Impact of gamma-ray irradiation on some aryl-amide-bridged Schiff-base complexes: spectral, TGA, XRD, and antioxidant properties

Article abstract of DOI:10.1007/s10967-019-06946-3

Some aryl amide Schiff base Co(II), Ni(II) and Cu(II) distance between Cu(II) and complexes (1–7) have been obtained and identified by various analytical and spectroscopic tools. To through a light on the probability of structure changes with γ-irradiation, powder samples of complexes 1, 3, 5 and 6 were irradiated with ⁶⁰Co γ-rays at dose of 100 kGy (hereafter referred to as 1F, 3F, 5F and 6F). Spectral, molar conductance, magnetic susceptibility, thermal, X-ray diffraction and antioxidant activity for the irradiated complexes were gained using similar methods used for the non-irradiated complexes. The data revealed that the irradiated complexes were not seriously affected by the utilized γ-irradiation dose.

Full text of DOI:10.1007/s10967-019-06946-3

Journal of Radioanalytical and Nuclear Chemistry
https://doi.org/10.1007/s10967-019-06946-3
Impact of gamma‑ray irradiation on some aryl‑amide‑bridged
Schif‑base complexes: spectral, TGA, XRD, and antioxidant properties
H. A. El‑Boraey1 · O. A. El‑Gammal2 · N. G. Abdel Sattar1
Received: 7 August 2019
© Akadémiai Kiadó, Budapest, Hungary 2019
Abstract
Some aryl amide Schif base Co(II), Ni(II) and Cu(II) distance between Cu(II) and complexes (1–7) have been obtained
and identifed by various analytical and spectroscopic tools. To through a light on the probability of structure changes with
γ-irradiation, powder samples of complexes 1, 3, 5 and 6 were irradiated with 60Co γ-rays at dose of 100 kGy (hereafter
referred to as 1F, 3F, 5F and 6F). Spectral, molar conductance, magnetic susceptibility, thermal, X-ray difraction and anti-
oxidant activity for the irradiated complexes were gained using similar methods used for the non-irradiated complexes. The
data revealed that the irradiated complexes were not seriously afected by the utilized γ-irradiation dose.
Keywords γ-Irradiation · Metal complexes · Spectral · Modeling · IC50
Introduction
disturbance of energy levels as well as distortion of elec-
tronic spectrum [18–21]. These changes provide essential
information about the physicochemical consequences of
radiation efects in solids materials [4, 22].
Studies on the efects produced in solids materials by the
interaction of ionizing radiation have received considerable
attention [1–5]. Energetic γ-radiation can afect on the color,
chemical composition, spectral, catalytic properties, mag-
netic, structural, optical, electrical, thermal and biological
behavior of variety of solids [6–8]. γ-irradiation can enhance
thermal decomposition process of the solids, owing to lat-
tice defects and chemical damage [8–10]. γ-irradiation also
afects on crystallinity leading to changes in lattice parame-
ters according to X-ray studies [11–14]. The specifc surface
areas, the particle size and the catalytic activities of certain
γ-irradiated catalytic systems can be altered upon irradiation
[15]. FT-IR and electronic spectral studies showed that the
position and intensity of the characteristic bands changed
upon irradiation [16, 17] and irradiation can encourage
The chemistry of aryl amide Schif base ligands is a fas-
cinating area of research and has attracted a lot of atten-
tion owing to their versatile bioactivities and their extensive
applications in many scientifc felds [23–29]. So, the liga-
tion of Schif base with transition metal ions is with great
signifcance in the range of bioinorganic chemistry and
medicine. However, over generation of free radicals may
encourage some oxidative damages to bio-molecules like
carbohydrates, proteins, lipids, DNA and so on. Antioxidants
interact with the free radicals, acting as electron donors
and prevent the damage by reactive oxygen species (ROS)
[30]. A lot of Schif base complexes have been examined as
potential scavengers of ROS [31–34]. In addition, synthetic
antioxidants are vastly used due to their efective and are
cheaper than natural antioxidants [35].
Recently, we have reported the impact of γ-irradiation on
spectral, X-ray difraction, SEM, DNA binding, molecular
modeling and antibacterial activity of some acetohydrazide
dervative metal(II) complexes [36]. The physicochemical
efect of γ-irradiation at 30 kGy dose on some transition
metal complexes with the tetraaza [N4] ligand (L) had been
reported by us [37]. Previously, we studied the impact of
high energetic ionizing radiation on hydrazine carbothioam-
ide derivative (H2L) and its Cu(II) complexes [10].
Electronic supplementary material The online version of this
article (https://doi.org/10.1007/s10967-019-06946-3) contains
supplementary material, which is available to authorized users.
* H. A. El-Boraey
helboraey@yahoomail.com
1
Department of Chemistry, Faculty of Science, Menoufa
University, Shebin El-Kom 32511, Egypt
2
Department of Pathology, University Hospital, Menoufa
University, Shebin El-Kom 32511, Egypt
Vol.:(0123456789)
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Journal of Radioanalytical and Nuclear Chemistry
With this regard and in continuation of our previous
studies on the impact of ionizing γ-irradiation on powder
solid samples of metal complexes, the present work aims
to study the impact of γ-irradiation on some aryl amide
bridged Schif base metal complexes. Spectral, molar con-
ductivity, magnetic susceptibility measurements, thermal
and XRD of both non-irradiated and irradiated samples
were studied. Moreover, the antioxidant activity of both
non-irradiated and irradiated samples was evaluated rela-
tive to ascorbic acid.
Synthesis of the metal complexes
0.5 g of (H2L) in 30 mL ethanol was magnetically stirred
in a bottom fask to which a dropwise addition of ethanolic
solution of CoCl2·6H2O, Co(CH3CO2)2·4H2O, NiCl2·6H2O,
Ni(CH3CO2)2·4H2O, CuCl2·2H2O, CuBr2 and CuN2O6·3H2O
for complexes (1–7), respectively in 1:1 molar ratio. The
reaction mixture was heated under refux near 12 h. The
reaction progress was confrmed by thin-layer chromatog-
raphy (TLC). The formed solid precipitate was removed
by fltration, washed with ethanol several times, dried and
stored in a desiccator at 25 °C under P4O10/CaCl2 for further
characterization.
Experimental
Materials
Physical measurements
All the reagents used were procured from Sigma-Aldrich
Company. Metal salts (E. Merck) were used without addi-
tional purifcation. All solvents were used as received.
Microanalyses (carbon, hydrogen and nitrogen), metals and
halide analyses, molar conductivity, magnetic measure-
ments, FT-IR, electronic, proton magnetic resonance, EPR
spectra and TG were all performed as described in the lit-
erature [36, 37, 39].
Synthesis of H2L ligand
N,N′-(1,2-phenylene)bis(2-aminobenzamide) (S) has
been prepared according to previous reported method
[38]. The current H2L ligand: N,Nʹ(1,2-phenylene)bis(2-
(((Z)-(2-hydroxynaphthalen-1-yl)methylene)amino)ben-
zamide) (Fig. 1) has been prepared by adding ethanolic
solution (20 mL) of (S) (0.5 g, 0.144 mmol) to a solu-
tion of 2-hydroxy-1-naphthaldehyde in the same solvent
(0.4976 g, 0.289 mmol) in 1:2 molar ratio, respectively.
The reaction mixture was allowed to refux with stirring
about 12 h at 70–80 °C. The yellow solid product formed
was isolated and washed many times with cold ethanol and
dried over P4O10/CaCl2.
Irradiation studies
For irradiation studies, powder samples of complexes 1, 3,
5 and 6 (hereafter referred to as 1F, 3F, 5F and 6F) were
irradiated at dose of 100 kGy with the 60Co γ-ray Indian
at a dose rate of 2.2 kGy h−1 cell type GE-4000 A. The
samples were irradiated at 25 °C in the absence of air, at
the Atomic Energy Authority of Egypt, Nasr City. For the
irradiated samples the FT-IR, electronic, EPR, XRD spectra,
molar conductance, magnetic measurements and TG were
performed by the same methods used for the non-irradiated
complexes [36, 37].
Antioxidant study
The antioxidant property of the ligand, non-irradiated com-
plexes (1, 3, 5 and 6) and their corresponding irradiated sam-
ples (1F, 3F, 5F and 6F) was evaluated by 1,1′-diphenyl-
2-picrylhydrazyl (DPPH) method [40] and compared with
standard (Ascorbic acid). To a diferent concentrations (100,
150 and 200 µg mL−1) in dimethylsulphoxide (DMSO) of
each sample solutions (2 mL), a solution of 400 μM DPPH
(2 mL) in methanol was added. The mixture was allowed to
stand in the dark 25 °C for 30 min. The absorbance values of
the mixture were then recorded at 517 nm. The percentage
of inhibition of the DPPH radical (%) was calculated using
equation reported elsewhere [40].
Fig. 1 Proposed structure of the ligand H2L
1 3

Journal of Radioanalytical and Nuclear Chemistry
Results and discussion
Microanalyses and molar conductance
The ligand H2L i.e.: N,Nʹ (1,2-phenylene)bis(2-(((Z)-(2-hy-
droxynaphthalen-1-yl)methylene)amino)benzamide) was
allowed to react with some transition metal(II) salts, in
1:1 molar ratio to yield the current complexes (1–7). All
isolated complexes are colored and air stable. They are
partially soluble in most popular organic solvents by heat-
ing but readily soluble in DMSO and dimethylformamide
(DMF). The elemental and physical data of the ligand and
its complexes were tabulated in Table 1. Microanalyses
data showed that all complexes are formed in 1M:1L molar
ratio and agree well with the suggested formula.
Conductivity measurements of 10−3 M solutions of the
complexes in DMF at 25 °C were recorded and the data
are given in Table 1. All complexes have molar conduct-
ance values in the range of 1–34 Ω−1 cm2 mol−1 and are
non-electrolytic in nature [41].
Color and molar conductivity of irradiated
complexes
Upon irradiation, color change was observed only for
cobalt(II) complex (1). Its color changed from red to
brown after γ-irradiation (1F). This change in color may
be owing to surface changes generated by γ-irradiation
[4]. The metal complexes exposed to γ-irradiation showed
slight change in values of Λm and there is no alteration in
their non-electrolytic behavior (Table 1) [41].
Spectroscopic studies
Proton nuclear magnetic resonance spectrum of the ligand
The spectrum (1H-NMR) of the ligand was measured in
1
DMSO-d6 solution. H-NMR spectrum showed singlet
at δ = 15.41 ppm corresponding to –OH protons which
corresponds to two protons. Singlet at δ = 10.42 ppm is
corresponded to the amide (–CO–NH–) protons, with
integration intensity equivalent to two hydrogens and
the appearance of a singlet at δ = 8.97 ppm is owing to
imine proton (–CH=N–) which integrated to two protons
1
[23–25]. Additionally, the H-NMR spectrum exhibits a
multiplets at δ = 6.7–8.21 ppm corresponding to aromatic
1
protons. Thus, the H-NMR data confrm the proposed
structure (Fig. 1).
1 3

Journal of Radioanalytical and Nuclear Chemistry
Table 2 FT-IR (cm−1), UV/vis (λmax, nm) and magnetic susceptibility data (µef, B.M.) of the compounds
No.
Compound
ν(OH/NH)
ν(C=N)
ν(C–O)
ν(M–O)
ν(M–N)
λmax (nm)
(B.M.)
H2L
[Co(L)]·2H2O
[Co(L)]·2H2O
3412, 3241(b)
3429(b)
3433(b)
3419(b)
3425(b)
3433(b)
3425(m)
3416(b)
3431(b)
3431(b)
3431(b)
3415(b)
1623(s)
1613(s)
1615(s)
1603(s)
1613(s)
1615(s)
1605(s)
1608(s)
1616(s)
1611(s)
1614(s)
1607(s)
1284(m)
1209 (w)
1210(s)
1260(m)
1270(m)
1284(s)
1210(m)
1286(m)
1284(s)
1284(m)
1285(s)
1274(m)
–
–
461, 444, 366, 321
460, 435, 320
458, 432, 319
486, 454, 430, 328
466, 441, 321
462, 440, 360, 320
458, 445, 323
465, 442, 365, 319
462, 440, 365, 320
475, 446, 325
471, 445, 365, 335
457, 445, 350, 323
–
1
1F
2
563(w)
542(s)
566(m)
562(w)
539(s)
572(m)
563(w)
539(s)
586(w)
539(s)
550(w)
472(w)
495(s)
495(m)
433(w)
496(s)
424(m)
437(w)
471(s)
450(w)
498(s)
467(w)
3.15
3.15
2.59
dia
[Co(L)(H2O)2]·3H2O
[Ni(H2L)Cl2]·H2O
[Ni(H2L)Cl2]·H2O
[Ni(L)(H2O)2]·H2O
[Cu(H2L)Cl2(H2O)2]
[Cu(H2L)Cl2(H2O)2]
[Cu(H2L)Br2(H2O)2]·H2O
[Cu(H2L)Br2(H2O)2]·H2O
[Cu(L)(H2O)2]·2H2O
3
3F
4
5
5F
6
6F
7
dia
3.60
2.12
2.12
2.10
2.10
2.10
s strong, m medium, w weak, b broad
except for complex (1F). This peak may be due to the exist-
ence of ketoamine-enolimine toutomerism in these com-
plexes due to transformation of the ligand molecule induced
by γ-irradiation [23, 42]. The absence of this peak in the
infrared spectrum of complex (1F) obviously confrms the
deprotonation of naphtholic hydroxyl groups. In addition,
pronounced changes in the intensities as well as position of
some characteristic peaks are observed. The broad bands
of ν(OH/NH) in the irradiated complexes (1F, 3F, 5F) are
observed at higher energy (Table 2). The imine stretching
vibration was shifted to higher energy to the extent of 8 cm−1
in some irradiated complexes. For bands corresponding to
the ν(M–O), these bands were shifted to lower energy upon
γ-irradiation whereas the bands due to the ν(M–N) were
shifted to higher energy. The shift observed in the FT-IR
bands may be owing to the deformity of lattice planes
induced by γ-irradiation [4].
FT‑IR
The characteristic FT-IR spectral data of the obtained
compounds are summarized and given in Table 2. In
the infrared spectrum of H2L the occurrence of peaks at
3412 and 3241 cm−1 is attributable to ν(OH) and ν(NH)
vibration modes, respectively. The strong band appeared
at 1623 cm−1 in the spectrum of the ligand is owing to
imine group vibration. The lowering of imine frequency
value in all complexes 1603–1613 cm−1 indicates the
involvement of imine nitrogen in the coordination [24].
The naphthalic ν(C–O) vibration band in the free ligand
appeared at 1284 cm−1. The shift of this band to lower fre-
quency 1209–1274 cm−1 in metal complexes (1, 2, 4 and
7) emphasis the coordination through deprotonated oxy-
gen atom [12]. New observed band at about 586–550 cm−1
is consistent with ν(M–O) vibrations. Another new band
at about 495–433 cm−1 was attributed to ν(M–N) vibra-
tions [30]. The presence of water of crystallization and/or
coordination in the compounds structure, as indicated by
microanalysis data, render it difcult to get information
from ν(OH) of the H2L ligand which will be interfered
by those of water molecules. Therefore, the above argu-
ments confrmed that the ligand coordinates as a dibasic
tertradentate one in complexes (1, 2, 4, 7) ligates through
the imine nitrogen atoms and the oxygen atoms of the
deprotonated hydroxyl groups or as a neutral bidentate
one in complexes (3, 5, 6) with imine nitrogen atoms.
UV–visible spectral studies and magnetic
susceptibility measurements
The UV/vis spectra of the ligand and its complexes were
done in DMF solution. The absorption bands showed by
the compounds alongside with their magnetic susceptibility
data at 25 °C (μef B.M.) are collected in Table 2. The elec-
tronic absorption spectrum of the free ligand shows strong
absorption bands with maxima at 321, 366, 444–461 nm,
respectively. The frst absorption with maxima at 321 nm
is assigned to the π → π*, transition through the aromatic
rings, imine and carbonyl groups. The other bands 366,
444–461 nm are attributed to the n→π* transition between
the lone pair of electrons of the imine and carbonyl groups
and the conjugated π bond of the aromatic rings and charge
transfer (CT) band [26].
FT‑IR of irradiated complexes
By comparing the FT-IR spectra of non-irradiated and
irradiated complexes (Fig. 2a, b; Table 2), it is noted that,
medium intensity band centered around 1670 cm−1 was
appeared in the FT-IR spectra of all irradiated complexes
1 3

Journal of Radioanalytical and Nuclear Chemistry
Fig. 2 a FT-IR spectra of complexes (1, 1F) and b FT-IR spectra of complexes (5, 5F)
The UV/vis spectrum of Co(II) complex (1) displays
bands with maxima at 460–435 nm which may be due
to ligand–metal charge transfer (LMCT) transition. The
value of magnetic moment is 3.15 B.M., so square planar
geometry was suggested for this complex [43]. Complex
(2) has electronic transition bands at 486–454 nm which
may be correlated to 4T1g(F)→4A2g(P) transition, its mag-
netic moment value is 2.59 B.M., confrming the low spin
octahedral confguration [26, 44].
The μef of all copper complexes is 2.10 B.M., that is cor-
related to the existence of one unpaired electrons [45].
UV–visible spectral studies of irradiated complexes
Comparing the electronic spectra of irradiated complexes
with that of non-irradiated complexes we observed that,
for irradiated [Co(L)].2H2O (1F) the broad peaks cor-
responded to LMCT transitions at 458, 432 nm were
recorded with a small shift in λmax to higher energy side
to the extent of 1–3 nm with no change in the measured
magnetic moment value of the irradiated sample (3.15
B.M), indicating that there is no change in the geometry
upon γ-irradiation and the observed color change (brown)
is due to surface changes and deformation of the complex
structure as a result of γ-irradiation [43]. When the LMCT
band of irradiated [Ni(H2L)Cl2]·H2O complex (3F) is com-
pared with that of non-irradiated [Ni(H2L)Cl2]·H2O (3), the
LMCT band, slightly shifted to higher energy side at 462,
440 nm was observed in complex (3F). Also the diamagnetic
The UV/vis spectrum of nickel(II) complex (3) displays
bands with maxima at 466–441 nm which correspond to
LMCT transition that hides the d–d transition. The dia-
magnetic behavior of this complex confrms its square pla-
nar geometry [43]. Nickel(II) complex (4) exhibits band at
458–445 nm which corresponds to LMCT transition. The
μef of this complex recorded at room temperature is 3.6
B.M., confrming the octahedral confguration [26].
The copper(II) complexes (5, 6, 7) showed UV/vis
broad spectral bands within 475–457 nm range due to
LMCT transition in a distorted octahedral confguration.
1 3

Journal of Radioanalytical and Nuclear Chemistry
behavior of the irradiated complex confrms its square planar
geometry so, there is no change in the confguration after
γ-irradiation [43]. The electronic spectra of the irradiated
(5F) and (6F) complexes also exhibited hypsochromic shift
in electronic absorption peaks. Also there is no change in the
magnetic moment values (2.10, 2.10 B.M.) for these com-
plexes indicating that there is no confguration change after
γ-irradiation.
the covalent character of the complexes [50]. The quotient
f=g∕∕/A// gives value of 194, 193 cm which correlated to a
marked distortion around the copper(II) site.
Thermal studies
Thermal properties have been carried out using TGA, at
heating rate 10 °C min−1 in N2 atmosphere from RT-800 °C
using platinum crucible. The results of the thermal analysis
for both non-irradiated and γ-irradiated metal complexes are
shown in Table 3. The TG thermograms of non-irradiated
and irradiated complexes have nearly the similar profle, it is
seen that the desolvated non-irradiated and irradiated com-
plexes decomposed in two or three steps.
EPR spectra of non‑irradiated and irradiated
copper(II) complexes
The room temperature (300 K) EPR spectra of the non-irra-
diated Cu(II) complex (6) and its irradiated (6F) were per-
formed on the X-band frequency 9.719 GHz. By comparing,
the EPR spectra of both non-irradiated and irradiated sample
were seen to be quite similar except slight decrease in the
intensity of the perpendicular component of the irradiated
sample (Fig. 1S). Both spectra displayed the parallel and the
perpendicular features indicating axially symmetric anisot-
ropy spectra. The g-tensor parameters with g∕∕=2.197 and
g⊥ = 2.026 for complex (6) and g∕∕ = 2.190, g⊥ = 2.036 for
complex (6F) i.e. g∕∕>g⊥>2.0023, indicated that the Cu(II)
center has a tetragonal distorted geometry with dx2–y2 ground
state for both samples [46]. The g∕∕ is less than 2.3 sug-
gesting covalent bond character around the Cu(II) ion. The
exchange interaction parameter G=g∕∕− 2.0023/g⊥− 2.0023
for complexes (6, 6F) is higher than 4 (7.579) for complex
(6) and (6.333) for complex (6F)) suggesting no exchange
coupling in the solid state. The bonding coefficients ꢀ2
(covalent in-plane σ-bonding), ꢀ2 and ꢀ2 (covalent in-plane
and out-of-plane π-bonding) have been computed for both
non-irradiated and irradiated samples, using Eqs. (2) and
(3) [47, 48].
The TG curve of Co(II) complex (1) (Fig. 3a) shows
mass loss of 4.8 (Calc. 4.8%) within the region 25–150 °C,
which agrees well with elimination of two water molecules.
The TG thermogram also reveals that complex (1) decom-
posed at 150 °C giving Co metal as a fnal residue. The
TG curve of Co(II) complex (2) shows weight loss of 6.72
(Calc. 6.72%) due to the removal of three water molecules
in RT-170 °C range. The coordinated water molecules were
removed with decomposition steps, where a gradual weight
loss appeared in 170–600 °C range, and CoO as is remain
as a fnal residue.
The TG thermograms of Ni(II) complexes (3, 4) (Fig. 3a)
displays weight loss of 2.3 (Calc. 2.3%) and 2.3 (Calc.
2.3%), respectively within RT-150 °C range, corresponding
to removal of one hydrated water molecule for both com-
plexes, after that the TG curves show that complex (3) starts
degradation at 150 °C, whereas complex (4) decomposed at
270 °C, followed by the oxidation to nickel oxide for both
complexes.
The TG thermogram of Cu(II) complex (5) (Fig. 3b)
shows no weight loss till 170 °C, confrming the absence
of H2O or solvent molecules outside coordination sphere.
However, The TG thermograms of Cu(II) complexes (6,
7) (Fig. 3b) show weight loss of 1.93 (Calc. 1.93%) in the
25–110 °C range; 4.5 (Calc. 4.5%) in the 25–170 °C range,
respectively correlated with release of one hydrated water
molecule (complex 6), two water molecules (complex 7).
The complexes (5, 7) start the decomposition process at
170 °C, while complex (6) decomposed at 160 °C. The
decomposition process ended with the air stable CuO as end
product for all Cu(II) complexes.
A∕∕
3
+ (g∕∕ − 2.0023) + (g⊥ − 2.0023) + 0.04
ꢀ2 =
(2)
0.036
7
ꢀ2 = (g∕∕ − 2.0023)E∕8ꢁꢂ2
(3)
where (λ = − 828 cm−1) and E is the electronic transition
energy. The smaller value of ꢀ2 (0.558, 0.5249) compared
to ꢀ2 (1.107, 1.146) showed that the in-plane σ-bonding has
greater covalent bond character than the in-plane π-bonding.
The values of ꢀ2 are 0.992 for complex (6), 1.021 for com-
plex (6F). For complex (6F) ꢀ2 > 1 shows considerable ionic
character of the out-of-plane π-bonding.
Thermal properties of irradiated complexes
The parallel K∕∕ and perpendicular K⊥ components of
orbital reduction factors were calculated by the expressions
notifed elsewhere [49]. The complexes (6, 6F) showed K∕∕,
K⊥ in the order K∕∕ > K⊥ due to considerable out-of-plane
π-bonding [49]. The small values of K (0.641, 0.613) suggest
To highlight the impact of γ-rays on the thermal behavior
of irradiated complexes, their TG thermograms were also
recorded (Table 3). The TG curve of irradiated Co(II) com-
plex (1F) (Fig. 3a) shows mass loss of 4.8 (Calc. 4.8%) in
the 25–150 °C range which corresponds to the elimination
1 3

Journal of Radioanalytical and Nuclear Chemistry
Table 3 TGA data of the
No
Compound
Temp. range/°C
Mass loss%
Calc.
Reaction
compounds
F.
4.807
1
[Co(L)]·2H2O
25–150
150–700
at 700
25–150
170–800
at 800
25–170
170–270
270–600
at 600
25–150
150–700
at 700
25–90
190–550
at 550
25–150
270–600
at 600
170–800
at 800
180–620
at 620
25–110
160–800
at 800
25–110
190–650
at 650
25–170
170–570
at 570
4.807
86.37
8.823
4.807
88.70
6.493
6.725
4.475
76.50
12.30
2.353
89.90
7.747
2.353
91.20
6.447
2.347
87.64
10.01
91.00
9.000
92.29
7.701
1.932
89.30
8.768
1.932
91.25
6.818
4.559
85.37
10.07
–2H2O
–decomp.
≡Co
–2H2O
–decomp.
≡Co
–3H2O
–2H2O
–decomp.
≡CoO
–H2O
–decomp.
≡NiO
–H2O
–decomp.
≡Ni
–H2O
–decomp.
≡NiO
–decomp.
≡ CuO
–decomp.
≡ Cu
–H2O
–decomp.
≡CuO
–H2O
–decomp.
≡Cu
86.37
8.901a
4.807
88.70
6.810a
6.725
4.48
1F
2
[Co(L)]·2H2O
[Co(L)(H2O)2]·3H2O
76.50
12.50a
2.353
89.90
7.810a
2.353
91.20
6.515 a
2.347
87.64
10.01a
91.50
8.500a
92.68
7.311a
1.932
90.00
8.068a
1.932
91.17
6.901 a
4.559
85.37
10.07a
3
[Ni(H2L)Cl2]·H2O
[Ni(H2L)Cl2]·H2O
[Ni(L)(H2O)2]·H2O
3F
4
5
[Cu(H2L)Cl2(H2O)2]
[Cu(H2L)Cl2(H2O)2]
[Cu(H2L)Br2(H2O)2]·H2O
5F
6
6F
7
[Cu(H2L)Br2(H2O)2]·H2O
[Cu(L)(H2O)2]·2H2O
–2H2O
decomp.
≡CuO
aFinal percent
of two hydrated water molecules. The complex starts decom-
position at 170 °C and the residual part was Co metal. The
complete sublimation of the organic ligand finished at
800 °C whereas for non-irradiated complex the sublimation
process fnished at 700 °C.
The TG thermogram of Cu(II) complex (5F) (Fig. 3b)
also shows no weight loss till 180 °C, confirming the
absence of H2O or solvent of crystallization. However,
The TG thermogram of Cu(II) complex (6F) (Fig. 3b)
shows mass loss of 1.93 (Calc. 1.93%) in the 25–110 °C
range related to release of one hydrated water molecule.
The complexes (5F, 6F) start the decomposition process
at 180, 190 °C, the sublimation of the organic ligand
ended at 620 and 650 °C, respectively leaving Cu as final
decomposition product. This indicates that irradiation
enhances the thermal stability for the irradiated com-
plexes (3F, 5F, 6F), this may be related to the intramo-
lecular and/or intermolecular hydrogen bonds present in
ketoamine –enolimine forms of these complexes [35].
The TG curve of irradiated Ni(II) complex (3F) (Fig. 3a)
displays mass loss of 2.3 (Calc. 2.3%) in the 25–90 °C range,
which agrees well with the elimination of one hydrated water
molecule. By comparison, complex (3F) lost its water mol-
ecule at lower temperature than complex (3). The complex
progressively decomposed at 190 °C, leaving Ni as a fnal
end residue. The decomposition process of irradiated (3F)
fnished at 550 °C, while for non-irradiated sample it com-
pletely fnished at 700 °C.
1 3

Journal of Radioanalytical and Nuclear Chemistry
Fig. 3 a TG curves of non-irradiated complexes (1 and 3) and their irradiated (1F and 3F) and b TG curves of non-irradiated complexes (5 and
6) and their irradiated (5F and 6F)
Fig. 4 XRD patterns of non-irradiated complexes (5 and 6) and their irradiated (5F and 6F)
few reflections indicating their amorphous nature [37].
The intensity of powder lines of irradiated Cu(II) complex
(6F) is found to be slightly different from non-irradiated
sample (6). While for (5, 5F) the intensities of powder
lines are almost the same.
X‑ray difraction studies of non‑irradiated
and irradiated complexes
The X-ray diffractograms for copper(II) complexes (5,
5F) and (6, 6F) before and after irradiation are given in
Fig. 4. It is noted that all samples are found to have very
1 3

Journal of Radioanalytical and Nuclear Chemistry
a
Fig. 5 3D structure of [Ni(H2L)Cl2]·H2O (3) (protons are omitted for
simplicity)
Molecular modeling studies of ligand and its Ni(II)
complex (3)
The model geometric structure of the ligand (Fig. 2S) and
its [Ni(H2L)Cl2]·H2O complex (3) (Fig. 5) was achieved uti-
lizing Hyper Chem Sketch 15.0 version [51]. The selected
bond lengths and bond angles of signifcant importance were
computed and the data are reported in Tables 1S, 2S. The
bond lengths of the azomethine (C=N): N(32)–C(34), and
N(31)–C(33) for the ligand are 1.262 and 1.267 Å, respec-
tively. Upon chelation, the bond length of these groups
altered to 1.267 and 1.289 Å. The bond lengths become
somewhat longer confirming the chelation with Ni(II)
ion which occurs via N atoms of the two imine (>C=N)
groups. Other changes have been noted in other bond
lengths. The actual bond angles of the azomethine (C=N):
C(34)–N(32)–C(30) and C(33)–N(31)–C(21) for the ligand
are 119.04° and 133.24°, respectively. These bond angles in
the complex changed to 123.23 and 120.11°. The values of
bond angles (Tables 1S, 2S) confrmed that Ni(II) ion has
square planar confguration [36, 48].
b
Based on the above discussions, the possible structures
for the metal complexes are shown in Fig. 6a, b.
Fig. 6 a Structure of the complexes (1, 2, 4 and 7) and b structure of
the complexes (3, 5 and 6)
Antioxidant activity of non‑irradiated and irradiated
samples
these values demonstrated that the non-irradiated com-
plexes have greater antioxidant activities than their free
ligand except for complex (1). Among the series stud-
ied, Cu(II) complex (5) possesses excellent antioxidant
activity (IC50 = 20.00 µg mL−1) better than ascorbic acid
(IC50 =28.21 µg mL−1). This confrmed the potential value
of metal ion in improving the antioxidant activity of the
ligand [52, 53]. The scavenging activity of the non-irradi-
ated compounds is in the order:
The antioxidant property of the synthesized ligand (H2L)
and its non-irradiated (1, 3, 5, 6) and irradiated (1F,
3F, 5F, 6F) complexes were determined by their scav-
enging ability on the stable 1,1′-diphenyl-2-picrylhy-
drazyl (DPPH) free radical [40]. As depicted in Fig. 7,
the calculated IC50 values = 253.15, 292.32, 75.13,
20.00, 41.28 µg mL−1 for H2L, 1, 3, 5, 6, respectively
1 3

Journal of Radioanalytical and Nuclear Chemistry
350
300
250
200
150
100
50
remove the hydrogen atom from it is higher than in the non
H-bonded one [35].
Conclusion
In our study, the impact of γ-ray irradiation on the physico-
chemical properties of some aryl amide Schif base Co(II),
Ni(II) and Cu(II) complexes was investigated by diferent
analytical, spectral, thermal and XRD tools. The results
showed the rigidity of the complexes to the applied dose
and can be summarized as follows:
0
1. Change in color was observed in the irradiated Co(II)
complex (1F).
Compound
2. New FT-IR side peaks, slight change in position, shape
and intensity of some FT-IR peaks were appeared after
irradiation in some irradiated complexes.
3. No change in geometry was observed.
4. XRD patterns of both non-irradiated and irradiated com-
plexes indicated their amorphous nature.
5. TGA results suggested that γ-irradiation enhanced
the dehydration process for Co(II) complex (1F) and
increases the thermal stability for complexes (3F, 5F,
6F).
Fig. 7 IC50 plot of the ligand, non-irradiated, irradiated compounds
and ascorbic acid as standard
Cu(II)(ꢀ) > Ascorbic acid > Cu(II)(ꢁ) > Ni(II)(ꢂ) > H2L > Co(II)(ꢃ)
It is worth to notify that γ-irradiation leaded to notewor-
thy change in the values of the antioxidant activity. The
irradiated samples (1F, 3F, 5F, 6F), with IC50 values
22.08, 153.03, 73.57, 196.57 µg mL−1, respectively and
based on data on Fig. 7, it was seen that the IC50 of com-
plex (1F) was enhanced upon γ-irradiation it presents an
excellent antioxidant activity better than ascorbic acid
(IC50 = 28.21 µg mL−1). Other exposed metal complexes
showed decrease in their antioxidant activity but still better
than their non-irradiated free ligand. The antioxidant scav-
enging activity after irradiation is in the order
6. Antioxidant activity was enhanced by γ-irradiation for
Co(II) complex(1F).
Compliance with ethical standards
Conflict of interest Authors have declared that no conficts of interest
Cu(II)(ꢀꢁ) > Ascorbic acid > Cu(II)(ꢂꢁ) >
Ni(II)(ꢃꢁ) > Co(II)(ꢄꢁ) > H2L
exist.
This pronounced property of the complexes may be due to
the chelating function of the organic ligand to the metal ions
[33]. The higher antioxidant activity of complexes (3, 5, 6)
than complex (1) may be due to the signifcant contribu-
tion of the hydroxyl groups [35]. The increased free radi-
cal scavenging action of the irradiated complex (1F) can be
assigned to the surface changes generated by γ-irradiation
which may facilitate the release of hydrogen atom or an
electron to reduce the DPPH radical [35]. However, the
decreased free radical scavenging action of the irradiated
complexes (3F, 5F, 6F) may be related to the intramolecular
and/or intermolecular hydrogen bonds present in ketoamine-
enolimine toutomeric forms of these complexes that dislikes
the DPPH scavenging activity, due to the enhanced bind-
ing of the hydrogen atoms. It was known that the H-bond
increases the structure stability, thus, the energy required to
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