New tetradentate Schiff bases of 2,2-dimethyl-1,3-diaminopropane and acetylacetone derivatives and their vanadyl complexes

Article abstract of DOI:10.1016/j.saa.2012.07.062

A series of new VO(IV) complexes with two new tetradentate Schiff base of 4,4′-(2,2-dimethylpropane-1,3-diyl)-bis(azan-1-yl-1-yldene) dipent-2-en-2-ol) [H₂L¹] and 3,3′-(2,2- dimethylpropane-1,3-diyl)azan-1-yl-1-ylidene)-bis(1-phenylbut-1-en-1-ol) [H ₂L²] (which have been derived from 2,2-dimethyl-1,3- diaminopropan, and diketones of acetylacetone and benzoylacetone) were synthesized and characterized by ¹H NMR, ¹³C NMR, FT-IR, mass and UV-Vis spectrophotometry. The electrochemical properties of the vanadyl complexes were investigated by means of cyclic voltammetry. The oxidation potentials are increased by increasing the electron-withdrawing properties of functional groups of the Schiff base ligands according to the trend of Me < Ph. The thermogravimetry (TG) and differential thermoanalysis (DTA) of the VO(IV) complexes were carried out in the range of 20-700 °C. The complexes were decomposed in two stages. Also, decomposition of the synthesized complexes is related to the Schiff base characteristics. The thermal decomposition of the studied reactions was first order. The kinetic parameters for the decomposition steps in vanadyl complexes thermograms have been calculated.

Full text of DOI:10.1016/j.saa.2012.07.062

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 97 (2012) 711–716
Contents lists available at SciVerse ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
New tetradentate Schiff bases of 2,2-dimethyl-1,3-diaminopropane
and acetylacetone derivatives and their vanadyl complexes
⇑
Khosro Mohammadi , Mina Rastegari
Chemistry Department, Faculty of Sciences, Persian Gulf University, Bushehr 75169, Iran
g r a p h i c a l a b s t r a c t
h i g h l i g h t s
The new tetradentate Schiff bases and their vanadyl complexes were synthesized and spectrally charac-
terized, Khosro Mohammadi and Sayedeh Mina Rastegari.
"
"
"
"
Two new symmetrical tetradentate
Schiff base ligands have been
synthesized.
Their oxovanadium(IV) complexes
have been synthesized and
characterized.
From TG curves, the order of thermal
stability for the complexes is
VOL1 > VOL2.
The electrochemical properties of
the vanadyl complexes were
investigated in DMF.
H3C
CH3
H3C
CH3
N
O
N
O
V
O
R
R
Complex
R
VOL1
VOL2
CH3
Ph
a r t i c l e i n f o
a b s t r a c t
A series of new VO(IV) complexes with two new tetradentate Schiff base of 4,40-(2,2-dimethylpropane
-1,3-diyl)-bis(azan-1-yl-1-yldene)dipent-2-en-2-ol) [H2L1] and 3,30-(2,2-dimethylpropane-1,3-diyl)azan-
1-yl-1-ylidene)-bis(1-phenylbut-1-en-1-ol) [H2L2] (which have been derived from 2,2-dimethyl-1,3-diami-
nopropan, and diketones of acetylacetone and benzoylacetone) were synthesized and characterized by 1H
NMR, 13C NMR, FT–IR, mass and UV–Vis spectrophotometry. The electrochemical properties of the vanadyl
complexes were investigated by means of cyclic voltammetry. The oxidation potentials are increased by
increasing the electron-withdrawing properties of functional groups of the Schiff base ligands according
to the trend of Me < Ph. The thermogravimetry (TG) and differential thermoanalysis (DTA) of the VO(IV)
complexes were carried out in the range of 20–700 °C. The complexes were decomposed in two stages. Also,
decomposition of the synthesized complexes is related to the Schiff base characteristics. The thermal decom-
position of the studied reactions was first order. The kinetic parameters for the decomposition steps in van-
adyl complexes thermograms have been calculated.
Article history:
Received 23 April 2012
Received in revised form 12 July 2012
Accepted 13 July 2012
Available online 22 July 2012
Keywords:
Schiff base
2,2-Dimethyl-1,3-diaminopropan
Acetylacetone
Vanadyl complex
Thermogravimetry
Electrochemistry
Ó 2012 Elsevier B.V. All rights reserved.
1. Introduction
Their ease of synthesis (by the condensation of an aldehyde/ketone
with an amine), multidenticity (from mono to hexadentate), com-
Schiff bases are one of the most versatile classes of ligands for
the study of the coordination chemistry of transition metals [1].
bination of donor atoms (coordination usually through the imine
nitrogen and other atoms like oxygen, sulfur or nitrogen) and sta-
bility have made them the preferred ligand systems in catalysis,
biological modeling, the design of molecular ferromagnets, liquid
crystals [2–4], medical imaging [5] and optical materials [6]. Schiff
⇑
Corresponding author. Tel.: +987714222340; fax: +987714541494.
E-mail
addresses:
Khmohammadi@pgu.ac.ir,
khmohammadi@gmail.com
(K. Mohammadi).
1386-1425/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.saa.2012.07.062

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K. Mohammadi, M. Rastegari / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 97 (2012) 711–716
base ligands are able to coordinate many different metals [7–10],
and to stabilize them in various oxidation states.
recrystallized with ethylacetate and n-hexane. Yield (80%), m.p.:
68 °C; 1HNMR (d, ppm, 500 MHz, CDCl3): 1.09 (s, 6H, CH3), 1.92
(s, 6H, CH3), 2.03 (s, 6H, CH3), 3.15 (d, J = 5, 4H, CH2), 5.00 (s, 2H,
HC@C), 11.20 (b, 2H, NH); 13CNMR (d, ppm, 125 MHz, CDCl3):
19.39, 24.00, 29.09, 36.18, 50.77, 95.91, 195.38; FT–IR (KBr,
The interest in vanadium coordination chemistry promoted by
the presence of this element in biological systems [11], and by cat-
alytic [12], and medicinal [13] properties of its compounds. The po-
tential catalytic abilities of vanadium compounds have led to an
increasing interest in vanadium coordination chemistry in recent
years [8]. Homogeneous catalysts of oxovanadium(IV) complexes
have been shown to induce organic reactions such as the oxidation
of sulfides and sulfones [14,15], the epoxidation of alkenes
[12,16,17], the hydroxylation of hydrocarbons [18], and the oxida-
tion of alcohols to aldehydes and ketones [19,20]. These studies are
indicative that oxovanadium(IV) complexes are potential catalysts
to influence the yield and selectivity in chemical transformation.
Furthermore, complexes of Schiff bases showed promising applica-
tions in biological activity and biological modeling applications
[21–23]. Besides the insulin-like activity of oxovanadium(IV) and
oxovanadium(V) compounds [24,25], its presence in vanadium
dependent haloperoxidases has particulary stimulated the search
for structural and functional models [26].
In the present study, we report acetylacetone derivative Schiff
base ligands. The structures of these compounds were studied by
1H NMR, 13C NMR, IR, UV–Vis and mass spectra. Then their vanadyl
complexes were prepared and the spectral and thermal properties
of these complexes were studied in details. Also the kinetic param-
eters for decomposition steps in thermograms of these complexes
were calculated. The electronic influence of acetylacetone deriva-
tives on electrochemical properties of vanadyl(IV) Schiff base com-
plexes were studied.
cmꢀ1): 3400 (
m
NAH), 3000, 2900 (
C@C); ESI–MS (m/z(%)): 266 [M+], 251, 182, 154, 124, 112, 98,
70, 55; UV–Vis: (kmax, nm, MeOH): 262, 311, 318.
mCAH), 1620 (mC@O), 1470, 1430
(m
2.2.2. Preparation of 3,30-(2,2-dimethylpropane-1,3-diyl)azan-1-yl-1-
ylidene)-bis(1-phenylbut-1-en-1-ol), [H2L2]
To a stirred n-heptane solution (30 ml) of benzoylacetone,
(1.62 g, 10 mmol) 2,2-dimethyl-1,3-diaminopropan (0.50 g,
5 mmol) was added. The bright yellow solution was stirred and
heated to reflux for 10 h. A white precipitate was obtained that
was filtered off, recrystallized with heated methanol. Yield (80%),
m.p.: 110 °C; 1HNMR (d, ppm, 500 MHz, CDCl3): 1.24 (s, 6H, CH3),
2.11 (s, 6H, CH3), 3.34 (d, J = 5, 4H, CH2), 5.70 (s, 2H, HC@C),
7.42–7.90 (m, 10H, Ar), 11.91 (b, 2H, NH); 13CNMR (d, ppm,
125 MHz, CDCl3): 19.98, 24.27, 36.30, 51.11, 93.02, 127.33–
140.71, 188.48; FT–IR (KBr, cmꢀ1): 3400 (
mNAH), 3100, 3000 (mCAH),
1610 ( C@O), 1470, 1440 (
m
m
C@C); ESI–MS (m/z(%)): 390 [M+], 285,
216, 174, 158, 105; UV–Vis: (kmax, nm, MeOH): 246, 346.
2.3. Preparation of vanadyl complexes
The complexes were prepared by a general procedure: the li-
gand, H2L1 (0.053 g, 0.2 mmol) or H2L2 (0.078 g, 0.2 mmol) was dis-
solved in 20 ml of methanol. A methanolic solution of vanadyl
acetylacetonate (0.05 g, 0.2 mmol) was added to above solution
and the reaction mixture was refluxed for 4 h. The colored solution
was concentrated to yield green powders. The products washed
with water and dried in vacuum. General structure of oxovana-
dium(IV) complexes has been shown in Fig. 1.
2. Experimental
2.1. Reagents and instruments
VOL1: yield: 60%, m.p.: >250 °C; FT–IR (KBr, cmꢀ1): 2925 (
mCAH),
All of the chemicals and solvents used for synthesis were of
commercially available reagent grade and used without purifica-
tion. They included 2,2-dimethyl-1,3-diaminopropan, acetylace-
tone, benzoylacetone, vanadyl acetylacetonate. Organic solvents
used included methanol, n-hexane, n-heptane and ethylacetate.
All reagents and solvents were commercially obtained from Merck,
Aldrich or Fluka.
1555 (mC@N), 1420 (mC@C), 1359 (mCAO), 998 (mVAO); ESI–MS (m/
z(%)): 331 [M+]; UV–Vis: (kmax, nm, MeOH): 273, 305, 400.
VOL2: yield: 50%, m.p.: >250 °C; FT–IR (KBr, cmꢀ1): 3056, 2962
(mCAH), 1597 (mC@N), 1450 (mC@C), 1294 (mCAO), 988 (mVAO); ESI–
MS (m/z(%)): 455 [M+]; UV–Vis: (kmax, nm, MeOH): 242, 342, 420.
Infrared spectra were recorded as KBr pellets using Shimadzu
FTIR-8300 spectrophotometer. 1H and 13C NMR spectra were
obtained in CDCl3 solutions with a Bruker Avance DPX-500 spec-
trometer. All of the scanning UV–Vis spectra were recorded on a Per-
kin–Elmer Lambda 25 spectrophotometer. Thermogravimetry (TG)
and differential thermoanalysis (DTA) were carried out by using a
PL-1500. The measurements were performed in air atmosphere.
The heating rate was held at 10 °C minꢀ1. A Metrohm 797 VA system
was employed to evaluate electrochemical measurements. Voltam-
metric measurements were performed at room temperature (25 °C)
in DMF solution with 0.1 M tetrabutylammonium tetrafluoroborate
as the supporting electrolyte. An Ag/AgCl (saturated KCl)/3 M KCl
reference electrode, a Pt wire as counter electrode and a glassy car-
bon electrode as working electrode (metrohm glassy carbon,
0.0314 cm2) were used for the electrochemical studies.
3. Results and discussion
3.1. 1H NMR spectra
The 1H NMR spectra of ligands were recorded in CDCl3. The 1H
NMR spectra of the ligands show a broad resonance at d 11.20,
11.91 ppm due to the hydrogen-bonded NAH moiety, indicating
that the ligands are in the keto–amine tautomers. Further, the
H3C
CH3
H3C
R
CH3
N
O
N
O
V
O
2.2. Synthesis of the ligands
R
R
2.2.1. The preparation of 4,40-(2,2-dimethylpropane-1,3-diyl)-bis(azan-
1- yl-1-yldene)dipent-2-en-2-ol), [H2L1]
To a stirred methanolic solution (30 ml) of acetylacetone (1 ml,
10 mmol) 2,2-dimethyl-1,3-diaminopropan (0.50 g, 5 mmol) was
added. The bright yellow solution was stirred and heated to reflux
for 12 h. A white precipitate was obtained that was filtered off,
Complex
VOL1
VOL2
CH3
Ph
Fig. 1. General structure of oxovanadium(IV) complexes.

K. Mohammadi, M. Rastegari / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 97 (2012) 711–716
713
Scheme 1. Tetradentate Schiff base tautomers.
Scheme 2. Mass fragmentation pattern of H2L1 compound.
spectrum shows the phenyl multiple at d 7.42–7.90 ppm for H2L2 li-
3.3. Infrared spectral studies of Schiff bases and their complexes
gand. The resonances about d 5.00 and 5.70 ppm are consistent with
a vinyl center. The signals observed at d 3.15 and 3.34 ppm are as-
signed to ACH2 protons of diamine, that coupling with the ANH.
The signals due to the methyl protons of the diketones are observed
at d 1.92, 2.03, 2.11 ppm. The sharp singlet signals observed at d 1.09
and 1.24 ppm are assigned to methyl protons of the propyl bridge.
Tetradentate Schiff base ligands, have been studied extensively
for more than 50 years [27,28]. Theoretically, this type of ligands
can exist in the three tautomeric forms shown in Scheme 1. Typical
R-groups have been AMe, APh. The most common backbones (BB)
have been straight alkyl chains containing 2–12 CH2 groups, short
branched alkyl chains [27–29].
The IR spectra of the free Schiff base ligands and the complexes
show several bands in the 400–4000 cmꢀ1 region. It would be dif-
ficult to elucidate the correct tautomer from the IR spectra of H2L1
and H2L2. The hydrogen-bonded NAH bands are extremely weak
and broad, spanning from about 2700 to 3700 cmꢀ1 with the center
somewhere 3400 cmꢀ1. The carbonyl stretch shows a strong band
about 1610 cmꢀ1. The CAN stretching mode shows up clearly as a
strong band about 1300 cmꢀ1. The comparison of the spectra of the
complexes with the ligands provides evidence for the coordination
mode of ligand in catalysts. Absence of NAH band in the spectra of
complexes indicates the breaking of hydrogen bonding followed by
coordination of nitrogen to the metal ion after deprotonation [30].
3.2. ESI–Mass spectral studies of Schiff bases and their complexes
A sharp band appearing at 1540–1619 cmꢀ1 due to
m(C@N) (azome-
thine) [30,31]. This indicates the involvement of azomethine nitro-
gen in coordination. Vanadyl complexes have the band which
appeared at 988–998 cmꢀ1 is assigned to m(V@O) [32,33]. The band
is observed as a new peak for the complexes and is not observed in
the spectra of free ligands. Tetradentate Schiff base oxovana-
dium(IV) complexes with m(V@O) around 970 cmꢀ1 are in a mono-
meric form. Thus, both of VOL1 and VOL2 are assigned to have
monomeric structure [34]. The IR spectra of H2L1 and VOL1 are
shown in Figs. 2 and 3.
The fragmentation mode of H2L1 occurs through three main
pathways in Scheme 2. The spectrum showed a molecular ion peak
at m/z 266 which is equivalent to its molecular weight. In case of
H2L2, the molecular ion peak at m/z 390 is ascribed to C25H30N2O2.
In the spectrum of VOL1 complex, the molecular ion peak M+, which
is equivalent to its molecular weight is observed at m/z 331. In the
spectrum of VOL2 complex, the molecular ion peak M+, which is
equivalent to its molecular weight is observed at m/z 455.

714
K. Mohammadi, M. Rastegari / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 97 (2012) 711–716
Fig. 2. IR spectrum of H2L1 compound.
Fig. 3. IR spectrum of VOL1 compound.
3.4. Electronic spectra
In solution, the electronic spectra of the Schiff base ligands con-
sist of a relatively intense band in the 250–300 nm region, involv-
ing intraligand
p ?
p⁄ transition [35]. The complexes show an
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
intense CT transition in 400–420 nm regions. Also, the d–d transi-
tion in this type of complexes appears in the range above of
500 nm. However, this band does not appear due to the low inten-
sity of the d–d transitions [36]. The electronic spectra of the H2L2
and VOL2 are shown in Fig. 4.
Ligand
Complex
3.5. The electrochemical study of vanadyl complexes
The cyclic voltammetry of VOL complexes were carried out in
DMF solution at room temperature. An oxidation peak is observed
at about Ca. ꢀ0.754 V. VOL1 is oxidized to [VOL1(solvent)]+ in a
quasireversible (peak-to-peak separation >100 mV) one electron
210
260
310
360
410
460
Wavelength/nm
Fig. 4. Electronic spectra of the H2L2 and VOL2.

K. Mohammadi, M. Rastegari / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 97 (2012) 711–716
715
Table 1
Electrochemical data for the oxidation of oxovanadium(IV) complexes in DMF.
3.7. Kinetic studies
Eap (V)
Ecp (V)
All the well-defined stages were selected to study the decompo-
sition kinetics of the complexes. Various methods exist for study-
ing the thermal decomposition of complexes. In this work,
Broido’s method was utilized [37]. Broido has suggested a simple
and sensitive graphical method for the treatment of TGA data.
According to this method, the weight at any time, t (Wt) is related
to the fraction of initial molecules not yet decomposed (y) by the
equation:
Complex
E1/2 (V)
DEp (V)
VOL1
VOL2
ꢀ0.754
ꢀ0.503
ꢀ0.900
ꢀ0.996
ꢀ0.827
ꢀ0.749
0.146
0.493
step [25]. The electron is removed from the nonbonding orbitals
and the V(V) complex is formed. Upon reversal of the scan direc-
tion, the V(V) complex is reduced to V(IV) at lower potentials. Mul-
tiple scans which resulted in nearly superposable cyclic
voltammograms show that the five coordinate geometry is stable
in both oxidation states, at least on the cyclic voltammetry time
scale. The oxidation potentials for complexes are shown in Table
1. The formal potentials (E1/2 (IV/V)) of the V(IV/V) redox couple
were calculated as the average of the cathodic Epc and anodic Epa
potentials peak of this process. The cathodic peak current of the
complexes were increased and the peak shifted to more negative
potentials direction with increasing the scan rates. To studying
the effect of functional groups of the Schiff base ligands on the oxi-
dation potentials of [VOL], two vanadyl Schiff base complexes were
studied by the cyclic voltammetry method. The results show that
the anodic peak potential Epa varies as can be expected from the
electronic effects of the substituents on Schiff base complexes.
Thus, Epa becomes more positive according to the sequence
Me < Ph, which reflect the variation of the electrode potential as
a function of the electron-withdrawing ability of the substituent.
N
ðWt ꢀ W1Þ
y ¼
¼
ð1Þ
N0 ðW0 ꢀ W1Þ
where W0 is the initial weight of the materials and W1 is the weight
of residue at the end of decomposition.
If the pyrolysis is carried out isothermically, the velocity of the
reaction is given by:
dy
dt
¼ kyn
ð2Þ
where n is the reaction order. The velocity constant k changes with
absolute temperature according to the equation of Arrhenius.
k ¼ A ꢁ eꢀE=RT
and if T is linear function of time t, therefore:
ð3Þ
ð4Þ
ð5Þ
T ¼ T0 þ u ꢁ t
u is the heating rate. The first derivative of this equation is:
dT ¼ u ꢁ dt
3.6. Thermal analysis
This rearranges to:
The thermal decomposition of the studied complexes presented
pathways which depend on the nature of the ligands. The TG and
DTA figures of another compound have the same trend. The ab-
sence of weight loss up to 80 °C indicates that the crystalline solids
have no water molecule. Also, in the studied complexes, the TG
showed no weight loss up to 150 °C indicating the absence of water
molecule coordinated to complexes [30,31]. The complexes were
decomposed in two steps. The DTA curve of VOL1 shows endother-
mic peak in the temperature range 200–275 °C which is due to
weight loss of 70.86 % (calculated weight loss for 1 mol of organic
part of the complex: 69.55%) corresponding to the elimination of
organic part. The second step of the thermal decomposition, which
occurs in the range 300–390 °C, is also endothermic, was assigned
to the loss of oxygen atom (observed 4.59 %) (calculated 4.84 %)
and VO3 formed. Finally, the metal oxide corresponds to V2O5
formed above 660 °C with exothermic peak. The DTA curve of
VOL2 shows endothermic peak in the temperature range 210–
290 °C which is due to weight loss of 31.04 % corresponding to
the elimination of partial organic part. The second step of the ther-
mal decomposition, which occurs in the range 385–475 °C, is also
endothermic, was assigned to the loss of residue of organic part
(observed 50.95 %). Finally, the metal oxide corresponds to V2O5
formed above 660 °C with exothermic peak. The temperature
range and the percent of loss weight calculated and found for
two steps are presented in Table 2.
ꢀ ꢁ
dy
yn
A
u
E
RT
¼ ꢀ
ꢁ eꢀ dt
ð6Þ
The thermogravimetric analysis curve for this reaction represents
the last equation integrated from a temperature T0, where y = 1, to
a temperature for another value of y.
Z
Z
Z
1
T
T0
dy
yn
A
u
A
u
E
RT
E
eꢀ dT ¼
eꢀ dT
ð7Þ
RT
¼ ꢀ
y
T0
T
The main consideration of this method is that the reaction is of the
first order. With this supposition, the left side of the reaction can be
resolved.
ꢀ ꢁ
Z
Z
1
1
dy
yn
dy
y
1
¼
¼ ꢀ ln y ¼ ln
ð8Þ
y
y
y
There are various methods for resolving the right side of the equa-
tion. Broido’s method is based on approximations done by other
authors. We have utilized the approximations introduced by
Wendland [38].
ꢀ
ꢁ
2
E
m
Tm
T
E
RT
eꢀ
ꢂ
eꢀ
ð9Þ
RT
Tm is the temperature at which the maximum reaction velocity oc-
curs. Introducing this approximation has
Table 2
Thermal and kinetics parameters for vanadyl complexes.
Compounds
VOL1
D
Ta (°C)
Reduce massb (%)
Ea (kJmolꢀ1
)
A (sꢀ1
)
D
S (Jmolꢀ1Kꢀ1
)
D
H (kJmolꢀ1
)
D )
G (kJmolꢀ1
200–275
300–390
210–290
385–475
69.55(70.86)
4.84(4.59)
30.12(31.04)
49.91(50.95)
323.78
34.47
77.51
1.82 ꢃ 109
1.05 ꢃ 10ꢀ4
3.20 ꢃ 10ꢀ3
8.90 ꢃ 10ꢀ2
ꢀ73.0
ꢀ327
ꢀ297
ꢀ273
319.22
28.95
72.83
359.06
245.76
240.04
320.47
VOL2
122.48
116.26
a
The temperature range of decomposition pathways.
Percent of weight lose calculated (found).
b

716
K. Mohammadi, M. Rastegari / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 97 (2012) 711–716
ꢀ
ꢁ
Z
2
for the complexes. The electrochemical properties of the vanadyl
complexes were investigated in DMF show the anodic peak poten-
tial becomes more positive according to the sequence Me < Ph.
1
y
A
u
Tm
T
E
eꢀ dT
ð10Þ
RT
ln
¼
changing variable has
ꢀ
ꢁ
Acknowledgements
1
T
1
1
x2
x ¼ ) dx ¼ dT ) dT ¼ ꢀ
dx
ð11Þ
ð12Þ
T2
The authors thank Persian Gulf University of Bushehr Research
Councils for financial support of this work.
ꢀ
ꢁ
Z
1
y
A
u
1
x2
E
R
ln
ln
ln
¼
T2m x2eꢀ X
ꢀ
dx
Appendix A. Supplementary data
1
y
A:R:T2m
E:u
E
R
¼
¼
ꢁ eꢀ X
ð13Þ
ð14Þ
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.saa.2012.07.062.
1
y
A:R:T2m
E:u
E
R
1
T
ꢁ eꢀ ð Þ
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ꢀ ꢁ
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R
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ð15Þ
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ꢀE#a ¼ slope ꢃ 2:303 ꢃ R
ð16Þ
where E#a is activation energy and R is the gas constant. Application
of this method used to determine the kinetic parameters for
complexes.
The entropy of activation
DS
# was calculated using the equation
#
kTm
h
S
eD
ð17Þ
R
A ¼
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D
H# ¼ E#a ꢀ RT
ð18Þ
D
G#
¼
D
H# ꢀ T
D
S#
ð19Þ
The activation energy E#a in the different stages is in the range of
34–323 kJmolꢀ1. The respective values of the pre-exponential factor
A vary from 1.05 ꢃ 10ꢀ4 to 1.82 ꢃ 109 sꢀ1. The corresponding values
of the entropy of activation,
D
S# , were in the range of ꢀ73 to
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D
S# values for complexes were found to be
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positive values of
endothermic. The corresponding values of the free energy of activa-
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G#, were in the range of 240–359 kJmolꢀ1
D
H#, values were in the range of 28–319 kJmolꢀ1. The
DH
# means that the decomposition processes are
D
.
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4. Conclusions
In this work, two new symmetrical tetradentate Schiff base li-
gands containing the N2O2 donor group have been synthesized
and spectrally characterized. Then, their oxovanadium(IV) com-
plexes have been synthesized and characterized by several spec-
troscopic methods. According to the results discussed from TG
curves, the order of thermal stability for the complexes is VOL1 > -
VOL2. The number of decomposition steps of the ligands depends
on the substituent group leading to differences in thermal process
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