Synthesis, structure, and magnetic property of organic-radical labeled carborane

Article abstract of DOI:10.1246/cl.2004.1460

A carborane derivative containing nitronyl nitroxide group was synthesized and was crystallographically and magnetically characterized. The X-ray structure analysis revealed that the molecules were crystallized in a head-to-tail dimer fashion. The intradimer ferromagnetic interaction (J/k_B = +4.26(2) K) was observed.

Full text of DOI:10.1246/cl.2004.1460

1460
Chemistry Letters Vol.33, No.11 (2004)
Synthesis, Structure, and Magnetic Property of Organic-radical Labeled Carborane
Fumiyasu Iwahori,y;yy Kengo Kamibayashi,y Yoshikazu Nishikawa,yyy Masahiro Yamashita,yy;yyyy and Jiro Abeꢀy
yDepartment of Chemistry, School of Science and Engineering, Aoyama Gakuin University,
5-10-1 Fuchinobe, Sagamihara, 229-8558
yyCREST, Japan Science and Technology Agency, Kawaguchi Center Building, 4-1-8, Honcho Kawaguchi, 332-0012
yyyDepartment of Applied Chemistry, Graduate School of Engineering, Tokyo Metropolitan University,
1-1 Minami-Osawa, Hachioji, Tokyo 192-0397
yyyyDepartment of Chemistry, Graduate School of Science, Tohoku University,
6-3 Aramaki-Aza-Aoba, Aoba-ku, Sendai, Miyagi 980-8578
(Received August 17, 2004; CL-040972)
A
carborane derivative containing nitronyl nitroxide
decacarboranyl)]benzaldehyde5 and 2,3-dimethyl-2,3-bis(hy-
droxylamino)butane, followed by the oxidation using an aque-
ous sodium meta-periodide (Scheme 1).6 The purification was
performed by a column chromatography on silica gel using di-
ethyl ether as an eluent. The eluent was kept standing for a
few days and slowly evaporated. An X-ray-quality blue single
crystal of 1 was obtained. The crystal structure of 1 is shown in
Figure 1a.7
group was synthesized and was crystallographically and magnet-
ically characterized. The X-ray structure analysis revealed that
the molecules were crystallized in a head-to-tail dimer fashion.
The intradimer ferromagnetic interaction (J=kB ¼ þ4:26ð2Þ K)
was observed.
Extensive researches have been demonstrated on the chem-
istry of carboranes.1 Taking advantage of the characteristic ico-
sahedral framework, the carborane derivatives were often used
for the modules for the molecular designing and crystal engi-
neering.2 The hydrogen-bonding affinity of the carborane deriv-
atives due to their polarized C–H vertices has been applied for
the crystal designing on the supramolecular chemistry.3 On the
one hand, constructions of organic magnetic materials are still
attracting much attention. A nitronyl nitroxide is a prominent or-
ganic radical which has been played an essential part in the de-
sign and synthesis of organic magnetic materials. The bulk mag-
netism of the nitronyl nitroxide derivatives is drastically affected
by the molecular alignment because intermolecular magnetic in-
teractions play decisive role for their magnetic properties. In par-
ticular, an intermolecular hydrogen-bond is often important for
the magnetic characters of the nitronyl nitroxide derivatives.4
The carborane derivatives can be considered as a novel spin-
coupler. However, the preparation of organic radical substituted
carboranes has not been mentioned up to date. In this paper, we
would like to describe the synthesis, isolation and characteriza-
tion of a carborane derivative containing a nitronyl nitroxide
group.
Figure 1. (a) An ORTEP drawing (50% of probability) of 1.
Hydrogen atoms of phenylene and methyl groups were deter-
mined by calculation. (b) A projection of the crystal packing
of 1. The broken lines represent the shortest contact described
in the text.
Compound 1 (=2-[40-[100-(100,200-o-dicarba-closo-dodeca-
carboranyl)]phenyl]-4,4,5,5-tetramethylimidazolin-2-yl-1-oxyl-
3-oxide) was synthesized from 4-[100-(100,200-o-dicarba-closo-do-
ꢀ
The B–B bond lengths range from 1.763(7) to 1.796(7) A.
ꢀ
The C–C bond length in the icosahedron is 1.655(5) A and the
ꢀ
B–C bonds are in the range of 1.691(6) to 1.738(6) A. Two N–
O distances in the nitronyl nitroxide moiety are 1.286(4) and
ꢀ
1.291(4) A. All of the bond lengths and angles found in 1 are rea-
O
OHC
N
N
O
(i) (ii)
sonable as compared with those found in the literature. In the
crystal lattice, the shortest intermolecular distance between O1
and C1i [symmetry operator; (i) 2 ꢁ x, 1 ꢁ y, 1 ꢁ z] was
H
H
C
C
C
C
ꢀ
3.160(5) A. This intermolecular distance is comparable to those
of the intermolecular hydrogen-bond lengths reported in the su-
pramolecular structure of the carborane derivative.3b Therefore a
significant intermolecular hydrogen-bonding will be expected.
Because of this intermolecular hydrogen bond, two molecules
of 1 are crystallized in a head-to-tail dimer manner as shown in
1
Scheme 1. (i)
2,3-Dimethyl-2,3-bis(hydroxylamino)butane,
MeOH, rt, 2 days. (ii) NaIO4(aq), dichloromethane, 0 ꢂC,
30 min.
Copyright Ó 2004 The Chemical Society of Japan

Chemistry Letters Vol.33, No.11 (2004)
1461
Figure 1b. The second nearest intermolecular distance lies be-
tween O1 and C4i reproduced by the same symmetry operation.
The dimer character observed in the magnetic measurement (see
below) can be explained based on these structural features.
Magnetic property of isotropically oriented crystalline sam-
ple of 1 was measured by a SQUID magnetometer. Figure 2
shows the temperature dependences of the ꢀmT product and
the reciprocal magnetic susceptibility.
for the experimental dimer structure of 1 (Figure 1b) was inves-
tigated by the single-point energy calculation at the UB3LYP/
6-31G** level of theory. The calculation revealed that the triplet
state is more stable in energy and is the ground state of the dimer.
Moreover, the opposite spin densities in sign were found be-
tween O1 and H–(C1i) and H–(C4i). Therefore the ferromagnet-
ic interaction is probably due to the spin polarization through
these intermolecular short contacts described above.
In conclusion, we have successfully synthesized a new car-
borane derivative containing a nitronyl nitroxide as a spin source
unit. Note that the ferromagnetic interaction was observed in this
system. This is the first detection of the ferromagnetic intermo-
lecular interaction in the hydrogen-bond network using a carbor-
ane cage. The isolation and characterization of 1 would help the
development of the magnetic material science.
This work was partly supported by a Grant-in-Aid for
Young Scientists B (No. 16750125) from the MEXT, Japan. This
work was also partially supported by a Grant-in-Aid for the 21st
Century COE program (Aoyama Gakuin University) from the
MEXT, Japan. F. I. and M. Y. thank the Japan Science and
Technology Agency (JST) for financial support.
References and Notes
1
a) J. F. Valliant, K. J. Guenther, A. S. King, P. Morel, P. Schaffer,
O. O. Sogbein, and K. A. Stephenson, Coord. Chem. Rev., 232,
173 (2002). b) R. B. King, Chem. Rev., 105, 1119 (2001). c) V. I.
Bregadze, Chem. Rev., 92, 209 (1992). d) J. Plesek, Chem. Rev.,
92, 269 (1992). e) L. A. Leites, Chem. Rev., 92, 279 (1992).
A. Maderna, A. Herzog, C. B. Knobler, and M. F. Hawthorne,
J. Am. Chem. Soc., 123, 10423 (2001); W. Jiang, I. T. Chizhevski,
M. D. Mortimer, W. Chen, C. B. Knobler, S. E. Johnson, F. A.
Gomez, and M. F. Hawthorne, Inorg. Chem., 35, 5417 (1996).
a) R. J. Blanch, M. Williams, G. D. Fallon, M. G. Gardiner, R.
Kaddour, and C. L. Raston, Angew. Chem., Int. Ed. Engl., 36,
504 (1997). b) M. G. Davidson, T. G. Hibbert, J. A. K. Howard,
A. Mackinnon, and K. Wade, Chem. Commun., 1996, 2285.
a) K. Doi, T. Ishida, and T. Nogami, Chem. Lett., 32, 544
(2003). b) F. M. Romero, R. Ziessel, M. Bonnet, Y. Pontillon, E.
Ressouche, J. Schweizer, B. Delley, A. Grand, and C. Paulsen, J.
Am. Chem. Soc., 122, 1298 (2000). c) R. Endtner, E. Rentschler,
D. Blaster, R. Boese, and R. Sustmann, Eur. J. Org. Chem., 19,
3347 (2000). d) T. Sugano, M. Kurmoo, H. Uekusa, Y. Ohashi,
and P. Day, J. Solid State Chem., 145, 427 (1999). e) M. M.
Matsushita, A. Izuoka, T. Sugawara, T. Kobayashi, N. Wada, N.
Takeda, and M. Ishikawa, J. Am. Chem. Soc., 119, 4369 (1997).
M. G. H. Vicent, S. J. Shetty, A. Wickramasinghe, and K. M. Smith,
Tetrahedron Lett., 41, 7623 (2000).
Figure 2. The temperature dependence of the magnetic
property of 1. The measurement was carried out under 0.5 T of
the applied field.
The ꢀmT value at room temperature (0.375 emu K molꢁ1
)
2
3
4
corresponds to the theoretical value of the isolated S ¼ 1=2 para-
magnetic spin. On cooling, the ꢀmT value gradually increased
and reached a maximum (0.412 emu K molꢁ1) at 5 K, followed
by the steep decrease in the lower temperature region. This mag-
netic behavior clearly implies the presence of two different inter-
molecular magnetic interactions: firstly a ferromagnetic interac-
tion that is predominant above ca. 5 K, secondly an antiferro-
magnetic one which dominates a bulk magnetism at cryogenic
temperature.
Two options were used to analyze the magnetic behavior. (i)
The reciprocal susceptibility of 1 was reproduced by means of
the Curie–Weiss law (ꢀm ¼ C=ðT ꢁ ꢁÞ) above 10 K. We ob-
tained positive Weiss constant ꢁ ¼ þ1:68ð4Þ K indicating a
small ferromagnetic intermolecular interaction. (ii) Taking into
account the result of the X-ray crystal structure analysis, a sin-
glet–triplet spin dimer model was used for the analysis. The
modified Bleaney–Bowers equation (Eq 1) for the Hamiltonian
H ¼ ꢁ2JS1ÁS2 was applied for the analysis of the magnetic
data.8 The parameter J is an intradimer magnetic interaction
and zJ0 describes a mean field intermolecular interaction.9 The
other symbols have their usual meanings. The best-fit parameters
by the least-squares method in the overall temperature range
were J=kB ¼ þ4:26ð2Þ K and zJ0=kB ¼ ꢁ0:61ð1Þ K. The theoret-
ical curve using these parameters is represented in Figure 2 by a
solid line.
5
6
IR (KBr) ꢃB-H ¼ 2545{2619 cmꢁ1
,
ꢃN-O ¼ 1365 cmꢁ1
;
UV
(CH2Cl2)
ꢄ
max/nm ("/Mꢁ1cmꢁ1) = 275(15300), 282(15200),
294(15100), 374(14500). ESR (benzene solution, rt) showed
characteristic five lines centered at g ¼ 2:006 with hyperfine
coupling constant aN ¼ 0:73 mT. Calcd For C15H27N2O2B10: C,
47.98; H, 7.25; N, 7.46%. Found: C, 47.57; H, 7.11; N, 7.56%.
Crystallographic data for 1: C15H27N2O2B10, fw ¼ 375:49, Mono-
7
ꢀ
ꢀ
ꢀ
clinic P21=c, a ¼ 7:363ð4Þ A, b ¼ 11:050ð6Þ A, c ¼ 25:74ð1Þ A,
ꢂ
ꢀ 3
ꢅ ¼ 92:015ð8Þ , V ¼ 2092:7ð1Þ A , Z ¼ 4, T ¼ 120ð1Þ K. RðRwÞ ¼
0:069ð0:185Þ, GOF ¼ 0:84 for 6073 unique reflections with
I > 2ꢆðIÞ and 295 parameters. Crystallographic data reported in
this manuscript have been deposited with CCDC as supplementary
publication No. CCDC 247437. Copies of the data can be obtained
free of charge via www.ccdc.cam.ac.uk/conts/retrieving.html.
B. Bleaney and K. D. Bowers, Proc. R. Soc. London, Ser. A, 214, 451
(1952).
1
ꢀm ¼
ð1Þ
ꢁ1
ꢀ
ꢁ 2zJ0=Ng2ꢂ2B
dimer
Ng2ꢂ2B
2
ꢀdimer
¼
8
9
kBT 3 þ expðꢁ2J=kBTÞ
The energy difference of two spin-states (singlet and triplet)
C. J. O’Conner, Prog. Inorg. Chem., 29, 203 (1982).
Published on the web (Advance View) October 9, 2004; DOI 10.1246/cl.2004.1460