The first one-dimensional molecular material featuring maleonitriledithiolate as a subunit exhibiting metamagnetic-like behavior

Article abstract of DOI:10.1002/ejic.200300108

An ion-pair complex [FBzPyNH₂][Ni(mnt)₂] {[FBzPyNH₂]⁺ = [1-(4′-fluorobenzyl)-4-amino]pyridinium and mnt^2- = maleonitriledithiolate} has been obtained by 12 oxidation of the corresponding dianion compl

Full text of DOI:10.1002/ejic.200300108

SHORT COMMUNICATION
The First One-Dimensional Molecular Material Featuring
Maleonitriledithiolate as a Subunit Exhibiting Metamagnetic-Like Behavior
Jingli Xie,[a] Xiaoming Ren,[a] Song Gao,[b] Wenwei Zhang,[a] Yizhi Li,[a] Changsheng Lu,[a]
Chunlin Ni,[a] Wenlong Liu,[a] Qingjin Meng,*[a] and Yuangen Yao[c]
Keywords: Nickel / Maleonitriledithiolate / Crystal structure / Magnetic properties
An ion-pair complex [FBzPyNH2][Ni(mnt)2] {[FBzPyNH2]+
[1-(4Ј-fluorobenzyl)-4-amino]pyridinium and
mnt2−
=
=
exhibits antiferromagnetic ordering below 2.5 K. It is the first
complex in this series of complexes containing a maleo-
maleonitriledithiolate} has been obtained by I2 oxidation nitriledithiolate dianion that exhibits metamagnetism.
of the corresponding dianion complex. It forms a well-
segregated stacking column structure in the solid state, and
( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2003)
Introduction
columns. A study of its magnetic properties shows anti-
ferromagnetic ordering below 2.5 K and metamagnetic-
like behavior.
Much effort has been devoted to the study of square-
planar M(dithiolene)2 complexes in the areas of conducting
and magnetic materials, dyes, non-linear optics and cataly-
sis.[1,2] Recently, we have employed a strategy of con-
structing one-dimensional molecule-based magnets based
on ion-pair complexes containing [M(mnt)]Ϫ (M ϭ NiIII
,
PtIII; mnt2Ϫ ϭ maleonitriledithiolate) anions with benzyl-
pyridinium derivatives as counterions. Interestingly, varying
the counterions led to a broader palette of complexes with
markedly different magnetic-exchange properties, although
they all have extremely similar molecular and stacking
structures. Versatile magnetic properties such as ferromag-
netic ordering at 2 K, unusual magnetic transitions from
ferromagnetic coupling to diamagnetism or from paramag-
netic to diamagnetic, or spin-Peierls-like transitions have
been witnessed.[3] In order to further understand the mag-
netic coupling mechanism in this series of complexes, we
should explore the relationship between stacking structures
and magnetic properties systematically. Within this frame-
work, we report the synthesis and crystal structure of an
ion-pair complex [1-(4Ј-fluorobenzyl)-4-aminopyridinium]-
[Ni(mnt)2] (Scheme 1), which has well-segregated stacking
Scheme 1. Molecular structure of 2
Results and Discussion
[FBzPyNH2]2[Ni(mnt)2] (1) was prepared by the direct
combination of NiCl2·6H2O, Na2mnt and [1-(4Ј-fluoro-
benzyl)-4-amino]pyridinium chloride in H2O in a 1:2:2 mo-
lar ratio. The title complex 2 was prepared by I2 oxidation
of 1,[4] and well-shaped single crystals were obtained by al-
lowing Et2O to diffuse into an MeCN solution of 2 for
about a week. Figure S1 depicts the molecular structure of
2. The coordination geometry of NiIII is square planar with
four sulfur donor atoms; the NiϪS bond lengths and
SϪNiϪS bond angles are in agreement with reported val-
ues.[3] The CN groups of the mnt2Ϫ ligand are bent away
from the plane defined by the Ni atom and four sulfur
atoms. The deviation of the four terminal N atoms from
[a]
State Key Laboratory of Coordination Chemistry,
Coordination Chemistry Institute, Nanjing University,
210093 Nanjing, P. R. China
˚
˚
˚
˚
the plane are 0.2926 A, 0.3666 A, 0.0802 A and 0.1736 A,
respectively. In the [FBzPyNH2]ϩ cation, the dihedral
angles between the C(15)ϪC(14)ϪN(5) reference plane and
the aryl rings are 80.5° for the phenyl ring and 106.6° for
the pyridine ring; these values are in line with previous re-
sults.[3] It should be noted that 2 possesses well-segregated
stacking column along the c-axis (Figure 1a). Within an
anion column, there exists a slipped nickel-over-sulfur con-
Fax: (internat.) ϩ86-25/331-4502
E-mail: njujlxie@yahoo.com
[b]
State Key Laboratory of Rare Earths Materials Chemistry and
Applications, College of Chemistry and Molecular Engineering,
Peking University, Beijing 100871 P. R. China
[c]
State Key Laboratory of Structural Chemistry, Fujian Institute
of Research on the Structure of Matter,
350002 Fuzhou, P. R. China
Supporting information for this article is available on the
WWW under http://www.eurjic.org or from the author.
Eur. J. Inorg. Chem. 2003, 2393Ϫ2396
DOI: 10.1002/ejic.200300108
 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
2393

Q. Meng et al.
SHORT COMMUNICATION
figuration of [Ni(mnt)2]Ϫ anions and the Ni···Ni distances
˚
between adjacent anions are identical (3.991 A); the nearest
˚
˚
S···S, S···Ni contacts are 3.797 A and 3.663 A, respectively.
These distances are larger than the sum of the van der
Waals radii of the corresponding atoms. The closest Ni···Ni
˚
separation between anion chains is 14.32 A, which is signifi-
cantly larger than the Ni···Ni separation within a chain.
Therefore, each [Ni(mnt)2]Ϫ anion column can be con-
sidered as a one-dimensional (1-D) magnetic chain from the
viewpoint of the crystal structure (Figure 1b). The
[FBzPyNH2]ϩ cations orient themselves in the solid state.
The pyridine rings of the neighboring cations are essentially
parallel to each other with an identical center-center
˚
Figure 2. Temperature dependence of χmT for 2 measured at 10
KOe; inset: temperature dependence of χm for 2 measured at 500 Oe
distance of 3.893 A (Figure S2).
(1)
A fit of the data to Equation (1) gives J ϭ Ϫ6.8 cmϪ1
and g ϭ 2.0 (fixed), which suggests there exists weak anti-
ferromagnetic coupling between adjacent S ϭ 1/2 NiIII spin
carriers within the anion chain. The χm/T curve at 500 Oe
field shows a sharp cusp at 2.5 K, suggesting a long-range
antiferromagnetic (AF) ordering (inset of Figure 2). The M
vs. H curve at 1.8 K exhibits a sigmoidal shape, indicating
a metamagnetic-like behavior (Figure 3), which switches
from an antiferromagnetic ground state to a ferrimagnetic-
like state upon the application of a large enough field. At
1.8 K, the critical field is approximately 1000 Oe because
the derivative dM/dH has an extremum (Figure S3). The
saturation magnetization of 2 at 1.8 K (the higher applied
magnetic field is 7 T) is 1310 emu·G·molϪ1, far from the
theoretical saturation value of 5585 emu·G·molϪ1, which is
usual in metamagnetic material if the temperature is not
much lower than TN.[7,8] The AF transition is further mani-
fested by the in-phase signal (χЈ) of zero-field ac magnetic
susceptibility, which has a maximum at about 2.5 K (TN).
No out-of-phase signal (χЈЈ) could be detected and their is
no frequency dependence, thus excluding any ferromagnetic
Figure 1. (a) Structure of anions and cations of 2 viewed along the
c-axis; (b) side view of the 1-D anion chain of 2 (symmetry codes:
A ϭ x, 1.5 Ϫ y, 0.5 ϩ z; B ϭ x, 1.5 Ϫ y, Ϫ0.5 ϩ z; C ϭ x, y, z ϩ 1)
The thermal variation of χmT, measured at a field of 1 T,
is shown in Figure 2. The observed χmT value at 308 K is
0.331 emu·K·molϪ1, slightly less than the theoretical value
of 0.375 emu·K·molϪ1 expected for a spin-only NiIII ion
with S ϭ 1/2 and g ϭ 2.0. Upon cooling down, the χmT
values decreases smoothly and reaches a minimum of 0.223
emu·K·molϪ1 at 24 K. This behaviour is characteristic of
ferrimagnetic-like behavior. With a further decrease in
temperature, the χmT values increase abruptly, reaching
a maximum of 0.343 emu·K·molϪ1 at 7.2 K, before
decreasing again. The data above 24 K are best fit by
the BonnerϪFisher model for
a uniformly spaced
chain of atoms with S ϭ 1/2 spin.[5] Equation (1) for H ϭ
Figure 3. M-H curve of 2 measured at 1.8 K; inset: enlargement of
the applied magnetic field range 0Ϫ20000 Oe
[6]
Ϫ2JS1·S2 with z ϭ J/kBT.
2394
 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Eur. J. Inorg. Chem. 2003, 2393Ϫ2396

One-Dimensional Molecular Material
SHORT COMMUNICATION
V ϭ 2296.7(6) A , Z ϭ 4, Dc ϭ 1.568 g cmϪ3, µ(Mo-Kα) ϭ 1.237
3
˚
phase or spin-glass behavior (Figure S4). The FCM curves
of 2 measured at lower fields (200 Oe and 1000 Oe) both
show a maximum in χm at about 2.5 K (Figure S5), suggest-
ing long-range magnetic ordering, whereas a higher field
(5000 Oe) leads to the absence of the peak down to 2.0 K
(inset of Figure S5).
Of all the commonly studied dithiolate systems, metam-
agnetism has been observed in some charge-transfer salts
such as [Fe(Cp*)2][Ni(edt)2] (edt ϭ ethylenedithiolate),
mmϪ1, λ ϭ 0.71073 A, Ϫ14 Յ h Յ 14, Ϫ31 Յ k Յ 22, Ϫ8 Յ l Յ
˚
8. A crystal of dimensions 0.20 ϫ 0.15 ϫ 0.10 mm3 was selected
for indexing and intensity data collection at 298 K. Data collection:
SMART (Bruker, 1997). ω-Scans covering reciprocal space up to
θmax 24.99° with 99.8% completeness, total of 11370 reflections
(4031 unique) with Rint ϭ 0.1139. Structure solution SHELXL-97,
full-matrix least-squares based on F2 using SHELXL-97, final R ϭ
0.058, wR ϭ 0.154, GOF ϭ 1.006. Final residual density was in
Ϫ3
˚
the range Ϫ0.497 to 0.923 e·A
.
[Mn(Cp*)2][M(tfd)2] [M
ϭ
Ni, Pd, Pt; tfd
ϭ
CCDC-201344 (2) contains the supplementary crystallographic
data for this paper. These data can be obtained free of charge at
www.ccdc.cam.ac.uk/conts/retrieving.html [or from the Cambridge
Crystallographic Data Centre, 12, Union Road, Cambridge
CB2 1EZ, UK; Fax: (internat.) ϩ44-1223/336-033; E-mail:
deposit@ccdc.cam.ac.uk].
bis(trifluoromethyl)ethylenedithiolate].[7Ϫ9] For complexes
containing the [Ni(mnt)2]Ϫ anion, previous studies have
shown that the magnetic coupling between [Ni(mnt)2]Ϫ
anions is very sensitive not only to intermolecular separ-
ation,[2a] but also to the degree of overlap of neighboring
[Ni(mnt)2]Ϫ anions.[10Ϫ12] Several shorter contact distances,
such as Ni···Ni, Ni···S, S···S, S···N, S···C and C···N, play
important roles in the superexchange pathway due to
extensive electron delocalization in the [Ni(mnt)2]Ϫ unit.[13]
At very low temperature, superexchange and/or through-
space intrachain antiferromagnetic couplings must be con-
sidered in order to yield a three-dimensional AF ordering
state below 2.5 K.
Supporting Information: ORTEP view, side view of cation chain,
dM/dH vs. H plot, in-phase signal (χЈ) and FCM curve for 2) is
available (see footnote on the first page of this article.
Acknowledgments
Financial support from the National Natural Science Foundation
(No. 2017022, No. 29831010, No. 20125104), Jiangsu Science and
Technology Department and The Center for Analysis and Determi-
nation of Nanjing University are gratefully acknowledged.
In summary, a metamagnetic-like behavior is observed in
the title complex, which, to the best of our knowledge, is the
first example of metamagnetism in this series of complexes
containing the maleonitriledithiolate dianion.
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[FBzPyNH2]2[Ni(mnt)2] (1): This compound was prepared by the
direct combination of NiCl2·6H2O, Na2mnt and [FBzPyNH2]Cl in
H2O in a 1:2:2 molar ratio. The red precipitate that formed was
filtered off, washed with water and dried under vacuum. Yield:
93%. C32H24F2N8NiS4 (745.5): calcd. C 51.55, H 3.24, N 15.03;
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,
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(150 mg, 0.59 mmol) was slowly added to an MeCN solution (20
mL) of [FBzPyNH2]2[Ni(mnt)2] (746 mg, 1.0 mmol), and stirred for
15 min. MeOH (90 mL) was then added, and the mixture allowed
to stand overnight. The microcrystals formed were filtered off,
washed with MeOH and dried in vacuo. Yield: 87%.
C20H12FN6NiS4 (542.3): calcd. C 44.30, H 2.23, N 15.50; found C
44.52, H 2.22, N 15.42. IR: ν(NH2) 3347.9 cmϪ1, 1654.4 vs; ν(CN)
2206.7 vs; ν(CϭC) of mnt2Ϫ 1453.3 m. Good-shaped single crystals
suitable for X-ray analysis were obtained by allowing Et2O to dif-
fuse into an MeCN solution of 2 for about a week.
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Eur. J. Inorg. Chem. 2003, 2393Ϫ2396