Synthesis and characterization of four new azo-Schiff base and their nickel(II) complexes

Article abstract of DOI:10.1016/j.poly.2021.115296

Four new azo-Schiff base ligands were prepared (H₂L_a-H₂L_d) via condensation of Methyl-2-{N-(2′-aminoethane)}-amino-1-cyclopentenedithiocarboxylate (Hcden) with derivatives of (E)-2-hydroxy-5-(phenyldiazenyl)benz

Full text of DOI:10.1016/j.poly.2021.115296

Polyhedron 205 (2021) 115296
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Synthesis and characterization of four new azo-Schiff base and their
nickel(II) complexes
b
c
d
Saeid Menati a, , Reza Azadbakht , Hadi Amiri Rudbari , Giuseppe Bruno
⇑
a Department of Chemistry, Khorramabad Branch, Islamic Azad University, Khorramabad, Iran
b Faculty of Chemistry, Bu-Ali Sina University, Hamedan 65174, Iran
c Department of Chemistry, University of Isfahan, 81746-73441 Isfahan, Iran
d Department of Chemical, Biological, Pharmaceutical and Environmental Sciences, University of Messina, Viale Ferdinando Stagno D’Alcontres 31, I-98166 Messina, Italy
a r t i c l e i n f o
a b s t r a c t
Four new azo-Schiff base ligands were prepared (H2La-H2Ld) via condensation of Methyl-2-{N-(20-ami-
noethane)}-amino-1-cyclopentenedithiocarboxylate (Hcden) with derivatives of (E)-2-hydroxy-5-
(phenyldiazenyl)benzaldehyde. The corresponding nickel(II) complexes were also synthesized. The struc-
tures of the azo-Schiff base ligands and the complexes were characterized by elemental analyses, UV–Vis,
IR and 1HNMR spectroscopies. The structures of [NiLa] and [NiLc] complexes have been determined by X-
ray crystallography. The Ni(II) metal complexes are formed by the coordination of the N, S and O atoms of
the ligands. The X-ray results confirm that the geometry of the Ni(II) metal complexes are slightly dis-
torted square-planar structures.
Article history:
Received 12 April 2021
Accepted 25 May 2021
Available online 29 May 2021
Keywords:
Azo compounds
Schiff base complexes
Square-planar structures
X-ray crystal structure
Nickel(II) complexes
Ó 2021 Published by Elsevier Ltd.
1. Introduction
starting material for the synthesis of asymmetric ligands contain-
ing NNOS coordination spheres.
Schiff base compounds are widely used as chelating ligands in
coordination chemistry [1]. They are also useful in catalysis, med-
icine as antibiotics, antiallergic and antitumor agents [2]. Azo com-
pounds have extensively been studied because of various
applications in organic synthesis and high technology areas such
as inkjet printers, liquid crystalline displays and laser [3–5]. Azo
dyes have excellent optical switching among the organic photoac-
tive materials [6–10]. Furthermore, azo metal complexes are used
in many biological process such as inhibition of RNA, DNA, and bio-
logical activity against fungi and bacteria [11,12]. Azo-Schiff base
ligands and their metal complexes have been extensively studied
over past few decades. It has been found that azo Schiff base com-
pounds have a widespread application both in biological activities
and in organic synthesis. They are increasingly employed in plastic,
leather and textile industries [13]. Azo Schiff bases have been
shown to coordinate with many metal ions and give stable com-
plexes. The coordination compounds of the azo Schiff bases are
used in medicine, for corrosion prevention, metal recovery as well
as to treat nuclear wastes [14]. Methyl-2-{N-(20-aminoethane)}-
amino-1-cyclopentenedithiocarboxilate (Hcden) is a convenient
The synthesis of Ni(II) complexes containing N and S donor
atoms is an important area of study with implications in bioinor-
ganic chemistry, catalysis, and medical chemistry [15–17]. Nickel
is present in the active sites of several important classes of metal-
loproteins, such as urease and Ni/Fe hydrogenases [16]. The nickel
coordination sphere in both of these metalloenzyme systems con-
tains N and S donor sets. These features led to increased interest in
the synthesis of nickel(II) complexes with mixed N, S donating che-
lates as structural and spectroscopic models of the active sites [17].
In this work, four new azo-Schiff base ligands were synthesized
(H2La-H2Ld) via condensation of Methyl-2-{N-(20-aminoethane)}-
amino-1-cyclopentenedithiocarboxylate (Hcden) with derivatives
of (E)-2-hydroxy-5-(phenyldiazenyl)benzaldehyde. The corre-
sponding nickel(II) complexes were also synthesized and the crys-
tal structures of [NiLa] and [NiLc] complexes have been determined
by X-ray crystallography.
2. Experimental
2.1. Reagents and solvents
All solvents were purchased commercially. Carbon disulfide,
⇑
cyclopentanone,
dimethylsulfate,
1,2-ethylendiamine,
2,4-
Corresponding author.
E-mail address: saiedmenati@gmail.com (S. Menati).
dichloroaniline, 3,4-dichloroaniline, 2-nitroaniline, 3-nitroaniline,
https://doi.org/10.1016/j.poly.2021.115296
0277-5387/Ó 2021 Published by Elsevier Ltd.

S. Menati, R. Azadbakht, Hadi Amiri Rudbari et al.
Polyhedron 205 (2021) 115296
sodium carbonate, sodium nitrite, nickel(II) chloride hexahydrate
and salicylaldehyde were obtained from Merck and Fluka and were
used without further purification.
2.3.2.4. (E)-5-((3,4-dichlorophenyl)diazenyl)-2-hydroxybenzaldehyde
(d). Yield: 70%. m.p 147 °C. IR (KBr, cmꢀ1): 3045
m
(OAH), 1670
(AN@NA, cis and trans),
(CAO). 1H NMR d (500 MHz; CDCl3): 11.46 (s, OH), 10.06
m
(C@O), 1619
m(C@C), 1571 and 1481 m
1284
m
(s, CHO), 8.23 (s, 1H), 8.19 (d, 1H, J = 8.01 Hz), 8.02 (s, 1H), 7.79
(d, 1H, J = 7.33 Hz), 7.62 (d, 1H, J = 7.58 Hz), 7.15 (d, 1H,
J = 7.19 Hz), Anal. Calc. for C13H8O2N2Cl2: C, 52.88; H, 2.71; N,
9.49 Found: C, 52.44; H, 2.58; N, 9.17%.
2.2. Instrumentation
The NMR spectra were obtained in a Brucker Avace DPZ-
500 MHz spectrometer. IR spectra were recorded by Perkin Elmer
RX1 FT-IR infrared spectrophotometer, Elemental analyses (C, H
and N) were measured with a Termo Finnigan-Flash 1200 analyzer
and UV–Vis measurements were recorded on a Jenus 5606 UV–Vis
spectrophotometer. Uv–Vis absorption spectra were obtained on a
Varian Cary Eclipse 300.
2.3.3. Synthesis of Schiff bases ligands (H2La-H2Ld)
Schiff base ligands (H2La-H2Ld) were prepared by addition of a-d
compounds (1 mmol, 0.271 g of a and/or b, 0.295 g of c and/or d) in
methanol (20 mL) to a methanolic solution of Hcden (1 mmol,
0.216 g). The mixtures were stirred for about 20 min and allowed
to react at room temperature for about 24 h. The color powders
were recrystallized by chloroform/methanol (1:1) v/v solution
(Scheme 1).
2.3. Synthesis
2.3.1. Synthesis of Methyl-2-{N-(2-aminoethane)}-amino-1-
cyclopentenedithiocarboxylate (Hcden)
Methyl-2-{N-(2-aminoethane)}-amino-1-cyclopentenedithio-
carboxylate was prepared by published method [18].
2.3.3.1. Methyl 2-((2-((E)-2-hydroxy-5-((E)-2-nitrophenyl)diazenyl)
benzylidene)amino)ethyl)ami-no)cyclopent-1-enecarbodithioate (H2-
La). Yield: 88%. m.p: 179 °C. IR (KBr, cmꢀ1): 1636
m
(C@N), 1589
m
(N@N), 1478 (Phenol ring), 1335 m(NO2), 1275 m(CAO), 1102, 852,
2.3.2. Preparation of Azo-aldehyde compounds (a-d)
603. 1H NMR d (500 MHz; CDCl3): 13.35 (s, 1H, OH), 12.17 (s, 1H,
NH), 8.39 (s, 1H, CH = N), 7–8.3 (Phenol ring), 3.82 (t, 2H,
J = 8.23 Hz), 3.72 (t, 2H, J = 8.18 Hz), 2.73 (m, 6H), 2.53 (s, -
SCH3). Anal. Calc. for C22H23N5O3S2: C, 52.21; H, 4.58; N, 14.93.
Found: C, 52.61; H, 4.19; N, 14.42%.
Azo-aldehydes (a-d) were synthesized according to the litera-
ture procedure [18]. A mixture of aniline derivatives (10 mmol,
1.38 g of 2-nitroaniline and/or 3-nitroaniline, 1.62 g of 2,4-
dichloroaniline and/or 3,4-dicheloroaniline) in hydrochloric acid
(36 mL), and water (16 mL) were heated. The solutions were
poured into an ice-water mixture, and were diazotized between
0 °C and 5 °C with sodium nitrite (10 mmol, 0. 69 g) dissolved in
water (5 mL). The cold diazo solutions were added to a solution
of salicylaldehyde (10 mmol, 1.29 g) in water (19 mL) containing
sodium hydroxide (10 mmol, 0.4 g) and sodium carbonate
(40 mmol, 4.24 g) during the period of 30 min at 0 °C. The products
were collected by filtration and washed with NaCl solution
(100 mL, 10% aq.) under vacuum. Then, the solids were dried under
vacuum at 80 °C overnight. The purity of the compounds were con-
trolled by TLC (n-hexane:ethylacetate/60:40).
2.3.3.2. Methyl 2-((2-((E)-2-hydroxy-5-((E)-(3-nitrophenyl)diazenyl)
benzyledeneamino)ethyl)ami-no)cyclopent-1-enecarbodithioate (H2-
Lb). Yield: 93%. m.p: 188 °C. IR (KBr, cmꢀ1): 1628
m
(C@N), 1583
m
(N@N), 1477 (Phenol ring), 1339 m(NO2), 1278 m(CAO), 1109, 848,
610. 1H NMR d (500 MHz; CDCl3): 13.40 (s, 1H, OH), 12.43 (s, 1H,
NH), 8.57 (s, 1H, CH@N), 7–8 (Phenol ring), 3.82 (t, 2H,
J = 8.23 Hz), 3.72 (t, 2H, J = 8.18 Hz), 2.73 (m, 6H), 2.53 (s, ASCH3).
Anal. Calc. for C22H23N5O3S2: C, 52.21; H, 4.58; N, 14.93. Found: C,
52.61; H, 4.19; N, 14.42%.
2.3.3.3. Methyl 2-((2-((E)-5-((E)-(2,4-dichlorophenyl)diazenyl)-2-
hydroxybenzylidene)amino)eth-yl)amino)cyclopent-1-enecarbod-
2.3.2.1. (E)-2-hydroxy-5-((2-nitrophenyl)diazenyl)benzaldehyde (a).
Yield: 86%. m.p 131 °C. IR (KBr, cmꢀ1): 3193
m
(OAH), 1668
(-N@N-, cis and trans),
m
(CAO). 1H NMR d (500 MHz; CDCl3):
m
ithioate (H2Lc). Yield: 79%. m.p: 170 °C. IR (KBr, cmꢀ1): 1633
m
(C@O), 1615
m
(C@C), 1579 and 1486
m
(C@N), 1582
m(N@N), 1485 (Phenol ring), 1288 m(CAO), 1103,
1348 and 1532
m(NO2), 1290
841, 613. 1H NMR d (500 MHz; CDCl3): 13.51 (s, 1H, OH), 12.35
(s, 1H, NH), 8.45 (s, 1H, CH@N), 7–8.2 (Phenol ring), 3.86 (t, 2H,
J = 8.20 Hz), 3.75 (t, 2H, J = 8.31 Hz), 2.73 (m, 6H), 2.51 (s, ASCH3),
Anal. Calc. for C22H22N4OS2Cl2: C, 57.26; H, 4.77; N, 12.15. Found: C,
56.87; H, 4.28; N, 11.79%.
11.48 (OH, s), 10.08 (s, CHO), 8.41 (t, 2H, J = 8.00 Hz), 8.31 (s, 1H),
8.24 (d, 1H, J = 7.83 Hz), 8.04 (d, 2H, J = 8.02 Hz), 7.19 (d, 1H,
J = 7.28 Hz), Anal. Calc. for C13H9O4N3: C, 57.56; H, 3.32; N, 15.50.
Found: C, 57.09; H, 3.47; N, 15.08%.
2.3.2.2. (E)-2-hydroxy-5-((3-nitrophenyl)diazenyl)benzaldehyde (b).
2.3.3.4. Methyl 2-((2-((E)-5-((E)-(3,4-dichlorophenyl)diazenyl)-2-
hydroxybenzylidene)amino)eth-yl)amino)cyclopent-1-enecarbod-
Yield: 91%. m.p 143 °C. IR (KBr, cmꢀ1): 3103
m
(OAH), 1662
(-N@N-, cis and trans), 1343 and
(CAO). 1H NMR d (500 MHz; CDCl3): 11.49
m(C@O),
1612
1528
m
m
(C@C), 1579 and 1486
m
ithioate (H2Ld). Yield: 68%. m.p: 187 °C. IR (KBr, cmꢀ1): 1635
m
(NO2), 1290
m
(C@N), 1577
m(N@N), 1479 (Phenol ring), 1283 m(CAO), 1107,
(s, OH), 10.10 (s, CHO), 8.43 (t, 2H, J = 7.76 Hz), 8.31 (s, 1H), 8.20
(d, 1H, J = 8.68 Hz), 8.09 (d, 2H, J = 7.82 Hz), 7.13 (d, 1H,
J = 8.17 Hz), Anal. Calc. for C13H9O4N3: C, 57.56; H, 3.32; N, 15.50.
Found: C, 57.25; H, 3.16; N, 15.19%.
839, 610. 1H NMR d (500 MHz; CDCl3): 13.48 (s, 1H, OH), 12.27
(s, 1H, NH), 8.49 (s, 1H, CH@N), 7–8 (Phenol ring), 3.86 (t, 2H,
J = 8.20 Hz), 3.75 (t, 2H, J = 8.31 Hz), 2.73 (m, 6H), 2.51 (s, ASCH3).
Anal. Calc. for C22H22N4OS2Cl2: C, 57.26; H, 4.77; N, 12.15. Found: C,
56.63; H, 4.45; N, 11.81%.
2.3.2.3. (E)-5-((2,4-dichlorophenyl)diazenyl)-2-hydroxybenzaldehyde
(c). Yield: 81%. m.p 128 °C. IR (KBr, cmꢀ1): 3086
m
(OAH), 1667
(-N@N-, cis and trans),
(CAO). 1H NMR d (500 MHz; CDCl3): 11.48 (s, OH), 10.08
m
2.3.4. General procedure for the synthesis of the complexes ([NiLa] –
[NiLd])
(C@O), 1620
m(C@C), 1577 and 1483 m
1285
m
To a solution of the appropriate (H2La-H2Ld) ligands (0.5 mmol,
0.235 g of H2La and/or H2Lb, 0.247 g of H2Lc and/or H2Ld) in cholo-
form/methanol (2:1 v/v) (30 mL), were added a solution of nickel
(II) chloride hexahydrate (0.5 mmol, 0.119 g) in methanol
(20 mL). The solutions were stirred for 30 min and then allowed
(s, CHO), 8.42 (d, 1H, J = 8.85 Hz), 8.36 (s, 1H), 8.31 (s, 1H), 8.17
(d, 1H, J = 8.48 Hz), 8.01 (d, 1H, J = 7.91 Hz), 7.21 (d, 1H,
J = 8.52 Hz), Anal. Calc. for C13H8O2N2Cl2: C, 52.88; H, 2.71; N,
9.49 Found: C, 52.21; H, 2.31; N, 9.04%.
2

S. Menati, R. Azadbakht, Hadi Amiri Rudbari et al.
Polyhedron 205 (2021) 115296
+
S-NH4
S
NH2
O
NH2
NH2
SCH3
S
SH
S
Me2SO4
20 O
HCl
NH4OH
CS2 , NH4OH
8h stir, 0 C
C
T
H2N NH2
R2
H3C
R2
O
N
N
S
NH2
NH
R1
N
N
OH
S
OH
R1
S
(a-d)
N
HN
S
(HLa-HLd)
Hcden
H
CH3
a = (R1=2-NO2, R2=H)
b = (R1=3-NO2, R2=H)
c = (R1=2-Cl, R2=4-Cl)
d = (R1=3-Cl, R2=4-Cl)
H2La = (R1=2-NO2, R2=H)
H2Lb = (R1=3-NO2, R2=H)
H2Lc = (R1=2-Cl, R2=4-Cl)
H2Ld = (R1=3-Cl, R2=4-Cl)
Scheme 1. Syntheses of the azo-dye ligands (H2La-H2Ld).
to stand at room temperature for 24 h. The resulting powders were
filtered and recrystallized from chloroform/methanol (1:1 v/v)
solution (Scheme 2).
J = 7.72 Hz), 2.64 (m, 6H), 2.61 (s, ASCH3). Anal. Calc. for C22H20N4-
OS2Cl2Ni: C, 48.03; H, 3.66; N, 10.18. Found: C, 48.15; H, 3.34; N,
10.33%.
2.3.4.1. [NiLa] complex. Yield: 67%. m.p: 267 °C. IR (KBr, cmꢀ1): 1618
2.4. X-ray crystallography
m
(C@N), 1462
m(Phenol ring), 1281 m(CAO), 489–558 m(NiAN),
413–448
m
(NiAO). 1H NMR d (500 MHz; CDCl3): 7.61 (s, 1H,
X-ray data for [NiLa] complex and [NiLc] complex were collected
CH@N), 7–7.9 (Phenol ring), 3.80 (t, 2H, J = 7.59 Hz), 3.70 (t, 2H,
J = 8.18 Hz), 2.81 (m, 6H), 2.62 (s, SCH3). Anal. Calc. for C22H21N5O3-
S2Ni: C, 53.52; H, 4.29; N, 14.19. Found: C, 53.39; H, 4.31; N,
14.25%.
at room temperature with a Bruker APEX II CCD area-detector
diffractometer using Mo Ka radiation (k = 0.71073 Å). Data collec-
tion, cell refinement, data reduction and absorption correction
were performed using multiscan methods with BRUKER software
[19]. The structures were solved by direct methods using
SIR2004 [20]. The non-hydrogen atoms were refined anisotropi-
cally by the full matrix least squares method on F2 using SHELXL
[21]. All the hydrogen (H) atoms were placed at the calculated
positions and constrained to ride on their parent atoms. Details
concerning collection and analysis are reported in Table 1.
For structure [NiLa], all obtained crystals of the compound had
low quality and also were weakly diffracting, with very broad
diffraction peaks. We collected the dataset but obtained data are
still insufficient for proper refinement. Weak data also led to a
number of additional problems. In spite of this, however, all the
non-H atoms could easily be located in the electron difference
map, and the overall shape of the molecule can be considered to
be reasonably determined.
2.3.4.2. [NiLb] complex. Yield: 58%. m.p: 242 °C. IR (KBr, cmꢀ1):
1619
(NiAN), 405–435
1H, CH@N), 7–7.9 (Phenol ring), 3.69 (t, 2H, J = 8.55 Hz), 3.61 (t,
2H, J = 8.41 Hz), 2.49 (m, 6H), 2.53 (s, -SCH3), Anal. Calc. for C22H21
m
(C@N), 1458
m(Phenol ring), 1280 m(CAO), 496–564 m
m
(NiAO). 1H NMR d (500 MHz; CDCl3): 8.02 (s,
-
N5O3S2Ni: C, 53.52; H, 4.29; N, 14.19. Found: C, 53.18; H, 4.17; N,
13.93%.
2.3.4.3. [NiLc] complex. Yield: 70%. m.p: 241 °C. IR (KBr, cmꢀ1): 1621
m
(C@N), 1473
m(Phenol ring), 1278 m(CAO), 496–564 m(NiAN),
415–435
m
(NiAO). 1H NMR d (500 MHz; CDCl3): 7.98 (s, 1H,
CH@N), 7–7.9 (Phenol ring), 3.76 (t, 2H, J = 8.01 Hz), 3.55 (t, 2H,
J = 7.78 Hz), 2.65 (m, 6H), 2.62 (s, ASCH3), 2.43 (q, ACH2,
J = 8.24 Hz), 1.54 (t, ACH3, J = 8.45 Hz). Anal. Calc. for C22H20N4OS2-
Cl2Ni: C, 48.03; H, 3.66; N, 10.18. Found: C, 47.81; H, 3.72; N,
10.49%.
3. Results and discussion
3.1. Synthesis
2.3.4.4. [NiLd] complex. Yield: 80%. m.p: 276 °C. IR (KBr, cmꢀ1):
1626
(NiAN), 438
m
(C@N), 1469
m
(Phenol ring), 1271
m
(CAO), 496–564
m
The azo-Schiff base ligands were prepared by direct reaction of
the azo-aldehydes (a-d) and Hcden in methanol. The infrared spec-
trum of the azo-Schiff base ligands exhibited a strong band at
m
(NiAO). 1H NMR d (500 MHz; CDCl3): 7.67 (s, 1H,
CH@N), 7–7.9 (Phenol ring), 3.65 (t, 2H, J = 7.41 Hz), 3.26 (t, 2H,
R2
R2
H3C
H3C
N
N
S
S
R1
R1
N
OH
N
N
O
N
S
S
Ni
+NiCl2.6H2O
HN
N
H
H
(H2La-H2Ld)
([NiLa] - [NiLd])
Scheme 2. General procedure for syntheses of Ni(II) complexes (([NiLa] – [NiLd])).
3

S. Menati, R. Azadbakht, Hadi Amiri Rudbari et al.
Polyhedron 205 (2021) 115296
Table 1
a fragment derived from the 2-((methylimino)methyl)phenolate
and another one derived from the 2-aminocyclopentenedithiocar-
boxylate methyl ester. The complexes have an ethylenic diimine
chain. The structures of complexes are depicted in Fig. 1. The anal-
ysis of the bond length within the metallocyclic part of the mole-
cule is indicative of a strong delocalization of the p-electron
density through the six member rings. For the cyclopentene frag-
ments of the [NiLa] and [NiLc] complexes, the mean value for the
S1AC1 bond lengths are 1.702(7) and 1.703(8)Å, respectively,
which is considerably lower than what is usually found for a single
SACsp3 bond, 1.808(10) Å, and similar to the 1.712(17) Å attributed
to the SACsp2 bond in thiophene, showing a high delocalization of
the p-electron density in this part of the molecules [22]; in addi-
tion, the distances found between the C3-C4 carbon atoms of the
cyclopentene rings of the [NiLa] and [NiLc] complexes have a mean
value 1.427(7) and 1.433(6) Å, respectively, that is similar to the
mean value for the Csp2ACsp2 bond in conjugated systems [22].
Finally, the similarity of the N1AC4 and N2AC7 bond length values
is indicative that this fragment coordinates in a Schiff base mode.
This electronic delocalization was reported for complexes contain-
ing this type of ligand with other metals [23,24] and for complexes
of related ligands [25,26]. The complexes show a square planar
geometry but with different degrees of tetrahedral distortion.
The degree of the distortion will be quantified by measuring the
dihedral angle, h, between planes formed by the N/Cu/O and N/
Cu/S atoms of the two semi-coordination spheres.
Crystal and structure data for the nickel complexes for [NiLa] and [NiLc].
Complex
[NiLa]
[NiLc]
Formula
C
46H42N10Ni2O7S4S2 C22H20Cl2N4NiOS2
Formula weight
Temperature/K
Wavelength k/Å
Crystal system
Space Group
a/Å
1092.55
298(2)
0.71073
Monoclinic
C2/c
18.0096(13)
8.4055(6)
32.631(2)
91.18(4)
4938.6(6)
4
1.469
1.248–29.721°
2256
566.15
298(2)
0.71073
Monoclinic
P21/c
13.5298(4)
23.1664(7)
7.7186(2)
96.172(2)
2405.27(12)
4
1.563
1.514–30.852
1160
b/Å
c/Å
b/°
Volume/Å3
Z
Density (calc.)/g cmꢀ1
h ranges for data collection
F(000)
Absorption coefficient
Index ranges
0.992
1.230
ꢀ24 ꢁ h ꢁ 24
ꢀ11 ꢁ k ꢁ 11
ꢀ45 ꢁ l ꢁ 45
36,025/6940
[R(int) = 0.0952]
6940/2/311
1.513
0.1433, 0.4189
0.2269, 0.4565
1.889 and ꢀ1.143
ꢀ19 ꢁ h ꢁ 19
ꢀ33 ꢁ k ꢁ 33
ꢀ11 ꢁ l ꢁ 10
55,183/7415
[R(int) = 0.0574]
7415/0/301
1.175
0.0752, 0.2266
0.1387, 0.2951
2.501 and ꢀ0.871
Reflections collected/unique
Data/restraints/parameters
Goodness-of-fit on F2a
R1/wR2 [I > 2
R1/wR2 (all data)b
Max./min. )
(e. Åꢀ3
r
(I)]b
c
D
q
P
Goodness-of-fit = [ [w(F2o – F2c)2]/(n – p)]1/2
.
a
b
c
P
P
P
P
R1 = [ (||Fo| – |Fc||)/ |Fo|]; wR2 = [ [w(F2o – Fc2)2]/ [w(Fo2)2]]1/2
.
Largest difference peak and hole.
3.2.1. [NiLa]
The ORTEP representation of the structure of [NiLa] complex,
including the atom numbering scheme is shown in Fig. 1. Selected
bond lengths and angles are given in Table 2. The crystal structure
determination revealed the existence of two independent mole-
cules in the asymmetric unit. The complex has tetrahedral distor-
tion relative to the square-planar geometry. The [NiLa] complex
presents a dihedral angle of 2.58(17). The geometry around the
coordination center is more planar than that in the homologous
N2S2 complex. The main bond lengths for the complexes studied
as well as for the homologous compounds with a symilar coordina-
tion sphere, are shown in Table 3. The bond lengths are within the
expected range for Nickel (II) complexes with Schiff base ligands
[27]. [Ni(cden)] that presents a dihedral angle of about 20 Å [27].
On the other hand, the analogous N2O2 [Ni(napen)] seems to be
more planar with h = 8Å [28]. The minimum distance between
the copper atoms is 3.661Aꢀwhich rules out the existence of an
interaction between them. The sum of the angles subtended by
the donor atoms at Ni(II) for [NiLa] is 360.10°. The plane containing
S1, N1, N2, O1 has r.m.s. values of 0.03803 Å. The nickel atom for
[NiLa] is close to co-planarity, being only 0.004 Å out of the plane
containing S1, N1, N2, O1.
about 1633 cmꢀ1, corresponding to the imine stretching vibration,
while there were no bands that could be attributed to the carbonyl
and primary amine groups, indicating that condensation of the
amine with the aldehyde, to form the azo-Schiff base ligands, has
completely occurred. FTIR spectrum of ligands did not show the
stretching frequency of phenolic (OAH) because of its involvement
in hydrogen bonding (Intra-ligand hydrogen bond) with lone elec-
tron pair of azo-Schiff base nitrogen atom (OAH. . .. . .N). The nickel
complexes were synthesized by direct reaction between azo-Schiff
base ligands with nickel(II) chloride hexahydrate in methanol.
The stretching frequency of azo-Schiff base in metal complexes
shifted to lower frequencies (10–12 cmꢀ1) compared with free
ligands. This confirms the participation of this group in coordina-
tion with metal ions. The stretching frequency of phenolic (CAO)
bond has been shifted by 14–20 cmꢀ1 to lower wave numbers in
spectra of prepared complexes. This also indicated the participa-
tion of phenolic oxygen atom in coordination with nickel ions after
losing its proton. New vibration bands have been noticed in spectra
of prepared complexes at wave number ranges 564–572 cmꢀ1 and
433–439 cmꢀ1 assigned to
respectively.
t(MAO) and t(MAN) vibrations,
3.2.2. [NiLc]
The NMR data are in agreement with the structures of the azo-
aldehydes. In the 1H NMR spectrum of azo-aldehydes, the presence
of the peaks related to imine protons at 8.39, 8.57, 8.45 and
8.49 ppm for a, b, c and d, respectively, and the related peaks to
other groups at the appropriate values are exactly matched with
the structure of the azo-aldehydes.
The molecular diagram of the complex, together with the atom
numbering scheme is depicted in Fig. 1. Selected bond lengths and
angles are given in Table 2. The molecular structure revealed that
the geometry around the coordination center is a square planar
one with a tetrahedral distortion. The dihedral angle is 3.80 (25),
higher than that observed for [NiLa]. The sum of the angles sub-
tended by the donor atoms at Ni(II) for [NiLc] is 360.14°. The plane
containing S1, N1, N2, O1 has r.m.s. values of 0.04803 Å. The nickel
atom for [NiLc] is close to co-planarity, being only 0.008 Å out of
the plane containing S1, N1, N2, O1.
3.2. Structures of the complexes
The X-ray structure determinations confirmed that the com-
plexes show the expected molecular structure. For complexes
[NiLa] and [NiLc], the Ni(II) is bonded to the two imine nitrogen
atoms, to the sulfur atom from the methyl dithiocarboxylate resi-
due and to the phenolic oxygen atom of the ligand, assuming a
cis configuration. The ligands are Schiff bases that are formed with
3.3. IR spectra
In the IR spectra of Ni(II) complexes, strong bands around 1618–
26 cmꢀ1 were observed, which assigned to the
m(C@N) band [33],
4

S. Menati, R. Azadbakht, Hadi Amiri Rudbari et al.
Polyhedron 205 (2021) 115296
(a) [NiLa]
(b) [NiLc]
Fig. 1. ORTEP representation of (a) [NiLa] and (b) [NiLc]. Displacement ellipsoids are drawn at the 30% probability level and H atoms are shown as small spheres of arbitrary
radii.
and the bands at 1230–1296 cmꢀ1 range are attributed to the phe-
Table 2
Selected bond distance (Å) and bond angles (°) for [NiLa] and [NiLc] and related
nolic (CAO) group vibrations [34,35]. The vibrations of C@S were in
complexes.
the region of 1440–1496 cmꢀ1 [36]. The bands in the range 700–
800 cmꢀ1 belongs to stretching vibrations of (CAS) and the bands
[NiLa]
[NiLc]
between 1103 and 1190 cmꢀ1 are due to the coupling of
(CAS) + (CAN) [37–39]. These data were compared with the
related ligands, indicate that the (C@N), (CAO) and (C@S) bands
m
Ni1AO1
Ni1AS1
Ni1AN1
Ni1AN2
N2AC7
N1AC4
O1AC19
S1AC1
O1ANi1AS1
N1ANi1AS1
N1ANi1AN2
O1ANi1AN2
O1ANi1AN1
S1ANi1AN2
1.854(8)
2.147(4)
1.864(9)
1.899(10)
1.288(14)
1.305(15)
1.330(13)
1.704(11)
81.6(3)
97.8(3)
86.7(4)
93.9(4)
178.1(4)
175.1(3)
1.851(4)
2.1577(17)
1.867(5)
1.880(5)
1.283(7)
1.318(7)
1.302(6)
1.716(6)
82.12(13)
98.21(15)
86.4(2)
m
m
m
m
are shifted to lower energy. These results show that Ni(II) ion is
coordinated through the nitrogen atoms of the imine group, oxy-
gen atom of the phenolic group and sulfur of the (C@S) group for
Ni(II) complexes.
3.4. 1H NMR spectra
93.39(19)
177.6(2)
174.46(15)
The 1H NMR spectra of the ligand (H2La-H2Ld) and the nickel
complex are mentioned in the experimental section. The resonance
Table 3
Selected geometric parameters for some nickel (II) complexes with Schiff base ligands.
Complex
NiAN
NiAO
NiAS
SAC
OAC
Reference
[Ni(cd5Clsalen)]
[Ni(cdsalen)]
[Ni(cd2en)]
[Ni(salen)]
[Ni(cdMeOsalen)]
[Ni(cdnapen)]
[Ni(cdsalpd)]
[Ni(t-salpd)]
[NiLa]
1.872 (10), 1.875(9)
1.872(5), 1.867(5)
1.893(6), 1.902(11)
1.853(2), 1.843(2)
1.867(4),1.871(3)
1.863(3), 1.856(3)
1.904.1(2), 1.930(2)
1.909(2), 1.916)
1.867(8)
1.860(4)
2.166(3)
2.163(3)
2.174(4), 2.170(2)
1.714(11)
1.725(6)
1.307(14)
1.311(7)
[29]
[30]
[29]
[29]
[30]
[30]
[31]
[32]
1.850(2), 1.855(2)
1.863(3)
1.853(2)
2.155(12)
2.156(2)
2.187.1(1)
2.1454(8), 2.1733(80)
2.147(4)
1.709(5)
1.707(7)
1.736(2)
1.708(3), 1.731(3)
1.704(11)
1.716(6)
1.297(5)
1.308(4)
1.312(2)
1.887(2)
1.864(9), 1.899(10)
1.867(5), 1.880(5)
1.854(8)
1.851(4)
1.330(13)
1.302(6)
This work
This work
[NiLc]
2.1577(17)
5

S. Menati, R. Azadbakht, Hadi Amiri Rudbari et al.
Polyhedron 205 (2021) 115296
Table 4
Appendix A. Supplementary data
UV–Vis spectral date of the ligands and Ni(II) complexes.
compound
(MLCT)
(n ?
p*)
(
p
?
p*)
CCDC 2046105 and 2046106 contains the supplementary crystallo-
graphic data for [NiLa] and [NiLc] complexes, respectively. These
data can be obtained free of charge via http://www.ccdc.cam.ac.
uk/conts/retrieving.html, or from the Cambridge Crystallographic
Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44)
1223-336-033; or e-mail: deposit@ccdc.cam.ac.uk. Supplementary
data to this article can be found online at https://doi.org/10.1016/j.
poly.2021.115296.
H2La
H2Lb
H2Lc
H2Ld
[NiLa]
[NiLb]
[NiLc]
[NiLd]
398
400
395
394
305
320
350
288
266
272
280
274
273
275
264
262
375
385
420
438
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Declaration of Competing Interest
The authors declare that they have no known competing finan-
cial interests or personal relationships that could have appeared
to influence the work reported in this paper.
6