Self-assembly of large multi-component systems is a common strategy for the bottom-up construction of discrete, well-defined, nanoscopic-sized cages. Icosahedral or pseudospherical viral capsids, built up from hundreds of identical proteins, constitute typical examples of the complexity attained by biological self-assembly. Chemical versions of the so-called 5 Platonic regular or 13 Archimedean semi-regular polyhedra are usually assembled combining molecular platforms with metals with commensurate coordination spheres. Here we report novel, self-assembled cages, using the conical-shaped carboxylic acid derivatives of calix[4]arene and calix[5]arene as ligands, and the uranyl cation UO22+ as a metallic counterpart, which coordinates with three carboxylates at the equatorial plane, giving rise to hexagonal bipyramidal architectures. As a result, octahedral and icosahedral anionic metallocages of nanoscopic dimensions are formed with an unusually small number of components.
A new cyclophane featuring two opposite anthracene units linked in 9,10-positions has been synthesized thanks to the template effect of the Me4N(+) ion. It forms pseudorotaxane complexes with alkylviologen ions and undergoes a fast and reversible reaction with tetracyanoethylene. A quantitative analysis has been carried out of the formation of Diels-Alder adducts, whose distribution can be controlled by host-guest complexation. These findings open interesting perspectives in the field of Dynamic Covalent Chemistry.
Three novel polymeric assemblages have been obtained from alkali metal salts of pyrazinetetracarboxylic acid (H4PZTC). In the complexes [Na2(H2PZTC)(H2O)2] (1), [K(H3PZTC)] (2), and [Cs2(H2PZTC)] (3), the cations are chelated in the O,N,O site of one (1) or two ligands (2 and 3),and further carboxylic/ate complexation results in the formation of two- (1) or three-dimensional (2 and 3) compact assemblages with alternate rows or planes of cations and ligands. The H4−x
PZTC
x− ligand is bound to 6, 4, and 12 cations in 1−3, respectively, with four oxygen atoms in the last case being coordinated to as many as four cesium atoms each. The crystal structure of complex 3 is particularly remarkable, with the cesium cation having a coordination number of 12 and a hexagonal prismatic environment. The Cs···Cs contacts in this compound are among the shortest reported. These compounds further illustrate the potential of H4PZTC for the building of metal−organic frameworks.
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