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1. Anion‐π Interactions: What's in the Name?

   https://doi.org/10.1002/cplu.202300350  

   Rosokha, Sergiy_V (August 2023, ChemPlusChem)

   Abstract The studies of the anion‐π interactions advanced during the last two decades from the discussion of the mere existence of this counter‐intuitive bonding to its utilization for anion recognition and transport, catalysis, and other applications. Yet, there are substantial differences in the interpretation of nature and the driving forces of anion‐π bonding. Most surprisingly, there are still different opinions about the meaning of this term (i. e., which associations can be considered anion‐π complexes). After a brief overview of the studies in this area (including early examples of such complexes), we suggested that anion‐π bonding occurs when there is evidence of a net attraction between a (close‐shell) anion and the face of an electrophilic π‐system. This definition encompasses fundamentally similar supramolecular complexes comprising diverse π‐systems and anions and its general acceptance would facilitate a discussion of the nature and distinct driving forces of this fascinating interaction. 

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2. Is the Chemisorbed CO ₂ in Ionic Liquid Electrolytes Active for Electrochemical Utilization? A Case Study on Carboxylate and Carbamate Speciation

   https://doi.org/10.1149/1945-7111/addf83  

   Coskun, Oguz_Kagan; Dongare, Saudagar; Gurkan, Burcu (June 2025, Journal of The Electrochemical Society)

   Abstract This study examines the activity of chemisorbed CO2 species in the microenvironment formed by bifunctional ionic liquids (ILs) in the reactive capture and conversion (RCC) of CO2 to CO on silver. Comparative electroanalytical measurements with imidazolium based ILs were performed to probe the impact of electrostatic interactions, anion and cation basicity, and hydrogen bonding on RCC. Particularly, ILs with 1-ethyl,3-methylimidazolium ([EMIM]+) and 1-ethyl, 2,3-methylimidazolium ([EMMIM]+) cations and aprotic heterocyclic anions of 2-cyanopyrrolide ([2-CNpyr]) and 1,2,4-triazolide ([1,2,4-Triz]) were examined for RCC. It was found that anion–CO2 carbamate complexes facilitate RCC at significantly lower overpotentials compared to cation–CO2 carboxylate complexes. Additionally, [EMIM]+ was found to better stabilize anion–CO2 complexes than [EMMIM]+. Furthermore, it was found that 2-CNpyrH that naturally forms in CO2 absorption competes for electrode surface adsorption with the anion–CO2 carbamate complex, thereby reducing the electrochemical activity of the anion–CO2 complex. These results highlight the importance of IL structure in tuning the interfacial interactions and suggest that ILs with anion-dominated CO2 chemisorption enhances CO2 utilization in RCC applications. 

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3. “Anti-electrostatic” halogen bonding in solution

   https://doi.org/10.1039/d1sc01863a  

   Loy, Cody; Holthoff, Jana M.; Weiss, Robert; Huber, Stefan M.; Rosokha, Sergiy V. (June 2021, Chemical Science)

   null (Ed.)

   Halogen-bonded (XB) complexes between halide anions and a cyclopropenylium-based anionic XB donor were characterized in solution for the first time. Spontaneous formation of such complexes confirms that halogen bonding is sufficiently strong to overcome electrostatic repulsion between two anions. The formation constants of such “anti-electrostatic” associations are comparable to those formed by halides with neutral halogenated electrophiles. However, while the latter usually show charge-transfer absorption bands, the UV-Vis spectra of the anion–anion complexes examined herein are determined by the electronic excitations within the XB donor. The identification of XB anion–anion complexes substantially extends the range of the feasible XB systems, and it provides vital information for the discussion of the nature of this interaction. 

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4. Mononuclear and Dinuclear Copper Complexes of Tridentate Redox‐active Ligands with Tunable H‐bonding Donors: Structure, Spectroscopy and H ⁺ /e ⁻ Reactivity

   https://doi.org/10.1002/asia.202100286  

   Wu, Tong; Musgrove, Justin; Siegler, Maxime_A; Garcia‐Bosch, Isaac (May 2021, Chemistry – An Asian Journal)

   Abstract In this research article, we describe the synthesis and characterization of mononuclear and dinuclear Cu complexes bound by a family of tridentate redox‐active ligands with tunable H‐bonding donors. The mononuclear Cu‐anion complexes were oxidized to the corresponding “high‐valent” intermediates by oxidation of the redox‐active ligand. These species were capable of oxidizing phenols with weak O−H bonds via H‐atom abstraction. Thermodynamic analysis of the H‐atom abstractions, which included reduction potential measurements, pK_adetermination and kinetic studies, revealed that modification of the anion coordinated to the Cu and changes in the H‐bonding donor did not lead to major differences in the reactivity of the “high‐valent” CuY complexes (Y: hydroxide, phenolate and acetate), which indicated that the tridentate ligand scaffold acts as the H⁺and e⁻acceptor. 

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5. Cluster self-assembly and anion binding by metal complexes of non-innocent thiazolidinyl–thiolate ligands

   https://doi.org/10.1039/D2DT01339H  

   Riffel, Madeline N.; Siegel, Lukas; Oliver, Allen G.; Tsui, Emily Y. (June 2022, Dalton Transactions)

   Zn II and Fe II chloride complexes of a di(methylthiazolidinyl)pyridine ligand were deprotonated to form the corresponding thiolate complexes supported by redox-active iminopyridine moieties. The thiolate donor groups are nucleophilic and reactive toward oxidants, electrophiles, and protons, while the pendant thiazolidine rings are available for hydrogen bonding. Anion exchange with the weakly-coordinating triflate anion resulted in self-assembly of the iminopyridine complexes to form a trimeric [M 3 S 3 ] cluster. Hydrogen bonding closely associates anions with this trimetallic core. 

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