Synthesis, thermal stability, electronic features, and antimicrobial activity of phenolic azo dyes and their Ni(II) and Cu(II) complexes

Article abstract of DOI:10.2478/s11696-013-0465-y

Four water soluble azo dyes, 4-(isopropyl)-2-[(E)-(4-chlorophenyl)diazenyl] phenol (L ¹), 4-(isopropyl)-2-[(E)-(2,4-dichlorophenyl)diazenyl] phenol (L²), 4-(sec-butyl)-2-[(E)-(4-chlorophenyl) diazenyl]phenol (L ³), 4-(sec-

Full text of DOI:10.2478/s11696-013-0465-y

Chemical Papers 68 (3) 352–361 (2014)
DOI: 10.2478/s11696-013-0465-y
ORIGINAL PAPER
Synthesis, thermal stability, electronic features, and antimicrobial
activity of phenolic azo dyes and their Ni(II) and Cu(II) complexes
a
a
b
aSelma Bal*, Sedat Salih Bal, Abdullah Erener, Hatice Nur Halipci,
aSeyhan Akar
aChemistry Department, bBiology Department, Science and Arts Faculty, Kahramanmaras Sutcu Imam University,
Avsar Kampusu, 46100, Kahramanmaras, Turkey
Received 7 March 2013; Revised 18 June 2013; Accepted 20 June 2013
Four water soluble azo dyes, 4-(isopropyl)-2-[(E)-(4-chlorophenyl)diazenyl]phenol (L1), 4-
(isopropyl)-2-[(E)-(2,4-dichlorophenyl)diazenyl]phenol (L2), 4-(sec-butyl)-2-[(E)-(4-chlorophenyl)
diazenyl]phenol (L3), 4-(sec-butyl)-2-[(E)-(2,4-dichlorophenyl)diazenyl]phenol (L4), and their Cu(II)
and Ni(II) complexes were synthesized and characterized using spectroscopic methods. Examination
of their thermal stability revealed similar decomposition temperature of approximately 260–300◦C
and that they were more thermally stable than their metal complexes. Ni(II) complexes of ligands L2
and L4 were more stable than the other coordination compounds. Among the synthesized ligands, L2
and the complexes Cu(L3)2 and Ni(L4)2 showed both antimicrobial and antifungal activity. How-
ever, the other ligands and the complexes were poorly active against selected microorganisms.
c
ꢀ 2013 Institute of Chemistry, Slovak Academy of Sciences
Keywords: azo, complexes, thermal, antimicrobial, electronic features
Introduction
for et al., 2009; Yazdanbakhsh et al., 2010). Azo
compounds, especially their metal(II) complexes are
generally more light-stable and this feature makes it
worthwhile to determine their thermal stability since
both azo dyes and their metal complexes have been
reported for use as optical recording media in digi-
tal versatile disc-recordable (DVD-R) media and in
many data storage devices (Ahmed et al., 2011; Li et
al., 2010; Park et al., 2002; Song et al., 2004). Addi-
tionally, color gels or generally known as color filters
are transparent colored materials used in photogra-
phy, videography, cinematography, and LCD displays.
Therefore, many dyes have been synthesized and their
potential for becoming color filters has been investi-
gated.
Azo dyes are an important class of organic col-
orants. It has been known for many years that azo
compounds are the most widely used class of dyes due
to their versatile applications in various fields such
as textile industry, biological-medical studies, and or-
ganic synthesis (Hartmann et al., 1991; Kılın¸carslan
et al., 2007; Peters & Chisowa, 1993; Song et al.,
2004). In addition, azo compounds are very impor-
tant chemicals for the inhibition of DNA, RNA, pro-
tein synthesis, and carcinogenesis (Badea et al., 2004;
Nejati et al., 2009). Efficacy of some azo dyes as lethal
photosensitisers was also investigated (Mackuľak et
al., 2012). Because they are highly colored materi-
als, they have been widely studied for their ther-
mal and optical properties in applications such as
optical data storage, photoswitching, non-linear op-
tics, and photochromic materials (Coelho et al., 2012;
Dinc¸alp et al., 2010; Essaidi et al., 2011; Huang et
al., 2004; Karipcin et al., 2010; Li et al., 2009; Lut-
There have been many systematic investigations
of the thermal stability of the water soluble azo dyes
and their metal complexes for the above mentioned
purposes. In this work, four water soluble azo dyes
and their Cu(II) and Ni(II) complexes were syn-
thesized. They were named as 4-(isopropyl)-2-[(E)-
*Corresponding author, e-mail: selmadagli9@hotmail.com

S. Bal et al./Chemical Papers 68 (3) 352–361 (2014)
353
Fig. 1. Reaction scheme and structures of the synthesized ligands and metal complexes including atom numbering. Reaction
conditions: i) NaNO2, HCl, –5◦C.
Table 1. Characterization data of the synthesized compounds
wi(calc.)/%
wi(found)/%
Yield
M.p.
Compound
Formula
Mr
C
H
N
%
76
70
64
76
72
66
68
80
72
66
68
80
◦C
L1
C15H15ClN2O
C15H14Cl2N2O
274.74
309.19
288.77
323.21
611.05
606.19
679.93
675.07
639.11
634.25
707.97
703.11
65.51
65.52
58.22
58.31
66.49
66.66
59.40
58.56
58.91
59.05
59.38
59.95
52.95
53.11
53.32
53.74
60.08
60.15
60.54
60.70
54.24
54.75
54.62
54.95
5.46
5.65
4.53
4.75
5.88
6.12
4.95
5.03
4.58
4.76
4.62
4.68
3.82
4.10
3.85
4.01
5.01
5.06
5.05
5.56
4.24
4.33
4.27
4.44
10.19
10.43
9.06
9.12
9.69
9.73
8.66
8.76
9.16
9.52
9.24
9.44
8.24
8.46
8.29
8.55
8.76
8.85
8.82
8.96
7.91
7.98
7.96
8.10
93.6
L2
98.1
L3
C16H17ClN2O
87.9
L4
C16H16Cl2N2O
75.9
Cu(L1)2
Ni(L1)2
Cu(L2)2
Ni(L2)2
Cu(L3)2
Ni(L3)2
Cu(L4)2
Ni(L4)2
C30H28N4O2Cl2Cu
C30H28N4O2Cl2Ni
C30H26N4O2Cl4Cu
C30H26N4O2Cl4Ni
C32H32N4O2Cl2Cu
C32H32N4O2Cl2Ni
C32H30N4O2Cl4Cu
C32H30N4O2Cl4Ni
122.9
120.5
125.3
140.8
116.7
119.0
132.4
138.5
(4-chlorophenyl)diazenyl]phenol (L1), 4-(isopropyl)-2-
[(E)-(2,4-dichlorophenyl)diazenyl]phenol (L2), 4-(sec-
butyl)-2-[(E)-(4-chlorophenyl)diazenyl]phenol (L3), 4-
(sec-butyl)-2-[(E)-(2,4-dichlorophenyl)diazenyl]
phenol (L4). Both synthesized ligands and their metal
complexes (Fig. 1) were examined for their thermal
behavior, cyclic voltametrics (CV), and antimicrobial
activity.
Experimental
Materials and instrumentation
4-Isopropylphenol, 4-sec-butylphenol, 4-chloro-
aniline, 2,4-dichloroaniline, NaNO2, HCl, and other
chemicals were purchased from Aldrich (USA) and
Merck (Germany). CuCl2 and NiCl2 metal salts were
obtained from Fluka (Switzerland). All solvents used

354
S. Bal et al./Chemical Papers 68 (3) 352–361 (2014)
Table 2. Spectral data of the synthesized compounds
Compound
Spectral dataa
L1
L2
L3
L4
IR, ν˜/cm−1: 3229 (OH), 2956, 2867 (CH), 1590 (ArCH), 1494 (N N)
UV-VIS, λmax/nm: 394, 294, 270
—
—
1H NMR (DMSO-d6), δ: 8.02 (d, J = 8.7 Hz, H-12, H-14), 7.64 (d, J = 8.7 Hz, H-11, H-15), 7.59 (d, J = 2.0 Hz,
H-3), 7.34 (dd, J = 8.5 Hz, J = 2.1 Hz, H-5), 7.01 (d, J = 8.5 Hz, H-6), 2.89 (m, H-7), 1.20 (d, J = 7.0 Hz, H-8,
H-9)
13C NMR (DMSO-d6), δ: 24.3 (C-8, C-9), 33.0 (C-7), 117–154 (Carom
MS, m/z: 274 (M+), 275 [M + 1]+
)
IR, ν˜/cm−1: 3489 (OH), 2952, 2868 (CH), 1579 (ArCH), 1491 (N N)
—
—
UV-VIS, λmax/nm: 472, 294, 260
1H NMR (DMSO-d6), δ: 7.94 (d, J = 8.76 Hz, H-15), 7.88 (d, J = 2.0 Hz, H-12), 7.66 (d, J = 2.0 Hz, H-3), 7.58
(dd, J = 8.76 Hz, J = 2.16 Hz, H-14), 7.39 (dd, J = 8.52 Hz, J = 2.0 Hz, H-5), 7.02 (d, J = 8.52 Hz, H-6), 2.91 (m,
H-7), 1.21 (d, J = 7.0 Hz, H-8, H-9)
13C NMR (DMSO-d6), δ: 118–153 (Carom), 32.9 (C-7), 24.2 (C-8, C-9)
MS, m/z: 310 [M + 1]+
IR, ν˜/cm−1: 3407 (OH), 2957, 2920, 2870 (CH), 1576 (ArCH), 1494 (N N)
—
—
UV-VIS, λmax/nm: 401, 309, 267
1H NMR (DMSO-d6), δ: 8.02 (d, J = 8.7 Hz, H-12, H-14), 7.64 (d, J = 8.6 Hz, H-11, H-15), 7.55 (d, J = 2.0 Hz,
H-3), 7.29 (dd, J = 8.4 Hz, J = 2.0 Hz H-5), 7.01 (d, J = 8.4 Hz, H-6), 2.60 (m, H-7), 1.21 (m, 2H-9), 1.19 (d, J=
7.0 Hz, H-8), 0.76 (t, J = 7.3 Hz, H-16)
13C NMR (DMSO-d6), δ: 115–155 (Carom), 40.63 (C-7), 31.0 (C-9), 22.16 (C-8), 12.49 (C-16)
MS, m/z: 288 (M+
)
IR, ν˜/cm−1: 3227 (OH), 2956, 2922, 2871(CH), 1579 (ArCH), 1512 (N N)
—
—
UV-VIS, λmax/nm: 452, 296, 259
1H NMR (DMSO-d6), δ: 7.95 (d, J = 8.8 Hz, H-15), 7.91 (d, J = 2.1 Hz, H-12), 7.63 (d, J = 2.0 Hz, H-3), 7.60 (dd,
J = 8.8 Hz, J = 2.2 Hz, H-14), 7.35 (dd, J = 8.5 Hz, J = 2.1 Hz, H-5), 7.03 (d, J = 8.5 Hz, H-6), 2.61 (m, H-7),
1.55 (m, H-9), 1.20 (d, J = 7.0 Hz, H-8), 0.78 (t, J = 7.4 Hz, H-16)
13C NMR (DMSO-d6), δ: 115–155 (Carom), 40.60 (C-7), 22.0 (C-8), 12.45 (C-16)
MS, m/z: 324 [M + 1]+
Cu(L1)2 IR, ν˜/cm−1: 2960, 2865 (CH), 1576 (ArCH), 1495 (N N), 545 (M—N), 460 (M—O)
—
—
UV-VIS, λmax/nm: 598, 365, 303, 273
Ni(L1)2 IR, ν˜/cm−1: 2956, 2870 (CH), 1575 (ArCH), 1495 (N N), 553 (M—N), 460 (M—O)
—
—
UV-VIS, λmax/nm: 596, 364, 302, 273
Cu(L2)2 IR, ν˜/cm−1: 2952, 2866 (CH), 1580 (ArCH), 1493 (N N), 558 (M—N), 486 (M—O)
—
—
UV-VIS, λmax/nm: 534, 462, 286, 264
Ni(L2)2 IR, ν˜/cm−1: 2951, 2869 (CH), 1579 (ArCH), 1492 (N N), 560 (M—N), 486 (M—O)
—
—
UV-VIS, λmax/nm: 595, 413, 289, 266
Cu(L3)2 IR, ν˜/cm−1: 2957, 2920, 2870 (CH), 1575 (ArCH), 1494 (N N), 550 (M—N), 461 (M—O)
—
—
UV-VIS, λmax/nm: 570, 345, 274, 254
Ni(L3)2 IR, ν˜/cm−1: 2957, 2919, 2870 (CH), 1576 (ArCH), 1494 (N N), 548 (M—N), 461 (M—O)
—
—
UV-VIS, λmax/nm: 587, 356, 294, 254
Cu(L4)2 IR, ν˜/cm−1: 2958, 2924, 2872 (CH), 1577 (ArCH), 1493 (N N), 558 (M—N), 487 (M—O)
—
—
UV-VIS, λmax/nm: 529, 472, 302, 272
Ni(L4)2 IR, ν˜/cm−1: 2958, 2921, 2871 (CH), 1577 (ArCH), 1492 (N N), 558 (M—N), 487 (M—O)
—
—
UV-VIS, λmax/nm: 517, 467, 302, 270
a) Ar means aryl; arom means aromatic; for atom numbering, see Fig. 1.
in this study were distilled before use.
mal analyses of ligands and their metal complexes
1H (400 MHz) and 13C (100 MHz) NMR spec-
tra were recorded on a Bruker AV 400 MHz spec-
trometer using DMSO-d6 as a solvent. FTIR spec-
tra (in KBr disc) were obtained on a Shimadzu
8300 FTIR spectrophotometer in the region of 400–
4000 cm−1. UV-VIS absorption spectra were mea-
sured in ethanol using a Schimadzu UV-160A spec-
trophotometer in the range of 200–600 nm. Mass spec-
tra of azo dyes were obtained on a VG Zab spec-
trometer. C, H, N elemental analyses were performed
on a LECO CHNS 932 elemental analyzer. Ther-
were carried out on a Perkin–Elmer TG/DTA 6300
thermogravimetric analyzer. Cyclic voltammetry was
performed in CH3CN (0.001–0.1 M NBu4BF4 as a
supporting electrolyte) at 293 K using an Iviumstat
electro-chemical workstation equipped with a low cur-
rent module (BAS PA-1) recorder. Unless otherwise
stated, all potentials quoted refer to the measurements
at the scan rates (ν) of 100 mV s−1, 150 mV s−1
,
,
200 mV s−1, 250 mV s−1, 500 mV s−1, 750 mV s−1
and 1000 mV s−1 and against an internal ferrocene–
ferrocenium standard.

S. Bal et al./Chemical Papers 68 (3) 352–361 (2014)
355
Synthesis of ligands and metal complexes
The ligands (1 : 1 mole ratio adducts of the amine
and the phenol (Fig. 1)) were prepared as follows: Aro-
matic amine (4-chloroaniline or 2,4-dichloroaniline,
1 g) was dissolved in HCl (2 M, 10 mL) and the
solution was kept in a salt/ice bath at –5◦C fol-
lowed by slow addition of NaNO2 (0.6 g) in water
(5 mL). The resulting mixture was stirred at –5◦C
for 2 h. Corresponding phenol (4-isopropylphenol or
4-sec-butylphenol) dissolved in an aqueous NaOH so-
lution (2 M, 5 mL) was added keeping the pH of the
final solution at 6. After stirring for 3 h, the precipitate
was collected and crystallized from ethanol. Physical
and chemical data of the products are summarised in
Table 1 and the spectral data are given in Table 2.
NiCl2 or CuCl2 was added to the respective azo
ligand dissolved in ethanol (50 mL) under heating
(ligand/metal mole ratio of 2 : 1) and the solution
was stirred under reflux for 5–6 h. The resulting com-
plex compounds were filtered, washed with ethanol
and dried at ambient temperature.
Antimicrobial activity testing
The microbial strains Streptococcus faecalis, Sta-
phylococcus aureus ATCC25923, Enterobacter cloacae
ATCC13047D, Micrococcus luteus NRLL B-4375, Es-
cherichia coli ATCC 11229, and the fungi Brusella
melitensis, Saccharomyces cerevisiae WET 136, and
Candida albicans 30114 were obtained from the Mi-
crobiology Division of the Biology Department of the
Kahramanmaras Sutcu Imam University in Kahra-
manmaras (Turkey).
The tested bacteria kept at 4◦C were injected into
Nutrient Buyyon and incubated at 37◦C for 24 h; the
yeasts were incubated in Sabouraud Dextrose Agar at
30◦C for 24 h. Mueller Hinton Agar (MHA) (Oxoid)
and Sabouraud Dextrose Agar (SDA) sterilized in a
flask and cooled to 45–50◦C were distributed to ster-
ilized Petri dishes with the diameter of 9 cm (15 mL)
after injecting cultures (0.1 mL) of bacteria and yeast
(106 bacteria per mL and 105 yeasts per mL, respec-
tively), and distributing medium in the Petri dishes
homogenously. The dishes injected with extracts were
located on the solid agar medium by pressing slightly
and kept at 4◦C for 2 h, placks injected with yeasts
were incubated at 25◦C, and the bacteria were incu-
bated at 37◦C for 24 h (Bradshaw, 1992; Collins et
al., 1995). At the end of the period, inhibition zones
(in mm) formed on the MHA and SDA were evaluated
(Uru¸s et al., 2005).
For antimicrobial activity testing, the azo com-
pounds and their metal complexes (0.02 g) were dis-
solved in chloroform (500 L) and saturated onto
10 mm diameter sterilized antibiotic discs.
Fig. 2. Absorption spectrum of L1 (a), L3 (b), and Cu(L3)2
(c).

356
S. Bal et al./Chemical Papers 68 (3) 352–361 (2014)
Table 3. Thermal analysis of the ligands
Compound
L1
Formula
Mr
T/◦C
Mass loss/%
Assignment
C15H15N2OCl
274.75
260–310
39.00
49.22
59.13
loss of C6H4Cl
loss of C9H11
loss of C9H11N2O
O
L3
L2
C16H17N2OCl
C15H14N2OCl2
288.78
309.19
260–300
265–300
37.23
48.30
61.29
loss of C6H4Cl
loss of C6H4N2Cl
loss of C10H13N2O
52.71
43.66
47.22
56.27
loss of C9H11N2O
loss of C9H11
O
loss of C6H3Cl2
loss of C6H3N2Cl2
L4
C16H16N2OCl2
323.21
260–300
45.17
46.10
54.76
loss of C6H3Cl2
loss of C10H13
O
loss of C10H13N2O
Results and discussion
NMR spectra of ligands
UV and IR spectra of ligands and complexes
1H and 13C NMR spectra of all ligands were very
similar. One exception was observed in the H NMR
1
The absorption bands observed in the range of
270–254 nm, 390–270 nm, and 472–390 nm can be
attributed to the δ–δ*, π–π*, and n–π* transitions,
respectively (Ceyhan et al., 2011). For all complexes,
the bands between 517 nm and 598 nm can be assigned
to the d–d transitions suggesting that the Cu(II)
and Ni(II) complexes of the ligands have square-
planar geometry (Tu¨mer et al., 1999, 2006). Although
the π–π* transitions of the non-substituted benzene
are generally observed at approximately 251 nm,
the activating hydroxyl group, alkyl groups and the
azobenzene chromophore caused red shift of the tran-
sition states to longer wavelengths. This was ob-
served in the UV spectra of both ligands and com-
plexes.
spectra: the signals of methylene protons of sec-butyl
group in L3 appeared at δ = 1.21, while the value of
δ = 1.55 was registered for analogous protons in L4.
More detailed relevant data are given in Table 2.
Thermal properties of ligands and complexes
Examination of the thermal spectra revealed that
azo dyes are more thermally stable than their metal
complexes.
The TGA curve of ligand L1 showed mass losses
over 260◦C related to the aromatic parts. Both Cu(II)
and Ni(II) complexes of ligand L1 exhibited simi-
lar decomposition temperatures; 220–290◦C and 235–
290◦C, respectively. Formation of the metal oxides
of these complexes was observed at over 400◦C. Lig-
and L2 was stable up to 265◦C. The Ni complex of L2,
however, overruns Cu(L2)2 in stability with the tem-
perature of up to 260◦C.
—
Azo group (—N N—) strechings observed in the
—
IR spectra of all ligands proved that the coupling
reaction was successful. In addition, the absence of
O—H (hydroxyl group) stretchings in the IR spectra
of the coordination compounds indicates the depro-
tonation of phenolic hydroxyl groups, thereby show-
ing its coordination to the metal ions. The Ar—H
bending vibrations in the para-substituted aromatic
ring in L3 and L1 were observed as sharp peaks at
854 cm−1 and 855 cm−1, respectively. In ligands L4
and L2, the bending vibrations of the ortho-positioned
aromatic hydrogens in meta-substituted rings exhib-
ited sharp signals at 839 cm−1 and 849 cm−1, respec-
tively.
Elemental analyses of the azo ligands and their
Cu(II) and Ni(II) complexes were in accordance with
the composition of the proposed structures supporting
the mole ratio of azo ligands to the metal(II) to be 2 : 1
as shown in Fig. 1. Selected absorption spectra of the
synthesized compounds are shown in Figs. 2a–2c.
Decomposition of L3 started at 260◦C; however, its
Cu(II) and Ni(II) coordination compounds (Cu(L3)2
and Ni(L3)2) were stable up to 210◦C. Formation of
the metal oxides of these coordination compounds was
recorded at above 350◦C and 490◦C, respectively. The
decomposition of L4 started at 260◦C and this ligand
was more stable than its metal complexes. However,
the Ni complex of L4 exhibited higher stability than
the corresponding Co complex whose decomposition
temperature was 200◦C with the decomposition tem-
perature starting at ∼ 245◦C. Formation of oxidized
Cu(L4)2 and Ni(L4)2 complexes was observed at over
480◦C.
Among the losses of aromatic parts of the azo com-
pounds, the loss of C9H11N2O was detected for lig-
ands L1 as 59.13 % and for L2 as 52.71 %. Similarly,

S. Bal et al./Chemical Papers 68 (3) 352–361 (2014)
Table 4. Thermal analysis of the complex compounds
357
Compound
Cu(L1)2
Formula
Mr
T/◦C
Mass loss/%
Assignment
C30H28N4O2Cl2Cu
611.05
220–290
45.12
26.89
13.12
loss of C15H14N2OCl
loss of C9H10N2O
formation of CuO
400–800
235–290
Ni(L1)2
Cu(L3)2
Ni(L3)2
Cu(L2)2
C30H28N4O2Cl2Ni
C32H32N4O2Cl2Cu
C32H32N4O2Cl2Ni
C30H26N4O2Cl4Cu
606.19
639.11
634.25
679.93
45.12
26.89
22.27
12.32
loss of C15H14N2OCl
loss of C9H10N2O
loss of C9H10
O
440–550
230–290
formation of NiO
45.11
17.42
27.65
12.43
loss of C16H16N2OCl
loss of C6H4Cl
loss of C10H12N2O
formation of CuO
350–700
210–290
45.46
17.55
27.86
11.75
loss of C16H16N2OCl
loss of C6H4Cl
loss of C10H12N2O
formation of NiO
490–620
220–300
45.40
25.55
21.44
23.95
11.68
loss of C15H13N2OCl2
loss of C6H3N2Cl2
loss of C6H3Cl2
loss of C9H10N2O
formation of CuO
360–650
260–300
Ni(L2)2
Cu(L4)2
C30H26N4O2Cl4Ni
C32H30N4O2Cl4Cu
675.07
707.97
45.73
25.74
21.60
11.05
loss of C15H13N2OCl2
loss of C6H3N2Cl2
loss of C6H3Cl2
350–700
200–370
formation of NiO
45.58
20.59
24.54
24.97
11.22
loss of C16H15N2OCl2
loss of C6H3Cl2
loss of C6H3N2Cl2
loss of C10H12N2O
formation of CuO
480–630
245–280
Ni(L4)2
C32H30N4O2Cl4Ni
703.11
45.90
20.50
24.71
25.14
10.60
loss of C16H15N2OCl2
loss of C6H3Cl2
loss of C6H3N2Cl2
loss of C10H12N2O
formation of NiO
480–660
Table 5. Antimicrobial activity of the ligands and complexes
Inhibition zone/mm
Compound
Bacteria
Fungi
S. faecalis
S. aureus
E. cloacae
M. luteus
E. coli
B. melitensis
S. cerevisiae
C. albicans
L1
20
13
nd
20
12
14
18
15
14
nd
17
17
14
17
13
12
15
12
17
13
17
12
16
14
18
19
12
20
12
22
15
15
17
12
13
16
13
24
12
20
13
14
21
17
19
14
18
16
16
nd
nd
14
15
20
19
14
20
nd
12
14
nd
16
13
15
nd
nd
18
nd
16
12
12
12
nd
nd
nd
nd
nd
nd
22
nd
24
nd
nd
nd
nd
12
12
16
nd
nd
nd
nd
12
nd
13
13
L2
L3
L4
Cu(L1)2
Ni(L1)2
Cu(L2)2
Ni(L2)2
Cu(L3)2
Ni(L3)2
Cu(L4)2
Ni(L4)2
nd – not determined.

358
S. Bal et al./Chemical Papers 68 (3) 352–361 (2014)
Table 6. Cyclic voltammetrya results for the ligands and complexes in CH3CN
Compound
ν/(mV s−1
)
Epa/V
Epc/V
E1/2/V
∆Ep/V
100
150
200
250
500
750
1000
0.31
0.34
0.36
0.37
0.46
0.52
0.56
0.95, 0.47
0.96, 0.43
0.99, 0.37
1.01, 0.36
1.03, 0.20
1.00, 0.18
0,99, 0.15
–
–
0.36
0.36
–
0.16
0.09
0.63
0.57
0.26
0.34
0.41
L1
–
–
100
150
200
250
500
750
1000
0.57
0.34
0.92, 0.46
0.93, 0.41
0.95, 0.41
0.99, 0.38
0.96, 0.31
0.97, 0.22
0.97, 0.17
–
–
–
0.37
–
–
0.11
0.07
0.06
0.01
0.10
0.23
0.47
–0.11, 0.35
–0.13, 0.37
0.41
–0.39, 0.45
–0.42, 0.50
Cu(L1)2
Ni(L1)2
L3
0.73
100
150
200
250
500
750
1000
0.68
0.57
0.37
0.52
0.40
0.87
0.88
–
–
0.37
–
–
–
0.19
0.31
0.01
0.11
0.07
0.05
0.28
0.93, 0.38
0.89, 0.41
0.89, 0.33
0.92, 0.29
0.87, 0.28
0.41, 0.97
–0.040
–
100
150
200
250
500
750
1000
–0.52, 0.41
–0.43, 0.47
0.50, 0.48
–0.49, 0.51
–0.48, 0.54
–0.45, 0.60
–0.41, 0.60
0.31
0.29
–
–
–
0.78
–
–
0.10
0.18
0.22
0.25
0.25
0.35
0.35
1.06, 0.26
1.05, 0.26
1.04, 0.23
0.95, 0.23
0.95, 0.21
–
100
150
200
250
500
750
1000
0.37
0.40
0.39
0.35
0.25
0.28
0.20
0.14
–
–
–
–
–
–
–
0.02
0.15
0.11
0.07
0.06
0.11
0.09
Cu(L3)2
Ni(L3)2
L2
–0.13, 0.38
–0.08, 0.41
–0.04, 0.42
–0.02, 0.44
0.15
0.11, -0.52
100
150
200
250
500
750
1000
0.42
0.38
0.39
0.42
0.45
0.50
0.49
0.36
0.36
0.33
–
–
–
–
–
0.06
0.02
0.06
0.15
0.22
0.31
0.31
0.27
1.02, 0.23
0.99, 0.19
0.95, 0.18
0.74
0.72
100
150
200
250
500
750
1000
–054, 0.43
–0.52, 0.47
0.42
0.49
0.56
–0.49, 0.61
–0.45, 0.62
0.24
0.22
0.22
–
–
–
–
–
–
–
0.19
0.25
0.20
0.28
0.34
0.34
0.35
0.22
1.05, 0.22
1.08, 0.27
1.07, 0.22
100
150
200
250
500
750
1000
0.42
0.42
0.47
045
0.42
–
–
–
–
–
–
–
0.05
0.03
0.02
0.43
0.21
0.35
0.22
–0.04, 0.44
–0.05, 1.19
0.05, 0.70
0.66, 1.29
0.06, 0.73
Cu(L2)2
0.38
1.38, 0.26
0.31
0.28

S. Bal et al./Chemical Papers 68 (3) 352–361 (2014)
359
Table 6. (continued)
Compound
ν/(mV s−1
)
Epa/V
Epc/V
E1/2/V
∆Ep/V
100
150
200
250
500
750
1000
0.44
0.42
0.43
0.48
0.55
0.57
0.63
0.20
0.17
–
–
–
–
–
–
–
0.24
0.25
0.28
0.34
0.36
0.34
0.35
1.07, 0.15
1.03, 0.14
0.99, 0.19
0.97, 0.23
0.93, 0.28
Ni(L2)2
100
150
200
250
500
750
1000
–0.52, 0.44
0.42
0.27, –0.25
0.30
–
–
–
0.76
–
–
0.17
0.12
0.25
0.29
0.36
0.38
0.16
0.45
0.49
0.59
0.61
1.08, 0.20
1.03, 0.20
1.07, 0.23
1.09, 0.23
1.04, 0.26, –0.28
L4
–0.44, 0.65
–
100
150
200
250
500
750
1000
0.39
0.40
0.41
0.40
–0.30
0.03
0.02
0.47
0.47
0.41
0.46
0.38
0.34
0.35
–
–
–
–
–
–
–
0.08
0.07
0.06
0.06
0.41
0.31
0.33
Cu(L4)2
100
150
200
250
500
750
1000
0.45
0.44
0.43
0.43
0.48
0.51
0.56
0.26
0.25
0.22
–
–
–
0.19
0.19
0.21
0.21
0.26
0.33
0.30
Ni(L4)2
0.22
–
1.02, 0.22
1.00, 0.18
0.98, 0.26
0.75
0.75
–
a) ν – scan rate; Epa – anodic peak potential; Epc – cathodic peak potential; E1/2 – half-wave potential; ∆Ep = Epa – Epc
.
the loss of C10H13N2O was assigned to ligands L3
and L4 as 61.29 % and 54.76 %, respectively. Over
260◦C, the loss of C6H4Cl (39 % and 37.23 %) was
attributed to ligands L1 and L3. The C6H3Cl2 loss
was recorded as 47.22 % and 45.17 % for the azo
ligands L2 and L4, respectively. Among the aromatic
losses of the complex compounds, the loss of 45.12 %
of C15H14N2OCl was assigned to Cu(II) and Ni(II)
complexes of ligand L1. Other data on the thermal
decomposition of both ligands and their metal com-
plexes is given in Tables 3 and 4.
both antibacterial and antifungal activities. On the
other hand, L3, Ni(L3)2, and Cu(L1)2 exhibited the
lowest activity against most microorganisms tested.
More details are given in Table 5.
Electronic features of ligands and complexes
The results of cyclic voltammetry measurements
are summarised in Table 6. As it can be seen, the
ligands L1–L4 exhibited two cathodic peak poten-
tials in the range of –0.42–0.75 V at all scan rates.
As the scan rate increased, the cathodic peak poten-
tials were shifted to the negative regions. In other
words, all ligands except for L1, had two anodic
Antimicrobial activity of ligands and com-
plexes
peak potentials at the 100 mV s−1, 150 mV s−1
200 mV s−1, 250 mV s−1, 500 mV s−1, 750 mV s−1
,
,
The results of antimicrobial activity testing re-
vealed that the highest activity was exhibited by the
following ligands and complexes: L1 and L4 against
S. faecalis; L2, Cu(L2)2, and Cu(L3)2 against S. au-
reus; Ni(L1)2 and L4 against E. cloacae; L2, Cu(L2)2,
and L4 against M. luteus; Ni(L1)2, Cu(L3)2, and
Cu(L2)2 against E. coli; Cu(L2)2, Cu(L3)2, and L2
against B. melitensis; Cu(L3)2 and Cu(L2)2 against
S. cerevisiae; L4 against C. albicans. Generally, ligand
L2 and metal complexes Cu(L3)2 and Ni(L4)2 showed
and 1000 mV s−1 scan rate. L1, L2, L3, and L4 showed
irreversible process at all scan rates.
L1 showed the reversible process (Ipa : Ipc = 1.0)
in a 0.001 M CH3CN solution at the 200 mV s−1 and
250 mV s−1 scan rates. Its potential ranges changed
from 0.36 V to 1.01 V (Epc) and from 0.36 V to
0.37 V (Epa). Ligand L1 showed the irreversible pro-
cess (Ipa : Ipc
ꢀ
at 100 mV s−1, 150 mV s−1, 500 mV s−1, 750 mV s−1

360
S. Bal et al./Chemical Papers 68 (3) 352–361 (2014)
and 1000 mV s−1. L2, L3, and L4 showed the irre-
versible process (Ipa : Ipc = 1.0) in a 0.001 M CH3CN
solution at scan rates of 250 mV s−1 and 500 mV s−1
Their potential ranges changed from 0.30 V to 1.10 V
(Epc) and from –0.50 V to 0.80 V (Epa).
New azo-derivative pigments and their Cu(II) complexes.
Journal of Thermal Analysis and Calorimetry, 77, 815–824.
10.1023/b:jtan.0000041
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All complexes showed strong irreversible cathodic
peaks in the range of 0.10–0.50 V and they had two
irreversible anodic peaks in the range of 0.30–0.80 V.
The complexes showed an irreversible process at all
scan rates considered. Although the forward peaks in
the reduction process in the CH3CN solution and re-
verse peaks in the oxidation processes in the CH3CN
solution are almost invariant, the position and broad-
ness of the return peak varied markedly depending
on the anion present. This suggests that close asso-
ciation of the anions with the metal(II) centres may
occur following the reduction at the electrode surface.
No M(I)–M(0) (M = Cu(II), Ni(II)) reduction was de-
tected for the metal complexes. As the ligand had an
electron donating benzyloxy group, the cathodic and
anodic peak potentials were shifted to the negative
regions. The ligands also had chloride atoms in ortho
and para positions and because the chloride atoms of-
fer their unpaired electrons by the mesomeric effect,
anodic and cathodic peak potentials were shifted to
the negative region.
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Phenolic azo dyes and their metal complexes were
synthesized and characterized. The results of their
thermal behavior examination indicate the possibil-
ity of their use in recordable media like DVDs, CDs,
and LCD displays. Azo dyes were found to be more
thermally stable than their metal complexes. Among
the coordination compounds, Ni(L2)2 and Ni(L4)2
were the most thermally stable. Antimicrobial activity
testing revealed that ligand L2 and metal complexes
Cu(L3)2 and Ni(L4)2 showed both antibacterial and
antifungal activities. The other ligands showed better
or poor activity against selected microorganisms. The
rest of the complexes generally exhibited lower activ-
ity than their ligands.
Acknowledgements. The authors would like to thank the K.
Maras Sutcu Imam University Research Projects Coordination
Unit for financial support and Prof. Dr. Mehmet Tu¨mer for
interpreting cyclic voltammograms.
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