Preparation and cis-to-trans transformation study of square-planar [Pt(Ln)2Cl2] complexes bearing cytokinins derived from 6-benzylaminopurine (Ln) by view of NMR spectroscopy and X-ray crystallography

Article abstract of DOI:10.1016/j.poly.2008.05.021

Mononuclear, square-planar platinum(II) complexes involving derivatives of aromatic cytokinins as the ligands, and having the general formula cis-[Pt(L_n)₂Cl₂] (1-3) and trans-[Pt(L_n)₂Cl₂] (4-6), where n = 1-3, L₁ = 2-chloro-6-(benzylamino)-9-isopropylpurine, L₂ = 2-chloro-6-[(4-methoxybenzyl)amino]-9-isopropylpurine and L₃ = 2-chloro-6-[(2-methoxybenzyl)-amino]-9-isopropylpurine, have been synthesized and characterized by elemental analysis, MALDI-TOF mass, FT IR, ¹H, ¹³C, ¹⁵N and ¹⁹⁵Pt NMR spectral measurements. Dynamic cis-to-trans isomerization process of complex 1 in N,N′-dimethylformamide (DMF) has been investigated by means of multinuclear NMR spectroscopy. The solid-state structures of 1, 4 · (DMF)₂, and 5 have been determined by single crystal X-ray analysis. X-ray structures revealed that the heterocyclic ligands are coordinated to platinum via nitrogen atom N(7) in all the complexes studied. In vitro cytotoxicity of the prepared complexes against MCF7, G361, K562, and HOS has been evaluated. Owing to low solubility of the complexes in water, the cytotoxicity has been only tested up to 5 μM concentration. Unfortunately, all complexes have been found to be non-cytotoxic in the accessible concentration range.

Full text of DOI:10.1016/j.poly.2008.05.021

Polyhedron 27 (2008) 2710–2720
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Polyhedron
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Preparation and cis-to-trans transformation study of square-planar [Pt(Ln)2Cl2]
complexes bearing cytokinins derived from 6-benzylaminopurine (Ln) by view
of NMR spectroscopy and X-ray crystallography
a
a,
Lucie Szücová , Zdenek Trávnícek , Igor Popa a,b, Jaromír Marek a,c
*
ˇ
ˇ
ˇ
a
´
Department of Inorganic Chemistry, Faculty of Science, Palacky University, CZ-771 47 Olomouc, Czech Republic
b Laboratory of Growth Regulators, Palacky´ University and Institute of Experimental Botany AS CR, CZ-783 71 Olomouc, Czech Republic
c Institute of Experimental Biology, Faculty of Science, Masaryk University, CZ-625 00 Brno, Czech Republic
a r t i c l e i n f o
a b s t r a c t
Article history:
Mononuclear, square-planar platinum(II) complexes involving derivatives of aromatic cytokinins as the
ligands, and having the general formula cis-[Pt(Ln)2Cl2] (1–3) and trans-[Pt(Ln)2Cl2] (4–6), where n = 1–
3, L1 = 2-chloro-6-(benzylamino)-9-isopropylpurine, L2 = 2-chloro-6-[(4-methoxybenzyl)amino]-9-iso-
propylpurine and L3 = 2-chloro-6-[(2-methoxybenzyl)-amino]-9-isopropylpurine, have been synthesized
and characterized by elemental analysis, MALDI-TOF mass, FT IR, 1H, 13C, 15N and 195Pt NMR spectral
measurements. Dynamic cis-to-trans isomerization process of complex 1 in N,N0-dimethylformamide
(DMF) has been investigated by means of multinuclear NMR spectroscopy. The solid-state structures of
1, 4 ꢀ (DMF)2, and 5 have been determined by single crystal X-ray analysis. X-ray structures revealed that
the heterocyclic ligands are coordinated to platinum via nitrogen atom N(7) in all the complexes studied.
In vitro cytotoxicity of the prepared complexes against MCF7, G361, K562, and HOS has been evaluated.
Received 8 April 2008
Accepted 20 May 2008
Available online 24 June 2008
Keywords:
Pt(II) complexes
Cytokinins
NMR spectroscopy
X-ray structures
In vitro cytotoxicity
Owing to low solubility of the complexes in water, the cytotoxicity has been only tested up to 5 lM con-
centration. Unfortunately, all complexes have been found to be non-cytotoxic in the accessible concen-
tration range.
Ó 2008 Elsevier Ltd. All rights reserved.
1. Introduction
plexes of the type [Pt(L)2X2] (where L = a monodentate N-donor
ligand, X = halide) in solid state as well as in solution. Above all,
Nowadays, there is indisputable fact that a platinum drug called
Cisplatin, i.e. cis-diamminedichloridoplatinum(II), of which the
cytotoxic effects were discovered by Rosenberg et al. in the
1960s [1], and some its derivatives, represent a unique class of
antineoplastic drugs used in current chemotherapy [2,3]. A high
number of recently prepared cis and/or trans-[Pt(L)2Cl2] (L = amine)
complexes showed the possibility to inhibit cell division and
growth of cancer cells [4]. This attribute initiated a great interest
in the potential application of these inorganic substances in the
treatment of tumors [4]. At present, novel potential platinum-
based anticancer agents are still intensively studied with the inten-
tion to improve their therapeutic profiles to overcome their side
effects and acquired resistance to the drugs [5,6]. Thus, an identi-
fication of cis/trans isomers was found to play a crucial role in
the characterization of the above mentioned types of Pt(II) com-
plexes because cis and trans isomers were found to possess sub-
stantially different cytotoxic effects when tested against various
cancer cell lines [7]. This fact gave rise the reason to study the ste-
reochemistry and geometric isomerism of square-planar com-
cis-to-trans isomerization of square–planar Pt(II) complexes in
solution is still a subject of great interest. The formation of the
trans isomer in a process which was supposed to give the cis isomer
gave impulse to focus on this phenomenon, especially if this effect
was already observed and determined, e.g. for [Pt(L)2Cl2] com-
plexes with L = aniline, 2,5-dimethyl-aniline or p-toluidine [8], cyc-
lobutylamine [9], cyclohexylamine [10], and cycloheptylamine
[11], Moreover, cis-to-trans isomerization reactions of [Pt(L)2X2]
complexes, where X = Cl, Br or NO3ꢁ, and L = pyridine or pyrimi-
dine [12,13], ketoxime [14], and pyridine [15], were also previously
reported. Generally, it may be concluded that the situation regard-
ing the isomerization process may be a bit complicated in a solu-
tion mainly because of the fact that trans-isomers may be formed
unexpectedly during the synthetic pathway or re-crystallization
of cis-isomers from some solvents [9,10]. For that reason, the mon-
itoring of cis-isomer behavior in solution was showed to be very
contributing. For instance, cis and trans-[Pt(amine)2I2] complexes
were studied using 195Pt NMR spectrometry in DMF and their cis-
to-trans isomerization was observed [16]. Similarly, the geometric
isomers distribution in case of platinum(II) complexes of the type
[M(L)2X2], where M = Pt or Pd, L = N-benzoyl-N0-propylthiourea,
X = Cl, Br or I, in chloroform was studied by 195Pt and 1H NMR
* Corresponding author. Tel.: +420 585634944; fax: +420 585634954.
ˇ
E-mail address: zdenek.travnicek@upol.cz (Z. Trávnícek).
0277-5387/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2008.05.021

ˇ
L. Szücová et al. / Polyhedron 27 (2008) 2710–2720
2711
spectrometry and their cis-to-trans isomerization process was also
investigated [17].
trans isomerization process was previously investigated in the case
of Pd(II) complexes of the type [Pd(L)2Cl2], where L = cytokinins de-
rived from 6-benzyalminopurine [34].
Besides the above-mentioned publications regarding the Cis-
platin-like complexes, there exists a great number of scientific pa-
pers concerning with the preparation, characterization and
biological activity testing of cis and trans Pt-complexes as well as
the papers describing the conditions and rules for their DNA bind-
ing. Among them, the following may be highlighted as examples,
e.g. [18–21].
In this paper, we describe the preparation of a series of isomer-
ically pure cis and trans-Pt(II) complexes of the general formula cis-
[Pt(Ln)2Cl2] and trans-[Pt(Ln)2Cl2], where n = 1–3, L1 = 2-chloro-6-
(benzylamino)-9-isopropylpurine (1, 4), L2 = 2-chloro-6-[(4-metho-
xybenzyl)-amino]-9-isopropylpurine ( 2, 5), L3 = 2-chloro-6-[(2-
methoxybenzyl)amino]-9-isopropylpurine (3, 6). The complexes
have been fully characterized by means of elemental analysis, MAL-
DI-TOF, FT IR and multinuclear NMR spectra, and complexes 1, 4
and 5 also by single crystal X-ray analysis. The complexes were also
investigated for their cytotoxic effects in vitro against four human
cancer cell lines: MCF7, K 562, G 361 and HOS. The cis-to-trans
isomerization process of the complexes in DMFA solutions was
studied by means of 1H, 13C, 15N and 195Pt NMR spectroscopy.
Based on these facts, we focused our attention on the prepara-
tion and characterization of isomerically pure Pt(II) complexes
bearing derivatives of plant growth hormones called cytokinins
as N-donor ligands and on their cis-to-trans isomerization pro-
cesses in solutions. One group of cytokinins, i.e. a class of natural
or artificial plant growth regulators discovered in the 1950s [22–
24], is represented by compounds bearing a 6-benzylaminopurine
moiety. Cytokinins play a very important role in plant growth and
development, including the promotion of cell division, senescence
and apical dominance regulation, and nutritional signals transmis-
sion [25–27]. Since the 1990s, some cytokinin derivatives based on
2,6,9-trisubstituted purine moiety have been extensively studied
due to their activity in the regulation of the eukaryotic cell cycle,
more specifically, due to their significant inhibition of cyclin-
dependent kinases (CDKs) [28,29]. The CDKs are protein kinase en-
zymes playing a considerable role in regulation of the cell cycle
[30]. Some of these CDK inhibitors, e.g. 2-[2-(hydroxyl-ethyl)ami-
no]-6-benzylamino-9-methylpurine (Olomoucine), 2-[3-(hydroxy-
propyl)amino]-6-benzylamino-9-isopropylpurine (Bohemine), and
2-{[1-(hydroxylmethyl)-propyl]-amino}-6-benzylamino-9-isopro-
pylpurine (Roscovitine, also named as seliciclib or CYC202) were
also found effective against the proliferation of some human cancer
cell lines both in vitro and in vivo [31,32]. The reason why we use
derivatives of aromatic cytokinins and/or cyclin-dependent kinase
inhibitors derived from 6-benzylaminopurine as the ligands for the
preparation of transition metal complexes is that the cytotoxicity
may be improved after the coordination of these organic molecules
to a suitable transition metal ion, e.g. to Pt(II) and Pd(II) [33,34],
Cu(II) [35], Zn(II) [36] or Co(II) [37], as we have found in the case
of complexes prepared previously in our laboratory. Up to now,
the dynamic cis-to-trans isomerization process of Pt(II) complexes
involving the above-discussed organic molecules has not been
investigated using NMR spectrometry yet. However, the cis-to-
2. Experimental
2.1. Materials
PtCl2 was used as received from Sigma–Aldrich Co. The organic
ligands 2-chloro-6-benzylamino-9-isopropylpurine (L1), 2-chloro-
6-[(4-methoxybenzyl)amino]-9-isopropylpurine (L2) and 2-
chloro-6-[(2-methoxybenzyl)amino]-9-isopropylpurine (L3) were
prepared by methods described in the literature [34]. Schematic
representations of all the ligands used in this study including atom
numbering are depicted in Fig. 1. Organic solvents used for the syn-
theses were purchased from Lachema Co., while N,N0-dimethyl-
formamide-d7 (99.5%) used for NMR spectroscopy was purchased
from Sigma–Aldrich Co.
2.2. Synthesis of the complexes
2.2.1. General procedure for the preparation of cis-[Pt(Ln)2Cl2] (1–3),
Ln = L1–L3
An appropriate ligand (1 mmol) was dissolved in chloroform
(15 mL) and added to a mixture of PtCl2 (0.09 g, 0.5 mmol) in the
same solvent (10 mL). The reaction mixture was stirred at ꢁ18 °C
for 15 days. Obtained yellow or light orange solutions were filtered
and the filtrate let to stand at room temperature. Yellowish or dark
Fig. 1. A representation of organic molecules, including atom numbering scheme, used as ligands L1–L3.

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L. Szücová et al. / Polyhedron 27 (2008) 2710–2720
2712
yellow precipitates appeared after several days, which were fil-
tered off, and dried in a vacuum desiccator over KOH.
[M+H]+) 928; 332 (calc. for [L+H]+) 332. Anal. Calc. for
32H36N10O2Cl4Pt: C, 41.3; H, 3.9; N, 15.1. Found: C, 41.0; H, 3.9;
C
N, 15.2%.
2.2.1.1. cis-[Pt(L1)2Cl2] (1). The complex was re-crystallized from
chloroform and yellowish crystals suitable for X-ray crystallogra-
phy were obtained by free evaporation of the solvent used. Yield:
2.2.2. General procedure for the preparation of trans-[Pt(Ln)2Cl2] (4–
6), Ln = L1–L3
76%. kM = 0.5
FT-IR (KBr, cmꢁ1): 3342 (s,
(C@N)ar), 1168 (m,
(C–Cl)ar). FT-IR (Nujol, cmꢁ1): 348 (s,
362 (vs, Pt–Cl), 532 (vs, Pt–N), 547 (s,
Pt–N). 1H NMR (300 MHz,
X
cm2 molꢁ1 in acetone, 0.8
N–H); 3092 (w,
X
cm2 molꢁ1 in DMF.
(C–H)ar); 1617 (vs,
Pt–Cl),
0.5 mmol of each of the cis-Pt isomers (1–3) was dissolved in
DMF (10 mL). The solution was heated up to 50 °C and stirred for
15 min. Then, the solution was filtered and let to crystallize at
the room temperature. The crystals of the complexes, in the case
of 4 suitable for X-ray analysis, were obtained after 21 days.
m
m
m
m
m
m
m
m
DMF-d7, 300 K): d 9.37 (1H, t, J = 6.0 Hz, N6H), d 9.25 (1H, bs,
C8H), d 7.46 (2H, d, J = 7.3 Hz, C11,15H), d 7.33 (2H, tt, Ja = 7.3 Hz,
Jb = 1.5 Hz, C12,14H), d 7.27 (1H, tt, Ja = 7.3 Hz, Jb = 1.5 Hz, C13H),
d 4.82 (1H, sep, J = 6.8 Hz, C16H), d 4.90 (2H, s, C9H), d 1.58 (6H,
d, J = 6.8 Hz, C17,18H). 13C NMR (75 MHz, DMF-d7, 300 K): 155.10
(C6), 154.23 (C2), 149.88 (C4), 142.17 (C8), 139.32 (C10), 128.94
(C12,14), 127.84 (C11,15), 127.57 (C13), 116.37 (C5), 49.64 (C16),
45.02 (C9), 22.14 (C17,18). 15N NMR (30 MHz, DMF-d7, 340 K):
231.92 (N1), 184.54 (N9), 141.62 (N7), 99.05 (N6). 195Pt (65 MHz,
DMF-d7, 300 K): ꢁ2017.88. MALDI-TOF-MS m/z: (positive mode)
906 (calc. for [M+K]+), 906; 890.1 (calc. for [M+Na]+) 890; 868.1
(calc. for [M+H]+) 868; 833 (calc. for [{MꢁCl}+H]+) 833; 798 (calc.
for [{Mꢁ2Cl}+H]+) 798; 302 (calc. for [L+H]+) 302. Anal. Calc. for
2.2.2.1. trans-[Pt(L1)2Cl2] (4). Dark yellow crystals suitable for X-ray
crystallography were obtained by slow evaporation of the solvent.
Yield: 50%. kM = 0.9
DMF. FT-IR (KBr, cmꢁ1): 3331 (s,
(vs, (C@N)ar), 1163 (m,
(C–Cl)ar). FT-IR (Nujol, cmꢁ1): 348 (vs,
542 (vs,
Pt–N). 1H NMR (300 MHz, DMF-d7, 300 K): d 9.05 (1H, t,
J = 6.0 Hz, N6H), d 8.97 (1H, s, C8H), d 7.56 (2H, dd, Ja = 7.3 Hz,
Jb = 1.5 Hz, C11,15H), 7.35 (2H, tt, Ja = 7.3 Hz, Jb = 1.5 Hz,
X X
cm2 molꢁ1 in acetone, 2.4 cm2 molꢁ1 in
m
N–H), 3110 (m,
m
(C–H)ar); 1623
Pt–Cl),
m
m
m
m
d
C12,14H), d 7.28 (1H, tt, Ja = 7.3 Hz, Jb = 1.5 Hz, C13H), d 4.95 (1H,
sep, J = 6.8 Hz, C16H), d 4.92 (2H, d, J = 6.2 Hz, C9H), d 1.63 (6H,
d, J = 6.8 Hz, C17,18H). 13C NMR (75 MHz, DMF-d7, 300 K): 155.15
(C6), 153.91 (C2), 149.60 (C4), 143.34 (C8), 138.77 (C10), 128.97
(C12,14), 128.05 (C11,15), 127.48 (C13), 115.99 (C5), 49.87 (C16),
45.24 (C9), 22.29 (C17,18). 15N NMR (30 MHz, DMF-d7, 340 K):
231.87 (N1), 224.80 (N3), 183.83 (N9), 133.20 (N7), 100.10 (N6).
195Pt (65 MHz, DMF-d7, 300 K): ꢁ2061.63. MALDI-TOF-MS m/z:
(positive mode) 890.1 (calc. for [M+Na]+) 890; 868 (calc. for
[M+H]+) 868; 833 (calc. for [{MꢁCl}+H]+) 833; 798 (calc. for
[{Mꢁ2Cl}+H]+) 798; 302 (calc. for [L+H]+) 302. Anal. Calc. for
C30H32N10Cl4Pt (1): C, 41.4; H, 3.7; N, 16.1. Found: C, 41.5; H,
3.7; N, 15.9%.
2.2.1.2. cis-[Pt(L2)2Cl2] (2). The complex was re-crystallized from
chloroform. Yield: 70%. kM = 0.9
X
cm2 molꢁ1 in acetone,
2.0
(m,
1176 (m,
X
m
cm2 molꢁ1 in DMF. FT-IR (KBr, cmꢁ1): 3316 (s,
(C–H)ar); 1614 (vs, (C@N)ar), 1226 (s, Car–O), 1033 (m,
). FT-IR (Nujol, cmꢁ1): 340 (s,
Pt–Cl), 349 (m,
Pt–N), 532 (s,
Pt–N). 1H NMR (300 MHz, DMF-d7, 300 K): d
9.29 (1H, t, J = 6.1 Hz, N6H), d 9.20 (1H, bs, C8H), d 7.41 (2H, d,
J = 8.6 Hz, C11,15H), 6.89 (2H, dd, Ja = 8.6 Hz, Jb = 2.2 Hz,
m
N–H), 3103
(C–O)alif),
Pt–Cl),
m
m
m
m
m
m
(C–Cl)ar
521 (s,
m
m
C30H32N10Cl4Pt (4): C, 41.4; H, 3.7; N, 16.1. Found: C, 41.5; H,
3.7; N, 16.0%.
d
C12,14H), d 4.81 (1H, sep, J = 6.8 Hz, C16H), d 4.82 (2H, s, C9H),
3.80 (3H, s, C19H), d 1.57 (6H, d, J = 6.8 Hz, C17,18H). 13C NMR
(75 MHz, DMF-d7, 300 K): 159.55 (C13), 155.10 (C6), 154.16 (C2),
149.84 (C4), 142.17 (C8), 131.00 (C10), 129.32 (C11,15), 116.38
(C5), 114.37 (C12,14), 55.51 (C19), 49.65 (C16), 44.55 (C9), 22.06
(C17,18). 15N NMR (30 MHz, DMF-d7, 340 K): 231.10 (N1), 184.47
(N9), 141.94 (N7), 100.70 (N6). 195Pt (65 MHz, DMF-d7, 300 K):
ꢁ2017.36. MALDI-TOF-MS m/z: (positive mode) 966 (calc. for
[M+K]+), 966; 950.0 (calc. for [M+Na]+) 950; 928 (calc.
for [M+H]+) 928; 893 (calc. for [{MꢁCl}+H]+) 893; 858 (calc. for
[{Mꢁ2Cl}+H]+) 858; 332 (calc. for [L+H]+) 332. Anal. Calc. for
2.2.2.2. trans-[Pt(L2)2Cl2] (5). Orange crystals suitable for X-ray
crystallography were obtained after slow evaporation of the sol-
vent used. Yield: 65%. kM = 0.8
X X
cm2 molꢁ1. kM = 2.5 cm2 molꢁ1
in acetone, 3.2
X
cm2 molꢁ1 in DMF. FT-IR (KBr, cmꢁ1): 3300 (s,
(C–H)ar); 1622 (vs, (C@N)ar), 1218 (s, Car–O), 1028
(C–Cl)ar). FT-IR (Nujol, cmꢁ1): 347 (s,
Pt–Cl),
Pt–N). 1H NMR (300 MHz, DMF-d7, 300 K): d 8.94 (1H, t,
mN–H), 3120 (m,
m
m
m
(m,
m(C–O)alif), 1177 (m,
m
m
525 (s,
J = 6.0 Hz, N6H), d 8.91 (1H, s, C8H), d 7.49 (2H, dd, Ja = 8.6 Hz,
Jb = 2.2 Hz, C11,15H), 6.90 (2H, dd, Ja = 8.6 Hz, Jb = 2.2 Hz,
m
d
C12,14H), d 4.94 (1H, sep, J = 6.8 Hz, C16H), d 4.81 (2H, d,
J = 6.06 Hz, C9H), 3.79 (3H, s, C19H), d 1.64 (6H, d, J = 6.8 Hz,
C17,18H). 13C NMR (75 MHz, DMF-d7, 300 K): 159.68 (C13),
155.28 (C6), 153.85 (C2), 149.60 (C4), 143.28 (C8), 130.45 (C10),
129.68 (C11,15), 116.06 (C5), 114.41 (C12,14), 55.51 (C19), 49.94
(C16), 44.95 (C9), 22.06 (C17,18). 15N NMR (30 MHz, DMF-d7,
340 K): 232.18 (N1), 224.68 (N3), 184.19 (N9), 133.66 (N7),
102.52 (N6). 195Pt (65 MHz, DMF-d7, 300 K): ꢁ2064.02. MALDI-
TOF-MS m/z: (positive mode) 928 (calc. for [M+H]+) 928; 893 (calc.
for [{MꢁCl}+H]+) 893; 858 (calc. for [{Mꢁ2Cl}+H]+) 858; 332 (calc.
for [L+H]+) 332. Anal. Calc. for C32H36N10O2Cl4Pt (5): C, 41.3; H, 3.9;
N, 15.1. Found: C, 41.4; H, 3.8; N, 15.4%.
C32H36N10O2Cl4Pt (2): C, 41.3; H, 3.9; N, 15.1. Found: C, 41.3; H,
3.9; N, 15.0%.
2.2.1.3. cis-[Pt(L3)2Cl2] (3). The complex was re-crystallized from
chloroform. Yield: 80%. kM = 1.5
cm2 molꢁ1 in DMF. FT-IR (KBr, cmꢁ1): 3317 (s,
(C–H)ar); 1620 (vs, (C@N)ar), 1243 (m, CarꢁO), 1029 (m,
(C–Cl)ar). FT-IR (Nujol, cmꢁ1): 336 (s,
Pt–Cl), 345 (s,
Pt–N), 549 (s,
Pt–N). 1H NMR (300 MHz, DMF-d7, 300 K): d
X
cm2 molꢁ1 in acetone, 1.8
X
m
m
N–H), 3101 (w,
(C–O)alif),
Pt–Cl),
m
m
m
1163 (m,
m
m
m
527 (s,
m
m
9.32t (1H, t, J = 6.2 Hz, N6H), d 9.15 (1H, bs, C8H), d 7.38 (1H, bs,
C15H), d 7.29 (1H, t, J = 7.9 Hz, C13H), d 7.06 (1H, d, J = 8.2 Hz,
C12H), d 6.86 (1H, t, J = 7.9 Hz, C14H), d 4.79 (1H, sep, J = 6.8 Hz,
C16H), d 4.91 (2H, d, J = 6.0 Hz, C9H), d 3.97 (3H, s, C19H), d 1.55
(6H, d, J = 6.4 Hz, C17,18H). 13C NMR (75 MHz, DMF-d7, 300 K):
158.15 (C11), 155.12 (C6), 154.27 (C2), 149.79 (C4), 142.24 (C8),
129.17 (C13), 128.49 (C15), 126.42 (C10), 120.64 (C14), 116.37
(C5), 111.02 (C12), 56.05 (C19), 49.66 (C16), 40.90 (C9), 22.04
(C17,18). 15N NMR (30 MHz, DMF-d7, 340 K): 231.68 (N1), 184.50
(N9), 142.53 (N7), 98.32 (N6). 195Pt (65 MHz, DMF-d7, 300 K):
ꢁ2023.06. MALDI-TOF-MS m/z: (positive mode) 966 (calc. for
[M+K]+), 966; 950.0 (calc. for [M+Na]+) 950; 928 (calc. for
2.2.2.3. trans-[Pt(L3)2Cl2] (6). Yield: 50%. kM = 0.9
acetone, 2.1
cm2 molꢁ1 in DMF. FT-IR (KBr, cmꢁ1): 3344 (s,
N–H), 3095 (w, (C–H)ar); 1619 (vs, (C@N)ar), 1244 (s, Car–O), 1027
(C–O)alif), 1166 (m, Pt–Cl),
(C–Cl)ar). FT-IR (Nujol, cmꢁ1): 340 (s,
Pt–N). 1H NMR (300 MHz, DMF-d7, 300 K): d 9.00 (1H, t,
X
cm2 molꢁ1 in
X
m
m
m
m
(m,
m
m
m
530 (s,
m
J = 6.2 Hz, N6H), d 9.02 (1H, s, C8H), d 7.49 (1H, d, J = 7.9 Hz,
C11,15H), d 7.38 (1H, t, J = 7.9 Hz, C13H), d 7.04 (1H, d, J = 8.2 Hz,
C12H), d 6.87 (1H, t, J = 7.9 Hz, C14H), d 4.95 (1H, sep, J = 6.8 Hz,
C16H), d 4.88 (2H, d, J = 6.0 Hz, C9H), d 3.82 (3H, s, C19H), d 1.64
(6H, d, J = 6.8 Hz, C17,18H). 13C NMR (75 MHz, DMF-d7, 300 K):

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L. Szücová et al. / Polyhedron 27 (2008) 2710–2720
2713
158.03 (C11), 155.28 (C6), 154.13 (C2), 149.69 (C4), 143.37 (C8),
129.28 (C13), 128.62 (C15), 126.26 (C10), 120.73 (C14), 116.11
(C5), 111.02 (C12), 55.78 (C19), 49.88 (C16), 40.90 (C9), 22.04
(C17,18). 15N NMR (30 MHz, DMF-d7, 340 K): 231.76 (N1), 184.20
(N9), 133.98 (N7), 99.34 (N6). 195Pt (65 MHz, DMF-d7, 300 K):
ꢁ2066.07. MALDI-TOF-MS m/z: (positive mode) 928 (calc. for
[M+H]+) 928; 893 (calc. for [{MꢁCl}+H]+) 893; 858 (calc.
for [{Mꢁ2Cl}+H]+) 858; 332 (calc. for [L+H]+) 332. Anal. Calc. for
plexes. All three structures were determined by direct methods
using SHELXS-97 and refined anisotropically on F2 using full-matrix
least-squares procedure by SHELXL-97 [39]. H-atoms were posi-
tioned geometrically, with C–H distances of 0.95–1.00 Å and N–H
distances of 0.88 Å, and with Uiso(H) values of 1.2Ueq(C,N). Most
of atoms of the L1 ligand in 1, methyl groups of the isopropyl moi-
ety in 4 ꢀ (DMF)2, and all atoms of the isopropyl moiety as well as
chlorine atom of the L2 ligand in 5 were refined as disordered over
two positions. Moreover, because of the disordered nature of the
part of the structure in the case of 1, isotropic restraints were
placed on the anisotropic thermal parameters of some atoms of
the L1 ligand. All structural figures were made with DIAMOND [40].
C
32H36N10O2Cl4Pt (6): C, 41.3; H, 3.9; N, 15.1. Found: C, 41.2; H,
4.0; N, 15.0%.
2.3. Physical measurements
Elemental analysis (C,H,N) was performed on the EA1112 Flash
analyzer (ThermoFinnigan). Thin layer chromatography (TLC) of
the prepared organic molecules was performed using a CHCl3/
CH3OH/NH4OH (8:2:0.1) mobile phase and carried out using Silica
Gel 60 WF254 plates (Merck Co.). Positive ion MALDI-TOF mass
spectra were measured in the reflection mode on a Microflex MAL-
DI-TOF LRF20 mass spectrometer equipped with a nitrogen laser
operating at 337 nm (Bruker Daltonik). MALDI-TOF-MS data of
the studied complexes were measured acetone solutions (0.5 mM
2.5. Cytotoxicity testing
Cytotoxicity values of IC50 for complexes 1–6 and for the ligands
L1–L3 were determined by a calcein AM assay. Human cancer cell
lines in vitro were used as follows: malignant melanoma (G361),
chronic myelogenous leukaemia (K562), osteogenic sarcoma
(HOS), and breast adenocarcinoma (MCF7). The technique of the
biological activity testing has been previously described in greater
detail [33]. All the experiments were repeated in triplicate. The
presented IC50 values are represented by arithmetic mean values,
with a maximal deviation of 15%. All the ligands and complexes
were first dissolved in DMF and then immediately diluted in water
to a final DMF concentration of 0.6%.
final concentration). Saturated solution of a-cyano-4-hydroxycin-
namic acid in a 50%/0.2% acetonitrile/trifluoroacetic acid solution
was used as a MALDI matrix. An aliquot of the sample solution in
acetone (5
l
L) and 5
lL of the matrix solution were premixed in
a test tube. Then, 0.5
l
L of the mixture was pipetted onto the target
plate and allowed to dry at ambient temperature. Spectra were
accumulated from 20 to 50 laser shots at a laser repetition rate
of 10 Hz. The instrument was calibrated externally using a mixture
of peptide standards. Acquired spectra were processed by FLEXANAL-
YSIS 2.4 software (Bruker Daltonik). Post-source decay (PSD) spectra
were recorded in 15 segments with each succeeding segment rep-
resenting a 10% reduction in reflectron voltage. About 100 shots
were averaged per segment. Segment spectra were pasted,
calibrated and smoothed using the program FLEXANALYSIS 2.4. Con-
ductivity measurements were performed on a Cond340i/SET con-
ductometer (WTW, Germany) in DMF solution (10ꢁ3 M) at 25 °C.
Far FT-IR spectra were measured using the Nujol technique in
the range of 150–600 cmꢁ1, whilst mid FT-IR spectra were ob-
3. Results and discussion
3.1. Synthetic aspects and conductivity measurement results
Scheme 1 illustrates the synthetic pathway that led to the prep-
aration both Ln organic molecules, used as ligands, and cis-
[Pt(Ln)2Cl2] (1–3) and trans-[Pt(Ln)2Cl2] (4–6) complexes. As the
first step of the complex syntheses, cis isomers were prepared. Yel-
low to light orange solutions appeared after mixing the reactants at
the temperature of ꢁ18 °C. Then, the reaction mixtures were fil-
tered off in order to remove visible residues originating from initial
PtCl2 and let to stand at the temperature of ꢁ18 °C for next few
days. Yellow precipitates, which appeared after this time period,
were collected by filtration and re-crystallized from chloroform
(1–3). Trans isomers were obtained after dissolving of the powdery
samples of the appropriate cis isomers in DMF. The whole proce-
dure was supported by heating up to 50 °C. Based on our next
experiences, trans isomers could be also obtained by elongation
of the reaction time by several weeks supported by heating (60–
70 °C). Generally, it is known that a cis-to-trans isomerization pro-
cess of square-planar Pt(II) complexes can be caused both by re-
crystallization of cis isomers from various solvents (e.g. acetone
[9–11], DMF [41], CHCl3 [17]) or solid state thermal heating [14].
All the complexes behave as non-electrolytes both in acetone
and DMF solutions with the conductivity values found within the
tained by the KBr pellets technique between 400 and 4000 cmꢁ1
,
both using a NEXUS 670 FT-IR spectrometer (Thermo Nicolet). 1H
and 13C NMR spectra were recorded on a Bruker Avance 300
spectrometer at 300 K. The samples were prepared by dissolving
the ligands L1–L3 and complexes 1–6 in deuterated N,N0-dimethyl-
formamide (DMF-d7). The internal reference standard used for 1H
and 13C NMR measurements was tetramethylsilane (TMS). 15N
NMR chemical shifts were measured relatively to the DMF-d7 sol-
vent (adjusted to 104.7 ppm). The individual 1H and 13C signals
were assigned and refined by means of 2D correlation experiments
of 1H–1H gs-COSY, 1H–13C gs-HMQC and 1H–13C gs-HMBC experi-
ments. 15N chemical shifts for the ligands L1–L3 and complexes
1–6 were obtained at natural abundance by 1H–15N gs-HMQC
and 1H–15N gs-HMBC experiments and the spectra were recorded
at 340 K.
interval of 0.5–2.5 and 1.2–3.2
X
cm2 molꢁ1 in acetone, and DMF,
respectively. The obtained conductivity values are consistent with
the literature data obtained for other complex non-electrolytes
[42].
2.4. X-ray crystallography
3.2. Mass and FT IR spectral studies
Diffraction data for single crystals of cis-Pt(II) complex of 1 and
trans-Pt(II) complexes of 4 ꢀ (DMF)2 and 5 were collected on an
The positive ion MALDI-TOF mass spectra were carried out for
all complexes 1–6. They showed molecular ion [M+H]+ peaks in
the spectra of complexes 1–3, and moreover, the [M+K]+ molecular
adduct ions also appeared. Fig. 2 depicts the isotopic distribution of
the molecular peak obtained for complex 1 compared to the calcu-
lated one obtained using the MASSLYNXTM software taking into
Xcalibur diffractometer (Oxford Diffraction) with Mo K
a
(mono-
chromator Enhance, Oxford Diffraction) radiation and
x-scan rota-
tion techniques. The data were collected to maximum h value of
25° and processed using the CRYSALIS software package (Oxford Dif-
fraction, Ltd.) [38]. A multi-scan absorption correction integrated
in the CRYSALIS software was applied on the data of all three com-

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L. Szücová et al. / Polyhedron 27 (2008) 2710–2720
Scheme 1. Schematic representation of the synthesis of ligands and cis (1–3) and trans (4–6) Pt(II) complexes.
account the isotopic representation of all the atoms within the
molecule [43]. For complexes 1–4, there were also found
[M+Na]+ molecular adduct ions. Generally, the formation of ad-
ducts with Na+ and K+ is typical for this type of complexes [44].
All the complexes, except for 3, showed at least two fragments,
i.e. [{MꢁCl}+H]+ and [{Mꢁ2Cl}+H]+. Moreover, the molecular peak
of the appropriate ligand, [L+H]+, appeared in all spectra of the
complexes.
between 150 and 600 cmꢁ1. Strong or very strong bands between
340 and 362 cmꢁ1 assignable to
(Pt–Cl) and between 521 and
549 cmꢁ1 attributable to
(Pt–N) were found [46]. For cis-complexes,
these bands were splitted into two peaks as compared to trans-iso-
mers which clearly supports the cis-to-trans transformation pro-
cess in case of the Pt(II) complexes studied.
m
m
3.3. Multinuclear NMR studies
FT-IR spectra of both the ligands L1–L3 and complexes 1–6 were
measured in the region of 150–4000 cmꢁ1. Characteristic bands
confirming the presence of organic ligands in complexes 1–6 were
observed in the region of 600–4000 cmꢁ1 [45]. The bands were
found and assigned as follows: strong bands between 3300 and
Multinuclear NMR study of complexes 1–6 and the ligands L1–
L3 was performed by means of 1H, 13C, 15N and 195Pt NMR spectros-
copy. Chemical shifts of the selected atoms of the free ligands L1–L3
and complexes 1–6, as found in 1H and 13C NMR spectra, are given
in Table 1, while the 15N NMR and 195Pt NMR spectral data are
given in Table 2. Observed signals were assigned and refined by
means of 1H–1H COSY, 1H–13C HMQC and 1H–13C HMBC experi-
ments. The signals found in 1H and 13C NMR spectra confirmed
the presence of organic ligands L1–L3 in complexes 1–6 and also
proved the coordination of these organic molecules to the central
Pt(II) ion. The manner of the ligand L1–L3 coordinations to Pt(II)
3342 cmꢁ1 are assignable to
m(N–H), weak to medium bands be-
tween 3092 and 3120 cmꢁ1 are assignable to
m(C–H)ar, very strong
bands between 1614 and 1623 cmꢁ1 may be attributed to m(C@N)ar
and medium bands between 1163 and 1177 cmꢁ1 are assignable
to
m(C–Cl)ar. The majority of the bands found between 660 and
900 cmꢁ1 can be assigned to skeletal vibrations of a purine moiety
of the organic ligands which is present in the complexes studied.
Medium to strong bands between 1218 and 1244 cmꢁ1 and 1027
can be deduced from the coordination shifts
Dd (Dd = dcomplex
ꢁ
and 1033 cmꢁ1 attributable to
m
(Car–O), and
m
(C–O)aliph, respectively,
dligand) as found in both 1H and 13C NMR spectra of the free ligands
and complexes. It is evident from 1H and 13C spectral data given in
Table 1 that the greatest coordination shifts in 1H NMR spectra
were found in FT IR spectra of complexes 2, 3, 5 and 6, containing
ligands L2 and L3. Some new bands appeared in the spectra of the
complexes in comparison with free organic ligands in the region
were found for the N6H (Dd = 0.35–0.94 ppm, downfield) and

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L. Szücová et al. / Polyhedron 27 (2008) 2710–2720
2715
found in 15N NMR spectra were obtained at natural abundance
by long-lasting two dimensional heteronuclear correlation
1H–15N gs-HMQC and 1H–15N gs-HMBC experiments. Presumable
coordination via the N7 atom can be also supported by 15N NMR
spectral data given in Table 2, from which it is obvious that the
greatest coordination shift as compared to the free ligands oc-
curred at the N7 atom (
chemical shifts of N1, N3, N6 and N9 remained without significant
changes, i.e. d were found to be within the interval of 0.80–
Dd = 97.67–106.55 ppm, upfield). The
D
10.07 ppm that means they are non-significantly influenced by
the organic ligand coordinations to platinum. The N7 atom chem-
ical shifts observable in the spectra of the ligands and complexes
demonstrably revealed that the coordination of the 6-benzylami-
nopurine derived ligands to the central platinum(II) ion proceeds
via the N7 position of the purine moiety.
Generally, it is known, that very important conclusions about
the oxidation state of the central Pt ion, stereochemistry, chromo-
phore and isomer types can be obtained from 195Pt NMR experi-
ments, where the significant differences between d(195Pt)
chemical shifts assignable to cis and trans complexes are supposed
to be observed. It can be evident from the d(195Pt) chemical shifts
listed in Table 2 that those ones assignable to cis isomers 1–3 ap-
peared within the interval of ꢁ2017.36 and ꢁ2023.06 ppm, while
the signals observed for trans isomers 4–6 were found between
ꢁ2061.63 and ꢁ2066.07 ppm. The values obtained for complexes
1–3 are in a good agreement with those found for similar com-
plexes of the type cis-[Pt(L)2Cl2] (L = methyl derivatives of pyri-
dine), where the d(195Pt) values were observed within the
interval between ꢁ1998 and ꢁ2021 ppm [16]. With regard to the
fact that we have already studied square-planar platinum(II) com-
plexes bearing 6-benzylaminopurine moiety recently, we can state
that the d(195Pt) chemical shift values found for cis-complexes 1–3
are in good agreement with those determined for Pt(II) complexes
of similar structural type and composition published previously
[33]. As for trans-complexes 4–6, it is interesting that the observed
d(195Pt) values between ꢁ2061.63 and ꢁ2066.07 ppm are shifted
to higher fields in comparison with literature data given for similar
type of complexes like trans-[Pt(L)2Cl2] (L = methyl derivatives of
pyridine) being ꢁ1948 and ꢁ1973 ppm [15]. On the other hand,
the achieved values are very close to those published elsewhere,
e.g. ꢁ2101 ppm for trans-[Pt(NH3)2Cl2] [47].
Fig. 2. A representation of the isotopic distribution of the molecular ion of 1
compared to the calculated one obtained using the MASSLYNX software taking into
account isotope representation of all the atoms within the molecule.
3.3.1. Cis-to-trans isomerization NMR study
It has been known for a long time that square-planar Pt(II) com-
plexes with cis arrangement of the type cis-[Pt(L)2X2] (where
L = NH3 or its derivatives, X = halide) can be transformed into trans
isomers by re-crystallization from various solvents or by their
heating [8–11]. That is why, we decided to prove this ability in
the case of the Pt(II) complexes 1–3 involving 6-benzylaminopu-
C8H (Dd = 0.65–0.97 ppm, downfield) atoms which are situated
close to the N7 atom, i.e. to a position where the coordination to
platinum(II) [33,34] or palladium(II) [34] can be expected on the
basis of our previous findings. These results could be also sup-
ported by 13C NMR spectral data, where the greatest chemical
shifts were observed for the C5 (
Dd = 3.28–3.69 ppm, upfield)
rine derivatives. A series of 1D (1H, 13C, 195Pt) and 2D (15
N
and C8 ( d = 2.13–3.33 ppm, downfield) atoms which are adjacent
D
gs-HMQC and 1H–15N gs-HMBC) NMR experiments were per-
to a coordination site represented by the N7 atom. The signals
Table 1
Selected 1H and 13C NMR spectral data (d, ppm) for L1–L3 and 1–6
Compound
1H NMR (ppm)
N6H
13C NMR (ppm)
C8H
C2
C4
C5
C6
C8
L1
8.67
8.28
153.96
150.57
119.68
156.11
140.04
L2
8.59
8.26
153.96
150.52
119.66
156.01
139.96
L3
8.38
8.29
154.02
150.54
119.75
156.35
140.04
1 cis-[Pt(L1)2Cl2]
2 cis-[Pt(L2)2Cl2]
3 cis-[Pt(L3)2Cl2]
4 trans-[Pt(L1)2Cl2]
5 trans-[Pt(L2)2Cl2]
6 trans-[Pt(L3)2Cl2]
9.37 (0.70)
9.29 (0.70)
9.32 (0.94)
9.05 (0.38)
8.94 (0.35)
9.00 (0.62)
9.25 (0.97)
9.20 (0.94)
9.15 (0.86)
8.97 (0.69)
8.91 (0.65)
9.02 (0.73)
154.23 (0.27)
154.16 (0.20)
154.27 (0.25)
153.91 (ꢁ0.05)
153.85 (ꢁ0.11)
154.13 (0.11)
149.88 (ꢁ0.89)
149.84 (ꢁ0.68)
149.79 (ꢁ0.75)
149.60 (ꢁ0.97)
149.60 (ꢁ0.92)
149.69 (ꢁ0.85)
116.37 (ꢁ3.31)
116.38 (ꢁ3.28)
116.37 (ꢁ3.38)
115.99 (ꢁ3.69)
116.06 (ꢁ3.60)
116.11 (ꢁ3.64)
155.10 (ꢁ1.01)
155.10 (ꢁ0.91)
155.12 (ꢁ1.23)
155.15 (ꢁ0.96)
155.28 (ꢁ0.73)
155.28 (ꢁ1.07)
142.17 (2.13)
142.17 (2.21)
142.24 (2.20)
143.34 (3.30)
143.28 (3.32)
143.37 (3.33)
Coordination chemical shifts (
D
d = dcomplex ꢁ dligand) are given in parentheses.

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L. Szücová et al. / Polyhedron 27 (2008) 2710–2720
2716
Table 2
Selected 15N NMR spectral data (d, ppm) for L1–L3 and 1–6 and 195Pt NMR chemical shifts obtained for 1–6
Compound
N1
N3
N6
N7
N9
195Pt
L1
L2
L3
227.30
227.32
227.47
224.00
223.69
223.97
93.57
95.32
89.27
239.75
240.15
240.20
178.70
178.57
178.73
1 cis-[Pt(L1)2Cl2]
2 cis-[Pt(L2)2Cl2]
3 cis-[Pt(L3)2Cl2]
4 trans-[Pt(L1)2Cl2]
5 trans-[Pt(L2)2Cl2]
6 trans-[Pt(L3)2Cl2]
231.92 (4.62)
231.10 (3.78)
231.68 (4.21)
231.87 (4.57)
232.18 (4.86)
231.76 (4.29)
99.05 (5.48)
100.70 (5.38)
98.32 (9.05)
100.10 (6.53)
102.52 (7.20)
99.34 (10.07)
141.62 (ꢁ98.13)
141.94 (ꢁ98.21)
142.53 (ꢁ97.67)
133.20 (ꢁ106.55)
133.66 (ꢁ106.49)
133.98 (ꢁ106.22)
184.54 (5.84)
184.47 (5.90)
184.50 (5.77)
183.83 (5.13)
184.19 (5.62)
184.20 (5.47)
ꢁ2017.88
ꢁ2017.36
ꢁ2023.06
ꢁ2061.63
ꢁ2064.02
ꢁ2066.07
224.80 (0.80)
224.68 (0.99)
Coordination chemical shifts (
D
d = dcomplex ꢁ dligand) are given in parentheses.
formed during six months to obtain necessary data for the study of
the cis-to-trans isomerization process in DMF. Although these mea-
surements were performed for all complexes 1–3, we decided to
describe and interpret NMR data regarding the process for complex
1 only because the obtained results were fully comparable for all
the studied complexes. Regarding the proper experiment, the sam-
ple was measured 20 min after dissolving complex 1 in DMF, and
subsequently after one, three and six months. An example of the
1H–15N gs-HMBC experiment performed for complex 1 taken one
month after the sample dissolution together with its comparison
to the spectra of the corresponding free ligand L1 is presented in
Fig. 1A (see Supplementary data). The presence of both cis and
trans isomers (i.e. complexes 1 and 3) can be clearly seen from
the last-mentioned figure. The same conclusion may be drawn
from the 1H NMR experiments of complex 1. The 1H NMR spectra
of complex 1, showing the integral intensities of hydrogen atoms
belonging to N6 and C8 atoms measured after 20 min, and 1, 3,
and 6 months, as well as proving the presence of both isomers
are depicted in Fig. 3. While a trace signal (3%) belonging to the
trans-isomer can be seen in the spectrum of complex 1 taken
20 min after dissolving of the sample in DMF, after one month,
the cis-to-trans ratio changed approximately to 6:3. Subsequently,
the content of trans isomer increased gradually and pure trans iso-
mer occurred six months after the beginning of the experiment. On
the basis of the above described experiments we can state that the
trans arrangement of the studied complexes is much more stable
than the cis one in the DMF solutions. Moreover, the performed
experiments gave us clear conclusions regarding the time-depen-
dent stability of cis complexes 1–3 in DMF and showed us another
possibility how to prepare trans isomers in a pure form.
In the quest to better describe the solution behavior of cis-com-
plexes 1–3, we were also trying to determine what is occurring
with the complexes in a DMF/water mixture. For that reason, com-
plex 1 was dissolved in DMF-d7:D2O mixture in 9:1 (v/v) ratio, and
we tried to obtain the signals of some hydroxo or aqua species {i.e
cis-[Pt(Ln)2(OH)2] or cis-[Pt(Ln)2(H2O)2]2+} that were expected to be
formed after dissolving the sample in the mentioned solvent mix-
ture. We could not use higher content of water in the mixture due
to low solubility of the prepared complexes in water. The sample
was measured in time intervals after 20 min, one week, and 1, 3,
and 6 months. We used nearly the same experiment formerly in
the case of analogous Pd(II) complexes bearing similar types of li-
gands, where the signals proving the presence of [Pd(L)2(OH)2]
species were detected [34]. Unfortunately, we were not successful
to observe any obvious NMR signals of (OH)ꢁ group in the case of
Pt(II)-complexes 1–3. This might be caused by the fact that the
studied Pt(II) complexes are even less soluble than analogous Pd(II)
ones in the same solvent mixture used and the complex concentra-
tions were under the detectable limit of the device used. However,
the formation of cis-[Pt(Ln)2(OH)2] or cis-[Pt(Ln)2(H2O)2]2+ species
in the mixture used may be supported by a simple, but very sensi-
tive, analytical experiment. AgNO3 was added to the solution of
complex 1 in the DMF/water (9:1) mixture after one week of stand-
ing in room temperature. After this time period, a white precipitate
originating from AgCl formed and it showed that chlorine anions
had to leave the complex in the solvent. To support assumption
that organic ligands remain coordinated to platinum, we simulta-
neously performed additional NMR experiments. It has been found
that complex 1 is sufficiently kinetically inert to hold the organic
ligands within the inner coordination sphere of platinum, because
signals belonging to the uncoordinated ligands were not detected
by means of 1H and 13C NMR measurements. It clearly supports
conclusion that cis-[Pt(Ln)2(OH)2] or cis-[Pt(Ln)2(H2O)2]2+ species
are forming in the mixture of solvents used.
3.4. X-ray molecular structures
Crystallographic data and refinement details for complexes 1,
4 ꢀ (DMF)2 and 5 are summarized in Table 3, while the selected
bond lengths and angles are given in Table 4. All important hydro-
gen-bonding interactions were generated by PARST95 [48].
3.4.1. Molecular and crystal structures of cis-[Pt(L1)2Cl2] (1)
The molecular structure of 1 is shown in Fig. 4 (DIAMOND) [40].
The central Pt(II) ion is coordinated by two chlorido and two L1 li-
gands through the N7 atoms of the adenine units forming a cis-
square-planar coordination around the central atom. The Pt–N
and Pt–Cl bond distances are comparable with the average bond
lengths of 2.027(4) and 2.291(1) Å, respectively, found in related
PtCl2N2 complexes deposited in the Cambridge Structural Database
[49]. Most of atoms of one of two L1 ligands are disordered over two
positions. A degree of the disorder can be seen from different posi-
tions of adenine moieties and phenyl rings (see Fig. 4). The adenine
moieties are turned in the plane of adenine to each other around the
center of rotation lying in the N7A atom about 10.3–13.7°. If Cg1
and Cg2 are defined as the centroids of the first and second disor-
dered phenyl rings, then the Cg1ꢀ ꢀ ꢀCg2 distance is 1.9948(2) Å
and the dihedral angle between the rings is 41.8(3)°. Two adenine
moieties originating from two L1 ligands (or three, if we consider
the disorder in the case of one L1 ligand) are almost perpendicular
to each other [dihedral angles are 93.6(1)° and 93.4(2)°], and the
angle between the platinum coordination plane (i.e. a PtCl2N2
chromophore) and the purine moiety is 65.13(7)°, 72.80(13)° and
71.99(14)°, respectively. The platinum atom deviates significantly
from the planarity of the imidazole ring of the first L1 ligand [the
out-of-plane deviation is 0.2807(3) Å] probably as the result of an
intramolecular hydrogen-bonding interactions (N6–Hꢀ ꢀ ꢀCl1:
N6ꢀ ꢀ ꢀCl1 = 3.275(5) Å; \DHA = 141°; where D = a donor atom,
H = the corresponding hydrogen atom, A = an acceptor atom), while
the deviations of platinum from the other two disordered imidazole
rings are notably lower [0.0636(3) and 0.0745(3) Å].
In the crystal packing, the individual molecules of 1 are con-
nected through strong intermolecular C–Hꢀ ꢀ ꢀCl hydrogen-bonding
interactions (C8–Hꢀ ꢀ ꢀCl1: Hꢀ ꢀ ꢀCl1 = 2.65 Å, \DHA 171°; 2.54 Å,

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L. Szücová et al. / Polyhedron 27 (2008) 2710–2720
2717
Fig. 3. Selected part of 1H NMR spectra of 1 showing the transformation of cis into trans isomer of the complex based on the changes of the N6H and C8H signals in
dependence on time.
178°; and 2.77 Å; 146°; respectively). The non-bonding intermo-
lecular interactions may be considered to be the main reason of
the ligand disorder. Whilst the first position of the disordered L1
N7 atoms of the adenine moieties [Pt–N: 2.009(2) Å; Pt–Cl:
2.2846(7) Å; N–Pt–Cl: 91.87(7)°]. The Pt(II) ion lies slightly out of
the plane of the imidazole ring [the out-of-plane deviation is
0.1332(4) Å]. Similarly to complex 1, the L1 ligand is also partially
disordered in methyl groups of the isopropyl moiety in the crystal
structure of 4 ꢀ (DMF)2, i.e. each of the two terminal methyl groups
is disordered over two positions. The corresponding methyl groups
are turned towards each other about 28° around the axis of rota-
tion lying on the N9–C16 bond. The purine moiety is slightly bent
[the dihedral angle between the imidazole and pyrimidine rings is
3.06(13)°] and almost perpendicular to the plane of phenyl group
[the dihedral angle is 88.4(1)°].
is stabilized by a
position is stabilized by a
p
interaction [Cl3Aꢀ ꢀ ꢀC5: 3.247(8) Å], the second
p–p
stacking interaction [the distance
between adjacent parallel imidazole planes is 3.3858 Å].
3.4.2. Molecular and crystal structures of trans-[Pt(L1)2Cl2]
(4 ꢀ (DMF)2)
The molecular structure of 4 ꢀ (DMF)2 (see Fig. 5) revealed a cen-
trosymmetric trans-square-planar complex in which the Pt(II) ion
is coordinated by two chlorido and two L1 ligands through the

ˇ
2718
L. Szücová et al. / Polyhedron 27 (2008) 2710–2720
Table 3
Crystallographic data and refinement for 1, 4 ꢀ (DMF)2 and 5
1
4 ꢀ (DMF)2
C36H46 l4N12O2Pt
5
Formula
M (g molꢁ1
T (K)
C
30H32
C
l4N10Pt
C
C32H36Cl4N10O2Pt
)
869.55
110(2)
1015.74
110(2)
0.71073
monoclinic
P21/n
9.2726(8)
19.8713(16)
11.0317(11)
90
96.886(7)
90
2018.0(3)
2
1.672
3.791
929.60
105(2)
0.71073
monoclinic
P21/c
8.1507(4)
15.6503(7)
14.1585(6)
90
101.086(4)
90
k (Å)
0.71073
triclinic
Crystal system
Space group
a (Å)
b (Å)
c (Å)
ꢀ
P1
11.2275(5)
12.4605(5)
14.1821(6)
85.638(3)
66.747(4)
69.128(4)
1698.46(14)
2
a
(°)
b (°)
c
(°)
V (Å3)
1772.37(14)
2
1.742
Z
Dcalc (g cmꢁ3
)
1.700
4.483
l
(Mo K
a
) (mmꢁ1
)
4.306
Crystal size (mm)
Crystal shape and
color
0.35 ꢂ 0.30 ꢂ 0.30 0.35 ꢂ 0.10 ꢂ 0.10 0.30 ꢂ 0.30 ꢂ 0.25
yellow prism
orange prism
orange prism
Tmin/Tmax
Number data
measured
Unique data (Rint
Observed data
0.82926/1.00000
14312
0.61972/1.00000
16816
0.84874/1.00000
12907
Fig. 4. Molecular structure of complex 1, showing the atom numbering scheme.
Thermal ellipsoids are drawn at the 40% probability level. Some of atoms are
disordered over two positions. Some of H-atoms were omitted for clarity.
)
5992 (0.0172)
5313
3555 (0.0155)
3175
3126 (0.0164)
2576
[I > 2
r(I)]
Final R1a, wR2
0.0310, 0.0772c
0.0375, 0.0800c
0.0206, 0.0475d
0.0245, 0.0493d
0.0251, 0.0626e
0.0358, 0.0689e
0.694, ꢁ0.586
b
(observed data)
Final R1a, wR2 (all
b
data)
qmax
,
qmin (e Åꢁ3
)
2.282, ꢁ1.813
0.710, ꢁ0.295
P
P
P
P
Where a R = (jFoj ꢁ jFcj)/ jFoj, b wR2 = [ w(jFoj ꢁ jFcj)2/ (Fo)2]1/2
, r
c w = 1/[ 2(Fo) +
(0.0375P)2 + 10P], d w = 1/[
10P] and P = (F2o + 2Fc2)/3.
r
2(Fo) + (0.015P)2 + 10P], e w = 1/[
r
2(Fo) + (0.025P)2
+
Table 4
Selected bond lengths (Å) and angles (°) for 1, 4 ꢀ (DMF)2 and 5
1
4 ꢀ (DMF)2
5
Bond lengths
Pt(1)–N(7)
Pt(1)–N(7A)
Pt(1)–Cl(1)
Pt(1)–Cl(1A)
Pt(1)–Cl(2)
2.032(4)
2.022(4)
2.2873(14)
2.009(2)
2.009(2)
2.2846(7)
2.2846(7)
2.008(4)
2.008(4)
2.2834(13)
2.2954(11)
Bond angles
N(7)–Pt(1)–Cl(2)
N(7)–Pt(1)–Cl(1A)
N(7A)–Pt(1)–N(7)
N(7A)–Pt(1)–Cl(1A)
N(7A)–Pt(1)–Cl(2)
N(7A)–Pt(1)–Cl(1)
N(7)–Pt(1)–Cl(1)
Cl(2)–Pt(1)–Cl(1)
Cl(1A)–Pt(1)–Cl(1)
Cl(2)–Pt(1)–Cl(2A)
178.63(12)
89.74(16)
91.02(11)
180.0
Fig. 5. Molecular structure of the centrosymmetric complex 4 ꢀ (DMF)2, showing
the atom numbering scheme [symmetry code: (i) 1 ꢁ x, 1 ꢁ y, 1 ꢁ z]. Some of atoms
are disordered over two positions. H-atoms belonging to the disordered part of the
molecule were omitted for clarity.
88.13(7)
180.0
91.87(7)
88.98(12)
179.17(13)
90.04(12)
91.25(5)
88.98(11)
88.13(7)
91.87(7)
with a trans-square-planar coordination around the central Pt(II)
ion which is coordinated by two chlorido and two L2 ligands via
the N7 atoms [Pt–N: 2.008(4) Å; Pt–Cl: 2.2954(11) Å; N–Pt–Cl:
91.02(11)°]. The platinum(II) ion lies significantly out of the plane
of the imidazole ring [the deviation is 0.1956(1) Å]. The isopropyl
group and chlorine atom of the L2 ligand is disordered over two
positions. Atoms of the isopropyl group are turned towards each
other around the N9–C16 rotation axis about 31.891(2)°. The pur-
ine moiety is also slightly bent [the dihedral angle between the
imidazole and pyrimidine rings is 5.23(2)°]. The main structural
differences between 4 ꢀ (DMF)2 and 5 are in intra- and intermolec-
ular interactions. While the interactions in the crystal structure of
4 ꢀ (DMF)2 are affected by the presence of DMF molecules, their ab-
sence in 5 result in a more compact molecular packing. The phenyl
180.0
180.0
Symmetry transformations used to generate equivalent atoms labelled
4 ꢀ (DMF)2: ꢁx + 1, ꢁy + 1, ꢁz + 1; for 5: ꢁx + 1, ꢁy + 1, ꢁz + 1.
A for
The crystal packing of 4 ꢀ (DMF)2 is stabilized by hydrogen-
bonding interactions involving chlorine and some atoms of DMF
(e.g. C8–Hꢀ ꢀ ꢀO1: Hꢀ ꢀ ꢀO1 = 2.16 Å; \DHA = 176°; C20–H20Cꢀ ꢀ ꢀCl1:
Hꢀ ꢀ ꢀCl1 = 2.78 Å; \DHA = 155°; C20–H20Aꢀ ꢀ ꢀCl1: Hꢀ ꢀ ꢀCl1 = 2.81 Å;
\DHA 148°) forming infinite linear complex–(DMF)2–complex
chains.
3.4.3. Molecular and crystal structures of trans-[Pt(L2)2Cl2] (5)
The central part of the molecular structure of 5 (see Fig. 6) is
very similar to that of 4 ꢀ (DMF)2. The complex is centrosymmetric
group of one L2 ligand in 5 is stabilized by p-interactions with the
purine of the other L2 ligand [if Cg1 is the centroid of the phenyl
ring of the first L2, H8ꢀ ꢀ ꢀCg1 distance is 3.07 Å, H8 distance from

ˇ
L. Szücová et al. / Polyhedron 27 (2008) 2710–2720
2719
molecular structures of the complexes cis-[Pt(L1)2Cl2] (1), trans-
[Pt(L1)2Cl2] (4 ꢀ (DMF)2), and trans-[Pt(L2)2Cl2] (5) have been deter-
mined and supported the composition and stereochemistry follow-
ing from other physical techniques used for the characterization of
the complexes. Moreover, the dynamic cis-to-trans isomerization
process in DMF solutions, as well as the behavior of the complexes
in a DMF/water solution has been investigated by the means of
multinuclear NMR spectroscopy. The obtained results elucidated
and extended our knowledge about time-dependent solution
behavior of these complexes. All the complexes were tested in vitro
against four human cancer cell lines (MCF7, G361, K562 and HOS).
The tested compounds could only be tested at low concentrations
(up to 5 lM) because of their low solubility in water which is a
necessary medium in the testing procedure used. Unfortunately,
at this concentration, the complexes, as well as the initial free li-
gands, showed no cytotoxicity.
Acknowledgements
Fig. 6. Molecular structure of the centrosymmetric complex 5, showing the atom
numbering scheme [symmetry code: (i) 1 ꢁ x, 1 ꢁ y, 1 ꢁ z]. Thermal ellipsoids are
drawn at the 50% probability level. Some of atoms are disordered over two
positions. H-atoms belonging to the disordered part of the molecule were omitted
for clarity.
This work was funded by The Ministry of Education, Youth and
Sports of the Czech Republic (a Grant No. MSM6198959218). The
authors thank to Assoc. Prof. Marek Šebela, PhD for performing of
MALDI-TOF experiments and Ms. Olga Hustáková for her help with
biological testing.
the plane of the phenyl ring is 3.04 Å, and the dihedral angle be-
tween the purine and phenyl moieties is 77.35(13)°]. The crystal
packing is further stabilized by intramolecular hydrogen bonds
N6–Hꢀ ꢀ ꢀCl2 [N6ꢀ ꢀ ꢀCl2 = 3.281(5) Å; \DHA = 139°] and intermolec-
Appendix A. Supplementary data
CCDC 683645, 683646 and 683647 contain the supplementary
crystallographic data for 1, 4 ꢀ (DMF)2, and 5. These data can be ob-
tained free of charge via http://www.ccdc.cam.ac.uk/conts/retriev-
ing.html, or from the Cambridge Crystallographic Data Centre, 12
Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-033;
or e-mail: deposit@ccdc.cam.ac.uk. Supplementary data associated
with this article can be found, in the online version, at doi:10.1016/
j.poly.2008.05.021.
ular Clꢀ ꢀ ꢀN
p–p
interactions [Cl2ꢀ ꢀ ꢀN1: 3.289(6) Å] arranging mol-
ecules of 5 into infinite linear chains.
3.4.4. Crystal structure summary
Generally, the Pt–N and Pt–Cl bond distances in complexes 1,
4 ꢀ (DMF)2 and 5 are in the range of 2.008–2.032 Å, and 2.2834–
2.2954 Å, respectively. They are quite comparable to those found
for the trans-[PtCl2(L)2] complex involving two coordinated 2-
chloro-6-[(3-hydroxybenzyl)amino]-9-isopropylpurine ligands (L)
[50] and also to the average bond lengths found for the Pt–N and
Pt–Cl bond lengths (2.02, and 2.29 Å, respectively) in related
PtCl2N2 complexes as reported in the Cambridge Structural Data-
base [49]. In all the discussed complexes, the central platinum
atom deviates significantly from the planarity of purine moieties.
The degree of deformation of organic ligands within the complexes
is markedly influenced by non-bonding intramolecular and inter-
molecular interactions.
References
[1] B. Rosenberg, L. Van Camp, T. Krigas, Nature 205 (1965) 698.
[2] E. Wong, Ch.M. Giandomenico, Chem. Rev. 99 (1999) 2451.
[3] R.R. Barefoot, J. Chromatogr. B 751 (2001) 205.
[4] Ch.X. Zhang, S.J. Lippard, Curr. Opin. Chem. Biol. 7 (2003) 481.
[5] L.R. Kelland, S.Y. Sharp, C.F. O’Neill, F.I. Raynaud, P.J. Beale, I.R. Judson, J. Inorg.
Biochem. 77 (1999) 111.
[6] Y. Najarjeh, J.M. Perez, C. Navarro-Ranninger, D. Gibson, J. Med. Chem. 45
(2002) 5189.
[7] Y.N. Kukushkin, Platinum Met. Rev. 35 (1991) 28.
[8] P.C. Kong, F.D. Rochon, Inorg. Chim. Acta 61 (1982) 269.
[9] C.J.L. Lock, M. Zvagulis, Inorg. Chem. 20 (1981) 1817.
[10] C.J.L. Lock, M. Zvagulis, Acta Crystallogr., Sect. B 36 (1980) 2140.
[11] J.P. Bradford, R. Faggiani, C.J.L. Lock, Acta Crystallogr., Sect. B 37 (1981) 243.
[12] P.C. Kong, F.D. Rochon, Can. J. Chem. 57 (1979) 526.
[13] P.C. Kong, F.D. Rochon, Can. J. Chem. 59 (1981) 3293.
[14] V.Y. Kukushkin, D. Tudela, Y.A. Izotova, V.K. Belsky, A.I. Stash, Polyhedron 17
(1998) 2455.
[15] Ch. Tessier, F.D. Rochon, Inorg. Chim. Acta 322 (2001) 37.
[16] F.D. Rochon, V. Buculei, Inorg. Chim. Acta 357 (2004) 2218.
[17] K.R. Koch, Y. Wang, A. Coetzee, J. Chem. Soc., Dalton Trans. (1999) 1013.
[18] J. Reedijk, PNAS 100 (2003) 3611.
3.5. Biological activity
Complexes 1–6 were screened for their cytotoxic effects in vitro
against four human cancer cell lines: MCF7, G361, K562 and HOS.
Based on the fact that the prepared complexes 1–6 were only
slightly soluble in water, and the testing procedure necessarily
uses water as a medium, we were limited by the solubility of the
complexes in water. That is why we could only prepare water solu-
tions with the complex concentrations being maximally 5 lM. At
higher concentrations, the complexes precipitated from the water
medium. Unfortunately, the complexes showed to be non-cyto-
toxic within this low concentration range.
[19] O. Nováková, J. Kašpárková, J. Malina, G. Natile, V. Brabec, Nucleic Acids Res. 31
(2003) 6450.
[20] G. McGowan, S. Pearsons, P.J. Sadler, Inorg. Chem. 44 (2005) 7459.
[21] J. Vinje, E. Sletten, AntiCancer Agents Med. Chem. 7 (2007) 35.
[22] D.S. Letham, New Zeal. J. Bot. 1 (1964) 336.
[23] C.O. Miller, F. Skoog, M.H. Von Saltza, F.M. Strong, J. Am. Chem. Soc. 77 (5)
(1955) 1392.
4. Conclusions
[24] F. Skoog, H.Q. Hamzi, A.M. Szweykowska, N.J. Leonard, K.L. Carraway, T. Fujii,
J.P. Helgeson, R.N. Leoppky, Phytochemistry 6 (9) (1967) 1169.
[25] P.J. Davies, Plant Hormones. Biosynthesis, Signal Transduction, Action, Kluwer
Academic Publishers, Dordrecht, The Netherlands, 2004.
[26] S. Gan, R.M. Amasino, Science 270 (1995) 1986.
We have prepared and fully characterized six new cis and trans
square-planar Pt(II) complexes involving derivatives of plant
growth hormones, called cytokinins, derived from 6-benzylamino-
purine moiety, and having a general formula of [Pt(Ln)2Cl2]. X-ray

ˇ
L. Szücová et al. / Polyhedron 27 (2008) 2710–2720
2720
[27] G. Haberer, J.J. Kieber, Plant Physiol. 128 (2002) 354.
[39] G.M. Sheldrick, Acta Crystallogr., Sect. A 46 (1990) 467.
[40] K. Brandenburg, DIAMOND (Release 3.1e), Grystal Impact GbR, Bonn, Germany,
2006.
[41] P.C. Kong, F.D. Rochon, Inorg. Chim. Acta 83 (1984) 65.
[42] W.J. Geary, Coord. Chem. Rev. 7 (1971) 81.
[28] M. Legraverend, P. Tunnah, M. Noble, P. Ducrot, O. Ludwig, D.S. Grierson, M.
Leost, L. Meijer, J. Endicott, J. Med. Chem. 43 (2000) 1282.
[29] M.J. Moon, S.K. Lee, J.W. Lee, W.K. Song, S. W Kim, J.I. Kim, C. Cho, S.J. Choi, Y.C.
Kim, Bioorg. Med. Chem. 14 (2006) 237.
[30] R.M. Goldsteyn, Cancer Lett. 217 (2005) 129.
[31] W.F. DeAzevedo, S. Leclerc, L. Meijer, L. Havlícek, M. Strnad, S.H. Kim, Eur. J.
[43] MASSLYNXTM, version 4.0, Waters, Milford, MA, USA, 2005.
[44] W. Henderson, J.S. McIndoe, Mass Spectrometry of Inorganic and
Organometallic Compounds, John Wiley & Sons, Ltd., Chichester, England,
2005.
[45] C.J. Pouchert, The Aldrich Library of Infrared Spectra, Aldrich Chemical
Company Press, Milwaukee, USA, 1981.
ˇ
Biochem. 243 (1997) 518.
[32] F.I. Raynaud, S.R. Whittaker, P.M. Fisher, S. McClue, M.I. Walton, S.E. Barrie,
M.D. Garrett, P. Rogers, S.J. Clarke, L.R. Kelland, M. Valenti, L. Brunton, S. Eccles,
D.P. Lane, P. Workman, Clin. Cancer Res. 11 (13) (2005) 4875.
ˇ
ˇ
[33] L. Szücová, Z. Trávnícek, M. Zatloukal, I. Popa, Bioorg. Med. Chem. 14 (2006)
479.
[46] K. Nakamoto, Infrared and Raman Spectra of Inorganic and Coordination
Compounds. Part B: Applications in Coordination, Organometallic and
Bioinorganic Chemistry, John Wiley & Sons Ltd., New York, England, 1991.
[47] F.H. Appleton, F.J. Pesch, M. Wienken, S. Menzer, B. Lippert, Inorg. Chem. 31
(1992) 4410.
ˇ
ˇ
[34] Z. Trávnícek, L. Szücová, I. Popa, J. Inorg. Biochem. 101 (2007) 477.
[35] M. Malon, Z. Trávnícek, M. Maryško, J. Marek, K. Dolezal, J. Rolcík, M. Strnad,
Transition Met. Chem. 27 (2002) 580.
ˇ
ˇ
ˇ
ˇ
ˇ
[36] Z. Trávnícek, V. Kryštof, M. Šipl, J. Inorg. Biochem. 100 (2006) 214.
[48] M. Nardelli, J. Appl. Crystallogr. 28 (1995) 659.
[49] F.H. Allen, Acta Crystallogr., Sect. B 58 (2002) 380.
ˇ
ˇ
ˇ
[37] A. Klanicová, Z. Trávnícek, I. Popa, M. Cajan, K. Dolezal, Polyhedron 25 (2006)
ˇ
ˇ
1421.
[50] Z. Trávnícek, J. Marek, L. Szücová, Acta Crystallogr., Sect. E 62 (2006) m1
482.
[38] CRYSALIS RED and CRYSALIS CCD, Version 1.171.23, Oxford Diffraction Ltd., Abingdon,
England, 2006.