Novel square planar copper(II) complexes with imino or nitronyl nitroxide radicals exhibiting large ferro- and antiferromagnetic interactions

Article abstract of DOI:10.1021/ic0005590

This paper reports the synthesis, crystal structures, and magnetic properties of two copper(II) complexes (1, 2) of general formula Cu(tfac)₂(radical)₂ (tfac = trifluoroacetate; radical = (1) 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (NITPh) or (2) 2-phenyl-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazoline-1-oxyl (IMPh)). They crystallize in the monoclinic P2₁/n space group with the following parameters: (1) a = 13.212(2) A, b = 9.136(1) A, c = 15.587(2) A, β = 114.61(1)°, Z = 2; (2) a = 11.059(2) A, b = 15.289(1) A, c = 10.694(2) A, β = 114.20(1)°, Z = 2. In both complexes the copper(II) ion is coordinated to two radicals in a slightly distorted square planar surrounding. The copper(II) - Radical exchange couplings are antiferromagnetic for the nitronyl nitroxide (NITPh) complex (1) and ferromagnetic in the case of the imino nitroxide (IMPh) analogue (2). The ground state has been found to be a spin-doublet for 1 and the spin-quartet for 2. No thermal population of the highest states has been observed, indicating copper(II) - Radical couplings of |J| > 500 cm^-1.

Full text of DOI:10.1021/ic0005590

5510
Inorg. Chem. 2000, 39, 5510-5514
Novel Square Planar Copper(II) Complexes with Imino or Nitronyl Nitroxide Radicals
Exhibiting Large Ferro- and Antiferromagnetic Interactions
Andre´ Cogne, Jean Laugier, Dominique Luneau,* and Paul Rey
Service de Chimie Inorganique et Biologique (UMR 5046), DRFMC, CEA-Grenoble,
17 Rue des Martyrs, 38054 Grenoble Cedex 09, France
ReceiVed May 23, 2000
This paper reports the synthesis, crystal structures, and magnetic properties of two copper(II) complexes (1, 2) of
general formula Cu(tfac)2(radical)2 (tfac ) trifluoroacetate; radical ) (1) 2-phenyl-4,4,5,5-tetramethylimidazoline-
1-oxyl-3-oxide (NITPh) or (2) 2-phenyl-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazoline-1-oxyl (IMPh)). They
crystallize in the monoclinic P21/n space group with the following parameters: (1) a ) 13.212(2) Å, b ) 9.136(1)
Å, c ) 15.587(2) Å, â ) 114.61(1)°, Z ) 2; (2) a ) 11.059(2) Å, b ) 15.289(1) Å, c ) 10.694(2) Å, â )
114.20(1)°, Z ) 2. In both complexes the copper(II) ion is coordinated to two radicals in a slightly distorted
square planar surrounding. The copper(II)-radical exchange couplings are antiferromagnetic for the nitronyl
nitroxide (NITPh) complex (1) and ferromagnetic in the case of the imino nitroxide (IMPh) analogue (2). The
ground state has been found to be a spin-doublet for 1 and the spin-quartet for 2. No thermal population of the
highest states has been observed, indicating copper(II)-radical couplings of |J| > 500 cm-1
.
Introduction
The past decade has triggered fast-growing interest in
nitroxide free radicals, as building blocks in the engineering of
molecular based magnet. The reasons are mainly that they are
among the most stable open shell organic molecules, even in
combination with metal ions, where they can also act as bridging
ligands. This has allowed a large extent of chemical modifica-
tions that have led to the efficient and specific formation of a
remarkable variety of magnetic species, which may be either
wholly organic compounds1-5 or based on metal-radical
complexes.6-10
Our contribution to this field focuses mainly on the metal-
radical approach11,12 with the aim of synthesizing compounds
exhibiting spontaneous magnetization. Accordingly, we work
at the synthesis of nitronyl nitroxide free radicals designed to
afford extended polynuclear complexes, with strong metal-
Figure 1. Chemical structure of (a) nitronyl nitroxide (NITPh) and
(b) imino nitroxide (IMPh).
radical magnetic interactions. In this frame we have recently
reported on lamellar compounds based on a 2D network of
alternatively bound nitronyl nitroxide radicals and manganese-
(II) ions which behave as a magnet below 50 K.9
Herein, we report on the structure and magnetic properties
of two novel copper(II)-radical complexes: one has been
obtained with the nitronyl nitroxide radical NITPh; the second
one, with the imino nitroxide IMPh analogue (Figure 1). Both
compounds exhibit opposite but large metal-radical magnetic
interactions: antiferromagnetic for the nitronyl nitroxide com-
plex; ferromagnetic in the case of the imino nitroxide analogue.
For both compounds, the nature of the magnetic interaction is
understood in relation with the copper(II)-radical coordination
geometry.
* To whom correspondence should be addressed. E-mail: luneau@
drfmc.ceng.cea.fr.
(1) Tamura, M.; Nakazawa, Y.; Shiomi, D.; Nozawa, K.; Hosokoshi, Y.;
Ishikawa, M.; Takahashi, M.; Kinoshita, M. Chem. Phys. Lett. 1991,
186, 401.
(2) Chiarelli, R.; Rassat, A.; Rey, P. J. Chem. Soc., Chem. Commun. 1992,
1081.
(3) Deumal, M.; Cirujeda, J.; Veciana, J.; Novoa, J. J. Chem. Eur. J. 1999,
5, 1631.
(4) Itoh, T.; Matsuda, K.; Iwamura, H.; Hori, K. J. Am. Chem. Soc. 2000,
122, 2567.
(5) Romero, F. M.; Ziessel, R.; Bonnet, M.; Pontillon, Y.; Ressouche,
E.; Schweizer, J.; Delley, B.; Grand, A.; Paulsen, C. J. Am. Chem.
Soc. 2000, 122, 1298.
(6) Caneschi, A.; Gatteschi, D.; Sessoli, R.; Rey, P. Acc. Chem. Res. 1989,
22, 392.
(7) Inoue, K.; Hayamizu, T.; Iwamura, H.; Hashizume, D.; Ohashi, Y. J.
Am. Chem. Soc. 1996, 118, 1803.
Experimental Section
Syntheses. 2,3-Bis(hydroxylamino)-2,3-dimethylbutane, 2-phenyl-
4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (NITPh), and 2-phenyl-
4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazoline-1-oxyl (IMPh) were
prepared according to literature methodes.13,14 Other compounds were
used as purchased.
(8) Takeda, K.; Awaga, K. Phys. ReV. B: Condens. Matter 1997, 56,
Cu(tfac)2(NITPh)2 (1). Bis(2-phenyl-4,4,5,5-tetramethylimidazoline-
1-oxyl-3-oxide)bis(trifluoroacetato)copper(II) was prepared by adding
14560.
(9) Fegy, K.; Luneau, D.; Ohm, T.; Paulsen, C.; Rey, P. Angew. Chem.,
Int. Ed. Engl. 1998, 37, 1270.
(10) Iwamura, H.; Inoue, K.; Koga, N. New J. Chem. 1998, 22, 201.
(11) Rey, P.; Luneau, D. NATO ASI Ser., Ser. C 1996, 484, 431.
(12) Rey, P.; Luneau, D. NATO ASI Ser., Ser. C 1999, 518, 145.
(13) Ullman, E. F.; Call, L.; Osiecky, J. H. J. Org. Chem. 1970, 35, 3623.
(14) Ullman, E. F.; Osiecky, J. H.; Boocock, D. G. B.; Darcy, R. J. Am.
Chem. Soc. 1972, 94, 7049.
10.1021/ic0005590 CCC: $19.00 © 2000 American Chemical Society
Published on Web 11/04/2000

Novel Cu(II) Complexes with Nitroxide Radicals
Inorganic Chemistry, Vol. 39, No. 24, 2000 5511
Table 1. Summary of the Crystal Structure Data Collection and
Refinement for 1 and 2
1
2
formula
fw
T (K)
CuC30H34N4O8F6
756.2
298(2)
CuC30H34N4O6F6
724.2
298(2)
space group
a (Å)
b (Å)
P21/n
P21/n
13.212(2)
9.136(1)
15.587(2)
114.61(1)
1710.5(4)
2
11.059(2)
15.289(1)
10.694(2)
114.20(1)
1649.3(4)
2
c (Å)
â (deg)
V (Å3)
Z
m(Mo KR) (mm-1
)
0.724
1.468
0.743
1.458
d
calc (cm3)
λ (Å)
0.71060
0.0394
0.1085
0.71060
0.0583
0.1280
R(I),a I > 2σ(I)
Rw(F2),a I > 2σ(I)
Figure 2. View of Cu(tfac)2(NITPh)2 (1) with ellipsoids drawn at the
30% probability level.
2
4
a R(F) ) Σ||Fo| - |Fc||/Σ|Fo|, Rw(F2) ) Σ[wFo - Fc2)2/ΣwFo ]1/2
.
145 mg of copper trifluoroacetate hydrate in 10 mL of diethyl ether in
which was dissolved 233 mg of NITPh. To the resulting green-brown
solution was added 10 mL of heptane. Concentration and cooling to
-18 °C yielded air-stable parallelepipedic dark green crystals. (250
mg, 66%). Anal. Calcd for C30H34N4O8F6Cu: C, 47.65; H, 4.53; N,
7.41; O, 16.93; F, 15.07; Cu, 8.40. Found: C, 47.49; H, 4.68; N, 7.44;
F, 14.27; Cu, 8.20
Cu(tfac)2(IMPh)2 (2). Bis(2-phenyl-4,4,5,5-tetramethyl-4,5-dihydro-
1H-imidazoline-1-oxyl)bis(trifluoroacetate)copper(II) was also prepared
as air-stable parallelepipedic dark-brown crystals (220 mg, 60%) in a
similar manner using 145 mg of copper trifluoroacetate hydrate and
218 mg of IMPh in a mixture of ethyl ether and heptane. Anal. Calcd
for C30H34N4O6F6Cu: C, 49.76; H, 4.73; N, 7.74; O, 13.26; F, 15.75;
Cu, 8.78. Found: C, 49.39; H, 4.79; N, 7.60; F, 15.36; Cu, 8.71
X-ray Crystallography. The intensity data were collected in the
ω-2θ mode, at room temperature, on an Enraf-Nonius CAD4 diffrac-
tometer equipped with a graphite monochromator for the Mo KR (λ )
0.7106 Å) radiation. Cell constants were derived from the least-squares
fit of the setting angles for 25 selected reflections with 10° e θ e 15°.
The structures were solved and refined using the SHELXTL15 software.
All non-hydrogen atoms were refined with anisotropic thermal param-
eters. The hydrogen atoms were included in the final refinement model
in calculated position with isotropic thermal parameters. Crystal
structure and refinement data for compounds 1 and 2 are summarized
in Table 1.
Figure 3. View of Cu(tfac)2(IMPh)2 (1) with ellipsoids drawn at the
30% probability level.
Table 2. Selected Bond Lengths (Å) and Angles (deg) for 1 and 2
1
2
Cu-O1
1.895(4)
1.956(4)
2.992(4)
1.948(4)
Cu-O4
Cu-O3
3.012(5)
1.995(2)
1.263(5)
Cu-N1
Magnetic Susceptibility Measurements. The magnetic susceptibili-
ties were measured on the bulk materials in the 2-300 K temperature
range with a Quantum Design MPMS superconducting SQUID mag-
netometer operating at a field strength of 0.5 T. The data were corrected
for diamagnetism of the constituent atoms using Pascal constants.
O2-N2
1.267(6)
1.308(5)
92.5(2)
O4-N1
O1-Cu-O4
O1-Cu-N1
88.7
observed for the uncoordinated N2-O2 in 1 and 2, respectively,
1.267(6) and 1.263(5) Å (Table 2). The lengthening of the N-O
bond is a general trend observed in the coordination of nitronyl
nitroxide radicals, and the N1-O4 bond length is in agreement
with previous reports.16 Generally the more marked is the
lengthening the stronger is the magnetic interaction. The torsion
angle between the nitronyl nitroxide fragment and the phenyl
ring is 24.84°. The geometrical features relevant for the
understanding of the magnetic properties are given hereafter.
The angle Cu-O4-N1 is 121.7(3)°. The O4-N1-C3-N2-
O2 plane containing the unpaired electron makes angles of 86.98
and 86.72° respectively with the Cu-O4-N1 and the O1-Cu-
O4 planes. The shortest intermolecular distances between the
uncoordinated NO groups are greater than 4 Å (O2-O2ii,
4.095(8) Å; O2-N2ii, 4.938(7) Å (ii: 1 - x, -y, -z)).
Cu(tfac)2(IMPh)2 (2). The molecular structure of 2 is similar
to that of 1, but with the imino nitroxide (IMPh) in place of the
Results and Discussion
Description of the Structures. Views of the molecular
structures of 1 and 2 are shown respectively in Figure 2 and
Figure 3. Selected bond lengths (Å) and angles (deg) are listed
in Table 2.
Cu(tfac)2(NITPh)2 (1). The molecular unit of 1 consists of
one (trifluoroacetate)copper(II) moiety (Cu(tfac)2) bound with
two radicals (NITPh) through an oxygen atom of one of their
NO groups (Figure 1). The molecule is centrosymmetrical with
the copper(II) ion at the inversion center. The Cu-O3-
(carboxylate) distance is 2.992(4) Å, so that the trifluoroacetate
(tfac) anion is unidentate with the copper(II) ion in a slightly
distorted square planar surrounding. The distances Cu-O1-
(carboxylate) and Cu-O4(nitroxyl) are 1.895(4) and 1.956(4)
Å, respectively, and the O1-Cu-O4 angle is 92.5(2)°. The N1-
O4 bond length is 1.308(5) Å and departs markedly from those
(15) SHELXTL, Ver. 5.030; Bruker AXS: 1994.
(16) Caneschi, A.; Gatteschi, D.; Rey, P. Prog Inorg. Chem. 1991, 30, 331.

5512 Inorganic Chemistry, Vol. 39, No. 24, 2000
Cogne et al.
Figure 4. Thermal dependence of the øT product for Cu(tfac)2(NITPh)2
(1) and Cu(tfac)2(IMPh)2 (2). The solid line for 2 is calculated with
the parameters reported in the text.
Figure 5. Geometrical parameters relevant to the magnetic interaction
between the two NO groups.
nitronyl nitroxide (Figure 2). As for 1, the molecular unit of 2
consists of one (trifluoroacetate)copper(II) (Cu(tfac)2) bound
with two radicals (IMPh). The radicals are coordinated to the
copper(II) ion through the imino nitrogen atom, due to its strong
donor character. Here again the trifluoroacetate (tfac) is uni-
dentate, and the molecule, centrosymmetrical at the copper(II)
ion in a square planar surrounding. The distances Cu-O1-
(carboxylate) and Cu-N1(imino) are respectively 1.948(4) and
1.995(4) Å, and the O1-Cu-N1 angle is 88.7(2)°. The torsion
angle between the imino nitroxide fragment and the phenyl ring
is 37.80°. The geometrical features relevant for the magnetic
properties are as follows: the copper plane O1-Cu-N1 makes
angles of 83.18 and 89.6° with the N1-C3-N2-O2 and Cu-
N1-C3 planes, respectively. The shortest intermolecular dis-
tances found between the uncoordinated NO groups for com-
pound 2 (O2-O2ii, 3.390(9) Å; O2-N2ii, 3.473(7) Å (ii: 1 -
x, -y, -z)) are noticeably shorter than those for 1.
Figure 6. Schematic representation of the interaction between the
magnetic orbital of square planar copper(II) and nitroxide radical (a)
in 1 and (b) in 2.
netic coupling between the magnetic centers must be a few
hundred of cm-1, to overcome the thermal population of the
higher spin states at room temperature. This allowed us to
eliminate case i. Indeed, from previous works we know that
the extent of the coupling between two NO groups relies, both
on the separation and on the relative orientation of their π*
orbitals16,18-19 (Figure 5). In 1, the intermolecular plane N2-
O2-N2ii-O2ii made by the two noncoordinated NO groups,
makes a â angle of 47.02° with the planes of the nitronyl
nitroxide radicals (ONCNO). This arrangement of the two NO
groups is unfavorable to the overlap of the π* orbitals, which
are perpendicular to the plane of the radical (ONCNO). This
together with the R angle N2-O2-N2ii of 104.25°, and the
large separation (O2-O2ii, 4.095(8) Å; O2-N2ii, 4.938(7) Å
(ii: 1 - x, -y, z), are not expected to favor antiferromagnetic
Magnetic Properties. The temperature dependence of the
magnetic susceptibility ø has been measured down to 2 K for
both complexes 1 and 2. The results are displayed in the form
of the product of the magnetic susceptibility with the temperature
(øT) versus the temperature (T) in Figure 4 for both compounds
1 and 2.
Cu(tfac)2(NIT2Ph)2 (1). øT ) 0.4 emu K mol-1 at room
temperature and obeys a Curie law when the temperature
1
decreases. Such a behavior exhibited by a three S ) /2 spin
system (rad-CuII-rad) is rather those of a magnetically
interaction greater than a few cm-1
.
1
independent S ) /2 spin. This could be explained in either of
On the contrary, regarding the geometrical parameters in
complex 1, a strong antiferromagnetic interaction between the
central copper(II) and the two radicals is quite realistic. Indeed,
the angle Cu-O4-N1 is 121.7(3)°, and the O4-N1-C3-N2-
O2 mean plane containing the unpaired electron of the radical
makes an angle of 86.98° with the O1-Cu-O4 plane. On the
basis of previous works,6,16 these geometrical parameters and
the short distance Cu-O4 of 1.956(4) Å, favor a strong overlap
of the π* magnetic orbital of the radical with the dx -y magnetic
orbital of the planar copper(II) ion (Figure 6). This is undoubt-
edly the origin of the strong antiferromagnetic copper(II)-
nitroxide interaction. The coupling is strong enough that it does
not allow the thermal population of the spin-quartet state ST )
3/2 (S23 ) 1) and of the spin-doublet state ST ) 1/2 (S23 ) 0). So
two ways, regarding which exchange coupling pathways are
predominant. (i) The main magnetic interactions are the
intermolecular antiferromagnetic couplings between the radicals,
and what we merely observe is the paramagnetism of the central
copper(II) ion. (ii) The prevalent magnetic interactions are the
antiferromagnetic couplings of the copper(II) ion (S1 ) 1/2) with
1
the two coordinated nitroxide radicals NITPh (S2 = S3 ) /2).
Indeed, according to Kambe’s approach,17 and neglecting the
exchange between the terminal radicals (S2, S3), there are for
such a three-spin system (S2-S1-S3) three spin states: two spin-
2
2
1
1
doublet states, ST ) /2 (S23 ) 1), ST ) /2 (S23 ) 0), and one
3
spin-quartet state, ST ) /2 (S23 ) 1), with the relative energy
given as 0, -2J, and -3J, respectively, where ST ) S1 + S2 +
S3 and S23 ) S2 + S3.
Moreover, the observed øT value at 300 K (0.4 emu K mol-1
)
(18) Cogne, A.; Grand, A.; Rey, P.; Subra, R. J. Am. Chem. Soc. 1989,
111, 3230.
implies that, whatever the exchange pathway, the antiferromag-
(19) Caneschi, A.; Ferraro, F.; Gatteschi, D.; Rey, P.; Sessoli, R. Inorg.
Chem. 1990, 29, 1756.
(17) Kambe, K. J. Phys. Soc. 1950, 5, 48.

Novel Cu(II) Complexes with Nitroxide Radicals
Inorganic Chemistry, Vol. 39, No. 24, 2000 5513
only the ground spin-doublet state ST ) 1/2 (S23 ) 1) is occupied,
which means that the CuII-radical antiferromagnetic exchange
interactions are greater than -500 cm-1. Such strong antiferro-
magnetic interaction is in agreement with previous founding
for copper(II)-nitroxide complexes.20-22
Cu(tfac)2(IM2Ph)2 (2). øT is 1.85 emu K mol-1 at 400 K
and then decreases continuously to a zero value when cooling.
3
This magnetic behavior is reminiscent of S ) /2 spins which
are antiferromagneticaly coupled. A total spin S ) 3/2, exhibited
by this other rad-CuII-rad system, means that the central
copper(II) ion is ferromagneticaly coupled with both radicals.
Indeed, in this case the order of the energy levels for a three-
spin system S2-S1-S3 (S1 = S2 = S3 ) 1/2) is reversed compare
with the antiferromagnetic case previously describe. The ground
spin state is then the spin-quartet state ST ) 3/2 (S23 ) 1), whose
associated øT value (1.875 emu K mol-1) corresponds to those
observed for compound 2 at 380 K. As for compound 1, this
means that the magnitude of the exchange interaction must be
a few hundred of cm-1 in order to overcome the thermal
population of the higher spin states at room temperature. A
strong ferromagnetic interaction is, in that case, also realistic,
and it has been previously observed in copper(II) complexes of
imino nitroxide.23 Considering the molecular structure of
compound 2, the coordination of the imino nitroxide by the
nitrogen atom occurs in such a way that the magnetic orbitals
are rigorously orthogonal. Indeed, the copper basal plane is
perpendicular to the plane Cu-N1-C3 from which the π*
orbital is perpendicular. In this geometry the overlap between
the copper(II) magnetic orbital and the π* orbital of the imino
nitroxide is forbidden, but because of the short Cu-N1 bond
length (1.995(4) Å) the overlap density is large. This explains
the strong ferromagnetic interaction observed in 2. A simplified
scheme of the interactions between the magnetic orbitals is
shown in Figure 6.
The continuous decrease of øT, which is then observed when
cooling, must be attributed to the intermolecular antiferromag-
netic couplings of the rad-CuII-rad complexes entities (ST )
3/2). Indeed, in compound 2 the shortest intermolecular distances
(O2-O2I, 3.390(9) Å; O2-N2I, 3.473(7) Å (i: 1 - x, -y, -z))
are found between the uncoordinated NO groups. Compare to
compound 1 these intermolecular distances are significantly
shorter, but overall the NO groups are favorably arranged in a
head-to-tail geometry (Figure 7). Indeed, the plane O2-N2-
C3-N1 containing the unpaired electron makes a â angle of
88.10° with the intermolecular plane N2-O2-N2i-O2i, and
the R angle N2-O2-N2i is 104.25° (Figure 5). These geo-
metrical parameters should favor a better overlap of the π*
orbitals of the radicals in compound 2, and hence stronger
intermolecular antiferromagnetic interactions than in compound
1. This explains that for 2 one observes a decrease of øT, which
was not evidenced for 1. Moreover, because the copper(II) ion
is at the inversion center, these intermolecular contacts are
symmetricaly experienced, and compound 2 must be considered
from the magnetic point of view as an infinite chain of weakly
Figure 7. View showing the close contacts between the noncoordinated
NO groups in 2.
The best fit of the experimental data with this equation was
obtained with g ) 2.12 and J ) -7.1 cm-1 (Figure 4). The
departure of g from 2.0 accounts for both the radicals and the
copper(II) ion contributions, while the exchange coupling
constant is in agreement with previous values found for such
an arrangement of intermolecular NO-NO contacts. To sum-
marize, in compound 2 the central copper(II) ion is ferromag-
netically coupled with both coordinated radicals. The ferro-
magnetic exchange interaction is so strong that at room
temperature the only occupied level is the spin-state quartet S
)
3/2, which means that the copper(II)-nitroxide coupling
constant is greater than +500 cm-1. Due to intermolecular
contacts between the uncoordinated NO groups, compounds 2
must be considered, from the magnetic point of view, as a chain
3
of antiferromagnetically coupled S ) /2 spins.
Conclusions
3
interacting S ) /2 spins. Accordingly, the temperature depen-
Significant magnetic exchange interactions between spin
carriers are of major concern, in view of the synthesis of
compounds exhibiting spontaneous magnetization. Our present
results are new examples that show how much metal-radical
dence of the magnetic susceptibility was fitted considering an
3
infinite chain of S ) /2 spins antiferromagnetically coupled
according to the reported equation24,25
ø ) (Ng2â2/3kT)S(S + 1)[(1 + U)/(1 - U)]
3
(22) Laugier, J.; Rey, P.; Benelli, C.; Gatteschi, D.; Zanchini, C. J. Am.
Chem. Soc. 1986, 108, 6931.
(23) Luneau, D.; Rey, P.; Laugier, J.; Fries, P.; Caneschi, A.; Gatteschi,
D.; Sessoli, R. J. Am. Chem. Soc. 1991, 113, 1245.
where U ) coth K - 1/K, K ) 2JS(S + 1)/kT, S ) /2, and H
) -2JS1S2.
(20) Lim, Y. Y.; Drago, R. S. Inorg. Chem. 1972, 11, 1334.
(21) Porter, C. L.; Doedens, R. J. Inorg. Chem. 1985, 24, 1006.
(24) Wagner, G. R.; Friedberg, S. A. Phys. Lett. 1964, 9, 11.
(25) Smith, T.; Friedberg, S. A. Phys. ReV. 1968, 176, 660.

5514 Inorganic Chemistry, Vol. 39, No. 24, 2000
Cogne et al.
complexes can favor large magnetic exchange couplings, which
may be either ferro- or antiferromagnetic, depending on the type
of radical used.
Joseph Fourier (UJF), and the 3MD Network of the TMR
program of the E.U. (Contract ERBFMRXCT980181).
Supporting Information Available: Crystallographic data for
compounds 1 and 2, in CIF format, are available free of charge via the
Internet at http://pubs.acs.org.
Acknowledgment. This work was supported by the Centre
National de la Recherche Scientifique (CNRS), the Commis-
sariat a` l’Energie Atomique (CEA), the Grenoble University
IC0005590