Synthesis and characterization of luminescent rhenium(l) tricarbonyl diimine complexes with a triarylboron moiety and the study of their fluoride ion-binding properties

Article abstract of DOI:10.1021/ic900803a

A serles of alkynylrhenium(l) tricarbonyl diimine complexes with a triarylboron moiety has been synthesized and characterized. The binding properties of the complex toward fluoride Ions have been studied using electronic absorption and emission spectroscopy and were further supported by ¹⁹F NMR binding experiments.

Full text of DOI:10.1021/ic900803a

9664 Inorg. Chem. 2009, 48, 9664–9670
DOI: 10.1021/ic900803a
Synthesis and Characterization of Luminescent Rhenium(I) Tricarbonyl
Diimine Complexes with a Triarylboron Moiety and the Study of Their Fluoride
Ion-Binding Properties
Siu-Tung Lam, Nianyong Zhu, and Vivian Wing-Wah Yam*
Centre for Carbon-Rich Molecular and Metal-Based Materials Research and Department of Chemistry,
The University of Hong Kong, Pokfulam Road, Hong Kong, P.R. China
Received April 25, 2009
A series of alkynylrhenium(I) tricarbonyl diimine complexes with a triarylboron moiety has been synthesized and
characterized. The binding properties of the complex toward fluoride ions have been studied using electronic
absorption and emission spectroscopy and were further supported by 19F NMR binding experiments.
Introduction
properties, a variety of investigations into triarylboron have
emerged.1 Because of their high Lewis acidity and electron-
accepting ability, this kind of materials has been found to show
potential applications in nonlinear optics,2 organic light-emit-
ting diodes (OLEDs),3 and particularly in anion sensing.4-6 By
introducing an electron-rich guest to the triarylboron system,
the pπ-π* conjugation through the vacant p-orbital of the
boron atom can be perturbed, and this provides an opportunity
to modify the electronic properties of these systems. In spite of
With the growing interest in the search for new advanced
materials that show novel responsive behavior and improved
*To whom correspondence should be addressed. E-mail: wwyam@hku.
hk. Fax: þ(852) 2857-1586. Phone: þ(852) 2859-2153.
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r
pubs.acs.org/IC
Published on Web 09/11/2009
2009 American Chemical Society

Article
Inorganic Chemistry, Vol. 48, No. 20, 2009 9665
the growing interest in this area, most of the works are focused
on the studies of organic systems,4,5 with transition metal
complex systems less extensively explored despite numerous
works on metal complexes with rich spectroscopic properties
being known.6 A particular class of transition metal complexes
that has aroused immense interest is the luminescent rhenium(I)
tricarbonyl diimine complexes that show rich and promising
photophysical properties.7 The metal-to-ligand charge-transfer
(MLCT) excited states of these luminescent organometallic
systems are well documented to show large responsive changes
toward host-guest complexation.8 Although there have been
some studies reporting the incorporation of the triarylboron
moiety into Pt(II) and Ir(III) MLCT complexes, most of the
reported complexes are connected to the boron moiety through
the polypyridine ligands.6 It is envisaged that upon incorpora-
tion of the triarylboron moiety through an alkynyl ligand to the
rhenium(I) complexes, the rich photophysical properties of the
MLCT excited state of these metal complex systems may be
capable of serving as versatile spectroscopic reporters and
probes for the fluoride ion. Interestingly, the use of rhenium(I)
tricarbonyl diimine complexes for anion sensing is relatively less
explored when compared with cation sensing and other metal
complex systems.9 Herein, we report the synthesis of triarylbor-
on-containing rhenium(I) tricarbonyl diimine complexes and
their anion-binding properties for fluoride ion.
Scheme 1. Synthesis of Complexes 1-3
driedand freshlydistilledbeforeuse. Therhenium(I)complex
precursors10 and tris(4-ethynyl-2,3,5,6-tetramethylphenyl)-
borane11 were synthesized according to reported procedures
or with slight modifications. Other materials and reagents
were of analytical grade and were used without further
purification.
Synthesis and Characterization of the Rhenium(I) Complexes
1-3. [Re(CO)3(2,9-Me2phen)(CtC-C6Me4-B(C6Me4-CtC-
H)2)] (1). This was prepared by modification of a previously
reported procedure for related alkynylrhenium(I) tricarbonyl
diimine complexes (Scheme 1).7g,12 A mixture of [Re(CO)3(2,9-
Me2phen)Br] (200 mg, 0.36 mmol), TlPF6 (138 mg, 0.39 mmol),
and tris(4-ethynyl-2,3,5,6-tetramethylphenyl)borane (260 mg,
0.54 mmol) in THF (100 mL) was heated under reflux in an
inert atmosphere of nitrogen in the presence of Et3N (5 mL) for
48 h. The yellowish orange suspension was then filtered to
remove the insoluble TlBr, and the orange filtrate was concen-
trated in vacuo. The residue was purified by column chroma-
tography on silica gel using dichloromethane as eluent. The
second band, which contains the desired product, was collected
and evaporated to dryness. Subsequent recrystallization by
layering hexane onto a concentrated dichloromethane solution
of the product gave 1 as analytically pure orange crystal. Yield:
Experimental Details
All reactions were carried out under an argon atmosphere
by using standard Schlenk techniques. The solvents were
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Lapinte, C.; Fathallah, S.; Costuas, K.; Kahlal, S.; Halet, J.-F. Inorg. Chem. 2003,
42, 7086. (n) Chong, S. H.-F.; Lam, S. C.-F.; Yam, V. W.-W.; Zhu, N.; Cheung,
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1
90 mg, 26%. H NMR (400 MHz, CD3CN, 298 K, relative to
Me4Si): δ 1.58 (s, 6H, -CH3), 1.68 (s, 6H, -CH3), 1.80 (s, 12H,
-CH3), 2.26 (s, 12H, -CH3), 3.29 (s, 6H, -CH3), 3.79 (s, 2H,
-CtCH), 7.86 (d, J = 8.2 Hz, 2H, 3- and 8-phenanthrolinyl
H’s), 7.99 (s, 2H, 5- and 6-phenanthrolinyl H’s), 8.50 (d, J = 8.2
Hz, 2H, 4- and 7-phenanthrolinyl H’s). Positive FAB-MS: m/z
959 [M]þ, 931 [M-CO]þ. IR (KBr disk, ν/cm-1): 1883 (s), 1903
(s), 2003 (s) ν(CtO) ; 2091 (w) ν(CtC), 2202 (w) ν(CtC).
Elemental analyses. Found (%): C 66.12, H 5.24, N 2.78. Calcd
for 1: C 66.36, H, 5.04, N 2.92.
[Re(CO)3(phen)(CtC-C6Me4-B(C6Me4-CtCH)2)] (2). This
was prepared according to a procedure similar to that described
for 1, except [Re(CO)3(phen)Br] (170 mg, 0.33 mmol) was used
in place of [Re(CO)3(2,9-Me2phen)Br] to give 2 as orange
crystals. Yield: 80 mg, 24%. 1H NMR (400 MHz, CDCl3, 298
K, relative to Me4Si): δ 1.58 (s, 6H, -CH3), 1.68 (s, 6H, -CH3),
1.80 (s, 12H, -CH3), 2.26 (s, 12H, -CH3), 3.79 (s, 2H,
-CtCH), 7.75 (m, 2H, 3- and 8-phenanthrolinyl H’s), 7.96 (s,
2H, 5- and 6-phenanthrolinyl H’s), 8.45 (d, J = 8.2 Hz, 2H, 4-
and 7-phenanthrolinyl H’s), 9.41 (d, J = 5.1 Hz, 2H, 2- and 9-
phenanthrolinyl H’s). Positive FAB-MS: m/z 930 [M]þ, 902
[M-CO]þ. IR (KBr disk, ν/cm-1): 1876 (s), 1911 (s), 2004 (s)
ν(CtO) ; 2095 (w) ν(CtC), 2202 (w) ν(CtC). Elemental
analyses. Found (%): C 65.52, H 5.35, N 2.75. Calcd for 2: C
65.50, H 5.17; N 2.99.
[Re(CO)3(5,6-Br2phen)(CtC-C6Me4-B(C6Me4-CtCH)2)]
(3). This was prepared according to a procedure similar to that
described for 1, except [Re(CO)3(5,6-Br2phen)Br] (230 mg, 0.33
mmol) was used in place of [Re(CO)3(2,9-Me2phen)Br] to give 3
(10) (a) Drew, M. G. B.; Davis, K. M.; Edwards, D. A.; Marshalsea, J.
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Chem. 2007, 46, 8484.

9666 Inorganic Chemistry, Vol. 48, No. 20, 2009
Lam et al.
as red microcrystalline solid. Yield: 78 mg, 20%. 1H NMR (400
MHz, CD3CN, 298 K, relative to Me4Si): δ 1.58 (s, 6H, -CH3),
1.68 (s, 6H, -CH3), 1.78 (s, 12H, -CH3), 2.26 (s, 12H, -CH3),
3.79 (s, 2H, -CtCH), 7.98 (dd, J = 3.9 and 5.1 Hz, 2H, 3- and
8-phenanthrolinyl H’s), 9.01 (d, J = 5.1 Hz, 2H, 4- and 7-
phenanthrolinyl H’s), 9.49 (d, J = 3.9 Hz, 2H, 2- and 9-
phenanthrolinyl H’s). Positive FAB-MS: m/z 1090 [M]þ, 1062
[M-CO]þ. IR (KBr disk, ν/cm-1): 1890 (s), 1915 (s), 2009 (s)
ν(CtO); 2091 (w) ν(CtC), 2202 (w) ν(CtC). Elemental ana-
employing the SHELXS-97 program14 on a PC. Re and many
non-H atoms were located according to the direct methods. The
positions of the other non-hydrogen atoms were found after
successful refinement by full-matrix least-squares using the
program SHELXL-9715 on a PC. For complex 1, there was
one formula unit in the asymmetric unit. Because of large
thermal parameters of the Re(Me2phen)(CO)3 group, the group
was treated with disorderness in the mode of shift. The shift
˚
started with the Re atom in amount of 0.290 A, and the ligands
lyses. Found (%): C 53.28, H 4.42, N 2.65. Calcd for 3 CH2Cl2:
3
shifted at the same time, that is, two sets of positions of the group
were located. The ratio of the occupancies at the two positions
was found to be 61:39 at the final stage of convergence of the
least-squares refinements. Non-H atoms of the first set of the
group were refined anisotropically. Only the Re atom of the
second set was refined anisotropically, with other non-H atoms
of the second set refined isotropically. Restraints were applied to
the disordered fragments, assuming the phenanthroline ligand
to be flat and the rings to be regular hexagons, with bond lengths
C 53.14, H 4.12, N 2.38.
Physical Measurements and Instrumentation. 1H NMR spec-
tra were recorded on either a Bruker DPX-300 (300 MHz) or a
Bruker AV400 (400 MHz) NMR spectrometer at 298 K with
chemical shifts (δ, ppm) relative to tetramethylsilane (Me4Si).
19F NMR (376.4 MHz) spectra were recorded on a Bruker
AV400 NMR spectrometer at 298 K with chemical shifts (δ,
ppm) relative to trichlorofluoromethane (CFCl3). Positive-ion
fast atom bombardment (FAB) mass spectra were recorded on a
Finnigan MAT95 mass spectrometer. Elemental analyses of the
new compounds were performed on a Carlo Erba 1106 elemen-
tal analyzer at the Institute of Chemistry, Chinese Academy of
Sciences, Beijing.
UV-Vis absorption spectra were recorded on a Hewlett-
Packard 8452A diode array spectrophotometer. Steady-state
emission and excitation spectra at room temperature were
recorded on a Spex Fluorolog-3 Model FL3-211 spectrofluo-
rometer. For solution emission and excitation spectra, samples
were rigorously degassed with no fewer than four free-
ze-pump-thaw cycles prior to the measurements.
˚
of 1.39 A. The corresponding bond lengths and distances of the
Re(Me2phen)(CO)3 group were also assumed to be similar, that
is, Re-C, C-O bonds and 1,3-Re O distances. For complex
3 3 3
2, there was one formula unit in the asymmetric unit. One
chloroform solvent molecule was located with disorderness.
The chloroform was disordered into two sets of positions (in
the ratio of 67:33). Restraints were applied to the disordered
chloroform, assuming similar C-Cl and 1,3-Cl Cl bond
3 3 3
distances. For crystallographic data in CIF, see the Supporting
Information.
Results and Discussion
The electronic absorption spectral titration was performed on
a Varian Cary 50 UV-vis spectrophotometer at room tempera-
ture while the emission titration was performed on a Spex
Fluorolog-3 Model FL3-211 spectrofluorometer. Supporting
electrolyte (0.1 M nBu4NPF6) was added to maintain a constant
ionic strength of the sample solution. Binding constants for 1:1
complexation were obtained by a nonlinear least-squares fit13 of
the absorbance (A) versus the concentration of the fluoride ion
added (cM) according to the following equation:
Crystal Structure Determination. Single crystals of 1
and 2 were obtained by layering of hexane onto a con-
centrated chloroform solution of the respective complex.
The structures of complexes 1 and 2 in the solid state are
depicted in Figures 1 and 2, respectively, and their crystal-
lographic data are summarized in Table 1. In both cases,
the three durene rings of the triarylboron ligand are
arranged in a propeller-like fashion, with the dihedral
angles between the trigonal planar coordination plane of
boron and the planes of the durene rings at 60-66°, and
the C-B-C angles close to the ideal 120°.11 The coordi-
nation geometry at the rhenium(I) center is distorted
octahedral, with the three carbonyl ligands arranged in
a facial fashion. The N-Re-N bond angles of 74.2(5)
-76.2(7)° were found to be less than 90°, as required by
the bite distance exerted by the steric demand of the
chelating phenanthroline ligands, as is commonly found
in other related complexes.7g,h The CtC bond lengths
Alim -Ao
2co
A ¼ Aoþ
½coþcMþ1=Ks -½ðcoþcM
2
1=2
þ1=KsÞ -4cocMꢀ
ꢀ
ð1Þ
where Ao and A 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 triarylboron-
containing rhenium(I) complex, cM is the concentration of the
added fluoride anion, Alim is the limiting value of absorbance at
saturation level, and Ks is the stability constant. For emission
titration studies, eq 1 can be modified to give eq 2, written as
˚
were found to be 1.102(17)-1.124(17) A, typical of those
found in other σ-bonded metal alkynyl systems.7g,h The
Re-CtC units were essentially linear with a Re-CtC
bond angle of 169.8(4)-172.3(7)°, similar to those found
in other related Re(I) alkynyl complex systems.7g,h
Ilim -Io
2co
2
1=2
I ¼ Ioþ
½coþcMþ1=Ks -½ðcoþcMþ1=KsÞ -4cocMꢀ
ꢀ
ð2Þ
Photophysical Properties. The electronic absorption
spectra of complexes 1-3 show intense high-energy ab-
sorption bands at about 270-360 nm, ascribed to an
admixture of intraligand (IL) π f π* transitions of the
diimine and alkynyl ligands. The low-energy absorptions
at about 370-420 nm with extinction coefficients in the
where Io and I are the emission intensities of the complex at a
selected wavelength in the absence and presence of the fluoride
ion, respectively, and Ilim is the limiting value of emission
intensity in the presence of excess fluoride ion.
X-ray Crystallography. Yellow crystals of complexes 1 and 2
with dimensions of 0.3 mm ꢁ 0.25 mm ꢁ 0.1 mm and 0.6 mm ꢁ
0.42 mm ꢁ 0.28 mm, respectively, mounted in glass capillary
were used for data collection at 28 °C on a Bruker Smart CCD
1000 using graphite monochromatized Mo-KR radiation (λ =
(14) Sheldrick, G. M. SHELXS97, SHELX97, Programs for Crystal
::
::
Structure Analysis (Release 97-2); University of Gottingen: Gottingen,
Germany, 1997.
˚
0.71073 A). The structures were solved by direct methods
(15) Sheldrick, G. M. SHELXL97, SHELX97, Programs for Crystal
::
::
Structure Analysis (Release 97-2); University of Gottingen: Gottingen,
(13) Bourson, J.; Pouget, J.; Valeur, B. J. Phys. Chem. 1993, 97, 4552.
Germany, 1997.

Article
Inorganic Chemistry, Vol. 48, No. 20, 2009 9667
Figure 1. Perspective drawing of complex 1 with atomic numbering. Hydrogen atoms are omitted for clarity. Thermal ellipsoids are shown at the 30%
probability level.
Table 1. Crystal and Structure Determination Data of 1 and 2 CHCl3
3
1
2 CHCl3
3
empirical formula
formula weight
temperature
C53H50BN2O3Re
959.96
301(2) K
0.71073 A
triclinic
C52H47BCl3N2O3Re
1051.28
301(2) K
0.71073 A
monoclinic
˚
˚
wavelength
crystal system
space group
P1 (No. 2)
9.463(2)
13.821(2)
20.383(4)
107.81(2)
98.15(2)
92.75(2)
P21/n
13.795(2) A
˚
˚
˚
a, A
˚
b, A
14.022(3) A
˚
c, A
˚
24.428(5) A
90
R, deg
β, deg
γ, deg
volume
Z
density
(calculated)
crystal size
102.43(2)
90
4614.5(15) A
3
3
˚
˚
2500.6(8) A
2
4
1.275 g cm-3
1.513 g cm-3
0.3 mm ꢁ
0.6 mm ꢁ 0.42 mm ꢁ
0.28 mm
1.71 to 25.68°
0.25 mm ꢁ 0.1 mm
2.13 to 25.68°
θ range for data
collection
index ranges
Figure 2. Perspective drawing of complex 2 with atomic numbering.
Hydrogen atoms are omitted for clarity. Thermal ellipsoids are shown at
the 40% probability level.
-11 e h e 11
-14 e k e 16
-24 e l e 24
15223/9170[R(int) =
0.0206]
-16 e h e 16
-17 e k e 15
-29 e l e 29
26696/8737[R(int) =
0.0200]
order of 104 dm3 mol-1 cm-1 were assigned to an ad-
mixture of intramolecular charge-transfer transitions
from the diarylalkynyl moiety to the triarylboron moiety
[π(aryl) f p(B)]11 and [dπ(Re) f π*(diimine)] metal-to-
ligand charge transfer (MLCT) transitions. In addition,
low-energy absorption tails at about 420-440 nm with
extinction coefficients in the order of 103 dm3 mol-1 cm-1
were observed, assigned to the [dπ(Re) f π*(diimine)]
metal-to-ligand charge transfer (MLCT) transition,
probably mixed with some [π(CtCR) f π*(diimine)]
alkynyl-to-diimine ligand-to-ligand charge transfer
reflections
collected/unique
Completeness to θ = 96.6%
25.68°
99.7%
goodness-of-fit on F2 0.944
1.020
R1 = 0.0344, wR2 =
0.0928
final R indicesa
[I > 2σ(I )]
R1 = 0.0667, wR2 =
0.2051
largest diff. peak and 2.200 and -0.792
1.076 and -0.688
-3
˚
hole (e A
)
P
P
P
P
a Rint
=
||Fo2- Fc (mean)|/ [Fo2], R1
=
||Fo| - |Fc||/ |Fo|,
2
P
P
wR2 = { w(Fo2 - Fc2)2/ w(Fo2)2}1/2
.
(LLCT) character.7g,h,l The assignment of the origin of
the absorption bands was further supported by the
solvatochromism studies, with the absorption energy
well correlated with the Dimroth’s solvent parameter16
(16) (a) Reichardt, C.; Dimroth, K. Fortschr. Chem. Forsch. 1968, 11, 1.
(b) Reichardt, C. Angew. Chem., Int. Ed. Engl. 1965, 4, 29. (c) Ng, C.-O.; Lo,
L. T.-L.; Ng, S.-M.; Ko, C.-C.; Zhu, N. Inorg. Chem. 2008, 47, 7447.

9668 Inorganic Chemistry, Vol. 48, No. 20, 2009
Lam et al.
Upon addition of F- ions to a solution of 1 (2.5 ꢁ 10-5
n
M) in acetonitrile (0.1 M Bu4NPF6), a decrease in the
absorbance of the low-energy band was observed.
Although the spectral changes in the UV-vis absorption
spectra was not very significant (Figure 4a), the dramatic
color changes could be readily noticeable by the naked
eye as shown in Figure 4b. The detection limit of the F-
ions was found to be 3.8 ( 0.2 ꢁ 10-6 M, estimated based
on the well-established technique of method detection
limit (MDL) as 3σ.19 Well-defined isosbestic points were
obtained and saturation was reached when the concen-
tration of F- ions was about 3 ꢁ 10-5 M. Figure 4a shows
the electronic absorption spectral traces of 1 in acetoni-
trile (0.1 M nBu4NPF6) upon addition of F- at 298 K. The
inset in Figure 4a showed the titration curve of 1 with F-
ions together with the theoretical fits to the equation for
the formation of a 1:1 adduct.13 Stoichiometry studies
indicated that 1 formed 1:1 complexes with F- ions under
the conditions studied, and the results are summarized in
Table 3. The log Ks values for the binding of F- ions to 1
were found to be 5.62, which is comparable to that
reported in the literature.5 The red shift in absorption
energies observed upon ion-binding is consistent with the
MLCT/LLCT assignment of the low-energy absorption,
since the binding of the negatively charged fluoride ion,
together with an increased electron-donating ability of
the alkynyl ligand upon fluoride ion-binding would cause
the MLCT/LLCT transition to occur at lower energies.
The changes in the luminescence response of 1 toward
F- ion were studied upon excitation at the isosbestic
wavelength of 430 nm in degassed acetonitrile (0.1 M
nBu4NPF6). The emission spectra showed a diminution of
the emission intensities (Figure 5) upon inclusion of the
F- ions, which is similar to their related organic counter-
parts.4,5 The inset in Figure 5 showed the emission titra-
tion curve of 1 with F- ions and the theoretical fits to the
equation for the formation of a 1:1 adduct.13 The origin of
the emission was assigned to be derived from an excited
Figure 3. (a) Normalized electronic absorption spectra of 1 in different
solvents at 298 K. (b) A plot of absorption energy of 1 in different solvents
versus Dimroth’s solvent parameter and its linear least-squares fit (solid
line).
(Figure 3). Negative solvatochromism was observed with
non-polar solvents causing a red shift in the MLCT/
LLCT transitions in the UV-vis absorption spectra,
similar to that of other related rhenium(I) polypyridine
systems.17 It has been reported that this may be due to
interactions of the solvent with the charge transfer excited
state.7a,f,18 The electronic absorption data of complexes
1-3 are collected in Table 2.
3
state of predominantly MLCT in character with some
3
mixing of a LLCT state, as was commonly observed in
other rhenium(I) tricarbonyl diimine systems.7,8 The
decrease in emission intensity could be rationalized by
the coordination of fluoride ion to the empty p orbital of
the boron atom, which would block the intramolecular
charge transfer and interrupt the π conjugation extended
through the boron atom, that led to phosphorescence
quenching. A log Ks value of 5.61 was obtained for the
binding of F- ions to 1. This result is in good agreement
with that obtained from UV-vis absorption binding
studies and further supported the 1:1 complexation mode.
Similar findings were observed in complexes 2 and 3.
In addition, the ion-binding properties of complex 1
have also been probed by 19F NMR spectroscopy by
addition of an excess of nBu4NF in solution. Two distinct
signals were observed at δ -120 ppm and δ -151 ppm,
which were assigned to the free fluoride ions and the
boron-bound fluoride, respectively, based on the chemi-
cal shifts of related compounds reported in the litera-
ture.4l Upon addition of the fluoride ions, dative coordi-
nation between the fluoride and the boron atom would
Upon excitation at λ g 350 nm, the complexes dis-
played a moderately intense emission band in degassed
THF solution at 550-750 nm. The long-lived emission
with lifetimes in the sub-microsecond range, typical of
rhenium(I) tricarbonyl diimine complexes,7g,h,l was sug-
gestive of a triplet parentage. With reference to previous
spectroscopic studies on other related rhenium(I) alkynyl
complexes,7g,h,l the luminescence was assigned as derived
from excited states of a 3MLCT [dπ(Re) f π*(diimine)]
origin, with some mixing of 3LLCT [π(CtCR) f
π*(diimine)] character.
Fluoride-Binding Studies. To explore their potential use
in anion recognition, the anion-binding abilities of these
alkynylrhenium(I) complexes were explored using
UV-vis absorption and emission spectrophotometry.
(17) (a) Lees, A. J. Chem. Rev. 1987, 87, 711. (b) Sullivan, B. P. J. Phy.
Chem. 1989, 93, 24. (c) Xue, W.-M.; Chan, M. C.-W.; Su, Z.-M.; Cheung, K.-K.;
Liu, S.-T.; Che, C.-M. Organometallics 1998, 17, 1622. (d) Heilmann, O.;
Hornung, F. M.; Fiedler, J.; Kaim, W. J. Organomet. Chem. 1999, 589, 2. (e)
::
Knor, G.; Leirer, M.; Vogler, A. J. Organomet. Chem. 2000, 610, 16.
(18) Pu, Y.-J.; Harding, R. E.; Stevenson, S. G.; Namdas, E. B.; Tedeschi,
C.; Markham, J. P. J.; Rummings, R. J.; Burn, P. L.; Samuel, I. D. W.
J. Mater. Chem. 2007, 17, 4255.
(19) MacDougall, D.; Crummett, W. B. Anal. Chem. 1980, 52, 2242.

Article
Inorganic Chemistry, Vol. 48, No. 20, 2009 9669
Table 2. Photophysical Data of Complexes 1-3
Complex
Absorption λabs /nm (ε /dm3mol-1cm-1 a
)
Medium (T /K)
λem/nm (τo /μs)
[Re(CO)3(2,9-Me2phen)(CtC-C6Me4-B-
(C6Me4-CtCH)2)] (1)
254 (62460), 272 (56190), 328 sh
(23825), 398 (25100)
THF (298)
673 (0.37)
solid (298)
solid (77)
glassb (77)
THF (298)
614 (<0.1)
600 (0.9)
570 (19.8)
690 (0.43)
[Re(CO)3(phen)(CtC-C6Me4-B-
(C6Me4-CtCH)2)] (2)
254 (50770), 272 (50140), 336 sh
(17925), 400 (20905)
solid (298)
solid (77)
glassb (77)
THF (298)
620 (<0.1)
610 (1.0)
582 (8.9)
730 (0.16)
[Re(CO)3(5,6-Br2phen)(CtC-C6Me4-B-
(C6Me4-CtCH)2)] (3)
248 (47900), 278 (45440), 340 sh
(14710), 396 (16675), 448 sh (2475)
solid (298)
solid (77)
glassb (77)
694 (<0.1)
620 (0.3)
588 (13.3)
a In THF. b Measured in EtOH-MeOH (4:1, v/v) glass.
Figure 5. Corrected emission spectral changes of 1 upon addition
of nBu4NF in CH3CN (0.1 M nBu4NPF6). Inset: A plot of emission
intensity upon excitation at 430 nm (9) as a function of the concentra-
tion of F- with theoretical fits (solid line) for the 1:1 binding of complex 1
with F-.
Figure 4. (a) UV-Vis spectral changes of 1 upon addition of various
concentrations of nBu4NF in CH3CN (0.1 M nBu4NPF6). Inset: A plot of
absorbance at 386 nm (9) as a function of the concentration of F- with
theoretical fits (solid line) for the 1:1 binding of complex 1 with F-. (b)
Photograph showing the color change of 1 before (left) and after (right)
the addition of fluoride ion.
Table 3. Binding Constants (log Ks) of Complexes 1-3 for Fluoride Ions in
Acetonitrile (0.1 M nBu4NPF6)
Log Ks
Figure 6. 19F NMR spectrum of 1 in the presence of an excess of
Complex
UV-Visible
Emission
nBu4NF in CD3CN.
1
2
3
5.62 ( 0.13
5.58 ( 0.15
5.29 ( 0.02
5.61 ( 0.12
5.58 ( 0.09
5.28 ( 0.04
decrease the electron density at the fluoride, causing a
downfield shift of the signal (Figure 6).

9670 Inorganic Chemistry, Vol. 48, No. 20, 2009
Lam et al.
Conclusion
The work described in this paper has been supported by a
Central Allocation Vote (CAV) Grant from the Research
Grants Council of Hong Kong Special Administrative
Region, China (Project No. HKU2/05C). S.-T.L. ac-
knowledges the receipt of a postgraduate studentship
from The University of Hong Kong.
In conclusion, an alkynylrhenium(I) tricarbonyl diimine
system was found to be capable of binding F- ions with
spectral changes in the UV-vis absorption and emission
spectra, and was further supported by 19F NMR bind-
ing experiment, which may find interesting applications in
the design of spectrochemical and luminescence chemosen-
sors.
Supporting Information Available: X-ray crystallographic
data in CIF format of complexes 1 and 2, table summarizing
data of absorption maxima of 1-3 and Dimroth’s solvent
parameter, and normalized absorption spectra in different
solvents at 298 K and titration spectra with fitting curves of
complexes 2-3 upon addition of fluoride ions by UV-vis and
emission spectroscopic methods. 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 of Hong Kong under the Distin-
guished Research Achievement Award Scheme. We also
acknowledge support from the Strategic Research Theme
on Molecular Materials of The University of Hong Kong.