Selective Synthesis of Molecular Borromean Rings: Engineering of Supramolecular Topology via Coordination-Driven Self-Assembly

Molecular Borromean
rings (BRs) is one of the rare topology among
interlocked molecules. Template-free synthesis of BRs via coordination-driven
self-assembly of tetracene-based Ru­(II) acceptor and ditopic pyridyl
donors is reported. NMR and single-crystal XRD analysis observed sequential
transformation of a fully characterized monomeric rectangle to molecular
BRs and vice versa. Crystal structure of BRs revealed that the particular
topology was enforced by the appropriate geometry of the metallacycle
and multiple parallel-displaced π–π interactions
between the donor and tetracene moiety of the acceptor. Computational
studies based on density functional theory also supported the formation
of BRs through dispersive intermolecular interactions in solution.