Theoretical studies and antibacterial activity for Schiff base complexes

Article abstract of DOI:10.1002/poc.3707

New ligand 4-((2-Hydroxy1-naphthyl) methylene amino)-1.5-dimethyl-2-phenyl-1H-pyrazol-3(2H)-one (HL) was synthesized from the reaction of 2-hydroxy-1-naphthaldehyde and 4-aminophenaz one. A complexes of this ligand [VO(II)(HL)(SO₄)], [Pt(IV)(L)

Full text of DOI:10.1002/poc.3707

Received: 7 October 2016
DOI: 10.1002/poc.3707
Revised: 14 March 2017
Accepted: 23 March 2017
R E S E A R C H A R T I C L E
Theoretical studies and antibacterial activity for Schiff base
complexes
Wail Al Zoubi1
Young Gun Ko1
| Abbas Ali Salih Al‐Hamdani2 | I Putu Widiantara1 | Rehab Ghalib Hamoodah2 |
1 School of Materials Science and
Engineering, Yeungnam University,
Gyeongsan 38541, Republic of Korea
2 Department of Chemistry, College of
Science for Women, University of Baghdad,
Baghdad, Iraq
Abstract
New ligand 4‐((2‐Hydroxy1‐naphthyl) methylene amino)‐1.5‐dimethyl‐2‐phenyl‐
1H‐pyrazol‐3(2H)‐one (HL) was synthesized from the reaction of 2‐hydroxy‐1‐
naphthaldehyde and 4‐aminophenaz one. A complexes of this ligand [VO(II)(HL)
(SO4)], [Pt(IV)(L)Cl3], [Re(V)(L)Cl3]Cl, and [M(II)(L)Cl] (M═Pd(II), Ni(II),
Cu(II)) were synthesized. The resulted compounds were characterized by IR,
NMR (1H and 13C), mass spectrometry, element analysis, and UV‐Vis spectroscopy.
Additionally, the spectroscopic studies revealed octahedral geometries for the
Re(V), Pt(IV) complexes, and square pyramidal for VO(II), square planar for Pd(II)
complex, and tetrahedral for the Ni(II) and Cu(II) complexes. Thermodynamic
parameters (ΔE*, ΔH*, ΔS*, ΔG*, and K) were calculated using from the TGA
curve Coats‐Red fern method. Therefore, hyper Chem‐8 program has been used to
predict structural geometries of compounds in the gas phase. Finally, the synthe-
sized Schiff base and its metal complexes were screened for their biological activity
against bacterial species, 2 Gram‐positive bacteria (Bacillus subtilis and Staphylo-
coccus aureus) and 2 Gram‐negative bacteria (Escherichia coli and Pseudomonas
aeruginosa).
Correspondence
Young Gun Ko, School of Materials Science
and Engineering, Yeungnam University,
Gyeongsan 38541, Republic of Korea.
Email: younggun@ynu.ac.kr
KEYWORDS
2‐hydroxy‐1‐naphthaldehyde, theoretical studies, thermal analysis, transition metal complexes
1 | INTRODUCTION
with various transition metal ions. Tridentate Schiff bases
with nitrogen, oxygen, and sulfur donor atoms have shown
The Schiff bases (also known as imine or azomethine) are
common ligands in coordination chemistry. Schiff bases
ligands are easily prepared and form complexes with almost
all metal ions. Schiff bases are known to be a sort of ligands
with strong coordinative ability, and almost all SBs can form
1:1 complexes with transition metal ions.[1] Besides interest-
ing structural features, Schiff bases complexes revealed
catalytical activity and some complexes are used as compo-
nents in the preparation of thin‐film organic solar cells or
self‐assembling layers.[2] Schiff bases have aroused many
investigators' interests because of their readiness to chelate
as bidentate ligands, through the nitrogen and oxygen atoms,
good coordination with various metal ions, rendering tremen-
dous attraction.[3,4]
The coordination of Schiff bases (2‐[(N.N‐
dimethylaminophenylimino)‐methyl]‐4‐xphenol)
toward
metal ions can enhance or minimize their activities.[5]
Schiff bases are a class of ligands capable of forming
coordinate bonds with many of metal ions through
both azomethine group and phenolic group or via
its azomethine or phenolic groups.[6–9] Heterocyclic
Schiff bases and their complexes receive significant inter-
est and attention of inorganic biochemists and organic
chemistry because of their biological activity including
J Phys Org Chem. 2017;e3707.
wileyonlinelibrary.com/journal/poc
Copyright © 2017 John Wiley & Sons, Ltd.
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https://doi.org/10.1002/poc.3707

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AL ZOUBI ET AL.
antitumor, antibacterial, fungicidal, and anticarcenogenic
properties.[10–13]
auto spec micromass spectrometer. The IR spectra (KBr disc)
were recorded on a JASCO FT‐IR 410 spectrophotometer in
In this paper, we report the synthesis, thermal analysis,
theoretical studies, and antibacterial screening of new transi-
tion metal complexes of Pd(II), Ni(II), Pb(II), and Cu(II) with
Schiff bases derived from condensation of 2‐hydroxy‐1‐
naphthaldehyde and 4‐aminophenaz. The complexes have
been characterized by several tools of analyses such as ele-
mental analyses, IR, and UV‐Vis spectra as well as thermal
gravimetric (TG) analysis. These complexes were assayed
by the disk diffusion method for antibacterial and antifungal
activity and compared with that of free Schiff bases.
the range of 4000 to 400 cm−1 1H NMR spectra were
.
recorded in DMSO with TMS as an internal standard on a Joel
GSX‐400 MHz, FT NMR spectrophotometer. The UV‐Vis
measurements were recorded on a Perkin‐Elmer k 20 UV‐
Vis Spectrometer. Conductivity measurements were made
with DMSO solutions using a Jenway 4071 digital conductiv-
ity meter at room temperature. Chlorine was determined using
potentiometer titration method on a 686‐Titro processor‐
665Dosimat‐Metrohm Swiss. Microanalyses were obtained
with an Elemental analyses system a Perkin‐Elmer automatic
equipment model 240 B. Melting points were recorded on an
Electrothermal 9200 apparatus and are uncorrected. Metal
ions were determined using a Shimadzu (A.A) 680 G atomic
absorption Spectrophotometer. Magnetic moments were mea-
sured with a magnetic susceptibility balance (Jonson Mattey
Catalytic System Division), and thermal analysis studies of
the compounds were performed on a Perkin‐Elmer Pyris Dia-
mond DTA/TG thermal system under nitrogen atmosphere at
a heating rate of 10°C/min from 25 to 700°C.
2 | EXPERIMENTAL
2.1 | Materials and methods
All chemicals were purchased from commercial sources and
were used without further purifications (CaCl2, VOSO4.
H2O, NiCl2.6H2O, PdCl2, CuCl2, ReCl5, H2PtCl6.6H2O,
2‐hydroxy‐1‐naphthaldehyde, 4‐amiophenazone, DMSO,
CH3OH, and C2H5OH from Merck).
2.3 | Synthesis of Schiff base (HL)
2.2 | Physical measurements
The ligand (Scheme 1) was prepared by condensing
2‐hydroxy‐1‐naphthaldehyde in hot ethanolic solution of
4‐aminophenazone in 1:1 molar ratio, and then, the reaction
mixture was heated to reflux for 3 hours. The 1H NMR spectra
of the Schiff base provide compelling evidence of the presence
of azomethine group. The product was dried and crystallized
from a mixture (water: ethanol) (1:1) at room temperature.
The electronic spectra were obtained by positive electron
impact and fast atom bombardment was recorded on a VG
1
Yield: 90%, mp = 212°C. H NMR (Figure 1) (DMSO,
1
ppm): 9.08 (s, –CH═N, H), 7.08 to 7.98 (m, arom), 10.99
(s, –OH, 1H), 3.1 (s, CH3, 3H), 3.39 (s, CH3, 3H), (2.5,
DMSO). 13C NMR (Figure 2) (DMSO, ppm): 161.3
(–CH═N), 111 to 136 (arom), 27.04 (C–CH3), 59.33(N–
CH3). FTIR (Figure 2) (cm−1): 3051 and 3024 (CH aro-
matic), 1639 (CH═N stretching), 1747 (C═O). The series
SCHEME
1
Structure of 4‐((2‐Hydroxy1‐naphthyl) methylene
amino)‐1.5‐dimethyl‐2‐phenyl‐1H‐pyrazol‐3(2H)‐one (HL)
1
FIGURE 1 A, H NMR and B, 13C NMR spectra of Schiff base

AL ZOUBI ET AL.
3 of 12
FIGURE 2 The FT‐IR spectra of Schiff base
of peaks (Figure 3) in the range, ie, 67, 96, 138, 158, 212, and
357 amu, may be assigned to fragments.
method by Al Zoubi and Al‐Hamdani. Thus, a solution of
4 mmol of metal salts in 10 mL of ethanol was added to an
ethanol solution containing 1 mmol Ligand(L) and was
refluxed for 5 hours. The resulting solution was concentrated
to a small volume (3 mL) on a rotary evaporator, and the
product was separated by the addition of small amount of
pet‐ether (Petroleum ether) (60‐80°C) mixture. Elemental
2.4 | Synthesis of Schiff base complexes
Ni(II), Cu(II), Pd(II), Vo(II), Re(V), and Pt(IV) complexes
(Scheme 2) were prepared in a similar manner using the
FIGURE 3 The MS spectra of Schiff base

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AL ZOUBI ET AL.
SCHEME 2 Preparation of Schiff base
and its complexes
analysis, colors, and yields for the complexes are given in
Table 1.
2.6 | The thermal analysis
From the curves recorded for the successive steps in the
decomposition process of these ligand and complexes, it was
possible to determine the following characteristic thermal
parameters for each reaction step: Initial point temperature of
decomposition (Ti): the point at which TG curve starts deviat-
ing from its base line. Final point temperature of decomposi-
tion (Tf): the point at which TG curve returns to its base line.
Peak temperature, ie, temperature of maximum rate of weight
loss (TDTG): the point obtained from the intersection of tan-
gents to the peak of TG curve. Mass loss at the decomposition
step (Dm): It is the amount of mass that extends from the point
Ti up to the reaction end point Tf on the curve, ie, the magni-
tude of the ordinate of a TG curve. The material released at
each step of the decomposition is identified by attributing
the mass loss (Dm) at a given step to the component of similar
weight calculated from the molecular formula of the investi-
gated complexes, comparing that with literatures of relevant
2.5 | Programs used in theoretical calculation
Hyper Chem‐8 program is a sophisticated molecular mod-
eler, editor, and powerful computational package that are
known for its quality, flexibility, and ease of use, uniting
2D visualization and animation with quantum chemical
calculations, molecular mechanics, and dynamics. In the
present work, parameterization method 3 (PM3) was used
for the calculation of the heat of formation and binding
energy for all metal complexes. The (PM3) and (AMBER)
are more popular than other semiempirical methods
because of the availability of algorithms, and these are
more accurate than other methods.[14] It has parameterized
primarily for organic molecules and selected transition
metals.[15]

AL ZOUBI ET AL.
5 of 12
TABLE 1 Colour, melting point, element microanalyses, and molar conductance values
Element Microanalysis Found (Calcd), %
Molecular
Formula, MWt
Molar Conductivity
mp, °C
Colour
M
C
H
H
Cl
(cm2·Ω‐1·mol‐1)
HL = C22H19N3O2
357
212
Yellow
crystals
‐
73.92 (73.94) 4.88 (5.36) 4.88 (5.36)
‐
‐
VOHL = 520.41
C22H19N3O7VS
295‐298d Greenish
10.0 (9.79)
51.09 (50.77) 3.11 (3.68) 3.11 (3.68)
‐
7
yellow
NiL = 450.54
265‐267 Green
13.98 (13.03) 59.06 (58.65) 4.87 (4.03) 4.87 (4.03)
8.08 (7.87)
8.54 (7.79)
7.77 (7.12)
12
15
9
C
22H18N3O2NiCl2
CuL = 455.40
C22H18N3O2CuCl2
250‐252 Greenish 14.14 (13.95) 58.77 (58.02) 4.44 (4.98) 4.44 (4.98)
yellow
PdL = 498.27
239‐241d Yellow
22.11 (21.36) 53.88 (53.03) 4.22 (3.64) 4.22 (3.64)
C22H18N3O2PdCl2
brown
Pt L = 657.83
C22H18N3O2PtCl3
277‐278d Dark
30.33 (29.65)
41.0 (40.17) 3.08 (2.76) 3.08 (2.76) 16.12 (16.17)
39.03 (38.61) 3.33 (2.65) 3.33 (2.65) 21.08 (20.72)
13
30
brown
Re L = 684.42
256‐257d Greenish
‐
C22H18N3O2ReCl4
Abbreviation: d, decomposition.
ꢂ
ꢃ
ꢂ
ꢀ
ꢁꢃ
compounds considering their temperature. This may assist
identifying the mechanism of reaction in the decomposition
steps taking place in the complexes under study. Activation
energy (E) of the composition step: The integral method used
is the Coats‐Red fern equation,[14] for reaction order n ≠ 1 or
n = 1, which when linear Z for a correctly chosen n yields
the activation energy from the slope. The equations are given
below: by plotting the appropriate left‐hand side of the below
equations 1/T, the slope equals –E/2.303R.
− logð1−αÞ
ZR
qEa
2RE
Ea
Ea
Log
¼ Log
1−
−
for n ¼ 1:
2:303RT
T2
ΔS* = 2.303R [log (Ah/KTmax)], ΔH* = E−RTmax
,
ΔG* = ΔH*−Tmax. ΔS*, where α = fraction of weight loss,
T = temperature (K), n = order of reaction, A or Z = per‐
exponential factor, R = molar gas constant, E = activation
energy, and q = heating rate. Order of reaction (n): It is the
one for which a plot of the Coats‐Red fern expression gives
the best straight line among various trial values of n that are
examined relative to that estimated by the Horovitz‐Metzger
method.[16]
"
#
ꢂꢀ
ꢁꢃ
1−n
1−ð1−αÞ
2RT
Ea
Ea
2:303RT
Log
¼ Log 1−
−
for n≠1;
T2ð1−nÞ
TABLE 2 The important infrared frequencies (cm‐1) of Schiff base and its complexes
Compound Name
υ(C═O)
υ(C═N)
H‐bonded υ(OH) Stretching
υ(M–N)
υ(M–O)
Other Bands
υ(C–H) = 3047 arom
HL
1747
1639
3429
υ(C–H) =2880 aliph
[CuL2Cl]
1690
1689
1785
1694
1700
1734
1616
1615
1615
1613
1616
‐
455
456
450
469
647
478
428
425
427
418
417
428
υ(C–H) = 3051 arom
υ(C–H) = 2943 aliph
[NiL2Cl]
‐
υ(C–H) = 3055 arom
υ(C–H) = 2943 aliph
[PdL2Cl]
‐
υ(C–H) = 3049 arom
υ(C–H) = 2943 aliph
[PtL2Cl3]
‐
‐
υ(C–H) = 3059 arom
υ(C–H) = 2943 aliph
[ReL2Cl3]Cl
[VOHL2(SO4)]
υ(C–H) = 3059 arom
υ(C–H) = 2943 aliph
1670
1629
3399
υ(C–H) = 3020 arom
υ(C–H) = 2934 aliph, υ(V═O) = 972
υ(SO4) = 914,1033, 1088, and 1184

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AL ZOUBI ET AL.
Cl, and [M(II)(L)Cl] (M═Ni(II), Cu(II) and Pd(II))
(Scheme 2).[18]
3 | RESULTS AND DISCUSSION
All the complexes are amorphous powder, insoluble in water
and ether whereas soluble in solvents such as CHCl3,
CH2Cl2, MeCN, DMF, and DMSO. The molar conductance
data (Table 1) indicate that all the complexes are nonelectro-
lytes (Scheme 2).[17]
The complexes are air‐stable solids, solution in DMF and
DMSO, sparingly soluble in MeOH, CHCl3, and CH2Cl2.
The analytical data (Table 1) agree well with the suggested
TABLE 4 The fragmentation pattern data for the Schiff base
The ligand was characterized by elemental analysis
(Table 1). IR (Table 2). and UV‐Vis (Table 3). respec-
tively. Monomeric complexes of the ligand with V(IV),
Ni(II), Cu(II), Pd(II), Re(V), and Pt(IV) were synthesized
by heating 1 mmol of the ligand with 1 mmol of metal
salt using ethanolic solution. However, deprotonation of
the ligand occur facilitating the formation of the com-
plexes [VO(II)(HL)(SO4)], [Pt(IV)(L)Cl3], [Re(V)(L)Cl3]
Ligand
Assignment
Peak, m/z Relative Abundance, %
HL
M═(C22H19N3O2)
M–C12H7O+═M1
M1–C4H5+═M2
M2–NH5+═M3
M3–CNO═M4
M4–CH2N+
357
212
158
138
96
94
34
17
24
15
91
67
TABLE 3 Magnetic and spectra data of the ligand and its metal complexes
Complex geometry
ʌm·cm2·Ω‐1·mol‐1
μeff B.M
ύ (cm‐1)
ABS
λmax, nm
ε
max·L·mol‐1·cm‐1
Assignments
[VOHL2(SO4)] (Sqy)
7
1.77
37 174.7
30 769.2
29 673.5
25 641
19 305
12 610
1.685
1.381
1.392
2.101
0.111
0.078
269
325
337
390
518
793
16 850
13 810
13 920
21 010
111
Ligand field
Ligand field
Ligand field
C.T
2
2B2 ! B1
2
78
2B2 ! E
[NiL2Cl](Th)
12
2.80
37 174.7
30 395
1.393
1.040
1.082
2.039
0.055
0.061
0.054
269
329
338
391
550
721
980
13 930
1040
1082
2039
550
Ligand field
Ligand field
Ligand field
Ligand field
M ! L(C.T)
3T1 ! 3 T2
29 585.7
25 575.4
18 181.8
13 869.6
10 204
61
54
3T1g ! 3 T1(P)
[CuL2Cl](Th)
[Pd L2Cl](Sq)
15
9
1.68
dia
36 496
28 985.5
23 419
12 642
1.407
0.856
1.203
0.036
274
345
427
791
1407
856
12 030
360
Ligand field
Ligand field
C.T
2
2T2 ! E
37 174.7
30 674.8
29 585.7
24 630.5
16 949
1.603
1.183
1.167
2.306
0.201
0.198
269
326
338
406
590
792
16 030
11 830
11 670
2306
Ligand field
Ligand field
Ligand field
M ! L(Ct)
1
201
198
1A1g ! B1g ν2
1
12 626
1A1g ! A2g ν1
[PtL2Cl3](Oh)
13
30
dia
36 496
28 985.5
25 510
17 094
14 326.6
12 150.6
2.072
2.217
2.421
0.621
0.465
0.248
274
345
392
585
698
823
20 720
22 170
2421
621
Ligand field
Ligand field
Ligand field + (CT)
1
1A1g ! T3g
1
465
248
1A1g ! T2g
1
1A1g ! T1g
[ReL2Cl3]Cl(Oh)
3.05
36 496
28 985.5
25 510
19 762.8
13 947
2.072
2.217
2.421
0.301
0.018
274
345
392
506
717
20 720
22 170
242
Ligand field
C.T
3
3T1g ! A2g
3
301
180
3T1g ! T1g (P)
3T1g ! 3 T2 g (F)
Abbreviations: dia, diamagnetic; Oh, octahedral; Sp, square planar; Spy, square pyramidal; Th, tetrahedral.

AL ZOUBI ET AL.
7 of 12
formulae. The most important infrared bands of the ligand
and its complexes together with their assignments are col-
lected in Table 2.
band in the region 3375 to 3399 cm‐1 and 2 weak bands in
the region 700 to 720 cm‐1 and 752 to 801 cm‐1 are attributed
to the presence of coordinated water molecules because of
υ(OH) rocking and wagging modes of vibrations, respec-
tively.[19–21] The reduction in bond order, upon complexa-
tion, can be attributed to delocalization of metal electron
density (t2g) to the π‐system of the ligand. These shifts con-
firm the coordination of the ligand via the nitrogen of the
azomethine group and oxygen of carbonyl and the phenol
groups to metal ions. At lower frequency the complexes
exhibited bands around 478 to 447 cm‐1 assigned to the
υ(M–N) and exhibited bands around 428 to 417 cm‐1
assigned to the υ(M–O) for complexes and new bands in
[VOHL (SO4)] complex the 927 cm‐1 assigned to the
υ(V═O). This indicates that the ligand was coordinated with
the V(IV) ion through the O atom and 1103, 1084, and
1022 cm‐1 assigned to the υ(SO4). This indicates that the
SO4 was coordinated with the V(IV) ion through the mono
O atom (mono dentate).[17,22] All these data are shown in
Table 2.
3.1 | The IR spectra
All peculiar features of the Infrared spectra are consistent
with the structural characteristics of the Schiff base and its
metal complexes. A characteristic stretching vibration
(Table 2) was observed in the region 1619 to 1640 cm‐1
attributed to υ(C═N). The broad bands around 3200 to
3429 cm‐1 are assigned to H‐bonded –OH starching vibra-
tions; a strong band at 1720 to 1747 cm‐1 and 1281 to
1284 cm‐1 in the IR spectra of the Schiff bases are assigned
to υ(C═O) and phenolic υ(C–O) vibrations, respectively. In
comparison with the vibrational spectra (Table 2) of the metal
complexes with the free ligands, the υ(C═N) and υ(C═O) are
shifted to the lower wave number ((C═N) (28‐22 cm‐1)
(C═O) (57‐13 cm‐1)), ie, in the range 1590 to 1593 cm‐1
shows the coordination of nitrogen of azomethine group to
the metal ion. This indicates that the ligand was coordinated
with the metal ions through the imine and carbonyl group.
The metal complexes (as shown in Table 2) showing broad
3.2 | Electronic spectra studies
The electronic spectral values of ligand and its complexes are
recorded in Table 3. The electronic spectra of VO complexes
generally showed 3 absorption bands in the region at 790,
518, and 390 nm, which are assigned to transitions
2
2
2
2B2 ! E, B2 ! B1, and M ! L(C.T) showing a square
pyramidal geometry[17,23] around the VO ion. The electronic
spectral data of Ni(II) complexes showed d–d bands in the
region 980, 721, and 550 nm, respectively, assigned to the
transitions 3T1g ! 3 T1(P), 3T1 ! 3 T2, M ! L(C.T), which
are characteristics of Ni(II) in tetrahedral geometry. The
SCHEME 4 Proposed thermal decomposition pathways of Schiff
SCHEME 3 The proposed mass fragmentation pathways of ligand
base (HL)
TABLE 5 Thermal analysis results of thermal decomposition of the EB
TGA
DTG
Ligand
Step
TG Range, °C
DTGmax, °C
Mass Loss Calcd (Estim), %
Total Mass Loss
ΔH (kJ·mol‐1)
Tdata
HL
1
2
3
33‐121.7
122.1‐429
460.3‐689
68.7
368
654
4.756 (5.27)
28.788 (28.82)
64.352 (64.09)
98.188
97.896
97.896
endo
endo
endo
49.3
313
607

8 of 12
AL ZOUBI ET AL.
FIGURE 4 Electrostatic potential (HOMO and LUMO) contours for ligand
electronic spectra of Cu(II) complexes exhibited low‐energy
590, and 406 nm, respectively, assigned to the transitions
1
1
absorption bands at 791 and 427 nm assigned to the transi-
1A1g ! A2g, 1A1g ! B1g, M ! L(C.T), which are charac-
teristic of Pd(II) in square planar geometry.[24–27] In addition,
The electronic spectral data of Pt(II) complexes showed d–d
bands in the region 823, 698, 585, and 392 nm, respectively,
2
2
tions T2 ! E and M ! L(C.T). The high‐energy band in
the region at 345 to 269 nm is due to the forbidden ligand,
on the basis of which a distorted octahedral geometry is sug-
gested for Cu(II) complexes.[17] The electronic spectral data
of Pd(II) complexes showed d–d bands in the region 792,
1
!1
1
!1
assigned to the transitions A1g T1g, A1g T2g,
1
1A1g ! T3g, and M ! L(C.T), which are characteristic of
TABLE 6 Conformation energy analysis in (K J.Mol‐1) for the ligand and its complexes
Complexes
Total Energy
Binding Energy
Heat of Formation
Electronic Energy
Dipole (Debyes)
HL
−91 542.629
−5133.684
73.9510
−740 230.728
6.297
3.57
[VOHL2(SO4)]
[NiL2 Cl]
[CuL2 Cl]
[Pd L2 Cl]
[Pt L2 Cl3]
[Re L2 Cl3]Cl
1042.548 (AMBER)
−119 271.432
−102 917.146
−103 087.391
−6453.444
−5375.758
−5397.259
−24.5877
−21.0218
−12.509
−5697.32
2.96
−867 067.15
−879 579.67
2.88
3.42
230.987 (AMBER)
1542.548 (AMBER)
40.15
38.83

AL ZOUBI ET AL.
9 of 12
Pt(II) in octahedral geometry. Additionally, The electronic
spectral data of Re(III) complexes showed d–d bands in the
region 717, 506, 392, and 345 nm, respectively, assigned to
64.352%), which may be attributed to the decomposition of
chemical formula C16H10N2 (mole mass = 230).
3
3
3
the transitions 3T1g ! T2g (F), 3T1g ! T1g (P), 3T1g ! A29,
and M ! L(C.T), which are characteristic of Re(II) in Octahe-
dral geometry.[28–30]
3.5 | Electrostatic potentials
Electron distribution governs the electrostatic potential of the
molecules. The electrostatic potential (E.P) describes the
interaction of energy of the molecular system with a positive
point charge. The E.P is useful for finding sites of reaction in
a molecule; positively charged species tend to attack a mole-
cule where the electro static potential is strongly negative
(electrophonic attack).[23,24] The E.P of the free ligand was
calculated and plotted as 2D contour to investigate the reac-
tive sites of the molecules, Figure 3. Therefore, one can inter-
pret the stereochemistry and rates of many reactions
involving “soft” electrophiles and nucleophiles in terms of
the properties of frontier orbital HOMO and LUMO. The
results of calculations show that the LUMO of transition
metal ions prefer to react with the HOMO of 3‐donor atoms
of 2 oxygen of carbonyl and nitrogen of imine group for free
ligand (as shown in Figure 4).[24]
3.3 | Mass spectra
The mass spectrum of the ligand HL is shown in Table 4
and Scheme 3, the peak at m/z = 357 due to the molecular
ion peak which coincides with its formula weight. The pro-
posed fragmentation pattern of the ligand is given below
(Scheme 3). The ligand spectrum shows M+–C12H7O and
M++C4H5 peaks, which are characteristics of aromatic
rings. Loss of one of the amino hydrogen atom of Schiff
base gives a moderately intense M+–1 peak; this effect is
more pronounced in amino group because of the better res-
onance stabilization of ion fragment by the nitrogen. This
molecular ion peak also has the good agreement with nitro-
gen rule of molecular fragmentation as well as their calcu-
lated value of molar mass = 357.[31–34] The measured
molecular weights were consistent with expected values
and the mass spectrum of the complex is shown in
Table 5 and Scheme 3.
All theoretically probable structures of free ligand and
their complexes have been calculated by (PM3) and
(ZINDO/1) methods in the gas phase to search for the most
probable model building stable structure, Table 6.
The vibrational spectra of the free ligand has been calcu-
lated, Table 7. The theoretically calculated wave numbers for
this ligand showed that some deviations from the experimen-
tal values; these deviations are generally acceptable in theo-
retical calculations. Calculation of parameters has been
optimized bond lengths of the free ligand and its metal com-
plexes which to give excellent agreement with the experimen-
tal data as shown in Figure 5.
3.4 | Thermal analysis studies
The thermal data of Scheme 4 and Table 5 refers to the
decomposition of this Schiff base in 3 steps of total estimated
mass loss of 100% (calcd 98.95%). The first step occurs
within the temperature range 33.2°C to 121.7°C and exactly
at 105.46°C (DTG) of estimated mass loss of 5.271%, (calcd
4.756%); which may be attributed to the decomposition of
chemical formula OH (mole mass = 17). The second step
occurs within the temperature range 122.1°C to 429°C and
exactly at 323.28°C (DTG). It refers to the estimated mass
loss of 28.821% (calcd 28.7), which may be attributed to
the decomposition of chemical formula C5H8NO (mole
mass = 98). Finally, the third step occurs within the temper-
ature range 460.3°C to 689°C and exactly at 579.43°C
(DTG). It refers to the estimated mass loss of 64.59% (calcd
3.6 | Antibacterial activates
The newly synthesized compounds were screened for anti-
bacterial activity. For antibacterial studies microorganisms
such as S. aureus NCIM 2079, Bacillus subtilis NCIM
2063, Escherichia coli NCIM 2918, P. aeruginosa NCIM
2036 were used (Table 8) and assayed by minimum inhibi-
tory concentration (MIC) by serial dilution technique. To
TABLE 7 Comparison of experimental and theoretical vibrational frequencies for ligand
Ligand
υ(OH)
υ(CH) aromatic
υ(CH) aliphatic
υ(CH) aldehyde
υ(C═O) ring
υ(C═N)
υ(C‐O‐H)
HL
3429a
3047a
2880a
2924a
1747a
1639a
1620a
1087a
3444b
3065b
2976b
2999b
1777b
1665b
1203b
−0.590c
−3.333c
−2.564c
−1.717c
−0.21c
−10.67c
aExperimental frequency.
bTheoretical frequency.
cError % due to main difference in the experimental measurements and theoretical treatments of vibration spectrum.

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AL ZOUBI ET AL.
FIGURE 5 Conformational structure of
ligand and their metal complexes

AL ZOUBI ET AL.
11 of 12
TABLE 8 Screening of minimal inhibitory concentration for sample with Gram‐positive bacteria and Gram‐negative bacteria
Minimal Inhibitory Concentration, μg/mL
Gram‐Positive Bacteria
Gram‐Negative Bacteria
Compounds
BS
SA
ES
PA
HL
1000
1800
2000
1600
2000
2000
1200
1000
1300
2000
1800
2000
2000
2000
1200
1800
1400
2000
2000
2000
1600
900
[VOHL(SO4)
[NiLCl]
1200
1400
1600
2000
1500
1000
[CuLCl]
[PdLCl]
[PtLCl3]
[ReLCl3]Cl
Dilutions for MIC
No of tubes for MIC
1
2
3
4
5
6
7
8
9
10
Concennration of drug (μg/ml)
4000
2000
1000
500
250
125
62.5
31.25
15.625
7.812
Abbreviations: BS, Bacillus subtilis NCIM 2063; EC, Escherichia coli NCIM 2911; PA, Pseudomonas aeruginosa NCIM 2036; SA, Staphylococcus aureus NCIM 2079.
[4] T. E. Olalekan, A. S. Ogunlaja, B. VanBrecht, G. M. Watkins,
determine the MIC, the compounds were dissolved in
dimethyl sulfoxide. Ciprofloxacin was used as the standard
and incubated for 24 hours at 37°C (Table 8).[17,20–24]
J. Mol. Struct. 2016, 1122, 72.
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[6] A. Muna, Acta Chim. Pharm. 2013, 3(2), 127.
4 | CONCLUSION
[7] A. A. S. Al‐Hamdani, A. M. Balkhi, A. Falah, S. A. Shaker,
J. Saudi Chem. Soc. 2016, 20, 487.
In this paper, we have explored the synthesis and coordina-
tion chemistry of some monomeric complexes obtained from
the reaction of the tridentate ligand L with some metal ions.
The mode of bonding and overall structure of the complexes
were determined through physicochemical and spectroscopic
methods. Complexes formation study via molar ratio has
been investigated, and results were consistent to those found
in the solid complexes with a ratio of (M:L) as (1:1). The
thermodynamic parameters, such as ΔE*, ΔH*, ΔS*, ΔG*,
and K are calculated from the TGA curve using Coats‐Red
fern method. Hyper Chem‐8 program was used to predict
structural geometries of compounds in the gas phase. The
heat of formation (ΔHf) and binding energy (ΔEb) at 298 K
for the A, free ligand, and its complexes were calculated by
PM3 method. The synthesized ligand and its metal com-
plexes were screened for their biological activity against
bacterial species, 2 Gram‐positive bacteria (B. subtilis and
S. aureus) and 2 Gram‐negative bacteria (E. coli and
P. aeruginosa).
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Theoretical studies and antibacterial activity for Schiff
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