Received 11 August 2008
Received in revised form 3 November 2008
Accepted 4 November 2008
Available online 18 November 2008
The [Ni(mnt)2] anions and the cations of 1 and 2 are alternately stacked and form 1D column via
pꢁ ꢁ ꢁp
stacking interactions between the [Ni(mnt)2] anions and the neighboring cations. Some weak Niꢁ ꢁ ꢁN,
Cꢁ ꢁ ꢁN interactions and CAHꢁ ꢁ ꢁBr, CAHꢁ ꢁ ꢁN hydrogen bonds between the adjacent columns further gener-
ate a 3D network structure. Magnetic susceptibility measurements show that both 1 and 2 exhibit the
typical magnetic behavior of a spin gap system with an energy gap of 1151.9 K for 1 and 73.9 K for 2.
Ó 2008 Elsevier B.V. All rights reserved.
Keywords:
Pyridinium
Isoquinolinium
Bis(maleonitriledithiolato)nickelate(III)
monoanion
Crystal structure
Spin gap system
1. Introduction
and magnetic properties, two new countercations, 1-(30,50-dibro-
mobenzyl)pyridinium (abbreviated as ([DiBrBzPy]+) and 1-(30,50-
Interest in coordination chemistry of square planar [M(mnt)2]
(M = Ni, Pd, or Pt, mnt = maleonitriledithiolate) complexes has
grown in recent years for their interesting and versatile magnetic
properties such as ferromagnetic ordering at low temperature,
magnetic transition, meta-magnetism, spin-Peierls-like transitions
and spin gap transition [1–6]. The 1D magnetic properties of these
complexes were attributed to the segregated columnar stacks of
anions and countercations, and intermolecular Niꢁ ꢁ ꢁS, Sꢁ ꢁ ꢁS, Niꢁ ꢁ ꢁNi
dibromobenzyl)isoquinolinium ([DiBrBzIQl]+), together with two
new molecular solids, [DiBrBzPy][Ni(mnt)2] (1) and [DiB-
rBzIQl][Ni(mnt)2] (2), were designed and prepared to gain more in-
sight into the magneto-structural relationship. To the best of our
knowledge, the Ni(mnt)2-based molecular solids exhibiting both
3D network structure and spin gap behavior are very rare.
2. Experimental
or
pꢁ ꢁ ꢁp interactions within the anionic columns [7–15]. Recently,
our efforts are to design new suitable multifunctional organic cat-
ions used as the countercation to tune the crystal stacking struc-
ture of [Ni(mnt)2]ꢀ anion, and establish the relationship between
the magnetic interactions and the stacking pattern of anions. Be-
cause the stacking pattern of the [M(mnt)2]ꢀ anions depends
strongly upon the molecular topology of the countercation, we
have introduced substituted benzylisoquinolinium into the system
containing [Ni(mnt)2]ꢀ anion and obtained some newly prepared
Ni(mnt)2-based molecular solids, as exemplified by [BzIQl][-
Ni(mnt)2] [16], [ClBzIQl][Ni(mnt)2] [16], [oFBzIQl][Ni(mnt)2] [17],
[BrFBzIQl][Ni(mnt)2] [18] and [NO2BzIQl][Ni(mnt)2] [19], which
exhibit versatile magnetic properties. With a view to investigating
the effect of substituted groups in the phenyl ring on the structure
2.1. General materials
3,5-Dibromobenzyl bromide, pyridine and isoquinoline were
purchased from Aldrich and were used without further purifica-
tion. 1-(30,50-dibromobenzyl)pyridinium bromide ([DiBrBzPy]Br)
and 1-(30,50-dibromobenzyl)isoquinolinium bromide ([DiB-
rBzIQl]Br) were prepared by the literature methods [20]. Disodium
maleonitriledithiolate (Na2mnt) was synthesized by a published
procedure [21].
2.2. Synthesis of [DiBrBzPy]2[Ni(mnt)2] and [DiBrBzIQl]2[Ni(mnt)2]
These two Ni(II) complexes were prepared by the direct combi-
nation of NiCl2 ꢁ 6H2O, Na2mnt and [DiBrBzPy]Br or [DiBrBzIQl]Br
in H2O in 1:2:2 molar ratio. The red or brown precipitate that
formed was filtered off, washed with water and dried under
* Corresponding authors. Tel.: +86 20 85282568; fax: +86 20 85282366.
E-mail addresses: jiarongzhou1965@163.com (J.-r. Zhou), niclchem@scau.edu.cn
(C.-l. Ni).
0020-1693/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2008.11.005

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Q. Huang et al. / Inorganica Chimica Acta 362 (2009) 2461–2466
Table 1
Table 2
Crystal data and structure refinement for 1 and 2.
Selected bond lengths, bond angles and dihedral angles for 1 and 2.
Compounds
Compounds
1
2
1
2
Empirical formula
Formula weight
T/K
Wavelength
Crystal system
Space group
a/Å
C20H10Br2N5NiS4
667.10
291(2)
C24H12Br2N5NiS4
717.16
291(2)
0.71073 Å
monoclinic
P21/c
Bond length (Å)
Ni(1)–S(1)
Ni(1)–S(2)
Ni(1)–S(3)
Ni(1)–S(4)
2.148(1)
2.143(1)
2.151(1)
2.155(1)
2.134(1)
2.143(1)
2.134(1)
2.137(1)
0.71073 Å
triclinic
ꢀ
P1
Bond angles (°)
S(1)–Ni(1)–S(2)
S(1)–Ni(1)–S(4)
S(2)–Ni(1)–S(3)
S(3)–Ni(1)–S(4)
8.014(1)
7.463(2)
92.63(5)
88.60(5)
85.90(5)
92.92(5)
92.89(5)
86.29(5)
88.25(5)
92.71(5)
b/Å
c/Å
11.006(2)
14.138(2)
80.59(2)
80.12(2)
85.88(2)
1210.7(3)
2
1.830
4.466
654
17.488(4)
21.295(5)
90
106.68(1)
90
2662.4(11)
4
1.789
a
/°
b/°
Dihedral angles (°)
c
/°
V/Å3
CAr–CH2–NPy(IQl) and UAr(h1)
CAr–CH2–NPy(IQl) and UPy(IQl)(h2)
UAr and UPy(IQl)(h3)
91.5
88.9
107.3
79.4
88.6
79.9
Z
Dcalc, Mg/m3
Absorption coefficient/mm1
F(000)
4.068
1412
Crystal size/mm3
Reflections collected
Independent reflections (Rint
Refinement method
0.32 ꢂ 0.25 ꢂ 0.21
0.35 ꢂ 0.25 ꢂ 0.20
vacuum. Yield: 90%. Anal. Calc. for C32H20Br4N6NiS4: C, 38.62; H,
8720
13957
2.03; N, 8.45; Ni, 5.90. Found: C, 38.59; H, 2.08; N, 8.41; Ni,
5.87%. IR spectrum (cmꢀ1): (C@C) of mnt2ꢀ
m(CN), 2216s, 2198s; m ,
)
4231 (0.022)
Full-matrix least-
squares on F2
4231/0/289
1.047
R1 = 0.0401,
wR2 = 0.1242
R1 = 0.0538,
wR2 = 0.1327
0.52 and ꢀ0.84
5191 (0.047)
Full-matrix least-
squares on F2
5191/0/326
0.978
R1 = 0.0394,
wR2 = 0.0849
R1 = 0.0646,
wR2 = 0.0911
0.42 and ꢀ0.65
1492s. ESI-MS (MeCN): 170.2, [Ni(mnt)2]2ꢀ; 328.1, [DiBrBzPy]+.
Yield: 88%. Anal. Calc. for C40H24Br4N6NiS4: C, 43.87; H, 2.19; N,
7.67; Ni, 5.36. Found: C, 43.85; H, 2.24; N, 7.63; Ni, 5.41%. IR spec-
Data/restraints/parameters
Goodness of fit on F2
trum (cmꢀ1): (C@C) of mnt2ꢀ, 1486s. ESI-MS
m(CN), 2214s, 2197s; m
Final R indices [I > 2
r
(I)]
(MeCN): 170.1, [Ni(mnt)2]2ꢀ; 378.2, [DiBrBzIQl]+.
Final R indices (all data)
2.3. [DiBrBzPy][Ni(mnt)2] (1) and [DiBrBzIQl][Ni(mnt)2] (2)
Largest difference in peak and
hole (e Åꢀ3
)
A MeCN solution (20 cm3) of I2 (160 mg, 0.62 mmol) was slowly
added to a MeCN solution (80 cm3) of [DiBrBzPy]2[Ni(mnt)2]
a
b
Fig. 1. (a) ORTEP plot (30% probability ellipsoids) showing the molecule structure of 1. (b) The [Ni(mnt)2]ꢀ anions and [DiBrBzPy]+ cations are alternately stacked and form a
column through stacking interactions between the pyridine rings and the planes of [Ni(mnt)2] ions for 1.
ꢁ ꢁ ꢁ
p
p

Q. Huang et al. / Inorganica Chimica Acta 362 (2009) 2461–2466
2463
(995 mg, 1 mmol) and the mixture was stirred for 4 h. MeOH
(90 cm3) was then added, and the mixture allowed to stand
overnight, 581 mg of black micro-crystals formed were filtered
off, washed with MeOH and dried in vacuum. Yield: 87%. Anal. Calc.
for C20H10Br2N5NiS4: C, 36.01; H, 1.51; N, 10.50; Ni, 8.80. Found: C,
were performed on a Model 240 Perkin–Elmer C H N instrument.
Nickel content was determined using Varian 220FS-220Z atomic
absorption spectrophotometer. Magnetic susceptibilities data on
crushed polycrystalline samples of 1 and 2 were collected over
the temperature range of 2–300 K using a Quantum Design
MPMS-5S super-conducting quantum interference device (SQUID)
magnetometer, and the experimental data were corrected for dia-
magnetism of the constituent atoms estimated from Pascal’s
constants.
36.04; H, 1.55; N, 10.43; Ni, 8.78%. IR spectrum (cmꢀ1):
2209s;
(C@C) of mnt2ꢀ
[Ni(mnt)2+H]ꢀ; 328.0, [DiBrBzPy]+.
m
(CN),
m
,
1484s. ESI-MS (MeCN): 340.1,
The procedure described for 1, except with [DiB-
rBzIQl]2[Ni(mnt)2] as the starting material, was followed to obtain
2. Yield: 81%. Anal. Calc. for C24H12Br2N5NiS4: C, 40.40; H, 1.69; N,
9.76; Ni, 8.18. Found: C, 40.37; H, 1.73; N, 9.67; Ni, 8.23%. IR spec-
2.5. Determination of crystal structure
trum (cmꢀ1):
m
(CN), 2204s;
m
(C@C) of mnt2ꢀ, 1475s. ESI-MS
The intensity data of 1 and 2 were collected using a SMART CCD
area detector (Mo Ka radiation, k = 0.71073 Å) at 291 K. The struc-
(MeCN): 340.2, [Ni(mnt)2+H]ꢀ; 378.3, [DiBrBzIQl]+.
ture was solved by direct method using SHELXS 97 and refined on F2
by full-matrix least-squares methods (SHELXL 97) [22]. All the non-
hydrogen atoms were easily found from Fourier map 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 of 1 and 2 are summarized in Table 1.
2.4. Physical measurements
Infrared spectra were collected on an IF66V FT-IR (400–
4000 cmꢀ1 region) spectrophotometer using KBr pellets of the
samples. The electrospray mass spectra [ESI-MS] were determined
on a Finnigan LCQ mass spectrograph, sample concentration
ca.1.0 mmol dmꢀ3. The elemental analyses (C, H and N contents)
a
b
Fig. 2. (a) The short Cꢁ ꢁ ꢁN and Niꢁ ꢁ ꢁN interactions between anions. (b) The packing diagram for 1 as viewed along a axis.

2464
Q. Huang et al. / Inorganica Chimica Acta 362 (2009) 2461–2466
The previous studies have indicated that the magnetic coupling
3. Results and discussion
between [Ni(mnt)2]ꢀ anions is very sensitive to the intermolecular
contacts and the overlap fashion of neighboring [Ni(mnt)2]ꢀ an-
ions, and small structural variations can lead to large changes in
the properties of molecular solids based on the [Ni(mnt)2]ꢀ anion
[3,5,6,9–11,14–19]. The stacking pattern of the [M(mnt)2]ꢀ anion
depends strongly upon the molecular topology of the counterac-
tion. Derivatives of benzylpyridinium or isoquinolinium (abbrevi-
ated as [RBzPy]+ or [RBzIQl]+) can serve as flexible cations which
can be adjusted via modifying the nature of the groups on the aro-
matic rings, and the molecular configuration was determined by
three dihedral angles (h1, h2, and h3) [23]. When we have fixed
two m-substituted Br atoms of the benzyl group and changed the
heterocyclic ring from pyridine to isoquinoline, the h2 is of compa-
rable value, but the value of h1 and h3 of 1 differ markedly from
those measured in 2 (Table 2). By comparing the structures of 1
and 2, although the geometry of the anion and the cation is essen-
tially identical, the intramolecular interactions and the stacking
modes of the anions and the cations are different. In addition, some
3.1. Crystal structure
The asymmetric unit within the unit cell of 1, which crystallizes
in triclinic system with space group P1, comprised of one
ꢀ
[Ni(mnt)2]ꢀ anion together with one [DiClBzPy]+ cation, is shown
in Fig. 1a. The Ni(III) center in the mononuclear complex is four
coordinate with NiS4 coordination and the geometry can be de-
scribed as approximately square planar. Most of the bond lengths
and angles (Table 2) are in agreement with those found in other
molecular solids based on the [Ni(mnt)2]ꢀ ion with other substi-
tuted benzylpyridinium cations [5,6,9–11]. The [DiBrBzPy]+ cation
adopts a conformation where both the phenyl and pyridine rings
are twisted to the C(14)-C(15)-N(5) reference plane, respectively.
The deviations of two Br atoms from the phenyl ring plane are
0.0972 Å for Br(1) and ꢀ0.0827 Å for Br(2). The dihedral angles that
the phenyl ring and the pyridine ring make with the C(14)-C(15)-
N(5) reference plane are 91.5°(h1) and 88.9°(h2). The phenyl ring
and the pyridine ring make a dihedral angle of 107.3°(h3). It is
interesting that the [Ni(mnt)2]ꢀ anions and [DiBrBzPy]+ cations
are alternately stacked as revealed by the projection along the
intermolecular contacts such as
p
ꢁ ꢁ ꢁ , Niꢁ ꢁ ꢁN, Cꢁ ꢁ ꢁN, CAHꢁ ꢁ ꢁBr or
p
CAHꢁ ꢁ ꢁN weak interactions in 1 and 2 play important roles in the
molecular stacking, and give exchange pathways of the magnetic
interaction for 1 and 2 from the structural point.
crystallographic a axis and form a column through
pꢁ ꢁ ꢁp stacking
interactions between the pyridine rings and the planes of
[Ni(mnt)2]ꢀ ions with the nearest distance of 3.645 Å between
the pyridine ring and the Ni(III) of the plane of [Ni(mnt)2]ꢀ anion
(Fig. 1b). Five weak interactions are observed between adjacent
columns (Fig. 2a and Table 3): (1) Cꢁ ꢁ ꢁN interactions of [Ni(mnt)2]ꢀ
anions with the contacts of C(1)ꢁ ꢁ ꢁN(2i) (symmetry code i = ꢀx + 2,
ꢀy + 1, ꢀz + 2) of 3.394 Å; (2) Niꢁ ꢁ ꢁN interactions of [Ni(mnt)2]ꢀ an-
ions with the contacts of Ni(1)ꢁ ꢁ ꢁN(2ii) (symmetry code ii = ꢀx + 1,
ꢀy + 1, ꢀz + 2) of 3.634 Å; (3) C(17)–H(17)ꢁ ꢁ ꢁN(3) hydrogen bond;
(4) C(18)–H(18)ꢁ ꢁ ꢁBr(1) hydrogen bond; (5) C(19)–H(19)ꢁ ꢁ ꢁN(2)
hydrogen bond. The effect of the combination of these Cꢁ ꢁ ꢁN, Niꢁ ꢁ ꢁN
short interactions and extensive CAHꢁ ꢁ ꢁN, CAHꢁ ꢁ ꢁBr hydrogen
bonds in the crystal generates a 3D network structure (Fig. 2b).
The crystal system and space group of 2 are significantly differ-
ent from those in 1. The plane of [Ni(mnt)2]ꢀ anion and the phenyl
ring of the cation are nearly parallel with the NiS4 plane of the an-
ion within the asymmetric unit cell with the dihedral angle of 2.8°.
The dihedral angles h1, h2, and h3 in [DiBrBzIQl]+ cation are 79.4°,
88.6° and 79.9° (Table 2), respectively. The [Ni(mnt)2]ꢀ anions
and [DiBrBzIQl]+ cation are alternately stacked as revealed by the
projection along the crystallographic a axis, and form a column
a
through
p p stacking interactions between the phenyl rings
ꢁ ꢁ ꢁ
and the planes of [Ni(mnt)2]ꢀ ions with the nearest distance of
3.624 Å between phenyl rings and the Ni(III) of the planes of
[Ni(mnt)2]ꢀ ions, which is different from that in 1. Weak Cꢁ ꢁ ꢁN
interactions with the shortest distance of 3.563 Å (Fig. 3a) and
extensive CAHꢁ ꢁ ꢁN hydrogen bonds (Table 3) observed between
adjacent columns of 2 generate a 3D network structure (Fig. 3b).
b
Table 3
Hydrogen bonds for 1 and 2 (Å and °).
D–Hꢁ ꢁ ꢁA
d(D–H)
d(Hꢁ ꢁ ꢁA)
d(Dꢁ ꢁ ꢁA)
<(DHA)
Compound 1
C(17)–H(17)ꢁ ꢁ ꢁN(3)#1
C(18)–H(18)ꢁ ꢁ ꢁBr(1)#2
C(19)–H(19)ꢁ ꢁ ꢁN(2)#3
0.930
0.930
0.930
2.410
2.930
2.460
3.193(8)
3.680(5)
3.290(7)
141.0
139.0
148.0
Compound 2
C(13)–H(13)ꢁ ꢁ ꢁN(1)#4
0.930
0.930
2.390
2.330
3.312(5)
3.255(5)
174.0
175.0
C(16)–H(16)ꢁ ꢁ ꢁN(4)#5
Symmetry transformations used to generate equivalent atoms: #1 = x + 1, yꢀ1, z;
#2 = x, y + 1, z; #3 = x, y, zꢀ1; #4 = ꢀx + 1, y + 1/2, ꢀz + 1/2; #5 = ꢀx + 1, y – 1/2,
ꢀz + 1/2.
Fig. 3. (a) The short anion–anion Cꢁ ꢁ ꢁN interactions and anion–cation C–Hꢁ ꢁ ꢁN
hydrogen bonds for 2. (b) The packing diagram for 2 as viewed along a axis.

Q. Huang et al. / Inorganica Chimica Acta 362 (2009) 2461–2466
2465
magnetic exchange for complexes containing [Ni(mnt)2]ꢀ anion
is very sensitive to not only the overlap fashion of neighboring
[Ni(mnt)2]ꢀ anions but also intermolecular contacts, and small
structural change can result in large changes in the materials prop-
erties of molecular solids based the [Ni(mnt)2]ꢀ anion [1,3]. There-
fore, the difference of weak interactions in crystal structures and
magnetic behaviors for 1 and 2 may also be understood.
a
1.4
1.2
1.0
0.8
0.6
4. Conclusion
In conclusion, two new molecular magnet, [DiBrBzPy[Ni(mnt)2]
(1) and [DiBrBzIQl][Ni(mnt)2] (2), have been structurally character-
ized and magnetically. The [Ni(mnt)2]ꢀ anions and the counterca-
tions of 1 and 2 are alternately stacked and form 1D column via
0
50 100 150 200 250 300
T (K)
p
ꢁ ꢁ ꢁ
p
stacking interactions. The weak Niꢁ ꢁ ꢁN, Cꢁ ꢁ ꢁN interactions
b
4.0
3.2
2.4
1.6
0.8
0.0
3.0
Tpeak=35 K
2.5
and CAHꢁ ꢁ ꢁBr, CAHꢁ ꢁ ꢁN hydrogen bonds between the adjacent col-
umns further generate a 3D network structure. Magnetic suscepti-
bility measurements for 1 and 2 indicate that two molecular solids
exhibit the typical magnetic behavior of a spin gap system.
2.0
1.5
1.0
0.5
0.0
-0.5
Acknowledgements
0
50 100 150 200 250 300
T(K)
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.
0
50 100 150 200 250 300
4
T (K)
Fig. 4. Plot of
vm versus T for 1 (a) and 2 (b) (inset: the plot d(vmT)/dT versus 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 color in this
figure legend, the reader is referred to the web version of this article.)
Appendix A. Supplementary material
CCDC-697337 and 294224 contain the supplementary crystallo-
graphic data for this paper. These data can be obtained free of
charge from the Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.
3.2. Magnetic properties and analyses
The magnetic behaviors of 1 and 2 have been determined using
polycrystalline samples under an applied field of 2000 Oe in the
temperature range 2–300 K. The results are given in Fig. 4 as
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vm = f(T) (vm is the magnetic susceptibility per nickel atom cor-
rected by the diamagnetic contribution). At 300 K, the
vmT values
of 1 and 2 are 0.294 and 0.128 emu K molꢀ1, and the values are sig-
nificantly lower than the expected for magnetically isolated Ni(III)
ions. As the temperature is lowered, compound 1 exhibits the typ-
ical magnetic behavior of a spin gap system (Fig. 4a) [23]. As shown
in Fig. 4b, upon cooling, firstly the vm values of 2 gradually increase
to a maximum at 65 K, and below the temperature the vm values
decrease abruptly to a minimum around 18 K, and finally increases
to 0.00374 emu molꢀ1 again upon further cooling to 2.0 K. It is
worthy to note that the vm values decrease exponentially around
35 K indicating that 2 undergoes a spin gap transition [24–27].
The transition is reversible without any sizable hysteresis. As
shown in the set of Fig. 4b, the transition temperature (ꢃ35 K) is
evaluated as the temperature at which the maximum of the
d(
v
mT)/dT derivative was observed.
The experimental data of 1 and 2 may be estimated by the for-
mula m = [ exp( /kBT)]/T + C/T + 0, where is a constant value
corresponding to the dispersion of excitation energy, is the mag-
nitude of the spin gap, 0 contributes from the core diamagnetism
v
a
D
v
a
[14] C.L. Ni, D.B. Dang, Y. Song, S. Gao, Y.Z. Li, Z.P. Ni, Z.F. Tian, L.L. Wen, Q.J. Meng,
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Lett. 5 (2005) 680.
D
v
and the possible Van Vleck paramagnetism, and the other symbols
[16] C.L. Ni, Z.F. Tian, Z.P. Ni, D.B. Dang, Y.Z. Li, Y. Song, Q.J. Meng, Inorg. Chim. Acta
359 (2006) 3927.
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(2005) 2680.
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(2007) 880.
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Struct. 317 (1994) 147.
have their usual meanings [28]. The best fitting yielded the param-
eters of
a
= 4.03,
D
/kb = 1151.9 K,
v
0 = ꢀ7.0 ꢂ 10ꢀ5 emu molꢀ1, C =
P
1.3 ꢂ 10ꢀ3 emu K molꢀ1 and
R
(defined as
ð
vcmalc
ꢀ
vombsd
=
2
ð
vombsdÞ Þ ¼ 5:3 ꢂ 10ꢀ5 for 1, and
a
= 0.18,
D
/kb = 73.90 K, v0
=
7.0 ꢂ 10ꢀ6 emu molꢀ1
,
C = 7.5 ꢂ 10ꢀ3 emu K mol1 and R = 5.1 ꢂ
10ꢀ6 for 2. The best fit curves are shown in the red solid lines of
[21] A. Davison, R.H. Holm, Inorg. Synth. 10 (1967) 8.
Fig. 4a and b. The theoretic studies using DFT have revealed that

2466
Q. Huang et al. / Inorganica Chimica Acta 362 (2009) 2461–2466
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5.10. Bruker Analytical X-ray Systems Inc. Madison Wisconsin, USA, 1997.
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Awaga, Z.P. Ni, J.L. Xie, Q.J. Meng, R.K. Kremer, J. Chem. Soc., Dalton Trans.
(2006) 1988.
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(2002) 408.
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(2002) 1607.
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State Chem. 168 (2002) 661.