0.8
0.6
0.4
+
× 1/10
whereas it has the highest quantum yield and longest lifetime in
dichloromethane. Importantly, addition of dichloromethane to a
methanol solution revives the emission. Thus, the decrease in
the 640 nm emission in polar solvents is consistent with the
UV–VIS absorption data. Because the low-energy emission at
640 nm is associated with a gold(i)···gold(i) interaction, the
reaction of Scheme 2 may well explain the apparent solvent-
induced quenching of the emission of 2BF4.
(a)
N
N
S
S
(c)
Au Au
Au
PPh3
1
(b)
(d)
(e)
Ph3P
PPh3
2
550 600 650 700 750 800
λ / nm
(a)
We acknowledge support from the University of Hong Kong,
the Hong Kong Research Grants Council, and the Croucher
Foundation.
0.2
0.0
(b)
(c)
Footnotes
300
350
400
λ / nm
450
500
† Syntheses: [Au(PPh3)(8-qnS)] 1: NEt3 was added dropwise to a methanol
solution (15 ml) of quinoline-8-thiol (8-HqnS, 99 mg). A dichloromethane
solution of [AuCl(PPh3)] (250 mg) was then added and stirred for 30 min.
Then Ag(CF3SO3) (130 mg) was added and the insoluble AgCl was filtered.
The pale yellow filtrate was reduced to ca. 2 ml to give the product
(yield = 50%).
Fig. 3 The absorption spectra of 1 in CH2Cl2 (a), 2BF4 in MeCN (b) and
2BF4 in CH2Cl2 (c); complex concentration = 9 3 1025 m. [Insert is the
emission spectra of 2BF4 (1 3 1024 m) in (a) CH2Cl2, (b) thf, (c) EtOH, (d)
MeOH and (e) MeCN; excitation at 320 nm].
[Au2(8-qnS)(PPh3)2] 2BF4: A solution of Na(8-qnS) was prepared by
adding 8-HqnS (99 mg) and NaOMe (30 mg) in CH2Cl2–MeOH (1:1, 25
ml). [AuCl(PPh3)] (500 mg, 25 ml in dichloromethane) was added to the
solution, which was stirred for 4 h at room temp. After addition of NaBF4
(60 mg) the pale yellow solution was evaporated to dryness. The resulting
solid was extracted with thf (yield = 45%).
which is assigned to S ? AuI charge transfer (LMCT) transi-
tion. For 2BF4 there is a distinct difference in the spectra
measured in dichloromethane and in acetonitrile. In dichloro-
methane, the complex shows an intense absorption band at ca.
320 nm, which is assigned to the 5d(ds*) ? 6p(ps) transition
modified by gold(i)···gold(i) interation. We suggest that coor-
dinating the electrophilic [Au(PPh3)]+ unit on the sulfur atom of
the [Au(8-qnS)] moiety would blue shift the S ? AuI transition
and hence explain the apparent blue shift of the spectrum of
2BF4 from that of 1. Notably, addition of acetonitrile to a
dichloromethane solution of 2BF4 increases the absorption at
ca. 386 nm with a concomitant decrease in the absorption at ca.
320 nm; the spectral changes with an isosbestic point at 352 nm.
Other solvents such as MeOH and EtOH also give similar
spectral changes. We rationalize this finding by the following
equilibrium reaction (Scheme 2).
‡ Crystal data: [Au(PPh3(8-qnS)] 1: C27H21AuNPS, M 619.47,
=
monoclinic, space group P21/n, 14.632(3), b = 10.424(1),
a
=
c = 16.360(3) Å, b = 110.08(1)°, U = 2344(1) Å3, Z = 4, Dc = 1.756
g cm23, crystal dimensions 0.2 3 0.15 3 0.25 mm, m(Mo-Ka) = 64.24
cm21, F(000) = 1200. Intensity data were collected on Rigaku AFC7R
diffractometer with graphite-monochromated Mo-Ka radiation
(l = 0.7107 Å) using w–2q scan mode with 2qmax = 45°. 3489 unique
reflections were measured and 1965 reflections with I > 3s(I) were used in
the refinement. Refinement of positional and anisotropic thermal para-
meters for all non-hydrogen atoms (281 variables) converged to R = 0.074
and Rw = 0.090. The final Fourier difference map showed residual extrema
in the range of 1.89 to 22.54 e Å23
[{Au(PPh3)}2(8-qnS)]BF4·0.5thf 2BF4·0.5thf: C47H40Au2BF4NP2SO0.5
.
,
–
+
+
M = 1201.58, triclinic, space group P1, a = 14.049(5), b = 17.319(6),
19.623(8) Å, a 90.09(3), b 108.72(3), g 101.20(3)°,
PPh3 AuPPh3
Ph3PAu
N
AuPPh3
c
=
=
=
=
S
Au
N
S
U = 4425(3) Å3, Z = 4, Dc = 1.805 g cm23, crystal dimensions 0.20 3
0.30 3 0.50 mm, m(Mo-Ka) = 67.28 cm21, F(000) = 2300. Intensity data
were collected on Enraf-Nonius CAD4 diffractometer with graphite-
monochromated Mo-Ka radiation (l = 0.7107 Å), 11585 unique reflection
(2q < 45°) were measured and 7758 with I > 2s(I) were used in the
refinement. Refinement of positional and anisotropic thermal parameters
for all non-hydrogen atoms (1046 variables) converged to R = 0.035 and
Rw = 0.037. The final Fourier difference map showed residual extrema in
K
D
E
Scheme 2
Form E would be isostructural to form B in Scheme 1 and
would show no intramolecular gold(i)···gold(i) interaction. Its
absorption spectrum, therefore, is anticipated to be similar to
that of 1. Thus the spectral changes shown in Fig. 3 could be
rationalized by a decrease in the equilibrium constant K
(K = [E]/[D]) from acetonitrile to dichloromethane. The
scrambling of the [Au(PPh3)]+ units is very fast on the NMR
timescale, since the 31P NMR spectrum of an acetonitrile
solution of 2BF4 shows only a single peak (d 34.12) at room
temperature and even at 235 °C (d 32.97).
the range of 1.34 to 22.34 e Å23
.
Atomic coordinates, bond lengths and angles, and thermal parameters
have been deposited at the Cambridge Crystallographic Data Centre
(CCDC). See Information for Authors, Issue No. 1. Any request to the
CCDC for this material should quote the full literature citation and the
reference number 182/310.
References
1 B.-C. Tzeng, W.-C. Lo, C.-M. Che and S.-M. Peng, Chem. Commun.,
1996, 181; B.-C. Tzeng, K.-K. Cheung, C.-M. Che and S.-M. Peng,
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C.-M. Che, J. Chem. Soc., Chem. Commun., 1994, 2561; S.-J. Shieh, H.
Xiao, S.-M. Peng and C.-M. Che, J. Chem. Soc., Dalton Trans., 1994,
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The reaction in Scheme 2 could also be shown by emission
spectroscopy. In solution, complex 1 shows a very weak
emission at 477 nm. Excitation of a dichloromethane solution of
2BF4 gives a very weak emission at 460 nm and an intense low-
energy one with a lifetime of 26 ms at 640 nm (Fig. 3, insert).
The low energy emission is absent in 1 and a gold(i)···gold(i)
interaction is most probably responsible for it. The excitation
spectrum of the 640 nm emission matches with the absorption
spectra. The excited state is tentatively assigned to come from
the metal-centred 5d(ds*) ? 6p(ps) excitation, although mixing
with some S ? Au charge-transfer character in the excited state
could not be precluded. Notably, the emission depends on
solvent polarity. Polar solvents such as MeCN, MeOH, EtOH
and thf were found to quench it with quenching rate constants in
the order MeCN > MeOH > EtOH > thf (kq = 1.25 3 105,
0.50 3 105, 0.32 3 105 and 0.24 3 105 m21 s21 respectively).
In acetonitrile, the 640 nm emission virtually disappears,
Received, 20th September 1996; Com. 6/06494I
136
Chem. Commun., 1997
Tzeng, Biing-Chiau
