Helical Polymer Complexes

This chapter describes the synthesis, structural features, and properties of polymer–metal complexes with various helical structures. Metal-containing helical structures can be obtained either by complexation of a pre-formed organic oligomer/polymer ligand with metal ions or by simultaneous formation of the oligomer/polymer main chain and the helical structure by metal complexation. In the first strategy, flexible linear oligomer/polymer molecules, such as bipyridine oligomers, are used to obtain self-assembled metal helicates with double and triple helical structures. The unique helical structures are based primarily on the well-defined coordination structures of the metal complex motifs. In addition, coordination bonds are used to form base pairs of DNA double helices instead of conventional hydrogen bonds. Single helical structures, such as metallo-foldamers, can also be obtained by metal complexation of linear oligomeric molecules. In the second strategy, oligomeric metal complexes with single and double helical structures are obtained by helically assembling small subunits by coordination bonds. In this case, metal complexation simultaneously leads to elongation of the main chain and formation of a helical structure. Helical metal complexes generally have dynamic features due to the reversibility of the coordination bonds. By exploiting these dynamic properties, various types of stimuli-responsive structural conversions have been achieved.