An ion-pair compound based on [Pd(mnt)2]- with strong antiferromagnetically coupled interaction: Synthesis, crystal structure, magnetic property

Article abstract of DOI:10.1016/j.molstruc.2004.08.009

An ion-pair compound, which constructs from the 1-(4′-F-benzyl) pyridinium with Λ-shaped (abbreviated as [FBzPy]⁺) and planar bis(maleonitrileditholato)palladium(III) (abbreviated as [Pd(mnt) ₂]^-), has been synthesized and

Full text of DOI:10.1016/j.molstruc.2004.08.009

Journal of Molecular Structure 733 (2005) 119–124
www.elsevier.com/locate/molstruc
An ion-pair compound based on [Pd(mnt)2]K with strong
antiferromagnetically coupled interaction: synthesis, crystal
structure, magnetic property
b
c
c
X.M. Rena,b, , H. Okudera , J.L. Xie , Q.J. Meng
*
aDepartment of Chemistry, Anqing Normal College, Anqing 246011, People’s Republic of China
b
¨
¨
Max-Planck-Institute fur Festkorperforschung, Heisenbergstrasse 1, Postfach 800665, D-70569 Stuttgart, Germany
cCoordination Chemistry Institute and State Key Laboratory, Nanjing University, Nanjing 210093, People’s Republic of China
Received 29 May 2004; revised 13 August 2004; accepted 16 August 2004
Available online 22 September 2004
Abstract
An ion-pair compound, which constructs from the 1-(40-F-benzyl)pyridinium with L-shaped (abbreviated as [FBzPy]C) and planar
bis(maleonitrileditholato)palladium(III) (abbreviated as [Pd(mnt)2]K), has been synthesized and structurally characterized. The cations and
anions in this compound stack into well-separated columns in the solid state, the adjacent anions exist the strong trend of dimerization within
˚
an anionic column, and the contacts between the neighbor Pd(III) ions alternate as 3.39 and 4.06 A, respectively. The weak p/p stacking
interactions were observed between adjacent benzene rings within a cationic column. The temperature dependence of magnetic susceptibility
measured in the temperature range of 1.8–330 K; indicates this compound is almost diamagnetic. The magnetic susceptibility was
successfully modeled by a spin dimer magnetic exchange scheme with sZ 12 to give rise to gZ2.1, and the energy gap between singlet ground
state and triplet excited state is about 1310 K.
q 2004 Elsevier B.V. All rights reserved.
Keywords: Bis(maleonitrileditholato)palladium(III) compound; Crystal structure; Magnetic property
1. Introduction
(M represents Ni(III), Pd(III) and Pt(III) ions; mnt2K is
maleonitriledithiolate), were constructed into the columnar
stack structures, in which intermolecular dz2 or p orbital
interactions give rise to 1-D electronic nature of these types
of compounds [8–11]. To build quasi-one-dimensional
molecular magnets based on the blacks of [M(mnt)2]K,
the key problem had to be solved is how to control
[M(mnt)2]K anions stacking into the columns. It is noted
that the counter cationic topology and size in [M(mnt)2]K
compounds play an important role in controlling the
stacking pattern of anions and cations, for instance, the
counter cations with bigger molecular size and approximate
sphere shape lead to form isolated dimers of anions, while
the planar cations induce to form the mixed stacking
columns with alternative overlapping of anions and
cations. In our current researches, the benzylpyridinium
derivatives ([RBzPy]C) with L-shaped molecular configur-
ation were selected as the counter cations for [Ni(mnt)2]K
Recently, lots of research interests have been paying
attentions to the low-dimensional spin systems [1–5] due to
more and more new quantum effects were found, such as,
slow relaxation of magnetization and hysteresis effects
which are not associated with 3-D ordering [6a–d], distinct
plateaus in the magnetization [6e], these findings also
stimulated theoretical investigations in the low-dimensional
spin systems [7].
It is possible that the molecular building blocks
with planar extended electronic structure, [M(mnt)2]K
* Corresponding author. Present address: Laboratory for Organic
Conductivity Materials Field, Research Institute for Electronic Science,
Hokkaido University, Sapporo 060-0812, Japan. Tel.: C86 81 11 706 2849;
fax: C86 81 11 706 4972.
E-mail address: xmren@es.hokudai.ac.jp (X.M. Ren).
0022-2860/$ - see front matter q 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2004.08.009

120
X.M. Ren et al. / Journal of Molecular Structure 733 (2005) 119–124
2.3. Synthesis of [FBzPy]2[Pd(mnt)2] (1)
This compound was prepared by the direct combination
of 1:2:2 mol equiv. of PdCl2, Na2mnt and [FBzPy]Br in
warm solution of water (w50 8C). A green precipitate given
was filtered off, washed by water and dried under vacuum.
Yield: 86% (Found: C, 50.3; H, 2.96; N, 10.8%. Calc. for
C32H22F2N6PdS4: C, 50.4; H, 2.91; N, 11.0%). IR spectra
data (cmK1): n(CN) of mnt2K 2196.5(vs) and 2229(sh).
2.4. Synthesis of [FBzPy][Pd(mnt)2] (2)
A MeCN solution (10 cm3) of I2 (205 mg, 0.80 mmol)
was slowly added to a MeCN solution (25 cm3) of
[FBzPy]2[Pd(mnt)2] (870 mg, 1.0 mmol), and stirred for
25 min. MeOH (150 cm3) was then added, and the mixture
allowed to stand overnight. The microcrystals formed were
filtered off, washed with MeOH and dried in vacuum. Yield:
76% (Found: C, 41.6; H, 1.95; N, 11.9%. Calc. for
C20H11FN5PdS4: C, 41.8; H, 1.93; N, 12.2%). IR(cmK1):
n(CN) of mnt2K 2201 (sh) and 2214.8(vs).
Scheme 1.
and [Pt(mnt)2]K anions, respectively. A series of ion-pair
compounds (Scheme1) with quasi-one-dimensional struc-
tural feature, which exhibit magnetic diversity, were
prepared by using this strategy. The investigations revealed
also the nature of both the substituent groups in the
benzylpyridinium derivatives and metal ions influence on
the overlap patterns of the anions within an anionic
column, and further tune the magnetic properties of these
types of compounds [12]. To extend our research and
understand the relationship between the magnetic properties
of these types of compounds and their stacking structures,
we are pursuing the study of the [RBzPy]C[Pd(mnt)2]K,
and [Pd(mnt)2]K anion is similar to both [Ni(mnt)2]K and
[Pt(mnt)2]K anions in the aspects of the molecular structure
and the electronic configuration. Herein we report synthesis,
crystal structure, magnetic property for the compound,
[FBzPy][Pd(mnt)2].
The single crystals suitable for X-ray analysis was
obtained by dispersing Et2O into MeCN solution of 2 about
4 days.
2.5. X-ray crystallography
Diffraction data of 2 were collected at 293 K on a CCD
area detector (Bruker-SMART) equipped with graphite-
monochromated Mo–Ka radiation. All computations were
carried out in a PC-586 computer using the SHELXTL-PC
Table 1
Summary of crystal and structure refinement data for 2
2. Experiments
Empirical formula
Formula weight
Temperature (K)
C20H10FN5PdS4
574.98
293(2)
2.1. Chemicals and reagents
˚
Wavelength (A)
0.71073
Crystalline system
Space group
˚
a (A)
˚
b (A)
˚
c (A)
Monoclinic
P21/c
All manipulations were carried out in air unless
otherwise noted. All chemicals and solvents were reagent
grade, and were used without further purification. 4-fluoro-
benzyl bromide is the product of Synica Chemicals, 1-(40-
fluorobenzyl)pyridinium bromide ([FBzPy]Br), Disodium
maleonitriledithiolate (Na2mnt) were synthesized following
the published procedures [13].
26.021(7)
12.607(3)
14.451(3)
b (deg)
3
V (A ), Z
103.42(2)
˚
4611.3(19), 8
1.656
Density (calc) (mg/m3)
Abs coeff. (mmK1
)
1.193
F(000)
2280
q range for data collection
1.80–25.04
Index ranges
K21%h%30, K15%k%13,
K17%l%16
8090
2.2. Physical measurements
Reflections collected
Independent reflns
Elemental analyses were performed with a Perkin-Elmer
240 analytical instrument. IR spectra were recorded on a
Fourier Transform Infrared Spectrometer (170SX) (KBr
pellet). Magnetic susceptibility data on powder-sample
were collected over the temperature range of 1.8–330 K
using a Quantum Design MPMS7 superconducting quantum
interference device (SQUID) magnetometer.
6013 [RintZ0.0322]
Full-matrix least-squares
6013/0/559
Refinement method on F2
Data/restraints/params
Goodness-of-fit on F2
Final R indices [IO2s(I)]
R indices (all data)
0.963
R1Z0.0348, wR2Z0.0813
R1Z0.0521, wR2Z0.0897
0.37 and K0.41
K3
˚
Largest diff peak and hole, (e A
)

X.M. Ren et al. / Journal of Molecular Structure 733 (2005) 119–124
121
program package [14]. The structure of 2 was solved by
direct method and refined on F2 by full-matrix least-squares
method. All non-hydrogen atoms were refined anisotropi-
cally. Hydrogen atoms were placed in their calculated
positions and refined following the riding model. Crystal-
lographic details for 2 are summarized in Table 1.
the results are summarized in Table 2. The average S–Pd–S
bond angle within the chelated ring is 90.098 for the moiety
of Pd(1)-contained (89.778 for the moiety of Pd(2)-
contained), and the Pd–S bond distances are from
˚
2.2637(10) to 2.2783(10) A for the entry of Pd(1)-contained
˚
(from 2.2618(10) to 2.2786(11) A for the entry of Pd(2)-
contained), these values are in agreement with that of
[Pd(mnt)2]K complexes reported [15]. The CN groups of
mnt2K ligand are out of the coordinating plane as the serials
of Ni(III)- and Pt(III)-based complexes with the deviations
3. Results and discussion
˚
˚
of 0.25 A of N(1), 0.14 A of N(2), 0.04 A of N(3) and
˚
3.1. Descriptions of crystal structure
˚
0.21 A of N(4) in the moiety of Pd(1)-contained, respect-
˚
ively (0.32 A of N(1), 0.30 A of N(2), 0.36 A of N(3) and
˚
˚
An ORTEP drawing of 2 in an asymmetric unit is shown
in Fig. 1a. Each Pd(III) ion in two crystallographic
independence [Pd(mnt)2]K moieties is coordinated by four
sulfur atoms, and exhibit square-planar coordination
geometry. The least-square planes with four sulfur
atoms were calculated for each of [Pd(mnt)2]K moieties,
˚
0.19 A of N(4) in the moiety of Pd(2)-contained). The two
crystallographic independence [Pd(mnt)2]K moieties are
almost parallel to each other (the angle between the two
coordination planes is only 2.28). The bond lengths and
angles of the two crystallographic independence [FBzPy]C
Fig. 1. (a) ORTEP view of 2 with 30% probability thermal ellipsoids. (b) Completely separated columnar stacking of 2 along the c-axis.

122
X.M. Ren et al. / Journal of Molecular Structure 733 (2005) 119–124
Table 2
Details of molecular planes (x, y, z are fractional atomic coordinates)
˚
Distances from the plane (A)
K0.0052a (4) S(1)
0.0068a (5) S(5)
0.0050a (4) S(2)
K0.0068a (5) S(6)
K0.0068a (5) S(7)
0.0068a (5) S(8)
0.0052a (4) S(3)
K0.0050a (4) S(4)
0.0001 (5) P(d1)
0.0172 (5) Pd(2)
K0.2459 (41) N(1)
K0.1399 (42) N(2)
0.0391 (45) N(3)
K0.2124 (40) N(4)
K0.1562 (39) C(1)
K0.0583 (34) C(2)
K0.0519 (32) C(3)
K0.1098 (40) C(4)
K0.0121 (41) C(5)
K0.0240 (33) C(6)
K0.0517 (36) C(7)
K0.1445 (42) C(8)
K0.3239 (47) N(5)
K0.2994 (48) N(6)
K0.3628 (49) N(7)
K0.1949 (44) N(8)
K0.2177 (45) C(21)
K0.1006 (38) C(22)
K0.0947 (35) C(23)
K0.2053 (44) C(24)
K0.2329 (44) C(25)
K0.1049 (35) C(26)
K0.0683 (34) C(27)
K0.1402 (41) C(28)
Equation of the plane for the entry of Pd(1): 11.6673 (81)xK0.1797 (36)yK
14.0667 (57)zZ0.8432 (19). Rms deviation of fitted atomsZ0.0051.
Equation of the plane for the entry of Pd(2): 11.8896 (82)xC0.2909
(37)yK14.0318 (57)zZ0.4558 (56). Rms deviation offitted atomsZ0.0068.
a
Indicates atom used to define plane.
cations are generally in close agreement with values
reported for the complex [FBzPy] [Ni(mnt)2] [12b]. Two
cations show L-shaped molecular configuration, the
dihedral angles between benzene, pyridine rings and the
reference plane, C(15)–C(14)–N(5) are 112.5 and 77.08 for
the entry of F(1)-contained, respectively, (corresponding
dihedral angles of 119.4 and 112.28 for the entry of F(2)-
contained).
The anionic and cationic columns with separated-well
stack along the direction of crystallographic c-axis as
displayed in Fig. 1b. The adjacent [Pd(mnt)2]K anions
exhibit two types of overlapping patterns within an anionic
column, the pattern with eclipsed plane over plane is labeled
as pattern A (Fig. 2a) and two superimposed monomers
rotated to each other as pattern B (Fig. 2b). Two
[Pd(mnt)2]K anions eclipse to lead the inter-plane (defined
˚
by four coordinated sulfur atoms) distance (3.39 A) is
almost identical to the separation of Pd/Pd, and the
adjacent S/S overlapping pairs exist very shorter separ-
ations (3.40 A of S(1).S(5) , 3.38 A of S(2)/S(6) , 3.45 A
Fig. 2. Patterns of overlapping of [Pd(mnt)2]K anions in 2 (a) side view (b)
top view.
i
i
˚
˚
˚
i
i
˚
of S(3)/S(7) and 3.43 A of S(4)/S(8) , symmetric code
iZ1Kx, 0.5Cy, 0.5Kz) in pattern A. The corresponding
3.2. Magnetic property of 2
˚
plane-to-plane distance is 3.64 A, the separation of Pd/Pd
is 4.06 A, and the nearest S/S, S/Pd contacts are of 3.60
˚
and 3.73 A in Pattern B. In a cationic column, the adjacent
˚
The temperature dependence of magnetic susceptibility
for 2 is shown in Fig. 4, which indicates very weak
paramagnetic property in temperature range of 1.8–330 K.
The magnetic susceptibilities in the temperature range of
30–330 K are negative, and exhibit weak paramagnetic
Curie tail below 30 K, so weak paramagnetic property
maybe arises from the magnetic impurities of the uncoupled
spins, that is, this compound actually is almost diamagnetic.
cations stack in a boat-type conformation-like, which is
shown in Fig. 3. The dihedral angles between the
overlapping benzene rings are same as 8.68, the correspond-
ing center-to-center distances between the face-to-face
˚
˚
stacking of aromatic rings are 4.01 A and 3.97 A, respect-
ively, and too long to be of energetic significance [16].

X.M. Ren et al. / Journal of Molecular Structure 733 (2005) 119–124
123
of the paramagnetic impurity deduced from C value is
w1.7%), c0ZK2.0!10K4 emu molK1, and the agreement
factor is 3.2!10K6
.
4. Conclusion and remarks
In summary, an ion-pair compound, 1-(40-F-benzyl)pyr-
idinium bis(maleonitriledithiolato)palladium(III), has been
synthesized. The crystal structural determination at room
temperature revealed that the anions and cations in this
compound stack into separated-well columns, which is
similar to the compounds of both [Ni(mnt)2]K and
[Pt(mnt)2]K series. Two types of anionic overlapping
patterns within an [Pd(mnt)2]K column were found, one is
two neighboring anions eclipses plane over plane (Pattern
A) and another is two adjacent superimposed monomers
rotates to each other (Pattern B), so the anionic column is
dimerized. By comparison, the stacking columns of
[Ni(mnt)2]K anions in these series of ion-pair compounds
are usually uniform, while the stacking columns of both
[Pd(mnt)2]K and [Pt(mnt)2]K anions favor to be dimerized.
These findings indicate the factors effecting on the stack
structure in the types of [RBzPy]C[M(mnt)2]K compounds
are not only from the cationic molecular configurations, but
also from the anionic structural properties (such as the ionic
radii of M, etc). The DC magnetic susceptibility measured
in the temperature range of 1.8–330 K shown the compound
2 is almost diamagnetic. The magnetic susceptibility was
modeled by using a spin dimer with sZ 12 to give the large
energy gap of ca. 1310 K between singlet ground state and
triplet excited state, which lead to the compound is nearly
diamagnetic. Presently, We have been studying the control
of the [M(mnt)2]K (MZNi, Pd or Pt) arrangements by
introduced the type of RBzPyC counter-cation with tunable
molecular geometry. Although the trend that the influence
of the substituent R- of the RBzPyC cation on the anionic
stacking structure and magnetic properties of the
[RBzPy][M(mnt)2] compounds for both [Pd(mnt)2]K and
[Pt(mnt)2]K series are not extremely clear due to the lack of
some crystal structural and magnetic data, some finding in
[RBzPy][Ni(mnt)2] compounds are significant, for example,
the separations between adjacent Ni/Ni within an anionic
column in those compounds decrease progressively as the
order of the substituent R–ZF–, Cl–, Br–, I– and NO2–
(zCN–), each compound of them undergo a phase
transition from the paramagnetic to the diamagnetic phase,
and the corresponding phase transition temperature increase
by degrees in the sequence of the substituent R–ZF–, Cl–,
Br–, I– and NO2– (zCN–) [12,17]. In order to gain more
information about the relationship of substituent effect,
anionic stacking structure and magnetic property of these
[RBzPy][M(mnt)2] compounds, the preparation of the new
compounds, the determination of crystal structures of them,
the investigation of their magnetic properties and the
relevant theoretic analyses are in progress.
Fig. 3. Stacking pattern with boat-conformation-like for the cations in 2.
The magnetic exchange scheme of a spin dimer with sZ 21
can be used to model the magnetic susceptibility for 2 based
on the structural analysis, and the function of the magnetic
susceptibility as temperature is described as the Eq. (1).
cm Z Ng2m2B=½kBTð3 CexpðD=kBTÞÞꢀ CC=T Cc0
(1)
where the first term contributes from the susceptibility of a
spin dimer with SZ 12 ; D is the energy difference between
triplet and singlet, C is Curie constant for the uncoupled
paramagnetic impurity, and c0 is the sum of both core
diamagnetic and temperature independent paramagnetic
contributions, and other symbols have normal meanings.
The fitting successfully give rise to the results of gZ2.1,
D/kBZ1310 K, CZ6.5!10K3 emu K molK1 (the fraction
Fig. 4. The variety of magnetic susceptibility versus temperature
(1.8–330 K) (circle is experimental data, and solid line is reproduced by
calculation with the parameters of gZ2.1, D/kBZ1310 K, CZ6.5!10K3
emu K molK1, c0ZK2.0!10K4 emu molK1).

124
X.M. Ren et al. / Journal of Molecular Structure 733 (2005) 119–124
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Crystallographic data (excluding structure factors) for
the structures reported in this paper have been deposited
with the Cambridge Crystallographic Data Center as
supplementary publications, and the CCDC numbers is
CCDC-208361. Copies of the data can be obtained free of
charge on application to CCDC, 12 Union Road, Cambridge
CB21EZ, UK (Fax: C44 1223 336 033; Email: deposit@
ccdc.cam.ac.uk).
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The authors thank Ms E. Bru¨cher for the magnetic
property determinations. This project was financially
supported from the National Natural Science Foundation
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