Sonochemical synthesis, structural inspection and semiconductor behavior of three new nano sized Cu(II), Co(II) and Ni(II) chelates based on tri-dentate NOO imine ligand as precursors for metal oxides

Article abstract of DOI:10.1002/aoc.4174

Three novel nanosized Cu(II), Co(II) and Ni(II) complexes of imine ligand attained from the condensation of 2-amino-3-hydroxypyridine and 3-methoxysalicylaldehyde have been prepared and investigated using diverse chemical methods such as NMR, CHN analysis

Full text of DOI:10.1002/aoc.4174

Received: 29 August 2017
DOI: 10.1002/aoc.4174
Revised: 18 October 2017
Accepted: 18 October 2017
F U L L P A P E R
Sonochemical synthesis, structural inspection and
semiconductor behavior of three new nano sized Cu(II),
Co(II) and Ni(II) chelates based on tri‐dentate NOO imine
ligand as precursors for metal oxides
1
1
1
Laila H. Abdel Rahman | Ahmed M. Abu‐Dief
| Rafat M. El‐Khatib |
1
2
2
Shimaa Mahdy Abdel‐Fatah | A.M. Adam | E.M.M. Ibrahim
1
Chemistry Department, Faculty of
Three novel nanosized Cu(II), Co(II) and Ni(II) complexes of imine ligand
Science, Sohag University, 82534 Sohag,
Egypt
attained from the condensation of 2‐amino‐3‐hydroxypyridine and 3‐
methoxysalicylaldehyde have been prepared and investigated using diverse
chemical methods such as NMR, CHN analysis, conductance, IR, Spectral stud-
ies, TGA and magnetic moment measurements. The obtained data confirmed
that the synthesized complexes have metal: ligand ratio of 1:1 and octahedral
geometry for Co(II) and Ni(II) complexes. Interestingly, The complexes are used
as precursors for producing CuO, Co O and NiO nanoparticles by calcination
2
Physics Department, Faculty of Science,
Sohag University, 82534 Sohag, Egypt
Correspondence
Ahmed M. Abu‐Dief, Chemistry
Department, Faculty of Science, Sohag
University, 82534 Sohag, Egypt
Email: ahmed_benzoic@yahoo.com
2
3
at 500 °C and their structures were described by powder x‐ray and transmit-
tance electron microscopy. Furthermore, to investigate the feasibility of using
the synthesized materials for semiconductor based nanodevices, the electrical
properties of the prepared imine complexes and their corresponding metal
oxides were investigated by measuring the electrical conductivity over a temper-
ature range 373‐593 K. The data confirm that the materials are semiconductor.
The electrical conduction process in the complexes is governed by intermolecu-
lar and intramolecular transfer of the charge carriers. But, the conduction
mechanism arises from the contribution of the phonon‐assisted small polaron
hopping in NiO nanoparticles and charge carrier hopping in CuO and Co O
2
3
nanoparticles. The results indicate that the complexes under study are promis-
ing candidates for wide scale of organic based semiconducting devices.
KEYWORDS
electrical properties, imines, nanoparticles, semiconductor, sonochemistry, thermal analyses
[
1–5]
1
| INTRODUCTION
fields.
Recently, there is great attention for prepara-
tion and description of novel nanosized semiconducting
organic compounds for several novel technologies. When
the size of semiconductor matters is decreased to nano-
scale, their physic‐ chemical properties alter significantly,
resulting in unique properties due to their high surface
Transition metal compounds with Schiff base have been
amid the most vastly investigated coordination com-
pounds of the past few years, since they are found to be
widely applicable in many domains such as biochemical
Appl Organometal Chem. 2017;e4174.
wileyonlinelibrary.com/journal/aoc
Copyright © 2017 John Wiley & Sons, Ltd.
1 of 12
https://doi.org/10.1002/aoc.4174

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ABDEL RAHMAN ET AL.
area. Although, appearance of many nanosized semicon-
ducting organic compounds is still in the research field,
some are committed for applications in different fields,
like solar cells, nanoscale electronic instruments, light‐
emitting diodes, laser technology, waveguide, chemical
and biosensors, packaging films, superabsorbents and cat-
2.1 | Synthesis of the investigated imine
ligand
The imine ligand was synthesized by the condensation of
3
3
‐methoxysalicylaldehyde (0.304 g, 2 mmol) and 2‐amino‐
‐hydroxypyridine (0.22 g, 2 mmol) (1: 1 molar ratio), dis-
[6]
solved in 20 ml ethyl alcohol. The mixture was refluxed
for 1 h. The progress and the purity of the prepared ligand
was checked by TLC. The orange precipitate of imine
obtained was filtered, scrubbed with distilled water, desic-
cated, recrystallized from ethanol and kept in a desiccator
alysts. In particular, Imine compounds could conduct as
photostabilizers, dyes for solar collectors, solar filters due
to their photochromic characteristics. They are also
[7,8]
extended in optical sound recording technology.
Also, transition metal oxide nanoparticles represent a
great class of materials that have been investigated exten-
sively. Several methods have been reported in order to
synthesize TMOs nanoparticles, including hydrothermal
(
yield: 88%) as shown in (Scheme 1).
2
.2 | Preparation of cu(II), co(II) and
[
9,10]
Ni(II) complexes with nano‐compositions
by sonochemical technique
route, thermal degradation, sonochemical route.
Transition metal oxides have gained great attention because
of their great applications in optoelectronic devices made
Forty milliliters of a 0.4 M ethyl alcohol solution of the
different metal salts [(Copper acetate, 0.796 g), (Cobalt
[11,12]
from organic semiconductors.
For example, in organic
light‐emitting diodes, they are used as anode modification
(
II) nitrate hexahydrate, 1.16 g) and (Nickel nitrate hexa-
[13–15]
interlayers,
which can substantially reduce the hole
hydrate, 1.16 g)] was placed in an ultrasonic probe, oper-
ating with a maximum force output of 400 W. Into this
solution, 40 ml of 0.4 M solution of the LH2 ligand
injection barrier. They are also opener components of
charge generation layer in tandem organic light‐emitting
diodes. In organic solar cells, they are employed as charge
extraction interlayer and recombination layer. Besides,
transition metal oxides have many unique properties, such
as high work function, semiconducting and good transpar-
ency, that are all very important for electrode interlayers
and/or as charge generation/recombination matters.
Among these characteristics, the high work function is
the main reason for efficient operation of transition metal
(
1.04 g) was added drop wise. The formed precipitate
was filtered off, scrubbed with ethyl alcohol and then des-
iccated in air (yield: 75‐84%) as shown in (Scheme 2).
2
.3 | Preparation of nano‐sized metal
oxides from their corresponding complexes
Nano‐sized metal oxides were got by calcination of (0.1 g)
of the various complexes in air at 500 °C with a heating
[16–18]
oxides based functional layers.
From this point of view, the aim of this research is to
prepare an imine derived from 2‐amino‐3‐hydroxypyridine
and 3‐methoxysalicylaldehyde and its Cu(II), Co(II) and
Ni(II) complexes in nanometer size. Furthermore, the pre-
pared nano‐sized complexes were used as starting materials
for preparation of Cu, Co and Ni oxide nanoparticles. More-
over, a comprehensive study has been presented about the
electrical properties of the synthesized imine complexes
and metal oxides with focus on the conduction mechanisms
governing their electrical properties.
2
| EXPERIMENTAL
All the utilized matters of chemicals in this paper
such as 3‐methoxysalicylaldehyde (97 %), 2‐amino‐3‐
hydroxypyridine (98%), the metal salts (Copper(II) acetate
(98%), Cobalt(II) nitrate hexahydrate (98%) and Nickel(II)
nitrate hexahydrate (98.5 %)) were got from Sigma‐Aldrich
Chemie, Germany. Spectroscopic grade ethyl alcohol,
dimethylformamide and HCl products were utilized.
SCHEME 1 synthesis of Schiff base ligand (LH ), where ahp = 2‐
amino‐3‐hydroxypyridine and v = 3‐methoxysalicylaldehyde
2

ABDEL RAHMAN ET AL.
3 of 12
(
TEM‐2100). An ultrasonic generator (Dr. Hielscher
UP400 S ultrasonic processor) equipped with a ‘H22’
sonotrode with diameter 22 mm was plied for the ultra-
sonic irradiation. The internal construction was sought
using x‐ray diffractmeter: model X’pert3‐Powder made
by PAnalytical with monochromatized CuKα radiation.
Particle size distribution of the synthesized imine com-
plexes and their corresponding metal oxides was esti-
mated utilizing image J Lanucher, broken‐symmetry
software, version (1.4.3.6.7).
2.5 | Electrical properties
To inspect the electrical characteristics of the synthesized
imine complexes and metal oxides, the temperature (T)
reliance of the electrical resistivity (ρ) by the so called
two prop technique within temperature domain 373‐
593 K was inspected. DC electrical resistance of the spec-
imen grains was standardized plying KEITHLEY 614
[22]
Electrometer, operating in the steady current pattern.
SCHEME 2 The suggested structures of LNi, LCo complexes
The electrical resistivity (ρ) is defined as:
average 10 °C min‐1.[19] The attained metal oxide is
scrubbed with ethyl alcohol and dried in desiccator. The
nano‐scale compounds were characterized by transition
electron microscopy and powder x‐ray.
ρ ¼ RA=d
(1)
Where R is the electrical resistance of an even speci-
men of the matter (measured in ohms, Ω), d and A are
the thickness and cross‐sectional area of the taking.
2.4 | Physical characterizations
Melting point of the imine ligand and degradation temper-
atures of the synthesized complexes were predestined
utilizing a melting point tool, Gallenkamp, England, UK.
Infra‐Red spectra of the acquired compounds were patent
by Shimadzu FTIR model 8101 spectrophotometer in KBr
granules in the domain of 4000‐400 cm . Conductivity
measurements were achieved by JENWAY conductivity
meter model 4320 at room temperature plying DMF
dimethylformamide as solvent. UV‐Vis spectra in
dimethylformamide were patent utilizing PG spectropho-
tometer model T+80. Proton NMR and Carbon‐13 NMR
spectra were procured by BRUKER NMR model
3
| RESULTS AND DISCUSSION
.1 | Physical and chemical
3
characteristics
‐
1
All the synthesized complexes are variegated, tough, fixed
at room temperature and non‐hygroscopic in kind. The
analytical and physicochemical data of ligand and its
complexes are patent in (Table 1). The metal complexes
manifested 1:1 (metal‐ligand) ratio.
4
00 MHz plying dimethylsulfoxide‐d6 as the solvent. The
1
13
3
.2 | H‐NMR and C‐NMR spectra
offered imine ligand and its complexes were undergone
to (C, H and N) analyses plying Elemental analyzer
Perkin‐Elmer (240c). The magnetic measurements were
anticipated by Gouy's balance route. Shimaduz corpora-
tion 60H analyzer was anticipated for doing the thermo-
gravimetric test under nitrogen with a heating average
The Proton NMR spectra of the LH ligand manifests sig-
nals at 6.85‐8.00 (m) δ for aromatic protons and 9.44(s) δ
for azomethine proton. The peak at 10.28(s) δ is imputed
2
to –OH group and it vanished upon addendum of D O.
2
The peak at 3.34(s) δ is attributed to methoxy group.
The Carbon‐13 NMR offers the signals coincide to
assorted non‐equivalent carbon atoms at assorted values
of δ as follows: at δ 169 ppm(CH=N) due to azomethine
and at δ 122‐156 ppm(11CH‐Ar) due to aromatic carbon
‐
1
‐3
1
0 °C min . The values of absorbance of 5 × 10 M for
complexes were measured at assorted pH levels. The pH
levels were checked by plying a series of Britton global
buffers.
[20,21]
The pH was measured plying HANNA 211
pH meter at room temperature. The morphology of the
matters was sought by transmission electron microscope
atoms. Also a signal evidences at δ 56 ppm(OCH ) due
3
[
23]
to carbon atom of –OCH group.
3

4
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ABDEL RAHMAN ET AL.
TABLE 1 The analytical and physical data of ligand and its metal complexes
M.p) Elemental analysis found(calculated)
(
Conductance Λ
‐
and
Dec. °
C
M.
Wt
m (Ω
μ
eff
B.M.
1
2
cm
‐
1
Compound
LH
Colour
Orange
C
H
N
mol )
3.67
2
250
>300
290
260
60.00 (60.15)
4.61 (4.71)
10.76 (10.64)
‐
LCu
LCo
LNi
Light green
Brick red
Brown
341.5
372.9
372.7
45.68 (45.53)
41.83 (41.70)
41.85 (41.77)
4.09 (4.22)
4.82 (4.89)
4.82 (4.73)
8.19 (8.05)
7.50 (7.65)
7.51 (7.65)
6.75
6.69
4.76
2.07
4.83
3.69
>300
3
.3 | Infrared spectra
electronic absorption spectra of the ligands and their com-
plexes were patent at the wavelength domain 800–200 nm
and at temperature of room temperature. The ligand
manifests absorption bands in UV–Vis zone around
The Infra‐Red hesitations of the LH ligand and its com-
plexes along with their assignments are manifested in
2
(Table S1). Bands due to –OH and –CH=N are discernible
3
55 nm which is assigned to n→π* transition creating
and bid proof respecting the structure of the ligand and its
bonding with metal. A band at 1613 cm‐ in the imine
ligand is due to −C=N stretching vacillation. On complex-
ation, this band is dislodged to a down hesitation. The
negative shift of this band is an obvious marker of the par-
ticipation of the azomethine nitrogen atoms in complex
[30]
from the imine group.
The absorption bands of com-
1
plexes at λmax=391‐414 nm is assigned to charge transfer
in imine ligands. Furthermore, an intense and broad band
‐1
2
lies in the zone 430–455 nm (ɛmax=1240‐850 mol cm ).
This band could be mainly attributed to the d → d
transition in the structure of the prepared complexes
[1,2,9,20,21,24–26]
consistence.
This is supported by the mani-
[31]
(
Figure S1).
festing of band at 527‐535 cm‐1 coinciding to the
stretching vacillation of M–N bond. The bands subsist at
32‐736 cm‐ coincide to the M‐O stretching vacillations.
1
7
3.5 | Magnetic moment measurements
‐
1
The band manifests at 3447 cm spotted in the ligand
spectrum is due to stretching vacillations of free –OH. In
the complexes, the patent Infra‐Red spectra of all the syn1-
thesized complexes manifest wide band at 3450–3510 cm‐
which have been assigned to υ(OH) stretching vacillation
of hydrated water molecules, in accordance with the find-
In the paramagnetic matters, the magnetic moments are
aligned in the effected magnetic field direction. Therefore,
the paramagnetic matters own positive susceptibilities.
Thus, the magnetic susceptibility measurements manifest
information on regard the geometric structure of the
compounds. Magnetic susceptibility measurements mani-
fested that all the prepared complexes have paramagnetic
property and octahedral geometry barring copper
ings of the CHN analysis patent in (Table 1). A band at
1
9
68‐976 cm– (OH rocking) proposes the subsist of coordi-
nated water in all three complexes. In the low hesitation
zone, the band spotted for imine ligand manifested an
absorption band at 1307 cm‐ which can result from the
[23,28,32]
complex which has tetrahedral geometry.
1
[
28]
stretching vacillation of the phenolic (C–O) group.
3.6 | Thermal analysis
The stir of that band to lower wave number values upon
complexation manifests that the oxygen atoms of the
phenolic groups are bonded to the metal ion. The bands
notified in the zones 3011–3100 cm‐1 can be assigned to
The thermograms of Copper, Cobalt and Nickel com-
plexes affirm the subsisting of one molecule of coordi-
nated water in case of copper and three coordinated
water molecules in case of Cobalt and Nickel com-
[1,2,4,5]
υ(C–H) aromatic stretching vacillations.
[33]
plexes. The thermal mode of the metal complexes man-
ifested that the hydrated complexes forfeit water
molecules of hydration in the first stage; then liberation
coordinated water molecules with degradation of the
ligand molecules in the subsequent stages as manifested
in (Table S2) and Figures (1,2). The LCu, LCo and LNi
have weight forfeits of 5.11, 4.85 and 4.78 %, respectively,
which are due to sweep of water molecules of hydration.
The weight forfeits of 27.48 and 48.11% coincide to the
sweep of the remaining thermally degradable fraction of
3
.4 | Electronic spectra
The molecular electronic absorption spectra are often very
leading for affirming the results attained by other tech-
niques of structural inspection. The electronic spectral
measurements were performed for specifying the stereo
chemistries of metal ions in the complexes reliance on
[29]
the sites and number of d–d transition peaks.
The

ABDEL RAHMAN ET AL.
5 of 12
Where W∞ is the mass forfeit at the completion of the
degradation process. W is the mass perishing up to tem-
perature T, R is the gas constant and φ is the heating aver-
age. Since (1‐2RT/E*) ≈ 1, the plot of the left side of
*
equation versus 1/T would offer a straight line. E was
then predestined from the slope and the Arrhenius con-
stant, A, was profited from the intercept. The other kinetic
*
parameters; the entropy of activation (S ), enthalpy of
*
activation (H ) and the free energy variance of activation
*
(
G ) were predestined using the following equations:
Ah
Sꢀ ¼ 2:303R log
kT
(3)
FIGURE 1 TGA curve of LCu complex
ꢀ
ꢀ
H ¼ E −RT
(4)
(5)
ꢀ
ꢀ
ꢀ
G ¼ H −TS
Where (k) and (h) are Boltzmann's and Plank's con-
stants, respectively. The Kinetic parameters are mani-
fested in (Table S3). It can be manifested that G* values
boosts with the growth of temperature. The positive
values of H* manifest that degradation operations are
endothermic. In most thermal stages, S* values are nega-
tive proposing a decomposition via abnormal passing at
those stages and the degradation operations are unfavor-
able. The negative activation entropy value proposes that
the activated complexes are more ordered than the reac-
tant and the reactions are overdue. The more ordered
kind is attributed to the polarization of bonds in the acti-
vated state which might procure through charge transfer
electronic transitions. Finally, positive values were offered
for H* and G* respectively representing endothermic
FIGURE 2 TGA curve of LCo complex
the complex at temperature domain 155.3‐501.0 °C with
respect to LCu complex. The weight forfeits of 22.82,
[37]
character for all thermal stages.
2
4.03 and 32.39% coincide to the sweep of the remaining
thermally degradable portion of the complex at tempera-
ture domain 153.5‐522.8 °C with respect to LCo complex.
The weight forfeits of 22.91, 31.51 and 24.83% coincide to
the sweep of the remaining thermally degradable portion
of the complex at temperature domain 166.1‐479.9 °C
with respect to LNi complex. The eventual product
explained from a horizontal curve has been attained sug-
[33,34]
gesting consistence of metal product.
3.7 | Kinetic aspects
The thermodynamic parameters of the degradation opera-
tions of the complexes were calculated plying the Coasts‐
[35,36]
Redfern equation,
ꢀ
ꢁ
ꢀ
ꢂ
ꢃꢁ
FIGURE
3
Continuous variation plots for the prepared
logðw −wÞ
AR
2RT
Eꢀ
Eꢀ
∞
‐3
log
¼ log
1−
−
(2)
complexes in aqueous‐alcoholic mixtures at [M] = [L] = 1 ×10
and 298 K
M
2
T
φEꢀ
2:303RT

6
of 12
ABDEL RAHMAN ET AL.
ꢄ
A
3
.8 | Spectrophotometric estimation of the
Am
A
K f ¼
À
Á
(6)
stoichiometry of the prepared complexes
3
4
C 2 1− =
Am
Stoichiometry of the synthesized complexes is predestined
plying the two techniques encompassing the utilize of
spectrophotometry, namely, continuous‐variations route
and mole‐ratio route. Reliance on the methods plied and
the experimental conclusion, the stoichiometry of the syn-
thesized complexes is 1:1. The curves of the continuous
variation technique (Figure 3) offered maximum absor-
bance at mole fraction Xligand = 0.5‐0.6 manifesting the
complexation of metal ions to ligand in molar ratio 1:1.
Moreover, the data resulted from applying the molar ratio
route prop the same metal to ligand ratio of the prepared
Where, Am is the absorption at the maximum consis-
tence of the complex, A is the arbitrary selected absor-
bance values on either hand of the absorbance mountain
col (pass) and C is the incipient concentration of the
metal. As acquired in (Table 2), the attained K values
manifest the great constancy of the synthesized com-
plexes. The values of K for the synthesized complexes
enhance in the following order: LCo > LNi > LCu. More-
over, the amount of the constancy constant (pK) and
f
f
≠
Gibbs free energy (ΔG ) of the complexes under study
[38–41]
complexes (Figure S2).
are predestined. The negative amount of Gibbs free energy
means that the reaction is spontaneous and favored. The
pH‐profile manifested in Figure 4 show perfect dissocia-
tion curves and a high constancy pH extent (4–9) of the
tested complexes. This shows that the consistence of the
complex greatly stabilizes the imine ligands. Conse-
quently, the suitable pH domain for the different applica-
tions of the tested complexes is from pH =4 to pH = 9.
Based on the data of CHN analyses, conductance, mag-
netic susceptibility, infrared and electronic spectra, the
suggested composition of the complexes was described.
3.9 | Estimation of the apparent formation
constants of the synthesized complexes
The consistence constants (K ) of the studied imine com-
f
plexes consisted in solution were attained from the spec-
trophotometric measurements by plying the continuous
variation route (Table 2) according to the following
[32,36,37]:
equation
TABLE 2 The formation constant (K
Gibbs free energy (ΔG ) values of the synthesized complexes in
aqueous‐ethanol at 298 K
f
), stability constant (pK) and
3
.10 | TEM and XRD of the prepared
≠
complexes and metal oxides
The Cobalt, Copper and Nickel oxides nanoparticles were
synthesized at 500 °C utilizing imine complexes as
starting materials and their properties studied with the
relief of a transmission electron microscope and x‐ray dif-
fraction. Dependence on TEM images and the predestined
histogram (see Figure 5 (a‐f) and see Figure 6 (a‐f)), it is
lucid that the average particle size equals 34 nm, 46 nm
and 65 nm for Cobalt, Copper and Nickel complexes,
respectively. Particle size of 25 nm, 42 nm and 16 nm
was predestined for Co O , CuO and NiO, respectively.
Complex Type of complex
K
f
pK
8.85 ‐50.48
ΔG≠ kJ mol‐1
8
1
9
LCu
LCo
LNi
1:1
1:1
1:1
7.15×10
1.10×10
9.60×10
0
10.04 ‐57.25
9.98 ‐56.91
3
4
These results manifest that the prepared compounds have
great surface area and this can lead to many leader cata-
[
42]
lytic and potential properties.
Figure 7 manifests the
XRD modes of the synthesized CuO, Co O and NiO
3
4
nanoparticles. The data also affirm that the synthesized
materials are CuO, Co O and NiO, that all the diffraction
3
4
peaks agreed with the reported standard data; no charac-
teristic peaks were manifested other than metal oxides.
The mean granule size (D) of the particles was
predestined from the XRD line broadening measurement
[
43–48]:
plying the Scherrer Equation
ꢄ
D ¼ 0:89λ cosθ
where λ is the wavelength (1.5406 Å), β is the full breadth
(7)
β
FIGURE 4 Dissociation curves of the prepared complexes in
aqueous alcohol mixtures at[M] = [L] = 1 ×10 M and 298 K
‐3

ABDEL RAHMAN ET AL.
7 of 12
FIGURE 5 (a): TEM image of the prepared LCu complex, (b): Calculated histogram or particle size of LCu complex, (c): TEM image of the
prepared LCo complex, (d): Calculated histogram for particle size distribution LCo complex, (e) TEM image of the prepared LNi complex, (f):
Calculated histogram for particle size of LNi complex

8
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ABDEL RAHMAN ET AL.
FIGURE 6 (a) TEM image of the prepared CuO nanoparticles, (b): Calculated histogram for particle size of CuO nanoparticles, (c): TEM
image of the prepared Co nanoparticles, (d) calculated histogram for particle size of Co nanoparticles
3
O
4
3 4
O
at the half‐ maximum of the CuO, Co O and NiO line
the domain of 16‐46 nm were predestined for the CuO,
3
4
and θ is the diffraction angle. Average crystallite size in
Co O and NiO nanoparticles.
3
4

ABDEL RAHMAN ET AL.
9 of 12
3 4
FIGURE 7 XRD patterns of CuO, Co O and NiO nanoparticles
FIGURE 9 Ln(ρ) vs. 1000/T plots of the co, Ni and cu complexes
bridge to facilitate the flow of current. To illustrate the
effect of the metal type on the electrical resistivity of the
ligand, isothermal resistivity values (determined at
520 K) of the all complexes are tabulated in Table 3. The
data reveal that the resistivity can be tuned by choosing
the proper metal for incorporation in the ligand. The ρ‐T
plots of Cobalt, Copper and Nickel complexes were found
to be well represented by the well‐known Arrhenius pat-
tern which depicts the thermally activated conduction.
According to this pattern, the resistivity reliance of tem-
[
49]
perature is depicted by the following relation:
ꢅ
ꢆ
ꢄ
Ea
ρ ¼ ρ0 exp
T
(8)
KB
FIGURE 8 The temperature dependence of resistivity of the co,
Ni and cu complexes
Where E is the activation energy of conduction, K is
a
B
TABLE 3 Isothermal resistivity at 520 K (ρ(520K)) and activation
energies correspond to the inter‐molecular (EaH) and intra‐molecu-
lar (EaL) conductions of the complexes
the Boltzmann constant and ρ is pre‐exponential constant
0
act the density of state and the charge carrier mobility. The
activation energies of the conduction were predestined
from the slope of the Ln(ρ) vs. 1000/T plots manifested in
Figure 9. Noteworthy, the Ln(ρ) vs. 1000/T plots of the
Co and Ni complexes manifest straight lines, each is
Complex
Ni(II)
E
aL (eV)
E
aH (eV)
ρ(520K) (MΩ.com)
0.021
0.031
0.017
0.037
0.054
‐‐
9.2
Co(II)
Cu(II)
24.7
0.063
4
| ELECTRICAL PROPERTIES
Figure 8 manifests the temperature reliance of resistivity
of the Co(II), Ni(II) and Cu(II) complexes. As seen, the
data reveal a semiconductor behavior where the resistivity
decreases with the increases of temperature. The decrease
of the electrical resistivity with increase of temperature is
resulted from the increase of the charge carriers that can
overcome the energy barrier and participate in the electri-
cal conduction where in metal complexes, the metal
atoms act as charge carriers reservoir supply the complex
with the free electrons and the metal ion can act as a
FIGURE 10 Temperature dependence of electrical resistivity of
the metal oxides nanostructures

10 of 12
ABDEL RAHMAN ET AL.
divided into two fractions with two slopes. This behavior
affirms that the conduction in these complexes consists of
two thermally activated mechanisms with two various acti-
vation energies. By taking in consider the structure of the
complex, the conduction mechanisms can be explained
reliance on two different transfer kinds of the charge car-
riers in the complex. The intra‐molecular transfer, where
the electrons hop from one atomic site to another if orbitals
subsist at these sites are with the same energy levels i.e. the
conduction procure due to the electron transfer between
the ligand and the metal ions in the complex molecule.
The other conduction mechanism, namely the inter‐
molecular conduction, originates from the electron trans-
fer between the neighboring complex molecules due to
the overlapping of their molecular orbitals i.e. π‐electrons
can transmit from one macromolecule to another if
orbitals with the same energy levels subsist between the
conduction can be assigned to the interaction between the
electrons in d‐orbitals of transition metal cations and the
[
54]
anti‐bonding π‐orbitals of the ligand. The intra‐molecu-
lar conduction mechanism is described by lower activation
energy EaL compared to the activation energy of the inter‐
molecular activation energy EaH due to the tying of the
excited free carriers within the molecule by the barriers
macromolecules. The activation energies of the inter‐
molecular and intra‐molecular conduction mechanisms
are patent in Table 3. Note that, the copper is characterized
by one value of the activation energy. Thus, the conduction
may be assigned to a combination of the two mechanisms
simultaneously within the whole domain of the tempera-
ture of measurement without a domination of a certain
one. The large change between activation energy values of
the complexes may be due to contact resistance resulting
from the various surface ratio of the three complexes.
Figure 10 shows the ρ ‐T plots of the metal oxides
[50–53]
complex molecules.
Accordingly, the intermolecular
(
Co O , NiO and CuO) nanostructures. The data affirm
2 3
that the materials have semiconductive properties where
the resistivity reduces dramatically as the temperature
raises. However, there is a clear difference between the
isothermal resistivity values of the oxides. To be specific,
the room temperature resistivity of Co O , NiO, and
2
3
CuO (ρ C3 0o 0O ; ρ and ρ ) where predestined to be 16.4,
NiO
CuO
300
300
2.3 and 1.1 Ω.cm . The semiconductor pattern of the sam-
ples under study is in well correspondance with the data
[
55–57]
published elsewhere.
To grasp the electrical conduc-
tion mechanisms, various theoretical models were applied
to the attained experimental data. It was found that, the
pattern of the resistivity variation with temperature fits
well with Equation 8.The well fit of the ρ‐T data to Equa-
tion 8 is evidenced by the linear pattern of the Ln(ρ) vs.
1
000/T plots manifested in Figure 11. The plots depicted
FIGURE 11 Ln (ρ) vs. 1000/T for co and cu oxides nanostructures
in Figure 11 allows predestin the activation energies Ea
which were found to be 0.098 and 0.12 for Co and Cu
oxides, respectively. These values are comparable to those
[
55]
published in other literature.
Although the tempera-
ture reliance of the temperature of NiO nanoparticles
exhibits typical semiconductor pattern like the other
oxides under study, the ρ‐T data do not fit well with Equa-
tion 9 where the accurate analyses affirm that the data are
better represented by the following equation:
Ea
K
T
ρ=T ¼ ρoe
B
(9)
This pattern affirms that the conduction in the NiO
oxide is band like type which can be assigned to the dom-
2
‐ [22,53]
ination of the large polarons in the 2p band of O .
Activation energy value of 0.13 eV was predestined from
temperature linear fits manifested in Figure 12 for the
NiO nanoparticles which is comparable with values
[
57]
FIGURE 12 Ln (ρ) vs. 1000/T for NiO nanoparticles
reported in other works.

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How to cite this article: Abdel Rahman LH,
Abu‐Dief AM, El‐Khatib RM, Abdel‐Fatah SM,
Adam AM, Ibrahim EMM. Sonochemical synthesis,
structural inspection and semiconductor behavior
of three new nano sized Cu(II), Co(II) and Ni(II)
chelates based on tri‐dentate NOO imine ligand as
precursors for metal oxides. Appl Organometal
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