Double-stranded dimetallic helicates: assembling-disassembling driven by the Cu(I)/Cu(II) redox change and the principle of homochiral recognition.

In the presence of d(10) metal ions, prone to tetrahedral coordination, ligands containing two bidentate subunits will give rise to double-stranded helical complexes (helicates). Upon electrochemical oxidation of Cu(I) to Cu(II), the helicate complex tends to disassemble, thus giving rise to two mononuclear Cu(II) complexes with tetragonal geometry. Upon subsequent Cu(II)-to-Cu(I) electrochemical reduction, two Cu(I) complexes instantaneously re-assemble to give the helicate complex. A helicand containing a chiral subunit (e.g. 1,2-substituted cyclohexanediamine) contains a racemic mixture of the R,R and S,S enantiomers. The racemic helicand, reacting with Cu(I), forms dimetallic helicates, in which the two strands show the same chirality, whether R,R or S,S, thus obeying the principle of homochiral recognition.