Abstract
Mono‐ or biscatechol esters with ether‐type substituents or spacers form either triple lithium bridged dimeric helicates or triple stranded helicates with the ability to bind three lithium cations in their interior. Hierarchical helicates with ether or thioether substituents show in solution a monomer‐dimer equilibrium which is independent of the heteroatom in the ester substituent. However, dimerization constants are significantly lower than for corresponding alkyl derivatives. Dinuclear helicates with oligoether spacers are well obtained in the presence of lithium cations. Upon removal of the cations the helicates expand and successive addition of LiCl results in compression again.
Highlights
Self-assembly provides a facile way to synthesise complex supramolecular structures starting from available building blocks
In 2005 we introduced hierarchically[3] formed triple lithium bridged helicates[4] based on dinuclear titanium catecholates,[5] which in solution represent a unique class of lithium dependent molecular switches (Figure 1a)
– Hierarchical helicates with ether or thioether-type substituents dissociate into the monomers more compared to the analogous alkyl derivatives
Summary
Self-assembly provides a facile way to synthesise complex supramolecular structures starting from available building blocks. Dynamic behavior of the obtained supramolecular aggregates, which ideally can be controlled by some external stimuli, leads into the world of molecular devices like machines or switches.[1]. Many chemical devices have been prepared e.g. based on rotaxane and catenane motifs, but other structural moieties have been successfully used as well.[2]. In 2005 we introduced hierarchically[3] formed triple lithium bridged helicates[4] based on dinuclear titanium catecholates,[5] which in solution represent a unique class of lithium dependent molecular switches (Figure 1a). NMR spectroscopy allows to observe the equilibrium between the monomeric and dimeric titanium(IV)triscatecholates.[6] The equilibrium mainly depends on the kind of carbonyl substituent
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