Preparation spectroscopy and conductivity of [Pt(SS)(NN)]-type complexes and their iodine oxidized complexes

Article abstract of DOI:10.1016/S0020-1693(98)00259-X

Complexes of the general formula [Pt(SS)(NN)] have been prepared, where SS is bbdt(1,2-bis(benzylthio)ethylene-1,2-dithiolate) or dpdt (5,6-dihydrophenyl-1,4-dithion-2,3-dithiolate) and NN is bipy (2,2′-bipyridine) or phen (1,10-phenanthroline). The UV-Vis spectra exhibit intense intramolecular ligand-to-ligand charge transfer absorption bands at 440-600 nm. Cyclic voltammograms show a reversible oxidation step assigned to [Pt(SS)(NN)]⁰/[Pt(SS)(NN)]⁺. On doping iodine into the complexes, partial oxidation occurs to afford [Pt(SS)(NN)]I_x (x=1.9(2.2). IR, Raman and ESR spectra of the iodine-doped complexes are discussed. Electrical conductivities of the neutral mixed-ligand complexes (10^-9-10^-10 S cm^-1) increase to 10^-6-10^-7 S cm^-1 upon I₂ doping.

Full text of DOI:10.1016/S0020-1693(98)00259-X

Inorganica Chimica Acta 284 (1999) 112±115
Note
Preparation spectroscopy and conductivity of [Pt(SS)(NN)]-type
complexes and their iodine oxidized complexes
Zhifeng Haoa, Zongxun Tangb,*, Qizhen Shib
a Department of Chemistry, Lanzhou University, Lanzhou 730000, China
b Department of Chemistry, Northwest University, Xi'an 710069, China
Received 12 March 1998; received in revised form 25 March 1998; accepted 30 April 1998
Abstract
Complexes of the general formula [Pt(SS)(NN)] have been prepared, where SS is bbdt(1,2-bis(benzylthio)ethylene-1,2-dithiolate) or dpdt
(5,6-dihydrophenyl-1,4-dithion-2,3-dithiolate) and NN is bipy (2,20-bipyridine) or phen (1,10-phenanthroline). The UV±Vis spectra exhibit
intense intramolecular ligand-to-ligand charge transfer absorption bands at 440±600 nm. Cyclic voltammograms show a reversible
‡
oxidation step assigned to [Pt(SS)(NN)]0/[Pt(SS)(NN)] . On doping iodine into the complexes, partial oxidation occurs to afford
[Pt(SS)(NN)]Ix (xˆ1.9(2.2). IR, Raman and ESR spectra of the iodine-doped complexes are discussed. Electrical conductivities of the
1
neutral mixed-ligand complexes (10 9±10 10 S cm 1) increase to 10 6±10 7 S cm upon I2 doping. # 1999 Elsevier Science S.A. All
rights reserved.
Keywords: Charge transfer; Platinum complexes; Mixed-ligand complexes
1. Introduction
trical conductivities. Spectroscopic, electrochemical and
magnetic properties as well as electrical conductivities
are discussed.
Partially oxidized planar metal complexes with one-
dimensional metal±metal interactions often exhibit high
electrical conductivity [1]. For example, sulfur-rich dithio-
late complexes, such as [M(dmit)2]n (dmitˆ1,3-dithiole-2-
thione-4,5-dithiolate) have recently attracted much attention
because of their high conductivities [2±6]. Another inter-
esting set of planar complexes having the formula
[Pt(SS)(NN)] contain both electron donor dithiolate and
ꢀ-electron acceptor diimine ligands [7]. These exhibit
intense electronic absorption bands due to intramolecular
ligand-to-ligand charge-transfer transitions [8]. They may
also assume columnar packing through SÁ Á ÁN electrostatic
interaction as well as PtÁ Á ÁPt contacts which form an effec-
tive conducting pathway when partially oxidized [8]. Polar-
ized, planar Pt(SS)(NN) complexes have been reported to be
electrical conductors [7±9].
2. Experimental
2.1. Materials
5H,10H-dithiolo[2,3-b][2,5]benzothionine-2-one and 4,5-
bis(benzylthio)-1,3-dithiole-2-one were prepared by the lit-
erature methods [10]. [PtCl2(bipy)] and [PtCl2(phen)] were
prepared by procedures similar to those for [PdCl2(bipy)]
[11].
2.2. Preparation of [Pt(dpdt)(L)] (Lˆbipy or phen)
Sodium metal (120 mg, 5.0 mmol) and 5H,10H-dithiolo-
[2,3-b][2,5]benzothionine-2-one (436 mg,1.5 mmol) were
dissolved in methanol (50 ml) under N2. To the resulting
dark red solution, PtCl2(bipy) (430 mg, 1.0 mmol) in
dimethyl sulfoxide (DMSO, 30 ml) was added dropwise.
A dark brown solid precipitated immediately. Stirring was
continued for 1 h at room temperature. Water (50 ml) was
added and the solid was collected by ®ltration, washed with
MeOH (50 ml) and dried in air. IR (KBr): 1610 m, 845 m,
746 m (aromatic), 1480 m, 1420 s, 1263 m, 1310 m,
This paper reports the preparation of new [Pt(SS)(NN)]-
type complexes containing bbdt or dpdt as electron donor
ligands and 2,20-bipyridine or 1,10-phenanthroline as elec-
tron acceptor ligands. This is the ®rst report of complexes
containing both bbdt and dpdt as the SS ligands. Partial
oxidation of the Pt(SS)(NN) complexes increase their elec-
*Corresponding author.
0020-1693/99/$ ± see front matter # 1999 Elsevier Science S.A. All rights reserved.
PII: S0020-1693(98)00259-X

Z. Hao et al. / Inorganica Chimica Acta 284 (1999) 112±115
113
1105 m, 960 m, 760 w cm 1. The reactions involving this
procedure are as follows:
Table 1
Elemental analyses of the [Pt(SS)(NN)] complexes and their iodine-doped
analogues a
Complex
Found (calc.) (%)
C
H
N
Pt(dpdt)(bipy)
Pt(dpdt)(phen)
39.42 (39.54)
41.89 (41.84)
45.74 (45.55)
47.40 (47.39)
26.93 (27.08)
29.27 (29.41)
33.54 (33.68)
34.03 (33.99)
2.52 (2.64)
2.52 (2.54)
3.15 (3.21)
3.25 (3.10)
1.80 (1.81)
1.80 (1.78)
2.40 (2.38)
2.20 (2.23)
4.39 (4.01)
4.36 (4.44)
4.01 (4.09)
4.07 (3.95)
3.25 (3.16)
3.10 (3.12)
3.05 (3.02)
2.65 (2.83)
Pt(bbdt)(bipy)
When [PtCl2(phen)] was used in place of [PtCl2(bipy)],
[Pt(dpdt)(phen)] was obtained by the same procedure. IR
(KBr): 1420 m, 830 s, 710 s (phenanthroline); 1620 m,
Pt(bbdt)(phen)
[Pt(dpdt)(bipy)]I2.2
[Pt(dpdt)(phen)]I2.1
[Pt(bbdt)(bipy)]I1.9
[Pt(bbdt)(phen)]I2.2
1
1415 s, 1260 m, 1120 m, 1090 m, 760 w cm
.
a Melting points > 2608C for both types of the complexes. Pt(SS)(NN)
complexes are dark brown and Pt(SS)(NN)Ix are black.
2.3. Preparation of [Pt(bbdt)(L)] (Lˆbipy or phen)
Sodium metal (120 mg, 5.0 mmol) and 4,5-bis(ben-
zylthio)-1,3-dithiole-2-one (543 mg, 1.5 mmol) were
allowed to react in MeOH (50 ml) under N2. The resulting
dark brown solution was added dropwise to a solution of
PtCl2(bipy) (430 mg, 1.0 mmol) in DMSO (30 ml). A dark
brown solid precipitated immediately. Stirring was contin-
ued for 1 h at room temperature. Water (50 ml) was added
and the solid was collected by ®ltration, washed with MeOH
(50 ml) and dried in air. IR (KBr): 1600 m, 850 s, 760 m
(aromatic); 1485 m, 1420 s, 1220 m, 1152 m, 920 m,
720 w cm 1. The reactions involving this procedure are
as follows:
as the auxiliary electrode and a standard calomel electrode
(SCE) as the reference electrode. IR spectra were recorded
on an IR-450 spectrophotometer. Raman spectra were
recorded on a SPEX 1403 laser spectrometer. Data were
obtained on KBr pellets. Electronic spectra were recorded
on an UV-1700 spectrophotometer. Electrical conductivities
for compacted pellets of the complexes were measured on a
HG high resistance meter by a four-probe technique. Ele-
mental analyses were performed with a PE-2400 analytical
instrument.
3. Results and discussion
3.1. Configuration, IR and electronic spectra of
Pt(SS)(NN)
When [PtCl2(phen)] was used in place of [PtCl2(bipy)],
[Pt(bbdt)(phen)] was obtained by the same procedure. IR
(KBr): 1420 s, 840 m, 720 s (phenanthroline); 1620 m,
The four neutral mixed-ligand complexes are stable in air
and water. All complexes are soluble in DMSO, dimethyl-
formamide (DMF) and dichloromethane, though they are
sparingly soluble in common organic solvents. The struc-
tures of the complexes are shown in Scheme 1.
1
1425 s, 1240 m, 1095 m, 940 m, 720 w cm
.
2.4. Reaction of Pt(dpdt)(L) or Pt(bbdt)(L) with iodine
The IR spectra of the complexes show ꢁC=C about
1420 cm 1, which is red-shifted compared with the corre-
1
sponding value of 1460 cm in the uncomplexed ligand.
Finely powdered Pt(dpdt)(L) (Lˆbipy or phen) was
suspended in a hexane solution containing a slight excess
of iodine. The solution was stirred at room temperature for
24 h to give an iodine-doped complex, which was washed
with hexane several times, collected by ®ltration and dried
in air. The iodine-doped complexes of [Pt(bbdt)(L)]
(Lˆbipy, phen) were obtained by the same method. Ele-
mental analyses for the [Pt(SS)(NN)] complexes and their
iodine-doped products are summarized in Table 1.
The absorptions of [Pt(dpdt)(bipy)] and [Pt(bbdt)(bipy)] at
1
1600, 850, 750 cm con®rm the presence of 2,20-bipyr-
2.5. Physical measurements
ESR spectra were recorded on a Bruker ER 200-D-SRC
spectrometer. Cyclic voltammetry (CV) was performed with
a model BAX 100 V-A analyser, with an electrochemical
cell containing a Pt wire as the working electrode, a Pt wire
Scheme 1.

114
Z. Hao et al. / Inorganica Chimica Acta 284 (1999) 112±115
Fig. 1. Electronic absorption spectrum of Pt(bbdt) (bipy) (1.1Â10 4 mol
dm 3) in dimethyl sulfoxide (ÐÐÐ) and in dichloromethane (- - -)
idine ligands, while the absorptions of [Pt(dpdt)(phen)] and
[Pt(bbdt)(phen)] at 1420, 835, 715 cm 1 can be attributed to
1,10-phenanthroline [12].
Fig. 2. Cyclic voltammograms of [Pt(dpdt)(bipy)] (top) and [Pt(bbdt)(bi-
4
py)] (bottom) measured at a Pt wire electrode in CH3CN, 1.0Â10
Fig. 1 shows the electronic absorption spectra of
[Pt(bbdt)(bipy)] in DMSO and in CH2Cl2. The intense
absorption bands centered at 450 nm in CH2Cl2 and
460 nm in DMSO are assignable to the ꢀ±ꢀ* transition
of the SS ligand. Note that the intense absorption band at
550 nm in DMSO is shifted to a longer wavelength
(590 nm) in CH2Cl2. This band may be assigned to the
intramolecular ligand-to-ligand charge transfer (LLCT)
transition (from electron-rich sulfur ligand to the ꢀ-electron
de®cient nitrogen ligand) as described for the corresponding
PtN2S2 complexes [13]. The negative solvatochromism
suggests the polar electronic structure of the complex in
the ground state. On the other hand, the low energy shifts
shown in Table 2 are smaller than those of [Pt(dmit)(Pri-
pia)] (Pri-piaˆN-isopropyl-2-picolinal diimine) (580 nm in
DMSO and 660 nm in CH2Cl2) [13]. Therefore, the title
complexes are less polar than [Pt(dmit)(Pri-pia)].
3
1
mol dm 3, 0.1 mol dm TNAP, sweep rate: 100 mV s
Table 3
Electrochemical data a
Complex
eV
Ref.
Pt(dpdt)(bipy)
Pt(dpdt)(phen)
Pt(bbdt)(bipy)
Pt(bbdt)(phen)
Pt(dmit)(bipy)
Pt(mnt)(bipy)
Pt(dddt)(bipy)
Pt(pddt)(bipy)
0.26
0.30
0.22
0.24
0.80
1.32
0.33
0.46
14
14
15
15
3
a Measured at a Pt wire electrode in CH3CN, 1.0Â10 4mol dm
,
3
1
0.1 mol dm [Bu4n][ClO4], sweep rate: 100 mV s
.
3.3. Properties of iodine-doped Pt(SS)(NN) complexes
3.2. Oxidation of Pt(SS)(NN) complexes
The value of x in iodine-doped complexes [Pt(SS)(NN)]Ix
is changeable depending on the nature of the SS ligand and
the NN ligand. The IR spectra of the iodine complexes show
remarkable low-frequency shifts and somewhat broadening
of the ꢁC=C band (from 1420 to 1380 cm 1) compared with
the neutral mixed-ligand complexes. This is indicative of the
occurrence of oxidation at the dithiolate ligands, since
similar low-frequency shifts of ꢁC=C bands were reported
for [Pt(dmit)(phen)]I1.9 [14]. The neutral mixed-ligand
complexes [Pt(SS)(NN)] exhibit no ESR signal. On the
other hand [Pt(dpdt)(bipy)]I2.2 exhibits a broad ESR signal
at g ˆ 1.93, g ˆ 2.06. Other iodine-doped complexes also
The cyclic voltammograms of Pt(dpdt)(bipy) and
Pt(bbdt)(bipy) measured in CH3CN are shown in Fig. 2.
Both complexes display a reversible redox process
‡
[Pt(SS)(NN)]0/[Pt(SS)(NN)] . The anodic potentials of
the title complexes are summarized in Table 3.
Complexes in Table 3 are oxidized at somewhat lower
potentials than their dmit, mnt, dddt and pddt analogues,
suggesting that they have more suitable redox potentials for
the preparation of conducting materials.
k
?
display broad ESR signals similar to those of [Pt(dpdt)(bi-
py)]I2.2
Table 2
Electronic absorptions of the [Pt(SS)(NN)] complexes
.
The iodine-doped complexes were investigated by
Raman spectroscopy. The spectrum of [Pt(dpdt)(bipy)]I2.2
shows characteristic features at 108 and 165 cm 1 (Fig. 3),
which are attributable to I3 [15] and I5 [16]. The formation
of I3 and I5 results from the oxidation of the complex by I2.
Complex
ꢀ-ꢀ* band (nm)
LLCT band (nm)
DMSO
CH2Cl2
DMSO
CH2Cl2
Pt(dpdt)(bipy)
Pt(dpdt)(phen)
Pt(bbdt)(bipy)
Pt(bbdt)(phen)
440
446
460
458
435
443
450
450
580
593
550
600
614
620
590
627
1
In addition, the absence of Raman bands around 250 cm
indicates that no free I2 is present.

Z. Hao et al. / Inorganica Chimica Acta 284 (1999) 112±115
115
University of China for ®nancial support and Professor D.F.
Shriver for helpful discussions.
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We thank the National Natural Science Foundation and
the Key Laboratory of Coordination Chemistry in Nanjing