Biological and electrochemical studies of Co2+, Ni2+, Cu2+, Zn2+ and Cd2+ metal complexes of Schiff base ligand derived from 4-amino benzoic acid and isonicotinic hydrazide

Article abstract of DOI:10.1007/s13738-020-02148-x

Ten metal complexes of Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺ and Cd²⁺ were synthesized by two novel Schiff bases derived from condensation of m-pthalaldehyde with 4-amino benzoic acid and isonicotinic hydrazide. The

Full text of DOI:10.1007/s13738-020-02148-x

Journal of the Iranian Chemical Society
https://doi.org/10.1007/s13738-020-02148-x
ORIGINAL PAPER
Biological and electrochemical studies of Co2+, Ni2+, Cu2+, Zn2+
and Cd2+ metal complexes of Schif base ligand derived from 4‑amino
benzoic acid and isonicotinic hydrazide
Pankaj Kosti1 · Gowhar Ahmad Naikoo2 · Ratnesh Das1 · Neha Mishra1 · Sushil Kashaw3
Received: 18 July 2020 / Accepted: 21 December 2020
© Iranian Chemical Society 2021
Abstract
Ten metal complexes of Co2+, Ni2+, Cu2+, Zn2+ and Cd2+ were synthesized by two novel Schif bases derived from conden-
sation of m-pthalaldehyde with 4-amino benzoic acid and isonicotinic hydrazide. The as-synthesized metal complexes were
characterized and explored by diferent spectroscopic techniques. FT-IR spectra have confrmed the presence of C=N bands
as well as UV–Vis spectroscopy in both Schif bases KM-1 and KM-2. All as-prepared compounds were evaluated for the
antimicrobial activities against the Escherichia coli and Propionibacterium acnes. KM-1 and its metal complexes have shown
efcient results compared to KM-2. The electrochemical study of M2+ complexes by cyclic voltammograms in electrolyte
solution (Pt electrode) demonstrated electrochemically irreversible oxidative and reductive responses.
Keywords Schif-base · Transition metal complex · 4-Amino benzoic acid · Isoniazid · Spectral and antibacterial study ·
Cyclic voltammograms
Introduction
including anti-bacterial, anti-fungal and anti-tumor activity
[3–6]. Schif base metal complexes show signifcant role in
diferent felds of synthetic chemistry like industrial chem-
istry, agricultural, etc. Schif bases could be a catalyst for
diferent synthetic organic reactions, biologically active
compound, dyes, plant growth regulators, etc. [7]. They dis-
play a phenomenal role in anti-fungal and anti-tubercular
activities [5, 6, 8–11]. Many metal complexes of Schif bases
show excellent catalytic activity in various aqueous reactions
at high temperature (>100 °C) which is ecofriendly [12].
Hugo Schif frstly synthesized Schif base compounds
by the nucleophile condensation of an aldehyde and an
amine in 1864 [13]. Schif base acts as a ligand and it is
able to coordinate metals through its imine nitrogen and
another donating group, usually bonded with aldehyde
group [14]. Research in invention of these Schif base
metal complexes is very fast-growing research feld due
to their wide range of possible structures as ligands which
depends on the structures of aldehydes and amines [15].
The structural changes via substitutions in the reactants
sometimes completely divert the desired reaction and
enforce to a completely diferent course of reactivity. The
changes in structure of aldehyde and amine can completely
change the reaction and it can show the entirely diferent
reactivity [16]. Schif base ligands and their complexes
Heterocyclic compounds are widely used as a pharmaceu-
tically indispensible compounds. Schif bases are one of
those heterocyclic compounds which are used as versatile
ligands. The ability of Schif bases for intermolecular hydro-
gen bonding between oxygen and nitrogen atoms leads to
ligand metal complexes in coordination chemistry [1]. A
large number of Schif bases and their metal complexes was
investigated in last decade because of their extreme biologi-
cal properties [2]. These organometallic complexes are key
active pharmaceutical gradient in medicinal and pharmaceu-
tical industries. They show various biological applications
* Ratnesh Das
ratneshdas1@gmail.com
1
Heterocyclic Synthesis and Electro-analytical Laboratory,
Department of Chemistry, Dr. Harisingh Gour Central
University, Sagar, India
2
Department of Mathematics and Sciences, College
of Arts and Applied Sciences, Dhofar University, Salalah,
Sultanate of Oman
3
Division of Medicinal and Computational Chemistry,
Department of Pharmaceutical Sciences, Dr. Harisingh Gour
Central University, Sagar, India
Vol.:(0123456789)
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Journal of the Iranian Chemical Society
are used as an intermediate in various enzymatic reactions
because of their interactions between amino groups and
enzymes [17]. Schif base ligand formed from the conden-
sation of KM-1 and KM-2 and its metal complexes were
reported in this paper. Moreover, an electrochemical and
antimicrobial evaluations of these complexes are also dis-
cussed in this paper.
Experimental
Materials
All reagents and solvents used in this work were purchased
from Sigma Aldrich. Solvents were analytical grad as per
receive, used purifed and dried as per standard procedure.
The Melting points of ligands and complexes were deter-
mined on electrochemical melting apparatus. Infrared spec-
troscopic analysis was done by FT-IR spectroscopy, Bruker
and UV absorption study by rigol-360-UV spectroscopy
instrument, NMR spectra obtained by Bruker 500 MHz
spectrometer in instrument. Mass spectra obtained by waters
xevo G2S QT of. The cyclic voltammograms obtained by
software NOVA version 1.10.1.9.
Isoniazid used as an amine, shows various biological
activities such as antibacterial, antiviral, antifungal and
anti-tuberculosis. Literature clearly demonstrates that the
metal complexes of this amine have also good activity.
Isoniazid based metal complexes can be efectively used
as anti-tuberculosis agents. They showed a vast variety of
antimicrobial activities such as antibacterial, antiviral and
antifungal [18].
The aim of the current study was to prepare new
ligands, derived from 4-amino benzoic acid and isonia-
zid. We have also explored complexes of certain 3d and 4d
series metals with the ligands KM-1 and KM-2. The novel
Schif bases were synthesized by the reaction of 4-amino
benzoic acid and isoniazidand with m-pthalaldehyde (2:1)
in ethanol. These ligands have excellent lone pair donor
ability with transition metals ion. The ligands along with
complexes of divalent metal ions such as Co2+, Ni2+, Cu2+,
Zn2+ and Cd2+ were characterized by spectroscopy and
physical methods for evaluation of their photo-physical,
biological and electrochemical studies.
Synthesis of Schif bases (KM)
KM-1 ligand was synthesized in ethanolic solution (20 mL)
of m-pthalaldehyde (0.134 g, 1 mmol) and 4-aminobenzoic
acid (0.274 g, 2 mmol) while as KM-2 was synthesized in
ethenolic solution (20 mL) of m-pthalaldehyde (0.134 g,
1 mmol) by adding of isonicotinic hydrazide (isoniazid)
(0.272 g, 2 mmol). To ethanolic solution of m-pthaladehyde
in a round bottom fask and fx on a heating magnetic stir-
rer was added amine solution as dropwise at 75–80 °C and
refuxed for 6–7 h. White/pale yellow colored precipitate
obtained and allowed to cool down at room temperature,
fltered and dried, then recrystallized from ethanol and water
(2:1 ratio). The progress of reaction was monitored by TLC
plate under UV–Vis chamber (Schemes 1, 2).
Electron donating and accepting ability of a ligands are
confrmed through electrochemical studies [19]. Our study
are based on the redox behavior of the Schif base and
metal complex chelates, where the electron accepting and
donating properties of the ligands were confrmed through
electrochemical studies. By varying several experimental
parameters such as the concentration, the speed of sweep
of the electric feld of study etc. diferent studies can be
made out of electrochemical studies [20]. Not only con-
centration of solution even the pH of solution also afects
the cyclic voltammograms or in other words its electro-
chemical behavior [21]. Scan rate may also change the
voltammograms behaviors [22]. Electrocatalytic activity
of various Schif bases have been also studied in recent
researches in diferent electrolytic solutions [23].
Synthesis of Complexes
To the methanolic solution of ZnNO2, CoNO2, CuNO2,
CdNO2 and NiNO2 (1 mmol, in 10 mL MeOH) was added
Schif base (KM-1 and KM-2) (1 mmol) in the presence of
4–5 mL KOH and was stirred for 6–7 h. After completion
of the reaction, the solution was concentrated to 10 mL
and was stirred for 3–4 h under refux. Then the reaction
mixture was cooled and the precipitated complexes was
fltered, washed with ethanol followed by hot water (2:1
Scheme 1 Synthesis
NH2
CHO
of 4,4′-(((1E,1′E)-1,3-
phenylenebis(methanylylidene))
bis(azanylylidene))dibenzoic
acid
Ethanol
N
N
Reflux
CHO
HO
OH
COOH
O
O
KM-1
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Journal of the Iranian Chemical Society
ratio) and dried. The reaction scheme for the synthesis of
metal complex is given below (Schemes 3, 4).
(N′,N″E,N′,N″E)‑N′,N″‑(1,3‑phenylenebis(methan‑1‑yl‑1‑y
lidene))diisonicotinohydrazide (KM‑2) White color powder,
m. p.: 228–231 °C, Yield; 0.333 g (81%), FT-IR (KBr):
v̄ = 3740.52 (O–H medium, broad), 1687.47 (–C=N–),
1508.15 (=C–H), 1338.43 (=C–H), 825.69 (C–H), 747.06,
(C–H), 1H NMR (500 MHz, DMSO-d6): δ=7.45 (d), 7.85
(s), 7.93 (d), 8.1 (d), 8.4 δ (m), 8.7 (s), 9.17 (m) ppm; UV–
Vis: λmax =210–307 nm; Chemical Formula: C20H16N6O2,
Molecular Weight: 372.38, Elemental Analysis: C, 64.51;
H, 4.33; N, 22.57; O, 8.5910.02.
Characterization of ligands
4,4′ ‑(((1E,1′ E)‑1,3‑phenylenebis(methanylylidene))
bis(azanylylidene))dibenzoic acid (KM‑1) Pale brownish color
powder; M. p.: 218–221 °C; Yield: 0.365 g (87%), FT-IR
(KBr): v̄ = 3852.58 (O–H medium, broad), 3739.95 (O–H
medium, broad), 3615.69 (O–H medium, broad), 3349.96
(O–H medium, broad), 2970.35(C–H aromatic proton
strong), 2875.07 (C–H aromatic proton strong), 2551.63
(C–H aromatic proton strong), 2358.68 (C–H aromatic pro-
ton strong), 1680.21 (–C=N–), 1633.76 (–C=N–), 1569.42
(C=C), 1444.90 (C=C), 1383.29 (C=C), 1288.26 (C=C),
1083.91 (C–H bending), 1040.73 (C–H bending), 918.41
(C–H bending), 880.28 (C–H bending), 785.49 (C–H bend-
ing), 746.23 (C–H bending), 674.18 (C–H bending) cm−1;
1H NMR (500 MHz, DMSO-d6): δ = 7.4 (m), 7.57δ (s),
7.85δ (s), 8.15 (s), 10.0δ (s), 8.2 (s) 8.37 (d) ppm; UV–
Vis: λmax = 205–275 nm; Chemical Formula: C22H16N2O4
Molecular Weight: 372.37 Elemental Analysis: C, 70.96; H,
4.33; N, 7.52; O, 17.19 s.
Characterization of complexes
4, 4′ ((1E, 1′ E)(1, 3phenylenebis(methanylylidene))
bis(azanylylidene))dibenzoic acid, cadmium(II) salt
(KM‑1[Cd]) Pale yellow color powder; M. p.: 269–272 °C;
Yield: 0.666 g (68%); FT-IR (KBr): v̄ =3852 (O–H medium,
broad), 3740.98 (O–H medium, broad, 3616.55 (O–H
medium), 2361.64 (H–C aromatic proton strong), 1744.40 (–
C=N–), 1687.64 (–C=N–), 1642.70 (C=O strong), 1525.81
(=C–H), 1462.13 (=C–H), 1389.39 (=C–H), 993.06 (–C–
H), 766.78 (–C–H), 679.94 (–C–H), 610.43 (C–H), 574.20
(N–Cd), 551.14 (N–Cd), 540.25 (O–Cd), 527.87 (O–Cd)
cm−1; UV–Vis: λmax = 207–264 nm, Chemical Formula:
C44H30CdN4O82+; Molecular Weight: 855.14, Elemental
Analysis C, 61.80; H, 3.54; Cd, 13.15; N, 6.55; O, 14.97.
Scheme 2 Synthesis of
N′,N‴-((1E,1′E)-1,3-
H
N
O
CHO
N
N
H2N
H
N
H
N
phenylenebis(methanylylidene))
di(isonicotinohydrazide)
N
N
Ethanol
Reflux
O
O
CHO
N
KM-2
Scheme 3 Synthesis of metal
complexes from ligand-
1(KM-1)
N
N
KOH
2+
M
N
N
M
HO
OH
Methanol, reflux
3-4 hr
HO
OH
O
O
O
O
Complexes of KM1
M = Co(II), Ni(II), Cu(II), Zn(II), Cd(II)
Scheme 4 Synthesis of metal
complexes from ligand-2
(KM-2)
N
O
N
O
KOH
N
N
N
N
M2+
N
N
M
Methanol, reflux
3-4 hr
HO
OH
N
N
N
N
Complexes of KM2
M= Co(II), Ni(II), Cu(II), Zn(II), Cd(II)
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Journal of the Iranian Chemical Society
Yield: 0.473 g (73%); FT-IR (KBr): v̄ = 3852.13 (O–H
medium, broad), 3740.36 (O–H medium, broad), 3680.67
(O–H medium, broad), 2358.73 (C–N=N strong), 1687.32
(–C=N–), 1457.30 (=C–H), 1170.88 (C–H), 1048.87
(C–H), 973.93 (C–H), 855.56 (C–H), 800.33 (C–H), 680.40
4,4′ ‑((1E,1′ E)‑(1,3‑phenylenebis(methanylylidene))
bis(azanylylidene))dibenzoic acid, cobalt(II) salt
(KM‑1[Co]) Pale brown color powder; M. p.: 275–277 °C;
Yield: 0.677 g (73%); FT-IR (KBr): v̄ = 3852.93 (O–H
medium, broad), 3741.12 (O–H medium, broad), 2360.71
(H–C aromatic proton strong), 1687.53 (–C=N–), 1548.33
(–C–H), 1387.51 (=C–H), 762.20 (–C–H), 679.20
(C–H), 609.23 (C–H), 552.65 (Co–N), 528.30 (Co–O)
cm−1; UV–Vis: λmax = 208–258 nm; Chemical Formula:
C44H30CoN4O82+; Molecular Weight: 801.66, Elemental
Analysis: C, 65.92; H, 3.77; Co, 7.35; N, 6.99; O, 15.97.
(C–H)568.18 (Cd–N), 527.03 (Cd–O) cm−1; UV–Vis:
2+
λmax =209–288 nm; Chemical Formula: C20H16CdN6O2
,
Molecular Weight: 486.04, Elemental Analysis: C, 49.55;
H, 3.33; Cd, 23.19; N, 17.34; O, 6.60.
(4Z,4′Z,N′,N″E,N′,N″E)N′,N″(1,3phenylenebis(meth
anylylidene))diisonicotinohydrazonic acid, cobalt salt
(KM‑2[Co]) Brownish color powder; M. p.: 257–260 °C;
Yield: 0.421 g (71%); FT-IR (KBr): v̄ = 3835.33 (O–H
medium, broad), 3740.04 (O–H medium, broad), 2358.09
(C–N=N strong), 1686.64 (–C=N–), 1503.75 (=C–H),
1386.90 (=C–H), 1169.28 (C–H), 973.82 (C–H), 848.87
(C–H), 794.33 (C–H), 682.24 (C–H), 585.04 (Co–N),
528.50 (Co–O) cm−1; UV–Vis: λmax =212–301 nm; Chemi-
cal Formula: C20H16CoN6O22+ Molecular Weight: 431.07,
Elemental Analysis: C, 55.69; H, 3.74; Co, 13.66; N, 19.48;
O, 7.42.
4 , 4 ′ ‑ ( ( 1 E , 1 ′ E ) ‑ ( 1 , 3 ‑ p h e n y l e n e b i s ( m e t h a n y l y l i d
ene))bis(azanylylidene))dibenzoic acid, zinc(II) salt
(KM‑1[Zn]) Brown color powder; M. p.: 265–268 °C;
Yield: 0.707 g (76%); FT-IR (KBr): v̄ =3435 (O–H medium,
broad), 2357.39 (H–C aromatic proton strong),1620.47 (–
C=N–), 1558.68 (–C–H), 1387.65 (=C–H), 1153.86 (–C–
H), 914.13 (C–H), 768.89 (C–H), 687.04 (C–H), 555.85 (N–
Zn) cm−1; UV–Vis: λmax =206–264 nm; Chemical Formula:
C44H30N4O8Zn2+; Molecular Weight: 806.134,Elemental
Analysis: C, 65.40; H, 3.74; N, 6.93; O, 15.84; Zn, 8.09.
(4Z,4′Z,N′,N″E,N′,N″E)N′,N″(1,3phenylenebis(methanylylid
ene))diisonicotinohydrazonic acid, zinc salt (KM‑2[Zn]) White
color powder; M. p.: 286–288 °C, Yield: 0.408 g (68%);
FT-IR (KBr): v̄ =3852.36 (O–H medium, broad), 3740.05
(O–H medium, broad), 3680.21 (O–H medium, broad),
3615.95 (O–H medium, broad), 2358.56 (C–N=N strong),
1744.46 (–C=N–), 1687.40 (–C=N–), 1652.66 (–C=N–),
1507.89 (–C–H), 1383.93 (=C–H), 1169.50 (–C–H),
1048.11 (–C–H), 973.26 (–C–H), 848.96 (–C–H), 677.73
4,4′ ‑((1E,1′ E)‑(1,3‑phenylenebis(methanylylidene))
bis(azanylylidene))dibenzoic acid, nickel(II) salt
(KM‑1[Ni]) Greenish color powder; M. p.: 276–279 °C;
Yield: 0.640 g (69%); FT-IR (KBr): v̄ = 3835.04 (O–H
medium, broad), 3741.20 (O–H medium, broad), 3616.79
(O–H medium, broad), 2361.55 (H–C aromatic proton
strong),1687.77 (–C=N–), 1620.51 (–C=N–), 1553.39
(–C–H), 1392.02 (=C–H), 1152.39 (–C–H), 921.11 (C–H),
770.95 (C–H), 687.76 (C–H), 609.78 (C–H), 562.33 (N–Ni),
528.51 (Ni–O) cm−1; UV–Vis: λmax =208–266 nm; Chemi-
cal Formula: C44H30N4NiO82+; Molecular Weight: 800.141,
Elemental Analysis: C, 65.94; H, 3.77; N, 6.99; Ni, 7.32;
O, 15.97.
(–C–H)554.89 (Zn–N), 527.72 (Zn–O) cm−1; UV–Vis:
2+
λmax =216–260 nm; Chemical Formula: C20H16ZnN6O2
,
Molecular Weight: 437.77, Elemental Analysis: C, 54.87;
H, 3.68; N, 19.20; O, 7.31; Zn, 14.94.
(4Z,4′Z,N′,N″E,N′,N″E)N′,N″(1,3phenylenebis(methanylylid
ene))diisonicotinohydrazonic acid, nickel salt (KM‑2[Ni]) Pale
green color powder, M. p.: 281–283 °C, Yield: 0.362 g
(61%); FT-IR (KBr): v̄ = 3852.24 (O–H medium, broad),
3740.33 (O–H medium, broad), 3680.97 (O–H medium,
broad), 3616.74 (O–H medium, broad), 2358.95 (C–N=N
strong), 1744.20 (–C=N–), 1687.23 (–C=N–), 1653.00 (–
C=N–), 1507.19 (–C–H), 1389.23 (=C–H), 1170.56 (=C–
H), 1048.91 (C–H), 973.58 (–C–H), 847.53 (–C–H), 797.61
(–C–H), 677.44 (–C–H),577.97 (Ni–N), 526.65 (Ni–O)
cm−1; UV–Vis: λmax = 217–265 nm; Chemical Formula:
C20H16NiN6O22+, Molecular Weight: 430.07, Elemental
Analysis: C, 55.72; H, 3.74; N, 19.50; Ni, 13.62; O, 7.42.
4,4′ ‑((1E,1′ E)‑(1,3‑phenylenebis(methanylylidene))
bis(azanylylidene))dibenzoic acid, copper(II) salt
(KM‑1[Cu]) Green color powder; M. p.: 275–278 °C; Yield:
0.653 g (70%); FT-IR (KBr): v̄ = 3852.46 (O–H medium,
broad), 3740.74 (O–H medium, broad), 3616.69 (O–H
medium, broad), 2361.34 (H–C aromatic proton strong),
1687.55 (–C=N–), 1525.05 (–C=N–), 1389.79 (=C–H),
755.86 (–C–H), 563.77 (N–Cu), 550.07 (N–Cu), 540.30
(Cu–O), 528.32 (Cu–O) cm−1; UV–Vis: λmax =210–270 nm;
Chemical Formula: C44H30CuN4O82+; Molecular Weight:
805.135, Elemental Analysis: C, 65.54; H, 3.75; Cu, 7.88;
N, 6.95; O, 15.87.
(4Z,4′Z,N′,N″E,N′,N″E)N′,N″(1,3phenylenebis(metha
nylylidene))diisonicotinohydrazonic acid, cadmium salt
(KM‑2[Cd]) Yellow color powder; M. p.: 293–296 °C;
(4Z,4′Z,N′,N″E,N′,N″E)N′,N″(1,3phenylenebis(meth
anylylidene))diisonicotinohydrazonic acid, copper salt
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Journal of the Iranian Chemical Society
Fig. 1 Anti-Microbial Activity of Compounds (KM-1)
Fig. 2 Anti-Microbial Activity of Compounds (KM-2)
(KM‑2[Cu]) Dark green color powder; M. p.: 297–299 °C;
Yield: 0.419 g (70%); FT-IR (KBr): v̄ = 3835.94 (O–H
medium, broad), 3739.61 (O–H medium, broad), 3680.57
(O–H medium, broad), 2358.50 (C–N=N strong), 1686.77
(–C=N–), 1506.07 (–C=N–), 2170.56 (=C–H), 1170.56
(C–H), 1046.86 (–C–H), 972.49 (–C–H), 848.46 (–C–H),
794.04 (–C–H), 679.70 (–C–H), 614.21 (–C–H), 566.72
(Cu–N), 523.64 (Cu–O) cm−1; UV–Vis: λmax =211–302 nm;
Chemical Formula: C20H16NiN6O22+, Molecular Weight:
435.07, Elemental Analysis: C, 55.10; H, 3.70; Cu, 14.58;
N, 19.28; O, 7.34.
Table 1 Anti-microbial activity of KM-1 and their metal complexes
Entry Compound
and com-
Escherichia coli
(MTCC 729)
(mm)
Propionibacterium
acnes (MTCC 1951)
(mm)
plexes
1
2
3
4
5
6
KM-1
16
19
15
16
19
17
15
16
15
18
17
20
KM-1[Co]
KM-1[Ni]
KM-1[Cu]
KM-1[Zn]
KM-1[Cd]
Biological study of compounds and their complexes
The antibacterial study of the explored compounds was car-
ried out by well difusion method by using Muller Hinton
agar. The synthesized ligands and metal complexes were
used as antimicrobial agents against bacterial cultures such
as Escherichia coli (MTCC 729) and Propionibacterium
acnes (MTCC 1951). First of all, we revived the deep freeze
bacterial culture on agar media of Luria burtani agar then
inoculated into broth media of Luria burtani and let them
stand for 24 h for incubation and at the turbidity of bacterial
culture by suspensions of microorganism (0.47 McFarland)
solution at 582 nm followed by Preparation of sterilized
Muller Hinton agar medium. We picked out the bacterial
suspension of broth culture 24 h old turbidity 0.47 and was
set at 582 nm and incubated for 10 min. 8 mm wells were
prepared aseptically and then the prepared solutions of com-
pounds and complexes (300 PPM/mL) 100/L were flled
in each well and let it to incubate at 37 °C for 48 h. The
inhibition of bacterial culture is illustrated in Figs. 1 and 2
(Tables 1, 2).
Table 2 Anti-microbial activity of KM-2 and their metal complexes
Entry Compound
and com-
Escherichia coli
(MTCC 729)
(mm)
Propionibacterium
acnes (MTCC 1951)
(mm)
plexes
1
2
3
4
5
6
KM-2
17
20
21
16
15
16
16
18
20
17
16
17
KM-2[Co]
KM-2[Ni]
KM-2[Cu]
KM-2[Zn]
KM-2[Cd]
software NOVA version 1.10.1.9., assembled with con-
ventional three electrode system of Ag/AgCl/KCl (3 M) as
reference electrode, a platinum wire as counter electrode
and glossy carbon electrode as a working electrode Elec-
trochemical analyzer in K4[Fe(CN)6] containing 0.1 M KCl
as the supporting electrolyte. A cyclic voltammogram of
KM-1[Zn] and KM-2[Ni] displays a reduction peak at Epc
−0.210 and −0.175 respectively and KM-1[Zn] and KM-
2[Ni] displays an oxidation peak at Epa 0.615 and 0.606
respectively. All the reported complexes have same pattern
of cyclic voltammograms but the position of KM-1[Zn] and
Electrochemical studies
Electrochemical properties of the complexes were performed
on Metrohm Autolab B.V. PGSTAT 128 N controlled with
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Journal of the Iranian Chemical Society
Fig. 3 Cyclic voltammograms of KM-1 and KM-2 and their metal complexes
KM-2[Ni] displays a reduction and oxidation peak diferent
Table 3 Electrochemical study of KM-1 and KM-2 and their metal
complexes
(Fig. 3, Table 3).
Entry Compounds
EPcv
IPc(A)
EPa
IPa(A)
and com-
plexes
Results and discussion
1
2
3
4
5
6
7
8
KM-1
−0.106
−0.128
−0.145
−0.210
−494×10−6 0.535 287×10−6
−483×10−6 0.537 284×10−6
−400×10−6 0.576 250×10−6
−410×10−6 0.615 220×10−6
The synthesized Schif bases (ligands) and their metal
complexes was purifed as solid and amorphous state, they
were stable at room temperature. The prepared ligands
were soluble in methanol and DMSO whereas metal com-
plexes were insoluble in methanol and ethanol but soluble
in DMSO. Their melting points were determined by elec-
trochemical melting point apparatus.
KM-1[Co]
KM-1[Cu]
KM-1[Zn]
KM-1[Ni]
KM-1[Cd]
KM-2
KM-2[Co]
KM-2[Cu]
KM-2[Zn]
KM-2[Ni]
KM-2[Cd]
−0.165 −420×10−6 0.542 227×10−6
−0.172 −407×10−6 0.576 259×10−6
−0.192 −431×10−6 0.610 233×10−6
−0.160 −420×10−6 0.603 237×10−6
−0.160 −415×10−6 0.593 235×10−6
−0.158 −418×10−6 0.579 238×10−6
−0.175 −419×10−6 0.606 239×10−6
−0.153 −416×10−6 0.579 238×10−6
9
(1) Infrared (IR) spectral studies
10
11
12
The synthesized compounds show characteristic
transitional band; stretching frequency of highly elec-
tronegative atom bond with electron withdrawing group
show maximum transition band at 3852–3600 cm−1
(O–H medium, broad) due to presence of acidic group,
the multiple bonded electron withdrawing group show
transitional bending frequency at 2358.73 cm−1 due
to presence of C–N=N strong group. Schif base for-
mation between aldehyde and amine group is due to
imine bond which show stretching frequency at 1687–
1655 cm−1 because of –C=N– bond and this is sig-
nifcantly shown by the formation of actual product,
1457.30 (=C–H), 1170.88 (=C–H), 1048.87 (=C–H),
973.93 (C–H), 855.56 (C–H), 800.33 (C–H), 680.40
(C–H), 568.18 (M–N), 527.03 (M–O) cm−1.
The synthesized ligand (KM-1) phenylenebis-
(methanylylidene))bis-(azanylylidene))di-benzoi-
cacid show absorption at λmax = 205–275 nm found
π–π* transition of electron in C=N bond and conju-
gated double in aromatic system similarly in ligand
(KM-2)3,3′-((1E,1′E)-(1,3 and (E)-N-((1H-indol-3-yl)
methylene)-4H-1,2,4-triazol-4-amine show absorption
on λmax = 205–260 nm. Complexes of these ligands
coordinate with empty d orbital of metal ions form dif-
ferent coordination sphere, complex of Cd having d9
confguration and show λmax =260–300 nm, complex
of Co having d7 confguration and show λmax = 258–
(2) UV–Vis spectral studies
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Journal of the Iranian Chemical Society
Table 4 Mass spectroscopic data for Schif base ligands and some metal complexes
Entry
Sample code
Molecular weight Molecular peak
Molecular peak
Molecular peak
Molecular peak
Molecular peak
(Calculated) M+
(Observed) M+
(Observed) M+1 (Observed) M+2 (Observed) M−1 (Observed)
M−3
1
2
3
4
5
6
7
KM-1
KM-2
KM-1[Co]
KM-1[Ni]
KM-1[Cu]
KM-2[Cd]
KM-2[Zn]
372.17
373.13
431.31
431.07
435.92
484.79
437.77
372.32
373.19
431.2
431.07
435.72
484.72
437.77
–
374.13
375.23
–
–
–
–
–
–
–
–
430.19
430.06
435.82
–
428.16
–
436.04
485.01
–
–
486.7
–
–
463.06
315 nm, complex of Zn having d9 confguration and
show λmax =300–306 nm, complex of Ni having d8 con-
fguration and show λmax =265–305 nm, complex of Cu
having d9 confguration and show λmax =310–325 nm.
Conclusion
In this study, we have explored some Schif bases com-
plexes successfully and characterized by IR spectroscopic
studies which observed the C=N bond formation with transi-
tion frequency in the range 1682 to 1650 cm−1. The FT-IR
signals of bond formation between metal and donor atoms
such as N or O exhibited in very low transition frequency at
580–540 cm−1 and the another important bands described
by this technique, too. The UV–Vis spectra provided note-
worthy information about the electronic transitions between
diferent energy levels in the wavelengths of 205–330 nm.
With help of 1HNMR the presence of Schif base (–CH=N–)
proton was verily confrmed. All of 1HNMR signals proved
that similar molecules have been formed. All prepared com-
pounds in this work showed antibacterial properties against
pathogenic bacteria. From the results obtained, it is con-
frmed that these as explored compounds and complexes
have a great phramaceutical importance.
(3) Nuclear magnetic resonance spectral studies
1HNMR spectra of compound are found as per
expected and predicted for structure of ligands. com-
pound having aromatic proton which is shown by the
chemical shift on 7.5–7.8 ppm (doublet and multiplet)
to determine the ring structure of m-pthalaldehyde core
of synthesized compound and in benzyl amine ring
show chemical shift at 8.10 ppm due to the presence of
electron withdrawing group, pyridine ring containing
proton show chemical shift at 9.3 (s), 8.1 (s) ppm and
this COOH (acidic proton) show chemical shift at 10.0
(s) ppm evidence for presence of acidic group. Schif
base (–CH=N–) proton show chemical shift at 8.1 to
8.5 ppm we determine the formation of bond between
aldehyde and amine group.
(4) Mass spectral study
Acknowledgements The authors express gratitude and thanks to the
Managing Board and Head of the Department of Chemistry, Dr. Hari
Singh Gour Central University for providing research facilities. CSIR-
UGC for providing scholarship. And Dr Rajiv Dua, Scientifc Ofcer,
State Forensic Science Laboratory, Department of Home, (M.P.) for
their voluble support.
Mass study of synthesized compounds and complex is
studies by mass spectroscopy instrument (microOTOF-Q II
10348 MS–ESI on 3000 m/z). These spectral data show fun-
damental mass peak of (M+) and some other isotopic peaks
(Table 4). In ligand compound KM-1 and KM-2 show M+
at 372.3 and 373.1 and some other isotopic peaks also. By
the complexation of these ligands with di-cationic transition
metal ion they form coordination complexes in which KM-1
form bidented and KM-2 form tetra-dented complexes with
1:1 ratio of ligand and metal ion. Mass of these complexes is
also analyzed and they give M+, M 1, M 2, M 3 peaks.
Funding Partially funded by University Grants Commission (UGC),
New Delhi, India.
Availability of data and material All data is given in the manuscript.
References
1. Y. Elerman, M. Kabak, A. Elmali, Z. Naturforsch. B 57, 651
(2002)
2. M.M.H. Khalil, M.M. Aboaly, R.M. Ramadan, Spectrochim. Acta
A 61, 157 (2005)
3. A.A.A. Abu-Hussen, J. Coord. Chem. 59, 157 (2006)
1 3

Journal of the Iranian Chemical Society
4. M.S. Karthikeyan, D.J. Parsad, B. Poojary, K.S. Bhat, B.S. Holla,
N.S. Kumari, Bioorg. Med. Chem. 14, 7482 (2006)
5. P. Panneerselvam, R.R. Nair, G. Vijayalakshmi, E.H. Subrama-
nian, S.K. Sridhar, Eur. J. Med. Chem. 40, 225 (2005)
6. O.M. Walsh, M.J. Meegan, R.M. Prendergast, T.A. Nakib, Eur. J.
Med. Chem. 31, 989 (1996)
16. K. Patel, S.S. Deshmukh, D. Bodkhe, M. Mane, K. Vanka, D.
Shinde, P.R. Rajamohanan, S. Nandi, R. Vaidhyanathan, S.H.
Chikkali, J. Org. Chem. 82, 4342 (2017)
17. A.D. Garnovskii, A.L. Nivorozhkin, V.I. Minkin, Coord. Chem.
Rev. 126, 1 (1993)
18. M.S. Hossain, M.A. Mannan, F.K. Camellia, A.K.B. Zaman, C.M.
Zakaria, M. Kudrat-E-Zahan, Sci. J. Chem. 5, 62 (2017)
19. B.K. Singh, P. Mishra, A. Prakash, N. Bhojak, Arab. J. Chem. 10,
72 (2017)
7. S. Kumar, D.N. Dhar, P.N. Saxena, J. Sci. Ind. Res. 68, 181 (2009)
8. K. Singh, M.S. Barwa, P. Tyagi, Eur. J. Med. Chem. 42, 394
(2007)
9. S.K. Sridhar, M. Saravan, A. Ramesh, Eur. J. Med. Chem. 36, 615
(2001)
20. A.A. Alothman, E.S. Al-Farraj, W.A. Al-Onazi, Z.M. Almarhoon,
A.M. Al-Mohaimeed, Arab. J. Chem. 13, 3889 (2020)
21. G. Ramamohan, P. Malleswarareddy, J. Sreeramulu, K.S. Babu,
B.R. Chaithanya, Pharm. Innov. J. 8, 919 (2019)
10. A. Hamil, K. Khalifa, A. Almutaleb, M. Nouradean, Adv. J. Chem.
A 3, 524 (2020)
11. R. Mladenova, M. Ignatova, N. Manolova, T. Petrova, I. Rashkov,
Eur. Polym. J. 38, 989 (2002)
22. A. Abayneh, T. Gebretsadik, S. Tadesse, M. Thomas, Adv. Chem.
Eng. Sci. 8, 241 (2018)
12. K.C. Gupta, A. Kumar Sutar, Coord. Chem. Rev. 252, 1420 (2008)
13. H. Schif, Ann. Suppl. 343, 1864 (1864)
14. P.G. Cozzi, Chem. Soc. Rev. 33, 410 (2004)
15. B.S. Tovrog, D.J. Kitko, R.S. Drago, J. Am. Chem. Soc. 98, 5144
(1976)
23. Z. Beigi, A.H. Kianfar, H. Farrokhpour, M. Roushani, M.H.
Azarian, W.A.K. Mahmood, J. Mol. Liq. 249, 117 (2017)
1 3