Synthesis, characterization and antibacterial activity of 2-p-tolyl-1h-imidazo[4,5-f][1,10]phenanthroline and its Co(II), Ni(II) and Cu(II) complexes

Article abstract of DOI:10.4314/bcse.v27i2.6

In this study, the ligand, 2-p-tolyl-1H-imidazo[4,5-f][1,10]phenanthroline (L) was synthesized by the reaction of 1,10-phenanthroline-5,6-dione with 4-methylbenzaldehyde. The complexes of L were prepared with Co(II), Ni(II) and Cu(II) chlorides. The ligan

Full text of DOI:10.4314/bcse.v27i2.6

Bull. Chem. Soc. Ethiop. 2013, 27(2), 213-220.
Printed in Ethiopia
ISSN 1011-3924
 2013 Chemical Society of Ethiopia
DOI: http://dx.doi.org/10.4314/bcse.v27i2.6
SYNTHESIS, CHARACTERIZATION AND ANTIBACTERIAL ACTIVITY OF
2-p-TOLYL-1H-IMIDAZO[4,5-f][1,10]PHENANTHROLINE AND ITS
Co(II), Ni(II) AND Cu(II) COMPLEXES
Mesut Gomleksiz1*, Cihan Alkan2 and Belgin Erdem3
1Ahi Evran University, Faculty of Science and Arts, Department of Chemistry, TR-40100,
Kirsehir, Turkey
2Firat University, Faculty of Science and Arts, Department of Chemistry, TR-23119, Elazig,
Turkey
3Ahi Evran University, Faculty of Science and Arts, Department of Biology, TR-40100,
Kirsehir, Turkey
(Received November 9, 2011; revised March 26, 2013)
ABSTRACT. In this study, the ligand, 2-p-tolyl-1H-imidazo[4,5-f][1,10]phenanthroline (L) was synthesized by
the reaction of 1,10-phenanthroline-5,6-dione with 4-methylbenzaldehyde. The complexes of L were prepared
with Co(II), Ni(II) and Cu(II) chlorides. The ligand and its complexes were characterized by IR, UV/VIS, 1H
NMR, TGA, elemental analyses, molar conductivity and magnetic susceptibility. The complexes were proposed to
be distorted octahedral geometry. Antibacterial activity of the ligand and its complexes were tested against
selected bacteria. The minimum inhibitory concentration (MIC) was determined for the ligand and its complexes.
KEY WORDS: 1,10-Phenanthroline, Imidazole, Cobalt complex, Nickel complex, Copper complex,
Antibacterial activity
INTRODUCTION
Metal complexes containing diimine ligands such as 1,10-phenanthroline and its derivatives
have gained importance because of their versatile roles as building blocks for the synthesis of
metallo-dendrimers and as molecular scaffolding for supramolecular assemblies, and in
analytical chemistry, catalysis, electrochemistry, ring-opening metathesis polymerization and
biochemistry [1-10].
1,10-Phenanthroline has a rigid framework and possesses a superb ability to coordinate
many metal ions, which show potential for technological applications, due to their strong
absorption in the ultraviolet spectral region, bright light-emission and good electro- and photo-
active properties [11-14]. The photochemical and redox properties of complexes can be varied
systematically through appropriate substitution on the phenanthroline rings [15-17]. 1,10-
Phenanthroline, as well as some of its derived complexes, do exhibit antimicrobial properties
[18, 19].
We report here the synthesis and characterization of new Co(II), Ni(II) and Cu(II) complexes
with 1,10-Phenanthroline imidazole derivative, which is 2-p-tolyl-1H-imidazo[4,5-f][1,10]
phenanthroline (L). These compounds were screened for antibacterial activity against these
bacterial strains; A. hydrophila, S. aureus, K. pneumoniae, P. aeruginosa, S. marcescens, E.
aerogenes, B. subtilis, E. coli and E. faecalis.
__________
*Corresponding author. E-mail: mesutgomleksiz@gmail.com

214
Mesut Gomleksız et al.
EXPERIMENTAL
Materials and physical measurements
1,10-Phenanthroline-5,6-dione was synthesized according to a published method [20]. Ethanol
was dried over anhydrous copper(II) sulfate and distilled over metallic sodium. All other
chemicals were of analytical grade and were used as purchased.
Elemental analyses (C, H, N) were performed by using a Leco 932 elemental analyzer
1
(Inonu University, Malatya, Turkey). H NMR spectra were recorded on a Bruker 300 MHz
spectrometer (Inonu University, Malatya, Turkey) in DMSO-d6. The IR spectra were obtained
using KBr discs on a Ati Unicam Mattson 1000 Series FT-IR spectrophotometer (Firat
University, Elazig, Turkey). The electronic absorption spectra in the 200-1100 nm range were
obtained in DMF on a Shimadzu UV-1700 UV-Visible spectrophotometer (Firat University,
Elazig, Turkey). Magnetic susceptibility were measured at room temperature with MK-1 model
Gouy balance (Firat University, Elazig, Turkey) using Hg[Co(SCN)4] as a reference for
calibrant. Conductivities of a 10-3 M solution of the complexes were measured in DMF at 25 oC
using a CMD 750 WPA model conductivity meter (Firat University, Elazig, Turkey).
Thermogravimetric analyses (TGA) were carried out by Shimadzu-50 thermal analyzer (Firat
o
University, Elazig, Turkey) in a dynamic nitrogen atmosphere in the 20-600 C and a heating
rate 20 oC min-1.
Antibacterial activity
The in vitro antibacterial screening effects of the compounds were tested against nine bacterial
strains namely A. hydrophila (ATCC 7966), S. aureus (ATCC 29213), K. pneumoniae (ATCC
21541), P. aeruginosa (ATCC 27853), S. marcescens (ATCC 21074), E. aerogenes (ATCC
5402), B. subtilis (ATCC 6633), E. coli (ATCC 25922) and E. faecalis (ATCC 29212).
All bacteria were inoculated into Nutrient Broth (Difco) and incubated for 24 h. In the agar
well diffusion method (Mueller Hinton Agar (Oxoid) for bacteria), the dilution plate method
was used to enumerate microorganisms (105 bacteria per mL) for 24 h [21, 22, 23]. By using a
sterilised cork borer (7 mm diameter), wells were dug in the culture plates. Compounds
dissolved in DMF (1000 µg/mL) were added (75 µL ) to these wells. The petri dishes were left
o
at 4 C for 2 h and then the plates were incubated at 37 oC for bacteria (18–24 h). At the end of
the period, inhibition zones formed on the medium were evaluated is milimeters (mm). DMF
was used as a negative control under similar conditions for comparison. Ampicillin (AMP) was
used as the reference drug in positive control. All the experiments were repeated three times and
the average values are presented.
The minimum inhibitory concentration (MIC) was determined by broth microdilution
method [21]. For MIC determination, suspensions of microorganism (0.5 McFarland), Muller-
Hinton broth, solutions of the substances to be tested (1000 µg/mL in DMF). An equal volume
of bacterial inoculum was added to each well on the microtitre plate. In this manner final
concentration of compounds range 1000-3.91 µg/mL in twofold dilution step. The inoculated
plates were then incubated at 37 °C for 18-24 h.
Synthesis of ligand (L)
The ligand (L) (Figure 1) was synthesized by a method similar to the one described previously
[24, 25]. A mixture of 1,10-phenanthroline-5,6-dione (0.4 g, 2 mmol), ammonium acetate (3.1
g, 40 mmol), 4-methylbenzaldehyde (0.27 g, 2.3 mmol) and glacial acetic acid (30 mL) was
refluxed for 2 h, then cooled to room temperature and diluted with water (60 mL). Dropwise
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2-p-Tolyl-1h-imidazo[4,5-f][1,10]phenanthroline and its Co(II), Ni(II) and Cu(II) complexes 215
addition of concentrated aqueous ammonia gave yellow precipitate, which was collected and
washed with water. The crude product dissolved in ethanol was purified by filtration on silica
gel. The principal yellow band was collected. Evaporation of the solution gave yellow crystals.
o
It was filtered, washed with ethanol and recrystallized from ethanol then dried at 80 C. Yield
1
0.384 g (62%). H NMR (300 MHz, DMSO-d6, δ ppm): 13.69 (s, 1H, NH), 9.05-9.01 (dd, 2H,
CAr-H), 8.95-8.89 (dd, 2H, CAr-H), 8.21-8.16 (d, 2H, CAr-H), 7.87-7.80 (m, 2H, CAr-H), 7.45-
7.39 (d, 2H, CAr-H), 2.41 (s, 3H, CH3).
Synthesis of complexes
[Co(L)2Cl2].H2O. A ethanolic (10 mL) solution of the CoCl2.6H2O (0.075 mmol, 0.019 g) was
added a hot solution of the L (0.047 g, 0.15 mmol) in ethanol (10 mL). The reaction mixture
was refluxed for 24 h. The mixture was cooled to room temperature, the resulting orange solid
o
was filtered, washed with ethanol and recrystallized in ethanol. The product was dried at 80 C
in a vacuum oven. Yield: 0.032 g (56 %).
[Ni(L)2Cl2].2H2O. A ethanolic (10 mL) solution of the NiCl2.6H2O (0.075 mmol, 0.018 g) was
added a hot solution of the L (0.047 g, 0.15 mmol) in ethanol (10 mL). The reaction mixture
was refluxed for 26 h. The mixture was cooled to room temperature, the resulting orange solid
o
was filtered, washed with ethanol and recrystallized in ethanol. The product was dried at 80 C
in a vacuum oven. Yield: 0.038 g (65 %).
[Cu(L)2Cl2].2H2O. A ethanolic (10 mL) solution of the CuCl2.H2O (0.075 mmol, 0.013 g) was
added a hot solution of the L (0.047 g, 0.15 mmol) in ethanol (10 mL). The reaction mixture
was refluxed for 20 h. The mixture was cooled to room temperature, the resulting green solid
o
was filtered, washed with ethanol and recrystallized in ethanol. The product was dried at 80 C
in a vacuum oven. Yield: 0.028 g (48 %).
RESULTS AND DISCUSSION
Elemental analyses indicate that the metal:ligand ratio are 1:2 in all the complexes (Table 1,
Figure 2). The ligand (L) and its complexes are soluble in EtOH, DMF and DMSO.
Figure 1. Structure of the ligand (L).
Figure 2. Structure of the [Co(L)2Cl2].H2O, [Ni(L)2Cl2].2H2O and [Cu(L)2Cl2].2H2O complexes.
Bull. Chem. Soc. Ethiop. 2013, 27(2)

216
Mesut Gomleksız et al.
IR spectra
In the IR spectra (Table 2) of [Co(L)2Cl2].H2O, [Ni(L)2Cl2].2H2O and [Cu(L)2Cl2].2H2O, the
bands were observed at the 3420, 3417 and 3428 cm-1 as broad bands, respectively, are due to
OH stretching vibrations of H2O molecules [26-28]. The presence of H2O is also confirmed by
TGA analyses.
The presence of broad bands in the IR spectra of the ligand and its complexes in the 3038-
3150 cm-1 range may be assigned to the N-H stretching vibrations. This is indicating hydrogen-
bonding between the molecules [29, 30].
The stretching vibration at 1604 cm-1 of the C=N (imidazole ring) group of the ligand not
affected in its complexes, indicating that the nitrogen atom of this group is not involved in
coordination for all the complexes. On the other hand, the bands observed in the 1503-1561
cm-1 range of the C=N (phenanthroline ring) and C=C (Ar) groups were shifted to higher
frequencies in the range 1522-1577 cm-1 in all the complexes of the ligand, that indicates the
participation nitrogen atom of the C=N (phenanthroline ring) groups in coordination of the
metal ion [31, 32].
The bands of the N-H and Ar(C-H) groups in all the complexes of the ligand shifted to
negative frequencies after complexations. The negative frequency shifts of these groups may be
attributed to flow of electrons from these groups to the phenanthroline ring due to electron flow
from the nitrogen atom of the phenanthroline ring to the metal ion after complexations.
Table 1. Some analytical data and physical properties of the ligand and its complexes.
Elemental analyses
calculated (found), %
ΛM (Ω-1.
Yield,
%
FW,
g/mol
Compound
Color Molecular formula
Yellow C20H14N4
cm2. mol-1)
C
-
H
-
N
-
L
62
56
310.35
768.56
-
62.51
3.93 14.58
[Co(L)2Cl2].H2O
Orange C40H30N8OCl2Co
Orange C40H32N8O2Cl2Ni
Green C40H32N8O2Cl2Cu
11.47
(61.96) (3.50) (15.03)
61.10 4.10 14.25
(60.47) (4.68) (13.77)
60.72 4.08 14.16
(60.20) (4.03) (13.58)
[Ni(L)2Cl2].2H2O
[Cu(L)2Cl2].2H2O
65
48
786.33
791.19
9.46
10.32
Table 2. Significant bands in the IR spectra (cm-1) of the ligand and its complexes.
(O-H)str.
H2O
(C=N)str.
Ar (C=C)str. and
Compounds
L
(N-H)str. Ar (C-H)str. Al (C-H)str.
imidazole ring phen ring (C=N)str.
-
3150 (br)
3010
2978
2851, 2912
2851, 2917
1604
1604
1561, 1519, 1503
1574, 1550, 1522
[Co(L)2Cl2].H2O 3420 (br) 3038 (br)
[Ni(L)2Cl2].2H2O 3417 (br) 3038 (br)
2978
2978
2851, 2912
2851, 2912
1604
1604
1574, 1550, 1522
1577, 1552, 1522
[Cu(L)2Cl2].2H2O 3428 (br) 3043 (br)
Abbreviations: str = stretching, Ar = aromatic, Al = Aliphatic, phen = phenanthroline, br = broad.
Electronic spectra and magnetic measurements
The electronic spectral data and magnetic moment of the compounds are given in Table 3. In the
electronic spectra of the ligand, the bands are observed in the 278-550 nm range. These bands
are attributed to π → π* and n → π* transitions [33-35].
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2-p-Tolyl-1h-imidazo[4,5-f][1,10]phenanthroline and its Co(II), Ni(II) and Cu(II) complexes 217
The magnetic moment value for the Co(II) complex at 4.78 BM reported here indicates a
high spin octahedral configuration with three unpaired electrons [36, 37]. The electronic
spectrum of the Co(II) complex gives two bands 410 and 500 nm. These bands may be assigned
to the transitions 4T1g(F)(D4h; 4Eg) → 4T1g(P)(D4h; 4A2g) and 4T1g(F)(D4h; 4Eg) → 4T1g(P)(D4h; 4Eg),
respectively. The positions of these bands suggest a tetragonal environment around Co2+ ion
[38]. The other bands of complex were not observed because they might be overlapped by the
bands of L ligand.
The magnetic moment value (2.93 BM) for the Ni(II) complex corresponds to two unpaired
electron [36, 39]. The absorption bands of this complex in the range 405-720 nm suggest a
tetragonal environment around Ni2+ ion [38].
The magnetic moment value (1.95 BM) for the Cu(II) complex corresponds to one unpaired
electron [36, 40]. The complex may be considered to have a tetragonal geometry. The electronic
2
2
spectrum of the Cu(II) complex shows two bands at 415 and 720 nm assigned to Eg(D4h; B1g)
→ 2T2g(D4h; 2B2g, 2Eg) and 2Eg(D4h; 2B1g) → 2Eg(D4h; 2A1g) transitions, respectively [38].
Table 3. Magnetic moment and electronic spectral data of the ligand and its complexes.
µeff
(BM)
Compound
λ (nm)
Assigned transitions
278, 291, 309, 320,
372, 445, 461, 550
L
-
π → π* and n → π*
410
500
4T1g(F)(D4h; 4Eg) → 4T1g(P)(D4h; 4A2g)
4T1g(F)(D4h; 4Eg) → 4T1g(P)(D4h; 4Eg)
3A2g(D4h; 3B1g) → 3T1g(P)(D4h; 3Eg)
3A2g(D4h; 3B1g ) → 3T1g(P)(D4h; 3A2g)
3A2g(D4h; 3B1g) → 3T1g(F)(D4h; 3Eg)
3A2g(D4h; 3B1g) → 3T1g(F)(D4h; 3A2g)
3A2g(D4h; 3B1g) → 3T2g(F)(D4h; 3Eg, 3B2g)
2Eg(D4h; 2B1g) → 2T2g(D4h; 2B2g, 2Eg)
2Eg(D4h; 2B1g) → 2Eg(D4h; 2A1g)
[Co(L)2Cl2].H2O
[Ni(L)2Cl2].2H2O
[Cu(L)2Cl2].2H2O
4.78
2.93
1.95
405
418
530
561
720
415
720
Thermal analysis (TGA)
o
According to the thermogravimetric results all the complexes were stable up to 50 C. In the
decomposition process of the complexes, the mass loss corresponded to one uncoordinated
water molecule for [Co(L)2Cl2].H2O (2.50% experimental; 2.29% calculated) and two
uncoordinated water molecule for [Ni(L)2Cl2].2H2O and [Cu(L)2Cl2].2H2O (4.58%
experimental; 4.57% calculated and 4.16 % experimental; 4.55 % calculated) in the temperature
range of 50-120 oC.
Conductance measurements
The molar conductivity values (Table 1) of all the complexes indicate that the complexes are
non-electrolytes [41].
Antibacterial activity
The results concerning in vitro antibacterial activity of the ligand and its complexes together
with the inhibition zone diameter (mm) and MIC values are presented in Tables 4 and 5.
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Mesut Gomleksız et al.
Table 4. Antibacterial activity of the ligand and its complexes (inhibition zone diameter, mm).
Antibacterial activity (IZD in mm)
Bacteria
Ampicillin
(AM10)
L
[Co(L)2Cl2].H2O [Ni(L)2Cl2].2H2O [Cu(L)2Cl2].2H2O DMF
A. hydrophila
ATCC 7966
S. aureus
19
21
18
14
15
19
20
14
22
11
14
17
7
−
−
16
15
17
8
−
7
−
−
ATCC 29213
K. pneumoni
ATCC 21541
P. aeroginose
ATCC 27853
S. marcescens
ATCC 21074
E. aerogenes
ATCC 5402
B. subtilis
17
−
14
11
13
7
16
18
18
16
8
16
11
15
11
16
7
15
14
17
8
−
−
7
ATCC 6633
E. coli
12
−
14
−
18
7
ATCC 25922
E. faecalis
20
ATCC 29212
IZD = Inhibition zone diameter.
Table 5. Antibacterial activity of the ligand and its complexes (MIC, µg/mL).
MIC (µg/mL)
Bacteria
Ampicillin
(AM10)
L
[Co(L)2Cl2].H2O
[Ni(L)2Cl2].2H2O [Cu(L)2Cl2].2H2O
A. hydrophila
ATCC 7966
S. aureus
250
250
250
250
31.25
125
125
125
62.5
125
250
−
−
250
125
_
_
ATCC 29213
K. pneumoni
ATCC 21541
P. aeroginose
ATCC 27853
S. marcescens
ATCC 21074
E. aerogenes
ATCC 5402
B. subtilis
250
62.5
−
125
3.91
7.81
3.91
7.81
15.63
15.63
7.81
31.25
62.5
125
31.25
62.5
62.5
125
31.25
−
125
−
ATCC 6633
E. coli
62.5
250
31.25
−
31.25
250
ATCC 25922
E. faecalis
ATCC 29212
Interestingly, the ligand was found to exhibit significant antibacterial activity against all the
bacteria tested. Ni(II) complex showed good antibacterial activity against E. coli and K.
pneumoniae, respectively. Cu(II) complex also displayed good antibacterial activity against the
tested bacteria. However, no effect was observed against P. aeruginosa and E. Coli by both the
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2-p-Tolyl-1h-imidazo[4,5-f][1,10]phenanthroline and its Co(II), Ni(II) and Cu(II) complexes 219
ligand and the complexes. Further, antibacterial activity Co(II) complex was found to be
significant effect against all bacteria. In contrast no effect was observed against P. aeruginosa.
The very high antibacterial activities of the ligand, Cu(II) complex and the Co(II) complex could
be further studied for the treatment of infections caused by any of the above organisms.
CONCLUSION
In this study, imidazole and phenanthroline containing 2-p-tolyl-1H-imidazo[4,5-
f][1,10]phenanthroline (L) and its complexes were synthesized and characterized. The analytical
data, physical and spectroscopic studies suggest that the complexes were of the general formula
[M(L)2Cl2].nH2O where M is Co(II), Ni(II) and Cu(II) and n corresponding to M is 1, 2, 2,
respectively. According to the IR data of the compounds, L is coordinated to the metal ions
through nitrogen atoms of the C=N (phenanthroline ring) groups. The biological activity test
results showed that the ligand and its metal complexes have good antibacterial activity against
the bacterial strains except for Ni(II) complex. We think that the ligand and the two metal
complexes (Cu(II) and Co(II)) might be effective as antibacterial agents.
ACKNOWLEDGEMENT
We would like to thank Firat University, Elazig, Turkey, for the financial support.
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