Paramagnetic semiconductors: Hybrid molecular materials based on ethyl- and methyl-pyridinium-substituted verdazyl radical cations and the Ni(dmit) 2 anion (dmit = 1,3-dithiol-2-thione-4,5-dithiolate)

Article abstract of DOI:10.1246/bcsj.78.2114

Four kinds of 1:1 salts of 3-(4- and 3-alkyl-pyridinium)-1,5- diphenylverdazyl (alkyl = ethyl and methyl) radical cations with the Ni(dmit)₂ anion ([p-EtPyDV]⁺[Ni(dmit)₂] ^- (1), [m-EtPyDV]⁺[Ni(dmit)₂]^- (2), [p-MePyDV]⁺[Ni(dmit)₂]^- (3), and [m-MePyDV]⁺[Ni(dmit)₂]^- (4)) have been prepared. The magnetic properties of salts 1-4 were discussed based on the results obtained by magnetic susceptibility and ESR measurements of 1-4 and the crystal structure analysis of 1. The results of the crystal structure analysis of salt 1 indicate the dimer formation in Ni(dmit)₂ anion molecules, and the dimers are sandwiched between two verdazyl cations [p-EtPyDV] ⁺, indicating the formation of a magnetic linear tetramer in 1. The magnetic susceptibility data for salt 1 have been fitted to a four-spin linear tetramer model using an end exchange interaction of 2J₁/k_B = -780 K and a central interaction of 2J₂/k_B = -200 K. The conductivity (σ) of salts 1, 2, 3, and 4 at room temperature was σ = 2:3 × 10^-5, 1:8 × 10^-4, 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 1:1 salts 1-4 are new molecular paramagnetic semiconductors.

Full text of DOI:10.1246/bcsj.78.2114

2
114 Bull. Chem. Soc. Jpn., 78, 2114–2123 (2005)
Ó 2005 The Chemical Society of Japan
Paramagnetic Semiconductors: Hybrid Molecular Materials Based
on Ethyl- and Methyl-pyridinium-Substituted Verdazyl Radical Cations
and the Ni(dmit) Anion (dmit = 1,3-Dithiol-2-thione-4,5-dithiolate)
2
ꢀ
Keishi Ohara, Yuko Hosokoshi, and Nagao Azuma
Kazuo Mukai, Daisuke Shiba, Kenji Yoshida, Kyohei Mukai, Hiroyuki Hisatou,
1
Department of Chemistry, Faculty of Science, Ehime University, Matsuyama 790-8577
1Department of Material Science, College of Integrated Arts and Sciences, Osaka Prefecture University, Sakai 599-8531
Received April 27, 2005; E-mail: mukai@chem.sci.ehime-u.ac.jp
Four kinds of 1:1 salts of 3-(4- and 3-alkyl-pyridinium)-1,5-diphenylverdazyl (alkyl = ethyl and methyl) radical cat-
þ
ꢁ
þ
ꢁ
þ
ꢁ
ions with the Ni(dmit)2 anion ([p-EtPyDV] [Ni(dmit)2] (1), [m-EtPyDV] [Ni(dmit)2] (2), [p-MePyDV] [Ni(dmit)2]
(
þ ꢁ
3), and [m-MePyDV] [Ni(dmit)2] (4)) have been prepared. The magnetic properties of salts 1–4 were discussed based
on the results obtained by magnetic susceptibility and ESR measurements of 1–4 and the crystal structure analysis of 1.
The results of the crystal structure analysis of salt 1 indicate the dimer formation in Ni(dmit)2 anion molecules, and the
þ
dimers are sandwiched between two verdazyl cations [p-EtPyDV] , indicating the formation of a magnetic linear tetra-
mer in 1. The magnetic susceptibility data for salt 1 have been fitted to a four-spin linear tetramer model using an end
exchange interaction of 2J1=kB ¼ ꢁ780 K and a central interaction of 2J2=kB ¼ ꢁ200 K. The conductivity (ꢀ) of salts 1,
ꢁ
5
ꢁ4
ꢁ5
ꢁ6
ꢁ1
2
, 3, and 4 at room temperature was ꢀ ¼ 2:3 ꢂ 10 , 1:8 ꢂ 10 , 1:4 ꢂ 10 , and 5:4 ꢂ 10 S cm with an activation
energy of EA ¼ 0:28, 0.52, 0.21, and 0.33 eV, respectively. The 1:1 salts 1–4 are new molecular paramagnetic semicon-
ductors.
Since the first molecular superconductor containing a tran-
and 3-alkyl-pyridinium)-1,5-diphenylverdazyl radical cations
(alkyl = ethyl and methyl) with the TCNQ anion were pre-
pared, and the magnetic and conducting properties of these
sition-metal complex, (TTF)[M(dmit)2]2 (M ¼ Ni and Pd,
TTF = tetrathiafulvalene, and dmit = 1,3-dithiol-2-thione-4,5-
dithiolato), was found by Brossard et al., extensive studies have
been performed for assembled metal complexes, [Donor]-
salts were studied.2
4,25
The 1:2 salts were found to be genuine
organic paramagnetic semiconductors. However, the examples
of the molecular complexes between the open-shell radical cat-
ion and the electron acceptor anion are very limited. In the
present work, we have prepared four kinds of 1:1 salts 1–4 of
3-(4- and 3-alkyl-pyridinium)-1,5-diphenylverdazyl (alkyl =
ethyl and methyl) radical cations with the Ni(dmit)2 anion
(see Fig. 1), and studied the structural, magnetic, and conduct-
ing properties of these radical salts.
Development of molecular ferromagnets and superconduc-
tors is two challenging goals in material science, and many
studies have been performed with great success in recent years.
On the other hand, examples of magnetic conductors, where
the superconducting (or metallic) state and antiferromagnetic
(AFM) (or FM) order coexist in a system, are very limited
[M(dmit)2]n, exhibiting insulating, metallic and superconduct-
ing phases at low temperature under high pressure.
1–5
Two
examples of magnetic semiconductors consisting of an open-
shell radical cation donor and a metal complex anion acceptor
ꢁ
have been reported for the 1:1 salt of [Ni(dmit)2] with
p-EPYNN (p-N-ethylpyridinium ꢁ-nitronyl nitroxide) and
Me3N -TEMPO (=N,N,N-trimethyl(1-oxyl-2,2,6,6-tetrameth-
þ
ylpiperidine-4-yl)ammonium) radical cations.6
It is well known that verdazyl radicals show high chemical
,7
and thermal stability and can be isolated as solvent-free pure
–10
radicals in crystalline states.8
The magnetic properties of
these verdazyl radical crystals have been studied recently,
and several interesting magnetic properties such as ferromag-
1
1,12
13–15
16
netism,
spin-Peierls transition,1
weak ferromagnetism,
7–19
antiferromagnetism,
and spin frustration20 have been
because of the difficulty in molecular design of these com-
26–31
plexes. In particular, there have been no examples of
molecular superconducting ferromagnets up to this time.
found, indicating comparatively strong intermolecular spin–
spin exchange interactions. Further, the intermolecular ferro-
magnetic (FM) interaction observed for these verdazyl radicals
was of high probability because of a very strong spin polariza-
tion effect in these verdazyl radicals.21
Experimental
Syntheses. The preparations of 3-(4-pyridyl)-1,5-diphenylver-
dazyl (p-PyDV) and 3-(3-pyridyl)-1,5-diphenylverdazyl (m-PyDV)
Recently, the first two examples of molecular paramagnetic
semiconductors consisting of verdazyl radical cations and met-
al complex anions have been reported for the Ni(dmit)2 salts
of 3-[4-(trialkylammonio)phenyl]-1,5-diphenyl-6-oxoverdazyl
radicals have been reported in a previous work.20 The preparations
of the iodide salts, 3-(4- and 3-alkyl-pyridinium)-1,5-diphenylver-
þ ꢁ
dazyl iodides (alkyl = ethyl and methyl), [p-EtPyDV] I (5), [m-
þ ꢁ
þ ꢁ
þ ꢁ
EtPyDV] I (6), [p-MePyDV] I (7), and [m-MePyDV] I (8),
2
2,23
have also been reported in previous papers.24,25 Preparations of the
radical cations.
Further, the 1:1 and 1:2 salts of 3-(4-
Published on the web December 9, 2005; DOI 10.1246/bcsj.78.2114

K. Mukai et al.
Bull. Chem. Soc. Jpn., 78, No. 12 (2005) 2115
+
Measurements. The magnetic susceptibility (ꢃ ) was mea-
sured in the temperature range of 1.8–300 K by a SQUID magne-
tometer. The ꢃM of all of the samples has been corrected for the
M
Ph
Ph
-
N
N
N
S
S
S
S
S
S
S
S
Et
N
S
Ni
S
diamagnetic contribution (ꢃ ¼ ꢁ0:399 ꢂ 10ꢁ emu/mol for
3
N
dia
ꢁ
.
3
salts 1 and 2 and ꢁ0:388 ꢂ 10 emu/mol for salts 3 and 4), cal-
culated by Pascal’s method. The conductivity measurements of
salts 1–4 were performed for pressed pellet samples of the salts,
using the standard dc four-probe method.
+
-
[
[
[
[
p-EtPyDV] [Ni(dmit) ] ( 1 )
2
+
Et
Ph
Structure Determination. The X-ray measurements of the
þ ꢁ
-
N
N
N
N
S
S
S
S
S
S
S
S
þ
[p-EtPyDV] [Ni(dmit)2] salt (1) and [p-EtPyDV] I salt (5) were
carried out on a Rigaku AFC5R diffractometer with graphite-
S
Ni
S
N
.
monochromated Mo Kꢁ (ꢂ ¼ 0:71069 A) radiations. The struc-
ꢀ
Ph
ture was solved by the direct method.
+
-
Crystallographic data for the structural analysis have been
deposited with the Cambridge Crystallographic Data Centre,
deposition numbers CCDC-249719 and -249720. Copies of this
information may be obtained free of charge from: The Direc-
tor, CCDC, 12 Union Road, Cambridge, CB2 1EZ, UK (Fax:
m-EtPyDV] [Ni(dmit) ] ( 2 )
2
+
Ph
-
N
N
N
S
S
S
S
S
S
S
S
Me
N
S
Ni
-
S
+44 1223 336033; e-mail: deposit@ccdc.cam.ac.uk or www:
http://www.ccdc.cam.ac.uk/conts/retrieving.html).
N
.
Ph
+
p-MePyDV] [Ni(dmit) ] ( 3 )
Results
2
UV and Visible Spectra of Salts 1–4. The absorption
spectra of salts 1–4 in acetonitrile can be well explained by
+
Me
Ph
-
N
N
N
N
S
S
S
S
S
S
S
þ
an addition of those of iodide salts 5–8 and [n-Bu4N] -
ꢁ
S
Ni
S
[
Ni(dmit)2] , respectively. The result suggests the 1:1 complex
N
S
.
22
formation between the verdazyl cation and Ni(dmit)2 anion.
The electronic structures of the verdazyl radical cation and
Ni(dmit)2 anion moieties in salts 1–4 are thought to be similar
Ph
+
-
m-MePyDV] [Ni(dmit) ] ( 4 )
2
þ
to those corresponding in iodide salts 5–8 and [n-Bu4N] -
ꢁ
Fig. 1. Chemical structures of the 1:1 salts of 3-(4- and
-alkyl-pyridinium)-1,5-diphenylverdazyl radical cations
alkyl = ethyl and methyl) with Ni(dmit)2 anion.
[Ni(dmit)2] , respectively.
3
(
Crystal Structures of Salts 1 and 5. The crystal structure
þ
ꢁ
was determined for the [p-EtPyDV] [Ni(dmit)2] salt (1) and
þ ꢁ
the [p-EtPyDV] I salt (5) (see Table 1). In Figs. 2a and b, we
charge-transfer salts 1–4 are as follows.
þ
ꢀ
[
EtPyDV] I (47.0 mg, 0.100 mmol) in methanol (50 mL), [n-
p-EtPyDV] [Ni(dmit)2] (1): To a stirred solution of [p-
þ ꢁ
show the molecular structures of salts 1 and 5, respectively.
Table 2 shows that the bond lengths and bond angles of verda-
zyl moieties (N1–N2–C1–N3–N4–C2) in salts 1 and 5 are sim-
ilar to those corresponding in neutral 1,3,5-triphenylverdazyl
(TPV),32 indicating that the verdazyl moieties in salts 1 and
þ
ꢁ
Bu4N] [Ni(dmit)2] (69.4 mg, 0.100 mmol) in methanol (250 mL)
was added, followed by stirring for 2 h under a nitrogen atmo-
sphere. The black-violet solids precipitated were filtered and
washed with diethyl ether. Recrystallization of the residue from
acetonitrile–diethyl ether afforded the product as black-violet pris-
matic crystals (43 mg, 54%): mp 190.0–191.5 C; UV (acetoni-
trile) ꢂmax (log ") 747 (3.37), 617 (3.59), 543 (4.03), 436 (4.26),
80 (4.56), 315 (4.59), 241 (4.64). Found: C, 40.58; H, 2.62; N,
8.46%. Calcd for C27H21N5S10Ni: C, 40.80; H, 2.66; N, 8.81%.
The radical salts 2, 3, and 4 were prepared similarly.
m-EtPyDV] [Ni(dmit)2] (2): Dark-green powder crystals:
mp 199.0–201.0 C; UV (acetonitrile) ꢂmax (log ") 735 (3.59), 625
3.64), 443 (4.31), 389 (4.39), 314 (4.64), 240 (4.58). Found: C,
33
5 are not oxidized. However, the dihedral angles (8.965
ꢃ
and 2.380 ) between the least-squares plane (N1–N2–N3–N4
plane) of the verdazyl ring and those of N1- and N4-phenyl
ꢃ
rings in salt 1 are much smaller than those of the iodide salt
ꢃ ꢃ
3
5
(9.255 and 28.925 ) and TPV (27.8(4) and 40.2(4) ), respec-
tively. In TPV, the verdazyl ring has an unsymmetrical boat
configuration, with both C1 and C2 out of the nitrogen plane
ꢀ
þ
ꢃ
ꢀ
[
on the same side. C1 is displaced by only þ0:099 A, while
ꢀ
C2 is displaced by þ0:590 A. The verdazyl ring in the iodide
(
salt 5 also shows a similar structure to that of TPV. On the
other hand, in salt 1, the verdazyl ring has an unsymmetrical
chair configuration, although the deviations (ꢁ0:007ð16Þ and
4
H, 2.66; N, 8.81%.
0.67; H, 2.61; N, 8.71%. Calcd for C27H21N5S10Ni: C, 40.80;
þ
ꢀ
[
p-MePyDV] [Ni(dmit)2] (3): Dark-green powder crystals:
ꢀ
ꢃ
þ0:140ð17Þ A) of the C1 and C2 atoms out of the N1–N2–
mp > 300:0 C; UV (acetonitrile) ꢂmax (log ") 747 (3.36), 619
3.59), 543 (4.13), 436 (4.26), 379 (4.56), 350 (4.51), 315 (4.60),
40 (4.65). Found: C, 40.82; H, 2.57; N, 9.14%. Calcd for
C26H19N5S10Ni: C, 39.99; H, 2.45; N, 8.97%.
N3–N4 plane are very small, indicating that the verdazyl mole-
ꢁ
(
2
cule has a planar structure. The iodide ion (I ) in salt 5 is
located at a position near the C12, C16, C8, and C18 atoms
of the phenyl rings; the I–C12, I–C16, I–C8, and I–C18 dis-
þ
ꢃ
ꢀ
[
m-MePyDV] [Ni(dmit)2] (4): Black-violet powder crys-
ꢀ
tances are 3.720(4), 3.929(4), 3.942(4), and 3.960(5) A, respec-
tals: mp > 300:0 C; UV (acetonitrile) ꢂmax (log ") 736 (3.34),
ꢁ
6
19 (3.61), 439 (4.30), 392 (4.41), 315 (4.58), 241 (4.63). Found:
tively. On the other hand, the distances between the I ions
and the neighboring nitrogen atoms (N5) having positive
C, 40.15; H, 2.55; N, 9.05%. Calcd for C26H19N5S10Ni: C, 39.99;
H, 2.45; N, 8.97%.
charge are I{N5 ¼ 4:204ð4Þ, 4.461(4), and 4.522(4) Aꢀ .

2
116 Bull. Chem. Soc. Jpn., 78, No. 12 (2005)
Paramagnetic Semiconductors Based on Verdazyl
Table 1. Crystal Data, Experimental Conditions, and Refinement Details of Salts 1 and 5
þ
ꢁ
þ ꢁ
[
p-EtPyDV] [Ni(dmit)2] (1)
[p-EtPyDV] I (5)
Empirical formula
Formula weight
Crystal color
Crystal system
Space group
C27H21N5NiS10
794.80
Black, prismatic
triclinic
C21H21N5I
470.33
Purple, prismatic
monoclinic
P21=c (#14)
8.771(2)
ꢁ
P1 (#2)
ꢀ
a/A
11.866(3)
16.556(4)
9.267(2)
105.94(2)
111.93(2)
79.72(3)
1618.0(8)
2
1.631
12.74 (Mo Kꢁ)
0:03 ꢂ 0:10 ꢂ 0:50
5999
ꢀ
b/A
8.851(3)
26.166(2)
ꢀ
c/A
ꢃ
ꢃ
ꢃ
ꢁ
ꢄ/
ꢅ/
/
96.83(1)
3
ꢀ
V/A
Z
2016.8(8)
4
1.549
16.04 (Mo Kꢁ)
0:25 ꢂ 0:23 ꢂ 0:10
5262
ꢁ
3
Dx/g cm
ꢁ1
ꢆ/cm
Crystal size/mm
3
No. of reflections measured
No. of unique reflections (Rint)
R, Rw
5745 (0.079)
0.180, 0.221
4641 (0.026)
0.067, 0.101
þ ꢁ
Table 2. Selected Structural Data of 1,3,5-Triphenylverdazyl (TPV), [p-EtPyDV] I Salt (5), and
þ
ꢁ
[
p-EtPyDV] [Ni(dmit)2] Salt (1)
þ ꢁ
þ
ꢁ
TPV
[p-EtPyDV] I (5)
[p-EtPyDV] [Ni(dmit)2] (1)
aÞ
bÞ
cÞ
ꢀ
N1–N2/A
1.351(3)
1.338(1)
1.443(3)
114.4(2)
126.8
117.8(4)
106.1
þ0:099
þ0:590
27.8(4)
1.350(5)
1.335(6)
1.452(6)
114.3(4)
128.3(4)
117.9(4)
107.4(4)
þ0:078ð6Þ
þ0:561ð7Þ
9.255
1.34(2)
1.33(1)
1.43(2)
115.4(9)
128(1)
123.7(9)
112(1)
ꢁ0:007ð16Þ
þ0:140ð17Þ
8.965
ꢀ
N2–C1/A
ꢀ
N1–C2/A
dÞ
eÞ
N1–N2–C1/deg
N2–C1–N3/deg
N3–N4–C2/deg
N1–C2–N4/deg
fÞ
fÞ
ꢀ
C1/A
ꢀ
C2/A
Dihedral angle/deg
N1–C3–(Phenyl)
Dihedral angle/deg
N4–C15–(Phenyl)
Dihedral angle/deg
C1–C9–(Phenyl)
40.2(4)
7.0(5)
28.925
3.757
2.380
7.148
a) Mean value of N1–N2 and N3–N4. b) Mean value of N2–C1 and N3–C1. c) Mean value of N1–
C2 and N4–C2. d) Mean value of N1–N2–C1 and N4–N3–C1. e) Mean value of N3–N4–C2 and
N2–N1–C2. f) Deviation out of the N1–N2–N3–N4 plane.
The bond lengths and bond angles of the Ni(dmit)2 anion in
þ
34
crystal. The Ni(dmit)2 anion dimers are connected to each
ꢀ
salt 1 are also similar to those corresponding in the [n-Bu4N] -
ꢁ
other through short S–S contacts (S8{S9 ¼ 3:566ð4Þ A, S9–
ꢀ
ꢀ
[Ni(dmit)2] salt (data are not shown). The result indicates
that the Ni(dmit)2 moiety in salt 1 is considered to exist as a
S9 = 3.811(7) A, and S5{S8 ¼ 3:934ð5Þ A) between Ni(A)
and Ni(C).
Conductivities of Salts 1–4. The room-temperature con-
ꢁ
6
mono anion [Ni(dmit)2] with S ¼ 1=2. The dihedral angle
ꢁ5
between the least-squares planes of the two dmit rings in salt
ꢃ
ductivities (ꢀRT’s) for salts 1, 2, 3, and 4 are 2:3 ꢂ 10 , 1:8 ꢂ
ꢁ4
ꢁ5
ꢁ6
ꢁ1
1
is 4.683 , indicating the planarity of the Ni(dmit)2 moiety.
Molecular packing of salt 1 is shown in Fig. 3a. The unit
cell of salt 1 contains two Ni(dmit)2 anions and two verdazyl
10 , 1:4 ꢂ 10 , and 5:4 ꢂ 10 S cm , respectively, as list-
ed in Table 4. The temperature dependency of the resistivities
of salts 1–4 are shown in Fig. 4. Under ambient pressure, salts
1–4 show semiconductive behavior with activation energy val-
ues (EA’s) of 0.28, 0.52, 0.21, and 0.33 eV at the temperature
range of 219–298, 250–283, 246–279, and 269–298 K, respec-
tively.
þ
cations [p-EtPyDV] . The Ni(dmit)2 anion molecules in salt
ꢁ ꢁ
1
intra-dimer contacts of ca. 3.6–3.8 A (see Table 3). The dimer
form a dimer ([Ni(dmit)2] (A)–[Ni(dmit)2] (B)) having
ꢀ
molecules are sandwiched between two verdazyl cation
þ
molecules, forming a linear tetramer ([p-EtPyDV] (A)–
ꢁ ꢁ þ
Magnetic Susceptibilities of Salts 1–4. Figure 5 shows a
plot of ꢃ T versus T for salts 1–4. The value of ꢃ T for the
[
Ni(dmit)2] (A)–[Ni(dmit)2] (B)–[p-EtPyDV] (B)) in the
M
M

K. Mukai et al.
Bull. Chem. Soc. Jpn., 78, No. 12 (2005) 2117
(
a)
(
a)
V(B)
Ni(C)
Ni(B)
Ni(A)
V(A)
(
b)
S
1
S
2
S
3
S
4
J
1
J
2
J
1
(
b)
[
V(A)]
[Ni(A)]
[Ni(B)]
[V(B)]
Fig. 3. (a) Molecular packing in salt 1, showing the forma-
tion of magnetic linear tetramer, [verdazyl cation (A)–
Ni(dmit)2 anion (A)–Ni(dmit)2 anion (B)–verdazyl cation
(
B)]. (b) Scheme 1.
þ ꢁ
ꢁ
þ
ꢁ
EtPyDV] I (6) and gNi ¼ 2:0472 for [n-Bu4N] [Ni(dmit)2]
(see Table 5)), respectively, suggesting that both the spins of
the verdazyl cation and the Ni(dmit)2 anion contribute to the
magnetism of salt 2. ꢃ T for salt 2 decreases gradually by
M
decreasing the temperature with a plateau between 60 and 30
K, followed by an increase with decreasing temperature. Below
Fig. 2. Molecular structures of (a) the Ni(dmit)2 salt (1) and
b) the iodide salt (5) with the atom numbering scheme.
3
with a Curie constant of 0.376 K emu mol and a positive
0 K, the susceptibility of salt 2 follows the Curie–Weiss law
(
ꢁ1
þ
ꢁ
ꢁ1
[p-EtPyDV] [Ni(dmit)2] salt (1) is 0.243 K emu mol at 300
K (see Table 4), and decreases by lowering the temperature,
Weiss constant of þ2:2 ꢄ 0:2 K (see Fig. 7b). The ꢃ T (0.388
M
ꢁ
1
K emu mol ) of salt 2 at the plateau (30–60 K) amounts to
ꢁ
1
indicating AFM interactions in salt 1. As shown in Fig. 6, the
ꢃ of salt 1 decreases slowly by lowering the temperature from
about one half of the value (0.768 K emu mol ) calculated on
the basis of two S ¼ 1=2 spins per one formula unit of the salt,
as shown in Fig. 7a. The additional susceptibility above 60 K
is considered to be a thermally activated species which is non-
magnetic at lower temperatures. This magnetic contribution is
M
3
00 K with a minimum at around 160 K, and increases rapidly
below 20 K.
The value of ꢃ T for the [m-EtPyDV] [Ni(dmit)2] salt (2)
þ
ꢁ
M
ꢁ1
ꢁ
is 0.685 K emu mol at 300 K, and is close to the sum of those
(
tentatively assigned to the dimer of the Ni(dmit)2 radical
22,23
0.376 and 0.392 K emu mol 1) expected for non-interacting
ꢁ
anions.
fore, attributed to the verdazyl radical cations.
The susceptibility at lower temperatures is, there-
þ
S ¼ 1=2 spin system with g-values (gV ¼ 2:0032 for [m-
þ
ꢁ
ꢀ
Table 3. Pertinent Intermolecular Contacts (r/A) in [p-EtPyDV] [Ni(dmit)2] (1)
Ni (A)–Ni (B)
Ni (A)–Ni (C)
Ni (A)–V (A)
V (A)–V (B)
Ni–Ni 4.278(3)
ꢀ
r < 4:00 A)
Ni{Ni > 5:00
ꢀ
(r < 4:00 A)
S5–S8 3.934(5)
S8–S9 3.566(4)
S9–S9 3.811(7)
N(i)–N(j) (i, j ¼ 1, 2, 3, and 4)
ꢀ
(r < 4:00 A)
ꢀ
(r < 5:00 A)
N1–N1 4.29(2)
(
Ni–S10 3.815(4)
Ni–C6 3.87(1)
S2–S7 3.970(5)
S3–S7 3.614(5)
S4–S8 3.819(5)
S4–C5 3.59(1)
S4–C6 3.81(1)
C2–C4 3.63(2)
Ni–N2 3.771(9)
Ni–N3 3.684(9)
S4–N1 3.936(9)
S4–N3 3.69(1)
S4–N4 3.30(1)
S5–N1 3.79(1)
S5–N2 3.67(1)
S10–N3 3.597(9)
C2–N1 3.62(2)
C2–N4 3.90(1)
C3–N1 3.56(1)

2
118 Bull. Chem. Soc. Jpn., 78, No. 12 (2005)
Paramagnetic Semiconductors Based on Verdazyl
Table 4. Conductivity (ꢀRT), Activation Energy (EA), ꢃ T Value (at 300 K), and Magnetism of Salts 1–4
M
ꢀ
RT
EA
ꢃ T
M
/K emu mol
Salts
Magnetism
ꢁ1
ꢁ1
/S cm
/eV
þ
ꢁ
ꢁ5
Linear tetramer
(2J1=kB ¼ ꢁ780 K, 2J2=kB ¼ ꢁ200 K)
[
[
p-EtPyDV]
Ni(dmit)2] (1)
2:3 ꢂ 10
(at 298 K)
0
.28
0.243
+
Curie impurity (5.3%)
þ
ꢁ
ꢁ4
[
[
[
[
m-EtPyDV]
Ni(dmit)2] (2)
1:8 ꢂ 10
1D-Ferro (2J=k ¼ þ2:5 K)
B
0
0
.52
.21
0.685
0.288
(at 283 K)
1:4 ꢂ 10
+ S–T (2J=kB ¼ ꢁ320 K)
Linear tetramer
þ
ꢁ5
p-MePyDV]
ꢁ
Ni(dmit)2] (3)
(at 279 K)
þ
ꢁ6
Alternating Chain (Tmax ¼ 100 ꢄ 2 K,
2J1=kB ¼ ꢁ165 K, ꢁ ¼ J2=J1 ¼ 0:6)
[
[
m-MePyDV]
ꢁ
5:4 ꢂ 10
0
.33
0.713
Ni(dmit)2] (4)
(at 298 K)
+
Curie impurity (5.4%)
þ
ꢁ
Table 5. The g-Value and Peak-to-Peak Line-Width (ꢂHPP) of Salts 1–8 and [(n-Bu)4N] [Ni(dmit)2]
3
00 K
77 K
Salts
g-Value
aÞ
ꢂHPP/mT
g-Value
cÞ
ꢂHPP/mT
þ
þ
þ
ꢁ
ꢁ
ꢁ
[
[
[
[
[
[
[
[
[
p-EtPyDV] [Ni(dmit)2] (1)
m-EtPyDV] [Ni(dmit)2] (2)
p-MePyDV] [Ni(dmit)2] (3)
m-MePyDV] [Ni(dmit)2] (4)
p-EtPyDV] I (5)
m-EtPyDV] I (6)
p-MePyDV] I (7)
m-MePyDV] I (8)
2.0221
2.0093
28.4
31.3
27.1
9.56
0.414
0.340
0.444
0.351
7.97
2.0231
2.0070
8.75
14.0
14.31
8.60
0.346
0.324
0.373
0.379
7.94
aÞ
dÞ
aÞ
aÞ
bÞ
bÞ
bÞ
bÞ
aÞ
dÞ
cÞ
2.0213
2.0206
2.0039
2.0032
2.0037
2.0033
2.0472
2.0241
2.0194
þ
ꢁ
þ ꢁ
þ ꢁ
þ ꢁ
2.0037
2.0032
2.0037
2.0034
2.0474
þ ꢁ
þ
ꢁ
(n-Bu)4N] [Ni(dmit)2]
a) Experimental error: ꢄ0:0005. b) Experimental error: ꢄ0:0001. c) The value at 103 K. At the temper-
ature below 103 K, the signal due to Curie impurity overlaps to that of salt 1, and the g-value and line-
width could not be determined. d) The value at 173 K.
6
1
0
0
0
0
.8
.6
.4
.2
0
0
.768
5
4
3
ρ
(2)
Salt (1)
0.376
Salt (2)
Salt (3)
Salt (4)
(4)
(
3)
(1)
3.4
3.6
3.8
T /10 K
4.0
4.2
4.4
0
50
100
150
200
250
300
−
1
−3
−1
T / K
Fig. 4. Temperature dependence of the resistivity (ꢇ) of the
Fig. 5. Temperature dependence of the product ꢃ T for
salts 1–4.
M
1:1 salts 1–4 at ambient pressure.
þ
ꢁ
The ꢃ of the [p-MePyDV] [Ni(dmit)2] salt (3) decreases
a broad maximum at Tmax ¼ 100 ꢄ 2 K, as shown in Fig. 8.
An increase in susceptibility below 26 K was observed, which
is probably due to Curie impurities. The value (0.713
M
gradually by decreasing temperature from 300 K with a mini-
mum at about Tmin ¼ 170 K (data are not shown). The suscep-
tibility increases below 170 K by decreasing temperature. The
ꢁ
1
K emu mol ) of ꢃ T at 300 K observed for salt 4 is similar
M
ꢁ
1
ꢁ1
value of ꢃ T for 3 is 0.288 K emu mol at 300 K, and de-
to the sum of those (0.376 and 0.392 K emu mol ) for a S ¼
M
1=2 spin system with gV ¼ 2:0033 and gNiꢁ ¼ 2:0472 (see
Table 5), suggesting that both the spins of the verdazyl cation
and Ni(dmit)2 anion contribute to the magnetism of salt 4.
ESR Measurements of Salts 1–8. The ESR measurements
þ
creases by lowering the temperature, indicating AFM interac-
tions in 3, as shown in Fig. 5. The magnetic behavior of salt 3
is very similar to that of salt 1.
þ
ꢁ
The ꢃM of the [m-MePyDV] [Ni(dmit)2] salt (4) shows

K. Mukai et al.
Bull. Chem. Soc. Jpn., 78, No. 12 (2005) 2119
1
0
0
0
0
.0
.8
.6
.4
.2
0
1.2
Exp. data
χM ( Tmax = 100 K )
1
0
0
0
0
.0
.8
.6
.4
.2
0
Linear Tetramer
1
(
D-Alt. Chain ( × 0.973 × 2 )
(
2J /k = −780 K, 2J /k = −200 K )
1 B 2 B
2J /k = −165 K , α = J /J = 0.6 )
1
B
2 1
+
Curie Imp. ( 2.6% × 2 )
+Curie Imp. ( 2.7% × 2 )
0
50
100 150 200 250 300
0
50
100 150 200 250 300
T / K
T / K
Fig. 8. Temperature dependence of the magnetic suscepti-
bility (ꢃ ) ( ) of salt 4. The dashed curve is the theoret-
ical susceptibility calculated by using Eq. 5.
Fig. 6. Temperature dependence of the magnetic suscepti-
bility of salt 1. The solid curve is the theoretical suscepti-
bility calculated using Eq. 2 in Ref. 35.
M
were carried out in powder samples of salts 1–8 and [n-
(
a)
þ
ꢁ
Bu4N] [Ni(dmit)2] in the temperature range of 77–300 K.
The g-value and the peak-to-peak line-width (ꢂHPP) of the
samples at 300 and 77 K are listed in Table 5. The ESR spectra
of the iodide salts 5–8 show an exchange-narrowed, Lorentz-
2
.5
1
χΜ
1
0
þ
χ1D-Ferro + χS-T
type absorption located at gV ¼ 2:0032{2:0039 with line-
widths (ꢂHPP) of 0.340–0.444 mT. Both the g-values and the
line-widths are nearly temperature independent (see Figs. 9
and 10), as observed for usual organic radical solids. The
0
0
.768
.376
þ
ꢁ
ESR spectrum of the [n-Bu4N] [Ni(dmit)2] salt exhibits
ꢁ
.5
0
one symmetric broad line with a gNi -value of 2.0472 and a
line-width of 7.97 mT at 300 K. Both the g-value and the
line-width are temperature-independent (see Fig. 9). A rela-
tively large g-value and line-width are characteristics of the
0
50
100 150 200 250 300
Ni(dmit)2 radical anion.6
T / K
The ESR spectra of salts 1–4 also exhibit one symmetric
broad line with a line-width of 28.4, 28.8, 27.1, and 9.56 mT
at 300 K, respectively. The temperature dependencies of the g-
value and line-width of salts 1–4 are shown in Figs. 9 and 10.
(
b)
8
0
0
0
0
0
0
0
0
0
1/χM
7
1
D-Ferro ( 2J/k = + 2.5 K )
B
Discussion
6
5
4
3
2
1
θ = +2.2 K
Magnetic Properties of Salts 1 and 3. The ꢃ of salt 1 is
M
shown in Fig. 6. 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 intra-dimer contacts of ca.
ꢀ
.6–3.7 A, suggesting strong AFM exchange interactions.
3
However, the ꢃM of 1 can not be explained by a dimer model.
In salt 1, the dimer molecules are sandwiched between two
þ
verdazyl cation [p-EtPyDV] molecules, forming a linear
þ
ꢁ
ꢁ
tetramer ([p-EtPyDV] (A)–[Ni(dmit)2] (A)–[Ni(dmit)2]
0
5
10
15
20
25
30
þ
(
B)–[p-EtPyDV] (B)) (see Fig. 3 and Table 3). As described
T / K
in a previous section, the verdazyl cation molecule in salt 1 has
a planar structure, and we can expect close contacts between
the 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 ¼ 1, 2,
3, and 4) in the hydrazidinyl moiety (N1–N2–C7–N3–N4–C8),
which have large unpaired spin densities, of verdazyl cations.20
The result suggests strong exchange interactions between the
Fig. 7. (a) Temperature dependence of the product ꢃMT
) for salt 2. The solid curve is the theoretical suscepti-
bility calculated using Eq. 2. (b) Inverse molar magnetic
susceptibility (1=ꢃ ) of salt 2 at low temperatures. The
observed values ( ) obey the theoretical results for the
1D isotropic Heisenberg ferromagnet (Eq. 3) with 2J=
(
M
kB ¼ þ2:5 K indicated by the solid line.

2
120 Bull. Chem. Soc. Jpn., 78, No. 12 (2005)
Paramagnetic Semiconductors Based on Verdazyl
(a)
(a)
2
2
2
2
2
2
.05
.04
.03
.02
.01
.00
30
2.05
40
g : (n-Bu N)[Ni(dmit) ]
g : (n-Bu N)[Ni(dmit) ]
4
2
35
4
2
25
2.04
2.03
2.02
2.01
2.00
∆
Hpp
3
0
+
-
∆
Hpp
20
g : [p-MePyDV] [Ni(dmit) ]
2
25
20
15
1
1
5
0
5
0
+
-
10
5
g : [p-EtPyDV] [Ni(dmit) ]
2
+
-
+ -
g : [p-EtPyDV] I
g : [p-MePyDV] I
0
300
1
00
150
200
250
100
150
200
T / K
250
300
T / K
(b)
(b)
2
2
2
2
2
2
.05
.04
.03
.02
.01
.00
40
35
2.05
12
10
8
g : (n-Bu N)[Ni(dmit) ]
g : (n-Bu N)[Ni(dmit) ]
4 2
4
2
2
2
2
.04
.03
.02
3
0
∆
Hpp
∆
Hpp
25
6
2
1
1
5
0
0
5
0
+
-
4
+
-
g : [m-MePyDV] [Ni(dmit) ]
g : [m-EtPyDV] [Ni(dmit) ]
2
2
+
-
g : [m-EtPyDV] I
2.01
2
+
-
g : [m-MePyDV] I
2
.00
0
300
1
00
150
200
T / K
250
100
150
200
T / K
250
300
Fig. 10. Temperature dependence of the g-value (gðTÞ) (
)
Fig. 9. Temperature dependence of the g-value (gðTÞ) (
)
and the line-width (ꢂHPPðTÞ) ( ) of the polycrystalline
sample of (a) salt 3 and (b) salt 4.
and the line-width (ꢂHPPðTÞ) ( ) of the polycrystalline
sample of (a) salt 1 and (b) salt 2.
verdazyl cation and the Ni(dmit)2 anion molecules.
When the exchange energy (2J=kB) between verdazyl cation
spin (S ¼ 1=2) and Ni(dmit)2 anion spin (S ¼ 1=2) is large
susceptibility. Using Eq. 2 in Ref. 36, we have fitted our data
to this model, where the g-value observed for 1 was used ten-
tatively for the calculation of the susceptibility. The calculated
susceptibility is shown by a solid curve in Fig. 6. The best
fit parameters obtained are 2J1=kB ¼ ꢁ780 K and 2J2=kB ¼
ꢁ200 K. The 2J2=kB value (ꢁ200 K) for the dimer is similar
to that (ꢁ320 K) for the Ni(dmit)2 dimer in salt 2, as described
later.
Recently, two examples of a magnetic linear tetramer with
(i) 2J1=kB ¼ ꢁ600 K and 2J2=kB ¼ ꢁ280 K and (ii) 2J1=kB ¼
ꢁ30 K and 2J2=kB ¼ ꢁ580 K have also been reported for the
salts of 6-oxo-verdazyl radical cations with the Ni(dmit)2
anion.23 Additionally, the formations of the Ni(dmit)2 dimer
have been reported for three kinds of salts of 6-oxo-verdazyl
radical cations with the Ni(dmit)2 anion, giving the 2J2=kB val-
þ
ꢁ
compared to the g-value difference (ꢂg ¼ jgV ꢁ gNi j) of
the parent verdazyl radical cation and Ni(dmit)2 anion, the
ESR spectrum from a solid of salt 1 is centered at a position
3
5
between the absorption lines from the parent species. In fact,
the g-value (2.0221) of 1 at 300 K is similar to the average
þ
value (gAV ¼ 2:0256) of the verdazyl radical cation (gV
¼
ꢁ
2
:0039) and Ni(dmit)2 anion (gNi ¼ 2:0472). The g-value
of salt 1 remains constant when lowering the temperature, as
shown in Fig. 9a.
In such a case, the ꢃM of salt 1 may be explained by a four-
spin Heisenberg Hamiltonian,
H ¼ ꢁ2J1ðS1S2 þ S3S4Þ ꢁ 2J2S2S3
S1 ¼ S2 ¼ S3 ¼ S4 ¼ 1=2;
ð1Þ
2
2,23
ues of ꢁ258, ꢁ274, and ꢁ354 K.
The 2J1=kB and 2J2=kB
values reported are similar to those (2J1=kB ¼ ꢁ780 K and
2J2=kB ¼ ꢁ200 K) obtained for salt 1.
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. 3b. This Hamiltonian has been solved exactly by
The Ni(dmit)2 (A) molecule connects with the Ni(dmit)2 (C)
molecule with short inter-dimer SꢅꢅꢅS contacts (see Fig. 3a and
Table 3). Therefore, we can expect some interaction between
the two Ni(dmit)2 molecules (A) and (C), that is, between
3
6
Rubenacker et al. to obtain the energy levels and magnetic

K. Mukai et al.
neighboring linear tetramers ([p-EtPyDV] (A)–[Ni(dmit)2]
Bull. Chem. Soc. Jpn., 78, No. 12 (2005) 2121
þ
ꢁ
ꢃ ¼ C1D-Altꢃ1D-Alt þ CCurieꢃCurie
;
ð5Þ
ꢁ þ
M
(A)–[Ni(dmit)2] (B)–[p-EtPyDV] (B)). The difference be-
tween the experimental and theoretical values of susceptibility
of salt 1 may be due to such an interaction. However, the de-
tails are not clear at present.
The susceptibility of the [p-MePyDV] [Ni(dmit)2] salt (3)
is similar to that of salt 1. The temperature dependencies of the
g-value and line-width of salt 3 are also similar to those of salt
where C1D-Alt þ CCurie ¼ 2, and the first and second terms rep-
resent the contributions from the 1D AFM Heisenberg alternat-
39
ing-chain system and from the Curie impurity, respectively.
Ci is the fraction of each term. The dashed curve in Fig. 8
is a theoretical curve with C1D-Alt ¼ 2 ꢂ 0:973 and CCurie ¼
þ
ꢁ
2
ꢂ 0:027 and 2J1=kB ¼ ꢁ165 K (alternation parameter ꢁ ¼
1
, as shown in Fig. 10a. The result suggests that salt 3 forms a
J2=J1 ¼ 0:6). The result shows that both the spins of the ver-
dazyl cation and Ni(dmit)2 anion contribute to the magnetism
of salt 4.
magnetic linear tetramer as observed for salt 1, although the
crystal structure of salt 3 has not been determined.
Magnetic Property of Salt 2. The susceptibility of salt 2
can be explained by two term contributions (Eq. 2).
As shown in Fig. 10b, the g-value (2.0206 at 300 K) of salt
is almost temperature-independent, and is similar to the
4
average value (gAV ¼ 2:0252) of the verdazyl radical cation
ꢃM ¼ ꢃ
1D-Ferro
þ ꢃS{T
;
ð2Þ
þ
ꢁ
(
gV ¼ 2:0033) and Ni(dmit)2 anion (gNi ¼ 2:0472), sug-
where the first and second terms represent the contributions
from the quasi-one-dimensional (1D) FM Heisenberg linear-
chain system and singlet–triplet (S–T) equilibrium system,
respectively. ꢃ1D-Ferro and ꢃS{T are given by Eqs. 3 and 4,
respectively.
gesting that the verdazyl cation and Ni(dmit)2 anion molecules
form a 1D alternating-chain in the crystal.35 The result shows
to be in good accordance with that obtained by susceptibility
measurements.
Conducting Properties of Salts 1–4. Recently, we pre-
pared several kinds of 1:1 and 1:3 salts of open-shell 6-oxo-
verdazyl radical cations with the Ni(dmit)2 anion, and found
3
7
2
2
ꢃ1D-Ferro ¼ ðNog ꢆ =4kBTÞ½1 þ ðJ=kBTÞꢆ;
ꢃS{T ¼ ðNog ꢆ =kBTÞ½1=ð3 þ e
ð3Þ
ð4Þ
B
2
2
ꢁ2J=kBT
that the 1:3 salts are molecular paramagnetic semiconduc-
2,23
Þꢆ:
B
tors.2
On the other hand, the 1:1 salts showed properties
The susceptibility of salt 2 follows the Curie–Weiss law
with a positive Weiss constant of þ2:2 K in the temperature
region between 10 and 40 K. A plot of 1=ꢃM against T is no
longer linear at low temperature (<10 K). Therefore, the low-
temperature behavior of the susceptibility of salt 2 was ana-
lyzed on the basis of the quasi-1D FM Heisenberg model. In
fact, the susceptibilities of salt 2 below 40 K are well repro-
duced by Eq. 3 with 2J=kB ¼ þ2:5 ꢄ 1:0 K and g ¼ 2:00 as
of paramagnetic insulators, as observed for the usual 1:1 salts
of the Ni(dmit)2 anion with closed-shell electron donor cat-
ions, such as tetraalkylammonium cations, alkali metal cations,
1–5
etc. However, in the present work, the 1:1 salts 1–4 studied
were found to be semiconductors, against to our expectation.
Generally, organic free radical solids display properties of
insulators. The semiconductive behavior of salts are due to
the existence of the Ni(dmit)2 anion moiety. As described ear-
lier, salt 1 forms a magnetic linear tetramer in which a strong
exchange interaction (2J1=kB ¼ ꢁ780 K) was observed be-
tween Ni(dmit)2 (A) anion and verdazyl (B) cation spins, in
addition to that (2J2=kB ¼ ꢁ200 K) between Ni(dmit)2 (A)
and (B) anion spins. As listed in Table 3, the Ni(dmit)2 anion
molecules in salt 1 form a dimer with short intra-dimer con-
shown in Fig. 7b. Above ca. 50 K, ꢃ T increases with increas-
M
ing temperature, as shown in Fig. 7a. This increase indicates
that thermal magnetic excitation occurs in addition to the 1D
FM linear-chain spins. The experimental data were interpreted
by the S–T model (Eq. 4) with 2J=kB ¼ ꢁ320 K. As shown
in Fig. 7a, the experimental curve can be well reproduced by
Eq. 2. The value of the exchange interaction (2J=kB ¼ ꢁ320
K) for salt 2 is similar to those of 2J2=kB (ꢁ258– ꢁ580 K)
observed for the Ni(dmit)2 anion dimers in the salts between
ꢀ
tacts of ca. 3.6–3.7 A, suggesting strong ꢈ–ꢈ interactions. In
salt 1, the dimer molecules are sandwiched between two ver-
dazyl cation molecules, forming a magnetic linear tetramer.
Actually, there are many short contacts between the atoms in
the Ni(dmit)2 anions and in verdazyl cations, indicating a
strong ꢈ–ꢈ interaction between the verdazyl cation and the
Ni(dmit)2 anion molecules. Such a strong ꢈ–ꢈ interaction in-
duces a delocalization of conduction electrons from Ni(dmit)2
anion moieties to verdazyl cation moieties, and thus, a de-
crease in the Coulomb repulsion. Further, comparatively short
S–S contacts were observed between Ni(dmit)2 (A) and (C)
anions (see Table 3). As a result, salt 1 may show semiconduc-
tive behavior. As salt 3 shows magnetic properties similar to
those of salt 1, we can expect strong ꢈ–ꢈ interactions in salt
3, resulting in a decrease in the Coulomb repulsion. Further,
a strong interaction between the verdazyl cation and Ni(dmit)2
anion was observed for salt 4, suggesting a decrease in the
Coulomb repulsion, and thus, an increase in the conductivity
in 4. Crystal structure analyses are necessary to discuss the
details of the semiconductive behavior observed for the 1:1
salts 2–4.
6
described above.
-oxo-verdazyl radical cations and the Ni(dmit)2 anion, as
2
2,23
Consequently, ꢃ1D-Ferro and ꢃS{T in Eq. 2
for salt 2 are due to the verdazyl radical cation and Ni(dmit)2
anion dimer, respectively.
If the verdazyl cation and Ni(dmit)2 anion spins form two
magnetically-independent subsystems in the crystal, the g-val-
ue will decrease from the average value (gAV ¼ 2:0252) of the
þ
verdazyl radical cation (gV ¼ 2:0032) and Ni(dmit)2 anion
ꢁ
þ
(
(
gNi ¼ 2:0472) at 300 K to that of the verdazyl radical cation
22,23,38
gV ¼ 2:0032) at 77 K.
In fact, the g-value (2.0070) of
salt 2 observed at 173 K is similar to that (2.0032) of the iodide
salt 6. However, the g-value (2.0093) of salt 2 observed at 300
K is much smaller than that expected, as shown in Fig. 9b. The
reason is not clear at present.
Magnetic Property of Salt 4. The susceptibility of the [m-
þ
ꢁ
MePyDV] [Ni(dmit)2] salt (4) shows a broad maximum at
Tmax ¼ 100 ꢄ 2 K. The susceptibility of 4 can be well ex-
plained by the sum of two contributions:

2
122 Bull. Chem. Soc. Jpn., 78, No. 12 (2005)
Paramagnetic Semiconductors Based on Verdazyl
As a conclusion, the present result shows that the 1:1 salts
–4 of verdazyl cations with the Ni(dmit)2 anion are new mo-
lecular magnetic semiconductors. However, the conductivities
observed for these 1:1 salts are not appreciably high. It is nec-
essary to prepare 1:2 and/or 1:3 salts to obtain magnetic con-
ductors with high conductivity.
Chem., 67, 691 (1964).
F. A. Neugebauer, H. Fisher, and C. Krieger, J. Chem.
Soc., Perkin Trans. 2, 1993, 535.
F. A. Neugebauer, H. Fisher, and R. Siegel, Chem. Ber.,
21, 815 (1988).
K. Mukai, K. Konishi, K. Nedachi, and K. Takeda, J. Phys.
1
9
1
0
1
1
1
Chem., 100, 9658 (1996).
12 K. Takeda, T. Hamano, T. Kawae, M. Hidaka, M.
Takahashi, S. Kawasaki, and K. Mukai, J. Phys. Soc. Jpn., 64,
Summary
In the present work, four new magnetic charge-transfer salts
–4 consisting of 3-(4- and 3-alkyl-pyridinium)-1,5-diphenyl-
2
343 (1995).
R. K. Kremer, B. Kanellakopulos, P. Bele, H. Brunner, and
F. A. Neugebauer, Chem. Phys. Lett., 230, 255 (1994).
S. Tomiyoshi, T. Yano, N. Azuma, M. Shoga, K. Yamada,
and J. Yamauchi, Phys. Rev. B, 49, 16031 (1994).
M. Mito, H. Nakano, T. Kawae, M. Hitaka, S. Takagi, H.
1
1
3
verdazyl (alkyl = ethyl and methyl) radical cations (S ¼ 1=2)
þ
ꢁ
ꢁ
and the Ni(dmit)2 anion (S ¼ 1=2) ([p-EtPyDV] [Ni(dmit)2]
1
4
þ ꢁ þ
(
(
1),[m-EtPyDV] [Ni(dmit)2] (2),[p-MePyDV] [Ni(dmit)2]
þ
ꢁ
3), and [m-MePyDV] [Ni(dmit)2] (4)) have been prepared,
1
5
and their magnetic, conducting, and structural properties have
been studied. Strong AFM exchange interactions between ver-
dazyl cation and Ni(dmit)2 anion molecules were observed for
these salts, in addition to that between Ni(dmit)2 anion mole-
cules. The magnetic susceptibilities of salts 1 and 3 were ex-
Deguchi, K. Suzuki, K. Mukai, and K. Takeda, J. Phys. Soc.
Jpn., 66, 2147 (1997).
1
C. Krieger, and F. A. Neugebauer, J. Phys. Chem., 101, 9517
6
M. Mito, K. Takeda, K. Mukai, N. Azuma, M. R. Gleiter,
(
1997).
17 K. Mukai, N. Wada, J. B. Jamali, N. Achiwa, Y. Narumi,
þ
plained by a four-spin linear tetramer model ([Verdazyl] ꢁ
ꢁ
ꢁ
þ
[
Ni(dmit)2] ꢁ[Ni(dmit)2] ꢁ[Verdazyl] ). Salts 1–4 are new
K. Kindo, T. Kobayashi, and K. Amaya, Chem. Phys. Lett., 257,
538 (1996).
18 K. Mukai, Y. Shimobe, J. B. Jamali, and N. Achiwa,
J. Phys. Chem. B, 103, 10876 (1999).
19 K. Mukai, M. Yanagimoto, S. Tanaka, M. Mito, T. Kawae,
and K. Takeda, J. Phys. Soc. Jpn., 72, 2312 (2003).
molecular paramagnetic semiconductors. In particular, FM
interactions were observed for salt 2 at 1.8–40 K. We can ex-
pect FM order for salt 2 at lower temperature. The examples of
organic/inorganic hybrid systems that show magnetism and
conductivity are very limited. The present work provides four
examples of new molecular paramagnetic semiconductors con-
sisting of the open-shell verdazyl radical cation and metal
complex anion.
2
0
K. Mukai, M. Matsubara, H. Hisatou, Y. Hosokoshi, K.
Inoue, and N. Azuma, J. Phys. Chem. B, 106, 8632 (2002).
K. Mukai, M. Nuwa, K. Suzuki, S. Nagaoka, N. Achiwa,
and J. B. Jamali, J. Phys. Chem. B, 102, 782 (1998).
K. Mukai, T. Hatanaka, N. Senba, T. Nakayashiki, Y.
2
1
2
2
We are very grateful to Prof. Yohji Misaki and Dr. Masateru
Taniguchi of Kyoto University for their help in the measure-
ment of the conductivity of salts 2 and 3. We are also very
grateful to Prof. Katsuya Inoue and Dr. Kentaro Suzuki of
the Institute for Molecular Science for their assistance in
SQUID measurements. This work was partly supported by
the Grant-in-Aid for Scientific Research on Priority Areas
Misaki, K. Tanaka, K. Ueda, T. Sugimoto, and N. Azuma, Inorg.
Chem., 41, 5066 (2002).
2
3
K. Mukai, N. Senba, T. Hatanaka, H. Minakuchi, K. Ohara,
M. Taniguchi, Y. Misaki, Y. Hosokoshi, K. Inoue, and N. Azuma,
Inorg. Chem., 43, 566 (2004).
2
4
K. Mukai, S. Jinno, Y. Shimobe, N. Azuma, Y. Hosokoshi,
K. Inoue, M. Taniguchi, Y. Misaki, and K. Tanaka, Polyhedron,
0, 1537 (2001).
K. Mukai, S. Jinno, Y. Shimobe, N. Azuma, M. Taniguchi,
(
1
B) of Molecular Conductors and Magnets (Area No. 730/
1224205) from the Ministry of Education, Culture, Sports,
2
2
5
Science and Technology, Japan. This work was partly support-
ed by the Joint Study Program (2002–2003) of the Institute for
Molecular Science.
Y. Misaki, K. Tanaka, K. Inoue, and Y. Hosokoshi, J. Mater.
Chem., 13, 1614 (2003).
26 M. Kurmoo, A. W. Graham, P. Day, S. J. Coles, M. B.
Hursthouse, J. L. Caulfield, J. Singleton, F. L. Pratt, W. Hayes,
L. Ducasse, and P. Guionneau, J. Am. Chem. Soc., 117, 12209
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