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Fig.
3
Corrected emission spectral changes of complex
1
(1.0 ꢄ 10ꢂ4 M) in CH2Cl2–MeOH (1 : 1 v/v; 0.1 M Bu4NPF6) upon
addition of Mg(ClO4)2. Inset shows the plot of emission intensity at
675 nm as a function of Mg2+ concentration.
n
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ion-encapsulated adduct.
Fig. 3 shows the emission spectral changes of 1 in
CH2Cl2–MeOH (1 : 1 v/v; 0.1 M nBu4NPF6) solution upon
addition of Mg2+. A new low-energy band at ca. 675 nm
appeared. The excitation spectra of 1 in the absence and in the
presence of Mg2+ ion revealed that the low-energy and the
high-energy bands were derived from different excited state
origin. The excitation spectrum in the presence of Mg2+ shows
a low-energy shoulder at 360 nm, which coincides with the new
absorption band at ca. 360 nm in the UV-vis spectrum
resulting from the switching on of the Auꢀ ꢀ ꢀAu interaction
upon Mg2+ binding. Thus, the low energy emission band at
675 nm has been attributed to originate from an excited state
associated with the switching on of the Auꢀ ꢀ ꢀAu interaction
upon the binding of Mg2+, that gives rise to a reduced
HOMO–LUMO energy gap.
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In summary, a novel tripodal alkynylgold(I) complex with
three oligoether pendants that shows selective binding towards
Mg2+, has been designed and synthesized. Optical reporting
based on the switching on of Auꢀ ꢀ ꢀAu interactions was
demonstrated and utilized as the mode of signal transduction.
V. W.-W. Y. acknowledges the support 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.
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Notes and references
z Crystal data for 3: C65H55Au3O0.5P3, M = 1527.90, monoclinic,
12 S. Watanabe, S. Ikishima, T. Matsuo and K. Yoshida, J. Am.
Chem. Soc., 2001, 123, 8402.
P21/c, a = 29.200(6), b = 13.992(2), c = 28.986(6) A, b = 96.25(2)1,
V = 11772 (4) A3, Z = 8, Dc = 1.724 g cmꢂ3, m = 7.579 mmꢂ1
,
13 It is believed that the –PPh2 groups on the tripodal ligand
would not pose large steric hindrance on the coming together of
the three gold(I) atoms to form short Auꢀ ꢀ ꢀAu contacts as
trinuclear Au(I) and Ag(I) complexes with a related tripodal
phosphine that show short metal–metal contacts are known.
See: C.-M. Che, H.-K. Yip, V. W.-W. Yam, P.-Y. Cheung,
T.-F. Lai, S.-J. Shieh and S.-M. Peng, J. Chem. Soc., Dalton
Trans., 1992, 427.
T = 301 K, 22 320 independent reflections, final R indices [I 4 2s(I)],
R1 = 0.0498, wR2 = 0.1189, Rint = 0.0452, GoF = 1.043.
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ꢁc
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4018 | Chem. Commun., 2009, 4016–4018