Thermal, spectroscopic studies and hydrogen bonding in supramolecular assembly of azo rhodanine complexes

Article abstract of DOI:10.1016/j.ica.2015.02.031

A novel series of Cu(II) complexes of azo rhodanine derivatives (HL_n) have been prepared and characterized by thermal analysis, spectral studies (IR, mass, UV-Vis, ESR) and magnetic measurements. IR spectra suggest that the HL_n acts as a bidentate ligands coordinating via (NN) and deprotonated enolized carbonyl oxygen (-C-O-). ESR spectra of the Cu(II) complexes show d_x2-y2 as a ground state, suggesting tetrahedral distorted or square planar geometries around Cu(II) center. The X-ray diffraction (XRD) patterns powder forms of Cu(II) complexes shows many diffraction peaks which indicates the polycrystalline phase. Thermal properties and decomposition kinetics of compounds are investigated. The thermodynamic parameters and evaluation of kinetic parameters (E_a, ΔS^?, ΔH^? and ΔG^?) of thermal decomposition stages have been evaluated using Coats-Redfern and Horowitz-Metzger methods. Cu(II) complexes are screened for their biological activity against bacterial and fungal species. The Cu(II) complexes showed antimicrobial activities against Staphylococcus aureus and Penicillium italicum.

Full text of DOI:10.1016/j.ica.2015.02.031

Accepted Manuscript
Thermal, spectroscopic studies and hydrogen bonding in supramolecular as-
sembly of azo rhodanine complexes
A.Z. El-Sonbati, M.A. Diab, A.A. El-Bindary, G.G. Mohamed, Sh.M. Morgan
PII:
S0020-1693(15)00124-3
http://dx.doi.org/10.1016/j.ica.2015.02.031
ICA 16449
DOI:
Reference:
Inorganica Chimica Acta
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26 December 2014
25 February 2015
27 February 2015
Please cite this article as: A.Z. El-Sonbati, M.A. Diab, A.A. El-Bindary, G.G. Mohamed, Sh.M. Morgan, Thermal,
spectroscopic studies and hydrogen bonding in supramolecular assembly of azo rhodanine complexes, Inorganica
Chimica Acta (2015), doi: http://dx.doi.org/10.1016/j.ica.2015.02.031
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Thermal, spectroscopic studies and hydrogen bonding in supramolecular
assembly of azo rhodanine complexes
A.Z. El-Sonbati1,+, M.A. Diab1, A.A. El-Bindary1, G.G. Mohamed2, Sh.M. Morgan1
1Chemistry Department, Faculty of Science, Damietta University, Damietta, Egypt
2Chemistry Department, Faculty of Science, Cairo University, Giza, Egypt
Abstract
A novel series of Cu(II) complexes of azo rhodanine derivatives (HLn) have been
prepared and characterized by thermal analysis, spectral studies (IR, mass, UV-
visible, ESR) and magnetic measurements. IR spectra suggest that the HLn acts as a
bidentate ligands coordinating via (N=N) and deprotonated enolized carbonyl oxygen
(-C-O-). ESR spectra of the Cu(II) complexes show dx2-y2 as a ground state,
suggesting tetrahedral distorted or square planar geometries around Cu(II) center. The
X-ray diffraction (XRD) patterns powder forms of Cu(II) complexes shows many
diffraction peaks which indicates the polycrystalline phase. Thermal properties and
decomposition kinetics of compounds are investigated. The thermodynamic
parameters and evaluation of kinetic parameters (Ea, ∆S*, ∆H* and ∆G*) of thermal
decomposition stages have been evaluated using Coast-Redfern and Horowitz-
Metzger methods. Cu(II) complexes are screened for their biological activity against
bacterial and fungal species. The Cu(II) complexes showed antimicrobial activities
against Staphylococcus aureus and Penicillium italicum.
Keywords: Azodye complexes; ESR; Thermal properties; Thermodynamic
parameters; Antimicrobial activity.
________________
+Corresponding author Tel.: +201060081581; fax: +20 572403868.
E-mail address: elsonbatisch@yahoo.com (A.Z. El-Sonbati).
1

1.
Introduction
Azodyes are an important class of organic colorants which consist of at least a
conjugated chromophore azo (-N=N-) group and the largest and most versatile class
of dyes. It has been known for many years that azo compounds are the most widely
used class of dyes due to their versatile application in various fields such as the dyeing
of textile fiber and coloring of different materials, and for plastics, biological-medical
studies, and advanced applications in organic synthesis [1-4].
Over the past decades, azodyes and their transition metal complexes have made
significant contribution in the development of co-ordination chemistry. The most
important step in the development of metal complexes was perhaps the preparation of
a new ligand which exhibit unique properties and novel reactivity. Since, the electron
donor and electron acceptor properties of the ligand, structural functional groups and
the position of the ligand in the coordination sphere together with the reactivity of
coordination compounds may be a factor of different studies [4-6]. Azodyes metal
complexes have been studied extensively [6-9] because of their attractive chemical
and physical properties and their wide range of applications such as catalysts,
antimicrobials and corrosion inhibitors. The presence of the nitrogen atoms of the azo
group makes the azodyes more significant chemically and biologically [5,10].
Azo compound based on rhodanine, play a central role as chelating agents for
a large numbers of metal ions, as they form a stable six- member ring after
complexation with a metal ion and also it could be used as analytical reagents [11,12].
The complex-formation equilibrium have been reported for several kinds of rhodanine
derivatives [4,13-15]. Potentiometry, conductivity and spectroscopy measurements on
the coordination ability biologically important azo derivatives have shown that their
complexes are very stable [16-18].
In this present study, we report the synthesis, characterization of Cu(II)
complexes of azo rhodanine derivatives ligands (HLn). The structure of the isolated
complexes is elucidated using elemental analyses, IR, mass spectra, magnetic
moment, ESR and thermogravimetric analysis. The activation thermodynamic
parameters were calculated using Coats–Redfern and Horowitz-Metzger methods.
Study of the antimicrobial activities of Cu(II) complexes.
2

2. Experimental
All the chemicals used were of British Drug House quality.
2.1. Synthesis of 5-(4'-derivatives phenylazo)-2-thioxothiazolidin-4-one (HLn)
In a typical preparation, 25 ml of distilled water containing 0.01 mol
hydrochloric acid were added to aniline (0.01 mol) or p-derivatives. To the resulting
mixture stirred and cooled to 0 ºC, a solution of 0.01 mole sodium nitrite in 20 ml of
water was added dropwise. The formed diazonium chloride was consecutively
coupled with an alkaline solution of 0.01 mol 2-thioxo-4-thiazolidinone, in 10 ml of
pyridine. The colored precipitate, which formed immediately, was filtered through
sintered glass crucible, washed several times with water and ether then dried in a
vacuum desiccator over P2O5. The elemental analyses of the ligands (HLn) are given
in Table 1.
2.2. Preparation of the complexes
CuCl2.2H2O (0.01 mol) in 30 ml ethanol was added to a solution of HLn (0.01
mol) in 30 ml ethanol. The mixture was then refluxed on a water bath for ~ 4 h and
allowed to cool whereby the solid complexes were separated, which filtered off,
washed several times with ethanol, the solid was dried in a vacuum desiccator over
P2O5.
2.3. Biological activity investigation
For this investigation the agar well diffusion method was applied [5,10]. The
antibacterial activities of the investigated compounds were tested against two local
Gram positive bacterial species (Bacillus cereus and Staphylococcus aureus) and two
local Gram negative bacterial species (Escherichia coli and Klebsiella pneumoniae)
on nutrient agar medium. Also, the antifungal activities were tested against four local
fungal species (Aspergillus niger, Alternaria alternata, Penicillium italicum and
Fusarium oxysporium) on DOX agar medium. The concentrations of each solution
were 150, 100 and 50 µg/ml in dimethyl formamide (DMF). By using a sterile cork
borer (10 mm diameter), wells were made in agar medium plates previously seeded
with the test microorganism. 200 µl of each compound was applied in each well. The
agar plates were kept at 4 °C for at least 30 min to allow the diffusion of the
compound to agar medium. The plates were then incubated at 37 °C or 30 °C for
bacteria and fungi, respectively. The diameters of inhibition zone were determined
after 24 h and 7 days for bacteria and fungi, respectively, taking the consideration of
3

the control values (DMF). Penicillin and miconazole were used as reference
substances against bacteria and fungi, respectively.
2.4. Analytical and physical measurements
Elemental microanalyses of the separated compounds for C, H, N and S were
determined on Automatic Analyzer CHNS Vario ELIII, Germany. The analyses were
repeated twice to check the accuracy of the analyzed data. The 1H-NMR spectra were
obtained with a JEOL FX90 Fourier transform spectrometer with DMSO-d6 as the
solvent and TMS as an internal reference. The infrared spectra were recorded as KBr
discs using a Perkin-Elmer 1340 spectrophotometer. Mass spectra were recorded by
the EI technique at 70 eV using MS-5988 GS-MS Hewlett-Packard. X-ray diffraction
analysis of complexes powder forms was recorded on X-ray diffractometer in the
range of diffraction angle 2θo = 4-70o. This analysis was carried out using CuKα
radiation (λ = 1.540598 Ả). The applied voltage and the tube current are 40 KV and
30 mA, respectively. Ultraviolet-visible (UV-Vis) spectra of the compounds were
recorded in nuzol solution using a Unicom SP 8800 spectrophotometer. The magnetic
moment of the prepared solid complexes was determined at room temperature using
the Gouy`s method. Mercury(II) (tetrathiocyanato)cobalt(II), [Hg{Co(SCN)4}], was
used for the calibration of the Gouy tubes. Diamagnetic corrections were calculated
from the values given by Selwood [19] and Pascal’s constants. Magnetic moments
were calculated using the equation, µeff. = 2.84 [TχMcoor.]1/2. Thermal studies were
computed on Simultaneous Thermal Analyzer (STA) 6000 system using
thermogravimetric analysis (TGA) method. Thermal properties of the samples were
o
analyzed in the temperature range from 30 to 800 °C at the heating rate of 10 C/min
under dynamic nitrogen atmosphere. ESR measurements of powdered samples were
recorded at room temperature using an X-band spectrometer utilizing a 100 kHz
magnetic field modulation with diphenyl picrylhydrazyle (DPPH) as a reference
material. The conductance measurement was achieved using Sargent Welch scientific
Co., Skokie, IL, USA.
3. Results and discussion
3.1. Stoichiometry of the copper(II) complexes
The stoichiometry of the complexes have been deduced from their elemental
analysis (Table 2), which indicates that the metal complexes fall into 1:1 (monomeric)
(metal:ligand). The ligands (HLn) are mononucleating and hence require one metal
4

ion for coordination. All the products were partially soluble in common organic
solvents. Microanalytical data are in good agreement with stoichiometry proposed for
complexes (Table 2). The elemental analysis correspond to the general formula
[Cu(Ln)(OH2)Cl].nH2O for all complexes. The principle HLn ligands undergoes mono
deprotonation to form Ln in Cu(II) complexes and acts as a bidentate ligand occupying
two positions of an geometrical structure. The formation of the complexes may be
represented by the following reaction:
CuCl2.2H2O + HLn → [Cu(Ln)(OH2)Cl].nH2O
+
HCl
where Ln represents the anion of HLn
3.2. Molar conductance of the complexes
The molar conductance of 10-3 M of solutions of the Cu(II) complexes in
DMSO is calculated at 25 2 oC. It is concluded from the results that Cu(II) chelates
under investigation were found to have molar conductance values of the compounds
(1:1)(M:Ln) shows that they are non-electrolytic. This indicates that the anions are
involved in the coordination sphere [18]. This is in accordance with the fact that
conductivity values for a non-electrolyte are below 50 Ω-1 mol-1 cm2 in DMSO
solution [8,14]. Such a non-zero molar conductance value for each of the complex in
the present study is most probably due to the strong donor capacity of DMSO, which
may lead to the displacement of anionic ligands and change of electrolyte type [18].
3.3. Infrared spectra and nature of coordination
The infrared spectra of ligands (HLn) give interesting results. The broad
absorption band located at ∼3400 cm–1 is assigned to υ(OH). The low frequency
bands indicate that the hydroxyl hydrogen atom is involved in keto ↔ enol
tautomerism through hydrogen bonding (A↔B, Fig. 1). The two bands located at
1330 and 1370 cm−1 are assigned to in-plane deformation and the band at 1130 cm−1
is due to υ(C–OH) (Fig. 1-C). The ligands give two bands at ∼3200_3040 cm–1
which can assigned to asymmetric and symmetric stretching vibrations of N–H
group and intramolecular hydrogen bonding NH····O systems (Fig. 1-D),
respectively. However, if such a mechanism is taking place in case of intermolecular
hydrogen bond, the OH····O and OH····N bond distances differ (Fig. 1-E and 1-F,
respectively).
5

By comparing the infrared spectra of the free ligands to that of the prepared
complexes the following points are observed:
1. The appearance of a new bands around ~3360 cm-1 and two sharp bands at ~715
and 430 cm-1, the latter two can be assigned to the wagging and rocking modes of
vibration of the water molecule, respectively, [14,18] in the prepared complexes (1-5)
may be taken as a strong evidence for the presence of coordinated water.
2. In the IR spectra of all the ligands, the band at ~1535 cm−1 due to the υ(–N=N–)
mode is observed. In the metal chelates, this frequency is lowered by 10–25 cm−1
indicating the bonding of the azo nitrogen to the copper atom. The υ(C–N) vibration
appearing at ~1480 cm−1 in the ligands suffers a downward shift of ~10 cm−1, thereby
supporting the assumption that the copper ion is coordinated to one of the azo
nitrogen atoms.
3. Further proof for the involvement of both enol oxygen and azodye-nitrogen atoms
in complexation is the appearance of weak bands in the complexes in the range of
465-500 and 430-445 cm-1 due to υ(Cu-O) and υ(Cu-N), respectively, [7,14] which
are absent in the free ligands.
According to the structure as shown in Fig. 2, the ligand (HLn) takes its usual
anionic form (Ln) to chelate Cu(II) through N- of azo group and oxygen atom of enol
group (Fig. 1-C).
3.4. 1H NMR spectra
The 1H NMR spectra of azo rhodanine and its derivatives show signal for CH (~
4.42 ppm), favoring formation of an intramolecular hydrogen bond with the N=N
(azodye) group. Electron-withdrawing substituents reduce the intramolecular
hydrogen bond as indicated by the marked shift of the hydroxyl signal to higher field
in the p-NO2 compounds. Electron-donating substituents give the opposite effect,
arising from the increasing basicity of the azonitrogen. The broad signals assigned to
the OH protons at ~11.36–11.88 ppm are not affected by dilution. The previous two
protons disappear in the presence of D2O. Absence of –CH proton signal of the ligand
moiety indicated the existence of the ligands in the azo-enol form. According to
El-Sonbati et al. [5-9], hydrogen bonding leads to a large deshielding of the protons.
The shifts are in the sequence: p-(NO2 > H > OCH3). In the meantime, the 1H NMR of
the HL1 exhibits signals at δ(ppm) [3.9 (s, 3H, OCH3)]. The aromatic protons have
resonance at 7.10–7.45 ppm for the ligands. The chemical shifts, δ, ppm owing to NH
proton (of rhodanine) remain practically unchanged in the complexes, indicating that
6

(NH of rhodanine) nitrogen does not involved in ligands coordination to the metal.
Absence of CH proton signal of the rhodanine azo moiety indicated the existence of
the ligands in the azo-enol form.
3.5. Mass spectra
The electron impact mass spectra of Cu(II) complexes (2-5) are recorded and
investigated at 70 eV of electron energy. The mass spectra of the studied Cu(II)
complexes are characterized by moderate to high relative intensity molecular ions
peaks at 70 eV. It is obvious that, the molecular ion peaks are in good agreement with
their suggested empirical formula as indicated from elemental analyses (Table 2). The
mass spectral fragmentation mode of Cu(II) complex (3) (Fig. 3) shows the exact
mass of 353, corresponding to the formula [CuC9H6N3OS2Cl (OH2)]. The ion of m/z =
353 undergoes fragmentation to a stable peak at m/z = 237 by losing chlorine atom, water
molecule and copper ion (structure I) as shown in scheme 1. The loss of C2HNOS molecule
leads to the fragmentation with m/z = 150 (structure II). The loss of sulpher atom leads to
the fragmentation with m/z = 118 (structure III). A breakdown of the backbone of
complex (3) gives the fragments (IV) and (V). The mass spectra of Cu(II) complexes
(2, 4 and 5) gives mass peaks at 385, 405 and 416, respectively, corresponding to the
formulae [CuC10H8N3OS2Cl (OH2)]H2O, [CuC9H5N3OS2Cl2 (OH2)]H2O and
[CuC9H5N4O3S2Cl (OH2)]H2O as shown in Figures S1, S2 and S3, respectively, in the
supplementary. The stable fragmentation of the mass spectra of the complexes is in
good agreement with the proposed molecular formula for these complexes.
3.6. X-ray diffraction
Single crystals of the complexes could not be prepared to get the XRD and
hence the powder diffraction data were obtained for structural characterization.
Structure determination by X-ray powder diffraction data has gone through a recent
surge since it has become important to get to the structural information of materials,
which do not yield good quality single crystals.
The X-ray diffraction (XRD) patterns powder forms of Cu(II) complexes (2-4)
are presented in Fig. 4. The XRD of Cu(II) complexes (2-4) shows many diffraction
peaks which indicates the polycrystalline phase. The average crystallite size (ξ) can be
calculated from the XRD pattern according to Debye-Scherrer equation [20,21]:
Kλ
ξ =
.
(1)
β1/ 2 cosθ
7

The equation uses the reference peak width at angle (θ), where λ is wavelength of X-
ray radiation (1.541874 Å), K is constant taken as 0.95 for organic compounds [21]
and β1/2 is the width at half maximum of the reference diffraction peak measured in
radians. The dislocation density,δ, is the number of dislocation lines per unit area of
the crystal. The value of δ is related to the average particle diameter (ξ) by the relation
[22]:
1
ξ 2
δ =
.
(2)
The values of ξ are calculated and found to be 210, 267 and 316 nm for complexes
(2), (3) and (4), respectively. The values of δ are 2.27 × 10-5, 1.40 × 10-5 and
1.00 × 10-5 nm-2 for complexes (2), (3) and (4), respectively.
3.7. Magnetic moment and electronic spectra
The magnetic moment of all the Cu(II) complexes at room temperature lie in
the range 1.84-1.94 B.M. corresponding to one unpaired electron [23]. This indicates
that these complexes are monomeric in nature and the absence of metal-metal
interaction. This behavior suggest square planar geometry for the Cu(II) complexes
[24]. The electronic spectra of complexes (1-5) showed two weak, low energy bands
in the region of 14980-15260 and 20865-21290 cm-1, respectively, which may be
2
2
2
assigned to B1g → A1g and B1g
→
2Eg transitions in a distorted square planar
ligands field [25].
3.8. ESR spectra
The spin Hamiltonian parameters of the complexes were calculated and
presented in Table 3. In axial symmetry the g-values are related by the expression G =
(gll-2)/(g⊥-2) = 4, where G is the exchange interaction parameter. According to
Hathaway and Billing [26], if the value of G is greater than 4, the exchange
interaction between Cu(II) centers in the solid state is negligible, whereas when is less
than 4, considerable exchange interaction is indicated in the solid complex. The
observed value for the exchange interaction parameter for the complex (1) (G = 3.1)
suggests the significant exchange coupling is present and the misalignment is
appreciable, and the unpaired electron is present in the dx2-y2 orbital. This result also
indicates that the exchange coupling effects are not operative in the present complex.
The tendency of All to decrease with an increase of gll is an index of an increase of the
8

tetrahedral distortion in the coordination sphere of copper. In order to quantify the
degree of distortion of the Cu(II) complexes. We selected the f factor gll/All obtained
from the ESR spectra. Although the factor, which is considered as an empirical index
of tetrahedral distortion [27]. Its value ranges between 105 and 135 for square planar
complexes, depending on the nature of the coordinated atoms. In the presence of a
tetrahedral distorted structure the values can be much larger [9]. For all copper(II)
complexes the gll/All quotient is demonstrating the presence of significant dihedral
angle distortion in the xy-plane and correlate well with the tetrahedral distortion from
square planar geometry arrangement around copper center. In a square planar Cu(II)
complex, the unpaired electron residue in the dx2-y2 orbital giving 2B1g as the ground
state with gll and g⊥ are given in the order gll > g⊥ > 2, while the unpaired electron lies
in the d2z orbital giving 2A1g as the ground state with g⊥ > gII > 2.
2
As shown in Table 3, the values of gll, α2 and Kll are related to the nature of
the p-substituent as they increase according to the following order p-(NO2 > H >
OCH3). This can be attributed to the fact that the effective charge increased due to the
electron withdrawing p-substituent in complex (5) while it decreased by the electrons
donating character of complex (1). This is in accordance with that expected from
2
Hammett’s constant (σR) as shown in Fig. 5, correlate the values of gll, α2 and Kll
with σR it is clear that all these values increase with increasing σR.
Significant information about the nature of bonding in the Cu(II) complexes can
be derived from the relative magnitudes of K2 and K2 . In the case of pure σ-bonding,
ll
⊥
K2 ≈ K2 = 0.77, whereas K2 < K2 implies considerable in-plane π-bonding, while
ll
⊥
ll
⊥
for out-of plane π-bonding K2ll > K2 . Molecular orbital coefficients α2 (in-plane σ-
⊥
bonding), β2 (in-plane π-bonding) and γ2 (out-plane π-bonding) were calculated. The
α2 values for the present copper complexes lie in the range of 0.58-0.72 supporting the
covalent nature of these complexes (Table 3). The observed β2 values (1.03, 1.00 and
0.91) and γ2 values (0.96, 1.01 and 1.17) shows that there is interaction in the out-of-
plane π-bonding, whereas the in-plane π-bonding is predominantly ionic. This is also
confirmed by orbital reduction factors [28] which were estimated from the simple
relations. For the present complexes, the observed order K2⊥ > K2 implies a greater
ll
contribution from in-plane π-bonding than for out-of-plane π-bonding in metal-ligand
π-bonding. Thus, the ESR study of the copper complexes has provided supporting
2
evidence for the optical results. We found that the values of Kll and K⊥2 increase with
increasing gll and g⊥ as shown in Fig. 6.
9

3.9. Thermogravimetric analysis study
The Thermogravimetric analysis (TGA) curves for the ligands (HLn) (where n =
1, 3 and 5) and their Cu(II) complexes (1, 3 and 5) are shown in Figs. 7 and 8. For
HL1 and HL3 there are two stages of the loss of masses, while for HL5 there are three
stages [17]. The first degradation stage for ligand (HL ) takes place in the range of
1
o
200-320 C was corresponding to the loss of C3H2S2N3O molecule, representing a
weight loss of 61.90% and its calculated value was 59.93%. The second degradation
o
stage takes place in the range of 320-655 C was corresponding to the loss of C7H7O
molecule, representing a weight loss of 38.10 % and its calculated value was 40.07%.
In HL3 ligand, the first degradation stage takes place in the range of 145-400 oC
was corresponding to the loss of C3H2S2N2O molecule, representing a weight loss of
59.80% and its calculated value was 61.60%. The second degradation stage takes
o
place in the range of 400-655 C was corresponding to the loss of C6H5N molecule,
representing a weight loss of 39.90% and its calculated value was 38.39%.
o
On the other hand, the first degradation stage in the range of 30-112 C for
ligand (HL5) was corresponding to the loss of solvent molecule [17]. The second
o
degradation stage takes place in the range of 112-284 C was corresponding to the
loss of C3H2S2 molecule, representing a weight loss of 35.60% and its calculated
o
value was 36.17%. The third degradation stage takes place in the range of 284-640 C
was corresponding to the loss of C6H4N4O3 molecule, representing a weight loss of
58.70% and its calculated value was 63.83%.
The TGA curves of Cu(II) complexes are taken as a proof for the existing of
water molecule as well as the anions to be coordination sphere. The temperature
intervals and the percentage of loss of mass are listed in Table 4. The first stage of
decomposition in the range ~30-80 ºC for Cu(II) complexes can be attributed to loss
of lattice water molecule [7,18] (Fig. 8). The second stage of decomposition
corresponds to the loss of coordinated water molecule, HCl molecule and
decomposition of a part of the ligand. The third stage of decomposition is due to
decomposition of a part of ligand leaving copper oxide as a residue. The third stage is
attributed to loss of a part of the ligand. The final weight losses are due to the
decomposition of the rest of the ligand leaving copper oxides residue (Table 4).
3.10. Kinetic studies
The kinetic parameters such as activation energy (Ea), enthalpy (∆H*), entropy
(∆S*), and Gibbs free energy change of the decomposition (∆G*) are evaluated
10

graphically by employing the Coast-Redfern [29] and Horowitz-Metzger [30]
methods. The thermodynamic data obtained with the two methods for the
decomposition stages for Cu(II) complexes (1, 3 and 5) are in harmony with each
other as shown in Table 5 and Figures 9 and 10. The kinetic data obtained from the
two methods are comparable and can be considered in good agreement with each
other.
The high values of the energy of activation (Ea) of the complexes reveal the
high stability of such chelates due to their covalent bond character [31]. The relation
between Ea and Hammett’s substituent coefficients (σR) for Cu(II) complexes (1, 3
and 5) is shown in Fig. 11. It is obvious that the values of Ea for Cu(II) complexes (1,
3 and 5) increase with increasing σR, attributable to the fact that the effective charge
experienced by the d-electrons.
The entropy of activation was found to be negative values in the Cu(II)
complexes (1, 3 and 5) which indicates more ordered activated complex than the
reactants or the reaction is slow [20,32]. The positive sign of ∆G* for the investigated
complexes reveals that the free energy of the final residue is higher than that of the
initial compound, and all the decomposition stages are non-spontaneous processes.
∆S* significantly from one stage to another which overrides the values of ∆H* [33].
The effect of the substituents on Gibbs free energy (∆G*) can be confirmed in
terms of Hammett’s substituent coefficients (σR) are shown in Fig. 12. It was found
that the values of ∆G* for Cu(II) complexes (1, 3 and 5) increase with increasing σR,
attributed to the fact that the effective charge experienced by the d-electrons increases
due to the electron withdrawing p-substituent NO2 while it decreases by the electron
donating character of OCH3.
3.11. Antimicrobial studies
Antibacterial and antifungal activities of Cu(II) complexes (1-5) were tested
against the Gram positive bacteria as S. aureus and B. cereus, Gram negative bacteria
as E. coli and K. pneumoniae and fungal species (A. niger, F. oxysporium, P. italicum
and A. alternata). The antimicrobial studies data reveal that the values of inhibition
clear zone for Cu(II) complexes are related to the nature of the p-substituent.
The results of the antibacterial activity of Cu(II) complexes (1-5) were listed in
Table 6. The Cu(II) complexes (1-5) have no antibacterial activity against B. cereus,
E. coli and K. pneumonia and have low antibacterial activity against S. aureus. It was
11

found that the complex (5) was more potent antibacterial activity than the other
complexes against S. aureus at high concentration (Table 6).
The results of the antifungal activity of the Cu(II) complexes (1-5) were listed in
Table 7. It was found that the Cu(II) complexes (1-5) have no antifungal activity
against A. niger, F, oxysporum and A. alternata but high antifungal activity against P.
italicum. From these results it is observed that the complex (5) is more potent
antifungal than the other complexes against P. italicum.
4. Conclusion
Spectroscopic studies of the complexation of metal ions with an azo dye showed
that the absorption maxima of the complexes are bathochromically shifted compared
with azo dyes. Five mononuclear copper(II) complexes have been synthesized by
thermal reaction between CuCl2.2H2O and monobasic NO bidentate azodye namely:
5-(4'-methoxyphenylazo)-2-thioxo-4-thiazolidinone (HL1), 5-(4'-methylphenylazo)-
2-thioxo-4-thiazolidinone (HL2), 5-(phenylazo)-2-thioxo-4-thiazolidinone (HL3), 5-
(4'-chlorophenylazo)-2-thioxo-4-thiazolidinone (HL4) and 5-(4'-nitrophenylazo) -2-
thioxo-4-thiazolidinone
(HL5), respectively. The novel complexes were fully
characterized by physicochemical and spectroscopic methods. Characterization of the
novel complexes have shown that, the Cu(II) formed square planar complexes with
1:1 (metal:ligand) stoichiometry. IR and thermal studies indicated that the fourth
position would be occupied by a water molecule and chloride ion in complexes. The
thermal analysis of the ligands (HLn) and thier Cu(II) complexes was studied by TGA
technique to give more information on the structure of the investigated complexes.
The thermodynamic parameters of the decomposition reaction were evaluated and
discussed. It was found that the change of substituent affects the thermal properties of
Cu(II) complexes. The tested complexes have good antibacterial activity against S.
aureus and have low antifungal activity against A. niger, F. oxysporium and A.
alternata. It was found that the complex (5) is more active than other complexes
against S. aureus and P. italicum.
Acknowledgement
The authors would like to thank Prof. Dr. M.I. Abou-Dobara and Miss. N.F. Omar
Botany Department, Faculty of Science, Damietta University, Egypt for their help
during testing antimicrobial activity.
12

Appendix A: Supplementary material
See the attached file.
13

Table 1
Elemental analysis (C, H, N and S) and physical data of the ligands (HLn).
Compounda
HL1
Color
Red
Yield (%)
37.45
m.p. (oC)
221
Experimental (calc.) (%)
C
H
N
S
44.82
3.25
15.85
23.65
(44.93) (3.39) (15.72) (23.97)
HL2
HL3
HL4
HL5
Dark Orange
Pale Yellow
Light Orange
Dark Yellow
47.81
42.19
51.37
66.09
231
237
248
245
47.88
3.76
16.61
25.23
(47.79) (3.61) (16.72) (25.50)
45.68
2.80
17.85
26.78
(45.55) (2.97) (17.71) (27.00)
39.65
2.35
15.58
23.24
(39.78) (2.23) (15.46) (23.57)
38.42
2.25
19.98
22.55
(38.29) (2.14) (19.85) (22.70)
aThe analytical data agree satisfactory with the expected formulae represented as
given in structures HL1-HL5. Air-stable, colored, insoluble in water, but soluble in
hot ethanol, and soluble in coordinating solvents.
14

Table 2
Elemental analysis data of Cu(II) complexesa (for molecular structure see Fig. 2)b.
Complexc
Experimental (calc.) (%)
Cl
C
H
N
S
[Cu(L1)(OH2)Cl]
(1)
31.14
2.45
10.76
16.44
9.11
(31.33) (2.61) (10.97) (16.71)
(9.27)
[Cu(L2)(OH2)Cl]H2O
(2)
31.04
2.52
10.66
16.44
9.01
(31.17) (2.60) (10.91) (16.62)
(9.22)
[Cu(L3)(OH2)Cl]
(3)
30.46
2.16
11.67
18.02
9.88
(30.59) (2.27) (11.90) (18.13) (10.06)
[Cu(L4)(OH2)Cl]H2O
(4)
26.59
1.66
10.06
15.52
16.89
(26.63) (1.73) (10.36) (15.78) (17.51)
[Cu(L5)(OH2)Cl]H2O
(5)
25.83
1.55
13.13 15.19
8.42
(25.96) (1.68) (13.46) (15.38)
(8.53)
aMicroanalytical data as well as metal estimations are in good agreement with the
stoichiometry of the proposed complexes, air stable, non-hydroscopic, high melting
temperature and colored, bThe excellent agreement between calculated and experimental
data supports the assignment suggested in the present work, c Ln are the anions
of the ligands (HLn).
15

Table 3
ESR spectral and bonding parameters of Cu(II) complexes
b
2
Complexa
(1)
(3)
gll
gav.
G
α2 All
f
β2
γ2
Kll
2
g⊥
K⊥
2.268 2.064 2.132 4.1 0.58 138 164 1.03 0.96 0.58 0.59
2.270 2.070 2.137 4.0 0.61 123 184 1.00 1.01 0.61 0.62
2.288 2.094 2.159 3.1 0.72 131 174 0.91 1.17 0.66 0.84
(5)
aNumbers as given in Table 2.
bA values in 10-4 cm-1.
16

Table 4
Thermal analysis data of Cu(II) complexes (1, 3 and 5).
Complexa Temp. range
(ºC)
Found mass loss (calc.)
(%)
Assignment
30-225
225-350
350-800
> 800
27.51 (27.54)
Loss of coordinated H2O molecule + HCl
molecule + decomposition of a part of the
ligand (C3HN).
(1)
18.33 (18.79)
28.73 (29.76)
24.93 (23.90)
4.78 (5.09)
Decomposition of a part of the ligand
(C2H2NS).
Decomposition of a part of the ligand
(C4H4NOS).
CuO residue + contaminated carbon atom.
Loss of coordinated H2O molecule.
100-200
(3)
200-370
370-800
> 800
45.67 (46.87)
26.53 (25.49)
23.02 (22.53)
Loss of HCl molecule + decomposition of a
part of the ligand (C3HN2S2).
Decomposition of a part of the ligand
(C6H4N).
CuO residue.
30-70
5.46 (4.33)
Loss of outer H2O molecule.
(5)
70-380
40.55 (40.98)
Loss of coordinated H2O molecule + HCl
molecule + decomposition of a part of the
ligand (C3H2NS2).
380-800
> 800
35.90 (35.57)
18.12 (19.12)
Decomposition of a part of the ligand
(C6H2N3O2).
CuO residue.
aNumbers as given in Table 2.
17

Table 5
Kinetic parameters of Cu(II) complexes (1, 3 and 5).
Complexa
Stage
Decomp.
Method
Parameter
Correlation
coefficient
(r)
temp. (oC)
Ea
(kJ mol−1)
83.9
A
∆S*
∆H*
∆G*
(s−1)
(J mol-1 K-1) (kJ mol−1) (kJ mol−1)
First
129-222
222-328
CR
HM
CR
2.27 × 107
3.88 × 108
2.92 × 103
4.91 × 104
-107
80.2
87.6
60.9
68.9
128
125
162
157
0.9834
0.9943
0.9843
0.9907
(1)
91.3
65.4
73.5
-84
-184
-160
Second
HM
First
120-264
264-465
CR
HM
CR
64.8
72.6
40.1
50.0
2.22 × 104
9.63 × 105
0.82 × 102
0.31 × 102
-165
60.9
68.8
34.8
44.7
138
131
190
187
0.9894
0.9927
0.9887
0.9945
(3)
(5)
-134
-243
-223
Second
HM
First
135-390
390-557
CR
HM
CR
29.3
36.4
134
145
1.05 × 102
0.90 × 102
4.24 × 106
7.89 × 107
-249
24.9
31.9
128
139
158
156
222
215
0.9982
0.9979
0.9949
0.9879
-232
-126
-101
Second
HM
aNumbers as given in Table 2.
Decomp. temp. = Decomposition temperature
18

Table 6
Antibacterial activity data of Cu(II) complexes (1-5). The results were recorded as the diameter
of inhibition zone (mm).
Gram positive bacteria
Gram negative bacteria
Complexa Conc.
(µg/ml)
Bacillus Staphylococcus Escherichia Klebsiella
cereus
-ve
-ve
-ve
-ve
-ve
-ve
-ve
-ve
3
aureus
-ve
-ve
1
coli
-ve
-ve
1
pneumoniae
-ve
50
(1)
100
150
-ve
-ve
50
-ve
2
-ve
-ve
-ve
-ve
-ve
-ve
1
-ve
(2)
100
150
-ve
3
-ve
50
-ve
-ve
-ve
-ve
3
-ve
(3)
100
150
-ve
-ve
50
-ve
-ve
-ve
-ve
-ve
-ve
1
-ve
(4)
100
150
-ve
-ve
-ve
-ve
1
-ve
4
-ve
50
1
-ve
(5)
100
150
50
3
-ve
5
-ve
2
1
-ve
Penicillin
100
3
2
3
-ve
150
3
2
3
-ve
aNumbers as given in Table 2.
19

Table 7
Antifungal activity data of Cu(II) complexes (1-5). The results were recorded as the diameter
of inhibition zone (mm).
Aspergillus Fusarium Alternaria Penicillium
Complexa
Conc.
niger
oxysporum alternata
italicum
(µg/ml)
50
100
150
50
-ve
-ve
-ve
-ve
-ve
-ve
-ve
-ve
-ve
-ve
-ve
-ve
-ve
-ve
-ve
1
-ve
-ve
-ve
-ve
-ve
-ve
-ve
-ve
-ve
-ve
-ve
-ve
-ve
-ve
-ve
2
-ve
-ve
-ve
-ve
-ve
-ve
-ve
-ve
-ve
-ve
-ve
-ve
-ve
-ve
-ve
1
-ve
3
(1)
4
5
(2)
(3)
(4)
(5)
100
150
50
3
3
6
100
150
50
4
2
-ve
-ve
-ve
4
100
150
50
100
150
50
5
7
-ve
-ve
-ve
Miconazole
100
150
3
2
3
3
2
3
aNumbers as given in Table 2.
20

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22

H
O H
O
H
O
H
N
H N
N
R
H N
N
N
R
S
N
N
R
S
N
S
S
S
S
(D )
(C )
(B )
S
S
C
O
H N
N H
N aN O
H C l
2
O
+
N
N
R
N H 2
-
R
N
C l
0 -5 o C
a lk a lin e so lu tio n
0 -5 o C
R
S
N
S
D ia z o n iu m S a lt
(A )
S
R
N
S
S
R
N
S
N
R
S
N
S
H N
N
N
O H
H
N H
N H
o r
O
H
O
o r
O
H
O
O H
H N
H N
H N
H
N
N
N
S
S
N
N
S
S
R
N
S
R
R
S
(E )
(G )
(F )
n = 1
n = 2
n = 3
n = 4
n = 5
R = OCH3
R = CH3
R = H
R = Cl
R = NO2
Fig. 1. The formation mechanism and tautomeric structures of ligands (HLn).
23

R
S
N
S
N
.n H 2
O
H 2
O
N H
C u
O
C l
Fig. 2. The structure proposed for Cu(II)-complexes.
24

100
95
90
85
80
75
70
65
60
55
50
45
40
35
30
25
20
15
10
5
0
40
60
80
100
120
140
160
180
200
220
240
260
280
300
320
340
360
380
m/z
Fig. 3. Mass spectrum of [Cu(L3)(OH2)Cl] (3) complex.
25

- H 2
- C l
- C u
O
S
N
S
N
- C 2 H N O S
S
N
S
N
N
S
N
H 2
O
N H
N H
C u
O
O
m /z = 1 5 0
m /z = 2 3 7
C l
S tru ctu re I I
S tru c tu re I
- S C N
- S
- C N
- N
N
N
C
N
m /z = 1 1 8
m /z = 7 7
m /z = 9 2
S tru c ture IV
S tru c tu re II I
S truc tu re V
Scheme 1. Fragmentation patterns of complex (3).
26

(2)
(3)
(4)
10
20
30
40
50
60
70
80
o
2θ
Fig. 4. X-ray diffraction patterns for powder forms of Cu(II) complexes (2-4).
27

(a)
2.290
(c)
(b)
(5)
(5)
(5)
0.72
0.69
0.66
0.66
2.285
2.280
0.63
g
2
2
ll
2.275
k
α
(3)
(3)
ll
0.63
0.60
0.57
g
0.60
ll
2
(3)
2.270
2.265
α
(1)
(1)
(1)
2
k
ll
0.57
-0.4
-0.2
0.0
0.2
0.4
0.6
0.8
R
Hammett's substituent coefficients (σ )
Fig. 5. The relation between Hammett’s substituent coefficients (σR) vs. a) gll, b) α2
2
and c) Kll of Cu(II) complexes (1, 3 and 5).
28

(a)
2.29
2.28
2.27
(5)
(3)
(1)
0.56
0.60
0.64
0.68
2
ll
k
(5)
(b)
2.094
2.088
2.082
2.076
2.070
2.064
(3)
(1)
0.60
0.66
0.72
0.78
0.84
2
k T
2
Fig. 6. The relation between a) Kll vs. gll and b) K⊥2 vs. g⊥ of Cu(II) complexes
(1, 3 and 5).
29