Helicates, Peptide-Helicates and Metal-Assisted Stabilization of Peptide Microstructures - Metallofoldamers: Supramolecular Architectures from Helicates to Biomimetics - page 284

The group of Lehn used a similar strategy for the formation of heteronuclear and heter-
oleptic helicates containing a high level of information.
Two strands of the bis-bipyridine/mono-terpyridine 16 bind two copper(I) ions and one
iron(II) ion to form a heterotrinuclear double-stranded helicate. The denticity of the coor-
dination site controls the position of the different metals. The two copper(I) coordinate
two bipyridine units, adopting tetrahedral coordination geometries, while iron(II) prefers
an octahedron formed by two terpyridine units. Ligand 17 leads to the opposite situation
in the helicate with two iron bis-terpyridine moieties and only one copper bis-bipyridine
moiety. This principle also works with the unsymmetrical ligand 18 , leading to a bis-cop-
per(I) mono-iron(II) complex.
The series of ligands 16-18 results in the formation of heterotrinuclear iron(II)-copper
(I) complexes with the sequence of the metals (Cu-Fe-Cu for 16 , Fe-Cu-Fe for 17 , Fe-Cu-
Cu for 18 ) programmed into the ligand strand (Figure 8.13). In addition, a mixture of
ligands 16 and 17 forms heteroleptic trinuclear double stranded helicates [( 16 )( 17 )Cu 3 ] 6þ
if copper(II) ions are added. Here the metal ions prefer a coordination number higher than
four, resulting in the binding of one bipyridine and one terpyridine to the same metal
Figure 8.13 Sequential bipyridine/ terpyridine ligands.