Spectroscopic and theoretical studies on Cr (III), Mn (II) and Cu (II) complexes of hydrazone derived from picolinic hydrazide and O-vanillin and evaluation of biological potency

Article abstract of DOI:10.1002/aoc.5408

Trivalent Cr (III) and divalent of both Mn (II) and Cu (II) complexes containing hydrazone ligands derived from the condensation of picolinohydrazide with O-vanillin were synthesised and characterized by elemental analysis, spectral and magnetic measurements. The suggested octahedral structures were confirmed by applying DFT optimization and conformational studies. The thermal decomposition behaviour of Mn (II) complex is discussed. The evaluation of kinetic parameters (E_a, A, ?H, ?S and ?G) of all thermal degradation stages have been evaluated using Coats-Redfern and Horowitz-Metzger approaches. The band gap results suggested that these complexes are semi-conductors and lie in same range of highly efficient photovoltaic materials. Antibacterial studies showed that higher activity of complexes than of ligands. Assay on the antioxidant activity (DPPH and SOD) of the above complexes revealed the high SOD-activity of Mn (II) complex and high DPPH-activity for ligand.

Full text of DOI:10.1002/aoc.5408

Received: 10 September 2019
DOI: 10.1002/aoc.5408
Revised: 1 November 2019
Accepted: 12 November 2019
F U L L P A P E R
Spectroscopic and theoretical studies on Cr (III), Mn (II)
and Cu (II) complexes of hydrazone derived from picolinic
hydrazide and O‐vanillin and evaluation of biological
potency
Gamil A.A. Al‐Hazmi1,2 | Khlood S. Abou‐Melha1 | Nashwa M. El‐Metwaly3,4
|
Ismail Althagafi3 | Fathy Shaaban5 | Marwa G. Elghalban3,4
|
Mohammed M. El‐Gamil6
1 Chemistry Department, Faculty of
Trivalent Cr (III) and divalent of both Mn (II) and Cu (II) complexes contain-
ing hydrazone ligands derived from the condensation of picolinohydrazide
with O‐vanillin were synthesised and characterized by elemental analysis,
spectral and magnetic measurements. The suggested octahedral structures
were confirmed by applying DFT optimization and conformational studies.
The thermal decomposition behaviour of Mn (II) complex is discussed. The
evaluation of kinetic parameters (Ea, A, ΔH, ΔS and ΔG) of all thermal degra-
dation stages have been evaluated using Coats‐Redfern and Horowitz‐Metzger
approaches. The band gap results suggested that these complexes are semi‐
conductors and lie in same range of highly efficient photovoltaic materials.
Antibacterial studies showed that higher activity of complexes than of ligands.
Assay on the antioxidant activity (DPPH and SOD) of the above complexes
revealed the high SOD‐activity of Mn (II) complex and high DPPH‐activity
for ligand.
Science, King Khalid University, P.O. Box
9004, Abha, Saudi Arabia
2 Chemistry Department, Faculty of
Applied Sciences, Taiz University, P.O.
Box 82, Taiz, Yemen
3 Department of Chemistry, Faculty of
applied science, Umm‐Al‐Qura
University, Makkah, Saudi Arabia
4 Department of Chemistry, Faculty of
Science, Mansoura University, El‐
Gomhoria Street, Egypt
5 Custodian of two holy mosques Institute
for Hajj and Umrah Research, Umm‐Al‐
Qura University, Makkah, Saudi Arabia
6 Department of Toxic and Narcotic Drug,
Forensic Medicine, Mansoura Laboratory,
Medico‐legal Organization,, Ministry of
Justice, Egypt
KEYWORDS
Correspondence
antioxidant activity, Hydrazone, molecular docking, spectral characterization, thermal degradation
Mohammed M. El‐Gamil, Department of
Toxic and Narcotic Drug, Forensic
Medicine, Mansoura Laboratory, Medico‐
legal Organization, Ministry of Justice,
Egypt.
Email: m_elgamil2004@yahoo.com
Funding information
Deanship of Scientific Research at King
Khalid University, Grant/Award Number:
R.G.P.1/126/40
Appl Organometal Chem. 2019;e5408.
wileyonlinelibrary.com/journal/aoc
© 2019 John Wiley & Sons, Ltd.
1 of 16
https://doi.org/10.1002/aoc.5408

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AL‐HAZMI ET AL.
(Continued)
1 | INTRODUCTION
Instrument/method Propose
Conditions
The hydrazones are a special series in the Schiff base
compounds because they have ‐NH‐N=CH‐ group in
their molecules. The picolinate hydrazones have addi-
tional donor sites like carbonyl oxygen and pyridine
nitrogen atoms. The multiplicity of donor sites facilitates
the formation of different manners of chelation with tran-
sition metal ions and then various applications can be
taken. The lone pair on trigonally hybridized nitrogen
atom of the azomethine group is responsible for the
chemical and biological activity.[1,2] Hydrazones are used
in the branch of analytical chemistry as selective metal
pull out agents in addition to in colorimetric determina-
tion of several ions of transition metal.[3] Hydrazone
derivatives are found to have pharmaceutical and biolog-
ical performances such as resistance of tumor growth[4,5]
antimicrobial,[6,7] anti‐inflammatory activities,[8,9] anti-
convulsant[10] and anti‐tubercular.[11] Moreover, the Cu
(II) complexes exhibited antioxidant activity of diphenyl
picryl hydrazyl (DPPH) scavenging[12,13] and superoxide
dismutase (SOD) like activity.[13–15] An extension of pre-
vious work,[13,16,17] this work purposes to prepare and
characterize Cr (III), Mn (II) and Cu (II) complexes of
metal and chloride
contents of
complexes
Shimadzu TGA‐50H
thermogravimetric
analyzer
Thermogravimetric
measurements
(TGA, DrTG)
• Temp. range:
20–800 °C
• heating rate:
10 °C/min
• nitrogen flow
rate:
for Mn (II) complex
30 ml/min
Shimadzu TGA‐50H
thermogravimetric
analyzer
Thermogravimetric
measurements
(TGA, DrTG)
for ligand, Cr (III)
and Cu (II)
• Temp. range:
20–700 °C
• heating rate:
15 °C/min
• nitrogen flow
rate:
complexes
15 ml/min
Sherwood Magnetic
Balance
Magnetic susceptibility • Room
temperature
Mattson 5000 FT‐IR
FT‐IR spectra
• Range: 4000–
400 cm−1
• Disc: KBr
spectrophotometer
(E)‐N‐(2‐hydroxy‐3‐methoxy
benzylidene)
Perkin Elmer Lamda 25 electronic spectra of
• Range: 200–
900 nm
• solvent:
DMSO
UV/Vis
complexes
picolinohydrazide (H2POV). The possible approaches of
chelation, geometries and the complexes bonding are
concluded by magnetic measurements, quantum calcula-
tions (DFT) and the various spectroscopic techniques (1H
NMR, 13C NMR, FT‐IR, EI‐Mass spectra, UV–visible and
EPR). In addition, thermodynamic and kinetics charac-
teristics of thermal degradation steps have been studied
by means of Coats–Redfern and Horowitz–Metzger
approaches. Also, their antibacterial and antioxidant
activity assays have been established.
Spectrophotometer
Mercury and Gemini
300 MHZ
1H‐NMR
measurements
• room
temperature
• solvent: d6‐
DMSO
spectrometer
Bruker 100 MHZ
spectrometer
13C‐NMR
measurements
• room
temperature
• solvent: d6‐
DMSO
Varian Mat 311
Mass spectra
• start‐end (m/
z) (40–1000)
• ionization
mode (EI)
2 | EXPERIMENTAL
2.1 | Materials
JEOL EPR spectrometer EPR spectra of Cu (II) • room
complex temperature
The analytical grade of metal chloride salts, hydrazine
hydrate, ethyl picolinate and O‐vanillin have been used.
• X‐band:
9.435 GHz
• modulation
frequency:
100 kHz
2.2 | Instrumentation
• microwave
power: 5 mW
Instrument/method Propose
Conditions
Perkin–Elmer 2400
series II analyzer
C, H and N elemental ‐‐‐‐
analyses
Standard methods[18]
‐‐‐‐

AL‐HAZMI ET AL.
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2.3 | Synthesis of ligand and its metal
2.4 | Biology
complexes
2.4.1 | Antimicrobial evaluation
The picolinic acid hydrazide was prepared from ethyl
picolinate and hydrazine hydrate as described earlier.[19]
The antibacterial activity of H2POV and its respective
metal complexes were established towards gram‐positive
Staphylococcus aureus, negative Escherichia coli bacterial
and Candida albicans fungal strain by the disc diffusion
method[20,21] as shown in Scheme 2.
The
(E)‐N‐(2‐hydroxy‐3‐methoxy
benzylidene)
picolinohydrazide (H2POV) and its metal complexes were
prepared by Scheme 1.
The precipitate of H2POV and complexes were
filtrated, cleaned with hot EtOH followed by Et2O and
dried out over anhydrous CaCl2 in a vacuum desiccator.
The analytical and physical data of separated complexes
are recorded in (Table 1) shows that complexes have high
melting points and stable in air.
Zone of inhibitionbytest compoundðdiameterÞ
%Activity Index ¼
x100
zone of inhibitionby standard ðdiameterÞ
2.4.2 | Molecular docking
Protein preparation
The Protein Data Bank structure of E. coli (PDB ID: 1C14‐
chain A) was downloaded.[22] and prepared via prepara-
tion wizard package for protein in the Schrödinger soft-
ware[23] by removing small molecules and water
molecules (> 5A radius) from the structure as well as
the addition of hydrogens and di‐sulphide bonds to
PDB. Restricted minimization was performed on the
structure with default options and optimized potentials
for liquid simulations (force field OPLS‐2005). The
obtained structure was used as a receptor grid generation
for docking.
Ligand preparation
The ligand compound (H2POV) planned to be used for
docking were organized by Schrödinger's suite‐Ligprep
module.[24] The docking studies of compounds occurs by
glide package[25] of the Schrödinger's suite to the target
protein by XP protocol without using post‐docking mini-
mization of metal complexes.
SCHEME
complexes
1
Synthesis of ligand (H2POV) and its metal
TABLE 1 Analytical and physical data of H2POV and its complexes
% Found (Calcd.)
M.P.;
oC
Compound
M.wt. Color
M
Cl
C
H
N
Yield%
(H2POV) C14H13N3O5
271.27 Buff
192
__
__
61.88 (61.98) 4.92 (4.83) 15.56 (15.49) 90
[Cr (POV)Cl2 (H2O)].
C14H15CrClN3O5
392.75 Brown
>300 13.78 (13.23) 9.86 (9.03) 42.94 (42.81) 3.50 (3.84) 10.29 (10.69) 82
[Mn(H2POV)Cl2(H2O)2].
H2O C14H17Cl2MnN3O5
433.23 Pale yellow >300 12.76 (12.68) 16.47 (16.38) 38.92 (38.81) 3.99 (3.95) 9.78 (9.69) 93
[Cu(HPOV)Cl(H2O)2].
H2O C14H18ClCuN3O6
423.351 Green
230
15.13 (15.00) 8.43 (8.38) 39.76 (39.72) 4.30 (4.28) 9.97 (9.92) 88

4 of 16
AL‐HAZMI ET AL.
SCHEME 2 Procedure of Antimicrobial evaluation
2.5 | Molecular modelling
2.4.3 | Antioxidant activity
The superoxide dismutase (SOD) like activity evaluated
by the procedure of Nishikimi et al.[26] and the decoloriz-
ing of the purple color of diphenylpicrylhydrazyl (DPPH)
in methanol as a result of electron donation ability com-
pounds was measured as showed in Scheme 3.
Calculations.
The geometry optimization was achieved with no symme-
try constraint based on DFT semi‐core pseudopods calcu-
lations (dspp) by double numerical basis sets with
polarization functional (DNP) and RPBE functional,[27,28]
based on the generalized gradient approximation (GGA),
using DMOL3 Module[29] in Materials Studio software.[30]
Delley et al. exhibited that the DNP basis sets are more
precise than the same size of Gaussian basis sets.[31,32]
SOD
ΔAcontrol − ΔAtest
%inhibition ¼
X100
ΔAcontrol
3 | RESULTS AND DISCUSSION
3.1 | 1H NMR spectra of the ligand
Such as.
A
and A
are the absorbance change at
test
control
The 1H NMR spectrum of H2POV in d6‐DMSO (Figure 1)
displays two signals at δ 12.50 and 11.21 ppm compara-
tive to TMS, which disappear on the addition of D2O.
These signals attributed to the NH and phenolic OH pro-
tons, respectively. The signals at δ 2.50 and 3.39 ppm
assigned to the C‐H and methoxy protons. The multi sig-
nals in the region 8.85–6.88 due to the C‐H protons in the
benzene and pyridine rings.
560 nm over 5 min after the addition of PMS in the
absence and presence of the investigated compounds,
respectively.
DPPH inhibition
A
blank − Asample
I% ¼
x100
Ablank

AL‐HAZMI ET AL.
5 of 16
SCHEME 3 Procedure of the
superoxide dismutase (SOD) like activity
C‐13, C‐14, C‐15, C‐16 and C‐77 of O‐vanillin ring moiety.
Finally, the sharp signal appeared at 56.26 ppm referred
to the methoxy group present at C‐20.
3.2 | IR spectra of ligand and complexes
Comparative infrared results of ligand and its metal com-
plexes are listed in (Table 2) and presented graphically in
(Figure S1, supplementary materials). In the IR spectrum
of H2POV, the bands of ν (OH) and ν (NH) appeared at
3345 and 3272 cm−1, respectively. Furthermore, the
strong bands at 1678 and 1626 cm−1 allocated to ν (CO)
and ν(C=N)az, respectively. Also, the bands observed at
1588 cm−1 attributed to ν(C=N)py. Whereas, the δ(C=N)
FIGURE 1 1HNMR spectra of H2POV
in‐plane and out of plane binding frequencies appears
py
at 630 cm−1 [33,34] The ν(N‐N) is detected at 997 cm−1
.
In the 13C‐NMR spectrum (Figure 2), the signals of
carbon resonance for ‐C=O and CH=N groups appeared
at δ = 160.86 and 149.02 ppm, respectively. The signal
of pyridyl ring appeared at 127.59, 149.63, 148.43, 123.30
and 138.47 ppm attributed to C‐1, C‐2, C‐4, C‐5 and C‐
6, respectively. Moreover, the signals at 119.22, 121.77,
119.48, 114.40, 148.07 and 147.90 ppm assigned to C‐12,
which shifts to higher wavenumber upon complexa-
tion.[35] The appearance of one OH and NH bands in both
1H NMR and IR spectra of ligand confirmed the predom-
inant of keto (Figure 3A).
In [Cr(POV)Cl(H2O)2] (Figure 3B), the H2POV acts as
bi‐negative tridentate ONO via (CN)az, enolized (CO) and
phenolic OH with displacement of H ions from the latter
two groups. These investigation is established by: (i) The
disappearance of ν(C=O), ν (OH) and ν (NH), (ii) appear-
ance of bands due to (CN)*and ν(C‐O) and (iii) shift of
ν(N‐N) and ν(C‐O) phenolic to higher wavenumber as
well as shift of ν (CN)az to lower wavenumber.
In [Mn(H2POV)Cl2(H2O)].H2O (Figure 3C), after care-
ful comparison with the ligand, the H2POV acts as neu-
tral tridentate NON via the (CN)az, the (CO) and the
(CN)py. These modes of chelation are proved by: (i)
appearance of ν (OH) at 3209 cm−1 in H2POV, (ii) shift
of ν(C=O) and ν(C=N) of both pyridine and azomethine
to lower wavenumber and (iii) shift of both δ(C=N)
py
and ν(N‐N) to higher wavenumbers.
While in [Cu(HPOV)Cl(H2O)2].H2O (Figure 3D),
H2POV behaves as univalent tridentate via enolized oxy-
gen of carbonyl group (=C‐OH) and N‐atoms of both
FIGURE 2 13C‐NMR spectra of H2POV

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AL‐HAZMI ET AL.
TABLE 2 Assignments of IR spectral bands of H2POV and its complexes
ν
ν(c‐o)
Compound
ν(C=O) υ(C=N)
ν(C=N)
δ(C=N) (NH) υ(C=N)* υ(C‐O)* ν (N‐N) ν (OH)
ν (M‐O) ν (M‐N)
azo
py
phenolic
(H2POV)
1678
‐
1626
1598
1592
1588
1588
1572
630
632
640
3272
‐
‐
‐
997
3345
‐
1077
1090
1074
‐
‐
[Cr (POV)Cl (H2O)2].
1538
1214
1030
1093
535
560
415
413
[Mn(H2POV)Cl2
(H2O)2].H2O
1641
3209
‐
‐
3416
[Cu(HPOV)Cl
(H2O)2].H2O
‐
1621
1579
648
‐
1643
1218
1017
3420
1076
545
462
FIGURE 3 Molecular modelling of (A) H2POV (B) [Cr(POV)Cl(H2O)2] complex (C) [Mn(H2POV)Cl2(H2O)2].H2O complex (D) [Cu
(HPOV)Cl(H2O)2].H2O complex
(C=N)pyridine and (C=N)azomethine groups. This behaviour
is revealed by the following observations: (i) change of
ν(C=N)py to lower wavenumber and positive shift of
assignable to π → π* and n → π* transitions of both C=O
and C=N (azomethine and pyridine) which changes
toward higher wavenumbers as result of coordination
with metal ion.
δ(C=N)
indicates it's coordination through
py
heteroaromatic nitrogen. (ii) absence of ν(C=O) band
with simultaneous appearance of bands at 1579, 1218
and 545 cm−1 due to ν(C=N*), ν(C‐O*) and ν (M‐O) vibra-
tions, respectively (iii) shift of ν(N‐N) modes to higher
wavenumbers.
In [Cr(POV)Cl2(H2O)] complex, (μeff = 3.7 B. M,
Dq = 1626 cm−1, β = 0.41 and B = 382 cm−1[36]) shows
two bands at 16260 and 20449 cm−1 attributed to
4
4
4
4A2g(F) → T2g(F) (ν1) and A2g(F) → T1g(F) (ν2) transi-
tions, respectively characterized for an octahedral
geometry.[37]
The μeff. Value of [Mn(H2POV)Cl2(H2O)].H2O complex
is 5.8 B. M lies in the range of high spin 3d5 arrangement.
The complex displayed weak and not observed electronic
transition bands thereby it was hard to assign them to
final transitions.
3.3 | Electronic spectra and magnetic
moments studies
Electronic spectral bands of H2POV and its complexes in
DMSO are represented graphically in (Figure S2, supple-
mentary materials). The spectra of ligand (Table 3) show
strong absorption bands at 32258, 28090 and 25641 cm−1
Electronic spectrum of [Cu(HPOV)Cl(H2O)2].H2O
complex, (1.7 B.M.) shows bands at 14598 and

AL‐HAZMI ET AL.
7 of 16
TABLE 3 Electronic spectral absorption bands of H2POV and its metal complexes and the ligand field parameter and magnetic moments
of the complexes
Ligand field parameters
Compound
Band position,cm−1
Assignment
Dq (cm−1
)
B (cm−1
)
β
μeff (B.M.)
H2POV
32258,28090 25641,23256 π → π* n → π*
‐
‐
‐
‐
4
4
4
[Cr(POV)Cl(H2O)2]
[Mn(H2POV)Cl2(H2O)].H2O
[Cu(HPOV)Cl(H2O)2]H2O
16260 20449
4A2g(F) → T2g(F) A2g (F) → T1g(F) 1626
382
0.41 3.7
‐
‐
‐
‐
‐
‐
‐
‐
5.8
1.7
2
2
2
14598 17361 23809
2B1g → B2g B1g → Eg LMCT
17361 cm−1 assignable to 2B1g → 2B2g and 2B1g → 2Eg tran-
sitions in an Oh environment. The high absorption at
23809 cm−1 may be attributed to L → M charge transfer
(LMCT). The band's wavelengths and the μeff value per
Cu atom are steady with Oh geometry of Cu (II)
complex.[38]
3.4 | Mass spectra
FIGURE 5 mass fragmentation path of H2POV
The mass spectrum of H2POV (Figure 4) showed the peak
of molecular ion [M]+ at m/z = 271.08 which was equiv-
alent to ligand molecular weight. The fragmentation path
of H2POV is given in Figure 5.
The mass spectrum of Cu(II) complex (Figure 6) pro-
vided good evidence for its molecular formula:
[Cu(HPOV)Cl(H2O)2].H2O (M.wt. 423.351). The molecu-
lar ion peak for Cu(II) complex at m/z = 423.00 (20.18%)
corresponding to (C14H18ClCuN3O6). The different frag-
ments of Cu(II) complex give the peaks with various
intensities at different m/z values like at 385.79
(16.99%)
(C14H13ClCuN3O4),
327.27
(15.84%)
(C9H12ClCuN2O5), 311.47 (11.86%) (C8H9ClCuN2O5),
269.73 (100.00%) (C7H8ClCuNO4) and 203.26 (34.21%)
(C2H5ClCuN2O3).
FIGURE
6
mass spectrum of [Cu(HPOV)Cl(H2O)2)].H2O
complex
3.5 | The optical band gap Eg
By the absorption of a photon of known energy, an elec-
tron is transferred from lower to higher energy position
resulting in a sudden increase in absorption, known as
absorption edge, which used to estimate the optical band
gap (Eg = hc/λ). To explain the conductivity of complexes
the optical band gap (Eg) of complexes has been calcu-
lated from α = 1/d ln A, where d is the width of cell.
The relation between optical band gap (Eg) and absorp-
tion coefficient (α) is used to calculate the band gap by
FIGURE 4 mass spectrum of H2POV
the following equation[39,40]
:

8 of 16
AL‐HAZMI ET AL.
À
Á
m
α hυ ¼ A hυ–Eg
where A is an energy‐independent constant, m is equal to
0.5 for direct transition and 2 for indirect transition. The
plot of (αhυ)2 vs. hυ (Figure 7) from which a direct band
gap was established by extrapolating the linear part of
curve to zero.
From the curve, the data of the direct band gap (Eg)
equal 3.04, 3.05 and 2.82 eV in complexes of [Cr(POV)
Cl2(H2O)], [Mn(H2POV)Cl2(H2O)].H2O and [Cu(HPOV)
Cl(H2O)2].H2O, respectively. The band gap data propose
that these compounds lie in the same range of highly
effective photovoltaic materials and semiconductors. So,
these complexes might be considered as potential mate-
rials for collecting solar radiation in solar cell
enforcement.[41]
FIGURE 8 Electron paramagnetic spectrum of [Cu(HPOV)
Cl(H2O)2].H2O complex
showing a considerable covalency of the metal–ligand
bonding with the ground‐state dx2‐y2[43,44] distinguishing
of square pyramidal or square planar or octahedral
stereochemistry.[45]
3.6 | Electron paramagnetic spectrum of
the cu (II) complex
3.7 | Thermogravimetric studies
The polycrystalline EPR spectrum of [Cu(HPOV)
Cl(H2O)2].H2O complex (Figure 8) shows only a strong
and wide signal at room temperature with unresolved
hyperfine couplings (giso = 2.096). Such isotropic spec-
trum, involving of a wide signal and only one g value
rises from extensive exchange connection via misalign-
ment of the local molecular axes between the unit cell
molecules (dipolar broadening) and improved spin–
lattice reduction.[42] The higher g value for Cu (II) com-
plex compared to the value of free electron (g = 2.0023)
The TG–DrTG data for solid H2POV and its metal com-
plexes are showed in Table 4, Figure 9 and Figure S3‐
S5, supplementary materials. The results are in accept-
able agreement with planned formulae accomplishes that
for example, the Mn (II) complex decompose in 3‐main
steps. The loss of hydrated H2O molecules at 24–105 °C,
followed by the loss of the coordinated H2O at 80–
282 °C, then the delegation process at 283–800 °C, finally
the formation of M (II)‐oxide.
FIGURE 7 The plots of (αhν)1/2 and (αhν)2 vs hν of (A) [Cr(POV)Cl(H2O)2], (B) [Mn(H2POV)Cl2(H2O)2].H2O and (C) [Cu(HPOV)
Cl(H2O)2].H2O complexes

AL‐HAZMI ET AL.
9 of 16
TABLE 4 Decomposition steps with the temperature range and weight loss for ligand and its metal complexes
Wt. Loss
Complex
Temp. Range, °C
Removed species
Found%
Calcd. %
H2POV
271–523
523–628
628–690
>700
‐(C8H8N3O3)
‐(C2H2)
‐(C2H3)
71.68
9.24
10.13
8.96
71.58
9.60
9.97
8.86
C2 (residue)
[Cr(POV)Cl(H2O)2]
145–339
339–460
460–612
612–691
>700
‐(2H2O+ C10H7O2)
‐(C2H2Cl)
‐(N2)
‐(C2H2N)
CrO (residue)
49.87
15.70
6.87
9.97
17.59
49.70
15.66
7.13
10.20
17.31
[Mn(H2POV)Cl2(H2O)].H2O
[Cu(HPOV)Cl(H2O)2].H2O
24–105
106–282
283–476
477–752
>800
‐(H2O)
4.193
23.436
36.028
15.718
20.625
4.158
22.183
37.659
16.853
19.144
‐(H2O + C5H4N)
‐(C8H7O2N2)
‐(2HCl)
MnO + C (residue)
34–93
‐(H2O)
‐(2H2O + C2H2)
‐(C2H2O)
‐(C5H4N)
CuO + C5H4ON2Cl (residue)
4.13
14.76
10.19
18.18
52.73
4.26
14.66
9.93
18.45
52.70
93–178
178–381
381–619
>700
iii. value of ΔG increases from step to another exhibited
that the rate of H2POV removal will be lower from
step to the successive step.[48,49] This may be attrib-
uted to the structural rigidity of the residual complex
after the removal of one or more ligands.
iv. ΔS is negative value indicates that the activated
complex more ordered than reactants i.e. reaction
are slow.[46]
v. ΔH is positive value showing that the endothermic
processes of decomposition.
vi. As a result of the previous results, the thermal stabil-
ity of the metal complexes decreases in the order:
FIGURE 9 Thermal analysis curves (TGA, DTG) of [Mn(H2POV)
Cl2(H2O)2].H2O complex
Â
Ã
Â
Ã
CrðPOVÞClðH2OÞ2 > CuðHPOVÞClðH2OÞ2 H2O >
½MnðH2POVÞCl2ðH2OÞꢀ:H2O:
3.8 | Kinetic data of thermal degradation
The kinetic parameters data of degradation steps have
been estimated by using two non‐isothermal methods,
Coats‐Redfern Figure 10a[46] and Horowitz‐Metzger
Figure 10b.[47] From the obtained data, the following
comments can be pointed out:
Commonly, the value of stepwise stability constants
reduced with an increase in the number of ligands
involved in the metal ion.[50,51] Thus, an opposite behav-
ior may take place throughout the degradation process.
Therefore, the rate of elimination of the remaining part
of ligand will be lesser than that of rate before the explo-
sion of one or two ligands.
i. The values of E, A, ΔH, ΔS and ΔG (Tables 5 and 6)
obtained from the two methods are quite equivalent.
Furthermore, all steps show the best fit for (n = 1)
related to a first‐order decomposition.
ii. The increases or decrease of Ea for the successive
decomposition steps depends on the stability of the
remaining species.
3.9 | Molecular modelling
3D‐structure of H2POV and its metal complexes with
atom numbering of are displayed in Structures (1–4).

10 of 16
AL‐HAZMI ET AL.
FIGURE 10 (a) Coats‐Redfern plot (b) Horowitz‐Metzger plot of the first degradation step for [Mn(H2POV)Cl2(H2O)2].H2O complex
TABLE 5 Kinetic Parameters evaluated by Coats‐Redfern equation ligand and its metal complexes
Ea
A
ΔH*
ΔS*
ΔG*
Mid
Temp(K)
Complex
peak
KJ/mol
(S−1
)
KJ/mol
KJ/mol. K
KJ/mol
H2POV
1st
2nd
3rd
618.67
816.06
938.07
214.6487
1531.0968
931.3157
1.67 × 1016
1.33 × 1096
6.51 × 1049
209.5051
1524.3121
923.5166
0.0596
1.5869
0.6992
172.6380
229.3168
267.6359
[Cr(POV)Cl(H2O)2]
1st
540.48
647.65
781.91
934.28
121.4163
145.5537
199.4360
585.0028
4.29 × 1009
1.04 × 1010
1.94 × 1011
6.28 × 1030
116.9227
140.1691
192.9352
577.2352
−0.0654
−0.0596
−0.0368
0.3352
152.2943
178.7838
221.7202
264.0782
2nd
3rd
4th
[Mn(H2POV)Cl2(H2O)].H2O
[Cu(HPOV)Cl(H2O)2].H2O
1st
333.41
497.12
697.83
932
76.1031
94.7406
220.6879
100.298
4.60 × 1010
1.63 × 1007
8.55 × 1013
7.62 × 1002
73.3311
90.6076
214.8861
92.5494
−0.04171
−0.11108
0.014734
−0.1992
87.2376
145.8286
204.6043
278.2057
2nd
3rd
4th
1st
341.14
398.6
488.76
723.43
102.5965
106.2102
127.7110
166.8116
4.73 × 1013
1.14 × 1012
4.29 × 1011
9.16 × 1009
99.7603
102.8962
123.6475
160.7970
0.0158
−0.0165
−0.0263
−0.0616
94.3798
109.4730
136.5084
205.3331
2nd
3rd
4th
TABLE 6 Kinetic Parameters evaluated by Horowitz‐Metzger equation ligand and its metal complexes
Ea
A
ΔH*
ΔS*
ΔG*
Mid
Temp(K)
Complex
peak
KJ/mol
(S−1
)
KJ/mol
KJ/mol. K
KJ/mol
H2POV
1st
2nd
3rd
618.67
816.06
938.07
223.9265
1525.7997
930.6976
9.76 × 1016
6.04 × 1095
5.9 × 1049
218.7829
1519.0150
922.8985
0.0743
1.5803
0.6984
172.8356
229.3733
267.7758
[Cr(POV)Cl(H2O)2]
1st
540.48
647.65
781.91
934.28
127.7919
161.4191
214.3634
597.2917
1.67 × 1010
1.99 × 1011
1.88 × 1012
2.99 × 1031
123.2984
156.0346
207.8626
589.5241
−0.0542
−0.0351
−0.0179
0.3482
152.5763
178.7475
221.8824
264.2459
2nd
3rd
4th
[Mn(H2POV)Cl2(H2O)].H2O
[Cu(HPOV)Cl(H2O)2].H2O
1st
333.41
497.12
697.83
932
91.187
96.1098
220.216
115.0724
1.27 × 1013
2.09 × 1007
7.49 × 1013
4.71 × 1003
88.4151
91.9768
214.4142
107.3238
0.0050352
−0.10903
0.013643
86.7363
146.1787
204.8939
278.8742
2nd
3rd
4th
−0.18407
1st
341.14
398.6
488.76
723.43
103.8402
110.5684
131.4424
177.6569
6.94 × 1013
4.03 × 1012
1.02 × 1012
5.29 × 1010
101.0040
107.2545
127.3788
171.6423
0.0189
−0.0060
−0.0191
−0.0470
94.5401
109.6487
136.7382
205.6284
2nd
3rd
4th

AL‐HAZMI ET AL.
11 of 16
The data analysis of bond lengths and angles in Tables
(S1–S8) (Supplementary materials) shows the following
remarks:
In [Mn(H2POV)Cl2(H2O)].H2O and [Cu(HPOV)
Cl(H2O)2)].H2O complexes the bond lengths of C(11)‐
N(10), N(10)‐N(9), C(7)‐C(4) and N(9)‐C(7) increased as
the coordination of N(10)az, carbonyl group in keto or
enol form and N(3)py. The carbonyl group bond distance
enlarged as the formation of the bond between the metal
and oxygen leads to the weakness of C‐O bond[52] as well
as N(3)‐C(2), N(3)‐C(4) distances of pyridine ring are
elongated due to M‐N bond formation that causes the
C‐N bond weaker.[53]
Decreasing of N(9)‐C(7) and N(10)‐N(9) bond lengths
in [Cr(POV)Cl(H2O)2] complex due to coordination
through N(10) az, enolized O(8)–(7) and C(17)‐O(18)
phe-
with metal atom. The C(7)‐O (8) and C(17)‐O(18)
nolic
bonds distance will be extended and C‐O bond will be
weaker as M‐O bond formation.
The complexes of H2POV can be organized according
to the bond lengths of M‐N azomethine and M‐O as follows:
Mn(21)‐N(10)
> Cu(21)‐N(10) > Cr(21)‐N(10) and
Mn(21)‐O(8) > Cu(21)‐O(8) > Cr(21)‐O(8) exhibiting the
excessive strength of the Cr‐O and Cr‐N bonds. The
change in bond angles of (H2POV) hydrazone moiety on
coordination exhibit the main alteration in angles of
C(7)‐N(8)‐N(9), O(11)‐C(7)‐N(8) and O(11)‐C(7)‐C(4)
which are compacted or enlarged on complexation.[42]
As the result of bond angles, the octahedral geometry of
all complexes lies in the range described for expecting
sp3d2 or d2sp3 hybridization.
DFT technique concept site selectivity and chemical
reactivity of the molecular structures. Table 7 display
frontier molecular orbitals (EHOMO, ELUMO) energies,
energy band gap that clarifies the ultimate charge allo-
cation in molecules, chemical potential (μ) and electro-
negativity (χ) as well as global (softness (S), hardness
(η) and electrophilicity index (ω)).[54,55] The overlap
between the HOMO and the LUMO (Figure 11) is
the main reason in many reactions. The energy gap
(EHOMO ‐ELUMO) is a significant stability index aids to
describe the kinetic stability and chemical reactivity of
FIGURE 11 3D plots frontier orbital energies using DFT method
for H2POV
compounds.[56] Soft molecules are molecules with a
small energy gap, more polarized and more reactive
than hard ones as they simply give electrons to an
acceptor. The Egap is small in H2POV due to groups
conjugation;[58] demonstrating that movement of charge
occurs easily leads to the influence of biological activity
of H2POV.
3.10 | Biological activity
3.10.1 | Antimicrobial evaluation
The ligand and its Cr (III), Mn (II) and Cu (II) complexes
were evaluated for their antimicrobial activity exhibits
TABLE 7 Calculated EHOMO, ELUMO, energy band gap (EH – EL), chemical potential (μ), electronegativity (χ), global hardness (η), global
softness (S) and global electrophilicity index (ω) for H2POV and its complexes
Compound
EH(eV)
EL(eV)
(EH ‐EL)(eV)
Χ(ev)
μ(eV)
η(eV)
S(eV−1
)
ω(eV)
σ(eV)
H2POV
−4.946
−4.423
−4.516
−3.802
−2.412
−2.735
−3.105
−2.577
−2.534
−1.688
−1.366
−1.225
3.679
3.579
3.810
3.190
−3.679
−3.579
−3.815
−3.190
1.267
0.844
0.705
0.613
0.633
0.422
0.352
0.306
5.340
7.588
0.789
1.184
1.418
1.633
[Cr(POV)Cl(H2O)2].
[Mn(H2POV)Cl2(H2O)]. H2O
[Cu(HPOV)Cl(H2O)2].H2O
10.290
8.304
H‐HOMO, L‐LUMO.

12 of 16
AL‐HAZMI ET AL.
that all tested compounds did not show antimicrobial
activity against S. aureus and C. Albicans (Table 8), while
Figures 12–15. From this interaction, H2POV plays inter-
actions with the active location residues (Figure 12) via
H‐bonds [LYS132 → (C=O) and H2O → (C=N)azomethine],
π‐cation stacking between PHE1 and pyridine ring as well
as π‐ π stacking of pyridine ring with TYR46. While hydro-
gen bonds interaction doesn't occur in metal complexes of
H2POV. the interaction of [Mn(H2POV)Cl2(H2O)].H2O
(Figure 13) through salt bridge between PHE1 and nega-
tive Cl− and π‐cation between PHE1‐(O‐vanillin ring).
Furthermore, [Cr(POV)Cl(H2O)2] shows only salt bridge
on negative charge of (C‐N−) with PHE1 (Figure 14).
Finally, [Cu(HPOV)Cl(H2O)2].H2O exhibits only π‐ π
stacking of O‐vanillin ring with TYR46 (Figure 15).
[Mn(H2POV)Cl2(H2O)2]H2O,
[Cr(POV)Cl(H2O)2],
[Cu(HPOV)Cl(H2O)2].H2O complexes and H2POV exhib-
ited moderate activity against Gram‐negative E. coli with
29.2, 25.0 and 20.8%, respectively compared to ampicillin.
The improved activity of complexes can be clarified by
the overtone impression and chelation theory.[21] Accord-
ing to chelation, the polarity of the metal ion is reduced
largely due to the ligand orbitals overlapping and the par-
tial distribution of the +ve charge of metal ion with donor
atoms rises the delocalization of electrons on completely
chelate ring and therefore improves the lipophilicity of
complex. Thus, improves the diffusion of complex through
lipid membrane and blocks the binding positions of metal
on enzymes of the micro‐organism. While negative results
could be attributed either to the failure of the complexes to
diffuse through the bacterium's cell wall or they can dif-
fuse and deactivated by unfamiliar cellular mechanism
i.e. defense proteins or bacterial enzymes.[58,59]
3.10.3 | Antioxidant activity
Oxidative stress, an imbalance between the antioxidant
resistance capacity of the body and the creation of reac-
tive oxygen species. Increased oxidative stress has been
exhibited to be amplified in both insulin and non‐insulin
dependent diabetes mellitus (IDDM and NIDDM) even in
patients without complications.[60] Reactive oxygen spe-
cies (ROS), which include hydrogen peroxide (H2O2),
superoxide radical (O2:−), singlet molecular oxygen (O2)
3.10.2 | Docking studies
The molecular interactions of investigated compounds for
inhibition against E. coli are displayed in Table 9 and
TABLE 8 Antibacterial activity for prepared ligand and its metal complexes
E. coli (mg/ml)
S. aureus (mg/ml)
C. Albicans (mg/ml)
Diameter of
inhibition
zone (in mm)
Diameter of
inhibition
zone (in mm)
Diameter of
inhibition
zone (in mm)
% Activity
index
% Activity
index
% Activity
index
Compound
H2POV
5
20.8
29.2
29.2
25
NA
NA
NA
NA
22
‐‐‐‐
‐‐‐‐
‐‐‐‐
‐‐‐‐
100
NA
NA
NA
NA
NA
NA
28
‐‐‐‐
‐‐‐‐
‐‐‐‐
‐‐‐‐
NA
100
[Cr(POV)Cl(H2O)2].
[Mn(H2POV)Cl2(H2O)].H2O
[Cu(HPOV)Cl(H2O)2].H2O
Ampicillin
7
7
6
24
NA
100
NA
Colitrimazole
NA
TABLE 9 Molecular interactions predicted for inhibitor binding to E.Coli
Docking
Hydrogen bonds
Donor Acceptor
Stacking
Compound
interaction
Type
H2POV
LYS132 → (C=O) H2O → (C=N)
PHE1‐‐‐‐pyridine ring TYR46‐‐‐‐pyridine π‐cation stacking π‐π
ring
stacking
azomethine
[Cr (POV)Cl(H2O)2].
‐‐‐‐
PHE1‐‐‐‐(C‐N−)
Salt bridge
[Mn(H2POV)Cl2(H2O)]. ‐‐‐‐
PHE1‐‐‐‐O‐vanillin ring PHE1‐‐‐‐Cl−
π‐cation stacking Salt
H2O
bridge
[Cu (HPOV)Cl(H2O)2].
H2O
‐‐‐‐
TYR46‐‐‐‐ O‐vanillin ring
π‐π stacking

AL‐HAZMI ET AL.
13 of 16
FIGURE 12 3D and 2D molecular
interaction of H2POV for inhibitor to E.
Coli
FIGURE 13 3D molecular interaction
of [Mn(H2POV)Cl2(H2O)2].H2O complex
for inhibitor to E. Coli

14 of 16
AL‐HAZMI ET AL.
FIGURE 14 3D molecular interaction
of [Cr(POV)Cl(H2O)2] complex for
inhibitor to E. Coli
FIGURE 15 3D molecular interaction
of [Cu(HPOV)Cl(H2O)2].H2O complex for
inhibitor to E. Coli
and hydroxyl radical (·OH), are constantly generated
intracellularly in aerobic organisms and are thought to
be the major mediators of oxygen metabolism.[51]
Superoxide dismutase like activity
All the investigated compounds were tested for antioxi-
dant activity using superoxide dismutase like activity
assay (Figure 16). The data indicate that Mn (II) and Cu
(II) complexes exhibit the higher antioxidative activity
for quenching phenazine methosulphate radicals at 98.4
and 92.2% inhibition, respectively. This high antioxidant
capacity might be due to structure–activity relationship
as they differ in the coordination geometries, stability
and distortion. Moreover, the difference in the dipole
moment of the complexes affects the stability, the distor-
tion and surely the activity of the complexes. These com-
pounds could be considered to be a significant set of
favorable antioxidants. They might aid the reduction of
oxidative stress and contribute in defense against the
destructive action of ROS, chiefly free radical of oxygen.
FIGURE 16 Superoxide dismutase scavenging radicals like
activity of the ligand and its metal complexes
DPPH free radical scavenging assay
The DPPH radical scavenging technique is considered to
be the effective, fast and standard technique for chemical
antioxidant property estimation of nutritious products
and chemicals through chain‐breaking. The results of

AL‐HAZMI ET AL.
15 of 16
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SUPPORTING INFORMATION
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