An asymmetric dinuclear copper(II) complex with phenoxo and acetate bridges: Synthesis, structure and magnetic studies

Article abstract of DOI:10.1016/j.poly.2010.10.029

The dinuclear (μ₂-acetate)bis(μ₂-phenoxide)di- copper(II) complex, 1 with a tetradentate ligand, L (L = 2,4-di-tert-butyl-6- {[(2-dimethylaminoethyl)-(2-hydroxybenzyl)-amino]-methyl}-phenol) has been synthesized and characterized. The single crystal X-ray structure of the dinuclear complex was determined. Variable temperature magnetic susceptibility measurement showed that the two copper(II) centres are strongly anti-ferromagnetically coupled. The structural study revealed that the Cu-Cu distance (2.911 ) is very close to the distance observed in dinuclear copper(II) acetate. The average Cu-O-Cu angles (～87°) are found to be the lowest amongst the examples reported so far.

Full text of DOI:10.1016/j.poly.2010.10.029

Polyhedron 30 (2011) 293–298
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Polyhedron
journal homepage: www.elsevier.com/locate/poly
An asymmetric dinuclear copper(II) complex with phenoxo and acetate
bridges: Synthesis, structure and magnetic studies
Gorachand Dutta, Rajib Kumar Debnath, Apurba Kalita, Pankaj Kumar, Moushumi Sarma,
⇑
R. Boomi Shankar, Biplab Mondal
Department of Chemistry, Indian Institute of Technology Guwahati, Assam 781039, India
a r t i c l e i n f o
a b s t r a c t
Article history:
The dinuclear (l2-acetate)bis(l2-phenoxide)di-copper(II) complex, 1 with a tetradentate ligand, L (L =
Received 3 September 2010
Accepted 22 October 2010
Available online 18 November 2010
2,4-di-tert-butyl-6-{[(2-dimethylaminoethyl)-(2-hydroxybenzyl)-amino]-methyl}-phenol) has been syn-
thesized and characterized. The single crystal X-ray structure of the dinuclear complex was determined.
Variable temperature magnetic susceptibility measurement showed that the two copper(II) centres are
strongly anti-ferromagnetically coupled. The structural study revealed that the Cu–Cu distance
(2.911 Å) is very close to the distance observed in dinuclear copper(II) acetate. The average Cu–O–Cu
angles (ꢀ87°) are found to be the lowest amongst the examples reported so far.
Keywords:
Copper complex
Phenoxo bridge
Structure
Ó 2010 Elsevier Ltd. All rights reserved.
Magnetic properties
Spectra
1. Introduction
one acetate bridge, having Cu–O–Cu angles of 87.22° and
89.61°. This is perhaps the lowest Cu–O–Cu angle reported so
Bridged dinuclear copper(II) complexes have been the subject of
continuing interest for chemists because of their magneto-struc-
tural properties. A considerable amount of work has been done
in recent years to correlate the structure and magnetic properties
of binuclear copper(II) complexes having alkoxo or hydroxo
bridges [1,2]. An increase in the strength of anti-ferromagnetic
coupling with an increasing Cu–O–Cu bridging angle has been ob-
served in doubly bridged systems with a Cu–O–Cu angle in the
range 90–105° and in single alkoxide or hydroxide bridged com-
pounds with larger angles (120–135°) [3,4]. The linear relationship
for the dihydroxide and alkoxide cases show that at an angle of
around 97°, the point of experimental accidental orthogonality,
the exchange integral approaches zero [3,4]. However, in the phen-
oxy bridged di-copper complexes, the linear least square fitting
suggests that anti-ferromagnetic exchange will dominate at angle
well below 97°, and the condition ꢁ2J = 0 cmꢁ1 should be achieved
with a Cu–O–Cu angle of ꢀ77°. However, this could not be proved
experimentally as there are not many examples of copper
complexes with a phenoxide bridged Cu–O–Cu angle less than
97° [5].
far. The compound exhibits very strong anti-ferromagnetic cou-
pling between the two Cu(II) centres, substantiating the theoret-
ical results.
2. Results and discussion
The ligand L was prepared through a modified Mannich reaction
of one equivalent of the phenol analogue, one equivalent of
the amine and an excess (four equivalents) of formaldehyde
(Scheme 1) [6–8]. The white solid product was precipitated out
from the reaction mixture, and this was then washed with cold
water and recrystallized from methanol to yield the pure product
as a white microcrystalline powder (see Section 3). The formation
of the ligand was authenticated by its FT-IR, 1H and 13C NMR spec-
tral analysis (see Section 3).
The dinuclear copper(II) complex 1 was prepared by the reac-
tion of equivalent amounts of copper(II) acetate tetrahydrate and
the ligand in methanol solution. The dark brown reaction mixture
was then kept for crystallization. The formation of the complex
was confirmed by UV–Vis and FT-IR spectroscopic studies, and fi-
nally by its single crystal structure determination. The complex
Here we report the synthesis, structure and magnetic study
of an asymmetric di-copper(II) complex with two phenoxo and
shows a room temperature magnetic moment,
leff, of 0.42 BM,
which is much less than the expected spin only calculated value.
This can be attributed to the very strong anti-ferromagnetic cou-
pling between the two copper(II) centres via the phenoxo and ace-
tate bridges [9].
⇑
Corresponding author. Tel.: +91 3612582317; fax: +91 3612582349.
E-mail address: biplab@iitg.ernet.in (B. Mondal).
0277-5387/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2010.10.029

294
G. Dutta et al. / Polyhedron 30 (2011) 293–298
OH
OH
MeOH
N
+
H2N
N
Stirring for 3h
N
CHO
MeOH
NaBH4
N
OH
1. MeOH/H2O (4:1)
2. HCHO (4 eq.)
OH
N
N
3. NEt3
N
H
4. 2,4-ditert-butyl
phenol (1 eq.)
(L/)
HO
5. refluxed for 60 h
(L)
Scheme 1. Synthesis of the ligand.
2.1. Crystallography
lato oxygen groups. It is clear from the structure that the O1-atom
from one phenolato group is coordinated to Cu1 through the apical
position, whereas it is equatorially coordinated to the Cu2 centre.
Similarly, O2 is coordinated to Cu2 through the axial position;
however it forms an equatorial coordination to the other Cu(II)
centre (Fig. 2).
A perspective ORTEP view, with the atom numbering scheme, of
the dinuclear complex 1 is given in Fig. 1. The crystallographic
data, selected bond lengths and angles are listed in Tables 1–3,
respectively. In complex 1, both the copper(II) centres adopt a
square pyramidal geometry, however they have different coordina-
tion environments (Fig. 2). The deviation from the square plane for
the Cu1 and Cu2 centres are 0.177 and 0.266 Å, respectively
The Cu–Ophenolato distances are observed to be in the range
1.9139–2.2622 Å. The axial Cu–Ophenolato distances {2.2066(17)
and 2.2622(17) Å} are found to be longer than the equatorial Cu–
Ophenolato ones {1.9450(16) and 1.9139(16) Å}, as expected [10–
(Fig. 3). Two
l-phenolato oxygen atoms and one bidentate bridg-
ing (l2 2)H3CCOOꢁ anion bridge the two copper(II) centres.
-
g1
:g
14]. The average Cu–Oacetate distance for the (l2 g1 2)H3CCOOꢁ
- :g
For Cu1, the other two positions of the coordination sphere are
group is 1.9547 Å, which is shorter than the average Cu–Oacetate
occupied by two amine N-donors, whereas in Cu2, a separate g2
-
distance {2.0095 Å} for the
g
2-acetate group, as found in other
acetate group completes the coordination sphere.
From the crystal structure, it has been found that in complex 1
the two inverted square pyramids are sharing a common apical-
cases [6]. The two Cu(II) centres are separated by 2.9111(4) Å. This
is much shorter than the values for other reported complexes by
Thompson et al. (e.g. ranging from 2.997 to 3.1184 Å) and is
comparable to the value of 2.903(3) Å reported by Ray et al. [15–
19]. It is worth mentioning that this Cu1–Cu2 distance is the short-
equatorial edge formed by the two
l-phenolato groups. For both
the Cu(II) centres, the apical positions are occupied by the pheno-
Table 1
Crystallographic data for complex 1.
Complex 1
Formula
Molecular weight
Crystal system
Space group
T (K)
C30H45Cu2N2O6
664.76
monoclinic
P21/c
296(2)
Wavelength (Å)
a (Å)
b (Å)
0.71073
9.1047(2)
16.8115(4)
22.0595(5)
101.434(10)
3309.50(13)
4
c (Å)
b (°)
V (Å3)
Z
Dcalc (mg mꢁ3
F(0 0 0)
)
1.334
1396
Total number of reflections
8136
Reflections [I > 2
r
(I)]
5141
Max. 2h (°)
28.39
Ranges (h, k, l)
ꢁ12 6 h 6 12
ꢁ22 6 k 6 21
ꢁ28 6 l 6 29
97.90
Complete to 2h (%)
Refinement method
wR2 (all data)
Full-matrix least-squares on F2
0.1213
Goodness-of-fit (GOF) (F2)
1.002
R indices [I > 2
R indices (all data)
r
(I)]
0.0403
0.0684
Fig. 1. ORTEP diagram for complex
numbering is shown only for the dinuclear core for clarity.
1 (50% thermal ellipsoid plot). The atom

G. Dutta et al. / Polyhedron 30 (2011) 293–298
295
Table 2
Selected bond lengths (Å).
Complex 1
Bond lengths (Å)
Cu1–Cu2
Cu1–O2
Cu1–O3
Cu1–N1
Cu1–N2
Cu1–O1
Cu2–O1
Cu2–O4
Cu2–O6
Cu2–O5
Cu2–O2
Cu2–C29
O1–C1
2.9111(4)
1.9450(16)
1.9629(18)
2.004(2)
2.047(2)
2.2066(17)
1.9139(16)
1.9465(19)
1.992(2)
2.0270(19)
2.2622(17)
2.351(3)
1.353(3)
O2–C10
O3–C27
O4–C27
O5–C29
O6–C29
1.343(3)
1.267(3)
1.260(3)
1.251(3)
1.267(3)
Table 3
Selected bond angles (°).
Bond angles (°)
O2–Cu1–O3
O2–Cu1–N1
O3–Cu1–N1
O2–Cu1–N2
N1–Cu1–O1
N2–Cu1–O1
O1–Cu2–O4
O1–Cu2–O6
O4–Cu2–O6
O1–Cu2–O5
O4–Cu2–O5
O6–Cu2–O5
O1–Cu2–O2
O4–Cu2–O2
89.74(7)
92.61(8)
174.32(8)
165.36(9)
93.46(7)
104.97(8)
92.67(8)
100.74(8)
162.09(8)
162.57(9)
99.84(8)
64.71(8)
88.82(7)
90.79(8)
O2–Cu1–N2
O3–Cu1–N2
N1–Cu1–N2
O4–Cu2–O2
O6–Cu2–O2
O5–Cu2–O2
C1–O1–Cu2
C1–O1–Cu1
Cu2–O1–Cu1
C10–O2–Cu1
C10–O2–Cu2
Cu1–O2–Cu2
O4–C27–O3
O5–C29–O6
165.36(9)
90.03(9)
86.39(9)
90.79(8)
101.23(7)
103.00(8)
127.68(15)
121.44(14)
89.61(7)
127.68(15)
120.50(16)
87.22(6)
Fig. 2. (a) The two square pyramidal cores and (b) the inverted square pyramids
sharing the axial-equatorial edge are shown.
125.8(3)
117.4(3)
est amongst the examples reported so far [15–19]. For a better
comparison, the Cu–Cu distances for some reported complexes
are given in Table 4. The distance between the two copper centres
in dimeric copper(II) acetate is found to be 2.6–2.7 Å. The Cu–Cu
distance in phenoxo bridged complexes becomes a little longer
than a direct Cu–Cu distance because of steric reasons [20]. For
open chain structures, this distance is reported to be ꢀ4.1 Å [20].
The Cu1–O1–Cu2 bridging angle is found to be 89.61°, whereas
the Cu1–O2–Cu2 angle is 87.22°, the smallest value found in this
series of complexes. These values are found to vary from 91.6° to
109.4° [20,21]. The sum of the angles at the phenoxide oxygen
atoms are 338.73° (O1) and 335.40° (O2), indicating a considerable
degree of pyramidal oxygen distortion. It is worth mentioning that
in [Cu2(L1)(H2O)2]F2(CH3OH)2, the Cu–O–Cu angle is ꢀ103.65(10)°
and sum of the angles at the phenoxide oxygen is almost exactly
360° (O1, 359.8°), indicating no pyramidal oxygen distortion [9].
Fig. 3. The deviation of the copper(II) centres from the square plane in complex 1.

296
G. Dutta et al. / Polyhedron 30 (2011) 293–298
Table 4
the presence of monomeric impurities (
the temperature independent paramagnetism.
q) [9,22,23], where N is
a
Structural and magnetic data for a series of related dinuclear copper(II) complexes 2–
10.
b
Compound Cu–Cu
(Å)
Cu–O–Cu
(°)
Cu–
Oa
/
(°) hc (°)
ꢁ2J
2Ng2b2
kT½3 þ expðꢁJ=kTÞꢂ
Ng2b2
2kT
(cmꢁ1
)
vM
¼
ð1 ꢁ
qÞ þ
q
þ Na
ð1Þ
2
3
4
5
6
7
8
3.154(2)
3.491(2)
3.495(2)
3.492(2)
3.395(7)
3.339(2)
3.642
107.1(1)
132.0(1)
133.3(2)
133.5(1)
123.6(2)
120.1(2)
143.7(2)
129.1
1.945
1.905
1.904
1.910
2.003
1.932
1.916
1.873
1.929
56.8
5.8
18.7
6.3
45.5
32.2
n.a.
n.a.
333.5 185.4
358.8 174.4
358.9 179.2
356.9 163.6
n.a.
n.a.
n.a.
n.a.
The isotropic exchange Hamiltonian used is ꢁ2JS1ꢃS2. The best
data fit results into g = 2.08, J = ꢁ398 10 cmꢁ1
, q = 0.028 and
20.2
55.6
1000
586
N
a
= 34 ꢄ 10ꢁ6 emu. The observed results indicate the copper(II)
centres present in complex 1 are strongly anti-ferromagnetically
coupled with a large negative J value, which is usual for phenoxo
bridged complexes (Table 4). The complex shows a maximum in
magnetic susceptibility at ꢀ185 K, which is typical of anti-ferro-
magnetic behaviour [24].
9
3.331
10
3.401
121.3
162.6 346.6 595
2, [Cu2(L)(O2CMe)]ꢃ(C3H7NO) (L = 1,3-bis(2,hydroxy-3-meythoxybenzlidene)pro-
pan-2-ol) [24]; 3, [Cu2(L1)(O2CMe)]1/2ꢃH2O [19]; 4, [Cu2(L2)(O2CMe)]1/2ꢃH2O [31];
5, [Cu2(L3)(O2CMe)]ꢃH2O [16]; 6, [Cu2(OH)(O2CMe)(H2O)2(dmen2)][ClO4]2ꢃ2NaClO4
[32,33]; 7, [Cu2(OH)(O2CMe)(tmen2)(ClO4)2] [3,33]; 8, [Cu2(OH)(ClO4)A](-
ClO4)2ꢃCHCl3 (A: bi-nucleating macrocycle) [34]; 9, [Cu2(L1)(pyd)]BF4ꢃH2O [35]; 10,
[Cu2(–L2)(prz)] [36]; n.a. = not available.
It is believed that several structural features of binuclear cop-
per(II) complexes regulate the strength of exchange coupling inter-
actions: (i) the dihedral angle between the two coordination
planes, (ii) the planarity of the bonds around the bridging atom,
and (iii) the Cu–O–Cu bridging angle [24–28]. Some interesting
correlations between structural and magnetic parameters emerge
from the data in Table 4 [24]. When we consider dinuclear cop-
per(II) complexes with a single hydroxide bridge and a double het-
ero bridge (pyrazolate or pyridazine instead of an acetate bridge), it
has been found that the structural properties of compounds 2–7
are not identical with those of the other compounds 8–10, their
anti-ferromagnetic super-exchange interactions being weaker (Ta-
ble 4). This may show that the presence of a second bridging ligand
affects the strength of the anti-ferromagnetic super-exchange
interaction differently. In addition, although the second bridging li-
gands of 6 and 7 are the same as those of 2–5, there is a significant
difference in the ꢁ2J values for these complexes.
a
Cu–O is the average distance between the copper and the bridging O atoms.
b
Dihedral angle between coordination planes.
Solid angle around the bridging oxygen atom.
c
A small deviation from the square pyramidal geometry is ob-
served in the case of the Cu2 centre, compared to Cu1, and this is
reflected in the O1–Cu1–O2 [89.66(7)°] and O1–Cu2–O2
[88.72(7)°] angles, which are very close to orthogonal.
The O1–C1 and O2–C10 distances, 1.353(3) and 1.343(3) Å
respectively, are very close to the C–O single bond distance, indi-
cating the phenolato character of the bridging O1 and O2 centres.
2.2. Magnetic properties
The dihedral angle between the two coordination planes is con-
sidered to be a key factor in determining the magnitude of the
spin-exchange coupling. However, as shown in Table 4, the dihe-
dral angle decreases in the order 10 > 2 > 6 > 7 > 4 > 5 > 3, while
ꢁ2J decreases in the order 10 > 2 > 4 > 3 > 5 > 7 > 6. This indicates
that the dihedral angle of the coordination sphere of unsymmetri-
cal doubly bridged complexes may play only a minor role in deter-
mining the exchange interaction. The planarity of the bonds about
the bridging oxygen atom has also been cited as factor influencing
the nature of the spin-exchange interaction [29,30]. In fact, there is
considerable variation in the planarity of the bonds around the
bridging oxygen of the complexes under consideration. In the pres-
ent case, the sum of the angles about the bridging oxygen atoms,
on average, is ꢀ337°, which is far from the idealized 360° angle ex-
pected for complete planarity. In the case of 4, the sum of the three
bond angles around the bridging oxygen is 358.9°, indicating the
bonds around the oxygen are practically coplanar, in spite of
the fact that the ꢁ2J value is lower than the present complex.
On the other hand, in the case of 5, whose ꢁ2J value is lower than
4, the deviation from the plane is larger than 4. Again this criterion
by itself does not accurately predict the trend in the ꢁ2J values.
Perhaps the most widely accepted criterion for correlating struc-
ture and magnetism is the Cu–O–Cu bridging angle [29,30]. This
factor has been invaluable in systematically correlating the degree
of interaction in both singly and doubly alkoxide (or hydroxide)
bridged copper complexes [37]. The Cu–O–Cu bridging angle de-
creases in the order 8 > 5 > 4 > 3 > 9 > 6 > 10 > 7 > 2, while the va-
lue of ꢁ2J does not decrease in the same order. But, in the
symmetric bridged Cu(II) dinuclear complexes, for small values
of Cu–O–Cu bridging angles (95–105°), Ruiz and co-workers ob-
served that the Cu–O–Cu angle decreases in the same order as
the value of ꢁ2J [3]. The Cu–O bridging distance may also be a
structural feature which determines the magnetic orbital overlaps,
leading to the size of the singlet–triplet separation. The average
The room temperature magnetic moment of complex 1 is found
to be very low (leff = 0.42 BM), indicating the presence of very
strong anti-ferromagnetic coupling between the two copper(II)
centres. Variable temperature magnetic moment studies were car-
ried out in the temperature range 77–300 K. The plot of the molar
susceptibility versus temperature for complex 1 is shown in Fig. 4.
The variable temperature susceptibility data (vM versus T) were fit-
ted to the modified Bleaney–Bowers equation (Eq. (1)), considering
Fig. 4. Magnetic susceptibility versus temperature plot of complex 1.

G. Dutta et al. / Polyhedron 30 (2011) 293–298
297
distance between the copper and the bridging O-atom of the dinu-
clear copper(II) complexes in Table 4 are quite similar (<1.9 Å), but
the ꢁ2J values show significant differences. Particularly, in com-
pounds 2–7, which have the same kind of bridges, the increase in
the average Cu–O bond lengths from 1.904 Å for 3 to 2.003 Å for
6 is connected with a decrease in the anti-ferromagnetic ex-
change-coupling constant from ꢁ179.2 to 220.2 cmꢁ1. The average
Cu–O bond lengths decreases in the order 6 > 7 > 5 > 3 > 2 while
the value of ꢁ2J increases in the same order, i.e. 6 < 7 < 5 < 3, ex-
cept for the present complex.
cation of the bidentate syn–syn bridging mode of the carboxylate
[39–42]. The phenolic mAr–O in the free ligand shows a strong band
at ꢀ1239 cmꢁ1. However, in the complex, this band is found at a
lower frequency, at 1127 cmꢁ1, which can be attributed to coordi-
nation to the metal ions through the deprotonated phenolic oxy-
gen atoms [43].
3. Experimental
3.1. General
2.3. Spectral properties
All reagents and solvents were purchased from commercial
sources and were of reagent grade. UV–Vis spectra were recorded
on a Perkin–Elmer Lambda 25 UV–Vis spectrophotometer. FT-IR
spectra were taken on a Perkin–Elmer spectrophotometer with
samples prepared as KBr pellets. Solution electrical conductivity
was checked using a Systronic 305 conductivity bridge. 1H NMR
spectra were obtained with a 400 MHz Varian FT spectrometer.
Chemical shifts (ppm) were referenced either with an internal
standard (Me4Si) for organic compounds or to the residual solvent
peaks. Elemental analyses were obtained from a Perkin–Elmer Ser-
ies II Analyzer. The magnetic moment of complex was measured on
a Cambridge Magnetic Balance. Variable temperature magnetic
moment studies were carried out in a Lakeshore 7410 vibrating
sample magnetometer.
The UV–Vis spectrum of complex 1 is recorded in methanol sol-
vent and is illustrated in Fig. 5. The complex exhibits intense
absorptions at 221 and 286 nm (
respectively) in the UV-region. These are attributed to the intra-li-
gand * and n ? * transitions. In the visible region, a weak
band is observed at kmax, 735 nm (
/molꢁ1 cm2: 830) which pre-
sumably corresponds to the d–d transition. The absorption at
/molꢁ1 cm2: 3100) is attributed to the phenolate ?
e
/molꢁ1 cm2: 33255, 19560,
p
?
p
p
e
ꢀ421 nm (
e
Cu(II) charge transfer [38].
The FT-IR spectrum of the complex 1 is recorded in a KBr pellet
and is shown in Fig. 6. The strong bands at ꢀ1603 and 1438 cmꢁ1
are assigned to the m(–COO) symmetric and asymmetric stretching,
respectively [20]. The difference between masym(COO–) and msym(-
, in the complex is about 165 cmꢁ1, which is a clear indi-
Single crystals were grown by the slow diffusion followed by
slow evaporation technique. The intensity data were collected
using a Bruker SMART APEX-II CCD diffractometer, equipped with
,
D
m
COO–)
fine focus 1.75 kW sealed tube Mo K
a radiation (k = 0.71073 Å) at
273(3) K, with increasing (width 0.3° per frame) at a scan speed
x
of 3 s/frame. The SMART software was used for data acquisition.
Data integration and reduction were undertaken with SAINT and
XPREP software [44]. Multi-scan empirical absorption corrections
were applied to the data using the program SADABS [45]. Structures
were solved by direct methods using SHELXS-97 and refined with
full-matrix least squares on F2 using SHELXL-97 [46]. All non-
hydrogen atoms were refined anisotropically. The hydrogen atoms
were located from the difference Fourier maps and refined.
Structural illustrations have been drawn with ORTEP-3 for Windows
[47].
3.2. Synthesis of the ligand
Fig. 5. UV–Vis spectrum of complex 1 in methanol solvent.
The Schiff base reaction was carried out using one equivalent
of N,N-dimethylethane-1,2-diamine (1.76 g, 20 mmol) and an
equivalent amount of salicylaldehyde (2.44 g, 20 mmol) in meth-
anol medium. A yellow coloured imine was formed. The imine
was reduced with 2.5 equivalents of sodium borohydride
(1.90 g, 50 mmol). After the complete reduction, a colourless
solution was obtained. The solution was stirred for 1 h. It was
then neutralized with acetic acid to pH 7 and subsequently ex-
tracted with chloroform to afford L/ (yield: 2.30 g, ꢀ60%). One
equivalent of formaldehyde (0.15 g, 5 mmol), one equivalent of
triethylamine (0.50 g, 5 mmol) and one equivalent of 2,4-diter-
tiarybutylphenol (1.03 g, 5 mmol) were added to L/ (0.97 g,
5 mmol) dissolved in a methanol–water mixture (1:4), and the
resulting mixture was refluxed for 3 days at 60 °C. A white pre-
cipitate was observed, which was filtered, washed with water
and dried (yield: 1.00 g, ꢀ50%). 1H NMR (400 MHz, CDCl3)
d(ppm): 7.160 (2H,t); 7.025 (1H,d); 6.89 (1H,d); 6.83 (1H,d);
6.744 (1H,t); 3.649 (2H,s); 3.576 (2H,s); 2.589 (4H,s); 2.317
(6H,s); 1.336 (9H,s); 1.239 (9H,s); 13C NMR (100 MHz, CDCl3)
d(ppm): 157.2; 153.2; 140.6; 136.01; 130.8; 129.6; 124.7;
123.4; 122.6; 121.6; 119; 117.3; 57.8; 56.3; 55.2; 49.1; 45.1;
Fig. 6. FT-IR spectrum of complex 1 in KBr pellet.

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G. Dutta et al. / Polyhedron 30 (2011) 293–298
35.1; 34.2; 31.8; 29.7. FT-IR in KBr (cmꢁ1): 2963; 2868; 2829;
2780; 1613; 1582; 1485; 1364; 1279; 1239; 1165.
References
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3.3. Preparation of the copper complex
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Cu2(H2O)2(OAc)4 (0.199 g, 0.5 mmol) was dissolved in 15 ml
methanol in a round bottom flask. To this blue solution, 262 mg
(0.5 mmol) of the ligand was added with constant stirring, which
was continued for 1 h. The blue colour of the solution immediately
changed to dark green. The volume of the solution was reduced to
5 ml on a rotary evaporator. To this, 15 ml diethyl ether was added
to make a layer and this was kept in the freezer overnight to yield a
dark blue crystalline solid (yield: 0.21 g, ꢀ64%). FT-IR in KBr
(cmꢁ1): 3430(s); 2952(s); 1603(s); 1438(s); 1305(m); 1270(m);
1127(m); 1034(m). UV–Vis. kmax, (nm): 221; 286; 421; 735.
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3.4. Crystal data
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CCDC No. 789702.
C30H45Cu2N2O6, M = 664.76, monoclinic,
a = 9.1047(2), b = 16.8115(4), c = 22.0595(5) Å, b = 101.4340(10)°,
V = 3309.50(13) Å3, space group P21/c, Z = 4, T = 296(2) K, l(Mo
Ka
) = 1.328 mmꢁ1, F(0 0 0) = 1396, Goodness-of-fit = 1.002; final R
indices: R1 = 0.0403 [I > 2r(I)], wR2 = 0.1149; R indices (all data):
R1 = 0.0684, wR2 = 0.1213.
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The present study demonstrates an example of a dinuclear
copper(II) complex with two phenoxo and one acetate bridge.
The coordination of the ligand around each of the two metal cen-
tres in complex 1 are found to be non-equivalent. A structural
study reveals that the Cu–Cu distance (2.911 Å) is very close to
the distance observed in dinuclear copper(II) acetate. The average
Cu–O–Cu angles (ꢀ87°) are found to be the lowest amongst the
examples reported so far. The variable temperature magnetic
moment studies indicate a very strong anti-ferromagnetic coupling
between the two copper centres. This can be attributed to the low
Cu–O–Cu angle.
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Acknowledgements
The authors would like to acknowledge their sincere gratitude
to the Department of Chemistry, Central Instrumentation Facility,
Indian Institute of Technology Guwahati, India. We are also thank-
ful to the Department of Science and Technology, India for the FIST
funded X-ray diffractometer.
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Chem. Res.(S) (2003) 642.
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Appendix A. Supplementary data
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Wisconsin, USA, 1995.
[45] G.M. Sheldrick, SADABS
University of Gottingen, Institut fur Anorganische Chemieder Universitat,
Tammanstrasse 4, D-3400 Gottingen, Germany, 1999–2003.
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CCDC 789702 contains the supplementary crystallographic data
for 1. These data can be obtained free of charge via http://
www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge
Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ,
UK; fax: (+44) 1223-336-033; or e-mail: deposit@ccdc.cam.ac.uk.
: software for Empirical Absorption Correction,