Assembled Columnar Structures from Bis‐Urea Macrocycles

Shimizu, Linda S.; Hughes, Alun D.; Smith, Mark D.; Samuel, Stevan A.; Ciurtin‐Smith, Delia

doi:10.1002/chin.200545279

Cited by 2 publications

(4 citation statements)

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“…Conditions: ( a ) slow cool from AcOH; ( b ) slow evaporation of a 10:1 CH 2 Cl 2 /MeOH. (b) Strained para -xylene derivative 4 shows an altered assembly motif with intervening water molecules when crystallized in slow cooling DMSO . (c) The bowl shape of 5 hinders the urea assembly motif.…”

Section: Designmentioning

confidence: 99%

“…The para-xylene spacer appears to induce strain within its corresponding macrocycle 4, 38 which reduces the macrocyclization efficiency and affects the subsequent assembled structure (Figure 5b). In this structure, one of the urea NH groups is twisted out of the plane to form a hydrogen bonding interaction with intervening water molecules.…”

Section: Columnar Assembly By Crystallizationmentioning

confidence: 99%

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Functional Materials from Self-Assembled Bis-urea Macrocycles

2014

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CONSPECTUS: This Account highlights the work from our laboratories on bis-urea macrocycles constructed from two C-shaped spacers and two urea groups. These simple molecular units assembled with high fidelity into columnar structures guided by the three-centered urea hydrogen bonding motif and aryl stacking interactions. Individual columns are aligned and closely packed together to afford functional and homogeneous microporous crystals. This approach allows for precise and rational control over the dimensions of the columnar structure simply by changing the small molecular unit. When the macrocyclic unit lacks a cavity, columnar assembly gives strong pillars. Strong pillars with external functional groups such as basic lone pairs can expand like clays to accept guests between the pillars. Macrocycles that contain sizable interior cavities assemble into porous molecular crystals with aligned, well-defined columnar pores that are accessible to gases and guests. Herein, we examine the optimal design of the macrocyclic unit that leads to columnar assembly in high fidelity and probe the feasibility of incorporating a second functional group within the macrocycles. The porous molecular crystals prepared through the self-assembly of bis-urea macrocycles display surface areas similar to zeolites but lower than MOFs. Their simple one-dimensional channels are well-suited for studying binding, investigating transport, diffusion and exchange, and monitoring the effects of encapsulation on reaction mechanism and product distribution. Guests that complement the size, shape, and polarity of the channels can be absorbed into these porous crystals with repeatable stoichiometry to form solid host-guest complexes. Heating or extraction with an organic solvent enables desorption or removal of the guest and subsequent recovery of the solid host. Further, these porous crystals can be used as containers for the selective [2 + 2] cycloadditions of small enones such as 2-cyclohexenone or 3-methyl-cyclopentenone, while larger hosts bind and facilitate the photodimerization of coumarin. When the host framework incorporates benzophenone, a triplet sensitizer, UV-irradiation in the presence of oxygen efficiently generates singlet oxygen. Complexes of this host were employed to influence the selectivity of photooxidations of 2-methyl-2-butene and cumene with singlet oxygen. Small systematic changes in the channel and bound reactants should enable systematic evaluation of the effects of channel dimensions, guest dimensions, and channel-guest interactions on the processes of absorption, diffusion, and reaction of guests within these nanochannels. Such studies could help in the development of new materials for separations, gas storage, and catalysis.

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Section: Designmentioning

confidence: 99%

Section: Columnar Assembly By Crystallizationmentioning

confidence: 99%

Functional Materials from Self-Assembled Bis-urea Macrocycles

2014

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“…38,43,44 The cross-section of 1 may be superficially described as elliptical, with dimensions 3.7 Å Â 4.8 Å for the interior van der Waals surface estimated from the crystal structure. 62 The minor axis of the elliptical center cavity of 1 is substantially smaller than the collision diameter of the Xe atom of 4.4 Å. Hence, passage of a Xe atom through the macrocycle 1 requires a correspondingly large distortion of its electron density.…”

Section: Resultsmentioning

confidence: 99%

“…Distortions from spherical symmetry resulting from intermolecular interactions induce paramagnetic excitations which deshield the 129 Xe nucleus relative to the free atom. Hence, the chemical shift anisotropy inside one-dimensional channels depends on Xe–channel and Xe–Xe interactions. ,, The cross-section of 1 may be superficially described as elliptical, with dimensions 3.7 Å × 4.8 Å for the interior van der Waals surface estimated from the crystal structure . The minor axis of the elliptical center cavity of 1 is substantially smaller than the collision diameter of the Xe atom of 4.4 Å.…”

Section: Resultsmentioning

confidence: 99%

Crystalline Bis-urea Nanochannel Architectures Tailored for Single-File Diffusion Studies

et al. 2015

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Urea is a versatile building block that can be modified to self-assemble into a multitude of structures. One-dimensional nanochannels with zigzag architecture and cross-sectional dimensions of only ∼3.7 Å × 4.8 Å are formed by the columnar assembly of phenyl ether bis-urea macrocycles. Nanochannels formed by phenylethynylene bis-urea macrocycles have a round cross-section with a diameter of ∼9.0 Å. This work compares the Xe atom packing and diffusion inside the crystalline channels of these two bis-ureas using hyperpolarized Xe-129 NMR. The elliptical channel structure of the phenyl ether bis-urea macrocycle produces a Xe-129 powder pattern line shape characteristic of an asymmetric chemical shift tensor with shifts extending to well over 300 ppm with respect to the bulk gas, reflecting extreme confinement of the Xe atom. The wider channels formed by phenylethynylene bis-urea, in contrast, present an isotropic dynamically average electronic environment. Completely different diffusion dynamics are revealed in the two bis-ureas using hyperpolarized spin-tracer exchange NMR. Thus, a simple replacement of phenyl ether with phenylethynylene as the rigid linker unit results in a transition from single-file to Fickian diffusion dynamics. Self-assembled bis-urea macrocycles are found to be highly suitable materials for fundamental molecular transport studies on micrometer length scales.

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Assembled Columnar Structures from Bis‐Urea Macrocycles

Abstract: Organic chemistry Z 0200 Assembled Columnar Structures from Bis-Urea Macrocycles -[9 refs.]. -(SHIMIZU, L. S.; HUGHES, A. D.; SMITH, M. D.; SAMUEL, S. A.; CIURTIN-SMITH, D.; Supramol. Chem. 17 (2005) 1-2, 27-30; Dep. Chem., Univ. S. C., Columbia, SC 29208, USA; Eng.) -Lindner 45-279

Cited by 2 publications

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Functional Materials from Self-Assembled Bis-urea Macrocycles

Functional Materials from Self-Assembled Bis-urea Macrocycles

Crystalline Bis-urea Nanochannel Architectures Tailored for Single-File Diffusion Studies

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