A Highly Entangled (M₃L₂)₈ Truncated Cube from the Anion-Controlled Oligomerization of a π-Coordinated M₃L₂ Subunit

The cooperation of weak acetylene π-coordination and relatively strong metal-heteroatom coordination has emerged as a promising strategy for the construction of highly complex but well-ordered nanostructures. Here, we report the formation of an (M₃L₂)₈ truncated cube (M = Ag^I) via the oligomerization of an M₃L₂ subunit stabilized by the secondary π-coordination of an acetylene spacer. This large framework cannot be obtained directly from its components (M and L) but is instead formed by counteranion exchange (BF₄^- to NO₃^-) of the presynthesized smallest oligomer, the dimeric (M₃L₂)₂ cage. Single-crystal X-ray diffraction analyses revealed that the cubic framework of (M₃L₂)₈ exhibits a π-coordination-supported highly entangled structure, which is formally constructed via alternation of the cubic corners and edges with helical M₃L₂ subunits and double lines with two twists, respectively. This observation enabled us to understand the complicated structures of the series of (M₃L₂) polyhedral cages (n = 2, 4, 6, 8) as a fundamentally new type of molecular entanglements based on trifurcate motifs, which can be obtained selectively by adjusting the self-assembly conditions.