Synthesis, characterization and antimicrobial studies of 2-{(E)-[(2-hydroxy-5-methylphenyl)imino]methyl}-4-[(E)-phenyldiazenyl]phenol as a novel azo-azomethine dye

Article abstract of DOI:10.1016/j.molstruc.2013.09.013

A novel dye, 2-{(E)-[(2-hydroxy-5-methylphenyl)imino]methyl}-4-[(E)- phenyldiazenyl]phenol dye was synthesized by the condensation reaction of 2-hydroxy-5-[(E)-phenyldiazenyl]benzaldehyde with 2-amino-4-methylphenol in methanol. The title dye was characte

Full text of DOI:10.1016/j.molstruc.2013.09.013

Journal of Molecular Structure 1053 (2013) 89–99
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Synthesis, characterization and antimicrobial studies of 2-{(E)-
[
(2-hydroxy-5-methylphenyl)imino]methyl}-4-[(E)-phenyldiazenyl]
phenol as a novel azo-azomethine dye
a
b
b
c
d
Muhammet Köse , Nurcan Kurtoglu , Özkan Gümü ßs su , Mustafa Tutak , Vickie McKee ,
e
a,
⇑
Duran Karaka sß , Mukerrem Kurtoglu
Department of Chemistry, Kahramanmaras Sutcu Imam University, Kahramanmaras 46050, Turkey
Department of Textile, Kahramanmaras Sutcu Imam University, Kahramanmaras 46050, Turkey
Department of Textile, Erciyes University, Kayseri 38000, Turkey
Department of Chemistry, Loughborough University, Leics. LE11 3TU, UK
Department of Chemistry, Faculty of Science, Cumhuriyet University, 58140 Sivas, Turkey
a
b
c
d
e
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
ꢀ
A novel azo-azomethine dye was
synthesized and characterized by
elemental analysis, FT-IR, 1H, 13
NMR and mass spectroscopy.
C
ꢀ
ꢀ
Molecular structure of the dye was
determined by single crystal X-ray
diffraction study.
The effect of various organic solvents
with different polarities on the UV–
Vis. spectra of the dye has been
studied.
ꢀ
Furthermore, the pathogenic
activities of the synthesized dye was
tested in vitro against the sensitive
organisms, Bacillus cereous and
Staphylococcus aureus, Escherichia coli,
and Klebsiella pneumoniae.
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 26 July 2013
Received in revised form 26 August 2013
Accepted 10 September 2013
Available online 14 September 2013
A novel dye, 2-{(E)-[(2-hydroxy-5-methylphenyl)imino]methyl}-4-[(E)-phenyldiazenyl]phenol dye was
synthesized by the condensation reaction of 2-hydroxy-5-[(E)-phenyldiazenyl]benzaldehyde with
2
-amino-4-methylphenol in methanol. The title dye was characterized by its melting point, elemental
1
13
analysis, FT-IR, H, C NMR and mass spectroscopic studies. Molecular structure of the title dye was
determined by single crystal X-ray diffraction study. X-ray data showed that the dye crystallizes in the
1
monoclinic space group P2 /c with cell parameters a = 18.541(2) Å, b = 4.7091(5) Å, c = 20.586(2) Å,
Keywords:
Synthesis
V = 1761.5(3) Å3 and Z = 4. The title dye adopts azo-enamine tautomer in the solid state. The molecules
crystallises as dimers assembled by two molecules of methanol via intermolecular hydrogen bonding
Azo-azomethine
X-ray structure
Tautomerism
Solvent effect
Biological activity
4
6
resulting in R ð18Þ hydrogen bonding motif. Additionally, there is an intramolecular keto-amine
hydrogen bond (NHꢁ ꢁ ꢁO) with a distance of 2.6172(17) Å. Optimized structures of the three possible
tautomers of the compound were obtained using B3LYP method with 6-311++G(d,p), 6-31G and 3-21G
basis sets in the gas phase. Thermal properties of the prepared dye were examined by thermogravimetric
analysis and results indicated that the framework of the dye is stable up to 172 °C. Furthermore, the
pathogenic activities of the synthesized dye were tested in vitro against the sensitive organisms, Bacillus
cereous (ATCC 33019) and Staphylococcus aureus (ATCC 25923) as gram positive bacteria, Escherichia coli
⇑
Corresponding author. Tel.: +90 344 280 1450; fax: +90 344 280 1352.
E-mail addresses: kurtoglu01@gmail.com, mkurtoglu@ksu.edu.tr (M. Kurtoglu).
0
022-2860/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.molstruc.2013.09.013

9
0
M. Köse et al. / Journal of Molecular Structure 1053 (2013) 89–99
(ATCC 11229), and Klebsiella pneumoniae (ATCC 13883) as gram negative bacteria and the results are
discussed. The results indicated that the prepared dye had antibacterial activities against gram-positive
bacteria (S. aureus and Bacillus cereuss), but it exhibited no activity against gram-negative bacteria (E. coli
and K. pneumoniae).
Ó 2013 Elsevier B.V. All rights reserved.
1
. Introduction
tomerism in solution [16,17]. 5-Arylazo-o-hydroxylimines have
been reported to show thermochromism and photochromism in
Compounds containing azo groups are of great interest because
of a wide range of applications such as organic dyes [1], indicators
2], radical reaction initiators [3] and therapeutic agents [4]. Azo
the solid state by a proton transfer from the hydroxyl O-atom to
the imine N-atom [17].
Recently, some compounds containing both imine and/or azo
groups have been reported by our group [18–21]. In this study,
we reported the synthesis, crystallographic and spectroscopic
studies as well as thermal investigation of a novel salicylaldi-
[
dyes are in use as dyestuffs for wool, leather and synthetic fabrics
due to their excellent coloring properties [5]. Compounds contain-
ing both imine (AC@NA) and azo (AN@NA) groups are also impor-
tant structures in medicinal and pharmaceutical chemistry and it
has been suggested that the azomethine linkage might be respon-
sible for the biological activities displayed by Schiff bases [6,7].
These compounds have also received special attention in coordina-
tion chemistry due to their mixed hard–soft donor character and
versatile coordination behavior [8–11].
Recently, the study of azo-azomethine dyes containing
hydroxyl groups has attracted considerable attention [12–17].
Inter- and intramolecular proton transfer from phenolic oxygen
to imine nitrogen is very common in polyhydroxy derivatives of
azo-azomethine dyes resulting in a self-isomerisation [13]. Due
to proton transfer ability of azo-azomethine dyes, these systems
have been of a special interest from practical viewpoint as the tau-
tomers showing different optical behavior and dyeing properties
mine-based
compound,
2-{(E)-[(2-hydroxy-5-methylphenyl)
13
imino]methyl}-4-[(E)-phenyldiazenyl]phenol dye (Scheme 1).
C
1
and H NMR spectra, UV–Vis spectroscopy, mass spectroscopy
and elemental analysis were obtained to determine the structure
of the azo-azomethine dye. The computational studies of the com-
pound were examined by Gauss View 5.0.8. Thermal properties of
the prepared compound were examined by thermogravimetric
analysis. The results indicated that the framework of the azo-
enamine dye is stable up to 172 °C. Additionally, antimicrobial
activity of the title compound was studied using both gram
positive and negative bacteria.
2
. Experimental
[
14]. Determination of which tautomeric structure favoured under
All reagents and solvents for synthesis and analysis were
certain conditions is important in terms of coloristic and techno-
logical properties of dyes. The presence of enol/imine, keto/amine
and hydrazone/azo-enaminone tautomerism in azo-azomethine
dyes affect their photo-physical and photo-chemical properties
purchased from commercial sources and used as received unless
otherwise noted. 2-Hydroxy-5-[(E)-phenyldiazenyl]benzaldehyde
was prepared according to the published paper [22]. IR
spectrum was performed on a Perkin Elmer Paragon 1000PC.
CHN analysis was performed using a CE-440 Elemental analyzer.
NMR spectra were performed using a Bruker Avance 400. Mass
spectrum was recorded on a Thermo Fisher Exactive + Triversa
[
15,16]. Self-isomerisation via proton transfer depends on several
factors such as temperature, the substituent structure and solvent
polarity. Dye–solvent interactions play an important role in tau-
Scheme 1. Synthesis of 2-{(E)-[(2-hydroxy-5-methylphenyl)imino]methyl}-4-[(E)-phenyldiazenyl]phenol dye and its tautomers. (i) (1) NaNO
2
, HCl, 0 °C, (2) salicylaldehyde;
(
ii) 2-amino-4-methylphenol, MeOH and reflux.

M. Köse et al. / Journal of Molecular Structure 1053 (2013) 89–99
91
Nanomate mass spectrometer. The UV–Vis spectra were measured
Table 2
Hydrogen bond parameters for the dye [Å and °].
with a T80+ UV–Vis. Spectrometer PG Instruments LTD spectrom-
eter. Data collection for X-ray crystallography was completed using
a Bruker APEX2 CCD diffractometer and data reduction was
performed using Bruker SAINT. SHELXTL was used to solve and
refine the structures [23].
DAHꢁ ꢁ ꢁA
d(DAH)
d(Hꢁ ꢁ ꢁA)
d(Dꢁ ꢁ ꢁA)
<(DHA)
N(1)AH(1A)ꢁ ꢁ ꢁO(2)
O(3)AH(3A)ꢁ ꢁ ꢁO(2)
O(1)AH(1)ꢁ ꢁ ꢁO(3A)
0.921(18)
0.91(2)
0.94(2)
1.842(18)
1.80(2)
1.67(2)
2.6172(17)
2.7108(16)
2.6095(16)
140.4(15)
176.3(19)
175.0(19)
Symmetry operations for equivalent atoms A: ꢂx, ꢂy, ꢂz.
2
5
.1. Synthesis, elemental and spectral analysis of 2-{(E)-[(2-hydroxy-
-methylphenyl)imino]methyl}-4-[(E)-phenyldiazenyl]phenol dye
optimized by using the best level in gas phase. The transition state
TS) method was used to find the transition states [31].
A solution of 2-hydroxy-5-[(E)-phenyldiazenyl]benzaldehyde
(
(
0.25 g, 1.1 mmol) in methanol (30 mL) was added dropwise to a
methanolic solution (20 mL) of 2-amino-4-methylphenol (0.14 g,
.1 mmol). The reaction mixture was refluxed for two hours, on
2.3. X-ray crystallography
1
cooling to room temperature red precipitate formed was collected
by filtration. Single crystal suitable for X-ray diffraction studies
were grown from the methanol solution of the dye by slow
evaporation.
3
A single crystal of dimensions 0.33 ꢃ 0.25 ꢃ 0.08 mm was cho-
sen for the diffraction experiment. Data were collected at 150(2) K
on a Bruker ApexII CCD diffractometer using Mo K radiation
k = 0.71073 Å). The structure was solved by direct methods and
a
(
Yield: 0.34 g 86%, color: red. M.p.: 178–179 °C. Anal. Calc. for
2
refined on F using all the reflections [32]. All the non-hydrogen
atoms were refined using anisotropic atomic displacement param-
eters and hydrogen atoms bonded to carbon atoms were inserted
at calculated positions using a riding model. Hydrogen atoms
bonded to oxygen and nitrogen atoms were located from differ-
ence maps and refined with temperature factors riding on the car-
rier atom. Details of the crystal data and refinement are given
Table 1. Hydrogen bond parameters are given in Table 2 and bond
lengths and angles are given in Tables 3 and 4, respectively.
C
20
H
17
N
3
O
2
ꢁCH
3
OH: C, 69.41; H, 5.82; N, 11.56%. Found: C, 69.24;
H, 5.67; N, 11.64%. ESI-MS (m/z (rel. intensity) assignment): 332
+
+
+ Na]+ (8%).
1
(
26%) [M + H] , 354 (100%) [M + Na] , 685 [M
2
H
NMR: (d-DMSO as solvent, d in ppm,): 15.07 (s, 1H, AN1AH),
9
4
.87 (s, 1H, O1AH), 9.25 (s, 1H, C8AH), 6.22–8.27 (11H, aromatic),
1
3
.17 (s, 1H, AO3AH), 3.22 (s, 3H, C21AH
3
), 2.16 (s, 3H, C5AH
3
).
C
NMR (d-DMSO as solvent, d in ppm): 167.33 (C8), 114.23–159.85
ꢂ1
(
C, aromatic), 48.57 (C21), 20.48 (C5). IR (cm ): 3370 (OAH
str.); 3190 (NAH str); 3060 (CAH str of aromatic); 2912 (CAH str
of aliphatic); 1614 (C10@O2 and C7AN1 str); 1588 (AC@CA str
of aromatic); 1480 (AN@NA str); 1207 (CAO str); 1141 and 877
2.4. Thermal analyses
(
aromatic CAH bond).
Thermal analysis of the dye was performed on SII Exstar
TG/DTA 6200. Thermal stability of the dye (ꢄ1 mg) was studied in
the temperature range of 30–1000 °C under nitrogen atmosphere
at a heating rate of 20 °C/min.
2
.2. Theoretical calculations
The structure of azo-enamine (1), azo-imine (2) and hydrozone-
imine (3) forms were prepared with GaussView 5.0.8 [24]. Calcula-
tions were made with Gaussian 09 AM64L-Revision-C.01 [25].
Density functional theory (DFT/B3LYP) method which is based on
Kohn–Sham theory was used for structure optimizations [26–30].
Tautomer (1) was fully optimized with 6-311G(d,p), 6-31+G(d,p)
and 3-21G basis sets in gas phase. The best level was found to be
B3LYP/6-311G(d,p). After that tautomers (2) and (3) were fully
2
.5. Antimicrobial tests
Cultures of the following four different bacteria were used in
the study: before the antimicrobial tests, all bacteria from the fresh
culture were grown in nutrient broth at 37 °C for 18 h. Each bacte-
rium culture had 10 cfu (colony forming unit)/mL cells.
Diffusion agar test method was used for the dye in dimethyl
sulfoxide and sterilized azo-azomethine solutions of four different
concentrations (1%, 2%, 3% and 4%) levels. A nutrient agar medium
7
Table 1
Crystallographic data for the dye.
(
2
g/L: peptone 5.0; beef extract 1.5; yeast extract 1.5; NaCl 5.0; agar
0; pH 7.5) was prepared and autoclaved at 121 °C for 15 min. Test
organisms were grown overnight at 37 °C, in 10 mL nutrient broth.
mL bacterial cultures were added to the cooled 100 mL nutrient
Identification code
Dye
Empirical formula
Formula weight
Crystal size (mm )
Crystal color
Crystal system
Space group
Unit cell
21 21 3 3
C H N O
363.41
1
3
0.33 ꢃ 0.25 ꢃ 0.08
agar (1%). Sterilized Petri plates with three wells opened (4 mm
in diameter) were prepared with an equal thickness of nutrient
agar. 60 lL of the dye solution was poured into wells on nutrient
agar. Escherichia coli, Klebsiella pneumoniae, Bacillus cereous, and
Staphylococcus aureus aureus test Petri plates were incubated at
37 °C for 24 h. At the end of this period, zone of inhibition formed
on the medium were measured in millimeters (mm).
Red
Monoclinic
P2 /c
1
a (Å)
b (Å)
c (Å)
18.541(2)
4.7091(5)
20.586(2)
90
101.460(2)
90
a
(°)
b (°)
(°)
m
3. Results and discussion
Volume (Å3)
Z
Abs. coeff. (mm
Refl. collected
1761.5(3)
4
0.093
ꢂ1
3.1. Basic properties of 2-{(E)-[(2-hydroxy-5-
methylphenyl)imino]methyl}-4-[(E)-phenyldiazenyl]phenol dye
)
16609
Completeness to h = 28.02°
Ind. Refl. [Rint
R1, wR2 [I > 2
R1, wR2 (all data)
CCDC number
99.6%
]
r
4253[0.0450]
0.0427, 0.0945
0.0701, 0.1083
950594
The red product is stable at room temperature in the solid state
without decomposition. The air-stable red product of the azo-azo-
methine dye is soluble in DMSO, DMF, methanol, ethanol, acetoni-
trile, and chloroform, and insoluble in hexane and water. Elemental
(I)]

9
2
M. Köse et al. / Journal of Molecular Structure 1053 (2013) 89–99
Table 3
Calculated and experimental bond lengths (Å) of tautomers.
Tautomer (1)
Tautomer (2)
Tautomer (3)
Expt.
6-311G(d,p)
6-31+G(d,p)
3-21G
6-311G(d,p)
6-311G(d,p)
O1AC1
C1AC7
C3AC4
C4AC5
C7AN1
C8AC9
C9AC10
C10AC11
C12AC13
C13AN2
N3AC15
C15AC16
C17AC18
C19AC20
C1AC2
C2AC3
C4AC6
C6AC7
N1AC8
C9AC14
C10AO2
C11AC12
C13AC14
N2AN3
C15AC20
C16AC17
C18AC19
1.3528(19)
1.398(2)
1.398(2)
1.511(2)
1.4120(19)
1.408(2)
1.446(2)
1.432(2)
1.425(2)
1.4148(18)
1.4268(19)
1.395(2)
1.385(2)
1.386(2)
1.391(2)
1.386(2)
1.389(2)
1.392(2)
1.3077(19)
1.410(2)
1.2811(17)
1.357(2)
1.372(2)
1.2617(17)
1.389(2)
1.381(2)
1.380(2)
1.366
1.409
1.403
1.512
1.406
1.405
1.475
1.446
1.434
1.407
1.418
1.403
1.397
1.392
1.395
1.395
1.398
1.402
1.329
1.417
1.262
1.367
1.384
1.263
1.408
1.396
1.402
1.366
1.409
1.403
1.512
1.406
1.405
1.475
1.446
1.434
1.407
1.418
1.403
1.397
1.392
1.395
1.395
1.398
1.402
1.329
1.417
1.262
1.367
1.384
1.263
1.408
1.396
1.402
1.382
1.412
1.399
1.519
1.406
1.404
1.473
1.445
1.433
1.411
1.426
1.401
1.397
1.39
1.39
1.396
1.4
1.396
1.33
1.41
1.363
1.41
1.362
1.413
1.394
1.511
1.398
1.466
1.503
1.473
1.448
1.318
1.403
1.4
1.393
1.39
1.391
1.395
1.399
1.4
1.274
1.363
1.219
1.346
1.442
1.315
1.399
1.39
1.386
1.511
1.402
1.452
1.429
1.403
1.406
1.41
1.418
1.389
1.383
1.377
1.382
1.393
1.396
1.389
1.286
1.386
1.332
1.372
1.385
1.256
1.403
1.381
1.388
1.281
1.363
1.381
1.298
1.404
1.393
1.401
1.395
Table 4
Calculated and experimental bond angles (°) of tautomers.
Tautomer (1)
Tautomer (2)
Tautomer (3)
Expt.
6-311G(d,p)
6-31+G(d,p)
3-21G
6-311G(d,p)
6-311G(d,p)
O1AC1AC2
C2AC1AC7
C2AC3AC4
C6AC4AC5
C4AC6AC7
C6AC7AN1
C8AN1AC7
C8AC9AC14
C14AC9AC10
O2AC10AC9
C12AC11AC10
C14AC13AN2
N2AC13AC12
N3AN2AC13
C20AC15AC16
C16AC15AN3
C16AC17AC18
C18AC19AC20
O1AC1AC7
C3AC2AC1
C6AC4AC3
C3AC4AC5
C6AC7AC1
C1AC7AN1
N1AC8AC9
C8AC9AC10
O2AC10AC11
C11AC10AC9
C11AC12AC13
C14AC13AC12
C13AC14AC9
N2AN3AC15
C20AC15AN3
C17AC16AC15
C19AC18AC17
C19AC20AC15
124.95(14)
118.91(14)
121.49(15)
121.42(14)
121.09(14)
123.87(13)
127.45(13)
119.34(14)
119.95(14)
121.60(14)
122.23(14)
117.26(13)
124.01(13)
113.95(12)
119.56(14)
124.91(13)
120.68(15)
119.86(15)
116.14(14)
120.20(15)
117.96(14)
120.62(14)
120.34(14)
115.79(13)
123.72(14)
120.71(13)
122.16(14)
116.24(13)
121.09(14)
118.65(14)
121.79(14)
114.39(12)
115.43(13)
119.56(14)
119.93(15)
120.37(15)
123.9
119.5
121.0
118.2
121.7
123.7
127.4
119.3
120.8
121.8
121.4
125.3
115.8
115.9
119.5
115.7
119.9
120.5
116.6
120.5
118.2
121.1
119.2
117.1
123.2
119.9
122.6
115.7
122.3
118.9
121.0
115.0
124.7
120.4
119.8
119.8
123.8
119.7
121.0
118.2
121.7
123.7
127.4
119.3
120.7
121.4
121.2
125.4
115.6
116.0
119.7
115.6
120.0
120.6
116.6
120.4
118.2
121.0
119.1
117.2
123.0
120.0
122.6
116.0
122.2
119.0
120.8
115.1
124.8
120.4
119.8
119.7
125.1
119.5
120.7
118.5
121.4
124.6
127.7
120.2
121.0
121.9
121.7
125.2
116.0
115.0
119.4
116.0
119.9
120.3
115.4
120.6
118.5
121.3
119.3
116.1
121.9
118.8
122.7
115.5
122.1
118.8
121.1
113.9
124.6
120.5
119.9
120.1
123.0
119.5
121.1
117.8
122.3
123.8
122.4
119.8
119.3
122.0
120.3
125.0
116.2
115.5
119.7
115.6
119.9
120.5
117.5
120.6
117.8
121.3
118.7
117.4
121.7
120.9
118.8
119.2
121.2
118.9
121.2
115.1
124.7
120.3
119.9
119.7
123.0
119.4
121.0
117.8
122.4
122.9
119.7
117.5
119.8
123.1
122.7
126.7
115.7
121.4
120.1
118.2
120.4
121.0
117.6
120.8
117.8
121.5
118.6
118.4
124.9
122.7
121.3
115.5
121.3
117.6
122.9
122.1
121.7
119.9
119.4
119.3

M. Köse et al. / Journal of Molecular Structure 1053 (2013) 89–99
93
Fig. 1. 1H NMR spectrum of the dye.
Fig. 2. 13C NMR spectrum of the dye.
analysis results are given in the experimental section and are in
good agreement with the calculated values. The data are in good
agreement with single crystal X-ray determination.
analysis and single crystal X-ray diffraction study. All aromatic
protons were observed in the range of d 6.22–8.27 ppm.
1
3
The C NMR spectrum of the compound exhibited the signals
due to the presence of aromatic and methylene carbons. Two
aliphatic carbon shifts were observed at d 20.19 and 48.57 ppm as-
signed to methyl groups in aromatic ring and methanol molecule,
respectively. The signal at d 167.33 ppm could be assigned to the
carbon (ANHAC@). All other aromatic carbon shifts were observed
3
3
2
.2. Spectral characterization
.2.1. NMR spectra
The 1H NMR spectrum of the title dye displays a singlet at d
in the range of d 114.23–159.85 ppm. H and C NMR spectra are
displayed in Figs. 1 and 2, respectively. The NMR data showed that
azo-enamine tautomer is maintained in DMSO and agreed with
values reported in literature [33].
1
13
3
.16 ppm corresponding to protons of methyl group (Ph-CH ). A
singlet at d 9.25 ppm was assigned to the proton of (ANACH@)
33]. Two broad signals at d 10.41 and 15.07 ppm could be assigned
[
to protons of enamine (ANHAC@) and phenol (Ph-OH), respec-
tively. The broad signal at the d 4.17 ppm and the singlet at the d
3.2.2. Mass spectrum
3
.22 ppm the corresponding to methanol protons are indicative
The ESI mass spectrum and mass fragmentation assignment of
the compound is shown in Fig. 3 and Scheme 2. Mass spectrum
of the dye showed signals at m/z 332 (26%) and 354 (100%)
of presence of methanol solvate in the compound. Presence of
methanol solvate in the compound was also confirmed by CHN

9
4
M. Köse et al. / Journal of Molecular Structure 1053 (2013) 89–99
Fig. 3. ESI mass spectrum of the dye.
Scheme 2. Mass fragmentation pattern of the dye.

M. Köse et al. / Journal of Molecular Structure 1053 (2013) 89–99
95
2
Fig. 6. Absorption spectra of the dye in DMF–H O mixtures.
Fig. 4. Absorption spectra of the dye in different organic solvents.
+
+
assigned to [M + H] and [M + Na] , respectively. The higher mass
+
peak at m/z 685 (8%) was attributed to [2M + Na] . In the mass
spectrum of the azo-azomethine compound, smaller fragmenta-
tions are also observed at m/z value of 200, 184, 172 and 142
and these fragmentations are assigned in Scheme 2.
3.2.3. IR spectrum
The IR spectrum of the dye shows several bands in 4000–
ꢂ1
4
50 cm region. The bands of the dye are also listed in experimen-
tal section. The functional groups of the dye have been identified
ꢂ1
from the infrared spectrum. The band at 1614 cm was assigned
Fig. 7. Dependence of electronic absorption spectra of the dye on temperature in
to C10@O2 and C7AN1 stretchings. Phenolic AOH group of the
dye containing AN@NA chromophore group was characterized
by an absorption band at 3370 cm . The aromatic and aliphatic
DMF.
ꢂ1
(
methyl) moieties in the compound were identified by the bands
ꢂ1
ꢂ1
at 3060 cm (aromatic CAH stretching) and 2912 cm (aliphatic
CAH stretching). Two bands at 1480 and 1588 cm were assigned
ꢂ1
to the azo group AN@NA and AC@CA (aromatic) stretchings,
ꢂ1
respectively. Bands at 1207 and 1141 cm were assigned to the
CAO and CAH (aromatic) stretchings, respectively. The synthe-
sized dye may exist in three possible tautomeric forms, in solid
state and solution namely (i) azo-imine form, (ii) azo-enamine
form and (iii) hydrazone-imine form as depicted in Scheme 1.
The single crystal X-ray diffraction study on the dye clearly indi-
cates that the present compound exists in azo-enamine form
rather than in azo-imine form and hydrazone-imine form in the
solid state.
3.2.4. Electronic absorption spectra
The UV–Vis absorption spectra of the synthesized dye were
measured in the range of 275–550 nm in three organic solvents
Fig. 8. Molecular structure with atom numbering thermal ellipsoid 50% probability.
ꢂ5
CHCl
Fig. 4). In CHCl
in the range of 345–355 nm were assigned to the
3
DMSO and DMF (C = 2.5 ꢃ 10 M) at room temperature
(
3
, DMSO and DMF, maximum absorptions observed
*
p
?
p
transi-
tions of
p
electrons in the structure. Absorption intensity of the
*
p
?
p
transitions decreased in order of CHCl
3
, DMSO and DMF
transitions in chloroform which
*
(
hyperchromic effect). The
p
?
p
is an apolar and aprotic solvent was observed at shorter wave-
length (hyposochromic effect) with higher absorption intensities
*
(
hyperchromic effect) than in DMF and DMSO. The
p
?
p
transi-
tions in DMSO and DMF were observed approximately in the same
Fig. 9. Intra- and intermolecular hydrogen bonding within the structure. Symmetry
code: ꢂx, ꢂy, ꢂz.
3
Fig. 5. Absorption spectra of the dye in DMF–CHCl .

9
6
M. Köse et al. / Journal of Molecular Structure 1053 (2013) 89–99
Table 5
ꢂ1
Total and Gibbs free energies (kJ mol ) of tautomers (1), (2) and (3).
Tautomer (1)
Tautomer (2)
Tautomer (3)
ꢂ1
E (kJ mol
)
ꢂ2853791.1
ꢂ2853991.4
ꢂ2853805.9
ꢂ2854003.2
ꢂ2853712.9
ꢂ2853914.8
ꢂ1
G° (kJ mol
)
*
the same absorption intensity in DMSO. However, n ?
p
transi-
tions were not seen in chloroform.
The UV–Vis absorption spectra of the dye at different volume
ꢂ5
Fig. 10.
p
ꢁꢁꢁ
p
interactions within the structure of the dye.
ratios of the applied pair solvents DMF/CHCl
3
(C = 2.5 ꢃ 10 M)
were also measured. The absorption curves of the dye in
DMF–CHCl mixtures are shown in Fig. 5. It can be seen from Fig. 5
3
that the absorption intensity at 350 nm decreased with increase
in polarity of the solutions. However, the absorption intensity at
4
50–500 nm increased with increase in polarity of the mixtures.
The UV–Vis absorption spectra of the dye at different volume
ratios of the applied pair solvents DMF/H
Fig. 6). No particular differences were observed in UV–Vis absorp-
tion spectra of the dye in water–DMF (25% and 50% Water/DMF)
2
O were also measured
(
*
solutions. The
p ? p transitions shifted to lower absorption inten-
*
sity (hypochromic effect). However, the n ?
p
transitions in the
range of 450–500 nm shifted higher absorption values.
The UV–Vis spectra of the compound in DMF solvent were
worked in the range of 300–530 nm at 8 °C, 40 °C and 80 °C,
respectively (Fig. 7). Absorption intensities of the compound
decreased with the increase in temperature (hypochromic effect).
3.3. X-ray structure
Perspective view of the compound is shown in Fig. 8. The com-
pound crystallizes in monoclinic crystal system, P2 /c space group
1
with unit cell parameters a = 18.541(2), b = 4.7091(5),
3
c = 20.586(2) Å, b = 101.460(2)°, V = 1761.5(3) Å and Z = 4 (final
refinement value R = 0.0427).
Fig. 11. Packing diagram, non-hydrogen bonded hydrogen atoms are omitted for
All bond lengths and angles are within the normal ranges. X-ray
investigation of the compound showed that azo-enamine tautomer
is favoured in the solid state. The C10AO2 bond length of
1.2811(17) Å indicates a double bond character, whereas the
C8AN1 bond length of 1.3077(19) Å is longer than a double bond
(C@N) character and the C8AC9 bond length of 1.408(2) Å is longer
than a double bond (C@C) character.
clarity; hydrogen bonds are shown as dashed lines.
region with higher wavelength (batochromic effect). In both DMF
and DMSO, an absorption band was observed in the 450–500 nm
*
range assigned to the n ?
p
transitions of azo-aromatic chromo-
phore and intermolecular charge transfer interaction [33,34]. The
*
absorption intensity of n ?
p transitions in DMF is higher than
Fig. 12. Optimized structures of tautomers (1), (2) and (3).

M. Köse et al. / Journal of Molecular Structure 1053 (2013) 89–99
97
Fig. 13. Contour diagrams of frontier molecular orbitals for tautomers (1), (2) and (3).
Fig. 14. The structure of transition state (upper) and IRC graphic (below).
Fig. 15. TGA–DTA curves for the dye.

9
8
M. Köse et al. / Journal of Molecular Structure 1053 (2013) 89–99
Table 6
Thermal analyses data for the dye.
Decomposition steps
DTA peak range (°C)
TG range (°C)
DTGmax (°C)
%Wt. loss Calcd. (Found)
Assignments
Loss of H O lattice
Loss of CH OH lattice
Loss of 4-methylphenol unit
I
II
III
IV
99 (endo)
–
197 (endo)
529 (endo)
649 (exo)
68–104
104–172
172–387
387–605
–
98
(3.1)
(8.8)
(33)
(4.6)
(50.5)
2
135
296
532
–
3
Residue
Table 7
Aromatic rings (C9AC14) and (C15AC20) adopt the trans config-
uration with regard to the azo double bond (AN2@N3A) with a
distance of 1.2617(17) Å the torsion angle C13AN2AN3AC15 of
Zone of inhibition for the dye against the selected microbes.
Concentration (%)
Zone of inhibition (diameter, mm)
Gram (ꢂ)
Gram (+)
1
[
74.54(12) Å which is in good agreement with published values
25].
The molecules crystallise as dimers, assembled by two metha-
E. coli
K. pneumoniae
B. cereous
S. aureus
1
2
3
4
–
–
–
–
–
–
–
–
–
–
26
28
28
30
–
22
24
28
29
–
nol molecules via intermolecular hydrogen bonding. A methanol
solvate involved in hydrogen bonding with both central (as donor)
and outer phenol groups (as acceptor) linking two molecules to-
DMSO(control)
4
6
gether resulting in a R ð18Þ hydrogen bonding motif. There is also
–: ineffective.
an intramolecular hydrogen bonding (NAHꢁ ꢁ ꢁO) in the molecule
forming a S(6) graph set motif (Fig. 9) (Table 2).
In the structure, the azo benzene ring slightly twisted with re-
spect to the central benzene ring. The mean planes of C1AC7 and
C15AC20 are at 6.31(9) and 24.94(7)° to the central (C9AC14) ring,
respectively. This is possibly a consequence of the intermolecular
interactions in the lattice. Dimeric units in the structure are linked
Contour diagrams of HOMO and LUMO can be used to predict
the reactive region of tautomers. Contour diagrams of frontier
molecular orbitals of tautomers were represented in Fig. 13. HOMO
and LUMO of tautomers are mainly delocalized on all atoms of
molecules.
via
.431 Å (under symmetry operation of x, ꢂ1 + y, z) (Fig. 10). Crystal
packing of the compound is determined by intermolecular hydro-
gen bonding and interactions. The packing plot of the com-
pound is shown in Fig. 11.
p–p interactions, C6 and C8 is separated by a distance of
3
3.6. Transition state
p–p
The transformation between tautomer (1) and tautomer (2) was
investigated by using transition state method. Because Gibbs free
energy and total energy of tautomer (1) and (2) are close to each
other. The transition state (TS) was calculated to explain the trans-
formation. Imaginary frequencies (IF) indicate that the calculated
structure is the transition state. The optimized structure of the
transition state and intrinsic reaction coordinate (IRC) versus total
energy graphic were represented in Fig. 14.
3.4. Optimized structures
Fig. 12 shows the optimized structures of tautomers (1), (2) and
(
(
3). Calculated bond lengths and angles of tautomers (1), (2) and
3) were given in Tables 3 and 4, respectively.
Compared with experimental and calculated bond lengths/
As can be seen from IRC graphic, the highest energy state corre-
sponds to optimal transition state. The optimal transition state has
angles of tautomer (1), it can be seen that B3LYP/6-311G(d,p) level
is the best level. The differences average between experimental
and calculated bond lengths of tautomer (1) is 0.009 Å. The
differences average between experimental and calculated bond
angles of tautomer (1) is 1.6°. These results show that there is a
good agreement between experimental and optimized structure
of tautomer (1).
ꢂ1
ꢂ1120.80 cm negative frequency. The distances between N1ꢁ ꢁ ꢁH
and O2ꢁ ꢁ ꢁH were obtained as 1.2029 Å and 1.2905 Å, respectively.
The structure of the TS are closer to the tautomer (1) than to the
tautomer (2). Because N1ꢁꢁꢁH distance is smaller than O2ꢁ ꢁ ꢁH dis-
tance [35]. This result indicates that tautomer (1) is more stable
than tautomer (2) in the gas phase.
3.5. The stability of tautomers
3.7. Thermal analyses
The total energy (E) and Gibbs free energy (G°) were calculated
to predict the stability of tautomers in gas phase and given in
Table 5.
The tautomer with the lowest energy has the most stability. The
stability ranking of tautomers should be:
Thermal analysis of the dye was performed on SII Exstar
TG/DTA 6200. Thermal stability of the dye (ꢄ1 mg) was studied
in the temperature range of 30–1000 °C under nitrogen atmo-
sphere at a heating rate of 20 °C/min. The thermal analysis curves
(TG and DTA) of the studied complex are shown in Fig. 15. Thermal
decomposition data for the compound is illustrated in Table 6. The
examination of TG and DTA curves that the compound has four
decomposition steps. It was found that the compound thermally
stable up to 172 °C and started to lose mass in the 68–104 °C
range (3%). In the second step, 8.8% of the compound was lost.
These two decomposition steps (3.3% and 8.8%) correspond to loss
of the hydrate water and methanol solvates in the structure,
respectively. Thermal decomposition of the framework of the title
dye starts at 172 °C. In the 172–387 °C range the mass loss was 33%
and this was assigned to the loss of 4-methylphenol unit of the dye.
(
(
2) > (1) > (3) (according to the E)
2) > (1) > (3) (according to the G°)
Taken into account E and G°, the most unstable tautomer is tau-
tomer (3). However, E and G° of tautomers (1) and (2) are close
each other. For E and G°, the differences of energies are 14.8 and
ꢂ1
1
1.8 kJ mol , respectively. These differences indicates that tau-
tomers (1) and (2) can be easily transformed each other. The deter-
mination of stability is difficult between tautomers (1) and (2).

M. Köse et al. / Journal of Molecular Structure 1053 (2013) 89–99
99
Further mass loss was observed in the 387–605 °C with a 4.6%
mass loss.
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[
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