Transition metal complexes of isonicotinic acid (2-hydroxybenzylidene)hydrazide

Article abstract of DOI:10.1016/j.saa.2007.07.023

A new series of transition metal complexes of Schiff base isonicotinic acid (2-hydroxybenzylidene)hydrazide, HL, have been synthesized. The Schiff base reacted with Cu(II), Ni(II), Co(II), Mn(II), Fe(III) and UO₂(II) ions as monobasic tridentat

Full text of DOI:10.1016/j.saa.2007.07.023

Available online at www.sciencedirect.com
Spectrochimica Acta Part A 70 (2008) 162–170
Transition metal complexes of isonicotinic acid
(2-hydroxybenzylidene)hydrazide
Khlood S. Abou-Melha
Education College for Girls, Scientific Departments, Department of Chemistry, Abha, Assir, Saudi Arabia (KSA)
Received 9 January 2007; received in revised form 28 June 2007; accepted 19 July 2007
Abstract
A new series of transition metal complexes of Schiff base isonicotinic acid (2-hydroxybenzylidene)hydrazide, HL, have been synthesized. The
Schiff base reacted with Cu(II), Ni(II), Co(II), Mn(II), Fe(III) and UO2(II) ions as monobasic tridentate ligand to yield mononuclear complexes
of 1:2 (metal:ligand) except that of Cu(II) which form complex of 1:1 (metal:ligand). The ligand and its metal complexes were characterized
by elemental analyses, IR, UV–vis, mass and 1H NMR spectra, as well as magnetic moment, conductance measurements, and thermal analyses.
All complexes have octahedral configurations except Cu(II) complex which has an extra square planar geometry distorted towards tetrahedral.
While, the UO2(II) complex has its favour hepta-coordination. The ligand and its metal complexes were tested against one strain Gram +ve
bacteria (Staphylococcus aureus), Gram −ve bacteria (Escherichia coli), and Fungi (Candida albicans). The tested compounds exhibited higher
antibacterial activities.
© 2007 Elsevier B.V. All rights reserved.
Keywords: Schiff base ligand; Metal complexes; Antimicrobial; IR spectra; UV–vis spectra
1. Introduction
hydrazones, we herein describe the synthesis and identifica-
tion of some transition metal complexes of isonicotinic acid
(2-hydroxybenzylidene)hydrazide, HL (Fig. 1).
Schiff bases play an important role in inorganic chemistry
as they easily form stable complexes with most transition metal
ions. The development of the field of bioinorganic chemistry
has increased the interest in Schiff base complexes, since it has
been recognized that many of these complexes may serve as
models for biologically important species [1–5]. The remark-
able biological activity of acid hydrazides R–CO–NH–NH2,
a class of Schiff base, their corresponding aroylhydrazones,
R–CO–NH–N CH–Rꢀ and the dependence of their mode of
chelation with transition metal ions present in the living sys-
tem have been of significant interest [6–12]. The coordination
compounds of aroylhydrazones have been reported to act as
enzyme inhibitors [13] and are useful due to their pharmaco-
logical applications [14–16]. Isonicotinic acid hydrazide (INH)
is a drug of proven therapeutic importance and is used as
bacterial ailments, e.g., tuberculosis [17]. Hydrazones derived
from condensation of isonicotinic acid hydrazide with pyridine
aldehydes have been found to show better antitubercular activ-
ity than INH [18,19]. In view of the versatile importance of
2. Experimental
2.1. Reagents and materials
Copper(II) chloride dihydrate, nickel(II) chloride mono-
hydrate, cobalt(II) acetate tetrahydrate, manganese(II) acetate
tetrahydrate, iron(III) chloride hexahydrate, uranyl(II) acetate
dihydrate, cadmium(II) acetate monohydrate, lithium hydrox-
ide monohydrate, salicylaldehyde and nicotinic acid hydrazide
were either BDH or Merck chemicals and were used without
further purification. Organic solvents were reagent grade.
2.2. Synthesis of the ligand
The ligand HL was synthesized as follows. Isonicotinic
acid hydrazide (1.4 g, 10 mmol) was dissolved in 10 mL abso-
lute ethanol. To this solution saclicylaldehyde (1.34 g (1.6 mL),
11 mmol dissolved in 5 mL absolute ethanol) was added. The
reaction mixture was refluxed for 2 h. After cooling, the pre-
cipitate solid was collected, filtered off and finally washed with
E-mail address: khold melha@yahoo.com.
1386-1425/$ – see front matter © 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2007.07.023

K.S. Abou-Melha / Spectrochimica Acta Part A 70 (2008) 162–170
163
of the complexes (10−3 M) using a model LBR, WTWD-812
Wilhelm conductivity meter fitted with a model LTA100 cell.
Analyses of the metals followed decomposition of their com-
plexes with concentrated nitric acid. The resultant solution was
diluted with distilled water, filtered to remove the precipitated
ligand. The solution was then neutralized with aqueous ammo-
nia solution and the metal ions titrated with EDTA. Analysis
of the uranyl complex was carried out at the Central Labora-
tory for Environmental Quality Monitoring, CLQM, Kalubia,
Cairo, Egypt. The complex was first dried and grind followed
by digestion by nitric-HF digestion mixture using Milestone
Microwave Digester Model MLS 1200 Mega. The digestible
uranium metal was analyzed using Perkin-Elmer ICP OES,
Model Optima-3000 coupled with an Ultra Sonic Nebulizer,
USN. Microanalyses of carbon, hydrogen, nitrogen and chlorine
were carried out at the Micro analytical Center, Cairo University,
Giza, Egypt. Chlorine in the Fe(III) complexes was determined
by ion chromatography using a (1C) Dionex 500 instrument
for anions at the Central Laboratory for Environmental Quality
Monitoring, El-Kanater, Cairo, Egypt.
Fig. 1. Structure of the ligand, Isonicotinic acid (2-hydroxybenzylidene)
hydrazide.
5–10 mL cold absolute ethanol and re-crystallized from ethanol
(yield 80%, m.p. 225 ◦C).
2.3. Synthesis of the metal complexes
A solution of metal salt dissolved in ethanol was added gradu-
ally to a stirred ethanolic solution of the ligand, HL, in the molar
ratio 1:2 (metal:ligand). The reaction mixture was further stirred
for 2–4 h to ensure the complete precipitation of the formed com-
plexes. The precipitated solid complexes were filtered, washed
several times with 50% (v/v) ethanol–water to remove any traces
of the unreacted starting materials. Finally, the complexes were
washed with diethyl ether and dried in vacuum desiccators over
anhydrous CaCl2. The reaction of uranyl salt was carried out in
methanol as it dissolved better in this solvent. The preparations
described were repeated in the presence of LiOH, as deproto-
nating agent, and its addition is must in order to obtain such
preparation with good yield. In most cases, the same yield was
obtained. Trials to prepare Cd(II) complex was unsuccessful and
start materials were recovered unreacted.
2.5. Pharmacology
The in vitro evaluation of antimicrobial activity was carried
out at Saudi Pharmacutical industries and Medical Appliance
Corporation. The purpose of the screening program is to pro-
vide antimicrobial activity and bacteriostatic and fungistatic
efficiency of the investigated metal complexes. The prepared
compounds were tested against one strain of Gram +ve bac-
teria (Staphylococcus aureu), Gram –ve bacteria (Escherichia
coli), and Fungi (Candida albicans) to provide the minimum
inhibitory concentration (MIC) for each complex. Bacteriostatic
and fungistatic efficiency is the lowest concentration of solution
to inhibit the growth of a test organism.
2.4. Physical measurements and analyses
3. Results and discussion
Electronic spectra were recorded for solution of the lig-
and, HL in DMF, and for the metal complexes as Nujol Mull
on a Jasco UV–vis spectrophotometer model V-550 UV–vis.
The 1R spectra were recorded using CsI discs on FT-IR 1650
3.1. Characterization of the Ligand, HL
The reaction of Co(II), Ni(II), Mn(II), UO2(II) and iron(III)
saltswiththe ligand, HL, resultsinthe formationof[ML2]·EtOH
for M = Ni(II), Co(II) and Mn(II) and [ML2Cl]·2EtOH for
M = Fe(III) and [UO2L2(MeOH)]·2MeOH. For Cu(II) salt, only,
[CuLCl]·EtOH was obtained (Table 1). All complexes are quite
stable and could be stored without any appreciable change. The
complexes do not have sharp melting points but decompose
above 260 ◦C. They are insoluble in common organic solvents,
such as ethanol, methanol, chloroform or acetone. However, they
are soluble in DMSO and DMF. The conductance measurement
indicates that all complexes are essentially non-electrolytes in
DMF.
Elemental analyses reflected that the ligand has the molecular
formula given in Table 1. The 1H NMR spectrum (Table 2) of
the ligand in deuterated dimethylformamide showed two signals
at δ 14.5 and 11.7 ppm for the proton of the phenolic OH and the
NH groups, respectively [20,21]. A signal is also observed at δ
1
Perkin-Elmer spectrometer. H NMR spectra were carried out
in DMF-d6 at room temperature using TMS as internal standard
on a Brucker 250 MHz spectrophotometer. Magnetic suscepti-
bilities of the complexes were measured by the Gouy method at
room temperature using a model MK1 Johnson Matthey. Alpha
products magnetic susceptibility balance. The effective mag-
netic moments were calculated using the relation (μeff = 2.828
(χm T)1/2 B.M.) where χm is the molar susceptibility corrected
using Pascal’s constants for diamagnetism of all atoms in the
compounds. The TG-DTA measurements were carried out on
a Shimadzu thermo gravimetric analyzer in dry nitrogen atmo-
sphere and a heating rate of 10 ◦C min−1 using the TA-50 WS1
program. Mass spectra were recorded at 70 eV and 300 ◦C on
an MS 5988 Hewlett–Packard mass spectrometer. Conductivity
measurements were measured in DMF or nitrobenzene solutions

164
K.S. Abou-Melha / Spectrochimica Acta Part A 70 (2008) 162–170
Table 1
Elemental analyses, colour, yield, melting points and molar conductance of HL and its corresponding metal complexes
Compund (F.wt.)
Elemental analysis, found/(calcd.) %
Colour
Yield (%)
C
H
N
Cl
–
M
–
HL
65.17
(64.73)
5.06
(4.56)
17.82
(17.43)
Pale Yellow
Green
94
60
55
76
60
66
72
C
13H11N3O2 (241)
[CuL(Cl]·EtOH
46.95
(46.75)
4.50
(4.16)
10.63
(10.90)
9.56
(9.22)
15.57
(16.50)
C15H16N3O3ClCu (385)
[NiL2]·EtOH
57.86
(57.44)
4.8.6
(4.44)
14.5.9
(14.36)
10.27
(10.09)
–
–
–
Pale Green
Yellowish Green
Brown
C28H26N6O5Ni (585)
[CoL2]·EtOH
57.76
(57.44)
4.91
(4.44)
14.72
(14.36)
10.34
(10.09)
C28H26N6O5Co (585)
[MnL2]·EtOH
58.13
(57.83)
4.93
(4.48)
14.92
(14.46)
9.97
(9.47)
C28H26N6O5Mn (581)
[FeL2(Cl)]·2EtOH
30H32N6O6ClFe (663.5)
54.81
(54.26)
8.60
(8.11)
13.15
(12.66)
6.10
(5.84)
9.12
(8.44)
Deep brown
C
[UO2L2(MeOH)]·2MeOH
29H32N6O7U (814)
43.19
(42.75)
3.45
(3.93)
10.52
(10.31)
28.81
(29.24)
–
Red
C
6.62 ppm for the HC N– group [20,21] (Table 2). Addition of
D2O to the previous solution results in diminishing the signals
due to the protons of phenolic OH and HN–N groups.
The UV–vis spectrum (Table 4) recorded for the ethano-
lic solution of the ligand showed absorption bands at 48,076
and 44,642 cm−1 assigned for ␲–␲ transitions within the aro-
*
The IR spectrum of the ligand (Table 3) shows a strong
band at 3530 cm−1 assigned to ␯OH of the phenolic group.
The deformation vibration, δ, of the phenolic OH group appears
at 1278 cm−1. The NH stretching [22–24] absorption appears
as weak bands at 3300 and 3220 cm−1. Another important
band occurs at 1585 cm−1 attributed to ␯(C N) (azomethine)
mode [21–24]. Carbonyl–amide and NH–amide absorption
bands appear at 1700 and 1655 cm−1, respectively. The strong
bands observed at 1520–1575 cm−1 and 1000–1080 cm−1 are
tentatively assigned [21–24] to asymmetric and symmetric
␯(C C) + ␯(C N) of pyridine ring and pyridine ring breathings
and deformations.
matic and pyridine rings. The band observed at 36,231 and
*
36,531 cm−1 would be due to the n–␲ transition of the C N
and C O groups, respectively. The absorption bands at 26,176
and 24,752 cm−1 assigned for CT transitions. The band at
24,752 cm−1 encroaches on the visible region [21] and impact
the ligand its colour.
Themass spectrum oftheligand (Fig. 2) showed itsmolecular
ion at m/e 241 which coincide with formula weight. Metastable
ion(s) is/are not observed. Scheme 1 represented the proposed
fragmentation pattern of the ligand.
The pH-metric measurement for 3 × 10−3 M of 75% (v/v)
ethanol–water solution of the ligand indicated that only one pro-
Table 2
1H NMR data of the ligand HL in DMF-d6
Isonicotinic acid (2-hydroxybenzylidene)hydrazide
Chemical shift, δTMS (ppm)
Assignmenta
14.5
[s, 1H] (1)
6.2
[s, 1H] (2)
11.7
[s, 1H] (3)
7.5–9.3
[m, 8 H, Ar-H and pyridine-H]
a
s: singlet, m: multiplet.
Fig. 2. Mass spectrum of the ligand HL.

K.S. Abou-Melha / Spectrochimica Acta Part A 70 (2008) 162–170
165
Table 3
Characteristic IR bands (cm−1) of HL and its corresponding metal complexes
Compound (F.wt.)
␯(C N)
␯(N–H)
␯(C O)
␯(N–N)
␯(M–N)
␯(M–O)
␯(OH)
Other bands
phenolic
HL C13H11N3O2 (241)
1585s
3300m
3314w
1700vs
1655vs
1140s
1136s
–
–
3530
–
1278 (␦OH)
[CuL(Cl]·EtOH
1530m
420w
540m
3385 (outer-sphere MeOH)
C15H16N3O3ClCu (385)
[NiL2]·EtOH C28H26N6O5Ni
1525m
1555s
1535m
1530s
1532s
3310s
1670vs
1680s
1620s
1670vs
1662s
1137w
1125w
1136s
1137s
1134s
425w
410w
445w
465w
460w
520m
515m
520w
520m
540w
–
–
–
–
–
3370 (outer-sphere MeOH)
3385 (outer-sphere MeOH)
3375 (outer-sphere MeOH)
3380 (outer-sphere MeOH)
3380 (outer-or inner-sphere
(585)
[CoL2]·EtOH C28H26N6O5Co
(585)
3300w
3310w
3315w
3314w
[MnL2]·EtOH C28H26N6O5Mn
(581)
[FeL2(Cl)]·2EtOH
C30H32N6O6ClFe (663.5)
[UO2L2(MeOH)]·2MeOH
C29H32N6O7U (814)
MeOH), 901 (␯3(O
U O)
s: strong, w: weak, m: medium, vs: very strong.
Table 4
Magnetic moment, molar conductance, and electronic spectral data (cm−1) for HL and its metal complexes
*
Compound (F.wt.)
μeff. (B.M.)
␲ → ␲*, n → ␲ and charge
d → d transitionsa
Molar
transfer transitionsa (cm−1
)
(cm−1
–
)
conductanceb
HL C13
H11N3O2 (241)
diac
48,067, 44,642, 36,231, 26,176,
24,752
–
[CuL(Cl]·EtOH C15H16N3O3ClCu (385)
[NiL2]·EtOH C28H26N6O5Ni (585)
[CoL2]·EtOH C28H26N6O5Co (585)
[MnL2]·EtOH C28H26N6O5Mn (581)
[FeL2(Cl)]·2EtOH C30H32N6O6ClFe (663.5)
[UO2L2(MeOH)]·2MeOH C29H32N6O7U (814)
1.75
2.85
5.13
5.92
5.89
diac
36,765, 28,612, 22,396
15,520, 15,850
1518.45, 11,957
15,250, 22,480
21,331.9, 11,733.33
14,331, 13,850
22,500, 19,040
3.7
2.6
2.4
5.0
3.6
3.7
37,037, 28,653, 22,371
370,307, 28,600, 22,271
37,085, 28,500, 22,471
37,137, 27,653, 22,571
37,537, 27,853, 22,871
a
As Nujol mull.
b
Measured for 10−3 M solution in DMF, ꢀ−1 cm2 mol−1
.
c
dia=diamagnetic.
Scheme 1. Mass fragmentation pattern of the ligand HL.

166
K.S. Abou-Melha / Spectrochimica Acta Part A 70 (2008) 162–170
␯3(O U O) appeared as a strong band at 901 cm−1 overlapping
with another band already present in the spectrum of the parent
ligand and thus gaining higher density [20,21].
The overall IR spectral evidence suggests that the HL
acts as monobasic tridentate ligand and coordinate through
amide–oxygen, azomethine–nitrogen and phenolic-oxygen
atoms forming a six-membered chelate ring. In all spectra, new
bands appeared, for all types of the complexes, at 515–540 cm−1
and 410–465 cm−1 that would be assigned to ␯M–O and ␯M–N,
respectively [25].
ton dissociates together with the value of pKa (10.63) suggesting
that the ligand behaves as a weak monobasic acid. The value of
pKa reveal that the proton dissociated from the phenolic OH
group rather than from the N-proton of the hydrazino moiety
which may dissociated at higher pH region.
3.2. IR spectra of the metal complexes
The ligand is expected to act as tetradentate one, the pos-
sible coordination sites being pyridinic-nitrogen, azomethine
nitrogen, phenolic oxygen and amide group. A study and com-
parison of the IR spectra of ligand and its metal complexes
imply that the ligand, HL, is monobasic tridentate in nature with
carbonyl–oxygen, azomethine–nitrogenandphenolic-oxygenas
three, ONO, coordination sites. The IR-data are presented in
Table 3.
3.3. Magnetic moments and electronic spectral data of the
metal complexes
The electronic spectra and magnetic moments of the metal
complexes are listed in Table 4. Generally, in all spectra of metal
complexes, the absorption bands due to ␲–␲* and n–␲* tran-
sitions that observed in the spectrum of the free ligand higher
than 22,300 cm−1 have shifted to lower frequencies due to the
coordination of the ligand with metal ions.
The IR spectra of the metal complexes showed that the band
due to phenolic OH group that appeared in the spectrum of the
ligand at 3530 cm−1 have disappeared in the spectra of the com-
plexes, may be due to the displacement of its proton by the metal
ion in accordance with the pH-metric and dissociation constant
of the ligand. The δ(COH)ip mode which appeared at 1355 cm−1
in the spectrum of the ligand, was not observed in the spectra of
the complexes and thus supported the suggestion that the ligand
coordinate to the metal through its deprotonated form. More-
over, the band observed at 1585 cm−1 in the spectrum of the
ligandwhichattributedto␯(C N)(azomethine)mode[21–24]is
shifted, in spectra of all the complexes to lower wave number and
appears at 1525–1555 cm−1 region indicating the involvement
of N-atom of the azomethine group in coordination [25–28].
In addition, in the spectra of the complexes, a considerable
negative shift in ␯(C O) is observed indicating a decrease in the
stretching force constant of C O as a consequence of coordina-
tion through the carbonyl–oxygen atom of the free ligand. The
NH stretching absorption in free ligand occurs [28] at 3300 and
3220 cm−1 which remains unaffected after complexation. This
precludes the possibility of coordination through imine nitrogen
atom.
The spectra of the Cu(II) complex (Table 4) showed absorp-
tion bands at 15,520–15,850 cm−1 which could be attributed
2
2
to the A1g → B1g transitions characterized Cu(II) ion in
a square-planar geometry [29]. The square-planar geometry
of Cu(II) ion in the complex is confirmed by the measured
magnetic moments values, 1.75 B.M. The square-planar geom-
etry is achieved by the coordination of two molecules of HL
each as monobasic tridentate ligand, to the copper(II) ion
[29–31]. The Cu(II) completed its four coordination by the
attachment of one chlorine ion. The shift of the absorption
band to lower energy than that expected for square-planar
geometry, at 18,191.8 cm−1 for square-planar N,Nꢀ-ethylenebis-
(salicylideneimine)copper(II), Cu(acacen) [21] may be due to
the distortion of the square-planar geometry towards tetrahedral
[21,29].
The electronic spectrum of the Ni(II) complex, Table 4,
showed broad absorption band at 16,220 cm−1 which may be
3
3
The strong bands observed at 1520–1575 cm−1 and
1000–1080 cm−1 are tentatively assigned [21–24] to asym-
metric and symmetric ␯(C C) + ␯(C N) of pyridine ring and
pyridine ring breathings and deformations remain practically
unchanged in frequency and band intensities revealing non
involvement of pyridinic-nitrogen and metal bond.
The IR spectrum of the mononuclear UO2(II) complex
showed a broad band at 3459 cm−1 assigned to ␯(OH) of the
coordinated methanol group and ␯(NH) of the uncoordinated
NH groups appeared as a shoulder at 3314 cm−1, exactly at the
same frequency as for the parent ligand. However, no splitting of
this band was observed, which may be due to the larger separa-
tion of the two ligand molecules, due to the larger volume of the
UO2(II) cation in the complex molecules. A well-characterized
band appeared at 1532 cm−1 assigned to the coordinated C N
group. The band recurs at a lower frequency compared to that
of the parent ligand indicating its involvement in coordinating
the UO2(II) cation, in addition to the phenolic-oxygen atoms
after replacing its hydrogen ions by the uranyl(II) cation. The
assigned to A1g(F) → T2g(F), while the absorption due to
3A2g(F) → T1g(P) is overlapped with the ligand absorption
3
bands. This indicates that the Ni(II) ion coordinated to NNO
sites in an octahedral geometry [29–33]. The third transition
due to 3A2g(F) → T1g(P) would be out of the scale of the used
3
spectrophotometer. Themagneticmomentofthecomplexis2.85
B.M. which agrees with the presence of Ni(II) ion in octahedral
geometry [21,29].
The measured magnetic moment of cobalt(II) complex is
given in Table 4. The theory of magnetic susceptibility of
cobalt(II) ion was given originally by Schlapp and Penney [30]
and the best summary of results on the magnetic behaviour
of cobalt compound is that of Figgis and Nyholm [31]. The
observed values of magnetic moments for cobalt(II) complexes
are generally diagnostic of the coordination geometry about
the metal ion. The low-spin square-planar cobalt(II) complexes
may be 2.9 B.M., arising from one unpaired electron plus
an apparently large orbital contribution [31]. Both tetrahedral
and high-spin octahedral cobalt(II) complexes possess three

K.S. Abou-Melha / Spectrochimica Acta Part A 70 (2008) 162–170
167
unpaired electrons but may be distinguished by the magni-
tude of the deviation of μeff from the spin-only value. The
magnetic moment of tetrahedral cobalt(II) complexes with an
orbitally non-generate ground term is increased above the spin-
only value via contribution from higher orbitally degenerate
terms and occurs in the range [31,33] 4.2–4.7 B.M. octahedral
cobalt(II) complexes, however, maintain a large contribution due
to 4Tg ground term and exhibit μeff in the range [31,33] 4.8–5.6
B.M. The magnetic measurement on the complex reported
herein is 5.1 B.M showing that it has three unpaired electrons
indicating a high-spin octahedral configuration. The electronic
spectrum of the complex showed two d–d transitions in the
range 15,250–15,390 cm−1 and 18,410–18,480 cm−1 due to the
from equatorial donor atoms of the ligand to the uranyl ion.
The second band observed at 19,040 cm−1 due to electronic
transitionsfromapicaloxygenatomtothef-orbitalsoftheuranyl
atom characteristic of the uranyl moiety [34].
On the other hand, the electronic spectra of Fe(II) complex
showed broad bands 14,331 and 13,850 cm−1. The former band
6
4
may be due to the spin forbidden transition A1g → T2g(G),
which may gain intensity as a result of the vibronic mechanism
in the octahedral field around ferric ion. The second bands may
6
4
be attributed to A1 → T1(G) transitions. In addition, a third
absorption band with high intensity observed at 25,252 cm−1
assigned for charge transfer transition. The magnetic moment
of complex is 5.89 B.M. [31,33].
4
4
transitions 4T1g(F) → A2g(F) and 4T1g(F) → A2g(P), respec-
tively, [31] indicating an octahedral configuration around Co(II)
3.4. Molar conductance of the metal complexes
4
4
ion. The T2g(F) → T1g(F) transition (9510 cm−1) would be
observed in near IR region [31]. This region is out of the scale
of our spectrophotometer [31,33].
The conductance measurements, recorded for 10−3 M solu-
tions of the metal complexes in DMF, are listed in Table 4. All
complexes, except two, are non-conducting and the measured
molar conductance ranged from ∼2.0 to 3.6 Ohm−1 cm2 mol−1
indicating their neutrality.
The spectrum of the Mn(II) complex showed a series of
weak bands in the range 21,331.96–11,733.33 cm−1. Mn(II)
ion is d5 system and its d–d transitions are both Laporte and
spin-forbidden. However, due to instantaneous distortion of the
octahedral structures around the metal cation, weak bands some-
times do appear [31,33] The magnetic moment of the complex is
5.94 B.M. and indicates antiferromagnetic interaction between
the adjacent metal cations.
3.5. 1H NMR spectrum of the uranyl complex
The uranyl complex was selected as it is diamagnetic. Its 1H
NMR spectrum in DMF and after deuteration are discussed. The
spectrum of the complex differs from that of the free ligand in
the following aspects:
The electronic spectra of the diamagnetic uranyl complex
showed two bands, in addition to the ligand bands. The first
band observed at 22,500 cm−1 corresponding to charge transfer
Table 5
Thermal analyses data for some metal complexes of HL
Compound (F.wt.)
Dissociation
stages
Temperature
range in TG ◦C
Weight loss
found (calcd.) %
Decomposition assignment
[CuL(Cl]·EtOH C15H16N3O3ClCu
Stage I
Stage II
Stage III
130–150
223–383
385–545
8.16 (7.79)
72.00 (71.56)
63.15 (62.60)
Loss of one mol outer-sphere EtOH
Loss of one mol of the ligand-Cl
Formation of CuO
(385)
[NiL2]·EtOH C28H26N6O5Ni (585)
[CoL2]·EtOH C28H26N6O5Co (585)
[MnL2]·EtOH C28H26N6O5Mn (581)
Stage I
120–135
234–373
375–438
439–510
5.73 (5.13)
42.00 (41.03)
41.70 (41.03)
13.20 (12.82)
Loss of one mol outer-sphere EtOH
Loss of one mol of the ligand
Loss of one mol of the ligand
Formation of NiO
Stage II
Stage III
Stage VI
Stage I
130–145
240–378
380–448
460–550
5.61 (5.16)
42.00 (41.31)
42.20 (41.31)
13.60 (12.82)
Loss of one mol outer-sphere EtOH
Loss of one mol of the ligand
Loss of one mol of the ligand
Formation of CoO
Stage II
Stage III
Stage VI
Stage I
125–155
234–375
380–438
459–510
4.45 (4.52)
37.20 (36.17)
36.73 (36.17)
13.00 (12.22)
Loss of one mol outer-sphere EtOH
Loss of one mol of the ligand
Loss of one mol of the ligand
Formation of MnO
Stage II
Stage III
Stage VI
[FeL2(Cl)]·2EtOH C30H32N6O6ClFe
Stage I
130–145
240–378
380–448
459–550
4.43 (4.52)
Loss of 2 mol outer-sphere EtOH
Loss of one mol of the ligand-Cl
Loss of one mol of the ligand
Formation of Fe2O3
(663.5)
Stage II
Stage III
Stage IV
41.10 (41.522)
37.21 (36.32)
23.90 (24.12)
[UO2L2(MeOH)]·2MeOH
Stage I
80–110
130–145
240–378
380–448
459–550
7.21 (7.37)
4.10 (3.68)
30.10 (29.48)
29.30 (29.48)
32.23 (33.17)
Loss of the 2 mol outer-sphere MeOH
Loss of one mol coordinated MeOH
Loss of one mol of the ligand
Loss of one mol of the ligand
Formation of UO2
C
29H32N6O7U (814)
Stage II
Stage III
Stage IV
Stage V

168
K.S. Abou-Melha / Spectrochimica Acta Part A 70 (2008) 162–170
Fig. 3. Suggested structures of [ML2]·EtOH (M = Co(II), Ni(II) or Mn(II); (b) [ML2Cl]·2EtOH (M = Fe(III); (c) [UO2L2(MeOH)]·2MeOH and (d) [CuL(Cl)]·EtOH.
1. The disappearance of the signal due to the phenolic OH group
is attributed to its involvement in coordinating the uranyl
cation, while the signal due to the NH group was broad and
appeared at δ = 12.4 ppm compared to that of the ligand which
appeared at, δ = 11.7 ppm, i.e. shifted to low-field. This signal
disappeared on deuteration.
2. The signals due to the aromatic and pyridine rings showed
fine structure and appear as four separate signals.
3. New signals for CH3 group of the coordinated and the
outer-sphere methyl alcohol molecule appeared at δ = 3.6 and
3.5 ppm, respectively, while the OH group of the alcohol did
not appear as it would be masked by other signals.
Table 6
Results of anti-microbial activity of some tested complexes
Compound
Concentration (%)
Staphylococcus aureus
ATCCa 6538 MICb 25%
Escherichia coli ATCC
8739 MIC 25%
Candida albicans ATCC
10,231 MIC 25%
1c
25
HL
+ve
−ve
−ve
−ve
−ve
+ve
−ve
+ve
+ve
50
100
[CuL(Cl)]·EtOH
[NiL2]·EtOH
1
25
50
+ve
+ve
+ve
−ve
+ve
+ve
+ve
−ve
+ve
+ve
−ve
−ve
100
1c
25
50
−ve
−ve
−ve
+ve
−ve
−ve
−ve
−ve
−ve
100
1c
25
50
[CoL2]·EtOH
−ve
−ve
−ve
−ve
−ve
−ve
−ve
−ve
−ve
100
[MnL2]·EtOH
1
25
50
+ve
+ve
+ve
−ve
−ve
+ve
−ve
−ve
−ve
−ve
−ve
−ve
100
[FeL2(Cl)]·2EtOH
UL2(MeOH)]·2MeOH
1
25
50
+ve
−ve
+ve
−ve
+ve
+ve
+ve
−ve
−ve
−ve
−ve
−ve
+ve
+ve
+ve
−ve
100
1
25
50
+ve
+ve
−ve
−ve
−ve
−ve
−ve
−ve
100
Key to symbols: Active and inhibit the growth of the strain: −ve; Inactive: +ve.
a
Number of strain in the American collection.
MIC is the lowest concentration of the product material solution to inhibit the growth of the microorganism.
Not tested in this concentration.
b
c

K.S. Abou-Melha / Spectrochimica Acta Part A 70 (2008) 162–170
169
3.6. Thermal analyses
exhibited for 25, and 50% concentrations. However, Cu(II) com-
plex [CuL(Cl)]·EtOH exhibited its activity only at its 100 and
50% concentration. The tested compounds showed an inhibitory
activity of 25%.
The TG-DTA results of the solid Ni(II), Co(II) and Mn(II)
complexes are listed in Table 5. The results show that all com-
plexes have similar decomposition pattern which is in good
agreement with the formulae suggested from the analytical data,
Table 1. A general decomposition patterns was concluded in
which the complexes decomposed in four stages except Cu(II)
complex which decomposed in three stages. Beside the four
stages, uranyl complex, which has coordinated MeOH molecule,
exhibited additional stage to be decomposed in five stages
(Table 5) and lost its outer-sphere MeOH molecule at rela-
tively low temperature, after that, the decomposition process
will started which is similar to the decomposition process of
the other complexes. All complexes lost one mol of the lig-
and at 230–370 ◦C. The second mol of the ligand was lost
at 380–4550 ◦C accompanied with the formation of the metal
oxides. Based on the above results, the structures in Fig. 3 are
suggested for the metal complexes.
4. Conclusion
The present study revealed octahedral geometry around
Ni(II), Co(II), Mn(II) and Fe(III) complexes. However,
square-planar geometry is suggested for copper ion in the Cu(II)-
complex, In all cases, the ligand HL acts as monobasic tridentate
coordinating through ONO coordination sites and thus form-
ing stable six- and four-membered chelates. The results of
antimicrobial activity show that the metal complexes exhibit
antimicrobial properties and it is important to note that they
show enhanced inhibitory activity compared to the parent lig-
and. It has also been proposed that concentration plays a vital
role in increasing the degree of inhabitation.
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previously [35]. A 0.02 g of each complex was dissolved in
100 ml dimethylsulfoxide, DMSO, to produce 0.02% solutions.
To a series of culture tubes, in which each tube containing ster-
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was added to each tube and mixed. To determine the bacterio-
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