Self-assembly of a supramolecular hexagram and a supramolecular pentagram

Abstract

Five- and six-pointed star structures occur frequently in nature as flowers, snow-flakes, leaves and so on. These star-shaped patterns are also frequently used in both functional and artistic man-made architectures. Here following a stepwise synthesis and self-assembly approach, pentagonal and hexagonal metallosupramolecules possessing star-shaped motifs were prepared based on the careful design of metallo-organic ligands (MOLs). In the MOL design and preparation, robust ruthenium-terpyridyl complexes were employed to construct brominated metallo-organic intermediates, followed by a Suzuki coupling reaction to achieve the required ensemble. Ligand LA (VRu²⁺X, V=bisterpyridine, X=tetraterpyridine, Ru=Ruthenium) was initially used for the self-assembly of an anticipated hexagram upon reaction with Cd²⁺ or Fe²⁺; however, unexpected pentagonal structures were formed, that is, [Cd₅LA₅]³⁰⁺ and [Fe₅LA₅]³⁰⁺. In our redesign, LB [V(Ru²⁺X)₂] was synthesized and treated with 60° V-shaped bisterpyridine (V) and Cd²⁺ to create hexagonal hexagram [Cd₁₂V₃LB₃]³⁶⁺ along with traces of the triangle [Cd₃V₃]⁶⁺. Finally, a pure supramolecular hexagram [Fe₁₂V₃LB₃]³⁶⁺ was successfully isolated in a high yield using Fe²⁺ with a higher assembly temperature.