Anion recognition in water

Abstract

Anion recognition by synthetic receptors in water is not a new field, indeed the first receptors that were shown to interact with anionic species exhibited high affinity in aqueous solutions. Anion recognition in aqueous solution was, however, for a long time the domain of receptors containing multiple positive charges and/or metal ions while interactions of neutral receptors with anions were believed to be too weak to be efficient in water. Independent work in several groups has recently shown that this assumption is not necessarily correct. As a consequence, a much wider range of receptors is now available with which anion recognition in competitive aqueous media can be achieved. This tutorial review presents selected examples of synthetic anion receptors active in aqueous solutions and guidelines to achieve anion recognition in water.

Anion-dependent spin crossover in solution for an iron(ii) complex of a 1H-pyrazolyl ligand

“…23 The sensitivity of and X -is expected to be weaker. 13 The fact that any correlation between T½ and X -is observed under our conditions is noteworthy for a monodentate hydrogen bond-donor like 1 2+ , and confirms that SCO in 1 2+ is sensitive to host:guest interactions.…”

“…Water tends to disrupt host:guest interactions to anions, all other things being equal, because of its polarity and strong hydrogen-bonding character. 13 and would be another rare observation of anion-dependent spin-crossover. This result required clarification, however, since SCO in 1 2+ in acetone:water is sensitive to the composition of the solvent mixture.…”

Anion Recognition in Water: Recent Advances from a Supramolecular and Macromolecular Perspective

“…Stefan Kubik, a pioneer in the use of neutral host molecules for anion binding in aqueous solutions, has reviewed the state of the art in the field of anion recognition in water using supramolecular host systems, the most recent of which was published in 2010 8, 9. However, in the past five years numerous exciting and significant advances in this rapidly expanding field have emerged, in particular exotic interactions such as C−H hydrogen bonding and halogen bonding have been exploited in anion host systems capable of operating in water.…”

The Effect of Ligand Design on Metal Ion Spin State—Lessons from Spin Crossover Complexes

“…This has been best studied in a series of complexes [Fe(bip) 2 [100] reported no measurable response to different anions in solution, that might reflect the aqueous solvents used for those measurements, which would disfavor intermolecular hydrogen-bonding and ion pairing [107]. 2+ , since in that study both electron-donating and -withdrawing substituents led to a similar reduction in T½ [98].…”