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

Abstract

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.

Symmetric tangled Platonic polyhedra

“…That feature is likely to be responsible for the formation of a molecule whose skeleton is equivalent to that of the simplest of all polyhedral tangles introduced in this paper, ( ) ( 1 ). More recent syntheses of entangled metal-organic molecules ( 2 – 5 ) have closely related and marginally less symmetric structures, which can also be described as (branched or unbranched) railways wound on polyhedra. Entangled infinite framework structures also emerge from these finite polyhedral tangles, which describe the embeddings of their quotient graphs [formed by replacing the infinite structure by a finite unit cell with periodic boundaries ( 42 )].…”

“…They are also promising candidates for (supra)molecular assemblies. For example, tangled symmetric structures are a feature of finite metal-organic molecules ( 1 – 5 ) and infinite catenated inorganic compounds, coordination polymers, covalent organic frameworks (COFs), and metal-organic frameworks (MOFs) ( 6 – 12 ).…”

Metallosupramolecular cages: from design principles and characterisation techniques to applications

“…metal-acetylene interactions 37,38 and the (M 3 L 2 ) 8 truncated cube can be self-assembled from the (M 3 L 2 ) 2 cage by anion exchange of BF 4 À for NO 3 À . 37 In a similar hierarchical selfassembly approach, Sun and co-workers reported Eu III 2 L 3 helicates self-assemble into a hexameric cage with a 4 nm diameter in the presence of anions. 16 2.2.4 Design of lower symmetry cages.…”

Heteroleptic metallosupramolecular aggregates/complexation for supramolecular catalysis

“…In search of supramolecular cavity-induced catalysis, chemists have become fascinated toward the design of large and sophisticated molecular vessels. In this context, Stang [ 54 ], Nitschke [ 55 ], Fujita [ 56 ], and others [ 57 ] have reported several template-free assemblies giving access to novel structures. The primary objective of these nanovessels as supramolecular catalysts is to encapsulate organic reactant/s to lower the activation barrier, thereby mimicking the functions of enzymes (without replicating their structures).…”