Selective Anion Extraction and Recovery Using a Fe^II₄L₄ Cage

Abstract

Selective anion extraction is useful for the recovery and purification of valuable chemicals, and in the removal of pollutants from the environment. Here we report that FeII 4L4 cage 1 is able to extract an equimolar amount of ReO4 −, a high‐value anion and a nonradioactive surrogate of TcO4 −, from water into nitromethane. Importantly, the extraction was efficiently performed even in the presence of 10 other common anions in water, highlighting the high selectivity of 1 for ReO4 −. The extracted guest could be released into water as the cage disassembled in ethyl acetate, and then 1 could be recycled by switching the solvent to acetonitrile. The versatile solubility of the cage also enabled complete extraction of ReO4 − (as the tetrabutylammonium salt) from an organic phase into water by using the sulfate salt of 1 as the extractant.

The Chaotropic Effect as an Assembly Motif in Chemistry

“…Understanding the driving forces between ions and concave binding sites is therefore of prime importance for the supramolecular design of synthetic receptors with defined affinity and selectivity.A ccordingly,t he unexpectedly high binding affinities of superchaotropic anions and the chaotropic effect as ag eneric driving force have recently found their entry into the important area of anion recognition. [44,65,117,[131][132][133][134][135][136][137][138][139][140][141][142][143] In follow-up studies with inclusion complexes,the affinity of dodecaborate clusters to cyclodextrins (CDs) has been extended to the larger CD homologues (Figure 3) [23] as well as other borate clusters, [14,144] both in solution and in the gas phase. [14,23,24] Theb inding propensity of borate clusters has also been demonstrated for calixarenes [21] and at etrathiafulvalene host [24] as an alternative macrocyclic host (Figure 3).…”

Synthesis and Applications of Endohedrally Functionalized Metal‐Ligand Cage Complexes

“… a) Stereocontrol in multicomponent self‐assembly; b) structural switching of M 4 L 4 cages via anion templation ,,…”

“…The interconversion of the complex ( T↔C 3 ) was sluggish, indicating a level of “short term memory” in the complex. The utility of this cage was further extended to the selective extraction of ReO 4 − and TcO 4 − anions from H 2 O which could be released via introduction of EtOAc to the system …”

Fluorometric Recognition of Nucleotides within a Water‐Soluble Tetrahedral Capsule

“…[4a] Many available receptors suffer from poor solubility in water, limited cavity space,o ral ack of specific recognition sites that promote electrostatic attraction. Although metal-organic cages have proven broadly useful as effective anion receptors, [5] those that can encapsulate anions in water remain scarce,possibly due to the difficulty of achieving solubility and stability in aqueous conditions. [4a, 6] Thes olubility of cages in water can be promoted by incorporating components with water-solubilizing groups; [7] however, this strategy requires additional synthetic steps and may limit the ability to incorporate additional functional organic moieties into the ligands of metal-organic capsules.…”