A new heterocyclic Schiff base and its metal complexes

Article abstract of DOI:10.1081/SIM-120030436

Cu(II), Co(II), Ni(II), and Zn(II) metal complexes of a new SNO tridentate heterocyclic Schiff base derived from the reaction of 1-amino-5-benzoyl-4- phenyl-1H-pyrimidine-2-thione with salicylaldehyde have been synthesized and characterized on the basis of elemental analyses, electronic, IR, and ¹H NMR spectra, and also by molar conductivity measurements, magnetic moment measurements and thermogravimetric analyses (TGA). It has been found that the Schiff base behaves as a neutral tridentate SNO ligand forming chelates with 1:2 or 1:1 (metal:ligand) stoichiometry. The complexes of Co(II), Ni(II), and Zn(II) are proposed to have an octahedral structure, while the Cu(II) complex is suggested to have a square - pyramidal geometry. All of the complexes show nonelectrolytic behavior.

Full text of DOI:10.1081/SIM-120030436

SYNTHESIS AND REACTIVITY IN INORGANIC AND METAL-ORGANIC CHEMISTRY
Vol. 34, No. 3, pp. 489–502, 2004
A New Heterocyclic Schiff Base and
Its Metal Complexes
1,
Mehmet Sonmez and Memet S¸ekerci
2
*
¨
1Department of Chemistry, Faculty of Science and Arts,
Yu¨zu¨ncu¨ Yıl University, Van, Turkey
2Department of Chemistry, Faculty of Science and Arts,
˘
Fırat University, Elazıg, Turkey
ABSTRACT
Cu(II), Co(II), Ni(II), and Zn(II) metal complexes of a new SNO tri-
dentate heterocyclic Schiff base derived from the reaction of 1-amino-5-
benzoyl-4-phenyl-1H-pyrimidine-2-thione with salicylaldehyde have been
synthesized and characterized on the basis of elemental analyses, elec-
tronic, IR, and 1H NMR spectra, and also by molar conductivity measure-
ments, magnetic moment measurements and thermogravimetric analyses
(TGA). It has been found that the Schiff base behaves as a neutral triden-
tate SNO ligand forming chelates with 1 : 2 or 1 : 1 (metal: ligand) stoichio-
metry. The complexes of Co(II), Ni(II), and Zn(II) are proposed to have
an octahedral structure, while the Cu(II) complex is suggested to have
*
¨
Correspondence: Mehmet Sonmez, Department of Chemistry, Faculty of Science and
Arts, Yu¨zu¨ncu¨ Yıl University, 65080 Van, Turkey; E-mail: vansonmez@hotmail.com.
489
DOI: 10.1081/SIM-120030436
0094-5714 (Print); 1532-2440 (Online)
www.dekker.com
Copyright # 2004 by Marcel Dekker, Inc.

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Sonmez and S¸ekerci
490
a square–pyramidal geometry. All of the complexes show nonelectrolytic
behavior.
Key Words: Synthesis; Salicylaldehyde Schiff base; Binuclear
complexes; Pyrimidine-2-thione.
INTRODUCTION
In recent years, heterocyclic Schiff bases containing NS and NSO donor
atoms and their 3d metal complexes have attracted considerable attention due
to their remarkable antifungal, antibacterial, and antitumor activities.[1,2]
Schiff base ligands are also chosen for their versatility in transition metal
chemistry,[3] and the coordination chemistry of heterocyclic thiones continues
to attract attention.[4,5] Specific systems studied include imidazolidine-2-
thiones, thiazole-thiones, neutral, and protonated forms of pyrimidine-2-thione
as well as 2-thiouracil.[6] Moreover, binuclear complexes with metal ions in
close proximity show interesting magnetic, catalytic, and electron-transfer
properties.[7]
The present investigation was undertaken in view of this and of the poten-
tial biological properties of complexes synthesized with this type of ligand.
We recently reported the synthesis and characterization of heterocyclic com-
plexes obtained from N-aminopyrimidine-2-one with salicylaldehyde[8] or
2-hydroxynaphthaldehyde.[9] In this study, a new Schiff base (Fig. 1) and its
complexes have been synthesized and characterized by elemental analyses,
1
IR, UV–VIS, and thermal studies and partly by H NMR, conductivity, and
magnetic measurements.
Figure 1. The ligand LH.

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491
EXPERIMENTAL
Materials and Methods
MeOH, EtOH, BuOH, CHCl3, DMF, DMSO, toluene, diethyl ether,
n-heptane, n-hexane, and salicylaldehyde were obtained from Fluka or
.
Aldrich. The metal salts, Cu(AcO)2 H2O, Co(AcO)2 4H2O, Zn(AcO)2 2H2O,
.
.
.
and NiCl2 6H2O, were obtained from E. Merck. All solvents were dried and
purified before use. 1-Amino-5-benzoyl-4-phenyl-1H-pyrimidine-2-thione
was prepared as described previously.[10]
Elemental analyses (C, H, N, S) were performed using a Carlo Erba 1106
elemental analyzer. The IR spectra were obtained using KBr discs
(4000–400) cm21 on a Bio-Rad-Win-IR spectrophotometer. The electronic
spectra in the 200–900 nm range were obtained in DMF solution on a Unicam
UV2-100 UV/Visible spectrophotometer. Magnetic measurements were
carried out by the Gouy method using Hg[Co(SCN)4] as calibrant. The molar
conductance of the Schiff base ligand and its transition metal complexes
were determined in DMF at room temperature using a model 4070 Jenway
1
conductivity meter. The H NMR spectra of the Schiff base and its Zn com-
plex were recorded on a Varian XL-200 NMR instrument. Thermogravimetric
analyses (TGA) measurements were carried out by a Shimadzu-50 thermal
analyzer.
Preparation of the Schiff Base (LH)
The new Schiff base ligand was prepared by the condensation of 1-amino-
5-benzoyl-4-phenyl-1H-pyrimidine-2-thione (0.3070 g, 1 mmol) with salicyl-
aldehyde (0.1220 g, 1 mmol) in n-butanol (40 mL) by boiling the mixture
under reflux for 2 hr. The resulting colored solid was filtered, recrystallized
from n-BuOH, and dried in a vacuum dessicator, providing HL (0.312g,
76%) as light-yellow solid, m.p. 205 8C. 1H NMR d (ppm): 7.02–7.85
(m, phenyl protons), 10.25 (s, phenolic proton), 9.17 and 8.96 (s, azomethine
protons).
Preparation of Cu(II) Complex [Cu2(L)2(OOCCH3)2]
HL (0.41 g, 1.0 mmol) was dissolved in 30 mL of chloroform. Then a
.
solution of Cu(OOCCH3)2 H2O (0.20 g, 1.0 mmol) in 15 mL methanol was
added drop-wise into the solution over a period of 2 min. After being stirred
at 50 8C for several hours, the reaction mixture was filtered. The obtained

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Sonmez and S¸ekerci
492
brown product was washed with cold ethanol and diethyl ether and then dried
in a vacuum dessicator providing [Cu2(L)2(OOCCH3)2] (0.745 g, 70%) as
solid, m.p. 233–235 8C (dec.).
Preparation of Co(II) Complex
.
[Co2(L)2(OOCCH3)2(H2O)2] H2O
HL (0.41 g, 1.0 mmol) was dissolved in 30 mL of chloroform. Then a
.
solution of Co(OOCCH3)2 4H2O (0.25 g, 1.0 mmol) in 15 mL methanol was
added drop-wise into the solution over a period of 2 min. The mixture was
stirred further for 1.5 hr at 50 8C. The resulting brown solid was then filtered,
washed with cold ethanol, followed by diethyl ether, and dried in a vacuum
.
dessicator providing [Co2(L)2(OOCCH3)2(H2O)2] H2O (0.754 g, 68%) as a
brown solid, m.p. 213–214 8C (dec.).
Preparation of Ni(II) Complex [Ni(L)2]
HL(0.41g, 1.0mmol)wasdissolvedin30 mLofchloroform. Thenasolution
.
of NiCl2 6H2O (0.24 g, 1.0mmol) in 15 mL methanol was added drop-wise over
a period of 2 min with continuous stirring. After being stirred at 508C for several
hours, the reaction mixture was filtered. The obtained green-brown solid product
was washed with cold ethanol, followed by n-hexane and dried in a vacuum des-
sicator providing [Ni(L)2] (0.685 g, 78%) as a green-brown solid, m.p. 223 8C.
Preparation of Zn(II) Complex
.
[Zn2(L)2(OOCCH3)2(H2O)2] 2H2O
HL(0.41 g,1.0 mmol)wasdissolvedin30mLofchloroform.Thenasolution
.
of Zn(OOCCH3)2 2H2O (0.22 g, 1.0 mmol) in 15mL methanol was added drop-
wise into the solution over a period of 2 min. The mixture was stirred further for
1 hr at 508C, The formed red solid was then filtered, washed with cold methanol,
followed by n-heptane, and dried in a vacuum dessicator to give [Zn2(L)2
.
(OOCCH3)2(H2O)2] 2H2O(0.980g,86%)asaredsolid,m.p.218–220 8C(dec.).
RESULTS AND DISCUSSION
The newly synthesized Schiff base ligand and its complexes are very
stable at room temperature in the solid state. The ligand is soluble in common

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493
organic solvents. But its metal complexes are generally soluble in DMF and
DMSO. Condensation of salicylaldehyde with 1-amino-5-benzoyl-4-phenyl-
1H-pyrimidine-2-thione readily gives rise to the corresponding imine as
1
shown in Fig. 1. LH was easily identified by the IR and H NMR spectra
(see Table 2 and the Materials and Methods section). Tridentate complexes
were obtained from 1 : 1 and 1 : 2 mole ratio reactions with metal ions and
.
the ligand. The ligand (LH) on reaction with Co(OOCCH3)2 4H2O,
.
.
.
Cu(OOCCH3)2 H2O, Zn(OOCCH3)2 2H2O, and NiCl2 6H2O yields com-
.
plexes corresponding to the formulas [Co2(L)2(OOCCH3)2(H2O)2] H2O,
.
[Cu2(L)2(OOCCH3)2], [Zn2(L)2(OOCCH3)2(H2O)2] 2H2O, and [Ni(L)2].
The complexes were prepared by the general reactions shown below.
methanol=chloroform
2LH þ 2M(OAc)2nH2O þ mH2O ꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀ!
½M2ðLÞ2ðOAcÞ2xH2OꢁyH2O þ 2CH3COOH þ zH2O
M
Cu(II) Co(II) Zn(II)
n
m
x
1
4
—
2
2
2
—
—
—
1
2
y
1
2
—
z
1
LH ¼ C24H17N3O2S
methanol=chloroform
2LH þ NiCl2 ꢂ 6H2O ꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀ! ½Ni(L)2ꢁ þ 2HCl þ 6H2O
The metal-to-ligand ratio of the Co(II), Cu(II), and Zn(II) binuclear com-
plexes was found to be 1 : 1 in addition to one or two acetate ligands. The
complexes of Co(II) and Zn(II) have two additional water molecules coordi-
nated. They also have one and two additional water molecules of crystalliza-
tion. The metal-to-ligand ratio of the mononuclear Ni(II) complex was found
to be 1 : 2. The analytical data and other spectral analyses are in good
agreement with the proposed stoichiometry of the complexes. The colors,
yields, melting points, IR, and electronic absorption spectral data of all the
compounds are presented in Table 1. The molar conductances of the solutions
of the complexes in DMF (1 mM) are in the range 4.0–6.3 V21 cm2 mol21
.
These observations suggest that all the complexes are nonelectrolytes in
DMF (1 ꢃ 1023 M) at room temperature.

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Sonmez and S¸ekerci
494
m

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Schiff Base Complexes
Proton Nuclear Magnetic Resonance Spectra
495
1
Deuterated chloroform was used as solvent to determine the H NMR
spectra of the ligand and its Zn(II) complex, but not the Cu(II), Co(II), and
Ni(II) because of their paramagnetic behavior. The sharp singlet observed at
about d 10.25 ppm is assigned to the phenolic proton of the ligand. The sing-
lets at d 9.17 and 8.96 ppm are assigned to the azomethine and pyrimidine ring
(C–H) protons, respectively, in the spectrum of the ligand. In the spectrum of
the Schiff base, the phenyl multiplet was observed between d 7.02–7.85 ppm.
1
The H NMR spectrum of Zn(II) complex shows approximately the same
peaks as those observed for the free ligand with the exception that the peak
due to the (2-OH) phenolic group resonance is absent. This is considered as
additional evidence for the deprotonation of the phenolic OH group.
Infrared Spectral Study
The most important infrared spectral bands of the investigated metal com-
plexes are summarized in Table 2. The free Schiff base ligand is characterized
by strong bands at 1640, 1288, and 3415 cm21 which may be ascribed to the
stretching vibrations of C55N (imine), C–O (phenolic), and OH (intramolecu-
lar H-bonded) groups, respectively.[8–12] The band at 1630 cm21 due to the
stretching mode of the C55N group in the spectrum of the free ligand shows
a remarkable shift to lower frequency with splitting in the 1600–1610 cm21
region in all the spectra of the complexes suggesting that the coordinating azo-
methine nitrogen atoms of the Schiff base are involved in complex for-
mation.[8,9,11] In the spectra of the binuclear complexes the phenolic band at
1260–1272 cm21 is shifted to lower frequency (16–28 cm21). It is suggested
that the oxygen atom of this phenolic (C–O) group is involved in bridging to
the metal ions. On the other hand, the band around 1050 cm21 may be attri-
buted to the predominant C55S (thione) stretching of the ligand. The decrease
of 15–30 cm21 in the frequency of this band in the complexes suggests the
coordination of sulfur of the C55S (thione) moiety. A broad band in the
3340–3495 cm21 range is observed in the spectra of the Co(II) and Zn(II)
complexes. An additional band at 840 cm21 suggests that water molecules
are coordinated to metal ions.[8,9,11] This band may be assigned to water
OH stretching frequencies confirming the elemental analyses and thermal
studies results that indicate water molecules are involved in the chemical com-
position of these metal complexes. On the other hand, the IR spectra confirm that
the acetate group at 1350–1420 cm21 is coordinated,[11] but it is impossible to
distinguish between mono or bidentate coordination. Moreover, a large number
of heterocyclic ring vibrations at 1580–1200 cm21 are seen for of the complexes,

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496
l

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497
these bands are shifted to lower wave length, suggesting that the nitrogen atom of
the azomethine group is coordinated to the metal ion. Bands of M–O, M–N, and
M–S appear, respectively, at 540–510, 460–470, 405–420 cm21
.
Electronic Spectra and Magnetic Measurements
The bands in the 300–250 nm range are attributed to the p ! pꢄ transition
of the benzenoid and pyrimidine rings. In the spectra of the complexes, these
bands are slightly shifted to shorter wave length. In the spectra of the com-
plexes, the less intense and broad bands in the 445–250 nm range result from
the overlap of low-energy p ! pꢄ transitions mainly localized within the
imine chromophore and the ligand to metal charge-transfer bands (LMCT) tran-
sition from the lone pairs of the phenolate oxygen donor to the M(II) ions.
On the basis of the magnetic data, the Cu(II) complex probably has a
binuclear structure with phenolic oxygen bridges. The Cu(II) complex with
LH, a tridentate, has been found to have an acetate group in the coordination
sphere. The magnetic moment at room temperature of the Cu(II) complex is
1.16 B.M.; this is abnormally small and consistent with a dimeric structure.
The complex exhibits a weak transition at 593 nm corresponding to
2
2B1g ! B2g which suggests the presence of a five-coordinate geometry.[13]
The magnetic moment value of 4.22 B.M. obtained for the brown Co(II)
complex was in the range expected for cobalt(II) in octahedral geometry. The
electronic spectra also showed a rather weak d–d transition in the visible
region of the spectrum. The bands at 485 and 520 nm may be assigned to
4
4
4
4T1g ! T1g(P) and T1g ! A2g transitions as expected for an octahedral
cobalt(II) complex.[8,9] The electronic spectrum of the Ni(II) complex
shows two d–d transitions at 593 and 490 nm which indicate an octahedral
environment around the metal ion (Fig. 2). The observed magnetic moment
of the Ni(II) complex is 1.48 B.M. The electronic spectrum of the Zn(II) com-
plex, which is diamagnetic, has bands in the 302–280 nm range, and these
bands may be due to the n ! pꢄ and p ! pꢄ transitions of the benzene
and pyrimidine rings and the azomethine group in a complex with octahedral
geometry. These data also support the conclusion that CH3COO2 and H2O
groups are coordinated axially to Zn(II). The binuclear Zn(II) complex also
shows a weak shoulder at 393 nm.
Thermal Studies
The thermal stability of the complexes was investigated using TGA. The
TGA curves were obtained at a heating rate of 10 8C/min in N2 atmosphere

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Figure 2. Suggested structure of the Ni(II) octahedral complex.
over the temperature range of 20–850 8C (Fig. 3). In the decomposition pro-
cess of the M(II) complexes, the mass losses corresponded to H2O, OOCCH3,
Ph-CH– and the other organic moieties leaving in the first, second, third,
fourth, and fifth stages of the decomposition, respectively. The five stages
of decomposition of the M(II) complex were irreversible.
The Ni(II) and Cu(II) complexes are thermally stable up to 174 and
240 8C, respectively, whereas the Co(II) and Zn(II) complexes are thermally
Figure 3. Thermogravimetric (TG) curve for the Zn(II) complex showing weight-
loss as a function of temperature in the range of ca. 20–850 8C.

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Sonmez and S¸ekerci
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Figure 4. Suggested structure for the Cu(II), Co(II), and Zn(II) complexes.
stable up to 30, and 42 8C, respectively. In the TGA curve of the Co(II) com-
plex, a 4.90% weight loss was observed up to 163 8C. In the TGA curve of the
Zn(II) complex, a 5.82% weight loss was observed up to 156 8C. This shows
that the complexes contain 3 or 4 mole of water of crystallization and coordi-
nation per complex molecule, respectively. The IR spectra of the complexes
are characterized by the appearance of a broad band in the region 3340–
3495 cm21 due to the n(O–H) frequency of water.[7,8,10–12,14] This water con-
tent was also identified by the elemental analyses.
This decomposition processes of the Cu(II), Ni(II), Co(II), and Zn(II)
complexes was confirmed by the TGA data. As the can be seen in Table 3,
the most stable complex is the Cu(II) complex. The weight losses for
Cu(II), Ni(II), Co(II), and Zn(II) complexes were found to be approximately
the same, when expressed as the percentages calculated stoichiometrically
from their chemical formulas given in Table 1. All of the complexes undergo
complete decomposition to the corresponding metal oxides, CuO, NiO,[8,9,15–18]
Co3O4,[16–18] or ZnO[8,9,14] (Table 3).
In conclusion, we report the synthesis and spectroscopic study of the new
LH heterocyclic Schiff base ligand and its metal complexes. However, single
crystals of the complexes could not be isolated from any solutions, thus no
definitive structure can be described. But, the analytical, spectroscopic, and mag-
netic data enable us to predict the possible structures as shown in Figs. 2 and 4.
ACKNOWLEDGMENT
We thank the Research Fund of the Yu¨zu¨ncu¨ Yıl University for financial
support.

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Received March 10, 2003
Accepted November 13, 2003
Referee I: T. R. Webb
Referee II: B. N. Storhoff

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