Synthesis, characterization and anticancer studies of bis-(N-methyl-1-phenyldithiocarbamato) Cu(II), Zn(II), and Pt(II) complexes: single crystal X-ray structure of the copper complex

Article abstract of DOI:10.1080/00958972.2018.1489537

Cu(II), Pt(II), and Zn(II) complexes of N-methyl-1-phenyldithiocarbamate were synthesized and characterized by FTIR, NMR, UV-visible spectroscopy and elemental analysis. The complexes were formulated as [Cu(L)₂], [Zn(L)₂] and [Pt(L)<

Full text of DOI:10.1080/00958972.2018.1489537

Journal of Coordination Chemistry
ISSN: 0095-8972 (Print) 1029-0389 (Online) Journal homepage: http://www.tandfonline.com/loi/gcoo20
Synthesis, characterization and anticancer studies
of bis-(N-methyl-1-phenyldithiocarbamato) Cu(II),
Zn(II) and Pt(II) complexes. Single crystal X-ray
structure of the copper complex
Fartisincha P. Andrew & Peter A. Ajibade
To cite this article: Fartisincha P. Andrew & Peter A. Ajibade (2018): Synthesis, characterization
and anticancer studies of bis-(N-methyl-1-phenyldithiocarbamato) Cu(II), Zn(II) and Pt(II)
complexes. Single crystal X-ray structure of the copper complex, Journal of Coordination
Chemistry, DOI: 10.1080/00958972.2018.1489537
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Publisher: Taylor & Francis
Journal: Journal of Coordination Chemistry
DOI: http://doi.org/10.1080/00958972.2018.1489537
Synthesis, characterization and anticancer studies of bis-(N-methyl-1-
phenyldithiocarbamato) Cu(II), Zn(II) and Pt(II) complexes. Single crystal
X-ray structure of the copper complex
FARTISINCHA P. ANDREW and PETER A. AJIBADE*
School of Chemistry and Physics, University of KwaZulu-Natal, Private Bag X01, Scottsville, Pietermaritzburg,
3209 South Africa
Cu(II), Pt(II) and Zn(II) complexes of N-methyl-1-phenyldithiocarbamate were synthesized and
characterized by FTIR, NMR and UV-visible spectroscopy and elemental analysis. The
complexes were formulated as [Cu(L)2], [Zn(L)2] and [Pt(L)2] (where L = N-methyl-1-
phenyldithiocarbamate) in which two molecules of the ligands coordinate to the metal ions in a
bidentate chelating fashion. This is confirmed by elemental analysis and the presence of strong
single band at 952, 951 and 955 cm-1 for Cu(II), Pt(II) and Zn(II) complexes, respectively, in the
FTIR spectra. The electronic spectra of Pt(II) and Cu(II) complexes are consistent with four-
coordinate square planar geometry. Single crystal X-ray of [Cu(N-mpDTC)2] confirmed square
planar structural arrangement (CuS4) in which the ligands are asymmetrically bonded to the
Cu(II) ion building a centrosymmetric monomer entity. The S-Cu-S bite angle is 77.95 (3)
whereas the intramolecular N-C bond length is 1.318 Å and trans S11-Cu-S1 = S21-Cu-S2 is
180, which are consistent with reported copper thiolates in square planar environment. In vitro
antiproliferative activity of the complexes against three human cancer cell lines showed that the
zinc complex has better activity compared to Cu and Pt complexes, with IC50 values of 14.28,
22.74 and 20.10 μM against TK10, UACC62 and MC7 cell lines, respectively.
Keywords: Dithiocarbamates; Metal complexes; Synthesis; Crystal structure; Anticancer
*Corresponding author. Email: ajibadep@ukzn.ac.za
1

1. Introduction
The development of transition metal complexes for the treatment of cancer has gained interest
since the successful clinical integration of cisplatin in 1978 [1-3]. Whereas cisplatin and its
derivatives are still the most used metal-based drugs for the treatment of various cancers, the side
effects associated with their application as a result of their severe toxicity, induced or intrinsic
resistance and narrow activity range have been serious pharmaceutical concerns [4-6]. Therefore,
there have been marked advances in the development of metal-based anticancer agents to
circumvent the side effect associated with the classical platinum drugs. A significant number of
metal complexes such as copper, nickel, ruthenium, silver, gold, zinc and platinum have been
evaluated both in vitro and in vivo with few at various stages of clinical trials [7-14]. Essential
elements such as copper and zinc have been proposed as promising anticancer agents. These
metal ions are found in all living organisms and act as catalytic cofactors or as structural
components of various biomolecules. They also play vital roles in various biological functions
such as oxygen transport, cell signaling, gene expression, protein stability and energy
metabolism; they also tend to raise the intracellular concentration, hence mediate cytotoxicity
[15-17].
Careful choice of metal ions, their oxidation states, the type and nature of the
coordination ligands and coordination geometry of metal-based drugs provide an efficient
strategy for designing effective metal-based anticancer agents [18]. Ligand exchange kinetics
that are a consequence of metal ligand coordination depict the stability of metal ligand bonds and
as a result play a great role in the overall biological activity of metallodrugs [19]. Metal
coordination compounds with slow metal-ligand exchange kinetics are known to be active
against cancer, although the nature of the ligand and the metal ion simultaneously account for the
mechanism of the exchange [19]. Ligands such as dithiocarbamates with strong binding
configuration to metal ions have been reported to limit ligand exchange reactions with thiol
containing renal proteins and enzymes and consequently inhibit cisplatin-like nephron and
gastrointestinal toxicity. [20, 21]. Consequently, metal dithiocarbamates have received
considerable attention as potential anticancer agents with documented evidence of various
degrees of DNA binding affinity, cytotoxicity and a broad spectrum of biological activity against
both plant and animal pathogens [4]. In view of this, we report here the synthesis,
characterization and in vitro cytotoxic studies of Cu(II), Zn(II) and Pt(II) complexes of
2

N-methyl-1-phenyldithiocarbamate. The synthesized ligand and its complexes were
characterized using FT-IR, UV-Visible, NMR and conductivity measurements. The single crystal
X-ray structure of the Cu(II) complex is presented and discussed. The anticancer potential of the
metal complexes were evaluated against human cancer cell lines TK10 (renal), UACC62
(melanoma) and MCF7 (breast).
2. Experimental
2.1. Material and method
All starting materials were purchased from Sigma-Aldrich and used without purification. The
1H and 13C NMR spectra were recorded on a Bruker Avance III 400 MHz spectrometer at room
temperature using TMS as internal reference. All the proton and carbon shifts are quoted in ppm
relative to the relevant solvent signal. FTIR spectra were recorded neat in the region 4000-
300 cm-1 using a Perkin Elmer spectrum 100 FTIR spectrometer. The UV-Visible spectra were
recorded using a Cary100-UV-Vis spectrophotometer from Agilent Technology. Molar
conductivities were measured with a Jenway 4510 conductivity meter using ~10-3 molL-1
solution of water and DMSO for the ligand and complexes, respectively. Human cancer cell lines
TK10 (renal), UACC62 (melanoma) and MCF7 (breast) were obtained from National Cancer
Institute (NCI) in the framework of a collaborative research program between the Council for
Scientific and Industrial Research (CSIR), South Africa and NCI. In vitro cytotoxic activity of
the compounds was tested using a sulforhodamine assay.
2.2. Synthesis of sodium N-methyl-1-phenyldithiocarbamate ligand (L)
The sodium salt of N-methyl-1-phenyldithiocarbamate was prepared by the reaction of
N-methylbenzylamine (6.0224 g, 50 mmol) dissolved in 20 mL methanol and NaOH (2.0 g,
50 mmol) followed by the addition of cold carbon disulfide (3.7980 g, 50 mmol). The reaction
mixture was stirred for 4 h at 0-4 C, the resulting white precipitate was filtered, washed
severally with diethyl ether and dried under vacuum over silica. Yield: 10.7457 g, 98%, m.p:
129 C, Anal. Calc. for Na(S2CNCH3CH2C6H5)·2H2O: C, 42.34; H, 5.53; N, 5.49; S, 25.12.
Found: C, 42.20; H, 5.60; N, 5.46; S, 25.54. 1H NMR (400 MHz, D2O, δ, ppm) (t, 2H), 7.50 (t,
2H), 7.42 (t, 1H), 7.36 (d, 2H), 5.50 (s, 2H), 3.50 (s, 3H). 13C NMR (400 MHz, D2O, δ, ppm),
210.14 (CS), 42.69 (N-CH3), 59.63 (N-CH2-(C6H5)), 136.79, 126.83, 127.40, 128.87 (-C6H5),
3

UV-Vis (H2O, λmax, nm) 258, 285. Selected IR (solid state, cm-1) 1625 (ѴN-CS2), 1374 (ѴCH3 bend),
949 (Ѵ(C-S)).
2.3. Synthesis of bis-N-methyl-1-phenyldithiocarbamato-S,S’ copper(II) [Cu(L)2] (1)
An aqueous solution of CuCl2·2H2O (3 mmol, 0.5114 g) was added dropwise to an aqueous
solution of the sodium salt of N-methyl-1-phenyldithiocarbamate (6 mmol, 1.1315 g) which
resulted in immediate formation of a brown precipitate. After stirring for 4 h at room temperature
it was filtered, washed several times with distilled water and dried under vacuum. Single clear
orange block-shaped crystals suitable for single crystal X-ray were obtained by layering a
dichloromethane solution of the complex with acetonitrile. Yield: 1.1988 g, 87%, m.p: 186 C,
brown solid, Anal. Calc. for [Cu(S2CNCH3CH2C6H5)2]: C, 47.39; H, 4.42; N, 6.14; S, 28.12.
Found: C, 47.45; H, 4.40; N, 5.84; S, 28.46. Selected IR (solid state, cm-1); 1509 (ѴN-CS2), 952
(Ѵ(C-S)), 1394 (ѴCH3 bend), 356 (Ѵ(M-S)), UV-Vis (CHCl3, λmax, nm) 276, 436, 630.
2.4. Synthesis of N-methyl-1-phenyldithiocarbamato-S,S’ platinum(II) [Pt(L)2] (2)
An aqueous solution of K2PtCl4 (0.3 mmol, 0.1245 g) was added dropwise to an aqueous
solution of the sodium salt of N-methyl-1-phenyldithiocarbamate (0.6 mmol, 0.1315 g). The
mixture was stirred at room temperature for 6 h, and the resulting yellow precipitate was filtered,
washed with water and dried under vacuum. Yield: 0.1364 g, 77%, m.p; 192 C, yellow solid,
Anal. Calc. for [Pt(S2CNCH3CH2C6H5)2]: C, 36.79; H, 3.43; N, 4.77; S, 21.82. Found: C, 36.87;
H, 3.44; N, 4.64; S, 22.26. Selected IR (solid state, cm-1); 1525 (ѴN-CS), 951 (Ѵ(C-S)), 1396
(ѴCH3 bend), 366 (Ѵ(M-S)), UV-Vis (CHCl3, λmax, nm), 257, 351, 430.
2.5. Synthesis of N-methyl-1-phenyldithiocarbamato-S,S’ zinc(II) [Zn(L)2] (3)
An ethanolic solution of ZnCl2 (2 mmol, 0.2726 g) was added dropwise to an aqueous solution of
N-methylbenzyl dithiocarbamate (4 mmol, 0.8772 g) ligand. The mixture was stirred at room
temperature for 3 h, and the white precipitate formed was filtered, washed with water and dried
under vacuum. Yield: 0.6961 g, 76%, m.p; 159 C, white solid, 1H NMR (400 MHz, CDCl3, δ,
ppm) 7.3562 (m, 10H), 5.1068 (s, 4H), 3.3524 (s, 6H), 13C NMR (400 MHz, CDCl3, δ, ppm)
205.18 (CS), 41.75 (N-CH3), 60.42 (N-CH2-(C6H5)), 134.73, 129.09, 128.41, 127.99 (-C6H5),
Anal. Calc. for [Zn(S2CNCH3CH2C6H5)2]: C, 47.20; H, 4.40; N, 6.40; S, 28.0. Found: C, 47.07;
4

H, 4.18; N, 6.04; S, 28.38. Selected IR (solid state, cm-1); 1493 (ѴN-CS), 955 (Ѵ(C-S)), 1392
(ѴCH3 bend), 375 (Ѵ(M-S)), UV-Vis (CHCl3, λmax, nm), 266.
2.6. Single crystal X-ray crystallography
A clear, orange, block-shaped crystal with dimensions 0.27×0.19×0.12 mm3 was mounted on a
MITIGEN holder in oil. X-ray diffraction data were collected using a Bruker APEX-II CCD
diffractometer equipped with an Oxford Cryosystems low-temperature device, operating at T =
100(2) K. The structure was solved in the space group P21/n (# 14) by direct methods using the
ShelXS [22] structure solution program and refined by least squares using version 2016/6 of
ShelXL [23]. All non-hydrogen atoms were refined anisotropically. Hydrogen atom positions
were calculated geometrically and refined using the riding model.
2.7. In vitro anticancer activity
The in vitro anticancer activities of the compounds were tested against three human cancer cell
lines viz; TK10 (renal), UACC62 (melanoma) and MCF7 (breast) using a sulforhodamine B
(SRB) assay. The cells were grown in RPMI 1640 containing 5 % fetal bovine serum, 2 mM
L-glutamine and 50 µg/ml gentamicin. In the experiment, cells were inoculated into 96 well
microtiter plates in 90 μl at plating densities of 7-10 000 cells per well and were incubated for
24 h. After cell inoculation, the microtiter plates were incubated at 37 C under 5 % CO2, 95%
air and 100 % relative humidity for 24 h prior to addition of the experiment drugs. The test
compounds were diluted from 10 mM stock in DMSO to give the desired concentrations. At the
time of experiment, fivefold serial dilutions were made using complete medium. 10 μl of these
different drug dilutions were added to the appropriate micro-titer wells already containing 90 μl
of medium. Cells without drug addition served as control. The blank contains complete medium
without cells. Parthenolide was used as a standard. The plates were incubated for 48 h after
addition of the compounds. Viable cells were fixed to the bottom of each well with cold 50 %
trichloroacetic acid, washed, dried and dyed by SRB. Unbound dye was removed and protein-
bound dye was extracted with 10 mM Tris base for optical density determination at the
wavelength 540 nm using a multiwell spectrophotometer [24]. Data analysis was performed
using GraphPad Prism software. 50 % of cell growth inhibition (IC50) was determined by non-
linear regression.
5

3. Results and discussion
3.1. Synthesis
The ligand and the complexes were synthesized as shown in scheme 1. They were all isolated as
air-stable, crystalline solids and melt in the range 129-192 C, in good yields of 87, 77 and 76 %
for the copper, platinum and zinc complexes, respectively (table 1).
H
S
S
Na
N
N
MeOH
0-4 oC
+ NaOH + CS2
2
M(II)
S
S
N
M
N
S
S
M = Cu(II), Pt(II) and Zn(II)
Scheme 1. Schematic route for the synthesis of N-methyl-1-phenyldithiocarbamate ligand and its
Cu(II), Pt(II) and Zn(II) complexes.
3.2. FTIR Spectra studies
Relevant FTIR spectra data of the ligand and the complexes are given in table 2. Generally,
FT-IR spectra of dithiocarbamate complexes exhibit three main characteristic stretching
vibrations [25-34]; the ν(N-CS2) 1450-1550 cm-1 band is typical of carbon nitrogen bond order
intermediate between the stretching frequencies associated with C—N single bond (1250-
1350 cm-1) and double bond (1640-1690 cm-1). The progressive shift > 50 cm-1 in ν(N-CS2),
1509, 1525 and 1493 for Cu(II), Pt(II) and Zn(II) complexes, respectively, relative to that of the
ligand 1625 cm-1, is consistent with the increased double bond character consequent of the
efficient involvement of the localized lone pair of electron on the carbon-nitrogen backbone in
resonance upon complexation [35].
6

The ν(C—S) 950-1050 cm-1 band(s) define the mode of coordination of the
dithiocarbamate moiety to the metal center. A single band in this region indicates a complete
symmetrical coordination of the dithiocarbamate ligand to the metal center, in other words it
indicates that the ligand acts in a bidentate mode, while two bands in this same region indicate
two non-equivalent C-S bonds for either monodentate (∆ν > 20 cm-1) or asymmetric bidentate
(∆ν < 20 cm-1) coordination [36]. In the three complexes, the presence of a strong single band at
952, 951 and 955 cm-1 for Cu(II), Pt(II) and Zn(II) complexes, respectively, confirms the
isobidentate coordination of the dithiocarbamate ligand to the metal center. The ν(M—S) 300-
400 cm-1 band observed at 358, 366 and 378 cm-1 was assigned to the metal sulfur stretching
frequency for complex Cu(II), Pt(II) and Zn(II), respectively.
3.3. 1H and 13C NMR Spectra
The 1H NMR data of the free dithiocarbamate ligand agrees with the proposed formulation. Two
separate singlets appear at 5.50 and 3.50 for methylene and methyl at the α-N position in relation
to the thioureide bond, respectively. The methylene protons are deshielded due to the electron
withdrawing effect of the aryl ring and the electronegative effect of the thioureide nitrogen atom
[26]. The aromatic protons appear at a higher frequency, thus, triplet signal at 7.5 ppm (1H),
triplet 7.42 ppm (2H) and doublet at 7.36 ppm (2H). Upon coordination to zinc (complex 3) a
downfield shift of the proton signals was observed with multiplets appearing at 7.35 ppm (10H)
(the aromatic region), and 5.10 ppm and 3.35 ppm for the methylene and free methyl group,
respectively.
Similarly, downfield shifts due to the coordination effect of the metal ion were also
observed in the 13C NMR spectra of the zinc complex compared to that of the ligand. The C-S
carbon, which was observed at 210.14 ppm in the ligand, shifted to 205.18 ppm in the complex.
The methyl carbon atom was 42.69 ppm in the ligand but shifted upon coordination to
41.75 ppm; the downfield shift observed is a consequence of the high electron density of the
electronegative thioureide nitrogen atom proximate to the methyl proton which brought about
shielding effect [26]. The carbon atoms of the aromatic ring give signals 136.79, 126.83, 127.40,
128.87 ppm and 134.73 ppm, 129.09, 128.41, 127.99 ppm for the ligand and complex,
respectively.
7

3.4. Molar conductivity
The molar conductivities of the ligand and the complexes were recorded in DMSO at 10-3 M at
room temperature. This provides the degree of ionization of the complexes, that is, the molecular
ions that a complex liberates in solution. The higher the number of the molecular ions liberated
the higher conductivity value and vice versa [37]. The lower conductivity value of the complexes
relative to that of the ligand (table) indicates a non-electrolytic nature of the complexes as a
consequence of a lack of counter ions around the coordination sphere of the complexes [38].
3.5. Electronic spectra
The electronic spectra of the ligand and its Cu(II), Pt(II) and Zn(II) complexes were recorded in
water and chloroform, respectively, at room temperature (table 3). The intraligand absorptions at
258 nm and 285 nm in the UV region are attributed to π-π* and n-π* transitions arising from the
aryl ring and azomethine (-C=N) in consequence of the partial double bond character in the free
ligand. These bands remained unchanged in all the complexes, although with slight shift in
wavelength, with the second band appearing as a shoulder in all the complexes. However, the
platinum complex showed an absorption in the UV region at 351 nm which as assigned to π-π*.
Absorptions in the visible region at 436 nm and 630 nm for Cu(II) complex arising from the
forbidden d-d transitions [39] were assigned to 2B1g – 2A1g, 2B1g – 2E1g which is typical of Cu(II)
in a square planar environment [40]. That of the Pt(II) complex at 430 nm was assigned to 1A1g –
1Eg and 1B1g transition which could be due to superposition of charge transfer and d-d transitions
[41]. The zinc complex is a d10 system and no d-d transition is expected. The observed bands are
assigned to the ligand to metal charge transfer transition [42].
3.6. Molecular structure of the copper complex, [Cu(N-mpDTC)2]
Single crystals of [Cu(N-mpDTC)2] complex were obtained by layering a dichloromethane
solution of the compound with acetonitrile. The summary of crystal data and structure refinement
is presented in table 4. The molecular structure and atom labeling are shown in figure 1, while
the unit cell packing is shown in figure S8. Bond angles (°) and bond lengths (Å) are shown in
table 5. The Cu(II) complex formed a centrosymmetric monomer with a square planar
coordination geometry comprising a CuS4 environment. The complex has four Cu-S equatorial
bonds [43] where the intramolecular Cu1-S1 bond length 2.2991 Å (8) is just slightly longer than
8

that of Cu1-S2 2.2930 Å (8). The dihedral angles of the chelating dithiocarbamate ligands
S2-Cu1-S11 77.95° (3) are the same. The N-C bond length 1.318 Å is consistent with the
thioureide resonance form [44-46], suggesting a partial double bond character because of higher
electron density expected upon complexation [31]. The trans S11-Cu-S1 = S21-Cu-S2 = 180°
which is perfectly consistent with expected value of usual square planar system [47].
3.7. Anticancer activity studies
The in vitro cytotoxicity, in terms of IC50 values of the complexes against TK10 (renal),
UACC62 (melanoma) and MCF7 (breast) human cancer cell lines, were determined using
Sulforhodamine B (SRB) assay. The IC50 values of the compounds in µM (table 6) indicate a
promising cytotoxic activity of the compounds against the three cancer cell lines, particularly the
zinc(II) complex with IC50 values of 14.28, 22.74 and 20.10 μM for TK10, UACC62 and MC7
cell lines, respectively (table 6), compared to the platinum(II) and copper(II) complexes which
are above 100 μM for the TK10 and UACC62 cell lines.
4. Conclusion
The complexes of Cu(II), Pt(II) and Zn(II) with N-methyl-phenyldithiocarbamate ligand were
prepared and characterized by FTIR, NMR, UV-visible spectroscopy and molar conductivity.
They were formulated as [Cu(L)2], [Zn(L)2] and [Pt(L)2], where L = N-methyl-1-
phenyldithiocarbamate. The spectroscopic data of the complexes showed a symmetrical
bidentate chelation of the dithiocarbamate ligand to the metal ions. These results are consistent
with complexes in a square planar environment for the Cu(II) and Pt(II) and tetrahedral for the
Zn(II) complex. The single crystal X-ray structure of the copper complex agreed with the
formulation [Cu(L)2] and confirms the square planar geometry around the Cu(II) ion. The
dithiocarbamate ligands are slightly asymmetrically bonded to the copper ion with
intramolecular Cu1-S1 bond length 2.2991 Å (8), Cu1-S2 2.2930 Å (8) and S2-Cu1-S11 bite
angle of 77.95 (3). These are consistent with copper thiolates in square planar environment. The
anticancer potencies of the complexes were evaluated against three cancer cell lines, TK10,
UACC62 and MCF7, with the zinc complex showing reasonable activity against the three cell
lines.
9

Supplementary material
CCDC 1821650 contains the supplementary crystallographic data for this paper. 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 Email: deposit@ccdc.cam.ac.uk.
Acknowledgements
The authors acknowledge the financial support of Sasol South Africa and FPA acknowledges
Tertiary Education Trust Fund (TETfund) and Modibbo Adama University of Technology,
Nigeria for the award of PhD scholarship.
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12

Figure 1. The molecular structure of [Cu(L)2] showing atomic labeling.
Table 1. Analytical data for ligand and complexes
Compound
Color
Yield %
Conductivity μЅ/cm
Melting point C
Free ligand
[Cu(L)2] (1)
[Pt(L)2] (2)
[Zn(L)2] (3)
White
Brown
Yellow
White
98
87
77
76
129
186
192
159
446
0.06
0.06
0.08
13

Table 2. FT-IR relevant data (cm-1) of free ligand and complexes.
Compound
Ѵ (N-CS2) (cm-1)
Ѵ(C-S) (cm-1)
ѴCH3 bend (cm-1)
Ѵ(M-S) (cm-1)
Free ligand
[Cu(L)2] (1)
[Pt(L)2] (2)
[Zn(L)2] (3)
1625
1509
1525
1493
949
952
951
955
1374
1374
1396
1392
356
366
375
Table 3. Electronic spectra of ligand and complexes.
Compound
Free ligand
Wavelength (λmax nm)
Wavenumber (cm-1)
Assignment
258
285
38760
35088
n-π*/π-π* intraligand
[Cu(L)2] (1)
[Pt(L)2] (2)
[Zn(L)2] (3)
276
436
630
36232
22936
15873
n-π*/π-π* intraligand
2B1g – 2A1g
2B1g – 2E1g
257
351
430
38911
28490
23256
n-π*/π-π* intraligand
π-π* transition
1A1g-1Eg and 1B1g
266
37594
M-L charge transfer band
14

Table 4. Summary of crystal data and structure refinement.
Compound
[Cu(L)2]
Formula
Dcalc./ g cm-3
/mm-1
C18H20CuN2S4
1.589
1.588
Formula weight
Color
456.14
Clear orange
Block
Shape
Size/mm3
0.27×0.19×0.12
100(2)
Monoclinic
P21/n
T/K
Crystal system
Space group
a/Å
6.5870(17)
6.5328(19)
22.397(6)
90
b/Å
c/Å
/°
/°
/°
98.513(7)
90
V/Å3
953.2(4)
2
Z
Z'
0.5
Wavelength/Å
Measured refl.
Independent refl.
Reflections used
Parameters
Restraints
Largest peak
Deepest hole
GooF
0.71073
1811
1811
1713
116
0
0.337
-0.450
1.066
wR2 (all data)
wR2
0.0670
0.0657
0.0293
0.0270
R1 (all data)
R1
15

Table 5. Bond angles in (°) and bond lengths in Å for [Cu(L)2].
Bond angle (°)
Bond length (Å)
N1-C1-S11
123.1(2)
123.5(2)
113.38(16)
112.9(2)
120.6(3)
119.2(3)
120.1(3)
120.6(2)
123.3(2)
115.8(2)
84.02(10)
83.92(11)
180.0
C1-N1
C1-S11
C1-S2
C2-N1
C3-C4
C3-N1
C4-C5
C4-C9
C5-C6
C6-C7
C7-C8
C8-C9
S1-Cu1
S2-Cu1
1.318(4)
1.721(3)
1.735(3)
1.468(4)
1.503(4)
1.466(4)
1.397(4)
1.394(4)
1.390(4)
1.383(5)
1.375(5)
1.389(4)
2.2991(8)
2.2930(8)
N1-C1-S2
S11-C1-S2
N1-C3-C4
C9-C4-C3
C9-C4-C5
C7-C8-C9
C1-N1-C2
C1-N1-C3
C3-N1-C2
C11-S1-Cu1
C1-S2-Cu1
S11-Cu1-S1 = S2-Cu1-S21
S21-Cu1-S1 = S2-Cu1-S1
S2-Cu1-S11 = S21-Cu1-S1
102.05(3)
77.95(3)
Table 6. Estimated IC50 (μM) on TK10, UACC62 and MCF7 cell lines.
Complex
TK10
UACC62
MCF7
[Cu(L)2] (1)
[Pt(L)2] (2)
[Zn(L)2] (3)
Parthenolide
>100
>100
14.28
4.64
>100
>100
22.74
11.37
62.93
66.82
20.10
3.52
16

Graphical abstract
H
N
S
S
Na
N
MeOH
0-4 o
+ NaOH + CS2
C
M(II)
S
S
S
N
M
N
S
M = Cu(II), Pt(II) and Zn(II)
17