Synthesis, luminescence, electrochemistry, and ion-binding studies of platinum(II) terpyridyl acetylide complexes

Article abstract of DOI:10.1021/om010336x

A series of platinum(II) terpyridyl acetylide complexes, [Pt(trpy)(C≡CR)]PF₆ (R = C₆H₅, C₆H₄Cl-4, C₆H₄CH₃-4, C₆H₄OCH₃-4, C₆H₄NO₂-4, benzo-15-crown-5, C₆H₃-(OCH₃)₂-3,4), have been synthesized and characterized. Their luminescence and electrochemical behaviors have been studied. The ion-binding properties of [Pt(trpy)(C≡C-benzo-15-crown-5)]PF₆ and the X-ray crystal structure of [Pt(trpy)(C≡CC₆H₅)]PF₆ are also reported.

Full text of DOI:10.1021/om010336x

4476
Organometallics 2001, 20, 4476-4482
Syn th esis, Lu m in escen ce, Electr och em istr y, a n d
Ion -Bin d in g Stu d ies of P la tin u m (II) Ter p yr id yl Acetylid e
Com p lexes
Vivian Wing-Wah Yam,* Rowena Pui-Ling Tang, Keith Man-Chung Wong, and
Kung-Kai Cheung
Department of Chemistry, The University of Hong Kong, Pokfulam Road,
Hong Kong SAR, People’s Republic of China
Received April 24, 2001
A series of platinum(II) terpyridyl acetylide complexes, [Pt(trpy)(CtCR)]PF6 (R ) C6H5,
C6H4Cl-4, C6H4CH3-4, C6H4OCH3-4, C6H4NO2-4, benzo-15-crown-5, C6H3-(OCH3)2-3,4), have
been synthesized and characterized. Their luminescence and electrochemical behaviors have
been studied. The ion-binding properties of [Pt(trpy)(CtC-benzo-15-crown-5)]PF6 and the
X-ray crystal structure of [Pt(trpy)(CtCC6H5)]PF6 are also reported.
In tr od u ction
weak metal-metal interactions.2 The platinum(II) terpy-
ridyl complexes have attracted considerable attention
in recent years, mainly due to their interesting spec-
troscopic behavior3 and useful physical and biological
properties.5 Despite the fact that a number of spectro-
scopic studies on the platinum(II) terpyridyl systems are
known,3 the utilization of such systems for applications
in molecular recognition and chemosensing work is
rare,5a-c,6 in particular, those related to the crown ether-
containing platinum(II) systems and their ion-binding
properties.6 The study of crown ethers and other related
inclusion compounds in molecular recognition, as well
as the design of molecular sensors and probes, has been
of growing interest in the field of host-guest chemistry,
and important review papers devoted to the chemistry
of crown ethers and their analytical, chemical, and
biological applications have been published.7 As a
continuation of our studies on the platinum(II) crown
ether-containing system,6 we have synthesized the first
platinum(II) alkynyl terpyridyl complex with ethynyl-
benzo-15-crown-5 as the ligand in this work. Although
alkynyl complexes of platinum(II) are known,4 most of
them are confined to platinum(II) phosphines4a-j and
diimines,4k-m with no reports on the platinum(II) terpy-
ridyl system. In addition, a series of noncrown ether-
containing analogues have been synthesized to provide
insights into the spectroscopic origin of the electronic
absorption and emission properties of this class of
compounds. Herein are reported the synthesis, elec-
tronic absorption, luminescence, electrochemical, and
The chemistry of square-planar platinum(II) com-
plexes has been extensively studied in the past few
decades due to their rich spectroscopic and photophysi-
cal behavior,1-4 as well as their propensity to exhibit
* To whom correspondence should be addressed. Tel: (852)2859-
2153. Fax: (852)2857-1586. E-mail: wwyam@hku.hk.
(1) (a) Schindler, J . W.; Fukuda, R. C.; Adamson, A. W. J . Am. Chem.
Soc. 1982, 104, 3596. (b) Biedermann, J .; Gliemann, G.; Klement, U.;
Range, K. J .; Zabel, M. Inorg. Chem. 1990, 29, 1884. (c) Chan, C. W.;
Lai, T. F.; Che, C. M.; Peng, S. M. J . Am. Chem. Soc. 1993, 115, 11245.
(d) Miskowski, V. M.; Houlding, V. H.; Che, C. M.; Wang, Y. Inorg.
Chem. 1993, 32, 2518. (e) Yam, V. W. W.; Yeung, P. K. Y.; Cheung, K.
K. J . Chem. Soc., Chem. Commun. 1995, 267. (f) Daws, C. A.; Exstrom,
C. L.; Sowa, J . R., J r.; Mann, K. R. Chem. Mater. 1997, 9, 363. (g)
Yersin, H.; Humbs, W.; Strasser, J . Coord. Chem. Rev. 1997, 159, 325.
(2) (a) Che, C. M.; Butler, L. G.; Gray, H. B. J . Am. Chem. Soc. 1981,
103, 7796. (b) Rice, S. F.; Gray, H. B. J . Am. Chem. Soc. 1983, 105,
4571. (c) Miskowski, V. M.; Houlding, V. H. Inorg. Chem. 1989, 28,
1529. (d) Miskowski, V. M.; Houlding, V. H. Inorg. Chem. 1991, 30,
4446. (e) Novoa, J . J .; Aullon, G.; Alemany, P.; Alvarez, S. J . Am. Chem.
Soc. 1995, 117, 7169. (f) Tzeng, B. C.; Fu, W. F.; Che, C. M.; Chao, H.
Y.; Cheung, K. K.; Peng, S. M. J . Chem. Soc., Dalton Trans. 1999, 1017.
(3) (a) Aldridge, T. K.; Stacy, E. M.; McMillin, D. R. Inorg. Chem.
1994, 33, 722. (b) Lai, S. W.; Chan, M. C. W.; Cheung, K. K.; Che, C.
M. Inorg. Chem. 1999, 38, 4262. (c) Bu¨chner, R.; Cunningham, C. T.;
Field, J . S.; Haines, R.; McMillin, D. R.; Summerton, G. C. J . Chem.
Soc., Dalton Trans. 1999, 711. (d) Bu¨chner, R.; Field, J . S.; Haines, R.
J .; Cunningham, C. T.; McMillin, D. R. Inorg. Chem. 1997, 36, 3952.
(e) Michalec, J . F.; Bejune, S. A.; McMillin, D. R. Inorg. Chem. 2000,
39, 2708.
(4) (a) Baralt, E.; Boudreaux, E. A.; Demas, J . N.; Lenhert, P. G.;
Lukehart, C. M.; McPhail, D. R.; Myers, J . B., J r.; Sacksteder, L.; True,
W. R. Organometallics 1989, 8, 2417. (b) Yam, V. W. W.; Chan, L. P.;
Lai, T. F. Organometallics 1993, 12, 2197. (c) Yam, V. W. W.; Yu, K.
L.; Cheung, K. K. J . Chem. Soc., Dalton Trans. 1999, 2913. (d) Yam,
V. W. W.; Yu, K. L.; Wong, K. M. C.; Cheung, K. K. Organometallics
2001, 20, 721. (e) Masai, H.; Sonogashira, K.; Hagihara, N. Bull. Chem.
Soc. J pn. 1971, 44, 2226. (f) Sacksteder, L.; Baralt, E.; DeGraff, B. A.;
Lukehart, C. M.; Demas, J . N. Inorg. Chem. 1991, 30, 3955. (g)
Sacksteder, L.; Baralt, E.; DeGraff, B. A.; Lukehart, C. M.; Demas, J .
N. Inorg. Chem. 1991, 30, 2468. (h) Kwok, W. M.; Phillips, D. L.; Yeung,
P. K. Y.; Yam, V. W. W. J . Phys. Chem. A 1997, 101, 9286. (i) 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. (j) Choi, C. L.; Cheng, Y. F.; Yip, C.; Phillips, D. L.; Yam, V. W.
W. Organometallics 2000, 19, 3192. (k) Chan, C. W.; Cheng, L. K.; Che,
C. M. Coord. Chem. Rev. 1994, 132, 87. (l) Adams, C. J .; J ames, S. L.;
Liu, X.; Raithby, P. R.; Yellowless, L. J . J . Chem. Soc., Dalton Trans.
2000, 63. (m) Hissler, M.; Connick, W. B.; Geiger, D. K.; McGarrah, J .
E.; Lipa, D.; Lachicotte, R. J .; Eisenberg, R. Inorg. Chem. 2000, 39,
447.
(5) (a) J ennette, K. W.; Gill, J . T.; Sadownick, J . A.; Lippard, S. J .
J . Am. Chem. Soc. 1976, 98, 6159. (b) Lippard, S. J . Acc. Chem. Res.
1978, 11, 211. (c) Peyratout, C. S.; Aldridge, T. K.; Crites, D. K.;
McMillin, D. R. Inorg. Chem. 1995, 34, 4484. (d) Wong, Y. S.; Lippard,
S. J . J . Chem. Soc., Chem. Commun. 1977, 824.
(6) Yam, V. W. W.; Tang, R. P. L.; Wong, K. M. C.; Ko, C. C.; Cheung,
K. K. Inorg. Chem. 2001, 40, 571.
(7) (a) Czarnik, A. W. Fluorescent Chemosensors for Ion and Mo-
lecular Recognition; American Chemical Society: Washington, DC,
1992. (b) Fabbrizzi, L.; Poggi, A. Chem. Soc. Rev. 1995, 197. (c) De
Silva, A. P.; Gunaratne, H. Q. N.; Gunnlaugsson, T.; Huxley, A. J . M.;
McCoy, C. P.; Rademacher, J . T.; Rice, T. E. Chem. Rev. 1997, 97, 1515.
(d) Yam, V. W. W.; Lo, K. K. W. Coord. Chem. Rev. 1999, 184, 157.
10.1021/om010336x CCC: $20.00 © 2001 American Chemical Society
Publication on Web 09/22/2001

Platinum(II) Terpyridyl Acetylide Complexes
Organometallics, Vol. 20, No. 22, 2001 4477
8.69 (d, 2H, J ) 5.0 Hz, trpy). IR (KBr disk, ν/cm-1): 2114
(w), ν(CtC). Positive ESI-MS: m/z 559 [M - PF6]+, 1263 [2M
- PF6]+. Anal. Calcd for C24H18F6N3OPPt: C, 40.90; H, 2.56;
N, 5.96. Found: C, 40.87; H, 2.52; N, 5.94.
ion-binding properties of a series of platinum(II) alkynyl
terpyridyl complexes. The X-ray crystal structure of [Pt-
(trpy)(CtCC6H5)]PF6 has also been determined.
[P t(tr p y)(CtCC6H4NO2-4)]P F 6 (5). The procedure was
similar to that for complex 1, except (4-nitrophenyl)acetylene
(58 mg, 0.43 mmol) was used in place of phenylacetylene.
Exp er im en ta l Section
Ma ter ia ls a n d Rea gen ts. Dichloro(1,5-cyclooctadiene)-
platinum(II) and 2,2′:6′,2′′-terpyridine were obtained from
Strem Chemicals Inc. Phenylacetylene and (4-chlorophenyl)-
acetylene were obtained from Aldrich Chemical Co. (4-Meth-
ylphenyl)acetylene and (4-methoxyphenyl)acetylene were pur-
chased from Maybridge Chemical Co. Ltd. (4-Nitrophenyl)-
acetylene,8 4-ethynylbenzo-15-crown-5,9 and (3,4-dimethoxy-
phenyl)acetylene9 were synthesized according to literature
methods. [Pt(trpy)(MeCN)](OTf)2 was synthesized by modifica-
tion of the literature method.3d All solvents were purified and
distilled using standard procedures before use. All other
reagents were of analytical grade and were used as received.
1
Yield: 70%. H NMR (300 MHz, (CD3)2SO, 298 K, relative to
Me4Si, δ/ppm): 7.68 (d, 2H, J ) 8.9 Hz, -C6H4-), 8.23 (d, 2H,
J ) 8.9 Hz, -C6H4-), 7.85 (t, 2H, J ) 6.6 Hz, trpy), 8.46 (t,
2H, J ) 7.9 Hz, trpy), 8.55 (m, 5H, trpy), 8.98 (d, 2H, J ) 5.6
Hz, trpy). IR (KBr disk, ν/cm-1): 2117 (s), ν(CtC). Positive
ESI-MS: m/z 573 [M - PF6]+, 1291 [2M - PF6]+. Anal. Calcd
for C23H14F6N4O2PPt: C, 38.44; H, 1.95; N, 7.80. Found: C,
38.46; H, 1.92; N, 7.65.
[P t(tr p y)(CtC-ben zo-15-cr ow n -5)]P F 6 (6). The proce-
dure was similar to that for complex 1, except 4-ethynylbenzo-
15-crown-5 (130 mg, 0.45 mmol) and triethylamine (60 mg,
0.59 mmol) was used in place of phenylacetylene and sodium
hydroxide. Yield: 73%. 1H NMR (300 MHz, CD3CN, 298 K,
relative to Me4Si, δ/ppm): 3.65 (m, 8H, -OCH2-), 3.85 (m,
4H, -OCH2-), 4.10 (m, 4H, C6H3OCH2-), 6.78 (s, 1H, -C6H3-),
6.87 (d, 2H, J ) 4.0 Hz, -C6H3-), 7.59 (t, 2H, J ) 6.6 Hz,
trpy), 7.97 (m, 4H, trpy), 8.21 (m, 3H, trpy), 8.75 (d, 2H, J )
4.9 Hz, trpy). IR (KBr disk, ν/cm-1): 2116 (w), ν(CtC). Positive
ESI-MS: m/z 719 [M - PF6]+, 1583 [2M - PF6]+. Anal. Calcd
for C31H30N3O5PtPF6: C, 43.06; H, 3.47; N, 4.86. Found: C,
43.11; H, 3.46; N, 4.91.
[P t(tr p y)(CtCC6H5)]P F 6 (1). To a stirred solution of
phenylacetylene (44 mg, 0.43 mmol) in methanol was added
sodium hydroxide (23 mg, 0.58 mmol). The resultant solution
was stirred at room temperature for 30 min. [Pt(trpy)(MeCN)]-
(OTf)2 (300 mg, 0.39 mmol) was added to the reaction mixture,
which turned to a deep red solution immediately and was then
stirred for 12 h at room temperature. The mixture was filtered,
and a saturated solution of ammonium hexafluorophosphate
in methanol was added. The product was isolated, washed with
methanol, and dried. Subsequent recrystallization by diffusion
of diethyl ether vapor into an acetonitrile solution of the
[P t(tr p y)(CtCC6H3-(OCH3)2-3,4)]P F 6 (7). The procedure
was similar to that for complex 1, except (3,4-dimethoxyphen-
yl)acetylene (70 mg, 0.43 mmol) was used in place of phenyl-
acetylene. 1H NMR (300 MHz, CD3CN, 298 K, relative to
Me4Si, δ/ppm): 3.87 (s, 3H, -OCH3), 3.89 (s, 3H, -OCH3), 6.95
(m, 3H, -C6H3-), 7.69 (t, 2H, J ) 6.7 Hz, trpy), 8.12 (t, 4H, J
) 8.5 Hz, trpy), 8.30 (m, 3H, trpy), 8.99 (d, 2H, J ) 5.1 Hz,
trpy). IR (KBr disk, ν/cm-1): 2109 (w), ν(CtC). Positive ESI-
MS: m/z 589 [M - PF6]+, 1323 [2M - PF6]+. Anal. Calcd for
1
product gave 1 as dark purple crystals. Yield: 60%. H NMR
(300 MHz, CD3CN, 298 K, relative to Me4Si, δ/ppm): 7.31 (m,
5H, -Ph), 7.55 (t, 2H, J ) 6.5 Hz, trpy), 8.13 (m, 7H, trpy),
8.67 (d, 2H, J ) 5.1 Hz, trpy). IR (KBr disk, ν/cm-1): 2125
(m), ν(CtC). Positive ESI-MS: m/z 529 [M - PF6]+, 1203 [2M
- PF6]+. Anal. Calcd for C23H16F6N3PPt: C, 40.90; H, 2.37; N,
6.23. Found: C, 40.87; H, 2.36; N, 6.23.
[P t(tr p y)(CtCC6H4Cl-4)]P F6 (2). The procedure was simi-
lar to that for complex 1, except (4-chlorophenyl)acetylene (59
mg, 0.43 mmol) was used in place of phenylacetylene. Yield:
C
25H20F6N3O2PPt: C, 40.87; H, 2.72; N, 5.72. Found: C, 40.81;
H, 2.76; N, 5.91.
1
59%. H NMR (300 MHz, (CD3)2SO, 298 K, relative to Me4Si,
P h ysica l Mea su r em en ts a n d In str u m en ta tion . UV/vis
spectra were obtained on a Hewlett-Packard 8452A diode array
spectrophotometer, IR spectra as KBr disks on a Bio-Rad
FTS-7 Fourier transform infrared spectrophotometer (4000-
400 cm-1), and steady-state excitation and emission spectra
on a Spex Fluorolog 111 spectrofluorometer. Solid-state pho-
tophysical studies were carried out with solid samples con-
tained in a quartz tube inside a quartz-walled Dewar flask.
Measurements of the butyronitrile glass or solid-state samples
at 77 K were similarly conducted with liquid nitrogen filled
in the optical Dewar flask. Excited-state lifetimes of solution
samples were measured 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
pulsed Nd:YAG laser (10 Hz). For self-quenching studies, the
rate constants of emission decay (kobsd ) 1/τ) are well modeled
by the Stern-Volmer expression (eq 1):
δ/ppm): 7.41 (d, 2H, J ) 8.3 Hz, -C6H4-), 7.49 (d, 2H, J )
8.3 Hz, -C6H4-), 7.87 (t, 2H, J ) 6.5 Hz, trpy), 8.46 (t, 2H, J
) 7.6 Hz, trpy), 8.57 (m, 5H, trpy), 9.04 (d, 2H, J ) 5.4 Hz,
trpy). IR (KBr disk, ν/cm-1): 2120 (m), ν(CtC). Positive ESI-
MS: m/z 564 [M - PF6]+, 1271 [2M - PF6]+. Anal. Calcd for
C
23H15ClF6N3PPt: C, 39.98; H, 2.12; N, 5.93. Found: C, 39.95;
H, 2.11; N, 5.92.
[P t(tr p y)(CtCC6H4CH3-4)]P F 6 (3). The procedure was
similar to that for complex 1, except (4-methylphenyl)acetylene
(51 mg, 0.43 mmol) was used in place of phenylacetylene.
Yield: 69%. 1H NMR (300 MHz, CD3CN, 298 K, relative to
Me4Si, δ/ppm): 2.41 (s, 3H, -CH3), 7.19 (d, 2H, J ) 7.8 Hz,
-C6H4-), 7.27 (d, 2H, J ) 7.8 Hz, -C6H4-), 7.64 (t, 2H, J )
6.0 Hz, trpy), 8.08 (t, 4H, J ) 7.6 Hz, trpy), 8.26 (m, 3H, trpy),
8.90 (d, 2H, J ) 5.6 Hz, trpy). IR (KBr disk, ν/cm-1): 2108
(w), ν(CtC). Positive ESI-MS: m/z 543 [M - PF6]+, 1231 [2M
- PF6]+. Anal. Calcd for C24H18F6N3PPt: C, 41.86; H, 2.62; N,
6.10. Found: C, 41.84; H, 2.65; N, 6.11.
kobsd ) kq[Pt] + k0
(1)
[P t(tr p y)(CtCC6H4OCH3-4)]P F 6 (4). The procedure was
similar to that for complex 1, except (4-methoxyphenyl)-
acetylene (57 mg, 0.43 mmol) was used in place of phenyl-
acetylene. Yield: 70%. 1H NMR (300 MHz, CD3CN, 298 K,
relative to Me4Si, δ/ppm): 3.86 (s, 3H, -OCH3), 6.92 (d, 2H, J
) 8.8 Hz, -C6H4-), 7.20 (d, 2H, J ) 8.8 Hz, -C6H4-), 7.54 (t,
2H, J ) 5.9 Hz, trpy), 7.93 (m, 4H, trpy), 8.15 (m, 3H, trpy),
where kq is the self-quenching rate constant, [Pt] is the
concentration of the platinum complex, and k0 ) 1/τ0 is the
rate constant of excited-state decay at infinite dilution. Lu-
minescence quantum yields were measured by the optical
dilute method reported by Demas and Crosby.10a The lumi-
nescence quantum yield of the sample was determined accord-
ing to eq 2
(8) Takahashi, S.; Kuroyama, Y.; Sonogashira, K.; Hagihara, N.
Synthesis 1980, 627.
(9) Kikukawa, K.; He, G. X.; Abe, A.; Goto, T.; Arata, R.; Ikeda, T.;
Wada, F.; Matsuda, T. J . Chem. Soc., Perkin Trans. 2 1987, 135.
(10) (a) Demas, J . N.; Crosby. G. A. J . Phys. Chem. 1971, 75, 991.
(b) van Houten, J .; Watts, R. J . Am. Chem. Soc. 1976, 98, 4853.

4478 Organometallics, Vol. 20, No. 22, 2001
φs ) φr(Br/Bs)(ns/nr)2(Ds/Dr)
Yam et al.
(2)
[Pt‚Mn+
]
K11
)
[Pt]1[Mn+
[Pt2‚Mn+
[Pt‚Mn+] [Pt]1
[Pt]T ) [Pt]1 + [Pt‚Mn+] + [Pt2‚Mn+
]
where the subscripts s and r refer to the sample and reference
solutions, respectively, B ) 1 - 10-AL, A is the absorbance at
the excitation wavelength, L is the path length, n is the
refractive index of the solvent, and D is the integrated emission
intensity. A degassed aqueous solution of [Ru(bpy)3]Cl2 (φem
) 0.042, excitation wavelength at 436 nm) was used as the
reference.10b
]
K21
)
]
K21[Pt‚Mn+ 2
]
[Pt‚Mn+
]
All solutions for photophysical studies were degassed on a
high-vacuum line in a two-compartment cell consisting of a
10 mL Pyrex bulb and a 1 cm path length quartz cuvette sealed
from the atmosphere by a Bibby Rotaflo HP6 Teflon stopper.
The solutions were subject to no less than four freeze-pump-
thaw cycles.
[Pt]T )
+ [Pt‚Mn+] +
K11[Mn+
]
K11[Mn+
]
a
[Pt‚Mn+] )
2K21
1H NMR spectra were recorded on a Bruker DPX-300 FT-
NMR spectrometer (300 MHz) in CD3CN or (CD3)2SO at 298
K, and chemical shifts are reported relative to Me4Si. Positive
ESI mass spectra were recorded on a Finnigan LCQ mass
spectrometer. Elemental analyses of the new complexes were
performed on a Carlo Erba 1106 elemental analyzer at the
Institute of Chemistry, Chinese Academy of Sciences. Cyclic
voltammetric measurements were performed by using a CH
Instruments, Inc. Model CHI 620 electrochemical analyzer,
which was interfaced to an IBM-compatible 486 personal
computer. The electrolytic cell used was a conventional two-
compartment cell. Electrochemical measurements were per-
where
a ) - 1 - K11[Mn+] + [(1 + K11[Mn+])2 +
4K21K11[Mn+][Pt]T]1/2
a
[Pt]1 )
2K21K11[Mn+
]
a2
[Pt2‚Mn+] )
4K21K11[Mn+
]
X0
Xlim
2Xlim
n
formed in acetonitrile solutions with 0.1 M Bu4NPF6 (TBAH)
X )
[Pt]1 +
[Pt‚Mn+] +
[Pt2‚Mn+
]
(4)
as supporting electrolyte at room temperature. The reference
electrode was a Ag/AgNO3 (0.1 M in acetonitrile) electrode,
and the working electrode was a glassy-carbon (Atomergic
Chemetal V25) electrode with a piece of platinum wire as
counter electrode in a compartment which is separated from
the working electrode by a sintered-glass frit. The ferrocenium/
ferrocene couple (FeCp2+/0) was used as the internal reference.
All solutions for electrochemical studies were deaerated with
prepurified argon gas just before measurements. Treatment
of the electrode surfaces was as reported elsewhere.11
[Pt]T
[Pt]T
[Pt]T
where [Pt]1 is the concentration of complex 6 in the unbound
state, [Pt‚Mn+] and [Pt2‚Mn+] are the concentrations of the 1:1
and 2:1 ion-bound adducts, respectively, and K11 and K21 are
the respective stability constants for 1:1 and 2:1 complexation.
It is assumed that the molar extinction coefficient of the 2:1
ion-bound adduct, (Pt2‚Mn+), is twice that of the 1:1 adduct
form, (Pt‚Mn+).
Cr ysta l Str u ctu r e Deter m in a tion . Single crystals of 1
were obtained by vapor diffusion of diethyl ether into an
acetonitrile solution of the complex. All the experimental
details are given in Table 1. A purple crystal of dimensions
0.35 × 0.07 × 0.07 mm in a glass capillary was used for data
collection at 28 °C on a Rigaku AFC7R diffractometer. The
space group was determined on the basis of systematic
absences and on a statistical analysis of intensity distribution,
and the successful refinement of the structure was solved by
Patterson methods and expanded by Fourier methods (PATTY13)
and refinement by full-matrix least squares using the software
package TeXsan14 on a Silicon Graphics Indy computer. One
crystallographic asymmetric unit consists of one formula unit
with the non-H atoms of CH3CN at special positions. The F
atoms of PF6- were disordered and were placed at 10 positions,
with F(1)-F(10) having occupation numbers of 0.8, 1.0, 0.45,
0.8, 0.8, 0.45, 0.5, 0.5, 0.3, and 0.4, respectively. In the least-
squares refinement, all 27 non-H atoms of the cation and P(1)
were refined anisotropically, the disordered F atoms and the
non-H atoms of CH3CN were refined isotropically, and 16 H
atoms at calculated positions with thermal parameters equal
to 1.3 times that of the attached C atoms were not refined. H
atoms bonded to the disordered methyl C atom in CH3CN were
not included in the calculation. The final difference Fourier
map was featureless, with maximum positive and negative
peaks of 0.90 and 0.53 e Å-3, respectively.
The electronic absorption spectral titration for binding
constant determination was performed with a Hewlett-Pack-
ard 8452A diode array spectrophotometer at 25 °C which was
controlled by a Lauda RM6 compact low-temperature ther-
mostat. Supporting electrolyte (0.1 mol dm-3 nBu4NPF6) was
added to maintain a constant ionic strength of the sample
solution, in order to avoid any changes arising from a change
in the ionic strength of the medium. Binding constants for 1:1
complexation were obtained by a nonlinear least-squares fit12
of the absorbance (X) vs the concentration of the metal ion
added ([Mn+]) according to eq 3
Xlim - X0
X ) X0 +
{[Pt]T + [Mn+] + 1/KS - [([Pt]T +
2[Pt]T
[Mn+] + 1/KS)2 - 4[Pt]T [Mn+]]1/2} (3)
where X0 and X are the absorbances of complex 6 at a selected
wavelength in the absence and presence of the metal cation,
respectively, [Pt]T is the total concentration of complex 6, [Mn+
]
is the concentration of the metal cation Mn+, Xlim is the limiting
value of the absorbance in the presence of excess metal ion,
and KS is the stability constant.
For systems involving Pt:Mn+ complexation in both 1:1 and
2:1 complexation stoichiometries, the binding constants were
determined by using eq 46
(13) PATTY: Beurskens, P. T.; Admiraal, G.; Beurskens, G.; Bosman,
W. P.; Garcia-Granda, S.; Gould, R. O.; Smits, J . M. M.; Smykalla, C.
The DIRDIF Program System; Technical Report of the Crystallography
Laboratory; University of Nijmegen, Nijmegen, The Netherlands, 1992.
(14) TeXsan: Crystal Structure Analysis Package; Molecular Struc-
ture Corp., The Woodlands, TX, 1985 and 1992.
(11) Che, C. M.; Wong, K. Y.; Anson, F. C. J . Electroanal. Chem.
Interfacial Electrochem. 1987, 226, 221.
(12) Bourson, J .; Pouget, J .; Valeur, B. J . Phys. Chem. 1993, 97,
4552.

Platinum(II) Terpyridyl Acetylide Complexes
Organometallics, Vol. 20, No. 22, 2001 4479
Ta ble 1. Cr ysta l a n d Str u ctu r e Deter m in a tion
Da ta for 1
mol formula
fw
(C23H16N3Pt)+PF6-‚0.5CH3CN
694.98
cryst color
cryst size (mm)
cryst syst
space group
a (Å)
purple
0.35 × 0.07 × 0.07
monoclinic
C2/ c (No. 15)
19.614(3)
20.62(2)
13.405(2)
117.60(1)
4805(2)
8
b (Å)
c (Å)
â (deg)
V (Å3)
Z
F(000)
2604
59.49
1.921
301
µ (cm-1
)
calcd density (g cm-3
T (K)
)
diffractometer
AFC7R
λ, (Å, graphite monochromated, 0.710 73
Mo KR)
collecn range (deg)
F igu r e 1. Perspective drawing of the complex cation of 1
with atomic numbering. Thermal ellipsoids were shown at
the 40% probability level.
2θmax ) 50 (h, 0-23; k, 0-24;
l, -15 to +14)
scan mode; scan speed
ω-2θ; 8
(deg min-1
)
Ta ble 2. Selected Bon d Dista n ces (Å) a n d Bon d
An gles (d eg) for 1
scan width (deg)
0.63 + 0.35 tan θ
0.038
0.047
0.05
1.74
4496
4360
2242
146
Ra
a
Rw
Pt(1)-N(1)
Pt(1)-N(2)
Pt(1)-N(3)
2.01(1)
1.97(10)
2.03(1)
Pt(1)-C(1)
C(1)-C(2)
1.98(1)
1.19(1)
max shift (∆/σ)max
goodness of fit
no. of data collected
no. of unique data
N(1)-Pt(1)-N(2)
N(2)-Pt(1)-N(3)
N(1)-Pt(1)-N(3)
N(2)-Pt(1)-C(1)
80.6(5)
81.0(4)
161.6(4)
178.8(4)
N(1)-Pt(1)-C(1)
N(3)-Pt(1)-C(1)
Pt(1)-C(1)-C(2)
99.5(5)
98.9(5)
179.0(1)
no. of data used in refinement
no. of params refined
residual extrema in final
0.09, 0.53
diff map (e Å-3
)
w ) 4Fo2/σ2(Fo2), where σ2(Fo2) ) σ2(I) + (0.02Fo
3σ(I).
)
with I >
a
2 2
binding of sodium ion into the crown cavity. The
identities of all the complexes have been confirmed by
IR spectroscopy, satisfactory elemental analyses, 1H
NMR spectroscopy, and ESI-mass spectrometry. The
crystal structure of [Pt(trpy)(CtCC6H5)]PF6 1 has also
been determined.
Sch em e 1. Syn th etic Rou te of Com p lexes 1-7
Cr ysta l Str u ctu r e Deter m in a tion . The perspective
drawing of the complex cation of 1 is shown in Figure
1. Selected bond distances and angles are tabulated in
Table 2. The coordination geometry about platinum is
essentially square planar with the bond distance of the
platinum to central nitrogen atom of the terpyridine
ligand slightly shorter than that to the other two outer
nitrogen atoms, as is required by the steric demand of
the terpyridine ligand. All the Pt-N distances are in
the range found for typical platinum terpyridine
complexes.2f,3a-d Not surprisingly, the N-Pt-N angles
(N(1)-Pt(1)-N(2), 80.6°; N(2)-Pt(1)-N(3), 81.0°; N(1)-
Pt(1)-N(3), 161.6°) deviate from the idealized values of
90 and 180° as a consequence of the geometric con-
straints imposed by terpyridine ligands. The Pt-C bond
distance is 1.98 Å, which compares well with a value
of 1.95 Å for the platinum bis(acetylide) diimine
complexes.4l,m The CtC bond length of 1.19 Å is
comparable to those of other related platinum(II) acetyl-
ide complexes.4a-d,l,m The phenyl ring of the acetylide
ligand is almost parallel to the plane of platinum-
terpyridine with a dihedral angle of 5.6°. The crystal
packing of 1 revealed a head-to-tail stacking between
pairs of complex cations (Figure 2). The intermolecular
Pt‚‚‚Pt distance of 3.36-3.38 Å is suggestive of inter-
molecular interaction between the two metal centers.
Electr on ic Absor p tion Sp ectr oscop y. The elec-
tronic absorption spectra of complexes 1-7 in acetoni-
Resu lts a n d Discu ssion
Syn th esis. The synthetic route for the formation of
platinum(II) terpyridyl acetylide complexes is sum-
marized in Scheme 1. The starting material [Pt(trpy)-
(MeCN)](OTf)2 was synthesized by modification of lit-
erature procedures3d using a large excess of AgOTf and
a much higher reaction temperature. Reaction of [Pt-
(trpy)(MeCN)](OTf)2 with HCtCR in methanol in the
presence of sodium hydroxide at room temperature,
followed by metathesis reaction using NH4PF6 and
subsequent recrystallization from MeCN-Et2O, af-
forded 1-5 and 7 as dark red to dark purple crystals.
For complex 6, the synthetic method is similar, except
that triethylamine was used as the deprotonating agent
instead of sodium hydroxide in order to prevent the

4480 Organometallics, Vol. 20, No. 22, 2001
Yam et al.
F igu r e 2. Crystal packing diagram of 1.
Ta ble 3. P h otop h ysica l Sp ectr a l Da ta for 1-7
emission
F igu r e 3. Emission (---) and excitation (s) spectra of 1 in
butyronitrile glass at 77 K.
absorptiona λabs/nm
(ꢀ/dm3 mol-1 cm-1
medium
λ
em/nmb
(τ0/µsc)
d
)
(T/K)
φem
1
2
3
4
272 (33 410), 286 (23 860), CH3CN (298) 630 (0.5)
0.0124
0.0073
0.0015
energy among the complexes. In general, the stronger
the electron-donating ability of the acetylide ligand is,
the lower will be the energy of the low-energy absorp-
tion. This observation is in line with an MLCT assign-
ment of the low-energy absorption band, since electron-
rich substituents on the phenyl ring of the acetylide
ligand would render the platinum metal center more
electron-rich and hence raise the dπ(Pt) orbital energy,
leading to a lower energy MLCT absorption. Although
an assignment of an acetylide-to-terpyridine ligand-to-
ligand charge transfer (LLCT) transition would also give
rise to such an energy trend, an assignment of MLCT
transition is favored, probably with some mixing of
LLCT character. The absorption spectral properties of
the complexes were found to obey Beer’s law in the
concentration range 10-5-10-2 mol dm-3 in dimethyl-
formamide solution, suggesting the lack of any signifi-
cant occurrence of complex aggregation.
Em ission P r op er ties. All the complexes show emis-
sion properties in 77 K butyronitrile glass, while at room
temperature in acetonitrile solutions, all complexes
except 4, 6, and 7 were found to exhibit luminescence
(Table 3). The large Stokes shifts and observed lifetimes
in the microsecond range for their emissions are sug-
gestive of a triplet parentage. The butyronitrile glass
of complexes 1-5 upon excitation at λ > 350 nm show
well-resolved vibronic structured emissions at 510-580
nm with progressional spacings of ca. 1300 cm-1, which
correspond to the aromatic vibrational mode of the
terpyridine ligands. Figure 3 shows the excitation and
emission spectra for 1 in 77 K butyronitrile glass. The
emission energies of the complexes in solution were
found to depend on the nature of the substituents on
the phenyl ring of the acetylide ligands. Complex 3,
which bears the electron-rich methyl substituent, shows
the lowest emission energy, while complex 5, with the
most electron-poor nitro group, shows the highest emis-
sion energy (Figure 4). This trend is consistent with a
3MLCT assignment. A shift in the emission energies to
the red was observed upon going from acetonitrile
solutions to the solid state at room temperature with
the exception of 4, 6, and 7 which were nonemissive in
solutions at 298 K. Such low-energy emissions at ca.
690-800 nm in the solid state are assigned as derived
312 (12 450), 28 (12 280), solid (298)
800 (<0.1)
342 (14 440), 432 (4430)
solid (77)
830 (0.7)
glasse (77)
530 (13.3)
272 (36 550), 286 (27 830), CH3CN (298) 620 (0.5)
312 (12 530), 328 (12 490), solid (298)
710 (<0.1)
342 (14 500), 432 (4790)
solid (77)
790 (0.8)
glasse (77)
530 (15.0)
272 (36 150), 312 (12 380), CH3CN (298) 665 (0.1)
330 (12 390), 344 (13 870), solid (298)
412 sh (3580), 456 (4380) solid (77)
glasse (77)
272 (39 310), 308 (13 920), CH3CN (298)
330 (13 500),344 (13 140), solid (298)
416 sh (3500), 474 (4700) solid (77)
glasse (77)
720 (<0.1)
740 (1.0)
545 (13.8)
f
-
f
-
f
-
580 (11.8)
5
6
7
272 (33 500), 286 (23 780), CH3CN (298) 560 (<0.1) 0.0011
310 (24 500), 326 (12 360), solid (298)
720 (<0.1)
790 (0.7)
510 (240)
340 (14 640), 417 (9740)
solid (77)
glasse (77)
f
288 (31 440), 308 (14 910), CH3CN (298)
330 (14 710), 344 (13 940), solid (298)
412 sh (2910), 476 (4180) solid (77)
glasse (77)
286 (40 690), 308 (19 000), CH3CN (298)
330 (15 780), 344 (15 760), solid (298)
412 sh (3890), 480 (5690) solid (77)
glasse (77)
-
f
-
f
-
585 (9.9)
f
-
f
-
f
-
590 (9.3)
a
b
In acetonitrile at 298 K. Emission maxima are corrected
values. c τ0 is the lifetime at infinite dilution. The luminescence
quantum yield, measured at room temperature using [Ru(bpy)3]2+
as a standard. e In butyronitrile glass (concentration 5 × 10-6 mol
dm-3). f Nonemissive.
d
trile solution exhibited intense vibronic-structured ab-
sorption bands at 300-350 nm with extinction coeffi-
cients (ꢀ) on the order of 104 dm3 mol-1 cm-1 and a less
intense band at ca. 456-480 nm with ꢀ on the order of
103 dm3 mol-1 cm-1 (Table 3). With reference to previous
spectroscopic work on platinum(II) terpyridine
complexes,3a-c the absorption bands at 300-350 nm are
most probably derived from the intraligand (IL) transi-
tion of the terpyridine ligands, while the low-energy
absorption band at 456-480 nm is tentatively assigned
to the dπ(Pt) f π*(trpy) metal-to-ligand charge transfer
(MLCT) transition. Complex 5, with the most electron-
withdrawing nitro group on the acetylide, shows an
absorption band at 456 nm, which is at the highest

Platinum(II) Terpyridyl Acetylide Complexes
Organometallics, Vol. 20, No. 22, 2001 4481
F igu r e 5. Electronic absorption spectral traces of 6 (2.6
× 10-4 mol dm-3) in dimethylformamide (0.1 mol dm-3
nBu4NPF6) upon addition of NaClO4 (path length ) 1 cm).
The insert shows a plot of absorbance vs [Na+] monitored
at λ ) 530 nm (9) and its theoretical fit (s).
F igu r e 4. Normalized solution emission spectra of 1 (‚‚‚
‚‚‚), 2 (---), 3 (‚‚ - ‚‚), and 5 (s), in acetonitrile at 298 K.
Ta ble 4. Electr och em ica l Da ta for 1-7a
oxidation Epa/V
reduction E1/2/V
from Pt(II) to Pt(III) is tentatively assigned. The oxida-
tion of complex 5 occurs at a more positive potential
than the others, which may be ascribed to the presence
of the most electron-withdrawing nitro group on the
phenylacetylide ligand, which lowers the energy of the
dπ(Pt) orbital. Thus, complex 5 is most difficult to be
oxidized among all the complexes studied.
Complex
vs SCEb
vs SCEc
1
+1.22
+1.28
+1.25
+1.02
+1.46
+0.96
+1.02
-0.97
-1.46
-1.00
-1.46
-1.03
-1.45
-1.05
-1.46
-1.18
-1.45
-1.06
-1.45
-1.08
-1.45
2
3
4
5
6
7
Cation -Bin din g P r oper ties. Upon addition of alkali-
metal cations to a dimethylformamide solution of 6, the
MLCT absorption band exhibits a blue shift in absorp-
tion energy. Figure 5 shows the UV-visible absorption
spectral traces upon addition of sodium cations to a
solution of 6, in which a well-defined isosbestic point
was observed. Spectrochemical recognition of guest
metal ions is confirmed by the absence of changes in
the absorption bands of the control complex 7. For
binding of Na+, a log KS value of 1.40((0.01) was
obtained according to eq 3. The 1:1 stoichiometry for
Na+ ion binding is evidenced by the close agreement of
the experimental data with the theoretical fit (Figure
5, insert) and has further been confirmed by the method
of continuous variation,17 where a break point at a mole
fraction 6/(6 + Na+) of 0.5 is observed. The much smaller
binding constant of 6 compared to that of a related [Pt-
(trpy)(S-benzo-15-crown-5)]PF6 complex in acetonitrile6
may be attributed to the difference in polarity of the
solvent. Since dimethylformamide is much more polar
than acetonitrile, the metal cations are already well
solvated or stabilized by the solvent molecules. The
binding of the cations in the crown cavity is therefore
less favored, leading to smaller binding constants. This
solvent effect on cation binding has also been reported
for other crown ether-containing compounds.18 In the
case of K+, complexes with stoichiometries of both 2:1
and 1:1 were formed. This binding mode is supported
In acetonitrile solution with 0.1 M nBu4NPF6 (TBAH) as
a
supporting electrolyte at room temperature; scan rate 100 mV s-1
.
b
Epa refers to the anodic peak potential for the irreversible
oxidation waves. E1/2 ) (Epa + Epc)/2; Epa and Epc are peak anodic
and peak cathodic potentials, respectively.
c
from triplet states of metal-metal bond-to-ligand charge
transfer (MMLCT) character, resulting from the sig-
nificant Pt‚‚‚Pt interaction in the solid state. When the
temperature is lowered to 77 K, the emission band in
the solid state shows a further red shift in emission
energies, which may be rationalized by the lattice
contraction at low temperatures, leading to a shortening
of the Pt‚‚‚Pt intermolecular separation and, hence, an
increased Pt‚‚‚Pt interaction. The self-quenching rate
constants for complexes 1-3 at room temperature are
1.73, 1.74, and 1.45 × 109 dm3 mol-1 s-1, respectively.
Electr och em ica l P r op er ties. The electrochemical
data for complexes 1-7 are summarized in Table 4. All
the complexes show two quasi-reversible couples at ca.
-1.05 and -1.45 V vs SCE. The relative insensitivity
of the potentials toward the nature of the acetylide
ligands with different substituents on the phenyl ring
suggests that these couples probably arise mainly from
the terpyridine-based reductions with some mixing of
the Pt(II) metal character. Similar assignment has also
been suggested in other platinum terpyridyl systems.15
Irreversible anodic waves are noted at ca. +1.02 to
+1.46 V vs. SCE. With reference to the previous studies
on other platinum complexes,16 metal-centered oxidation
(15) (a) Hill, M. G.; Bailey, J . A.; Miskowski, V. M.; Gray, H. B. Inorg.
Chem. 1996, 35, 4585. (b) Crites, D. K.; Cunningham, C. T.; McMillin,
D. R. Inorg. Chim. Acta 1998, 273, 346.
(16) (a) Blanton, C. B.; Murtaza, Z.; Shaver, R. J .; Rillema, D. P.
Inorg. Chem. 1992, 31, 3230. (b) von Zelewsky, A.; Gremaud, G. Helv.
Chim. Acta 1988, 84, 85.
(17) (a) J affe, H. H.; Orchin, M. Theory and Applications of
Ultraviolet Spectroscopy; Wiley: New York, 1962. (b) Peyman, A.;
Uhlmann, E.; Wagner, K.; Augustin, S.; Weiser, C.; Will, D. W.;
Breipohl, G. Angew. Chem., Int. Ed. Engl. 1997, 36, 2809.

4482 Organometallics, Vol. 20, No. 22, 2001
Yam et al.
Ta ble 5. Ion Clu ster s Obser ved in th e P ositive ESI
Ma ss Sp ectr a of 6 w ith Na ClO4, KP F 6, a n d Ba ClO4
in Aceton itr ile Solu tion
m/z
ion cluster
842
903
1767
1055
{[Pt(trpy)(CtC-benzo-15-crown-5)‚Na]ClO4}+
{[Pt(trpy)(CtC-benzo-15-crown-5)‚K]PF6}+
{{[Pt(trpy)(CtC-benzo-15-crown-5)]2‚K}(PF6)2}+
{[Pt(trpy)(CtC-benzo-15-crown-5)‚Ba](ClO4)2}+
nitrile at room temperature were found to depend on
the nature of the acetylide ligands with different sub-
stituents on the phenyl ring, i.e., the more electron-
withdrawing the group on the phenylacetylide ligand
is, the higher is the emission energy. This trend is
consistent with an assignment of a triplet metal-to-
terpyridine metal-to-ligand charge transfer (3MLCT)
state, probably mixed with some acetylide-to-terpyridine
ligand-to-ligand charge transfer (3LLCT) character.
From the electrochemical studies, all the complexes
showed two quasi-reversible terpyridine-based reduction
couples with some mixing of the Pt(II) metal character
and one irreversible metal-based oxidation wave. The
cation-binding properties for a crown ether-containing
complex have also been studied. The spectral change
upon addition of guest metal ions was monitored by
electronic absorption studies. For Na+, a 1:1 binding
mode with log KS of 1.40((0.01) was observed, while for
K+, both complexes with stoichiometries of 2:1 and 1:1
were formed with log K11 and log K21 of 1.99((0.05) and
2.79((0.05), respectively. The ion-binding properties
have further been confirmed by positive ESI mass
spectrometry.
F igu r e 6. Plot of absorbance of 6 (2.5 × 10-4 mol dm-3
)
in dimethylformamide (0.1 mol dm-3 nBu4NPF6) vs [K+]
monitored at λ ) 520 nm (9) and its theoretical fit (s).
by the close resemblance of the experimental data with
the theoretical fit (Figure 6) and also the lack of well-
defined isosbestic points on the UV-visible spectral
traces. Log K11 and log K21 values of 1.99((0.05) and
2.79((0.05) were obtained, respectively, according to eq
4. However, no satisfactory fit for eqs 3 and 4 can be
obtained for the binding studies of Ba2+. The blue shift
in absorption energies observed upon ion binding is
consistent with the MLCT assignment of the low-energy
absorption, since a reduced electron-donation ability of
the acetylide would occur upon ion binding, causing the
MLCT to occur at higher energies.
The ion-binding studies have further been confirmed
by positive ESI mass spectrometry. A 1:1 adduct was
observed for the binding of 6 with Na+ and Ba2+, while
for K+, both 1:1 and 2:1 adducts were observed (Table
5). This is fully consistent with the binding properties
studied by UV-visible spectroscopy. Similar to the
absorption studies, control experiments with the crown-
free analogue 7 did not show the presence of such ion-
bound species upon the addition of metal ions, providing
further supporting evidence for the binding of cations
to the crown moieties.
Ack n ow led gm en t. V.W.-W.Y. acknowledges sup-
port from The University of Hong Kong and the receipt
of a Croucher Senior Research Fellowship (2000-2001)
from the Croucher Foundation. The work described in
this paper has fully been supported by a grant from the
Research Grants Council of the Hong Kong Special
Administrative Region, People’s Republic of China
(Project No. HKU 7123/00P). R.P.-L.T. acknowledges the
receipt of a postgraduate studentship, administered by
The University of Hong Kong, and K.M.-C.W. the receipt
of a University Postdoctoral Fellowship from The Uni-
versity of Hong Kong.
Con clu sion
A series of platinum(II) terpyridyl acetylide complexes
were successfully synthesized and shown to exhibit long-
lived emissive states. The emission energies in aceto-
Su ppor tin g In for m ation Available: Tables giving atomic
coordinates, anisotropic thermal parameters, bond lengths,
and bond angles for complex 1. This material is available free
of charge via the Internet at http://pubs.acs.org.
(18) (a) Frensdorf, H. K. J . Am. Chem. Soc. 1971, 93, 600. (b)
Kauffmann, E.; Lehn, J . M.; Sauvage, J . P.; Helv. Chim. Acta 1976,
59, 1099. (c) Yam, V. W. W.; Lee, V. W. M.; Ke, F.; Siu, M. K. W. Inorg.
Chem. 1997, 36, 2124.
OM010336X