Solubilizing Sodium Fluoride in Acetonitrile: Synthesis, Molecular Structure, and Complexation Behavior of Bis(organostannyl)methyl-Substituted Crown Ethers

Enhancement of Ion Pairing of Sr(II) and Ba(II) Salts by a Tritopic Ion-Pair Receptor in Solution

Tritopic ion-pair receptors can bind bivalent salts in solution; yet, these salts have a tendency to form ion-pairs even in the absence of receptors. The extent to which such receptors can enhance ion pairing has however remained elusive. Here, we study ion pairing of M2+ (Ba2+ , Sr2+ ) and X- (I- , ClO4- ) in acetonitrile with and without a dichlorooxacalix[2]arene[2]triazine-related receptor containing a pentaethylene-glycol moiety. We find marked ion association already in receptor-free solutions. When present, most of the MX+ ion-pairs are bound to the receptor and the overall degree of ion association is enhanced due to coordinative, hydrogen-bonding, and anion-π interactions. The receptor shows higher selectivity for iodides but also stabilizes perchlorates, despite the latter are often considered as weakly coordinating anions. Our results show that ion-pair binding is strongly correlated to ion pairing in these solutions, thereby highlighting the importance of taking ion association in organic solvents into account.

Macrocycles as Ion Pair Receptors

Cation and anion recognition have both played central roles in the development of supramolecular chemistry. Much of the associated research has focused on the development of receptors for individual cations or anions, as well as their applications in different areas. Rarely is complexation of the counterions considered. In contrast, ion pair recognition chemistry, emerging from cation and anion coordination chemistry, is a specific research field where co-complexation of both anions and cations, so-called ion pairs, is the center of focus. Systems used for the purpose, known as ion pair receptors, are typically di- or polytopic hosts that contain recognition sites for both cations and anions and which permit the concurrent binding of multiple ions. The field of ion pair recognition has blossomed during the past decades. Several smaller reviews on the topic were published roughly 5 years ago. They provided a summary of synthetic progress and detailed the various limiting ion recognition modes displayed by both acyclic and macrocyclic ion pair receptors known at the time. The present review is designed to provide a comprehensive and up-to-date overview of the chemistry of macrocycle-based ion pair receptors. We specifically focus on the relationship between structure and ion pair recognition, as well as applications of ion pair receptors in sensor development, cation and anion extraction, ion transport, and logic gate construction.

Organotin-based receptors for anions and ion pairs

The field of anion recognition has developed into an area of tremendous significance over the recent decades due to the role of anions in biological and environmental systems, contributing significantly to the more general domain of supramolecular chemistry. So far, a number of receptors have been designed for anion recognition, synthesized and evaluated, most involving hydrogen bonding donors (urea, amide, pyrrole, imidazolium and hydroxyl groups), π-acidic aryl rings, Lewis acidic metals (boron, tin, aluminium, mercury and uranium) and positively charged polyammonium moieties. With the rapid progress in this field, the role of counterions in modulating the binding strength and selectivity of a specific ion has been recognized, leading to the design and discovery of more robust ion pair receptors. Among various recognition strategies that are presently available for anions and ion pairs, the development of Lewis acidic element-based receptors offers an attractive alternative to the hydrogen bond donor-based receptors, by which both anion and Lewis base recognition can be achieved. Consequently, researchers have focused a great deal of attention on such receptors and this sub-branch of recognition chemistry is expanding rapidly. In recent years, the desired selectivity and binding strength have been achieved for various anions by tuning the Lewis acidity through variation of substituents about the metal center. The easy access, rich molecular diversity and strong Lewis acidity of organotin compounds led to the development of organotin-based molecular receptors for anions and ion pairs. This feature article highlights the advances in the design, synthesis and applications of organotin-based receptors, mainly focusing on our group's contributions.

Tritopic ion-pair receptors based on anion–π interactions for selective CaX2 binding

Selective ion-pair binding of CaX₂ (X = Br⁻ and I⁻) was realized by a tritopic receptor incorporating two homoditopic anion–π binding sites and a pentaethylene glycol moiety.

Liquid membrane transport of potassium fluoride by the organotin-based ditopic host Ph2FSnCH2SnFPh-CH2-[19]-crown-6

A novel tin-based ditopic host efficiently transports KF through an organic membrane.

Relay recognition of F−and a nerve-agent mimic diethyl cyano-phosphonate in mixed aqueous media: discrimination of diethyl cyanophosphonate and diethyl chlorophosphate by cyclization induced fluorescence enhancement

F⁻to DCNP detection by relay recognition has been designed and realized for the first time with sequence specificity (F⁻→ DCNP)viaa fluorescence “off–on–on” mechanism.

A turn-on fluorescent chemosensor for selective responses of copper(ii) ion pairs

New piperazine-based aminonaphthalimide imidazolium podands as fluorescent chemosensor was designed and synthesized for selectively sensing Cu(ClO₄)₂ and Cu(NO₃)₂ over a wide range of tested metal ion pairs.

Probing the origin of opposite ion-pair binding behavior for two new calix[4]pyrrole bis-phosphonate receptors

The origin of opposite ion-pair binding behavior for two new calix[4]pyrrole bis-phosphonate receptors has been explored.

A selective, colorimetric, and fluorescent chemodosimeter for relay recognition of fluoride and cyanide anions based on 1,1'-binaphthyl scaffold

The reaction-based relay recognition of fluoride and cyanide anions was demonstrated for the first time, with rapid response and unique triple (fluorescence color, intensity and absorption band) output modes in either of two sequential sensing events. Ratiometric determination of these two anions by fluorescence and/or absorbance spectra is also achieved.

Ion pair receptors

Compared with simple ion receptors, which are able to bind either a cation or an anion, ion pair receptors bearing both a cation and an anion recognition site offer the promise of binding ion pairs or pairs of ions strongly as the result of direct or indirect cooperative interactions between co-bound ions. This critical review focuses on the recent progress in the design of ion pair receptors and summarizes the various binding modes that have been used to accommodate ion pairs (110 references).

Charge separation by ditopic complexation in the solid state: molecular structure of {Ph2(I)SnCH2Sn(Ph)(I)CH2-[16]-crown-5}.NaF.CH3OH

An intramolecular O-H-F hydrogen bridge involving a methanol molecule provides communication between the strongly separated sodium cation and fluoride anion in sodium fluoride that is, for the first time and despite its high lattice energy, ditopically complexed by an organotin-substituted crown ether.