Synthesis, characterization and in vitro cytotoxicity of Co(II) complexes with N6-substituted adenine derivatives: X-ray structures of 6-(4-chlorobenzylamino)purin-di-ium diperchlorate dihydrate and [Co 6(μ-L6)4Cl8(DMSO)10] ? 4DMSO

Article abstract of DOI:10.1016/j.poly.2005.09.032

Cobalt(II) complexes of the composition [Co(L₁)Cl(H ₂O)₂] ? H₂O (1), [Co(L₂) Cl(H₂O)₂] ? 2H₂O (2), [Co(L ₃)Cl(H₂O)₂] ? H₂O (3), [Co(L₄)Cl(H₂O)₂] ? H₂O (4), [Co(L₅)Cl(H₂O)₂] ? H₂O (5) and [Co(L₆)Cl(H₂O)₂] ? H₂O (6), where HL₁ = 6-(3-chlorobenzylamino)purine, HL₂ = 6-(4-chlorobenzylamino)purine, HL₃ = 6-(2,3-dimethoxybenzylamino) purine, HL₄ = 6-(3,4-dimethoxybenzylamino)purine, HL₅ = 6-(3-fluorobenzylamino)purine and HL₆ = 6-(4-fluorobenzylamino) purine, have been prepared. The compounds have been characterized by elemental analyses, ES+ mass, UV-Vis, IR and NMR spectroscopies, magnetic measurements, molar conductances and thermogravimetric analysis as mononuclear tetrahedral high-spin cobalt(II) complexes. In vitro cytotoxicities of the complexes were tested by a Calcein AM assay against the following human tumour cell lines: malignant melanoma (G361), chronic myelogenous erythroleukemia (K562), osteogenic sarcoma (HOS) and breast adenocarcinoma (MCF7). The molecular structures of 6-(4-chlorobenzylamino)purin-di-ium diperchlorate dihydrate, [H²⁺L₂](ClO₄)₂ ? 2H ₂O, and a hexanuclear Co(II) complex, [Co₆(μ-L ₆)₄Cl₈(DMSO)₁₀] ? 4DMSO (7), have been determined by a single crystal X-ray analysis. To elucidate the manner of the organic ligand coordination to cobalt, the geometry of the complex 2 was optimized using DFT calculations at the B3LYP/6-311+G* level of the theory.

Full text of DOI:10.1016/j.poly.2005.09.032

Polyhedron 25 (2006) 1421–1432
www.elsevier.com/locate/poly
Synthesis, characterization and in vitro cytotoxicity of Co(II)
complexes with N6-substituted adenine derivatives: X-ray structures
of 6-(4-chlorobenzylamino)purin-di-ium diperchlorate dihydrate
and [Co6(l-L6)4Cl8(DMSO)10] Æ 4DMSO
a
a,b,
b
b
b
ˇ
*, Igor Popa , Michal Cajan , Karel Dolezˇal
´
ˇ
´ ´ˇ
Alena Klanicova , Zdenek Travnıcek
a
Department of Inorganic Chemistry, Palacky´ University, Krˇı´zˇkovske´ho 10, Olomouc, CZ-771 47, Czech Republic
ˇ
Laboratory of Growth Regulators, Palacky´ University and Institute of Experimental Botany ASCR, Slechtitelu 11, Olomouc CZ-783 71, Czech Republic
b
˚
Received 21 July 2005; accepted 30 September 2005
Available online 7 November 2005
Abstract
Cobalt(II) complexes of the composition [Co(L1)Cl(H2O)2] Æ H2O (1), [Co(L2)Cl(H2O)2] Æ 2H2O (2), [Co(L3)Cl(H2O)2] Æ H2O (3),
[Co(L4)Cl(H2O)2] Æ H2O (4), [Co(L5)Cl(H2O)2] Æ H2O (5) and [Co(L6)Cl(H2O)2] Æ H2O (6), where HL1 = 6-(3-chlorobenzylamino)purine,
HL2 = 6-(4-chlorobenzylamino)purine, HL3 = 6-(2,3-dimethoxybenzylamino)purine, HL4 = 6-(3,4-dimethoxybenzylamino)purine,
HL5 = 6-(3-fluorobenzylamino)purine and HL6 = 6-(4-fluorobenzylamino)purine, have been prepared. The compounds have been char-
acterized by elemental analyses, ES+ mass, UV–Vis, IR and NMR spectroscopies, magnetic measurements, molar conductances and
thermogravimetric analysis as mononuclear tetrahedral high-spin cobalt(II) complexes. In vitro cytotoxicities of the complexes were
tested by a Calcein AM assay against the following human tumour cell lines: malignant melanoma (G361), chronic myelogenous eryth-
roleukemia (K562), osteogenic sarcoma (HOS) and breast adenocarcinoma (MCF7). The molecular structures of 6-(4-chlorobenzyla-
mino)purin-di-ium diperchlorate dihydrate, [H2+L2](ClO4)2 Æ 2H2O, and a hexanuclear Co(II) complex, [Co6(l-L6)4Cl8(DMSO)10] Æ
4DMSO (7), have been determined by a single crystal X-ray analysis. To elucidate the manner of the organic ligand coordination to
cobalt, the geometry of the complex 2 was optimized using DFT calculations at the B3LYP/6-311+G* level of the theory.
ꢀ 2005 Elsevier Ltd. All rights reserved.
Keywords: Cobalt(II) complexes; X-ray structures; Cytokinins; Cytotoxicity; DFT calculations
1. Introduction
human cancer cell lines). It can be supposed that the mod-
ification of a cytokinin molecule could cause an extensive
change of cytokinin action in growth and developmental
control [2]. It has been found that some of cytokinin deriv-
atives, substituted suitably at C2, N6 and N9 positions,
{e.g., olomoucine = (6-(benzylamino)-2-[(2-hydroxyethyl)
amino]-9-methyl-purine), bohemine = (6-(benzyl-amino)-2-
[(3-hydroxypropyl)amino]-9-isopropylpurine), roscovitine =
(6-(benzylamino)-2-[(1-hydroxymethylpropyl)amino]-9-
isopropylpurine)}, inhibit some of cyclin-dependent kinases
(i.e., enzymes which play key role in the cell cycle regula-
tion) at micromolar concentrations and show cytotoxic
activity against some human carcinoma cell lines [3]. A
few years ago, it has been found that the cytotoxicity may
N6-Substituted adenine derivatives belong to a group of
both natural and artificial growth regulators, called cytoki-
nins, whose main physiological effect is the support of cell
division [1]. However, these adenine derivatives can behave
differently in regulation of the cell cycle: they may stimulate
a cell division (this process is known in plants and their tis-
sues) as well as show strong inhibitory effect with the ability
to arrest cell cycle in its specific points (as found for some of
*
Corresponding author. Tel.: +420 58 5634944; fax: +420 58 5634954.
´
´ˇ
E-mail address: trav@risc.upol.cz (Z. Travnıcek).
0277-5387/$ - see front matter ꢀ 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2005.09.032

1422
A. Klanicova´ et al. / Polyhedron 25 (2006) 1421–1432
Scheme 1.
be increased by coordination of cytokinin-derived com-
pounds to a suitable transition metal. Recently, we have fo-
cused our interest on the preparation of Pt(II), Pd(II),
Cu(II), Ni(II) and Co(II) complexes with the above-
mentioned organic derivatives [4–8].
To date, only a few of cobalt complexes with purine and
adenine derivatives as ligands have been structurally char-
acterized and deposited at Cambridge Crystallographic
Data Centre (CCDC) [9]. The coordination variability both
the purine and adenine moieties, relating to their four or
five nitrogen-donor atoms, can be shown, among others,
on the following examples. In 1D-polymeric chain
octahedral cobalt complexes of formulae [CoII(l-ox)-
(H2O)(purH-N9)]n, [CoII(l-ox)(H2O)(purH-N9)0.76(adeH-
high-spin Co(II) complexes bearing the cytokinin-derived
compounds as ligands [8]. Herein, we describe the
preparation, characterization and cytotoxicity of the Co(II)
complexes with 6-(3-chlorobenzylamino)purine (HL1),
6-(4-chlorobenzylamino)purine (HL2), 6-(2,3-dimethoxy-
benzylamino)purine (HL3), 6-(3,4-dimethoxybenzyla-
mino)purine
(HL4),
6-(3-fluorobenzylamino)purine
(HL5) and 6-(4-fluorobenzylamino)purine (HL6) (see
Scheme 1).
2. Experimental
2.1. Materials
N9)0.24 n
]
(ox = oxalate(2ꢀ), purH = purine, adeH = ade-
CoCl2 Æ 6H2O, 6-chloropurine, 3-chlorobenzylamine,
4-chlorobenzylamine, 2,3-dimethoxybenzylamine, 3,4-
dimethoxybenzylamine, 3-fluorobenzylamine, 4-fluoroben-
zylamine and the solvents {dimethyl sulfoxide (DMSO),
N,N-dimethylformamide (DMF), etc.} were purchased
from Aldrich Co. and were used as received.
nine), purine and/or adenine are coordinated to cobalt
through the N9 atom of an imidazole ring [10]. The same
manner of the ligand coordination was found in
monomeric complexes cis-[CoIII(ade-N9)Cl(en)2]Br Æ H2O
(en = 1,2-diaminoethane) [11] and (adeH+)2[CoII(H2O)4-
(adeH-N9)2] (SO4)2 Æ 6H2O [12]. On the other hand, the
adenine can be also bound via N3 as determined
in {[CoII(l-ox)(H2O)(adeH-N3)] Æ 2(adeH) Æ (H2O)}n [10].
From general point of view, other nitrogen atoms of purine
(i.e., N1 and N7) and adenine (i.e., N1, N6 and N7) deriv-
atives can be also used for coordination to cobalt. This was
found in some Co(III) complexes which X-ray structures
were determined. For example, the coordination through
N7 was found in [Co(acac)2(NO2)(tca-N7)] Æ H2O Æ DMF
(acacH = acetylacetone, tca = tricanthine) [13], [Co(acac)2
(NO2)(1,9-dimethyl-adeH+-N7)][Co(acac)2(NO2)2] [14] and
[Co(3-benzyl-ade-N7)(dmg)2(dmp)] Æ H2O Æ EtOH (dmg =
dimethylglyoximate, dmp = dimethylphosphonate) [15].
Moreover, in the tetrahedral [CoII(ade-N6,N7)Cl(H2O)] Æ
H2O complex, adenine acts probably as a bidentate ligand
through N6 and N7 atoms [16]. Unfortunately, the conclu-
sion relating to a mode of coordination in the latter com-
plex is not supported by results following from a single
crystal X-ray analysis and was deduced from IR data only.
In our previous work, we have published the first prep-
aration and biological activity of mononuclear tetrahedral
2.2. Syntheses
2.2.1. 6-(3-Chlorobenzylamino)purine (HL1), 6-(4-chloro-
benzylamino)purine (HL2), 6-(2,3-dimethoxybenzylamino)
purine (HL3), 6-(3,4-dimethoxybenzylamino)purine (HL4),
6-(3-fluorobenzylamino)purine (HL5), 6-(4-fluorobenzyl
amino)purine (HL6) and [H2+L2](ClO4)2 Æ 2H2O
Compounds HL1–HL6 were prepared by the reaction of
6-chloropurine with an appropriate benzylamine in n-
butanol with the addition of triethylamine by the procedure
similar to that as described previously [17]. Yields ranged
from 65% to 70%. The purity and composition of the com-
1
pounds were proved by elemental analyses, H and 13C
NMR spectra, thin-layer chromatography using a Silica
gel 60 F254 (Merck) precoated aluminum plates with
CHCl3:CH3OH:conc. NH4OH (8:2:0.2, v/v/v) as a mobile
phase, and melting points (data shown in Dolezˇal et al., Bio-
org. Med. Chem. 2005, submitted). Crystals of
[H2+L2](ClO4)2 Æ 2H2O were obtained by recrystallization
of HL2 from 2 M HClO4.

A. Klanicova´ et al. / Polyhedron 25 (2006) 1421–1432
1423
HL1. Anal. Calc. for C12H10N5Cl: C, 55.5; H, 3.9; N,
27.0. Found: C, 55.3; H, 4.0; N, 27.2%. IR (cmꢀ1):
3429m, 3260m, 3077m, 2939m, 1622vs, 1538w, 1485w,
d 12.95 (s, 1H, N9H), 8.26 (s, 1H, C2H), 8.21 (s, 1H,
C8H), 8.13 (s, 1H, N6H), 7.50 (q, 2H, C12H, C16H),
7.13 (t, 2H, C13H, C15H), 4.89 (s, 2H, C10H). 13C NMR
(DMF-d7, ppm): 162.32 (C14), 155.11 (C6), 153.22 (C2),
151.66 (C4), 139.94 (C8), 137.43 (C11), 130.13 (C12),
130.01 (C16), 119.20 (C5), 115.64 (C13), 115.35 (C15),
43.48 (C10). MS: m/z 244 [HL6]+.
1
1158w. H NMR (DMF-d7, ppm): d 13.00 (s, 1H, N9H),
8.24 (s, 1H, C2H), 8.20 (s, 1H, C8H), 7.50 (s, 1H,
C12H), 7.42 (d, 1H, C16H), 7.36 (t, 1H, C15H), 7.24 (d,
1H, C14H), 4.90 (s, 2H, C10H). 13C NMR (DMF-d7,
ppm): 155.02 (C6), 152.96 (C2), 150.58 (C4), 143.53
(C11), 139.67 (C8), 133.80 (C13), 130.50 (C12), 127.63
(C16), 127.13 (C15), 126.44 (C14), 119.51 (C5), 43.33
(C10). ES+ MS: m/z 261 [HL1]+. HL2. Anal. Calc. for
C12H10N5Cl: C, 55.5; H, 3.9; N, 27.0. Found: C, 55.5; H,
4.1; N, 26.8%. IR (cmꢀ1): 3430m, 3261w, 3048w, 2997w,
1626vs, 1567m, 1491w, 1155w. 1H NMR (DMF-d7,
ppm): d 12.98 (s, 1H, N9H), 8.23 (s, 1H, C2H), 8.19 (s,
1H, C8H), 8.11 (s, 1H, N6H), 7.48 (dd, 2H, C12H,
C16H), 7.38 (dd, 2H, C13H, C15H), 4.88 (s, 2H, C10H).
13C NMR (DMF-d7, ppm): d 155.41 (C6), 153.25 (C2),
152.79 (C4), 140.41 (C11), 139.69 (C8), 132.32 (C14),
129.94 (C12, C16), 128.91 (C13, C15), 119.69 (C5), 43.59
(C11). ES+ MS: m/z 261 [HL2]+. HL3. Anal. Calc. for
C14H15N5O2: C, 58.9; H, 5.3; N, 24.5. Found: C, 58.5; H,
5.2; N, 24.7%. IR (cmꢀ1): 3422w, 3262w, 3067w, 2995w,
2.2.2. [Co(L1)Cl(H2O)2] Æ H2O (1), [Co(L2)Cl(H2O)2]
Æ 2H2O (2), [Co(L3)Cl(H2O)2] Æ H2O (3), [Co(L4)Cl-
(H2O)2] Æ H2O (4), [Co(L5)Cl(H2O)2] Æ H2O (5),
[Co(L6)Cl(H2O)2] Æ H2O (6) and [Co6(l-L6)4Cl8-
(DMSO)10] Æ 4DMSO (7)
Co(II) complexes 1–6 were synthesized by the following
general method: a solution of an appropriate organic li-
gand (1 mmol) in EtOH (15 cm3) and triethylamine
(0.14 cm3) were mixed with stirring. Then, a solution of Co-
Cl2 Æ 6H2O (0.24 g, 1 mmol) was added. The pale blue pre-
cipitate formed immediately. This reaction mixture was
refluxed at 70 ꢁC and stirred for 5 h. All the synthetic steps
proceeded under nitrogen atmosphere. Then, the precipi-
tate was filtered off, washed with EtOH (3 · 10 cm3),
Et2O (2 · 10 cm3) and dried under an infrared lamp at
40 ꢁC. Yields ranged from 60% to 75%.
1
2835w, 1623vs, 1539w, 1480s, 1274m. H NMR (DMF-
d7, ppm): d 13.01 (s, 1H, N9H), 8.24 (s, 1H, C2H), 8.20
(s, 1H, C8H), 7.83 (s, 1H, N6H), 6.98 (t, 1H, C15H),
6.97 (dd, 2H, C14H, C16H), 4.92 (s, 2H, C10H), 3.87 (d,
6H, C17H, C18H). 13C NMR (DMF-d7, ppm): 155.00
(C6), 152.71 (C2), 149.63 (C4), 149.35 (C14), 148.43
(C13), 139.64 (C8), 132.70 (C11), 121.93 (C12), 120.31
(C5), 119.89 (C16), 111.96 (C15), 56.81 (C17), 48.89
(C18), 43.23 (C10). MS: m/z 286 [HL3]+. HL4. Anal. Calc.
for C14H15N5O2: C, 58.9; H, 5.3; N, 24.5. Found: C, 58.7;
H, 5.2; N, 24.7%. IR (cmꢀ1): 3430m, 3288w, 3072w, 2992w,
Crystals of [Co6(l-L6)4Cl8(DMSO)10] Æ 4DMSO (7) suit-
able for single crystal X-ray analysis were obtained by
recrystallization of the complex 6 from DMSO. In more
details, complex 6 was dissolved in DMSO and dark green
crystals were obtained by slow evaporation of the solvent
after several months.
[Co(L1)Cl(H2O)2] Æ H2O (1). Anal. Calc. for CoC12H15-
N5O3Cl2: C, 35.4; H, 3.7; N, 17.2; Co, 14.5. Found: C,
35.1; H, 3.7; N, 16.9; Co, 14.2%. IR (KBr) (cmꢀ1): 3397s,
1621vs, 1532w, 1474m, 1170m. IR (Nujol) (cmꢀ1): 449,
1
1
2834w, 1623vs, 1515s, 1464w, 1255m. H NMR (DMF-d7,
315, 303. H NMR (DMF-d7, ppm): d 8.77 (s, 1H, C8H),
ppm): d 12.92 (s, 1H, N9H), 8.25 (s, 1H, C2H), 8.18 (s, 1H,
C8H), 7.95 (s, 1H, N6H), 7.13 (s, 1H, C12H), 6.95 (d, 1H,
C16H), 6.91 (d, 1H, C15H), 4.81 (s, 2H, C10H), 3.79 (d,
6H, C17H, C18H). 13C NMR (DMF-d7, ppm): 155.00
(C6), 152.71 (C2), 149.63 (C4), 149.35 (C14), 148.43
(C13), 139.64 (C8), 132.70 (C11), 121.93 (C12), 120.31
(C5), 119.89 (C16), 111.96 (C15), 56.81 (C17), 48.89
(C18), 43.23 (C10). ES+ MS: m/z 286 [HL4]+. HL5. Anal.
Calc. for C12H10N5F: C, 59.3; H, 4.1; N, 28.8. Found: C,
59.1; H, 3.9; N, 28.4%. IR (cmꢀ1): 3456vs, 3267s, 3085w,
8.21 (s, 1H, C2H), 7.56 (s, 1H, C12H), 7.50 (s, 1H, C16H),
7.41 (s, 1H, C15H), 7.34 (s, 1H, C14H), 5.01 (s, 2H,
C11H). 13C NMR (DMF-d7, ppm): 155.62 (C6), 152.69
(C2), 147.10 (C4), 142.82 (C11), 145.70 (C8), 134.71 (C13),
131.65 (C12), 127.39 (C16), 127.41 (C15), 125.45 (C14),
119.20 (C5), 42.37 (C10). ES+ MS: m/z 391 [Co(L1)Cl-
(H2O)2]+, 354 [Co(L1)Cl]+, 260 [HL1]+. [Co(L2)Cl-
(H2O)2] Æ 2H2O (2). Anal. Calc. for CoC12H17N5O4Cl2: C,
33.9; H, 4.0; N, 16.5; Co, 13.9. Found: C, 33.5; H, 3.9; N,
16.4; Co, 13.5%. IR (KBr) (cmꢀ1): 3409m, 1620vs, 1540w,
1
1
2941m, 1630vs, 1567w, 1485w, 1253w. H NMR (DMF-
1473w, 1171w. IR (Nujol) (cmꢀ1): 435, 315, 303. H NMR
d7, ppm): d 12.99 (s, 1H, N9H), 8.25 (s, 1H, C2H), 8.21
(s, 1H, C8H), 8.17 (s, 1H, N6H), 7.36 (qui, 1H, C12H),
7.29 (d, 1H, C16H), 7.26 (t, 1H, C15H), 7.04 (1H,
C14H), 4.92 (s, 2H, C10H). 13C NMR (DMF-d7, ppm):
163.41 (C13), 155.31 (C6), 153.23 (C2), 151.01 (C4),
144.46 (C11), 139.89 (C8), 130.77 (C15), 123.98 (C16),
119.75 (C5), 114.64 (C12), 113.97 (C14), 43.66 (C10).
ES+ MS: m/z 244 [HL5]+. HL6. Anal. Calc. for
C12H10N5F: C, 59.3; H, 4.1; N, 28.8. Found: C, 59.2; H,
4.0; N, 28.3%. IR (cmꢀ1): 3447s, 3259m, 3044s, 2950m,
(DMF-d7, ppm): d 8.61 (s, 1H, C8H), 8.46 (s, 1H, C2H),
7.49 (s, 2H, C12, C16), 7.33 (s, 2H, C13, C15), 5.01 (s, 2H,
C10H). 13C NMR (DMF-d7, ppm): d 155.65 (C6), 153.09
(C2), 148.70 (C4), 141.82 (C11), 145.98 (C8), 134.09 (C14),
131.21 (C12, C16), 129.30 (C13, C15), 118.72 (C5), 45.31
(C10). ES+ MS: m/z 391 [Co(L2)Cl(H2O)2]+, 354
[Co(L2)Cl]+, 260 [HL2]+. [Co(L3)Cl(H2O)2] Æ H2O (3). Anal.
Calc. for CoC14H20N5O5Cl: C, 38.9; H, 4.7; N, 16.2; Co,
13.6. Found: C, 38.6; H, 4.5; N, 16.0; Co, 13.3%. IR (KBr)
(cmꢀ1): 3414s, 1622vs, 1541w, 1479m, 1275m IR (Nujol)
(cmꢀ1): 430, 315, 303. 1H NMR (DMF-d7, ppm): d 8.62 (s,
1
1630vs, 1568vs, 1489s, 1256m. H NMR (DMF-d7, ppm):

1424
A. Klanicova´ et al. / Polyhedron 25 (2006) 1421–1432
1H, C8H), 8.36 (s, 1H, C2H), 7.86 (s, 1H, N6H), 7.05 (s, 1H,
C15H), 7.01 (s, 2H, C14H, C16H), 5.01 (s, 2H, C10H), 3.90
(d, 6H, C17H, C18H). 13C NMR (DMF-d7, ppm): 155.78
(C6), 153.70 (C13), 154.15 (C2), 148.52 (C4), 147.63 (C12),
145.38 (C8), 133.12 (C11), 125.01 (C16), 121.48 (C15),
119.12 (C5), 111.92 (C14), 62.81 (C17), 55.24 (C18), 41.00
(C10). ES+ MS: m/z 414 [Co(L3)Cl(H2O)2]+, 379
[Co(L3)Cl]+, 286 [HL3]+. [Co(L4)Cl(H2O)2] Æ H2O (4). Anal.
Calc. for CoC14H20N5O5Cl: C, 38.9; H, 4.7; N, 16.2; Co,
13.6. Found: C, 38.7; H, 4.6; N, 15.9; Co, 13.2%. IR (KBr)
(cmꢀ1): 3429s, 1621vs, 1516s, 1465m, 1266m. IR (Nujol)
(cmꢀ1): 436, 314, 303. 1H NMR (DMF-d7, ppm): d 8.61 (s,
1H, C8H), 8.35 (s, 1H, C2H), 8.25 (s, 1H, N6H), 7.28 (s,
1H, C12H), 7.04 (s, 1H, C16H), 6.96 (s, 1H, C15H), 4.98
(s, 2H, C10H), 3.81 (6H, C17H, C18H). 13C NMR (DMF-
d7, ppm): 155.33 (C6), 151.15 (C2), 145.68 (C4), 149.23
(C14), 148.46 (C13), 145.21 (C8), 132.62 (C11), 121.36
(C12), 120.98 (C5), 120.01 (C16), 112.57 (C15), 56.01
(C17), 47.53 (C18), 43.91 (C10). ES+ MS: m/z 414
[Co(L4)Cl(H2O)2]+, 379 [Co(L4)Cl]+, 286 [HL4]+.
[Co(L5)Cl(H2O)2] Æ H2O (5). Anal. Calc. for CoC12H15-
N5O3ClF: C, 36.9; H, 3.9; N, 17.9; Co, 15.1. Found: C,
36.5; H, 3.6; N, 18.2; Co, 15.0%. IR (KBr) (cmꢀ1): 3409m,
1621vs, 1537w, 1474w, 1250w. IR (Nujol) (cmꢀ1): 441,
plexes were obtained on a Perkin–Elmer Lambda40
spectrometer in the 11000–25000 cmꢀ1 range. Diffuse-
reflectance spectra were recorded using a Perkin–Elmer
Lambda35 spectrometer in the same range. Magnetic sus-
ceptibilities were measured by the Faraday method at
room temperature using Hg[Co(SCN)4] as a calibrant,
corrections for diamagnetism were calculated from Pas-
calꢀs constants [18]. ES+ mass spectra of the ligands
and complexes were recorded on a Waters ZMD 2000
mass spectrometer using a flow injection mode in mass
monitoring interval 30–900 m/z. The spectra were col-
lected using 3.0 s cyclical scans with cone voltage 20
and 40 V, at the source block temperature 80 ꢁC, desol-
vation temperature 150 ꢁC and desolvation gas flow rate
200 l/h. Conductances of 10ꢀ3 M solutions of the com-
plexes in DMF were measured using a WTW Con-
d340i/SET conductometer at 25 ꢁC. Thermogravimetric
(TG) measurements were made in the temperature range
of 20–1000 ꢁC using a THASS TGA XP-10 thermal ana-
lyser. Melting points of the ligands used were determined
on a Buchi Melting point B-540 apparatus and were
¨
uncorrected.
2.4. X-ray structure determinations
1
324, 307. H NMR (DMF-d7, ppm): d 8.80 (s, 1H, C8H),
8.63 (s, 1H, C2H), 7.38 (m, 3H, C12H, C15H, C16H), 7.07
(t, 1H, C14H), 5.02 (s, 2H, C10H). 13C NMR (DMF-d7,
ppm): 156.00 (C6), 153.70 (C2), 148.23 (C4), 145.02 (C11),
146.12 (C8), 129.16 (C15), 125.01 (C16), 120.13 (C5),
115.16 (C12), 112.57 (C14), 44.28 (C10). MS: m/z 337
[Co(L5)Cl]+, 244 [HL5]+. [Co(L6)Cl(H2O)2] Æ H2O (6). Anal.
Calc. for CoC12H15N5O3ClF: C, 36.9; H, 3.9; N, 17.9; Co,
15.1. Found: C, 36.6; H, 3.5; N, 17.6; Co, 14.8%. IR (KBr)
(cmꢀ1): 3416m, 1622vs, 1510m, 1474w, 1272w. IR (Nujol)
(cmꢀ1): 436, 317, 310. 1H NMR (DMF-d7, ppm): d 8.59 (s,
1H, C8H), 8.38 (s, 1H, C2H), 7.56 (s, 2H, C12H, C16H),
7.16 (s, 2H, C13H, C15H), 4.95 (s, 2H, C10H). 13C NMR
(DMF-d7, ppm): 156.45 (C6), 154.28 (C2), 146.23 (C4),
144.13 (C8), 136.20 (C11), 130.30 (C12), 128.12 (C16),
120.50 (C5), 114.31 (C13), 113.78 (C15), 43.14 (C10). MS:
m/z 337 [Co(L6)Cl]+, 244 [HL6]+.
Diffraction data for [H2+L2](ClO4)2 Æ 2H2O and [Co6(l-
L6)4Cl8(DMSO)10] Æ 4DMSO (7) were collected on an Ox-
ford Diffraction Xcalibur2 diffractometer equipped with
Sapphire2 CCD detector at 100 K. The CRYSALIS software
package (Version 1.171.24) was used for data collection
and reduction. Both structures were solved by the SIR97
program [19] incorporated in the WINGX system (Version
1.70.00) [20]. All non-hydrogen atoms were refined
anisotropically by the full-matrix least-squares procedure
SHELXL-97 [21] on F2 with weight: w = 1/[r2(Fo)2 +
(0.0869P)2 + 1.9024P] for [H2+L2](ClO4)2 Æ 2H2O and
w = 1/[r2(Fo)2 + (0.1875P)2 + 8.3404P] for 7, where P ¼
ðF 2o þ 2F 2cÞ=3. In [H2+L2](ClO4)2 Æ 2H2O, H-atoms at-
tached to C and N atoms were found from difference
Fourier maps and refined using a ꢁridingꢀ model with
˚
C–H distances of 0.95 and 0.99 A, the N–H distances
˚
of 0.88 A with Uiso values derived from Ueq of the corre-
2.3. Physical measurements
sponding C and N atoms, respectively. Uiso(H) = 1.2Ueq
(CH, CH2 and NH). The H-atoms of water molecules
were refined freely. The largest peak and hole on the final
All compounds were characterized by elemental analy-
ses (C, H, N) using a ThermoFinnigan Flash EA-1121
Elemental Analyser. The cobalt content was determined
by a chelatometric (EDTA) titration on murexide as an
indicator. IR spectra of all compounds were recorded
on a ThermoNicolet Nexus 670 FT-IR spectrometer as
KBr pellets (400–4000 cmꢀ1) and using Nujol (150–
500 cmꢀ1) and DRIFT (4000–10000 cmꢀ1) techniques
˚
difference map were 0.632 [0.90 A from O(4)] and ꢀ0.606
[0.87 A from Cl(2)] e Aꢀ3, respectively. In 7, H-atoms
belonging to all ligands, except for those of disordered
DMSO molecules, were positioned theoretically and
H-atoms of solvated DMSO were not included into cal-
culation. In connection with overall bad crystal data
quality [Rint = 0.1333], statistical data relating to this
structure are not satisfactory. Nevertheless, the molecular
structure of 7 was determined unambiguously from chem-
ical point of view. The crystal data and structure refine-
ments for [H2+L2](ClO4)2 Æ 2H2O and 7 are given in
Table 1.
˚
˚
(only in case of the complexes). H and 13C NMR data
1
of the ligands and Co(II) complexes in DMF-d7 were col-
lected on a Bruker 300 MHz NMR spectrometer Avance
600 with tetramethylsilane as an internal standard. Elec-
tronic absorption spectra of DMF solutions of the com-

A. Klanicova´ et al. / Polyhedron 25 (2006) 1421–1432
1425
Table 1
Crystal data and structure refinements for [H2+L2](ClO4)2 Æ 2H2O and [Co6(l-L6)4Cl8(DMSO)10] Æ 4DMSO (7)
[H2+L2](ClO4)2 Æ 2H2O
(7)
Empirical formula
Formula weight
Temperature (K)
C
12H16Cl3N5O10
C76H90Cl8Co6F4N20O17S14
2717.70
100(2)
496.65
100(2)
0.71073
˚
Wavelength (A)
0.71073
ꢀ
Crystal system, space group
Unit cell dimension
triclinic, P1
monoclinic, P21/n
˚
a (A)
8.273(5)
8.306(5)
14.798(5)
78.721(5)
80.048(5)
75.441(5)
957.0(9)
2, 1.724
13.559(5)
25.212(5)
17.437(5)
90
100.820(5)
90
5855(3)
2, 1.542
1.333
˚
b (A)
˚
c (A)
a (ꢁ)
b (ꢁ)
c (ꢁ)
3
˚
Volume (A )
Z, Calculated density (Mg mꢀ3
)
Absorption coefficient (mmꢀ1
F(000)
)
0.544
580
2760
Crystal size (mm)
h range for data collection (ꢁ)
Index ranges
Reflections collected/unique
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I > 2r(I)]
R indices (all data)
0.30 · 0.30 · 0.25
2.57–25.00
ꢀ9 6 h 6 9, ꢀ9 6 k 6 6, ꢀ17 6 l 6 17
6920/3237 [Rint = 0.0806]
3237/4/288
0.30 · 0.30 · 0.25
2.70–25.00
ꢀ16 6 h 6 14, ꢀ28 6 k 6 29, ꢀ20 6 l 6 20
42659/10293 [Rint = 0.1333]
10293/2/664
1.101
1.141
R1 = 0.0481, wR2 = 0.1221
R1 = 0.0586, wR2 = 0.1498
0.632 and ꢀ0.606
R1 = 0.1111, wR2 = 0.2889
R1 = 0.1458, wR2 = 0.3231
2.189 and ꢀ1.650
ꢀ3
˚
Largest difference peak and hole (e A
)
2.5. Cytotoxicity testing
the case of described complexes, a band centered at ca.
16000 cmꢀ1 is splitted into two peaks what is probably
due to the interaction with the doublet state through
spin–orbit coupling and may be attributed to the m3 transi-
Cytotoxicity of the starting compounds (i.e., HL1–HL6
and CoCl2 Æ 6H2O) and complexes 1–6 was assessed by a
Calcein AM assay. The following human tumour cell lines
were used: malignant melanoma (G361), chronic myeloge-
nous erythroleukemia (K562), osteogenic sarcoma (HOS)
and breast adenocarcinoma (MCF7). IC50 values, i.e., the
drug concentration lethal to 50% of the tumour cells, were
estimated. Our experimental setup relating to the cytotox-
icity testing was described previously in greater details [7].
4
4
tion, i.e., A2 ! T1(P) [27–31]. The calculated values of
molar absorption coefficients range from 103 to
527 Mꢀ1 cmꢀ1 and correspond to d–d transitions [32].
Additionally, the next two d–d transitions were observed
in the NIR region. The broadbands at ca. 7560 cmꢀ1 can
4
4
be attributed to the spin allowed transition A2 ! T1(F)
(m2) [33], while weak peaks near 4450 cmꢀ1 were assigned
4
4
to the m1 transition, i.e. A2 ! T2(F). The curve shapes
and maxima positions both in the solution and solid-state
spectra are almost identical, and so, it can be expected that
the prepared complexes are sufficiently chemically inert and
do not change their coordination spheres in the solvent
used. The ligand field parameters 10Dq and the Racah
parameters B were calculated from Tanabe–Sugano matri-
ces described in the literature [34,35]. To calculate 10Dq
and B values, the maximal intensity of the relevant m2
and m3 bands were used. Calculated values for degree of
covalent binding of ligands b (ꢁ 0.69) and ligand field
strength 10Dq (4420–4430 cmꢀ1) as well as Racah parame-
3. Results and discussion
3.1. Magnetic, conductivity data, electronic spectra
Magnetic, conductivity and electronic spectral data of
the prepared complexes are given in Table 2. The effective
magnetic moment values vary from 4.4 to 4.7 leff/lB, which
correspond with the values expected for tetrahedral high-
spin (d7) Co(II) complexes [22–25] (see Scheme 2). The
molar conductivity values of the complexes (10ꢀ3 M in
DMF) at 25 ꢁC range from 11.0 to 18.7 S cm2 molꢀ1 and
show on their non-ionic character [26].
ters
B ) are comparable for all the
(668–671 cmꢀ1
Both absorption (DMF solutions) and diffuse-reflec-
tance (solid state) electronic spectra of all the complexes
are similar and exhibit three maxima at ca. 15700, 16100
and 18700 cmꢀ1, and 15600, 16000 and 18100 cmꢀ1. The
electronic spectra of compound 2 are shown in Fig. 1. As
it is generally known, regular tetrahedral Co(II) complexes
should have only one d–d transition in the visible region. In
complexes. However, these values differ to those described
for some tetrahedral complexes in the literature,
e.g., [Co(Th4DM)(OH)(H2O)] (10Dq = 4110 cmꢀ1, B =
709 cmꢀ1 and b = 0.73), where HTh4DM = 4-acetamido-
benzaldehyde-N(4)-dimethyl-thiosemicarbazone [36], and
[CoCl2(TdTn)] (10Dq = 4861 cmꢀ1
,
B = 754 cmꢀ1 and
b = 0.78), where TdTn = 2-(3,4-dichlorophenyl)imino-N-

1426
A. Klanicova´ et al. / Polyhedron 25 (2006) 1421–1432
Table 2
Magnetic, conductivity and electronic spectral data of the complexes 1–6
Compound
leff/lB (293 K)
kM (S cm2 molꢀ1
a
)
Absorption maxima (cmꢀ1)/e
(Mꢀ1 cmꢀ1
10Dq (cmꢀ1
)
B (cmꢀ1
)
b
)
DMF solution
Solid state
1
4.4
4.4
4.6
4.6
4.7
4.7
18.7
7570
15710/470
16090/454
18640/125
4430
668
0.69
15420
15960
18030
2
3
4
5
12.1
11.0
13.0
14.4
11.2
7570
15710/464
16100/449
18660/127
4430
4420
4420
4430
4420
669
671
670
670
670
0.69
0.69
0.69
0.69
0.69
15460
15910
18000
7560
15700/445
16090/439
18660/130
15450
15970
18050
7550
15700/414
16100/405
18650/103
15500
15920
18130
7570
15720/527
16100/518
18720/144
15710
16190
18070
6
7550
15730/515
16100/502
18690/137
15740
16110
18070
a
Measured in 10ꢀ3 M DMF solutions.
Scheme 2.
(2-thiazolin-2-yl)thiazolidine [37]. The difference of spectral
parameters is caused by dissimilarity of chromophores, i.e.
CoNClO2 versus CoNSO2 or CoN2Cl2. Thus, the results
following from electronic spectral data are in agreement
with the conclusions from magnetic measurements.
Fig. 1. Absorption electronic solution (—) and diffuse-reflectance spectra
(ꢂ ꢂ ꢂ) of complex 2.
3.2. NMR measurements
The 1H and 13C NMR spectra of the free cytokinin deriv-
atives as well as the complexes were measured in DMF-d7
and the chemical shifts are summarized in Section 2.2. Dif-
ferences between NMR spectra of the complexes and free
ligands provide circumstantial evidence on a complex
formation. The largest coordination shifts Dd (Dd =
0.59 ppm. The largest coordination shifts were also found
for C8 and C4 signals in 13C NMR spectra. The C8 signals
were shifted downfield by ca. 6.29 ppm, while the C4 signals
were shifted upfield by ca. 4.09 ppm. On the basis of this
fact, we can conclude that the ligands are deprotonated at
the N9 position of an imidazole ring and moreover, the
coordination of the cytokinin derivatives to cobalt proceeds
1
dcomplex ꢀ dligand) were observed in H NMR spectra for
the H8 protons, which were shifted downfield by 0.38–

A. Klanicova´ et al. / Polyhedron 25 (2006) 1421–1432
1427
via the same atom in all the complexes (see Scheme 2). The
similar conclusion can be made in case of the measurement
in methanol-d4. However, the interpretation of the spectra
is somewhat complicated due to limited solubility of the
complexes as well as free ligands in methanol-d4. We have
also measured NMR spectra in DMSO-d7 and acetone-d6.
Unfortunately, reproducible NMR data in DMSO-d7 and
acetone-d6 have not been obtained, probably in connection
with the decomposition of the complexes in these solvents.
This conclusion was proved in the case of 6 by a single crys-
tal X-ray analysis, where the recrystallization of the com-
plex from DMSO led to formation of complex 7 (see
Section 3.8).
group, and complex 2 is not probably formed by this
way. The optimized geometries of complex 2 with the pos-
sible monodentate coordination modes of the 6-(4-chloro-
benzylamino)purine ligand are shown in Fig. 2. Similar
to the N1 coordination, the benzyl functional group par-
tially hinders the bidentate coordination to cobalt(II) ion
via the N6 and N7 donor atoms. Mutual orientation of
purine ring and benzylamino group leads to the different
spatial orientation of the lone electron pairs of N6 and
N7 atoms. This arrangement makes impossible effective a
bidentate binding of the organic ligand to cobalt(II) ion.
On the other hand, the N3 and N9 positions are in essence
equivalent from both the geometrical and sterical perspec-
tives, and moreover, both donor atoms are well uncovered
for the coordination with the cobalt ion.
3.3. Computational analysis
The elꢀectron distribution within the purine skeleton of
anion L2 gives preference rather to the coordination via
the N7 atom with highest negative partial charge. The
remaining three nitrogen atoms (i.e., N1, N3 and N9) have
comparable charges. On the other hand, the greatest
changes in the charge distribution have been observed in
case of the coordination via the N9 atom (for details, see
Table 3).
Bond distances between the corresponding nitrogen and
cobalt atoms are nearly identical in all three studied sys-
tems (Table 4). All three suggested models also offer the
strong hydrogen bond interaction between one water mol-
ecule coordinated to the cobalt(II) ion and the correspond-
ing adjacent nitrogen atom, i.e., N3 for the N9-coordinated
complex, N9 for the N3-coordinated complex and N6 for
the N7-coordinated complex (see Fig. 2). Selected
calculated hydrogen bond parameters are also summarized
in Table 3.
Theoretical calculations using the DFT (B3LYP) ap-
proach were performed with the aim to suggest a possible
coordination mode of the studied 6-benzylaminopurine
derivatives to the cobalt(II) ion. This approach partially
substitutes the absence of crystallographic data of any of
the studied Co(II) complexes. All calculations were done
using the GAUSSIAN03 program [38]. As a model system,
complex 2 was chosen. Preliminary optimized data were
prepared on the HF/6-31* level of the theory. Then, the ob-
tained geometries were fully optimized at the B3LYP level
with 6-311++G** (for ligands) and 6-311+G* (for com-
plexes) basis sets. Harmonic-frequency analysis was used
to verify the nature of found stationary points as the min-
ima as well as for the calculation of zero-point vibrational
energies. Calculated infrared frequencies of the ligands, as
shown in Table 3, were not scaled. Natural-bond orbital
analysis (NBO) was used for investigation of the electron
distribution in the studied complexes [39].
Difference between DSCF energies of the N3 and N9
coordinated complexes is 1.01 kcal molꢀ1 in favour of
the N9 coordination. The energy of the N7 complex is
higher by 15.7 kcal molꢀ1, also in comparison with the
From general point of view, each of the 6-benzylamin-
opurine derivatives used in this study offers several possible
binding sites for the cobalt complex formation, e.g., N1,
N3, N7 or N9 for the monodentate binding, N6–N7 for
bidentate one, and N7–N9 or N3–N9 for bridging coordi-
nation [9,16]. The N1 binding site is strongly sterically hin-
dered by the methylene hydrogens of the benzylamino
ꢀ
N9 complex. It is supposable that the L2 anion is coor-
dinated to cobalt via N9 or N3 atom in complex 2, and
some dynamic equilibrium should be expected in the
solution.
Table 3
Selected calculated partial charges and geometrical parameters of the complex 2
˚
Coordination site
Partial charges (Mulliken/NBO)
Interatomic parameters (A, ꢁ)
N1
N3
N7
N9
Co–N
1.98
Co–Cl
2.23
Co–O
O–Hꢂ ꢂ ꢂNb
2.67
\DHAc
N7
N3
N9
ꢀ0.07/ꢀ0.54
ꢀ0.08/ꢀ0.47
ꢀ0.01/ꢀ0.77
ꢀ0.10/ꢀ0.50
2.10
154.3
2.02a
2.09
ꢀ0.09/ꢀ0.56
ꢀ0.15/ꢀ0.57
ꢀ0.19/ꢀ0.61
0.11/ꢀ0.70
ꢀ0.50/ꢀ0.62
ꢀ0.16/ꢀ0.53
ꢀ0.18/ꢀ0.53
ꢀ0.17/ꢀ0.52
ꢀ0.27/ꢀ0.60
ꢀ0.50/ꢀ0.66
0.19/ꢀ0.74
2.02
1.99
2.23
2.22
2.54
2.62
155.3
155.5
2.01a
2.09
2.06a
ꢀ
Free L2
ꢀ0.20/ꢀ0.59
a
The value belongs to the Co–O bond with oxygen atom participating in the HO(H)ꢂ ꢂ ꢂN hydrogen bond.
The distance between donor (D) and acceptor (A) atoms.
The O–Hꢂ ꢂ ꢂN angle.
b
c

1428
A. Klanicova´ et al. / Polyhedron 25 (2006) 1421–1432
Fig. 2. Optimized geometries of possible structures of complex 2. The most probable structure is depicted in a variant c.
Table 4
Comparison of calculated and experimental infrared frequencies (cmꢀ1) of the ligands HL1–HL6 and their assignment
HL1
HL2
HL3
HL4
HL5
HL6
Assignment
Calcd.
Exp.
Calcd.
Exp.
Calcd.
Exp.
Calcd.
Exp.
Calcd.
Exp.
Calcd.
Exp.
3648
3612
3241
3091
3017
1630
1636
3648
3613
3240
3093
3019
1630
1614
3650
3609
3239
3137
3046
1629
1622
1240
3649
3619
3240
3081
3014
1629
1615
1292
3648
3612
3240
3092
3018
1632
1626
3648
3613
3240
3096
3016
1630
1636
m(N9–H)
m(N6–H)
m(C8–H)
mas(CH2)
ms(CH2)
m(C@N)
m(C@C)ar
m(Car–O)
m(Car–X)
3429
3260
3077
2985
1622
1538
3430
3261
3048
2997
1626
1567
3422
3262
3067
2995
1623
1539
1274
3430
3288
3072
2992
1623
1515
1255
3455
3267
3085
2941
1630
1567
3447
3259
3082
2950
1630
1568
1099
1157
1100
1155
1269
1253
1240
1256
3.4. IR spectra
among molecules were ignored, differences between exper-
imental and theoretical values appeared. In spite of this,
values correspond sufficiently.
In the IR spectra of all the ligands as well as the com-
plexes, the maxima belonging to the m(C@N) vibration
appeared in the 1620–1630 cmꢀ1 region, while the bands
at 1465–1491 and 1510–1568 cmꢀ1 belong to m(C@C)
vibration. The broadbands between 3339 and 3447 cmꢀ1
are associated with the m(N–H) vibration. The characteris-
tic bands of the Car–Cl, Car–F and Car–O groups are ob-
served in the 1155–1174, 1250–1272, and 1255–1275 cmꢀ1
regions, respectively. All the bands discussed above con-
firm the presence of the ligands in complexes 1–6 [40].
The far-IR spectra of the complexes revealed absorptions
in the 430–449 and 314–324 cmꢀ1 ranges, which may be as-
signed to the m(Co–N), and m(Co–O) stretching bands,
respectively. The bands between 303 and 310 cmꢀ1 can be
attributed to the m(Co–Cl) stretching vibration [41–45].
The comparison of measured frequencies with calcu-
lated values is given in Table 4. Because of the fact that cal-
culations were carried out in vacuum, and thus interactions
3.5. Mass spectroscopy
The ES+ mass spectra of complexes 1 and 2 showed a
peak at 260 m/z identifying the presence of HL1 and HL2
molecule in these complexes. The presence of HL3 and
HL4 in compounds 3 and 4 is obvious from the maximum
at 286 m/z. The maxima observed at 244 m/z confirmed the
presence of the ligands HL5 and HL6 in compounds 5 and
6. The peaks observed at 136 and 121 m/z correspond to
the fragments of adenine and purine, respectively. The
peaks for fragments [Co(L1)Cl(H2O)2]+ and [Co(L2)Cl-
(H2O)2]+ appeared at 391 m/z, while peaks observed at
414 m/z belong to fragments [Co(L3)Cl(H2O)2]+ and
[Co(L4)Cl(H2O)2]+. The peaks observed at 354 m/z for
compounds 1 and 2 are associated with fragments
[Co(L1)Cl]+ and [Co(L2)Cl]+, respectively. The peaks

A. Klanicova´ et al. / Polyhedron 25 (2006) 1421–1432
1429
appeared at 379 m/z correspond with fragments
[Co(L3)Cl]+ and [Co(L4)Cl]+. In case of the complexes 5
and 6, the maxima appeared at 337 m/z agree with the frag-
ments [Co(L5)Cl]+ and [Co(L6)Cl]+.
3.6. Thermal analyses
Thermal decomposition of all complexes is very similar.
TG curves showed that compounds 1 and 3–6 are monohy-
drates while the complex 2 exists as a dihydrate. The curves
of thermal degradation of compounds 2 and 4 are shown in
Fig. 3. In the case of 2, the first weight loss is apparent be-
tween 40 and 138 ꢁC and can be attributed to the loss of
one crystal water molecule (found/calc. 4.1/4.2%) and the
existence of the compound having formula of [Co(L2)Cl-
(H2O)2] Æ H2O, which is stable between 138 and 196 ꢁC.
The weight loss connected with the elimination of the sec-
ond crystal water molecule can be observed between 196
and 280 ꢁC. A plateau occurs on the TG curve in the
280–305 ꢁC temperature interval and it can be associated
with formation of an anhydrous complex [Co(L2)Cl(H2O)2]
(found/calc. 8.7/8.5%). It is evident from the TG curves of
1 and 3–6 that the weight loss between ca. 35 and 140 ꢁC is
connected with the release of one crystal water molecule.
Thermal decomposition of all complexes is finished at ca.
960 ꢁC, giving Co3O4/CoO mixture in ratio 4:1 which
was determined by means of X-ray powder diffraction anal-
ysis and PDF2 database [46] in the case of 3 and 6.
Fig. 4. The molecular structure of [H2+L2](ClO4)2 Æ 2H2O with the atom
labelling scheme. The non-H atoms are drawn as displacement ellipsoids
at the 50% probability level and H atoms are shown as small spheres at
arbitrary radii. Dashed lines indicate possible hydrogen bonds. The H1A
and H3A positions belong to the identical hydrogen atom, which is
disordered over two positions with the probability of 34% for the H1A
position and 66% for the H3A one.
3.7. X-ray structure of 6-(4-chlorobenzylamino)purin-di-ium
diperchlorate dihydrate, [H2+L2](ClO4)2 Æ 2H2O
The crystal structure of 6-(4-chlorobenzylamino)purin-
di-ium diperchlorate dihydrate is composed of 6-(4-chloro-
benzylamino)purin-di-ium cation, two perchlorate anions
and two water molecules of crystallization. The molecular
structure together with the atom numbering scheme is
shown in Fig. 4. The cation is clearly protonated at the
N7 and N9 positions, and a combination of N1 and N3
ones. However, the positions of the latter proton are statis-
tically disordered over two positions with probability of
34% (for N(1)–H), and 66% (for N(3)–H), respectively.
The position of the hydrogen atoms differs from free bases,
where the protonation occurs only at the N9 position. The
molecular structure of [H2+L2](ClO4)2 Æ 2H2O represents
the (N1,N3), N9-protonated N7 tautomer. There are signif-
icant deviations from planarity in both purine and phenyl
rings [47]. Maximum deviation from the LSQ-plane is
˚
˚
0.0119(3) A for C2 of the purine ring and 0.0077(3) A for
C14 of the phenyl ring. The dihedral angle between
the above-mentioned rings is equal to 53.45(1)ꢁ. It is
significantly lower in comparison to that found for 6-(2-
chlorobenzylamino)purine dihydrate [79.5(2)ꢁ] [5], 6-(4-
chlorobenzylamino)purinium perchlorate [86.19(1)ꢁ] [6]
and
6-(4-methoxybenzylamino)purin-3-ium
chloride
[77.46(5)ꢁ] [48]. Selected bond lengths and angles are given
in Table 5, while hydrogen bond parameters are summa-
rized in Table 6. The C2–N3–C4, C8–N7–C5 and C8–
N9–C4 bond angles in a purine skeleton of [H2+L2]-
(ClO4)2 Æ 2H2O are 116.1(3)ꢁ, 108.3(3)ꢁ and 107.5(3)ꢁ and
are slightly different from the values obtained for
the above-mentioned compounds. All the above-
discussed differences are probably caused by a degree of
Fig. 3. Thermogravimetric curves of the complexes 2 (—) and 4 (ꢂ ꢂ ꢂ).

1430
A. Klanicova´ et al. / Polyhedron 25 (2006) 1421–1432
Table 5
protonation and substitution of the whole 6-benzylaminop-
Selected bond lengths (A) and angles (ꢁ) for [H2+L2](ClO4)2 Æ 2H2O
˚
urine moiety. The Cg1ꢂ ꢂ ꢂ Cg2, Cg1ꢂ ꢂ ꢂCg3 and Cg2ꢂ ꢂ ꢂCg3
˚
Bond lengths
Bond angles
distances are 6.311(2), 7.0208(21) and 2.1086(7) A,
respectively, where Cg1, Cg2 and Cg3 are the centroids of
benzene, purine and imidazole rings. Torsion angles of
C9–N6–C6–C5, C6–N6–C9–C10 and N6–C9–C10–C15
are 178.8(3)ꢁ, 157.6(3)ꢁ, and 138.7(3)ꢁ, respectively.
N(1)–C(2)
N(1)–C(6)
C(2)–N(3)
N(3)–C(4)
C(4)–N(9)
C(4)–C(5)
C(5)–N(7)
C(5)–C(6)
N(6)–C(6)
N(7)–C(8)
C(8)–N(9)
1.307(5)
1.359(5)
1.334(5)
1.357(5)
1.358(5)
1.370(5)
1.381(4)
1.415(5)
1.310(4)
1.313(4)
1.335(5)
C(2)–N(1)–C(6)
N(1)–C(2)–N(3)
C(2)–N(3)–C(4)
N(3)–C(4)–C(5)
N(9)–C(4)–C(5)
C(4)–C(5)–N(7)
C(4)–C(5)–C(6)
N(1)–C(6)–C(5)
C(8)–N(7)–C(5)
N(7)–C(8)–N(9)
C(8)–N(9)–C(4)
120.1(3)
126.2(3)
116.1(3)
121.2(3)
108.1(3)
106.0(3)
119.8(3)
116.7(3)
108.3(3)
110.2(3)
107.5(3)
3.8. X-ray structure of [Co6(l-L6)4-
Cl8(DMSO)10] Æ 4DMSO (7)
The interatomic and geometrical parameters of complex
7 are not discussed in detail in connection with the overall
bad crystal data quality and consequently with the low
quality of the refinement. Thus, the discussion regarding
to the molecular structure of 7 is focused on the description
of the stereochemistry in the vicinity of the central Co(II)
ions and on the manner of coordination of organic ligands
only. The molecular structure of the centrosymmetric hexa-
nuclear complex [Co6(l-L6)4Cl8(DMSO)10] Æ 4DMSO is de-
picted in Fig. 5. Four of the six central atoms, Co(1),
Co(1A), Co(2) and Co(2A), are surrounded by six atoms
in a distorted octahedral arrangement, while the geometry
around Co(3) and Co(3A) atoms is tetrahedral. Thus, HL6,
i.e., 6-(4-fluorobenzylamino)purine, acts as a tridentate
bridging ligand in this complex. There is a direct metal–me-
tal interaction between Co(1) and Co(1A) atoms with the
Table 6
Hydrogen bonds for [H2+L2](ClO4)2 Æ 2H2O (A, ꢁ)
˚
D–Hꢂ ꢂ ꢂA
d(D–H)
d(Hꢂ ꢂ ꢂA)
d(Dꢂ ꢂ ꢂA)
\(DHA)
N(3)–H(3A)ꢂ ꢂ ꢂO(4)i
N(3)–H(3A)ꢂ ꢂ ꢂO(7)ii
N(6)–H(6A)ꢂ ꢂ ꢂO(10)
N(7)–H(7A)ꢂ ꢂ ꢂO(10)
N(9)–H(9A)ꢂ ꢂ ꢂO(4)iii
N(9)–H(9A)ꢂ ꢂ ꢂO(7)ii
N(9)–H(9A)ꢂ ꢂ ꢂO(7)iv
O(9)–H(9V)ꢂ ꢂ ꢂO(5)v
O(9)–H(9V)ꢂ ꢂ ꢂO(5)vi
O(9)–H(9W)ꢂ ꢂ ꢂO(1)vii
O(10)–H(10V)ꢂ ꢂ ꢂO(9)
O(10)–H(10W)ꢂ ꢂ ꢂO(6)
O(10)–H(10W)ꢂ ꢂ ꢂO(3)vii
0.88
0.88
0.88
0.88
0.88
0.88
0.88
0.85(3)
0.85(3)
0.88(3)
0.89(3)
0.85(3)
0.85(3)
2.16
2.31
2.09
1.87
2.09
2.34
2.46
2.17(4)
2.34(4)
2.08(3)
1.80(3)
2.38(4)
2.55(3)
2.919(4)
2.910(4)
2.943(4)
2.680(4)
2.862(4)
2.900(4)
3.009(4)
2.953(5)
3.009(4)
2.874(4)
2.684(4)
2.995(4)
3.243(4)
143.5
125.2
161.8
153.1
145.3
121.3
120.8
153(5)
136(5)
150(4)
170(6)
130(4)
139(4)
˚
bond length of 2.667(2) A. Furthermore, these two cobalt
atoms are connected with four bridging organic ligands
HL6, which are coordinated via N3 and N9 donor atoms.
One chlorine atom is bonded to Co(2) and Co(2A), respec-
Symmetry transformations used to generate equivalent atoms: (i) x + 1, y,
z; (ii) x, y + 1, z; (iii) ꢀx + 1, ꢀy + 1, ꢀz + 2; (iv) ꢀx + 2, ꢀy, ꢀz + 2; (v)
ꢀx + 1, ꢀy, ꢀz + 2; (vi) x ꢀ 1, y, z; (vii) x, y ꢀ 1, z.
Fig. 5. The molecular structure of [Co6(l-L6)4Cl8(DMSO)10] Æ 4DMSO (7). Hydrogen atoms and solvated DMSO molecules were omitted for clarity.

A. Klanicova´ et al. / Polyhedron 25 (2006) 1421–1432
1431
Table 7
Table 8
˚
Selected bond lengths (A) and angles (ꢁ) for [Co6(l-L6)4Cl8-
(DMSO)10] Æ 4DMSO (7)
The cytotoxicity of the studied compounds, expressed as IC50 values (lM)
assessed by a Calcein AM assay
Co(1)–N(9A)
Co(1)–N(3A)i
Co(1)–N(3)
Co(1)–N(9)i
Co(1)–Cl(4)
Co(1)–Co(1A)i
Co(1)–Co(2)
Co(1)–Co(3)
Co(2)–O(4)
Co(2)–O(2)
Co(2)–O(1)
Co(2)–O(3)
Co(2)–N(7A)
Co(2)–O(5)
Co(2)–Co(3)
Co(2)–Co(2A)i
Co(3)–N(7)
Co(3)–Cl(3)
1.926(7)
1.933(7)
1.938(7)
1.932(7)
2.456(2)
2.667(2)
5.9575(19)
7.0505(19)
2.079(7)
2.079(6)
2.092(7)
2.103(7)
2.137(6)
2.144(6)
9.838(2)
12.877(3)
2.027(7)
2.237(3)
Co(3)–Cl(1)
Co(3)–Cl(2)
Co(3)–Co(3A)i
2.255(3)
2.267(3)
12.757(3)
172.2(3)
172.6(3)
175.45(9)
171.7(3)
172.3(3)
176.9(3)
110.6(2)
111.4(2)
112.56(15)
103.9(2)
110.07(15)
107.93(14)
Compound
Cell linea
G361
HOS
K562
MCF7
N(9A)–Co(1)–N(3A)i
N(3)–Co(1)–N(9)i
Cl(4)–Co(1)–Co(1A)i
O(2)–Co(2)–O(1)
O(4)–Co(2)–O(3)
N(7A)–Co(2)–O(5)
N(7)–Co(3)–Cl(3)
N(7)–Co(3)–Cl(1)
Cl(3)–Co(3)–Cl(1)
N(7)–Co(3)–Cl(2)
Cl(3)–Co(3)–Cl(2)
Cl(1)–Co(3)–Cl(2)
HL1
HL2
HL3
HL4
HL5
HL6
1
>50
>50
>50
>50
>50
>50
>50
>50
>50
>50
42
>50
>50
>50
>50
>50
>50
28
>50
27
22
>50
>50
>50
>50
>50
>50
>50
>50
>50
>50
>50
>50
>50
>50
>50
>50
>50
>50
>50
>50
>50
>50
>50
>50
>50
>50
2
3
4
5
10
7
>50
6
>50
>50
CoCl2 Æ 6H2O
a
G361 – human malignant melanoma, K562 – human chronic myelog-
enous erythroleukemia, HOS – human osteogenic sarcoma, MCF7 –
human breast adenocarcinoma.
Symmetry transformations used to generate equivalent atoms: (i) ꢀx + 1,
ꢀy + 1, ꢀz + 2.
these values are comparable and even better than those ob-
tained for Roscovitine (CYC202) (20 lM) [7], a cytokinin-
derived compound, currently undergoing Phase IIb clinical
trials for lung cancer and cancer from a group of B-cell
hematological malignancies [49]. The obtained IC50 values
in the case of all complexes, except for 2, in connection
with the HOS cell line show that higher cytotoxicity of
the Co(II) complexes as compared to free cytokinins is
probably caused by the complex formation.
tively, and it appears as a terminal ligand. Each of the
Co(2) and Co(2A) atoms are coordinated by five oxygen
atoms of DMSO and the N7 atom of the purine moiety.
Coordination spheres of Co(3) and Co(3A) are formed
by three chlorine atoms and the N7 atom originating from
6-(4-fluorobenzylamino)purine. Selected bond lengths and
angles are given in Table 7. It is evident, that the octahedral
surrounding of Co(1) atom is slightly deformed as can be
obvious from angle values in the vicinity of the central
atom, i.e., N(9A)–Co(1)–N(3A), N(3)–Co(1)–N(9) and
Cl(4)–Co(1)–Co(1A), which were found to be 172.2(3)ꢁ,
172.6(3)ꢁ and 175.45(9)ꢁ, respectively. As for the
Co(2) atom, the O(2)–Co(2)–O(1), O(4)–Co(2)–O(3) and
N(7A)–Co(2)–O(5) bond angles are 171.7(3)ꢁ, 172.3(3)ꢁ
and 176.9(3)ꢁ, respectively. A tetrahedral surrounding of
the Co(3) atom is slightly deformed which can be seen from
the bond angle values N(7)–Co(3)–Cl(3) [110.6(2)ꢁ], N(7)–
Co(3)–Cl(1) [111.4(2)ꢁ], Cl(3)–Co(3)–Cl(1) [112.56(15)ꢁ],
N(7)–Co(3)–Cl(2) [103.9(2)ꢁ], Cl(3)–Co(3)–Cl(2) [110.07
(15)ꢁ] and Cl(1)–Co(3)–Cl(2) [107.93(14)ꢁ].
4. Supplementary material
Crystallographic data of the structural analysis have
been deposited with the Cambridge Crystallographic Data
Centre as supplementary publication numbers CCDC:
269650 {for [H2+L2](ClO4)2 Æ 2H2O} and 269651 {for 7}.
Copies of this information may be obtained free of charge
from The director, CCDC, 12 Union Road, Cambridge,
CB2 1EZ, UK (fax: +44 1223-336-033; e-mail: deposit
@ccdc.cam.ac.uk or http://www.ccdc.cam.ac.uk).
Acknowledgements
3.9. Testing for cytotoxicity
This financial support from The Ministry of Education,
Youth and Sports (MSM6198959218) and the Grant
Agency of the Czech Republic (203/04/1168) is acknowl-
The cytotoxicity of the prepared complexes as well as
the starting compounds, i.e., CoCl2 Æ 6H2O and ligands
HL1–HL6, was tested against malignant melanoma
(G361), chronic myelogenous erythroleukemia (K562),
osteogenic sarcoma (HOS) and breast adenocarcinoma
(MCF7) human cancer cell lines. As can be seen from Table
8, G361, K562 and MCF7 cell lines were insensitive to all
the assayed compounds in tested concentrations. HOS cell
line was insensitive to starting compounds and 2, whereas
complexes 1 and 3–6 showed increased cytotoxic activity
against this cell line. IC50 values of these compounds range
from 7 to 28 lM and are close to that for similar Co(II)
complexes we had described previously [8]. Moreover,
´
edged. The authors thank Dana Vychodilova and Eva Hir-
ˇ
´
ˇ
´ˇ
nerova for technical assistance and Dr. Zdenek Sindelar for
magnetochemical measurements.
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