Synthesis and NMR characterization of the novel mixed-ligand Pt(II) complexes cis- and trans-Pt(Ypy)(pyrimidine)Cl2 and trans,trans-Cl2(Ypy)Pt(μ-pyrimidine)Pt(Ypy)Cl2 (Ypy = pyridine derivative)

Article abstract of DOI:10.1016/j.ica.2008.07.003

Mixed-ligand complexes of the type cis- and trans-Pt(Ypy)(pm)Cl₂ where Ypy = pyridine derivative and pm = pyrimidine were synthesized and characterized by IR spectroscopy and by multinuclear (¹⁹⁵Pt, ¹H and ¹³C) magnetic resonance spectroscopy. The cis compounds were prepared from the reaction of K[Pt(Ypy)Cl₃] with pyrimidine (1:1 proportion) in water, while most of the trans isomers were synthesized from the isomerization of the cis compounds. The cis isomers could not be isolated with the Ypy ligands containing two -CH₃ groups in ortho positions. When the aqueous reaction of K[Pt(Ypy)Cl₃] with pyrimidine was performed in a Pt:pm ratio = 2:1, the pyrimidine-bridged dinuclear species were formed. Only the most stable trans-trans isomers could be isolated pure. In IR spectroscopy, the cis monomers showed two ν(Pt-Cl) bands, while the trans monomers and dimers showed only one ν(Pt-Cl) band. The ¹⁹⁵Pt NMR signals of the cis monomers were found at slightly higher fields than those of the corresponding trans isomers. The δ(¹⁹⁵Pt) of the dimers were found close to those of the trans monomers. The NMR results were interpreted in relation to the solvent effect, which seems important in these complexes. The coupling constants J(¹⁹⁵Pt-¹H) and J(¹⁹⁵Pt-¹³C) are larger in the cis geometry. The crystal structures of the compounds cis-Pt(2,4-lut)(pm)Cl₂, trans-Pt(2,6-lut)(pm)Cl₂ and trans,trans-Cl₂(2,6-lut)Pt(μ-pm)Pt(Ypy)Cl₂ were studied by X-ray diffraction methods and the results have confirmed the configurations suggested by IR and NMR spectroscopies.

Full text of DOI:10.1016/j.ica.2008.07.003

Inorganica Chimica Acta 362 (2009) 1455–1466
Contents lists available at ScienceDirect
Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Synthesis and NMR characterization of the novel mixed-ligand
Pt(II) complexes cis- and trans-Pt(Ypy)(pyrimidine)Cl2 and
trans,trans-Cl2(Ypy)Pt(l-pyrimidine)Pt(Ypy)Cl2 (Ypy = pyridine derivative)
*
Fernande D. Rochon , Majd Fakhfakh
Chemistry Department, Université du Québec à Montréal, C. P. 8888, Succ. Centre-ville, Montréal, Canada H3C 3P8
a r t i c l e i n f o
a b s t r a c t
Article history:
Mixed-ligand complexes of the type cis- and trans-Pt(Ypy)(pm)Cl2 where Ypy = pyridine derivative and
pm = pyrimidine were synthesized and characterized by IR spectroscopy and by multinuclear (195Pt, 1H
and 13C) magnetic resonance spectroscopy. The cis compounds were prepared from the reaction of
K[Pt(Ypy)Cl3] with pyrimidine (1:1 proportion) in water, while most of the trans isomers were synthe-
sized from the isomerization of the cis compounds. The cis isomers could not be isolated with the Ypy
ligands containing two –CH3 groups in ortho positions. When the aqueous reaction of K[Pt(Ypy)Cl3] with
pyrimidine was performed in a Pt:pm ratio = 2:1, the pyrimidine-bridged dinuclear species were formed.
Only the most stable trans–trans isomers could be isolated pure. In IR spectroscopy, the cis monomers
Received 31 May 2008
Accepted 4 July 2008
Available online 11 July 2008
Keywords:
Platinum complexes
Pyridine
Pyrimidine
X-ray crystal structure
NMR
showed two m(Pt–Cl) bands, while the trans monomers and dimers showed only one m(Pt–Cl) band.
The 195Pt NMR signals of the cis monomers were found at slightly higher fields than those of the corre-
sponding trans isomers. The d(195Pt) of the dimers were found close to those of the trans monomers. The
NMR results were interpreted in relation to the solvent effect, which seems important in these com-
plexes. The coupling constants J(195Pt–1H) and J(195Pt–13C) are larger in the cis geometry. The crystal
structures of the compounds cis-Pt(2,4-lut)(pm)Cl2, trans-Pt(2,6-lut)(pm)Cl2 and trans,trans-Cl2(2,6-
IR
lut)Pt(l-pm)Pt(Ypy)Cl2 were studied by X-ray diffraction methods and the results have confirmed the
configurations suggested by IR and NMR spectroscopies.
Ó 2008 Elsevier B.V. All rights reserved.
1. Introduction
also indicate that dinuclear Pt(II) complexes might have a promis-
ing future in chemotherapy [7].
The antitumor activity of cisplatin (cis-Pt(NH3)2Cl2) has been
known for decades and the compound is still one of the most com-
monly used drug for cancer treatment, even though its side effects
are important. Its mechanism of action has been studied by several
authors. It is extremely complex and there are still many uncer-
tainties, although the antitumor properties are known to be related
to a reaction with the bases (particularly guanine) of cellular DNA.
A few good reviews have been published [1,2]. When the NH3 li-
gands of cisplatin are replaced by pyridine (py), the compound
cis-Pt(py)2Cl2 is not active, but the cytotoxicity of the trans isomer
is comparable to the one of cisplatin in Leukemia L1210 cells [3].
The mixed-ligand compound cis-Pt(2-picoline)(NH3)Cl2 is quite ac-
tive and it is in clinical trials [4,5]. The pyrazine-bridged dinuclear
Pyrimidine (pm) is a diazine like pyrazine and can form bridges
between two Pt atoms. A few pyrimidine-bridged-Pt(II) compounds
were reported, like K2[Cl3Pt(l-pm)PtCl3] and Cl2(R2SO)Pt(l-pm)Pt-
(R2SO)Cl2 [8]. Pyrimidine and its derivatives are interesting
molecules, since they play an important role in many biological pro-
cesses. The molecule contains some empty pꢀ orbitals, which could
accept electron density from a soft metal like Pt(II), but the nature of
the Pt–pyrimidine bond has not yet been studied in the literature.
However, only a few papers were published on platinum com-
pounds with non-substituted pyrimidine. Fazakerley and Koch [9]
synthesized and characterized cis-[Pt(NH3)2(pm)2](ClO4)2 by 13C
NMR spectroscopy while Rochon and coworkers [10] prepared cis-
and trans-Pt(pm)2X2 (X = Cl and Br) and determined the crystal
structures of the two trans isomers. Kaufmann et al. characterized
trans-Pt(PEt3)(pm)Cl2 by 31P and 1H NMR, although they were not
able to isolate the compound [11]. These authors also reported the
Pt(II) complex cis,cis-[Cl(NH3)2Pt(l-pz)Pt(NH3)2Cl]Cl2 was recently
found to possess good anticancer properties and seems to over-
come the cross-resistance of cisplatin [6]. The dinuclear compound
has the appropriate Pt–Pt distance and the flexibility to react with
a minimum of distorsion of the DNA molecule. A few other studies
pm-bridged compound trans,trans-Pt(PBu3)Cl2(
More recently, we have published the synthesis of cis- and trans-
Pt(R2SO)(pm)Cl2 [12], the dinuclear species K2[Cl3Pt( -pm)PtCl3]
and Cl2(R2SO)Pt( -pm)Pt(R2SO)Cl2 (cis–cis and trans–trans) [8] and
trans-Pt(R2SO)(pm)I2 [13,14].
l-pm)Pt(PBu3)Cl2.
l
l
* Corresponding author. Tel.: +1 514 987 3000/4896; fax: +1 514 987 4054.
E-mail address: rochon.fernande@uqam.ca (F.D. Rochon).
0020-1693/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2008.07.003

1456
F.D. Rochon, M. Fakhfakh / Inorganica Chimica Acta 362 (2009) 1455–1466
Table 1
We have now started a new study of mixed-ligand Pt(II) com-
Crystal data and experimental details
pounds containing a pyridine derivative (Ypy) and pyrimidine. Pyr-
idine and its derivatives also contain empty pꢀ orbitals, which are
1
2
3 ꢂ 2CHCl3
able to accept electron density from the metal, but p-bonding does
Compound
cis-Pt(2,4-
lut)(pm)Cl2
C11H13Cl2N3Pt
453.23
trans-Pt(2,6-
lut)(pm)Cl2
C11H13Cl2N3Pt
453.23
{PtCl2(2,6-
lut)}2(l-pm)
not seem to play an important role in the Pt–pyridine bond.
The Ypy ligands used in this work are unsubstituted pyridine,
different picolines, (pic), lutidines (lut) and collidines (col). The
influence of the methyl groups on Ypy was studied, especially
when the methyl substituents are in ortho positions, where steric
hindrance is quite important and is a major factor in the geometry
of the mixed-ligand compounds. We have developed methods to
synthesize cis- and trans-Pt(Ypy)(pm)Cl2. The formation of pm-
bridged dinuclear species was also studied. The new compounds
were characterized by IR and multinuclear magnetic resonance
spectroscopies. We have found that these techniques are usually
good methods to determine the geometry of the different isomeric
forms. A few compounds were also characterized by X-ray diffrac-
tion methods. The results of this study are reported below.
Chemical formula
Mw
Space group
a (Å)
b (Å)
C20H24Cl10N4Pt2
1065.11
C2/c
22.139(5)
7.6870(18)
21.372(5)
120.405(2)
3136.9(13)
4
2.255
9.781
54.00
17621
P21/n
P21/c
11.3334(7)
9.9095(6)
11.9392(7)
91.646(1)
1340.33(14)
4
2.246
10.848
52
14082
8.1614(9)
7.8291(9)
21.1282(8)
96.285(1)
1341.9(2)
4
2.243
10.835
52
3526
c (Å)
b (°)
Volume (Å3)
Z
qcalc. (g cmꢁ3
)
l
(mmꢁ1
)
2h Maximum (°)
Measured
reflections
Independent
reflections (Rint
2621 (0.022)
2774
3405 (0.024)
)
Observer reflections
R1 (I > 2 (I))
wR2 (all data)
2397
2647
3178
r
0.0168
0.0416
1.081
0.0414
0.1353
1.121
0.0179
0.0444
1.021
2. Experimental
S
K2[PtCl4] was obtained from Johnson Matthey Inc. and was puri-
fied by recrystallization in water before use. Pyrimidine and the pyr-
idine derivatives were obtained from Aldrich. CDCl3 was purchased
from CDN Isotopes, while CD2Cl2 was bought from Acros Organics.
The decomposition points were measured on a Fisher–Johns
instrument and were not corrected. The IR spectra were recorded
in the solid state (KBr pellets) on a FTIR Nicolet 4700 spectrometer
between 4000 and about 280 cmꢁ1. All the NMR spectra were mea-
sured in CDCl3 (except a few, which were measured in CD2Cl2) on a
Varian Gemini 300BB spectrometer operating at 300.07, 75.460
and 64.267 MHz for 1H, 13C and 195Pt, respectively. For 195Pt, the
external reference was K2[PtCl4] in D2O, adjusted at ꢁ1628 ppm
from K2[PtCl6] (d(Pt) = 0 ppm).
parentheses and the frequencies are in cmꢁ1. The pyrimidine and
m
(Pt–Cl) bands are shown in Tables 2 and 7. The chemical shifts
in 1H and 13C NMR are listed in the Supplementary material.
2.2.1. cis-Pt(Ypy)(pm)Cl2 (Ypy = py, 2-pic, 3-pic, 2,3-lut, 2,4-lut, 2,5-
lut, 3,4-lut, 3,5-lut and 2,3,5-col)
K[Pt(Ypy)Cl3] (0.1 mmol) is dissolved in 0.5 mL of a 0.1 M NaCl
solution and added dropwise (while stirring) to pyrimidine
(0.11 mmol) dissolved in 4 drops of water. The mixture is filtered
after 2 h and the residue is washed with water, dried, washed with
diethylether, dried in air and finally dried under vacuum in a des-
iccator. The compounds are light yellow.
2.1. Crystallographic studies
cis-Pt(py)(pm)Cl2: Yield = 42%, dec. 259–275 °C. IR m(C–H) aro-
matic 3104sh, 3093w, 3085w, 3070vw, 3041w, 3026w, 3002vw,
py (8a) 1606m, (19a) 1481w (19b) 1449w, (9a) 1242w, 1208w,
(15) 1147sh, (18a) 1073m, (12) 1057w, (1) 1019w, (10b) 776sh,
765 m, (4) 689sh, (16b) 462w, other bands 1220w, 982vw, 957vw.
cis-Pt(3-pic)(pm)Cl2: Yield = 70%, m.p. 127–140 °C, dec. 255–
The crystals cis-Pt(2,4-lut)(pm)Cl2 (1), trans-Pt(2,6-lut)(pm)Cl2
(2) and trans,trans-Pt(2,6-lut)Cl2(l-pm)Pt(2,6-lut)Cl2 (3) were
mounted on a glass fiber using Paratone N hydrocarbon oil. Mea-
surements were made at 200(2) K on a Bruker APEX II area detector
diffractometer, equipped with graphite monochromated MoK
(k = 0.71073 Å) radiation. Frames corresponding to an arbitrary
hemisphere of data were collected using scans of 0.5° counted
a
280 °C. IR
3037sh, 3009vw, 3-pic
das(CH3) 1449sh, ds(CH3) 1384m,
m
(C–H) aromatic 3109sh, 3095w, 3073m, 3061m,
as(CH3) 2959sh, 2948vw, s(CH3) 2927w,
(CH3) 1043w, (8a) 1607w, (8b)
m
m
x
q
for a total of 30 s per frame. The program used for retrieving the
cell parameters and data collection was APEX 2 [15]. The data were
integrated using the program SAINT [16]. The data were corrected
for Lorentz and polarization effects and a multiscan absorption cor-
rection was performed using the SADABS program [17]. The struc-
tures were solved and refined using SHELXS-97 and SHELXL-97
programs [18]. Crystal 2 was twinned with 20–80% proportions.
All non-H atoms were refined anisotropically and the H positions
were placed at idealized positions. Neutral atom scattering factors
were taken from the International Tables for X-ray Crystallography
[19]. All calculations and drawings were performed using the SHEL-
XTL package [20]. The final model was checked for missing symme-
try or voids in the crystal structure using the PLATON software [21].
The structures gave satisfactory checkcif reports. The crystal data
and the most important experimental details are shown in Table 1.
1582sh, (19a) 1481m, (13) 1247w, (9a) 1187w, (15) 378w, 370w,
(18a) 1073w, (12) 1034w, (18b) 1114m, (14) 1342w, (1) 1046w,
(17a) 996w, (5) 934w, (10b) 809m, 798m, (11) 501w, (6b) 670w,
(6a) 538vw, (16a) 427w, other bands 955vw, 919vw.
cis-Pt(2,3-lut)(pm)Cl2: Yield = 61% m.p. 146–152 °C, dec. 265–
270 °C. IR
3030tw, 3006tw, 2,3-lut
2905sh, das(CH3) 1450s, ds(CH3) 1387m,
m
(C–H) aromatic 3121tw, 3088w, 3069w, 3052w,
as(CH3) 2987tw, 2960w, s(CH3) 2915w,
(CH3) 979w, (8a)
m
m
q
1590vs, (8b) 1578sh, (19a) 1466vsF, (19b) 1437sh, (10b) 805vs,
796sh, (4) 718m, (11) 525w, 518sh, (10a) 447w, other bands
1366w, 1267sh, 1262w, 1245w, 1193vw, 1080m, 1069w, 1019sh,
988w, 935vw, 762vw, 614vw, 485vw, 371w.
cis-Pt(2,4-lut)(pm)Cl2: Yield = 83%, m.p. 146–150 °C, dec. 258–
260 °C. IR
3035w, 3007w, 2,4-lut
das(CH3) 1450m, ds(CH3) 1376w,
m
(C–H) aromatic 3118vw, 3096w, 3070w, 3057w,
as(CH3) 2984w, 2957w, s(CH3) 2919w,
(CH3) 1036m 995vw, (8a)
m
m
q
2.2. Synthesis of the complexes
1625s, 1618sh, (8b) 1579sh, (19a) 1492w, 1485w, (10b) 812m,
(4) 723w, (11) 545w, (10a) 459w, 449w, other bands 1359w,
1346sh, 1301w, 1272w, 1240vw, 1185vw, 1072w, 1036w,
974vw, 929w, 893w, 752vw, 572vw, 559vw, 374w, 314w.
cis-Pt(2,5-lut)(pm)Cl2: Yield = 59%, m.p. 143 °C, dec. 238–
The K[Pt(Ypy)Cl3] complexes were synthesized according to the
methods described in the literature [22,23].
In the following data, the IR assignments are based on several
papers in the literature [24], the vibration numbers are placed in
258 °C. IR
m(C–H) aromatic 3122vw, 3097w, 3087vw, 3064w,

F.D. Rochon, M. Fakhfakh / Inorganica Chimica Acta 362 (2009) 1455–1466
1457
Table 2
Tentative assignment of the pyrimidine vibration modes in cis- and trans-Pt(Ypy)(pm)Cl2
Mode
Free pm [24d]
py
3-pic
2,3-lut
2,4-lut
2,5-lut
3,4-lut
3,5-lut
2,3,5-col
2,6-lut
2,4,6-col
2,3,6-col
8b
8a
19b
19a
1576
1566
1476
1403
1589vs
1551m
1463w
1407vs
1592vs
1556m
1469m
1409vs
1590vs
1558m
1466vs
1408vs
1592vs
1557s
1467m
1404vs
1590vs
1553m
1461m
1404vs
1592sh
1557s
1469s
1593vs
1556m
1469m
1408vs
1590vs
1560s
1468s
1410vs
1593s
1559m
1592s
1558m
1593vs
1557m
1477s
1405vs
1408vs
1400m
1223w
1163m
1134vw
1406vs
1407vs
3
15
9a
1237
1161
1143
1227w
1174w
1131w
1225w
1174w
1133w
1228w
1175w
1138m
1132sh
1091w
1056m
1028m
823m
1223w
1174w
1126w
1220w
1172w
1128vw
12vs
1226w
1176w
1136vw
1231m
1177w
1137w
1226w
1176w
1221w
1175w
1132vw
1171m
1133vw
1128vw
1089m
1060m
1027m
812s
18b
12
1
1084
1064
991
1090vw
1057m
1027w
827w
820w
706sh
697s
1091vw
1060w
1029w
826sh
1089vw
1060m
1030m
832s
1086vw
1058w
1028m
819s
1092vw
1059w
1028w
819m
805w
707s
1094w
1061w
1031m
816m
1091vw
1060w
1030w
815m
1094w
1060w
1029w
818m
1058m
1031m
827m
10b
832
815m
699vs
4
721
702vs
701vs
704vs
701vs
704vs
700vs
701s
702s
699s
6a
6b
676
642
685sh
643m
685sh
643m
685sh
644m
684w
642m
684w
643m
684sh
643m
685sh
646m
682sh
644m
684w
644w
684w
643w
642w
m(Pt–Cl)
345m
334m
337s
331s
342s
335s
340s
330s
339s
344vs
336vs
336m
329m
331s
327s
340s
354m
341m
3051w, 3038w, 3012vw, 3000vw, 2,5-lut
2979vw, 2960vw, s(CH3) 2925tw, 2912sh, das(CH3) 1449sh,
ds(CH3) 1384m, (CH3) 1043w, 1012sh, 973w, (8a) 1616w, (8b)
m
as(CH3) 2985vw,
is stirred for 12 h and the mixture is then filtered. The yellow res-
idue is washed with water, dried, washed with diethylether, dried
in air and finally in a dessicator under vacuum.
m
q
1575w, (19a) 1499vs, (19b) 1429w, (10b) 832sh, (4) 720w, (11)
517sh, 510m, (10a) 458w, 446w, other bands 1366tw, 1357sh,
1349w, 1260vw, 1224sh, 1247w, 1142w, 1070w, 1034w, 983w,
916vw, 845w, 675vw, 372w.
trans-Pt(2,6-lut)(pm)Cl2: Yield = 54%, color change at 247 °C, dec.
292–300 °C. IR
m
(C–H) aromatic 3121vw, 3095w, 3082w, 3075w,
as(CH3) 2987w, 2956w,
s(CH3) 2923sh, 2914w, das(CH3) 1458sh, ds(CH3) 1375m, 1370m,
3061vw, 3050vw, 3037w, 3009vw, 2,6-lut
m
m
cis-Pt(3,4-lut)(pm)Cl2: Yield = 81%, m.p. 145–152 °C, dec. 262–
q(CH3) 1031m, (8a) 1611m, (8b) 1569w, (19a) 1473s, (19b)
270 °C. IR
3007vw, 3,4-lut
2905sh, das(CH3) 1453m, 1445m, ds(CH3) 1384m,
m
(C–H) aromatic 3115vw, 3088w, 3068w, 3050w,
as(CH3) 2978w, 2954w, 2946w, s(CH3) 2924w,
(CH3) 1045vw,
1425m, (10b) 798s, 784sh, (4) 730sh, other bands 1499vw,
1432sh, 1360w, 1271vw, 1249vw, 1177w, 1119w, 1077vw,
1043vw, 1005w, 997w, 968vw, 946vw, 909vw, 539w, 375w.
m
m
q
1020w, 1001sh. (8a) 1616m, (19a) 1492s, (19b) 1425sh, (10b)
833s, (4) 714m, (11) 551w, (10a) 431w, other bands 1363w,
1351sh, 1304sh, 1251w, 1207w, 1175sh, 1074w, 995vw, 966vw,
890w, 755vw, 620w, 530vw, 378w, 319sh.
trans-Pt(2,3,6-col)(pm)Cl2: Yield = 34%, dec. 238–148 °C. IR
H) aromatic 3118vw, 3098w, 3083vw, 3076sh, 3072w, 3035w,
3009vw, 2,3,6-col as(CH3) 2977w, 2955w, 2949sh, s(CH3)
2920w, das(CH3) 1444w, ds(CH3) 1388sh, 1377m, 1365w, (CH3)
m(C–
m
m
q
cis-Pt(3,5-lut)(pm)Cl2: Yield = 67%, color change at 247 °C, dec.
1029w, 994w, (8a) 1604m, (19a) 1472s, (19b) 1428w, (10b)
843w, 835w (4) 729vw, other bands 2860w, 1255vw, 1185sh,
1158w, 1152w, 1078vw, 1060w, 997vw, 994vw, 935vw, 787sh,
562w, 504w, 499w, 373vw, 319w.
270–295 °C. IR
3046sh, 3036sh, 3010vw, 3,5-lut
2949vw, s(CH3) 2919w, das(CH3) 1445sh, ds(CH3) 1385w,
m
(C–H) aromatic 3116vw, 3095sh, 3080w, 3069w,
as(CH3) 2991vw, 2977vw,
(CH3)
m
m
q
1047w, (8b) 1579sh, (19b) 1435sh, (10b) 867m, (11) 509sh,
499w, (10a) 451vw, 431vw, other bands 1378sh, 13634vw,
1282vw, 1254w, 1156w, 1078vw, 985vw, 942vw, 380vw.
cis-Pt(2,3,5-col)(pm)Cl2: Yield = 16%; color change 167 °C, dec.
trans-Pt(2,4,6-col)(pm)Cl2: Yield = 10%, m.p. 103–135 °C, dec. 233–
240 °C. IR
3051w, 3036w, 3007tw, 2,4,6-col
2917w, ds(CH3) 1375m, (CH3) 1030w, (8a) 1627s, (19a) 1466s,
m(C–H) aromatic 3119tw, 3102w, 3095w, 3085w, 3070w,
m
as(CH3) 2981w, 2959w, s(CH3)
m
q
265–275 °C. IR
2,3-lut as(CH3) 2976vw, 2953w,
ds(CH3) 1388w, (CH3) 1031m, 1006w, (8a) 1613w, (8b) 1576w,
m
(C–H) aromatic 3097m, 3074m, 3035w, 3010w,
(19b) 1428m, (10b) 855m, (4) 726w, other bands 2851w, 1246sh,
1152w, 1114vw, 895vw, 668vw, 548vw, 502vw, 376vw, 324w.
m
ms(CH3) 2922w, das(CH3) 1459w,
q
(19a) 1477w, (10b) 881m, 871sh, (4) 716m, (11) 534w, other bands
1545w, 1437w, 1356m, 1255w, 1215w, 1151w, 951vw, 790w,
745vw, 557vw, 507w, 344sh.
2.2.4. Cl2(Ypy)Pt(l-pm)Pt(Ypy)Cl2 (Ypy = 2-pic, 3-pic, 2,3-lut, 2,4-lut,
2,5-lut, 3,4-lut, 2,3,5-col)
K[Pt(Ypy)Cl3] (0.11 mmol) is dissolved in 1 mL of a NaCl solu-
tion (0.1 M), while pyrimidine (0.05 mmol) is dissolved in 3 drops
in the same NaCl solution. The two solutions are stirred together
for 2 days. The precipitate is filtered and washed with water. The
product is then refluxed in dichloromethane for 25 to 35 days
and filtered to remove the decomposed product. The filtrate was
evaporated to dryness and the yellow residue washed with dieth-
ylether and dried under vacuum.
2.2.2. trans-Pt(Ypy)(pm)Cl2 (Ypy = py, 2-pic, 3-pic, 2,3-lut, 2,4-lut, 2,5-
lut, 3,4-lut, 3,5-lut and 2,3,5-col)
These complexes were prepared from the isomerization of the
cis analogues in chloroform at 40 °C. The reaction takes a few
weeks and the product always contains a small quantity of dimers
trans,trans-Cl2(Ypy)Pt(l-pz)Pt(Ypy)Cl2, Pt(Ypy)2Cl2 and Pt(pm)2Cl2.
Therefore the IR spectra of the complexes were not recorded. The
NMR signals of the impurities were removed from the data shown
in the Supplementary material.
Cl2(2-pic)Pt(
140 °C, dec. 205–245 °C.
Cl2(3-pic)Pt( -pm)Pt(3-pic)Cl2: Yield 57%, color change at
130 °C, dec. 230–255 °C. IR (C–H) aromatic 3002sh, 3-pic as(CH3)
2962w, 2951sh, s(CH3) 2928sh, 2923vw, das(CH3) 1455w, ds(CH3)
1376w, (8a) 1606w, (8b) 1580w, (19a) 1480w, (10b) 796s, 760sh,
other bands 1538w, 1505w, 1260m, 1092m, 1016m, 668w, 660w,
503w, 492w, 412sh, 398vs, 385sh, 376sh, 357w, 337w, 326w.
l-pm)Pt(2-pic)Cl2: Yield 80%, color change at
l
m
m
2.2.3. trans-Pt(Ypy)(pm)Cl2 (Ypy = 2,6-lut, 2,3,6-col and 2,4,6-col)
The salt K[Pt(Ypy)Cl3] (0.1 mmol) is dissolved in 0.5 mL of a
NaCl (0.1 M) solution and added dropwise to pyrimidine
(0.11 mmol) dissolved in 4 drops of the same solution. The mixture
m

1458
F.D. Rochon, M. Fakhfakh / Inorganica Chimica Acta 362 (2009) 1455–1466
Cl2(2,3-lut)Pt(
102–118 °C, dec. 196–215 °C. IR
3108vw, 3090w, 3081sh, 3075sh, 3072sh, 3037vw, 2,3-lut
2963w, s(CH3) 2917vw, das(CH3) 1454s, ds(CH3) 1374m, (8a)
1603s, (10b) 794s, (4) 717s, other bands 1366w, 1267sh, 1262w,
1245w, 1193w, 1080w, 1069w, 1028m, 1019sh, 988w, 935w,
762vw, 614w, 485w, 371w.
l
-pm)Pt(2,3-lut)Cl2: Yield = 80%, color change at
(C–H) aromatic 3118w,
as(CH3)
solved in dichloromethane and filtered. The filtrate is evaporated to
dryness and the yellow residue is washed with diethylether and
dried under vacuum. Yield = 24%, color change at 190 °C, dec.
m
m
m
230–255 °C. IR
2,3,6-col as(CH3) 2986w, 2955w,
ds(CH3) 1387m, 1377m, 1366sh,
m
(C–H) aromatic 3119w, 3087w, 3068sh, 3035vw,
s(CH3) 2920w, das(CH3) 1444w,
(CH3) 1027w, (8a) 1604vs, (8b)
m
m
q
1583sh, (19a) 1475vs, (19b) 1428m, (10b) 822m, other bands
2868w, 2851w, 1348w, 1323sh, 1226w, 1152w, 1138w, 1090w,
970w, 935w, 897vw, 704vw, 665w, 645vw, 563w, 493vw, 423w,
402w, 317w.
Cl2(2,4-lut)Pt(l-pm)Pt(2,4-lut)Cl2: Yield 62%, dec. 150–165 °C.
IR 2,4-lut as(CH3) 2993 sh 2979sh, 2963w,
m
m
s(CH3) 2928w,
2915w, das(CH3) 1456w, ds(CH3) 1377w, (8a) 1623w, (10b) 790s,
other bands 2905w, 2877w, 2869w, 2840w, 1717vw, 1653vw,
1540vw, 1508vw, 1358sh, 1260w, 1095m, 1018m, 862w, 751sh,
667vw, 658vw, 562w, 546w, 507w, 451w, 394vs.
3. Results and discussion
Cl2(2,5-lut)Pt(
IR 2,5-lut (C–H) aromatic 3127sh, 3124sh, 3119w, 3112sh, 3092w,
3081sh, 3077sh, 3073sh, 3048w, 3044w, 3039w, 2,5-lut as(CH3)
2975vw, 2972w, 2963vw, s(CH3) 2921w, das(CH3) 1457w, (8a)
1617w, (8b) 1575vw, (19a) 1500m, (19b) 1464w, (10b) 832s, other
bands 2869w, 2861w, 1538vw, 1533sh, 1344w, 1266vw, 1246vw,
1226vw, 1217sh, 1186vw, 1112vw, 1030vw, 733w, 642vw, 514w,
452w.
l-pm)Pt(2,5-lut)Cl2: Yield = 76%, dec. 245–255 °C.
3.1. Complexes Pt(Ypy)(pm)Cl2
m
m
3.1.1. Synthesis
m
The complexes cis-Pt(Ypy)(pm)Cl2 (Ypy = py, 2-pic, 3-pic, 2,3-
lut, 2,4-lut, 2,5-lut, 3,4-lut, 3,5-lut and 2,3,5-col) were synthesized
from the aqueous reaction of K[Pt(Ypy)Cl3] with pyrimidine (pro-
portion 1:1) in the presence of NaCl. The Pt(II) salt is added slowly
to the pyrimidine solution in order to always have an excess of
pyrimidine to prevent the formation of pyrimidine-bridged spe-
cies. The reaction is stopped after 2 h. In these conditions, only
the cis isomer is produced, since the trans effect of the chloro ligand
is larger than the one of the pyridine ligand.
Cl2(3,4-lut)Pt(
122–130 °C, dec. 198–212 °C. IR
3096vw, 3085vw, 3076vw, 3041vw, 3025vw, 3,4-lut
2991sh, 2962w, s(CH3) 2923w, das(CH3) 1450m, ds(CH3) 1388w,
l
-pm)Pt(3,4-lut)Cl2: Yield = 59%, color change at
(C–H) aromatic 3123vw,
as(CH3)
m
m
m
(8a) 1604w, (19a) 1495m, (10b) 834m, 817sh, other bands 2870w,
2851w, 1377w, 1304vw, 1201w, 1168w, 1137w, 1123sh, 1089vs,
1045sh, 1022vs, 909w, 864w, 749m, 664w, 400w, 387w, 314w.
K½PtðYpyÞCl3ꢃ þ pm N!aCl cis-PtðYpyÞðpmÞCl2 # þKCl
H2
O
Cl2(3,5-lut)Pt(
230 °C. IR (C–H) aromatic 3094vw, 3,5-lut
s(CH3) 2924w, das(CH3) 1456w, ds(CH3) 1384w, (8a) 1604w, (8b)
l-pm)Pt(3,5-lut)Cl2: Yield = 25%, dec. 210–
K[Pt(Ypy)Cl3] is not very stable in water without the presence of
NaCl. If the time of reaction is longer, trans isomers will be formed.
The yields vary between 42 and 83%, except for the 2,3,5-col com-
pound, which was isolated in lower yields. The subsequent charac-
terization of the products has shown pure compounds except
cis-Pt(2-pic)(pm)Cl2, which contained a small quantity of the trans
isomer. Attempts to isolate the 2-pic product at lower temperature
in order to reduce the isomerization have slowed down the reac-
tion, but mixtures of isomers were also obtained. The cis ? trans
isomerization is faster with 2-pic, because of the presence of a sub-
stituent in ortho position. If the time of reaction is increased, the
thermodynamically more stable trans compound is formed in larger
quantities.
The complexes trans-Pt(Ypy)(pz)Cl2 (Ypy = py, 2-pic, 3-pic, 2,3-
lut, 2,4-lut, 2,5-lut, 3,4-lut, 3,5-lut and 2,3,5-col) were prepared
from the isomerization of the corresponding cis compound in chlo-
roform at 40 °C. The reaction is very slow (few weeks) and the
products are always contaminated by the complexes trans-Pt
(Ypy)2Cl2 [25], a small quantity of trans-Pt(pm)2Cl2 [10] and the
m
mas(CH3) 2963m,
m
1575w, (19a) 1464w, (10b) 863m, other bands 2907w, 1569w,
1521vw, 1506vw, 1261s, 1156sh, 1093s, 1019s, 693m, 668m,
660m, 504vw, 394s, 349s. Cl2(2,3,5-col)Pt(l-pm)Pt(2,3,5-col)Cl2:
Yield = 11%, dec. 150–165 °C.
Cl2(2,3,5-col)Pt(l-pm)Pt(2,3,5-col)Cl2: Yield = 15%, dec. 150–
165 °C.
2.2.5. Cl2(Ypy)Pt(l-pm)Pt(Ypy)Cl2 (Ypy = 2,6-lut and 2,4,6-col)
Pyrimidine (0.05 mmol) dissolved in 3 drops of an NaCl 0.1 M
solution was added to K[Pt(Ypy)Cl3] (0.11 mmol) dissolved in
1 mL of the same solution. The mixture was stirred for five days.
The pale precipitate was then filtered, washed with water, dried,
washed with diethylether, dried in air and finally in a dessicator
under vacuum.
Cl2(2,6-lut)Pt(
120 °C, dec. 220–250 °C. IR
3081w, 3052vw, 3030vw, 2,6-lut
l
-pm)Pt(2,6-lut)Cl2: Yield = 70%, color change at
(C–H) aromatic 3113w, 3095w,
as(CH3) 2980w, 2954w, s(CH3),
m
m
m
dinuclear compound Cl2(Ypy)Pt(l-pm)Pt(Ypy)Cl2 (to be discussed
later in the text). All these neutral compounds have similar solubil-
ities and could not be separated.
2916w, (8a) 1610s, (8b) 1581w, (19a) 1474vs, (19b) 1427m, (10b)
782vs, other bands 2852w, 1567w, 1542vw, 1500vw, 1350w,
1253vw, 1186sh, 1137w, 1118vw, 1096w, 999w, 934w, 893vw,
738vw, 730w, 707vw, 501vw, 406w, 354m, 313w.
The complexes trans-Pt(Ypy)(pm)Cl2 (Ypy = 2,6-lut, 2,3,6-col et
2,4,6-col) were prepared pure by the reaction described above to
synthesize the cis isomers, but the time of reaction was longer
(ꢄ12 h). The cis isomer is first formed since the trans effect of the
chloro ligand is larger than the one of the pyridine derivative,
but it rapidly isomerizes to the trans isomer because of steric hin-
drance caused by the presence of two –CH3 groups in ortho
positions.
Cl2(2,4,6-col)Pt(
213 °C. IR (C–H) aromatic 3114vw, 3091w, 3045vw, 3025vw,
3003w, 2,4,6-col as(CH3) 2983w, 2955w, s(CH3) 2918w, ds(CH3)
1375m, (CH3) 1031w, (8a) 1627s, (8b) 1583sh, (19a) 1464s,
l-pm)Pt(2,4,6-col)Cl2: Yield = 33%, dec. 193–
m
m
m
q
(19b) 1428m, (10b) 852m, other bands 2850vw, 1507vw, 1226w,
1183w, 1173w, 1137w, 1085w, 1014w, 937vw, 897vw, 830w,
750m, 662w, 546w, 327m.
H2
O
K½PtðYpyÞCl3ꢃ þ pm ! cis-PtðYpyÞðpmÞCl2ðcannot be isolatedÞ
2.2.6. Cl2(2,3,6-col)Pt(l-pm)Pt(2,3,6-col)Cl2
ꢁKCl
Pirimidine (0.05 mmol) dissolved in 3 drops of an NaCl 0.1 M
solution is added very slowly to K[Pt(2,3,6-col)Cl3] (0.11 mmol) dis-
solved in 1 mL of the same solution. The mixture is stirred during 5
days. The precipitate is filtered out, washed with water, dried,
washed with diethylether and dried in air. The product is then dis-
! trans-PtðYpyÞðpmÞCl2
If the time of reaction is longer than 12 h, dinuclear species will be
formed. The yields are lower (ave. 33%) than those of the cis
isomers.

F.D. Rochon, M. Fakhfakh / Inorganica Chimica Acta 362 (2009) 1455–1466
1459
3.1.2. IR spectroscopy
signal of the cis compounds was found at higher field than the one
of the corresponding trans analogue. The average difference be-
The IR spectrum of free pyrimidine (C2v
) was published
[24a,24b,24c,24d]. There are 22 vibration modes (A1, B1 and B2)
which are active in IR spectroscopy, while the two other modes
(A2) are active in Raman only. Coordination of pyrimidine to a
metal reduces its symmetry to Cs and all the vibration modes are
now active in IR [26]. Four of these vibrations are mainly stretching
tween the two isomers (Ddtrans–cis) is 38 ppm. The complexes listed
in Table 3 were separated into 3 different groups depending on the
Ypy ligands. The complexes of group 1 contain pyridine derivatives
which do not have any substituent in ortho positions, while those of
group 3 contain Ypy with two –CH3 substituents in ortho positions.
In the group 2 compounds, the Ypy ligand has only one –CH3 substi-
m
(C–H) vibrations. There is no IR study in the literature on Pt–
pyrimidine complexes.
tuent in ortho position. The difference (
ger for group 2 compounds (41 ppm) than for group 1 (35 ppm). For
the complexes Pt(Ypy)2Cl2, the d value is about 52 ppm [25]. A
smaller difference for the mixed-ligand complexes Pt(Ypy)(pm)Cl2
might indicate the presence of a slightly stronger -bond between
Ddtrans–cis) seems slightly lar-
The IR spectra of only the pure compounds were recorded. A ten-
tative assignment of bonded pyrimidine is shown in Table 2. In the
D
1630–1400 cmꢁ1 region, the stretching
m
(C–C) and
(8a, 8b, 19a, 19b) coupled to deformation d(C–H) modes are strong
bands. There are several weak bands between 1250 and 1200 cmꢁ1
m(C–N) modes
p
,
pyrimidine and Pt(II) than between pyridine and Pt(II).
one was assigned to the 3 mode. The region 1200–900 cmꢁ1 con-
tains the deformation modes in the heterocyclic plane, where the
modes 9a, 15, 12, 18a and 1 were assigned. Mode 1 is the vibration
of the complete aromatic ring, while 10b is the umbrella mode (1 or
2 bands) and 4 is the intense out of plane vibration mode. The 6a and
6b modes are out of plane deformations.
There is no relation between the d(195Pt) and the pKa values [27]
of the protonated pyridine derivative. The most basic ligands are the
collidines, which should form stronger
r (ligand ? Pt) bonds and
the complexes should be observed at higher fields than the other
compounds. In fact, the compounds of group 3 are observed at lower
fields than the others. Therefore the electron density on the Pt atom
is lower in group 3 compounds than in the others. Unfortunately, we
cannot prepare cis complexes with pyridine derivatives containing
two –CH3 substituents in ortho position because of steric hindrance,
but we can compare the results obtained in the trans series. We ex-
plain these results by the solvent effect, as suggested in the com-
pounds K[Pt(Ypy)Cl3], which were studied in D2O [23]. Chloroform
is not as good as water as a coordinating solvent, but its influence
should not be neglected. The molecules of solvent normally ap-
proach the Pt(II) atom on both sides of the square plane, which in-
creases the electron density in the close environment of the metal
atom, resulting in a 195Pt chemical shift towards higher fields. When
one of the ligand is a pyridine derivative containing two –CH3 sub-
stituents in ortho position, the planar ligand will be perpendicular to
the Pt(II) plane, in order to reduce steric hindrance with the cis
neighbours. In this conformation, the two –CH3 substituents will
be above and below the coordination plane, directly above and be-
low the Pt atom, which will reduce the approach of the molecules of
solvent. The electron density on the metal atom will thus be re-
duced, which will cause the 195Pt signal to shift towards lower field,
as observed in our group 3 complexes.
It is interesting to note that the complexes containing Ypy with
–CH3 substituents in both positions 2 and 3 (2,3-lut, 2,3,5-col and
2,3,6-col) are observed at slightly lower field than the other com-
plexes of their respective group.
The symmetry of free pyrimidine is C2v. Its proton chemicals
shifts are: H2 9.226, H4 and H6 8.737 and H5 7.328 ppm in CDCl3.
This order can be explained by the different ionic resonance struc-
tures and by the inductive effect of the N atoms. H5 is a doublet of
triplet with 3J(Pt–H4,6) = 4.9 Hz and 5J(Pt–H2) = 1.59 Hz, H4,6 is a
doublet and H2 is a singlet. The presence of the two neighboring
N atoms with strong quadrupolar magnetic moments is probably
responsible for the absence of couplings on H2.
The Ypy bands are shown in the experimental section and the
assignments are based on several literature reports [24]. The defor-
mation modes das(CH3) were found around 1450 cmꢁ1, while the
ds(CH3) were observed at lower energies (1387–1365 cmꢁ1).
IR spectroscopy seems a good method to determine the geom-
etry of these compounds. Two stretching m(Pt–Cl) bands (A1 and
B1, C2v skeleton symmetry) are observed for the cis compounds be-
tween 327 and 345 cmꢁ1, while only one band (B3u, D2h skeleton
symmetry) was detected between 339 and 354 cmꢁ1 for the trans
isomers.
3.1.3. Multinuclear magnetic resonance spectroscopy
The 195Pt NMR spectra of all the compounds were measured in
CDCl3. There are only three 195Pt NMR papers in the literature on
Pt-pm compounds. These are on the complexes cis and trans-
Pt(R2SO)(pm)Cl2 [12], trans-Pt(R2SO)(pm)I2 [13], K2[Cl3Pt(
PtCl3] and Cl2(R2SO)Pt( -pm)Pt(R2SO)Cl2I2 [8]. The chemical shifts
l-pm)-
l
(d(195Pt)) of the compounds Pt(Ypy)(pm)Cl2 are shown in Table 3.
The cis compounds are pure (also confirmed by 1H and 13C NMR), ex-
cept cis-Pt(2-pic)(pm)Cl2. The trans compounds containing Ypy = 2,
6-lut, 2,3,6-col et 2,4,6-col are also pure, but those prepared from
the isomerization of the cis compounds contain other impurities
as discussed above. The assignments for the latter trans compounds
were made at the beginning of the isomerization process, when
there were only cis- and trans-Pt(Ypy)(pm)Cl2.
The d(195Pt) vary between ꢁ2026 and ꢁ2054 for the cis isomers
and between ꢁ1966 and ꢁ2014 ppm for the trans analogues. The
Table 3
d(195Pt) and
Ddtrans–cis (ppm) of Pt(Ypy)(pm)Cl2 and the pKa of protonated Ypy
Ypy
pKa [27]
cis
trans
Ddtrans–cis
The binding of pyrimidine to Pt(II) in a monodentate fashion re-
duces its symmetry to Cs and all the H atoms are different as shown
in Scheme 1. Therefore 4 different signals are observed in 1H NMR.
py
3-pic
3,4-lut
3,5-lut
Ave. gr. 1
5.22
5.63
6.46
6.15
ꢁ2041
ꢁ2040
ꢁ2042
ꢁ2041
ꢁ2041
ꢁ2008
ꢁ2005
ꢁ2005
ꢁ2007
ꢁ2006
33
35
37
34
35
2-pic
5.96
6.57
6.63
6.40
ꢁ2052
ꢁ2029
ꢁ2047
ꢁ2054
ꢁ2026
ꢁ2042
ꢁ2012
ꢁ1983
ꢁ2006
ꢁ2014
ꢁ1987
ꢁ2000
ꢁ1992
ꢁ1987
ꢁ1966
ꢁ1982
40
46
41
40
39
41
Pt
H6
N1 C6
2,3-lut
2,4-lut
2,5-lut
2,3,5-col
Ave. gr. 2
H2 C2
H5
C5
N3 C4
2,6-lut
6.72
7.48
7.40
2,4,6-col
2,3,6-col
Ave. gr. 3
H4
Scheme 1.

1460
F.D. Rochon, M. Fakhfakh / Inorganica Chimica Acta 362 (2009) 1455–1466
In the complexes Pt(Ypy)(pm)Cl2, the signal of H2 is a doublet of
the cis compounds are the first example where the order of the
doublets with 5J(1H2–1H5) and 4J(1H2–1H6) are ꢄ1.2 Hz. It is not
always seen because of the presence of the two neighbouring N
atoms. It does not couple with H4, probably because of the pres-
ence of the non-coordinated N3 atom between the two atoms.
The signal of H4 is a doublet of doublets with 3J(1H4–1H5)
ꢄ4.8 Hz and 4J(1H4–1H6) ꢄ2.1 Hz. H5 is also a doublet of doublets
with 3J(1H5–1H6) ꢄ6.0 Hz. Finally, the signal of H6 is a doublet of
doublets of doublets, since it couples with H2, H4 and H5. This cou-
pling pattern has also been observed in the complexes cis- and
trans-Pt(R2SO)(pm)Cl2 [12].
chemical shifts of H2 and H6 is reversed upon coordination.
Table 4 shows also the ave.
Dd values for each group of com-
pounds. The values seem to slightly increase from group 1 to group
3 in the trans isomers. The influence of the –CH3 substituents in
ortho positions on the pyridine ligand located in trans position
seems to affect the electron density on the protons of the pyrimi-
dine ligand. In the cis compounds, the steric hindrance is the most
important factor.
The proton coupling constants with 195Pt could be measured for
most of the compounds and they depend on the geometry (Table
4). The 3J(195Pt–1H6) values are much larger in the cis compounds
(41 Hz) than in the trans isomers (32 Hz). The 3J(195Pt–1H2) values
are also larger in the cis geometry (23 Hz vs. 19 Hz), although the
difference is much smaller. Similar values were observed for cis-
and trans-Pt(R2SO)(pm)Cl2 [12], and trans-Pt(R2SO)(pm)I2 [13].
The proton chemical shifts of the pyridine ligands are shown in
The signals of pyrimidine have shown a downfield shift upon
coordination, since the formation of the
tron density on the ligand, while it is increased on the Pt atom.
The chemical shifts differences
r bond reduces the elec-
D
d(dligand ꢁ dfree pm) (where the
spectrum of free pm was measured in the same solvent) are shown
in Table 4. The values of H2 for the cis isomers do not follow the
expected pattern. The H–H coupling patterns of these atoms are
different, therefore the assignments seem correct. A large down-
the Supplementary material and the
Dd values are listed in Table 5.
The average d values for the three groups of complexes are also
D
field shift is observed for H6 (ave.
D
d = 0.753 ppm), while the posi-
shown in the table. All the signals are shifted towards lower field
upon coordination. It is difficult to compare the signals of the dif-
ferent Ypy ligands because of the local effects caused by the pres-
ence of methyl groups in different positions. The most deshielded
atoms are the –CH3 protons located in ortho positions, followed
by H6.
tion of H2 is almost not affected by coordination in the cis isomers.
For the trans complexes, the expected values are observed. The sig-
nals of H2 and H6 are deshielded by ꢄ0.42 ppm, while those of H4
and H5 are not very affected. The assignments in the cis and trans
isomers were confirmed by 2D 1H NMR studies.
In the trans isomers, the deshielding order is H2 > H6 > H4 > H5,
while in the cis isomers, it is H6 > H2 > H4 > H5. In the complexes
cis-et trans-Pt(R2SO)(pm)Cl2 (measured in CD2Cl2) [12], the order
was the same for the two isomers (H2 > H6 > H4 > H5). In the latter
For the trans complexes, the values seem to increase from group
1 to group 3. The latter group contains the most basic ligands.
These results are therefore in agreement with the pKa values of
the protonated ligands. The strength of the
r bond should be larger
complexes, the ave.
D
d are H2 = 0.217, H6 = 0.255 ppm (cis), and
in the group 3 complexes, thus the electron density on the Ypy li-
gand should be smaller for this group. For the cis compounds, the
trend seems similar, although steric hindrance should play a more
important role.
H2 = 0.304, H6 = 0.313 ppm (trans), except for cis-Pt(dibenzylsulf-
oxide)(pm)Cl2, where all the signals were observed at higher fields
than in free pyrimidine. In the ionic compound cis-
[Pt(NH3)2(pm)2](ClO4)2, the
H6 = 0.36 ppm in D2O [9]. It seems therefore that our results on
D
d values are: H2 = 0.45 ppm and
Several 3J(195Pt–1H) couplings were observed. They vary from
36 to 42 Hz (ave. 38 Hz) for the cis isomers and between 27 and
33 Hz (ave. 30 Hz) for the trans analogues. It seems therefore that
this value is a good criterion to determine the geometry of these
complexes. A few couplings 4J(195Pt–1H) could also be measured
and they vary between 10 and 12 Hz. Similar values were observed
for the compounds Pt(Ypy)2Cl2 [25].
Table 4
D
d (ppm) and 3J(Pt–H) (Hz) of pm in Pt(Ypy)(pm)Cl2
Ypy
H2
9.226 8.737 7.328 8.737
ꢁ0.055 0.048 0.127 0.644 0.191 22
H4
H5
H6
ave.
3J(Pt–H2) 3J(Pt–H6)
As in 1H NMR, four signals will be observed in 13C NMR for Pt-
Free pm
py
bonded pyrimidine. The
D
d values (dpm ꢁ dfree
in CDCl3) are
pm
cis
trans
cis
trans
cis
trans
cis
40
33
42
shown in Table 6. The trans compounds obtained from the isomer-
ization of the cis isomers showed the presence of other Pt com-
plexes, which could be substracted from the spectra only for a
few ligands. The compound trans-Pt(2,3-lut)(pm)Cl2 was acciden-
tally obtained pure when the reaction of K[Pt(2,3-lut)Cl3] and
pyrimidine was performed in a very large excess of NaCl. This re-
sult could not be reproduced with the other ligands.
a
0.407 0.039
0.403
19
3-pic
ꢁ0.032 0.034 0.162 0.824 0.252 23
0.403 0.045 0.043 0.399 0.223
ꢁ0.024 0.005 0.167 0.941 0.272
0.402 0.035 0.032 0.401 0.218 18
3,4-lut
3,5-lut
42
29
42
ꢁ0.047 0.025 0.161 0.855 0.249 24
b
trans
0.403 0.044
0.397
19
Ave. gr. 1 cis
trans
ꢁ0.040 0.028 0.154 0.816 0.240 23
42
31
0.404 0.041 0.038 0.400 0.221 19
All the pm signals were observed at lower field than those of
free pyrimidine. The
ences between the cis and trans isomers are in the position of C2
and C5. The signal of C2 is more shielded in the cis compounds
Dd values are larger for C6. The main differ-
2-pic
cis
trans
cis
trans
cis
trans
cis
ꢁ0.077 0.027 0.130 0.642 0.181 22
0.441 0.046 0.039 0.440 0.242 19
ꢁ0.078 0.009 0.159 0.738 0.207 23
0.448 0.048 0.039 0.444 0.245 18
ꢁ0.075 0.013 0.133 0.688 0.190 23
0.433 0.073 0.029 0.434 0.242 19
ꢁ0.093 0.034 0.140 0.657 0.185 25
0.439 0.048 0.039 0.436 0.241 22
ꢁ0.095 0.010 0.201 0.790 0.227 24
0.442 0.040 0.031 0.442 0.239 17
ꢁ0.084 0.019 0.153 0.703 0.197 23
0.441 0.051 0.035 0.439 0.242 19
42
2,3-lut
2,4-lut
2,5-lut
38
32
39
32
43
33
39
32
40
32
(ave.
D
d values = 1.16 vs. 2.53 ppm), while the one of C5 is more
d values = 0.12 vs. 1.66 ppm).
shielded in the trans isomers (ave.
D
The total average values of the four C atoms are very similar in
the two geometries. Therefore the total electron density on the
four C atoms of the pm ligand seems identical in the two isomers.
In the series Pt(R2SO)(pm)Cl2 [12], all the C atoms are more
trans
2,3,5-col cis
trans
Ave. gr. 2 cis
trans
deshielded in the cis geometry, probably because
p-bonding is
more important in the R2SO-pm complexes and it is more effective
in the cis geometry.
2,6-lut
trans
0.460 0.048 0.037 0.465 0.253 19
33
33
30
32
2,4,6-col trans
2,3,6-col trans
Ave. gr. 3 trans
0.455 0.042 0.027 0.460 0.246 18
b
0.467 0.049
0.472
19
The average
Dd values were calculated for the three different
0.461 0.046 0.032 0.466 0.251 19
groups of Ypy ligands and the results are shown in Table 6. These
values were compared with the d(195Pt) and there is an agreement,
although there are few results on some groups of complexes. In the
a
Hidden by impurities.
Hidden by H4 of Ypy.
b

F.D. Rochon, M. Fakhfakh / Inorganica Chimica Acta 362 (2009) 1455–1466
1461
Table 5
d (ppm) and J(195Pt–1H) (Hz) for Ypy in Pt(Ypy)(pm)Cl2
D
Ypy
H2
2Me
H3
3Me
H4
4Me
H5
5Me
H6
6Me
3J(Pt–H2/6)
4J(Pt–H2,6–Me)
H2
H6
Pyridine
3-pic
cis
trans
cis
trans
cis
trans
cis
trans
cis
trans
0.262
0.310
0.277
0.137
0.108
0.208
0.186
0.112
0.101
0.137
0.108
0.024
0.262
0.310
0.239
36
30
36
30
42
ꢁ0.028
0.032
3,4-lut
3,5-lut
Ave. gr. 1
0.314
0.258
0.239
0.194
0.273
0.226
ꢁ0.004
0.049
0.102
0.073
0.076
0.303
0.240
0.239
0.194
0.268
0.248
0.060
27
36
31
ꢁ0.038
0.027
0.023
0.079
0.038
0.027
0.038
0.027
36
31
0.137
0.108
0.160
0.144
0.049
0.102
0.105
0.092
0.040
2-pic
cis
trans
cis
trans
cis
trans
cis
trans
cis
trans
cis
0.603
0.713
0.799
0.849
0.566
0.680
0.631
0.750
0.780
0.894
0.676
0.777
0.149
0.089
0.165
0.127
0.165
0.101
0.169
0.084
0.169
0.072
0.371
0.842
0.450
0.705
0.320
0.687
0.425
0.731
0.474
0.741
0.408
2,3-lut
2,4-lut
2,5-lut
2,3,5-col
Ave. gr. 2
0.088
0.111
40
33
40
33
36
27
36
29
11
11
0.150
0.133
0.225
0.190
0.057
0.080
0.168
0.115
0.161
0.128
0.161
0.115
0.086
0.092
0.060
0.087
0.073
0.090
12
0.049
0.075
0.069
0.093
0.188
0.162
0.057
0.080
0.169
0.076
trans
2,6-lut
trans
trans
trans
trans
0.906
0.907
0.977
0.930
0.198
0.209
0.081
0.198
0.209
0.181
0.196
0.906
0.907
1.045
0.953
11
10
2,4,6-col
2,3,6-col
Ave. gr. 3
0.127
0.112
0.112
0.130
0.106
0.204
0.127
Table 6
D
group and for the methyl groups located in ortho positions. It is
not possible to compare the results, since the local effects
caused by the methyl substituents at different positions are too
important.
d(13C) (ppm) of pm in cis- and trans-Pt(Ypy)(pm)Cl2
Ypy
Geometry
C2
C4
C5
C6
Ave.
Free pm
py
3-pic
3,4-lut
3,5-lut
159.06
1.18
1.52
1.70
1.46
2.68
1.47
156.78
1.45
1.33
1.19
1.27
1.24
1.31
121.42
1.56
1.72
1.76
1.67
0.19
1.68
156.78
3.38
3.35
3.34
3.31
3.33
3.35
Very few couplings of the Ypy C atoms with the 195Pt isotope
were observed. In cis-Pt(3,4-lut)(pm)Cl the 3J(195Pt–13C3,5) is
38 Hz, while it is 28 and 30 Hz, respectively, for the trans 2,6-lut
and 2,4,6-col analogues. Therefore it seems again larger for the
cis isomers. A 3J(195Pt–13C2,6–Me) coupling of 23 Hz could be cal-
culated in the trans 2,6-lut compound. These results are similar
to the few values reported in the literature [9,12,13].
cis
cis
cis
cis
trans
cis
1.89
1.98
2.00
1.93
1.86
1.95
1.86
Ave. gr. 1
trans
2.68
1.24
0.19
3.33
2,3-lut
cis
trans
cis
cis
cis
1.07
2.61
0.80
0.86
0.66
0.85
2.61
1.20
1.20
1.16
1.19
1.14
1.17
1.20
1.71
0.13
1.45
1.56
1.82
1.64
0.13
3.08
3.23
3.02
3.00
3.00
3.03
3.23
1.77
1.80
1.61
1.65
1.66
1.67
1.79
2,4-lut
2,5-lut
2,3,5-col
Ave. gr. 2
3.2. Cl2 (Ypy)Pt(l-pm)Pt(Ypy)Cl2
cis
trans
3.2.1. Synthesis
2,6-lut
trans
trans
trans
trans
2.44
2.44
2.49
2.46
1.10
1.02
1.05
1.06
0.11
0.09
0.10
0.10
3.06
3.05
3.10
3.07
1.68
1.65
1.69
1.67
The pyrimidine-bridged dimers (Ypy = 2-pic, 3-pic, 2,3-lut, 2,4-
lut, 2,5-lut, 3,4-lut, 3,5-lut and 2,3,5-col) were synthesized from
the aqueous reaction of K[Pt(Ypy)Cl3] with pm using a Pt:pm ratio
of 2:1 in the presence of NaCl. After two days of reaction, the mix-
ture contains cis and trans monomers and dimers of different
geometries. The mixture was refluxed in dichloromethane for 5
to 34 days (depending on the Ypy ligand), until only one product
was obtained. The mixture can be periodically monitered by 1H
NMR. The final product was characterized by IR and multinuclear
magnetic resonance spectroscopy and identified as the pyrimi-
2,4,6-col
2,3,6-col
Ave. gr. 3
Total ave.
Total ave.
cis
trans
1.16
2.53
1.24
1.12
1.63
0.12
3.19
3.15
1.81
1.73
trans series, the d(195Pt) were found at lower fields for group 3
complexes (ave. ꢁ1982 ppm), while the ave. d(13C) of the four C
atom of pm in group 3 complexes (Dd = 1.67 ppm) is at higher field
dine-bridged dinuclear species Cl2(Ypy)Pt(l-pm)Pt(Ypy)Cl2.
than for the two other groups. Therefore the –CH3 substituents on
the Ypy group located in trans position influence the electron den-
sity on the pyrimidine ligand. The C2 and C6 atoms close to the
binding site are the most affected.
The aqueous reaction of K[Pt(Ypy)Cl3] (Ypy = 2,6-lut, 2,3,6-col
and 2,4,6-col) with pyrimidine in a 2:1 proportion produced the
trans–trans dimer after 5 days. The product of the reaction with
2,3,6-col contained some decomposed product, which could be re-
moved by dissolving in dichloromethane and filtering out the
impurities.
Coupling with the 195Pt isotope was rarely observed. The
2J(195Pt–13C2) coupling constants could be calculated for the cis
3,4-lut and the trans 2,3,6-col complexes. These values are 14
and 15 Hz.
The d(13C) of the Ypy ligands in the complexes are shown in the
3.2.2. IR spectroscopy
The symmetry of the pyrimidine ligand in the dinuclear species
is identical to the one of free pm. The A2 modes are not active in IR.
Supplementary material, and the
Table S1. The values are larger for the C atoms bonded to a methyl
D
d(13C) values are shown in

1462
F.D. Rochon, M. Fakhfakh / Inorganica Chimica Acta 362 (2009) 1455–1466
Table 7
IR bands (cmꢁ1) of free pm and pm in the complexes Cl2(Ypy)Pt(
l-pm)Pt(Ypy)Cl2
Mode
pm [24d]
3-pic
2,3-lut
2,4-lut
2,5-lut
3,4-lut
1592sh
3,5-lut
2,6-lut
1603s
2,4,6-col
1602s
2,3,6-col
1592sh
8b
8a
19b
19a
1576
1566
1467
1403
1595sh
1557vw
1593w
1559w
1473w
1412w
1557w
1465w
1412w
1560w
1414w
1466s
1410s
1403m
1232w
1180w
820s
1461m
1414m
1403m
1225sh
1463sh
1411
1412m
1411s
1402
1224w
1168m
825m
1411m
3
15
10b
1237
1161
832
1180w
790s
1175w
824s
1184m
822m
816sh
800vs
818sh
799vs
704sh
683m
829m
820sh
4
6a
721
676
695m
683m
681s
342s
701w
684m
699m
684S
702w
687m
687s
343s
684m
358m
683s
m(Pt–Cl)
348vs
344vs
345s
349m
347vs
There are 22 active A1, B1 and B2 modes, but only 9 were assigned
(Table 7). The different assignments have already been discussed in
the monomer section.
Pt
H6
N1 C6
The stretching m(Pt–Cl) are strong and only one band was ob-
H2 C2
C5 H5
served between 342 and 358 cmꢁ1. These results strongly suggest
a trans–trans geometry for these dinuclear species.
N3 C4
Pt
H4
3.2.3. Multinuclear magnetic resonance spectroscopy
The compounds were studied by 195Pt NMR in CDCl3. The results
are listed in Table 8. Only one resonance was observed for all the
compounds indicating isomeric purity, which was also confirmed
by 1H and 13C NMR spectroscopy.
Scheme 2.
the one of H4,6 is a doublet of doublets and the one of H5 is a doublet
of triplets. The latter doublets are due to coupling with H2. In our
compounds Cl2(Ypy)Pt(l-pm)Pt(Ypy)Cl2, there were no proton cou-
For the same Ypy ligand, the d(Pt) of the dinuclear compound is
very close to the one of the trans monomer. It seems that the elec-
tron density on the Pt atom in the dinuclear species is the same as
in the trans monomers. The results in Table 8 have been separated
into three groups as discussed previously. The group 3 complexes
containing YPy ligands with two –CH3 substituents in ortho posi-
tions were found at lower fields (ave. ꢁ1979 ppm) than those of
group 2 (ave. ꢁ1998 ppm) and group 1 (ave. ꢁ2004 ppm), as ob-
served in the monomers. The solvent effect is responsible for this
observation. Since the Ypy planar ring is mainly perpendicular to
the Pt plane, the –CH3 substituents are located on both sides of
the square plane in the close environment of the Pt atom. These
substituents reduce the approach of the molecules of solvent close
to the metal center, thus reducing the electron density on the Pt
atom. As a result, the d(195Pt) will be shifted to lower field for group
3 compounds. The complexes of group 2 are observed at interme-
diate field. The signals of the dinuclear complexes containing Ypy
ligands with –CH3 substituents in positions 2 and 3 are always ob-
served at slightly lower field than the others of their respective
group, as observed for the monomers.
pling with H2, although it was observed in the monomers discussed
above.
The
The atom H2 is very shifted to lower field (
pected from the binding of its two neighbouring N atoms to two
metal centers. The H4,6 atoms are also shifted similarly ( da-
ve. = 0.66 ppm), while H5 is not very influenced by coordination
D
d(1H) values of bonded pyridimine are shown in Table 9.
D
dave. = 1.09 ppm) as ex-
D
(D
dave. = 0.04 ppm).
The shifts towards lower fields are larger for group 3 compounds
(ave. for C2 and C4,6, 1.123 and 0.702 ppm) than for group 2 (ave.
1.089 and 0.661 ppm) and group 1 (ave. 1.053 and 0.621 ppm) as re-
ported above for the monomers. The
much smaller than those reported in the series Cl2(R2SO)Pt
-pm)Pt(R2SO)Cl2 (0.291 6 d 6 0.381 ppm) [8]. It seems that
the presence of a strong -accepting ligand (R2SO) changes the elec-
Dd values for H5 are small,
(l
D
p
tron density distribution on the pm-bridging ligand.
In these pm-bridged species, the atoms H4 and H6 are equiva-
lent (C2v symmetry) and only 3 signals will be observed in 1H
and 13C NMR (see Scheme 2).
The H2 signal of pm in these compounds is a singlet, while the
signal of H4 and H6 is a doublet and H5 a triplet. This pattern was
Table 9
D
d(1H) (ppm) for pm in Cl2(Ypy)Pt(
l
-pm)Pt(Ypy)Cl2
Ypy
H2
H4,6
H5
3J(Pt–H2)
3J(Pt–H4,6)
3-pic
1.055
1.048
1.056
1.053
0.626
0.619
0.619
0.621
0.051
18
18
17
18
27
also reported in the ionic complex [Cl(NH3)2Pt(l-pm)Pt(NH3)2Cl]Cl2
3,4-lut
3,5-lut
Ave. Gr. 1
0.026
a
33
30
[6]. In Cl2(R2SO)Pt(l-pm)Pt(R2SO)Cl2 [8], the signal of H2 is a singlet,
0.039
2-pic
1.095
1.097
1.074
1.093
1.088
1.089
0.669
0.669
0.652
0.658
0.657
0.661
0.050
0.041
0.026
0.041
0.033
0.038
21
21
21
22
19
21
33
31
33
33
37
35
Table 8
2,3-lut
2,4-lut
2,5-lut
2,3,5-col
Ave. Gr. 2
d(195Pt) (ppm) of the compounds Cl2(Ypy)Pt(
l-pm)Pt(Ypy)Cl2
Ypy
d (ppm)
Ypy
d (ppm)
Ypy
d (ppm)
3-pic
3,4-lut
3,5-lut
ꢁ2005
ꢁ2003
ꢁ2004
2-pic
ꢁ2010
ꢁ1984
ꢁ2005
ꢁ2008
ꢁ1982
2,6-lut
2,4,6-col
2,3,6-col
ꢁ1990
ꢁ1984
ꢁ1962
2,3-lut
2,4-lut
2,5-lut
2,3,5-col
2,6-lut
1.128
1.110
1.132
1.123
0.706
0.693
0.708
0.702
0.037
20
19
20
20
33
29
2,4,6-col
2,3,6-col
Ave. Gr. 3
0.015
a
0.026
31
Ave. gr. 1
ꢁ2004
Ave. gr. 2
ꢁ1998
Ave. gr. 3
ꢁ1979
a
Hidden by H4 of YPy.

F.D. Rochon, M. Fakhfakh / Inorganica Chimica Acta 362 (2009) 1455–1466
1463
The coupling constants 3J(195Pt–1H4,6) vary between 27 and
Table 11
J(195Pt–13C) values (Hz) observed in Cl2(Ypy)Pt(
l
-pm)Pt(Ypy)Cl2
37 Hz and the 3J(195Pt–1H2) are small (17–22 Hz), which seem to
suggest a trans–trans geometry. A value of 15.8 Hz was reported
in the literature for 3J(195Pt–1H2) in trans,trans-Cl2(PBu3)Pt
3,4-lut 3,5-lut 2-pic 2,3-lut 2,4-lut 2,5-lut 2,6-lut 2,4,6-col
3J(Pt–C–Meortho
3J(Pt–Cmeta
2J(Pt–Cortho
)
26
23
24
33
14
23
24
26
27
23
(l-pm)Pt(PBu3)Cl2 [11]. In the Cl2(R2SO)Pt(l-pm)Pt(R2SO)Cl2 ser-
)
)
)
30
25
21
9
27/27 33/27 28
ies [8], 3J(195Pt–1H2) varies from 20 to 24 Hz for the trans–trans
species and between 25 and 26 Hz for the cis–cis isomers, while
the constants 3J(195Pt–1H6) are between 28 and 32 Hz for the
trans–trans compounds and between 40 and 42 Hz for the cis–cis
analogues. All these results strongly suggest a trans–trans geome-
15/17
14
15
4J(Pt–Cpara
2J(Pt–C4,6 pm)
3J(Pt–C5 pm)
14
13
25
try for our novel compounds Cl2(Ypy)Pt(
The
d(1H) values of Ypy in the dinuclear compounds are
shown in Table S2. The results are close to those observed for the
trans monomers. The largest d values are for the methyl substit-
l-pm)Pt(Ypy)Cl2.
D
(3) were determined by X-ray diffraction methods. The results have
confirmed the configuration of the three compounds. The crystallo-
graphic data (Table 12) are slightly less precise for crystal 2, which
was found to be twinned. The trans–trans pyrimidine-bridged com-
plex (3) contains a twofold axis and the atoms C2 and C5 of pyrim-
idine are located on the axis. It contains also 2 molecules of CHCl3
per dimer. The conformation of the different molecules are shown
on the labelled diagrams of the three compounds (Figs. 1–3).
The coordination around the Pt(II) atoms is square planar and
the angles are close to the expected values. The Pt–Cl distances
are normal (2.2945(9) - 2.3079(7) Å), while the Pt–N bonds are
similar in the three crystals and they vary between 2.012(9) and
2.0228(18) Å. There is no difference between the bonds located
in trans position to a chloro ligand or to a N-bonded ligand. These
values agree with similar distances in the literature [8,12,14,25].
The Pt–N (pm) bonds (ave. 2.018(4) Å) do not seem shorter than
the Pt–N (Ypy) bonds (ave. 2.021(4) Å).
D
uents located in ortho positions. The same trend is also observed
for the three groups of complexes. The coupling constants
3J(195Pt–1H6) are between 28 and 33 ppm.
The
10. The latter are very large for C2 (
C4,6 ( dave = 4.13 ppm), while C5 is not affected by coordination
D
d(13C) values of pm in these complexes are shown in Table
D
dave = 5.69 ppm), smaller for
D
(D
dave = 0.13 ppm).
Table 10 shows that the ave.
D
d(13C) value for each group of
complexes decreases from group 1 to group 3. These results are
in agreement with those observed in 195Pt NMR, where group 3
compounds were observed at lowest fields. In 13C NMR, the C
atoms of pm were observed at highest field for the group 3 com-
pounds. When there is a reduction of electron density on the Pt
atom (d(195Pt) at lower field), there is an increase of electron den-
sity on the pm ligand (d(13C) at higher field).
The d(13C) of the Ypy ligands are shown in the Supplementary
material and the
D
d(13C) values are listed in Table S3. The results
Table 12
are very similar to those observed for the trans monomers.
Coupling of the pm C atoms with 195Pt are rarely observed. The
2,3-lut compound showed a 3J(195Pt–13C5) of 25 Hz, while a few
2J(195Pt–13C4,6) (13–15 Hz) could be evaluated (Table 11). Several
3J(195Pt–13C) coupling were observed for the Ypy ligands, also
shown in Table 11. The largest are with the C atoms located in meta
positions (23–33 Hz), followed by the coupling with the methyl
groups located in ortho positions (23–27 Hz). The couplings
2J(195Pt–13C) are between 14 and 21 Hz and finally the couplings
4J(195Pt–13Cpara) are 9 and 14 Hz. These values are consistent with
a trans–trans geometry, although there are very few such data in
the literature.
Bond distances and angles
cis-Pt(2,4-lut)(pm)-
Cl2 (1)
trans-Pt(2,6-lut)-
(pm)Cl2 (2)
{PtCl2(2,6-lut)}2-
-pm) (3)a
(l
Pt–Cl
2.2945(9)
2.3021(10)
2.018(3)
2.021(3)
1.352(4)
1.380(5)
1.498(5)
1.338(5)
1.342(5)
1.318(6)
1.324(6)
1.363(6)
1.367(5)
2.2961(14)
2.3069(15)
2.012(9)
2.3014(7)
2.3079(7)
2.0228(18)
2.0206(18)
1.358(3)
1.379(4)
1.489(4)
1.330(2)
Pt–N1
Pt–N2
N2–C (ave.)
C–C (ave. Ypy)
C–CH3 (ave.)
N1–C2
N1–C6
N3–C2
N3–C4
C4–C5
2.022(8)
1.364(11)
1.383(11)
1.498(9)
1.361(12)
1.353(13)
1.326(9)
1.331(10)
1.398(15)
1.360(15)
1.352(3)
3.3. Crystal structures
C5–C6
1.376(3)
1.760(3)
C1–Cl (ave.)
The crystal structures of cis-Pt(2,4-lut)(pm)Cl2 (1), trans-Pt(2,6-
lut)(pm)Cl2 (2) and trans,trans-Cl2(2,6-lut)Pt(l-pm)Pt(2,6-lut)Cl2
Cl1–Pt–Cl2
Cl1–Pt–N1
Cl1–Pt–N2
Cl2–Pt–N1
Cl2–Pt–N2
N1–Pt–N2
C12–N2–C16
Pt–N2–C (ave.)
N2–C–CH3 (ave.)
N2–C–Cmeta (ave.)
C–C–C (ave. Ypy)
C–C–CH3 (ave.)
Pt–N1–C2
Pt–N1–C6
C2–N1–C6
N1–C2–N3
N1–C6–C5
93.35(4)
177.16(8)
88.18(8)
178.63(6)
90.3(2)
89.89(19)
89.0(2)
177.89(3)
90.036
88.71(5)
90.41(6)
90.80(5)
178.20(7)
120.4(2)
119.73(15)
118.6(2)
120.1(2)
119.8(2)
89.20(9)
Table 10
176.65(8)
89.21(11)
118.9(3)
116.1(2), 125.0(2)
118.6(3)
119.8(3), 122.9(3)
119.4(3)
121.4(4)
120.6(3)
122.9(2)
116.5(3)
125.5(4)
90.8(2)
D
d(13C) (ppm) of pm in Cl2(Ypy)Pt(
l
-pm)Pt(Ypy)Cl2
C4,6
177.8(2)
119.5(7)
120.3(6)
118.4(6)
120.8(7)
119.7(8)
120.9(6)
119.3(6)
123.3(7)
117.3(9)
125.1(7)
120.6(10)
116.8(6)
122.0(7)
119.1(10)
Ypy
C2
C5
Ave.
3-pic
5.99
5.97
5.99
5.98
4.39
4.31
4.31
4.37
0.23
0.22
0.20
0.22
3.75
3.70
3.70
3.72
3,4-lut
3,5-lut
Ave. gr. 1
118.03(16)
123.75(16)
118.2(2)
124.3(3)
120.3(2)
2-pic
5.68
5.73
5.63
5.69
5.74
5.69
4.18
4.20
4.10
4.12
4.13
4.15
0.16
0.17
0.14
0.14
0.15
0.15
3.55
3.58
3.49
3.52
3.54
3.54
2,3-lut
2,4-lut
2,5-lut
2,3,5-col
Ave. gr. 2
121.4(4)
116.6(4)
122.8(4)
117.1(4)
C2–N3–C4
N3–C4–C5
C6–C5–C4
Cl–C1–Cl (ave.)
118.7(3)
110.23(15)
2,6-lut
5.39
5.40
5.45
5.41
3.91
3.85
3.91
3.89
0.04
0.00
0.04
0.03
3.31
3.28
3.33
3.31
2,4,6-col
2,3,6-col
Ave. gr. 3
a
Labelling on crystal 3 is slightly different for the pm ligand, which contains a
twofold axis.

1464
F.D. Rochon, M. Fakhfakh / Inorganica Chimica Acta 362 (2009) 1455–1466
of –CH3 groups reduces the internal C–C–C angles, as observed in
the angle C13–C14–C15 in the 2,4-lut crystal (1) (117.1(3)°). In
the same compound, N2–C12–C13 is smaller (119.8(3)°) than the
N2–C16–C15 angle (122.9(3)°).
The ave. Pt–N1–C2 angles in the pyrimidine are smaller
118.03(16) to 120.6(3)° than the Pt–N1–C6 angles 122.9(2) to
123.75(16)°. In the monomers, the ave. N1–C bond distance is
slightly longer (1.348(9) Å) than the N3–C bonds (ave. 1.325(8)
Å). In the dimer where the two N atom are bonded to Pt, these dis-
tances are identical by symmetry (ave. 1.346(7) Å). The C–C dis-
tances are slightly longer (ave. 1.373(8) Å). These distances are in
agreement with those determined in free pyrimidine (1.33(1)
and 1.37(1) Å, respectively) [28]. The internal angles N–C–C (ave.
121.3(5)°) and N1–C2–N3 angles (ave. 125.0(3)°) are larger than
the C–N1/3-C (ave. 117.3(4)°) and C–C–C angles (ave. 118.3(6)°).
All these angles are similar to those of the free ligand [28] and
the values reported in trans-Pt(pm)2X2 [10], Pt(R2SO)(pm)X2 [12–
14] and in Cl2(R2SO)Pt(l-pm)Pt(R2SO)Cl2 [8]. The binding of the
N to the Pt atom does not change the internal angle at the N atom
as it does in the hydrochlorides of pyrimidine and pyrimidin-2-one
[29,30]. The protonation at N1 in the latter compounds increased
the ring angle at the N atom by about 6°. This effect is not observed
when Pt is the exocyclic bonded group. In the monomers (crystals
1 and 2) the angles C–N1–C and C–N3–C are identical. Therefore,
contrary to protonation, coordination to the platinum atom does
not affect the structure of the pyrimidine ligand. For the pyrazine
ligand, different results were reported. In cis- and trans-
Pt(Ypy)(pyrazine)Cl2 [31], the binding of pyrazine to platinum
through the N1 atom slightly increased the internal C–N1–C angle,
(ave. 117.6(3)°), while the non-bonded angle C–N4–C (ave.
115.6(3)°) is identical to the one in free pyrazine (115.1°) [32]. In
the two Pt-pyrazine compounds, the N1–C–C angles are smaller
(ave. 120.5(3)°) than the N4–C–C angles (ave. 123.1(4)°). In free
pyrazine, these angles are 122.4° [32].
Fig. 1. Labelled diagram of cis-Pt(2,4-lut)(pm)Cl2, (1). The ellipsoids correspond to
40% probability.
Planar ligands such as pyridine derivatives and pyrimidine are
often perpendicular to the platinum plane in order to reduce the ste-
ric hindrance, especially for ortho-substituted pyridine ligands. For
2,6-lutidine, the most stable conformer is the one where the ligand
is perpendicular to the Pt plane. The orientation of the planar rings is
particularly important in cis isomers, where steric factors are usu-
ally very important. For cis-Pt(2,4-lut)(pz)Cl2, where the Ypy ligand
contains one ortho substituent, the dihedral angle between the
platinum and the pyrimidine planes is 70.13(9)°, while the angle
between the Pt and the 2,4-lutidine plane is 80.73(7)°. In the trans
geometry, these angles should be smaller. For trans-Pt(2,6-lut)-
(pz)Cl2, where the Ypy ligand contains two ortho substituents, the
dihedral angle between the Pt(II) plane and the 2,6-lutidine plane
is 76.38(15)°, while the angle between the Pt(II) and pyrimidine
Fig. 2. Labelled diagram of trans-Pt(2,6-lut)(pm)Cl2 (2). The ellipsoids correspond
to 40% probability.
For the pyridine derivative, the ave. Pt–N2–C angles are
120.3(6) (2) and 120.4(2)° (3) for the compounds containing 2,6-
lutidine. For crystal 1 which contains 2,4-lutidine, the external an-
gle with C12, which is bonded to a –CH3 substituent is larger
(125.0(2)°) than the Pt–N2–C16 angle (116.1(2)°). The presence
Fig. 3. Labelled diagram of trans,trans-Cl2(2,6-lut)Pt(
l-pm)Pt(Ypy)Cl2 (3). The ellipsoids correspond to 40% probability.

F.D. Rochon, M. Fakhfakh / Inorganica Chimica Acta 362 (2009) 1455–1466
1465
planes is 60.12(15)°. In the pyrimidine-bridged dimer, the dihedral
angle between the Pt(II) and the 2,6-lut planes is much larger
(87.98(6)°) than the one between the Pt(II) and pyrimidine planes
(43.97(9)°).
Packing forces are probably the more determining factors in the
orientation of the pyrimidine or pyridine rings, when there is no
important steric hindrance. It has also been suggested that the pres-
there is an electron density reduction on the pm ligand. The influ-
ence of the –CH3 substituents in ortho positions of the pyridine li-
gand was also observed in 1H NMR.
Several couplings of the types J(195Pt–1H) and J(195Pt-13C) are
reported. The 3J values are always larger in the cis compounds than
in the trans isomers. A few 2J and 4J are also reported. These values
are quite small.
ence of
p
-bonding between Pt(II) and the aromatic ligand would
The crystal structures of three compounds were determined by
crystallographic methods. The results have confirmed the configu-
rations suggested by IR and multinuclear magnetic resonance
spectroscopies for the three new types of Pt(II) compounds.
tend to decrease this angle [23]. An intermediate angle would be a
compromisebetween thetwofactors, sterichindrance, whichwould
tend to increase the dihedral angle and more effective Pt–N
ing, which would tend to reduce the angle. We are not suggesting
that -bonding is very important in these types of complexes, but
p-bond-
p
Acknowledgment
it might be present, since pyridine and pyrimidine contains empty
pꢀ orbitals, which can accept electron density from a soft metal like
Pt(II). Therefore, when steric factors are less important, the orienta-
tion of these planes results from several smaller factors.
The authors are grateful to the Natural Sciences and Engineer-
ing Engineering Research Council of Canada for financial support
of the project.
The dinuclear species (3) crystallized with two molecules of
chloroform per dimer. It does not seem to influence the structure
of the Pt(II) molecule. The average C–Cl distance is 1.760(3) Å
and the average angle Cl–C–Cl is 110.23(15)°.
Appendix A. Supplementary material
CCDC 689624, 689625 and 689626 contain the supplementary
crystallographic data for this paper. These data can be obtained
free of charge from The Cambridge Crystallographic Data Centre
via www.ccdc.cam.ac.uk/data_request/cif. The supplementary
material includes a list of the NMR spectra of the complexes,
4. Conclusion
Novel mixed-ligand Pt(II) complexes containing pyrimidine and
a pyridine derivative were synthesized and characterized in the so-
lid state by IR spectroscopy and in solution by multinuclear mag-
netic resonance spectroscopy. Monomers of the types cis- and
trans-Pt(Ypy)(pm)Cl2 and pyrimidine-bridged dinuclear species
D
d(13C) (ppm) for Ypy in Pt(Ypy)(pm)Cl2 (Table S1), the
(ppm) of Ypy in Cl2(Ypy)Pt(
d(13C) (ppm) for Ypy in Cl2(Ypy)Pt(
D
d(1H)
-pm)Pt(Ypy)Cl2 (Table S2) and the
-pm)Pt(Ypy)Cl2 (Table S3).
l
D
l
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.ica.2008.07.003.
Cl2(Ypy)Pt(l-pm)Pt(Ypy)(pm)Cl2 were studied. The cis monomers
containing Ypy with two –CH3 substituents in ortho position can-
not be synthesized because of steric hindrance. The cis monomers,
the trans monomers containing Ypy with two methyl substituents
in ortho positions and the dinuclear compounds were prepared
pure, while the other trans monomers contain other species. The
latter compounds were prepared from the isomerization of the
cis isomers in dichloromethane. The cis ? trans isomerization is
very slow and the product is usually contaminated with the pm-
bridged dimer and other species such as trans-Pt(pm)2Cl2 and
trans-Pt(Ypy)2Cl2. IR and NMR spectroscopies indicated strongly
that the dinuclear species have the trans–trans geometry.
The NMR results were interpreted in relation to the solvent ef-
fect. For each series of complexes, the compounds were classified
into three groups depending on the Ypy ligand. Group 1 complexes
contains pyridine derivatives which have no –CH3 substituent in
ortho position, group 2 includes Ypy which have one –CH3 substi-
tuent in ortho position, while group 3 contains the Ypy ligands
which have two –CH3 substituents in ortho positions. The solvent
normally weakly binds the metal atom on both sides of the square
plane, which increases the electron density on the metal center.
Planar ligands such as pyridine derivatives are usually perpendic-
ular to the square plane in order to reduce steric hindrance with
the cis neighbours. This is particularly true when the pyridine
derivative contains –CH3 substituents in ortho positions. In this
conformation, the –CH3 substituents are directly on top and bot-
tom of the coordination plane, thus preventing the approach of
the molecules of solvent towards the Pt atom. The presence of
these substituents will therefore reduce the electron density on
the metal center, reflected by a downfield shift in 195Pt NMR.
The d(195Pt) of group 1 complexes were observed at highest
fields, while the group 3 compounds were found at lowest fields
for the three series of new compounds (the cis and trans monomers
and the trans–trans dinuclear species). The d(13C) of the pyrimidine
C atoms of the three groups of compounds are in the reverse order
as expected. When the electron density on the Pt atom increases,
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