C O M M U N I C A T I O N S
tions, empty tube 224+ possesses considerable kinetic stability.5c,10
The empty tube is, of course, capable of binding other molecules
in the cavity. Guests 3 and 4 reentered the tube within 1 h at room
temperature when they were suspended in the solution of 224+ 11
. A
small rodlike guest, sodium biphenylcarboxylate (Na•5), was also
22+
included, giving 2•(5)2
complex (Figure 3c). The two guest
1
molecules were equivalently observed by H NMR spectroscopy,
indicating symmetrical inclusion, in which COO- groups are
exposed outside at both ends of the tube. Particularly interesting is
that the 2•(5)222+ complex can be efficiently formed only via 2•424+
complex. This fact clearly demonstrates the “chaperoning effect”
22+
of 4 in the self-assembly of kinetically stabilized 224+ and 2•(5)2
complexes.12
Acknowledgment. We thank S. Adachi (KEK) for supporting
X-ray measurement. This work has been approved by the Photon
Factory Program Advisory Committee (Proposal No. 2003G186).
Note Added after ASAP Posting. After this paper was posted
ASAP on August 17, 2004, an error in the compound numbers in
the first sentence of the third paragraph was corrected. The corrected
version was posted August 18, 2004.
Supporting Information Available: Preparation and physical
properties of 1, 3, 5, 224+, 2•324+, 2•424+, and 2•(5)222+. This material
Figure 2. Crystal structure of 2•324+. For clarity, H atoms, solvent
molecules, and anions are omitted.
References
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(9) X-ray crystallographic measurement was performed on PF-AR NW2
beamline at High Energy Accelerator Research Organization (KEK), Japan.
Crystal data for 2•324+: orthorhombic, space group Fdd2, λ(synchrotron)
) 0.68900 Å, T ) 88(2) K, a ) 49.2540(12) Å, b ) 122.86(4) Å, c )
27.6620(5) Å, V ) 167395(55) Å3, Z ) 16, dcalcd ) 1.138 Mg/m3. The
detailed crystallographic information was described in a CIF file deposited
in CCDC 238715.
Figure 3. 1H NMR observation of guest removal/reinclusion in tube 224+
(500 MHz, D2O-CD3CN). (a) 2•424+ complex. (b) Empty 224+ after
extraction of template 4 with CDCl3. (c) 2•(5)222+ obtained by reinclusion
of Na•5 into the empty tube. Circles indicate guest signals.
by six Pd(II) ions via π-π stacking and CH-π contact. The
diethylene glycol linker is essential because the tube did not
assemble efficiently when anthracene or anthracenecarboxylate was
employed as a template. Probably, Pd(II)-linked frameworks at both
ends of 224+ are simultaneously assembled by dual templating at
the two anthracene moieties of 3.
In the presence of another linear molecule 4 (in Figure 3), the
high-yield formation of 2•424+ was also observed (Figure 3a). Guest
4 seems, however, less effectively bound than 3 because 4 was
easily replaced by 3 in 1 h at room temperature when 3 (1.0 equiv)
was added to the solution of 2•424+. This result is remarkable
because the guest exchange requires the movement of 3 and 4 by
more than 3 nm within the tubular cavity of 224+. The guest
exchange probably takes place by an SN2-like mechanism, as
previously discussed.5b
Template molecule 4 could be removed by extracting it with
CHCl3 (Figure 3b). After removal of the guest, the framework
remained unchanged at room temperature, in sharp contrast to the
behavior of previously reported shorter tubes that immediately
collapsed when the template was removed.5a This fact indicates
that, being cooperatively sustained by 24 Pd(II)-pyridine interac-
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