A luminescent supermolecule with gold(I) quinoline-8-thiolate: Crystal structure, spectroscopic and photophysical properties

Article abstract of DOI:10.1021/ic034041i

The trinuclear complex [(8-QNS)₂Au(AuPPh₃) ₂]·BF₄ (8-QNS = quinoline-8-thiolate), with intramolecular gold(I)...gold(I) distances of 3.0952(4) and 3.0526(3) A, is aggregated to form a novel hexanuclear supermolecule, {[(8-QNS) ₂Au(AuPPh₃)₂]}₂·(BF ₄)₂, via a close intermolecular gold(I)...gold(I) contact of 3.1135(3) A. The beautiful hexanuclear supermolecule has an inversion center, and the six metal centers can be viewed as roughly coplanar. Six gold(I) ions are embedded in an ellipse and surrounded by 4 quinoline and 12 phenyl rings. The title compound shows interesting spectroscopic and luminescence properties dependent on the solvent polarity; i.e., it emits at ca. 440 and 636 nm in CH₂Cl₂ and only at ca. 450 nm in CH₃CN. The long-lived emission at ca. 636 nm (16.2 μs) in CH ₂Cl₂ is quenched by polar solvents such as CH ₃CN and CH₃OH with quenching constants as 1.00 × 10⁵ and 3.03 × 10⁴ s^-1 M^-1, respectively, which is suggested to be related to the presence or absence of gold(I)...gold(I) interactions due to scrambling of the [AuPPh ₃]⁺ units, isolobal to H⁺.

Full text of DOI:10.1021/ic034041i

Inorg. Chem. 2003, 42, 6008−6014
A Luminescent Supermolecule with Gold(I) Quinoline-8-thiolate: Crystal
Structure, Spectroscopic and Photophysical Properties
,†
Biing-Chiau Tzeng,* Hsien-Te Yeh,† Yung-Chi Huang,† Hsiu-Yi Chao,† Gene-Hsiang Lee,‡ and
Shie-Ming Peng‡
Department of Chemistry and Biochemistry, National Chung Cheng UniVersity, 160 San-Hsin,
Min-Hsiung, Chia-Yi, Taiwan 621, and Department of Chemistry, National Taiwan UniVersity,
Taipei, Taiwan
Received January 15, 2003
The trinuclear complex [(8-QNS)2Au(AuPPh3)2]‚BF4 (8-QNS ) quinoline-8-thiolate), with intramolecular
gold(I)‚‚‚gold(I) distances of 3.0952(4) and 3.0526(3) Å, is aggregated to form a novel hexanuclear supermole-
cule, {[(8-QNS)2Au(AuPPh3)2]}2‚(BF ) , via a close intermolecular gold(I)‚‚‚gold(I) contact of 3.1135(3) Å. The
4 2
beautiful hexanuclear supermolecule has an inversion center, and the six metal centers can be viewed as roughly
coplanar. Six gold(I) ions are embedded in an ellipse and surrounded by 4 quinoline and 12 phenyl rings. The title
compound shows interesting spectroscopic and luminescence properties dependent on the solvent polarity; i.e., it
emits at ca. 440 and 636 nm in CH Cl2 and only at ca. 450 nm in CH CN. The long-lived emission at ca. 636 nm
2
3
(16.2 µs) in CH Cl2 is quenched by polar solvents such as CH CN and CH OH with quenching constants as
2
3
3
1.00 × 105 and 3.03 × 104 s-1 M-1, respectively, which is suggested to be related to the presence or absence of
+
gold(I)‚‚‚gold(I) interactions due to scrambling of the [AuPPh3]+ units, isolobal to H .
Introduction
by following the “aurophilicity principle”8 and also intrigued
both theoretical and experimental chemists.9-17
Gold(I) thiolates are the most extensively used gold(I)
complexes in medicine and in surface technology.1,2 Virtually
all of the classical and modern drugs based on gold(I) for
arthritis and rheumatism have been gold(I)-sulfur com-
pounds.3-5 The pastes known as “liquid gold” used for gold-
plating of glass and ceramics are mixtures of gold(I) thiolates
derived from natural products. Furthermore, precursors of
advanced gold thin film technology are still relying mainly
on the special properties of the gold(I)-sulfur system.6
Surprisingly, it is only recently that major progress has been
made regarding the full characterization of specific gold(I)
thiolates.7 Most of the research leading to new gold(I)
aggregates with interstitial metalloid elements was initiated
The study of the solvent and/or medium effects on
gold(I)‚‚‚gold(I) interactions may pave the way for molecular
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R. C.; Bruce, A. E.; Bruce, M. R. M. Inorg. Chem. 1995, 34, 1996.
(b) Narayanaswamy, R.; Young, M. A.; Parkhurst, E.; Ouellette, M.;
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* To whom correspondence should be addressed. E-mail: chebct@
ccu.edu.tw.
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† National Chung Cheng University.
‡ National Taiwan University.
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6008 Inorganic Chemistry, Vol. 42, No. 19, 2003
10.1021/ic034041i CCC: $25.00 © 2003 American Chemical Society
Published on Web 08/16/2003

A Luminescent Supermolecule with Au(I) 8-QNS
Scheme 1
self-assembly of gold(I) ions leading to the formation of
novel gold(I) supermolecules.17 This is particularly important
for understanding the chemistry of gold(I) drugs,18 where
such interactions might occur under biological conditions.
The presence of aurophilic contacts may be recognized not
only from short gold(I)‚‚‚gold(I) distances and novel struc-
tural features but also intriguing electronic absorption and
luminescence properties.19 It is becoming clear that the
gold(I)‚‚‚gold(I) bonding interaction is responsible for the
relevant transitions, and luminescence has thus become an
important diagnostic tool for aurophilicity. Recently, a
spectacular experiment carried out by Balch et al.13a has
demonstrated that luminescence of gold(I) complexes can
be triggered by the solvation of the donor-free solid substrate
either from the vapor phase or by dissolving the material in
a solvent. An unusual chromic luminescence behavior linked
to a structural change in the solid state induced by exposure
to the vapor phase of volatile organic compounds (VOCs)
was also observed by Eisenberg and co-workers.20 The
“luminescent switch” for the detection of VOCs using
gold(I) dimers following the pioneering work by Mann and
co-workers21 on absorption and emission spectra of vapo-
chromic platinum(II) and palladium(II) compounds shows
that the phenomena of these kinds of luminescent gold(I)
compounds hold great potential for analytical applications.
8-thiolate in polar solvents such as CH3CN and CH3OH is
attributed to an equilibrium between two forms 1A and 1B
of the complexes (Scheme 1) of which only the former
displays emission. Herein is described the molecular struc-
tures and photophysical properties of a novel complex,
[(8-QNS)2Au(AuPPh3)2]‚BF4, 2‚BF4, isolated from a pro-
posed rearrangement reaction of 1‚BF4. This huge gold(I)
cluster shows interesting spectroscopic and luminescence
properties dependent on the solvent polarity as those in
1‚BF4, which is suggested to be related to the presence or
absence of gold(I)‚‚‚gold(I) bonding interactions due to
scrambling of the [AuPPh3]+ units, isolobal to H+.
Experimental Section
General Information. All reactions were performed under
a nitrogen atmosphere and solvents for syntheses (analytical
grade) were used without further purification. NMR: Bruker
DPX 400 MHz NMR; deuterated solvents with the usual
standards. MS: Positive ion FAB mass spectra were recorded
on a Finnigan MAT95 mass spectrometer. Quinoline-8-thiol
(8H-QNS) was purchased from Aldrich Chemicals, and Au-
(PPh3)Cl was prepared by literature methods.23 Solvents for
photophysical studies were purified by literature methods.
Synthesis of [(8-QNS)2Au(AuPPh3)2]‚BF4 2‚BF4. A solu-
tion of Na(8-QNS) was prepared by adding NaOMe (30 mg)
to 8H-QNS (50 mg) in CH2Cl2/CH3OH (1:1, 25 mL). Au-
(PPh3)Cl (250 mg, 25 mL in CH2Cl2) was then added to the
solution, which was stirred for 4 h at room temperature. After
the addition of NaBF4 (60 mg), the pale yellow solution was
stirred for another 10 min and then evaporated to dryness.
The resulting solid was extracted with THF and then layered
with hexanes. Pale-yellow single crystals were obtained in
55% yield in 1 week. MS (FAB): [(8-QNS)(AuPPh3)2]+,
m/e ) 1080, 100%; [(8-QNS)2Au(AuPPh3)2]+, m/e ) 1436,
10%. {1H}31P NMR (CDCl3, 25 °C): δ 33.75 (s). Anal. Calcd
for Au3C54H42N2S2P2BF4: C, 42.56; H, 2.76; N, 1.84. Found:
C, 43.01; H, 2.92; N, 1.52.
A remarkable example of the strong solvent dependence
of the luminescence of a gold(I) compound in solution has
been previously communicated by Che et al.22 The quenching
of the luminescence of the simple dinuclear gold(I) quinoline-
(13) (a) Vickery, J. C.; Olmstead, M. M.; Fung, E. Y.; Balch, A. L. Angew.
Chem., Int. Ed. Engl. 1997, 36, 1179. (b) Vickery, J. C.; Balch, A. L.
Inorg. Chem. 1997, 36, 5978. (c) Calcar, P. M. V.; Olmstead, M. M.;
Balch, A. L. Inorg. Chem. 1997, 36, 5231. (d) Calcar, P. M. V.;
Olmstead, M. M.; Balch, A. L. J. Chem. Soc., Chem. Commun. 1995,
1773.
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Laguna, M. Organometallics 1996, 15, 4939. (b) Gimeno, M. C.;
Laguna, A. Chem. ReV. 1997, 97, 511. (c) Jones, P. G.; Ahrens, B.
New J. Chem. 1998, 104. (d) Chem. Ber./Recueil 1997, 130, 1813.
(e) Vicente, J.; Chicote, M.-T.; Abrisqueta, M.-D.; Guerrero, R.; Jones,
P. G. Angew. Chem., Int. Ed. Engl. 1997, 36, 1203.
(15) (a) Mingos, D. M. P.; Yau, J.; Menzer, S.; Williams, D. J. Angew.
Chem., Int. Ed. Engl. 1995, 34, 1894. (b) Mingos, D. M. P. J. Chem.
Soc., Dalton Trans. 1996, 561.
(16) (a) Yam, V. W.-W.; Lo, K. K.-W. Chem. Soc. ReV. 1999, 28, 323. (b)
Yam, V. W.-W.; Cheng, E. C.-C. Angew. Chem., Int. Ed. 2000, 39,
4240. (c) Yam, V. W.-W.; Cheng, E. C.-C. Gold Bull. 2001, 34, 20.
(17) (a) Tzeng, B.-C.; Lo, W.-C.; Che, C.-M.; Peng, S.-M. Chem. Commun.
1996, 181. (b) Tzeng, B.-C.; Cheung, K.-K.; Che, C.-M. Chem.
Commun. 1996, 1681. (c) Tzeng, B.-C.; Che, C.-M.; Peng, S.-M. J.
Chem. Soc., Dalton Trans. 1996, 1769. (d) Tzeng, B.-C.; Che, C.-M.;
Peng, S.-M. Chem. Commun. 1997, 1771.
(18) (a) Shaw, C. F., III; Coffer, M. T.; Klingbeil, J.; Mirabelli, C. K. J.
Am. Chem. Soc. 1988, 110, 729. (b) Coffer, M. T.; Shaw, C. F., III;
Eidsness, M. K.; Watkins, J. W., II; Elder, R. C. Inorg. Chem. 1986,
25, 333. (c) Isab, A. A.; Sadler, P. J. J. Chem. Soc., Dalton Trans.
1982, 135.
(19) (a) Che, C.-M.; Kwong, H.-L.; Yam, V. W.-W.; Cho, K.-C. J. Chem.
Soc., Chem. Commun. 1989, 885. (b) King, C.; Wang, J. C.; Khan,
M. N. I.; Fackler, J. P., Jr. Inorg. Chem. 1989, 28, 2145. (c) Fu, W.-
F.; Chan, K.-C.; Miskowski, V. M.; Che, C.-M. Angew. Chem., Int.
Ed. 1999, 38, 2783.
(20) Mansour, M. A.; Connick, W. B.; Lachicotte, R. J.; Gysling, H. J.;
Eisenberg, R. J. Am. Chem. Soc. 1998, 120, 1329.
Physical Measurements and Instrumentation. UV/vis
spectra were recorded on a Perkin-Elmer Lambda 19
spectrophotometer, and steady-state emission spectra, on a
SPEX Fluorolog-2 spectrophotometer. Emission lifetime
measurements were performed with a Quanta Ray DCR-3
Nd:YAG laser (pulse output 355 nm, 8 ns). The decay signal
was recorded by a R928 PMT (Hamamatsu), which was
connected to a Tektronix 2430 digital oscilloscope. Solutions
(21) Exstrom, C. L.; Sowa, J. R., Jr.; Daws, C. A.; Janzen, D.; Moore, G.
A.; Stewart, F. F.; Mann, K. R. Chem. Mater. 1995, 7, 15.
(22) Tzeng, B.-C.; Chan, C.-K.; Cheung, K.-K.; Che, C.-M.; Peng, S.-M.
Chem. Commun. 1997, 135.
(23) Schmidbaur, H.; Wohlleben, A.; Wagner, F.; Orama, O.; Huttner, G.
Chem. Ber. 1977, 110, 1748.
Inorganic Chemistry, Vol. 42, No. 19, 2003 6009

Tzeng et al.
Table 1. Crystallographic Data for 2‚BF4
interesting metal thiolate clusters or supermolecules can be
formed easily. In addition to the novel structural properties,
the rich electrooptical properties related to visible photo-
luminescence arising from S f Au charge-transfer excitation
can also be anticipated. The preliminary result regarding
solvent effects on the spectroscopic and photophysical
properties of dinuclear gold(I) quinoline-8-thiolate (1‚BF4)
is striking,22 and it prompted us to continue to explore the
study about structural chemistry on the basis of aurophilic
interactions and potential chemosensing applications. In this
work, the novel supramolecular structure of 2‚BF4 has been
characterized and interesting solvent effects on spectroscopic
and photophysical properties as those in 1‚BF4 also studied.
2‚BF4
empirical formula
fw
C
110H92Au6B2F8N4O2P4S4
3109.42
cryst system
space group (No.)
a (Å)
b (Å)
c (Å)
triclinic
P1h(2)
11.5200(5)
15.2049(6)
16.7176(7)
72.1283(8)
85.2163(9)
79.0915(9)
2735.6(2), 1
1.887
R (deg)
â (deg)
γ (deg)
V (Å3), Z
F
calc (g cm-3
)
F(000) (e)
1476
82.12
295(2)
µ(Mo KR) (cm-1
T (K)
)
Description of Crystal Structure. The structure of
complex 2 cation shown in Figure 1(a) features a trinuclear
gold(I) complex with two intramolecular gold(I)‚‚‚gold(I)
distances of 3.0952(4) and 3.0526(3) Å, which are further
aggregated to form a novel hexanuclear supermolecule,
{[(8-QNS)2Au(AuPPh3)2]}2‚(BF4)2 shown in Figure 1(b),
through a close intermolecular gold(I)‚‚‚gold(I) contact of
3.1135(3) Å. The beautiful hexanuclear supermolecule has
an inversion center, and the six metal centers can be viewed
as roughly coplanar as shown in Figure 1(c). The least-square
plane is calculated from the six gold ions with deviations
from the plane as follows: -0.1364 Å, Au(1); 0.3350 Å,
Au(2); 0.0469 Å, Au(3); 0.1364 Å, Au(1A); -0.3351 Å,
Au(2A); -0.0468 Å, Au(3A). Six gold(I) ions are embedded
in an ellipse and surrounded by 4 quinoline and 12 phenyl
rings. There are six significant aurophilic interactions
(3.0526(3)-3.1135(3) Å) in this supermolecule, which are
expected to stabilize this novel supramolecular structure in
the solid state. The structure can be inferred from Scheme 2
that two molecules of 1‚BF4 underwent a proposed rear-
rangement (discussed in the following section) to lead to the
formation of trinuclear complex 2‚BF4 by loss of one
Au(PPh3)2+ cation. In 1‚BF4, 8-QNS is bonded to two nearly
equivalent [AuPPh3]+ units through the sulfur atom. The
central gold(I) ion (isolobal to H+) in complex 2 cation acts
as a bridge between two sulfur atoms of 8-QNS(AuPPh3)
with an almost linear S(1)-Au(2)-S(2) (174.84(6)°) bond
and two different P(1)-Au(1)-S(1) (156.91(6)°) and P(2)-
Au(3)-S(2) (171.52(6)°) bonds. The difference of 14.6°
between the two P-Au-S moieties may be only due to the
steric constraint or structural packing in the solid state. It is
noted that there are two Au‚‚‚N interactions in the structure.
The Au(1)‚‚‚N(1) distance of 2.555 Å is quite shorter than
the Au(3)‚‚‚N(2) distance of 3.274 Å, where the former is
indicative of a strong bonding interaction and the latter is a
weak one. The hexanuclear gold(I) supermolecule may be
regarded as an ellipse, which is surrounded with 4 quinoline
and 12 phenyl rings. Thus, we guess the surrounding
quinoline and phenyl rings outside the Au6 core possibly
make this supramolecular structure flexible due to the
possible rotation of C-S or C-C single bonds of the
quinoline and phenyl rings, and this is in accordance with
the shorter lifetime and lower quantum yield of 2‚BF4
compared to those in 1‚BF4.
reflcns collcd
35 916
12 553
618
0.0368, 0.1017
1.488/-0.931
1.052
obsd reflcns (Fo g 2σ(Fo))
refined params
b
R,a wR2
F
fin(max/min) (e Å-3
)
goodness-of-fit on F2
a R )∑||Fo| - |Fc||/∑|Fo|. b wR2 ) {[∑w(Fo - Fc )2/∑[w(Fo )2]}1/2
.
2
2
2
for photophysical experiments were degassed by at least four
freeze-pump-thaw cycles.
X-ray Crystallography. A pale-yellow crystal of ap-
proximately 0.25 × 0.25 × 0.20 mm3 was mounted on a
glass capillary. Data collection was carried out on a Bruker
SMART CCD diffractometer with Mo radiation at low
temperature. A preliminary orientation matrix and unit cell
parameters were determined from 3 runs of 15 frames each,
each frame corresponding to 0.3° scan in 15 s, followed by
spot integration and least-squares refinement. Data were
measured using an ω scan of 0.3°/frame for 20 s until a
complete hemisphere had been collected. Cell parameters
were retrieved using SMART24 software and refined with
SAINT25 on all observed reflections. Data reduction was
performed with the SAINT software and corrected for
Lorentz and polarization effects. Absorption corrections were
applied with the program SADABS.26 The structure was
solved by direct methods with the SHELX9327 program and
refined by full-matrix least-squares methods on F2 with
SHEXLTL-PC V 5.03.27 All non-hydrogen atomic positions
were located in difference Fourier maps and refined aniso-
tropically. The hydrogen atoms were placed in their geo-
metrically generated positions. Detailed data collection and
refinement of the complex are summarized in Table 1.
Results and Discussion
Owing to the versatility of the coordination modes of
quinolinethiolate such as monodentate (through S donor),
bidentate (µ2-bridging and/or chelate through S and N
donors), and tridentate (µ3-bridging through S and N donors),
(24) SMART V 4.043 Software for the CCD Detector System; Siemens
Analytical Instruments Division: Madison, WI, 1995.
(25) SAINT V 4.035 Software for the CCD Detector System; Siemens
Analytical Instruments Division: Madison, WI, 1995.
(26) Sheldrick, G. M. SHELXL-93, Program for the Refinement of Crystal
Structures; University of Gottingen: Gottingen, Germany, 1993.
(27) SHELXTL 5.03 (PC-Version), Program Liberary for Structure Solution
and Molecular Graphics; Siemens Analytical Instruments Division:
Madison, WI, 1995.
6010 Inorganic Chemistry, Vol. 42, No. 19, 2003

A Luminescent Supermolecule with Au(I) 8-QNS
Scheme 2
whereas there is a weaker absorption band at ca. 320 nm as
well as an additional absorption band at ca. 380 nm in CH3-
CN. The absorption spectra measured in CHCl3, THF, and
CH3OH are quite similar to that measured in CH2Cl2, except
with a low-energy absorption band at ca. 400 nm measured
in THF. This low-energy absorption is red-shifted to the
above measured in CH3CN, and the red shift is also observed
in 1‚BF4. In the inset of Figure 2, the spectral change with
two isosbestic points at 357 and 366 nm shows a decrease
in the absorption at ca. 320 nm concomitant with an increase
in the absorption at ca. 380 nm upon addition of CH3CN to
a CH2Cl2 solution of 2‚BF4. The absorption at ca. 380 nm
of 2‚BF4 measured in CH3CN strongly resembling in that
of [8-QNS(AuPPh3)] (ca. 386 nm) as well as that in 1‚BF4
(ca. 386 nm) measured in CH3CN is tentatively assigned to
an intraligand transition of thiolates and/or a S f Au charge-
transfer transition. Indeed, the absorption spectra measured
in CH2Cl2, CHCl3, and CH3OH also show a very weak
absorption in this spectral range. Notably, the absorption at
ca. 320 nm of 2‚BF4 is similar to that in 1‚BF4 and is also
in energy relative to the low-energy 5d(dσ*) f 6p(pσ)
transitions in a number of dinuclear and trinuclear gold(I)
phosphine complexes such as [Au2(dppm)2]2+ (295 nm)28 and
[Au3(dpmp)2]3+ (326 nm).29 This may be a major difference
between the forms in Schemes 1 and 2 (discussed in the
following section) with or without gold(I)‚‚‚gold(I) interac-
tions, as reflected by the presence or absence of the
absorption at ca. 320 nm. However, none of the spectra
exclusively shows only one absorption band at ca. 320,
suggesting that there is no pure isomeric form of 2‚BF4 (with
or without gold(I)‚‚‚gold(I) interactions) in the solutions but
a mixture at an equilibrium. Surprisingly, the huge complex
structure of 2‚BF4 with six gold(I) ions connected by six
significant aurophilic interactions in the solid state leading
Figure 1. (a) Perspective view of complex 2 cation (bond lengths in Å,
angles in deg): Au(1)‚‚‚Au(2) 3.0952(4), Au(2)‚‚‚Au(3) 3.0526(3), Au-
(1)-S(1) 2.3789(16), Au(2)-S(2) 2.3188(16), Au(3)-S(2) 2.3502(16), Au-
(1)-P(1) 2.2420(16), Au(3)-P(2) 2.2633(16); S(1)-Au(1)-P(1) 156.91(6),
S(1)-Au(2)-S(2) 174.84(6), S(2)-Au(3)-P(2) 171.52(6). (b) Dimeric
aggregate of complex 2 cations leading to the formation of a hexanuclear
gold(I) supermolecule connected by intermolecular Au(2)‚‚‚Au(3A) contact
of 3.1135(3) Å. For clarity only the ipso carbons of the phenyl rings are
shown. (c) The six metal centers can be viewed as roughly coplanar.
UV-Visible Absorption and Emission Spectra. The
absorption spectra of 2‚BF4 measured in CH2Cl2, CHCl3,
THF, CH3OH, and CH3CN are shown in Figure 2. Table 2
summarizes the spectroscopic and photophysical data of
2‚BF4 in various solvents. It is somewhat surprising that
although 2‚BF4 is a huge structure, its absorption spectra
measured in the same solvent are almost identical to those
of dinuclear 1‚BF4, except the latter has weaker absorptions.
There is a distinct difference in the absorption spectra of
2‚BF4 measured in CH2Cl2 and in CH3CN. In CH2Cl2, this
complex shows an intense absorption band at ca. 320 nm,
(28) Che, C.-M.; Kwong, H.-L.; Poon, C.-K.; Yam, V. W.-W. J. Chem.
Soc., Dalton Trans. 1990, 3215.
(29) Li, D.; Che, C.-M.; Peng, S.-M.; Liu, S.-T.; Zhou, Z.-Y.; Mak, T.
C.-W J. Chem. Soc., Dalton Trans. 1993, 189.
Inorganic Chemistry, Vol. 42, No. 19, 2003 6011

Tzeng et al.
Figure 2. Electronic absorption spectra of 2‚BF4 measured in various solvents (CH2Cl2, CHCl3, THF, CH3OH, and CH3CN) at 298 K. Inset is the spectral
change upon addition of CH3CN to a CH2Cl2 solution (9 × 10-5 M) with a v (CH3CN)/v (CH2Cl2) ratio from 0/5, 1/4, 2/3, 3/2, 4/1, to 5/0 leading to a
decrease in the absorption at ca. 320 nm concomitant with an increase in the absorption at ca. 386 nm when the CH3CN content increases.
Table 2. Spectroscopic and Photophysical Data for 2‚BF4
λ
em (nm)/τ (µs)
solid state (RT)
587/27.4
(510, 545, 590/283.7)a
λ
abs (nm)/
kq
solvents
CH2Cl2
ꢀ (dm3 mol-1 cm-1
)
solution
(s-1 M-1
)
320/11 310
(320/8060)a
380/2180
440/0.8
(430/0.3)a
636/16.2
(640/26.0)a
425/0.7
(386/230)a
320/9840
CHCl3
THF
1.10 × 103
380/2460
320/11 420
400/2040
636/11.3
425/0.7
636/2.5
425/0.7
636/1.8
1.84 × 104
(3.2 × 104)a
3.03 × 104
(5.0 × 104)a
1.00 × 105
(1.25 × 105)a
CH3OH
CH3CN
320/10 390
380/1,960
320/7260
450/0.7
(320/5870)a
380/3710
(440/0.3)a
(386/1450)a
a Data in parentheses represent the related values of 1‚BF4.
to the formation of a supramolecular structure also shows a
proposed scrambling of [Ph3PAu]+ units in polar solvents.
emission energy and the gold(I)‚‚‚gold(I) interaction was
studied by Fackler and co-workers30 on a series of monomeric
gold(I) complexes containing phosphine and thiolate (aro-
matic) ligands. All of the compounds synthesized by Fackler
et al. luminesce at 77 K (485-702 nm) in the solid state,
and the excitation was also assigned to a S f Au charge-
transfer transition. According to their studies, the emission
energy can be tuned either by changing the substituents on
the thiolates or by the presence of gold(I)‚‚‚gold(I) interac-
tions in the solid state. Since there are six intra- and
intermolecular gold(I)‚‚‚gold(I) interactions for the solid-state
structure of 2‚BF4, the emission at ca. 587 nm assigned to a
S f Au charge-transfer transition strongly modified by a
metal-centered 5d(dσ*) f 6p(pσ) transition is anticipated.
The solid-state emission spectra of 2‚BF4 measured in
CH2Cl2, CHCl3, THF, CH3OH, and CH3CN at room tem-
perature are shown in Figure 3. For a purpose of comparison,
the solid-state emission spectrum of 1‚BF4 is also included.
At room temperature and in the solid state, complex 2‚BF4
displays a red-orange emission at ca. 587 nm with a lifetime
of 27.4 µs upon photoexcitation at 355 nm, whereas 1‚BF4
shows a bright yellow and vibronic-structured emission with
peak maxima at ca. 508, 545, and 590 nm with a lifetime of
283.7 µs. This progression with a spacing at 1300-1400
cm-1 is mostly due to the CdC or CdN stretching mode of
the 8-QNS ligand, and the emission is most likely due to a
S f Au excitation and possibly with modification of
gold(I)‚‚‚gold(I) interactions. The correlation between the
(30) Forward, J. M.; Bohmann, D.; Fackler, J. P., Jr.; Staples, R. J. Inorg.
Chem. 1995, 34, 6330.
6012 Inorganic Chemistry, Vol. 42, No. 19, 2003

A Luminescent Supermolecule with Au(I) 8-QNS
Figure 3. Solid-state emission spectra of 1‚BF4 (dash line) and 2‚BF4
(solid line) measured at 298 K. Excitation is at 355 nm.
Figure 5. Representative example shows the spectral change upon addition
of CH3OH to a CH2Cl2 solution of 2‚BF4 (7.72 × 10-5 M) with excitation
at 320 nm. The lifetime change according to the Stern-Volmer equation is
shown in the inset.
at ca. 425-450 nm are suggested to be due to an intraligand
transition of PPh3, but it should be noted that the possibility
of having the emission contributed from the Au-PPh3
portion could not be excluded, since the complex Au(PPh3)X
(X ) halide) also shows photoluminescence in this spectral
region.31 Notably, these emissions depend on the solvent
polarity as those in 1‚BF4. Polar solvents such as CH3CN,
CH3OH, THF, and CHCl3 were found to quench the low-
energy emissions with Stern-Volmer quenching rate con-
stants in the order: CH3CN > CH3OH > THF > CHCl3
(kq ) 1.00 × 105, 3.03 × 104, 1.84 × 104, and 1.10 × 103
s-1 M-1, respectively), which are comparable to those in
1‚BF4. In CH3CN, the ca. 636 nm emission virtually
disappears, whereas it has the highest quantum yield
(QY ) 0.001) and longest lifetime (τ ) 16.2 µs) in CH2Cl2,
and both are smaller than those in 1‚BF4 (QY ) 0.02, τ )
26.0 µs). In Figure 5, a representative example shows the
spectral change upon addition of CH3OH to a CH2Cl2
solution of 2‚BF4, which causes emission intensities de-
creased and lifetimes shortened. The quenching plot is shown
in the inset of Figure 5, and the quenching constant is
obtained from the slope of the Stern-Volmer plot. The
quenching constants of 1‚BF4 and 2‚BF4 are also summarized
in Table 2.
Figure 4. Emission spectra of 2‚BF4 measured in various solvents (CH2Cl2,
CHCl3, THF, CH3OH, and CH3CN) at 298 K. Complex concentration )
9 × 10-5 M. Excitation is at 320 nm.
As shown in Figure 4, photoexcitation of a CH2Cl2 solution
of 2‚BF4 gave an intense emission at ca. 450 nm and a weak
one at ca. 636 nm, and a similar emission in CHCl3 was
also observed. It is somewhat different from those measured
in CH2Cl2 and CHCl3 that the emission spectra measured in
THF and CH3OH show only very weak high- (ca. 424 nm)
and low-energy (ca. 636 nm) emissions. However, the low-
energy emission is absent upon photoexcitation of a CH3-
CN solution of 2‚BF4 with only a high-energy emission at
ca. 440 nm. The low-energy emission of 2‚BF4 measured in
CH2Cl2 is similar to that in 1‚BF4, except the former having
a weaker emission intensity and a shorter lifetime. Because
there is only a weak- and high-energy emission at ca. 477
nm for [8-QNS(AuPPh3)] without any aurophilic interaction,
the excited state is supposed to originate from a S f Au
charge-transfer transition, and an intraligand transition of the
thiolate ligand cannot be excluded. On the basis of the only
weak- and high-energy emission for [8-QNS(AuPPh3)] as
well as Fackler’s work, the low-energy excited state of 2‚BF4
is tentatively assigned to a S f Au charge-transfer transition
modified by a metal-centered 5d(dσ*) f 6p(pσ) transition
as the solid-state excitation origin. The high-energy emissions
In a proposed rearrangement process (Scheme 2), 2‚BF4
is serendipitously isolated and characterized by the X-ray
crystallographic and spectroscopic study. Scrambling of
+
AuPPh3 unit causing a structural change or isomerization
is suggested to be responsible for the dramatic spectroscopic
and luminescence change in various solvents with the
different polarity. Scheme 1 shows an equilibrium reaction
between 1A and 1B with the equilibrium constant K1
()[1B]/[1A]), where the former is supposed to have a
(31) Larson, L. J.; McCauley, E. M.; Weissbart, B.; Tinti, D. S. J. Phys.
Chem. 1995, 99, 7218.
Inorganic Chemistry, Vol. 42, No. 19, 2003 6013

Tzeng et al.
gold(I)‚‚‚gold(I) interaction and the latter has none. Since
there is only a weak- and high-energy emission at ca. 477
nm for [8-QNS(AuPPh3)], it does not show any aurophilic
interaction. Thus, the gold(I)‚‚‚gold(I) interaction is suggested
to be responsible for the low-energy emission at ca. 640 nm
for 1‚BF4. The solvent polarity could affect the charge
localization or delocalization over the 8-QNS ligand as well
as the isomer formation of the 1A (2A) or 1B (2B) forms.
The Au(I)‚‚‚N interactions are anticipated to play a key role
in facilitating the formation of 2B in CH3CN, although how
the polarity influences the isomer formation is sill unclear.
In an earlier communication, Che et al.17d reported a novel
luminescent gold(I) supermolecule with trithiocyanuric acid,
[(LAu)(AuPPhMe2)2]2 (H3L ) trithiocyanuric acid), which
has a novel two-dimensional framework via intermolecular
gold(I)‚‚‚gold(I) interactions and possesses interesting pho-
toluminescence properties. It is unexpected that the hexa-
nuclear supermolecule is obtained by slow diffusion of Et2O
into a CH2Cl2/CH3OH solution of [L(AuPPhMe2)3]. Presum-
ably, two trinuclear [L(AuPPhMe2)3] molecules undergo a
rearrangement process upon loss of two PPhMe2 molecules
to form [(LAu)(AuPPhMe2)2]2. In a rationale based on the
above example and Scheme 1, the absorption similarity
between [8-QNS(AuPPh3)] (ca. 386 nm) and 1‚BF4 (ca. 386
nm) or 2‚BF4 (ca. 380 nm) measured in CH3CN is proposed
to explain the formation scheme of 2‚BF4, shown in Scheme
2. In Scheme 2, we propose that two 1‚BF4 molecules
undergo a rearrangement process to give rise to 2‚BF4
with loss of one [Au(PP3)2](BF4). 2A shows close
gold(I)‚‚‚gold(I) interactions which are suggested to be
responsible for the low-energy emission for 2‚BF4. Accord-
ingly, 2B has no close aurophilic interaction as well as low-
energy emission. K2 ()[2B]/[2A]) represents the equilibrium
reaction between 2A and 2B. Thus, Schemes 1 and 2 have
a similar rationale to explain the dramatic solvent effect on
spectroscopic and luminescence properties of both 1‚BF4 and
2‚BF4 dependent on the solvent polarity. However, the
spectrum of 2‚BF4 measured in CH2Cl2, since it shows only
one strong absorption band and a very weak band at ca. 380
nm. However, the absorption band at ca. 320 and 380 nm
measured in CH3CN cannot obey the Beer law in the same
concentration range. This distinction of the absorption spectra
may be helpful to elucidate that the species in CH2Cl2 is
mostly in a 2A form, responsible for the low-energy
emission, and, in CH3CN, 2A,B are both present in a
significant amount. Thus, the undergoing isomerization
(2A T 2B) is most likely responsible for the distinction of
absorption behavior, obeying or not obeying the Beer law,
between solvents CH2Cl2 and CH3CN, respectively. A self-
quenching rate constant for the ca. 636 nm emission is also
measured in CH2Cl2 as 2.88 × 108 s-1 M-1 but not show
any energy change for concentration-dependence emission
study in CH2Cl2 and CH3CN.
Conclusion
The beautiful hexanuclear supermolecule has 6 gold(I) ions
embedded in an ellipse and surrounded by 4 quinoline and
12 phenyl rings. It is somewhat surprising that although
2‚BF4 is a huge supramolecular structure with six gold(I)
atoms connected by six significant aurophilic interactions
in the solid state, it still shows scrambling of [Ph3PAu]+ units.
Not only is the supramolecular structure of 2‚BF4 novel, but
an interesting family of compounds containing both 1‚BF4
and 2‚BF4 showing a dramatic solvent effect on spectroscopic
and luminescence properties dependent on the solvent
polarity have also been built up. We anticipate that given
this property of luminescence, gold(I) compounds could find
useful applications in the future design of new luminescence
sensors and molecular light-switch devices. Studies of the
detection of volatile organic compounds (VOCs) using
optical-fiber technology in combination with solvent-induced
luminescence properties of this interesting family of com-
pounds are in progress.
+
identification about Au(PPh3)2 units is still unsuccessful,
Acknowledgment. We thank the National Science Coun-
cil and National Chung Cheng University of the Republic
of China for financial support (NSC 90-2113-M-194-028 and
91-2113-M-194-019).
but the isolated [Au(PPh3)Cl] may be obtained from
-
[Au(PPh3)2]‚BF4 + Cl- f [Au(PPh3)Cl] + BF4 + PPh3.
A concentration-dependence UV-vis absorption study in
CH2Cl2 and CH3CN has been performed. The absorption
band at ca. 320 nm measured in CH2Cl2 obeys the Beer law
in the concentration range 10-6-10-3 M suggesting that no
dimerization, oligomerization, or isomerization of the metal
complex occurs. This is in accordance with the absorption
Supporting Information Available: Crystallographic data in
CIF format. This material is available free of charge via the Internet
at http://pubs.acs.org.
IC034041I
6014 Inorganic Chemistry, Vol. 42, No. 19, 2003