Comparative studies of mononuclear Ni(II) and UO2(II) complexes having bifunctional coordinated groups: Synthesis, thermal analysis, X-ray diffraction, surface morphology studies and biological evaluation

Article abstract of DOI:10.1016/j.saa.2011.11.037

Two Schiff base ligands derived from condensation of phthalaldehyde and o-phenylenediamine in 1:2 (L¹) and 2:1 (L²) having bifunctional coordinated groups (NH₂ and CHO groups, respectively) and their metal complexes with N

Full text of DOI:10.1016/j.saa.2011.11.037

Spectrochimica Acta Part A 88 (2012) 10–22
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Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Comparative studies of mononuclear Ni(II) and UO2(II) complexes having
bifunctional coordinated groups: Synthesis, thermal analysis, X-ray diffraction,
surface morphology studies and biological evaluation
Abeer A. Fahema,b,∗
a Chemistry Department, Faculty of Science (Girl’s), Al-Azhar University, P.O. Box 11754, Nasr-City, Cairo, Egypt
b Chemistry Department, College of Education and Science (Khurma), Taif University, Al-khurma, Taif, Saudi Arabia
a r t i c l e i n f o
a b s t r a c t
Article history:
Two Schiff base ligands derived from condensation of phthalaldehyde and o-phenylenediamine in 1:2
(L1) and 2:1 (L2) having bifunctional coordinated groups (NH2 and CHO groups, respectively) and their
metal complexes with Ni(II) and UO2(II) have been synthesized and characterized by elemental analysis,
molar conductance, magnetic susceptibilities and spectral data (IR, 1H NMR, mass and solid reflectance)
as well as thermal, XRPD and SEM analysis. The formula [Ni(L1)Cl2]·2.5H2O, [UO2(L1)(NO3)2]·2H2O,
[Ni(L2)Cl2]·1.5H2O and [UO2(L2)(NO3)2] have been suggested for the complexes. The vibrational spectral
data show that the ligands behave as neutral ligands and coordinated to the metal ions in a tetradentate
manner. The Ni(II) complexes are six coordinate with octahedral geometry and the ligand field parame-
ters: Dq, B, ˇ and LFSE were calculated while, UO2(II) complexes are eight coordinate with dodecahedral
geometry and the force constant, FU O and bond length, RU O were calculated. The thermal decomposition
of complexes ended with metal chloride/nitrate as a final product and the highest thermal stability is
displayed by [UO2(L2)(NO3)2] complex. The X-ray powder diffraction data revealed the formation of nano
sized crystalline complexes. The SEM analysis provides the morphology of the synthesized compounds
and SEM image of [UO2(L2)(NO3)2] complex exhibits nano rod structure. The growth-inhibiting potential
of the ligands and their complexes has been assessed against a variety of bacterial and fungal strains.
© 2011 Elsevier B.V. All rights reserved.
Received 31 August 2011
Received in revised form
10 November 2011
Accepted 15 November 2011
Keywords:
N4 and N2O2 donor ligands
Ni(II) and UO2(II) complexes
Spectroscopic study
Thermal investigation
X-ray and biological study
1. Introduction
attention and it has been reported that chelation causes drastic
change in the biological properties of the ligands and also the metal
The use of coordination compounds as pharmaceutical agents
represents one of the most successful applications of bioinorganic
chemistry after the discovery of the antitumor activity of cis-
diamminedichloroplatinum (II) which is one of the best selling
anticancer drugs [1,2]. In recent decades, metallocomplexes have
received much attention in chemistry, biochemistry, and pharmacy
as promising compounds for the creation of novel drugs. On the
one hand, using such complexes, it is possible to avoid some neg-
ative effects inherent in drug compositions containing inorganic
salts, which can dissociate with the formation of metal ions. On the
other hand, metal ions can modify both magnitude and direction
of the pharmacological activity of the initial organic compounds
(ligands) as a result of changes in their size, shape, charge density
distribution, and redox potentials[3]. During recent years coordina-
tion compounds of biologically active ligands have received much
moiety, moreover, many drugs possess modified pharmacologi-
cal and toxicological properties when administered in the form of
transition metal complexes [4–6].
In this article, the coordination mode of the two Schiff base lig-
ands bearing two functions; NH2 and CHO groups, toward Ni(II) and
UO2(II) ions have been investigated. The possible modes of coordi-
nation, the geometry and the nature of bonding of the complexes in
addition to the thermal stability and surface morphology were dis-
cussed on the basis of various spectroscopic methods. Furthermore,
all synthesized compounds were screened for their antimicrobial
activity in an attempt to understand the influence of metal ion and
ligand nature on the biological properties.
2. Experimental
2.1. Analysis and physical measurements
All chemicals used were BDH, Analar or Merck products. The
chemicals used were phthalaldehyde, o-phenylenediamine, nickel
(II) chloride hexahydrate and uranyle (II) nitrate hexahydrate. The
∗
Correspondence address: Chemistry Department, Faculty of Science (Girl’s), Al-
Azhar University, P.O. Box 11754, Nasr-City, Cairo, Egypt. Tel.: +20 0163550402.
E-mail address: aafwafy@hotmail.com
1386-1425/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2011.11.037

A.A. Fahem / Spectrochimica Acta Part A 88 (2012) 10–22
11
mineral acids utilized were perchloric, and nitric acids. The organic
solvents used were ethanol, dimethylformamide (DMF), dimethyl-
sulfoxide (DMSO) and diethylether.
Carbon, hydrogen and nitrogen contents were determined using
Perkin-Elmer 2408 CHN analyzer. Nickel contents were determined
by titration against standard EDTA after complete decomposition of
the complexes with concentrated nitric and perchloric acid [7]. The
uranium content was determined gravimetrically by igniting a def-
inite mass of the solid complex in a muffle furnace at ∼800 ◦C and
weighing the residue as U3O8 [8,9]. Chloride content was deter-
mined gravimetrically as AgCl after decomposing the complexes
with HNO3 acid [7]. 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 spectrophotome-
ter using KBr disks. Mass spectra were recorded in a range of m/e
ratio between 0 and 1000 at Jeol JMSAX-500 mass spectrometer.
The electronic spectra of metal complexes were recorded on a Jasco
model V-550 UV-Vis spectrophotometer. Magnetic susceptibility
of the metal complexes was measured by the Gouy method at
room temperature using a Johnson Matthey, Alpha products, model
MKI magnetic susceptibility balance. Molar conductance measure-
ments were measured in solutions of the metal complexes in DMF
and DMSO (10−3 M) using WTWD-812 Weilheium-Conductivity
meter model LBR, fitted with a cell model LTA100. The TG anal-
ysis (20–1000 ◦C) was carried out in dynamic nitrogen atmosphere
(20 ml min−1) with heating rate of 10 ◦C min−1 on a Shimadzu
Thermogravimetric Analyzer (TGA-50H). X-ray powder diffraction
(XRD) measurements were performed at ambient temperature
using a D8 Advance X-ray diffractometer (Bruker AXS, Germany).
The diffraction pattern was recorded for 2ꢀ from 4◦ to 80◦ at room
˚
temperature using CuK␣ monochromated radiation (ꢁ = 1.54060 A)
with the following measurement conditions: tube voltage of 40 kV,
tube current of 40 mA, step scan mode with a step size of 0.02◦
2ꢀ. Scanning electron microscopy (gold coating, Edwards Sputter
Coater, UK) was performed using a Jeol 6310 (Jeol Instruments,
Tokyo, Japan) system running at 5–10 keV. The agar-disk diffusion
technique was followed to determine the activity of the synthesized
compounds against some sensitive organisms [10].
2.2. Synthesis of Schiff base ligands, L1 and L2
2.2.1. Synthesis of Schiff base ligands, L1
The Schiff base ligand (L1) was obtained by refluxing an
ethanolic solution of
a mixture of phthalaldehyde and o-
phenylenediamine in molar ratio 1:2, respectively, on a water bath
for 5 h. The color of the solution turned to yellow. After cooling the
solution, the resulting precipitate was filtered, washed with cold
ethanol then diethylether and finally dried over anhydrous calcium
chloride.
2.2.2. Synthesis of Schiff base ligands, L2
The Schiff base ligand (L2) was obtained by refluxing an
ethanolic solution of
a mixture of phthalaldehyde and o-
phenylenediamine in molar ratio 2:1, respectively, on a water bath
for 5 h. The color of the solution turned to yellow. After cooling the
solution, the resulting precipitate was filtered, washed with cold
ethanol then diethylether and finally dried over anhydrous calcium
chloride.
The microanalytical data of the two ligands, L1 and L2, Fig. 1 are
listed in Table 1.
2.3. Synthesis of metal complexes
A solution of metal salt, namely, NiCl2·6H2O or UO2(NO3)2·6H2O
dissolved in the least amount of bidistilled water was added drop-
wise to a stirred ethanolic solution of the ligands, L1 or L2 in the

12
A.A. Fahem / Spectrochimica Acta Part A 88 (2012) 10–22
Fig. 1. Structures of N4 and N2O2 tetradentate Schiff base ligands under study, L1 and L2, respectively.
molar ratio 1:1. The reaction mixture was further stirred for 3 h to
ensure the complete precipitation of the formed complexes. The
precipitated solid complexes were filtered off while the solution
was still hot, washed several times with 50% (v/v) ethanol–water
to remove any excess of the unreacted starting materials. Finally,
the complexes were washed with ethyl alcohol and diethyl ether
and dried in vacuum desiccators over anhydrous CaCl2.
The microanalytical data of the isolated complexes (1–4) are
listed in Table 1.
determined the antimicrobial activity of the compound. The mean
value obtained for three individual replicates was used to calculate
the zone of growth inhibition of each sample.
3. Results and discussion
Condensation of the aldehyde with amine readily gives rise to
Schiff-base ligands. Their reactions with Ni(II) and UO2(II) ions
afford mononuclear metal complexes in which the microanalyt-
ical data as well as metal and chloride estimations are in good
agreement with proposed stoichiometries, Table 1. These com-
plexes are found to be insoluble in common organic solvents
but soluble in DMF and DMSO. The elemental analyses confirm
that the complexes are mononuclear and may be formulated as:
[M(L1)X2]·yH2O{M = Ni(II); X = Cl; y = 2.5 and M = UO2(II); X = NO3;
y = 2} and [M(L2)X2]·yH2O{M = Ni(II); X = Cl; y = 1.5 and M = UO2(II);
X = NO3; y = nil}. The reactions follow:
L1 + MX2 · nH2O → [M(L1)X2] · yH2O
M = Ni(II); X = Cl; n = 6; y = 2.5
UO2(II); X = NO3; n = 6; y = 2
L2 + MX2 · nH2O → [M(L2)X2] · yH2O
M = Ni(II); X = Cl; n = 6; y = 1.5
UO2(II); X = NO3; n = 6; y = nil
2.4. Antimicrobial screening
The two Schiff base ligands, L1 and L2, and their metal complexes
(1–4) were screened for antibacterial and antifungal activity against
the sensitive organisms Staphylococcus aureus and Streptococcus
pyogenes as Gram-positive bacteria; Pseudomonas phaseolicola and
Pseudomonas fluorescens as Gram-negative bacteria, and the fungi;
Fusarium oxysporum and Aspergillus fumigatus. The antibiotics;
Chloramphenicol, Cephalothin and Cycloheximide were used as stan-
dard references for Gram-positive bacteria, Gram-negative bacteria
and fungi, respectively, using the agar-disk diffusion technique [10]
described below.
The tested compounds were dissolved in DMF, which has no
inhibition activity to get concentrations of 2 mg/ml. The test was
performed on medium potato dextrose agar (PDA), which contains
an infusion of 200 g potatoes, 6 g dextrose, and 15 g agar. Uniform
size filter paper disks (3 disks per compound) were impregnated
by an equal volume (10 ␮l) from the specific concentration of dis-
solved tested compounds and carefully placed on inoculated 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, the inhibition zone diameter
produced by these compounds against the particular test organism
3.1. Infrared spectra and nature of coordination
The relevant infrared bands of the ligands (L1 and L2) and their
metal complexes (1–4) are presented in Table 2. The assignments
of the infrared bands were made by comparing the spectra of the
prepared compounds with reported literature on similar systems.
The absence of C O and N H stretching vibrations in the spectra
Table 2
Main IR and 1H NMR data with their assignment for ligands, L1 and L2 and their complexes.
b
Compd.a No
IR bands (cm−1
)
1H NMR (ı, ppm)c
ꢃ(NH2)
ꢃ(C O)
ꢃ(C N)
ꢃ(M O)
ꢃ(M N)
Additional bands
L1
3476br; 3371br
–
1593s
–
–
–
8.372 (2H, s, HC N); 7.915–6.978
(12H, m, Ar H); 6.141 (4H, s, NH2).
–
8.651 (2H, s, CH N); 7.994–7.108
(12H, m, Ar H); 6.432 (4H, s, NH2).
10.079 (2H, s, CHO); 8.763 (2H, s,
CH N); 8.090–7.021 (12H, m, Ar H).
–
1
2
3368br; 3216br
3420br; 3255br
–
–
1508s
1520s
510m
499m
440m
424m
–
1490, 1244 and 1035 (coord.
NO3); 927 and 832 (O
–
U O)
L2
–
1670s
1584s
–
–
3
4
–
–
1612s
1609s
1497s
1560s
500m
496m
442m
433m
–
1485, 1250 and 1044 (coord.
NO3); 922 and 830 (O O)
10.319 (2H, s, CHO); 8.972 (2H, s,
CH N); 7.913–6.884 (12H, m, Ar H).
U
a
L1 and L2 represent the Schiff base ligands and 1–4 represent the complex number as in Table 1.
sStrong; mmedium; brbroad (IR data).
b
c
sSinglet; mmultiple (1H NMR data).

A.A. Fahem / Spectrochimica Acta Part A 88 (2012) 10–22
13
Fig. 2. Mass spectra of: (a) Schiff base ligand, L1; (b) Schiff base ligand, L2; (c) [Ni(L1)Cl2]·2.5H2O; (d) [UO2(L1)(NO3)2]·2H2O.
of the ligands, L1 and L2, related to aldehyde and amino groups,
respectively, indicate occurrence of Schiff base condensation and
formation of the proposed skeleton of ligands. Instead, the two lig-
ands exhibit a strong band at 1593 and 1584 cm−1, respectively,
attributable to ꢃ(C N) supports the formation of ligands structure
[11,12]. The IR spectrum of the free ligand, (L1), shows a medium
intensity bands at 3476 and 3371 cm−1 assigned to ꢃas(NH2) and
ꢃs(NH2), of o-phenylenediamine [13,14], moreover the IR spectrum
of the free ligand, (L2), shows a strong band at 1670 cm−1 assigned
to ꢃ(C O) of the CHO group of phthalaldehyde [15,16] even after
the formation of both ligands. This could be due to one of the two
NH2 groups as well as one of the two CHO groups participates in
the condensation process while the other group is still free [14].
The IR spectra of the Ni(II) and UO2(II) complexes of each ligand
are similar suggesting similar structural geometry. In the spectra
of all metal complexes (1–4) a number of changes are observed:
the dioxouranium ion [19,20]. The calculated force constant, FU
O
and the bond length, RU values are 7.094–7.018 mdyn/Å and
O
˚
1.732–1.734 A, respectively, fall in the usual range of the uranyl
complexes and are in good agreement with the data found from
various uranyl complexes [21].
•
It seems that, the existence of water molecules associated with
complex formation (lattice/coordinated) in the IR spectra of the
metal complexes render it difficult to get conclusion from the
amino or aldehyde groups of ligands; L1 and L2, respectively,
which will be overlapped by those of the water molecules. The
thermal data confirms the nature of water molecules. The thermal
study will be discussed in detailed manner later.
3.2. 1H NMR spectra
Additional structural information can be deduced from the 1H
NMR spectra (300 MHz, DMSO-d6 and ı in ppm) of the free ligands
(L1 and L2), and their diamagnetic UO2(II) complexes (2,4). The aro-
matic region is a set of multiplets in the range 8.090–6.978 (m, 12H,
Ar CH) for the two Schiff base ligands, while the methine protons
of the azomethine group was observed as a singlet in the region
The strong bands at 1593 and 1584 cm−1, characteristic of azome-
thine group, ꢃ(C N), in the free ligands are shifted to lower
frequencies at 1560–1497 cm−1 in the IR spectra of the corre-
sponding complexes, due to coordination of the imine nitrogen.
The peaks due to free amino and carbonyl groups in ligands, L1
and L2 undergoes shift to lower frequency regions in metal com-
plexes (1,2) and (3,4), respectively, indicating their involvement
in coordination with the metal ions, moreover the non-ligand
bands observed in the regions 510–496 cm−1 and 442–424 cm−1
are assigned to ꢃ(M–O) and ꢃ(M–N) stretching vibrations,
respectively, in metal complexes and is indicative of the forma-
tion of metal–ligand bonds [17,18].
•
8.763–8.372 (s, 2H, CH
N
) [22,23]. Additionally, 1H NMR spec-
•
tra exhibit a peak at 6.141 and 10.079 ppm due to NH2 protons
(s, 4H, NH2) and HC O protons (s, 2H, HC O) for L1 and L2,
respectively [24,25]. In the spectra of the UO2(II) complexes (2,4),
the signals due to CH
N , NH2 and HC O protons are slightly
shifted to downfield suggesting the involvement of these groups in
coordination. The chemical shifts of the different types of protons
in the 1H NMR spectra of the ligands and their diamagnetic UO2(II)
complexes are listed in Table 2.
•
In the IR spectrum of UO2(II) complexes (2,4), there are addi-
tional bands not present in the spectra of free ligands. The
strong bands at 1490–1485 cm−1 and 1250–1244 cm−1 in addi-
tion to medium band around 1044–1035 cm−1 are assignable
to ꢃ4, ꢃ1 and ꢃ2 vibration modes of unidentate coordinated
NO3 group while, the characteristic bands at 927–922 cm−1 and
832–830 cm−1 assigned to ꢃ3 and ꢃ1 vibrations, respectively, of
3.3. Conductivity measurements
Conductivity measurements have been used in structural elu-
cidation of metal complexes (mode of coordination) within the
limits of their solubility. The molar conductance values of the metal

14
A.A. Fahem / Spectrochimica Acta Part A 88 (2012) 10–22
Scheme 1. Mass fragmentation pathway of Schiff base ligand, L1.
complexes in DMF and DMSO (10−3 M solution) were measured at
room temperature and the results are listed in Table 1. The molar
conductance values of all complexes (1–4) are found in the range
ꢄM = 39.42–8.55 ꢂ−1 cm2 mol−1. A comparison of these relatively
low values with literature data indicates that all complexes are
non-electrolytes and there is no counter ion present outside their
coordination sphere [26].
target compounds with the series of peaks corresponding to the
various fragments. Their intensity gives an idea of stability of frag-
ments. The pathway fragmentation pattern of the mass spectra of
the ligands is described in Schemes 1 and 2.
3.4.2. Mass spectra of metal complexes
The recorded mass spectra of the metal complexes (1–4)
and the molecular ion peaks have been used to confirm the
proposed formula. The mass spectra of [Ni(L1)Cl2]·2.5H2O (1)
and [UO2(L1)(NO3)2]·2H2O (2) show maximum peaks at m/z
(%) = 490.00 (28.25) (calcd. 489.06 amu) and 746.00 (9.96) (calcd.
744.51 amu) corresponds to the moiety NiC20H18N4Cl2·2.5H2O and
UO2C20H18N6O6·2H2O, respectively, indicative of the monomeric
nature of the complexes under study. Moreover, the mass spectra
have a common prominent peak at m/z (%) = 313.00 (13.00) and
314.00 (17.86) (calcd. 314.42 amu) for (1) and (2), respectively,
which shows a peak of ligand, L1. In addition, the mass spectra
of these complexes have similar degradation pattern. Both com-
plexes, give a loss of water molecules followed by the anions. The
peak observed at 445.00 (18.78) (calcd. 444.01 amu) and 376.00
(33.04) (calcd. 373.11 amu) in complex (1) are due to the loss of
the hydrated water molecules followed by the two coordinated
3.4. Mass spectra
The mass spectra of the two Schiff base ligands; L1 and L2 and
their Ni(II) and UO2(II) complexes (1–4) have been recorded. The
proposed molecular formula of the ligands and their complexes was
confirmed by comparing their molecular formula weight with m/z
values.
3.4.1. Mass spectra of Schiff base ligands
The mass spectra of L1 and L2 (Fig. 2a and b) show the molec-
ular ion peak at m/z (%) = 314.00 (34.15) and 340.40 (35.37) (calcd.
314.42 and 340.40 amu) corresponding to the moieties, C20H18N4
and C22H16N2O2 for L1 and L2, respectively. The pattern of mass
spectra gives an impression of the successive degradation of the

A.A. Fahem / Spectrochimica Acta Part A 88 (2012) 10–22
15
Scheme 2. Mass fragmentation pathway of Schiff base ligand, L2.
chloride ions, respectively. Instead, the peak observed at 710.00
(15.00) (calcd. 708.47 amu) and 582.00 (17.77) (calcd. 584.45 amu)
in complex (2) are due to the loss of the hydrated water molecules
followed by the two coordinated nitrate ions, respectively.
(12.53) (calcd. 610.00 amu) in complex (4) are due to the elimina-
tion of one of the two coordinated nitrate ions followed by the other
one, respectively.
The mass spectra of the metal complexes (1) and (2) are depicted
in Fig. 2c and d as representative example.
The mass spectra of [Ni(L2)Cl2]·1.5H2O (3) and [UO2(L2)(NO3)2]
(4) show maximum peaks at m/z (%) = 499 (5.73) (calcd.
497.02 amu) and 733.00 (20.00) (calcd. 734.45 amu) correspond-
ing to the moiety NiC22H16N2O2Cl2·1.5H2O and UO2C22H16N4O8,
respectively, indicative of the monomeric nature of the complexes
under study. Moreover, the mass spectra have a common promi-
nent peak at m/z (%) = 343.00 (2.76) and 338.00 (4.91) (calcd.
340.40 amu) for (3) and (4), respectively, which shows a peak of
ligand, L2. In addition, the mass spectra of these complexes have
different patterns of degradation. The peak observed at 470.00
(7.56) (calcd. 469.99 amu) and 400.00 (10.00) (calcd. 399.09 amu) in
complex (3) are due to the loss of the hydrated water molecules fol-
lowed by the two coordinated chloride ions, respectively. Instead,
the peak observed at 672.00 (15.00) (calcd. 672.44 amu) and 611.00
3.5. Electronic spectroscopy and magnetic measurements
The observed magnetic moment values for Ni(II) complexes
(1,3) are in close agreements with their electronic spectral data
which further supports their proposed geometry while the UO2(II)
complex (2,4) are diamagnetic [27–29]. Ni(II) complexes, (1,3), have
ꢅeff values 3.02–2.89 B.M., Table 3 corresponding to two unpaired
electrons suggesting high spin configuration, sp3d2-hybridization
and in tune with an octahedral environment around the Ni(II) ion.
The nickel (II) ion in an octahedral field is expected to give a spin
only moment of 2.83 B.M. [30].

16
A.A. Fahem / Spectrochimica Acta Part A 88 (2012) 10–22
Table 3
The magnetic properties of Ni(II) complexes.
a
b
Complex No
ꢅeff
ꢅSO
No. of unpaired electronsc
Hybrid orbitals
Suggested structure
Theo.
Exp.
(1)
(3)
3.02
2.89
2.83
2.83
2
2
2.18
2.06
sp3d2
sp3d2
Octahedral
Octahedral
a
ꢅeff is an experimental effective magnetic moment calculated.
b
c
ꢅso is spin – only magnetic moment = [n(n + 2)]1/2
Number of unpaired electrons per metal ion calculated from ꢅeff = [n(n + 2)]1/2
.
.
The electronic absorption spectra of the free ligands (L1 and
L2) in DMF solution have been recorded in the 800–200 nm range.
The electronic spectra of the free ligands displayed two absorption
bands in the region 43,103–41,667 cm−1 and 32,154–27,778 cm−1
.
The first one can be attributed to ␲–␲* transitions in the benzene
rings and azomethine (C N) groups while the other is most prob-
ably due to the transitions of n–␲* of azomethine groups [31,32].
A comparison of the electronic spectra of the free ligands with
those of Ni(II) and UO2(II) complexes show some blue or red shifts
that can be considered as evidence for the complex formation. Addi-
tionally a new bands were observed in the spectra of complexes
corresponding to certain transition which suggests the geometry
of the complexes [33,34].
The nickel (II) complexes (1,3) are paramagnetic pre-
cluding square planar configuration, their solid reflectance
spectra exhibit three transition bands at 13,003–12,953,
3
3
19,685–19,417 and 22,779–22,321 cm−1 due to A2g(F) → T2g(F)
3
3
3
3
(ꢃ1), A2g(F) → T1g(F) (ꢃ2) and A2g(F) → T1g(P) (ꢃ3) transition,
respectively, suggesting high-spin octahedral Ni(II) [35,36]. The
magnetic moment value (ꢅeff = 3.02–2.89 B.M.) is an additional
evidence for octahedral geometry. The octahedral geometry is
further supported by ligand field parameters like Dq, B, ˇ, ˇ% and
LFSE values, Table 4 [37–39]. UO2(II) complex (2,4) are diamagnetic
and their spectra are dominated only by the ligand bands [40].
According to the empirical formulae of these complexes and in
analogy with those described for UO2(II) complexes having similar
structure, the complexes has a coordination number 8 and exists
in dodecahedral geometry [41].
Fig. 3. TG profiles of metal complexes: (1) [Ni(L1)Cl2]·2.5H2O; (2)
[UO2(L1)(NO3)2]·2H2O; (3) [Ni(L2)Cl2]·1.5H2O; (4) [UO2(L2)(NO3)2].
On the basis of observed thermal decomposition studies, it can
be inferred that all the metal complexes except one lose the water
molecules in one step below 100 ◦C supporting the presence of
water molecules in the outer sphere of these complexes corre-
sponding to the lattice water. The exception was the complex (4),
which was found to be stable to 275 ◦C suggesting its non involve-
ment of water molecules.
3.6. Thermal studies
The aim of our thermal analyses was to obtain information con-
cerning the thermal stability of the complexes investigated (1–4)
and to decide whether water molecules are in the inner or outer
coordination sphere of metal ion. Thermogravimetric studies were
carried out within the temperature range 20–1000 ◦C at a heating
rate of 10 ◦C min−1. The TG curves of metal complexes are depicted
in Fig. 3, while Table 5 lists the initial and final temperatures (◦C)
and the partial mass losses (%) together with the assignments of
each decomposition stage based on mass calculation. The thermal
decomposition is suggested to proceed as shown in Scheme 3 and
the results obtained are in good agreement with the theoretical
formulae suggested from the elemental analysis.
The complex (1) [Ni(L1)Cl2]·2.5H2O gives decomposition pat-
tern of four stages. The first stage within the temperature range
of 27–50 ◦C, is related to the evolution of two and half hydrated
water molecules with a found mass loss of 9.06% (calcd. 9.21%). The
second stage between 50–275 ◦C representing the decomposition
of the organic part of the ligand, L1 and loss of N2 and HCN with
found mass loss of 10.94% (calcd. 11.26%). The third stage within
the temperature range 275–409 ◦C may attribute to loss of 2C6H6
with found mass loss of 31.98% (calcd. 31.95%). The fourth stage
Table 4
Electronic parameters data of nickel (II) complexes.a
Complex No
Absorption bands (cm−1)/peak assignment
Dq (cm−1
)
B (cm−1
)
ˇ
ˇ%
LFSE (cm−1
)
ꢃ1
ꢃ2
ꢃ3
(1)
(3)
13,003
12,953
19,417
19,685
22,779
22,321
13,003
12,953
706
769
0.65
0.71
34.63
28.80
15,604
15,544
3
3
3
3A2g(F) → T2g(F)
3A2g(F) → T1g(F)
3A2g(F) → T1g(P)
a
The ligand field splitting energy (Dq), interelectronic repulsion parameter (B), nephelauxetic ratio (ˇ) and ligand field stabilization energy(LFSE).
The lowering in the (B) values compared to the free metal ion value, 1080 suggests appreciable amount of the covalent character in the metal–ligand bonds. Additionally,
(ˇ) value is less than unity suggesting a largely covalent bond between the organic ligands and metal (II) ions in these complexes.

A.A. Fahem / Spectrochimica Acta Part A 88 (2012) 10–22
17
Table 5
Thermoanalytical results of Ni(II) and UO2(II) complexes.
Complex No
Stage
Temp. range (◦C)
Mass loss
found (calcd.) %
Total mass loss
found (calcd.) %
Evolved moiety
Residue
(1) [Ni(L1)Cl2]·2.5H2O
NiC20H18N4Cl2·2.5H2O
I
27–50
50–275
275–409
409–650
25–80
80–113
113–350
350–430
25–75
75–125
125–400
400–460
275–390
390–450
9.06(9.21)
10.94(11.26)
31.98(31.95)
21.87 (21.09)
5.00(4.84)
20.32(20.71)
11.33(11.02)
11.22(10.49)
5.12(5.44)
2.5H2O (hydr.)
N2 and HCN
2C6H6
NiC20H18N4Cl2
NiC19H17NCl2
NiC7H5NCl2
NiCl2
UO2C20H18N6O6
UO2C8H8N6O6
UO2C6H6N2O6
UO2(NO3)2
II
III
IV
I
II
III
IV
I
II
III
IV
I
73.85(73.51)
47.87(47.06)
C6H5CN
(2) [UO2(L1)(NO3)2]·2H2O
UO2C20H18N6O6·2H2O
2H2O (hydr.)
C6H5 C6H5
N2 and 2HCN
C6H6
1.5H2O (hydr.)
O2
(3) [Ni(L2)Cl2]·1.5H2O
NiC22H16N2O2Cl2
NiC22H16N2Cl2
NiC20H14Cl2
NiCl2
6.88(6.44)
NiC22H16N2O2Cl2·1.5H2O
11.14(10.88)
51.17(49.98)
23.00(23.17)
22.87(23.17)
2HCN
73.12(73.93)
45.87(46.34)
The remaining of organic part
1/2L2
[UO2(1/2L2)(NO3)2]
UO2(NO3)2
(4) [UO2(L2)(NO3)2]
UO2C22H16N4O8
II
1/2L2
L1 and L2 represent the Schiff base ligands.
at 409–650 ◦C representing loss of C6H5CN leaving NiCl2 residue
(found 27.12%, calcd. 26.50%).
25–75 ◦C, is related to the evolution of one and half hydrated water
molecules with a found mass loss of 5.12% (calcd. 5.44%). The sec-
ond stage between 75 and 125 ◦C representing the decomposition
of the organic part of the ligand, L2 and loss of O2 with found mass
loss of 6.88% (calcd. 6.44%). The third stage within the temperature
range 125–400 ◦C may attribute to loss of 2HCN with found mass
loss of 11.14% (calcd. 10.88%). The fourth stage at 400–460 ◦C rep-
resenting loss of the remaining part of the organic ligand leaving
NiCl2 residue (found 27.12%, calcd. 26.07%).
The complex (2) [UO2(L1)(NO3)2]·2H2O gives decomposition
pattern of four stages. The first stage within the temperature range
of 25–80 ◦C, is related to the evolution of two hydrated water
molecules with a found mass loss of 5.00% (calcd. 4.84%). The sec-
ond stage between 80 and 113 ◦C representing the decomposition
of the organic part of the ligand, L1 and loss of C6H5–C6H5 with
found mass loss of 20.32% (calcd. 20.71%). The third stage within
the temperature range 113–350 ◦C may attribute to loss of N2 and
2HCN with found mass loss of 11.33% (calcd. 11.02%). The fourth
stage at 350–430 ◦C representing loss of C6H6 leaving UO2(NO3)2
residue (found 53.21%, calcd. 52.93%).
The complex (4) [UO2(L2)(NO3)2] gives decomposition pat-
tern of two stages. The first one within the temperature range of
273–390 ◦C, is related to the decomposition of the organic part of
the ligand, L2 and loss of half L2 with a found mass loss of 23.00%
(calcd. 23.17%). The second stage between 390 and 450 ◦C repre-
senting the loss of the other half L2 with found mass loss of 22.87%
The complex (3) [Ni(L2)Cl2]·1.5H2O gives decomposition pat-
tern of four stages. The first stage within the temperature range of
Scheme 3. The thermal decomposition pathway for metal complexes (1–4).

18
A.A. Fahem / Spectrochimica Acta Part A 88 (2012) 10–22
Fig. 4. X-ray diffraction pattern of the synthesized compounds: (a) Schiff base ligand, L1; (b) [Ni(L1)Cl2]·2.5H2O; (c) [UO2(L1)(NO3)2]·2H2O; (d) Schiff base ligand, L2; (e)
[Ni(L2)Cl2]·1.5H2O; (f) [UO2(L2)(NO3)2].
(calcd. 23.17%) leaving UO2(NO3)2 residue (found 53.66%, calcd.
53.65%).
increasing thermal stability was observed as:
Comparing the thermal stabilities of metal complexes on the
basis of initial temperature of decomposition [42], the highest ther-
mal stability is displayed by the complex (4) and the sequence of
[Ni(L1)Cl2]·2.5H2O < [Ni(L2)Cl2]·1.5H2O < [UO2(L1)(NO3)2]·2H2O
< [UO2(L2)(NO3)2]
Table 6
X-ray diffraction data of ligand (L1) and its complexes.
Peak No.
L1
(1) [Ni(L1)Cl2]·2.5H2O
(2) [UO2(L1)(NO3)2]·2H2O
d (Å)
Intensity (%)
2ꢀ
4.64
4.88
9.33
d (Å)
Intensity (%)
2ꢀ
5.78
8.48
9.40
d (Å)
Intensity (%)
2ꢀ
7.39
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
19.04
18.70
9.47
9.00
6.30
5.98
4.90
4.73
4.49
4.27
4.09
3.97
3.84
3.69
3.60
3.61
3.26
38.90
100.00
3.90
13.90
17.50
42.70
25.30
14.80
14.80
9.90
15.28
10.43
9.40
7.83
6.97
6.53
6.36
5.92
5.45
5.19
4.85
4.60
4.45
4.16
3.93
3.81
3.46
3.34
3.17
3.11
2.95
2.62
2.39
2.31
2.27
2.12
2.06
1.98
1.91
1.57
11.50
100.00
28.60
13.10
36.50
45.40
28.20
12.20
49.70
19.70
17.20
19.10
40.60
99.10
22.10
39.20
17.40
32.80
24.70
24.30
24.60
28.90
14.00
18.80
22.00
17.70
7.40
11.96
6.53
6.37
6.03
5.57
5.27
4.88
4.75
4.35
4.24
3.97
3.58
3.29
2.93
2.77
100.00
43.00
25.60
32.20
24.60
15.80
32.10
17.80
26.00
15.80
22.20
65.40
18.40
20.00
11.40
13.56
13.88
14.68
15.91
16.80
18.15
18.68
20.41
20.91
22.40
24.83
27.10
30.48
32.30
9.82
11.29
12.69
13.55
13.92
14.95
16.26
17.07
18.27
19.28
19.95
21.33
22.63
23.35
25.76
26.66
28.09
28.72
30.25
34.26
37.64
38.90
39.59
42.64
44.01
45.89
47.67
58.71
14.04
14.80
18.07
18.76
19.75
20.77
21.69
22.38
23.13
24.08
24.71
26.50
27.36
8.20
10.10
15.00
18.30
10.30
18.30
7.30
13.10
8.00
5.00

A.A. Fahem / Spectrochimica Acta Part A 88 (2012) 10–22
19
Table 7
X-ray diffraction data of ligand (L2) and its complexes.
Peak no.
L2
(3) [Ni(L2)Cl2]·1.5H2O
(4) [UO2(L2)(NO3)2]
d (Å)
Intensity (%)
2ꢀ
5.77
d (Å)
Intensity (%)
2ꢀ
8.01
d (Å)
Intensity (%)
2ꢀ
6.24
6.95
8.84
11.89
17.70
19.70
24.81
25.43
27.60
28.08
34.06
44.28
50.87
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
15.29
10.37
6.98
6.35
5.83
5.41
4.60
4.16
3.74
3.52
3.37
2.83
2.36
2.26
100.00
5.10
1.70
11.02
8.14
7.69
6.48
5.99
5.52
4.99
4.66
4.51
4.34
4.22
4.08
3.82
3.71
3.61
3.49
3.36
3.27
3.05
2.98
2.910
2.40
2.33
2.22
1.92
1.73
1.68
5.20
8.90
12.50
34.50
3.40
14.14
12.70
9.99
7.43
5.00
4.50
3.58
3.49
3.22
3.17
2.58
2.04
1.79
32.90
42.40
37.80
43.90
36.60
40.30
100.00
53.00
97.90
70.90
35.40
43.40
33.20
8.51
12.65
13.93
15.16
16.36
19.26
21.32
23.74
25.21
26.41
31.49
38.09
39.81
10.85
11.49
13.63
14.77
16.01
17.75
18.99
19.65
20.43
20.99
21.76
23.22
23.94
24.62
25.49
26.46
27.24
29.19
29.95
30.69
37.33
38.56
40.49
47.22
52.62
54.64
2.60
17.70
10.30
6.10
4.90
35.90
28.70
7.20
5.80
9.60
17.00
6.10
9.40
6.60
8.30
100.00
9.40
4.30
12.60
7.10
7.40
6.10
6.50
5.40
2.60
7.80
19.20
17.60
8.50
4.20
8.00
5.00
4.10
3.7. Powder X-ray diffraction characterization
of the metal ions to the donor sites of the ligands. Moreover,
SEM images of the metal complexes revealed that the surface
morphology of metal complexes changes by changing the metal
ions. From SEM, we can say that, granule-like shape is observed
in [Ni(L1)Cl2]·2.5H2O, the image of [UO2(L1)(NO3)2]·2H2O shows
sponge-like shape, [Ni(L2)Cl2]·1.5H2O has hexagonal shaped mor-
phology and [UO2(L2)(NO3)2] has rode like shape.
Based on the chemical and spectroscopic results, a schematic
structure for Ni(II) and UO2(II) complexes with formation of an
octahedral and dodecahedral geometries, respectively, is proposed,
Figs. 6 and 7.
Although single crystal X-ray crystallographic investigation is
the most precise source of information regarding the structure of
a complex, the difficulty of obtaining crystalline complexes ren-
ders this method unsuitable for such a study. However, a variety of
other spectroscopic techniques could be used with good effect for
characterizing the metal complexes as X-ray power diffraction. So,
X-ray powder diffraction (XRD) measurements of the two ligands
and their complexes were performed. The diffractograms obtained
of the ligands and their complexes have been given in Fig. 4 and
the observed diffraction data, i.e., interplanar spacing d (Å), rela-
tive intensities (I/I0) and (2ꢀ) observed of the samples have been
given in Tables 6 and 7. Comparing the X-ray diffraction patterns
of each ligand with its corresponding metal complexes indicate
that the interplanar spacing, d (Å) and the relative intensities (I/I0)
are different which could be attributed to the complex forma-
tion. Moreover, the diffractogram of [Ni(L1)Cl2]·2.5H2O records
30 reflections with maxima at 2ꢀ = 8.48 ◦ corresponding to d-
3.9. Antibacterial and antifungal properties
The agar disk diffusion method was employed for the determi-
nation of antimicrobial capacities of the synthesized ligands and
their metal complexes. The test microbes represented the stan-
dard strains of S. aureus and S. pyogenes as Gram-positive bacteria;
P. fluorescens and P. phaseolicola as Gram-negative bacteria, and
the fungi: F. oxysporum and A. fumigatus. The antibiotics; Chlo-
ramphencol, Cephalothin and Cycloheximide were used as standard
references for Gram-positive bacteria, Gram-negative bacteria and
fungi, respectively. The results are listed in Table 9 in addition to the
calculated percent activity index data [45,46]. Figs. 8 and 9 explain
1
˚
value 10.43 A. The diffractogram of [UO2(L )(NO3)2]·2H2O shows
15 reflection with maxima at 2ꢀ = 7.39 ◦ corresponding to d-value
2
˚
11.96 A. The diffractogram of [Ni(L )Cl2]·1.5H2O consists of 27
reflections with maxima at 2ꢀ = 26.46 ◦ corresponding to d-value
2
˚
3.36 A. The diffractogram of [UO2(L )(NO3)2] shows 13 reflections
with maxima at 2ꢀ = 24.81◦ corresponding to d-value 3.58 A. With
˚
Table 8
the help of the data obtained from the powder XRD, the crystallite
size calculations were performed using Scherrer equation [43,44]
and the values obtained for crystallite size, Table 8 indicated that
the particles were of nano-sized.
Particle sizes of the synthesized metal complexes.
Complex no.
2ꢀ
8.48
7.39
26.46
24.81
d (Å)
FWHM
Cry. sizea
(1)
(2)
(3)
(4)
10.43
11.96
3.49
0.002
0.001
0.002
0.003
59.29
118.94
59.37
3.8. Scanning electron micrographs (SEM)
3.58
40.47
a
Crystallite size obtained using Scherrer’s equation, D = Kꢁ/(ˇ cos ꢀ), where D is
the particle size in nm of the crystal gain has been calculated using maximum inten-
sity peak; K is the Scherrer’s constant; ꢁ is the wavelength of target used; ˇ is the
full width at half maximum reflection height in terms of radian and ꢀ is the Bragg
diffraction angle at peak position in degree.
The scanning electron micrography (SEM) is used to evaluate
the surface morphology of the synthesized ligands and their metal
complexes. SEM images, Fig. 5 of synthesized ligands differ signifi-
cantly from that of the metal complexes due to the coordination

20
A.A. Fahem / Spectrochimica Acta Part A 88 (2012) 10–22
Fig. 5. Scanning electron microscope (SEM) image of the synthesized compounds: (a) Schiff base ligand, L1; (b) [Ni(L1)Cl2]·2.5H2O; (c) [UO2(L1)(NO3)2]·2H2O; (d) Schiff base
ligand, L2; (e) [Ni(L2)Cl2]·1.5H2O; (f) [UO2(L2)(NO3)2].
the antimicrobial antifungal screening data. Analyzing the potent
action of all synthesized compounds allows us to conclude that:
This result is possible due to the difference in the structure of
the cell wall between Gram-positive and Gram-negative bacte-
ria. The cell wall of the Gram-positive bacteria is composed of a
thick layer of peptidoglycan, consisting of linear polysaccharide
chains cross-linked by short peptides thus forming more rigid
structure leading to difficult penetration of the compounds com-
pared to the Gram-negative bacteria where the cell wall possesses
thinner layer of peptidoglycan [47].
•
The synthesized compounds; the ligands and their metal com-
plexes are found to be more susceptible toward the fungal strains
as compared to the bacterial strains. Additionally, the growth
inhibition activity toward the bacterial strains was observed for
the Gram-negative bacteria more than Gram-positive bacteria.

A.A. Fahem / Spectrochimica Acta Part A 88 (2012) 10–22
21
Fig. 6. Proposed structure of metal complexes of Schiff base ligands, L1.
Fig. 7. Proposed structure of metal complexes of Schiff base ligands, L2.
•
•
Both the ligands and their metal complexes individually exhib-
ited varying degrees of inhibitory on the growth of the organisms
tested. This may attributed to the nature of the ligands, the nature
of the metal ions, and the combined effect of the metal and the
ligand [48].
result of complexation enhances the biological activity of the lig-
ands. This enhancement of activity can be rationalized on the
basis of:
(a) The effect of the metal ion on the normal cell process; the
bounded metal may block enzymatic activity of the cell or else
it may catalyze toxic reactions among cellular constituents
[49,50].
(b) The change in structure due to coordination, it is known
that chelation tends to make the ligand acts as more pow-
erful and potent agents. Furthermore, chelation reduces
the polarity of the metal ion mainly due to the par-
tial sharing of its positive charge with the donor groups
within the chelate ring system increasing the lipophilic
nature of the central metal atom, which favors its per-
meation more efficiently through the lipid layer of the
On comparison of the two ligands, the Schiff base ligand, L2 having
bifunctional CHO groups (with N2O2 donor) was the most potent
antimicrobial agent against all tested organisms than the Schiff
base ligand, L1 having bifunctional NH2 groups (with N4 donor),
this may be due the variation of the donor site in the ligand skele-
ton. The same will be true for their metal complexes indicating
that the donor sites play an important role in the antimicrobial
activity.
•
The metal complexes are more potent bactericides and fungicides
than their parent ligands, so the presence of metal ions as the
Table 9
Antimicrobial screening results of all compounds under study.
Compd. No
Diameter of the inhibition zone (mm) against microorganisms
Antibacterial
Antifungal
S.a.
S.p.
P.f.
P.p.
F.o.
A.f.
L1
8(19)
14(33)
24(57)
9(21)
16(38)
26(62)
42
7(18)
18(47)
22(58)
10(26)
14(37)
27(71)
38
10(28)
19(53)
28(78)
11(31)
19(53)
29(81)
36
9(24)
20(53)
25(66)
13(34)
22(58)
27(71)
38
11(28)
27(68)
30(75)
12(30)
30(75)
34(85)
40
10(25)
23(58)
29(73)
12(30)
27(68)
37(93)
40
(1) [Ni(L1)Cl2]·2.5H2O
(2) [UO2(L1)(NO3)2]·2H2O
L2
(3) [Ni(L2)Cl2]·1.5H2O
(4) [UO2(L2)(NO3)2]
Control
Test done using agar-disk diffusion method.
(S.a.) is Staphylococcus aureus and (S.p.) is Streptococcus pyogenes (Gram-positive bacteria).
(P.f.) is Pseudomonas fluorescens and (P.p.) is Pseudomonas phaseolicola (Gram-negative bacteria).
(F.o.) is Fusarium oxysporum and (A.f.) is Aspergillus fumigatus (fungi).
Control: Chloramphenicol, Cephalothin and Cycloheximide were used as Gram-positive bacteria, Gram-positive bacteria and antifungal, respectively.
Inhibition values: –, no effect; 3–12, low activity; 13–21, intermediate activity; 22–30, high activity and <30, very high activity.
% activity index values are given in parenthesis.

22
A.A. Fahem / Spectrochimica Acta Part A 88 (2012) 10–22
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[51].
•
Moreover, the metal complexes are also found to inhibit the
tested organisms at different rates. Sensitivity of metal complexes
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UO2(II) complexes > Ni(II) complexes which may correlate to the
increase in the coordination number from six in Ni(II) complexes
to eight in UO2(II) [52].
The % activity index data indicate that the ligands show lower
activity than their metal complexes and [UO2(L2)(NO3)2] shows
the highest activity against all tested microbes, in addition, the
activity follows the following order:
•
A. fumigatus (93%) > F. oxysporum (85%) > P. fluorescens (81%) > S.
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The complexes of Ni(II) and UO2(II) with two Schiff base ligands,
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atoms. The remaining coordination positions being occupied by
two chloride ions as well as two nitrate ions to achieve an octa-
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respectively. The bioactivity of these synthesized compounds is
a complex phenomenon related to different factors as described
above and the metal complexes are more active than the free lig-
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