Ion-Pair Recognition by Metal - Salophen and Metal - Salen Complexes

Abstract

The development of heteroditopic receptor systems that can simultaneously bind cationic and anionic species is one of the most challenging research topics in supramolecular chemistry, attracting the attention of a large number of research groups worldwide. Such an interest is due especially to the fact that the overall receptor–ion-pair complex is neutral and this can be advantageous in many situations, such as salt solubilization and extraction, and membrane-transport applications. Receptors designed for ion-pair complexation are molecules comprising well-known anion-binding motifs and familiar cation-binding sites. An important family of compounds that can use metal Lewis-acidic centres for anion recognition and that can be easily derivatized to introduce an additional binding site for the cation is metal–salophen and metal–salen complexes. This short review shows that the high versatility of salen and salophen ligands and of the corresponding metal complexes allows, through simple modifications of the basic skeleton, the obtention of highly efficient receptors for ion pairs.

Supramolecular Detection of a Nerve Agent Simulant by Fluorescent Zn–Salen Oligomer Receptors

“…Non-linear curve fit plots were performed by using a 1:1 stoichiometry, supported by our previous studies on CWA recognition by Metal–Salen complexes [31,32,33,34,35,36,37]. Interestingly, moving from longer to shorter oligomer distribution, an increase of the affinity was observed (see Table 2).…”

“…Metal–Salen complexes are well known in literature for their use as catalysts [26,27,28,29,30] and supramolecular hosts [31,32,33,34,35,36,37,38], where the Lewis acid metal center is exploited for the recognition of Lewis base species. Furthermore, recently we also demonstrated the high efficiency of metal-Salen complexes as receptors for NA simulants [25,39].…”

Solution and Solid‐State Studies on the Halide Binding Affinity of Perfluorophenyl‐Armed Uranyl–Salophen Receptors Enhanced by Anion–π Interactions

“…Thus, the development of novel artificial anion receptors represents an important researchf ield, and the study of the non-covalent interactions on whichh ostanion recognitionr elies is crucialf or the understanding of the biological processes and designing systems for environmental monitoring. [3] For example,t he presence of appended benzyloxy groups in the ortho-positions of the salicylimine shown in Figure1 results in the cooperative ion-pair binding. [2] The large number of synthetic routes to ortho-substituted phenols and to the corresponding ortho-salicylaldehydes gives access to av arietyo fs tructures with subtle steric and electronic variations on the receptor structure,t hus making them perfect candidates for systematic studies.…”

From Heteroditopic to Multitopic Receptors for Ion‐Pair Recognition: Advances in Receptor Design and Applications

“…[22] As a consequence of the structurally welldefined electron rich interior of these macrocycles, in particular pillar [5]arene, facilitating the formation of strong inclusion complexes with a series of cationic aromatic and aliphatic molecules, pillar [5]arenes have found extensive application in the development of novel host frameworks for organic cation recognition. [23] In general, these have been limited to monotopic receptor systems, however, more recently Huang has exploited rim-functionalised pillar [5]arene derivatives to provide recognition environments for ion-pairs. In a 2019 report, Huang investigated a series of peralkylated pillar [5]arenes 8 a-c as hosts for the complexation of silver trifluoroacetate (Figure 7a).…”

“…[1] Examples are chosen to highlight progress, new developments and challenges in the design as well as applications of ion-pair receptors. For more detailed treatments of particular classes of ion-pair receptors, the reader's attention is drawn to many excellent recent reviews on calix [4]pyrrole, [2] macrocyclic, [3] organotin, [4] metal-salophen and -salen, [5] pyrrole, [6] imidazole [6] and triazole [6] ion-pair receptors.…”