Design, synthesis, photophysics, and ion-binding studies of a ditopic receptor based on goid(i) phosphine thiolate complex functionalized with crown ether and urea binding units

Article abstract of DOI:10.1021/ic9021068

A ditopic receptor based on gold(l) phosphine thiolate complex [(B15C5Ph₂P)Au(SC₆H₄NHCONHC₆H ₅)] (1) together with a related crown-free analogue, [(Ph ₃P)Au(SC₆H₄NHCON

Full text of DOI:10.1021/ic9021068

Inorg. Chem. 2010, 49, 2273–2279 2273
DOI: 10.1021/ic9021068
Design, Synthesis, Photophysics, and Ion-binding Studies of a Ditopic Receptor
Based on Gold(I) Phosphine Thiolate Complex Functionalized with Crown Ether
and Urea Binding Units
Xiaoming He and Vivian Wing-Wah Yam*
Centre for Carbon-Rich Molecular and Nano-Scale Metal-Based Materials Research,
Department of Chemistry, and HKU-CAS Joint Laboratory on New Materials, The University of Hong Kong,
Pokfulam Road, Hong Kong, P.R. China
Received October 24, 2009
A ditopic receptor based on gold(I) phosphine thiolate complex [(B15C5Ph2P)Au(SC6H4NHCONHC6H5)] (1) together
with a related crown-free analogue, [(Ph3P)Au(SC6H4NHCONHC6H5)] (2), have been designed and synthesized and
their photophysical properties studied. Complex 1 featured both a benzo-15-crown-5 cation-binding unit in the auxiliary
phosphine ligand and a urea-functionalized thiolate as an anion receptor moiety. The anion- and cation-binding study, salt
extraction ability, as well as the cooperativity have been studied using 1H NMR and ESI-MS techniques.
Introduction
and as a carrier transportation reagent for environmentally
important ion-pair species.4-8 The ditopic hosts are expected
to exhibit allosteric and cooperative effects, where the bind-
ing of one ion alters the association affinity of the counterion
through electrostatic and conformational effects. The ion-
pair recognition can also play an important role in control-
ling the geometry in supramolecular chemistry. Most of the
studies on the heteroditopic hosts have focused on the
organic molecules.4 There has also been increasing interest
in the use of inorganic and organometallic transition metal
complexes as chemosensors for cations and anions, due to the
diversity of their geometry, redox activity, and rich photo-
physical properties.3,9,10 However, ion-pair receptors based
on metal complexes have been relatively much less explo-
red.11
Since Pedersen’s discovery of crown ethers in 1967,1a
supramolecular host-guest chemistry has attracted much
attention that goes beyond the complexation of cations to
more comprehensive views that include anion sensing.1-3
Recently, much effort on the development of a heteroditopic
receptor, which incorporates both individual cation- and
anion-binding sites within a single molecule, has been driven
by its great potential applications, such as in efficient extraction
*To whom correspondence should be addressed. E-mail: wwyam@
hku.hk.
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r
2010 American Chemical Society
Published on Web 01/25/2010
pubs.acs.org/IC

2274 Inorganic Chemistry, Vol. 49, No. 5, 2010
He and Yam
Gold(I) chemistry has been the subject of extensive study
due to its wide range of potential applications, such as in
biological activity,12 catalysis,13 and surface technology.14
Intriguing luminescence and interesting supramolecular
structures are also prominent properties. The presence of
to be responsible for the construction of a wide range of
fascinating supramolecular architectures.17 A number of
luminescent mono-, di-, and polynuclear gold(I) complexes
have been reported,16-25 many of which show fascinating
supramolecular structures as a result of Au Au inter-
3 3 3
Au Au interactions15 has been shown to play animportant
actions.16-25
3 3 3
role in governing the unique electronic absorption and
On the basis of our interest in the study of luminescent
gold(I) complexes and their supramolecular and host-guest
chemistry, a number of homotopic receptors based on gold(I)
complexes, such as di- and tetranuclear gold(I) alkynyl-
crown18 and alkynylcalixcrown complexes,17 which have
been shown to exhibit interesting photophysical and cation-
binding properties, have been reported. Recently, a novel
dipicolylamine-containing alkynylgold(I) complex has been
successfully synthesized and structurally characterized,
which has been shown to exhibit rich photoluminescence
properties and to function as a selective sensor for Cu2þ, as
revealed by the large UV-vis change and significant emission
quenching.20 In addition, the utilization of the switching on
emission features in these complexes16 but also is believed
(12) (a) Hill, D. T.; Sutton, B. M. Cryst. Struct. Commun 1980, 9, 679.
(b) Sutton, B. M.; McGusty, E.; Ealz, D. T.; DiMartino, M. J. J. Med. Chem.
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Gold Bull. 2000, 33, 3. (c) Pyykko, P. Angew. Chem., Int. Ed. 2004, 43, 4412.
€
(d) Pyykko, P.; Zhao, Y. Angew. Chem., Int. Ed. 1991, 30, 604. (e) McCleskey,
T. M.; Gray, H. B. Inorg . Chem. 1992, 31, 1733. (f) Vickery, J. C.; Olmstead,
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(b) Yam, V. W. W.; Cheng, E. C. C. Top. Curr. Chem. 2007, 281, 269.
(17) (a) Yu, S. Y.; Zhang, Z. X.; Cheng, E. C. C.; Li, Y. Z.; Yam, V. W. W.;
Huang, H. P.; Zhang, R. J. Am. Chem. Soc. 2005, 127, 17994. (b) Yu, S. Y.; Sun,
Q. F.; Lee, T. K. M.; Cheung, E. C. C.; Li, Y. Z.; Yam, V. W. W. Angew. Chem., Int.
Ed. 2008, 47, 4551. (c) Sun, Q. F.; Lee, T. K. M.; Li, P. Z.; Yao, L. Y.; Huang, J. J.;
Huang, J.; Yu, S. Y.; Li, Y. Z.; Cheng, E. C. C.; Yam, V. W. W. Chem. Commun.
2008, 5514.
and off of Au Au interactions has been successfully
3 3 3
demonstrated as a novel strategy of optical signal transduc-
tion for chemosensing.21-23
Given the two-coordinate nature of gold(I) complexes, the
rich photophysical properties, as well as the good affinity of
gold(I) to a variety of ligands, it is envisaged that a gold(I)
complex would provide an ideal platform to construct ditopic
receptors. As an extension of our previous work on host-
guest chemistry, herein are reported the design and synthesis
of a simple but novel ditopic receptor based on the gold(I)
phosphine thiolate complex [(B15C5Ph2P)Au(SC6H4NH-
CONHC6H5)] (1), together with its related crown-free ana-
logue [(Ph3P)Au(SC6H4NHCONHC6H5)] (2), and the study
of their photophysical properties. Complex 1 featured both a
benzo-15-crown-5 cation-binding unit in the auxiliary phos-
phine ligand and a urea-functionalized thiolate as an anion
receptor moiety. With such a design, it is envisaged that
complex 1 could bind both cations and anions simultane-
ously. The anion- and cation-binding properties, salt extrac-
tion ability, and the cooperativity have also been studied
using 1H NMR and ESI-MS techniques.
(18) Lu, X. X.; Li, C. K.; Cheng, E. C. C.; Zhu, N.; Yam, V. W. W. Inorg.
Chem. 2004, 43, 2225.
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Angew. Chem., Int. Ed. 2004, 43, 4954. (b) Yam, V. W. W.; Cheung, K. L.; Yuan,
L. H.; Wong, K. M. C.; Cheung, K. K. Chem. Comm. 2000, 1513. (c) Yam,
V. W. W.; Yip, S. K.; Yuan, L. H.; Cheung, K. L.; Zhou, N.; Cheung, K. K.
Organometallics 2003, 22, 2630.
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(b) Yam, V. W. W.; Chan, C. L.; Li, C. K.; Wong, K. M. C. Coord. Chem. Rev.
2001, 216-217, 173. (c) Yam, V. W. W.; Li, C. K.; Chan, C. L. Angew. Chem.,
Int. Ed. 1998, 37, 2857. (d) Li, C. K.; Lu, X. X.; Wong, K. M. C.; Chan, C. L.;
Zhu, N.; Yam, V. W. W. Inorg. Chem. 2004, 43, 7421.
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15, 8842.
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2009, 4016.
(24) Gold(I) alkynyl complexes: (a) Koshevoy, I. O.; Koshinen, L.;
Haukka, M.; Tunik, S. P.; Serdobintsev, P. Y.; Melnikov, A. S.; Pakkanen,
T. A. Angew. Chem., Int. Ed. 2008, 47, 3942. (b) Wei, Q. H.; Zhang, L. Y.; Yin,
G. Q.; Shi, L. X.; Chen, Z. N. J. Am. Chem. Soc. 2004, 126, 9940. (c) Li, D.;
Hong, X.; Che, C. M.; Lo, W. C.; Peng, S. M. J. Chem. Soc., Dalton Trans. 1993,
2929. (d) Che, C. M.; Chao, H. Y.; Miskowski, V. M.; Li, Y.; Cheung, K. K. J. Am.
Chem. Soc. 2001, 123, 4985. (e) Mingos, D. M. P.; Yan, J.; Menzer, S.; Williams,
D. J. Angew. Chem., Int. Ed. 1995, 34, 1894. (f) Puddephatt, R. J. Coord. Chem.
Rev. 2001, 216-217, 313. (g) McArdle, C. P.; Van, S.; Jennings, M. C.;
Puddephatt, R. J. J. Am. Chem. Soc. 2002, 124, 3959. (h) Bruce, M. I.; Hall,
B. C.; Skelton, B. W.; Smith, M. E.; White, A. H. J. Chem. Soc., Dalton Trans.
2002, 995. (i) Abu-Salah, O. M.; Al-Ohaly, A.; Knobler, C. B. J. Chem. Soc.,
Chem.Commun. 1985, 1502. (j) de la Riva, H.; Nieuwhuyzen, M.; Fierro, C. M.;
Raithby, P. R.; Male, L.; Lagunas, M. C. Inorg. Chem. 2006, 45, 1418.
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Lett. 1988, 150, 135. (b) Bardaji, M.; Laguna, A.; Jones, P. G.; Fischer, A. K.
Inorg. Chem. 2000, 39, 3560. (c) Mansour, M. A.; Connick, W. B.; Lachicotte,
R. J.; Gysling, H. J.; Eisenberg, R. J. Am. Chem. Soc. 1998, 120, 1329. (d) Lee,
Y. A.; McGarrah, J. E.; Lachicotte, R. J.; Eisenberg, R. J. Am. Chem. Soc. 2002,
124, 10662. (e) Lee, Y. A.; Eisenberg, R. J. Am. Chem. Soc. 2003, 125, 7778.
(f) Forward, J. M.; Bohmann, D.; Fackler, J. P., Jr.; Staples, R. J. Inorg. Chem.
Experimental Section
ꢀ
1995, 34, 6330. (g) van Zyl, W. E.; Lopez-de-Luzuriaga, J. M.; Mohamed, A. A.;
Staples, R. J.; Fackler, J. P., Jr. Inorg. Chem. 2002, 41, 4579. (h) Vicente, J.;
Materials and Reagents. Potassium tetrachloroaurate(III)
and triphenylphosphine were purchased from Strem Chemicals
Inc. 2,20-Thiodiethanol, chlorodiphenylphosphine, lithium alumi-
num hydride, phenyl isocyanate, and tetra-n-butylammonium
hexafluorophosphate were purchased from Aldrich Chemical
Co., and the latter was recrystallized three times from hot
absolute ethanol and dried under a vacuum for 12 h prior to
use. Tetra-n-butylammonium chloride, tetra-n-butylammonium
ꢀ
Chicote, M. T.; Gonzalez-Herrero, P.; Jones, P. G. J. Chem. Soc., Chem.
Commun. 1995, 745. (i) Jones, W. B.; Yuan, J.; Narayanaswamy, R.; Young,
M. A.; Elder, R. C.; Bruce, A. E.; Bruce, M. R. M. Inorg. Chem. 1995, 34, 1996.
(j) Chiari, B.; Piovewsana, O.; Tarantelli, T.; Zanazzi, P. F. Inorg. Chem. 1985, 24,
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Dalton Trans. 1977, 8. (l) Hanna, S. D.; Khan, S. I.; Zink, J. I. Inorg. Chem.
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Inorg. Chem. 1997, 36, 2294.

Article
Inorganic Chemistry, Vol. 49, No. 5, 2010 2275
bromide, and tetra-n-butylammonium iodide were purchased
from Fluka. 4-Aminophenyl disulfide,26 40-diphenylphosphino-
benzo-15-crown-5 (Ph2P-B15C5),27 and the gold thiolate poly-
mer [Au-SR]¥28 were synthesized according to modified proce-
dures. Dichloromethane, tetrahydrofuran, diethyl ether, and
methanol were purified using standard procedures before use.29
All other reagents were of analytical grade and were used as
received. All reactions were carried out under strictly anhydrous
and anaerobic conditions using standard Schlenk techniques
under an inert atmosphere of nitrogen.
-OCH2-), 3.93 (t, J = 4.0 Hz, 2 H; -OCH2-), 4.09 (m, 2 H;
-OCH2-), 6.95 (t, J = 7.3 Hz, 1 H; -C6H5), 7.02 (dd, J = 8.4
and 2.4 Hz, 1 H; -C6H3-), 7.10 (dd, J=13.3 and 1.8 Hz, 1 H;
-C6H3-), 7.15 (dd, J=8.4 and 2.4 Hz, 1 H; -C6H3-), 7.20 (d,
J =8.6 Hz, 2 H; -SC6H4-), 7.26 (t, J =7.6 Hz, 2 H; -C6H5),
7.33 (d, J = 8.6 Hz, 2 H; -SC6H4-), 7.43 (d, J = 8.5 Hz, 2 H;
-C6H5), 7.50-7.62 (m, 10 H; PPh2), 8.48 (s, 1 H; -NH), 8.59
(s, 1 H; -NH). 31P NMR (202 MHz, d6-DMSO, relative to 85%
H3PO4): δ 38.2. FAB-MS: m/z 892 [M]þ, 649 [M - L]þ, 1101
[B15C5Ph2P-Au-PPh2B15C5]þ. Elem anal. found (%): C,
53.41; H, 5.16; N, 2.96. Calcd. for C39H40AuN2O6PS C4H10O:
Synthesis. [C6H5NHCONHC6H4-4-S-]2. To a solution of
4-aminophenyl disulfide (0.62 g, 2.5 mmol) in anhydrous CH2Cl2
(40 mL) was slowly added phenyl isocyanate (0.6 g, 5.0 mmol) in
CH2Cl2 (10 mL) over 10 min, and the mixture was heated to
reflux overnight under a nitrogen atmosphere. The precipitate
was collected by filtration and washed twice with CH2Cl2 to
yield the product as a white solid. Yield: 1.1 g, 91%. 1H NMR
(400 MHz, DMSO-d6, 298 K, relative to Me4Si): δ 6.97 (t, J =
7.6 Hz, 2 H; -C6H5), 7.27 (t, J = 7.6 Hz, 4 H; -C6H5), 7.45
(m, 12 H; -C6H5 and -SC6H4-), 8.73 (s, 2 H; -NH), 8.86 (s, 2 H;
-NH). Positive-ion FAB-MS: m/z 487 [M þ 1]þ. Elem anal.
found (%): C, 62.82; H, 5.15; N, 11.00. Calcd. for C26H22-
3
C, 53.42; H, 5.21; N, 2.90.
[(Ph3P)Au(SC6H4NHCONHC6H5)] (2). This was synthe-
sized according to a procedure similar to that of 1 except PPh3
(60 mg, 0.23 mmol) was used in place of PPh2B15C5. Subse-
quent recrystallization by the diffusion of diethyl ether vapor
into a dichloromethane solution of the product gave 2 as a pale
yellow solid. Yield: 128 mg, 80%. 1H NMR (400 MHz, DMSO-
d6, 298 K, relative to Me4Si): δ 6.95 (t, J=7.3 Hz, 1 H; -C6H5),
7.20 (d, J = 8.5 Hz, 2 H; -SC6H4-), 7.26 (t, J = 7.7 Hz, 2 H;
-C6H5), 7.31 (d, J=8.5 Hz, 2 H; -SC6H4-), 7.42 (d, J=7.7 Hz,
2 H; -C6H5), 7.54-7.64 (m, 15 H; PPh3), 8.46 (s, 1 H; -NH),
8.57 (s, 1 H; -NH). 31P NMR (202 MHz, d6-DMSO, relative to
85% H3PO4): δ 38.3. Positive-ion FAB-MS: m/z 459 [M - L]þ,
702 [M]þ. Elem anal. found (%): C, 53.48; H, 4.05; N, 3.93.
N4O2S2 CH3OH: C, 62.53; H, 5.05; N, 10.80.
3
HSC6H4NHCONHC6H5. To a suspension of [C6H5NHCO-
NHC6H4-4-S-]2 (0.8 g, 1.65 mmol) and triphenylphosphine (0.45 g,
1.72 mmol) in a dioxane-water mixture (17:3 v/v, 40 mL) was
added 5 drops of concentrated HCl, and the mixture was
allowed to stir overnight at 60 ꢀC in a nitrogen atmosphere.
The solvent was evaporated under reduced pressure, and the resi-
due was dissolved in an aqueous NaOH solution (5%, 20 mL)
and washed with diethyl ether three times. To the aqueous layer
collected was added HCl (10%, 20 mL) to precipitate out the
desired product, which was filtered and washed with water.
Subsequent drying gave the product as a white solid. Yield: 0.5 g,
62%. 1H NMR (400 MHz, DMSO-d6, 298 K, relative to Me4Si):
δ 5.17 (s, 1 H; -SH), 6.96 (t, J=7.6 Hz, 1 H; -C6H5), 7.21 (d,
J = 8.4 Hz, 2 H; -SC6H4-), 7.27 (t, J = 7.6 Hz, 2 H; -C6H5),
7.35 (d, J = 8.4 Hz, 2 H; -SC6H4-), 7.43 (d, J = 8.0 Hz, 2 H;
-C6H5), 8.63 (s, 2 H; -NH). Positive ESI-MS: m/z 244 [M]þ.
Elem anal. found (%): C, 64.05; H, 4.95; N, 11.54. Calcd. for
C13H12N2OS: C, 63.91; H, 4.95; N, 11.47.
Calcd. for C31H26AuN2OPS 0.5C4H10O: C, 53.59; H, 4.22; N,
3
3.79.
Physical Measurements and Instrumentation. The UV-vis
spectra were recorded on a Hewlett-Packard 8452 A diode array
spectrophotometer. 1H NMR spectra with chemical shifts rela-
tive to tetramethylsilane (Me4Si) were recorded on a Bruker
Avance 400 FT-NMR spectrometer. Positive-ion fast atom
bombardment (FAB) mass spectra were recorded on a Finnigan
MAT95 mass spectrometer. Positive electrospray-ionization
(ESI) mass spectra were obtained on a Finnigan LCQ mass
spectrometer. Elemental analysis of the new complexes was per-
formed on a Carlo Erba 1106 elemental analyzer at the Institute
of Chemistry of the Chinese Academy of Sciences in Beijing.
Steady-state excitation and emission spectra were recorded
on a Spex Fluorolog-3 Model FL3-211 fluorescence spectro-
fluorometer equipped with a R2658P PMT detector. All solu-
tions for photophysical studies were prepared under a high
vacuum in a 10-cm3 round-bottomed flask equipped with a
side-arm 1-cm fluorescence cuvette and sealed from the atmos-
phere with a Rotaflo HP6/6 quick-release Teflon stopper.
Solutions were rigorously degassed on a high-vacuum line in a
two-compartment cell with no less than four successive freeze-
pump-thaw cycles. Solid-state photophysical measurements
were carried out with the solid sample loaded in a quartz
tube inside a quartz-walled Dewar flask. Measurements of the
ethanol-methanol-dichloromethane (4:1:1, v/v) glass or solid
samples at 77 K were conducted by using liquid nitrogen filled in
the optical Dewar flask. Excited-state lifetimes of samples in
fluid solutions or in the solid states were measured using a
conventional laser system. The excitation source used 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).
Luminescence decay signals were detected by a Hamamatsu
R928 photomultiplier tube, recorded on a Tektronix Model
TDS-620 A (500 MHz, 2 GS s-1) digital oscilloscope, and
analyzed by using a program for exponential fits. The concen-
trations of the gold complexes employed in the UV-vis and
emission spectral studies are typically in the range of 2.5 ꢀ 10-5
[Au(SC6H4NHCONHC6H5)]¥. To the solution of KAuCl4
(189 mg, 0.5 mmol) in CH3OH (15 mL) and water (1 mL) was
added dropwise 2,20-thiodiethanol (0.5 mL). The stirring was
maintained until the solution turned colorless. HSC6H4NH-
CONHC6H5 (122 mg, 0.5 mmol) in THF (2 mL) was added, and
a white precipitate began to form immediately from the reaction
mixture. After stirring for 30 min, the solid was separated;
washed with water, CH3OH, and diethyl ether; and dried under
a vacuum to give the product as a white solid. Yield: 215 mg,
98%. Elem anal. found (%): C, 35.61; H, 2.77; N, 6.33. Calcd.
for C13H11AuN2OS: C, 35.46; H, 2.52; N, 6.36.
[(B15C5Ph2P)Au(SC6H4NHCONHC6H5)] (1). A mixture of
[Au{SC6H4NHCONHC6H5}]¥ polymer (100 mg, 0.23 mmol)
and PPh2B15C5 (103 mg, 0.23 mmol) in CH2Cl2 (15 mL) was
stirred for 2 h under N2. The mixture was then filtered, and the
solvent was removed under reduced pressure. The residue was
redissolved in CH2Cl2 and was recrystallized by layering n-hexane
onto a CH2Cl2 solution of the product and washed with diethyl
ether to give 1 as a white solid. Yield: 134 mg, 65%. 1H NMR
(400 MHz, DMSO-d6, 298 K, relative to Me4Si): δ 3.60 (m, 8 H;
-OCH2-), 3.72 (t, J = 4.0 Hz, 2 H; -OCH2-), 3.77 (m, 2 H;
to 2.0 ꢀ 10-4 mol dm-3
.
(26) Price, C. C.; Stacy, G. W. Organic Syntheses, 1955, 3, 86.
(27) Okano, T.; Iwahara, M.; Konishi, H.; Kiji, J. J. Organomet. Chem.
1988, 346, 267.
Results and Discussion
(28) Antonella, B.; Oliver, B.; Pietro, D.; Serena, L.; Fabio, M.; Piero, Z.
Eur. J. Inorg. Chem. 2007, 865.
(29) Perrin, D. D.; Armarego, W. L. F. Purification of Laboratory
Chemicals, 3rd ed.; Pergamon: Oxford, U. K., 1988.
Synthesis and Characterization. The synthetic route of
complexes 1 and 2 is summarized in Scheme 1. 4-Amino-
phenyl disulfide was first allowed to react with isocyanate

2276 Inorganic Chemistry, Vol. 49, No. 5, 2010
Scheme 1. Synthetic Route of Complexes 1-2
He and Yam
to give the corresponding urea disulfide. This was fol-
lowed by reduction of the disulfide with triphenylphos-
phine to give the desired air- and moisture-stable urea-
containing thiol in relatively high yield.
Table 1. Photophysical Data of Complexes 1 and 2
absorptiona λ/nm
medium
(ε ꢀ 10-4/dm3
emission
em/nm (τ0/μs)
complex
mol-1 cm-1
288 (3.12)
)
(T/K)
λ
The gold(I) phosphine thiolate complexes with a urea
receptor were prepared by the reaction of the gold(I)
thiolate polymer with the different phosphine ligands. All
the newly synthesized complexes have been characterized
by 1H NMR, 31P NMR, FAB-MS or ESI-MS, and gave
satisfactory elemental analyses. In the positive FAB-mass
spectra, besides the parent molecular ion peak [M]þ, the
[M - L]þ ion cluster which corresponded to the loss of
one urea-containing thiolate ligand has always been ob-
served. For complex 1, the ion cluster due to [Au(PR3)2]þ
was also present in the spectra with significant intensity.
Electronic Absorption and Emission Properties. The
electronic absorption spectra of complexes 1 and 2 show
intense high-energy absorption bands at ca. 288-290 nm,
with lower-energy tails extending to ca. 400 nm in CH2-
Cl2. The photophysical data are tabulated in Table 1.
According to the previous studies on the related phos-
phinogold(I) thiolate systems,25 the high-energy absorp-
tion bands are tentatively assigned as the intraligand
transitions of the phosphine and urea-functionalized
thiolate ligands. The low-energy tail, which is absent in
the spectra of the corresponding phosphinogold(I) chlo-
ride and free ligand, is characteristic of the phosphino-
gold(I) thiolate systems and is tentatively assigned to the
thiolate-to-gold ligand-to-metal charge transfer (LMCT)
transition.
1
DCM (298)
solid (298)
solid (77)
451, 530 (<0.1)
530 (0.5)
511 (15.0, 3.4)
451 (70.6, 17.6)
426, 534 (0.1, 0.34)
573 (0.64, 0.1)
535 (13.4)
glassb (77)
DCM (298)
solid (298)
solid (77)
2
290 (2.35)
glassb (77)
530 (20.2)
a In dichloromethane solution. b In EtOH-MeOH-CH2Cl2 (4:1:1, v/v).
Figure 1. Normalized emission spectra of 1 (----) and 2 (—) in dichloro-
methane at 298 K.
at 298 K. With reference to previous spectroscopic work
on gold(I) phosphine thiolate complexes,25 the lower
energy emissions with lifetime in the microsecond range
are tentatively assigned as originating from a thiolate-to-
gold ligand-to-metal charge transfer (LMCT) excited
state of phosphorescence nature. The high-energy emis-
sion, which has a lifetime in the nanosecond regime, is
tentatively assigned to states arising from the metal-per-
turbed intraligand transition of fluorescence nature. The
relatively weak low-energy emission of complex 1 might be
due to the photoinduced electron transfer (PET) quench-
ing effectof the electron-donating oligoether oxygen atoms
on the crown ether moiety, as is commonly observed in
Excitation of complex 2 in degassed CH2Cl2 solution at
room temperature gives rise to intense long-lived low-
energy emission at ca. 534 nm, with a shoulder at 564 nm,
with vibrational progressional spacings of ca. 1000 cm-1
,
which are tentatively ascribed to the vibrational mode of
the N-C-N group on the urea moiety and/or the aro-
matic C-H deformation modes. A high-energy emission
band at ca. 426 nm is also obvious, but with a lower
intensity. Unlike its crown-free analogue 2, excitation of
complex 1 in a degassed dichloromethane solution pro-
duces an intense high-energy emission at ca. 451 nm, with
a low-energy emission shoulder at ca. 530 nm. Figure 1
shows the emission spectra of 1 and 2 in dichloromethane

Article
Inorganic Chemistry, Vol. 49, No. 5, 2010 2277
Figure 2. (a) 1H NMR spectral changes of 1 (4.8 mM) upon addition of tetra-n-butylammonium chloride in CD3CN-DMSO-d6 (9:1, v/v). (b) 1H NMR
titration curves of 1 with the three different anions (Cl-, Br-, and I-) in CD3CN-DMSO-d6 (9:1, v/v), where the changes of proton chemical shift of NHd are
monitored. (c) Job’s plots for 1:1 binding of 1 with Cl- and Br-, showing a 1:1 stoichiometry. The changes of proton chemical shift of NHd are monitored.
crown ether-containing luminophores.30 In the solid state
at 298 and 77 K, complex 1 is found to exhibit higher
energy emission compared to that of 2. The reason may be
due to the fact that the crown ether unit with stronger
electron-donating ability is expected to render the gold(I)
atom in complex 1 more electron-rich and hence increases
the thiolate-to-gold LMCT transition energy. The rela-
tively large Stokes shift together with the observed lumi-
nescence lifetimes in the microsecond range are suggestive
of a triplet parentage.
follow the trend Cl->Br->I- (Figure 2b), reflecting the
decrease in charge density of the anionic guest species,
since the ionic radii of Cl-, Br-, and I- are 1.81, 1.95, and
˚
2.16 A, respectively.
A 1:1 binding mode has been proposed and confirmed
by the method of continuous variation. Figure 2c shows
the Job’s plots for the binding of 1 with Cl- and Br- ions.
A plot of the changes of proton chemical shift of NHd
versus X1 (= [ 1]/([G] þ [1])) shows a break point at a
molar ratio of ca. 0.5, indicative of a 1:1 complexation
stoichiometry. The binding constants Ks for 1 toward
Cl-, Br-, and I- are determined to be 599 ( 90, 109 ( 15,
and 16 ( 2 M-1, respectively, using the EQNMR pro-
gram for a 1:1 binding model (Table 2).31 The order of
anion-binding affinity of complex 1 is found to be Cl- >
Br- . I-, consistent with the decrease in charge density of
the anionic guest species. The experimental data are
found to be in good agreement with the theoretical fits
obtained from the EQNMR program using a 1:1 binding
model.31 The anion-binding properties of complex 1 with
various halides (Cl-, Br-, and I-) have also been studied
using UV/vis and emission spectroscopy. However, in-
significant spectral changes in the UV-vis absorption
and emission spectra were observed.
Ion-Binding Studies. The anion-binding properties of
1
complex 1 have been quantitatively investigated by H
NMR spectroscopy. Figure 2a shows the 1H NMR
spectral changes of complex 1 upon the addition of Cl-
(as tetra-n-butylammonium salt) in CD3CN-DMSO-d6
(9:1, v/v). The tetra-n-butylammonium counterion with
its large size is expected not to bind to the crown ether.
Upon the addition of chloride, the signals of the two
NH protons show a considerable downfield shift of up to
1.7 ppm, while the other proton signals are found to
undergo essentially negligible changes, suggesting that
the Cl- ion would bind to the urea group of complex 1
through a hydrogen bonding interaction. Analogous
investigations have also been carried out with larger
halides such as Br- and I-, which show similar spectral
1
Cation binding has also been studied using the H
1
changes in the H NMR spectroscopy. However, the
magnitude of the complexation-induced H NMR shift
NMR titration experiment. The addition of a Naþ ion
in the form of perchlorate salt to 1 leads to a slight
downfield shift by ca. 0.1 ppm of the proton signals of
the crown ether, as a result of the decrease in the electron
1
is found to be smaller than that of Cl- and is found to
(30) deSilva, 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.
(31) Hynes, M. J. J. Chem. Soc., Dalton Trans. 1993, 311.

2278 Inorganic Chemistry, Vol. 49, No. 5, 2010
He and Yam
Table 2. Summary of Binding Constants of the Ditopic Receptor 1 for Halides
in the Absence and in the Presence of 1 equiv of NaClO4 in CD3CN-d6-DMSO
(9:1, v/v) at 298 Ka
halidesb
Cl-
Naþ additive
binding constant (Ks/M-1
)
none
Naþ
none
Naþ
none
Naþ
599 ( 90
155 ( 20
109 ( 15
c
16 ( 2
34 ( 5
Br-
I-
a The binding constants were analyzed on the basis of the downfield
shift of the urea NH signals. Errors in the binding constants were less
than 15%. b Halides employed were as tetra-n-butylammonium salts.
c Not determined.
Figure 4. Expanded ion cluster of (a) [1 Na]þ at m/z 915 from the
3
Figure 3. 1H NMR spectra of 1 (5.6 mM) (a) in the unbound state and
(b) as the [1 NaCl] adduct in CDCl3.
positive ESI-mass spectrum and (b) [1 Cl]- at m/z 926 from the negative
ESI-mass spectrum, in chloroform solution, and simulated isotopic
3
3
patterns of (c) [1 Na-1]þ and (d) [1 Cl-1]-.
3
3
density upon Naþ binding to the crown cavity. These
changes are also accompanied by a slight upfield shift of
the urea NH protons by ca. 0.1 ppm, probably due to the
binding of the Naþ ion into the crown unit that destroys
the intermolecular hydrogen bonding interaction bet-
ween the NH of the urea unit and O atoms in the crown
ether moiety. The binding event also shows a 1:1 stio-
chiometry by the method of continuous variation, and the
binding constant Ks for Naþ has been determined to be
with an excess of solid NaCl for 20 h. The changes in the
1H NMR chemical shifts of 1 suggest a rapid exchange
process. Compared with the free complex, the proton
resonances of the two urea NH signals of the [1 NaCl]
3
adduct show a large downfield shift, suggesting the pre-
sence of hydrogen bonding interaction of the NH group
with Cl-. Meanwhile, the protons of the crown ether
show a slight upfield shift, which is rather unusual and
might be due to a ring current effect resulting from the
π-stacking of the phenyl urea group with the benzocrown
ether because of the ion pairing, which would bring the
two binding units into close proximity. Complex 1 also
shows good ability in the extraction of solid NaI, as
revealed by the large downfield shift of the two urea
NH signals. However, with KI and CsOTf, no obvious
ca. 34 M-1
.
Experiments to study the cooperative effect of the
presence of Naþ on the halide binding have also been
carried out by repeating the H NMR titration experi-
1
ments for anions in the presence of 1 equiv of NaClO4.
Different cooperativities have been observed for different
halides. The addition of I- to the [1 Na]þ adduct gives a
1
change in the H NMR spectra can be observed, which
3
binding constant of 34 ( 5 M-1, 2-fold larger than the
binding constant for I- with the free receptor 1, indicating
a positive cooperativity. For Cl-, however, a negative
cooperativity has been observed, and the binding con-
stant in the presence of Naþ is found to be smaller than
that with free complex 1. The above results agree with the
trend that an anion with larger size tends to give the larger
cation-induced affinity, which is consistent with the study
reported by Smith and co-workers.5
may be due to the large cation size of Kþ and Csþ that
cannot fit well into the cavity of the benzo-15-crown-5
unit. Although Kþ is well-known to be capable of binding
to two benzo-15-crown-5 units in a sandwich binding
mode,21,22,32 the large steric bulk of the crown moiety
(-PPh2B15C5) in complex 1 might hinder the intermole-
cular sandwich binding with Kþ. As a control, the crown-
free analogue 2 has been investigated, which essentially
shows negligible 1H NMR spectral changes upon similar
The binding property of the ditopic complex 1 has also
been assessed by determining if the ditopic receptor 1 is
capable of extracting solid salt, such as NaCl, into chloro-
form. Figure 3 shows the typical 1H NMR spectral
changes of complex 1 in CDCl3 solution after stirring
(32) (a) Xia, W. S.; Schmehl, R. H.; Li, C. J. J. Am. Chem. Soc. 1999, 121,
5599. (b) Cacciapaglia, R.; Di Stefano, S.; Mandolini, L. J. Am. Chem. Soc.
2003, 125, 2224. (c) Yamauchi, A.; Hayashita, T.; Nishizawa, S.; Watanabe, M.;
Teramae, N. J. Am. Chem. Soc. 1999, 121, 2319.

Article
Inorganic Chemistry, Vol. 49, No. 5, 2010 2279
solid-liquid extraction, suggesting that the heteroditopic
structure that could simultaneously bind the cation and
anion is essential for salt transport.
presence of Naþ have been carried out using 1H NMR
spectroscopy. The results show good 1:1 binding of 1 with
anions, with a stability trend of Cl->Br- . I-. In addition,
for I- with the largest size, the presence of Naþ shows a
positive cooperativity effect, giving a larger binding cons-
tant. The ditopic receptor 1 also shows a good ability to
solubilize NaCl and NaI salts in organic chloroform solu-
The adduct of NaCl salt has also been confirmed by
positive and negative ESI-MS experiments. After liquid-
solid extraction, complex 1 exhibits intense signals at m/z
915 corresponding to the [1 þ Na]þ adduct in the positive
mode, and at m/z 928 corresponding to the [1 þ Cl]- in the
negative mode (Figure 4). The close resemblance of
the isotopic pattern of the two expanded ion clusters with
the simulated patterns further supports the salt complex-
ation. For the extraction of NaI salt, the signal at m/z 915
corresponding to the [1 þ Na]þ could also be obser-
ved. However, the signal of the [1 þ I]- cannot be detec-
table, which may be due to the weak hydrogen bonding
interaction between 1 and the I- anion.
1
tion, as evidenced by the H NMR and ESI-MS experi-
ments. Crown-free complex 2 shows essentially negligible
capability in such solid-liquid transport of NaCl, suggesting
the ditopic composition is essential for the complexation of
simple salt.
It is envisaged that d10 gold(I) complexes, with rich
photophysical properties and the two-coordinate nature, as
well as the good affinity of gold with a variety of ligands,
would provide an ideal platform to construct ditopic recep-
tors. The design of various ditopic gold(I) complexes by
incorporating different ligands with special receptor sites for
recognition of guest molecules is in progress.
Conclusion
In summary, a novel ditopic receptor 1 based on a gold(I)
phosphine thiolate complex has been successfully designed
and synthesized, which contains a urea-functionalized thio-
late as an anion-binding site, and a benzo-15-crown-5 ether
unit in the phosphine auxiliary ligand for cation binding. In
the solid state at 298 and 77 K, complex 1 is found to exhibit a
slightly higher LMCT emission energy compared to that of 2,
which might be due to the presence of the stronger electron-
donating crown ether moiety on the phosphine ligand of
complex 1, rendering the gold(I) atom more electron-rich,
and hence increases the thiolate-to-gold LMCT transition
energy. The anion-binding studies in the absence and in the
Acknowledgment. V.W.-W.Y. acknowledges the sup-
port from The University of Hong Kong under the
Distinguished Research Achievement Award Scheme
and the URC Strategic Research Theme on Molecular
Materials. This work has been supported by a General
Research Fund (GRF) grant from the Research Grants
Council of Hong Kong Special Administrative Region,
P. R. China (HKU 7050/08P). X.H. acknowledges the
receipt of a postgraduate studentship, administered by
The University of Hong Kong.