One-, two- and three-periodic metal-organic rotaxane frameworks (MORFs): Linking cationic transition-metal nodes with an anionic rotaxane ligand

Article abstract of DOI:10.1002/chem.201002542

A new singly charged pyridinium axle was prepared and combined with disulfonated dibenzo[24]crown-8 ether to form a [2]pseudorotaxane. The reaction of this new, anionic ligand with Zn^II ions, under various crystallization conditions, resulted i

Full text of DOI:10.1002/chem.201002542

DOI: 10.1002/chem.201002542
One-, Two- and Three-Periodic Metal–Organic Rotaxane Frameworks
(MORFs): Linking Cationic Transition-Metal Nodes with an Anionic
Rotaxane Ligand
V. Nicholas Vukotic and Stephen J. Loeb*[a]
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Chem. Eur. J. 2010, 16, 13630 – 13637

FULL PAPER
Abstract: A new singly charged pyridi-
nium axle was prepared and combined
with disulfonated dibenzo[24]crown-8
ether to form a [2]pseudorotaxane. The
reaction of this new, anionic ligand
with ZnII ions, under various crystalli-
zation conditions, resulted in the for-
mation of three metal–organic rotax-
ane framework (MORF) solids; a one-
periodic ML coordination polymer and
two, two-periodic ML2 square grid
frameworks. The layers of square grids
can be pillared to create full three-peri-
oidic MORF structures, which have
completely neutral frameworks and are
porous. These three-perioidic materials
represent the first examples of neutral
porous MOFs in which one (or more)
of the linkers is a mechanically inter-
locked molecule (MIM).
Keywords: metal–organic
frame-
works · rotaxanes · supramolecular
chemistry · zinc
Introduction
of counterions in the lattice, which not only hindered any
potential dynamic behavior of the wheel component, but
also limited the stability of the frameworks. More recently,
we have shown that by using an anionic wheel, the anti-
isomer of disulfonated dibenzo[24]crown-8, DSDB24C82ꢁ,
in conjunction with the dicationic axle 12+, a neutral
[2]pseudorotaxane can be generated.[10] The zwitterionic
linker [1ꢀDSDB24C8] was combined with neutral metal
nodes, such as the classic Cu2OBn4 paddlewheel, to form
neutral one-periodic MORFs that were free of independent
counterions.[11] However, due to the limited number of neu-
tral metal nodes available, creating permanent porosity by
increasing the periodicity of this system proved to be diffi-
cult.
The great majority of MOFs, such as those pioneered by
Yaghi and co-workers, rely on organic anions to link posi-
tively charged metals or clusters,[4] so another way to create
a neutral MORF would be to design an anionic [2]pseudoro-
taxane ligand. Since, we have previously shown that
DSDB24C82ꢁ has a high affinity for axle 12+ in MeOH[10]
(Ka >105 mꢁ1 at 298 K), it was reasoned that it should be pos-
sible to replace one of the internal pyridinium rings of axle
12+ with a simple phenyl ring, thereby removing one of the
positive charges, but still achieving significant [2]pseudoro-
taxane formation. A similar, singly charged pyridinium
based axle has previously been reported by Quintela to
The development of new materials that have technologically
important physical properties, such as nonlinear optics or
ferroelectrics, is of great interest.[1] A new and relatively un-
explored avenue for creating these materials is to incorpo-
rate mechanically interlocked molecules (MIMs),[2] such as
catenanes or rotaxanes into metal–organic frameworks
(MOFs).[3] MOFs are a well-established class of porous ma-
terial consisting of inorganic metal nodes and organic bridg-
ing ligands arranged in one-, two-, or three-periodic net-
works.[4] The incorporation of MIMs into MOFs would
allow for a unique way to manipulate the properties of ma-
terials by having control over motion at a molecular level;
reminiscent of “crystalline molecular motors” first demon-
strated by Garcia-Garibay.[5] Since a component of the lat-
tice, the wheel, would be quite flexible, this new type of
framework material could be thought of as a class of “soft
porous crystal” as defined by Kitigawa.[6] Alternately, given
the dynamic nature of the wheel in a framework pore, the
concept of “robust dynamics”, as recently proposed by Stod-
dart and Yaghi might be more appropriate.[7] By any defini-
tion, these are materials that have yet to be realized, but
have significant potential and are only just beginning to be
explored.
We have previously shown that combining a 1,2-bis(4,4’bi-
pyridinium)ethane (12+) axle and a dibenzo[24]crown-8
(DB24C8) wheel yields a [2]pseudorotaxane [1ꢀDB24C8]2+
that can act as a linker between d-block or lanthanide
metals for the construction of 1-, 2-, and 3-periodic solids.[8]
We have called these materials, metal–organic rotaxane
frameworks or MORFs.[9] In order to observe molecular dy-
namics in the solid state, the wheel component must be able
to “operate” in well-defined “space”. These preliminary re-
sults, while establishing the concept of MORFs, did not
meet this requirement. A primary reason was the presence
form catenated structures with {Pd
ACHTUNGERTN(NUNG diamine)} corners and
various crown ether macrocycles.[12]
Herein, we present the preparation of [2]pseudorotaxanes
utilizing a singly charged pyridinium axle 2+ and its benzy-
lated derivative 33+ with DB24C8 and DSDB24C82ꢁ
(Scheme 1). The combination of 2+ and DSDB24C82ꢁ cre-
ates
a
negatively charged [2]pseudorotaxane ligand
[2ꢀDSDB24C8]ꢁ that can be used to create unique one-,
two- and three-periodic MORFs that are neutral and
porous; significant steps towards the goal of creating a
robust and porous MOF with truly dynamic components.
[a] V. N. Vukotic, Prof. S. J. Loeb
Department of Chemistry and Biochemistry
University of Windsor, Windsor, Ontario
Canada N9B 3P4 (Canada)
Results and Discussion
Fax : (+1)519-973-7098
E-mail: loeb@uwindsor.ca
The synthesis of 2+ was accomplished by conversion of the
alcohol 4-[4-(a-hydroxyethyl)phenyl]pyridine[13] to the corre-
sponding bromo derivative, 4-[4-(a-bromoethyl)phenyl]pyri-
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201002542.
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13631

S. J. Loeb and V. N. Vukotic
and verify that [2ꢀDSDB24C8]ꢁ should be capable of acting
as a pseudorotaxane linker between metal ions in a MORF.
At this point, it seems prudent to discuss the result of
combining an axle such as 2+, which is unsymmetrical along
its long axis (has direction), with
a wheel such as
DSDB24C82ꢁ, which has a center of symmetry but no C2
primary axis. The result is two different [2]pseudorotaxanes
that are cyclochiral enantiomers designated as C for clock-
wise and A for anticlockwise (Figure 1).
Scheme 1. The pyridinium axles (12+
, ) and crown ethers
2+, 33+
(DB24C8, DSDB24C82) used in this study to form [2]pseudorotaxanes
with varying charge.
dine, followed by alkylation with 4,4’-bipyridine and subse-
quent anion exchange to the triflate salt (Scheme 2). In
order to investigate the extent of [2]pseudorotaxane forma-
1
tion, H NMR studies were conducted using 2+ as the axle
and DB24C8 or DSDB24C82ꢁ as the wheel at 2.0ꢁ10ꢁ3 m in
CD3OD. There was an order of magnitude increase in asso-
Figure 1. Enantiomers of [2ꢀDSDB24C8]ꢁ. For enantiomer C, the sulfo-
nate group is on the left hand side of the positively charged end of the
axle. Conversely, for enantiomer A, the sulfonate group is on the right
hand side.
The initial investigation into utilizing [2ꢀDSDB24C8]ꢁ as
a linker for MORF formation involved combining equimo-
lar amounts of [2]
ACHTUGTNREN[NGU OTf], anti-[Me4N]2ACHTUNGTREN[NGUN DSDB24C8] and Zn-
AHCUTNERTGG(NNUN NO3)2·4H2O in CH3OH. The resulting solution was left to
stand for three days, after which a crop of pale yellow, X-
ray quality crystals were isolated (50% yield). A single-crys-
tal X-ray diffraction analysis showed the resulting material,
MORF-1, to be
a
one-periodic solid with formula
[Zn(2ꢀDSDB24C8)
N
E
ACHTUNGTRENNUNG
(CH3OH)]+ units of opposite chirality are joined to-
ACHUTNGREN(NUG H2O)2ACHTUNGTRENNGUN
gether in a head-to-tail fashion by coordination of a sulfo-
nate group of one unit to the ZnII center of a neighboring
unit; the closest Zn···Zn distance is 9.17 ꢂ. The crown
ethers wrap around the charged pyridinium end of the axle,
which presumably optimizes the noncovalent interactions
between axle and wheel. Linking cations of the same chirali-
Scheme 2. Reagents and conditions: i) PBr3 in THF/CH2Cl2, 24 h, 08C; ii)
20 equiv 4,4’-bipyridine, n-butanol, 48 h, reflux followed by anion ex-
change with NaOTf in MeNO2/H2O; iii) 2 equiv benzylbromide, NaOTf,
MeNO2/H2O, 80 8C, 24 h.
ciation
constant
between
[2ꢀDB24C8]2+
and
ty through Zn N coordination results in propagation of this
ꢁ
[2ꢀDSDB24C8]ꢁ from 3.5ꢁ101 to 3.0ꢁ102 mꢁ1 due to the ad-
dition of increased electrostatic attraction from the sulfonate
groups. Since coordination of [2ꢀDSDB24C8]ꢁ to a Lewis
acidic, transition-metal center should increase the interac-
tion between the axle and wheel, similar to alkylation, it
was also of interest to study these interactions with benzy-
lated axle 33+. As expected, there was a substantial increase
in association constant upon benzylation; from 8.0ꢁ101 to
2.3ꢁ103 mꢁ1 comparing DB24C8 to DSDB24C82ꢁ. These
values compare well to those observed for similar systems[14]
dimeric unit into a racemic, double-stranded, one-periodic
framework with Zn···Zn distances of 22.0 ꢂ (Figure 2b, 2c).
Although, this interesting material verified that the nega-
tively charged rotaxane [2ꢀDSDB24C8]ꢁ could be com-
bined with a positively charged metal ion (ZnII), the result-
ing one-periodic framework was not neutral as non-coordi-
nating nitrate ions were required for charge balance.
To increase the periodicity of the resulting MORF and
generate a neutral framework, the amount of axle and
wheel were doubled and a less coordinating solvent mixture
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Supramolecular Chemistry
FULL PAPER
Figure 2. a) Two cyclochiral enantiomers joined by ZnII···SO3 coordina-
tion (NO3 ions and hydrogen atoms removed for clarity). b) Schematic
showing how each strand consists of a single enantiomer. c) Space-filling
model of MORF-1 (coordinated solvent and NO3 ions omitted for clari-
ty). Key: blue=2+ axle; red=DSDB24C82ꢁ wheel; yellow=sulfur;
grey=ZnII ions; green=coordinated H2O and MeOH ligands.
ꢁ
Figure 3. a) Space-filling model of MORF-2 showing an enantiomerically
pure square grid (solvent omitted for clarity). b) Schematic diagram of
an enantiomerically pure square grid. c) Ball and stick representation of
how the square grids are layered, through hydrogen-bonding (hydrogen
atoms have been removed for clarity). Key: blue=2+ axle; red=
DSDB24C82ꢁ wheel; yellow=sulfur; grey=Zn2+; green=H2O; hydrogen
bonds=dashed black lines.
was used; two equivalents each of [2]
[Me4N]2A[DSDB24C8] were combined with one equivalent of
Zn(NO3)2·4H2O in a 1:9 CH3OH/CH3NO2 solvent mixture.
ACHTUNGTREN[NUNG OTf] and anti-
CHTUNGTRENNUNG
ACHTUNGTRENNUNG
The resulting solution was left to stand for five days, after
which a crop of pale yellow, X-ray quality crystals were iso-
lated (64% yield). A single-crystal X-ray diffraction analysis
showed the material, MORF-2, to be neutral and two-peri-
MORF-1, in which the sulfonate groups interact directly
with the ZnII centers, in MORF-2 the sulfonates are in-
volved in hydrogen-bonding to the bridging H2O molecules.
The as-synthesized samples of MORF-2 readily lose
CH3NO2 at room temperature and immersion of the crystal-
line material in CHCl3 followed by treatment under mild
vacuum at room temperature yielded a solvent-free sample.
Thermal gravimetric analysis (TGA) and variable-tempera-
ture powder X-ray diffraction (VT-PXRD) studies showed
the sample to be moderately stable with loss of bridging and
coordinated H2O molecules in the range 80–1008C, followed
by decomposition of the metal–ligand network above
2258C. The PXRD patterns recorded below 808C matched
well with that predicted from the single-crystal data and at
1008C were consistent with formation of a new layered
structure, presumably due to loss of the weak interlayer hy-
drogen-bonding, but retention of the much stronger square
odic with formula [Zn(2ꢀDSDB24C8)
2ACHTUNGRTNE(NUNG H2O)2]·H2O·
21CH3NO2.
MORF-2 contains a neutral, square grid of ZnII nodes
linked by anionic [2ꢀDSDB24C8]ꢁ rotaxanes with a Zn···Zn
distance of 22.0 ꢂ. Figures 3a and 3b show that each of
these layers is enantiomerically pure, since each ligand
adopts the same cyclochirality. These layers are stacked in
an alternating AB fashion through hydrogen bonding be-
tween bridging and axially coordinated H2O molecules to
yield a racemic solid (Figure 3c). The layer spacing is 7.82 ꢂ
between closest Zn centers. The void space of the resulting
channels was calculated to be 42% by PLATON and a final
PLATON/SQUEEZE[15] refinement of the model accounted
for 21 molecules of CH3NO2 per formula unit. Unlike
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S. J. Loeb and V. N. Vukotic
2ꢁ
grid structure. Attempts to perform standard BET measure-
ments were unsuccessful as the conditions required for full
evacuation of the pores also resulted in collapse of the pil-
laring hydrogen bonds.
During the initial preparations of MORF-2, we were able
to isolate a small amount (ꢂ10%) of another crystalline
material. Single-crystal X-ray diffraction analysis showed
this colorless material, MORF-3, to be neutral and three-pe-
SO4 ions. Pillaring with this [{ZnACHTUNGTERU(GNNN CH3OH)2AHCUTNRTEG(NGUNN H2O)2ACHTUNGTRENNUNG(SO4)}2]
cluster results in a much larger layer spacing of 11.0 ꢂ be-
tween Zn centers of the square grids. Figure 4b illustrates
another difference between MORF-2 and MORF-3; the ar-
rangement of cyclochiral linkers is such that each layer is
comprised of an identical racemic mixture with adjacent C
and A linkers in the same grid rather than the alternating,
enantiomeric layers observed for MORF-2.
riodic with formula [Zn(2ꢀDSDB24C8)2][{Zn
A
The void space of the resulting channels in MORF-3 was
calculated to be 55% by PLATON and a final PLATON/
SQUEEZE[15] refinement of the model accounted for 42
molecules of CH3NO2 per formula unit. Unlike MORF-2,
which is pillared with weak, noncovalent hydrogen bonding,
A
CHTUNGTRENNUNG
tral, square grid of ZnII nodes and [2ꢀDSDB24C8]ꢁ rotax-
anes as MORF-2 (Figure 4a), but the pillaring groups are
very different. In place of the simple coordinated and hydro-
gen-bonded H2O molecules is a much more robust fragment
2ꢁ
the direct coordination of bridging SO4 ions between the
made of two {Zn
G
N
two different types of ZnII ions leads to a truly three-period-
ic coordination polymer with increased stability between
layers.
Unfortunately, it was not possible to synthesize and iso-
late MORF-3 free from contamination with MORF-2. In
the synthesis of these materials, MORF-2 is by far the domi-
2ꢁ
nant species. It was determined that the source of the SO4
ions for creating MORF-3 was contamination of samples of
the crown ether salt [Me4N]
[SO4], as the synthesis involves treatment of DB24C8 with
excess H2SO4 and neutralization with [Me4N][OH]. Elimina-
tion of the [Me4N]2A[SO4] contaminate resulted in only
2ACHTUNGTREN[NUNG DSDB24C8] with [Me4N]2-
AHCTUNGTRENNUNG
CTHUNGTRENNUNG
MORF-2 being produced. Attempts to purposefully produce
2ꢁ
MORF-3 by the addition SO4 ions were successful, but
these samples were always mixtures of MORF-2 and
MORF-3. To date no successful method for separation and
isolation of bulk samples of pure MORF-3 has been de-
vised.
Although this problem precluded a complete analysis of
the stability and thermal properties of MORF-3, some gen-
eral observations could be made. Crystals of MORF-3 readi-
ly lose CH3NO2 at room temperature and could be washed
with CHCl3 and evacuated under mild vacuum with no evi-
dent change in structure; similar to the behavior of MORF-
2 under the same conditions. Similar to MORF-2, TGA of
mixtures of MORF-2 and MORF-3 lost coordinated sol-
vents in the range 80–1008C and decomposed above 2258C.
Although it is reasonable to speculate that, even with the
loss of coordinated solvents, the moderately strong coordi-
nation bonds of the square grid and pillar would be suffi-
cient to maintain a three-periodic structure, it was not possi-
ble to unambiguously determine whether the structure ob-
served by single-crystal X-ray analysis was retained above
1008C.
Finally, although MORF-2 and MORF-3 both contain a
neutral, square grid as designed, there are some interesting
structural differences in addition to the pillaring groups and
ligand cyclochirality. In MORF-2, the axle and wheel are p-
stacked (see Figure 3c) in a fashion similar to that observed
for almost every other X-ray structure determined for this
type of rotaxane[9c,10] and charge transfer between these
components give rise to the yellow color of the material.[14a]
In stark contrast, the axle in MORF-3 is rotated ꢂ908 and is
Figure 4. a) Space-filling model of MORF-3 showing a racemic square
grid (solvent omitted for clarity). b) Schematic diagram of a racemic
square grid. c) Ball and stick representation of how the square grids are
pillared by [Zn
moved for clarity). Key: blue=2+ axle; red=DSDB24C82ꢁ wheel;
yellow=sulfur; grey=Zn2+
ACHTUNGTRENNUNG(H2O)4ACHTUNGTRENNUNG(SO4)]2 clusters (hydrogen atoms have been re-
.
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Supramolecular Chemistry
FULL PAPER
for free and complexed axle. These concentration values were then used
to calculate an association constant with an estimated error of 10%.
better described as being involved in a CH···p interaction
with the crown ether aromatic ring. This perpendicular ori-
entation negates any charge transfer interaction and this ma-
terial is colorless. This very subtle difference in orientation
of the aromatic rings in MORF-2 and MORF-3 begs the
question; is it possible for these orientations to interconvert
in the solid state, that is, display robust dynamics. Although
an unambiguous answer to this question will have to wait
for more detailed experiments, it should be noted that
gentle heating of the colorless crystals of MORF-3 produced
a yellow material, which we believe could be the result of
reorientation of the MIM components from a perpendicular
CH–p to a p-stacked rotaxane.
Synthesis of 4-[4-(a-bromoethyl)phenyl]pyridine: 4-[4-(a-Hydroxyethyl)-
phenyl]pyridine (3.50 g, 0.0176 mol) was dissolved in a 1:1 mixture of
THF/CH2Cl2 (200 mL) under a nitrogen atmosphere and placed on ice.
Phosphorustribromide (13.4 mL of
a 1.0m solution, 0.0132 mol) was
added to the reaction vessel by syringe and the reaction left to stir for
24 h. The reaction was then quenched with H2O, and the solvent removed
via a rotary evaporator. A separation was performed with H2O/CHCl3
and the solution basified with Na2CO3 to pH 10. The organic layer was
washed with H2O (3ꢁ20 mL), dried over MgSO4, and the solvent re-
moved to yield a yellow oil; crude yield by NMR analysis was 75%. The
product was purified by flash column chromatography using Teledyne
Ultra Pure Silica/RP-C18 Silica Gel, with a solvent gradient of hexanes
with 0–70% EtOAc. The product was isolated as a white crystalline
solid. Yield, 2.51 g, 60%; m.p. 180–1828C (decomp); 1H NMR (CDCl3):
3
3
3
d=8.66 (d, J=4.4 Hz, 2H), 7.62 (d, J=8.0 Hz, 2H), 7.51 (d, J=4.4 Hz,
2H), 7.35 (d, 3J=8.0 Hz, 2H), 3.62 (t, 3J=7.4 Hz, 2H), 3.24 ppm (t, 3J=
7.4 Hz, 2H); ESI-MS: m/z calcd for [M+H]+: 262.0226; found: 262.0225.
Conclusion
Synthesis of
2ACTHUNGTERNNU[G OTf]: 4-[4-(a-Bromoethyl)phenyl]pyridine (1.00 g,
0.00379 mol) was dissolved in n-butanol (250 mL) and slowly added over
24 h through a syringe pump, to a solution of 20 equivalents of 4,4’-bipyr-
idine (11.9 g, 0.0763 mol) in n-butanol (200 mL). The solution was re-
fluxed for 48 h, cooled to room temperature and placed in the freezer for
2 h to allow for precipitation of the product. The precipitate was filtered
by vacuum filtration, dried and stirred in CHCl3 to remove any excess
4,4’-bipyridine. (the product is approx. 95% pure at this point with a 5%
impurity from the reaction of 4-[4-(a-bromoethyl)phenyl]pyridine with
itself. The crude product was further purified by column chromatography
on silica gel using a 7:1:2 mixture of MeOH/2m NH4Cl(aq)/MeNO2. The
product was isolated as an off-white solid (yield: 1.00 g, 63%). The prod-
uct was anion exchanged from the bromide salt to the OTfꢁ salt by way
In conclusion, we have prepared and characterized the first
examples of neutral porous MOF materials containing a
component that is only linked to the MOF framework by
virtue of a mechanical bond (a MIM). In addition, we have
shown that although the two-periodic nature of the square
grid reported herein limits the stability of the MORF, this
strategy has the potential to make the realization of robust,
three-periodic MOFs containing dynamic MIM components
a reality. Work towards this goal is ongoing.
of
a two-layer NaOTf (aq)/MeNO2 extraction. Yield, 0.902 g, 90%;
1
3
m.p.>2008C (decomp); H NMR (CD3OD): d=8.99 (d, 2H, J=6.5 Hz),
8.79 (d, 3J=5.4 Hz, 2H), 8.68 (d, 3J=5.4 Hz, 2H), 8.46 (d, 3J=6.5 Hz,
2H), 8.00 (d, 3J=5.4 Hz, 2H), 7.95 (d, 3J=5.4 Hz, 2H), 7.83 (d, 3J=
8.0 Hz, 2H), 7.45 (d, 3J=8.0 Hz, 2H), 4.99 (t, 3J=7.1 Hz, 2H), 3.48 ppm
(t, 3J=7.1 Hz, 2H); ESI-MS: m/z calcd for [2]+: 338.1652; found:
338.1658.
Experimental Section
General comments: 4-Pyridineboronic acid, 4-bromophenethyl alcohol,
tetrakis(triphenylphosphine)palladium(0), phosphorus tribromide, 4,4’-bi-
pyridine, sodium trifluoromethanesulfonate, benzylbromide and DB24C8
were purchased from Aldrich and used as received. Deuterated solvents
were obtained from Cambridge Isotope Laboratories and used as re-
ceived. Solvents were dried using an Innovative Technologies Solvent Pu-
rification System. Thin-layer chromatography (TLC) was performed
using Teledyne Silica gel 60 F254 plates and viewed under UV light.
Column chromatography was performed using Silicycle Ultra Pure Silica
Gel (230–400 mesh). Flash column chromatography was performed using
Teledyne Ultra Pure Silica/RP-C18 Silica Gel (230–400 mesh) on a Tele-
dyne Isco Combiflash Rf. 1H NMR 1D and 2D experiments were per-
formed on a Brꢃker Avance 500 instrument, with working frequency of
500.13 MHz. Chemical shifts are quoted in ppm relative to tetramethylsi-
lane, using the residual solvent peak as a reference standard. 2D NMR
Synthesis of 3ACHTNUTRGENNG[U OTf]3: Compound 2HCATUNGTRENN[UGN OTf] (100 mg, 0.205 mmol), benzyl-
bromide (140 mg, 0.821 mmol), and NaOTf (140 mg 0.820 mmol) were
dissolved in a 1:1 mixture of MeNO2/H2O (50 mL) and heated at 808C
for 24 h. Solvent was removed by a rotary evaporator and a two-layer ex-
traction was performed using MeNO2 and H2O. The MeNO2 layer was
isolated, and the solvent removed. The resulting material was then stirred
in EtOAc overnight to precipitate the product and remove excess benzyl-
bromide. The product was isolated as an off-white solid. Yield: 80 mg,
40%; m.p.>2008C (decomp); 1H NMR (CD3OD): d=9.29 (d, 3J=
6.4 Hz, 2H), 9.16 (d, 3J=6.2 Hz, 2H), 8.99 (d, 3J=6.4 Hz, 2H), 8.62 (d,
3J=6.4 Hz, 2H), 8.60 (d, 3J=6.2 Hz, 2H), 8.39 (d, 3J=6.4 Hz, 2H), 7.97
3
3
(d, J=8.1 Hz, 2H), 7.56 (d, J=8.1 Hz, 2H), 7.56–7.47 (m, 10H), 5.94 (s,
2H), 5.80 (s,2H), 5.03 (t, 3J=7.0 Hz, 2H), 3.51 ppm (t, 3J=7.0 H, 2Hz).
1
analysis (1H-1H COSY) were used to assign all H NMR peaks. High-res-
ESI-MS: m/z calcd for [3ACHTNUTGRNEUNG
(OTf)2]+: 818.1793; found: 818.1805.
olution mass spectrometry (HR-MS) experiments were performed on a
Micromass LCT electrospray ionization (ESI) time-of-flight (ToF) mass
spectrometer. Solutions with concentrations of 1.0ꢁ10ꢁ3 m were prepared
in methanol, and injected for analysis at a rate of 5 mLminꢁ1 by using a
syringe pump. 4-[4-(a-Hydroxyethyl)phenyl]pyridine was prepared by the
literature method;[13] m.p. 1058C, no m.p. data were cited in the litera-
ture. The 1H NMR spectral data were consistent with the formulation
and subsequent conversion to the bromo species (below) verified the suc-
cessful preparation of this compound.
X-ray diffraction analysis: Single crystals were frozen in paratone oil
inside a cryoloop. Reflection data were integrated from frame data ob-
tained from hemisphere scans on a Bruker APEX diffractometer with a
CCD detector. Decay was monitored by 50 standard data frames mea-
sured at the beginning and end of each data collection. Diffraction data
and unit-cell parameters were consistent with assigned space groups. Lor-
entzian polarization corrections and empirical absorption corrections,
based on redundant data at varying effective azimuthal angles, were ap-
plied to the data sets. The structures were solved by direct methods, com-
pleted by subsequent Fourier syntheses and refined using full-matrix
least-squares methods against jF2 j data. All non-hydrogen atoms were
refined anisotropically. Hydrogen atoms were treated as idealized contri-
butions. Scattering factors and anomalous dispersion coefficients are con-
tained in the SHELXTL 5.03 program library (Sheldrick, G. M., Madi-
son). The SHELXTL library[16] of programs was used for X-ray solutions
[2]Pseudorotaxane formation and measurement of association constants:
A
1H NMR spectrum of an equimolar solution (2.0ꢁ10ꢁ3 m) of pyridini-
um axle (as the triflate salt) and disulfonated dibenzo[24]crown-8 ether
(as the Me4N+ salt) was recorded in CD3OD at 298 K for each axle.
Since these equilibria were slow on the NMR timescale, the concentra-
tions of all species at equilibrium were determined using the initial crown
and axle concentrations and integration of the aromatic NCH resonance
Chem. Eur. J. 2010, 16, 13630 – 13637
ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
13635

S. J. Loeb and V. N. Vukotic
and figures were drawn with DIAMOND software.[17] CCDC-786890
(MORF-1), 7868921 (MORF-2) and 786892 (MORF-3) contain the sup-
plementary crystallographic data for this paper. These data can be ob-
tained free of charge from The Cambridge Crystallographic Data Centre
via www.ccdc.cam.ac.uk/data_request/cif.
V.N.V. would like to thank NSERC for support of his graduate work in
the form of a PGS-M scholarship.
Synthesis of MORF-1: Compound 2
ACHTUNGTRENNUNG
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7, 4391.
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Yaghi, Science 2009, 325, 855.
[Me4N]2A[DSDB24C8] (15.8 mg, 0.0205 mmol), and ZnCAHTUNGTRENNUNG
G
(5.4 mg, 0.0205 mmol) were dissolved in CH3OH (3 mL). The resulting
solution was partially covered and left to stand for three days after which
a
crop of pale yellow, X-ray quality crystals with formula
[Zn(2ꢀDSDB24C8)(H2O)2A(CH3OH)][NO3]·2CH3OH were isolated
A
U
ACHTUNGTRENNUNG
(12.5 mg, 50% yield). X-ray data: C50H65N4O22S2Zn, Mr =1203.55, pale
¯
yellow prisms (0.32ꢁ0.26ꢁ0.14 mm), triclinic, P1, a=11.353(2), b=
15.891(2), c=17.369(3) ꢂ, a=111.098(2), b=97.685(2), g=104.313(2)8,
V=2745.5(7) ꢂ3, Z=2, 1calcd =1.456 gcmꢁ3
,
m=0.607 mmꢁ1
,
min/max
transmission=0.8931, MoKa l=0.71073 ꢂ, T=173.0(2) K, 26089 total re-
flections (RACHTUNGTRENNUNG(int)=0.1180), R1=0.0987, wR2=0.2281 [I>2s(I)], R1=
0.1784, wR2=0.2842 [all data], GoF(F2)=1.009, data/variables/re-
straints=9623/713/16.
Synthesis of MORF-2: Compound 2
ACHTUNGTRENNUNG
[Me4N]2A[DSDB24C8] (31.6 mg, 0.0410 mmol), and ZnCAHTUNGTRENNUNG
G
(5.4 mg, 0.0205 mmol) were dissolved in a 1:9 CH3OH/CH3NO2 solvent
mixture (3 mL). The resulting solution was left partially covered to stand
for five days after which a crop of pale yellow, X-ray quality crystals with
formula [Zn(2ꢀDSDB24C8)
(43.6 mg, 64% yield). X-ray data:
yellow prisms (0.34ꢁ0.30ꢁ0.22 mm), monoclinic, C2/c, a=28.756(3), b=
33.394(4), c=15.572(2) ꢂ, b=98.303(2)8, V=14796(3) ꢂ3, Z=4, 1calcd
1.485 gcmꢁ3, m=0.334 mmꢁ1, min/max transmission=0.7459, MoKa l=
0.71073 ꢂ, T=173.0(2) K, 67226 total reflections (R(int)=0.0833). The
unit cell included a large region of disordered CH3NO2 solvent molecules
in addition to the single hydrogen-bonded water molecule which connects
the layers. The water was located and refined, but the CH3NO2 molecules
were severely disordered and could not be modeled. We therefore em-
ployed the program SQUEEZE[15] to calculate the diffraction contribu-
tion of the solvent molecules and produce a data set with solvent-free dif-
fraction intensities. With no solvent contribution, before SQUEEZE:
R1=0.2066, wR2=0.5118 [I>2s(I)], R1=0.2564, wR2=0.5427 (all
data), GoF(F2)=1.633, data/variables/restraints=13022/654/145. After
SQUEEZE; R1=0.0736, wR2=0.1850 [I>2s(I)], R1=0.1133, wR2=
0.2044 (all data), GoF(F2)=0.985, data/variables/restraints=13029/654/
104.
(H2O)2]·H2O·21CH3NO2 were isolated
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C
115H169N27O74S4Zn, Mr =3307.38,
=
AHCTUNGTRENNUNG
Synthesis of MORF-3: During the crystallization of MORF-2, as de-
2ꢁ
scribed above but with SO4 impurities (see text for explanation), a
small crop of colorless crystals with formula [Zn(2ꢀDSDB24C8)2][{Zn-
A
N
G
X-ray data: C140H250N48O128S6Zn3, Mr =5042.35, colorless prisms (0.38ꢁ
0.14ꢁ0.12 mm), orthorhombic, Cmc21, a=35.882(6), b=24.607(4), c=
21.956(4) ꢂ, V=19386(5) ꢂ3, Z=4, 1calcd =1.728 gcmꢁ3, m=0.570 mmꢁ1
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min/max transmission=0.5789, MoKa l=0.71073 ꢂ, T=173.0(2) K,
61667 total reflections (R(int)=0.1675). The unit cell included a very
AHCTUNGTRENNUNG
large region of severely disordered CH3NO2 molecules which could not
be modeled. We therefore employed the program SQUEEZE[15] to calcu-
late the diffraction contribution of the solvent molecules and produce a
data set with solvent-free diffraction intensities. With no solvent contri-
bution, before SQUEEZE: R1=0.2030, wR2=0.4679 [I>2s(I)], R1=
0.2957, wR2=0.5078 (all data), GoF(F2)=2.593, data/variables/re-
straints=10313/258/17. After SQUEEZE; R1=0.0853, wR2=0.2037 [I>
2s(I)], R1=0.1376, wR2=0.2304 (all data), GoF(F2)=0.962, data/varia-
bles/restraints=10311/694/506.
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Acknowledgements
This research work was supported by a Discovery Grant to S.J.L. from
the Natural Sciences and Engineering Research Council of Canada.
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13636
www.chemeurj.org
ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2010, 16, 13630 – 13637

Supramolecular Chemistry
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Received: September 2, 2010
Published online: November 23, 2010
Chem. Eur. J. 2010, 16, 13630 – 13637
ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
13637