Synthesis and study of Pt(II)-aromatic amines complexes of the types cis- and trans-Pt(amine)2(NO3)2 and cis-Pt(amine)2(R(COO)2)

Article abstract of DOI:10.1016/j.ica.2007.09.024

Complexes of the types cis- and trans-Pt(amine)₂(NO₃)₂ with amines containing a phenyl group were synthesized and studied mainly by IR and multinuclear magnetic resonance spectroscopies. The cis complexes could be synthesized pure only with the amines of the type Ph-R-NH₂ (R = alkyl), while pure trans compounds were synthesized with all the studied amines. In ¹⁹⁵Pt NMR spectroscopy, the dinitrato complexes of the amines Ph-R-NH₂ were observed around -1700 ppm for the cis isomers and at about -1580 for the trans complexes. For the other amines, where a phenyl ring is directly attached to the amino group, the signals were observed at lower fields, -1528 ppm for cis-Pt(PhNH₂)(NO₃)₂ and around -1450 ppm for all the trans isomers. There is a linear relationship between the δ(Pt) of the Pt(amine)₂(NO₃)₂ complexes and the pK_a of the protonated amines. The coupling constants ²J(¹⁹⁵Pt-¹HN) are larger in the cis compounds (ave. 76 Hz) than in the trans isomers (ave. 63 Hz). The complexes cis-Pt(amine)₂(R(COO)₂) with bidentate dicarboxylato ligands were also synthesized and characterized mainly by IR spectroscopy. The compounds apparently decompose in DMF and are too insoluble in other solvents for solution studies.

Full text of DOI:10.1016/j.ica.2007.09.024

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Inorganica Chimica Acta 361 (2008) 1437–1446
www.elsevier.com/locate/ica
Synthesis and study of Pt(II)-aromatic amines complexes of the types
cis- and trans-Pt(amine)2(NO3)2 and cis-Pt(amine)2(R(COO)2)
*
Fernande D. Rochon , Gassan Massarweh, Catherine Bonnier
`
´ ´
De´partement de chimie, Universite´ du Que´bec a Montreal, C.P. 8888, Succ. Centre-ville, Montreal, Canada H3C 3P8
Received 10 September 2007; accepted 17 September 2007
Available online 21 September 2007
Abstract
Complexes of the types cis- and trans-Pt(amine)2(NO3)2 with amines containing a phenyl group were synthesized and studied mainly
by IR and multinuclear magnetic resonance spectroscopies. The cis complexes could be synthesized pure only with the amines of the type
Ph–R–NH2 (R = alkyl), while pure trans compounds were synthesized with all the studied amines. In 195Pt NMR spectroscopy, the dinit-
rato complexes of the amines Ph–R–NH2 were observed around ꢀ1700 ppm for the cis isomers and at about ꢀ1580 for the trans com-
plexes. For the other amines, where a phenyl ring is directly attached to the amino group, the signals were observed at lower fields,
ꢀ1528 ppm for cis-Pt(PhNH2)(NO3)2 and around ꢀ1450 ppm for all the trans isomers. There is a linear relationship between the
2
d(Pt) of the Pt(amine)2(NO3)2 complexes and the pKa of the protonated amines. The coupling constants J(195Pt–1HN) are larger in
the cis compounds (ave. 76 Hz) than in the trans isomers (ave. 63 Hz). The complexes cis-Pt(amine)2(R(COO)2) with bidentate dicarb-
oxylato ligands were also synthesized and characterized mainly by IR spectroscopy. The compounds apparently decompose in DMF and
are too insoluble in other solvents for solution studies.
Ó 2007 Elsevier B.V. All rights reserved.
Keywords: Platinum; Aromatic amine; Nitrato; Carboxylato; NMR; IR
1. Introduction
lysis reactions, which have been studied in a few
laboratories.
The antitumor drug cisplatin (cis-Pt(NH3)2Cl2) is still
one of the most widely used drugs in chemotherapy. Its
mechanism of action has been studied by several authors,
but there are still many uncertainties, since its reactions
are extremely complex [1,2]. The drug remains mostly
unchanged in the plasma in the presence of a high chloride
concentration (103 mM) and can cross the cell membrane
because of its neutrality. The chloride ion concentration
is much lower inside the cells (4 mM) and in these condi-
tions, cis-Pt(NH3)2Cl2 produces different ionic species,
which can bind to DNA [3] leading to the eventual cell
death. Its mechanism of action involves aquation or hydro-
A good review of the influence of the structure on the
activity of Pt drugs has been published [4]. When the
ligands NH3 in cisplatin are replaced by primary amines,
the antitumor properties can increase, especially with cyclic
amines [5–7], but the latter compounds have often a more
limited activity spectrum. Furthermore, several of the most
active compounds are quite insoluble [8]. In the amine sys-
tem, the most active compounds usually have the cis geom-
etry, although a few trans compounds have been shown to
possess some antitumor properties.
Our research group has recently undertaken a systematic
study on complexes of the types cis- and trans-Pt(ami-
ne)2X2 (X = I or Cl) with different aliphatic amines
[9,10]. These complexes have been known for a long time,
but their purity has not been well investigated. We have
found that multinuclear magnetic resonance spectroscopy
is an excellent technique to determine the purity of 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 Ó 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2007.09.024

1438
F.D. Rochon et al. / Inorganica Chimica Acta 361 (2008) 1437–1446
complexes and also their geometry. The purity of the iso-
mers is important since in the amine system, the antitumor
properties are related to the isomeric form of the com-
pound. We have transformed these complexes into cis-
and trans-Pt(amine)2(NO3)2, which have also been studied
in the solid state by IR and in acetone solution by 195Pt, 1H
and 13C NMR spectroscopy [10,11]. Conductivity measure-
ments in acetone have shown that the dinitrato complexes
are not dissociated.
We have now started to extend the study to aromatic
amines. We have recently reported the results on complexes
of the types cis- and trans-Pt(amine)2I2 with different types
of amines containing a phenyl group [12]. The compounds
were characterized by IR and by multinuclear magnetic
resonance spectroscopies in order to determine the purity
of the compounds. Most compounds were pure, except
for cis-Pt(PhNH2)2I2, which contained some trans isomers
when dissolved in acetone. But it was not possible to isolate
cis complexes with other amines containing a phenyl group
directly on the binding N atom because of steric hindrance.
We have now transformed these diiodo compounds into
the dinitrato complexes. The latter compounds are not very
stable in air, but they could be characterized by IR and
multinuclear magnetic resonance spectroscopies.
We have also prepared the compounds Pt(amine)2(R-
(COO)2) with the same amines. Three dicarboxylate ligands
were chosen to form bidentate complexes. These ligands are
1,1-cyclopropyldicarboxylate (1,1-CPDCA), 1,1-cyclo-
butyldicarboxylate (1,1-CBDCA) and 1,2-cyclobutyldi-
carboxylate (1,2-CBDCA). Therefore only cis compounds
were isolated. The latter are very insoluble in most solvents.
Therefore solution NMR studies were not possible. The IR
spectra were measured in the solid state. The results on these
aromatic amines Pt(II) complexes are described below.
ne)2(NO3)2 were synthesized by slight variations of the
methods described for aliphatic amines [10,11]. The com-
pounds Pt(amine)2I2 (0.5 mmol) were dissolved in a mini-
mum quantity of acetone (EtOH: CHCl3 1:1 for
cis-Pt(PhNH2)2I2).
A slight excess of silver nitrate
(1.05 mmol, 178.4 mg) was added and the mixture was stir-
red in the dark and at low temperature (5 °C) until the
reaction was complete (clear colorless solution and a yellow
precipitate of AgI). The mixture was filtered and the filtrate
was evaporated to dryness. The product was dried under
vacuum in a dessicator.
cis-Pt(PhMeNH2)2(NO3)2: IR (cmꢀ1): m4(NO3) 1512 m,
m2(NO3) 1274w, m1(NO3) 980s, m6(NO3) 783w, m5(NO3)
722m, m(Pt–N) 385w, m(Pt–O) 350w, 347w. NMR
1
2
(d(ppm)): H: NH, 5.612s + d J(195Pt–NH) = 73 Hz, H1
4.036t, H2–H3–H4 7.430mult.
trans-Pt(PhMeNH2)2(NO3)2: IR (cmꢀ1): m4(NO3) 1508w,
m2(NO3) 1268m, m1(NO3) 976m, m6(NO3) 758m, m5(NO3)
1
722vs, m(Pt–N) 369w, m(Pt–O) 352w. NMR (d(ppm)): H:
2
NH, 5.400s, J(195Pt–NH) = 63 Hz, H1 3.848t, H2–H3–H4
7.429mult.
cis-Pt(PhEtNH2)2(NO3)2: yield = 11%, m.p. = 123–
169 °C (dec). IR (cmꢀ1): m(N–H) 3229m, 3136w, m(@C–
H) 3060w, m(C–H) 2938w, d NH2 1586s, m4(NO3) 1507m,
m2(NO3) 1270s, m1(NO3) 958m, m6(NO3) 775w, m5(NO3)
701s, other bands 1495m, 1455w, 1180w, 1156w, 1086w,
1028s, 1001s, 751vs, 701s, 613w, 547w, 591w, 438w, m(Pt–
N) 374w, m(Pt–O) 342w. NMR (d(ppm)): 1H: NH
5.468s + d, 2J(195Pt–NH) = 72 Hz, H1 4.045t, H2 3.116t,
H3–H4–H5 7.285mult.
trans-Pt(PhEtNH2)2(NO3)2: yield = 48%, m.p. = 106–
157 °C (dec). IR (cmꢀ1): m(N–H) 3279w, 3234m, 3126w,
m(@C–H) 3043m, m(C–H) 2941w, 2852w, d NH2 1576m,
m4(NO3) 1524m, m2(NO3) 1279m, m1(NO3) 959w, m6(NO3)
763m, m5(NO3) 701s, other bands 1496 s, 1454vs, 1176m,
1052w, 1077w, 1032m, 833m, 804w, 751s, 592w, 549w,
2. Experimental
1
438w, m(Pt–N) 358w, m(Pt–O) 325w. NMR (d(ppm)): H:
2
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 and CD3COCD3 were obtained from
CDN Isotopes.
NH 4.468s + d J(195Pt–NH) = 65 Hz, H1 4.350mult, H2
2.628mult, H3–H4–H5 7.045mult.
cis-Pt(PhPrNH2)2(NO3)2: yield 78%, m.p. = 100–112 °C
(dec). IR (cmꢀ1): m(N–H) 3283w, 3254m, 3221m, 3200m,
3125w, m(@C–H) 3085w, 3062w, 3025w, m(C–H) 2923w,
2887w, 2855w, dNH2 1584m, m4(NO3) 1519m, m2(NO3)
1271m, m1(NO3) 988m, m6(NO3) 780w, m5(NO3) 731m, other
bands 1602m, 1496m, 1455w, 1474w, 1382s, 1353vs, 1206w,
966m, 746m, 698s, 576w, m(Pt–N) 494w, 462w, m(Pt–O)
325w. NMR (d(ppm)): 1H: NH 5.240s + d 2J(195Pt–
NH) = 80 Hz, H1 2.711mult, H2 2.089mult, H3 2.686mult,
H4-H5-H6 7.232mult.
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) was the
external standard. The NMR spectra of the dinitrato
complexes were measured in CD3COCD3, while the carb-
oxylato compounds were studied particularly in D2O and
DMF. Other organic solvents were tried for the latter com-
pounds without success.
trans-Pt(PhPrNH2)2(NO3)2: yield 69%, m.p. = 108–
161 °C (dec). IR (cmꢀ1): m(N–H) 3282m, 3250m, 3170w,
m(@C–H) 3082w, 3060w, 3024w, m(C–H) 2946w, 2924w,
2860w, dNH2 1582w, m4(NO3) 1502s, m2(NO3) 1259s,
m1(NO3) 960s, m6(NO3) 794w, m5(NO3) 715w, other bands
1601w, 1528s, 1453m, 1362m, 1286m, 1205m, 1379m,
1174w, 1153w, 1078w, 1030m, 847w, 759m, 704s, 777w,
2.1. Pt(amine)2(NO3)2
The compounds cis- and trans-Pt(amine)2I2 were pre-
pared as described in our recent publication on aromatic
amines [12]. The dinitrato complexes cis- and trans-Pt(ami-
1
579w, m(Pt–N) 362w, m(Pt–O) 332f. NMR (d(ppm)): H:

F.D. Rochon et al. / Inorganica Chimica Acta 361 (2008) 1437–1446
1439
2
NH 4.846s + d J(195Pt–NH) = 67 Hz, H1 2.717mult, H2
trans-Pt(4-tBuPhNH2)2(NO3)2: yield 59%, m.p. = 84–
144 °C (dec). IR (cmꢀ1): m(N–H) 3240s, 3214m, 3137m,
m(@C–H) 3056w, m(C–H) 2957m, 2866w, dNH2 1598s,
m4(NO3) 1513m, m2(NO3) 1277m, m1(NO3) 974m, m6(NO3)
780w, m5(NO3) 716w, other bands 1492vs, 1353vs, 1256s,
1204w, 1189w, 1018w, 836s, 802w, 740w, 700w, 584m,
530w, 451w, m(Pt–N) 369w, m(Pt–O) 353w. 1H NMR
(d(ppm)): NH 7.134s + d, 2J(195Pt–NH) = 62 Hz, H1
7.339d, H2 7.227d, H3 1.284s.
trans-Pt(4-tBuPhNH2)2(NO3)2: yield 59%, m.p. = 84–
144 °C (dec). IR (cmꢀ1): m(N–H) 3240s, 3214m, 3137m,
m(@C–H) 3056w, m(C–H) 2957m, 2866w, dNH2 1598s,
m4(NO3) 1513m, m2(NO3) 1277m, m1(NO3) 974m, m6(NO3)
780w, m5(NO3) 716w, other bands 1492vs, 1353vs, 1256s,
1204w, 1189w, 1018w, 836s, 802w, 740w, 700w, 584m,
530w, 451w, m(Pt–N) 369w, m(Pt–O) 353w. 1H NMR
(d(ppm)): NH 7.134s + d, 2J(195Pt–NH) = 62 Hz, H1
7.339d, H2 7.227d, H3 1.284s.
2.138q, H3, 2.691mult, H4–H5–H6 7.220mult.
cis-Pt(PhBuNH2)2(NO3)2: yield = 43%, m.p. = 97–
111 °C (dec). IR (cmꢀ1): m(N–H) 3261m, 3236m, 3157w,
m(@C–H) 3083w, 3061w, 3023w, m(C–H) 2933w, 2858w, d
NH2 1587w, m4(NO3) 1507m, m2(NO3) 1275s, m1(NO3)
988m, m6(NO3) 793w, m5(NO3) 722w, other bands 1603f,
1495s, 1454w, 1216w, 1465w, 1354vs, 1180w, 1155w,
1084w, 1028w, 976m, 833w, 743m, 698m, 580w, m(Pt–N)
376w, m(Pt–O) 352w, 328w. NMR (d(ppm)): 1H: NH
5.172s + d, 2J(195Pt–NH) = 77 Hz, H1 2.748q, H2
1.689mult, H3 1.780mult, H4 2.620t, H5–H6–H7 7.202mult.
trans-Pt(PhBuNH2)2(NO3)2: yield 25%, m.p. = 132–
162 °C (dec). IR (cmꢀ1): m(N–H) 3266s, 3244s, 3173m,
m(@C–H) 3082w, 3057w, 3021w, m(C–H) 2971w, 2953w,
2932w, 2894w, 2863w, dNH2 1600s, m4(NO3) 1498s,
m2(NO3) 1267vs, m1(NO3) 967vs, m6(NO3) 784m, m5(NO3)
717m, other bands 1487s, 1456m, 1400w, 1356w, 1383m,
1205m, 1154m, 1080w, 1031w, 1094w, 747m, 691m,
trans-Pt(4-BuPhNH2)2(NO3)2: yield 59%, m.p. = 96–
190 °C (dec). IR (cmꢀ1): m(N–H) 3249s, 3161m, m(@C–H)
3054w, 3022w, m(C–H) 2958w, 2920m, 2872w, 2855w,
dNH2 1605s, m4(NO3) 1513m, m2(NO3) 1273m, m1(NO3)
973vs, m6(NO3) 782w, m5(NO3) 716w, other bands 1492s,
1451w, 1361m, 1261s, 1207m, 1164w, 1090w, 1021w,
823s, 802w, 760w, 574m, 544w, 472m, m(Pt–N) 371w,
1
520w, m(Pt–N) 390w, m(Pt–O) 344w. NMR (d(ppm)): H:
2
NH 4.779s + d, J(195Pt–NH) = 57 Hz, H1–H4, 2.634mult,
H2 1.697tt, H3 1.847tt, H5–H6–H7 7.186mult.
cis-Pt(PhNH2)2(NO3)2: yield: 53%, m.p. = 92–118 °C
(dec). IR (cmꢀ1): m(N–H) 3256m, 3240m, m(@C–H):
3044w, d NH2 1599vs, m4(NO3) 1510m, m2(NO3) 1260w,
m1(NO3) 970m, m6(NO3) 784w, m5(NO3) 716w, other
bands1612s, 1494m, 1467w, 1393m, 1193w, 1178w,
1070w, 1027w, 922w, 832m, 802s, 756s, 732w, 689w,
619w, 577w, 554w, 447m, m(Pt–N) 386w, m(Pt–O) 338m,
1
m(Pt–O) 344m. H NMR (d(ppm)): H1 7.219d, H2 7.119d,
H3 2.551t, H4 1.568tt, H5 1.344qt, H6 0.904t.
trans-Pt(PhNHMe)2(NO3)2: yield 66%, m.p. = 97–
116 °C (dec). IR (cmꢀ1): m(N–H) 3226s, 3183s, m(@C–H)
3038w, m(C–H) 2944w, dNH2 1600s, m4(NO3) 1525m,
m2(NO3) 1261s, m1(NO3) 965s, m6(NO3) 780m, m5(NO3)
712w, other bands 1493w, 1470w, 1407m, 1355m, 1181w,
1156w, 1130m, 1066m, 1076m, 1066m, 1032w, 832w,
761w, 690m, 617w, 576w, 420w, m(Pt–N) 351w, m(Pt–O)
326w. 1H NMR (d(ppm)): NH 7.631s + d, 2J(195Pt–
NH) = 71 Hz, H1 2.850s + d, 3J(195Pt–H1) = 24 Hz, H2–
H3–H4 7.291m.
1
330w. NMR (d(ppm)): H: H1–H2–H3, 7.278mult.
trans-Pt(PhNH2)2(NO3)2: yield = 19%, m.p. = 133–
173 °C (dec). IR (cmꢀ1): m(N–H): 3256m, 3162m,m(@C–
H): 3037w, d NH2 1599s, m4(NO3) 1508Fs, m2(NO3)
1276w, m1(NO3) 970s, m6(NO3) 784w, m5(NO3) 716w, other
bands 1613s, 1493s, 1466m, 1383m, 1197w, 1167w,
1069w, 1027w, 1152w, 833w, 802w, 756vs, 688sv, 626w,
556w, 578s, 448m, m(Pt–N) 387m, m(Pt–O) 347m. NMR
1
(d(ppm)): H: H1–H2–H3, 7.260mult.
trans-Pt(4-EtPhNH2)2(NO3)2: yield 58%, m.p. = 107–
170 °C (dec). IR (cmꢀ1): m(N–H) 3256s, 3238s, 3166s,
m(@C–H) 3074w, 3042w, m(C–H) 2969m, 2929w, 2874w,
2841w, dNH2 1593m, m4(NO3) 1512s, m2(NO3) 1273s,
m1(NO3) 975s, m6(NO3) 786m, m5(NO3) 716m, other bands
1608s, 1484w, 1452m, 1442m, 1374m, 1228s, 1208s,
1157w, 1113w, 1047w, 1019w, 942s, 830s, 636w, 580s,
540w, 486m, 457w, m(Pt–N) 384w, m(Pt–O) 346m. NMR
2.2. Ag2R(COO)2
These compounds were synthesized by the recently pub-
lished method (13).
Ag2(1,1-CBDCA): yield 71%, dec. 199–300. IR (cmꢀ1
)
m(C@O) 1596, m(C–O) 1345.
Ag2(1,2-CBDCA): yield quantitative, dec. 228–300. IR
(cmꢀ1) m(C@O) 1556, m(C–O) 1396.
1
(d(ppm)): H: H1 7.225d, H2 7.133d, H3 2.571q, H4 1.180t.
Ag2(1,1-CPDCA): yield 45%, dec. 194–300. IR (cmꢀ1
)
trans-Pt(4-isoPrPhNH2)2(NO3)2: yield 56%, m.p. = 108–
253 °C (dec). IR (cmꢀ1): m(N–H) 3243vs, 3204s, 3134s,
m(@C–H) 3042m, m(C–H) 2957m, 2888w, dNH2 1599s,
m4(NO3) 1512m, m2(NO3) 1278m, m1(NO3) 978s, m6(NO3)
780m, m5(NO3) 719w, other bands 1488s, 1440m, 1381m,
1363m, 1290s, 1258s, 1183m, 1144w, 1053w, 1019m,
883m, 841m, 735w, 639w, 584s, 549w, 459w, m(Pt–N)
m(C@O) 1589, 1569, m(C–O) 1391, 1373.
2.3. cis-Pt(amine)2(R(COO)2)
The two compounds cis-Pt(amine)2I2 and Ag2R(COO)2
were mixed together in acetone in a 1:1.15 proportion.
The mixture is stirred in the dark until the formation of
AgI is complete (several hours). The yellow precipitate is
filtered out and the filtrate is evaporated to dryness and
the residue is dried in a dessicator under vacuum.
1
392w, m(Pt–O) 352w. H NMR (d(ppm)): NH 7.120s + d,
2J(195Pt–NH) = 57 Hz, H1 7.231d, H2 7.171d, H3 2.842h,
H4 1.204d.

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F.D. Rochon et al. / Inorganica Chimica Acta 361 (2008) 1437–1446
cis-Pt(PhMeNH2)2(1,1-CBDCA):
yield
41%,
3062w 3026w, m(C–H) 2937m 2857w, m(C@O) 1617s
1604s, m(C–O) 1364m, other bands 1496w, 1454w, 1221w,
1158w, 1085w, 1029w, 1116w, 905w, 748m, 699m, 569w,
m(Pt–O) 469w, m(Pt–N) 352w, 329w.
cis-Pt(PhBuNH2)2(1,2-CBDCA): yield 39%, m.p. = 93–
121 °C. IR (cmꢀ1): m(N–H) 3208m 3122w, m(@C–H)
3085w 3061w 3025w, m(C–H) 2933m 2855w, m(C@O)
1604s, m(C–O) 1373m, other bands 1495w, 1453w, 1227w,
1178w, 1155w, 1083w, 1046w, 1029w, 912w, 748m, 699m,
619w, 569w, m(Pt–O) 462w, m(Pt–N) 351w, 328w.
cis-Pt(PhBuNH2)2(CPDCA): yield 52%, m.p. = 110–
142 °C. IR (cmꢀ1): m(N–H) 3214m, m(@C–H) 3086w
3062w 3025w, m(C–H) 2932m 2857w, m(C@O) 1621s
1604s, m(C–O) 1380m, other bands 1496w, 1453w, 1239w,
1197w, 1085w, 1030w, 972w, 810w, 748m, 699m, 612w,
530w, 570w, m(Pt–O) 496w, m(Pt–N) 366w, 325w.
cis-Pt(PhNH2)2(1,1-CBDCA): yield 38%, m.p. = 102–
147 °C (dec.). IR (cmꢀ1): m(N–H) 3191m, m(@C–H)
3046m, m(C–H) 2990m 2944m 2868w, m(C@O) 1619s
1600s, m(C–O) 1352m, other bands 1494vs, 1225w, 1469w,
1199w, 1156w, 1072w, 1028w, 904w, 801w, 756m, 690s,
620w, 550w, 593w, m(Pt–O) 458w, m(Pt–N) 353w, 303w.
m.p. = 138–157°C. IR (cmꢀ1): m(N–H) 3209m 3115w,
m(@C–H) 3063w 3031w, m(C–H) 2942w 2855w m(C@O)
1608vs, m(C–O) 1360s, other bands 1497w, 1455m, 1224w,
1116w, 1156w, 1077w, 1029w, 988w, 842w, 751m, 698s,
619w, 576w, m(Pt–O) 481w, m(Pt–N) 357w, 329w.
cis-Pt(PhMeNH2)2(1,2-CBDCA): yield 19%, m.p. = 92–
171 °C. IR (cmꢀ1): m(N–H) 3202m, 3111w, m(@C–H) 3062w
3030w, m(C–H) 2943w 3871w, m(C@O) 1604s, m(C–O)
1368m, other bands 1496m, 1454m, 1293w, 1267w,
1225w, 1177w, 1076w, 1029w, 983w, 752s, 699vs, 621w,
575w, m(Pt–O) 480w, m(Pt–N) 354w, 326w.
cis-Pt(PhMeNH2)2(CPDCA): yield 51%, m.p. = 103–
149 °C. IR (cmꢀ1): m(N–H) 3208m 3111m, m(@C–H)
3064w 3030w, m(C–H) 2949w 2878w, m(C@O) 1619s, m(C–
O) 1377s, other bands 1497w, 1455w, 1197m, 1077w,
1030w, 973w, 916w, 808w, 751s, 698vs, 619w, 530w, m(Pt–
O) 480w, m(Pt–N) 374w, 326w.
cis-Pt(PhEtNH2)2(1,1-CBDCA): yield 41%, m.p. = 112–
139 °C. IR (cmꢀ1): m(N–H) 3210m 3125fw, m(@C–H) 3087w
3062w 3027w, m(C–H) 2943w 2855w, m(C@O) 1621s 1604s,
m(C–O) 1360m, other bands 1496m, 1454m, 1220w, 1180w,
1157w, 1078w, 1033w, 1002w, 904w, 749w, 699m, 552w,
m(Pt–O) 470w, m(Pt–N) 352w, 323w.
cis-Pt(PhEtNH2)2(1,2-CBDCA): yield 24%, m.p. = 103–
124 °C. IR (cmꢀ1): m(N–H) 3206m 3122w, m(@C–H) 3086w,
3062w, 3027w, m(C–H) 2945w, 2855w, m(C@O) 1604s,
m(C–O) 1370m, other bands 1496m, 1454w, 1265w,
1225w, 1178, 1156w, 1079w, 1032w, 748m, 699s, 619w,
550w, m(Pt–O) 494w, m(Pt–N) 345w, 327w.
cis-Pt(PhEtNH2)2(CPDCA): yield 57%, m.p. = 96–
163 °C. IR (cmꢀ1): m(N–H) 3204m 3123m, m(@C–H)
3026w, m(C–H) 2918m, 2850w, m(C@O) 1619s 1591s, m(C–
O) 1398s, other bands 1496w, 1454w, 1421m, 1227w,
1195w, 1157w, 1079w, 1033w, 964w, 933w, 770w, 747m,
699m, 558w, 530w, m(Pt–O) 488w, m(Pt–N) 366w, 326w.
cis-Pt(PhPrNH2)2(1,1-CBDCA): yield 62%, m.p. = 122–
157 °C. IR (cmꢀ1): m(N–H) 3213m, m(@C–H) 3086w 3062w
3026w, m(C–H) 2941m 2856w, m(C=O) 1619s 1604s, m(C–O)
1360m, other bands 1496m, 1454m, 1220w, 1157w, 1082w,
1029m, 1115w, 908w, 746m, 699m, 581w, 565w, m(Pt–O)
470w, m(Pt–N) 352w, 323w.
cis-Pt(PhPrNH2)2(1,2-CBDCA): yield 37%, m.p. = 97–
141 °C. IR (cmꢀ1): m(N–H) 3207m 3121w, m(@C–H)
3085w 3061w 3025w, m(C–H) 2941m, 2858w, (C@O)
1604vs, m(C–O) 1399m 1373m, other bands 1495m,
1453w, 1225w, m(C–N) 1178w, 1155w, 1082w, 1029w,
910w, 746m, 699s, 620w, 563w, m(Pt–O) 494w, m(Pt–N)
364w, 330w.
3. Results and discussion
3.1. Pt(amine)2(NO3)2
3.1.1. Synthesis of the compounds
The dinitrato compounds were synthesized from the dii-
odo complexes. Two series of primary amines were studied
in this project. The amines of the first series are of the type
Ph–R–NH2, with an alkyl group between the phenyl and
amine groups. The second series includes PhNH2 and
4-R–PhNH2 (R = Et, isoPr, tert-Bu and n-Bu in para posi-
tion). A secondary amine (PhNHMe) was also included in
the study. The amines of the second series contain a phenyl
group on the binding atom and are more sterically hin-
dered than the amines of the first series. The secondary
amine is the most sterically demanding ligand.
The compounds Pt(amine)2I2 with these ligands were
synthesized as recently reported [12]. The cis diiodo isomers
were synthesized only with the amines of the first series and
PhNH2. The diiodo complexes containing the other amines
could not be synthesized because of steric hindrance.
Therefore the compounds cis-Pt(amine)2(NO3)2 were syn-
thesized only with the amines of the first series and PhNH2.
The dinitrato complexes were prepared by the reaction
(in the dark around 5 °C) of the diiodo complexes with a
slight excess (10–15%) of silver nitrate in acetone, as
reported for aliphatic amines [10,11].
cis-Pt(PhPrNH2)2(CPDCA): yield 62%, m.p. = 108–
153 °C. IR (cmꢀ1): m(N–H) 3213m, m(@C–H) 3085w
3061w 3025w, m(C–H) 2939m 2857w, m(C@O) 1617s
1603s, m(C–O) 1362m, other bands 1495m, 1454m,
1245tw, 1220w, 1157w, 1082w, 1029w, 1114w, 746m,
698m, 566w, m(Pt–O) 468w, m(Pt–N) 353w, 321w.
PtðamineÞ2I2 þ 2AgðNO3Þ ! PtðamineÞ2ðNO3Þ2 þ 2AgI #
The time of reaction varied between 4 and 8 h. For the cis
PhNH2 compound, the reaction was performed in a 1:1
mixture of ethanol and chloroform, since the cis compound
isomerizes in acetone. Souchard et al. [14] have reported
cis-Pt(PhBuNH2)2(1,1-CBDCA): yield 49%, m.p. =
122–211 °C. IR (cmꢀ1): m(N–H) 3213m, m(@C–H) 3086w

F.D. Rochon et al. / Inorganica Chimica Acta 361 (2008) 1437–1446
1441
Table 1
the compound cis-Pt(PhNH2)2(NO3)2 which was synthe-
sized in acetone. We have repeated their procedure and
we have found by NMR spectroscopy that cis and trans
complexes were present. The reported compound was not
characterized by NMR by the authors [14]. Following
our procedure, only the cis isomer was detected when the
preparation was performed in a 1:1 mixture of ethanol
and chloroform.
These dinitrato complexes are not very stable at room
temperature. For the PhMeNH2 compound, all the manip-
ulations were done in the cold, the solution was evaporated
at 5 °C and kept below this temperature to avoid
decomposition.
D(m4 ꢀ m2) and Dm1 (cmꢀ1) in the complexes cis- and trans-Pt(amine)2-
(NO3)2
Amine
cis-Pt(amine)2(NO3)2
trans-Pt(amine)2(NO3)2
D(m4 ꢀ m2)
Dm1
D(m4 ꢀ m2)
Dm1
PhMeNH2
PhEtNH2
PhPrNH2
PhBuNH2
PhNH2
4-EtPhNH2
4-iPrPhNH2
4-tBuPhNH2
4-BuPhNH2
PhNHMe
237
237
248
232
250
69
91
61
61
79
240
245
243
231
232
239
234
236
240
264
73
90
89
82
79
74
71
75
76
84
The cis dinitrato complexes were synthesized with the
amines of the first series Ph–R–NH where R = CH3,
C2H5, n-C3H7, and n-C4H9 and also with PhNH2. The
trans dinitrato compounds were prepared with all the
studied amines. The yields varied between 11% and 78%.
In general, the decomposition points (shown in the Section
2) of the cis complexes are lower than those of the trans
isomers and also than the corresponding diiodo
analogues.
aromatic amines, the difference between the cis and trans
isomers does not seem very significant.
The position of m1 for our compounds is slightly different
in the two geometries (ave. Dm1 72 cmꢀ1 for cis and 83 cmꢀ1
for trans, using only the five complexes whose spectra of
both isomers are available). For cyclic amines, these values
are 71 and 86 cmꢀ1 [10]. For the compounds cis and trans-
Pt(pyridine derivative)2(NO3)2, the m1 band was also found
less energetic in the trans complexes (ave. Dm1 = 90 cmꢀ1
(cis), 120 cmꢀ1 (trans)), suggesting a more covalent charac-
ter of the Pt–O bonds in the trans geometry [19]. For
amines, the difference is smaller than in pyridine com-
plexes. Our previous results on the aliphatic amines system
seemed to indicate that the covalency of the Pt–O bonds in
the cis and trans compounds is not very different in the two
isomers [10,11]. The aromatic amines studied here, seem
very similar to the results obtained on aliphatic and cyclic
amines complexes.
The stretching energy of a slightly more covalent bond
should increase and these results can be compared to the
energies of the m(Pt–O) vibrations. For the cis complexes,
two m(Pt–N) and two m(Pt–O) bands are expected from
group theory for the skeleton PtN2O2 (C2v symmetry),
while one m(Pt–N) and one m(Pt–O) are predicted for the
trans analogues (20). A study on cis-Pt(NH3)2(NO3)2 has
shown that these vibrations are often coupled with other
vibrations [23]. The bands assigned to these vibrations
are shown in Table 2. Only one band was observed for
the m(Pt–O) vibrations in the trans compounds, between
325 and 353 cmꢀ1, while one or two bands were observed
in the range 325–352 cmꢀ1 in the cis configuration. The
energy of these vibrations are quite low and close to the
energy of m(Pt–Cl) vibrations, but they are difficult to
assign with certainty, since the intensity of the bands are
weak. They are probably not pure and might couple with
other vibrations. Similar results were reported for dinitrato
aliphatic amines complexes [10,11].
3.1.2. IR spectroscopy
The compounds were characterized in the solid state in
KBr pellets by IR spectroscopy. The main bands were
assigned based on published work on similar compounds
[15–19] and are shown in Section 2. The notation of
Nakamoto [20] was used for the bands involving the nitra-
to ligands. The symmetry of the free nitrate ion is D3h with
a bond order of 1 13, while in the monodentate coordinated
nitrato ligand, the N–O(Pt) bond order is close to 1. The p
electron density is then delocalized on only two N–O bonds
resulting in a bond order of 1 12 for the two latꢀter bonds.
The approximate symmetry of coordinated NO3 (monod-
entate) is C2v. It has been suggested that the position of the
m1 band (at 1049 cmꢀ1 [20] in free NO3ꢀ) gives important
information on the covalent character of the Pt–O bond
[21]. Because of the reduction in symmetry of the coordi-
nated nitrato ligand, some of the vibration modes, which
were degenerate in the free ion, will be split. This is the case
for the m3 stretching mode in D3h(E), which will separate
into the m2(A1) and m4(B2) stretching modes in C2v symme-
try [20]. The energy difference between the two latter modes
(D = m4 ꢀ m2) should also give additional information on
the covalent character of the Pt–O bond [21,22]. For ionic
nitrate D = 0 cmꢀ1, while it is 385 cmꢀ1 in CH3ONO2 a
totally covalent compound [22].
The D values as well as the energy difference (Dm1)
between the m1 band for free nitrate and the coordinated
nitrato ligands are shown in Table 1. The average value
D(m4 ꢀ m2) was calculated using the five complexes for
which the two isomers could be measured. These values
are 241 cmꢀ1 (cis) and 238 cmꢀ1 (trans). For the aliphatic
aminesꢀs1ystem [11], the values were 252 cmꢀ1 (cis) and
The m(Pt–N) bands assignments are based on some pub-
lished works [9–11,20,23–25]. We have assigned only one
band for the cis isomers (ms) and only one band (mas)
for the trans compounds around 380 cmꢀ1 (Table 2). The
238 cm
(trans) and for cyclic amines, they were
227 cmꢀ1 (cis) and 240 cmꢀ1 (trans) [10]. In this study on

1442
F.D. Rochon et al. / Inorganica Chimica Acta 361 (2008) 1437–1446
[10,11]. The 195Pt chemical shifts of the other compounds
were observed at lower fields. The cis-Pt(PhNH2)2(NO3)2
was found at lower fields than the other cis compounds
(about 75 ppm), probably due to the solvent effect. In the
complexes of the amines of the first series, there is an alkyl
group separating the phenyl group from the binding atom.
Steric hindrance close to the binding side is thus reduced,
permitting the approach of molecules of solvents close to
the Pt atom, which increases the electron density on the
Pt atom. In the cis PhNH2 complex, the two phenyl groups
are very close to the metal atom, which hinders the
approach of molecules of solvent towards the Pt atom.
The electron density on the Pt atom will thus be reduced
and its d(195Pt) will be shifted towards lower fields. The
chemical shifts of the trans compounds of the second series
and of the secondary amines are more uniform (ꢀ1436 to
ꢀ1484 ppm) and are observed at lower fields than the trans
complexes of the first series also because of the solvent
effect.
Table 2
m(Pt–O) and m(Pt–N) (cmꢀ1) for the complexes Pt(amine)2(NO3)2
Amine
m(Pt–O)
m(Pt–N)
cis
trans
cis
trans
PhMeNH2
PhEtNH2
PhPrNH2
PhBuNH2
PhNH2
4-EtPhNH2
4-iPrPhNH2
4-tBuPhNH2
4-BuPhNH2
PhNHMe
350, 347
342
325
352, 328
338, 330
352
325
332
344
347
346
352
353
344
326
385
374
369
358
362
390
387
384
392
369
377
351
376
386
second band for the cis complexes is probably hidden by
the m(Pt–O) bands. The m(Pt–N) vibrations are observed
at similar or slightly higher energies than in the corre-
sponding diiodo compounds [12].
The solvent effect is an important factor in these studies,
especially for solvents like water or acetone which can
coordinate to platinum in solution. The dinitrato com-
plexes were measured in deuterated acetone, a solvent
which can coordinate to Pt, but not as easily as water.
Therefore the solvent effect should be reduced compared
to water, but it should still be an important factor. For
square planar complexes, the molecules of solvent can nor-
mally approach and weakly bind to the Pt atom on both
sides of the coordination plane. For complexes containing
more bulky ligands close to the binding site, the molecules
of solvent cannot approach the Pt atom easily, resulting in
a decrease of the electron density around the Pt nucleus.
Nitrato ligands are more bulky than iodo or chloro ligands.
Therefore the presence of the nitrato ligands should have
an influence of the solvation of the Pt atom. There are a
few studies published in the literature on dinitrato com-
plexes. For the NH3 dinitrato [26] complexes, the Dd value
between the cis and trans isomers is ꢀ179 ppm (in DMF),
for primary amines [10,11] the ave. reported value is
3.1.3. NMR spectroscopy
The complexes Pt(amine)2(NO3)2 were characterized by
195Pt and 1H magnetic resonance in acetone. The com-
plexes were pure and are not dissociated in acetone as
shown by conductivity measurements of the cyclic amine
complexes [10].
The 195Pt chemical shifts of the dinitrato complexes are
listed in Table 3. The nitrato ion is a weak ligand and its
polarisability is smaller than the one of the iodo ligand.
Therefore the Pt d orbital coefficient in the Ramsey equa-
tion is larger for the dinitrato complex and the Pt signals
will be observed at much lower field than for the diiodo
compounds. The cis dinitrato isomers of the complexes
containing the amines of the first series were observed at
higher fields (ave. ꢀ1702 ppm) than their trans analogues
(ave. ꢀ1582 ppm). The difference (Dd) between the cis
and trans isomers (ave. 120 ppm) is quite constant for the
different ligands and it is much larger than the value (ave.
10 ppm [12]) published for the corresponding diiodo com-
pounds. The results on these dinitrato compounds are sim-
ilar to those reported for aliphatic and cyclic primary
amines (around ꢀ1695 (cis) and ꢀ1570 (trans) ppm)
ꢀ125 ppm (in acetone), for secondary amines [11] Ddave
=
ꢀ44 ppm (in acetone) and for pyridine derivatives [19] Ddave
= ꢀ59 ppm (in CDCl3 or CD2Cl2). Therefore the Dd values
seem to depend on the solvent and the N-ligands. Our
values are close to those reported on the aliphatic amines
and cyclic amines [10,11].
Table 3
d(195Pt) and Dd = dcis ꢀ dtrans (ppm) of the complexes Pt(amine)2(NO3)2 in
The d(195Pt) of the complexes of the first series shift
slightly towards higher fields as the length of the alkyl
chain increases for both isomers. This is again explained
by the solvent effect. For the PhMeNH2 ligand, the phenyl
group is closer to the binding site than in PhBuNH2 ligand.
The proximity of the phenyl groups close to the Pt atom
reduces the approach of the molecules of solvent in the
close environment of the metal centre. Therefore the elec-
tron density on the Pt atom is reduced when the phenyl
groups are close to the binding atom. In 195Pt NMR, the
chemical shifts will be observed at lower fields (lower elec-
tron density of the Pt atom) when the alkyl chain is shorter.
CD3COCD3
Amine
pKa
9.62
Proton affinity (kJ/m) cis
trans
Dd
PhMeNH2
PhEtNH2
PhPrNH2
PhBuNH2
PhNH2
913
936
ꢀ1691 ꢀ1571 ꢀ120
ꢀ1703 ꢀ1582 ꢀ121
ꢀ1706 ꢀ1587 ꢀ119
ꢀ1708 ꢀ1589 ꢀ119
9.83
10.28a
10.66a
4.603 883
5.09a
ꢀ1528 ꢀ1436
ꢀ1451
ꢀ92
4-EtPhNH2
4-iPrPhNH2
4-tBuPhNH2
4-BuPhNH2
PhNHMe
a
5.01a
ꢀ1449
4.93a
ꢀ1441
4.90a
ꢀ1462
4.85
917
ꢀ1484
These values were calculated [27].

F.D. Rochon et al. / Inorganica Chimica Acta 361 (2008) 1437–1446
1443
Table 4
For the four ligands of the first series, the difference is
about 18 ppm between R = Me and R = Bu for both
isomers.
d(1HN), Dd(dcomplex ꢀ dfree
)
(ppm) and 2J(195Pt–1HN) (Hz) of
amine
Pt(amine)2(NO3)2 in CD3COCD3 (for a few complexes, the NH2 signal
was hidden by other signals)
Attempts were made to correlate the d(195Pt) of the com-
plexes with the basicity of the protonated amines. These
ligands cannot accept electron density from the Pt atom.
Therefore, in the formation of the r(amine ! Pt) bond,
electron density is transferred from the amine ligand to
the metal atom, resulting in a shielding on the Pt nucleus
Amine
NH
5.612 1.187
trans 5.400 0.974
cis 5.468 1.782
trans 4.468 0.782
cis 5.240 2.125
trans 4.846 1.731
Dd(NH) 2J(195Pt–1HN) 3J(195Pt–1H3C)
PhMeNH2
cis
73
PhEtNH2
PhPrNH2
PhBuNH2
72
65
80
67
77
57
57
62
71
(
195Pt NMR) and a deshielding effect on the ligand (1H
a
cis
5.172
NMR). The pKa values of the ligands are not all available.
A few were calculated using the software SOLARIS V4.67 [27]
and are shown in Table 3. The d(Pt) values were plotted
versus the pKa of the protonated amines and a very good
correlations could be observed, especially with the cis com-
pounds. The relation is shown in Fig. 1. For the trans com-
plexes, there is also a good relation, especially if we do not
include the secondary amine compound. Therefore the
d(Pt) values of these complexes are influenced by the basi-
city of the ligands. For the aliphatic amines systems, the
correlations were poor [10,11]. For the latter compounds,
better correlations were observed with the proton affinity
values, which are measured in the gas phase. But these val-
ues are not very common in the literature. A few values for
aromatic amines are known and are shown in Table 3. For
the primary amines, only three values are available and
there seems to be a good correlation for both the cis- and
trans-Pt(amine)2(NO3)2 complexes.
a
trans 4.779
4-iPrPhNH2 trans 7.120 2.817
4-tBuPhNH2 trans 7.134 2.790
PhNHMe
trans 7.631 2.825
24
a
d(NH2) of free amine hidden by other signal.
field). The NH2 signals of the PhNH2, 4-EtPhNH2 and
4-BuPhNH2 were hidden by other resonances.
The 1H NMR spectra of the free amines were also mea-
sured in acetone and the Dd (dcomplex ꢀ damine) values calcu-
lated (shown in Table 4) in order to evaluate the effect of
platinum coordination on the ligands. As already men-
tioned, the values for the NH signals are larger in the cis
geometry. The d(1H) of the NH2 resonance shifts towards
higher fields as the lengths of the alkyl chain increases in
the complexes of the first series (5.61 and 5.40 ppm for
cis- and trans-Pt(PhMeNH2)(NO3)2 to 5.17 and 4.78 ppm
for cis- and trans-Pt(PhBuNH2)(NO3)2), which might
appear surprising since PhBuNH2 should be a better donor
than PhMeNH2. But if the Dd values are considered, these
data seem to increases as the length of the alkyl chain
increases in the complexes of the first series (Table 4).
For the other trans compounds, the value seems more uni-
form (ꢁ2.8 ppm).
The 1H NMR chemical shifts of the complexes are listed
in Section 2. There are very few dinitrato complexes stud-
ied by NMR in the literature. For the complexes of the
amines of the first series, the NH signals of the cis com-
plexes were observed at lower fields (5.2–5.6 ppm) than
those of the trans isomers (4.8–5.4 ppm) as shown in
Table 4. This observation is in agreement with the d(Pt)
values, where the cis compounds were observed at higher
fields than the corresponding trans isomers. A larger reduc-
tion of electron density on the ligand in the cis compounds
(d(H) at lower field) should be associated with a greater
electron density on the platinum atom (d(Pt) at higher
The 2J(195Pt–1HN) coupling constants are shown in
Table 4. They are larger in the cis configuration with an
average value of 76 Hz compared to 63 Hz (ave.) for the
trans isomers. The average values were found to be 68 Hz
(cis) and 62 Hz (trans) for the corresponding diiodo com-
plexes [12]. In the dinitrato primary aliphatic amines these
values were 67 (cis) and 58 (trans) Hz [11].
-1500
R2 = 0.99
PhNH2
The 3J(195Pt–1H) coupling constants usually also depend
on the geometry of the complex. They are difficult to
observe in these complexes because of the multiplicity of
the signals. But it was observed for trans-
Pt(PhNHMe)2(NO3)2 (24 Hz) since the –CH3 signal is a
singlet. In the aliphatic and cyclic amines systems, these
values were 35–47 Hz for the cis compounds and 27–
33 Hz for the trans isomers [10,11].
-1550
-1600
-1650
PhMeNH2
PhEtNH2
PhPrNH2
PhBuNH2
-1700
-1750
3.2. cis-Pt(amine)2(R(COO)2)
4
5
6
7
8
9
10
11
pKa
3.2.1. Synthesis of the compounds
A few methods have been reported for the synthesis of
Pt(II)-carboxylato complexes. The different methods have
Fig. 1. d(195Pt) (ppm) of the complexes cis-Pt(amine)2(NO3)2 vs. pKa of
the protonated amines.

1444
F.D. Rochon et al. / Inorganica Chimica Acta 361 (2008) 1437–1446
Table 5
been summarized recently along with our new method pub-
lished recently [13]. This new synthetic procedure is more
rapid and produces pure compounds contrary to most of
the other published methods. In this method, the silver
dicarboxylate compound is first synthesized and reacted
with cis-Pt(amine)2I2 and the reaction is performed in ace-
tone. We have used only bidentate carboxylate ions in this
study, therefore all the Pt(II) complexes have the cis geom-
etry. Three dicarboxylate ligands were studied: 1,1-cyclo-
propyldicarboxylate, 1,1-cyclobutyldicarboxylate and
1,2-cyclobutyldicarboxylate.
msymC@O,
m
asymC–O and D(msym ꢀ masym
) ) in cis-Pt(amine)2
(cmꢀ1
(R(COO)2)
Amine
R(COO)2
msymC@O
masymC–O
Da
PhNH2
1,1-CBDCA
1619, 1600
1352
263
PhMeNH2
1,1-CPDCA
1,1-CBDCA
1,2-CBDCA
1619
1608
1604
1377
1360
1368
242
248
236
PhEtNH2
PhPrNH2
PhBuNH2
1,1-CPDCA
1,1-CBDCA
1,2-CBDCA
1619
1621, 1604
1604
1398
1360
1370
221
253
234
1,1-CPDCA
1,1-CBDCA
1,2-CBDCA
1617, 1603
1619, 1604
1604
1362
1360
1399, 1373
248
252
218
cis-PtðamineÞ2I2 þ Ag2ðRðCOOÞ2Þ
! cis-PtðamineÞ2ðRðCOOÞ2Þ þ 2AgI #
1,1-CPDCA
1,1-CBDCA
1,2-CBDCA
1621, 1604
1617, 1604
1604
1380
1364
1373
233
247
231
The crystal structure of one of the silver intermediate
Ag2(1,1-CBDCA) was recently published [13]. The yields
of cis-Pt(amine)2(R(COO)2) varied between 19% and
62%. They are quite low, because the preparations were
done on a micro scale. They were the lowest with 1,2-
CBDCA, since this ligand forms a 7-membered chelate ring
with the Pt atom, which reduces its stability compared to
the other carboxylates, which form the more stable 6-mem-
bered chelates. The decomposition points of the complexes
are also the lowest with the 1,2-CBDCA ligand (experimen-
tal section) showing the importance of the chelate effect in
the stability of the Pt complexes.
The cis-Pt(amine)2(R(COO)2) complexes were prepared
with the four amines of the first series. We have shown that
the complex cis-Pt(PhNH2)2I2 partly isomerizes in acetone
[12]. Therefore its reaction was studied in chloroform and it
seems that with the ligand 1,1-CBDCA, the compound was
formed. With other carboxylates, the cis-Pt(PhNH2)2I2
solution decomposed.
The dicarboxylato compounds are very insoluble and
could not be characterized in solution by NMR spectros-
copy. DMF seemed the best solvent, but the spectra of
the solution indicated that the complexes were decom-
posed. There are several products formed, since the 1H
NMR spectra contained a great number of new signals.
Furthermore, the signals were very large probably caused
by the presence of solid particles in suspension.
NH3 [32]
EtNH2 [32]
a
1,1-CBDCA
1,1-CBDCA
1610
1620
1378, 1360
1365
241
255
When two bands, the average value was used.
1370 cmꢀ1. The Dm values were calculated and they vary
between 218 and 263 cmꢀ1. These values agree with the
results reported in the literature [28–31]. For comparison,
two of these reports [32] are also shown in Table 5. The
Dm values are larger than in the free carboxylates, but much
lower than in the acids. These bonds are usually involved in
H-bonding and these will influence the energy of the car-
boxyl vibrations.
The m(Pt–N) and m(Pt–O) vibrations are usually weak
bands which are difficult to assign. There are very few
examples in the literature found on this type of complex.
A few metallic complexes with glycine have been reported.
For Pt(glycine)2, the m(Pt–N) and m(Pt–O) vibrations have
been located at 549 and 415 cmꢀ1, respectively, [20]. In a
few examples with 1,1-CBDCA the authors have assigned
the m(Pt–O) vibrations between 460 and 480 cmꢀ1 [33–35].
In these cis compounds, only one m(Pt–O) band was
observed, although theoretically, there should be two.
These vibrations seem to be very dependent on the metal
and are affected by intermolecular interactions. We have
used these references to make tentative assignments for
the m(Pt–N) and m(Pt–O) vibrations in our complexes and
these are shown in Table 6. One weak band observed
between 458 and 496 cmꢀ1 was assigned to the m(Pt–O)
vibrations, while two weak bands observed between 303
and 374 cmꢀ1 were assigned to the m(Pt–N) modes. Two
bands were observed for the latter vibrations as expected
for cis compounds. The m(Pt–N) vibrations seem to absorb
at quite low energy, in the same region as the m(Pt–Cl)
vibrations, but similar values were reported for the com-
pounds Pt(amine)2I2 with the same amines [12] and for
the Pt(amine)2(NO3)2 compounds discussed in the above
section. It seems that the m(Pt–N) vibrations absorb at
lower energy for amines containing an aromatic group
compared to aliphatic amines, where these vibration modes
are observed at higher energy [9,10].
3.2.2. IR spectroscopy
All the isolated complexes were characterized by IR
spectroscopy and the results are shown in the experimental
section. The carboxylate region is of special interest for this
type of compounds. For the carboxylate ions, the m(C@O)
vibrations absorb between 1595 and 1565 cmꢀ1, while the
m(C–O) vibrations range between 1410 and 1330 cmꢀ1
.
The difference between the two vibration modes (Dm) is
smaller in the carboxylates (ꢂ180 cmꢀ1) than in the acids
(ꢂ400 cmꢀ1), where the resonance is much reduced.
The m(C@O) and m(C–O) vibrations modes of the cis
dicarboxylato Pt(II) complexes are shown in Table 5. A
few bands are split. The m(C@O) vibrations absorb around
1610 cmꢀ1, while the m(C–O) mode was observed around

F.D. Rochon et al. / Inorganica Chimica Acta 361 (2008) 1437–1446
1445
Table 6
pension, but no change was observed after filtering. It
might be caused by the presence of paramagnetic species.
Furthermore, there were more signals than expected, sug-
gesting the presence of decomposition products. Therefore,
the solution NMR study was not pursued for the moment.
Efforts were made to obtain crystals of good quality for
X-ray diffraction studies, but again without success.
Monodentate carboxylato ligands might produce
slightly more soluble Pt(II) complexes. The research project
is continuing along this line, but isomerization of the cis
compounds usually occur in organic solvents, especially
when slightly heated, which is usually required to slightly
dissolve these species.
Tentative m(Pt–O) and m(Pt–N) vibrations (cmꢀ1) in the complexes cis-
Pt(amine)2(R(COO)2)
Amine
R(COO)2
m(Pt–O)
m(Pt–N)
PhNH2
1,1-CBDCA
458
353, 303
PhMeNH2
1,1-CPDCA
1,1-CBDCA
1,2-CBDCA
480
481
480
374, 326
357, 329
354, 326
PhEtNH2
PhPrNH2
PhBuNH2
1,1-CPDCA
1,1-CBDCA
1,2-CBDCA
488
490
490
366, 326
350, 326
345, 327
1,1-CPDCA
1,1-CBDCA
1,2-CBDCA
468
470
494
353, 321
352, 323
364, 330
1,1-CPDCA
1,1-CBDCA
1,2-CBDCA
496
469
462
366, 325
352, 329
351, 328
Acknowledgement
The authors are grateful to the Natural Sciences and
Engineering Research Council of Canada for financial sup-
port of the project.
4. Conclusion
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