Synthesis, characterization, and electrochemical study of some novel, azo-containing Schiff bases and their Ni(II) complexes

Article abstract of DOI:10.1016/j.dyepig.2013.04.009

Five novel azo-azomethine ligands with NN'OS coordination spheres were prepared by reaction of methyl-2-{N-(2′-aminoethane)}-amino-1- cyclopentenedithiocarboxylate (Hcden) with (E)-2-hydroxy-5-(phenyldiazenyl) benzaldehyde and its substituted derivatives

Full text of DOI:10.1016/j.dyepig.2013.04.009

Accepted Manuscript
Synthesis, characterization, and electrochemical study of some novel, azo-containing
Schiff bases and their Ni(II) complexes
Saeid. Menati, Azadeh Azadbakht, Reza Azadbakht, Abbas Taeb, Ali Kakanejadifard
PII:
S0143-7208(13)00136-8
10.1016/j.dyepig.2013.04.009
DYPI 3908
DOI:
Reference:
To appear in: Dyes and Pigments
Received Date: 3 December 2012
Revised Date: 31 March 2013
Accepted Date: 5 April 2013
Please cite this article as: Menati S, Azadbakht A, Azadbakht R, Taeb A, Kakanejadifard A, Synthesis,
characterization, and electrochemical study of some novel, azo-containing Schiff bases and their Ni(II)
complexes, Dyes and Pigments (2013), doi: 10.1016/j.dyepig.2013.04.009.
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ACCEPTED MANUSCRIPT
Synthesis, characterization, and electrochemical study of some novel, azo-
containing Schiff bases and their Ni(II) complexes
Saeid.Menatia,*, Azadeh Azadbakhta, Reza Azadbakhtb Abbas Taebc, Ali Kakanejadifardd
aDepartment of Chemistry, Khorramabad Branch, Islamic Azad University, Khorramabad, Iran
bDepartment of chemistry, Payame Noor Universtiy, PO BOX 19395-3697 Tehran, Iran
cDepartment of Chemistry, Science and Research Branch, Islamic Azad University, Tehran, Iran
dDepartment of Chemistry, University of Lorestan, Lorestan, Iran
Five novel azo-azomethine ligands with NN'OS coordination spheres were prepared
and then the corresponding nickel(II) complexes were synthesized.The crystal structure
analysis of nickel(II) complexes by using X-ray crystallography confirmed the
complexes are slightly distorted square-planar structures.

ACCEPTED MANUSCRIPT
Synthesis, characterization, and electrochemical study of some novel,
azo-containing Schiff bases and their Ni(II) complexes
Saeid.Menatia,*, Azadeh Azadbakhta, Reza Azadbakhtb, Abbas Taebc, Ali Kakanejadifardd
aDepartment of Chemistry, Khorramabad Branch, Islamic Azad University, Khorramabad, Iran
bDepartment of chemistry, Payame Noor Universtiy, PO BOX 19395-3697 Tehran, Iran
cDepartment of Chemistry, Science and Research Branch, Islamic Azad University, Tehran, Iran
dDepartment of Chemistry, University of Lorestan, Lorestan, Iran
Abstract
Five novel azo-azomethine ligands with NN'OS coordination spheres were prepared by
reaction of methyl-2-{N-(2'-aminoethane)}-amino-1-cyclopentenedithiocarboxylate (Hcden) with
(E)-2-hydroxy-5-(phenyldiazenyl)benzaldehyde and its substituted derivatives and then the
corresponding nickel(II) complexes were synthesized. The structures of ligands and the
1
complexes were characterized by elemental analyses, IR, UV-Vis, HNMR spectroscopy and
cyclic voltammetry. The structures of (methyl 2-(2-((E)-2-hydroxy-5-((E)-p-tolyldiazenyl)benzyli
deneamino)ethylamino)cyclopent-1-enecarbodithioato)nickel(II) and (methyl 2-(2-((E)-5-((E)-(4-
chlorophenyl)diazenyl)-2-hydroxybenzylideneamino)ethylamino)cyclopent-1-enecarbodithioato)-
nickel(II) have been determined by X-ray crystallography. The X-ray results confirm that the
geometry of the complexes are slightly distorted square-planar structures. The nickel(II) ions
coordinate to two nitrogen atoms from the imine moiety of the ligand, a sulfur atom from the
methyl dithiocarboxylate moiety and a phenolic oxygen atom.
*Corresponding author: Saeid.Menati, Tel: +98 661 6200460
E-mail: saiedmenati@gmail.com
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Keyword: Schiff base complexes; Azo dyes; Azo-azomethine compounds; X-ray crystal structure
; Nickel(II) complexes: Asymmetry Schiff bases.
1. Introduction
Azo compounds are the oldest and largest class of industrial synthesized organic dyes due to
their versatile application in various fields, such as biomedical studies, advanced application in
organic synthesis, dyeing textile fibers and high technology areas such as electro-optical devices,
liquid crystalline displays, laser and ink-jet printers[1-3]. The great majority of azo dyes are
monoazo compounds, which have the common structure unit of the azo chromophore, -N=N-,
linking two aromatic systems. The textile industry is the largest consumer of dyestuffs. Although
some azo dyes have been reported to be toxic, dozens of additional monoazo dyes are permitted in
drugs and cosmetics [4]. The oxidation-reduction behaviours of these compounds play an
important role in its biological activity [5]. The pharmaceutical importance of compounds
including an arylazo group has been extensively reported in the literature [6,7].
Schiff bases are an important class of ligands in coordination chemistry and find extensive
applications in different fields. There is a continuing interest in transition metal complexes of
asymmetrical Schiff bases because of the presence of soft sulphur, hard nitrogen and oxygen
donor atoms in the backbones of these ligands. Some of these complexes exhibit interesting
physical and chemical properties [8] and potentially useful biological activities [9]. Also, these
transition metal complexes are used in analytical fields [10] and as model molecules for biological
oxygen carrier systems [11]. Tetradentate Schiff base complexes are well known to form stable
complexes, where the coordination takes place through the NN'OS donor set [12]. The number of
the Schiff bases derived from condensation of various aldehyds with methyl-2-{N-(2'-
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aminoethane)}-amino-1-cyclopentenedithiocarboxylate (Hcden) and their transition metal
complexes with Ni(II) have been reported in the literature [13-17].
We reported herein the syntheses and structural characterization of some novel, azo-
containing Schiff bases derivatives ligands (H2L) [(6a=methyl 2-(2-((E)-2-hydroxy-5-((E)-
phenyldiazenyl)benzylideneamino)ethylamino)cyclopent-1-enecarbodithioate); (6b=methyl 2-(2-
((E)-2-hydroxy-5-((E)-p-tolyldiazenyl)benzylideneamino)ethylamino)cyclopent-1-enecarbodithio-
ate); (6c=methyl 2-(2-((E)-5-((E)-(4-ethylphenyl)diazenyl)-2-hydroxybenzylideneamino)ethylam-
ino)cyclopent-1-enecarbodithioate); (6d=methyl 2-(2-((E)-5-((E)-(4-chlorophenyl)diazenyl)-2-hy-
droxybenzylidenamino)ethylamino)cyclopent-1-enecarbodithioate); (6e=methyl 2-(2-((E)-5-((E)-
(4-nitrophenyl)diazenyl)-2-hydroxybenzylidenamino)ethylamino)cyclopent-1-enecarbodithioate);
1
(Scheme 1) and their nickel(II) complexes (Scheme 2). Elemental analyses, IR, UV-Vis HNMR
spectra and cyclic voltammetry were obtained to determine the structure of the ligands derived
from condensation of azo-containing aldehyde with Hcden and their complexes with Nickel(II). In
addition the complexes 7b= (methyl 2-(2-((E)-2-hydroxy-5-((E)-p-tolyldiazenyl)benzylideneami-
no)ethylamino)cyclopent-1-enecarbodithioato)nickel(II) and 7d= (methyl 2-(2-((E)-5-((E)-(4-chl-
orophenyl)-diazenyl)-2-hydroxybenzylideneamino)ethylamino)cyclopent-1-enecarbodithioato)ni-
ckel(II) were characterized in the solid state by X-ray diffractometry in order to elucidate their
molecular and crystal structures and to evaluate their degree of tetrahedral distortion to the square
planar geometry.
2. Experimental
2.1. Reagents and solvents
All solvents were purchased commercially. 1,2-ethylendiamine, aniline, 4-chloroaniline, 4-
nitroaniline, 4-methylanilin, 4-ethylanilin, sodium carbonate, sodium nitrite, carbon disulfide,
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cyclopentanone, dimethylsulfate, nickel(II) chloride hexahydrate and salicylaldehyde were
obtained from Merck and were used without further purification.
2.2. Instrumentation
Elemental analyses (C, H and N) were measured with a Termo Fininngan-Flash 1200
analyzer and UV-Vis measurements were recorded on a Jenus 5606 UV-Vis spectrophotometer.
The NMR spectra were obtained in a Brucker Avance DPZ-500 MHz spectrometer. IR spectra
were recorded by Perkin Elmer RX1 FT-IR infrared spectrophotometer. Electrochemical
experiments were performed using an Autolab modular electrochemical system (Eco Chem.
Utrecht, The Netherlands) equipped with PSTA 20 model and driven by GPES software (Eco
Chem.). A conventional three-electrode cell was used with a saturated Ag|AgCl as reference
electrode, a Pt wire as counter electrode and a modified carbon paste as working electrode. All
experiments were carried out at ambient temperature of 20 ± 1 °C. A Metrohm pH-meter (model
691) was also applied for the pH measurements
2.3. Synthesis
2.3.1. Synthesis of methyl-2-{N-(2-aminoethane)}-amino-1-cyclopentenedithiocarboxylate(Hcden)
Hcden was prepared by published method [18,19].
2.3.2. Preparation of Azo compounds (4a-e).
Azo dyes (4a-e) were synthesized according to the well-known literature procedure [20]. A
mixture of aniline (10 mmol) or its derivatives in hydrochloric acid (36 mL), and water (16 mL)
were heated to 70 ˚C. The clear solutions were poured into an ice-water mixture, and were
diazotized between 0 ˚C and 5 ˚C with sodium nitrite (10 mmol) dissolved in water (5 mL). The
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cold diazo solutions were added to a solution of salicylaldehyde (10 mmol) in water (19 mL)
containing sodium hydroxide (10 mmol) and sodium carbonate (40 mmol) during the period of 30
min at 0 ˚C. during the adding process, the diazo solutions were vigorously stirred. The products
were collected by filtration and washed with 100 mL of NaCl solution (10%) under vacuum.
Then, the solids were dried under vacuum at 80 ˚C overnight. The purity of the compounds were
controlled by TLC (n-hexane:ethylacetate/60:40).
2.3.2.1 (E)-2-hydroxy-5-(phenyldiazenyl)benzaldehyde (4a)
Yield: 91%. m.p 120 ˚C. IR (KBr, cm-1): 3200 ν(O-H)ꢀ 1667 ν(C=O)ꢀ 1620 ν(C=C)ꢀ 1569 and
1478 ν(-N=N-, cis and trans)ꢀ 1285 ν(C-O)ꢀ 1171, 1106, 849, 764. 1H NMR δ (500MHz; CDCl3):
11.36 (OH, s), 10.05 (s, CHO), 8.23 (d, 1H, J=8.87 Hz), 8.21 (d, 1H, J=7.91 Hz), 7.93 (d, 1H,
J=7.58 Hz), 7.92 (d, 1H, J=7.01 Hz), 7.55 (t, 2H, J=8.00 Hz), 7.51 (t, 1H, J=7.78 Hz), 7.15 (d,
1H, J=8.80 Hz). Anal. Calc. for C13H10O2N2: C, 69.02; H, 4.42; N, 12.39. Found: C, 69.24; H,
4.71; N, 11.99%
2.3.2.2 (E)-2-hydroxy-5-(paratolyldiazenyl)benzaldehyde (4b)
Yield: 75%. m.p 150 ˚C . IR (KBr, cm-1): 3182 ν(O-H)ꢀ 1656 ν(C=O)ꢀ 1619 ν(C=C)ꢀ 1573
1
and 1479 ν(-N=N-, cis and trans)ꢀ 1278 ν(C-O)ꢀ 1171, 1106, 849, 764. H NMR δ (500MHz;
CDCl3): 11.33 (s, OH), 10.03 (s, CHO), 8.19 (s, 1H), 8.17 (d, 1H, J=8.68 Hz), 7.83 (d, 2H, J=8.22
Hz), 7.35 (d, 2H, J=8.12 Hz), 7.13 (d, 1H, J=8.52 Hz), 2.46 (s, CH3). Anal. Calc. for C14H12O2N2:
C, 73.13; H, 4.48; N, 10.45. Found: C, 72.55; H, 4.86; N, 10.73%.
2.3.2.3 (E)-5-((4-ethylpheny)ldiazenyl)-2-hydroxybenzaldehyde (4c)
Yield: 60%. m.p 90 ˚C . IR (KBr, cm-1): 3036 ν(O-H)ꢀ 1651 ν(C=O)ꢀ 1622 ν(C=C)ꢀ 1578 and
1478 ν(-N=N-, cis and trans)ꢀ 1275 ν(C-O)ꢀ 1171, 1106, 849, 764. 1H NMR δ (500MHz; CDCl3):
11.33 (s, OH), 10.02 (s, CHO), 8.19 (s, 1H), 8.17 (d, 1H, J=8.48 Hz), 7.85 (d, 2H, J=8.24 Hz),
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7.36 (d, 2H, J=8.21 Hz), 7.13 (d, 1H, J=8.52 Hz), 2.76 (q, CH2, J=7.59 Hz). 1.32 (t, CH3, J=7.60
Hz). Anal. Calc. for C15H14O2N2: C, 73.94; H, 4.93; N, 9.86 Found: C, 74.21; H, 5.28; N, 9.64%.
2.3.2.4 (E)-5-((4-chloropheny)ldiazenyl)-2-hydroxybenzaldehyde (4d)
Yield: 80%. m.p 204 ˚C . IR (KBr, cm-1): 3208 ν(O-H)ꢀ 1633 ν(C=O)ꢀ 1613 ν(C=C)ꢀ 1581
1
and 1479 ν(-N=N-, cis and trans)ꢀ 1283 ν(C-O)ꢀ 1171, 1106, 849, 764. H NMR δ (500MHz;
CDCl3): 11.38 (s, OH), 10.06 (s, CHO), 8.22 (s, 1H), 8.19 (d, 1H, J=9.00 Hz), 7.87 (d, 2H, J=8.73
Hz), 7.51 (d, 2H, J=8.72 Hz), 7.15 (d, 1H, J=8.88 Hz). Anal. Calc. for C13H9O2N2: C, 72.51; H,
3.59; N, 11.16. Found: C, 72.85; H, 3.21; N, 11.33%.
2.3.2.5 (E)-2-hydroxy-5-((4-nitrophenyl)diazenylbenzaldehyde (4e)
Yield: 90%. m.p 184 ˚C . IR (KBr, cm-1): 3103 ν(O-H)ꢀ 1657 ν(C=O)ꢀ 1620 ν(C=C)ꢀ 1577
and 1478 ν(-N=N-, cis and trans)ꢀ 1342 ν(NO2)ꢀ 1284 ν(C-O), 1171, 1106, 849, 764. 1H NMR δ
(500MHz; CDCl3): 11.48 (s, OH), 10.08 (s, CHO), 8.41 (d, 2H, J=9.00 Hz), 8.31 (s, 1H), 8.24 (d,
1H, J=8.95 Hz), 8.04 (d, 2H, J=8.97 Hz), 7.19 (d, 1H, J=8.94 Hz). Anal. Calc. for C13H9O4N3: C,
57.56; H, 3.32; N, 15.50. Found: C, 57.28; H, 3.67; N, 15.18%.
2.3.3 Synthesis of azo-containing Schiff bases(6a-e)
Schiff bases (6a-e) were prepared by addition of (4a-e) compounds (1 mmol) in methanol (10
mL) to a methanolic solution of Hcden (1 mmol). The mixtures were stirred for about 30 min and
allowed to react at room temperature for about 24 h. The colour powders were recrystallized from
chloroform/methanol (1:1) v/v solution.
2.3.3.1. Methyl 2-(2-((E)-2-hydroxy-5-((E)-phenyldiazenyl)benzyledeneamino)ethyleamino)cyclo-
pent-1-ene-carbodithioate (6a)
Yield: 93%. m.p: 145 ˚C. IR (KBr, cm-1): 1628 ν(C=N), 1587 ν(N=N), 1479 (Phenol ring),
1
1272 ν(C-O), 1109, 841, 603. H NMR δ (500 MHz; CDCl3): 13.42 (s, 1H, OH), 12.40 (s, 1H,
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NH), 8.51 (s, 1H, CH=N), 7-7.9 (Phenol ring), 3.85 (t, 2H, J=8.23 Hz), 3.73 (t, 2H, J=8.18 Hz),
2.73 (m, 6H), 2.53 (s, -SCH3). Anal. Calc. for C22H24N4OS2: C, 62.23; H, 5.69; N, 13.19. Found:
C, 62.34; H, 5.37; N, 13.29 %.
2.3.3.2. Methyl 2-(2-((E)-2-hydroxy-5-((E)-para-tolyldiazenyl)benzyledeneamino)ethyleamino)cy-
clopent-1-ene-carbodithioate (6b)
Yield: 70%. m.p: 170 ˚C. IR (KBr, cm-1): 1630 ν(C=N), 1584 ν(N=N), 1486 (Phenol ring),
1
1270 ν(C-O), 1107, 844, 601. H NMR δ (500 MHz; CDCl3): 13.39 (s, 1H, OH), 12.40 (s, 1H,
NH), 8.51 (s, 1H, CH=N), 7-7.9 (Phenol ring), 3.87 (t, 2H, J=8.19 Hz), 3.76 (t, 2H, J=8.16 Hz),
2.73 (m, 6H), 2.56 (s, -SCH3), 2.43 (s, -CH3). Anal. Calc. for C23H26N4OS2: C, 62.97; H, 5.97; N,
12.77. Found: C, 62.69; H, 5.81; N, 12.67 %.
2.3.3.2. Methyl 2-(2-((E)-5-((E)-(4-ethylphenyl)diazenyl)-2-hydroxybenzylideneamino)ethylam-
ino)cyclopent-1-enecarbodithioate (6c)
Yield: 74%. m.p: 150 ˚C. IR (KBr, cm-1): 1633 ν(C=N), 1582 ν(N=N), 1485 (Phenol ring),
1
1285 ν(C-O), 1106, 845, 602. H NMR δ (500 MHz; CDCl3): 13.46 (s, 1H, OH), 12.35 (s, 1H,
NH), 8.49 (s, 1H, CH=N), 7-7.9 (Phenol ring), 3.86 (t, 2H, J=8.20 Hz), 3.75 (t, 2H, J=8.31 Hz),
2.73 (m, 6H), 2.52 (s, -SCH3), 2.47 (q, -CH2, J=7.64 Hz), 1.53 (t, -CH3, J=7.79 Hz). Anal. Calc.
for C24H28N4OS2: C, 63.67; H, 6.23; N, 12.38. Found: C, 63.70; H, 6.20; N, 12.48 %.
2.3.3.4. Methyl 2-(2-((E)-5-((E)-(4-chlorophenyl)diazenyl)-2-hydroxybenzylideneamino)ethylam-
ino)cyclopent-1-enecarbodithioate (6d)
Yield: 68%. m.p: 187 ˚C. IR (KBr, cm-1): 1633 ν(C=N), 1581 ν(N=N), 1479 (Phenol ring),
1
1283 ν(C-O), 1107, 842, 601. H NMR δ (500 MHz; CDCl3): 13.46 (s, 1H, OH), 12.35 (s, 1H,
NH), 8.49 (s, 1H, CH=N), 7-7.9 (Phenol ring), 3.86 (t, 2H, J=6.82 Hz), 3.75 (t, 2H, J=7.50 Hz),
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2.73 (m, 6H), 2.52 (s, -SCH3). Anal. Calc. for C22H23N4OS2Cl: C, 57.43; H, 5.03; N, 12.18.
Found: C, 57.30; H, 5.21; N, 12.07 %.
2.3.3.5. Methyl 2-(2-((E)-5-((E)-(4-nitrophenyl)diazenyl)-2-hydroxybenzylideneamino)ethylamin-
o)cyclopent-1-enecarbodithioate (6e)
Yield: 75%. m.p: 219 ˚C. IR (KBr, cm-1): 1633 ν(C=N), 1584 ν(N=N), 1484 (Phenol ring),
1
1336 ν(NO2), 1261 ν(C-O), 1102, 852, 603. H NMR δ (500 MHz; CDCl3): 13.47 (s, 1H, OH),
12.45 (s, 1H, NH), 8.56 (s, 1H, CH=N), 7-7.9 (Phenol ring), 3.84 (t, 2H, J=7.19 Hz), 3.72 (t, 2H,
J=7.83 Hz), 2.73 (m, 6H), 2.53 (s, -SCH3). Anal. Calc. for C22H23N5O3S2: C, 52.21; H, 4.58; N,
14.93. Found: C, 52.34; H, 4.26; N, 14.28 %.
2.3.4. General procedure for the synthesis of the complexes(7a-e)
To a solution of the appropriate (6a-e) ligand (0.1 mmol) in choloform/methanol (2:1 v/v) (15
mL), were added a solution of nickel(II) chloride hexahydrate (0.1 mmol) in methanol (.15 mL) The
solutions were stirred for 15 min and then allowed to stand at room temperature for 24 h. The
resulting powders were filtered and recrystallized from chloroform/methanol (1:1 v/v) solution.
2.3.4.1. (Methyl 2-(2-((E)-2-hydroxy-5-((E)-phenyldiazenyl)benzyledeneamino)ethyleamino)cyclo-
pent-1-ene-carbodithioato)nickel(II) complex, (7a).
Yield: 84%. m.p: 280 ºC. IR (KBr, cm-1): 1626 ν(C=N), 1469 ν(Phenol ring), 1283 ν(C-O),
1
496-564 ν(Ni-N), 415-435 ν(Ni-O). H NMR δ (500 MHz; CDCl3): 7.71 (s, 1H, CH=N), 7-7.9
(Phenol ring), 3.72 (t, 2H, J=7.64 Hz), 3.63 (t, 2H, J=8.31 Hz), 2.83 (m, 6H), 2.63 (s, SCH3).
Anal. Calc. for C22H22N4OS2Ni: C, 54.91; H, 4.57; N, 11.65. Found: C, 55.32; H, 4.32; N,
11.25%.
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2.3.4.2. (Methyl 2-(2-((E)-2-hydroxy-5-((E)-para-tolyldiazenyl)benzyledenamino)ethyleamino)cy-
clopent-1-ene-carbodithioato)nickel(II) complex, (7b).
Yield: 49%. m.p: 274 ºC. IR (KBr, cm-1): 1616 ν(C=N), 1467 ν(Phenol ring), 1283 ν(C-O),
1
496-564 ν(Ni-N), 415-435 ν(Ni-O). H NMR δ (500 MHz; CDCl3): 7.76 (s, 1H, CH=N), 7-7.9
(Phenol ring), 3.72 (t, 2H, J=8.92 Hz), 3.66 (t, 2H, J=8.58 Hz), 2.51 (m, 6H), 2.56 (s, -SCH3),
2.43 (s, -CH3. Anal. Calc. for C23H24N4OS2Ni: C, 55.79; H, 4.85; N, 11.31. Found: C, 55.89; H,
4.51; N, 11.75%.
2.3.4.3. (Methyl 2-(2-((E)-5-((E)-(4-ethylphenyl)diazenyl)-2-hydroxybenzylideneamino)ethylam-
ino)cyclopent-1-enecarbodithioato)nickel(II) complex, (7c).
Yield: 76%. m.p: 285 ºC. IR (KBr, cm-1): 1630 ν(C=N), 1460 ν(Phenol ring), 1285 ν(C-O),
1
496-564 ν(Ni-N), 415-435 ν(Ni-O). H NMR δ (500 MHz; CDCl3): 7.87 (s, 1H, CH=N), 7-7.9
(Phenol ring), 3.81 (t, 2H, J=7.99 Hz), 3.72 (t, 2H, J=8.09 Hz), 2.69 (m, 6H), 2.62 (s, -SCH3),
2.47 (q, -CH2, J=8.66 Hz), 1.55 (t, -CH3, J=8.51 Hz). Anal. Calc. for C24H26N4OS2Ni: C, 56.61;
H, 5.11; N, 11.00. Found: C, 56.82; H, 5.24; N, 11.25%.
2.3.4.4 (Methyl 2-(2-((E)-5-((E)-4-chlorophenyl)diazenyl)-2-hydroxybenzylidenamino)ethylamino-
)ethyleamino)cyclopent-1-ene-carbodithioato)nickel(II) complex. (7d).
Yield: 75%. m.p: 293 ºC. IR (KBr, cm-1): 1628 ν(C=N), 1466 ν(Phenol ring), 1284 ν(C-O),
496-564 ν(Ni-N), 438 ν(Ni-O). 1H NMR δ (500 MHz; CDCl3): 7.59 (s, 1H, CH=N), 7-7.9 (Phenol
ring), 3.92 (t, 2H, J=7.31 Hz), 3.81 (t, 2H, J=7.94 Hz), 2.64 (m, 6H), 2.64 (s, -SCH3). Anal. Calc.
for C22H21N4OS2ClNi: C, 57.83; H, 4.60; N, 12.27. Found: C, 58.11; H, 4.35; N, 12.43%.
2.3.4.5. (Methyl 2-(2-((E)-5-((E)-(4-nitrophenyl)diazenyl)-2-hydroxybenzylideneamino)ethylamin-
o)cyclopent-1-enecarbodithioat)nickel(II) complex, (7e).
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Yield: 88%. m.p: 291 ºC. IR (KBr, cm-1): 1626 ν(C=N), 1469 ν(Phenol ring), 1333 ν(NO2),
1283 ν(C-O), 496-564 ν(Ni-N), 437 ν(Ni-O). 1H NMR δ (500 MHz; CDCl3): 7.54 (s, 1H, CH=N),
7-7.9 (Phenol ring), 3.87 (t, 2H, J=7.69 Hz), 3.70 (t, 2H, J=8.09 Hz ), 2.65 (m, 6H), 2.61 (s, -
SCH3). Anal. Calc. for C22H21N5O3S2Ni: C, 50.22; H, 3.99; N, 13.31. Found: C, 50.47; H, 4.21; N,
13.11%.
2.4. X-ray Crystallography
The X-ray diffraction studies were obtained on a STOE IPDS IIT diffractometer with graphite
monochromated Mo-Kα radiation. A dark red plate crystal (complex 7b) with a dimension of 0.27
× 0.11 × 0.05 mm and A dark red plate crystal (complex 7d) with a dimension of 0.42 × 0.08 ×
0.03 mm were mounted on a glass fiber and used for data collection. Structures determination
were obtained by least-squares refinement of diffraction data from 3047 unique reflections for
complex 7b and 4073 unique reflections for complex 7d. Data were collected at a temperature of
291(2) K to a maximum 2θ value of 51.00° and in a series of ω scans in 1° oscillations and
integrated using the Stoe X-AREA [21] software package. The numerical absorption coefficient,
ꢀ, for Mo-Kα radiation are 1.076 mm-1 (complex 7b) and 1.204 mm-1 (complex 7d). A numerical
absorption correction was applied using X-RED [22] and X-SHAPE [23] software's. The data
were corrected for Lorentz and Polarizing effects. The structure was solved by direct methods [24]
and subsequent difference Fourier map and then refined on F2 by a full-matrix procedure using
anisotropic displacement parameters. All of hydrogen atoms were positioned geometrically in
ideal positions and then after refined isotropically. Atomic factors are taken from International
Tables for X-ray Crystallography [25]. All refinements were performed using the X-STEP32
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crystallographic software package [26]. A summary of the crystal data, experimental details and
refinement results for complexes 7b and 7d are given in Table 1.
3. Results and discussion
Methyl-2-{N-(2'-aminoethane)}-amino-1-cyclopentenedithiocarbooxylate is a convenient
starting material for the synthesis of asymmetric ligands containing NNOS coordination spheres.
Schiff base condensation of the methyl-dithiocarboxylate ester with azo-substituted aldehydes
yields the desired ligand in a facile manner and with high yields.
The complexes have a sulfur donor atom that can act as a π acceptor, an oxygen donor atom
as a π donor and the coordination around the nickel ion allows for π electronic delocalization, as
depicted in Scheme 2. The compounds were characterized by elemental analysis, IR, UV-Vis and
NMR. The 7b and 7d complexes were characterized further by X-ray crystallography in order to
determine their molecular and crystal structures to evaluate the degree of tetrahedral distortion in
square planar geometry. The structures and the electrochemical results are compared with those
obtained for the corresponding symmetric N2O2 and N2S2 formulations in order to correct possible
dietary deficiencies. Also, it has been implicated as a Ni(II) complexes.
3.1. Crystal structures of 7b and 7d complexes
Selected bond distances and bond angles for 7b and 7d complexes are collected in Table 2.
The ORTEP representation of the structures of 7b and 7d complexes with atomic numbering
Scheme and their unit cell diagrams are presented in Figs. 1-4, respectively. The bond distances
and bond angles are within the expected range for nickel(II) complexes with Schiff base ligands.
7b and 7d complexes are crystalliz in the space group Pbca with eight molecules per unit cell. The
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nickel(II) ions are coordinate to a sulfur atom the methyl dithiocarboxylate moiety, phenolic
oxygen atom and two nitrogen atoms from the imine moiety of the ligands,. In these complexes,
the Ni center and its four neighbors (O(1), N(1), N(2) and S(1)) are nearly coplanar. The
deviations from the mean coordination plane are at the best 0.002 Å for the donors and equal to
0.005(4) Å for the metal ion. Tetrahedral distortion relative to the square-planar geometry are
4.05(9)˚ in 7b complex and 3.94(3)˚ in 7d complex. In these complexes, the geometry around the
coordination centre are more planar than that in the homologous N2OS complex with the dihedral
angle of 5.28˚ and 11.52˚ (for the two crystallographically independent molecules) [14],
homologous N2S2 complex with the dihedral angle of about 20˚[27-28], and analogous N2O2
complex with dihedral angle of about 7˚ [29].
3.2. IR Spectra
In the IR spectrum of Ni(ІІ) complexes a strong band around 1600-1630 cm-1 is assigned to
the ν(C=N) band [30], and the bands in the range 1230-1296 cm-1 can be related to the phenolic
(C-O) group vibrations [31-32]. The ring skeletal vibrations (C=S) were in the region of 1440-
1496 cm-1 [33]. The bands in the range 700-800 cm-1 belong to (C-S) and the bands between 1103
and 1190 cm-1 are due to the coupling of ν(C-S)+ν(C-N) [34-35]. These data compared with those
of the ligands, indicate that the ν(C=N), ν(C-O), ν(C=C), ν(C-S), and ν(C-S)+ν(C-N) bands are
shifted to lower energy. These results show that Ni(ІІ) ions are coordinated through the nitrogen
atoms of the amine group, oxygen atom of the phenolic group and sulfur of the (C-S) group for
Ni(ІІ) complexes[30-35]. These data are in accord to the proposed structures.
3.3. 1H NMR Spectra
The 1H NMR resonance of azomethine proton (CH=N) in ligands (8.49-8.56 ppm), are shifted
to higher field in the Ni(ІІ) complexes, confirming the coordination of the metal ion to that group.
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1
In the H NMR spectra of the free ligands, OH, NH, or SH exhibit single resonance at δ= 13.39-
13.46 ppm, and δ= 12.35-12.45 ppm, respectively, which disappear in the nickel(ІІ) complexes,
indicating that the OH and NH or SH groups have been deprotonated and bonded to the Ni(ІІ)
ions[36].
3.4. The electronic spectra
The UV-Vis absorption spectra of the ligands (6a-e) and related nickel complexes (7a-e) in
DMF solution at 298 K are shown in Fig. 5 and Fig. 6, respectively. The electronic spectra of the
ligands are similar to each other. The UV-Vis absorption spectra of the ligands show three bands.
The first band appearing at ca 260 nm is attributed to the π-π* transition of the benzene rings, the
second band appearing around 300-424 nm arose from a transition involving electron migration
along the entire conjugate system of the ligands. The entire conjugate system includes both the
aryl rings and azo groups. The broadness of the intramolecular CT band is quite common for azo
or azomethine dyes having a hydroxyl group in opposition to the N=N or C=N bond on the
aromatic ring [37]. The third band observed in the range 430–500 nm can be assigned to an n-π*
electronic transition of azo-aromatic chromophore [37,38].
The UV-Vis absorption spectra of the complexes were compared to the spectra of the ligands. In
all spectra of the metal complexes, the n-π* absorption bands of the free ligand has shifted to
lower frequencies upon the coordination of ligand with metal ions.
3.5. Cyclic voltammetry studies
Because the Ni-complexes(7a-e) are insoluble in water, the bulk-modified carbon paste
electrode (Ni-CPE) becomes the optimal choice to investigate their redox properties of it. Cyclic
voltammograms of the 7b complex carbon paste electrode (1-CPE) and 7d complex carbon paste
electrode (2-CPE) were carried out at room temperature.
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The modified 1-CPE and 2- CPE were fabricated as following: 10 mg of each 7b and 7d
complex, 50 mg graphite powder and proper amount of anhydrous ethanol were mixed to form a
uniform mixture, which was left to evaporate the solvent at room temperature in the air. Then 20
ml paraffin oil was added into the graphite-Ni complex mixture.
The 1-CPE and 2-CPE were packed into a piston glass tube electrode (3 mm in diameter).
Prior to the measurements the 1-CPE and 2-CPE were smoothed out on a piece of transparent
paper to get a fresh surface. All the potentials reported in this work were versus Ag|AgCl
electrode. Unmodified carbon paste electrode was prepared by adding 20 ml paraffin oil to 50 mg
graphite powder. A cyclic voltammograms of modified 1-CPE, 2-CPE were similar, therefore just
cyclic voltammogram of 1- CPE was shown.
A cyclic voltammograms of modified 1-CPE and unmodified carbon paste electrodes at scan
rate of 50mVs−1 are shown in Fig.7.
As can be seen, there is no redox peak at the surface of bare CPE in the potential range of -0.5
to 0.9V. A pair of well-defined redox peaks with formal potential of 0.18 V versus Ag|AgCl
electrode was observed when Ni-CPE was used. This anodic and cathodic peaks are due to redox
reaction of the Ni(III)/Ni(II) couple at the electrode surface. The cyclic voltammograms of Ni-
CPE electrode in 0.1 M NaOH solution at different scan rates are shown in Fig.8. The potential
was cycled between -0.4 and 0.6 mV in 0.1 M NaOH aqueous solution. The peaks current of the
voltammograms are linearly proportional to the scan rate (ν) up to 300 mV s-1 for the redox
couples (Fig. 8B). According to the following equation this results confirms a surface type
reactions [39]:
Ip = n2F2νAC/4RΓ
(1)
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4. Conclusions
In the present work five novel, azo-containing Schiff bases were obtained by condensation
reaction of methyl-2-{N-(2'-aminoethane)}-amino-1-cyclopentenedithiocarboxylate (Hcden) with
azo-containing aldehydes that are favorable to formation of the complexes with Ni(II) ion. IR,
1H NMR and UV-Vis spectra and cyclic voltammogram of the nickel(II) complexes were
recorded and compared with together. The crystal structure analysis of nickel(II) complexes by
using X-ray crystallography confirmed the complexes are slightly distorted square-planar
structures based on experimental studies.
5. Supplementary data
CCDC 836471 and 836470 are contain the supplementary crystallographic data for 7b and 7d
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.
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Table 1
Crystal and structure data for the nickel complexes
7b
7d
Formula
Formula weight
C23 H24 N4 Ni O S2
495.29
C22 H21 Cl N4 Ni O S2
515.71
Temperature /K
Wavelength λ /Å
Crystal system
Space Group
Crystal size /mm3
a /Å
291(2)
291(2)
0.71073
0.71073
orthorhombic
Pbca
orthorhombic
Pbca
0.27 x 0.11 x 0.05
22.380(5)
7.8917(16)
25.366(5)
4480.0(16)
8
0.42 x 0.08 x 0.03
22.674(3)
7.7860(7)
25.170(2)
4443.5(8)
8
b /Å
c /Å
Volume / Å3
Z
Density (calc.) /g cm-1
θ ranges for data collection
F(000)
1.469
1.542
1.82-25.25°.
2064
1.80-25.50°..
2128
Absorption coefficient
Index ranges
1.076
1.204
-26 ≤ h ≤ 24
-8 ≤ k ≤ 8
-30 ≤ l ≤ 26
7091
-27 ≤ h ≤ 26
-9 ≤ k ≤ 8
-26 ≤ l ≤ 30
11925
Data collected
Unique data (Rint)
Parameters, restrains
3047, (0.0863)
282
4073, (0.0878)
281
a
Final R1, wR2 (Obs. data)
0.0429, 0.0453
0.1531, 0.0590
0.717
0.0509, 0.0887
0.1099, 0.1033
0.878
a
Final R1, wR2 (All data)
Goodness of fit on F2 (S)
Largest diff peak and hole /e.Å-3
0.182, -0.177
0.311, -0.526
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Table 2
Selected bond distance (Å) and bond angles (˚) for 7b and 7d complexes
7b
7d
Ni1-N1
Ni1-N2
1.858(4)
1.867(4)
1.870(3)
1.868(4)
Ni1-O1
1.879(3)
2.1524(17)
173.12(17)
176.3(2)
93.16(19)
82.22(14)
97.9(2)
1.882(3)
Ni1-S1
2.1505(12)
173.64(13)
176.94(15)
93.26(14)
82.30(9)
N1-Ni1-S1
N2-Ni1-O1
N1-Ni1-O1
O1-Ni1-S1
S1-Ni1-N2
N2-Ni1-N1
97.82(13)
86.86(17)
87.0(2)
Figure Captions:
Fig. 1. Graphical representations of 7b complex with the adopted numbering scheme.
Fig. 2. Graphical representations of 7d complex with the adopted numbering scheme
Fig. 3. Stereoview of the unit cell of 7b complex.
Fig. 4. Stereoview of the unit cell of 7d complex.
Fig. 5. UV-Vis absorption spectra of the ligands (6a-e)
Fig. 6. UV-Vis absorption spectra of the complexes (7a-e)
Fig.7. Cyclic voltammetric responses of unmodified carbon paste elctrode (a) and 1-CPE (b) at scan rate
50mVs−1.
Fig.8. Cyclic voltammograms of Ni-CPE at various scan rates: 10, 25,50,75,100,150, 200,300,400,500,600
and 700 mVs-1 , respectively. (B) the variation of anodic and cathodic peak currents vs. potential scan rate.
22

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Figure 1
Figure 2
23

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Figure 3
Figure 4
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0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
6a
6C
6b
6d
6e
250
300
350
400
450
500
550
600
Figure 5
1
7a
7b
7c
7d
7e
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
250
350
450
550
Figure 6
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100
b
a
0
-100
-0.5
0.2
0.9
E vs (Ag|AgCl) / V
Figure 7
150
A
200
0
B
0
-200
0
400
800
ν / mVs-1
-150
-0.4
0.1
0.6
E vs (Ag|AgCl) / V
Figure 8
26

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Scheme 1. General syntheses of azo-containing Schiff bases (6a-e)
27

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Scheme 2. Syntheses of (7a-e) complexes.
28