Molecular Paramagnetic Semiconductor: Crystal Structures and Magnetic and Conducting Properties of the Ni(dmit)2 Salts of 6-Oxoverdazyl Radical Cations (dmit = 1,3-Dithiol-2-thione-4,5-dithiolate)

Article abstract of DOI:10.1021/ic030068q

Four kinds of 1:1 and 1:3 salts of 3-[4-(trimethylammonio)phenyl]-l,5-diphenyl-6-oxoverdazyl radical cation ([1]⁺) and its mono- and dimethyl derivatives ([2]⁺ and [3]⁺) with Ni(dmit)₂ anions (dmit = 1,3-dithiol-2-thione-4,5-dithiolate) ([1]⁺[Ni(dmit)₂] ^- (4), [2]⁺[Ni(dmit)₂]^- (5), [3]⁺[Ni(dmit)₂]^- (6), and [1] ⁺[Ni(dmit)₂]₃^- (7)) have been prepared, and the magnetic susceptibilities (Xm) have been measured between 1.8 and 300 K. The Xm values of salts 5 and 7 can be well reproduced by the sum of the contributions from (i) a Curie-Weiss system with a Curie constant of 0.376 (K emu)/mol and negative Weiss constants (Θ) of -0.4 and -1.7 K and (ii) a dimer system with strong negative exchange interactions of 2J/k_B = -354 and -258 K, respectively. The dimer formations in Ni(dmit)₂ anions have been ascertained by the crystal structure analyses of salts 4-6. In salts 4 and 6, Ni(dmit)₂ dimer molecules are sandwiched between two verdazyl cations, indicating the formation of a linear tetramer in 4 and 6. The magnetic susceptibility data for salts 4 and 6 have been fitted to a linear tetramer model using an end exchange interaction of 2J₁/k _B = -600 K and a central interaction of 2J₂/k_B = -280 K for 4 and 2J_l/kB = -30 K and 2J₂/k_B = -580 K for 6, respectively. The results of the temperature dependence of the g(T) value in salts 4-6 obtained by ESR measurement also support the above analyses. The 1:1 salts 4-6 are insulators. On the other hand, the conductivity of the 1:3 salt 7 at 20 °C was σ= 0.10 S cm^-1 with an activation energy E_A = 0.099 eV, showing the semiconductor property. Salt 7 is a new molecular paramagnetic semiconductor.

Full text of DOI:10.1021/ic030068q

Inorg. Chem. 2004, 43, 566−576
Molecular Paramagnetic Semiconductor: Crystal Structures and
Magnetic and Conducting Properties of the Ni(dmit)2 Salts of
6-Oxoverdazyl Radical Cations (dmit ) 1,3-Dithiol-2-thione-4,5-dithiolate)
,†
K. Mukai,* N. Senba,† T. Hatanaka,† H. Minakuchi,† K. Ohara,† M. Taniguchi,‡ Y. Misaki,‡
Y. Hosokoshi,§ K. Inoue,§ and N. Azuma†
Department of Chemistry, Faculty of Science, Ehime UniVersity, Matsuyama 790-8577,
Graduate School of Engineering, Kyoto UniVersity, Kyoto 606-8501, and
Institute for Molecular Science, Okazaki 444-8585, Japan
Received February 18, 2003
Four kinds of 1:1 and 1:3 salts of 3-[4-(trimethylammonio)phenyl]-1,5-diphenyl-6-oxoverdazyl radical cation ([1]+)
and its mono- and dimethyl derivatives ([2]+ and [3]+) with Ni(dmit)2 anions (dmit ) 1,3-dithiol-2-thione-4,5-dithiolate)
([1]+[Ni(dmit)2]- (4), [2]+[Ni(dmit)2]- (5), [3]+[Ni(dmit)2]- (6), and [1]+[Ni(dmit)2]3- (7)) have been prepared, and the
magnetic susceptibilities (øM) have been measured between 1.8 and 300 K. The øM values of salts 5 and 7 can
be well reproduced by the sum of the contributions from (i) a Curie−Weiss system with a Curie constant of 0.376
(K emu)/mol and negative Weiss constants (Θ) of −0.4 and −1.7 K and (ii) a dimer system with strong negative
exchange interactions of 2J/kB ) −354 and −258 K, respectively. The dimer formations in Ni(dmit)2 anions have
been ascertained by the crystal structure analyses of salts 4−6. In salts 4 and 6, Ni(dmit)2 dimer molecules are
sandwiched between two verdazyl cations, indicating the formation of a linear tetramer in 4 and 6. The magnetic
susceptibility data for salts 4 and 6 have been fitted to a linear tetramer model using an end exchange interaction
of 2J1/kB ) −600 K and a central interaction of 2J2/kB ) −280 K for 4 and 2J1/kB ) −30 K and 2J2/kB ) −580
K for 6, respectively. The results of the temperature dependence of the g(T) value in salts 4−6 obtained by ESR
measurement also support the above analyses. The 1:1 salts 4−6 are insulators. On the other hand, the conductivity
of the 1:3 salt 7 at 20 °C was σ ) 0.10 S cm-1 with an activation energy EA ) 0.099 eV, showing the semiconductor
property. Salt 7 is a new molecular paramagnetic semiconductor.
Introduction
coexist has been reported for (BEDT-TTF)4(H2O)[Fe(C2O4)3]-
(C6H5CN) [BEDT-TTF ) bis(ethylenedithio)tetrathiaful-
valene] (TC ) 7 K).1 Coexistence of ferromagnetism and
metallic conductivity has been found for a similar system,
[BEDT-TTF]3[MnCr(C2O4)3].2 Further, it has been reported
that κ-BETS2FeBr4 (BETS ) bis(ethylenedithio)tetraselena-
fulvalene) undergoes the transition from an antiferromagnetic
(AFM) metal phase to a superconducting phase at 1.1 K.3,4
Development of the molecular ferromagnet and that of the
superconductor are two challenging targets in material
science, and many studies have been performed with great
success in recent years. Superconductivity and magnetism
have long been considered incompatible with each other,
because Cooper pairs are destroyed by an external field (or
by the internal field generated in ferromagnets). Conse-
quently, it is very interesting to establish superconductivity
in a composite system containing localized magnetic mo-
ments. The first example of an organic/inorganic hybrid
system in which paramagnetism and superconductivity
(1) Kurmoo, M.; Graham, A. W.; Day, P.; Coles, S. J.; Hursthouse, M.
B.; Caulfield, J. L.; Singleton, J.; Pratt, F. L.; Hayes, W.; Ducasse,
L.; Guionneau, P. J. Am. Chem. Soc. 1995, 117, 12209.
(2) Coronado, E.; Galan-Mascaros, J. R.; Gomez-Garcia, C. J.; Laukhin,
V. Nature 2000, 408, 447.
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K.; Kobayashi, H.; Kobayashi, A.; Tokumoto, M.; Cassoux, P. J. Am.
Chem. Soc. 2001, 123, 306.
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Kobayashi, A.; Tokumoto, M.; Cassoux, P. J. Am. Chem. Soc. 1999,
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* Author to whom correspondence should be addressed. E-mail: mukai@
chem.sci.ehime-u.ac.jp. Phone: 81-89-927-9588. Fax.: 81-89-927-9590.
† Ehime University.
‡ Kyoto University.
§ Institute for Molecular Science.
566 Inorganic Chemistry, Vol. 43, No. 2, 2004
10.1021/ic030068q CCC: $27.50 © 2004 American Chemical Society
Published on Web 12/23/2003

Molecular Paramagnetic Semiconductor
Chart 1
However, the examples of the organic/inorganic hybrid
system in which the magnetism and conductivity coexist are
very limited, because of the difficulty in molecular design
of the complexes.
Extensive studies have been performed for the assembled
metal complexes (cation)[M(dmit)2]2 (M ) Ni and Pd, and
dmit ) 1,3-dithiol-2-thione-4,5-dithiolate) of a closed-shell
cation with an M(dmit)2 anion, exhibiting insulating, metallic,
and superconducting phases at low temperature under high
pressure.5-10 Two examples of molecular magnetic semi-
conductors consisting of an open-shell radical cation donor
and a metal complex anion acceptor have been reported for
the 1:1 salts of (i) the p-EPYNN (p-N-ethylpyridinium
R-nitronyl nitroxide) and (ii) the Me3N+-TEMPO (N,N,N-
trimethyl(1-oxyl-2,2,6,6-tetramethylpiperidine-4-yl)ammo-
nium) radical cations with a Ni(dmit)2 anion.11,12
Verdazyl radicals are well-known as one type of the
representative stable free radicals. Several interesting mag-
netic properties, such as ferromagnetism,13,14 weak ferro-
magnetism,15-17 antiferromagnetism,18 spin-Peierls transi-
tion,19,20 and spin frustration,21 have been found for the
verdazyl radical crystals in recent years. The magnetic
properties of the transition-metal and hydroquinone com-
plexes of the verdazyl radicals have been investigated by
Brook et al.23,24 and Hicks et al.25,26
In a previous work, we reported the preparation of the
1:1 and 1:2 salts of ethylpyridinium verdazyl radical cations
with TCNQ anion. The 1:2 salts were found to be genuine
organic paramagnetic semiconductors.27 Further, the 1:1 and
1:3 salts of Ni(dmit)2 anion with 6-oxoverdazyl radical cation
[V]+ (V ) 3-[4-(diethylmethylammonio)phenyl]-1,5-di-
phenyl-6-oxoverdazyl radical) were prepared.28 The 1:1 and
1:3 salts were found to be a paramagnetic insulator and
semiconductor, respectively. However, the examples of the
molecular complexes consisting of the open-shell radical
cation and Ni(dmit)2 anion are very limited. In the present
work, we prepared four kinds of Ni(dmit)2 salts (4-7)
of 3-[4-(trimethylammonio)phenyl]-1,5-diphenyl-6-oxover-
dazyl radical cation ([1]+) and its mono- and dimethyl
derivatives ([2]+ and [3]+) (see Chart 1), and studied the
structural, magnetic, and electric properties of these radical
salts.
(5) Brossard, L.; Ribault, M.; Valade, L.; Cassoux, P. Physica B+C
(Amsterdam) 1986, 143, 378.
(6) Brossard, L.; Ribault, M.; Valade, L.; Cassoux, P. J. Phys. (Paris)
1989, 50, 1521.
(7) Kobayashi, A.; Kim, H.; Sasaki, Y.; Murata, K.; Kato, R.; Kobayashi,
H. J. Chem. Soc., Faraday Trans. 1990, 86, 361.
(8) Cassoux, P.; Valade, L.; Kobayashi, H.; Kobayashi, A.; Clark, R. A.;
Underhill, A. E. Coord. Chem. ReV. 1991, 110, 115.
(9) Pullen, A. E.; Olk, R.-M. Coord. Chem. ReV. 1999, 188, 211 and
references are cited therein.
(10) Kato, R.; You-Liang, L.; Hosokoshi, Y.; Aonuma, S.; Sawa, H. Mol.
Cryst. Liq. Cryst. 1997, 296, 217.
(11) Imai, H.; Otsuka, H.; Naito, T.; Awaga, K.; Inabe, T. J. Am. Chem.
Soc. 1999, 121, 8098.
(12) Aonuma, S.; Casellas, H.; Faulmann, C.; Garreau de Bonneval, B.;
Malfant, I.; Cassoux, P.; Lacroix, P. G.; Hosokoshi, Y.; Inoue, K. J.
Mater. Chem. 2001, 11, 337.
(13) Mukai, K.; Konishi, K.; Nedachi, K.; Takeda, K. J. Phys. Chem. 1996,
100, 9658.
(14) Takeda, K.; Hamano, T.; Kawae, T.; Hidaka, M.; Takahashi, M.;
Kawasaki, S.; Mukai, K. J. Phys. Soc. Jpn. 1995, 64, 2343.
(15) Kremer, R. K.; Kanellakopulos, B.; Bele, P.; Brunner, H.; Neugebauer,
F. A. Chem. Phys. Lett. 1994, 230, 255.
(16) Tomiyoshi, S.; Yano, T.; Azuma, N.; Shoga, M.; Yamada, K.;
Yamauchi, J. Phys. ReV. B 1994, 49, 16031.
(17) Mito, M.; Nakano, H.; Kawae, T.; Hitaka, M.; Takagi, S.; Deguchi,
H.; Suzuki, K.; Mukai, K.; Takeda, K. J. Phys. Soc. Jpn. 1997, 66,
2147.
(18) Mito, M.; Takeda, K.; Mukai, K.; Azuma, N.; Gleiter, M. R.; Krieger,
C.; Neugebauer, F. A. J. Phys. Chem. 1997, 101, 9517.
(19) Mukai, K.; Wada, N.; Jamali, J. B.; Achiwa, N.; Narumi, Y.; Kindo,
K.; Kobayashi, T.; Amaya, K. Chem. Phys. Lett. 1996, 257, 538.
(20) Mukai, K.; Shimobe, Y.; Jamali, J. B.; Achiwa, N. J. Phys. Chem. B
1999, 103, 10876.
Experimental Section
2. Experimental Section. Syntheses. 3-(4-Dimethylamino-
phenyl)-1,5-diphenyl-6-oxoverdazyl radical (p-DaDpOV) and its
methyl derivatives (p-DaPTOV and p-DaDtOV) were prepared
according to a procedure similar to that used by Neugebauer et
al.29 to prepare a 1,3,5-triphenyl-6-oxoverdazyl (TOV) radical. The
precursors of the above verdazyl radicals, that is, 1,4,5,6-tetrahydro-
2,4-diphenyl-6-(4-dimethylaminophenyl)-1,2,4,5-tetrazin-3(2H)-
one and its methyl derivatives, were also prepared according to a
method used by Neugebauer et al.29
3-(4-Dimethylaminophenyl)-1,5-diphenyl-6-oxoverdazyl, p-
DaDpOV. To a stirred solution of 1,4,5,6-tetrahydro-6-(4-dimethyl-
aminophenyl)-2,4-diphenyl-1,2,4,5-tetrazin-3(2H)-one (958 mg, 2.6
mmol) in dimethyl sulfoxide (5 mL) was added lead dioxide (4 g),
and stirring was continued for 12 h. The reaction mixture was
(21) Mukai, K.; Matsubara, M.; Hisatou, H.; Hosokoshi, Y.; Inoue, K.;
Azuma, N. J. Phys. Chem. B 2002, 106, 8632.
(22) Mukai, K.; Nuwa, M.; Suzuki, K.; Nagaoka, S.; Achiwa, N.; Jamali,
J. B. J. Phys. Chem. B 1998, 102, 782.
(23) Brook, D. J. R.; Lynch, V.; Conklin, B.; Fox, M. A. J. Am. Chem.
Soc. 1997, 119, 5155.
(24) Brook, D. J. R.; Fornell, S.; Stevens, J. E.; Noll, B.; Kock, T. H.;
Eisfeld, W. Inorg. Chem. 2000, 39, 562.
(26) Hicks, R. G.; Lemaire, M. T.; Ohrstrom, L.; Richardson, J. F.;
Thompson, L. K.; Xu, Z. J. Am. Chem. Soc. 2001, 123, 7154.
(27) Mukai, K.; Jinno, S.; Shimobe, Y.; Azuma, N.; Hosokoshi, Y.; Inoue,
K.; Taniguchi, M.; Misaki, Y.; Tanaka, K. Polyhedron 2001, 20, 1537.
(28) Mukai, K.; Hatanaka, T.; Senba, N.; Nakayashiki, T.; Misaki, Y.;
Tanaka, K.; Ueda, K.; Sugimoto, T.; Azuma, N. Inorg. Chem. 2002,
41, 5066.
(25) Hicks, R. G.; Lemaire, M. T.; Thompson, L. K.; Barclay, T. M. J.
Am. Chem. Soc. 2000, 122, 8077.
(29) Neugebauer, F. A.; Fischer, H.; Krieger, C. J. J. Chem. Soc., Perkin
Trans. 2 1993, 535.
Inorganic Chemistry, Vol. 43, No. 2, 2004 567

Mukai et al.
Table 1. Conductivity (σRT), Activation Energy (EA), øMT Value (at 300 K), Magnetism, and Pascal’s Diamagnetism (ødia) of Salts 4-10
σRT
øMT
[(K emu)/mol]
ø
dia/10-3
(emu/mol)
salt
(S cm-1
)
magnetism
[1]+[Ni(dmit)2]-‚1/2CH3CN (4‚1/2CH3CN) 1.9 × 10-7 a,c
0.323 (0.391)e linear tetramer (Tmax ≈ 360 K, 2J1/kB ) -600 K,
-0.440
2J2/kB ) -280 K) + Curie impurity (3.0%)
[2]+[Ni(dmit)2]- (5)
[3]+[Ni(dmit)2]- (6)
[1]+[Ni(dmit)2]3- (7)
[1]+I-‚1/2H2O (8‚1/2H2O)
[2]+I- (9)
1.8 × 10-7 a,c
1.0 × 10-1 b,d (EA ) 0.10 eV) 0.642
0.650
0.540
Curie-Weiss (Θ ) -0.4 K) + S-T (2J/kB ) -354 K)
linear tetramer (2J1/kB ) -30 K, 2J2/kB ) -580 K)
Curie-Weiss (Θ ) -1.7 K) + S-T (2J/kB ) -258 K)
Curie-Weiss (Θ ) -2.9 K)
-0.428
-0.440
-0.786
-0.287
-0.297
-0.312
4.7 × 10-5 b,d
0.331
0.357
0.346
Curie-Weiss (Θ ) -3.8 K)
[3]+I- (10)
Curie-Weiss (Θ ) -0.6 K)
a Single crystal. b Pressed pellet. c Two-probe ac method. d Four-probe ac method. e The value at 350 K.
filtered. After addition of water and chloroform to the filtrate the
organic layer was separated, washed with water, dried (MgSO4),
and evaporated under reduced pressure. The residue was chromato-
graphed on silica gel using chloroform as eluent. Recrystallization
of the residue from ethyl acetate/n-hexane (1:3, v/v) afforded the
product as dark-green thin needle crystals (787 mg, 83%): mp 184-
186 °C; UV (dioxane) λmax (log ꢀ) 628 (3.01), 315 (4.60) nm. Anal.
Found: C, 71.46; H, 5.48; N, 18.96. Calcd for C22H20N5O: C,
71.33; H, 5.44; N, 18.91.
mg, 80%) precipitated were filtered and recrystallized from
acetonitrile. The salt 4 includes a CH3CN molecule in the crystal
with a ratio of 1:0.5, as the crystal structure analysis indicates. Dark-
green prismatic crystals were obtained: mp > 300 °C; UV (CH3-
CN) λmax (log ꢀ) 618 (3.53), 572 (3.59), 540 (3.57), 438 (4.25),
392 (4.35), 314 (4.56), 238 (4.67) nm. Anal. Found: C, 42.09; H,
2.86; N, 8.98. Calcd for C29H23N5OS10Ni‚1/2CH3CN: C, 42.03; H,
2.88; N, 8.98.
The following Ni(dmit)2 salts were prepared similarly.
[2]+[Ni(dmit)2]- Salt (5). Dark-green prismatic crystals were
obtained: mp > 300 °C; UV (CH3CN) λmax (log ꢀ) 615 (3.50),
574 (3.60), 547 (3.57), 440 (4.23), 392 (4.32), 316 (4.52), 237 (4.66)
nm. Anal. Found: C, 42.23; H, 2.86; N, 8.31. Calcd for C30H25N5-
OS10Ni: C, 42.34; H, 2.96; N, 8.23.
The following radicals were prepared similarly.
3-(4-Dimethylaminophenyl)-1-phenyl-5-tolyl-6-oxoverdazyl,
p-DaPTOV. Light green thin needle crystals were obtained: mp
155-157 °C; UV (dioxane) λmax (log ꢀ) 625 (3.10), 315 (4.59) nm.
Anal. Found: C, 71.94; H, 5.82; N, 18.13. Calcd for C23H22N5O:
C, 71.85; H, 5.77; N, 18.22.
3-(4-Dimethylaminophenyl)-1,5-ditolyl-6-oxoverdazyl, p-DaD-
tOV. Dark green needle crystals were obtained: mp 163-164 °C;
UV (dioxane) λmax (log ꢀ) 625 (3.07), 316 (4.57) nm. Anal.
Found: C, 72.50; H, 6.19; N, 17.55. Calcd for C24H24N5O: C,
72.34; H, 6.07; N, 17.57.
[3]+[Ni(dmit)2]- Salt (6). Dark-green platelet crystals were
obtained: mp > 300 °C; UV (CH3CN) λmax (log ꢀ) 614 (3.48),
575 (3.58), 551 (3.56), 438 (4.20), 395 (4.28), 318 (4.49), 237 (4.63)
nm. Anal. Found: C, 43.00; H, 3.12; N, 8.24. Calcd for C31H27N5-
OS10Ni: C, 43.04; H, 3.15; N, 8.10.
-
[1]+[Ni(dmit)2]3 Salt (7). For the preparation of 7, the air
Preparations of the iodide salts 8-10 were as follows.
oxidation of a solution containing 4 (39 mg), acetic acid (15 mL),
and acetic anhydride (15 mL) in acetone (150 mL) was carried out
at room temperature.8,9 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, 7.9 mp > 300 °C. Anal. Found: C, 28.24; H, 1.58; N, 3.66.
Calcd for C41H23N5OS30Ni3: C, 28.30; H, 1.33; N, 3.20.
Susceptibility and Conductivity Measurements. The magnetic
susceptibility was measured in the temperature range of 1.8-300
K by a SQUID magnetometer. The susceptibility of all samples
has been corrected for the diamagnetic contribution (ødia), calculated
by Pascal’s method (see Table 1).
The conductivity measurements were performed for the single
crystals of salts 4 and 5 and the pressed pellet samples of salts 6
and 7, using the standard two- or four-probe ac technique. Electrical
contacts were achieved with gold paste.
Structure Determination and Crystal Data. The X-ray mea-
surements of the Ni salts 4-6 and iodide salt 8 were carried out
on a Rigaku AFC5R diffractometer with graphite-monochromated
Cu KR (λ ) 1.54178 Å) and Mo KR (λ ) 0.71069 Å) radiations.
The structure was solved by the direct method. The crystallographic
data and the parameters of structure refinement are given in Table
2.
[1]+I- Salt (8), [1]+ ) 3-[4-(Trimethylammonio)phenyl]-1,5-
diphenyl-6-oxoverdazyl Radical Cation. A 1.03 g sample of
p-DaDpOV radical was dissolved in 20 mL of CH3I, and the
solution was stirred for 1 week at room temperature. The red crystals
precipitated were filtered and washed with diethyl ether. Recrys-
tallization of the residue from acetonitrile-diethyl ether solution
afforded the product as dark-red plate crystals (1.35 g, 95%). The
salt 8 includes a H2O molecule in the crystal with a ratio of 1:0.5,
as the crystal structure analysis indicates: mp 174-176 °C; UV
(CH3CN) λmax (log ꢀ) 535 (3.30), 424 (3.18), 314 (4.07), 248 (4.49)
nm. Anal. Found: C, 53.37; H, 4.52; N, 13.42. Calcd for C23H23N5-
OI‚1/2H2O: C, 52.98; H, 4.64; N, 13.43.
The following iodide salts were prepared similarly.
[2]+I- Salt (9), [2]+ ) 3-[4-(Trimethylammonio)phenyl]-1-
phenyl-5-tolyl-6-oxoverdazyl Radical Cation. Dark-red plate
crystals were obtained: mp 150-152 °C; UV (CH3CN) λmax (log
ꢀ) 535 (3.35), 428 (3.23), 318 (4.07), 247 (4.50) nm. Anal. Found:
C, 54.54; H, 4.83; N, 13.07. Calcd for C24H25N5OI: C, 54.78; H,
4.78; N, 13.31.
[3]+I- Salt (10), [3]+ ) 3-[4-(Trimethylammonio)phenyl]-1,5-
ditolyl-6-oxoverdazyl Radical Cation. Dark-red plate crystals were
obtained: mp 162-164 °C; UV (CH3CN) λmax (log ꢀ) 535 (3.40),
433 (3.29), 322 (4.12), 247 (4.53) nm. Anal. Found: C, 55.31; H,
5.01; N, 13.00. Calcd for C25H27N5OI: C, 55.56; H, 5.04; N, 12.96.
Preparations of the Ni(dmit)2 salts 4-6 were as follows.
[1]+[Ni(dmit)2]- Salt (4). To a solution of [1]+I- (16.1 mg,
0.0313 mmol) in acetonitrile (10 mL) was added slowly [n-Bu4N]+-
[Ni(dmit)2]- (21.7 mg, 0.0313 mmol) in acetonitrile (20 mL), and
the reaction mixture was kept for one night at room temperature
under a nitrogen atmosphere. The dark green crystals of 4 (21.0
Results
UV and Visible Spectra of Salts 4-6. As reported in a
previous work,28 the absorption spectra of salts 4-6 in
acetonitrile can be well explained by an addition of those of
iodide salts 8-10 and [n-Bu4N]+[Ni(dmit)2]-, respectively,
suggesting 1:1 complex formation between verdazyl cation
568 Inorganic Chemistry, Vol. 43, No. 2, 2004

Molecular Paramagnetic Semiconductor
Table 2. Crystal Data, Experimental Conditions, and Refinement Details of the 1:1 Ni(dmit)2 Salts 4-6 and the Iodide Salt 8
[1]+[Ni(dmit)2]-‚1/2CH3CN
[2]+[Ni(dmit)2]-
[3]+[Ni(dmit)2]-
[1]+I-‚1/2H2O
empirical formula
fw
2(C23H23N5O)2(C6NiS10)‚C2H3N
1714.74
C30H25N5OS10Ni
850.94
C31H27N5OS10Ni
864.97
C23H23N5OI‚1/2H2O
521.38
cryst color
cryst syst
space group
a/Å
b/Å
c/Å
R/deg
â/deg
γ/deg
V/Å3
dark green, prismatic
triclinic
P1h (No. 2)
12.533(1)
15.012(2)
9.983(1)
97.632(10)
107.299(8)
89.890(10)
1775.9(4)
dark green, prismatic
triclinic
black, plate
monoclinic
P21/c (No. 14)
9.641(3)
22.435(4)
16.989(3)
red, prismatic
monoclinic
P21/n (No. 14)
13.114(4)
11.332(3)
18.437(7)
P1h (No. 2)
13.281(3)
13.930(5)
10.618(4)
109.72(3)
95.72(2)
96.19(2)
1818.9(11)
2
93.37(2)
108.67(3)
3668(1)
4
1.566
11.33 (Mo KR)
0.50 × 0.38 × 0.08
4.7-55.0
9147
8429 (0.058)
6252 (I > 2σ(F2)
14.44
2595.7(15)
4
1.334
12.57 (Mo KR)
0.430 × 0.230 × 0.130
4.7-55.0
6504
5970 (0.052)
4908 (I > 0.00)
17.53
Z
1
Dx/(g cm-3
)
1.603
1.554
µ/cm-1
65.76 (Cu KR)
0.280 × 0.180 × 0.150
4.7-123.1
11.41 (Mo KR)
0.300 × 0.200 × 0.150
4.7-55.1
cryst size/mm
range of 2θ/deg
no. of reflns measured
no. of unique reflns (Rint
no. of reflns obsd
5813
8694
)
5527 (0.015)
5527 (all, 2θ < 123.10°)
12.94
0.041, 0.142
0.98
8377 (0.028)
8377 (I > 0.00)
19.76
0.059, 0.156
1.18
no. or reflns/no. of params ratio
R, Rw
S (goodness of fit)
0.087, 0.188
1.22
0.069, 0.212
1.15
max shifts/error
0.001
-0.52 to +0.40
0.00
-0.65 to +0.87
0.000
-1.18 to +1.57
0.002
-0.93 to +1.44
residual electron density/(e Å-3
)
Table 3. Selected Structural Data for 1,3,5-triphenyl-6-oxoverdazyl
(TOV), [1]+[Ni(dmit)2]- salt 4, and 8
of verdazyl moieties in salts 5 and 6 are also similar to those
of TOV (data are not shown). The structures of the Ni(dmit)2
anion moiety in salts 4-6 are also similar to those in the
[n-Bu4N]+[Ni(dmit)2]- salt (data are not shown).31 The
dihedral angles between least-squares planes of two dmit
rings in salts 4-6 are 4.38°, 8.11°, and 7.21°, respectively,
indicating the planarity of the Ni(dmit)2 moiety.
Molecular packing of salt 4 is shown in Figure 3. The
unit cell of salt 4 contains two Ni(dmit)2 anions and two
verdazyl cations [1]+. The Ni(dmit)2 anion molecules in salt
4 form a dimer ([Ni(dmit)2] (A)-[Ni(dmit)2] (B)) having
intradimer contacts of ca. 3.6-3.7 Å along the b axis. The
dimer molecules are sandwiched between two verdazyl cation
[1]+ molecules, forming a linear tetramer ([1]+-[Ni(dmit)2]
(A)-[Ni(dmit)2] (B)-[1]+) in the crystal (see Figure 3 and
Table 4). The Ni(dmit)2 anion dimers are connected to each
other through short S-S contacts (S1-S1 ) 3.632(2) Å and
S1-S2 ) 3.643(1) Å).
[1]+[Ni(dmit)2]-‚
[1]+I-‚
TOV
1/2CH3CNf
1/2H2O
O-C2/Å
1.208(2)
1.381(1)
1.368(1)
1.330(1)
1.212(4)
1.388(4)
1.366(4)
1.327(4)
1.500(4)
115.3(3)
127.1(3)
124.4(3)
113.5(3)
30.2(2)
1.214(10)
1.39(1)
1.378(9)
1.34(1)
1.504(9)
113.7(7)
128.9(7)
124.9(7)
113.7(7)
41.3(3)
N1-C2/Åa
N1-N2/Åb
N2-C1/Åc
N5-C12/Å
N1-N2-C1/degd
N2-C1-N3/deg
N3-N4-C2/dege
N4-C2-N1/deg
115.3
127.0
124.0
114.4
dihedral angle/deg, N1-phenyl 34.5(1)
dihedral angle/deg, N4-phenyl 34.5(1)
dihedral angle/deg, C1-phenyl 12.3
53.8(1)
9.5(1)
48.2(3)
11.1(3)
a Mean value of N1-C2 and N4-C2. b Mean value of N1-N2 and N3-
N4. c Mean value of N2-C1 and N3-C1. d Mean value of N1-N2-C1
and C1-N3-N4. e Mean value of N3-N4-C2 and C2-N1-N2. f C7, C8,
and C18 atoms in salt 4 correspond to C1, C2, and C12 atoms in salt 8,
respectively.
and [Ni(dmit)2]- anion. The 7 crystals are insoluble in the
usual organic solvents, and we could not measure the optical
spectrum of salt 7 in solution.
Crystal Structures of Salts 4-6 and 8. The crystal
structure could be determined for the 1:1 [V]+[Ni(dmit)2]-
(V ) 1-3) salts 4-6 and the salt 8 (see Table 2). Salts 4
and 8 include CH3CN and H2O molecules in the crystal with
a ratio of 1:0.5, respectively. In parts a-c of Figure 1 and
in Figure 2, we show the solid-state structures of salts 4-6
and 8, respectively.
Table 3 shows that the bond lengths and bond angles of
verdazyl moieties in the Ni(dmit)2 salt 4 and iodide salt 8
are similar to those of the neutral 1,3,5-triphenyl-6-oxover-
dazyl (TOV),29 indicating that the verdazyl moieties in salts
4 and 8 are not oxidized.30 The bond lengths and bond angles
Molecular packing of salt 5 is shown in Figure 4. The
unit cell of salt 5 contains two Ni(dmit)2 anions and two
verdazyl cations [2]+. The Ni(dmit)2 anion molecules in salt
5 also form a dimer ([Ni(dmit)2] (A)-[Ni(dmit)2] (B)) having
intradimer contacts of ca. 3.6-3.8 Å along the c axis (see
Table 5). However, the interdimer distances are larger than
6.509(2) Å (S5-S10), as shown in Figure 4.
Molecular packing of salt 6 is shown in Figure 5. The
unit cell of salt 6 contains four Ni(dmit)2 anions and four
verdazyl cations [3]+. The Ni(dmit)2 anion molecules in salt
6 form a dimer ([Ni(dmit)2] (A)-[Ni(dmit)2] (B)) having
intradimer contacts of ca. 3.6-3.8 Å presented in Table 6.
The dimer molecules are sandwiched between two verdazyl
cation [3]+ molecules, forming a linear tetramer ([3]+-[Ni-
(dmit)2] (A)-[Ni(dmit)2] (B)-[3]+) in the crystal, as ob-
served for salt 4 (see Figure 5 and Table 6). The dimers are
(30) Nakatsuji, S.; Kitamura, A.; Takai, A.; Nishikawa, K.; Morimoto, Y.;
Yasuoka, N.; Kawamura, H.; Anzai, H. Z. Naturforsch. 1998, 53b,
495.
(31) Lindqvist, O.; Anderson, L.; Sieler, J.; Steimecke, G.; Hoyer, E. Acta
Chem. Scand., Ser. A 1982, 36, 855.
Inorganic Chemistry, Vol. 43, No. 2, 2004 569

Mukai et al.
Figure 2. Molecular structure of the iodide salt 8 with the atom numbering
scheme.
Figure 3. Molecular packing in salt 4, showing the formation of a linear
tetramer [verdazyl cation-Ni(dmit)2 anion (A)-Ni(dmit)2 anion (B)-
verdazyl cation] along the b axis.
Figure 4. Molecular packing of salt 5.
In the iodide salt 8, the interatomic distances between the
nitrogen atoms in the central hydrazidinyl moiety (N1-N2-
C1-N3-N4-C2) having large unpaired spin densities are
larger than 6.46(1) Å, indicating weak intermolecular
exchange interaction, as described later.32 The iodide ion (I-)
in salt 8 is located near the N3 and C1 atoms of the verdazyl
ring; the I--N3 and I--C1 distances are 3.776(7) and
Figure 1. Molecular structure of (a) salt 4, (b) salt 5, and (c) salt 6 with
the atom numbering scheme.
connected to each other through four short S-S contacts
(S1-S8 ) 3.803(4) Å, S5-S9 ) 3.574(3) Å, S5-S8 )
3.747(4) Å, and S9-S9 ) 3.586(5) Å), as shown in Figure
5.
(32) Mukai, K.; Suzuki, K.; Ohara, K.; Jamali, J. B.; Achiwa, N. J. Phys.
Soc. Jpn. 1999, 68, 3078.
570 Inorganic Chemistry, Vol. 43, No. 2, 2004

Molecular Paramagnetic Semiconductor
Table 4. Pertinent Intermolecular Contacts (r/Å) in [1]+[Ni(dmit)2]- 4‚1/2CH3CN
[Ni(dmit)2]‚‚‚[Ni(dmit)2]
[Ni(A)‚‚‚Ni(B)]
[Ni(dmit)2]‚‚‚[Ni(dmit)2]
[Ni(A)‚‚‚Ni(C)]
[Ni(dmit)2]‚‚‚verdazyl
[Ni(A)‚‚‚V(A)]
[Ni(dmit)2]‚‚‚verdazyl
[Ni(A)‚‚‚V(B)]
verdazyl‚‚‚verdazyl
Ni‚‚‚Nj, >5
Ni‚‚‚Ni, 5.540(1)
Ni‚‚‚S1, 3.679(1)
Ni‚‚‚C3, 3.789(3)
S2‚‚‚C5, 3.877(4)
S3‚‚‚S9, 3.893(1)
S4‚‚‚S5, 3.945(1)
S5‚‚‚C2, 3.628(4)
S5‚‚‚C3, 3.772(4)
S9‚‚‚C1, 3.660(4)
Ni‚‚‚Ni, 9.98
Ni‚‚‚N2, 3.853(3)
Ni‚‚‚N3, 3.905(3)
S5‚‚‚N3, 3.511(3)
S9‚‚‚N4, 3.429(3)
S9‚‚‚N1, 3.680(3)
S9‚‚‚N3, 3.791(3)
S9‚‚‚N2, 3.958(3)
C5‚‚‚N1, 3.584(4)
C6‚‚‚N1, 3.944(4)
S7‚‚‚N3, 3.690(3)
S7‚‚‚N4, 3.971(3)
S1‚‚‚S1, 3.632(2)
S1‚‚‚S2, 3.643(1)
S1‚‚‚C1, 3.834(4)
Table 5. Pertinent Intermolecular Contacts (r/Å) in 5
[Ni(dmit)2]‚‚‚[Ni(dmit)2]
[Ni(A)‚‚‚Ni(B)]
[Ni(dmit)2]‚‚‚verdazyl
[Ni(dmit)2]‚‚‚verdazyl
[Ni(A)‚‚‚V(A)]
[Ni(A)‚‚‚V(B)]
verdazyl‚‚‚verdazyl
Ni‚‚‚Nj, >5
Ni‚‚‚Ni, 4.390(2)
Ni‚‚‚S4, 3.836(2)
S1‚‚‚S10, 3.916(2)
S2‚‚‚S6, 3.872(2)
S2‚‚‚S8, 3.918(2)
S3‚‚‚S9, 3.581(2)
S4‚‚‚S5, 3.767(2)
Ni‚‚‚Ni, >5
S6‚‚‚N2, 3.779(4)
S7‚‚‚N4, 3.510(4)
S7‚‚‚N3, 3.570(4)
S7‚‚‚N1, 3.765(4)
S7‚‚‚N2, 3.825(4)
S1‚‚‚N2, 3.598(4)
S2‚‚‚N2, 3.716(4)
S2‚‚‚N4, 3.970(4)
Table 6. Pertinent Intermolecular Contacts (r/Å) in 6
[Ni(dmit)2]‚‚‚[Ni(dmit)2]
[Ni(A)‚‚‚Ni(B)]
[Ni(dmit)2]‚‚‚[Ni(dmit)2]
[Ni(dmit)2]‚‚‚verdazyl
[Ni(dmit)2]‚‚‚verdazyl
[Ni(A)‚‚‚V(B)]
[Ni(A)‚‚‚Ni(C)]
[Ni(A)‚‚‚V(A)]
verdazyl‚‚‚verdazyl
Ni‚‚‚Nj, >5
Ni‚‚‚Ni, 4.603(3)
Ni‚‚‚C2, 3.651(9)
Ni‚‚‚S4, 3.754(3)
S1‚‚‚S10, 3.826(4)
S2‚‚‚S6, 3.987(6)
S4‚‚‚S5, 3.702(4)
S10‚‚‚C3, 3.773(9)
S10‚‚‚C1, 3.91(1)
S10‚‚‚C2, 3.944(9)
Ni‚‚‚Ni, 6.516(3)
S1‚‚‚S8, 3.803(4)
S5‚‚‚S9, 3.574(3)
S5‚‚‚S8, 3.747(4)
S9‚‚‚S9, 3.586(5)
Ni‚‚‚N4, 3.725(7)
Ni‚‚‚N3, 3.821(8)
S4‚‚‚N1, 3.971(7)
S9‚‚‚N3, 3.836(8)
S10‚‚‚N2, 3.657(8)
S10‚‚‚N1, 3.809(8)
C6‚‚‚N2, 3.87(1)
S7‚‚‚N2, 3.642(8)
S7‚‚‚N3, 3.682(8)
S7‚‚‚N1, 3.745(7)
S7‚‚‚N4, 3.789(7)
3.765(8) Å, respectively. These values just correspond to the
sum (3.73 and 3.83 Å) of the ionic radius (2.16 Å) of the I-
ion and the van der Waals radius (1.57 and 1.67 Å) of the
N2 and C1 atoms, showing close contact between the I- ion
and N2 and C1 atoms, respectively. The increase of the g
value in iodide salt 8 may be induced by the existence of
the iodide ion. On the other hand, the distances (I--N5+ )
4.439(6), 4.591(6), and 5.069(6) Å) between the I- ions and
the neighboring nitrogen atoms (N5+) having positive charge
are larger than the above distances.
Conductivities of Salts 4-7. The room temperature
conductivities (σRT) for salts 4-7 are 1.9 × 10-7, 1.8 × 10-7,
4.7 × 10-5, and 1.0 × 10-1 S cm-1, respectively, as listed
in Table 1. Salts 4-6 are insulators as expected for the 1:1
salts. On the other hand, the 1:3 salt 7 has higher conductivity
than the 1:1 salts. The temperature dependency of the
resistivity of the 1:3 salt is shown in Figure 6. Under ambient
pressure, the 1:3 salt 7 shows semiconductive behavior with
Figure 5. Molecular packing in salt 6, showing the formation of a linear
tetramer [verdazyl cation-Ni(dmit)2 anion (A)-Ni(dmit)2 anion (B)-
verdazyl cation].
Figure 6. Temperature dependence of the resistivity (F) of the 1:3 salt 7
at ambient pressure.
Inorganic Chemistry, Vol. 43, No. 2, 2004 571

Mukai et al.
Table 7. g value and Peak-to-Peak Line Width (∆HPP) of Salts 4-10
and Related Compounds
300 K
77 K
∆HPP
(mT)
∆HPP
(mT)
salt
g value
g value
4
5
6
7
2.0126a 24.9
2.0159a 25.1
2.0162a 21.4
2.0049d 13.8d
2.0044
2.0043
0.869
0.647
0.603
0.910
0.918
8 (powder)
8 (in EtOH)
9 (powder)
2.0048b 0.584
2.0048
2.0052
2.0060
2.0036c aN ) 0.57 mT
2.0051b 0.854
9 (in EtOH)
10 (powder)
10 (in EtOH)
TOV (powder)
TOV (in EtOH)
2.0036c aN ) 0.57 mT
2.0061b 0.795
2.0035c aN ) 0.57 mT
2.0039b
Figure 7. Temperature dependence of the product øMT for salts 4-7.
2.0036c aN ) 0.56 mT
[n-Bu4N]+[Ni(dmit)2]- 2.0472a 7.97
2.0474
7.94
a Experimental error (0.0005. b Experimental error (0.0002. c Experi-
mental error (0.0001. d The value at 123 K. At temperatures below 123
K, the anisotropic signal due to salt 4 appears, and the g value and line
width could not be determined.
Figure 8. Temperature dependence of the magnetic susceptibility of salt
4. The solid curve is the theoretical susceptibility calculated using eq 2 in
ref 33.
an activation energy (EA) of 0.10 eV in the temperature range
of 165-300 K.
Magnetic Susceptibilities of Salts 4-10. Figure 7 shows
a plot of øMT versus T for three kinds of 1:1 salts (4-6) and
a kind of 1:3 salt (7). The values of øMT for 4-6 at 300 K
are 0.323 (0.391 at 350 K), 0.650, and 0.540 K emu/mol,
respectively. These values are larger than that (0.376 K emu/
mol) for the S ) 1/2 free spin system, suggesting that both
spins of the verdazyl cation (S ) 1/2) and Ni(dmit)2 anion
(S ) 1/2) contribute to the magnetism of salts 4-6. The øM
of salt 4 shows a broad maximum at Tmax ≈ 360 K (see
Figure 8). The susceptibilities of salts 5 and 6 increase
monotonically with decreasing temperature from 300 K, and
no peaks were observed in the susceptibilities. The suscep-
tibility of the 1:3 salt 7 showed a behavior similar to that of
the 1:1 salt 5. The value (0.642 K emu/mol) of øMT at 300
K observed for salt 7 also suggests that both the spins of the
verdazyl cation (S ) 1/2) and [Ni(dmit)2]3- anion (S ) 1/2)
contribute to the magnetism of salt 7.
The susceptibilities of the iodide salts 8-10 follow the
Curie-Weiss law (see Table 1). The small value of the
negative Weiss constant (θ ) -2.9 K) in salt 8 indicates
weak AFM interaction. This agrees with the absence of short
direct distances between the verdazyl moieties in salt 8.
ESR Measurements of Salts 4-10. The ESR measure-
ments were carried out in powder samples of salts 4-10
and [n-Bu4N]+[Ni(dmit)]- in the temperature range of 77-
300 K. The g value and the peak-to-peak line width (∆HPP)
of the samples at 300 and 77 K are listed in Table 7. The g
values of the iodide salts 8-10 are nearly temperature
independent (see Figure 9), while the line widths show a
Figure 9. Temperature dependence of the g value (g(T)) (O) and the line
width (∆HPP(T)) (4) of the polycrystalline sample of (a) salt 4, (b) salt 5,
and (c) salt 6. The solid line is the theoretical g(T) value calculated by
using eq 4.
small increase with decreasing temperature. The g value and
hyperfine splitting aN of the iodide salts 8-10 in ethanol
572 Inorganic Chemistry, Vol. 43, No. 2, 2004

Molecular Paramagnetic Semiconductor
Chart 2
are similar to each other, and are similar to those (g ) 2.0036
and aN ) 0.56 mT) of TOV radical. On the other hand, the
g values (g ) 2.0048, 2.0051, and 2.0061) of powder samples
of salts 8-10 are larger than that (2.0039) of TOV. The I-
ion having a negative charge is located near the verdazyl
ring in salt 8, as described above. This negative charge may
affect the increase of the g value of salt 8. The [n-Bu4N]+-
[Ni(dmit)2]- salt exhibits one symmetric broad line (g )
2.0472 and ∆HPP ) 7.97 mT) at 300 K. Both the g value
and the line width are temperature independent (see Table 7
and Figure 9).
In such a case, the øM of salt 4 may be explained by a
four-spin Heisenberg Hamiltonian
H ) -2J1(S1S2 + S3S4) - 2J2S2S3
S1 ) S2 ) S3 ) S4 ) 1/2
(1)
The ESR spectrum of salt 6 shows a symmetric broad line
with a g value of 2.0162 and a line width of 21.4 mT at 300
K. However, in addition to the broad ESR signal of salt 6,
a symmetric single line (g ) 2.0045 and ∆HPP ) 1.58 mT)
with a narrow line width which is attributable to the Curie
impurity due to verdazyl radical cation was observed at 300
K. The integrated signal intensity of the Curie impurity was
about 0.6% of that of salt 6. The g value and the line width
of salt 6 show notable temperature dependence, as shown in
Figure 9c. Similarly, the salts 4 and 5 show a broad
symmetric ESR absorption, and both the g value and the
line width decrease with decreasing temperature, as shown
in Figure 9a,b. On the other hand, the 1:3 salt 7 shows
anisotropic absorption with an anomalous line shape at 77-
300 K, and we could not determine the g value of salt 7.
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 Chart 2. This Hamiltonian has been solved
exactly by Rubenacker et al.,33 to obtain the energy levels
and magnetic susceptibility. Using eq 2 in ref 33, we have
fitted our data to this model, where, as the g value of salt 4,
+
the average value (gav ) 2.0254) of gV ) 2.0036 for the
-
verdazyl cation and gNi ) 2.0472 for the Ni(dmit)2 anion
was used tentatively for the calculation of the susceptibility.
The calculated susceptibility is shown by the solid curve in
Figure 8, where øCurie due to the Curie impurity (3.0%)
included in the crystal was added to the theoretical suscep-
tibility. The best fit parameters obtained are 2J1/kB ) -600
K and 2J2/kB ) -280 K. The 2J2/ kB value (-280 K) for
the dimer compares well with those (-354 and -580 K)
for the Ni(dmit)2 dimer in salts 5 and 6, respectively, as
described later.
Discussion
Magnetic Property of Salt 4. The susceptibility of the
salt shows a maximum at Tmax ≈ 360 K, and increases again
below ca. 100 K with decreasing temperature, as shown in
Figure 8. The increase in øM is probably due to the Curie
impurity (3.0%) included in the crystal. The g value of salt
4 decreases from 2.0126 at 300 K to 2.0049 at 123 K by
lowering the temperature, as shown in Figure 9a. The g value
(2.0126) of 4 at 300 K is larger than that of verdazyl cation
Magnetic Properties of Salts 5 and 6. The susceptibilities
of salts 5 and 6 can be reproduced by the sum of the two
contributions, as shown in Figure 10a,b, respectively
øM(T) ) øCurie-Weiss(T) + øS-T(T)
(2)
where the first and second terms represent the contributions
from (i) the Curie-Weiss system and (ii) the singlet-triplet
(S-T) equilibrium system (dimer system), respectively.
+
-
(gV ) 2.0036) and smaller than that of Ni(dmit)2 anion (gNi
) 2.0472) at 300 K, suggesting that both the spins of the
cation and anion contribute to the magnetism of salt 4. The
g value (2.0049) of 4 at 123 K is similar to that (2.0036 in
ethanol) of verdazyl radical cation. The result indicates that
the verdazyl cation spins contribute mainly to the øM of salt
4 at 123 K.
ø
S-T(T) is given by eq 3.
S-T(T) ) (Nog2µB /kBT)[1/(3 + e-2J/kBT)]
The solid curve in Figure 10a is a theoretical curve ((i)
2
ø
(3)
CCurie ) 0.376 (K emu)/mol and Θ ) -0.4 K and (ii) 2JA-B
/
The molecular packing of salt 4 is shown in Figure 3. As
described in a previous section, the Ni(dmit)2 anion mol-
ecules in salt 4 form a dimer (Ni(dmit)2 (A)-Ni(dmit)2 (B))
with short intradimer contacts of ca. 3.6-3.7 Å, suggesting
strong AFM exchange interaction. However, the øM of 4
cannot be explained by a dimer model. In salt 4, the dimer
molecules are sandwiched between two verdazyl cation [1]+
molecules, forming linear tetramer ([1]+-[Ni(dmit)2]- (A)-
[Ni(dmit)2]- (B)-[1]+) (see Figure 3 and Table 4). We can
expect strong exchange interaction between the Ni(dmit)2
anions and the verdazyl cations [1]+, because there are many
short contacts between the Ni, Si, and Ci atoms in the
Ni(dmit)2 anions and the Nj atoms (j ) 1-4) in the
hydrazidinyl moiety (N1-N2-C7-N3-N4-C8), having
large unpaired spin densities, of verdazyl cations [1]+.32
kB ) -354 K) calculated for salt 5. Similarly, the solid curve
in Figure 10b is a theoretical curve ((i) CCurie ) 0.376 (K
emu)/mol and Θ ) -0.3 K and (ii) 2JA-B/kB ) -580 K)
calculated for salt 6. The results show that the susceptibilities
can be explained approximately by eq 2. The susceptibilities
of salts 5 and 6 at the low-temperature region are due to the
spins of verdazyl cations [2]+ and [3]+, respectively, because
the Ni(dmit)2 anions form a dimer in the crystal lattice, as
described below.9,11,12
Figure 4 shows a projection of the structure of salt 5 along
the a axis. The Ni(dmit)2 anion molecules form a dimer,
Ni(dmit)2 (A)-Ni(dmit)2 (B), having short interatomic
(33) Rubenacker, G. V.; Drumheller, J. E.; Emerson, K.; Willet, R. D. J.
Magn. Magn. Mater. 1986, 54, 1483.
Inorganic Chemistry, Vol. 43, No. 2, 2004 573

Mukai et al.
C-C distances were observed for the Ni(A)-Ni(B) pair, as
listed in Table 6, indicating dimer formation. Further, short
S-S distances were observed for the Ni(A)-Ni(C) pair. In
salt 6, the dimer molecules are sandwiched between two
verdazyl cation [3]+ molecules, forming a linear tetramer
([3]+-[Ni(dmit)2]- (A)-[Ni(dmit)2]- (B)-[3]+) (see Figure
5 and Table 6). There are some comparatively short distances
between the V(A) cation and Ni(A) anion, suggesting
considerable interaction between the verdazyl radical spin
and Ni(dmit)2 anion spin. Therefore, the øM of salt 6 was
calculated by using eq 2 (that is, the linear tetramer model)
in ref 33. The best fit parameters obtained are 2J1/kB ) -30
K and 2J2/kB ) -580 K, as shown in Figure 10b. The value
of the exchange interaction (2J1/kB ) -30 K) between the
Ni(dmit)2 anion and verdazyl cation estimated is not so small,
but is much smaller than that (2J2/kB ) -580 K) between
Ni(dmit)2 anions A and B. Consequently, the susceptibility
of salt 6 can be explained by a simple dimer model, as a
first-order approximation.
On the other hand, the Ni-Nj contacts (i, j ) 1-4)
between the nitrogen atoms in the central hydrazidinyl moiety
(N1-N2-C7-N3-N4-C8) are larger than 5 Å in salts 5
and 6, suggesting weak intermolecular exchange interaction
+-V+
(JV
) between verdazyl cation molecules. In fact, the
susceptibilities of salts 5 and 6 below approximately 50 and
100 K can be well described by the Curie-Weiss law with
small Weiss constants (Θ ) -0.4 and -0.3 K), respectively.
The Lorentzian shape of the single ESR absorption line,
which suggests the strong magnetic exchange interaction
between the verdazyl cation and Ni(dmit)2 anion spins, was
observed for salt 6. The øM of salt 6 was explained by eq 2,
as a first-order approximation. In such a case, the temperature
dependence of the g value of salt 6 is given by eq 4,34,35
g(T) ) [1 - R(T)]gV+ + R(T)gNi-
(4)
where R(T) is the fraction of the susceptibility of the
Ni(dmit)2 anion dimer and gV and gNi are the g values of
the verdazyl cation and Ni(dmit)2 anion, respectively.
Figure 10. Temperature dependence of the product øMT (O) for (a) the
1:1 salt 5, (b) the 1:1 salt 6, and (c) the 1:3 salt 7. The solid curve is the
theoretical susceptibility calculated using eq 2. The dashed curve in (b) is
the theoretical susceptibility calculated using eq 2 in ref 33.
+
-
R(T) ) øNi-(T)/[øV+(T) + øNi-(T)]
(5)
contacts of ca. 3.6-3.8 Å, as listed in Table 5. The two dimer
units are related by an inversion center. The dimers are
stacked along the c axis, and are separated by two verdazyl
(A and B) cation molecules. The interdimer distance, that
is, the distance between Ni(A) and Ni(A′), is 6.693(1) Å for
salt 5. The large AFM exchange interaction (2JA-B/kB) -354
K) observed for salt 5 may be explained by the short
interplanar distances of Ni(dmit)2 molecules in the crystal.
The Ni(dmit)2 (A) anion molecule connects with the two
verdazyl radical cations (V(A) and V(B)) with short inter-
molecular contacts. Therefore, we can expect some interac-
tion between cation and anion molecules. The difference
between the experimental and theoretical values of the
susceptibility of salt 5 above 100 K may be due to such an
interaction.
+
-
where øV (T) and øNi (T) correspond to øCurie-Weiss and øS-T
in eq 2, respectively. As the g values of the cation and anion
moieties, we used the g values of [3]+I- (gV ) 2.0035 in
+
ethanol) and [n-Bu4N]+[Ni(dmit)2]- (gNi ) 2.0472), respec-
-
tively. These values are temperature independent. The
observed g(T) curve (77 K < T < 300 K) can be well
reproduced by the effective g(T) value calculated by using
+
-
eq 4, if we use the relations øV ) øCurie-Weiss and øNi
)
ø
S-T, as shown in Figure 9c. The result suggests that the
spins of cation and anion moieties in salt 6 independently
contribute to the magnetic susceptibility.
Similarly, the g value of salt 5 decreases from 2.0159 at
300 K to 2.0044 at 77 K by lowering the temperature, as
(34) Tomkiewicz, Y.; Taranko, A. R.; Torrance, J. B. Phys. ReV. Lett. 1976,
In salt 6, the Ni-Ni distances of the Ni(dmit)2 anions are
4.603(3) Å for the Ni(A)-Ni(B) pair and 6.516(3) Å for
the Ni(A)-Ni(C) pair. The short Ni-S, S-S, S-C, and
36, 751.
(35) Takahashi, M.; Sugano, T.; Kinoshita, M. Bull. Chem. Soc. Jpn. 1984,
57, 26.
574 Inorganic Chemistry, Vol. 43, No. 2, 2004

Molecular Paramagnetic Semiconductor
However, the magnetic properties of the complexes have not
been reported, as far as we know. On the other hand, in the
case of the crystal of (TPP)[Ni(dmit)2]3 (TPP ) tetraphen-
ylphosphonium), two of the three Ni(dmit)2 units form
columns, the remaining unit exists almost perpendicular to
the stack, and the conducting sheets of the Ni(dmit)2 anions
are separated by layers of large countercations.38 The
susceptibility follows Curie-Weiss law with C ) 0.40 (K
emu)/mol and Θ ) 1.6 K. The Curie constant corresponds
to one spin per three Ni(dmit)2 units. The result obtained
for salt 7 also suggests the existence of one spin per three
Ni(dmit)2 units. However, the exchange interaction (2J/kB
) -258 K) observed is much larger than that in the (TPP)-
[Ni(dmit)2]3 complex. Crystal structure analysis of salt 7 is
necessary to discuss the difference in the magnetic properties.
Conducting Properties of Salts 4-7. As described in a
previous section, the three 1:1 salts 4-6 are insulators, as
expected for the 1:1 complexes. On the other hand, the 1:3
salt 7 is a semiconductor (σRT ) 0.10 S cm-1) with activation
energy EA ) 0.10 eV. The result indicates that salt 7 is a
new molecular paramagnetic semiconductor.
Recently, we reported the first example of 1:1 and 1:3
salts of the Ni(dmit)2 anion with the 6-oxoverdazyl radical
cation [V]+ (V ) 3-[4-(diethylmethylammonio)phenyl]-1,5-
diphenyl-6-oxoverdazyl radical).28 The øM of the 1:1 salt
[V]+[Ni(dmit)2]- was explained by the sum of the contribu-
tions from (i) a Curie-Weiss system (Θ ) -1.6 K) and (ii)
the one-dimensional Heisenberg AFM alternating-chain
system with 2JA-B/kB ) -274 K (alternation parameter R
) JA-C/JA-B ) 0.2). The øM of the 1:3 salt was also explained
by the two-term contributions from (i) the Curie-Weiss
system (Θ ) -5.0 K) and (ii) the dimer system with 2J/kB
) -258 K. The 1:1 and 1:3 salts were a paramagnetic
insulator and semiconductor, respectively. The structural,
magnetic, and conducting properties of the salts reported are
similar to those obtained in the present work. The magnetic
interactions between the verdazyl radical cations and between
the verdazyl cation and Ni(dmit)2 anion observed were
weaker than expected, except for the case of salt 4. To obtain
the organic/inorganic hybrid system which shows the fer-
romagnetism (or antiferromagnetism) and superconductivity
(or metallic conductivity), it is necessary to use the different
types of verdazyl radical cations with smaller molecular size,
such as 1,5-dimethyl-6-oxo- and 1,5-dimethyl-6-thioxover-
dazyls, for which we can expect stronger magnetic interac-
tion.13,19,20
Figure 11. Temperature dependence of the R(T) values for salts 5 and 6.
shown in Figure 9b. The result shows that both the spins of
the verdazyl cation and Ni(dmit)2 anion contribute to the
magnetism of salt 5 at 300 K. The g value (2.0044) of 5 at
77 K is similar to that (2.0036 in ethanol) of the verdazyl
radical cation [2]+, indicating that the spins of the verdazyl
cation contribute mainly to the øM of salt 5 at 77 K. As shown
in Figure 9b, the temperature dependence of the g value
cannot be explained by eq 4, if we use the value of 2J/kB )
-354 K obtained by the susceptibility measurement. There
are two reasons for the inaccordance: (i) we cannot
determine the correct g values for salt 5 because the Curie
impurity signal of the radical cation overlaps the signal of
salt 5, and (ii) the value of the exchange interaction
determined by the susceptibility measurement is not correct,
because of the interaction between the Ni(dmit)2 and verdazyl
cation molecules. However, the detailed reason is not clear
at present.
As shown in Figure 11, the values of R(T) for salts 5 and
6 are 0.281 and 0.292 at 300 K, respectively. The values
decrease by lowering the temperature and approach zero at
77 K, suggesting that the contributions of Ni(dmit)2 anion
spins to the susceptibility disappear almost at 77 K in these
salts. The AFM exchange interactions between Ni(dmit)2
anion molecules are strong for these salts.
Magnetic Property of Salt 7. As described in a previous
section, the value of øMT for the 1:3 salt 7 is 0.642 (K emu)/
mol at 300 K, and decreases by lowering the temperature,
as shown in Figure 7. The magnetic behavior is similar to
that of salts 5 and 6. As shown in Figure 10, the experimental
curve can be approximately reproduced by the two-term
contributions (eq 2) with (i) C ) 0.376 (K emu)/mol and Θ
) -1.7 K and (ii) 2J/kB ) -258 K. The difference between
the experimental and theoretical values of susceptibility may
be due to the interaction between the verdazyl cation and
Summary
-
[Ni(dmit)2]3 anion spins. We can expect stronger AFM
In the present work, four magnetic charge-transfer salts
(4-7) of 3-[4-(trimethylammonio)phenyl]-1,5-diphenyl-6-
oxoverdazyl radical cation ([1]+) and its mono- and dimethyl
derivatives ([2]+ and [3]+) with [Ni(dmit)]- and [Ni(dmit)2]3-
-
exchange interaction between the [Ni(dmit)2]3 anion mol-
ecules than that between verdazyl radical cations, as observed
for salts 4-6. Therefore, the susceptibility of salt 7 below
ca. 30 K is due to the spins of the verdazyl radical cation.
Several kinds of 1:3 complexes (cation)[Ni(dmit)2]3 of a
closed-shell cation with Ni(dmit)2 species have been pre-
pared, and the structural and conducting properties have been
studied.9,36,37 The complexes show semiconducting and
metallic behavior. The Ni(dmit)2 units generally form trimers.
(36) Verdhuizen, Y. S. J.; Smeets, W. J. J.; Veldman, N.; Spek, A. L.;
Faulmann, C.; Auban-Senzier, P.; Jerome, D.; Paulus, P. M.; Haasnoot,
J. G.; Reedijk, J. Inorg. Chem. 1997, 36, 4930.
(37) Xu, W.; Zhang, D.; Yang, C.; Jin, X.; Li, Y.; Zhu, D. Synth. Met.
2001, 122, 409.
(38) Nakamura, T.; Underhill, A. E.; Coomber, A. T.; Friend, R. H.; Tajima,
H.; Kobayashi, A.; Kobayashi, H. Inorg. Chem. 1995, 34, 870.
Inorganic Chemistry, Vol. 43, No. 2, 2004 575

Mukai et al.
anions ([1]+[Ni(dmit)2]- (4), [2]+[Ni(dmit)2]- (5), [3]+[Ni-
(dmit)2]- (6), and [1]+[Ni(dmit)2]3- (7)) have been prepared,
and their structural, magnetic, and conducting properties have
been studied. The results of the crystal structure analyses of
the 1:1 salts 4-6 indicate dimer formation of the Ni(dmit)2
anion moiety in the salts. The separate contributions of the
verdazyl cation (S ) 1/2) and Ni(dmit)2 anion (S ) 1/2)
subsystems to the total magnetic susceptibility of the salts
were evaluated from the measurements of the temperature
dependence of the susceptibility (øM(T)) and the g value
(g(T)) of the 1:1 salt 5 and the 1:3 salt 7. Fraction R(T) values
of the Ni(dmit)2 anion in the susceptibility of salts 5 and 6
decrease by lowering the temperature, and approach zero at
77 K, suggesting that the magnetic gaps of the spin pair in
the Ni(dmit)2 anion in the salts are larger than those in the
verdazyl cation. On the other hand, the magnetic susceptibili-
ties of salts 4 and 6 were explained by the four-spin linear
tetramer model ([1 (or 3)]+-Ni(dmit)2-Ni(dmit)2-[1 (or
3)]+). The 1:1 salts 4-6 are insulators. On the other hand,
the 1:3 salt 7 is a semiconductor. The examples of the
organic/inorganic hybrid system which shows magnetism and
conductivity are very limited, because of the difficulty in
the molecular design of the complexes. The present work
provides an example of a new molecular paramagnetic
semiconductor consisting of an open-shell verdazyl radical
cation and a metal complex anion.
Acknowledgment. We are very grateful to Prof. K.
Tanaka and Mr. T. Nakayashiki of Kyoto University for their
kind help in the measurement of conductivity. We are also
very grateful to Dr. K. Suzuki of the Institute for Molecular
Science and Prof. T. Ishida of the University of Electro-
Communications for their kind help in the SQUID measure-
ments and the analysis of the susceptibility of salt 4,
respectively. We are also very grateful to Prof. T. Sugano
of Meiji Gakuin University for his helpful discussions. This
work was partly supported by a 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 supported by the Joint Studies Program (2000-2002)
of the Institute for Molecular Science.
Supporting Information Available: Tables listing detailed
crystallographic data, atomic positional parameters, and bond
lengths and angles of salts 4-6 and 8 in CIF format. This material
is available free of charge via the Internet at http://pubs.acs.org.
IC030068Q
576 Inorganic Chemistry, Vol. 43, No. 2, 2004