Synthesis and characterization of new Cu(II) complexes derived from benzilic and mandelic hydrazones

Article abstract of DOI:10.1081/SIM-100001935

Two new sets of Cu(II) complexes with newly synthesised benzilic and mandelic hydrazone derivatives were prepared in the mole ratios 1:1 and 1:2 (Cu:L). The structure of the complexes was identified on the basis of the data obtained from elemental and the

Full text of DOI:10.1081/SIM-100001935

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SYNTHESIS AND CHARACTERIZATION OF NEW Cu(II)
COMPLEXES DERIVED FROM BENZILIC AND MANDELIC
HYDRAZONES
R. M. Issa a , S. A. Abdel-Latif b & H. A. Abdel-Salam a
a Chemistry Department, Faculty of Science, Tanta University, Tanta, Egypt
b Chemistry Department, Faculty of Science, Helwan University, Cairo, Egypt
Published online: 20 Aug 2006.
To cite this article: R. M. Issa , S. A. Abdel-Latif & H. A. Abdel-Salam (2001): SYNTHESIS AND CHARACTERIZATION OF NEW
Cu(II) COMPLEXES DERIVED FROM BENZILIC AND MANDELIC HYDRAZONES, Synthesis and Reactivity in Inorganic and Metal-
Organic Chemistry, 31:1, 95-105
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SYNTH. REACT. INORG. MET.-ORG. CHEM., 31(1), 95–105 (2001)
SYNTHESIS AND CHARACTERIZATION OF
NEW Cu(II) COMPLEXES DERIVED FROM
BENZILIC AND MANDELIC HYDRAZONES
R. M. Issa,1 S. A. Abdel-Latif,2,∗
and H. A. Abdel-Salam1
1Chemistry Department, Faculty of Science,
Tanta University, Tanta, Egypt
2Chemistry Department, Faculty of Science,
Helwan University, Cairo, Egypt
ABSTRACT
Two new sets of Cu(II) complexes with newly synthesised
benzilic and mandelic hydrazone derivatives were prepared in the
mole ratios 1:1 and 1:2 (Cu:L). The structure of the complexes
was identified on the basis of the data obtained from elemental and
thermal analyses as well as IR, UV-visible, ESR spectra, and X-ray
diffraction. The results indicate that the ligands are tightly bound
to the metal ion through the phenolic OH oxygen, the azomethine
nitrogen, and the enolic OH oxygen in case of the 1:1 complexes
while for the 1:2 complexes the enolic OH group did not participate
in bonding. The complexes have elongated octahedral as well as
square-planar symmetries.
∗Corresponding author. E-mail: saalatif@halpha.hun.euu.eg
95
Copyright ꢀ 2001 by Marcel Dekker, Inc.
www.dekker.com
C

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ISSA, ABDEL-LATIF, AND ABDEL-SALAM
O
O
C
C
Cu++
Cu++
NH
N
N
N
(I)
(II)
Figure 1. Ketonic (I) and enolic (II) structures of the hydrazone part of the complexes
with copper ions.
INTRODUCTION
The interest in studying the hydrazides of organic acids and their deriva-
tives arises from the fact that most of these compounds have relevant biological
properties such as virus inhibitors (1), analgesics (2), antitumor agents (3), anti-
radiation drugs (4), and other pharmacological activities. The biological activity
of hydrazides was ascribed to their ability to form chelates with transition metal
ions (5). Transition metal ion complexes with arylhydrazones have found many
applications as catalysts in various chemical and photochemical reactions as well
as in some biological systems (6). The use of arylhydrazone complexes in a given
reaction depends to a great extent on their molecular structure. The structure of
metal chelates with arylhydrazones drew the attention of many investigators, since
the ligand can retain its ketonic structure (I) or react with the metal ion in the enolic
form (II) as shown in Figure 1 for copper ions.
The reactivity of the metal complex in biological systems was found to de-
pend on its structure. The structure of the ligand in the complex was also found to be
dependent on the nature of the anion of the metal salt used and the alkalinity of the
medium (7–10). Also, arylhydrazones have been used for the spectrophotometric
determination of some metal ions (11,12).
The present work is concerned with the preparation of some new Cu(II)
complexes of benzilic and mandelic hydrazones (Fig. 2)
OH
O
HO
H
C
C
X
C
Y
NH
N
Figure 2. Structure of benzilic and mandelic hydrazones. X = C6H5 for benzilic hydra-
zones and H for mandelic hydrazones; Y = H (H3L1), 4-OH (H4L2) or C6H4 (H3L3) for
benzilic hydrazones; Y = H (H3L4), 4-OH (H4L5) or C6H4 (H3L6) for mandelic hydrazones.

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97
The complexes were identified on the basis of the data obtained from ele-
mental and thermal analyses, IR, UV-visible, ESR spectra, and X-ray diffraction.
EXPERIMENTAL
All chemicals used in the present work were chemically pure from BDH
Chemicals. The ligands utilised were prepared by the condensation of benzilic
or mandelic hydrazide with salicylaldehyde, 2,4-dihydroxybenzaldehyde, or 2-
hydroxy-1-naphthaldehyde following a known procedure using ethanol as solvent
(13,14). After refluxing the reaction mixture for 2 h on a water bath, the respec-
tive hydrazones separated on cooling. The compounds were filtered, recrystallized
from ethanol and then dried in a desiccator over silica gel. The purity of the lig-
ands under investigation has been confirmed by a sharp melting point, elemental
analyses (Table 1), IR, electronic, and 1H NMR spectra.
The Cu(II) complexes were prepared by mixing the ligands (0.01 or 0.02 mol
in 100 mL ethanol) with anhydrous Cu(II) acetate (0.01 mol, 1.8164 g) in 100
mL ethanol. The mixture was refluxed for 8 h on a water bath, then cooled to
a room temperature. The solid complexes which separated were filtered, washed
with ethanol, and dried in a desiccator over silica gel. The apparatus and working
procedures were the same as described previously (15).
RESULTS AND DISCUSSION
The 1:1 and 1:2 (Cu:L) complexes were prepared as shown in the experi-
mental part according to the following equations:
Table 1. Analytical Data of Benzilic and Mandelic Hydrazone Derivatives
%C
%H
%N
Melting
Point
(◦C)
Empirical Formula
Formula
%
Found
(Calc.)
Found
(Calc.)
Found
(Calc.)
Cpd.
Weight Yield Colora
Benzilic hydrazone derivatives
H3L1 C21H18N2O3
H4L2 C21H18N2O4
H3L3 C25H20N2O3
346
362
396
75
80
65
p.y. 211–212 72.39 (72.83) 5.09 (5.20) 7.57 (8.09)
p.y. 261–262 69.45 (69.61) 5.09 (4.97) 7.66 (7.73)
y.
265–267 75.42 (75.76) 5.70 (5.05) 7.16 (7.07)
Mandelic hydrazone derivatives
H3L4 C15H14N2O3
H4L5 C15H14N2O4
H3L6 C19H16N2O3
270
286
320
70
65
75
w.
p.o. 215–216 62.84 (62.94) 5.01 (4.90) 9.72 (9.79)
y. 242–243 70.99 (71.25) 5.49 (5.00) 8.73 (8.75)
180–181 66.53 (66.67) 5.30 (5.19) 10.55 (10.37)
ap.y.: pale yellow, Y.: yellow, w.: white, p.o.: pale orange.

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ISSA, ABDEL-LATIF, AND ABDEL-SALAM
For benzilic hydrazone (1:1) complexes:
H3L1 + Cu2+ → [Cu(HL1)] + 2H+
H4L2 + Cu2+ → [Cu(H2L2)] + 2H+
H3L3 + Cu2+ → [Cu(HL3)] + 2H+
for 1:2 complexes as follows:
2H3L1 + Cu2+ → [Cu(H2L1)2] + 2H+
2H4L2 + Cu2+ → [Cu(H3L2)2] + 2H+
2H3L3 + Cu2+ → [Cu(H2L3)2] + 2H+
while for mandelic hydrazone (1:1) complexes:
H3L4 + Cu2+ → [Cu(HL4)] + 2H+
H4L5 + Cu2+ → [Cu(H2L5] + 2H+
H3L6 + Cu2+ → [Cu(HL6)] + 2H+
for 1:2 complexes as follows:
2H3L4 + Cu2+ → [Cu(H2L4)2] + 2H+
2H4L5 + Cu2+ → [Cu(H3L5)2] + 2H+
2H3L6 + Cu2+ → [Cu(H2L6)2 + 2H+
The physico–chemical data of the ligands are summarized in Table 1. The results
of elemental analyses of the complexes (Table 2) show that they include one or
more water or ethanol molecules. These solvent molecules are not removed in
vacuo for three hours at room temperature.
Thermogravimetric and Differential Thermal Analyses
Thermogravimetric(TG) and differential thermal (DTA) analyses of the
[Cu(H2L6)2(EtOH)2] complex (Table 3) indicated that the ethanol molecules as-
sociated with the complex are removed within the 100–240 and 240–260◦C tem-
perature ranges. Hence, these solvent molecules are involved in the coordination
sphere. Decomposition of the nonsolvated complex started at 375◦C, the DTA
curve of the complex exhibits two exothermic peaks at 220 and 250◦C. The first
is due to the removal of the ethanol molecules leading to the desolvated complex
which underwent some lattice rearrangement at the second step. Finally, thermal
decomposition of the complex gave a broad exothermic peak in the 330–375◦C
range leading to CuO as the final product.

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99

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ISSA, ABDEL-LATIF, AND ABDEL-SALAM
Table 3. TG-DTA of Mandelic Hydrazone Cu(II) 1:2 Complexes
Temperature, ◦C
%loss
Decomp.
Init
Temp.
TG
DTA
Complex
Cu-lig. Core Thermal step Exo Found Calc. Assignment
[Cu(H2L6)2
(EtOH)2]
50
–
280
–
100–240
240–260
260–280
280–375
375
220
5.84 5.81 Coordinated
EtOH
[Cu(H2L6)2
EtOH]
250 11.67 11.62 Coordinated
EtOH
[Cu(H2L6)2]
–
–
–
–
–
–
–
Thermal
stability
[Cu(H2L6)+
–
–
51.56 51.80 One molecule
of ligand
–
–
–
–
Decomp. and
formation of
Cu2O
Infrared Spectra
The IR spectra (Table 4) of all of the complexes exhibit a broad band within
the range 3550–3300 cm−1, which is assigned to ν(OH) of solvent (ethanol or
water) molecules associated with the Cu(II) ions in the complexes; the ν(NH)
band at 3301–3260 cm−1 and the ν(C O) band at 1674–1650 cm−1 in the spectra
=
of the free ligands are absent in the spectra of the (1:1) complexes with HL1,
H2L2, HL4, H2L5, HL6 indicating that they are bound to Cu(II) ions in the enolic
form. The ν(OH) bands of the phenolic (3230–3180 cm−1) and enolic groups
(3070–3050 cm−1) in the spectra of the free ligands are absent in those of the
Cu(II) complexes. This denotes that Cu(II) ions are bound to the ligands through
displacement of protons of these two OH groups. This assumption finds support
in the disappearance of the ν(C–H) ligand bands at 1060–1050 cm−1 and δ(OH)
−1
at 1350–1270 cm−1 on complex formation. The ν(C N) band at 1640 cm in
=
the spectra of the ligands is split into two bands, one at 1640 cm−1 while the
second is located at 1617–1609 cm−1; this shift denotes the coordination of Cu(II)
through one azomethine nitrogen, most probably that of the hydrazone. The ν(OH)
of the alcoholic group at 3270–3220 cm−1 in the spectra of the free ligands is still
observed at the same position for the Cu(II) complexes, indicating that this group
does not participate in the bonding between the ligands and Cu(II) ions.
According tothe results of the IR spectral study of the 1:1 complexes, the
bonding of Cu(II) to the ligands takes place through two covalent bonds, with
the oxygen of the phenolic and enolic OH groups and a coordinative bond to
the azomethine nitrogen atom of the hydrazone. Thus, the hydrazones behave as
dibasic tridentate ligands. The suggested mode of bonding is further supported by

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101

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ISSA, ABDEL-LATIF, AND ABDEL-SALAM
the appearance of two new bands at 532–465 and 377–329 cm−1 in the spectra of
–
–
the complexes, which are assigned to ν(Cu O) and ν(Cu N), respectively (16).
The spectra of the 1:2 complexes display a behaviour that is somewhat different
from that of the 1:1 complexes. The bands due to ν(OH) alcohol, ν(OH) enol,
ν(NH) (3300–3260 cm−1), and ν(C O) display only small changes in their posi-
tions, indicating that these groups do not coordinate to Cu(II). Also, the ligand is
coordinated to the central metal ion in the ketonic form.
=
=
The ν(OH)phenolic is absent in the spectra of the complexes and the ν(C N)
band is shifted to lower wave numbers by 32–21 cm−1 which reveals that Cu(II)
is bonded to the ligands through coordination bonds with the azomethine nitrogen
of the hydrazone part and the oxygen of the deprotonated phenolic group. This is
confirmed by the appearance of two new bands at 479–450 and 380–330 cm−1 in
–
–
the spectra of the complexes which are assigned to ν(Cu O) and ν(Cu N) modes
(16). Thus, in the 1:2 complexes the hydrazones behave as monobasic bidentate
ligands.
Electronic Absorption Spectra
The electronic absorption spectra of the complexes under study were mea-
sured as Nujol mulls and in DMF solution. The results (Table 4) are very similar,
indicating that no changes in their geometry occur on going from the solid state
to solution. The spectra exhibit one or two broad bands at 600–650 nm (2B1g
→
2B1g) and 800–850 nm (2B1g →2Eg). The spectral patterns indicate a tetragonally
elongated octahedral geometry.
Electron Spin Resonance
The X-band ESR spectra of the Cu(II) hydrazone complexes at room tem-
perature generally show one broad signal which is split in some cases into two or
three signals (Table 2). These complexes are not magnetically dilute, therefore, ex-
change and/or dipolar forces are expected to operate in such a case, the anisotropy
is likely to be reduced. This appears to be the case for [Cu(H2L1)2]EtOH and
[Cu(HL4)H2O complexes, where only a single EPR line is observed. The appar-
ent broadening of the EPR signals may be due to an interaction between Cu(II)
ions which are probably present in nonequivalent lattice positions. The giso value
forcomplexes([Cu(H2L5)H2O(EtOH)2], [Cu(H3L5)2(EtOH)2], [Cu(H2L1)2EtOH,
and [Cu(H3L2)2(H2O)2]2H2O, relative to the other complexes, [Cu(HL1)EtOH],
[Cu(H2L2)EtOH]H2O, [Cu(H2L3)2]-EtOH, [Cu(H2L4)2]H2O, [Cu(HL6)]EtOH,
and [Cu(H2L6)2(EtOH)2], may be attributed to a varied electron donating effect
of the group attached to the hydrazone molecule (17,18). The positive shift of giso

ORDER
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NEW Cu(II) COMPLEXES
103
from that of the free electron (2.0023) indicates a high covalent character of the
bonding between the Cu(II) ions and the hydrazone ligands (19).
X-Ray Diffraction
On comparing the X-ray diffraction pattern of the complexes under study
with those of the free ligands, the following may be pointed out: The diffraction
patterns of the Cu(II) complexes are totally different in terms of the interplanar
❛
❛
distances d, Aand relative intensities I/I from those of the corresponding ligands.
This proves complex formation between Cu(II) ions and the hydrazone ligands.
❛
❛
The change in d, A, and I/ Iis attributed to differences in the structures, such
as the contribution of solvent molecules to the lattice structure and the different
orientation of the ligands around the metal ion (20), the various spherical rotations
around the lattice axes, diffraction planes, and transition group operations (21,22).
The relatively high background and the broadening of the diffraction lines in
the patterns of the complexes reflect a crystalline structure and strain occurring
in the crystal lattice. This results from the orientation of the ligand molecules
around the central Cu(II) ions or the distortion of the coordination polyhedron
around the central metal ion (16). The diffraction patterns of the 1:1 complexes
[Cu(HL1)EtOH] and [Cu(HL4)H2O] differ completely from the corresponding 1:2
complexes [Cu(H2L1)2]EtOH and [Cu(H2L4)2]H2O.
CONCLUSION
Based on the knowledge gained from the results of the various methods used,
the structures of the Cu(II) complexes with Benzilic and Mandelic hydrazones for
the 1:1 complexes are square-planar for [Cu(HL1)-EtOH], [Cu(H2L2)EtOH]H2O,
[Cu(HL4)H2O] and [Cu(HL6)EtOH] as shown in Figure 3 and for the 1:2 com-
plexes [Cu(H2L1)2]EtOH, [Cu(H2L4)2]H2O and [Cu(H2L3)2]EtOH as shown in
S
O
O
S
OH
Cu
N
S
C
X
C
Y
N
CH
S = solvent (H2O or EtOH)
Figure 3. The structural formula of the 1:1 complexes formed between Cu(II) ions and
the benzilic or mandelic hydrazones.

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ISSA, ABDEL-LATIF, AND ABDEL-SALAM
O
C
C
N
NH
OH
CH
Y
S
Cu
S
O
O
N
CH
Y
OH
C
NH
C
O
X
S = solvent (H2O or EtOH)
Figure 4. The 1:2 complexes of Cu(II) ions with benzilic or mandelic hydrazones.
Figure 4, while for the 1:1 complex [Cu(H2L5) H2O(EtOH)2] and the 1:2 com-
plex [Cu(H3L2)2(H2O)2]2H2O, [Cu(H3L5)2-(EtOH)2] and [Cu(H2L6)2(EtOH)2]
an elongated octahedral structure is assigned as shown in Figures 3 and 4.
Axial solvent molecules are present in case of the 1:1 complexes [Cu(H2L5)-
H2O(EtOH)2] and [Cu(H3L2)2(H2O)2]2H2O, [Cu(H3L5)2(EtOH)2] and [Cu-
(H2L6)2(EtOH)2] but no solvent molecules are present in the other complexes.
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Received June 16, 2000
Accepted October 27, 2000
Referee I: R. C. Thompson
Referee II: S. E. Lincoln

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