Molecular design of luminescence ion probes for various cations based on weak gold(I)...gold(I) interactions in dinuclear gold(I) complexes

Article abstract of DOI:10.1021/ic049094u

A series of luminescent dinuclear gold(I) complexes with different crown ether pendants, [Au₂(P∧P)(S-B15C5)₂] [S-B15C5 = 4′-mercaptobenzo-15-crown-5, P∧P = bis(dicyclohexylphosphino)methane (dcpm) (1), bis(diphenylphosphino)methane (dppm) (2)] and [Au ₂(P∧P)(S-B18C6)₂] [S-B18C6 = 4′-mercaptobenzo- 18-crown-6, P∧P = dcpm (3), dppm (4)], and their related crown-free complexes, [Au₂(P∧P)(SC₆H₃(OMe) ₂-3,4)₂] [P∧P = dcpm (5), dppm (6)], were synthesized. The low-energy emission of the mercaptocrown ether-containing gold(I) complexes are tentatively assigned as originated from states derived from a S → Au ligand-to-metal charge transfer (LMCT) transition. The crown ether-containing gold(I) complexes showed specific binding abilities toward various metal cations according to the ring size of the crown pendants. Spectroscopic evidence was provided for the metal-ion-induced switching on of the gold...gold interactions upon the binding of particular metal ions in a sandwich binding mode.

Full text of DOI:10.1021/ic049094u

Inorg. Chem. 2004, 43, 7421−7430
Molecular Design of Luminescence Ion Probes for Various Cations
Based on Weak Gold(I)‚‚‚Gold(I) Interactions in Dinuclear Gold(I)
Complexes
Chi-Kwan Li, Xiao-Xia Lu, Keith Man-Chung Wong, Chui-Ling Chan, Nianyong Zhu, and
Vivian Wing-Wah Yam*
Open Laboratory of Chemical Biology of the Institute of Molecular Technology for Drug
DiscoVery and Synthesis, Centre for Carbon-Rich Molecular and Nanoscale Metal-Based
Materials Research, and Department of Chemistry, The UniVersity of Hong Kong, Pokfulam Road,
Hong Kong SAR, People’s Republic of China
Received July 9, 2004
A series of luminescent dinuclear gold(I) complexes with different crown ether pendants, [Au2(P
[S-B15C5 bis(dicyclohexylphosphino)methane (dcpm) (1), bis(diphe-
-mercaptobenzo-15-crown-5, P∧P
nylphosphino)methane (dppm) (2)] and [Au2(P∧P)(S-B18C6)2] [S-B18C6
dcpm (3), dppm (4)], and their related crown-free complexes, [Au2(P∧P)(SC6H3(OMe)2-3,4)2] [P∧P
∧
P)(S-B15C5)2]
)
4′
)
)
4′
-mercaptobenzo-18-crown-6, P∧P
)
)
dcpm (5),
dppm (6)], were synthesized. The low-energy emission of the mercaptocrown ether-containing gold(I) complexes
are tentatively assigned as originated from states derived from a S Au ligand-to-metal charge transfer (LMCT)
f
transition. The crown ether-containing gold(I) complexes showed specific binding abilities toward various metal
cations according to the ring size of the crown pendants. Spectroscopic evidence was provided for the metal-ion-
induced switching on of the gold‚‚‚gold interactions upon the binding of particular metal ions in a sandwich binding
mode.
Introduction
spectroscopic detection upon ion-binding.4-6 However, most
of them were focused on systems with metal-to-ligand charge
transfer (MLCT) excited states,4,5 with relatively few studies
or exploitations on other systems.6
Since the first discovery of macrocyclic crown polyethers
by Pedersen et al.,1 the study of their binding abilities toward
alkali metal, alkaline earth metal, and transition metal ions
has aroused much attention.2 There are extensive applications
of crown ethers in the field of metal ion probes, pH sensors,
molecular recognitions, photocontrol of ion extractions and
transport, and construction of chemical switches.3 Although
various types of luminescent chemosensors have been
developed, most of them are mainly confined to systems that
are organic in nature, while relatively little have been
explored in the field of inorganic/organometallic compounds.
Recently, there have been an increasing number of transition
metal-based metalloreceptors reported which can provide
Recently, there has been a growing interest in the study
of polynuclear gold(I) complexes, in particular with regard
to the phenomenon of aurophilicity associated with these
complexes, which results from weak gold‚‚‚gold interac-
tions.7,8 Gold(I) thiolates containing phosphine ligands
(4) (a) MacQueen D. B.; Schanze, K. S. J. Am. Chem. Soc. 1991, 113,
6108. (b). Shen, Y.; Sullivan, B. P. Inorg. Chem. 1995, 34, 6235. (c)
Bushell, K. L.; Couchman, S. M.; Jeffery, J. C.; Ress, L. H.; Ward,
M. D. J. Chem. Soc., Dalton Trans. 1998, 3397. (d) Encinas, S.;
Bushell, K. L.; Couchman, S. M.; Jeffery, J. C.; Ward, M. D.; Flamigni,
L.; Barigelletti, F. J. Chem. Soc., Dalton Trans. 2000, 1783.
(5) (a) Yam, V. W. W.; Lee, V. W. M. J. Chem. Soc., Dalton Trans.
1997, 3005. (b) Yam, V. W. W.; Lee, V. W. M.; Ke, F.; Siu, K. W.
M. Inorg. Chem. 1997, 36, 2124. (c) Yam, V. W. W.; Tang, R. P. L.;
Wong, K. M. C.; Cheung, K. K. Organometallics 2001, 20, 4476. (d)
Yam, V. W. W.; Pui, Y. L.; Cheung, K. K. Inorg. Chim. Acta 2002,
335, 77.
* Author to whom correspondence should be addressed. E-mail:
wwyam@hku.hk. Tel.: (852)2859-2153. Fax: (852)2857-1586.
(1) Pedersen, C. J. J. Am. Chem. Soc. 1967, 89, 2495.
(2) Izatt, R. M.; Bradshaw, J. S.; Nielsen, S. A.; Lamb, J. D.; Christensen,
J. J.; Sen, D. Chem. ReV. 1985, 85, 271.
(3) (a) Xia, W. S.; Schmehl, R. H.; Li, C. J. Tetrahedron 2000, 56, 7045.
(b) Gunnlaugsson, T.; Davis, A. P.; Glynn, M. Chem. Commun. 2001,
2556. (c) Valeur, B.; Leray, I. Coord. Chem. ReV. 2000, 205, 3. (d)
Lehn, J. M. Angew. Chem., Int. Ed. Engl. 1988, 27, 89. (e) Gokel, G.
W.; Mukhopadhyay, A. Chem. Soc. ReV. 2001, 30, 274.
(6) (a) Yam, V. W. W.; Tang, R. P. L.; Wong, K. M. C.; Ko, C. C.;
Cheung, K. K. Inorg. Chem. 2001, 40, 571. (b) Yam, V. W. W.; Pui,
Y. L.; Cheung, K. K.; Zhu, N. New. J. Chem. 2002, 26, 536. (c) Yam,
V. W. W.; Tang, R. P. L.; Wong, K. M. C.; Lu, X. X.; Cheung, K.
K.; Zhu, N. Chem.sEur. J. 2002, 8, 4066.
10.1021/ic049094u CCC: $27.50
Published on Web 10/14/2004
© 2004 American Chemical Society
Inorganic Chemistry, Vol. 43, No. 23, 2004 7421

Li et al.
Chart 1
Figure 1. Perspective drawing of [Au2(dcpm)(S-B15C5)2] (1) with atomic numbering scheme. Hydrogen atoms are omitted, and only the ipso carbons of
the cyclohexyl rings are shown for clarity. Thermal ellipsoids are shown at the 30% probability level.
represent a class of polynuclear d10 metal complexes which
exhibits rich luminescence properties.9 In view of the rich
spectroscopic and luminescence properties exhibited by
gold(I) phosphine complexes, together with the unique and
attractive property of Au‚‚‚Au interactions resulting from
aurophilicity, it is anticipated that the incorporation of
macrocycles to dinuclear gold(I) building block would serve
as an ideal candidate for the design of luminescence
chemosensors as well as molecular optoelectronic switching
devices based on the switching on and off of the
gold‚‚‚gold interactions. A series of dinuclear gold(I) crown
ether-containing complexes which can act as luminescence
ion probe for potassium ions have been reported by us
previously.10 These complexes demonstrated a novel concept
of the utilization of the on/off switching of gold‚‚‚gold
interactions for metal ion sensing. To extend the work of
the novel gold(I) complexes containing benzo-15-crown-5
moieties,10 gold(I) phosphine thiolate complexes con-
taining benzo-18-crown-6 pendants are synthesized, so as
to investigate the effect of crown size on the specificity of
metal ion-binding by such systems. Herein we report the
synthesis of a series of dinuclear gold(I) complexes with
different crown ether pendants, [Au2(P∧P)(S-B15C5)2]
[S-B15C5 ) 4′-mercaptobenzo-15-crown-5, P∧P ) bis-
(dicyclohexylphosphino)methane (dcpm) (1), bis(diphenyl-
phosphino)methane (dppm) (2)] and [Au2(P∧P)(S-B18C6)2]
[S-B18C6 ) 4′-mercaptobenzo-18-crown-6, P∧P ) dcpm
(3), dppm (4)], and their related crown-free analogues,
[Au2(P∧P)(SC6H3(OMe)2-3,4)2] [P∧P ) dcpm (5), dppm (6)];
the crystal structures of 1 and 3 have been determined.
Complexes 1, 2, 5, and 6 have previously been com-
municated. On the basis of a judicious choice of an
appropriate size match between the crown ether moiety and
the metal cations of interest, metal ion-binding in an
intramolecular sandwich binding fashion has been demon-
strated, as confirmed by ESI-mass spectrometry, when the
size of the metal cations is larger than that of the crown
ether cavities. Complexes 1-4 displayed low-energy ligand-
to-metal-metal charge transfer (LMMCT) emission, which
was induced upon the binding of metal cations that are larger
than the size of the crown cavity. Their binding constants,
log Ks, with various metal cations, i.e., K+, Cs+, and Rb+,
have been determined by UV-vis absorption and lumines-
cence spectroscopies.
(7) (a) Schmidbaur, H. Gold Bull. 1990, 23, 11. (b) Scherbaum, F.;
Grohmann, A.; Huber, B.; Kru¨ger, C.; Schmidbaur, H. Angew. Chem.,
Int. Ed. Engl. 1988, 27, 1544. (c) Pyykko¨, P. Chem. ReV. 1997, 97,
597. (d) Jiang, Y.; Alvarez, S.; Hoffmann, R. Inorg. Chem. 1985, 24,
749. (e) Mingos, D. M. P. J. Chem. Soc., Dalton Trans. 1976, 1163.
(f) Harwell, D. E.; Mortimer, M. D.; Knobler, C. B.; Anet, F. A. L.;
Hawthorne, M. F. J. Am. Chem. Soc. 1996, 118, 2679. (g) Naraya-
naswany, R.; Young, M. A.; Parkhurst, E.; Ouellette, M.; Kerr, M.
E.; Ho, D. M.; Elder, R. C.; Bruce, A. E.; Bruce, M. R. M. Inorg.
Chem. 1993, 32, 2506.
(8) Zhang, H. X.; Che, C. M. Chem.sEur. J. 2001, 7, 4887.
(9) (a) Assefa, Z.; McBurnett, B. G.; Staples, R. J.; Fackler, J. P., Jr.;
Assmann, B.; Angermaier, K.; Schmidbaur, H. Inorg. Chem. 1995,
34, 75. (b) 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. (c) Forward, J. M.; Bohmann, D.; Fackler, J. P., Jr.; Staples,
R. J. Inorg. Chem. 1995, 34, 6330. (d) Hanna, S. D.; Zink, J. I. Inorg.
Chem. 1996, 35, 297.
Results and Discussion
Syntheses and Characterization. Complexes 1-6 (Chart
1) were prepared by the direct ligand substitution reactions
of [Au2(P∧P)Cl2] with the mercaptocrown ligand in the
presence of triethylamine as the base. All the complexes are
stable both in the solid state and in solution. Repeated
recrystallization of the complexes from dichloromethane-
diethyl ether to remove the triethylammonium chloride gave
X-ray-quality single crystals of 1 and 3, which have been
structurally determined.
Crystal Structure Determination. Figures 1 and 2 show
the perspective drawings of 1 and 3, respectively. The
respective crystal structure determination data and selected
(10) (a) Yam, V. W. W.; Li, C. K.; Chan, C. L. Angew. Chem., Int. Engl.
1998, 37, 2857. (b) Yam, V. W. W.; Chan, C. L.; Li, C. K.; Wong,
K. M. C. Coord. Chem. ReV. 2001, 216, 173.
7422 Inorganic Chemistry, Vol. 43, No. 23, 2004

Dinuclear Gold(I) Complexes
Figure 2. Perspective drawing of [Au2(dcpm)(S-B18C6)2] (3) with atomic numbering scheme. Hydrogen atoms are omitted, and only the ipso carbons of
the cyclohexyl rings are shown for clarity. Thermal ellipsoids are shown at the 30% probability level.
Table 1. Crystal and Structure Determination Data for 1 and 3
1
3
empirical formula
fw
temp (K)
wavelength (Å)
cryst system
space group
a (Å)
C53H84Au2O10P2S2
1401.24
301
0.710 73
monoclinic
P21/a
16.459(1)
19.956(2)
17.772(2)
90
91.516(9)
90
5835.1(10)
4
1.595
5.219
C57H92Au2O12P2S2
1487.28
293 (2)
0.710 69
monoclinic
P21/c
18.934(4)
20.287(4)
16.638(3)
90
91.51(3)
90
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
6389(2)
4
1.546
4.758
Z
D(calcd) (mg m-3
)
abs coeff (mm-1
F(000)
)
2808
2992
cryst size (mm)
collecn range, 2θmax (deg)
index ranges
0.2 × 0.1 × 0.3
0.3 × 0.2 × 0.1
50
50.68
0 e h e 19
0 e k e 23
-20 e l e 20
10 977
-21 e h e 21
-23 e k e 23
-18 e l e 17
27 329
reflcns collcd
indpndt reflcns
10 587 [R(int) ) 0.045]
9324 [R(int) ) 0.0601]
no. of data for struct anal.
no. of params
4415
4821
307
2.60
545
0.877
goodness-of-fit on F2
final R indices
R1 ) 0.047 [I > 3σ(I)]
wR2 ) 0.0693
0.87, -0.84
R1 ) 0.0475 [I > 2σ(I)]
wR2 ) 0.1223
1.270, -1.458
largest diff peak and hole (e Å-3
)
Table 2. Selected Bond Lengths (Å) and Angles (deg) with Estimated
Standard Deviations (esd’s) in Parentheses for 1 and 3
basically similar. Each gold atom of the complexes is two-
coordinate, with one side bound to the sulfur atom of the
thiolate group and the other side bound to the phosphorus
atom of the diphosphine ligand. The two gold(I)-mercapto-
crown ether moieties, bridged by a diphosphine ligand, are
directed away from each other, probably to relieve the
repulsion between the two sterically bulky crown ether
pendants. The bond angles of P-Au-S in complex 1 are
178.25(13) and 177.77(12)°, while those of complex 3 are
178.25(13) and 177.77(12)°; all of them only show a slight
deviation from ideal linearity, typical of the sp hybridization
in gold(I). The intramolecular Au‚‚‚Au separation of complex
3 (3.2256(8) Å) is slightly shorter than the benzo-15-crown-5
analogue 1 (3.28 Å), which indicates the presence of weak
Au‚‚‚Au interactions in both complexes in the solid state. It
is likely that the steric requirement of the bulky crown ether
pendants prevents shorter Au‚‚‚Au contacts. The Au-S bond
distances in the range of 2.301(3)-2.292(5) Å and Au-P
distances of 2.274(3)-2.262(4) Å are normal and typical
of two-coordinate gold(I) complexes.9b The angles of
C(26)-S(1)-Au(1) and C(32)-S(2)-Au(2) are 109.1(4) and
1
3
Au(1)-P(1)
Au(1)-S(1)
Au(1)‚‚‚Au(2)
Au(2)-P(2)
Au(2)-S(2)
S(1)-C(26)
S(2)-C(40)
S(2)-C(32)
2.262(4)
2.295(4)
3.284(1)
2.265(4)
2.292(5)
1.72(2)
2.274(3)
2.301(3)
3.2556(8)
2.267(3)
2.293(3)
1.732(15)
1.75(2)
1.788(12)
P(1)-Au(1)-S(1)
P(2)-Au(2)-S(2)
C(26)-S(1)-Au(1)
C(40)-S(2)-Au(2)
C(32)-S(2)-Au(2)
C(1)-P(1)-Au(1)
C(1)-P(2)-Au(2)
C(8)-P(1)-Au(1)
C(2)-P(1)-Au(1)
C(20)-P(2)-Au(2)
C(14)-P(2)-Au(2)
P(2)-C(1)-P(1)
176.7(2)
178.25(13)
177.77(12)
109.1(4)
177.3(2)
108.8(7)
108.1(7)
108.1(4)
113.6(3)
117.1(3)
114.6(3)
112.2(4)
113.5(3)
112.0(4)
116.3(5)
115.2(5)
113.0(5)
111.3(5)
113.4(5)
111.9(6)
115.1(5)
120.3(8)
bond distances and angles are summarized in Tables 1 and
2. The molecular structures of complexes 1 and 3 are
Inorganic Chemistry, Vol. 43, No. 23, 2004 7423

Li et al.
Table 3. Electronic Absorption and Emission Spectral Data for the
Mercaptocrown Ether-Containing Gold(I) Complexes
transition and similar assignment has been reported in the
related (thiolato)gold(I) phosphine system.11 For the com-
plexes with the same diphosphine ligands, i.e. 1, 3, and 5
with dcpm ligands and 2, 4, and 6 with dppm ligand, the
close resemblance of their UV-visible absorption spectra
is understandable since a variation in the size of the crown
cavity or a modification to the methoxy groups in the crown-
free analogues would have very little influence on the
electronic effect and hence very little influence on the
spectroscopic properties of the compounds.
emission
abs [λ/nm
medium
(T/K)
corrected
[λem/nm (τo/µs)]
(ꢀ/dm3 mol-1 cm-1)]a
complex 1
solid (298)
solid (77)
CH2Cl2 (298)
CH2Cl2 (77)
274 sh (20 200)
298 (15 700)
324 sh (9700)
b
512
520 (<0.1)
620
complex 2
solid (298)
solid (77)
CH2Cl2 (298)
CH2Cl2 (77)
266 (33 000)
298 sh (16 000)
327 (5330)
650 (<0.1)
628
580 (<0.1)
645
Emission Properties. All the (thiolato)gold(I) phosphine
complexes exhibit luminescence upon photoexcitation in
dichloromethane solution or in the solid state. The measured
lifetimes in the sub-microsecond range suggest that the
emission is derived from a spin-forbidden transition and is
probably of triplet parentage, giving rise to phosphorescence.
The photophysical data are collected in Table 3. The emission
bands at 492-580 nm observed in complexes 1-6 in
dichloromethane solution at 298 K are assigned as derived
from a S f Au LMCT origin, probably with minimal
perturbation by Au‚‚‚Au interactions. It is likely that any
modification of this type would be insignificant given the
relatively large Au‚‚‚Au separations of 3.28 and 3.23 Å
observed in the solid-state structures of 1 and 3, respectively,
the separations of which are believed to be even larger in
solution due to the floppy nature of the molecule. When
compared to similar systems containing significant interac-
tions, the Au‚‚‚Au separations are usually in the range of
ca. 2.90- 3.00 Å.7c,9b,13-16 The result matches well with the
previous works of Fackler, Bruce, and Yam, in which the
emission maxima for S f Au LMCT emissions of gold(I)
thiolate complexes without Au‚‚‚Au interactions are reported
to be at ca. 480-520 nm.7c,9b,13-16 Some modifications due
to Au‚‚‚Au interactions may exist in the solid state, leading
to a slight red shift in the emission maxima. The excitation
and emission spectra of 3 in dichloromethane at room
temperature are depicted in Figure 3. The slightly lower
emission energies of the complexes with the dppm than the
dcpm-containing analogues are in accord with the poorer
electron-donating ability of dppm than dcpm, rendering the
Au(I) metal-centered acceptor orbital lower lying in energy,
complex 3
solid (298)
solid (77)
CH2Cl2 (298)
CH2Cl2 (77)
273 sh (25 300)
298 (19 075)
341 sh (7100)
b
508
492 (<0.1)
530
complex 4
solid (298)
solid (77)
CH2Cl2 (298)
CH2Cl2 (77)
266 (32 680)
302 sh (15 900)
336 (8105)
660 (<0.1)
601
580 (<0.1)
554
complex 5
solid (298)
solid (77)
CH2Cl2 (298)
CH2Cl2 (77)
275 sh (23 500)
300 (15 670)
330 sh (9300)
627 (<0.1)
647
553 (<0.1)
565
complex 6
solid (298)
solid (77)
CH2Cl2 (298)
CH2Cl2 (77)
266 (32 570)
302 sh (14 700)
332 (7740)
650 (<0.1)
640
580 (<0.1)
583
a Measured in dichloromethane at 298 K. b Nonemissive.
108.1(4)°, respectively, in complex 3, while the angles of
C(26)-S(1)-Au(1) and C(40)-S(2)-Au(2) are 108.8(7) and
108.1(7)°, respectively, in complex 1. This indicates that the
two crown moieties of each complex are directed away from
each other. Moreover, due to the steric bulkiness of the
cyclohexyl rings and the crown ether pendants, the shortest
intermolecular Au‚‚‚Au contact is longer than 8 Å in both
complexes, which is too long for any interaction to be
considered.
Electronic Absorption Spectroscopy. The electronic
absorption spectra of all the complexes show high-energy
absorption bands at ca. 266-302 nm and low-energy
absorption shoulders at ca. 324-341 nm with tails extending
to ca. 400 nm. The electronic absorption data for complexes
1-6 are summarized in Table 3. Basically, the electronic
absorption spectra of complexes 3 and 4 are similar to that
of their corresponding analogues 1 and 2. In view of the
similar absorption energies found in the corresponding chloro
analogues, Au2(dcpm)Cl2 and Au2(dppm)Cl2, and in the free
mercaptocrown ether ligands, the high-energy absorption
bands are tentatively assigned as intraligand transitions of
the diphosphine and mercaptocrown ether. The low-energy
absorption shoulders, which are absent in the chloro ana-
logues, Au2(dcpm)Cl2 and Au2(dppm)Cl2, are characteristic
of the (thiolato)gold(I) phosphine system.7g,11,12 Accordingly,
the low-energy absorption shoulders are assigned to a
thiolate-to-gold ligand-to-metal charge transfer (LMCT)
(11) (a) El-Etri, M. M.; Scovell, W. M. Inorg. Chem. 1990, 29, 480. (b)
Jaw, H. R. C.; Mason, W. R. Inorg. Chem. 1989, 28, 4370. (c) Savas,
M. M.; Mason, W. R. Inorg. Chem. 1987, 26, 301. (d) Tzeng, B. C.;
Chan, C. K.; Cheung, K. K.; Che, C. M.; Peng, S. M. Chem. Commun.
1997, 135.
(12) Yam, V. W. W.; Cheng, E. C. C.; Zhou, Z. Y. Angew. Chem., Int.
Ed. 2000, 39, 1683.
(13) (a) Vogler, A.; Kunkely, H. Chem. Phys. Lett. 1988, 150, 135. (b)
Che, C. M.; Kwong, H. L.; Yam, V. W. W.; Cho, K. C. Chem.
Commun. 1989, 885. (c) Che, C. M.; Kwong, H. L.; Poon, C. K.;
Yam, V. W. W. J. Chem. Soc., Dalton Trans. 1990, 3215. (d) Yam,
V. W. W.; Lee, W. K. J. Chem. Soc., Dalton Trans. 1993, 2097.
(14) (a) Pyykko¨, P.; Zhao, Y. Angew. Chem., Int. Ed. Engl. 1991, 30, 604.
(b) Pyykko¨, P.; Li, J.; Runeberg, N. Chem. Phys. Lett. 1994, 218,
133. (c) Go¨rling, A.; Ro¨sch, N.;. Ellis, D. E.; Schmidbaur, H. Inorg.
Chem. 1991, 30, 3986. (d). Ha¨berlen, O. D.; Schmidbaur, H.; Ro¨sch,
N. J. Am. Chem. Soc. 1994, 116, 8241. (e) Burdett, J. K.; Eisenstein,
O.; Schweizer, W. B. Inorg. Chem. 1994, 33, 3261.
(15) (a) Jaw, H. C.; Savas, M.; Rogers, R. D.; Mason, W. R. Inorg. Chem.
1989, 28, 1028. (b) Chastain, S. K.; Mason, W. R. Inorg. Chem. 1982,
21, 1, 3717.
(16) Yam, V. W. W.; Lai, T. F.; Che, C. M. J. Chem. Soc., Dalton Trans.
1990, 3747.
7424 Inorganic Chemistry, Vol. 43, No. 23, 2004

Dinuclear Gold(I) Complexes
Table 4. Binding Constants of Mercaptocrown Ether-Containing
Gold(I) Complexes with Metal Cations Determined by UV-Vis
Spectrophotometric Titration at 298 K
binding consts, log Ksa
complex
K+
Rb+
Cs+
[Au2(dcpm)(S-B15C5)2] (1)
[Au2(dppm)(S-B15C5)2] (2)
[Au2(dcpm)(S-B18C6)2] (3)
[Au2(dppm)(S-B18C6)2] (4)
4.0b
3.4
2.9 (2.9)
4.5
d
3.4
2.3 (2.6)
5.5
3.4b (3.2)
c
c
4.6 (4.6)
a Binding constants, log Ks, are determined from UV-vis spectropho-
tometric method while data in parentheses are determined from emission
spectrophotometric method. b From ref 6a. c Cannot be determined. d Not
measured.
of the complexes rather than resulting from changes in the
solvent polarity.
Figure 3. Excitation (s) and corrected emission (---) spectra of [Au2-
(dcpm)(S-B18C6)2] (3) in dichloromethane at room temperature.
To gain more insight into the cation-binding properties of
the complexes, stability constants (Ks) for the binding of
metal ions to the complexes have been determined. Binding
constants for 1:1 complexation were obtained by a nonlinear
least-squares fit17 of the absorbance versus the concentration
of the metal ion added. The close agreement of the
experimental data with the theoretical fits indicates that the
complexation of a Cs+ ion to the dinuclear Au(I) complex
was in a 1:1 ratio. Since the ionic diameter of Cs+ ion (3.34
Å) is too large to fit into the cavity size of a benzo-18-
crown-6 (diameter: 2.6-3.2 Å), a 1:1 complexation ratio
would indicate that the Cs+ ion is sandwiched between two
benzo-18-crown-6 units within the dinuclear Au(I) complex.
Similar binding studies have been made for complexes 1-4
with CsOTf and RbOTf. The stability constants (Ks) for
complexes 1-4 with various metal ions are summarized in
Table 4. For complexes 1 and 2 with benzo-15-crown-5
pendants, the highest stability constant has been obtained in
the case of binding of K+. The absence of spectral change
in complexes 3 and 4 with benzo-18-crown-6 pendants upon
addition of Na+ or K+ is ascribed to the fact that no sandwich
binding could occur because Na+ or K+ would be bound
inside the benzo-18-crown-6 cavity.
The changes in the luminescence response of the dinuclear
gold(I) complexes toward metal ion binding were found to
be more strikingly pronounced. Figure 5a shows the corrected
emission spectral changes of 4 with excitation at 320 nm
which is the isosbestic wavelength upon addition of CsOTf.
The band at ca. 410 nm showed a drop in intensity with the
concomitant formation of a new low-energy emission band
at ca. 790 nm upon addition of Cs+ ions. An isoemissive
point was obtained at ca. 590 nm. Similar to the electronic
absorption studies, the crown-free analogues of 5 and 6
showed no changes in the emission characteristics upon the
addition of Cs+ ions, indicating that the crown pendants of
the complexes are responsible for the association with Cs+
ions. The stability constants were also obtained from the
emission ion-binding data. The close resemblance of the
experimental data to the theoretical fits further confirmed
that the complexation of Cs+ ion to the dinuclear Au(I)
complex was in a 1:1 ratio. The log Ks value of 4.6 is in
agreement with the value obtained from absorption measure-
Figure 4. Electronic absorption spectral traces of [Au2(dcpm)(S-B18C6)2]
(3) in CH2Cl2-MeOH (1:1 v/v) upon addition of CsOTf at 298 K. The
inset shows a plot of absorbance vs [Cs+] monitored at λ ) 318 nm (9)
and its theoretical fit (s).
leading to a lower energy emission of substantial LMCT
character. Some mixing of a metal-pertubed intraligand
phosphine phosphorescence may also be possible.
Cation Binding Studies. Unlike previous binding studies
of complexes 1 and 2,6 in which their electronic absorption
spectra in CH2Cl2-MeOH (1:1, v/v) mixture containing 0.1
mol dm-3 tetra-n-butylammonium hexafluorophosphate as
supporting electrolyte show spectral changes upon addition
of potassium hexafluorophosphate, no such spectral changes
were observed for complexes 3 and 4 upon addition of
potassium ion under the same condition. However, upon
addition of cesium trifluoromethanesulfonate to 3 and 4,
spectral changes in the UV-vis absorption spectra were
observed. The electronic absorption spectral traces of 3 upon
addition of cesium ions are illustrated in Figure 4. The inset
in Figure 4 shows the changes of absorbance at 318 nm as
a function of Cs+ ion concentration, reaching saturation at
higher concentrations. Clean isosbestic points at 240 and 360
nm for 3 and at 256 and 320 nm for 4 were observed in the
electronic absorption spectra, indicating that the reaction is
clean and probably involves only two absorbing species in
equilibrium present in the solution. Spectrochemical recogni-
tion of guest metal ions is confirmed by the absence of
spectral changes in the absorption bands of the corresponding
crown-free analogues, 5 and 6, upon addition of metal ions
under the same condition. The changes are ascribed to the
specific association of metal cations to the polyether cavity
(17) Bourson, J.; Pouget, J.; Valeur, B. J. Phys. Chem. 1993, 97, 4552.
Inorganic Chemistry, Vol. 43, No. 23, 2004 7425

Li et al.
Figure 6. Excitation spectra of 2 in the absence (s) and in the presence
(---) of potassium ions, monitored at 502 and 790 nm, respectively. (An
asterisk denotes an instrumentation artifact.)
Figure 5. Corrected emission spectra of (a) [Au2(dppm)(S-B18C6)2] (4)
upon addition of various concentrations of CsOTf in CH2Cl2-MeOH (1:1,
v/v) and (b) [Au2(dppm)(S-B15C5)2] (2) upon addition of various concen-
trations of KPF6 in CH2Cl2-MeOH (1:1, v/v).
ments. It is interesting to note that the lifetime of the excited
state for the emission band at 790 nm was determined to be
0.14 µs, while the emission lifetime of the band at 410 nm
in the absence of Cs+ ions was found to be less than 0.1 µs.
Although K+ ions (ionic diameter: 2.66 Å) are well-known
to have a high binding affinity to benzo-18-crown-6, addition
of K+ ions to [Au2(P∧P)(S-B18C6)2] did not give rise to the
growth of a new emission band at 790 nm. Similarly, only
a very small spectral change was observed in the UV-vis
spectra, and no isosbestic points were obtained. The failure
of the fit of the experimental data to a 1:1 complexation
model suggested that the binding mode of K+ ion may be in
a 2:1 (2 K+:Au2) ratio, in which the K+ ion would fit into
the cavity of the benzo-18-crown-6 units.
In the case of [Au2(P∧P)(S-B15C5)2] (where P∧P ) dcpm,
dppm) reported previously,10 the unique luminescence re-
sponse of these gold(I) thiolate complexes toward K+ ion
binding indicates the importance of metal-metal interactions
in reporting the selective binding of metal ions into the bis-
(crown) pocket. As shown in the corrected emission spectrum
in Figure 5b, upon the successive addition of K+ ions to 2,
a drop in emission intensity at ca. 502 nm with a concomitant
formation of a new low-energy emission band at ca. 790
nm (uncorrected wavelength at 720 nm in ref 10) was
observed, with an isoemissive point at ca. 600 nm. Figure 6
shows the excitation spectra of 2 in the absence and in the
presence of potassium ions. The excitation spectra revealed
that the high-energy emission band and the low-energy
emission band came from different origins. The 502-nm
emission band is originated from a higher energy absorption
at 350 nm while the 790-nm emission band is derived from
a lower energy absorption at ca. 400 nm. This observation
is in agreement with the changes observed in the electronic
absorption spectral traces upon addition of potassium ion.
Addition of either Cs+ or Rb+ ions to 1 and 2 also gave
similar emission spectral changes, with log Ks values of 3.4
and 2.3 obtained for 1 and 2, respectively, upon addition of
Cs+ ions, while log Ks values of 3.4 and 2.9 were obtained,
respectively, in the case of Rb+ ions. These values are smaller
Figure 7. Corrected emission spectra of [Au2(dppm)(S-B15C5)2] (2) upon
addition of various concentrations of (a) CsOTf and (b) RbOTf in CH2-
Cl2-MeOH (1:1, v/v). (An asterisk denotes an instrumentation artifact.)
than the respective values obtained from K+ ion-binding
measurements. It is understandable that the cavity of benzo-
15-crown-5 with diameter of 1.7-2.2 Å is most suitable to
sandwich K+ ion (ionic diameter: 2.66 Å) than either Cs+
or Rb+ ions which have larger ionic diameters of 3.34 and
2.98 Å, respectively. As a consequence, the log Ks values
for [Au2(P∧P)(S-B15C5)2] with Cs+ or Rb+ ion-binding
are found to be smaller than those with K+ ions. The
corrected emission spectral changes of 2 upon addition of
various concentrations of CsOTf (a) and RbOTf (b) in
CH2Cl2-MeOH (1:1, v/v) are depicted in Figure 7. The
growth of a new low-energy emission band at ca. 790 nm
upon addition of Cs+ and Rb+ ions was also observed. These
observations were in line with the expectations when crown
ethers with different cavity size were deliberately chosen in
the design of such molecules, as variation in the crown size
could alter the specificity toward various metal cations. In
[Au2(P∧P)(S-B18C6)2], upon addition of Cs+ or Rb+ ions,
which have ionic diameters too large to fit into the cavity of
the benzo-18-crown-6, the Cs+ or Rb+ ions would tend to
sandwich between the two crown moieties, similar to the
sandwich binding mode that occurs in the case of benzo-
15-crown-5 analogues with K+ ions. As a result, the two
Au(I) centers would be brought into close proximity,
resulting in Au‚‚‚Au interactions. As shown in Figure 8, the
7426 Inorganic Chemistry, Vol. 43, No. 23, 2004

Dinuclear Gold(I) Complexes
Table 5. Ion Clusters Observed in the Positive ESI-Mass Spectra of
Various Complexes with Different Metal Cations
m/z
ion cluster
1415
1597
1641
771
[Au2(dppm)(S-B15C5)2‚K]+
[Au2(dppm)(S-B18C6)2‚Cs]+
[{Au2(dppm)(S-B18C6)2‚K2}(ClO4)]+
[Au2(dppm)(S-B18C6)2‚K2]2+
of metal ions, i.e. benzo-15-crown-5 for K+, while benzo-
18-crown-6 for Cs+, through the on/off switching of Au‚‚‚
Au interactions, reported as luminescence signaling.
Apart from spectrophotometric measurements, ESI-mass
spectrometry provides another piece of evidence for the bind-
ing of metal cations to the complexes. The ESI-mass spectro-
metric results for the binding of various metal ions with dif-
ferent complexes were summarized in Table 5. Upon addition
of various metal cations to the gold complexes, either 1:1
or 1:2 complexation adducts were observed, depending on
the size of the metal ion and the preferred mode of binding.
Only the 1:1 bound species, [Au2(dppm)(S-B18C6)2‚Cs]+,
was observed upon addition of excess cesium ion
while mainly 1:2 adducts, [Au2(dppm)(S-B18C6)2‚K2]2+ and
[{Au2(dppm)(S-B18C6)2‚K2}(ClO4)]+, were found in the case
of potassium ion addition. Similar findings have been
observed in the mercaptobenzo-15-crown-5 analogues, in
which the sandwich adduct, [Au2(dppm)(S-B15C5)2‚K]+,
was detected. These further support the complexation stoi-
chiometry obtained from electronic absorption and emission
studies.
Figure 8. Schematic diagram of the orbital splittings and the proposed
sandwich binding mode for cesium ion in [Au2(dcpm)(S-B18C6)2] (3) and
[Au2(dppm)(S-B18C6)2] (4).
2
filled 5dz and empty 6s and 6pz orbitals on each Au atom
would overlap with each other resulting from Au‚‚‚Au
interactions, which then gave rise to bonding and antibonding
combinations of dσ, dσ*, sσ, sσ*, pσ, and pσ* character. A
net stabilization of the dinuclear Au acceptor orbital of pσ
parentage would result, leading to a new emission band in
the red, characteristic of the thiolate-to-gold-gold ligand-
to-metal-metal charge transfer (LMMCT) excited state. This
is in accord with the observation of an excitation band at
ca. 400 nm, attributed to a LMMCT absorption. On the con-
trary, in the absence of K+ ions, complex 2 only shows an
excitation band at ca. 350 nm, ascribed to a LMCT transition.
Conclusion
As an extension of the work on novel dinuclear gold(I)
phosphine complexes containing 4′-mercaptomonobenzo-15-
crown-5 pendants, [Au2(P∧P)(S-B15C5)2] (P∧P ) dcpm,
dppm), a series of gold(I) complexes with crown ethers of
different cavity size have been synthesized so as to elucidate
the perturbation of the ion-binding properties by different
crown pendants.
Although different metal cations (of different sizes) would
be expected to give rise to a variation in the Au‚‚‚Au
distances in the sandwich adduct and hence emission
energies, the observation that addition of K+, Rb+, and Cs+
to 2 gave rise to an emission band of similar energy at ca.
790 nm is indicative of a similar Au‚‚‚Au interaction
irrespective of the size of the metal cation. This may be
rationalized by the rather remote disposition of the ben-
zocrown units from the Au(I) centers and the flexibility of
the thiolate ligand which would become less effective in
affecting the Au‚‚‚Au distance, as well as the rigidity of the
diphosphine bridging ligand as governed by the bite distance
to afford a Au‚‚‚Au separation that is rather preorganized
and predetermined to give the best possible metal-metal
interaction.
All the dinuclear gold(I) complexes exhibited low-energy
emissions in dichloromethane solution at room temperature,
which have been assigned as originating from states derived
from a S f Au ligand-to-metal charge transfer (LMCT)
origin. The ion-binding properties of these complexes with
various metal cations have been studied. Well-defined
isosbestic points in the UV-vis absorption spectra were
observed and the stability constants of the complexes with
the metal cations have been determined. In the mercapto-
crown ether-containing complexes, spectroscopic evidence
has been provided for the metal ion-induced switching on
of the gold‚‚‚gold interactions upon metal ion binding. The
corrected emission spectra of [Au2(dppm)(S-B18C6)2] showed
a drop in intensity at ca. 410 nm with the concomitant
formation of a new low-energy emission band at ca. 790
nm upon addition of cesium ions. An isoemissive point was
obtained at ca. 590 nm. The low-energy band was believed
to originate from a thiolate-to-gold-gold ligand-to-metal-
metal charge transfer (LMMCT) excited state as a result of
the switching on of the Au‚‚‚Au interaction upon cesium
ion binding to the bis(benzo-18-crown-6) moiety which was
On the contrary, addition of an excess of free benzo[15]-
crown-5 to the mixture of 2 and K+ ions extracted the
sandwiched K+ ions from 2, with a breaking of the short
Au‚‚‚Au contact and a reversal of the emission trend.
Similarly, addition of Na+ ions to a mixture of 2 and K+
ions also caused a drop in the intensity of the emission band
at 790 nm, probably as a result of the high affinity of the
benzo[15]crown-5 unit for Na+ ions, which displace the K+
ions.
The variation of crown size on the gold(I) thiolate
complexes is found to be useful for the specific recognition
Inorganic Chemistry, Vol. 43, No. 23, 2004 7427

Li et al.
Fluorolog-2 model F111 fluorescence spectrophotometer with or
without Corning filters and were corrected for instrumental
deliberately chosen in the design for the recognition of
cesium ions, similar to the use of benzo-15-crown-5 in [Au2-
(P∧P)(S-B15C5)2] for the selective recognition of potassium
ions. The binding of various metal cations to the complexes
was further confirmed by ESI-mass spectrometry.
responses. All solutions for photophysical studies (∼10-5 mol dm-3
)
were prepared under high vacuum in a 10-cm3 round-bottomed flask
equipped with a sidearm 1-cm fluorescence cuvette and sealed from
the atmosphere by 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. Liquid nitrogen was placed into the Dewar
flask for low-temperature (77 K) solid-state and glass photophysical
measurements. Emission-lifetime measurements were performed
using a conventional laser system. The excitation source was the
355 nm output (third harmonic) of a Spectra-Physics Quanta-Ray
Q-switched GCR-150-10 pulsed Nd:YAG laser. Luminescence
decay signals from a Hamamatsu R928 photomultiplier tube were
converted to voltage changes by connecting to a 50Ω load resistor
and were then recorded on a Tektronix model TDS-620A digital
oscilloscope. The lifetime τ was determined by a single-exponential
fitting of the luminescence decay trace with the relationship I ) Io
exp(-t/τ), where I and Io are the luminescence intensity at time )
t and 0, respectively. Solution samples for luminescence lifetime
measurements were degassed by no less than four successive
freeze-pump-thaw cycles.
It is envisaged that with the rich spectroscopic and
luminescence properties exhibited by d10 gold(I) complexes,
together with the propensity of gold(I) centers to form weak
Au‚‚‚Au interactions resulting from aurophilicity, various
gold(I) complexes capable of luminescence signaling could
be designed by employing the appropriate bridging and
ancillary ligands with special functions for the recognition
of guest molecules. All this characteristic luminescence
behavior would render the dinuclear gold(I) building block
as an ideal candidate for the design of luminescence
chemosensors as well as molecular optoelectronic switching
devices on the basis of the switching on and off of the metal‚
‚‚metal interactions.
Experimental Section
Materials and Reagents. Benzo-15-crown-5,18 4′-mercapto-
benzo-15-crown-5,19 4′-mercaptobenzo-18-crown-6,19 HAuCl4‚
XH2O,20 and [Au2(P∧P)Cl2] (P∧P ) dcpm, dppm)21-23 were
prepared according to reported procedures. 2,2′-Thiodiethanol,
benzo-18-crown-6, bis(diphenylphosphino)methane, bis(dicyclo-
hexylphosphino)methane, and tetra-n-butylammonium hexafluoro-
phosphate were purchased from Aldrich Chemical Co., and the latter
was recrystallized three times from hot ethanol prior to use. 3,4-
Dimethoxybenzenethiol was obtained from Maybridge Chemical
Co. Ltd. Dichloromethane (Lab Scan, AR) and diethyl ether (Lab
Scan, AR) were purified and distilled using standard procedures
before use.24 All other reagents were of analytical grade and were
used as received.
Binding Constant Determination. The concentrations of the
gold complexes employed in the UV-vis and emission titration
studies are typically in the range of 4 × 10-5 to 1 × 10-4 mol
dm-3. The electronic absorption spectral titration for binding
constant determination was performed on a Hewlett-Packard 8425A
diode-array spectrophotometer at 25 °C which was controlled by a
Lauda RM6 compact low-temperature thermostat. Supporting
electrolyte (0.1 mol dm-3 nBu4NPF6) was added to maintain the
ionic strength of the sample solution constant during the titration
to avoid any changes in the ionic strength of the medium.
Binding constants for 1:1 complexation were obtained according
to17
All reactions were carried out under strictly anhydrous and
anaerobic conditions using standard Schlenk technique under an
atmosphere of nitrogen.
Xlim - X
o([Co] + [Cm] + 1/Ks - {([Co] + [Cm] +
Physical Measurements and Instrumentation. 1H NMR spectra
were recorded on a Bruker DPX-300 (300 MHz) FT-NMR
spectrometer with chemical shifts reported relative to tetramethyl-
silane, SiMe4. Positive ion fast-atom bombardment (FAB) mass
spectra were recorded on a Finnigan MAT95 mass spectrometer.
All electrospray-ionization (ESI) mass spectra were recorded on a
Finnigan LCQ mass spectrometer. Elemental analyses of all newly
synthesized metal complexes were performed on a Carlo Erba 1106
elemental analyzer at the Institute of Chemistry of the Chinese
Academy of Sciences in Beijing. The electronic absorption spectra
were recorded on a Hewlett-Packard 8452A diode-array spectro-
photometer. Steady-state emission and excitation spectra recorded
at room temperature and at 77 K were obtained on a Spex
X ) Xo +
2[Co]
1/Ks)2 - 4[Co][Cm]}1/2) (1)
where Xo and X are the absorbance of the complex at a selected
wavelength in the absence and presence of the metal cation,
respectively, [Co] is the total concentration of the complex, [Cm] is
the concentration of the metal cation, Xlim is the limiting value of
absorbance in the presence of excess metal ion, and Ks is the
stability constant.
From the emission binding data, binding constants were also
obtained using eq 3 by the modification of eq 2 as follows:17
Ilim - Io
I ) Io +
([Co] + [Cm] + 1/Ks - {([Co] + [Cm] + 1/Ks)2 -
4[Co][Cm]}1/2) (2)
2[Co]
(18) Pedersen, C. J. J. Am. Chem. Soc. 1967, 89, 7017.
(19) (a) Shinkai, S.; Minami, T.; Araragi, Y.; Manabe, O. J. Chem. Soc.,
Perkin Trans. 1985, 503. (b) Nabeshima, T.; Hanami, T.; Akine, S.;
Saiki, T. Chem. Lett. 2001, 560.
Here Io and I are the emission intensity of the complex at a selected
wavelength λ in the absence and presence of the metal cation,
respectively, [Co] is the total concentration of the complex, [Cm] is
the concentration of the metal cation, Ilim is the limiting value of
absorbance in the presence of excess metal ion, and Ks is the
stability constant.
(20) Block, B. P.; Bartkiewicz, S. A.; Chrisp, J. D. Inorg. Synth. 1953, 4,
14.
(21) Yam, V. W. W.; Chan, C. L.; Cheung, K. K. J. Chem. Soc., Dalton
Trans. 1996, 4019.
(22) Yam, V. W. W.; Choi, S. W. K. J. Chem. Soc., Dalton Trans. 1994,
2057.
(23) Schmidbaur, H.; Wohlleben, A.; Wagner, F.; Orama, O.; Huttner, G.
Chem. Ber. 1977, 110, 1748.
Syntheses of Mercaptocrown Ether-Containing Complexes.
[Au2(dcpm)(S-B15C5)2] (1). To a solution of [Au2(dcpm)Cl2] (30
(24) Perrin, D. D.; Armarego, W. L. F. Purification of Laboratory
Chemicals, 3rd ed.; Pergamon: Oxford, U.K.
7428 Inorganic Chemistry, Vol. 43, No. 23, 2004

Dinuclear Gold(I) Complexes
mg, 0.034 mmol) in dichloromethane (5 mL) was added a mixture
of 4′-mercaptomonobenzo-15-crown-5 (21 mg, 0.071 mmol) and
triethylamine (40 µL, 0.29 mmol). The reaction mixture was stirred
for 30 min at room temperature, after which the solvent was
removed under reduced pressure. The pale yellow residue was
dissolved in dichloromethane. Recrystallization of the complex by
the diffusion of diethyl ether vapor into a dichloromethane solution
yielded 1 as pale yellow crystals (32 mg, 0.022 mmol, 67% yield).
1H NMR (300 MHz, CDCl3, 298 K): δ 1.10-2.23 (m, 44H,
-C6H11; 2H, -PCH2P-), 3.74 (m, 16H, -OCH2-), 3.90 (m, 8H,
-C6H3OCH2CH2-), 4.10 (m, 8H, -C6H3OCH2-), 6.62 (d, 2H, J
) 8.3 Hz, aryl H meta to S), 7.05-7.10 (m, 4H, aryl H ortho to
S). Positive-ion FAB mass spectrum: m/z 1101, [M - (S-B15C5)]+.
Anal. Found: C, 44.28; H, 5.88. Calcd for C53H84Au2O10P2S2‚
1/2CH2Cl2: C, 44.53; H, 5.89.
(SC6H3(OMe)2)]+. Anal. Found: C, 40.21; H, 5.21. Calcd for
C41H64Au2O4P2S2‚CH2Cl2‚H2O: C, 40.57; H, 5.47.
[Au2(dppm)(SC6H3(OMe)2-3,4)2] (6). The procedure was similar
to that described for the preparation of 2 except 3,4-dimethoxy-
benzenethiol (12 mg, 0.071 mmol) was used in place of 4′-
mercaptomonobenzo-15-crown-5. Recrystallization of the complex
by the diffusion of diethyl ether vapor into dichloromethane solution
1
yielded 6 as yellow solid (24 mg, 0.021 mmol, 65% yield). H
NMR (300 MHz, CDCl3, 298 K): δ 3.70 (s, 2H, -PCH2P-), 3.80
(s, 12H, -OCH3), 6.60 (d, 2H, J ) 8.0 Hz, aryl H meta to S),
7.05-7.10 (m, 4H, aryl H ortho to S), 7.20-7.40, 7.60-7.70 (m,
20H, -PPh2). Positive-ion FAB mass spectrum: m/z 947, [M -
(SC6H3(OMe)2)]+. Anal. Found: C, 43.94; H, 3.67. Calcd for
C41H40Au2O4P2S2: C, 44.11; H, 3.58.
Crystal Structure Determination. Single crystals of [Au2-
(dcpm)(S-B15C5)2] (1) and [Au2(dcpm)(S-B18C6)2] (3) were
obtained from the slow diffusion of diethyl ether vapor into the
dichloromethane solution of the corresponding compounds. For 1,
X-ray diffraction data were collected at 28 °C on a Rigaku AFC7R
diffractometer with graphite-monochromatized Mo KR radiation
(λ ) 0.710 73 Å) using ω-2θ scans with ω-scan angle (0.73 +
0.35 tan θ)° at a scan speed of 8.0 deg min-1 (up to 6 scans for
reflections with I < 15σ(I)). Intensity data (in the range of 2θmax
) 50°; h, 0 to 19; k, 0 to 23; l, -20 to 20; 3 standard reflections
measured after every 300 reflections showed decay of 0.71%) were
corrected for Lorentz and polarization effects. A total of 10 977
reflections were measured, of which 10 587 were unique and Rint
) 0.045. A total of 4415 reflections with I > 3σ(I) were considered
observed and used in the structural analysis. The space group was
uniquely determined on the basis of systematic absences, and the
structure was solved by Patterson methods and expanded by Fourier
methods (PATTY25) and refinement by full-matrix least-squares
using the software package TeXsan.26 Convergence for 307 variable
[Au2(dppm)(S-B15C5)2] (2). The procedure was similar to that
described for the preparation of 1 except [Au2(dppm)Cl2] (29 mg,
0.034 mmol) was used in place of [Au2(dcpm)Cl2]. Recrystallization
of the complex by the diffusion of diethyl ether vapor into a
dichloromethane solution yielded 2 as yellow solid (35 mg,
1
0.025 mmol, 74% yield). H NMR (300 MHz, CDCl3, 298 K):
δ 3.70 (m, 16H, -OCH2-; 2H, -PCH2P-), 3.90 (m, 8H,
-C6H3OCH2CH2-), 4.10 (m, 8H, -C6H3OCH2-), 6.62 (d, 2H, J
) 8.3 Hz, aryl H meta to S), 7.05-7.10 (m, 4H, aryl H ortho to
S), 7.24-7.70 (m, 20H, -PPh2). Positive-ion FAB mass spec-
trum: m/z 1077, [M - (S-B15C5)]+. Anal. Found: C, 42.89; H.
3.91. Calcd for C53H60Au2O10P2S2‚2CH2Cl2: C, 42.71; H, 4.14.
[Au2(dcpm)(S-B18C6)2] (3). The procedure was similar to that
described for the preparation of 1 except 4′-mercaptomonobenzo-
18-crown-6 (25 mg, 0.073 mmol) was used in place of 4′-
mercaptomonobenzo-15-crown-5. Recrystallization of the complex
by the diffusion of diethyl ether vapor into a dichloromethane
solution yielded 3 as pale yellow crystals (32 mg, 0.022 mmol,
1
2
parameters by least-squares refinement on F with w ) 4Fo /σ2-
65% yield). H NMR (300 MHz, CDCl3, 298 K): δ 1.10-2.25
2
2
2 2
(Fo ), where σ2(Fo ) ) [σ2(I) + (0.026Fo ) ] for 4415 reflections
with I > 3σ(I), was reached at R ) 0.047 and wR ) 0.069 with a
goodness-of-fit of 2.60. (∆/σ)max ) 0.05 except for atoms of the
two crown ether parts having large temperature factors. For 3, X-ray
diffraction data were collected at 20 °C on a MAR diffractometer
with a 300 mm image plate detector using graphite-monochroma-
tized Mo KR radiation (λ ) 0.710 73 Å). Data collection was made
with 2° oscillation step of æ, 600 s exposure time, and scanner
distance at 120 mm. A total of 90 images were collected. The
images were interpreted and intensities integrated using program
DENZO.27 The structure was solved by direct methods employing
the SIR-9728 program. Gold, sulfur, phosphorus, and many non-
hydrogen atoms were located according to the direct methods and
the successive least-squares Fourier cycles. According to the
SHELXL-9729 program, all 9324 independent reflections (Rint equal
(m, 44H, -C6H11; 2H, -PCH2P-), 3.70 (m, 24H, -OCH2-), 3.85
(m, 8H, -C6H3OCH2CH2-), 4.10 (m, 8H, -C6H3OCH2-), 6.61
(d, 2H, J ) 8.3 Hz, aryl H meta to S), 7.05-7.15 (m, 4H, aryl H
ortho to S). Positive-ion FAB mass spectrum: m/z 1488, [M +
H]+. Anal. Found: C, 45.35; H, 6.15. Calcd for C57H92Au2O12P2S2‚
1/2CH2Cl2: C, 45.09; H, 6.12.
[Au2(dppm)(S-B18C6)2] (4). The procedure was similar to that
described for the preparation of 2 except 4′-mercaptomonobenzo-
18-crown-6 (25 mg, 0.073 mmol) was used in place of 4′-
mercaptomonobenzo-15-crown-5. Recrystallization of the complex
by the diffusion of diethyl ether vapor into an acetone solution
yielded 4 as pale yellow solid (32 mg, 0.022 mmol, 65% yield).
1H NMR (300 MHz, CDCl3, 298 K): δ 3.70 (m, 24H, -OCH2-;
2H, -PCH2P-), 3.85 (m, 8H, -C6H3OCH2CH2-), 4.10 (m, 8H,
-C6H3OCH2-), 6.65 (d, 2H, J ) 8.3 Hz, aryl H meta to S), 7.05-
7.15 (m, 4H, aryl H ortho to S), 7.25-7.65 (m, 20H, -PPh2).
Positive-ion FAB mass spectrum: m/z 1122, [M - (S-B18C6)]+.
Anal. Found: C, 47.14; H, 4.75. Calcd for C57H92Au2O12P2S2‚
(CH3)2CO: C, 47.31; H, 4.90.
2
to 0.0601, 4821 reflections larger than 4σ(Fo), where Rint ) Σ|Fo
2
2
- Fo (mean)|/Σ[Fo ]) from a total 27 329 reflections were partici-
(25) Beurskens, P. T.; Admiraal, G.; Beurskens, G.; Nosman, 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.
(26) Crystal Structure Analysis Package; Molecular Structure Corp.: The
Woodlands, TX, 1985 and 1992.
(27) Otwinowski, Z.; Minor, W. Methods Enzymol. 1997, 276, 307.
(28) Sir97: a new tool for crystal structure determination and refinement.
Altomare, A.; Burla, M. C.; Camalli, M.; Cascarano, G.; Giacovazzo,
C.; Guagliardi, A.; Moliterni, A. G. G.; Polidori, G.; Spagna, R. J.
Appl. Crystallogr. 1998, 32, 115.
[Au2(dcpm)(SC6H3(OMe)2-3,4)2] (5). The procedure was similar
to that described for the preparation of 1 except 3,4-dimethoxy-
benzenethiol (12 mg, 0.071 mmol) was used in place of 4′-
mercaptomonobenzo-15-crown-5. Recrystallization of the complex
by the diffusion of diethyl ether vapor into dichloromethane solution
1
yielded 5 as yellow solid (23 mg, 0.021 mmol, 61% yield). H
NMR (300 MHz, CDCl3, 298 K): δ 1.10-2.20 (m, 44H, -C6H11;
2H, -PCH2P-), 3.79 (s, 6H, -OCH3), 3.84 (s, 6H, -OCH3), 6.60
(d, 2H, J ) 8.2 Hz, aryl H meta to S), 7.02-7.10 (m, 4H, aryl H
ortho to S). Positive-ion FAB mass spectrum: m/z 971, [M -
(29) SHELXL97: Sheldrick, G. M. SHELXL97: Programs for Crystal
Structure Analysis, release 97-2; University of Go¨ttingen: Goo¨ttingen,
Germany, 1997.
Inorganic Chemistry, Vol. 43, No. 23, 2004 7429

Li et al.
pated in the full-matrix least-squares refinement against F2. These
reflections were in the range -21 e h e 21, -23 e k e 23, and
-18 e l e 17 with 2θmax equal to 50.68°. Convergence ((∆/σ)max
) -0.001, average 0.001) for 545 variable parameters by full-matrix
least-squares refinement on F2 reaches R1 ) 0.0475 and wR2 )
0.1223 with a goodness-of-fit of 0.877.
administered by The University of Hong Kong. The work
has been supported by a CERG Grant from the Research
Grants Council of the Hong Kong Special Administrative
Region of China (Project No. HKU 7020/02P).
Supporting Information Available: Tables giving atomic
coordinates, anisotropic thermal parameters, bond lengths, and bond
angles for complexes 1 and 3 (CIF) and a positive ESI mass
spectrum of a CH2Cl2-MeOH (1:1, v/v) solution of 4 and excess
CsOTf. This material is available free of charge via the Internet at
http://pubs.acs.org.
Acknowledgment. V.W.-W.Y. acknowledges support
from the University Grants Committee of Hong Kong Special
Administration Region, China (Project AoE/P-10/01); the
University Development Fund of The University of Hong
Kong; and The University of Hong Kong Foundation for
Education Development and Research Limited, and C.-K.L.
acknowledges the receipt of a Postgraduate Studentship,
IC049094U
7430 Inorganic Chemistry, Vol. 43, No. 23, 2004