Metal complexes of azo coumarin derivative: Synthesis, spectroscopic, thermal, and antimicrobial studies

Article abstract of DOI:10.1080/00958972.2010.508519

Cu(II), Co(II), Ni(II), Cd(II), and Zn(II) complexes of 6-(2-phenyldiazenyl)-7-hydroxy-4-methyl coumarin (PAHC) are characterized based on elemental analyses, infrared, 1H NMR, magnetic moment, molar conductance, mass spectra, UV-Vis analysis, thermogravi

Full text of DOI:10.1080/00958972.2010.508519

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Metal complexes of azo coumarin
derivative: synthesis, spectroscopic,
thermal, and antimicrobial studies
Samir Alghool a
a Department of Chemistry, Faculty of Science , Port Said
University , Port Said, Egypt
Published online: 09 Aug 2010.
To cite this article: Samir Alghool (2010) Metal complexes of azo coumarin derivative: synthesis,
spectroscopic, thermal, and antimicrobial studies, Journal of Coordination Chemistry, 63:18,
3322-3333, DOI: 10.1080/00958972.2010.508519
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Journal of Coordination Chemistry
Vol. 63, No. 18, 20 September 2010, 3322–3333
Metal complexes of azo coumarin derivative: synthesis,
spectroscopic, thermal, and antimicrobial studies
SAMIR ALGHOOL*
Department of Chemistry, Faculty of Science, Port Said University, Port Said, Egypt
(Received 10 December 2009; in final form 11 May 2010)
Cu(II), Co(II), Ni(II), Cd(II), and Zn(II) complexes of 6-(2-phenyldiazenyl)-7-hydroxy-4-
methyl coumarin (PAHC) are characterized based on elemental analyses, infrared, 1H NMR,
magnetic moment, molar conductance, mass spectra, UV-Vis analysis, thermogravimetric
analysis (TGA), and X-ray powder diffraction. From the elemental analyses, it is found that the
complexes have formulae [M(L)2(H2O)n] Á xH2O (where M ¼ Cu(II), Co(II), Ni(II), Cd(II), and
Zn(II), n ¼ 0–2, x ¼ 1–4). The molar conductance data reveal that all the metal chelates are
non-electrolytes. From the magnetic and solid reflectance spectra, it is found that the structures
of these complexes are octahedral or tetrahedral. The synthesized ligand and metal complexes
were screened for antibacterial activity against some Gram-positive and Gram-negative
bacteria.
Keywords: Coumarin; Metal complexes; Bacterial
1. Introduction
Coumarins, both naturally occurring and synthetic derivatives, have found widespread
applications as anticoagulant, spasmolytic, and bacteriostatic agents [1–4] and represent
an important group of organic compounds used as antibiotics [5, 6], fungicides [7],
anti-inflammatory [8], anticoagulant [9], and antitumor agents [10–13].
While coumarin is colorless, some of its derivatives exhibit color and intense
fluorescence [14]. Such coumarins have been reported to be useful in solar energy and
lasers [15]. The presence of perfluoroalkyl groups in coumarin dyes causes an increase in
their photostability and creates bathochromic shifts [16]. The application of coumarin
dyes to polyester fabrics gave greenish-yellow to orange shades [17]. A number of
coumarins have been investigated for complexing ability [18, 19]. A recent review
summarizes advances in the field of cytotoxic properties of coumarins and their
coordination complexes [20]. Different coordination compounds and the mechanism of
cytotoxic action have been discussed with regard to the development of new antitumor
agents. A broad array of medicinal applications of metal complexes of coumarins has
been investigated. In some cases the metal complexes obtained had higher biological
activity than their ligands [12–23]. In this study new azo dyes were synthesized by
*Email: alghools@yahoo.com; samalph2020@yahoo.com
Journal of Coordination Chemistry
ISSN 0095-8972 print/ISSN 1029-0389 online ß 2010 Taylor & Francis
DOI: 10.1080/00958972.2010.508519

Azo coumarin derivative
3323
coupling 7-hydroxy-4-methyl coumarin with diazonium salts, obtained by diazotization
of aniline, which is an efficient route for the synthesis of new Cu(II), Co(II), Ni(II),
Cd(II), and Zn(II) complexes. Thermal decomposition of their complexes is used to
infer the structure. The biological activity of this ligand and metal complexes are
evaluated.
2. Experimental
2.1. Materials and methods
Purifying and drying of compounds and solvents were performed according to
common procedure. Liquid and solid aromatic amines were purified by distilla-
tion and recrystallization, respectively. CuCl2 Á 4H2O, CoCl2 Á 6H2O, NiCl2 Á 6H2O,
ZnCl2 Á 6H2O, CdCl2 Á 2H2O, and other chemicals were purchased from Fluka and
Merck companies, and were used without purification.
2.2. Analysis
Elemental analyses (C, H, and N) were performed using a Perkin-Elmer CHN 2400
elemental analyzer. The content of metal ions was calculated gravimetrically as metal
oxides. Molar conductance measurements of the ligand and their complexes with
1.0 ꢀ 10ꢁ3 mol Lꢁ1 in DMSO were carried out using a Jenway 4010 conductivity meter.
Magnetic measurements were carried out on a Sherwood Scientific magnetic balance
1
using the Gouy method. H-NMR spectra from a Varian 200 MHz spectrometer using
DMSO as solvent are given as chemical shifts in ppm relative to tetramethylsilane.
Electron impact mass spectra were recorded on a Jeol, JMS, DX-303 mass spectro-
meter. The UV-Vis spectra were obtained in DMSO (1.0 ꢀ 10ꢁ3 mol Lꢁ1) for the ligand
and metal complexes with a Jenway 6405 Spectrophotometer using 1 cm quartz cell
from 200 to 600 nm. Infrared (IR) spectra (4000–400 cmꢁ1) were recorded as KBr pellets
on a Bruker FT-IR Spectrophotometer. Thermogravimetric analyses (TGA; TG/DTG)
were carried out from 25 to 800ꢂC in a steam of nitrogen using Shimadzu TGA 50H
TGA. The experimental conditions were: platinum crucible, nitrogen atmosphere with a
30 mL minꢁ1 flow rate, and a heating rate of 10ꢂC minꢁ1. X-ray powder diffraction
analyses were carried out using a Rigku Model ROTAFLEX Ru-200. Radiation was
provided by copper target (Cu anode 2000 W) high-intensity X-ray tube operated at
40 kV and 35 mA. Divergence slit and receiving slit were 1 and 0.1, respectively. The
scanning electron microscope (SEM) images were taken in Jeol-840 equipment with an
accelerating voltage of 15 kV.
2.3. Microbiological investigations
For these investigations the filter paper disc method was applied according to Gupta
et al. [24]. The investigated bacteria were seeded in tubes with nutrient broth (NB).
The seeded NB (1 cm3) was homogenized in the tubes with 9 cm3 of melted (45ꢂC)
nutrient agar (NA). The homogeneous suspensions were poured into Petri dishes.

3324
S. Alghool
CH
3
H C
3
O
PPA,
+
Stirred at 70°C for 20 min
O
O
O
HO
OH
HO
O
CH
3
Scheme 1. Preparation of 7-hydroxy-4-methyl coumarin.
Discs of filter paper (diameter 4 mm) were arranged on the cool medium. After cooling
the formed solid medium, 2 ꢀ 10ꢁ5 dm3 of the investigated compounds were applied
using a micropipette. After incubation for 24 h at 25–27ꢂC, the inhibition (sterile) zone
diameters (including disc) were measured and expressed in millimeter. An inhibition
zone diameter over 7 mm indicates that the tested compound is active against the
bacteria under investigation. The antibacterial activities of the investigated compounds
were tested against Escherichia coli, Pseudomonas aeruginosa as Gram negative, Bacillus
subtilis and Staphylococcus aureus as Gram positive. The concentration of each solution
was 1.0 ꢀ 10ꢁ3 mol dm3. Commercial DMF was employed to dissolve the tested
samples.
2.4. Synthesis of the ligand
The preparation of 6-(2-phenyldiazenyl)-7-hydroxy-4-methyl coumarin) (PHM)
involves the following two steps.
2.4.1. Preparation of 7-hydroxy-4-methyl coumarin. A mixture of polyphosphoric acid
(160 g, obtained by dissolving 126 g of P2O5 in 70 g of orthophosphoric acid), resorcinol
(11 g, 0.1 mol), and ethylacetoacetate (13 g, 0.1 mol) was stirred and heated at 75–80ꢂC
for 20 min (scheme 1). It is poured into ice water and the solid separated was filtered,
washed with cold water, and recrystallized from dilute ethanol [25]. Yield: 97%, m.p.:
184ꢂC.
2.4.2. Preparation of azo dyes. To an ice-cooled stirred solution of aromatic amine
(10 mmol) in HCl (6 N, 25–30 mL) a cold solution of NaNO2 (7 mL, 10 wt%) was added
during 15 min and the reaction mixture was stirred for 45 min at the same temperature.
Finally, excess HNO2 was eliminated by adding solid urea (0.5 g). To a vigorously
stirred cold (0–5ꢂC) solution of diazonium salt, a solution of 7-hydroxy-4-methyl
coumarin (10 mmol) dissolved in 10 wt% aqueous solution of NaOH (15 mL) was
added. After stirring for 30 min, the mixture was neutralized by adding HCl (15 mL,
10 wt%). The obtained precipitate was isolated by filtration and washed with water and
cold ethanol. The crude dye was purified by recrystallization.

Azo coumarin derivative
2.5. Synthesis of metal complexes
3325
All Cu(II), Co(II), Ni(II), Cd(II), and Zn(II) complexes were synthesized by adding
appropriate metal chlorides (1.0 mmol, in 20 mL ethyl alcohol : water (50 : 50) volume to
a hot solution of ligand (2.0 mmol, in 30 mL ethyl alcohol (95%)). The resulting
solutions were stirred and refluxed on a hot plate at 80ꢂC for 3 h and the colored solid
formed was filtered, washed with ethanol and diethyl ether, and finally dried under
vacuum. All complexes were prepared and isolated as amorphous solids.
3. Results and discussion
The azo dye of coumarin was prepared by coupling 7-hydroxy-4-methyl coumarin with
diazotized aniline. Selected physical properties and characteristic data of the synthe-
sized dye and metal complexes are listed in table 1. All the complexes show 1 : 2
metal : ligand stoichiometry. The isolated solid complexes are stable in air and insoluble
in water or ethyl alcohol, but soluble in DMF and DMSO. Molar conductance
indicates that all the complexes are nonelectrolytes. The ligand was decomposed at
temperatures higher than 200ꢂC. Elemental analyses were in good agreement with those
required for the formulas.
3.1. Mass spectra
Mass spectra of 6-(2-phenyldiazenyl)-7-hydroxy-4-methyl coumarin shown in
Supplementary material confirm the proposed formula with the appearance of a peak
at 280 amu (C12H11O2N3S, calculated atomic mass 280 amu) and other peaks at 77, 92,
105, 147, 189, and 203 amu due to different fragments.
3.2. Molar conductance measurements
The molar conductivities for the coumarin azo dye complexes in DMSO
(10ꢁ3 mol dmꢁ3) were in the range 14–22 ꢀꢁ1 cm2 molꢁ1, suggesting them to be
nonelectrolytes (table 1). This was confirmed from the chemical analysis (elemental
analysis data), where Clꢁ are not precipitated by the addition of AgNO3.
3.3. UV-Vis spectra and magnetic measurements
UV-Vis spectra of the ligand and its metal complexes are recorded in DMF from 200 to
800 nm. The ligand shows three bands at 215, 317, and 355 nm, which may be attributed
to ꢀ–ꢀ*, ꢀ–ꢀ*, and n–ꢀ* transitions. These bands are shifted to 221–236, 301–307, and
360–368 nm, respectively, upon coordination.
The electronic spectral data of the Cu complex, [Cu(PAHC)2] Á H2O, gave d–d
2
transition at 584 nm assigned to the transition 2E ! T2. Its magnetic moment
ꢁeff ¼ 1.73 B.M. is very close to tetrahedral geometry. Electronic spectra of Co complex,
[Co(PAHC)2(H2O)2] Á 2H2O, gave visible d–d electronic spectral bands at 454, 575,

3326
S. Alghool

Azo coumarin derivative
3327
4
4
4
4
4
4
and 641 nm assigned to T1g(F) ! T2g(P), T1g(F) ! A2g(F), T1g(F) ! T2g(F), and
its effective room temperature magnetic moment ꢁeff ¼ 5.12 B.M. is typical of high spin
octahedral [26, 27]. The [Ni(PAHC)2(H2O)2] Á 2H2O complex showed d–d electronic
3
3
3
bands at 497, 571, and 640 nm assigned to 3A2g ! T1g(P), 3A2g ! T1g(F), 3A2g ! T2g.
The ꢁeff ¼ 3.26 B.M. supported the existence of octahedral geometry [28–33].
[Cd(PAHC)2(H2O)2] Á H2O and [Zn(PAHC)2] Á 2H2O complexes are diamagnetic as
expected.
3.4. IR spectra and mode of bonding
The IR spectral bands of the ligand and complexes are listed in table 2 together with
assignments. The functional groups of the azo-linked ligand and the metal complexes
have been detected by IR spectra (Supplementary material).
A comparison of IR spectra of the ligand and complexes reveals the disappearance of
absorptions associated with OH stretch of the phenol, indicating loss of phenolic proton
on complexation, forming a metal–oxygen bond. This was further supported by the
decrease in ꢂ(C–O) frequency by 8–36 cmꢁ1 [34].
Bands at 1602 cmꢁ1 were assigned to the stretching vibration of the azo of PAHC
[35], which shifted in the complexes by ca ꢃ20 cmꢁ1 to lower wavenumber because of
nitrogen coordination, withdrawing electrons from nitrogen.
IR spectra of the complexes have a broad band at 3421–3438 cmꢁ1 attributed to OH
of crystal water [36], while ꢂ(H2O) of coordinated water appear at 837–844 cmꢁ1 [37].
In the far IR spectra of all the complexes, non-ligand bands at 510–523 and
410–459 cmꢁ1 can be assigned to ꢂ(M–O) and ꢂ(M–N), respectively [38, 39]. Therefore,
the IR spectra reveal that PAHC coordinates to metals via azo-N and phenolic-O of
coumarin.
3.5. 1H NMR spectra
Proton spectra of the compounds recorded at 250 MHz in DMSO-d6 confirm the
formation of the complex; typical chemical shifts of the 1H NMR spectra in DMSO-d6
are summarized in ‘‘Supplementary material’’. Different chemical shifts in the Zn(II)
1
complex were attributed to coordination. Comparison of the H NMR spectra of the
complex with the ligand reveals that the resonances are considerably broadened and
1
also shifted on complexation. The H NMR spectrum of the ligand shows a singlet at
2.4 ppm due to –CH3 group, phenyl rings at ꢃ ¼ 6.8–8.4 ppm, and a broad signal near
14.2–14.4 ppm, indicating
a NH resonance of the hydrazone (scheme 2 in
Supplementary material). In the 1H NMR spectrum of Zn(II) complex, the –CH3
is at 2.2 ppm and aromatic protons at 6.9–9.00 ppm. Disappearance of the
broad signal at 14.2–14.4 ppm indicates that coordination takes place through nitrogen
of azo.
3.6. Thermogravimetric analysis
Thermal properties of Cu(II), Co(II), Ni(II), Cd(II) and Zn(II) complexes are
summarized in Supplementary material. The data from TGA clearly indicate that

3328
S. Alghool

Azo coumarin derivative
3329
CH
3
N
N
H
O
O
O
CH
3
N
O
N
H
O
O
Scheme 2. Resonance of the hydrazone form.
decomposition of the complexes proceeds in three or four steps (table 3). Crystal water
molecules were lost between 25 and 160ꢂC and coordinated water between 160 and
250ꢂC. The decomposition of all complexes ended with the metal or stoichiometric
oxide formation and carbon residue.
.
3.6.1. Thermal properties of [Cu(PAHC)2] H2O. [Cu(PAHC)2] Á H2O gives
three stages of decomposition. The first stage, 25–120ꢂC, represents loss of one
hydrated water molecule. The temperature range 280–385ꢂC corresponds to the loss of
organic molecules. The final products, formed above 700ꢂC, consist of copper oxide and
carbon residue.
.
.
3.6.2. Thermal properties of [Co(PAHC)2(H2O)2] 2H2O and [Ni(PAHC)2(H2O)2] 2H2O
complexes. The TGA of [Co(PAHC)2(H2O)2] Á 2H2O and [Ni(PAHC)2(H2O)2] Á 2H2O
give four stages. The first at 25–120ꢂC represents loss of two crystal water molecules,
the second at 120–200ꢂC represents loss of two coordinated water molecules. The final
decomposition products are metal oxide and carbon residue.
.
.
3.6.3. Thermal properties of [Cd(PAHC)2(H2O)2] 4H2O and [Zn(PAHC)2] 2H2O
complexes. Thermal decompositions of and
[Cd(PAHC)2(H2O)2] Á 4H2O
[Zn(PAHC)2] Á 2H2O are in three or four decomposition steps. The first stage, at
40–140ꢂC, is from loss of four crystal water molecules for Cd(II) and two for Zn(II).
The second stage for Cd(II) at 140–200ꢂC corresponds to loss of two coordinated water
molecules; Zn(II) shows no weight loss for coordinated water. From 250ꢂC to 450ꢂC,

3330
S. Alghool
Table 3. Thermal data of PAHC and metal complexes.
Temperature range DTG peak
TG Weight
loss (%) Calcd/Found
Compounds
(ꢂC)
(ꢂC)
Assignments
H2O
Organic moiety
CuO þ 5C
2H2O
2H2O
Organic moiety
1/2(Co2O3) þ 5C
2H2O
[Cu(PAHC)2]
25–120
120–600
4600
77
465
2.81(3.11)
75.44(75.82)
21.75(21.07)
[Co(PAHC)2(H2O)2] Á 2H2O 25–120
75
180
371
5.22(5.43)
5.22(5.55)
68.67(67.41)
20.89(21.61)
120–200
200–600
4600
[Ni(PAHC)2(H2O)2] Á 2H2O 25–120
75
174
384
5.23(5.28)
5.23(5.65)
69.92(70.11)
19.62(18.96)
120–200
200–600
4600
2H2O
Organic moiety
NiO þ 5C
4H2O
2H2O
Organic moiety
Cd
[Cd(PAHC)2(H2O)2] Á 4H2O 25–140
80
160
377
9.91(10.00)
4.95(4.81)
69.44(68.93)
15.70(16.26)
140–200
200–600
4600
[Zn(PAHC)2] Á 2H2O
25–120
120–600
4600
70
380
5.47(5.58)
77.06(76.55)
17.47(17.87)
2H2O
Organic moiety
ZnO þ 3C
25–140°C
Dehydration
.
[M(L)2(H2O)n] mH 2O
[M(L) (H O) ] + mH O
2 2 n 2
140–400°C
[M(L)
2(H2O)n]
[M(L) ]+nH O
2 2
400–700°C
Final decomposition
[M(L) ]
Metal oxide + L+ carbon residue
2
M=Cu, Co, Ni, Cd or Zn; L=PAHC; n=0 or 2; m=1, 2 or 4
Scheme 3. Thermal degradation steps of PAHC ligand and their metal complexes.
organic part is lost. The final products, formed above 700ꢂC, consist of Cd metal and
zinc oxide and carbon residue.
In general, the stages of thermal decomposition of the complexes can be written as in
scheme 3.
3.7. X-ray powder diffraction
Single crystals of the complexes could not be isolated; however, the spectroscopic data
and elemental analyses enable us to predict structures.
X-ray powder diffraction patterns in the 5ꢂ52ꢄ590ꢂ were carried out in order to
obtain lattice dynamics of the compound. The obtained X-ray powder diffraction
patterns are shown in the ‘‘Supplementary material’’. This identification of the
complexes was done by the known method [40] and suggests that the prepared
compounds are amorphous.

Azo coumarin derivative
3331
Table 4. Antibacterial activity data of PAHC and metal complexes, inhibition zone (mm).
Bacillus subtili Staphylococcus aureus Escherichia coli Pseudomonas aeruginosa
Compounds
Gþ
Gþ
Gꢁ
Gꢁ
PAHC
[Cu(PAHC)2]
18
20
26
24
24
20
18
0
18
16
23
26
21
24
19
0
18
17
24
26
26
23
17
0
17
18
24
22
21
23
17
0
[Co(PAHC)2(H2O)2] Á 2H2O
[Ni(PAHC)2(H2O)2] Á 2H2O
[Cd(PAHC)2(H2O)2] Á 4H2O
[Zn(PAHC)2] Á 2H2O
Norfloxacin
Control (DMSO)
Less than 10 mm ¼ inactive, 10–15 mm ¼ weakly active, 15–20 mm ¼ moderately active; more than 20 mm ¼ highly active
(error limits 1–2 mm).
3.8. Microbiological investigation
Biological activities of the azo coumarin ligand and metal complexes were tested against
bacteria. The organisms used in the present investigation include two Gram-positive
bacteria (B. subtillis and S. aureus) and two Gram-negative bacteria (E. coli and
P. aereuguinosa). Norfloxacin was used as the standard against respective bacteria.
DMSO was used as the control. The concentration of DMSO used for testing was
1 mg mLꢁ1, whereas Norfloxacin solution was 1.0 ꢀ 10ꢁ3 mol dmꢁ1. The antimicrobial
activity was estimated on the basis inhibition zone. The results of the bactericidal
screening of the synthesized compounds are recorded in table 4. The complexes have
enhanced activity compared to the azo coumarin ligand itself (Supplementary material).
The ligands and their complexes havehigh activity toward Bacillus subtili (Gþ) in the order
[Co(PAHC)2(H2O)2] Á 2H2O4[Ni(PAHC)2(H2O)2] Á 2H2O ¼ [Cd(PAHC)2(H2O)2] Á H2O4
[Zn(PAHC)2] Á 2H2O ¼ [Cu(PAHC)2]4PAHC4Norfloxacin. In the case of Escherichia
coli
(Gꢁ),
[Ni(PAHC)2(H2O)2] Á 2H2O ¼ [Cd(PAHC)2(H2O)2] Á H2O4[Co(PAHC)2
(H2O)2] Á2H2O4[Zn(PAHC)2] Á 2H2O4PAHC4[Cu(PAHC)2] ¼ Norfloxacin.
3.9. Structure of complexes
CH3
N
N
O
O
O
OH2
N
H2O
O
xH O
2
M
N
O
O
CH3
M=Co; Ni or Cd, x=2 or 4

3332
S. Alghool
CH3
N
N
O
O
O
N
M
O
N
xH O
2
O
O
CH3
M
=
Cu or Zn, x=1 or 2
4. Conclusion
The coordination ability of 6-(2-phenyldiazenyl)-7-hydroxy-4-methyl coumarin has
been proved in complexation with Cu(II), Co(II), Ni(II), Cd(II), and Zn(II).
1
The elemental analysis and TGA confirmed the compositions of the compounds. H
NMR, IR, UV-Vis spectra and magnetic measurements of the ligand and metal
complexes confirmed the suggested coordination of the ligands through azo-N and
phenolic-O of coumarin. Under experimental conditions employed, only 1 : 2 (M : L)
complexes have been found.
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Azo coumarin derivative
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