Ditopic bis(oxazolines): Synthesis and structural studies of zinc(II), copper(II) and nickel(II) complexes

Article abstract of DOI:10.1016/j.ica.2011.06.029

The synthesis, crystal structures, magnetic and spectroscopic properties of zinc(II), nickel(II) and copper(II) dinuclear complexes 2-4 of a novel dinucleating polyoxazoline ligand 1 are reported. X-ray analysis revealed that the three complexes are centr

Full text of DOI:10.1016/j.ica.2011.06.029

Inorganica Chimica Acta 376 (2011) 285–289
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Inorganica Chimica Acta
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Ditopic bis(oxazolines): Synthesis and structural studies of zinc(II), copper(II)
and nickel(II) complexes
Adela Nano a, Lydia Brelot b, Guillaume Rogez a, Aline Maisse-François a, Stéphane Bellemin-Laponnaz a,
⇑
a Institut de Physique et Chimie des Matériaux de Strasbourg, CNRS-Université de Strasbourg, 23, rue du Loess, 67034 Strasbourg Cedex 2, France
b Service de Radiocristallographie, Institut de Chimie, CNRS-Université de Strasbourg, 1, rue Blaise Pascal, 67070 Strasbourg, France
a r t i c l e i n f o
a b s t r a c t
Article history:
The synthesis, crystal structures, magnetic and spectroscopic properties of zinc(II), nickel(II) and cop-
per(II) dinuclear complexes 2–4 of a novel dinucleating polyoxazoline ligand 1 are reported. X-ray anal-
ysis revealed that the three complexes are centrosymmetric dinuclear species with an overall S shape, the
bisoxazoline moieties pointing toward the aromatic core of the molecule. Magnetic susceptibility mea-
surements suggest that there is a very weak exchange interaction between the copper or nickel ions in
complexes 3 and 4.
Received 31 January 2011
Received in revised form 14 June 2011
Accepted 16 June 2011
Available online 25 June 2011
Keywords:
Ditopic bis(oxazoline)
Zinc
Ó 2011 Elsevier B.V. All rights reserved.
Nickel
Copper
1. Introduction
oxazoline-based ligand, called DiBox. In the present paper, we have
synthesized zinc, copper and nickel complexes bearing DiBox as
Because of their features, oxazolines are among the most widely
used ligands in asymmetric catalysis and coordination chemistry
[1]. They are readily accessible, stable and offer a simple and
straightforward way to efficiently control the chiral environment
around the metal [2]. These advantages constitute the base for
the development of efficient enantioselective catalytic systems
and now successful ligands incorporating an oxazoline include bis-
oxazolines, trisoxazolines or oxazoline ligands with an additional
donating element [3].
ditopic ligand. All these complexes were characterized by standard
analytical methods and their molecular structures were deter-
mined by X-ray crystallography, revealing an S conformation of
the complexes. The magnetic study suggests a very weak antiferro-
magnetic interaction between the paramagnetic ions (Cu and Ni
complexes).
2. Experimental
More recently, there have been growing interests to form
potentially dinucleating oxazoline-based ligands, the goal being
the development of bifunctional or recyclable catalysts [4]. Thus,
chiral ditopic azabis(oxazoline) ligands have shown interest in
cobalt-catalyzed enantioselective conjugate reduction [5], cyclo-
propanation [6], or Henry reaction [7]. However, in all these cases,
the coordination chemistry of the related ligand has not been
investigated and information about it would be instructive.
In recent years, we have been exploring the coupling of an addi-
tional ‘sidearm’ to the bridging carbon atom of bisoxazoline by
using simple synthetic strategies. Thus, we found that monolithiat-
ed methyl-bis(oxazolinyl)methane was easily functionalized with
the appropriate electrophile [8]. We now have investigated the
reactivity with biselectrophile giving rise to a new type of ditopic
2.1. General details
All manipulations were carried out under an inert gas atmo-
sphere of dry nitrogen using standard Schlenk techniques, unless
notified. Solvents were purified and dried by standard methods.
All reagents were commercially available and used as received.
1H and 13C NMR spectra were recorded on a Bruker Avance 300
spectrometer at 300 MHz and 75 MHz and were referenced using
the residual proton solvent (1H) or carbon solvent (13C) resonance.
Infrared spectra were recorded on a Perkin–Elmer 1600 FT-IR spec-
trometer. Mass spectra and elemental analysis were recorded by
the analytical service of the Chemistry Department. 1,1-Bis[4,4-
dimethyl-1,3-oxazolin-2-yl]ethane was synthesized according to
literature procedure [9]. Magnetic measurements were performed
using a Quantum Design MPMS-XL SQUID magnetometer. The sus-
ceptibility measurements were performed in the 300 to 1.8 K tem-
perature range with an applied field of 5 kOe. Magnetization
⇑
Corresponding author. Tel.: +33 388 107 166; fax: +33 388 107 246.
E-mail address: bellemin@unistra.fr (S. Bellemin-Laponnaz).
0020-1693/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2011.06.029

286
A. Nano et al. / Inorganica Chimica Acta 376 (2011) 285–289
measurements at different fields at a given temperature confirm
the absence of ferromagnetic impurities. Data were corrected for
the sample holder and diamagnetism was estimated from Pascal
constants.
MS (ESI): m/z (%) 869.4 [Mꢀ(OAc)+Na+1]+ (1 0), 853.4
[Mꢀ2(OAc)+Na+1]+ (1 5), 551.4 [Mꢀ2Cu(OAc)2+1] (1 0 0). Anal.
Calc. C40H58Cu2N4O12 (914.00): C, 52.56; H, 6.40; N, 6.13. Found:
C, 51.47; H, 6.28; N, 5.96%. FT-IR (cmꢀ1): 1659 (C@N), 1590
(acetate).
2.2. Synthesis of the ligand 1
2.6. X-ray crystal structures for compounds 2ꢂ2(CH3OH), 3 and
4ꢂ2(H2O)
To
a solution of bis[4,4-dimethyl-1,3-oxazolin-2-yl]ethane
(1.06 g, 4.8 mmol) in THF (30 mL) was added dropwise nBuLi
(3.0 mL, 4.8 mmol, 1.6 M in hexanes) at ꢀ78 °C and the mixture
was stirred for 15 min. 1,4-Bis(bromomethyl)benzene (596 mg,
2.26 mmol, 0.47 equiv.) was then added and the resulting solution
was stirred for additional 12 h at room temperature. Dichloro-
methane was added and the organic phase was washed with aque-
ous ammonium chloride and then dried with Na2SO4 and
concentrated in vacuo. Flash column chromatography (methanol/
ethyl acetate) afforded 0.66 g of DiBox (53%) as off-white solid.
1H NMR (CDCl3, 300 MHz) d: 7.03 (s, 4H), 3.92 (s, 8H, O–CH2–),
3.21 (s, 4H), 1.37 (s, 6H), 1.25 (s, 12H, C(CH3)(CH3)), 1.19 (s, 12H,
C(CH3)(CH3)). 13C NMR (CDCl3, 75 MHz) d: 166.3 (O–C@N), 134.9,
130.1, 79.3 (O–CH2–), 67.1 (C(CH3)2), 42.8 (CH2), 41.6(CH2), 28.2
(C(CH3)(CH3)), 28.0 (C(CH3)(CH3)), 21.2 (CH3). Anal. Calc. for
Suitable crystals of 2ꢂ2(CH3OH) were obtained as colorless
prisms from (CH3)2CO/MeOH. Suitable crystals of 4ꢂ2(H2O) were
obtained as turquoise-blue blocks from CH2Cl2/Et2O. Suitable crys-
tals of 3 were obtained as purple prisms from MeOH/Et2O. The
crystals were placed in oil, and a single crystal was selected,
mounted on a glass fiber and placed in a low-temperature N2
stream.
Compound 2ꢂ2(CH3OH) and 4ꢂ2(H2O): X-ray diffraction data
collection was carried out on a Nonius Kappa-CCD diffractometer
equipped with an Oxford Cryosystem liquid N2 device, using Mo
Ka radiation (k = 0.71073 Å). The crystal-detector distance was
36 mm. The cell parameters were determined (Denzo software)
from reflections taken from one set of 10 frames (1.0° steps in
phi angle), each at 20 s exposure [10].
Compound 3: X-ray diffraction data collection was carried out
on a Bruker APEX II DUO Kappa-CCD diffractometer equipped with
C
32H46N4O4 (550.73): C, 69.79; H, 8.42; N, 10.17. Found: C, 69.68;
H, 8.46; N, 10.08%. MS (ES): m/z (%) 551.361 [M++1] (1 0 0). FT-IR
(cmꢀ1): 1666 (C@N).
an Oxford Cryosystem liquid N2 device, using Mo K
a radiation
(k = 0.71073 Å). The crystal-detector distance was 38 mm. The cell
parameters were determined (APEX2 software) [11] from reflec-
tions taken from three sets of 12 frames, each at 10 s exposure.
The structures were solved by Direct methods using the pro-
gram SHELXS-97 [12]. The refinement and all further calculations
were carried out using SHELXL-97 [13]. The H-atoms were included
in calculated positions and treated as riding atoms using SHELXL de-
fault parameters, except for the water molecule (4) and for the OH
group of the methanol molecule (2) where the H-atoms were lo-
cated from Fourier difference maps and refined isotropically. The
non-H atoms were refined anisotropically, using weighted full-ma-
trix least-squares on F2. For complexes 2ꢂ2(CH3OH) and 4ꢂ2(H2O), a
semi-empirical absorption correction was applied using the MUL-
2.3. Synthesis of [(DiBox)(ZnCl2)2] 2
ZnCl2 (49 mg, 0.36 mmol) and DiBox (100 mg, 0.18 mmol) were
dissolved in dry methanol (25 mL) under nitrogen and the solution
was stirred at room temperature for one night. After filtration and
evaporation to dryness, the resulting white solid was washed with
pentane (2 ꢁ 15 mL). Recrystallization from acetone/methanol
afforded complex 2 as colorless crystals (118 mg, 80% yield).
1H NMR (DMSO, 300 MHz) d: 7.12 (s, 4H), 4.29 (d, J = 7.5 Hz,
4HO–CHH–), 4.19 (d, J = 7.5 Hz, 4HO–CHH–), 3.30 (s, 4H, CH2),
1.60 (s, 6H, CH3), 1.39 (s, 12H, C(CH3)(CH3)), 1.28 (s, 12H,
C(CH3)(CH3)). The 13C NMR was not recorded due to its low solubil-
ity. MS (ESI): m/z (%) 845.1 [M+Na]+ (4), 787.1 [MꢀCl]+ (10), 687.2
[MꢀZnCl2+1]+ (18), 551.4 [Mꢀ2(ZnCl2)+1]+ (1 0 0). Anal. Calc.
scanABS routine in PLATON [14]; transmission factors: Tmin
/
Tmax = 0.581/0.899 and 0.574/0.737, respectively. For complex 3,
a semi-empirical absorption correction was applied using SADABS
in APEX2 [10]; transmission factors: Tmin/Tmax = 0.270/0.471.
C
32H46Cl4N4O4Zn2 (823.36): C, 46.68; H, 5.63; N, 6.80. Found: C,
46.59; H, 5.72; N, 6.72%. FT-IR (cmꢀ1): 1659 (C@N).
2.4. Synthesis of [(DiBox)(NiBr2)2] 3
3. Results and discussion
NiBr2(PPh3)2 (134 mg, 0.18 mmol) and ligand
1 (50 mg,
3.1. Ligand synthesis
0.09 mmol) were dissolved in dry dichloromethane (10 mL) under
nitrogen and the solution was stirred at room temperature for one
night. After filtration and evaporation to dryness, the resulting pur-
ple solid was washed several times with diethyl ether. Recrystalli-
The ditopic bis(oxazoline) DiBox was obtained in one step
starting from methyl-bis(oxazolinyl)methane derivative [9].
Deprotonation with nBuLi followed by reaction with 1,4-bis(bro-
momethyl)benzene gave the desired ligand in 53% yield (Scheme
1). Spectroscopic data are consistent with the proposed structure
for 1. The product was also characterized by X-ray diffraction.
However, the preliminary X-ray data obtained were of insufficient
quality for a refinement of the structure; only the basic connectiv-
ities were verified (see supporting information for details).
zation from diethyl ether/methanol afforded complex
quantitative yield.
3 in
MS (ESI): m/z (%) 851.4 [Mꢀ(2Br+Na)]+ (5), 551.3 [Mꢀ2
(NiBr2)+1]+ (1 0 0). Anal. Calc. C32H46Br4N4Ni2O4 (987.73): C, 38.
91; H, 4.69; N, 5.67. Found: C, 38.86; H, 4.75; N, 5.59%. FT-IR
(cmꢀ1): 1663 (C@N).
2.5. Synthesis of (DiBox)[Cu(OAc)2]2
4
3.2. Synthesis and characterization of dinuclear complexes 2–4
Cu(OAc)2 (67 mg, 0.37 mmol) and ligand 1 (100 mg, 0.18 mmol)
were dissolved in methanol (15 mL) under nitrogen and the solu-
tion was stirred at room temperature for 1 h. After filtration and
evaporation to dryness, the resulting blue solid was washed three
times with pentane. Recrystallization from diethyl ether/dichloro-
methane afforded complex 4 in quantitative yield.
The reaction of ZnCl2 with half- equivalent of DiBox ligand in
methanol results in the formation of air-stable, dinuclear complex
2 (Scheme 2). The formation of the complex was confirmed by
NMR spectroscopy, IR spectroscopy and mass spectrometry. In par-
ticular, the IR spectrum indicates that the oxazolines are coordi-

A. Nano et al. / Inorganica Chimica Acta 376 (2011) 285–289
287
N
O
O
N
Me
(i)
O
O
O
Me
(ii)
N
N
N
H2N
OH
O
N
Dibox (1)
Scheme 1. Synthesis of the ditopic ligand DiBox 1. Reaction conditions: (i) Ref. [8]; (ii) nBuLi, THF, ꢀ78 °C then bis(bromomethyl)benzene (0.5 equiv.), r.t. overnight (53%
yield).
Table 1
O
Cl
Cl
X-ray experimental data of compounds 2, 3 and 4.
N
N
Zn
2ꢂ2(CH3OH)
3
4ꢂ2(H2O)
O
Formula
Molecular weight 887.35
(g molꢀ1
Crystal system
Space group
a (Å)
C34H54Cl4N4O6Zn2 C32H46Br4N4Ni2O4 C40H62Cu2N4O14
DiBox + 2 ZnCl2
987.79
950.02
MeOH, r.t.
)
O
2
Cl
Cl
triclinic
monoclinic
P21/c
8.2890(2)
17.2633(4)
14.6589(4)
90.00
105.6990(10)
90.00
2019.37(9)
2
triclinic
N
N
Zn
ꢀ
ꢀ
P1
P1
O
8.7656(4)
9.3900(3)
12.9860(7)
102.371(3)
105.910(2)
93.728(2)
995.30(8)
1
9.3476(2)
9.8673(3)
13.6214(5)
69.069(2)
71.417(2)
73.661(2)
1092.21(6)
1
b (Å)
c (Å)
Scheme 2. Synthesis of the dinuclear zinc complex 2.
a
(°)
b (°)
c
(°)
V (Å3)
nated to the Zn center (slight coordination shift of m(CN) band of
7 cmꢀ1). The complexation is also highlighted by the 1H NMR spec-
tra, which displays an AB quartet, assigned to the protons of the
methylene of the oxazoline ring (J = 7.5 Hz).
An X-ray diffraction study of complex 2 established its struc-
tural details. Fig. 1 displays its molecular structure along with
the principal bond lengths and angles. The crystallographic data
are shown in Table 1. It crystallizes in the triclinic space group
Z
q
calc(g cmꢀ3
)
1.480
462
1.625
988
1.444
500
F(0 0 0)
Crystal size(mm) 0.38 ꢁ 0.18 ꢁ 0.15 0.36 ꢁ 0.20 ꢁ 0.18 0.40 ꢁ 0.30 ꢁ 0.12
l
(mmꢀ1
Temperature (K) 173(2)
)
1.520
4.927
173(2)
1.86–30.03
1.043
173(2)
1.65–27.47
h minimum–
maximum
Dataset [h,k,l]
1.68–27.47
ꢀ11/10,ꢀ12/
12,ꢀ14/16
0.71073
ꢀ11/11,ꢀ24/
23,ꢀ20/20
0.71073
Mo Ka graphite
monochromated
ꢀ12/12,ꢀ12/
12,ꢀ17/15
0.71073
ꢀ
P1. The zinc atoms adopt a tetrahedral coordination with Zn–N
bond length average of 2.032(3) Å and Zn–Cl bond length average
of 2.238(11) Å. They both are within the range found for related
Wavelength (Å)
Radiation
Number of data
measurements
Number of data
4547
4068
236
5888
4985
4484
286
4651
213
with I > 2
Number of
variables
R1
r(I)
0.0305
0.0852
1.198
0.0346
0.0793
1.041
0.0372
0.1036
1.146
wR2
Goodness-of-fit
(GOF)
Largest peak in
final difference
(eÅ3)
0.482
1.763
0.543
blue
Color
colorless
purple
bisox complexes reported in the literature [15]. The six-membered
ring moieties form a nearly planar metallacycle and the Zn atom
deviates from the N(1)–C(3)–C(11)–C(8)–N(2) plane by
0.233(2) Å. Interestingly, the molecule is a centrosymmetric dinu-
clear species and the overall shape resembles the letter S with the
bisoxazoline moieties pointing toward the aromatic core and the
apical methyl groups pointing to the outside of the molecule. As
a result, the Zn(1)–Zn(1)0 distance was found to be only 8.9627
(6) Å, which is relatively short if you consider the possibility to
have a more extended linear arrangement of the ligand.
Fig. 1. Molecular structure of dinuclear zinc complex 2 (ellipsoids are drawn at 50%
probability level). Selected bond lengths (Å) and angles (°): Zn(1)–Cl(1), 2.2457(6);
Zn(1)–Cl(2), 2.2295(6); Zn(1)–N(1), 2.0296(16); Zn(1)–N(2), 2.0336(17); Cl(1)–
Zn(1)–Cl(2), 113.50(2); N(1)–Zn(1)–N(2), 90.72(7); Zn(1)–N(1)–C(3)–C(11), 5.4(3);
N(1)–C(3)–C(11)–C(8), 3.0(3); Zn(1)–Zn(1)0, 8.9627(6). Symmetry transformation
used to generate equivalent atoms: 0ꢀx + 1, ꢀy + 1, ꢀz + 1. H atoms have been
omitted for clarity.
The reaction of the Dibox ligand
1 with 2 equivalents
(Ph3P)2NiBr2 in dichloromethane led to the purple, stable and iso-
lable dinuclear nickel complex 3 in quantitative yield (Scheme 3).
IR and mass spectrometry confirmed the formation of the expected
dinuclear complex. Recrystallization from MeOH/diethyl ether led

288
A. Nano et al. / Inorganica Chimica Acta 376 (2011) 285–289
Br
O
O
Ni
N
N
O
O
O
Br
Cu
N
O
N
O
O
DiBox + 2 (Ph3P)2NiBr2
CH2Cl2, r.t.
DiBox + 2 Cu(OAc)2
O
3
MeOH, r.t.
N
N
Br
Br
O
4
O
Cu
O
N
N
Ni
O
O
O
O
Scheme 3. Synthesis of the dinuclear nickel complex 3.
Scheme 4. Synthesis of the dinuclear copper complex 4.
to single crystals for X-ray diffraction studies (Fig. 2). The complex
3 crystallizes in the monoclinic space group P21/c and the arrange-
ment of the dinuclear species is identical to complex 2. The nickel
atoms adopt a tetrahedral coordination with Ni–N bond length
average of 1.975(6) Å and Ni–Br bond length average of 2.37(2) Å
[16]. The six-membered ring moieties is boat shaped and the nickel
atom deviates from the N(1)–C(3)–C(8)–N(2) plane by 0.460(4) Å.
As a result, the metal-metal distance is significantly longer than
the previous zinc complex (11.3411(7) Å versus 8.9627(6) Å).
Finally, we investigated the coordination chemistry of the
ligand with copper(II) acetate. Thus, reacting half equivalent of
Dibox with Cu(OAc)2 in methanol lead to complex
4 as a
turquoise-blue powder in nearly quantitative yield (Scheme 4).
Recrystallization from methanol/diethyl ether gave single crystals
of sufficient quality for X-ray diffraction study (Fig. 3). The complex
ꢀ
4 crystallizes in the triclinic space group P1 and the overall shape
of the complex is matching with previous complexes 2 and 3. The
geometry around copper atoms is distorted octahedral with two
acetate oxygen atoms and the nitrogen atoms in equatorial posi-
tions and two oxygen atoms in axial positions (Cu–N bond distance
average 2.01(2) Å and equatorial Cu–O bond distance average
1.979(2) Å, and axial Cu–O bond distance average 2.55(3) Å). The
Oeq–Cu–Oeq and the Oax–Cu–Oax angles are 87.76(7)° and
141.44(6)°, respectively, the N–Cu–N angle being 90.92(7)° [17].
The six-membered ring metallacycle is relatively flat akin to com-
plex 2 and the intramolecular metal–metal distance is 9.4315(5) Å.
Fig. 3. Molecular structure of dinuclear copper complex 4 (ellipsoids are drawn at
50% probability level). Selected bond lengths (Å) and angles (°): Cu(1)–N(1),
1.9978(17); Cu(1)–N(2), 2.0196(17); Cu(1)–O(3), 1.9777(16); Cu(1)–O(4),
2.5304(18); Cu(1)–O(5), 1.9800(16); Cu(1)–O(6), 2.5707(18); O(4)–Cu(1)–O(6),
141.44(6); O(3)–Cu(1)–O(5), 87.76(7); N(1)–Cu(1)–N(2), 90.92(7); Cu(1)–N(1)–
C(3)–C(11), 10.9(3); N(1)–C(3)–C(11)–C(8), ꢀ4.7(3); Cu(1)–Cu(1)0, 9.4315(5). Sym-
metry transformation used to generate equivalent atoms: 0 ꢀx, ꢀy, ꢀz + 1. H atoms
have been omitted for clarity.
3.3. Magnetic properties
Given the unusual S shape of the complexes, it was interesting
to study the magnetic interaction between the spin-carriers, possi-
bly relayed by the aromatic cycle in-between. The Curie constants,
C = 2.74 emu K molꢀ1 for 3 and C = 0.83 emu K molꢀ1 for 4, deter-
mined from the fit of the data using the Curie–Weiss law, are in
good accordance with the expected values for two Ni(II) ions
(2.42 emu K molꢀ1 assuming g = 2.2) and for two Cu(II) ions
(0.83 emu K molꢀ1 assuming g = 2.1), respectively (Fig. 4) [18].
For both compounds the
vT product remains almost constant,
down to about 80 K and 20 K for 3 and 4, respectively. Then it
decreases slightly upon decreasing the temperature down to
1.67 emu K molꢀ1 and 0.75 emu K molꢀ1 at 1.8 K for 3 and 4,
respectively, indicating the occurrence of very weak antiferromag-
netic interactions.
Fig. 2. Molecular structure of dinuclear nickel complex 3 (ellipsoids are drawn at
50% probability level). Selected bond lengths (Å) and angles (°): Ni(1)–Br(1),
2.3830(5); Ni(1)–Br(2), 2.3505(4); Ni(1)–N(1), 1.9704(19); Ni(1)–N(2), 1.979(2);
Br(1)–Ni(1)–Br(2), 120.413(18); N(1)–Ni(1)–N(2), 90.05(8); Ni(1)–N(2)–C(8)–C(11),
–9.0(4); N(2)–C(8)–C(11)–C(3), ꢀ16.4(4); Ni(1)–N(1)–C(3)–O(2), ꢀ172.36(18);
Ni(1)–Ni(1)0, 11.3411(7). Symmetry transformation used to generate equivalent
Neglecting all possible intermolecular interactions, the vT = f(T)
curves can be fit using the following spin Hamiltonian where all
parameters have their usual meaning and the spin operator S is de-
fined as S = SM1 + SM2 (where M = Ni or Cu) [19]:
0
H ¼ ꢀJSM1SM2 þ gbHS
atoms: ꢀx + 2, ꢀy + 1, ꢀz + 1. H atoms have been omitted for clarity.

A. Nano et al. / Inorganica Chimica Acta 376 (2011) 285–289
289
4. Conclusion
In conclusion, we have shown that methyl-bis(oxazoli-
nyl)methane was easily converted into ditopic oxazoline-based
ligand. The coordination chemistry of the new ligand with zinc,
nickel and copper was investigated and the structures were deter-
mined by X-ray crystallography revealing an S conformation of the
complexes. Finally, the magnetic studies suggest a very weak anti-
ferromagnetic interaction between the ions (Cu and Ni). Further
work will focus on the development of chiral ditopic oxazoline-
based ligands and their use in asymmetric catalysis.
Acknowledgments
This work was supported by the CNRS and the Université de
Strasbourg.
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Fig. 4.
vT = f(T) for 3 (open squares) and 4 (open circles), full black lines: best fit
considering intra and inter-dimer interactions for 3 and only intra-dimer interac-
tion for 4 (see text).
The fit leads the following values for 3 and 4, respectively:
J = ꢀ3.5(1) cmꢀ1, g = 2.36(2) and J = ꢀ0.48(2) cmꢀ1, g = 2.11(2) with
good agreement factors R = 2.7 ꢁ 10ꢀ4 and R = 1.7 ꢁ 10ꢀ5
,
respectively.1
Yet considering the structure (and above all the M–M dis-
tances), it does not seem reasonable to neglect interdimer interac-
tion (for 3 the intradimer Ni–Ni distance is 11.34 Å whereas the
smallest interdimer Ni–Ni distance is 7.82 Å, for 4 the intradimer
Cu–Cu distance is 9.43 Å and the smallest interdimer Cu–Cu dis-
tance is 7.64 Å). Therefore, one has to consider intermolecular
interactions in the fitting procedure.
For 3, the fit performed using a mean-field approach leads
J = ꢀ3.3(3) cmꢀ1, g = 2.36(2) and zJ = ꢀ0.2(1) cmꢀ1 with a good
agreement factor R = 2.9 ꢁ 10ꢀ4
. Nevertheless, the hypothesis
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1888.
underlying the use of the mean-field approach (zJ ꢃ J) is actually
hardly fulfilled. Therefore the present fit can just give very approx-
imate values of the interactions. For 4, considering the weakness of
the (supposed) intramolecular interaction, the mean field approach
is clearly not applicable.
The complete and careful fit of the magnetic properties would
require a full analysis of the 3D arrangement of the dimers within
the crystal, which is clearly beyond the scope of this study. DFT cal-
culations would also enable to understand more clearly the
exchange pathways within the dimers, for instance determining
the spin density distribution in the ground state, in order to precise
the possible role of the aromatic cycle in-between the two
paramagnetic metals [20].
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Eur. J. Inorg. Chem. (2010) 4450;
(b) I. Fernández, R. Ruiz, J. Faus, M. Julve, F. Lloret, J. Cano, X. Ottenwaelder, Y.
Journaux, M.C. Muñoz, Angew. Chem., Int. Ed. 40 (2001) 3039.
P
vexp ꢀvcalc
1
P
R is defined as R ¼
.
v2exp