Sandwich species, supramolecular

We showed in Chapter 3 that half-sandwich complexes with three-legged piano stool geometry with different substituents are archetypal examples of optically active chiral-at-metal centre. Such species are ubiquitous in organometallic synthesis and catalysis however, more recently it has become clear that they can be very interesting building blocks for supramolecular chemistry (Figure... 

When the coordination bonds that hold these assemblies together are both stable and inert, their formation from the components occurs under kinetic rather than thermodynamic control and it is thus disputable if they can be truly defined as supramolecular systems. On the other hand, owing to their kinetic stability, some of these species can be further exploited as building blocks in the construction of higher order architectures through a hierarchical self-assembly approach (see for example the molecular sandwiches 13-15). Through this modular approach, multichromophore systems become easily accessible on demand, with a limited synthetic effort. 

The trigonal bipyramidal coordination geometry around the Cu ion in [Cu(H20)5] species (Figs. 29 and 30) is decided by its participation in forming a supramolecular sandwich with two crown ethers that involves hydrogen... 

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