Mononuclear metal complexes of organic carboxylic acid derivatives: Synthesis, spectroscopic characterization, thermal investigation and antimicrobial activity

Article abstract of DOI:10.1016/j.saa.2006.05.038

Two Schiff base ligands bearing organic acid moiety, vis., N-(2-thienylmethylidene)-2-amino-4-chlorobenzoic acid (HL¹) and N-(2-hydroxybenzylidene)-2-amino-4-chlorobenzoic acid (H₂L²) have been synthesized by the interaction of 2-thiophenecarboxaldehyde and 2-hydroxybenzaldehyde with 2-amino-4-chlorobenzoic acid. Co(II), Ni(II), Cu(II) and Zn(II) complexes of these ligands have been prepared. They are characterized on the basis of analytical data, molar conductance, IR, ¹H NMR, UV-vis, mass spectra, magnetic measurements, thermal analysis and X-ray powder diffraction technique. The molar conductance data reveal that these complexes are non-electrolytes. The ligands are coordinated to the metal ions in a terdentate manner with ONO/ONS donor sites of the carbonyl oxygen, azomethine nitrogen and phenolic oxygen or thiophenic sulphur. An octahedral structure is proposed for the prepared metal complexes and some ligand field parameters (D_q, B and β) in addition to CFSE were calculated. The thermal stability of the metal complexes is evaluated. The Schiff base ligands and their metal complexes have been tested against four species of bacteria as well as four species of fungi and the results have been compared with some known antibiotics.

Full text of DOI:10.1016/j.saa.2006.05.038

Spectrochimica Acta Part A 67 (2007) 25–38
Mononuclear metal complexes of organic carboxylic acid derivatives:
Synthesis, spectroscopic characterization, thermal
investigation and antimicrobial activity
Zeinab H. Abd El-Wahab
Chemistry Department, Faculty of Science (Girl’s), Al-Azhar University, Nasr City, P.O. Box 11754, Cairo, Egypt
Received 17 April 2006; accepted 5 May 2006
Abstract
Two Schiff base ligands bearing organic acid moiety, vis., N-(2-thienylmethylidene)-2-amino-4-chlorobenzoic acid (HL1) and N-(2-
hydroxybenzylidene)-2-amino-4-chlorobenzoic acid (H2L2) have been synthesized by the interaction of 2-thiophenecarboxaldehyde and 2-
hydroxybenzaldehyde with 2-amino-4-chlorobenzoic acid. Co(II), Ni(II), Cu(II) and Zn(II) complexes of these ligands have been prepared.
They are characterized on the basis of analytical data, molar conductance, IR, 1H NMR, UV–vis, mass spectra, magnetic measurements, thermal
analysis and X-ray powder diffraction technique. The molar conductance data reveal that these complexes are non-electrolytes. The ligands are
coordinated to the metal ions in a terdentate manner with ONO/ONS donor sites of the carbonyl oxygen, azomethine nitrogen and phenolic oxygen
or thiophenic sulphur. An octahedral structure is proposed for the prepared metal complexes and some ligand field parameters (Dq, B and β) in
addition to CFSE were calculated. The thermal stability of the metal complexes is evaluated. The Schiff base ligands and their metal complexes
have been tested against four species of bacteria as well as four species of fungi and the results have been compared with some known antibiotics.
© 2006 Elsevier B.V. All rights reserved.
Keywords: Schiff base ligands; Metal chelates; Spectral characterization; Thermal analysis; XRD and antimicrobial activity
1. Introduction
As an extension of our work on the structural characteriza-
tion of Schiff base ligands and their metal complexes [9–15],
the main target of the present article is to study the coordination
behavior of the two ligands, HL1 and H2L2 that incorporate sev-
eral binding sites towards Co(II), Ni(II), Cu(II) and Zn(II) ions,
also to evaluate the relative thermal stability of the synthesized
complexes and to examine their antimicrobial activity against
different species of bacteria and fungi.
Schiff bases are compounds containing the azomethine group
(RC N–) and are usually formed by the condensation of a pri-
mary amine with an active carbonyl compound [1,2]. Schiff
bases have been used extensively as ligands in the field of coordi-
nation chemistry, some of the reasons are that the intramolecular
hydrogen bonds between the (O) and the (N) atoms which play
an important role in the formation of metal complexes and
that Schiff base compounds show photochromism and ther-
mochromism in the solid state by proton transfer from the
hydroxyl (O) to the imine (N) atoms [3]. A large number of
Schiff bases and their complexes have been investigated for
their interesting and important properties, such as their ability
to reversibly bind oxygen, catalytic activity in the hydrogena-
tion of olefins, photochromic properties and complexing ability
towards some toxic metals, furthermore complexes of Schiff
bases showed promising applications in biological activity and
biological modeling applications [4–8].
2. Experimental
2.1. Reagents and instruments
All chemicals used were of highest available purity. They
include 2-thiophenecarboxaldehyde, 2-hydroxybenzaldehyde
and 2-amino-4-chlorobenzoic acid (BDH). The metal chloride
salts, namely, cobalt and nickel chloride hexahydrates (Sigma),
cupric chloride dihydrate (Merck) and zinc chloride (Adwic)
products. Organic solvents used included absolute ethyl alcohol,
diethylether, dimethylformamide (DMF) and dimethylsulfoxide
(DMSO) were purchased from Merck or Sigma. Concentrated
E-mail address: zhabdelwahab@yahoo.com.
1386-1425/$ – see front matter © 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2006.05.038

26
Z.H. Abd El-Wahab / Spectrochimica Acta Part A 67 (2007) 25–38
nitric and perchloric acid were reagent grade and were used as
supplied.
The elemental analysis was made using Perkin-Elmer 2408
CHN analyzer. Metal contents were determined by titration
against standard EDTA solution after complete decomposition
of the complexes with nitric and perchloric acid in kjeldahl flask
several times and the chloride contents were determined gravi-
metrically. Melting or decomposition points were carried out
on a melting point apparatus, Gallenkamp, England. IR spectra
were recorded on a Perkin-Elmer FT-IR type 1650 spectropho-
tometer using KBr discs. 1H NMR spectra were recorded using
Brucker ARX-300 spectrometer using DMSO-d6 as a solvent,
chemical shifts are reported in parts per million downfield from
tetramethylsilane. Mass spectra were recorded at 70 eV and
300 ◦C on a MS 5988 Hewlett-Packard mass spectrometer. Elec-
tronic spectra of solutions of both ligands in DMF and the solid
reflectance spectra of their metal complexes were recorded on
a Jasco model V-550 UV–vis spectrophotometer. Magnetic sus-
ceptibility of the metal complexes were measured by the Gouy
method at room temperature using a Johnson Matthey, Alpha
products, model MKI magnetic susceptibility balance and the
effective magnetic moments were calculated using the relation
μeff = 2.828(χmT)1/2 B.M., where χm is the molar susceptibility
corrected using Pascal’s constants for diamagnetism of all atoms
in the compounds. The molar conductance measurements were
measured in solutions of the metal complexes in DMF (10−3 M)
using WTWD-812 Weilheium-Conductivity meter model LBR,
fitted with a cell model LTA100. A Shimadzu TGA-50H ther-
mal analyzer was used to record simultaneously the TG and
DTG curves, the experiments were carried out in dynamic nitro-
gen atmosphere (20 ml min−1) with a heating rate 10 ◦C min−1
in the temperature range 20–1000 ◦C using platinum crucibles.
Highly sintered ␣-Al2O3 was used as a reference. The X-ray
powder diffraction analysis of the two ligands and their Ni(II)
and Cu(II) complexes were carried out by using Rigku Model
ROTAFLEX Ru-200. Radiation was provided by copper target
(Cu anode 2000 W) high intensity X-ray tube operated at 40 kV
and 35 MA. Divergence slit and the receiving slit were 1 and
0.1, respectively. The antimicrobial activity of both ligands and
their metal complexes were screened using the diffusion agar
technique at the Medical Mycology Laboratory in the Regional
Center for Mycology and Biotechnology at Al-Azhar University.
Fig. 1. Structure of Schiff base ligands used (HL1) and (H2L2). N-
(2-Thienylmethylidene)-2-amino-4-chlorobenzoic acid (HL1), N-(2-hydroxy-
benzylidene)-2-amino-4-chlorobenzoic acid (H2L2).

Z.H. Abd El-Wahab / Spectrochimica Acta Part A 67 (2007) 25–38
27
Table 2
IR spectral assignment for schiff base ligands (HL1) and (H2L2) and their metal complexes (υcm
)
−1
Compound no. υC (carboxy.) ꢁυ (υasy. − υsy.
)
υC (azome.) υC–C (thioph.) υCSC (ring) υO–H (pheno.) υC–O (pheno.) υM–O υM–N υM–S
N
O
HL1
1668 sh
1610sh
1584sh
1586sh
1600sh
1589sh
1612sh
1576sh
1586sh
1592sh
1586sh
1550m
1536w
1534w
1530m
850sh
836sh
838sh
840sh
–
–
–
–
–
–
–
–
–
–
–
–
–
1
2
3
4
1614, 1400
1612, 1348
1620, 1398
1632, 1400
1668 sh
214
264
222
232
520s 500s 468w
550w 494w 474w
519s 498w 479s
553s 502s 444s
1539w
837sh
H2L2
–
–
–
–
–
–
–
–
–
–
3288br
3240br
3149br
3122br
3250br
1248sh
1236sh
1236sh
1230sh
1158sh
–
–
–
–
–
–
–
5
6
7
8
1614, 1402
1614, 1400
1600, 1378
1612, 1346
212
214
222
266
520w
526w
526s
540w
468s
474w
484s
446w
sh, sharp; s, small; m, medium; br, broad; w, weak.
2.2. Schiff base ligands synthesis
where M = Co(II): x = 2, n = 6, y = 2H2O, z = 4H2O + 2HCl;
M = Ni(II): x = 2, n = 6, y = 2H2O, z = 4H2O + 2HCl; M = Cu(II):
x = n = 2, y = nil, z = 2H2O + 2HCl; M = Zn(II): x = 2, n = nil,
y = H2O, z = 2HCl.
The two Schiff base ligands, HL1 and H2L2 (Fig. 1) were
prepared by adding a solution of 2-thiophenecarboxaldehyde
(9.35 ml, 0.1 mol) or 2-hydroxybenzaldehyde (10.66 ml,
0.1 mol) in ethanol (25 ml) to 2-amino-4-chlorobenzoic acid
(17.16 g, 0.1 mol) in ethanol (50 ml) in presence of few drops
of piperidine. The mixture was kept under reflux for 4 h on
a water bath and then allowed to cool to room temperature.
The product was filtered off, recrystallized from ethanol and
dried in a desciccator over anhydrous CaCl2 to give orange
powder of Schiff base ligand, HL1 in 89% yield or reddish
brown powder of Schiff base ligand, H2L2 in 76% yield.
Some physico-chemical characteristic of both ligands and their
elemental analysis is collected in Table 1.
2H2L2 + M(Cl)x·nH2O → [M(HL2)2]y + z
(2)
where M = Co(II): x = 2, n = 6, y = H2O, z = 5H2O + 2HCl;
M = Ni(II): x = 2, n = 6, y = nil, z = 6H2O + 2HCl; M = Cu(II):
x = n = 2, y = nil, z = 2H2O + 2HCl; M = Zn(II): x = 2, n = nil,
y = 2H2O, z = 2HCl.
3.1. IR spectra
The mode of binding of both Schiff base ligands to the metal
ions was elucidated by recording the IR spectra of the com-
plexes as compared with the spectra of the free ligands. The
small difference between the infrared spectra of both Schiff
base ligands indicates that, the ligands have a similar structure
but the spectra of the free ligands differ obviously from that of
their complexes as clear from Table 2. The spectra of both free
ligands show twostrongbandsat1610and1612 cm−1 character-
istics of the υC N (azomethine) stretching mode for (HL1) and
(H2L2), respectively [9,16,17] indicating the formation of the
Schiff base products. These bands are shifted towards lower fre-
quencies in the spectra of all metal complexes 1600–1576 cm−1
compared with the free Schiff base indicating the involvement
of the azomethine nitrogen in chelation with the metal ions, the
coordination of nitrogen to the metal ion would be expected to
reduce the electron density of the azomethine link and thus cause
a shift in the υC N group [11]. The intense band at 1668 cm−1
present in the IR spectra of the free ligands may be assigned to
the υC O (carboxylic group), similar band was observed at the
same frequency region in the IR spectra of some organic acid
ligands [18,19]. However, the spectra of all complexes show
the absence of this band accompanied by the appearance of
two characteristic bands at 1632–1600 and 1402–1346 cm−1
attributed to υasy.(COO−) and υsy.(COO−), respectively, indi-
cating the participation of the carboxylate oxygen atom in the
complexes formation. The mode of coordination of carboxylate
group (Fig. 2) has often been deduced from the magnitude of the
observed separation between the υasy.(COO−) and υsy.(COO−),
2.3. Metal complexes synthesis
A hot ethanolic solution of the appropriate metal chloride
(0.1 mol) namely, CoCl2·6H2O, NiCl2·6H2O, CuCl2·2H2O and
ZnCl2 was added to a hot ethanolic solution of the Schiff base
ligands, HL1 or H2L2 (0.2 mol). The resulting mixture was
stirred under reflux for 2 h where upon the metal complexes
wereprecipitated. Theprecipitatedsolidcomplexeswerefiltered
recrystallized and dried in vacuum desiccator over anhydrous
CaCl2. These complexes are stable in air, soluble in DMF and
DMSO, insoluble in most organic solvents and its elemental
analysis are in accordance with the proposed stoichiometry and
agree well with the suggested molecular formula. Their micro-
analytical data are listed in Table 1.
3. Results and discussion
Condensation of the aldehydes with amine readily gives rise
to the corresponding imines “Schiff base ligands, HL1 and
H2L2”. Their reaction with the metal ions Co(II), Ni(II), Cu(II)
and Zn(II), afford the metal complexes (1–8), the general reac-
tion for the preparation of the metal complexes of HL1 and H2L2
is shown below:
2HL1 + M(Cl)x·nH2O → [M(L1)2]y + z
(1)

28
Z.H. Abd El-Wahab / Spectrochimica Acta Part A 67 (2007) 25–38
Table 3
1H NMR spectra data of Schiff base ligands (HL1) and (H2L2) and their dia-
magnetic Zn(II) complexes (δ, ppm)
Compound
no.
COOH(s)
OH(s)
HC N(s)
Aromatic (and/or)
thiophene protons(m)
HL1
4
11.43
–
11.41
–
–
–
8.93
8.99
8.92
8.96
7.94–6.95
7.65–6.79
7.68–6.94
7.65–6.95
Fig. 2. Possible coordination modes of the carboxylate group.
H2L2
8
10.20
10.35
the separation value (Δ) between υasy.(COO−) and υsy.(COO−)
in metal complexes was more than 200 cm−1 (266–212 cm−1
)
s, singlet; m, multiple.
suggests the coordination of carboxylate group in all metal com-
plexes of the two ligands in a monodentate fashion [20–23].
The Schiff base ligand (HL1), its spectrum displays two
bands at 1550 and 850 cm−1 ascribed to υC–C and υC–S–C
(thiophene moiety) [24] which shifts to lower frequencies in
the spectra of metal complexes (1–4) in the region 1539–1530
and 840–836 cm−1, respectively, suggesting the coordination of
metal ions through the sulphur atom of thiophene moiety sup-
ported from 1H NMR data.
The observed broad band at 3288 cm−1 in the IR spectrum
of the ligand, H2L2 was assigned to υO–H (phenolic) of alde-
hyde moiety [13,14,17]. The observed low value of this band
is due to the intramolecular hydrogen bonding between the
hydrogen atom of OH group and the azomethine nitrogen atom,
O–H· · ·N, where the free υO–H is generally observed between
3650 and 3500 cm−1 according to the assignment made by Son-
mez and Sekerci [25]. This band was shifted to lower frequencies
in metal complexes (5–8) at 3250–3122 cm−1 suggesting the
involvement of O–H group in coordination. Additionally, the IR
spectrum exhibits a strong band at 1248 cm−1 may be referred
to υC–O (phenolic), the same band was observed at the same
frequency in the IR spectrum of salicylidene thiophenol Schiff
base [6] which undergoes a shift toward lower frequencies in
the region 1236–1158 cm−1 in the metal complexes (5–8). This
shift confirms the participation of the oxygen atom of aldehyde
moiety in coordination to the metal ion.
Fig. 3. Proposed molecular structure of metal complexes (1–4). In complex
(1): M = Co2+, x = 2H2O; in complex (2): M = Ni2+, x = 2H2O; in complex (3):
M = Cu2+, x = nil; in complex (4): M = Zn2+, x = H2O.
11.43–11.41 ppm (s, 1H) [29] is completely disappeared in the
spectrum of the Zn(II) complexes indicating the deprotonation
of carboxylic group and its involvement in chelation through
the displacement of the COOH proton. The shift to higher field
of the CH N– proton signal which appears in the free ligands
Conclusive evidence of the bonding is also shown by the
observation that new bands in the spectra of all metal complexes
appear in the low frequency regions at 553–519, 502–494 and
484–444 cm−1 characteristic to υM–O, υM–N and υM–S stretch-
ingvibrations, respectively, thatarenotobservedinthespectraof
bothfreeligands[15,26]. Furthermore, theobservedbroadbands
appear at 3452–3400 cm−1 in some complexes may attributed
to OH stretching vibration of lattice water molecules, another
bands observed at 900–844 cm−1 due to bending vibration of
H2O indicating that these complexes are hydrated supported
from thermal analysis study [27,28].
3.2. 1H NMR spectra
The NMR spectra of the free Schiff base ligands (HL1)
and (H2L2) and their diamagnetic Zn(II) complexes (4 and 8)
were recorded in d6-dimethylsulfoxide (DMSO) solution using
tetramethylsilane (TMS) as internal standard. The 1H NMR
spectra of zinc(II) complexes are compared with those of the
free ligands (Table 3). Upon complexation, the signal due to
the carboxylic proton which appears in the free ligands at δ
Fig. 4. Proposed molecular structure of metal complexes (5–8). In complex (5):
M = Co2+, x = H2O; in complex (6): M = Ni2+, x = nil; in complex (7): M = Cu2+
x = nil; in complex (8): M = Zn2+, x = 2H2O.
,

Z.H. Abd El-Wahab / Spectrochimica Acta Part A 67 (2007) 25–38
29
Fig. 5. Proposed fragmentation route of Schiff base ligand, HL1.
at δ 8.93–8.92 ppm (s, 1H) [30] suggesting the coordination to
the metal ions via the azomethine nitrogen. The upfield shift of
the signal due to phenolic proton in zinc(II) complex (8) which
appears in the free ligand (H2L2) at δ 10.20 ppm (s, 1H) [25]
supports the involvement of OH group in coordination to the
metal ions. The signals at δ 7.94–6.79 ppm (multiplets) are due
to the aromatic and thiophenic protons [31]. The downfield shift
of the thiophenic protons in zinc(II) complex (4) indicating that
the thiophenic sulphur taking part in complexation to metal ions.
Depending on the IR and 1H NMR Spectra, the suggested struc-
tures of the complexes are given in Figs. 3 and 4 which are
confirmed by the other techniques.
Fig. 6. Proposed fragmentation route of Schiff base ligand, H2L2.

30
Z.H. Abd El-Wahab / Spectrochimica Acta Part A 67 (2007) 25–38
Fig. 7. Proposed fragmentation route of: (a) [Zn(L1)2]·H2O and (b) [Zn(HL2)2]·2H2O.
Table 4
Electronic spectral data, magnetic moment values and ligand field parameters of the paramagnetic metal complexes
Compound no.
μeff
(B.M.)
Absorption bands (cm−1)/peak assignment
Ligand field parameters
CFSE
(cm−1
)
υ1
υ2
υ3
Dq (cm−1
)
B (cm−1
)
β
β (%)
Co(II) complexes
(1) [Co(L1)2]·2H2O
4.93
13.33 × 103
12.90 × 103
15.90 × 103
14.43 × 103
18.35 × 103
18.05 × 103
4
2086.50
2022
837
831
0.85 15.03
0.84 15.63
16.69 × 103
16.18 × 103
(5) [Co(HL2)2]·H2O 4.56
4
4
4T1g(F) → T2g(F)
4T1g(F) → A2g(F) 4T1g(F) → T1g(P)
Ni(II) complexes
(2) [Ni(L1)2]·2H2O
3.06
2.93
12.50 × 103
18.52 × 103
17.39 × 103
21.28 × 103
20.83 × 103
3
1250
1220
653
531
0.60 39.65
0.49 50.92
15 × 103
(6) [Ni(HL2)2]
12.20 × 103
14.64 × 103
3
3
3A2g(F) → T2g(F) 3A2g(F) → T1g(F) 3A2g(F) → T1g(P)
Cu(II) complexes
(3) [Cu(L1)2]
1.99
1.96
15.93 × 103
15.82 × 103
16.11 × 103
16.33 × 103
18.22 × 103
17.91 × 103
(7) [Cu(HL2)2]
2
2
2
2B1g → B2g
2B1g → Eg
2B1g → A1g

Z.H. Abd El-Wahab / Spectrochimica Acta Part A 67 (2007) 25–38
31
bands in the region (25.00–50.00) × 103 cm−1 assigned to π–π*
and n–π* transition, involving the molecular orbitals of the C N
and both benzene and thiophene rings [8]. In metal complexes,
these transitions were found to be shifted to lower or higher
energy region compared to the free ligands transitions confirm-
ing the coordination of the ligands to metal ions, in addition to
d–d transitions and the intramolecular charge transfer transitions
between the ligands and metal ions. The spectra data (Table 4)
includes absorption regions, band assignment and magnetic sus-
ceptibility values.
3.3. Mass spectra
The mass spectra of the ligands used, HL1 and H2L2 exhibit
the molecular ion peaks at m/e (264.00 and 277.00) (calculated
265.73and275.70)withabundance18.19%and11.01%, respec-
tively. Their proposed pathway fragmentation pattern is depicted
in Figs. 5 and 6. The mass spectra of the metal complexes (1–8)
have been investigated in which the molecular ion peaks are
detected. All metal complexes show similar fragmentation pat-
tern and Fig. 7 shows the proposed fragmentation pattern of the
zinc(II) complexes as representative example.
At room temperature, Co(II) complexes (1 and 5) show mag-
netic moment values in the range 4.93–4.56 B.M., which higher
than the spin only value (3.87) due to the orbital angular momen-
tum contribution in d7-system and close to the value required for
an octahedral structure [11]. The magnetic moment values for
the Ni(II) complexes (2 and 6) were found to be 3.06–2.93 B.M.,
which is in the normal range (2.80–3.80) for an octahedral envi-
ronment [1]. Cu(II) complexes (3 and 7) show magnetic values
of 1.99–1.96 B.M. falls within the range normally observed for
octahedral Cu2+ complexes [15]. Zn(II) complexes (4 and 8) are
found to be diamagnetic as expected for d10 configuration.
The metal ion, Co(II) (d7) gives rise to the free ion
terms 4F, 4P and a number of doublet states [33], the
electronic spectra of Co(II) complexes (1 and 5) dis-
play three bands at (13.33–12.90) × 103, (15.90–14.43) × 103
and (18.35–18.05) × 103 cm−1 wave number regions, respec-
3.4. Molar conductance data
The metal complexes discussed herein were dissolved in
DMF and the molar conductivities of 10−3 M of their solutions
at room temperature were measured to establish the charge of
the metal complexes. The conductance data, Table 1 indicate
that, all the metal complexes having conductivity values in the
range characteristic for the non-electrolytic nature suggesting
that these complexes are neutral [32].
3.5. Magnetic susceptibility measurements and electronic
absorption spectra
The electronic spectra of both free ligands under study in
DMF solution were characterized mainly by two absorption
4
4
tively, may assigned to the transition T1g(F) → T2g(F) (υ1),
Table 5
Thermal behavior of metal complexes (1–8) of the Schiff base ligands (HL1) and (H2L2)
Compound no.
Temperature range (◦C)
Loss in weight found (calcd.) (%)
Decomposition product loss
Mass loss
Total mass loss
(1) [Co(L1)2]·2H2O
(2) [Ni(L1)2]·2H2O
40–450
88.56 (88.00)
2H2O (lattice) and 2L1 leaving CoO residue
25–88
88–234
234–425
425–600
8.67 (8.57)
14.43 (14.43)
28.75 (28.88)
33.64 (34.24)
H2O (lattice) and Cl
H2O (lattice), CO2 and CO
CN and biphenyl fragment
CN, O, Cl, 2CH CH and thiophene fragment leaving NiS residue
85.49 (86.12)
87.78 (87.60)
50–100
100–375
375–500
8.19 (7.76)
41.26 (41.88)
38.33 (37.96)
NO2
(3) [Cu(L1)2]
CN, CO, CH CH and two thiophene fragment
2C6H5Cl leaving CuO residue
50–130
130–325
325–425
425–600
3.24 (2.94)
30.03 (30.06)
22.14 (22.54)
30.82 (30.53)
H2O (lattice)
NO and biphenyl fragment
O2, CN, CO and 2CH CH
Cl2, S and thiophene fragment leaving ZnC2 residue
(4) [Zn(L1)2]·H2O
86.23 (86.07)
79.46 (79.92)
38–127
127–265
265–450
450–800
6.58 (6.23)
13.91 (13.91)
31.35 (31.65)
27.62 (28.13)
(1/2)H2O (lattice) and NO
(1/2)H2O (lattice) and C6H6
CO2 and biphenyl fragment
CO2, CO, CN and C6H6 leaving CoCl2 residue
(5) [Co(HL2)2]·H2O
(6) [Ni(HL2)2]
34–108
108–246
246–434
434–600
11.54 (11.66)
9.68 (9.54)
29.76 (29.97)
33.26 (35.56)
2Cl
CO and NO
CO and biphenyl fragment
O2, NO and biphenyl fragment leaving NiC2 residue
84.24 (86.73)
89.71 (89.96)
98.90 (100.00)
100–350
350–581
43.08 (43.91)
46.63 (46.05)
CO2, Cl2 and biphenyl fragment
CO2, O2, 2CN and biphenyl fragment leaving Cu residue
(7) [Cu(HL2)2]
100–300
300–596
89.97 (89.95)
8.93 (10.05)
2H2O (lattice) and 2HL2
Zn and no residue
(8) [Zn(HL2)2]·2H2O

32
Z.H. Abd El-Wahab / Spectrochimica Acta Part A 67 (2007) 25–38
4
4
4
4T1g(F) → A2g(F) (υ2) and T1g(F) → T1g(P) (υ3), respec-
tively of the d7-system suggesting Co(II) high-spin complexes
octahedral environment of donor atoms with a ground state term
symbol 4F, its magnetic moment values confirm the octahedral
structure [15]. The ligand field parameters (Dq, B and β) where
Dq is the crystal field splitting parameter, B the Racah inter-
electronic repulsion parameter and β is the nephelauxtic param-
tionally, the crystal field stabilization energy (CFSE) for Co(II)
in a crystal field with Oh symmetry was calculated.
The free ion terms for Ni(II) ion (d8) are 3F, 3P, 1G, 1D and 1S
[33]. The electronic spectra of Ni(II) complexes (2 and 6) exhibit
three electronic spectra bands in the range (12.50–12.20) × 103,
(18.52–17.39) × 103 and (21.28–20.83) × 103 cm−1 suggest-
ing high-spin Ni(II) complexes with octahedral configura-
tion with a ground state term symbol 3F. These bands are
eter were calculated [34]. The smaller B value (837–831 cm−1
)
3
3
3
3
compared to the free metal ion (985 cm−1) is due to the strong
interaction between the reactive sites of the organic com-
pound with cobalt(II) ion which indicate a reduction of about
15.63–15.03% from the free ion value, also (β) value is less than
unity (0.85–0.84) suggesting a largely covalent bond between
the organic ligand and cobalt(II) ion in these complexes. Addi-
assigned to A2g(F) → T2g(F) (υ1), A2g(F) → T1g(F) (υ2)
and 3A2g(F) → T1g(P) (υ3) transition, respectively for an octa-
3
hedral geometry [35]. The ligand field parameters (Dq, B and β)
were calculated [36] and the smaller B value (653–531 cm−1
)
compared to the free metal ion (1082 cm−1) is due to the
strong interaction between the reactive sites of the organic com-
Fig. 8. TG and DTG curve of: (a) [Ni(L1)2]·2H2O and (b) [Ni(HL2)2].

Z.H. Abd El-Wahab / Spectrochimica Acta Part A 67 (2007) 25–38
33
Fig. 9. X-ray diffraction pattern of: (a) Schiff base ligand, HL1, (b) [Ni(L1)2]·2H2O and (c) [Cu(L1)2].

34
Z.H. Abd El-Wahab / Spectrochimica Acta Part A 67 (2007) 25–38
pound with nickel(II) ion which indicate a reduction of about
50.92–39.65% from the free ion value, also (β) value is less than
unity (0.60–0.49) suggesting a largely covalent bond between
the organic ligand and nickel(II) ion in these complexes. Addi-
tionally, the crystal field stabilization energy (CFSE) for Ni(II)
in a crystal field with Oh symmetry was calculated.
The metal complexes (3 and 7) for Cu(II) ion (d9), their
spectra consist of a broad, low intensity shoulder band centered
Fig. 10. X-ray diffraction pattern of: (a) Schiff base ligand, H2L2, (b) [Ni(HL2)2] and (c) [Cu(HL2)2].

Z.H. Abd El-Wahab / Spectrochimica Acta Part A 67 (2007) 25–38
35
Table 6
X-ray diffraction data of Schiff base ligand (HL1) and its Ni(II) and Cu(II) complexes (2, 3)
HL1
[Ni(L1)2]·2H2O
[Cu(L1)2]
˚
˚
˚
d (A)
2θ
7.48
I/I0
16.60
3.80
5.00
2.50
12.50
9.40
100.00
44.40
5.10
17.80
28.00
2.60
15.80
6.20
2.00
d (A)
2θ
5.86
I/I0
89.80
d (A)
2θ
5.71
I/I0
11.81
10.38
8.73
7.71
6.69
6.03
4.89
3.89
3.74
3.40
3.19
2.99
2.86
2.74
2.56
2.43
2.32
2.20
2.10
1.90
1.85
1.81
15.07
4.46
3.79
3.41
3.25
3.06
2.66
2.50
2.35
2.10
2.02
1.69
1.50
1.36
1.24
15.48
11.87
7.69
5.14
4.88
4.51
3.83
3.57
3.44
3.09
2.67
2.50
2.35
2.12
2.04
1.99
1.89
1.70
1.36
100.00
8.00
8.51
10.12
11.46
13.22
14.68
18.13
22.85
23.79
26.21
27.98
29.87
31.27
32.63
35.01
37.03
38.74
41.00
43.13
47.77
49.14
19.90
23.46
26.14
27.44
29.14
33.71
35.96
38.30
43.14
44.78
54.37
62.02
68.79
76.49
100.00
15.40
44.50
51.40
18.30
19.20
19.90
8.30
5.10
7.90
13.70
3.70
7.70
7.44
11.50
17.24
18.15
19.67
23.20
24.89
25.89
28.90
33.49
35.86
38.19
42.54
44.39
45.64
47.99
53.82
68.83
18.70
14.10
26.40
50.40
10.60
10.60
26.50
20.00
8.20
7.70
5.60
9.80
7.60
14.30
13.60
4.10
1.90
5.10
3.50
6.30
6.20
9.50
4.50
2.10
1.80
at (18.22–15.93) × 103 and (17.91–15.82) × 103 cm−1, respec-
tate donor ligands [1,13,25,26,37] and according to the empirical
formula of these complexes, we propose an octahedral geom-
etry for the Zn(II) complexes. Their electronic spectra show
an absorption bands at (26.32–25.00) × 103 cm−1 attributed to
LMCT transition which is compatible with octahedral structure
[38].
2
2
tively, may be assigned to the transitions B1g → B2g and
2
2
2
2B1g → Eg and B1g → A1g, respectively, corresponding to
a distorted octahedral geometry of Cu(II) ion [15].
Zn(II) complexes (4 and 8) are diamagnetic and in analogy
with the previously described Zn(II) complexes of some triden-
Table 7
X-ray diffraction data of Schiff base ligand (H2L2) and its Ni(II) and Cu(II) complexes (6, 7)
H2L2
[Ni(HL2)2]
[Cu(HL2)2]
˚
˚
˚
d (A)
2θ
5.86
I/I0
6.80
9.60
6.70
100.00
19.20
24.90
18.50
15.10
43.40
89.00
1.60
11.20
5.00
0.70
6.50
4.00
8.50
0.90
6.70
4.10
d (A)
2θ
5.84
I/I0
d (A)
2θ
5.80
I/I0
15.07
11.64
6.67
4.89
4.52
3.87
3.69
3.52
3.39
3.18
2.98
2.87
2.73
2.57
2.42
2.31
2.20
2.11
1.90
1.64
15.12
4.46
3.78
3.40
3.24
3.06
2.34
2.10
1.69
1.63
1.60
1.26
100.00
83.90
21.00
46.40
77.20
21.80
17.60
16.20
7.90
15.21
11.81
8.34
7.56
5.03
4.57
4.29
3.74
3.49
3.03
2.79
2.71
2.61
2.51
2.41
2.23
2.14
2.07
1.81
1.70
1.51
1.46
100.00
7.70
0.70
15.30
10.80
19.20
16.40
10.00
15.70
5.20
0.40
4.60
7.00
4.60
4.00
5.20
6.30
3.80
7.59
13.26
18.11
19.64
22.94
24.07
25.30
26.24
28.03
29.92
31.17
32.79
34.89
37.12
38.91
40.99
42.88
47.80
55.91
19.89
23.50
26.15
27.51
29.18
38.37
43.14
54.28
56.42
57.66
75.20
7.48
10.60
11.69
17.61
19.41
20.69
23.77
25.53
29.43
32.01
33.01
34.36
35.81
37.26
40.46
42.29
43.71
50.42
53.72
61.51
63.55
5.50
15.30
19.30
2.50
2.20
2.00
1.60

36
Z.H. Abd El-Wahab / Spectrochimica Acta Part A 67 (2007) 25–38
3.6. Thermogravimetric analysis
Thermal analysis plays an important role in studying the
properties of metal complexes to obtain a useful data on the
metal–ligand bonds. The thermal decomposition of all metal
complexes (1–8) was studied using the TG-technique. During
the heating of the metal complexes, the TG-curves undergo a
series of thermal changes associated with a weight loss of the
samples. Analysis of the obtained TG-curves is given in Table 5
and the correlations between the different decomposition steps
of the complexes with the corresponding weight losses are dis-
cussed in terms of the proposed formulae of the complexes.
Fig. 8 is a representative example for thermal analysis of the
metal complexes under study.
3.7. X-ray diffraction study
Single crystals of the complexes under study could not be
obtained because the metal complexes wear isolated as powder
ratherthansinglecrystals, inaddition to theirinsolubility in most
organic solvents, thus no definitive structure can be described.
X-ray diffraction patterns of both ligands, HL1 and H2L2 and
their Ni(II) and Cu(II) complexes (2, 3, 6 and 7) were recorded
between 4◦ and 80◦ (2θ) and are given in Figs. 9 and 10. The
˚
value of (2θ), interplanar spacing d (A) and the relative inten-
sities (I/I0) of the compounds under study were recorded in
Tables 6 and 7. Comparing the X-ray diffraction patterns of each
ligand with its corresponding metal complexes indicate that the
0
˚
interplanar spacing, d (A) and the relative intensities (I/I ) are
different which could be attributed to the complex formation.
Furthermore, correlation the analytical, spectroscopic and mag-
netic data enables us to predict the possible structure for the
metal complexes.
3.8. Antimicrobial studies
The two Schiff base ligands, HL1 and H2L2 and their metal
complexes (1–8) have been tested against four species of bacte-
ria; Staphylococcus aureus, Pseudomonas aeruginosa, Bacillus
subtilis and Escherichia coli as well as four species of fungi;
Aspergillus fumigatus, Penicillium italicum, Syncephalastrum
racemosum and Candida albicans. The test was done using the
diffusion agar technique [39] and both chloramphenicol and
Terbinafin were used as standard antibacterial and antifungal
agents, respectively. The compounds to be tested were dissolved
in dimethylformamide at a different concentration 1, 2.5 and
5 mg/ml and the diameter (cm) of the inhibitation zone was mea-
sured, all data were collected in Tables 8 and 9.
On comparing the biological activity of the Schiff base
ligands and their metal complexes the following results are
obtained:
(1) The ligands and their metal complexes, all have the capacity
of inhibiting the metabolic growth of the investigated bac-
teria and fungi to different extent. This inhibitory capacity
is reinforced with the increment of concentration.

Z.H. Abd El-Wahab / Spectrochimica Acta Part A 67 (2007) 25–38
37
Table 10
Antibacterial activity of some known antibiotics
Antibiotic
name
Staphylococcus
aureus
Pseudomonas
aerruguinosa
Escherichia
coli
Amikacin
Doxycllin
Augmantin
Sulperazon
Unasyn
R
+++
R
R
+++
R
R
++
R
+++
R
++
R
+++
+++
+++
+++
R
Septrin
Cefobid
R
R
R
Ampicillin
Nitrofurantion
Traivid
R
+++
R
++
R
R
++
R
+++
R
Erythromycin
+++
R
R = resistance.
(2) Thedifferentcoordinatedmetalionshavedifferentinfluence
towards the tested bacteria and fungi. This result reflects the
difference of the way and mechanism that the complexes
interact with bacteria and fungi due to the difference in metal
ions.
(3) The inhibitation zone of the metal chelates generally is
higher than that of the free ligands.
(4) The two ligands and their metal complexes were found to
be more effective against the fungi than bacteria species.
Comparison of the antibacterial activity of the synthe-
sized compounds with some known antibiotics shows some
metal complexes possess remarkable antimicrobial activity
equal to or higher than some possess antibiotics as clear from
Table 10.
4. Concluding remarks
In this work, the coordination chemistry of the two Schiff
base ligands, HL1 and H2L2 and their metal complexes with
cobalt(II), nickel(II), copper(II) and zinc(II) metal ions were
described and characterized on the basis of analytical, magnetic
and spectral data as well as thermal gravimetric studies. The two
Schiff base ligands act as monobasic tridentate, coordinated to
the metal ions in a terdentate manner with ONO/ONS donor sites
of the carbonyl oxygen, azomethine nitrogen and phenolic oxy-
gen or thiophenic sulphur and in both, the coordination mode
of carboxylate group is the unidentate mode. Correlating the
experimental data, one can suggest the octahedral structure for
the prepared metal complexes. Additionally some metal com-
plexes posses antibacterial and antifungal activity against the
selected species of bacteria or fungi more than the free Schiff
base ligands which is in accordance with the fact that the chelat-
ing of metal to ligands increase the biological activity of the
molecule. Theseresultswerecomparedwithsomeknownantibi-
otics showing that, the free ligands or some their metal com-
plexes possess a higher degree of antibacterial activity than the
antibiotics itself. The importance of this lies in the fact that these
complexes could be applied in the treatment of some common
diseases.

38
Z.H. Abd El-Wahab / Spectrochimica Acta Part A 67 (2007) 25–38
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