Solid-state molecular rotators of anilinium and adamantylammonium in [Ni(dmit)2]- salts with diverse magnetic properties

Article abstract of DOI:10.1021/ic800271m

Supramolecular rotators of hydrogen-bonding assemblies between anilinium (Ph-NH₃⁺) or adamantylammonium (AD-NH₃ ⁺) and dibenzo[18]crown-6 (DB[18]crown-6) or meso-dicyclohexano[18] crown-6 (DCH[18]crown-6) were introduced into [Ni(dmit)₂] salts (dmit^2- is 2-thioxo-1,3-dithiole-4,5-dithiolate). The ammonium moieties of Ph-NH₃⁺ and AD-NH₃⁺ cations were interacted through N-H⁺～O hydrogen bonding with the six oxygen atoms of crown ethers, forming 1:1 supramolecular rotator-stator structures. X-ray crystal-structure analyses revealed a jackknife-shaped conformation of DB[18]crown-6, in which two benzene rings were twisted along the same direction, in (Ph-NH₃⁺)(DB[18]crown-6)[Ni(dmit) ₂]^- (1) and (AD-NH₃⁺)(DB[18]crown-6) [Ni(dmit)₂]^- (3), whereas the conformational flexibility of two dicyclohexyl rings was observed in (Ph-NH3⁺)(DCH[18]crown-6) [Ni(dmit)₂]^- (2) and (AD-NH₃ ⁺)(DCH[18]crown-6)[Ni(dmit)₂]^_ (4). Sufficient space for the molecular rotation of the adamantyl group was achieved in the crystals of salts 3 and 4, whereas the rotation of the phenyl group in salts 1 and 2 was rather restricted by the nearest neighboring molecules. The rotation of the adamantyl group in salts 3 and 4 was evidenced from the temperature-dependent wide-line ¹H NMR spectra, dielectric properties, and X-ray crystal structure analysis, ab initio calculations showed that the potential energy barriers for the rotations of adamantyl groups in salts 3 (ΔE ≈ 18 kJmol^-1) and 4 (ΔE ≈ 15 kJmol ^-1) were similar to those of ethane (～12 kJmol^-1) and butane (17-25 kuJmol^-1) around the C-C single bond, which were 1 order of magnitude smaller than those of phenyl groups in salts 1 (ΔE ≈ 180 kJmol^-1) and 2 (ΔE ≈ 340 kJmol^-1). 1D or 2D [Ni(dmit)2]^- anion arrangements were observed in the crystals according to the shape of crown ether derivatives. The 2D weak intermolecular interactions between [Ni(dmit)₂]^- anions in salts 1 and 3 led to Curie-Weiss behavior with weak antiferromagnetic interaction, whereas 1D interactions through lateral sulfur-sulfur atomic contacts between [Ni(dmit)₂]^- anions were observed in salts 2 and 4, whose magnetic behaviors were dictated by ferromagnetic (salt 2) and singlet-triplet (salt 4) intermolecular magnetic interactions, respectively.

Full text of DOI:10.1021/ic800271m

Inorg. Chem. 2008, 47, 5951-5962
Solid-State Molecular Rotators of Anilinium and
Adamantylammonium in [Ni(dmit)2]- Salts with Diverse Magnetic
Properties
Tomoyuki Akutagawa,*,†,‡,§ Daisuke Sato,‡ Hiroyuki Koshinaka,‡ Masaaki Aonuma,‡
Shin-ichiro Noro,†,‡ Sadamu Takeda,| and Takayoshi Nakamura*,†,‡,§
Research Institute for Electronic Science, Hokkaido UniVersity, Sapporo 060-0812, Japan,
Graduate School of EnVironmental Earth Science, Hokkaido UniVersity, Sapporo 060-0810, Japan,
CREST, Japan Science and Technology Agency (JST), Kawaguchi 332-0012, Japan, and Graduate
School of Science, Hokkaido UniVersity, Sapporo 060-0810, Japan
Received February 13, 2008
Supramolecular rotators of hydrogen-bonding assemblies between anilinium (Ph-NH3+) or adamantylammonium
(AD-NH3+) and dibenzo[18]crown-6 (DB[18]crown-6) or meso-dicyclohexano[18]crown-6 (DCH[18]crown-6) were
introduced into [Ni(dmit)2] salts (dmit2- is 2-thioxo-1,3-dithiole-4,5-dithiolate). The ammonium moieties of Ph-NH3+
and AD-NH3+ cations were interacted through N-H+∼O hydrogen bonding with the six oxygen atoms of crown
ethers, forming 1:1 supramolecular rotator-stator structures. X-ray crystal-structure analyses revealed a jackknife-
shaped conformation of DB[18]crown-6, in which two benzene rings were twisted along the same direction, in
(Ph-NH3+)(DB[18]crown-6)[Ni(dmit)2]- (1) and (AD-NH3+)(DB[18]crown-6)[Ni(dmit)2]- (3), whereas the confor-
mational flexibility of two dicyclohexyl rings was observed in (Ph-NH3+)(DCH[18]crown-6)[Ni(dmit)2]- (2) and
(AD-NH3+)(DCH[18]crown-6)[Ni(dmit)2]- (4). Sufficient space for the molecular rotation of the adamantyl group
was achieved in the crystals of salts 3 and 4, whereas the rotation of the phenyl group in salts 1 and 2 was rather
restricted by the nearest neighboring molecules. The rotation of the adamantyl group in salts 3 and 4 was evidenced
from the temperature-dependent wide-line 1H NMR spectra, dielectric properties, and X-ray crystal structure analysis.
ab initio calculations showed that the potential energy barriers for the rotations of adamantyl groups in salts 3 (∆E
≈ 18 kJmol-1) and 4 (∆E ≈ 15 kJmol-1) were similar to those of ethane (∼12 kJmol-1) and butane (17-25
kJmol-1) around the C-C single bond, which were 1 order of magnitude smaller than those of phenyl groups in
salts 1 (∆E ≈ 180 kJmol-1) and 2 (∆E ≈ 340 kJmol-1). 1D or 2D [Ni(dmit)2]- anion arrangements were observed
in the crystals according to the shape of crown ether derivatives. The 2D weak intermolecular interactions between
[Ni(dmit)2]- anions in salts 1 and 3 led to Curie-Weiss behavior with weak antiferromagnetic interaction, whereas
1D interactions through lateral sulfur-sulfur atomic contacts between [Ni(dmit)2]- anions were observed in salts 2
and 4, whose magnetic behaviors were dictated by ferromagnetic (salt 2) and singlet-triplet (salt 4) intermolecular
magnetic interactions, respectively.
Introduction
conformations, are among the useful building blocks for
constructing molecular machines, such as motors and
shuttles.1 Coupling the molecular conformational change,
especially molecular rotational motion, with electronic func-
Flexible molecules such as rotaxanes and catenanes, which
possess several thermodynamically stable and/or metastable
* To whom correspondence should be addressed. Phone: +81-11-706-
2884,Fax:+81-11-706-4972,E-mail:takuta@es.hokudai.ac.jp(A.T.),tnaka@
es.hokudai.ac.jp (T.N.).
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Systems; Stoddart, J. F., Ed.; RSC: Cambridge, 2000. (b) Molecular
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Berlin, 2001. (d) Molecular DeVices and Machines; Balzani, V.,
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†
Research Institute for Electronic Science, Hokkaido University.
‡ Graduate School of Environmental Earth Science, Hokkaido University.
§
CREST, Japan Science and Technology Agency (JST).
Graduate School of Science, Hokkaido University.
|
10.1021/ic800271m CCC: $40.75  2008 American Chemical Society
Inorganic Chemistry, Vol. 47, No. 13, 2008 5951
Published on Web 05/28/2008

Akutagawa et al.
tions will enable us to construct molecular machines, whose
intramolecular rotary motion is controllable through outer
stimuli, such as electromagnetic field, photoirradiation, and
redox reactions.1,2 A large number of molecular rotary
machines have already been developed that allow unidirec-
tional rotation in the solution phase using rotaxane and
catenane structures.1–4 Molecular machines have a potential
to realize collective transport systems of electrons, protons,
ions, and so forth. For example, ATPase in cell membranes
is a well-known biological molecular motor,5 in which the
ionic channel, proton relay, and unidirectional molecular
rotation are coupled to each other, forming a proton pump
with high-energy conversion efficiency.5 One important
feature of biological motors is that they are aligned in the
same direction in the cell membrane so that they achieve
directional proton transport through unidirectional rotation
by consuming ATP. Although such a complex molecular
system is difficult to construct artificially, solid-state mo-
lecular motors are promising model systems for mimicking
biological functions from the viewpoint of directional align-
ment of rotators. To the best of our knowledge, unidirectional
molecular rotation has not yet been achieved in the solid
state. In the solid state, structural isomerizations such as
thermal, photo-, and chemical reactions for achieving
unidirectional molecular rotations are very difficult, owing
to the steric hindrance between the nearest-neighboring
molecules. An entirely different approach from that for the
solution phase is necessary to construct solid-state molecular
motors.
the way to solid-state molecular motors.6,8 The potential
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5952 Inorganic Chemistry, Vol. 47, No. 13, 2008

Solid-State Molecular Rotators
Scheme 1. Molecular Structures of Anilinium (Ph-NH3+), Adamantylammonium (AD-NH3+), Dibenzo[18]crown-6 (DB[18]crown-6),
meso-Dicyclohexano[18]crown-6 (DCH[18]crown-6), and [Ni(dmit)2]a
a
+
+
Molecular structures of bottom Ph-NH3 and AD-NH3 were shown in the CPK representation.
possibility.9 In plastic crystals, relatively large molecules,
such as cyclohexane, adamantane (AD), and C60, can rotate,
keeping the center of gravity in the crystal lattice.9 A peculiar
feature of these plastic crystals is their high conformational
flexibility and/or isotropic molecule shape. Such molecules
are suitable candidates for constructing crystalline rotators.
We have employed the supramolecular cation approach
based on crown ethers to construct rotators in the crystals
of magnetic [Ni(dmit)2] salts (dmit2- is 2-thioxo-1,3-dithiole-
4,5-dithiolate).8,13 The crown ether supramolecular
cation-[Ni(dmit)2] approach has several advantages: (i) the
combination of organic and/or inorganic cations and crown
ethers yields diverse molecular rotator structures, (ii) one-
pot synthesis of rotator-stator structures by self-assembly
processes through selective cation recognition by crown
ethers becomes possible, and (iii) magnetically and electri-
cally active [Ni(dmit)2] anions can coexist with the rotators.
Such hybrid solids between the molecular rotators and
magnetic spin (or conduction electrons of [Ni(dmit)2]) has a
potential to show peculiar electronic functions coupled with
the molecular motion.14
the salt Cs+ ([18]crown-6)3[Ni(dmit)2]- .8a In this salt, the
2 2
rotation of [18]crown-6 was coupled with the magnetic
properties of the [Ni(dmit)2]- assembly. More recently, we
reported the supramolecular rotators in (Ph-NH3+)([18]cown-
6)[Ni(dmit)2]- and (AD-NH3 )([18]crown-6)[Ni(dmit)2]-
+
+
+
(Ph-NH3 and AD-NH3 were anilinium and adamanty-
lammonium, respectively).8c,d In these salts, dual-mode
rotations, that is, organic ammoniums and [18]crown-6 with
different rotation frequencies, were confirmed by solid-state
2
1H and H NMR measurements. Reflecting the isotropic
molecular structure of the adamantyl group, the rotation
speed of the adamantyl group was much faster than that of
the phenyl group in the solid state.8c,d However, in previous
salts, the [18]crown-6 itself acted as the rotator and/or stator
simultaneously. Here, we report new supramolecular solid-
state rotators of phenyl and adamantyl groups fixed on
bulky stators of dibenzo[18]crown-6 (DB[18]crown-6) and
meso-dicyclohexano[18]crown-6 (DCH[18]crown-6). Four
+
new single crystals of (Ph-NH3 )(DB[18]crown-6)[Ni(d-
mit)2]- (1), (Ph-NH3+)(DCH[18]crown-6)[Ni(dmit)2]-
(2), and (AD-NH3+)(DB[18]crown-6)[Ni(dmit)2]- (3),
and (AD-NH3 )(DCH[18]crown-6)[Ni(dmit)2]- (4) were
+
We first reported the molecular rotator of [18]crown-6 in
prepared (Scheme 1). The rotation of bulky crown ethers
was completely suppressed in the solid state, whereas an
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extremely low potential energy barrier (15-18 kJmol-1
)
for the rotation of the adamantyl group was confirmed in
the solid state. Diverse magnetism from antiferromagnetic
to ferromagnetic coupling depended on the [Ni(dmit)2]-
1
˜
(S ) /2) arrangements through the lateral S–S contacts
within the crystals.
Experimental Section
(Ph-NH3+)(BF4-). An aqueous 42% solution of HBF4 (9.8
mmol) was slowly dropped into aniline (10 mmol) in CH3CN (30
mL) over a period of 20 min. The reaction solvent was removed
by reducing of pressure, and then white powder was recrystallized
from CHCl3-CH3CN. Elemental analysis. Calcd C: 39.82, H: 4.46,
N: 7.74. Found. C: 39.71, H: 4.45, N: 7.74.
(AD-NH3+)(BF4-). An aqueous 42% solution of HBF4 was
slowly dropped into adamantylamine (0.76 g, 5 mmol) in CH3OH
(20 mL) over a period of 20 min. During this reaction, the reaction
solution was adjusted to pH ∼7 and stirred for 30 min at room
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Inorganic Chemistry, Vol. 47, No. 13, 2008 5953

Akutagawa et al.
Table 1. Crystal Data, Data Collection, and Reduction Parameter of Salts 1-4
1
2
3
4
chemical formula
fw
No.
a, Å
b, Å
c, Å
C32H32NO6S10Ni
908.93
C2/c (#15)
22.846(5)
8.0691(20)
21.662(4)
C32H44NO6S10Ni
918.00
P1 (#2)
C36H42NO6S10Ni
964.03
Cmcm (#63)
21.49(4)
9.091(15)
22.55(4)
C36H54NO6S10Ni
976.13
P21/n (#14)
13.770(3)
15.988(4)
19.762(5)
j
12.396(6)
12.624(5)
14.281(7)
93.843(15)
104.802(17)
105.375(17)
2061.2(16)
2
1.479
253
10.19
19 926
9259
R, deg
ꢀ, deg
101.702(5)
92.027(8)
γ, deg
V, Å3
3910.3(14)
4
1.544
273
10.73
18 381
4446
4407(12)
4
1.453
298
4347.9(16)
4
1.491
123
Z
Dcalcd, g·cm-1
T
µ, cm-1
reflns measured
independent reflns
reflns used
9.57
9.71
20 156
2632
1583
0.038
0.074
0.947
41 918
9935
6602
0.036
0.068
0.944
2518
5230
0.043
0.076
1.039
a
R
0.143
0.134
1.041
a
Rw(F2)
GOF
a R ) Σ|Fo| - |Fc|/Σ|Fo| and Rw ) (Σω|Fo| - |Fc|)2/ΣωFo )1/2
.
2
temperature. The reaction solvent was removed by reducing the
pressure, then oil products were recrystallized from CHCl3-hexane.
White powder was precipitated, which was washed with cold ether
(1.19 g) and recrystallized from CHCl3-hexane (0.82 g). Elemental
analysis. Calcd C: 50.24, H: 7.59, N: 5.86. Found. C: 50.10, H:
7.68, N: 5.65.
could not be determined using the atomic coordinates of the X-ray
structural analysis of salt 3 due to the orientational disorders of
+
the AD-NH3 cation. Thus, the geometry optimization of the
+
disordered AD-NH3 structure was first carried out by empirical
PM3 calculation of salt 3. The relative energy of the structures
was obtained by evaluating the rigid rotation of phenyl and/or
adamantylunitsaroundthePh-NH3+and/orAD-NH3+carbon-nitrogen
bonds. Rotations were performed at every 30°, and the relative
energies were calculated using fixed atomic coordinates. The
transfer integrals (t) between the [Ni(dmit)2]- anions were calculated
within the tight-binding approximation using the extended Hu¨ckel
molecular orbital method. The LUMO of the [Ni(dmit)2]- molecule
was used as the basis function.18 Semiempirical parameters for
Slater-type atomic orbitals were obtained from the literature.18 The
t values between each pair of molecules were assumed to be
proportional to the overlap integral (S) via the equation t ) -10S
eV.
Preparation of Salts 1-4. The precursor monovalent (n-
Bu4N)[Ni(dmit)2] salt was prepared according to the literature.15a
The single crystals of salts 1-4 were obtained by the standard
diffusion method in an H-shaped cell (∼50 mL).15b The green
solution of (n-Bu4N)[Ni(dmit)2] (20 mg) in CH3CN (∼20 mL) was
-
poured into a solution of (Ph-NH3+)(BF4-) or (AD-NH3+)(BF4
)
(∼60 mg) and DB[18]crown-6 or DCH[18]crown-6 (∼200 mg) in
CH3CN (∼30 mL) (detailed conditions of the single-crystal
preparation are shown in Table S1 in the Supporting Information).
After two weeks, single crystals (typical dimensions: 0.4 × 0.4 ×
0.3 mm) were obtained as black blocks. The stoichiometry of
crystals was determined by X-ray structural and elemental analyses
(Table S2 in the Supporting Information).
Crystal Structure Determination. Crystallographic data (Table
1) were collected by a Rigaku RAXIS-RAPID diffractometer using
Mo KR (λ ) 0.71073 Å) radiation from a graphite monochromator.
Structure refinements were made using the full-matrix least-squares
method on F2. Calculations were performed using Crystal Structure
software packages.16 Parameters were refined using anisotropic
temperature factors except for the hydrogen atom.
Dielectric Measurements. Temperature-dependent dielectric
constants were measured by the two-probe AC impedance method
at the frequency of 100 × 103 Hz (HP4194A). A single crystal
was placed into a cryogenic refrigerating system (Daikin PS24SS).
The electrical contacts were prepared using gold paste (Tokuriki
8560) to attach the 10 µm Α gold wires to the single crystal. The
measurement axes of salts 1, 2, 3, and 4 were perpendicular to the
+
+
rotation axis of Ph-NH3 and AD-NH3 cations.
1
1
Solid-State H NMR Measurements. Solid-state wide-line H
Calculations. The relative energy of the structures was calculated
NMR spectra under static sample conditions were measured by solid
using the RHF/6-31(d) basis set.17 The nearest-neighboring
+
molecules around the phenyl ring of Ph-NH3 and/or adamantyl
(17) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb,
M. A.; Cheeseman, J. R.; Montgomery, J. A., Jr.; Vreven, T.; Kudin,
K. N.; Burant, J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi, J.; Barone,
V.; Mennucci, B.; Cossi, M.; Scalmani, G.; Rega, N.; Petersson, G. A.;
Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa,
J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Klene,
M.; Li, X.; Knox, J. E.; Hratchian, H. P.; Cross, J. B.; Bakken, V.;
Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev,
O.; Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Ayala,
P. Y.; Morokuma, K.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.;
Zakrzewski, V. G.; Dapprich, S.; Daniels, A. D.; Strain, M. C.; Farkas,
O.; Malick, D. K.; Rabuck, A. D.; Raghavachari, K.; Foresman, J. B.;
Ortiz, J. V.; Cui, Q.; Baboul, A. G.; Clifford, S.; Cioslowski, J.;
Stefanov, B. B.; Liu, G.; Liashenko, A.; Piskorz, P.; Komaromi, I.;
Martin, R. L.; Fox, D. J.; Keith, T.; Al-Laham, M. A.; Peng, C. Y.;
Nanayakkara, A.; Challacombe, M.; Gill, P. M. W.; Johnson, B.; Chen,
W.; Wong, M. W.; Gonzalez, C.; Pople, J. A. Gaussian 03, Revision
C.02; Gaussian, Inc.: Wallingford, CT, 2004.
+
group of AD-NH3 were included in the calculations of the
potential energy curves. The structural units of salts 1, 2, 3, and 4
in the calculations were (Ph-NH3+)(DB[18]crown-6)[Ni(dmit)2]2,
(Ph-NH3+)(DCH[18]crown-6)3, (AD-NH3+)(DB[18]crown-6)[Ni(d-
mit)2]2, and (AD-NH3+)(DCH[18]crown-6)[Ni(dmit)2]2, respec-
tively (Figures S5-S8 in the Supporting Information), which were
different from the real stoichiometries of salts 1-4. The atomic
coordinates of salts 1, 2, and 4 based on the X-ray crystal structural
analysis were used for the calculations. The potential energy curve
(16) (a) Crystal Structure: Single Crystal Structure Analysis Software, Ver.
3.6; Rigaku Corporation and Molecular Structure Corporation, 2004.
(b) Sheldrick, G. M. SHELX97 Programs for Crystal Structure
Analysis; Universitat Go¨ttingen: Go¨ttingen, Germany, 1998.
5954 Inorganic Chemistry, Vol. 47, No. 13, 2008

Solid-State Molecular Rotators
pendent supramolecular cation units in salts 1 and 3. The
DB[18]crown-6 in salts 1 and 3 had a jackknife-type
conformation, where the folding angles between two benzene
rings were 128.4 and 123.4°, respectively (parts a and c of
Figure 1). The C-N bonds of Ph-NH3+ and AD-NH3+ in
salts 1-4 were almost perpendicular to the mean oxygen
planes of crown ethers. Average hydrogen-bonding N∼O
distances between the nitrogen and oxygen atoms of salts 1
and 3 were 2.97 and 2.98 Å, respectively, which were
comparable to the standard N-H+∼O hydrogen bond
length.19 AlthoughthejackknifeconformationsofDB[18]crown-
6 in salts 1 and 3 were similar (parts a and c of Figure 1),
the magnitude of the thermal fluctuation and orientation of
ammonium cations were quite different. The orientational
Figure 1. Supramolecular cation structures of (a) (Ph-NH3+)(DB[18]-
crown-6) in salt 1, (b) (Ph-NH3+)(DCH[18]crown-6) in salt 2, (c)
(AD-NH3+)(DB[18]crown-6) in salt 3, and (d) (AD-NH3+)(DCH[18]crown-
6) in salt 4 viewed parallel to the mean oxygen plane of [18]crown-6.
Hydrogen atoms are omitted in the figures.
+
disorder of AD-NH3 was observed in salt 3 (section of
packing structure), which was intrinsic because the same
disorder arrangement was confirmed in structural analyses
echo pulse sequence π/2 - τ - π/2 (the π/2 pulse width and τ were
+
x
y
with low crystal symmetry of C2 (full AD-NH3 was the
1.3 and 10 µs, respectively) using a Bruker DSX 300 spectrometer
with an operating frequency of 300 MHz for protons.
crystallographically independent unit, as seen in Figures S9
and S10 in the Supporting Information).
Magnetic Susceptibility. The temperature-dependent magnetic
susceptibility and the magnetization magnetic field dependence were
measured using a Quantum Design MPMS-XL5 SQUID magne-
tometer using polycrystalline samples. The applied magnetic field
was 1 T for all temperature-dependent measurements.
The conformations of DCH[18]crown-6 in salts 2 and 4
were slightly different. Two cyclohexane rings in salt 2
adopted the jackknife-like conformation, whereas those in
salt4werealmostparalleltoeachother.The(Ph-NH3+)(DCH-
+
[18]crown-6) and (AD-NH3 )(DCH[18]crown-6) units were
Results and Discussion
both crystallographically independent, indicating the non-
centrosymmetrical supramolecular cation structure of salts
2 and 4. The average hydrogen bonding Ñ–O distances in
salts 2 and 4 were 2.92 and 3.02 Å, respectively, which were
almost the same as those in salts 1 and 3. The supramolecular
cation structures of salts 1-4 were constructed from the
standard N-H+∼O hydrogen bonding interactions.19 The
adamantyl group of salt 4 had a C3V symmetry without
orientational disorder, suggesting a 120° rotational symmetry.
Thesimilarsupramolecularcationstructuresof(Ph-NH3+)(DB-
Cation exchange reactions from (n-Bu4N+)[Ni(dmit)2]- to
Ph-NH3+ or AD-NH3+ in the presence of DB[18]crown-6
or DCH[18]crown-6 yielded monovalent [Ni(dmit)2]- salts
of(Ph-NH3+)(DB[18]crown-6)[Ni(dmit)2]-(1),(Ph-NH3+)(DCH-
[18]crown-6)[Ni(dmit)2]- (2), (AD-NH3 )(DB[18]crown-
+
6)[Ni(dmit)2]- (3), and (AD-NH3+)(DCH[18]crown-6)[Ni(d-
mit)2]- (4). The 1:1 adducts of supramolecular cations
between organic ammonium and crown ether were con-
structed by six N-H+∼O hydrogen bonds, forming a stand-
up configuration of the C-N bond of phenyl and adamantyl
groupswithrespecttothemeanoxygenplaneofDB[18]crown-
6 or DCH[18]crown-6. Although the crystal symmetry of
salt 3 (C/mcm) was higher than that of salt 1 (C2/c),
isostructural cation and anion arrangements were observed
in both crystals.
+
[18]crown-6) and (AD-NH3 )(DB[18]crown-6) yielded iso-
structural [Ni(dmit)2]- arrangements in salts 1 and 3, whereas
the slight conformational difference between cyclohexane
rings in salts 2 and 4 led to the different [Ni(dmit)2]-
arrangements and magnetic behaviors (sections of packing
structure and magnetic properties).
Packing Structures of Cations and [Ni(dmit)2]- Anions.
Cation Conformations. The structural flexibility of two
dicyclohexyl rings in DCH[18]crown-6 was higher than that
of two benzene rings in DB[18]crown-6, whereas the
molecular surfaces of phenyl and adamantyl groups were
constructed from π-electrons and sp3 carbon-hydrogen
bonds, respectively. These differences affected the supramo-
lecular structure as well as intermolecular interactions
between the cations and [Ni(dmit)2]- anions. Figure 1 shows
the supramolecular cation structures of salts 1-4 viewed
along the mean oxygen plane of DB[18]crown-6 and
DCH[18]crown-6. The 1:1 adducts between the organic
ammoniums and crown ethers had similar stand up config-
uration of organic ammonium on bulky crown ethers.
1
Each [Ni(dmit)2]- anion had one S ) /2 spin, and the
arrangement of [Ni(dmit)2]- anions directly determined the
magnetism. Transfer integrals based on extended Hu¨ckel
molecular orbital calculations were used to evaluate the
magnitude of the intermolecular interactions between [Ni(d-
mit)2]- anions within the crystals.20 The magnetic exchange
energy (J) is proportional to the square of the transfer
integral, J ∼ 4t2/Ueff, where Ueff is the effective on-site
(19) (a) Jeffrey, G. A. An Introduction to Hydrogen Bonding; Truhlar, D. G.,
Ed.; Oxford University Press: New York, 1997. (b) Pimentel, G. C.;
McClellan, A. L. The Hydrogen Bond; Freemann: San Francisco, 1960.
(c) Hamilton, W. C.; Ibers, J. A. Hydrogen Bonding in Solids; Breslow,
R.; Karplus, M., Eds.; Benjamin Inc: New York, 1968.
+
A half (Ph-NH3 )(DB[18]crown6) and a quarter (AD-
(20) (a) Scott, J. C. Semiconductor and Semimetals. Highly Conducting
Quasi-One-Dimensional Organic Crystals; Conwell, E. Ed.; Academic
Press: New York, 1988, 385. (b) Carlin, R. L. Magnetochemistry;
Springer-Verlag: Heidelberg, 1986. (c) Kahn, O. Molecular Magne-
tism; VCH: New York, 1993.
+
NH3 )(DB[18]crown-6) were the crystallographically inde-
(18) Mori, T.; Kobayashi, A.; Sasaki, Y.; Kobayashi, H.; Saito, G.; Inokuchi,
H. Bull. Chem. Soc. Jpn. 1984, 57, 627.
Inorganic Chemistry, Vol. 47, No. 13, 2008 5955

Akutagawa et al.
two nearest-neighboring [Ni(dmit)2]- anions interacted with
the π plane of Ph-NH3 , which prevented the rotation of
Table 2. Transfer Integrals (t) and Magnetic Parameters of Salts 1-4
+
1
2
3
4
t1, meVa
t2, meVa
14.2
2.0
1.7
-1.6
1D
9.12
4.09
-0.76
1D
the phenyl ring with 2-fold 180° flip-flop motion. The
uniform stack of jackknife-shaped (Ph-NH3+)(DB[18]crown-
6) cations arranged the direction of dipole moments of
[Ni(dmit)2]- arrangement 2D
2D
g (298 K)b
2.04622 2.03943 2.06135 2.04599
0.46
0.38
+
∆H (298 K), mTb
C, emu K mol-1
θ or J/kB, K
2.78
0.39
1.54
0.37
6.00
0.39
Ph-NH3 cations within the ab plane (part c of Figure 2).
However, the total dipole moment canceled out due to the
inverted dipole arrangement of cation layers along the c axis.
Although sufficient crystalline void space was achieved for
the phenyl ring along the a axis, molecular rotation was rather
restricted by the effective intermolecular interactions between
the π plane of Ph-NH3+ and lateral sulfur atoms of the two
nearest-neighboring [Ni(dmit)2]- anions along the c axis (part
a of Figure S14).
-1.3
+0.9
-0.4
-39.5
magnetismc
C-Wc
C-Wc
C-Wc
S-Tc
a The transfer integrals (t) were obtained by the LUMO of [Ni(dmit)2]-
based on the extended Hu¨ckel calculation (t ) -10S eV, where S is the
overlap integral). b The g value (g) and line-width (∆H) of the [Ni(dmit)2]-
anion were determined from the electron spin resonance spectra for single
crystals at 298 K. c S-T and C-W are the singlet-triplet thermal excitation
and Curie-Weiss models, respectively.
The crystal structure of salt 3 was isomorphous to that of
salt 1, where the alternate cation and anion layer arrangement
was observed along the c axis, as shown in part a of Figure
2. Because of the higher crystal symmetry of salt 3 (Cmcm)
as compared to that of salt 1 (C2/c), one intermolecular
interaction (t1 ) t2 ) 9.12 meV) was observed in the ab
plane (part b of Figure 2). In the cation layer, an average
structure of two kinds of molecular orientations (I and II in
part b of Figure 3), where orientation II was generated by a
60° rotation from orientation I around the C-N bond of
+
AD-NH3 , was confirmed in the X-ray crystal structural
analysis (parts a and b of Figure 3). The rotation of the
adamantyl group was affected by the intermolecular interac-
tions between the lateral sulfur atoms of the [Ni(dmit)2]-
anions along the c axis. The isotropic molecular structure of
+
AD-NH3 was effective in constructing the space for
molecular rotation in the crystal. Sufficient crystalline space
for the adamantyl ring was achieved, although the molecular
rotation was somewhat restricted by the intermolecular
interactions between the AD-NH3+ and lateral sulfur atoms
of the two nearest-neighboring [Ni(dmit)2]- anions along the
c axis (part b of Figure S14). It should be noted that the
+
rotation of the NH3 moiety around the C-N bond of
+
AD-NH3 was also expected to occur in the solid state.
Because the magnitude of the potential barrier for the rotation
of NH3+ moiety was less than ∼2 kJmol-1,8d the rotation of
+
the -NH3 moiety was negligible in comparison with that
of the adamantyl group in salt 3.
The packing structure of cations and anions in salt 2 was
different from those of salts 1 and 3. Parts a and b of Figure
4 show the unit cells of salt 2 viewed along the a and c
axes, respectively. The alternate cation and anion layers
within the ac plane were arranged along the b axis. In the
anion layer, two kinds of lateral sulfur-sulfur intermolecular
interactions between the [Ni(dmit)2]- anions (t1 ) 1.7 and
t2 ) -1.6 meV) were elongated along the a axis. Almost
the same magnitude of t1 and t2 interactions formed a uniform
1D chain. Along the c axis, the shortest sulfur-sulfur
distance between the [Ni(dmit)2]- anions (5.931 Å) was far
from the effective intermolecular interaction. The supramo-
lecular cations were arranged within the ac plane, where the
Figure 2. Crystal structures of salt 1. (a) Unit cell viewed along the b
+
axis. Ph-NH3 cations without hydrogen atoms were drawn by CPK
representation. (b) [Ni(dmit)2]- anion arrangement within the ab plane. Two
kinds of intermolecular interactions (t1 and t2) were observed along the a
+ b- and -a + b axes, respectively. (c) (Ph-NH3+)(DB[18]crown-6)
cation arrangement within the ab plane viewed along the c axis.
Coulomb repulsive energy in the solid.20 Table 2 summarizes
the transfer integrals and magnetic parameters of salts 1-4.
Part a of Figure 2 shows the unit cell of salt 1 viewed
along the b axis. The [Ni(dmit)2]- anion arrangement in the
ac plane yielded the 2D intermolecular interactions t1 ) 14.2
meV and t2 ) 2.0 meV (part b of Figure 2). An alternate
arrangement of cation and anion layers was elongated along
the c axis (parts b and c of Figure 2), which isolated each
2D [Ni(dmit)2]- layer. In salt 1, the lateral sulfur atoms of
+
dipole moments of Ph-NH3 cations were arranged in
antiparallel manner with respect to each other (part a of
+
Figure 4). The π plane of the Ph-NH3 cation was
5956 Inorganic Chemistry, Vol. 47, No. 13, 2008

Solid-State Molecular Rotators
Figure 3. Supramolecular cation structure of (AD-NH3+)(DB[18]crown-6) in salt 3 (T ) 298 K). (a) Orientational disorder of the adamantyl group (yellow-
colored thermal ellipsoid) viewed along the C-N bond of AD-NH3+. (b) Two kinds of orientations (I and II) rotated by 60° with respect to each other. An
average structure of orientations I and II yielded the cation structure. (c) 2D layer of (AD-NH3+)(DB[18]crown-6) cations within the ab plane (CPK
representation).
observed between the π plane of Ph-NH3+ and [Ni(dmit)2]-
along the b axis.
Parts a and b of Figure 5 show the unit cell of salt 4 viewed
along the a and b axes, respectively. The 1D intermolecular
interaction through the lateral sulfur-sulfur contacts between
[Ni(dmit)2]- anions was observed along the a axis. Because
the magnitude of the t1 interaction (4.09 meV) was about
five times larger than that of the t2 interaction (-0.76 meV),
the lateral [Ni(dmit)2]- dimer was arranged along the a axis
as a result of the weak t2 interactions (part b of Figure 5).
The 1D cation arrangement was also observed along the a
+
axis, where the alternate dipole arrangement of AD-NH3
cations canceled the net dipole moment. Because the
intermolecular interactions between [Ni(dmit)2]- anions were
not observed along the b and c axes, the lateral [Ni(dmit)2]-
chains were isolated from each other. The relatively flat
conformation of the two cyclohexane rings of (DCH[18]crown-
+
6 in (AD-NH3 )(DCH[18]crown-6) (part d of Figure 1) did
+
not affect the rotation of the AD-NH3 cation because of
reduction of the steric repulsion between cyclohexane rings
and the adamantyl group. Around the AD-NH3+ cation, the
weakly interacting terminal sulfur atoms of [Ni(dmit)2]-
anions affected the rotation of AD-NH3+ (part d of Figure
Figure 4. Crystal structure of salt 2. Unit cell viewed along the (a) a axis
and (b) c axis. Two intermolecular interactions (t1 and t2) were observed
along the a axis. Hydrogen atoms are omitted in the figure.
S14 in the Supporting Information).
Potential Energy of Cation Rotations. The rotation mode
and frequency of phenyl and adamantyl groups in the solid
state were determined by the potential energy curve and the
magnitude of the potential energy barrier (∆E). The potential
energy curves of the molecular rotation of phenyl and
adamantyl groups in salts 1, 2, 3, and 4 were calculated using
the RHF/6-31(d) basis set.17 Beside the supramolecular
surrounded by the two nearest-neighboring DCH[18]crown-
6 molecules along the c axis, which prevented the rotation
+
of Ph-NH3 (part c of Figure S14 in the Supporting
Information). No effective intermolecular interaction was
Inorganic Chemistry, Vol. 47, No. 13, 2008 5957

Akutagawa et al.
6)[Ni(dmit)2]- (i.e., 40 kJmol-1), where the symmetrical 180°
+
flip-flop motion of Ph-NH3 with a flip-flop frequency of
∼106 Hz was confirmed at room temperature.8d
The rotational angle dependence of ∆E for the structural
+
unit of (AD-NH3 )(DB[18]crown-6)[Ni(dmit)2]2 and (AD-
+
NH3 )(DCH[18]crown-6)[Ni(dmit)2]2 in salts 3 and 4 were
different from those in salts 1 and 2 from the viewpoints of
rotational symmetry and potential-energy barrier height. For
rotational angle φ, the initial atomic coordinates from the
X-ray crystal structural analysis corresponded to the first
potential energy minimum at φ ) 0°, whereas the second
and third potential-energy minima were observed at around
φ ) 120° and φ ) 240°, respectively. The triple minimum
potential energy curve suggested the 120° rotation of the
adamantyl group. The one orientation of the adamantyl group
in the X-ray crystal structural analysis of salt 4 was consistent
with the 120° periodicity in the calculation of the potential
energy curve. Because the magnitude of ∆E in salt 4 (∼15
kJmol-1) was 1 order of magnitude smaller than that of salt
1 (∼180 kJmol-1), the 120° rapid rotation of the adamantyl
group is expected to occur at room temperature. The
orientational disorder of the adamantyl group in salt 3 was
prevented to determine the potential energy curve, thus, the
optimized molecular structure of the adamantyl group in the
+
(AD-NH3 )(DB[18]crown-6)[Ni(dmit)2]2 structure was used
for the calculation. The triple minimum potential energy
curve with a ∆E of ∼18 kJmol-1 was similar to those of
salt 3, suggesting rapid rotation of the adamantyl group at
room temperature. It should be noted that the symmetry
breaking of the potential energy curve was assumed in
salt 4 due to an asymmetrical intermolecular interaction
between the adamantyl group and two cyclohexane rings
of meso-DCH[18]crown-6.
Figure 5. Crystal structure of salt 4. Unit cell viewed along the (a) a
and (b) b axes. Alternate cation and cation layers were elongated along
the c axis. The AD-NH3 cations without the hydrogen atoms in part
b of Figure 5 were drawn by CPK representation. Two intermolecular
interactions (t1 and t2) were observed between the [Ni(dmit)2]- anions
along the a axis.
+
cation, the nearest-neighboring molecules of [Ni(dmit)2]- or
crown ethers were included in the calculations (Figures
S5-S8 in the Supporting Information). The relative energies
as a function of the rotational angle φ around the C-N bond
of Ph-NH3+ and AD-NH3+ were determined at every 30°
rotation.
Extremely low potential-energy barriers for the rotation
of the adamantyl group were achieved in salts 3 (∆E ∼18
kJmol-1) and 4 (∆E ∼15 kJmol-1), which were comparable
to those of ethane (∆E ∼12 kJmol-1) and butane (∆E )
17-25 kJmol-1) for rotation around the C-C single bond.21
The potential-energy barriers for rotation around the C-C
bond of ethane and butane are dominated by the steric
hindrance and hyperconjugation effects, whereas the ∆E of
salts 3 and 4 were determined by the steric hindrance of the
Part a of Figure 6 shows the rotational angle dependence
+
of the relative energy (∆E) of (Ph-NH3 )(DB[18]crown-
+
6)[Ni(dmit)2]2 and (Ph-NH3 )(DCH[18]crown-6)3 in salts
1 and 2, where the relative energy at φ ) 0° is defined as
zero. For the rotational angle φ, the initial atomic coordinates
from the X-ray crystal structural analysis corresponded to
the first potential energy minimum at φ ) 0°, whereas the
second potential energy minimum was observed around φ
) 180°. The double-minimum potential with two stable
molecular orientations suggested a 180° flip-flop motion of
the phenyl ring in salts 1 and 2, which is consistent with
˜
intermolecular S–H interaction between [Ni(dmit)2] and
+
AD-NH3 . In the plastic crystalline state, the rotation of
adamantane (and cyclohexane) has been examined by tem-
perature-dependent solid-state 1H NMR spectra. The activa-
tion energy for the rotation of adamantane (and cyclohexane),
which keeps its center of gravity during the rotation, was
12.9 kJmol-1 (and 6.4 kJmol-1, respectively).22 This is almost
similar to the potential energy barriers of salts 3 and 4,
suggesting the similar rotation of the adamantyl group in
that in (Ph-NH3 )([18]crown-6)[Ni(dmit)2]-.8d The fact that
+
only one position was observed for the phenyl ring in the
crystal structural analysis presumably indicates the 180°
periodicity of the potential-energy curve. The magnitude of
∆E of salt 2 (∼340 kJmol-1) was about twice that of salt 1
(21) (a) Eyring, H.; Grant, D. M.; Hecht, H. J. Chem. Educ. 1962, 39,
466. (b) Lowe, J. P. Science 1973, 179, 527. (c) Verma, A. L.; Murphy,
W. F.; Bernstein, H. J. J. Chem. Phys. 1974, 60, 1540. (d) Pophristic,
V.; Goodman, L. Nature 2001, 411, 565. (e) Mo, Y.; Gao, J. Acc.
Chem. Res. 2007, 40, 113.
(∼180 kJmol-1), suggesting that the rotation of Ph-NH3
+
in salt 2 was much hindered to the presence of the two
nearest-neighboring DCH[18]crown-6. The ∆E in salt 1
(∼180 kJmol-1) was larger than that in (Ph-NH3+)([18]crown-
(22) (a) Resing, H. A. Mol. Cryst. Liq. Cryst. 1969, 9, 101. (b) O’Reilly,
D. E.; Peterson, E. M.; Hogenboom, D. L. J. Chem. Phys. 1972, 57,
3969.
5958 Inorganic Chemistry, Vol. 47, No. 13, 2008

Solid-State Molecular Rotators
Figure 6. Potential-energy curves of phenyl and adamantyl group rotations in the cation structures. The rotations of (a) the phenyl group around the C-N
+
bond of Ph-NH3 in salts 1 and 2 and of (b) the adamantyl group in salts 3 and 4. The structural units for the calculations of salts 1, 2, 3, and 4 were
(Ph-NH3+)(DB[18]crown-6)[Ni(dmit)2]2, (Ph-NH3+)(DCH[18]crown-6)3, (AD-NH3+)(DB[18]crown-6)[Ni(dmit)2]2, and (AD-NH3+)(DCH[18]crown-
6)[Ni(dmit)2]2, respectively. The solid and dashed lines are guides for the eye.
Figure 7. Temperature-dependent dielectric constants (ꢀ1) of salts (a) 1 and 2, and (b) 3 and 4. The measurement frequency was fixed at 100 kHz. The
+
+
electric field was applied perpendicular to the rotation axis of the Ph-NH3 and AD-NH3 cations.
salts 3 and 4 in comparison with the plastic crystalline state
of adamantane. An extremely low activation energy for
molecular rotation has been reported for the C60 crystal (∆E
∼6 kJmol-1) at 298 K,23 which is almost equal to those of
salts 3 and 4. The suitable size and shape of the adamantyl
group with respect to the space created by DB[18]crown-6
and DCH[18]crown-6 is presumably one reason for the low
potential-energy barrier. Another possible reason for the low
potential energy barrier of the adamantyl group in salts 3
and 4 is the rigid framework of the crystal. Because the
crystal lattice of salts 3 and 4 was mainly constructed by
the electrostatic Coulomb interaction between the anionic
[Ni(dmit)2]- and cationic -NH3 group of AD-NH3 , the
crystalline rotation space of the adamantyl group in salts 3
and 4 was kept within the rigid framework of the crystals.
Dielectric Properties. Temperature-dependent dielectric
constants (ꢀ1) of salts 1-4 were evaluated to obtain informa-
tion on the molecular motions.24 Figure 7 plots ꢀ1 vs T for
salts 1-4 at a measurement frequency (f) of 100 kHz. The
electric field was applied perpendicular direction to the
+
+
rotation axis of the Ph-NH3 and AD-NH3 cations. The
thermally activated molecular rotations of the cations affect
the dielectric response when the temperature is lowered.
When the rotation frequency of the rotator was almost equal
to the measurement frequency (f ) 100 kHz), a great
enhancement in the dielectric response appeared in the ꢀ1
versus T plots.24 The structural fluctuation of the cations
enhanced the magnitude of ꢀ1, which was suppressed by
lowering the temperature owing to the reduced thermal
motion at lower temperatures. Because the room-temperature
ꢀ1 of salts 1 and 3 (∼3000) was larger than those of salts 2
and 4 (∼1000), the introduction of DB[18]crown-6 molecules
has a tendency to enhance the magnitude of ꢀ1 relative to
that of DCH[18]crown-6. A gradual enhancement of ꢀ1
without an anomaly was observed in salts 1 and 2 upon
increasing the temperatures to 300 K, whereas anomalies of
ꢀ1 were observed in salts 3 and 4 at around 230 and 80 K,
respectively.
+
+
From the isomorphous crystal structures of salts 1 and 3,
the phenyl and adamantyl groups were expected to have
similar crystalline rotation environments. However, the
potential energy barrier for the rotation of the adamantyl
group in salt 3 (∆E ∼18 kJmol-1) was 1 order of magnitude
lower than that of the phenyl group in salt 1 (∆E ∼180
(23) (a) Tycko, R.; Dabbagh, G.; Fleming, R. M.; Haddon, R. C.; Makhija,
A. V.; Zahurak, S. M. Phys. ReV. Lett. 1991, 67, 1886. (b) Johnson,
R. D.; Bethune, D. S.; Yannoni, C. S. Acc. Chem. Res. 1992, 25, 169.
(c) Johnson, R. D.; Yannoni, C. S.; Dorn, H. C.; Salem, J. R.; Bethune,
D. S. Science 1992, 255, 1235.
(24) Kao, K. C. Dielectric Phenomena in Solids; Elsevier: Amsterdam,
2004.
Inorganic Chemistry, Vol. 47, No. 13, 2008 5959

Akutagawa et al.
1
Figure 8. Temperature-dependent solid-state wide-line H NMR spectra of salt 3. (a) Spectral changes (left) and the first derivative of the spectra (right)
obtained by decreasing the temperatures from (i) 360 K, (ii) 320 K, (iii) 270 K, (iv) 230 K, (v) 190 K, (vi) 150 K to (vii) 120 K. (b) Temperature-dependent
line-width (∆HA) of salts 3 and 4 along with that of Cs+2([18]crown-6)3[Ni(dmit)2]2 (5).
kJmol-1), owing to the loose molecular packing and isotropic
molecular structure of the adamantyl group. In fact, a
dielectric anomaly was observed at around ∼230 K in salt
3. A notable structural difference between salts 1 and 3 was
assumed to be the packing structure of cations, suggesting
that the ꢀ1 anomaly around 230 K of salt 3 was related to a
changing of the rotational freedom of the adamantyl group
induced by lowering of the temperature. In salt 1, the
molecular rotation of the phenyl ring was ignored within the
limit of measuring frequencies and temperatures. Because
the height of ∆E for salt 2 (∼340 kJmol-1) was almost twice
that of salt 1, the rotation of the phenyl ring in salt 2 is
restricted at room temperature. Thus, no anomaly appeared
in the temperature-dependent dielectric properties of salt 2.
On the other hand, the ∆E of salts 3 (∼18 kJmol-1) and 4
(∼15 kJmol-1) was almost on the order of the thermal energy
at room temperature (kBT ≈ 2.5 kJmol-1), assuming a rapid
rotation of the adamantyl group at room temperature.
However, lowering of the temperature resulted in a decrease
in the rotation frequency of the adamantyl group in salts 3
and 4, which became comparable to the measurement
frequency (100 kHz) at 80 and 230 K, respectively.
independent of temperature. Because a distinct temperature-
dependent spectral change in the line-width of the 1H NMR
spectra of salt 3 could not be seen in the left figure in part
a of Figure 8, the first derivative of the spectrum was
employed to distinguish between the line-width components
+
of AD-NH3 (∆HA: narrow line-width component) and
DB[18]crown-6 (∆HB: wide line-width component). The
peak-to-peak line width of the wide-line-width component
(DB[18]crown-6) was ∼65 kHz and was almost temperature-
independent, which was consistent with that of the frozen
[18]crown-6 (60 kHz) in the crytsal.8a In (Cs+)2([18]crown-
6)3[Ni(dmit)2]2 (5), the rotation of [18]crown-6 was frozen
at around 220 K upon decreasing the temperature, where a
dramatic change in line width was observed from ∼10 kHz
(motional state) to ∼60 kHz (freeze state).8a The negligible
motion of protons in DB[18]crown-6 from 120 to 360 K
resulted in a temperature-independent line-width of ∼60 KHz
in salt 3.
The temperature-dependent narrow line width (∆HA) was
+
assigned to the protons of AD-NH3 in salt 3. Increasing
the temperature slightly increased the ∆HA of salt 3 from
20 kHz (T ) 350 K) to 30 kHz (T ) 120 K). A discontinuous
increase in ∆HA was confirmed at around 250 K, which was
almost where the consistent ꢀ1 anomaly appeared. The
temperature-dependent line-width of salt 4 was basically
similar to that of salt 3, where two kinds of temperature-
independent line-widths (∆HA and ∆HB) were observed over
the temperature range studied. The nearly temperature-
independent line widths ∆HA and ∆HB were observed at ∼20
and ∼65 kHz, respectively. Because the dielectric peak of
salt 4 was observed at ∼80 K, the rotation frequency of the
adamantyl group over the temperature range from 360 to
120 K in the 1H NMR spectra was faster than the measure-
ment frequency of dielectric behavior (f ) 100 kHz).
Assuming the dielectric peak in salt 4 arose from the rotation
of the adamantyl group, the rotation frequency of the
adamantyl group was estimated to be around 100 kHz at 80
K. Thus, the spectral change in the temperature-dependent
1H NMR spectra was not observed due to the change in the
rotational frequency of the adamantyl group.
1
Solid-State H NMR of Salts 3 and 4. On the basis of
the crystal structures, ab initio calculations, and dielectric
properties, salts 3 and 4 were assumed to contain the
crystalline rotator of the adamantyl group. The temperature-
1
dependent solid-state wide-line H NMR spectra of salts 3
and 4 were evaluated to confirm the rotations of the
adamantyl group. Part a of Figure 8 shows the temperature-
dependent spectral changes (left figure) and the first deriva-
1
tive (right figure) of the wide line H NMR spectra of
salt 3.
Because the rotation of bulky DB[18]crown-6 and
DCH[18]crown-6 should be suppressed in salts 3 and 4, the
rotations of the adamantyl group contributed to the temper-
1
ature-dependent spectral changes in the wide-line H NMR
+
spectra. In salt 3, 18 protons of AD-NH3 and 32 protons
1
of DB[18]crown-6 were overlapped in the H NMR spec-
trum. The 18 protons showed a temperature-dependent
behavior, whereas the behavior of the 32 protons was almost
5960 Inorganic Chemistry, Vol. 47, No. 13, 2008

Solid-State Molecular Rotators
Figure 9. Temperature-dependent magnetic susceptibility of salts 1-4. (a) ꢁmolT vs T plots of salts 1 (red), 2 (black), and 3 (blue) per [Ni(dmit)2]- anion.
(b) ꢁmol vs T plots for salt 4 per [Ni(dmit)2]-. The blue and red lines represent the fits obtained using the 1D alternate antiferromagnetic Heisenberg model
and singlet-triplet thermal excitation model, respectively (text).
Magnetic Properties. The temperature-dependent molar
magnetic susceptibility (ꢁmol) per [Ni(dmit)2]- anion was
directly affected by the anion arrangements in the crystals.
Part a of Figure 9 plots ꢁmolT versus T for salts 1, 2, and 3.
In salts 1 and 3, 2D intermolecular interactions in the
[Ni(dmit)2]- layers were observed within the magnitude of
transfer integrals below 15 meV, which led to a weak
antiferromagnetic interaction between [Ni(dmit)2]- anions.
The ꢁmol versus T plots for salts 1 and 3 exhibited typical
Curie-Weiss behavior with a Weiss temperature (θ) of -1.3
and -0.4 K, respectively (Table 2).20 The magnetic spins
on the [Ni(dmit)2]- anion within the 2D layer of salts 1 and
3 were almost identical to each other.
(intradimer J1 . interdimer J2). First, we applied the alternate
antiferromagnetic Heisenberg model for the ꢁmol versus T
behavior of salt 4,25 which almost reproduced the temper-
ature-dependent magnetic behavior using the fitting param-
eters’ intradimer J1 ) -20 K and interdimer J2 ) -7.4 K.
However, the J1/J2 ratio of ∼3:1 was inconsistent with the
ratio from the calculation. Thus, we used the singlet-triplet
(S-T) thermal excitation model.20c Although a slight devia-
tion from the theoretical model was observed above 150 K,
the ꢁmol versus T behavior of salt 4 was in good agreement
with this theoretical model. From the crystal structure,
theoretical calculations, and fitting results of magnetic
susceptibility, the magnetic properties of salt 4 could be
explained by the lateral [Ni(dmit)2]- dimer.
Although similar 1D lateral intermolecular interactions
through the sulfur-sulfur contacts between the [Ni(dmit)2]-
anions were observed in salts 2 and 4, the magnetic exchange
interactions of salts 2 and 4 were ferromagnetic and
antiferromagnetic, respectively. Although constant ꢁmolT
values were observed in salt 2 above 30 K, an enhancement
in the ꢁmolT value was found below 30 K. A ferromagnetic
interaction with a Weiss temperature of θ ) +0.9 K was
observed at low temperatures (T < 30 K). The ferromagnetic
ordering could not be confirmed by the magnetization -
magnetic field (M - H) and AC susceptibility measurements.
The M - H curve (-5 T < M < +5 T) at 2 K showed a
nonlinear behavior with a saturation of M to ∼1.73 µB at 5
T (Figure S15 in the Supporting Information). On the other
hand, the θmol versus T behavior of salt 4 clearly showed
the antiferromagnetic interaction between the [Ni(dmit)2]-
anions (part b of Figure 9). The ꢁmol versus T plots around
room temperature exhibited Curie-Weiss behavior. Further
lowering of the temperature resulted in a broad ꢁmol
maximum around 25 K, and a rapid decrease in ꢁmol was
observed below 25 K. This kind of temperature dependence
has been typically observed in the 1D antiferromagnetic
Heisenberg chain or singlet-triplet dimer. The magnitude
of intrachain transfer integrals (t1 ) 4.09 meV and t2 ) 0.76
meV) of salt 4 suggested the formation of an alternate 1D
chain or isolated lateral [Ni(dmit)2]- dimer, which depended
on the ratio of intra- (J1) to interdimer magnetic exchange
energy (J2). Assuming the relationship J ∼ t2, the J1/J2 ratio
based on the transfer integrals of salt 4 was about 30
Although 1D [Ni(dmit)2]- anion arrangements were ob-
served in salts 2 and 4 (Figure S16 in the Supporting
Information), different magnetic interactions appeared as
ferromagnetic and antiferromagnetic interactions. The [Ni(d-
mit)2]- anions of salt 2 were arranged in the up and down
configurations with almost equal t1 and t2 interactions,
whereas those of salt 4 were constructed from a nonuniform
[Ni(dmit)2]- dimer arrangement with t1 . t2 interactions.
Another notable structural difference was observed in the
largely deformed conformation of the [Ni(dmit)2]- anion in
salt 4. The uniform 1D chain along the long axis of the
[Ni(dmit)2]- anion typically yielded a linear antiferromag-
netic Heisenberg chain,13 whereas the uniform 1D chain
through the lateral sulfur∼sulfur contacts between the
[Ni(dmit)2]- anions yielded a ferromagnetic interaction.
Conclusions
Hydrogen bonding molecular assemblies between anilin-
+
+
ium (Ph-NH3 ) or adamantylammonium (AD-NH3 ) and
bulky crown ethers of dibenzo[18]crown-6 (DB[18]crown-
6) or meso-dicyclohexano[18]crown-6 (DCH[18]crown-6)
formed supramolecular rotators in [Ni(dmit)2]- salts (dmit2-
is 2-thioxo-1,3-dithiole-4,5-dithiolate). Different types of
crystalline rotators, namely, a 180° flip-flop rotator of Ph-NH3+
(25) (a) Duffy, W., Jr.; Barr, K. P. Phys. ReV. 1968, 165, 647. (b) Hall,
J. W.; Marsh, W. E.; Weller, R. R.; Hatfield, W. E. Inorg. Chem.
1981, 20, 1033.
Inorganic Chemistry, Vol. 47, No. 13, 2008 5961

Akutagawa et al.
and a 120° symmetrical rotator of AD-NH3+, were constructed
on the bulky DB[18]crown-6 and DCH[18]crown-6 stator units.
Because of the isotropic molecular structure of the adamantyl
group, the potential energy barrier for the rotation of the
adamantyl group was lower than that of the phenyl ring.
The 2-fold symmetrical intermolecular interaction between
the π plane of Ph-NH3+ and sulfur atoms of [Ni(dmit)2]-
anions yielded a 2-fold symmetrical potential energy curve
with a relatively large potential energy barrier. The bulky
crown ethers (DB[18]crown-6 and DCH[18]crown-6)
served to keep the crystalline space for the rotators. The
potential energy barriers for the rotation of the adamantyl
groupin(AD-NH3+)(DB[18]crown-6)and(AD-NH3+)(DCH-
[18]crown-6) supramolecular cations were extremely low.
They were comparable to the rotation barriers of ethane
and butane and lower than that of adamantane in the
plastic crystalline state. The adamantyl group was effective
in constructing the rotation environment in the solid state.
The structure of the supramolecular rotators directly affected
the [Ni(dmit)2] arrangements and the magnetic behavior. 2D
[Ni(dmit)2]- anion arrangements were observed in (Ph-NH3+)-
(DB[18]crown-6) and (AD-NH3+)(DB[18]crown-6) cations,
whereas 1D lateral [Ni(dmit)2]- interactions through the sulfur-
sulfur contacts were observed in (Ph-NH3+)(DCH[18]crown-
6) and (AD-NH3+)(DCH[18]crown-6) cations. A uniform 1D
magnetic interaction through the lateral sulfur-sulfur contacts
resulted in a ferromagnetic interaction in salt 3. The deformation
from the uniform chain of salt 2 to salt 4 changed the magnetic
interaction dramatically, from ferromagnetic to antiferromag-
netic coupling. Precise control of the [Ni(dmit)2]- anion
arrangement is necessary to control the magnetic properties in
the solid state. On the other hand, the partially oxidized
[Ni(dmit)2] anion is effective in preparing electrically conducting
salts, where supramolecular rotators can be introduced as cation
structures that couple with the conduction electrons.
Acknowledgment. This work was partly supported by a
Grant-in-Aid for Science Research from the Ministry of
Education, Culture, Sports, Science, and Technology of
Japan.
Supporting Information Available: Atomic numbering scheme,
structural analysis of salts 1-4, calculated structural units, 1H NMR
of salt 4, vibrational spectra, nearest neighboring packing of the
rotators in salts 1-4, M - H curve of salt 2 at 2 K, and ESR spectra
at room temperature. This material is available free of charge via
the Internet at http://pubs.acs.org.
IC800271M
5962 Inorganic Chemistry, Vol. 47, No. 13, 2008