A one-dimensional nickel(III) chain complex showing ferromagnetic ordering: Crystal structure and magnetic property

Article abstract of DOI:10.1246/cl.2002.576

A ferromagnetic complex [BrFBzPy][Ni(mnt)₂], where [BrFBzPy]⁺ = 1-(4′-bromo-2′-fluorobenzyl)pyridinium and mnt^2-= maleonitriledithiolate, has been prepared. The [Ni(mnt)₂]^- anions and [BrFBzPy]⁺ cations form a well-separated stacking column and [Ni(mnt)₂]^- anions are uniformly spaced to give a one-dimensional (1-D) chain structure. Its magnetization studies shown it ferromagnetically ordered around 2 K.

Full text of DOI:10.1246/cl.2002.576

576
Chemistry Letters 2002
A One-dimensional Nickel(III) Chain Complex Showing Ferromagnetic Ordering: Crystal
Structure and Magnetic Property
Jingli Xie, Xiaoming Ren, Song Gao,y and Qingjin MengÃ
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 February 13, 2002; CL-020146)
A
ferromagnetic complex [BrFBzPy][Ni(mnt)2], where
The anion and cation possess the stacking structure with well-
separated column along the direction of c axis (Figure 1a). When the
Ni...Ni separation between anion chains is of the same magnitude as
the distance of the Ni...Ni separation within a anion chain and
interchain interaction becomes appreciable, 1-D character are
damped.11 The nearest S...S, S...Ni and ÀNi...Ni distances are of 3.73,
[BrFBzPy]þ ¼ 1-(40-bromo-20-fluorobenzyl)pyridinium
and
mnt2À ¼ maleonitriledithiolate, has been prepared. The
[Ni(mnt)2]À anions and [BrFBzPy]þ cations form a well-separated
stacking column and [Ni(mnt)2]À anions are uniformly spaced to
give a one-dimensional (1-D) chain structure. Its magnetization
studies shown it ferromagnetically ordered around 2 K.
ꢀ
3.63 and 3.96 A within the [Ni(mnt)2] anion chain, respectively.
...
ꢀ
While the closest inter-chain Ni Ni separation (11.89 A) is
significantly longer than intra-chain one (Figure 1b). Moreover,
the magnetic interaction between two anion columns separated by a
sizable diamagnetic cation column is generally weak. The cations
also form a 1-D chain through the Br-ꢀ interactions between Br
atoms and adjacent benzene rings similar to some complexes.12
Therefore, this complex is a 1-D magnetic chain system.
Widespread attention has been paid on one-dimensional (1-D)
compounds because they show novel physical properties such as
Peierls transition, spin-Peierls transition, charge-density-wave
states, spin-density-wave states, molecular bistabilities, etc.1{4 1-
D transition metal complexes containing [M(mnt)2]À (M ¼ Ni(III),
Pd(III) or Pt(III), mnt2À ¼ maleonitriledithiolate) ions have been
studied extensively. In these complexes, the constituent planar
molecules [M(mnt)2]À form columnar stack structures, in which
intermolecular dz2 or ꢀ orbital interaction results in 1-D electronic
nature.5;6 We have developed
a new class of complexes
[RBzPy]þ[Ni(mnt)2]À ([RBzPy]þ ¼ benzylpyridinium deriva-
tive).7 Here we report the crystal structure and magnetic properties
of
a
1-D chain [BrFBzPy]þ[Ni(mnt)2]À ([BrFBzPy]þ
¼
1-(40-bromo-20-fluorobenzyl)pyridinium) complex, which is ferro-
magnetically ordered around 2 K.
Firstly, [BrFBzPy]2[Ni(mnt)2] was prepared by the direct
combination of 1 : 2 : 2 mol ratio of NiCl2Á6H2O, Na2mnt and
[BrFBzPy]Br in H2O. Then, the title complex was prepared by
oxidation of the [BrFBzPy]2[Ni(mnt)2] by I2,8 good shaped single
crystals were obtained by dispersing Et2O into MeCN solution of
the complex about a week. Diffraction data were collected on a FR
590 CAD4 diffractometer equipped with graphite-monochromated
Mo Kꢁ radiation. Magnetic data on powder-sample were collected
over the temperature range of 1.8–300 K using a Quantum Design
MPMS-5S superconducting quantum interference device (SQUID)
magnetometer (the molar diamagnetic contributions of the
molecule is À3:04 Â 10À4 emuÁmolÀ1).
Figure 1. a) The packing diagram of
a
unit cell of
[BrFBzPy]þ[Ni(mnt)2]À viewed along the c axis. b) The side view of
1-D anion chain for [BrFBzPy]þ[Ni(mnt)2]À.
Figure 2a shows its magnetic properties, in which ꢂm is the
molar magnetic susceptibility. The value of ꢂmT at 300 K is
estimated at 0.412 emuÁKÁmolÀ1, and slightly larger than that of
spin-only of one s ¼ 1=2 spin per formula unit. The ꢂmT values
increase with the temperature decreasing and reach a maximum at
3.7 K (ꢂmT ¼ 2:55 emuÁKÁmolÀ1). These results demonstrate the
presence of ferromagnetic exchange interaction between the
localized spins. When the temperature is below 3.7 K, the ꢂmT
values decrease and drop to 1.58 emuÁKÁmolÀ1 at 1.82 K. From
these results, short-range ferromagnetic correlation is present in this
1-D chain system, and it may develop into a long range ordering
The X-ray structure of title complex has been characterized9
and the Ni(III) ion is co-ordinated to four sulfur atoms of two mnt2À
ligands, exhibiting square-planar coordination geometry. The CN
groups of mnt2À ligand are bent away from the coordinating plane
defined by four sulfur atoms and the five-membered nickel-
containing rings are slightly puckered, as have been found with
other [M(mnt)2]nÀ structures.10 The average S–Ni–S bond angle
within the five-membered ring is 92.6 ꢀ, and the average Ni–S bond
ꢀ
distance is 2.14 A, these values are in agreement with that of
[Ni(mnt)2]À complexes reported.7
Copyright Ó 2002 The Chemical Society of Japan

Chemistry Letters 2002
577
state in low temperature.
1. Below 5 K, the ꢂFCT
SeffðTÞ ¼ À
From its ac susceptibility measurements, ꢂ0 show a maximum
around 2 K indicating that the magnetic ordering may occur, and the
nonzero ꢂ00 was also observed below 2 K (inset of Figure 2a).
Ferromagnetic ordering is demonstrated further by the field
dependence of isothermal magnetization performed at 2 K, 5 K
and 10 K, respectively (Figure 2b). The magnetization at 2 K
increases very rapidly in low field, and reaches the saturation value
of ca. 5400 emuÁGÁmolÀ1 at 50 kOe, which agree well with the
theoretical saturation value of a S ¼ 1=2, g ¼ 2 system(Ni(III) is in
low spinstate). The rapid riseand approach to saturationin theM(H)
data is typical for long range ferromagnetic coupling around 2 K. On
the contrary, the magnetization at 5 K and 10 K increases slowly as
magnetic field increases. Cycling the applied field between þ5 kOe
and À5 kOe at 2 K, an observable hysteresis loop characteristic of
ferromagnetic behavior arises and it is so small that it seem to
intersect at 0 Oe (inset of Figure 2b). Similar phenomenon has been
reported by K. Hashimoto.13
pffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
1
2
1
2
ð2Þ
þ
1 þ 8ꢂFCT
values are quite large (ꢂFCT > 2:3) so that the Seff value derived
from eq 2 is large enough (Seff > 1:7) to be treated as a classic
spin.15 So the classic spin model (eq 3) derived by Fisher16 was used
to treat the magnetic susceptibility (ꢂ2D) of this ‘‘chain of chains’’
model. From modified eq 3, the full fitting
Ng2ꢃ2
3kT
ð1 þ uÞ
ð1 À uÞ
ꢂm ¼
Seff ðSeff þ 1Þ
ð3Þ
u ¼ coth½JeffSeffðSeff þ 1Þ=kTꢁ À kT=SeffðSeff þ 1Þ
parameters are as following: g ¼ 2:09, J ¼ 42:2 cmÀ1, geff ¼ 2:0
(fixed), Jeff ¼ À4:78 cmÀ1, R ¼ 6:4 Â 10À5 (cf. Figure 2a). The
sign of fitting results indicated that there exist ferromagnetically
coupled interactions within [Ni(mnt)2]À anion chain, and anti-
ferromagnetically coupled interactions between [Ni(mnt)2]À anion
chains.
In conclusion, to our best knowledge, the uniformly spaced 1-D
chain complex with ferromagnetism is rare for [Ni(mnt)2]À anion.
The origin of the ferromagnetic interactions is similar to previous
reports on (EDO-TTFI2)M(mnt)2(M ¼ Ni, Pt).5 The orthogonality
of the molecular orbitals suppresses the antiferromagnetic interac-
tion between spin localized on the Ni(mnt)2 molecules. Moreover,
ferromagnetic interactions arise from the spin polarization effect
(McConnell’s theory17) between large positive spin densities on the
Ni(III) ions and small negative spin densities on the S atom of
adjacent [Ni(mnt)2]À ions.
We thank the National Nature Science Foundation of China for
financial support.
References and Notes
´
1
2
3
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Figure 2. a) Plots of ꢂmTðÃÞ of [BrFBzPy]þ[Ni(mnt)2]À measured
at 5 kOe field. The solid line represents the best fit. Inset: ac
susceptibility obtained at zero external magnetic field. b) M-H plot at
2 K, 5 K and 10 K. Inset: Small hysteresis loop exhibited for
[BrFBzPy]þ[Ni(mnt)2]À at 2 K.
6
7
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8
9
In the temperature range 5–300 K, the ꢂmT data was fitted by
the Baker equation14 (expression 1) to give g ¼ 2:09,
J ¼ 42:2 cmÀ1, TIP ¼ 3:7 Â 10À4 emuÁmolÀ1 with a final agree-
Crystallographic data of [BrFBzPy][Ni(mnt)2] are: C20H10BrFN5NiS4, mono-
ꢀ
clinic, P21=c, fw ¼ 606:19, a ¼ 11:989ð2Þ, b ¼ 26:363ð5Þ, c ¼ 7:4860ð15Þ A,
P
ꢀ
ꢀ 3
ꢃ ¼ 101:63ð3Þ , V ¼ 2317:5ð8Þ A , Z ¼ 4, dcalc ¼ 1:737 g cmÀ3, T ¼ 273 K,
2
ment factor R ¼ 3:7 Â 10À5 ½R ¼ ðꢂmTobs À ꢂmTcalcÞ =
P
R ¼ 0:079 [I > 2ꢄðIÞ], and 4022 independent reflections.
2
ðꢂmTobsÞ ].
10 K. W. Plumlee, B. M. Hoffman, and J. A. Ibers, J. Chem. Phys., 63, 1926 (1975).
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c) the coefficients are: C ¼ 1:0 þ 5:7979916y þ 16:902653y2 þ 29:376885y3þ
ꢀ
ꢁ
2=3
Ng2ꢃ2
4kT
C
D
¨¨
ꢂm ¼
ð1Þ
y ¼ J=2kT
Moreover, a two-dimensional model involving a ‘‘chain of
chains’’15 was attempted to fit the data from 300 K to 3 K. In this
model, at a given temperature, an effective total spin associated with
each chain in the structure, Seff, can be calculated as eq 2, where ꢂFC
is the susceptibility calculated for the ferromagnetic chain from eq
29:832959y4 þ 14:036918y5,
8:653644y3 þ 4:5743114y4.
D ¼ 1:0 þ 2:7979916y þ 7:0086780y2þ
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