Crystalline O,O′-di-sec-butyl and O,O′-diethyl dithiophosphate platinum(II) complexes: Synthesis, 13C and 31P CP/MAS NMR, single crystal X-ray diffraction studies and thermal behaviour

Article abstract of DOI:10.1016/j.poly.2011.05.050

Crystalline bis(O,O′-di-sec-butyldithiophosphato)platinum(II) was prepared and studied by means of ¹³C, ³¹P CP/MAS NMR spectroscopy and single-crystal X-ray diffraction. The unit cell of the platinum(II) compound is comprised of one centrosymmetric mononuclear molecule [Pt{S₂P(O-sec-C₄H₉)₂}₂], in which the dithiophosphate groups display structural equivalence in both ³¹P NMR and XRD data. A pair of the dithiophosphate ligands exhibit the same S,S′-bidentate chelating structural function and form two planar four-membered chelate rings, [PtS₂P], in this molecule. The planar configuration of the [PtS₄] chromophore in structure 1 is governed by the dsp²-hybrid state of platinum(II). The structural states of the dithiophosphate groups in two different samples of complex 1 (one crystallised from ethanol and the other one precipitated from an aqueous solution) are all characterised by almost rhombic ³¹P chemical shift tensors. The observed essential dispersion of the ³¹P NMR chemical shift is caused by a coexistence of six optical isomers of molecule 1. The thermal behaviour of this compound was studied by means of simultaneous thermal analysis (a combination of TG and DSC) under an argon atmosphere. The thermal behaviour shows that the mass of 1 is lost in three steps, involving successive thermal decompositions of the organic and inorganic parts of this compound with platinum(II) dithio-meta-phosphate and reduced metallic platinum as the intermediate and the final products, respectively.

Full text of DOI:10.1016/j.poly.2011.05.050

Polyhedron 30 (2011) 2210–2217
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Crystalline O,O0-di-sec-butyl and O,O0-diethyl dithiophosphate platinum(II)
complexes: Synthesis, 13C and 31P CP/MAS NMR, single crystal X-ray
diffraction studies and thermal behaviour
b
a
a
Tatyana A. Rodina a, Alexander V. Ivanov a, , Andrey V. Gerasimenko , Irina A. Lutsenko , Maxim A. Ivanov ,
⇑
John V. Hanna c, Oleg N. Antzutkin c,d, Valentin I. Sergienko b
a Institute of Geology and Nature Management, Far Eastern Branch of the Russian Academy of Sciences, 675000 Blagoveschensk, Amur Region, Russia
b Institute of Chemistry, Far Eastern Branch of the Russian Academy of Sciences, 690022 Vladivostok, Russia
c Department of Physics, Warwick University, Coventry CV47AL, UK
d Chemistry of Interfaces, Luleå University of Technology, S-97187 Luleå, Sweden
a r t i c l e i n f o
a b s t r a c t
Crystalline bis(O,O0-di-sec-butyldithiophosphato)platinum(II) was prepared and studied by means of 13C,
31P CP/MAS NMR spectroscopy and single-crystal X-ray diffraction. The unit cell of the platinum(II) com-
pound is comprised of one centrosymmetric mononuclear molecule [Pt{S2P(O-sec-C4H9)2}2], in which the
dithiophosphate groups display structural equivalence in both 31P NMR and XRD data. A pair of the
dithiophosphate ligands exhibit the same S,S0-bidentate chelating structural function and form two pla-
nar four-membered chelate rings, [PtS2P], in this molecule. The planar configuration of the [PtS4] chromo-
phore in structure 1 is governed by the dsp2-hybrid state of platinum(II). The structural states of the
dithiophosphate groups in two different samples of complex 1 (one crystallised from ethanol and the
other one precipitated from an aqueous solution) are all characterised by almost rhombic 31P chemical
shift tensors. The observed essential dispersion of the 31P NMR chemical shift is caused by a coexistence
of six optical isomers of molecule 1. The thermal behaviour of this compound was studied by means of
simultaneous thermal analysis (a combination of TG and DSC) under an argon atmosphere. The thermal
behaviour shows that the mass of 1 is lost in three steps, involving successive thermal decompositions of
the organic and inorganic parts of this compound with platinum(II) dithio-meta-phosphate and reduced
metallic platinum as the intermediate and the final products, respectively.
Article history:
Received 18 April 2011
Accepted 31 May 2011
Available online 25 June 2011
Keywords:
O,O0-dialkyl dithiophosphate platinum(II)
complexes
Molecular structures
Multinuclear 13C, 31P CP/MAS NMR
spectroscopy
31P chemical shift anisotropy
Inorganic four-membered metallocycles
Simultaneous thermal analysis
Ó 2011 Elsevier Ltd. All rights reserved.
1. Introduction
cytotoxic activity against myelogenous leukaemia cell lines com-
pared to cisplatin [9]. Therefore, transition metal complexes with
Ionic O,O0-dialkyl dithiophosphates are the main components of
commercial flotation reagents such as Aerofloats, Danafloats, etc.
Therefore, dialkylsubstituted derivatives of dithiophosphoric acid
are widely used as selective reagents. These derivatives function
as collectors in froth flotation enrichment of non-ferrous sulphide
ores, including serving a special purpose in improving the recovery
of platinum group elements, which are strongly associated with
sulphide minerals [1,2]. Furthermore, some O,O0-dialkyl dithio-
phosphate transition metal complexes, as well as ashless dithio-
phosphates, displaying both outstanding antiwear and
antioxidant properties, have long been used as lubricating oil addi-
tives [3–7] and as antioxidants in polyolefins [8]. Recently, it was
also discovered that heteroleptic platinum(II) complexes with
other related dithioligands (i.e., dithiocarbamates) display greater
dithioligands have long been a focus of interest in coordination
and applied chemistry.
Recently, we have reported the successful use of 195Pt NMR
spectroscopy (both static and MAS) for the study of platinum min-
erals with single crystal cooperite1 (natural PtS) as an example
[10,11]. In cooperite, platinum(II) is situated in a central position
within the square-planar chromophore [PtS4]. A structurally similar
pattern has been established in platinum(II) complexes with various
ionic O,O0-dialkyl dithiophosphates [12–15] and cyclic O,O0-alkylene
dithiophosphates [16]: the central platinum atom is surrounded by
four sulphur atoms, forming a slightly distorted square-planar coor-
dination polygon. The final product of thermal decomposition of
these dithiophosphate complexes is also PtS [11,15]. However, most
of the presently known and characterised O,O0-dialkyl dithiophos-
1
⇑
Corresponding author. Tel.: +7 4162 225 329; fax: +7 4162 225 325.
E-mail address: alexander.v.ivanov@chemist.com (A.V. Ivanov).
Natural PtS was discovered in South Africa and characterised by R.A. Cooper in
1928.
0277-5387/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2011.05.050

T.A. Rodina et al. / Polyhedron 30 (2011) 2210–2217
2211
phate platinum(II) complexes are liquid compounds [12].
1, [Pt{S2P(O-sec-C4H9)2}2] (1:1:1:1): 78.2, 77.4 (1:1, –OCH@);
31.8, 31.1 (–CH2–); 23.9, 22.3, 22.7 (–CH3); 12.1 (–CH3).
1a, [Pt{S2P(O-sec-C4H9)2}2] (1:1:1:1): 78.3, 77.2 (–OCH@); 32.1,
31.1 (–CH2–); 24.0, 22.6 (–CH3); 12.1, 11.4 (–CH3) (powdered
sample).
The present article describes the preparation, multinuclear (13C,
31P) CP/MAS NMR and single-crystal X-ray diffraction studies of a
novel crystalline platinum(II) complex with
a symmetrically
substituted O,O0-di-sec-butyl dithiophosphate ligand, ꢀS(S)P(O-
sec-C4H9)2. In the centrosymmetric molecule of [Pt{S2P(O-sec-
C4H9)2}] (1), the central platinum atom links two Dtph groups in
an almost S,S0-isobidentate coordination mode, forming two
small-sized four-membered rings [PtS2P]. Therefore, the platinum
atom has four sulphur atoms in its neighbouring environment
and two phosphorus atoms in the second coordination sphere. At
relatively low spinning frequencies (2.8 and 2.3 kHz), the 31P CP/
MAS NMR spectra of the isolated platinum(II) complex display
manifolds of spinning sidebands, whose intensities have been used
to calculate the 31P chemical shift anisotropy (CSA) parameters: da-
2, [Pt{S2P(OC2H5)2}2] (1:1): 65.5, 65.4 (1:1, –OCH2–); 18.7, 17.5
(1:1, –CH3).
2.3. Physical measurements
2.3.1. 13C and 31P NMR spectroscopy
Solid state 13C and 31P magic-angle-spinning (MAS) NMR spectra
were recorded on a Varian/Chemagnetics InfinityPlus CMX-360
(B0 = 8.46 T) spectrometer, using cross-polarisation (CP) from the
protons together with phase modulated proton decoupling [17].
The 13C/31P operating frequencies were 90.52/145.72 MHz, respec-
niso and g
. The 31P CSA parameters, as well as the isotropic chemical
shift (diso), were used to characterise the structural state of the ter-
minal O,O0-di-sec-butyl dithiophosphate groups in the platinum(II)
complex 1, in comparison with platinum(II) O,O0-diethyl dithio-
phosphate (complex 2). Simultaneous thermal analysis (STA), as
a combination of TG and DSC techniques, has been also used to
study the thermal behaviour of complex 1 under an argon
atmosphere.
tively. Theproton
time was 2.0/3.0 ms and the nutation frequency of protons during
decoupling was nut/2 = 38/32 kHz. For the studied sample, 100–
2400/32–600 transients, spaced by relaxation delays of 3/3 s, were
accumulated. The polycrystalline sample (ca. 80–100 mg) was
packed in zirconiumdioxidestandarddouble bearing 7.5 mm rotors.
Thespinningfrequenciesrangedfrom3600to 4600/2300to3800 Hz
and were stabilised to 2 Hz using a built-in stabilisation device. All
13C and 31P MAS NMR spectra were recorded at room temperature
(ca. 295 K).
p/2 pulse durationswere 6.0/7.0 ls, the CPcontact
x
p
2. Experimental
13C isotropic chemical shifts (in the deshielding, d-scale) were
externally referenced to the least shielded resonance of solid ada-
mantane [18] at 38.48 ppm [19] relative to tetramethylsilane.
Chemical shifts and integrated intensity ratios for overlapping sig-
nals in the 13C NMR spectra were additionally refined by fragment-
by-fragment simulation with consideration of line positions and line
widths, as well as of the Lorentzian and Gaussian contributions to
the line shapes. All 31P chemical shift data are given with respect
to 85.5% H3PO4 [20] (here, 0 ppm, externally referenced), which
wasmountedinashort1 mmglasstubeandplacedina7.5 mmrotor
to avoid errors due to differences in the magnetic susceptibility.
2.1. Materials
Potassium tetrachloroplatinate(II), K2[PtCl4] >99% (‘Merck’), was
used without additional purification. Two potassium salts of sym-
metrically disubstituted O,O0-dialkyl dithiophosphoric acids, which
constitute the major components of the commercial Danafloat col-
lectors, were provided by ‘CHEMINOVA AGRO A/S’:
O,O0-di-sec-butyl dithiophosphate
– K[S2P(O-sec-C4H9)2] –
Danafloat-345 K.
Drifts in the 13C/31P frequencies (B0-drift) were 0.051/0.11 Hz hꢀ1
,
O,O0-diethyl dithiophosphate – K[S2P(OC2H5)2] – Danafloat-
respectively. The homogeneity of the magnetic field was monitored
by measuring the width of the reference signal of crystalline ada-
mantane at d (13C) = 38.48 ppm, which was 2.6 Hz.
123 K.
Both original potassium salts were additionally characterised by
The anisotropy, daniso = dzz ꢀ diso, and the asymmetry parameter
solid state 13C CP/MAS NMR (d, ppm):
of the 31P chemical shift tensor (CST),
g
= (dyy ꢀ dxx)/(dzz ꢀ diso), were
estimated from the determined ratios between the integrated side-
band intensities for each phosphorous site in the NMR spectra re-
corded at two different spinning frequencies [21,22] using a
simulation program in the Mathematica front end [23]. To increase
the number of spinning sidebands in the 31P NMR spectra, which
are needed for more accurate estimation of CSA parameters, the
spectra were recorded at relatively low spinning frequencies (2.3
and 2.8 kHz).
K{S2P(O-sec-C4H9)2} (1:1:1:1): 77.5 (–OCH=); 31.7, 31.5, 31.1
(–CH2–); 22.0, 21.2 (–CH3); 12.0 (–CH3).
K{S2P(OC2H5)2} (1:1): 63.2 (–OCH2–); 18.1, 18.0 (1:1, –CH3).
2.2. Synthesis of complexes 1 and 2
The crystalline complexes 1 and 2 were prepared by reacting
aqueous solutions of K2[PtCl4] with the appropriate dithiophos-
phate salts, K{S2P(OR)2} (R = sec-C4H9 and C2H5, respectively). The
reaction mixtures were heated at 60 °C for 10 min and left over-
night. The resulting yellow precipitates were filtered off, washed
with water, and air-dried. Additional crops were obtained by
extraction of the complexes from the mother liquors using chloro-
form. For X-ray diffraction studies, suitable single crystals of
bis(O,O0-di-sec-butyldithiophosphato-S,S0)platinum(II), [Pt{S2P(O-
sec-C4H9)2}2] (1) were isolated by means of slow evaporation of
ethanol at room temperature. Complex 1 was isolated as transpar-
ent, yellowish prismatic crystals. The yield was 92% (the structural
data on complex 2 were previously established in [12]). Solid state
13C CP/MAS NMR data (d, ppm) for compounds 1 and 2 are given
below:
2.3.2. Crystal structure determination
A suitable single crystal of [Pt{S2P(O-sec-C4H9)2}2] was selected
and mounted on a glass capillary with epoxy glue. Experimental
intensity data were collected at T = 173(2) K on a BRUKER SMART
1000 CCD diffractometer with graphite monochromated Mo K
a
radiation (k = 0.71073 Å) in the range of a semi-sphere [24] (crys-
tal-detector distance 45 mm). Intensity data were corrected for
absorption using the crystal face indices. The unit cell dimensions,
additional crystallographic data and refinement results of complex
1 are given in Table 1.
The structure was solved by direct methods and refined by least-
squarescalculations in anisotropic approximationfor non-hydrogen
atoms. Hydrogen atoms were added at ideal positions and refined
using a riding model. Each dithiophosphate ligand has both

2212
T.A. Rodina et al. / Polyhedron 30 (2011) 2210–2217
Table 1
Table 2
Selected crystal data for [Pt{S2P(O-sec-C4H9)2}2] (1).
Selected bond lengths (Å), bond angles (°) and torsion angles (°) in the molecule of
[Pt{S2P(O-sec-C4H9)2}2] (1).
Empirical formula
Formula weight
Crystal system
Space group
Crystal shape
Crystal size (mm)
Unit cell dimensions
a (Å)
C16H36O4P2S4Pt
677.72
Bond lengths
Pt–S(1)
S(1)–P
P–O(1A)
P–O(2A)
O(1A)–C(1A)
C(1A)–C(2A)
C(1A)–C(3A)
C(3A)–C(4A)
O(2A)–C(5A)
C(5A)–C(6A)
C(5A)–C(7A)
C(7A)–C(8A)
triclinic
2.3210(7)
1.9900(1)
1.582(3)
1.606(3)
1.445(5)
1.475(8)
1.504(7)
1.532(8)
1.474(5)
1.486(8)
1.491(6)
1.545(9)
Pt–S(2)
S(2)–P
P–O(1B)
P–O(2B)
O(1B)–C(1B)
C(1B)–C(2B)
C(1B)–C(3B)
C(3B)–C(4B)
O(2B)–C(5B)
C(5B)–C(6B)
C(5B)–C(7B)
C(7B)–C(8B)
2.3244(7)
1.9984(1)
1.578(3)
1.575(3)
1.483(6)
1.569(1)
1.451(8)
1.504(1)
1.477(5)
1.493(8)
1.498(7)
1.510(8)
ꢀ
P1
prism
0.21 ꢁ 0.17 ꢁ 0.15
7.2213(7)
8.7625(8)
11.9319(1)
106.2410(1)
90.863(2)
111.483(2)
668.66(1)
1
1.683
173(2)
5.696
2.62–28.31
ꢀ9 ? 8,
ꢀ10 ? 11,
ꢀ14 ? 15
336
b (Å)
c (Å)
a
(°)
b (°)
c
(°)
V (Å3)
Z
Bond angles
Dcalc (g cmꢀ3
T (K)
)
S(1)–Pt–S(1)a
180.0
S(2)–Pt–S(2)a
180.0
S(1)–Pt–S(2)
83.32(3)
96.68(3)
87.23(3)
101.47(4)
121.18(2)
107.91(1)
124.12(9)
105.82(1)
95.15(2)
97.29(2)
125.0(3)
108.3(5)
109.6(4)
112.6(4)
114.7(4)
124.0(2)
109.6(3)
106.5(3)
114.1(5)
113.5(4)
S(1)–Pt–S(2)a
96.68(3)
83.32(3)
86.94(3)
16.46(2)
108.02(2)
122.69(1)
106.34(1)
124.40(1)
92.73(2)
96.64(2)
118.5(3)
105.4(5)
107.0(5)
106.0(6)
109.7(7)
121.3(3)
110.1(4)
106.6(3)
114.5(4)
111.4(5)
l
(Mo K
a
) (mmꢀ1
)
S(1)a–Pt–S(2)
S(1)a–Pt–S(2)a
P–S(2)–Pt
O(1B)–P–O(1A)
O(1B)–P–S(1)
O(1B)–P–S(2)
h Range
Range of h, k and l
P–S(1)–Pt
S(1)–P–S(2)
O(1A)–P–S(1)
O(1A)–P–S(2)
O(2A)–P–S(1)
O(2A)–P–S(2)
O(1A)–P–O(2A)
O(1A)–P–O(2B)
C(1A)–O(1A)–P
O(1A)–C(1A)–C(2A)
O(1A)–C(1A)–C(3A)
C(2A)–C(1A)–C(3A)
C(1A)–C(3A)–C(4A)
C(5A)–O(2A)–P
O(2A)–C(5A)–C(6A)
O(2A)–C(5A)–C(7A)
C(5A)–C(7A)–C(8A)
C(6A)–C(5A)–C(7A)
F(0 0 0)
Rint
Number of observations
Criterion of significance
Number of parameters
Weighting scheme
O(2B)–P–S(1)
O(2B)–P–S(2)
0.0129
3228
I > 2r(I)
224
O(1B)–P–O(2B)
O(1B)–P–O(2A)
C(1B)–O(1B)–P
O(1B)–C(1B)–C(2B)
O(1B)–C(1B)–C(3B)
C(2B)–C(1B)–C(3B)
C(1B)–C(3B)–C(4B)
C(5B)–O(2B)–P
O(2B)–C(5B)–C(6B)
O(2B)–C(5B)–C(7B)
C(5B)–C(7B)–C(8B)
C(6B)–C(5B)–C(7B)
W = 1/[s2(F2o) + (0.0251P)2 + 0.2529P]
where P = (F2o + 2Fc2)/3
1.087
0.0206, 0.0486
0.897, ꢀ0.463
S (Goodness-of-fit)
R1, wR2 (F2 > 2
D
r
(F2))
qmax, D
qmin (e/Å3)
sec-C4H9O– groups that were modelled as disordered. Oxygen atoms
O(1A), O(2A), O(1B), O(2B) and carbon atoms C(1A), C(2A), C(3A),
C(4A), C(5A), C(6A), C(7A), C(8A) and C(1B), C(2B), C(3B), C(4B),
C(5B), C(6B), C(7B), C(8B) have the same (0.50) site occupation fac-
Torsion angles
Pt–S(1)–S(2)–P
ꢀ168.79(5)
S(1)–Pt–P–S(2)
ꢀ169.44(4)
a
ꢀx, ꢀy, ꢀz + 2.
ꢀ
tors. Comparedto thespacegroup P1, therefinementofthestructure
in the non-centrosymmetric space group P1 does not allow us to re-
move the disorder of the sec-C4H9O– groups or to improve R-values
essentially, while the refined (using SHELXTL) BASF parameter was
close to 0.50. Therefore, the final refinement of the structure has
dispersive X-ray (EDX) spectra were recorded using a JEOL JSM-
6390 LV scanning electron microscope attached to an Oxford
INCAEnergy EDX instrument.
ꢀ
been executed in the centrosymmetric space group P1.
3. Results and discussion
Data collection and editing, as well as the refinement of the unit
cell parameters, was performed with the SMART and SAINT-PLUS pro-
gram packages [24]. The structure solution and refinement were
3.1. Heteronuclear (13C, 31P) CP/MAS NMR data
performed with the SHELXTL/PC program packages [25]. Selected
Fig. 1 shows the 13C CP/MAS NMR spectra of the polycrystalline
dialkyl dithiophosphate platinum(II) complexes 1 [Pt{S2P(O-sec-
C4H9)2}2] (Fig. 1a and b) and 2, [Pt{S2P(OC2H5)2}2] (Fig. 1c). There
are four and two sets of expected resonance lines (see Fig. 1a–c,
respectively), which can be attributed to 13C sites in CH3–, –CH2–,
–OCH2– and –OCH@ groups of the alkyl substituents in the Dtph
ligands of compounds 1 and 2. However, these spectra also reveal
that the samples of di-sec-butyl platinum(II) dithiophosphate,
which were crystallised from ethanol solution (1) and precipitated
from aqueous solution (1a), are spectrally non-identical. Fig. 2
exhibits the 31P CP/MAS NMR spectra of the recrystallised com-
plexes 1 (Fig. 2a and a0) and 2 (Fig. 2b and b0). Single 31P resonance
multiplet lines (2J(31P–195Pt)-couplings are also clearly visible) are
observed in these experimental CP/MAS NMR spectra as central
bands flanked by spinning sidebands. This observation indicates
that there is structural equivalence of the Dtph groups in both
compounds 1 and 2. It is also necessary to note that there is a
superposition of two resonance lines in the 31P CP/MAS NMR spec-
trum of the sample 1a, which was precipitated from aqueous solu-
tion (see Fig. 3). The central band of this spectrum was
bond lengths, bond angles and torsion angles are listed in Table 2.
Complete crystallographic details are included in the Supporting
Information.
2.3.3. Thermal analysis
The thermal behaviour of complex 1 was studied using the simul-
taneousthermalanalysis(STA)techniqueforparallelrecordingofTG
(thermogravimetry) and DSC (differential scanning calorimetry)
curves. The study was performed on an STA 449C Jupiter instrument
(‘NETZSCH’)incorundumcruciblesunderalidwithaholetoensurea
vapour pressure of 1 atm during the thermal decomposition of the
sample. Therateofheatingto1200 °Cwas5 °C minꢀ1 underan argon
atmosphere. The sample mass was in the range of 3.43–5.47 mg. The
accuracy of the temperature measurements was 0.7 °C, and that of
mass changes was 1 ꢁ 10ꢀ2 mg.
2.3.4. Elemental microanalysis
Qualitative determination of the elements was carried out on
the basis of electron-probe X-ray microanalysis. The energy

T.A. Rodina et al. / Polyhedron 30 (2011) 2210–2217
2213
31
Fig. 3. P CP/MAS NMR (145.72 MHz) spectra of platinum(II) O,O0-di-sec-butyl
dithiophosphate, whose sample was precipitated from aqueous solution. The MAS
frequencies were 2.8 (a) and 2.3 kHz (b); the number of transients being 1024 in the
each case. The central band is denoted by an asterisk.
result is consistent with our previous 31P NMR studies of other
dithiophosphate transition and post-transition metal complexes
[26–43]: nickel(II) [26–28], zinc(II) [26,29,30], cadmium(II)
[31–34], lead(II) [35–37], silver(I) [38], thallium(I) [39,40] and
antimony(V) [41–43]. Therefore, the additional shielding of the
31P nuclei arises due to the formation of covalent linkages between
the Dtph groups and platinum atoms in complexes 1 and 2.
There are clearly visible two equidistant satellite signals sym-
metrically located from both sides of the 31P resonance line in
the latter case (Fig. 2b and b0). The discussed 31P resonance line
was de-convoluted as a triplet with relative integral intensities of
1:4:1. Platinum has one naturally occurring NMR active nuclide
Fig. 1. 13C CP/MAS NMR spectra (90.51 MHz) of O,O0-dialkyl dithiophosphate
platinum(II) complexes, [Pt{S2P(OR)2}]: R = sec-C4H9 (a and b) and R = C2H5 (c). In
the cases of ‘a’ and ‘b’, the samples of complex 1 were precipitated from aqueous
solution and crystallised from ethanol, respectively. The MAS frequencies were 4.6
(a and b) and 3.6 kHz (c); the number of transients being 1600 (a), 3700 (b) and 100
(c). The sidebands are denoted by ‘s’.
de-convoluted as two 31P resonances at 104.1 and 102.9 ppm
2J(31P–195Pt)-couplings were also taken into account) with almost
equal line widths and integral intensities. The former, less shielded
resonance is characterised by the same chemical shift value (i.e.,
104.1 ppm) as the phosphorus sites in sample 1, which was crystal-
lised from ethanol. The latter 31P resonance line at 102.9 ppm dem-
onstrates the existence of the second polymorph of complex 1,
which shows complete transformation to the first polymorph, 1
(104.1 ppm) in the crystallisation course from ethanol. Comparing
the isotropic 31P chemical shift values for the above-mentioned
platinum(II) complexes and the initial potassium dithiophosphates
[26] (see Table 3), more shielded phosphorus sites (smaller values
in the deshielded d-scale) were revealed in the former case. This
with nuclear spin I = ½ ꢀ 195Pt (
l = 0.60950 l/lN), therefore the
two-bond spin–spin interaction 2J(31P–195Pt) is the basis of the ob-
served multiplicity of the 31P resonance. The integral intensities of
the discussed satellites are also in good agreement with the natural
abundance of the 195Pt nuclide (33.832 at.%). In contrast, the ex-
pected multiplicity of the 31P resonance is not directly visible for
the considerably broadened 31P CP/MAS NMR spectra of complex
1, [Pt{S2P(O-sec-C4H9)2}2] (Figs. 2a and a0 and 3a and b). For exam-
ple, the discussed 31P NMR signal (lw = 370 Hz) is broadened
approximately tenfold with respect to the spectra of the diethyl
dithiophosphate platinum(II) complex (lw = 35 Hz). This unusually
31
Fig. 2. P CP/MAS NMR spectra (145.72 MHz) of platinum(II) O,O0-dialkyl dithiophosphates, [Pt{S2P(OR)2}]: R = sec-C4H9 (a and a0) and R = C2H5 (b and b0). The MAS
frequencies were 2.8 (a), 3.8 (b) and 2.3 kHz (a0 and b0); the number of transients being 600 and 32 for the cases a, a0 and b, b0, respectively. The central bands are denoted by
asterisks.

2214
T.A. Rodina et al. / Polyhedron 30 (2011) 2210–2217
large broadening can be explained by the presence of two chiral
centres in the (sec-C4H9O)2P(S)Sꢀ ligand (i.e., the asymmetric car-
bon atoms of the –OCH(CH3)(C2H5) groups bound to a tetrahedral
array of four different substituents). Inasmuch as the original li-
gand is not stereospecific and is represented, according to the ran-
dom distribution of l and d groups, by a mixture of three optical
isomers: ld (50%), ll (25%) and dd (25%), the sample of the complex
theoretically should be a set of six isomers: (ll)–(ll) (6.25%), (ll)–(ld)
(25.0%), (ll)–(dd) (12.5%), (ld)–(ld) (25.0%), (ld)–(dd) (25.0%) and
(dd)–(dd) (6.25%). The coexistence of these structurally similar
optical isomers results in the aforementioned dispersion of the
31P NMR chemical shift.
To characterise quantitatively the Dtph groups with terminal
chelating structural functions in complexes 1 and 2, both 31P iso-
tropic chemical shifts (diso) and the chemical shift anisotropy
(CSA) parameters were used. From the relative intensities of the
sidebands in the spinning sideband manifolds (see Figs. 2 and 3),
v2-statistics as a function of the two 31P CSA parameters: the
chemical shift anisotropy, daniso = dzz ꢀ diso, and the asymmetry
parameter of the chemical shift tensor (CST),
g
= (dyy ꢀ dxx)/
(dzz ꢀ diso), were calculated using the MATHEMATICA program [23].
The global minimum of this statistic, v2min, gives values for the
two CSA parameters, daniso and
is the measure of the errors for these parameters [23]. Fig. 4 shows
joint confidence limits for daniso and
, while the 31P CSA data given
in Table 3 correspond to the minima of the v2-plots [23] (it is
necessary to note that the zero asymmetry parameter, = 0,
corresponds to the axially symmetric CST, while an increase in
g, while the joint confidence limit
g
g
the
g-value from 0 to 1 reflects an enhanced contribution of
rhombicity). The 31P CSTs of both samples of complex 1 (both crys-
tallised from ethanol and precipitated from water solution) are
close to being rhombic (
g = 0.89 and 0.85). These data are very
similar to the -values of the previously studied crystalline
g
di-cyclo-hexyl- (0.98) [14], di-iso-propyl- (0.75) [14] and di-iso-
butyl (0.73) dithiophosphate platinum(II) complexes [15].
However, complex 2, unexpectedly, shows the least contribution
of the rhombic component to CST (g = 0.57) among all of the stud-
ied crystalline platinum(II) dialkyl dithiophosphates.
In order to confirm the validity of these conclusions derived
from heteronuclear (31P, 13C) CP/MAS NMR, the crystal and molec-
ular structure of the mononuclear O,O0-di-sec-butyl dithiophos-
phate platinum(II) complex has been successfully resolved using
single-crystal X-ray diffraction analysis.
Fig. 4. v2 Statistics as a function of the 31P CSA parameters daniso and
g. Graphs
exhibit simulations for P-sites of [Pt{S2P(O-sec-C4H9)2}2] samples (a and b) and
[Pt{S2P(OC2H5)2}2] (c). In ‘a’ and ‘b’ cases, complex 1 was precipitated from aqueous
media and crystallised from ethanol solution, respectively. The 68.3% joint
confidence limit (solid) and 95.4% joint confidence limit (dashed) for the two CSA
parameters are shown. In each case simulations were performed for one P-site but
at two different spinning frequencies: 2.3 kHz (thick lines) and 2.8 kHz (thin lines).
S,S0-isobidentate coordination mode (Fig. 6): Pt–S 2.3210(7) and
2.3244(7) Å. This type of coordination results in the formation of
two four-membered chelate rings [PtS2P] with a common platinum
atom. A slight tetrahedral distortion of the planar geometry of
these metallocycles is shown by the corresponding Pt–S–S–P and
S–Pt–P–S torsion angle values, which deviate noticeably from
180° (see Table 2). This distortion is due to a slight bend in the
aforementioned four-membered rings [PtS2P] along the S–S axis:
the dihedral angle between the [PtSS] and [SSP] half-rings is equal
to 168.79(5)°. In the dithiophosphate ligands, both values of the P–
S bond lengths (1.9900(1) and 1.9984(1) Å) are intermediate
3.2. Structural description of [Pt{S2P(O-sec-C4H9)2}2] (1)
The unit cell of platinum(II) O,O0-di-sec-butyl dithiophosphate
comprises one centrosymmetric molecule of [Pt{S2P(O-sec-
C4H9)2}2] (Fig. 5) (selected bond lengths, angles and torsion angles
for 1 are given in Table 2) The central platinum atom, exhibiting
fourfold coordination, links two Dtph ligands almost in an
Table 3
31P NMR chemical shift parametersa for O,O0-dialkyl dithiophosphate compounds.
b
Compound
diso (ppm)
2J(31P–195Pt) (Hz)
daniso (ppm)
gb
1, [Pt{S2P(O-sec-C4H9)2}2]
1a, [Pt{S2P(O-sec-C4H9)2}2]
K{S2P(O-sec-C4H9)2} [26]
104.1
102.9
113.8
114.8
(1:1)
ꢂ456
ꢂ443
ꢀ43.3 0.2
ꢀ42.3 0.2
ꢀ114.0 1.0
ꢀ112.4 1.7
0.89 0.02
0.85 0.02
0.33 0.04
0.28 0.03
2, [Pt{S2P(OC2H5)2}2]
K{S2P(OC2H5)2} [26]
105.0
108.5
444.4
ꢀ35.1 0.2
0.57 0.03
0.10 0.06
ꢀ107.6 1.0
a
Relative to 85.5% H3PO4 (0 ppm, externally referenced), deshielding scale.
Definitions: daniso = dzz ꢀ diso; g = (dyy ꢀ dxx)/(dzz ꢀ diso). (1) The crystalline sample was isolated from ethanol solution. (1a) The powdered sample was precipitated from
b
aqueous solution.

T.A. Rodina et al. / Polyhedron 30 (2011) 2210–2217
2215
Fig. 5. Crystal structure of [Pt{S2P(O-sec-C4H9)2}2] (projection onto the bc plane).
between hypothetical single (2.14 Å) and double (1.94 Å) P–S
bonds [44]. This is evidence of delocalisation of the -electron den-
S(1)–Pt–S(2) and S(1)–Pt–S(2)a (83.32(3)° and 96.68(3)°, respec-
tively) are noticeably deviated from 90° because of the formation
of the two sterically strained four-membered chelate rings [PtS2P].
Complex 1 is also characterised by the lowest value of the S–P–S
angle (101.47°) among various platinum(II) dialkyl dithiophos-
phates: R = C2H5 (102.4° [12]), iso-C3H7 (101.9° [13]), iso-C4H9
(102.39° [15]), cyclo-C6H11 (101.79° [14]).
p
sity over the four-membered metallocycles [PtS2P], whose small
sizes are illustrated by unusually short interatomic Ptꢃ ꢃ ꢃP
(2.983 Å) and Sꢃ ꢃ ꢃS (3.088 Å) distances. The latter values are much
shorter than the sum of the van der Waals radii of the correspond-
ing pairs of atoms: 3.55 and 3.60 Å, respectively [45–47]. Thus, the
positions of the platinum and phosphorus atoms are essentially
drawn together in the chelate rings, which can be attributed to a
direct trans-annular interaction between them. The phosphorus
atoms in both Dtph groups are in a tetrahedral neighbouring
[O2S2] environment.
3.3. Thermal analysis and elemental microanalysis data
Fig. 7 shows both the TG and DSC traces. Thermogravimetry
data reflect the thermal stability of complex 1 below 157 °C and
the stepwise mass loss in the range of 157–795 °C. There are three
distinct steps exhibiting mass loss on the TG curve: (i) in the range
157–170 °C, (ii) at 170–425 °C and (iii) at 425–795 °C (see Fig. 7a).
The first and second steps of the TG curve reflect thermal decom-
position of the organic parts of the Dtph ligands: a 38.5% total loss
The planar configuration of the [PtS4] chromophore in structure
1
is due to the dsp2-hybrid state of platinum(II).
A slight
non-equivalence of the Pt–S bonds results in a slight rhombic dis-
tortion of the discussed chromophore. In contrast to the [PtS4]
chromophore in cooperite [10,11], the values for both angles
Fig. 6. Molecular structure of [Pt{S2P(O-sec-C4H9)2}2]. Displacement ellipsoids are shown at the 50% probability level.

2216
T.A. Rodina et al. / Polyhedron 30 (2011) 2210–2217
The thermal transformations of dialkyldithiophosphate plati-
num(II) complexes, usually, lead to platinum(II) sulphide as the fi-
nal product [12]. However, in our case, there was a 38.6%
remaining mass that clearly did not correspond to PtS (calc.
33.52%). Therefore, to establish qualitatively the elemental compo-
sition of the end-product particles, which were characterised by a
heterogeneous surface, energy dispersive X-ray analysis was used.
The EDX spectral pattern (Fig. 8a) supports the existence of plati-
num particles as the main end-product with dark inclusions of a
slag at its bright metallic surface (Fig. 8b). Form the EDX spectros-
copy data, these dark areas are characterised by the presence of the
sulphur, phosphorus, oxygen, carbon and platinum.
4. Conclusion
Crystalline bis(O,O0-di-sec-butyldithiophosphato)platinum(II)
was prepared and studied by means of heteronuclear 13C, 31P CP/
MAS NMR spectroscopy and single-crystal X-ray diffraction. The
unit cell of this platinum(II) compound comprises of one molecule
of [Pt{S2P(O-sec-C4H9)2}2], in which Dtph ligands, playing the same
terminal chelating function, exhibit structural equivalence in both
Fig. 7. TG (a) and DSC (c) curves of complex 1. A close-up view of the inner surface
of the crucible with the end-product particles (b). An enlarged fragment of TG curve
around the melting endotherm (d).
31
solid state P NMR and XRD data. A terminal S,S0-bidentate
coordination of the Dtph groups leads to the formation of two
four-membered planar chelate rings [PtS2P] with a platinum atom
displaying a ‘spiro’ function. In the dithiophosphate complexes, the
structural states of the phosphorus atoms are characterised by 31P
chemical shift tensors that are close to being rhombic. The thermal
behaviour of compound 1 was studied by means of the STA meth-
od, as a combination of TG and DSC techniques taken under an ar-
gon atmosphere. The mass of complex 1 is lost in three steps: first
at 157–170 °C and then in the temperature intervals of 170–425
and 425–795 °C. The thermal decomposition of the organic parts
of the Dtph ligands over the first and second steps with a 38.5% to-
tal loss, corresponding to the relative mass of two sec-C4H9– and
two sec-C4H9O– groups (the calculated loss is 38.43%), yields
bis(dithio-meta-phosphato)platinum(II), [Pt(S2PO)2] (calc. 61.57%),
as the intermediate product; whereas reduced metallic platinum
is the main final product.
corresponds to the relative mass of two sec-C4H9– and two sec-
C4H9O– groups (the calculated loss is 38.43%). The mass remaining
after the second step at 425 °C (61.5%) corresponds, as expected, to
the mass of bis(dithio-meta-phosphato)platinum(II), [Pt(S2PO)2]
(calc. 61.57%) as the intermediate product [12]. Hence, a 25.1% loss
at the first step is probably connected with the thermal cleavage of
the C–C(H)O– bonds when both di-sec-butyl dithiophosphate li-
gands lose alkyl groups of terminal carbon atoms, which are not di-
rectly linked to the oxygen atom (calc. 26.02%). The third step
exhibits a 22.9% loss defining a 38.6% final mass (at 900 °C) of
metallic bright rounded particles (Fig. 7b).
Fig. 7c shows a DSC curve with two main endotherms. The first,
low-temperature one, which is observed in a region of the thermal
stability of 1 (i.e., before the beginning of mass loss), is the melting
endotherm of compound 1 (the extrapolated m.p. is 83.5 °C). The
second endotherm arises on the DSC curve at 165.1 °C, at the start
of the first step of the intense thermal decomposition of the organ-
ic part of the Dtph ligands in complex 1. Besides that, there is one
more, very low intense and non-reversible endotherm on the TG
curve before the m.p. (see Fig. 7d). This endotherm was attributed
to a phase transition of complex 1 at 74.2 °C.
Acknowledgements
We are grateful to ‘CHEMINOVA AGRO A/S’ (Denmark) for the
dithiophosphate chemicals that were kindly supplied for this
study. One of the authors (I.M.A.) acknowledges financial support
from the Presidium of Far Eastern Branch of the Russian Academy
of Sciences (project no. 11–III–B–04–244). The Varian/Chemagnet-
ics CMX-360 NMR spectrometer was purchased with a grant from
the Swedish Council for Planning and Coordination of Research
(FRN). We thank the foundation in memory of J.C. and Seth M.
Kempe for grants JCK-2003, JCK-2307 and JCK-2701 from which
some of the NMR equipment was purchased.
Appendix A. Supplementary data
CCDC 821345 contains the supplementary crystallographic data
for complex 1. These data can be obtained free of charge via http://
www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge
Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ,
UK; fax: (+44) 1223-336-033; or e-mail: deposit@ccdc.cam.ac.uk.
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