Organic synthesis, anion-directed assembly

Although the chanistry of anion directed assemblies is a flourishing field that can profit from the geometrical properties of anions similar to those of cations, examples of tanplated synthesis assisted by anion coordination are far less common than cationic examples. A pioneer example came from Beer s group. The authors took advantage of the tetrahedral organization of a sulfate anion coordinated to two hydrogen atoms of secondary amides (Scheme 17.3). 

Amouri has reported the anion-directed synthesis of a series of coordi-natively unsaturated metallo-cages with general formula [Co2(L )4(RCN)2C (BF4)](BF4)3 (R = Me, Ft, Ph) [35]. The X-ray crystal structures of some of these assemblies (see Fig. 7 for an example) have revealed the presence of an encapsulated BF4 anion which interacts with the coordinatively unsaturated cobalt(ll) centres. Interestingly when analogous reactions were performed in the presence of other anions (such as Cl and NO3) different metal-organic assemblies were formed [36]. 

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