Anion coordination and anion-directed assembly: highlights from 1997 and 1998

Supramolecularly Built Local Electric Field Microenvironment around Cobalt Phthalocyanine in Covalent Organic Frameworks for Enhanced Photocatalysis

The local electric field (LEF) plays an important role in the catalytic process; however, the precise construction and manipulation of the electric field microenvironment around the active site remains a significant challenge. Here, we have developed a supramolecular strategy for the implementation of a LEF by introducing the host macrocycle 18-crown-6 (18C6) into a cobalt phthalocyanine (CoPc)-containing covalent organic framework (COF). Utilizing the supramolecular interaction between 18C6 and potassium ion (K+), a locally enhanced K+ concentration around CoPc can be built to generate a LEF microenvironment around the catalytically active Co site. The COF with this supramolecularly built LEF realizes an activity of up to 7.79 mmol mmolCo-1 h-1 in the photocatalytic CO2 reduction reaction (CO2RR), which is a 180% improvement compared to its counterpart without 18C6 units. The effect of LEF can be subtly controlled by fully harnessing the K+@18C6 interaction by changing the potassium salts with different counterions. In situ spectroscopy and density functional theory calculations show that the complexation of K+ by 18C6 creates a positive electric field that stabilizes the critical intermediate *COOH involved in CO2RR, which can be tuned by the halide ion-mediated K+@18C6 interaction and hydrogen-bonding interaction, consequently leading to improved catalytic performance to varying degrees.

Macrocyclic receptors for anion recognition

Macrocyclic receptors have emerged as versatile and efficient molecular tools for the recognition and sensing of anions, playing a pivotal role in molecular recognition and supramolecular chemistry. The following review provides an overview of the recent advances in the design, synthesis, and applications of macrocyclic receptors specifically tailored for anion recognition. The unique structural features of macrocycles, such as their well-defined structures and pre-organised binding sites, contribute to their exceptional anion-binding capabilities that have led to their application across a broad range of the chemical and biological sciences.

Spectroscopic and Density Functional Studies on the Interaction of a Naphthalene Derivative with Anions

This article highlights the investigation of anion interactions and recognition abilities of naphthalene derivative, [(E)-1-(((4-nitrophenyl)imino)methyl)naphthalen-2-ol], (NIMO) by UV-visible spectroscopically and colorimetrically. NIMO shows selective recognition of F^- ions colorimetrically, and a visual color change from yellow to pink is observed by the naked eye. The F^- ions recognition is fully reversible in the presence of HSO₄^- ions. The limit of F^- ions detection by NIMO could be possible down to 0.033 ppm-level. A paper strips-based test kit has been demonstrated to detect F^- ions selectively by the naked eye, and a smartphone-based method for real sample analysis in the non-aqueous medium has also been demostrated. Spectroscopic behavior is well supported by pK_a value calculation and DFT analysis, to find a correlation with receptor analyte interaction. The optical response of NIMO towards the accumulation of F^- ions and, subsequently, HSO₄^- ions as chemical inputs provides an opportunity to construct INH and IMP molecular logic gates.

Quinoline based thiosemicarbazones as colorimetric chemosensors for fluoride and cyanide ions and DFT studies

High toxicity and extensive accessibility of fluoride and cyanide ions in diverse environmental media encouraged attention for scheming well-organized probes for their detection. Keeping in mind we have designed and synthesized thiosemicarbazone-based chemosensors RB-1, RB-2 and RB-3 for the detection of fluoride and cyanide ions. The structural elucidation of the synthesized chemosensors is done by employing different analytical techniques including nuclear magnetic resonance and electronic absorption specrtoscopies. Admirable detection limit, binding constant and fast response time (2 s) to F- and CN- ions enlarged the applications of these chemosensors. Additional confirmation of the sensing ability of these chemosensors is derived from DFT and TDDFT calculations with M06/6-311G(d,p) method by performing FMO, UV-Vis, QTAIM and global reactivity parameters elucidation. Overall results point out that investigated chemosensors are suitable candidates for sensing the F- ions. These chemosensors were successfully applied to detect F- ions in a commercial toothpaste sample.

N-Confused Porphyrin - A Unique "Turn-On" Chemosensor for CN- and F- ions and "Turn-Off" Sensor for ClO4 - ions

N-Confused meso-tetrakis(4-carbomethoxyphenyl)porphyrin (1) and its Ni(II) complex (1 a) have been synthesized and utilized for anion sensing studies, and the results are compared with N-confused meso-tetraphenylporphyrin (NCTPP). Anion susceptibilities of 1 and 1 a were investigated using spectroscopic, electrochemical, and DFT studies. Porphyrins 1 and 1 a were able to detect CN^- , F^- , and ClO₄ ^- ions selectively over the tested set of anions even at ppm level. Interestingly, the addition of ClO₄ ^- ions resulted in fluorescence quenching (turn off) whereas the addition of F^- or CN^- resulted in fluorescence enhancement (turn on). Notably, the TFA addition resulted in fluorescence quenching, whereas the fluorescence enhancement was observed while adding TBAOH. The higher association constant (K_a ) values with anions, lower detection limit, and shifts in redox potentials are due to the electron-withdrawing effect of the -COOCH₃ group at the para-position of the meso-phenyl ring. This electron-withdrawing nature is crucial for the higher affinity towards anions. The anion sensing description in this article may not only unveil the built-in nature of N-confused porphyrins, but may also provide a general proposal for the development of novel anion sensors based on porphyrinoids. The electron-deficient porphyrin framework, large polarisable π-system, and anion binding through the outer NH or a combination of the above factors serve as a foundation for N-confused porphyrin to act as an anion sensor.

The simultaneous recognition mechanism of cations and anions using macrocyclic–iodine structures: insights from dispersion-corrected DFT calculations

The design of structures to recognize ions is growing in recent years. Here, the simultaneous recognition of cations and anions by a macrocycle comprising a simple crown ether and an iodine-triazole unit has been investigated using DFT calculations.

Dynamic optical activity induction in the N-alkyl-N'-trityl ureas and thioureas

Considered to be rigid, the urea and thiourea functionalities, often used in material chemistry and in asymmetric organocatalysis, are able to transmit information regarding 3D structure from a permanently chiral inducer part to a dynamically chiral (reporter) part of the molecule. Despite a considerable distance between the inducer and the reporter parts of the molecule, the chirality transfer phenomenon has been demonstrated for a series of secondary N-alkyl-N'-trityl ureas and thioureas. The induction of helicity in a stereodynamic trityl propeller is revealed by rising non-zero Cotton effects in the area of trityl absorption. The information regarding the 3D structure of the inducer is transferred to the reporter part of the system through a set of weak but complementary electrostatic interactions. The presence of two supramolecular motifs in the same molecule, characterized by opposite properties, significantly affected the molecular solid state structure of the thioureas and their abilities to assemble. In the crystalline phase, the model, a chiral N-tert-butyl-thiourea derivative that retains the extended Z,Z conformation of the linker, is prone to form a supramolecular network typical of secondary ureas and thioureas. In contrast, the presence of the hydrophobic trityl group suppresses the thioamide NHS[double bond, length as m-dash]C hydrogen bonds. Therefore, trityl acts as a supramolecular protecting group for thioamide functionality, hampering the formation of hydrogen bonded networks in the solid state.

Knock-on synthesis of tritopic calix[4]pyrrole host for enhanced anion interactions

Interactions of anionic guests with a tritopic peripherally functionalized conjugated calix[4]pyrrole host (1) prepared using a regioselective synthetic method is reported. The regioselectivity of synthesis relies on selective N-alkylation of the calix[4]pyrrole caused by peripheral substitution of one pyrrole group with subsequent N-alkylation at the opposing pyrrole group termed by us 'knock-on' regioselectivity. The resulting host molecule exhibits anion interactions with common chloride and nitrate anions enhanced by an order of magnitude over the parent conjugated calix[4]pyrrole. Combined analysis of ¹H NMR and UV-vis spectroscopic titration data enabled an evaluation of binding strengths of anions with the host K_A in a binding model where the salt dissociation process is also incorporated in the form of its dissociation constant K_d. Anions could be classified as two types based on their interactions with 1: Type A anions (chloride, nitrate, perchlorate, hydrogensulphate) associate as 1 : 1 complexes through hydrogen bonding while interactions involving Type B anions (acetate, fluoride, dihydrogenphosphate) are complicated by host deprotonation and/or countercation association. Hosts based on rim-functionalized calix[4]pyrroles such as 1 represent a promising new family of chromophores for estimation of biologically relevant anions or other species.

Exotic Hydrogen Bonding in Compressed Ammonia Hydrides

Hydrogen-rich compounds attract significant fundamental and practical interest for their ability to accommodate diverse hydrogen bonding patterns and their promise as superior energy storage materials. Here, we report on an intriguing discovery of exotic hydrogen bonding in compressed ammonia hydrides and identify two novel ionic phases in an unusual stoichiometry NH₇. The first is a hexagonal R3̅ m phase containing NH₃-H⁺-NH₃, H^-, and H₂ structural units stabilized above 25 GPa. The exotic NH₃-H⁺-NH₃ unit comprises two NH₃ molecules bound to a proton donated from a H₂ molecule. Above 60 GPa, the structure transforms to a tetragonal P4₁2₁2 phase comprising NH₄⁺, H^-, and H₂ units. At elevated temperatures, fascinating superionic phases of NH₇ with part-solid and part-liquid structural forms are identified. The present findings advance fundamental knowledge about ammonia hydrides at high pressure with broad implications for studying planetary interiors and superior hydrogen storage materials.

Selective detection of fluoride via amplified donor-acceptor interaction of 6H-indolo[2,3-b]quinoline

In this report, 6H-indolo[2,3-b]quinoline (hereafter 2a) was synthesized and employed as an optical chemosensor for fluoride. The sensitivity of 2a towards fluoride was established from the change in both the absorption and emission signals. The various in-situ¹H NMR, UV-Vis, and density functional studies indicate that the 1:2 binding interaction between 2a and fluoride followed by deprotonation to its corresponding di-anion (2a^2-), which in turn boosted the donor-acceptor interaction between indole and quinoline moiety in 2a^2-via expansion of torsion angle by 10.2° as compared to 2a. Consequently the significant changes in both the absorption and emission signal of 2a allow us to detect and estimate the concentration of fluoride up to 0.2 μM from the mixture of different anions.

A concise treatment of pterins: some recent synthetic and methodology aspects and their applications in molecular sensors

A concise account of pterins in chemistry and biology and their applications in molecular sensors including their optical spectroscopic properties are described. Different natural, synthetic, biological and photophysical aspects are also discussed. Synthetic access to direct functionalised pterins and a recently reported new thiophene annulation technique are described for the synthesis of Form B of molybdenum cofactor. The receptor properties of fluorescent pterin molecules including selenopyrimidines which are rarely reported for their binding of anions and neutral molecules are also of major importance in this review. For such an old and still so young, unexplored pterin system on its power to be sensitive for physical studies especially the interaction with cations, anions and neutral molecules are fascinating and research in this area is relatively new and expected to increase fast. Pterin based receptors are for the first time put into a useful review for the advantage of those who want to explore pterin and modified pterin as chromogenic and fluorogenic sensors.

Miranda M, Busschaert N, Howe ENW, Clarke HJ, Haynes CJE, Kirby IL, Rodilla AM, Pérez-Tomás R, Gale PA, Félix V. Full elucidation of the transmembrane anion transport mechanism of squaramides using in silico investigations

The anion carrier mechanism promoted by squaramide-based molecules has been elucidated by molecular dynamics and chloride efflux studies.

Filling the gap between the quantum and classical worlds of nanoscale magnetism: giant molecular aggregates based on paramagnetic 3d metal ions

In this review, aspects of the syntheses, structures and magnetic properties of giant 3d and 3d/4f paramagnetic metal clusters in moderate oxidation states are discussed. The term "giant clusters" is used herein to denote metal clusters with nuclearity of 30 or greater. Many synthetic strategies towards such species have been developed and are discussed in this paper. Attempts are made to categorize some of the most successful methods to giant clusters, but it will be pointed out that the characteristics of the crystal structures of such compounds including nuclearity, shape, architecture, etc. are unpredictable depending on the specific structural features of the included organic ligands, reaction conditions and other factors. The majority of the described compounds in this review are of special interest not only for their fascinating nanosized structures but also because they sometimes display interesting magnetic phenomena, such as ferromagnetic exchange interactions, large ground state spin values, single-molecule magnetism behaviour or impressively large magnetocaloric effects. In addition, they often possess the properties of both the quantum and the classical world, and thus their systematic study offers the potential for the discovery of new physical phenomena, as well as a better understanding of the existing ones. The research field of giant clusters is under continuous evolution and their intriguing structural characteristics and magnetism properties that attract the interest of synthetic Inorganic Chemists promise a brilliant future for this class of compounds.

Piperazine linked salicylaldoxime and salicylaldimine-based dicopper(ii) receptors for anions

The syntheses and single crystal X-ray analyses of five strapped salicylaldoxime/salicylaldimine based dicopper(ii) receptors utilising a new piperazine linker are described. The complexes form 2 + 2 metallocycles and the molecular structures of all four complexes possess a small internal cavity with the utilisation of a short piperazine linker. The molecular structures of complexes [Cu2(L(4) - H)(L(4) - 2H) ⊂ DMF]BF4·DMF, and [Cu2(L(4) - H)2Br]Br·1.25DMSO·H2O·MeOH, show that intramolecular H-bonding interactions due to the presence of -OH (oxime moiety) groups lead to a Pacman-like cleft arrangement of the two metal coordinating subunits in the metallo-macrocycle. The geometrical constraints brought about by this constrained cleft make the receptor coordinate strongly to a bromide anion involving both metal centres as evidenced by whereas in the larger tetrafluroborate anion is excluded. Absence of the oxime moiety around the metal coordination site of the ligand as demonstrated in the complexes [Cu2(L(5))2BF4](BF4)3, and [Cu2(L(5))2Br]Br3·2MeOH, resulted in less constrained dicopper(ii) helicate forms. For these complexes no anion size discrimination was observed. The addition of pyridine solvent to a slightly modified piperazine-linked ligand produces an expanded 3 + 3 tube-like tricopper complex [Cu3(L(4a) - H)3Py3](BF4)2·(MeOH)3·PF6·(H2O)3, , with two coordinated pyridine molecules occupying the newly formed cavity.

Anion binding, electrochemistry and solvatochromism of β-brominated oxoporphyrinogens

Effects of macrocycle bromination on the structural, electrochemical and anion binding properties of 5,10,15,20-tetrakis(3,5-di-t-butyl-4-oxo-cyclohexa-2,5-dienylidene)porphyrinogen, OxP, are reported. Bromination of 5,10,15,20-tetrakis(3,5-di-t-butyl-4-hydroxyphenyl)-porphinatocopper(II), [T(DtBHP)P]Cu(II) yielded β-Br8OxP, which was N-alkylated to β-Br8OxPBz2 and β-Br8OxPBz4 (where Bz = 4-bromobenzyl). β-Br8OxPBz2 crystallizes in orthorhombic space group Pccn [a = 23.5535(17) Å, b = 19.3587(14) Å c = 20.9760(15) Å, V = 9564.3(12) Å3]. It has a calix[4]pyrrole-like structure with a saddle conformation and two molecules of methanol occupy a central binding site made up of the non-alkylated pyrrole N–H groups. Computational and electrochemical studies revealed widening HOMO–LUMO band gaps for the brominated compounds over the non-brominated analogues consistent with the observed hypsochromic shifts in electronic absorption spectra. Solvatochromic and chromogenic effects on anion binding were both observed for β-Br8OxP and β-Br8OxPBz2 with binding affinities of anions being greater than those observed for the corresponding OxP and OxPBz2. Colorimetric sensor studies suggest that the OxP compounds reported here are possible candidates for use in the design of optoelectronic noses for detection of anions and anionic analyte species of biological interest.

Tri-color emission and colorimetric recognition of acetate using semicarbazide and thio-semicarbazide derivatives: Experimental and computational studies

Two new fluorescence probes having semicarbazide (DSC) and thio-semicarbazide (DTSC) units have been derived upon reaction with 2-hydroxy-5-methylbenzene-1,3-dialdehyde. Both the probes show excellent selectivity for acetate ion in DMSO medium whereby DTSC generates tricolor emission. The association constants of DSC and DTSC for acetate are 6.6×10(4)M(-1) and 2×10(3)M(-1) respectively with corresponding detection limits, 1.06×10(-7)M and 2.5×10(-6)M. Density functional theoretical (DFT) studies nicely demonstrate the interaction between the DTSC and acetate ion.

An NHC silver(i) macrometallocycle: synthesis, structure and selective recognition of iodide anions

An NHC silver(i) crown ether 1 has been synthesized, and the recognition of I⁻ using 1 as a receptor was studied.

A “turn on” fluorescent and chromogenic chemosensor for fluoride anion: experimental and DFT studies

A simple, convenient “turn on” fluorescent and chromogenic chemosensor for fluoride anion detection in acetonitrile as well as in water has been developed.

A sandwich-type zinc complex from a rhodamine dye based ligand: a potential fluorescent chemosensor for acetate in human blood plasma and a molecular logic gate with INHIBIT function

Zn-R1 exhibits reversible binding with acetate yielding different optical and fluorescence outputs on alternate addition of zinc and acetate ions.

Theoretical Study of the Interaction between the Guanidinium Cation and Chloride and Sulfate Anions

The interactions between the guanidinium cation and the chloride and sulfate anions have been explored theoretically. As a basis for this study, the structure of the guanidinium cation has been reexamined and confirmed to possess a nonplanar propeller structure. Thus, computations at the MP2/6-31+G* level yielded several guanidinium-chloride complexes in 1:1 and 2:1 stoichiometry, with the most stable being those in which the guanidinium cation(s) interact in pincerlike form with the spherical chloride anion. In the case of guanidinium-sulfate complexes, a large number of stable 1:1 dimers and 2:1 trimers were found at the same level of computation. The nature of all the interactions established has been analyzed by means of the AIMs and NBO approaches, and several correlations have been found between electron density at the bond critical points, hydrogen bond distances, and orbital interaction energies. The guanidinium moiety has been widely exploited as an anion receptor in supramolecular chemistry and bears relation to the arginine amino acid, which interacts with anionic substrates within proteins. Thus, the current study provides insight into the nature of the interactions involving the guanidinium cation within both abiotic and natural systems.

Sulfate recognition by a hexaaza cryptand receptor

A hexamine macrobicycle with pyrrolyl spacers was evaluated as an anion receptor in its protonated forms. The protonation constants of the receptor, as well as its association constants with Cl(-), NO3(-), AcO(-), ClO4(-), H2PO4(-), and SO4(2-) were determined by potentiometry at 298.2 ± 0.1 K in H2O-MeOH (50 : 50 v/v) and at an ionic strength of 0.10 ± 0.01 M in KTsO. These studies revealed that the Hnpyrr(n+) receptor has a very high effective association constant value for the SO4(2-) at pH 4.0 (log Keff = 6.42), and it is selective for the uptake of this anion in the presence of the other studied anionic substrates. In particular, the receptor showed very high SO4(2-)/NO3(-) selectivity. Using the indicator-displacement approach the receptor is able to signal the presence of sulfate by a change of color. Single crystal X-ray diffraction determination of [(H6pyrr)(SO4)(H2O)3](SO4)2·9.3H2O revealed the presence of one sulfate anion inside the receptor cavity and showed that the encapsulation of the anion is favored by an array of nine hydrogen bonding interactions, including N-HO, C-HO and water-mediated ones.

A simple and effective 1,2,3-triazole based “turn-on” fluorescence sensor for the detection of anions

1,2,3-Triazole based chemosensor is synthesized using “Click chemistry” approach. Addition of fluoride ion “turn-on” the fluorescence response of probe.

A selective ratiometric fluoride ion sensor with a (2,4-dinitrophenyl)hydrazine derivative of bis(indolyl) methane and its mode of interaction

An easy-to-synthesis chemosensor was synthesized and employed as a selective optical chemosensor for fluoride through naked eye detection, which allow us to detect and estimate the concentration of fluoride ion accurately up to 2 μM via ratiometric responses.