Heteroleptic Metallosupramolecular Racks, Rectangles, and Trigonal Prisms: Stoichiometry-Controlled Reversible Interconversion

A simple
approach toward preparation of heteroleptic two-dimensional (2D) rectangles
and three-dimensional (3D) triangular prisms is described utilizing
the HETPYP (HETeroleptic PYridyl and Phenanthroline metal complexes)
concept. By mixing metal-loaded linear bisphenanthrolines of varying
lengths with diverse (multi)­pyridine (py) ligands in a proper ratio,
six different self-assembled architectures arise cleanly and spontaneously
in the absence of any template. They are characterized by 1H and DOSY NMR, ESI-FT-ICR mass spectrometry as well as by Job plots
and UV–vis titrations. Density functional theory (DFT) computations
provide information about each structure. A stoichiometry-controlled
supramolecule-to-supramolecule interconversion based on the relative
amounts of metal bisphenanthroline and bipyridine forces the rectangular
assembly to reorganize to a rack architecture and back to the rectangle,
as clearly supported by variable temperature and DOSY NMR as well
as dynamic light scattering data. The highly dynamic nature of the
assemblies represents a promising starting point for constitutional
dynamic materials.