Synthesis, spectral studies, NLO, and biological studies on metal(II) complexes of s-triazine-based Ligand

Article abstract of DOI:10.1080/15533174.2013.818018

A series of metal(II) complexes of [ML.H₂O] type [where MCu(II), Ni(II), Co(II), and Zn(II); L2,4-bis(1-(2-hydroxyphenyl)ethylideneamino)-6- phenyl-1,3,5-triazine] have been synthesized and characterized by using analytical and spectral studies. Spectroscopy and other data show octahedral geometry for metal(II) complexes. The redox behavior of the copper(II) complex has been studied by using cyclic voltammetry. The second harmonic generation (SHG) efficiency of the ligand and metal(II) complexes has been found to be higher than that of urea and KDP. The in vitro antimicrobial activities of the compounds were tested and the results revealed that metal(II) complexes exhibit higher activity than the ligand. Copyright

Full text of DOI:10.1080/15533174.2013.818018

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Synthesis, Spectral Studies, NLO, and Biological Studies
on Metal(II) Complexes of s-Triazine-Based Ligand
R. Shanmuga kalaa, P. Tharmaraja & C. D. Sheelab
a Department of Chemistry, Thiagarajar College, Madurai, India
b Department of Chemistry, The American College, Madurai, India
Accepted author version posted online: 10 Feb 2014.Published online: 02 Jun 2014.
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To cite this article: R. Shanmuga kala, P. Tharmaraj & C. D. Sheela (2014) Synthesis, Spectral Studies, NLO, and Biological
Studies on Metal(II) Complexes of s-Triazine-Based Ligand, Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-
Metal Chemistry, 44:10, 1487-1496, DOI: 10.1080/15533174.2013.818018
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Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry, 44:1487–1496, 2014
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ISSN: 1553-3174 print / 1553-3182 online
DOI: 10.1080/15533174.2013.818018
Synthesis, Spectral Studies, NLO, and Biological Studies
on Metal(II) Complexes of s-Triazine-Based Ligand
R. Shanmuga kala,1 P. Tharmaraj,1 and C. D. Sheela2
1Department of Chemistry, Thiagarajar College, Madurai, India
2Department of Chemistry, The American College, Madurai, India
ity is noncentrosymmetric and the presence of D–π–A system.
In addition to organic materials, transition metal complexes
have also been found to be effective in this regard. In view
of the above advantages a lot of attention has been focused
especially on s-triazine derivatives because of their high first-
order hyperpolarizabilities and better transparency.[15] Besides
the easily polarizable aromatic π-system, another characteristic
of s-triazine is that due to its π-deficient nature, it can act as an
auxiliary acceptor in NLO chromophores. Further advantages
in considering the s-triazine as central moiety is its symmet-
ric nature by which it will be possible to chemically tune its
NLO nature by mono- or di-substitution.[16–18] Hence s-triazine
derivatives are found to be the right choice in this regard.
In order to study the effect of π-conjugated system on
NLO activity, we are prompted to synthesize and char-
acterize the metal(II) complexes of ligand 2,4-bis(1-(2-
hydroxyphenyl)ethylideneamino)-6-phenyl-1,3,5-triazine de-
rived from s-triazine and 2-hydroxyacetophenone. Because of
the presence of π-conjugation between donor and acceptor unit,
the present ligand is expected to have largerhyperpolarisability
compared to standard. Fluorescence, electrochemical behavior,
and biological activity of the ligand and its metal complexes are
also examined.
A
series of metal(II) complexes of [ML.H2O] type
[where M Cu(II), Ni(II), Co(II), and Zn(II); L 2,4-bis(1-
(2-hydroxyphenyl)ethylideneamino)-6-phenyl-1,3,5-triazine] have
been synthesized and characterized by using analytical and spec-
tral studies. Spectroscopy and other data show octahedral geome-
try for metal(II) complexes. The redox behavior of the copper(II)
complex has been studied by using cyclic voltammetry. The second
harmonic generation (SHG) efficiency of the ligand and metal(II)
complexes has been found to be higher than that of urea and KDP.
The in vitro antimicrobial activities of the compounds were tested
and the results revealed that metal(II) complexes exhibit higher
activity than the ligand.
Keywords antimicrobial activity, hydroxyacetophenone, metal com-
plexes, NLO, triazine
INTRODUCTION
S-triazine and its derivatives display a wide range of phar-
macological properties, including antibacterial, antiviral, an-
timalarial, antiinflammatory activities and exhibit promising
anticancer, antileukemia, and anti-HIV activities.[1–6] Triazine
analogues can be utilized as a building block for the construc-
tion of multisite ligand systems.[7,8] During the last few years, the
potential of s-triazine derivatives in agrochemical and medicinal
properties has been subjected to investigations.[9–12] The amino-
substituted s-triazine derivatives are associated with a number
of pronounced antibacterial activities.[13]
EXPERIMENTAL
Reagents and Measurements
All the chemicals and solvents used were purchased from
Aldrich Chemicals & Co. Microanalytical data were recorded
at Central Drug Research Institute (CDRI), Lucknow. The mass
spectra of the ligand and its metal complexes were recorded
In recent years, there is a quest to design and develop the
nonlinear optical materials to meet the present demand due
to their widespread applications such as high-speed informa-
tion processing, optical communications and optical data stor-
age.[14] Generally, molecule with conjugated π-electron system
can have large nonlinear polarizabilities. Many researchers have
shown that the criterion for the compound to exhibit NLO activ-
1
at the Indian Institute of Technology, Madras. H NMR spec-
trum of the ligand was recorded in DMSO-d6 by employing
TMS as internal standard at the Madurai Kamaraj University,
Madurai. IR spectra of the samples were recorded on JASCO
FT-IR spectrophotometer in 4000–400 cm−1 range using KBr
pellet. The UV-Vis spectra were recorded on a JASCO V-530
spectrophotometer using DMSO as a solvent. The ESR spec-
tra of the complexes were recorded at 300 and 77 K at IIT,
Mumbai using DPPH (diphenylpicrylhydrazyl) as internal stan-
dard. Magnetic susceptibility of the complexes was measured
Received 27 March 2013; accepted 11 June 2013.
Address correspondence to P. Tharmaraj, Department of Chemistry,
Thiagarajar College, Madurai, India. E-mail: tharmatc5@gmail.com
Color versions of one or more of the figures in the article can be
found online at www.tandfonline.com/lsrt.
1487

1488
R. SHANMUGA KALA ET AL.
N
N
CH3
OH
CH3
C
H3C
N
N
N
O
N
N
Reflux
Ethanol
2
+
HO
OH
H2N
N
NH2
o-hydroxy acetophenone
2,4-diamino-6-phenyl-triazine
BHPTZ
FIG. 1. Synthesis of ligand.
by Gouy balance using copper sulphate as calibrant. Effective cipitated were collected by filtration, washed thoroughly with
magnetic moments were calculated using the formula μeff
=
ethanol, and dried in vacuum (Yield: 73–78%).
2.28(χMT)1/2, where χM is the corrected molar susceptibility.
Cyclic voltammetric measurements of copper complexes were
carried out at room temperature in acetonitrile under nitrogen
atmosphere using three electrode cell containing a Ag/AgCl
reference electrode, platinum wire auxiliary electrode, and a
glassy carbon working electrode in acetonitrile with tetrabuty-
lammonium perchlorate (TBAP) as supporting electrolyte. The
molar conductance of the complexes was measured using a
Systronic conductivity bridge at room temperature in DMSO.
Thermogravimetric studies were carried out using a Shimadzu
TGA-50 thermal analyser. Fluorescence spectra were recorded
with an ELICO SL174 Spectrofluorometer. The antimicrobial
activities of the ligand and its metal complexes were carried out
by well-diffusion method. The SHG (Second Harmonic Gen-
eration) efficiency of the ligand and its complexes were deter-
mined by the modified version of powder technique at IISc,
Bangalore.
Nonlinear Optical Property
The SHG efficiency of the ligand and its metal(II) complexes
were determined by the modified version of the powder tech-
nique developed by Kurtz and Perry. The samples were ground
into powder and packed between two transparent glass slides.
An Nd :YAG laser beam of wavelength 1064 nm was passed
through the sample cell. The transmitted fundamental wave was
absorbed by a copper(II) sulphate solution, which removes the
incident 1064 nm light and Filter BG-38 removing any residual
1064 nm light. Interference filter band width is 4 nm and for
Synthesis of Ligand
A mixture of 2-hydroxy acetophenone (2.72 g, 20 mmol),
2,4-diamino-6-phenyl-1,3,5-triazine (1.87 g, 10 mmol) and
piperidine (0.05 cm3) in 25 mL of ethanol was stirred under
reflux for 6 h. The solution was concentrated and the white
crystalline solid obtained was filtered and recrystallized from
ethanol. (Yield: 70%). m.p. 153–155◦C.
N
N
H3C
CH3
N
O
N
N
O
M
Synthesis of Metal(II) Complexes
OH2
The metal(II) complexes were prepared by the addition of hot
solution of the appropriate metal(II) chloride (1 mmol) [M =
Cu(II), Ni(II), Co(II), and Zn(II)] in 25 mL of ethanol to the hot
ethanolic solution of the ligand (0.423 g, 1 mmol). The resulting
mixture was stirred under reflux for 4 h and the complex pre-
M = Cu(II), Ni(II), Co(II) , Zn(II)
FIG. 2. Suggested structure of metal(II) complexes.

METAL COMPLEXES WITH TRIAZINE BASED LIGAND
1489
TABLE 1
Physical characterization, analytical, and molar conductance data of the ligand and metal(II) complexes
Elemental Analyses Calculated (found). (%)
Compounds/Empirical
Formula
Color
C
H
N
M
λm (ꢀ−1 cm2 mol−1) M.P. (◦C)
Ligand C25H21N5O2
CuL(H2O)
[Cu(C25H21N5O2)H2O] (1)
NiL(H2O)
[Ni(C25H21N5O2)H2O] (2)
CoL(H2O)
[Co(C25H21N5O2)H2O] (3)
ZnL(H2O)
White 70.92 (70.94) 4.96 (4.97) 16.54 (16.52)
—
—
5.7
153
209
Blue 59.46 (59.48) 4.55 (4.52) 13.87 (13.82) 12.59 (12.51)
Green 60.00 (60.04) 4.60 (4.68) 14.00 (14.03) 11.78 (11.74)
Violet 60.01 (60.05) 4.61 (4.67) 14.01 (14.03) 11.74 (11.78)
White 59.24 (59.29) 4.54 (4.52) 13.82 (13.86) 12.91 (12.96)
8.2
7.9
9.1
192
178
183
[Zn(C25H21N5O2)H2O] (4)
central wavelength of 532 nm. Green light is finally detected RESULTS AND DISCUSSION
by the photomultiplier tube and displayed on the oscilloscope.
The second harmonic signal was detected by a photomultiplier
tube and displayed on a storage oscilloscope. The efficiency of
the sample was compared with microcrystalline powder of KDP
(Potassium dihydrogenphosphate) and urea. The input energy
used in this particular set-up was 2.2 mJ/pulse.
The ligand is synthesized by the condensation of 2,4-
diamino-6-phenyl-1,3,5-triazine and 2-hydroxyacetophenone
(Figure 1). The metal(II) complexes of copper(II), nickel(II),
cobalt(II), and zinc(II) of general formula [ML.H2O] were ob-
tained in good yield through the reaction of ligand with the cor-
responding metal chlorides (Figure 2). The analytical data and
physical properties of the ligand and metal(II) complexes are
listed in Table 1. The molar conductance of the metal(II) com-
plexes were measured to establish the charge of the metal(II)
complexes and implies that all the complexes are nonelec-
trolytes.[19] The metal(II) complexes are stable in air and nonhy-
groscopic in nature. They are freely soluble in organic solvents
such as DMSO, DMF, and acetonitrile.
Antimicrobial Activity
The in vitro biological screening effects of the synthesized
compounds were evaluated by well diffusion method. Staphylo-
coccus aureus, Salmonella typhi, Escherichia coli, and Bacillus
subtilis were used for bacterial test. Antifungal activity was eval-
uated against Aspergillus niger and Candida albicans. All the
bacterial strains mentioned above were incubated in Nutrient
Broth (NB) at 37◦C for 24 h and fungal isolates were incubated
in PDA broth at 28◦C for 2 to 3 days. The wells each of 5 mm in
diameter were made in Muller Hinton agar using cork borer. The
test solution was prepared in 10−3 mL−1 concentration (DMSO)
and then 100 μL of the solution was transferred into each well.
The plates were incubated for 24 h at 37◦C and examined for
clear inhibition zone around the well.
IR Spectra
Important IR spectral bands of the free ligand and metal
complexes are listed in Table 2. The IR spectrum of the ligand
shows a broad band centered at 3188 cm−1 which is characteris-
tic of ν(OH). This band disappears in all the complexes, which
can be attributed to the involvement of phenolic OH in coor-
dination.[20] The involvement of deprotonated phenolic moiety
in complexes is confirmed by the shift of ν(C O) stretching
band observed at 1212 cm−1 in the free ligand to a lower fre-
quency[21,22] to the extent of 10 to 20 cm−1. The shift of ν(C O)
band at 1212 cm−1 to a lower frequency suggests the weakening
of ν(C O) and formation of stronger M O bond. The band ob-
served at 1646 cm−1 in the ligand is assigned to ν(C N) mode.
The shift of ν(C N) vibration in all the complexes to a lower
frequency suggests the coordination of azomethine nitrogen to
the metal ion.[23,24] The ligand shows a strong band at 1425 cm−1
which is a characteristic of the ν(C N) group in s-triazine. This
band which is shifted to lower frequency of 1417–1408 cm−1
upon complexation indicates that the above group is one of the
coordinating atoms in the ligand.[25] The presence of coordi-
nated water in the complexes is confirmed by a broad band
TABLE 2
Characteristic of IR bands (cm−1) of the ligand and its
metal(II) complexes
Vibrational frequencies (cm−1
)
ν
ν(C N) ν(OH)
ν
ν
ν
Compounds
Ligand
[Cu(L)H2O] (1) 1635
[Ni(L)H2O] (2) 1632
[Co(L)H2O] (3) 1630
[Zn(L)H2O] (4) 1639
(C N) triazine ring (OH) of H2O (M N) (M O)
1646
1425
1408
1411
1417
1415
3188
—
—
—
—
3380
3406
3392
3410
420
460
442
438
540
520
515
528
—
—
—

1490
R. SHANMUGA KALA ET AL.
TABLE 3
Electronic absorption spectral data (nm) and magnetic susceptibility data of metal(II) complexes
Frequency
μeff
(B.M.)
Compounds
(nm) (ε, M−1 cm−1
)
Assignment
ILCT∗
Geometry
[Cu(L)H2O] (1)
447 (210)
852 (78)
999 (68)
749 (105)
410 (132)
1040 (128)
630 (183)
525 (222)
Distorted octahedral
1.86
3.23
2Eg → T2g
2
3
[Ni(L)H2O] (2)
[Co(L)H2O] (3)
3A2g → T2g
Distorted octahedral
Distorted octahedral
3
3A2g → T1g(F)
3
3A2g → T1g(P)
4
4T1g(F) → T2g(F)
4.78
4
4T1g(F) → A2g(F)
4
4T1g(F) → T1g (P)
*Intraligand charge transfer.
around 3400 cm−1 and weak band around 850 cm−1 indicating
the binding of water to the metal.[26] The lower ν(C N) fre-
quency also indicates stronger M N bonding. In the IR spectra
of the complexes, a band observed between 420 and 460 cm−1
is attributed to the ν(M N) stretching vibrations.[27] Another
band appeared between 515 and 540 cm−1 which is assigned to
the interaction of phenolic oxygen to the metal atom, i.e., the
stretching vibrations of ν(M O).[28]
on complexation compared with the free ligand. C17 and C19
show a downfield shift to 189 ppm on complexation. The other
ring carbons did not show significant shifts.
Electronic Absorption Spectra and Magnetic Susceptibility
The electronic absorption spectral regions, assignments, and
the proposed geometry of the complexes are given in Table 3.
The electronic absorption spectrum of the ligand displayed
bands at 219 nm and 400 nm which can be assigned to Intra-
ligand charge transfer transition. The electronic absorption spec-
trum of the copper(II) complex (1) displayed bands at 447 nm
and 852 nm which are assigned as an intra-ligand charge trans-
1H NMR Spectra
The 1H NMR spectra of ligand and nickel(II), zinc(II) com-
plexes recorded in DMSO-d6 show well-resolved signals. The
1H NMR spectrum of ligand shows that a singlet at 2.57 ppm is
due to six methyl protons, singlet at 6.6–8.3 ppm corresponding
to aromatic protons, and singlet at 11.5 ppm observed for pheno-
lic hydroxyl group. The 1H NMR spectra of both the complexes
show the resonance with expected integrated intensities. In both
complexes, no signal is recorded for phenolic hydrogen in the
11.5 ppm region. This indicates deprotonation of the ortho-
hydroxyl group on complexation. The singlet at 3.45–3.72 ppm
shows thepresenceof water moleculeinthemetal complexes.[29]
No appreciable changes were found in other signals of the com-
plex.
2
fer band (ILCT) and a d–d band due to 2Eg → T2g transition,
respectively.[30] This band strongly favors an octahedral geom-
etry; the same is further supported by the magnetic susceptibil-
ity value (1.86 B.M.).[31,32] The nickel(II) complex (2) exhibits
three d–d bands at 999 nm, 749 nm, and 419 nm which can be
3
3
3
3
assigned to 3A2g → T2g, A2g → T1g(F), and 3A2g → T1g(P)
transitions, respectively.[33] Moreover, the ratio ν2/ν1 is (1.38)
indicative of octahedral geometry for nickel(II) complex.[34] The
magnetic moment for nickel(II) complex is 3.23 B.M. which is
well within the range expected for octahedral geometry around
the central metal ion.[35] The electronic spectrum of cobalt(II)
complex (3) exhibits three d–d bands at 1040 nm, 630 nm, and
The 13C NMR spectrum of the ligand that exhibits a singlet
peak at 172 ppm is attributed to three equivalent carbons of
triazine ring and aromatic carbons are observed in the region
117–167 ppm and azomethine carbon at 170 ppm. From the 13C
NMR spectrum of the Co(II) complex, the signal for C3 and C4
carbon showed an upfield shift to 109, 152 ppm, respectively,
525 nm due to the 4T1g(F) → T2g(F), 4T1g(F) → A2g(F), and
4
4
4T1g(F) → T1g(P) transitions, respectively, and has magnetic
4
moment value 4.78 B.M.[36] These transitions suggest octahe-
dral geometry and the assignments are in good agreement with
the reported values.[37]
The coordination field parameters 10Dq, B, and β and β0
were calculated using the secular equation given by E. Konig[38]
for nickel(II) and cobalt(II) complexes and the results are given
in Table 4. Observed ν2/ν1 values are in agreement with the
calculated ones. This indicates that the assignments are reason-
able and are additional evidence for octahedral structure.[39] In
addition, the β value for cobalt(II) complex is ≈0.7 showing
that the bonding is moderately covalent.[40]
TABLE 4
Ligand field parameters of metal(II) complexes
Complexes
ν2/ν1
B (cm−1
)
β
β0
10 Dq
[Ni(L)H2O] (2)
[Co(L)H2O] (3)
1.38
1.64
478
704
0.46
0.72
54
28
10010
10562

METAL COMPLEXES WITH TRIAZINE BASED LIGAND
1491
FIG. 3. Mass spectrum of ligand.
Mass Spectra
electron process. The cyclic voltammogram of the copper(II)
complex (1) is shown in Figure 5.
The EI mass spectra of the ligand and copper(II) complex
were recorded. Mass spectrum of the ligand shows a molecu-
lar ion peak at m/z 423 and the molecular ion peak for cop-
per(II) complex (1) is observed at 504 m/z confirms the stoi-
chiometric composition of the metal(II) complexes as being of
the [ML.H2O] type. Mass spectra of the ligand and copper(II)
complex are given in Figures 3 and 4.
ESR Spectra
The ESR spectrum of copper(II) complex (1) was recorded at
300 K and 77 K. The spin Hamiltonian parameters calculated for
the copper(II) complex is given in Table 5. The “g” tensor values
of this copper(II) complex can be used to derive the ground state.
The observed spectral parameters show g|| > g ⊥ value that is
characteristic of an axially elongated octahedral geometry. The
Electrochemical Behavior
The redox behavior of the copper(II) complex was studied covalent character of metal-ligand bond is inferred from the giso
using cyclic voltammetry at 10−3 M concentration in DMSO. value 2.094, which support the fact that the unpaired electron lies
The Cyclic voltammogram of copper(II) complex (1) shows one predominantly in the dx2−y2 orbital. The geometric parameter G
reduction peak at −0.385 V in cathodic side and oxidation peak is estimated from the expression G g|| − 2.0023/ g ⊥ − 2.0023.
at 0.377 V in anodic side. The peak separation, Ep = 0.762 V The observed value for the exchange interaction parameter for
which is greater than required for reversible process (59 mV) the copper(II) complex (G = 6.45) suggest that no appreciable
indicates that the redox couple is irreversible[41] and the ratio exchange coupling is present. Kivelson and Nielson pointed out
of cathodic to anodic peak current corresponds to a simple one that g|| value is moderately sensitive function of metal-ligand
FIG. 4. Mass spectrum of copper(II) complex.

1492
R. SHANMUGA KALA ET AL.
From the experimental data, ligand shows 1.3 and 5.8 times
more activity than urea and KDP, respectively. Metal(II) com-
plexes show SHG intensity as high as 1.8–3.5 times as that
of urea and 5.2–6.9 times than that of KDP, which concludes
that metal(II) complexes exhibit better SHG efficiency than the
ligand. The second order nonlinearity for the metal(II) com-
plexes follows the order (1) > (2) > (4) > (3). Thus, among the
metal(II) complexes, (1) has the largest hyperpolarisabilty. The
magnitude of the optical nonlinearities depends on the strengths
of the donor-acceptor groups and also the nature of π-bonding
sequence.
Fluorescence Studies
The ligand displays a fluorescence excitation maximum at
λex 496 nm and an emission maximum at λem 501 nm in
DMSO solvent. The Cu(II), Ni(II), and Co(II) complexes ex-
hibit emission bands at 540 nm, 544 nm, and 471 nm upon
photo excitation at 535 nm, 538 nm, and 465 nm, respectively
(Table 6). Usually, metal(II) complexes showed a decrease in
fluorescence intensities compared to the ligand due to the de-
localization of π-electrons within the system.[44] However, the
increase in fluorescence intensity may be explained by metal
to ligand charge transfer. The fluorescence quantum yields of
the ligand and its metal(II) complexes were obtained using the
following relation,[45]
FIG. 5. Cyclicvoltammogram of [Cu(L)H2O].
covalency. The observed g|| value is less than 2.3 which is an
indication of a strong covalent environment in the copper(II)
complex.
The spin-orbit coupling constant, λ value calculated using
the relations,
gav = 1/3 (g|| + 2 g⊥)
gav = 2(1 − 2λ)/10Dq
is less than that of free Cu(II) ion (−832 cm−1) which sup-
ports covalent character of metal-ligand bond in the complex.
The covalency parameter α2 is calculated using the following
equation.
ꢁS = As/A × (Abs)R/(Abs)s × ꢁR
Where ꢁs and ꢁR are the fluorescence quantum yield of the
sample and reference respectively, AS and AR are the area under
the fluorescence spectra of the sample and reference and (Abs)S
and (Abs)R are the respective optical densities of the sample
and the reference solution at the wavelength of excitation. The
closed shell Zn(II) ion is known to be nonquenching in nature
as it does not allow a fluorophore-metal oxidative photoelec-
tron transfer.[46] The emission spectrum of ligand is given in
Figure 6.
α2 = −(A||/0.036)+(g||−2.0023)+3/7(g⊥−2.0023)+0.04
The observed value of α2 = 0.75 of the complex is less
than unity, which indicates that the complex has some covalent
character in the ligand environment.[42] The calculated value of
g||/A|| (145 cm) for the complex indicates that the structure is
strongly distorted.
NLO Property
Thermal Analysis
Thus, the second-order nonlinear optical property of ligand
and all the four complexes were investigated using modified
Thermogravimetric studies of ligand, Cu(II), and Ni(II) com-
version of powder technique developed by Kurtz and Perry.[43] plexes were carried out in the temperature range 30 to 800◦C
The efficiency of the ligand and metal(II) complexes were com- (Table 7). The TG curve for ligand shows weight change be-
pared with microcrystalline powder of KDP and urea. The input tween 120 to 150◦C. This is in conformity with indefinite
energy used in this particular setup is 2.2 mJ/ pulse.
stability of ligand at room temperature compared to metal(II)
TABLE 5
ESR spectral data of the copper(II) complex (1)
Compound
g||
g⊥
2.043
g iso
A|| (10−4 cm−1
156.93
)
A⊥ (10−4 cm−1
)
α2
β2
g||/A|| cm
145
[Cu(L)H2O] (1)
2.26
2.095
80.25
0.75
1.70

METAL COMPLEXES WITH TRIAZINE BASED LIGAND
1493
FIG. 6. Fluorescence spectrum of ligand.
prepared in 10−3 mL−1 concentration (DMSO) and then 100 μL
of the solution was transferred into each well. The plates were
incubated for 24 h at 37◦C and examined for clear inhibition
zone around the well. The inhibition zone was developed and it
was measured. Zone of inhibition of the investigated compounds
against the bacteria and fungi are summarized in Table 8. The
biospectrum of ligand and its metal complexes are shown in
Figure 7.
complexes. In the nickel(II) complex, the TG curve is indicative
of 3.57% weight loss in the temperature range 30 to 140◦C which
could be ascribed to the elimination of water molecule. The de-
hydrated product remains stable between 140 and 320◦C. The
second step corresponds to removal of two hydroxyacetophe-
none moiety in the temperature range 320 to 506◦C and the
third step corresponds to lose of triazine moiety at 432 to 685◦C
leaving NiO residue.
All the tested compounds showed a remarkable biological
activity against different types of bacteria and fungi species. On
comparing the biological activity of the ligand and its metal(II)
complexes with the standard, it is inferred that, the metal(II)
complexes have shown potential antibacterial activity against
all the bacterial strains. In case of antifungal activity, all the
metal(II) complexes were found to be highly active than the free
ligand. In general, all the metal(II) complexes possess higher
Biological Activity
Antimicrobial activity of the compounds were tested in vitro
by well diffusion method[47] against the bacteria Staphylococ-
cus aureus, Salmonella typhi, Escherichia coli, Bacillus subtilis,
and antifungal activity against the fungi Candida albicans and
Aspergillus niger. Amikacin and Ketokonazole were used as ref-
erences for antibacterial and antifungal studies. All the bacterial
strains were incubated in Nutrient Broth (NB) at 37◦C for 24 h
and fungal isolates were incubated in PDA broth at 28◦C for
2 to 3 days. The wells each of 5 mm in diameter were made
in Muller-Hinton agar using cork borer. The stock solution was
TABLE 7
Thermal analysis data of metal(II) complexes
Metal
complex
Temperature,
(◦C)
% Weight
loss
Decomposition
product
TABLE 6
Fluorescence spectral parameters of the ligand and metal(II)
complexes
[Ni(L)H2O]
30–140
320–506
432–685
>685
90–186
276–318
318–800
>800
3.57
53.17
30.75
residue
3.59
54.22
31.07
residue
H2O
2(C8H8NO)
C9N3H5
NiO
Compounds
λexc (nm)
λem (nm)
Quantum yield
Ligand
496
535
538
465
501
540
544
471
0.29
0.72
0.96
0.95
[Cu(L)H2O]
H2O
[Cu(L)H2O] (1)
[Ni(L)H2O] (2)
[Co(L)H2O] (3)
2(C8H8NO)
C9N3H5
CuO

1494
R. SHANMUGA KALA ET AL.
1
2
3
4
Standard
Ligand
30
25
20
15
10
5
0
S. aureus
S. typhi
E. coli
B. subꢀlis
C. albicans
A. niger
FIG. 7. Graphical representation of antimicrobial activity of ligand and metal(II) complexes.
antimicrobial activity than ligand and this may be due to the atom with the active centre of the cell constituents resulting in
change in structure due to coordination and chelation tends to interference with normal cell process.[50]
make metal complexes act as more powerful and potent bac-
teriostatic agents, thus inhibiting the growth of the microor-
CONCLUSIONS
ganisms.[48] Moreover, coordination reduces the polarity of the
The metal(II) complexes of Cu(II), Ni(II), Co(II), and Zn(II)
metal ion mainly because of the partial sharing of its positive
obtained from 2,4-bis(1-(2-hydroxyphenyl)ethylideneamino)-
charge with the donor groups within the chelate ring system
6-phenyl-1,3,5-triazine were synthesized and characterized by
formed during the coordination.[49] This process, in turn in-
spectral and analytical methods. The spectral and analytical
creases the lipophilic nature of the central metal atom, which
data confirm the bonding of ligand to metal(II) ions and the
favors its permeation more efficiently through the lipid layer
octahedral geometry of metal(II) complexes. The ligand and its
of the microorganism, thus destroying them more aggressively.
metal(II) complexes were found to exhibit appreciable nonlin-
The mode of action of ligand and complexes may involve the
ear optical property in comparison with KDP and urea, hence
formation of a hydrogen bond through the azomethine nitrogen
the compound can be studied for optical sensing material. Lig-
and and its metal(II) complexes are fluorescent in nature. Most
of the metal chelates show better antimicrobial activity than
ligand, particularly Ni(II) complex has higher antimicrobial
activity compared to other complexes.
TABLE 8
Antimicrobial activity data of the ligand and metal(II)
complexes
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