Synthesis, characterization and thermal behavior of some Zn(II) complexes with ligands having 1,3,4-thiadiazole moieties

Article abstract of DOI:10.1002/hc.20572

Some new zinc(II) complexes of the type [Zn(L¹) ₂(C₂H₅OH)₂]·C ₂H₅OH, [Zn(L²)₂ Cl ₂]·H2O, and [Zn₂(L³)₂(H _2<

Full text of DOI:10.1002/hc.20572

Heteroatom Chemistry
Volume 21, Number 1, 2010
Synthesis, Characterization and Thermal
Behavior of Some Zn(II) Complexes with
Ligands Having 1,3,4-Thiadiazole Moieties
Nevin Turan1 and Memet S¸ ekerci2
1Chemistry Department, Faculty of Arts and Sciences, Mus¸ Alparslan University, 49100, Mus¸,
Turkey
2Chemistry Department, Faculty of Arts and Sciences, Firat University, 23119, Elazig˘, Turkey
Received 22 July 2008; revised 13 November 2009
complexes of Schiff bases containing nitrogen and
ABSTRACT: Some new zinc(II) complexes of the type
other donors [1–3]. Since the first preparation of
[Zn(L1)2(C2H5OH)2]·C2H5OH, [Zn(L2)2 Cl2]·H2O, and
thiadiazole, numerous research investigations have
[Zn2(L3)2(H2O)4Cl4], where HL1 = N-[5ꢀ-amino-2,
focused on thiadiazoles and their derivatives. It is
2ꢀ-bis(1,3,4-thiadiazole)-5-yl]-2-hydroxybenzaldehyde
known that the thiadiazole themselves and their
imine, L2 = N-(5-ethyl-1,3,4-thiadiazole-2-yl)tereph-
derivatives have been used as antibacterial, antifun-
thalaldehyde imine, and L3 = N,Nꢀ-bis[5-(4-nitro
gal, insecticidal [4,5], herbicidal, pesticidal, and an-
phenyl)-1,3,4-thiadiazole-2-yl]terephthalaldehydedii-
titumor agents [6,7]. The ligands used in this work
mine have been synthesized and characterized by IR,
(Figs. 1–3) have two different and important func-
1H NMR spectra, elemental analyses, magnetic sus-
tionalities: thiadiazole and azomethine.
ceptibility, UV–vis. and thermogravimetry-differential
The present investigation is concerned with the
thermal analysis (TGA-DTA). On the basis of elec-
preparation and characterization of Zn(II) chelates
tronic spectral studies, an octahedral environment
with the bidentate Schiff bases derived from 1,3,4-
1
around the Zn(II) ion has been suggested. H NMR
thiadiazole derivatives with salicylaldehyde and
spectra of the metal complexes of ligands were found
terephthalaldehyde.
to be in agreement with the proposed stoichiometry.
The presence of water molecules and ethanol in the
Zn(II) complexes is also indicated by the thermal
studies. 2010 Wiley Periodicals, Inc. Heteroatom Chem
EXPERIMENTAL
ꢁ
C
Reagents and Instrumentation
21:14–23, 2010; Published online in Wiley InterScience
(www.interscience.wiley.com). DOI 10.1002/hc.20572
All solvents were analytical-grade reagents, used as
purchased. The metal salt ZnCl2 and starting materi-
als for the ligand were obtained from Merck, Aldrich,
Fluka, and Alfa Aesar (Ankara, Turkey). Compounds
(HL1, L2, L3) were synthesized as described in the
literature [8–10].
Elemental analyses were carried out on a Leco
CHNS-O model 932 elemental analyzer. 1H NMR
spectra were recorded using a model Bruker GmbH
DPX-300 MHz FT spectrometer. IR spectra were
recorded on Perkin Elmer Precisely Spectrum One
spectrometer on KBr disks in the wave number
range of 4000–400 cm−1. Electronic spectral studies
INTRODUCTION
During the past two decades, considerable attention
has been paid to the chemistry of the transition metal
Correspondence to: Nevin Turan; e-mail; nevintrn@hotmail.
com.
Contract grant sponsor: Management Unit of Scientific
Research Projects of Firat University (FUBAP).
Contract grant number: 1275.
2010 Wiley Periodicals, Inc.
c
ꢀ
14

Synthesis, Characterization and Thermal Behavior of Some Zn(II) Complexes with Ligands Having 1,3,4-Thiadiazole Moieties 15
FIGURE 1 Synthesis of the ligand: N-[5ꢀ-Amino-2,2ꢀ-bis(1,3,4-thiadiazole)-5-y1]-2-hydroxybenzaldehyde imine (HL1).
were conducted on a Shimadzu model UV-1700
spectrophotometer in the wavelength 1100–200 nm.
Magnetic susceptibilities measurements were per-
formed using the standard Gouy tube technique us-
ing Hg[Co(SCN)4] as a calibrant. Thermal analyz-
ers (TGA and DTA) were carried out in nitrogen
atmosphere with a heating rate of 15◦C/min using
Shimadzu DTG-60 AH (Shimadzu DSC 60 A) ther-
mal analyzers.
Synthesis of N-(5-Ethyl-1,3,4-thiadiazole-2-
yl)terephthalaldehyde Imine(L2)
2-Amino-5-ethyl-1,3,4-thiadiazole 0.26 g (0.002 mol)
in ethanol 20 mL was added to a hot ethanol solu-
tion 15 mL of terephthalaldehyde 0.27 g (0.002 mol).
The pH was adjusted to ≈5 using glacial acetic acid
(3 mL). The resultant solution was heated in an
electro-magnetic stirring apparatus to reflux for 8 h.
After cooling, the solution of the Schiff base was
stirred for an additional 10 min and finally poured
into a beaker containing 100 mL of water. The new
mixture was stirred for 20 min, and the resulting
dark yellow solid was collected by filtration, washed
several times with water, and dried in air for 48 h.
The product was recrystallized from ethanol and
washed with cold ethanol [9].
Synthesis of 2-Amino-5-(2-amino-1,3,4-
thiadiazoleyl)-1,3,4-thiadiazole (1)
A mixture of acid (0.04 mol), thiosemicarbazide
(0.104 mol), and POCl3 (0.104 mol) was warmed at
60◦C for 1 h, than the temperature was raised to
95◦C for an additional 3 h. The mixture was then
poured into the least amount of required crushed
ice, cooled to 15◦C and the pH was adjusted to ≈5
with 10 M NaOH. The resulting solid was crystallized
from DMF-ethanol to get HL1 [8].
Synthesis of N,Nꢀ-bis[5-(4-Nitrophenyl)-1,3,4-
thiadiazole-2-yl]terephthalaldehydediimine (L3)
Terephthalaldehyde (5.42 g, 0.01 mol) in hot ethanol
(20 mL) was added to a hot DMF solution (30 mL)
of 5-nitrophenyl-1,3,4-thiadiazole-2-amine (4.44 g,
0.02 mol). Then 2–3 drops of conc. H2SO4 were
added, and the mixture was refluxed for 3 h. The pre-
cipitated ligand was filtered off, recrystallized from
ethanol, and dried in air at room temperature [10].
Some properties of the synthesized ligands are given
in Table 1.
Synthesis of N-[5ꢀ-Amino–2,2ꢀ-bis(1,3,4-
thiadiazole)-5-yl]-2-hydroxybenzaldehyde Imine
(HL1)
A
solution
of
2-amino-5-(2-amino-1,3,4-
thiadiazoleyl)-1,3,4-thiadiazole (1) 4 g (0.02 mol) in
15 mL EtOH was added slowly and dropwise into
a solution of salicylaldehyde 2.44 g (0.02 mol). The
mixture was stirred at 60◦C for 30 min Five drops
of 3 mL glacial acetic acid (AcOH) were added to
the above-mentioned solution to keep pH ∼5. The
resultant solution was heated in an electro-magnetic
stirring apparatus to reflux for 3 h. A poor yellow
colored precipitation was filtered and washed with
EtOH, then dried in air [8].
Synthesis of Complexes
Synthesis of the [Zn(L1)2(C2 H OH)2] · C2 H OH
5
5
Complex. The ligand HL1 0.61 g (0.002 mol) was dis-
solved in 20 mL DMF in a 100-mL round-bottomed
flask. A solution of 0.41 g (0.001 mol) metal salt ZnCl2
in 10 mL of absolute ethanol was added dropwise
FIGURE 2 Synthesis of the ligand: N-(5-ethyl-1,3,4-thiadiazole-2-yl)terephthalaldehyde imine (L2).
Heteroatom Chemistry DOI 10.1002/hc

16 Turan and S¸ekerci
FIGURE 3 Synthesis of the ligand: N,Nꢀ-bis[5-(4-nitrophenyl)-1,3,4-thiadiazole-2-yl]terephthal aldehyde diimine (L3).
for 15 min with continuous stirring at room tem-
perature. The reaction mixture was then further re-
fluxed for 6 h at 100–120◦C. The resulting precipitate
was filtered off and washed with DMF and absolute
ethanol, respectively, then dried in air.
20 mL DMF in a 100-mL round-bottomed flask. A
solution of 0.14 g (0.001 mol) metal salt ZnCl2 in
10 mL of absolute ethanol was added dropwise for
15 min with continuous stirring at room temper-
ature. The reaction mixture was then further re-
fluxed for 8 h at 100–120◦C. The resulting precip-
itate was filtered off and washed with DMF and
absolute ethanol, respectively, then dried at room
temperature.
Synthesis of the [Zn(L2)2Cl2] · H O Complex.
2
1.49 g (0.006 mol) of ligand L2 was dissolved in 20 mL
absolute ethanol in a 100-mL round bottomed flask.
A solution of 0.41 g (0.003 mol) of ZnCl2 in 10 mL
absolute ethanol was added dropwise for 10 min
with continuous stirring at room temperature. The
mixture was refluxed overnight. Then the volume of
the solutions was reduced to about 10 mL and com-
plex was precipitated with chloroform–acetone (1:2)
to give a gray product. The precipitate was filtered,
washed with methanol, and then dried at room tem-
perature.
RESULTS AND DISCUSSION
This study was completed in four stages. In
the first stage, the 2-amino-5-(2-amino-1,3,4-
thiadiazoleyl)-1,3,4-thiadiazole (1) compound, as
stated in the Experimental section, was synthesized
according with to the method described in the
literature [8]. Then, N-[5ꢀ-amino–2,2ꢀ-bis(1,3,4-
thiadiazole)-5-yl]-2-hydroxybenzaldehyde
imine
Synthesis of the [Zn2(L3)2(H O)4Cl4] Complex.
(HL1) was obtained by the reaction of 2-amino-5-(2-
2
The ligand L3 0.70 g (0.001 mol) was dissolved in
amino-1,3,4-thiadiazoleyl)-1,3,4-thiadiazole (1) and
TABLE 1 Colors, Formula, Formula Weight, Yields, Melting Points, Magnetic Moments, and Elemental Analysis Results of the
Ligands HL1, L2, and L3 and Their Complexes
Elemental Analyses/(%) Calculated (Found)
Compounds
FW (g/mol)
304.00
245
Mp (oC)
330
Yield (%)
μeff(BM)a
C
H
N
S
[HL1] C11H8N6S2O
(pale yellow)
66
60
62
50
–
–
43.42
(43.31)
58.76
(58.72)
53.14
(52.98)
41.51
(40.97)
2.63
(2.44)
4.49
(4.22)
2.58
(2.53)
3.95
(3.88)
27.63
(26.49)
17.14
(17.20)
20.66
(20.48)
20.76
(20.64)
21.05
(21.02)
13.06
(13.32)
11.81
(12.09)
15.82
(15.66)
[L2] C12H11N3SO
(orange)
170
[L3] C24H14N8S2O4
(dark red)
542
325
–
[Zn(L1) (C2H5OH)2]
·C H25OH (yellow)
809.38
340
Dia
C228H32N12S O5Zn
4
[Zn(L2)2Cl2]·H2O (gray)
C24H24N6S2O3Cl2Zn
[Zn2(L3)2(H2O)4Cl4]
(brownish yellow)
644.28
834.66
230
358
52
64
Dia
Dia
44.70
(44.95)
32.49
3.73
(3.51)
2.48
13.04
(12.88)
12.63
9.93
(9.89)
7.22
(32.15)
(2.30)
(12.54)
(6.98)
C24H22N8S2O8Cl4Zn2
Heteroatom Chemistry DOI 10.1002/hc

Synthesis, Characterization and Thermal Behavior of Some Zn(II) Complexes with Ligands Having 1,3,4-Thiadiazole Moieties 17
salicylaldehyde. In the second stage, the N-(5-
ethyl-1,3,4-thiadiazole-2-yl) terephthalaldehyde
ligand ratio of 1:1 and 1:2 according to the elemental
analyses results. In addition, there are ethanol and
water molecules.
imine (L2) compound was synthesized by the
reaction of terephthalaldehyde and 2-amino-5-
ethyl-1,3,4-thiadiazole, which was provided by
Merck chemical company. In the third stage, the
N,Nꢀ-bis[5-(4-nitrophenyl)-1,3,4-thiadiazole-2-yl]
terephthalaldehydediimine (L3) compound was
synthesized by the reaction of 5-nitrophenyl-1,3,4-
thiadiazole-2-amine and terephthalaldehyde. In the
last stage, the complexes were synthesized by the
reaction of these ligands (HL1, L2, L3) with ZnCI2
metal salt.
Infrared Spectra
The IR data of the spectra of Schiff bases and their
complexes are listed in Table 2. The IR spectra of
the complexes are compared with those of the free
ligands to determine the coordination sites that may
involve chelation. There are some guide peaks in the
spectra of the ligands, which are helpful in achieving
this goal. The position and/or the intensities of these
peaks are expected to change upon chelation.
The spectra of all complexes exhibited intense
broad bands at 3615–3363 cm−1 due to ν(OH) of
lattice and coordinated water or ethanol molecules
[11]. The presence of hydrate or/and coordinated
water molecules or ethanol molecule was also con-
firmed by elemental analyses and thermogravimetric
analyses [12].
Schiff bases and their metal complexes are stable
toward air and moisture. The Schiff bases are solu-
ble in dimethylformamide, whereas the complexes
are sparingly soluble in hot dimethylformamide and
dimethylsulfoxide.
The ligands (HL1, L2, L3) and their new com-
plexes were characterized by elemental analyses
(Table 1) and the spectral data that allowed us to as-
sign the coordination mode of ligands in these com-
plexes. As seen from the data given in Table 1, the
elemental analyses data of the new complexes are
within 0.4% of the theoretical data calculated for
the proposed formulas. The complexes have a metal:
In the IR spectrum of 2-amino-5-(2-amino-1,3,4-
thiadiazoleyl)-1,3,4-thiadiazole (1) the characteris-
tic peaks are at 3340 and 3280 cm−1 νas(NH2)
and νs(NH2), 1628 cm−1ν(C N) in thiadiazole and
1514 cm−1δ (NH), respectively [8].
TABLE 2 Spectral Data of Ligands LH1, L2, and L3 and Their Complexes
Compounds
Spectral Data
Ligand LH1
IR: ν (cm−1): (OH) 3379, (NH2) 3284, (C H)arom 3119, (CH N) 1679, (C C) 1610,
(>C N N C<) 1492–1430, (C O) 1302, (N N) 1060–948, (C S C) 758–754 IR:
δ (cm−1): (NH) 1570
1H NMR (DMSO-d6) δ: 11.20 (s, 1H, Ar-OH), 9.00 (s, 1H, CH N), 6.50–8.50 (m, 4H,
Ar-CH), 8.40 ( 2H, NH2)
[Zn(L1)2(C2H5OH)2]·C2H5OH
IR, ν (cm−1): (OH) 3615–3406, (NH2) 3270, (C H)arom 3127, (CH N) 1664, (C C) 1601,
(>C N N C<) 1489–1432, (C-O) 1286, (N N) 1063–949, (C S C) 760-758, (M O)
567, (M N) 465; IR, δ (cm−1): (NH) 1572
1H NMR (DMSO-d6), δ: 9.20 (s, 1H, CH N), 6.60–8.58 (m, 4H, Ar-CH), 8.42 ( 2H, NH2),
1.12 (3H, CH3), 3.45 (2H, CH2)
Ligand L2
IR: ν (cm−1): (C H)arom 3090–3082, (C H)alift 2865–2806, (C O) 1692, (CH N) 1629,
(>C N N C<) 1498–1444, (N N) 1045–980, (C S C) 772
1H NMR (DMSO-d6), δ: 10.10 (s, 1H, –COH), 9.10 (s, 1H, CH N), 8.20–6.80 (m, 4H,
Ar-CH ), 3.40 (2H, CH2), 1.20 (3H, CH3)
[Zn(L2)2Cl2]·H2O
IR, ν (cm–1): (OH) 3505–3363, (C H)arom 3070, (C H)
2860–2800, (C O) 1690,
(CH N) 1610, (>C N N C<) 1496–1430, (N N) 1a0li1ft3–1004, (C S C) 770 ν(M N):
522
1H NMR (DMSO-d ), δ: δ = 10.80 (s, 1H, COH), 9.15 (s, 1H, CH N), 8.10–6.90 (m, 4H,
H
6
Ar-CH), 3.30 (2H, CH2), 1.36 (3H, CH3)
Ligand L3
IR: ν (cm–1): (C H)arom3154–3006, (C H)alift 2945–2791, (CH N) 1676–1624,
(>C N N C<) 1568–1482, (NO2) 1349, (C S C) 752–687
1H NMR (DMSO-d6), δ: 9.20 (s, 2H, CH N), 8.50–7.70 (m, 12H, Ar-CH)
IR: ν (cm–1): (OH) 3500–3384, (C H)arom 3116–3026, (C H)alift 2923–2750, ν(CH N)
1660-1612, (>C N N C<) 1565–1483, (NO2) 1347, (C S C) 740–673, (M N) 460
1H NMR (DMSO-ds6), δ: 9.30 (s, 2H, CH N), 8.55–7.78 (m, 12H, Ar-CH)
[Zn2(L3)2(H2O)4Cl4]
Heteroatom Chemistry DOI 10.1002/hc

18 Turan and S¸ekerci
In the IR spectra of the ligand HL1, the most
characteristic bands are at 3379 cm−1ν(OH) and
1679 cm−1 azomethine ν(HC N) and 3284 cm−1
ν(NH2). The absence of ν(C O), and ν(NH2) peaks
in the spectra of ligand indicates that the ex-
pected imino compound was formed by condensa-
tion from 2-amino-5-(2-amino-1,3,4-thiadiazoleyl)-
1,3,4-thiadiazole (1) and salicylaldehyde, and it is
also shown that there are no residual starting mate-
rials left in the ligand compound as well [12,13].
The IR spectrum of the 2-amino-5-(2-amino-
1,3,4-thiadiazoleyl)-1,3,4-thiadiazole (1) exhibits a
NH2 peak at 3280 cm−1. The position of this band re-
mains almost unaffected, showing only minor shifts
to lower frequency in the spectra of metal complex
indicating thereby the noninvolvement of the NH2
group in the coordination [14].
ing materials) and the appearance of a strong new
band at 1629 cm−1 assigned to azomethine ν(C N)
vibration [18].
The spectra of the free ligand L2 display band at
1692 cm−1 due to ν(C O). The position of ν(C O) is
found to be dependent on the electronic nature of the
p-substituents [19]. The ν(C O) stretching vibration
that is useful for diagnosis of coordination located
at 1692 cm−1 for ligand remains at the same position
as in L2, indicating that the ν(C O) group does not
coordinate with the metal atoms [20].
The infrared spectra of the ligand show bands
1629 and 1498–1444 cm−1, which may be as-
signed to be ν(C N) (the azomethine group)
and ν(>C N N C<) (ring), respectively. The first
band is shifted toward the lower frequency region
(19 cm−1) in the [Zn(L2)2Cl2]·H2O complex, indi-
cating the coordination of the azomethine nitro-
gen atom of the Schiff base. However, the second
band ν(>C N N C<) (ring) is found to split into
two: one almost located at the original position, in-
dicating noncoordinated at the ν(C N), and other
shifted to lower frequency 1430 cm−1, arising due
to the coordinated ν(C N) mode. The splitting of
the ν(>C N N C<) (ring) absorption band sug-
gests that only one of the ring nitrogen is involved in
coordination and other is free and noncoordinated.
This is further supported by a new band at 522 cm−1
assignable to ν(M N) in the complex. The ν(C S C)
band in the ligand occurs at 772 cm−1, which remains
unaltered in the spectra of the complex, indicating
the noncoordination of sulfur atom of the thiadia-
zole ring [21].
The IR spectra of the [Zn(L1)2(C2H5OH)2]·
C2H5OH complex indicated the disappearance of the
OH band from the spectra of complex displacement
of phenolic proton by a metal ion. The IR spectrum
for intensity of the OH band indicates partial re-
moval of proton from the OH group [13].
In the Schiff base ligand HL1, the strong band
observed 1679 cm−1can be assigned to the ν(C N)
azomethine stretching vibration. On complexation,
this band was shifted (1664 cm−1) to lower frequency
of the azomethine nitrogen atom to the central metal
ion [15].
The ν(C O) phenolic band in the [Zn(L1)2(C2H5
OH)2]·C2H5OH complex was shifted to lower fre-
quency in the 1286 cm−1range, indicating the coor-
dination of the phenolic oxygen atom with the metal
ion [16].
In the IR spectrum of the ligand L3,
In the complexes, weak bands in the 465− and
567 cm−1 range can be attributed to ν(M N) and
ν(M O), respectively. From the IR results, it may be
concluded that the Schiff base ligand HL1 is biden-
tate and coordinates with the metal ion through
the phenolic oxygen and azomethine nitrogen
atoms [17].
most
characteristic
bands
are
at
1568–
1482 cm−1 ν(>C N N C<) in thiadiazole, 1676–
1624 cm−1 ν(C N), 1349 cm−1ν(NO2), and 752–
687 cm−1 ν(C S C). The Absence of ν(C O), and
ν(NH2) peaks in the spectra of the ligand indicates
that the expected imino compound was formed by
condensation from 5-nitrophenyl-1,3,4-thiadiazole-
2-amine and terephthalaldehyde. And it is also
shown that no residual starting materials were left
in the ligand compound as well [22].
Other characteristic IR bands observed in
the spectra of the Schiff bases at 1492–1430,
1060–948, and 758–754 cm−1 are assigned to the
ν(>C N N C<), ν(N N), and ν(C S C) modes of
vibrations, respectively, of the thiadiazole ring. In
the spectra of the complex, the ν(>C N N C<),
ν(N N), and ν(C S C) vibrations remain almost
unchanged, indicating, thereby, noninvolvement of
the ring nitrogen and sulfur in the coordination
[13].
The azomethine ν(C N) bands in the spectra of
ligand L3 lying at 1676–1624 cm−1 displayed a shift
to lower wave numbers (1660–1612) in the spectra
of [Zn2(L3)2(H2O)4Cl4] complex, indicating that the
C N nitrogen atom coordinates to the metal ion in
this complex [18].
The band due to ν(NO2) in the spectra of ligand
was observed at the same positions in the spectra
of the complexes, showing that the NO2 group in
these complexes did not participate in the complex
formation [19].
The IR spectra of the Schiff base (L2) re-
ported here showed the absence of bands at ≈1700,
3287, and 3108 cm−1 due to carbonyl ν(C O) and
ν(NH2) stretching vibrations (present in the start-
Heteroatom Chemistry DOI 10.1002/hc

Synthesis, Characterization and Thermal Behavior of Some Zn(II) Complexes with Ligands Having 1,3,4-Thiadiazole Moieties 19
FIGURE 4 Suggested structure of the octahedral Zn(II) complex of the ligand HL1.
In the spectra of the [Zn2(L3)2(H2O)4Cl4] com-
plex, the ν(>C N N C<) vibrations remain almost
unchanged indicating, thereby, noninvolvement of
the ring nitrogen in-coordination. The ν(C S C) un-
dergoes a negative shift in the complex, indicating
the coordination of ring sulfur to copper [4]. The
coordination through the azomethine nitrogen and
sulfur is further supported by the occurrence of new
bands at 460 and 360 cm−1 in the spectra of the
complex, which may be assigned to ν(M → N) and
ν(S → M) vibration, respectively [23,24]. However,
the IR spectrum of the complex (M S) bands could
not be observed, that we have studied in 4000–
400 cm−1 range.
The IR bands of ν(H2O) of coordinated water
appeared at 820–840 cm−1, indicating the binding of
water molecules to the metal ions [25].
The coordinated halogen in the complexes
shows a far IR absorption peak in the range 294–
230 cm−1, which may be attributed to ν(M Cl)
[15,26]. However, the IR spectrum of the complexes
(M CI) bands could not be observed, which we have
studied in 4000–400 cm−1 range.
In the Zn(II) complexes of the HL1, L2, and L3
ligands, the chloride ions are coordinate with the
metal ions (see Figs. 5 and 6). In the CI− test with
AgNO3, precipitation of white AgCI salt does not im-
mediately become evident.
1H NMR Spectrum
1
The H NMR spectrum of Schiff bases as well as
their Zn(II) complexes was recorded in dimethylsul-
foxide (DMSO-d6) solution using tetramethylsilane
(TMS) as an internal standard. The 1H NMR spectra
of the Schiff bases (HL1, L2, L3), their diamagnetic
Zn(II) complexes, and the chemical shifts of the dif-
ferent types of protons are listed in Table 2. The
Schiff base exhibited signals due to all expected pro-
tons in their expected regions. These were compared
FIGURE 5 Suggested structure of the octahedral Zn(II) complex of the ligand L2.
Heteroatom Chemistry DOI 10.1002/hc

20 Turan and S¸ekerci
FIGURE 6 Suggested structure of the octahedral Zn(II) complex of the ligand L3.
with the reported signals of known structurally re-
lated compounds and give further support for the
composition of Schiff bases as well as their com-
plexes suggested by their IR and elemental analyses
data. A comparison of the chemical shifts of the un-
complexed Schiff bases shows that the resonances
are shifted upon complexation. Upon examination,
it was found that the phenolic-OH signal, appeared
in the spectrum of ligand HL1 at 11.20 ppm, is com-
pletely disappeared in the spectra of its Zn(II) com-
plex, indicating that the OH proton was removed
by the chelation with the Zn(II) ion. In the spectra of
Schiff bases, protons of the azomethine group down-
field shifted in the Zn(II) complexes, indicating par-
ticipation of this group in coordination of the metals
ions. The signals observed at 3.45 and 3.70 ppm with
an integration corresponding to protons in the case
of [Zn(L2)2Cl2]·H2O and [Zn2(L3)2(H2O)4Cl4] com-
plexes, respectively, are assigned to water molecules.
The band appearing in the range of 218–318 nm
is attributed to π → π∗transition of the benzene ring
of the ligand HL1. This band is redshifted to 265–
328 nm. The other bands observed in the region 318–
387 nm in the free ligand are reasonably accounted
for π → π∗and n → π∗ transitions for the phenolic-
OH and azomethine moieties, respectively [8]. In the
[Zn(L1)2(C2H5OH)2]·C2H5OH complex, these bands
are shifted to longer wavelength as a result of the
coordination to the metal, confirming the formation
of the Schiff base metal complex.
The diamagnetic [Zn(L1)2(C2H5OH)2]·C2H5OH
complex of the HL1 ligand did not show any d–d
bands, and their spectra are only dominated by
charge transfer bands. The charge transfer band at
2
2
377–460 nm was assigned to Eg → T2gtransitions,
possibly in an octahedral environment.
In the spectrum of the ligand L2, the bands 350–
390 nm range are assigned to the n → π∗ transitions
of the azomethine group and thiadiazole ring. Dur-
ing the formation of the complex, these bands are
shifted to lower wavelength, suggesting that the ni-
trogen atoms of the azomethine group and thiadia-
zole ring are coordinated to the metal ion. The values
in the 300–350 nm range are attributed to the π →
π∗ transition of the aromatic and thiadiazole ring. In
the spectra of the complex, these bands are shifted
slightly to lower wavelength [9,27].
Magnetic Susceptibility and Electronic Spectra
Measurements
The UV–vis spectra of the ligands and their com-
plexes were recorded in the DMF solution in the
wavelength range from 200 to 800 nm. The cor-
responding electronic transitions are presented in
Table 3.
TABLE 3 Electronic Spectral Data of the Ligands HL1, L2, and L3 and Their Complexes (nm) (in DMF)
Compounds
Wavelength (nm) (ε)
[HL1]
218–318, 387 (1125, 160) π → π∗, n→ π∗
[L2]
304–354a, 390 (1400a, 150) π → π∗, n → π∗
304, 370 (30100, 22300) π → π∗, n→ π∗
265 (1100) π → π∗
[L3]
[Zn(L1)2(C2H5OH)2]·C2H5OH
[Zn(L2)2Cl2]·H2O
[Zn2(L3)2(H2O)4Cl4]
377, 460 (7300–330) L → M 2Eg → T2g
2
301–313 (1600–1200) π → π∗, n → π∗
360 (6900) L → M
265, 330 (31100,16100) π → π∗, n → π∗
345–350 (12500) L → M
ε = Molar extinction coefficient (L mol−1 cm−1).
amaximum wavelength in 340 nm.
Heteroatom Chemistry DOI 10.1002/hc

Synthesis, Characterization and Thermal Behavior of Some Zn(II) Complexes with Ligands Having 1,3,4-Thiadiazole Moieties 21
350.35◦C is assigned to the elimination of 2C2H5OH
The electronic spectrum of the [Zn(L2)2Cl2]·H2O
groups from the ligand accompanied by weight loss
(% experimental weight 11.37; calculated weight
11.11) [31]. The third step (350.35–458.16◦C) can
be ascribed to the removal of the remaining C4N4S2
group by weight loss of (% experimental weight
24.71; calculated weight 23.70).
complex shows an absorption band at 360 nm, at-
tributed to the L → M transition, which is com-
patible with this complex having an octahedral
structure [28].
The spectrum of the ligand L3 shows an intense
band at 304 nm, which is attributed to π → π∗ tran-
sition within the benzene ring and a double bond of
the azomethine group. The band around 370 nm is
due to the n → π∗ transition of the nonbonding elec-
trons present in the nitrogen of the thiadiazole group
in the Schiff base. In the complex, this band under-
goes a hypsochromic shift due to coordination of
the Schiff base ligand to metal ion [10,29]. The elec-
tronic spectra of the [Zn2(L3)2(H2O)4Cl4] complex
exhibited only high-intensity band at 345–350 nm,
which is assigned to a ligand metal charge transfer.
The [Zn2(L3)2(H2O)4Cl4] complex is diamagnetic and
has an octahedral geometry.
The ligand L2 is stable up to 115.26, but then it
decomposes in three steps 115.26–200.46◦, 200.46–
300.24,◦ and 300.24–620.88◦C. In the decomposition
of the ligand, the weight losses correspond to the re-
moval of the –CH2CH3, –CHO, and thiadiazole group
at the first, second, and third stages of decomposi-
tion, respectively. The DTA curve of the ligand ex-
hibits three endothermic peaks at 104.35, 190.30,
and 217.25◦C, and one exothermic peak at 313.58◦C.
The three stages of the ligand decomposition are ir-
reversible [9,10].
The [Zn(L2)2Cl2]·H2O complex was stable up to
87.0◦C, and its decomposition started at this tem-
perature. The first step in the temperature range
87.35–121.42◦C was accounted for the loss of wa-
ter molecules of hydration (% experimental weight
2.79; calculated weight 2.96). The second step of de-
composition within the temperature range 121.42–
200.28◦C corresponds to the loss of 2Cl, 2CH2CH3,
and C8H5O groups (% experimental weight 56.63;
calculated weight 57.03). In the DTA curve, a
sharp endothermic peak observed in the range
120.34◦C for the complex of Zn(II), in conjunction
with the mass loss in the TGA curve correspond-
ing to water molecule, confirms the stoichiometry
[Zn(L2)2Cl2]·H2O of the Zn(II) complex [32,33].
The ligand L3 is stable up to 150.34◦C but then it
decomposes in two steps corresponding to the tem-
perature range 150.34–495.12◦ and 495.12–800.46◦C.
In the decomposition of the ligand, the weight losses
correspond to the removal of the 2C6H4NO2and the
other parts of the ligand at the first and second stages
of decomposition, respectively. The TGA curve of the
ligand exhibits three exothermic peaks at 217.43,
495.56, 626.24◦C. The two stages of the ligand de-
composition are irreversible [10,34].
Thermal Studies
The thermal stability of the ligands and their com-
plexes was investigated by a combination of TGA and
DTA. The TGA and DTA curves were obtained at a
heating rate of 15◦C/min in a nitrogen atmosphere
over the temperature range of 25–800◦C. The ther-
mal data are summarized in Table 4. The results are
in good agreement with the theoretical formula sug-
gested by the elemental analyses. The weight losses
for ligand and complexes were calculated within the
corresponding temperature ranges.
The ligand HL1 is stable up to 50.37◦C, and its
decomposition started at this temperature. The lig-
and shows five-step weight loss. The loss of the OH
and NH2 groups and simultaneously in the first and
second steps between 50.37 and 333.56◦C with one
endothermic DTA peak at 83.35◦C and violently one
exothermic peak at DTA 219.48◦C. The 30 step in the
333.56–470.18◦C range corresponds to the exother-
mic elimination of the second thiadiazole rings. The
experimental mass loss of 55.55% agrees well with
the calculated mass loss of 55.56%. The 40 step in the
470.18–645.25◦C range corresponds to the exother-
mic elimination of the benzene ring. The experimen-
tal mass loss of 25.18% agrees well with the cal-
culated mass loss of 25.33%. The final step in the
645.25◦C step shows elimination of one of the CH N
group. The experimental mass loss of 7.41% agrees
well with the calculated mass loss of 8.88% [8,30].
The decomposition curve of Zn(L1)2(C2H5OH)2]·
C2H5OH begins by a step at 75.12–175.46◦C, display-
ing (% experimental weight 5.68; calculated weight
5.19) weight loss corresponding to the removal
of C2H5OH. The second stage ending at 175.46–
The [Zn2(L3)2(H2O)4Cl4] complex was stable up
to 110.00◦C, and its decomposition started at this
temperature. The first step in the temperature range
110.00–285.25◦C was accounted for the loss of co-
ordinated water molecules (% experimental weight
8.12; calculated weight 8.15). In the DTA curve, a
sharp endothermic peak observed in range 160.8◦C
for the complex of Zn(II), in conjunction with
the mass loss in the TGA curve corresponding to
four water molecules, confirms the stoichiometry
[Zn2(L3)2(H2O)4Cl4] of the Zn(II) complex. The sec-
ond step of decomposition within the temperature
Heteroatom Chemistry DOI 10.1002/hc

22 Turan and S¸ekerci
TABLE 4 Proposed Decomposition Steps and the Respective Mass Losses of Ligands HL1, L2, and L3 and their Complexes
Percent Loss in
Weight Percent
Found (Percent
Calculated),
Temperature
(◦C)
Decomposition
Products
Equation
C11H8N6S2O [HL1]
50.37–333.56
333.56–470.18
10.85 (11.11)
55.56 (55.55)
OH vs. NH2
N
N
N N
S
S
C11H5N5S2
C7H5N
CHN
470.18–645.25
645.25
25.50–115.26
115.26–200.46
200.46–300.24
300.24–620.88
620.88
25.33 (25.18)
8.88 (7.41)
–
11.84 (11.85)
11.84 (11.85)
34.29 (34.81)
N CH
C12H11N3SO [L2]
C12H11N3SO
C10H6N3SO
C H5N S
Thermal stability
CH2CH3
CHO
C2N2S
C97H5N3
C24H14N8S2O4[L3]
25.00–150.34
–
Thermal stability
NO2
2
C24H14N8S2O4
150.34–495.12
45.01(44.44)
N
N
and
CH
N
CH
2
S
C12H6N6S2
495.12–810.46
75.12–175.46
175.46–350.35
54.98(54.07)
5.68(5.19)
11.37(11.11)
[Zn(L1)2(C2H5OH)2] ·C2H5OH C28H32N12S4O5Zn
C2H5OH
2C2H5OH
C26H26N12S4O4Zn
N
N
H2N
2
S
C22H12N12S4O2Zn
350.35–458.16
458.16-
87.35–121.42
121.42–200.28
24.71(23.70)
C18H8N6S2O2Zn
[Zn(L2)2Cl2]·H2O C24H24Cl2ZnN6S2O3
2.79 (2.96)
56.63 (57.03)
Two hydrated water
C24H20Cl2ZnN6S2O
2CH2CH3,2Cl and
O
CH
CH
2
C16H4ZnN6S2
200.28
[Zn2(L3)2(H2O)4Cl4] C24H22N8S2O8Cl4Zn2
25.00–110.00
110.00–285.25
285.25–420.40
Thermal stability
Four coordinated water
4Cl
C24H22N8S2O8Cl4Zn2
24H14N8S2O4Cl4Zn2
8.15(8.12)
15.99(15.15)
C
NO2
2
C
24H14N8S2O4Zn2
420.40–480.65
480.65
29.62(29.13)
C12H8N6S2Zn2
range 285.25–420.40◦C corresponds to the loss of
Cl ligands (% experimental weight 15.15; calculated
weight 15.99). In the Zn(II) complex, the endother-
mic peak at 360.4◦C is related to the decomposition
of Cl ligands [35,36]. The 30 step in the 420.40–
480.65◦C range corresponds to the exothermic elim-
ination of the 2C12H8N2O4 (% experimental weight
29.13; calculated weight 29.62).
The final products during thermal analysis of
the ligand and its complexes were not identified
because ligand and its complexes could not com-
pletely decomposed until 800◦C temperature. The
continuation of the decomposition indicates that a
higher thermal stability of the complexes. Such sta-
bility may refer to the presence of one or/two five-
membered rings [31].
could be described. However, the analytical, spectro-
scopic, and magnetic data enable us to propose the
possible structure.
REFERENCES
˙
˙
[1] Refat, M. S.; El-Deen, I. M.; Ibrahim, H. K.; El-Ghool,
S. Spectrochim Acta A 2006, 65, 1208–1220.
[2] So¨nmez, M.; Levent, A.; S¸ ekerci, M. Russ J Coord
Chem 2004, 30 (9), 655–659.
[3] Tuncel, M.; Serin, S. Synth React Inorg Met Org Nano
Met Chem 2005, 35, 203.
[4] Nath, M.; Goyal, S.; Eng, G.; Whalen, D. Bull Chem
Soc Jpn 1996, 69, 605–612.
[5] Foroumadi, A.; Kargar, Z.; Sakhteman, A.; Shar-
ifzadeh, Z.; Feyzmohammadi, R.; Kazemi, M.;
Shafiee, A. Bioorg Med Chem Lett 2006, 16, 1164–
1167.
Single crystals of the complexes could not be iso-
lated from any solutions, thus no definite structure
Heteroatom Chemistry DOI 10.1002/hc

Synthesis, Characterization and Thermal Behavior of Some Zn(II) Complexes with Ligands Having 1,3,4-Thiadiazole Moieties 23
˙
[6] Spalinska, K.; Foks, H.; Kedzia, A.; Wierzbowska,
M.; Kwapisz, E.; Gebska, A.; Zilkolwska-Klinkosz, M.
Phosphorus, Sulfur Silicon 2006, 181, 609–625.
[7] Go¨rgu¨lu¨, O.; C¸ ukurovali, A. Synth React Inorg Met-
Org Chem 2002, 32(6), 1033–1042.
[8] Turan, N.; S¸ ekerci, M. Spectrosc Lett 2009, 42, 258–
267.
[22] Ilhan, S.; Temel, H.; Yilmaz, I.; S¸ ekerci, M. J
Organomet Chem 2007, 692, 3855–3865.
[23] Philip, V.; Suni, V.; Kurup, M. R. P.; Nethaji, M. Poly-
hedron 2006, 25, 1931–1938.
[24] Masoud, M. S.; Soayed, A. A.; Ali, A. E.; Sharsherh,
O. K. J Coord Chem 2003, 56(8), 725–742.
[25] Sharaby, C. M. Spectrochim Acta A 2007, 66, 1271–
1278.
[26] Chohan, H. Z.; Pervez, H.; Rauf, A.; Scozzafava, A.;
Supuran, C. T. J Enz Inhib Med Chem 2002, 17(2),
117–122.
[27] Turan, N.; C¸ olak, N.; S¸ ekerci, M. Int J Nat Eng Sci
2008, 2(3), 28–32.
[9] Turan, N.; S¸ ekerci, M. Synth React Inorg Met-Org
Chem 2009, 39(10), 637–651.
[10] Turan, N. Ph.D. Thesis, Firat University, Institute of
Sciences, Elazig˘, Turkey, 2008.
¨
¨
[11] Oztu¨rk, O. F.; Cansız, A.; KoparıR, M. Transit Met
Chem 2007, 32, 224–227.
˙
[12] Abu-El-Wafa, S. M.; El-Wakiel, N. A.; Issa, R. M.;
Mansour, R. A. J Coord Chem 2005, 58(8), 683–
694.
[13] El-Haty, M. T.; Adam, F. A. Bull Soc Chim France
1986, 5, 729–732.
[14] Rastogi, R. B.; Yadav, M.; Singh, K. Synth React Inorg
Met-Org Chem 2001, 31(6), 1011–1022.
[28] Temel, H.; Ilhan, S. and S¸ ekerci, M. Synth React In-
org Met-Org Chem 2002, 32, No. 9, 1625–1634.
[29] Ko¨ksal, H.; Tu¨mer, M.; Serin, S. Synth React Inorg
Met-Org Chem 1996, 26(9), 1577–1588.
[30] (a) Donia, A. M.; Gouda, M. M.; Ayad, M. I. Ther-
mochim Acta 1992, 194, 155–163; (b) Ayad, M. I.
Monat Chem 1993, 124, 981–986.
[15] Nath, M.; Kumar, A.; Vashistha, S. Synth React Inorg
Met-Org Chem 1998, 28(6), 893–906.
[16] Sivasankaran Nair, M.; Selwin Joseyphus, R. Spec-
trochim Acta 2008, 70, 749–753.
[17] Mohamed, G. G.; Sharaby, M. C. Spectrochim Acta A
2007, 66, 949–958.
[18] Saydam, S. Synth React Inorg Met-Org Chem 2002,
32(3), 437–447.
[19] Al-Awadi, N.; Shuaib, N. M.; El-Dissouky, A. Spec-
trochim Acta A 2006, 65, 36–43.
[20] Balaban, A.; S¸ ekerci, M. and Erk, B. Synth Reactivity
Inorg Met-Org Chem 2003, 33(10), 1775–1786.
[21] Srivasvata, A. K.; Pandey, O. P.; Sengupta, S. K.
Bioinorg Chem Appl 2005, 3(3–4), 289–297.
[31] El-Metwally, N. M.; Gabr, I. M.; Shallaby, A. M.;
El-Asmy, A. A. J Coord Chem 2005, 58(13), 1145–
1159.
[32] S¸ ekerci, M. Russ J Inorg Chem 2000, 45, No. 10,
1525–1530.
[33] S¸ ekerci, M.; Alkan, C. Synth Reactivity Inorg, Met-
Org Chem 1999, 29(10), 1685–1697.
[34] S¸ ekerci, M. Russian J Inorg Chem 1999, 45, No. 10,
1525–1530.
[35] Cami, G. E.; Liu Gonzalaz, M.; Sanz Ruiz, F.;
Pedregosa, J. C. J Phys Chem Solids 2005, 66, 936–
945.
[36] S¸ ekerci, M.; Temel, H. Synth React Inorg Met-Org
Chem 2001, 31(5), 849–857.
Heteroatom Chemistry DOI 10.1002/hc