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 = AgI) 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)n 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.