Ni(II), Cu(II), and Zn(II) complexes of tetradentate schiff base containing two thiadiazoles units: Structural, spectroscopic, magnetic properties, and molecular modeling studies

Article abstract of DOI:10.1002/hc.20496

Four new mononuclear metal complexes with a mononucleating Schiff base ligand containing two thiadiazoles units have been synthesized. The ligand and metal complexes were characterized by elemental analyses, IR, ¹H, and ¹³C NMR, UV-vis, ESR, electrospray ionization mass spectra, and magnetic susceptibility measurements. Electronic spectra, magnetic susceptibility measurement, and molecular modeling studies support octahedral geometry around the Ni(II), Cu(II), and Zn(II) ions. The magnetic properties were investigated, and ferromagnetic coupling is observed in Cu(II) and Ni(II) complexes. In addition, total energy and heat of formation calculated for conformers of the Schiff base ligand by the semiempirical AM1 calculations have shown that E,Z-isomer of the ligand is more stable (about 5.3 kcal/mol) than E,E- and Z,Z-isomers.

Full text of DOI:10.1002/hc.20496

Heteroatom Chemistry
Volume 19, Number 7, 2008
Ni(II), Cu(II), and Zn(II) Complexes of
Tetradentate Schiff Base Containing Two
Thiadiazoles Units: Structural, Spectroscopic,
Magnetic Properties, and Molecular Modeling
Studies
Kerim Serbest,1 Hakan Kayi,2 Mustafa Er,3 Kemal Sancak,3
3
˙
and Ismail Deg˘irmenciog˘lu
1Department of Chemistry, Rize University, 53100 Rize, Turkey
2Computer-Chemie-Centrum, Friedrich-Alexander-Universita¨t Erlangen-Nu¨ rnberg, Na¨gelsbachstr.
25, 91052 Erlangen, Germany
3Department of Chemistry, Karadeniz Technical University, 61080 Trabzon, Turkey
Received 3 December 2007; revised 12 May 2008
of the ligand is more stable (about 5.3 kcal/mol) than
ABSTRACT: Four new mononuclear metal com-
ꢀ
C
E,E- and Z,Z-isomers.
2008 Wiley Periodicals, Inc.
plexes with a mononucleating Schiff base ligand con-
taining two thiadiazoles units have been synthesized.
The ligand and metal complexes were characterized
Heteroatom Chem 19:700–712, 2008; Published online
in Wiley InterScience (www.interscience.wiley.com). DOI
10.1002/hc.20496
1
by elemental analyses, IR, H, and 13C NMR, UV–vis,
ESR, electrospray ionization mass spectra, and mag-
netic susceptibility measurements. Electronic spectra,
magnetic susceptibility measurement, and molecular
modeling studies support octahedral geometry around
the Ni(II), Cu(II), and Zn(II) ions. The magnetic prop-
erties were investigated, and ferromagnetic coupling
is observed in Cu(II) and Ni(II) complexes. In addi-
tion, total energy and heat of formation calculated for
conformers of the Schiff base ligand by the semiem-
pirical AM1 calculations have shown that E,Z-isomer
INTRODUCTION
Tetradentate Schiff bases derived from 2 equiv of
salicylaldehyde and 1 equiv of a variety of alkyl or
aryl diamines have been known for decades. Schiff
base complexes containing different central metals
such as Co, Ni, Cu, and Zn play a central role as
chelating ligands in main group and transition metal
coordination chemistry [1–4]. Transition metal com-
plexes of tetradentate Schiff base ligands have been
used as model analogues of certain metal enzymes
[5–7], in catalysis and material chemistry [8–11], in
various other fields such as illness treatment, bio-
chemical reaction, and biological regulator [12], and
have specific activities in pharmacology and physi-
ology. Furthermore, the 1,3,4-thiadiazole ring sys-
tem is known to possess several biological activities
Correspondence to: Kerim Serbest; e-mail: kerimserbest@yahoo.
com; Hakan Kayi; e-mail; kayi@chemie.uni-erlangen.de.
Contract grant sponsor: Scientific and Technical Research
Council of Turkey (TUBITAK).
Contract grant number: 106T237.
Contract grant sponsor: The Research Fund of Karadeniz Tech-
nical University.
c
ꢀ
2008 Wiley Periodicals, Inc.
700

Ni(II), Cu(II), and Zn(II) Complexes of Tetradentate Schiff Base Containing Two Thiadiazoles Units 701
SCHEME 1 Synthetic route to Schiff base ligand (3).
and its antibacterial properties have been widely de-
scribed [13–15]. Therefore, people have a great in-
terest in Schiff bases synthesis, structure, and appli-
cation of this kind of complexes.
EXPERIMENTAL
Materials
Salicylaldehyde was purchased from Merck
(Frankfurten, Germany) and was used without
further purification. 2-[2-(Cyanomethoxy)phenoxy]-
acetonitrile (1) was synthesized according to the
procedure described in [19].
Although a large number of complexes of struc-
tural types such as M(N2O2) have been synthesized
and characterized, complexes of the mononucle-
ating Schiff base ligand derived from salicylalde-
hyde containing a thiadiazole unit are rather scarce.
Through the loss of the two hydroxyl protons, these
ligands have been used to form neutral complexes
with a number of divalent metal ions [16–18].
Here we focus on the preparation, characteri-
zation, and molecular modeling calculations of a
tetradentate Schiff base ligand, 1,2-bis[2-[(5-meth-
oxy-[1,3,4]thiadiazol-2-ylimino)-methyl]-phenol]-
benzene (H2L) containing two thiadiazoles units
(Scheme 1), and its mononuclear Cu(II), Ni(II),
and Zn(II) complexes. The characterization of
the ligands and complexes by elemental analyses,
mass, NMR, UV–vis, ESR, IR spectra, and magnetic
susceptibilities was also investigated in detail.
Physical Measurements
Melting points (mp) were determined on a Bu¨chi
530 apparatus in open capillary tubes and are un-
corrected. IR spectra were recorded on a Matson
1000 model FTIR spectrophotometer as KBr pel-
1
lets. H and 13C NMR spectra were recorded on a
Varian Gemini 200 spectrometer using DMSO-d6 as
a solvent. Chemical shifts (δ) are reported in parts
per million (ppm) relative to an internal standard
of Me4Si. Electronic spectra were obtained on an
ATI Unicam UV2 model UV–vis spectrophotometer.
Room temperature (20◦C) magnetic susceptibilities
Heteroatom Chemistry DOI 10.1002/hc

702 Serbest et al.
(Sherwood Scientific MXI model Gouy magnetic bal-
ance) were recorded at Department of Chemistry, 19
Mayis University, Samsun, Turkey. Elemental anal-
yses were determined on a LECO CHNSO-932 au-
toelemental analyses apparatus. Copper and nickel
were determined by atomic absorption spectral tech-
niques using standard flames [20]. Zinc was esti-
mated in complexometric titration against EDTA
[21]. The ESR spectra were recorded on a Varian
model E 109C spectrometer in X-band with 100 kHz
modulation frequencies. The g value was determined
in comparison with a diphenylpicrylhydrazyl sam-
ple of g = 2.0036. Errors for g and A parameters
of the complexes are 0.001 and 0.05 G, respec-
tively. Electrospray ionization mass spectrometry
(ESI-MS) was performed on a VG 7070 spectrom-
eter at Department of Chemistry, Karadeniz Techni-
cal University, Trabzon, Turkey.
then a canary yellow microcrystalline solid product
precipitated. It was filtered off, washed with water,
EtOH, and Et2O to remove excess of salicylaldehyde
and dried over P2O5 in vacuo. mp 196–198◦C.
Preparation of Metal Complexes (4–7)
The complexes [CuL(H2O)2], [NiL(H2O)2], and
[ZnL]·2H2O were obtained according to the follow-
ing procedure:
A solution of NaOH (4 mmol) in 4 cm3 water was
added to a suspension of H2L (2 mmol) in 5 cm3 hot
EtOH. After stirring for 30 min at 50◦C, a solution
of metal nitrates [Cu(NO3)2 · 3H2O, Ni(NO3)2 · 6H2O,
and Zn(NO3)2 · 6H2O] was added to the solution of
sodium salt of the ligand. The mixture was then re-
fluxed for 6 h, the precipitate was filtered off, washed
with water, EtOH, and Et2O, and dried over P2O5 in
vacuo. mp of all complexes was >300◦C.
Synthesis of the Ligand
RESULTS AND DISCUSSION
5-({2-[(2-Amino-1,3,4-thiadiazole-5-yl)methoxy]-
The ligand was derived from the condensation of 2
with salicylaldehyde without using any solvent and
is abbreviated as H2L (3). Cu(II), Ni(II), and Zn(II)
complexes have been synthesized by the reaction of
the ligand mixture in EtOH with an aqueous solution
of NaOH and metal nitrates. In the proposed struc-
ture of the Schiff base (3), N2O2 units are available
for the complexation of a metal ion in a square–
planar coordination geometry. The structural for-
mula of the Schiff base ligand, as a canary yellow
solid material, and metal complexes was verified
phenoxy}methyl)2-amino-1,3,4- thiadiazoles (C12 H
12
N6 O2 S ; 2). A mixture of compound 1 (0.01 mol)
2
and thiosemicarbazide (2.73 g, 0.03 mol) in triflu-
oroacetic acid (5 cm3) at 60–70◦C was stirred for
4 h. The reaction mixture was poured into 200-cm3
ice-cold water and neutralized with aq. ammonia.
The precipitate was filtered and washed with hot
water and then dried. The resulting white product
recrystallized in DMSO–water (1:4) and isolated
with 89% yield. mp 247–248◦C.
1
by elemental analysis, H NMR, 13C NMR, IR, UV–
1,2-Bis[2-[(5-myethoxy-[1,3,4]thiadiazol-2-ylimi-
vis, and mass spectral data presented in Tables 1–3.
All the complexes and the ligand are very stable
at room temperature in air, insoluble in water and
common organic solvent such as EtOH, CHCl3, and
CH3CN. The complexes have low solubility, whereas
the ligand has high solubility in DMSO, DMF, and
pyridine. The characterization of the complexes
no)-methyl]-phenol]benzene (C26 H N6 O4 S ; 3). Sal-
20
2
icylaldehyde (35 mmol; 3.7 cm3) was added to 2
(3.36 g, 10 mmol) under nitrogen atmosphere. After
stirring for 5 h at 160◦C, the mixture was kept in
the refrigerator for 30 min. Cold diethyl ether was
then added to a reddish brown reaction mixture and
TABLE 1 Observed Frequencies and Proposed Mode of Assignments for the H2L and Its Metal Complexes
ν(C N) ν(C N)
Azomethine Thiadiazole
Compound
ν(OH)
ν(CH2)
ν(C O)
ν(NH2)
ν(M O)
ν(M N)
2
3
4
5
6
–
–
1513
1497
1496
1496
1496
2980
2917
2925
2923
2923
1124
1185
1150
1185
1157
3301, 3115
–
–
536
520
532
–
–
435
422
434
3412
3409
3400
3360
1607
1615
1622
1613
–
–
–
–
Heteroatom Chemistry DOI 10.1002/hc

Ni(II), Cu(II), and Zn(II) Complexes of Tetradentate Schiff Base Containing Two Thiadiazoles Units 703
includes elemental analysis, ESI mass, IR, UV–vis,
ESR, and magnetic susceptibilities. Elemental anal-
ysis and ESI mass spectral data show that all the
complexes have a 1:1 metal:ligand ratio and contain
two water molecules.
n)m
(
,
Spectral Characterization
M
The condensation of 2 with salicylaldehyde has been
indicated by the elimination of two equally intense,
sharp IR bands at 3301 and 3115 cm−1 correspond-
ing to ν (NH2) in free aminothiadiazole. An in-
tense band that appears at 1607 cm−1 in the con-
densed product, H2L, is assigned to ν(C N) and a
medium intensity band centered around 3412 cm−1
for ν (OH). The IR bands that are most useful for
determining the mode of thiadiazole uncoordina-
tion are shown in Table 1. The ν (C N) azome-
thine bands of the Schiff base (1607 cm−1) undergo
small shifts to higher frequencies in the spectra of
the complexes (1615–1622 cm−1), indicating coor-
dination of the azomethine [22]. All the complexes
exhibit medium intense broad bands centered at
3400–3360 cm−1 assigned to coordinated water. All
the complexes show medium intense bands at 536–
520 cm−1 and 441–422 cm−1, suggesting the presence
of the ν (M O) and ν(M N), respectively. That any
absorption bands belonging to nitrates are not seen
in the spectra of all the complexes, indicating that
neutral complexes were formed. In general, the com-
plexes exhibited very similar IR features indirectly,
evidencing that complexes of the Schiff base have
similar structures.
()%
(aClcd.)
N
onud
F
H
C
B)M
(
K
Mcoule
pre
279
The electronic absorption spectra of the com-
plexes in pyridine less than 400 nm are dominated by
the intense bands due to intraligand transition of the
Schiff base (H2L) or/and a charge-transfer transition.
The pyridine solution of Cu(II) complex (4) displays
a broad absorption at 584 nm and a weak shoulder
at 730 nm. The position of the band and their weak
intensity (ε = 80–220 M−1 cm−1) has been assigned
at
()%
iled
Y
2
2
2
2
to d–d transition Eg → B1g and Eg → A1g. This
supports the distorted octahedral Cu(II) complex,
which is usual in the d9 case [23,24]. Nickel(II) com-
plex (5) exhibits transitions at 809, 603, and 590 nm.
Three bands in the Ni(II) complex may correspond
Colr
3
3
3
3
3
to A2g(F) → T2g(F), A2g(F) → T1g (F), and A2g(F)
3
→ T1g (P) transitions, respectively. This supports
the octahedral orientation of donor centers around
the metal ion. No d–d transition is expected for d10
Zn(II) complex (6), and a square-planar structure
is very unlikely because Zn(II) ion generally forms
tetrahedral complexes because of its d10 electronic
configuration. The absorption maxima at 299 and
Cpmound
Heteroatom Chemistry DOI 10.1002/hc

704 Serbest et al.
TABLE 3 1H NMR and 13C NMR Data for 2 and 3
1H NMR Data for 2
13C NMR Data for 2
1H NMR Data for 3
13C NMR Data for 3
5.25s. (OCH2, 4H)
6.94–7.16d. (Ph, 4H)
7.30s. (NH2, 4H)
65.1(OCH2), 169.8, 154.1(Het.C)
147.3, 122.0, 115.2 (Ph)
5.428 and 5.505s. ( OCH2, 2H)
6.946–7.248m. (Ar H, 8H, and OH, 2H)
7.534–7.738m. (Ar H, 4H)
C-1,2
C-3,6
136.405
115.11
122.522
64.888
160.690
191.581
160.696
119.434
146.813
117.181
129.038
122.211
136.40
C-4,5
8.407 and 10.319s. (N CH , 2H)
C7,7ꢁ
C8,8ꢁ
C-9,9ꢁ
C-10,10ꢁ
C-11,11ꢁ
C-12,12ꢁ
C-13,13ꢁ
C-14,14ꢁ
C-15,15ꢁ
C-16,16ꢁ
s: Singlet, d: doublet, m: multiplet.
(Table 3). The careful analyses of the 1H NMR spec-
tra of the ligand show the presence of two com-
ponents. These are assigned as (E,Z)- and (E,E)-
diasteromers. In the 1H NMR (DMSO-d6, δ) spectrum
of the ligand, two singlets were observed at δ 5.428
and 5.505 ppm (–OCH2, 4H), a multiplet at δ 6.946–
7.248 ppm (Ar-H, 8H, and OH, 2H), a multiplet
at δ 7.534–7.738 ppm (Ar-H, 4H), two singlets at δ
8.407 and 10.319 ppm ( N C H, 2H) (Fig. 3). After
D2O was added, a decrease in the integrated intensity
of the multiplet at δ 6.946–7.248 ppm was observed
because of the absence of the OH proton signals.
Each of OCH2 and N C H protons having two
different chemical shifts show that the ligand is the
(E,Z)- and (E,E)-isomeric mixture (Fig. 3). This is
consistent with the results of the semiempirical AM1
calculations. The E,Z/E,E isomer ratio can also be
FIGURE 1 Proposed structure for the mononuclear Cu(II),
Ni(II), and Zn(II) complexes.
377 nm can be attributed to intraligand transitions
only [25].
1
The H NMR spectra of DMSO-d6 solution of
the ligand (3) show well-resolved signals as expected
FIGURE 2 ESR spectra of the Cu(II) complex.
Heteroatom Chemistry DOI 10.1002/hc

Ni(II), Cu(II), and Zn(II) Complexes of Tetradentate Schiff Base Containing Two Thiadiazoles Units 705
FIGURE 3 1H NMR spectra of the ligand in DMSO-d6.
easily quantified by the NMR techniques. The inten-
sities of the H signals at δ 8.407 and 10.319 have
netic moment than that of spin-only values. The
magnetic moment data of the Cu(II) complex at
room temperature correspond to one unpaired elec-
tron. Paramagnetic behavior of the Ni(II) complex
supports octahedral geometry [23].
The X-band powder ESR spectrum of the Cu(II)
complex (4) shown in Fig. 3 was recorded at room
temperature. The spin Hamiltonian parameters of
[CuL(H2O)2] (4) are listed in Table 4. The ESR spec-
tra for polycrystalline sample of [CuL(H2O)2] (4) at
300 K is characterized by an axial symmetric g ten-
sor with g|| > g⊥ > 2.03 [26–28] (Table 4 and Fig. 2.
1
allowed us to measure the ratio of E,Z/E,E isomers,
and the percentage of the isomers in DMSO-d6 is
71.26% E,Z- and 28.74% E,E-isomers. Because of
the fact that the distance between OH-based H atom
and N C-based N atom in the E-part is shorter than
˚
˚
it is in the Z-part (2.14 A in the Z-part, 4.82 A in the
E-part from the AM1 calculation), stronger hydro-
gen bond can be formed in the E-part of the ligand.
So, the proton signal of the azomethine in the E-
part shifts to the lower field. 13C NMR spectral data
are also consistent with the structure of the ligand
(Table 3).
Computational Studies
An analysis by ESI-mass data of the molecular
ion of H2L and its Cu(II), Ni(II), Zn(II), and Co(II)
complexes indicated at m/z 545.1 (87%) [M + 1]+ (a
base peak at m/z 223.9), at m/z 643.2 (15%) [M + 2]+,
at m/z 636.0 (34%) [M]+, and at m/z 644.0 (28%)
[M + 2]+, respectively. The mass spectra and frag-
mentation pattern of Cu(II) complex are shown in
Figs. 8 and 9. These mass spectral data show that
mononuclear metal complexes were formed.
Semiempirical Calculations. To obtain the most
probable molecular conformations and stabilization
of the ligand and to explain 1H NMR spectra, energy
minimization studies of the ligand were carried out,
using the molecular mechanics MM+ module and
AM1 semiempirical calculations in a HyperChem
7.01 program package on a Pentium 4 computer [29].
The semiempirical AM1 calculations have shown
ESR and Magnetic Properties
TABLE 4 X-Band ESR Spectral Data of the Cu(II) Complex
The magnetic susceptibility measurements exhibit
the paramagnetic behavior of the complexes. The
Zn(II) complex is expectedly diamagnetic (Table 2).
The magnetic moment per metal ion follows 4, 1.98
and 54.74 (Table 2). The results exhibit higher mag-
Complex
g
||
g
⊥
A
A
⊥
||
[CuL(H2O)2] (4)
2.277
2.068
25
166
A
and A values are given of G (Gauss).
||
⊥
Heteroatom Chemistry DOI 10.1002/hc

706 Serbest et al.
FIGURE 4 The lowest energy conformations by AM1 optimized geometries (a) E,E-isomer, (b) E,Z-isomer, (c) Z,Z-isomer of
the Schiff base ligand, and its Etot, ꢀHf energies (kcal/mol) and dipole moments (Debye).
that the E,Z-isomer of the Schiff base ligand is more
stable at 0.5 and 5.3 kcal/mol than E,E- and Z,Z-
isomers, respectively (Fig. 4).
worthwhile to obtain structural information. Molec-
ular modeling studies were carried out by using
hybrid density functional theory. Support of the
experimental data and findings is the main concern
of the theoretical investigation. All calculations were
performed with the Gaussian program [30] using
DFT Calculations. Because single crystals could
not be obtained for these complexes, it was thought
Heteroatom Chemistry DOI 10.1002/hc

Ni(II), Cu(II), and Zn(II) Complexes of Tetradentate Schiff Base Containing Two Thiadiazoles Units 707
FIGURE 5 Energy minimized, hexacoordinated, octahedral copper complex.
Heteroatom Chemistry DOI 10.1002/hc

708 Serbest et al.
FIGURE 6 Energy minimized, hexacoordinated, octahedral nickel complex.
Heteroatom Chemistry DOI 10.1002/hc

Ni(II), Cu(II), and Zn(II) Complexes of Tetradentate Schiff Base Containing Two Thiadiazoles Units 709
FIGURE 7 Energy minimized, hexacoordinated, octahedral zinc complex.
FIGURE 8 The mass spectra of Cu(II) complex.
Heteroatom Chemistry DOI 10.1002/hc

710 Serbest et al.
FIGURE 9 Fragments observed in the mass spectrum of the Cu(II) complex.
Heteroatom Chemistry DOI 10.1002/hc

Ni(II), Cu(II), and Zn(II) Complexes of Tetradentate Schiff Base Containing Two Thiadiazoles Units 711
TABLE 5 Total Energy of Geometry Optimized Tetra-, Penta-
of the complexes, we investigated about the lowest
energy conformations, bond lengths, and coordinate
covalent bond angles of the complexes. As it has
been shown in Table 5, Ni(II), Cu(II), and Zn(II)
complexes having hexacoordination are more sta-
ble than those having tetra- and pentacoordination,
because they have the lowest energy conformation.
Theoretically calculated geometrical parameters are
presented in Table 6. All the coordinative covalent
bond lengths and bond angles are in accordance with
the octahedral geometry (Figs. 5–7).
, and Hexacoordinated Metal Complexes
Total Energy
(in Hartrees)
Complex
Ni tetracoordinated
Ni pentacoordinated
Ni hexacoordinated
Cu tetracoordinated
Cu pentacoordinated
Cu hexacoordination
Zn tetracoordinated
Zn pentacoordinated
Zn hexacoordinated
−1820.195
−1896.623
−1973.064
−1847.026
−1923.446
−1999.903
−1716.515
−1792.954
−1869.407
CONCLUSIONS
TABLE 6 Geometrical Parameters for Hexacoordinated
Tetradentate Schiff base ligand obtained from the
condensation of 2 with salicylaldehyde. Mononu-
clear complexes of Cu(II), Ni(II), and Zn(II) have
been synthesized, and structural investigation us-
ing spectral, magnetic data, and molecular model-
ing calculations suggests the octahedral geometry
for Cu(II), Ni(II), and Zn(II) complexes. ESR spectra
of Cu(II) complex also show the distorted octahedral
geometry. The magnetic properties of the complexes
were investigated, and ferromagnetic coupling is ob-
served in Cu(II) and Ni(II) complexes.
Metal Complexesa
Theoretical
(B3LYP/LANL2DZ)
Parameter
Ni(1)–O(3)
Ni(1)–O(4)
Ni(1)–O(5)
Ni(1)–O(6)
Ni(1)–N(5)
Ni(1)–N(6)
O(5)–Ni(1)–O(6)
C(16)–O(3)–Ni(1)–O(6)
O(5)–Ni(1)–N(5)–C(10)
Cu(1)–O(3)
Cu(1)–O(4)
Cu(1)–O(5)
Cu(1)–O(6)
Cu(1)–N(5
1.889
1.870
4.062
2.580
1.967
1.970
100.7
133.4
139.2
1.966
1.952
4.224
1.994
2.341
2.078
127.3
105.3
139.4
2.017
2.027
2.121
2.118
2.395
2.358
155.5
117.9
53.2
ACKNOWLEDGMENTS
We are thankful to Dr. Bu¨nyamin Karabulut for
recording ESR spectra.
Cu(1)–N(6)
O(5)–Cu(1)–O(6)
C(16)–O(3)–Cu(1)–O(6)
O(5)–Cu(1)–N(5)–C(10)
Zn(1)–O(3)
Zn(1)–O(4)
Zn(1)–O(5)
Zn(1)–O(6)
Zn(1)–N(5)
Zn(1)–N(6)
REFERENCES
[1] Garoufis, A.; Kasselouri, S.; Mitsopoulou, C.-A.; Slet-
ten, J.; Papadimitriou, C.; Hadjiliadis, N. Polyhedron
1999, 18, 39.
[2] Garg, B. S.; Kumar, D. N. Spectrochim Acta, Part A
2003, 59, 229.
[3] Venkatachalam, G.; Ramesh, R. Spectrochim Acta,
Part A 2005, 61, 2081.
[4] Kasumov, V. T.; Ko¨ksal, F. Spectrochim Acta, Part A
2005, 61, 225.
O(5)–Zn(1)–O(6)
C(16)–O(3)–Zn(1)–O(6)
O(5)–Zn(1)–N(5)–C(10)
[5] Chattopadhyay, T.; Islam, S.; Nethaji, M.; Majee, A.;
Das, D. J Mol Catal A: Chem 2007, 267, 255.
[6] Taylor, M. K.; Stevenson, D. E.; Berlouis, L. E. A.;
Kennedy, A. R.; Reglinski, J. J Inorg Biochem 2006,
100, 250.
aThe atomic-numbering scheme is given in Figs. 5–7.
[7] Utz, D.; Heinemann, F. W.; Hampel, F.; Richens, D.
T.; Schindler S. Inorg Chem 2003, 42, 1430.
[8] Amirnasr, M.; Mahmoudkhani, A. H.; Gorji, A.; De-
hghanpour, S.; Bijanzadeh, H. R. Polyhedron 2002,
21, 2733.
[9] Abbo, H. S.; Titinchi, S. J. J.; Prasad, R.; Chand, S. J
Mol Catal A: Chem 2005, 225, 225.
[10] Venkataramanan, N. S.; Kuppuraj, G.; Rajagopal, S.
Coord Chem Rev 2005, 249, 1249.
[11] Nag, J. K.; Pal, S.; Sinha, C. Transition Met Chem
2005, 30, 523.
Becke three-parameters hybrid exchange functional
combined with Lee–Yang–Parr correlation func-
tional [31,32]. DFT geometry optimizations were
performed using LANL2DZ basis set [33].
Elemental analysis and mass spectral data show
that all the complexes have two water molecules in
the structure. To decide whether water molecules
are coordinated to the metal ions in the structures
Heteroatom Chemistry DOI 10.1002/hc

712 Serbest et al.
[12] Li, L.-Z.; Zhao, C.; Xu, T.; Ji, H.-W.; Yu, Y.-H.; Guo,
G.-Q.; Chao, H. J Inorg Biochem 2005, 99, 1076.
[13] Foroumadi, A.; Asadipour, A.; Mirzaei, M.; Karimi,
J.; Emami, S. Il Farmaco 2002, 57, 765.
[14] Mamolo, M. G.; Falagiani, V.; Zampieri, D.; Vio, L.;
Banfi, E. Il Farmaco 2001, 56, 587.
[27] Hathaway, B. J.; Billing, D. E. Coord Chem Rev 1970,
5, 1.
[28] Bhadbhade, M. M.; Srinivas, D. Inorg Chem 1993, 32,
6122.
[29] HYPERCHEM for Wimdows, Release 7.01, Hyper-
cube Inc., Gainesville, FL.
[15] Servi, S.; Genc, M.; Gu¨r, S.; Koca, M.; Eur J Med
Chem 2005, 40, 687.
[16] Akilan, P.; Thirumavalavan, M.; Kandaswamy, M.
Polyhedron 2003, 22, 3483.
[17] Azevedo, F.; Freire, C.; Castro, B. Polyhedron 2002,
21, 1695.
[30] Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria,
G. E.; Robb, M. A.; Cheeseman, J. R.; Montgomery,
J. A.; Jr., Vreven, T.; Kudin, K. N.; Burant, J. C.;
Millam, J. M.; Iyengar, S. S.; Tomasi, J.; Barone,
V.; Mennucci, B.; Cossi, M.; Scalmani, G.; Rega, N.;
Petersson, G. A.; Nakatsuji, H.; Hada, M.; Ehara,
M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida,
M.; Akajima, T.; Honda, Y.; Kitao, O.; Nakai, H.;
Klene, M.; Li, X.; Knox, J. E.; Hratchian, H. P.;
Cross, J. B.; Adamo, C.; Jaramillo, J.; Gomperts,
R.; Stratmann, R. E.; Yazyev, O.; Austin, A. J.;
Cammi, R.; Pomelli, C.; Ochterski, J. W.; Ayala,
P. Y.; Morokuma, K.; Voth, G. A.; Salvador, P.;
Dannenberg, J. J.; Zakrzewski, V. G.; Dapprich, S.;
Daniels, A. D.; Strain, M. C.; Farkas, O.; Malick,
D. K.; Rabuck, A. D.; Raghavachari, K.; Foresman,
J. B.; Ortiz, J. V.; Cui, Q.; Baboul, A. G.; Clifford, S.;
Cioslowski, J.; Stefanov, B. B.; Liu, G.; Liashenko,
A.; Piskorz, P.; Komaromi, I.; Martin, R. L.; Fox,
D. J.; Keith, T.; Al-Laham, M. A.; Peng, C. Y.;
Nanayakkara, A.; Challacombe, M.; Gill, P. M. W.;
Johnson, B.; Chen, W.; Wong, M. W.; Gonzalez, C.;
Pople, J. A.; GAUSSIAN-03, Revision C.02, Gaussian
Inc., Pittsburgh PA, 2003.
[18] Torzilli, M. A.; Colquhoun, S.; Doucet, D.; Beer, R. H.
Polyhedron 2002, 21, 697.
¨
[19] Ustaba, R.; C¸ oruh, U.; Sancak, K.; Er, M.; Unver, Y.;
Yavuz, M. Acta Crystallogr, Sect E: Struct Rep Online
2004, 60, o968.
[20] Skoog, D. A.; Holler, F. J.; Nieman, A. T. Principles
of Instrumental Analysis, 5th ed.; Harcourt Brace:
London, 1998. p. 206.
[21] Gato, V. J.; Arnold, K. A.; Viscariello, A. M.; Miller, S.
R.; Morgan, C. R.; Gokel, G. W. J Org Chem 1986, 51,
5373.
[22] Karabo¨cek, N.; Karabo¨cek, S.; Mazlum, H.;
˙
Deg˘irmenciolu, I.; Serbest, K. Turk J Chem 2004, 28,
87.
[23] Lever, A. B. P. Inorganic Electronic Spectroscopy;
Elsevier: Amsterdam, 1984: p. 19.
[24] Karabo¨cek, S.; Karabo¨cek, N. Polyhedron 1998, 17,
319.
[25] Tarafder, M. T. H.; Jin, K. T.; Crouse, K. A.; Ali, A.
M.; Yamin, B. M.; Fun, H.-K. Polyhedron 2002, 21,
2547.
[26] Kasumov, V. T.; Ko¨ksal, F. Spectrochim Acta, Part A
2005, 61, 225.
[31] Becke, A. D. J Chem Phys 1993, 98, 5646.
[32] Lee, C.; Yang, W.; Parr, R. G. Phys Rev B: Condens
Matter Mater Phys 1988, 37, 785.
[33] Wadt, W. R.; Hay, P. J. J Chem Phys 1985, 82,
284.
Heteroatom Chemistry DOI 10.1002/hc