A new quasi-one-dimensional molecular solid based on Ni(mnt)2 anion: Crystal structure and spin-gap transition

Article abstract of DOI:10.1016/j.jpcs.2006.09.016

A new molecular solid, [1-(4′-bromo-2′-fluorobenzyl)-4-dimetylaminopyridinium]-bis(maleonitriledithiolato)nickel(III), (BrFBzPyN(CH₃)₂(Ni(mnt)₂)(1), has been prepared and characterized by elemental analyses, IR, ESI-MS spe

Full text of DOI:10.1016/j.jpcs.2006.09.016

ARTICLE IN PRESS
Journal of Physics and Chemistry of Solids 68 (2007) 59–65
www.elsevier.com/locate/jpcs
A new quasi-one-dimensional molecular solid based
on Ni(mnt)2 anion: Crystal structure and spin–gap transition
Ã
Chunlin Ni , Xiaoping Liu, Linliang Yu, Lemin Yang
Department of Applied Chemistry, Centre of Inorganic Functional Materials, College of Science,
South China Agricultural University, 510642 Guangzhou, PR China
Received 22 June 2006; received in revised form 23 August 2006; accepted 8 September 2006
Abstract
A new molecular solid, [1-(40-bromo-20-fluorobenzyl)-4-dimetylaminopyridinium]-bis(maleonitriledithiolato)nickel(III), (BrFBzPyN
(CH3)2(Ni(mnt)2)(1), has been prepared and characterized by elemental analyses, IR, ESI-MS spectra, single crystal X-ray diffraction
˚
˚
and magnetic measurements. Compound 1 crystallizes in the orthorhombic space group Pnma, a ¼ 20.579(4) A, b ¼ 7.078(1) A,
3
˚
˚
c ¼ 17.942(4) A, a ¼ b ¼ g ¼ 901, V ¼ 2613.3(9) A , Z ¼ 4. The Ni(III) ions of 1 form a quasi-one-dimensional Zigzag magnetic chain
within a Ni(mnt)ꢀ2 column through Ni?S, S?S, Ni?Ni, or p?p interactions with an Ni?Ni distance of 4.227 A. Magnetic
˚
susceptibility measurements in the temperature range 2–300 K show that 1 exhibits a spin–gap transition around 200 K, and
antiferromagnetic interaction in the high-temperature phase (HT) and spin gap in the low-temperature phase (LT). The transition for 1 is
second-order phase transition as determined by DSC analyses.
r 2006 Elsevier Ltd. All rights reserved.
Keywords: A. Magnetic materials; D. Crystal structure; D. Magnetic properties
1. Introduction
benzylpyridinium derivatives as the counteraction that can
effectively mediate the magnetic coupling between the
spin carriers [Ni(mnt)2] anions, and establish a relation-
ship between the magnetic interactions and the stacking
pattern of anions or cations [10–15]. Recently, we
reported the preparation, crystal structure and magnetic
properties of a new ion-pair complex, [BrFBzPyNH2]
[Ni(mnt)2] [BrFBzPyNH2+ ¼ 1-(40-bromo-20-flurobenzyl)-
4-aminopyridinium] that exhibits interesting magnetic prop-
erties: the occurrence of significant ferromagnetic interaction
in the high-temperature phase (HT), spin–gap transition in
the low-temperature phase (LT) and weak ferromagnetism
due to spin canting below 5 K [16].With a view to obtaining
molecular solid with novel properties and to investigate
methyl groups in amino group of 4-aminopyridine, we
selected organic cation [BrFBzPyN(CH3)2]+ to tune the
crystal stacking structure of [M(mnt)2] anion, and obtained
a new quasi-one-dimensional molecular solid, (1-(40-bromo-
20-fluorobenzyl)-4-dimetylaminopyridinium)-bis(maleonitri-
ledithiolato)nickel, [BrFBzPyN(CH3)2][Ni(mnt)2](1) show-
ing a spin–gap transition around 200 K and a spin gap
below this temperature. To the best of our knowledge, the
Molecular solids based on transition metal dithiolene
complexes have attracted intense interest in recent years, not
only owing to the fundamental research of magnetic
interactions and magneto-structural correlations but also
to the development of new functional molecule-based
materials [1]. Much work has been performed in molecular
solids based on [M(mnt)2]ꢀ(mnt2ꢀ ¼ maleonitriledithiolate,
M ¼ Ni(III) or Pt(III)) ions) owing to their application as
building blocks in molecular-based materials showing
magnetic, superconducting, and optical properties [2–8].
Especially, the discovery in 1996 of the ferromagnetic
complex containing Ni(mnt)ꢀ2 ion, NH4 ꢁ Ni(mnt)2 ꢁ H2O,
strongly stimulated the study on Ni(mnt)2 complexes as
building blocks for new molecular magnets [9].The emphasis
on synthesizing these molecular solids is to search for
suitable multifunctional organic cations such as substituted
Ã
Corresponding author. Fax: +86 20 85282366.
E-mail address: niclchem@scau.edu.cn (C. Ni).
0022-3697/$ - see front matter r 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.jpcs.2006.09.016

ARTICLE IN PRESS
C. Ni et al. / Journal of Physics and Chemistry of Solids 68 (2007) 59–65
60
1D chain exhibiting a spin–gap transition above 200 K is
very rare for the Ni(mnt)2 complexes.
on F2 by full-matrix least-squares methods (SHELXL 97)
[19]. 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 are summarized in
Table 1.
2. Experimental
2.1. Synthesis
The starting materials were commercial 40-bromo-20-fluor-
obenzyl bromide (Fluka, 98%) and 4-dimetylaminopyridine
(Aldrich, 99%).1-(40-bromo-20-fluorobenzyl)-4-dimetylamino-
pyridinium bromide and disodium maleonitriledithiolate
(Na2mnt) were synthesized following the published
procedures [17,18]. (1-(40-bromo-20-fluorobenzyl)-4-dimetyla-
minopyridinium)2[Ni(mnt)2] was prepared by the direct
combination of 1:2:2 mol equiv of NiCl2 ꢁ 6H2O, Na2mnt
and 1-(40-bromo-20-fluorobenzyl)-4-dimetylaminopyridinium
bromide in water by a similar method described in the
literature [18]. (1-(40-Bromo-20-fluorobenzyl)-4-dimetylamino-
pyridinium)2[Ni(mnt)2] (960 mg, 1.0 mmol) was dissolved in
60 ml MeCN, then a MeCN solution (10 ml ) of I2 (180 mg,
0.71 mmol) was slowly added, the mixture was stirred for 4 h,
and then 80 ml MeOH was added. After the mixture was
allowed to stand overnight, 556 mg dark microcrystals
produced were filtered off, washed with MeOH and Et2O
and dried in a vacuum. Single crystals suitable for X-ray
structure analyses were obtained by evaporating solution of 1
in mixtures of MeCN and i-PrOH (1:2 v/v). Yield: 85.7 %.
Anal. Calc. for C22H15BrFN6NiS4: C, 40.70; H, 2.33; N, 12.94;
Ni, 9.04%. Found: C, 40.58; H, 2.47; N, 12.82; Ni, 8.97%. IR
(cmꢀ1): 2208.9 s, n(CN); 1487.8 s,n(CQC) of mnt2ꢀ. ESI-MS
(MeCN): 340.1, [Ni(mnt)2+H]ꢀ; 310.2, [BrFBzPyN(CH3)2]+.
3. Results and discussion
3.1. Crystal structure
The molecular structure of 1 with non-hydrogen atomic
labeling in an asymmetric unit is shown in Fig. 1a. An
asymmetric unit in a cell comprises an ion pair of
[Ni(mnt)2]ꢀ and [BrFBzPyN(CH3)2]+.The Ni(III) ion in
the [Ni(mnt)2]ꢀ anion is coordinated by four sulfur atoms
of two mnt2ꢀ ligands, and exhibits square-planar coordi-
nation geometry. All atoms of [Ni(mnt)2]ꢀ anion are in a
plane and the bond lengths and angles within the anion are
in fair agreement with those of [BrFBzPyNH2][Ni(mnt)2]
[16]. Selected bond distances, bond angles, and intermole-
cular Ni?Ni, Ni?S, and S?S distances of 1 are
summarized in Table 2. In the [BrFBzPyN(CH3)2]+
moiety, the C14-C15-N5 reference plane shares a plane
with the benzene ring, which is completely perpendicular to
the pyridine ring. Both anions and cations form segregated
stacks whose directions are parallel to the b-axis as shown
in Fig. 1b. Face-to-face overlap (Fig. 2a) involves an
anionic pair containing Ni(1) and Ni(1A) (symmetric code
A ¼ 3/2–x, ꢀy, 3/2+z), in which the distance between the
2.2. Physical measurements
The elemental analyses (C, H, and N contents) were
performed on a Model 240 Perkin Elmer C H N
instrument. Nickel content was determined using a Varian
220FS/220Z atomic absorption spectrophotometer. An
infrared spectrum was collected on an IF66 V FT-IR
(400–4000 cmꢀ1 region) spectrophotometer using KBr
pellets of the samples. DSC was carried out with a
Perkin–Elmer calorimeter, and thermal analysis of crushed
polycrystalline sample for 1 placed in an aluminum crucible
was performed on warming (rate of 20 K minꢀ1) from 100
to 300 K. Magnetic susceptibilities data on crushed
polycrystalline sample of 1 were collected over the
temperature range 2.0–300 K using a Quantum Design
MPMS-5S super-conducting quantum interference device
(SQUID) magnetometer, and the experimental data were
corrected for diamagnetism of the constituent atoms
estimated from Pascal’s constants.
Table 1
Crystallographic data for 1
Temperature (K)
Empirical formula
Crystal size (mm)
Space system
293(2)
C22H15BrFN6NiS4
0.45 ꢂ 0.38 ꢂ 0.30
Orthorhombic
649.27
Formula weight
Space group
Unit cell dimensions
Pnma
˚
a(A)
20.579(4)
7.078(1)
˚
b(A)
˚
c(A)
17.942(4)
2613.3(9), 4
1.650
3
Volume (A ), Z
˚
Density (g cmꢀ3
)
˚
l (A)
0.71073
2y range (1)
3.96o2yo50.0
2.622
12628
m (Mo Ka)(mmꢀ1
)
Reflection collected
Unique reflection, Rint
Goodness of fit on F2
Observed data [I42s(I)]
R1
2508, 0.080
1.008
1783
2.3. Determination of crystal structure
The intensity data of the Ni(III) complex 1 were
collected using a Siemens SMART CCD area detector
0.0362, 0.0580
0.0686, 0.0730
0.45, ꢀ0.39
wR2
˚
(Mo–Ka radiation, l ¼ 0.71073 A) at 293 K. The structure
ꢀ3
˚
Largest diff peak and hole (eA
)
was solved by direct method using SHELXS 97 and refined

ARTICLE IN PRESS
C. Ni et al. / Journal of Physics and Chemistry of Solids 68 (2007) 59–65
61
(a)
(b)
Fig. 1. (a) ORTEP plot (30% probability ellipsoids) showing the molecule structure of complex 1. (b) The packing diagram of a unit cell for 1 as viewed
along b-axis.
˚
˚
3.699 A, respectively) (Fig. 3a). The most interesting fact
Ni ions is 4.227 A and the nearest Ni?S and S?S contacts
˚
˚
have 3.618 A and 3.714 A, respectively. Therefore, the
Ni(III) ions form a quasi-one-dimensional zigzag uniform
magnetic chain within a Ni(mnt)ꢀ2 column through Ni?S,
S?S, Ni?Ni, or p ꢁ ꢁ ꢁ p interactions (Fig. 2b). In a
cationic column, the adjacent cations are stacked and form
a quasi-one-dimensional column through weak p?p
stacking interactions among the phenyl rings of neighbor-
ing cations (the contact distances of C(9)?C(11),
C(10)?C(11), and C(10)?C(12) are 3.582, 3.631,
in 1 is that the four columns of cations create a cubic-like
large channel (extending along the crystallographic
b-direction) (Fig. 3b) in which the Ni(mnt)ꢀ2 columns are
located (Fig. 1b). This geometry and stacking pattern for
[BrFBzPyN(CH3)2]+ in 1 are significantly different from
those of [BrFBzPyNH2][Ni(mnt)2] [16], and it is very rare in
the conformation of cation for the Ni(mnt)ꢀ2 complexes.
Because the cationic columns mediate the anionic columns,
˚
the shortest intercolumn Ni?Ni distance of 12.373 A is

ARTICLE IN PRESS
C. Ni et al. / Journal of Physics and Chemistry of Solids 68 (2007) 59–65
62
Table 2
Selected bond parameters and intermolecular contacts for 1
significantly greater than the intracolumn distance. As a
result, 1 is a quasi-one-dimensional magnetic chain system
from the point of view of the structure analysis. It is worth
noting that two intermolecular hydrogen bonds between
anions and cations were observed in the crystal structure of
1 as listed in Table 3. The anion–anion, anion–cation, and
cation–cation contacts may play important roles in the
crystal packing and stabilizing of 1.
˚
Bond distances (A)
Ni(1)–S(1)
Ni(1)–S(2)
Ni(1)–S(3)
Ni(1)–S(4)
S(1)–C(2)
S(2)–C(3)
S(3)–C(6)
S(4)–C(7)
2.139(1)
2.146(1)
2.138(1)
2.139(1)
1.726(4)
1.705(4)
1.713(5)
1.700(5)
3.2. Magnetic property
Bond angles (1)
S(1)–Ni(1)–S(2)
S(1)–Ni(1)–S(4)
S(2)–Ni(1)–S(3)
S(3)–Ni(1)–S(4)
92.31(4)
88.06(4)
87.65(4)
91.98(4)
The temperature dependence of the magnetic suscept-
ibility for 1 is measured under an applied field of 2000 Oe in
a temperature range 2–300 K. The plots of wm versus T and
wmT versus T for 1 are shown in Fig. 4, where wm is the
magnetic susceptibility per nickel atom corrected by the
diamagnetic contribution. The overall magnetic behavior
of 1 corresponds to a paramagnetic system with an
antiferromagnetic coupling interaction. The wmT value at
300 K is only 0.250 emu K molꢀ1, which is significantly
˚
Intrachain distances (A)
Ni?Ni (nearest separation)
Ni?S
S?S
4.227
3.681
3.714
˚
Interchain distances (A)
Ni?Ni (nearest separation)
12.373
(a)
(b)
Fig. 2. (a) Mode of overlapping of [Ni(mnt)2]ꢀ anions for 1. (b) The chain of [Ni(mnt)2]ꢀ anions with equal Ni?Ni distances viewing along the b-axis.

ARTICLE IN PRESS
C. Ni et al. / Journal of Physics and Chemistry of Solids 68 (2007) 59–65
63
2.5
0.8
T = 201.4 K
2.0
1.5
1.0
0.5
0.0
0.6
0.4
0.2
0.0
0
50 100 150 200 250 300
T (K)
(a)
0
50
100
150
200
250
300
(a)
T (K)
0.30
0.25
0.20
0.15
0.10
0.05
0.00
0
50
100
150
200
250
300
(b)
T (K)
Fig. 4. (a) Plot of wm versus T for 1 (inset: plot of d(wmT)/dT versus T).
The solid lines are reproduced from the theoretic calculations and detailed
fitting procedure described in the text. (b) Plot of wmT versus T for 1.
(b)
Fig. 3. (a) The 1D column of cations through weak p?p stacking
interactions. (b) The cubic-like channel formed by four columns of cations
along the crystallographic b-direction.
d(wmT)/dT derivative, that is, ꢃ200 K for 1 (inset of
Fig. 4a). It is very rare for Ni(mnt)2 complexes with a
spin–gap transition above 200 K [24,25]. The magnetic
susceptibility for 1 may be simulated by the formula [26]:
Table 3
˚
Hydrogen bonds for 1 (A and 1)
D–H ꢁ ꢁ ꢁ A
d(D–H) d(H?A) d (D?A) o(DHA)
wm ¼ a expðꢀD=kbTÞ=T þ C=T þ w0,
C(10)–H(10) ꢁ ꢁ ꢁ N(2)#1 0.93
C(19)–H(19C) ꢁ ꢁ ꢁ N(1)#2 0.96
2.48
2.62
3.398(6)
3.552(5)
169.0
165.0
where a is a constant corresponding to the dispersion of
excitation energy, D is the magnitude of the spin gap, kb is
the Boltzmann constant, C is a constant corresponding to
the contribution of the magnetic impurity, w0 contributes
from the core diamagnetism and the possible Van Vleck
paramagnetism. A reasonable fit to the data within the
range of 2–200 K for 1 are shown in Fig. 4(a) (the solid
line), and the corresponding parameters are given as
Symmetry transformations used to generate equivalent atoms: #1 ¼ x+1/2,
ꢀy+1/2, ꢀz+1/2; #2 ¼ ꢀx+3/2, ꢀy, z+1/2.
lower than the spin-only value expected for a S ¼ 1/2
Ni(III) system (0.375 emu K molꢀ1). When the temperature
decreases, the value of wm slightly decreases. Below around
200 K, the wm values decrease exponentially (Fig. 4a),
indicating that 1 exhibits the characteristics of a spin gap
system [20–23]. On increasing the temperature from 2 K
back to 300 K, the same wmꢀT curves are obtained without
hysteresis that indicates that complex 1 undergoes a
reversible spin transition. The spin transition temperature
is evaluated as the temperature at the maximum of the
follows:
w0 ¼ 1.0 ꢂ 10ꢀ5 emu molꢀ1
a ¼ 4.88,
D/kb ¼ 755.31 K,
,
C ¼ 3.1 ꢂ 10ꢀ4 emu K molꢀ1
,
P
and R ¼ 5.3 ꢂ 10ꢀ6 (R is defined as
((wmcꢀalcdwmobsd)2/
(wmobsd)2). Magnetic impurity from the uncoupled
Ni(mnt)ꢀ2 anions was estimated as 0.083%, based on the
C value. The value of the parameter 2D/kbTc (Tc is the
transition temperature) is estimated to be 7.51 for 1, which

ARTICLE IN PRESS
C. Ni et al. / Journal of Physics and Chemistry of Solids 68 (2007) 59–65
64
ꢀ
˚
with the Ni?Ni distance being 4.227 A in the Ni(mnt)2
stacking column by intermolecular Ni?S, S?S, Ni?Ni,
or p?p interactions at room temperature. The measure-
ment of the temperature dependence of the magnetic
susceptibility reveals that the title complex undergoes a
spin–gap transition around 200 K, and exhibits antiferro-
magnetic interaction in the HT and spin gap in the LT. The
spin–gap transition is a second-order phase transition as
determined by DSC analyses.
30
24
18
12
6
5. Supplementary materials
Supplementary crystallographic data are available from
the Cambridge Crystallographic Data Center, CCDC No.
601745. 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; depos-
it@ccdc.cam.ac.uk or http://www.ccdc.cam.ac.uk).
0
80
120
160
200
240
280
320
T (K)
Fig. 5. DSC plot for 1.
is higher than the ideal value of 3.53 derived from the BCS
formula in a weak coupling regime. This result thus
indicates that the spin transition is not a pure spin-Peierls
transition [16], and are attributed to the cooperative
interactions of Ni?S bonding, interplane repulsion of
the [Ni(mnt)2]ꢀ anions, p?p stacking interactions between
adjacent cations, spin–lattice interactions and spin–spin
coupled interaction between nearest-neighbor anions
[27–29].
Acknowledgments
We thank financial support from the president’s science
foundation of South China Agricultural University
(No. 2005K092).
References
[1] N. Robertson, L. Cronin, Coord. Chem. Rev. 227 (2002) 93.
[2] Z.P. Ni, X.M. Ren, J. Ma, J.L. Xie, C.L. Ni, Z.D. Chen, Q.J. Meng,
J. Am. Chem. Soc. 127 (2005) 143301.
Thermodynamic property of the phase transition for 1
was determined, and the power-compensated DSC trace
for 1 from 100 to 300 K at a warming rate of 20 K minꢀ1 is
displayed in Fig. 5. No detectable endothermic peak in the
corresponding temperature region was observed, indicating
that the spin–gap transition of 1 is a second-order phase
transition [11,13].
As for complexes containing Ni(mnt)ꢀ2 anion, previous
studies have shown that the magnetic coupling between
Ni(mnt)ꢀ2 anions is very sensitive to not only the overlap
fashion of neighboring Ni(mnt)ꢀ2 anions but also inter-
molecular contacts, and small structural change can result
in large changes in the material properties of the Ni(mnt)2ꢀ
complexes [3,4]. The theoretic studies using DFT have also
revealed that magnetic exchange nature depend highly on
the interplane distance (d) and the rotation angle (y) [2].
Therefore, the magnetic behavior for 1 different from
[BrFBzPyNH2][Ni(mnt)2] [16] may be understood as
below, on the temperature being 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.
[3] J. Nishijo, E. Ogura, J. Yamaura, A. Miyazaki, T. Enoki, T. Takano,
Y. Kuwatani, M. Iyoda, Solid State Commun. 116 (2000) 661.
[4] N. Robertson, C. bergemann, H. Becher, P. Agarwal, S.R. Julian,
R.H. Friend, N.J. Hatton, A.E. Underhill, A. Kobayashi, J. Mater.
Chem. 9 (1999) 1713.
[5] A.E. Pullen, C. Faulmann, K.I. Pokhodnya, P. Cassoux, M.
Tokumoto, Inorg. Chem. 37 (1998) 6714.
[6] M. Urichi, K. Yakushi, Y. Yamashita, J. Qin, J. Mater. Chem. 8
(1998) 141.
[7] J.F. Weiher, L.R. Melby, R.E. Benson, J. Am. Chem. Soc. 86 (1964)
4329.
[8] P.I. Clemenson, A.E. Underhill, M.B. Hursthouse, R.L. Short,
J. Chem. Soc. Dalton Trans. (1988) 1689.
[9] A.T. Coomber, D. Beljonne, R.H. Friend, J.L. Bredas, A. Charlton,
´
N. Robertson, A.E. Underhill, M. Kurmoo, P. Day, Nature 380
(1996) 144.
[10] J.L. Xie, X.M. Ren, Y. Song, Y. Zou, Q.J. Meng, J. Chem. Soc.
Dalton Trans. (2002) 2868.
[11] X.M. Ren, Q.J. Meng, Y. Song, C.S. Lu, C.J. Hu, Inorg. Chem.
41 (2002) 5686.
[12] J.L. Xie, X.M. Ren, S. Gao, W.W. Zhang, Y.Z. Li, C.S. Lu, C.L. Ni,
W.L. Liu, Q.J. Meng, Y.G. Yao, Eur. J. Inorg. Chem. (2003) 2393.
[13] J.L. Xie, X.M. Ren, C. He, Y. Song, Q.J. Meng, R.K. Kremer,
Y.G. Yao, Chem. Phys. Lett. 369 (2003) 41.
[14] X.M. Ren, Q.J. Meng, Y. Song, C.L. Lu, C.J. Hu, X.Y. Chen,
Z.L. Xue, Inorg. Chem. 41 (2002) 5931.
[15] J.L. Xie, X.M. Ren, Y. Song, W.W. Zhang, W.L. Liu, C. He,
Q.J. Meng, Chem. Commun. (2002) 2346.
4. Conclusion
[16] 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, Chem. Phys. Lett. 396 (2004) 353.
[17] S.B. Bulgarevich, D.V. Bren, D.Y. Movshovic, P. Finocchiaro,
S. Failla, J. Mol. Struct. 317 (1994) 147.
In conclusion, we present a new molecular solid
containing Ni(mnt)ꢀ2 anion in which the anions in solid
state form completely segregated uniform stacking columns
[18] A. Davison, R.H. Holm, Inorg. Synth. 10 (1967) 8.

ARTICLE IN PRESS
C. Ni et al. / Journal of Physics and Chemistry of Solids 68 (2007) 59–65
65
[19] G.M. Sheldrick, SHELXTL, Structure Determination Software
Programs, Version 5.10. Bruker Analytical X-ray Systems Inc.
Madison, Wisconsin, USA, 1997.
[24] C.L. Ni, Y.Z. Li, D.B. Dang, Z.P. Ni, Z.F. Tian, Z.R. Yuan, Q.J.
Meng, Inorg. Chem. Commun. 8 (2005) 105.
[25] D.B. Dang, C.L. Ni, Y. Bai, Z.F. Tian, Z.P. Ni, L.L. Wen, Q.J.
Meng, S. Gao, Chem. Lett. 5 (2005) 680.
[20] Y. Fujii, T. Goto, W. fujita, K. Awaga, Pysica B 329–333 (2003) 973.
[21] C. Yasuda, S. Todo, M. Matsumoto, H. Takayama, J. Phys. Chem.
Solids 63 (2002) 1607.
[26] L.C. Isett, D.M. Rosso, G.L. Bottger, Phys. Rev. B 22 (1980) 4739.
[27] S. Alvarez, R. Vicente, R. Hoffman, J. Am, Chem. Soc. 107 (1985)
6253.
[22] S. Nishihara, T. Akutagawa, T. Hasegawa, T. Nakamura, Chem.
Comm. (2002) 408.
[28] E. Pytte, Phys. Rev. B 10 (1974) 4637.
[29] M.E. Itkis, X. Chi, A.W. Cordes, R.C. Haddon, Science 296 (2002)
1443.
[23] S. Nishihara, T. Akutagawa, T. Hasegawa, S. Fujiyama, T.
Nakamura, J. Solid State Chem. 168 (2002) 661.