The X-ray structure and spectroscopy of platinum(II) complexes with 1,2,4-triazolo[1,5-a]pyrimidines and dimethylsulfoxide

Article abstract of DOI:10.1016/S0020-1693(02)00771-5

Platinum(II) complexes with 1,2,4-triazolo[1,5-a]pyrimidines of general formula trans-[PtCl₂(dmso)(L)], where L=1,2,4-triazolo[1,5-a] pyrimidine (tp), 5,7-dimethyl-1,2,4-triazolo[1,5-a]pyrimidine (dmtp), 5,7-diphenyl-1,2,4-triazolo[1,5-a]pyrimidine (dptp), 5,7-ditertbutyl-1,2,4- triazolo[1,5-a]pyrimidine (dbtp) have been prepared by direct reaction between cis-[PtCl₂(dmso)₂] and respective 1,2,4-triazolo[1,5-a] pyrimidine in molar ratio M:L=1:1. All new platinum(II) compounds were characterized by ¹H, ¹³C, ¹⁵N, ¹⁹⁵Pt NMR and IR. Significant ¹⁵N NMR upfield shifts (75-87 ppm) were observed for N(3) atom indicating this nitrogen atom as a coordination site. Crystal structure of trans-[PtCl₂(dmso)(dmtp)] (2) has been determinated. The molecular structure indicates that Pt(II) ion has the square-planar geometry with N(3) bonded dmtp, S-bonded dimethylsulfoxide and two trans chloride anions.

Full text of DOI:10.1016/S0020-1693(02)00771-5

Inorganica Chimica Acta 333 (2002) 93Á99
/
www.elsevier.com/locate/ica
The X-ray structure and spectroscopy of platinum(II) complexes with
1,2,4-triazolo[1,5-a]pyrimidines and dimethylsulfoxide
Edward Sz lyk a, Iwona Lakomska a,*, Andrzej Surdykowski a, Tadeusz G lowiak b,
Leszek Pazderski a, Jerzy Sitkowski c, Lech Kozerski c
a Faculty of Chemistry, Nicholas Copernicus University, Gagarina 7, 87-100 Torun´, Poland
b Institute of Chemistry, University of Wroclaw, F. Joliot-Curie 14, 50-383 Wroc law, Poland
c Drug Institute, Chelmska 30/34, 00-725 Warsaw, Poland
Received 18 October 2001; accepted 14 January 2002
Abstract
Platinum(II) complexes with 1,2,4-triazolo[1,5-a]pyrimidines of general formula trans-[PtCl2(dmso)(L)], where Lꢀ1,2,4-
/
triazolo[1,5-a]pyrimidine (tp), 5,7-dimethyl-1,2,4-triazolo[1,5-a]pyrimidine (dmtp), 5,7-diphenyl-1,2,4-triazolo[1,5-a]pyrimidine
(dptp), 5,7-ditertbutyl-1,2,4-triazolo[1,5-a]pyrimidine (dbtp) have been prepared by direct reaction between cis-[PtCl2(dmso)2]
and respective 1,2,4-triazolo[1,5-a]pyrimidine in molar ratio M:Lꢀ
/
1:1. All new platinum(II) compounds were characterized by 1H,
87 ppm) were observed for N(3) atom indicating this nitrogen
13C, 15N, 195Pt NMR and IR. Significant 15N NMR upfield shifts (75Á
/
atom as a coordination site. Crystal structure of trans-[PtCl2(dmso)(dmtp)] (2) has been determinated. The molecular structure
indicates that Pt(II) ion has the square-planar geometry with N(3) bonded dmtp, S-bonded dimethylsulfoxide and two trans chloride
anions. # 2002 Elsevier Science B.V. All rights reserved.
Keywords: Pt(II) complexes; 1,2,4-triazolo[1,5-a]pyrimidine; NMR; Crystal structures; 15N NMR; IR
1. Introduction
complexes with 1,2,4-triazolo[1,5-a]pyrimidines can be
related to a metalÁligand interactions similar to one
/
The chemistry of heterocycles with a purine ring
skeleton is of wide interest [1]. Usually, such ligands
have multiple coordination sites, hence different vari-
eties of coordination modes are possible. This prompted
us to study 1,2,4-triazolo[1,5-a]pyrimidine, a ligand
whose skeleton differs from the purine ring system in
having a pyrimidine atom in a bridgehead position with
disappearance of the acidic H-proton of the five-
membered ring. The figure below (Fig. 1) compares
these two bicyclic systems. These triazolopyrimidines
have also influence on the behavior of other auxiliary
ligands, either by electronic or steric reasons, giving rise
observed in biological systems [3]. The 1,2,4-triazole
derived ligands show a remarkable resemblance to
imidazole, although some differences appear in the
coordination behavior of these ligands [4]. Studies on
the naturally-occurring bases (guanine, adenine) have
revealed that the purine prefers the imidazole N(9) atom
for coordination, however ligation via N(7) atom is also
observed [5]. In order to better elucidate the influence of
steric effects on the coordination sites, we have char-
acterized some metal complexes using 5,7-disubstituted-
1,2,4-triazolo[1,5-a]pyrimidines.
Reported studies of triazolopyrimidines complexes
with mono-, di- and multinuclear structures exhibited
the influence of the central ion, inorganic anions and
in some cases to compounds with interesting metalÁ
/
metal interaction [2]. In addition, the transition metal
heterocycle ligand on the complex geometry [6Á10].
/
However, platinum(II) complexes with triazolopyrimi-
dines have been studied to a much less extent. The
chemistry of platinum group metals and 1,2,4-tria-
zolo[1,5-a]pyrimidine ligands has been dominated by
* Corresponding author. Tel.: ꢁ48-56-611 4302; fax: ꢁ48-56-654
2477.
E-mail address: dziubek@cc.uni.torun.pl (I. L akomska).
0020-1693/02/$ - see front matter # 2002 Elsevier Science B.V. All rights reserved.
PII: S 0 0 2 0 - 1 6 9 3 ( 0 2 ) 0 0 7 7 1 - 5

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E. Sz lyk et al. / Inorganica Chimica Acta 333 (2002) 93Á99
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2.2. Instrumentation
IR spectra were measured with a PerkinÁ
/Elmer
Spectrum 2000 FT IR spectrometer, using KBr (400Á
/
4000 cmꢂ1) and polyethylene discs (100Á400 cmꢂ1). 1H,
/
13C, 15N, 195Pt NMR spectra were performed on a
Varian INOVA 500 spectrometer equipped with inverse
Nalorac Z gradient shielded probe. 15N NMR was
detected by 2D 1HÁ15
N gradient selected Heteronuclear
/
Fig. 1. IUPAC numbering of (a) 5,7-disubstituted-1,2,4-triazolo[1,5-
a]pyrimidine, where R-H, CH3, C6H5, C(CH3)3, and (b) adenine
molecule.
Multiple Quantum Correlation (HMQC) in the absolute
value mode. 195Pt NMR of Pt(II) species were measured
by 1D technique optimized for fast relaxing nuclei
(acquisition time 10 ms, relaxation delay 10 ms, flip
angle 208, spectral width 100 kHz). The solvent was d7-
dmf, the concentration of samples 0.05 M, the tempera-
ture 298 K. The reference standard was TMS for 1H and
13C; CH3NO2 for 15N and K2PtCl6 for 195Pt.
Pt(II) [6,11,12], Pd(II) [13,14] and Ru(III) [15] com-
pounds, because these complexes often show biological
activity. Some coordination compounds of Pt(II), Pd(II)
and Ru(III) were described: cis-[Pt(II)(HmtpO)2-
C, H, N were determined by semimicroanalysis
whereas platinum was determinated by spectrophoto-
(NH3)2](NO3)2×
/
2H2O,
[Pt(II)(dmtp)4][Pt(IV)(SCN)6],
CH3OH, mer-[Ru(III)(dmtp)2-
H2O and mer-[Ru(III)(2-amino-dmtp)2-
trans-[Pd(II)(dmtp)2Br2]×
/
metric method on Specord M40 Carl Zeiss Jena (lꢀ400
/
Cl3(H2O)]×
/
nm).
Cl3(H2O)]×
/
H2O [6,11,13,15,16], but the high antitumor
activity was exhibited only for cis-[Pt(II)(HmtpO-
N3)2Cl2]×
2H2O [12]. The intention of our research is to
2.3. Syntheses
/
find new platinum(II) compounds which show similar
activity to cisplatin and carboplatin, but have an
additional functional group where they may be linked
to carrier substances. For our study, we choose triazo-
lopyrimidines, which have a similar structure to purine
ring and dimethylsulfoxide as labilizing ligand. It is a
first report of mixed Pt(II) complexes with 1,2,4-
triazolo[1,5-a]pyrimidines and dimethylsulfoxide. In
this paper we study four platinum(II) complexes with
unsubstituted tp and its 5,7-substituted derivatives
(dmtp, dptp, dbtp): trans-[PtCl2(dmso)(tp)] (1), trans-
[PtCl2(dmso)(dmtp)] (2), trans-[PtCl2(dmso)(dptp)] (3)
and trans-[PtCl2(dmso)(dbtp)] (4).
The compound cis-[PtCl2(dmso)2] was prepared by
the known method [19].
The new platinum(II) complexes were prepared by
reaction of cis-[PtCl2(dmso)2] with 1,2,4-triazolo[1,5-a]-
pyrimidines (tp, dmtp, dptp) in molar ratio M:Lꢀ1:1 in
/
ethanol solution. The details of particular syntheses are
given below.
2.3.1. trans-[PtCl2(dmso)(tp)] (1)
A suspension of cis-[PtCl2(dmso)2] (0.201g; 0.5 mmol)
in 20 ml of ethanol was treated with the stoichiometric
amount of tp (0.060 g; 0.5 mmol) in 10 ml of the same
solution and the reaction mixture stirred at room
temperature (r.t.) for 1 h. The yellow precipitate was
filtered, washed with ethanol, acetone, diethyl ether and
dried in vacuum over P2O5. Yield 0.197 g (85%). Anal.
Found: C, 18.0; H, 2.2; N, 12.1, Pt 39.8%. Calc. for
C7H10Cl2N4OSPt: C, 18.1; H, 2.2; N, 12.1; Pt, 42.0%.
2. Experimental
2.1. Materials
The melting point (m.p.) of the complexes is ꢀ250 8C
/
Dipotassium
tetrachloroplatinum(II),
1,2,4-tria-
(dec.).
zolo[1,5-a]pyrimidine and dimethylsulfoxide, 3-amino-
1,2,4-triazole (98%), 2,4-pentanedione (99%) and 1,3-
diphenyl-1,3-propanedione (99%), 2,2,6,6-tetramethyl-
3,5-heptanedione (98%), were purchased from Aldrich,
whereas the inorganic salts of analytical grade from
POCh Gliwice (Poland).
5,7-Disubsituted derivatives of 1,2,4-triazolo[1,5-a]-
pyrimidines were prepared according to the Bulow and
¨
Haas method [17] by the reaction of 3-amino-1,2,4-
triazole with 2,4-pentanedione for dmtp, 1,3-diphenyl-
1,3-propanedione for dptp and 2,2,6,6-tetramethyl-3,5-
heptanedione for dbtp [18].
2.3.2. trans-[PtCl2(dmso)(dmtp)] (2)
A suspension of cis-[PtCl2(dmso)2] (0.201g; 0.5 mmol)
in 20 ml of ethanol was treated with the stoichiometric
amount of dmtp (0.070 g; 0.5 mmol) in 10 ml of the
same solution. The reaction mixture was stirred at r.t.
for 30 min. The yellow precipitate was filtered, washed
with ethanol, acetone, diethyl ether and dried in vacuum
over P2O5. Yield 0.196 g (80%). Anal. Found: C, 22.4;
H, 2.9; N, 11.4; Pt, 39.4%. Calc. for C9H14Cl2N4OSPt:
C, 22.0; H, 2.9; N, 11.4; Pt, 39.6%. The m.p. of the
complex is ꢀ250 8C (dec.).
/

E. Sz lyk et al. / Inorganica Chimica Acta 333 (2002) 93Á
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95
Table 1
Crystallographic date for complex 2
2.3.3. trans-[PtCl2(dmso)(dptp)] (3)
A suspension of cis-[PtCl2(dmso)2] (0.102 g; 0.2
mmol) in 20 ml of ethanol was treated with the
stoichiometric amount of dptp (0.048 g; 0.2 mmol) in
the ethanol. The reaction mixture was heated by stirring
at 50 8C, for 2 h. The yellow precipitate was filtered
directly from hot solution, washed with boiling ethanol
and then dried in vacuum over P2O5. Yield 0.111 g
(75%). Anal. Found: C, 36.8; H, 3.0; N, 8.8; Pt 31.5%.
Calc. for C19H18Cl2N4OSPt: C, 37.0; H, 2.9; N, 9.1; Pt
Empirical formula
M
C9H14Cl2N4OPtS
492.29
Crystal system
Temperature
Space group
orthorhombic
100(1) K
Pbca
˚
a (A)
10.542(2)
12.661(3)
21.334(4)
2847.5(10)
8
˚
b (A)
˚
c (A)
3
V (A )
˚
Z
31.6%. The m.p. of the complexes is ꢀ
/
250 8C (dec.).
Density (calculated) (mg mꢂ3
)
2.297
10.370
m (mmꢂ1
F(000)
Crystal size (mm)
)
2.3.4. trans-[PtCl2(dmso)(dbtp)] (4)
1856
0.10ꢃ0.10ꢃ0.15
A suspension of cis-[PtCl2(dmso)2] (0.201 g; 0.5
mmol) in 20 ml of ethanol was treated with the
stoichiometric amount of dbtp (0.116 g; 0.5 mmol) in
10 ml of the same solution. The reaction mixture was
stirred at r.t. for 2 h. The yellow precipitate was filtered,
washed with ethanol, acetone, diethyl ether and dried in
vacuum over P2O5 0.202 g (70%). Anal. Found: C, 31.2;
H, 4.7; N, 9.3; Pt, 33.5%. Calc. for C15H26Cl2N4OSPt:
C, 31.2; H, 4.6; N, 9.7; Pt, 33.8%. The m.p. of the
u Range for data collection (8)
Index ranges
3.2Á25.0
/
ꢂ125h 512, ꢂ155k 59,
ꢂ255l 525
14 031
Reflections collected
Reflections unique
Goodness-of-fit on F2
Data/parameters
2480 [Rintꢀ0.064]
1.173
2411/167
Final R1, wR2 indices
[I ꢀ2s(I)]
All data
0.051, 0.14
0.052, 0.14
4.02 and ꢂ2.91
complexes is ꢀ250 8C (dec.).
/
Largest difference peak and hole
ꢂ3
˚
(e A
)
2.4. Crystal structure determination of (2)
The crystals of 2 were obtained by slow crystallization
from ethanolÁ
were collected on a Kuma KM4 CCD diffractometer
with graphite-monochromated Mo Ka radiation, lꢀ
/
hexaneÁCH2Cl2 solution. The X-ray data
/
/
˚
0.71069 A using Á2u method. No absorption correction
/
was applied. Data reduction on analysis was carried out
with the Kuma Diffraction programs. The structure was
solved by direct methods (program SHELXS-97) [20] and
refined by the full-matrix least-squares method on all F2
data using the SHELXL-97 programs [21]. Non-hydrogen
atoms were refined with anisotropic-thermal para-
meters. Hydrogen atoms were included from geometry
of molecule. During refinement, they were rated as rigid
groups with fixed interatomic distances. The atomic
scattering factors were taken from International Tables
for Crystallography [22]. The crystal data of compound
2 are listed in Table 1.
Fig. 2. The ORTEP [23] drawing of the [PtCl2(dmso)(dmtp)] (2)
molecule.
best weighted plane of the ligating atoms are: Cl(1), ꢂ
/
0.0545(15); Cl(2), ꢂ0.0563(15); S, 0.0515(14); N(3),
/
˚
0.0593(16) and Pt, 0.0089(15) A. The dmtp ligand is
monodentately bonded via N(3). The relatively high
trans effect of the sulfur donor atom results in elonga-
˚
N(3) distance [2.048(5) A in (2)] which is
longer than the ones in cis-[PtCl2(dmtp)2] [2.020(3) and
tion of the Ptꢀ
/
3. Results and discussion
˚
2.024(3) A] [24]. In [Pt(dmtp)4][Pt(SCN)6] the Ptꢀ
distances have been even shorter [1.97(3) and 2.03(3) A]
but the data have been of low accuracy [6]. The Ptꢀ
/
N(3)
3.1. Discussion of the crystal structure
˚
/
S
The crystal structure of 2 consists of monomeric
[PtCl2(dmso)(dmtp)] units. The projection of the mole-
cule with the atomic numbering scheme is presented in
Fig. 2, whereas the relevant bond distances and bond
angles are listed in Table 2.
˚
distance of 2.221(2) A is similar to the reported for other
PtÁdmso complexes [25]. Sulfur atoms in dimethylsulf-
oxide are in an approximate tetrahedral environment
although the biggest deviation has been observed for the
/
Ptꢀ
/
Sꢀ
/
O (114.7(2)8) and Cꢀ
/
Sꢀ
/
C (100.1(3)8) angles.
Cl distances
The Pt atom has the square-planar geometry slightly
distorted towards tetrahedron. The deviations from the
Chloride ions are in trans position, the Ptꢀ
/

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E. Sz lyk et al. / Inorganica Chimica Acta 333 (2002) 93Á99
/
Table 2
model, which exhibits the one preferred site for co-
ordination to metal ion in biological system.
˚
Selected bond lengths (A) and angles (8) for 2
Bond lengths
3.2. NMR spectroscopy
PtꢀN(3)
PtꢀS
PtꢀCl(2)
PtꢀCl(1)
SꢀO(1)
SꢀC(11)
SꢀC(12)
N(1)ꢀC(2)
N(1)ꢀN(8)
2.048(5)
2.221(2)
2.295(2)
2.303(2)
1.470(5)
1.765(6)
1.780(8)
1.322(9)
1.379(8)
N(3)ꢀC(3A)
N(3)ꢀC(2)
N(4)ꢀC(3A)
N(4)ꢀC(5)
N(8)ꢀC(3A)
N(8)ꢀC(7)
C(5)ꢀC(6)
C(5)ꢀC(9)
C(6)ꢀC(7)
C(7)ꢀC(10)
1.339(8)
1.360(8)
1.332(8)
1.346(8)
1.352(8)
1.381(8)
1.417(10)
1.504(9)
1.373(10)
1.483(9)
The 1H, 13C and 15N NMR spectra of the ligands were
reported by many authors, however, the data concerned
CDCl3 or dmso-d6 solutions [18,34Á45]. During this
/
work we had to perform all the measurements in dmf-d7,
due to insolubility or decomposition of the complexes in
the former solvents. The assignment of the signals for
both ligands and complexes was based on heteronuclear
correlation methods (HETCOR), analogous to those
described by us in earlier reports [14,18,45]. In the case
of dptp complex, we have observed the two forms 3a
and 3b, differing in their NMR spectra, the former
existing shortly after dissolving the sample in d7-dmf
and the latter appearing after 24 h. Probably we
Bond angles
N(3)ꢀPtꢀS
N(3)ꢀPtꢀCl(2)
SꢀPtꢀCl(2)
N(3)ꢀPtꢀCl(1)
SꢀPtꢀCl(1)
Cl(2)ꢀPtꢀCl(1)
O(1)ꢀSꢀC(11)
O(1)ꢀSꢀC(12)
C(11)ꢀSꢀC(12)
C(2)ꢀN(1)ꢀN(8)
C(3A)ꢀN(3)ꢀC(2)
C(3A)ꢀN(4)ꢀC(5)
C(3A)ꢀN(8)ꢀN(1)
176.9(2)
89.2(2)
88.95(6)
C(3A)ꢀN(8)ꢀC(7)
N(1)ꢀN(8)ꢀC(7)
N(1)ꢀC(2)ꢀN(3)
122.7(6)
125.7(6)
115.0(6)
128.1(6)
124.3(6)
107.5(5)
122.4(6)
117.6(6)
119.9(6)
121.2(6)
114.1(6)
127.2(6)
118.7(6)
87.63(15) N(4)ꢀC(3A)ꢀN(3)
94.33(6)
175.46(5)
108.7(3)
109.1(4)
100.1(3)
101.4(5)
104.6(5)
115.3(5)
111.5(5)
N(4)ꢀC(3A)ꢀN(8)
N(3)ꢀC(3A)ꢀN(8)
N(4)ꢀC(5)ꢀC(6)
N(4)ꢀC(5)ꢀC(9)
C(6)ꢀC(5)ꢀC(9)
C(7)ꢀC(6)ꢀC(5)
C(6)ꢀC(7)ꢀN(8)
C(6)ꢀC(7)ꢀC(10)
N(8)ꢀC(7)ꢀC(10)
observed trans 0/cis isomerisation under the influence
of dmf alone. Isomerization catalyzed by pyridine and
another nucleophilic agent is a fairly common phenom-
enon and occurs either via pseudorotation of five-
coordination intermediate or through a consecutive
displacement of ligands [46,47].
1
The H and 13C NMR data of the studied complexes
are listed in Table 3.
˚
being 2.295(2) and 2.303(2) A as expected for this type
of compounds. The analysis of the dmtp ligand planar-
ity data indicates that the fused-ring system is essentially
planar. The nine atoms comprising the triazolopyrimi-
For 1Á4 the chemical shifts changes pattern is very
/
clear. The coordination of triazolopyrimidine molecules
by Pt(II) ions results in the downfield shift of H(2) and
H(6) resonances (0.3Á
N(3) coordination site, i.e. C(2) and C(3a) are shifted
upfield (1.5Á3.7 ppm) whereas the others, C(5), C(6) and
C(7)-downfield (2Á4.4 ppm). The shielding of the
/
0.9 ppm). The carbons adjacent to
˚
dine core have the rms deviation of 0.014 A from the
least-squares plane. This ring system is slightly bent
/
/
along the N(8)ꢀ
/
C(3a) bond as indicated by the inter-
carbon atoms, adjacent to the coordination site N(3),
as well as the deshielding of the other carbons and the
protons inside the heterocyclic ring was already de-
scribed by us for some Pd(II) chloride complexes with tp
planar angle of 2.0(3)8 between the planes calculated for
six atoms of the pyrimidine ring and five atoms of the
triazole moiety. The mean plane through the nine-
framework of the dmtp ligand makes the dihedral angle
with the mean basal coordination plane of 61.7(1)8. The
bond distances in the coordinated ligand are similar to
the ones found in solvated dmtp [26]. In contrast the
bond angles within the imidazole ring exhibit important
differences. They are larger at N(3) [104.6(5)8] and
smaller at C(2) [115.0(6)8] and C(3a) [107.5(5)8] as
compared with the neutral ligand, 102.2(3), 117.6(4)
and 109.5(3)8, respectively.
and its derivatives [14].
1
In the H NMR spectra of 1Á
/4, we also observe the
signal of CH3 groups of dmso molecules. Its d value,
3.50Á3.56 ppm, is typical for those sulfur-bonded
ligands [48]. In the case of 1 and 4 it appears as a
spin interaction has been
/
singlet and no 195Pt{1H} spinÁ
/
detected whereas for 2 and 3 the 195Pt{1H} coupling was
observed. A single CH3 resonance with 195Pt satellites
indicates the absence of the detectable ligand dissocia-
tion and retention of the S-bonded structure in this
Previous crystallographic studies carried out on
metalÁdmtp complexes have indicated that the N(3)
/
3
solvent. The calculated values of the JPtꢀH coupling
atom in the unidentate form is the most preferred
binding site. This coordination mode was found for
Pt(II) [6], Pd(II) [13,14], Cd(II) [27], Hg(II) [28], Co(II)
[28], Cu(II) [29], Ni(II) [30], Zn(II) [31], and Ru(III) [15]
complexes. The N(3), N(4) bridging bidentate coordina-
tion has been found only in a cluster [Cu4(dmtp)4-
constants, being 10.3 Hz for 2 and 9.9 Hz for 3 are lower
than for analogous coordination compounds with other
heterocycle ligands (thiazole [49] and quinoline [50]).
The 15N and 195Pt NMR data for the ligands and
complexes are collected in Table 4.
During this work, we have measured 15NÁ1
H HET-
/
Cl2][Cu2Cl4] [32] and in some dimeric Ag(I)Á
/
dmtp
compounds [33]. This proves that dmtp can be a good
COR spectra for all discussed ligands and new plati-
num(II) complexes, assigning all 15N resonances.

E. Sz lyk et al. / Inorganica Chimica Acta 333 (2002) 93Á
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97
Table 3
1H and 13C NMR chemical shifts (d) of platinum(II) complexes in dmf-d7 (coordination shifts in parentheses)
Compound
H(2)
H(6)
C(2)
C(3a)
C(5)
C(6)
C(7)
1
9.17 (ꢁ0.45)
9.00 (ꢁ0.41)
9.08 (ꢁ0.59)
9.17 (ꢁ0.68)
9.11 (ꢁ0.47)
7.79 (ꢁ0.32)
7.53 (ꢁ0.34)
8.48 (ꢁ0.87)
8.50 (ꢁ0.89)
7.54 (ꢁ0.27)
155.1 (ꢂ1.6)
153.7 (ꢂ2.2)
154.4 (ꢂ2.4)
155.0 (ꢂ1.8)
153.8 (ꢂ1.5)
152.5 (ꢂ3.5)
152.3 (ꢂ3.5)
153.5 (ꢂ3.6)
153.4 (ꢂ3.7)
152.8 (ꢂ3.7)
159.7 (ꢁ3.6)
169.5 (ꢁ4.1)
164.4 (ꢁ2.7)
164.7 (ꢁ3.3)
180.0 (ꢁ4.4)
114.7 (ꢁ3.1)
114.6 (ꢁ3.1)
110.3 (ꢁ2.8)
110.6 (ꢁ3.1)
108.2 (ꢁ3.6)
140.0 (ꢁ2.0)
150.2 (ꢁ2.2)
150.3 (ꢁ1.7)
150.4 (ꢁ1.8)
159.7 (ꢁ1.8)
2
3a
3b
4
Table 4
15N NMR and 195Pt chemical shifts (d) of platinum(II) complexes in d7-dmf (coordination shifts in parentheses)
a
Compound
N(1)
N(3)
N(4)
N(8)
Pt
1
ꢂ105.9 (ꢁ0.1)
ꢂ110.9 (ꢁ0.1)
ꢂ110.6 (ꢁ0.1)
ꢂ111.0 (ꢂ0.5)
ꢂ108.6 (ꢂ1.0)
ꢂ236.2 (ꢂ84.9)
ꢂ228.6 (ꢂ74.7)
ꢂ227.8 (ꢂ77.1)
ꢂ237.4 (ꢂ86.7)
ꢂ238.4 (ꢂ85.3)
ꢂ108.6 (ꢂ5.4)
ꢂ118.6 (ꢂ2.8)
ꢂ125.8 (ꢂ5.4)
ꢂ128.5 (ꢂ8.1)
ꢂ122.0 (ꢂ6.2)
ꢂ157.7 (ꢂ3.4)
ꢂ157.6 (ꢂ2.3)
ꢂ161.9 (ꢂ2.6)
ꢂ163.3 (ꢂ4.0)
ꢂ162.2 (ꢂ3.5)
ꢂ2953 (ꢁ523)
ꢂ3008 (ꢁ468)
ꢂ2954 (ꢁ522)
ꢂ3066 (ꢁ410)
ꢂ2955 (ꢁ521)
2
3a
3b
4
a
For 195Pt the value in parentheses is the shift related to starting material cis-[Pt(dmso)2Cl2] (dꢀꢂ3476 ppm).
In the case of 1Á
significantly N(3) signal, shifting it upfield 74.7Á
ppm. Such a diamagnetic shift unambiguously indicates
that the complexation occurs via N(3). The absolute
values of the coordination shifts are smaller than for
/
4 the Pt(II) coordination affects most
86.7
comparing to those found for [PtCl4]2ꢂ ions (ca. 110
Hz) [57], which can be explained, most likely, by the
quadrupolar interactions between 195Pt and 14N nuclei.
/
Pd(II) (78Á90 ppm) complexes [14]. The increased
/
3.3. Infrared studies
shielding of the Pt(II) coordinated nitrogen nucleus is,
most likely, the result of the decrease of the absolute
value of the paramagnetic term in its 15N NMR
shielding constant. Such a phenomenon was already
reported for several Pt(II) complexes with ammonia, the
Characteristic bands of the whole triazolopyrimidine
ring skeletal vibrations appeared at 1619 (1), 1633 (2),
1618 (3) and 1618 cmꢂ1 (4), whereas those of the
pyrimidine ring at 1565 (1), 1555 (2), 1555 (3), 1543
cmꢂ1 (4). In the spectra of free ligands the former band
was found at 1620 (tp), 1633 (dmtp), 1611 (dptp), 1615
cmꢂ1 (dbtp) and the latter one at 1553 (tp), 1550
(dmtp), 1539 (dptp), 1530 cmꢂ1 (dbtp) [45]. The two
most characteristic bands, assigned previously by us as
triazolopyrimidine ring skeletal vibration and pyrimi-
dine ring skeletal vibration are shifted not more than 13
cmꢂ1. Similar effect has already been observed for
different complexes with tp, dmtp or dptp, where the
N(3) coordination occurred. The strong absorption
coordination shifts varying from ꢂ
Single 195Pt resonance appeared in the range (ꢂ
to ꢂ
3066 ppm). Such values of 195Pt chemical shifts are
typical for Pt(II) complexes with N-donor heteroaro-
matic compounds [51Á55]. Spectra of the complexes
under discussion exhibit 195Pt resonances shifted down-
field 410Á523 ppm in relation to the starting platinum
/
70 to ꢂ
/
90 ppm.
/2953
/
/
/
complex, cis-[PtCl2(dmso)2]. Downfield coordination
shift can be explained by the charge shift from ligand
to the metal center caused by Ptꢀ/N bond formation.
bands at 1142Á
dmso, as expected for this typical soft coordination
center [48,49,58]. Far-IR spectroscopy of 1Á4 has
exhibited one new absorption band of high intensity in
a narrow range 338Á
347 cmꢂ1. Its position is similar to
/
1147 cmꢂ1 range indicate S-bonded
The majority of 5,7-disubsituted derivatives of 1,2,4-
triazolo[1,5-a]pyrimidines revealed downfield shift at
195Pt resonance in relation to their unsubstituted coun-
terpart. This feature is in favor of the smaller donor
strength of the unsubstituted heterocycles. Presented
complexes generally exhibit a higher downfield shift of
the platinum signals than that observed for complexes
with pyridine and non-bulky pyridines [56]. The 195Pt
/
/
that found for some chloride complexes of Pt(II) with
thiazole (347 cmꢂ1) [49], mercaptoimidazole [59] and
mercaptopyrimidine [59] derives, most likely, from a Ptꢀ
Cl stretching vibration. The IR spectra contain also the
bands at 289Á
282 cmꢂ1, those can be assigned to Ptꢀ
stretching modes [59,60].
/
signals of Pt(II) complexes 1Á
broad singlets, their half-line widths being approxi-
mately 200Á420 Hz. Such values are relatively high,
/4 have been detected as
/
/N
/

98
E. Sz lyk et al. / Inorganica Chimica Acta 333 (2002) 93Á99
/
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273 (1998) 259.
4. Conclusion
The present study describes a series of trans-dichloro
complexes of Pt(II) with dimethylsulfoxide and 1,2,4-
triazolo[1,5-a]pyrimidines. The platinum(II) complexa-
tion results in a large upfield shift of 15N NMR signals
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[19] J.H. Price, A.S. Williamson, R.S. Schramm, B.B. Wayland, Inorg.
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a]pyrimidines occurs via N(3). The observed coordina-
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these heterocycles and analogous to N(9) complexion
purines. The crystal structure of 2 indicates that Pt(II)
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dmtp, S-bonded dimethylsulfoxide and two trans chlo-
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