Synthesis, characterisation and X-ray crystal structure of copper(II) complexes with unsymmetrical tetradentate schiff base ligands: First evidence of Cu(II) catalysed rearrangement of unsymmetrical to symmetrical complex

Article abstract of DOI:10.1016/S0277-5387(02)01435-3

The mononuclear copper(II) complexes, [CuL¹](ClO₄) (1), and [CuL²](ClO₄) (2) with unsymmetrical quadridentate Schiff base ligands derived from the 1:1:1 condensation of 2,4-pentanedione, pyridine-2-carboxaldehyde and 1,2-ethanediamine (HL¹) or 1,3-propanediamine (HL²) have been prepared and characterised. Complex 2 undergoes Cu(II)/H⁺ catalysed rearrangement to [CuL³](ClO₄)₂ (3) where L³ is a symmetrical tetradentate Schiff base involving 1,3-propanediamine and pyridine-2-carboxaldehyde. Structures of all the three compounds have been verified by single crystal X-ray analysis. The geometry around Cu(II) is square-planar in I and 2 whereas that in 3 is distorted octahedral with two axially coordinated perchlorate ions.

Full text of DOI:10.1016/S0277-5387(02)01435-3

Polyhedron 22 (2003) 617ꢁ624
/
www.elsevier.com/locate/poly
Synthesis, characterisation and X-ray crystal structure of copper(II)
complexes with unsymmetrical tetradentate Schiff base ligands: first
evidence of Cu(II) catalysed rearrangement of unsymmetrical to
symmetrical complex
Mau Sinha Ray a, Rahul Bhattacharya a, Siddhartha Chaudhuri b, Lara Righi c,
Gabriele Bocelli c, Gurucharan Mukhopadhyay d,*, Ashutosh Ghosh a,*
a Department of Chemistry, University College of Science and Technology, University of Calcutta, 92, A.P.C. Road, Kolkata 700 009, India
b R.S.I.C. Bose Institute, 92, A.P.C. Road, Kolkata 700 009, India
c CSSD-CNR, Palazzo Chimico Parco Area delle Scienze, Parma, Italy
d Department of Chemistry, Presidency College, Kolkata 700 073, India
Received 5 September 2002; accepted 16 December 2002
Abstract
The mononuclear copper(II) complexes, [CuL1](ClO4) (1), and [CuL2](ClO4) (2) with unsymmetrical quadridentate Schiff base
ligands derived from the 1:1:1 condensation of 2,4-pentanedione, pyridine-2-carboxaldehyde and 1,2-ethanediamine (HL1) or 1,3-
propanediamine (HL2) have been prepared and characterised. Complex 2 undergoes Cu(II)/Hꢀ catalysed rearrangement to
[CuL3](ClO4)2 (3) where L3 is a symmetrical tetradentate Schiff base involving 1,3-propanediamine and pyridine-2-carboxaldehyde.
Structures of all the three compounds have been verified by single crystal X-ray analysis. The geometry around Cu(II) is square-
planar in 1 and 2 whereas that in 3 is distorted octahedral with two axially coordinated perchlorate ions.
# 2003 Elsevier Science B.V. All rights reserved.
Keywords: Asymmetrical tetradentate Schiff base; Copper(II); X-ray crystallography; Cu(II) catalysed hydrolysis
1. Introduction
ligands capable of binding transition metal ions. Such
singly condensed units have been prepared by several
Since the first reports on the synthesis of 7-amino-4-
methyl-5-azahept-3-en-2-one (AMAH) [1] and 8-amino-
4-methyl-5-azaoct-3-en-2-one (AMAO), [2] the mono-
condensation products of 2,4-pentanedione with 1,2-
ethanediamine and or 1,3-propanediamine, respectively,
the compounds have been used as precursors for the
preparation of unsymmetrical quadridentate Schiff base
ligands [3]. The monocondensation products of dia-
mines, here after referred to as ‘half-units’ where one
primary amine group forms an imine or enamine bond
and the other is unchanged, have a potential to react
with other carbonyl moieties to form unsymmetrical
routes [1ꢁ4]. Reacting the constituents under high
/
dilution which was employed in the present study, is a
route employed earlier [1,4]. In transition-metal biosites
the metal ions are often found in chemically or
geometrically distinct environments. Such compounds
have been suggested as useful probes for the study of
low symmetry complexes related to the low symmetry
sites found in metalloprotins [5]. The unsymmetrical
nature of the dicopper site in hemocyanin was estab-
lished [6].
In this paper we report the synthesis and character-
isation of copper(II) complexes of quadridentate un-
symmetrical ligands HL1 and HL2 derived from AMAH
and AMAO by condensation of the free amine group
with pyridine-2-carboxaldehyde (Scheme 1). The com-
plex, [CuL2]ClO4, has been found to rearrange into the
symmetrical complex [CuL3](ClO4)2 (where L3 is the
* Corresponding author. Tel.: ꢀ
9755.
E-mail address: ghosh_59@yahoo.com (A. Ghosh).
/
91-33-350-8386; fax: ꢀ91-33-351-
/
0277-5387/03/$ - see front matter # 2003 Elsevier Science B.V. All rights reserved.
doi:10.1016/S0277-5387(02)01435-3

618
M.S. Ray et al. / Polyhedron 22 (2003) 617ꢁ624
/
4.07; N, 10.69; Cu, 16.16. Found: C, 39.91; H, 4.17; N,
10.70; Cu 15.83%; lmax (nm) (omax (dm3 molꢂ1 cmꢂ1))
(acetonitrile), 539 (255), 367 (1639); meff, 1.73 BM.
2.1.2. [CuL2]ClO4 (2) and [CuL3] (ClO4)2 (3)
Complex 2 was prepared by similar method to 1
except that AMAO was used instead of AMAH. The
immediately separated product was a brown solid which
was collected by filtration and was recrystallised from
CH3CNꢁMeOH (1:1 v/v) mixture to give dark brown
/
single crystals of 2 suitable for X-ray diffraction (yield:
1.222 g, 30%). Calc. for C14H18CuClN3O5: C, 41.27; H,
4.42; N, 10.32; Cu, 15.6. Found: C, 41.43; H, 4.67; N,
10.35; Cu, 15.02%. lmax (nm) (omax (dm3 molꢂ1 cmꢂ1))
(acetonitrile), 533 (130), 373 (1170); meff, 1.77 BM.
A mixture of brown and green products started to
separate out from the filtrate after approximately 20 min
and only the green crystalline product after 1 h. The
green product was identified as 3 and single crystals
suitable for X-ray studies were obtained by diffusion of
diethylether to an acetonitrile solution of the compound
at room temperature (r.t.). Calc. for C15H16CuCl2N4O8:
C, 34.97; H, 3.11; N, 10.88; Cu, 12.34. Found: C, 35.35;
H, 3.04; N, 11.12; Cu, 11.71%. The same product 3 was
also obtained as a green solid by refluxing 1,3-propane-
diamine (0.74 g, 10 mmol) and pyridine-2-carboxalde-
hyde (2.2 g, 20 mmol, 1:2 molar ratio) for 2 h and then
Scheme 1.
symmetrical Schiff base ligand involving 1,3-propane-
diamine and pyridine-2-carboxaldehyde). Unsymmetri-
cal to symmetrical rearrangement of similar type of
ligands was observed in the presence of Mn3ꢀ during
the synthesis of such type of complexes [7]. However, to
our knowledge, till date there is no report of investiga-
tion as to whether this type of rearrangement (i) is
catalysed by any other metal ion or (ii) is dependent on
the ligand systems. In the present systems, we observed
the first copper catalysed rearrangement, which is
dependent upon the ligand systems. The structures of
all the three complexes have been verified by single
crystal X-ray analysis.
adding Cu(ClO4)2×/6H2O (3.7 g, 10 mmol) to the
mixture. It was recrystallised from CH3OH. (yield:
4.118 g, 80%). Calc. for C15H16CuCl2N4O8: C, 34.97;
H, 3.11; N, 10.88. Found: C, 35.21; H, 2.90; N, 11.02%.
lmax (nm) (omax (dm3 molꢂ1 cmꢂ1)) (acetonitrile), 624
(119); meff, 1.72 BM.
2.1.3. Synthesis of 3 from 2
2. Experimental
All other chemicals were of reagent grade and used
without further purification. The ‘half-units’ AMAH
and AMAO were prepared as viscous oil by reported
methods [1,4].
2.1.3.1. Catalysed by Hꢀ. Two drops of 1 M perchloric
acid was added to a solution of complex 2 (0.5 mmol, 0.2
g) in methanolꢁ
water (9:1 v/v) mixture (50 cm3) and put
/
under reflux. Within 30 min, the colour of the solution
started to change into green and the green compound 3
deposited along with the brown compound 2 just above
the upper meniscus of the boiling solution indicating the
occurrence of the rearrangement. The solid compounds
were taken back into the solution by occasional stirring.
After approximately 10 h of reflux the solvent was
evaporated to make the final volume approximately 2
cm3 and cooled at r.t. when a mixture of compound 2, 3
and Cu(acac)2 were precipitated. Compound 3 was
separated from the mixture by dissolving it in cold
water. The residue was washed with little amount of dmf
(5 cm3) to dissolve out the unreacted 2. The yield of
compound 3 and Cu(acac)2 were approximately 50 and
35%, respectively.
2.1. Synthesis of the complexes
2.1.1. [CuL1]ClO4 (1)
AMAH (10 mmol) was dissolved in methanol (50
cm3) and pyridine-2-carboxaldehyde (1.1 g, 10 mmol)
was mixed with it. The mixture was warmed at 50ꢁ
/
60 8C
for 1 h and cooled to ambient temperature. To the
6H2O (3.7
solution was added a solution of Cu(ClO4)2×
/
g, 10 mmol) in methanol (20 cm3) to precipitate
immediately dark red solid of 1 which was recrystallised
from CH3CNꢁMeOH (1:1 v/v) mixture to obtain dark
/
red single crystals suitable for X-ray diffraction. (yield:
3.146 g, 80%). Calc. for C13H16CuClN3O5: C, 39.69; H,

M.S. Ray et al. / Polyhedron 22 (2003) 617ꢁ
/
624
619
2.1.3.2. Catalysed by Cu2ꢀ. The same experiment was
performed by adding 0.005 g of Cu(ClO4)2×6H2O to the
3. Results and discussions
/
solution instead of perchloric acid. Here also partial
rearrangement was found to occur with approximately
30 and 20% yield of 3 and Cu(acac)2, respectively.
3.1. Infrared and electronic spectra
In the IR spectra of all the complexes no bands due to
nNH could be observed indicating the condensation of
the free amine groups. The bands corresponding to
2
2.1.3.3. Catalysed both by Hꢀ and Cu2ꢀ. The experi-
ment was again performed with the addition of both two
azomethine (CÄ
/
N) group are distinct and occurs within
1573 cmꢂ1. The lowering of the positions of the
1649ꢁ
/
bands indicate their coordination to the metal centres.
The sharp single peak at 1088 cmꢂ1 for both 1 and 2
give evidence of ionic perchlorate present in both of
them. The splitting of the band at 1090 cmꢂ1 for 3 is
indicative of coordinated perchlorate ions as substan-
tiated in the crystal structure.
drops of perchloric acid and 0.005 g of Cu(ClO4)2×
/
6H2O. The yield of compound 3 was found to be
much higher in this case (75%) along with a yield of
50% Cu(acac)2.
The electronic spectral data in acetonitrile solution
suggest basically square planar geometry for compounds
1 and 2. In general square-planar complexes are known
to exhibit two or more band [14]. Complex 1 shows two
bands at 18 553 and 27 248 cmꢂ1 while the correspond-
ing peaks for complex 2 are at 18 762 and a shoulder at
26 809 cmꢂ1. The octahedral nature of complex 3 is
evident by appearance of a single broad peak at 16 026
cmꢂ1 substantially lower than the two square-planar
complexes [15].
2.2. Physical measurements
Elemental analyses (carbon, hydrogen and nitrogen)
were performed using a PerkinꢁElmer 240C elemental
/
analyser and the copper contents in all the complexes
were estimated spectrophtometrically [8]. IR spectra in
KBr (4500ꢁ
Elmer RXI FT-IR spectrophotometer. Electronic spec-
tra in acetonitrile (1200ꢁ350 nm) were recorded in a
/
500 cmꢂ1) were recorded using a Perkinꢁ
/
/
Hitachi U-3501spectrophotometer. Electrochemical stu-
dies were done using PAR Versastat-2. The effective
magnetic moments were calculated from magnetic
susceptibility measurements with an EG & G PAR
vibrating sample magnetometer model 155 at r.t. and
diamagnetic corrections were made using Pascal’s con-
stants.
3.2. Cyclic voltammetry
The cyclic voltammograms of the Cu(II) complexes
show oxidation peaks at high potentials thereby suggest-
ing stable Cu(II) complexes. The oxidation peak of
complex 3 at 1.205 V is quasi reversible with the
corresponding reduction peak at 1.058 V versus AgCl
(DEPꢃ
initial anodic scan or the corresponding cathodic part.
On initial cathodic scan a reduction peak at ꢂ0.17 V
Cu(I) reduction with no
corresponding anodic peak. The initial anodic scan of
complex 1 and 2 is at 1.3 V with a corresponding
/
147 mV ). No other peaks are observed on the
2.3. Structure determination
/
versus AgCl is due to Cu(II)Ã
/
The X-ray single-crystal diffraction measurements
were carried out using an EnrafꢁNonius CAD4 single
/
crystal diffractometer for complex 1 and 3 and a Bruker
AXS Smart single crystal diffractometer with CCD for
complex 2. The data were corrected for Lorentz,
polarisation and absorption effects. The crystal struc-
tures of the three complexes were solved by direct
methods using the programs SIR-97 [9] and SHELXS-97
[10] and refined by using SHELXL-97 [10]. The non-
hydrogen atoms were refined anisotropically while the
hydrogen atoms, either located from difference electron
density maps or placed geometrically, were refined with
isotropic thermal parameters. Neutral atom scattering
factors were taken from Cromer and Weber [11] and
anomalous dispersion effects were included in Fcalc [12].
The crystallographic data are summarised in Table 1.
Selected bond lengths and bond angles are shown in
Table 2. The crystallographic illustrations were prepared
using ORTEP-3 [13].
cathodic peak at 1.142 V (DEPꢃ
/
158 mV) indicative of a
0.23
quasi-reversible nature. Initial cathodic scan is at ꢂ
/
V.
3.3. Crystal structures of complexes 1, 2 and 3
The X-ray analysis verified the structures of unsym-
metrical copper(II) complexes 1 and 2 and the symme-
trical complex, 3. The ORTEP-3 views of the three
complexes with atom numbering schemes are shown in
Figs. 1ꢁ3. In both the complexes 1 and 2, the
/
deprotonated ligands L1 and L2 are quadridentate
forming one six-membered chelate ring, and two five-
membered chelate rings (6ꢁ
six-membered chelate rings and one five-membered
chelate ring (6ꢁ6ꢁ5) in 2.
/
5ꢁ
/
5) in 1 and two adjacent
/
/

620
M.S. Ray et al. / Polyhedron 22 (2003) 617ꢁ624
/
Table 1
Crystal data and structure refinement of complexes 1ꢁ
/
3
[CuL1](ClO4) (1)
[CuL2](ClO4) (2)
[CuL3](ClO4)2 (3)
Formula
M
C13H16CuClN3O5
393.29
C14H18CuClN3O5
407.29
C15H16CuCl2N4O8
514.77
Crystal system
Space group
triclinic
P1
triclinic
P1
monoclinic
C2/c
˚
a (A)
10.439(3)
10.959(2)
7.674(2)
92.54(3)
91.27(2)
117.77(2)
775.1(4)
2
7.743(2)
10.767(2)
10.997(2)
63.62(2)
84.64(2)
88.66(2)
817.6(3)
2
14.037(3)
10.220(3)
15.138(4)
˚
b (A)
˚
c (A)
a (8)
b (8)
115.15(2)
g (8)
3
V (A )
˚
1965.8(9)
4
1.739
Z
Dcalc (g cmꢂ3
m (mmꢂ1
Number of unique data
)
1.685
3.852[Cu Ka]
2940
1.654
1.529[Mo Ka]
3483
)
4.565[Cu Ka]
1760
Number of data with I ꢀ
R1, wR2
/2s(I)
2478
0.0539, 0.1758
2584
0.0963, 0.2723
1440
0.0515, 0.1684
Table 2
Selected bond lengths (A) and bond angles (8) for complexes 1ꢁ
˚
/
3
1
2
3
Bond lengths
CuÃ
CuÃ
CuÃ
CuÃ
CuÃ
/
N1
N2
N3
O
2.004(3)
1.922(5)
1.907(3)
1.866(4)
2.047(5)
1.977(6)
1.955(5)
1.884(5)
2.026(3)
1.982(4)
/
/
/
/O1
2.510(5)
1.406(5)
1.375(9)
1.404(5)
1.377(7)
ClÃ
ClÃ
ClÃ
ClÃ
ClÃ
ClÃ
ClÃ
/
O1
1.382(9)
1.419(7)
1.357(12)
1.371(14)
1.351(9)
/
O2
1.341(11)
1.359(10)
1.315(11)
1.322(13)
1.309(11)
1.369(17)
/
O3
/
O4
/
O2A
O3A
O4A
1.418(10)
1.355(15)
1.393(15)
/
/
Bond angles
N1Ã
N2Ã
N3Ã
N1Ã
N1Ã
N2Ã
N2Ã
N2*Ã
N1ÃCuÃ
N1ÃCuÃ
/
CuÃ
CuÃ
CuÃ
CuÃ
CuÃ
CuÃ
CuÃ
/
N2
N3
O
80.8(2)
85.4(2)
97.5(2)
96.5(1)
165.2(2)
176.7(2)
79.2(2)
98.6(2)
94.9(2)
87.3(2)
174.6(2)
166.5(2)
81.3(2)
/
/
Fig. 1. ORTEP-3 view of complex 1 with the atom labelling scheme.
Thermal ellipsoids are shown at 50% probability. Only the major
fractions of the disordered perchlorate oxygen atoms are shown.
/
/
/
/O
/
/N3
/
/O
deviation of copper(II) from the same plane are
/
/N2*
92.6(2)
81.3(2)
˚
0.0337(5) and 0.0463(7) A in complex 1 and 2, respec-
tively.
/
CuÃN1*
/
/
/
N1*
104.9(2)
173.1(2)
/
/
N2*
In complex 1, the five-membered chelate ring, CuÃ
N(2)ÃC(7)ÃC(8)ÃN(3), has a half chair conformation
with the puckering parameters [16] q2ꢃ0.253(6) and
f2ꢃ 83.2(9)8. In complex 2, the carbon atom C(8) of
the six-membered chelate ring, CuÃN(2)ÃC(7)ÃC(8)Ã
C(9)ÃN(3), is disordered with the C(8) atom having
/
* Designates the symmetry related atom at 1ꢂ
complex 3.
/
x, y, 3/2ꢂ
/
z for
/
/
/
/
/
ꢂ
/
The copper(II) ions have square-planar co-ordination
with a slight tetrahedral distortion in both the com-
plexes 1 and 2. The deviations of the co-ordinating
atoms O, N(3), N(2), N(1) from the least-square mean
/
/
/
/
/
two alternate positions, C(8) with an occupancy of
0.475(19) and C(8?) with an occupancy of 0.525(19).
This causes the six-membered ring to flip between two
plane through them are 0.042(3), ꢂ
/
0.060(3), 0.083(4),
0.046(3) A in complex 1 and 0.049(6), ꢂ0.040(6),
0.036(5) A in complex 2, respectively. The
˚
ꢂ
/
/
envelope conformations [17] with fꢃ
/
359.0(14)8 for
˚
0.050(6), ꢂ
/
CuÃN(2)ÃC(7)ÃC(8)ÃC(9)ÃN(3) and fꢃ
/
/
/
/
/
/
180.2(9)8 for

M.S. Ray et al. / Polyhedron 22 (2003) 617ꢁ
/
624
621
Fig. 2. ORTEP-3 view of complex 2 with the atom labelling scheme. Thermal ellipsoids are shown at 50% probability. Only the major fraction of the
disordered carbon atom, C(8), of the six-membered puckered ring is shown.
rings are invariably smaller than those associated with
six-membered rings. The corresponding values observed
in related structures range from 818 to 848 for five-
membered rings and from 928 to 988 for six-membered
rings [3,18]. The values found in the present system are
within these ranges. The larger value of the N(2)Ã
/
CuÃ
/
N(3) angle in complex 2 is attributed in part to the steric
strain imparted to the system by the presence of the two
adjacent six-memberd rings. The rather long CuÃ
/N
distances (Table 2) in complex 2 compared with those in
1 are also consistent with this.
Crystal structure of 3 reveal that the copper atom lies
on a twofold axis of symmetry passing through the
copper(II) and C(8). The co-ordination polyhedron
around the copper atom is best described as a distorted
octahedron. The four nitrogen atoms N(1), N(2) and
N(2)*, N(1)* (* designates a symmetry related atom) of
the quadridentate symmetrical ligand define the equa-
torial plane and two oxygen atoms O(1) and O(1)* of
the perchlorate groups are semi-coordinated in trans
axial position. The deviations of the component atoms
Fig. 3. ORTEP-3 view of complex 3 with the atom labelling scheme. An
* denotes a symmetry related atom. For clarity, thermal ellipsoids are
given at 20% probability and only the major fractions of the disordered
perchlorate oxygen atoms are shown.
N(1), N(2), N(2)*, N(1)* from the equatorial plane are
˚
0.048(4), 0.059(5), ꢂ0.059(5), 0.048(4) A, respectively,
ꢂ
/
/
from the least-square mean plane defined by themselves.
The copper atom lies in that plane. Unlike complex 2,
the saturated six-membered ring is not disordered and
exhibits twist-boat with the puckering parameters [15]
CuÃ
/
N(2)Ã
/
C(7)Ã
/
C(8?)Ã
/
C(9)Ã
/
N(3). The displacements of
C(8) and C(8?) from the least-squares mean plane
through Cu, N(2), C(7), C(9), N(3) are, respectively,
˚
0.727(14) A.
q3ꢃ
/
0, q2ꢃ
/
Q, f2ꢃ
/
90(11)8, u2ꢃ
/
90(18)8. The N(2)Ã
/
ꢂ
/
0.534(19) and ꢀ
/
CuÃN(2)* angle is 92.6(17)8 and is typical of six-
/
The general features of the copper co-ordination
membered chelate [3,18]. However, in comparison to
the complex 2, the angle is smaller and that is expected
as its adjacent chelate rings are five-membered, causing
less steric strain. It is to be mentioned here that the
geometry of the complexes with other symmetrical
sphere are not unusual. The observed angular distor-
tions from a regular square-planar geometry are con-
sistent with similar distortions seen in related
compounds [3,18]. For example the angles around the
copper atom associated with five-membered chelate

622
M.S. Ray et al. / Polyhedron 22 (2003) 617ꢁ624
/
tetradentate Schiff base ligands are different from the
present one e.g. ligand involving 1,2-ethanediamine and
2,4-pentanedione shows a square-planar metal environ-
ment [19] whereas that derived from 1,2-ethanediamine
and 2-pyrollecarboxaldehyde gives a binuclear cop-
per(II) complex in which both ends of the Schiff base
act as bis(bidentate) ligands [20].
For complexes 1 and 2 the molecules are packed in
pairs; one on top of the other giving rise to infinite
stacks along c and a directions, respectively (Figs. 4 and
5). The two molecules in each pair are centrosymme-
trically related and exhibit significantly short CuÃ
/
Cu
˚
distances, 3.335(1) and 3.491(1) A for 1 and 2, respec-
tively. The comparatively large distance in 2 is probably
due to the presence of disorder in the saturated six-
membered chelate ring preventing the molecules to be
closer.
Fig. 5. Stacking of the molecules of complex 2 along the a-axis.
period of time. However, during the synthesis all the
constituents i.e. the metal ion, the ligand, the complex
and most importantly the Hꢀ which is released during
the complex formation are present in the solution.
Therefore, it is very difficult to conclude whether the
rearrangement took place with free ligand, the ligand
bound to the metal ion and if it was catalysed by the free
metal ion or by Hꢀ. To verify the role of Hꢀ and Cu2ꢀ
ion in the hydrolysis scheme, complex 2 (0.5 mmol; 0.2
3.4. Cu(II) catalysed rearrangement of the
unsymmetrical ligand, HL2
The rearrangement was first noticed during the
preparation of the complex. Addition of HL2 to the
methanolic solution of Cu(ClO4)2×
/
6H2O results imme-
diately in the formation of the brown unsymmetrical
complex 2. When the resulting mixture was put under
reflux for approximately 2 h all the brown compounds
disappear and on cooling crystalline symmetrical com-
plex 3 was isolated as sole product. It was filtered and
the mother liquor was concentrated to about one-eighth
of the original volume and left overnight at r.t. The
crystalline product which was separated from this
solution was found to be a mixture of 3 and bis(acety-
lacetonato)Cu(II) but no compound of the Schiff base of
symmetrical combination of pent-2,4-dione with the
diamine could be isolated. Such rearrangement was
reported earlier by Bermijo et al. [7] for Mn(III)
complexes during their synthesis which took a long
g) was dissolved in methanolꢁwater (9:1 v/v) mixture (50
/
cm3) and put under reflux for several hours but no
rearrangement or colour change of the solution was
observed. However, the same reaction by addition of
two drops of 1 M perchloric acid or of 0.005 g of
Cu(ClO4)2×/6H2O showed the rearranged products
within 1 h as described in the Section 2.1. Thus we can
infer that the presence of either free Hꢀ or Cu2ꢀ is
necessary for the rearrangement of 2 i.e. both of them
can catalyse the hydrolysis of compound 2.
It is well known that Schiff bases are subject to
hydrolysis in acidic or basic conditions to reform the
constituent carbonyl and amine precursors [21]. The
hydrolysis of compound 2 is believed to follow the
similar path as proposed by Bermijo et al. [7] However,
the Mn(III) acetylacetonato complex was not isolated
by this group. The isolation of the Cu(acac)2 in our
study substantiate the formation of the constituents in
the initial stage. From Scheme 2 although it is apparent
that there is an excess of Cu(II) (0.005 g, added for
hydrolysis) and diamine left in the solution, we were
unable to isolate any Cu(II) diamine complex.
It is to be mentioned here that no rearrangement was
observed for HL1 under similar conditions either during
synthesis or in the presence of Cu(II) ion. The suscept-
ibility of the complex with HL2 towards hydrolysis can
be attributed to the steric strain imparted to the system
by the presence of two adjacent six-membered chelate
rings (vide crystal structures, Section 3.3).
Fig. 4. Stacking of the molecules of complex 1 along the c-axis.

M.S. Ray et al. / Polyhedron 22 (2003) 617ꢁ
/
624
623
Scheme 2.
4. Conclusion
Acknowledgements
In the present study we first noticed that Cu(II) can
also catalyse the unsymmetrical to symmetrical rearran-
gement of the tetradentate Schiff base ligand and the
rearrangement can take place with ligand which is
complexed with metal ion in the presence of some free
Cu(II) or Hꢀ ions. The nature of the ligand is also very
important. Rearrangement was observed with complex 2
where the chelate rings around the copper ion were
under more strain in comparison to complex 1 where no
such rearrangement was observed during the study.
We are thankful to Dr. Shyamal Chattopadhyay,
Department of Chemistry, B.E. College (Deemed Uni-
versity), Shibpur, Howrah, for providing facilities for
electrochemical studies. One of the authors (M.S.R.) is
thankful to UGC, India for awarding a Junior Research
Fellowship (Sanction no. UGC/750/Jr. Fellow Sc.2000/
2001).
References
[1] (a) J.-P. Costes, G. Cros, M.-H. Darbieu, J.-P. Laurent, Inorg.
Chim. Acta 60 (1982) 111;
5. Supplementary material
(b) G. Cros, J.-P. Costes, C.R. Acad. Sci. II 294 (1982) 173.
[2] M. Kwiatkowski, E. Kwiatkowski, A. Olechnowiez, D.M. Ho, E.
Deutsch, Inorg. Chim. Acta 150 (1988) 65.
Crystallographic data for the structural analysis have
been deposited with the Cambridge Crystallographic
data Centre, CCDC Nos. 179038 (complex 1), 179837
(complex 2), 179039 (complex 3). Copies of this
information may be obtained free of charge from The
Director, CCDC, 12 Union Road, Cambridge, CB2
[3] (a) J.-P. Costes, Inorg. Chim. Acta 130 (1987) 17;
(b) E. Kwiatkowski, M. Kwiatkowski, A. Olechnowiez, Inorg.
Chim. Acta 90 (1984) 145;
(c) H. Adams, N.A. Bailey, I.S. Bard, D.E. Fenton, J.-P. Costes,
G. Cros, J.-P. Laurent, Inorg. Chim. Acta 101 (1985) 7;
(d) E. Kwiatkowski, M. Kwiatkowski, Inorg. Chim. Acta 117
(1986) 145;
1EZ, UK (fax: ꢀ
/
44-1223-336033; e-mail: deposit@
ccdc.cam.ac.uk or www: http://www.ccdc.cam.ac.uk).
(e) M. Kwiatkowski, G. Bandoli, J. Chem. Soc., Dalton Trans.

624
M.S. Ray et al. / Polyhedron 22 (2003) 617ꢁ624
/
(1992) 379.;
[9] A. Altomare, G. Cascarano, C. Giacovazzo, A. Guagliardi,
A.G.G. Moliterni, M.C. Burla, G. Polidori, M. Camalli, R.
Spagna, Private Communication, 1997.
(f) M. Kwiatkowski, E. Kwiatkowski, A. Olechnowiez, D.M. Ho,
E. Deutsch, J. Chem. Soc., Dalton Trans. (1990) 2497.;
(g) M. Kwiatkowski, E. Kwiatkowski, A. Olechnowiez, D.M. Ho,
E. Deutsch, J. Chem. Soc., Dalton Trans. (1990) 3063.;
(h) N. Matsumoto, S. Yamashita, A. Ohyoshi, S. Kohata, H.
Okawa, J. Chem. Soc., Dalton Trans. (1988) 1943.;
(i) N. Matsumoto, H. Murakami, T. Akui, J. Honto, H. Okawa,
A. Ohyoshi, Bull. Chem. Soc. Jpn. 59 (1986) 1609;
(j) T. Nagahara, M. Suzuki, K. Kasuga, Inorg. Chim. Acta 149
(1988) 279;
[10] G.M. Sheldrick, in: SHELX 97, Program for the Refinement
of Crystal Structure, University of Gottingen, Germany,
1997.
¨
[11] D.T. Cromer, J.T. Weber, International Tables for X-ray Crystal-
lography, vol. IV (Table 2.2A), The Kynoch Press, Birmingham,
UK, 1994, p. 2.
[12] J.A. Ibers, W.C. Hamilton, Acta Crystallogr. 17 (1964) 781.
[13] L.J. Farrugia, ORTEP-3 for WINDOWS, University of Glasgow,
Scotland, UK, 1999.
(k) C.T. Brewer, G. Brewer, J. Chem. Soc., Chem. Commun.
(1988) 85.;
[14] (a) F.A. Cotton, J.J. Wise, Inorg. Chem. 5 (1967) 1200;
(b) B.J. Hathaway, D.E. Billing, R.J. Dudly, J. Chem. Soc. A
(1970) 1420.
(l) E. Kwiatkowski, M. Kwiatkowski, Inorg. Chim. Acta 82
(1984) 101.
[4] N. Matsumoto, T. Akui, H. Murakami, J. Kanesaka, A. Ohyoshi,
H. Okawa, J. Chem. Soc., Dalton Trans. (1988) 1021.
[5] R.C. Elder, E.A. Blubaugh, Jr., W.R. Heinmann, P.J. Brukeand,
R.D. McMillian, Inorg. Chem. 22 (1983) 2771.
[15] R. Shukla, S. Mondal, P.K. Bharadwaj, Polyhedron 11 (1992)
1837.
[16] D. Cremer, J.A. Pople, J. Am. Chem. Soc. 97 (1975) 1354.
[17] J.C.A. Boyens, J. Cryst. Mol. Struct. 8 (1978) 31.
[18] (a) E.O. Schlemper, R.K. Murmann, M.S. Hussain, Acta
Crystallgr., Sect. C 42 (1986) 1739;
[6] (a) W.P.J. Gaykema, A. Volveda, W.J.H. Hol, J. Mol. Biol. 187
(1985) 2255;
(b) W.P.J. Gaykema, W.G.H. Hol, J. Mol. Biol. 209 (1989) 249.
[7] (a) M.R. Bermejo, A.G. Deibe, M. Rey, J. Sanmartin, A. Sousa,
N. Aurangzeb, C.E. Hulme, C.A. McAuliffe, R.G. Pritchard, M.
Watkinson, M. Helliwell, J. Chem. Soc., Dalton Trans. (1994)
1265;
(b) M.S. Hussain, E.O. Schlemper, Inorg. Chem. 18 (1979)
2275;
(c) J.F. McConnel, M.J. Lacey, C.G. Macdonald, J.S. Shanon,
Acta Crystallogr., Sect. B 29 (1973) 2477.
[19] M. Calligaris, G. Nardin, L. Randaccio, Coord. Chem. Rev. 7
(1972) 385.
(b) A.G. Deibe, A. Sousa, M.R. Bermejo, P.P. MacRory, C.A.
McAuliffe, R.G. Pritchard, M. Helliwell, J. Chem. Soc., Chem.
Commun. (1991) 728.
[20] T. Kikuchi, C. Kabuto, H. Yokoi, M. Iwaizumi, W. Mori, J.
Chem. Soc., Chem. Commun. (1983) 1306.
[8] Vogel’s A Text Book of Quantitative Analysis, fifth ed., Longman
Scientific and Technical, New York, 1989, p. 689.
[21] R.J. Fessenden, J.S. Fessenden, Organic Chemistry, 3rd ed,
Brooks/Cole Publishing Company, Monterey, CA, 1986.