Computational studies of the first order kinetic reactions for mononuclear copper(II) complexes having a hard-soft NS donor ligand

Article abstract of DOI:10.1016/j.saa.2014.02.173

The chelation behaviour of 4-((E)-2-(1-(thiophen-2-yl)ethylidene) hydrazinyl)-1-(4-methoxyphenyl)-1H-pyrrole-3-carbonitrile (HL) towards Cu(II) ions has been investigated. These Cu(II) complexes are characterized by elemental analyses, molar-solid conductance, ESR, FTIR and electronic spectral studies. Also, the kinetic and thermodynamic parameters (E_a, A, ΔH, ΔS, ΔG) for all thermal decomposition steps have been evaluated using Coats-Redfern and Horowitz-Metzger methods. Furthermore, antimicrobial activity of the ligand and its complexes were studied against Gram-negative bacteria: Escherichia coli, Gram-positive Bacillus cereus, Bacillus subtilis and pathogenic fungi Pseudomonas aeruginosa by using minimum inhibitory concentrations (MICs) method.

Full text of DOI:10.1016/j.saa.2014.02.173

Accepted Manuscript
Computational studies of the first order kinetic reactions for mononuclear cop-
per(II) complexes having a hard-soft NS donor ligand
R.R. Zaky, T.A. Yousef, A.M. Abdelghany
PII:
S1386-1425(14)00372-2
http://dx.doi.org/10.1016/j.saa.2014.02.173
SAA 11804
DOI:
Reference:
Spectrochimica Acta Part A: Molecular and Biomo-
lecular Spectroscopy
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Revised Date:
Accepted Date:
24 October 2013
23 February 2014
25 February 2014
Please cite this article as: R.R. Zaky, T.A. Yousef, A.M. Abdelghany, Computational studies of the first order kinetic
reactions for mononuclear copper(II) complexes having a hard-soft NS donor ligand, Spectrochimica Acta Part A:
Molecular and Biomolecular Spectroscopy (2014), doi: http://dx.doi.org/10.1016/j.saa.2014.02.173
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Computational studies of the first order kinetic reactions for
mononuclear copper(II) complexes having a hard-soft NS
donor ligand
R. R. Zaky a*, T. A. Yousef b, A. M. Abdelghany c
a Department of Chemistry, Faculty of Science, Mansoura University, Mansoura, Egypt.
b
Department of Toxic and Narcotic drug, Forensic Medicine, Mansoura Laboratory, Medicolegal
organization,Ministry of Justice, Egypt.
c Spectroscopy Department, Physics division, National Research Centre, Cairo, Egypt.
ABSTRACT
The chelation behaviour of 4-((E)-2-(1-(thiophen-2-yl)ethylidene)hydrazinyl)-
1-(4-methoxyphenyl)-1H-pyrrole-3-carbonitrile (HL) towards Cu(II) ions has been
investigated. These Cu(II) complexes are characterized by elemental analyses, molar-
solid conductance, ESR, FTIR and electronic spectral studies. Also, the kinetic and
thermodynamic parameters (Ea, A, ∆H, ∆S, ∆G) for all thermal decomposition steps
have been evaluated using Coats-Redfern and Horowitz-Metzger methods.
Furthermore, antimicrobial activity of the ligand and its complexes were studied
against Gram-negative bacteria: Escherichia coli, Gram-positive Bacillus cereus,
Bacillus subtilis and pathogenic fungi pseudomonas aeruginosa by using minimum
inhibitory concentrations (MICs) method.
Keywords: Copper(II) complexes; FTIR; ESR; Thermal analysis; Antimicrobial
activity
∗
Corresponding author: Department of Chemistry, Faculty of Science, Mansoura
University, Mansoura, Egypt. Tel: 00200105193223. Fax number: 0020502219214.
E-mail address: rania.zaky@yahoo.com
1

1. Introduction
A literature survey reveals that the pyrrolidine ring is important for
antimycobacterial activity [1]. In addition, many hetero-nitrogen and sulfur
derivatives exhibit a wide variety of biological activities, such as antimicrobial [2],
anti-inflammatory [3], antihistaminic [4], antihypertensive [5], hypnotic [6] and
anticonvulsant [7] activity. From previous work, Schiff bases are known to possess at
least antimicrobial and genotoxicity activities [8–13]. Also, transition metal ions with
different oxidation state have a strong role in bio-inorganic chemistry and redox
enzyme systems and may provide the basis of models for active sites of biological
systems [14]. Copper is the third most abundant metallic element in the human body,
following iron and zinc. It also plays a role in the action of a multitude of enzymes
that catalyze a great variety of reactions [15–17]. Superoxide dismutase has normal
Cu(II) enzyme active sites containing tetragonally coordinated Cu(II) ion. DTA and
TG were used to study the modes of thermal decomposition of some divalent copper
complexes of Schiff bases [18, 19]. In this work we aim to study the thermal analysis
(DTA and TG) as well as the kinetic parameters of decomposition of some Cu(II)
complexes prepared from 4-((E)-2-(1-(thiophen-2-yl) ethylidene) hydrazinyl)-1-(4-
methoxyphenyl)-1H-pyrrole-3-carbonitrile Schiff base.
2. Experimental
2.1. Materials and reagents
All manipulations were performed under aerobic conditions. All metal salts
and other reagents used were pure (Fluka, Aldrich, or Merck). They included
thiophene-2-carboxaldehyde;
4-hydrazinyl-1-(4-methoxyphenyl)-1H-pyrrole-3-
carbonitrile, Cu(CH3COO)2.H2O, CuCl2.2H2O, Cu(NO3)2.3H2O and CuSO4.5H2O.
Organic solvents used included absolute ethyl alcohol, diethyl ether and dimethyl
sulphoxide. These solvents were spectroscopic pure from BDH.
2.2. Apparatus
The molar conductance of the complexes were determined by preparing 10-3
M solutions of the complexes in DMSO at room temperature and measured on an YSI
Model 32 conductivity bridge. The electrical conductivity was measured using
METRISO 5000A electrometer. The samples were in the form of discs of diameter 13
2

mm and thickness of 1-3 mm which were pressed under a pressure of ca 300 kg/cm-2.
Good contact area was achieved by liquid silver painting on the two opposite surfaces
of each disc. The temperature was measured in air using Cu-CuNi thermocouple
placed close to the sample. Thermogravimetric analysis was performed using an
automatic recording thermobalance type (DuPont 951 instrument). Magnetic moment
values were evaluated at room temperature (25+1°C) for triplet samples using a
Johnson Matthey magnetic susceptibility balance using Hg[Co(SCN)4] as calibrant.
The electronic spectra of the complexes were recorded in DMSO solution on a
Unicam UV2-UV–visible spectrometer, in the range 200–900 nm. Infrared spectra of
the complexes and parent ligand were recorded on Mattson 5000 FTIR
spectrophotometer, in the range 4000–400 cm-1 in KBr disk. ESR spectra of Cu(II)
complexes were obtained on a Bruker EMX Spectrometer working in the X-band
(9.78 GHz) with 100 kHz modulation frequency. The microwave power was set at 1
mW and modulation amplitude was set at 4 Gauss. The low-field signal was obtained
after four scans with a tenfold increase in the receiver gain. A powder spectrum was
obtained in a 2 mm quartz capillary at room temperature. Carbon and hydrogen
content for the ligand and its complexes were performed with a Perkin-Elmer 2400
2-
series II analyzer. Cu(II), Cl- and SO4 contents in the complexes were determined by
the well known standard methods [20].
2.3. Synthesis of ligands
The 4-((E)-2-(1-(thiophen-2-yl)ethylidene)hydrazinyl)-1-(4-methoxyphenyl)-
1H-pyrrole-3-carbonitrile (Scheme 1- Supplementary Materials) was prepared by
condensing 1:1 molar ratios of thiophene-2-carboxaldehyde in absolute ethanol with
4-hydrazinyl-1-(4-methoxy-phenyl)-1H-pyrrole-3-carbonitrile in ethanolic solutions.
The reaction mixtures were refluxed in a water bath for 3 h in the presence of few
drops of glacial acetic acid. On heating, pale yellow crystals were formed, filtered off,
washed with absolute ethanol and diethyl ether and recrystallized from EtOH. The
purity of the compound was checked by TLC. The proposed formula of the ligand is
in good agreement with the stoichiometric concluded from its analytical data (Table
1).
2.4. Synthesis of copper(II) complexes
3

The complexes were prepared by mixing equimolar amounts of 4-((E)-2-(1-
(thiophen-2-yl)ethylidene)hydrazinyl)-1-(4 methoxyphenyl)-1H-pyrrole-3-carbonitrile
(HL) with ethanolic and/or aqueous solution of CuSO4.5H2O, CuCl2.2H2O,
Cu(NO3)2.3H2O and Cu(CH3COO)2.H2O. The reaction mixture was refluxed on a
water bath for 1–3 h. The precipitate was filtered off, washed with hot water, hot
absolute ethanol and diethyl ether and finally dried in a vacuum desiccator over
anhydrous CaCl2.
2.5. Antimicrobial activity
The minimum inhibitory concentration (MIC) was carried out using the micro
dilution susceptibility method in Muller-Hinton Broth and sabouraud liquid medium.
The compounds, ampicillin and gentamycin were dissolved in DMSO at
concentration of 1mg/ml. The twofold dilutions of the solution were prepared. The
microorganism suspensions at 10 CFU/ml (colony forming unit/ml) concentrations
were inoculated to the corresponding wells. The plates were incubated at 36 ºC for 24
and 48 h for the bacteria and fungi, respectively. The MIC values were determined as
the lowest concentration that completely inhibited visible growth of the
microorganism as detected by unaided eye.
3. Results and Discussion
The isolated solid complexes are stable in air and easily soluble in DMF and
DMSO. The complexes decompose on heating in the range 235-300 ºC. The molar
conductance values in DMSO are 3-9 Ohm-1cm2mol-1 indicating that all complexes
are non-electrolytes. The colors, melting points and elemental analyses of the isolated
complexes are listed in Table 1.
3.1. IR spectra
The bonding of the ligand to Cu(II) ion has been judged by a careful
comparison of the infrared spectra of the complexes with that of the free ligand (Table
2). A few significant bands have been selected to observe the effect on ligand
vibration in the complexes. Ligand show a medium-intensity broad band, due to
ν(NH) at 3240 cm-1 [21]. In all Cu(II) complexes ν(NH) appears at nearly the same or
slightly higher frequencies, suggesting that this group does not take part in bonding.
Whereas, the bands attributed to thiophen sulfur (C=S) and azomethine nitrogen
(C=N) groups appears at 805 and 1644 cm-1, respectively [22]. In all the complexes
4

ν(C=N) and ν(C=S) is shifted to lower frequency indicating coordination of thiophen
sulphur and azomethine nitrogen to the metal. So, the ligand acts as a neutral
bidentate ligand via the thiophen sulphur and azomethine nitrogen. Also, the spectra
of Cu(II) complexes show new bands in (503–512) and (405–423) cm-1 region
assignable to ν(Cu–O) and ν(Cu–N), respectively [23,24]. The appearance of new
bands in [Cu(HL)2(SO4)] complex at 1055 and 917 cm-1 assignable to the SO
stretching vibrations
suggest bidentate sulphate [25]. In addition,
[Cu(HL)(OAc)2].3H2O complex shows two bands at 1448 and 1541 cm-1 attributable
to the νas(O–C–O) and νs(O–C–O) of the acetate group. The difference (93 cm-1)
between those two bands indicating the bidentate bonding for the acetate group [26].
3.2. Magnetic moments and electronic spectra
The magnetic susceptibility (µeff) varies between 1.75 and 2.20 B.M., when
spin–spin coupling between unpaired electrons belonging to different copper ions is
absent, depending on the geometries of the complexes due to the difference in orbital
contribution [27]. The observed µeff values for the copper(II) complexes in this study
are in the 1.92–2.05 B.M. range, corresponding to one unpaired electron. Electronic
absorption spectra arise from the electronic transitions within a molecule or ion from
a lower to a higher electronic energy level. The transition metal ions generally show a
number of d–d transition bands depending on their electronic configuration from d1 to
d9 in UV–vis regions. The copper(II) complexes generally show a broad band in the
2
2
2
2
13000–18000 cm-1 region assigned to the envelop of B1g → Eg + B2g + A1g
transitions [28]. In the present study, all of the isolated complexes show a broad band
in the 16000–16667 cm-1 region in DMSO with a shoulder in the 14184–14285 cm−1
regions (Table 3), suggesting a distorted octahedral geometry for all the complexes.
3.3. ESR spectra
The room temperature solid state spectra of copper complexes (Fig. 1) exihibit
axially symmetric g-tensor parameters with g|| >g >2.0023. The g values reflect that
⊥
Cu(II) center has a tetragonally distorted octahedral geometry with the unpaired
electron residing in the dx2-y2 orbital [29].
No band corresponding to the forbidden magnetic dipolar transition for the
complexes were observed at half-field (ca. 1500 G, g = 4.0), ruling out any Cu–Cu
5

interaction and indicating that the complex is mononuclear Cu(II) complex. The g-
values in axial symmetry given by, G = (g|| – 2)/(g⊥–2) = 4 which measure the exchange
interaction between copper centers in solid.
According to Hathaway [30], if the value of G is greater than 4, the exchange
interaction between Cu(II) centres in the solid state is negligible, whereas when G is
less than 4, a considerable exchange interaction is indicated in the solid complex. The
calculated G values were given in Table 3. The G values are greater than four
Gsuggesting no copper–copper exchange interaction and these results are well
consistence with the values of effective magnetic moments.
In hexacoordinated Cu(II) complexes, tetragonal distortion from the octahedral
symmetry due to the Jahn-Teller distortion is very common. Such complexes with
different ligands are attractive mainly due to the variation in the coordination geometry
and the spectral features. [31, 32].
Superhyperfine structures for complexes were not seen at higher fields excluding
any interaction of the nuclear spins of the nitrogen (I = 1) with the unpaired electron
density on Cu(II). The absence of 14N hyperfine coupling may be due to a relatively
higher tetrahedral distortion for this complex [33]. Molecular orbital coefficients, α2 (A
measure of the covalency of the in-plane σ-bonding between a copper 3d orbital and
the ligand orbitals) and β 2 (covalent in-plane π-bonding), were calculated by using the
following equations, [34–37].
where α2 = 1 indicates complete ionic character, whereas α2= 0.5 denotes
100% covalent bonding, with the assumption of negligibly small values of the overlap
integral.
A//
3(
g⊥ − 2.0023
)




α2 =
+
(
g// − 2.0023
)
+
+ 0.04
0.036
7


(
g// − 2.0023)E
β2 =
− 8λα2
where λ = -828 cm–1 for the free copper ion and E is the electronic transition
energy. From table 4, the α2 and β2 values indicate that there is a substantial
interaction in the in-plane σ-bonding whereas the in-plane π -bonding is almost ionic.
The higher value of β2 compared to α2 indicates that the in-plane π-bonding is less
6

covalent than the in-plane σ-bonding. The α2 value for Cu(II) complex indicates a
considerable covalency in the bonding between the copper(II) ion and the ligand.
3.4. Thermal analysis
The TG of the isolated complexes was taken as a proof for the existing of H2O
molecules as well as the anions to be outside and/or inside the coordination sphere.
The water of crystallization lost in 30–110 ºC regions. The complexes show thermal
stability rather than the ligand where the beginning of its decomposition shifts to
higher temperature (252–320 ºC). In general, all complexes are thermally stable;
[Cu(HL)2(NO3)2](H2O)2 is the highest one. It is thermally stable up to 320 ºC. In the
temperature range 320–716 ºC, the TG curve displays 47.4% weight loss which could
be ascribed to the elimination of the two loosely bound (C12H10ON3) fragments. The
final weight loss of 27.4% ending at 860 ºC, is largely attributed to complete
decomposition of the remaining more two tightly bound fragment (C6H6NS). The
remaining final fired product is Cu metal, representing 7.1%. The data of the different
decomposition steps of all isolated complexes are shown in Table 4.
A realistic explanation for the anion effect can be provided by defect diffusion
model [38]. When a reaction takes place in a solid, the formation of transition state
results in a point defect in the lattice. These defects are analogous to the substituted
ion Schotty and Frenkel defects [39]. When a volatile ligand like water is lost from a
complex, a situation analogous to the Frenkel defect is formed. This introduces
distortion in the structure of the crystal leading to transition state. The fraction of free
space in crystal increases as the difference between the size of the cation and anion
increases [40, 41]. The activation energies in Tables 5, 6 of the reported Cu(II)
complexes for deaquation reaction decreases in the order sulphate > chloride >
acetate > nitrate. The fraction of free space is much lower when cation and anions are
of equal size.
3.5. Kinetic data
Non-isothermal calculations were used extensively to evaluate the
thermodynamic and kinetic parameters for the different thermal decomposition steps
of the Cu(II) complexes were determined using the Coats-Redfern [42] and Horowitz-
Metzger [43].
7

The rate of decomposition of a solid depends upon the temperature and the
amount of material. The expression for the thermal decomposition of a homogeneous
system has the following general form:
dα
= K
(T
)
g
(α)
dt
(1)
Where t is the time, T is the absolute temperature and α is the degree of
transformation defined as:
w − w
o
w − w
t
α =
o
∞
In which wo, wt and w∞ are the weights of the sample before the degradation,
at temperature t and after total conversion, respectively. K(T) is the rate coefficient
that usually follows the Arrhenius equation. The differential conversion function, g(α)
may present various functional forms but its most commonly form for solid-state
reactions is g(α)=(1-α)n, where n is the reaction order, assumed to remain constant
during the reaction [44, 45].
The rate constant is normally expressed by the Arrhenius equation:
Ea



K = Aexp −

RT


(2)
Where Ea is the activation energy, A is the Arrhenius pre-exponential factor which
indicates how fast the reaction occurs and R is the gas constant in (Jmol-1K).
Substituting in equation 1, we get:
Ea
dα



= Aexp −

g
(α )
dt
RT


(3)
(4)
T
A
E
ln(1−α) = −
Exp(−
) dT
∫
β
RT
T
o
On the basis of equation (4), it is possible to analyze experimental data by the
integral method, in order to determine the degradation kinetic parameters A and Ea.
8

The temperature integral in the right-hand side of equation (4) has no exact analytical
solutions and several kinds of approximations are generally used. Two methods that
differ on the way of resolving equation (4) are compared using the TGA data of the
studied complexes. These methods are:
3.5.1. Coats-Redfern method:
The Coats-redfern [42] method is as follows:








g(α)
2
AR
Ea
ln[
]= ln
−
βE
RT
T
(5)
Where g(α) = 1-(1-α)1-n/1-n for n≠ 1 and g(α) = -ln(1-α) for n=1, R is the universal
gas constant. The correlation coefficient, r, was computed using the least square's
g(α)
2
ln[
]
T
method for different values of n (n=0.33, 0.5, 0.66 and n=1) by plotting
versus 1/T for the investigated metal complexes are shown in Figures from 2–4. The
n-value which gave the best fit (r ≈1) was chosen as the order parameter for the
decomposition stage of interest. The slope of the straight line equal (Ea/R) and the
intercept the pre-exponential factor, A can be determined (Fig. S1–Supplementary
Materials). The data obtained are represented in Table 4.
3.5.2. Horowitz-Metzger method:
The Horowitz-Metzger [43] relation was used to evaluate the degradation
kinetics is
Ea θ
ln[−ln(1 − α)] =
2
RT
s
For n=1
(6)
1−n
)
RT2
Ea Eaθ
RT2
RT









(
1− 1−α
A
S

ln
=ln
−
+
S
S
For n≠1


1−n
β E


(7)
Where θ=T-Ts, Ts is the DTG peak temperature, T the temperature corresponding to
weight loss Wt. In this method a straight line should be observed between
Ea
2
s
RT
ln[−ln(1−α)]
and θ with a slope of
. The figures 5 & 6 show the Horowitz-
9

Metzger plots for the metal complexes under study (Figs. 2S, 3S - Supplementary
Materials). The obtained data are recorded in Table 6.
3.5.3 Thermodynamic parameters:
The other thermodynamic parameters of activation can be calculated by
Eyring equation [46, 47]:
∆H= Ea-RT
(8)
(9)
hA
k T
∆S = R (ln
−1)
B
∆G = ∆H-T∆S
(10)
Where ∆H is the enthalpy of activation (kJ/mol), ∆S is the entropy of
activation (kJ/mol.K) and ∆G is the Gibbs free enthalpy of activation (kJ/mol), h is
the Planck constant and kB the Boltzmann constant. The kinetic parameters evaluated
by Coats-Redfern (CR) and Horowitz-Metzger (HM) methods are listed in Tables 5
and 6, respectively. From the results the following remarks can be pointed out:
i) The kinetic parameters (Ea, A, ∆H, ∆S and ∆G) of all isolated complexes have been
calculated by using CR and HM methods (Table 5 and 6). The values obtained from
the two methods are quite comparable.
ii) The thermodynamic data obtained with the two methods are in harmony with each
other.
iii) The correlation coefficients of the Arrhenius plots of the thermal decomposition
steps were found to lie in the range 0.9820–0.9996, showing a good fit with linear
function.
iv) The activation energy Ea increases somewhat through the degradation steps
revealing the high stability of the remaining part suggesting a high stability of
complexes characterized by their covalence.
v) The negative value of the entropy of activation, ∆S of some decomposition steps in
case of the ion exchanger and its metal complexes with all investigated metal ions
indicates that the activated fragments have more ordered structure than the
undecomposed ones and the later are slower than the normal [48, 49].
10

vi) The positive sign of activation enthalpy change, ∆H indicates that the
decomposition stages are endothermic processes.
vii) The high values of the energy of activation, Ea of the complexes reveals the high
stability of such chelates due to their covalent bond character [50].
viii) 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 hence all
the decomposition steps are non-spontaneous processes. Moreover, the values of ∆G
increase significantly for the subsequent decomposition steps of a given compound.
This results from increasing the T∆S clearly from one step to another which override
the values of ∆H reflecting that the rate of removal of the subsequent species will be
lower than that of the precedent one [51]. This may be attributed to the structural
rigidity of the remaining complex after the expulsion of one or more ligands, as
compared with the precedent complex, which requires more energy, T∆S, for its
rearrangement before undergoing any decomposition change.
3.6. Electrical conductivity measurements
The relation between solid state electric conductivity (log σ) and temperature
(1000/T) was found to be Arrhenius (σ = σo exp (-∆Ea /KT)) where σο is the pre-
exponential factor given by (σο = nq2d2f/2KT) where n is the concentration of mobile
ions, q is the ionic charge, d is the average distance between the holes, f is the
vibration frequency of the ion, ∆Ea is the activation energy, K Boltzman constant and
T is the absolute temperature. The activation energy was calculated from the linear
portion of obtained data [52].
The electrical resistivity can be expressed by Kuivalainen et al. [53] model:
(yp + ybp )2
Ro2
KT
0.45e2α(T)2
1
ρ =
(11)
− 2.78Ro
ξ
yp ybp
exp(
)
ξ
where, yp and ybp are the concentration of polarons and bipolarons, respectively;
ζ
Ro is the hopping distance (separation) between impurities;
is the average
decay length of the polaron and bipolaron wave function. The electronic
transition rate (T) between polaron and bipolaron states can be expressed as
[54]:
11

T
n
α(T) = A(
)
(12)
300K
where A, is a constant equal to 1.2×1017.
By using a computer-aided program, the order of magnitude of in the
present system was adjusted. Taking y =y for simplicity, which is an acceptable
p
bp
approximation, and using equations (11) and (12), we can obtain the values of the
hopping distance Ro [55].
The calculated values of R was found to range from 8.04 nm to 12.10 nm
o
depending on chemical composition. It was found also that the electrical
conductivity and activation energies of metal complexes were lower than the ligand
itself. This may be due to the increased electron delocalization or depends on the ionic
radius of the cation and its ligand field's strength.
The inflection observed can be attributed to a change in conduction mechanism. It
is assumed that at lower temperatures the conduction process is essentially due to the
electronic conduction through π–electron delocalization while the conduction at
higher temperatures is due to the excitation of an electron from the upper most filled
π–molecular orbital to the lowest unfilled π–molecular orbital of these compounds
(Table 1).
3.7. Antimicrobial Activity
Minimum inhibitory concentration (MIC) [56, 57] was determined for each of
the active compounds along with ampicillin and gentamycin as standard controls;
results are shown in tables 7, 8. This screening was performed against the Gram-
negative Escherechia coli and the Gram-positive Bacillus cereus, Bacillus subtilis in
addition to pseudomonas aeruginosa. The tested compounds were dissolved in
DMSO at a concentration of 8 mg/ml. Amongst all the compounds tested,
[Cu(HL)(OAc)2].3H2O demonstrated the most potent antimicrobial activity against
Bacillus subtilis, Escherechia coli and pseudomonas aeruginosa and
[Cu(HL)2Cl2].3H2O against Escherechia coli. It is noteworthy that the observed
antimicrobial activity was highly dependent on the metal complex, in which copper
complexes played an important role in achieving an excellent level of biological
activity. It is observed from these studies that most of the metal chelates have a higher
12

activity than the free ligand. Such increased activity of the metal chelates can be
explained on the basis of Overtone’s concept and chelation theory [58]. According to
Overtone’s concept of cell permeability the lipid membrane that surrounds the cell
favours the passage of only lipid soluble materials due to which liposolubility is an
important factor that controls antimicrobial activity. On chelation, the polarity of the
metal ion is reduced to a greater extent due to the overlap of the ligand orbital and
partial sharing of the positive charge of the metal ion with donor groups. Further, it
increases the delocalization of p-electrons over the whole chelate ring and enhances
the lipophilicity of the complex. This increased lipophilicity enhances the penetration
of the complexes into lipid membranes and blocking of metal binding sites on the
enzymes of the microorganism.
4. Conclusion
4-((E)-2-(1-(thiophen-2-yl)ethylidene)hydrazinyl)-1-(4-methoxyphenyl)-1H-
pyrrole-3-carbonitrile (HL) and its Cu(II) complexes were prepared and characterized.
It is obvious from this study that the ligand acts as a neutral bidentate via the thiophen
sulphur and azomethine nitrogen. Also, the ESR, electronic spectra of the complexes
and their magnetic moments suggesting octahedral geometry around Cu(II) center.
The stability of complexes was explained and kinetic parameters (Ea, A, ∆H, ∆S, ∆G)
of all thermal decomposition stages have been evaluated using Coats–Redfern method
and Horowitz-Metzger methods. Moreover, the biological activities of the ligand and
its complexes against bacterial and fungal organisms have been evaluated by using
minimum inhibitory concentrations (MICs) method.
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16

Fig. 1. Solid state X-band ESR spectra for (A) [Cu(HL)(OAc)2](H2O)3, (B)
[Cu(HL)2Cl2](H2O)3, (C) [Cu(HL)2(NO3)2](H2O)2 and (D) [Cu(HL)2(SO4)] complexes
at room temperature.

lnX n=1
lnX n=1
lnX n=0.66
lnX n=0.33
lnX n=0
lnX n=0.66
lnX n=0.33
lnX n=0
-11
-12
-13
-14
-15
-16
-17
( B )
-11
-12
-13
-14
-15
-16
-17
-18
( A )
lnX n = 0.5
lnX n = 0.5
0.0024
0.0026
0.0028
1000/T
0.0030
0.0018
0.0019
1000/T
0.0020
lnX n=1
lnX n=1
lnX n=0.66
lnX n=0.33
lnX n=0
lnX n=0.66
lnX n=0.33
lnX n=0
-11
-12
-13
-14
-15
-16
( D )
( C )
-12
-13
-14
-15
lnX n = 0.5
lnX n = 0.5
0.0015
0.0016
1000/T
0.0017
0.0018
0.0011
0.0012
1000/T
0.0013
Fig. 2. Coats-Redfern plots of [Cu(HL)(OAc)2](H2O)3 (A) first step, (B) second step,
(C) third step and (D) fourth step.

lnX n=1
lnX n=1
lnX n=0.66
lnX n=0.33
lnX n=0
lnX n=0.66
lnX n=0.33
lnX n=0
-11.5
-12.0
-12.5
-13.0
-13.5
-11
-12
-13
-14
-15
-16
( B )
( A )
lnX n = 0.5
lnX n = 0.5
0.00242
0.00244
0.00246
0.00248
0.0019
0.0020
0.0021
0.0022
1000/T
1000/T
lnX n=1
lnX n=0.66
lnX n=0.33
lnX n=0
( C )
-13
-14
-15
lnX n = 0.5
0.0010
0.0011
1000/T
0.0012
Fig. 3. Coats-Redfern plots of [Cu(HL)2Cl2](H2O)3 (A) first step, (B) second step, (C)
third step and (D) fourth step.

lnX n=1
lnX n=1
lnX n=0.66
lnX n=0.33
lnX n=0
lnX n=0.66
lnX n=0.33
lnX n=0
-11
-12
-13
-14
-15
-12
-13
-14
-15
( A )
( B )
lnX n = 0.5
lnX n = 0.5
0.0022 0.0023 0.0024 0.0025 0.0026 0.0027 0.0028
1000/T
0.0016
0.0017
0.0018
1000/T
0.0019
0.0020
lnX n=1
lnX n=1
lnX n=0.66
lnX n=0.33
lnX n=0
lnX n=0.66
lnX n=0.33
lnX n=0
-13
-14
-15
-16
-17
-18
-19
( C )
( D )
lnX n = 0.5
lnX n = 0.5
-14
-15
-16
0.0010
0.0011
0.0012
1000/T
0.0013
0.0014
0.00090 0.00092 0.00094 0.00096 0.00098 0.00100
1000/T
Fig. 4. Coats-Redfern plots of [Cu(HL)2(NO3)2](H2O)2 (A) first step, (B) second step,
(C) third step and (D) fourth step.

lnX n=1
1
0
ln X=1
lnX n=0.66
lnX n=0.33
lnX n=0
( B )
( A )
ln X=0.66
ln X=0.33
ln X=0
1
0
lnX n = 0.5
lnX=0.5
-1
-2
-3
-1
-2
-40 -30 -20 -10
0
10 20 30 40 50 60
T-Ts
-60 -50 -40 -30 -20 -10
T-Ts
0
10 20 30 40
lnX n=1
1.5
lnX n=1
lnX n=0.66
lnX n=0.33
lnX n=0
lnX n=0.66
lnX n=0.33
lnX n=0
( D )
( C )
1
0
1.0
0.5
lnX n = 0.5
lnX n = 0.5
0.0
-0.5
-1.0
-1.5
-2.0
-1
-2
-125 -100
-75
-50
-25
0
25
50
-30 -20 -10
0
10
20
30
40
50
60
T-Ts
T-Ts
Fig. 5. Horowitz-Metzger plots of [Cu(HL)(OAc)2](H2O)3 (A) first step, (B) second step, (C) third
step and (D) fourth step.

lnX n=1
lnX n=1
1.0
0.5
lnX n=0.66
lnX n=0.33
lnX n=0
lnX n=0.66
lnX n=0.33
lnX n=0
( B )
( A )
1.0
0.5
lnX n = 0.5
lnX n = 0.5
0.0
-0.5
-1.0
-1.5
-2.0
-2.5
0.0
-0.5
-1.0
-150
-100
-50
0
50
100
150
-150
-100
-50
0
T-Ts
50
100
T-Ts
Fig. 6. Horowitz-Metzger plots of [Cu(HL)2(SO4)] (A) first step, (B) second step.

Table 1
Analytical and physical data of ligand and its Cu(II) complexes.
Molar
conductance
%Found (Calcd.)
Electrical conductance
Compound
M.P.
(°C)
Yield
(%)
Colour
Λm
Empirical Formula (F.W.)
Ro
X
C
H
M
-
Ea (eV)
0 (S/cm)
Cl- or SO42-
in DMSO (-1cm2 mol-1)
HL
C18H16ON4S
[Cu(HL)(OAc)2](H2O)3
CuC22H28O8N4S
(1)
(2)
(3)
(4)
(5)
64.50
(64.43)
46.27
(46.29)
50.31
(50.20)
48.34
(48.24)
51.83
(51.94)
4.54
(4.79)
4.88
(4.93)
4.39
(4.45)
4.12
(4.10)
3.90
(3.87)
8.04
9.11
Pale Yellow
Green
215
> 300
> 300
235
80
75
75
79
83
-
-
-
2.35
1.18
1.38
1.06
1.19
11.52
11.12
11.07
10.98
11.15
(336.419)
11.14
(11.1)
7.45
(7.38)
7.04
(7.10)
7.51
(7.63)
3
7
9
4
(572.094)
[Cu(HL)2Cl2](H2O)3
8.19
(8.24)
10.82
12.10
11.92
Green
CuC36H38O5N8SCl2 (861.424)
[Cu(HL)2(NO3)2](H2O)2
CuC36H36O10N10S2 (896.409)
[Cu(HL)2(SO4)]
Brown
-
11.42
(11.5)
Brown
243
CuC36H32O6N8S2
(832.442)

Table 2
Infrared data for the ligand and its Cu(II) complexes (cm-1).
Compound
ν(C=N) ν(C=S) ν(NH) ν(N-N) ν(M-S) ν(M-N)
1
2
3
4
5
1644
1635
1630
1633
1636
805
783
793
790
785
3240
3251
3244
3249
3242
1030
1034
1033
1042
1040
-
-
512
510
503
508
423
405
420
417

Table 3
Magnetic moment, electronic spectra and ESR data of Cu(II) Complexes.
A (cm-1)
159
g/ A
2
2
Compound
μeff. (B.M.) Band position (cm-1)
G
g
g
2
3
4
5
1.98
1.92
2.05
1.98
14211; 16667
14285; 16393
14285; 16667
14184; 16000
2.25 2.07
2.21 2.06
2.30 2.08
2.27 2.06
3.5
6.3
4.6
4.5
141 0.75 0.86
136 0.72 0.63
164 0.75 0.99
140 0.78 0.84
162
140
162
Table 4
Thermal behavior of Cu(II) complexes of HL.
Complex
2
Temp. range (°C)
Decomp. prod.
(Formula wt.)
Wt. loss (%)
Found Calcd.
35-150
150-285
285-396
396-641
> 641
3H2O
(54.045)
9.40
20.8
37.0
21.8
11.0
9.5
20.6
37.1
21.7
11.1
2C2H3O2
C12H10ON3
C6H6NS
(118.090)
(212.234)
(124.122)
(63.540)
Residue, Cu
3
4
117-156
156-252
252-670
670-850
> 850
3H2O
Cl2
2C12H10ON3
2C6H6NS
Residue, Cu
(54.045)
(71.000)
(424.468)
(248.243)
(63.540)
6.4
8.0
49.4
28.7
7.5
6.3
8.2
49.3
28.9
7.4
35-161
161-320
320-716
716-860
> 860
2H2O
NO3
2C12H10ON3
2C6H6NS
Residue, Cu
(36.030)
(124.013)
(424.468)
(248.243)
(63.540)
4.0
13.8
47.4
27.7
7.1
4.0
13.8
47.4
27.7
7.1
5
200-598
598-875
> 875
SO4+2C12H10ON3 (520.468)
62.3
29.9
7.9
62.5
29.8
7.7
2C6H6NS
(248.243)
(63.540)
Residue, Cu

Table 5
Kinetic Parameters of Cu(II) complexes evaluated by Coats-Redfern equation.
Mid.
Ea
A
∆H*
∆S*
∆G*
Complex
2
peak
Temp(K) kJ\mol
(S-1)
kJ\mol kJ\mol.K kJ\mol
215.05 -0.34823 342.16
171.78 -0.36395 350.49
1st
2nd
3rd
4th
365
491
614
790
218.08
175.86
4.90E-6
9.95E-7
1011.29 4.11E-6 1006.18 -0.35401 1223.55
1643.33 1.09E-5 1636.76 -0.34800 1911.69
3
4
5
1st
2nd
3rd
4th
411
478
780
329.87
239.18
415.62
3.10E-5
3.10E-6
5.24E-7
326.45 -0.33388 463.68
235.21 -0.35427 404.55
409.13 -0.37312 700.17
1057
3037.01 1.94E-6 3028.22 -0.36477 3413.79
1st
2nd
3rd
4th
371
515
791
147.42
523.93
5.83E-8
1.51E-5
144.33 -0.38521 287.25
519.65 -0.34172 695.63
1093.80 2.41E-6 1087.23 -0.36054 1372.42
3552.21 5.59E-6 3543.51 -0.35590 3916.14
1047
1st
672
997
429.38
3.93E-7
423.79 -0.37427 675.31
2nd
1310.33 1.22E-6 1302.04 -0.36811 1669.05

Table 6
Kinetic Parameters of Cu(II) complexes evaluated by Horowitz-Metzger equation.
Complex
2
Peak
Mid.
Ea
A
∆H*
∆S*
∆G*
Temp(K) kJ\mol
(S-1)
kJ\mol kJ\mol.K kJ\mol
215.92 -0.34786 342.89
170.99 -0.36346 349.46
1st
2nd
3rd
4th
365
491
614
790
218.96
175.08
5.13E-6
1.06E-6
1011.83 3.99E-6 1006.72 -0.35426 1224.25
1642.24 1.01E-5 1635.68 -0.34860 1911.07
3
4
5
1st
2nd
3rd
4th
411
478
780
329.28
239.90
414.98
3.29E-5
4.06E-6
5.09E-7
325.79 -0.33338 462.81
235.92 -0.35204 404.21
408.49 -0.37338 699.73
1057
3037.63 2.03E-6 3028.84 -0.36442 3414.04
1st
2nd
3rd
4th
371
515
791
148.96
515.08
6.32E-8
1.93E-5
145.88 -0.38455 288.55
510.80 -0.33972 685.76
1093.49 2.69E-6 1086.92 -0.35965 1371.40
3553.68 5.86E-6 3544.98 -0.35551 3917.21
1047
1st
672
997
428.16
3.94E-7
422.57 -0.37428 674.09
2nd
1309.38 1.21E-6 1301.09 -0.36818 1668.17

Table 7
Antimicrobial activities of ligand and Cu(II) its complexes.
Inhibition zone (mm)
Pseudomonas Aeruginosa
Bacillus Cereus
Bacillus Subtillis
Esherichia Coli
Compounds
1
2
3
4
5
3.5
6.5
5.5
6.5
3.5
0
17
1
5
3
3
12
11
7
2.5
12
12.5
5.5
4
4
Ampicillin
7.5
12
13.5
18
11
16.5
11.5
Gentamicin
16.5

Table 8
Antimicrobial activities of ligand and Cu(II) its complexes in terms of MIC (µg/mL).
Minimum inhibitory concentration (MIC) (µg/ml)
Compounds
Bacillus
Cereus
3000
375
1500
750
Bacillus
Subtillis
6000
93.75
3000
Pseudomonas Esherichia
Aeruginosa
3000
Coli
3000
93.75
93.75
750
1
2
3
4
187.5
93.75
1500
1500
5
1500
187.5
93.75
3000
187.5
93.75
1500
187.5
187.5
1500
93.75
375
Ampicillin
Gentamicin