Study of the chemical structure and their nematicidal activity of N2O2 tetradentate Schiff base metal complexes

Article abstract of DOI:10.1002/aoc.5010

Coordination compounds of Cu (II), Y (III), Zr (IV) and La (III) with the tetradentate Schiff base (H₂L) obtained through the condensation of p-phenylenediamine with salicylaldehyde under reflux conditions. The complexes were characterized by elemental analysis, magnetic susceptibility, molar conductance and also, with various spectroscopic techniques such as ¹H NMR, UV–Vis., IR and XRD techniques. Electrolytic nature of complexes was ascertained by molar conductance values. In these four complexes, the ligand chelates act in a tetradentate manner via azomethine nitrogen and oxygen atoms of phenolic groups. Electronic spectroscopic data are in agreement with an octahedral geometrical structure. Thermal degradation analyses in nitrogen gas were used to investigate the number and location of water molecules. The chemical formulae of metal complexes were confirmed by microanalytical data. The activation thermodynamic parameters, such as, E^*, ΔH^*, ΔS^* and ΔG^* were calculated from the DTG curves using Coats Redfern (CR) and Horowitz–Metzeger (HM) methods at n?=?1 or n?≠?1. Nematicidal activities indicate that the ligand exhibit greater activity when compared to its complexes. In addition metal complexes displayed good moderate nematicidal activities.

Full text of DOI:10.1002/aoc.5010

Received: 12 January 2019
DOI: 10.1002/aoc.5010
Revised: 1 May 2019
Accepted: 3 May 2019
F U L L P A P E R
Study of the chemical structure and their nematicidal
activity of N2O2 tetradentate Schiff base metal complexes
S.M. Abd El‐Hamid1
| S.A. Sadeek1 | N.S. Abd El‐Lattif2
1 Department of Chemistry, Faculty of
Science, Zagazig University, Zagazig,
Egypt
2 Department of Pesticides Formulation,
Central Agricultural Pesticides
Laboratory, Cairo, Egypt
Coordination compounds of Cu (II), Y (III), Zr (IV) and La (III) with the
tetradentate Schiff base (H2L) obtained through the condensation of p‐
phenylenediamine with salicylaldehyde under reflux conditions. The com-
plexes were characterized by elemental analysis, magnetic susceptibility, molar
conductance and also, with various spectroscopic techniques such as 1H NMR,
UV–Vis., IR and XRD techniques. Electrolytic nature of complexes was
ascertained by molar conductance values. In these four complexes, the ligand
chelates act in a tetradentate manner via azomethine nitrogen and oxygen
atoms of phenolic groups. Electronic spectroscopic data are in agreement with
an octahedral geometrical structure. Thermal degradation analyses in nitrogen
gas were used to investigate the number and location of water molecules. The
chemical formulae of metal complexes were confirmed by microanalytical
data. The activation thermodynamic parameters, such as, E*, ΔH*, ΔS* and
ΔG* were calculated from the DTG curves using Coats Redfern (CR) and
Horowitz–Metzeger (HM) methods at n = 1 or n ≠ 1. Nematicidal activities
indicate that the ligand exhibit greater activity when compared to its com-
plexes. In addition metal complexes displayed good moderate nematicidal
activities.
Correspondence
S.M. Abd El‐Hamid, Department of
Chemistry, Faculty of Science, Zagazig
University, Zagazig, Egypt.
Email: sherifmohamed85@yahoo.com
KEYWORDS
H2L, IR, Nematicidal activity, thermal analysis, XRD
1 | INTRODUCTION
Transition metals assume significant parts in different
biological activities because of the exceptionally wide
Schiff bases are named organic ligands got from the con-
densation reactions of amines and corresponding alde-
hydes or ketones (RCH=NR, where R and R represent
alkyl/or aryl substitutes).[1] Schiff's base nucleus contain-
ing compounds made their own character significance in
pharmaceutical, medicinal, biochemical, industrial and
agricultural sciences. They indicated scopes of biological
activities, for example, herbicidal, anti‐bacterial, anti‐
viral, anti‐fungal, anti‐inflammatory and antioxidant
activities.[2–7]
range of reactivity available and have been especially
attractive.[8] It is additionally realized that the existence
of metal ions bonded to biologically active compounds
may enhance their biological activities, such as antibacte-
rial,[9] anticonvulsant,[10] antifungal,[11] anti‐HIV,[12] anti-
viral, anticancer,[13] antimicrobial[14] and numerous other
biological activities.
Transition metal complexes of Schiff base ligand had
gain a growing interest in pharmacological field for the
utilization as antimicrobial agents and show great
Appl Organometal Chem. 2019;e5010.
wileyonlinelibrary.com/journal/aoc
© 2019 John Wiley & Sons, Ltd.
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https://doi.org/10.1002/aoc.5010

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ABD EL‐HAMID ET AL.
biological activities against pathogenic microorganisms.
It had been seen with several experimental results that
the metal complexes had more significant antimicrobial
action than their parent ligands .[15–17] The reaction of
tetradentate Schiff bases got from salicylaldehyde and
diamine has been the subject potential as catalysts for
the inclusion of oxygen into an organic substrate of numer-
ous studies.[18–26]
Orange precipitate was filtered off, washed several times
by ethanol and dried under vacuum over CaCl2.
2.3 | Synthesis of Schiff base metal
complexes
The dark brown solid complex [Cu(H2L)(H2O)2]
(CH3COO)2.2H2O was prepared by adding 1 mmol
(0.182 g) of Cu (CH3COO)2 in 30 ml absolute ethanol
drop‐wise to a stirred suspended solution 1 mmol
(0.316 g) of H2L in 30 ml ethanol. The reaction mixture
was boiled and stirred under reflux for 12 hr. The formed
solid product was separated by filtration and washed
thoroughly with ethanol and dried under vacuum over
anhydrous CaCl2. The orange and red [Y(H2L)(H2O)2]
Cl3.3H2O, [ZrO(H2L)(H2O)]Cl2·3H2O and [La(H2L)
(H2O)2]Cl3.7H2O were prepared in a similar manner
described above by using ethanol as solvent.
To continue our investigation in the field of Schiff
base complexes,[27–29] we reported here the synthesis
of tetradentate Schiff base N, N/−p‐phenylenebis
(salicylideneimine) (H2L) (scheme 1) and its metal com-
plexes. The compounds have been characterized by using
1
the microanalytical, conductance, (IR, electronic and H
NMR) spectra, magnetic data with Bohr magnetons, ther-
mogravimetric analyses as well as XRD techniques. The
activation energies and other kinetic parameters were
computed from the Coats‐Redfern and Horowitz‐Metzger
equations and nematicidal evaluated.
• [Cu(H2L)(H2O)2](CH3COO)2.2H2O complex.
N,N/−p‐phenylenebis (salicylideneimine)diaqua cop-
per acetate dihydrate.
2 | EXPERIMENTAL
2.1 | Materials
• [Y(H2L)(H2O)2]Cl3.3H2O complex.
N,N/−p‐phenylenebis
(salicylideneimine)
Salicylaldehyde,
absolute
ethanol,
FeCl3.6H2O,
diaquayttrium chloride trihydrate.
ZrOCl2.8H2O (99.9%), AgNO3 were purchased from Fluka
chemical Co. CoCl2.6H2O, Cu (CH3COO)2, YCl3.6H2O
and LaCl3.7H2O from Aldrich Chemical Co. p‐
phenylenediamine purchased from EL‐Shorouk Scientific
chemical Co. This is all chemicals used for the synthesis
of compounds were of the analytical reagent grade, com-
mercially available from different sources and highest
purity available. All the chemicals and solvents were used
as purchased.
• [ZrO(H2L)(H2O)]Cl2·3H2O complex.
N,N/−p‐phenylenebis (salicylideneimine)oxoaquo zir-
conium chloride trihydrate.
• [La(H2L)(H2O)2]Cl3.7H2O complex.
N,N/−p‐phenylenebis (salicylideneimine)diaqua lan-
thanum chloride heptahydrate.
2.2 | Synthesis of N,N/−p‐phenylenebis
(salicylideneimine) Schiff base
(C20H16N2O2) H2L
2.4 | Physical measurements
The elemental analysis for C, H and N was done by a
Perkin Elmer CHN 2400. The ratio of the metal ions were
specified gravimetrically by transforming the solid prod-
ucts into metal oxide and also specified by using atomic
absorption method. Spectrometer model PYE‐UNICAM
SP 1900 fitted with the corresponding lamp was used for
this purpose. The infrared spectra of H2L and its metal
complexes were recorded from KBr discs using FTIR
460 plus spectrophotometer in the range from 4000 to
400 cm−1. The electronic absorption spectra were mea-
sured as solutions in DMSO in the region 200‐800 nm
The Schiff base (H2L) was synthesized via mixing 1 mmol
(0.108 g) of p‐phenylenediamine in 30 ml absolute etha-
nol with 2 mmol (0.244 ml) salicylaldehyde 30 ml abso-
lute ethanol into round bottomed flask equipped with a
magnetic stirrer. The reaction mixture was boiled under
reflux for 10 hr. The resulting solution was concentrated
to 8 ml on a water bath and allowed to cool at 0 °C.
1
using UV‐3101PC Shimadzu. H NMR spectra were mea-
sured on Varian Mercury VX‐300 NMR Spectrometer
using DMSO‐d6 as solvent. TGA‐DTG measurements
SCHEME 1 N,N/−p‐phenylenebis (salicylideneimine) (H2L)

ABD EL‐HAMID ET AL.
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were keeping running under N2 atmosphere within the
temperature range from room temperature to 1000 C
2.5.2 | Bioassay technique
ο
using TGA‐50H Shimadzu, the mass of sample was pre-
cisely weighted out in an aluminum crucible. XRD analy-
ses were carried out by using a Philips Analytical X‐ray
BV, diffractometer type PW 1840. Radiation was given
by a copper target (Cu anode 2,000 W) high intensity X‐
ray tube operated at 40 kV and 25 mA. Magnetic suscep-
tibilities of the powdered samples were done on a Sher-
wood scientific magnetic balance using Gouy balance at
room temperature using Hg[Co (CSN)4] as calibrant.
The molar conductance of 1 × 10−3 M solutions of the
ligands and its metal complexes in DMSO was measured
at room temperature using CONSORT K410. All mea-
surements were carried out at ambient temperature with
freshly prepared solutions. Melting points were recorded
on a Buchi apparatus.
Evaluation of tested ligand and its complexes as nemati-
cides was distributed consistent with migration
method.[30] Bioassay unit consists of polyethylene tube
protracted 1.3 cm and 2.4 cm diameter lined at one end
with two layers; the primary one is paper handkerchief
then muslin cloth. It stuffed with washed dry sand of par-
ticle size 250 μ and placed upright in a petri‐dish (5 cm
diameter) tested ligand and its complexes were prepared
in ethanol with 5000 ppm concentration. One milliliter
of tested concentration was pipetted on surface of sand
in every tube and kept at 25 2 °C to evaporate the sol-
vent. After 24 hr, one milliliter of water was pipetted on
surface of sand in every tube, then one milliliter of water
containing second stage larvae of one hundred
Meloidgyne javanica was pipetted on the surface of the
sand in every tube. Each bioassay unit was transferred
to petri‐dish (9 cm diameter) containing filter paper
soaked with two milliliter water to serve as humidity
room to stop evaporation. After 24 hr the bioassay unit
took up from humidity room and eight milliliter distilled
water was added in petri‐dish of bioassay unit. The num-
ber of second stage larvae that had migrated in bioassay
dish was recorded 72 hr later. The numbers of migrated
second stage larvae in treatments were expressed as pro-
portion of number in control each treatment was repli-
cated fourfold. The Inhibition ratios were counted.
2.5 | Nematicidal investigation
2.5.1 | Culture technique
Nematicidal activity of ligand and its metal complexes
was investigated.[30] Root‐Knot worm (Meloidgyne
javanica) propagated in pure culture in central Agricul-
tural Pesticides Laboratory. Individual egg‐masses with
their mature females were far away from galls of the
infected roots. Every egg‐mass was placed in ten cubic
centimeter glass capsule containing distilled water. The
feminine below the actual egg‐mass was far away from
root tissue, dissected and known by magnifier examina-
tion of its perineal pattern system. Identification was
recorded in keeping with its corresponding egg‐mass of
previously known females. Egg‐mass were individually
placed on root system of two weeks old tomato seed
plant race variety (CV). Pritchard in fifteen cm clay pots
filled with steam sterilized sandy loam soil. The inocu-
lated pots were watered completely and kept in green
3 | RESULTS AND DISCUSSION
The tetradentate Schiff base (H2L) and its Cu (II), Y
(III), Zr (IV) and La (III) complexes are colored, solid,
stable at room temperature toward air and moisture
and soluble in DMSO and DMF. Analytical results of
the complexes are consistent with the proposed molecu-
lar formulas and confirm the formation of 1:1 were
established on the basis of elemental chemical metal
ions: H2L complexes (Table 1). Molar conductance of
prepared Schiff base metal complexes were measured
in DMF (1x10−3 M) at room temperature and found in
the range 172.4 to 273.4 S cm2 mol−1 revealing their
electrolyte.[31] Qualitative reactions also agree well with
the molar conductance data which revealed the pres-
ence of chloride and acetate ions as counter ions. The
magnetic moment value of Cu (II) complex is 2.11 B.
M. According to the above data the complexes have
octahedral geometry. Crystallinity and unit cell structure
were estimated by XRD. Nematicidal activity were per-
formed with standard protocols and methodologies as
described in previous section.
house at 25
5 °C. Two months after inoculation the
plants were far away from the pots and therefore the
rootage of every plant was examined for nematodes
infection and reproduction. Sample was from the
infected roots that contained adult females and egg‐
masses for identification to verify the worm species to
their original patterns. The infected roots were used
for inoculation of tomato seedlings CV. Pritchard
growth in twenty five cm pots filled with 3:1 blend of
sandy and muddy soil. New tomato seed plant was
transplanted to the pots as required. By repetition this
procedure enough quantities of inoculate from pure cul-
ture were obtained.

4 of 13
ABD EL‐HAMID ET AL.
TABLE 1 Elemental analysis and physico‐analytical data for H2L and its metal complexes
% found (calc.)
Color
(yield) % (°C)
M.P.
Λ S
Compounds M.Wt. (MF.)
C
H
N
Cl
M
cm2 mol−1
H2L 316.35 (C20H16N2O2)
Dark
Orange
219 75.90 (75.93) 5.07 (5.09) 8.84 (8.86)
‐
‐
15.3
[Cu(H2L)(H2O)2](CH3COO)2.2H2O
570.05 (C24H30N2O10Cu)
Dark
brown
300 50.55 (50.57) 5.27 (5.30) 4.89 (4.91)
‐
11.14 (11.15) 172.4
[Y(H2L)(H2O)2]Cl3.3H2O 601.69
(C20H26N2O7Cl3Y)
Orange
320 39.89 (39.92) 4.33 (4.36) 4.64 (4.66) 17.67 (17.68) 14.77 (14.78) 271.6
345 42.38 (42.40) 4.25 (4.27) 4.91 (4.94) 12.50 (12.52) 16.09 (16.10) 188.3
330 33.16 (33.19) 4.71 (4.73) 3.84 (3.87) 14.68 (14.70) 19.17 (19.19) 273.4
[ZrO(H2L)(H2O)]Cl2·3H2O 566.54
(C20H24N2O7Cl2Zr)
Red
[La(H2L)(H2O)2]Cl3.7H2O 723.76
(C20H34N2O11Cl3La)
Red
TABLE 2 Infrared frequencies (cm‐1) and tentative assignments for H2L and its metal complexes
Compounds
ν(O‐H); phenolic and H2O
ν(C=N)
ν (Zr = O)
ν(C‐O)
υ(M‐O) and υ(M‐N)
H2L
3419br
3430 m
3368br
3382br
3421br
1606 ms
1611s
‐
1061s
‐
[Cu(H2L)(H2O)2](CH3COO)2.2H2O
[Y(H2L)(H2O)2]Cl3.3H2O
[ZrO(H2L)(H2O)]Cl2·3H2O
[La(H2L)(H2O)2]Cl3.7H2O
‐
1019w
1036w
1077w
1019w
673vw,500w,593w, 527w
611 m, 551vw, 519w
674sh, 652sh, 543sh
569vw, 544w, 522vw
1613vs
1620s
‐
827w
1623s
‐
Keys: s = strong, w = weak, v = very, m = medium, br = broad, sh = shoulder, ν = stretching.
3.1 | FT IR absorption spectra
The FT‐IR spectra of the complexes were done (Figure
S1) and compared with that of free Schiff base in order
to investigate the mode of bonding the ligand to the metal
ions (Table 2). There are some main peaks in the Schiff
base spectrum which are changed upon complex forma-
tion. The broad band at 3419 cm−1 in the spectrum of free
Schiff base corresponds to O‐H stretching vibrations.
Medium and broad bands observed in the complexes at
3368–3430 cm−1 can be assigned to the O–H stretching
vibrations of water molecules or hydrogen bonds.[32] This
bonding behavior is supported by the following
evidences.
SCHEME 2 The coordination mode of Cu (II), Y (III), Zr (IV)
and La (III) with H2L
i. The band at 1606 cm−1 assigned to C=N stretch in
the spectrum of free ligand is slightly shifted to
higher wavenumbers in the complexes, sustaining
the above mentioned affirmation.[33]
ii. The shifting in the frequency of ν(C‐O) which
appeared in the complexes spectra in the 1019–
1077 cm−1 range.[34]
iii. New bands spotted in the 673–527, 611–519, 674–543
and 569–522 cm−1 regions which referring to ν(M‐O)
and ν(M‐N) vibrations respectively.[35–37]
The proposed structures for complexes are represented in
Scheme 2. The ν (Zr = O) found as a medium band at
827 cm−1. The above results together with elemental
analysis indicate that the ligand acted as tetradentate
fashion bind to metal ions via oxygen atom of hydroxyl
group and azomethine nitrogen.

ABD EL‐HAMID ET AL.
5 of 13
FIGURE 1 Electronic absorption spectra for (A) H2L, (B) Cu (II), (C) Y (III), (D) Zr (IV) and (E) La (III)
peak attributed to n‐π* transition of azomethine
group.[38,39] The two bands (274 and 364 nm) are shifted
in all complexes to lower or higher values in the range
of 273–385 nm. The complexes show an additional
strong shoulder in the region of 520–570 nm are
assigned to have their charge transfer character arising
from the transfer of charge from the ligand to the metal
centre. This data gave good indication in coordination
of the azomethine nitrogen to the metal ions. The elec-
3.2 | Electronic absorption spectra
The electronic absorption spectral data of H2L and its
complexes in DMSO are showed in Figure 1 and
Table 3. The electronic spectra are used to assign the
stereochemistry of the metal ion in the complexes based
on the position and number of d‐d transition bands. The
electronic absorption spectrum of ligand displays two
bands in the UV at 274 and 364 nm. The first peak of
shortest wavelength may be assignable to the π‐π* tran-
sition in the benzenoid moieties. However, the second
tronic absorption spectral band of Cu (II) complex, gives
2
band at 633 nm. The band is assigned to B1g
2Eg

6 of 13
ABD EL‐HAMID ET AL.

ABD EL‐HAMID ET AL.
7 of 13
transition typified octahedral geometry.[40,41] The mag-
netic moment value is 2.11 B.M. in favor of octahedral
geometry.
3.4 | Thermal analysis of Schiff base
ligand and its metal complexes
Thermal degradation of ligand and its complexes was
studied in the range of 30–1000 °C to elucidate the nature
of water molecules in these complexes (Figure 3). The
solid complexes showed mode of stability at room tem-
perature and subjected to gradual decomposition ending
up with formation of their respective metal or metal
oxides. The thermal decomposition process of H2L ligand
(C20H16N2O2) involved one decomposition step. The
decomposition step started at 300 °C and finished at
700 °C with maxima peaks temperatures at 326 and
3.3 | 1H NMR spectra
1
The detected H NMR chemical shifts of the ligand and
its complexes in DMSO‐d6 are depicted in Table 4. The
1H‐NMR spectrum of ligand exhibited multiplet signals
at 7.02–7.69 ppm which corresponded to –CH aromatic
(Figure 2) and singlet around 11.88 and 13.05 ppm related
to the hydroxyl proton. The azomethine proton (–HC=N)
signal in the spectrum of ligand showed singlet at
618
°C,
which
involved
the
removal
of
8C2H2 + 2CO + C2N2. The overall weight loss amounted
to 99.57% (calc. = 100%) (Table 5).
1
6.97 ppm. By comparison of the H NMR of the ligand
Cu (II) and Y (III) complexes decomposed in two
stages. The first one occurred in 50–240 °C and 30–
186 °C ranges with 6.63% and 9.25% weight loss (calc.
6.32%) and (calc. 8.98%) corresponding to loss of two
and three water molecules. The second step occurred at
241–700 °C and 187–700 °C, represent the complete deg-
radation of complexes with 75.17% and 58.35% weight
loss (calc. 75.51%), and (calc. 58.28%) ending with metal
oxide formation (CuO +2C and YO1.5 + 7C).
and that of complexes, it was found that the signal of
hydroxyl proton not disappeared in the spectra of this
complexes indicating that the ligand bonded with metal
ion in the protonated form. In addition, the noteworthy
chemical shift of the azomethine proton signal in com-
parison to the free ligand is a good proof for involvement
of the azomethine nitrogen atom in the coordination via
donation of a lone pair of electrons of the nitrogen atom
to the central metal atom resulting in the formation of a
coordinated bond (N → M).[42,43] Also, the signals
observed at 3.18–3.61 ppm with an integration corre-
sponding to protons of complexes, is assigned to water
molecules.
In order to make sure for the presence of the proton of
–OH in all complexes. The spectrum of Zr (IV) complex
as an example was done in presence of D2O which indi-
cated the presence of the –OH protons in the complex
(Figure 2).
TABLE 4 1H NMR values (ppm) and tentative assignments for
(A) H2L, (B) [Cu(H2L)(H2O)2](CH3COO)2.2H2O, (C) [Y(H2L)
(H2O)2]Cl3.3H2O, (D) [ZrO(H2L)(H2O)]Cl2·3H2O and (E) [La(H2L)
(H2O)2]Cl3.7H2O
13.05,
A
11.88
13.08, 11.81 7.00–7.86
13.00 11.02 7.14–8.86
7.02–7.69 6.97
‐
B
C
D
E
F
6.72–6.97 3.18–3.31
6.63–6.98 3.48
13.03, 10.95 7.01–8.85
13.00, 11.26 7.01–8.92
6.61–6.96 3.32–3.34
6.41–6.96 3.40–3.61
6.87–6.95 3.33–3.42
‐
7.09–8.93
Assignments δ, OH(s)
δ, –CH(m) δ, –CH(s) δ, H2O
aromatic HC=N
FIGURE 2 1H NMR spectra for (A) H2L, (B) Cu (II), (C) Y (III),
(D) Zr (IV), (E) La (III) were done in DMSO and (F) Zr (IV)
complex was done in D2O
Where (F) is Zr (IV) complex was done in D2O.

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ABD EL‐HAMID ET AL.
FIGURE 3 TGA and DTG diagrams for (A) H2L, (B) Cu (II), (C) Y (III), (D) Zr (IV) and (E) La (III)
3.5.1 | Coats‐Redfern equation[44]
The thermal decomposition of Zr (IV)and La (III) com-
plexes were occurred via two degradation steps. The first
step of decomposition was occurred within the tempera-
ture range 30–243 °C and 30–183 °C with maxima peaks
at 89, 177 °C and 120, 152 °C which correspond to loss
of three and seven water molecules of hydration with
weight loss of 9.74% (calc. 9.54%) and 17.76%, (calc.
17.42%). The last step of decomposition was occurred
within the temperature range of 244–850 °C and 184–
750 °C with weight loss of 53.82% (calc. 53.87%), and
63.12% (calc. 63.38%) leaving ZrO2 + 7C and La as
residue.
The Coats‐Redfern equation (1), which is a typical integral
method, can be represented as:
ꢀ
ꢁ
α
T2
T1
dα
ð1−αÞ
A
φ
−E*
RT
∫
¼
∫
exp
dT
(1)
n
0
For convenience of integration, the lower limit T1 is usu-
ally taken as zero. This equation on integration gives:
ꢂ
ꢃ
ꢂ
ꢃ
− lnð1 − αÞ
−E*
RT
AR
φE*
ln
¼
þ ln
(2)
T2
A plot of left‐hand side (LHS) against 1/T was drawn, E*
is the energy of activation in kJ mol−1 and calculated
from the slope and A in (s−1) from the intercept. The
entropy of activation ΔS* in (kJ K−1 mol−1) was calcu-
lated by using equation (3):
3.5 | The kinetic studies
In the present investigation the general thermal behavior
of ligand and its complexes in terms of stability ranges,
peak temperatures and values of kinetic parameters, are
shown in Table 6 and Figure S2. The kinetic parameters
have been evaluated using the following methods[44,45]
and the results obtained by these methods are compared
with one another.
ꢀ
ꢁ
Ah
KBTs
ΔS* ¼ R ln
(3)
Where KB is the Boltzmann constant, h is the Plank's con-
stant and Ts is the DTG peak temperature.

ABD EL‐HAMID ET AL.
9 of 13
TABLE 5 The maximum temperature Tmax (°C) and weight loss values of the decomposition stage for (H2L), Cu (II), Y (III), Zr (IV)
and La (III)
Weight loss (%)
Compounds
Decomposition
Tmax(°C) Calc.
Found Lost species
H2L C20H16N2O2
First step
Total loss
Residue
326, 618 100
99.57
99.57
8C2H2 + 2CO + C2N2
100
100
[Cu(H2L)(H2O)2](CH3COO)2.2H2O
(C24H30N2O10Cu)
First step
Second step
Total loss
Residue
143 281,
368, 618
6.32
6.63
2H2O
75.51 75.17
81.83 81.80
18.16 18.20
10C2H2 + 3H2O + 2CO + 2NO
CuO + 2C
3H2O
[Y(H2L)(H2O)2]Cl3.3H2O
(C20H26N2O7Cl3Y)
First step
50, 120
297,
8.98
9.25
Second step
550, 667
58.28 58.35
6C2H2 + 2.5H2O +
NCCl+Cl2 + NH3
Total loss
Residue
67.26 67.60
32.74 32.40
YO1.5 + 7C
[ZrO(H2L)(H2O)]Cl2·3H2O
(C20H24N2O7Cl2Zr)
First step
89, 177
317,
9.54
9.74
3H2O
Second step
Total loss
Residue
747
53.87 53.82
63.41 63.56
36.59 36.44
6C2H2 + CH4 + 2NO + 2HCl
ZrO2 + 7C
[La(H2L)(H2O)2]Cl3.7H2O
(C20H34N2O11Cl3La)
First step
53, 120,
152
17.42 17.76
7H2O
Second step
Total loss
Residue
288, 341,
723
63.38 63.12
80.80 80.88
19.20 19.12
9C2H2 + 2NO + 2CO + 2HCl + 0.5Cl2
La
to be linear from the slope of which E* was calculated.
The pre‐exponential factor, A, was calculated from the
equation:
3.5.2 | Horowitz‐Metzger equation[45]
The Horowitz‐Metzger equation is an illustrative of the
approximation methods. These authors derived the rela-
tion:
E*θ
RT2s
A
¼
(6)
ꢂ
ꢀ
ꢁꢃ
E*
RTs
"
#
ꢄ
ꢅ
φ exp −
1−n
1 − ð1−αÞ
ð1 − nÞ
E*θ
2:303RT2s
log
¼
for n ≠ 1
(4)
The entropy of activation, ΔS*, was calculated from equa-
tion (3). The enthalpy of activation, ΔH*, and Gibbs free
energy, ΔG*, were calculated from;
When n = 1, the LHS of equation 4 would be log[−log
(1‐α)]. For a first‐order kinetic process the Horowitz‐
Metzger equation may be written in the form:
ΔH* ¼ E*–RT
(7)
ꢂ
ꢀ
ꢁꢃ
wα
wγ
E*θ
2:303RT2s
and
log log
¼
− log 2:303
(5)
ΔG* ¼ ΔH*–TΔS*
(8)
Where θ = T‐Ts, wγ = wα–w, wα = mass loss at the com-
pletion of the reaction; w = mass loss up to time t. The
plot of log[log (wα/wγ)] versus θ was drawn and found
It is clear that the thermal decomposition process of the
complexes indicate that the complexes are thermally

10 of 13
ABD EL‐HAMID ET AL.

ABD EL‐HAMID ET AL.
11 of 13
FIGURE 4 Powder XRD pattern for (A) H2L, (B) Cu (II), (C) Y (III), (D) Zr (IV) and (E) La (III)
TABLE 7 XRD spectral data of free ligand H2L and its complexes
d value
(Angstrom)
Relative Intensity
(%)
Full width at half maximum (FWHM)a
The crystallite
size
Compounds
H2L
2θ (°)
14.385
26.652
27.672
6.593
6.158
3.345
3.224
13.406
7.797
100
100
100
100
100
0.138
0.217
0.197
0.119
0.157
60.65
39.31
43.40
69.87
53.14
Cu (II) complex
Y (III) complex
Zr (IV) complex
La (III) complex
11.349
aThe maximum diffraction patterns according to the highest value of intensity.
stable. The positive ΔH* values postulate an endothermic
nature of the formed complexes. These results showed that
all the decomposition steps show a best fit for n = 1. The
negative value of the entropy of activation, ΔS*, for some
of the decomposition steps indicated that the activated
fragments have a more ordered structure than some com-
pounds are slower than normal.[46] The greater positive
values of E* indicate that the processes involving in trans-
lational, rotational, vibrational states and a changes in
mechanical potential energy for complexes.

12 of 13
ABD EL‐HAMID ET AL.
of nematode, it recorded 86.9% inhibition (% I). On con-
trast the inhibition of Cu (II), Y (III), Zr (IV) and La
(III) less than the inhibition % of H2L the descending
order of complexes depending on their inhibition % Y
(III), Zr (IV) and Cu (II) its % I 27.1, 10.4 and 0.48
whereas La (III) increased the migration of second stage
larvae 28.1%.
3.6 | X‐ray diffraction analysis
Since several attempts to obtain single crystal of com-
plexes was unsuccessful, so the crystallinity of these com-
plexes was established X‐ray powder diffraction analysis.
X‐ray diffraction pattern of all the newly prepared com-
pounds were scanned in the range 10–80° at wavelength
1.542 Å. Cu (II) complex was found amorphous in nature
(non‐crystalline). The X‐ray diffraction pattern of com-
pounds was found with well resolved crystalline peaks
as given in Figure 4. The definite diffraction data, like
angle (2θ), interplanar spacing (d value, Angstrom), and
relative intensity (%), are summarized in Table 7. The
maximum diffraction patterns of H2L, Y (III), Zr (IV)
and La (III) complexes exhibited at 2θ [d value
(A°)] = 14.385 (6.158), 27.673 (3.224), 6.593 (13.406),
and 11.349 (7.797), respectively. The particle size was cal-
culated by Debye–Scherrer's formula:
4 | CONCLUSION
Novel Cu (II), Y (III), Zr (IV) and La (III) complexes with
tetradentate Schiff base ligand were synthesized and then
characterized by various physicochemical and spectro-
scopic techniques. From elemental analysis, it was indi-
cated that Schiff base ligand reacted with metal ions in
1:1 molar ratio. The spectroscopic data showed that the
H2L ligand acted as tetradentate ligand and it coordinated
to metal ions through azomethine nitrogen and oxygen
atom of phenolic group. All the prepared complexes have
octahedral structures and were electrolytes. The stability
of the complexes was explained and kinetic parameters
(Ea, ΔH, ΔS, ΔG) of the thermal decomposition stages
have been evaluated using the Coats–Redfern and
Horowitz–Metzger methods. Nematicidal studies were
carried out on migration of second stage larvae of root
knot nematode Meloidogyne javanica. The nematicidal
effect of ligand changed to stimulation effect in case of
La (III) complex that increased migration of nematode.
D ¼ 0:9 λ=ß:cos θ
where, λ is the wavelength of radiation, ß is the full width
with half maximum (FWHM) of characteristics peak and
θ is the diffraction angle of the hkl plane.[47,48]
3.7 | Nematicidal activity
Plant parasitic nematodes are the main pathogens on
most fiber crops, horticultural, food and vegetable crops
and without adequate control; they cause loss of yield
and quality. Nematode Meloidogyne species is known
to attack almost all types of plants and cause consider-
able damage.[49] M. incognita produces galls on the
roots of many host plants and is also responsible for
44.87% of yield loss in brinjal.[50] The past literature
works concerning nematode problems have indicated
that there is a need to check this pest by control prac-
tices, using various chemicals. The nematicidal activity
of the metal complexes is depicted in Table 8 and
details are given in Figure S3. From the results, ligand
alone shows a high nematicidal effect against migration
CONFLICT OF INTEREST
The authors declare that they have no conflicts of
interest.
ORCID
S.M. Abd El‐Hamid
https://orcid.org/0000-0002-3658-
3629
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How to cite this article: Abd El‐Hamid SM,
Sadeek SA, Abd El‐Lattif NS. Study of the chemical
structure and their nematicidal activity of N2O2
tetradentate Schiff base metal complexes. Appl
Organometal Chem. 2019;e5010. https://doi.org/
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