Self-assembly of a double calix[6]arene pseudorotaxane in oriented channels.
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.
Arduini
Arturo
A
Dipartimento di Chimica Organica e Industriale, Università di Parma via G.P. Usberti 17/a, 43100 Parma, Italy. arturo.arduini@unipr.it
Credi
Alberto
A
Faimani
Giovanni
G
Massera
Chiara
C
Pochini
Andrea
A
Secchi
Andrea
A
Semeraro
Monica
M
Silvi
Serena
S
Ugozzoli
Franco
F
D047250:Calixarenes / Q000138:chemical synthesis / Q000737:chemistry*; D018360:Crystallography, X-Ray; D008958:Models, Molecular; D015394:Molecular Structure; D010636:Phenols / Q000138:chemical synthesis / Q000737:chemistry*; D043862:Rotaxanes / Q000737:chemistry*; D013053:Spectrophotometry
D010636:Phenols; D043862:Rotaxanes; C476540:calix(6)arene; D047250:Calixarenes