Cation- and Anion-Exchanges Induce Multiple Distinct Rearrangements within Metallosupramolecular Architectures

Abstract

Different anionic templates act to give rise to four distinct Cd(II)-based architectures: a Cd2L3 helicate, a Cd8L12 distorted cuboid, a Cd10L15 pentagonal prism, and a Cd12L18 hexagonal prism, which respond to both anionic and cationic components. Interconversions between architectures are driven by the addition of anions that bind more strongly within a given product framework. The addition of Fe(II) prompted metal exchange and transformation to a Fe4L6 tetrahedron or a Fe10L15 pentagonal prism, depending on the anionic templates present. The equilibrium between the Cd12L18 prism and the Cd2L3 triple helicate displayed concentration dependence, with higher concentrations favoring the prism. The Cd12L18 structure serves as an intermediate en route to a hexafluoroarsenate-templated Cd10L15 complex, whereby the structural features of the hexagonal prism preorganize the system to form the structurally related pentagonal prism. In addition to the interconversion pathways investigated, we also report the single-crystal X-ray structure of bifluoride encapsulated within a Cd10L15 complex and report solution state data for J-coupling through a CH···F(-) hydrogen bond indicating the strength of these interactions in solution.

[C–H⋯anion] interactions mediate the templation and anion binding properties of topologically non-trivial metal–organic structures in aqueous solutions

“…An analogous system in which both cations and anions influence the distribution of several metallosupramolecular products by templation has been described by Nitschke and coworkers 54. In that system a set of cages, helicates and prisms were formed.…”

Anion Receptor Chemistry

“…Riddell et al 70 have continued their work on metallosupramolecular assemblies and have demonstrated anion-driven structural transformations between a number of metal complexed assemblies of the bis-imine formed between 3,3 0 -diformyl-6,6 0 -bypyridine and p-toluidine. This includes the formation of a Cd 10 complex templated by bifluoride (HF 2 À ) ( Figure 48).…”

Anion-directed self-assembly of a 2,6-bis(2-anilinoethynyl)pyridine bis(amide) scaffold

“…Self-assembled receptors or sensors are also capable of selecting guests by an “induced fit” model (10, 11), not just the restrictive lock and key method. The self-assembly of many such complexes has been effected using metal ions (12, 13), small molecules (14), and anions (15, 16). Advancing the use of anions as directing elements and/or templates in self-assembling systems requires an improved understanding of conformational preferences of the flexible receptors comprising these assemblies (5, 8).…”