Synthesis, spectral, thermal and theoretical studies of Cu(II) complexes with 3-[4′-dimethylaminophenyl]-1-(2-pyridyl)prop-2-en-1-one (DMAPP)

Article abstract of DOI:10.1016/j.molstruc.2009.01.042

Cu(II) complexes of 3-[4′-dimethylaminophenyl]-1-(2-pyridyl) prop-2-en-1-one (DMAPP) are prepared and characterized by elemental analysis as well as spectral studies (IR and UV-vis), ESR, magnetic susceptibilities and thermal studies. The effect of differ

Full text of DOI:10.1016/j.molstruc.2009.01.042

Journal of Molecular Structure 922 (2009) 51–57
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Journal of Molecular Structure
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Synthesis, spectral, thermal and theoretical studies of Cu(II) complexes
0
with 3-[4 -dimethylaminophenyl]-1-(2-pyridyl)prop-2-en-1-one (DMAPP)
M. Gaber, S.A. El-Daly, Y.S.Y. El-Sayed *
Chemistry Department, Faculty of Science, Tanta University, El-Bahre Street, Tanta 11113, Egypt
a r t i c l e i n f o
a b s t r a c t
0
Article history:
Cu(II) complexes of 3-[4 -dimethylaminophenyl]-1-(2-pyridyl) prop-2-en-1-one (DMAPP) are prepared
and characterized by elemental analysis as well as spectral studies (IR and UV–vis), ESR, magnetic suscep-
tibilities and thermal studies. The effect of different alcoholic solvents as well as the temperature on the
complex formation is studied. The effect of Cu(II) ion on the emission spectrum of the free chalcone is also
assigned. The stoichiometry, stability constant, absorption maximum and molar absorptivity of the metal
complexes as well as the effect of pH, temperature on complex formation are determined spectrophoto-
metrically. Adherence to Beer’s law and Ringbom optimum concentration ranges are determined. The
thermal decomposition of the metal complexes is studied by TGA technique. The kinetic parameters like
activation energy, pre-exponential factor and entropy of activation are estimated. The structure of com-
Received 26 March 2008
Received in revised form 10 January 2009
Accepted 20 January 2009
Available online 31 January 2009
Keywords:
Chalcones
Complexes
Spectral
Thermal studies
Effect of viscosity on the complexes
+
plexes was energetically optimized through molecular mechanics applying MM force field coupled with
molecular dynamics simulation.
Ó 2009 Elsevier B.V. All rights reserved.
1
. Introduction
Chalcones, the bichromophoric molecules separated by a keto-
In this paper, we are reporting the synthesis and spectroscopic
characterization as well as magnetic and conductance measure-
ments of Cu(II) complexes with chalcone ligand (DMAPP) Fig. 1.
vinyl chain, constitute an important class of naturally occurring
flavonids exhibiting a wide spectrum of biological activities
2
. Experimental
[
1–3]. Also, chalcones have potential applications as artificial
sweeteners, new drugs and agrochemicals [4–6]. The importance
of this class of compounds is not only due to their biological activ-
ities but also to their colors, usually give yellow to orange colors to
the tissues in which they are located [2,7]. So, they are attractive to
insects in such a way that they contribute to the flower’s pollina-
tion [8]. In addition, chalcones are widely used for various optical
applications including second harmonic generation materials in
non-linear optics [9], photorefractive polymers [10], holographic
recording materials [11] and fluorescent probes for sensing of
metal ions [12–15]. Therefore, the photophysical properties of
chalcones containing alkyl amino groups as electron donors have
been studied by numerous researchers [16–21]. In an earlier work,
the photophysical properties, excitation energy transfer and laser
activity of DMAPP. The photophysical properties such as singlet
absorption, molar absorptivity, fluorescence spectra, fluorescence
The ligand (DMAPP) was synthesized and characterized accord-
ing to the method reported previously [22]. All the chemicals used
were of Analar grade. Solvents were purified according to standard
procedures before use.
2
.1. Synthesis of metal complexes
A solution of the appropriate metal ion (0.01 mol) in ethanol
10 ml) was mixed with a solution of the chalcone (0.01 mol) in
(
the same solvent (30 ml) and the resulting mixture was stirred un-
der reflux for 12 h where upon the complexes precipitated after
cooling. The solid complexes were then filtered off, washed several
times with ethanol, dried and kept in desiccators over dried silica
gel. The analytical and spectral data are collected in Table 1.
quantum yield (/
were measured in different media [22].
f
) and transition dipole moment (l12) of DMAPP
2.2. Measurements
Microanalyses of C, H and N were made using Heraeus CHN
elemental analyzer. The IR spectra were recorded as KBr discs on
ꢀ
1
a Perkin Elmer 1430 spectrophotometer in the 4000–200 cm
range. The electronic spectra were recorded using a Shimadzu 160
UV–vis spectrometer. The X-band ESR spectra of the complexes
*
Corresponding author. Tel.: +20 40 3331359; fax: +20 40 3350804.
E-mail address: Yousifchem@yahoo.com (Y.S.Y. El-Sayed).
0
022-2860/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2009.01.042

5
2
M. Gaber et al. / Journal of Molecular Structure 922 (2009) 51–57
tions and same process was repeated five times to ensure the energy
minimum had been reached. A bath of relaxation time of 0.1 ps and
a step size of 0.001 ps were used for dynamics simulation.
N
CH3
CH3
3. Results and discussion
O
N
3.1. Study of metal complexes in solution
The reaction of the ligand with metal ions was carried out to
Fig. 1. The structure of chalcone ligand.
establish the most favorable conditions to give increased color
intensity and to achieve maximum color development in the quan-
titative determination of the metal ions. The optimum pH value for
the complex formation was detected by scanning the absorption
spectra of the complexes using universal buffer solutions. The com-
plexes are formed instaneously and the color of the complexes is
stable for 24 h. Temperature exhibits no apparent influence on
the color development. The suitable wavelength for the complex
formation was also determined and listed in Table 2. The composi-
tion of the Cu(II) complexes in solution was established at the opti-
mum conditions described above using the molar ratio (MRM) and
continuous variations (CVM) methods. The results indicate the
presence of Cu(II) complex in solution having the stoichiometric ra-
tio 1:1 (M:L). The conditional formation constants were calculated
were recorded at room temperature on a JOEL-X-band spectrome-
ter equipped with an E 101 microwave bridge. Diphenyl picryl
hydrazide free radical (DPPH) was used as internal standard
(g = 2.0023). The fluorescence measurements were recorded with
the aid of Shimadzu RF-510 spectrofluorometer.
Excitation, emission bandwidth, scan rate and excitation wave-
length are 10 nm, 100 nm/min and 370 nm, respectively. Magnetic
susceptibilities were measured by employing the Faraday balance
4
technique. The equipment was calibrated with Hg[Co(CNS) ].
Diamagnetic corrections were made from Pascal constants. The
thermal analysis (TGA) was carried out using computerized Shima-
dzu TG-50 thermal analyzer up to 800 °C at a heating rate 10 °C/
using Harvey and Manning equation applying the data obtained
*
min. in an atmosphere of N
2
.
from the MRM and CVM methods. The free energy (
D
G ) of complex
formation was also calculated. The limits of validity to Beer’s law,
molar extinction coefficient, specific absorptivity [24], standard
deviation and correlation coefficient were calculated. These values
confirmed the possible application of the method for the determi-
nation of the metal ions. Ringbom [25] concentration range was
also determined and the results are listed in Table 2.
The effect of Cu(II) ions on the emission spectrum of DMAPP was
also studied by steady-state emission measurements. The emission
spectral patterns of the ligand do not change by adding the metal
ion while a decrease in emission intensities was observed as shown
in Fig. 2. This implies the absence of emitting excited state
complexes. By applying the Stern–Volmer [26] relation:
2
.3. Computational procedures
All calculations were carried out on a Pentium IV 3.2 GHz ma-
chine on windows XP environment using Hyperchem release 7
23]. The geometry of complex was energetically optimized through
[
+
molecular mechanics applying MM force field in vacuo with the
polka Ribiere (conjugated gradient) algorithm and RMS gradient
0
is performed without any constrains allowing all atoms, bonds,
dihedral angles to change simultaneously. The dynamic simulation
was done up to 2000k followed by molecular mechanics calcula-
.001 kal/mol followed by molecular dynamics. The optimization
Table 1
Analytical data of the isolated complex.
a
ꢀ1
ꢀ1
No.
Formula
% Elemental analysis
K
m
leff (BM)
IR spectra (cm
)
Electronic spectra (cm )
C Cal. (F)
H Cal. (F)
N Cal. (F)
M Cal. (F)
vꢀ M!N
vꢀ M!O
1
2
3
4
[CuLXAc]AcꢁX
[CuLXCl]ClꢁX
[CuLXZ]ZꢁX
51.06 (51.24)
45.39 (45.51)
34.88 (35.0)
42.86 (42.8)
5.53 (5.64)
4.73 (4.8)
3.63 (3.7)
4.47 (4.43)
5.96 (6.0)
6.62 (6.64)
5.09 (5.1)
6.26 (6.3)
13.5 (13.56)
15.01 (14.95)
11.53 (11.6)
14.19 (14.1)
110
119
108
121
1.72
1.78
1.94
1.80
547
555
550
532
617
616
629
626
28,571
26,455
27,027
28,571
22,222
21,978
21,277
23,256
17,241
16,949
16,667
16,949
2 4
[CuLX ]SO
ꢀ
ꢀ
L = DMAPP; X = H
2
O Z ¼ClO Ac = CH
3
COO .
4
a
ꢀ1
2
ꢀ1
X
cm mol .
Table 2
Analytical parameters for chalcone (DMAPP) complexes.
Parameter
Complex 1
Complex 2
Complex 3
Complex 4
k
max (nm)
570
560
560
563
Buffer
pH
Universal
3.2
Universal
3.0
Universal
3.5
Universal
3.2
Logb
n
4.996
6.813
32,715
515
0.0791
0.996
4.998
7.225
33,412
618
0.0781
0.996
4.6
5.246
7.323
33,752
623
0.0663
0.998
4.799
6.413
33,515
641
0.0651
0.989
5.0
*
D
G
e )
(dm3 mol cm
ꢀ1
ꢀ1
Molar absorptivity,
Specific absorptivity, a (g cm
Standard deviation
Correlation coefficient
Beer’s limits (ppm)
ꢀ
1
ꢀ1
)
4.0
5.1
Ringbom range (ppm)
ꢀ0.197–0.253
ꢀ0.17–0.244
ꢀ0.166–0.333
ꢀ0.21–0.343

M. Gaber et al. / Journal of Molecular Structure 922 (2009) 51–57
53
-
3
[
CuAc ] mol.dm .
2
a
0
1
2
3
5
8
.0E-5
.0E-5
.0E-5
.0E-5
.0E-5
.0E-5
40
30
20
10
400
440
480
520
560
600
640
680
Wavelength (nm)
b
Fig. 2. Fluorescence quenching of 2 ꢃ10 mol dm DMAPP using Cu2+, acetate in
ꢀ
5
ꢀ3
0.0004
MeOH
EtOH
methanol at room temperature.
n-PrOH
n-BuOH
0
0
0
.0003
.0002
.0001
I
I
0
¼
1 þkSV ½Qꢂ
where I and I represent the fluorescence intensities in the absence
o
and presence of metal ions (quencher), [Q] is the concentration of
quencher and kSV is the second-order quenching rate constant;
the Stern–Volmer plot as shown in Fig. 3,is not linear, indicating a
static type mechanism via ground-state complex formation be-
tween DMAPP and Cu(II) ions [27].
0.0000
ꢀ5
ꢀ3
0
20000
40000
60000
/[M ]
80000 100000
Fluorescence quenching of 1 ꢃ10 mol dm DMAPP by Cu(II)
salt with different anions (acetate, chloride, perchlorate and sul-
phate) have been studied in some alcoholic solvents (e.g. methanol,
ethanol, n-propanol and n-butanol) at room temperature. As
shown in Fig. 3, the Stern–Volmer plots are not linear and the
quenching efficiency increases in the order of MeOH > EtOH >
n-PrOH > n-BuOH. This is may be attributed to the solvent viscosity
and the quenching is diffusion controlled process [28].
1
o
ꢀ5
ꢀ3
Fig. 4. (a) Absorption spectra of CuAc
MeOH at room temperature. (b) Plot of (L
solvents at room temperature (20 °C).
2
complex with 1 ꢃ10 mol dm DMAPP in
)/(A ꢀA ) vs. 1/[M ] in different alcoholic
o
o
o
The stability constant of the complexes was estimated from the
following equation [29,30]:
ꢀ5
ꢀ3
The electronic absorption spectra of 1 ꢃ10 mol dm DMAPP
when adding different concentrations of Cu(II) ions of different
anions (acetate, chloride, perchlorate and sulphate) have been
studied in different alcoholic solvents (e.g. methanol, ethanol,
n-propanol and n-butanol). The absorption spectrum of DMAPP
changed when metal ion is added (Fig. 4a) where the initial absorp-
tion band of DMAPP decreased on adding the metal ion and a new
absorption band appears with a clear isosbestic point at 482 nm in
methanol using Cu(II) acetate, chloride, perchlorate and shifted to
½L
o
ꢂ
1
ꢀ
1
¼
þ
e
A ꢀA
o
e
ML
e
L
ð
ML
ꢀ
e
L
ÞK½M ꢂ
o
where A
with metal complex at a given wavelength;
extinction coefficients of the DMAPP and the metal complex, and [L
o
and A are absorbance’s of the free DMAPP solution and that
e
L
and ML are the molar
e
o
]
is the initial concentration of DMAPP. The stability constants (K)
values for the complexes of DMAPP with Cu(II) ion in different alco-
holic solvents (MeOH, EtOH, n-PrOH and n-BuOH) are calculated
4
84 nm for Cu(II) sulphate, indicating a single equilibrium in
from the plots of [L
o
]/(A ꢀA
o o
) vs. 1/[M ] (Fig. 4b) and the values were
solution.
collected in Table 3. The data indicated that the stability constant
decreases with increasing solvent viscosity and are close to the cor-
responding diffusion rate constant (kdiff) values. The values of kdiff
were calculated by the following equation [31].
MeOH
EtOH
5
4
3
2
1
n-PrPH
n-BuOH
8
000
RT
k
diff ¼2
g
The viscosity dependence of k for diffusion-controlled bimolecular
reactions is described by [32]:
o
I /I
ꢀ
a
k ¼A
g
where the parameters A and
a
are assumed to be constants that are
invariant with . Values of
reported [33] for a number of bimolecular chemical reactions. A plot
of ln k vs. ln yielded a straight line from which the value of was
calculated, and found between 0.13 and 0.39 for all complexes.
Also, the absorption spectra of Cu(II)–DMAPP complexes in
methanol have been studied in the temperature range 20–50 °C.
Using Benesi–Hildebrand method [30], the values of the equilib-
rium constants K of the complexes were estimated (Table 3). The
g
a ranging from zero to unity have been
g
a
0.00000
0.00005
0.00010
0.00015
0.00020
2+
-3
[
Cu ] mol.dm
Fig. 3. Stern–Volmer plots for fluorescence quenching of 1 ꢃ10ꢀ5 mol dm
ꢀ3
2
DMAPP in different alcoholic solvents using CuAc at room temperature.

5
4
M. Gaber et al. / Journal of Molecular Structure 922 (2009) 51–57
Table 3
Stability constant (logK) of complexes of Cu(II) of different anions in different alcoholic solvents at different temperature and thermodynamic parameters.
Solvent
T (°C)
Stability constant of Cu2+ complexes
Thermodynamic parameters
ꢀ
ꢀ
4ꢀ
2ꢀ
ꢀ
ꢀ1
ꢀ1
ꢀ1
Ac
Cl
ClO
SO
ꢀ
D
H° (KJ mol)
ꢀ
D
G° (KJ mol
)
D
S° (J mol deg )
4
ꢀ
ꢀ
4ꢀ
2ꢀ
ꢀ
ꢀ
ꢀ
2ꢀ
ꢀ
ꢀ
ꢀ
2ꢀ
Ac
Cl
7.91
ClO
5.26
SO
Ac
Cl
22.9
ClO
SO
Ac
Cl
51.1
ClO
SO
4
4
4
4
4
MeOH
20
4.06
3.98
3.92
3.88
4.09
4.01
3.99
3.95
4.16
4.13
4.11
4.07
4.03
3.95
3.84
3.73
11.1
17.9
22.7
23.4
22.7
39.8
61.7
16.3
3
4
5
0
0
0
EtOH
20
20
20
3.98
3.86
3.77
4.06
4.01
3.97
4.12
4.09
4.07
3.97
3.91
3.84
–
–
–
–
–
–
–
–
–
PrOH
n-BuOH
stability constant of the complexes decreased with increasing the
temperature. The thermodynamic parameters (the enthalpy
ground state [40]. This band may be assigned to the transition
2
2
T
2g ? E
g
[39,41].
2
+
change (
D
H°), entropy change (
D
S°) and Gibbs free energy
D
G°)
The Cu complexes showed magnetic moments 1.72, 1.78, 1.94
were calculated from Van’t Hoff equation plot. The plot of the nat-
ural logarithm of the equilibrium constant measured for a certain
equilibrium vs. the reciprocal of temperature gives a straight line,
and 1.80 BM for Cu(II) complexes 1, 2, 3 and 4, respectively, indi-
cating the presence of only one unpaired electron [41]. The slightly
higher value of observed magnetic moment of Cu(II) complex (3) is
consistent [42] with an orbitally non-degenerate ground state of
Cu(II) ion.
the slope of which is the negative of the
DH° divided by the gas
constant and the intercept of which is equal to the
by the gas constant, then it is possible to determine
values are reported in Table 3.
D
S° divided
D
G° and the
The ESR spectra of Cu(II) complexes are recorded as poly crystal-
line samples at room temperature. The g-values are taken to calcu-
late the exchange interaction, G = (g|| ꢀ2)/(g ꢀ2). According to
\
Hathaway [43], if G < 4 a considerable exchange interaction in the
solid complexes occurs, while, G > 4 indicates that a negligible inter-
action. The G-value of Cu(II) complexes 3 and 4 are 2.15 and 2.0994,
respectively. These values leads to spin exchange interaction be-
tween Cu(II) ions in the solid state. The g|| values in Cu(II) complexes
can be used as a measure of the covalent character of metal ligand
bond [44]. If the value of g|| < 2.3, the environment is essentially
covalent, but if g|| > 2.3, the ionic environment is assigned. The g||
value of complex 3, showed considerable ionic character while com-
plex 4 is covalent in nature. For complex 1, the hyperfine splitting
signals is absent, instead only a single signal appeared. The absence
of hyperfine signal may be due to the strong dipolar and exchange
interaction between Cu(II) ion in the unit cell [45].
3
.2. Characterization of the solid complexes
Structure elucidation of Cu(II) complexes was accomplished on
the basis of elemental analyses, IR, UV–vis, ESR spectra, conduc-
tance and magnetic measurements as well as the thermal analysis
(
TGA). The analytical data of the isolated solid complexes are given
in Table 1 which is in a good agreement with the proposed struc-
ture. The solid complexes were found to be stable in air and soluble
in most organic solvents. The high molar conductance values of the
isolated complexes measured in DMF solution (10 M) at room
temperature suggested their ionic nature [34] indicating that the
anion is present outside the coordination sphere.
ꢀ3
A comparison of the IR spectrum of the free chalcone ligand
The thermal behavior of the prepared complexes (Fig. 5a) are
summarized in Table 4. The Cu(II) complex (1) exhibited the first
mass loss in the temperature range 25–120 °C; it may be attributed
to the liberation of the hydrated water molecule. The second mass
loss at 120–172 °C, is due to the liberation of the coordinated water
molecule. The third mass loss at 172–305 °C, is due to the liberation
of two acetate molecules. Copper oxide was found as the final prod-
uct at 305–620 °C. The Cu(II) complexes (2–4) decomposed in three
steps. The first step in the range 25–166 °C which may attribute to
the loss of hydrated water. The second step in the range 95–420 °C
may be due to the liberation of anion in and/or outside the coordi-
nation sphere and the CuO formed as a final product in the last step.
The kinetic parameters of decomposition process of the complexes
(
DMAPP) with those of its metal complexes was carried out to
investigate the mode of bonding between the chalcone ligand
and Cu(II) ion. In the IR spectrum of the free ligand, the band at
1
ꢀ1
661 cm characteristic for C@O bond was shifted to lower fre-
ꢀ1
quency by 6–19 cm upon coordination to the metal ions with
ꢀ1
the appearance of another mode of vibration at 541–547 cm cor-
responding to bond [35]. The IR spectra of the complexes
showed a new band at 617–625 cm
resulting from the interaction between carbonyl oxygen atom
and the metal ion. A broad band at 3402–3422 cm is present in
the spectra of the metal complexes; this band is associated with
coordinated and/or hydrated water molecule [37]. The other
stretching vibrations of the free chalcone is less affected by com-
plex formation indicating that the chalcone ligand behaves as
bidentate ligand via the nitrogen atom of pyridine ring and car-
bonyl oxygen atom. In the IR spectra of the complexes, bands
t
M N
ꢀ1
due to
M O
t bond [36]
ꢀ1
*
*
*
namely, activation energy (E ), enthalpy (
D
H ), entropy (
D
S ) and
*
free energy of the decomposition (
D
G ) as well as the order (n) were
evaluated graphically by using Coats–Redfern equations [46].
due to
s
tas and t of the acetate group are displayed within the
ꢀ1
ꢄCoats–Redfern equation
ranges 1610–1625 and 1380–1390 cm , respectively. This fre-
quency separation is characteristic of monodentate acetate groups
for 1:1 (M:L) complexes [38].
The Nujol mull electronic spectra of the Cu(II) complexes under
investigation showed bands within the range 26,455–28,571 cm
"
ꢀn#
1
1
ꢀð1 ꢀ
a
Þ
M
T
ln
ln
¼
þB for n–1
2
ð1 ꢀnÞT
ꢀ1
ꢀꢀ
Þꢁ
.
lnð1 ꢀ
a
m
These bands would be assigned to the intra-ligand charge transfer
transitions [39] type. The spectra of Cu(II) complexes showed the
visible d–d electronic spectral bands within the range 16,667–
¼
þB for n ¼1
T
2
T
where M = ꢀE/R and B = ln(ZR/uE) where E, R, Z and u are the acti-
vation energy, gas constant, pre-exponential factor and heating rate,
respectively.
7,241 cm , assigned to 2
ꢀ1
B
1g ? A2g transition, characteristic of
2
1
the square planner geometry of the Cu(II) complex with dx2ꢀy2

M. Gaber et al. / Journal of Molecular Structure 922 (2009) 51–57
55
activation energy values, one can concluded that the water mole-
cules are easy to be eliminated from the complexes according to
the following order 4 < 3 < 1 < 2. Also, the energy of activation for
the second stage of decomposition for complexes is less than that
of the first stage, due to the high steric strain in the intermediate
a
1
00
3
0
80
60
40
20
compounds obtained after the first stage of decomposition. The
*
D
S values were found to be negative. This indicates that the acti-
vated complex is more ordered than the reactants and/or the reac-
tions are slow [47]. The values of G increase significantly for the
subsequently decomposition stages due to increasing the values of
S from one step to another which override the values of H. This
-3
D
TD
D
-
6
9
increase reflects that the rate of removal of the subsequent ligand
will be lower than that of the precedent ligand [48]. This may be
attributed to the structural rigidity of the remaining complex after
the expulsion of one and more ligands, as compared with the prec-
edent complex, which requires more energy for its rearrangement
before undergoing any compositional change. The positive values
-
0
100 200 300 400 500 600 700 800
o
Temp. C.
of
D
H means that the decomposition processes are endothermic.
From all of the above observations, the structure of the com-
plexes is given as follows:
b
-11.2
12.0
-
+
step 1
step 2
step 3
step 4
-12.8
C
N
NMe
2
Z-.X
-
13.6
14.4
15.2
16.0
16.8
X
Cu
Z
O
Y -
-
-
-
-
X= H
2
O and Z = CH
3
COO for complex 1
-
Z = Cl
for complex 2
-
4
Z = ClO
for complex 3.
++
1
.2
1.5
1.8
2.1
2.4
2.7
3.0
3.3
-
1
C
O
NMe
2
SO4--.
1000/T K
N
X
Cu
Fig. 5. (a) TGA curve of CuAc
2
–DMAPP complex. (b) Coats–Redfern plots for
h
i
1
ꢀn
aÞ
2
1
ꢀð1ꢀ
ð1ꢀnÞT
the decomposition steps of CuAc
2
–DMAPP complex: Y ¼ln
for
X
h
Þi
ꢀ
lnð1ꢀ
a
n–1 or ln
2
for n ¼1.
T
Complex 4.
The correlation coefficient r was computed by using the least
square method for the above equations. Linear curves were drawn
for different values of n equal 0, 0.33, 0.5, 0.66 and 1. The value of n,
which gave the best fit, was chosen as the order parameter for the
decomposition stage of interest. The kinetic parameters were cal-
culated from the plots of the L.H.S. vs. 1/T of Coats–Redfern equa-
3
.3. Molecular modeling
Since our efforts to obtain crystalline samples of the compounds
of X-ray diffraction were unsuccessful, we decided to carry out
molecular modeling studies in order to gain a better understanding
of all structures. The structures for the Cu-complexes were pre-
dicted through strain energy, calculated through the molecular
*
*
*
tion, as shown in (Fig. 5b). The calculated values of n, E , A,
DS , DH
*
and
D
G for the decomposition steps are given in Table 5. From the
+
mechanics (MM ) coupled with molecular dynamics calculations.
Although, the molecular mechanics calculations cannot predict
the electronic properties, still it has enormous applications in the
field of coordination chemistry [49–51]. The molecular mechanics
calculate the strain energy, which partition into stretching, bend-
ing and torsion and non-bonded interactions for the molecule
and give stable structure with least strain energy. It provides an
ideal tool to evaluate the degree to which a ligand is structurally
organized for metal complexation. Energy minimization was re-
peated to find the global minimum.
Table 4
Thermal decomposition data of Cu(II) DMAPP complexes.
Complex
Temp. (°C)
Mass loss (%)
Estimate
Assignment
Calc.
1
25–120
3.5
4.2
24.7
53.5
3.7
4.94
24.9
51.2
Loss of 1H
Loss of 1H
2
O
O
120–172
172–305
305–620
2
Loss of 2AcO
Loss of ligand
The results of energy minimization of square planar and tetra-
hedral structures of Cu-complexes without restriction indicate that
the strain energies of square planar of Cu(II) complexes are less
than that of tetrahedral structures in all cases. This result is in an
agreement with the experimental results. Fig. 6 shows the ball
and stick model of the optimized geometries of complexes (1–4).
The bond lengths (CuAO)C for complexes 1–4 are 1.728, 1.8,
2
3
4
25–160
8.23
17.1
55.9
8.5
16.8
58.2
Loss of 2H
Loss of 2Cl
Loss of ligand
2
O
1
3
60–355
55–600
25–95
3.53
40.0
46.2
3.4
39.6
47.1
Loss of 1H
Loss of 1H
2
O
95–380
O, 2ClO
2 4
380–630
Loss of ligand
Loss of 2H
Loss of SO
Loss of ligand
80–166
7.82
21.5
54.5
8.09
21.4
56.3
2
O
1
4
66–420
20–630
4
1
2
.804 and 1.807 Å, respectively, while (CuAO)H are 1.871, 1.842,
1
.844 and 1.841 Å, respectively, in the case of (CuAN) are 1.875,

5
6
M. Gaber et al. / Journal of Molecular Structure 922 (2009) 51–57
Table 5
Temperatures of decomposition and activation parameters (kJ molꢀ1) of decomposition for the chelates under investigation.
Complex
Steps
T (K)
Coats–Redfern
*
D *
S*a
*
n
r
E
H
ꢀ
D
DG
1
1
2
3
4
335.2
451.3
510
1
1
0.66
1
0.99610
0.98507
0.99626
0.95280
30.6
30.9
29.9
43.6
27.8
27.1
25.7
39.6
0.121
0.118
0.115
0.115
68.2
80.3
84.2
98.2
753.5
2
1
2
3
4
375.7
442.5
510.4
747
0
1
1
1
0.94543
0.98436
0.94917
0.96861
27.8
28.4
29.5
25.3
24.7
24.7
25.3
19.1
0.105
0.113
0.114
0.099
64.24
74.5
83.3
93.0
3
4
1
2
3
445.4
509.6
759.2
1
1
1
0.98932
0.95054
0.98168
33.5
35.7
41.9
29.8
31.4
35.6
0.123
0.125
0.117
84.7
94.9
124.7
1
2
3
4
330.2
486.9
618.3
930.9
1
1
1
0
0.97110
0.95695
0.99753
0.96025
26.1
21.8
37.4
44.2
23.3
17.7
32.2
36.4
0.117
0.096
0.114
0.105
62.0
64.4
102.8
133.8
a
ꢀ1 ꢀ1
KJ mol
K .
1
1
.864, 1.866 and 1.861 Å, respectively, and (CuAO)Ac for complex
is 1.809 Å , (CuACl) for complex 2 is 1.165 Å, (CuAClO ) for com-
4
plex 3 is 1.844 Å. The bond angles of the complexation parts of
Cu(II) of different anions with the ligand in the range 75–87° which
are stable angles with minimum strain energy.
4
. Conclusion
The electronic spectrum of the chalcone (DMAPP) was re-
corded in methanol. The various optimum conditions for com-
plex formation were detected. The stoichiometric ratios of
Cu(II) complexes with DMAPP were determined. The fluores-
cence of the chalcone was quenched in presence of Cu(II) ions.
The calculated Stern–Volmer second order rate constant de-
creases with increasing the viscosity of the solvent. The solid
complexes were prepared and characterized on the basis of ele-
mental analysis, molar conductance, magnetic moments, spec-
tral and thermal studies. The proposed chemical structures of
the metal chelates suggested the square planar for all Cu(II)
chelate.
Acknowledgement
We are grateful to Dr. M. Khaled for his helpful is the part of
theoretical studies.
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