Pendant ligand metal-binding sites

Conceptually, a similar strategy may be applied to introduce chiral auxiliary ligands with well-defined binding and catalytic centers to MOPMs that have pendant reactive centers or open metal coordination sites (Fig. 9). Though no CMOPM has been synthesized by this strategy until now, it certainly appears to be quite a feasible and promising strategy. 

Ligands with three donor groups may bind to three sites of a metal as a tridentate ligand, although didentate chelation with one donor group pendant and unbound is also observed. Complex stability is usually enhanced by coordination of aU three donor groups. Examples appear below in Figures 11,13, and 14. 

A brief report showed that molecular square IZn could be used to detect binding of sodium and potassium cations by a crown ether featuring a pendant pyridine [32], The crown ether ligand was observed to bind via the pendant pyridine to the available Zn(II) sites of the porphyrin square. Accompanying the binding was a decrease in fluorescence intensity that was reversed upon capture of an alkali metal cation by the crown. 

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