Anion-directed assembly templates, anions

Since the first examples of anion-directed assemblies were reported in the 1990s, a wide range of molecular and supramolecular systems have been successfully prepared using anions as templates. This section has been divided by the type of molecular or supramolecular species formed and, as mentioned before, it will mainly focus on systems that have been recently reported in the literature (making reference to previous examples when important for the sake of clarity and completion). 

Anion-Directed Assembly, p. 51 Enzymes Characteristics and Mechanisms, p. 554 Hydrogen Bonding, p. 658 Molecular Squares, Boxes, and Cubes, p. 909 Molecular-Level Machines, p. 931 Protein Supramolecular Chemistry, p. 1161 Racks, Ladders, and Grids, p. 1186 Self-Assembling Catenanes, p. 1240 Self-Assembly Definition and Kinetic and TTjermot/ynam-ic Considerations, p. 1248 Self-Assembly in Biochemistiy, p. 1257 The Template Effect, p. 1493... 

De Mendoza reported the first example of anion-directed helix formation in 1996 [91]. The assembly of this helical structure relies, not only on electrostatic interactions between the anionic template and the positively charged strands, but also on hydrogen bonding. The tetraguanidinium strand 69 (see Scheme 34) self-assembles around a sulfate anion via hydrogen bonding to produce a double helical structure. The formation of this assembly and its anion-dependence was proposed on the basis of NMR and CD spectroscopic studies. 

The interest in rotaxanes, pseudorotaxanes, and catenanes (i.e., molecules that contain non-covalently interlocked components) stems from their potential use as building blocks in molecular devices. Their syntheses usually rely on some sort of template assistance, such as the preorganization of the assembly s components around a metal center. While cationic templates have been widely used in this context, only a few examples of anion-directed synthesis of interlocked molecules have been reported. In fact, although rotaxanes and pseudorotaxanes have been prepared in this way (as discussed in this section), to date there is no reported example of anion-directed synthesis of catenanes. 

Further studies by the same authors have demonstrated that PFj acts a hydrogen bond-acceptor template in the assembly of several other interwoven structures. In an extensive study aimed at using a combination of hydrogenbonding motifs to self-assemble pseudorotaxanes into more complex structures it was discovered that PFj assists on the organization of the components that yield the final superstructure [74]. Particularly, it was found that this anion dictates the orientation of the two carboxylic acid groups of the [3]pseudorotaxanes 58 and 59 (see Schemes 27 and 28) when these groups are co-directional with respect to each other the formation of discrete hydrogen-bonded dimers is observed. 

For a number of years the research interests of the Beer group have covered many areas of macrocychc coordination and supramolecular chemistry. This article reviews our latest results of current research by focusing on three major sections sensing of cations and anions anion templated assembly of pseudorotaxanes and rotaxanes, and metal-directed self-assembly using the dithiocaibamate ligand. 

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