Two Cu(I) complexes based on semicarbazone ligand: synthesis, crystal structure, Hirshfeld surface and anticancer activity evaluation against human cell lines

Article abstract of DOI:10.1007/s11224-019-01379-w

Two novel Cu(I) complexes with the 2-acetylpyridine-N(4)-phenyl semicarbazone (HL) ligand, [CuCl (HL)(PPh₃)]?CH₃CN (1) and [CuBr (HL)(PPh₃)] (2), were investigated by single-crystal X-ray analysis, Hirshfeld surface, and p

Full text of DOI:10.1007/s11224-019-01379-w

Structural Chemistry
https://doi.org/10.1007/s11224-019-01379-w
ORIGINAL RESEARCH
Two Cu(I) complexes based on semicarbazone ligand: synthesis,
crystal structure, Hirshfeld surface and anticancer activity evaluation
against human cell lines
Pedro H. O. Santiago1 & Mahmi Fujimori2 & Marcio A. S. Chagas1 & Eduardo L. França2 & Adenilda C. Honorio-França2
&
Claudia C. Gatto1
Received: 9 April 2019 /Accepted: 13 June 2019
#
Springer Science+Business Media, LLC, part of Springer Nature 2019
Abstract
Two novel Cu(I) complexes with the 2-acetylpyridine-N(4)-phenyl semicarbazone (HL) ligand, [CuCl (HL)(PPh3)]∙CH3CN (1)
and [CuBr (HL)(PPh3)] (2), were investigated by single-crystal X-ray analysis, Hirshfeld surface, and physicochemical and
spectroscopic methods. In both cases, the Schiff base was coordinated by the bidentate ligand via the pyridine nitrogen and the
iminic nitrogen atoms. A molecule of triphenylphosphine and a halide ion (Cl− or Br−) completed the coordination sphere of the
metal centers. The geometry around the copper atoms was distorted tetrahedral geometry. The secondary coordination sphere of
Cu(I) is pentacoordinated and has weak interactions Cu···O of 2.906(1) Å and 2.783(1) Å. The 3D Hirshfeld surface and the 2D
fingerprint plots of the complexes were analyzed quantitatively to verify the presence of intermolecular interactions. By their
crystal structure of (2), it is possible to observe π···π stacking interactions between the pyridyl and phenyl rings from HL and also
between phenyl rings and the triphenylphosphine ligands forming a 1D network. The biological activity of the Cu(I) salts, the free
semicarbazone, and its Cu(I) complexes was evaluated against human cancer cell lines MCF-7 and nontumor cell lines PBMC.
.
.
.
.
Keywords Copper(I) complexes Semicarbazone Crystal structure Hirshfeld surface Cytotoxicity
Introduction
semicarbazones in the synthesis of metal complexes with
more variety of structures and applications [3–8]. Some metal
complexes based on semicarbazone ligands can exhibit anti-
tumor, antimicrobial, and other biological activities, an indic-
ative of the chelation of metal ions with bioactive ligands is an
effective way to develop new compounds with interesting
pharmacological properties [9–12].
Copper is an essential element for many living organisms,
responsible for different biological processes: energy metabo-
lism, oxygen transport, and antioxidant activity [13, 14]. The
Cu+ and Cu+2 ions have good affinity with O-, N-, and S-
containing ligands and are capable to form stable coordination
compounds with pronounced biological activity [14–19].
Previous studies have shown that copper (II) complexes with
salicylaldehyde semicarbazones have good anticancer poten-
tial and high selectivity [20, 21], and the modulation in the
semicarbazone structures with the coordination of these com-
pounds to the copper (II) ion can improve the biological ac-
tivity of the semicarbazones [22].
Semicarbazones are organic compounds with the structure
composed by the R2C=N-NH-C(O)-NR2 group, which insti-
gate great interest due their anticonvulsant, antimicrobial, and
antineoplasic activity [1, 2]. The presence of nitrogen and
oxygen atoms in semicarbazone structures motivated the use
of these compounds as ligands in coordination chemistry. The
keto-enol tautomerism and the possibility of these ligands to
coordinate in neutral or anionic form enable the use of
Electronic supplementary material The online version of this article
(https://doi.org/10.1007/s11224-019-01379-w) contains supplementary
material, which is available to authorized users.
* Claudia C. Gatto
ccgatto@gmail.com
1
Laboratory of Inorganic Synthesis and Crystallography, University of
Brasilia (IQ-UnB), Campus Universitário Darcy Ribeiro,
Brasilia, DF CEP 70904-970, Brazil
Due to our interest in compounds based on semicarbazones
[23, 24], this present work describes the synthesis, structural,
and spectroscopic characterization of two new copper(I)
2
Institute of Biological and Health Science, Federal University of
Mato Grosso, Barra do Garças CEP 78600-000, Brazil

Struct Chem
complexes with 2-acetylpyridine-N(4)-phenyl semicarbazone.
The crystal structures of the complexes were determined by
single-crystal X-ray diffraction method. Hirshfeld surface, FT-
IR, electronic spectroscopy, and 1H NMR, as well as the cy-
totoxicity assays against human cancer cell lines, are
discussed here.
λmax = 251, 296 and 391 nm. 1H NMR (DMSO-d6,
δ/ppm): 2.35 (s, 3H, CH3), 8.-7.0 (m, 24H, H-Ar), 9.1 (s,
1H, N3–H), and 7.6 (s, 1H, N4–H).
Synthesis of the complex (2-acetylyridine-N(4)-
p h e n y l s e m i c a r b a z o n e ) b r o m o
(triphenylphosphine)copper(I), [CuBr (HL)(PPh3)] (2)
Complex 2 was synthesized in a similar procedure as de-
scribed for complex 1, but [CuBr (PPh)3] (0.1 mmol, 41 mg)
replaced [CuCl (PPh3)]. Orange single-crystals were obtained
from mother liquor after a few days. Yield, 39 mg (59%).
Melting point, 191–193 °C. Elemental analysis, calcd for
C32H29ON4BrCuP: C, 58.23%; H, 4.43%; N, 8.49% and
found C, 58.05%; H, 4.19%; N, 8.90%. Selected IR bands
(KBr, ν/cm−1): ν(N–H) 3245, 3194; ν(C=O), 1714;
ν(C=N), 1596; ν(N–N), 1195; ν(P–C), 1095; and δ (py),
Experimental section
Materials, methods, and instruments All the reagents and
solvents were obtained from commercial sources. FT-IR
spectra were recorded in a FT-IR Varian 640 spectrometer,
using KBr pellets. Electronic spectra were obtained using a
UV-Vis-NIR Varian Cary 5000 spectrophotometer using
ethanolic solutions of the compounds, with concentration
of 20 μM. CHN elemental analysis was performed with a
Perkin Elmer/Series II 2400 analyzer. The 1H NMR spectra
of the compounds were obtained in solutions prepared in
DMSO-d6 using a Bruker Advance III HD (600 MHz), with
TMS as an internal reference. The copper(I) complexes
[CuCl (PPh3)] and [CuBr (PPh3)] were synthesized based
on previous method [25].
1
695. UV-vis (EtOH): λmax = 251, 296 and 391 nm. H
NMR (DMSO-d6, δ/ppm): 2.35 (s, 3H, CH3), 8.-7.0 (m,
24H, H-Ar), 9.1 (s, 1H, N3–H), and 7.6 (s, 1H, N4–H).
Crystal structure determination X-ray data collection was ac-
complished on a Bruker CCD SMARTAPEX II single-crystal
diffractometer with Mo Kα radiation (0.71073 Å) at 296 K.
The data were processed with SAINT [27] and were corrected
for absorption using SADABS [28]. The structures were
solved with SHELXS-97 option using the direct methods
[29], and the positions of the nonhydrogen atoms were deter-
mined with subsequent Fourier-difference map analysis. The
refinement was performed using SHELXL-18 [30]. The ma-
terial used for publication was prepared with Olex2 [31]. The
crystal data, experimental details, and refinement results are
summarized in Table 1. Some bond lengths and bond angles
of the compounds are listed in Table 2.
Synthesis of the ligand 2-acetylpyridine-N(4)-
phenylsemicarbazone (HL) The semicarbazone ligand (HL)
was synthesized with the pattern procedure [23, 24, 26]. Ten
microliters of an ethanolic mixture of 2-acetylpyridine
(1.8 mmol, 218 mg) and 4-phenylsemicarbazide (2 mmol,
302 mg) was refluxed for 3 h. The product was obtained after
a few days. Yield, 379 mg (82%). Melting point, 207–209 °C.
Elemental analysis, calcd for C14H14ON4: C, 66.12%; H,
5.55%; N, 22.03% and found C, 65.95%; H, 5.57%; N,
21.85%. Selected IR bands (KBr, ν/cm−1): ν(N–H) 3381,
3361; ν(C=O), 1690; ν(C=N), 1593; ν(N–N), 1150; and δ
Computational details Hirshfeld surfaces (HS) and related
2D-fingerprint plots [32, 33] were generated with the crystal-
lographic information files (CIFs) obtained from single-
crystal X-ray experiment, using the CrystalExplorer 17.5 pro-
gram [34]. The 3D dnorm surfaces (normalized contact dis-
tance) were mapped over a fixed color scale of − 0.4686
(red) to 1.5667(blue) for 1 and − 0.4686 (red) to 1.6626
(blue) for 2. The dnorm property, Eq. (1), is a sum of two
distances, di and de, which are normalized by the Van der
Waals radii of the involved atoms. di is the closest internal
distance from a given point on the surface and de is the closest
external contact. The 2D fingerprint cards are plots of di ver-
sus de that were used to indicate and quantify different types of
intermolecular contacts. The combination of di and de in the
form of a 2D fingerprint plot summarizes the intermolecular
contacts in the crystals and was used in the translated 0.4–
3.0 Å range, including reciprocal contacts. The shape index
S range of − 1.0 to 1.0 for 2 and is defined as indicated in Eq.
(2).
1
(py), 624. UV-vis (EtOH): λmax = 236 and 296 nm. H
NMR (DMSO-d6, δ/ppm): 2.35 (s, 3H, CH3), 8.6–7.0 (m,
9H, H-Ar), 9.6 (s, 1H, N3–H), and 9.0 (s, 1H, N4–H).
Synthesis of the complex (2-acetylyridine-N(4)-
phenylsemicarbazone) chloro (triphenylphosphine)copper(I)
acetonitrile solvate, [CuCl (HL)(PPh3)]∙CH3CN (1) A solution
of [CuCl (PPh3)] (36 mg, 0.1 mmol) in 7 mL of acetonitrile
was added to a hot solution of HL (25 mg, 0.1 mmol) in
acetonitrile (3 mL). The mixture was stirred under reflux
for 2 h. Orange crystals suitable for single-crystal X-ray dif-
fraction analysis were obtained after a few days, from the
mother solution. Yield, 33 mg (51%). Melting point, 165–
167 °C. Elemental analysis, calcd for C32H29ON4ClCuP: C,
62.43%; H, 4.75%; N, 9.10% and found C, 62.46%; H,
4.41%; N, 9.12%. Selected IR bands (KBr, ν/cm−1): ν(N–
H) 3248, 3194; ν(C=O), 1716; ν(C=N), 1596; ν(N–N),
1195; ν(P–C), 1095; and δ (py), 692. UV-vis (EtOH):

Struct Chem
Table 1 X-ray diffraction data collection and refinement parameters for
1 and 2
and
−2
π
K1 þ K2
K1−K2
S ¼
tan−1
ð2Þ
1
2
Chemical formula
M (g mol−1
C34H32ON4CuClP C32H29ON4CuBrP
)
656.60
660.01
Cell culture MCF-7 human breast cancer cells were obtained
from the American Type Culture Collection (ATCC, USA).
The cells were maintained as monolayer cultures in 75 cm2
plastic culture flasks in RPMI 1640 medium supplemented
with 10% fetal bovine serum (Sigma, St. Louis, Mo., USA),
penicillin (20 U/ml), and streptomycin (20 μg/ml; Sigma) at
37 °C in a humid atmosphere containing 5% CO2. The cells
were subcultured every 5 2 days. Subconfluent [80%]
monolayers of MCF-7 cells were treated with a concentra-
tion of trypsin [Sigma, St. Louis, USA] for 5 min at room
temperature and adjusted for 1 × 106 cells/mL. Then, the
cells co-cultures were washed twice and used for cells via-
bility assay.
Crystal system
Space group
Unit cell
a (Å)
Monoclinic
P21/c
Monoclinic
P21/c
20.869(2)
9.997(1)
14.988(1)
10.099(1)
21.218(1)
109.903(1)
3019.8(1)
4
b (Å)
c (Å)
22.246(2)
136.115(4)
3217.2(4)
4
β (°)
V (Å3)
Z
Density/g cm−3
1.356
1.452
Index ranges
− 28 ≤ h ≤ 27
− 13 ≤ k ≤ 13
− 26 ≤ l ≤ 30
0.847
− 17 ≤ h ≤ 21
− 14 ≤ k ≤ 12
− 28 ≤ l ≤ 30
2.131
Absorption coefficient/mm−1
Absorption correction
Max/min transmission
Measured reflections
Independent reflections/Rint
Refined parameters
Peripheral blood mononuclear cells After receiving informed
consent, 8 mL samples of blood were collected from 24 clin-
ically healthy men ranging from 18 to 35 years of age. The
volunteers signed an informed consent form before entering
the study, which was approved by the local ethics committee
of the Campus Araguaia on Federal University of Mato
Grosso [Protocol Number CAAE: 62417016.6.000.5587].
The blood samples were collected and heparinized in
aliquoted (25 U/mL) tubes, and fractionated by Ficoll–Paque
density gradient (density 1.077 g/L; centrifugation 160×g;
30 min) (Pharmacia, Upsala, Sweden). This procedure result-
ed in 98% pure mononuclear (MN) phagocytes preparations
as analyzed morphologically by light microscopy. Purified
MN phagocytes were resuspended independently in serum-
free medium 199 at a final concentration of 2 × 106 cells/mL
[35].
Multi-scan
0.842 and 0.639
30,920
Multi-scan
0.737 and 0.459
35,713
8331/0.0442
390
9267/0.0411
362
R1 (F)/wR2 (F2) (I > 2σ(I))
0.041/0.091
1.006
0.039/0.075
1.013
GooF
Largest diff. peak and hole
0.33 and − 0.26
0.46 and − 0.29
(eÅ−3
)
di–rvi dW de–rvedW
rvi dW
dnorm
¼
þ
ð1Þ
rvedW
Table 2 Selected bond distances (Å) and bond angles (°) for the
complexes 1 and 2
1
2
Table 3 Cytotoxic activity of phorbol 12-myristate 13-acetate (PMA)
and the compounds are shown as the inhibition concentration that caused
a 50% decrease in cell growth (IC50), in μM (95% CI), treated for 24 h at
concentrations in the range from 0.2 to 200 μM and selectivity index (SI)
against cancer (MCF-7) and normal (PBMC) cells. (mean standard
error of the mean).
Cu1–N1
2.064(2)
2.219(2)
2.200(1)
2.411(1)
1.213(3)
1.379(3)
1.284(3)
1.361(2)
2.123(2)
2.146(2)
2.200(1)
2.469(1)
1.208(2)
1.380(3)
1.294(3)
1.363(2)
Cu1–N2
Cu1–P1
Cu1–X*
C8–O1
Compound
MCF-7
PBMC
SI
C8–N3
C6–N2
[CuCl (PPh3)]
[CuBr (PPh3)]
HL
76.57 ( 3.44)
72.87 ( 2.47)
48.19 ( 4.40)
34.43 ( 2.21)
7.66 ( 2.27)
73.24 ( 6.70)
75.37 ( 3.44)
45.20 ( 4.25)
36.61 ( 3.87)
58.50 ( 3.66)
193.91 ( 2.51)
1.0
1.0
0.9
1.1
7.7
1.0
N2–N3
N1–Cu1–P1
N2–Cu1–P1
N1–Cu1–X*
N2–Cu1–X*
130.79(6)
131.36(5)
97.73(5)
113.10(5)
132.29(5)
103.71(5)
108.63(4)
[CuCl (HL)(PPh3)] (1)
[CuBr (HL)(PPh3)] (2)
PMA
104.58(5)
185.95 ( 1.73)
* X = Cl for 1 and Br for 2
Mean SD standard error of at least three independent experiments

Struct Chem
Scheme 1 Synthesis of the ligand 2-acetylpyridine-N(4)-phenylsemicarbazone (HL) and their copper(I) complexes.
Cell viability assay (MTT assay) The cytotoxic effects of the
five compounds and the positive control PMAwere evaluated
using the colorimetric method MTTassay [36] with peripheral
blood mononuclear cells (PBMC) cells and MCF-7 human
breast tumor cells. Initially, MCF-7 and PBMC cells were
placed separately on plaques of a 96-well tissue culture plate
and treated with different concentrations of the five com-
pounds and the control (0.2–200 μM) for 24 h. After this
treatment, 10 μL of MTT (5 mg mL−1) was added to each
well, and the plates were incubated at 37 °C for additional
3 h. The purple formazan crystals were dissolved in 50 μL
of solubilization solution [sodium dodecyl sulfate (SDS) and
Fig. 1 Molecular structure of 1 with crystallographic labelling (30%
probability displacement ellipsoids). Intramolecular interaction is shown
as a dashed line. Acetonitrile solvent was omitted for clarity
Fig. 2 Molecular structure of 2 with crystallographic labelling (30%
probability displacement ellipsoids). Intramolecular interaction is shown
as a dashed line

Struct Chem
Fig. 3 Dimeric aggregate
generated in 1 by hydrogen bonds
0.01 M HCl at pH = 4.7]. After that, the absorbance was de-
termined at 545 nm using a ELx800 microplate reader
(BioTek’s™ Instruments, Winooski, Vermont, USA). The cell
viability was calculated according to the following equation:
n = 3 of each independent experiment. Correlation tests were
performed to determine the effects of the concentration of the
complex on the growth of tumor cell line. The IC50 was graph-
ically obtained from the dose-response curves.
ꢀ
ꢁ
Abst
Absc
V ¼
 100
ð3Þ
Results and discussion
where V, Abst, and Absc are, respectively, the percentage of cell
viability (%) obtained from three independent experiments,
each done in triplicates, the absorbance of the treated wells,
and absorbance of the control wells. The software GraphPad
Prism 4.02 for Windows (GraphPad Software, San Diego,
CA, USA) was used to determine the half-maximal (50%)
inhibitory concentration (IC50) and was obtained from dose-
response curves. The selectivity index (SI) was calculated
using the formula previously described [37]. The IC50 values
obtained are listed in Table 3.
The complexation reaction of copper(I) precursors [CuX
(PPh3)], where X = Cl− or Br−, with the ligand 2-
acetylpyridine-N(4)-phenylsemicarbazone (HL) yielded two
new copper(I) complexes, [CuCl (HL)(PPh3)]∙CH3CN (1)
and [CuBr (HL)(PPh3)] (2), represented in Scheme 1.
Spectroscopic analysis
Some bands at 1690, 1593, 1150, and 624 cm−1 were ob-
served in the FT-IR spectra of HL, which correspond to the
vibrational modes of ν(C=O), ν(C=N), ν(N–N) and in-plan
deformation of pyridine ring, respectively. The infrared
Statistical analysis Statistical products were described as the
mean standard deviation of the measurements obtained from
Fig. 4 One-dimensional aggregate generated in 2 by hydrogen bonds and π∙∙∙π stacking interactions

Struct Chem
complexes spectra, observed in 296 nm, the same as it is in
the free ligand spectra [16, 41].
The 1H NMR spectra of the semicarbazone ligand and the
complexes were obtained in DMSO-d6. The spectrum of HL
presents a singlet at δ 2.35 ppm and a multiplet set between δ
8.6–7.0 ppm, corresponding to the hydrogen atoms of methyl
group and the pyridyl and phenyl aromatic rings, respectively.
Two singlets are observed at δ 9.0 ppm and δ 9.9 ppm due the
N-H groups in the ligand structure. The copper(I) complexes
spectra also exhibit a singlet at δ 2.35 ppm of the methyl
group, and multiplets in the range of δ 8.0–7.0 ppm, corre-
sponding to the hydrogen atoms of the pyridyl, phenyl and
triphenylphosphine groups. The N-H signals in the copper(I)
complexes are observed at δ 9.1 ppm and δ 7.6 ppm and
indicate the coordination of the HL to the copper(I) atom
through the ketonic tautomer and in neutral form. Some sig-
nals are displaced in the complexes spectra, compared to the
free ligand spectra, due the change of electronic density in the
atoms of semicarbazone after the coordination to the copper(I)
atom.
Fig. 5 Hirshfeld surface mapped in dnorm for 1
spectra of the complexes show the ν(C=O) at 1715 cm−1 ap-
proximately and that is expected for an uncoordinated carbon-
yl group. A positive shift of ν(C=N) and ν(N–N) bands to
1596 and 1195 cm−1, respectively, was observed in the spectra
of the complexes, being an indicative of the coordination of
HL to the metal ion through the azomethine nitrogen atom.
The in-plan deformation mode at 692 cm−1 suggests the coor-
dination of the semicarbazone ligand also happens through the
pyridine nitrogen atom [38–40]. A band of ν(P–C) from the
triphenylphosphine ligand is observed at 1095 cm−1 in both
the spectra of copper(I) complexes.
The UV-Vis spectra of HL show two absorption bands at
236 and 296 nm and are attributed to π → π* and n → π*
transition, respectively. The π → π* transition band is
displaced to 251 nm in the copper(I) complexes, indicating
the coordination of the semicarbazone to the metal ion.
Ligand-metal charge-transfer (LMCT) transition is observed
in the spectra of the complexes since the absorption band in
391 nm also indicates the coordination of the semicarbazone
ligand. The n → π* transition remains unchanged in the
Crystal structures of the copper(I) complexes
The crystal structures of the complexes 1 and 2 were charac-
terized by single-crystal X-ray diffraction, with the ORTEP
graphics represented in the Figs. 1 and 2. Both the complexes
crystallize in monoclinic crystal system and P21/c space
group.
The complexes 1 and 2 are isostructural, with a distorted
tetrahedral geometry for the copper(I) atom. The
semicarbazone acts as bidentated and neutral ligand, coordi-
nated to the metal atom through the N-pyridyl and N-iminic
atoms from HL, which compose the chelating system. The
others two coordination positions are occupied by the phos-
phorus atom from the triphenylphosphine ligand, and the ha-
lide X ion (X = Cl− for 1 or Br− for 2). An acetonitrile solvent
Fig. 6 Hirshfeld surface mapped
in dnorm (a) and shape index (b)
for 2

Struct Chem
Fig. 7 2D fingerprint plot derived from HS of 1
molecule is also observed in the asymmetric unit of 1. The
geometry index τ4 [42] is used to distinguish the tetrahedral or
square planar geometry for the tetracoordinated complexes,
where the τ4 value for the ideal tetrahedral geometry is one
and is zero for an ideal square planar geometry. The τ4 was
calculated utilizing the N2–Cu1–P1 (131.36(5)°) and N1–
Cu1–P1 (130.79(6)°) angles values for 1, and the N2–Cu1–
P1 (132.29(5)°) and P1–Cu1–Br1 (113.67(2)°) angles for 2.
The geometry indexes τ4 calculated are 0.692 and 0.751 for 1
and 2, respectively, and these results indicate a distorted tetra-
hedral geometry for both the copper(I) complexes. The distor-
tion observed in the coordination polyhedron of the com-
plexes was probably caused by the size of the semicarbazone
and triphenylphosphine ligands, which can cause a stereo im-
pediment in the environment around of the copper(I) atom. An
intramolecular interaction between the Cu1 and O1 atoms is
observed in the crystal structure of both the complexes and
their distance is 2.906(1) Å in 1 and 2.783(1) Å in 2, indicat-
ing a weaker interaction to the complex 1.
pentacoordinated sphere is considered for the metal centers,
with Cu-O interactions, we find the BVS very close to 1.0, as
expected. The BVS calculated for (1) and (2) were 0.905 and
0.994, respectively, indicating the oxidation state +1 to the
metal center and the intramolecular interactions.
The HL is coordinated to the copper(I) atom in the geomet-
ric isomer E, in relation to the iminic bond C6–N2, and by its
ketonic tautomer. That is indicated by the presence of the
carbonyl bond C8–O1 [1.211(3) Å in 1 and 1.209(2) Å in 2]
and the hydrogen atom bonded to the nitrogen N3 atom in the
complexes. The bond lengths in the coordination sphere of the
complexes are comparable to similar copper(I) complexes [45,
46].
The intermolecular hydrogen bonds N3–H3a∙∙∙Cl1’
[2.56(2) Å and 155(2)°] and N4–H4a∙∙∙Cl1’ [2.44(2) Å and
165(2)°], with the symmetry operations (‘): –x +1, –y +1, –z
are observed in the structure of the complex 1, while the in-
termolecular interactions found in complex 2 are between N3–
H3a∙∙∙Br1’ [2.70(2) Å and 159(2)°] and N4–H4a∙∙∙Br1’
[2.59(2) Å and 170(2)°] with the symmetry operations (‘): –
x, −y, −z. The π∙∙∙π stacking interactions between the pyridyl
ring and phenyl ring from HL and between the phenyl rings of
the triphenylphosphine ligands are also observed in the struc-
ture of 2, with a distance of 3.776(1) Å and 3920(1) Å [47].
These interactions stabilize the structures of the complexes
The bond valence sum (BVS) is a method used to predict
the oxidation state of metal ions. The BVS of the copper atom
of the complexes was determined summing the values of s for
each metal-ligand bond [43]. We calculated the BVS using the
Cu-donor bond distances tabulated in Table 2 and published
R0 values [44]. For the two complexes, when the secondary

Struct Chem
Fig. 8 2D fingerprint plot derived from HS of 2
and enable the formation of a pseudo-dimeric arrangement in
1 (Fig. 3) and an unidimensional organization of the mole-
cules of the complex 2 in its crystalline lattice (Fig. 4).
each contact in the crystal structure of the complexes. The
fingerprint plots of the complexes indicate that the H∙∙∙H and
C∙∙∙H interactions have the most contribution for 1 and 2, with
the H∙∙∙H interaction contributed with 51.9% for 1 and 54.3%
for 2, and the C∙∙∙H interaction contributed with 25.9% for 1
and 26.1% for 2. The Cl∙∙∙H and Br∙∙∙H interactions appear like
spikes in the fingerprint plots of complexes 1 and 2, respec-
tively, with contribution of 8.4% for Cl∙∙∙H in 1 and 9.9% for
Br∙∙∙H in 2. The spike of Cl∙∙∙H interactions in 1 is more in-
tense and longer than the spike of Br∙∙∙H in 2, observed in
regions with smaller values of di and de and indicates the
Cl∙∙∙H interactions are stronger than the Br∙∙∙H interactions.
Hirshfeld surface
The Hirshfeld surface (HS) is a technique currently used to
analyze and verify the types of intermolecular interactions in a
crystal lattice [32, 33]. The HS of 1 and 2 are shown in Figs. 5
and 6, respectively. The dnorm surface shows regions with red,
blue, and white colors, which indicate contacts with smaller,
larger, and closer distances to the sum of van der Waals radii,
respectively. Red spots are observed in the dnorm surfaces of 1
and 2, indicating the presence of close-contacts in the crystal
structure of both the complexes, such as classical hydrogen
bonds N–H∙∙∙X (Cl− for 1 and Br− for 2) in the structure of 1
and 2 and non-classical interactions, such as C–H∙∙∙Cl and C–
H∙∙∙C in the structure of 1, and C–H∙∙∙C and C–H∙∙∙H in the
structure of 2. The shape index surface of 2 indicate the pres-
ence of π∙∙∙π stacking interactions in the crystal structure of
this complex, observed by the detached red and blue triangles.
Fingerprint plots of 1 and 2 are represented in Figs. 7 and 8,
respectively, and display the intermolecular contacts present in
the crystalline solid of these complexes. The decomposition of
the fingerprints plots was made to verify the contributions of
Cytotoxic activity
The cytotoxic effects of the free semicarbazone (HL), their
copper(I) complexes 1 and 2, and the complexes [CuCl
(PPh3)] and [CuBr (PPh3)] were evaluated against human
breast cancer cells (MCF-7) and peripheral blood mononucle-
ar cells (PBMC). The tests were performed with the MTT
assay, using phorbol 12-myristate-13-acetate (PMA) as posi-
tive control. Table 3 shows the cytotoxic activity of the tested
compounds, expressed in the concentration which caused the
inhibition of 50% in cell growth.

Struct Chem
3. Patel RN, Shukla KK, Singh A et al (2009) Copper (II) complexes
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The tested compounds showed antitumor activity against
MCF-7 cells line, with better activity for HL (48.19
4.4 μM), 1 (34.43 2.21 μM), and 2 (7.66 2.27 μM. It
was observed an increase in the antitumor activity of the
semicarbazone after the complexation to the copper(I) ion,
which indicates that the chelation of semicarbazone with a
metal ion causes a synergic effect that can improve the cyto-
toxic activity of the semicarbazone. Interestingly, the change
of the chloride ligand in 1 for a bromide ligand in 2 resulted in
a better antitumor activity for 2. All the compounds showed a
similar cytotoxicity against the PBMC cells line if compared
against MCF-7 cancer cells, with selectivity index (SI) in the
range of 0.9 to 1.1, except for 2, which showed less cytotox-
icity against the PBMC cells line, with its IC50 of 58.50
3.66 μM and SI value of 7.7. Therefore, 2 demonstrated a
better selectivity against the MCF-7 cells lines.
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characterization, biological screening, and theoretical studies of
organotin (IV) complexes of semicarbazone and
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Conclusions
The 2-acetylpyridine-N(4)-phenylsemicarbazone ligand was
used for the synthesis of two new copper(I) complexes. The
structural and spectroscopic analysis indicated in both com-
plexes the copper(I) atoms is tetracoordinated, and the
semicarbazone acts as bidentate and neutral ligand. The results
obtained in the biological analysis show that the copper(I)
complexes demonstrate more cytotoxicity in comparison to
the free semicarbazone and enable the development of similar
compounds which can be used as promising antitumor agents.
Acknowledgments All funding agencies are acknowledged for partial
financial support.
Funding sources The authors wish to thank FAPDF (process number
0193.001545/2017). This study was financed in part by the Coordenação
de Aperfeiçoamento de Pessoal de Nível Superior—Brasil (CAPES)—
Finance Code 001, FINEP/CTINFRA, CNPq and DPP-UnB.
Author contributions The manuscript was written with contributions
from all authors. All authors have approved the final version of the
manuscript.
13. Denoyer D, Masaldan S, La Fontaine S, Cater MA (2015) Targeting
copper in cancer therapy: “Copper That Cancer”. Metallomics 7:
1459–1476. https://doi.org/10.1039/C5MT00149H
14. Duncan C, White AR (2012) Copper complexes as therapeutic
agents. Metallomics 4:127–138. https://doi.org/10.1039/
C2MT00174H
15. Krishnamoorthy P, Sathyadevi P, Butorac RR et al (2012) Copper(i)
and nickel (ii) complexes with 1 : 1 vs. 1 : 2 coordination of
ferrocenyl hydrazone ligands: do the geometry and composition
of complexes affect DNA binding/cleavage, protein binding, anti-
oxidant and cytotoxic activities? Dalt Trans 41:4423. https://doi.
org/10.1039/c2dt11938b
Compliance with ethical standards
Conflict of interest The authors declare that they have no conflicts of
interest.
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