Crystal Structures and Magnetic Properties of m-Phenylenebis(imidazole) Derivatives Having Two Nitronyl Nitroxide or Iminyl Nitroxide Radicals. The Two Kinds of Antiferromagnetic Interaction Alternating along One-Dimensional Chains

Article abstract of DOI:10.1021/jo971438t

1,3-Bis{2-(1-oxyl-3-oxo-4,4,5,5-tetramethylimidazolin-2-yl)imidazol-1-yl } benzene (1), 1,3-bis{2-(1-oxyl-4,4,5,5-tetramethylimidazolin-2-yl)imidazol-1-yl}benzene (2), and their chloro derivatives (3 and 4) were prepared. Both diradicals 1, 2 and 3, 4 crystallized in orthorhombic, space group Pbcn and in monoclinic, space group P2₁/c, respectively. The molecular structures of diradicals 1 and 2 were similar to each other and had C₂ symmetry. Intra- and intermolecular average distances between the two NO groups of the nitronyl nitroxide (NN) moieties in 1 and those of the N-N and NO-NO of the iminyl nitroxide (IN) moieties in 2 were found to be 4.26 and 3.49 ? for 1 and 4.38 and 3.54 ? for 2, respectively, suggesting the formation of magnetically linear chain structures along the c axis. An alternating antiferromagnetic one-dimensional chain model (H = -2J Σ{S_A2iSA_2i-1 + αS_A2iSA_2i+1}) was applied to the spin systems 1 and 2 and a theoretical equation derived therefrom was fitted to the observed Χ_molT vs T plots to give the exchange coupling parameters, J/k_B = -158 ± 2 and -239 ± 8 K and α = 0.22 ± 0.02 and 0.11 ± 0.04, respectively. The molecular structures of 3 and 4 were also similar to each other, in which two NN and IN groups are far away from each other by the nearest intramolecular average distance between radical centers being 4.54 and 4.72 ? for 3 and 4, respectively. One of the latter has a disorder with respect to the position of the oxygen atom in IN. One of the two NNs and INs in both diradicals had intermolecular short distances between the radical centers in the neighboring molecules; average distances 3.56 ? for 3 and 3.82 ? for 4, to form magnetic dimer structures. The exchange coupling parameters for 3 and 4 were determined to be J/k_B = -4.85 ± 0.15 and -37.3 ± 0.3 K (one triplet species for the singlet - triplet model; H = -2JS₁S₂, and isolated two doublets in a ratio of 1:1), respectively.

Full text of DOI:10.1021/jo971438t

8854
J . Org. Chem. 1997, 62, 8854-8861
Cr ysta l Str u ctu r es a n d Ma gn etic P r op er ties of
m -P h en ylen ebis(im id a zole) Der iva tives Ha vin g Tw o Nitr on yl
Nitr oxid e or Im in yl Nitr oxid e Ra d ica ls. Th e Tw o Kin d s of
An tifer r om a gn etic In ter a ction Alter n a tin g a lon g On e-Dim en sion a l
Ch a in s
Ryuji Akabane, Masakazu Tanaka, Kenji Matsuo, and Noboru Koga*
Faculty of Pharmaceutical Sciences, Kyushu University, Fukuoka, 812-82 J apan
Kenji Matsuda and Hiizu Iwamura*
Institute for Fundamental Research of Organic Chemistry, Kyushu University, Fukuoka, 818-81 J apan
Received August 4, 1997X
1,3-Bis{2-(1-oxyl-3-oxo-4,4,5,5-tetramethylimidazolin-2-yl)imidazol-1-yl}benzene (1), 1,3-bis{2-(1-
oxyl-4,4,5,5-tetramethylimidazolin-2-yl)imidazol-1-yl}benzene (2), and their chloro derivatives (3
and 4) were prepared. Both diradicals 1, 2 and 3, 4 crystallized in orthorhombic, space group
Pbcn and in monoclinic, space group P21/c, respectively. The molecular structures of diradicals 1
and 2 were similar to each other and had C2 symmetry. Intra- and intermolecular average distances
between the two NO groups of the nitronyl nitroxide (NN) moieties in 1 and those of the N-N and
NO-NO of the iminyl nitroxide (IN) moieties in 2 were found to be 4.26 and 3.49 Å for 1 and 4.38
and 3.54 Å for 2, respectively, suggesting the formation of magnetically linear chain structures
along the c axis. An alternating antiferromagnetic one-dimensional chain model (H ) -2J
Σ{SA2iSA2i-1 + RSA2iSA2i+1}) was applied to the spin systems 1 and 2 and a theoretical equation
derived therefrom was fitted to the observed ømolT vs T plots to give the exchange coupling
parameters, J /kB ) -158 ( 2 and -239 ( 8 K and R ) 0.22 ( 0.02 and 0.11 ( 0.04, respectively.
The molecular structures of 3 and 4 were also similar to each other, in which two NN and IN
groups are far away from each other by the nearest intramolecular average distance between radical
centers being 4.54 and 4.72 Å for 3 and 4, respectively. One of the latter has a disorder with
respect to the position of the oxygen atom in IN. One of the two NNs and INs in both diradicals
had intermolecular short distances between the radical centers in the neighboring molecules; average
distances 3.56 Å for 3 and 3.82 Å for 4, to form magnetic dimer structures. The exchange coupling
parameters for 3 and 4 were determined to be J /kB ) - 4.85 ( 0.15 and -37.3 ( 0.3 K (one triplet
species for the singlet-triplet model; H ) -2J S1S2, and isolated two doublets in a ratio of 1:1),
respectively.
Free radicals capable of serving as bridging ligands for
and developing these metal-radical systems, it is im-
portant to explore new biradicals having two bidentate
ligating sites. 1,3-Bis{2-(1-oxyl-3-oxo-4,4,5,5-tetrameth-
ylimidazolin-2-yl)imidazol-1-yl}benzene (1) and 1,3-bis{2-
(1-oxyl-4,4,5,5-tetramethylimidazolin-2-yl)imidazol-1-yl}-
benzene (2) were designed and synthesized in this work.
NN- and IN-imidazole groups in 1 and 2, respectively,
are expected to serve as bidentate ligands6 and interact
magnetically to each other through bonds and/or space.
We wish to describe the analyses of their crystal struc-
tures and the measurements of their magnetic properties
by means of EPR spectroscopy and SQUID magneto/
susceptometry. Similar studies have been carried out in
the corresponding chloro derivatives 3 and 4.
magnetic metal ions are recent subjects of great interest
in designing and constructing metal-radical hybrid spin
systems that exhibit meta-, ferri-, and ferromagnetism
depending on the dimension of the extended structure
and mode of the exchange interaction. Metal complexes
ligated with nitronyl nitroxides (NN),1 di- and trinitrox-
ides,2 nitrogen bases carrying free radicals3 and carbenes4
and semiquinones5 are typical examples. For extending
X Abstract published in Advance ACS Abstracts, November 15, 1997.
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Caneschi, A.; Chiesi, P.; David, L.; Ferraro, F.; Gatteschi, D.; Sessoli,R.
Inorg. Chem. 1993, 32, 1445. (e) Stumpf, H. O.; Ouahab, L.; Pei, Y.;
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1994, 1693. (b) Inoue, K.; Iwamura, H. J . Chem. Soc., Chem. Commun.
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Burdukov, A. B.; Ovcharenko, V. I.; Ikorski, V. N.; Pervukhina, N. V.;
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B. Inorg. Chem. 1991, 30, 972.
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Engl. 1996, 36, 755. (b) Sano, Y.; Tanaka, M.; Koga, N.; Matsuda, K.;
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S0022-3263(97)01438-2 CCC: $14.00 © 1997 American Chemical Society

m-Phenylenebis(imidazole) Derivatives
J . Org. Chem., Vol. 62, No. 25, 1997 8855
Ta ble 1. Cr ysta l Da ta a n d Exp er im en ta l P a r a m eter s of X-r a y Cr ysta l An a lyses of 1-4
1
2
3
4
formula
M
C26H32N8O4
520.59
C26H32N8O2
488.59
C26H31N8O4Cl
555.04
C26H31N8O2Cl
523.04
crystal system
space group
orthorhombic
Pbcn
orthorhombic
Pbcn
monoclinic
P21/c
monoclinic
P21/c
a, Å
b, Å
c, Å
10.448(6)
13.859(4)
18.147(4)
10.617(3)
13.082(2)
18.371(4)
11.859(2)
11.369(2)
20.368(2)
95.05(1)
2735.5(7)
4
11.924(1)
11.314(5)
20.344(2)
96.191(7)
2728.6(9)
4
â, deg
V, A3
2627(1)
4
1.316
2551(1)
4
1.272
Z
D, g/cm3
1.348
1.273
no. of observations
no. of variables
R(I)
436 (I > 3.00σ(I))
678 (I > 3.00σ(I))
2653 (I > 3.00σ(I))
1756 (I > 3.00σ(I))
174
165
353
345
0.049
0.030
0.060
0.055
0.068
0.060
0.069
0.066
Rw(I)
Ta ble 2. Selected Tor sion An gles, Bon d An gles, Bon d
Len gth s, a n d Non bon d ed Con ta cts for Bir a d ica l 1 a n d 2
Sch em e 1
1
2
Torsion Angles, deg
N1-C1-C8-N4
N1-C1-C8-N3
N2-C1-C8-N4
N2-C1-C8-N3
C8-N4-C12-C11
C8-N4-C12-C13
C10-N4-C12-C11
C10-N4-C12-C13
137
-44
-46
130
-38
144
131
-44
137.1
-47
-45
130.1
-33
146.6
135.4
-45
Bond Angles, deg
O1-N1-C1
O1-N1-C2
O2-N2-C1
O2-N2-C3
125
122
126
121
O1-N2-C1
O1-N2-C3
126
123.8
Bond Lengths, Å
O1-N1
O2-N2
1.24
1.27
O1-N2
1.29
Nonbonded Contacts, Å
O1-O*1
N1-N*1
O2-O2a
N2-N2a
3.97
4.54
3.22
3.75
N1-N*1
O1-O1a
N2-N2a
4.38
3.24
3.84
a
Intermolecular distance.
Resu lts a n d Discu ssion s
imidazole rings in a disrotatory fashion: the dihedral
angles between the phenylene and imidazole ring, and
imidazole ring and the radical plane are 36-49 and 43-
50° for 1 and 33-45 and 43.9-49.9° for 2, respectively.
P r ep a r a tion s of Bir a d ica ls. Routes to biradicals
1-4 are summarized in Scheme 1. Starting 1,3-di(N-
imidazolyl)benzene and its chloro derivative were selec-
tively lithiated at position 2 of the imidazole rings with
n-butyllithium followed by the reaction with N,N-dimeth-
ylformamide to afford diformyl derivatives. Biradicals
having NN and IN groups were prepared by a standard
procedure7 reported previously.
The biradicals obtained were very stable in solution
and solid states. Biradicals 1-4 were obtained by
recrystallization as single crystals that were subjected
to X-ray crystal and molecular structure analyses.
Cr ysta l Str u ctu r es. Pertinent crystallographic pa-
rameters and refinement data are listed in Table 1.
Selected torsion angles, bond angles, bond lengths, and
nonbonded contacts are reported in Tables 2 and 3 for
biradical 1 and 2, and for 3 and 4, respectively.
Intramolecular through-space average distance (rO1N1-O′1N′1
)
of rO1-O′1 and rN1-N′1 for 1 and distance (rN1-N′1) for 2 are
4.26 and 4.38 Å, respectively. As shown in Figure 2, the
crystal structure for both radicals are also similar. The
molecules aligned alternatively along the c axis with the
intermolecular average distance (rO2N2-O2N2) between the
oxygen and nitrogen atoms of the nitroxide by 3.49 Å for
1 and 3.54 Å for 2. Taking the short distances (rO1N1-O′1N′1
) 4.26 Å and rN1-N′1 ) 4.38 Å for 1 and 2, respectively)
between the two radical centers within a molecule into
account, these radicals in crystals, especially for 1, are
considered to have a magnetically one-dimensional chain
structure. The nearest distance of the radical centers
between the chains is 5.84 for 1 and 7.74 Å for 2,
indicating that interchain magnetic interaction is less
significant.
As shown in the ORTEP drawings for 1 and 2 in
Figures 1a and b, respectively, both the radicals have C2
symmetry axes through C11 and C14 of the benzene ring
and have similar molecular structures in which two
radical centers are close to each other by twisting the
As observed in ORTEP drawing of Figure 3, the
molecular structure of chloro derivatives 3 and 4 are also
similar to each other and have no symmetry axis. The
two NN and IN groups in a molecule are away from each
other and largely twisted toward the imidazole rings; the
dihedral angles between the phenylene and imidazole
(7) Ullman, E. F.; Osiecki, J . H.; Boocok, D. G. B.; Darcy, R. J . Am.
Chem. Soc. 1972, 94, 7049.

8856 J . Org. Chem., Vol. 62, No. 25, 1997
Akabane et al.
F igu r e 1. ORTEP drawings of biradicals 1 (a) and 2 (b) (ellipsoids at 30% probability).
Ta ble 3. Selected Tor sion An gles, Bon d An gles, Bon d
Len gth s, a n d Non bon d ed Con ta cts for Bir a d ica l 3 a n d 4
other, respectively, in 4. Intramolecular through-space
average distance (rO2O4-N4N7) of rO2-O4 and rN4-N7 for 3 is
4.54 Å. One of the two INs in 4 indicated by dashed
square in Figure 3b is disordered in 1:1 probability and
the intramolecular average distances between the radical
centers (rN4-N8 and rN4-N7O3) are 4.71 and 4.72 Å. As
indicated in the crystal structure of Figure 4, both radical
molecules have the nearest ones in which average
intermolecular distances (rO1N3-N1O3) between the radical
centers are 3.56 Å for 3 and 3.82 Å for 4 to form the dimer
structure. The average distances between the nearest
radical centers of the dimers are 4.66 and 5.53 Å for 3
and 4, respectively.
3
4
Torsion Angles, deg
N1-C7-C10-N3
N1-C7-C10-N4
N2-C7-C10-N3
N2-C7-C10-N4
C4-C5-N2-C7
C4-C5-N2-C9
C6-C5-N2-C7
C6-C5-N2-C9
N5-C17-C20-N7
38.5
-133.8
-145.1
42.6
N1-C7-C10-N3
36
N1-C7-C10-N4 -140.2
N2-C7-C10-N3 -151.6
N2-C7-C10-N4
32
-137.3
C4-C5-N2-C7 -133.7
38.3
C4-C5-N2-C9
C6-C5-N2-C7
39
46
43.5
-140.9
C6-C5-N2-C9 -140.6
67.4
N5-C17-C20-N7 -136
N5-C17-C20-N8 -115.8
N6-C17-C20-N7 -109.4
N5-C17-C20-N8
N6-C17-C20-N7
46
46
EP R Sp ectr a . EPR spectra of 1, 2, 3, and 4 in
2-methyltetrahydrofuran (MTHF) solution at room tem-
perature consisted of five (aN/2 ) 7.26 and 7.17 G for 1
and 3, respectively) and seven lines (aN/4 ) 4.30 and 4.29
G for 2 and 4, respectively) due to hyperfine coupling with
the nitrogen nuclei overlapped with one broad signals at
g ) 2.0069, 2.0062, 2.0070, and 2.0066, respectively.
N6-C17-C20-N8
C2-C3-N5-C17
C2-C3-N5-C18
C4-C3-N5-C17
C4-C3-N5-C18
67.5
-128.6
53
51.2
-127.2
N6-C17-C20-N8 -130
C2-C3-N5-C17 -127
C2-C3-N5-C18
C4-C3-N5-C17
56
51
C4-C3-N5-C18 -125
Bond Angles, deg
O1-N3-C10
O1-N3-C11
O2-N4-C10
O2-N4-C12
O3-N8-C20
O3-N8-C21
O4-N7-C20
O4-N7-C22
126.8
122.8
127.3
120.6
125.9
122.1
124.6
123.4
O1-N3-C10
127.4
123.9
125
O1-N3-C11
O2-N7-C20
O2-N7-C21
Ground powder samples showed one broad signal (Hpp
)
121
1.46, 3.25, 0.80, and 1.24 mT) at g ) 2.009, 2.012, 2.007,
and 2.007 for 1, 2, 3, and 4, respectively.
EPR spectra (ν0 ) 9.411 GHz) in frozen MTHF solu-
tions were obtained in the temperature range 10-100
K. All the four EPR spectra contained two sets of signals
characteristic of triplet species at ca. g ) 2.00 in addition
to the signals due to ∆mS ) ( 2 transitions. The
spectrum of 1 at 10 K is shown in Figure 5a as an
example and was simulated8 (Figure 5b) by a sum of two
triplet spectra in a 1:4 ratio with zero-field splitting
parameters |D/hc| ) 0.00726, 0.00270 and |E/hc| )
0.00002, 0.00002 cm-1, respectively.
The intramolecular average distances between the
radical centers were estimated to be 7.1 Å by applying a
point dipole approximation to the former |D/hc| value
(0.00726 cm-1). This value is different from the intramo-
lecular through-space distance of 4.26 Å revealed by
X-ray analysis, suggesting that the molecular structure
Bond Lengths, Å
O1-N3
O2-N4
O3-N8
O4-N7
1.27
1.29
1.25
1.26
O1-N3
O2-N7
1.28
1.26
Nonbonded Contacts, Å
O1-O1a
N3-N3a
O4-O2
N7-N4
O3-O3a
N8-N8a
3.30
3.81
3.90
O1-O1a
N3-N3a
N4-N8
3.62
4.01
4.71
5.18
4.04
5.28
(N4-O2)
(4.73)
a
Intermolecular distance.
rings, and the imidazole ring and the radical plane are
51.2-53 and 64.2-70.6° for the side indicated by dashed
square and 38.3-43.5 and 34.9-46.2° for the other,
respectively, in 3. Those dihedral angles are 51-56 and
44-50° for the one and 39.0-46.3 and 28.4-39.8° for the
(8) The simulation of the EPR fine structure was performed by using
a program based on the second-order perturbation theory and provided
by Professors K. Ito and T. Takui of Osaka City University.

m-Phenylenebis(imidazole) Derivatives
J . Org. Chem., Vol. 62, No. 25, 1997 8857
F igu r e 2. Views of the unit cell of biradicals 1 (a) and 2 (b). Methyl groups have been omitted for the sake of clarity. Average
distances between the radical centers: (i) 4.26 Å, (ii) 3.49 Å, (iii) 4.38 Å, and (iv) 3.54 Å.
Sch em e 2
in frozen solution and in crystalline state might be
different and the former may not be unique but consist
of at least two conformers (rotamers). Similarly, the
triplet spectra for the other biradicals were interpreted
not by single species but two conformers with different
composition. The two radical centers in these molecules
interact magnetically to each other through-space and/
or through-bond to produce triplet species. The intensi-
ties (I) of the observed triplet signals linearly decreased
with increasing temperature (T) from 13 to 100 K in I vs
T-1 plot; the temperature dependence of triplet signal
intensities suggested either that triplet states are ground
states or they are degenerate with singlet states.
Ma gn etic Su scep tibility. The paramagnetic suscep-
tibilities of microcrystalline samples were measured at
2-350 K for 1 and 2, and 2-300 K for 3 and 4 at a
constant field of 500 mT. Temperature dependence of
the molar paramagnetic susceptibility ømol was obtained
and presented as ømolT vs T plots for biradicals 1 and 2
and their chloro derivatives 3 and 4 in Figures 6 and 7,
respectively.
lated for a spin only value either of two isolated S ) 1/2
or degenerate singlet-triplet spin systems. As the
temperature was lowered from 350 K, ømolT values for 1
and 2 decreased gradually to nearly zero at ca. 30 and
50 K, respectively, as shown in Figure 6. The observed
thermal behavior of ømolT values for both samples indi-
cates that strong antiferromagnetic interactions took
place in crystalline states and that their magnitude was
greater for 2 than 1.
To understand these magnetic interactions quantita-
tively, an antiferromagnetic alternating one-dimensional
chain model9,10 (Scheme 2) suggested by the X-ray crystal
structure data (Figure 2) was applied to the spin systems
of radicals 1 and 2, in which intramolecular through-bond
interaction were insignificant by large dihedral angles
(9) (a) Duffy, W.; 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.
(10) Kahn, O. Molecular Magnetism; VCH: New York, 1993; Chap-
ter 11.
(A) Bir a d ica l 1 a n d 2. ømolT values of 0.651 and 0.613
emu‚K‚mol-1 at 350 K for 1 and 2, respectively, are
already smaller than those of 0.751 emu‚K‚mol-1 calcu-

8858 J . Org. Chem., Vol. 62, No. 25, 1997
Akabane et al.
F igu r e 3. ORTEP drawings of biradicals 3 (a), and 4 (b) (ellipsoids at 30% probability).
between the benzene and imidazole rings, and the
imidazole and radical units.
The spin Hamiltonian for such systems is given by
either the presence of a high-spin state with a consider-
ably large energy gap to the next lower state or a mixture
of species having two different negative J value, one large
and the other small.
H ) -2J Σ{SA2iSA2i-1 + RSA2iSA2i+1
}
(1)
The crystal structures (Figure 4a,b) of 3 and 4 suggest
two kinds of spin models: a combination of the singlet-
triplet model (H ) -2J (S1S2)) and the isolated doublet
model in a ratio of 1:1 on one hand, and a four-spin model
which depends on the presence or absence of the intra-
molecular interaction on the other. The experimental
data were fitted by Bleaney-Bowers equation12 (S-T
model) plus an isolated doublet term to give g ) 1.966 (
0.003, 1.930 ( 0.020, J /kB ) -4.85 ( 0.15, -37.3 ( 0.3
K, θ ) 0, -0.45 ( 0.02 K for 3 and 4, respectively. The
best-fit curves are shown in Figure 7 as solid curves.
When intramolecular interactions are significant, their
spin system become four spin linear chain (H ) -2J (S1S2
+ S3S4) -2RJ (S2S3), where J and RJ mean intra- and
intermolecular exchange coupling constants, respec-
tively). Theoretical equations13 were fitted to the experi-
mental data by means of a least-squares method to give
the best fitted parameters: g ) 1.970 ( 0.003, 1.932 (
0.02, J /kB ) -0.95 ( 0.40, -0.27 ( 0.30 K, θ ) 0, -0.46
( 0.03 and R ) 4.05 ( 2.31, 136 ( 152, for 3 and 4,
respectively. The obtained intramolecular J /kB values
are very small indicating that intramolecular through-
space interaction (4.54 and 4.72 Å for 3 and 4, respec-
tively) was insignificant.
Com p a r ison s of J in ter /kB Va lu es betw een Bir a d i-
ca ls 1, 2 a n d 3, 4. Intermolecular J inter/kB values
obtained by fitting theoretical equations to the experi-
mental data and the average distances between radical
centers revealed by X-ray analysis for four biradicals are
summarized in Table 4.
The magnitude of the J /kB values are considerably
different in unsubstituted biradicals 1 and 2 and their
chloro derivatives 3 and 4, while their intermolecular
average distances between the radical centers are nearly
where R is an alternation parameter smaller than unity.
The equations9 derived from the eigenvalues of this
Hamiltonian for 0 < R < 0.4 and 0.4 < R were fitted to
the experimental data from 350 to 2 K. For the fitting,
g value of 2.009 and 2.012 for 1 and 2, respectively,
obtained from EPR spectra of their ground samples were
employed. Although theoretical curves slightly deviated
from experimental data in the low-temperature region,
the best fit parameters; J /kB ) -158 ( 2, -239 ( 8 K,
and R ) 0.22 ( 0.02, 0.11 ( 0.04 for 1 and 2, respectively,
were obtained. The best-fit curves are shown in Figure
6 as solid curves. Taking the distance between the
radical centers in crystal structures of 1 and 2 into
account, we find that the J and RJ values are due to the
inter- (J inter) and intramolecular (J intra) through-space
interactions; J inter/kB ) -158, -239 K and J intra/kB
)
-34.8, -26.3 K for 1 and 2, respectively. The difference
in the R values between 1 and 2 was explained by
assuming that the spins in biradical 2 are mainly
localized on the N-O atoms in IN moieties11 in addition
to that the intermolecular distance between N-N of IN
in a molecule 2 is slightly longer than the one of NO-
NO in 1 (rN1-N′1 ) 4.38 Å for 2 and rO1N1-N′1O′1 ) 4.26 Å
for 1).
(B) Bir a d ica l 3 a n d 4. As shown in the ømolT vs T
plot for biradical 3 (Figure 7a), ømolT values above 60 K
are constant at 0.74 emu‚K‚mol-1 and those below 60 K
decreased with decreasing temperature. The observed
ø
molT vs T profile showed an ordinary antiferromagnetic
interaction. On the other hand, the ømolT values of
biradical 4 decreased gradually from 300 to 20 K and in
a slightly stepwise manner below 20 K as temperature
was decreased (Figure 7b). The step-shaped decrease
cannot be explained by a simple S-T model but suggests
(12) Bleaney, B.; D. Bowers, K. Proc. R. Soc. London 1952, A214,
451.
(11) Akita, T.; Mazaki, Y.; Kobayashi, K.; Koga, N.; Iwamura, H. J .
Org. Chem. 1995, 60, 2092.
(13) Mitsumori, T.; Inoue, K.; Koga, N.; Iwamura, H. J . Am. Chem.
Soc. 1995, 117, 2467.

m-Phenylenebis(imidazole) Derivatives
J . Org. Chem., Vol. 62, No. 25, 1997 8859
F igu r e 5. (a) X-band EPR(9.411 GHz) spectrum of 1 in frozen
MTHF solution at 10 K. (b) Simulated spectrum of a randomly
oriented triplet species for 1.
centers revealed by X-ray analysis in four biradicals is
given in Figure 8 where one set of radical planes of NN
and IN unit are found to be nearly parallel to each other
and the π-orbitals containing the radical spins take an
orthogonal position to the radical plane (to the paper
plane).
As seen in Figure 8, the radical center units of
biradicals 1 and 2 have the appropriate geometry in
which π-orbitals of radical centers overlapped to each
other more ideally than those for 3 and 4. Therefore,
they give rise to a large difference in the negative J /kB
values between 1, 2 and 3, 4.
F igu r e 4. View of the crystal structure of biradical 3 (a) and
4 (b). Average distances between the radical centers: (i) 4.54
and 4.72 Å, (ii) 3.56 and 3.82 Å, (iii) 4.66 and 5.53 Å for 3 and
4, respectively.
Ta ble 4. In ter m olecu la r Exch a n ge P a r a m eter s
(-J in ter /KB) a n d Dista n ces for Bir a d ica l 1-4
Con clu sion
1
2
3
4
The through-bond interaction between the two radical
centers was not dominant due to large dihedral angles
between phenylene-imidazole rings and between imid-
azole-radical planes in crystalline state of biradicals
1-4. Both 1 and 2 have similar crystal structure as well
as molecular structure and show alternating antiferro-
-J inter/kB (K)
158
3.49
239
3.54
4.85
3.56
37.3
3.83
distances (Å)a
a
Intermolecular average distances between radical centers.
equal (slightly longer in 1 and 2 than in 3 and 4). These
NO-NO short contacts were also observed in the crystal
structure of imidazole,14 1-methylimidazole,15 N-meth-
ylpyridine16 derivatives having NN groups at position 2
and produced strong intermolecular antiferromagnetic
interactions between the NNs. Although those observed
in this work were also considered to be caused by short
NO-NO contact, this large difference in the J inter/kB
values cannot be explained only by the average distances
of radical centers. Relative orientation of the radical
magnetic one-dimensional chain interaction with J inter
kB ) -158 K, J intra/kB ) -35 K and J inter/kB ) -239 K,
intra/kB ) -26 K, respectively. Biradical 3 and 4 also
/
J
have similar molecular and crystal structure in which
J /kB values for the intramolecular interaction were
insignificant, while those for the intermolecular one were
-4.85 and -37.3 K, respectively. When the magnitude
of the intermolecular exchange interaction between radi-
cal centers was considered, it was found to be important
to know not only the distance between radical centers
but also the direction and overlap of π-orbitals occupied
by radical spins.
(14) Yoshioka, N.; Irisawa, M.; Mochizuki, Y.; Kato, T.; Inoue, H.;
Ohba, S. Chem. Lett. 1997, 251.
(15) Hanayama, H.; Tanaka, M.; Koga, N., unpublished result.
(16) Yamaguchi, A.; Awaga, K.; Inabe, T.; Nakamura, T.; Matsu-
moto, M.; Maruyama, Y., Chem. Lett. 1993, 1443.
The complex formation will be expected to make planar
imidazole-radical plane by coordination of metal ions.

8860 J . Org. Chem., Vol. 62, No. 25, 1997
Akabane et al.
F igu r e 7.
ø
molT - T plots for 3 (a) and 4 (b). Solid curves
F igu r e 6.
ømolT - T plots for 1 (a) and 2 (b). Solid curves
were calculated by means of the theoretical equation based
on S-T model and isolated two doublets with optimized
parameters.
were calculated by means of the theoretical equation9 based
on alternating linear-chain spin systems with optimized
parameters.
Magnetic susceptibilities were measured on Quantum De-
sign MPMS2 and MPMS-5S SQUID susceptometers. Data
were corrected for the magnetization of a sample holder and
capsule used and for diamagnetic contributions which were
estimated from Pascal’s constants.
Ma ter ia ls. Unless otherwise stated, the preparative reac-
tions were carried out under a high purity dry nitrogen
atmosphere. Tetrahydrofuran (THF) and 2-methyltetrahy-
drofuran (MTHF) were distilled from sodium benzophenone
ketyl. 2,3-Bis(hydroxyamino)-2,3-dimethylbutane was pre-
pared by the procedure17 reported previously. 1,3-Di-1-imid-
azolylbenzene and 1,3-di-1-imidazolyl-5-chlorobenzene were
prepared via four steps from 1,3-diaminobenzene and 1,3-
diamino-5-chlorobenzene, respectively, in a manner similar to
the procedure for phenylimidazole derivatives reported by
J ohnson et al.18
Efforts are underway toward preparation of magnetic
metal complexes using these ligands.
Exp er im en ta l Section
Gen er a l Meth od s. Infrared spectra were recorded on a
Hitachi 270-30 IR spectrometer. UV-vis spectra were recorded
on a J ASCO UVDEC 610C spectrometer. 1H NMR spectra
were measured on a J EOL 270 Fourier transform spectrometer
using CDCl3 as solvent and referenced to TMS. FAB mass
spectra (FAB MS) were recorded on a J EOL J MS-SX102
spectrometer. Melting points were obtained with a MEL-
TEMP heating block and are uncorrected. Elemental analyses
were performed in the Analytical Center of Faculty of Science,
Kyushu University.
X-r a y Cr ysta l a n d Molecu la r Str u ctu r e An a lyses. All
the X-ray data were collected using Cu KR radiation on a
Rigaku AFC5R four circle diffractometer. The structures were
solved in Pbcn for both biradical 1 and 2 in P21/c for 3 and 4
by direct methods and refinement converged using the full-
matrix least squares of the TEXAN Ver. 1.6 program (Molec-
ular Structure Corp.). All non-hydrogen atoms were refined
anisotropically; hydrogen atoms were included at standard
positions (C-H 0.96 Å, C-C-H 109.5°, 120°, or 180°) and
refined isotropically using a rigid model.
1,3-Bis{1-(2-for m ylim id a zolyl)}ben zen e (6). To the so-
lution of 1.49 g (7.09 mmol) of 1,3-di-N-imidazolylbenzene 7
in 90 mL of anhydrous THF was added 14.6 mL of a 1.6 M
solution of n-butyllithium in n-hexane at -78 °C. After
stirring for 80 min, 1.81 mL (23.4 mmol) of dimethylformamide
was added dropwise. The reaction mixture was stirred for 1
h at -78 °C and then left overnight at room temperature. After
the usual workup, 0.97 g (3.65 mmol) of a dialdehyde 6 was
obtained in 51.7% yield: mp 204-205 °C, IR (KBr) 1682 cm-1
,
EP R Sp ectr a a n d Ma gn etic Mea su r em en ts. EPR spec-
tra were recorded on a Bruker ESP 300 X-band (9.4 GHz)
spectrometer equipped with a Hewlett-Packard 5350B micro-
wave frequency counter. An Air Products LTD-3-110 liquid
helium transfer system was attached for the low-temperature
measurements. Sample solutions were placed in 5 mm o.d.
quartz tubes, degassed by three freeze-and-thaw cycles, and
sealed.
1H NMR (500 MHz, DMSO-d6) δ 9.71 (s, 2H), 7.84 (s, 2H), 7.81
(s, 1H), 7.66 (s, 1H), 7.66 (d, J ) 1.37 Hz, 2H), 7.46 (d, J )
0.69 Hz, 2H), FAB MS (m-nitrobenzyl alcohol): M + 1 267.
(17) J ohnson, A. L.; Kauer, J . C.; Sharma, D. C.; Dorfman, R. I. J .
Med. Chem. 1969, 12, 1024.
(18) Siegle, L. W.; Hass, H. B. J . Org. Chem. 1940, 5, 100.

m-Phenylenebis(imidazole) Derivatives
J . Org. Chem., Vol. 62, No. 25, 1997 8861
derivative was prepared in a manner similar to the procedure
of 5 using 9 in place of 6. The mixture of hydroxyamine 8
containing the corresponding biradicals was used for the next
oxidation reaction without further purification.
1,3-Bis{2-(1-oxyl-3-oxo-4,4,5,5-tetr a m eth ylim id a zolin -
2-yl)im id a zol-1-yl}ben zen e (1). To a solution of 0.27 g (0.48
mmol) of 3 in 20 mL of CHCl3 and 2 mL of MeOH was added
20 mL of aqueous solution of 1.02 g of NaIO4 in H2O. The
suspension was stirred at room temperature for 5 min. After
the usual workup, crude residue was chromatographed on
aluminum oxide to afford 0.15 g (0.30 mmol) of 1 in 62% yield.
Recrystallization from cyclohexane-CH2Cl2 gave bis(nitronyl
nitroxide) 1 as a blue brick: mp 227-228 °C, UV-vis (in
CH2Cl2) 552, 330 nm, FAB MS (m-nitrobenzyl alcohol ma-
trix): 521 (M + 1, 100), 520 (69). Anal. Calcd for C26H32N8-
O4: C, 59.97; H, 6.20; N, 21.53. Found: C, 60.05; H, 6.18; N,
21.49.
1,3-Bis{2-(1-oxyl-4,4,5,5-tetr a m eth ylim id a zolin -2-yl)im -
id a zol-1-yl}ben zen e (2). To a solution of 0.20 g of 1 in 60
mL of CH2Cl2 was added 0.6 g of NaNO2 in 2 mL of acetic
acid. Reaction solution was stirred for 2 min at room tem-
perature. After the usual workup, crude residue was chro-
matographed on silica gel to afford 0.16 g (0.33 mmol) of 1 in
85.2% yield. Recrystallization from n-hexane-CH2Cl2 gave
bis(iminyl nitroxide) 2 as orange bricks: mp 228-229 °C, UV-
vis (in CH2Cl2) 421, 330 nm, FAB MS (m-nitrobenzyl alcohol):
490 (M + 2, 100), 489 (57.6). Anal. Calcd for C26H32N8O2: C,
63.90; H, 6.61; N, 22.94. Found: C, 63.82; H, 6.56; N, 22.93.
1-Ch lor o-3,5-bis{2-(1-oxyl-3-oxo-4,4,5,5-tetr a m eth ylim -
id a zolin -2-yl)im id a zol-1-yl}ben zen e (3) a n d 1-Ch lor o-3,5-
bis{2-(1-oxyl-4,4,5,5-tetr am eth ylim idazolin -2-yl)im idazol-
1-yl}ben zen e (4). Biradicals 3 and 4 were prepared in a
manner similar to the procedure for 1 using crude 8 in place
of 6. The mixture of both radicals was chromatographed on
aluminum oxide with n-hexane/CH2Cl2 as eluent to afford 3
and 4 in 16.4 and 30.2% yield, respectively. The obtained
biradicals were crystallized from n-hexane/CH2Cl2/ethyl ac-
etate and n-hexane/CH2Cl2 to give 3 and 4 as blue bricks and
brown plates, respectively.
F igu r e 8. Ball-and-stick models for intermolecular contacts
(ON-ON) of radical center units in 1 (a), 2 (b), 3 (c), and 4 (d)
viewed along the direction perpendicular to ONCNO plane of
a radical center. Black balls and dotted balls indicate the
oxygen and nitrogen atoms, respectively.
Anal. Calcd for C14H10N4O2: C, 63.14; H, 3.79; N, 21.05.
Found: C, 62.95; H, 3.83; N, 20.96.
3: mp 210-211 °C. Anal. Calcd for C26H31N8O4Cl: C, 56.3;
H, 5.64; N, 21.21. Found: C, 56.36; H, 5.69; N, 20.08.
4: mp 224-225 °C. Anal. Calcd for C26H31N8O2Cl: C,
59.63; H, 6.16; N, 21.41. Found: C, 59.35; H, 5.96; N, 21.16.
1-Ch lor o-3,5-bis{1-(2-for m ylim id a zolyl)}ben zen e (9).
The compound was prepared in a manner similar to the
procedure of 6 using 1-chloro-3,5-di-1-imidazolylbenzene, 10,
in place of 7. Formyl derivative 9 was obtained in 91.8% yield:
mp 204-205 °C, IR (KBr) 1698 cm-1 1H NMR (270 MHz,
,
Ack n ow led gm en t. This work was supported by a
Grant-in-Aid for Scientific Research (B) (no. 06453035)
from Ministry of Education, Science and Culture, J apan.
We appreciate Dr. Max Dobler of ETH who provided the
program for the molecular model obtained by X-ray
crystal analysis.
CDCl3) δ 9.85 (s, 2H), 7.50 (d, J ) 2.02 Hz, 2H), 7.46 (d, J )
1.10 Hz, 2H), 7.39 (d, J ) 0.92 Hz, 2H), 7.33 (d, J ) 1.92 Hz,
1H), FAB MS (m-nitrobenzyl alcohol): M + 1 301. Anal.
Calcd for C14H10N4O2Cl‚2/9H2O: C, 55.26; H, 3.13; N, 18.42.
Found: C, 55.16; H, 3.25; N, 18.28.
1,3-Bis{2-(1,3-h yd r oxy-4,4,5,5-tetr a m eth ylim id a zolin -
2-yl)im id a zol-1-yl}ben zen e (5). To a solution of 0.58 g (2.17
mmol) of dialdehyde 6 in 30 mL of MeOH was added 1.37 g
(9.30 mmol) of free 2,3-bis(hydroxyamino)-2,3-dimethylbutane.
Reaction mixture was heated at 30 °C for 6 h. After the usual
workup, 0.97 g (1.15 mmol) of dihydroxyamine 5 containing
small amounts of the nitronyl nitroxide were obtained in 53%
yield. This mixture was used for oxidation without further
purification.
Su p p or tin g In for m a tion Ava ila ble: Details of X-ray
analysis for birdical 1-4 including tables of atomic coordinates,
anisotropic displacement parameters, bond lengths, bond
angles, torsion angles, and nonbonding contacts out to 3.60 Å
(80 pages). This material is contained in libraries on micro-
fiche, immediately follows this article in the microfilm version
of the journal, and can be ordered from the ACS; see any
current masthead page for ordering information.
1-Ch lor o-3,5-bis{2-(1,3-h yd r oxy-4,4,5,5-tetr a m eth ylim -
idazolin -2-yl)im idazol-1-yl}ben zen e (8). The hydroxyamine
J O971438T