Structural, spectral and biological studies of binuclear tetradentate metal complexes of N3O Schiff base ligand synthesized from 4,6-diacetylresorcinol and diethylenetriamine

Article abstract of DOI:10.1016/j.saa.2010.04.036

The binuclear Schiff base, H₂L, ligand was synthesized by reaction of 4,6-diacetylresorcinol with diethylenetriamine in the molar ratio 1:2. The coordination behavior of the H₂L towards Cu(II), Ni(II), Co(II), Zn(II), Fe(III), Cr(III

Full text of DOI:10.1016/j.saa.2010.04.036

Spectrochimica Acta Part A 77 (2010) 117–125
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Structural, spectral and biological studies of binuclear tetradentate metal
complexes of N3O Schiff base ligand synthesized from 4,6-diacetylresorcinol and
diethylenetriamine
Adel A.A. Emara∗
Faculty of Education, Department of Chemistry, Ain Shams University, Roxy, Cairo 11341, Egypt
a r t i c l e i n f o
a b s t r a c t
Article history:
The binuclear Schiff base, H2L, ligand was synthesized by reaction of 4,6-diacetylresorcinol with
diethylenetriamine in the molar ratio 1:2. The coordination behavior of the H2L towards Cu(II), Ni(II),
Co(II), Zn(II), Fe(III), Cr(III), VO(IV) and UO2(VI) ions has been investigated. The elemental analyses,
magnetic moments, thermal studies and IR, electronic, 1H NMR, ESR and mass spectra were used to char-
acterize the isolated ligand and its metal complexes. The ligand acts as dibasic with two N3O-tetradentate
sites and can coordinate with two metal ions to form binuclear complexes. The bonding sites are the nitro-
gen atoms of the azomethine and amine groups and the oxygen atoms of the phenolic groups. The metal
complexes exhibit either square planar, tetrahedral, square pyramid or octahedral structures. The Schiff
base ligand and its metal complexes were tested against four pathogenic bacteria (Staphylococcus aureus
and Streptococcus pyogenes) as Gram-positive bacteria, and (Pseudomonas fluorescens and Pseudomonas
phaseolicola) as Gram-negative bacteria and two pathogenic fungi (Fusarium oxysporum and Aspergillus
fumigatus) to assess their antimicrobial properties. Most of the complexes exhibit mild antibacterial and
antifungal activities against these organisms.
Received 22 February 2010
Received in revised form 26 March 2010
Accepted 28 April 2010
Keywords:
Tetradentate Schiff base
Binuclear complexes
Antimicrobial activities
ESR spectra
© 2010 Elsevier B.V. All rights reserved.
1. Introduction
cytotoxic activity [15,20], where the metal complexes have higher
antimicrobial and antifungal activities than the free ligands. Also,
Schiff base ligands played central role as chelating ligands in
the main group and transition metal coordination chemistry [1,2].
Transition metal complexes of tetradentate Schiff base ligands find
applications as model analogues of certain metal enzymes [3] and
catalyst in oxidative addition reactions [4,5], modifier for selective
electrodes, and different uses in material chemistry [6]. A bimetallic
core is versatile at the active site of many metalloenzymes and plays
an essential role in biological systems by the interplay of a pair of
metal ions [7]. In the last decade, a large number of bimetallic Schiff
base complexes of different structural types have been synthesized
and characterized [8,9]. These complexes span the gamut in their
new applications, donating types, structures [10] and biological
activities [11].
Recently, a wide varieties of the Co(II), Ni(II), Cu(II) and Zn(II)
complexes of Schiff base derivatives including compartmental and
macrocyclic ligands were tested in vitro for their antibacterial activ-
ities against human pathogenic bacteria (using disc diffusion (DD)
method [12–15,19] or minimum inhibitory concentration (MIC)
method [16,17,20,21]), fungal activities [13,14,16–18,20–23] and
a survey highlights structural properties and biological studies
of transition metal complexes derived from 4-aminoantipyrine
were reported [24]. The most important results of extensive stud-
ies (syntheses, spectral, magnetic, redox, structural characteristics,
antimicrobial and DNA cleavage) of the metal complexes with het-
erocyclic Schiff bases of 4-aminoantipyrine with some aldehydes
and oximes are reviewed.
In the present work, this field is extended in synthesis of
novel tetradentate binuclear Schiff base complexes, which could
be used in numerous applications. The ligand was prepared by
the condensation of 4,6-diacetylresorcinol (DAR), as starting mate-
rial, with diethylenetriamine (DET) to afford the corresponding
Schiff base, H2L, ligand. The reaction of this ligand with copper(II),
nickel(II), cobalt(II), cadmium(II), zinc(II), iron(III), chromium(III),
oxovanadium(IV) and dioxouranium(VI) ions, in the 1:2 molar ratio
(ligand:metal ion) was studied. The newly prepared metal com-
plexes of this ligand were identified by different physicochemical
and spectroscopic techniques.
The H2L ligand acts as dibasic with two N3O-tetradentate
sites and can coordinate with two metal ions to form bin-
uclear complexes. Copper(II), cobalt(II), iron(III) and Cr(III)
complexes are octahedral. Nickel(II) is square planar while
zinc(II) is tetrahedral. Oxovanadium(IV) complex is square pyra-
∗
Tel.: +20 2 24551530; fax: +20 2 22581243.
E-mail addresses: adelaemara@yahoo.com, adelaemara@gmail.com.
1386-1425/$ – see front matter © 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2010.04.036

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A.A.A. Emara / Spectrochimica Acta Part A 77 (2010) 117–125
Fig. 1. Formation of Schiff base, H2L, ligand.
midal, while the dioxouranium(VI) complex is an octahedral
[25].
ethylamine:ligand) and heated to reflux for 30 min. The appropriate
weight of 10.00 mmol of the metal salts was added to the ionic
deprotonated ligand to form the metal complexes.
The following detailed preparation is given as an example and
the other complexes were obtained similarly.
The Schiff base, H2L, ligand and its metal complexes were
investigated for antibacterial and antifungal properties. Two
Gram-positive bacteria (Staphylococcus aureus and Streptococcus
pyogenes), two Gram-negative bacteria (Pseudomonas fluorescens
and Pseudomonas phaseolicola) and two fungi (Fusarium oxyspo-
rum and Aspergillus fumigatus) were used in this study to assess
their antimicrobial properties. Most of the complexes exhibit mild
antibacterial and antifungal activities against these organisms and
some of them were more effective than the free ligand.
2.3.1. Reaction of Cu(II) with H2L ligand
Copper(II) nitrate tetrahydrate, Cu(NO3)2·4H2O (2.596 g,
10.0 mmol) in methanol (30 mL) was added gradually with con-
stant stirring to a solution of the deprotonated, H2L, ligand (1.822 g,
5.0 mmol) in methanol (60 mL). The pH of the mixture was 2.2.
The stoichiometry of the metal ion to ligand was 2:1. The solution
was heated to reflux for 3 h. A green precipitate was formed and
washed with small amount of methanol then ether. The yield was
2.307 g (75.6%), m.p. > 250 ◦C.
2. Experimental
2.1. Materials
4,6-Diacetylresocinol (DAR) was synthesized according to the
literature method [26]. Diethylenetriamine and triethylamine
were Merck. Copper(II), nickel(II), cobalt(II), cadmium(II), zinc(II),
iron(III) and chromium(III) were used as nitrate salts and were
Merck or BDH. Oxovanadium(IV) sulfate monohydrate and diox-
ouranium(VI) acetate dihydrate were Fluka. Organic solvents
(ethanol, absolute ethanol, methanol, diethylether, dimethylfor-
mamide and dimethylsulfoxide) were reagent grade and were used
as supplied.
2.4. Physical measurements
Carbon, hydrogen and nitrogen contents were carried out at
the Microanalytical Center, Cairo University. Analyses of metal
ions after the dissolution of the solid complex in hot concen-
trated nitric acid, HNO3, then diluting with distilled water and
filtering to remove the precipitated ligand. The solution was neu-
tralized with ammonia solution and the metal ions were then
titrated with EDTA [27–29]. The FT-IR spectra (4000–400 cm−1
)
of the compounds were recorded as KBr discs using FT-IR (Shi-
madzu) spectrophotometer model 4000. 1H NMR spectra (TMS
was used as an internal standard reference) were recorded using
a Varian spectrometer, EM-390, 90 MHz. Electronic spectra of the
ligand and its metal complexes were carried out in 10−3 M DMF
solution on a JASCO model V-550 UV–Visible spectrophotometer
in the range 200–900 nm. Magnetic susceptibilities of the com-
plexes were measured by the Gouy method at room temperature
using a magnetic susceptibility balance (Johnson Matthey, Alfa
product, Model No. (MKI)). Effective magnetic moments were cal-
culated from the expression ꢀeff = 2.828 (ꢁMT)1/2 B.M., where ꢁM is
the molar susceptibility corrected using Pascal’s constants for the
diamagnetism of all atoms in the compounds and T is the abso-
lute temperature [30]. ESR spectra of compounds were recorded
on a Bruker model EMX, X-band spectrometer (9.78 GHz) with
100 kHz modulation frequency. Mass spectra of the compounds
were recorded on a Hewlett Packard mass spectrometer model
MS 5988. Samples were introduced directly to the probe and the
fragmentations were carried out at 300 ◦C and 70 eV. Thermal gravi-
metric analysis (TGA) data were measured from room temperature
to 800 ◦C at a heating rate 20 ◦C/min in dynamic N2 atmosphere.
The data were obtained using a Shimadzu TGA-50H instrument.
Thermal analyzer equipped with a thermo-balance. The sample was
contained in a boat-shaped platinum pan suspended in the center
of a furnace. Molar conductance of millimolar solutions of the solid
complexes in DMF was measured on Corning conductivity meter
model NY 14831 (USA). Melting points were not corrected and were
measured using a Stuart melting point instrument.
2.2. Synthesis of the Schiff base, H2L, ligand
The ligand was synthesized by adding 4,6-diacetylresorcinol
(DAR) (3.88 g, 20 mmol) dissolved in hot absolute ethanol (30 mL)
to diethylenetriamine (DET) (3.00 g, 40 mmol) in absolute ethanol
(30 mL). The reaction mixture was heated to reflux for 4 h. The yel-
low product was filtered off and washed with a few amount of
ethanol then ether and air dried. Fine crystals were obtained by
recrystallization from ethanol. The ligand was kept in a desicca-
tor until used. The yield was 4.98 g (80.4%), m.p. > 250 ◦C. The Schiff
base, H2L, ligand was characterized by elemental analyses, 1H NMR
and electronic spectra in DMF solution and in the solid state by IR
and mass spectra. The formation of H2L ligand is illustrated in Fig. 1.
2.3. Synthesis of the Schiff base metal complexes
A methanolic solution of the metal salt (30 mL) was added grad-
ually to a methanolic solution of the deprotonated ligand (60 mL)
in the molar ratio 2:1. Triethylamine was used to affect the depro-
tonation of the ligand. The reaction mixtures of the deprotonated
H2L ligand with metal salts were stirred on cold for 30 min, and then
heated to reflux, for 3 h. The resulting precipitates were filtered off,
washed with methanol then ether. The complexes are insoluble in
most common solvents and soluble only in DMF and DMSO.
In each case, triethylamine (0.610 g, 10.0 mmol) dissolved
in methanol (20 mL) which was added to the ligand (1.822 g,
5.00 mmol) in methanol (30 mL), i.e., in the molar ratio 2:1 (tri-

A.A.A. Emara / Spectrochimica Acta Part A 77 (2010) 117–125
119
2.5. Antimicrobial activities
The in vitro evaluation of antimicrobial activity was carried
out at Faculty of Agricultural, Al-Azhar University. The standard-
ized disc-agar diffusion method [31] was followed to determine
the activity of the synthesized compounds against the sensitive
organisms S. aureus (ATCC 25923) and S. pyogenes (ATCC 19615)
as Gram-positive bacteria, P. fluorescens (S 97) and P. phaseolicola
(GSPB 2828) as Gram-negative bacteria and the fungi F. oxysporum
and A. fumigatus.
The antibiotic chloramphencol was used as standard reference
in the case of Gram-negative bacteria, cephalothin was used as
standard reference in the case of Gram-positive bacteria and cyclo-
heximide was used as standard antifungal reference.
The tested compounds were dissolved in DMF (which have no
inhibition activity), to get concentrations of 2 and 1 mg mL−1. The
test was performed on medium potato dextrose agar (PDA) which
contains infusion of 200 g potatoes, 6 g dextrose and 15 g agar
[32,33]. Uniform size filter paper disks (3 disks per compound)
were impregnated by equal volume (10 ␮L) from the specific con-
centration of dissolved tested compounds and carefully placed on
incubated agar surface.
After incubation for 36 h at 27 ◦C in the case of bacteria and for
48 h at 24 ◦C in the case of fungi, inhibition of the organisms which
evidenced by clear zone surround each disk was measured and used
to calculate mean of inhibition zones.
The activity of tested compounds was categorized as (i) low
activity = mean of zone diameter is ≤1/3 of mean zone diameter
of control, (ii) intermediate activity = mean of zone diameter ≤2/3
of mean zone diameter of control and (iii) high activity = mean of
zone diameter >2/3 of mean zone diameter of control.
3. Results and discussion
3.1. Schiff base ligand
The structure of the Schiff base, H2L, ligand is identified by ele-
mental analysis, infrared, UV–Visible, 1H NMR and mass spectra.
Table 1 lists the physical and analytical data of the Schiff base, H2L,
ligand and its metal complexes. From the investigation, H2L ligand
can be represented as shown in Fig. 1.
The infrared spectrum is consistent with the formation of H2L
ligand. The vibrational assignments were aided by comparison
with the vibrational frequencies of the related compounds, such
as, the Schiff bases of 2-hydroxy-acetophenone [34]. The fun-
damental stretching mode of the azomethine moiety, ꢂ(–C N–),
is readily assigned by comparison with the infrared spectra
of 4,6-diacetylresorcinol (DAR) and diethylenetriamine (DET).
The absorption band of the C O in the 4,6-diacetylresorcinol
disappeared, but the absorption band of the NH2 in the diethylen-
etriamine, still persists, which may be due to the condensation of
the one NH2 has occurred while the other NH2 still as it is. The most
intense band at 1578 cm−1 is assigned to the –C N– stretching fre-
quency of the H2L ligand and is characterized for the azomethine
moiety of most Schiff base compounds. On the other hand, other
fundamental bands were assigned in the infrared spectrum of the
H2L ligand.
The mass spectrum of the Schiff base, H2L, ligand, revealed the
molecular ion peak at m/e 364 which is coincident with the for-
mula weight (364.4) and support the identity of the structure. Fig. 2
depicts the mass spectrum of the H2L ligand.
1H NMR spectra of H2L ligand in DMSO-d6, shows the chemical
shifts of the proton signals. Table 2 lists the 1H NMR chemical shifts
(ppm) of the Schiff base, H2L, ligand and its [Zn2(L)](NO3)2 complex
(4) in DMSO-d6 and their assignments. The signals of the –NH and
–NH2 for the diethylenetriamine moiety (4.62 and 10.12 ppm) and

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A.A.A. Emara / Spectrochimica Acta Part A 77 (2010) 117–125
5.86 and 8.17 ppm. The signal at 5.86 ppm is shifted to down field
based on the shielding by electrons due to the electron-repelling
effect of the two hydroxyl groups, i.e., mesomeric (+M) effect. The
other proton which observed at 8.17 ppm which is in the meta-
position for the two hydroxyl groups and have no mesomeric effect,
was deshielded by the inductive (−I) effect of the two acetyl groups
and two hydroxyl groups. These two protons did not disappear in
the presence of D2O. On the other hand, each of these two bands
showed related bands in slightly higher frequency which is due to
the tautometric isomers of the H2L ligand in solution. This is inter-
preted by the presence of three different tautometric isomers for
the H2L ligand.
Electronic spectral data of the ligand were recorded in DMF solu-
tion and four absorption bands at 272, 324, 335 and 417 nm were
1
characterized. The former and third bands correspond to 1La → A1
and 1Lb → A1 transitions of the phenyl ring [36]. The second band
1
corresponds to the ␲ → ␲* transition of the azomethine group, and
the last band corresponds to the n → ␲* transitions of the oxygen
and nitrogen atoms which are overlapped with the intermolecular
CT from the phenyl ring.
Fig. 2. Mass spectrum of the Schiff base, H2L, ligand.
Table 2
1H NMR chemical shifts (ppm)a of the Schiff base, H2L, ligand and [Zn2(L)(NO3)2]
3.2. Schiff base complexes
complex in DMSO-d6 and their assignments.
The Schiff base, H2L, ligand behaves as a dibasic ligand with
two N3O-tetradentate sites. The ligand reacted with Cu(II), Ni(II),
Co(II), Zn(II), Cr(III), Fe(III), VO(IV) and UO2(VI) ions to yield the
corresponding binuclear transition metal complexes. The geomet-
rical structures of the complexes were identified and characterized
using elemental analyses and infrared, UV–Visible, 1H NMR, ESR
and mass spectra. Also, TGA and molar conductivity measurements
were conducted to add more proofs in identifying the structures.
Chemical shifts (ppm)
H2L
Assignments
[Zn2(L)](NO3)2 complex (4)
1.59
1.58
[s, 6H, 2CH3]
[m, 8H, 4CH2]
[s, br, 4H, 2NH2]
[s, 1H, Ar-H]
[s, 1H, Ar-H]
[s, 2H, NH]
1.79, 2.41 and 3.20
1.80, 2.41 and 3.23
4.62b
5.86
3.31b
5.65
8.00
10.11b
–
8.17
10.12b
17.28b
[s, 2H, 2OH]
Chemical shifts (ppm) were referenced internally at 25 ◦C with respect to TMS;
s = singlet, br = broad, m = multiplet.
a
3.2.1. IR spectra
The characteristic vibrational frequencies and their tentative
assignments for the H2L ligand and its transition metal complexes
are listed in Table 3. The assignments were aided by comparison
with the vibrational frequencies of the free ligand and its related
compounds [26,37,38].
The shift of the stretching frequencies of the azomethine
ꢂ(–C N–) group of the metal complexes to lower frequencies which
lie in the range of 1570–1530 cm−1, compared with the free lig-
b
The bands disappeared after the addition of D2O.
the –OH phenolic (17.28 ppm) protons disappear in the presence
of D2O, which indicates that the –OH phenolic groups are acidic
and can participate in the coordination with the metal ions. The
signals of the CH3 and CH2 groups were observed in the range
1.59–3.20 ppm [35]. The two aromatic protons were observed at
Table 3
Characteristic of the vibrational frequencies (cm−1) of the Schiff base, H2L, ligand and its metal complexes and their assignments.
Ligand/complex
H2L
ꢂ(OH) H2O
ꢂas(NH2) and ꢂs(NH2)
ꢂs(NH)
ı(H2O)
ꢂ(C C) and ꢂ(C N)
ꢂ(M–O)
ꢂ(M–N)
Other bands
–
–
3357 s, 3293 s
3275 s
–
1578 vs, br
–
–
1
2
3
–
–
–
3315 s, 3274 s
3167 m
3222 m
3146 m
–
–
–
1570 s, br
1567 vs, br
1546 vs
596 w
601w
598 w
510 w
496 w
519 w
1546 m, 1350 vs, 812 w;
bidentate NO3 groups.
1742 s, 1357 s, 1055s,
810 w, sh; NO3 groups.
1542 m, 1352 vs, 810 w,
sh; bidentate NO3
3312 s, br, 3254
3309 s, 3251 s, br,
groups.
4
5
–
3310 s 3252 s, br
3298 s, 3258 s, br
3210 m
3198 m
–
1567 vs
598 w
580 w
498 w
492 w
1755 s, 1356 s, 1054 s,
810 w; NO3 groups.
1420 s, sh, 1311 s, br, 810
w, sh; unidentate NO3
groups.
3445 s, br
1578 vs, br
1556 s, sh
6
7
8
3415 s, br
3305 m 3255 m, br
3293 s 3208 s, br
3187 m
3144 m
3176 m
1599 s, br
1540 s, br
1564 vs
561 m
591 sh
587 vw
484 m
1381 vs, 1356 s, 810 w,
sh; unidentate NO3
groups.
1124 s, 1095 s, sh, 1056 s,
sh, 625 m,; SO4 groups,
942 m, sh; ꢂ(V O).
1575 vs, 1428 s, sh, 811
w; OAc groups and 897
m; ꢂ 3(UO2).
–
–
–
–
500 w, sh
419 w
3250 s, sh 3210 s, br
1530 s, sh
s, strong; m, medium; w, weak; vs, very strong; sh, shoulder; br, broad; ꢂ, stretching.

A.A.A. Emara / Spectrochimica Acta Part A 77 (2010) 117–125
121
and band at 1578 cm−1, may be due to the coordination of the two
azomethine groups to metal ions [26,37]. The broad bands in the
range of 3445–3415 cm−1 is assigned to the stretching frequencies
of the ꢂ(OH) of the water molecules associated to the complexes
which are also confirmed by the elemental analyses and TGA data.
The two bands at the ranges 3315–3293 and 3293–3210 cm−1 are
due to the stretching frequencies, ꢂas(NH2) and ꢂs(NH2), of the
NH2 groups. Also, the stretching frequency of the ꢂ(NH) for the NH
groups in the metal complexes were observed as one sharp band
at 3222–3144 cm−1. The weak bands in the two ranges 601–561
and 519–419 cm−1 are assigned to the stretching frequencies of
the ꢂ(M–O) [39] and ꢂ(M–N) bands [40], respectively, supporting
that the bonding of the ligand to the metal ions is achieved by the
phenolic oxygen atoms and the azomethine and amine nitrogen
atoms of the ligand.
−
The NO3 ions are coordinated to the metal ion as unidentate
for the complexes (5) and (6) with C2v symmetry. Each unidentate
nitrate group possesses three non-degenerated modes of the vibra-
tions (ꢂs, ꢂs and ꢂas), which appeared at 1420–1381, 1356–131−1
and 810 cm−1, respectively. The ꢂs(NO3−) of the unidentate NO3
is markedly shifted to lower frequencies compared to that of the
free nitrate (1700–1800 cm−1) [41]. This could be a factor measur-
ing the covalent bond strength which is formed due to the transfer
of an electron den−sity from NO3− to the metal ion. In complexes (1)
and (3), two NO3 ions behave as bidentate ligand. These nitrate
groups possesses three non-degenerated modes of the vibrations
(ꢂ, ꢂa and ꢂs), which appeared at ca. 1546–1542, 1352–1352 and
812–810 cm−1. Beside, there are two ionic NO3− groups in the Ni(II)
(2) and Zn(II) (4) complexes, where their vibrations appeared at
1755–1742, 1357–1356 and 1055–1054 cm−1
.
In oxovanadium(IV) complex (7), several bands were observed
at 1124, 1095, 1056 and 625 cm−1 which are assigned to the coor-
dinated sulfate group [42]. In [(UO2)2(L)(OAc)2] complex (8), the
bands observed at 1575, 1428 and 811 cm−1 are assigned to the
acetate group in the complex and overlapped by the ligand vibra-
tions.
The IR spectrum of VO(IV) complex displays a band at 942 cm−1
which has no counterpart in the spectrum of the ligand and is
assigned to the stretching frequency of the ꢂ(V O) [43]. Also,
the IR spectrum of the UO2(VI) complex displays a strong band
at 897 cm−1 which is assigned to the stretching frequency of the
ꢂ(UO2) [44].
3.2.2. Electronic spectra, magnetic and molar conductance
measurements
It is possible to draw up the electronic transitions and predict
the geometry with the aid of magnetic moments of most metal ions.
Table 4 lists the characteristic electronic absorption bands, mag-
netic moments and molar conductance of the H2L ligand and its
metal complexes in DMF solutions. The electronic transitions due
to the organic ligand in the metal complexes, showed the absorp-
tion bands of the ␲ → ␲* and n → ␲* transitions results from the
C
N and C O groups and appeared at 318–315 and 412–407 nm
regions, respectively. These values are lower than the correspond-
ing absorption bands for the H2L ligand, which observed at 324
and 417 nm, respectively. This may be due to the coordination of
the nitrogen and oxygen atoms of the ligands to the metal ions.
Also, other two bands were observed in all electronic spectra of
the complexes, which persist at the same positions compared to
the electronic spectra of the free H2L ligand, which are the two
1
1
bands due to the 1La → A and 1Lb → A transitions of the phenyl
ring transitions which were observed at 273–272 and 337–334 nm,
respectively.
The electronic spectrum of the green Cu(II) complex (1)
showed one unsymmetrical band at 712 nm which is assigned to
3T2g(G) ← Eg transition in distorted octahedral geometry. The mea-

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A.A.A. Emara / Spectrochimica Acta Part A 77 (2010) 117–125
sured value of the magnetic moment for Cu(II) complex was 1.81
B.M., which confirm the octahedral structure [45].
The electronic spectrum of the red Ni(II) complex (2) showed
1
1
a band at 525 nm and is assigned to the A2g ← A1g transition.
The diamagnetic value of the Ni(II) complex agrees with the square
planar structure.
The electronic spectrum of the brownish-rose Co(II) complex (3)
in DMF solution showed that the complex has an octahedral geom-
etry. Two bands were observed in the visible region, the former one
4
is due to 4A2g(F) ← T1g(F) transition, which is observed at 647 nm.
4
The second band due to 4T1g(P) ← T1g(F) transition is observed at
463 nm. The Co(II) complex showed the magnetic moment at 4.90
B.M. at room temperature where the usual octahedral complexes
are around 4.8–5.2 B.M.
The electronic spectrum of the dark brown Fe(III) complex (5)
showed a strong band at 519 and a weak band at 830 nm. It was not
possible to identify the type of the d–d transition. This is due to a
strong charge transfer (CT) band tailing from the UV-region to the
visible region. Generally, from the elemental analyses and infrared
spectrum which gives a significant proof for the nitrate anion to
act as a unidentate ligand, it is expected that the Fe(III) complex
has the octahedral arrangement. Magnetic moment of the Fe(III)
complex (5) was measured and gives 5.94 B.M. This value is the
2
range of the magnetic moment of the high spin octahedral, t2g3 eg
arrangement, which has the amounts to 5.92 B.M. [46].
The electronic spectrum of the green Cr(III) complex (6) showed
that it has an octahedral geometry. The transition can be inter-
preted using Tanab-Sugano diagram. In the Cr(III) octahedral
complexes, the splitting of the free ion ground F term along with the
presence of the excited P term of the same multiplicity provides the
possibility of three spin allowed d–d transition [47]. The first band
4
4
which observed at 572 nm is due to T2g(F) ← A2g(F) transition,
while the second band due to 4T1g(F) ← A2g(F) transition was not
4
observed. The third band which is due to 4T1g(P) ← A2g(F) transi-
4
tion lies in the range of the ligand transitions and is not possible to
identify. The magnetic moment is expected to be very close to the
spin-only value for three unpaired electrons (3.87 B.M.) and also
because of the absence of any orbital contribution. In the present
work, the magnetic moment of the Cr(III) complex is 3.87 B.M.
The electronic spectrum of the green VO(IV) complex (7) showed
one band at 587 nm which corresponds to b1 ← b2 electronic tran-
sition. With the aid of the elemental analysis and the infrared
spectrum, the VO(IV) complex (7) structure is 5-coordinate, thus
its geometry would be square pyramidal. Although most oxo-
vanadium(IV) complexes are magnetically simple which having
virtually ‘spin-only’ moments of 1.73 B.M. corresponding to one
unpaired electron. In this study, the actual magnetic moment was
1.41 B.M. This value is less than the expected and is less eas-
ily understood. But, this could be due to antiferromagnetic effect
between vanadium atoms of adjacent molecules linked together
through oxygen atoms. The mass spectrum of the VO(IV) complex,
[(VO)2(L)]SO4, showed the molecular ion peak at m/e 495 which
agree well with the formula weight of the cationic complex after
Fig. 3. X-bands of the ESR spectra of (a) Cu(II) and (b) VO(IV) complexes of the Schiff
base, H2L, ligand.
means that all the phenolic groups in the ligand were deprotonated
to coordinate with the Zn(II) ions. The mass spectrum of the Zn(II)
complex, [Zn2(L)](NO3)2, showed the molecular ion peak at m/e 491
which agree well with the formula weight of the cationic complex
−
after releasing the NO3 anions.
The values of the molar conductivity for all complexes were
measured within the range 95–235 ꢄ−1 cm2 mol−1, for complexes
(1)–(8), which are higher than the expected value for most cases.
This may be due to the fact that the DMF solvent replaced the
coordinated anions in the complexes, which results in the higher
electrolytes due to the uncoordinated anions [48].
2−
releasing the SO4 anions.
3.2.3. ESR spectra and thermal analysis
The electronic spectrum of the yellow UO2(VI) complex (8)
arise from the electronic transition of metal → ligand charge trans-
fer. This is an allowed transition and produces broad, intense
absorption at 600 nm tailing into the visible region which produce
the intense yellow color. The UO2(VI) complex is diamagnetic as
expected [47].
Zn(II) complex (4) is diamagnetic as expected and its geometry is
most probably tetrahedral. The 1H NMR spectrum of [Zn2(L)](NO3)2
complex (4) in DMSO-d6 showed the chemical shifts of the proton
signals in the spectrum. The assignments are listed in Table 2. It
is worthnoting that the proton signals of the phenolic group were
not observed in the 1H NMR spectrum of the Zn(II) complex, which
X-band ESR spectra of [Cu2(L)(NO3)2] complex (1) and
[(VO)2(L)]SO4 complex (7) were recorded in the solid state at 25 ◦C
(Fig. 4). The Cu(II) spectrum exhibited two bands. One of them
is strong sharp band with gꢀ = 2.1081 and the other is weak with
g
⊥
= 2.1120 (Fig. 3a). The shape of the spectrum is consistent with
the octahedral geometry around each Cu(II) ion in the complex
[49,50].
The gꢀ value is an important function for indicating the cova-
lent character of (M–L) bonds. For ionic character, the gꢀ value is
<2.0023 and for covalent characters the gꢀ value is >2.0023. In the
present complex, gꢀ is more than 2.0023 indicating covalent char-
acter for Cu–L bond. In axial symmetry, the g-values are related

A.A.A. Emara / Spectrochimica Acta Part A 77 (2010) 117–125
123
Table 5
Antimicrobial activity of the Schiff base, H2L, ligand and 1–8 complexes.
Organisms
Mean of zone diametera (mm)
Gram-positive bacteriab
Gram-negative bacteriab
Fungic
S. aureus
(ATCC 25923)
S. pyogenes
(ATCC 19615)
P. phaseolicola
(GSPB 2828)
P. fluorescens
(S 97)
F. oxysporum
A. fumigatus
A
B
A
B
A
B
A
B
A
B
A
B
H2L
1
2
3
4
5
6
7
8
22
18
30
19
18
20
10
18
32
13
11
20
14
10
14
4
18
15
34
22
16
20
10
18
31
11
9
26
14
8
13
6
13
25
28
22
26
23
22
23
12
10
32
22
14
18
16
15
16
7
22
24
28
20
22
20
10
12
35
12
16
23
10
13
13
5
27
15
27
18
15
29
9
10
10
20
10
16
20
4
23
20
29
20
16
31
8
16
12
20
12
10
23
4
12
22
7
28
6
30
20
22
14
15
23
22
15
17
Control #
42
28
38
30
36
25
38
30
40
28
40
31
a
Chloramphencol in the case of Gram-positive bacteria, cephalothinin in the case of Gram-negative bacteria, and cycloheximide in the case of fungi. The concentration of
A is 2 mg mL−1 and B is 1 mg mL−1
.
b
Calculated from 3 values.
Identified depending on morphological and microscopical characteristics.
c
Fig. 4. Representative structures of the metal complexes of the Schiff base, H2L, ligand.

124
A.A.A. Emara / Spectrochimica Acta Part A 77 (2010) 117–125
to the G-factor by the expression G = (gꢀ − 2)/(g⊥ − 2) = 4. According
to Hathaway [51], if G > 4, the exchange interaction between Cu(II)
centers in the solid state is negligible, on the other hand, when
G < 4, a considerable exchange interaction is indicated. The G value
of the complex (0.965) suggests the exchange coupling between
Cu(II) centers in the solid state [51]. The powder ESR spectrum of
Cu(II) complexes is typical of the octahedral [52]. The value of the
magnetic moment (1.81 B.M), beside, the spectral data (712 nm)
agrees well with the proposed structures.
Oxovanadium(IV) complex (7) (ꢀeff = 1.41 B.M. at room temper-
ature) exhibits three bands, g1 = 2.1081, g2 = 2.041 and g3 = 2.144
(Fig. 3b). The resolution of the ESR spectra may be due to superex-
change interaction between two oxovanadium(IV) ions which lead
to a configuration in which the two electron spins have an anti-
ferromagnetic character. The shape of the spectrum as well as the
spectral studies agreed with the square pyramid structure.
Thermal gravimetric analysis for [Fe2(L)(NO3)2]·2H2O (5) and
[Cr2(L)(NO3)2]·3H2O (6) complexes were obtained to give informa-
tion concerning the thermal stability of the complex and to decide
whether the water molecules are in the inner or outer coordina-
tion sphere of the central metal ion [37,53]. TGA/DrTGA studies
were carried out from 25 to 800 ◦C, which showed four stages of
weight loss and the complete decomposition at 670 ◦C. TGA for the
Fe(III) complex showed a weight loss at 90 ◦C for the two water
molecules, Calcd. (Found)%; 5.68 (5.69)%, also, the first stage in the
TGA in Cr(III) complex showed a weight loss at 108 ◦C for three
water molecules, Calcd. (Found)%; 8.37%; 8.39%.
4. Conclusions
In the present study, the Schiff base, H2L, ligand is dibasic with
two sets of N3O-tetradentate sites. The Schiff base, H2L, ligand
was allowed to react with copper(II), nickel(II), cobalt(II), zinc(II),
cadmium(II), iron(III), chromium(III), oxovanadium(IV) and diox-
ouranium(VI) ions, with 1:2 molar ratio (ligand:metal ion). All
reactions afforded binuclear complexes except cadmium(II) for
H2L, which gave oily product which was difficult to isolate. For this
ligand, nickel(II) complex exhibits a square planar geometry and
zinc(II) complex exhibits tetrahedral geometry while copper(II),
cobalt(II), iron(III) and chromium(III) complexes exhibit an octa-
hedral geometry which contain coordinated nitrate ions as either
unidentate or bidentate ligands. The oxovanadium(IV) complex
showed a square pyramidal geometry and dioxouranium(VI) com-
plex is an octahedral. The bonding sites are the azomethine nitrogen
and the amino nitrogen atoms and the phenolic oxygen atoms. The
ligand and its metal complexes enhanced a significant antimicro-
bial activity compared with standard antifungal and antibacterial
agents.
Appendix A. Supplementary data
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.saa.2010.04.036.
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complexes. Fig. 4 depicts the representative structures of the metal
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