Synthesis, characterization and antibacterial activity of nanocrystalline Ni(II)-6-methyl-4-oxo-4H-chromene-3-carbaldehyde complex

Article abstract of DOI:10.14233/ajchem.2017.20152

The methyl substituted 3-formyl chromones was synthesized by Vilsmeier-Haack reaction. Nickel(II) complex was synthesized by refluxing the mixture of ligand solution taken into ethanol:acetic acid as 1:1 ratio and Ni(II) salt solution. The nature of bonding and geometry of the Ni(II) complex have been characterized from elemental analysis, FTIR, UV-visible spectral studies, thermal methods like TGA, the magnetic susceptibility, XRD, SEM, ESI-MS and molar conductance measurement, etc. Nickel(II) chloride is forming 1:2 (M:L) complex. The FTIR spectrum shows characteristic frequency band at 1614 cm^-1 and 1695 cm^-1, which belongs to carbonyl of pyron ring and neighboring aldehyde carbonyl in ligand respectively. The Ni(II)-ligand complex shows characteristic frequency of M-O- bonding in 545-466 cm^-1 region. The electronic spectrum shows three absorption bands and confirmed complex has octahedral geometry. The formation of nanocrystalline complex and their bird feather like morphology was identified by powder XRD and SEM. Finally, NiO residue was obtained in thermogravimetric study of the complex. The ligand and its Ni(II) complex were screened for antimicrobial activities by the agar well diffusion technique.

Full text of DOI:10.14233/ajchem.2017.20152

Asian Journal of Chemistry; Vol. 29, No. 1 (2017), 119-123
A
SIAN
J
OURNAL OF HEMISTRY
C
http://dx.doi.org/10.14233/ajchem.2017.20152
Synthesis, Characterization and Antibacterial Activity of Nanocrystalline
Ni(II)-6-methyl-4-oxo-4H-chromene-3-carbaldehyde Complex
1
1,*
1
2
1
N.H. KOLHE , S.S. JADHAV , S.J. TAKATE , D.V. AWARE and A.E. ATHARE
1Department of Chemistry and Research Centre, New Arts, Commerce and Science College, Ahmednagar-414 001
2Department of Chemistry, Arts, Commerce and Science College Sonai, Tal. Newasa, Dist. Ahmednagar-414 603, India
*Corresponding author: Fax: +91 241 2324715; Tel: +91 241 2324023; E-mail: ssjadhav1957@gmail.com
Received: 22 June 2016;
Accepted: 21 September 2016;
Published online: 29 October 2016;
AJC-18110
The methyl substituted 3-formyl chromones was synthesized byVilsmeier-Haack reaction. Nickel(II) complex was synthesized by refluxing
the mixture of ligand solution taken into ethanol:acetic acid as 1:1 ratio and Ni(II) salt solution. The nature of bonding and geometry of
the Ni(II) complex have been characterized from elemental analysis, FTIR, UV-visible spectral studies, thermal methods like TGA, the
magnetic susceptibility, XRD, SEM, ESI-MS and molar conductance measurement, etc. Nickel(II) chloride is forming 1:2 (M:L) complex.
The FTIR spectrum shows characteristic frequency band at 1614 cm-1 and 1695 cm-1, which belongs to carbonyl of pyron ring and
neighboring aldehyde carbonyl in ligand respectively. The Ni(II)-ligand complex shows characteristic frequency of M-O- bonding in 545-
466 cm-1 region. The electronic spectrum shows three absorption bands and confirmed complex has octahedral geometry. The formation
of nanocrystalline complex and their bird feather like morphology was identified by powder XRD and SEM. Finally, NiO residue was
obtained in thermogravimetric study of the complex. The ligand and its Ni(II) complex were screened for antimicrobial activities by the
agar well diffusion technique.
Keywords: Substituted 3-formylchromones, Nanocrystalline complex, Antibacterial activity.
synthesis, characterization of Ni(II)-6-methyl-4-oxo-4H-
chromene-3-carbaldehyde and its antibacterial activity. The
Ni(II)-chromone complex antibacterial activity was checked
by well diffusion methods [9,10] and the inhibition zone was
measured in mm-scale.
INTRODUCTION
Several metal complexes are known to accelerate the drug
action and efficacy of the organic therapeutic agent. The
original observations that cisplatin complex had antibacterial
properties led to the discovery of their antitumor properties
and the development of the highly successful platinum anti-
cancer drugs cisplatin and nidoplatin [1]. The complexes of
gold have also been reported to have a wide range of antimicro-
bial activities [2]. Compounds containing the chromones
skeleton are an important chelating agents belonging to the
flavonoid group that occur naturally in different parts of the
plants. They are minor constituents of the human as well as
wild animal diet and have been reported to exhibit bioactivities
[3]. The bioactivities like antifungal, antibacterial, antitumor
[4], antioxidant [5], anti-HIV [6], antiallergenic and antiviral
[7] are common.
EXPERIMENTAL
Nickel chloride hexahydrate, phenol, acetic anhydride,
pyridine, anhydrous sodium sulphate, anhydrous AlCl3, aryl
acetate, acetophenone, dimethyl formide, POCl3, dimethyl
sulfoxide and ethanol and solvent were of A.R. grade quality
and were purchase from Loba Chem and Merck chemicals.
Fourier transformer infrared spectra were recorded in KBr
disc on a IRAffinity-1 FTIR-Spectrophotometer Shimadzu in
the range 4000-400 cm-1. The electronic spectra was obtained
using UV-1800 Shimadzu Spectrophotometer at 25 °C in 10-3
M concentration in DMSO solvent. Elemental analysis of C,
H, N, O was done using Perkin Elmer analyzer. Magnetic
properties were determined from Gouy balance method using
analytical single pan balance. The solubility of the prepared
complex was checked using solvent DMSO, acetonitrile, water
In order to begin our efforts for such new medicines as
effective anti-infective agents against bacteria and fungi, we
thought of substituted heterocyclic chromones derivatives to
β-diketones ligand with best complex forming ability with
d-block metals [8]. The present research work deals with the

120 Kolhe et al.
Asian J. Chem.
and ethanol. The conductivity of metal complexes was measured
in DMF:H2O using Conductivity Bridge, Model Systronics
type 304 and a dip type cell which is calibrated with KCl
solution. Thermal study was recorded on TGA-50, Shimadzu,
thermogravimetric analyzer having TGA-50 H thermal
analyzer detector. The synthesized complex was characterized
by powder X-ray diffraction patterns recorded on a model Philips
X-ray diffract meter with diffraction angle 2θ in between 20°
to 80° using CuKα radiation of wavelength 1.54058 Å. The grain
size was calculated by Scherer’s formula. The Surface morpho-
logy and elemental analysis of the samples were carried out
using scanning electron microscopy characterization conducted
using a JEOL-JEM-6360A analytical scanning electron micro-
scope (Oxford). Also the complex was analyzed by the ESI-
Mass Bruker Impact QTOF to gives the information about
molecular weight and the possible structures of complex.
Synthesis of 6-methyl-4-oxo-4H-chromene-3-carbal-
dehyde: The ligand 6-methyl-4-oxo-4H-chromene-3-carbal-
dehyde was synthesized using theVilsmeir-Haack reaction by
reported methods [11-15] (Scheme-I). Yield 76.03 %, m.w.
188.17.
appropriate Ni(II) chloride solution (0.25 g) was added drop
by drop with continuous stirring and the resulting reaction
mixture was further refluxed for 3 h and allow to stand for
overnight. The spring green solid was separate out and it was
filtered, washed with methanol. The complex was dried at room
temperature in vacuum (Scheme-II). Anal. calcd. (found) for
C22H20O8Cl2Ni: C, 48.75 % (48.09 %); H, 3.69 % (3.28 %); O,
27.05 % (27.17 %); Ni, 10.41 % (10.83) %, Colour: Spring
green, m.w. 541.98, m.p. 251 °C,Yield: 69.48 %. The complex
is soluble in chloroform, DMF and DMSO.
Antimicrobial activity: in vitro Antibacterial activity of
the synthesized ligand 6-methyl-4-oxo-4H-chromene-3-
carbaldehyde and the its Ni(II) complex was checked against
Gram-negative bacteria Escherichia coli and Gram-positive
bacteria Bacillus subtilis. The antibacterial activity was
measured by agar well diffusion method at 100 µg/mL concen-
tration [16-18]. Bacterial cultures were prepared in nutrient
broth. 100 µL of 24 h old bacterial culture was spread on sterile,
solidified nutrient agar plates. Wells were made using borer
of 7 mm diameter. 100 µL samples were loaded in respective
wells. Ciprofloxacin and DMSO were also loaded as positive
and negative control respectively. The plates were incubated
overnight at 37 °C in incubator. Next day zone of inhibition
were observed and measured. All the experiments were per-
formed in duplicate.
Synthesis of Ni(II) complex: 6-Methyl-4-oxo-4H-
chromene-3-carbaldehyde ligand (0.395 g) was dissolved in
25 mL acetic acid: ethanol (1:1) and was reflux for 0.5 h. To
this reflux ligand solution an 25 mL methanolic solution of
O
OH
O
O
Dry
+
Pyridine
O
O
4-methylphenol
4-methylphenyl acetate
Acetic anhydride
Anhydrous AlCl3
∆
OH
O
O
O
H
POCl3
DMF
O
6-methyl-4-oxo-4H-chromene-3-carbaldehyde
1-(2-hydroxy-5-methylphenyl)ethanone
Scheme-I
OH2
H
OH
H
Cl2
O
O
O
O
O
O
O
Ni
Reflux
NiCl2.6H2O
2
+
O
H
CH3OH
Nickel(II) complex
OH2
Scheme-II

Vol. 29, No. 1 (2017) Synthesis,AntibacterialActivity of Nanocrystalline Ni(II)-6-methyl-4-oxo-4H-chromene-3-carbaldehyde Complex 121
Thermal analysis:The thermal stability of Ni(II) complex
is studied by controlling heating rates 8 °C per min under static
air atmosphere. The first decomposition temperature start from
102.20 °C and end with 125.64 °C with % weight loss 7.52 %
is attributed with calculated % weight loss 7.63 % indicates
the presence of coordinated water molecules [27,28] (Fig. 2).
In second step, the % weight loss was 54.44 % was attributed
with calculated % weight loss 53.57 % indicate the loss of
four C11H6O4 molecules at 199.79 to 260.98 °C. The final
decomposition product was only 3.17 % which was attributed
to weight loss 3.21 % indicate formation of C9H6O. The final
residue was form of NiO. Which was stable at > 650 °C.
RESULTS AND DISCUSSION
Infrared spectra: The free ligand shows a high intensity
band observed at 1651 cm-1 is assigned to ν(C=O) vibration
suggesting the pyron carbonyl group [19]. The sharp intense
band around 1695 cm-1 is assigned to ν(C=O) of the aldehyde
carbonyl of the ligand [20]. The band at 1566-1485 cm-1 is
assigned to the combination of ν(C=C) of the aromatic ring.
A high intensity band in the region 1350-1336 cm-1 is assigned
to oxo ν(C-O) vibration.
In the IR of Ni2+ complex, the band of ν(C=O) was shifted
from 1651 to 1614 cm-1 indicates the bonding towards Ni2+.
The another band at 1695 cm-1 was shifted toward 1604 cm-1
which is attributed to donation of electron from ν(C=O) group
of cyclic ketone. The frequency was decreased by 69-83 cm-1
unit toward 1267 cm-1 from 1350-1336 cm-1. The infrared of
prepared complexes have shown weak bands in the range of
545-486 cm-1. This band was attributed to the ν(Ni-O) coordi-
nation [21].
100
75
2
(a)
(b)
0
-2
-4
-6
Electronic spectra: The electronic spectrum of Ni(II)
complex (Fig. 1) shows bands at 9670, 14415 and 24465 cm-1
assignable to 3A2g (F) - 3T2g (F) (ν1), 3A2g (F) - 3A1g (F) (ν2) and
3A2g (F) - 3T1g (P) (ν3) transitions respectively, in an octahedral
environment [22]. The band ν1 (10 Dq) was observed at
27472.50 cm-1. However, it is calculated by using equation
suggested by Billing and Underhill. Racha parameter B1 is
382.67 cm-1, which is less than the free ion value of 1030 cm-1
indicating the covalent character of the complex (β = 0.371).
The ratio ν2/ν1 and 1.15 % are further support the octahedral
geometry [23,24] around the Ni(II) ion, The electronic spectra
of ligand was shown at 277-384 nm indicate n–π* and π–π*
transition.
50
25
200
400
600
800
Temperature (°C)
Fig. 2. Thermogram of complex (a) TG and (b) DTG
X-ray diffraction analysis: The confirmation of structure
of the complex by taking the powder XRD recorded at 2θ ranges
from 20-80° was performed. The complex XRD pattern shows
sharp peak, indicating the complex are crystalline in nature.
The line broadening of the XRD diffraction peaks in complex
show formation of fine nanocrystalline particles (Fig. 3). By
using Scherer’s equation, average size of nanocrystalline
complex is found to be 17 nm. The decrease in the size indicates
the surface to volume ratio goes on increases.
3.629
3.000
2.000
1.000
1000
800
600
400
200
0
200
400
Wavelength (nm)
Fig. 1. Electronic spectra of Ni(II) complex
600
800
Magnetic susceptibility: The magnetic susceptibility of
the nickel(II) complex in the solid state was determined by
Gouy balance using Hg[Co(SCN)4] as a calibrate at room
temperature. The magnetic moment of Ni(II)-6-methyl-4-oxo-
4H-chromene-3-carbaldehyde complex has been found to be
µeff 3.23 BM, suggesting that the octahedral geometry of the
complex and the magnetic moment goes on increases due to
the second order Zeeman effect [25].
Molar conductance: Molar conductance of the complex
was measured in DMF:H2O (90:10) water at a concentration
of 0.0002 M. The observed conductance value for nickel
complex is 154.1 Ohm-1 cm2 mol-1, indicates that the complex
is 1:2 electrolyte [26].
20
30
40
50
(°)
60
70
80
2
θ
Fig. 3. Powder XRD pattern of Ni(II) complex
The crystallographic data of Ni(II) complex are summa-
rized in Table-1. The complex is stable at room temperature.

122 Kolhe et al.
Asian J. Chem.
TABLE-1
CRYSTALLOGRAPHIC DATA OF Ni(II) COMPLEX
2.0
1.5
1.0
0.5
0
Empirical formula
Formula weight
Crystal colour
Temperature (K)
C22H20O8Cl2Ni
541.98
Spring green
298
Wavelength (Å)
Radiation
1.54050
CuKα
Crystal system
Space group
Monoclinic (P)
P21/c (14)
1.9630
2.0556
4
A
C
Z
a (Å)
b (Å)
c (Å)
α (°)
β (°)
γ (°)
a/b
10.6
5.4
11.1
90.00
106
90
600 650 700 750 800 850 900 950 1000
m/z
Fig. 5. ESI-mass spectra of complex
against E. coli and B. subtilis (Table-2). In the present investi-
gation the coordination of ligand with Ni(II) ion the activity
go on decrease or the complex become biologically inactive.
According to overtone theory and chelation theory on the
complexation the polarity decrease and lipophilic nature of
metal atom increases. Hence the increase in biological activity.
But here in this complex the biological activity decrease due
to the formation of ionic complex and this is again showed by
electrolytic nature of complex. The antimicrobial activity of
ligand get decrease by forming the complex with Ni(II) metal
ion and the complex is found to biologically inactive.
2.0556
1.9630
610.75
c/b
Volume (Å3)
Scanning electron microscopy: The complex Ni(II)-6-
methy-4-oxo-4H-chromene-3-carbaldehyde shows the nano-
birds feather like morphology [29] (Fig. 4). The nanocrystalline
complex has smaller particles with a high tendency to crysta-
llization and homogeneous size distribution.
ESI-mass studies: Electrospray ionization spectra of
complex are shown in Fig. 5. The ESI-mass spectra were
measured in order to confirm the composition and the purity
of the complexes. The complex was dissolved in DMSO and
the spectra of complex displayed the molecular ion peak at
m/z 628.2466, which is attributable to [M+1]+ corresponding
to the molecular weight of the complex formed during the
measuring the ESI-mass spectra. The empirical formula of this
complex is C26H32NiO10S2. The parent molecular weight of the
complex is 541.98. But in the ESI-mass spectra shows m/z
628.2466 this is due the DMSO attack on the pyron ring. The
successive degradation of the coordinate water molecules from
the complex. The mass spectra obtained at m/z 589.30324
corresponding to the formation of stable ion C26H28NiO8S2.
Antimicrobial activity:The 6-methyl-4 oxo-4H-chromene-
3-carbaldehyde as ligand and their Ni(II) complexes were
evaluated for antibacterial activity with different strains of
bacteria. The ligand exhibits higher antibacterial activity
TABLE-2
ANTIMICROBIAL ACTIVITY OF
LIGAND AND Ni(II)-COMPLEX
Diameter of zone (mm) of inhibition
Compound
E. coli
B. subtilis
23
00
40
24
00
39
22
00
35
22
00
35
1c
2a
Ciprofloxacin
Conclusion
Ni(II) complex have been synthesized using 6-methyl-
4-oxo-4H-chromene-3-carbaldehyde and characterized by
various analytical and spectral data. Based on the electronic
spectra, magnetic moment and elemental analysis data, octa-
hedral geometry was proposed for Ni(II) complex. The Ni(II)
(a)
(b)
(c)
Fig. 4. Scanning electron micrograph of Ni(II) complex with different scales (a) 10 µm, (b) 5 µm and (c) 1 µm

Vol. 29, No. 1 (2017) Synthesis,AntibacterialActivity of Nanocrystalline Ni(II)-6-methyl-4-oxo-4H-chromene-3-carbaldehyde Complex 123
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shows the formation of NiO as a residue. The antimicrobial
activity data has shown that the ligand 6-methyl-4-oxo-4H-
chromene-3-carbaldehyde displayed higher activity but the
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ACKNOWLEDGEMENTS
The authors are grateful to Management ofAhmednagar Jilha
Maratha Vidya Prasarak Samaj’s, Principal Dr. B.H. Zaware,
New Arts Commerce and Science College, Ahmednagar for
providing laboratory facilities. Two of the authors (Kolhe and
Jadhav) also gratefully acknowledged the financial support
of BCUD-Savitribai Phule Pune University, Pune, India
(14SCI000295 and 14SCI000729).
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