Magnetic semiconductors: Molecular materials based on alkyl-pyridinium- substituted verdazyl radical cations and Ni(dmit)2 anion

Article abstract of DOI:10.1016/j.poly.2005.03.073

Five kinds of (1:1) and (1:3) salts of 3-(4- and 3-alkyl-pyridinium)-1,5- diphenylverdazyl (alkyl = ethyl and methyl) radical cations with Ni(dmit) ₂ anion ([p-EtPyDV]⁺[Ni(dmit)₂]^- (1), [m-EtPyDV]⁺[Ni(dmit)₂]^- (2), [p-MePyDV]⁺[Ni(dmit)₂]^- (3), [m-MePyDV] ⁺[Ni(dmit)₂]^- (4), and [p-MePyDV]+[Ni(dmit)2]3- (5)) (dmit = 1,3-dithiol-2-thione-4,5-dithiolate) have been prepared, and the magnetic susceptibilities (χ_M's) have been measured between 1.8 and 300 K. The χ_M of salt 1 can be well explained by a four-spin linear tetramer model ([p-EtPyDV]⁺-[Ni(dmit)₂] ^--[Ni(dmit)₂]^--[p-EtPyDV]⁺) with an end exchange interaction 2J₁/k_B = -780 K and a central interaction 2J₂/k_B = -200 K. The formation of magnetic tetramer in salt 1 has been ascertained by the crystal structure analysis of 1. The χ_M of salt 2 was explained by the sum of the contributions from: (i) a dimer system (2J/k_B = -320 K) due to Ni(dmit)₂ anions and (ii) the one-dimensional (1D) Heisenberg ferromagnetic linear-chain system (2J k_B = +2.5 K) due to verdazyl cations. The χ_M of salt 3 is similar to that of salt 1, suggesting a formation of magnetic tetramer in salt 3. The χ_M of salt 4 shows a broad maximum at T_max = 100 ± 2 K, and can be explained by a 1D Heisenberg antiferromagnetic alternating-chain model with 2J₁/k _B = -165 K (alternation parameter α = J₂/J ₁ = 0.6). The conductivity (σ) of salts 1, 2, 3 and 4 at 293 K was σ = 2.3 × 10^-5, 1.1 × 10^-3, 1.4 × 10^-5 and 5.4 × 10^-6 S cm^-1 with an activation energy of E_A = 0.28, 0.52, 0.21 and 0.33 eV, respectively. The (1:3) salt 5 (σ = 1.0 S cm^-1, E_A = 0.048 eV) showed three to five orders of magnitude higher conductivity than those of the (1:1) salts 1-4 at room temperature. All the (1:1) and (1:3) salts 1-5 are new molecular paramagnetic semiconductors.

Full text of DOI:10.1016/j.poly.2005.03.073

Polyhedron 24 (2005) 2513–2521
www.elsevier.com/locate/poly
Magnetic semiconductors: Molecular materials
based on alkyl-pyridinium-substituted verdazyl radical cations
and Ni(dmit)2 anion
a,
a
a
a
a
Kazuo Mukai *, Daisuke Shiba , Kyohei Mukai , Kenji Yoshida , Hiroyuki Hisatou ,
a
Keishi Ohara , Yuko Hosokoshi , Nagao Azuma
b
a
a
Department of Chemistry, Faculty of Science, Ehime University, Bunkyo-cho 2-5, Matsuyama 790-8577, Japan
b
Department of Material Science, College of Integrated Arts & Sciences, Osaka Prefecture University, Sakai 599-8531, Japan
Received 5 October 2004; accepted 25 March 2005
Available online 24 May 2005
Abstract
Five kinds of (1:1) and (1:3) salts of 3-(4- and 3-alkyl-pyridinium)-1,5-diphenylverdazyl (alkyl = ethyl and methyl) radical
cations with Ni(dmit)2 anion ([p-EtPyDV]+[Ni(dmit)2]ꢀ (1), [m-EtPyDV]+[Ni(dmit)2]ꢀ (2), [p-MePyDV]+[Ni(dmit)2]ꢀ (3),
þ
[m-MePyDV]+[Ni(dmit)2]ꢀ (4), and ½p-MePyDVꢁ ½NiðdmitÞ ꢁ ð5Þ) (dmit = 1,3-dithiol-2-thione-4,5-dithiolate) have been prepared,
ꢀ
2 3
and the magnetic susceptibilities (vMÕs) have been measured between 1.8 and 300 K. The vM of salt 1 can be well explained by a
four-spin linear tetramer model ([p-EtPyDV]+–[Ni(dmit)2]ꢀ–[Ni(dmit)2]ꢀ–[p-EtPyDV]+) with an end exchange interaction
2J1/kB = ꢀ780 K and a central interaction 2J2/kB = ꢀ200 K. The formation of magnetic tetramer in salt 1 has been ascertained
by the crystal structure analysis of 1. The vM of salt 2 was explained by the sum of the contributions from: (i) a dimer system
(2J/kB = ꢀ320 K) due to Ni(dmit)2 anions and (ii) the one-dimensional (1D) Heisenberg ferromagnetic linear-chain system
(2J kB = +2.5 K) due to verdazyl cations. The vM of salt 3 is similar to that of salt 1, suggesting a formation of magnetic tetramer
in salt 3. The vM of salt 4 shows a broad maximum at Tmax = 100 2 K, and can be explained by a 1D Heisenberg antiferromagnetic
alternating-chain model with 2J1/kB = ꢀ165 K (alternation parameter a = J2/J1 = 0.6). The conductivity (r) of salts 1, 2, 3 and 4 at
293 K was r = 2.3 · 10ꢀ5, 1.1 · 10ꢀ3, 1.4 · 10ꢀ5 and 5.4 · 10ꢀ6 S cmꢀ1 with an activation energy of EA = 0.28, 0.52, 0.21 and
0.33 eV, respectively. The (1:3) salt 5 (r = 1.0 S cmꢀ1, EA = 0.048 eV) showed three to five orders of magnitude higher conductivity
than those of the (1:1) salts 1–4 at room temperature. All the (1:1) and (1:3) salts 1–5 are new molecular paramagnetic
semiconductors.
ꢀ 2005 Elsevier Ltd. All rights reserved.
Keywords: Verdazyl radical; Ni(dmit)2 complex; Magnetism; Conductivity; Magnetic semiconductor; Crystal structure
1. Introduction
(or metallic) state and antiferromagnetic (AFM) (or fer-
romagnetic (FM)) order coexist in a system, are very
limited because of the difficulty in molecular design of
the complexes [1–5]. Especially, there has been no exam-
ple of superconducting ferromagnet up to this time. It is
well known that the assembled metal complexes, [Do-
nor][M(dmit)2]n (M = Ni and Pd, and dmit = 1,3-
Development of the molecular ferromagnet and the
superconductor is two challenging targets in material
science, and many studies have been performed with
great success in recent years. On the other hand, exam-
ples of magnetic conductors, where the superconducting
dithiol-2-thione-4,5-dithiolate),
exhibit
insulating,
*
metallic and superconducting phases at low temperature
under high pressure [6,7]. Two examples of magnetic
Corresponding author. Tel.: +81 89 927 9588; fax: +81 89 927 9590.
E-mail address: mukai@chem.sci.ehime-u.ac.jp (K. Mukai).
0277-5387/$ - see front matter ꢀ 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2005.03.073

2514
K. Mukai et al. / Polyhedron 24 (2005) 2513–2521
semiconductors consisting of open-shell radical cation
donor and metal complex anion acceptor have been re-
ported for the (1:1) salt of Ni(dmit)2 anion with the
p-EPYNN (p-N-ethylpyridinium a-nitronyl nitroxide)
and the Me3N+–TEMPO (=N,N,N-trimethyl(1-oxyl-
2,2,6,6-tetramethylpiperidine-4-yl)ammonium) radical
cations [8,9].
+
−
S
S
N N
NN
S
S
S
S
S
S
S
Ni
S
R N
R = C2H5 : [p−EtPyDV]+[Ni(dmit)2]− (1)
R = CH3 : [p−MePyDV]+[Ni(dmit)2]− (3)
Verdazyl radicals show a high chemical and thermal
stability and can be isolated as solvent-free pure radi-
cals in crystalline states [10]. The magnetic properties
of these verdazyl radical crystals have been studied
extensively, and several interesting magnetic properties
such as ferromagnetism, weak ferromagnetism, antifer-
romagnetism, spin-Peierls transition, and spin frustra-
tion have been reported [11–17]. Recently, first two
examples of molecular paramagnetic semiconductors
consisting of verdazyl radical cation and metal complex
anion have been reported for the Ni(dmit)2 salts of
3-[4-(trialkylammonio)phenyl]-1,5-diphenyl-6-oxover-
dazyl radical cations [18,19]. Further, we prepared the
(1:1) and (1:2) salts of 3-(4- and 3-alkyl-pyridinium)-
1,5-diphenylver-dazyl (alkyl = ethyl and methyl) radical
cations with TCNQ anion, and found that the (1:2)
salts are genuine organic paramagnetic semiconductors
[20,21]. However, the examples of the molecular com-
plexes between the open-shell radical cation and elec-
tron acceptor anion are very limited. In the present
work, we prepared five kinds of (1:1) and (1:3) salts
1–5 of 3-(4- and 3-alkyl-pyridinium)-1,5-diph-
enylverdazyl (alkyl = ethyl and methyl) radical cations
with Ni(dmit)2 anion (see Fig. 1), and studied the
structural, magnetic and conducting properties of these
radical salts.
+
R
−
S
S
N
N N
NN
S
S
S
S
S
Ni
S
S
S
R = C2H5 : [m−EtPyDV]+[Ni(dmit)2]− (2)
R = CH3 : [m−MePyDV]+[Ni(dmit)2]− (4)
+
−
N N
NN
S
S
S
S
S
S
S
S
Ni
H3C N
S
S
3
[p-MePyDV]+[Ni(dmit)2]3− (5)
Fig. 1. Chemical structures of the (1:1) and (1:3) salts of 3-(4- and
3-alkyl-pyridinium)-1,5-diphenylverdazyl radical cations (alkyl = ethyl
and methyl) with Ni(dmit)2 anion.
2. Experimental
and washed with diethyl ether. Recrystallization of the
residue from acetonitrile–diethyl ether afforded the
product as black-violet prismatic crystals (43 mg,
54%): m.p. = 190.0–191.5 ꢁC; UV (acetonitrile) kmax
(loge): 747 (3.37), 617 (3.59), 543 (4.03), 436 (4.26),
380 (4.56), 315 (4.59), 241 (4.64). Anal. Calc. for
C27H21N5S10Ni: C, 40.80; H, 2.66; N, 8.81. Found: C,
40.58; H, 2.62; N, 8.46%.
2.1. Syntheses
The preparations of 3-(4-pyridyl)-1,5-diphenyl-ver-
dazyl (p-PyDV) and 3-(3-pyridyl)-1,5-diphenyl-verdayl
(m-PyDV) radicals were reported in a previous work
[17]. The preparations of the iodide salts, 3-(4- and 3-al-
kyl-pyridinium)-1,5-diphenylverdazyl iodides (alkyl =
ethyl and methyl), [p-EtPyDV]+Iꢀ (6), [m-EtPyDV]+Iꢀ
(7), [p-MePyDV]+Iꢀ (8), and [m-MePyDV]+Iꢀ (9), were
reported in previous papers [20,21].
The radical salts 2, 3, and 4 were prepared similarly.
2.1.2. [m-EtPyDV]+[Ni(dmit)2]ꢀ (2)
Dark-green powder crystals: m.p. = 199.0–201.0 ꢁC;
UV (acetonitrile) kmax (loge) 735 (3.59), 625 (3.64), 443
(4.31), 389 (4.39), 314 (4.64), 240 (4.58). Anal. Calc.
for C27H21N5S10Ni: C, 40.80; H, 2.66; N, 8.81. Found:
C, 40.67; H, 2.61; N, 8.71%.
Preparations of the charge transfer salts 1–5 are as
follows.
2.1.1. [p-EtPyDV]+[Ni(dmit)2]ꢀ (1)
To stirred solution of [p-EtPyDV]+[I]ꢀ (47.0 mg,
0.100 mmol) in methanol (50 ml), [n-Bu4N]+[Ni(dmit)2]ꢀ
(69.4 mg, 0.100 mmol) in methanol (250 ml) was added
and stirring was continued for 2 h under nitrogen atmo-
sphere. The black-violet solids precipitated were filtered
2.1.3. [p-MePyDV]+[Ni(dmit)2]ꢀ (3)
Dark-green powder crystals: m.p. > 300.0 ꢁC; UV
(acetonitrile) kmax (loge) 747 (3.36), 619 (3.59), 543
(4.13), 436 (4.26), 379 (4.56), 350 (4.51), 315 (4.60),

K. Mukai et al. / Polyhedron 24 (2005) 2513–2521
2515
240 (4.65). Anal. Calc. for C26H19N5S10Ni: C, 39.99; H,
2.45; N, 8.97. Found: C, 40.82; H, 2.57; N, 9.14%.
2.0
1.5
1.0
0.5
0
[m-MePyDV]+[Ni(dmit)2]-
[m-MePyDV]+I- + [n-Bu4N]+[Ni(dmit)2]-
2.1.4. [m-MePyDV]+[Ni(dmit)2]ꢀ (4)
Black-violet powder crystals: m.p. > 300.0 ꢁC; UV
(acetonitrile) kmax (loge) 736 (3.34), 619 (3.61), 439
(4.30), 392 (4.41), 315 (4.58), 241 (4.63). Anal. Calc.
for C26H19N5S10Ni: C, 39.99; H, 2.45; N, 8.97. Found:
C, 40.15; H, 2.55; N, 9.05%.
2.1.5. [p-MePyDV ]þ[Ni(dmit)2]3 (5)
ꢀ
For the preparation of (1:3) salt 5, the air oxidation
of a solution containing the [p-MePyDV]+[Ni(dmit)2]ꢀ
(3) (30 mg), acetic acid (20 ml) and acetic anhydride
(20 ml) in acetone (300 ml) was carried out at room tem-
perature [6,7]. Black fine crystals obtained show a high
melting point and are insoluble in the usual organic
solvents. The result of the elemental analysis indicates
the formation of a (1:3) salt, ½p-MePyDVꢁþ½Niꢀ
200
300
400
500
600
700
800
900
λ / nm
Fig. 2. UV–Vis spectra of the (1:1) [m-MePyDV]+[Ni(dmit)2]ꢀ salt (4)
in acetonitrile.
ðdmitÞ ꢁ ð5Þ [7]. M.p. > 300 ꢁC; Anal. Calc. for
[Ni(dmit)2]ꢀ anion [18]. Similarly, the absorption spec-
tra of salts 1–3 in acetonitrile can be well explained by
an addition of those of corresponding iodide salts and
[n-Bu4N]+[Ni(dmit)2]ꢀ, respectively. The electronic
structures of the verdazyl radical cation and Ni(dmit)2
anion moieties in salts 1–4 are thought to be similar
to those in corresponding iodide salts 6–9 and
[n-Bu4N]+[Ni(dmit)2]ꢀ, respectively. The (1:3) salt 5
crystals are insoluble in the usual organic solvents, and
we could not measure the optical spectrum of salt 5 in
solution.
ꢀ
2 3
C38H19N5S30Ni3: C, 27.11; H, 1.14; N, 4.16. Found: C,
26.85; H, 1.27; N, 3.97%.
2.2. Measurements
The magnetic susceptibility (vM) was measured in the
temperature range of 1.8–300 K by a SQUID magne-
tometer. The vM of all samples has been corrected for
the diamagnetic contribution (vdia = ꢀ0.399 · 10ꢀ3
emu/mol for salts 1 and 2, ꢀ0.388 · 10ꢀ3 emu/mol for
salts 3 and 4, and ꢀ0.757 · 10ꢀ3 emu/mol for salt 5), cal-
culated by PascalÕs method. The conductivity measure-
ments of salts 1–5 were performed for the pressed
pellet samples of salts, using the standard dc four-probe
method.
3.2. Crystal structures of salts 1 and 6
The crystal structure could be determined for the
[p-EtPyDV]+[Ni(dmit)2]ꢀ salt (1) and the [p-EtPyDV]+-
Iꢀ salt (6) (see Table 1). The crystal structures of salts
1 and 6 are shown in Fig. 3(a) and (b), respectively.
The bond lengths and bond angles of verdazyl moieties
(N1–N2–C1–N3–N4–C2) in salts 1 and 6 are similar to
corresponding those of the neutral 1,3,5-trip-
henylverdazyl (TPV) (data are not shown) [22]. How-
ever, the dihedral angles (8.965ꢁ and 2.380ꢁ) between
least-squares plane (N1–N2–N3–N4 plane) of verdazyl
ring and those of N1- and N4-phenyl rings in salt 1
are much smaller than those of the iodide salt 6
(9.255ꢁ and 28.925ꢁ) and TPV (27.8(4)ꢁ and 40.2(4)ꢁ),
respectively. In TPV, the verdazyl ring has an unsym-
metrical boat configuration, with both C1 and C2 out
of the nitrogen plane on the same side. C1 is displaced
2.3. Structure determination
The X-ray measurements of the [p-EtPyDV]+
[Ni(dmit)2]ꢀ salt (1) and [p-EtPyDV]+Iꢀ salt (6) were
carried out on a Rigaku AFC5R diffractometer with
˚
graphite-monochromated Mo Ka (k = 0.71069 A) radia-
tions. The structure was solved by the direct method.
3. Results
3.1. UV–Vis spectra of salts 1–5
Absorption spectra of [m-MePyDV]+[Ni(dmit)2]ꢀ (4),
[m-MePyDV]+Iꢀ (9), and [n-Bu4N]+[Ni(dmit)2]ꢀ salts
are measured in acetonitrile solvent. As shown in
Fig. 2, the absorption spectrum of 4 can be well
explained by the addition of [m-MePyDV]+Iꢀ (9) and
[n-Bu4N]+[Ni(dmit)2]ꢀ, suggesting the (1:1) complex for-
mation between the [m-MePyDV]+ cation and the
˚
˚
by only +0.099 A, while C2 is displaced by +0.590 A.
The verdazyl ring in iodide salt 6 also shows similar
structure to that of TPV. On the other hand, in salt 1,
˚
the deviations (ꢀ0.007(16) and +0.140(17) A) of C1
and C2 atoms out of N1–N2–N3–N4 plane are very
small, indicating that the verdazyl molecule has planar
structure.

2516
K. Mukai et al. / Polyhedron 24 (2005) 2513–2521
Table 1
Crystal data, experimental conditions, and refinement details of salts 1
and 6
[p-EtPyDV]+[Ni(dmit)2]ꢀ [p-EtPyDV]+Iꢀ
(1)
(6)
Empirical formula
Formula weight
Crystal color
C
794.80
27H21N5NiS10
C21H21N5I
470.33
black, prismatic
triclinic
purple, prismatic
monoclinic
P21/c(#14)
Crystal system
Space group
Unit cell dimensions
ꢀ
P1ð#2Þ
˚
a (A)
11.866(3)
16.556(4)
9.267(2)
105.94(2)
111.93(2)
79.72(3)
1618.0(8)
2
8.771(2)
8.851(3)
26.166(2)
˚
b (A)
˚
c (A)
a (ꢁ)
b (ꢁ)
c (ꢁ)
96.83(1)
3
˚
V (A )
2016.8(8)
4
1.549
Z
Dx (g cmꢀ3
l (cmꢀ1) (Mo Ka)
Crystal size/mm
)
1.631
12.74
16.04
0.25 · 0.23 · 0.10
5262
0.03 · 0.10 · 0.50
Number of reflections 5999
measured
Number of unique
reflections (Rint
R, Rw
5745 (0.079)
4641 (0.026)
0.067; 0.101
)
0.180, 0.221
The bond lengths and bond angles of the Ni(dmit)2
anion in salt 1 are also similar to corresponding those
in the [n-Bu4N]+[Ni(dmit)2]ꢀ salt (data are not shown)
[23]. The result indicates that the Ni(dmit)2 moiety in
salt 1 is considered to exist as monoanion [Ni(dmit)2]ꢀ
with S = 1/2 [8]. The dihedral angles between least-
squares planes of two dmit rings in salt 1 is 4.683ꢁ,
indicating the planarity of the Ni(dmit)2 moiety.
Molecular packing of salt 1 is shown in Fig. 4. The
unit cell of salt 1 contains two Ni(dmit)2 anions and
two verdazyl cations [p-EtPyDV]+. The Ni(dmit)2 an-
ion molecules in salt 1 form a dimer ([Ni(dmit)2] (A)–
[Ni(dmit)2] (B)) having intra-dimer contacts of ca.
˚
3.6–3.8 A (see Table 2). The dimer molecules are sand-
wiched between two verdazyl cation molecules, forming
a linear tetramer ([p-EtPyDV]+ (A)–[Ni(dmit)2] (A)–
[Ni(dmit)2] (B)–[p-EtPyDV]+ (B)) in the crystal. The
Ni(dmit)2 anion dimers are connected to each other
Fig. 3. Molecular structures of (a) the Ni salt 1 and (b) the iodide salt 6
with the atom numbering scheme.
˚
through short S–S contacts (S8–S9 = 3.566(4) A, S9–
˚
˚
S9 = 3.811(7) A, and S5–S8 = 3.934(5) A) between
Ni(A) and Ni(C).
and 269–298 K, respectively. The conductivity of the
(1:3) salt 5 at 20 ꢁC was r = 1.0 S cmꢀ1 with an activa-
tion energy EA = 0.048 eV (data are not shown), and
is three to five orders of magnitude larger than those
of the (1:1) salts 1–4.
3.3. Conductivities of salts 1–5
The room-temperature conductivities (rRTÕs) for
salts 1, 2, 3, and
,
4
are 2.3 · 10ꢀ5
,
1.1 · 10ꢀ3
respectively, as
,
1.4 · 10ꢀ5 and 5.4 · 10ꢀ6 S cmꢀ1
,
3.4. Magnetic susceptibilities of salts 1–5
listed in Table 3. As shown in Fig. 5, the salts 1, 2,
3 and 4 show semiconductive behavior with activation
energy values (EAÕs) of 0.28, 0.52, 0.21 and 0.33 eV at
the temperature range of 219–298, 250–283, 246–279
Fig. 6 shows a plot of vMT versus T for salts 1–5. The
value of vMT for the [p-EtPyDV]+[Ni(dmit)2]ꢀ salt (1) is
0.243 K emu/mol at 300 K (see Table 3), and decreases

K. Mukai et al. / Polyhedron 24 (2005) 2513–2521
2517
The value of vMT for the [m-EtPyDV]+[Ni(dmit)2]ꢀ
salt (2) is 0.685 K emu/mol at 300 K, and is close to
the sum of those (0.376 and 0.392 K emu/mol) expected
for non-interacting S = 1/2 spin system with g-values
gþV ¼ 2.0032 for [m-EtPyDV]+Iꢀ [21] and gNꢀi ¼ 2.0472
for [n-Bu4N]+[Ni(dmit)2]ꢀ [18], respectively, suggesting
that both the spins of verdazyl cation and Ni(dmit)2 an-
ion contribute to the magnetism of salt 2. vMT for salt 2
decreases gradually by decreasing the temperature,
shows the plateau between 30 and 60 K, and increases
by decreasing the temperature. Below 30 K, the suscep-
tibility of salt 2 follows the Curie–Weiss law with a
Curie constant of 0.376 K emu/mol and a positive Weiss
constant of +2.2 0.2 K (see Fig. 8(b)). The vMT
(0.388 K emu/mol) of salt 2 at the plateau (30–60 K)
amounts to about one half of the value (0.768 emu
K/mol) calculated on the basis of two S = 1/2 spins per
one formula unit of the salt, as shown in Fig. 8(a).
The additional susceptibility above 60 K is considered
to be a thermally activated species which is nonmagnetic
at lower temperatures. This magnetic contributꢀion is
Fig. 4. Molecular packing in salt 1, showing the formation of magnetic
linear tetramer, [verdazyl cation (A)–Ni(dmit)2 anion (A)–Ni(dmit)2
anion (B)–verdazyl cation (B)].
tentatively assigned to the dimer of the NiðdmitÞ rad-
2
ical anions. The susceptibility at lower temperatures is,
therefore, attributed to the verdazyl radicaꢀl cations.
The vM of the [p-MePyDV]+[Ni(dmit)2] salt (3) de-
creases gradually by decreasing temperature from
300 K, and shows a minimum at about Tmin = 170 K
(data are not shown). The susceptibility increases by
by lowering the temperature, indicating AFM interac-
tion in salt 1. As shown in Fig. 7, the vM of salt 1 de-
creases slowly by lowering the temperature from
300 K, shows a minimum around 160 K, and increases
rapidly below 20 K.
Table 2
Pertinent intermolecular contacts (r/A) in [p-EtPyDV] [Ni(dmit)2] (1)
+
ꢀ
˚
Ni(A)–Ni(B)
Ni–Ni 4.278(3)
Ni(A)–Ni(C)
Ni–Ni > 5.00
Ni(A)–V(A)
V(A)–V(B)
N(i)–N(j) (i, j = 1,2,3,4)
˚
(r < 4.00 A)
˚
(r < 4.00 A)
˚
(r < 4.00 A)
˚
(r < 5.00 A)
Ni–S10
Ni–C6
S2–S7
S3–S7
S4–S8
S4–C5
S4–C6
C2–C4
3.815(4)
3.87(1)
3.970(5)
3.614(5)
3.819(5)
3.59(1)
3.81(1)
3.63(2)
S5–S8
S8–S9
S9–S9
3.934(5)
3.566(4)
3.811(7)
Ni–N2
Ni–N3
S4–N1
S4–N3
S4–N4
S5–N1
S5–N2
S10–N3
C2–N1
C2–N4
C3–N1
3.771(9)
3.684(9)
3.936(9)
3.69(1)
3.30(1)
3.79(1)
3.67(1)
3.597(9)
3.62(2)
3.90(1)
3.56(1)
N1–N1
4.29(2)
Table 3
Conductivity (rRT), activation energy (EA), vMT value (at 300 K), and magnetism of salts 1–5
Salts
rRT (S cmꢀ1
2.3 · 10ꢀ5
)
EA (eV)
v
MT (K emu/mol)
magnetism
[p-EtPyDV]+[Ni(dmit)2]ꢀ (1)
0.28
0.243
linear tetramer
(2J1kB = ꢀ780 K, 2J2kB = ꢀ200 K) + Curie impurity (5.3%)
1D-Ferro (2J/kB = +2.5 K) + S–T (2J/kB = ꢀ320 K)
linear tetramer
[m-EtPyDV]+[Ni(dmit)2]ꢀ (2)
[p-MePyDV]+[Ni(dmit)2]ꢀ (3)
[m-MePyDV]+[Ni(dmit)2]ꢀ (4)
1.1 · 10ꢀ3
1.4 · 10ꢀ5
5.4 · 10ꢀ6
0.52
0.21
0.33
0.685
0.288
0.713
alternating chain (Tmax = 100 2 K, 2J1kB = ꢀ165 K,
a = J2J1 = 0.6) + Curie impurity (5.4%)
½p-MePyDVꢁþ½NiðdmitÞ2ꢁ3 ð5Þ
1.0
0.048
0.641
Curie–Weiss law (C = 0.684 (emu K)/mol, h = ꢀ17 K)
ꢀ

2518
K. Mukai et al. / Polyhedron 24 (2005) 2513–2521
6
5
4
3
(a)
0.01
0.008
0.006
0.004
0.002
0
Exp. data
Linear Tetramer
( 2J1/kB = -780 K, 2J2/kB = -200 K )
+ Curie Imp. ( 2.6 % 2 )
Salt (1)
Salt (2)
Salt (3)
Salt (4)
0
50
100
150
T / K
200 250 300
3.4
3.6
3.8
4.0
4.2
4.4
S1
S2
S3
S4
(b)
1000 / T
J1
J2
J1
Fig. 5. Temperature dependence of the resistivity (q) of the (1:1) salts
1–4 at ambient pressure.
[V(A)]
[Ni(A)]]
[Ni(B)]
[V(B)]
Fig. 7. (a) Temperature dependence of the magnetic susceptibility of
salt 1. The solid curve is the theoretical susceptibility calculated using
Eq. (2) in [24]. (b) Scheme 1.
1
0.8
0.768
The vM of the ½p-MePyDVꢁþ½NiðdmitÞ ꢁ salt ð5Þ in-
ꢀ
2 3
(5)
(2)
0.6
0.4
0.2
0
creases monotonically by lowering the temperature, and
follows the Curie–Weiss law with C = 0.684 K emu/mol
and h = ꢀ17.0 K.
0.376
(4)
(3)
4. Discussion
(1)
250
4.1. Magnetic properties of salts 1 and 3
0
50
100
150
200
300
T / K
The vM of salt 1 is shown in Fig. 7. As described in a
previous section, the Ni(dmit)2 anion molecules in salt 1
form a dimer (Ni(dmit)2 (A)–Ni(dmit)2 (B)) with short
Fig. 6. Temperature dependence of the product vMT for salts 1–5.
˚
intra-dimer contacts of ca. 3.6–3.7 A, suggesting strong
AFM exchange interaction. However, the vM of 1 can
not be explained by a simple dimer model. In salt 1,
the dimer molecules are sandwiched between two
verdazyl cation molecules, forming linear tetramer
([p-EtPyDV]+ (A)–[Ni(dmit)2]ꢀ (A)–[Ni(dmit)2]ꢀ (B)–
[p-EtPyDV]+ (B)) (see Fig. 4 and Table 2). As described
in a previous section, the verdazyl cation molecule in salt
1 has planar structure, and we can expect close contacts
between verdazyl cation and Ni(dmit)2 anion molecules.
In fact, there are many short contacts between the Ni,
S(i) and C(i) atoms in the Ni(dmit)2 anions and the
N(j) atoms (j = 1, 2, 3, and 4) in the hydrazidinyl moiety
(N1–N2–C7–N3–N4–C8), having large unpaired spin
densities, of verdazyl cations [17]. The result suggests
strong exchange interaction between the verdazyl cation
and the Ni(dmit)2 anion molecules.
decreasing temperature below 170 K. The value of vMT
for 3 is 0.288 K emu/mol at 300 K, and decreases by
lowering the temperature, indicating AFM interaction
in 3, as shown in Fig. 6. The magnetic behavior of salt
3 is very similar to that of salt 1.
The vM of the [m-MePyDV]+[Ni(dmit)2]ꢀ salt (4)
shows a broad maximum at Tmax = 100 2 K, as shown
in Fig. 9. An increase in susceptibility below 26 K was
observed, which is probably due to Curie impurities.
The value (0.713 K emu/mol) of vMT at 300 K observed
for salt 4 is similar to the sum of those (0.376 and
0.392 K emu/mol) for S = 1/2 spin system with
gþV ¼ 2.0033 [21] and gNꢀi ¼ 2.0472 [18], suggesting that
both the spins of verdazyl cation and [Ni(dmit)2]ꢀ anion
contribute to the magnetism of salt 4.

K. Mukai et al. / Polyhedron 24 (2005) 2513–2521
2519
In such a case, the vM of salt 1 may be explained by a
four-spin Heisenberg Hamiltonian,
2
1.5
1
H ¼ ꢀ2J1ðS1S2 þ S3S4Þ ꢀ 2J2S2S3;
S1 ¼ S2 ¼ S3 ¼ S4 ¼ 1=2;
χM
1D-Ferro + χS-T
χ
ð1Þ
where J1 is the exchange interaction between an edge
verdazyl cation and a central Ni(dmit)2 anion and J2 is
the interaction between two central Ni(dmit)2 anions.
The model is shown in Fig. 7(b). This Hamiltonian
has been solved exactly by Rubenacker et al. [24] to ob-
tain the energy levels and magnetic susceptibility. Using
the Eq. (2) in [24], we have fitted our data to this model,
where the g-value (g = 2.0221 at 300 K) observed for salt
1 was used tentatively for the calculation of the suscep-
tibility. The calculated susceptibility is shown by solid
curve in Fig. 7(a). The best fit parameters obtained are
2J1/kB = ꢀ780 K and 2J2/kB = ꢀ200 K. The 2J2/kB va-
lue (ꢀ200 K) for the dimer is similar to that (ꢀ320 K)
for the Ni(dmit)2 dimer in salt 2, as described later.
The Ni(dmit)2 (A) molecule connects with the Ni(dmit)2
(C) molecule with short inter-dimer Sꢂ ꢂ ꢂS contacts (see
Fig. 4 and Table 2). Therefore, we can expect some
interaction between two Ni(dmit)2 molecules (A) and
(C). The difference between the experimental and theo-
retical values of susceptibility of salt 1 may be due to
such an interaction.
0.768
0.376
0.5
0
0
50
100 150 200 250 300
(a)
T / K
80
1/χM
70
60
50
40
30
20
10
0
1D-Ferro ( 2J / kB = + 2.5 K )
θ = + 2.2 K
The susceptibility of the [p-MePyDP]+[Ni(dmit)2]ꢀ
salt (3) is similar to that of salt 1. The result suggests
that salt 3 also forms a magnetic linear tetramer as ob-
served for salt 1.
0
5
10
15
T / K
20
25
30
(b)
Fig. 8. (a) Temperature dependence of the product vMT (s) for salt 2.
The solid curve is the theoretical susceptibility calculated using Eq. (2).
(b) Inverse molar magnetic susceptibility (1/vM) of salt 2 at low
temperatures. The observed values (open circles) obey the theoretical
results for the 1D isotropic Heisenberg ferromagnet (Eq. (3)) with
2J/kB = +2.5 K indicated by the solid line.
4.2. Magnetic property of salt 2
The susceptibility of salt 2 can be explained by the
two term contributions (Eq. (2)).
vM ¼ v1D-Ferro þ vS–T
;
ð2Þ
where the first and second terms represent the contribu-
tions from quasi one-dimensional (1D) FM Heisenberg
linear-chain system [25] and singlet–triplet (S–T) equilib-
rium system, respectively. v1D-Ferro and vS–T are given by
Eqs. (3) and (4), respectively.
1.2
χ
M ( Tmax = 100 K )
1.0
0.8
0.6
0.4
0.2
0
1D-Alt. Chain ( 0.973 2 )
( 2J1/kB = -165K , α = J2/J1 = 0.6 )
Curie Imp. ( 2.7 % 2 )
v1D-Ferro ¼ ðNog2lB2 =4kBT Þ½1 þ ðJ=kBTÞꢁ;
ð3Þ
ð4Þ
BT
vS–T ¼ ðNog2lB2 =kBT Þ½1=ð3 þ eꢀ2J=k Þꢁ.
The susceptibility of salt 2 follows the Curie–Weiss law
with positive Weiss constant of +2.2 K in the tempera-
ture region between 10 and 40 K. A plot of 1/vM against
T is no longer linear at low temperature (<10 K). There-
fore, the low-temperature behavior of the susceptibility
of salt 2 was analyzed on the basis of the quasi-1D FM
Heisenberg model. In fact, the susceptibilities of salt 2
below 40 K are well reproduced by Eq. (3) with 2J/kB
= +2.5 1.0 K and g = 2.00, as shown in Fig. 8(b).
Above ca. 50 K, however, vMT increases with increasing
0
50
100 150 200 250 300
T / K
Fig. 9. Temperature dependence of the magnetic susceptibility (vM
(s) of salt 4. The dashed curve is the theoretical susceptibility
calculated by using Eq. (5).
)

2520
K. Mukai et al. / Polyhedron 24 (2005) 2513–2521
temperature, as shown in Fig. 8(a). This increase indi-
cates that thermal magnetic excitation occurs in addition
to the 1D FM linear-chain spins. The experimental data
are interpreted by the S–T model (Eq. (4)) with 2J/kB =
ꢀ320 K. As shown in Fig. 8(a), the experimental curve
can be well reproduced by Eq. (2).
5 at 20 ꢁC was r = 1.0 S cmꢀ1 with an activation energy
EA = 0.048 eV. This value is three to five orders of
magnitude larger than those of the (1:1) salts 1–4.
The examples of the organic/inorganic hybrid system
which shows the magnetism and conductivity are very
limited, because of the difficulty in molecular design of
the complexes. The present work provides five examples
of new molecular magnetic semiconductors consisting of
open-shell verdazyl radical cation and metal complex
anion. Especially, FM interaction was observed for salt
2 at 1.8–40 K. We may expect FM order for salt 2 at
lower temperature.
4.3. Magnetic property of salt 4
The susceptibility of salt 4 shows a broad maximum
at Tmax = 100 2 K. The susceptibility of 4 can be well
explained by the sum of the two contributions;
vM ¼ C1D-Altv1D-Alt þ CCurievCurie
;
ð5Þ
where C1D-Alt + CCurie = 2, and the first and second
terms represent the contributions from the 1D AFM
Heisenberg alternating-chain system [26] and from the
Curie impurity, respectively. Ci is the fraction of each
term. The dashed curve in Fig. 9 is a theoretical curve
with C1D-Alt = 2 · 0.973 and CCurie = 2 · 0.027 and
2J1/kB = ꢀ165 K (alternation parameter a = J2/J1 =
0.6). The result shows that both the spins of verdazyl
cation and Ni(dmit)2 anion contribute to the magnetism
of salt 4.
5. Supplementary material
Crystallographic data for the structural analysis have
been deposited with the Cambridge Crystallographic
Data Centre, deposition number CCDC No. 249719.
Copies of this information may be obtained free of
charge from: The Director, CCDC, 12 Union Road,
Cambridge CB2 1EZ, UK, fax: +44 1223 336 033, e-mail:
deposit@ccdc.cam.ac.uk or www: http://www.ccdc.
cam.ac.uk), or on the web http://www.ccdc.cam.ac.uk.
4.4. Conducting properties of salts 1–5
Acknowledgements
Recently, we prepared several kinds of (1:1) and (1:3)
salts of open-shell 6-oxoverdazyl radical cations with
Ni(dmit)2 anion, and found that the (1:3) salts are
molecular paramagnetic semiconductors [18,19]. On
the other hand, the (1:1) salts showed the property as
paramagnetic insulators, as observed for the usual
(1:1) salts of Ni(dmit)2 anion with closed-shell electron
donor cations, such as tetra-alkyl-ammonium cations,
alkali metal cations, etc [6,7].
However, in the present work, all the (1:1) salts 1–4
studied were found to be semiconductors, against to
our expectation. As described above, salt 1 forms a mag-
netic linear tetramer in which the strong exchange inter-
action between Ni(dmit)2 (A) and verdazyl (B) spins in
addition to that between Ni(dmit)2 (A) and (B) spins
was observed. Such an interaction will induce a delocal-
ization of conduction electron from Ni(dmit)2 dimer
moieties to verdazyl moieties, and, thus, a decrease in
the on-site Coulomb repulsion. Further, comparatively
short S–S contacts were observed between Ni(dmit)2
(A) and (C) anions, as listed in Table 2. As a result, salt
1 may show semiconductive behavior. Salt 3 showed
the magnetic property similar to that of salt 1. Further,
strong interaction between verdazyl cation and Ni(dmit)2
anion was observed for salt 4, suggesting a decrease in
the on-site Coulomb repulsion in 4. The crystal structure
analyses will be necessary to discuss the details of the
semiconductive behavior observed for the (1:1) salts
2–4. On the other hand, the conductivity of the (1:3) salt
We are very grateful to Prof. Yohji Misaki and Dr.
Masateru Taniguchi of Kyoto University for their kind
help in the measurement of conductivity of salts 2 and
3. We are also very grateful to Prof. Katsuya Inoue and
Dr. Kentaro Suzuki of Institute for Molecular Science
for their kind help in SQUID measurement. This work
was partly supported by the Grant-in-Aid for Scientific
Research on Priority Areas (B) of Molecular Conductors
and Magnets (Area No. 730/11224205) from the Ministry
of Education, Science, Sports and Culture, Japan. This
work was partly supported by the Joint Study Program
(2002–2003) of the Institute for Molecular Science.
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