Synthesis and characterization of Pt(II) complexes with amine and carboxylato ligands. Crystal structure of (1,1-cyclobutanedicarboxylato)di(ethylamine)platinum(II)·H2O

Article abstract of DOI:10.1016/S0020-1693(00)00171-7

Two methods for the synthesis of compounds of the type cis-PtA₂X₂ (A₂ = bidentate amine or two monodentate amines and X₂ = bidentate or two monodentate carboxylato ligands) were evaluated. The compounds were characterized by multinuclear NMR and IR spectroscopies. The ¹⁹⁵PT NMR chemical shifts were in the range - 1615 to - 1976 ppm, the higher field values corresponding to the complexes containing bidentate ligands. The coupling constants ³J(¹⁹⁵Pt-¹H) are approximately 35 Hz, while the ²J(¹⁹⁵Pt-¹HN) are about 70 Hz. One coupling constant ²J(¹⁹⁵Pt-¹³C) (53 Hz) was also measured. The crystal structure of the compound, cis-Pt(1,1-cyclobutanedicarboxylato)(C₂H₅NH₂)₂·H₂O belongs to the P2₁/n space group with a=9.468(5), b =9.365(4), c = 16.473(7) A?, β = 105.08(3)°, Z = 4 and R₁ = 0.0576. The Pt-N bond distances are 1.992(5) and 2.020(5) A?, while the Pt-O bonds are 2.000(4) and 2.015(4) A?. The molecules are held together by intermolecular H-bonds involving the lattice water molecules and the two free carbonyl O atoms and between the amino H atoms and the Pt-bonded C-O groups. (C) 2000 Elsevier Science S.A.

Full text of DOI:10.1016/S0020-1693(00)00171-7

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Inorganica Chimica Acta 306 (2000) 193–204
Synthesis and characterization of Pt(II) complexes with amine and
carboxylato ligands. Crystal structure of
(1,1-cyclobutanedicarboxylato)di(ethylamine)platinum(II)·H2O
Fernande D. Rochon *, Letitia M. Gruia
Department of Chemistry, Uni6ersite´ du Que´bec a` Montre´al, C.P. 8888, Succ. Centre-6ille, Montre´al, Canada, H3C 3P8
Received 13 January 2000; accepted 28 April 2000
Abstract
Two methods for the synthesis of compounds of the type cis-PtA2X2 (A2=bidentate amine or two monodentate amines and
X2=bidentate or two monodentate carboxylato ligands) were evaluated. The compounds were characterized by multinuclear
NMR and IR spectroscopies. The 195Pt NMR chemical shifts were in the range −1615 to −1976 ppm, the higher field values
corresponding to the complexes containing bidentate ligands. The coupling constants 3J(195Pt–1H) are approximately 35 Hz, while
2
2
the J(195Pt–1HN) are about 70 Hz. One coupling constant J(195Pt–13C) (53 Hz) was also measured. The crystal structure of the
compound, cis-Pt(1,1-cyclobutanedicarboxylato)(C2H5NH2)2·H2O belongs to the P21/n space group with a=9.468(5), b=
,
,
9.365(4), c=16.473(7) A, i=105.08(3)°, Z=4 and R1=0.0576. The PtꢀN bond distances are 1.992(5) and 2.020(5) A, while the
,
PtꢀO bonds are 2.000(4) and 2.015(4) A. The molecules are held together by intermolecular H-bonds involving the lattice water
molecules and the two free carbonyl O atoms and between the amino H atoms and the Pt-bonded CꢀO groups. © 2000 Elsevier
Science S.A. All rights reserved.
Keywords: Crystal structures; Platinum complexes; Carboxylato complexes; Amine complexes
strong antitumor effect, but at a markedly higher
dosage due to the delayed formation of the active
aquated metabolites [2]. A few other amine–carboxy-
lato Pt(II) complexes also have good antitumor activi-
ties like Pt(dach)(oxalato) (oxaliplatin), Pt(dach)-
(malonato) (where dach=1,2-diaminocyclohexane) and
Pt(ethylenediamine)(malonato) (malonatoplatin) [3].
Although these types of compound have been studied
by several researchers in the biological sciences, the
chemical knowledge related to the synthesis and charac-
terization of these molecules is limited, especially for
complexes with amines other than NH3, dach or
ethylenediamine.
1. Introduction
Cis-Pt(NH3)2Cl2 (cisplatin) is well known as an anti-
tumor drug [1]. However, there are still difficulties
related to its use, because of its numerous side effects
and toxicity, although several methods have been devel-
oped in the last ten years which have considerably
reduced these side effects. Cisplatin is not very soluble
in water and it tends to hydrolyze at neutral pH,
producing several species, including toxic hydroxo-
bridged oligomers. Replacement of the chloro ligands
by carboxylato groups reduces the toxicity of the plat-
inum compounds and increases their solubility in water.
We have recently undertaken a study of the synthesis
and characterization of platinum(II) complexes, with
various amines and several carboxylato ligands in order
to establish the purity of the products, which has not
always been studied in the literature, except for elemen-
tal analysis. The latter method is not a good criterion
for the purity of the Pt complexes, since the products
might contain isomers. We have found that multinu-
A
second generation antitumor Pt compound,
Pt(NH3)2(1,1%-cyclobutanedicarboxylato) (carboplatin)
is now commercially available in several countries. It is
more soluble than cisplatin and produces an equally
* Corresponding author. Tel.: +1-514-9873000 ext. 4896; fax:
+1-514-9874054.
E-mail address: rochon.fernande@uqam.ca (F.D. Rochon).
0020-1693/00/$ - see front matter © 2000 Elsevier Science S.A. All rights reserved.
PII: S0020-1693(00)00171-7

194
F.D. Rochon, L.M. Gruia / Inorganica Chimica Acta 306 (2000) 193–204
clear NMR (195Pt, 1H and 13C) spectroscopy is an
effective and underused method to detect both the
chemical and most important the isomeric purity of
these types of compound. The choice of a solvent is
usually a problem for solution studies of Pt complexes,
but in the present case, most of the complexes are
sufficiently soluble in water. However, some Pt(II) com-
plexes hydrolyze or are aquated in water and the results
of aqueous studies in such cases must be interpreted
with care. The results of this study are reported below.
in a minimum quantity of acetone and filtered and
diethylether was added to the filtrate until a slight
turbidity occurred. The mixture was cooled to about
3°C for several hours. The crystals were filtered, washed
with diethylether and dried under vacuum. The yields
of the dinitrato complexes were around 85% (from
K2[PtCl4]). These compounds are dissolved in about 20
ml of water to obtain the diaqua species. The sodium
carboxylate compounds were prepared in situ by react-
ing 1 mmol of the carboxylic acid with 1 mmol (mono-
acid) or 2 mmol (diacid) of NaOH. The required
stoichiometric quantity of sodium carboxylate was then
added to the diaqua species prepared above. The mix-
ture was stirred for 4–5 days and then filtered. The
filtrate was evaporated to dryness and methanol added
to the residue in order to dissolve the free ligand. The
insoluble Pt complex was filtered, washed with di-
ethylether and dried in vacuum. The yields varied be-
tween 11 and 51% (from K2[PtCl4]).
2. Experimental
K2[PtCl4] was purchased from Johnson Matthey and
Co. and was recrystallized from water before use. The
amines, the carboxylic acids, sodium acetate, sodium
benzoate, D2O and DMF-d7 were obtained from
Aldrich. The silver salts were bought from Anachemia
and CDCl3 from Merck Frosst.
The melting or decomposition points of the platinum
compounds were measured on a Fisher–Johns instru-
ment. The IR spectra were recorded in KBr pellets on a
Perkin–Elmer model 783 spectrometer between 4000
and 250 cm−1. The NMR spectra were measured in
D2O (unless specified otherwise) on a Varian Gemini
300 BB spectrometer operating at 300.1 MHz (1H), 75.5
MHz (13C) and at 64.4 MHz (195Pt, spectral window=
1500 ppm). The external references were DSS (DSS in
D2O placed in an inner small tube adjusted to 0 ppm)
for 1H and 13C. K2[PtCl4] with KCl (adjusted to −1628
ppm from Na2PtCl6, (l=0 ppm)) was used for 195Pt
NMR. For the spectra measured in CDCl3, CHCl3 was
adjusted at 77.00 ppm (relative to TMS l=0.00 ppm)
for the 13C spectra and at 7.27 ppm (relative to TMS
2.1.2. cis-PtA2X2 Method 2
cis-PtA2I2 (1 mmol) was added to a 40 ml aqueous
solution containing 0.98 mmol of AgSO4 and the mix-
ture was stirred for 4 h in the dark. The mixture was
then filtered to remove the AgI precipitate and the
diaqua filtrate was set aside for the reaction with the
carboxylate ligands. The barium carboxylate com-
pounds were prepared in situ by reacting 0.98 mmol of
Ba(OH)2 with 15 ml of an aqueous solution containing
1.125 mmol of the dicarboxylic acid or 2.25 mmol of
monocarboxylic acid. The mixture (which contains bar-
ium carboxylate) was slowly added to the ionic diaqua
species prepared above. BaSO4 precipitated immedi-
ately and the mixture was stirred for 20 min (2 h for the
acetato complexes) and then filtered. The filtrate was
evaporated to dryness and methanol added to the
residue in order to dissolve the free ligand. The insolu-
ble Pt complex was filtered, washed with diethylether
and dried in vacuum. The yields varied between 45 and
88% (from K2[PtCl4]).
1
l=0.00 ppm) for the H spectra.
2.1. Syntheses
cis-PtA2I2 (A=amine): these complexes were pre-
pared by Dhara’s method [4]. The yields varied between
87 and 95%.
cis-Pt(NH3)2(Ac)2: Yield 32% (Method 1) 60%
(Method 2), dec. 168–175°C; IR (cm−1): 3260m,
2940w, 1650s, 1610s, 1580sh, 1565sh, 1390s, 1055m,
1
2.1.1. cis-PtA2X2 Method 1
1045m, 865br, 705s, 622w, 550br, 330w; H NMR: l
cis-PtA2I2 (1 mmol) was added to 15 ml of water and
1.95 mmol of solid pulverized AgNO3 was added to the
suspension. After 24 h of stirring in the dark, the AgI
precipitate was filtered off and the diaqua filtrate was
set aside for the reaction with the carboxylate ligands.
The diaqua solution was also prepared by a faster
reaction as follows: cis-PtA2I2 (1 mmol) was dissolved
in a minimum quantity of acetone. A slight excess (2.2
mmol) of solid pulverized AgNO3 was added to the
solution which was stirred for 10–20 min. The AgI
precipitate was filtered and the filtrate was evaporated
to dryness. The residue cis-PtA2(ONO2)2 was dissolved
(ppm) 1.96s, 4.08(NH3); 13C NMR: l (ppm) 24.79,
184.71. cis-Pt(NH3)2(PhCOO)2: Yield 26% (Method 1)
57% (Method 2), dec. 270–280°C; IR (cm−1): 3280m,
1645s, 1625s, 1560s, 1455w, 1380s, 1075m, 1030m,
900br, 830br, 715s, 690sh, 680sh, 540w, 430br, 360w.
cis-Pt(NH3)2(Ox): Yield 30% (Method 1), dec. 179–
190°C; IR (cm−1): 3280s, 3200sh, 3140sh, 1670s, 1615s,
1395s, 1355s, 850s, 795s, 570m, 480s, 395m, 370w,
300m. cis-Pt(NH3)2(Mal): Yield 35% (Method 1) 53%
(Method 2), dec. 196–210°C; IR (cm−1): 3280s,
3130sh, 2930w, 1660s, 1630s, 1585sh, 1460m, 1390s,
1330s, 1300m, 1150m, 960m, 940m, 850m, 840m, 585m,

F.D. Rochon, L.M. Gruia / Inorganica Chimica Acta 306 (2000) 193–204
195
1
468w, 375m, 340w. cis-Pt(NH3)2(Bumal): Yield 61%
(Method 2), dec. 215–227°C; IR (cm−1): 3118s, 3085s,
2960s, 2875m, 1665s, 1640s, 1470br, 1440w, 1400s,
1360s, 1310m, 1267m, 1248m, 1140m, 968br, 900m,
865m, 830m, 809m, 755m, 723w, 595m, 540w, 400w,
410sh, 389m, 340w; H NMR: l (ppm) 1.26t, 2.64q,
3.21s, 3.78s, 7.36m; 13C NMR: l (ppm) 17.68, 44.24,
39.48, 62.32, 129.72, 131.48, 140.92, 182.62. cis-
Pt(EtNH2)2(CBDCA): Yield 82% (Method 2), dec.
238–245°C; IR (cm−1): 3220m, 3140br, 2985m, 2950sh,
1660s, 1620s, 1470w, 1450w, 1408sh, 1365s, 1362sh,
1266w, 1252w, 1109m, 1082m, 1040w, 905m, 770m,
1
345w; H NMR: l (ppm) 0.92t, 1.39m, 2.56m, 3.53t,
4.22(NH3); 13C NMR: l (ppm) 15.83, 24.38, 31.92,
33.63, 60.77, 183.92. cis-Pt(NH3)2(Benzmal): Yield 76%
(Method 2), dec. \300°C; IR (cm−1): 3240m, 2960br,
1670s, 1630s, 1490m, 1430br, 1395s, 1270sh, 1170br,
1075w, 1025w, 958m, 905w, 860m, 750m, 695s, 570m,
540br, 465m, 398w. cis-Pt(NH3)2(CBDCA): Yield 41%
(Method 1) 80% (Method 2) dec. 241–250°C; IR
(cm−1): 3285s, 3000w, 2960m, 1655s, 1610m, 1378s,
1360s, 1286w, 1202br, 1112m, 1045w, 900m, 863m,
762w, 655w, 615w, 572w, 474m, 350m; 1H NMR: l
1
700w, 560w, 470m, 345m, 328m; H NMR: l (ppm)
1.23t, 1.88quintet, 2.65q, 2.87t; 13C NMR: l (ppm)
17.65, 18.03, 33.67, 44.18, 58.88, 184.50.
cis-Pt(Me2NH)2(Ac)2: Yield 30% (Method 1) 52%
(Method 2), dec. 174–185°C; IR (cm−1): 3190s, 3120s,
2960m, 1650s, 1610s, 1460sh, 1380s, 1330sh, 1127w,
1
1085m, 1010m, 895m, 687m, 545w, 395w; H NMR: l
(ppm) 1.96s, 2.49s J(195Pt–1H)=36 Hz; 13C NMR: l
3
(ppm) 24.88, 46.18, 184.33. cis-Pt(Me2NH)2(PhCOO)2:
Yield 15% (Method 1) 57% (Method 2), dec. 159–
170°C; IR (cm−1): 3190s, 3000w, 2950w, 1700sh, 1645s,
1620s, 1580s, 1500w, 1470m, 1432w, 1370s, 1312w,
1180m, 1138m, 1108m, 1075m, 1030m, 1021m, 902s,
2
(ppm) 1.87quintet, 2.86t, 4.18(NH3) J(195Pt–1H)=69
Hz; 13C NMR: l (ppm) 18.00, 33.78, 58.97, 184.61.
cis-Pt(EtNH2)2(Ac)2: Yield 50% (Method 2), dec.
148–157°C; IR (cm−1): 3220m, 3130w, 3000w, 2950w,
1645s, 1610s, 1570sh, 1453w, 1435sh, 1390s, 1328s,
1270w, 1253w, 1090s, 1045m, 1020m, 935m, 805br,
760s, 690s, 530br, 380w, 360w; 1H NMR: l (ppm)
1.31t, 2.00s, 2.88q, 5.12s; 13C NMR: l (ppm) 17.65,
25.14, 44.30, 184.91. cis-Pt(EtNH2)2(PhCOO)2: Yield
45% (Method 2), dec. 153–165°C; IR (cm−1): 3210m,
2990w, 2945w, 1640s, 1620s, 1578s, 1498w, 1454m,
1370s, 1180m, 1090m, 1075m, 1030m, 850m, 755m,
723s, 688s, 623br, 530w, 408w, 335w; 1H NMR: l
(ppm) 1.25t, 2.87q, 6.15s, 7.30t, 7.40t, 7.97d; 13C NMR:
l (ppm) 16.21, 42.50, 128.51, 129.43, 130.93, 134.24,
175.27. cis-Pt(EtNH2)2(Ox): Yield 43% (Method 1),
dec. 203–215°C; IR (cm−1): 3210s, 3130s, 3000m,
1670s, 1615sh, 1455m, 1423w, 1395s, 1265br, 1100m,
1075m, 900br, 810s, 560m, 550m, 425w, 385m, 322m;
1
850m, 724s, 700s, 610w, 548w, 447w, 362w; H NMR:
l (ppm) 2.70d, 3.46s, 7.29t, 7.38t, 7.98d; 13C NMR: l
(ppm) 44.84, 128.66, 129.71, 131.43, 135.29, 175.86.
cis-Pt(Me2NH)2(Ox): Yield 35% (Method 1), dec. 205–
217°C; IR (cm−1): 3200s, 2980w, 1680s, 1630s, 1520br,
1470m, 1325sh, 1390s, 1123s, 1080m, 1020m, 900s,
855s, 578m, 550m, 465m, 395w, 362m; 1H NMR: l
(ppm) 2.57d J(195Pt–1H)=36 Hz; 13C NMR: l (ppm)
3
46.64, 171.37. cis-Pt(Me2NH)2(Mal): Yield 33%
(Method 1) 63% (Method 2), dec. 160–173°C; IR
(cm−1): 3170s, 3000w, 1660s, 1635s, 1470m, 1430sh,
1405sh, 1385s, 1315w, 1298w, 1220w, 1112s, 1105s,
1025w, 970s, 937m, 865s, 750s, 575m, 460m, 378m,
335w; H NMR: l (ppm) 2.57d J(195Pt–1H)=36 Hz,
1
3
3.71s, 5.65s J(195Pt–1H)=69 Hz; 13C NMR: l (ppm)
2
3
1H NMR: l (ppm) 1.25t, 2.65q J(195Pt–1H)=30 Hz;
45.96, 50.28, 180.97. cis-Pt(Me2NH)2(Bumal): Yield
64% (Method 2), dec. 168–179°C; IR (cm−1): 3150s,
2960m, 2940m, 1660s, 1630s, 1465m, 1430sh, 1385s,
1338w, 1203br, 1130w, 1090m, 1018m, 860s, 800br,
618w, 525br, 400w, 355w; 1H NMR: l (ppm) 0.94t,
13C NMR:
l (ppm) 17.66, 44.53, 171.63. cis-
Pt(EtNH2)2(Mal): Yield 68% (Method 2), dec. 187–
193°C; IR (cm−1): 3200s, 3120s, 2970w, 1655s, 1625s,
1480w, 1400sh, 1375sh, 1390s, 1278m, 1140w, 1080m,
1035w, 950m, 935m, 860m, 730s, 595m, 420w, 360m,
1.42m, 2.58t, 2.77m, 3.48t, 5.68s J(195Pt–1H)=68 Hz;
2
325w; H NMR: l (ppm) 1.26t, 2.63q, 3.68s J(195Pt–
13C NMR: l (ppm) 15.85, 24.41, 32.01, 33.82, 46.09,
60.84, 183.69. cis-Pt(Me2NH)2(Benzmal): Yield 68%
(Method 2), dec. 182–195°C; IR (cm−1): 3170s, 3000w,
2940w, 1730sh, 1675s, 1630s, 1610sh, 1500sh, 1482m,
1435m, 1385s, 1280m, 1192m, 1170m, 1100s, 1025w,
1015w, 960w, 904m, 865m, 852m, 750s, 695s, 610sh,
600m, 565w, 475w, 380m, 330w; 1H NMR: l (ppm)
2.57d 3J(195Pt–1H)=33 Hz, 3.18s, 3.88t, 5.67s
2J(195Pt–1H)=68 Hz, 7.35m; 13C NMR: l (ppm) 39.67,
46.11, 62.19, 129.77, 131.53, 140.83, 182.56. cis-
Pt(Me2NH)2(CBDCA): Yield 50% (Method 1) 83%
(Method 2), dec. 179–190°C; IR (cm−1): 3230s,
2960br, 1660s, 1615s, 1475sh, 1462m, 1370s, 1308br,
1282br, 1250m, 1204m, 1112m, 1085m, 1040m, 1019m,
1
3
1H)=36 Hz, 4.91s J(195Pt–1H)=72 Hz; 13C NMR: l
2
(ppm) 17.67, 44.09, 50.21, 181.00. cis-Pt(EtNH2)2-
(Bumal): Yield 57% (Method 2), dec. 213–221°C; IR
(cm−1): 3230s, 3140s, 2970s, 2940s, 1665s, 1635s,
1482w, 1458w, 1395s, 1315br, 1280br, 1200w, 1085m,
1038m, 960m, 902m, 802w, 815m, 770m, 585w, 390w;
1H NMR: l (ppm) 0.93t, 1.25t, 1.40m, 2.64m, 2.67q,
3.48t, 4.93s; 13C NMR: l (ppm) 15.83, 17.59, 24.42,
32.00, 33.86, 44.19, 60.93, 183.80. cis-Pt(EtNH2)2-
(Benzmal): Yield 52% (Method 2), dec. 198–215°C; IR
(cm−1): 3220s, 3140s, 2990m, 2940w, 1730sh, 1675s,
1630sh, 1600sh, 1503m, 1470m, 1460m, 1440sh, 1390s,
1350sh, 1257br, 1170w, 1085br, 1035w, 960m, 870m,
860m, 820w, 761s, 705s, 615m, 602m, 565m, 470br,
1
949m, 903s, 875s, 700w, 614w, 553w, 470m, 348m; H

196
F.D. Rochon, L.M. Gruia / Inorganica Chimica Acta 306 (2000) 193–204
NMR:
l
(ppm) 2.89t, 1.90quintet, 2.58d, 5.63s
1475sh, 1390s, 1350w, 1295w, 1145wm, 1040w, 1015m,
960m, 820m, 780m, 650m, 555m, 510m, 360w; 1H
NMR: l (ppm) 1.98s, 2.75s, 2.79s; 13C NMR: l (ppm)
2J(195Pt–1H)=67 Hz; 13C NMR: l (ppm) 18.03, 33.47,
46.08, 58.78, 184.38.
2
cis-Pt(Me2en)(Ac)2: Yield 19% (Method 1) 75%
(Method 2), dec. 201–210°C; IR (cm−1): 3240s,
2940br, 1650s, 1615s, 1585sh, 1470m, 1430sh, 1390s,
1330s, 1210m, 1060m, 990m, 950m, 790m, 695s, 560br,
24.93. 54.56, 67.65, 184.04 J(195Pt–13C)=53 Hz. cis-
Pt(Me4en)(PhCOO)2: Yield 11% (Method 1) 63%
(Method 2), dec. 225–233°C; IR (cm−1): 3080s, 3010w,
1720sh, 1650s, 1585s, 1465m, 1455m, 1375s, 1310sh,
1137m, 1070m, 1032m, 1010m, 962m, 845m, 820s,
775w, 727s, 700s, 610w, 535w, 445w, 335w; 1H NMR: l
(ppm) 2.58s, 2.93s, 7.24t, 7.31t, 7.95d; 13C NMR: l
(ppm) 52.72, 65.30, 128.52, 129.55, 130.59, 135.29,
172.81. cis-Pt(Me4en)(Ox): Yield 51% (Method 1), dec.
230–238°C; IR (cm−1): 2960s, 1680s, 1480m, 1470m,
1360br, 1390s, 1300m, 1255m, 1215w, 1140w, 1040m,
1020s, 965s, 840sh, 830sh, 815s, 775m, 560m, 530m,
400w, 360w, 330m; 1H NMR: l (ppm) 2.84s, 2.91s
3J(195Pt–1H)=30 Hz; 13C NMR: l (ppm) 54.94, 67.18,
171.43. cis-Pt(Me4en)(Mal): Yield 83% (Method 2), dec.
227–234°C; IR (cm−1): 3000m, 2930w, 1660s, 1465br,
1410s, 1385s, 1300w, 1205w, 1115br, 1010m, 957m,
942m, 812s, 775m, 750s, 615m, 530w, 465br, 355m,
1
365w, 325w; H NMR: l (ppm) 2.02s, 2.64m, 2.68m,
2.73s; 13C NMR: l (ppm) 25.25, 47.68, 54.56, 70.84,
184.89. cis-Pt(Me2en)(PhCOO)2: Yield 23% (Method 1)
58% (Method 2), dec. 247–255°C; IR (cm−1): 3220m,
3125m, 2989w, 2890w, 1645s, 1630s, 1580s, 1498w,
1455br, 1375s, 1310sh, 1202w, 1175w, 1153m, 1072w,
1030m, 990w, 848m, 792w, 720s, 698s, 615br, 560w,
1
445w, 330w; H NMR: l (ppm) 2.89s, 2.78m, 5.28s,
7.22t, 7.32t, 7.91d; 13C NMR: l (ppm) 45.23, 51.43,
68.76. cis-Pt(Me2en)(Ox): Yield 49% (Method 1), dec.
208–219°C; IR (cm−1): 3250s, 2950w, 1670s, 1620sh,
1470sh, 1405br, 1385s, 1230br, 1170sh, 1055m, 990m,
950m, 900m, 840m, 830m, 818s, 790s, 780m, 560br,
1
500br, 395w, 330w; H NMR: l (ppm) 2.64m, 2.73m,
2.89s 3J(195Pt–1H)=33 Hz, 5.52s 2J(195Pt–1H)=66
Hz; 13C NMR: l (ppm) 47.45, 54.79, 70.15, 171.44.
cis-Pt(Me2en)(Mal): Yield 80% (Method 2), dec. 210–
223°C; IR (cm−1): 3200s, 3095s, 2960sh, 1655s, 1630s,
1470m, 1405sh, 1375s, 1360sh, 1235w, 1150br, 1070m,
1000w, 953m, 918w, 807m, 758m, 635m, 615w, 570br,
340m; H NMR: l (ppm) 2.82s J(195Pt–1H)=33 Hz,
2.86s, 3.69s; 13C NMR: l (ppm) 50.41, 54.14, 67.32,
180.81. cis-Pt(Me4en)(Bumal): Yield 85% (Method 2),
dec. 218–227°C; IR (cm−1): 2970s, 2940s, 1670s,
1475m, 1448sh, 1385s, 1346m, 1285w, 1135w, 1040m,
1012m, 963m, 900w, 822s, 780w, 605w, 540br, 390m;
1H NMR: l (ppm) 0.93t, 1.41m, 2.67m, 2.82s, 2.84s,
2.88s, 3.48t; 13C NMR: l (ppm) 15.90, 24.48, 32.09,
34.07, 54.39, 54.15, 60.99, 67.34, 183.63. cis-
Pt(Me4en)(Benzmal): Yield 81% (Method 2), dec. 240–
252°C; IR (cm−1): 3030s, 3000sh, 1730sh, 1675s,
1610sh, 1502m, 1475m, 1460sh, 1380s, 1350m, 1312m,
1280m, 1243m, 1170m, 1040m, 1014m, 960s, 917w,
862m, 850m, 820s, 745s, 700s, 614m, 602sh, 563w,
474w, 387m, 330w; 1H NMR: l (ppm) 2.80s, 2.81s,
2.84s, 3.18s, 3.75s, 7.35m; 13C NMR: l (ppm) 39.84,
54.10, 54.44, 62.21, 67.32, 129.85, 131.59, 140.67,
182.54. cis-Pt(Me4en)(CBDCA): Yield 45% (Method 1)
88% (Method 2), dec. 221–235°C; IR (cm−1): 3000s,
1660s, 1592sh, 1475s, 1445w, 1365s, 1285w, 1250w,
1210w, 1125s, 1042s, 1015m, 965s, 904m, 823s, 780m,
621m, 566m, 480s, 350s; 1H NMR: l (ppm) 1.89quintet,
2.81s, 2.83s, 2.86t; 13C NMR: l (ppm) 18.04, 33.48,
54.24, 58.71. 67.32, 184.29.
1
3
1
460m, 385m, 345w; H NMR: l (ppm) 2.70m, 2.75m,
2.80s 3J(195Pt–1H)=34 Hz, 3.65s, 5.52s 2J(195Pt–1H)=
66 Hz; 13C NMR: l (ppm) 47.48, 50.18, 54.07, 70.84,
180.81. cis-Pt(Me2en)(Bumal): Yield 81% (Method 2),
dec. 214–225°C; IR (cm−1): 3220s, 3100sh, 2970m,
2945m, 1660s, 1640s, 1470m, 1450sh, 1385s, 1350sh,
1280w, 1135w, 1055m, 990m, 950m, 900m, 790m,
610br, 560w, 405w, 390w; 1H NMR: l (ppm) 0.93t,
1.41m, 2.59m, 2.72m, 2.80s, 2.82s, 3.47t, 5.57s; 13C
NMR: l (ppm) 15.86, 24.48, 32.08, 33.98, 47.43, 54.12,
54.26, 61.04, 70.83, 183.66. cis-Pt(Me2en)(Benzmal):
Yield 81% (Method 2), dec. 236–248°C; IR (cm−1):
3180s, 3080sh, 2940w, 1730sh, 1670s, 1640s, 1500m,
1465m, 1440sh, 1385s, 1350sh, 1320w, 1270m, 1098w,
1055m, 1002m, 985m, 948m, 902m, 855m, 790m, 758m,
700s, 602m, 560m, 480br, 382m, 362w; 1H NMR: l
(ppm) 2.72m, 2.79s, 2.81s, 3.18s, 3.82t, 5.52s, 7.37m;
13C NMR: l (ppm) 39.60, 47.56, 54.40, 54.11, 62.25,
70.86, 129.77, 131.50, 140.87, 182.43. cis-Pt(Me2en)-
(CBDCA): Yield 30% (Method 1) 85% (Method 2), dec.
227–235°C; IR (cm−1): 3200s, 2995m, 2905sh, 1655s,
1615s, 1470m, 1430w, 1375s, 1360m, 1260w, 1200w,
1123s, 1050m, 945s, 902s, 855m, 789s, 766m, 620w,
2.2. Crystallographic measurements and structure
resolution
The crystal was selected after examination under a
polarizing microscope for homogeneity. The unit cell
parameters were obtained by least-squares refinement
of the angles for 29 well-centered reflections, on a
Siemens P4 diffractometer using graphite-monochroma-
tized Mo Ka radiation. The Siemens XSCANS program
[5] was used for the crystal centering, the data collec-
1
601w, 563br, 480m, 372m, 357m; H NMR: l (ppm)
1.89quintet, 2.71m, 2.81s, 2.87t, 5.56s 2J(195Pt–1H)=70
Hz; 13C NMR: l (ppm) 18.03, 33.57, 47.55, 54.18,
58.79, 70.79, 184.42.
cis-Pt(Me4en)(Ac)2: Yield 23% (Method 1) 58%
(Method 2), dec. 174–182°C; IR (cm−1): 2940s, 1650s,

F.D. Rochon, L.M. Gruia / Inorganica Chimica Acta 306 (2000) 193–204
197
tion and the data reducing process. The background
time to scan time ratio was 0.5.
Two methods were used to prepare the compounds.
The first method has been reported to prepare com-
plexes with similar ligands [7]. The reactions in water
are as follows:
The intensity data were corrected for absorption
(Gaussian integration) and for Lorentz and polariza-
tion effects. The coordinates of the Pt atom were
determined from a Patterson map calculation, and the
positions of all the other non-hydrogen atoms were
found by the usual Fourier methods. The refinement of
the structure was done on F2 by full-matrix least-
squares analysis. The H atoms were fixed at their
calculated positions (riding model) with Ueq=1.2 (1.5
for CH3 groups) Ueq of the atom to which it is bonded.
The crystal belongs to the monoclinic P21/n space
H O
2
cis-PtA2I2+2AgNO3 “ cis-[PtA2(H2O)2](NO3)2
+2AgI¡
cis-[PtA2(H2O)2](NO3)2+2NaX
“cis-PtA2X2+2NaNO3
The cis-PtA2I2 complexes were prepared by Dhara’s
method [4]. The silver salt should not be in excess in the
mixture, since other species will be produced. For this
reason, a Pt–Ag molar ratio of 1:1.95 was used. Since
the diiodo Pt compound is very sparingly soluble in
water, the reaction with the silver salt is very slow.
Acetone has been used in the literature for a similar
reaction [8]. We have found that if the above reaction
with the silver salt is done in acetone, it is much faster.
A slight excess of the silver salt can then be used, which
,
group with a=9.468(5), b=9.365(4), c=16.473(7) A,
3
,
i=105.08(3)°, V=1410.4(11) A , Z=4, z=2.098 g
cm−3, v=9.964 mm−1, F(000)=856, Mw=445.4.
The refinement of the scale factor, coordinates and
anisotropic temperature factors of all the non-hydrogen
atoms converged to R1 (3038 reflections F\2|(I))=
0.0576 and wR2 (all data, 3728 reflections)=0.1396. All
the calculations were done using the Siemens SHELXTL
system [6].
considerably increased the yields.
acetone
cis-PtA2I2+2AgNO3 ꢀꢀꢀꢁ cis-PtA2(NO3)2+2AgI¡
The AgI is filtered together with the excess of silver
nitrate, which is not very soluble in cold acetone. The
acetone is then evaporated and the residue is again
dissolved in acetone to remove the last traces of the two
silver compounds. The solid dinitrato Pt compound is
finally dissolved in a small quantity of water to produce
the diaqua species which is then reacted with sodium
carboxylate as described above.
The reaction with sodium carboxylate is quite slow
and depends on the ligands (4–5 days). It is very
difficult to evaluate the extent of the reaction, since all
the reactants and products are soluble in water. Fur-
thermore, the separation of the Pt complexes from
sodium nitrate is difficult. For these reasons, the overall
yields for this method are not very high, ranging be-
tween 11 and 51% (from K2[PtCl4]).
3. Results and discussion
A few methods for the synthesis of carboxylato–
amine Pt(II) complexes are available in the literature,
but the yields are usually low and we have found that
the products are not always of high purity. We have
therefore studied these methods in a view of developing
the experimental conditions to obtain a more general
method, adaptable to different kinds of amines and
carboxylato ligands. Higher yields and a great purity of
the products were a high priority in this project.
We have now synthesized several complexes cis-
PtA2X2 where A2=bidentate or two monodentate
amine and X2 is a bidentate or two monodentate car-
boxylato ligands. We have chosen various types of
ligand with different bulkiness. Five amines were cho-
sen: NH3, a primary amine, ethylamine (EtNH2), a
secondary amine, dimethylamine (Me2NH) and two
We have therefore examined a second method for the
preparation of amine–carboxylato Pt complexes, which
eventually proved to produce much purer compounds
and with considerable increased yields. Silver sulfate is
used instead of the nitrate salt and barium carboxylate
(prepared in situ) is used instead of the sodium salt.
This method was adapted from the published method
used to prepare similar complexes [9]. The reactions
were done in H2O.
bidentate
amines,
N,N-dimethylethylenediamine
(Me2en) and N,N,N%,N%-tetramethylethylenediamine
(Me4en). For each of these amines, Pt(II) complexes
were synthesized with two monodentate carboxylato
ligands, acetato (Ac) and benzoato (PhCOO) and five
bidentate carboxylato ligands, namely oxalato (Ox),
malonato (Mal), n-butylmalonato (Bumal), benzyl-
malonato (Benzmal) and 1,1-cyclobutanedicarboxylato
(CBDCA). Complexes containing dimethylamine were
also synthesized with two other carboxylato ligands,
1,1-cyclopentanediacetato (CPDA) and 1,1-cyclohex-
anediacetato (CHDA). All the compounds were charac-
terized by IR and multinuclear NMR spectrocopies.
H O
2
cis-PtA2I2+Ag2SO4 “ cis-[PtA2(H2O)2](SO4)+2AgI¡
H O
2
cis-[PtA2(H2O)2](SO4)+BaX2 “ cis-PtA2X2+BaSO4¡
The diaqua species contain also some PtA2(H2O)(SO4).
This second method is much faster, is easy to control,
since we can see the precipitate of BaSO4 and the
products are much easier to purify. The yields varied
between 45 and 88% (from K2[PtCl4]). This method is

198
F.D. Rochon, L.M. Gruia / Inorganica Chimica Acta 306 (2000) 193–204
not applicable to the synthesis of the oxalato com-
plexes, since barium oxalate is too insoluble in water.
The first method produced a mixture of several Pt
complexes, while the second method produced pure
complexes as will be shown below. Therefore, the com-
pounds synthesized in the latter part of the project were
prepared only by the second method.
tures of a few complexes of this type were reported in
the literature. These compounds are Pt(NH3)2(CBDCA)
[10,11], Pt(NH3)2(Mal) [12], Pt(NH3)2(Ox) [12],
Pt(en)(Mal) [11] and Pt(dach)(Ac)2 [13]. The results of
the X-ray diffraction study has shown that the crystal
Pt(EtNH2)2(1,1-cyclobutanedicarboxylato)·H2O
con-
tains a molecule of lattice water, which was not found
in the NH3 complex. A labeled diagram of the molecule
is shown in Fig. 1. The bond distances and angles are
listed in Table 1.
3.1. Structure of Pt(EtNH2)2(CBDCA)·H2O
The compound Pt(EtNH2)2(1,1-cyclobutanedicarb-
oxylato) gave crystals suitable for crystallographic
studies. It was recrystallized in water. The crystal struc-
The coordination around the platinum atom is pla-
nar. The best plane through the five atoms was calcu-
lated and the mean deviation of the atoms is 0.014(3)
,
A. The PtꢀO bond distances are 2.000(4) and 2.015(4)
,
,
A, while the PtꢀN bonds are 1.992(5) and 2.020(5) A, in
agreement with published values on similar complexes
[10–14]. The angles around the Pt atom vary between
86.5(2) and 92.1(2)° for the cis angles, while the trans
angles are 177.2(2) and 177.6(2)°. The PtꢀNꢀC angles
are larger (118.2(4) and 116.8(4)°) than the tetrahedral
value as observed in other Ptꢀamine compounds. The
PtꢀOꢀC angles are even larger (121.8(4) and 123.4(4)°)
as observed in Pt(NH3)2(CBDCA) [10,11]. As expected,
the coordinated CꢀO bonds are longer (average
,
1.290(7) A) than the other CꢂO bonds (average 1.234(7)
,
A). The average angle around C(1) and C(2) is
120.0(6)°. The angles inside the four-membered ring
vary between 88.6(5) and 92.0(6)°. The best plane was
calculated through the four atoms forming the ring and
Fig. 1. Labeled diagram of the atoms in the crystal
Pt(EtNH2)2(CBDCA)·H2O (the ellipsoids correspond to 30% proba-
bility).
,
the mean deviation is 0.013(4) A. The Pt atom is also in
the plane of the four-membered ring with a deviation of
,
0.098(22) A. The dihedral angle between the cyclobu-
tane ring and the Pt coordination plane is 84.4(4)°.
It is interesting to note the conformation of the
molecule. The two ethylamine ligands and the cy-
clobutyl ring are all on the same side of the Pt coordi-
nation plane. The six-membered malonate chelate ring
has a boat conformation as seen in Fig. 1. The best
plane was calculated through the four atoms O(1),
O(2), C(1) and C(2). The mean deviation of the four
Table 1
,
Bond distances (A) and bond angles (°) in the crystal
Pt(EtNH2)2(CBDCA)·H2O
PtꢀO(1)
PtꢀN(1)
2.015(4)
2.020(5)
1.277(8)
1.229(7)
1.483(9)
1.547(9)
1.542(9)
1.545(12)
1.538(12)
PtꢀO(2)
PtꢀN(2)
2.000(4)
1.992(5)
1.313(7)
1.238(7)
1.499(9)
1.536(9)
1.561(9)
1.512(11)
1.521(13)
O(1)ꢀC(1)
O(3)ꢀC(1)
N(1)ꢀC(7)
C(1)ꢀC(3)
C(3)ꢀC(4)
C(4)ꢀC(5)
C(7)ꢀC(8)
O(2)ꢀC(2)
O(4)ꢀC(2)
N(2)ꢀC(9)
C(2)ꢀC(3)
C(3)ꢀC(6)
C(5)ꢀC(6)
C(9)ꢀC(10)
,
atoms is 0.049(3) A and Pt and C(3) are on one side of
the plane with deviations of −0.561(9) and −0.655(9)
,
A, respectively. The two carbonyl atoms O(3) (devia-
,
,
tion=0.278(11) A) and O(4) (deviation=0.608(10) A)
are oriented towards the other side of the plane and
form intermolecular H-bonds with the water molecule
located in the lattice. The O(3)···Ow distance is 2.808(7)
O(1)ꢀPtꢀO(2)
91.5(2)
86.5(2)
O(1)ꢀPtꢀN(1)
O(2)ꢀPtꢀN(1)
N(1)ꢀPtꢀN(2)
PtꢀO(2)ꢀC(2)
PtꢀN(2)ꢀC(9)
O(2)ꢀC(2)ꢀO(4)
O(4)ꢀC(2)ꢀC(3)
O(2)ꢀC(2)ꢀC(3)
C(1)ꢀC(3)ꢀC(4)
C(1)ꢀC(3)ꢀC(6)
C(4)ꢀC(3)ꢀC(6)
C(4)ꢀC(5)ꢀC(6)
N(1)ꢀC(7)ꢀC(8)
177.6(2)
89.9(2)
92.1(2)
O(1)ꢀPtꢀN(2)
O(2)ꢀPtꢀN(2)
PtꢀO(1)ꢀC(1)
177.2(2)
123.4(4)
118.2(4)
122.6(6)
119.1(6)
118.3(5)
111.4(5)
113.5(5)
112.7(5)
88.6(5)
121.8(4)
116.8(4)
122.1(6)
120.2(5)
117.6(5)
114.5(5)
113.2(5)
90.2(5)
PtꢀN(1)ꢀC(7)
,
,
A while the O(4)···Ow distance is 2.801(7) A. The angle
O(3)···Ow···O(4) is 131.5(3)°. The molecules are further
held together by H-bonds involving the amine groups,
which form intermolecular H-bonds with the Pt-bonded
O(1)ꢀC(1)ꢀO(3)
O(3)ꢀC(1)ꢀC(3)
O(1)ꢀC(1)ꢀC(3)
C(1)ꢀC(3)ꢀC(2)
C(2)ꢀC(3)ꢀC(4)
C(2)ꢀC(3)ꢀC(6)
C(3)ꢀC(4)ꢀC(5)
C(3)ꢀC(6)ꢀC(5)
N(2)ꢀC(9)ꢀC(10)
,
CꢀO groups. The N(1)···O(1) distance is 3.081(7) A
,
while the N(2)···O(2) distance is 2.972(7) A, with angles
92.0(6)
112.2(7)
PtꢀN(1)···O(1)=108.1(3),
PtꢀN(2)···O(2)=119.2(3),
C(7)ꢀN(1)···O(1)=99.1(4) and C(9)ꢀN(2)···O(2)=
89.1(5)
110.7(7)
109.7(4)°.

F.D. Rochon, L.M. Gruia / Inorganica Chimica Acta 306 (2000) 193–204
199
3.2. IR spectra
absorption bands in the 600–300 cm−1 region, as
shown in Section 2.
The IR (4000–250 cm−1) spectra of all the com-
plexes prepared by Method 2 were measured in the
solid phase. Multinuclear NMR spectroscopy (see later)
has shown that these compounds were pure. With the
exception of the complexes Pt(Me4en)X2, all the com-
pounds exhibit one or two w(NꢀH) stretching vibrations
between 3285 and 3080 cm−1. The deformation vibra-
tions l(NꢀH) were observed between 1650 and 1545
cm−1. These vibrations absorb at lower frequencies
than in the free ligands. The carboxylate region is of
special interest for this type of complex. Besides the IR
spectra of the complexes, we have measured for com-
parison purposes the IR spectra of the free acids and
the sodium carboxylate salts in the solid state, except
for benzoic acid [15] and acetic acid (measured in the
gas phase) [16] where the literature values were used. In
the free acids, the w(CꢂO) bands are between 1799 and
1685 cm−1, while the w(CꢀO) vibrations are observed
between 1314 and 1250 cm−1. For H2Mal and
H2BuMal, two w(CꢂO) have been observed. For the
carboxylate ions, the w(CꢂO) vibration absorbs between
1595 and 1565 cm−1, while the w(CꢀO) vibrations
range between 1410 and 1330 cm−1. The values of the
Dw (w(CꢂO)−w(CꢀO)) for the free acids and for the
carboxylate ions were calculated. The value is much
larger in the carboxylic acids where the resonance is
much reduced. The percentage resonance can be ap-
proximately related to the value of Dw [16]. The values
for the acids vary between 395 and 520 cm−1, while it
is much reduced for the carboxylate salts (155–260
cm−1). The value seems also slightly larger for dianions
(average 254 cm−1) than for monoanions (average 163
cm−1). These Dw values were compared to those of the
carboxylato Pt complexes. For the latter compounds,
the values are slightly larger than those of the carboxyl-
ate salts, but smaller than those observed for the acids.
The Dw values for the complexes vary between 255 and
295 cm−1. For the carboxylato ligands, the w(CꢂO)
vibrations absorb between 1680 and 1640 cm−1, while
the w(CꢀO) vibrations range between 1400 and 1360
cm−1. The CꢂO and CꢀO bonds in these types of
complex are often involved in H-bonding as shown
earlier in the crystal structure of Pt(EtNH2)2-
(CBDCA)·H2O. These H-bonds will usually influence
the energy of the carboxyl vibrations.
3.3. 195Pt NMR
All the complexes prepared by the two methods were
characterized by NMR spectroscopy. The purity of the
products can be verified by 195Pt NMR spectroscopy,
since each species will show a different signal. In this
study, long accumulation times were used in order to
detect small quantities of secondary products. 1H NMR
is even more sensitive to impurities and these spectra
will be discussed later.
Many factors influence the shielding of a heavy atom
like the 195Pt nucleus, as expressed in the modified
Ramsey equation [18,19]. Since the l(Pt) chemical
shifts depend on the electronic density on the Pt atom,
it is possible to observe the variation of the electronic
effects caused by the presence of different ligands
bonded to the Pt atom. An increase of the basicity of
the ligand or a stronger s bond, should in theory
increase the electronic density on the Pt atom and
should cause the Pt signal to be shifted towards higher
field (more negative) if all other factors are equal. The
presence of p-interaction in the Ptꢀligand bond should
produce the opposite effect. For complexes containing
only amines, p-backbonding is not possible, which sim-
plifies the interpretation of the spectra. For amines, the
strength of the s bond can be related to the pKa (or
pKb) values, which are thermodynamic values charac-
teristic of the electronic density on the N atom (basic
basicity) and steric effects. The pKa values (measured in
water) for the amines used in this study are available in
the literature [20]. The effect of the presence of car-
boxylato ligands bonded to Pt is not so straightfor-
ward, since the situation is complicated by the presence
of p-bonds on the ligands. The latter influence on the
l(Pt) values is probably not very important, although it
may be different in 13C NMR spectroscopy. Other
factors like the solvent effect will influence the l(Pt)
values. Coordinating solvents like water will slightly
increase the electronic density on the Pt atom and the
signals of the Pt compounds dissolved in water are
usually observed at higher fields than those dissolved in
neutral organic solvents. Steric effects close to the
binding site of the ligand are another factor, although it
has been suggested that this factor is also due to the
solvent effect [21]. The presence of bulky ligands re-
duces the number of molecules of solvent in the close
environment of the Pt atom, resulting in a reduction of
electronic density on the metal. Bulkiness will also alter
slightly the bond distances and angles. All these factors
will have important effects in the Ramsey equation.
The 195Pt NMR chemical shifts of all the products
obtained by the two methods are presented in Table 2.
When several signals were observed, the one of cis-
The w(PtꢀN) and w(PtꢀO) vibrations are usually weak
bands which are difficult to assign. We have not found
any IR study on this type of complex. A few metallic
complexes with glycine have been reported. These vi-
brations are very dependent on the metal and are
affected by intermolecular interactions. For Pt(glyc-
ine)2, the w(PtꢀN) and w(PtꢀO) vibrations have been
located at 549 and 415 cm−1, respectively [17]. The
complexes studied in this project have shown several

200
F.D. Rochon, L.M. Gruia / Inorganica Chimica Acta 306 (2000) 193–204
Table 2
Chemical shifts (l195Pt (ppm)) of the products synthesized by the two methods (% if different from 100%) measured in D2O a
Ligand
Ac
Method NH3
1
EtNH2
Me2NH
Me2en
Me4en
−1364 (9), −1693 (82), −1745 (9)
−1693
−1456 (30),
−1838 (70)
−1456 (10),
−1838 (90)
−1469 (40),
−1777 (60)
−1469 (15),
−1777 (85)
Ac
2
−1615 (70),
−1705
−1563 (30),
−1565 b
PhCOO
PhCOO
Ox
Mal
Mal
Bumal
Benzmal
CBDCA
1
2
1
1
2
2
2
1
−1552 b [−1602]
−1816 c [−1866] −1706 c [−1756]
−1706 c [−1756]
−1988
−1730 c [−1780] −1615 c [−1665]
−1872
−1873
−1887
−1722 (30), −1882 (70)
−1882
−1826
−1835
−1720 (13), −1745 (12),
−1869 (75)
−1869
−1970
−1974
−1923
−1926
−1964
−1976
−1922
−1930
−1966
−1686
−1720
−1720
−1827
−1833
CBDCA
CPDA
2
1
−1860
−1964
−1966
−1358 (10), −1692 (20), −1708 (50),
−1741 (20)
CPDA
CHDA
2
1
−1683
−1360 (23), −1675 (25), −1705 (30),
−1738 (22)
−1675
CHDA
2
a The bold value is for cis-PtA2X2 when several species are present in solution.
b In DMF-d7.
c In CDCl3.
PtA2X2 is printed in bold letters and the percentage of
each species is indicated. The spectra were measured in
D2O, except for a few compounds which were not
sufficiently soluble. In these cases, CDCl3 or DMF-d7
was used as indicated in Table 2. The chemical shifts
are slightly solvent dependent, since the signals in
CDCl3 or DMF-d7 were observed at lower field than
those in D2O. For example, cis-Pt(NH3)2(Ac)2 was
observed at −1615 ppm in D2O and at −1565 ppm in
DMF-d7. Therefore, it is more difficult to compare
values measured in different solvents. For comparison
purposes, we have added −50 ppm to the values
measured in an organic solvent for the benzoato com-
plexes (values in square parentheses in Table 2). The
195Pt NMR spectra of all the cis-PtA2X2 complexes
displayed signals between −1602 and −1988 ppm in
D2O (Table 2). These results are similar to those pub-
lished in the literature for the complexes Pt(NH3)2(Ac)2
(−1581 ppm) [22], Pt(NH3)2(ethylmalonato) (−1694
ppm) [10] and Pt(NH3)2(CBDCA) (−1723 ppm) [10].
The Pt chemical shifts should be dependent on the
ligands. An increase in basicity of the ligand should
lead to a higher field chemical shift for Pt, as observed
for the complexes cis-Pt(py)(DMSO)Cl2 (py=pyridine
derivatives, pKa of py ranging from 1.9 to 9.7) [23].
However, no correlation was observed for other types
of Ptꢀpy complex [21,23–25]. We have examined the
possibility of a correlation between the Pt chemical
shifts of the complexes prepared in this study and the
pKa of the amines in water [20] for each of the carboxyl-
ato ligand. No correlation was found, probably due to
the large difference in the nature of the amines used in
our study (NH3, one primary amine, a secondary amine
and two bidentate amines). A linear relationship be-
tween the l(Pt) and the pKa of the protonated amines
was observed in the literature [26] for the monoamine
complexes [Pt(amine)Cl3]− with three primary amines,
but the secondary amine Me2NH, was found to be out
of the linear relationship, because of steric factors close
to the binding site of the amine. Pregosin [27] had
earlier observed a downfield shift when the ligand be-
came sterically larger close to the binding atom. This
phenomenon is probably caused by a solvent effect.
With ligands containing bulky substituents close to the
binding site, the solvent (water) cannot approach effi-
ciently the platinum atom, reducing considerably the
electronic density around the platinum atom. Proton
affinities of the ligands (determined in the gas phase)
are intrinsic measures of the basicity of ligands and
could bring a better understanding of how steric hin-
drance and solvent effects are related to the chemical
shifts. Unfortunately, the proton affinities [28] of most
of the ligands used in this work are not available in the
literature.
Another factor which influence the l(Pt) is the nature
of the ligand. It has been observed that dichloro com-
plexes containing bidentate amines (e.g. Pt(en)Cl2) are
observed at higher fields [29] than similar complexes
containing monodentate amines [26]. A brief survey of
Table 2 indicates that all the Me2en and Me4en com-

F.D. Rochon, L.M. Gruia / Inorganica Chimica Acta 306 (2000) 193–204
201
pounds are observed at higher fields than the equivalent
complexes with monodentate amines. The difference is
about 100 ppm. The chelate effect of the bidentate
amine increases the electronic density on the platinum
atom. NH3 has been shown to produce complexes
which are usually observed at lower fields than the
compounds containing primary amines, probably be-
cause NH3 is a slightly weaker base and it also is more
susceptible to H-bonding with the solvent. The com-
pounds containing bidentate carboxylato ligands are
also observed at higher fields (ꢀ100 ppm) than those
containing monodentate carboxylato ligands. Therefore
complexes containing both bidentate ligands are ob-
served at the highest fields.
−1464 ppm (Me4en) [31]. These dimeric species are
formed in small quantities.
Table 2 shows that Method 1 produced less pure
products, especially for the secondary amine Me2NH
and for the acetate ligand. The latter part of the project
was therefore carried out using only the second prepar-
ative method, since it produced purer compounds by a
faster method and in greater yields. Consequently, some
results are not available with Method 1.
The results on the Me2NH complexes synthesized by
Method 1 are of special interest. The spectra have
shown the presence of one to three other species present
in the aqueous solution. A separate study was made of
the products of hydrolysis of cis-Pt(Me2NH)2I2 and the
results will be published later. This study has permitted
us to identify the signals observed in this project. The
species observed at much lower field (around −1360
ppm) was ascribed to the hydroxo-bridged dimer
[Pt(Me2NH)2(m-OD)]22+. The signal observed around
−1742 ppm was assigned to the diaqua species
It is of interest to note that the 195Pt resonances of
the butylmalonato and benzylmalonato complexes are
identical, indicating that the presence of an electrore-
pulsive or electroattracting group on the carboxylato
ligand does not seem to have an important influence on
the 195Pt chemical shifts. The other factors mentioned
above seem to play a much greater role. The 195Pt
signals of the butylmalonato and benzylmalonato com-
plexes were observed at slightly lower fields (ꢀ50 ppm)
than the malonato complexes. The latter results could
be explained again by a solvent effect. The presence of
bulky substituents on the malonato ligand (n-butyl or
benzyl) reduces the extent of hydration around the Pt
atom, reducing considerably the electronic density
around the Pt atom, when compared to the unsubsti-
tuted malonato ligand.
[Pt(Me2NH)2(D2O)2]2+
, while the peak at about
−1714 ppm is caused by the presence of the bridged-
monohydroxy diaqua ionic species [(Me2NH)2-
(D2O)Pt(m-OD)Pt(D2O)(Me2NH)2]3+. These peaks are
observed in small quantities except for the ligands
CPDA and CHDA. These two ligands form eight-mem-
bered chelates, which are much less stable than the
normal five- or six-membered chelates. Their l(Pt) are
not in the same region as the other Me2NH–bidentate
carboxylato Pt complexes. The l(Pt) for the other five
Pt(Me2NH)2(R(COO)2) complexes varies between
−1826 and −1887 ppm, while it is −1692 and
−1675 ppm for Pt(Me2NH)2(CPDA) and Pt(Me2NH)2-
(CHDA), respectively. The chemical shifts of the two
latter compounds are close to the one of the complex
which contains a monodentate carboxylato ligand,
Pt(Me2NH)2(Ac)2 (−1693 ppm).
The reaction of the Pt diaqua complex with sodium
carboxylate used in Method 1 is quite slow (several
days) and leads to the formation of several products,
while the reaction with barium carboxylate (Method 2)
is much faster due to the rapid precipitation of BaSO4.
For Me2NH, Method 2 has produced only one com-
pound. The latter method has now been adapted by our
laboratory for the synthesis of diaminodicarboxylato
Pt(II) compounds, except for oxalate ligands, which
must be synthesized by Method 1. The oxalate com-
pounds with EtNH2, Me2NH, Me2en and Me4en were
found to be pure. The NH3 compound was not suffi-
ciently soluble for NMR studies.
The 195Pt NMR spectra of all the products have
shown only one signal for the compounds synthesized
by the second method, except for those containing the
acetate ligand with NH3, Me2en and Me4en, where a
second minor signal was observed. The second peak
observed at −1563 ppm for the NH3 compound
(ꢀ30%) was attributed to cis-Pt(NH3)2(D2O)(Ac).
There is no reference in the literature to support this
suggestion. The diaqua species cis-[Pt(NH3)2(D2O)2]
has been reported at −1590 [30] and at −1583 ppm
[22]. In order to confirm our hypothesis, we have
remeasured the 195Pt NMR spectrum of the product in
another solvent, DMF-d7. We have observed only one
species at −1565 ppm (−1615 ppm after the 50 ppm
correction for the solvent). Therefore, we can conclude
that cis-Pt(NH3)2(Ac)2 was pure. The second product
cis-Pt(NH3)2(D2O)(Ac) observed at −1563 ppm was
formed when it was dissolved in D2O. We have elimi-
nated the possibility that this species was the trans
isomer, since we have detected free acetate ligand in the
1H NMR spectrum. The second species observed for
the Me2en (10%) and Me4en (15%) complexes are quite
different. These were observed at −1456 and −1469
ppm, respectively. These signals were assigned to the
hydroxo-bridged dimers, [A2Pt(m-OD)2PtA2]+2 which
have been reported in D2O at −1454 (Me2en) and at
1
3.4. H and 13C NMR
The coordination of amines to platinum reduces the
electronic density on the ligand and the interpretation
1
of the H and 13C NMR should be relatively simple

202
F.D. Rochon, L.M. Gruia / Inorganica Chimica Acta 306 (2000) 193–204
since amines cannot accept p-back-donation from the
metal. The chemical shifts of the atoms in the ligands
should be deshielded compared to the ones of the free
amines, and the atoms closer to the Pt atom are usually
more affected. The presence of electrorepulsive groups
(e.g. alkyl) on the amine should produce a greater
deshielding effect, while the presence of electroattract-
ing groups (e.g. phenyl) should reduce the deshielding
effect. The binding of carboxylates to platinum should
also produce a deshielding effect on the carboxylato
ligands, although the situation is more complicated by
the presence of p-bonds on the ligands. The 13C NMR
signals are very influenced by the presence of p elec-
trons, which should be redistributed on the ligand upon
binding to Pt(II). The IR spectra of the Pt–carboxylato
complexes have shown that the resonance on the car-
boxyl groups is intermediate between the ion (where the
resonance is close to 100%) and the acid, where the
resonance is closer to zero. Therefore the p-system in
the bonded carboxylato ligand is different from the
ones of the free ligands. The presence of an electrore-
pulsive group on the carboxylate ligand should increase
the electronic density on the COO− group, while the
presence of an electroattracting group should reduce it.
The results will be discussed in relation to the Dl (l
of the complex−l of the ligand) values. Table 3 sum-
marizes the chemical shift data of the amines. For each
one, the average Dl value was calculated from the
spectra of seven different carboxylato ligands. The Dl
for the benzoato complexes measured in CDCl3 were
not different from the other Dl values measured in
1
D2O. Most of the H results are similar to those found
in complexes of the type cis-PtA2Cl2 [26,29] or
[PtACl3]− [32]. For the EtNH2 complex, the ꢀCH3
1
group is more deshielded in H NMR than the ꢀCH2
group, which is closer to the Pt atom, as observed for
K[Pt(EtNH2)X3] [32]. Surprisingly, the l(C) of the
ꢀCH3 group in the EtNH2 complexes are more shielded
upon coordination. The average Dl value is −1.75
ppm. 13C NMR studies on similar Pt compounds are
not very common in the literature. These results have
been attributed to the presence of the second ligand
(carboxylato) which will be discussed later. For the
bidentate amines, Me2en and Me4en, the ꢀCH3 groups
1
are more affected than the ꢀCH2 groups in H NMR.
Furthermore, the ꢀCH2 group close to the methyl
groups in Me2en is more deshielded than the second
ꢀCH2 group. These results resemble those reported for
Pt(Me2en)Cl2, Pt(Me2en)(D2O)22+, and Pt(Me2en)(OD)2
[29].
1
We have measured the H and 13C NMR of the pure
Pt compounds (in D2O except for the benzoato com-
plexes which were measured in CDCl3) and compared
their chemical shifts with those of the free ligands
(amines and sodium carboxylate) and also with those of
the corresponding carboxylic acid. The NMR spectra
of the free ligands were measured in the same solvent as
the complexes. All the 1H and 13C NMR chemical shifts
are shown in Section 2. The results will be briefly
summarized below. First, the spectra of the bonded
amines will be discussed. These results should be sim-
pler to interpret, since the PtꢀN bond cannot be of
multiple nature. An attempt to discuss the spectra of
the bonded carboxylato ligands will then follow. Rela-
tively few studies have been done in the literature,
especially using 13C NMR spectroscopy. There are
many factors affecting the chemical shifts of C atoms,
especially in the presence of p-bonding.
The 195Pt NMR spectra of the acetato complexes
have shown the presence of a second species, which we
1
have assigned to cis-[PtA2(Ac)(D2O)]+. The H spectra
have shown the presence of free acetate ligand reinforc-
ing our hypothesis. Furthermore an additional set of
signals attributed to the mono aqua complex was also
detected. The 1H and 13C NMR signals of the
monoaqua monoacetato complex were observed at
higher fields than those of the diacetato complexes.
This is in agreement with the 195Pt NMR results, where
cis-[PtA2(Ac)(D2O)]+ was observed at lower field than
cis-PtA2(Ac)2.
For the ligands butylmalonato and benzylmalonato
with Me2en and Me4en, two singlets of equal intensity
could be observed for the ꢀCH3 groups of the amines in
1
both the H and 13C NMR spectra. The presence of
crowded ligands like butylmalonato and benzyl-
malonato creates different environments around the
ꢀCH3 groups located above and below the Pt plane.
Table 4 summarizes the carboxylato ligand data in
the complexes. Again, the average Dl values were cal-
culated from the spectra of the different amines. For
comparison purposes, the Dl values for the free acids
have also been listed in the table. Most of the latter
signals are observed at higher fields than those of the
carboxylate ions in water or in CDCl3. The formation
of H bonds with the solvent is probably an important
factor especially in water, but it is difficult to evaluate
the difference between the carboxylate ions and the
carboxylic acid. Carboxylic acids are weak acids and
are partially dissociated in water.
Table 3
Average Dl (lcomplex−lligand) for the 1H and 13C NMR amine
resonances for the cis-PtA2X2 complexes
A
Dl 1H (ppm)
Dl 13C (ppm)
CH3
CH2
0.08
CH3
CH2
EtNH2
Me2NH
Me2en
0.21
0.29
0.63
−1.75
6.94
7.58
6.28
0.03
6.82
(near NH2)
0.32
(near NH2)
7.47
(near CH3)
0.36
(near CH3)
9.16
Me4en
0.64
7.68

F.D. Rochon, L.M. Gruia / Inorganica Chimica Acta 306 (2000) 193–204
203
Table 4
almost absent, indicating that the H atoms exchanged
quite rapidly with the solvent. The spectrum showed a
low intensity multiplet for the ꢀCH2 (or ꢀCDH or
ꢀCD2) group. Normal spectra were observed when the
spectra were measured in CDCl3. The same behavior
was observed for the ꢀCH group of the butylmalonate
and benzylmalonate ions and in all the Pt(II) malonato,
butylmalonato and benzylmalonato complexes mea-
sured in D2O. A comparison of the chemical shifts of
the malonato, butylmalonato and benzylmalonato lig-
ands in the complexes has not shown any difference.
Therefore, the presence of an electrorepulsive or elec-
troattracting group on the ligand is less important than
the redistribution of the p-electrons upon binding to Pt.
A special effort was made to measure coupling con-
stants with 195Pt, which are not very common in the
literature and not easy to measure, especially on a
higher field instrument. Coupling constants 3J(1H–
195Pt) of Pt with the amine ligands could be measured
for several complexes and they varied between 30 and
36 Hz. These values are close to those observed for
Average Dl (lcomplex−lligand) of the 1H and 13C NMR carboxylato
resonances for the cis-PtA2X2 complexes measured in D2O
X
Dl 1H (ppm)
average
Dl 13C (ppm)
COO
Average others
AcH
Ac
0.02
0.08
0.02
−0.95
0.48
−0.85
2.25
−0.05
−0.99
−0.05
0.53
PhCOOH a
PhCOO a
OxH2
−0.20
−2.43
3.26
Ox
MalH2
Mal
BumalH2
Bumal
BenzmalH2
Benzmal
CBDCAH2
CBDCA
0.28
0.45
0.10
0.34
0.12
0.15
0.07
0.19
−4.33
2.82
−4.61
2.88
−5.68
1.31
−3.89
1.89
−0.92
6.10
−1.04
1.18
−1.93
0.05
−0.72
1.04
a Measured in CDCl3.
3
PtA2Cl2 [26,29] and [PtACl3]− [32]. No such J cou-
pling was seen between 195Pt and the atoms in the
carboxylato ligands. Long accumulation times on
acetato complexes did not show any 4J(1H–195Pt)
couplings. These values are usually too small (B15 Hz)
to be seen on a 300 MHz instrument. We tried to
measure the 3J(13C–195Pt) couplings on the acetato
compounds, but an accumulation of 3 days did not
Table 4 indicates that the carboxylato ligands in the
Pt complexes are not as deshielded as expected in 13C
NMR. Some signals have been shifted to higher fields
(Dl is negative) when compared to the free carboxylate
ions. The Dl values of the carboxyl C atom vary
between 0.48 and 3.26 ppm, which seem quite low when
compared to amine compounds. For complexes of the
type PtA2Cl2, these values are usually \6 ppm for C
atoms not too far from the binding site. We suggest
that the signals of the carboxylato ligands, which are
observed at higher fields than expected, probably result
from the redistribution of the p electrons in the car-
boxylato ligand upon binding to Pt(II). The p electrons
have a greater influence on the 13C chemical shifts than
the s electrons. Cooper and Powell [33] have studied
compounds of the type trans-Pt(CO)(Ypy)Cl2 where
Ypy=para-substituted pyridine derivative. They have
suggested an inverse polarization of the CꢃO ligand to
explain their 13C NMR signals. The coordination of the
CꢃO ligand to Pt produces a displacement of the p-elec-
tronic density from the O atom to the C atom in the
CꢃO bond. This inverse polarization of the CO bond
would be responsible for the shielding observed for the
carbonyl C atom in 13C NMR spectrum. This explana-
tion is interesting and could be applied to our com-
plexes. We suggest that the same phenomenon might be
an important factor in our 13C NMR results. The Dl
values are smaller than expected because of inverse
polarization of the p CꢂO bond, which reduces the p
electronic density on the free O atom and increases it
on the C atom and on most of the other atoms of the
ligand.
2
show any coupling. We were able to observe a J(13C–
195Pt) coupling of 53 Hz, for the complex
Pt(Me4en)(Ac)2 after a 3 day accumulation. However, a
long accumulation time produces aquation or hydroly-
sis of several of the complexes. The chemical shifts of
the amine protons in the complexes were observed
between 4.99 and 5.66 ppm in D2O and between 3.46
2
and 6.15 ppm in CDCl3. Several J(1H–195Pt) coupling
constants with the amine protons could be measured
although these signals are quite large. Their approxi-
mate values varied between 66 and 72 Hz in D2O.
4. Conclusions
Two methods for the synthesis of complexes of the
type cis-PtA2X2 were evaluated. The method involving
the use of barium carboxylate was found to be superior,
except for the oxalate ligand. It is faster, the yields are
1
higher and the 195Pt, H and 13C NMR spectra have
shown that the products are chemically and isomeri-
cally pure. No correlation was found between the 195Pt
chemical shifts of the complexes and the pKa of the
protonated amines, probably because the amines are
too different. A systematic study with a series of pri-
mary amines for example might show a correlation.
The intrinsic basicity of the different ligands could be
1
The H NMR spectrum of sodium malonate mea-
sured in D2O has shown that the ꢀCH2 group was

204
F.D. Rochon, L.M. Gruia / Inorganica Chimica Acta 306 (2000) 193–204
[3] S.J. Lippard, S.E. Sherman, Chem. Rev. 87 (1987) 1153.
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evaluated from the gas phase protonic affinities or by
the Hammett constants but these values are not easily
accessible.
[5] XSCANS
, Version 2.2, Siemens Analytical Instruments Inc.,
Madison, WI, USA.
Bidentate amines or bidentate carboxylato ligands
produce complexes whose 195Pt signals were observed at
much higher fields than those containing monodentate
ligands, due to the chelate effect. In 13C NMR, some
resonances of the carboxylato atoms were found at
higher fields than the corresponding atoms in the free
carboxylate ions. The Dl values for the carboxylato C
atoms (Table 4) are smaller than the values observed
for the amines (Table 3). This difference probably
results from the redistribution of the p electrons upon
binding to Pt(II), since p electrons have a greater
influence on the 13C chemical shifts than the s elec-
trons. Inverse polarization of the CꢂO bond has been
suggested, as observed in the literature for Pt(CO)
complexes [33].
[6] SHELXTL
,
Version 5, Siemens Analytical Instruments Inc.,
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A few coupling constants 3J(195Pt–1H) (around 35
2
Hz) and one J(195Pt–13C) could be calculated (53 Hz).
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5. Supplementary material
The crystallographic tables have been deposited to
the Cambridge Data File. Copies of this information
may be obtained free of charge from: The Director,
CCDC, 12 Union Road, Cambridge, CB2 1EZ, UK
(fax: +44-1223-336033; e-mail: deposit@ccdc.cam.
ac.uk or www: http://www.ccdc.cam.ac.uk), quoting the
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Acknowledgements
The authors are grateful to the Natural Sciences and
Engineering Research Council of Canada for financial
support.
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