Self‐Assembly of a Double Calix[6]arene Pseudorotaxane in Oriented Channels

Abstract

A synthetic study to disclose the more appropriate manner by which two calix[6]arene units could be connected for the construction of an extended tubular structure was undertaken. As a result, a head-to-tail double calix[6]arene having the structure of an oriented nanotube that is about 2.6 nm long and 1.6 nm wide was prepared and characterized. This molecule is able to act as a wheel-type host and forms a supramolecular complex with an axle-type molecule, derived from 4,4'-bipyridinium (viologen), through very efficient self-assembly in solution. The properties of such a pseudorotaxane-type complex, which is stabilized by a combination of noncovalent interactions, were investigated in solution by UV/Vis absorption spectroscopy and voltammetric methods. These observations provide a clue about the location of the bipyridinium unit along the nanotube. In the solid state, the complex undergoes a further stage of self-assembly, thereby initiating extended oriented tubular structures. Crystallographic studies revealed that the positioning of the viologen dication in this asymmetric wheel is addressed by a complicated pattern of cooperative noncovalent intermolecular interactions that involve only one half of the host, whereas the remaining (more polar) half of the host is exploited to create long-range structural order that leads to a "secondary" structure of extended supramolecular channels that, in turn, self-assemble in the lattice, thus giving rise to a "tertiary" structure of parallel sandwiches of nanotubes.

Towards Controlling the Threading Direction of a Calix[6]arene Wheel by Using Nonsymmetric Axles

“…[11,13,21] The titration curves (see, e.g., Figure 6, inset) were satisfactorily fitted with a 1:1 association model; the corresponding apparent stability constants are gathered in Table 1. On the basis of the results of the NMR spectroscopy characterisation, these values are obviously referred to the up orientational isomers.…”

C3v (Trimethyl) p‐(Benzyloxy)calix[6]arene: A Versatile Platform for the Synthesis of Functionalized C3v Calix[6]arenes

“…Some already described examples of "large-rim"-functionalized calix [6]arenes. [27,29,30,[34][35][36] Scheme 1. Synthesis of C 2v -tetramethylated 3 and C 3v -trimethylated 4 p-(benzyloxy)calix [6]arenes.…”

“…[28][29][30][31][32][33][34] These new calixarene receptors, functionalized at both rim positions, hold great promise for the synthesis of new supramolecular hosts (Figure 2). [27,29,30,[34][35][36][37] Up to now, these useful C 3v platforms are only described starting from the parent (p-tBu)calix [6]arene (Figure 1). [28][29][30][31][32][33][34] In this case, the substitution of the p-(tBu) group is usually obtained by electrophilic cleavage.…”

Light-Operated Machines Based on Threaded Molecular Structures

“…In the next section a strategy similar to that just described is applied to supramolecular assemblies based on three-dimensional non-symmetric macrocycles whose lengths can approach the thickness of a bilayer membrane, [97] and in which face-selective threading can be realized.…”