Coordination-driven self-assembly of metallamacrocycles via a new Pt II2 organometallic building block with 90° geometry and optical sensing of anions

Article abstract of DOI:10.1021/om100202c

A new Pt^II ₂ organometallic building block with 90° geometry, 3,6-bis[trans-platinum(triethylphosphine)₂(nitrate) (ethynyl)]carbazole (5), containing an ethynyl functionality is synthesized in reasonable yield by employing a Sonagashira coupling reaction. Multinuclear NMR and electrospray ionization mass spectrometry (ESI-MS) including a single-crystal X-ray diffraction study characterized this 90° building unit. The self-assembly of 5 with three flexible ditopic donors (L_a-L _c) afforded [2 + 2] metallamacrocycles (6a-c) [where L_a = 1,3-bis(4-pyridyl)isophthalamide; L_b = 1,3-bis(3-pyridyl) isophthalamide, and L_c = 1,2-di(4-pyridyl)ethane]. All three [2 + 2] self-assembled macrocycles were characterized by various spectroscopic techniques, and the molecular structure of 6a was determined by the single-crystal X-ray diffraction method. The square-type macrocycle 6a was designed using amide-based ligand L_a to make it a suitable system composed of a fluorophorereceptor combination. The amide functional group is the receptor site for the anions, which can bind through hydrogen-bonding interaction, whereas the carbazole-based 90° building unit is the fluorophore unit. Macrocycle 6a was found to be fluorescent in nature and showed dramatic fluorescence enhancement in a DMF/H₂O solvent mixture upon titration with P₂O₇^4-, which plays important roles in various biological functions such as energy transduction in organisms and controls metabolic processes by participating in various enzymatic reactions. Interestingly, the nonresponsive nature of the fluorescence intensity of 6a upon addition of the anions F^-, ClO₄^-, and H₂PO₄^- makes it a suitable fluorescent sensor for pyrophosphate anion (P₂O₇^4-).

Full text of DOI:10.1021/om100202c

Organometallics 2010, 29, 2971–2980 2971
DOI: 10.1021/om100202c
Coordination-Driven Self-Assembly of Metallamacrocycles via a
II
2
New Pt Organometallic Building Block with 90° Geometry and
Optical Sensing of Anions
†
†
Sankarasekaran Shanmugaraju, Arun Kumar Bar, Ki-Whan Chi, and
‡
,†
Partha Sarathi Mukherjee*
†
Department of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore-560 012, India, and
Department of Chemistry, University of Ulsan, Ulsan 680-749, Republic of Korea
‡
Received March 16, 2010
II
A new Pt organometallic building block with 90° geometry, 3,6-bis[trans-platinum(triethyl-
2
phosphine) (nitrate)(ethynyl)]carbazole (5), containing an ethynyl functionality is synthesized in
2
reasonable yield by employing a Sonagashira coupling reaction. Multinuclear NMR and electro-
spray ionization mass spectrometry (ESI-MS) including a single-crystal X-ray diffraction study
characterized this 90° building unit. The self-assembly of 5 with three flexible ditopic donors (L -L )
a
c
afforded [2 þ 2] metallamacrocycles (6a-c) [where L =1,3-bis(4-pyridyl)isophthalamide; L =1,3-
a
b
bis(3-pyridyl)isophthalamide, and L = 1,2-di(4-pyridyl)ethane]. All three [2 þ 2] self-assembled
c
macrocycles were characterized by various spectroscopic techniques, and the molecular structure of
6
a was determined by the single-crystal X-ray diffraction method. The square-type macrocycle 6a
was designed using amide-based ligand L to make it a suitable system composed of a fluorophore-
a
receptor combination. The amide functional group is the receptor site for the anions, which can bind
through hydrogen-bonding interaction, whereas the carbazole-based 90° building unit is the fluoro-
phore unit. Macrocycle 6a was found to be fluorescent in nature and showed dramatic fluorescence
4
7
-
enhancement in a DMF/H O solvent mixture upon titration with P O , which plays important
2
2
roles in various biological functions such as energy transduction in organisms and controls metabolic
processes by participating in various enzymatic reactions. Interestingly, the nonresponsive nature
-
-
-
of the fluorescence intensity of 6a upon addition of the anions F , ClO , and H PO makes it a
4
2
4
4
suitable fluorescent sensor for pyrophosphate anion (P O ).
-
2
7
Introduction
diverse number of structural motifs accessible via coordina-
tion chemistry of transition metals. The architectural advan-
tage of the rigid square-planar coordination environment of
Pd(II) and Pt(II) has long been utilized for the purpose of
several molecular architectures by several groups. More-
over, an easy way of functionalization of these coordination
For more than a decade, abiological self-assembly of
discrete supramolecular structures has received considerable
attention due to their potential for applications as sensors
1-3
1
and in host-guest chemistry. Of the various self-assembly
protocols, metal-ligand coordination driven self-assembly
is especially appealing and effective because of the large and
(
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*
Corresponding author. Fax: 91-80-2360-1552. Tel: 91-80-2293-3352.
E-mail: psm@ipc.iisc.ernet.in.
1) (a) Leininger, S.; Olenyuk, B.; Stang, P. J. Chem. Rev. 2000, 100,
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r 2010 American Chemical Society
Published on Web 06/08/2010
pubs.acs.org/Organometallics

2
972 Organometallics, Vol. 29, No. 13, 2010
Shanmugaraju et al.
Scheme 1. Self-Assembly of Molecular Squares 6a-c via the New Organometallic 90° Building Block 5 and Flexible Ditopic Donors
(
L -L )
a
c
assemblies by incorporating suitable functional groups is
also an important aspect of this methodology. Several
functional groups such as porphyrine, calixarene, and
others have been incorporated into discrete supramole-
possible to obtain from cis-blocked square-planar
4
,5
acceptors.
On the other hand, anions play fundamental roles in a wide
range of chemical and biological processes, and considerable
efforts have been devoted to the development of abiotic
2
cules. Among the several kind of linkers used to design
6
receptors for anionic species. In particular, phosphate
polynuclear transition metal complexes, the ones that con-
tain ethynyl spacers in the backbones have shown to be good
members to design a variety of supramolecules with poten-
3
(PO4 ) and pyrophosphate (P O ) play vital roles in
-
4-
2
7
various biological functions such as energy transduction in
organisms and controlling metabolic processes by partici-
pating in enzymatic reactions. Moreover, pyrophosphate is
the product of ATP hydrolysis under cellular conditions. In
this regard, detection of phosphate-based anions has been
the main focus of several groups over the last several years
with particular attention being paid to fluorescent chemo-
4
tial applications in optical electronics. In the majority of the
cases, finite assemblies of these metal ions are the derivatives
of cis-blocked 90° acceptors. In the past few years, indepen-
dently and in parallel, we, Stang, and others have reported
II
II
several shape-selective di-/polynuclear Pt /Pd linkers and
their self-assembly of various architectures such as rectan-
gle, hexagon, pentagon, and dodecahedron, which are not
7
sensors for this kind of anion.
Here, we report the synthesis and characterization of a new
organometallic shape-selective linker, 3,6-bis[trans-platinum-
(triethylphosphine) (nitrate)(ethynyl)]carbazole (5), repre-
(
4) (a) Yam, V. W-W.; Tao, C.-H.; Zhang, L.; Wong, K. M-C.;
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2
II
senting the first example of a Pt organometallic building
2
2
2
unit with 90° geometry. Self-assembly of 5 with flexible ditopic
donors (L ) resulted in the formation of [2 þ 2] molecular
a-c
1
squares (6a-c) (Scheme 1). Metallamacrocycles 6a-c show
luminescent behavior in solution due to the presence of a Pt-
ethynyl functionality and conjugated π-electrons. Macro-
cycle 6a is an interesting system of fluorophore-receptor-
fluorophore combination composed of carbazole-based
fluorophore and amide receptor. The solution-state fluores-
cence of the molecular square 6a was enhanced efficiently
4-
upon titration with pyrophosphate (P O ) solution. Inter-
2
7
estingly, no such noticeable enhancement in fluorescence
intensity was observed upon titration with other anions such
(
l) Grosshenny, V.; Harriman, A.; Hissler, M.; Ziessel, R. J. Chem. Soc.,
-
-
-
2þ
as F , ClO , and H PO . Although several Zn -based
4 2 4
Faraday Trans. 1996, 92, 2223. (m) Ziessel, R.; Hissler, M.; El-ghayoury,
A.; Harriman, A. Coord. Chem. Rev. 1998, 178-180, 1251.
(
8
optical sensors for pyrophosphate are known, macrocycle
5) (a) Schweiger, M.; Seidel, R. S.; Schmitz, M.; Stang, P. J. Org.
Lett. 2000, 2, 1255. (b) Olenyuk, B.; Whiteford, J. A.; Stang, P. J. Nature
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2
Ko, S. O. J. Inorg. Chem. 2005, 44, 7886. (e) Elsegood, M. R. J.; Smith,
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J. Org. Chem. 2005, 70, 9603. (g) Ojida, A.; Nonaka, H.; Miyahara, Y.;
Tamaru, S.-I.; Sada, K.; Hamachi, I. Angew. Chem., Int. Ed. 2006, 45, 5518.
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6) (a) Gale, P. A. Acc. Chem. Res. 2006, 39, 465. (b) Yoon, J.;
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Article
Organometallics, Vol. 29, No. 13, 2010 2973
II
6a represents a new class of Pt fluorescent sensor for this
anion.
(1:1) as eluent. Yield: 900 mg, 40%. Anal. Calcd for C40
NP Pt : C, 36.13; H, 5.08; N, 1.05. Found: C, 35.86; H, 5.36; N,
67 2
H I -
4
4
2
1
1
.29. H NMR (CDCl , 400 MHz): δ 8.20 (s, NH), 7.94 (s, 2H),
3
7
.36 (d, 2H, J=8.4 Hz), 7.28 (d, 2H, J=6.8 Hz), 2.29 (m, 24H,
Experimental Section
3
1
2 3 3
CH -ethyl), 1.24 (m, 32H, CH -ethyl). P NMR (CDCl , 120
MHz): δ 8.63 (s, JPt-P = 1728.7 Hz). IR (KBr): ν 2113.3 cm
for the ethynyl group.
1
-1
Materials and Methods. The building block 5 was synthesized
under a dry nitrogen atmosphere using standard Schlenk tech-
niques. Solvents were dried and distilled according to stand-
ard literature procedures. 1,2-Bis(4-pyridyl)ethane, isonicotinyl
chloride hydrochloride, 3-aminopyridine, and 4-aminopyridine
were purchased from Aldrich (USA) and were used without
2
Synthesis of 3,6-Bis[trans-platinum(triethylphosphine) (nitrate)-
(
(
ethynyl)]carbazole (5). A 20 mL vial was charged with 0.3 g
0.22 mmol) of 4 and 10 mL of dry chloroform. A yellow pre-
cipitate of AgI was formed upon treatment of the above solution
with 80.4 mg (0.47 mmol) of AgNO in 5 mL of methanol. After
further purification. 1,3-Bis(4-pyridyl)isophthalamide (L ) and
a
3
3 h of stirring at room temperature in the dark, the suspension
was filtered through Celite using a glass fiber. To the concen-
1
ing the reported procedures. NMR spectra were recorded on a
,3-bis(3-pyridyl)isophthalamide (L ) were synthesized follow-
b
9
1
Bruker 400 MHz spectrometer. The chemical shifts (δ) in the H
NMR spectra are reported in ppm relative to tetramethylsilane
(Me Si) as internal standard (0.0 ppm) or the proton resonance
resulting from incomplete deuteration of the NMR solvents:
CD NO (4.33). P NMR spectra were recorded at 120 MHz,
and the chemical shifts (δ) are reported in ppm relative to
external 85% H PO at 0.00 ppm. Mass spectra of the self-
4
assembled macrocycles were recorded on an ESI-MS spectro-
meter using standard spectroscopic grade solvents. IR spectra
and electronic absorption spectra were recorded on a Bruker
ALPHA FT-IR spectrometer and Perkin-Elmer LAMBDA 750
UV/visible spectrophotometer, respectively. Fluorescence emis-
sion studies were carried out on a Horiba JOBIN YVON
Fluoromax-4 spectrometer.
Synthesis of 3,6-Diethynylcarbazole (3). In a flame-dried
00 mL round-bottom Schlenk flask 3,6-dibromocarbazole (1)
1.0 g, 3.07 mmol) and 2 mL of trimethylsilylacetylene were
trated solution (5 mL) was added diethyl ether to isolate 5 as an
off-white powder. Yield: 220 mg, 82%. Anal. Calcd for C40
N
N, 3.71. H NMR (CDCl
(s, 2H), 7.28 (d, 4H, J=7.2 Hz), 2.01 (m, 24H, CH
2
(m, 32H, CH
67
H -
O
6
P
4
Pt : C, 40.03; H, 5.63; N, 3.50; Found: C, 39.96; H, 5.80;
2
4
3
1
3
, 400 MHz): δ 8.01 (s, NH), 7.86
-ethyl), 1.28
, 120 MHz): δ 20.09
3
1
3
2
3
1
3
-ethyl). P NMR (CDCl
3
1
-1
3
(s, J
Pt -P
=1848.36 Hz). IR (KBr): ν 2124.6 cm for the ethynyl
-
þ
group. ESI-MS (m/z): 1156.03 [5 - NO þ H O] , 538.01 [5 -
3
- þ
]
2
-
2þ
2NO3
]
, 430.03 [5 - 6PEt - NO
.
3
3
General Procedure for the Synthesis of 6a-c. To a stirred
slurry of the corresponding flexible ditopic donor (L -L ) in
acetone (2 mL) was added a clear solution of 5 in acetone (2 mL)
in 1:1 molar ratio. Initially, a clear solution was formed, which
upon further stirring at 50 °C for 5 h yielded the product as a
precipitate. The solid product was washed several times with
acetone and finally washed with diethyl ether.
6a. Building block 5 (30.0 mg, 0.02 mmol) and 1,3-bis(4-
pyridyl)isophthalamide L (7.94 mg, 0.02 mmol) were reacted in
acetone (4 mL) to obtain 6a. Isolated yield: 66%. Anal. Calcd
for C116H162N O P Pt : C, 45.88; H, 5.38; N, 6.46. Found: C,
a
c
1
(
dissolved in 40 mL of freshly distilled dry triethylamine. A
mixture of 100 mg of [(PPh ) PdCl ] (0.14 mmol), 20 mg of
a
3
2
2
triphenylphosphine (0.07 mmol), and 20 mg of CuI (0.1 mmol)
was added, and the suspension was refluxed with stirring under a
nitrogen atmosphere for 12 h. After removal of the volatile
solvents, the product was extracted with 100 mL of dichloro-
methane. The solvent was removed under reduced pressure to
obtain 3,6-bis[trimethylsilylethynyl]carbazole (2) as an off-
white solid in 98% yield. Anal. Calcd for C H NSi (2): C,
3.48; H, 7.01; N, 3.89. Found: C, 73.38; H, 7.15; N, 3.58. H
, 400 MHz): δ 8.96 (s, NH), 8.18 (s, 2H,), 7.55 (d,
H, J=8.4 Hz), 7.34 (d, 2H, J=8.0 Hz), 0.32 (s, 18H). IR (KBr):
14
16
8
4
1
45.56; H, 5.76; N, 6.70. H NMR (CD NO , 400 MHz): δ 10.95
3
2
(s, NHamide), 9.28 (s, NHcarbazole), 8.65 (d, 8H, Py-H , J =
R
6.0 Hz), 8.52 (d, 8H, Py-H , J = 6.0 Hz), 8.12 (s, 2H, H -
β
carbazole, J=5.6 Hz), 7.98 (s, 2H, H -amide), 7.77 (d, 4H, H -
1
4
5
amide, J=8.4 Hz), 7.49 (d, 8H, H2,3-carbazole, J=5.2 Hz), 7.39
(m, 2H, H-amide), 1.89 (m, 48H, CH -ethyl), 1.28 (m, 64H,
CH -ethyl). P NMR (CD NO , 120 MHz): δ 14.00 (s, JPt-P=
3 3 2
1
1699.68 Hz). IR (KBr): ν 2110.8 cm for the ethynyl group.
2
2
25
2
2
1
31
1
7
NMR (CDCl
-
3
-
2þ
-
2
ESI-MS (m/z): 1456.03 [6a - 2NO
]
, 1279.03 [6a - 2NO3-
-
-
-
3
-
1
2þ
-
2þ
ν 2138.8 cm for the ethynyl group. Desilylation of 2 was
achieved by stirring 2 (1.25 g, 3.4 mmol) with anhydrous K CO
(1.0 g, 7.3 mmol) in 100 mL of methanol under a nitrogen
3PEt ] , 1102.03 [6a - 2NO3 - 6PEt ] , 714.02[6a - 3NO3
3
3
3
þ
- 4þ
-
2
3
6PEt3] , 697.01 [6a - 4NO
3
]
, 579.01 [6a - 4NO3
4
þ
4PEt3]
.
atmosphere at room temperature for 48 h followed by complete
removal of the solvent. The product (3) was extracted with 100
mL of toluene. Subsequent removal of toluene yielded the
product as a yellow powder. Yield: 600 mg, 80%. Anal. Calcd
for C H N (3): C, 89.28; H, 4.21; N, 6.51. Found: C, 89.12; H,
6b. Building block 5 (15.2 mg, 0.01 mmol) and 1,3-bis(3-
pyridyl)isophthalamide L (3.97 mg, 0.01 mmol) were reacted in
b
acetone (4 mL) to obtain 6b. Isolated yield: 70%. Anal. Calcd
for C116H162N O P Pt : C, 45.88; H, 5.38; N, 6.46. Found: C,
14
16
8
4
1
16
9
45.52; H, 5.59; N, 6.80. H NMR (CD NO , 400 MHz): δ 10.89
3
2
1
4
.29; N, 6.77. H NMR (CDCl
s, 2H), 7.58 (d, 2H, J=8.4 Hz), 7.38 (d, 2H, J=8.4 Hz), 3.08 (s,
3
, 400 MHz): δ 8.76 (s, NH), 8.24
R1
(s, NHamide), 9.52 (s, 4H, Py-H ), 9.34 (s, NHcarbazole), 9.00 (d,
4H, Py-H , J=8.4 Hz), 8.80 (s, 2H, H -amide), 8.49 (d, 4H, Py-
R2 4
H ), 8.34 (s, 4H, H -carbazole), 8.25 (m, 4H, H -amide), 8.03 (d,
γ 1 β
(
2
H, ethynyl). IR (KBr): ν 2100.5 cm- for the ethynyl group.
1
Synthesis of 3,6-Bis[trans-platinum(triethylphosphine) (iodide)-
(ethynyl)]carbazole (4). To a 100 mL round-bottom Schlenk
flask were added trans-(PEt PtI (3.2 g, 4.6 mmol) and 3,6-
diethynylcarbazole (3) (400 mg, 1.8 mmol). Then 40 mL of
freshly distilled toluene and 20 mL of dry diethylamine were
added to the above mixture through a syringe under a nitrogen
atmosphere. The mixture was stirred for 15 min at room
temperature before 40 mg of CuI was added in one portion.
5 6
4H, H -amide), 7.79 (m, 2H, H -amide), 7.55 (d, 8H, H2,3-
carbazole), 1.98 (m, 48H, CH -ethyl), 1.27 (m, 64H, CH -ethyl).
2 3
2
3
1
1
3
)
2
2
P NMR (CD NO , 120 MHz): δ 17.16 (s, JPt-P=1735.92 Hz).
3 2
-
1
IR (KBr): ν 2117.2 cm for the ethynyl group. ESI-MS (m/z):
-
2þ
-
1456.03 [6b - 2NO
3
]
, 1417.53 [6b - 2NO - PEt3
3
þ
2
þ
-
2þ
3
CH CN] , 1279.33 [6b - 2NO - 3PEt ] , 1102.27 [6b -
3
3
-
2þ
-
3þ
2NO3 - 6PEt ] , 832.20 [6b - 3NO3 - 3PEt3] , 697.01
3
4þ
-
[6b - 4NO3
]
.
6c. Building block 5 (15.1 mg, 0.01 mmol) and 1,2-bis(4-
After 32 h of stirring at room temperature, a small amount of
was precipitated out. The solvent was removed
þ -
Et
2
NH
2
I
pyridyl)ethane L (2.4 mg, 0.01 mmol) were reacted in acetone
c
under vacuum, and the resulting residue was separated by
column chromatography (silica gel) using toluene/chloroform
(4 mL) to obtain 6c in 58% isolated yield. Anal. Calcd for
C104H158N O P Pt : C, 45.12; H, 5.75; N, 5.06. Found: C,
10
12
8
4
1
4
4.96; H, 5.90; N, 6.70. H NMR (CD NO , 400 MHz): δ 8.75
3 2
(
s, NHcarbazole), 8.59 (d, 8H, Py-H ), 8.05 (d, 8H, Py-H ),
(
9) (a) Nancy, L. S.; Dana, E. J.; Jennings, M. C.; Puddephatt, R. J.
R
β
-ethyl),
Inorg. Chem. 2004, 43, 7671. (b) Ghosh, S.; Mukherjee, P. S. Organome-
tallics 2008, 27, 316.
7.65-7.25 (m, 12H, H1,2,3-carbazole), 1.96 (m, 48H, CH
1.72 (s, 4H, H -ethane), 1.20 (m, 64H, CH -ethyl). P NMR
4 3
2
3
1

2
974 Organometallics, Vol. 29, No. 13, 2010
Shanmugaraju et al.
Scheme 2. Schematic Representation of the Synthesis of 3,6-Bis[trans-platinum(triethylphosphine)
,6-Dibromocarbazole (1)
2
(nitrate)(ethynyl)]carbazole (5) from
3
1
(
CD
3
NO
2
, 120 MHz): δ 17.42 (s, JPt-P=1125.6 Hz). IR (KBr):
was added in an incremental fashion. Their corresponding
UV-vis absorption and fluorescence spectra were recorded at
298 K. Each titration was repeated at least three times to get
consistent values. For all measurements λexc = 325 nm and the
emission wavelength was monitored at 335 nm. Both excitation
and emission slit widths were 5 nm. Relative fluorescence
intensities were measured for solution of receptor host 6a in
DMF, and the pyrophosphate anion was used as guest. There
was no change in shape of the emission spectra except enhance-
ment of the fluorescence emission intensity upon addition of
anion solution. Analysis of the normalized fluorescence inten-
-
1
ν 2118 cm
for the ethynyl group. ESI-MS m/z: 1322.27
-
2þ
, 850.27 [6c - 2NO3- - 8PEt3] , 630.13 [6c
2þ
[
-
6c - 2NO
]
3
-
4þ
.
4NO
3
]
X-ray Data Collection and Structure Refinements. The diffrac-
tion data of 6a were collected with synchrotron radiation (λ =
.69998 A) at the wiggler beamline 4A, Pohang Accelerator
Laboratory. This multipole wiggler has 28 magnet poles with
.02 T, and its periodic length and gap size are 14 cm and 14 mm,
˚
0
2
respectively. A fast speed CCD is installed for multiwavelength
anomalous diffraction (MAD) experiments in the energy range
6
-18 keV. Crystal data for 4 were collected on a Bruker
sity (I
was well described by the Stern-Volmer equation I
[G]. K was calculated from the slope of the Stern-Volmer
0
/I) as a function of increasing guest concentration ([G])
SMART APEX CCD diffractometer using the SMART/
SAINT software. X-ray quality crystals were mounted on a
glass fiber with traces of viscous oil. Intensity data were collected
0
/I = 1 þ
10
K
SV
plot.
SV
˚
using graphite-monochromated Mo KR radiation (0.7107 A) at
150 K. The structures were solved by direct methods using
SHELX-97 incorporated in WinGX. Empirical absorption
Results and Discussion
11
12
1
3
corrections were applied with SADABS. All non-hydrogen
atoms were refined with anisotropic displacement coefficients.
Hydrogen atoms were assigned isotropic displacement coeffi-
cients, U(H) = 1.2U(C) or 1.5U(C-methyl), and their coordi-
nates were allowed to ride on their respective carbons.
Synthesis and Characterization of the 90° Building Block
5). Substituted and heterocyclic aromatic compounds have
(
16
proven to be useful rigid building blocks in self-assembly.
Incorporation of a 90° angle into the organic framework is a
challenging task since this angle cannot be provided by the
hybridization of simple s and p orbitals. However, the com-
bination of proper carbon framework and various substitu-
tion patterns can result in a plethora of angles, including the
elusive 90° angle necessary for the predesigned square. Cis-
blocked mononuclear Pt(II)/Pd(II) building units have been
widely used as 90° corners to design interesting architectures.
To develop a new kind of 90° building unit containing two
metal centers, we have selected 3,6-dibromocarbazole as the
skeleton for the 90° building block. The activity of C-H
bonds in alkynes induced by transition metals has received
1
4
Structures were drawn using either ORTEP-3 for Windows
1
5
or DIMOND or PLATON.
UV-Vis and Fluorescence Titrations. Stock solutions (1 mM)
-
-
of the tert-butylammonium/potassium salts of F , ClO
4
,
-
4-
-3
H PO , and P O7 (1 ꢀ 10 M) in H O and that of 6a (1.0 ꢀ
2
4
2
2
-
4
1
was placed in a quartz cell of 1 cm width, and K solution
0
M) in DMF were prepared. A 2 mL stock solution of 6a
4 2 7
P O
(
(
10) SMART/SAINT; Bruker AXS, Inc.: Madison, WI, 2004.
11) Sheldrick, G. M. SHELX-97, Program for the Solution and
Refinement of Crystal Structures; University of G €o ttingen: G €o ttingen,
Germany, 1998.
17
(12) Farrugia, L. J. WinGX: An Integrated System of Windows
considerable attention in organometallic chemistry.
large number of oligomeric and polymeric transition metal
A
Programs for the Solution, Refinement and Analysis for Single Crystal
X-ray Diffraction Data, version 1.65.04; Department of Chemistry: Uni-
versity of Glasgow, 2003. (Farrugia, L. J. J. Appl. Crystallogr. 1999, 32, 837).
(13) Sheldrick, G. M. SADABS, Bruker Nonius Area Detector
Scaling and Absorption Correction, version 2.05; University of G €o ttingen:
G €o ttingen, Germany, 1999.
(16) (a) Kuehl, C. J.; Huang, S. D.; Stang, P. J. J. Am. Chem. Soc.
2001, 123, 9634. (b) Kuehl, C. J.; Mayne, C. L.; Arif, A. M.; Stang, P. J. Org.
Lett. 2000, 2, 3727. (c) Hall, J.; Loeb, S. J.; Shimizu, G. K. H.; Yap, G. P. A.
Angew. Chem., Int. Ed. 1998, 37, 121. (d) Sautter, A.; Schmid, D. G.; Jung,
G.; Wurthner, F. J. Am. Chem. Soc. 2001, 123, 5424.
(
14) Farrugia, L. J. ORTEP-3 for Windows, version 1.08. J. Appl.
Crystallogr., 1997, 30, 565.
15) Spek, A. L. Acta Crystallogr. 1990, A46, C34.
(

Article
Organometallics, Vol. 29, No. 13, 2010 2975
1 31
Figure 1. H NMR (left) and P NMR (right) spectra of the building block 5 in CDCl with the peak assignments.
3
complexes containing acetylene units have been prepared,
and their applications in the field of materials science have
1
been studied. Here, we utilized the coupling reaction of
8
trans-PtI (PEt ) with the C-H bonds in alkynes as the key
2
3 2
step to synthesize the 90° building block. 3,6-Diethynylcar-
bazole 3 was prepared by the coupling reaction of 3,6-dibromo-
carbazole (1) with trimethylsilylacetylene and subsequent
desilylation of 2 (Scheme 2) by K CO in methanol at room
2
3
temperature under a nitrogen atmosphere. Compound 3 was
then reacted with 2.5 equiv of trans-PtI (PEt ) to give 3,6-
bis[trans-Pt(PEt ) (I)(ethynyl)]carbazole (4). Subsequent de-
2
3 2
3
2
halogenation using 2.1 equiv of AgNO in a chloroform/
3
methanol solvent mixture resulted in the isolation of accep-
tor 5 in high yield (Scheme 2).
The building unit 5 was fully characterized by various
II
2
Figure 2. Molecular structure of the 90° Pt -diiodide complex
4 (color codes: green = Pt, purple = I, magenta = P, blue = N,
black = C).
1
31
spectroscopic techniques such as IR, NMR { H and P},
and ESI-MS. The IR spectrum showed an intense peak at
-1
2
functional group. The diplatinum linker 5 showed a singlet at
124.6 cm corresponding to the presence of an ethynyl
Table 1. Crystallographic Data and Refinement Parameters of
6a and 4
1
0.09 ppm accompanied by concomitant Pt satellites in
the P NMR spectrum (Figure 1). The H NMR spectrum of
exhibited characteristic peaks for carbazole protons in the
95
2
6
a
4
3
1
1
5
empirical formula
fw
C
116
H
162
N
14
20
O P
8
Pt
4
40 67 2 4 2
C H I NP Pt
3100.7
triclinic
P1
150
0.69998
10.404(2)
17.934(4)
19.064(4)
81.16(3)
86.77(3)
85.21(3)
3499.01(12)
1
1.472
4.139
1.016
1329.8
monoclinic
P2 /c
150
aromatic region (Figure 1). Electrospray ionization (ESI-
MS) mass spectrometric analysis of the building block 5
showed (Figure S5, Supporting Information) several peaks
at m/z = 1156.03, 538.01, and 430.03 corresponding to the
cryst syst
space group
T, K
1
˚
λ (Mo KR), A
a, A
0.71073
9.6127(17)
36.807(7)
15.011(3)
90
107.460(3)
90
5066.5(15)
4
1.743
-
- 2þ
˚
fragments [5 - NO þ H O], [5 - 2NO
] , and [5 -
3
2
3
˚
b, A
˚
c, A
-
þ
6
PEt - NO ] , respectively.
3
3
Finally, the molecular structure of the 90° building unit (5)
was unambiguously established by X-ray single-crystal dif-
fraction analysis of iodide analogue 3,6-bis[trans-platinum-
R, deg
β, deg
γ, deg
3
˚
V, A
Z
(triethylphosphine) (iodide)(ethynyl)]carbazole (4). Suitable
single crystals of 4 for X-ray diffraction study were grown by
2
-1
F
calcd, g cm
-1
μ, mm
GOF
6.886
1.029
0.1267(3714)
0.3054(11965)
a
(
17) (a) Werner, H.; Bachmann, P.; Martin, M. Can. J. Chem. 2001,
9, 519. (b) John, K. D.; Hopkins, M. D. Chem. Commun. 1999, 589.
c) Werner, H.; Bachmann, P.; Laubender, M.; Gevert, O. Eur. J. Inorg.
b
7
(
R1 [I > 2σ(I)]
wR2 [I > 2σ(I)]
0.0851(4851)
0.2611(6056)
c
Chem. 1998, 1217. (d) Wong, W.-Y.; Wong, C.-K.; Lu, G.-L.; Lee, A. W.-M.;
Cheah, K.-W.; Shi, J.-X. Macromolecules 2003, 36, 983. (e) Berenguer, J. R.;
Bernechea, M.; Fornies, J.; Lalinde, E.; Torroba, J. Organometallics 2005,
P
a
2
2 2
1/2
GOF = { [w(F
o
- F ) ]/(n - p)} , where n and p denote the
c
b
number of data points and the number of parameters, respectively. R1 =
P
P
P
P
c
|. wR2 = { [w(F
2
o
2 2
2 2 1/2
) ]/ [w(F
o
(
||F
o
| - |F
c
||)/ |F
o
- F
c
) ]} , where
]/3.
2
4, 431. (f) Vicente, J.; Chicote, M.-T.; Alvarez-Falcon, M. M.; Jones, P. G.
Organometallics 2005, 24, 2764.
18) (a) Paul, F.; Lapinte, C. Coord. Chem. Rev. 1998, 178-180, 431.
b) Ziessel, R.; Hissler, M.; El-ghayoury, A.; Harriman, A. Coord. Chem.
2
2
2
2
2
w = 1/[σ (F
o
) þ (aP) þ (bP)] and P = [max (0,F
o
) þ 2F
c
(
(
slow evaporation of a solution of 4 in a dichloromethane/n-
hexane (1:1) mixture at ambient temperature. A ball-and-
stick representation of the structure of 4 (Figure 2) shows
that it is indeed a 90° building unit with the Pt-N-Pt angle
Rev. 1998, 178-180, 1251. (c) Nguyen, P.; Go'mez-Elipe, P.; Manners, I.
Chem. Rev. 1999, 99, 1515. (d) Dembinski, R.; Bartik, T.; Bartik, B.; Jaeger,
M.; Gladysz, J. A. J. Am. Chem. Soc. 2000, 122, 810. (e) Long, N. J.;
Williams, C. K. Angew. Chem., Int. Ed. 2003, 42, 2586.

2
976 Organometallics, Vol. 29, No. 13, 2010
Shanmugaraju et al.
1
31
3 2
Figure 3. H NMR (left) and P NMR (right) spectra of the macrocycle 6a recorded in CD NO with the peak assignments.
˚
Table 2. Selected Bonds Distances (A) and Angles (deg) for 6a and 4
6
a
Pt(1)-C(3)
Pt(1)-P(2)
Pt(2)-P(4)
1.87(2)
2.282(8)
2.309(8)
Pt(1)-N(5)
Pt(2)-C(4)
Pt(2)-P(1)
2.055(16)
1.92(3)
2.331(7)
Pt(1)-P(3)
Pt(2)-N(6)
P(1)-C(38)
2.240(11)
2.069(17)
1.76(2)
C(3)-Pt(1)-N(5)
N(5)-Pt(1)-P(3)
N(5)-Pt(1)-P(2)
C(4)-Pt(2)-N(6)
N(6)-Pt(2)-P(4)
N(6)-Pt(2)-P(1)
177.3(8)
C(3)-Pt(1)-P(3)
86.9(9)
88.6(9)
170.2(5)
88.2(7)
86.7(6)
174.1(3)
93.5(6)
91.5(5)
177.9(8)
93.8(6)
91.3(5)
C(3)-Pt(1)-P(2)
P(3)-Pt(1)-P(2)
C(4)-Pt(2)-P(4)
C(4)-Pt(2)-P(1)
P(4)-Pt(2)-P(1)
4
Pt(1)-C(8)
1.96(2)
2.635(2)
2.298(8)
Pt(1)-P(1)
Pt(2)-C(15)
Pt(2)-I(2)
2.303(7)
1.96(3)
2.611(3)
Pt(1)-P(2)
Pt(2)-P(4)
2.311(6)
2.247(9)
Pt(1)-I(1)
Pt(2)-P(3)
C(8)-Pt(1)-P(1)
P(1)-Pt(1)-P(2)
P(1)-Pt(1)-I(1)
C(15)-Pt(2)-P(4)
P(4)-Pt(2)-P(3)
P(4)-Pt(2)-I(2)
88.3(7)
C(8)-Pt(1)-P(2)
88.9(6)
178.5(6)
90.84(17)
86.2(7)
178.3(7)
92.8(2)
172.1(3)
91.78(19)
89.4(7)
175.3(4)
91.5(3)
C(8)-Pt(1)-I(1)
P(2)-Pt(1)-I(1)
C(15)-Pt(2)-P(3)
C(15)-Pt(2)-I(2)
P(3)-Pt(2)-I(2)
being approximately 93°. The distance between the platinum
NMR spectra of 6a, 6b, and 6c exhibited a sharp singlet
[14.00 ppm (6a), 17.16 (6b), 17.42 ppm (6c)] shifted upfield
with respect to the starting platinum building unit 5 by 2.7-6
ppm, respectively. The upfield shifts of the phosphorus peaks
indicated a ligand to Pt electron donation due to metal-
ligand coordination. Moreover, a decrease in coupling of the
˚
centers is 12.6 A. All of the atoms except the PEt groups lie
approximately on the same plane. The coordination geome-
3
II
try around each Pt is square-planar with a “P CI” environ-
2
ment. Crystallographic data and refinement parameters are
summarized in Table 1, while selected bond lengths and
angles are assembled in Table 2. The dihedral angle between
the Pt-ethynyl units is about 29°, which may be caused by the
1
95
flanking Pt satellites (ca. ΔJ = -112.44 Hz for 6a, ΔJ =
-148.68 Hz for 6b, ΔJ=-1732.76 Hz for 6c) was consistent
with the back-donation from Pt(II). In the H NMR spec-
1
strong steric interaction between the PEt units in the
3
molecule.
Synthesis and Characterization of the Macrocycles 6a-c.
The 90° building block 5 was treated with the flexible ditopic
trum of 6a, hydrogen atoms of the pyridine rings exhibited a
small downfield shift due to the loss of electron density upon
coordination of the pyridine-N atom to the platinum center
(Figure 3). A similar observation was also noticed for the
other two assemblies 6b and 6c.
Formation of [2 þ 2] self-assembled macrocyles (6a-c)
was further indicated by ESI-MS spectrometric analysis,
where multiply charged molecular ions corresponding to
macrocycles were observed (Supporting Information). The
ESI-MS experiments were performed in an acetonitrile/
nitromethane (4:1) mixture of the corresponding macro-
cycle. The multiply charged molecular ions for 6a at
donors L
[L = 1,3-bis(4-pyridyl)isophthalamide; L =
a b
a-c
,3-bis(3-pyridyl)isophthalamide; L =1,2-di(4-pyridyl)ethane]
1
in 1:1 molar ratio in acetone (2 mL) to obtain the self-
c
assembled molecular squares (6a-c) after 5 h of stirring at
5
IR, H and P NMR, and ESI mass spectrometry. Multi-
0 °C (Scheme 1). All the assemblies were characterized by
1 31
1
31
nuclear NMR ( H, P) spectra of the assemblies (6a-c) were
consistent with the formation of single and symmetrical
3
1
P
products (Figure 3 and Supporting Information). The

Article
Organometallics, Vol. 29, No. 13, 2010 2977
packing shows the presence of square-type channels occu-
pied by one nitrate anion and an assigned water molecule.
Several efforts to obtain good-quality single crystals of
macrocycles 6b and 6c were unsuccessful. On the basis of the
mass spectrometric results, these are confirmed to be [2 þ 2]
self-assembled macrocycles. Due to the almost identical
nature of the ligands L and L , 6b is expected to have a
a
b
similar structure. The optimization of the macrocycle 6c has
been done using density functional theory (DFT) calcula-
tions to obtain a view of the shape of macrocycle 6c. The
B3LYP functional was used for the DFT calculations, which
were performed with the Gaussian 03 program. Two basis
sets were employed, 6-31G for lighter elements (C, H, N, and
O) and LanL2DZ for the heavier elements (Pt and P). A view
of the optimized structure of the macrocycle 6c is shown in
Figure 6. An energy-minimized view of the molecule indi-
cated the formation of a square-type macrocycle of around
2.1 nm diameter, which was almost identical to the size of
macrocycle 6a obtained from X-ray analysis.
UV-Vis Absorption and Fluorescence Studies. Photophy-
sical data of the diplatinum building block 5 and its macro-
cycles (6a-c) are summarized in Table 3. The absorption
-
6
-6
spectra of 5 (5.0ꢀ10 M) and macrocycles 6a-c (5.0ꢀ10
Figure 4. Molecular structure of 6a (green = Pt, magenta = P,
blue = N, red = O, black C). Counter anions and hydrogen
atoms are omitted for the sake of clarity.
M) in DMF show peaks at λ=289 and 325 nm for building
block 5; λ=288 and 323 nm for 6a; λ=286 and 322 nm for
6
b; and λ=325 nm for 6c (Figure 7). The peaks in the range
-
2þ
-
m/z = 1456.03 [6a - 2NO
]
, 1279.03 [6a - 2NO
-
322-325 nm are ascribed to metal-to-ligand charge transfer
(MLCT), whereas the peaks in the range 288-290 nm are
due to intra-/intermolecular π-π* transitions. The emission
3
3
2
þ
-
2þ
3
PEt3] , 1102.03 [6a - 2NO - 6PEt3] , 714.02 [6a -
3
-
3þ
- 4þ
] ; for 6b at
3
3
NO3 - 6PEt3] , 697.01 [6a - 4NO
-
2þ
-
II
-6
m/z 1456.03 [6b - 2NO
]
, 1417.53 [6b - 2NO
-
spectra (Figure 7) of the Pt building block 5 (1.0ꢀ10 M)
3
3
2
2þ
-
2þ
3
-6
PEt þCH CN] , 1279.33 [6b - 2NO - 3PEt ] , 1102.27
and macrocycles 6a-c (1.0ꢀ10 M) were recorded in DMF
3
3
3
-
2þ
-
3þ
[
6
8
6b - 2NO - 6PEt ] , 832.02 [6b - 3NO3 - 3PEt3]
,
,
at room temperature. All the emission spectral data are given
in Table 3. 5 and 6b were excited at 325 nm, while 6a and 6c
were excited at 290 nm. Both excitation and emission slit
widths were 5 nm.
3
3
4þ
-
- 2þ
97.01 [6b - 4NO3
]
; for 6c at m/z 1322.27 [6c - 2NO
]
3
-
2þ
- 4þ
50.27 [6c - 2NO3 - 8PEt3] , 630.13 [6c - 4NO3
]
were
found in the mass spectra.
Crystal Structure of the Macrocycle 6a. The X-diffraction
quality single crystals of 6a were grown by slow vapor
diffusion of diethyl ether into a chloroform/methanol (1:1)
Anion Binding Study of 6a by UV-Visible Spectroscopy.
Recognition of anions has attracted growing attention be-
cause they play fundamental and important roles in a wide
range of chemical, biological, and environmental processes.
Most of the chemosensors developed so far are chromogenic
and/or fluorescent probes, which can efficiently respond by
changing their photophysical properties in the presence of
solution. Single-crystal X-diffraction analysis confirmed the
II
formation of an expected Pt
(
that two (I-PtC ) arms are not coplanar with the carbazole
square-type macrocycle
Figure 4). The solid-state structure of 4 (Figure 2) revealed
4
2
1
9
moiety. Due to high thermal disorder in the ethyl groups in
the PEt moieties, the carbon atoms in these groups are
anions. In this context, several efforts have been made to
employ a large variety of structural motifs to design efficient
anion sensors. Hydrogen bonding or other supramolecular/
electrostatic interactions between the receptors and analytes
are commonly being used. For this kind of receptor, the
polarized N-H functional group represents a very commonly
3
treated with one cycle refinement for both 4 and 6a. Inter-
estingly, although Pt-metal centers are almost 29° apart with
respect to the plane of the carbazole moiety, the bite angle
(
Pt-N-Pt) is almost orthogonal (93.9°) in 4.
2
0
Because of the cyclization effect, the torsion angle between
used anion interacting moiety. In general, hydrogen bond-
induced π-electron delocalization or basic anion-induced
N-H deprotonation serves as the signaling output of the
two arms (I-PtC ) of the 90° building block in complex 6a is
2
reduced drastically to almost 7°. Although the centroids of
the carbazole moieties and that of the phenyl moieties of the
donor in complex 6a formed an almost square-planar geo-
2
1
anion receptor interaction.
˚
˚
metry with dimensions 20.0 Aꢀ21.4 A, due to such a strong
torsion angle strain, the macrocycle 6a assumes a sigmoidal-
like shape instead of an ideal planar square. The N atoms of
(
19) (a) Beer, P. D.; Gale, P. A. Angew. Chem., Int. Ed. 2001, 40, 486.
(
(
b) Martnez-Manez, R.; Sancenon, F. Chem. Rev. 2003, 103, 4419.
c) Amendola, V.; Esteban-Gomez, D.; Fabrizzi, L.; Lichelli, M. Acc. Chem.
the carbazole moieties are almost 13.5° above/below the Pt -
Res. 2006, 39, 343. (d) Gunnlaugsson, T.; Glynn, M.; Tocci, G. M.; Kruger,
P. E.; Peffer, F. M. Coord. Chem. Rev. 2006, 250, 3094. (e) Gale, P. A. Acc.
Chem. Res. 2006, 39, 343.
4
plane, while the phenyl rings of the donor are almost 8°
above/below the Pt -plane in complex 6a. The coordination
4
(
20) Sessler, J. L.; Gale, P.; Cho, W.-S. Anion Receptor Chemistry;
environment around the Pt-metal centers deviates slightly
from the ideal square-planar geometry. The angles P-Pt-C
are in the range 85-89°, while the angles P-Pt-N are in
the range 92-94°. The solid-state packing diagram of 6a
through the crystallographic a-axis is shown in Figure 5. The
RSC Publishing: Cambridge, UK, 2006.
(21) (a) Chou, P. T.; Yu, W. S.; Chen, Y. C.; Wei, C. Y.; Martinez,
S. S. J. Am. Chem. Soc. 1998, 120, 12927. (b) Kumar, N.; Chakravorti, S.;
Chowdhury, P. J. Mol. Struct. 2008, 891, 351. (c) Chowdhury, P.; Panja, S.;
Chatterjee, A.; Battacharya, P.; Chakravorti, S. J. Photochem. Photobiol. A
2006, 173, 106.

2
978 Organometallics, Vol. 29, No. 13, 2010
Shanmugaraju et al.
Figure 5. Solid-state packing diagram of 6a along a-axis.
Table 3. Photophysical Data of the Building Unit 5 and Macro-
cycles 6a-c
molar extinction
coefficient
fluorescence
emission
maxima
absorption
maxima
complex solvent [λmax (nm)]
3
-1
-1
ε ꢀ 10 M cm
[λmax (nm)]
[λmax (nm)]
5
6
6
6
DMF
DMF
DMF
DMF
289, 325
288, 323
286, 322
325
275 (325)
129 (323)
106 (322)
33 (325)
414, 435
413, 434
411, 432
406, 434
a
b
c
DNA polymerization and synthesis of cyclic adenosine mono-
22,23
phosphate (c-AMP) catalyzed by DNA polymerase.
Therefore, the detection of trace amounts of pyrophosphate
is an important task. However, only a few examples of
Zn(II)-based effective fluorescent chemosensors for these
2
4
oxoanions have so far been reported.
Since effective detection of trace amounts of anions
through fluorescence quenching/enhancing is highly sensi-
tive and cost-effective, the design of efficient luminescent
receptors is a continuing challenge to synthetic chemists. The
(
23) Ronaghi, M.; Karamohamed, S.; Petterson, B.; Uhlen, M.;
Nyren, P. Anal. Biochem. 1996, 242, 84.
24) (a) Xu, S.; He, M.; Yu, H.; Cai, X.; Tan, X.; Lu, B.; Shu, B. Anal.
(
Biochem. 2001, 299, 188. Fabbrizzi, L.; Marcotte, N.; Stomeo, F.; Taglietti,
A. Angew. Chem., Int. Ed. 2002, 41, 3811. (b) Gunnalaugsson, T.; Davis,
A. P.; O'Brien, J. E.; Glynn, M. Org. Lett. 2002, 4, 2449. (c) Lee, D. H.; Kim,
S. Y.; Hong, J.-I. Angew. Chem., Int. Ed. 2004, 43, 4777. (d) Kanekiyo, Y.;
Naganawa, R.; Tao, H. Chem. Commun. 2004, 1006. (e) Cho, H. K.; Lee,
D. H.; Hong, J.-I. Chem. Commun. 2005, 1690. (f) Jang, Y. J.; Jun, E. J.; Lee,
Y. J.; Kim, Y. S.; Kim, J. S.; Yoon, J. J. Org. Chem. 2005, 70, 9603.
Figure 6. View of the optimized structure of 6c (green = Pt,
orange = P, blue = N, black = C).
Pyrophosphate and related oxoanions play an important
role in energy transduction in organisms and control several
metabolic processes involving several enzymatic reactions.
ATP hydrolysis with the release of pyrophosphate is an
important step in many biochemical reactions such as
(
g) McDonough, M. J.; Reynolds, A. J.; Lee, W. Y.G.; Jolliffe, K. A. Chem.
Commun. 2006, 2971. (h) Bazzicalupi, C.; Biagini, S.; Bencini, A.; Faggi, E.;
Giorgi, C.; Matera, I.; Valtancoli, B. Chem. Commun. 2006, 4087. (i) Lee,
H. N.; Swamy, K. M. K.; Kim, S. K.; Kwon, J.-Y.; Kim, Y.; Kim, S.-J.; Yoon,
Y. J.; Yoon, J. Org. Lett. 2007, 9, 242. (j) Lee, H. N.; Xu, Z.; Kim, S. K.;
Swamy, K. M. K.; Kim, Y.; Kim, S.-J.; Yoon, J. J. Am. Chem. Soc. 2007,
129, 3828. (k) Swamy, K. M. K.; Kwon, S. K.; Lee, H. N.; Shantha Kumar,
S. M.; Kim, J. S.; Yoon, J. Tetrahedron Lett. 2007, 48, 8683.
(
22) (a) Lipscombe, W. N.; Strater, N. Chem. Rev. 1996, 96, 2375.
b) Tabary, T.; Lu, L. J. Inmunol. Methods 1992, 156, 55. (c) Nyren, P. Anal.
Biochem. 1987, 167, 235.
(

Article
Organometallics, Vol. 29, No. 13, 2010 2979
Figure 7. UV-visible (left) and fluorescence (right) spectra of 5 and 6a-c in DMF solution.
4-
Figure 8. Changes in the absorption spectra of receptor 6a in DMF upon addition of increasing amounts of P
changes in absorption (right) after addition of various anions. Excitation slit width = 2 nm.
2
O
7
2
in H O (left) and
molecular square 6a was designed for the following reasons:
2
isosbestic point at 329 nm, indicating a neat interconversion
between the uncomplexed and complexed states (Figure 8).
Anion Binding Study of 6a by Fluorescence Spectroscopy.
Receptor square 6a did not undergo any considerable change
5
(
a) the carbazole functionality can act as a fluorophore,
and it has also been well established that compounds with a
Pt-ethynyl functionality generally show luminescence beha-
2
6
-
-
vior; (b) an amide-containing ligand was introduced to
make an effective receptor site that could effectively bind the
anions through hydrogen-bonding interaction; (c) the bulky
in its emission spectrum upon addition of F , ClO , and
4
-
-3
H PO anions (1.0ꢀ10 M) (Figure 9). However, gradual
2
4
4
7
-
addition of aqueous P O
2
to a DMF solution of receptor
PEt groups attached to Pt(II) centers help to avoid inter-
3
6a (1 μM) induced a dramatic enhancement in the fluores-
cence emission intensity (Figure 9). The shape of the emission
molecular stacking and thus prevent the chance of self-
quenching of fluorescence. The solution-state fluorescence
of macrocycle 6a was enhanced upon gradual addition
4-
spectrum was unaltered upon addition of P O . The final
2
7
fluorescence enhancement factor (FEF = IPPi/I ) was
6a
4
-
of aqueous pyrophosphate (P O ) solution. Absorption
2
approximately 3.5 times that of the emission intensity of
macrocycle 6a. Binding assays calculation from the fluores-
cence titration data using the method of continuous varia-
tion (Jobs plot) suggests a 1:1 mode of binding (Figure 10),
and the Stern-Volmer binding constant was calculated to be
7
-
5
studies were performed using a DMF solution (1.0ꢀ10 M)
of the receptor 6a and the corresponding anions in H O
2
-
3
(
1.0 ꢀ 10 M). It is worth mentioning that no significant
change was noticed in the absorption spectrum of the
receptor 6a upon addition of F , ClO , and H PO .
4
-
-
-
3
-1
4
2
24 ꢀ 10 M . Macrocycle 6a is composed of a carbazole-
based fluorophore and an amide-based receptor. In their
electronic excited states, a strong interaction develops in the
form of an electron transfer from the anion-free amide
receptor to the excited state of carbazole-based fluorophore
subunit.
However, considerable red-shift in the absorption spectrum
of 6a was observed upon gradual addition of P O
4-
solution,
indicating a strong hydrogen-bonding interaction between
2
7
the cleft of 6a and the anion (Figure 8). Thus, the addition
4
of increasing amounts of P O7 solution to a solution of
-
2
6
a caused the progressive appearance of a well-defined
As a result, due to the photoinduced electron transfer
PET) process, molecular square 6a shows weak fluorescence
(
(
25) (a) Donat-Bouillud, A.; L ꢀe vesque, I.; Tao, Y.; D’Iorio, M.;
emission (Figure 9) in the anion-free situation. However, the
efficiency of the PET process could be suppressed effectively
by the binding of the anion into the amide receptor through a
hydrogen-bonding interaction. Such a suppression of the
PET process results in enhancement of fluorescence emission
of the excited carbazole-based fluorophore upon gradual
addition of aqueous pyrophosphate anion.
Beaupr ꢀe , S.; Blondin, P.; Ranger, M.; Bouchard, J.; Leclerc, M. Chem.
Mater. 2000, 12, 1931. (b) Weinfurtner, K.-H.; Fujikawa, H.; Tokito, S.;
Taga, Y. Appl. Phys. Lett. 2000, 76, 2502. (c) Kl
Chen, W.-D.; Scott, J. C.; Miller, R. D. Adv. Mater. 1998, 10, 993.
26) (a) Zhang, L.; Niu, Y.-H.; Jen, A. K.-Y.; Lin, W. Chem.
Commun. 2005, 1002. (b) Jiang, H.; Lin, W. J. Am. Chem. Soc. 2003,
25, 8084. (c) Hu, J.; Lin, R.; Yip, J. H. K.; Wong, K.-Y.; Ma, D.-L.; Vittal,
J. J. Organometallics 2007, 26, 6533.
€
arner, G.; Davey, M. H.;
(
1

2
980 Organometallics, Vol. 29, No. 13, 2010
Shanmugaraju et al.
4
7
-
Figure 9. Changes in the fluorescence spectra (left) of receptor 6a in DMF (red line) upon addition of increasing amounts of P O
2
in
2
H O. Change in fluorescence intensity (right) of the receptor 6a, in relation to the free ligand, after addition of the anions.
Figure 10. Stern-Volmer plot (left) of the increase in fluorescence intensity of 6a upon gradual addition of pyrophosphate anion and
Jobs plot (right). λexc = 325 nm, λemi = 335 nm, excitation and emission slit widths = 5 nm.
Conclusions
reports, to the best of our knowledge, of phosphate-sensing
Pt(II) macrocycles derived via coordination-driven self-assem-
bly. The use of a specially designed shape-selective metal-
based linker and the incorporation of various functional groups
suitable for sensing trace analytes through noncovalent inter-
actions have the potential to considerably expand the range of
directional bonding paradigms in self-assembly.
In conclusion, we report here the first example of a shape-
II
selective Pt organometallic 90° building block, 5. Self-
2
assembly of this building block with flexible ditopic donors
(
L
a-c
) resulted in the formation of [2 þ 2] macrocycles 6a-c.
Despite the possibility of open-chain oligomers, we demon-
strated that closed macrocycles containing an ethynyl func-
tionality are preferred. Macrocycles 6a-c were characterized
by various spectroscopic techniques, and the structure of 6a
was determined by single-crystal X-ray diffraction. Macro-
cycles 6a-c show luminescent behavior in solution due to
the presence of a Pt-ethynyl functionality and conjugated
π-electrons. The square 6a is a system composed of a
fluorophore-receptor-fluorophore combination, which is re-
quired for a fluorescence sensor. A carbazole-based acceptor
was used as the fluorophore, while the amide-based flexible
Acknowledgment. S.S. gratefully acknowledges the
Council of Scientific and Industrial Research, New Delhi,
India, for the award of a research fellowship. We thank
Mr. P. Duraipandi, IISc, Bangalore, for his helpful dis-
cussions on fluorescence measurement and data analysis.
P.S.M. thanks the Department of Science and Techno-
logy (DST), India, for the financial support. The authors
are grateful to Johnson Mathey Pvt. Ltd. U.K. for
supplying K PtCl as a loan. K.-W.C. acknowledges
2
4
ditopic donor L was introduced to make a receptor site for
a
Pohang Accelerator Laboratory, Pohang 790-784 (Korea),
for the X-ray diffraction data and appreciates the financial
support of the WCU program (R33-2008-000-10003) in
Korea.
pyrophosphate. The square 6a shows weak fluorescent beha-
vior compared to free building block 5. The fluorescence
intensity of the molecular square 6a was dramatically enhanced
4
-
upon titration with aqueous P O
2
anion in DMF solution.
Interestingly, no such perturbation in fluorescence intensity
was observed when the titration was carried out with other
7
Supporting Information Available: Crystallographic details of
4 and 6a in CIF format, NMR spectra of 2-4, 6b, and 6c, and
mass spectra of 5 and 6a-c are available free of charge via the
Internet at http://pubs.acs.org.
-
-
-
anions (F , ClO , H PO ). Although a large number of
2
4
4
2
þ
phosphate sensors based on Zn are reported, there are no