Ni(II), Pd(II) and Cu(II) complexes with N-(dialkylthiocarbamoyl)-N′- picolylbenzamidines: Structure and activity against human MCF-7 breast cancer cells

Article abstract of DOI:10.1016/j.poly.2012.08.088

N-(Dialkylthiocarbamoyl)-N′-picolylbenzamidines (HL^Et and HL^Morph) react with NiCl₂, CuCl₂ and [PdCl ₂(MeCN)₂] with the formation of complexes of the general composition [M(L^R)Cl] (M = Ni (1), Pd (2)) and the dimeric complexes [{Cu(L^R)Cl}₂] (3). The molecular structures of complexes 1 and 2 exhibit a square-planar coordination sphere, in which the organic ligands coordinate in a S,N,N coordination mode. The two subunits of 3, the arrangement of each is similar to those of 1 and 2, are connected via two weak Cu-Cl′ bonds. The copper complexes [{Cu(L^R)Cl}₂] (3) are slowly oxidized under aerobic conditions to give [{Cu(^*L ^R)Cl}₂] complexes (4), where H^*L ^R = N-(dialkylthiocarbamoyl)-N′-picolinoylbenzamidines. Complexes 1 and 2 show a very weak reduction of the growth of human MCF-7 breast cancer cells. Complexes 4, however, possess a remarkable cytotoxicity with IC₅₀ values within the range 0.40-1.05 μM. Compounds 3 are likely converted to 4 under the conditions of the cytotoxicity assay, and consequently exhibit IC₅₀ values very similar to those found for 4.

Full text of DOI:10.1016/j.poly.2012.08.088

Polyhedron 48 (2012) 181–188
Contents lists available at SciVerse ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Ni(II), Pd(II) and Cu(II) complexes with N-(dialkylthiocarbamoyl)-
N0-picolylbenzamidines: Structure and activity against human
MCF-7 breast cancer cells
b
a
a
c
Hung Huy Nguyen a, , Canh Dinh Le , Chien Thang Pham , Thi Nguyet Trieu , Adelheid Hagenbach ,
⇑
Ulrich Abram c,
⇑
a Department of Chemistry, Hanoi University of Science, 19 Le Thanh Tong, Hanoi, Viet Nam
b Department of Chemistry, Quy Nhon University, 170 An Duong Vuong, Quy Nhon, Viet Nam
c Institute of Chemistry and Biochemistry, Freie Universität Berlin, Fabeckstraße 34-36, D-14195 Berlin, Germany
a r t i c l e i n f o
a b s t r a c t
N-(Dialkylthiocarbamoyl)-N0-picolylbenzamidines (HLEt and HLMorph
) react with NiCl2, CuCl2 and
Article history:
[PdCl2(MeCN)2] with the formation of complexes of the general composition [M(LR)Cl] (M = Ni (1), Pd
(2)) and the dimeric complexes [{Cu(LR)Cl}2] (3). The molecular structures of complexes 1 and 2 exhibit
a square-planar coordination sphere, in which the organic ligands coordinate in a S,N,N coordination
mode. The two subunits of 3, the arrangement of each is similar to those of 1 and 2, are connected via
two weak Cu–Cl0 bonds. The copper complexes [{Cu(LR)Cl}2] (3) are slowly oxidized under aerobic
conditions to give [{Cu(⁄LR)Cl}2] complexes (4), where H⁄LR = N-(dialkylthiocarbamoyl)-N0-picolinoyl-
benzamidines. Complexes 1 and 2 show a very weak reduction of the growth of human MCF-7 breast
cancer cells. Complexes 4, however, possess a remarkable cytotoxicity with IC50 values within the range
Received 18 May 2012
Accepted 28 August 2012
Available online 23 September 2012
Keywords:
Tridentate ligands
Thiocarbamoyl benzamidines
Cytotoxicity
Ni(II) complex
Pd(II) complex
0.40–1.05
consequently exhibit IC50 values very similar to those found for 4.
Ó 2012 Elsevier Ltd. All rights reserved.
lM. Compounds 3 are likely converted to 4 under the conditions of the cytotoxicity assay, and
Cu(II) complex
1. Introduction
of Cu(II) and Ni(II) with tetradentate benzamidines derived from
o-phenylenediamine [10] and a few complexes of Au(III) with tri-
dentate benzamidines derived from 4,4-dialkylthiosemicarbazide
[11].
Bidentate N-(dialkylthiocarbamoyl)benzamidines (S,N-type li-
gands of Scheme 1) (I) are well known chelators, which can be
readily prepared by the reactions of N-(dialkylthiocarbamoyl)
benzimidoylchlorides with ammonia or primary amines [1,2]. Dur-
ing recent decades, a large number of bidentate benzamidine li-
gands and their complexes with most transition metal ions have
been extensively studied [3]. In principle, thiocarbamoylbenzami-
dines with higher denticity can readily be achieved by the intro-
duction of functionalized primary amines into the ligand
synthesis. However, surprisingly less is known about the chemistry
of such multidentate benzamidine-type ligands. Only a few triden-
tate benzamidines having S,N,N [4], S,N,O [4–6], S,N,S [7,8] and S,N,P
[9] donor sets (II) and a tetradentate benzamidine with an S,N,N,S
donor set [10] (Scheme 1) (III) have been recently reported. The
coordination chemistry of these ligands is mainly restricted to
their rhenium and technetium complexes [4–9]. For other transi-
tion metals, hitherto, there are only reports about two complexes
Recently, we have pursued investigations on the biological acti-
vitiy of multidentate benzamidines and their transition metal com-
plexes. In fact, derivatives of thiosemicarbazides and their {ReVO}3+
and Au(III) complexes were found promising for the inhibition of
the growth of human MCF-7 breast cancer cells [8,11]. Addition-
ally, it is evident that the properties of the compounds can easily
be tuned by convenient modifications to the periphery of their che-
lating systems, which allows systematic SAR studies [4–11]. Here,
we report on the synthesis and characterization of complexes
of potentially tridentate N-(dialkylthiocarbamoyl)-N0-picolyl
benzamidine ligands (HLR, Chart 1) with transition metal ions such
as Ni(II), Pd(II) and Cu(II), as well as the first evaluation of their
in vitro cytotoxic activity.
2. Results and discussion
⇑
Corresponding authors. Address: Department of Inorganic Chemistry, Hanoi
University of Science, 19 Le Thanh Tong, Hanoi, Viet Nam (H.H. Nguyen). Tel.: +84
1294849543; fax: +84 43 8241140.
N-(Dialkylthiocarbamoyl)-N0-picolyl benzamidines readily react
with NiCl2 in MeOH to give red solutions, from which red crystals
of the composition [Ni(LR)Cl] (1) were isolated in high yields
(Scheme 2).
E-mail addresses: nguyenhunghuy@hus.edu.vn (H.H. Nguyen), abram@chemie.
fu-berlin.de (U. Abram).
0277-5387/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.poly.2012.08.088

182
H.H. Nguyen et al. / Polyhedron 48 (2012) 181–188
R3
N
R1
N
H
N
HN-X =
HN
Ph2P
HN
HN
R4
R1
N
N
N
N
R1
N
R2
S
N
{S,N,N}
{S,N,S}
{S,N,P }
R2
N
NH
NH
S
S
R2
NH
X
S
NRH
S
HN
HOOC
HN
HO
H
N
R2
N
HN
R = H, alkyl, aryl
O
R1
{S,N,N,S}
(III)
I
( )
(II)
{S,N,O}
Scheme 1. Bi- tri- and tetradentate thiocarbamoyl benzamidines.
R1
N
R1
N
N
N
R2
R2
NH
S
O
NH
S
H2C
C
HLEt : R1 = R2 = Et
H*LEt : R1 = R2 = Et
N
N
HLMorph : NR1R2 = morpholine
H*LMorph : NR1R2 = morpholine
Chart 1. Ligands used in this study.
R1
N
R1
N
N
NH
N
1a : M = Ni, R1 = R2 = Et
R2
R2
1b : M = Ni, NR1R2 = morpholine
2a : M = Pd, R1 = R2 = Et
S
N
N
S
+ NiCl2 or [Pd(MeCN)2Cl2]
- HCl
H2C
H2C
M
Cl
2b : M = Pd, NR1R2 = morpholine
N
Scheme 2. Synthesis of [Ni(LR)Cl] (1) and [Pd(LR)Cl] (2).
IR spectra of complexes 1 exhibit strong bands in the 1500 cmꢀ1
central Ni atom and the pyridine N atom is indicated by a significant
low field shift of about 0.4 ppm of the signal assigned to the proton
in the ortho position to this N atom. This consequently leads to a
five-membered chelate ring and results in a high field shift about
0.3 ppm of the resonance corresponding to the two methylene pro-
tons in the ring. Furthermore, the observation of a singlet for the
CH2 protons of the five-membered chelate ring reveals their mag-
netic equivalence, which is consistent with a square-planar coordi-
nation environment for the Ni(II) complexes. In contrast, in
octahedral complexes of {ReVO}3+, these two methylene protons
are magnetically unequal. Their resonances are observed as two
doublets with typical geminal coupling patterns [4].
The proposed composition and structure of the complexes 1, de-
rived from spectroscopic analysis, are supported by X-ray single
crystal diffraction studies. The molecular structure of 1b is shown
in Fig. 1 as a representative for this type of complex. Because the
structure of 1a is identical, with the exception of the dialkylamino
residue, no extra Figure is given. Table 1 contains selected bond
lengths and angles for both compounds. In both complexes, the
Ni atom reveals the expected square-planar environment. Three
positions in the coordination sphere are occupied by the S1, N5,
N56 donor atoms of the monoanionic {LR}ꢀ ligand and the remain-
ing position is occupied by a chlorido ligand. The formed square
planes are slightly distorted with maximum deviations of
0.045(1) and 0.038(1)/0.065(1) Å from the mean least-square plane
for the N5 atoms in 1a and 1b, respectively. The Ni-N5 bonds are
slightly shorter (about 0.06 Å) than the Ni-N56 bonds. This is in
good agreement with the expected deprotonation of the ligands
and the formation of mononanionic benzamidine chelate rings.
Nevertheless, all the Ni-N and Ni-S bond lengths are in the typical
ranges found for nickel–nitrogen and nickel–sulfur single bonds. In
both complexes, the six-membered benzamidine chelate rings are
region, but no absorptions in the range between 1608 and
1620 cmꢀ1, where the mC@N stretches in the spectra of the non-
coordinated benzamidines typically appear. This corresponds to a
strong bathochromic shift of about 110 cmꢀ1 and reflects chelate
formation with a large degree of
p-electron delocalization within
the chelate rings, as has been observed for other benzamidine com-
plexes [3]. The absence of absorption bands in the region around
3215 cmꢀ1, which are assigned to
mN–H vibrations in the uncoordi-
nated HL, indicates the expected deprotonation of the ligands upon
complex formation.
1H NMR spectra of 1 are characterized by broad signals for most
of the protons. The hindered rotation around the R2N–CS bonds,
commonly discussed in 1H NMR studies of related complexes,
may cause the poor resolution of the signals corresponding to the
aliphatic protons in the dialkylamino groups [12]. However, the de-
scribed pattern is most likely due to the labile character and/or dis-
tortion of the square planar Ni(II) complexes since the broadening is
extended to the signals of the aromatic protons in the phenyl as
well as in the pyridyl rings [13]. Nevertheless, the rigid model of
the R2N–CS moiety, which results in magnetic inequivalence of
the alkyl groups, is also found in the spectra of the Ni(II) complexes
under study. Thus, in the 1H NMR spectrum of 1a, four broadened
singlets, two in the region of 1.0–1.2 ppm and two others in the re-
gion around 3.6 ppm are assigned to the resonances of CH3 and
NCH2 protons, respectively. The resonances corresponding to the
four methylene groups of the Morph residue in 1b are observed
as four broad signals between 3.7 and 4.2 ppm. More importantly,
the absence of the broad N–H resonance, found in the region of
6.9 ppm for the free ligands, in the 1H NMR spectra of 1 confirms
the deprotonation of the coordinated benzamidines and formation
of {N,S} chelate rings. An additional coordination bond between the

H.H. Nguyen et al. / Polyhedron 48 (2012) 181–188
183
also results in two magnetically unequal ethyl groups, which is
indicated by well resolved signals including two triplets and two
other quartets with almost the same chemical shifts as the corre-
sponding resonances in 1a. The most significant differences are
the resonances corresponding to the proton in the ortho position
to the pyridine N atom and the methylene protons in PyCH2ꢀ.
These signals are low field shifted by approx. 0.3 ppm in the 1H
NMR spectra of 2 compared to those of complexes 1.
Compounds 2 are well soluble in chlorinated solvents like CHCl3
and CH2Cl2, but almost insoluble in alcohols. Slow evaporation of a
CH2Cl2/MeOH solution of 2a gave single crystals suitable for X-ray
studies. An ORTEP diagram of 2a (Fig. 2) confirms an analogous
bonding situation as discussed for complexes 1. The corresponding
bond lengths and angles are compared to those of the structurally
characterized nickel complexes in Table 1. The coordination sphere
of the palladium atom is best described as almost ideal square-
planar, with a main distortion of only 0.046(1)/0.021(1) Å for atom
N5 from the mean least-squares plane formed by the Pd, S1, N5,
N56 and Cl atoms. The planar feature can be extended to include
both the six-membered benzamidine ring and the five-membered
ring, with a maximum deviation from the mean least-squares
plane of 0.103(3)/0.091(3) Å for atom S1.
Fig. 1. ORTEP representation of 1b (50% thermal ellipsoids) [22]. Hydrogen atoms
have been omitted for clarity.
The reactions of the ligands HLR and CuCl2 in MeOH lead to the
rapid formation of dark blue microcrystalline solids of the compo-
sition [{Cu(LR)Cl}2] (3) (Scheme 3). IR spectra of complexes 3,
which mainly exhibit the same patterns as described for the nickel
complexes 1, indicate a similar bonding situation as discussed for
the nickel complexes. Compounds 3 are stable in the solid state.
Solutions of 3 in CH2Cl2/MeOH, however, gradually change their
color from blue to light blue under aerobic conditions. Thus, X-
ray quality single crystals of 3a could only be obtained by slow dif-
fusion of MeOH into a CH2Cl2 solution of the complex under N2
atmosphere. Fig. 3 illustrates the dimeric structure of the com-
pound. Selected bond lengths and angles of the two crystallograph-
ically independent molecules found in the asymmetric unit cell of
3a are summarized in Table 2. In each monomer, the arrangement
of the organic ligand and the chlorido ligand around the central
copper atom is analogous to those described for the Ni(II) and
Pd(II) complexes. The two subunits, which are related by a center
of inversion, are connected by two very weak Cu-Cl0 bonds with
the distances of 2.978(1)/2.947(1) Å for the two symmetry-
independent molecules. Thus, each of the copper atoms has a dis-
torted square pyramidal environment (Addison distortion index,
Table 1
Selected bond lengths and angles in [Ni(LEt)Cl] (1a), [Ni(LMor)Cl] (1b) and [Pd(LEt)Cl]
(2a).
1a
1b*
2a*
Bond lengths (Å)
M–S1
M–N5
M–N56
M–Cl
S1–C2
C2–N3
N3–C4
C4–N5
C2–N41
2.136(1)
1.868(2)
1.928(2)
2.196(1)
1.733(3)
1.339(3)
1.332(3)
1.316(3)
1.340(3)
2.137(1)/2.138(1)
1.875(2)/1.868(2)
1.944(2)/1.942(2)
2.212(1)/2.193(1)
1.717(3)/1.714(3)
1.330(3)/1.333(3)
1.342(3)/1.340(3)
1.312(4)/1.315(4)
1.354(4)/1.359(4)
2.228(3)/2.233(3)
1.981(7)/1.976(6)
2.042(8)/2.048(8)
2.325(2)/2.315(2)
1.722(8)/1.732(8)
1.34(1)/1.32(1)
1.34(1)/1.33(1)
1.29(1)/1.33(1)
1.34(1)/1.35(1)
Angles (°)
S1–M–N5
N5–M–N56
N56–M–Cl
Cl–M–S1
95.6(1)
85.1(1)
94.0(1)
85.3(1)
179.4(1)
175.8(1)
95.5(1)/95.9(1)
85.6(1)/86.1(1)
94.1(1)/93.5(1)
84.8(1)/84.6(1)
178.5(1)/175.5(1)
177.3(1)/177.4(1)
95.9(2)/96.2(2)
83.2(3)/82.7(3)
94.6(2)/94.2(2)
86.3(1)/87.0(1)
179.0(2)/178.6(2)
175.9(2)/176.6(2)
S1–M–N56
N5–M–Cl
*
Two crystallographically independent species.
s
= 0.11/0.12) with the distance from the central atom to the apical
slightly distorted, with main deviations of 0.184(1) Å (for S1 in 1a)
and 0.094(1)/0.099(1) Å (for Ni in 1b) from the mean least-square
planes. A considerable delocalization of
p-electron density inside
the chelate rings is observed and indicated by the C–S and C–N
bond lengths, which are all within the range between typical C–S
(1.80 Å), C–N (1.47 Å) single bonds and C@S (1.67 Å), C@N
(1.28 Å) double bonds [14]. The bond length equalization is even
extended to the C2–N41 bonds, which are significantly shorter
than that expected for single bonds. This observation is consistent
with the hindered rotation around the CS–NR2 bond, as revealed by
the 1H NMR analysis.
Reactions of HLR with [PdCl2(MeCN)2] in CH2Cl2/MeOH (Scheme 2)
are much slower than those with NiCl2. The addition of a support-
ing base like Et3N accelerates the reaction rate, which can be
detected by a rapid color change from brown–yellow to bright
yellow. Crystalline yellow solids of the composition [Pd(LR)Cl] (2)
are isolated as the sole products in excellent yields.
The IR spectra of complexes 2 are very similar to those of 1, ex-
cept that the absorption bands of the mC@N stretches appear at
higher frequencies by about 10 cmꢀ1. The 1H NMR spectra of 2 ex-
hibit a compatible pattern, but with a better resolution. In the case
of 2a, for instance, the hindered rotation around the CS–NEt2 bond
Fig. 2. ORTEP representation of 2a (50% thermal ellipsoids) [22]. Hydrogen atoms
have been omitted for clarity.

184
H.H. Nguyen et al. / Polyhedron 48 (2012) 181–188
R1
N
R1
N
N
N
R1
N
R2
R2
O
N
R2
N
N
S
N
N
S
H2C
C
Cu
Cu
NH
S
+
+
O2
CuCl2
Cl
H2C
Cl
- H2O
- HCl
Cl
S
N
Cl
S
N
N
Cu
Cu
CH2
C
N
N
O
R2
R2
N
N
N
N
R1
R1
3a : R1 = R2 = Et
4a : R1 = R2 = Et
3b : NR1R2 = morpholine
4b : NR1R2 = morpholine
Scheme 3. Synthesis of [{Cu(LR)Cl}2](3) and [{Cu(⁄LR)Cl}2](4).
having a similar ligand sphere, such as [Cu(HL)Cl2] complexes
where HL are {N,N,S} tridentate, 2-pyridineformamide N(4)-
dialkylthiosemicarbazone [16]. ESI(+) mass spectra of 3 show no
molecular peak for the dimeric structure, but peaks of moderate
intensity are obtained which can be assigned to the monomeric
ions [Cu(LR)Cl+H]+ (m/z = 424 for 3a, m/z = 438 for 3b) with the ex-
pected isotopic patterns. More intense peaks are assigned to
[Cu(LR)]+ fragments, which result from the loss of the chlorido li-
gands from the monomeric ions.
Slow evaporation of a CH2Cl2/MeOH solution of 3 in air results
in the formation of light blue crystals of 4. The IR spectra of these
compounds are characterized by a very strong absorption band in
the 1660 cmꢀ1 region. Such bands are indicative of mC=O stretches,
which is a strong hint for the oxidation of the main skeleton of the
organic ligands{LR}ꢀ by atmospheric oxygen and the formation of
an amide. This assumption is supported by the ESI(+) mass spectra
of 4. They show the same fragmentation pattern as the correspond-
ing complexes 3, but at m/z values, which are each higher by 14
mass units. The visible spectra of 4 reveal a single band in the
600 nm region. This corresponds to a red shift of about 25 nm
compared to the corresponding bands of 3 and reflects a smaller
elongation of the coordination sphere toward the z axis [17].
An X-ray structural study confirmed the expected oxidation of
the ligand {LR}ꢀ, in which the methylene group attached to the pyr-
idine ring was converted to a carbonyl group to form a new tride-
nate monoanionic ligand {⁄LR}ꢀ. The described air oxidation of the
benzylic carbon in HLR is unprecedented. In the solid state, com-
pounds 4 are also in a dimeric form, with the general composition
[{Cu(⁄LR)Cl}2]. The dimerization in 4a (Fig. 4) is very similar to that
in 3a except that the coordination bond between the central Cu(II)
atom and the axial chlorido ligand is about 0.3 Å shorter. This re-
sults in an increase of the deviation of central Cu atom out of the
Fig. 3. ORTEP representation of 3a (50% thermal ellipsoids) [22]. Hydrogen atoms
have been omitted for clarity.
position being much elongated. Although the basal plane of 3a is
distorted, the central Cu atom is displaced from the plane of the
four in-plane donor atoms by only 0.083(1)/0.087(1) Å toward
the axial ligand. This distance is not in the common range (0.1–
0.5 Å) for square-pyramidal Cu(II) complexes, but is consistent
with the previously reported inverse correlation between the devi-
ation out of the basal plane and the distance to the apical donor
atom (L5) of a central Cu atom, i.e. the longer the Cu–L5 distance
the smaller the deviation [15].
The electronic spectra of 3 in CHCl3 show a broad band centered
at 575 nm with low extinction coefficient values that correspond to
the d–d transition. These absorption bands are in the same region
reported for distorted square pyramidal [Cu{N2S}Cl2] complexes
Table 2
Selected bond lengths and angles in [{Cu(⁄LEt)Cl}2] (3a) and [{Cu(⁄LEt)Cl}2] (4a).
Bond lengths (Å)
3a⁄
4a
3a⁄
4a
Cu–S1
Cu–N5
Cu–N56
Cu–Cl
Cu-Cl10
C6–O7
2.224(1)/2.227(1)
1.948(2)/1.941(2)
2.028(2)/2.030(3)
2.276(1)/2.271(1)
2.978(1)/2.947(1)
2.286(1)
1.956(4)
2.040(3)
2.289(1)
2.689(1)
1.225(6)
S1–C2
C2–N3
C2–N41
N3–C4
C4–N5
N5–C6
1.716(3)/1.719(3)
1.344(4)/1.341(4)
1.342(4)/1.353(4)
1.335(4)/1.344(3)
1.306(4)/1.309(4)
1.468(4)/1.469(4)
1.726(5)
1.358(6)
1.322(5)
1.294(5)
1.367(5)
1.359(5)
Angles (°)
S1–Cu–N5
N5–Cu–N56
N56–Cu–Cl
Cl–Cu–S1
95.4(1)/96.0(1)
83.0(1)/83.0(1)
93.8(1)/94.3(1)
88.1(1)/87.0(1)
169.8(1)/169.5(1)
176.5(1)/176.9(1)
93.3(1)
81.2(1)
94.8(1)
88.4(1)
158.7(1)
173.0(1)
N(5)–Cu–Cl10
N(56)–Cu–Cl10
S(1)–Cu–Cl10
Cl–Cu–Cl10
87.2(1)/82.7(1)
84.4(1)/91.2(1)
105.6(1)/99.1(1)
91.1(1)/96.1(1)
88.9(1)/83.9(1)
96.2(1)
96.0(1)
105.1(1)
89.9(1)
90.1(1)
S1–Cu–N56
N5–Cu–Cl
Cu–Cl–Cu10
Symmetry transformations used to generate equivalent atoms: for 3a (1 ꢀ x,1 ꢀ y,ꢀz)/(1 ꢀ x,ꢀy,1 ꢀ z), (0) for 4a (ꢀx,ꢀy + 2,ꢀz).

H.H. Nguyen et al. / Polyhedron 48 (2012) 181–188
185
of HLEt (>400
l
M), this value is still far too high for a promising
bioactive substance. The complexation of HLR with metal ions is
expected to increase the cytotoxicity of the compound. In fact, all
the complexes of HLR studied herein exhibit IC50 values, which
are lower than those of the free ligands (Table 3). The Ni(II) and
Pd(II) complexes have IC50 values higher than 70 lM, reflecting
low cytotoxicity. While the antiproliferative effect of [Ni(LEt)Cl] is
stronger than that of [Pd(LEt)Cl], the activities of the two
{LMorph ꢀ complexes 1b and 2b are similar. For the Ni(II) and Pd(II)
}
complexes, the IC50 values of the complexes with {LMorph ꢀ are low-
}
er than those with {LEt}ꢀ. Surprisingly, the replacement of the metal
ion by Cu(II) in 3 results in a dramatic decrease of their IC50 values
(3a: IC50 = 0.42; 3b: IC50 = 1.14), which are much lower than that of
cisplatin (IC50 = 7.10, determined under the same experimental
conditions) [18]. This is particularly interesting due to the fact that
the uncomplexed Cu2+ ion has almost no effect on the growth of
MCF-7 cancer cells [19]. Additionally, the structural effect of the
dimeric form of 3 can be excluded due to the very weak bridging
Cu–Cl0 bond which should be readily cleaved during exchange reac-
tions with plasma components. Under the conditions present in the
cytotoxicity assay, however, the oxidation of complexes 3 by oxy-
gen to 4 cannot be excluded. Thus, the cytotoxic effects of 4 were
additionally studied. The obtained results show very compatible
IC50 values between the respective complexes 3 and 4, which
strongly suggests that oxidation of complexes 3 occurs during the
determination of the cytotoxicity. For the Cu(II) complexes of these
new ligand systems, the replacement of the Morph substituent (4b:
IC50 = 1.05) by an N,N-diethyl group (4a: IC50 = 0.40) increases the
activity by more than a factor 2.
The interesting cytotoxic properties of 4 should involve the nat-
ure of the new ligand framework {⁄LR}ꢀ and it will be worth study-
ing the bioactivity of these ligands as well as their complexes with
other metal ions. However, up until now all our attempts to isolate
reasonable amounts of pure H⁄LR by the decomposition of 4 with
H2S failed. Currently, we are trying to synthesize larger amounts
of H⁄LR directly from the reaction of benzimidoyl chloride. The bio-
activity of these ligands and their metal complexes will be studied
in the future.
Fig. 4. ORTEP representation of 4a (50% thermal ellipsoids) [22]. Hydrogen atoms
have been omitted for clarity.
square basal plane by about 0.2 Å. The Cu atom is placed about
0.254(2) Å above the plane defined by the three donor atoms S1,
N5, N56 of the organic ligand {⁄L}ꢀ and one chlorido ligand to-
wards the apical bridging chlorido ligand. The six membered ben-
zamidine chelate ring in 4a is significantly distorted (with a
maximum distortion of 0.322(3) Å for N5 atom). This is in good
agreement with unequal distances of the C–N bonds in the ben-
zamidine chelate ring, in which the C4–N3 bond with a length of
1.294(5) Å is considerably shorter and reflects more double bond
character than the other C–N bonds. The C6-O7 bond distance of
1.225(6) Å is within the typical range of carbon–oxygen double
bonds. Conjugation between this carbonyl group and the adjacent
nitrogen atom N5 is also found and indicated by the N5-C6 bond
length of 1.359(5) Å, which is significantly shorter than the corre-
sponding bond in 3a. Some other selected bond lengths and angles
of 4a are compared to those of 3a in Table 2.
It is well-known that the cytotoxic properties of a bioactive li-
gand can be influenced by chelate formation. Several mechanisms
of antitumor activity of metal complexes have been proposed.
Changed activity of a thermodynamically stable and kinetically in-
ert metal complex is due to the difference in the nature of mole-
cules, while that of labile metal complexes may be assigned to
the effect of a metal-assisted transport and consequent complex
dissociation inside the cell which releases the biologically active
species. We investigated the antiproliferative effects of the ligands
HLR, their complexes with different metal ions (compounds 1–3)
and complexes 4 on human MCF-7 breast cancer cells in a concen-
tration response assay. This allows the determination of their IC50
values. In the cell, compounds 3 and 4 can undergo ligand exchange
reactions, during which the very weak and labile Cu–Cl0 bond is pri-
marily cleaved by interaction with biological ligands. Thus, the IC50
values of 3 and 4 are reported based on the concentration of their
monomeric complexes. The compounds HLR only cause a very weak
reduction of the growth of human MCF-7 breast cancer cells.
3. Experimental
3.1. Materials
All reagents used in this study were reagent grade and used
without further purification. Solvents were dried and freshly dis-
tilled prior to use unless otherwise stated. [PdCl2(MeCN)2] was
synthesized by a literature procedure [20].
3.2. Physical Measurements
Infrared spectra were measured as KBr pellets on a Shimadzu
FTIR-spectrometer between 400 and 4000 cmꢀ1. Positive ESI mass
spectra were measured with an Agilent 6210 ESI–TOF. All MS re-
sults are given in the form: m/z, assignment. Elemental analysis
of carbon, hydrogen, nitrogen and sulfur were determined using
a Heraeus vario EL elemental analyzer. Electronic spectra were
measured in CHCl3 with a Shimadzu UV-1650PC.
Although the IC50 value of HLMorph (94
lM) is much lower than that
Table 3
3.3. Preparation of the ligands
Cytotoxic effects of the ligands HL and their complexes against MCF-7 Cells.
The N-(dialkylthiocarbamoyl)-N0-picolylbenzamidines were
prepared following our previously published procedure with slight
modifications [4]. N-(N0,N0-Dialkylylaminothiocarbonyl)-benzimi-
IC50
HLR
(
l
M)
[Ni(LR)Cl]
[Pd(LR)Cl]
[Cu(LR)Cl]
[{Cu(⁄LR)Cl}2]
R = Et
R = Morph
>400
94
117
75
274
76
0.42
1.14
0.40
1.05
doyl chloride (4 mmol) was added to
a mixture containing
picolylamine (4 mmol) and Et3N (12 mmol) in 10 mL of dry THF.

186
H.H. Nguyen et al. / Polyhedron 48 (2012) 181–188
The mixture was stirred for 3 h at room temperature. The colorless
precipitate of NEt3ꢁHCl was filtered off, and the solvent of the
filtrate was removed under reduced pressure. The residue was
dissolved in 5 mL of a MeOH/diethyl ether mixture (1/1) and stored
at ꢀ20 °C. The colorless solid of H2L, which deposited from this
solution, was filtered off, washed with diethyl ether, and dried
under vacuum.
3.4.2. Synthesis of [Pd(LR)Cl] (2)
[PdCl2(MeCN)2] (0.2 mmol) was dissolved in 5 mL of CH2Cl2 and
added to a solution of HLR (0.2 mmol) in 5 mL methanol. After stir-
ring for 5 min at room temperature, three drops of NEt3 were
added. The reaction mixture was stirred for additional 10 min until
its brown-yellow color turn to bright yellow. Large yellow crystals
of 2 were obtained from the reaction mixture by slow evaporation
of the solvent.
3.3.1. Data for HLEt
3.4.2.1. Data for [Pd(LEt)Cl] (2a). Yield: 78% (73 mg). Elemental anal-
ysis: Calc. for C18H21ClN4PdS: C, 46.26; H, 4.53; N, 11.99; S, 6.86.
Found: C, 46.04; H, 4.87; N, 12.12; S, 6.77%. IR (KBr, cmꢀ1): 3058
(w), 2983 (w), 2925 (w), 1514 (vs), 1485 (vs), 1457 (vs), 1436
(vs), 1418 (vs), 1350 (s), 1254 (m), 1138 (m), 1075 (m), 772 (w),
713 (w). 1H NMR (500 MHz, CDCl3, ppm): 1.08 (t, 7.0 Hz, 3H,
CH3), 1.29 (t, 7.0 Hz, 3H, CH3), 3.57 (q, 7.0 Hz, 2H, CH2), 3.82 (q,
7.0 Hz, 2H, CH2), 4.83 (s, 2H, CH2-Py), 7.20 (d, J = 8.0 Hz, 1H, py),
7.26–7.45 (m, 6H, Ph + py), 7.78 (t, 8.0 Hz, 1H, py), 9.14 (d,
5.5 Hz, 1H, py). ESI(+)MS (m/z, assignment): 469 ([M+H]+).
Yield: 85% (1.108 g). Elemental analysis: Calc. for C18H22N4S: C,
66.22; H, 6.79; N, 17.16; S, 9.82. Found: C, 65.72; H, 6.58; N, 16.82;
S, 9.05%. IR (KBr, cmꢀ1): 3217 (m), 3065 (m), 2980 (w), 2928 (w),
1608 (vs), 1582 (s), 1535 (s), 1482 (s), 1355 (m), 1292 (s), 1254
(m), 1112 (s), 1080 (m), 1025 (m), 946 (w), 925 (w), 779 (m),
687 (m). 1H NMR (500 MHz, CDCl3, ppm): 1.18 (t, J = 7.0 Hz, 3H,
CH3), 1.25 (t, J = 7.0 Hz, 3H, CH3), 3.64 (q, J = 7.0 Hz, 2H, CH2),
3.93 (q, J = 7.0 Hz, 2H, CH2), 4.73 (s, 2H, CH2-Py), 6.89 (s, br, 1H,
NH), 7.21 (t, J = 6.1 Hz, 1H, py), 7.38–7.45 (m, 4H, Ph + py), 7.52
(d, J = 6.8 Hz, 2H, Ph), 7.70 (t, J = 7.5 Hz, 1H, py), 8.53 (d,
J = 4.8 Hz, 1H, py).
3.4.2.2. Data for [Pd(LMorph)Cl] (2b). Yield: 80% (77 mg). Elemental
analysis: Calc. for C18H19ClN4PdOS: C, 44.92; H, 3.98; N, 11.64; S,
6.66. Found: C, 45.10; H, 4.09; N, 11.32; S, 6.54%. IR (KBr, cmꢀ1):
2954 (w), 2886 (w), 1524 (vs), 1474 (vs), 1426 (s), 1343 (s), 1200
(m), 1115 (m), 1023 (m), 783 (m), 762 (m), 723 (w). 1H NMR
(500 MHz, CDCl3, ppm): 3.70 (s, br, 4H, NCH2), 4.02 (s, br, 4H,
NCH2), 4.84 (s, 2H, CH2-Py), 7.22 (d, J = 8.0 Hz, 1H, py), 7.31(d,
J = 7.5 Hz, 2H, Ph), 7.35 (t, J = 7.0 Hz, 1H, Ph), 7.43–7.48 (m, 3H,
Ph + py), 7.80 (t, J = 8.0 Hz, 1H, py), 9.16 (d, J = 5.5 Hz, 1H, py).
ESI(+)MS (m/z, assignment): 483 ([M+H]+).
3.3.2. Data for HLMorph
Yield: 70% (0.952 g). Elemental analysis: Calc. for C18H20N4OS:
C, 63.50; H, 5.92; N, 16.46; S, 9.42. Found: C, 64.01; H, 5.61; N,
16.42; S, 9.26%. IR (KBr, cmꢀ1): 3215 (m), 3051 (w), 2948 (w),
2894 (w), 2851 (w), 1620 (vs), 1597 (s), 1550 (s), 1435 (m), 1420
(s), 1350 (m), 1308 (s), 1288 (s), 1130 (m), 1112 (s), 1017 (m),
937 (w), 900 (w), 780 (m). 1H NMR (500 MHz, CDCl3, ppm): 3.63
(s, br, 2H, NCH2), 3.73 (s, br, 2H, NCH2), 3.81 (s, br, 2H, OCH2),
4.20 (s, br, 2H, OCH2), 4.73 (s, 2H, CH2-Py), 6.93 (s, br, 1H, NH),
7.17 (t, J = 6.4 Hz, 1H, py), 7.30–7.38 (m, 4H, Ph + py), 7.45 (d,
J = 6.8 Hz, 2H, Ph), 7.66 (t, J = 7.6 Hz, 1H, py), 8.46 (d, J = 4.5 Hz,
1H, py).
3.4.3. Synthesis of [{Cu(LR)Cl}2] (3) and [{Cu(⁄LR)Cl}2] (4)
The [{Cu(LR)Cl}2] complexes were prepared following a proce-
dure similar to that for 1, except that CuCl2 4H2O was used instead
of nickel chloride. The compounds 3 precipitated directly from the
reaction solutions as dark blue crystalline solids. Large dark blue
crystals of 3 were obtained by slow diffusion of MeOH into a solu-
tion of 3 in CH2Cl2 under N2 atmosphere. Light blue single crystals
of 4 were obtained by slow evaporation of a solution of 3 in MeOH/
CH2Cl2 under aerobic conditions.
3.4. Synthesis of the complexes
3.4.1. Synthesis of [Ni(LR)Cl] (1)
NiCl2 6 H2O (0.4 mmol) was dissolved in 5 mL of methanol and
added to a solution of HLR (0.4 mmol) in 5 mL methanol. A deep red
solution was obtained immediately, which was stirred at room
temperature for 15 min and then evaporated slowly to give large
red crystals of 1.
3.4.3.1. Data for [{Cu(LEt)Cl}2] (3a). Yield: 78% (132 mg). Elemental
analysis: Calc. for C36H42Cl2Cu2N8S2: C, 50.93; H, 4.99; N, 13.20;
S, 7.55. Found: C, 51.04; H, 4.80; N, 13.07; S, 7.63%. IR (KBr,
cmꢀ1): 3053 (w), 2971 (w), 2928 (w), 1519 (s), 1484 (vs), 1439
(vs), 1411 (vs), 1344 (s), 1257 (m), 1138 (w), 1075 (w), 764 (w),
712 (w). ESI(+)MS (m/z, assignment): 424 ([Cu(LEt)Cl+H]+), 388
3.4.1.1. Data for [Ni(LEt)Cl] (1a ). Yield: 80% (134 mg). Elemental
analysis: Calc. for C18H21ClN4NiS: C, 51.52; H, 5.04; N, 13.35; S,
7.64. Found: C, 51.06; H, 5.33; N, 13.72; S, 7.51%. IR (KBr, cmꢀ1):
3075 (w), 2976 (w), 2927 (w), 1503 (vs), 1486 (vs), 1425 (vs),
1347 (m), 1255 (m), 1141 (m), 1074 (m), 760 (w), 708 (w). 1H
NMR (500 MHz, CDCl3, ppm): 1.07 (s, br, 3H, CH3), 1.27 (s, br, 3H,
CH3), 3.55 (m, br, 2H, CH2), 3.78 (m, br, 2H, CH2), 4.48 (s, 2H,
CH2-Py), 7.04 (d, br, J = 7.0 Hz, 1H, py), 7.22–7.40 (m, 6H, Ph + py),
7.69 (m, br, 1H, py), 8.89 (s, br, 1H, py). ESI(+)MS (m/z, assignment):
419 ([M+H]+).
([Cu(LEt)]+). UV–Vis [CHCl3; kmax (nm),
e
(dm3 molꢀ1 cmꢀ1)]: 575
(280).
3.4.3.2. Data for [{Cu(LMorph)Cl}2] (3b). Yield: 83% (145 mg). Elemen-
tal analysis: Calc. for C36H38Cl2Cu2N8O2S2: C, 49.31; H, 4.37; N,
12.78; S, 7.31. Found: C, 49.19; H, 4.12; N, 12.85; S, 7.51%. IR
(KBr, cmꢀ1): 2910 (w), 2843 (w), 1509 (s), 1470 (vs), 1438 (vs),
1417 (vs), 1342 (s), 1263 (m), 1227 (m), 1205 (m), 1111 (m),
1029 (m), 788 (m), 765 (m). ESI(+)MS (m/z, assignment): 438
([Cu(LMorph)Cl+H]+), 402 ([Cu(LMorph)]+). UV–Vis [CHCl3; kmax
3.4.1.2. Data for [Ni(LMorph)Cl] (1b). Yield: 81% (140 mg). Elemental
analysis: Calc. for C18H19ClN4NiOS: C, 49.86; H, 4.42; N, 12.92; S,
7.40. Found: C, 49.70; H, 5.03; N, 13.12; S, 7.35%. IR (KBr, cmꢀ1):
3053 (w), 2961 (w), 2890 (w), 2853 (w), 1509 (vs), 1475 (vs),
1436 (s), 1346 (s), 1265 (m), 1227 (m), 1210 (m), 1115 (m), 1027
(m), 902 (w), 781 (m), 761 (m), 722 (m). 1H NMR (500 MHz, CDCl3,
ppm): 3.68 (s, br, 2H, NCH2), 3.74 (s, br, 2H, NCH2), 3.81 (s, br, 2H,
OCH2), 4.18 (s, br, 2H, OCH2), 4.43 (s, 2H, CH2-Py), 7.07 (d, br,
J = 7.0 Hz, 1H, py), 7.20–7.40 (m, 6H, Ph + py), 7.72 (m, br, 1H,
py), 8.86 (s, br, 1H, py). ESI(+)MS (m/z, assignment): 433 ([M+H]+).
(nm),
e
(dm3 molꢀ1 cmꢀ1)]: 574 (273).
3.4.3.3. Data for [{Cu(⁄LEt)Cl}2] (4a). Elemental analysis: Calc. for
C
36H38Cl2Cu2N8O2S2: C, 49.31; H, 4.37; N, 12.78; S, 7.31. Found:
C, 49.15; H, 4.41; N, 12.90; S, 7.50%. IR (KBr, cmꢀ1): 3059 (w),
2972 (w), 2932 (w), 1661 (vs), 1584 (s), 1568 (vs), 1525 (vs),
1446 (m), 1352 (vs), 1307 (m), 1280 (m), 1244 (m), 1136 (w),
1078 (w), 760 (w), 703 (w). ESI(+) MS (m/z, assignment): 438

H.H. Nguyen et al. / Polyhedron 48 (2012) 181–188
187
Table 4
Crystal data and structure refinement parameters.
1a
1b
2a
3a
4a
Formula
Mw
Crystal system
a (Å)
b (Å)
c (Å)
C
18H21ClN4NiS
C18H19ClN4NiOS
433.59
triclinic
C18H21ClN4PdS
467.30
triclinic
12.645(1)
12.923(1)
14.283(1)
64.46(1)
C18H21ClCuN4S
424.44
triclinic
11.713(1)
11.916(1)
17.001(1)
75.85(1)
C18H19ClCuN4OS
438.44
monoclinic
8.928(1)
21.334(1)
10.287(1)
90
419.61
monoclinic
8.086(1)
19.600(1)
12.224(1)
90
9.053(1)
11.073(1)
19.911(1)
87.25(1)
a
(°)
b (°)
105.75(1)
90
1864.6(3)
P21/n
83.64(1)
66.78(1)
66.83(1)
71.94(1)
70.00(1)
60.70(1)
99.16(1)
90
1934.4(3)
P21/n
c
(°)
V (Å3)
1823.0(3)
1908.1(2)
1935.9(3)
ꢀ
ꢀ
ꢀ
Space group
P1
P1
P1
Z
4
4
4
4
4
Dc (g cmꢀ3
)
1.495
1.304
12692
4985
227
1.580
1.341
22325
9810
470
0.0500/0.1258
0.939
1.627
1.230
1.456
1.382
1.505
1.389
14044
5160
236
0.0583/0.1315
0.962
l
(mmꢀ1
)
No. of reflections
No. of independent
No. parameters
R1/wR2
21463
10214
452
0.0677/0.1284
0.944
21035
10351
451
0.0463/0.0965
0.949
0.0549/0.1434
1.002
Goodness-of-fit
([Cu(⁄LEt)Cl+H]+). UV–Vis [CHCl3; kmax (nm),
601 (157).
e
(dm3 molꢀ1 cmꢀ1)]:
precipitate. The optical density of the solution was determined
by a plate reader (TECAN) at 540 nm. The inhibition ratio was
calculated on the basis of the optical densities obtained from three
replicate tests.
3.4.3.4. Data for [{Cu(⁄LMorph)Cl}2] (4b). Elemental analysis: Calc. for
C
36H34Cl2Cu2N8O4S2: C, 47.79; H, 3.79; N, 12.38; S, 7.09. Found: C,
48.04; H, 3.53; N, 12.32; S, 7.01%. IR (KBr, cmꢀ1): 3065 (w), 2997
(w), 2856 (w), 1658 (vs), 1584 (s), 1562 (vs), 1523 (s), 1447 (m),
1358 (vs), 1308 (m), 1278 (m), 1250 (m), 1141 (w), 1110 (w),
1026 (w), 762 (w), 703 (w). ESI(+) MS (m/z, assignment): 452
Acknowledgement
We thank Vietnam’s National Foundation for Science and Tech-
nology Development for financial support through Project 104.02–
2010.31.
([Cu(⁄LMorph)Cl+H]+). UV–Vis [CHCl3; kmax (nm),
e -
(dm3 molꢀ1
cmꢀ1)]: 603 (150).
Appendix A. Supplementary data
3.5. X-ray crystallography
CCDC 881132 (1a), 881130 (1b), 881131 (2a), 881133 (3a) and
881134 (4a) contain the supplementary crystallographic data.
These data can be obtained free of charge via http://www.ccdc.ca-
m.ac.uk/conts/retrieving.html, or from the Cambridge Crystallo-
graphic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK;
fax: +44 1223 336 033; or e-mail: deposit@ccdc.cam.ac.uk.
The intensities for the X-ray determinations were collected on a
STOE IPDS 2T instrument with Mo K radiation (k = 0.71073 Å).
Standard procedures were applied for data reduction and absorp-
tion correction. Structure solution and refinement were performed
with SHELXS-97 and SHELXL-97 [21]. Hydrogen atoms were calculated
for idealized positions and treated with the ‘riding model’ option of
a
S
HELXL [21].
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