[2]Pseudorotaxanes from T-Shaped Benzimidazolium Axles and [24]Crown-8 Wheels

A new templating motif for the formation of [2]pseudorotaxanes is described in which T-shaped axles with a benzimidazolium core and aromatic substituents at the 2-, 4-, and 7-positions interact with [24]crown-8 ether wheels ([24]crown-8, dibenzo[24]crown-8, and dinaphtho[24]crown-8). The T-shape greatly enhances the association between axle and wheel when compared to simple imidazolium or benzimidazolium cations. A series of interpenetrated molecules are characterized by ¹H NMR spectroscopy and single crystal X-ray crystallography

[2]Pseudorotaxanes from T-Shaped Benzimidazolium Axles and [24]Crown-8 Wheels

A new templating motif for the formation of [2]pseudorotaxanes is described in which T-shaped axles with a benzimidazolium core and aromatic substituents at the 2-, 4-, and 7-positions interact with [24]crown-8 ether wheels ([24]crown-8, dibenzo[24]crown-8, and dinaphtho[24]crown-8). The T-shape greatly enhances the association between axle and wheel when compared to simple imidazolium or benzimidazolium cations. A series of interpenetrated molecules are characterized by ¹H NMR spectroscopy and single crystal X-ray crystallography

Metal–Organic Frameworks with Mechanically Interlocked Pillars: Controlling Ring Dynamics in the Solid-State via a Reversible Phase Change

Metal–organic framework (MOF) materials have been prepared that contain a mechanically interlocked molecule (MIM) as the pillaring strut between two periodic Zn-carboxylate layers. The MIM linker is a [2]­rotaxane with a [24]­crown-6 (<b>24C6</b>) macrocycle and an aniline-based axle with terminal pyridine donor groups. The single-crystal X-ray structures of MOFs <b>UWDM-2</b> (1,4-diazophenyl-dicarboxylate) and <b>UWDM-3</b> (1,4-biphenyl-dicarboxylate) show that both frameworks are large enough to contain the free volume required for rotation of the interlocked <b>24C6</b> macrocycle, but the frameworks are interpenetrated (<b>UWDM-2</b>, three-fold, and <b>UWDM-3</b>, two-fold). In particular, for <b>UWDM-</b>3 the <b>24C6</b> rings of the pillaring <b>MIM</b> are positioned directly inside the square openings of neighboring zinc dicarboxylate layers. Variable-temperature (VT) ²H SSNMR demonstrated that the <b>24C6</b> macrocycles in <b>UWDM-2</b> and <b>UWDM-3</b> can only undergo restricted motions related to ring flexibility or partial rotation but are incapable of undergoing free rotation. VT-powder X-ray diffraction studies showed that upon activation of <b>UWDM-3</b>, by removing solvent, a phase change occurs. The new β-phase of <b>UWDM-3</b> retained crystallinity, and ²H SSNMR demonstrated that the <b>24C6</b> macrocyclic ring of the pillared MIM strut is now free enough to undergo full rotation. Most importantly, the phase change is reversible; the β version of the MOF can be reverted to the original α state by resolvation, thus demonstrating, for the first time, that the dynamics of a MIM inside a solid material can be controlled by a reversible phase change

Trust and institutional work:a framing perspective

A series of metal–organic framework (MOF) materials has been prepared, each containing a mechanically interlocked molecule (MIM) as the linker and a copper­(II) paddlewheel as the secondary building unit (SBU). The MIM linkers are [2]­rotaxanes with varying sizes of crown ether macrocycles ([22]­crown-6, <b>22C6</b>; [24]­crown-6, <b>24C6</b>; [26]­crown-6, <b>26C6</b>; benzo[24]­crown-6, <b>B24C6</b>) and an anilinium-based axle containing four carboxylate donor groups. Herein, the X-ray structures of MOFs <b>UWCM-</b>1 (no crown) and <b>UWDM-1</b>_<b>(22)</b> are compared and demonstrate the effect of including a macrocycle around the axle of the linker. The rotaxane linkers are linear and result in nbo-type MOFs with void space that allows for motion of the interlocked macrocycle inside the MOF pores, while the macrocycle-free linker is bent and yields a MOF with a novel 12-connected bcc structure. Variable temperature ²H solid-state nuclear magnetic resonance showed that the macrocycles in <b>UWDM-1</b>_<b>(22)</b>, <b>UWDM-1</b>_<b>(24)</b>, and <b>UWDM-1</b>_<b>(B24)</b> undergo different degrees and rates of rotation depending on the size and shape of the macrocycle

Supramolecular Micelles Constructed by Crown Ether-Based Molecular Recognition

A novel supramolecular amphiphilic polymer constructed by crown ether-based molecular recognition has been fabricated and demonstrated to self-assemble into core–shell supramolecular micelles in water. The reversible transition between assembled and disassembled structures can be achieved by changing the pH. This transition was used to realize the controlled release of small molecules. The supramolecular micelle was characterized by various techniques including conductivity, transmission electron microscopy (TEM), dynamic laser light scattering (DLS), and fluorescence titration. TEM images showed dark gray spherical aggregates, and the mean size of the micelles was 50 nm in diameter and of uniformly dispersed size, in good agreement with the DLS results. The release of hydrophobic molecules from the micelles was realized by adding acid (aqueous HCl), weakening the host–guest interactions and leading to disassembly of the supramolecular micelles

Mechanically Interlocked Linkers inside Metal–Organic Frameworks: Effect of Ring Size on Rotational Dynamics

A series of metal–organic framework (MOF) materials has been prepared, each containing a mechanically interlocked molecule (MIM) as the linker and a copper­(II) paddlewheel as the secondary building unit (SBU). The MIM linkers are [2]­rotaxanes with varying sizes of crown ether macrocycles ([22]­crown-6, <b>22C6</b>; [24]­crown-6, <b>24C6</b>; [26]­crown-6, <b>26C6</b>; benzo[24]­crown-6, <b>B24C6</b>) and an anilinium-based axle containing four carboxylate donor groups. Herein, the X-ray structures of MOFs <b>UWCM-</b>1 (no crown) and <b>UWDM-1</b>_<b>(22)</b> are compared and demonstrate the effect of including a macrocycle around the axle of the linker. The rotaxane linkers are linear and result in nbo-type MOFs with void space that allows for motion of the interlocked macrocycle inside the MOF pores, while the macrocycle-free linker is bent and yields a MOF with a novel 12-connected bcc structure. Variable temperature ²H solid-state nuclear magnetic resonance showed that the macrocycles in <b>UWDM-1</b>_<b>(22)</b>, <b>UWDM-1</b>_<b>(24)</b>, and <b>UWDM-1</b>_<b>(B24)</b> undergo different degrees and rates of rotation depending on the size and shape of the macrocycle