Synthesis, multinuclear magnetic resonance and crystal structures of Pt(II) complexes containing amines and bidentate carboxylate ligands

Article abstract of DOI:10.1016/j.ica.2006.04.014

A novel synthetic method for the synthesis of the complexes cis-Pt(amine)₂R(COO)₂ is compared to two other methods involving the use of either barium dicarboxylate or sodium carboxylate. Pt(II) compounds with monodentate and bidentate amines were studied. The reaction involves the use of a silver dicarboxylato complex, which is the intermediate in the new synthetic procedure. The crystal structure of the silver intermediate with the ligand 1,1-cyclobutanedicarboxylate (1,1-CBDCA) was determined by X-ray diffraction. The crystal Ag₂(1,1-CBDCA) has a very interesting 3-D extended structure. The complexes cis-Pt(amine)₂R(COO)₂ were studied in solution by multinuclear (¹H, ¹³C and ¹⁹⁵Pt) magnetic resonance spectroscopy, but the solubilities are very low. D₂O was found to be the best solvent. In ¹⁹⁵Pt NMR, the complexes containing bidentate amines forming five-membered chelates were observed at higher fields than those containing monodentate amines. The resonances of the NH₃ compounds were also found at lower fields than the primary amine complexes. All the dicarboxylato ligands form six-membered chelates except 1,2-CBDCA, whose Pt(II) compounds were observed at lower fields than the others. The crystal structures of Pt(en)(1,1-CBDCA), Pt(Meen)(1,1-CBDCA) and Pt(en)(benzylmalonato) were confirmed by X-ray diffraction methods. Several compounds are disordered. The crystals are stabilized by intermolecular hydrogen bonds between the -NH₂ groups and the carboxylato O atoms.

Full text of DOI:10.1016/j.ica.2006.04.014

Inorganica Chimica Acta 359 (2006) 4095–4104
www.elsevier.com/locate/ica
Synthesis, multinuclear magnetic resonance and crystal structures of
Pt(II) complexes containing amines and bidentate carboxylate ligands
*
Fernande D. Rochon , Gassan Massarweh
`
´ ´ ´
Universite´ du Que´bec a Montreal, Departement de chimie, C. P. 8888, Succ. Centre-ville, Montreal, Canada H3P 3P8
Received 28 March 2006; accepted 10 April 2006
Available online 22 April 2006
Abstract
A novel synthetic method for the synthesis of the complexes cis-Pt(amine)2R(COO)2 is compared to two other methods involving the
use of either barium dicarboxylate or sodium carboxylate. Pt(II) compounds with monodentate and bidentate amines were studied. The
reaction involves the use of a silver dicarboxylato complex, which is the intermediate in the new synthetic procedure. The crystal struc-
ture of the silver intermediate with the ligand 1,1-cyclobutanedicarboxylate (1,1-CBDCA) was determined by X-ray diffraction. The crys-
tal Ag2(1,1-CBDCA) has a very interesting 3-D extended structure. The complexes cis-Pt(amine)2R(COO)2 were studied in solution by
multinuclear (1H, 13C and 195Pt) magnetic resonance spectroscopy, but the solubilities are very low. D2O was found to be the best sol-
vent. In 195Pt NMR, the complexes containing bidentate amines forming five-membered chelates were observed at higher fields than
those containing monodentate amines. The resonances of the NH3 compounds were also found at lower fields than the primary amine
complexes. All the dicarboxylato ligands form six-membered chelates except 1,2-CBDCA, whose Pt(II) compounds were observed at
lower fields than the others. The crystal structures of Pt(en)(1,1-CBDCA), Pt(Meen)(1,1-CBDCA) and Pt(en)(benzylmalonato) were con-
firmed by X-ray diffraction methods. Several compounds are disordered. The crystals are stabilized by intermolecular hydrogen bonds
between the –NH2 groups and the carboxylato O atoms.
ꢀ 2006 Elsevier B.V. All rights reserved.
Keywords: Platinum; Amine; Carboxylato; Silver; Crystal structure; NMR
1. Introduction
antitumor compound Pt(NH3)2(1,1-cyclobutanedicarboxy-
lato) (carboplatin) is now commercially available in a few
countries. It is more soluble in water than cisplatin and pro-
duces an equally strong antitumor effect, but at a markedly
higher dosage due to the delayed formation of the active
aquated metabolites. Several other amine-carboxylato
Pt(II) compounds have also good antitumor activities like
Pt(dach)(oxalato) (oxaliplatin) [3] or Pt(dach)(malonato)
(dach = 1,2-diaminocyclohexane) and Pt(en)(malonato)
(malonatoplatin) [4] (en = ethylenediamine).
Two methods have been used in the literature to synthe-
size diamine dicarboxylato Pt(II) complexes and these were
discussed in a previous paper [5]. These methods involve
the use of a silver salt to remove the dihalo ligands from Pt-
(amine)2X2. The product is usually the diaqua compound
(in slightly acidic medium) which is very reactive. In basic
pH, the diaqua Pt species are hydrolyzed to the dihydroxo
The compound cis-Pt(NH3)2Cl2 (cisplatin) is still one of
the most extensively used anticancer drug in the world [1],
although it has numerous side effects and toxicity. It is not
very soluble in water and it can hydrolyze inside the cell,
where the chloride concentration is low and the pH is neu-
tral, to produce several species, including toxic hydroxo-
bridged dimers or other oligomers. A good review of the
influence of structure on the activity and toxicity of Pt
anti-cancer drugs has been published [2]. The replacement
of the chloro ligands by carboxylato ligands produces less
toxic compounds, with increased solubility in water. The
*
Corresponding author. Tel.: +1 514 987 3000x4896; fax: +1 514 987
4054.
E-mail address: rochon.fernande@uqam.ca (F.D. Rochon).
0020-1693/$ - see front matter ꢀ 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2006.04.014

4096
F.D. Rochon, G. Massarweh / Inorganica Chimica Acta 359 (2006) 4095–4104
compound, while in neutral pH, the monoaquamonohy-
droxo compound, along with hydroxo-bridged dimers and
other oligomers, are formed. In these reactions, the quantity
of the silver salt is very critical, since a small excess can react
with the reactive Pt-aqua species. The crystal structure of one
such complex was reported [6]. The structure is a tetranuclear
compound containing platinum–silver bonds. Therefore, the
quantity of the reactants must be carefully controlled and
usually a small deficit of the silver salt is used. Furthermore,
the reaction must be done in basic medium to deprotonate
the carboxylic acid, where sometimes the ligands might be
sensitive to the use of base.
We have now developed a new method, which was com-
pared to the two reported methods. The method involves
the formation of a silver carboxylato intermediate, which
is then reacted with the diaminodiiodo Pt complex. Com-
pounds with different types of monodentate and bidentate
amines were studied. Only bidentate dicarboxylate ligands
were chosen. Therefore, all the compounds have the cis
configuration. The products were analyzed by multinuclear
magnetic resonance and a few by crystallographic methods.
The silver intermediate was also characterized by X-ray dif-
fraction methods.
Pt(amine)2R(COO)2: The two compounds cis-Pt(ami-
ne)2I2 and Ag2R(COO)2 were mixed together in water in
a 1:1 proportion. The mixture is stirred in the dark during
2–3 days until the formation of AgI is complete. The yellow
precipitate is filtered out and the filtrate is evaporated to
dryness.
Pt(NH3)2(1,1-CBDCA): d(H) (ppm), 1.716quintet,
2.700t, d(C) (ppm), 15.41, 31.19, 56.37, 182.0.
Pt(NH3)2(1,2-CBDCA): d(H) (ppm), 1.806, 3.011, 3.517,
d(C) (ppm), 21.86, 44.20. Pt(NH3)2(malonato): d(H)
(ppm), 3.018. Pt(NH3)2(Bumalonato): d(H) (ppm), 0.77,
1.187, 1.254, 1.77, 2.41, 3.392t, d(C) (ppm), 13.21, 21.9,
29.30, 31.01, 58.17, 181.32. Pt(NH3)2(Bzmalonato): d(H)
(ppm), 2.914d, 3.267t, 7.18m, d(C) (ppm), 36.6, 61.8,
126.2, 128.6, 128.81, 180.7.
Pt(cpa)2(1,1-CBDCA): d(H) (ppm), 1.753quintet, 2.258t,
(cpa) 1.38, 1.48, 1.72, 1.90, 2.66, d(C) (ppm), 15.61, 29.37,
30.64, 58.0, 179.6, (cpa) 23.51, 33.16, 59. Pt(cpa)2(1,2-
CBDCA) in D2O-DMF: d(H) (ppm), 1.82, 3.04, (cpa)
1.53, 1.95, d(C) (ppm), 21.77, 43.38, 164.8, (cpa) 23.53,
32.92, 57.78. Pt(cpa)2(malonato): d(H) (ppm), 3.52, (cpa)
1.42, 1.56, 1.98, 3.05, d(C) (ppm), 48.0, 178.0 (cpa) 23.64,
33.11, 57.83. Pt(cpa)2(Bumalonato) measured in D2O/
MeOH d(H) (ppm), 0.73, 1.17, 3.50, (cpa) 1.48, 1.56,
1.70, 1.90, 3.05, d(C) (ppm) 13.24, 21.94, 29.0, 30.64,
52.23, 181.76, (cpa) 23.64. Pt(cpa)2(Bzmalonato): d(H)
(ppm), 3.05, 3.40, 7.17, d(C) (ppm), 36.6, 61.8, 126.98,
129.38, 130.23, 179.9, (cpa) 23.73, 31.87, 52.34.
2. Experimental
2.1. Chemicals and instrumentation
K2[PtCl4] was purchased from Johnson–Matthey and
was recrystallized in water before use. The amines were
bought from Aldrich, while silver nitrate was purchased
from Analar. D2O, DMF-d7, MeOD, CDCl3 and
CD3COCD3 were obtained from CDN Isotopes.
Pt(en)(1,1-CBDCA): d(H) (ppm), 1.7, 2.4, d(C) (ppm),
15.41, 31.03, 56.20, 180.0 (en) 48.02. Pt(en)(1,2-CBDCA):
d(H) (ppm), 1.86, 3.03, 3.50, (en) 2.33, 2.41,
3J(195Pt–1H) = ꢁ48 Hz, d(C) (ppm), 22.07, 44.06, 180.2,
(en) 48.22. Pt(en)(malonato): d(H) (ppm), 3.46, (en) 2.40,
3J(195Pt–1H) = ꢁ46 Hz, d(C) (ppm) 48.01. Pt(en)(Bumalo-
nato): d(H) (ppm), 0.99t, 1.43, 1.51, 2.01, 3.58t, (en) 2.64,
2.70, 3J(195Pt–1H) = ꢁ47 Hz, d(C) (ppm), 13.2, 22.06,
29.02, 31.55. Pt(en)(Bzmalonato): d(H) (ppm), 3.06, 3.6,
7.2m, (en) 2.50, 2.83, d(C) (ppm), 36.40, 60.33, 126.25,
128.65, 128.80, 140.9, 179.10, (en) 48.09, 46.97.
Pt(Meen)(1,1-CBDCA): d(H) (ppm), 1.695quintet,
2.648t, 2.695t, (Meen) 1.102d, 2.15m, 2.45m, 2.63m, d(C)
(ppm), 15.31, 30.80, 31.26, 56.21, 181.74, (Meen) 15.41,
52.58, 55.82. Pt(Meen)(1,2-CBDCA): d(H) (ppm), 1.78,
2.98, (Meen) 1.14, 2.23, 2.42, 2.84, d(C) (ppm), 21.8,
43.33, 184.03 (Meen) 15.25, 52.81, 56.04. Pt(Meen)(malo-
nato): d(H) (ppm), 3.468, 3.51, (Meen) 1.147d, 2.25dd,
2.50dd, 2.87m, d(C) (ppm) 48.3, 177.13, (Meen) 15.30,
52.62, 55.87. Pt(Meen)(Bumalonato): d(H) (ppm), 0.751t,
0.810t, 1.28, 1.722t, 2.46, 3.342t, 3.357t, (Meen) 1.116d,
1.184d, 2.26, 2.53, 2.87, d(C) (ppm), 13.4, 21.83, 29.34,
31.12, 52.8, 179.3. Pt(Meen)(Bzmalonato): d(H) (ppm),
3.03d, 3.61t, 7.2, (Meen) 1.14d(minor), 1.15d(major),
2.22(minor), 2.37(major), 2.46(minor), 2.56(major),
2.98(CH2).
The NMR spectra were measured on a Varian Gemini
300BB. The fields were 300.070, 75.460 and 64.395 MHz
1
for H, 13C and 195Pt, respectively. For the 195Pt NMR
spectra, K2[PtCl4] (ꢀ1628 ppm in D2O with KCl, relative
to K2[PtCl6] which was assigned a d(Pt) = 0 ppm) was the
external standard. Most of the NMR spectra of the com-
plexes were measured in D2O. The solutions were often
heated to about 40–45ꢁ in order to increase the solubility.
For the less soluble compounds, several organic solvents
like CD3COCD3, DMF-d7, MeOD and CDCl3 were used,
often without success.
2.2. Synthesis
cis-Pt(amine)2I2: These compounds were prepared as
described in the literature [7,8].
Ag2R(COO)2: Two millimoles of aqueous NaOH are
added to 1 mmol of the dicarboxylic acid dissolved in a
small quantity of water. Two millimoles of AgNO3 are then
added to the sodium dicarboxylate solution in the dark. A
white precipitate forms immediately. The mixture is stirred
for 15–30 min and the silver compound is filtered, washed
with water, dried in air and finally in a dessicator. The
yields are between 60% and 80%.
Pt(Me2en)(1,1-CBDCA): d(H) (ppm), 1.70, 2.65, d(C)
(ppm), 15.43, 30.96, 56.17, 181.67, 181.83 (Me2en) 44.69,
51.57, 68.14. Pt(Me2en)(1,2-CBDCA): d(H) (ppm), 1.92d,

F.D. Rochon, G. Massarweh / Inorganica Chimica Acta 359 (2006) 4095–4104
4097
Table 1
Crystallographic details of the crystals
Name
{Ag2(1,1-CBDCA)}n
Pt(en)(1,1-CBDCA)
Pt(Meen)(1,1-CBDCA)
Pt(en)(Bzmal)
Crystal
1
2
3
4
Chemical formula
Molecular weight
Space group
C6H6O4Ag2
(357.85)n
I41/a (No. 88)
22.5966(16)
22.5966(16)
11.692(2)
C8H14N2O4Pt
397.30
Pnma (No. 62)
8.663(2)
9.618(2)
12.713(2)
C9H16N2O4Pt
411.33
Pnma (No. 62)
9.686(3)
9.986(3)
11.753(5)
C12H16N2O4Pt
447.36
P2/1 (No. 4)
4.603(3)
10.792(5)
12.916(6)
93.61(5)
640.3(6)
2
2.320
10.968
424
˚
a (A)
˚
b (A)
˚
c (A)
B (ꢁ)
3
˚
V (A )
5970.0(12)
32
3.185
5.212
5376
1059.3(4)
4
2.491
13.243
744
1136.8(7)
4
2.403
12.344
776
Z
qcalcd (g cmꢀ3
)
l(Mo Ka) (cmꢀ1
F(000)
)
Measured reflections
Independent reflections (Rint
Observed reflections [I > 2r(I)]
10634
2919 (0.0488)
2507
11754
1637 (0.0577)
1464
8442
1186 (0.1513)
964
4512
2262 (0.0949)
1812
)
R1 [F > 2r(I)]
wR2 (all data)
S
0.0268
0.0597
1.070
0.0289
0.0704
1.064
0.0459
0.1072
1.045
0.0575
0.1327
1.074
P
P
P
P
2
2
1=2
R1 = (|Fo ꢀ Fc|)/ |Fo|, wR2 ¼ ½ ðwðF 2o ꢀ F c2Þ Þ= ðwðF o2Þ Þꢂ
.
3.10, (Me2en) 2.43, 2.52, 2.566, d(C) (ppm), 21.50, 41.54,
179.76, (Me2en) 45.42, 51.91, 68.50. Pt(Me2en)(malonato):
d(H) (ppm), 3.55, (Me2en) 2.58, 2.687, d(C) (ppm) 47.81,
178.5, (Me2en) 44.71, 51.48, 68.22. Pt(Me2en)(Bumalo-
nato): d(H) (ppm), 0.80, 1.28, 2.55, 3.36, (Me2en) 2.43,
2.94, d(C) (ppm), 13.24, 21.83, 29.40, 31.24, 58.22, (Me2en)
44.70, 51.59, 68.22. Pt(Me2en)(Bzmalonato): d(H) (ppm),
2.60d, 3.65t, 7.19m, (Me2en) 2.50, d(C) (ppm), 37.00,
59.65, 127.17, 128.90, 129.02, 138.26, 179.86.
were found by the usual Fourier methods. The intensity data
were corrected for absorption (Gaussian integration for
crystal 4 and semi-empirical for the others) and for the effects
of Lorentz and polarization. The H atoms were fixed at their
calculated positions (riding model) with Ueq = 1.2 · Ueq of
the C atom to which they are bonded, except where there
are disorders. In crystals 2, there are two positions (occu-
pancy of 0.5 each) for the ethylene groups in ethylenedia-
mine, while in crystal 3, there are two positions for the
methylene and the CH3 groups (occupancy of 0.5 each) of
the methyl derivative of ethylenediamine. The refinement
of the structures was done on F2 by full-matrix least-squares
analysis. The calculations were done with a SHELXTL system
[10]. The crystallographic data and other pertinent informa-
tion are summarized in Table 1.
Pt(dach)(1,1-CBDCA): d(H) (ppm), 1.735q, 2.713t,
(dach) 0.99, 1.13, 1.42, 2.22, 2.32, d(C) (ppm), 15.41,
31.04, 56.28, 181.75, (dach) 23.98, 31.82, 62.48.
Pt(dach)(1,2-CBDCA): d(H) (ppm), 1.82, 3.05, 3.46, (dach)
0.94, 1.08, 1.36, 2.20, d(C) (ppm in D2O–CH3OD), 20.48,
43.95, (dach) 23.85, 31.5, 63.10. Pt(dach)(malonato): mea-
sured in CDCl3, d(H) (ppm), 3.46, (dach) 0.86, 1.19, 1.23,
2.15, d(C) (ppm) 181.8, (dach) 23.94, 31.78, 62.48.
Pt(dach)(Bumalonato): d(H) (ppm), 0.97, 1.12, 1.41, 1.73,
1.86d, 2.23, 2.71t. Pt(dach)(Bzmalonato): d(H) (ppm),
2.60, 2.98d, 3.14, 3.36, 7.11m.
3. Results and discussion
3.1. Synthetic procedures
Pt(sec-butylamine)(Bzmalonato): d(H) (ppm), 3.13, 3.3,
7.17m, (sec-butylamine) 0.823t, 1.129d. 1.49m, 3.01.
Two different methods have been used in the literature
for the synthesis of amine-carboxylato Pt(II) complexes.
These have been discussed in a previous publication [5].
The standard method involves the use of sodium carboxyl-
ate (NaX or Na2X2) which reacts with the diaquadiamine
Pt(II) complex in water.
2.3. Crystallographic measurements and structure resolution
The four crystals were recrystallized in water or a mixture
of water and acetone. They were selected after examination
under a polarizing microscope for homogeneity. The data
collection was made at room temperature on a Bruker P4 dif-
fractometer equipped with graphite-monochromatized Mo
Ka radiation. The XSCANS program [9] was used for centering
the crystals, the data collections and the reducing process.
The unit cell parameters were obtained by least-squares
refinement of the angles 2h, x and v for well-centered reflec-
tions. The coordinates of the heavy atoms were determined
from direct methods and the positions of all the other atoms
H2O
___
cis-PtA2I2
+
2AgNO3
→
cis-[PtA2(H2O)2] (NO3)2
↓ Na2X2
+ 2AgI ↓
cis-PtA2X2 + 2NaNO3
In this reaction, the silver salt should not be in excess, since
other species will be produced. Furthermore, since the

4098
F.D. Rochon, G. Massarweh / Inorganica Chimica Acta 359 (2006) 4095–4104
diaminediiodo compound is very insoluble in water, the
reaction in water is very slow. The reaction is faster in ace-
tone and a small excess of the silver salt can then be used,
which can increase the yield of the intermediate ionic com-
pound. The second step is done in water and the reaction is
quite long depending on the two ligands. It is difficult to
evaluate the extent of the reaction since all the products
are soluble in water. Furthermore, the complete separation
of the Pt compound from sodium nitrate is difficult. There-
fore, the overall yields (from K2[PtCl4]) for this method are
not very high, usually between 10% and 50% in water
(depending on the two ligands) or slightly higher when
the reaction with the silver salt is performed in acetone.
A study of the products by 195Pt NMR spectroscopy has
shown the presence of more than one species for a few pairs
of ligands [5].
ceeding to the second step of the reactions. The overall
yields (from K2[PtCl4]) are about 75%.
The crystal structure of one of the intermediate silver
compounds was determined by X-ray diffraction methods.
The results have shown that the crystal Ag2(1,1-CBDCA)
(1,1-CBDCA = 1,1-cyclobutyldicarboxylate) which was
recrystallized in water is not hydrated. Three diaminedi-
carboxylato Pt(II) compounds were also studied by crystal-
lographic methods. The results have confirmed the
expected structures. The three Pt(II) complexes do not con-
tain any water of hydration contrary to the reported struc-
ture Pt(EtNH2)2(1,1-CBDCA) Æ H2O [5].
Compounds with the following amines were studied:
NH3, cyclopentylamine (cpa), ethylenediamine (en), 1,2-
diaminopropane (Meen), N,N-dimethylethylenediamine
(Me2en) and 1,2-diaminocyclohexane (dach). Only dicarb-
oxylate ligands were studied: 1,1-cyclobutanedicarboxy-
late, trans-1,2-cyclobutanedicarboxylate (1,2-CBDCA),
malonate (mal), butylmalonate (Bumal) and benzylmalo-
nate (Bzmal). Several other compounds were synthesized
(ex. with sec-butylamine), but most of these could not be
characterized in solution by NMR spectroscopy, since their
solubility is too low. A few experiments were performed
with the ligand 1,1-cyclohexanediacetate. This ligand forms
an eight-membered chelate and the Pt(II) complexes do not
seem very stable. Multinuclear magnetic resonance studies
of the products have shown the presence of several species
in solution, most without the presence of the diacetate
ligand.
In the second method, silver sulfate is used instead of sil-
ver nitrate and barium carboxylate (prepared in situ) is
used instead of the sodium salt. The reaction is done in
water.
cis-PtA2I2
+
Ag2SO4
cis-[PtA2(H2O)2] (SO4) + 2AgI↓
↓ BaX2
cis-PtA2X2
+ BaSO4 ↓
The diaqua species contains also some cis-PtA2(H2O)-
(SO4). This method is faster, easier to control since the pres-
ence of BaSO4 can be observed and the products are easier
to purify. The yields (from K2[PtCl4]) vary between about
45% and 88%. We have shown that this method is superior
to the above one, since it produces pure complexes, while
the method described above often lead to a mixture of com-
pounds with some of the different ligands. But this second
method cannot be used for the synthesis of the oxalate
complexes, since barium oxalate is too insoluble in water.
Furthermore, these two methods cannot be used for li-
gands containing groups which can be attacked in basic
medium.
3.2. Crystal structures
3.2.1. Ag2(1,1-CBDCA) (1)
The results of the crystal structure determination of the
1,1-CBDCA silver complex have shown that there are four
independent Ag atoms and two 1,1-CBDCA ligands in the
unit cell. The compound did not crystallize with any mole-
cule of solvent and the stoichiometry of the compound is
Ag2(1,1-CBDCA). The independent pattern and a few
more atoms (Ag30, Ag40, O30, O40 and C20) are shown in
Fig. 1.
The most important bond distances and angles are listed
in Table 2. The compound has an interesting 3-D extended
structure. There seems to be metal–metal bonds although it
is difficult to evaluate. The sum of the van der Waals radii
We have now developed a new method where the
intermediate is the silver carboxylato compound which
can be isolated and characterized. The reactions are as
follows:
H2O
2AgNO3 þ M2X2 ! Ag2X2 # þ2MðNO3Þ ðM ¼ Na or KÞ
0
˚
of Ag atoms is about 3.4 A. The Ag1–Ag2 and Ag3–Ag3
˚
H2O
distances are relatively short, 2.9284(6) and 2.9519(7) A,
respectively. The other distances are longer, with Ag4–
Ag4 and Ag3–Ag3 = 3.1962(8) and 3.2835(7) A, respec-
tively, probably too long to suggest metal–metal bonds.
cis-PtA2I2 þ Ag2X2 ! cis-PtA2X2 þ 2AgI #
0
00
˚
The second reaction takes about 2 days in water. The addi-
tion of acetone will accelerate the reaction in the formation
of the diaminedicarboxylato complex. In a water–acetone
ratio of 1:4, the reaction time was reduced to about 2 h.
If the carboxylate and the amine are monodentate ligands,
the addition of acetone is not recommended, since the cis-
Pt(II) compound can isomerize to the trans isomer in ace-
tone. The intermediate silver carboxylato compound must
be isolated and purified by washing with water before pro-
˚
Therefore, the Ag–Ag distances shorter than 2.96 A were
linked in Fig. 1.
The environment around each Ag atom is quite differ-
ent. Again, it is difficult to evaluate some bonds since the
distances Ag–O vary. In the following discussion, we will
˚
assume a maximum Ag–O bond distance of 2.32 A. There
are two such Ag–O bonds around each Ag atom, with O–

F.D. Rochon, G. Massarweh / Inorganica Chimica Acta 359 (2006) 4095–4104
4099
Table 2
˚
Selected bond distances (A) and angles (ꢁ)
Ag2(C4H6(COO)2) (1)
Ag1–O1
Ag1–O(6)
Ag1–O(60)
Ag3–O30
Ag3–O4
Ag3–O50
Ag3–O70
Ag3–Ag30
O2–C1
2.195(3)
2.267(3)
2.454(3)
2.282(3)
2.293(3)
2.556(3)
2.569(3)
2.9520(6)
1.241(5)
1.261(5)
1.259(5)
1.263(5)
Ag2–O2
Ag2–O5
Ag2–O30
Ag4–O8
Ag4–O70
Ag4–O700
Ag1–Ag2
O1–C1
O3–C2
O5–C3
O7–C4
C–C (ave.)
2.165(3)
2.195(3)
2.535(3)
2.235(3)
2.310(3)
2.591(3)
2.9284(6)
1.248(5)
1.263(5)
1.255(5)
1.267(5)
1.537(7)
O4–C2
O6–C3
O8–C4
O1–Ag1–O6
154.00(12)
151.19(12)
82.90(9)
O2–Ag2–O5
O70–Ag4–O8
Ag1–Ag2–O (ave.)
Ag–O–C
165.76(12)
151.19(11)
82.90(9)
111.6(3)–
128.1(3)
88.5(3)–
90.7(4)
O30–Ag3–O4
Ag1–Ag2–O (ave.)
Ag30–Ag3–O (ave.)
77.00(9)
O–C–O (ave.)
125.1(4)
C–C–C (four-
membered ring)
C–C–C (others)
106.4(3)–
118.2(3)
Fig. 1. Labeled diagram of Ag2(1,1-CBDCA) (the ellipsoids correspond to
˚
30% probability). Ag–Ag distances shorter than 2.96 A were linked.
Pt(en)(1,1-CBDCA) (2)
Pt–O1
O1–C5
N1–C6
C1–C5
C1–C4
C3–C4
2.009(4)
1.302(7)
1.537(13)
1.512(8)
1.538(12)
1.497(19)
Pt–N1
O2–C5
N1–C7
C1–C2
C2–C3
C6–C70
2.028(5)
1.226(8)
1.505(12)
1.565(12)
1.479(19)
1.486(16)
Ag–O angles ranging from 151.2ꢁ to 165.8ꢁ (Table 2). In
addition, there are a few other O atoms around each Ag
˚
atom at distances between 2.45 and 2.59 A, suggesting
some weaker bonds. Furthermore, if we assume Ag–Ag
O1–Pt–O10
N1–Pt–N10
Pt–O1–C5
Pt–N1–C7
C5–C1–C4
C2–C1–C4
C1–C4–C3
O1–C5–O2
O1–C5–C1
N1–C7–C60
91.8(3)
84.8(3)
123.5(4)
108.1(5)
114.3(4)
88.6(7)
O1–Pt–N1
O1–Pt–N10
Pt–N1–C6
C5–C1–C50
C5–C1–C2
C1–C2–C3
C2–C3–C4
O2–C5–C1
N1–C6–C70
91.6(2)
175.2(2)
105.8(6)
112.8(7)
112.3(4)
88.8(9)
93.5(9)
121.0(6)
106.9(9)
˚
bonds for distances shorter that 2.96 A, we can suggest
metal–metal bonds between Ag1 and Ag2 and between
Ag3 and another Ag3. The angles Ag–Ag–O for these
atoms are between 71.18(9)ꢁ and 83.04(9)ꢁ. The fourth sil-
ver atom Ag4 does not seem to be involved in metal–metal
bonds.
89.2(8)
120.1(7)
118.9(6)
105.1(8)
Each carboxylato group forms bonds with two different
Ag atoms as clearly shown in Fig. 1. The angles Ag–O–C
vary between 111.6(3)ꢁ and 128.1(3)ꢁ. The C–O bonds are
˚
Pt(Meen)(1,1-CBDCA) (3)
Pt–O1
O1–C5
N1–C61
C1–C5
in the range 1.241(5)–1.267(5) A and the average carboxy-
2.021(8)
1.286(12)
1.50(3)
Pt–N1
O2–C5
N1–C62
C–C (cyclobut.
ave.)
2.033(9)
1.239(12)
1.49(3)
lato O–C–O angle is 125.1(4)ꢁ. The C atoms of the four-
membered rings are in a plane (mean deviation of 0.094
˚
and 0.087 A) and the internal C–C–C angles vary between
1.534(12)
1.56(2)
88.5(3)ꢁ and 90.7(4)ꢁ. The dihedral angles between the two
carboxylato planes with its four-membered ring plane are
110.6ꢁ and 129.3ꢁ for the C11 ring and 46.3ꢁ and 84.4ꢁ
for the C21 ring plane. The two independent four-mem-
bered rings are almost co-planar with a dihedral angle of
10.9ꢁ. The two carboxylato groups on each 1,1-CBDCA
ligand are almost perpendicular to each other. The dihedral
angle between the C1 O1 O2 and the C2 O3 O4 planes is
91.2ꢁ, while it is 104.9ꢁ between the C3 O5 O6 and C4
O7 O8 planes.
C61–C620
1.61(3)
C6–C7 (ave.)
1.45(4)
O1–Pt–O10
N1–Pt–N10
Pt–O1–C5
87.8(5)
83.4(5)
O1–Pt–N1
O1–Pt–N10
Pt–N1–C61
C5–C1–C50
C5–C1–C2
C1–C2–C3
C2–C3–C4
O2–C5–C1
N1–C61–C620
N1–C61–C7
94.3(4)
177.2(3)
109.2(12)
111.1(11)
111.1(7)
93.6(12)
89.9(10)
119.6(9)
104(2)
119.1(6)
112.5(11)
116.0(7)
89.7(10)
86.9(10)
121.9(9)
118.5(9)
105(2)
Pt–N1–C62
C5–C1–C4
C2–C1–C4
C1–C4–C3
O1–C5–O2
O1–C5–C1
N1–C62–C610
N1–C62–C7
114(2)
115(2)
3.2.2. cis-Pt(amine)2 (dicarboxylato)
The crystal structure of the compounds Pt(en)(1,1-
CBDCA) (2), Pt(Meen)(1,1-CBDCA) (3) and Pt(en)(Bz-
mal) (4) were studied by X-ray diffraction methods. The
three crystals were recrystallized in water or water–acetone
Pt(en)(Bzmal) (4)
Pt–O1
Pt–N1
2.046(5)
2.043(9)
Pt–O2
Pt–N2
1.986(7)
2.007(7)
(continued on next page)

4100
F.D. Rochon, G. Massarweh / Inorganica Chimica Acta 359 (2006) 4095–4104
Table 2 (continued)
are 105.1(8)ꢁ and 106.9(9)ꢁ. In the second chelate, the strain
is smaller, since it is a six-membered ring. The internal
angles are 123.5(4)ꢁ at O1, 118.9(6)ꢁ at C5 and 112.8(7)ꢁ
at C1. The angles inside the four-membered cyclobutane
ring are much smaller and vary between 88.6(7)ꢁ and
93.5(9)ꢁ.
Pt(en)(Bzmal) (4)
O@C (ave.)
N1–C5
1.227(12)
1.480(12)
1.533(15)
O–C (ave.)
N1–C6
C–C (ave.
aromatic)
1.310(11)
1.449(12)
1.367(15)
C–C (ave.)
O1–Pt–O2
N1–Pt–O1
N2–Pt–O2
90.5(2)
94.5(3)
91.1(3)
N1–Pt–N2
N1–Pt–O2
N2–Pt–O1
Pt–O2–C2
Pt–N2–C6
C1–C3–C2
C3–C4–C11
C1–C3–C2
83.8(3)
174.9(3)
172.6(2)
124.7(5)
111.0(5)
108.1(6)
115.1(10)
108.1(6)
The conformation of the molecule is clearly seen on
Fig. 2. The six-membered carboxylato chelate ring has a
boat conformation. The best plane was calculated through
the four atoms O1, O10, C5 and C50 and the Pt and C1
atoms are on the same side of the plane with deviations
Pt–O1–C1
Pt–N1–C5
O–C–O (ave.)
N–C–C (ave.)
O–C–C (ave.)
120.8(4)
104.2(6)
121.4(7)
107.9(7)
116.2(8)
˚
of 0.444 and 0.623 A, respectively. This boat conformation
was also observed in the structure of Pt(EtNH2)2(1,1-
CBDCA) Æ H2O [5]. The two carbonyl atoms O2 are ori-
ented towards the other side of the plane (deviation of
C–C3–C2 (ave.) 112.2(13)
C–C–C (ave. aromatic) 120.0(10)
˚
mixture, but the structures do not contain any molecule of
solvent.
ꢀ0.470 A).
The environment around the –NH2 groups was exam-
ined for possible intermolecular H-bonds. There are two
The crystal Pt(en)(1,1-CBDCA) (2) was shown to belong
to a centrosymmetric space group. The Pt atom and the
four C atoms of the cyclobutyl ring are located in a crystal-
lographic plane, resulting in disorders of the two methylene
groups of the ethylenediamine ligand. Its structure is
shown in Fig. 2, including the disorder on the amine ligand.
The best coordination plane around the Pt atom was calcu-
0
˚
short
0contacts
with
N1ꢃ ꢃ ꢃO1 = 2.944 A
and
˚
N1ꢃ ꢃ ꢃO2 = 2.879 A. The angles are favorable for H bonds
involving N1 with O10 with Pt–N1ꢃ ꢃ ꢃO10 = 119.0ꢁ, C6(or
7)–N1ꢃ ꢃ ꢃO10 = 107.4ꢁ (ave.) and C50–O10ꢃ ꢃ ꢃN1 = 107.9ꢁ.
The angles involving possible H-bonds with O20 are less
favorable with Pt–N1ꢃ ꢃ ꢃO20 = 126.4ꢁ, C6(or 7)–
N1ꢃ ꢃ ꢃO20 = 84.6ꢁ (ave.) and C50–O10ꢃ ꢃ ꢃN1 = 159.8ꢁ. The
reported compound Pt(EtNH2)2(1,1-CBDCA) crystallized
with a molecule of water, which was involved in an exten-
sive H-bonding system. There are no molecules of solvent
in crystal 2, as observed also in the reported structure of
Pt(NH3)2(1,1-CBDCA) [11].
˚
lated (mean deviation of 0.023 A) and its dihedral angle
with the cyclobutane ring is 90ꢁ (by symmetry).
The bond lengths and angles are listed in Table 2. The
angles around the Pt angles are normal with the five-mem-
bered chelate angle of 84.8(3)ꢁ and the dicarboxylato six-
membered chelate angle is 91.8(3)ꢁ. The other cis angles
are 91.6(2)ꢁ, while the trans angles are 175.2(2)ꢁ. The Pt–
O bond distances are 2.009(4), while the Pt–N bonds are
In the crystal structure of Pt(Meen)(1,1-CBDCA) (3),
the –CH3 group on the amine ligand is located on a C atom
and the molecule is chiral. The compound belongs to a cen-
trosymmetric space group and the crystal is disordered.
Two positions (50:50) were found for the methylene and
the methyl groups of the Meen ligand. The disorder is
shown in Fig. 3. Again, the Pt atom and the four C atoms
of the cyclobutyl group are on a mirror plane. Therefore,
the dihedral angle between the Pt plane (mean deviation
˚
2.028(5) A, in agreement with published values on similar
complexes [5,11–15]. The carbonyl bonds O2–C5 are
shorter (1.226(8) A) than the O1–C5 (1.302(7) A) distances
as expected. The N–C bond lengths are slightly long
˚
˚
˚
(1.505(12) and 1.537(13) A) probably due to the strain
inside the chelate five-membered ring. The disorder on
the C atoms increases the standard deviations on these
bonds. The internal chelate ring angles at the N atoms
are 108.1(5)ꢁ and 105.8(6)ꢁ, while those at the C atoms
˚
is 0.0126 A) and the cyclobutyl ring is again 90ꢁ by
symmetry.
Fig. 2. Labeled diagram of Pt(en)(1,1-CBDCA) (2 conformations for the
C atoms of en, and the ellipsoids correspond to 30% probability).
Fig. 3. Labeled diagram of Pt(Meen)(1,1-CBDCA) (2 conformations for
the C atoms of Meen and the ellipsoids correspond to 30% probability).

F.D. Rochon, G. Massarweh / Inorganica Chimica Acta 359 (2006) 4095–4104
4101
The bond distances and angles in crystal 3 are shown in
Table 2. The chelate angles around the Pt atom are smaller
than the other cis angles, although the five-membered che-
late angle is smaller (83.4(5)ꢁ) than the six-membered che-
late angle (87.8(5)ꢁ). The other cis angles are 94.3(4)ꢁ and
the trans angles are 177.2(3)ꢁ. The Pt–O bond distances
plane and the coordination plane is 19.7ꢁ. The two car-
bonyl atoms O3 and O4 are oriented towards the other side
˚
of the plane (deviations of 0.283 and 0.781 A, respectively)
and form intermolecular H-bonds with the –NH2 groups.
The distance N1ꢃ ꢃ ꢃO40 is 2.859 A with angles Pt–
˚
N1ꢃ ꢃ ꢃO40 = 115.1ꢁ and C5–N1ꢃ ꢃ ꢃO40 = 91.7ꢁ, while the
angle C20–O40ꢃ ꢃ ꢃN1 is 136.5ꢁ. The distance N2ꢃ ꢃ ꢃO300 is
˚
˚
are 2.021(8) A, while the Pt–N bonds are 2.033(9) A. The
average internal angle inside the cyclobutyl ring is
00
˚
2.971 A with favorable angles Pt–N2ꢃ ꢃ ꢃO3 = 110.23ꢁ,
90.0(11)ꢁ. The O1–C5 bond is longer (1.286(12) A) than
C6–N2ꢃ ꢃ ꢃO300 = 109.9ꢁ
and
C100–O300ꢃ ꢃ ꢃN2 = 131.2ꢁ.
˚
˚
the C5–O2 bond (1.239(12) A) as expected.
Therefore, each amine group is involved in the intermolec-
ular H-bonding system with the carbonyl O atoms. This H-
bonding pattern is slightly different from those of crystals 2
and 3. The aromatic ring forms a dihedral angle of 43.5ꢁ
with the Pt plane and 34.7ꢁ with the plane of the 4 planar
atoms of the boat conformer.
The carboxylato chelate ring has also a boat conforma-
tion as in crystal 2. The best plane was calculated through
the four atoms O1, O10, C5 and C50 and the Pt and C1
atoms are on the same side of the plane with deviations
˚
of ꢀ0.907 and ꢀ0.627 A, respectively. The two carbonyl
atoms O2 are oriented towards the other side of the plane
˚
(deviation of 0.458 A) and form intermolecular H-bonds
3.3. NMR
0
˚
with the –NH2 groups. The distance N1ꢃ ꢃ ꢃO2 is 2.977 A
with angles Pt–N1ꢃ ꢃ ꢃO20 = 105.4ꢁ, C6–N1ꢃ ꢃ ꢃO20 = 101.2ꢁ
(ave.) and C5–O2ꢃ ꢃ ꢃN1 = 121.6ꢁ, while the distance
The majority of the multinuclear magnetic resonance
spectra of the diamine dicarboxylato complexes were mea-
sured in D2O. Since most of the compounds are only spar-
ingly soluble in water, very long accumulating times were
required especially for the 195Pt and 13C NMR spectra.
The solutions were often heated to about 40–45ꢁ in order
to increase the solubility. One 1H NMR spectrum was mea-
sured at 50ꢁ. Even then, some weaker signals (especially in
13C NMR) could not be detected. A few compounds were
too insoluble for NMR spectroscopy. Several organic sol-
vents were tested, but the solubilities were even lower. A
few spectra were measured in a mixture of D2O with an
organic solvent. Some of the complexes decomposed when
heated.
N1ꢃ ꢃ ꢃO200 is 2.995 A with favorable angles Pt–
˚
N1ꢃ ꢃ ꢃO200 = 116.2ꢁ, C6–N1ꢃ ꢃ ꢃO200 = 101.9ꢁ (ave.) and
C5–O200ꢃ ꢃ ꢃN1 = 127.2ꢁ. Therefore, all the amine protons
are involved in the H-bonding system with the carbonyl
O2 atoms. This H-bonding pattern is quite different from
the one of the ethylenediamine analogue described above
(crystal 2).
The third Pt(II) compound Pt(en)(Bzmal) (4) belongs to
a non-symmetric space group. A drawing of the molecule is
shown in Fig. 4. The quality of this crystal was not as good
as for the others. The average bond distances are Pt–
˚
N = 2.025(8) and Pt–O = 2.016(6) A. The N–Pt–N chelate
angle is smaller (83.8(3)ꢁ) than the six-membered chelate
ring angle O–Pt–O (90.5(2)ꢁ). The other cis angles are
92.8(3)ꢁ (ave.), while the average trans angle is 173.8(3)ꢁ.
3.3.1. 195Pt NMR
Most of the 195Pt NMR spectra were recorded over-
night. The 195Pt chemical shifts of the Pt(II) compounds
are shown in Table 3. Most of the complexes have shown
only one signal. They can be approximately classified into
three groups according to the amines. The complexes con-
taining NH3 are observed at lowest fields (ꢀ1610 to
ꢀ1742 ppm), those containing a monodentate primary
amine (cyclopentylamine) (ꢀ1646 to ꢀ1861 ppm) and
finally the bidentate amines, ethylenediamine, its methyl
derivatives and dach (ꢀ1851 to ꢀ1978 ppm) compounds.
The presence of a five-membered chelate (like ethylenedia-
mine) moves the chemical shifts to higher fields because of
the strain inside the ring and the increased electron density
on the Pt atom caused by the chelate effect. All the carb-
oxylato ligands are bidentate and form six-membered che-
late rings, except the ligand 1,2-CBDCA, which forms a
seven-membered chelate ring upon complexation. This
removes the strain inside the dicarboxylate chelate ring
along with a decrease of stability due to the chelate effect
and the chemical shifts of all the 1,2-CBDCA complexes
are observed at lower fields than the others.
˚
The average C@O bond is shorter (1.227(12) A) than the
˚
two other C–O bonds (ave. 1.310(11) A) as expected. The
other bond distances and angles are listed in Table 2.
The carboxylato chelate ring has also a boat conforma-
tion as in crystals 2 and 3. The best plane was calculated
through the four atoms O1, O2, C1 and C2 (mean devia-
˚
tion = 0.039 A) and the Pt and C3 atoms are on the same
side of the plane with deviations of ꢀ0.528 and
˚
ꢀ0.752 A, respectively. The dihedral angle between this
It is difficult to compare the chemical shifts of the differ-
ent compounds, since several are very different. We might
Fig. 4. Labeled diagram of Pt(en)(Bzmalonato) (the ellipsoids correspond
to 30% probability).

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F.D. Rochon, G. Massarweh / Inorganica Chimica Acta 359 (2006) 4095–4104
Table 3
d(Pt) (ppm), d(H) (ppm) and 2J(195Pt–1HN) (Hz) of the complexes in D2O
Amine
Carboxylato
d(Pt)
d (1HN)
2J(195Pt–1H)
NH3
NH3
NH3
NH3
cpa
cpa
cpa
en
en
1,1-CBDCA
1,2-CBDCA
malonato
Bumalonato
1,2-CBDCA
malonato
Bzmalonato
1,1-CBDCA
1,2-CBDCA
malonato
Bumalonato
Bzmalonato
1,1-CBDCA
1.2-CBDCA
malonato
Bumalonato
Bzmalonato
1,1-CBDCA
1,2-CBDCA
malonato
Bumalonato
Bzmalonato
1,1-CBDCA
1,2-CBDCA
malonato
ꢀ1742
4.025
3.945
5.3
72
99
ꢀ1610, ꢀ1506 (30%)
ꢀ1686
4.077
90
ꢀ1647, ꢀ1720 (20%)
ꢀ1861
5.4
ꢀ1908
ꢀ1860
4.094
5.310
en
en
en
ꢀ1997
68
65
ꢀ1954
5.28 (D2O), 4.80 (acetone)
5.15, 5.47, 5.58
5.5, 5.3
5.05, 5.25, 5.44
5.4
ꢀ1907
Meen
Meen
Meen
Meen
Meen
Me2en
Me2en
Me2en
Me2en
Me2en
dach
dach
dach
dach
ꢀ1951
ꢀ1867
ꢀ1963
72
70
ꢀ1914
ꢀ1916
ꢀ1968
5.56
5.21
ꢀ1851
ꢀ1978
ꢀ1930
ꢀ1928
5.33
ꢀ1946
ꢀ1888, ꢀ1713 (35%)
5.43
4.28, 4.39
5.56
63
62
Bumalonato
look at the malonato complexes and its benzyl and butyl
derivatives. The presence of a butyl or benzyl group on
the malonato ligand seems to shift the resonance towards
lower fields. This might be caused by the solvent effect.
For the malonato compounds, the solvent (water) can
approach the metal atom on both sides of the Pt(II) plane,
which increases the electron density on the Pt atom. For
the benzyl and butyl malonato derivatives, the bulkiness
of these ligands reduces the extent of hydration around
the Pt atom, thus reducing the electron density around
the metal atom, when compared to the unsubstituted malo-
nato ligand. A shift towards lower fields is often observed
when the bulkiness around the Pt atom increases. Similar
results were obtained for the Me2NH and Me4en com-
plexes [5]. It is interesting to note that the 195Pt resonances
of the butylmalonato and benzylmalonato complexes are
almost identical indicating that the presence of an electro-
repulsive or electroattracting group on the carboxylato
ligand does not seem to have an important influence on
the 195Pt chemical shifts. But the butyl or the benzyl groups
are quite far for the Pt atom.
It might be different for the amine ligand. For the 1,1-
CBDCA complexes of ethylenediamine (d = ꢀ1908 ppm)
and its methyl (d = ꢀ1951 ppm) and dimethyl
(d = ꢀ1972 ppm) derivatives, a shift towards higher fields
can be observed when methyl groups are present. For the
Me4en complex, the reported value is ꢀ1966 ppm [5]. The
presence of electrorepulsive groups on the amine should
increase the strength of the Pt–N r bond, therefore increas-
ing the electron density on the Pt atom resulting in a shield-
ing on the metal as observed in 195Pt NMR.
The NH3, cpa, and dach Pt(II) complexes containing
1,2-CBDCA have shown a second signal (Table 3), which
could be attributed to some hydrolyzed or aqua species.
In the Pt(NH3)2 system, the diaqua compound cis-
[Pt(NH3)2(D2O)2]2+ has been reported at ꢀ1590 [16], the
monohydroxo-bridged
dimer
cis-[Pt(NH3)2(D2O)(l-
OH)Pt(NH3)2(D2O)]3+ between ꢀ1516 and ꢀ1547 depend-
ing on the pH [17] and the cyclic trimer at ꢀ1499 ppm [17–
19]. The cis-[Pt(cpa)2(D2O)2]2+ compound was found at
ꢀ1721 ppm [20] very close to the second peak observed
for the cpa-1,2-CBDCA compound (ꢀ1720 ppm). For the
dach compound, we have not found any report on mono-
hydroxo-bridged dimers, but their chemical shifts should
be around the observed second signal (ꢀ1713 ppm).
In the first experiment on the synthesis of the complex
Pt(Me2en)(1,2-CBDCA), three signals were observed in
195Pt NMR at ꢀ1861, ꢀ1851 and ꢀ1738 ppm. The sample
was probably heated for a longer time before the measure-
ment in order to dissolve it. The monohydroxo-bridged
dimer with Me2en was reported between ꢀ1740 and
ꢀ1764 (several isomers [21]), close to the lowest field value
observed in the NMR spectrum of Pt(Me2en)(1,2-CBDCA)
(ꢀ1738 ppm). The diaqua compound [Pt(Me2en)(D2O)2]2+
was reported at ꢀ1867 ppm [21], close to the ꢀ1861 found
here.
The bidentate ligand 1,2-CBDCA forms upon coordina-
tion a seven-membered chelate, whose stability is much
decreased compared to five or six-membered chelates.
Therefore, its reaction with Pt(II) is probably slower and
other hydrolyzed or aqua species are observed in solution.
Similar results were reported for two other dicarboxylato

F.D. Rochon, G. Massarweh / Inorganica Chimica Acta 359 (2006) 4095–4104
4103
ligands, (1,1-cyclopentanediacetato and1,1-cyclohexanedi-
acetato) which form eight-membered chelates [5].
weaker peaks were doubtful and are not included in Sec-
tion 2. For this reason, no J(195Pt–13C) coupling constants
are reported. The carboxylato C atoms are observed at
around 180 ppm and the signal is extremely low. In the
Meen and Me2en complexes, the two carboxylato C atoms
are not equivalent. For Pt(Me2en)(1,1-CBDCA), two well
resolved signals were observed at 181.67 and 181.83 ppm.
As mentioned earlier, we have performed several exper-
iments with the ligand 1,1-cyclohexanediacetate. Multinu-
clear magnetic resonance studies of the products have
shown the presence of several species in solution, most
without the presence of the diacetate ligand.
1
3.3.2. H and 13C NMR
4. Conclusion
1
The H NMR signals are listed in Section 2. For a few
complexes, the malonate protons exchange with the D atoms
of the solvent. Therefore, the signals of –CH2 or –CH groups
of the malonato derivatives were often weaker than
expected. The N–H groups of the bonded amines could be
observed for several complexes and are shown in Table 3.
Their chemical shifts vary between 3.95 and 5.58 ppm.
Exchange with D2O is usually limited for Pt(II) bonded
amines. For several compounds, they were not observed.
The long accumulation times along with slight heating of
the solutions in order to dissolve as much sample as possible
increased the amine proton exchange with D2O. A few cou-
The already reported method for the synthesis of Pt-
(amine)2(RCOO)2 using silver sulfate and barium carboxyl-
ate has been found superior to the conventional method
involving the reaction of the diaqua species [Pt(amine)2-
(H2O)2](NO3)2 with the carboxylate salt of sodium or
potassium. This latter method produces usually a mixture
of products and the yields of Pt(amine)2(RCOO)2 are low
(ꢁ30%), especially for monodentate ligands. The yields
using the barium carboxylate method are better, usually
40–60% and with a few bidentate ligands up to 85%. The
new method described in this paper is slightly different,
since it involves synthesizing the silver carboxylate interme-
diate, which is formed quite rapidly. The crystal structure
of Ag2(1,1-cyclobutyldicarboxylate) was determined. Sur-
prisingly, this complex is quite stable (few months) in the
presence of light. It was recrystallized in water and the
compound is free from molecules of solvent. Its reaction
with Pt(amine)2I2 in water is simple. Both reactants are
dried and can be easily weighed. If the reaction is done in
a mixture of water and acetone, the reaction is faster, but
acetone should be used with care when monodentate
amines and carboxylate ligands are used, since isomeriza-
tion may occur. The product Pt(amine)2(RCOO)2 is pure
after the removal of AgI. The yields with bidentate carbox-
ylate ligands are excellent (ꢁ80%).
2
pling constants J(195Pt–1HN) could be calculated, but the
values in Table 3 are very approximate. These vary between
62 and 99 Hz. For cis-Pt(amine)2I2 complexes with monod-
entate amines, values between 65 and 70 Hz were reported
[8].
The ligand 1,2-diaminopropane (Meen) is a chiral mole-
cule. When bonded to Pt(II), the H atoms on the –NH2
and –CH2 groups are not equivalent, since one H atom is
located on the same side as the –CH3 group and the second
is on the opposite side. In the complex, Pt(Meen)(mal), the
two H atoms in the malonato ligand are not equivalent, since
one H atom is on the same side as the –CH3 group and the
second is on the opposite side. These are observed at 3.47
and 3.51 ppm, with relative intensity, respectively, of 2:1.
Furthermore, in the Pt(II)–Meen complexes, the CH group
in the n-butylmalonate and benzylmalonate ligands is pro-
chiral. Therefore, the complexes Pt(Meen)(Bumal or Bzmal)
will have four diastereoisomers with two pairs of enantio-
The NMR characterization of these compounds is diffi-
cult due to their low solubility. Water was found to be the
best solvent, although the spectra of several compounds
could not be measured, since the aqueous concentration
was too low. For the monodentate amine ligands, the com-
plexes containing the moiety Pt(NH3)2 were found more
soluble than the Pt(cyclopentylamine)2 species. The ethy-
lenediamine complexes and its derivatives are slightly more
soluble than the Pt(NH3)2 and Pt(cpa)2 species. In the eth-
ylenediamine series, the Meen complexes were found to be
the least soluble. Finally, the dach complexes are probably
the least soluble in the reported series.
1
mers. This is clearly seen in the H NMR spectra of these
molecules, especially for the two –CH3 groups. Two well-
defined triplets at 0.751 and 0.810 ppm (–CH3 of Bumal)
and two doublets at 1.166 and 1.188 ppm (–CH3 of Meen)
are observed in the 1H spectrum of Pt(Meen)(Bumal). Two
triplets at 3.342 and 3.357 ppm are also observed for the
CH butylmalonato ligand.
The coupling constants 3J(195Pt–1H) are usually difficult
to determine for these type of complexes on a 300 MHz
instrument, especially since the compounds are quite insol-
uble. They were well observed in the complex of Pt(en)-
The 195Pt chemical shifts are observed at higher fields
when complexation involves the formation of five-mem-
bered chelates as observed for the ethylenediamine deriva-
tives, compared to the monodentate cyclopentylamine
complexes. The same observation can be made for the
dicarboxylato complexes. The signals of the six-membered
chelates are found at higher fields than the seven-mem-
bered chelates as observed for the 1,1-CBDCA and the
1,2-CBDCA complexes. The 1,2-CBDCA compounds
might contain other Pt(II) species, especially aqua or
3
(mal) where the J(195Pt–1H) was found to be 46 Hz. They
could also be calculated for the compound Pt(en)(1,2-
CBDCA) (48 Hz). For comparison, values between 44
and 54 Hz have been reported in the literature for other
complexes containing the moiety Pt(en) [22].
The accumulation times for the 13C NMR spectra were
48–72 h. The background noise was still important. Several

4104
F.D. Rochon, G. Massarweh / Inorganica Chimica Acta 359 (2006) 4095–4104
[8] F.R. Rochon, V. Buculei, Inorg. Chim. Acta 357 (8) (2004) 2218.
[9] XSCANS, Version 2.2, Siemens Analytical Instruments Inc., Madison,
WI, USA.
hydrolyzed compounds, where the dicarboxylato ligand is
absent.
[10] SHELXTL, Version 5, Siemens Analytical Instruments Inc., Madison,
WI, USA.
5. Supplementary material
[11] B. Beagley, D.W.J. Cruickshank, C.A. McAuliffe, R.G. Pritchard,
A.M. Zaki, R.L. Beddoes, R.J. Cernik, O.S. Mills, J. Mol. Struct.
130 (1985) 97.
[12] S. Neidle, I.M. Ismail, P.J. Sadler, J. Inorg. Biochem. 13 (1980)
205.
[13] F.D. Rochon, R. Melanson, J.-P. Macquet, F. Belanger-Gariepy,
A.L. Beauchamp, Inorg. Chim. Acta 108 (1985) 1.
[14] F.D. Rochon, R. Melanson, J.-P. Macquet, F. Belanger-Gariepy,
A.L. Beauchamp, Inorg. Chim. Acta 108 (1985) 17.
[15] S.D. Cutbush, R. Kuroda, S. Neidle, A.B. Robins, J. Inorg. Biochem.
18 (1983) 213.
The four CIF lists have been deposited at the Cambridge
Structural Database, CCDC 298125–298128.
Acknowledgement
The authors are grateful to the Natural Sciences and
Engineering Research Council of Canada for financial sup-
port of the project.
[16] I.M. Ismail, P.J. Sadler, Platinum, Gold and Other Metal Chemo-
therapeutic Agents, American Chemical Society, Washington, DC,
1983, pp. 171–190.
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