Self-Assembly, Structure, and Dynamic Interconversion of Metallosupramolecular Architectures Generated by Pb(II) Binding-Induced Unfolding of a Helical Ligand

The binding of lead(II) cations to the terpyridine-type subunits of the helical ligand 1 leads to the
self-assembly of different polynuclear metallosupramolecular architectures of nanometric size. Three different
entities are generated and may be interconverted as a function of metal/ligand stoichiometry:  a [4 × 4]Pb16II grid-type array 2, a [4 # 4]Pb12II double-cross species 4, and an intermediate complex 3. The structures
of 2 and 4 have been confirmed by X-ray crystallography; that of 3 is based on NMR spectral data. The
interconversion of the three species generates dynamic diversity and represents an expression of
constitutional dynamic chemistry. In the course of ion binding, the helical molecules of ligand 1 unwrap to
yield fully extended strands arranged in perpendicular fashion in the architectures 2−4 generated. This
process amounts to molecular motions in two directions which confer to the present systems characteristics
of two-dimensional nanomechanical devices, capable of performing 2D-contraction/extension motions. The
triple features of self-organization, dynamic interconversion, and potential addressability displayed by the
processes described trace a self-fabrication approach to nanoscience and nanotechnology.