Helical nanostructures of an optically active metal-free porphyrin with four optically active binaphthyl moieties: Effect of metal-ligand coordination on the morphology

Article abstract of DOI:10.1002/ejic.201000358

An optically active metal-free porphyrin (1) with four chiral binaphthyl units attached at the meso-phenyl substituents through crown ether moieties has been designed, synthesized, and characterized. Its self-assembly behavior in the absence and presence of K⁺ was comparatively investigated by electronic absorption and circular dichroism (CD) spectra, transmission electron microscopy (TEM), scanning electron microscopy (SEM), atom force microscopy (AFM), and energy-dispersive X-ray (EDX) spectroscopy. In the absence of K ⁺, metal-free porphyrin self-assembles into nanoparticles depending mainly on the van der Waals interaction among neighboring metal-free molecules. In the presence of K⁺, additionally formed metal-ligand K-O _crown coordination bonds between K+ and crown units of (R)-and (S)-1 molecules, together with chiral discrimination of chiral side chains and intermolecular van der Waals interactions, induce a righthanded and left-handed helical arrangement in a stack of (R)-and (S)-1 molecules, respectively, with an ordered head-to-tail internal molecular arrangement. This then further hierarchically self-assembles into highly ordered fibrous nanostructures with a helicity opposite to that of the original porphyrin stack. This clearly reveals the effect of the metal-ligand coordination bonding interaction on the morphology and handedness of self-assembled nanostructures.

Full text of DOI:10.1002/ejic.201000358

FULL PAPER
DOI: 10.1002/ejic.201000358
Helical Nanostructures of an Optically Active Metal-Free Porphyrin with Four
Optically Active Binaphthyl Moieties: Effect of Metal–Ligand Coordination on
the Morphology
Jitao Lu,[a] Lizhen Wu,[a] Jianzhuang Jiang,*[a,b] and Xiaomei Zhang*[a]
Keywords: Chirality / Porphyrinoids / Self-assembly / Optical activity / Nanostructures
An optically active metal-free porphyrin (1) with four chiral
binaphthyl units attached at the meso-phenyl substituents
through crown ether moieties has been designed, synthe-
sized, and characterized. Its self-assembly behavior in the
absence and presence of K+ was comparatively investigated
by electronic absorption and circular dichroism (CD) spectra,
transmission electron microscopy (TEM), scanning electron
microscopy (SEM), atom force microscopy (AFM), and en-
ergy-dispersive X-ray (EDX) spectroscopy. In the absence of
K+, metal-free porphyrin self-assembles into nanoparticles
depending mainly on the van der Waals interaction among
neighboring metal-free molecules. In the presence of K+, ad-
ditionally formed metal–ligand K–Ocrown coordination bonds
between K+ and crown units of (R)- and (S)-1 molecules, to-
gether with chiral discrimination of chiral side chains and
intermolecular van der Waals interactions, induce a right-
handed and left-handed helical arrangement in a stack of
(R)- and (S)-1 molecules, respectively, with an ordered
“head-to-tail” internal molecular arrangement. This then
further hierarchically self-assembles into highly ordered fi-
brous nanostructures with a helicity opposite to that of the
original porphyrin stack. This clearly reveals the effect of the
metal–ligand coordination bonding interaction on the mor-
phology and handedness of self-assembled nanostructures.
molecular-based electronic and optical devices such as elec-
tronic wires, switches, electroluminescence devices, field-ef-
fect transistors, and photovoltaic devices.[8] Hollow capsules
with potential applications as drug-delivery agents were
fabricated from a designed amphiphilic porphyrin com-
pound.[9] Monomer, trimer, tetramer, and extended wirelike
nanostructures were produced from a cyano-substituted
porphyrin on a gold surface.[10] Very recently, the successful
tuning control over the morphology of self-assembled
nanostructures of porphyrin derivatives has been achieved
by means of molecular design and synthesis through the
introduction of metal–ligand coordination or hydrogen-
bonding interactions according to this group.[11] Among
these extensive investigations, great effort has been paid to
the construction of helical supramolecular architectures
with both achiral and, in particular, chiral porphyrin pre-
cursors due to their great potential applications.[11–15] This
resulted in the synthesis of a large number of chiral por-
phyrins that contain different stereocenters such as chiral
amino acids and chiral hydrocarbons. Nevertheless, some
investigations have indicated that installing stereocenters
into the periphery of a porphyrin molecule merely provides
a possibility for the fabrication of helical supramolecular
structures instead of ensuring it outright. Actually, quite a
small fraction of nanostructures fabricated from porphyrin
compounds with peripheral substituents that contain
stereocenters exhibit helicity on the nanoscale.[16] In fact,
some porphyrin compounds that bear peripheral chiral sub-
stituents with stereocenters that are even circular dichroism
Introduction
Nature is amazing when it comes to being able to create
various kinds of functional architectures with a preferred
helicity, such as DNA with a double-helix structure and
motifs in protein with an α-coiled helical structure.[1] In-
spired by the elegance of fascinating biological supramolec-
ular structures, numerous artificial assemblies that comprise
helical fibers and twisted ribbons of sugars,[2] helicenes,[3]
metal complexes,[4] optically active π-conjugated systems,[5]
and chiral block copolymers[6] have been fabricated with
the assistance of noncovalent interactions such as hydrogen
bonding, metal–ligand coordinate bonding, electrostatic in-
teractions, van der Waals forces, and π–π stacking.
As one of the most important typical representative of
π-conjugated systems, porphyrin compounds have been in-
tensively studied over the past century due to their wide
range of biological relevance and industrial applications.[7]
In recent years, the self-assembly behavior and nanostruc-
tures of porphyrin compounds have attracted extensive
research interest with an eye toward the construction of
[a] Department of Chemistry, Shandong University,
Jinan 250100, China
E-mail: jianzhuang@ustb.edu.cn
[b] Department of Chemistry, University of Science and Technol-
ogy Beijing,
Beijing 100083, China
E-mail: jianzhuang@ustb.edu.cn
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.201000358.
View this journal online at
wileyonlinelibrary.com
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Optically Active Metal-Free Porphyrin
(CD) active at the supramolecular level do not display heli- ties of the (R)- and (S)-1 molecules, together with chiral
cal nanostructures, probably due to the lack of long-range discrimination of chiral side chains, induce a right-handed
molecular ordering as a result of the weak intermolecular and left-handed helical arrangement in a stack of (R)- and
interactions.[17] The delicate balance between noncovalent (S)-1 molecules with an ordered “head-to-tail” internal mo-
interactions and chiral discrimination during the self-as- lecular arrangement, respectively, which then further hierar-
sembly process therefore appears to play an important role chically self-assembles into highly ordered fibrous nano-
in the fabrication of helical supramolecular nanostructures. structures with the opposite helicity to the stack. This re-
This is indeed exemplified by the double-stranded helixes veals the effect of the metal–ligand coordination bonding
that have been fabricated from porphyrins decorated with interaction on the morphology and handedness of self-as-
optically active BisPYBOX [PYBOX = 2,6-bis(2-oxazolyl)- sembled nanostructures. The results will be helpful in pro-
pyridine] units in the presence of oligomers that have two viding new insight into chiral information transfer and the
or three secondary dialkylammonium cations.[17b] However, expression of synthetic conjugated systems on the supra-
synergistic interplay among noncovalent interactions and molecular level.
chiral discrimination during the self-assembly process and
its effect on the morphology and dimension of nanostruc-
tures formed from porphyrin compounds still remains po-
orly understood.
It is well known that the significant absorption over the
ultraviolet and visible region of porphyrin derivatives ren-
ders it possible to investigate the self-assembly process of
Results and Discussion
Synthesis and Characterization of Optically Active Metal-
Free Porphyrin Enantiomers (R)- and (S)-1
To enhance the asymmetric perturbation to the por-
these tetrapyrrole compounds, in particular chiral por- phyrin chromophore, optically active binaphthyl units
phyrins, by means of electronic absorption and CD spec- were chosen to be attached onto the porphyrin ring through
troscopy. However, at the molecular level quite a large meso-attached benzene, thereby resulting in the target
number of porphyrins with peripheral subsitutents contain- metal-free porphyrin enantiomers (R)- and (S)-1
ing stereocenters do not display any circular dichroism sig- (Scheme 1). Meanwhile, crown ether substituents were also
nal in the whole absorption range of porphyrins. This is due introduced between meso-attached benzene substituents
to the weak perturbation of the central porphyrin core by and binaphthyl units, which were expected to provide an
the peripheral substituents with chiral stereocenters.[18] In additional opportunity to tune the morphology and dimen-
this paper, we describe the synthesis and characterization of sion of aggregates based on the formation of additional co-
a novel optically active metal-free porphyrin. Optically ordination bonding interactions between the crown ether
active binaphthyl units were introduced onto the porphyrin units and the added K+ ion. The metal-free porphyrin
periphery to enhance the asymmetric perturbation enantiomers (R)- and (S)-1 were prepared from (R)/(S)-
(Scheme 1). The self-assembly properties of this metal-free 2,2Ј-dihydroxy-1,1Ј-binaphthyl derivatives 6. As shown in
porphyrin were also comparatively studied. In the absence Scheme 1, (R)-/(S)-6 were obtained from the Williamson
of K+, both enantiomers of this optically active metal-free ether synthesis reaction between (R)-/(S)-2,2Ј-dihydroxy-
porphyrin self-assemble into nanoparticles. However, with 1,1Ј-binaphthyl and 3,4-bis{2Ј-[2ЈЈ-(p-tolylsulfonyloxy)-
the assistance of K+, additional metal–ligand K–Ocrown co- ethoxy]ethoxy}benzaldehyde (5) generated from an aro-
ordination bonds formed between K+ and the crown moie- matic nucleophilic substitution reaction and tosylation re-
Scheme 1. Synthesis of optically active metal-free porphyrin enantiomers (R)- and (S)-(1).
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action of 3,4-dihydroxybenzaldehyde. Then treatment of bi- tically active binaphthyl groups, which are believed to play
naphthyl derivatives 6 in propionic acid, heated to reflux, important roles in the construction of helical nanostruc-
with pyrrole led to the isolation of optically active metal- tures.
free porphyrin enantiomers (R)- and (S)-1 in good yields.
In line with the previous results, racemization of the corre-
sponding optically active compounds at each reaction step
under the depicted reaction conditions did not occur.[19]
Satisfactory elemental analysis results were obtained for the
newly prepared metal-free porphyrin enantiomers of 1 after
purification through column chromatography followed by
repeated recrystallization from chloroform/methanol (it is
worth noting that the purple crystalline solid of 1 contains
0.5 equiv. solvated CHCl3). The compound was further
1
characterized by MALDI-TOF mass and H NMR spec-
troscopic methods (Figures S1 and S2 in the Supporting In-
formation). The MALDI-TOF mass spectrum of the com-
pound clearly shows an intense signal for the protonated
molecular ion [M + H]+. The isotopic pattern closely re-
semble the simulated one, as shown in Figure S2. This com-
pound was also characterized by electronic absorption and
IR spectroscopy.
Electronic Absorption and CD Spectroscopy
The electronic absorption and circular dichroism spectra
of the metal-free porphyrin derivatives (R)- and (S)-1 in
chloroform are shown in Figure 1. As can be seen from Fig-
ure 1B, similar to other metal-free porphyrins, compound 1
shows a typical molecular electronic absorption spectrum
with the Soret band at 421 nm and Q bands at 511, 547,
582, and 637 nm, thereby revealing the nonaggregated mo-
lecular spectroscopic nature of the compound in CHCl3.
An intense band below 270 nm is also observed, which can
be attributed to the absorption of binaphthyl groups with
evidence by the observation of the corresponding CD signal
in the same region for either (R)-1 or (S)-1 in their CD
Figure 1. Circular dichrorism (CD) spectra of (S)- and (R)-1 (A)
as a dilute solution in chloroform and (C) their nanostructures
formed in the presence of potassium ions dispersed in methanol.
(B) Electronic absorption spectra of a dilute solution of metal-free
porphyrin 1 in chloroform (solid line) and its nanostructures
formed in the presence of potassium ions dispersed in methanol
(dashed line).
The electronic absorption and circular dichroism spectra
spectra (Figure 1A).[20] As clearly shown in the CD spectra of the aggregates formed from (R)- and (S)-1 in n-hexane
of (R)- and (S)-1, the introduction of the optically active in the absence and presence of potassium ions are also re-
binaphthyl moieties through the crown ether unit onto the corded and shown in Figures 1 and S3 (in the Supporting
meso-attached phenyl groups of the porphyrin ring induces Information), respectively, which are different from the
the appearance of CD signals of the porphyrin ligand in spectra of the corresponding compounds in CHCl3. As
both the Soret and Q absorption regions (Figure 1A); this shown in Figure S3A, in comparison with the electronic ab-
indicates an effective chiral information transfer from the sorption spectra of homogeneous solutions of (R)- and (S)-
optically active binaphthyl moieties to the porphyrin chro- 1 in chloroform, when (R)- and (S)-1 self-assemble into ag-
mophore at the molecular level. In detail, in the case of (S)- gregates, both the Soret and Q bands for (R)-1 or (S)-1 lose
1, the sign of the circular dichroism is negative over almost their intensity in the aggregate phase. In particular, the So-
the entire Soret and Q bands, whereas conversely (R)-1 ret band shifts to a longer wavelength with a maximum at
shows a positive circular dichroism sign. According to the 432 nm, and the Q band redshifts to 518, 553, 584, and
chiral exciton theory, (S)-1 is right-handed, whereas (R)-1 643 nm in n-hexane. In contrast, addition of K+ induces
is left-handed on the basis of the circular dichroism pattern further redshift for the porphyrin Soret band during the
in the range of 250–270 nm. It is noteworthy that, despite self-assembly process of 1, with a maximum at 441 nm and
the optically active binaphthyl groups being linked remotely a shoulder around 404 nm. This reveals the further en-
to the porphyrin core, the circular dichroism intensity of 1 hanced intermolecular interaction due to the additionally
at the porphyrin Soret band [∆ε = –3.0727 (λ = 421 nm, c introduced metal–ligand coordination bonds between
= 2ϫ10–6 molL–1 in CHCl3)] is not weaker than that of crown ether units and K+. The porphyrin Q absorption is
other optically active porphyrin derivatives,[21] thereby indi- redshifted to 518, 550, 582, and 638 nm. On the basis of
cating the relatively stronger chiral perturbation of the op- Kasha’s exciton theory,[22] redshifts in the main absorption
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Optically Active Metal-Free Porphyrin
bands of compound 1 upon aggregation with and without Aggregate Morphology
the presence of K+ reveals that the porphyrin molecules
self-assemble into the J aggregates with a head-to-tail mo-
The morphology of the aggregates formed was examined
lecular arrangement in their nanostructures. However, ob- by transmission electron microscopy (TEM), scanning elec-
servation of a larger degree of the redshift in the main elec- tron microscopy (SEM), and AFM. Samples were prepared
tronic absorptions for (R)-1 and (S)-1 upon aggregation in by casting a drop of sample solution onto a carbon-coated
the presence of K+ indicates a stronger intermolecular in- grid. In line with the electronic absorption result, different
teraction in the direction parallel to the porphyrin ring than morphologies were observed for nanostructures formed in
in the aggregates formed in the absence of K+ due to the the presence and absence of potassium ions. Figure 2A dis-
formation of additional metal–ligand coordination bonds. plays a large-area SEM image of nanostructures fabricated
These are expected to improve the chiral discrimination be- from (R)-1 in the absence of potassium ions. As can be seen,
tween adjacent porphyrin molecules, thus resulting in the spherical particles with an average radius of approximately
formation of nanostructures with helicity. This was indeed 500 nm were formed from (R)-1. This is also true for (S)-
verified by their circular dichroism spectroscopic and elec- 1. A statistical analysis, conducted by measuring over 200
tronic microscopic results as detailed below.
particles in this SEM image, indicated that the particles are
In the circular dichroism spectra of aggregates fabricated quite uniform in dimension (Figure 2B). AFM was also
from (R)- and (S)-1 in the absence of K+ (Figure S3A in used to evaluate the integrity of these nanoparticles on sil-
the Supporting Information), both porphyrin enantiomers ica in the absence of solvent (Figure 2C), thereby showing
experience a similar intensity decrease in almost the whole that the height of these nanoparticles is in the range of 450–
Soret and Q regions upon aggregation. Nevertheless, no 550 nm. This result is in good agreement with that observed
Cotton effect was observed in the circular dichroism spectra by SEM.
of (R)-1 or (S)-1 aggregates, thereby indicating the lack of
Contrary to the self-assembly of metal-free porphyrin in
effective chiral discrimination between the porphyrin mole- the absence of K+, both (R)- and (S)-1 self-assemble into
cules during the self-assembly process. However, perfect fibrous nanostructures with nanometer-sized diameter and
mirroring bisignate Cotton effect is observed with a zero micrometer-sized length in the presence of K+ (Figure 3A
crossing at 441 nm that is close to the absorption maximum and B). These fibrous nanostructures consist of bundles of
(Figure 1C). According to the semiempirical method devel- single twisted strands, as clearly revealed by the magnified
oped by Nakanishi and co-workers,[23] the sign of the cou- TEM image (Figure 3a). Further inspection with AFM in-
pling and the direction of dipole moments can be used to dicates that these fibrous nanostructures with left- and
determine the chirality of stacked porphyrin molecules in right-handed helicity were formed from (R)- and (S)-1
aggregates. In general, the circular dichroism spectrum that enantiomers, respectively, which are clearly revealed by two
features a bisignate Cotton effect showing positive features high-magnification AFM images chosen simultaneously
at longer wavelengths and negative ones at shorter wave- from (R)- and (S)-1 aggregates (Figure 3C and D). Careful
lengths would indicate right-handed chirality of the dipole analysis of a single fibrous nanostructure fabricated from
moments (positive chirality), whereas the opposite would (R)- and (S)-1 enantiomers shows the average helical pitch
be true for left-handed chirality (negative chirality). In the to be about 125 nm with an angle (the angle of the groove
present case, the negative chirality of (S)-1 aggregates corre- with respect to the main fiber axis) of about 46°. It is worth
sponds to a left-handed stacking and the positive chirality noting that, as mentioned above, the circular dichroism
of (R)-1 aggregates indicates a right-handed stacking of chi- spectroscopic results demonstrate that a right-handed and
ral metal-free porphyrin molecules in aggregates. The for- a left-handed helical arrangement was formed from (R)-
mation of the supermolecular helicity, observed from the and (S)-1, respectively, in a stack of the metal-free por-
circular dichroism spectrum, is unequivocally confirmed by phyrin molecules in aggregates. However, according to the
atom force microscopy (AFM) analysis of the (R)-1 or (S)- AFM results, observation of nanostructures with opposite
1 aggregates as detailed below.
helicity to the stack fabricated from either the (R)- or the
Figure 2. TEM and SEM images of nanostructures fabricated from optically active metal-free porphyrin 1 in the absence of K+. (A) TEM
image of nanoparticles formed from optically active metal-free porphyrin 1 in the absence of potassium ions. (B) Diameter distribution of
nanoparticles. (C) Topographic AFM image of nanoparticles on silica.
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(S)-1 enantiomer clearly reveals the hierarchical self-as-
sembly nature of this compound. In detail, the (R)-1 mole-
cules first self-assemble into one-dimensional right-handed
helices with positive chirality depending on the synergistic
interplay of intermolecular van der Waals interactions, ad-
ditionally introduced metal–ligand coordination bonding,
and chiral discrimination among neighboring porphyrin
molecules, which, acting as elementary building blocks, fur-
ther stack into highly ordered fibrous nanostructures with
left-handed helicity (Figure 3C). In the case of the (S)-1 en-
antiomer, the left-handed helices with negative chirality are
formed at the first stage of aggregation and then stack into
highly ordered nanofibers with right-handed helicity (Fig-
ure 3D).
Figure 4. EDX spectrum of (A) nanostructures formed from op-
tically active metal-free porphyrin 1 in the presence of potassium
ions and (B) nanostructures formed from optically active metal-
free porphyrin 1 in the absence of potassium ions.
X-ray Diffraction Patterns
The internal structure of self-assembled nanostructures
was further investigated by X-ray diffraction (XRD) tech-
niques (Figure 5). As can be seen from Figure 5A, in the
absence of K+, there exists no diffraction peak in the X-ray
diffraction pattern of the nanoparticles self-assembled from
metal-free porphyrin 1, thereby indicating a lack of ordered
molecular packing in this nanostructure due to the lack of
effective intermolecular π–π interaction. In contrast, three
broad diffraction peaks at 2θ = 1.26° (corresponding to
7.01 nm), 1.96° (4.51 nm), and 2.50° (3.53 nm) were ob-
served in the X-ray diffraction pattern of the nanostructures
fabricated from 1 in the presence of K+, thereby indicating
regular molecular stacking (Figure 5B). These peaks are as-
cribed to the refractions from the (001), (010), and (002)
planes, respectively. On the basis of the geometry optimiza-
tion and energy-minimized molecular structure of por-
phyrin 1 with the Gaussian 98 program at the B3LYP/6-
31G(d) level,[24] the molecular dimensional size is 3.2 nm
(length)ϫ4.5 nm (diagonal length) (Figure 5C). According
Figure 3. TEM, SEM, and topographic AFM images of nanostruc-
tures fabricated from optically active metal-free porphyrin 1 in the
presence of K+. (A) TEM image of nanostructures formed from
optically active metal-free porphyrin 1 in the presence of potassium
ions; (a) high-magnification TEM image of metal-free porphyrin 1
in the presence of K+, which shows the nanostructures being
formed by several fibers together. (B) SEM image of nanostructures
formed from optically active metal-free porphyrin 1 in the presence
of potassium ions. (C) AFM height image of a single left-handed
fibrous nanostructure fabricated from (R)-1; (D) AFM height im-
age of a single right-handed fibrous nanostructure fabricated from
(S)-1.
Energy-Dispersive X-ray (EDX) Spectroscopy
To understand the role of potassium ions in the forma-
tion of nanofibers, EDX spectroscopy was used to detect
the composition of the sample. Observation of the elemen-
tal signature for C, N, and O atoms in the EDX spectrum
of the nanostrucutres fabricated from (R)- or (S)-1 in the
presence and absence of K+ (Figure 4A and B) confirms the
composition of nanoparticles and nanofibers from por-
phyrin derivative 1. In addition, observation of the elemen-
tal signature for the potassium atom in addition to C, N,
and O atoms in the EDX spectra of (R)- or (S)-1 aggregates
formed in the presence of K+ (Figure 4A) indicates the exis-
tence and the coordination role of K+ during the self-as-
sembly process of the optically active porphyrin 1 enantio-
mers in the presence of K+.
Figure 5. (A) XRD profile of the nanostructures fabricated from
metal-free porphyrin 1 in the absence of K+. (B) XRD profile of
the nanostructures fabricated from metal-free porphyrin 1 in the
presence of K+. (C) Schematic representation of a metal-free por-
phyrin 1 molecule and K+. (D) Schematic representation of a 1/K+
dimer.
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Optically Active Metal-Free Porphyrin
to the XRD results and the simulated molecular structure, those of the metal-free porphyrin, unambiguously confirm
a unit cell that consists of two porphyrin molecules with the composition of both nanoparticles and nanofibers fab-
cell parameters of a = 7.01 nm and b = 4.51 nm is given for ricated from the metal-free porphyrin. However, in the IR
compound 1 (Figure 5D).
spectrum of the metal-free porphyrin, two relatively sharp
absorptions at around 1260 and 1133 cm–1 are assigned to
the symmetric and asymmetric C–O–C bonding stretching
vibration, respectively. Similar absorption peaks at 1257
and 1134 cm–1 are also observed in the IR spectrum of
nanoparticles fabricated from 1 in the absence of K+. How-
ever, in the IR spectrum of the aggregates formed from 1
in the presence of K+, these two absorption bands are
broadened and shifted to a lower frequency at 1257 and
1124 cm–1, respectively, thereby indicating the formation of
coordination bonds between crown ether units and added
K+ ion. These results are in line with the electronic absorp-
tion result as detailed above.
Assembly Mechanism
On the basis of the experimental results described above,
a formation mechanism of nanofibers from both enantio-
mers of metal-free porphyrin 1 in the presence of potassium
ions was proposed and is depicted in Figure 6. As described
above, to increase the chiral perturbation and intermo-
lecular interaction, four bulky chiral binaphthyl units as
well as crown ether moieties were incorporated onto the
meso-attached phenyl groups of the porphyrin ring, which,
however, interfere with the effective intermolecular π–π in-
teraction, thereby preventing stacking of porphyrin mole-
cules from assembling along one dimension to form one-
dimensional nanostructures. As a result, nanoparticles were
formed from both enantiomers of metal-free porphyrin 1 in
the absence of potassium ion. However, in the event that
K+ ions were added to the system, additional metal–ligand
coordination bonding interactions between K+ and crown
ether moieties facilitate the linear stacking of porphyrin
molecules in a “head-to-tail” manner.[25] This, in combina-
tion with the van der Waals interaction between the por-
phyrin rings and the chiral discrimination among the op-
tically active binaphthyl units during the self-assembly pro-
cess, dominates the formation of a helix with a right- and a
left-handed helical arrangement of (R)- and (S)-1, respec-
tively, which then further hierarchically self-assembles into
highly ordered fibrous nanostructures with a helicity oppo-
site to that of the original porphyrin stack.
Conclusion
We have designed and prepared both enantiomers of an
optically active metal-free porphyrin decorated with four bi-
naphthyl units linked at the meso-attached phenyl groups
through crown ether moieties. The self-assembly properties
of these two enantiomers were comparatively investigated
in the absence and presence of potassium ions. Without
adding K+, both enantiomers self-assemble into nano-
particles. In the presence of K+, additional metal–ligand
K–Ocrown coordination bonds formed between K+ and the
crown units of (R)- and (S)-1 together with chiral discrimi-
nation of chiral side chains, and intermolecular
van der Waals interactions induce the formation of a right-
handed and left-handed helix, respectively, with an ordered
“head-to-tail” internal molecular arrangement at the first
stage of aggregation; this then further hierarchically stacks
into highly ordered fibrous nanostructures with the oppo-
site helicity. The present results not only reveal the effect
of additionally formed metal-coordination bonding on the
morphology of self-assembled nanostructures but is also
helpful in providing new insight into chiral information
transfer and expression for synthetic conjugated systems at
the supramolecular level.
Experimental Section
Figure 6. Schematic illustration of the hierarchical formation of
nanofibers with right-handed helicity through a one-dimensional
left-handed helix with negative chirality determined by the periph-
eral chiral side chains of the porphyrin ring in the molecule of the
(R)-1 enantiomer.
Measurements: Electronic absorption spectra were recorded with a
Hitachi U-4100 spectrophotometer. MALDI-TOF mass spectra
were taken with a Bruker BIFLEX III ultra-high resolution Fourier
transform ion cyclotron resonance (FT-ICR) mass spectrometer
with α-cyano-4-hydroxycinnamic acid as matrix. Q-TOF mass spec-
tra were recorded with an Agilent Technologies 6510 mass spec-
trometer. All melting points were determined with an X-4 appara-
IR Spectra
1
tus. H and 13C NMR spectra were recorded with a Bruker DPX
IR spectroscopy was also employed to investigate the
composition of the nanostructures. The IR spectra of the
metal-free porphyrin itself, nanoparticles, and nanofibers of
1 are compared in Figure S4 in the Supporting Information.
Similar features, except for the decreased intensity in the IR
300 spectrometer. Elemental analyses were performed by the Beij-
ing Institute of Chemistry. Circular dichroism (CD) measurements
were carried out with a JASCO J-810 spectropolarimeter. Trans-
mission electron microscopic (TEM) images were measured with
a JEOL-100CX II electron microscope operated at 100 kV. High-
spectra of both nanoparticles and nanofibers relative to resolution TEM (HRTEM) measurements and energy-dispersive
Eur. J. Inorg. Chem. 2010, 4000–4008
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J. Lu, L. Wu, J. Jiang, X. Zhang
FULL PAPER
X-ray (EDX) spectra were performed with a JEOL-2010 instru-
ment working at 200 kV. Scanning electron microscopic (SEM)
images were obtained with a JEOL JSM-6700 F. Atom force micro-
scopy (AFM) images were collected in air under ambient condi-
tions by using the tapping mode with a Nanoscope III/Bioscope
scanning probe microscope from Digital Instruments. For TEM
imaging, a drop of sample solution was cast onto a carbon copper
grid. For SEM imaging, Au (1–2 nm) was sputtered onto these
grids to prevent a charging effect and to improve the image clarity.
fate, and concentrated. The residue was purified by silica gel
chromatography with ethyl acetate/petroleum ether (60–90 °C) (1:1)
as eluent, thereby giving the product as a viscous oil (3.67 g,
61.7%). 1H NMR (300 MHz, CDCl3, 25 °C): δ = 2.38 (s, 6 H,
CH3), 3.75–3.83 (m, 8 H, OCH2), 4.07–4.19 (m, 8 H, OCH2), 6.96–
6.98 (d, J = 8 Hz, 1 H, Ar-H), 7.28–7.33 (d, J = 20 Hz, 4 H, Ar-
H), 7.37 (s, 1 H, Ar-H), 7.44–7.46 (d, J = 8 Hz, 1 H, Ar-H), 7.76–
7.78 (d, J = 8 Hz, 4 H, Ar-H), 9.83 (s, 1 H, CHO) ppm. 13C NMR
(100 MHz, CDCl3, 25 °C): δ = 21.31, 53.60, 60.25, 68.66, 68.70,
68.85, 69.40, 69.43, 69.45, 69.51, 111.89, 112.62, 126.61, 157.84,
129.81, 130.28, 132.93, 144.82, 149.01, 154.20, 190.53 ppm. MS:
calcd. for C29H38NO11S2 [M + NH4]+ 640.2; found 640.2.
Chemicals: DMF was freshly distilled just before use. 3,4-Di-
hydroxybenzaldehyde was purchased from Shanghai Zhixin Co.
Both chloroform and methanol (HPLC grade) were purchased
from Tianjin Kermel Co. Column chromatography was carried out
on silica gel (Merck, Kieselgel 60, 70–230 mesh) with the indicated
eluents. Optically pure (R)- and (S)-2,2Ј-dihydroxy-1,1Ј-binaphthyl
(Ͼ99% ee) were obtained from Dalian Reagent Company. All the
other chemicals were of reagent grade and used as received without
further purification. 5-Tosyloxy-3-oxa-1-pentanol (3) was prepared
according to a published procedure.[19b]
Preparation of (R)- or (S)-6: A mixture of compound 5 (3 g,
4.82 mmol), (R)- or (S)-2,2Ј-dihydroxy-1,1Ј-binaphthyl (1.15 g,
4.0210 mmol), and potassium carbonate (0.6 g, 4.35 mmol) in
DMF (25 mL) was stirred at room temperature under nitrogen for
72 h. The reaction mixture was concentrated under reduced pres-
sure, and the residue was shaken with water and extracted with
dichloromethane (3ϫ100 mL). The combined organic layers was
washed with water (3ϫ50 mL) and dried with anhydrous sodium
sulfate. The solvent was removed by evaporation under reduced
pressure, and the residue was purified by silica gel chromatography
with ethyl acetate/petroleum ether (60–90 °C) (1:6) as eluent, thus
leading to a white solid as the target compound 6 (0.63 g, 27.6%).
1H NMR (300 MHz, CDCl3, 25 °C): δ = 3.49–3.89 (m, 8 H,
OCH2), 3.90–4.23 (m, 8 H, OCH2), 6.85–6.88 (d, J = 9 Hz, 1 H,
Ar-H), 7.13–7.22 (m, 4 H, Ar-H), 7.27–7.43 (m, 6 H, Ar-H), 7.80–
7.83 (m, 4 H, Ar-H), 9.83 (s, 1 H, CHO) ppm. 13C NMR
(100 MHz, CDCl3, 25 °C): δ = 69.25, 69.45, 69.49, 69.55, 69.62,
69.76, 70.21, 70.30, 111.09, 111.95, 116.04, 120.60, 120.71, 123.58,
123.64, 215.35, 125.36, 126.15, 126.18, 126.61, 127.67, 127.70,
129.03, 129.06, 129.33, 129.38, 130.16, 134.04, 149.22, 154.14,
154.17, 154.21, 190.69 ppm. M.p. 80–83 °C. MS: calcd. for
C35H36NO7 [M + NH4]+ 582.2; found 582.2.
Nanostructure Fabrication: The self-assembled nanostructures of
the optically active metal-free porphyrin were fabricated by the
solution mixture method according to the following procedure.[26]
A saturated solution of potassium acetate in n-hexane was injected
into a solution of optically active metal-free porphyrin in chloro-
form (3 ϫ10–4 m) to give a solution with a final chloroform/n-
hexane ratio of 1:1 (v/v) in a small flask. After the solution had
slowly concentrated at room temperature, some loose aggregates
remained at the bottom of the flask. Then a small amount of n-
hexane was added into the flask to suspend the aggregates in the
solvent. Successive drops of the solution were cast onto a grid (Cu
with a carbon film). The aggregated behavior in the solid state was
observed after the solvent was evaporated. The nanoparticles were
prepared according to the same method except for using pure n-
hexane instead of the saturated n-hexane solution of potassium
acetate. The experimental results were stable and reproducible un-
der the experimental conditions described above.
Preparation of (R)- and (S)-1: A solution of pyrrole (0.20 g,
3.0 mmol) in propionic acid (13 mL) was added dropwise to a solu-
tion of compound 5 (1.15 g, 2.0 mmol) in propionic acid (17 mL)
at reflux for 30 min. Then the reaction mixture was cooled to room
temperature. Methanol (100 mL) was added, and the solution was
left standing overnight. The crystalline residue separated from the
bulk solution was collected by filtration, washed with methanol,
and then purified by silica gel chromatography. After the first green
band eluted with chloroform, the desired metal-free porphyrin was
subsequently eluted with chloroform/methanol (100:1) as eluent,
thereby giving the product as a purple crystalline solid (1 g, 20%).
Satisfactory elemental analysis results were obtained by repeated
recrystallization from chloroform/methanol or chloroform/n-hex-
Preparation of 4: Potassium carbonate (3.79 g, 27.43 mmol) was
added into
a solution of 3,4-dihydroxybenzaldehyde (1.87 g,
13.6 mmol) and compound 3 (5.02 g, 29.88 mmol) in CH3CN
(169 mL). The mixture was heated at reflux under a nitrogen atmo-
sphere for 16 h. After being cooled to room temperature, the mix-
ture was concentrated under reduced pressure, and water (200 mL)
was added. Then the product was extracted with dichloromethane
(3ϫ100 mL). The combined organic layers were washed with brine,
dried with anhydrous sodium sulfate, filtered, and concentrated.
The residue was purified by silica gel chromatography with ethyl
acetate/petroleum ether (60–90 °C) (1:2) as eluent to give the prod-
uct as a viscous oil (3.59 g, 84%). 1H NMR (300 MHz, CDCl3,
25 °C): δ = 3.69–3.76 (m, 8 H, OCH2), 3.92–4.01 (m, 4 H, OCH2),
4.21–4.26 (m, 4 H, OCH2), 6.97–7.00 (d, J = 9 Hz, 1 H, Ar-H),
7.42–7.47 (m, 2 H, Ar-H), 9.84 (s, 1 H, CHO) ppm. 13C NMR
(100 MHz, CDCl3, 25 °C): δ = 61.90, 68.17, 68.20, 68.51, 68.67,
72.28, 72.33, 110.80, 111.67, 112.10, 126.33, 129.77, 148.44, 153.56,
190.46 ppm. MS: calcd. for C15H23O7 [M + H]+ 315.1; found 315.1.
1
ane. H NMR (300 MHz, CDCl3, 25 °C): δ = 3.60–3.87 (m, 32 H,
OCH2), 4.11–4.31 (m, 32 H, OCH2), 7.18–7.36 (m, 33 H, Ar-H),
7.52–7.57 (m, 6 H, Ar-H), 7.76–7.84 (m, 6 H, Ar-H), 7.86–8 (m,
15 H, Ar-H), 8.93 (s, 8 H, Ar-H) ppm. M.p. 195–200 °C. MS:
calcd. for C156H134N4O24 [M
+
H]+ 2449.8; found 2449.6.
C156H134N4O24·0.5CHCl3 (2508.4): calcd. C 74.93, H 5.40, N 2.23;
found C 74.59, H 5.07, N 2.15.
Preparation of 5: A solution of compound 4 (3.0 g, 9.42 mmol) in
pyridine (6 mL) was cooled to –10 °C, and a solution of p-tolu-
enesulfonyl chloride (4.0 g, 20.72 mmol) in pyridine (6 mL) was
added dropwise whilst stirring. The mixture was then stirred at
Supporting Information (see footnote on the first page of this arti-
cle): Experimental and simulated isotopic patterns for the molecu-
lar ion of optically active metal-free porphyrin 1. 1H NMR spectro-
scopic data for the optically active metal-free porphyrin 1 recorded
–10 °C for 2 h and at 0 °C for 12 h. The reaction mixture was in CDCl3. Electronic absorption spectra and CD spectra of a dilute
poured onto ice, acidified with aqueous hydrogen chloride, and ex-
tracted with dichloromethane (3ϫ100 mL). The combined organic
layers were washed with water, dried with anhydrous sodium sul-
solution of 1 in chloroform and its nanoparticle aggregates formed
in the absence of potassium ions dispersed in methanol. Electronic
absorption data for a dilute solution of 1 in chloroform. IR spectra
4006
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Eur. J. Inorg. Chem. 2010, 4000–4008

Optically Active Metal-Free Porphyrin
X. Li, J. Jiang, Chem. Eur. J. 2009, 15, 13241–13252; c) G. Lu,
Y. Chen, Y. Zhang, M. Bao, Y. Bian, X. Li, J. Jiang, J. Am.
Chem. Soc. 2008, 130, 11623–11630; d) G. Lu, X. Zhang, X.
Cai, J. Jiang, Eur. J. Inorg. Chem. 2010, 753–757.
a) H. Ogoshi, T. Mizutani, Acc. Chem. Res. 1998, 31, 81–89;
b) X. Huang, K. Nakanishi, N. Berova, Chirality 2000, 12,
237–255.
a) X. Huang, B. H. Richman, B. Borhan, N. Berova, K. Nak-
anishi, J. Am. Chem. Soc. 1998, 120, 6185–6186; b) G. Proni,
G. Pescitelli, X. Huang, K. Nakanishi, N. Berova, J. Am.
Chem. Soc. 2003, 125, 12914–12927; c) T. Kurtán, N. Nesnas,
Y. Li, X. Huang, K. Nakanishi, N. Berova, J. Am. Chem. Soc.
2001, 123, 5962–5973; d) T. Kurtán, N. Nesnas, F. E. Koehn,
Y. Li, K. Nakanishi, N. Berova, J. Am. Chem. Soc. 2001, 123,
5974–5982.
a) D. Mansuy, Coord. Chem. Rev. 1993, 125, 129–142; b) J. P.
Collman, X. Zhang, V. J. Lee, E. S. Uffelman, J. I. Brauman,
Science 1993, 261, 1404–1411; c) Z. Gross, S. Ini, J. Org. Chem.
1997, 62, 5514–5521.
E. Bellacchio, R. Lauceri, S. Gurrieri, L. M. Scolaro, A. Ro-
meo, R. Purrello, J. Am. Chem. Soc. 1998, 120, 12353–12354.
a) S.-i. Kawano, S.-i. Tamaru, N. Fujita, S. Shinkai, Chem. Eur.
J. 2004, 10, 343–351; b) T. Sugimoto, T. Suzuki, S. Shinkai, K.
Sada, J. Am. Chem. Soc. 2007, 129, 270–271; c) M. Wolffs,
F. J. M. Hoeben, E. H. A. Beckers, A. P. H. J. Schenning, E. W.
Meijer, J. Am. Chem. Soc. 2005, 127, 13484–13485.
a) X. M. Guo, C. Jiang, T. S. Shi, Inorg. Chem. 2007, 46, 4766–
4768; b) J.-H. Fuhrhop, C. Demoulin, C. Boettcher, J. Köning,
U. Siggels, J. Am. Chem. Soc. 1992, 114, 4159–4169; c) S. Ari-
mori, M. Takeuchi, S. Shinkai, J. Am. Chem. Soc. 1996, 118,
245–246; d) T. Ishi-I, J. H. Jung, S. Shinkai, J. Mater. Chem.
2000, 10, 2238–2240.
a) S. Tamaru, M. Takeuchi, M. Sano, S. Shinkai, Angew. Chem.
Int. Ed. 2002, 41, 853–856; b) S.-i. Tamaru, M. Nakamura, M.
Takeuchi, S. Shinkai, Org. Lett. 2001, 3, 3631–3634.
a) X. Zhang, A. Muranaka, W. Lv, Y. Zhang, Y. Bian, J. Jiang,
N. Kobayashi, Chem. Eur. J. 2008, 14, 4667–4674; b) H. Liu,
C. Chen, M. Ai, A. Gong, J. Jiang, F. Xi, Tetrahedron: Asym-
metry 2000, 11, 4915–4922; c) H. Liu, Y. Liu, M. Liu, C. Chen,
F. Xi, Tetrahedron Lett. 2001, 42, 7083–7086.
of optically active metal-free porphyrin itself, nanoparticles formed
from optically active metal-free porphyrin in the absence of potas-
sium ions, and nanofibers formed from optically active metal-free
porphyrin in the presence of potassium ions in the region of 400–
1800 cm–1 with 2 cm–1 resolution. Schematic illustration for the
hierarchical formation of nanofibers with left-handed helicity
through one-dimensional right-handed helix with negative chirality
determined by the peripheral chiral side chains of porphyrin ring
in the molecule of (S)-1 enantiomer.
[12]
[13]
Acknowledgments
Financial support from the Natural Science Foundation of China
(grant nos. 20931001 and 20801031), the Ministry of Education of
China, the Independent Innovation Foundation of USTB and
SDU, and the Beijing Municipal Commission of Education is
gratefully acknowledged.
[14]
[15]
[16]
[1] a) R. A. Garoff, E. A. Litzinger, R. E. Connor, I. Fishman,
B. A. Armitage, Langmuir 2002, 18, 6330–6337; b) M. Wang,
G. L. Silva, B. A. Armitage, J. Am. Chem. Soc. 2000, 122,
9977–9986; c) R. F. Pasternack, A. Giannetto, P. Pagano, E. J.
Gibbs, J. Am. Chem. Soc. 1991, 113, 7799–7800; d) K. C. Han-
nah, B. A. Armitage, Acc. Chem. Res. 2004, 37, 845–853; e) X.
Chen, M. Liu, J. Inorg. Biochem. 2003, 94, 106–113.
[2] a) J. H. Fuhrhop, W. Helfrich, Chem. Rev. 1993, 93, 1565–1582;
b) S. I. Tamaru, M. Nakamura, M. Takeuchi, S. Shinkai, Org.
Lett. 2001, 3, 3631–3634; c) S. Tamaru, S. Uchino, M. Takey-
chi, M. Ikeda, T. Hatano, S. Shinkai, Tetrahedron Lett. 2002,
43, 3751–3755.
[3] a) C. Nuckolls, T. J. Katz, T. Verbiest, S. V. Elshocht, H. G.
Kuball, S. Kiesewalter, A. J. Lovinger, A. Persoons, J. Am.
Chem. Soc. 1998, 120, 8656–8660; b) J. M. Fox, T. J. Katz, S. V.
Elshocht, T. Verbiest, M. Kauranen, A. Persoons, T. Thong-
panchang, T. Krauss, L. Brus, J. Am. Chem. Soc. 1999, 121,
3453–3459.
[4] a) Z. Wu, G. Yang, Q. Chen, J. Liu, S. Yang, J. S. Ma, Inorg.
Chem. Commun. 2004, 7, 249–252; b) S. Shinoda, T. Okazaki,
T. N. Player, H. Misaki, K. Hori, H. Tsukube, J. Org. Chem.
2005, 70, 1835–1843; c) T. Kawamoto, B. S. Hammes, B. Hag-
gerty, G. P. A. Yap, A. L. Rheingold, A. S. Borovik, J. Am.
Chem. Soc. 1996, 118, 285–286.
[5] a) H. Engelkamp, S. Middlebeek, R. J. M. Nolte, Science 1999,
284, 785–788; b) D. Adam, P. Schumacher, J. Simmerer, L.
Häusling, K. Siemensmeyer, K. H. Etzbach, H. Ringsdorf, D.
Harrer, Nature 1994, 371, 141–143; c) J. Wu, M. D. Watson, L.
Zhang, Z. Wang, K. Müllen, J. Am. Chem. Soc. 2004, 126,
177–186; d) V. Dehm, Z. Chen, U. Baumeister, P. Prins,
L. D. A. Siebbeles, F. Würthner, Org. Lett. 2007, 9, 1085–1088.
[6] a) H. Goto, H. Q. Zhang, E. Yashima, J. Am. Chem. Soc. 2003,
125, 2516–2523; b) K. Morino, M. Oobo, E. Yashima, Macro-
molecules 2005, 38, 3461–3468; c) R. Nonokawa, E. Yashima,
J. Am. Chem. Soc. 2003, 125, 1278–1283.
[17]
[18]
[19]
[20]
a) N. Kobayashi, Y. Kobayashi, T. Osa, J. Am. Chem. Soc.
1993, 115, 10994–10995; b) N. Kobayashi, Chem. Commun.
1998, 4, 487–488.
L. D. Bari, G. Pescitelli, G. Reginato, P. Salvadori, Chirality
2001, 13, 548–555.
M. Kasha, H. R. Rawls, M. A. EI-Bayoumi, Pure Appl. Chem.
1965, 11, 371–392.
[21]
[22]
[23]
a) N. Berova, K. Nakanishi, R. Woody, Circular Dichroism:
Princples and Applictions, 2nd ed., Wily-VCH, New York, 2000,
pp. 337–382; b) A. L. Hofacker, J. R. Parquette, Angew. Chem.
Int. Ed. 2005, 44, 1053–1057; c) M. Balaz, A. E. Holmes, M.
Benedetti, P. C. Rodriguez, N. Berova, K. Nakanishi, G. Proni,
J. Am. Chem. Soc. 2005, 127, 4172–4173; d) V. V. Borovkov,
J. M. Lintuluoto, M. Fujiki, Y. Inoue, J. Am. Chem. Soc. 2000,
122, 4403–4407.
M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria,
M. A. Robb, J. R. Cheeseman, J. A. Montgomery Jr., T.
Vreven, K. N. Kudin, J. C. Burant, J. M. Millam, S. S. Iyengar,
J. Tomasi, V. Barone, B. Mennucci, M. Cossi, G. Scalmani, N.
Rega, G. A. Petersson, H. Nakatsuji, M. Hada, M. Ehara, K.
Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y.
Honda, O. Kitao, H. Nakai, M. Klene, X. Li, J. E. Knox, H. P.
Hratchian, J. B. Cross, C. Adamo, J. Jaramillo, R. Gomperts,
R. E. Stratmann, O. Yazyev, A. J. Austin, R. Cammi, C. Pom-
elli, J. W. Ochterski, P. Y. Ayala, K. Morokuma, G. A. Voth, P.
Salvador, J. J. Dannenberg, V. G. Zakrzewski, S. Dapprich,
A. D. Daniels, M. C. Strain, O. Farkas, D. K. Malick, A. D.
Rabuck, K. Raghavachari, J. B. Foresman, J. V. Ortiz, Q. Cui,
A. G. Baboul, S. Clifford, J. Cioslowski, B. B. Stefanov, G. Liu,
A. Liashenko, P. Piskorz, I. Komaromi, R. L. Martin, D. J.
[24]
[7] K. Kadish, K. M. Smith, R. Guilard (Eds.), The Porphyrin
Handbook, Academic Press, New York, 1999.
[8] a) M. Kimura, H. Narikawa, K. Ohta, K. Hanabusa, Chem.
Mater. 2002, 14, 2711–2717; b) X. Huang, F. Zhao, Z. Li, Y.
Tang, F. Zhang, C. Tung, Langmuir 2007, 23, 5167–5172; c) A.
de la Escosura, M. V. M. Díaz, P. Thoedarson, A. E. Rowan,
R. J. M. Nolte, T. Torres, J. Am. Chem. Soc. 2003, 125, 12300–
12308; d) P. Chen, X. Ma, M. Liu, Macromolecules 2007, 40,
4780–4784.
[9] Y. Li, X. Li, Y. Li, H. Liu, S. Wang, H. Gan, J. Li, N. Wang,
X. He, D. Zhu, Angew. Chem. Int. Ed. 2006, 45, 3639–3643.
[10] T. Yokoyama, S. Yokoyama, T. Kamikado, Y. Yoshi-
shige Okuno, T. Mashiko, Nature 2001, 413, 619–621.
[11] a) Y. Gao, X. Zhang, C. Ma, X. Li, J. Jiang, J. Am. Chem. Soc.
2008, 130, 17044–17052; b) Y. Gao, Y. Chen, R. Li, Y. Bian,
Eur. J. Inorg. Chem. 2010, 4000–4008
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
4007

J. Lu, L. Wu, J. Jiang, X. Zhang
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Fox, T. Keith, M. A. Al-Laham, C. Y. Peng, A. Nanayakkara,
M. Challacombe, P. M. W. Gill, B. Johnson, W. Chen, M. W.
Wong, C. Gonzalez, J. A. Pople, Gaussian 03, Revision B.05,
Gaussian, Inc., Pittsburgh, PA, 2003.
7398; b) W. Su, Y. Zhang, C. Zhao, X. Li, J. Jiang, ChemPhys-
Chem 2007, 8, 1857–1862; c) Y. Li, X. Li, Y. Li, H. Liu, S.
Wang, H. Gan, J. Li, N. Wang, X. He, D. Zhu, Angew. Chem.
Int. Ed. 2006, 45, 3639–3643; d) X. Gong, T. Milic, C. Xu, J. D.
Batteas, C. M. Drain, J. Am. Chem. Soc. 2002, 124, 14290–
14291.
[25] F. D’Souza, R. Chitta, S. Gadde, M. E. Zandler, A. L.
McCarty, A. S. D. Sandanayaka, Y. Araki, O. Ito, J. Phys.
Chem. A 2006, 110, 4338–4347.
[26] a) K. Balakrishnan, A. Datar, T. Naddo, J. Huang, R. Oitker,
M. Yen, J. Zhao, L. Zang, J. Am. Chem. Soc. 2006, 128, 7390–
Received: March 31, 2010
Published Online: July 13, 2010
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Eur. J. Inorg. Chem. 2010, 4000–4008