UV-visible spectroscopic study of the salicyladehyde benzoylhydrazone and its cobalt complexes

Article abstract of DOI:10.1016/j.saa.2005.12.032

Salicyladehyde benzoylhydrazone (SBH) has three groups suitable for forming coordination bond with transition metal. The UV-vis absorption spectra of SBH and its Co(II) complexes in various media were studied by using the deconvolution method. It is found that the structure of complex in solution is different from those in solid crystals. The nature of complexes in solution depends on acidity of the phenolic proton of SBH and on the medium. In neutral or slightly acid medium, the SBH is a non-charged bidentate ligand. And the free hydroxyl group on the SBH molecule makes it possible to form hydrogen bonds in solution. In basic medium, the SBH is a mono, negatively charged tridentates ligand.

Full text of DOI:10.1016/j.saa.2005.12.032

Spectrochimica Acta Part A 65 (2006) 695–701
UV–visible spectroscopic study of the salicyladehyde
benzoylhydrazone and its cobalt complexes
Yi-Heng Lub, Yu-Wei Lua,∗, Cheng-Li Wub, Qun Shaob, Xiao-Ling Chenb,
Rosa Ngo Biboum Bimbonga
a Laboratoire de Chimie Physique, Electrochimie et Photoe´lectrochimie, CNRS UMR 8000, Baˆtiment 350, Universite´ Paris XI, 91405 Orsay Cedex, France
b Department of Chemical Engineering, Anhui University of Science and Technology, 232001 Huainan, Anhui, China
Received 14 October 2005; received in revised form 15 December 2005; accepted 16 December 2005
Abstract
Salicyladehyde benzoylhydrazone (SBH) has three groups suitable for forming coordination bond with transition metal. The UV–vis absorption
spectra of SBH and its Co(II) complexes in various media were studied by using the deconvolution method. It is found that the structure of complex
in solution is different from those in solid crystals. The nature of complexes in solution depends on acidity of the phenolic proton of SBH and on
the medium. In neutral or slightly acid medium, the SBH is a non-charged bidentate ligand. And the “free” hydroxyl group on the SBH molecule
makes it possible to form hydrogen bonds in solution. In basic medium, the SBH is a mono, negatively charged tridentates ligand.
© 2005 Elsevier B.V. All rights reserved.
Keywords: Gaussian deconvolution; UV–vis spectra; Hydrogen bond; Ligand; Salicyladehyde benzoylhydrazone
1. Introduction
SBH can also be used as an analogue to understand the reaction
mechanism of vitamin B12 [6].
In recent years, the metallic complexes of salicyladehyde
benzoylhydrazone (or N-salicylidene benzoylhydrazine), abbre-
viated as SBH, continues to generate considerable attention for
its biological activities, physicochemical properties and indus-
trial applications. SBH is one of the important Schiff bases,
which can react with a large variety of transition metal cations
and thus, form a great number of complexes [1]. It is reported
that SBH facilitates the trace metal analysis as a fluorescence
chromophore [2]. And also, as iron-chelating agent, SBH can
eliminate the excess of iron from the human body caused
by repeated blood transfusion, genetic disorders such as tha-
lassemia or cancers. It is a reference in the pharmacological
study for pyridoxal isonicotinoyl hydrazone, which is a substi-
tute of the drug “Desferrioxamine” [3]. The SBH complex of
copper has an antitumour activity; it is a potential inhibiter of
DNA synthesis and cell growth in a variety of human and rodent
cell lines [4]. The vanadium complexes can imitate the action
of some enzymes and are used in the treatment of diabetes [5].
The biological studies showed that the hydrogen bond plays
an extremely important role in these biological processes [4,7],
but for the SBH complexes, such as those described above, they
do not have any chance to form hydrogen bond (Scheme 1).
Indeed, in the solid state, each of the three chelating groups of
SBH, the hydroxyl of phenol, the nitrogen of azomethine and the
carbonyl of benzoylhydrazine, form a coordination bond with
metallic cation [1,4,9]. If the hydrogen bonds are formed with
the complexes M(SBH), it means that the structure of the com-
plexes in solution is different from those in solid state that are
reached by X-ray analysis. However, to the best of our knowl-
edge, no publication tried to show the structure of the complexes
in solution. The majority of the interesting complexes are para-
magnetic, which makes it difficult to use NMR to study the
structure in solution [1].
We are more particularly interested in the behaviour of the
intra and intermolecular hydrogen bond of SBH [8,10]. We
analysed the composition of the UV–vis absorption spectra of
the SBH and its complexes of cobalt formed in solution. The
comparison of SBH spectra in various media with those of the
complexes enabled us to identify the chromophore groups and
to deduce the nature of coordination bond formed between SBH
and cobalt.
∗
Corresponding author. Tel.: +33 1 69 15 47 32; fax: +33 1 69 15 43 28.
E-mail address: yuwei.lu@lcp.u-psud.fr (Y.-W. Lu).
1386-1425/$ – see front matter © 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2005.12.032

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Y.-H. Lu et al. / Spectrochimica Acta Part A 65 (2006) 695–701
Scheme 1. Structure of complex M–SBH.
2. Experimental section
The SBH and the complex Co(SBH)(AcO) were synthesized
and characterized by the methods described in the literature
[8,10].
All reagents (NaClO4, AcONa, NaOH, MeOH, Co(AcO)2
are Normapur quality of VWR.
Fig. 1. Evolution of UV–vis absorption spectra of SBH in the presence of 0,
0.5, 1 and 1.5 times of equivalent of cobalt(II). The figure presents only the most
interesting part of the spectra between 200 and 500 nm.
The solutions electrolytes containing 0.1 M NaClO4, 0.1 M
AcONa and 0.1 M NaClO4 + 10−3 M NaOH in MeOH are pre-
pared from NaClO4, AcONa and NaOH without titration. The
mother solution of SBH is prepared by dissolution of SBH in
MeOH. It was titrated by NaOH in MeOH containing 0.1 M
NaClO4. The mother solution of Co(AcO)2 is prepared by dis-
solution of Co(AcO)2 in MeOH, and is titrated by flame atomic
spectroscopy.
3.2. Comprehension of spectrum of SBH
To deduce the complex SBH–Co structure in solution, it is
necessary to understand the UV–vis spectrum of the ligand. SBH
is formed by condensation between salicylaldehyde and ben-
zoylhydrazine, thus UV–vis spectrum of SBH must have some
resemblance with the spectra of original molecules. Figs. 4 and 5
show the UV–vis spectra of SBH, benzoylhydrazine and sali-
cylaldehyde with concentration of 2 × 10−5 M in MeOH. The
benzoylhydrazine gives only one peak at 225 nm in the domain
from 200 to 800 nm. The salicylaldehyde has three absorption
bands in the same region, which are at 213, 255 and 324 nm,
respectively. The absorption band of the aromatic ring is located
at a wavelength lower than 200 nm. The ␲→␲* transition of
C O on the aldehyde group is located at 255 nm. Because
of the presence of intramolecular hydrogen bond between the
phenolic hydroxyl and the carbonyl of aldehyde, the molecule
presents a dienyl ␲→␲* transition of HC CH CH CH around
217 nm and enonyl transition of C C C O around 325 nm.
One of the absorption band of benzoylhydrazone is around
224 nm that for C O on amide group and another absorption
band for the aromatic ring is lower than 200 nm. By comparison
of the absorption bands, Scheme 2 gives the attribution of the
absorption bands. The SBH presents four important transitions,
which are at 212, 234, 282, 328 nm, respectively, and two small
bands at 286 and 297 nm. The replacement of C O by C N
reinforces the intramolecular hydrogen bonding, the absorp-
tion band shifts to red and the intensity increases. This tran-
sition has more characteristic of O C C C (NH) than that of
(HO) C C C N, indicating that the nitrogen has more affinity
for hydrogen than oxygen. The band at 328 nm is then assigned
to the enonyl transition of O C C C (NH) and the band at
212 nm is assigned to the dienyl transition of HC CH CH CH.
The band at 286 nm is attributed to azomethine C N bond
and the band at 234 nm is assigned to C O of benzoylhydra-
zone.
The UV–vis spectra were recorded using Perkin Elmer
Lamda 19 spectrometer controlled by computer. The experi-
ments were carried out at the ambient temperature.
2.1. Preparation of solution for the spectroscopic study
Firstly, 3 ml MeOH or electrolyte solution were added in
a spectroscopic quartz cell with 1000 cm optical path, then
4–10 ␮l of SBH mother solution (approximately 1.2 × 10−3 M)
was added in, after that, cobalt mother solution (1.6 × 10−3 M)
was added step by step. The UV–vis spectra are recorded after
each addition of cobalt solution.
3. Result and discussion
3.1. Evolution of UV–vis spectra of the SBH in the presence
of cobalt
Fig. 1 illustrates the evolution of the UV–vis spectra of the
SBH in the presence of cobalt. In the exploited wavelength
domain from 200 to 800 nm, SBH in MeOH gives four max-
imum of absorption at 234.4, 286.1, 297.2 and 329.1 nm. When
cobalt(II) solution was added, the absorbance of SBH peaks
decrease and two last peaks have a red shift. New peaks at 226.7,
258.5, 300.7 and 382.5 nm appeared. The intensity of these new
peaks increased with the increase of cobalt(II) concentration and
reaches a maximum when the volume of equivalence reached.
Beyondthevolumeofequivalence, thespectrumdoesnotchange
any more, even in the presence of 2.5 times of cobalt(II) equiv-
alence. The evolution of spectra indicates that the Co(II)–SBH
complexes were formed during the addition of cobalt(II), and
the reaction is almost complete at equivalence volume.

Y.-H. Lu et al. / Spectrochimica Acta Part A 65 (2006) 695–701
697
Scheme 2. Distribution of the absorption bands to the molecules BSH in MeOH.
3.3. Gaussian deconvolution of the UV–vis absorption
spectra of SBH [11–13]
Fig. 2 shows that the UV–vis spectrum of SBH in MeOH
can be regarded as a sum of seven Gaussian peaks. Table 1
gathers the parameters of each Gaussian peak. Due to the limited
data number, it is difficult to distinguish the peak at 212 nm and
the transitions at wavelength lower than 200 nm mathematically.
The first Gaussian peak is then used to correct the baseline,
which comprises all absorptions with low wavelength. From
deconvolution, it can be observed that there are four important
transitions at 238.33, 285.41 and 330.36 nm, and three weak
transitions at 286.49, 298.11 and 393.99 nm.
3.4. Influence of media on the UV–vis spectrum of SBH and
identification of chromophore group
Fig. 2. Deconvolution of the UV–vis spectrum of SBH in MeOH
(CSBH = 4.16 × 10−5 M). The figure presents only the most interesting part of
the spectrum between 200 and 600 nm.
Fig. 3 shows the UV–vis spectra and their deconvolution of
the SBH in three different methanol solutions containing 0.1 M
NaClO4, 0.1 M NaAcO and 0.1 M NaClO4 + 10−3 M NaOH,
respectively. The peak at 286.49 nm is very weak, particu-
larly, in diluted solutions; it is difficult to assign a Gaussian
peak mathematically. Thus, it is then neglected at the time of
deconvolution. Table 3 gathers the characteristic parameters of
Gaussian peaks, which compose the UV–vis spectra of SBH. For
SBH in MeOH, the characteristic values in Table 2 are slightly
different from those in Table 1 because these values are recal-
culated without taking into account the influence of peak at
286.49 nm. But the variations are negligible for the important
transitions.
Table 1
Characteristics of Gaussian peaks composing the UV–vis spectrum of the SBH
in MeOH (CSBH = 4.16 × 10−5 M)
λ
ω
A
ε
1
2
3
4
5
6
7
186.24
238.33
285.41
286.49
298.11
330.36
393.99
30.66
7.65
15.41
3.15
3.31
15.00
12.25
0.85506
0.25345
0.53465
0.08992
0.18614
0.44404
0.00888
6.09 × 103
12.85 × 103
2.16 × 103
4.47 × 103
10.67 × 103
0.23 × 103
Table 2
Characteristic values of Gaussian peaks composing the UV–vis spectra of SBH
MeOH
NaClO4 0.1 M
AcONa 0.1 M
NaClO4 0.1 M + NaOH 10−3 M
Chromophore concerned
1
2
3
4
5
6
238.19 (6.90)
286.74 (14.11)
298.52 (2.65)
330.29 (14.96)
237.74 (7.10)
286.62 (13.89)
298.47 (2.70)
329.83 (14.91)
237.39 (7.64)
286.69 (13.95)
298.54 (2.71)
330.09 (15.25)
225.57 (21.30)
291.23 (18.40)
298.12 (2.47)
333.75 (14.08)
372.41 (26.56)
435.05 (15.21)
C
C
O amide
N-
Aromatic nucleus
O
C
C
C
C
C-N (H)
C–C
C C N(H) (cyclic)
(−O)
(H)O
N
397.80 (12.32)
397.27 (11.36)
391.70 (14.07)

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Y.-H. Lu et al. / Spectrochimica Acta Part A 65 (2006) 695–701
Scheme 3. Equilibrium of deprotonated SBH.
In MeOH alone or in the presence of NaClO4, AcONa, the
UV–vis spectra of the SBH are similar. The Gaussian peaks
that composed them have similar positions and widths. This
suggests that in these neutral and slightly basic media, SBH
always has the same form and the chromophore groups are not
influenced either by the presence of sodium or by the presence
of acetate or perchlorate. This result confirms the existence
of intramolecular hydrogen bond between the phenolic pro-
ton and the nitrogen of azomethine, because acetate is a weak
base and is not capable to take the proton from OH of phe-
nol.
In MeOH containing NaOH, the spectrum of SBH changed.
A new band appeared at 373 nm, which is certainly due to the
deprotonation of phenol. The ionization makes the hydrogen
bond between phenol and azomethine disappear.
By examining the position and the width of Gaussian remain-
ing, it can be concluded that SBH approximately keeps its non-
ionic characteristics. Ionization primarily influenced the absorp-
tion of chromophore at 238 nm (−13 nm), 286 nm (+5 nm) and
330 nm (+3 nm). It does not affect the absorption of chro-
mophore at 298 nm, which indicated that this chromophore is
not concerned by the resonance effect in the molecule. The
coexistence of the peaks at 334 and 373 nm shows an equi-
librium (Scheme 3). Another group that is more influenced
by this equilibrium is the carbonyl benzoylhydrazine, which
reacted preferably with sodium. It was reported that the carbonyl
group in SBH molecular reacted preferably with potassium,
and then the hydroxyl group in SBH interacted with hydrox-
ide of the potassium hydroxide when an aqueous potassium
hydroxide was dropped in the SBH solution of DMSO–H2O
[8].
The evolution of the peak width reinforces this deduction.
Indeed, the peak width changes in the same direction as the
displacement of the peak position following the interaction. It
passes from 7 to 21 nm (+15 nm) for the peak at 238 nm and
from 14 to 18 nm (+4 nm) for the peak at 286 nm. It varies little
for the group at 298 nm (0.2 nm) and the chromophore at 330 nm
(1 nm). However the peak width depends on the degeneracy of
the levels. The larger the width, the more are the intermediate
states.
Fig. 3. Deconvolution of UV–vis absorption spectrum of SBH in MeOH,
from top to bottom, containing (a) 0.1 M NaClO4, CSBH = 1.60 × 10−5 M; (b)
0.1 M AcONa, CSBH = 2.00 × 10−5 M; and (c) 0.1 M NaClO4 + 10−3 M NaOH,
CSBH = 2.00 × 10−5 M. The figure presents only the most interesting part of the
spectrum between 200 and 500 nm.
3.5. Reactivity of SBH groups
SBH has three groups suitable for forming coordination bond
with transition metallic cation like as Co(II). It is necessary
to know which group is the most active. Figs. 4 and 5 show
the reactivity of benzoylhydrazine, acetate and salicylaldehyde
with cobalt(II), respectively. It should also be known if the com-
plex SBH–Co(II) obtained by mixture of SBH and Co(AcO)2

Y.-H. Lu et al. / Spectrochimica Acta Part A 65 (2006) 695–701
699
Scheme 4. Equilibrium of salicylaldehyde and its cobalt complex.
Fig. 4. UV–vis spectra of the complex Co(SBH)(AcO) (2 × 10−5 M in MeOH),
the benzoylhydrazine 2 × 10−5 M and in the presence of 1 eq. of cobalt(II),
and 2 × 10−5 M Co(AcO)2 in 0.1 M AcONa. The figure presents only the most
interesting part of the spectra from 200 to 500 nm.
in solution is the same as the real Co(SBH)(AcO) complex
dissolved.
Fig. 4 shows the UV–vis spectrum of the authentic com-
plex Co(SBH)(AcO) in MeOH. It is composed of four important
absorptions peaks, which are similar with that obtained by reac-
tion between the SBH and Co(AcO)2 in MeOH (see Fig. 1),
indicating that the complex obtained in solution is the same as
the dissolved Co(SBH)(AcO) complex.
Fig. 6. Deconvolution of the UV–vis absorption spectrum of SBH in the pres-
ence of 1.5 times of equivalent of cobalt(II) in MeOH (CSBH = 4.16 × 10−5 M).
The figure presents only the most interesting part of the spectrum between 200
and 600 nm.
In MeOH, two spectra two spectra of benzoylhydrazone can
be seen that are almost the same, which suggests that the ben-
zoylhydrazone does not react with Co(AcO)2.
coordinated by salicylaldehyde. Two forms are in equilibrium
(Scheme 4). All the peaks are split and widened because the
mode of resonance does not change. A new peak at 265 nm,
which is increased with the Co(II) concentration, indicated the
presence of the complexed acetate.
The absorption of acetate in MeOH is lower than 200 nm. In
2−
0.1 M AcONa, complex Co(AcO)4 gives a peak at 274 nm.
This means that only complexed acetate is observable.
Fig. 5 shows the reactivity of salicylaldehyde with increas-
ing amount of Co(AcO)2. Cobalt(II) replaces the proton and is
The trace of complexed acetate is also observable in the spec-
trum of the complex Co(SBH)(AcO) in Figs. 1 and 4.
The reactivity of the salicylidene is close to that of salicy-
laldehyde. Thus, the salicylidene group might be more reactive
than the benzoylhydrazine group in SBH.
3.6. Gaussian deconvolution of UV–vis spectra of
SBH–Co(II)
The UV–vis spectrum of SBH–Co(II) is less complex than
that of SBH. Fig. 6 shows the spectrum of SBH in the presence of
Table 3
Characteristics of Gaussian peaks composing the UV–vis spectrum of the SBH
in the presence of 1.5 eq. of cobalt(II) in MeOH (CSBH = 4.16 × 10−5 M)
λ
ω
A
1
2
3
4
5
6
198.24
226.15
259.32
299.67
378.88
400.72
6.78
26.35
7.81
18.96
27.46
13.05
0.44206
0.57209
0.11896
0.42442
0.31435
0.04154
Fig. 5. UV–vis spectra of involved salicylaldehyde with an increasing quantity
of Co(AcO)2. The figure presents only the most interesting part of the spectra
between 200 and 500 nm.

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Y.-H. Lu et al. / Spectrochimica Acta Part A 65 (2006) 695–701
1.5 times of equivalent of cobalt in MeOH. It is also made up of
six Gaussian peaks. Table 3 gathers the characteristic parameters
of each Gaussian peak. The reaction is almost complete with one
equivalence of cobalt(II); there is no detectable SBH with 1.5
times of equivalence. The deconvolution of the spectrum with
the Gaussian characteristics of the SBH becomes mathemati-
cally impossible. The UV–vis spectrum observed is absolutely
those of Co(SBH)(AcO) complex. The spectrum of the com-
plex is also made up of three important transitions at 226.15,
299.67 and 378.88 nm and two weak transitions at 259.32 and
400.72 nm.
By comparing the position of each chromophore with that of
SBH, the peak at 330 nm of the SBH moves to 378 nm (+48 nm
shift to red) and the width passes from 15 to 27 nm (+12 nm),
and C N absorption band shifts from 286 nm to 299 nm and
widens of +4 nm, which indicates that the salicylidene group
reacts with Co(AcO)2. The band of benzoylhydrazine shifts to
blue (−12 nm) and widens of 14 nm, which indicates that ben-
zoylhydrazineparticipatesinthecomplexformation. Thepeakat
259 nm, non-existent initially in SBH, is assigned to complexed
acetate (Table 4).
3.7. Influence of media on the UV–vis spectra of complexes
Co(II)–SBH
Fig. 7 illustrates the UV–vis spectra and their deconvolution
of the complexes SBH–Co(II) in three methanol solution
containing 0.1 M NaClO4, 0.1 M sodium acetate and 0.1 M
NaClO4 + 10−3 M NaOH, respectively. The first two spectra
are recorded in the presence of 1.5 times of equivalence of
cobalt(II). The last is in the presence of 1 eq. of cobalt(II) in
the mixture NaClO4 + NaOH. The excess cobalt(II) causes an
invisible precipitation.
In the presence of NaClO4, SBH and cobalt(II) form
the same complex as that in MeOH. Compared with that
of SBH, the peaks of amide and C N absorption shift to
red for −2 and −3 nm, respectively, and that the peak of
salicylidene has more characteristic of HO C C C N than
O C C C N. It can be noticed that the carbonyl of amide
and the nitrogen of azomethine take more part in the coordi-
nation than the phenol oxygen when the hydroxyl group is not
ionised.
In the presence of AcONa or NaOH, the spectrum of the
complex is different from those in neutral medium, the peaks
of the carbonyl of amide and the peak of the azomethine shift
to red for more than 3 nm and on the other hand, the peak
of salicylidene shift to blue for about 4–7 nm. That is, the
hydroxyl group looses its proton and that oxygen take more
part in the coordination than the carbonyl and azomethine
groups.
The benzoylhydrazine strongly participates in the coordi-
nation of cobalt(II) in all solutions. It has a higher reactiv-
ity than the phenolic hydroxyl. The phenolic hydroxyl takes
part only in basic medium. The nature of complex thus
depends on the acidity of phenolic proton and the medium
(Scheme 5).
Fig. 7. UV–vis spectra and deconvolution of spectrum of the SBH in the pres-
ence of cobalt(II) in MeOH, from top to bottom containing as (a) 0.1 M NaClO4,
CSBH = 1.60 × 10−5 M, 1.5 eq.; (b) 0.1 M AcONa, CSBH = 2.00 × 10−5 M,
1.5 eq.; and (c) 0.1 M NaClO4 + 10−3 M NaOH, CSBH = 2.00 × 10−5 M, 1 eq.
The figure presents only the most interesting part of the spectrum between 200
and 600 nm.

Y.-H. Lu et al. / Spectrochimica Acta Part A 65 (2006) 695–701
701
Table 4
Characteristics values of Gaussian peaks composing the UV–vis spectra of the SBH in the presence of cobalt
MeOH
NaClO4 0.1 M
AcONa 0.1 M
NaClO4 0.1 M + NaOH 10−3 M
Chromophor concerned
1
2
3
4
5
226.15 (26.37)
259.32 (7.80)
299.67 (18.96)
378.88 (27.46)
400.71 (13.05)
224.33 (25.45)
256.38 (8.16)
296.33 (18.67)
381.16 (27.94)
402.23 (15.38)
229.98 (19.17)
263.39 (9.78)
302.50 (20.78)
374.85 (26.18)
399.00 (14.03)
232.15 (26.39)
263.60 (8.89)
301.83 (20.65)
371.16 (32.33)
399.11 (17.25)
C
C
O amide
O acetate
N
C
(HO)C
LMCT
C C N
Scheme 5. Deprotonation of Co(SBH) complex in solution.
4. Conclusion
(h) C.C. Gatto, E.S. Lang, A. Kupfer, A. Hagenbach, U. Abram, Z. Anorg.
Allg. Chem. 630 (2004) 1286–1295;
(i) P.B. Sreeja, M.R. Prathapachandra Kurup, Spectrochim. Acta, Part A
(2005) 331–336.
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762.
In summary, the UV–vis spectra of the SBH and its com-
plexes of cobalt(II) were studied and the chromophores in the
molecules were identified. It rises that the carbonyl benzoylhy-
drazine and is strongly involved in the formation of the complex
Co(SBH)(AcO). The reactivity of phenolic hydroxyl strongly
depends on the medium. SBH behaves as a neutral bidentate lig-
and in the neutral or slightly acid medium and is monoanionic
tridentate ligand in basic medium. The structure of complex in
solution is different from the solid crystalline state. The pres-
ence of “free” hydroxyl group allows the formation of hydrogen
bonding in neutral or slightly acid solution.
[8] (a) Y.-H. Lu, Y.-W. Lu, Chin. J. Spectrosc. Lab. 21 (5) (2004) 999–
1004;
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