X-ray crystal structural and spectral studies of copper(II) and nickel(II) complexes of functionalized bis(thiosemicarbazone) ligands and investigation of their electrochemical behavior

Article abstract of DOI:10.1016/j.ica.2018.04.053

Neutral bivalent copper and nickel bis(thiosemicarbazone) complexes bearing the methoxy and bromine substituents on the dialdehyde-backbone of the ligand have been synthesized. All of them have been characterized by spectroscopic methods and in two cases

Full text of DOI:10.1016/j.ica.2018.04.053

Accepted Manuscript
Research paper
X-ray crystal structural and spectral studies of copper(II) and nickel(II) com-
plexes of functionalized bis(thiosemicarbazone) ligands and investigation of
their electrochemical behavior
L.A. Saghatforoush, S. Hosseinpour, M.W. Bezpalko, W. Scott Kassel
PII:
S0020-1693(18)30170-1
https://doi.org/10.1016/j.ica.2018.04.053
ICA 18244
DOI:
Reference:
To appear in:
Inorganica Chimica Acta
Received Date:
Revised Date:
Accepted Date:
29 January 2018
7 April 2018
25 April 2018
Please cite this article as: L.A. Saghatforoush, S. Hosseinpour, M.W. Bezpalko, W.S. Kassel, X-ray crystal structural
and spectral studies of copper(II) and nickel(II) complexes of functionalized bis(thiosemicarbazone) ligands and
investigation of their electrochemical behavior, Inorganica Chimica Acta (2018), doi: https://doi.org/10.1016/j.ica.
2
018.04.053
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X-ray crystal structural and spectral studies of copper(II) and
nickel(II) complexes of functionalized bis(thiosemicarbazone) ligands
and investigation of their electrochemical behavior
a, *
a
b
b
L.A. Saghatforoush , S. Hosseinpour , M. W. Bezpalko , W. Scott Kassel
a
Department of Chemistry, Payame Noor University, PO Box 19395-4697, Tehran, Iran
b
Department of Chemistry, Villanova University, 800 Lancaster Avenue, Villanova, PA
1
9085, USA
1

Abstract
Neutral bivalent copper and nickel bis(thiosemicarbazone) complexes bearing the methoxy
and bromine substituents on the dialdehyde-backbone of the ligand have been synthesized.
All of them have been characterized by spectroscopic methods and in two cases by X-ray
crystallography. Upon formation of these complexes, the each two bis(thiosemicarbazone)
arms is deprotonated, acting as dianionic, tetradentate N
2
2
S ligands. The geometrical
distortion from square planar in the copper complex is very greater than the nickel complex.
Cyclic voltammetry studies of Cu(II) and Ni(II) complexes in DMF show that all complexes
are able to stabilize low oxidation states of Cu(I) and Ni(I). The introduction of different
substitutions on the aromatic ring attached to the imine carbon led to two consequences. First,
I
II
I
II
The E1/2 values for the Cu /Cu and Ni /Ni redox couples were cathodically shifted in
comparison with the unsubstituted analog. Second, the copper complexes underwent a quasi-
II
III
reversible one-electron oxidation (Cu /Cu ).
Keywords: Nickel, Copper, Functionalized bis(thiosemicarbazones), Structure–activity
relationship, Cyclic voltammetry.
Introduction
The bis(thiosemicarbazone) family of ligands and their transition metal complexes have been
investigated for several decades in a wide range of biological activities [1- 3]. The Study on
the mechanism of action of copper bis (thiosemicarbazone) complexes shows that they unlike
copper mono thiosemicarbazone complexes don't manifest cytotoxicity mainly through ROS
generation [4-6]. Indeed, these complexes represent a class of compounds that have recently
been the subject of intense research because of their potential as radiopharmaceuticals for the
specific targeting of hypoxic tissue [7, 8]. Fujibayashi and coworkers suggest that the high
hypoxia selectivity of some compounds (i.e. Cu(II)ATSM) is accounted for by its
considerably lower Cu(II/I) redox potential [9]. Recently, a series of Cu(II) complexes of
substituted bis(thiosemicarbazone) ligands have been reported, in which subtle changes to the
backbone of the ligand can dramatically alter their electrochemical behavior [10-12] and
biological activity [13, 14]. A close relationship between the electrochemical behavior and
biological activity has been noted [15- 18]. Studies show electrochemical behavior is
significantly affected by the substitution pattern on the imine carbon compared to substitution
at the terminal nitrogen (N(3)) [12,15]. Therefore, to extend a previous investigations [19,
2
0], we report here the synthesis and evaluation of four uncharged distorted square-planar
2

copper(II) and nickel(II) chelates share π-conjugated ligand backbones and differ only in
various substitutions placed on the aromatic ring attached to the imine carbon.
O
R
1
R
1
O
O
S
1
,3-dibromopropane
NaOH
2
Cl
NH NHNH
2
2
R2
OH
+
R2
R
2
R
1
O
O
R
1
R1
R
1
R1
O
O
O
O
M(CH
3 2
COO)
R2
R2
R
2
R2
M = Cu, Ni
N
S
N
N
S
N
S
N
N
HN
NH
Cl
M
Cl
Cl
Cl
S
N
H
N
H
N
H
N
H
R1 = OMe,R2 = H (H
R1 = H, R2 = Br (H
2
L')
L")
2
Scheme 1. Preparation steps of H
2
L' and H L" and corresponding complexes.
2
2
2
4
. Experimental
. 1. Materials and general procedures
-chlorophenyl thiosemicarbazide was prepared according to literature methods [19, 21].
Other reagents and solvents were obtained from Alfa Aesar and Merck and were used as
received. Elemental Analysis (C, H and N) were carried out on a Vario EL elemental
1
analyzer. H NMR spectra were recorded on Bruker Avance 400 in DMSO-d
6
solvent and
chemical shifts are relative to residual solvent protons as internal standard at room
temperature. Infrared spectra were obtained on a Bruker Tensor 27 FT-IR spectrometer in the
–
1
region 4000-400 cm using KBr pellets. UV-Vis spectra were recorded with an Analytik
Jena Specord 250 spectrophotometer in the region 230-1100 nm in CH Cl . Melting points
2
2
were obtained with an Electrothermal 9100 and are uncorrected. Cyclic voltammograms were
measured using a glassy carbon as working electrode, a platinum wire auxiliary electrode,
+
and an Ag/AgCl reference electrode. The ferrocene/ferrocenium couple (Fc/Fc , ∆E
p
= 125
mV) was used as a standard. All potentials are referenced to the Ag/AgCl reference electrode.
-3
All scans were recorded in deoxygenated DMF containing 3 × 10 M complexes and 0.1 M
LiClO as supporting electrolyte.
4
3

2
2
.2 Synthesis of the ligands
.2.1 Synthesis of 2-[3-(2-Formyl-6-methoxyphenoxy)propoxy]-3-methoxybenzaldehyde
(dialdehyde 1)
Dialdehyde 1 was prepared according to literature methods [22, 23] with minor modification.
Sodium hydroxide (2.63 g, 0.066 mol) in water (200 ml) was added to 2-hydroxy-3-
methoxybenzaldehyde (10 g, 0.066 mol) in ethanol (30 ml). The mixture was warmed and
1
,3-dibromopropane (6.63 g, 0.033 mol) was added. Sufficient ethanol (250 ml) to produce a
homogeneous solution was then added. The solution was refluxed under nitrogen for 96 h,
then cooled and let stand at 0 C. The cream-colored solid product was washed with water.
The solid product was recrystallized in 2:1 (ethanol/water). The resulting crystals were
̊
collected by filtration and dried in a vacuum desiccator over P
26 ˚C. Anal. Calc. (Found) for C19
MHz, CDCl
Hz, ArH); 4.15 (t, 4H, J = 5.92 Hz, -OCH
4
O
10. Yield 3.75 g (33%), m.p.
1
1
H
20
O
6
: C, 66.27 (66.21); H, 5.85 (5.68)%. H NMR (400
3
) δ 10.26 (s, 2H, ArCHO); 7.81 (t, 2H, J = 4.72 Hz, ArH); 7.12 (d, 4H, J = 4.72
); 3.81 (s, 6H, OCH ), 2.43 (quintet, 2H, J = 5.92 Hz,
) ppm. Selected FT-IR (KBr disc, cm ): 3295w, 2953w, 1689m, 1594s, 1482s, 1457m,
371m, 1294m, 1248s, 1199s, 1092m, 1062s, 628m, 574s.
2
3
-1
CH
2
1
2
.2.2
Synthesis
of
5-bromo-2-[3-(4-bromo-2-formylphenoxy)propoxy]benzaldehyde
(dialdehyde 2)
Dialdehyde 2 was prepared by a similar procedure to that of dialdehyde 1 with minor
modification. Sodium hydroxide (1.99 g, 0.05 mol) in water (150 ml) was added to 2-
hydroxy-5-bromobenzaldehyde (10 g, 0.05 mol) in ethanol (40 ml). The mixture was warmed
and 1,3-dibromopropane (5.02 g, 0.025 mol) was added. Then 150 ml of ethanol was added.
A yellow solution containing milky precipitate was formed after a day of reflux. The
refluxing under nitrogen was continued for a total of 30 hours. The cooled mixture was
filtered and the precipitate was washed with water to give dialdehyde 2. The resulting
products were dried in a vacuum desiccator over P
Anal. Calc. (Found) for C17
MHz, CDCl
4
O
10. Yield 4.98 g (45%), m.p. 134 ˚C.
1
H14Br
2
O
4
: C, 46.18 (46.16); H, 3.19 (3.14) %. H NMR (400
3
) δ 10.39 (s, 2H, ArCHO); 7.91 (d, 2H, Jmeta = 2.52 Hz, ArH); 7.62 (dd, 2H, J =
.88 Hz, Jmeta = 2.52 Hz, ArH); 6.92 (d, 2H, J = 8.88 Hz, ArH); 4.30 (t, 4H, J = 5.95 Hz, -OCH );
) ppm. Selected FT-IR (KBr disc, cm ): 3144w, 2932m,
8
2
1
2
-1
.43 (quintet, 2H, J = 5.95 Hz, CH
2
687m, 1538s, 1487s, 1369w, 1268s, 1204s, 1057s, 925w, 764m, 648w, 568w.
4

2
.2.3 Synthesis of H
2
L'
4
-chlorophenyl thiosemicarbazide was dissolved (0.28 g, 1.7 mmol) in 150 ml of hot
methanol. Dialdehyde 1 (0.4 g, 0.85 mmol) was dissolved in 20 mL of dichloromethane and
slowly added to the reaction content at reflux. After the mixture was heated on reflux for 5 h,
a pale yellow solid precipitated, it was filtered off and washed with methanol and then diethyl
-1
ether. Yield 0.53 g (88 %). m.p. 239˚C (dec.). FT-IR (KBr disc, cm ): 2927 w, 1597 s, 1546
1
m, 1477 s, 1401 m, 1326 s, 1252 s, 1171 m, 1108 m, 1052 m, 750 s. H NMR (400 MHz,
DMSO-d6): δ 2.23 (quintet, 2H, J = 6.4 Hz, CH
OCH ), 7.10 (d, 4H, J = 4.7 Hz, ArH), 7.42 (d, 2H, J = 8.72 Hz, ArH), 7.61 (d, 4H, J = 8.72 Hz,
ArH), 7.88 (t, 2H, J = 4.7 Hz, ArH), 8.53 (s, 2H, ArCHN), 10.12 (s, 2H, NH), 11.98 (s, 2H, NH) ppm.
2 3
), 3.81 (s, 6H, OCH ), 4.15 (t, 4H, J = 6.4 Hz, -
2
2
2
.2.4 Synthesis of H L"
H
2
L" ligand was prepared by a similar procedure to that of H
2
L'. The resulting yellow-
colored solid product was formed, filtered, and dried. Yield 0.58 g (85 %). m.p. 248˚C (dec.).
-
1
FT-IR (KBr disc, cm ): 3441s, 3146w, 2988 w, 1597 m, 1542 s, 1388 w, 1321 w, 1259 m,
1
1
195 m, 1123 w, 1079 w, 816 m, 510w. H NMR (400 MHz, DMSO-d6): δ 2.26 (quintet, 2H, J =
5
8
2
2 2
.88 Hz, CH ), 4.29 (t, 4H, J = 5.88 Hz, -OCH ), 7.08 (d, 2H, J = 8.92 Hz, ArH), 7.43 (d, 4H, J =
.68 Hz, ArH), 7.50-7.59 (m, 6H, J = 8.68 Hz, J = 8.92 Hz, Jmeta = 2.5 Hz, ArH), 8.43 (d, 2H, Jmeta
.4 Hz, ArH), 8.54 (s, 2H, ArCHN), 10.25 (s, 2H, NH), 11.93 (s, 2H, NH) ppm.
=
2
2
.3. Synthesis of the complexes
.3.1. General procedure
H
2
L' and H L" (1 mmol) was suspended in dichloromethane. To this refluxing suspension
2
2
+
2+
solution of the metal acetates of Cu and Ni (1 mmol) dissolved in the methanol was added
and refluxing was continued for 4 h with the color changing to dark green and red-brown for
copper (II) and nickel(II) complexes, respectively. The obtained suspension was concentrated
and products were filtered off, washed with methanol and then with diethyl ether. The
complexes were isolated as air-stable solids and soluble in chloroform, DMF and slightly
soluble in ethanol and methanol.
2
.3.2. [CuL'].0.87H
2
O
Dark green crystals. Yield 0.43 g (55%). m.p. 190 ˚C (dec.). Anal. Calc. for
C
33
H
32Cl
2
CuN
6
O
S
4.87 2
: C, 50.24; H, 4.06; N, 10.65. Found: C, 50.21, H, 4.01: N, 10.63%.
5

-
1
FT-IR (KBr disc, cm ): 3444 w, 2925 m, 2855 w, 1592 w, 1518 s, 1462 s, 1387 m, 1300 w,
1
243 m, 1107 w, 1093 m, 813 m, 748 m.
2
.3.3. [NiL']
Red-brown crystals. Yield 0.48 g (62%). m.p. 190 ˚C (dec.). Anal. Calc. for
NiO : C, 51.58; H, 3.94; N, 10.94. Found: C, 51.57, H, 3.91: N, 10.92%. FT-
C
33
H
30Cl
2
N
6
4 2
S
-1
IR (KBr disc, cm ): 3324 m, 2927 w, 1593 m, 1485 s, 1387 m, 1301 m, 1244 m, 1110 w,
1
037 m, 818 m, 748 m.
2
.3.4. [CuL"]
Dark green crystals. Yield 0.50 g (58%). m.p. 190 ˚C (dec.). Anal. Calc. for
Cl CuN : C, 42.75; H, 2.78; N, 9.65. Found: C, 42.74, H, 2.73: N, 9.63%. FT-
C
31
H26Br
2
2
6 2 2
O S
-
1
IR (KBr disc, cm ): 3423 s, 2925 s, 2855 m, 1597 m, 1510 s, 1390 m, 1300 m, 1245 m, 1163
w, 1110 w, 1041 m, 817 m, 749 m.
2
.3.5. [NiL"]
Red crystals. Yield 0.60 g (69%). m.p. 190 ˚C (dec.). Anal. Calc. for C31
H26Br
2
Cl
2
N
6
2 2
NiO S :
-
1
C, 42.99; H, 2.79; N, 9.70. Found: C, 42.99, H, 2.77: N, 9.68%. FT-IR (KBr disc, cm ): 3399
m, 3324 m, 2954 w, 2883 w, 1593 m, 1486 s, 1388 m, 1302 m, 1246 m, 1112 m, 1062 m, 620
m, 751 m.
2
.4. Single-crystal X-ray diffraction
X-Ray data collection, solution, and refinement for [CuL'].0.87H
2
O: Single crystals were
grown by slow evaporation of dichloromethane/ethanol 96% solvent mixture. All operations
were performed on a Bruker-AXS Kappa Apex II CCD diffractometer with 0.71073 Å
MoKα radiation. All diffractometer manipulations, including data collection, integration,
scaling, and absorption corrections were carried out using the Bruker Apex2 software [24].
Unit cell parameters were obtained from 60 data frames, 0.5˚ φ, from three different sections
of the Ewald sphere. Data collection was carried out at 120K, using a frame time of 50 sec
and a detector distance of 50 mm. The optimized strategy used for data collection consisted
of one phi and three omega scan sets, with 0.5˚ steps in phi or omega; completeness was
9
9.9%. A total of 1055 frames were collected. Final cell constants were obtained from the
xyz centroids of 7281 reflections after integration.
6

From the systematic absences, the observed metric constants and intensity statistics, space
group Pccn was chosen initially; subsequent solution and refinement confirmed the
correctness of this choice. The structure was solved using SIR-92 [25], and refined (full-
matrix-least squares) using the Oxford University Crystals for Windows program [26, 27].
The asymmetric unit contains a molecule of the complex, two disordered water solvate
molecules (see below) (for the complex, Z = 8; Z’=1). All of the non-hydrogen atoms were
refined using anisotropic displacement parameters. After location of H atoms on electron-
density difference maps, the H atoms were initially refined with soft restraints on the bond
lengths and angles to regularize their geometry (C-H in the range 0.93-0.98 Å and Uiso(H) in
the range 1.2-1.5 times Ueq of the parent atom), after which the positions were refined with
riding constraints [28]. During the structure solution, electron density difference maps
revealed that there were two disordered water solvent molecules which could be modeled.
One water solvate (O(5)) was found to be located on a two-fold (1/4, 1/4, 0) and was set to an
occupancy value of 0.5. The other water solvate (O(6)) had only partial occupancy which was
refined to a value of 0.369(6). Due to partial occupied oxygen atoms, all attempts to
find/place hydrogen atoms were unsuccessful. All the modeled disordered components were
refined using isotropic displacement parameters. The final least-squares refinement
2
converged to R = 0.0329(I> 2σ(I), 4951 data) and wR = 0.0837 (F , 6867 data, 450
1
2
parameters). The final CIF is available as supporting material.
X-Ray data collection, solution, and refinement for [NiL"]: Single crystals were grown by
slow evaporation of dichloromethane/methanol solvent mixture. All operations were
performed on a Bruker-AXS Kappa Apex II CCD diffractometer with 0.71073 Å MoKα
radiation. All diffractometer manipulations, including data collection, integration, scaling,
and absorption corrections were carried out using the Bruker Apex2 software [24]. Unit cell
parameters were obtained from 60 data frames, 0.5˚ φ, from three different sections of the
Ewald sphere. Data collection was carried out at 120K, using a frame time of 10 sec and a
detector distance of 50 mm. The optimized strategy used for data collection consisted of two
phi and five omega scan sets, with 0.5˚ steps in phi or omega; completeness was 99.8%. A
total of 1818 frames were collected. Final cell constants were obtained from the xyz centroids
of 9954 reflections after integration.
From the systematic absences, the observed metric constants and intensity statistics, space
group P2 /n was chosen initially; subsequent solution and refinement confirmed the
1
correctness of this choice. The structure was solved using SIR-92 [25], and refined (full-
matrix-least squares) using the Oxford University Crystals for Windows program [26, 27].
7

The asymmetric unit contains one molecule of the complex (Z = 4; Z’=1). All of the non-
hydrogen atoms were refined using anisotropic displacement parameters. After location of H
atoms on electron-density difference maps, the H atoms were initially refined with soft
restraints on the bond lengths and angles to regularize their geometry (C-H in the range 0.93-
0
.98 Å and Uiso(H) in the range 1.2-1.5 times Ueq of the parent atom), after which the
positions were refined with riding constraints [28]. The final least-squares refinement
2
converged to R = 0.0305(I> 2σ(I), 7412 data) and wR = 0.0720 (F , 9449 data, 423
1
2
parameters). The final CIF is available as supporting material.
3
. Results and discussion
3
.1. Synthesis of compounds
Scheme 1 illustrates the reaction scheme used to obtain H
2
L' and H L" ligands. The
2
synthesis of 4-substituted thiosemicarbazides can be achieved in a one-pot synthesis by the
reaction of 4-substituted phenylisothiocyanate with hydrazine. Dialdehydes 1 and 2 were
prepared by Williamson condensation 1,3-dibromopropane with 3-methoxysalicylaldehyde
and 5-bromosalicylaldehyde, respectively as outlined in Scheme 1. The IR and NMR data are
in accord with the proposed structure. The infrared spectrum shows a carbonyl mode at 1687
-
1
-1
1
cm and 1682 cm , and in H NMR spectrum (Fig. S1 and S2) resonances attributable to
aldehydic functions appear as a singlet at 10.26 ppm and 10.39 ppm for dialdehydes 1 and 2,
respectively [23]. In dialdehyde 1, the protons of the methoxy group located on the aromatic
rings appeared as a singlet at δ 3.81 ppm integrating for six protons [29]. A condensation
reaction between two equivalents 4-chlorophenyl thiosemicarbazide and one equivalent of
dialdehyde 1 or 2 gave two bis(thiosemicarbazone) ligands H
2
L' and H L", respectively, in
2
1
high yield. H NMR spectra of H
2
L' and H L" (Fig. S3 and S4) show singlets at 8.53 ppm
2
assigned to the HC=N protons [30, 31]. The chemical shift of NH–N and NH–Ar protons
observed as singlets, respectively, at 11.98 and 10.14 ppm for H L', and 11.93 and 10.25
ppm for H L" [19, 20]. If we consider the strongest peak at 1549 cm for H
L" corresponding to imine bond, these peaks will shift to lower wavenumbers
2
-
1
2
2
L' and at 1543
-
1
cm for H
upon coordination (1518, 1510, 1485 and 1487 cm ) for ([NiL'], [NiL"], [CuL'].0.87H
CuL"]), respectively - indicating coordination of the azomethine nitrogens, N(1). This band
2
-1
2
O and
[
is generally at a lower energy for the copper(II) complexes than for the corresponding
nickel(II) complexes. Furthermore, the thioamide {which is partly ν(C=S)} stretching
vibrations of these ligands, has considerable ν(C=S) character, and is observed in the 1320-
-
1
-1
1
340 cm range. This band also shifts to lower energy, 1300-1305 cm , in the spectra of the
8

complexes, due to the loss of the N(2)H hydrogen, which formally reduces the C=S bond
from a double to a single bond and results in coordination of the sulfur [32-34].
3
.2. Crystal structure of compounds
An ORTEP view of the copper complex [CuL'].0.87H
distances and angles are given in Table 2. In this complex, ligand H
2
O is given in Fig. 1 and selected bond
L' has lost hydrazinic
2
hydrogen atoms and therefore acts as a dianion. The ligand is tetradentate and coordinated to
Cu(II) through two imine nitrogen atoms (N3 and N4) and two sulfur atoms (S1 and S2).
According to the geometrical parameter τ
between square planar and tetrahedral [35]. The Cu–Nimine bond distances (1.975(2) and
.000(2) Å) and Cu–S bond distances (2.2451(8) and 2.2279(7) Å) are comparable to
4
index = 0.45, the metal center has a geometry
2
corresponding distances in related complexes [19, 20, 36]. The bond distances of N5–C27
and N2–C7 at 1.301(3) and 1.300(3) Å, respectively, are close to the distances of the C=N
double bonds N4–C26 and N3–C8 which are 1.285(3) and 1.286(3) Å, respectively. So, the
newly formed azomethine bond distances are short enough to imply a partial double bond.
These observations are consistent to electronic delocalization through the thiosemicarbazone
backbone, enhanced upon deprotonation. Also the C7–S1 and C27–S2 bond distances of
1
.772(3) and 1.769(3) Å, respectively, are not in the range of double bond character,
indicating the negative charges is delocalized on sulfur atoms that are coordinated to copper
cation. These bonds are comparable to corresponding distances in other thiosemicarbazone
complexes [19, 20, 36].
The molecular structure of the nickel complex [NiL"] is given in Fig. 2 with selected
distances and angles listed in the Table 2. This complex, like the complex [CuL"], was
analyzed as the neutral nickel complexes, [NiL"], where the ligand has been doubly
deprotonated. The nickel is four-coordinate with the N
complex [CuL"], according to τ index = 0.15, the amount of distortion from square planar is
very less for the nickel complex.
The Ni–Nimine distances (1.900(2) and 1.918(2) Å) and Ni–S distances (2.1527(7) and
.1523(6) Å) are smaller than their corresponding bonds for the complex [CuL"]. Double
2 2
S coordination mode. Unlike the
4
2
bond character of the newly formed C–Nimine bonds with distances (1.298(3) and 1.296(3) Å),
and single-bond character of the C–Sthiolate bonds with distances (1.756(2) and 1.748(2) Å)
show that after deprotonation at N2 and N5 atoms, electron density delocalize over the
molecular skeleton [19, 20, 32, 36].
2
Table 1. Crystal data and structure refinement for [CuL'].0.87H O and [NiL"]
9

[
CuL'].0.87H
2
O
[NiL"]
Crystal data
Chemical formula
Mr
Dx ( Mg m )
Crystal system, space group
λ (Å)
C
33
H
30Cl
2
CuN
6
O
4.87
S
2
31 2 2 6 2 2
C H24Br Cl N NiO S
866.13
1.788
787.13
1.507
Orthorhombic, Pccn
0.71073
120
17.4626 (7), 28.1351 (13), 14.1237 (6) 10.2401 (10), 27.651 (3), 11.5171 (11)
90°
6939.1 (5)
8
−3
Monoclinic, P2
0.71073
1
/n
Temperature (K)
a, b, c (Å)
120
β (°)
V (Å )
99.469 (5)°
3216.6 (5)
4
3
Z
Radiation type
µ (mm )
Mo Kα
0.95
Mo Kα
3.43
−
1
Crystal size (mm)
0.27 × 0.09 × 0.06
26.1°, 1.4°
3231.628
h = 0→21
k = 0→34
l = 0→17
0.23 × 0.14 × 0.13
30.1°, 1.9°
1728
h = −14→14
k = −38→38
l = −16→16
θmax , θmin
F(000)
Index ranges
Data collection
Diffractometer
Absorption correction
Bruker Kappa Apex2
Numerical
0.92, 0.94
6867, 0, 450
0.081
Bruker Kappa Apex2
Numerical
0.62, 0.64
9449/0/423
0.055
T
min, Tmax
Data/restraints/parameters
R
int
−
1
(sin θ/λ)max (Å )
0.618
0.705
Refinement
R[F > 2σ(F )], wR(F ), S
2
2
2
0.033, 0.084, 1.02
0.77, −0.82
0.031, 0.072, 1.00
0.98, −0.79
−3
∆
ρ
max, ∆ρmin (e Å )
2
2
2
2
2
2
w = 1/[σ (F ) + (0.03P) + 7.85P], where P = (max(F
w = 1/[σ (F ) + (0.03P) + 2.62P],where P = (max(F
o
,0) + 2F
c
)/3 for [CuL
)/3 for [NiL"]
'
2
].0.87H O
2
2
2
2
o
,0) + 2F
c
2
Fig. 1. Molecular structure of [CuL'].0.87H O complex. Solvent molecule is omitted
.
1
0

Fig. 2. Molecular structure of [NiL"] complex.
2
Table 2. Selected bond distances (Å) and angles (°) for [CuL'].0.87H O and [NiL"]
Bond distances
[CuL'].0.87H
2
O
Bond distances
[NiL"]
Bond angles
2
[CuL'].0.87H O
Cu1–S1
Cu1–S2
Cu1–N3
Cu1–N4
C28–N6
C27–N6
C27–N5
C5–N4
C26–N4
C1–N1
C7–N1
C7–N2
N2–N3
C8–N3
C7–S1
2.2451(8)
2.2279(7)
1.975(2)
2.000(2)
1.414(4)
1.364(3)
1.301(3)
1.394(3)
1.285(3)
1.400(3)
1.362(3)
1.300(3)
1.393(3)
1.286(3)
1.772(3)
1.769(3)
1.394(3)
Ni1–N4
Ni1–S2
Ni1–N3
Ni1–S1
C26–N6
C25–N6
C25–S2
C25–N5
N5–N4
C24–N4
C7–S1
C7–N1
C1–N1
C7–N2
N3–N2
C8–N3
1.900(2)
2.1527(7)
1.918(2)
2.1523(6)
1.400(3)
1.362(3)
1.756(2)
1.298(3)
1.412(2)
1.289(3)
1.748(2)
1.369(3)
1.400(3)
1.296(3)
1.413(2)
1.292(3)
N3–Cu1–N4
N3–Cu1–S2
N4–Cu1–S2
N4–Cu1–S1
N3–Cu1–S1
S1–Cu1–S2
Bond angles
S1–Ni1–S2
S1–Ni1–N3
S1–Ni1–N4
S2–Ni1–N3
S2–Ni1–N4
N3–Ni1–N4
97.87(9)
148.34(6)
84.82(6)
147.73(6)
84.18(6)
110.11(3)
[NiL"]
93.27(2)
85.18(5)
168.51(5)
169.62(5)
84.48(5)
99.02(7)
C27–S2
N4–N5
The unit cell of [CuL'].0.87H
2
O complex consists of eight units of CuL' and about seven
H
2
O molecules, held together in the crystal packing by intermolecular hydrogen bonds and
short contacts. The molecules form dimmers via an offset face-to-face interaction between
one of the substituted phenyl ring with methoxy group by O1…H81–C81 hydrogen
interactions with distances 2.604 Å. The dimers are arranged in chains by N1–H11…S1
hydrogen interactions with distances 2.699 Å along the crystallographic a axis (Fig. 3 (a)).
The chains then close-pack through H161…C23 short contact with distances 2.834 Å along
the c direction. The presence of the water molecules and Cl1…H152–C15 hydrogen
interactions with distance H152. . .Cl1 = 2.856 Å lead an extensive packing interconnecting
1
1

the adjacent layers in the b direction. The uncoordinated water molecules act as hydrogen
acceptor from N6-H16 with distance H16. . .O5 = 2.217 Å (Fig. 3 (b)).
2
Fig. 3. Intermolecular hydrogen bonds and short contacts in [CuL'].0.87H O
Intermolecular hydrogen bonds and short contacts in [NiL"] are different from
CuL'].0.87H O (Fig. 4). In complex [NiL"], The π–π (Cg(3)–Cg(31) 3.212 Å) and C31–
[
2
H311…π-ring (Cg5 = C1, C2, C3, C4, C5 and C6 3.149 Å) interactions link the complexes to
form infinite 1D zigzag chains running parallel to the crystallographic c axis. The formed
zigzag chains are extended through hydrogen interactions C21–Br2…H51 and N1–H1…Cl2
with distance 2.854 and 2.838 Å along the b direction, respectively. Then, in the third
dimension (the a direction) the molecules is stacked together through an extended network of
intermolecular hydrogen bonds involving sulfur atoms with distance (C19–H191…S1 2.905
Å and C17–H171…S2 2.924 Å) (Fig. 4).
1
2

Fig. 4. Intermolecular hydrogen bonds and short contacts in [NiL"]
3
.3. UV–Vis spectroscopy
The electronic spectra are taken in CH
The uv spectra of H L' and H L" show the following intra-ligand absorption maxima: π–π*
2
2
Cl , and the spectral data are tabulated in Table 3.
2
2
of the phenyl rings, together with the imine function at ca. 234 and 254 (sh) nm. Their n–π*
transitions for imine function and thione portions of the ligands are found at ca. 295(sh) and
3
11 nm for H
2
L' and 315(sh) and 341 nm for H
2
L". The n–π* transitions of H
2
L" with
brome substituent is shift towards higher wavelength compared to H
2
L' with methoxy
substituent. But the π–π* transitions have not undergone significant changes as a result of
replacing the methoxy group with bromine. In the electronic spectra of the
thiosemicarbazones, the band maximum related to the π-π* absorptions at ca. 234 and
2
54(sh) nm are not modified upon complexation. But this absorption band is broaded at
higher wavelength due to mixing with a shoulder. Most likely, this shoulder is due to an
overlap with part of n–π* transitions. Also, in the spectra of complexes a broad band with a
shoulder was observed in the range of 308-500 nm and 370-685 nm for the nickel and copper
complexes, respectively. The bands appearing in such ranges are assignable to n-π*, S–M(II)
charge-transfer and d-d transitions. Indeed, the strong intra-ligand and charge-transfer bands
mask the absorptions due to d–d transitions in the all of these metal complexes. Generally,
the relatively high energy d-d band maxima is a characteristic feature of the four-coordinate
copper(II) and nickel(II) complexes with square planar geometry [37, 38].
1
3

Table 3. Electronic spectral data of compounds in CH
2
Cl
2
Compound
Intraligand, charge-transfer and d-d
234, 254 (sh), 295 (sh), 311
234, 254 (sh), 315 (sh), 341
H
2
L'
H
2
L"
[
[
[
[
CuL'].0.87H
2
O
233, 254 (sh), 265 (sh), 352, 467 (sh), 595
234, 253 (sh), 274 (sh), 362, 442 (sh), 554
235, 254 (sh), 269 (sh), 338, 378(sh), 411
234, 256 (sh), 272 (sh), 348, 367(sh), 384
CuL"]
NiL']
NiL"]
3
.4. Cyclic voltammetry
To investigate the redox properties of the complexes, the cyclic voltammograms were recorded for all
the complexes in DMF using the same cell set up. The electrode potential is firstly scanned in
the negative direction and then in the positive direction. The electrochemical behavior of
copper(II) and nickel(II) complexes is compared with the corresponding unsubstituted analog
in dialdehyde backbone [19] (Figs 5 and 6). Results are summarized in Table 4 and in Figs. 5,
6
and S5. Neither ligands were electroactive within the potential range studied. All of the
complexes showed reversible one-electron reductions with anodic/cathodic peak separations
ranged from 75 to 96 mV except the complex NiL" that has the value ∆E = 249 mV. The
p
investigation of variations in the Cu(II/I) and Ni(II/I) redox potential with varying the ligand
substituents is studied in this paper. In our two previous works [19, 20], the effects of
chlorine and bromine substituted on the N(4)-phenyl is investigated. Now, we investigated
the effects of various substitutions placed on the aromatic ring attached to the imine carbon.
In a study conducted on bisthiosemicarbazones derived from diketone, it has been shown that
complexes with two substituent groups on the diketone backbone showed reversible one
electron oxidative processes (CuIII/CuII), while those with less than two were not oxidisable
within the potential range studied [39]. Interestingly, we achieved the same result in this
research work. This means that the substituted complexes in the dialdehyde backbone, unlike
the corresponding unsubstituted ones, were oxidisable within the potential range studied (Fig.
S5). Also, it is frequently reported in literatures that small modifications on the diketone
backbone changes the redox potential to a large extent [10-12]. A similar process was
I
II
observed in this work, meaning that the E1/2 values for the Cu /Cu redox couples of
CuL'].0.87H O and [CuL"] was cathodically shifted by 257 and 295 mV relative to the
[
2
unsubstituted analog [CuL1].MeOH respectively. A similar trend was observed for [NiL']
and [NiL"], with a cathodic shift by 313 and 319 mV when compared to the complex
[
NiL1].EtOH, respectively. But it should be noted that in this study, contrary to previous
1
4

studies, the substituents are not directly connected to the imine carbon, but also located on an
aromatic ring bound to the imine carbon. Despite the fact that the substituents are located in
the meta position relative to the imine carbon (consequently, negligible inductive effects),
nevertheless, the observed changes are dramatic.
The introduction of the methoxy and bromine groups on aromatic rings in the [CuL1].MeOH
4
and [NiL"] [19] produced an increase in the τ index from 0.36 to 0.45, and a decrease from
0
.23 to 0.15, respectively. According to the above results, it can be argued that a large part of
the variation in the E1/2 values is probably due to the change in geometry around the metal
center, not because of the inductive effects of the constituents. Nonetheless, for obtaining an
exact result, we should use the theoretical studies on the electronic structure and molecular
orbitals, especially the frontier molecular HOMO and LUMO orbitals.
-
1
Table 4. Cyclic voltammetry data for complexes in DMF solutions at 100 mVs scan rate.
complex
E
pc(V)
E
pa(V)
∆E
77
152
94
156
86
84
p
(mV)
E
1/2 (V)
|Ipc|/|Ipa
1.05
0.92
0.99
0.96
1.03
1.02
|
II
I
Cu /Cu
-0.269
0.353
-0.288
0.340
-1.110
-1.116
-0.192
0.505
-0.194
0.496
-1.024
-1.032
-0.234
0.429
-0.272
0.418
-1.06
[CuL'].0.87H
2
O
III
II
II
Cu /Cu
II
I
Cu /Cu
[CuL"]
III
Cu /Cu
II
I
I
[NiL']
Ni /Ni
II
[NiL"]
Ni /Ni
-0.998
The ferrocenium–ferrocene couple shows a peak separation of 125 mV under the same experimental conditions.
∆E = Epa - Epc and E1/2 = (Epc + Epa)/2.
p
[NiL1].EtOH
[
NiL']
5
.00
[NiL"]
-2.00
-9.00
-16.00
-23.00
-
1.50
-1.30
-1.10
-0.90
-0.70
-0.50
-0.30
E(V)
II
I
-1
Fig. 5. Ni /Ni redox wave of [NiL'], [ NiL"] and [NiL1].EtOH [19] in DMF solution at 100 mVs scan rate
1
5

8
4
0
.00
.00
.00
[
[
CuL"]
CuL1].MeOH
[CuL']
-
-
4.00
8.00
-12.00
-0.80
-0.60
-0.40
-0.20
0.00
0.20
0.40
0.60
E(V)
II
I
Fig. 6. Cu /Cu redox wave of [CuL'].0.87H
2
O, [CuL"] and [CuL1].MeOH [19] in DMF solution at
-1
100 mVs scan rate
Conclusion
Two new bis(thiosemicarbazone) ligands have been synthesized via incorporation different
substituents on the aromatic rings attached to the imine carbons. The copper(II) and nickel(II)
complexes of both ligands, have been synthesized and fully characterized using a range of
spectroscopic techniques, including IR, CHN, UV/Vis and in two cases by X-ray
crystallography. The results indicated that ligands lose hydrazinic hydrogen atoms upon
2 2
coordination to act as dianions and coordinating to the metal center as N S donor set.
Bromine and methoxy substitutions at the meta-position of the phenyl rings relative to the
imine carbon have affected the electrochemical behavior of these copper and nickel
I
II
complexes and also the geometrical parameter τ
4
index. The E1/2 value of the M /M redox
wave has cathodically shifted for all complexes. Copper complexes have showed a new redox
II
III
couple Cu /Cu within the potential range studied. Distortion from square planar has
increased for [CuL'].0.87H O and has decreased for [NiL"] complex.
2
Acknowledgement
This work was supported by Payame Noor University. The authors are grateful for the
financial support.
Appendix A. Supplementary material
CCDC 1818951 and 1818952 contain the supplementary crystallographic data for [NiL"] and
[
CuL'].0.87H
2
O complexes, respectively. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/ data_request/cif.
1
6

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1
8

Highlight
Neutral bivalent copper and nickel bis(thiosemicarbazone) complexes bearing the methoxy and
bromine substituents on the dialdehyde-backbone of the ligand have been synthesized.
Incorporating these substitutions at the meta-position of the phenyl rings relative to the imine
carbon has affected the electrochemical behavior of the copper and nickel complexes and also
I
II
the geometrical parameter τ
4
index. The E1/2 value of the M /M redox wave has cathodically
II
III
shifted for all complexes. Copper complexes have showed a new redox couple Cu /Cu within
the potential range studied. Distortion of square planar has increased for [CuL'].0.87H
2
O and has
decreased for [NiL"] complex

Graphical abstract
I
II
The E1/2 values for the M /M redox couples for the functionalized copper (II) and nickel (II)
bis(thiosemicarbazone) complexes on the dialdehyde backbone was cathodically shifted
relative to the unsubstituted analogs. Also, the modified copper complexes were oxidisable
within the potential range studied.
R1
R1
O
O
R2
R2
N
S
N
N
N
Cl
M
Cl
S
N
N
H
H