Synthesis, structure, and magnetic property of manganese(II) complex of 1,2-closo-carboranyl biradical with S = 3/2 ground state

Article abstract of DOI:10.1246/cl.2006.68

Three-spin magnetic cluster consists of manganese(II) and ortho-carboranyl biradical OCB-BNN have been synthesized and characterized as the first example of the carborane containing paramagnetic complex. The crystal structure of discrete 1:1 complex Mn(hf

Full text of DOI:10.1246/cl.2006.68

6
8
Chemistry Letters Vol.35, No.1 (2006)
Synthesis, Structure, and Magnetic Property of Manganese(II) Complex
of 1,2-closo-Carboranyl Biradical with S ¼ 3=2 Ground State
1
;2
1
2;3
ꢀ1
Fumiyasu Iwahori, Kazunari Matsumura, Masahiro Yamashita, and Jiro Abe
Department of Chemistry, School of Science and Engineering, Aoyama Gakuin University, 5-10-1 Fuchinobe, Sagamihara 229-8558
1
2
CREST, Japan Science and Technology Agency, Kawaguchi Center Building, 4-1-8 Honcho, Kawaguchi 332-0012
Department of Chemistry, Graduate School of Science, Tohoku University, 6-3 Aramaki-Aza-Aoba, Aoba-ku, Sendai 980-8578
3
(Received September 29, 2005; CL-051248; E-mail: jiro abe@chem.aoyama.ac.jp)
.
Three-spin magnetic cluster consists of manganese(II) and
ortho-carboranyl biradical OCB-BNN have been synthesized
and characterized as the first example of the carborane contain-
ing paramagnetic complex. The crystal structure of discrete 1:1
In the usual way, 7.8 mg (15 mmol) of Mn(hfac)2 2H2O was
azeotropically dehydrated in n-heptane. After the solution (ca.
5 mL) was cooled to room temperature, a solution of 9.6 mg of
OCB-BNN (14 mmol) in 3 mL of dichloromethane was added
and stirred 5 min. The color of the solution changed immediately
from blue to green. The solution was concentrated to remove
dichloromethane under reduced pressure then kept standing
20 min. The precipitation was filtered off and dried in vacuo to
.
complex Mn(hfac)2 OCB-BNN was unambiguously deter-
mined. In the crystal structure, OCB-BNN behaves as the
molecular tweezers that bind to manganese(II) ion. The strong
antiferromagnetic interaction (J=kB ¼ ꢁ181ð2Þ K) was found
between nitronyl nitroxides and manganese(II) ion.
.
give 12.1 mg (11 mmol) of Mn(hfac)2 OCB-BNN as green block
ꢁ1
crystals (yield; 79%). IR (KBr): ꢀB{H ¼ 2593 cm , ꢀN{O ¼
ꢁ
1
ꢁ1
.
1
362 cm , ꢀC{F ¼ 1148{1254 cm
There have been a number of reports on the syntheses and
magnetic properties of the spin clusters containing organic rad-
icals. The direct overlap between the magnetic orbitals of para-
magnetic transition-metal ion and organic radical ensures signif-
icant magnetic exchange interaction. Because of the great ad-
vantage of the chelate effect that enforces the coordination of ni-
troxide, most organic radical ligands in spin-cluster complexes
The molecular structure revealed by X-ray crystallographic
9
i
analysis is shown in Figure 1. The long C1–C1 [symmetry op-
ꢀ
erator; (i) ꢁx þ 1, y, ꢁz þ 1=2] distance (1.718(6) A) that result
from the characteristic electronic state of carborane cage was
found in the complex, however, there is no significant difference
in the distance compared to that of free OCB-BNN (1.727(4)
7
ꢀ
A). Manganese(II) ion is comprised of trans-coordination by
ꢀ
nitroxides with 2.132(2) A of bond lengths. The N–O distances
ꢀ
are 1.272(3) A (uncoordinated) and 1.302(3) A (coordinated)
1
2
bear coordination subunits such as pyridine, bipyridine, ethyl-
3
4
5
6
ꢀ
enediamine, imidazole, triazole, phosphine oxides, and so
on. Recently, we have reported the synthesis and magnetic prop-
erty of ortho-carboranyl biradical (OCB-BNN; Chart 1) having
a weak through-space dipole intramolecular antiferromagnetic
ꢂ
and the N2–O2–Mn angle is 123.6(2) . These bond lengths
and angle are reasonable as compared with those found in man-
1
0
ganese(II)-coordinated nitroxides in the literature. The O2–
7
i
i
ꢂ
interaction. Two nitroxide arms that held together by ortho-car-
Mn–O2 and O3–Mn–O4 angles are 157.1(1) and 157.40(8) ,
respectively. The coordination environment of the manga-
nese(II) is severely distorted from the octahedron. Although
ꢀ
3.542(4) A of intermolecular contact in the adjacent uncoordi-
nated NOꢃꢃꢃON was found [symmetry operator; (ii) ꢁx þ 1=2,
borane cage might be suitable for the coordination to transition-
metal ions with the aid of the chelate effect, therefore OCB-
BNN should behave like molecular tweezers that can bind tran-
sition-metal ions, in spite of the absence of the assistance of the
ii
8
coordination sites. The carborane framework is sometimes used
for the construction of the supramolecular structures, however,
the synthesis of carborane cluster compound having nonzero
spin ground state is unexplored. The construction of magnetic
carborane cluster is one of the productive approaches to the
development of the boron material science. For the construction
of the magnetic metal complex of OCB-BNN, we have chosen
6
manganese(II) ion having S5=2 ground state. The aim of our
work in this communication is the synthesis, structural and
magnetic investigation of the manganese(II) complex of ortho-
carboranyl biradical as the first example of the transition-metal
complex of the carborane derivative with nonzero spin ground-
state.
O
R
R
N
C
C
R =
=
N
O
.
Figure 1. ORTEP view of Mn(hfac)2 OCB-BNN. Hydrogen
BH
atoms are determined by calculation except those in carborane
cage. The selected atom numbers are given in the figure.
Chart 1.
Copyright ꢀ 2006 The Chemical Society of Japan

Chemistry Letters Vol.35, No.1 (2006)
69
structure.1
–6,10,11a
A weak intermolecular antiferromagnetic
0
interaction (zJ =kB ¼ ꢁ3:4ð1Þ K) was taken into account by the
mean-field approximation to reproduce the sudden decrease
1
2
below 30 K. The strong antiferromagnetic interactions between
.
manganese(II) and nitroxides cause Mn(hfac)2 OCB-BNN to be
the magnetic cluster molecule with S ¼ 3=2 ground state.
In conclusion, we have successfully synthesized three-spin
magnetic system consists of manganese(II) and ortho-carboranyl
biradical OCB-BNN as the first example of the carborane
containing paramagnetic cluster. The construction of the spin-
cluster molecule using OCB-BNN will contribute to the devel-
opment of the boron material science and the supramolecular
chemistry by means of carborane units.
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.
.
Figure 2. ꢁ T–T plot of Mn(hfac)2 OCB-BNN. The solid
m
curve is the theoretical fitting value that described in the text.
ꢁ
y þ 1=2, ꢁz þ 1], there is no effectual overlap between their
magnetic orbitals in the molecular arrangement. Hence, a small
contribution of the direct exchange is expected for the intermo-
lecular magnetic interaction. On the other hand, a fluorine atom
References and Notes
iii
iii
ꢀ
of hfac anion (F3) is held in close to O2 (3.241(3) A), N2
ꢀ
3.560(3) A), and C14 (3.337(4) A) of the other neighboring
1
H. Oshio, M. Yamamoto, T. Ito, H. Kawauchi, N. Koga, T.
Ikoma, S. T.-Kubota, Inorg. Chem. 2001, 40, 5518; G.
Francese, F. M. Romero, A. Neels, H. S.-Evans, S. Deurtins,
Inorg. Chem. 2000, 39, 2087.
iii
ꢀ
(
molecule [symmetry operator; (iii) ꢁx þ 3=2, ꢁy þ 1=2,
ꢁ
z þ 1]. Therefore, the intermolecular magnetic interaction
through the superexchange path might play more important role
2
D. Luneau, F. M. Romero, R. Ziessel, Inorg. Chem. 1998, 37,
5078; C. Stroh, E. Belorizky, P. Turek, H. Bolvin, R. Ziessel,
Inorg. Chem. 2003, 42, 2938.
.
for the magnetic behavior of Mn(hfac)2 OCB-BNN rather than
the direct exchange.
The temperature dependence of the product of magnetic sus-
ceptibility and temperature is shown in Figure 2. The magnetic
interaction between manganese(II) and nitroxide radical is
expected to be strongly antiferromagnetic due to the symmetry
of the electronic ground state of the manganese(II).
3
4
5
6
7
K. E. Vostrikova, E. Belorizky, J. P e´ caut, P. Rey, Eur. J.
Inorg. Chem. 1999, 1181.
K. Fegy, N. Sanz, D. Leneau, E. Belorizky, P. Rey, Inorg.
Chem. 1998, 37, 4718.
M. L. Kahn, J.-P. Sutter, S. Golhen, P. Guionneau, L. Ouahab,
O. Kahn, D. Chasseau, J. Am. Chem. Soc. 2000, 122, 3413.
C. Rancurel, D. B. Lenznoff, J.-P. Sutter, S. Golhen, L.
Ouahab, J. Kliava, O. Kahn, Inorg. Chem. 1999, 38, 4753.
F. Iwahori, Y. Nishikawa, K.-i. Mori, M. Yamashita, J. Abe,
Dalton Trans. 2006, in press; Proceedings of the Conference
on the Science and Technology of Synthetic Metals: F.
Iwahori, K. Kamibayashi, K.-i. Mori, Y. Nishikawa, M.
Yamashita, J. Abe, Synth. Met. 2005, 153, 485.
ꢁ
1
At 300 K, ꢁ T value is 3.0 emu K mol much lower than
m
ꢁ
1
the calculated uncorrelated spin-only value, 5.1 emu K mol
This fact indicates that manganese(II) ion and nitroxide radicals
.
are strongly coupled in antiferromagnetic manner in Mn(hfac)2.
OCB-BNN. The ꢁ T value showed a gradual decrease as
m
decreasing temperature, followed by the abrupt decrease attrib-
utable to the intermolecular interaction below 50 K to a value
ꢁ1
of 0.359 emu K mol
at 1.8 K. The magnetic interaction
8
9
M. Tanaka, K. Matsuda, T. Itoh, H. Iwamura, Angew. Chem.,
Int. Ed. 1998, 37, 810.
between the radicals through the carborane cage is probably
very small in comparison with the direct exchange interaction
between manganese(II) and radicals. Therefore, we carried
out the analysis with linear three-spin model. On the basis of
.
Crystallographic data for Mn(hfac)2 OCB-BNN: C38H44N4-
O8B10F12Mn, fw ¼ 1075:81, monoclinic C2=c (#15), a ¼
ꢀ
ꢂ
ꢀ
3
ꢀ
1
1
0
7:460ð5Þ A, b ¼ 20:740ð5Þ A, c ¼ 14:710ð4Þ A, ꢃ ¼
the Hamiltonian H ¼ ꢁJðSrad
susceptibility data were analyzed by following equation
Eq 1), where J=kB is intramolecular magnetic interaction
between manganese(II) and radicals and the other symbols have
ꢃ
SMn þ SMn
ꢃ
SRadÞ, the magnetic
ꢀ
10:160ð4Þ , V ¼ 5000:4ð2Þ A , Z ¼ 4, T ¼ 93ð1Þ K. R1 ¼
:059, RðRwÞ ¼ 0:074ð0:131Þ (for all data), G.O.F. ¼ 1:32
(
for 4322 unique reflections with I > 2ꢄðIÞ and 345 variable
parameters. Crystallographic data reported in this manuscript
have been deposited with CCDC, No. CCDC-285276. Copies
of the data can be obtained free of charge via www.ccdc.
cam.ac.uk/conts/retrieving.html.
1
1
their usual meaning. The Lande factors were fixed to 2.0.
2
2
Nꢂ g 35 þ 35 expðꢁJ=kBTÞ þ 10 expðꢁ7J=2kBTÞ þ 84 expð5J=2kBTÞ
0
B
ꢁ
¼
4
kBT
3 þ 3 expðꢁJ=kBTÞ þ 2 expðꢁ7J=2kBTÞ þ 4 expð5J=2kBTÞ
0
ꢁ
T
10 A. Caneschi, D. Gatteschi, P. Rey, Prog. Inorg. Chem. 1991,
39, 331, and references therein.
ꢁmT ¼ 1
ð1Þ
0
2
2
B
0
ꢁ ð2zJ =Ng ꢂ Þꢁ
A best-fit result is obtained as shown by the solid curve in
11 a) M. H. Dickman, L. C. Porter, R. J. Doedens, Inorg. Chem.
1986, 25, 2595. b) I. M.-Badarau, H. H. Wickman, Inorg.
Chem. 1985, 24, 1889.
Figure 2 with J=kB ¼ ꢁ181ð2Þ K. The large antiferromagnetic
coupling constant is similar to other systems reported previously,
and is consistent with the expectation based on the X-ray
12 C. J. O’Connor, Prog. Inorg. Chem. 1982, 29, 203.
Published on the web (Advance View) December 10, 2005; DOI 10.1246/cl.2006.68