Synthesis and characterization of Cu(II) complexes of tetradentate and tridentate symmetrical Schiff base ligands involving o-phenelenediamine, salicylaldehyde and diacetylmonoxime

Article abstract of DOI:10.1007/s11243-009-9314-9

A mononuclear complex [CuL] (1), a binuclear complex [Cu ₂LCl₂(H₂O)] (2), a trinuclear complex [Cu ₃L₂](ClO₄)₂ (3) involving o-phenylenediamine and sal- icylaldehyde and another

Full text of DOI:10.1007/s11243-009-9314-9

Transition Met Chem (2010) 35:197–204
DOI 10.1007/s11243-009-9314-9
Synthesis and characterization of Cu(II) complexes
of tetradentate and tridentate symmetrical Schiff base
ligands involving o-phenelenediamine, salicylaldehyde
and diacetylmonoxime
•
Debdulal Maity Michael G. B. Drew Jeffrey F. Godsell
•
•
•
Saibal Roy Gurucharan Mukhopadhyay
Received: 14 July 2009 / Accepted: 17 November 2009 / Published online: 9 December 2009
Ó Springer Science+Business Media B.V. 2009
Abstract A mononuclear complex [CuL] (1), a binuclear
complex [Cu2LCl2(H2O)] (2), trinuclear complex
realization that ligands systems around the central metal
a
ions in many living systems are unsymmetrical. The use of
unsymmetrical ligands is more advantageous over their
symmetrical analogues to explain the metal ion–binding
site in metalloproteins and in efforts to mimic the enzy-
matic efficiency and selectivity of natural systems with
synthetic materials [1–6]. The work in our laboratory with
unsymmetrical ligands stems from the above observations
[7–11]. Unsymmetrical ligands involving an oxime func-
tionality exhibit an interesting chelating property in the
area of complex chemistry [11–14]. The importance of
oxime moiety in the ligand environment has been described
in detail in our earlier publications where we have intro-
duced an oxime function in the unsymmetrical ligand
environment [11, 12]. Nevertheless, we have noted that
unsymmetrical Schiff base ligands containing an oxime
moiety are quite rare to date, more so with aromatic dia-
mines [15, 16], our interest arises therefore to synthesize an
unsymmetrical Schiff base ligand involving o-phenylene-
diamine as aromatic amine and diacetylmonoxime with
salicylaldehyde as the other carbonyl compound. The
process applied to synthesize this unsymmetrical ligand
was via the single condensation of o-phenylenediamine
with salicylaldehyde following the method mentioned in
our earlier communication [8].
[Cu3L2](ClO4)2 (3) involving o-phenylenediamine and sal-
icylaldehyde and another binuclear complex of a tridentate
ligand (H2L1) [Cu2L21](CH3COO)2 (4) involving o-phenyl-
enediamine and diacetylmonoxime have been synthesized,
where H2L = N,N0-o-phenylenebis(salicylideneimine) and
H2L1 = 3-(2-aminophenylimino)butan-2-one oxime. All
the complexes have been characterized by elemental analy-
ses, spectral and magnetic studies. The binuclear complex
(2) was characterized structurally where the two Cu(II)
centers are connected via an oxygen-bridged arrangement.
Introduction
Present trends in the design, synthesis, isolation and crystal
structure characterization of unsymmetrical Schiff base
type complexes of transition metals stem from the
D. Maity ꢀ G. Mukhopadhyay (&)
Department of Chemistry, Presidency College,
Kolkata 700073, India
e-mail: gcmukhopadhyay@rediffmail.com
The free amine group of the single condensed product
was then reacted with diacetylmonoxime.
M. G. B. Drew
School of Chemistry, The University of Reading,
P.O. Box 224, Whiteknights, Reading RG6 6AD, UK
However, it was observed that any attempt to synthesize
a Cu(II) complex of the unsymmetrical Schiff base derived
from one mole of the said amine with the two above car-
bonyl compounds, yielded only the symmetrical complex
of the Schiff base (H2L) as the sole product. Thus, the
present paper is devoted to the synthesis, structural features
and spectroscopic characterizations of some Cu(II) com-
plexes of symmetrical bis-Schiff base ligands (H2L).
J. F. Godsell ꢀ S. Roy
Microsystems Center, Tyndall National Institute,
University College Cork, Cork, Ireland
D. Maity
Department of Chemistry, Darjeeling Government College,
Darjeeling 734101, India
123

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Transition Met Chem (2010) 35:197–204
could be synthesized yielding a binuclear copper(II)
complex 4 (Scheme 1). The composition of this complex
was confirmed by mass spectrometric study (found m/z
(M?H)? = 508.0; Mcalcd = 507.7).
OH
N
HO
N
It is therefore observed that the symmetrical tetradentate
Schiff base complex 2 with salicylaldehyde was the most
stable product that could be isolated as the one and only
variety even in the presence of diacetylmonoxime. The
reactivity of different carbonyl functions with diamines has
been studied by Tan et al. [17], who carried out the syn-
thesis of unsymmetrical Schiff base complexes by the
displacement of one carbonyl function from the complexes
replacing it with a new carbonyl moiety. We tried in our
laboratory to get the unsymmetrical complex from the
symmetrical Schiff base complex 1 by replacing salicyl-
aldehyde with diacetylmonoxime, but the symmetrical
complex was reluctant to react with diacetylmonoxime.
We have isolated a binuclear complex 2 and a trinuclear
complex 3 using CuCl2 and Cu(ClO4)2 as the metal salts,
respectively. A 1:1 molar proportion of the ligand and
copper(II) perchlorate yielded the mononuclear complex 1,
but reaction in 2:3 molar (ligand:metal) ratio gave the tri-
nuclear compound 3. On the other hand, CuBr2 and
Cu(CH3COO)2 always yielded the mononuclear variety
and no dinuclear or trinuclear species could be isolated
even if the reaction was carried out with different stoichi-
ometry of ligand and metal and varying the solvent med-
ium. The dinuclear CuCl2 complex 2 was isolated in
chloroform even when Cu(CH3COO)2 was used as the
starting material. Probably, the hydrochloric acid present in
the undistilled chloroform gave the chloro complex. This
was substantiated by using distilled, pure chloroform that
yielded monomeric complex 1 with copper(II)acetate. The
monomeric complex 1 isolated from CuBr2 and Cu(CH3-
COO)2 was allowed to react with CuCl2 that yielded the
binuclear complex 2 (Scheme 2). This reaction failed to
give a similar binuclear complex when reacted with CuBr2
and Cu(CH3COO)2. Therefore, the mononuclear complex
was acting as a bidentate ligand with respect to CuCl2 or
Cu(ClO4)2 but not with CuBr2 or Cu(CH3COO)2. The
structural pattern of the monomeric moiety plays a signif-
icant role for further reaction with another metal center.
Several compounds of this type were extensively studied
by Gruber et al. [18] in particular Cu-complexes involving
ethylenediamine and 1,2-diaminopropane but none were
structurally characterized. To the best of our knowledge,
the symmetrical Schiff base complex 2 involving o-phen-
ylenediamine has not been structurally characterized untill
now. Complex 1, which acts as a bidentate complex ligand
to form adducts with CuCl2 and Cu(ClO4)2, failed to do so
with CuBr2 or Cu(CH3COO)2. Gruber et al. [18] observed
that if the complex ligand is planar, then the metal to which
it coordinates is unlikely to have a planar configuration.
H
H
2
1
H2L
H
2L
We had attempted to synthesize the unsymmetrical
Schiff base Cu(II) complex involving both the diacetyl-
monoxime and salicylaldehyde via the high dilution tech-
nique in chloroform. In this case also, only complex 2 was
isolated. This same compound was isolated as expected
involving o-phenylenediamine and salicylaldehyde in 1:2
proportion taking ethanol as solvent. Complex 2 is binu-
clear with two metal centers brought into combination via
an oxygen-bridged structure. Irrespective of the nature of
co-anion present, complex 2 separated out when the
unsymmetrical variety was attempted to be isolated via
single condensation in chloroform medium. But with eth-
anol as solvent, only the neutral Cu(II) complex 1 sepa-
rated out as the most stable species with bromide,
perchlorate and acetate as counter anion. A trinuclear
complex 3 involving an analogous metal environment has
been synthesized using a similar method, but with nonco-
ordinating anion, namely perchlorate in place of the
halogen atom in stoichiometric molar proportion. Spec-
trophotometric and elemental analyses support the pro-
posed structures of complex 1, 2 and 3. Several attempts to
obtain suitable single crystals of 1 and 3 for structural
analysis were futile. Our continuing study reveals that
when complex 1 was reacted with CuCl2, again the binu-
clear complex 2 was synthesized as expected. But several
approaches to prepare binuclear bromo variety were
unsuccessful.
Results and discussion
Though the initial aim of this work was to synthesize an
unsymmetrical Schiff base ligand involving o-phenylene-
diamine and the corresponding Cu(II) complexes, the
products obtained were complexes of a symmetrical
Schiff base ligand. The two different carbonyl compounds
chosen to synthesize an unsymmetrical Schiff base were
salicylaldehyde and diacetylmonoxime. In all the attempts
where the above two carbonyl moieties were allowed to
react with the diamine, namely o-phenylenediamine, no
oxime function gets incorporated into the ligand moiety.
However, in the absence of salicylaldehyde, when o-
phenylenediamine was reacted with diacetylmonoxime,
the tridentate Schiff base with the oxime function (H2L1)
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Transition Met Chem (2010) 35:197–204
199
NH2
H2
N
N
N
O
N
NH
2 Cu(CH3COO)2
Cu
Cu
+
(CH3COO)2
Methanol solvent
N
O
N
H2
O
N
OH
Scheme 1 Schematic representation for the preparation of complex 4
CHO
OH
NH2
2
+
NH2
Stirred in
Ethanol
OH
HO
N
N
H
H
CuCl2 in
Ethanol
Cu(ClO4)2
in Ethanol
(2:3)
H
H
N
O
N
O
H
H
Cu
Cu
O
N
N
Cl
Cu
Cl
Cu
Cu(ClO4)2
(1:1) or CuBr2 or
Cu(CH3COO)2
(ClO4)2
O
OH2
O
N
O
N
Cu
Ethanol
H
H
Complex 2
Cu(ClO4)2
(1:2)
Complex 3
CuCl2 in Ethanol
(1:1)
O
N
O
Cu
N
H
H
Complex 1
Scheme 2 Preparation of the complexes 1, 2 and 3
Two adjacent metal atoms are unlikely to be bridged
together as perfect tetrahedra, because of the very short
metal to metal separation that would be required. There is a
greater distortion from planarity of the bromine-bonded
copper atom than the chlorine-bonded one. This distortion
toward tetrahedral configuration brings the two copper
atoms too close, leading to instability. As the deviation
from planarity of the metal outside the complex ligand in a
binuclear complex increases, more distortion from planar-
ity should be observed in the complex ligand itself.
The bridging therefore is controlled by the stereochemistry
of the metal outside the Schiff base complex. For
123

200
Transition Met Chem (2010) 35:197–204
NH2
H
single
HO
condensation
diacetyl
monoxime
N
N
Cl
Cl
O
NH2
Cu
+
Cu
N
H2N
CHCl3
CHO
Cu(CH3COO)2
OH2
O
H
OH
H
(E)-2-((2-aminophenylimino)methyl)phenol
[monocondensed]
Complex-2
O
Cu(CH3COO)2
N
OH
OH
O
N
N
Cu
(CH3COO)
N
H
Scheme 3 Synthetic scheme of alternate way to prepare complex 2
noncoordinating anion, e.g. ClO4-, where the anion is not
positioned inside the metal complex, a trinuclear variety
separated out since the copper atom at the center coordi-
nated to the two complex ligands do not enforce any steric
requirement of the copper centers at the complex ligands.
Though it is suggested in the absence of structural studies
that the three metal equatorial planes cannot be coplanar,
but should deviate from planarity either in the complex
ligand or the metal ion at the center, it seems probable that
since acetate-bonded copper atom also is distorted from
planarity to a pseudo tetrahedral center, a dinuclear or
trinuclear compound should be unstable since the metal
atoms come too close to form a stable complex (Scheme 2,
3). The steric requirement of the acetate ion should be more
or less like the bromide.
complex 4. The bands for azomethine (C=N) groups
present in all the compounds are distinct and occur within
1,639–1,603 cm-1. General lowering of this band in all the
compounds substantiates the coordination of the Cu(II)
centers with the azomethine nitrogen. Usually, stretching
vibration for water appears above 3,400 cm-1. Hence, the
appearance of a broad band in the range of 3,430 cm-1 for
complex 2 indicates the presence of a water molecule. This
nature and lowering of the position indicates that the H
atoms are involved in an intermolecular H-bond network.
The appearance of a sharp intense band at 1,090 cm-1
for complex 3 is consistent with the proposed structure.
The mononuclear compound
1 obtained by using
Cu(ClO4)2ꢀ6H2O as the starting material does not show any
band in this region, indicating that it is the same compound
obtained when chloride and acetate are used as the counter
anions.
Spectroscopic studies
The electronic spectra of the complexes are consistent
with the square-planar geometry around the Cu(II) center.
Two d–d transitions are expected to appear between 500
and 430 nm absorption around 430 nm with a shoulder
around 400 nm. These two bands can be assigned to
The IR spectra for complexes 1, 2 and 3 show no bands for
t
the stretching frequency of free amine group appears at
3,228 cm-1 along with NH2 bending at 1,660 cm-1 for
(NH2) indicating the condensation of free amine groups but
123

Transition Met Chem (2010) 35:197–204
201
2B1g-2A1g and 2B1g-2Eg [19]. More intense bands from 300
to 200 nm are charge transfer in origin. The broadness of
the d–d band at 430 nm for the binuclear compound 2
indicates an overlapping of the d–d band in trigonal bipy-
ramidal geometry in this region. The intense band around
250 nm for the binuclear compound, which is absent in the
other two compounds probably accounts the difference in
color. The distortion in the trigonal bipyramidal geometry
from regular square-planar configuration can account for a
ligand to metal charge transfer, which should be absent in
the other two complexes. The other higher energy bands for
the three complexes occur in the same region.
´
o
Table 1 Selected bond lengths (A) and bond angles ( ) for complex 2
˚
Cu(1)–O(11)
1.966(4)
1.980(4)
2.262(2)
2.266(2)
2.354(5)
1.872(4)
1.920(6)
1.925(5)
1.942(5)
174.7(2)
89.5(2)
Cu(1)–O(100)
Cu(1)–Cl(1)
Cu(1)–Cl(2)
Cu(1)–O(25)
Cu(2)–O(25)
Cu(2)–N(26)
Cu(2)–O(11)
Cu(2)–N(19)
O(11)–Cu(1)–O(100)
O(11)–Cu(1)–Cl(1)
O(100)–Cu(1)–Cl(1)
O(11)–Cu(1)–Cl(2)
O(100)–Cu(1)–Cl(2)
Cl(1)–Cu(1)–Cl(2)
O(11)–Cu(1)–O(25)
O(100)–Cu(1)–O(25)
Cl(1)–Cu(1)–O(25)
Cl(2)–Cu(1)–O(25)
O(25)–Cu(2)–N(26)
O(25)–Cu(2)–O(11)
N(26)–Cu(2)–O(11)
O(25)–Cu(2)–N(19)
N(26)–Cu(2)–N(19)
O(11)–Cu(2)–N(19)
90.8(2)
Crystal structure results
92.7(2)
89.0(2)
Complex 2
158.0(1)
72.4(2)
The structure determination reveals that complex 2 repre-
sents a binuclear species [Cu2LCl2(H2O)] as shown in
Fig. 1, and the selected bond lengths and angles are given
in Table 1. The Cu(2) atom is four-coordinated being
bonded to the four donor atoms O(11), O(25), N(19) and
N(26) of the symmetrical tetradentate ligand. The four
102.4(2)
102.6(1)
99.0(1)
94.8(2)
85.2(2)
˚
donor atoms are planar with a r.m.s. deviation of 0.003 A.
177.8(2)
178.2(2)
85.6(2)
The copper atom deviates from the mean plane by
˚
0.033(3) A. The tetrahedral distortion is not so apparent
94.2(2)
since all the four donor atoms lie almost in the same plane.
The dihedral angles between the two planes [N(l9)–Cu(2)–
N(26) and O(25)–Cu(2)–O(11)] is 2.70° compared with 0°
for a perfectly square-planar arrangement and 90°for a
perfect tetrahedral arrangement. The two oxygen atoms
O(11) and O(25) in the ligand also bridge to Cu(1). Cu(1) is
five-coordinated with a distorted square-pyramidal geom-
etry. The basal plane is occupied by two chlorine atoms
with equivalent bond lengths, Cu(1)–Cl(1) 2.262(2) Cu(1)–
˚
Cl(2) 2.266(2) A,
a water molecule Cu(1)–O(100)
˚
1.980(4) A and a bridging oxygen atom Cu(1)–O(11)
˚
1.966(4) A. The apical position is occupied by a second
bridging oxygen atom that bonds less strongly, Cu(1)–
˚
O(25) 2.354(5) A. The four donor atoms in the basal plane
˚
show a r.m.s. deviation of 0.261 A. The copper atom Cu(1)
˚
is deviated from the mean plane by 0.171(2) A in the
direction of the axial atom O(25). The extent of distortion
of coordination polyhedron from the square pyramid to the
trigonal bipyramid has been calculated applying the
Addison parameter (s) [20] as an index of the degree of
trigonality, and s is defined as (b - a)/60 where b and a
are the two trans-basal angles. For a perfectly square-
pyramidal geometry, s is equal to zero, while it becomes
unity for perfectly trigonal–bipyramidal geometry. The
Addison parameter (s = 0.278) for the complex indicates
that the penta coordinated geometry is square pyramidal
with a considerable distortion toward trigonal bipyramid.
Although the hydrogen atoms on the water molecule could
not be located, it seems likely that O(100) is involved in
intermolecular hydrogen-bonded chains with Cl(10)(x ? 1,
0
˚
y, z) and Cl(2 )(1.5 - x, y - 0.5, 0.5 - z) at 3.175 A and
Fig. 1 ORTEP-3 picture for complex 2 with a limited atom
numbering scheme. Thermal ellipsoids are shown at 30% probability
˚
3.175 A, respectively (Fig. 2).
123

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Transition Met Chem (2010) 35:197–204
considering inter-dimer interaction. The data fitted
reasonably well using the following Bleaney–Bowers
expression considering small paramagnetic impurity.
vM ¼ 2Ng2b2ð1 ꢁ qÞ=½3 þ expðꢁJ=KTÞꢂðKTÞ
þ Ng2b2q=2KT ꢁ vdia
The best-fit parameters obtained are the following: J =
-217.095 cm-1, g = 2.09889 and R2 = 2.003 9 10-5
R = 1.158 9 10-5 (R is the agreement factor defined
as R = R[(vm)obs - (vm)calcd]2/R[(vm)obs]2).
q
(% of
paramagnetic impurity) = 0.48682. vdia (diamagnetic
contribution) = 0.00026 cm3 mol-1
.
From the structural data, it is clear that the complex 2 is
a phenoxo-bridged dimer in which the magnetic orbital,
d2x2-yof two Cu(II) ions interact via the two bridging
phenoxo groups. Magnetostructural correlation of such
complexes has been reported [9, 21, 22]. The average
bridging Cu–O–Cu angle in this complex is
100.81°(Cu(2)–O(25)–Cu(1) = 94.70° and Cu(2)–O(11)–
Cu(1) = 106.92°) and the Cu2O2 ring is nearly planar (no
Fig. 2 Proposed H-bonded chains of complex 2
Variable temperature magnetic study
´
Variable temperature magnetic study was done with com-
plex 2. According to the structural data, complex 2 is a
binuclear complex, in which the two Cu(II) ions are
bridged by two phenoxo-oxygen atoms. The magnetic
properties of the complex are very simple and correspond
to an almost isolated binuclear entity, in line with the
structural data. The magnetic susceptibility data were col-
lected on polycrystalline samples over the temperature
range of 300–2 K using an applied magnetic field of 10
Oersted. The plot of temperature dependence of vM (vM is
the molar magnetic susceptibility for 2 Cu(II) ions) is
shown in Fig. 3. To fit the temperature dependence mag-
netic susceptibility data, we used the dimeric model
˚
atom deviates more than 0.06 A from the least square mean
´
˚
plane). The Cu–Cu distance is 3.126 A. All these data are
in agreement with the strong antiferromagnetic coupling in
the complex.
Experimental
Elemental analyses (carbon, hydrogen and nitrogen) were
performed using a Perkin–Elmer 240C elemental analyzer.
IR spectra in KBr (4,500–500 cm-1) were recorded using a
Perkin–Elmer RXI FT-IR spectrophotometer. Electronic
spectra in acetonitrile (1,200–350 nm) were recorded on a
Hitachi U-3501 spectrophotometer. The magnetic suscep-
tibility measurements were done with a MPMS XL5
SQUID magnetometer (QUANTUM DESIGN) and dia-
magnetic corrections were made using Pascal’s constants.
All chemicals were of reagent grade and used without
further purification.
0.04
0.03
0.02
0.01
0.00
Caution! Metal perchlorates in the presence of organic
ligands are potentially explosive. Only a small amount of
the material should be prepared, and it should then be
handled with care.
Synthesis of the [CuL] (1)
Salicylaldehyde (10 mmol, 1.1 mL) was added to a solu-
tion of o-phenylenediamine (5 mmol, 0.54 g) in ethanol
(25 mL) with stirring. To the resulting mixture, an etha-
nolic solution (20 mL) of CuBr2ꢀ2H2O (5 mmol, 1.30 g)
was added dropwise. This was stirred continuously for 3 h.
Gradually, the color of the solution changed to deep blue.
A deep blue compound precipitated out and was filtered
0
100
200
300
T (K)
Fig. 3 Plot of vM versus T data for complex 2. Solid line represents
the fitting using the inter-dimer model
123

Transition Met Chem (2010) 35:197–204
203
off. Due to its highly insoluble nature, no single crystals
suitable for X-ray diffraction were obtained. Yield: (*90%).
Anal. found: C, 62.9; N, 6.9; H, 3.7; Cu, 16.5. Calc. for
C20N2O2H14Cu: C, 63.6; N, 7.4; H, 3.7; Cu, 16.8%. HRMS
(ESI): found m/z (M?H)? = 395.9; Mcalcd = 396.5; mag-
netic moment (at 25 °C) leff = 1.7 BM.
The same product was obtained when Cu(ClO4)2ꢀ6H2O
(5 mmol, 1.89 g) or Cu(CH3COO)2ꢀH2O (5 mmol, 1.00 g)
were used instead of CuBr2ꢀ2H2O.
(M?H)? = 819.4; Mcalcd = 819.5. Magnetic moment (at
25 °C) leff = 1.63 BM.
[Cu2L12](CH3COO)2 (4)
A mixture of diacetylmonoxime (5 mmol, 0.505 g) and
o-phenylenediamine (5 mmol, 0.54 g) in ethanol (25 mL)
was refluxed for about 3 h. An ethanolic solution (10 mL)
of Cu(CH3COO)2ꢀH2O (5 mmol, 1.00 g) was added drop-
wise to the resulting mixture. This was stirred continuously
for 3 h. Gradually, the color of the solution changed to
brown. A brown crystalline compound precipitated out and
was filtered off and recrystallised from ethanol but no
single crystals suitable for X-ray diffraction could be
obtained. Yield: (*80%). Anal. found: C, 45.9; N, 13.4; H,
4.7; Cu, 19.9. Calc. for C24N6O6H30Cu2: C, 46.1; N, 13.4;
H, 4.8; Cu, 20.3%.
[Cu2LCl2(H2O)] (2)
Complex 2 was prepared by the same procedure as complex 1
but using CuCl2ꢀ2H2O (5 mmol, 0.85 g) instead of
CuBr2ꢀ2H2O. Gradually, the color of the solution changed to
reddish brown. A reddish brown compound precipitated out
and was filtered off, and the filtrate was kept at room tem-
perature. Overnight, brown-colored single crystals suitable
for X-ray diffraction were obtained. Yield: (*70%). Anal.
found: C, 44.9; N, 4.9; H, 2.9; Cu, 23.5. Calc. for
C20N2O3H16Cu2Cl2 : C, 45.3; N, 5.3; H, 3.0; Cu, 23.9%.
The same product was obtained by the following process
in the presence of diacetylmonoxime.
X-ray crystallography
Crystal data are given in Table 2. A total of 4,892 inde-
pendent reflections were collected with Mo Ka radiation at
A solution of salicylaldehyde (10 mmol, 1.1 mL) in
chloroform (50 mL) was added dropwise to a solution of
o-phenylenediamine (10 mmol, 1.08 g) in chloroform
(50 mL). After completion of the addition, the solution was
stirred for an additional 3 h, and chloroform was evapo-
rated under reduced pressure, yielding the monocondensed
2-[(2-amino-phenylimino)-methyl]-phenol as a viscous
liquid. It was dissolved in methanol (10 mL). Solid dia-
cetylmonoxime (10 mmol, 1.011 g.) was added, and the
mixture was stirred for 24 h. A solution of Cu(CH3COO)2ꢀ
H2O(10 mmol, 1.99 g) in methanol (20 mL) was added to
the resulting solution with continuous stirring to precipitate
a brown-red solid. It was recrystallized from ethanol
solution to obtain single crystals of 2 suitable for X-ray
diffraction. Yield: (*70%).
Table 2 Crystal data and refinement details of complex 2
Crystal data
2
Formula
C20H16C12Cu2N2O3
530.33
fw
Temp (K)
150
Space group
Crystal system
Crystal dimensions (mm)
Monoclinic
P21/n
0.24 9 024 9 0.05
11.886(6)
7.7456(15)
20.684(4)
(90)
˚
a/A
˚
b/A
˚
c/A
a/deg
b/deg
c/deg
93.68(3)
(90)
3
˚
V(A )
1900.3(11)
4
[Cu3L2](ClO4)2 (3)
Z
DCalc (gm cm-3
)
1.854
l (mm-1
)
2.545
Salicylaldehyde (10 mmol, 1.1 mL) was added to a solu-
tion of o-phenylenediamine (5 mmol, 0.54 g) in ethanol
(25 mL) with stirring. An ethanolic solution (10 mL) of
Cu(ClO4)2ꢀ6H2O (15 mmol, 5.67 g) was added dropwise to
the resulting mixture. This was stirred continuously for 3 h.
Gradually, the color of the solution changed to deep green.
A deep green crystalline compound precipitated out and
was filtered off and recrystallised from ethanol. Unfortu-
nately, no single crystals suitable for X-ray diffraction
could be obtained. Yield: (*90%). Anal. found: C, 46.9;
N, 5.4; H, 2.7; Cu, 18.5. Calc. for C40N4O12H28Cu3Cl2: C,
47.2; N, 5.5; H, 2.8; Cu, 18.7%. HRMS (ESI): found m/z
F(000)
1,064
Total reflections
Unique reflections
Observed data [I [ 2r(I)]
No. of parameters
Refined
7,405
4,892
1,411
257
R (int)
0.0841
R indices (all data)
R indices
R1 = 0.0979 wR2 = 0.2598
R1 = 0.0721
[I [ 2r(I)]
wR2 = 0.0775
123

204
Transition Met Chem (2010) 35:197–204
150 K using the Oxford Diffraction X-Calibur CCD Sys-
tem. The crystal was positioned at 50 mm from the CCD.
Three hundred twenty-one frames were measured with a
counting time of 10 s. Data analysis was carried out with
the CrysAlis program [23]. An empirical absorption cor-
rection was carried out using Abspack [24]. The structure
was solved using direct methods with the Shelxs97 pro-
gram [25]. The nonhydrogen atoms were refined with
anisotropic thermal parameters. The hydrogen atoms bon-
ded to carbon were included in geometric positions and
given thermal parameters equivalent to 1.2 times those of
the atom to which they were attached. The hydrogen atoms
on the water molecule were not located. The structure was
refined using all data on F2 using Shelxl97 [25] to R1
0.0721, wR2 0.0775 for 1,411 reflections with I [ 2r(I)
and R1 0.0979, wR2 0.2598 for all data.
No 721696 (complex 2). Copies of this information may
be obtained free of charge from CCDC, 12 Union Road,
Cambridge, CB21EZ, UK (fax:?441223336033; email:-
deposit@ccdc.cam.ac.uk or www: http://www.ccdc.cam.
ac.uk).
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Three symmetrical Schiff base complexes have been
studied and one of them has been characterized structur-
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involving o-phenylenediamine, salicylaldehyde and diace-
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diacetylmonoxime, only the symmetrical complex was
isolated. Mononuclear, binuclear and trinuclear compounds
were obtained by varying the counter anions. It seems
probable, therefore, that the salicylaldehyde symmetrical
Schiff base complex was the most stable species that sep-
arated out even in the presence of diacetylmonoxime. The
Schiff base compound derived from diacetylmonoxime
could only be isolated in the absence of salicylaldehyde.
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Acknowledgments We thank EPSRC and the University of Read-
ing for funds for the X-Calibur system. Thanks are also due to Prof.
Ashutosh Ghosh, Department of Chemistry, University College of
Science, University of Calcutta, 92, A.P.C. Road, Kolkata-700 009,
India, for his valuable suggestions during preparation of the manu-
script and Sri Sanjib Giri of Indian Association for the Cultivation
of Science, Jadavpur, Kolkata-700 032, India, for the magnetic
measurements.
23. CrysAlis (2008) Oxford Diffraction Ltd., Abingdon, UK
24. Abspack Program (2007) Oxford Diffraction Ltd., Abingdon, UK
25. Sheldrick GM, Shelxs97 and Shelxl97, Programs for Crystallo-
graphic solution and refinement Acta Crystallogr A64:112 (2008)
Appendix A. Supplementary data
Crystallographic data for the analysis have been deposited
with the Cambridge Crystallographic data Centre, CCDC
123