Synthesis and characterization of self-assembled nanoscopic metallarectangles capable of binding fullerenes with size-selective responses

Article abstract of DOI:10.1021/ic401685s

Two new metallarectangles, 4 and 5, were obtained from the self-assembly of areneruthenium-based molecular clips 2 and 3 with a new dipyridyl donor ligand 1 containing a diamide core and ethynyl spacers. The metallarectangles were characterized by multinuclear NMR, electrospray ionization mass spectrometry, and UV-vis spectroscopy, and the molecular structure of 4 was unambiguously determined by single-crystal X-ray diffraction analysis. Because of the presence of an extended π-electron aromatic surface, the tetracene-containing molecular rectangle 5 was capable of binding C₆₀ and C₇₀ fullerenes as quantified by UV-vis, emission, and ¹H NMR experiments, providing an example of a supramolecular host capable of recognizing large guest molecules.

Full text of DOI:10.1021/ic401685s

Article
pubs.acs.org/IC
Synthesis and Characterization of Self-Assembled Nanoscopic
Metallarectangles Capable of Binding Fullerenes with Size-Selective
Responses
Anurag Mishra,† Hyunji Jung,† Min Hyung Lee,† Myoung Soo Lah,‡ and Ki-Whan Chi*,†
†Department of Chemistry, University of Ulsan, Ulsan 680-749, Republic of Korea
‡Interdisciplinary School of Green Energy, Ulsan National Institute of Science & Technology, Ulsan 689-798, Korea
S
* Supporting Information
ABSTRACT: Two new metallarectangles, 4 and 5, were
obtained from the self-assembly of areneruthenium-based
molecular clips 2 and 3 with a new dipyridyl donor ligand 1
containing a diamide core and ethynyl spacers. The metal-
larectangles were characterized by multinuclear NMR, electro-
spray ionization mass spectrometry, and UV−vis spectroscopy,
and the molecular structure of 4 was unambiguously
determined by single-crystal X-ray diffraction analysis. Because
of the presence of an extended π-electron aromatic surface, the
tetracene-containing molecular rectangle 5 was capable of binding C60 and C70 fullerenes as quantified by UV−vis, emission, and
1H NMR experiments, providing an example of a supramolecular host capable of recognizing large guest molecules.
a certain size and shape.5 Such rectangles are obtained when a
INTRODUCTION
■
molecular clip assembles with a linear ditopic donor, with
The formation of new nanoscopic supramolecular coordination
dimensions determined by the height of the molecular clip and
complexes (SCCs) via coordination-driven self-assembly has
the length of the donor. While a number of such species have
been a cornerstone of the modern supramolecular chemistry
been synthesized,6 elongated structures containing extended
commmunity.1 Over the last 2 decades, an expansive library of
linear ligands are relatively rare. Obtaining such ligands through
SCCs has been filled by various synthetic approaches,
the use of ethynyl spacers is attractive in that the electron-rich π
ultimately relying on predictable directional interactions
systems that are necessarily present in such designs may endow
between carefully selected metal acceptors and organic donors.2
interesting photophysical properties and rigidity to supra-
Because coordination-driven self-assembly is guided by the
molecules.7
structural information encoded in rigid molecular subunits,
structures of predetermined shape, size, and functionality may
be designed with internal cavities that are capable of
Herein, we report two new large molecular rectangles, 4 and
5, from the combination of a symmetrically elongated
dipyridiyldiethynyl ligand centered on a diamide core with
encapsulating guest molecules through electrostatic and/or
two areneruthenium acceptors. The rectangular nature of these
dispersion forces. As such, considerable efforts have been made
SCCs, the first made using this ligand, was confirmed via X-ray
to develop functional macrocyclic assemblies that show promise
in molecular recognition, catalysis, sensing, and photo-
diffraction analysis on a single crystal of 4. The propensity of
both assemblies to form inclusion complexes with large C60 and
luminescence, all applications that can utilize host/guest
C70 guest molecules in solution was demonstrated by
interactions.3
absorption and fluorescence quenching experiments. The
Among the suite of metal-containing acceptor building
blocks, areneruthenium complexes are especially suitable for
use as molecular clips, wherein two Ru centers are bridged by a
bis-chelating moiety and capped with a η6-arene group, leaving
a final coordination site to interact with an organic spacer,
oftentimes pyridyl-based. Using such acceptors, [2 + 2]
metallacycles and [2 + n] prisms may be generated, where n
is the number of molecular clips required, as determined by the
number of Lewis basic sites of the two donors, which will be
held cofacially; a planar tritopic donor (n = 3) will furnish a
trigonal prism using three molecular clips.4 Recently, we
reported rigid and shape-persistent [2 + 2] molecular rectangles
as host structures for the selective binding of guest molecules of
design of sensing hosts from these discrete rectangles provides
a new rationale for the recognition of π-electronic surfaces.
RESULTS AND DISCUSSION
■
Synthesis and Characterization of the Ligand. The new
N,N′-bis[4-(pyridin-4-ylethynyl)phenyl]terephthalamide (1)
was synthesized in two steps (Scheme 1). The starting ligand
precursor N,N′-bis(4-iodophenyl)terephthalamide was synthe-
sized by coupling 4-iodoaniline and terephthaloyl dichloride in
Received: March 18, 2013
© XXXX American Chemical Society
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1H NMR spectra of 4 and 5 were shifted downfield about ∼0.5
ppm relative to 2 and 3 in nitromethane-d3 (Figures S3 and S4
in the SI).
Scheme 1. Synthesis of Ligand 1
Electrospray ionization mass spectrometry (ESI-MS) spectra
of 4 and 5 confirmed the [2 + 2] stoichiometry of the
complexes. In the mass spectrum of assembly 4, peaks at m/z
801.31 and 563.96 corresponded to the [M − 3OTf]3+ and [M
− 4OTf]4+ charge states (see Figure S5 in the SI), while the
spectrum of 5 showed a peak at m/z 639.62, corresponding to
the [M − 4OTf]4+ charge state (see Figure S6 in the SI). These
peaks were all isotopically resolved and matched well with their
theoretical isotopic distributions.
The molecular structure of 4 was unequivocally determined
by single-crystal X-ray diffraction analysis. A single crystal
suitable for X-ray diffraction was obtained by the slow vapor
diffusion of diethyl ether into a nitromethane/methanol (1:1)
solution of 4. As expected, the molecular structure of 4
included a large cavity (8.5 × 32.43 Å2), as shown in Figure 1.
Two dipyridyl ligands bridge two [Ru2(arene)2(2,5-dihydroxy-
1,4-benzoquinonato)2]4+ building blocks to form a [2 + 2]
M4L2 rectangle. Each cymene-capped ruthenium coordination
sphere was further coordinated by a N atom from the ditopic
ligand and two O atoms from the bridging moiety. The Ru−
Npyridine bond distances were ∼2.019 Å, comparable to the
distances found within other tetracationic rectangles.5,6 The
central diamide cores of the ligands were oriented such that the
NH groups were directed inward, with the carbonyls directed
away from the internal cavity. The distance between the
opposing carbonyls was ∼11.12 Å, while the NH groups were
held closer at ∼6.57 Å. The extended nature of the ditopic
ligand results in a 32.43 Å separation between the two
ruthenium-based acceptors, with an 11.12 Å spacing between
ligands. In the solid state, two triflate anions occupy the internal
cavity bound through weak hydrogen-bonding interactions
(Figure S7 in the SI). The hydrogen-bonding distances
between the H atoms of the amide groups (NH) and the O
atoms of the triflate anion were in the range of 2.18−3.03 Å for
4.
CH2Cl2 in the presence of triethylamine followed by
recrystallization from methanol/H2O (yield 90%). The
resulting product was then used under standard Sonogashira
coupling conditions with the hydrochloride salt of 4-
ethynylpyridine in N,N-dimethylformamide (DMF) to generate
1
1 in ca. 77% overall yield. H NMR showed one sharp singlet
for the NH at δ 10.81 in dimethyl sulfoxide (DMSO)-d6, and
five aromatic resonances were found, indicating the presence of
20 protons (Figure S2 in the Supporting Information, SI). In
the IR spectrum of ligand 1, the NH and CO vibration
stretching peaks for the amide linkage were observed at 3368
and 1692 cm−1, respectively, while the CC vibration
stretching peak was obtained at 2215 cm−1.
Synthesis and Characterization of Molecular Rectan-
g l e s . D i n u c l e a r r u t h e n i u m c o m p l e x e s
[Ru2(arene)2(OO∩OO)Cl2] [OO∩OO = 2,5-dihydroxy-1,4-
benzoquinonato (2) and 6,12-dihydroxytetracene-5,11-dionato
(3)] were mixed at room temperature in a nitromethane/
CH2Cl2 (1:1) solution with 1, and silver triflate furnished
metallacycles 4 and 5 as triflate salts with the coformation of
silver chloride (Scheme 2). Filtration and precipitation via the
addition of diethyl ether yielded 4 and 5 as analytically pure
solids.
1
The H NMR spectra of both metallarectangles 4 and 5
clearly showed the formation of a symmetrical species with
typical resonance shifts relative to those of the free acceptors
due to metal complexation.7a,8 The CH and Me signals in the
Scheme 2. Synthesis of Nanoscopic Metallarectangles
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Figure 3. Normalized emission spectra of 3 and 5 in methanol (1 ×
10−5 M).
was to develop a novel class of fullerene receptors, which could
bind strongly and efficiently with potential size selectivity, in
analogy to known porphyrin-containing covalent macrocycles9
and supramolecular cages,10 which exhibit strong binding
interactions. Given the extended π systems of these rectangles
and the suitable dimensions revealed from the structural studies
of 4, interactions with fullerenes were expected. Because the
tetracene bridging moiety of 5 resulted in easily monitored
photophysical properties, it was selected for titrations with C60
and C70 using UV−vis absorption and fluorometric methods in
a 1,1,2,2-tetrachloroethane (TCE) solution. Upon the gradual
addition of C60 to a solution of 5 in TCE, the intensity of the
absorption peaks of 5 at 277 and 332 nm increased (Figure 4).
Figure 1. Crystal structure of 4. (a) Schematic diagram showing the
two Ru2+ ions (green) coordinated by four pyridine N atoms (blue).
(b) Side view shown as a space-filling model. The triflate anion and
solvent molecules are omitted for clarity.
Absorption and Emission Studies. The electronic
absorption spectra of 4 and 5, along with their corresponding
metal acceptors (2 and 3) were investigated in methanol
solutions at 1 × 10−5 M (Figure 2). The absorption spectra
Figure 2. Electronic absorption spectra of 2−5 in methanol (1 × 10−5
M).
Figure 4. Changes in the absorption spectra of 5 in a TCE solution (1
× 10−5 M) upon the addition of 4.0 equiv of C60 in a TCE solution (1
× 10−4 M). Inset: Job’s plot of metallarectangle 5 with C60 in a TCE
solution.
exhibit bands at λabs = 502 nm for 4 and λabs = 526, 565, and
610 nm for 5. The dinuclear areneruthenium acceptors also
exhibited energy absorption bands at 485 nm and 521, 553, and
599 nm for 2 and 3, respectively. These bands are likely a
combination of intra/intermolecular π → π* transitions mixed
with metal-to ligand charge-transfer transitions. As such, these
areneruthenium-based bands are also preserved upon self-
assembly, giving rise to strong absorption for 4 and 5.
Rectangle 4 gives a strong absorption band red-shifted with
respect to acceptor 2 by ∼17 nm. Similar red shifts are
observed for bands in 5 that correspond to absorption in donor
3.
The metallarectangle 5 exhibits fluorescence emission at 530
and 570 nm upon photoexcitation at 390 nm. This fluorescence
originated from the acceptor because the emission wavelengths
matched well with the emission bands observed for the
acceptor alone (Figure 3). The emission intensity of 5 was
notably quenched compared with the acceptor 3. The
intramolecular photoinduced electron transfer in 5 from the
acceptor 3 to the donor 1 could be responsible for the observed
emission quenching.5
A similar trend in the UV−vis titration curve at 277 and 332
nm was observed when a solution of 5 in TCE was titrated with
C70 (Figure 5). According to the Job plot, 5 formed a 1:1 host/
guest complex with C60 (see the inset in Figure 4) and C70 (see
the inset in Figure 5), respectively.
Additional evidence in support of C60 and C70 binding with 5
came from fluorescence titration experiments. The ethynyl-
containing donors with areneruthenium acceptors make 5
particularly electron-rich, which was manifested in strong
fluorescence emission centered at 527 and 560 nm (Figure 3).
The assembly 5 was titrated with incremental amounts of C60
and C70 in a TCE solution. The change in the fluorescence
intensity at 527 nm was monitored with the 390 nm excitation
at which the change in the molar absorption of the host/guest
solution is marginal during titration. As shown in Figures 6 and
7, the emission intensity of 5 gradually decreased upon the
addition of C60 and C70, respectively. Because both C60 and C70
were nonemissive at the same excitation, such changes in the
Fullerene Binding Studies. One of the major motivations
for constructing such rigid, ethynyl-containing metallacycles
C
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spectroscopy: a 1:1 mixture solution of 5 and C60 in TCE-d2
showed significant shifts of the proton resonances for the donor
ligand that are distinctly different from the signals of free
rectangle 5. This result confirms the binding interaction
between C60 and metallarectangle 5 (Figure 8).
CONCLUSION
■
In conclusion, we report the syntheses of two new self-
assembled metallarectangles, 4 and 5, with adaptable cavities via
new π-electron-rich N,N′-bis[4-(pyridin-4-ylethynyl)phenyl]-
terephthalamide donor 1 and areneruthenium acceptors 2
and 3. The formation of both molecular rectangles was
established by various spectroscopic techniques, and the
molecular structure of metallarectangle 4 was determined by
single-crystal X-ray diffraction analysis. Because of its extended
aromatic surface, metallarectangle 5 was capable of interacting
with C60 and C70, providing a basis for host/guest chemistry
using SCCs with large substrates by exploiting π interactions.
Currently, the binding behavior and charge-transfer chemistry
of such metallarectangles with higher-order fullerenes are being
investigated and will be reported in due course.
Figure 5. Change in the absorption spectra of 5 in a TCE solution (1
× 10−5 M) upon the addition of 4.0 equiv of C70 in a TCE solution (1
× 10−4 M). Inset: Job’s plot of metallarectangle 5 with C70 in a TCE
solution.
EXPERIMENTAL SECTION
■
Materials and Methods. All chemicals used in this work were
purchased from commercial sources and used without further
purification. Starting areneruthenium chlorides were prepared as
previously described.13,14 1H and 13C NMR spectra were recorded on a
1
Bruker 300 MHz NMR spectrometer. H NMR chemical shifts are
reported relative to residual solvent signals. Mass spectra were
recorded on a Micromass Quattro II triple-quadrupole mass
spectrometer using ESI running the MassLynx software suite. IR
spectra (in KBr pellets) were recorded using a Varian 2000 FTIR
spectrometer. Elemental analyses were performed using an Elemental
GmbH Vario EL-3 instrument. Absorption spectra were recorded
using a CARY 100 Conc UV−vis spectrophotometer. Fluorescence
titration studies were carried out on a Horiba FluoroMax-4
fluorimeter.
Figure 6. Changes in the emission spectra of 5 in a TCE solution (1 ×
10−5 M) upon the addition of 15 equiv of C60 in TCE (1 × 10−3 M;
λexc = 390 nm).
UV−Vis Binding Study. A stock solution of 5 in a TCE solution
(2.0 mL, 1 × 10−5 M) was prepared and placed in a quartz cell. Stock
solutions (1 × 10−4 M) of the corresponding fullerenes in TCE were
added incrementally, and the absorption spectra were recorded at
room temperature.
Fluorescence Sensing Study. A 2 mL stock solution (1 × 10−5
M) of metallacycle 5 was placed in a 1-cm-wide quartz cell, and C60
and C70 stock solutions (1 × 10−3 M) were added incrementally.
Titration experiments were carried out at 298 K, and each
measurement was repeated at least three times to acquire concordant
values. Both the excitation and emission slits were 5 nm. An excitation
wavelength (λexc) of 390 nm for 5 was used for all measurements, and
emission was monitored at 527 nm. The association constant (K) was
estimated from the change in the emission intensity using Benesi−
Figure 7. Changes in the emission spectra of 5 in a TCE solution (1 ×
10−5 M) upon the addition of 12 equiv of C70 in TCE (1 × 10−3 M;
λexc = 390 nm).
Hildebrand analysis; the insets in Figures 6 and 7 are plots of (Imin
−
emission intensity were consistent with the formation of a
charge-transfer inclusion complex between the metallacyclic
host and C60 or C70.11
I0)/(I − I0) vs 1/[G], where I0 is the fluorescence intensity of the host,
I is the observed intensity, Imin is the lowest intensity, and G is C60 or
C70.
Furthermore, the association constants of 5 were estimated
from the fluorescence intensity changes using Benesi−
Hildebrand analysis,12 which afforded K values of 5.0 × 103
M−1 for C60 and 1.1 × 104 M−1 for C70 (insets in Figures 6 and
7). It may be noted though that the K values could not be
adequately approximated from the absorption titration because
of large absorption by free C60 and C70 guests. The observed K
values further indicate that the binding ability of 5 with C70 is
better than that with C60.
Crystallographic Data Collection and Refinement of Metal-
lacycle 4. A crystal of 4 was coated with paratone oil, and diffraction
data were measured at 173 K with Mo Kα radiation on an X-ray
diffraction camera system using an imaging plate equipped with a
graphite crystal incident beam monochromator. RapidAuto software15
was used for data collection and data processing. The structure was
solved by the direct methods and was refined by full-matrix least-
squares calculation with the SHELXTL software package.16 One
ligand, two Ru atoms, two p-cymene ligands, two triflate anions, and a
lattice water molecule were observed in the asymmetric unit cell. All
non-H atoms were refined anisotropically; the H atoms were assigned
isotropic displacement coefficients U(H) = 1.2U(C,N) and
In order to further understand the binding interaction of 5
1
with fullerenes, the binding was also examined by H NMR
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1
Figure 8. Comparative H NMR spectra of 5 and 5 + C60 in a TCE-d2 solvent.
1.5U(Cmethyl), and their coordinates were allowed to reside on their
respective atoms. H atoms attached to the lattice water molecule were
not included in the least-squares refinement. The least-squares
refinement of the structural model was performed under the geometry
constraint AFIX for phenyl and pyridyl portions of the ligand and
under geometry restraints and displacement parameter restraints such
as DFIX, DANG, and ISOR. Refinement of the structure converged at
final R1 = 0.1819 and wR2 = 0.4658 for 2992 reflections with I > 2σ(I)
and R1 = 0.2392 and wR2 = 0.4952 for all 5365 reflections. The largest
difference peak and hole were 1.902 and −0.707 e Å−3, respectively.
Synthesis of N,N′-Bis(4-iodophenyl)terephthalamide. A
solution of terephthaloyl dichloride (1 g, 4.90 mmol) and triethyl-
amine (3 mL) in 20 mL of CH2Cl2 was prepared and chilled to 4 °C in
an ice bath for 5 min, and then 4-iodoaniline (2.26 g, 10.30 mmol) was
added slowly to the cold solution over a period of 10 min. The
reaction mixture was stirred at room temperature overnight. The
resulting precipitate was collected on a frit, recrystallized with MeOH/
H2O, and dried in a vacuum oven. Yield: ca. 90% (2.60 g). Anal. Calcd
for C20H14I2N2O2: C, 42.28; H, 2.48; N, 4.93. Found: C, 42.08; H,
2.26; N, 4.50. 1H NMR (DMSO-d6, 300 MHz, δ, ppm): 10.50 (s, 2H,
CONH), 8.08 (d, 4H, Hc), 7.70−65 (d, 8H, Ha/Hb).
was removed under reduced pressure. The crude product thus
obtained was redissolved in nitromethane/CH3OH (10 mL, 1:1) and
subjected to vapor diffusion of diethyl ether. This resulted in a highly
red crystalline product within 1 week.
Yield: ca. 90%. Anal. Calcd for C124H104F12N8O24Ru4S4: C, 52.24;
H, 3.68; N, 3.93. Found: C, 52.18; H, 3.70; N, 3.90. FTIR (KBr, ν,
selected peaks): 3341 (NH), 2241 (CC), 1632 (CO) cm−1. ESI-
MS peaks at m/z 801.31 and 563.96 corresponding to [M − 3OTf]3+
and [M − 4OTf]4+ charge states. respectively. 1H NMR (nitro-
methane-d3, 300 MHz, δ, ppm): 9.06 (s, 4H, CONH), 8.22 (d, 8H, J =
6.6 Hz, Ha), 7.82 (s, 8H, He), 7.57 (d, 8H, J = 9.0 Hz, Hd), 7.47−7.43
(m, 16H, Hb/Hc), 5.98 (d, 8H, J = 6.3 Hz, −C6H4), 5.77−5.75 (m,
12H, −C6H4/bz), 2.98−2.86 (m, 4H, −CH(CH3)2), 2.22 (s, 12H,
−CH3), 1.36 (d, 12H, −CH(CH3)2).
Synthesis of Metallacycle 5. A mixture of starting complex 3
(0.0083 g, 0.01 mmol) and 2 equiv of AgCF3SO3 (0.0052, 0.02 mmol)
in 6 mL of methanol was stirred at room temperature for 2 h and
filtered to remove AgCl. The corresponding donor ligand 1 (0.0052 g,
0.01 mmol) was added to the filtrate. The mixture was then stirred at
room temperature for 6 h, and the solvent was removed under reduced
pressure. The crude product was redissolved in nitromethane and
subjected to vapor diffusion of diethyl ether. This resulted in a highly
crystalline product. The product was filtered and dried under vacuum.
Yield: ca. 90%. Anal. Calcd for C148H116F12N8O24Ru4S4: C, 56.41; H,
3.71; N, 3.56. Found: C, 56.60; H, 3.73; N, 3.45. FTIR (KBr, ν,
selected peaks): 3349 (NH), 2242 (CC), 1629 (CO) cm−1. ESI-
MS peaks at m/z 639.62 corresponding to the [M − 4OTf]4+ charge
Synthesis of Ligand N,N′-Bis[4-(pyridin-4-ylethynyl)phenyl]-
terephthalamide (1). In a flame-dried Schlenk flask, 4-ethynylpyr-
idine hydrochloride (0.615 g, 4.4 mmol) and triethylamine (10 mL)
were vigorously stirred for 30 min. During this time, a white
precipitate formed. Next, DMF (30 mL), Pd(PPh3)2Cl2 (0.062 g, 0.09
mmol), PPh3 (0.024 g, 0.09 mmol), CuI (0.018 g, 0.09 mmol), and
H2I (1.0 g, 1.76 mmol) were successively added. The Schlenk flask was
wrapped in aluminum foil to keep the reaction mixture in the dark.
The reaction mixture was refluxed for 24 h at 80 °C. The resulting
brown mixture was filtered on a frit, the solvent was removed, and the
residue was recrystallized with CH3OH/H2O (1:1). The compound
was filtered and dried under vacuum. Yield: ca. 77% (0. 700 g). Anal.
Calcd for C34H22N4O2: C, 78.75; H, 4.28; N, 10.80. Found: C, 78.62;
H, 4.21; N, 10.69. IR (KBr, ν, selected peaks): 3368 (NH), 2215 (C
1
state. H NMR (nitromethane-d3, 300 MHz, δ, ppm): 9.01 (s, 4H,
CONH), 8.76 (d, 8H, J = 6.6 Hz, Har), 8.54 (d, 8H, J = 6.6 Hz, Har),
7.96 (d, 8H, J = 6.6 Hz, Ha), 7.76 (s, 8H, He), 7.69 (d, 8H, J = 8.7 Hz,
Hd), 7.36 (d, 8H, J = 8.7 Hz, Hc), 7.27 (d, 8H, J = 6.6 Hz, Hb), 5.97 (d,
8H, J = 6.3 Hz, −C6H4), 5.76 (d, 8H, J = 6.3 Hz, −C6H4), 3.09−3.04
(m, 4H, −CH(CH3)2), 2.30 (s, 12H, −CH3), 1.39 (d, 12H,
−CH(CH3)2).
1
C), 1692 (CO) cm−1. H NMR (DMSO-d6, 300 MHz, δ, ppm):
10.67 (s, 2H, CONH), 8.62 (d, 4H, J = 4.8 Hz, Ha), 8.11 (s, 4H, He),
7.93 (d, 4H, J = 8.7 Hz, Hd), 7.64 (d, 4H, J = 8.4 Hz, Hc), 7.52 (d, 4H,
J = 5.4 Hz, Hb).
ASSOCIATED CONTENT
■
S
* Supporting Information
Synthesis of Metallacycle 4. A mixture of starting complex 2
(0.0068 g, 0.01 mmol) and 2 equiv of AgCF3SO3 (0.0052 g, 0.02
mmol) in nitromethane/CH3OH (4 mL, 1:1) was stirred at room
temperature for 2 h and filtered to remove AgCl. The corresponding
donor ligand 1 (0.0052 g, 0.01 mmol) was added to the filtrate. The
mixture was then stirred at room temperature for 12 h, and the solvent
1H NMR spectra of the starting precursor and ligand 1 and of 4
and 5 in nitromethane-d3, ESI-MS of both metallarectangles, an
ORTEP diagram of metallarectangle 4, and a table of bond
lengths and angles for 4. This material is available free of charge
via the Internet at http://pubs.acs.org.
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J.; Mukherjee, P. S. Inorg. Chem. 2012, 51, 4817. (b) Samanta, D.;
Shanmugaraju, S.; Joshi, S. A.; Patil, Y. P.; Nethaji, M.; Mukherjee, P.
S. Chem. Commun. 2012, 48, 2298.
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: kwchi@ulsan.ac.kr.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work was supported by the Basic Science Research
program through the National Research Foundation of Korea
(NRF) funded by the Ministry of Science, ICT, and Future
Planning (Grant NRF-2013R1A1A2006859). A Priority Re-
search Centers program (2009-0093818) through the NRF is
also financially appreciated. X-ray diffraction experiments using
synchrotron radiation were performed at the Pohang
Accelerator Laboratory in Korea. We thank Prof. Peter J.
Stang, Department of Chemistry, University of Utah, for help
with ESI-MS experiments.
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dx.doi.org/10.1021/ic401685s | Inorg. Chem. XXXX, XXX, XXX−XXX