Synthesis and Characterization of VO2+, Co2+, Ni2+, Cu2+ and Zn2+ Complexes of a Schiff base ligand derived from ethyl 2-amino-6-ethyl-4,5,6,7-tetrahydrothieno[2,3-c]pyridine-3-carboxylate and their Investigation as fungicide Agents

Article abstract of DOI:10.1002/aoc.4581

Complexes of VO²⁺, Co²⁺, Ni²⁺, Cu²⁺, and Zn²⁺ ethyl-6-ethyl-2-((2-hydroxybenzylidene)amino)-4,5,6,7-tetrahydrothieno[2,3-c]pyridine-3-carboxylate were synthesized and characterized via different spectroscopic techniques. The whole results declared that the complexes assembled in 1:1 mole ratio furthermore, the spectroscopic data analysis proved the present ligand adhered to the different metal ions in neutral or monobasic tridentate ligand via azomethine nitrogen, carbonyl oxygen atoms and protonated/deprotonated phenolic hydroxyl group. The UV–Vis. and ESR spectroscopic data analysis proposed a distorted octahedral or octahedral structure for all complexes. The ESR spectra for Cu²⁺ complexes (5–6) revealed an axial symmetry with g‖?>?g_┴?>?g_e, denoting to distorted octahedral Cu²⁺ complex and the free electrons in the M shell exist in a d_(x2-y2) orbital with a remarkable covalent bond aspect. The synthesized complexes showed moderate to superb fungicide activity. All complexes are more active than both standard drug and ligand against C. albicans where complexes (5–7) are more active against A. flavus and compounds (1), (4–5), (7) against S. cerevisiae whereas only complex (6) is more active against A niger.

Full text of DOI:10.1002/aoc.4581

Received: 23 May 2018
DOI: 10.1002/aoc.4581
Revised: 3 August 2018
Accepted: 8 August 2018
F U L L P A P E R
Synthesis and Characterization of VO2+, Co2+, Ni2+, Cu2+
and Zn2+ Complexes of a Schiff base ligand derived from
ethyl 2‐amino‐6‐ethyl‐4,5,6,7‐tetrahydrothieno[2,3‐c]
pyridine‐3‐carboxylate and their Investigation as fungicide
Agents
Mohamad M.E. Shakdofa1,2
Hanan A. Mousa2
| Ammar A. Labib2
| Naglaa A. Abdel‐Hafez3
|
1 Chemistry Department, Faculty of
Science and Arts, Khulais, University of
Jeddah, Saudi Arabia
2 Inorganic Chemistry Department,
National Research Center, P.O. 12622,
Dokki, Cairo, Egypt
3 Applied Organic Chemistry Department,
National Research Center, P.O. 12622,
Dokki, Cairo, Egypt
Complexes of VO2+
, , , ,
Co2+ Ni2+ Cu2+ and Zn2+ ethyl‐6‐ethyl‐2‐((2‐
hydroxybenzylidene)amino)‐4,5,6,7‐tetrahydrothieno[2,3‐c]pyridine‐3‐carboxylate
were synthesized and characterized via different spectroscopic techniques.
The whole results declared that the complexes assembled in 1:1 mole ratio fur-
thermore, the spectroscopic data analysis proved the present ligand adhered to
the different metal ions in neutral or monobasic tridentate ligand via
azomethine nitrogen, carbonyl oxygen atoms and protonated/deprotonated
phenolic hydroxyl group. The UV–Vis. and ESR spectroscopic data analysis
proposed a distorted octahedral or octahedral structure for all complexes.
The ESR spectra for Cu2+ complexes (5–6) revealed an axial symmetry with
g‖ > g > ge, denoting to distorted octahedral Cu2+ complex and the free elec-
trons in the M shell exist in a d(x2‐y2) orbital with a remarkable covalent bond
aspect. The synthesized complexes showed moderate to superb fungicide
activity. All complexes are more active than both standard drug and ligand
against C. albicans where complexes (5–7) are more active against A. flavus
and compounds (1), (4–5), (7) against S. cerevisiae whereas only complex
(6) is more active against A niger.
Correspondence
Mohamad M. E. Shakdofa, Chemistry
Department, Faculty of Science and Arts,
Khulais, University of Jeddah, Saudi
Arabia.
┴
Email: mshakdofa@gmail.com;
Ammar A. Labib, Inorganic Chemistry
Department, National Research Center,
P.O. 12622 Dokki, Cairo, Egypt.
Email: ammar_al@yahoo.com
KEYWORDS
ESR, fungicide activities, metal complexes, Schiff base
1 | INTRODUCTION
to their structures; furthermore, these have an imperative
role in the theme of coordination chemistry, particularly
Schiff bases resulted from the condensation of primary
amines and carbonyl compounds which discovered by
Hugo Schiff in 1894 are structurally recognized as imine
or azomethine.[1,2] These possess a vital role in organic,
inorganic, medicinal chemistry and biological field owing
in the development of complexes owing to its facility to
produce stable organo‐metal compounds with transition
metal ions. Schiff bases and their complexes are versatile
extensively used for industrial goals and expose a con-
trasting broad range of biological activities[3–6] include,
Appl Organometal Chem. 2018;e4581.
wileyonlinelibrary.com/journal/aoc
© 2018 John Wiley & Sons, Ltd.
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https://doi.org/10.1002/aoc.4581

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SHAKDOFA ET AL.
antifungal,[7] antibacterial,[7,8] Anti‐leishmanial,[9] anti‐
molluscicidal,[8] antimalarial,[10] anti‐proliferative,[11]
anti‐inflammatory, antitumor,[12] anti‐amoebic,[13] antivi-
ral,[14] antioxidant[15] and antipyretic properties. The
Schiff base ligands derived from o‐vanillin connected
with Pd atom forming metal complexes showed a cyto-
toxic effect on three cancer cell lines: breast (MCF‐7),
lung (A549) and ovarian (SKOV3).[16] While Cu (II) com-
plexes of Schiff bases of the pyrrolizine‐5‐carboxamides
displayed cytotoxic effect on the breast (MCF‐7), ovary
(A2780) and colon (HT29) human adenocarcinoma, in
addition to MRC5 (normal human fetal lung fibroblast)
cells.[17] Niu et al. reported that the Zn2+ complexes of
o‐vanillin Schiff Bases exhibited efficient DNA interaction
and furthermore, showed in vitro cytotoxic effect against
four different sets of human cancer cell lines (HL‐60,
HeLa, K562 and A549,).[18] Recently, Venkateswarlu
et al. stated DNA binding, DNA cleavage, In addition to
many other biological studies of Co2+ Ni2+ and Cu2+
complexes with “2‐((furan‐2‐yl) methylimino)methyl)‐6‐
ethoxyphenol Schiff Base,[19] were also carried out.
Ghorai et al. reported the preparation and characteriza-
tion of Cu2+ and Zn2+ complexes of “3‐methoxy
propylimino) methyl)‐6‐methoxyphenol” and reported
studies related to their capability to DNA binding,
DNA cleavage.[20] Numerous of Schiff base complexes
show superb catalytic behavior in numerous dissimilar
reactions particularly at elevated temperature and in
dampness.[21–24]
3 | INSTRUMENTATION AND
MEASUREMENTS
The ligand and its metal complexes were analyzed for C,
H, N, and S at the Micro‐analytical Laboratory, Cairo
University, Egypt. 1H NMR (500 MHz) spectra were
recorded in DMSO‐d6 on JEOL ECA‐500 MHz spectrom-
eter. Chemical shifts (δ) are reported in ppm using TMS
as the internal standard. Standard analytical methods
were used to determine the metal ion content.[31–34] Mass
spectra of the solid ligand and its metal complexes
recorded using JEOL JMS‐AX‐500 mass spectrometer pro-
vided with the data system. TLC confirmed the purity of
all prepared compounds. IR spectra of the ligand and its
metal complexes were measured using a Jasco FT/IR
6100 type A infrared spectrophotometer covering the
range 400–4000 cm−1. Nujol mull electronic absorption
spectra (EAS) were measured using Whatman filter paper
No.1 and referenced against another similar filter paper
saturated with paraffin oil in the 200–1100 nm regions
on a Shimadzu 2600 spectrophotometer. The thermal
analysis (TG) was carried out on Shimadzu DT‐50 ther-
mal analyzer from room temperature to 800 °C at a
heating rate of 10 °C/min. Magnetic susceptibilities were
measured at 25 °C by the Gouy method using mercuric
tetrathiocyanatocobaltate (II) as the magnetic susceptibil-
ity standard. Diamagnetic corrections were estimated
from Pascal's constant. The magnetic moments were
calculated from the equation (1):
Due to the above mentioned applications of
Schiff bases and in extension of group preceding work,
on the synthesizing of biologically active metal com-
plexes.[25–28] This work devoted to the preparation of a
novel Schiff base ligand, Ethyl 6‐ethyl −2 ‐(2‐ hydroxyl‐
benzylideneamino)‐4,5,6,7‐tetrahydrothieno[2,3‐c]pyri-
pffiffiffiffiffiffiffiffiffi
μeff¼2:84 χcMorr:T
(1)
Molar conductance was measured on a Tacussel
type CD6NG conductivity bridge using 10−3 M DMF solu-
tions. The resistance measured in ohms and the molar
conductivities were calculated according to the
equation (2):
dine‐3‐carboxylate and its complexes with VO2+, Co2+
,
Ni2+, Cu2+, and Zn2+. The chemical structure of the
recent ligand and metal complexes was investigated by
elemental analysis and spectroscopic data. In addition,
the fungicide activity for the synthesized complexes
was assessed by Well diffusion method.
V × K × Mw
ΛM
¼
(2)
g × Ω
Where: ΛM = molar conductivity/ Ω−1 cm2 mol−1
,
2 | MATERIALS AND METHODS
V = volume of the complex solution/mL, K = cell con-
stant (0.92/cm−1), Mw = molecular weight of the
complex, g = weight of the complex in gram, Ω= resis-
tance. The solid ESR spectra of the complexes were
recorded with Varian E‐109 spectrophotometer operating
at 9.8 GHz with 100 kHz modulation in CW mode in
3‐mm Pyrex tubes at 298 °K. Diphenyl picryl hydrazide
(DPPH) used as a g‐marker for the calibration of the
spectra.
All metal salts were purchased from commercial sup-
pliers and used without further purification.
Salicylaldehyde was provided from SIGMA‐ALDRICH
Company as well as DMSO (assay 99.7%) and absolute
ethanol (assay ≥99.8%). Ethyl 2‐amino‐6‐ethyl‐4,5,6,7‐
tetrahydrothieno[2,3‐c]pyridine‐3‐carboxylate was pre-
pared according to a known method.[29,30]

SHAKDOFA ET AL.
3 of 12
(358.5 mg, 1 mmol, in 30 ml of absolute ethanol) in the
presence of 3 ml of triethylamine except in case of
vanadyl complex a 3 ml of distilled water was added.
The mixture refluxed for three hours with stirring. The
resulting solid complexes filtered off while heated,
washed several times with hot ethanol and finally dried
over P4O10.
3.2.1 | VO2+‐complex (2)
FIGURE
1
Preparation
of
ethyl‐6‐ethyl‐2‐((2‐
hydroxybenzylidene)amino)‐4,5,6,7‐tetrahydrothieno[2,3‐c]
pyridine‐3‐carboxylate
Yield (61%), m.p. >300 °C; color: green; μeff = 1.81; molar
conductivity (Λm): 28.9 ohm−1cm2mol−1. Elemental anal-
ysis for [VO (HL)(SO4)H2O]·2H2O, C19H24VS2N2O8,
(559.50): calcd. (Found) %C 40.79(40.48), %H 5.04(4.91),
%N 5.01(4.85), %S 5.04(4.91), %V 9.10 (8.79). IR (KBr,
cm−1), 3435 ν (H2O), 1691 ν (C=O), 1602 ν (C=N), 1536
ν (C‐Ophenolic), 1120, 1038 and 727 ν (SO4), 541 ν
(V ← O), 457 ν (V ← N), 984 ν (V=O).
3.1 | Synthesis of Schiff base (HL)
The ligand, (HL) was prepared by refluxing ethanolic
solution
of
ethyl
2‐amino‐6‐ethyl‐4,5,6,7‐
tetrahydrothieno[2,3‐c]pyridine‐3‐carboxylate (254 mg,
1.0 mmol) with ethanolic solution of 2‐hydroxy benzalde-
hyde (122 mg, 1.0 mmol), Figure 1. The mixture stirred
and refluxed for three hours, then left to cool to room
temperature. The solid product which formed was filtered
off, washed with cold ethanol, followed by crystallization
from ethanol and finally dried under vacuum over anhy-
drous CaCl2. The color was yellow and yield 59%. Elemen-
tal microanalyses, Calc. for ligand (H2L) = C19H22N2O3S
(FW = 358.45): C, 63.31; H, 5.97; N, 7.56% S, 8.56%.
Found: C, 63.66; H, 6.19; N, 7.82%, S, 8.95%. IR data,
3435(br), 1691, 1601, 1560, 1277 cm−1 assigned to υ(OH,
3.2.2 | Co2+‐complex (3)
Yield (67%), m.p. >300 °C; color: reddish brown; μeff = 396;
molar conductivity (Λm): 14.9 ohm−1cm2mol−1. Elemental
analysis
C21H38NiN2O12S,
for
[Co
(529.23):
(L)(CH3COO)(H2O)2].5H2O,
calcd. (Found) %C
41.93(41.28), %H 6.37(6.09), %N 4.66 (4.57), %S
5.33(5.29), %Co 9.80(9.67). IR (KBr, cm−1), 3432 ν (H2O),
1632 ν (C=O), 1596 ν (C=N), 1323 ν (C‐Ophenolic), 1542/
1347(Δ= 195) ν (CH3COO), 541 ν (Co‐O), 478 ν (Co ← N).
1
C=O, C=N, C=C, C‐Oph). H NMR data (500 MHz, δ
3.2.3 | Ni2+‐complex (4)
ppm DMSO‐d6): 1.06 (3H, t, JHH 6.9,7.60, O–16CH2–17-
CH3); 1.29 (3H, t, JHH 6.90,7.65, N–7CH2–8CH3); 2.65
Yield (66%), m.p. >300 °C; color: reddish brown; μeff = 3.11;
molar conductivity (Λm): 15.5 ohm−1cm2mol−1. Elemental
(2H, t, N–10CH2 CH2); 2.75 (2H, t, N–10CH2 CH2); 3.39
9
9
(2H, s, N–7CH2 CH3); 4.14 (2H, s, N–6CH2); 4.28 (2H,
8
analysis
C21H30NiN2O8S,
for
[Ni
(529.23):
(L)(CH3COO)(H2O)2].H2O,
calcd. (Found) %C
q, O–7CH2); 7.65 (1H, d, JHH 7.6, 23C‐H); 7.40 (1H,
d, JHH 8, 8.05 22C‐H); 6.94 (2H, m, 3&4C‐H); 8.76 (1H,
s, N = 18C‐H); 12.56 (1H, S, OH). The positive (EI) mass
spectrum of ligand showed the parent ion peak at m/z
358(100%) corresponding to (M+) and the following frag-
ments; 301 (45%) (M‐2CH3CH2)+, 285.3 (15%) [M‐
2CH2CH2‐OH]+, 257 (13%) [M‐2CH3CH2‐OH ‐CHO]+,
165 (8%) [M‐2CH3CH2‐OH–CHO‐C6H5]+.
47.66(47.49), %H 5.71(5.51), %N 5.29 (5.36), %S
6.06(5.89), %Ni 11.09(10.85). IR (KBr, cm−1), 3413 ν
(H2O), 1600 ν (C=O), 1585 ν (C=N), 1314 ν (C‐Ophenolic),
1532/1347(Δ= 185) ν (CH3COO), 531 ν (Ni‐O), 499 ν
(Ni ← N).
3.2.4 | Cu2+‐complex (5)
Yield (58%), m.p. >300 °C; color: deep brown; μeff = 161;
molar conductivity (Λm): 35.6 ohm−1cm2mol−1. Elemen-
3.2 | Preparation of metal complexes (2‐7)
The complexes (2–7) were prepared by adding metal
tal
analysis
for
[Cu
(HL)Br2(H2O)].H2O,
salts
[VOSO4]·2H2O,
[Co
(CH3COO)2]·6H2O,
C21H26CuN2O5SBr2, (617.84): calcd. (Found) %C
36.94(36.67), %H 4.24(4.17), %N 4.53 (4.58), %S 5.19
(4.98), %Cu 10.29(10.22). IR (KBr, cm−1), 3418 ν (H2O),
1611 ν (C=O), 1586 ν (C=N), 1326 ν (C‐Ophenolic), 534 ν
(Cu ← O), 442 ν (Cu ← N).
[Ni (CH3COO)2]·6H2O, [Cu (CH3COO)2]·2H2O, CuBr2,
[Zn (CH3COO)2]·2H2O (1 mmol, in 30 mL of ethanol)
to Ethyl 6‐ethyl‐2‐(2‐hydroxybenzylideneamino)‐4,5,6,7‐
tetrahydrothieno[2,3‐c]pyridine‐3‐carboxylate
(HL)

4 of 12
SHAKDOFA ET AL.
3.2.5 | Cu2+‐complex (6)
(20 mg\ ml) using a micropipette and the plate was incu-
bated at 37 °C for 72 hr. During the test the solution dif-
fused, and the growth of the inoculated fungi or bacteria
was affected. The inhibition zone (MIZ) developed on the
plate was recorded. Each test took place for three times
and the activity index for the complexes was calculated
by following formula.[39]
Yield (53%), m.p. >300 °C; color: brown; μeff = 1.87; molar
conductivity (Λm): 11.5 ohm−1cm2mol−1. Elemental analy-
sis for [Cu (L)(CH3COO)(H2O)2], C19H28CuN2O7S,
(516.07): calcd. (Found) %C 48.87(48.73), %H 5.47(5.27),
%N 5.43 (4.62), %S 6.21(5.99), %Cu 12.31(11.99). IR (KBr,
cm−1), 3423 ν (H2O), 1602 ν (C=O), 1578 ν (C=N), 1353
ν (C‐Ophenolic), 1531/1317(Δ= 214) ν (CH3COO), 536
ν (Cu‐O), 457 ν (Cu ← N).
Diameter of inhibition zone by test compound
Activity index ¼
× 100
Diameter of inhibition zone by standard
3.2.6 | Zn2+‐complex (7)
4 | RESULTS AND DISCUSSION
Yield (55%), m.p. >300 °C; color: yellow; μeff = Dia.;
molar conductivity (Λm): 7.5 ohm−1cm2mol−1. Elemental
analysis for [Zn (L)(CH3COO)].H2O, C21H26ZnN2O6S,
(499.89): calcd. (Found) %C 50.46(49.93), %H 5.24(5.17),
%N 5.60 (5.62), %S 6.41(6.09), %Zn 13.08(12.99). IR
(KBr, cm−1), 3400 ν (H2O), 1642 ν (C=O), 1589 ν
(C=N), 1311 ν (C‐Ophenolic), 1555/1355(Δ= 200) ν
(CH3COO), 503 ν (Zn‐O), 465 ν (Zn ← N).
The whole attained complexes (2–7) are stable in air and
have comparable colors, the test of solubility showed that
the complexes are water insoluble and soluble in the
polar aprotic solvents. Ligand (1) Ethyl 6‐ethyl‐2‐(2‐
hydroxy‐benzylideneamino)‐4,5,6,7‐tetra‐hydrothieno[2,3‐
c]‐pyridi‐ne‐3‐carboxylate (HL) was prepared by reaction
of salicylaldehyde with 3 Ethyl 2‐amino‐6‐ethyl‐4,5,6,7‐
tetrahydrothieno[2,3‐c]pyridine‐3‐carboxylate in refluxed
ethyl alcohol with glacial acetic acid as a catalyst for four
hours to give 79% as a yellow solid crystal (Figure 1). The
prepared metal compounds had a molar conductivity
located within 7.5–35.6 Ω−1cm2mol−1 range indicating
their non‐electrolytes nature.[40] The whole spectroscopic
analysis and thermal gravimetric data are presented in
the experimental part and Tables 1–3. The data displayed
that all complexes were formed in a molar ratio
(1 L:1 M) (Figure 2).
3.3 | Biological activity
Well diffusion method used to measure the antifungal
activity. Lab. of microbiology, Biology Department,
Faculty of Science and Arts, University of Jeddah,
KSA.[35–38] Both positive (Amphotericin B) and negative
(solvent, DMSO) controls were used in the technique.
The complexes and ligand were tested against four fungal
strains Aspergillus niger (A. niger), Aspergillus flavus
(A. flavus), Saccharomyces cerevisiae (S. cerevisiae) and
Candida albicans (C. albicans) cultured on Czapek Dox's
agar as a medium. In a typical procedure, a well was
made on the agar medium inoculated with the fungal
strains. The well was filled with the test solution
4.1 | 1H‐NMR spectrum
1
The H NMR for the Schiff base, Ethyl −6‐ethyl‐2‐(2‐
hydroxybenzylideneamino)‐4,5,6,7‐tetrahydrothieno[2,3‐
TABLE 1 The UV–Vis spectra and magnetic moments for the prepared complexes and the parent ligand
No.
π–π*, n–π*, CT and d‐d bands
d–d Transition
Geometry
μeff (BM)
(1)
(2)
272, 298, 338, 407
‐‐
‐‐
‐
2
275, 290, 338, 406, 483, 642, 860
2B2 → E(dxy → dxz,dyz)
distorted
octahedral
1.81
2B2 → B1(dxy → dx2 − y2
)
2
2B2 → A1(dxy → dz2)
2
3
(3)
(4)
273, 296, 338, 384, 404, 485, 509, 1031
274, 300,339, 386, 454, 539, 1073
3T2g(F) ← A2g(F)
octahedral
3.11
3.96
3
3T1g(F) ← A2g(F)
3
3T1g(P) ← A2g(F)
4
4T2g(F) ← T1g(F)
4
4A2(F) → T1(F)
4
4T1g(P) ← T1g(F)
2
(5)
(6)
275, 295, 336, 384, 520, 749, 1099
275, 295, 336, 384, 520, 749, 1099
2A1g ← B1g
distorted
octahedral
1.61
1.87
2
2B2g ← B1g
2
2Eg ← B1g
(7)
270, 300, 340, 410
‐‐‐
Dia.

SHAKDOFA ET AL.
5 of 12
TABLE 2 ESR parameters of VO2+and Cu2+ complexes
Complex No.
(2)
1.965
(5)
2.260
(6)
2.258
g||
g
2.040
1.99
2.057
2.125
2.056
2.123
┴
giso
A|| × 10−4 (cm−1
)
14.3
137.2
142
14.4
A
× 10−4 (cm−1
)
96.4
24
┴
FIGURE 2 Structure representation of metal complexes (2‐7)
Aiso × 10−4 (cm−1
)
69.7
59.4
164.7
54.5
g||/A||(cm)
‐
‐
158.6
This hydrogen chemical shift observed at high values of
δ characteristic to their bonding to the oxygen atom that
is lean to electronegativity in nature. This consequence
was confirmed by the signal chart of the prepared ligand
which showed that the notable decrease of the strength of
the signals (Figure 4). While the azomethine proton
H‐18C=N appeared as the singlet at δ = 8.76 ppm. The
aromatic protons H‐C21&24 can be observed as a doublet
at δ = 7.65 and 7.40 ppm with JHH equal to 7.6 and 8
G
4.56
4.64
ΔExy (cm−1
)
13717
19230
0.534
0.636
0.602
0.776
0.702
0.76
14684
21786
0.567
0.70
ΔExz (cm−1
)
‐
‐
2
K||
2
K⊥
‐
K2
‐
0.658
0.81
K
‐‐
&
8.05 consecutively while the aromatic protons
α2
β2
γ
0.415
0.714
0.79
H‐C22&23 appeared as multiple at 6.94.
0.959
‐
0.91
0.98
4.2 | Mass spectrum
b
agiso = (2g⊥+g||)/3 G = (g||‐2)/(g⊥‐ 2).
The spectrum of mass MS for the ligand (1) proof the sug-
gested chemical structure for the molecular ion peak m/z
equal 358 (100%) (Figure 5). Furthermore, many frag-
ments can be observed at 343, 329, 315, 301, 285 and
c]pyridine‐3‐carboxylate (HL) was measured in DMSO‐
d6. 1H‐NMR spectrum for the ligand (1) (Figure 3)
displayed a peak of hydroxyl proton at δ = 12.56 ppm.
TABLE 3 Thermogravimetric data of Schiff base complexes (2‐7)
Temp. range (°C) Loss in weight Found (calcd.) assignment
Composition of the residue
(2)
(3)
(4)
(5)
30–100
100–170
245–260
260–490
6.50 (6.88)
3.7 (3.44)
17.76 (18.34)
63.63 (53.97)
Dehydration process (2H2O)
[VO (HL)(SO4)(H2O)]
[VO (HL)(SO4)]
[VO (HL)]
Loss of coordinated water molecule
Loss of one sulphate ion (H2SO4)
Complex decomposition forming V2O5
V2O5
50–95
115–200
200–235
390–515
14.89 (14.97)
5.67 (5.99)
9.51 (9.88)
Dehydration process (5H2O)
[Co (L)(CH3COO) H2O)2]
[Co (L)(CH3COO)]
[Co (L)]
Loss of two coordinated water molecule
Loss of one acetate ion (CH3COOH)
Complex decomposition forming CoO
58.55 (56.70)
CoO
40–100
110–190
240–265
350–480
3.13 (3.4)
6.61 (6.81)
11.08 (11.23)
65.77 (64.44)
Dehydration process (H2O)
Loss of two coordinated water molecules [Ni (L)(CH3COO)]
Loss of one acetate ion (CH3COOH)
Complex decomposition forming NiO
[Ni (L)(CH3COO)(H2O)2]
[Ni (L)]
NiO
40–90
110–150
230–255
350–450
100–170
2.79 (2.92)
3.03 (2.92)
24.88 (25.78)
57.10 (55.43)
6.58 (6.98)
Dehydration process (2H2O)
[Cu (HL)Br2(H2O)]
[Cu (HL)Br2]
[Cu (HL)]
Loss of coordinated water molecule
Loss of two bromide ions (2HBr)
Complex decomposition forming CuO
CuO
Loss of two coordinated water molecules [Cu (L)(CH3COO)]
(6) 210–230
370–470
11.63 (11.5)
68.23 (66.09)
Loss of one acetate ion (CH3COOH)
Complex decomposition forming CuO
[Cu (L)]
CuO
(7)
30–60
220–271
275–375
4.1 (3.60)
11.39 (11.89)
67.57 (68.22)
Dehydration process (H2O)
Loss of one acetate ion (CH3COOH)
Complex decomposition forming ZnO
[Zn (L)(CH3COO)]
[Zn (L)]
ZnO

6 of 12
SHAKDOFA ET AL.
1
FIGURE 3 The HNMR spectrum of
the Schiff base (1)
1
FIGURE 4 The Deuterated HNMR spectrum of the Schiff base (1)
255 owing to the loss of methyl, ethyl and finally carbox-
ylic group. In addition, there are main fragments
appeared at m/z 238 belong to fragment ethyl 6‐ethyl‐
4,5,6,7‐tetrahydro‐[2,3‐c]‐thieno[5,4‐c]pyridine‐3‐carbox-
ylate, the second peak at m/z = 121 owing to the presence
of fragment 2‐(iminomethyl)phenol. The peaks at m/
z = 135, 105, 94, 77 expected to be for fragment 4,7‐
dihydrothieno[2,3‐c] pyridine, phenylmethanimine, phe-
nol and benzene respectively.
4.3 | IR spectra
The data of infrared spectra of the Schiff base (1)
displayed a broad band at 3435 cm−1 and a band at
1278 which ascribed to the hydroxyl and C‐OH of pheno-
lic moiety. The carbonyl group ν(C=O) of carboxylate
moiety was detected at 1692 cm−1, while the azomethine
group ν(C=N) appeared at 1602 cm−1. The manner of
chelation can be recognized by matching the IR spectrum

SHAKDOFA ET AL.
7 of 12
FIGURE 5 Mass spectrum of the Schiff base (1)
of the complexes with the original IR spectrum of Schiff
base (1). The matching clear that the Schiff base (1)
works either as:
(N atom) and carbonyl (O atom) groups as found in
complexes (3–4) and (6–7). This type of coordination
was recommended by four pieces of evidences as
follow:
1. Neutral tridentate ligand chelated to the VO2+ and
Cu2+ ion via the azomethine (N atom), and the pro-
tonated hydroxyl group (O atom) of phenolic moie-
ties as in complexes (2) and (5). This type of
coordination was recommended by four pieces of evi-
dences as follow:
i. The misplaced of ν(OH) band signifying the
engagement of the deprotonated phenolic
hydroxyl group which was confirmed by the posi-
tive shift in the position of the phenolic C‐O band.
ii. The azomethine group shows a negative shift in
both location and intensity for (C=N) groups by
17–42 cm−1, respectively.
2.
i. The shift toward the negative of the υ (OH) group
and the positive shift of phenolic C‐OH proof the
contribution of the hydroxyl group.
iii. The carbonyl group in the azomethine showed a
negative shift in both location and intensity by
(41–91 cm−1).
ii. The azomethine group showed a shift towards
negative in both position and intensity, valued
by 16 and 46 cm−1 consecutively.[41–44]
iii. The carbonyl group showed a shift towards nega-
tive in both position and intensity, valued by 28
and 80 cm−1 consecutively.
iv. The existence of new bands at 541, 534 and 457,
442 cm−1 for complexes (2) and (5) can be
signified to the ν(M ← O) and ν(M ← N)
consecutively.[45]
iv. The existence of IR bands located at the ranges
503–541 and 457–499 cm−1 for the prepared com-
plexes can be ascribe to the ν(M–O) and ν(M ← N)
consecutively.[45]
In case of VO2+ complex, a recent band signal
appeared at 984 cm−1, that ascribed to ν(V=O).[46] The
presence of two new bands in the acetate complexes
(3–4) and (6–7) in the 1531–1555 and 1339–1351 cm−1
are imputing to both the symmetric and asymmetric
stretching band vibration of the acetate ion [(νas (COO−)
and νs (COO−))]. The difference values (Δ) between νas
(COO−) and νs (COO−) in (3–4) and (6–7) were in range
183–206 cm−1 implying to mono‐chelated acetate
3. Monobasic tridentate ligand, forming a covalent
bond by the (O atom) of deprotonated hydroxyl group
of phenolic moieties and coordinated via azomethine

8 of 12
SHAKDOFA ET AL.
group.[47–49] The sulfate complex (2) demonstrated bands
at 1120, 1038 and 727 cm−1 distinctive for the mono‐che-
lated sulfate group, where the low conductance values of
the compounds affirmed the later state.[25,47]
are equal to 3.11 and 3.96 BM consecutively, which con-
firmed electronic configuration with two and three
unpaired electrons in an octahedral environment.[60,61]
4.6 | ESR spectra of VO2+ and Cu2+
complexes
4.4 | Electronic Absorption Spectra of the
prepared complexes and parent ligand
The ESR spectra for VO2+ and Cu2+ complexes provide
more information about their geometry. The compounds
were recorded on ESR at 9.8 GHz in polycrystalline state
at 25 °C Table 2.The ESR of VO2+ complex (d1, 51V,
I = 7/2) shows axially anisotropic spectrum with eight
line investigating to g⊥>g||and A||> > A⊥relationship,
this is true for a distorted octagonal structure that refers
to the dxy ground state.[62] It demonstrates two sets of res-
onance components, due to the parallel (g||) and perpen-
dicular (g⊥) features which a signifying to axially
symmetric anisotropy. These data demonstrating that
there is an interaction between the spin of both vanadium
nucleus and electron. The super‐hyperfine splitting of
nitrogen atom does not appear on vanadium signals,
demonstrating that the interactive happens between the
spin of electron and ligand.[63] Such values are demon-
strating that the VO2+ has a deformed octahedral struc-
ture.[55,64] The α2 and β2 (molecular orbital coefficient)
of VO2+ complex were evaluated utilized the subsequent
equations.[54]
The EAS of the compounds are outlined in Table 1. The
UV–Vis. spectrum of Schiff base (1) demonstrated, three
absorption bands at 272, 298, 338 nm because of the
intra‐ligand π‐π* transition in the benzenoid moiety that
nearly unchanged on chelation and n → π* transitions of
the azomethine and carbonyl groups.[50,51] The
bathochromic shift of these absorption bands on chela-
tion may be owing to the participation of a lone pair of
electrons of N and O atoms to the metal ion, demonstrat-
ing the participation of azomethine and carbonyl groups
in chelation.[52] Additionally, the band at 407 nm may
be assigned to the transition within the molecule, actually
an intramolecular charge transfer interaction.[52,53]
The VO2+ complex UV–Vis. spectrum demonstrated
three beaks located at 860, 642 and 483 nm, attributed
to the electronic transition “2B2→2E(dxy→dxz,dyz),
2
2B2→2B1(dxy→dx2−y2) and B2→2A1(dxy→dz2)” (Table 1)
which are harmonious to an octahedral skeletal for
VO2+complexes (Figure 2).[54–57] However, the Co2+ com-
plex (3) spectrum demonstrated three bands at 1073, 539
and 454 nm which is ascribable to “4T2g(F)←4T1g(F),
À
Á
2:0023 − g‖ E
α2 ¼
8λβ2
4
4A2(F)→4T1(F) and T1g(P)←4T1g(F)” transition in octa-
hedral ligand field.[56] The UV–Vis. spectrum for Ni2+
complex demonstrated three peaks originates at 1031,
539 and 485 that ascribable to electronic transitions
“3T2g(F)←3A2g(F), 3T1g(F)←3A2g(F) and 3T1g(P)←3A2g(F)”
which are compatible with a Ni2+ion in an octahedral
skeletal (Figure 2).[56,58] The UV–Vis. spectra of Cu2+
complexes (5) and (6) demonstrated three bands origi-
nates at 1083, 749 and 520 nm and 1068, 681, 459 nm con-
secutively which are ascribable to electronic transitions
ꢀ
ꢁ
ꢀ
ꢁ
À
Á
A‖
P
A⊥
P
β2 ¼ 1:17 −
þ
þ g‖ − 0:36g⊥ − 0:64ge
“where P = 128 × 10−4 cm−1, λ = 135 cm−1 and E is the
electronic transition energy of 2B2
→
2E”. The higher
value for β2 with respect to α2 denoted that in‐plane π‐
bonding is less covalent than in‐plane σ‐bonding.[54,65]
The β2 (in‐plane π‐bonding parameter) value is compati-
ble with the data of VO2+ complexes of acetyl acetone
and Schiff base published by Walter, Patron McGarvey,
Dodwad and Raman.[64–68]
2
“2A1g←2B1g, B2g←2B1g, 2Eg←2B1g” denoting the com-
plexes has a strong tetragonal distorted octahedral geom-
etry around metal ion (Figure 2).[56]
The Cu2+‐complexes (5–6) ESR spectra displayed that
the complexes demonstrate anisotropic signals with g||
(2.260, 2.258), g⊥(2.057, 2.056) and giso (2,124, 2,123)
values which are distinguishing to a types with a d9
arrangement and having an axial symmetry specie of a
d(x2‐y2) ground state, that is recognized for Cu2+ com-
plexes.[39,69] This g‐values support that the Cu2+‐com-
plexes (5–6) adopted an octahedral or square‐planar
geometry.[70,71] The ESR data shows g|| > g > 2.0023,
signifying that the structure around the Cu2+ ion are
deformed.[72] The term G is related to g‐values “G =
4.5 | Magnetic moment (μeff)
measurements
The μeff data of polycrystalline metal complexes at 298 °K
are shown in Table 1. The data showed that VO2+, Co2+
,
Ni2+ and Cu2+ are paramagnetic but Zn2+ is diamagnetic.
The μeff for VO2+ and Cu2+complexes (2) and (5–6) were
found to have values lying between 1.61 to 1.87 BM corre-
sponding to one unpaired electron system (1.73 BM).[59]
The μeff values for Co2+ and Ni2+ complexes (3) and (4)
┴

SHAKDOFA ET AL.
9 of 12
(g||‐2)/(g ‐2)”.[73] If G < 4.0, significantly the exchange
bonding.[81] The γand βcoefficients (out‐of‐plane and in‐
plane π‐bonding) can be could be assessed utilized the
subsequent equations.[76]
┴
coupling is present, if G > 4.0, thus domestic tetragonal
axes are align parallel or only partially misalign. Cu2+
‐
complexes (5–6) demonstrate G equal to 4.56 and 4.64,
signifying the occurrence of tetragonal axes. In addition,
the value of g||/A||can be used as a diagnostic of stereo-
chemistry.[74] If the value ranged from 105 to 135 the
geometry is square‐planar while if it is ranged from 150
to 250 the geometry is tetrahedrally distorted octahedral
150–250 cm−1. The g||/A||for complexes (5–6) are 164.7
and 158.6 confirmed that the geometry of Cu2+ com-
plexes (5–6) are tetragonally distorted octahedral.[48,73]
Kivelson and Neiman display that for the Cu2+‐com-
plexes the g||‐valuable can be utilized to depict the
metal–ligand bond aspect. If the g||‐valuable is larger than
2.3 the environmental is principally ionic while if it is
smaller than 2.3 the environmental is principally cova-
lent.[75] For Cu2+ complexes (5–6) the g||‐values are
2.260 and 2.258 which signify that the bonds are princi-
pally covalent bonds.[74] The g‐values could be concerned
to the parallel (k||) and perpendicular (k⊥) parts of the
orbital reduction factor (k) as in these equations.[76–79]
α2γ2 ¼ K⊥
2
2
2
α2β ¼ K‖
The Cu2+ complexes (5–6) γ2 values are 0.91 and 0.98
while the β2 values are 0.76 and 0.79 consecutively, sug-
gesting the covalency nature of out‐of‐plane and in‐plane
π‐bonding.[48,76]
4.7 | Thermal analysis
To attain additional informative data concerned with the
stability and nature of water molecules in the complexes,
the TG analysis for (2–7) scanned in the temperatures 25
to 800 °C. The data of thermo‐analysis are cited in Table 3
and demonstrated that there is a clear correspondence
between the weight loss of the calculating and proposed
formulae. These are signified that the (2–7) are generally
decayed in three or four phases that could be understood
as follows:
ꢂ
ꢃ
ꢃ
Á
2
k∥ ¼ g∥ − 2:0023 ΔExy=8λ°
1. The dehydration process occurs through 30–100 °C
accompanied by weight loss ranged from 2.79(2.92)
to 14.89(14.97) % matching to the evolution of one,
two or five water molecules as in complexes (2–5)
and (7).
2. The second phase appears in (2–6) occur at 100 and
200 °C with losing in weight ranged from 3.03(2.92)
to 6.58(6.98) % which ascribed to the excluding of
the chelated water molecules.
3. The anions (sulfate, bromide or acetate) eliminated
from the complexes at temperature range 200 to
271 °C with weight lose 9.51(9.88) to 24.88(25.78) %.
4. Finally, the complete disintegration of the complexes
through the oxidation of the organic part occur
through 260–515 °C range forming metal oxide.
ꢂ
k⊥ ¼ g∥ − 2:0023 ΔExz=2λ°
2
À
2
2
¼ k∥ þ 2k⊥ =3
“Where λo is free Cu2+ ion for the spin orbit coupling
(‐828 cm‐1) ΔExy and ΔExz are the electronic transitions
2B1g→ 2Eg and 2B1g→ 2B2g consecutively”. The calculating
values of k|| , k⊥ and k2 demonstrated that k|| < k2
supporting that the ground state for complexes (5–6) is
2B1. Additionally, when the environmental is covalent,
k < 1 but if more than 1 the environmental is ionic.
The k value for complexes (5–6) are 0.776 and 0.810 con-
secutively which are smaller than the unity denoting the
covalency nature of the environmental that agrees with
the data given by the g||‐values.[78–80]
2
2
2
4.8 | Biological activity
Fungicide activity of the compounds was assessed by Well
Diffusion technique against A. niger, A. flavus, S.
cerevisiae and C. albicans. The screening data (Table 4)
showed that the activity of the parent Schiff base‐(1)
equal or more than Amphotericin B against C. albicans
and S. cerevisiae within inhibition zone, (MIZ, mm)/activ-
ity index (AI%) equal to 14(100) and 23(104.5). while the
parent Schiff base‐(1) activity against A. niger, A. flavus, is
less than Amphotericin B. Some complexes were more
effective than both Amphotericin B and the parent Schiff
base‐(1). The most biologically active compounds against
A. niger is complex (6) with MIZ equal to 20 (AI 117.6),
The α2 (in‐plane sigma bonding parameters) valuable
could be assessed by the subsequent equations.[39,71]
ꢀ
ꢁ
ꢂ
ꢃ
3
7
A∥
P
α2 ¼ g∥ − 2:0023 þ ðg⊥ − 2:0023Þ −
þ 0:04
“Where P is the free ion dipole expression equal
0.036”. If α2 equal to 1, the bond could be pure ionic
but if it is equal to 0.5, the bond could be pure covalent,
assumption that P = 0.036 cm−1 and K = 0.43.[39,71] The
Cu2+‐complexes (5–6) α2 values are 0.702 and 0.714 sug-
gesting the covalency nature of in‐plane sigma

10 of 12
SHAKDOFA ET AL.
TABLE 4 Antifungal activities of ligand and its complexes against A. niger, A. Flavus, S. cerevisiae and C. albicans
A. niger
A. flavus
S. cerevisiae
C. albicans
Compound
No.
inhibition
zone (mm)
Activity
Index (%)
inhibition
zone (mm)
Activity
Index (%)
inhibition
zone (mm)
Activity
Index (%)
inhibition
zone (mm)
Activity
Index (%)
Amphotericin B
17
14
11
14
13
15
20
16
100
19
14
19
13
15
28
26
30
100
22
23
21
17
30
25
15
29
100
14
14
16
16
15
20
24
21
100
Ligand
(2)
82.4
64.7
82.4
76.5
88.2
117.6
94.1
73.7
100
104.5
95.5
100
114.3
114.2
107.1
142.9
171.4
150
(3)
68.4
78.9
147.4
136.8
157.9
77.3
(4)
136.3
113.6
68.2
(5)
(6)
(7)
131.8
complex (7) against A. Falvus with MIZ equal to 30 (AI
157.9), complex (4) against S. cerevisiae with MIZ equal
to 30 (AI 136.3), and complex (6) against C. albicans with
MIZ equal to 24 mm (AI 171). The rest complexes showed
a medium activity against the four species with MIZ in
the ranges of 11–16 mm (AI 64.7–94.1), 13–28 mm (AI
68.4–147.4), 15–29 mm (AI 68.2–131.8) and 15–21 mm
(AI 107.1–150). The activity order is sorted in Figure 6.
The high biological activity of the prepared complexes
may attribute to the central metal ion lipophilicity that
build on the bases of Overtone's concept and Tweedy's
chelation theory. In conventionality with Overtone's con-
cept of cell permeability, the lipophilic soluble complexes
can traverse across the cell membrane, so the lipo‐
solubility are consisting a fundamental factor that affect
the antimicrobial activity. On chelation, the polarity of
metal ion become remarkably more restrictive due to
the obstructing of the orbital in the ligand, along with
the engagement of the positive charge of the metal ion
partially with donor atoms. Additionally, this encourages
the allocation of π‐electrons across the chelating ring and
this fundamentally increases the complexes lipophilicity,
which leading to raising the capability of the complexes
to penetrate the membranes of the lipid and hinder the
metal binding sites of the cell enzymes. The synthesized
complexes also break down the respiratory operation of
the cells, which lead to the generation of the proteins,
and intercept microbe cells growth.[82–84]
FIGURE 6 The fungicide activity order for the ligand and its complexes against A. niger, A. Flavus, S. cerevisiae and C. albicans

SHAKDOFA ET AL.
11 of 12
[8] E. S. A. El‐Samanody, S. A. AbouEl‐Enein, E. M. Emara, Appl.
Organomet. Chem. 2018, 32, e4262.
5 | CONCLUSION
A series of VO2+, Co2+, Ni2+, Cu2+, and Zn2+ complexes
(Schiff base parent ligand) prepared under mild condi-
tions. The Schiff base and the new six complexes have
been characterized by using different analytical and spec-
troscopic techniques. The entire spectroscopic and ana-
lytic data revealed that the Schiff base (1) combined
with the metal ions as a neutral or as a monobasic
tridentate ligand via azomethine nitrogen, ketonic car-
bonyl oxygen atoms and protonated/deprotonated pheno-
lic hydroxyl group that give finally an octahedral or
distorted octahedral geometry. The antifungal screening
assignment were tested for the whole synthesized com-
pounds against A. niger, A. Flavus, S. cerevisiae and C.
albicans. The resulted data displayed that, the whole
compounds had a positive activity towards many fungi
under study particularly C. albicans. While only complex
(6) showed a good antifungal activity against A. niger
with MIZ, mm (IA%) equal 20 (117.6%), even as com-
plexes (5–7) showed also a well satisfying biological activ-
ity against A. Falvus with MIZ, mm (IA%) 28(147.4),
26(136.8) and 30(157.9) respectively. In contrast com-
pounds (1), (4–5) and (7) displayed an exceptional good
result against S. cerevisiae with MIZ, mm (IA%)
23(104.5), 30(136.3), 25(113.6) and 29(131.8). These
results encourage our teamwork to continue preparing
more complexes from a Schiff base with a 4,5,6,7‐
tetrahydrothieno[2,3‐c] pyridine moiety in the future.
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How to cite this article: Shakdofa MME, Labib
AA, Abdel‐Hafez NA, Mousa HA. Synthesis and
Characterization of VO2+, Co2+, Ni2+, Cu2+ and
Zn2+ Complexes of a Schiff base ligand derived from
ethyl 2‐amino‐6‐ethyl‐4,5,6,7‐tetrahydrothieno[2,3‐
c]pyridine‐3‐carboxylate and their Investigation as
fungicide Agents. Appl Organometal Chem. 2018;
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