Synthesis, structural characterization, and photophysical study of luminescent face-to-face dinuclear platinum(II) alkynyl phosphine complexes and their tetranuclear mixed-metal platinum(II)-silver(I) and -copper(I) complexes

Article abstract of DOI:10.1021/om100473q

A series of luminescent face-to-face dinuclear platinum(II) alkynyl phosphine complexes with trimethoxyphenyl and carbazole moieties have been synthesized by phosphine exchange reaction. Two mixed-metal tetranuclear platinum(II)-silver(I) and -copper(I) c

Full text of DOI:10.1021/om100473q

5558 Organometallics 2010, 29, 5558–5569
DOI: 10.1021/om100473q
Synthesis, Structural Characterization, and Photophysical Study
of Luminescent Face-to-Face Dinuclear Platinum(II) Alkynyl Phosphine
Complexes and Their Tetranuclear Mixed-Metal Platinum(II)-Silver(I)
and -Copper(I) Complexes†
Sammual Yu-Lut Leung, Wai Han Lam, Nianyong Zhu, and Vivian Wing-Wah Yam*
Institute of Molecular Functional Materials and Department of Chemistry, The University of Hong Kong,
Pokfulam Road, Hong Kong, Republic of China
Received May 15, 2010
A series of luminescent face-to-face dinuclear platinum(II) alkynyl phosphine complexes with
trimethoxyphenyl and carbazole moieties have been synthesized by phosphine exchange reaction.
Two mixed-metal tetranuclear platinum(II)-silver(I) and -copper(I) complexes have also been
synthesized. The complexes are well characterized by 1H, 13C, and 31P NMR spectroscopy, positive
ion FAB mass spectrometry, IR spectroscopy, and elemental analysis. Most of them have been
structurally characterized by X-ray crystallography. All the complexes are found to show emissive
behavior. Correlations of the emissive property with the Pt Pt distance, the nature of the alkynyl
3 3 3
and bridging phosphine ligands, and the nature of the encapsulated metal ions on the alkynyl ligands
have been made. TDDFT/CPCM calculations have been performed to provide further insight into
the origin of the absorption and emission properties.
Introduction
sandwich fashion6a,b have been reported, and these compounds
have been shown by us to show rich luminescence behavior.
The [Pt2(μ-dppm)2(CtCR)4] unit has further been demon-
strated to function as versatile building blocks for the construc-
tion of multinuclear platinum(II) assemblies through the
incorporation of a pyridyl ligating group to give hexanuclear
[Pt2(μ-dppm)2(CtCC5H4N)4{Pt(trpy)}4](CF3SO3)8 (trpy =
2,20:60,200-terpyridine).6c
Supramolecular chemistry involving metal coordination
has been one of the most popular subjects over the past
decade.1,2 Organometallic supramolecular arrays with tran-
sition metal corner and difunctional organic ligand bridges
have attracted growing attention.2,3 With the unique and
interesting spectroscopic and luminescence properties asso-
ciated with metal-metal interactions, dinuclear d8-d8 metal
complexes have attracted much attention.4 Early works by
Pringle and Shaw have shown that face-to-face dinuclear
platinum(II) alkynyl complexes bridged by bis(diphenyl-
phoshino)methane (dppm) could be isolated by the reaction
of [Pt(dppm-P,P0)Cl2] with alkynyllithium.5 Extension of the
synthesis to various [Pt2(μ-dppm)2(CtCR)4] derivatives6,7 and
the use of these face-to-face dinuclear platinum(II) alkynyls as
metalloligands to encapsulate metal ions in a tweezer-like/
While the [Pt2(μ-dppm)2(CtCR)4] system has been fairly
well studied,5-7 corresponding spectroscopic studies involving
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28, 2908. (e) Smith, D. C.; Gray, H. B. Coord. Chem. Rev. 1990, 100, 169.
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1995, 99, 7977. (h) Lewis, N. S.; Mann, K. R.; Gordon, J. G., II; Gray, H. B.
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C.-M. J. Chem. Soc., Dalton Trans. 1993, 2939. (j) Yam, V. W.-W.; Chan,
L.-P.; Lai, T.-F. Organometallics 1993, 12, 2197. (k) Kwok, W. M.; Phillips,
D. L.; Yeung, P. K.-Y.; Yam, V. W.-W. J. Phys. Chem. A 1997, 101, 9286.
(l) Yam, V. W.-W.; Yeung, P. K.-Y.; Chan, L.-P.; Kwok, W. M.; Phillips, D. L.;
Yu, K.-L.; Wong, R. W.-K.; Yan, H.; Meng, Q.-J. Organometallics 1998, 17,
2590. (m) Bennett, M. A.; Bhargava, S. K.; Cheng, E. C.-C.; Lam, W. H.; Lee,
† Part of the Dietmar Seyferth Festschrift.
*To whom correspondence should be addressed. E-mail: wwyam@
hku.hk.
(1) (a) Lehn, J. M. Supramolecular Chemistry; VCH Publishers:
NewYork, 1995. (b) Baxter, P.; Lehn, J. M.; DeCian, A. Angew. Chem., Int.
Ed. Engl. 1993, 32, 69. (c) Amabilino, D. B.; Stoddart, J. F. Chem. Rev.
1995, 95, 2725. (d) Leininger, S.; Olenyuk, B.; Stang, P. J. Chem. Rev. 2000,
100, 853.
(2) (a) Fujita, M.; Umemoto, K.; Yoshizawa, M.; Fujita, N.; Kusukawa,
T.; Biradha, K. Chem. Commun. 2001, 509. (b) Caulder, D. L.; Raymond, K. N.
Acc. Chem. Res. 1999, 32, 975. (c) Leininger, S.; Olenyuk, B.; Stang, P. J. Chem.
Rev. 2000, 100, 853.
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M. G. B.; Dent, S. W.; Maestri, M. J. Am. Chem. Soc. 1997, 119,
11864. (b) Belanger, S.; Hupp, J. T. Angew. Chem., Int. Ed. 1999, 38, 2222.
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ꢀ
T. K.-M.; Priver, S. H.; Wagler, J.; Wills, A. C.; Yam, V. W.-W. J. Am. Chem.
Soc. 2010, 132, 7094.
(5) Pringle, P. G.; Shaw, B. L. Chem. Commun. 1982, 581.
(6) (a) Yam, V. W.-W.; Yu, K.-L.; Wong, K. M.-C.; Cheung, K.-K.
Organometallics 2001, 20, 721. (b) Yam, V. W.-W.; Hui, C.-K.; Wong, K.
M.-C.; Zhu, N.; Cheung, K.-K. Organometallics 2002, 21, 4326. (c) Hui,
C.-K.; Chu, B. W.-K.; Zhu, N.; Yam, V. W.-W. Inorg. Chem. 2002, 41, 6178.
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r
pubs.acs.org/Organometallics
Published on Web 10/14/2010
2010 American Chemical Society

Article
Organometallics, Vol. 29, No. 21, 2010 5559
diphosphines other than dppm have not been made. These,
together with the previous report by Gladysz and co-workers
on the preparation of tetranuclear platinum(II) alkynyls using
phosphine exchange reactions,8 have prompted us to explore
the study of the bis(dimethylphosphino)methane (dmpm) ana-
logues, given the more electron-rich and more optically trans-
parent nature of the dmpm ligand. It is envisaged that the
incorporation of dmpm bridging ligands other than that of
dppm will provide an opportunity for the systematic variation
of the electronic and structural properties of the ligands, which
would have an important influence on the spectroscopic prop-
erties of this class of compounds. In addition, incorporation
of carbazole, a well-known hole-transporting9a,b and electro-
luminescent molecule9c,d with simple functionization,10 into the
face-to-face dinuclear platinum(II) alkynyl phosphine system
has also been explored.
Herein we report the synthesis and photophysical study of
several face-to-face dinuclear platinum phosphine alkynyl
complexes, [Pt2(μ-dppm)2{CtCC6H2(OMe)3-3,4,5}4] (1),
[Pt2(μ-dppm)2(CtCC6H4-Carb-9)4] (2), [Pt2(μ-dmpm)2{Ct
CC6H2(OMe)3-3,4,5}4] (3), and [Pt2(μ-dmpm)2(CtCC6H4-
Carb-9)4] (4), using the phosphine exchange approach, and
their mixed-metal tetranuclear complexes, [Pt2(μ-dppm)2-
trans-[Pt(PPh3)2{CtCC6H2(OMe)3-3,4,5)4}2]. It was synthe-
sized by the modification of literature procedures.14 cis-[Pt(PPh3)2-
Cl2] (1.0 g, 1.27 mmol) was dissolved in HNEt2 (60 mL) contain-
ing CuI (3.8 mg, 0.038 mmol) followed by the addition of
5-ethynyl-1,2,3-trimethoxybenzene (0.73 g, 3.81 mmol). The
reaction mixture was then heated to reflux for 8 h with stirring.
The white organic ammonium salt formed during the course of
the reaction was then filtered off, and the solvent was removed
under reduced pressure. Dichloromethane was added to dissolve
the yellow residue, and the solution was washed successively with
ammonium chloride solution and deionized water to remove the
copper(I) catalyst. The organic layer was then dried over anhydrous
MgSO4, filtered, and concentrated under reduced pressure.
Subsequent recrystallization from dichloromethane-diethyl ether
afforded pale yellow crystals. Yield: 60.4 mg, 65.0%. 1H NMR
(400 MHz, CDCl3, 298 K, relative to Me4Si): δ 3.58 (s, 12H,
-OCH3-m), 3.65 (s, 6H, -OCH3-p), 5.50 (s, 4H, -C6H2-),
7.35-7.83 (m, 30H, -PPh3). 13C NMR (100.6 MHz, CDCl3,
298 K, relative to Me4Si): δ 55.70 (-OCH3-m), 60.67 (-OCH3-p),
101.34 (Pt-CtC-C), 103.56 (Pt-CtC-C), 105.65, 121.76, 134.10,
and 149.25 (-C6H2-), 125.45, 126.23, 127.91, and 130.89
(-PPh3). 31P NMR (161 MHz, CDCl3, 298 K, relative to 85%
H3PO4): δ 18.82 (s, J(Pt-P) = 2635 Hz). IR (KBr disk, ν/cm-1):
2084 ν(CtC). Positive FAB-MS: ion clusters at m/z 1103 {M}þ,
913 {M - CtCC6H2(OMe)3-3,4,5}þ, 719 {M - 2CtCC6-
H2(OMe)3-3,4,5}þ. Anal. Found (%): C, 63.10; H, 4.70. Calcd
for trans-[Pt(PPh3)2{CtCC6H2(OMe)3-3,4,5)4}2]: C, 63.21; H,
4.76.
{CtCC6H2(OMe)3-3,4,5}4 {Ag(MeCN)}2](BF4)2 (5) and
3
[Pt2(μ-dppm)2{CtCC6H2(OMe)3-3,4,5}4 {Cu(MeCN)}2]-
3
(PF6)2 (6). The influence of the Pt Pt distance, the nature
3 3 3
trans-[Pt(PPh3)2(CtCC6H4-Carb-9)2]. The title compound
was prepared according to a procedure similar to that described
for the preparation of trans-[Pt(PPh3)2{CtCC6H2(OMe)3-
3,4,5)4}2], except 9-(4-ethynylphenyl)-9H-carbazole (52.0 mg,
0.19 mmol) was used in place of 5-ethynyl-1,2,3-trimethoxy-
benzene to give a yellow solid. Yield: 54.7 mg, 66.0%. 1H NMR
(400 MHz, CDCl3, 298 K, relative to Me4Si): δ 6.45 (d, 4H,
JHH = 9.0 Hz, H’s at 5-position of carbazole), 7.08 (d, 4H, H’s at
1-position of -C6H4-), 7.10-7.30 (m, 8H, H’s at 3- and
4-position of carbazole), 7.35 (d, 4H, JHH = 7.0, H’s at 2-position
of the diphosphine and alkynyl ligands, and the metal
encapsulation on the spectroscopic and luminescence prop-
erties have also been explored and supported by the TDDFT/
CPCM calculations.
Experimental Section
Materials and Reagents. Bis(diphenylphosphino)methane
(dppm) and bis(dimethylphosphino)methane (dmpm) were pur-
chased from Strem Chemical Inc. [Ag(MeCN)4]BF4, Cu(BF4)2
6H2O, and PtCl2 were purchased from Aldrich Chemical Co.
Trimethylsilylacetylene was purchased from GFS Chemical Co.
3
of -C6H4-), 7.43-7.92 (m, 30H, -PPh3), 8.10 (d, 4H, JHH
=
8.0 Hz, H’s at 2-position of carbazole). 13C NMR (100.6 MHz,
CDCl3, 298 K, relative to Me4Si): δ 101.18 (Pt-CtC-C), 104.25
(Pt-CtC-C), 111.00, 117.27, 119.19, 119.67, 119.88, 120.65, 121.74,
130.86, 132.78, and 140.16 (-C6H4-Carb), 128.54, 128.67, 133.47,
and 137.56 (-PPh3). 31P NMR (161 MHz, CDCl3, 298 K, relative
to 85% H3PO4): δ 18.98 (s, J(Pt-P) = 2624 Hz). IR (KBr disk,
ν/cm-1): 2090 ν(CtC). Positive FAB-MS: ion clusters at m/z
1263 {M}þ, 985 {M - CtCC6H4-Carb-9}þ. Anal. Found (%): C,
73.00; H, 4.43; N, 2.30. Calcd for trans-[Pt(PPh3)2(CtCC6H4-
Carb-9)2]: C, 72.89; H, 4.35; N, 2.24.
11
Ltd. [Cu(MeCN)4]PF6 and 9-(4-ethynylphenyl)-9H-carbazole12
were prepared according to literature procedures. Tetrahydro-
furan (Lab-Scan, AR) was purified by Pure Solv-MD (Multiple
Dispensing System, Innovative Technology). Methanol (Merck,
GR), acetonitrile (Lab Scan, AR), diethyl ether (Scharlau, AR),
and dichloromethane (Lab Scan, AR) were purified and distilled
using standard procedures before use.13 All other reagents were
of analytical grade and were used as received. Dichloromethane
(Sigma-Aldrich, spectrophotometric grade) was used for spec-
troscopic studies without further purification.
Synthesis and Characterization of the Mononuclear Platinum(II)
Alkynyl Precursor Complexes. All reactions were carried out
under an inert atmosphere of nitrogen using standard Schlenk
techniques.
Synthesis and Characterization of the Dinuclear Platinum(II)
Alkynyl Complexes 1-4. All reactions were carried out under an
inert atmosphere of nitrogen using standard Schlenk techniques.
Pt2(μ-dppm)2{CtCC6H2(OMe)3-3,4,5}4] (1). The precursor
complex trans-[Pt(PPh3)2{CtCC6H2(OMe)3-3,4,5)4}2] (50.0 mg,
0.045 mmol) and bis(diphenylphosphino)methane (20.9 mg,
0.054 mmol) were placed in a 250 mL two-necked round-bottomed
flask. Degassed THF (160 mL) was transferred into the mixture. The
reaction mixture was stirred for two days. The resulting mixture
was evaporated to dryness, and the residue was purified by column
chromatography on silica gel (70-230 mesh) using dichlorometh-
ane-acetone (8:2 v/v) as the eluent. Subsequent diffusion of diethyl
ether vapor to the concentrated dichloromethane solution of the
product gave 1 as yellow crystals. Yield: 53.7 mg, 62.0%. 1H NMR
(400 MHz, CDCl3, 298 K, relative to Me4Si): δ 3.39 (s, 24H,
-OCH3-m), 3.72 (s, 12H, -OCH3-p), 4.62-4.64 (m, 4H,
-PCH2P-), 5.72 (s, 8H, -C6H2-), 7.00-7.85 (m, 40H, -PPh2).
13C NMR (100.6 MHz, CDCl3, 298 K, relative to Me4Si): δ 30.87
(8) (a) Owen, G. R.; Hampei, F.; Gladysz, J. A. Organometallics 2004,
23, 5889. (b) Owen, G. R.; Hampei, F.; Gladysz, J. A. Organometallics 2004,
23, 5893. (c) Quadras, L.; Hampei, F.; Gladysz, J. A. Dalton Trans. 2006, 24,
2929. (d) Owen, G. R.; Gauthier, S.; Weisbach, N.; Hampei, F.; Bhuvanesh,
N.; Gladysz, J. A. Dalton Trans. 2010, 39, 5260.
(9) (a) Tao, X.; Zhang, Y.; Wada, T.; Sasabe, H.; Suzuki, H.;
Watanabe, T.; Miyata, S. Adv. Mater. 1998, 10, 226. (b) Maruyama, S.;
Tao, X.; Hokari, H.; Noh, T.; Zhang, Y.; Wada, T.; Sasabe, H.; Suzuki, H.;
Watanabe, T.; Miyata, S. J. Mater. Chem. 1999, 9, 893. (c) Brizius, G.;
Kroth, S.; Bunz, U. H. F. Macromolecules 2002, 35, 3517. (d) Zhu, Z.;
Moore, J. S. J. Org. Chem. 2000, 65, 116.
(10) Coffey, S. In RODDs Chemistry of Carbon Compounds, 2nd ed.;
Elsevier Scientific: New York, 1964; Vol. IV, Part A, pp 491-499.
(11) Jian, H.; Tour, J. M. J. Org. Chem. 2003, 68, 509.
(12) Kubas, G. J. Inorg. Synth. 1979, 19, 90.
(13) Perrin, D. D.; Armarego, W. L. F. Purification of Laboratory
Chemicals, 3rd ed.; Pergamon: Oxford, U.K., 1998.
(14) Leininger, S.; Strang, P. J.; Huang, S. Organometallics 1998, 17,
3981.

5560 Organometallics, Vol. 29, No. 21, 2010
Leung et al.
(-PCH2P-), 55.76 (-OCH3-m), 60.68 (-OCH3-p), 104.56 (Pt-
CtC-C), 105.34 (Pt-CtC-C), 107.79, 124.43, 135.01, and 152.20
(-C6H2-), 127.48, 128.67, 129.82, and 133.90 (-PPh2). 31P NMR
(161 MHz, CDCl3, 298 K, relative to 85% H3PO4): δ 2.37
(s, J(Pt-P) = 2829 Hz). IR (KBr disk, ν/cm-1): 2097 ν(CtC).
Positive FAB-MS: ion clusters at m/z 1922 {M}þ, 1732 {M -
CtCC6H2(OMe)3-3,4,5}þ, 1541 {M - dppm}þ, 1159 {M -
2dppm}þ. Anal. Found (%): C, 58.52; H, 4.88. Calcd for 1: C,
58.69; H, 4.61.
[Pt2(μ-dppm)2(CtCC6H4-Carb-9)4] (2). The title compound
was prepared according to a procedure similar to that described
for the preparation of 1, except trans-[Pt(PPh3)2(CtCC6H4-
Carb-9)2] (50.0 mg, 0.040 mmol) was used in place of trans-
[Pt(PPh3)2{CtCC6H2(OMe)3-3,4,5)4}2] to give 2 as a bright
yellow solid. Yield: 50.9 mg, 57.2%. 1H NMR (400 MHz, CDCl3,
298 K, relative to Me4Si): δ 4.78-4.80 (m, 4H, -PCH2P-), 6.78
(d, 8H, JHH = 8.4 Hz, H’s at 5-position of carbazole), 7.04-7.30
(m, 32H, H’s at 3- and 4-position of carbazole, H’s at 1- and
2-position of -C6H4-), 7.09-7.95 (m, 40H, -PPh2), 8.04 (d, 8H,
JHH = 7.3 Hz, H’s at 2-position of carbazole). 13C NMR
(100.6 MHz, CDCl3, 298 K, relative to Me4Si): δ30.89 (-PCH2P-),
102.56 (Pt-CtC-C), 105.34 (Pt-CtC-C), 109.57, 119.69, 120.12,
123.23, 125.74, 126.43, 128.00, 132.28, 134.44, and 140.66 (-C6H4-
Carb), 127.50, 128.70, 130.01, and 133.92 (-PPh2). 31P NMR
(202 MHz, CDCl3, 298 K, relative to 85% H3PO4): δ 2.59 (s,
J(Pt-P) = 2840 Hz). IR (KBr disk, ν/cm-1): 2104 ν(CtC).
Positive FAB-MS: ion clusters at m/z 2224 {M}þ, 1959 {M -
CtCC6H4)-Carb-9}þ. Anal. Found (%): C, 69.81; H, 4.15; N,
2.99. Calcd for 2: C, 70.20; H, 4.17; N, 2.89.
[Pt2(μ-dmpm)2{CtCC6H2(OMe)3-3,4,5}4] (3). The precursor
complex trans-[Pt(PPh3)2{CtCC6H2(OMe)3-3,4,5)4}2] (50.0 mg,
0.045 mmol) was placed in a 250 mL two-necked round-bottomed
flask. Degassed THF (160 mL) was transferred into the mixture.
Bis(dimethylphosphino)methane (12 μml, 0.079 mmol) was then
added. The reaction mixture immediately turned to a clear yellow
solution and was stirred for two days. The resulting mixture was
evaporated to dryness under reduced pressure, and the residue was
purified by column chromatography on silica gel (70-230 mesh)
using dichloromethane-acetone (8:2 v/v) as the eluent. Sub-
sequent diffusion of diethyl ether vapor to the concentrated
dichloromethane solution of the product gave 3 as pale yellow-
green crystals. Yield: 45.7 mg, 73.7%. 1H NMR (400 MHz, CDCl3,
298 K, relative to Me4Si): δ 2.01 (t, 24H, -PMe2), 3.06 (m, 4H,
-PCH2P-), 3.54 (s, 24H, -OCH3-m), 3.76 (s, 12H, -OCH3-p),
6.51 (s, 8H, -C6H2-). 13C NMR (100.6 MHz, CDCl3, 298 K,
relative to Me4Si): δ 15.57 (-PCH3-), 30.88 (-PCH2P-), 55.72
(-OCH3-m), 60.82 (-OCH3-p), 105.76 (Pt-CtC-C), 106.96
(Pt-CtC-C), 108.22, 124.05, 136.67, and 152.71 (-C6H2-). 31P
NMR (161 MHz, CDCl3, 298 K, relative to 85% H3PO4):
δ -18.68 (s, J(Pt-P) = 2517 Hz). IR (KBr disk, ν/cm-1): 2081
ν(CtC). Positive FAB-MS: ion clusters at m/z 1428 {M}þ, 1237
{M - CtCC6H2(OMe)3-3,4,5}þ, 1045 {M - 2CtCC6H2(OMe)3-
3,4,5}þ, 853 {M - 3CtCC6H2(OMe)3-3,4,5}þ. Anal. Found (%):
C, 45.78; H, 5.16. Calcd for 3: C, 45.72; H, 4.87.
120.12, 123.23, 125.74, 126.43, 128.00, 132.28, 134.44, and 140.66
(-C6H4-Carb). 31P NMR (161 MHz, CDCl3, 298 K, relative to
85% H3PO4): δ -18.70 (s, J(Pt-P) = 2480 Hz). IR (KBr disk,
ν/cm-1): 2097 ν(CtC). Positive FAB-MS: ion clusters at m/z 1729
{M}þ, 1461 {M - CtCC6H4-Carb-9}þ, 1195 {M - 2CtCC6H4-
Carb-9}þ, 921 {M - 3CtCC6H4-Carb-9}þ, 662 {M - 4CtCC6-
H4-Carb-9}þ. Anal. Found (%): C, 58.33; H, 4.22; N, 3.90. Calcd
for 4 2CH2Cl2: C, 58.23; H, 4.25; N, 3.78.
3
Synthesis and Characterization of the Mixed-Metal Tetranuclear
Platinum(II)-Silver(I) and -Copper(I) Alkynyl Complexes 5 and 6.
All reactions were carried out under an inert atmosphere of nitrogen
using standard Schlenk techniques.
[Pt2(μ-dppm)2{CtCC6H2(OMe)3-3,4,5}4 {Ag(MeCN)}2]-
3
(BF4)2 (5). This was synthesized by modification of a literature
procedure for the related mixed-metal complexes of [Pt2(μ-dppm)2-
(CtCPh)4].6a To a yellow suspension of 1 (48.0 mg, 0.025 mmol)
in dichloromethane (10 mL) was added dropwise [Ag(MeCN)4]-
BF4 (19.7 mg, 0.055 mmol) in acetone solution (10 mL). The
reaction mixture immediately turned to a clear greenish-yellow
solution and was allowed to stir for 30 min. After removal of the
solvent under vacuum, a greenish-yellow solid was obtained.
Subsequent recrystallization from acetone-n-hexane afforded 5
as air-stable greenish-yellow rod-shaped crystals. Yield: 30.0 mg,
50.4%. 1H NMR (400 MHz, CDCl3, 298 K, relative to Me4Si):
δ 1.30 (s, 6H, CH3CN), 3.50 (s, 24H, -OCH3-m), 3.81 (s, 12H,
-OCH3-p), 5.20-5.22 (m, 4H, -PCH2P-), 5.47 (s, 8H,
-C6H2-), 7.35-8.07 (m, 40H, -PPh2). 31P NMR (161 MHz,
CDCl3, 298 K, relative to 85% H3PO4): δ 5.16 (s, J(Pt-P) =
2580 Hz). IR (KBr disk, ν/cm-1): 2024 ν(CtC). Positive FAB-
MS: ion clusters at m/z 2033 {M - Ag - 2MeCN}þ. Anal. Found
(%): C, 48.27; H, 4.05. Calcd for 5: C, 48.50; H, 4.10.
[Pt2(μ-dppm)2{CtCC6H2(OMe)3-3,4,5}4 {Cu(MeCN)}2]-
3
(PF6)2 (6). This was synthesized by modification of a literature
procedure for the related mixed-metal complexes of [Pt2(μ-dppm)2-
(CtCPh)4].6b To a yellow suspension of 1 (52.8 mg, 0.027 mmol)
in dichloromethane (10 mL) was added dropwise [Cu(MeCN)4]-
PF6 (21.5 mg, 0.058 mmol) in acetone solution (10 mL). The
reaction mixture immediately turned to a clear yellow solution
and was stirred for 30 min. After removal of the solvent under
vacuum, a yellow solid was obtained. Subsequent recrystalliza-
tion from acetone-n-hexane afforded 6 as air-stable yellow rod-
1
shaped crystals. Yield: 35.0 mg, 52.0%. H NMR (400 MHz,
CDCl3, 298 K, relative to Me4Si): δ 1.81 (s, 6H, CH3CN), 3.51 (s,
24H, -OCH3-m), 3.79 (s, 12H, -OCH3-p), 5.00-5.04 (m, 4H,
-PCH2P-), 5.32 (s, 8H, -C6H2-), 7.26-8.00 (m, 40H, -PPh2).
31P NMR (400 MHz, CDCl3, 298 K, relative to 85% H3PO4): δ
5.00 (s, J(Pt-P) = 2543 Hz). IR (KBr disk, ν/cm-1): 2005
ν(CtC). Positive FAB-MS: ion clusters at m/z 1988 {M - Cu
- 2MeCN}þ, 1025 {M - 2MeCN}2þ. Anal. Found (%): C,
44.08; H, 3.97. Calcd for 6: C, 44.55; H, 3.66.
Physical Measurements and Instrumentation. 1H, 13C, and
31P NMR spectra were recorded on either a Bruker DPX300
or a Bruker AV400 FT-NMR spectrometer. The chemical shifts
(δ, ppm) were reported relative to tetramethylsilane (Me4Si)
[Pt2(μ-dmpm)2(CtCC6H4-Carb-9)4] (4). The title compound
was prepared according to a procedure similar to that described
for the preparation of 3, except trans-[Pt(PPh3)2(CtCC6H4-
Carb-9)2] (50.0 mg, 0.040 mmol) was used in place of trans-
[Pt(PPh3)2{CtCC6H2(OMe)3-3,4,5)4}2] to give 4 as greenish-
for 1H and 13C NMR and 85% phosphoric acid (H3PO4) for 31
P
NMR studies. Positive ion fast atom bombardment (FAB) mass
spectra were recorded on a Finnigan MAT95 mass spectro-
meter. IR spectra were obtained as KBr disks on a Bio-Rad
FTS-7 Fourier transform infrared spectrophotometer (4000-
400 cm-1). Elemental analyses of the new compounds were
performed on a Carlo Erba 1106 elemental analyzer at the
Institute of Chemistry, Chinese Academy of Sciences, Beijing.
UV-vis absorption spectra were recorded on a Hewlett-Packard
8452A diode array spectrophotometer. Steady-state emission and
excitation spectra recorded at room temperature and 77 K were
obtained on a Spex Fluorolog-2 model F111 fluorescence spec-
trophotometer equipped with a Hamamatsu R928 photomulti-
plier tube with or without Corning filters. All solution samples for
photophysical studies were degassed on a high-vacuum line in a
two-compartment cell consisting of a 10 cm-3 Pyrex bulb and a
1
yellow crystals. Yield: 39.9 mg, 60.0%. H NMR (400 MHz,
CDCl3, 298 K, relative to Me4Si): δ 2.19 (t, 24H, -PMe2), 3.28
(m, 4H, -PCH2P-), 7.03 (t, 8H, JHH=8.1 Hz, H’s at 4-position
of carbazole), 7.03 (t, 8H, JHH =7.1 Hz, H’s at 3-position of
carbazole), 7.21 (d, 8H, JHH = 8.3 Hz, H’s at 2-position of
-C6H4-), 7.28 (d, 8H, JHH = 6.5 Hz, H’s at 5-position of
carbazole), 7.50 (d, 8H, JHH = 8.3 Hz, H’s at 1-position
of -C6H4-), 8.03 (d, 8H, JHH = 7.7 Hz, H’s at 2-position
of carbazole). 13C NMR (100.6 MHz, CDCl3, 298 K,
relative to Me4Si): δ 15.58 (-PCH3-), 30.92 (-PCH2P-),
107.86 (Pt-CtC-C), 109.36 (Pt-CtC-C), 109.57, 119.69,

Article
Organometallics, Vol. 29, No. 21, 2010 5561
Table 1. Crystal and Structure Determination Data
1
3
4
5
6
formula
fw
C
94H88O12P4Pt2
6CH2Cl2
C54H72O12P4Pt2
C90H76N4P4Pt2
4CH2Cl2
2067.31
C98H94Ag2B2F8N2O12P4Pt2
4(CH3)2CO
2627.48
23.472(2)
23.370(2)
21.290(2)
90.00
102.184(1)
90.00
11415.9(18)
4
C
98H94Cu2F12N2O12P6Pt
4(CH3)2CO
3
3
3
3
2433.26
13.8451(6)
15.0585(6)
15.7499(6)
61.876(1)
77.895(1)
64.178(1)
2606.75(18)
1
1427.18
8.412(1)
11.037(2)
15.715(3)
92.82(2)
100.90(2)
99.52(2)
1408.0(4)
1
2655.14
23.973(2)
22.983(2)
21.570(2)
90.00
102.229(2)
90.00
11615(2)
4
˚
a, A
11.9617(9)
12.8784(10)
15.8100(12)
104.444(1)
100.856(1)
93.525(1)
2301.2(3)
1
˚
b, A
˚
c, A
R, deg
β, deg
γ, deg
3
˚
V, A
Z
cryst syst
color/habit
space group
Dc, g cm-3
T, K
triclinic-P
yellow block
P1 (No. 2)
1.550
297(2)
3.11
triclinic-P
yellow block
P1 (No. 2)
1.683
301(2)
5.14
triclinic-P
yellow block
P1 (No. 2)
1.492
301(2)
3.38
monoclinic-C
yellow rod
C2/c (No. 15)
1.529
298 (2)
2.91
monoclinic-C
yellow block
C2/c (No. 15)
1.518
297(2)
2.93
μ, mm-1
F(000)
1216
17 798
11 532
0.0184
0.0277, 0.0701
0.0328, 0.0729
1.020
708
8190
5234
0.0279
0.0317, 0.0832
0.0342, 0.0865
1.061
5248
15 665
10 206
0.0219
0.0388, 0.0984
0.0541, 0.1068
1.016
5248
31 572
10 050
0.0191
0.0349, 0.0967
0.0443, 0.1056
1.048
5328
29 002
10 214
0.0223
0.0358, 0.1005
0.0484, 0.1109
1.055
no. of reflns
no. of indep reflns
Rint
R1,a wR2b (I > 2(I))
R1, wR2 (all data)
GoFc
P
P
P
P
P
a R1 = ||Fo| - |Fc||/ |Fo|. b wR2 = [ w(|Fo2| - |Fc2|)2/ w|Fo2|2]1/2
.
c GoF = [ w(|Fo| - |Fc|)2/(Nobs - Nparam)]1/2
.
1 cm path length quartz cuvette and sealed from the atmosphere
by a Rotaflo HP6/6 quick-release Teflon stopper. Solution
samples were rigorously degassed with no fewer than four
successive freeze-pump-thaw cycles prior to the measurements.
Low-temperature glass photophysical measurements were car-
ried out with the samples loaded in a quartz tube inside a quartz-
walled Dewar flask with liquid nitrogen. Emission lifetime mea-
surements were performed using a conventional laser system. The
excitation source was the 355 nm output (third harmonic, 8 ns)
of a Spectra-Physics Quanta-Ray Q-switched GCR-150-10
pulsed Nd:YAG laser. Luminescence decay signals from a Ha-
mamatsu R928 photomultiplier tube were converted to voltage
changes by connecting to a 50 Ω load resistor and were then
recorded on a Tektronix model TDS 620A digital oscilloscope.
The lifetime τo was determined by a single-exponential fitting of
the luminescence decay trace with the relationshipI=Io exp(-t/τo),
where I and Io are the luminescence intensity at time=t and 0,
respectively. Solution samples for luminescence lifetime measure-
ments were degassed with no fewer than four successive freeze-
pump-thaw cycles.
fined by full-matrix least-squares on F2 using the SHELXL-97
program.17 In the final stage of least-squares refinement, non-H
atoms of the solvent molecules were refined isotropically; other
non-H atoms were refined anisotropically. H atoms were gener-
ated by the program SHELXL-97.17 The positions of H atoms
were calculated on the basis of the riding mode with thermal
parameters equal to 1.2 times that of the associated C atoms and
participated in the calculation of final R-indices (see Supporting
Information).
Computational Details. Using Gaussian 03,18 time-dependent
density functional theory (TDDFT)19 at the hybrid Perdew,
Burke, and Ernzerhof (PBE0) functional level20 associated with
the conductor-like polarizable continuum model (CPCM)21
using CH2Cl2 as the solvent was employed to compute the first
three lowest lying singlet-singlet transitions of [Pt2(μ-dppm)2-
{CtCC6H2(OMe)3-3,4,5}4] (1), [Pt2(μ-dmpm)2{CtCC6H2(OMe)3-
3,4,5}4] (3), and [Pt2(μ-dmpm)2(CtCC6H4-Carb-9)4] (4) on the
basis of the experimentally determined geometry obtained from
(18) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.;
Robb, M. A.; Cheeseman, J. R.; Montgomery, J. A., Jr.; Vreven, T.;
Kudin, K. N.; Burant, J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi, J.;
Barone, V.; Mennucci, B.; Cossi, M.; Scalmani, G.; Rega, N.; Petersson,
G. A.; Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.;
Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai,
H.; Klene, M.; Li, X.; Knox, J. E.; Hratchian, H. P.; Cross, J. B.; Bakken,
V.; Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev,
O.; Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Ayala,
P. Y.; Morokuma, K.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.;
Zakrzewski, V. G.; Dapprich, S.; Daniels, A. D.; Strain, M. C.; Farkas,
O.; Malick, D. K.; Rabuck, A. D.; Raghavachari, K.; Foresman, J. B.;
Ortiz, J. V.; Cui, Q.; Baboul, A. G.; Clifford, S.; Cioslowski, J.; Stefanov,
B. B.; Liu, G.; Liashenko, A.; Piskorz, P.; Komaromi, I.; Martin, R. L.;
Fox, D. J.; Keith, T.; Al-Laham, M. A.; Peng, C. Y.; Nanayakkara, A.;
Challacombe, M.; Gill, P. M. W.; Johnson, B.; Chen, W.; Wong, M. W.;
Gonzalez, C.; Pople, J. A. Gaussian 03; Revision E.01; Gaussian, Inc.:
Wallingford, CT, 2004.
X-ray Diffraction Measurement. Single crystals of 1, 3, and 4
suitable for X-ray crystallographic studies were obtained by the
diffusion of diethyl ether vapor into a concentrated dichloro-
methane solution of the respective complexes, while single
crystals of 5 and 6 for X-ray crystallographic studies were
obtained by the diffusion of diethyl ether vapor into a concen-
trated acetone solution of the respective complexes. Crystal and
structure determination data of 1 6CH2Cl2, 3, 4 4CH2Cl2, 5 4-
3
3
3
(CH3)2CO, and 6 4(CH3)2CO are summarized in Table 1. Se-
3
lected bond distances and bond angles of 1 and 3-6 are collected
in Tables 2 and 3. The crystals were mounted in a glass capillary,
and the intensity data were collected on a Bruker SMART 1000
CCD diffractometer using graphite-monochromated Mo KR
˚
radiation (λ=0.71073 A). Raw frame data were integrated using
the SAINT15 program. Semiempirical absorption corrections
with SADABS16 were applied. The structures were solved by
direct methods employing the SHELXS-97 program17 and re-
(19) (a) Stratmann, R. E.; Scuseria, G. E.; Frisch, M. J. J. Chem.
Phys. 1998, 109, 8218. (b) Bauernschmitt, R.; Ahlrichs, R. Chem. Phys.
Lett. 1996, 256, 454. (c) Casida, M. E.; Jamorski, C.; Casida, K. C.; Salahub,
D. R. J. Chem. Phys. 1998, 108, 4439.
(20) (a) Ernzerhof, M.; Scuseria, G. E. J. Chem. Phys. 1999, 110, 5029.
(b) Ernzerhof, M.; Perdew, J. P.; Burke, K. Int. J. Quantum Chem. 1997,
64, 285.
(21) (a) Barone, V.; Cossi, M. J. Phys. Chem. A 1998, 102, 1995.
(b) Cossi, M.; Rega, N.; Scalmani, G.; Barone, V. J. Comput. Chem. 2003,
24, 669.
(15) SAINTþ, SAX area detector integration program, Version 7.34A;
Bruker AXS, Inc.: Madison, WI, 2006.
(16) Sheldrick, G. M. SADABS, Empirical Absorption Correction
€
€
Program; University of Gottingen: Gottingen, Germany, 2004.
(17) Sheldrick, G. M. Acta Crystallogr. 2008, A64, 112.

5562 Organometallics, Vol. 29, No. 21, 2010
Leung et al.
Table 2. Selected Bond Distances and Angles with Estimated
Standard Deviations in Parentheses
Table 3. Pt Pt Distances of Dinuclear Pt(II) Alkynyl
3 3 3
Complexes with Estimated Standard Deviations in Parentheses
˚
d(Pt Pt), A
complex
3 3 3
[Pt2(μ-dppm)2{CtCC6H2(OMe)3-3,4,5}4] (1)
[Pt2(μ-dppm)2{CtCC6H2(OMe)3-3,4,5}4] (1)
[Pt2(μ-dmpm)2{CtCC6H2(OMe)3-3,4,5}4] (3)
[Pt2(μ-dmpm)2(CtCC6H4-Carb-9)4] (4)
3.3686(2)
3.3082(5)
3.2045(4)
3.2022(2)
˚
Bond Distances (A)
Pt(1)-P(1)
Pt(1)-P(2)
Pt(1)-C(1)
Pt(1)-C(12)
2.293(1)
2.297(1)
2.001(3)
2.000(3)
C(1)-C(2)
C(12)-C(13)
P(1)-C(23)
P(2)-C(23)
1.206(5)
1.220(5)
1.837(3)
1.832(3)
[Pt2(μ-dppm)2{CtCC6H2(OMe)3-3,4,5}4
{Ag(MeCN)}2](BF4)2 (5)
3
[Pt2(μ-dppm)2{CtCC6H2(OMe)3-3,4,5}4
{Cu(MeCN)}2](PF6)2 (6)
3.0117(2)
3
Bond Angles (deg)
crystallographic data. For complex 6, calculation was performed
on the basis of its X-ray crystal structure with the Cu-N-C and
N-C-CH3 angles in each of the acetonitrile coordinations set
at 180°. In the present study, all the C-H bond lengths of
Pt(1)-C(1)-C(2)
Pt(1)-C(12)-C(13)
C(1)-Pt(1)-P(1)
172.0(3)
174.4(3)
92.17(9)
P(1)-Pt(1)-P(2)
P(1)-Pt(1)-C(12)
C(1)-Pt(1)-C(12)
174.12(3)
84.61(9)
170.42(13)
˚
the complexes were set at 1.09 A. The Stuttgart effective core
potentials and the associated valence basis set were applied for
Pt22a and Cu22b with f polarization functions [ζf(Pt)=0.993 and
ζf(Cu)=3.525],23 while the 6-31G(d) basis set24 was used for P, O,
N, C, and H atoms. All TDDFT calculations were performed
with a larger grid size (99590). Mulliken population analyses were
done using MullPop.25
[Pt2(μ-dmpm)2{CtCC6H2(OMe)3-3,4,5}4] (3)
˚
Bond Distances (A)
Pt(1)-P(1)
Pt(1)-P(2)
Pt(1)-C(1)
Pt(1)-C(12)
2.290(1)
2.280(1)
1.994(5)
2.001(5)
C(1)-C(2)
C(12)-C(13)
P(1)-C(23)
P(2)-C(23)
1.222(7)
1.222(7)
1.826(5)
1.833(5)
Results and Discussion
Bond Angles (deg)
Synthesis and Characterization. The face-to-face diplatinum-
(II) alkynyl complex [Pt2(μ-dppm)2(CtCPh)4] was first synthe-
sized by Pringle and Shaw5 by the reaction of [Pt(dppm-P,P0)-
Cl2] with LiCtCPh in THF-benzene under reflux conditions
for 24 h. In this synthesis, LiCtCR was generated in situ from
the corresponding RCtCH and nBuLi and was added drop-
wise to [Pt(dppm-P,P0)Cl2] in benzene at -78 °C. Until more
recently, an alternative synthetic procedure was reported by
Chen and co-workers.7 It was suggested that this class of face-
to-face diplatinum(II) complexes could be prepared by the
stirring of [Pt(dppm-P,P0)Cl2] with the corresponding alkynes
in the presence of a base at room temperature for five days
without the need for the use of lithiating reagents.7 However,
this synthetic approach required a relatively long reaction time
as compared to the former one. Alternatively, based on the
previous experience in phosphine exchange reaction suggested
by Gladysz and co-workers,8 an improved synthetic route
involving two steps that require a common mononuclear
platinum(II) bis-alkynyl precursor for the subsequent synthesis
of a variety of face-to-face dinuclear platinum(II) alkynyl com-
plexes with various diphosphine ligands has been employed.
The first step involves the syntheses of mononuclear platinum-
(II) bis-alkynyl complexes with triphenylphosphine as auxiliary
ligands, trans-[Pt(PPh3)2(CtCR)2] (R = CtCC6H2(OMe)3-
3,4,5 and CtCC6H4-Carb-9), according to the well-documented
procedures.14 In the second step, the corresponding mono-
nuclear platinum(II) bis-alkynyl intermediate is subjected to a
facile phosphine exchange reaction with various diphosphines,
which has to be done under very dilute conditions in order to
avoid the formation of insoluble polymers. The purification of
Pt(1)-C(1)-C(2)
Pt(1)-C(12)-C(13)
C(1)-Pt(1)-P(1)
171.1(4)
170.7(4)
85.98(14)
P(1)-Pt(1)-P(2)
P(1)-Pt(1)-C(12)
C(1)-Pt(1)-C(12)
176.23(4)
91.40(14)
171.81(18)
[Pt2(μ-dmpm)2(CtCC6H4-Carb-9)4] (4)
˚
Bond Distances (A)
Pt(1)-P(1)
Pt(1)-P(2)
Pt(1)-C(1)
Pt(1)-C(21)
2.284(2)
2.279(2)
1.986(5)
1.993(5)
C(1)-C(2)
C(21)-C(22)
P(1)-C(41)
P(2)-C(41)
1.217(7)
1.204(7)
1.855(8)
1.785(7)
Bond Angles (deg)
Pt(1)-C(1)-C(2)
Pt(1)-C(21)-C(22)
C(1)-Pt(1)-P(1)
173.0(5)
178.0(5)
89.99(17)
P(1)-Pt(1)-P(2)
P(1)-Pt(1)-C(21)
C(1)-Pt(1)-C(21)
177.65(5)
90.39(16)
172.98(19)
[Pt2(μ-dppm)2{CtCC6H2(OMe)3-3,4,5}4 {Ag(MeCN)}2](BF4)2 (5)
3
˚
Bond Distances (A)
Pt(1)-P(1)
Pt(1)-P(2)
Ag(1)-C(1)
Ag(1)-C(2)
Ag(1)-N(1)
2.321(1)
2.303(1)
2.305(5)
2.343(5)
2.389(9)
Pt(1)-C(1)
Pt(1)-C(12)
C(1)-C(2)
C(12)-C(13)
P(1)-C(27)
2.012(5)
2.005(5)
1.222(7)
1.219(7)
1.840(5)
Bond Angles (deg)
P(1)-Pt(1)-P(2)
P(1)-Pt(1)-C(1)
Pt(1)-C(1)-C(2)
175.37(4)
93.87(15)
165.8(4)
P(1)-Pt(1)-C(12)
P(2)-Pt(1)-C(12)
Pt(1)-C(12)-C(13)
89.86(14)
93.97 (14)
168.2 (4)
[Pt2(μ-dppm)2{CtCC6H2(OMe)3-3,4,5}4 {Cu(MeCN)}2](PF6)2 (6)
3
˚
Bond Distances (A)
€
(22) (a) Andrae, D.; Haussermann, U.; Dolg, M.; Stoll, H.; Preuss, H.
Pt(1)-P(1)
Pt(1)-P(2)
Cu(1)-C(1)
Cu(1)-C(2)
Cu(1)-N(1)
2.317(1)
2.304(1)
2.087(5)
2.100(5)
2.077(8)
Pt(1)-C(1)
Pt(1)-C(12)
C(1)-C(2)
C(12)-C(13)
P(1)-C(27)
2.012(5)
2.009(5)
1.230(7)
1.220(7)
1.839(5)
Theor. Chim. Acta 1990, 77, 123. (b) Dolg, M.; Wedig, U.; Stoll, H.; Preuss,
H. J. Chem. Phys. 1987, 86, 866.
€
€
(23) Ehlers, A. W.; Bohme, M.; Dapprich, S.; Gobbi, A.; Hollwarth,
A.; Jonas, V.; Kohler, K. F.; Stegmann, R.; Veldkamp, A.; Frenking, G.
€
Chem. Phys. Lett. 1993, 208, 111.
(24) (a) Hehre, W. J.; Ditchfield, R.; Pople, J. A. J. Chem. Phys. 1972,
56, 2257. (b) Hariharan, P. C.; Pople, J. A. Theor. Chim. Acta 1973, 28, 213.
(c) Francl, M. M.; Pietro, W. J.; Hehre, W. J.; Binkley, J. S.; Gordon, M. S.;
Defrees, D. J.; Pople, J. A. J. Chem. Phys. 1982, 77, 3654.
(25) Pis Diez, R. MullPop; National University of La Plata: Argentina,
2003.
Bond Angles (deg)
P(1)-Pt(1)-P(2)
P(1)-Pt(1)-C(1)
Pt(1)-C(1)-C(2)
176.03(5)
92.01(16)
165.2(5)
P(1)-Pt(1)-C(12)
P(2)-Pt(1)-C(12)
Pt(1)-C(12)-C(13)
90.17(14)
93.50(14)
166.6(4)

Article
Organometallics, Vol. 29, No. 21, 2010 5563
Scheme 1. Synthetic Route of Complexes 1-4 by Phosphine Exchange Reaction
Scheme 2. Synthetic Route of Complexes 5 and 6 by Metal Ion Encapsulation
complexes 1-4 was accomplished by column chromatography
on silica gel using dichloromethane as eluent. Subsequent
recrystallization from dichloromethane-diethyl ether afforded
the products as pure air-stable greenish-yellow crystals. Scheme
1 summarizes the synthetic routes for complexes 1-4.
tetranuclearplatinum(II)-silver(I)and-copper(I) complexes
5 and 6, respectively. The selected bond distances and angles
of 1 and 3-6 are summarized in Table 2 and the Pt Pt
3 3 3
distances in Table 3.
In general, the dinuclear platinum(II) alkynyl complexes
show a face-to-face arrangement with two mutually eclipsed
platinum square planes bridged by two dppm ligands or
dmpm ligands to form an eight-membered ring (Pt-P-C-
P-Pt-P-C-P). Each platinum atom exhibits a distorted
square-planar geometry with the two alkynyl groups
[C-Pt-C, 170.42(13)-172.98(19)°] and the two bridging
dppm or dmpm phosphorus atoms [P-Pt-P, 174.12(3)-
177.65(5)°] arranged in a trans disposition. In the mixed-
metal complexes 5 and 6, each of the silver(I) and copper(I)
centers is π-coordinated to one pair of the preorganized
alkynyl groups that serve as η2-ligands and is coordinated
to one acetonitirile molecule in a trigonal-planar geometry.
The average CtC bond distances of complexes 5 and 6 are in
The structure of the face-to-face dinuclear complexes
shows two pairs of adjacent alkynyl ligands that have been
preorganized for the ready incorporation of other metal ions
through π-coordination.6a,b By the reaction of [Pt2(μ-dppm)2-
{CtCC6H2(OMe)3-3,4,5}4] with [M(MeCN)4]þ (M=Cu or
Ag), the tetranuclear mixed-metal platinum(II)-silver(I)
and -copper(I) complexes [Pt2(μ-dppm)2{CtCC6H2(OMe)3-
3,4,5}4{Ag(MeCN)}2](BF4)2 (5) and [Pt2(μ-dppm)2{Ct
CC6H2(OMe)3-3,4,5}4{Cu(MeCN)}2](PF6)2 (6) have been
prepared and isolated, in which the metal ions are sand-
wiched between the alkynyl groups within the same dinuclear
face-to-face complexes (Scheme 2).6a,b In contrast to the
homometallic dinuclear platinum(II) face-to-face com-
plexes, which are only sparsely soluble in dichloromethane,
the mixed-metal complexes are found to have good solubil-
ities in dichloromethane.
˚
the range 1.219(7)-1.230(7) A, slightly longer than the CtC
˚
bond distances (1.206(5)-1.220(5) A) in the related [Pt2-
(μ-dppm)2{CtCC6H2(OMe)3-3,4,5}4] (1) precursor. The
weakening of the CtC bond upon silver(I) or copper(I)
coordination is in accord with the π-coordination mode
of the alkynyl group and is in agreement with the observa-
tion of a lower CtC stretching frequency {2024(w) cm-1
X-ray Crystal Structures. The structures of 1 and 3-6
have been determined by X-ray crystallography. Figures 1 and 2
show the perspective drawings of the dinuclear platinum(II)
alkynyl phosphine complexes 1, 3, and 4 and the mixed-metal

5564 Organometallics, Vol. 29, No. 21, 2010
Leung et al.
Figure 1. Perspective drawings of (a) 1, (b) 3, and (c) 4 with atomic numbering scheme. The H atoms have been omitted for clarity.
Thermal ellipsoids are shown at the 30% probability level.
two Pt centers to approach each other more closely due to
the reduced electron density around the Pt centers as well
as the steric crowdedness of the two adjacent alkynyl
groups. Comparatively stronger Pt Pt interactions have
3 3 3
˚
been observed in the mixed-metal complexes, 5 [3.2022(2) A]
˚
and 6 [3.0117(2) A], in which the Pt Pt distances are
3 3 3
found to be significantly shorter than in their precursor
complex [Pt2(μ-dppm)2{CtCC6H2(OMe)3-3,4,5}4] (1)
˚
[3.3686(2) A]. The substantial decrease in the Pt Pt
3 3 3
distance upon metal ion encapsulation is ascribed to the
encapsulation of a silver(I) or copper(I) metal ion into the cleft
between the two alkynyl groups, which pushes the platinum
atoms into close proximity as a result of the reduced donor
strength of the alkynyl ligands as well as the steric demands
required upon silver(I) or copper(I) coordination. The larger
ionic radius of the silver(I) ion compared to that of the copper(I)
ion as well as the weaker Lewis acidity of Ag(I) than Cu(I) may
account for the longer Pt Pt distance in the silver(I)
analogue, 5, than that in the copper(I) analogue, 6.
Figure 2. Perspective drawings of complex cation of (a) 5 and
(b) 6 with atomic numbering scheme. The H atoms, counter-anions
and the phenyl rings of dppm have been omitted for clarity.
Thermal ellipsoids are shown at the 30% probability level.
3 3 3
Electronic Absorption Study. The electronic absorption
spectra of the face-to-face dinuclear platinum(II) phosphine
alkynyl complexes and mixed-metal tetranuclear platinum(II)-
silver(I) and -copper(I) complexes show intense absorp-
tion bands at ca. 272-282 and 342-432 nm in dichloro-
methane solution. A summary of the electronic absorption
spectral data is tabulated in Table 4. The high-energy
absorption bands at 272-282 nm of complexes 1-2 and
5-6 are assigned as π f π* (phosphine) and π f π*
(alkynyl ligand) intraligand (IL) transitions that are
slightly perturbed by the metal centers. This is because
the free phosphine ligands and alkynyl ligands also absorb
strongly in this region. In addition, the very large extinc-
tion coefficients of the complexes in this region, which
are much larger than those found in the free diphosphine
and alkynyl ligands, further support the assignment of
the high-energy absorption bands as IL transitions of
the diphosphine and alkynyl ligands, resulting from
the presence of multiple phosphine and alkynyl moieties.
in 5; 2005(w) cm-1 in 6 versus 2097 cm-1 in 1} in the IR
spectroscopy.
The Pt Pt distances of 1 and 3-6 are summarized
3 3 3
in Table 3. The Pt Pt distances in the range 3.0117(2)-
3.3686(2) A, which are comparable to that of the related
3 3 3
˚
6a
˚
[Pt2(μ-dppm)2(CtCPh)4] (Pt Pt 3.437(1) A) and [Pt2-
3 3 3
(μ-dppm)2(CN)4] (Pt Pt 3.301(1) A),4d suggest the presence
˚
3 3 3
of weak Pt Pt interaction. It is interesting to note that
3 3 3
the X-ray crystal structure of the dmpm analogue of
complex 3 shows a slight decrease in Pt
Pt distance by
0.06 A when compared to the dppm analogue of complex 1.
3 3 3
˚
In addition, it is found that the Pt Pt distances vary
3 3 3
with the nature of the alkynyl ligands. A shorter Pt Pt
3 3 3
distance has been found for complex 4 (Pt Pt distance
3 3 3
˚
3.2045(4) A), with the less electron-rich and more bulky
carbazole-based alkynyl ligand. The lower electron den-
sity and the bulkiness of the alkynyl ligand would cause the

Article
Organometallics, Vol. 29, No. 21, 2010 5565
Table 4. Electronic Absorption and Emission Data
absorption
emission
complex
λ/nm (ε/dm3 mol-1cm-1
)
medium (T/K)
λ/nm (τ0/μs)
1
274 sh (117 345), 342 (48 930), 378 (56 090)
CH2Cl2 (298)
solid (298)
solid (77)
643 (0.4)
470 (0.9)
465 (1.0)
460 (5.8)
648 (0.1)
615 (<0.1)
660 (4.8)
638 (10.2)
612 (0.4)
462 (0.5)
458 (8.5)
453 (6.6)
619 (0.2)
495 (0.3)
504 (3.8)
465 (11.7)
647 (0.3)
524 (1.3)
520 (5.1)
483 (5.4)
659 (0.2)
548 (1.4)
542 (7.2)
550 (5.8)
glass (77)a
CH2Cl2 (298)
solid (298)
solid (77)
2
3
4
5
6
296 (166 315), 312 sh (119 850), 346 sh (94 990), 380 (71 410)
280 (78 810), 318 sh (28 250), 342 sh (25 855)
296 (145 530), 316 (106 320), 344 (100 880), 372 sh (46 610)
282 sh (91 760), 368 (50 500), 404 (59 435)
glass (77)a
CH2Cl2 (298)
solid (298)
solid (77)
glass (77)a
CH2Cl2 (298)
solid (298)
solid (77)
glass (77)a
CH2Cl2 (298)
solid (298)
solid (77)
glass (77)a
CH2Cl2 (298)
solid (298)
solid (77)
282 sh (115 200), 388 (52 610), 432 (74 110)
glass (77)a
a In EtOH-MeOH (4:1 v/v).
The lowest energy absorption is found to be sensitive to the
nature of the alkynyl ligands, similar to those observed in
previous spectroscopic studies,6 suggesting the involvement of
the π*(CtCR) character in the LUMO. The absorption energy
in the order of [Pt2(μ-dppm)2{CtCC6H2(OMe)3-3,4,5}4] (1)
(342-378 nm)>[Pt2(μ-dppm)2(CtCC6H4-Carb-9)4] (2) (346-
380 nm) as well as Pt2(μ-dmpm)2{CtCC6H2(OMe)3-3,4,5}4]
(3) (318-342 nm) > [Pt2(μ-dmpm)2(CtCC6H4-Carb-9)4] (4)
(344-372 nm) seems to be dependent on the π-accepting ability
of RCtC, in which R=C6H2(OMe)3-3,4,5 < C6H4-Carb-9. The
lower π* orbital energy of CtCC6H4-Carb-9 could be attributed
to the more extended π-conjugation of the carbazole moiety.
{CtCC6H2(OMe)3-3,4,5}4] (3) (318-342 nm)>[Pt2(μ-dppm)2-
{CtCC6H2(OMe)3-3,4,5}4] (1) (342-378 nm) indicates that the
HOMO-LUMO energy gap becomes larger when the bridging
diphosphine ligand is changed from dppm to dmpm. A similar
trend has also been observed in the carbazole-based alkynyl
complexes, in which the energy follows the order [Pt2(μ-dmpm)2-
(CtCC6H4-Carb-9)4] (4) (344-372 nm) > [Pt2(μ-dppm)2-
(CtCC6H4-Carb-9)4] (2) (346-380 nm). It is worth
mentioning that the dppm and dmpm bridging diphosphine
ligands do not alter the structure of the system much, as reflected
by the similar Pt Pt distances observed in the X-ray crystal
3 3 3
structures of [Pt2(μ-dppm)2{CtCC6H2(OMe)3-3,4,5}4] (1)
˚
As mentioned previously, a shorter Pt Pt distance has
been found for the carbazole-based complex 4 (Pt Pt dis-
(3.3686(2) A) and [Pt2(μ-dmpm)2{CtCC6H2(OMe)3-3,4,5}4]
3 3 3
˚
(3) (3.3082(5) A). Given the less obvious role of the substituent
3 3 3
˚
tance 3.2045(4) A) relative to the trimethoxylphenyl-based
˚
complexes 1 (3.3686(2) A) and 3 (3.3082(5) A). In general,
groups on the diphosphine ligands, the effect of the nature of the
bridging diphosphine ligands on the low-energy absorption band
will be probed by the computational study (vide infra).
˚
previous spectroscopic works on dinuclear platinum(II)
systems6 show that a shorter Pt Pt distance would lead to a
Apart from the nature of the alkynyl and bridging ligands,
the coordination of d10 metal centers, namely, Ag(I) and
Cu(I), also has an influence on the energy of the low-energy
absorption bands. Figure 3 shows the overlaid electronic
absorption spectra of complexes 1, 5, and 6, which indicates a
red shift in the low-energy absorption band upon the co-
ordination of Ag(I) and Cu(I). In general, the mixed-metal
complexes always show a lower energy absorption band than
the dinuclear platinum(II) face-to-face precursor. The red
shift of the absorption band upon encapsulation of silver(I)
ions in 5 (368-404 nm) and copper(I) ions in 6 (388-432 nm)
compared to their precursor complex, [Pt2(μ-dppm)2(Ct
CC6H2(OMe)3-3,4,5)4] (1), may be ascribed to the narrower
HOMO-LUMO energy gap as a consequence of an increase
in the alkynyl π-acceptor ability as well as an increase in the
3 3 3
smaller HOMO-LUMO gap as a result of a stronger Pt Pt
3 3 3
interaction due to the antibonding overlap of the metal-filled d
orbitals in the HOMO and the bonding overlap of the metal
empty p orbitals in the LUMO. Computational studies in this
system showed that the effect of the Pt Pt distance on the
3 3 3
energy level of the LUMO would be more significant than that of
the HOMO, as the antibonding combination of the metal-filled
d orbitals is in either π or δ symmetry, while the bonding
combination of the metal empty p orbitals is in σ symmetry
(vide infra). Both the stronger π-accepting ability of CtCC6H4-
Carb-9 and the shorter Pt Pt distance for the carbazole-based
3 3 3
complexes would cause a narrowing of the HOMO-LUMO
energy gap. Such a red shift of the absorption band appears to be
in line with an assignment of the transition that contains a metal-
to-ligand charge transfer (MLCT) character perturbed by metal
d-p character resulting from the metal-metal interaction.
Interestingly, the bridging diphosphine ligands also have
been shown to have an effect on the electronic absorption
energy. The absorption energy in the order of [Pt2(μ-dmpm)2-
Pt Pt interaction upon metal ion coordination. The Lewis
3 3 3
acid Ag(I) and Cu(I) would withdraw electron density from
the alkynyl ligands upon coordination. Thus, this would give
rise to a lower lying π*(CtCR) orbital for the mixed-metal
tetranuclear platinum(II)-silver(I) and -copper(I) complexes.

5566 Organometallics, Vol. 29, No. 21, 2010
Leung et al.
Figure 4. Normalized emission spectra of [Pt2(μ-dppm)2{Ct
CC6H2(OMe)3-3,4,5}4] (1) (blue) and [Pt2(μ-dppm)2(CtCC6H4-
Carb-9)4] (2) (red) in CH2Cl2 at 298 K.
Figure 3. Electronic absorption spectra of [Pt2(μ-dppm)2{Ct
CC6H2(OMe)3-3,4,5}4] (1) (black), [Pt2(μ-dppm)2{CtCC6H2-
(OMe)3-3,4,5}4 {Ag(MeCN)}2](BF4)2 (5) (blue), and [Pt2-
3
(μ-dppm)2{CtCC6H2(OMe)3-3,4,5}4 {Cu(MeCN)}2](PF6)2 (6)
(red) in CH2Cl2 at 298 K.
3
Moreover, the antibonding combination of the Pt d orbitals
would be higher lying in energy, while the bonding combination
of the Pt empty p orbitals would be lower lying in energy when
the complexes show a stronger Pt Pt interaction, as reflected
3 3 3
by the shorter Pt Pt distance observed in the study of the
3 3 3
X-ray crystal structures of complexes 1, 5, and 6, in which the
˚
Pt Pt distances are 3.3686(2), 3.2022(2), and 3.0117(2) A,
3 3 3
respectively. As a result, the increase in the π-acceptor ability of
alkynyl ligands and the decrease in the Pt Pt distances would
3 3 3
cause a narrowing of the HOMO-LUMO energy gap. Such a
red shift of the absorption band is in accord with an assignment
of the transition that contains MLCT mixed with metal-centered
(MC) d-p character. The higher absorption energy of the bands
observed in 5 relative to its copper(I) analogue, 6, is ascribed to
the weaker Lewis acidity of AgI than CuI as well as the larger
ionic radius of Ag(I) than Cu(I), which would lead to a weaker
Figure 5. Normalized emission spectra of [Pt2(μ-dppm)2-
(CtCC6H2(OMe)3-3,4,5)4] (1) (black), [Pt2(μ-dppm)2(CtCC6H2-
(OMe)3-3,4,5)4 {Ag(MeCN)}2](BF4)2 (5) (blue), and [Pt2(μ-
3
dppm)2(CtCC6H2(OMe)3-3,4,5)4 {Cu(MeCN)}2](PF6)2 (6) (red)
in the solid state at 298 K.
3
π-accepting ability of the alkynyl ligands and a longer Pt Pt
3 3 3
separation upon AgI coordination, and hence a higher MLCT/
MC transition energy.
2012-2142 cm-1, typical of the phenyl ring deformation,
ν(C3-3 3 C) and ν(CtC) stretching modes in the ground state,
suggesting the involvement of the R-CtC moiety in the emissive
state. Similar spectroscopic assignments have also been sug-
gested in other related face-to-face diplatinum(II) systems.6
The emission band is also found to be sensitive to the
nature of the alkynyl ligands. A red shift in emission energy
for complexes 1 (643 nm) and 2 (648 nm) when compared to
[Pt2(μ-dppm)2(CtCPh)4] (620 nm)6a has been observed.
This has been similarly rationalized by the presence of the
more π-conjugated carbazole-based substituents in 2, which
would lower the π*(CtCR) orbital energy, as well as the
Luminescence Study. Upon excitation at λ > 350 nm, the
carbazole-based complexes 2 and 4 exhibit strong luminescence
in room-temperature fluid solution, room- and low-temperature
solid state, and low-temperature glass state, while the trimethox-
ybenzene-based complexes 1, 3, 5, and 6 are found to be weakly
emissive in room-temperature fluid solution. In general, all the
face-to-face dinuclear platinum(II) phosphine alkynyl com-
plexes 1-6 display emissions at ca. 612-659 nm in degassed
dichloromethane solution. 3 and 4, with dmpm as the bridging
ligand, are found to exhibit emissions at ca. 612-619 nm, which
are more blue-shifted with respect to their dppm analogues 1
and 2, which display the emission at ca. 643-648 nm in the fluid
solution. Moreover, mixed-metal tetranuclear platinum(II)-
silver(I) and -copper(I) complexes 5 (647 nm) and 6 (659 nm)
show a red-shifted emission as compared to that of their
precursor, 1 (643 nm), in the fluid solution. All complexes
exhibit relatively long-lived emissive states in the microsecond
range and are suggestive of their triplet parentage. An assign-
ment of the low-energy emission to an excited state of
3MLCT/3MC d-p origin is suggested. The emission and
excited-state lifetime data are summarized in Table 4, and
selected overlaid emission spectra of the complexes are depicted
in Figures 4 and 5. In the solid and glass state at 77 K, the
emission spectra are dominated by vibronic structures with
vibrational progressional spacings of ca. 1585-1618 and
presence of a shorter Pt Pt separation in complex 1
˚
3 3 3
(3.36861(18) A) than that in [Pt2(μ-dppm)2(CtCPh)4]
5a
˚
(3.437 A). Both the increase in the π-accepting ability of
the alkynyl group and the shortening of the Pt Pt distance
3 3 3
would lead to the narrowing of the HOMO-LUMO energy
gap, as discussed in the electronic absorption studies, and
thus a lower emission energy is observed for both complexes
1 and 2. Furthermore, it is interesting to note that the emis-
sion energy in the fluid solution is in the order of [Pt2(μ-dppm)2-
{CtCC6H2(OMe)3-3,4,5}4] (1) (643 nm) > [Pt2(μ-dppm)2-
(CtCC6H4-Carb-9)4] (2) (648 nm) and [Pt2(μ-dmpm)2{Ct
CC6H2(OMe)3-3,4,5}4] (3) (612 nm) > [Pt2(μ-dmpm)2(Ct
CC6H4-Carb-9)4] (4) (619 nm), similar to the trend observed
in the electronic absorption studies.

Article
Organometallics, Vol. 29, No. 21, 2010 5567
Figure 6. Spatial plot (isovalue value = 0.02) of selected molecular orbitals in 1.
In line with the shift observed in the electronic absorption
spectral studies, a lower emission energy of the bands in the
dppm analogues (643-648 nm) relative to the dmpm coun-
terparts (612-619 nm) has been observed in the fluid solu-
tion. The emission energy in the order of [Pt2(μ-dmpm)2{Ct
CC6H2(OMe)3-3,4,5}4] (3) (612 nm) > [Pt2(μ-dppm)2{Ct
CC6H2(OMe)3-3,4,5}4] (1) (643 nm) in the room-temperature
fluid solution indicates a larger transition energy when the
bridging diphosphine ligand is changed from dppm to dmpm.
A similar trend has also been observed in the carbazole-based
alkynyl complexes, in which the emission energy follows the
order [Pt2(μ-dmpm)2(CtCC6H4-Carb-9)4] (4) (619 nm) >
Pt2(μ-dppm)2(CtCC6H4-Carb-9)4] (2) (648 nm) in the room-
temperature fluid solution.
energy of 5 and 6 was observed. As in the electronic absorp-
tion studies, the slightly higher emission energy of the mixed-
metal silver(I)-platinum(II) complex 5 (647 nm) than its
copper analogue 6 (659 nm) has been similarly ascribed to the
weaker Lewis acidity of Ag(I) as well as the larger ionic
radius of Ag(I) than Cu(I).
Computational Study. In order to provide an in-depth under-
standing of the origin of the low-energy electronic absorption
band of the face-to-face dinuclear platinum(II) complexes,
time-dependent density functional theory (TDDFT) calcula-
tions associated with the conductor-like polarizable continuum
model (CPCM) were performed to compute the first three
lowest lying singlet-singlet transitions of [Pt2(μ-dppm)2-
{CtCC6H2(OMe)3-3,4,5}4] (1), [Pt2(μ-dmpm)2{CtCC6H2-
(OMe)3-3,4,5}4] (3), and [Pt2(μ-dmpm)2(CtCC6H4-Carb-9)4]
(4) on the basis of the experimentally determined geometries
obtained from X-ray crystallographic diffraction data (for
details, see the Experimental Section).
In general, the first four highest lying occupied orbitals
in each of 1, 3, and 4 are dominated by the four linear
combinations of the highest occupied π orbitals of the four
CtCR ligands. In the HOMO and HOMO-1 orbitals,
orbital mixing from the metal dπ orbitals in an out-of-phase
fashion can be found. The LUMO is the σ-bonding combi-
nation of the empty metal p orbitals from the two metal
centers with the P-C σ* orbitals26 of the bridging diphos-
phine ligands and π* orbitals of the alkynyl ligands con-
tributing in a bonding fashion. Figure 6 and Figure S1 depict
these orbitals for complexes 1, and 3 and 4, respectively.
Upon encapsulation of the Lewis acid metal ions Ag(I)
and Cu(I), a lower emission energy of 5 and 6 than the
precursor complex 1 in room-temperature fluid solution is
observed, consistent with the trend observed in the electronic
absorption studies. The coordination of Ag(I) and Cu(I) ions
would lead to a shortening of the Pt Pt distance since the
3 3 3
bending of the C-Pt-C bond would force the two Pt centers
into close proximity. This, together with the reduction of
electron density at the Pt center as a result of the reduction of
the donor strength of the alkynyl ligands upon π-donation to
Ag(I) and Cu(I), would further bring the two Pt centers into
close proximity. In addition, the coordination of the Lewis
acidic Ag(I) and Cu(I) centers to the alkynyl unit would also
lower the π* orbital energy of the alkynyls. Both the contrac-
tion of the Pt Pt distance and the increase in π-accepting
3 3 3
ability of the alkynyl group would result in a narrowing of
the HOMO-LUMO energy gap, and hence a lower emission
(26) Vogler, A.; Kunkely, H. Coord. Chem. Rev. 2002, 230, 243.

5568 Organometallics, Vol. 29, No. 21, 2010
Leung et al.
Table 5. TDDFT/CPCM Vertical Excitation Wavelength (nm) of
the First Three Lowest Lying Singlet Excited States of 1, 3, and 4
Table 6. Mulliken Percentage Compositions of Selected Molecular
Orbitals (H = HOMO and L = LUMO) of the Complexesa
vertical
excitation
1
3
4
transition
coefficient
wavelength
(nm)
Pt dppm CtCR Pt dmpm CtCR Pt dmpm CtCR
complex
Sn
excitationa
fb
L
H
22
15
48
1
1
5
4
31
84
86
82
95
36
12
10
13
16
28
1
1
3
2
37
87
89
84
82
29
14
19
21
1
20
0
1
3
1
51
86
81
76
98
1
S1
S2
S3
S1
S2
S3
S1
S2
S3
H-1 f L
H f L
H-2 f L
H f L
H-1 f L
H-3 f L
H f L
H-1 f L
H-2 f L
0.68
0.68
0.65
0.68
0.67
0.65
0.67
0.63
0.62
0.000
0.590
0.184
0.323
0.000
0.000
0.001
1.221
0.809
362
362
338
341
337
325
365
357
344
H-1 13
H-2 13
3
4
H-3
1
a The compositions were expressed in terms of contributions from the
two Pt metal centers (Pt), four alkynyl ligands (CtCR), and two bridging
diphosphine ligands (dppm for 1 and dmpm for 3 and 4).
ligand, the decrease in the Pt Pt separation and increase in
3 3 3
a Orbitals involved in the major excitation (H = HOMO and L =
the contribution of the alkynyl ligand upon coordination of
the metal ions would decrease the LUMO level to a more
significant extent relative to the decrease in the HOMO level,
leading to the red shift of the low-energy absorption and
emission bands upon coordination of the metal ions. As the
acetonitrile ligands in the X-ray crystal structures of the
mixed-metal complexes 5 and 6 showed cross-like disorder,
with the acetonitrile ligands largely deviated from linear
geometry, showing average N-C-CH3 angles of 158° for
5 and 150° for 6, and a bent coordination to the metal center
with average M-N-C angles of 130° and 131° for 5 and 6,
respectively, attempts have been made to perform the
TDDFT/CPCM calculation for 6 on the basis of its X-ray
crystal structure with the Cu-N-C and N-C-CH3 angles
in each of the acetonitrile coordination set at 180°. While the
computational results have reproduced the trend in the
electronic absorption spectral shift of 6 relative to that of 1
and the larger decrease in the LUMO level relative to the
HOMO level upon coordination of the metal ion, the calcu-
lated data based on the crystal structure of 6 did not provide
a good match with the experimental data, probably due to
the distorted solid-state structure, which could not well
represent the structure in solution.27
LUMO). b Oscillator strengths.
The computed singlet-singlet transitions and the percent-
age composition of selected molecular orbitals for 1, 3, and 4
are listed in Tables 5 and 6, respectively. These transitions
involve the excitation from the π orbitals of the alkynyl
ligand mixed with the metal d orbitals to the LUMO. The
transitions for 1 (S0 f S2) and 3 (S0 f S1) with the largest
oscillator strength are mainly the excitation from the HOMO
to the LUMO, while for 4 the S0 f S2 transition with the
largest oscillator strength involves the HOMO-1 f LUMO
excitation. The excitation wavelengths for the transitions in
1, 3, and 4 are computed to be 362, 341, and 357 nm,
respectively. The red shift of the calculated transitions upon
going from 3 to 1 and from 3 to 4 is in agreement with the
trend of the low-energy absorption band observed in the
electronic absorption spectra.
The energy level of the LUMO in 3 (-0.87 eV) is found to
be higher lying than that of 1 (-0.98 eV). Based on the
calculated percentage composition of the molecular orbitals
in Table 6, the contribution of the bridging diphosphine
ligands to the LUMO in 1 is larger than that in 3. As
mentioned above, the LUMO is composed of the P-C σ*
antibonding orbitals of the diphosphine ligands. The mixing
of the π* orbitals from the phenyl rings into the P-C σ*
antibonding orbitals would stabilize the LUMO in the dppm
system. It is interesting to note that the HOMO level in 3
(-5.29 eV) is found to be lower lying in energy than that in 1
(-5.12 eV). This is in contrast to the expectation that the
stronger σ-donating dmpm ligand when compared to the
dppm ligand would raise the HOMO that contains the metal
and alkynyl characters. These unexpected findings might be
ascribed to the greater degree of conjugation in the com-
plexes with the phenyl rings attached to the P atoms in the
dppm ligands, which is in contrast to the methyl groups in the
dmpm ligands. Both the decrease in the HOMO level and
the increase in the LUMO level in 3 would increase the transi-
tion energy. For 4, the red shift of the transition energy rela-
tive to 3 is due to the fact that the LUMO level in 4 (-1.11 eV)
is lower in energy than that in 3. More alkynyl contribution
to the LUMO for 4 relative to 3 is found (Table 6), consistent
with a stronger π-accepting ability of the carbazole-containing
alkynyl ligand.
On the basis of the spectroscopic studies and TDDFT/
CPCM calculations, the lowest energy absorption of the face-
to-face diplatinum alkynyl complexes can be assigned as an
admixture of the MLCT transition from the Pt d orbitals to the
π* orbitals of the alkynyl ligands and the P-Cσ*orbitalsofthe
bridging diphosphine ligands and the intraligand π-π* transi-
tion of the alkynyl ligands. For these transitions, some mixing
of the MC d-p transition can also be found. Similarly, the low-
energy emission has been assigned to be derived from triplet
states of a mixture of MLCT, IL, and MC character.
Conclusion
In summary, the synthesis, structures, and luminescent
behavior of a series of face-to-face dinuclear platinum(II)
alkynyl complexes bridged by the two diphosphine ligands
together with their mixed-metal tetranuclear platinum(II)-
silver(I) and -copper(I) complexes have been studied. The
origin and the energy of the lowest energy absorption and
emission in the complexes depend on the nature of both
the alkynyl and bridging diphosphine ligands, the Pt Pt
3 3 3
The coordination of the Lewis acid metal ions Agþ and
Cuþ to the alkynyl ligands of 1 would lead to the decrease of
both the energy level of the filled and unfilled orbitals, due to
the electron-withdrawing properties of the cations. How-
ever, since the LUMO consists of the bonding combination
of the metal p orbitals with the π* orbitals of the alkynyl
(27) The first singlet-singlet transition of 6 was computed at 374 nm,
which is mainly contributed from the HOMO f LUMO excitation, and
was found to show a red shift when compared to 1 (362 nm), in line with
the trend observed in the electronic absorption spectra. The small shift of
the calculated transitions from 1 to 6 was probably due to the fact that
the crystal structure for 6 could not represent the structure in solution.

Article
Organometallics, Vol. 29, No. 21, 2010 5569
separation, and the nature of the encapsulated metal ions on the
alkynyl ligands. In general, stronger π-accepting abilities of the
alkynyl ligands, greater degree of π-conjugation of the sub-
stituent groups attached to the P atoms of the bridging diphos-
W.H.L. acknowledges the support by the Seed Funding
Programme for Basic Research from The University of
Hong Kong (200905159002). S.Y.-L.L. acknowledges the
receipt of a postgraduate studentship, administered by
The University of Hong Kong. Technical assistance in
the crystallographic data refinement at the later stage by
Dr. L. Szeto is gratefully acknowledged. We also thank the
Computer Center at The University of Hong Kong for
providing the computational resources.
phine ligands, and shorter Pt Pt separations will lead to a red
3 3 3
shift in the lowest energy absorption and emission. The TDDFT/
CPCM calculations support the spectroscopic assignments.
Acknowledgment. V.W.-W.Y. acknowledges the sup-
port from The University of Hong Kong under the Dis-
tinguished Research Achievement Award Scheme and the
URC Strategic Research Theme on Molecular Materials.
This work has been supported by the University Grants
Committee Areas of Excellence Schemes (AoE/P-03/08).
Supporting Information Available: Crystallographic data and
details for complexes 1, and 3-6. Figure S1, containing selected
molecular orbitals for complexes 3 and 4. This material is
available free of charge via the Internet at http://pubs.acs.org.