Synthesis and characterization of liquid platinum compounds

Article abstract of DOI:10.1016/S0020-1693(99)00499-5

Liquid platinum complexes were obtained with a ligand with alkyl chains that attach to the coordination plane perpendicularly and herewith render a close packing of the molecules difficult for certain chain lengths. Bis(O,O'-dialkyldithiophosphato)platinum(II) complexes, Pt(C(x)dtp)₂, where the alkyl chains are methyl (x = 1), ethyl (x = 2), propyl (x = 3), butyl (x = 4), pentyl (x = 5), hexyl (x = 6), heptyl (x = 7), dodecyl (x = 12), and octadecyl (x = 18), were investigated. The platinum compounds were synthesized via two routes: reaction of tetrachloroplatinate(II) with ammonium-O,O'-dialkyldithiophosphates or oxidative addition of (O,O'-dialkylthiophosphoryl)disulfides to tris(styrene)platinum(0). The melting temperatures as a function of the alkyl chain length show a minimum for the complex with pentyl groups. The complexes with pentyl and hexyl groups are liquid at room temperature, and the complexes with butyl and heptyl groups melt only slightly above room temperature. Depending on the complex, the low melting temperatures are induced by an unfavorable packing of the molecules in the solid state, reflected in a low melting enthalpy, or melting entropy. The molecular weights of the liquid complexes are between 700 and 800 and, therefore, extraordinarily high for liquid metal compounds. Depending on the alkyl groups, the complexes decompose at 172-241°C. Crystals of bis(O,O'-diethyldithiophosphato)platinum(II), Pt(C₂dtp)₂, are monoclinic, space group P2₁/n, a = 8.90, b = 8.70, c = 12.45 A?, α = γ = 90°, β = 100.89°, and Z = 4. (C) 2000 Elsevier Science S.A.

Full text of DOI:10.1016/S0020-1693(99)00499-5

www.elsevier.nl/locate/ica
Inorganica Chimica Acta 299 (2000) 199–208
Synthesis and characterization of liquid platinum compounds
Michel Gianini, Walter R. Caseri *, Volker Gramlich, Ulrich W. Suter
Eidgeno¨ssische Technische Hochschule, Uni6ersita¨tstrasse 41, ETH Zentrum NW E 88.2, CH-8092 Zurich, Switzerland
Received 5 July 1999; accepted 4 October 1999
Abstract
Liquid platinum complexes were obtained with a ligand with alkyl chains that attach to the coordination plane perpendicularly
and herewith render a close packing of the molecules difficult for certain chain lengths. Bis(O,O%-dialkyldithiophos-
phato)platinum(II) complexes, Pt(Cxdtp)2, where the alkyl chains are methyl (x=1), ethyl (x=2), propyl (x=3), butyl (x=4),
pentyl (x=5), hexyl (x=6), heptyl (x=7), dodecyl (x=12), and octadecyl (x=18), were investigated. The platinum compounds
were synthesized via two routes: reaction of tetrachloroplatinate(II) with ammonium-O,O%-dialkyldithiophosphates or oxidative
addition of (O,O%-dialkylthiophosphoryl)disulfides to tris(styrene)platinum(0). The melting temperatures as a function of the alkyl
chain length show a minimum for the complex with pentyl groups. The complexes with pentyl and hexyl groups are liquid at room
temperature, and the complexes with butyl and heptyl groups melt only slightly above room temperature. Depending on the
complex, the low melting temperatures are induced by an unfavorable packing of the molecules in the solid state, reflected in a
low melting enthalpy, or melting entropy. The molecular weights of the liquid complexes are between 700 and 800 and, therefore,
extraordinarily high for liquid metal compounds. Depending on the alkyl groups, the complexes decompose at 172–241°C.
Crystals of bis(O,O%-diethyldithiophosphato)platinum(II), Pt(C2dtp)2, are monoclinic, space group P21/n, a=8.90, b=8.70,
,
c=12.45 A, h=k=90°, i=100.89°, and Z=4. © 2000 Elsevier Science S.A. All rights reserved.
Keywords: Crystal structures; Platinum complexes; Dithiophosphato complexes; Liquid complexes
complexes of the type bis(O,O%-dialkyldithiophos-
1. Introduction
phato)platinum(II), where the alkyl chains are posi-
tioned perpendicularly to the coordination plane. The
intermolecular interactions in such complexes are domi-
nated by van der Waals interactions, and hence, the
resulting melting temperatures might be governed by
critical balances between steric effects (crystal packing)
in the solid structure and the melting entropy, both
depending on the alkyl chain lengths.
In the following, we describe liquid platinum com-
plexes with O,O%-dialkyldithiophosphate ligands. Dithio-
phosphoric acids and their derivatives have been exten-
sively studied since the beginning of this century [7–9].
O,O%-Dialkyldithiophosphoric acids have been em-
ployed as flotation reagents for the recovery of metals
from their solutions [10,11] and O,O%-dialkyldithio-
phosphates have been used as pesticides and for chemi-
cal warfare [12–14], while metal complexes with
O,O%-dialkyldithiophosphates have found application
as antioxidants, oil-additives [15–19], coloring and bio-
active agents [15–21]. Finally, O,O%-dialkyldithio-
Transition metal compounds are usually solid under
ambient conditions. Liquid transition metal complexes
are also known and they find interest, e.g. in the
preparation of thin layers by chemical vapor deposition
(CVD) [1] or of polymer-inorganic nanocomposites [2].
Examples of liquid transition metal compounds are
TiCl4, VCl4, SnCl4, VOCl3, CrO2Cl2, ReO3Cl, MoF6,
ReF6, H2Fe(CO)4, Fe(CO)5, Ni(CO)4, Ru(CO)5,
Os(CO)5, Zn(CH3)2, Cd(CH3)2, Hg(CH3)2, Zn(CH2-
CH3)2, Cd(CH2CH3)2, Hg(CH2CH3)2, Ti(N(CH3)2)4, Ti-
(N(CH2CH3)2)4, Zr(N(CH2CH3)2)4, Nb(OCH2CH2CH2-
CHꢀCH2)5, Ta(OCH2CH2CH2CHꢀCH2)5, and alkyl-
substituted ferrocenes [1,3–6]. To our knowledge, liq-
uid complexes of platinum have not been described to
date. Here, we present a study of liquid platinum
* Corresponding author. Tel.: +41-1-632 2218; fax: +41-1-632
1178.
E-mail address: wcaseri@ifp.mat.ethz.ch (W.R. Caseri)
0020-1693/00/$ - see front matter © 2000 Elsevier Science S.A. All rights reserved.
PII: S0020-1693(99)00499-5

200
M. Gianini et al. / Inorganica Chimica Acta 299 (2000) 199–208
phosphate complexes have been reported for almost
each of the naturally occurring metals [22–31]. In the
case of platinum(II), only the bis(O,O%-diethyldithio-
phosphate) complex has been well characterized [29],
although X-ray crystal data have not been presented. To
our knowledge, the possibility of preparing liquid metal
complexes with bis(O,O%-dialkyldithiophosphate) as lig-
ands has not yet been recognized.
(3.00 g, 6.3 mmol) in distilled styrene (120 ml) was
treated with triphenylsilane (3.29 g, 12.6 mmol). The
solution was stirred for 30 min. Thereafter a solution of
concentrated ammonia (30 ml) and water (250 ml) was
added and the solution was stirred vigorously for 90 min.
The two phases were separated in a separation funnel.
The organic phase was shaken with 250 ml water and
again separated from the aqueous phase. The organic
phase was percolated through a column of 4 cm diameter
filled with 15 cm Alox basic (activity I). After the
solution had passed the Alox, the column was washed
with distilled styrene (150 ml), and this eluate was
combined with the first fraction, yielding a solution of
tris(styrene)platinum(0) in styrene. To analyze the plat-
inum content, 5 g of the solution were evaporated and
the black residue was dissolved in aqua regia (10 ml).
The orange solution was diluted with 0.1 M hydrochloric
acid (700 g) and analyzed with atomic absorption spec-
troscopy. The platinum mass concentrations in the
styrene solutions fell in the range of 0.47–0.58%.
Elemental analyses were performed by the Laborato-
rium fu¨r Organische Chemie of ETH Zu¨rich. NMR
spectra were obtained on Bruker dpx 200 and Bruker
dpx 300 spectrometers (300.1, 81.0 and 64.5 MHz for 1H,
31P and 195Pt NMR spectra, respectively). For 1H NMR
spectra, tetramethylsilane (TMS) was used as internal
standard and for 31P and 195Pt NMR spectra, H3PO4
85% and Na2PtCl6, respectively, as external standard.
Thermogravimetric analyses (TGA) and differential
scanning calorimetry (DSC) were performed on a
Perkin–Elmer Series 7 apparatus. UV–Vis spectra were
measured on a Perkin–Elmer Lambda 900 device.
2. Experimental
2.1. General
Phosphorus pentasulfide and the different alcohols
were bought from Fluka (Buchs, Switzerland). Potas-
sium tetrachloroplatinate(II) was either prepared ac-
cording to the literature [32,33] or purchased, as was
platinum(II) dichloride, from Johnson–Matthey
(Zurich, Switzerland).
Tris(styrene)platinum(0) was synthesized and purified
in situ by slightly modifying a procedure from the
literature [34,35]. cis-Dichlorobis(styrene)platinum(II)
Table 1
Crystal data and structure refinement for Pt(C2dtp)2
Empirical formula
Formula weight
Temperature (K)
C8H20O4P2PtS4
282.76
293(2)
,
Wavelength (A)
0.71073
monoclinic
P21/n
Crystal system
Space group
Unit cell dimensions
,
a (A)
8.899(6)
8.695(5)
12.454(10)
90
100.89
90
946.3(11)
4
,
b (A)
2.2. X-ray crystallography
,
c (A)
h (°)
i (°)
k (°)
Suitable crystals for X-ray analysis were grown by
diffusion of hexane into a solution of bis(diethyldithio-
phosphato)platinum(II), Pt(C2dtp)2, in dichloro-
methane at room temperature (r.t.). Crystal data and
details of the structure refinement of Pt(C2dtp)2 are
summarized in Table 1. The data were collected on a
Syntex P21 four circles diffractometer (graphite-
monochromated Mo Ka radiation) at r.t. using the ꢀ/q
scan mode. Absorption correction was applied to the
data using integration. Transmission factors were 0.413
(min.) and 0.534 (max.). The structure was solved using
the program SHELXS-86 [36] and refined by full-matrix
least-squares on F2 using SHELXL-93 [37]. The H atoms
were included in calculated positions and treated as
‘riding atoms’.
3
,
Volume (A )
Z
Dcalc (g cm−3
)
1.985
8.028
544
Absorption coefficient (mm−1
F(000)
)
Crystal size (mm)
q Range for data collection (°)
0.5×0.1×0.1
2.60–22.02
Index ranges
−85h59, 05k58,
05l511
Reflections collected
Independent reflections
Absorption correction
Max./min. transmission
Refinement method
890
890 [Rint=0.0000]
integration
0.534, 0.413
full-matrix least-squares on
F2
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I\2|(I)]
R indices (all data)
890/0/89
0.966
R1=0.0339, wR2=0.0777
R1=0.0396, wR2=0.0793
0.028(2)
2.3. Preparation of ammonium (O,O%)-dialkyldithio-
phosphates
Extinction coefficient
Largest difference peak and hole
1.363 and −1.642
−3
Phosphorus pentasulfide (4.44 g, 20 mmol) and the
respective alcohols (70 mmol) were stirred at 70°C for 3 h.
,
(e A
)

M. Gianini et al. / Inorganica Chimica Acta 299 (2000) 199–208
201
The suspensions were filtered and the residues were
washed with dichloromethane (50 ml). Greenish oils
(white solid in the case of the substance with octadecyl
chains) were isolated after removal of the solvent, and
it is assumed that these substances predominantly con-
sist of the (O,O%)-dialkyldithiophosphoric acids 1. They
were diluted with hexane (50 ml), and anhydrous ammo-
nia was subsequently bubbled through the solution for
5 min under stirring. The white ammonium (O,O%)-di-
alkyldithiophosphates (2) precipitated and were filtered,
washed with hexane (2×50 ml) and dried. The overall
yields of 2 were ca. 50%, consistent with those of similar
reactions reported by Wystrach et al. [38]. Elemental
analyses and NMR data are collected in Tables 2 and 3.
Table 2
Elemental analysis of ammonium (O,O%)-dialkyldithiophosphates
Alkyl group
C
H
O
S
Calc.
Found
Calc.
Found
Calc.
Found
Calc.
Found
Methyl
Ethyl
Propyl
Butyl
Pentyl
Hexyl
Heptyl
Dodecyl
Octadecyl
13.71
23.64
31.16
37.05
41.79
45.69
48.95
59.58
66.31
13.65
23.64
31.07
36.95
41.73
45.75
48.76
59.43
66.12
5.75
6.94
7.84
8.55
9.12
9.58
9.98
11.25
12.06
5.65
6.77
7.71
8.37
9.13
9.56
9.81
11.03
12.13
18.26
15.74
13.83
12.34
11.13
10.14
9.31
18.20
15.84
14.09
12.36
11.32
10.35
9.08
36.60
31.55
27.72
24.72
22.31
20.33
18.67
13.25
9.83
36.54
31.66
27.81
24.45
22.28
20.53
18.71
13.02
9.62
6.61
4.91
6.88
4.90
Table 3
NMR chemical shifts (ppm) and coupling constants, J (Hz), in DMSO-d6 of ammonium (O,O%)-dialkyldithiophosphates a
Alkyl group
1H b
31P
a-CH2
b-CH2
ꢁCH2ꢁ
ꢁCH3
NH4+
Methyl
Ethyl
3.38
7.12
4H, s
118.7
s
6H, d
J=14.3
1.12
6H, t
J=7.1
0.85
6H, t
J=7.4
0.88
6H, t
J=7.2
0.87
6H, t
J=6.7
0.86
6H, t
J=6.6
0.86
6H, t
J=6.5
0.84
6H, t
J=6.4
0.84
3.79
7.11
4H, s
114.4
s
4H, d×q
J=9.0, 7.1
3.69
4H, d×t
J=8.5, 6.8
3.73
4H, d×t
J=8.4, 6.5
3.72
4H, d×t
J=8.4, 6.6
3.72
4H, d×t
J=8.4, 6.6
3.72
4H, d×t
J=8.4, 6.6
3.70
4H, d×t
J=8.5, 6.6
3.69
4H, d×t
J=8.5, 6.5
Butyl
1.52
4H, m
7.11
4H, s
114.7
s
Propyl
Pentyl
Hexyl
1.49
4H, m
1.31
4H, m
7.11
4H, s
114.7 s
1.50
4H, m
1.28
8H, m
7.13
4H, s
114.8
s
1.49
4H, m
1.27
12H, m
7.09
4H, s
114.7
s
Heptyl
Dodecyl
Octadecyl
1.49
4H, m
1.26
16H, m
7.09
4H, s
114.7
s
1.47
4H, m
1.23
36H, m
7.07
4H, s
114.6
s
1.47
4H, m
1.22
60H, m
7.07
4H, s
114.6
s
6H, t
J=6.4
a s, singlet; d, doublet; t, triplet; m, multiplet.
b J refers to J(1H–1H).

202
M. Gianini et al. / Inorganica Chimica Acta 299 (2000) 199–208
2.4. Preparation of bis(O,O%-dialkylthiophosphoryl)-
disulfides
products were purified by flash chromatography (SiO2/
CH2Cl2) and dried. Yields 90–95%. The elemental
analyses and NMR data of the complexes are presented
in Tables 6 and 7, respectively.
(b) The respective bis(O,O%-diethyldithiophospho-
ryl)disulfides (3) (190 mg, 0.51 mmol) were added to a
solution of tris(styrene)platinum(0) [35] (2% Pt in
styrene, 5 g, 0.51 mmol) and stirred for 15 min. The
styrene was removed under reduced pressure at r.t. and
the solid residue was purified by chromatography (SiO2,
1:1 CH2Cl2/hexane). The yields of the bis(O,O%-dialkyl-
dithiophosphate)platinum(II) complexes (4) were 85–
90%.
O,O%-dialkyldithiophosphoric acids 1 were prepared
as described above and diluted with water (100 ml). The
pH value was adjusted with 1 M KOH to 8, and KNO2
(3.86 g, 40 mmol) was added to the solution to which
95% sulfuric acid (4.96 g, 40 mmol) was slowly ad-
mixed. The solutions were stirred at 50°C for 2 h. The
bis(O,O%-dialkylthiophosphoryl)disulfides (3) were ex-
tracted with CH2Cl2 (3×100 ml) and dried over
MgSO4. The solvent was then removed, yielding green-
ish oils (white solid in the case of the substance with
octadecyl chains), which were purified by flash chro-
matography (SiO2/CH2Cl2). The global yields of 3 were
50%. Elemental analyses and NMR data are collected
in Tables 4 and 5, respectively.
3. Results and discussion
3.1. Syntheses and chemical analyses
2.5. Preparation of bis(O,O%-dialkyldithiophosphato)-
platinum(II)
The preparation of metal O,O%-dialkyldithiophos-
phate complexes usually involves the reaction of metal
halides or acetates with dithiophosphoric acids or their
salts [22,23]. We have prepared the bis(O,O%-dialkyl-
dithiophosphato)platinum(II) complexes 4 by two dif-
ferent reaction paths (Fig. 1). The first route follows
(a) Potassium tetrachloroplatinate(II) (415 mg, 1
mmol) and the respective ammonium (O,O%)-dialkyl-
dithiophosphates (2) (3 mmol) were stirred in water (50
ml) at 60°C for 1 h. The water was removed and the
Table 4
Elemental analysis of bis(O,O%-dialkyldithiophosphoryl)disulfides
Alkyl group
C
H
O
S
Calc.
Found
Calc.
Found
Calc.
Found
Calc.
Found
Ethyl
Hexyl
Dodecyl
Octadecyl
25.94
48.46
61.89
68.19
25.66
48.55
61.69
67.97
5.44
8.81
10.82
11.76
5.38
8.52
10.88
11.59
17.28
10.76
6.87
17.06
10.49
7.06
34.62
21.56
13.77
10.11
34.40
21.31
14.06
10.00
5.05
5.04
Table 5
NMR chemical shifts (ppm) and coupling constants, J (Hz), in CDCl3 of bis(O,O%-dialkyldithiophosphoryl)disulfides a
Alkyl group
1H b
31P
a-CH2
b-CH2
ꢁCH2ꢁ
ꢁCH3
Methyl
Hexyl
4.24
8H, m
1.41
86.0
s
12H, d×t
J=7.1, 0.8
0.90
12H, t
J=6.5
0.88
12H, t
J=6.4
0.88
12H, t
J=6.4
4.16
8H, m
1.74
8H, m
1.34
24H, m
86.7
s
Dodecyl
Octadecyl
4.16
8H, m
1.74
8H, m
1.27
72H, m
86.7
s
4.16
8H, m
1.74
8H, m
1.26
120H, m
86.7
s
a s, singlet; d, doublet; t, triplet; m, multiplet.
b J refers to J(1H–1H).

M. Gianini et al. / Inorganica Chimica Acta 299 (2000) 199–208
203
Table 6
Elemental analysis of bis(O,O%-dialkyldithiophosphate)platinum(II) complexes
Alkyl group
C
H
O
S
Calc.
Found
Calc.
Found
Calc.
Found
Calc.
Found
Methyl
Ethyl
Propyl
Butyl
Pentyl
Hexyl
Heptyl
Dodecyl
Octadecyl
9.43
16.99
23.19
28.36
32.73
36.49
39.75
51.17
59.10
9.62
17.11
23.21
28.20
32.81
36.69
40.01
51.18
59.69
2.37
3.56
4.54
5.35
6.04
6.63
7.15
8.95
10.02
2.13
3.41
4.41
5.23
6.07
6.58
7.02
8.80
9.85
12.56
11.32
10.30
9.44
8.72
8.10
7.56
5.68
4.37
12.77
11.51
10.26
9.64
8.91
8.29
7.60
5.83
4.38
25.17
22.68
20.63
18.92
17.48
16.24
15.16
11.38
8.76
25.23
22.60
20.64
19.13
17.39
16.04
14.96
11.24
8.72
Table 7
Chemical shift values (ppm) and coupling constants, J (Hz), in CDCl3 for bis(O,O%-dialkyldithiophosphate)platinum(II) complexes a
b
1H
31P c
195Pt c
a-CH2
b-CH2
ꢁCH2ꢁ
ꢁCH3
Pt(C1dtp)2 (4.1)
Pt(C2dtp)2 (4.2)
Pt(C3dtp)2 (4.3)
Pt(C4dtp)2 (4.4)
Pt(C5dtp)2 (4.5)
Pt(C6dtp)2 (4.6)
Pt(C7dtp)2 (4.7)
Pt(C12dtp)2 (4.12)
Pt(C18dtp)2 (4.18)
3.91
8H, d
3.91
108.0
d
J=449
102.5
d
J=445
102.2
d
J=445
102.7
d
J=444
102.7
d
J=444
102.1
d
J=444
101.9
d
J=444
102.7
d
−4005
t
J=449
−3987
t
J=445
−3992
t
J=445
−3991
t
J=444
−3991
t
J=444
−3991
t
J=444
−3989
t
J=444
−3991
t
12H, d
J=14.9
1.42
12H, t
J=7.1
0.99
12H, t
J=7.4
0.95
12H, t
J=7.3
0.92
12H, t
J=7.0
0.90
12H, t
J=6.8
0.89
12H, t
J=6.8
0.88
12H, t
J=6.7
0.88
J=14.9
4.31
8H, d×q
J=9.4, 7.1
4.19
8H, d×t
J=8.9, 6.6
4.23
8H, d×t
J=8.8, 6.6
4.22
8H, d×t
J=8.8, 6.7
4.22
8H, d×t
J=8.9, 6.7
4.21
8H, d×t
J=8.9, 6.7
4.21
8H, d×t
J=8.8, 6.7
4.21
1.79
8H, m
1.74
8H, m
1.43
8H, m
1.76
8H, m
1.25–1.45
16H, m
1.75
8H, m
1.28–1.45
24H, m
1.75
8H, m
1.28–1.42
32H, m
1.75
8H, m
1.26–1.45
72H, m
J=444
102.0
d
J=444
−3991
t
1.75
8H, m
1.25–1.45
120H, m
8H, d×t
J=8.7, 6.7
12H, t
J=6.7
J=444
J=444
a s, singlet; d, doublet; t, triplet; m, multiplet.
b J refers to J(1H–1H).
c J refers to J(195Pt–31P).
the common procedure for short-chain compounds
[9,23,38], which we have modified for longer alkyl
chains in order to avoid solubility and emulsion prob-
lems during the syntheses: an excess of phosphorus
pentoxide reacts with primary alcohols to produce
O,O%-dialkyldithiophosphoric acids 1. Since compounds
1 are slowly oxidized by atmospheric oxygen, no at-
tempt was made to purify them; they were used as
crude products for the conversion into the ammonium
O,O%-dialkyldithiophosphates (2) with anhydrous am-
monia. The complexes 4 were prepared from 2 and
potassium tetrachloroplatinate(II). The compounds 2
have to be present in excess in order to avoid the
formation of dichloro-bridged complexes [27].
As an alternative reaction, bis(O,O%-dialkylthiophos-
phoryl)disulfides (3) were first formed by oxidation of

204
M. Gianini et al. / Inorganica Chimica Acta 299 (2000) 199–208
1. This conversion can be induced by irradiation with
visible light [39] or oxidative agents [21,40]. We selected
the method involving nitrous acid [40] and modified the
procedure in order to facilitate the handling of the
long-chain products. As a result, higher yields than
those reported in the literature were obtained. The
compounds 3 were converted into the platinum com-
plexes 4 by oxidative addition to tris(styrene)platin-
um(0). As can be expected, the sulfurꢁsulfur bond,
which mimics the cysteine CSSC skeleton [41], is very
sensitive towards reduction.
In the following, the individual bis(O,O%-dialkyl-
dithiophosphato)platinum(II) complexes are designated
as Pt(Cxdtp)2, where x denotes the number of carbon
atoms in the respective alkyl chains. Complexes with
x=1, 2, 3, 4, 5, 6, 7, 12, and 18 were prepared. Their
elemental composition agrees with the expected values
(Table 6). The purity of the substances is also mani-
fested in 1H, 31P, and 195Pt NMR spectra. Chemical
shifts and coupling constants are collected in Table 7.
The spectra fully agree with the surmised structures.
1
Fig. 1. Reaction scheme for the preparation of Pt(Cxdtp)2 complexes.
For example, the H NMR spectra confirm the pres-
ence of the alkyl chains and the 195Pt–31P couplings
(J=440–450 Hz) are visible in both the 31P and 195Pt
spectra. The 195Pt spectra are characterized by a triplet
at around −4000 ppm, proving that the platinum
atoms are coordinated with two of the bidentate lig-
ands, and the 31P spectrum shows the corresponding
platinum satellites. The chemical shifts in the 31P spec-
tra lie close together except that of Pt(C1dtp)2. The
195Pt shifts are practically identical for the complexes
with x\1 and differ slightly but not relevantly for
Pt(C1dtp)2. As the electronic structure around the plat-
inum atoms is very similar in all complexes, all
Pt(Cxdtp)2 compounds exhibit virtually identical UV–
Vis spectra and molar extinction coefficients. As an
example, Fig. 2 shows the absorption spectrum of
Pt(C6dtp)2. Despite the apparent simplicity of this spec-
trum, the interpretation is not easy due to contradictory
explanations in the literature stemming from different
energy level sequences in the molecular orbital scheme
[25,42]. Due to their lone pair electrons, the Cxdtp−
ligands exert a strong nephelauxetic effect [24,27]. The
character of the binding in complexes 4 is dominated by
s-type bonds, while p interactions are of minor impor-
tance [24,25,27].
Fig. 2. UV–Vis spectrum of Pt(C6dtp)2 in dichloromethane. Also
indicated in the Figure are the absorption maxima and extinction
coefficients (in brackets, M−1 cm−1).
Pt(C2dtp)2 was obtained as crystals suitable for ex-
amination with X-ray diffraction. Fig. 3 shows the
elucidated structure, Table 8 lists selected bond lengths
and angles, and Table 1 contains the crystal data for
Pt(C2dtp)2. The molecule consists of a square-planar
platinum(II) complex with a crystallographic center of
inversion and a non-crystallographic C2 axis. The phos-
phorus atoms are out of the plane defined by the four
,
PtꢁS bonds. The PtꢁS distances (2.33 A) are longer
Fig. 3. Molecular structure and selected bond lengths and bond
angles of Pt(C2dtp)2. Hydrogen atoms are omitted for clarity.
,
than the NiꢁS distances (2.23 A) in Ni(C2dtp)2 [43,44],

M. Gianini et al. / Inorganica Chimica Acta 299 (2000) 199–208
205
Table 8
respective temperatures. The melting process is accom-
panied by a vanishing of birefringence. The melting
process is reversible in DSC and optical microscopy
except for Pt(C1dtp)2, which obviously melts under
decomposition at 171°C (as a result, the enthalpy
change at 171°C is negative (−174 kJ mol−1) in the
calorimetric measurements, and the mass of Pt(C1dtp)2
in TGA decreases at 172°C). In the other cases, how-
ever, decomposition occurs at least 68°C above the
melting temperature of the respective complexes (cf.
Figs. 5 and 6). No mass loss was observed below 190°C,
i.e. the substances do not contain significant amounts
of low-boiling compounds, e.g. solvents. As an exam-
ple, Fig. 7 shows the mass loss of Pt(C6dtp)2, in a range
50–800°C. Mass is lost in two steps. The loss at 225°C
corresponds to the mass of the alkyl groups, suggesting
that predominantly bis(dithio-meta-phosphato)plati-
num(II) is left. The mass remaining after the second
step at 650°C corresponds to the mass of platinum(II)
sulfide which might be finally left. The stability of the
Pt(Cxdtp)2 complexes increases with the length of the
alkyl chains. There is a 69°C difference between the
temperature of decomposition of Pt(C1dtp)2 and that of
Pt(C18dtp)2, the latter being more stable.
Fig. 5 presents the melting temperatures of the
Pt(Cxdtp)2 complexes as a function of the length of the
alkyl chains. For compounds with alkyl chains ranging
from methyl (x=1) to pentyl (x=5), the melting tem-
peratures decrease with increasing alkyl chain length.
This effect is probably connected with less favorable
packing in the solid state with increasing chain length.
An increase in melting entropy induced by the increased
conformational freedom of the longer chains in the melt
must also be considered and is discussed below. There
is only a barely perceptible odd–even effect in contrast
to that observed in the melting temperatures of alkanes
and many substituted alkanes with low chain lengths.
For x]7, differences in the packing of the molecules
in the solid state become probably less important and
the melting temperatures increase with increasing
molecular weight; the longer chains might enhance the
van der Waals interactions and render the melting
temperatures higher. The melting temperatures of
Pt(C7dtp)2, 1-octanoic acid, 1-heptanol, 1-aminohep-
tane, and heptane (29, −8, −34, −18, and −91°C,
respectively) markedly differ from each other. However,
the melting temperature of Pt(C18dtp)2 (67°C) is close
to the melting temperatures of 1-nonadecanoic acid
(69°C), and to the values of 1-octadecanol (60°C) and
1-aminooctadecane (53°C), and differs only by 29°C
from octadecane. The influence of the alkyl chains
seems to dominate in Pt(C18dtp)2; indeed it is expected
from standard bond lengths and angles that roughly
90% of the volume of Pt(C18dtp)2 is filled by alkyl
groups.
,
Bond lengths (A) and angles (°) for Pt(C2dtp)2 (atomic coordinates
will be deposited in the Cambridge Crystallographic Data Center) a
Bond lengths
PtꢁS(2)c1
2.325(3)
2.325(3)
2.332(4)
2.332(4)
1.998(4)
1.558(7)
1.564(7)
2.007(4)
1.462(14)
1.444(13)
1.33(2)
PtꢁS(2)
PtꢁS(1)c1
PtꢁS(1)
S(2)ꢁP
PꢁO(1)
PꢁO(2)
PꢁS(1)
O(1)ꢁC(1)
O(2)ꢁC(3)
C(3)ꢁC(4)
C(2)ꢁC(1)
1.42(2)
Bond angles
S(2)c1ꢁPtꢁS(2)
S(2)c1ꢁPtꢁS(1)c1
S(2)ꢁPtꢁS(1)c1
S(2)c1ꢁPtꢁS(1)
S(2)ꢁPtꢁS(1)
S(1)c1ꢁPtꢁS(1)
PꢁS(2)ꢁPt
O(1)ꢁPꢁO(2)
O(1)ꢁPꢁS(2)
O(2)ꢁPꢁS(2)
O(1)ꢁPꢁS(1)
O(2)ꢁPꢁS(1)
S(2)ꢁPꢁS(1)
C(1)ꢁO(1)ꢁP
C(3)ꢁO(2)ꢁP
C(4)ꢁC(3)ꢁO(2)
C(2)ꢁC(1)ꢁO(1)
PꢁS(1)ꢁPt
180.0
84.19(10)
95.81(10)
95.81(10)
84.19(10)
180.0
86.89(14)
96.8(4)
114.3(3)
114.8(4)
115.1(3)
114.1(4)
102.4(2)
121.6(7)
122.4(7)
112.8(13)
110.4(10)
86.51(14)
a Symmetry transformations used to generate equivalent atoms:
c1 −x, −y, −z.
as expected since platinum(II) has a larger diameter
than the nickel(II) cation [3]. Otherwise, the PꢁS and
PꢁO bond lengths (2.00 and 1.56 A, respectively) and
the SꢁPꢁS, OꢁPꢁO and SꢁPꢁO bond angles (102.4, 96.8
and 114.8°, respectively) are similar to those in related
compounds [43–47]. Fig. 4 shows the packing of the
Pt(C2dtp)2 molecules in the unit cell. The shortest inter-
,
,
molecular PtꢁPt distance is 8.19 A, which excludes any
metal–metal interaction. The tetrahedral arrangement
around the phosphorus atoms hinders any overlap of
the metal orbitals and prevents a parallel stacking of
the planar units around the platinum atoms. As a
consequence, the structure and the intermolecular inter-
actions in the solid state and, therefore, the melting
temperatures are expected to be influenced significantly
by the packing of the alkyl chains.
3.2. Thermal analyses
Melting temperatures were measured with DSC after
careful purification of the products. The phase transi-
tions were also observed with optical microscopy at the

206
M. Gianini et al. / Inorganica Chimica Acta 299 (2000) 199–208
Fig. 4. Crystal structure of Pt(C2dtp)2 in the (010) and (100) orientations.
A more detailed picture of the melting behavior of
temperatures of these complexes (17°C) are due to the
melting enthalpy, which is a few percent lower for
Pt(C6dtp)2, i.e. the packing in Pt(C2dtp)2 seems to be
somewhat less favorable than that of Pt(C4dtp)2. In the
Pt(Cxdtp)2 complexes with x=3–6, the melting en-
thalpies and entropies of the compounds with even x
are roughly 3 and 2.5 times, respectively, above the
corresponding values of the compounds with odd x.
This suggests that the packing of the molecules in
Pt(C3dtp)2 and Pt(C5dtp)2 in the solid state allows a
relatively high disorder of the alkyl groups (provided
the entropy differences are not due to a restricted
mobility of the ‘odd’ complexes in the melt). The
melting entropy is particularly low for Pt(C5dtp)2, even
50% below that of Pt(C4dtp)2, while for Pt(C5dtp)2 it is
10% below that of Pt(C3dtp)2. This might mean that the
the Pt(Cxdtp)2 complexes arises from the energy re-
quired for the melting of the substances (Table 9). The
melting enthalpy was determined by DSC and the
calorimetric data were further used to calculate the
melting entropy (Table 9). For x56, the melting en-
thalpies exhibit an odd–even effect. They are similar
for x=2, 4, and 6 (ca. 35 kJ mol−1). However, the
melting entropies of Pt(C4dtp)2 and Pt(C6dtp)2 are ca.
50% above the value of Pt(C2dtp)2. This implies that
the sharp decrease in the melting temperatures from
Pt(C2dtp)2 to Pt(C4dtp)2 and Pt(C6dtp)2 (ca. 100°C) is
mainly due to the entropy gained by the increased
conformational freedom of the longer alkyl chains. The
melting entropies of Pt(C4dtp)2 and Pt(C6dtp)2 are vir-
tually identical, and the slight difference of the melting
Fig. 5. Melting temperatures (°C) of Pt(Cxdtp)2 complexes.
Pt(C1dtp)2 melts under decomposition. The dotted line represents an
empirical fit.
Fig. 6. Decomposition temperatures (°C) of Pt(Cxdtp)2 complexes.
The dotted line represents an empirical fit.

M. Gianini et al. / Inorganica Chimica Acta 299 (2000) 199–208
207
only slightly above r.t. (30 and 29°C, respectively). To
our knowledge, liquid metal complexes have not been
reported so far with any platinum complex or with
O,O%-dialkyldithiophosphates as ligands. Compared
with the other liquid transition metal complexes, the
molecular weights of Pt(C5dtp)2 and Pt(C6dtp)2 are
extraordinarily high (733.83 and 789.94, respectively). It
is often anticipated that the alkyl groups in metal
compounds should be very short (methyl or ethyl) to
obtain liquids since the van der Waals interactions
increase with increasing molecular weight. However,
steric effects may render close packing of the molecules
more difficult with increasing chain length, and the
melting entropy can also contribute to a decrease in
melting temperature for intermediate chain lengths. The
results with bis(O,O%-dialkyldithiophosphato)platin-
um(II) complexes suggest that intermediate alkyl chain
lengths might generally render transition metal com-
pounds liquid.
Fig. 7. TGA diagram of Pt(C6dtp)2.
Table 9
Melting enthalpies (DH) and melting entropies (DS) of bis(O,O%-di-
alkyldithiophosphato)platinum(II) complexes
Alkyl group
DH (kJ mol−1
)
DS (J mol−1 K−1
)
Ethyl
Propyl
Butyl
Pentyl
Hexyl
Heptyl
Dodecyl
Octadecyl
32.2
18.3
37.1
12.4
34.3
41.7
150
80.9
54.0
122
47.7
120
138
474
550
4. Conclusions
Bis(O,O%-dialkyldithiophosphato)platinum(II) com-
pounds with alkyl chains containing 1–18 carbon
atoms can be synthesized by reaction of tetrachloro-
platinate(II) with ammonium-O,O%-dialkyldithiophos-
phates or oxidative addition of (O,O%-dialkylthio-
phosphoryl)disulfides to tris(styrene)platinum(0). The
course of the melting temperatures of bis(O,O%-di-
alkyldithiophosphato)platinum(II) complexes exhibits a
minimum at the complex with pentyl groups. This
compound and the one with hexyl groups are liquid at
r.t. (melting temperatures −14 and 13°C, respectively).
The crystal structure of Pt(C2dtp)2 implies that the
tetrahedral arrangement around the phosphorus atoms
hinders any stacking of the molecules, which makes the
formation of a dense packing of the molecules in the
crystal more difficult for intermediate chain lengths,
resulting in a decrease in melting temperature. In addi-
tion, the melting entropy can also contribute to the low
melting temperatures. In Pt(C5dtp)2 the low melting
enthalpy and in Pt(C6dtp)2 the relatively high melting
entropy seem to be the decisive factors for the low
melting temperatures. We expect that the concept ap-
plied here will also be useful for the development of
other liquid metal complexes.
187
marked difference in the melting temperature of
Pt(C3dtp)2 and Pt(C5dtp)2 (79°C) is due to an unfavor-
able packing of the Pt(C5dtp)2 molecules in the solid
state.
The melting enthalpy and entropy of Pt(C7dtp)2 is 3.5
and 3 times, respectively, above the values of Pt(C5dtp)2
but only 25 and 15%, respectively, higher than the
corresponding values of Pt(C6dtp)2. It seems that the
molecules can fill the space between the planar units in
Pt(C7dtp)2 better than in Pt(C5dtp)2. While the differ-
ences in melting enthalpy per mole of alkyl group
between Pt(C7dtp)2 and heptane [3] is distinct (10.4 vs.
14.2 kJ mol−1), the value of Pt(C12dtp)2 approaches
that of dodecane [3] (37.6 vs. 36.6 kJ mol−1). This
suggests that the packing of the molecules in
Pt(C12dtp)2 is largely determined by the alkyl chains.
Since the alkyl chains are attached to a common central
unit, the melting entropy per mole of alkyl chains of
Pt(C12dtp)2 (119 J mol K−1) is below the entropy
gained upon melting of dodecane (139 J mol K−1).
Remarkably, the complexes with pentyl (x=5) and
hexyl (x=6) chains are liquid at r.t. They crystallize at
−14 and 13°C, respectively, which is not only evident
from DSC but also clearly visible with an optical
microscope equipped with a temperature control unit
and a cooling stage. The complexes with butyl (x=4)
and hexyl (x=6) chains are isolated as solids that melt
References
[1] A. Gebauer, Plasmagestu¨tztes CVD mit metallorganischen und
analogen Verbindungen (Fortschritt-Berichte VDI, Reihe 5:
Grund- und Werkstoffe, Nr. 344), VDI, Du¨sseldorf, 1994.
[2] T. Kyprianidou-Leodidou, P. Margraf, W. Caseri, U.W. Suter,
P. Walther, Polym. Adv. Technol. 8 (1997) 505.
[3] D.L. Lide (Ed.), Handbook of Chemistry and Physics, 76th ed.,
CRC Press, Boca Raton, FL, 1995.

208
M. Gianini et al. / Inorganica Chimica Acta 299 (2000) 199–208
[4] N.N. Greenwood, A. Earnshaw, Chemie der Elemente, VCH,
[24] C.K. Jørgensen, Inorg. Chim. Acta Rev. (1968) 65.
[25] E. Ciliberto, S. Di Bella, I. Fragala`, G. Granozzi, N.A. Burton,
I.H. Hillier, J. Kendrick, M.F. Guest, J. Chem. Soc., Dalton
Trans. (1990) 849.
[26] T.J. Cardwell, P.S. McDonough, Inorg. Nucl. Chem. Lett. 10
(1974) 283.
Weinheim, 1988.
[5] C. Wohlfarth, B. Wohlfahrt, in: M.D. Lechner (Ed.), Landolt-
Bo¨rnstein Numerical Data and Functional Relationship in Sci-
ence and Technology, Group III, vol. 38A, Springer, Berlin,
1996.
[6] H.O. Pierson, Handbook of Chemical Vapor Deposition (CVD),
Noyes Publications, Park Ridge, NJ, 1992.
[27] C.K. Jørgensen, J. Inorg. Nucl. Chem. 24 (1962) 1571.
[28] P.J. Marriott, T.J. Cardwell, J. Chromatogr. 234 (1982) 157.
[29] R.G. Cavell, W. Byers, E.D. Day, P.M. Watkins, Inorg. Chem.
11 (1972) 1598.
[30] J.P. Maier, D.A. Swaigart, Inorg. Chem. 15 (1976) 1989.
[31] R. Colton, T.A. Stephenson, Polyhedron 3 (1984) 231.
[32] S.E. Livingstone, Synth. Inorg. Met. Org. Chem. 1 (1971) 1.
[33] G.B. Kauffman, D.O. Cowan, Inorg. Synth. 6 (1960) 211.
[34] A. Albinati, W.R. Caseri, P.S. Pregosin, Organometallics 6
(1987) 788.
[35] W. Caseri, P.S. Pregosin, Organometallics 7 (1988) 1373.
[36] G.M. Sheldrick, Acta Crystallogr., Sect. A 46 (1990) 467.
[37] G.M. Sheldrick, SHELXL93, Program for crystal structure refine-
ment, University of Go¨ttingen, Germany.
[38] V.P. Wystrach, E.O. Hook, G.L.M. Christopher, J. Org. Chem.
21 (1956) 705.
[7] P.J. Pishchimuka, J. Russ. Phys. Chem. 44 (1912) 1406.
[8] L. Malatesta, R. Pizzotti, Chim. Ind. 27 (1945) 6.
[9] L. Malatesta, Gazz. Chim. Ital. 81 (1951) 596.
[10] N.A. Borshch, O.M. Petrukin, Yu. A. Zolotov, Zh. Anal. Khim.
33 (1978) 1120.
[11] N.A. Ulakhovich, G.K. Budnikiv, N.K. Shakurova, Zh. Anal.
Khim. 35 (1980) 1081.
[12] G.A. Johnson, J.H. Fletcher, K.G. Nolan, J. Econ. Entomol. 45
(1952) 279.
[13] Analytical Methods for Pesticides Plant Growth Regulators and
Food Additives, Academic Press, New York, a series of volumes.
[14] G.S. Hartley, T.F. West, Chemicals for Pest Control, Pergamon,
New York, 1969.
[15] S.L. Lawton, G.T. Kokotailo, Inorg. Chem. 8 (1969) 2410.
[16] S.L. Lawton, W.J. Rohrbaugh, G.T. Kokotailo, Inorg. Chem. 11
(1972) 2227.
[39] A. Deronzier, J. Chem. Soc., Chem. Commun. (1982) 329.
[40] B. Miller, Tetrahedron 20 (1964) 2069.
[17] S.L. Lawton, Inorg. Chem. 10 (1971) 328.
[18] S.L. Lawton, G.T. Kokotailo, Inorg. Chem. 11 (1972) 363.
[19] S.L. Lawton, W.J. Rohrbaugh, G.T. Kokotailo, Inorg. Chem. 11
(1972) 612.
[20] S.E. Livingstone, A.E. Mihkelson, Inorg. Chem. 9 (1970) 2545.
[21] T. Miyamoto, I. Yamamoto, Agric. Biol. Chem. 45 (1981) 1991.
[22] R.C. Mehrotra, G. Srivastava, B.P.S. Chauhan, Coord. Chem.
Rev. 55 (1984) 207.
[41] P. Knopik, L. Luczak, M.J. Potrzebowski, U. Michalski, J.
Blaszczyk, M.W. Wieczorek, J. Chem. Soc., Dalton Trans.
(1993) 2749.
[42] J.P. Maier, D.A. Sweigart, Inorg. Chem. 15 (1976) 1989.
[43] Q. Fernando, C.D. Green, J. Inorg. Nucl. Chem. 29 (1967) 647.
[44] J.F. McConnel, V. Kastalsky, Acta Crystallogr. 22 (1967) 853.
[45] V.V. Tkachev, L.O. Atovmyan, Koord. Khim. 8 (1982) 215.
[46] V. Kastalsky, J.F. McConnel, Acta Crystallogr., Sect. B 25
(1969) 909.
[23] J.R. Wasson, G.M. Woltermann, H.J. Stoklosa, Fortschr. Chem.
Forsch. 35 (1973) 65.
[47] S. Ooi, Q. Fernando, Inorg. Chem. 6 (1967) 1558.
.