2-Hydroxybenzaldehyde-(4,6-dimethylquinolin-2-yl)- hydrazone (HBDH), synthesis, characterization, and ligational behavior towards some metals

Article abstract of DOI:10.1080/15533174.2010.494271

2-Hydroxybenzaldehyde-(4,6-dimethylquinolin-2-yl)-hydrazone, and itsmetal complexes with Cu(II),Co(II),Ni(II), and Zn(II) have been synthesized and characterized using elemental analyses, spectral analyses (IR, UV, 1H-NMR, MS), thermal analyses (TGA and DTG), conductance and magnetic measurements. The results showed that 2-hydroxybenzaldehyde-(4,6-dimethylquinolin-2-yl)- hydrazone acts as mononegative tridentate ligand coordinating to the metal ions through quinoline nitrogen, azomethine nitrogen and phenolic oxygen after deprotonation. The difference between ν_as and ν_as stretching vibrations indicates that acetate group binds to the metal ions in a bi-dentate fashion. An octahedral stereochemistry has been suggested for all metal ions. The vibrational spectra of the ligand and its metal complexes have been calculated using semi-empirical calculations, AM1, PM3 and ZINDO/1 methods, to facilitate the assignments of the experimental spectra. Also, the optical band gap (E_g) of the metal complexes has been calculated. The optical transition energy (E_g) is direct and equals 2.40, 2.62 and 2.71 ev for Co, Ni and Cu complexes, respectively. Taylor & Francis Group, LLC.

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2-Hydroxybenzaldehyde-(4,6-Dimethylquinolin-2-yl)-
Hydrazone (HBDH), Synthesis, Characterization, and
Ligational Behavior Towards Some Metals
Nasser Mohammed Hosny a , Mohamed Abdel-Moneim Mahmoud a & Mohamed R.E. Aly a b
a Chemistry Department, Faculty of Science , Port-Said University , Port-Said, Egypt
b Chemistry Department, Faculty of Science , Taif University , Taif, Saudi Arabia
Published online: 15 Jul 2010.
To cite this article: Nasser Mohammed Hosny , Mohamed Abdel-Moneim Mahmoud & Mohamed R.E. Aly (2010) 2-
Hydroxybenzaldehyde-(4,6-Dimethylquinolin-2-yl)-Hydrazone (HBDH), Synthesis, Characterization, and Ligational Behavior
Towards Some Metals, Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry, 40:7, 439-446
To link to this article: http://dx.doi.org/10.1080/15533174.2010.494271
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Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry, 40:439–446, 2010
Copyright © Taylor & Francis Group, LLC
ISSN: 1553-3174 print / 1553-3182 online
DOI: 10.1080/15533174.2010.494271
2-Hydroxybenzaldehyde-(4,6-Dimethylquinolin-2-yl)-
Hydrazone (HBDH), Synthesis, Characterization, and
Ligational Behavior Towards Some Metals
Nasser Mohammed Hosny,1 Mohamed Abdel-Moneim Mahmoud,1 and Mohamed
R. E. Aly1,2
1Chemistry Department, Faculty of Science, Port-Said University, Port-Said, Egypt
2Chemistry Department, Faculty of Science, Taif University, Taif, Saudi Arabia
properties, liquid-crystal properties, and non-linear optical
properties.[7,8] Metal complexes of the polypyridine family
have attracted a great deal of attention from the photochemical
community.[9] Another strategy found in the literature to
improve the light harvesting efficiency and sensitivity at longer
wavelengths of mononuclear pyridyl metal complexes sensi-
tizers is the introduction of phenyl groups in the chromophoric
ligands.[10] The diversity of applications and in continuation
to our previous work on hydrazones[11−15] has prompted us
to synthesis a new series of hydrazones metal complexes
containing quinoline moiety. The structure of the ligand and its
metal complexes have confirmed by different physicochemical
techniques. The vibrational spectra of the most important
bands of the ligand and its metal complexes were calculated
theoretically using semi-empirical methods to facilitate the
assignments of the experimental results. Also, the optical band
gap of the isolated complexes has been calculated to shed more
light on the conductivity of these complexes.
2-Hydroxybenzaldehyde-(4,6-dimethylquinolin-2-yl)-hydra-
zone, and its metal complexes with Cu(II), Co(II), Ni(II), and Zn(II)
have been synthesized and characterized using elemental analyses,
spectral analyses (IR, UV, 1H-NMR, MS), thermal analyses (TGA
and DTG), conductance and magnetic measurements. The results
showed that 2-hydroxybenzaldehyde-(4,6-dimethylquinolin-2-yl)-
hydrazone acts as mononegative tridentate ligand coordinating to
the metal ions through quinoline nitrogen, azomethine nitrogen
and phenolic oxygen after deprotonation. The difference between
νas and νas stretching vibrations indicates that acetate group binds
to the metal ions in a bi-dentate fashion. An octahedral stereo-
chemistry has been suggested for all metal ions. The vibrational
spectra of the ligand and its metal complexes have been calculated
using semi-empirical calculations, AM1, PM3 and ZINDO/1
methods, to facilitate the assignments of the experimental spectra.
Also, the optical band gap (Eg) of the metal complexes has been
calculated. The optical transition energy (Eg) is direct and equals
2.40, 2.62 and 2.71 ev for Co, Ni and Cu complexes, respectively.
Keywords 2-hydroxybenzaldehyde-(4,6-dimethylquinolin-2-yl)-
hydrazone, metal complexes, spectral analyses, optical
band gap
EXPERIMENTAL
Reagents
INTRODUCTION
All the chemicals used were of analytical grade and used
without further purifications.
Aroyl hydrazones are an important class of compounds
containing azomethine group. Hydrazides and their corre-
sponding hydrazones can function as anti-tuberculoses and
anti-oxidants.[1−5] The anti-tuberculoses activity of hydrazides
comes from their ability to form metal chelates with tran-
sition metal ions. This category of compounds has not only
pharmacological activity, but also extensive applications.[6]
Polyazomethines have been widely studied for their high ther-
mal stability, mechanical properties, electrical and magnetic
Analysis and Equipment
Carbon and hydrogen contents were determined at the Mi-
croanalytical Unit of Mansoura University. The metal analyses
were carried out by standard methods.[16] Molar conductance
measurements of the complexes (10−3 M) in DMSO were car-
ried out with a conductivity bridge YSI model 32. Infrared
spectra were measured using KBr discs on a Mattson 5000
FTIR spectrometer. Calibration with the frequency reading was
made with polystyrene film at Mansoura University. Electronic
spectra were recorded on UV2 Unicam UV/vis. Spectrometer
using 1 cm Stoppard silica cells at Mansoura University. Mag-
netic measurements were carried out on a Sherwood magnetic
Received 22 July 2009; accepted 15 May 2010.
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
439

440
N. M. HOSNY ET AL.
Preparation of Metal Complexes
CH3
N
The metal complexes were prepared by adding equimolar
amounts (1 mmol) of the metal (II) acetate in 25 ml absolute
EtOH to a hot solution of the ligand (1 mmol, 0.29 gm) in 25 ml
absolute EtOH. The precipitate formed was filtered immediately
and washed with hot absolute EtOH to ensure the isolation of
pure complexes then kept in a vacuum desiccator over fused
CaCl2.
HO
H3C
N
N
H
FIG. 1. Structure of the ligand (HBDH).
RESULTS AND DISCUSSION
balance at Mansoura University. Thermal analysis measure-
ments (TGA) were recorded on a Schimadzu model 50 instru-
ment using 20 mg samples. The nitrogen flow rate and heating
were 20 cm3/ min. and 10◦C /min., respectively. The 1H-NMR
spectrum of the ligand was recorded in d6-DMSO on a Gemini-
200 spectrometer at Cairo University. Mass spectra of the ligand
were recorded on Shimadzu GC-MS-QP 1000 Ex at 70 ev mass
spectrometer at Cairo University.
The reaction of Cu(II), Co(II), Ni(II), and Zn(II) ac-
etates with the ligand (HBDH) results in the formation
of [MLAc.H2O] (M = Cu(II), Co(II) Ni(II) or Zn(II);
L = 2-hydoxybenzaldehyde-(4,6-dimethylquinolin-2-yl)-hyd-
razone]. One type of metal complexes has been formed from
the reaction of 2-hydroxybenzaldehyde-(4,6-dimethylquinolin-
2-yl)-hydrazone with Cu, Co, Ni and Zn acetates. The ligand is
chelated to all the metal ions as mono negative tridentate after
replacement of one hydrogen atom from the phenolic oxygen.
Ethanol was used as a solvent in the preparation of all the metal
complexes.
Computational Details
Molecular geometries of all forms of the ligand and its metal
complexes were optimized using molecular mechanics and the
semi-empirical ZINDO/1, PM3 and AM1 methods using the hy-
perchem series of programs.[17] Molecular mechanics technique
was used to investigate rapidly the geometries of the suggested
structures of the ligand. The low lying conformers obtained from
this search were then optimized at AM1, ZINDO/1 and PM3,
(Polak-Ribiere) RMS 0.01kcal.
The formation of metal chelate may be represented by the
following equation:
HBDH + M(CH3COO)2
EtOH
−−−−−−→ [M(HBDH)OAc.H2O] + CH3COOH
3−6 h reflux
(where M = Cu(II), Co(II), Ni(II) and
Zn(II), OAc = CH3COO−)
Preparation of the Ligand
A mixture of 2-hydrazino-4,6-dimethylquinoline (4.2 mmol,
0.8 g) and salicylaldehyde (7.6 mmol, 0.8 ml) in benzene
(8 ml) was heated under reflux for 2 h then left to be cooled
to ambient temperature. The orange-yellow crystals formed
were filtered in vacuum, washed with petroleum ether and dried
well to afford 2-hydoxybenzaldehyde-(4,6-dimethylquinolin-2-
yl)-hydrazone; (1.07 g, 86 %) (Figure 1).
All the complexes are quite stable in air. These complexes
are generally insoluble in common organic solvents, but solu-
ble in coordinating solvents as DMSO and DMF. The conduc-
tance measurements (∼ 7.0 ohm−1cm2 mol−1 in 10−3M DMF)
indicate that the complexes are essentially nonelectrolytes.[18]
The elemental analyses and some physical data are collected in
Table 1.
TABLE 1
Analytical data and physical properties of the the ligand (HBDH) and its complexes
% Found (calcd.)
Compound
Color
M.P. ◦C
C
H
M
HL
orange-yellow
green
228
75.0 (74.6)
56.0 (55.8)
57.0 (56.5)
56.9 (56.5)
55.2 (55.6)
5.9 (5.5)
4.7 (4.7)
4.8 (4.7)
5.0 (4.7)
5.1 (4.6)
-
[CuL.Ac H2O]
[NiL. Ac H2O]
[CoL.Ac H2O]
[ZnL.Ac H2O]
>300
>300
>300
>300
14.7 (14.9)
14.0 (13.8)
13.5 (13.9)
14.8 (15.1)
green
yellow
brown

METAL COMPLEXES OF DIMETHYLQUINOLINE DERIVATIVE
441
Zn
Ni
Co
Cu
L
FIG. 2. Mass spectrum of the ligand (HBDH).
Mass Spectra
The mass spectral fragmentation mode of (HBDH) has been
investigated. The mass spectrum (Figure 2) shows an intense
molecular ion peak at m/z = 291, corresponding to the molec-
ular formula C18H17N3O. The ion of m/z = 291, undergoes
fragmentation to produce a stable peak at m/z = 274, by losing
hydroxyl group (OH). The loss of phenyl group from the ion
4000
3500
3000
2500
2000
1500
1000
500
Wavelength (cm-1)
FIG. 4. IR spectra of the ligand and its metal complexes.
with m/z = 274, with rearrangement results in the formation of the anisotropy of the endocyclic-nitrogen. The aromatic protons
methyl diazoquinoline gives ion at m/z = 198. The loss of CN appear as multiplet in the 6.91–7.72 ppm region. Just next to the
group from the ion at m/z =198 gives the base peak at m/z = aromatic protons at 8.40 ppm the methane protons of the imine
172. The base peak undergoes loss of ammonia molecule to give moiety appeared as singlet. The broad singlet peak in the far
the peak at m/z =155, followed by loosing of HCN molecule downfieled region in the range 10.45–11.4 ppm was assigned
to give the ion at m/z =128. It further undergoes loss of CH, for the H-bonded NH and OH groups with an integration that
C2H4and C2H2 to give peaks at m/z = 115, 91 and 65, respec- fits for two protons.
tively (Scheme 1).
IR Spectra
1H-NMR
The most important IR band assignments of the experimen-
The 1H-NMR spectrum (Figure 3) of the ligand (HBDH), in tally and theoretically calculated for the optimized structures
DMSO-d6 shows two singlets signals in the upfieled region at are included in Table 2.
2.51 and 2.67 ppm, corresponding to the two methyl groups,
IR spectra of the ligand and its metal complexes are collected
C4-CH3 and C6-CH3 with C4-CH3being more desheielded by in Figure 4.
FIG. 3. 1H-NMR spectrum of the ligand (HBDH).

442
N. M. HOSNY ET AL.
CH3
H3C
m/z = 65 (10.3 %)
- C2H2
N
N
N
H
HO
m/z = 291 (32.4 %)
-OH
m/z = 91 (7.8)
-C2H4
CH3
H3C
N
N
N
H
H3C
m/z = 274 (20.0 %)
- C6H4
m/z = 115 (9.5%)
CH3
- CH
H3C
N
CH
CH2
N
N
H
H3C
m/z = 198 (43.6 %)
- CN
m/z = 128 (7.5%)
CH3
- HCN
H3C
- NH3
CH3
N
NH2
H3C
m/z = 172 (100 %)
N
m/z = 155 (8.0 %)
SCH. 1. Fragmentation pattern of the ligand (HBDH).
The IR spectrum of the ligand shows a band at 3420 cm−1 as- tively. The bands located at 1611, 1032, 651 and 420 cm−1, may
signed to ν (OH). Also, another band is observed at 1353 cm−1 be assigned to ν (C=C) +ν (C=N)Q , the ring skeletal mode, in
assigned to δ (OH).[14] The presence of a broad band at 2853 plane and out of plane ring deformation modes, respectively.[19]
cm−1 which may be assigned to OH....O stretching vibration, These bands are of considerable importance in deciding whether
indicates the possibility of intermolecular hydrogen bonding of the quinoline nitrogen is involved in the coordination with the
the phenolic OH group. The bands observed at 3182, 1590 and metal ion.[20] The spectra of all metal complexes show a broad
1580 cm−1 are assigned to ν (NH), δ (NH) and ν (C=N), respec- band located at 3430 cm−1 assigned to ν (OH) of water. The

443

444
N. M. HOSNY ET AL.
category of metal complexes. The thermal measurements (TGA
H
O
H
N
and DTG) were carried out within a temperature range from
25 up to 800◦C. The thermograms of Zn complex show that it
is stable up to 200◦C. It decomposes in three steps; the first is
endothermic, lies in the temperature range 200–359◦C and cor-
responds to the loss of one coordinated H2O and acetate (mass
loss is 17.1%; close to the calculated 17.8%). The second step
is an endothermic, lies in temperature range 359 – 443◦C and
corresponds to the loss of Ph, HCN and N (mass loss is 27.6%;
calculated 27.0%). The last step is an endothermic, corresponds
to the loss of the remaining organic (quinoline and 2 CH3) the
observed mass loss is 34.5%; calculated 36%. This step lies in
the temperature range 443 – 575◦C. The remaining is assigned
to ZnO (mass loss is 19.7%; calculated 18.8%).
N
H3C
N
M
H2O
O
O
CH3
H3C
FIG. 5. Suggested structure of metal complexes.
Electronic Spectra and Magnetic Moments
band assigned to δ OH of phenolic group disappeared in the
spectra of metal complexes indicating the participation of this
group in bonding after deprotonation. The bands at 1580 and 905
cm−1 assigned to azomethine group ν (C=N) and ν (N-N), re-
spectively, are shifted to lower wavenumber due to the decrease
of electron density on the nitrogen atom, suggesting the partic-
ipation of the azomethine group in bonding. On contrary, the
bands assigned to quinoline ring are shifted to higher wavenum-
ber due to the increase of electron density on the quinoline
nitrogen through back donation. This behavior indicates that
quinoline nitrogen is one of the active sites that take part in
coordination to the metal ion.[15] Two new bands are observed
at 1470 and ∼ 1307 cm−1 assigned to νas and νs of the acetate
group, respectively. The difference between these two bands
indicates the bi-dentate nature of this group.[21,22] Several new
weak bands are observed in the regions 478–487 and 526–533
cm−1 assigned to ν (M-N) and ν (M-O), respectively.[23] On
the basis of the above evidence, it could be suggested that the
ligand acts as mononegative tridentate ligand coordinating to
the metal ions through quinoline nitrogen, azomethine nitrogen
and phenolic oxygen after deprotonation of phenolic oxygen
(Figure 5).
The electronic spectrum of Cu(II) complex in Nujol shows
a band at 18181 cm−1. The position of this band suggests the
presence of distorted octahedral around Cu(II).[24] The band
observed at 23256 cm−1 may be LMCT transition.
The magnetic moment value is 1.80 B.M. in the range sug-
gested for monomeric copper complexes.[14]
The electronic spectra of Co(II) complexes exhibit two bands
4
4
at 15723 and 18868 cm−1 assigned to T1g (F) → A2g (F)
4
4
and T1g (F) → T1g (P) transitions, respectively.[25] The band
recorded at 23148 cm−1 may be attributed to LMCT.
The magnetic moment value 4.9 B.M. supports the presence
of an octahedral geometry around Co(II). The ligand field pa-
rameters [B = 839, β = 0.86 and 10 Dq = 8390 cm−1] fall in
the range suggested for octahedral geometry of Co(II).
Electronic spectrum of Ni(II) complex in Nujol shows two
3
3
bands at 13054 and 22522 cm−1 assigned to A2g → T1g (ν2)
3
and 3A2g → T1g (P) (ν3) transitions, respectively. The presence
of these bands indicates an octahedral geometry around Ni(II)
ion[25]. The ligand field parameters [B = 789, β = 0.75 and
10 Dq = 7890 cm−1] support the presence of an octahedral
geometry.
The magnetic moment value 2.90 B.M. is consistent with
octahedral configuration around Ni(II).
From Table 2, it is clear that AM1 and PM3 methods agree
well with the characteristic group frequencies in case of the free
ligand and Zn complex, while PM3 and ZINDO/1 agree well
for Co(II) and Ni(II) complexes. Also, PM3 agrees well with
the experimental data for the Ni(II) complex.
The experimental data are obtained in the solid state where
the calculated frequencies are estimated in the gas phase. This
may be the reason for the difference observed between the cal-
culated and experimental values.
Optical Band Gap (Eg)
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 the following equations: α = 1/d ln A
(1) where, (α) is the absorption coefficient and (d) is the width
of the cell. The optical band gap (Eg) is calculated from the
relation:
αhν = A (hν- Eg)m (2), where m is equal to 1/2 and 2 for
Thermal Analyses
Thermal analysis plays an important role in studying the direct and indirect transition respectively, A is an energy inde-
properties of metal complexes to obtain a useful data on the pendent constant.[26,27] The values of α calculated from relation
thermal stability and metal–ligand bonds. The thermal analyses 1 was used to plot (α hν)2 and (α hν)1/2 vs. hν from which a
TGA and DTG of Zn complex were studied as a representative direct band gap was found (Figure 6), by extrapolating the linear
example to shed more light on the thermal decomposition of this portion of the curve to (α hν)2 = 0. From the curve it is clear

METAL COMPLEXES OF DIMETHYLQUINOLINE DERIVATIVE
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