A novel schiff base ligand and its Ni(II) complex: synthesis and characterization

Article abstract of DOI:10.1007/s00706-016-1727-5

Abstract: In this paper, synthesis of a novel Schiff base ligand based on bis(2-amino-4-pheny1-5-thiazolyl)disulfide and its corresponding Ni(II) complex was reported. This ligand was prepared through the formation of an imine bond between 2-hydroxy-1-naphthaldehyde and bis(2-amino-4-phenyl-5-thiazol)disulfide in absolute methanol as solvent. The characterizations were performed by FT-IR, ¹H NMR, ¹³C NMR, elemental analysis, and single crystal X-ray analysis. In the molecular structure, the ligand possessed anti-conformation around –S–S– bond and monomeric moieties were linked into the chains through the C–H?O and π?π interactions. The reaction of the synthesized ligand with NiCl₂ in methanol afforded the corresponding Ni(II) complex. The resulting product was further investigated by thermal gravimetric and differential thermal analysis, which confirmed the formation of desired polymeric complex. The electrochemical behavior and formation of Ni(II) complex in dimethyl sulfoxide (DMSO) solution were investigated by means of cyclic voltammetry and UV–Vis titration, respectively. Graphical abstract: [Figure not available: see fulltext.]

Full text of DOI:10.1007/s00706-016-1727-5

Monatsh Chem
DOI 10.1007/s00706-016-1727-5
ORIGINAL PAPER
A novel schiff base ligand and its Ni(II) complex: synthesis
and characterization
Jafar Attar Gharamaleki1 Houra Sadat Bolouhari1 Atousa Goodarzi1
•
•
•
Ali Javadi2 Behrouz Notash3
•
Received: 6 June 2015 / Accepted: 7 March 2016
Ó Springer-Verlag Wien 2016
Abstract In this paper, synthesis of a novel Schiff base
ligand based on bis(2-amino-4-pheny1-5-thiazolyl)disul-
fide and its corresponding Ni(II) complex was reported.
This ligand was prepared through the formation of an imine
bond between 2-hydroxy-1-naphthaldehyde and bis(2-
amino-4-phenyl-5-thiazol)disulfide in absolute methanol as
solvent. The characterizations were performed by FT-IR,
1H NMR, 13C NMR, elemental analysis, and single crystal
X-ray analysis. In the molecular structure, the ligand pos-
sessed anti-conformation around –S–S– bond and
monomeric moieties were linked into the chains through
the C–H_O and p_p interactions. The reaction of the
synthesized ligand with NiCl2 in methanol afforded the
corresponding Ni(II) complex. The resulting product was
further investigated by thermal gravimetric and differential
thermal analysis, which confirmed the formation of desired
polymeric complex. The electrochemical behavior and
formation of Ni(II) complex in dimethyl sulfoxide (DMSO)
solution were investigated by means of cyclic voltammetry
and UV–Vis titration, respectively.
Graphical abstract
Keywords Schiff base Á Thiazoline Á Disulfide bond Á
Transition metal complex Á UV/Vis spectroscopy Á
Cyclic voltammetry
Introduction
Schiff bases (known as azomethines), possessing a carbon–
nitrogen double bond (C=N) functional group, are consid-
ered as important organic compounds. These systems play
a critical role in coordination chemistry due to their ability
to encapsulate metal ions using donor atoms in their
backbones [1, 2]. So far, many biologically important
Schiff bases possessing antibacterial, antifungal, anti-HIV,
herbicidal, antitubercular, and anticancer activities have
been reported in the literature [3–8]. These materials can
easily coordinate with a wide range of transition metal
ions, yielding stable and intensely colored metal complexes
which exhibit interesting physical, chemical, biological,
and catalytic properties [9–14]. Most commonly used
Schiff bases have NO or N2O2-donor atoms. However, the
oxygen atoms can be replaced by other atoms such as
sulfur, nitrogen, or selenium atoms. To improve the
& Jafar Attar Gharamaleki
attar_jafar@yahoo.com
1
Faculty of Chemistry, Kharazmi University, Tehran, Iran
2
Department of Polymer Engineering, University of Akron,
Akron, OH 44325, USA
3
Chemistry Department, Shahid Beheshti University, G. C.,
Evin, Tehran 1983963113, Iran
123

J. A. Gharamaleki et al.
medicinal properties of Schiff bases, the incorporation of
thiazoline groups as chelating moieties in ligands is con-
sidered as effective models for executing important
biological reactions [15].
Results and discussion
The molecular structure together with the crystallographic
numbering scheme of 2 is shown in Fig. 1, with thermal
ellipsoids drawn at 50 % probability level. A summary of
crystal data, experimental details, and refinement results is
also given in Table 1. As shown, the molecule adopts anti
configuration with respect to the disulfide (–S–S–) bond.
The torsion angle of C14–S2–S2i–C14i is 63.32(19)°
[symmetry code (i): -x ? 1, y, -z ? 1/2] and supports the
anti configuration of this molecule and indicates that it is
twisted around the disulfide bond.
Thiazole is a five-membered heterocycle having two
hetero atoms (S, N) and one –C=N– bond. In recent
years, thiazole and its derivatives have been the struc-
tural motif of many natural compounds including
vitamin B1 (thiamine), penicillin, and carboxylase.
Among them, 2-aminothiazole derivatives possess an
antitumor activity through the inhibition of the kinases
[16]. They have also been employed in the preparation
of different drugs required for treatment of allergies,
hypertension, inflammation, schizophrenia, bacterial and
HIV infections [17]. From the chemistry point of view,
the structure of 2-amino-4-phenylthiazole Schiff base
derivatives has already been investigated in detail [18].
In addition, the molecular structures of two corre-
In comparison with the average S–S bond length
˚
reported for almost similar structures (2.02 0.03 A) [25–
28], the S–S bonds in this present Schiff base were
˚
somewhat elongated as 2.0969(18) A (Table 2). The
dihedral angle between the planes of phenyl and naphthyl
groups with thiazole ring is 32.95(16)° and 22.07(14)°,
respectively. The C12–S1–C14 angle is smaller with that of
2-amino-4-phenylthiazole hydrobromide monohydrate
(89.4° vs. 90.17°) [19]. The exocyclic (C11–N1 and C12–
N1) and heterocyclic (C12–N2 and C13–N2) bond dis-
sponding
compounds,
2-amino-4-phenylthiazole
hydrobromide monohydrate and 2-aminothiazole have
been reported [19, 20]. Recently, some multi-substituted
Schiff base-type ligands derived from 2-(2-aminothiazol-
4-yl)-4-methylphenol and anisaldehyde have been
developed [21]. Moreover, the complexes of Zn(II),
Co(II), and Cu(II) with these ligands were synthesized
and characterized. The prepared metal complexes were
tested in vitro to their antibacterial activities against
bacteria E. coli, S. aureus, P. aeruginosa, K. pneumo-
niae, and fungi C. albicans and S. cerevisiae [22]. In
another study, 2-amino-4-phenyl-5-phenylazothiazole
was prepared by coupling of phenyldiazonium chloride
with 2-amino-4-phenylthiazole and was screened for
antibacterial activity against Escherichia coli and Sta-
phylococcus aureus [23].
˚
tances are 1.297(5), 1.370(5), 1.314(5), and 1.383(5) A,
respectively, in which an excellent agreement is observed
between Fehlmann’s data and those of 2 [29, 30].
It was expected that the C–N bond distances would be
dissimilar as a consequence of different bond order
between these atoms. The C13–C15 bond distance in 2 is
˚
˚
1.473(5) A. Compared with the value of 1.506 A found in
2-amino-4-phenylthiazole hydrobromide monohydrate,
there is a greater double bond character of the C13–C15
bond in 2. The inter-ring distance of C13–C14 is 1.389(5)
˚
A. The internal bond angles show the characteristic
reduction from 120° which is usual in five-membered
heterocyclic molecules. The angle of 89.4(2)° at the sulfur
atom (C12–S1–C14) is common for substituted thiazole
molecules.
Although the biological and medicinal functions of
thiazole have been widely noticed, to our knowledge,
studies on substituted bi(thiazole) Schiff base systems and
their related complexes have been limited. Quite recently,
we found that a disulfide compound, bis(2-amino-4-phe-
nyl-5-thiazolyl)disulfide, could be obtained and separated
as a by-product during the previously reported reaction for
the preparation of bis(2-amino-4-phenyl-5-thiazolyl)sulfide
[24].
As shown in Table 3, the structure of 2 contains an
intermolecular hydrogen bond between the hydrogen atom
of the phenolic group and the nitrogen atom of imine
fragment. In addition, non-classic C20–H20_S2 hydrogen
˚
bond with D_A distance of 3.330(4) A is present. An
interesting feature of this compound is the formation of a
chain structure through the connection of individual
molecules to each other by C3–H3_O1ii [(ii): x - 1/2,
y ? 1/2, z] hydrogen bond in [11] direction (Fig. 2).
Furthermore, the symmetric p–p stacking interaction
Here we report the synthesis and characterization of a
novel Schiff base ligand prepared by the condensation
reaction between this disulfide compound and 2-hy-
droxy-1-naphthaldehyde.
The
structure
of
the
˚
synthesized Schiff base is then investigated by single
crystal X-ray analysis (Scheme 1). The Ni(II) complex
of this ligand is also prepared and characterized by
several analytical methods.
with centroid–centroid distance of 3.777(3) A exists
between parallel aromatic naphthyl rings of Cg1_Cg2
(Fig. 3); Cg1 and Cg2 are centroids for C5–C10 and C1–
C5,C10 rings, respectively.
123

A novel schiff base ligand and its Ni(II) complex: synthesis and characterization
Scheme 1
Fig. 1 The molecular structure together with the crystallographic numbering of 2, with thermal ellipsoids drawn at 50 % probability level
absorption range 420–700 cm-1 due to (M–N) and (M–O)
FT-IR study
vibrations [31].
In the FT-IR spectrum of 1, absorptions at 3281, 3191, and
1628 cm-1 suggested the presence of NH2, CH, and C=C
NMR study
functionalities, respectively. The intense band at
1570 cm-1 is assigned to vꢀ(C=N). Also, the bands near
3423 and 1318 cm-1 are assigned to vꢀ(O–H) and vꢀ(C–O)
1
In the H NMR spectra of 1, the signal at 7.05 ppm is
assigned to the amino groups. The protons of the pendant
stretching of the phenolic group. The downfield shift of the
vꢀ(C=N) vibration (1538 cm-1) suggests that the nitrogen
atom of imine group participates in coordination to the
Ni(II) atom. Also, the band at 1318 cm-1, which is ascri-
bed to the stretching vibration of the phenolic oxygen,
undergoes a shift toward higher frequency (1362 cm-1) in
the Ni(II) complex spectra. The complex formation is
further proved by the appearance of new bands around the
phenyl ring are also observed at 7.28–7.66 ppm. Since only
seven signals are observed in the 13C NMR spectrum of 1,
1
a symmetry element is present in this molecule. In the H
NMR spectrum of 2, the broad signal at 13.53 ppm is
assigned to the proton of the OH group. The single proton
of –CH=N has chemical shift at 8.79 ppm. In the 13C NMR
spectrum, the carbon atoms of –CH=N and C–O groups
show resonances at 162.3 and 158.8 ppm, respectively. As
123

J. A. Gharamaleki et al.
investigation, magnetization measurements on Ni(II)
complex are performed using vibrating sample magne-
tometer (VSM) at room temperature. Figure 4 shows the
hysteresis loop obtained from the magnetization M versus
field H data for Ni(II) complex. The shape of the hysteresis
loop is characteristic of superparamagnetic (weak ferro-
magnetic) behavior. From Fig. 4, the coercive field (Hc)
and the remanent magnetization (Mr) are estimated to be
only 60 Oe and 0.003 emu/g.
Table 1 Crystallographic and structure refinement data for com-
pound 2
Formula
C40H26N4O2S4
722.93
Formula weight/g mol-1
Crystal system
Space group
Monoclinic
C2/c
˚
a/A
16.136 (3)
10.567 (2)
20.949 (4)
111.32 (3)
3327.5 (13)
1.311
˚
b/A
˚
c/A
b/°
Volume/A
D/g cm-3
Thermal study
3
˚
The Ni(II) complex is thermally investigated by TGA and
DTA analysis and its thermal degradation is shown in
Fig. 5. The decomposition process of the Ni(II) complex
occurs in two steps. At the beginning, the weight loss of
8 % at 200 °C corresponds to removal of the hydrated and
coordinated solvent molecules from the complex which can
be supported with an exothermic peak in the thermogram.
The Ni(II) complex is stable up to 200 °C and its decom-
position starts after this temperature and ends at 500 °C.
The loss percentage of Schiff base ligand is found as 82 %
(calculated = 81 %). The process of removal of this frag-
ment can be explained with the sharp exothermic peaks
between 200 and 450 °C. By further heating above 500 °C,
it decomposes to stable metal oxides as final products.
F(000)
1496
Temperature/K
Crystal size/mm
h range for data collection/8
Index ranges
120 (2)
0.23 9 0.15 9 0.11
2.36–29.16
-21 B h B 22,
-14 B k B 12,
-28 B l B 28
4
Z
˚
Wavelength/A
Absorption coefficient/mm-1
0.71073
0.33
Data collected
4482
Unique data (Rint
)
2535, 0.1298
230/0
Parameters/restraints
Final R indices [I [ 2r(I)]
R indices (all data)
Goodness of fit on F2 (S)
R1 = 0.0827, wR2 = 0.1187
R1 = 0.1609, wR2 = 0.1392
1.018
UV–Vis studies
-3
˚
Largest diff. peak and hole/e A
0.43 and -0.36
The electronic absorption spectral bands of the Schiff base
and its Ni(II) complex are recorded over the range
200–600 nm in DMSO as solvent. The electronic spectrum
of the Schiff base ligand shows two absorption bands at
343 and 428 nm. The short-wave band may be attributed to
electron transitions in the aromatic rings (intraligand (IL)
n–p*), and the longer wavelength band at 428 nm is
assigned to p–p* transition in the azomethine chromo-
spheres in the Schiff base ligand [32, 33]. On
complexation, the absorption band at 428 nm undergoes a
bathochromic shift compared to the free ligand as a result
1
the nickel(II) complex exhibits extremely broad H NMR
signals, hence no analysis can be performed in this regard.
VSM study
1
As mentioned before, elementary H NMR study reveals
that this complex should be paramagnetic. For further
Table 2 Selected bond distances and angles for 2
S2–S2i
C8–O1
C12–S1
C14–S1
C14–S2
2.0969 (18)
1.336 (5)
1.748 (4)
1.731 (4)
1.733 (4)
C11–N1
1.297 (5)
1.370 (5)
1.383 (5)
1.314 (5)
1.383 (5)
1.471 (5)
119.9 (2)
100.83 (12)
63.32 (19)
C12–N1
C13–N2
C12–N2
C13–C14
C13–C15
C11–N1–C12
C13–C14–S2
C12–S1–C14
120.0 (3)
129.8 (3)
89.4 (2)
S1–C14–S2
S2i–C14–S2
C14– S2–S2i–C14i
Symmetry code (i): -x?1, y, -z?1/2
123

A novel schiff base ligand and its Ni(II) complex: synthesis and characterization
Table 3 Selected hydrogen bonding geometries for 2
˚
d(D–H)/A
˚
˚
D–H_A
d(H_A)/A
d(D_A)/A
\(D–H_ÁA)/°
O1–H1A_N1
C3–H3_O1ii
C20–H20_S2
0.86
0.95
0.95
1.76
2.53
2.79
2.538 (4)
3.386 (5)
3.330 (4)
150
149
117
Symmetry code (ii): x - 1/2, y ? 1/2, z
of coordination via the nitrogen atoms of the azomethine
groups. The Ni(II) complex displays absorption bands at
330 nm and 474 nm, respectively.
(5.0 9 10-5 mol dm-3) in one cell and then this addi-
tion continues up to 40 times. The absorbance spectrum of
the mixture is recorded after each addition. Therefore, the
numbers of obtained points are higher in this method and
the accuracy would definitely be better. Performing all
additions in one UV–Vis quartz cell compared to using ten
cells in Jobs analysis is another advantage of the method
utilized in this present study.
In a typical procedure, 2.0 cm3 of ligand solution in
methanol is placed in the spectrophotometer cell and the
absorbance of the solution is measured. Then an appro-
priate amount of the concentrated solution of NiCl2 in
methanol is added in a stepwise manner using a 10-mm3
Hamilton syringe. The absorbance spectrum of the solution
is recorded after each addition. The Ni(II) solution was
continually added until the desired metal to ligand mole
ratio was achieved. The electronic absorption spectra of the
Schiff base ligand 2 in the presence of increasing con-
centration of NiCl2 in MeOH at room temperature are
shown in Fig. 6. The resulting absorbance against [HL]/
[Ni2?] mole ratio plot is shown in the inset of Fig. 6. As
mentioned, the injection point at ligand-to-metal molar
ratio of about ten indicates the formation of polymeric
compound [34]. It seems that these compounds have dif-
ferent behavior in the solid state and in solution.
Solution studies
In this study, we also represent further support for the
polymeric character of Ni(II) complex. It is important to
note that the method used in this research has some
advantages over the Jobs analysis. In fact, a limited number
of samples (10 samples for instance) with different volume
ratios should be prepared in Jobs analysis. However, in the
UV–Vis titration desired amount of metal (5 9 10-3
mol dm-3) is added to the ligand solution
Electrochemical studies
Electrochemical experiments are performed with a lAU-
TOLAB TYPE III electrochemical workstation (ECO
CHEMIE, the Netherlands). A standard three-electrode cell
is used for the electrochemical experiments and a 2-mm-
Fig. 2 The individual molecules of 2 are connected to each other by
C3–H3_O1ii (symmetry code (ii): x - 1/2, y ? 1/2, z) hydrogen
bond in [11] direction, forming a chain structure. Hydrogen atoms not
involved in hydrogen bonding are omitted for clarity
˚
Fig. 3 p–p stacking interaction with face-to-face distance of 3.776(3) A between parallel aromatic naphthyl rings
123

J. A. Gharamaleki et al.
Fig. 4 Magnetization versus
applied magnetic field at room
temperature and hysteresis loop
of Ni(II) complex
Fig. 5 The TGA and DTA analysis and decomposition process of the Ni(II)
diameter GC is utilized as the working electrode. A silver/
silver chloride (Ag/AgCl) electrode and a platinum elec-
trode are also used as the reference and the counter
electrodes, respectively.
The measurements are carried out in a dimethyl sulf-
oxide and 0.1 mol dm-3 tetrabutylammonium perchlorate
as a supporting electrolyte at room temperature. Figure 7
represents the cyclic voltammetry curve of the synthesized
123

A novel schiff base ligand and its Ni(II) complex: synthesis and characterization
Fig. 6 a Electronic absorption
spectra of the ligand 2 in MeOH
in the presence of increasing
concentration of NiCl2 at room
temperature. b Corresponding
mole ratio plot of HL/NiII
Schiff base (curve T1). As shown, a pair of redox peak
attributes to the phenolic moiety in which the anodic peak
appears at 0.06 V and cathodic peak appears at -0.35 V
vs. Ag/AgCl. Moreover, one total irreversible cathodic
peak appears at -0.82 V which can be arisen from the
reduction of sulfur moiety. The cyclic voltammetry curve
of the Ni(II) complex is also recorded and shown in Fig. 7
(curve T2). It seems that this complex has the same feature
of the free ligand and is not an electro-active solid.
Experimental
All chemicals were purchased from Merck and used
without further purification. The required starting material,
4-phenylthiazol-2-amine, was prepared from acetophe-
none, iodine, and thiourea following the procedure
developed by Dodson and King [24].
FT-IR spectra were recorded in the frequency range of
4000–400 cm-1 using Perkin-Elmer RXI spectrometer
using KBr disks at room temperature. Elemental analysis
was carried out using a Perkin-Elmer 2400(II) CHNS/O
1
analyzer. H NMR and 13C NMR spectra were recorded
Conclusion
with Bruker Avance 300 spectrometer using DMSO-d6 as
solvent. UV–Vis spectra were recorded with a Perkin-
Elmer Lambda 25 spectrophotometer, using two matched
10-mm quartz cells. Thermal gravimetric analysis (TGA)
and differential thermal analysis (DTA) were carried out
with a STA-1500 Instrument at a heating rate of 10 °C/min
in air.
In summary, a novel Schiff base ligand based on bis(2-
amino-4-phenyl-5-thiazolyl)disulfide was synthesized and
fully characterized including X-ray crystallography. Non-
covalent forces such as C–H_O hydrogen bonding and
p_p interactions in 2 connect the monomeric moieties into
chains and help to stabilize the constructed framework. The
Ni(II) complex of this ligand was prepared and the obtained
product was further investigated by TG and DT analysis.
Finally, in this study, UV–Vis data support a square planar
Ni(II) ion, while paramagnetism (from NMR and VSM
study) suggests octahedral geometry for a d8 configuration.
Therefore, it seems that the actual structure of the Ni(II)
complex is ambiguous. We suppose that the structure might
have a highly distorted octahedral geometry with two elon-
gated bonds of coordinated solvent molecules, hence
approaching a square planar environment.
5,50-Disulfanediylbis(4-phenylthiazol-2-amine)
(1, C18H14N4S4)
2-Amino-4-phenylthiazole (3.6 g) and 1.52 g of thiourea
were dissolved in 50 cm3 mixture of warm ethanol and
distilled water. Iodine (7.6 g) was then added slowly to this
solution with occasional stirring. After the addition was
completed, the resultant red-brown mixture was refluxed
for 3 h and then poured into cooled distilled water. The
mixture was extracted with CH2Cl2 (3 9 50 cm3). The
123

J. A. Gharamaleki et al.
Fig. 7 The cyclic voltammetry
curve of the synthesized Schiff
base ligand (T1 curve) and its
Ni(II) complex (T2 curve)
filtrate was concentrated and the crude product purified by DMSO-d6): d = 109.7, 119.2, 122.0, 124.4, 127.7, 127.9,
column chromatography (silica gel, CH2Cl2/n-hexane, 2/3 128.5, 128.9, 129.2, 129.3, 132.3, 132.9, 137.9, 158.8,
v/v). The first and major fraction was then made alkaline 162.3 ppm; UV–Vis (DMSO, c = 2.10-5 mol dm-3):
with sodium hydroxide solution and was identified as bis(2- kmax = 428, 343 nm.
amino-4-phenyl-5-thiazolyl)sulfide. The second fraction
1,10-[(1E,10E)-[[5,50-Disulfanediylbis(4-phenylthiazole-
containing the desired bis(2-amino-4-phenyl-5-thia-
5,2-diyl)]bis(azanylylidene)]bis(methanylylidene)]-
zolyl)disulfide was then made alkaline with sodium
bis(naphthalen-2-olate)-dimethanol-nickel(II)
hydroxide solution. A yellow precipitate was formed which
(C15H15N3NiO2)
further crystallized from water/acetic acid (3:1) to give 1 as
A solution of 0.1 g NaOH (2 mmol) in 5 cm3 MeOH was
a
yellow solid. M.p.: 180–182 °C; FT-IR (KBr):
vꢀ = 3281(m), 3191(m), 2425(br), 1682(s), 1628(s),
added to a suspension of 0.7 g Schiff base (1 mmol) in
absolute methanol to obtain a clear solution. To this
solution, NiCl2 salt was slowly added in absolute methanol.
Subsequently, the reflux was continued overnight. The
black precipitates were obtained from the reaction mixture.
At the end, the precipitates were filtered and washed
several times with methanol and then dried in vacuum.
Regardless of testing several methods, our attempts to get
suitable crystals for X-ray analysis were unsuccessful. FT-
IR (KBr): vꢀ = 3338(br), 1618(s), 1576(s), 1538(s),
1515(s), 1471(s), 1438(w), 1355(m), 1277(s), 771(s),
1
690(s) cm-1; H NMR (300 MHz, DMSO-d6): d = 7.05
(2H, NH2), 7.28–7.66 (5H, aromatic) ppm; 13C NMR
(75 MHz, DMSO-d6): d = 109.9, 128.4, 128.8, 129.8,
134.7, 159.4, 171.9 ppm.
1,10-[(1E,10E)-[[5,50-Disulfanediylbis(4-phenylthiazole-
5,2-diyl)]bis(azanylylidene)]bis(methanylylidene)]-
bis(naphthalen-2-ol) (2, C40H26N4O2S4)
To a stirred solution of 0.35 g 2-hydroxy-1-naphthaldehyde 1477(m), 1362(s), 833(s), 771(s), 695(s), 456(w) cm-1
;
(2 mmol) in 25 cm3 absolute methanol, 0.4 g bis(2-amino- UV–Vis (DMSO, c = 2.10-3 mol dm-3): kmax = 474,
4-phenyl-5-thiazolyl)disulfide (1 mmol) in methanol was 330 nm.
added in presence of 2–3 drops of glacial acetic acid. After
the addition, the prepared solution was refluxed overnight. Crystal structure determination and refinement
Difficulties resulting from the poor chemical reactivity of
the starting materials were overcome with azeotropical The X-ray diffraction measurements were made on a STOE
removal of water by a Dean-Stark trap. The obtained IPDS-II diffractometer with graphite monochromated Mo-
˚
orange precipitation was filtered, washed with methanol Ka radiation (k = 0.71073 A). Cell constants and orienta-
and dried in vacuum. The orange plate-like crystals of the tion matrices for data collection were obtained by least-
compound suitable for X-ray analysis were obtained by squares refinement of diffraction data from 2535 unique
slow evaporation of the solvent (DMSO) within several reflections for 2. Data were collected to a maximum 2h
weeks. M.p.: 240–242 °C; FT-IR (KBr): vꢀ = 3423(br), value of 29.16° for 2 in a series of x scans in 1° oscillations
1620(s), 1601(s), 1570(s), 1480(s), 1444(s), 1318(s), and integrated using the Stoe X-AREA [35] software
1
1186(s), 8229 s), 775(s), 752(m), 695(s) cm-1; H NMR package. A numerical absorption correction was applied
(300 MHz, DMSO-d6): d = 8.79 (1H, N=CH), 7.21–8.13 using X-RED [36] and X-SHAPE [37] software. The data
(11H, aromatic), 13.53 (1H, OH) ppm; 13C NMR (75 MHz, were corrected for Lorentz and Polarizing effects. The
123

A novel schiff base ligand and its Ni(II) complex: synthesis and characterization
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full-matrix least-squares procedure using anisotropic dis-
placement parameters [39]. The atomic factors were taken
from the International Tables for X-ray Crystallography
[40]. All refinements were performed using the X-STEP32
crystallographic software package [41].
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CCDC number of 1059282 contains the supplementary
crystallographic data for compound 2. These data can be
obtained free of charge via http://www.ccdc.cam.ac.uk/
conts/retrieving.html, or from the Cambridge Crystallo-
graphic Data Centre, 12 Union Road, Cambridge CB2
1EZ, UK; fax: (?44) 1223-336-033; or e-mail:
deposit@ccdc.cam.ac.uk.
28. Schroth W, Hintzsche E, Jordan H, Jende T, Spitzner R, Thondorf
I (1997) Tetrahedron 53:7509
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