Synthesis and characterization of transition metal complexes derived from (E)-N-(1-(Pyridine-2-yl)ethylidiene)benzohydrazide (PEBH)

Article abstract of DOI:10.1080/15533174.2011.591296

Three metal complexes derived from (E)-N-(1-(pyridine-2-yl)ethylidene) benzohydrazide (PEBH) with Cu(II), Co(II), and Ni(II) have been synthesized and characterized using elemental analyses, spectral analyses (infrared [IR], ultraviolet [UV], mass spectroscopy [MS], nuclear magnetic resonance [ ¹H-NMR]), thermal analyses, conductance, and magnetic measurements. The results showed that 1:1 (M:L) chelates with the general formula [M L Ac]nH₂O have been formed. IR and ¹H-NMR spectra of the ligand (E)-N-(1-(pyridine-2-yl)ethylidene)benzohydrazide (PEBH) showed that the free ligand exists in the keto form, while it binds to the metal ions in the enol form. The difference between as and s stretching vibrations of the acetate group suggests the monodentate nature of this group. Some semiempirical calculations of the vibrational spectra have been done using AM1, PM3, and ZINDO/1 methods to assist in the assignments of the experimental results. The optical band gap (E_g) values of Co, Ni, and Cu were found to be 3.4, 1.45, and 1.20 eV, respectively, arising from direct transitions. These values indicate the semiconductivity nature of these complexes. Copyright Taylor &Francis Group, LLC.

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Synthesis and Characterization of Transition Metal
Complexes Derived from (E)-N-(1-(Pyridine-2-
yl)ethylidiene)benzohydrazide (PEBH)
a
Nasser Mohammed Hosny
a
Chemistry Department, Faculty of Science , Port-Said University , Port-Said, Egypt
Published online: 11 Aug 2011.
To cite this article: Nasser Mohammed Hosny (2011) Synthesis and Characterization of Transition Metal Complexes Derived
from (E)-N-(1-(Pyridine-2-yl)ethylidiene)benzohydrazide (PEBH), Synthesis and Reactivity in Inorganic, Metal-Organic, and
Nano-Metal Chemistry, 41:7, 736-742, DOI: 10.1080/15533174.2011.591296
To link to this article: http://dx.doi.org/10.1080/15533174.2011.591296
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Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry, 41:736–742, 2011
Copyright ꢀC Taylor & Francis Group, LLC
ISSN: 1553-3174 print / 1553-3182 online
DOI: 10.1080/15533174.2011.591296
Synthesis and Characterization of Transition
Metal Complexes Derived from
(
E)-N-(1-(Pyridine-2-yl)ethylidiene)benzohydrazide (PEBH)
Nasser Mohammed Hosny
Chemistry Department, Faculty of Science, Port-Said University, Port-Said, Egypt
overload disease and cancer.[9] Two series of ligands based on
Three metal complexes derived from (E)-N-(1-(pyridine-2- the very active 2-pyridylcarboxaldehyde isonicotinoyl hydra-
yl)ethylidene)benzohydrazide (PEBH) with Cu(II), Co(II), and
Ni(II) have been synthesized and characterized using elemental
analyses, spectral analyses (infrared [IR], ultraviolet [UV], mass
spectroscopy [MS], nuclear magnetic resonance [ H-NMR]), ther-
mal analyses, conductance, and magnetic measurements. The re-
[10]
zone were synthesized and tested as potent antitumor agents.
The increasing applications in medicine, analytical chemistry,
syntheses of novel heterogeneous catalysts of oxido-reduction
processes, and molecular semiconductors, as well as in numer-
ous fields of science and technology,[ make these compounds
of special interest.
In view of the versatile importance of hydrazones, we herein
describe the synthesis and identification of (E)-N-(1-(pyridine-
-yl)ethylidene)benzohydrazide (PEBH) and its metal com-
1
11]
sults showed that 1:1 (M:L) chelates with the general formula
1
[
M L Ac]nH
2
O have been formed. IR and H-NMR spectra of the
ligand (E)-N-(1-(pyridine-2-yl)ethylidene)benzohydrazide (PEBH)
showed that the free ligand exists in the keto form, while it binds to
the metal ions in the enol form. The difference between νas and ν
stretching vibrations of the acetate group suggests the monoden-
s
2
tate nature of this group. Some semiempirical calculations of the plexes with Cu(II), Co(II), and Ni(II). The ligand and its metal
vibrational spectra have been done using AM1, PM3, and ZINDO/1
methods to assist in the assignments of the experimental results.
The optical band gap (E ) values of Co, Ni, and Cu were found to
g
be 3.4, 1.45, and 1.20 eV, respectively, arising from direct transi-
tions. These values indicate the semiconductivity nature of these
complexes.
complexes have been characterized by different spectral tech-
niques. The optical band gap of the isolated complexes has been
calculated to shed light on the conductivity of these complexes.
EXPERIMENTAL
Keywords metal complexes, spectral characterization, (E)-N-(1-
Reagents
(pyridine-2-yl)ethylidene)benzohydrazide
All the chemicals used were of analytical grade and used
without further purifications.
INTRODUCTION
Analysis and Equipment
Carbon and hydrogen contents were determined at the Mi-
croanalytical Unit of Mansoura University. The metal analyses
Interest in the study of hydrazones has been growing be-
cause of their anti- tuberculosis, anti-oxidant and anti-tumor
activity.[
1–4]
Hydrazones derived from condensation of isonico-
[
12]
were carried out by standard methods.
Molar conductance
measurements of the complexes (10 M) in dimethyl sulfoxide
DMSO) were carried out with a conductivity bridge YSI model
32. Infraredspectra were measured using KBr discs ona Mattson
000 Fourier-transform infrared (FTIR) spectrometer. Calibra-
tinic acid hydrazide with pyridinealdehydes have been found to
show better anti-tubercular activity than INH. A novel class
−3
[5]
(
of anti-cancer compounds derived from quinoxaline hydrazides
has been reported.[6] The remarkable biological activity of acid
5
hydrazides R−CO−NH−NH2 and their corresponding aroyl-
ꢁ
tion with the frequency reading was made with polystyrene film.
Electronic spectra were recorded on the UV2 Unicam ultravi-
olet/visible (UV/Vis) spectrometer using 1-cm stoppered silica
cells. Magnetic measurements were carried out on a Sherwood
magnetic balance at Mansoura University. Thermal analyses
measurements (TGA and DTG) were recorded on a Schimadzu
model 50 instrument using 20-mg samples. The nitrogen flow
rate and heating were 20 cm /min and 10 C/min, respectively.
The nuclear magnetic resonance ( H-NMR) spectrum of the lig-
and was recorded in d6-DMSO on a Gemini-200 spectrometer
hydrazones R−CO−NH−N=CH−R comes from their ability
to bind with the transition metal ions present in the living sys-
tem.[
7,8]
Aroylhydrazones are highly effective in terms of their
ability to bind Fe, and have been used for the treatment of Fe
Received 17 July 2009; accepted 25 February 2011.
3
◦
Address correspondence to Nasser Mohammed Hosny, Chemistry
Department, Faculty of Science, Port-Said University, 23 December
Street, Port-Said, Egypt. E-mail: Nasserh56@yahoo.com
1
736

TRANSITION METAL COMPLEXES FROM PEBH
737
at Cairo University. Mass spectra of the ligand were recorded
on a Shimadzu GC-MS-QP 1000 Ex mass spectrometer at 70
eV at Cairo University.
Computational Details
Molecular geometries of the ligand and its metal complexes
were optimized using molecular mechanics and the semiempir-
ical ZINDO/1, PM3, and AM1 methods (Polak-Ribiere), RMS
.01 kcal, using the hyperchem series of programs.[ Results
13]
0
of a recent literature study indicate that frequencies computed
using semiempirical PM3, and AM1 methods compare well to
values obtained at the ab initio level using medium-size basis
sets. Of these methods, PM3 showed the closest correspondence
to experimental values, which is generally about 10% too high
FIG. 1. Suggested structure of the metal complexes, with M=Cu(II), Co(II),
or Ni(II), and n = 1 or 4.
The formation of metal chelate may be represented by the
following equation:
[
14]
in value from stretches.
Preparation of the Ligand
EtOH
The ligand was prepared by refluxing solution of benzoylhy-
drazide (6.75 g; 0.05 M) with 2-acetylpyridine (6.05 mL; 0.05
M) in absolute EtOH. The reaction mixture was refluxed on wa-
ter bath for 3 h and then left to cool. Yellowish brown crystals
were separated. The product was filtered off, washed several
times with ethanol, and then kept to dry in a desiccator over
CaCl2; yield, 7.5 g (63.0%).
PEBH + M(CH3COO)2 −−−−−−−→[M(PEBH)OAc]nH2O
6
hours reflux
+
CH3COOH,
-
where M=Cu(II), Co(II), or Ni(II), OAc=CH3COO and n = 1
or 4.
The elemental analyses measurements of the ligand and its
metal complexes confirm the 1:1 (M:L) composition for the
synthesized complexes (Figure 1). Data of the elemental anal-
yses and some physical properties for the ligand and its metal
complexes are illustrated in Table 1.
All the metal complexes are colored and stable in air, insol-
uble in most common organic solvents, but soluble in coordi-
nating solvents as dimethylformamide (DMF) and DMSO. The
Preparation of the Metal Complexes
The metal complexes were prepared by adding stoichiometric
quantities of (1 mmol) of the metal(II) acetate in 20 mL absolute
EtOH to a hot solution of the ligand (1 mmol, 0.24 gm) in 20
mL absolute EtOH. A direct change in color was observed. The
mixture was refluxed on a water bath for 3 h. The precipitate
is formed on reflux. To ensure the isolation of pure complexes
the resulting solid complexes were filtered immediately, washed
several times with hot EtOH, and kept in a vacuum desiccator
over CaCl2.
−1
2
−1
−3
molar conductivity values (∼3.0 ohm cm mol ) in 1 × 10
◦
M DMF at 25 C show that all the complexes are nonconduct-
ing.[
15]
Mass Spectra
RESULTS AND DISCUSSION
The mass spectrum (Figure 2) of the ligand (PEBH) gives
+
In this study, one type of metal complexes has the molecular ion peak [M ] at m/z = 240. The fragmentation
been isolated from the reaction of (E)-N-(1-(pyridine-2- pattern of the ligand is represented in Scheme 1.
yl)ethylidene)benzohydrazide (PEBH) with Cu, Co, and Ni ac-
Two fragmentation pathways are followed by the molecular
etates. The ligand is chelated to all the metal ions in the enol ion of (PEBH). The first includes the cleavage of the azome-
form with replacement of one hydrogen atom. Ethanol was used thine group –C=N-, leading to the formation of the base peak
as a solvent in the preparation of all the metal complexes.
resulting from the fragment PhCONHN at m/z = 134 (100%).
TABLE 1
Analytical data and physical properties of the the ligand (PEBH) and its complexes
Percent found (calculated)
◦
Compound
HL
Color
m.p. ( C)
C
H
M
Yellowish brown
Green
160
71.4(71.2)
44.6(44.4)
51.5(51.4)
45.3(44.9)
4.6(4.2)
5.8(5.3)
5.0(4.5)
5.7(5.3)
—
[Cu L Ac]4H2O
[Co L Ac]H2O
[Ni L Ac]4H2O
>300
>300
>300
15.1(14.7)
15.4(15.8)
14.0(13.7)
Brown
Brown

738
N. M. HOSNY
FIG. 2. Mass spectrum of the ligand (PEBH).
SCH. 1. Fragmentation pattern of the ligand (PEBH).
The IR spectrum of (PEBH) shows a band at 3179 cm 1
−
Then it is cleaved through the amide group –CO–NH– leading
to benzoyl fragment at m/z = 105 (97%). The elimination of assigned to the ν (NH) of the amino group. The bands at 1658,
−1
CO from the benzoyl group leads to the formation of phenyl 1630, 1620, 1544, 1373, and 984 cm can be assigned to the
radical with peak at m/z = 77 (34%). Liberation of acetylene amide (1) ν (C=O), amide (2) ν (CONH), ν (NH), ν (C=N),
from the phenyl group can be observed at m/z = 51 (37%). The amide (3) ν (C-N) and ν (N–N) modes, respectively.[
16,17]
The
second pathway involves the removal of methyl group and the presence of the bands assigned to ν (C=O), amide (2) ν (CONH)
liberation of acetylene from the phenyl group; as a result of this and ν (NH) confirms the presence of the free ligand in the keto
−1
fragmentation the peak at m/z = 198 (23%) is formed.
form. The bands located at 1578, 1052, 620, and 433 cm may
be assigned to ν (C=N)py, ring skeletal, and in and out of plane
1
[18,19]
H-NMR
ring deformation modes, respectively.
These bands are of
1
considerable importance in deciding whether the pyridyl nitro-
The H-NMR spectrum (Figure 3) of the ligand (PEBH),
[20]
gen participates in coordination to the metal ions or not. The
in d6-DMSO shows a singlet signal at 3.38 ppm, downfield
with respect to tetramethylsilane (TMS), and is assigned to the
protons of the CH3. The multiplet signals in the 7.47–8.68 ppm
region are assigned to the protons of pyridyl and phenyl rings.
The spectrum shows also a singlet signal at 10.92 ppm, due to
the NH proton. The presence of this signal indicates that the
ligand exists in the keto form.
−1
bands observed at 1544 and 984 cm in the spectra of the ligand
[
21]
can be assigned to ν (C=N) and ν (N–N), respectively.
In
the spectra of the metal complexes all the amide bands (amide
1
1
and amide 2) disappear, while new bands appear in the region
631–1650 and 1417–1428 cm due to ν (C=N) and ν (C-O),
−1
∗
respectively. This indicates the transformation of carbonyl oxy-
gen to the enol form with subsequent coordination of the oxy-
gen upon deprotonation. The band suggested to the azomethine
group is shifted to lower frequency in all the metal complexes.
Also, the bands assigned to ν (C=N) and ν (C=N)py are shifted
to higher wavenumber in the spectra of all complexes, indicating
the possibility of back donation and the participation of nitro-
gen atoms in bonding. The IR spectra of all metal complexes
show that (PEBH) behaves as a mononegative tridentate ligand,
coordinating to the metal ions through carbonyl oxygen in the
enol form after deprotonation, azomethine nitrogen, and pyridyl
nitrogen. This suggestion is supported by the positive shift of
IR Spectra
The assignments of some of the observed and calculated IR
bands are included in Table 2. (PEBH) can be represented by
two tautomeric forms, the keto form (Structure I) and enol form
(
Structure II).
−1
the band assigned to ν (C=N) from 1544 cm in the free ligand
−1
to 1565 and 1580 cm in the metal complexes. Also, the shift to

TRANSITION METAL COMPLEXES FROM PEBH
739
FIG. 3. 1H-NMR spectrum of the ligand (PEBH).
higher frequency of the band at 984 cm−1 due to ν (N-N) can be lation between the positions of the asymmetric and symmetric
taken as an addition evidence that the azomethine group takes stretching vibrations of the acetate group and the type of coor-
part in bonding. Participation of pyridyl nitrogen in coordination dination of this group was earlier studied.[ It was concluded
is suggested on the basis of the observed changes in the bands from these studies that the frequency difference between the two
23]
−
1
at 1578, 1052, 620, and 433 cm assigned to ν (C=N)py, ring carboxyl stretching vibrations in the case of ionic acetate groups
−1
skeletal, and in-plane ring deformation mode and out-of-plane is usually in the interval ∼167 cm ; longer values were found
[
22]
[24]
ring deformation mode, respectively.
in the regions 435–480 and 552–565 cm can be assigned to ν respondingly, the split of 178–215 cm in the case of Cu(II),
M-N) and ν (M-O), respectively. The spectra of all metal com- Co(II), and Ni(II) complexes may be evidence for the monoden-
The new weak bands for monodentate and lower values for bidentate groups. Cor-
−
1
−1
(
−1
plexes show a band centered at 3440 cm assigned to ν OH of tate nature of the acetate group.
water.
The results showed that AM1 and PM3 methods agree well in
The spectra of the complexes show two bands in the region the case of the ligand and ZINDO/1 agrees with the Co complex,
− −1
1
1
438–1458 cm and 1245–1260 cm assigned to νas and νs while ZINDO/1 and PM3 agree to the same extent in the case
stretching vibrations of acetate group, respectively. The corre- of Cu and Ni complexes.
TABLE 2
−1
Observed and calculated wavenumbers (cm ) of the ligand (PEBH) and its metal complexes
APBH Cu complex Co complex Ni complex
Exp. AM1 PM3 ZINDO/1 Exp PM3 ZINDO/1 Exp PM3 ZINDO/1 Exp PM3 ZINDO/1
Vibration
ν(NH)
3179
—
—
—
1581
1526
—
1073,
652,
431
—
—
—
—
—
—
—
—
—
ν(C=N)py
1578 1593 1600
1544 1547 1535
—
1607 1618
1565 1577
1635 1631
1060, 1063,
625, 638,
1600
1574
1658
1048,
615,
437
1596 1462
1567 1400
1632 1682
1066, 1071,
624, 650,
1591
1521
1625
1055,
654,
410
1631 1639
1580 1598
1650 1681
1062, 1073,
629, 636,
1634
1622
1664
1072,
644,
434
ν (C=N)
∗
ν(C=N)
—
—
Py skeletal
1052, 1062, 1102,
20, 642, 646,
33 427 455
6
4
437
440
440
425
422
440
∗Nitrogen of the new azomethine group; py = pyridine nitrogen.

740
N. M. HOSNY
SCH. 2. Thermal decomposition of Ni complex.
Thermal Analyses
magnetic moment value (2.85 BM), which indicates a low-spin
Thermal analyses give useful data about the thermal stability square-planar cobalt(II) complex[ may be arising from one
of metal complexes and the metal–ligand bonds. The thermal unpaired electron plus an apparently large orbital contribution.
measurements (TGA and DTG) were carried out within a tem- The electronic spectrum of Ni complex shows two bands at
27]
−
1
3
3
3
perature range from 25 up to 800C. The nickel complex is taken 17,412 and 10,050 cm assigned to T1 → T1 (P) and T1
3
as a representative example to clarify the thermal stability of → A2 transitions, respectively, in a tetrahedral geometry of
this type of complexes. The decomposition pattern of the nickel Ni(II).[ Another band is observed at 20,920 cm and assigned
27]
−1
3
1
complex is represented in Scheme 2. The nickel complex is to the forbidden transition T1→ T2. The spectrum shows also a
◦
−1
thermally stable up to 140 C. It decomposes in four steps. The band at 25,906 cm assigned to LMCT. The magnetic moment
◦
first is endothermic and starts from 54–138 C, corresponding to value (3.80 BM) is taken as an additional evidence of tetrahedral
the liberation of four molecules of water of hydration, the mass Ni(II). The ligand field parameters (B = 906, β = 0.87, and 10
−
1
loss is 16.1%; calculated 16.7%. The second stage represents Dq = 5431 cm ) are in agreement with the values reported for
the decomposition of acetate group. This step is endothermic tetrahedral Ni(II) complexes.[
26]
◦
and lies in the temperature range 140–270 C; the loss is 13.4%,
which is close to the theoretically calculated 13.7%. The next
step is exothermic and lies in the range 270–358 C. It represents
the decomposition of a phenyl group, and the loss in weight is
Optical Band Gap (Eg)
The conductive and semiconductive properties of molecular
materials formed from organometallic or metal-organic species
◦
17.3%; calculated 17.9%. The final step corresponds to the loss
give them potential use in molecular electronics. They have
been used in optoelectronic devices, organic transistors, and
sensors.[
of the remaining of the organic ligand. This process is endother-
◦
mic and starts from 358 to 475 C with mass loss 34.0%, which is
28]
close to the calculated 33.8%. The remaining residue is 18.6%,
calculated 17.5%, and corresponds to NiO.
To clarify the conductivity of the isolated complexes, the
optical band gap (Eg) of Cu(II), Co(II), and Ni(II) complexes
has been calculated from absorption spectra. The measured ab-
sorbance (A) was used to calculate approximately the absorption
Electronic Spectra and Magnetic Moments
The electronic spectrum of the copper(II) complex in Nujol coefficient (α) by using the relation α = 1/d ln A (Eq. 1), where,
−
1
shows a broad band at 14,000 cm , which can be assigned d is the width of the cell. The optical band gap (Eg) is calculated
2
2
2
2
m
to B1g → A1g and B1g → Eg transitions in a square-planar from the relation: α hν = A (hν- Eg) (Eq. 2), where m is equal
geometry.[ The band recorded at 24,630 cm is suggested to and 2 for direct and indirect transition, respectively, and A
25]
−1
1
2
[
29,30]
as LMCT. The magnetic moment (2.1 BM) of copper complex is an energy-independent constant.
is in the range expected for monomeric copper(II) complexes. lated from relation (1) were used to plot (α hν) and (α hν)
The values of α calcu-
2
1/2
The high magnetic moment value of the square-planar complex versus hν, from which a direct band gap was found (Figure 4),
2
compared with the observed values for the distorted octahedron by extrapolating the linear portion of the curve to (α hν) =
may be taken as an additional evidence for the presence of a 0. From the curve it is clear that the values of the direct band
square-planar geometry.
gap (Eg) equal 3.40, 1.45, and 1.20 eV in the case of Co, Ni,
The electronic spectrum of cobalt complex shows a d–d band and Cu complexes, respectively. There is a trend between the
−
1
1
1
at 20,000 cm assigned to A1g → B1g transition, which con- atomic number of the central atoms and (Eg) values, indicating
[
26]
firms square-planar geometry. This is further confirmed by its that (Eg) depends on the electronic configuration of the d orbital

TRANSITION METAL COMPLEXES FROM PEBH
741
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CONCLUSION
The free ligand (E)-N-(1-(pyridine-2-yl)ethylidene)
benzohydrazide exists in the keto form, while it coordinates to
the investigated metal ions Cu(II), Co(II), and Ni(II) in the enol
17. Rana, V.B.; Sahni, S.K.; Gupta, S.P.; Songal, S.K. Some 5-coordinate
nickel(II) complexes of dipicolinic acid hydrazide. J. Inorg. Nucl. Chem.
1
977, 39, 1098.
form. Coordination number four is suggested for all the isolated 18. Alpert, N.L.; Keiser, W.E.; Szymonski, H.A. Theory and Practical Infrared
Spectroscopy; Plenum: New York, 1970.
metal complexes. Both Cu(II) and Co(II) form square-planar
1
9. Sakamoto, M. Synthesis and characterization of lanthanoid(III) complexes
with a pentadentate ligand derived from 2,6-diacetylpyridine and benzoyl-
hydrazide. Inorg. Chim. Acta 1987, 131, 139.
complexes, while Ni(II) forms a tetrahedral one. Optical band
gap calculations indicate that the transition is direct and the
complexes have semiconducting nature.
2
0. Bellamy, L.J. Advance in Infrared Group Frequency; Methuen: London,
1
969.
2
1. Hosny, N.M.; Shalaby, A.M. Spectroscopic characterization of some metal
complexes derived from 4-acetylpyridine nicotinoylhydrazone. Transition
Met. Chem. 2007, 32, 1085.
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