Transition metal complexes of N-1-tosylcytosine and N-1-mesylcytosine

Article abstract of DOI:10.1016/j.poly.2009.06.088

The syntheses as well as chemical and X-ray structural characterization of dichlorobis[1-(p-toluenesulfonyl)cytosine]copper(II) (2), its solvated pseudopolymorph containing two methanol molecules (3), dichlorobis[1-(p-toluenesulfonyl)cytosine]cadmium(II)

Full text of DOI:10.1016/j.poly.2009.06.088

Polyhedron 28 (2009) 3101–3109
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Transition metal complexes of N-1-tosylcytosine and N-1-mesylcytosine
a
b
b,
*
ˇ
´
Aleksandar Višnjevac , Nikola Biliškov , Biserka Zinic
a
ˇ
Division of Physical Chemistry, Ruder Boškovi´c Institute, Bijenicka 54, 10000 Zagreb, Croatia
Division of Organic Chemistry and Biochemistry, Ruder Boškovi´c Institute, Bijenicka 54, 10000 Zagreb, Croatia
b
ˇ
a r t i c l e i n f o
a b s t r a c t
Article history:
The syntheses as well as chemical and X-ray structural characterization of dichlorobis[1-(p-toluenesulfo-
nyl)cytosine]copper(II) (2), its solvated pseudopolymorph containing two methanol molecules (3),
dichlorobis[1-(p-toluenesulfonyl)cytosine]cadmium(II) (4), 1-methanesulfonylcytosine (6) and its copper
complex dichlorobis(1-methanesulfonylcytosine)copper(II) (7) are described. In addition, spectroscopic
studies of dichlorobis[1-(p-toluenesulfonyl)cytosine]cobalt(II) (5), as well as of dichlorobis(1-mesylcyto-
sine)cadmium(II) (8) are presented. Pseudopolymorphs 2 and 3, as well as their 1-mesylcytosine analog
7, reveal square-planar coordination spheres, almost ideal in the case of 2, but considerably distorted in
the case of 3 and 7. In all cases, the Cu(II) ion is coordinated by two endocyclic N3 atoms from two ligand
molecules and by two chlorine atoms. The analogous coordination sphere was found in complex 4, where
Cd(II) lies in the center of a slightly distorted tetrahedron formed by two endocyclic N3 atoms and by two
chlorine atoms.
Received 14 May 2009
Accepted 24 June 2009
Available online 3 August 2009
Keywords:
Transition metal complexes
N-1-Substituted cytosine
X-ray diffraction
IR spectroscopy
NMR spectroscopy
Ó 2009 Elsevier Ltd. All rights reserved.
1. Introduction
biological activity, these compounds are also a very good and sim-
ple model for investigating the coordination properties of N-1
The interaction of various metal ions with nucleobases as struc-
tural elements of nucleic acids is of considerable interest for a
number of reasons. Metal ions participate in nucleic acid–enzyme
interactions during replication and transcription [1] and their role
in inducing carcinogenesis and mutagenesis is very well
documented [2]. It is also well known that the affinity of some
transition metal ions to bind at a specific site of the nucleotide
molecule has a deeper impact on the conformation and overall
stability of the DNA molecule in solution [3]. It was found that
Cu(II), Hg(II) and Cd(II), due to their high affinity for coordination
to nitrogen sites of the nucleotide base, help break the hydrogen
bonds involved in nucleobase pairing and, consequently, disrupt
the structure of the double helix. On the other hand, ions like Co(II),
Zn(II) and Mg(II), which prefer to bind to phosphate groups, leave
the hydrogen bonding arrangements inside the DNA structure
intact and thus do not destabilize the DNA structure [4].
To study the latter phenomenon, in our current study we report
on the Cu(II), Cd(II) and Co(II) coordination to 1-(p-toluenesulfo-
nyl)cytosine (1) [1-tosylcytosine or TsC] and 1-methanesulfonylcy-
tosine (6) [1-mesylcytosine or MsC], two ligand compounds
belonging to the series of N-sulfonylpyrimidine derivatives which
reveal intriguing biological activity both in vitro and in vivo and
are the subject of our comprehensive studies [5]. Besides their
substituted pyrimidine nucleobases, as reported in our previous
paper [6] and herein. According to the above cited previous reports,
Cu(II) and Cd(II) readily formed complex compounds with our li-
gands, while the formation of Co(II), and Ni(II) complexes with
the same ligands was not easy or was impossible to achieve.
2. Experimental
2.1. General remarks
1H and 13C NMR spectra were recorded in DMSO-d6 and CD3CN
on Bruker AV 300 and 600 MHz spectrometers using CD3CN
(d = 1.94 ppm) or DMSO-d6 (d = 2.5 ppm) as internal standards. Ele-
mental analyses were done on a Perkin–Elmer 2400 Series II CHNS
analyzer. Infrared spectra were collected using an ABB Bomem
MB102 spectrometer. CsI pellets of all samples were prepared in
order to record spectra at room temperature as an average of 10
co-added scans with a nominal resolution of 4 cmÀ1. Temperature
dependent IR spectra and thermogravimetry data are in the Sup-
plementary material (general Figs. S1a and S1b). Positive ion mass
spectra were acquired using a Micromass Q-Tof2 hybrid quadru-
pole time-of-flight mass spectrometer, equipped with a Z-spray
interface, over a mass range of 100–2000 Da, with a scan time of
1.5 s and an interscan delay of 0.1 s in the continuum mode. NaCsI
was used as the external mass calibrant lock mass. Ionization was
achieved with a capillary voltage of 3.50 kV, a cone voltage of 30 V,
* Corresponding author. Tel.: +385 1 4561066; fax: +385 1 4680195.
ˇ
E-mail address: bzinic@irb.hr (B. Zinic
´).
0277-5387/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2009.06.088

3102
A. Višnjevac et al. / Polyhedron 28 (2009) 3101–3109
and with cone and desolvation gas flows of 5–10 and 500 L/h,
respectively (details and spectra Figs. S2–S12 in Supplementary
material).
Cl]+ (C33H33N9O9S3CuCl): calc. 893.0548, found: 893.0547
(0.1 ppm).
2.3.2. Cd(1-TsC-N3)2Cl2 (4)
2.2. Preparation of the ligands
Starting materials: solutions of 1-(p-toluenesulfonyl)cytosine
(1) (133 mg, 0.5 mmol) in methanol (23 mL), 2 M aqueous solution
of CdCl2 (0.125 mL, 0.25 mmol). The colorless solution was stirred
overnight and was then left to evaporate at room temperature. After
4 days, colorless prisms were obtained. One transparent colorless
crystal was picked for the X-ray diffraction study, and the remaining
crystals were filtered off and dried in vacuum to give 131 mg (77%)
of white powder 4: 1H NMR (DMSO-d6) d/ppm: 8.75 (brs, 1H, NH),
8.26 (brs, 1H, NH), 8.22 (d, 1H, J6,5 = 8.0 Hz, H-6), 7.88 (d, 2H,
Jb,c = 8.3 Hz, Ph-b), 7.48 (d, 2H, Jc,b = 8.1 Hz, Ph-c), 6.06 (d, 1H,
J5,6 = 8.0 Hz, H-5), 2.41 (s, 3H, CH3); 1H NMR (CD3CN) d/ppm: 8.19
(brd, 1H, H-6), 8.08 (brs, 1H, NH), 7.90 (brd, 2H, Ph-b), 7.43 (brd,
2H, Ph-c), 7.39 (brs, 1H, NH), 6.10 (brd, 1H, H-5), 2.45 (brs, 3H,
CH3); 13C NMR (DMSO-d6) d/ppm: 163.35 (s, C-4), 148.38 (s, C-2),
146.02 (s, Ph-d), 140.38 (d, C-6), 133.29 (s, Ph-a), 129.71 (d, Ph-c),
129.01 (d, Ph-b), 97.13 (d, C-5), 21.17 (q, CH3). ESI-HRMS (m/z):
[MÀTsCÀCl]+ (C11H11N3O3SCdCl): calc. 413.9243, found: 413.9225
(4.3 ppm); [MÀCl]+ (C22H22N6O6S2CdCl): calc. 678.9764, found:
678.9730 (5.0 ppm); [M+TsCÀCl]+ (C33H33N9O9S3CdCl): calc.
944.0286, found: 944.0291 (0.5 ppm).
A mixture of cytosine (1 mmol) and N,O-bis(trimethylsilyl)acet-
amide (BSA) (3 mmol) was heated under reflux in dry acetonitrile
(3.3 mL) for 1 h. The solution was cooled to 0 °C and sulfonyl chlo-
ride (1.2 mmol) was added. The reaction mixture was heated for
16 h at 80 °C, cooled and treated with a small amount of methanol.
The resulting solid was filtered off and recrystallized.
2.2.1. 1-(p-Toluenesulfonyl)cytosine (1)
Synthesis of ligand 1 was performed according to the procedure
reported by Kašnar-Šamprec et al. [7]. [1H NMR (DMSO-d6) d/ppm:
8.14 (d, 1H, J6,5 = 7.8 Hz, H-6), 7.95 (brd, 2H, NH2), 7.87 (d, 2H,
Jb,c = 8.1 Hz, Ph-b), 7.46 (d, 2H, Jc,b = 8.1 Hz, Ph-c), 5.98 (d, 1H,
J5,6 = 7.8 Hz, H-5), 2.42 (s, 3H, CH3); 13C NMR (DMSO-d6) d/ppm:
166.27 (s, C-4), 151.22 (s, C-2), 145.61 (s, Ph-d), 139.73 (d, C-6),
134.47 (s, Ph-a), 129.80 (d, Ph-c), 129.02 (d, Ph-b), 97.50 (d, C-5),
21.20 (q, CH3)]. Anal. Calc. for C11H11N3O3S (Mr = 265.30): C,
49.80; H, 4.18; N, 15.84. Found: C, 50.09; H, 4.02; N, 15.89%.
Additional data for 1-(p-toluenesulfonyl)cytosine (1): 1H NMR
(CD3CN) d/ppm: 8.13 (d, 1H, J6,5 = 7.9 Hz, H-6), 7.92 (brd, 2H,
Jb,c = 8.4 Hz, Ph-b), 7.46 (d, 2H, Jc,b = 8.0 Hz, Ph-c), 6.42 (brd 2H,
NH2), 5.98 (d, 1H, J5,6 = 7.8 Hz, H-5), 2.49 (s, 3H, CH3).
2.3.3. Co(1-TsC-N3)2Cl2 (5)
Starting materials: solutions of 1-(p-toluenesulfonyl)cytosine
(1) (130 mg, 0.5 mmol) in methanol (40 mL), CoCl2 Â 6H2O
(60 mg, 0.25 mmol) in methanol (4 mL). The resulting dark violet
solution was left to slowly evaporate at room temperature yielding
112 mg of blue powder 5: 1H NMR (DMSO-d6) d/ppm: 8.10 (d, 1H,
J6,5 = 8 Hz, H-6), 7.90 (brd, 2H, NH2), 7.84 (d, 2H, Jb,c = 8.4 Hz, Ph-
b), 7.44 (d, 2H, Jc,b = 8.4 Hz, Ph-c), 5.93 (d, 1H, J5,6 = 7.9 Hz, H-5),
2.40 (s, 3H, CH3); 1H NMR (CD3CN) d/ppm: 8.05 (brd, 1H, H-6),
7.85 (brd, 2H, Ph-b), 7.40 (brd, 2H, Ph-c), 6.33 (brs, 2H, NH2), 2.42
(brs, 3H, CH3). ESI-HRMS (m/z): [MÀCl]+ (C22H22N6O6S2CoCl): calc.
624.0063, found: 624.0041 (3.5 ppm); [M+TsCÀCl]+ (C33H33N9O9-
S3CoCl): calc. 889.0584, found: 889.0582 (0.2 ppm).
2.2.2. 1-Methanesulfonylcytosine (6)
1-Methanesulfonylcytosine (6) was prepared according to the
literature method [8]. [1H NMR (DMSO-d6) d/ppm: 8.21 (brs, 1H,
NH), 8.05 (brs, 1H, NH), 7.87 (d, 1H, J6,5 = 7.8 Hz, H-6), 5.96 (d,
1H, J5,6 = 7.9 Hz, H-5), 3.63 (s, 3H, CH3); 13C NMR (DMSO-d6) d/
ppm: 165.44 (s, C-4), 151.42 (s, C-2), 139.45 (d, C-6), 96.64 (d,
C-5), 41.13 (q, CH3)]. Anal. Calc. for C5H7N3O3S (Mr = 189.20): C,
31.74; H, 3.73; N, 22.21. Found: C, 31.92; H, 4.01; N, 22.02%.
2.3. Preparation of the complexes
To a water or methanol solution of MCl2 Â nH2O (1 equiv.), the
1-sulfonylcytosine ligand (2 equiv.) in methanol was added and
the reaction mixture was left stirring. The solid product obtained
by evaporation was filtered off, washed with methanol and dried.
2.3.4. Cu(1-MsC-N3)2Cl2 (7)
Starting materials: solutions of 1-methanesulfonylcytosine (6)
(113 mg, 0.6 mmol) in methanol (40 mL), CuCl2 Â 2H2O (51 mg,
0.3 mmol) in methanol (2 mL). The resulting turquoise solution
was left to slowly evaporate at room temperature in order to ob-
tain high quality single crystals. After 5 days, dark green prisms
were obtained, one of which was picked for X-ray diffraction mea-
surements, while the others were filtered off, yielding 137 mg
(89%) of dark green powder 7: 1H NMR (DMSO-d6) d/ppm: 7.97
(brs, 2H, NH2), 7.32 (brs, 1H, H-6), 3.67 (s, 3H, CH3); 13C NMR
(DMSO-d6) d/ppm: 136.06 (d, C-6), 39.01 (q, CH3). ESI-HRMS (m/
z): [MÀCl]+ (C10H14N6O6S2CuCl): calc. 475.9401, found: 475.9388
(2.7 ppm).
2.3.1. Cu(1-TsC-N3)2Cl2 (2)
Starting materials: solutions of 1-(p-toluenesulfonyl)cytosine
(1) (133 mg, 0.5 mmol) in methanol (23 mL), CuCl2 Â 2H2O
(43 mg, 0.25 mmol) in methanol (5 mL). The resulting dark green
solution was left to slowly evaporate at room temperature in order
to obtain high quality single crystals. After 7 days, two types of sin-
gle crystals were present in the crystallization vessel – deep blue
prisms (X-ray structure 2) and turquoise plates [methanol solvate
of 2, X-ray structure 3 (2 Â 2CH3OH)]. After selection of single
crystals suitable for X-ray diffraction experiments, the remaining
crystals were filtered off and dried in vacuum to remove the
methanol yielding 110 mg (66%) of the blue-green complex 2: 1H
NMR (DMSO-d6) d/ppm: 8.25 (brs, 1H, H-6), 7.89 (brs, 2.5H,
Ph-b + part of NH2), 7.42 (brs, 3.5H, Ph-c + part of NH2), 2.34 (brs,
3H, CH3); 1H NMR (CD3CN) d/ppm: 9.48 (brs, 1H), 8.71 (brs, 2H),
7.79 (brs, 2H), 2.59 (brs, 3H, CH3); 13C NMR (DMSO-d6) d/ppm:
143.22 (s, Ph-d), 132.13 (s, Ph-a), 127.58 (d, Ph-c), 126.75 (d,
Ph-b), 19.27 (q, CH3). Anal. Calc. for C22H22Cl2CuN6O6S2 Â 2H2O
(Mr = 701.06): C, 37.69; H, 3.74; N, 11.99. Found: C, 37.29; H,
4.10; N, 11.74%. ESI-HRMS (m/z): [MÀTsCÀCl]+ (C11H11N3O3SCuCl):
calc. 362.9506, found: 362.9494 (3.3 ppm); [MÀCl]+ (C22H22N6-
O6S2CuCl): calc. 628.0027, found: 627.9995 (5.1 ppm); [M+TsC –
2.3.5. Cd(1-MsC-N3)2Cl2 (8)
Starting materials: solutions of 1-methanesulfonylcytosine (6)
(113 mg, 0.6 mmol) in methanol (40 mL), 2 M aqueous solution
of CdCl2 (0.15 mL, 0.3 mmol). After 1 h, a white precipitate was
formed. It was filtered off and dried in vacuum to give 131 mg
(77%) of snow-white powder 8. The mother liquor was left to crys-
tallize, but the colorless prisms formed after four days turned out
to be single crystals of ligand 6. Complex 8: 1H NMR (DMSO-d6)
d/ppm: 7.92 (brs, 1H, NH), 7.89 (brs, 1H, NH), 7.84 (d, 1H,
J6,5 = 7.8 Hz, H-6), 5.90 (d, 1H, J5,6 = 7.8 Hz, H-5), 3.62 (s, 3H,
CH3); 13C NMR (DMSO-d6) d/ppm: 166.06 (s, C-4), 152.08 (s, C-2),
139.08 (d, C-6), 96.68 (d, C-5), 41.05 (q, CH3). ESI-HRMS (m/z):
[MÀClÀHCl]+ (C10H13N6O6S2Cd): calc. 490.9372, found: 490.9345

A. Višnjevac et al. / Polyhedron 28 (2009) 3101–3109
3103
(5.5 ppm); [MÀClÀHCl+TsC]+ (C15H20N9O9S3Cd): calc. 679.9580,
Two forms of copper complexes with the 1-tosylcytosine ligand
1 were isolated in the process of crystal growth from a diluted
methanolic solution: Cu(1-TsC-N3)2Cl2 (2) and its solvated pseud-
opolymorph Cu(1-TsC-N3)2Cl2 Â 2CH3OH (3), with suitable mono-
crystals for X-ray diffraction studies. Crystals suitable for X-ray
crystallography were also obtained in the reaction of copper(II)
chloride with 1-mesylcytosine 6, yielding the complex Cu(1-MsC-
N3)2Cl2 (7), and yielding the complex Cd(1-TsC-N3)2Cl2 (4) in the
reaction of cadmium(II) chloride with 1-tosylcytosine 1. On the
other hand, the IR and NMR studies suggested the existence of
the Co(II) complex with ligand 1 and the Cd(II) complex with li-
gand 2, for which we assume them to be the N3 coordinated spe-
cies Co(1-TsC-N3)2Cl2 (5) and Cd(1-MsC-N3)2Cl2 (8); their
molecular formulas were confirmed by HRMS spectrometry.
found: 679.9556 (3.5 ppm).
2.4. X-ray structural analysis
Crystal data, data collection and refinement parameters are
summarized in Table 1. Data collections were performed on an En-
raf Nonius CAD4 diffractometer using graphite monochromated Cu
Ka radiation (k = 1.54179 Å) (structures 2, 3 and 4) and on an Ox-
ford Diffraction Xcalibur Nova R diffractometer with a microfocus-
ing Cu tube (structures 6 and 7). The X-ray structure of ligand 1
was reported in our previous paper [6]. Data reduction and cell
refinement were carried out using the procedures incorporated
into the WINGX package [9] for structures 2, 3 and 4, while, CRYSALIS
software [10] was used for the structures 6 and 7. Intensities were
measured at room temperature. All structures were solved using
direct methods with SIR2002 [11] and refined using full matrix
least-squares refinement based on F2, with SHELX97 [12]. Molecular
illustrations were prepared with ORTEP-3 [13] and PLATON [14]. All
non-hydrogen atoms in the structures were refined anisotropically
and hydrogen atoms were included in their geometrically calcu-
lated positions (except for some hydrogen atoms included in
hydrogen bonding), and refined according to the riding model.
3.2. NMR Spectroscopy
In the 1H NMR spectrum (measured in DMSO-d6), complex
Cd(1-TsC-N3)2Cl2 (4) displays a slight downfield shift of the signals
for two sets of doublets in the aromatic region corresponding to
the H-6 and H-5 protons (d 8.22 and 6.06 ppm) and phenyl Ph-b
and Ph-c protons (d 7.88 and 7.48 ppm) relative to the free ligand
1. The H-6 (Dd 0.03 ppm), H-5 (Dd 0.06 ppm) and NH (Dd 0.28 and
0.16 ppm) signals in the Cd(1-MsC-N3)2Cl2 (8) complex are slightly
shifted to higher frequencies compared to those of the free cyto-
sine ligand 6, which is in accord with coordination via N3. These
very small changes are in agreement with other cytosine com-
plexes [15].
3. Results and discussion
3.1. Synthesis
NMR peak positions are particularly sensitive to the presence of
paramagnetic species and ‘‘diamagnetic” 1H NMR spectroscopy has
not been applied extensively to Cu(II) and Co(II) coordination com-
plexes because of their paramagnetism, which complicates the
spectra acquisition and interpretation. On the other hand, almost
all signals for complexes Cu(1-TsC-N3)2Cl2 (2), Co(1-TsC-N3)2Cl2
(5) and Cu(1-MsC-N3)2Cl2 (7) were registered in the ‘‘diamagnetic”
(in the range d = 0–14 ppm) part of the 1H NMR spectra, showing
broad resonances (doublets collapsed into broad singlets). The
The organic ligands were synthesized by procedures described
in the literature [7,8]. Condensation of silylated cytosine with
p-toluenesulfonyl chloride (TsCl) or methanesulfonyl chloride
(MsCl) gave the corresponding ligands 1-tosylcytosine, 1 (1-TsC),
and 1-mesylcytosine, 6 (1-MsC). The mononuclear complexes de-
scribed in this paper were prepared by the reaction of Cu(II), Cd(II)
and Co(II) chlorides with the corresponding ligands in a 1:2 molar
ratio of reactants in methanol and led to complexes of the M(L)2Cl2
type (Scheme 1).
Table 1
Crystallographic parameters for compounds 2, 3, 4, 6, and 7.
Compound
2
3
4
6
7
Formula
C22H22Cl2CuN6O6S2
665.02
blue plate
0.25 Â 0.11 Â 0.09
P21/c
11.909(2)
13.247(2)
8.7883(8)
90.00
100.44(2)
90.00
C22H22Cl2CuN6O6S2 Â 2CH3OH C22H22Cl2CdN6O6S2
C5H7N3O3S
189.2
colorless prism
0.20 Â 0.18 Â 0.15
P21/n
5.1275(3)
24.675(1)
6.3307(5)
90.00
106.32(1)
90.00
C10H14Cl2CuN6O6S2
512.8
green prism
0.12 Â 0.10 Â 0.10
P21/c
22.1814(3)
7.0616(1)
12.4291(2)
90.00
103.152(1)
90.00
Formula weight (g molÀ1
Crystal color and habit
)
727.08
713.88
turquoise plate
0.25 Â 0.15 Â 0.10
P21/n
colorless prism
0.25 Â 0.18 Â 0.15
P-1
Crystal dimensions (mm)
Space group
a (Å)
b (Å)
c (Å)
14.244(1)
14.096(1)
16.003(2)
90.00
104.75(1)
90.00
8.7910(3)
13.0760(5)
13.3430(4)
113.641(3)
97.747(3)
97.840(3)
1361.25(9)
2
a
(°)
b (°)
c
(°)
V (Å3)
1363.5(3)
2
4.803
3107.3(5)
4
768.68(9)
4
3.567
1895.78(5)
4
6.680
Z
l
(Cu K
a
) (mmÀ1
)
4.317
10.105
Absorption correction
h max (°)
W
76.59
-scan
W
76.18
-scan
W
76.39
-scan
multi-scan
75.88
multi-scan
76.24
hkl
0,15; À16,16; À11,10 À17,17; À17,0; À20,0
À10,11; À16,0; À15,16 À6,6; À29,30; À7,7 À27,26; À8,8; À15,15
Number of reflections collected
Number of reflections unique
Number of reflections observed [I > 2
Rint
5856
2865
6725
5958
4440
10 263
3881
6493
5702
1593
r
(I)] 2474
4430
5106
1534
3357
0.0417
0.0380
187
0.0357
0.0453
404
0.0194
0.0256
384
0.0162
0.0135
126
0.0232
0.0211
262
R
r
Parameters
R1 [I > 2
R1, all
wR2
r
(I)]
0.0421
0.0491
0.1134
1.095
0.0649
0.1058
0.1970
1.067
0.0415
0.0479
0.1168
1.025
0.0356
0.0364
0.1152
1.081
0.0354
0.0410
0.1023
1.081
Goodness-of-fit, S
qmax
,
qmin (e ÅÀ3
)
0.53, À0.77
0.88, À0.65
1.37, À1.77
0.27, À0.28
0.79, À0.55

3104
A. Višnjevac et al. / Polyhedron 28 (2009) 3101–3109
O
R
N
O
S
N
NH2
O
NH2
4
NH2
Cl
MCl2 x nH2O
3 eq BSA /CH3CN
2. 1.2 eq TsCl or MsCl
5
6
1.
N3
N
M
2
1
N
MeOH
or
MeOH/H2O
N
O
O
NH2
N
H
Cl
S
N
S
O
O
O
R
cytosine
2 R = a, M = Cu(II)
3 = 2 x 2CH3OH
4 R = a, M = Cd(II)
5 R = a, M = Co(II)
7 R = b, M = Cu(II)
8 R = b, M = Cd(II)
O
R
1 R = a
6 R = b
O
CH3
R =
b
R =
CH3
a
a
d
b
c
MsCl = methanesulfonyl chloride
BSA = N,O-bis(trimethylsilyl)acetamide, TsCl = p-toluenesulfonyl chloride,
Scheme 1.
signal of H-5, a proton of the cytosine moiety, which is not in the
nearest neighborhood to the coordination center, disappeared from
the range of ‘‘diamagnetic” spectra for complexes 2, 5 and 7 (Figs.
S13 and S14 Supplementary material).
The spectrum of complex Co(1-TsC-N3)2Cl2 (5) exhibits signals
of the free ligand 1 in DMSO-d6 solution (Figs. S13), indicating
low stability of the complex in polar coordinative solvent. How-
ever, the 1H NMR spectrum of 5 measured in CD3CN shows the dis-
appearance of the H-5 signal, as can be seen for the paramagnetic
Cu(II) complex 2; all other broad resonances are slightly shifted to
higher field compared to the spectrum of the free ligand 1 (Figs.
S14). Due to the lack of an X-ray structure for the Co(II) complex
5, we can only suggest that the binding probably takes place at
the N-3 atom of the cytosine moiety.
3.3. Infrared spectroscopy
The infrared spectra of the free ligands, 1-tosylcytosine 1 and
1-mesylcytosine 6, together with their complexes with copper,
cadmium and cobalt, are shown in Figs. 1 and 2, while the band
assignments are given in Table 2. Direct evidence of complexation
is the presence of absorption bands due to the metal–chlorine
stretching vibration in the spectral region below 500 cmÀ1. In the
region corresponding to m(NH) vibrations, the spectra of 1-tosylcy-
tosine 1 and 1-mesylcytosine 6 undergo prominent changes due to
complexation, both in the band positions and intensities.
3.4. The molecular and crystal structures of 1-tosylcytosine complexes
2, 3 and 4
The molecular structures of the Cu(II) complexes, pseud-
opolymorphs 2 and 3, as well as of the Cd(II) complex 4 are given
in Figs. 3–5, respectively. The geometries of the pyrimidine rings in
complexes 2, 3 and 4 are given in Table 3. As the Cu(II) ion in com-
plex 2 lies on an inversion center, and consequently the molecule
possesses Ci symmetry, the two cytosine rings have identical
geometries. This is, however, not the case of complexes 3 and 4.
Moreover, in the cytosine ring 1 (cy1) of complex 3, the values of
bond lengths N3–C4 and C4–N4 suggest an increase of the single
bond character of the former, and an increase of the double bond
character of the latter, compared to complexes 2 and 4 as well as
to the other cytosine ring (cy2) of the same complex (Table 3). They
Fig. 1. Infrared spectra of (a) 1-tosylcytosine 1, (b) Cu(1-TsC-N3)2Cl2 x 2CH3OH (3),
(c) Cd(1-TsC-N3)2Cl2 (4) and (d) Co(1-TsC-N3)2Cl2 (5).
are, in fact, in very good accord with the analogous average values
extracted from the current version of CSD [16] for a set of 14 struc-
tures containing the iminooxo form of N-1-substituted cytosine
[N3–C4, 1.359(5) Å; C4–N4, 1.300(4) Å]. This is due to charge delo-
calization over the bonds N3–C4 and C4–N4, caused by the copper
coordination. Search of the same version of the CSD has revealed

A. Višnjevac et al. / Polyhedron 28 (2009) 3101–3109
3105
Fig. 3. ORTEP drawing of 2. Thermal ellipsoids are scaled at the 50% probability level.
correspond to the analogous values in complexes 2 and 4, and also,
approximately, to the bond lengths revealed by the cytosine ring 2
(cy2) of complex 3.
In both copper complexes 2 and 3, the central ion forms a
square-planar coordination sphere, almost ideal in the case of 2,
and considerably distorted in the case of 3 (Table 4). On the other
hand, while the two coordinated pyrimidine rings are in a trans-
arrangement with respect to the central Cu(II) ion [N3–Cu1–N3i,
180(11)°, see Table 4] and are virtually coplanar (head-to-tail
oriented), they are mutually cis-oriented in complex 3 [N3–Cu1–
N23, 90.88(14)°, see Table 4], and their corresponding ls planes
Fig. 2. Infrared spectra of (a) 1-mesylcytosine 6, (b) Cu(1-MsC-N3)2Cl2 (7) and (c)
Cd(1-MsC-N3)2Cl2 (8).
291 structures containing the preferred amino-oxo form of N-1-
substituted cytosine. In this set, the average values for these bond
lengths are: N3–C4, 1.346(1) Å, and C4–N4, 1.323(1) Å, which
Table 2
Characteristic infrared bands (wavenumbers in cmÀ1) in the 4000–200 cmÀ1 range and with tentative band assignments.
1
3
4
5
6
7
8
Assignation
3621 wa
Adsorbed MeOH
Adsorbed water
m
(OH)
3608 mb
3441 s
3311 s
m(OH)
3372s
3355 s, b
3374 s
3325 m
3418 s
3418 s
3369 s, b
m
m
m
m
m
m
asym(NH)
(NH)
(NH)
(NH)
sym(NH)
(NH)
3358 m
3306 m
3188 w, sh
3155 s
3096 m
1729 m
1677 vs
1668 vs
1655 w, sh
1626 s
3381 sh
3300 w
3193 w, sh
3162 s
3318 w, b
3192 m
3102 s
3186 w, sh
3101 m
3217 m
3109 m
3186 m
3091 m
3200 m
3100 m
3110 m
1702 m, sh
1673 vs
1662 vs
1648 m, sh
1601 m
d(NH2)
1667 vs
1671 vs
1656 vs
1641 vs
1623 m, sh
1595 m
1506 s
1684 vs
1655 vs
1663 vs
1650 s, sh
1663 vs
1648 s, sh
m(C@O)
m(C@C),
m(ring),
1647 m, sh
1620 m, sh
1596 m
m(C@N), d(NH2)
m
(C@N), d(NH)
1596 m
1626 s
1629 vs
1511 s
d(NH)
d(NH)
1523 s
1490 s
1377 m
1354 s
1286 s
1186 m
1174 s
1139 m
765 m
554 s
1511 s
1512 s
1499 s
1371 s
1353 s
1287 s
1191 s
1175 vs
1137 w, sh
775 s
1509 s
1493 s
1366 m
1345 s
1293 s
1513 s
1496 m
1365 s
1344 s
1294 s
1180 m
1172 m
1145 m
775 s
m(ring),
m
(C–NH2), d(NH)
d(NH),
m(C–N), m(ring), d(CH)
1379 m, sh
1367 m
1293 s
1194 m
1173 s
1142 m
774 m
1380 m
1359 m
1281 s
1362 m
1350 s
1298 m
m
m
(SO2)
(SO2)
Cytosine breathing
mring
mring
1177 s
1137 w, sh
770 m
549 s
1171 s
1145 m
1171 m
1143 m
775 w, sh
520 s
q(NH2)
c(NH2)
s(NH2)
s(NH2)
557 s
543 s
554 vs
542 vs
520 s
523 s
509 s
542 s
538 s
387 m
387 m
311 m
389 m
227 m
d(CO) or d(CN)
(MCl)
302 m
249 m
227 w
m
vs: very strong; s: strong; m: medium; w: weak: stretching; : deformation;
c
: out-of-plane bending; s: torsion.
M: Cu(II) (complexes 3 and 7); Cd(II) (complexes 4 and 8); Co(II) (complex 5).
a
Thermogravimetry of 3 shows a continuous mass loss of 6.45%. This, together with the IR band position, shows that methanol is only weakly adsorbed to the crystal of 3
(Figs. S1a).
b
The thermogram of the complex 5 reveals a continuous mass loss of 2.66%, which corresponds to one water molecule per formula unit. This, together with the IR band
position, indicates that water is only weakly adsorbed to the crystal of 5 (Figs. S1b).

3106
A. Višnjevac et al. / Polyhedron 28 (2009) 3101–3109
Table 4
Geometry of the coordination spheres in complexes 2, 3, 4, and 7.
2
3
4
7
Bond (Å)
M–N3
M–N3i (N23)
M–Cl1
1.988(2)
1.988(2)
2.2547(7)
2.2547(7)
2.033(4)
2.030(3)
2.2349(14)
2.2216(15)
2.260(3)
2.278(3)
2.4490(10)
2.4707(9)
2.0176(19)
2.0333(19)
2.2173(8)
2.2267(8)
M–Cl1i (Cl2)
Angle (°)
N3–M–N3i (N23)
N3–M–Cl1
N3–M–Cl1i (Cl2)
N3i (N23)–M–Cl1
N3i (N23)–M–Cl1i (Cl2)
Cl1–M–Cl1i (Cl2)
180.00(11)
90.76(6)
89.24(6)
89.24(6)
90.76(6)
180.00(3)
90.88(14)
157.87(11)
91.04(11)
90.23(10)
156.70(11)
96.59(6)
129.66(11)
101.19(8)
108.37(8)
107.84(8)
98.95(8)
91.21(8)
91.12(6)
156.54(6)
161.08(7)
88.29(6)
96.90(4)
110.33(4)
Fig. 4. ORTEP drawing of 3. Thermal ellipsoids are scaled at the 40% probability level
Hydrogen bonds are given by dashed lines.
are not included in the model. They might however extend the
hydrogen bonding network in this structure.
Complex 4 is a neutral complex where the positive charge of the
central Cd(II) ion is compensated by two chlorine anions, forming
together with two endocyclic N3 atoms that belong to cytosine
rings of the two ligand molecules a slightly distorted tetrahedral
coordination sphere (Table 4 and Fig. 5). Its crystal structure is
characterized by a complex hydrogen bonded three-dimensional
molecular network. Two ligand molecules coordinated to the cen-
tral Cd(II) ion form different hydrogen bonds via their amino
groups, thus creating an asymmetric environment around the
Cd(II) cation (Table 5a). While cytosine 1 of complex 4 forms one
intramolecular H-bond via N4-H4A, and one intermolecular hydro-
gen bond with the chlorine from the neighboring molecule via
N4-H4B, cytosine 2 forms, besides these two hydrogen bonds, an
form an angle of 72.5(2)°. The crystal structure of 2 is characterized
by a complex three-dimensional hydrogen bonded molecular net-
work where each complex molecule is connected to two others
through amino-group protons forming hydrogen bonds towards
O2i and O3i of the neighboring molecule (Table 5a and Fig. 6).
The crystal packing is less complicated by far in the structure of
complex 3, where a single complex molecule is connected through
intermolecular hydrogen bonds to only two neighboring solvent
molecules, forming with them discrete hydrogen bonded units (Ta-
ble 5a and Fig. 4). The refinement of the OH group hydrogens of
both solvent molecules does not converge, and consequently they
Fig. 5. ORTEP drawing of 4. Thermal ellipsoids are scaled at the 50% probability level.
Table 3
Bond distances in the cytosine ring (Å).
Bond
2
3 (cy1)
3 (cy2)
4 (cy1)
4 (cy2)
6
7 (cy1)
7 (cy2)
N1–C2
C2–O2
C2–N3
N3–C4
C4–N4
C4–C5
C5–C6
C6–N1
1.409(3)
1.222(3)
1.360(3)
1.339(3)
1.320(4)
1.428(4)
1.333(4)
1.383(3)
1.400(6)
1.228(6)
1.351(6)
1.355(6)
1.299(7)
1.417(7)
1.316(8)
1.383(6)
1.410(6)
1.223(6)
1.349(6)
1.328(6)
1.310(7)
1.440(7)
1.323(8)
1.375(7)
1.412(4)
1.214(5)
1.362(5)
1.339(4)
1.319(5)
1.436(5)
1.335(6)
1.377(5)
1.403(5)
1.224(5)
1.360(5)
1.338(4)
1.320(5)
1.435(5)
1.329(6)
1.378(5)
1.433(2)
1.227(2)
1.341(2)
1.337(2)
1.317(2)
1.437(2)
1.323(2)
1.391(2)
1.394(3)
1.237(3)
1.344(3)
1.345(3)
1.310(4)
1.426(4)
1.318(4)
1.388(3)
1.404(3)
1.226(3)
1.349(3)
1.333(3)
1.313(4)
1.432(4)
1.327(4)
1.383(3)

A. Višnjevac et al. / Polyhedron 28 (2009) 3101–3109
3107
Table 5a
Hydrogen bonds in 1-tosylcytosine complexes 2, 3 and 4.
D–HÁ Á ÁA
d (D–H)/Å
d (HÁ Á ÁA)/Å
d (DÁ Á ÁA)/Å
\ (D–HÁ Á ÁA)/°
Symm. operation
Complex 2 [Cu(1-TsC-N3)2Cl2]
N4–H4AÁ Á ÁO3i
0.86(4)
0.72(4)
2.49(4)
2.41(4)
2.991(3)
3.086(3)
118(3)
157(4)
(i) Àx, 1/2 + y, 1/2 À z
(i) Àx, 1/2 + y, 1/2 À z
N4–H4BÁ Á ÁO2i
Complex 3 [Cu(1-TsC-N3)2Cl2 Â 2CH3OH]
N4–H4AÁ Á ÁO35i
N4–H4BÁ Á ÁO22
N24–H24AÁ Á ÁO2
N24–H24BÁ Á ÁO36ii
0.76(6)
2.21(6)
2.24(6)
2.30(10)
2.07(7)
2.951(9)
2.986(7)
3.031(7)
2.847(9)
166(6)
156(6)
153(9)
159(7)
(i) 1 À x, Ày, Àz
0.80(6)
0.79(10)
0.81(7)
(ii) 1 À x, Ày, 1 À z
Complex 4 [Cd(1-TsC-N3)2Cl2]
N4–H4AÁ Á ÁCl1
0.90(7)
0.90(6)
0.93(8)
0.93(8)
0.79(7)
2.36(7)
2.44(6)
2.61(8)
2.40(7)
2.51(6)
3.247(4)
3.296(4)
3.371(4)
3.141(5)
3.273(4)
168(5)
158(5)
139(6)
136(6)
164(5)
N4–H4BÁ Á ÁCl2i
(i) Àx,1 Ày, Àz
N24–H24AÁ Á ÁCl2
N24–H24AÁ Á ÁO21ii
N24–H24BÁ Á ÁCl2iii
(ii) À1 + x, y, z
(iii) Àx, 2 À y, Àz
Fig. 7. Hydrogen bonding in 6.
sphere. Four ligand atoms (N3, N23, Cl1 and Cl2) reveal strong
deviations from the ls plane calculated through them and the cen-
tral Cu(II) ion, with the average absolute value of 0.38(2) Å. The an-
gle between the planes defined by Cl1, Cu1 and Cl2 and by N3, Cu1
and N23 is 28.97(4)°. These values describe the coordination
sphere of complex 7 as a severely distorted square plane, rather
than as a severely distorted tetrahedron. Angles N3–Cu1–N23
and Cl1–Cu1–Cl2 [91.21(8)° and 96.26(4)°, see Table 4] further
support this conclusion and, moreover, suggest a cis-arrangement.
An obvious result is the angle of 73.56(6)° formed by the ls planes
of two pyrimidine rings, which are, hence, close to a mutual per-
pendicular arrangement, similarly as in complex 3, and unlike in
complex 2, where the two pyrimidine rings are coplanar and trans
oriented with respect to the central Cu(II) ion (vide supra). The
crystal structure of 7 is characterized by endless hydrogen bonded
molecular chains along the crystallographic b axis (Fig. 9). These
chains are formed by the N4–H4AÁ Á ÁO2i hydrogen bond (Table
5b). Through its remaining hydrogen, H4B, N4 forms an intramo-
lecular hydrogen bond, N4–H4BÁ Á ÁO22, symmetrical (with respect
to Cu(II)) with the hydrogen bond N24–H24BÁ Á ÁO2 (Fig. 8). Hence,
O2 acts as a double acceptor, taking part in one intramolecular and
one intermolecular hydrogen bond. Nevertheless, two exocyclic
nitrogen atoms from two cytosine rings, N4 and N24, reveal an
asymmetrical hydrogen bonding pattern. N4 forms an intermolec-
ular bond to O2i and an intramolecular one to O22 (vide supra),
while N24 forms an intramolecular hydrogen bond to O2, and an
Fig. 6. Crystal packing of 2.
additional hydrogen bond N24–H24AÁ Á ÁO21ii, thus creating a
bifurcated hydrogen bond via the H24A proton.
3.5. The molecular and crystal structures of 1-mesylcytosine 6 and its
Cu(II) complex 7
The hydrogen bonding pattern of ligand 6 is given in Fig. 7. The
molecular structure of this ligand reveals no unexpected features.
The geometry of the pyrimidine ring is typical of an N1-substituted
cytosine in the preferred aminooxo form [6]. The hydrogen bond-
ing pattern (Table 5b) reveals centrosymmetric dimers formed by
the H-bond N4–H4AÁ Á ÁN3i. These dimers are further connected
into endless chains via the N4–H4BÁ Á ÁO2ii hydrogen bond. The OR-
TEP drawing of complex 7 is given in Fig. 8 and its crystal packing
is displayed in Fig. 9. In complex 7, the Cu(II) ion resides in the cen-
ter of a rather unusual, severely distorted coordination sphere that
could be described as a transition state between a square planar
and a tetrahedral arrangement, and strongly resembles the coordi-
nation sphere of Cu(II) in complex 3. Relevant geometry parame-
ters are given in Table 4. Both of these complexes lack molecular
Ci symmetry, unlike complex 2 where the central Cu(II) ion lies
on an inversion center and reveals a square-planar coordination

3108
A. Višnjevac et al. / Polyhedron 28 (2009) 3101–3109
Table 5b
Hydrogen bonds in 1-mesylcytosine 6 and its Cu(II) complex 7.
D–HÁ Á ÁA
d (D–H)/Å
d (HÁ Á ÁA)/Å
d (DÁ Á ÁA)/Å
\ (D–HÁ Á ÁA)/°
Sym. operation
Ligand 6 (MsC)
N4–H4AÁ Á ÁN3i
0.90(2)
0.80(2)
2.04(2)
2.24(2)
2.938(2)
3.011(2)
175(2)
162(2)
(i) 1 À x, Ày, 2 À z
(ii) x À 1, y, z À 1
N4–H4BÁ Á ÁO2ii
Complex 7 [Cu(1-MsC-N3)2Cl2]
N4–H4AÁ Á ÁO2i
0.80(3)
0.76(2)
0.85(5)
0.81(4)
2.27(4)
2.23(5)
2.33(8)
2.23(7)
3.056(2)
2.950(3)
3.172(4)
2.998(6)
167(1)
157(1)
171(1)
159(1)
(i) x, À1 + y, z
N4–H4BÁ Á ÁO22
N24–H24AÁ Á ÁCl2ii
N24–H24BÁ Á ÁO2
(ii) x, 5/2 À y, À1/2 + z
Two forms of copper complexes with 1-tosylcytosine ligand 1
were isolated in the process of crystal growth from a diluted meth-
anolic solution: Cu(1-TsC-N3)2Cl2 (2) and its solvated pseud-
opolymorph Cu(1-TsC-N3)2Cl2 Â 2CH3OH (3). The X-ray structure
of the complex 3 revealed charge delocalization inside the cytosine
ring, prompted by metal coordination, which is the first step to-
wards tautomerization. This, to the best of our knowledge, has
not been observed previously with the copper complexes of N-1
substituted cytosine.
Acknowledgments
We appreciate the financial support of the Ministry of Science,
Education and Sports of the Republic of Croatia through Grant
Nos. 098-0982914-2935, 098-1191344-2943 and 098-0982904-
2927. We also thank Renata Kobetic´ and Dubravka Gembarovski
for HRMS, Ernest Sanders for TG measurements, and Krešimir Mol-
Fig. 8. ORTEP drawing of 7. Thermal ellipsoids are scaled at the 50% probability level.
ˇ
canov for X-ray data collection for compounds 6 and 7.
Appendix A. Supplementary data
CCDC 729010, 729011, 729012, 729013 and 729014 contains
the supplementary crystallographic data for 2, 3, 4, 6 and 7. These
data can be obtained free of charge via http://www.ccdc.cam.ac.uk/
conts/retrieving.html, or from the Cambridge Crystallographic
Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44)
1223-336-033; or 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.2009.06.088.
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