Antiferromagnetic interactions in 1D Heisenberg linear chains of 7-(4-fluorophenyl) and 7-phenyl-substituted 1,3-diphenyl-1,4-dihydro- 1,2,4-benzotriazin-4-yl radicals

Article abstract of DOI:10.1002/chem.201202784

7-(4-Fluorophenyl) and 7-phenyl-substituted 1,3-diphenyl-1,4-dihydro-1,2,4- benzotriazin-4-yl radicals were characterized by X-ray diffraction analysis and variable-temperature magnetic susceptibility studies. The radicals pack in 1D π stacks of equally s

Full text of DOI:10.1002/chem.201202784

FULL PAPER
DOI: 10.1002/chem.201202784
Antiferromagnetic Interactions in 1D Heisenberg Linear Chains of
7-(4-Fluorophenyl) and 7-Phenyl-Substituted 1,3-Diphenyl-1,4-dihydro-
1,2,4-benzotriazin-4-yl Radicals
Christos P. Constantinides,[a, b] Panayiotis A. Koutentis,*[a] and Jeremy M. Rawson[b]
Abstract: 7-(4-Fluorophenyl) and 7-
phenyl-substituted 1,3-diphenyl-1,4-di-
hydro-1,2,4-benzotriazin-4-yl radicals
were characterized by X-ray diffraction
analysis and variable-temperature mag-
netic susceptibility studies. The radicals
pack in 1D p stacks of equally spaced
slipped radicals with interplanar distan-
ces of 3.59 and 3.67 ꢀ and longitudinal
angles of 40.97 and 43.478, respectively.
Magnetic-susceptibility studies showed
that both radicals exhibit antiferromag-
netic interactions. Fitting the magnetic
data revealed that the behavior is con-
sistent with 1D regular linear antiferro-
magnetic chain with J=À12.9 cmÀ1,
zJ’=À0.4 cmÀ1, g=2.0069 and J=
À11.8 cmÀ1, zJ’=À6.5 cmÀ1, g=2.0071,
respectively. Magnetic-exchange inter-
actions in benzotriazinyl radicals are
sensitive to the degree of slippage, and
inter-radical separation and subtle
changes in structure alter the fine bal-
ance between ferro- and antiferromag-
netic interactions.
Keywords: benzotriazinyls · hetero-
cycles · heterocyclic radicals · mag-
netic properties · stacking interac-
tions
Table 1. Table for Scheme 1.
Introduction
Radical
R1
R2
R3
The quest for new multifunctional molecular materials
based on open-shell molecules has been intensively pursued
over the past couple of decades.[1] Although numerous radi-
cal families are known, and a plethora of persistent organic
radicals have been synthesized, their magnetic properties,
which depend on their crystal packing, are difficult to pre-
dict and control.[2] Research ef-
1
2
3
4
5
6
7
Ph
Ph
Ph
4-BrC6H4
4-ClC6H4
Ph
Ph
Ph
thien-2-yl
CF3
H
H
3-vinyl C6H4
3-vinyl C6H4
Ph
Ph
Ph
H
4-FC6H4
Ph
Ph
forts to develop “magnetostruc-
tural relationships” aimed to
understand the effects of molec-
ular structure on solid-state
try of 1,2,4-benzotriazine, we developed a short synthetic
route to access a range of derivatives functionalized at the
C7 position of the benzo-fused ring.[4]
packing and their resultant
magnetic behavior. Ultimately,
these efforts can assist in the
design of radicals with favora-
ble properties.
1,3-Diphenyl-7-(thien-2-yl)-1,4-dihydro-1,2,4-benzotriazin-
4-yl (1)[5] was a 1D alternating ferromagnetic chain (J1 = +
7.12 cmÀ1, J2 = +1.28 cmÀ1, g=2.0071) and 1,3-diphenyl-7-
Scheme 1. 1,2,4-Benzotriazinyl
radicals 1–7 with IUPAC num-
bering of the ring system.
trifluoromethyl-1,4-dihydro-1,2,4-benzotriazin-4-yl (2)[6]
a
1D regular ferromagnetic chain (J= +1.05 cmÀ1, g=2.0000)
with weaker antiferromagnetic interchain interactions.
Three other radicals 3–5 have also been reported by other
groups.[7,8] Radicals 3 and 4 have similar magnetic behavior
as radical 2 (J= +7.38 and 6.90 cmÀ1, respectively),[7] where-
as radical 5 has strong 1D alternate linear-chain antiferro-
magnetic interactions (J1 =À76.50 cmÀ1, J2 =À22.90 cmÀ1).[8]
In all cases, the benzotriazinyl radicals exhibited p-slipped
stacked structures, but in some cases, the interactions are
ferromagnetic and in others antiferromagnetic. Herein, we
present the solid-state characterization of two new benzo-
triazinyls: 1,3-diphenyl-7-(4-fluorophenyl)-1,4-dihydro-1,2,4-
benzotriazin-4-yl (6) and 1,3-diphenyl-7-phenyl-1,4-dihydro-
1,2,4-benzotriazin-4-yl (7) and provide a magnetostructural
correlation for the series 1–7 based on the degree of slip-
page of the p stacks.
1,2,4-Benzotriazinyls, despite their exceptional air and
moisture stability, have received little attention (Scheme 1
and Table 1).[3] As part of our efforts to explore the chemis-
[a] C. P. Constantinides, Dr. P. A. Koutentis
Deptartment of Chemistry
University of Cyprus
P.O. Box 20537, 1678 Nicosia (Cyprus)
Fax : (+357)22892809
E-mail: koutenti@ucy.ac.cy
[b] C. P. Constantinides, Prof. J. M. Rawson
Deptartment of Chemistry
The University of Cambridge
Lensfield Road, Cambridge, CB2 1EW (UK)
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201202784.
Chem. Eur. J. 2012, 18, 15433 – 15438
ꢁ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
15433

Results
Synthesis and characterization: Radicals 6 and 7 were pre-
pared by Suzuki–Miyaura reactions of 7-iodo-1,2,4-benzo-
triazinyl (8, Scheme 2)[4a] with 4-FC6H4B(OH)2 and
Scheme 2. Synthesis of radicals
(1.6 mol%), CH2Cl2 (1 mL), approximately 208C under air atmosphere,
4–9 h (81%); b) 4-FC6H4B(OH)2 or PhB(OH)2 (3 equiv), [Pd(OAc)2]
6 and 7. a) DBU (0.1 equiv), Pd/C
AHCTUNGTRENNUNG
(5 mol%), dry DMF (2 mL), approximately 1008C, under argon, 30 min
(47 and 93%, respectively).
PhB(OH)2 by using PdACTHNUGTRNE(NUG OAc)2 (5 mol%) in dry toluene
(2 mL) at 1008C under argon with yields of 47 and 93%, re-
spectively (Scheme 2).[4b]
Cyclic voltammetry and EPR spectroscopy: The redox be-
havior of radicals 6 and 7 was similar to that of radicals 1–
5[5–8] exhibiting two fully reversible waves, which correspond
to the À1/0 and 0/+1 processes (Figures S1 and S2 in the
Supporting Information). Oxidation potentials in radicals 6
and 7 occurred at +0.16 and +0.15 V versus ferrocene/fer-
rocenium, whereas the corresponding reduction potentials
occurred at À0.95 and À0.96 V, respectively. Solution EPR
spectra of radicals 6 and 7 have the typical seven-line spec-
trum consistent with the coupling of the unpaired electron
with three similar but slightly inequivalent 14N nuclei. Radi-
cals 6 and 7 have hyperfine coupling constants (hfcc) similar
to radicals 1–5 (Figures S3 and S4 in the Supporting Infor-
mation).[5–8] Simulated first- and second-derivative modes
gave hfcc aN(1)=7.47, aN(2)=4.84, aN(3)=4.70, and g=
2.0069 for radical 6 and aN(1)=7.49, aN(2)=4.89, aN(3)=
4.65, and g=2.0071 for radical 7.
Figure 1. Solid-state packing of the 7-(4-fluorophenyl)benzotriazinyl radi-
cal 6. Top: 1D p-slipped stacks of radicals along the a axis (N-phenyls
are omitted for clarity). Bottom: lamellar sheets formed along the bc di-
agonal.
À
ring being located between the phenyl substituent and a C
C bond of neighboring molecules within the stack. The in-
trastack distance between the centroids of the triazinyl ring
and the phenyl ring is 3.624 ꢀ with a closest inter-ring con-
tact of 3.411(2) ꢀ [C(17)···N(3)]. The intrastack distance be-
X-ray diffraction studies: Suitable single crystals of 6 and 7
for X-ray diffraction studies (Table S1 in the Supporting In-
formation) were obtained by slow cooling of concentrated
hot hexane solutions. Radicals 6 and 7 crystallize in the
À
tween the centroids of the triazinyl ring and the C C bond
is 3.769 ꢀ with the closest contact being C(1)···C(6) at
3.705(2) ꢀ. Neighboring stacks, pack along the c axis in an
antiparallel orientation to form chains, in which the N-phe-
¯
monoclinic space groups P1 and Pna21, respectively, with
À
one molecule in the asymmetric unit. Intramolecular dimen-
sions of radicals 6 and 7 are similar to those of radicals 1–5
with the 1,2,4-amidrazonyl moiety close to planarity with
the N-phenyl rotated out of the plane to minimize steric in-
teractions.
1,2,4-Benzotriazinyl radicals tend to form 1D p-slipped
stacked columns, and radicals 6 and 7 are no exception.
Molecules of the 7-(4-fluorophenyl)benzotriazinyl 6 are re-
lated by translation parallel to the crystallographic a axis
with a longitudinal slippage of 40.978 and an intraplane dis-
tance of 3.59 ꢀ (Figure 1, top). This leads to the triazinyl
nyls of one stack form edge-to-face C H···p interactions
with the 3-phenyls of the neighboring stacks. This causes al-
ternation in the interchain distances of 6.591 and 6.364 ꢀ. In
À
À
the latter case, centrosymmetric C H···H C contacts, with a
C···C distance of 3.869(2) ꢀ for C(5)···C(19), causes neigh-
boring chains to form lamellar sheets (Figure 1, bottom).
The 7-phenylbenzotriazinyl 7 packs similarly to radical 6:
The molecules of radical 7 are related by translation parallel
to the crystallographic c axis with a longitudinal slippage of
43.478 and an intraplane distance of 3.67 ꢀ (Figure 2, top).
The triazinyl ring is again located between the phenyl sub-
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Chem. Eur. J. 2012, 18, 15433 – 15438

Antiferromagnetic Interactions in Heisenberg Linear Chains
FULL PAPER
both rings align perpendicular to the channel this pore
closes to approximately 2.4 ꢀ. The pore is too small to be
accessible by the solvent molecules (hexane), and there was
no evidence of residual electron density in the channel
region in the final difference map.
Magnetic properties: The p-based nature of the benzotri-
azinyl radical coupled with the 1D p-slipped stacked col-
umns of radicals 6 and 7 suggest that both 6 and 7 will ex-
hibit strongly uni-dimensional magnetic interactions propa-
gating parallel to the stacking direction, because overlap be-
tween singly-occupied molecular orbitals is maximized par-
allel to the stacking direction.
Variable-temperature magnetic-susceptibility measure-
ments on radicals 6 and 7 were obtained by using a Quan-
tum Design SQUID magnetometer in the region 5–300 K in
an applied field of 0.5 T. The data were corrected for both
sample diamagnetism (Pascalꢂs constants) and the diamag-
netism of the sample holder.
Radical 6 demonstrated Curie–Weiss behavior above 50 K
with C=0.374 emuKmolÀ1, which is close to that expected
for an S=1= radical with g=2.0069 (C=0.375 emuKmolÀ1
;
2
Figure 3, upper inset). The Weiss constant (q=À11.3 K) is
consistent with local antiferromagnetic interactions. From
the mean-field approach, a first estimate of the intrachain
interaction was J/k=À11.3 K (q=2zJS
ACHTUNGTREN(NUNG S+1)/3k) [Eq. (1)].
The magnetic data were modeled by using the Bonner–
Fisher expression (Figure 3, top) for a linear chain of anti-
Figure 2. Solid-state packing of 7. Top: 1D p-slipped stacks of radicals
along the c axis (N-phenyls are omitted for clarity). Bottom: antiparallel
chains along the a axis form voids (opaque light diamonds). Pinwheel ori-
entation of radicals around the voids.
ferromagnetically coupled S=1= spins by using the g value
2
(2.0069) from EPR data.[9] A close examination of the low-
temperature data revealed a deviation from the simple iso-
lated chain model. Inclusion of a mean field approximation
[Eq. (1)] to take into account weak interchain interactions
led to a marginally improved fit with J=À12.9 cmÀ1, zJ’=
À
stituent and a C C bond of neighboring molecules within
the stack. The intrastack distances between the centroids of
the triazinyl ring and the phenyl ring is 3.822 ꢀ with a clos-
est inter-ring contact of 3.663(2) ꢀ [C(17)···N(3)]. The intra-
stack distance between the centroids of the triazinyl ring
À0.4 cmÀ1,
R=6.21ꢃ10À4
(correlation
factor
R=
S[(cT)obsÀ(cT)calcd]2/S[(cT)obs]2). This fit reproduces both the
position and maximum in c extremely well, and the magni-
tude of J in relation to zJ’ indicates that radical 6 is well de-
scribed as a 1D antiferromagnetic linear chain of equally
À
and the C C bond is 3.779 ꢀ, and the closest contact is
C(2)···C(8) at 3.803(2) ꢀ. In the packing of radical 6, the
longitudinal slippage angle can accommodate the N-phenyl
substituent without disorder at a torsional angle of 69.528.
In contrast, the smaller longitudinal slippage angle in radical
7 brings the N-phenyl substituents closer. Because there is
only one molecule in the asymmetric unit, the phenyl ring
appears disordered over two sites with torsion angles at
spaced S=1= radicals.
2
Radical 7 showed similar magnetic behavior with radical
6: It demonstrated Curie–Weiss behavior above 50 K with
C=0.379 emuKmolÀ1, which is close to that expected for an
S=1= radical. The Weiss constant (q=À19.2 K) indicates
2
local antiferromagnetic interactions. Fitting the magnetic
data in the Bonner–Fisher model provided J=À11.8 cmÀ1,
zJ’=À6.5 cmÀ1, R=5.14ꢃ10À4 (Figure 3, bottom). The mag-
nitude of the interchain interactions indicates that the anti-
parallel chains along the a axis are not well isolated from
each other (Figure 2, bottom). Each benzotriazinyl radical
generates two crystallographically equivalent contacts to
molecules in the neighboring stack; the N atom points be-
À
50.48 and 97.718 affording favorable C H···p (edge-to-face)
interactions between the N-phenyls.
Neighboring stacks pack along the a axis in a head-to-tail
orientation to form chains. Neighboring chains run antipar-
allel in the ab plane so that the N-phenyls of one stack form
À
edge-to-face C H···p interactions with the 7-phenyls of the
À
neighboring stacks. The packing of these chains gives rise to
small voids in the structure, which generate pores parallel to
the c axis (Figure 2, bottom). The centroid···centroid dis-
tance for the disordered N-phenyl substituent is 8.481 ꢀ,
which acts as an upper limit to the pore size. Conversely, if
tween a pair of C H bonds to one molecule and offers a
À
pair of C H bonds to another one.
Chem. Eur. J. 2012, 18, 15433 – 15438
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15435

P. A. Koutentis et al.
radicals 3 and 4 both adopt p-slipped stacks similar to 6 and
7, yet the interactions in 3 and 4 are both ferromagnetic,
whereas those in 6 and 7 are antiferromagnetic. A direct
comparison between these four radicals is more complex,
because there are three molecules in the asymmetric unit of
4 leading to a more complex set of geometric parameters;
nevertheless, the maximum orbital overlap occurs in a per-
fectly eclipsed geometry, favoring an antiferromagnetic in-
teraction. In this regard, the degree of slippage in 6 and 7 is
somewhat less than that observed in 3 and 4, in qualitative
agreement with the observed exchange interaction in 6 and
7 being antiferromagnetic (Table 2, Figure 4).
Table 2. Geometric parameters and exchange interactions in p-slipped
stacked benzotriazinyls. Parameters are defined in Figure 4.
Molecule Longitudinal [o]
Latitudinal [o] Distance [ꢀ]
J [cmÀ1
]
3
4
45.07
46.09
59.68
40.97
43.47
77.32
68.71
69.90
75.84
79.15
3.44
3.28
3.25
3.59
3.67
+7.4
+6.9
6
7
À12.9
À11.8
Figure 3. Temperature dependence of
c for radical 6 (top) and 7
(bottom). The solid line represents the best fit to the 1D antiferromag-
netic regular linear chain model. J=À12.9 cmÀ1, zJ’=À0.4 cmÀ1, g=
2.0069 for radical 6; J=À11.8 cmÀ1, zJ’=À6.5 cmÀ1, g=2.0071 for radical
7. Inset: Curie–Weiss behavior in the 50–300 K region, C=0.374 emuK
molÀ1, q=À11.3 K for 6 and C=0.379 emuKmolÀ1, q=À19.2 K.
Discussion
The magnetic behavior of radicals 6 and 7 can be rational-
ized by using the molecular orbital model,[10] because DFT
studies performed on the X-ray geometries of benzotriazin-
yls did not describe accurately the electronic structure of the
ground state and, therefore, the magnitude of the exchange
interaction within the radical stacks. Because the size of the
overlap between the SOMO orbitals (Figures S5 and S6 in
the Supporting Information) is proportional to the exchange
coupling interaction, the latitudinal and longitudinal slip-
page angles as well as the distances between radicals deter-
mine the nature of the magnetic exchange along the p-stack-
ing direction. In related p-stacked systems, Oakley has
shown that there is a fine balance between ferro- and anti-
ferromagnetic interactions, because the degree of slippage is
adjusted through chemical or mechanical pressure.[2h,11]
The structures of radicals 1 and 5 adopt an alternating p
stack, whereas 2 adopts a twisted stack of radicals, and so
neither are directly comparable with 6 and 7. Conversely,
Figure 4. Parameters used to define the degree of longitudinal and lateral
slippage. Top: the longitudinal slippage a is defined as the plane formed
between the central C atoms of two benzotriazinyl rings and the benzo-
triazinyl ring plane. Bottom: the latitudinal slippage b defined the angle
between the plane linking atoms N(2) and C(7) on each of the two neigh-
boring benzotriazinyl radicals and the benzotriazinyl ring plane.
Of particular note in the design of future radicals is the
larger interplanar distance in radicals 6 and 7 in relation to
3 and 4, which is likely to lead to reduced magnetic-ex-
change interactions (either ferro- or antiferromagnetic);
both radicals 6 and 7 can be considered as biphenyl deriva-
tives and exhibit twist angles between the two phenyl rings
of 31.79 and 26.128, respectively. This lack of coplanarity
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Chem. Eur. J. 2012, 18, 15433 – 15438

Antiferromagnetic Interactions in Heisenberg Linear Chains
FULL PAPER
the temperature region of 5–300 K and in an applied magnetic field of
5000 G. X-ray diffraction data were collected on an Nonius Kappa-CCD
diffractometer, equipped with a CCD area detector and graphite mono-
chromated MoKa radiation (l=0.71073 ꢀ). A suitable crystal (black plate
of dimensions 0.32ꢃ0.18ꢃ0.10 mm) was attached to a glass fiber by using
paratone-N oil and transferred to a goniometer, in which it was cooled to
180(2) K for data collection by using an Oxford Instruments cryostream.
Unit cell dimensions were determined and refined by using 17991 (1.02<
q<27.488), reflections. An empirical absorption correction was applied
by using multiscan based on symmetry-related measurements by using
Sortav.[14] The structure was solved by direct methods and refined on F2
by using full-matrix least squares with SHELXL97.[15] Programs used:
HKL Denzo and Scalepack for cell refinement and data reduction[16a]
and MERCURY[16b] for molecular graphics. The nonhydrogen atoms
were treated anisotropically, whereas the hydrogen atoms were placed in
calculated, ideal positions and refined by using a riding model.
may lead to larger intermolecular separations along the p-
stacking direction. Further modifications to the benzotria-
zinyl framework are in progress to optimize both the intra-
stack separation and the degree of lateral and longitudinal
slippage.
Conclusion
The crystal structures and magnetic properties of 1,3-di-
phenyl-7-(4-fluorophenyl)-1,4-dihydro-1,2,4-benzotriazin-4-
yl (6) and 1,3-diphenyl-7-(4-phenyl)-1,4-dihydro-1,2,4-benzo-
triazin-4-yl (7) have been investigated. The radicals form
regular 1D p stacks and magnetic-susceptibility studies
showed local 1D antiferromagnetic interactions within the
stacks. The reduced slippage of the stacks in both 6 and 7 in
relation to 3 and 4 favored a net antiferromagnetic interac-
tion. Clearly subtle fine tuning of the steric effects of the
substituents is required to control the degree of slippage
and inter-radical separation, which dictate the nature of the
resultant magnetic-exchange interaction. Further studies are
underway.
Acknowledgements
We thank the University of Cyprus (medium-sized grants), the Cyprus
Research Promotion Foundation (grant No. YGEIA/BIOS/0308ACHTUNGTRENNUNG(BIE)/
13), and the following organizations in Cyprus for generous donations of
chemicals and glassware: the State General Laboratory, the Agricultural
Research Institute, the Ministry of Agriculture, and Biotronics Ltd. Fur-
thermore, we thank the A. G. Leventis Foundation for helping to estab-
lish the NMR spectroscopic facility in the University of Cyprus.
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General synthetic procedure: A stirred mixture of 7-iodo-1,3-diphenyl-
1,4-dihydro-1,2,4-benzotriazin-4-yl (8),[4a] arylboronic acid (3 equiv),
K2CO3 (3 equiv) and PdACHTUNGTRENNUNG(OAc)2 (5 mol%) was heated to about 1008C in
dry toluene for 1–3 h under argon until all the starting material was con-
sumed (TLC). Dry flash chromatography (Et2O/hexane 1:3) of the reac-
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1,3-Diphenyl-7-(4-fluorophenyl)-1,4-dihydro-1,2,4-benzotriazin-4-yl (6):
Black needles; m.p. 194–1958C (from pentane); v˜max =3066vw, 3039vw,
1593w, 1487 m, 1450w, 1431w, 1390 (m), 1328 (w), 1315 (w), 1219 (m),
1163 (w), 1066 (w), 1024 (w), 900 (w), 862 (w), 837 (w), 821 (s), 779 (m),
758 cmÀ1 m; lmax (CH2Cl2; loge) 293 (3.52), 382 (2.81), 513 nm (2.14); MS
(EI): m/z (%) 379 [M+ +1] (32), 378 [M+] (100), 180 (6), 170 (25), 120
(44), 77 (45), 51 (21); elemental analysis calcd (%) for C25H17FN3
(378.42): C 79.35, H 4.53, N 11.10; found: C 79.41, H 4.57, N 11.05; g=
2.0069.
1,3-Diphenyl-7-phenyl-1,4-dihydro-1,2,4-benzotriazin-4-yl (7): Black nee-
dles; m.p. 152–1548C (cyclohexane); v˜max =3062 (vw), 3032 (vw), 2953
(vw), 2924 (vw), 1595 (w), 1510 (w), 1481 (m), 1448 (w), 1415 (w),
1392 (m), 1317 (w), 1278 (w), 1247 (w), 1199 (w), 1168 (w), 1080 (w),
1066 (w), 1022 (w), 898 (w), 839 (w), 776 cmÀ1 (m); lmax (CH2Cl2;
loge)=293 (3.50), 323 inf (2.88), 385 (2.78), 443 (2.46), 514 (2.20); MS
(EI): m/z (%): 361 [M+ +1] (37), 360 [M+] (100), 255 (12), 180 (12), 152
(26), 126 (5), 102 (46), 77 (51), 57 (5), 51 (22); elemental analysis calcd
(%) for C25H18N3 (360.43): C 83.31, H 5.03, N 11.66; found: C 83.45, H
5.12, N 11.68; g=2.0071.
Instrumental analyses: Cyclic voltammetry (CV) measurements were per-
formed on a Princeton Applied Research Potentiostat/Galvanostat 263 A
apparatus. The concentration of the benzotriazinyl radical used was 1 mm
in CH2Cl2. A 0.1m CH2Cl2 solution of tetrabutylammonium tetrafluoro-
borate (TBABF4) was used as electrolyte. The reference electrode was
Ag/AgCl, and the scan rate was 50 mVsÀ1. Ferrocene was used as an in-
ternal reference; the E1/2(ox) of ferrocene in this system was 0.352 V.[12]
EPR measurements were carried out on a Bruker EMX spectrometer by
using an X band (9.8 GHz) microwave bridge at 290 K. The EPR spec-
trum was simulated by using the Winsim Spectral Simulation for MS
Windows 9x, NT v0.98.[13] Magnetic-susceptibility measurements were
performed on a Quantum Design MPMS-XL SQUID magnetometer in
Chem. Eur. J. 2012, 18, 15433 – 15438
ꢁ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
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[16] a) H. K. L. Scalepack, Z. Otwinski, W. Minor, Methods in Enzymol.
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[12] M. Dietrich, J. Heinze, J. Am. Chem. Soc. 1990, 112, 5142–5145.
[13] Public EPR software tools: Winsim spectral simulation for MS Win-
dows 9x, NT v0.98, D. A. OꢂBrien, D. R. Duling, Y. C. Fann,
NIEHS, National Institute of Health, USA.
Received: August 3, 2012
[14] SORTAV, R. H. Blessing, Acta. Cryst. 1995, A51, 33–38.
Published online: October 12, 2012
15438
www.chemeurj.org
ꢁ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2012, 18, 15433 – 15438