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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S0022-3263(97)01438-2 CCC: $14.00 © 1997 American Chemical Society