Synthesis and Characterization of Metal Complexes of a New Unsymmetrical Tridentate NNS Schiff Base Ligand: X-ray Crystal Structure Determination of Nickel(II) Complex

Article abstract of DOI:10.1002/jccs.201700068

A new unsymmetrical tridentate NNS Schiff base ligand, 2-(2-nitrophenylthio)-N-((pyridine-2-yl)methylene)benzenamine (L), and its Mn(II), Ni(II), Cu(II), and Zn(II) complexes were synthesized. These compounds were characterized by different physicochemica

Full text of DOI:10.1002/jccs.201700068

JOURNAL OF THE CHINESE
CHEMICAL SOCIETY
Article
Synthesis and Characterization of Metal Complexes of a New Unsymmetrical
Tridentate NNS Schiff Base Ligand: X-ray Crystal Structure Determination of Nickel(II)
Complex
a
a
b
*
Ahmad Ali Dehghani-Firouzabadi, Samaneh Sepehri and Behrouz Notash
aDepartment of Chemistry, Faculty of Science, Yazd University, 89195-741Yazd, Iran
bChemistry Department, Shahid Beheshti University, G. C. Evin, Tehran 1983963113, Iran
(Received: February 26, 2017; Accepted: June 3, 2017; DOI: 10.1002/jccs.201700068)
A new unsymmetrical tridentate NNS Schiff base ligand, 2-(2-nitrophenylthio)-N-((pyridine-2-yl)
methylene)benzenamine (L), and its Mn(II), Ni(II), Cu(II), and Zn(II) complexes were synthesized.
These compounds were characterized by different physicochemical and spectroscopic techniques.
The molecular structure of [NiL2](ClO4)2 was determined by single-crystal X-ray diffraction. In
this complex, two ligands coordinate through azomethine-N, pyridine-N, and thioether-S, forming
a mononuclear 6-coordinate distorted octahedral geometry about a nickel.
Keywords: NNS donor; Tridentate ligand; Unsymmetrical ligand; Schiff base complexes;
Thioether ligand; Ni(II) complex.
INTRODUCTION
and/or 1:2 complexes. In most complexes, the Schiff
base ligand behaves as an NNS-tridentate ligand or
NN-bidentate ligand.15–18 We report here the synthesis
and characterization of a new unsymmetrical tridentate
NNS Schiff base ligand derived from pyridine-2-carbal-
Schiff base ligands have been studied extensively
and played a major role in the development of coordi-
nation chemistry. The synthesis of Schiff base ligands
and their complexes is one the main areas of interest in
the active sites and the role of metal ions in biological
systems, catalysis, magnetic phenomena, anticancer
properties, transport and separation phenomena, etc.1–5
Unsymmetrical Schiff base ligands with hard nitrogen
and soft sulfur donor atoms have been widely investi-
gated, and they readily form stable complexes with
most of the transition- and non-transition-metal ions.
The synthesis of these complexes is an important area
of study with implications in bioinorganic chemistry,
catalysis, and medical chemistry.6–9 Also, unsymmetri-
cal Schiff base ligands with N and S donors have been
able to provide diverse possibilities in structure and
chemical properties, and these complexes are the most
abundant in and dominate the field.10–15
dehyde,
2-aminothiophenol,
and
1-chloro-2-
nitrobenzene and its metal complexes. The complexa-
tion reaction of manganese(II), nickel(II), copper(II),
and zinc(II) chloride with this NNS Schiff base ligand
gave complexes with a metal:ligand ratio 1:1,whereas
nickel(II) perchlorate with this ligand gave a complex
with a metal:ligand ratio 1:2. The structure of the latter
complex has been determined by X-ray diffraction. This
ligand was bonded to the nickel(II) center as an NNS-
tridentate ligand in the metal:ligand ratio 1:2, indicating
a distorted octahedral structure.
EXPERIMENTAL
The interest of tridentate unsymmetrical Schiff
base ligands with NNS donating sites in coordination
chemistry has increased due to their capabilities of
forming stable four-, five-, and six-coordinated com-
Materials and instrumentation
2-Aminothiophenol, pyridine-2-carbaldehyde, and
1-chloro-2-nitrobenzene were purchased from Merck
and used as received. Other reagents and solvents were
of analytical grade and used without any further purifi-
cation. Elemental analyses were performed on a Perkin-
Elmer CHNS-O-2400 II analyzer. Infrared spectra were
plexes and have
a
broad range of biological
properties.10,16–22 Tridentate NNS donor unsymmetri-
cal Schiff base ligands have been able to provide 1:1
*Corresponding author. Email: aadehghani@yazd.ac.ir
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1

Article
Dehghani-Firouzabadi et al.
recorded in the ATR (attenuated total reflection) mode
using a Bruker Equinax-55 FT-IR spectrophotometer
(4000–400 cm−1). MS spectra were obtained using a
Shimadzu QP-1100EX GC-MS instrument (EI at
spectrophotometer with a 1-cm quartz cell in the range
200–1100 nm at 25ꢀC.
X-ray crystal structure determination
Slow crystallization from an ethanolic solution of
[NiL2](ClO4)2 yielded brown crystals. The X-ray dif-
fraction data were collected on a STOE IPDS-II dif-
fractometer with graphite-monochromated Mo Kα
radiation (λ = 0.71073 Å). A crystal with dimensions
0.50 × 0.30 × 0.10 was used for data collection. Cell
constants and orientation matrix for data collection
were obtained by least-squares refinement of the diffrac-
tion data from 5004 unique reflections. Data were col-
lected at a temperature of 298(2) K to a maximum 2θ
value of 58.42ꢀ and in a series of ω scans in 1ꢀ oscilla-
tions and integrated using the Stoe X-AREA software
package.23 The numerical absorption coefficient μ for
Mo Kα radiation is 0.849 mm−1. A numerical absorp-
tion correction was applied using the X-RED and
X-SHAPE software.24,25 The data were corrected for
Lorentz and polarizing effects. The crystal structure
was solved by direct methods and subsequent difference
Fourier maps and then refined by the full matrix least-
squares procedure on F2 using anisotropic displacement
parameters.26 All the hydrogen atoms were located in
their calculated positions and refined using a riding
model. Subsequent refinement then converged with the
R-factors. Atomic factors were taken from the Interna-
tional Tables for X-ray Crystallography.27 All refine-
1
70 eV). H and 13C NMR spectra were recorded on a
Bruker AC-300 NMR spectrometer using CDCl3 as the
solvent and TMS as the internal standard. Conductivity
measurements were carried out in 10−3 mol dm−3 meth-
anol and DMF solutions at 25ꢀC using a Metrohm
660 conductivity meter. The electronic spectra were
recorded on
a
GBC Cintra 101 UV–visible
Table 1. Crystallographic and structure refinements data for
[NiL2](ClO4)2
Complex
[NiL2](ClO4)2
Empirical formula
Formula weight
Temperature (K)
Wavelength λ (Å)
Crystal system
Space group
a (Å)
C36H26Cl2N6NiO12S2
928.34
298(2)
0.71073
Monoclinic
C 2/c
24.937(5)
8.4416(17)
19.400(4)
90
113.79(3)
90
3736.9(16)
4, 1.650
0.849
b (Å)
c (Å)
α (ꢀ)
β (ꢀ)
γ (ꢀ)
Volume (Å)3
Z, Calculated density (Mg/m3)
Absorption coefficient (mm−1
F(000)
)
ments
were
performed
using
the
X-STEP
1896
32 crystallographic software package.28 Crystal data,
experimental details, and structure refinement results
are given in Table 1.
Crystal size (mm)
0.50 × 0.30 × 0.10
Theta range for data collection 2.27–29.21
(ꢀ)
Limiting indices
−33 < =h < =34
Synthesis
−11 < =k < =10
−26 < =l < =26
12691/5004 [R
(int) = 0.0742]
98.7%
Synthesis of the 2-((nitrophenyl)thio)aniline.
2-Amino-
Reflections collected/unique
thiophenol (5.0 g, 40 mmol), 1-chloro-2-nitrobenzene
(6.3 g, 40 mmol), and potassium carbonate (5.5 g,
40 mmol) were mixed and then fused together at
130–140ꢀC with constant stirring for 4 h. The mixture
was then cooled, and absolute ethanol (70 mL) was
added. The mixture was stirred for 15 min and then fil-
tered off. The filtrate volume was reduced to about
10 mL and resulted in the formation of a green precipi-
tate. The precipitate was decanted and washed twice
with diethyl ether (2 × 10 mL) (Scheme 1). Yield:
7.94 g, 81%, m.p.: 85ꢀC. IR (ATR, cm−1) 3451, 3360
Completeness to theta
Absorption correction
Max. and min. transmission
Refinement method
Numerical
0.9199 and 0.6763
Full-matrix least-squares on
F2
5004/0/267
0.990
R1 = 0.0567, wR2 = 0.1218
R1 = 0.0984, wR2 = 0.1368
0.624 and −0.341
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I > 2sigma(I)]
R indices (all data)
Largest diff. peak and hole
(eÅ−3
)
2
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Synthesis and Characterization of Metal Complexes
ν(NH2); 1504, 1305 ν(NO2); 734 ν(C S); 1H NMR
(CDCl3, ppm): δH 4.34 (2H, br), 6.62 (1H, t), 6.63 (1H,
t), 6.72 (1H, d), 6.73 (1H, d), 7.19 (4H, m); EI-MS
(m/z, M+): 248 [M]+.
[NiL2](ClO4)2
Yield: 476 mg (68%). Anal. Calc. for
C36H26Cl2N6NiO12S2: C, 46.58; H, 2.82; N, 9.05%.
Found: C, 45.32; H, 3.04; N, 8.78%; IR (ATR, cm−1
)
1616 ν(C N); 1513, 1305 ν(NO2); 1080 ν(ClO4);
776 ν(C S); UV–vis in DMF (λ, nm) 270 (log
ε = 6.64), 340 (log ε = 6.28), 520 (log ε = 2.20),
750 (log ε = 1.09), 990 (log ε = 1.03); Λm (DMF)
Synthesis of the 2-(2-nitrophenylthio)-N-((pyridine-2-yl)methyl-
ene)benzenamine (L).
A solution of 2-((nitrophenyl)
thio)aniline (2.46 g, 10 mmol) in ethanol (40 mL) was
added dropwise to solution of pyridine-2-
162.0 Ω−1 cm2 mol−1
.
a
carbaldehyde (1.07 g, 10 mmol) in the same solvent
(20 mL). The solution was refluxed for 8 h. Then, the
solution was cooled and concentrated to dryness. The
resulting brown oil was rubbed and washed twice with
diethyl ether (2 × 10 mL) (Scheme 1). Yield: 2.11 g,
[NiLCl]Cl ꢁ EtOH
Yield: 470 mg (92%). Anal. Calc. for
C20H19Cl2N3NiO3S: C, 47.00; H, 3.75; N, 8.22%.
Found: C, 46.42; H, 4.05; N, 8.07%; IR (ATR, cm−1
63%.IR (ATR, cm−1
) 1619 ν(C N); 1509, 1304
)
1
1606 ν(C N); 1495, 1305 ν(NO2); 759 ν(C S); UV–vis
in MeOH (λ, nm) 260 (log ε = 4.07), 350 (log ε = 3.89),
526 (log ε = 2.80), 730 (log ε = 1.64); EI-MS (m/z,
M+): 431 [NiLCl + 2H]+; Λm (MeOH) 128.2 Ω−1
ν(NO2); 737 ν(C S); H NMR (CDCl3, ppm): δH 6.87
(1H, d), 7.22 (2H, d), 7.02 (1H, d), 7.34 (2H, t), 7.48
(1H, t), 7.51 (1H, t), 7.86 (1H, d), 7.96 (1H, t), 8.24
(1H, t), 8.39 (1H, d), 8.72 (1H, s), 8.80 (1H, d);13C
NMR (CDCl3, ppm): δC 119.0, 122.0, 123.5, 125.1,
125.6, 125.7, 126.1, 127.3, 132.4, 133.8, 137.1, 137.4,
137.8, 147.6, 149.3, 149.6, 154.2, 160.0; UV–vis in
MeOH (λ, nm) 243 (log ε = 3.44), 295 (log ε = 2.71),
364 (log ε = 2.64); EI-MS (m/z, M+): 335 [L]+; Λm
cm2 mol−1
.
[CuLCl2]
Yield: 385 mg (82%). Anal. Calc. for
C18H13Cl2CuN3O2S: C, 46.01; H, 2.79; N, 8.94%.
Found: C, 45.62; H, 2.74; N, 8.88%; IR (ATR, cm−1
(MeOH) 15.2 Ω−1 cm2 mol−1
.
)
1607 ν(C N); 1514, 1305 ν(NO2); 758 ν(C S); UV–vis
in MeOH (λ, nm) 270 (log ε = 4.35), 308 (log ε = 4.33),
350 (log ε = 4.25), 556 (log ε = 3.36); EI-MS (m/z,
M+): 429 [CuLCl-3H]+; Λm (MeOH) 65.1 Ω−1
General synthesis of the complexes.
A solution of MCl2
(M Mn, Ni, Cu, Zn) or Ni(ClO4)2(1 mmol) in ethanol
(40 mL) was added dropwise to a refluxing solution of
2-(2-nitrophenylthio)-N-((pyridine-2-yl)methylene)benze-
namine (L) (0.335 g, 1 mmol) in ethanol (40 mL). After
refluxing for 2 h, the reaction mixture was cooled and
concentrated to ~5 mL, and the resulting solid was fil-
tered, washed with cold ethanol, and air-dried.
cm2 mol−1
.
[ZnLCl(H2O)]Cl
Yield: 348 mg (69%). Anal. Calc. for
C18H15Cl2N3O3SZn: C, 44.15; H, 3.09; N, 8.58%.
Found: C, 42.51; H, 3.60; N, 8.27%; IR (ATR, cm−1
)
3350–3450 ν(H2O); 1604 ν(C N); 1487, 1304 ν(NO2);
1
764 ν(C S); H NMR (DMSO-d6, ppm): δH 5.48 (br),
6.45 (1H, t), 6.75 (1H, d), 7.02 (1H, d), 7.11 (1H, t),
7.5–7.7 (3H, m), 8.07 (1H, t), 8.13 (1H, d), 8.19 (1H,
d), 8.36 (1H, d), 8.75 (1H, s);13C NMR (DMSO-d6,
ppm): δC 111.2, 115.3, 116.6, 117.0, 120.9, 123.0,
123.8, 126.5, 126.6, 127.1, 131.6, 135.9, 138.4, 150.2,
150.4, 150.7, 154.2, 169.4; UV–vis in MeOH (λ, nm)
232 (log ε = 3.34), 313 (log ε = 2.93); EI-MS (m/z,
M+): 451 [ZnLCl(H2O)]+; Λm (MeOH) 69.0 Ω−1
Scheme 1 Synthesis of the 2-(2-nitrophenylthio)-N-
cm2 mol−1
.
((pyridine-2-yl)methylene)benzenamine (L).
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Article
Dehghani-Firouzabadi et al.
[MnLCl(H2O)]Cl
to the aromatic ring protons in the region
6.75–8.80 ppm.13,17,33 In the 13C NMR spectra of the
ligand (L) and Zn(II) complex, the HC N carbon reso-
nance is observed at 160.0 and 169.4 ppm, respectively,
and those of the aromatic carbons in the region
1121.2–154.2 ppm.
Yield: 359 mg (75%). Anal. Calc. for
C18H15Cl2MnN3O3S: C, 45.11; H, 3.15; N, 8.77%.
Found: C, 45.61; H, 3.14; N, 8.66%; IR (ATR, cm−1
)
1604 ν(C N); 1500, 1304 ν(NO2); 763 ν(C S); UV–vis
in MeOH (λ, nm) 245 (log ε = 3.32), 309 (log ε = 3.27),
364 (log ε = 2.48), 516 (log ε = 0.88); EI-MS (m/z,
M+): 429 [MnLCl + 3H]+; Λm (MeOH) 129.0 Ω−1
Electronic spectra
cm2 mol−1
.
The electronic spectrum of 0.001 M solutions of the
ligand (L) in MeOH shows absorption bands at 243 nm
(log ε = 3.44), 295 nm (log ε = 2.71), and 364 nm (log
ε = 2.64), which can be attributed to π ! π* and n ! π*
transitions.34 The electronic spectra of 0.001 M solutions
of complexes in MeOH and DMF show bands
232–270 nm corresponding to π ! π* transitions and at
309–364 nm corresponding n ! π* and/or charge-
transfer transitions. In general, the electronic transitions
for Zn(II) (d10) complex are spin-forbidden and hence
cannot be observed. The Cu(II) complex shows only one
band at 556 nm (log ε = 3.36) and the Mn(II) complex
shows only one band at 516 nm (log ε = 088) corre-
sponding to the d ! d transition. In the absorption spec-
trum of [NiLCl]+, the absence of any electronic transition
at longer wavelengths indicates a significant crystal-field
splitting and is consistent with the square-planar geome-
try of Ni(II) complexes. The appearance of two bands at
526 nm (log ε = 2.80) and 730 nm (log ε = 1.64) in the
absorption spectrum of [NiLCl]+ is consistent with the
square-planar geometry of Ni(II).35–37 The appearance of
three bands at 520 nm (log ε = 2.20), 750 nm (log
ε = 1.09), and 990 nm (log ε = 1.03) in the absorption
spectrum of [NiL2]2+ is in good agreement with those
reported for a pseudo-octahedral geometry around the
Ni(II) ion.30,38
RESULTS AND DISCUSSION
IR spectra
The IR spectrum of 2-((nitrophenyl)thio)aniline
shows bands at 3451 and 3360 cm−1 assignable to the
aromatic primary amine vibrations and a band at
734 cm−1 due to the thioether stretch. Also, the vibra-
tion peaks of NO2 are observed at 1504 and 1305 cm−1
.
The IR spectrum for the ligand (L) confirms the pres-
ence of imine (1619 cm−1) and the absence of carbonyl
and amine functional groups of the starting materials.
The vibration peak of C S in the IR spectrum of
ligand (L) is observed in 737 cm−1, and those of NO2
are observed in 1509 and 1304 cm−1. In the IR spectra
of Mn(II), Ni(II), Cu(II), and Zn(II) complexes, the
bands in the range 1604–1616 cm−1 are associated with
ν(C N) vibration. Also, the vibration peaks of NO2 are
seen in the ranges 1487–1514 and 1304–1305 cm−1 and
those of C S are seen in the range 758–776 cm−1. The
vibration peaks of C S are shifted similar to the bands
of the ligand, which shows that the thioether sulfur
atom is coordinated to the metal ions.12,29–32
NMR spectra
The 1H NMR and 13C NMR results were
obtained for prepared compounds at ambient tempera-
ture in CDCl3 and DMSO-d6 as mentioned in
Section Experimental. The 1H NMR spectrum of 2-
((nitrophenyl)thio)aniline shows a significant signal at
4.34 ppm corresponding to the NH2 protons and shows
doublet and triplet signals in the 6.62–7.19 ppm range
corresponding to the aromatic ring protons. The 1H
and 13C NMR spectra of the 2-(2-nitrophenylthio)-N-
((pyridine-2-yl)methylene)benzenamine (L) confirm the
Mass spectra
The electrospray ionization (EI) mass spectra of
the 2-((nitrophenyl)thio)aniline, the ligand (L), and the
complexes provide strong evidence for the formation of
these compounds. The molecular peak in the spectra of
2-((nitrophenyl)thio)aniline and the ligand (L) are
observed at m/z 248 and 335, respectively. The EI mass
spectra of Mn(II), Ni(II), and Cu(II) complexes exhibit
a peak at m/z 429 or 431, which confirms the presence
of a metal ion, Cl−, and the ligand (L). The presence of
several peaks at higher molecular weights in the EI
1
successful synthesis of this compound. The H NMR
spectra of the ligand (L) and the Zn(II) complex exhibit
singlets at 8.72 and 8.75 ppm, respectively, which have
been assigned to the HC N resonance, and signals due
4
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JOURNAL OF THE CHINESE
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Synthesis and Characterization of Metal Complexes
Table 3. Hydrogen bonds (Å and deg) for [NiL2](ClO4)2
D–H…A
d(D–H) d(H…A) d(D…A) <(DHA)
C(6)–H(6)…O(3)
C(11)–H(11)…O(6)
C(15)–H(15)…O(5)
C(17)–H(17)…O(4)
C(10)–H(10)…O(2)
0.93
0.93
0.93
0.93
0.93
2.585
2.521
2.495
2.817
2.649
3.506
3.154
3.255
3.174
3.492
171.2
125.5
139.0
104.0
151.1
[NiL2]2+ (162.0 Ω−1 cm2 mol−1) forms a 1:2 electrolyte
in DMF.39 These data support the formulations of the
complexes. Results of the elemental analyses of these
complexes are in good agreement with the above molec-
ular formula. In all the complexes, it has been observed
that the Schiff base behaves as an NNS-tridentate
ligand in the 1:1 and 1:2 complexes and both chloride
or perchlorate ions from the starting compounds are
consistent with the molecular formula.
Fig. 1. View of the cationic part and one perchlorate
ion of [NiL2](ClO4)2 showing 50% displace-
ment ellipsoids.
X-ray crystallography
mass spectrum of Zn(II) complex (e.g., m/z 604) indi-
Single crystals of the Ni(II) complex were
obtained by slow evaporation of an ethanolic solution
of this compound. Then, the structures of Ni(II) and
the complex were determined by single-crystal X-ray
diffraction. The molecular structure of [NiL2](ClO4)2 is
shown in Figure 1. The crystallographic and measure-
ment data are shown in Table 1. Selected bond lengths
and bond angles are listed in Table 2. The complex
[NiL2]2+ crystallizes in the monoclinic space group
C 2/c with Z = 4. In the compound [NiL2]2+, the
nickel(II) atom is six-coordinated in a distorted octahe-
dral geometry by two Schiff base ligands. Each of the
Schiff bases acts as a meridional tridentate ligand
through the thioether sulfur atom, the imine N, and the
pyridine N atom. In this complex, the S(1), N(1), S(1)
#1, and N(1)#1 (Symmetry code: #1 –x + 1,y,–z + 1/2)
donors define the equatorial plane and the nickel(II)
atom lies in this plane. Also, the N(2) and N(2)#1
donors occupy the apical positions. The Ni(1)–S(1),
Ni(1) –N(1), and Ni(1) –N(2) bond lengths are 2.4949
(10), 2.056(3), and 2.034(2) Å, respectively (Table 2),
which are in agreement with the reported values for
such bonds [12,31]. The N(2) –Ni–N(2)#1 and N(1)–
Ni–S(1) or N(1)#1–Ni–S(1)#1 bond angles are 178.31
(15) and 161.27(7)ꢀ, respectively. Other angles around
nickel(II) are 80.73, 81.35, 97.37, 100.43ꢀ (judged
angles) and 82.87, 94.05, 94.05, 94.51ꢀ (bite angles),
cates that this complex is polynuclear.
Molar conductivity and elemental analysis
The molar conductance values for the ligand
(L) and the Cu(II) and Zn(II) complexes measured in
MeOH solution (1 × 10−3 mol dm−3) fall in the range
15.2–69.0 Ω−1 cm2 mol−1. These values are well within
the expected range for non-electrolytes. The molar
conductance values of [NiLCl]+ (128.2 Ω−1 cm2 mol−1
)
and [MnLCl(H2O)]+ (129.0 Ω−1 cm2 mol−1
)
suggest
that these complexes form 1:1 electrolytes in MeOH.
Table 2. Selected bond lengths (Å) and bond angles (ꢀ) for
[NiL2](ClO4)2
Bond lengths (Å)
Bond angles (ꢀ)
Ni(1) –S(1)
Ni(1) –N(1)
Ni(1)–N(2)
N(2) –C(6)
N(2) –C(7)
N(3)–C(18)
N(1)–C(5)
N(1)–C(1)
S(1)–C(13)
S(1)–C(12)
C(5)–C(6)
2.4949(10) N(2) –Ni–N(2)#1
178.31(15)
161.27(7)
161.27(7)
2.056(3)
2.034(2)
1.273(4)
1.418(4)
1.462(5)
1.356(4)
1.339(4)
1.776(3)
1.786(3)
1.456(5)
N(1) –Ni–S(1)
N(1)#1–Ni–S(1)#1
N(2)#1–Ni(1) –N(1)#1 80.73(10)
N(2) –Ni(1) –S(1)
N(2)#1–Ni(1)–S(1)
N(2) –Ni(1)–N(1)#1
S(1) –Ni(1)–S(1)#1
N(1) –Ni(1)–S(1)#1
N(1)#–Ni(1) –S(1)
N(1) –Ni(1)–N(1)#1
81.35(8)
97.37(7)
100.43(10)
82.87(5)
94.05(8)
94.05(8)
94.51(15)
Symmetry code: #1 –x + 1, y, –z + 1/2.
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Article
Dehghani-Firouzabadi et al.
CONCLUSIONS
In this work, we have successfully designed, synthe-
sized, and characterized the unsymmetrical amine and
then the NNS unsymmetrical tridentate Schiff base ligand
(L) containing the NO2 group and/or hard–soft donors.
Then, manganese(II), copper(II), nickel(II), and zinc(II)
complexes with this ligand were prepared and character-
ized by analytical and spectroscopic methods. The molec-
ular structure of [NiL2](ClO4)2 was determined by single-
crystal X-ray crystallography. The nickel(II) complex
showed the distorted octahedral geometry about the metal
center. Also, this ligand can be bonded to metal center as
an NNS–tridentate ligand in the 1:1 and 1:2 complex.
Fig. 2. View of the crystal packing of [NiL2]2+ in the
b-direction. Dashed lines indicate some of
hydrogen bonds.
which deviate significantly from 90ꢀ, indicating the dis-
tortion from a regular octahedron. Each molecule in
[NiL2]2+ is involved in intermolecular hydrogen bond-
ing interactions between the hydrogen of the aromatic
carbon atoms (H11, H15, H17) and the hydrogen of
ACKNOWLEDGMENTS
−
We are grateful to the Faculty of Chemistry, Yazd
University, and the Ministry of Science, Research and
technology of Iran, for financial support.
azomethine carbon atoms (H6) with the ClO4 groups
and between the hydrogen of aromatic carbon atoms
(H10) of a unit with the NO2 groups (O2) of another
unit. Crystal packing structure of the complex is stabi-
lized by intermolecular hydrogen bonding interactions
(Table 3 and Figure 2). The angle between the plane
calculated through S(1), N(3), and C(13)–C(18) of
ligand and the plane calculated through N(1), N(2),
and C(1)–C(12) of the same ligand is 71.24ꢀ. The angle
between the plane calculated through S(1), N(3), and C
(13) –C(18) of the ligand and the plane calculated
through S(1), N(3), and C(13)–C(18) of the another
ligand is 18.03ꢀ and shows ligand–ligand interactions.
The shortest and longest atom-atom distances between
phenyl and pyridine rings are 3.22 and 4.03 Å, respec-
tively. The mean distance is 3.62 Å, which indicates
weak π–π intramolecular interactions (Figure 3).40 The
close contact and parallel configuration of the two rings
on different ligands may be a result of forced packing
or possible π−π ligand interaction.
Supporting information
CCDC 1483020 contain the supplementary crys-
tallographic data for [NiL2](ClO4)2. These data can be
obtained free of charge via http://www.ccdc.cam.ac.uk/
conts/retrieving. html, or from the Cambridge Crystal-
lographic Data Centre.
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