Synthesis, molecular modeling, thermal and spectral studies of metal complexes of hydrazone derived from 5-acetyl-4-hydroxy-2H-1,3-thiazine-2,6(3H)- dione and thiosemicarbazide

Article abstract of DOI:10.1016/j.saa.2011.04.058

Metal complexes with the general formula [ML(H₂O)(CH ₃OH)_x]·nH₂O·(CH ₃OH)_y(NO₃)_z [M = Cu(II), Ni(II), Co(II), VO(IV), Cr(III), Cd(II), Zn(II) or UO₂(VI); x = 0-2; y = 0,1; z = 0,1; n = 0-2, 6 and L = hydrazone (H₂L) derived from condensation of thiosemicarbazide with 5-acetyl-4-hydroxy-2H-1,3-thiazine-2, 6(3H)-dione. The synthesized ligand and its metal complexes have been characterized on the basis of elemental analyses, spectral and magnetic studies as well as thermal gravimetric analysis (TGA). The deprotonated ligand acts as a dibasic tridentate (ONS) via phenolate oxygen, azomethine (CN), and thiolate (C-S) groups. Copper(II) complex exhibits square planar geometry. Nickel(II), chromium(III) and dioxouranium(VI) complexes exhibit octahedral geometry. Cobalt(II), cadmium(II) and zinc(II) complexes showed tetrahedral geometry, whereas oxovanadium(IV) reveals square pyramidal geometry. Thermal analysis are investigated and showed either three or four thermal decomposition steps. Kinetic parameters (E_a, A, ΔH, ΔS and ΔG) of the thermal decomposition stages have been evaluated using Coats-Redfern equations. The molecular parameters of the ligand and its metal complexes have been calculated and correlated with the experimental data such as IR and TGA results.

Full text of DOI:10.1016/j.saa.2011.04.058

Spectrochimica Acta Part A 79 (2011) 1295–1303
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Synthesis, molecular modeling, thermal and spectral studies of metal complexes
of hydrazone derived from 5-acetyl-4-hydroxy-2H-1,3-thiazine-2,6(3H)-dione
and thiosemicarbazide
Omima M.I. Adly∗
Department of Chemistry, Faculty of Education, Ain Shams University, Roxy, Cairo 11711, Egypt
a r t i c l e i n f o
a b s t r a c t
Article history:
Metal complexes with the general formula [ML(H2O)(CH3OH)x]·nH2O·(CH3OH)y(NO3)z [M = Cu(II), Ni(II),
Co(II), VO(IV), Cr(III), Cd(II), Zn(II) or UO2(VI); x = 0–2; y = 0,1; z = 0,1; n = 0–2, 6 and L = hydrazone (H2L)
derived from condensation of thiosemicarbazide with 5-acetyl-4-hydroxy-2H-1,3-thiazine-2,6(3H)-
dione. The synthesized ligand and its metal complexes have been characterized on the basis of elemental
analyses, spectral and magnetic studies as well as thermal gravimetric analysis (TGA). The deprotonated
ligand acts as a dibasic tridentate (ONS) via phenolate oxygen, azomethine (C N), and thiolate (C–S)
groups. Copper(II) complex exhibits square planar geometry. Nickel(II), chromium(III) and dioxoura-
nium(VI) complexes exhibit octahedral geometry. Cobalt(II), cadmium(II) and zinc(II) complexes showed
tetrahedral geometry, whereas oxovanadium(IV) reveals square pyramidal geometry. Thermal analysis
are investigated and showed either three or four thermal decomposition steps. Kinetic parameters (Ea, A,
ꢀH, ꢀS and ꢀG) of the thermal decomposition stages have been evaluated using Coats–Redfern equa-
tions. The molecular parameters of the ligand and its metal complexes have been calculated and correlated
with the experimental data such as IR and TGA results.
Received 8 January 2011
Received in revised form 16 April 2011
Accepted 27 April 2011
Keywords:
Thiosemicarbazone
Tridentate ligand
5-Acetyl-4-hydroxy-2H-1,3-thiazine-
2,6(3H)-dione
Molecular modeling
Thermal degradation kinetics
© 2011 Elsevier B.V. All rights reserved.
1. Introduction
mal gravimetric analysis (TGA). Molecular modeling carried out for
the free ligand and its complexes and the theoretical results were
Thiosemicarbazones are well established as an important class
of sulfur donor Schiff base ligands particularly for transition metal
ions [1,2]. Metal complexes of thiosemicarbazones are a class of
important compounds in medicinal and pharmaceutical field, they
show various biological activities such as antibacterial [3,4], anti-
fungal [5,6], anticancer [7,8], antitumoral [9], antimalarial [10],
antimicrobial [11], antiamebic [12] and pharmacological activi-
ties [13]. Also, thiosemicarbazones have been a subject of interest
due to their variable applications in industry and analytical chem-
istry [14,15]. In view of their interesting structural properties and
wide ranging uses, studies of the thiosemicarbazone complexes
have attracted the attention of many investigators [16–19]. The
present work aims to synthesize and characterization of a new
thiosemicarbazone ligand (H2L), derived from the condensation of
5-acetyl-4-hydroxy-2H-1,3-thiazine-2,6(3H)-dione with thiosemi-
carbazide, and its complexes with the first row transition metals:
Cr(III), Co(II), Ni(II), Cu(II), Zn(II), Cd(II); and oxy-metals: VO(IV)
and UO2(VI) ions. These compounds have been characterized by
elemental analyses, spectral and magnetic studies as well as ther-
correlated with the experimental data.
2. Experimental
2.1. Materials
Copper(II),
nickel(II),
cobalt(II),
cadmium(II),
zinc(II),
chromium(III) and iron(III) were used as nitrate salts and were
Merck or BDH. Oxovanadium(IV) sulphate monohydrate and
dioxouranium(VI) acetate dihydrate were BDH. Organic solvents
(ethanol, absolute ethanol, methanol, diethylether, dimethylfor-
mamide (DMF) and dimethylsulfoxide (DMSO)) were reagent
grade.
2.2. Synthesis of 2-[1-(4-hydroxy-2,6-dioxo-3,6-dihydro-2H-1,3-
thiazin-5-yl)ethylidene] hydrazinecarbothioamide, H2L,
ligand
5-Acetyl-4-hydroxy-2H-1,3-thiazine-2,6(3H)-dione
(AHTD)
was prepared as described elsewhere [20]. A mixture of AHTD
(1.87 g, 10.0 mmol) and thiosemicarbazide (0.91 g, 10.0 mmol) in
absolute ethanol (25 mL) was heated under reflux for 1 h. Yellow
product was obtained after cooling to room temperature, then
∗
Tel.: +20 108693220.
E-mail address: omima adly@yahoo.com
1386-1425/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2011.04.058

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O.M.I. Adly / Spectrochimica Acta Part A 79 (2011) 1295–1303
O
CH3
O
CH3
H
H
N
NH2
N
NH2
S
O
EtOH
S
N
H2N
+
S
S
O
N
H
OH
O
N
OH
H
Scheme 1. Formation of the hydrazone, H2L, ligand.
filtered and washed with a few portions of ethanol. The fine yellow
crystals were recrystallized from ethanol. The yield was 1.53 g
(59%) and m.p. 232–233 ◦C. Scheme 1 illustrates the formation of
the H2L ligand.
complexes with Cu(II), Ni(II), Co(II), VO(IV), Cr(III), Cd(II), Zn(II)
and UO2(VI) are presented in Table 1. The ligand (H2L) might
exhibits two tautomeric, thione and thiol, forms. It behaves as a
dibasic tridentate with ONS sites as shown in structures of the
thione–thiol forms of the free ligand (Fig. 1).
2.3. Synthesis of the metal complexes
The mass spectrum of the present free ligand (H2L) showed
the molecular ion peak at m/e = 259 (M − 1) corresponding to the
molecular formula (C7H8N4O3S2, F.W. 260.29 amu). The fragmen-
tation pattern of the mass spectrum is depicted in Scheme 2.
1H NMR spectrum of the H2L ligand in DMSO-d6 showed sin-
glet signal at 2.51 ppm which might attributed to the methyl
protons, and broad signals exchangeable with D2O at 7.26 ppm
which assignable to NH protons, in addition to 10.02 and 10.09 ppm
attributed to CSNH2 protons. The absence of the signal at ∼4.0 ppm
attributable to the S–H proton provides strong evidence of the
thione form even in solution. The signal of the –OH for the phenolic
proton was not observed in the range of the spectrum as previously
reported for the starting material [20].
Methanolic solutions of the deprotonated ligand (0.78 g,
3 mmol, 20 mL) were added gradually to methanolic solutions of the
appropriate metal salt (3 mmol, 20 mL) in the molar ratio 1:1. The
ligand was firstly deprotonated by lithium hydroxide, LiOH·H2O
(0.246 g, 6 mmol) in the molar ratio 1:2. The reaction mixture of
the deprotonated ligand with metal salts was stirred for 3 h at room
temperature, except in cases of Cr(III) and UO2(VI) were heated to
reflux for 2 h. The resulting precipitates were filtered and washed
with methanol then diethyl ether.
Trials to prepare iron(III) complex of the hydrazone, H2L, ligand
was unsuccessful, it gave oily product and was difficult to isolated
in its pure form.
The main characteristic IR absorption frequencies of the free
ligand (H2L) showed stretching vibrational modes at 3435, 3288,
3162, 1681, 1606 and 1558 cm−1 assigned for OH, NH2, NH, C O,
2.4. Molecular modeling
C
N and C C, respectively, in the light of IR data of similar
An attempt to gain a better insight on the molecular struc-
ture of the ligand and its complexes, geometric optimization
and conformation analysis has performed using PM3 forcefield as
implemented in hyperchem 7.5 [21].
compounds [25,26]. These assignments further supported by the
comparison the IR spectrum of the current hydrazone ligand with
that of the corresponding 5-acetyl-4-hydroxy-2H-1,3-thiazine-
2,6(3H)-dione (AHTD) and thiosemicarbazide. The intense band at
1606 cm−1 assigned to the azomethine group (C N) [25,26]. This
assignment confirmed by disappearance of the absorption band
that assigned to acetyl C O of AHTD at 1659 cm−1, emphasizing the
condensation between the C O of the later compound with NH2 of
the thiosemicarbazide as suggested in Scheme 1. The absence of the
IR band around 2600 cm−1 due to ꢁ(SH) supports the presence of
the current ligand (H2L) in the thione form which agree well with
1H NMR data.
2.5. Physical measurements
Elemental analyses of (C, H, N, S) were carried out at the National
Research Center, Dokki, Giza, Egypt. Analyses of the metal ions
were carried out complexometrically [22,23]. The FT-IR spectra
(4000–400 cm−1) of the ligand and its complexes were recorded
as KBr discs using FT-IR-4000 (Shimadzu) spectrophotometer. 1H
NMR spectra were recorded using a Gemini spectrometer, 200 MHz.
Dimethylsulphoxide, DMSO-d6, was used as a solvent and tetram-
ethylsilane (TMS) as an internal reference. The electronic spectra
of the ligand and its metal complexes were carried out on a JASCO
model V-550 UV–vis spectrophotometer in the range 200–900 nm.
ESR spectra were recorded on the Bruker, Model: EMX, X-band
spectrometer. Mass spectra were recorded on a Hewlett Packard
mass spectrometer model MS 5988. Samples were introduced
directly to the probe, and the fragmentations were carried out at
300 ◦C and 70 eV.
Magnetic susceptibilities of the complexes were measured by
the Gouy method at room temperature using Johnson Matthey, Alfa
product, Model No. (MKI), the diamagnetic corrections were calcu-
lated from Pascal’s constants for all atoms in the compounds [24].
Thermal gravimetric analysis (TGA) data was measured from room
temperature up to 800 ◦C at a heating rate of 10 ◦C/min. The data
were obtained using a Shimadzu TGA-50H instrument. All melting
points were recorded on a Stuart SMP3 melting point apparatus.
Electronic spectral data of the H2L ligand in DMF solu-
tion displays two absorption bands at 35,842 and 29,411 cm−1
assigned to the ␲→␲* (K-band), and n→␲* transitions (R-band)
[27].
3.1. Metal complexes of H2L ligand
The results of the elemental analyses and physical data of
the current solid complexes recorded in Table 1 are in good
agreement with the suggested tentative molecular formula;
[ML(H2O)(CH3OH)x]·nH2O·(CH3OH)y(NO3)z; n = 0–2, 6; x = 0–2;
y = 0,1; z = 0,1.
The thione form of the ligand is the dominant form in either
solid state or solution, while the thiolate form is mainly dominant
in presence of a base such as LiOH as concluded from IR and 1H NMR
spectral data of the ligand and its metal complexes, respectively.
The deprotonated hydrazone ligand behaves as a dibasic with
tridentate ONS sites during the reaction with Cu(II), Ni(II), Co(II),
VO(IV), Cr(III), Cd(II), Zn(II) or UO2(VI) ions yielding the corre-
sponding metal complexes. The isolated complexes were further
characterized by FT-IR, mass, UV–vis, ESR spectroscopy and ther-
mal gravimetric analysis (TGA), as well as magnetic susceptibility
measurements.
3. Results and discussion
The analytical and physical data of the free ligand,
2-[1-(4-hydroxy-2,6-dioxo-3,6-dihydro-2H-1,3-thiazin-5-
yl)ethylidene]hydrazinecarbothioamide (H2L), and its solid

O.M.I. Adly / Spectrochimica Acta Part A 79 (2011) 1295–1303
1297
Table 1
Physical and analytical data of the hydrazone, H2L, ligand and its transition metal complexes.
Ligand/complex
Molecular formula
M. wt. yield (%)
Color
M.P. (◦C)
Elemental analyses found (calcd.) %
C
H
N
S
M
–
H2L
C7H8N4O3S2
260.29
(59)
357.93
(80)
435.19
(60)
367.31
65
360.99
(49)
548.52
(75)
359.76
(73)
406.79
(69)
Yellow
Brown
Green
Cumin
Brown
Grey
232–233
256
32.28
3.18
21.37
24.60
(32.30)
23.60
(23.48)
25.00
(24.83)
26.28
(26.15)
24.16
(23.29)
18.78
(19.70)
23.25
(23.37)
20.05
(20.66)
14.65
(3.10)
2.75
(2.81)
4.34
(4.63)
3.54
(3.29)
2.98
(2.79)
5.28
(5.14)
2.74
(2.80)
2.74
(2.47)
1.74
(21.52)
15.70
(15.67)
12.78
(12.89)
16.12
(15.27)
15.35
(15.54)
10.95
(10.22)
15.79
(15.59)
13.86
(13.79)
9.79
(24.63)
17.90
(17.92)
14.89
(14.73)
17.04
(17.45)
17.80
(17.76)
11.60
(11.69)
17.65
(17.82)
15.63
(15.76)
11.28
(1)
(2)
(3)
(4)
(5)
(6)
(7)
(8)
[CuL(H2O)]·H2O
C7H10N4O5 S2Cu
C9H20N4O8S2Ni
C8H12N4O5S2Co
C7H10N4O6S2V
C9H28N4O15S2Cr
C7H10N4O5S2Zn
C7H10N4O5S2Cd
C7H10N4O7S2U
17.76
(17.75)
13.26
(13.48)
16.23
(16.03)
NA
[NiL(CH3OH)2(H2O)]·2H2O
[CoL(H2O)]·CH3OH
[VOL(H2O)]·H2O
>300
>300
260
(14.01)
9.52
[CrL(CH3OH)2(H2O)]·(NO3) 6H2O
[ZnL(H2O)]·H2O
256
(9.46)
18.32
(18.17)
27.58
(27.63)
NA
Yellow
Yellow
Orange
240
[CdL (H2O)]·H2O
280
[UO2L(H2O)]·H2O
564.41
(67)
>300
(14.89)
(1.78)
(9.94)
(11.36)
(42.17)
NA: not analyzed.
Fig. 1. Molecular modeling of the thione-thiol forms of H2L ligand.
+
+.
O
CH3
O
O
CH3
+.
H
.
CH3
N
NH2
NH
-OH
S
S
N
-HSCN
S
N
N
S
N
H
N
O
O
N
H
OH
O
N
H
OH
H
259 (M-1; 1%)
183 (13%)
-CH3CN
200 (6%)
.
-H
O
+.
S
S
+.
N
O
78 (100%)
O
O
N
H
141 (7%)
Scheme 2. Mass fragmentation pattern of the hydrazone, H2L, ligand.
3.1.1. Infrared spectra
free ligand. All complexes showed a broad band in the range of
3462–3420 cm−1 assignable to the stretching frequencies of ꢁ(OH)
of water and/or solvated molecules. The band at 1606 cm−1 belong-
ing to ꢁ(C N) stretching was shifted to a lower frequencies in the
range (1600–1586 cm−1) supporting the participation of C N in
The main characteristic IR vibrational frequencies and their
assignments for the current free ligand and its complexes are given
in Table 2. The sites of coordination are deduced from the com-
parison of the IR data of the metal complexes with that of the

1298
O.M.I. Adly / Spectrochimica Acta Part A 79 (2011) 1295–1303
Table 2
a
Characteristic infrared frequencies (cm−1
)
of hydrazone, H2L, ligand and its transition metal complexes.
Ligand/complex
H2L
ꢁ(OH)
ꢁ(NH2)
ꢁ(NH)
ꢁ(C O)
ꢁ(C N)
ꢁ(C C)
ꢁ(C–S)
ꢁ(M–N)
ꢁ(M–O)
Other band
3435 s
3422 s
3288 s
3162 s
3210 w
–
1681 s
1670 m
1616 s
–
1667 s
1638 m
–
1606 s
1590 s
1590 s
1600 s
1593 s
1587 s
1595 s
1598 s
1586 s
1558 w
1517 m
1517 m
1510 m
1513 s
1535 s
1518 s
1517 s
1543 m
–
–
–
1340 (C S)
–
–
–
1009 w (V O)
1384,832 (NO3)
–
–
(1)
(2)
(3)
(4)
(5)
(6)
(7)
(8)
[CuL(H2O)]·H2O
3332 w
3322 w
3329 w
3329 m
3329 w
3331 w
3328 s
695 w
692 w
691 w
693 w
691 w
688 w
683 w
681 w
507 w
529 w
507 w
525 w
568 w
568 w
525 w
508 w
485 w
444 w
430 w
489 w
487 w
479 w
470 w
435 w
[NiL(CH3OH)2(H2O)]·2H2O
[CoL(H2O)]·CH3OH
[VOL(H2O)]·H2O
3420 br, s
3430 br, s
3426 s
3437 br, s
3432 s
–
3194 w
–
–
3326 s
3324 s
[CrL(CH3OH)2(H2O)]·(NO3)·6H2O
[ZnL(H2O)]·H2O
[CdL (H2O)]·H2O
3435 s
3462 s
–
–
[UO2L(H2O)]·H2O
3330 w
904 w (U O)
a
s = strong, m = medium, w = weak, br = broad.
the coordination mode. The disappearance of ꢁ(C S) band of the
free ligand at 1340 cm−1, and appears of new bands in the range
(695–681 cm−1) which attributed to ꢁ(C–S) providing strong evi-
dence that the sulfur participates as thiolate [28]. The weak bands in
the ranges (489–430) cm−1 and (586–507) cm−1 were assigned to
the ꢁ(M–O) and ꢁ(M–N) stretching frequencies for the metal com-
plexes of the H2L ligand [29]. Hence, the ligand behaves as dibasic
tridentate (ONS) via the phenolate oxygen, azomethine nitrogen
and thiolate sulfur atoms.
The anion coordinating modes are inferred from the IR data of
the complexes. Nitrate complex (5) of Cr(III) exhibits two bands at
1384, 832 cm−1 characterized the presence of ionic nitrate (D3h),
ꢁ3(Eꢀ), [ꢁch(NO)] mode. This might indicate that the nitrate group
in complex 5 is ionic [29]. The IR spectrum of VO(IV) complex (4)
displayed a band at 1009 cm−1 due to the stretching vibration of
the ꢁ(V O) band in five coordinate structure [30,31]. Similarly, the
strong band located at 904 cm−1 for complex (8) was assigned to
are calculated (Table 3) according to the equations reported for the
tetrahedral Co(II) complexes.
ꢂeff = 3.87(1 − 4ꢃ/10 Dq), ꢃ = −178 cm−1
B = [4(ꢁ3 − 15 Dq)2 − 10 Dq2]/[60(ꢁ3 − 15 Dq) − 18 Dg]
ꢁ1 = 10 Dq
The electronic spectrum of the brown oxovanadium(IV) com-
plex (4) showed one band at 16,750 cm−1 due to b1 ← b2 electronic
transition suggesting a penta coordinated structure, which would
be square pyrimidal [40]. This conclusion agree well with the
data obtained from elemental analysis and IR spectrum of VO(IV)
complex (4) [41]. Although most oxovanadium(IV) complexes are
magnetically simple which having virtually ‘spin-only’ moments
of 1.73 B.M. corresponding to one unpaired electron. In this study,
the ꢂeff = 1.43 B.M., suggesting a vanadyl polymeric complex with
a variety of nucleotides such as reported by Katsaros [42] and
Dutta [43].
ꢁ3(asym) of the O
U O group indicate the six coordinate for the
The electronic spectrum of the grey Cr(III) complex (5) showed
two absorption bands at 17,301 and 23,584 cm−1, suggesting an
octahedral geometry for the Cr(III) complex (5) attributing to
uranyl complex [32,33].
4
4
4T2g(F) ← A2g(F) and 4T1g(F) ← A2g(F) transitions, respectively. In
the Cr(III) octahedral complexes, the splitting of the free ion ground
F term along with the presence of the excited P term of the same
multiplicity provides the possibility of three spin allowed d–d tran-
sitions [44]. The third band expected for Cr(III) octahedral which
3.1.2. Electronic spectra and magnetic moment measurements
The electronic spectra of the current colored metal complexes
in the range 200–900 nm, were carried out as Nujol mulls, since the
metal complexes are sparingly soluble in most common solvents.
Table 3 shows the electronic spectral bands and their assignments,
in addition to the magnetic moments of the current complexes.
The electronic spectrum of the brown Cu(II) complex (1)
[CuL(H2O)]·H2O showed one broad band in the visible region at
4
4
is due to T1g(P) ← A2g(F) transition not observed which might
lies in the range of the ligand transitions. The ligand field param-
eters of Cr(III) complex is calculated on the basis Tanab–Sugano
diagrams (Table 3) and also predict that the third transition band
found to be 37,174 cm−1. The magnetic moment of Cr(III) com-
plex (5) ꢂeff = 3.58 B.M. corresponding to the spin-only for three
unpaired electrons, due to the absence of any orbital contribution.
The yellow [CdL(H2O)]·H2O (6) and [ZnL(H2O)]·H2O (7) com-
plexes, are diamagnetic as expected and are likely to be tetrahedral
structure for Cd(II) and Zn(II) complexes. The mass spectra of Zn(II)
and Cd(II) complexes showed the molecular ion peak at m/e 359
and 406, respectively. This finding which is consistent with the for-
mula weight, indicated from elemental analysis, and supports the
identity of structures.
17,543 cm−1 might assigned to dxy → dx2-y2 (2T2g(G) ← Eg) tran-
2
sition, suggesting square planar geometry around the Cu(II) ion
[34,35]. The magnetic moment of Cu(II) complex (1) was 1.66 B.M.
[36].
The electronic spectrum of the green Ni(II) complex (2)
[NiL(CH3OH)2(H2O)]·2H2O, showed two absorption bands at
16,393 cm−1 and 23,866 cm−1. Since the spectra of octahedral Ni(II)
consist of three bands as a result of the splitting of the free ion
in ground state 3F term and the presence of 3P term [37]. These
3
3
3
3
bands were assigned as T2g(F) ← A2g(F), T1g(F) ← A2g(F) and
3T1g(P) ← A2g(F); the first band is out of the instrument mea-
3
The electronic spectrum of the orange UO2(VI) complex (8)
arises from the electronic transitions of metal → ligand charge
transfer and/or appical oxygen → Fo (U) transition [45]. This is
an allowed transition and produces a broad, intense absorption
band at 20,000 cm−1 for complex (8) tailing into the visible region,
producing the intense yellow color. The magnetic moment mea-
surement suggested that the UO2(VI) complex is diamagnetic as
expected [46].
surements range. The ligand field parameters of Ni(II) complex is
calculated and the first transition band in the spectrum can also
predicted, at 10,718 cm−1 on the basis Tanab–Sugano diagrams
(Table 3). This finding further emphasized by the measured mag-
netic moment at 3.27 B.M., which lies in the range (2.9–3.3 B.M.) of
the Ni(II) octahedral complexes [27].
The electronic spectrum of the cumin Co(II) complex (3) showed
a single band in the visible region at 16,528 cm−1 indicating tetra-
hedral geometry [38]. The tetrahedral structure of Co(II) complex
(3) was further confirmed by the magnetic moment measurements,
ꢂeff = 4.4 B.M. which agree well with the tetrahedral structure
around Co(II) ion [39]. The ligand field parameter (B, ˇ and 10Dq)
3.1.3. ESR Spectra
The X-Band ESR spectrum of [CuL(H2O)]·H2O (1) complex at
room temperature exhibits one broad band with geff = 1.98. The
spectrum is consistent with the square planar geometry around

O.M.I. Adly / Spectrochimica Acta Part A 79 (2011) 1295–1303
1299
Table 3
Characteristic electronic transition bands and magnetic moments of the transition metal complexes of the hydrazone, H2L, ligand.
a
Complex
␲–␲*
n–␲*
ꢃmax (cm−1) Nujol
d–d transition assignments
10 Dq
B
ˇ
ꢂeff
H2L
35,842
33,557
33,670
29,411
27,700
29,069
–
–
–
–
1020
–
–
447
–
–
0.41
–
1.66
3.27
(1)
(2)
[CuL(H2O)]·H2O
17,543
23,866
16,393
16,528
20,000
17,301
–
3T2g(G) ← Eg
3
[NiL(CH3OH)2(H2O)]·2H2O
3T1g(P) ← A2g(F)
3T1g(F) ← A2g(F)
3
(3)
(4)
(5)
(6)
(7)
(8)
[CoL(H2O)]·CH3OH
[VOL(H2O)]·H2O
34,482
33,670
35,971
33,898
33,670
35,335
28,735
26,525
28,985
28,735
28,985
28,818
4T1(P) ← 4A2(F)
b1 ← b2
5199
–
1809
–
–
–
582
–
605
–
–
–
0.60
–
0.58
–
–
–
4.40
1.43
3.58
Diam
Diam
Diam
4
[CrL(CH3OH)2(H2O)]·(NO3)·6H2O
[ZnL(H2O)]·H2O
4T2g(F) ← A2g(F)
–
–
[CdL(H2O)]·H2O
–
[UO2L(H2O)]·H2O
20,000
Charge transfer
a
ꢂeff is the magnetic moment of one metal ion in the complex.
-10
-11
-12
-13
-14
Cu(II) ion in the complex as concluded from UV/vis spectra [47]. The
ESR spectrum of the oxovanadium(IV) complex (4), exhibits one
band at geff = 2.06, without hyperfine structure indicating square
pyramidal geometry around VO(IV) ion. This finding agrees with
that concluded from the IR and UV/vis spectra. The absence of vana-
dium’s hyperfine coupling might attributed to the strong exchange
interactions, which average out the interaction with the nuclei or
due to simultaneous flipping of neighboring electron spin [48].
R2 = 0.9814
2.3
2.5
2.7
1000/T
First stage
2.9
3.1.4. Thermal analysis and kinetic studies
The thermal gravimetric analysis (TGA) for the ligand (H2L) and
its metal complexes was carried out within the temperature range
from room temperature up to 800 ◦C.
The main aim of the thermal analysis is to obtain information
concerning the thermal stability of the investigated complexes, to
decide the number of water or solvent molecules and whether they
are inside or outside the coordination sphere. Moreover, the kinetic
and thermodynamic parameters using Coats–Redfern method have
been also calculated.
Thermograms of the current complexes showed the removal of
the lattic water or methanol molecules at 69 ◦C up to 118 ◦C. The
anhydrous complexes are thermally stable in the range 118–180 ◦C.
The removals of the coordinated water and/or methanol molecules
are completed at 180–250 ◦C. The decomposition of the complexes
to CuO, NiO, CoO, VO2, Cr2O3, ZnO, CdO and UO2 starts within the
temperature ranging from 500 to 800 ◦C.
The stages of decomposition, temperature ranges and decom-
position product loss as well the found and calculated weight loss
percentages of the ligand and its metal complexes are given in
Table 4.
-13
-13.5
-14
-14.5
-15
-15.5
-16
R2 = 0.983
1.8
1.9
2
2.1
2.2
2.3
2.4
1000/T
Second stage
-11.4
-11.6
-11.8
-12
R2 = 0.981
`
-12.2
-12.4
The kinetic and thermodynamic parameters of the thermal
degradation of the complexes namely, activation energy (Ea),
enthalpy (ꢀH), entropy (ꢀS) and free energy changes (ꢀG) were
calculated using Coats–Redfern method [49]. The Coats–Redfern
equations are in the following form:
1.6
1.65
1.7
1.75
1.8
1.85
1000/T
Third stage
ꢀ
ꢁ
1 − (1 − ˛)1−n
(1 − n)T2
M
Fig. 2. Coats–Redfern plots for [CuL(H2O)]·H2O (1), where Y = ln[−ln(1 − ˛)/T2].
ln
ln
=
for n =/ 1
(1)
(2)
T + B
(Figs. 2 and 3). The n value which gave the best fit (r ≈ 1) was
chosen as the order parameter for the decomposition stage of
interest. From the intercept and linear slope of such stage, the
A and Ea values were determined. The other kinetic parameters,
ꢀH, ꢀS and ꢀG were also computed using the relationships;
ꢀH = Ea − RT, ꢀS = R[ln(Ah/kT) − 1] and ꢀG = ꢀH − T ꢀS, where k
is the Boltzmann’s constant and h is the Plank’s constant. The
following remarks can be pointed out on the kinetic parame-
ters listed in Table 5. (1) All complexes decomposition stages
show a best fit for (n = 1) indicating a first order decomposition
in all cases. (2) Non-spontaneously (endergonic reactions) and the
endothermicity of the desolvation process. (3) The negative values
of activation entropies ꢀS indicate a more order activated complex
ꢂ
ꢃ
− ln(1 − ˛)
M
=
for n = 1
T2
T + B
where ˛ represents the fraction of sample decomposed at time t,
defined by: ˛ = (wo − wt)/(wo − w ), wo, wt and w are the weight
∞
∞
of the sample before the degradation, at temperature t ◦C and after
total conversion, respectively. T is the derivative peak temperature.
M = −Ea/R and B = ln AR/˚Ea; Ea, R, A and ˚ are the heat of the activa-
tion, the universal gas constant, pre-exponential factor and heating
rate, respectively.
The correlation coefficient, r, was computed using the least
square method for different values of n (n = 0.33, 0.5, 0.66 and
1), by plotting the left-hand side of Eqs. (1) or (2) versus 1000/T

1300
O.M.I. Adly / Spectrochimica Acta Part A 79 (2011) 1295–1303
Table 4
Thermal gravimetric results of H2L and its metal complexes.
Compound (molecular weight)
DTG peak (◦C)
Temperature range (◦C)
Decomposition product lost (formula weight)
Weight loss (%) found
(calculated)
H2L
237
279
535
91
236
521
77–253
253–328
328–800
49–155
154–278
278–800
Residue
35–137
138–470
470–637
Residue
34–116
118–357
357–750
Residue
24–104
105–322
322–800
Residue
32–92
93–325
325–679
Residue
24–143
144–345
345–712
Residue
25–162
162–340
340–800
Residue
31–148
148–239
239–495
497–684
Residue
−NH4SCN
32.14 (29.19)
48.53 (48.84)
20.00 (22.28)
5.0 (5.02)
25.40 (25.70)
38.00 (38.09)
31.60 (31.20)
8.80 (8.27)
45.54 (45.26)
15.27 (16.31)
30.00 (30.00)
8.14 (8.71)
25.45 (26.20)
41.92 (41.93)
25.00 (24.48)
5.00 (4.98)
36.40 (36.84)
35.00 (35.18)
23.70 (22.88)
19.70 (19.68)
18.75 (18.04)
25.62(26.43)
35.29 (35.96)
5.00 (5.00)
25.00 (25.57)
45.54 (46.69)
22.96 (22.61)
4.32 (4.42)
−C4HOS
−(CH3CN + OH)
[CuL(H2O)]·H2O
−H2O
−(H2O + NH2SCN)
−C5H6N2O
−(CuO + S)
[NiL(CH3OH)2(H2O)]·2H2O
[CoL(H2O)]·CH3OH
[VOL(H2O)]·H2O
85
384
536
−2H2O
−(2CH3OH + H2O + C3H5N3S + 2CO + NH)
−(NiO + C2S)
68
308
508
−CH3OH
−(H2O + NH2SCN)
−C6H3NO2S
−(NH + CoO)
−H2O
85
289
618
−(H2O + C3H5N3S)
−C4O2NHS
−VO2
[CrL(CH3OH)2(H2O)]·(NO3) 6H2O
[ZnL(H2O)]·H2O
82
290
491
−6H2O
−(2CH3OH + H2O + NH3)
−(C3H3N2S + NO2)
−(C4O3NHSCr)
−H2O
85
290
622
−(H2O + NH2SCN)
−(CH3CN + C4O2NHS)
−ZnO
[CdL (H2O)]·H2O
86
296
500
−H2O
−(H2O + NH2SCN)
−C6H4O2N2
−(CdO + S)
23.33 (22.61)
33.65 (33.49)
40.00(39.33)
3.07 (3.18)
6.66 (6.20)
25.42 (25.15)
9.66 (9.21)
[UO2L(H2O)]·H2O
118
180
297
555
−H2O
−(H2O + NH3)
−(CH3CN + SCN + HNCO)
−(CO + 2C)
−(UO2 + O + S)
56.00 (56.34)
Table 5
Temperatures of decomposition and the kinetic parameters of H2L ligand and its metal complexes.
Compound
H2L
Step
T (K)
A (S−1
)
ꢀE (kJ mol−1
)
ꢀH (kJ mol−1
)
ꢀS (J mol−1 K−1
)
ꢀG (kJ mol−1
)
First
Second
First
Second
Third
First
Second
Third
First
Second
Third
First
Second
Third
First
Second
Third
First
Second
Third
First
510
552
364
507
794
358
657
809
345
581
781
342
562
891
355
563
764
349
563
895
359
569
773
391
453
570
828
2.74 × 1027
4.41 × 1010
4.98 × 105
5.84 × 1013
6.99 × 106
5.94 × 105
1.99 × 108
6.63 × 107
4.79 × 105
5.38 × 106
2.11 × 108
3.82 × 107
1.09 × 1015
2.74 × 108
1.56 × 1017
7.80 × 106
5.63 × 108
9.64 × 104
2.13 × 105
1.08 × 107
1.05 × 105
6.58 × 106
8.62 × 106
1.36 × 1014
8.66 × 104
6.69 × 107
6.16 × 108
270.25
114.11
29.49
22.04
31.79
35.33
41.10
35.90
41.23
37.74
24.19
52.87
164.79
32.08
114.90
31.93
12.30
23.86
54.12
62.60
34.32
80.98
12.88
32.17
47.93
24.61
17.00
266.00
109.52
26.46
17.82
25.18
32.35
35.63
28.77
38.36
32.91
17.69
50.02
160.11
24.67
111.94
27.24
5.94
20.95
49.43
55.15
31.33
76.24
6.45
28.92
44.16
19.87
10.11
270
−54
128.3
137.12
79.24
14.82
128.4
(1)
(2)
(3)
(4)
(5)
(6)
(7)
(8)
[CuL(H2O)]·H2O
−145
5.90
−130
−144
−100
−103
−145
−130
−101
−109
29
[NiL(CH3OH)2(H2O)]·2H2O
[CoL(H2O)]·CH3OH
[VOL(H2O)]·H2O
83.87
101.31
112.04
88.32
108.05
96.57
87.27
143.81
113.77
138.21
101.09
76.99
−100
[CrL(CH3OH)2(H2O)]·(NO3)·6H2O
[ZnL(H2O)]·H2O
74
−131
−93
−159
−159
−127
−158
−128
−128
15
76.48
138.94
168.82
88.02
149.07
106.32
23.06
117.54
26.026
87.55
[CdL·(H2O)]·H2O
Second
Third
First
Second
Third
Fourth
[UO2L(H2O)]·H2O
−162
−108
−93
than reactant and/or the reaction are slow. (4) The positive values
of ꢀH means that the decomposition processes are endothermic
[50].
The linear relationship between ꢀH values of the second
stages against to the ꢁM–O vibrational frequencies of the cur-
rent complexes: ꢀH2 = 492.56 2.61 − 0.46ꢁM–O 0.05, r = 0.99,
except Ni(II) and Co(II) complexes. This finding suggests that
the breaking of it becomes difficult with the increase of
the M–O bond strength (the source of oxygen is water or
methanol).

O.M.I. Adly / Spectrochimica Acta Part A 79 (2011) 1295–1303
1301
Table 6
Molecular parameters of the ligand and its complexes.
Property
H2L thione (thiol)
Cu(II)
Ni(II)
Co(II)
Cr(III)
Zn(II)
Cd(II)
Total energy (kcal/mol)
Binding energy (kcal/mol)
Electronic energy (kcal/mol)
Heat of formation (kcal/mol)
Dipole moment (D)
HOMO (eV)
−65,784 (−65,799)
−2399 (−2414)
−382,145 (−38,002)
−22.75 (−37.44)
7.22 (5.58)
−96,184
−2388
−489,922
−199
−139,311
−5561
−115,754
−494
−90,882
−2892
−536,951
−354
−120,864
−5276
−73,232
−2542
−436,195
−75
−73,094
−2519
−421,075
−56
−11,120,262
−216
3.208
6.58
6.56
12.31
6.12
7.84
−8.88 (−9.00)
−9.43
−8.79
−4.14
−7.36
−8.98
−8.39
LUMO (eV)
−1.19 (−1.26)
−1.57
−1.01
−1.36
−0.63
−1.24
−0.97
Table 7
Calculated bond lengths (Å) of the free ligand and its complexes.
Compound
C
N
NH2
NH
N–N
C
–
Na
C–S
OH
OHsolv.
M–S
M–OL
M–N
M–Osolv.
C S
H2L
1.32
1.33
1.31
1.33
1.34
1.33
1.34
0.994
0.991
0.99
0.990
0.99
1.005
1.004
1.009
0.996
1.00
1.403
1.444
1.37
1.378
1.45
1.78 ring
1.80
1.74
1.81
1.80
1.324
–
–
–
–
–
1.64
–
–
–
–
Cu(II)
Ni(II)
Co(II)
Cr(III)
Zn(II)
Cd(II)
1.34
1.36
1.357
1.32
1.335
1.32
–
–
–
–
–
–
0.956
0.96
0.964
0.968
0.95
0.95
2.13
2.50
2.17
2.28
2.29
2.40
1.85
1.84
1.85
1.84
1.96
2.16
1.88
1.81
1.86
1.92
2.00
2.37
1.82
1.93
1.99
2.05
2.30
4.49
0.993
0.995
1.005
1.004
1.40
1.41
1.80
1.79
–
–
aBond length of HN–C.
3.1.5. Molecular orbital calculations
cal optimization of the structures of free ligand and its complexes
are given in Table 6. A comparison between the bond lengths of
the ligand and its metal complexes demonstrated in Table 7. The
theoretical data were compared with the experimental data, molec-
ular orbital calculations for vanadyl and uranyl-complexes are
failed.
The experimental results were compared with theoretical data
which were obtained from molecular mechanical calculations on
the basis of the semi-empirical PM3 level provided by HyperChem
7.5 software. The calculated heat of formation, dipole moment,
HOMO and LUMO energies as well as bond lengths after geometri-
The calculated bond lengths of M–O, M–N and M–S
coordinated bonds of the current complexes are lin-
early correlated with their measured IR frequencies:
-10
M–O
bond
lengths = 11.25 0.72 − 0.0194 V
0.0015,
М–O
R2 = 0.985
r = 0.99 except Ni(II) and Co(II)-complexes and M–S bond
lengths = 17.68 3.48 − 0.022 ꢁC–S 0.005, r = 0.99, except Ni(II)
complex. The deviation of Ni(II) complex bond lengths could be
explained as a result of presence it as an octahedral structure. The
negative slopes reveal increase of the bond strength, as indicated
from their vibrational frequencies, with the shortness of the
calculated coordinated bond lengths of M–O and M–S. This finding
supports the assignment of the IR vibrational modes of M–O and
M–S.
-11
-12
-13
-14
2.2
2.4
2.6
2.8
3
3.2
1000/T
First stage
The calculated energies of the high occupied molecular orbital
(HOMO) and low unoccupied molecular orbital (LUMO) are lin-
early correlated with the IR data of the corresponding complexes:
-11
-11.5
-12
R2 = 0.984
-12.5
-13
-13.5
-14
-14.5
1.3
1.4
1.5
1.6
1.7
1.8
1000/T
Second stage
R2 = 0.9845
-12.2
-12.3
-12.4
-12.5
-12.6
-12.7
-12.8
1.14
1.16
1.18
1.2
1.22
1.24
1.26
1000/T
Third stage
Fig. 3. Coats–Redfern plots for [NiL(CH3OH)2(H2O)]·2H2O (2), where
Y = ln[−ln(1 − ˛)/T2].
Fig. 4. Molecular modeling of [NiL(CH3OH)2(H2O)]·2H2O (2).

1302
O.M.I. Adly / Spectrochimica Acta Part A 79 (2011) 1295–1303
Fig. 5. Molecular modeling of [CoL(H2O)]·CH3OH (3).
Fig. 8. Molecular modeling of [CdL(H2O)]·H2O (7).
with the increase of ELUMO. However, the increase of EHOMO is
accompanied by weakness (elongation) of metal–ligand bonds
which leading to strengthen (shortness) of the sites adjacent to
the metal ligand centers. This interpretation agrees well with the
Gutmann’s variation rules “the bond strength increases as the
adjacent bonds becomes weaker” such as found by Linert et al.
[51].
On the other hand, the calculated dipole moment values (ꢂ)
are related along the activation parameters values obtained from
thermal gravimetric analysis (ꢀH1: hydration water) given the
following relation: ꢂ = −4.28 0.35 + 0.071 0.005 ꢀH1, r = 0.97
except Zn(II) and Cd(II) complexes. The positive slope indicates
increasing the possibility of hydration/solvation (outer sphere)
with the increase of the dipole moment of the complex, which
support the proposed structures for these complexes and their ten-
tative TGA assignments.
4. Conclusion
Fig. 6. Molecular modeling of [CrL(CH3OH)2(H2O)]·(NO3)·6H2O (5).
The condensation reaction of thiosemicarbazide with 5-
acetyl-4-hydroxy-2H-1,3-thiazine-2,6(3H)-dione afforded the cor-
responding thiosemicarbazone, H2L, ligand. Reaction of the newly
synthesized ligand with Cu(II), Ni(II), Co(II), VO(IV), Cr(III), Cd(II),
Zn(II) and UO2(VI) in the molar ratio (1:1) gave the correspond-
ing mononuclear metal complexes with the general formula
[ML(H2O)(CH3OH)x]·nH2O·(CH3OH)y(NO3)z. In the absence of X-
ray single crystal data of the current complexes and based on the
physicochemical studies and geometrical optimization discussed
above, a tentative mononuclear structure could be proposed as
shown in Figs. 4–8.
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Ni(II)
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Cr(III)
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and Cr(II) complexes). The positive slopes indicate increase of
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