Heteroleptic binuclear palladium(ii) and platinum(ii) complexes containing 1,2-bis(diphenylphosphino)acetylene and 1,2-benzenedithiolates: Syntheses, crystal structures, electrochemistry and photoluminescence properties

Article abstract of DOI:10.1039/b815013c

A series of heteroleptic binuclear Pd(ii) and Pt(ii) complexes, [M(bdts)]₂(μ-dppa)₂ (M = Pd (3) and Pt (4); dppa = 1,2-bis(diphenylphosphino)acetylene = Ph₂PCCPPh₂; bdts = 1,2-benzenedithiolate (bdt: a), 3,4-toluenedithiolate (tdt: b) and 1,4-dichloro-2,3-benzenedithiolate (Cl₂bdt: c), containing two square-planar MP₂S₂ cores were prepared using (MCl ₂)₂(μ-dppa)₂ (M = Pd (1) and Pt (2)) and the corresponding 1,2-benzenedithiols, and characterized by spectroscopic methods including FT-IR, Raman, UV-vis, MALDI-TOF-MS, ³¹P{¹H} and/or ¹⁹⁵Pt{¹H} NMR spectroscopy. X-Ray crystal structure analyses for complexes 3 and 4 revealed that C1C2C4C3 is twisted in two ways with a torsion angle of 21.6-30.7° for 3a, 3b, 4a and 4b and about 42° for 3c and 4c, and that their crystals are racemic mixtures. Due to the more electronegative chloride atoms in the ligand, complexes 3c and 4c show higher ν(M-S) vibrational frequencies in their Raman spectra, smaller spin-spin coupling constants (J_Pt-P) in their ¹⁹⁵Pt{³¹P} NMR spectra and higher anodic potentials (E_pa) in their cyclic voltammograms than complexes 3a, 3b, 4a and 4b. Moreover, only complex 4c containing the chlorinated ligand and Pt(ii) ion exhibits luminescence (λ_ob = 610 nm and λ_ex = 440 nm) in the solid state at 298 K. This emissive transition can be assigned as the d-π*_dithiolate metal-to-ligand charge transfer (MLCT) and the feasibility of this spin-forbidden transition is ascribed to the effective spin-orbit coupling of ligand c containing heavy chloride atoms and the large spin-orbit coupling in Pt(ii).

Full text of DOI:10.1039/b815013c

View Article Online / Journal Homepage / Table of Contents for this issue
PAPER
www.rsc.org/dalton | Dalton Transactions
Heteroleptic binuclear palladium(II) and platinum(II) complexes containing
1,2-bis(diphenylphosphino)acetylene and 1,2-benzenedithiolates: syntheses,
crystal structures, electrochemistry and photoluminescence properties†
Kyong-Soon Shin,a Kyung-In Son,a Jae Il Kim,b Chang Seop Hong,b Myungkoo Suh‡c and Dong-Youn Noh*a
Received 28th August 2008, Accepted 28th November 2008
First published as an Advance Article on the web 28th January 2009
DOI: 10.1039/b815013c
A series of heteroleptic binuclear Pd(II) and Pt(II) complexes, [M(bdts)]2(m-dppa)2 (M = Pd (3) and Pt
∫
(4); dppa = 1,2-bis(diphenylphosphino)acetylene = Ph2PC CPPh2; bdts = 1,2-benzenedithiolate
(bdt: a), 3,4-toluenedithiolate (tdt: b) and 1,4-dichloro-2,3-benzenedithiolate (Cl2bdt: c), containing two
square-planar MP2S2 cores were prepared using (MCl2)2(m-dppa)2 (M = Pd (1) and Pt (2)) and the
corresponding 1,2-benzenedithiols, and characterized by spectroscopic methods including FT-IR,
1
1
Raman, UV-vis, MALDI-TOF-MS, 31P{ H} and/or 195Pt{ H} NMR spectroscopy. X-Ray crystal
structure analyses for complexes 3 and 4 revealed that C1C2C4C3 is twisted in two ways with a torsion
angle of 21.6–30.7◦ for 3a, 3b, 4a and 4b and about 42◦ for 3c and 4c, and that their crystals are racemic
mixtures. Due to the more electronegative chloride atoms in the ligand, complexes 3c and 4c show
higher n(M–S) vibrational frequencies in their Raman spectra, smaller spin–spin coupling constants
31
(JPt–P) in their 195Pt{ P} NMR spectra and higher anodic potentials (Epa) in their cyclic voltammograms
than complexes 3a, 3b, 4a and 4b. Moreover, only complex 4c containing the chlorinated ligand and
Pt(II) ion exhibits luminescence (lob = 610 nm and lex = 440 nm) in the solid state at 298 K. This
emissive transition can be assigned as the d–p*dithiolate metal-to-ligand charge transfer (MLCT) and the
feasibility of this spin-forbidden transition is ascribed to the effective spin–orbit coupling of ligand c
containing heavy chloride atoms and the large spin–orbit coupling in Pt(II).
Introduction
A considerable amount of interests has been devoted to the
chemistry of palladium(II) and platinum(II) complexes, mostly
focusing on their structural diversity, anticancer activity, cat-
alytic effect and photochemical properties, as well as their
superconductivity.1–35 These properties are basically related to
the characteristic coordination preference of Pd(II) and Pt(II)
ions for square-planar geometry. These complexes are mostly
mononuclear system with C2MP2,3 S2MN2,4,5 MP46 and S2MP2
7–13
Scheme 1
cores where M = Pd(II) or Pt(II), and the ligands are monodentate
or chelate systems. One of the relevant diphosphine chelate ligands
is 1,1¢-bis(diphenylphosphino)ferrocene (dppf) (Scheme 1), which
is frequently comprised of (dppf)MS2 complexes where S2 is
dithiolate ligand such as 1,2-benzenedithiolates,14 1,2-ethylenedi-
thiolates,15 or tetrathiafulvalene-2,3-dithiolates.16 These com-
plexes show considerable interactive redox behaviors among
the redox-active centers such as dppf, M(II) ions and dithi-
olate ligands. Linear diphosphine ligands such as trans-1,2-
bis(diphenylphosphino)ethane (trans-dppen),17 1,4-bis(diphenyl-
phosphino)butadiyne (dppby),18 1,4-bis(diphenylphosphino)-
benzene (dppb)19 and 4,4¢-bis(diphenylphosphino)biphenylene
(dpbp)20 are also used as bridging ligands between two metal ions,
mostly resulting in a binuclear complex as the main product. The
dppby ligand also adopts a trinuclear system as a minor product.18
It is interesting to note that the complexes with trans-dppen and
dppby ligands undergo intramolecular cyclization when subjected
to UV-irradiation or elevated temperatures.
aDepartment of Chemistry, Seoul Women’s University, Seoul, 139-774,
Korea. E-mail: dynoh@swu.ac.kr; Fax: +82 2 970 5972; Tel: +82 2 970
5656
bDepartment of Chemistry, Korea University, Seoul, 136-701, Korea. E-mail:
cshong@korea.ac.kr; Fax: +82 2 3290 3121; Tel: +82 2 3290 3138
cDepartment of Chemistry, Sungkyunkwan University, Suwon, 440-746,
Korea. E-mail: msuh@skku.edu; Fax: +82 31 290 7075; Tel: +82 31 290
5941
† Electronic supplementary information (ESI) available: Cyclic voltam-
mograms of 2, 3 and 4, the crystal packing diagrams of 3 and 4, and UV-
Vis, 31P NMR and 195Pt NMR spectra of 1, 2, 3 and 4. CCDC reference
numbers 699934–699939. For ESI and crystallographic data in CIF or
other electronic format see DOI: 10.1039/b815013c
‡ Present address: Department of Chemistry and Advanced Materials
Science, Kyung Hee University, Yongin 446-701, Korea.
Another linear diphosphine ligand that we are interested in
∫
is 1,2-bis(diphenylphosphino)acetylene (dppa: Ph2PC CPPh2). It
was utilized for the first time by Carty, as a bridging ligand between
two metal ions.21,22 Following these reports, many binuclear
complexes, together with mono- and multi-nuclear complexes,
This journal is
The Royal Society of Chemistry 2009
Dalton Trans., 2009, 1767–1775 | 1767
©

View Article Online
1
Table 1 31P{ H} NMR data for the complexes 1 and 3a
of Ni(0), Cr(0), Mo(0), W(0), Os(0), Cu(I), Ag(I), Au(I), Mn(I),
Ru(II), Hg(II) and mixed Pd(II)/Pt(II) ions have been reported,
which comprise 1 ~ 4 dppa bridging ligands and diverse terminal
ligands such as halides (Cl, Br, I, SCN), CO, cyclopentadienyl,
alkyl, acetylacetonato (acac), phosphine, monothiol and so on.21–33
All of these reports, however, deal solely with the synthesis, X-ray
crystal structure analysis and electrochemical properties (only in
some reports) of the complexes, whereas the specific properties of
the complexes, such as their luminescence, have not been reported.
Very recently, we investigated and reported the X-ray structure
analysis and luminescence properties of binuclear Pt(II)-dppa com-
plexes with the bidentate 1,2-ethylenedithiolate ligands, ([Pt(1,2-
dithiolate)]2(m-dppa)2).34,35 To the best of our knowledge, this is
the first, albeit preliminary, report concerning the luminescence
properties of binuclear metal–dppa complexes. Furthermore, the
luminescence properties of Pt-complexes with a P2PtS2 core have
dHb/ppm
dPc/ppm
nJH–H/Hz
1
7.53468 (16H, q; H1)
7.48212 (8H, t; H3)
7.25642 (16H, t; H2)
7.48693 (16H, q; H1)
7.42107 (8H, t; H3)
7.21785 (16H, t; H2)
7.14599 (4H, dd; H4 + H7)
6.82061 (4H, dd; H5 + H6)
7.48316 (16H, m; H1)
7.41270 (8H, t; H3)
7.20997 (16H, t; H2)
7.01595 (2H, d; H4)
6.96357 (2H, s; H7)
6.63725 (2H, d; H5)
2.16880 (6H, s; H6)
7.49647 (16H, q; H1)
7.44636 (8H, t; H3)
7.24612 (16H, t; H2)
6.91114 (4H, s; H5 + H6)
4.873
3J = 7.47
3a
1.757
1.676
3J = 7.40
3J = 7.40
3J = 5.95, 4J = 3.22
3J = 5.95, 4J = 3.22
3b
3J = 7.40
3J = 7.40
3J = 8.00
3J = 8.00
3c
1.943
3J = 7.40
3J = 7.40
4,5
not been investigated as much as those with an N2PtS2 or
3
C2PtS2 core. In this paper, we describe the results of our system-
atic investigation of the [M(1,2-dithiolate)]2(m-dppa)2 complexes
where M = Pd(II) or Pt(II), and the 1,2-dithiolate ligand is 1,2-
benzenedithiolate (a), 3,4-toluenedithiolate (b) or 1,4-dichloro-
2,3-benzenedithiolate (c). The luminescence properties of the
complexes are explained in correlation with the FT-IR, Raman
a
31
and 195Pt{ P} NMR spectra, cyclic voltammetry results and X-
ray crystal structure analysis, and are compared with those of
other luminescent complexes with a P2PtS2 core.
b d: doublet; t: triplet; q: quartet; dd: doublet of doublets; m: multiplet.
c Positive chemical shifts are downfield from the standard (85% H3PO4).
Experimental
electrolyte, Ag/Ag+ as the reference electrode, a Pt-button working
electrode (r = 1 mm), a Pt-wire as the counter electrode and with
a scan rate of 50 mV s-1. All redox potentials were referenced
against the Fc/Fc+ couple (E1/2 = +0.687 V). The UV-Vis spectra
were obtained at ambient temperature in acetonitrile on an HP
8452A diode array spectrophotometer. The emission spectra of the
microcrystalline samples were acquired at ambient temperature
using an Amico-Bowman Series 2 spectrofluorometer equipped
with a 7 W pulsed Xe Lamp. The Pt(II) samples were excited with
440 nm light and the luminescence was collected for 5 ms after
a 10 ms delay in order to reduce the scattering excitation light.
The reagent-grade chemicals used for the syntheses were com-
mercially purchased and used without further purification. For
example, commercially obtained 3,6-dichloro-1,2-benzendithiol
(H2c) containing an inseparable 5% 1,2-benzenedithiol impurity
was used without further purification. The solvents were degassed
by Ar-bubbling prior to use. All reactions and recrystallizations
involving the Pd(II) and Pt(II) complexes were performed under
protection from light and air.
The measurements of the MALDI-TOF-MS and elemental
analyses were carried out at the National Center for Inter-
University Research Facilities (NCIRF) in Seoul. The Raman
spectra were recorded with a Raman microscope spectrometer
The excitation spectra were observed with the parameters lobs
=
˚
(Renishaw, Ltd.) equipped with a He–Ne laser (lo = 6328 A). A
610 nm, a 16/16 band pass filter and 700 V. The emission spectra
were observed with the parameters lex = 440 nm, a 16/16 band
pass filter and 680 V.
low laser power of ca. 0.06 mW focused on a 1 mm2 area was
used. The infrared spectra were recorded by the KBr method
on a MIDAC FT-IR spectrophotometer in the range of 4000–
400 cm-1. The 1H NMR spectra were recorded using an Avance 500
(Bruker) spectrometer with the samples dissolved in CDCl3. The
X-Ray crystal structure determinations
1
1
31P{ H} and 195Pt{ H} NMR spectra of the complexes dissolved in
CDCl3 or CD2Cl2 were recorded using an Avance 500 (Bruker) or
DMX 600 (Bruker) spectrometer at 202.46 MHz and 128.38 MHz,
respectively. The positive chemical shifts are downfield from
Single crystals of complexes 3 and 4 suitable for the X-ray
structure analysis were obtained by the recrystallization of the
purified complexes from CHCl3–MeOH or CH2Cl2–MeOH. The
X-ray crystallographic data for these complexes were collected
on a Bruker SMART APEXII diffractometer equipped with
1
external standards, viz 85% H3PO4 for the 31P{ H} resonances
1
and 1.0 M K2PtCl4 in D2O for the 195Pt{ H} resonances. The
graphite-monochromated Mo-Ka radiation (l = 0.71073 A).
˚
1
1
31P{ H} and 195Pt{ H} NMR data and coupling parameters for
complexes 1, 2, 3 and 4 are summarized in Tables 1 and 2.
The cyclic voltammetry (CV) measurements were performed at
room temperature with a CHI 620A Electrochemical Analyzer
(CHI Instrument Inc.) in 10 mL CH2Cl2 solution containing
a 1.0 mM sample, using 0.1 M n-Bu4NBF4 as a supporting
The preliminary orientation matrix and cell parameters were
determined from three sets of w/y or w scans at different starting
angles. The data frames were obtained at scan intervals of 0.5◦
with an exposure time of 10 s per frame for complexes 3a, 3b,
4a and 4b, and 20 s per frame for complexes 3c and 4c. The
reflection data were corrected for Lorentz and polarization factors.
1768 | Dalton Trans., 2009, 1767–1775
This journal is
The Royal Society of Chemistry 2009
©

View Article Online
1
1
Table 2 195Pt{ H} and 31P{ H} NMR data for the complexes 2 and 4a
dHb/ppm
dPc/ppm
dPtc/ppm
-4431
nJH–H/Hz
1JPt–P/Hz
2
7.55808 (16H, q; H1)
7.47198 (8H, t; H3)
7.24063 (16H, t; H2)
7.49668 (16H, q; H1)
7.39078 (8H, t; H3)
7.33699 (4H, dd; H4 + H7)
7.21153 (16H, t; H2)
6.76139 (4H, dd; H5 + H6)
7.49291 (16H, m; H1)
7.39078 (8H, t; H3)
7.20348 (18H, t; H2 + H4)
7.14535 (2H, s; H7)
6.58692 (2H, d; H5)
2.18978 (6H, s; H6)
7.50837 (16H, q; H1)
7.42373 (8H, t; H3)
7.24070 (16H, q; H2)
6.88700 (4H, s; H5 + H6)
-13.753
3660
3J = 7.35
3J = 7.35
4a
-4.504
-4.502
-4729
2814
3J = 7.33
3J = 5.85, 4J = 3.22
3J = 7.33
3J = 5.85, 4J = 3.22
4b
4c
-4726
2813
3J = 7.33
3J = 8.11
3J = 7.33
-4.947
-4700
2800
a Proton numbering scheme is found in Table 1. b d: doublet; t: triplet; q: quartet; dd: doublet of doublets; m: multiplet. c Positive chemical shifts are
downfield from the standards (85% H3PO4 and 1.0 M K2PtCl4 solutions for the 31P and 195Pt resonances, respectively).
Absorption corrections were carried out using SADABS.36 The
structures were solved by direct methods and refined by full-matrix
least-squares analysis using anisotropic thermal parameters for
the non-hydrogen atoms with the SHELXTL program.37 The
chloroform molecules in complex 3a were restrained by means
of the SAME instruction. Two methylene chloride molecules
for complex 3b and two water molecules for complex 3c were
significantly disordered and could not be modeled properly, thus
the program SQUEEZE,38 a part of the PLATON package39
of crystallographic software, was used to calculate the solvent
disorder area and remove its contribution to the overall intensity
data. Hydrogen atoms of the water molecules in complexes 4a, 4b
and 4c were not found in the difference map and then not included.
One of three water molecules in complex 4a was disordered and
assigned with an occupancy factor of 0.5. The carbon atoms
(C8 and C63) for complex 4b was disordered and assigned with
an occupancy factor of 0.4 : 0.6. The rigid group fittings and
refinements (AFIX 66) were performed on the two disordered
phenyl rings (from C47 to C58) for complex 4c, which were placed
with 0.58 : 0.42 and 0.51 : 0.49 occupancy factors, respectively.
The crystallographic data and the details of the data collection are
listed in Table 3, and the selected bond distances and angles are
summarized in Table 4.
Preparation of the Pd(II) and Pt(II) complexes
(PdCl2)2(l-dppa)2 (1). An ethanol solution (75 mL) of
Na2PdCl4 (2.4 mmol, 0.71 g) was slowly added to an ethanol
solution (75 mL) of dppa (2.4 mmol, 0.95 g) with stirring at room
temperature for 1 h. The yellow product was filtered off, washed
Table 3 Crystallographic data for 3a·3CHCl3, 3b, 3c, 4a·3H2O·CHCl3, 4b·2H2O·CHCl3 and 4c·H2O
3a·3CHCl3
3b
3c
4a·3H2O·CHCl3
4b·2H2O·CHCl3
4c·H2O
Formula
Mf
C67H51Cl9P4Pd2S4
1640.05
293(2)
Monoclinic
P21/n
13.7964(3)
14.0504(3)
36.1985(8)
90.00(0)
93.538(1)
90.00(0)
7003.6(3)
4
C66H52P4Pd2S4
1310.00
293(2)
Triclinic
¯
P1
10.8273(7)
14.6236(10)
21.0611(13)
97.031(2)
97.023(2)
91.372(2)
3282.2(4)
2
0.1 ¥ 0.08 ¥ 0.07
54698
16198
0.0692
C64H44Cl4P4Pd2S4
1419.71
293(2)
Monoclinic
C2/c
26.9243(13)
17.0332(13)
17.4498(13)
90.00(0)
124.389(5)
90.00(0)
6603.9(8)
4
0.20 ¥ 0.12 ¥ 0.03
32067
8196
0.0380
0.0447
C65H55Cl3O3P4Pt2S4
1632.74
293(2)
Triclinic
¯
P1
10.6227(12)
14.2985(12)
23.709(3)
74.885(1)
86.509(1)
71.508(1)
3296.2(6)
2
0.19 ¥ 0.18 ¥ 0.17
32798
13065
0.0290
C67H57Cl3O2P4Pt2S4
1642.78
293(2)
Triclinic
¯
P1
10.8814(8)
14.7267(12)
21.2919(16)
97.397(2)
96.961(2)
92.179(3)
3353.6(4)
2
0.1 ¥ 0.07 ¥ 0.07
55310
16442
0.0423
C64H46Cl4OP4Pt2S4
1615.11
293(2)
Monoclinic
C2/c
42.3763(16)
11.0230(4)
31.0144(12)
90.00(0)
118.554(2)
90.00(0)
12725.1(8)
8
0.12 ¥ 0.08 ¥ 0.06
59345
15807
0.0665
0.0517
T/K
Crystal system
Space group
˚
a/A
˚
b/A
˚
c/A
a/◦
b/◦
g /◦
V/A
Z
3
˚
Crystal size/mm
Refl. collected
Refl. unique
Rint
0.36 ¥ 0.12 ¥ 0.15
69043
17498
0.0633
Ra
0.0525
0.0472
0.0393
0.0418
ꢀ
ꢀ
a R = ꢀFo| - |Fcꢀ/ |Fo|.
This journal is
The Royal Society of Chemistry 2009
Dalton Trans., 2009, 1767–1775 | 1769
©

View Article Online
◦
◦
a
˚
Table 4 Selected bond distances (A), bond angles ( ) and torsion angles ( ) for complexes 3 and 4
3a
3b
3c
4a
4b
4c
M(1)–P(1)
M(1)–P(2)
M(2)–P(3)
M(2)–P(4)
M(1)–S(1)
M(1)–S(2)
M(2)–S(3)
M(2)–S(4)
C(1)–C(2)
C(3)–C(4)
2.301(1)
2.291(1)
2.297(1)
2.283(1)
2.282(1)
2.280(1)
2.287(2)
2.279(1)
1.194(6)
1.190(6)
2.278(1)
2.294(1)
2.282(1)
2.308(1)
2.293(1)
2.289(1)
2.291(1)
2.277(1)
1.186(5)
1.195(4)
2.312(1)
2.289(1)
2.258(2)
2.278(2)
2.260(2)
2.282(2)
2.313(2)
2.303(2)
2.303(2)
2.301(2)
1.198(9)
1.200(9)
2.260(2)
2.280(2)
2.258(2)
2.279(2)
2.306(2)
2.295(2)
2.307(2)
2.302(2)
1.187(8)
1.201(8)
2.284(2)
2.273(2)
2.293(2)
2.275(2)
2.300(2)
2.297(2)
2.314(2)
2.293(2)
1.191(9)
1.177(9)
2.291(1)
2.286(1)
1.206(6)b
1.183(6)b
P(1)–M(1)–P(2)
P(1)–M(1)–S(2)
P(2)–M(1)–S(2)
P(1)–M(1)–S(1)
P(2)–M(1)–S(1)
S(2)–M(1)–S(1)
P(3)–M(2)–P(4)
P(3)–M(2)–S(4)
P(4)–M(2)–S(4)
P(3)–M(2)–S(3)
P(4)–M(2)–S(3)
S(4)–M(2)–S(3)
95.12(4)
173.34(5)
87.46(4)
88.48(4)
176.29(5)
89.07(5)
94.23(4)
171.48(5)
89.45(5)
87.57(5)
177.28(5)
89.05(5)
95.16(3)
172.76(3)
89.97(3)
86.02(4)
177.64(3)
88.68(4)
96.34(3)
169.01(4)
89.29(4)
85.82(4)
177.81(4)
88.53(5)
96.78(3)
175.45(3)
87.76(3)
86.84(3)
171.76(3)
88.70(4)
94.18(6)
172.66(6)
90.72(6)
86.42(6)
174.58(6)
88.19(6)
95.00(6)
172.25(7)
89.86(7)
86.50(7)
177.24(7)
88.41(8)
95.39(5)
170.22(7)
89.72(7)
86.52(7)
177.86(7)
88.25(8)
94.68(5)
173.27(6)
90.27(6)
86.34(6)
176.97(6)
88.49(6)
97.34(7)
172.79(7)
88.19(7)
86.19(7)
172.86(7)
88.83(7)
95.75(7)
174.48(8)
86.98(8)
89.13(7)
175.12(7)
88.16(8)
C(1)–C(2)–C(4)–C(3)
-30.67
27.51
-41.51c
21.65
-24.61
-42.13
a M = Pd for 3a, 3b and 3c, and M = Pt for 4a, 4b and 4c. b Bond distances corresponding to C(1)–C(1)# and C(2)–C(2)#, respectively (#: -x + 1, y,
-z + 3/2). c Torsion angle for C(1)–C(1)#–C(2)#–C(2).
with cyclohexane and dried in vacuum. Recrystallization from
CHCl3–MeOH afforded yellow crystals.21 Yield: 80% (1.10 g).
Anal. Calc. for C52H40Cl4P4Pd2·2CHCl3: C 46.92; H 3.06. Found:
complex 1 (0.10 mmol, 110 mg) or 2 (0.10 mmol, 134 mg) with
stirring for 2 h under an argon atmosphere. The orange or brown
solution was dried under reduced pressure. The solid products,
obtained in quantitative yield, were recrystallized from CHCl3–
MeOH or CH2Cl2–MeOH, and subjected to elemental analyses
and X-ray structure analyses. The same process was followed
when [M(OTf)2]2(m-dppa)2 (0.1 mmol) in nitromethane (5 mL)
was used instead of (MCl2)2(m-dppa)2 in chloroform resulting in
spectroscopically identical products.
C 46.57; H 3.01%. MALDI-TOF-MS (m/z): 1144.6663 (M+
+
5), 1109.6650 (M+ - Cl + 5), 1073.6875 (M+ - 2Cl + 4). FT-IR
(KBr, cm-1): 3054 (C–H str), 1479, 1437 (Ar ip str), 1185, 1162,
1097 (oop CH def), 1027, 998 (P–Ph str), 840, 744 (oop def),
689 (ring oop def), 533, 512, 490, 475 (oop ring def). Raman
-1
∫
(He–Ne, cm ): 2148, 2132 (C C), 1584, 1095, 1028, 1000, 697,
618, 570, 325, 301 (Pd–Cl), 190, 158. UV-vis (CH3CN, l/nm
3a. Yield >95%. MALDI-TOF-MS (m/z): 1283.8241 (M+
4). Anal. Calc. for C64H48P4Pd2S4·0.25CHCl3: C 58.82; H 3.71; S
9.78. Found: C 59.02; H 3.68; S 9.98%. FT-IR (KBr, cm-1): 3050
(C–H str), 1550, 1479, 1437 (Ar ip str), 1098 (ip CH def), 1024,
+
(10-4emax/M-1 cm-1)): 266 (6.65), 326 (2.38).
(PtCl2)2(l-dppa)2 (2). To 24 mL of an ethanol suspension
of K2PtCl4 (2.0 mmol, 0.84 g) was added a minimum amount
of degassed solvent water until the suspension became clear. A
benzene solution (10 mL) of dppa (2.0 mmol, 0.79 g) was dropped
into this solution, and stirred for 6 h. The white product was filtered
off, and washed with distilled water and methanol consecutively.
Recrystallization from CHCl3–MeOH afforded yellow crystals.34
Yield: 93% (1.23 g). Anal. Calc. for C52H40Cl4P4Pt2: C 47.29;
H 3.05. Found: C 47.30; H 3.05%. MALDI-TOF-MS (m/z):
1284.7332 (M+ - Cl + 2). FT-IR (KBr, cm-1): 3054 (C–H str), 1480,
1437 (Ar ip str), 1185, 1161, 1099 (oop CH def), 1027, 998 (P–Ph
998 (P–Ph str), 840, 740 (oop CH def), 690, 526, 510, 490, 433
-1
∫
(oop ring def). Raman (He–Ne, cm ): 2134 (C C), 1584, 1103,
1027, 998, 697, 665, 618, 561, 353 (Pd–S). UV-vis (CH3CN, l/nm
(10-4emax/M-1 cm-1)): 260 (7.02), 304 (5.35).
3b. Yield >95%. MALDI-TOF-MS (m/z): 1310.7959 (M+
3). Anal. Calc. for C66H52P4Pd2S4·CHCl3: C 56.29; H 3.74; S 8.97.
Found: C 56.07; H 3.64; S 8.94%. FT-IR (KBr, cm-1): 3052 (C–
H str), 2915 (–CH3), 1542, 1480, 1458, 1436 (Ar ip str), 1097 (ip
+
CH def), 1026, 998 (P–Ph str), 836, 743 (oop CH def), 690, 526,
-1
str), 838, 745 (oop def), 689 (ring oop def), 545, 515, 497, 445 (oop
∫
511, 491 (oop ring def). Raman (He–Ne, cm ): 2146, 2131 (C C),
-1
∫
ring def). Raman (He–Ne, cm ): 2144 (C C), 1584, 1323, 1096,
1586, 1109, 1028, 998, 556, 348 (Pd–S). UV-vis (CH3CN, l/nm
(10-4emax/M-1 cm-1)): 268 (2.63), 320 (0.83).
1025, 997, 699, 614, 578, 325, 299 (Pt–Cl), 179. UV-vis (CH3CN,
l/nm (10-4emax/M-1 cm-1)): 274 (1.98), 328 (0.26).
3c. Yield >95%. MALDI-TOF-MS (m/z): 1421.7075 (M+ + 6).
Anal. Calc. for C64H44Cl4P4Pd2S4: C 54.14; H 3.12; S 9.03. Found:
C 53.28; H 2.94; S 9.43%. FT-IR (KBr, cm-1): 3053 (C–H str),
1526, 1480, 1436 (Ar ip str), 1396, 1345, 1272, 1158, 1096 (oop
CH def), 1066 (C–Cl str), 1027, 998 (P–Ph str), 838, 821, 743 (oop
[M(1,2-dithiolate)]2(l-dppa)2 where M = Pd (3) and Pt (4).
Each of the 1,2-benzenedithiol compounds (0.20 mmol, 29 mg for
H2a; 31 mg for H2b; 42 mg for H2c) dissolved in a minimum amount
of chloroform was dropped into a chloroform solution (5 mL) of
1770 | Dalton Trans., 2009, 1767–1775
This journal is
The Royal Society of Chemistry 2009
©

View Article Online
CH def), 690, 526, 510, 489 (oop def). Raman (He–Ne, cm-1):
∫
2130 (C C), 1583, 1000, 560, 362 (Pd–S). UV-vis (CH3CN, l/nm
(10-4emax/M-1 cm-1)): 266 (10.7), 308 (7.37).
4a. Yield >95%. MALDI-TOF-MS (m/z): 1461.0226 (M+
+
3). Anal. Calc. for C64H48P4Pt2S4·CHCl3: C 49.45; H 3.13; S 8.12.
Found: C 48.86; H 3.18; S 8.14%. FT-IR (KBr, cm-1): 3048 (C–
H str), 1550, 1480, 1437 (Ar ip str), 1099 (ip CH def), 1025, 998
(P–Ph str), 838, 741 (oop CH def), 689, 538, 513, 436 (oop ring
-1
∫
def). Raman (He–Ne, cm ): 2149, 2133 (C C), 1583, 1323, 1286,
1102, 1024, 996, 570, 366 (Pt–S), 211 (Pt–P), 172. UV-vis (CH3CN,
l/nm (10-4emax/M-1 cm-1)): 262 (1.91), 320 (0.30), 356 (0.26).
4b. Yield >95%. MALDI-TOF-MS (m/z): 1489.0203 (M+
+
3). Anal. Calc. for C66H52P4Pt2S4·CHCl3: C 50.08; H 3.32; S 7.98.
Found: C 50.78; H 3.50; S 8.18%. FT-IR (KBr, cm-1): 3053 (C–H
str), 2918, 2859 (–CH3), 1459, 1436 (Ar ip str), 1098 (ip CH def),
1029, 998 (P–Ph str), 837, 744 (oop CH def), 690, 538, 514, 496,
-1
∫
434 (oop ring def). Raman (He–Ne, cm ): 2152, 2133 (C C), 1582,
1323, 1283, 1205, 1109, 1024, 996, 864, 570, 365 (Pt–S), 258 (Pt–P),
167. UV-vis (CH3CN, l/nm (10-4emax/M-1 cm-1)): 266 (1.07), 326
(0.25), 358 (0.04).
4c. Yield >95%. MALDI-TOF-MS (m/z): 1598.0262 (M+ + 4).
Anal. Calc. for C64H44Cl4P4Pt2S4: C 48.13; H 2.78; S 8.03. Found:
C 48.05; H 2.85; S 8.07%. FT-IR (KBr, cm-1): 3055 (C–H str),
1479, 1436 (Ar ip str), 1397, 1343, 1276, 1160, 1098 (oop CH def),
1070 (C–Cl str), 1029, 999 (P–Ph str), 839, 823, 743 (oop CH def),
690, 538, 514, 494 (oop ring def). Raman (He–Ne, cm-1): 2137
∫
(C C), 1587, 1342, 1276, 1142, 1109, 1029, 1001, 572, 384 (Pt–S),
Scheme 2
259 (Pt–P), 152. UV-vis (CH3CN, l/nm (10-4emax/M-1 cm-1)): 266
(2.22), 322 (0.25), 348 (0.24).
formation of a mixed-solvent system (water–ethanol–benzene).
It can be supposed that the two reactants are completely dissolved
in the mixed-solvent system and can readily react with each other,
and actually a high yield of the product of about 93% was obtained.
The reaction was almost completed after 1 h, and the chemical
compositions of the products were confirmed by elemental analysis
and MALDI-TOF-MS measurements. The synthesis of complex
1 was, however, achieved following the reported method21 and
afforded a fairly high yield (80%).
[M(OTf)2]2(l-dppa)2 where M = Pd (5) and Pt (6). An
acetonitrile solution of Ag(OTf) (4 mmol, 1.03 g) was added
to a methylene chloride solution (40 mL) of (MCl2)2(m-dppa)2
(1 mmol, 1.14 g for M = Pd and 1.32 g for M = Pt) with
stirring for 4 h under an argon atmosphere. The white precipitate
(AgCl) was separated by filtration through a fine glass filter and
washed with a minimum amount of acetonitrile, and the filtrate
was centrifuged at 15 000 rpm for 2 h. The filtrate was dried under
reduced pressure and recrystallized. The crystalline products were
obtained in quantitative yield and used directly in the synthesis of
complexes 3 or 4.
5. Yield >95%. FT-IR (KBr, cm-1): 3057 (C–H str), 1481, 1437
(Ar ip str), 1261, 1173, 1099 (ip CH def), 1033 (SO3CF3), 998
(P–Ph str), 840, 744 (oop CH def), 689, 512, 493, 474 (oop ring
def).
6. Yield >95%. FT-IR (KBr, cm-1): 3056 (C–H str), 1481, 1438
(Ar ip str), 1262, 1173, 1099 (ip CH def), 1034 (SO3CF3), 998
(P–Ph str), 840, 745 (oop CH def), 689, 515, 497, 442 (oop ring
def).
Complexes
3 and 4 were synthesized by reacting 1,2-
benzenedithiolates (bdts) with [M(OTf)2]2(m-dppa)2, as well as
(MCl2)2(m-dppa)2, in a high yield as shown in Scheme 2. The
products prepared through the two different pathways were
spectroscopically identical. One merit for the use of [M(OTf)2]2(m-
dppa)2 is that the pure products can be obtained even before the
chromatographic purification step. Complexes 3 and 4 dissolved
in an appropriate solvent were treated either with UV-radiation
or elevated temperatures to induce intramolecular cyclization in a
similar manner to that observed with binuclear Pt-(trans-dppen)17
and Pt-dppby18 complexes. Our complexes, however, did not show
any evidence of cyclization under these conditions, possibly due
to the lack of the flexibility of the dppa ligand.
Results and discussion
The Pd(II) and Pt(II) complexes synthesized in this research
=
give very rich IR and Raman spectra exhibiting P–C, C C,
∫
Synthesis and vibrational spectroscopic analysis
C C and C–H vibrations from the ligands and M–Cl, M–P
As shown in Scheme 2, complex 2 was prepared by mixing equal
amounts of K2PtCl4 in H2O and dppa in benzene using a minimum
amount of ethanol as a mediator:15 Even though H2O and benzene
do not normally mix with each other, the ethanol solvent facilitates
the mixing of these two immiscible solvents, resulting in the
and M–S vibrations from the coordination sphere. All of the
=
complexes show strong C C vibrational bands of aromatic rings
at ca. 1480–1430 cm-1 and C–H stretching bands at ca. 830–
680 cm-1. The P–Ph vibrations are observed at an almost fixed
position (997–1000 cm-1) in the IR/Raman spectra, regardless
This journal is
The Royal Society of Chemistry 2009
Dalton Trans., 2009, 1767–1775 | 1771
©

View Article Online
of whether they have MP2Cl2 or MP2S2 cores, which indicates
that the P–Ph vibrations are completely free from the influence
of the central metals and the other coordination ligands such
ligand,8 and increased in the following order: 4c < 4b ª 4a. This
can also be explained by the inductive effect of the substituted
ligands. The amount of P→Pt donation is inversely proportional
to the electron-withdrawing ability of the 1,2-dithiolate ligands
resulting in a higher field resonance and a weaker Pt–P coupling.
as Cl and S (from 1,2-dithiolate). The IR-inactive but Raman-
40
∫
active vibrational mode of the symmetric C C bond appears at
2100 cm-1 in the spectra of free dppa, but those of complexes 1–4
are detected as strong peaks in the range of 2130–2152 cm-1. The
wavenumber shifts of about 30–52 cm-1 indicate the coordination
X-Ray crystal structure determinations
The X-ray structure determination for single crystals of 3 and 4 was
performed at room temperature. The crystal data and the infor-
mation used for the structure refinements a◦re listed in Table 3, and
∫
of M(II) to the phosphorus atom, not the C C bond, because the
P→M coordination can cause the weakening of the pp–dp overlap
∫
on the C–P bond and the consequent increase of the vibrational
˚
the selected bond lengths (A) and angles ( ) are listed in Table 4.
∫
∫
frequency of the C C bond. When the C C bond instead of a
Fig. 1–6 show the X-ray crystal structures of complexes
phosphine ligand is coordinated to a metal ion, the local symmetry
is generally lowered and n(C C) usually shifts to a lower frequency
˚
3 and 4. The observed Pd–P (2.278(1)–2.312(1) A), Pd–
∫
˚
˚
by 200–400 cm-1. For the structures having C2v symmetry, such
as cis-MP2Cl2 core, group theory predicts that the Raman active
n(M–X) vibrational modes (A1 + B1) will be found at around
300 cm-1.41 These halogen-sensitive absorptions were observed in
the Raman spectra at 325 and 301 cm-1 for the n(Pd–Cl) vibrations
of complex 1 and at 325 and 299 cm-1 for the n(Pt–Cl) vibrations of
complex 2. The n(M–S) vibrations of the cis-MP2S2 core with the
1,2-dithiolate ligand are generally observed in the range of 300–
400 cm-1.15,16,34,35 As regards the Raman spectra of complexes 3 and
4, the n(Pd–S) vibrations were observed at 348 cm-1 (3b), 353 cm-1
(3a) and 362 cm-1 (3c), while the n(Pt–S) vibrations were observed
at 365 cm-1 (4b), 366 cm-1 (4a) and 384 cm-1 (4c). It is clearly
shown from these data that the n(M–S) vibrational frequencies
are very sensitively proportional to the electron-donating ability
of the 1,2-dithiolate ligands with the order of tdt (b) ª bdt (a) >
Cl2bdt (c).
S (2.277(1)–2.293(1) A), Pt–P (2.258(2)–2.293(2) A) and Pt–
˚
S (2.293(2)–2.314(2) A) bond lengths of the complexes are
slightly shorter than the sum of their covalent radii (2.34,
43
˚
2.30, 2.36 and 2.32 A, respectively). The Pt–P and Pt–S
bond distances are similar to those of [Pt(MET)]2(m-dppa)2
˚
(2.264(3) and 2.288(3) A, respectively) where MET is (Z)-1,4-
dimethoxy-1,4-dioxobut-2-ene-2,3-bis(thiolate).35 On the other
˚
hand, the Pt–S bond length of [Pt(PFBT)2]2(m-dppa)2 (2.349(3) A;
PFBT = pentafluorobenzenethiolate)24 is longer than those of 4a
˚
˚
˚
(2.305(2) A), 4b (2.303(2) A) and 4c (2.301(2) A), possibly due to
the presence of the mono-dentate PFBT ligand and the effect of
the five electronegative fluorides on the PFBT ligand, while the
˚
Pt–P bond lengths (2.272(3) A) are similar to those of 4 (2.258(2)–
1H, 31P and 195Pt NMR spectroscopic analyses
Complexes 1–4 were characterized by 31P{ H} and/or 195Pt{ P}
NMR spectroscopies and their parameters are collected in Table 1
and 2. The 31P NMR spectra of complex 3 give a singlet at 1.676–
1.943 ppm with an approximately 3 ppm up-field shift relative to
that of complex 1. On the other hand, complex 4 shows the typical
1 : 4 : 1 signals with a down-field shift of about 9 ppm in its 31P
NMR spectra and an up-field shift of about 269–298 ppm in its
195Pt NMR spectra relative to complex 2, surely due to the electron-
donating properties of the 1,2-dithiolate ligands. Furthermore, the
1,2-benzenedithiolate ligand with an electron-withdrawing moiety
in complex 4c would be expected to exhibit the lowest electron
donating ability among the three dithiolates. It is evidenced from
the observations that the value of dPt for complex 4c (-4700 ppm)
is significantly downfield shifted. However, the methyl moiety
on the ligand b does not play a significant role in the variation
of the dPt value between complexes 4a and 4b. These results
coincide well with the vibrational spectroscopic results, in that the
n(Pt–S) vibrations for 4a and 4b are very close to each other (366
and 365 cm-1, respectively), whereas that of 4c was observed in a
higher frequency region (384 cm-1).
1
31
∫
Fig. 1 Molecular structure of [Pd(bdt)]2(m-Ph2PC CPPh2)2 (3a) with
thermal ellipsoids drawn at the 50% probability level. Solvent molecules
and hydrogen atoms are omitted for clarity.
The magnitude of the Pt–P coupling (JPt–P) for complex 4 fell
in the range of 2800–2814 Hz, suggesting the cis coordination of
the phosphine ligands, as observed in cis-(Ph3P)2Pt(dithiolates).8,42
The variation of the NMR parameters is closely related to the
electron-donating ability of the dithiolate ligands. The JPt–P values
are sensitive to the electron-donating properties of the dithiolate
∫
Fig. 2 Molecular structure of [Pd(tdt)]2(m-Ph2PC CPPh2)2 (3b) with
thermal ellipsoids drawn at the 50% probability level. Hydrogen atoms
are omitted for clarity.
1772 | Dalton Trans., 2009, 1767–1775
This journal is
The Royal Society of Chemistry 2009
©

View Article Online
∫
Fig. 6 Molecular structure of [Pt(Cl2bdt)]2(m-Ph2PC CPPh2)2 (4c) with
∫
Fig. 3 Molecular structure of [Pd(Cl2bdt)]2(m-Ph2PC CPPh2)2 (3c) with
thermal ellipsoids drawn at the 50% probability level. Solvent molecules
and hydrogen atoms are omitted for clarity. The disordered phenyl groups
are shown in the figure.
thermal ellipsoids drawn at the 50% probability level. Hydrogen atoms are
omitted for clarity (symmetry transformations used to generate equivalent
atoms: # -x + 1, y, -z + 3/2).
as the distance between them (that is, the Pt–P bond length) is
increased.
The P–M–S trans angles are within the range of 170.22(7)–
177.86(7)◦, which reveals that the P2MS2 core slightly deviates
∫
from the complete square-planar geometry, and the C C bond
˚
distances (1.177(9)–1.206(6) A) are also slightly shorter than that
˚
in acetylene (1.21 A). The two acetylenic moieties in one molecule
are staggered relative to each other with a torsion angle of C(1)–
C(2)–C(4)–C(3), as shown in Table 4, where the torsion angles of
complexes 3c and 4c containing ligand c are larger (about 42◦)
◦
∫
than those of the other complexes (22–31 ). The P–C C bond
angles deviate from linearity, with their average values of 172.9◦–
173.6◦ (3a, 3b, 4a and 4b), 175.9◦ (3c) and 175.4◦ (4c) being
larger than those of the bis(monothiolate) derivatives such as
[Pt(PFBT)2]2(m-dppa)2 (171.3(7)◦).24 These observations indicate
that complexes 3 and 4, especially complexes 3c and 4c, are totally
distorted, which is common in the complexes of (MLn)2(m-dppa)2
where MLn is Pt(MET),35 Ru(acac)2,33 Pt(C6F5)2,32 Pt(PFBT)2,24
and Mo(CO)4.31 Furthermore, they are distorted in right- and
left-handed modes and their crystals are racemic, as shown in Fig.
S4–S9 (see ESI†).
∫
Fig. 4 Molecular structure of [Pt(bdt)]2(m-Ph2PC CPPh2)2 (4a) with
thermal ellipsoids drawn at the 50% probability level. Solvent molecules
and hydrogen atoms are omitted for clarity.
Electrochemical study
The electrochemical properties of complexes 1, 2, 3 and 4 were
investigated by cyclic voltammetry (CV). The potentials were
swept forward from -1.0 to +2.0 V and then back again. The
cyclic voltammograms of complexes 2, 3 and 4 are shown in ESI
(Fig. S1–S3),† and their electrochemical parameters are listed
and compared in Table 5. Complex 1 exhibits one irreversible
oxidation peak at Epa = 1.102 V, but it seems to be unstable
in solution, because of the lack of reproducibility of the results.
One quasi-reversible cycle with Epa = 1.334 V and Epc = 1.028 V,
however, was observed for complex 2, in which the anodic peak
can be attributed to the Pt-centered oxidation. On the contrary,
complexes 3 and 4 show two irreversible anodic peaks in the range
of 0.9–1.5 V, as summarized in Table 5. It is worthwhile comparing
them with the previously reported [Pt(1,2-ethylenedithiolate)]2(m-
dppa)2 complexes.34 These complexes showed two redox peaks
∫
Fig. 5 Molecular structure of [Pt(tdt)]2(m-Ph2PC CPPh2)2 (4b) with
thermal ellipsoids drawn at the 50% probability level. Solvent molecules
and hydrogen atoms are omitted for clarity. The disordered methyl groups
are shown in the figure.
˚
2.293(2) A). When the electronegative chloride ions are directly
ligated to the Pt(II) ion as in [PtCl2]2(m-dppa)2, however, the average
Pt–P bond distance (2.239(2) A) becomes much shorter than
those of 4 because of the inductive effect of the electronegative ions.
The averaged bond lengths of Pt–P (2.270(2) A for 4a, 2.269(2) A
for 4b, and 2.281(2) A for 4c) are inversely correlated with the
34
˚
˚
˚
˚
value of the Pt–P coupling constant (JPt–P: 2814, 2813 and 2800 Hz,
respectively; Table 2). This can be explained by the simple rationale
that the degree of spin-coupling of the Pt and P nuclei is decreased
in which one reversible cycle that appears at around E1/2
=
0.745–1.010 V (vs. Ag/Ag+) is attributable to the redox process
of the 1,2-ethylenedithiolate ligand and the other one found at
This journal is
The Royal Society of Chemistry 2009
Dalton Trans., 2009, 1767–1775 | 1773
©

View Article Online
Table 5 Cyclic voltammetry parameters for complexes 1, 2, 3 and 4a
Complex
Epa1/Vb
Epa2/Vb
1
—
1.102
1.334
1.091
1.030
1.371
1.247
1.204
1.480
2
1.028c
0.983
0.972
1.142
1.073
1.046
1.230
3a
3b
3c
4a
4b
4c
a Samples are dissolved in CH2Cl2 (1.0 mM, 10 mL) containing 0.1 M
n-Bu4NBF4 electrolyte and measured with a scan rate of 50 mV s-1. Ag/Ag+
reference electrode, a Pt-button working electrode (r = 1 mm) and a Pt-wire
counter electrode are used. b Fc/Fc+: E1/2 = +0.687 V. c Epc1/V.
Fig. 7 Absorption (dashed blue), excitation (solid purple) and emission
(dotted orange) spectra of complex 4c in the solid state at 298 K
around Epa = 1.420–1.506 V (vs. Ag/Ag+) is ascribed to the Pt-
centered oxidation. In the present system (complexes 3 and 4)
also, the first irreversible anodic peak (Epa1) corresponds to the
oxidation process of the 1,2-benzenedithiolate ligands and the
second one (Epa2) corresponds to the Pt-center. Moreover, the
anodic potentials of 3a, 3b, 4a and 4b are 0.16–0.34 V lower
than those of the corresponding complexes 3c and 4c. This clearly
indicates the ease of oxidation of the 1,2-benzendithiolate ligands
in the order of b ª a ꢁ c, based on the electrochemical results.
(time-resolved detection: 5 ms flash period, 10 ms decay; excitation: lob
=
610 nm, 16/16 band pass, 700 V; emission: lex = 440 nm, 16/16 band pass,
680 V).
electronegativity than both a and b as evidenced by the fact
that the 195Pt NMR chemical shift of 4c is the most downfield
shifted. The highest oxidation potential of 4c, as measured by
cyclic voltammetry, supports this assignment as well.
In addition, there are many indications that this emission
involves a spin-forbidden transition. The 430 nm excitation band is
not observed in the absorption spectrum of 4c in solution, implying
that its extinction coefficient is small. Also, we found that the
luminescence lifetime is moderately long (≥5 ms), which strongly
signifies that it has spin-forbidden characteristics. Therefore, we
can assign the emissive state of 4c as 3{d–p*dithiolate}. Undoubtedly,
the more effective spin–orbit coupling of ligand c in complex
4c containing heavy chlorine atoms, as compared to that in the
ligands a and b, contributed to the feasibility of this spin-forbidden
transition. The larger spin–orbit coupling in platinum than that
in palladium may also contribute to the transition probability.
It should be noted that our findings and the assignment for
the emission band are similar to those previously reported for
Pt(II) complexes containing dithiolate ligands.10,44 In the previous
studies, the luminescence of the synthesized complexes was
observed only in the solid state and the luminescent platinum
complexes exhibited a long luminescence lifetime and a small
extinction coefficient, confirming that the emissive state was
Absorption and emission spectra
The absorption spectra of the synthesized complexes showed a
band centered at ~265 nm and additional small bands between
304 and 360 nm in solution, as shown in the Experimental section.
Overall, the observed spectra of the platinum complexes are
similar to those of the dithiol ligands except a ~40 nm red shift
upon complex formation. The lowest energy band at 360 nm was
observed with 4a and no additional absorption band was observed
in the wavelength region longer than ~400 nm for all complexes
(see ESI†).
Among the six metal-dithiolate complexes prepared in this
study, only complex 4c was luminescent at room temperature in
the solid state whereas no emission was observed in solution.
This emission band was broad with a maximum at 615 nm.
However, the excitation spectrum was structured so as to exhibit
vibrational progressions and centered at 430 nm (Fig. 7). The
Stokes shift (~7000 cm-1) was relatively large. The metal-metal-to-
ligand charge transfer transition (MMLCT) can be ruled out for 4c
since there is no direct interaction between the platinum metals as
3
{d–p*dithiolate}.
Conclusions
˚
evidenced by the large metal-to-metal distance (7.265 and 8.007 A
for the shortest Pd ◊ ◊ ◊ Pd and Pt ◊ ◊ ◊ Pt distances, respectively)
determined from its X-ray crystal structure. In addition, it is highly
unlikely that this emission originates from the transition between
the ligands. Neither the analogous palladium complexes nor the
ligands by themselves showed luminescence at 615 nm. The X-ray
crystal structure also revealed that the formation of an excimer or
exciplex between the ligands is unfeasible.
Based on the fact that only the complex containing the ligand
c and Pt(II) ion exhibited luminescence, the transition required to
generate the emissive state can be assigned as the d–p*dithiolate metal-
to-ligand charge transfer (MLCT). The transition probability of
the MLCT band is known to increase as the ligand becomes
more reducible or electronegative. The ligand c has a larger
As part of a serial investigation of Pd(II) and Pt(II) co-
ordination complexes, the heteroleptic binuclear complexes,
[M(bdts)]2(m-dppa)2 (M = Pd (3) and Pt (4); dppa = 1,2-
∫
bis(diphenylphosphino)acetylene = Ph2PC CPPh2; bdts = 1,2-
benzenedithiolate (bdt; a), 3,4-toluenedithiolate (tdt; b) and 1,4-
dichloro-2,3-benzenedithiolate (Cl2bdt; c)) were prepared using
(MCl2)2(m-dppa)2 (M = Pd (1) and Pt (2)). The X-ray crystal
structure analyses of 3 and 4 show that they are twisted in two
ways and, thus, their single crystals are racemic mixtures. The more
electronegative ligand c (and its complexes 3c and 4c), as compared
to ligands a and b, leads to higher n(M–S) vibrational frequencies
in the Raman spectra, a smaller spin–spin coupling constant (JPt-P
)
31
in the 195Pt{ P} NMR spectra, higher anodic potentials (Epa) in
1774 | Dalton Trans., 2009, 1767–1775
This journal is
The Royal Society of Chemistry 2009
©

View Article Online
the cyclic voltammograms and larger torsion angles than those of
complexes 3a, 3b, 4a and 4b. Moreover, only complex 4c exhibits
luminescence (lob = 610 nm and lex = 440 nm) in the solid state at
298 K, assigned as the d–p*dithiolate metal-to-ligand charge transfer
(MLCT).
19 D. Liu, Q. Feng, X. L. Feng and J. W. Cai, Inorg. Chem. Commun.,
2003, 6, 361–364.
20 C. H. Chou, W. Y. Yeh, G. H. Lee and S. M. Peng, Inorg. Chim. Acta,
2006, 359, 4139–4143.
21 A. J. Carty and A. Efraty, Inorg. Nucl. Chem. Lett., 1968, 4, 427–431.
22 A. J. Carty and A. Efraty, Chem. Commun. (London), 1968, 1559–
1561.
23 W. Oberhauser, C. Bachmann, T. Stampfl and P. Bru¨ggeller, Inorg.
Acknowledgements
Chim. Acta, 1997, 256, 223–234.
24 A. Singhal, V. K. Jain and R. J. Butcher, J. Coord. Chem., 1999, 46,
355–363.
25 A. J. Carty and A. Efraty, Inorg. Chem., 1969, 8, 543–550.
26 H. C. Clark, G. Ferguson, P. N. Kapoor and M. Parvez, Inorg. Chem.,
1985, 24, 3924–3928.
This work was supported by Korea Research Foundation Grant
(KRF-2003-070-C00029).
27 J.-L. Chen, L.-Y. Zhang, Z.-N. Chen, L.-B. Gao, M. Abe and Y.
Sasaki, Inorg. Chem., 2004, 43, 1481–1490; E. Louattani and J. Suades,
J. Organomet. Chem., 2000, 604, 234–240; B. F. G. Johnson, J. Lewis,
A. D. Massey, P. R. Raithby and W. T. Wong, J. Organomet. Chem.,
1990, 397, C28–C30; O. Orama, J. Organomet. Chem., 1986, 314, 273–
279; G. R. Eaton and R. H. Holm, Inorg. Chem., 1971, 10, 805–811;
A. J. Carty, A. Efraty, T. W. Ng and T. Birchall, Inorg. Chem., 1970, 9,
1263–1268; A. J. Carty, A. Efraty and T. W. Ng, Can. J. Chem., 1969, 47,
1429–1431; W. A. Anderson, A. J. Carty and A. Efraty, Can. J. Chem.,
1969, 47, 3361–3366.
Notes and references
1 V. K. Jain and L. Jain, Coord. Chem. Rev., 2005, 249, 3075–3197.
2 E. I. Stiefel, Dithiolene Chemistry: Syntheses, Properties and Applica-
tions, Prog. Inorg. Chem., 2004, 52, 315–368.
3 K. M. Wong, C. Hui, K. Yu and V. W. Yam, Coord. Chem. Rev., 2002,
229, 123–132.
4 M. Hissler, J. E. McGarrah, W. B. Connick, D. K. Geiger, S. D.
Cummings and R. Eisenberg, Coord. Chem. Rev., 2000, 208, 115–137.
5 W. Paw, S. D. Cummings, M. A. Mansour, W. B. Connick, D. K. Geiger
and R. Eisenberg, Coord. Chem. Rev., 1998, 171, 125–150.
6 A. Vogler and H. Kunkely, Coord. Chem. Rev., 2002, 230, 243–251.
7 C. J. Smith, V. S. Reddy, S. R. Karra, K. V. Katti and L. J. Barbour,
Inorg. Chem., 1997, 36, 1786–1791.
8 C. E. Keefer, R. D. Bereman, S. T. Purrington, B. W. Knight and P. D.
Boyle, Inorg. Chem., 1999, 38, 2294–2302; C. E. Keefer, S. T. Purrington,
R. D. Bereman, B. W. Knight, D. R. Bedgood and P. D. Boyle, Inorg.
Chim. Acta, 1998, 282, 200–208.
9 J. M. Bevilacqua and R. Eisenberg, Inorg. Chem., 1994, 33, 2913–2923.
10 J. M. Bevilacqua, J. A. Zuleta and R. Eisenberg, Inorg. Chem., 1994,
33, 258–266.
11 S. P. Kaiwar, A. Vodacek, N. V. Blough and R. S. Pilato, J. Am. Chem.
Soc., 1997, 119, 3311–3316.
12 K. A. Van Houten, D. C. Heath, C. A. Barringer, A. L. Rheingold and
R. S. Pilato, Inorg. Chem., 1998, 37, 4647–4653; K. A. Van Houten,
N. V. Blough and R. S. Pilato, Inorg. Chim. Acta, 2003, 353, 231–237.
13 N. Lardies, E. Cerrada and M. Laguna, Polyhedron, 2006, 25, 2785–
2790.
28 A. J. Carty and A. Efraty, Can. J. Chem., 1969, 47, 2573–2578.
29 K. S. Wheelock, J. H. Nelson and H. B. Jonassen, Inorg. Chim. Acta,
1970, 4, 399–403.
30 C. M. Bolinger and T. B. Rauchfuss, Inorg. Chem., 1982, 21, 3947–
3954.
31 G. Hogarth and T. Norman, Polyhedron, 1996, 15, 2859–2867.
32 L. R. Falvello, J. Fornies, J. Gomez, E. Lalinde, A. Martin, F. Martinez
and M. T. Moreno, J. Chem. Soc., Dalton Trans., 2001, 2132–2140.
33 M. A. Bennett, M. J. Byrnes and A. C. Willis, Dalton Trans., 2007,
1677–1686.
34 K. S. Shin and D. Y. Noh, Bull. Korean Chem. Soc., 2004, 25, 130–132.
35 D. Y. Noh, K. S. Shin and K. I. Son, Bull. Korean Chem. Soc., 2007,
28, 343–346.
36 G. M. Sheldrick, SADABS, A Program for Area Detector Absorption
Corrections, University of Gottingen, Germany, 1994.
37 G. M. Sheldrick, SHELXTL, version 5, Bruker AXS, Madison, WI,
1995.
¨
38 P. van der Sluis and A. L. Spek, Acta Crystallogr., Sect. A: Found.
14 L. L. Maisela, A. M. Crouch, J. Darkwa and I. A. Guzei, Polyhedron,
Crystallogr., 1990, 46, 194–201.
2001, 20, 3189–3200.
39 A. L. Spek, J. Appl. Crystallogr., 2003, 36, 7–13.
40 R. M. Silverstrein, G. C. Bassler and T. C. Morrill, Spectroscopic
Identification of Organic Compounds, Wiley, Singapore, 5th edn, 1991,
pp. 107–108.
15 D. Y. Noh, E. M. Seo, H. J. Lee, H. Y. Jang, M. G. Choi, H. Y. Kim
and J. Hong, Polyhedron, 2001, 20, 1939–1945.
16 K. S. Shin, Y. K. Han and D. Y. Noh, Bull. Korean Chem. Soc., 2003,
24, 235–238.
17 W. Oberhauser, T. Stampfl, C. Bachmann, R. Haid, C. Langes, H.
Kopacka, K.-H. Ongania and P. Bru¨ggeller, Polyhedron, 2000, 19, 913–
923; W. Oberhauser, C. Bachmann, T. Stampfl, R. Haid, C. Langes, H.
Kopacka, A. Rieder and P. Bru¨ggeller, Inorg. Chim. Acta, 1999, 290,
167–179.
41 K. Nakamoto, Infrared and Raman Spectra of Inorganic and Coordina-
tion Compounds, Part A, John Wiley & Sons, NY, 5th edn, 1997.
42 S. O. Grim, R. L. Keiter and W. Mcfarlane, Inorg. Chem., 1967, 6,
1133–1137.
43 J. A. Dean, in Lange’s Handbook of Chemistry, McGraw Hill, NY, 15th
edn, 1999.
18 M. P. Martin-Redondo, L. Scoles, B. T. Sterenberg, K. A. Udachin and
A. J. Carty, J. Am. Chem. Soc., 2005, 127, 5038–5039.
44 J. M. Bevilacqua, J. A. Zuleta and R. Eisenberg, Inorg. Chem., 1993,
32, 3689–3693.
This journal is
The Royal Society of Chemistry 2009
Dalton Trans., 2009, 1767–1775 | 1775
©