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1. Orthogonal, modular anion–cation and cation–anion self-assembly using pre-programmed anion binding sites

   https://doi.org/10.1039/D2SC05121D  

   Dhara, Ayan; Fadler, Rachel E.; Chen, Yusheng; Köttner, Laura A.; Van Craen, David; Carta, Veronica; Flood, Amar H. (March 2023, Chemical Science)

   Subcomponent self-assembly relies on cation coordination whereas the roles of anions often only emerge during the assembly process. When sites for anions are instead pre-programmed, they have the potential to be used as orthogonal elements to build up structure in a predictable and modular way. We explore this idea by combining cation (M + ) and anion (X − ) binding sites together and show the orthogonal and modular build up of structure in a multi-ion assembly. Cation binding is based on a ligand (L) made by subcomponent metal-imine chemistry (M + = Cu + , Au + ) while the site for anion binding (X − = BF 4 − , ClO 4 − ) derives from the inner cavity of cyanostar (CS) macrocycles. The two sites are connected by imine condensation between a pyridyl-aldehyde and an aniline-modified cyanostar. The target assembly [LM-CS-X-CS-ML], + generates two terminal metal complexation sites (LM and ML) with one central anion-bridging site (X) defined by cyanostar dimerization. We showcase modular assembly by isolating intermediates when the primary structure-directing ions are paired with weakly coordinating counter ions. Cation-directed (Cu + ) or anion-bridged (BF 4 − ) intermediates can be isolated along either cation–anion or anion–cation pathways. Different products can also be prepared in a modular way using Au + and ClO 4 − . This is also the first use of gold( i ) in subcomponent self-assembly. Pre-programmed cation and anion binding sites combine with judicious selection of spectator ions to provide modular noncovalent syntheses of multi-component architectures. 

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2. Heterogeneous Cation–Lattice Interaction and Dynamics in Triple-Cation Perovskites Revealed by Infrared Vibrational Nanoscopy

   https://doi.org/10.1021/acsenergylett.0c00522  

   Nishida, Jun; Alfaifi, Amani H.; Gray, Thomas P.; Shaheen, Sean E.; Raschke, Markus B. (May 2020, ACS Energy Letters)
3. Directing cation-cation interactions in thiamine compounds: Analysis of a series of organic salts based on vitamin B1

   https://doi.org/10.1016/j.molstruc.2021.130046  

   Traver, Joseph; Chenard, Erica; Zeller, Matthias; Guillet, Gary L.; Lynch, Will E.; Hillesheim, Patrick C. (May 2021, Journal of Molecular Structure)

   null (Ed.)
4. Communication—Capillary Effects on Metal Cation Solubility

   https://doi.org/10.1149/1945-7111/ad0e48  

   Sieradzki, Karl (November 2023, Journal of The Electrochemical Society)

   The effect of capillarity on the chemical equilibrium between a dissolved metal cation and the corresponding metal oxide is determined within the framework of Gibbssian thermodynamics. We examined the equilibrium between Cr³⁺and Cr₂O₃and found that for 10⁻⁶M Cr³⁺in the electrolyte and a curvature of −2 × 10⁹m⁻¹, the equilibrium pH is −1.8. The corresponding potential-pH diagram shows that chromium passivates in strong acids. This analysis potentially resolves a long-standing issue in corrosion science. 

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5. Forbidden ion transport through cation exchange membranes

   https://doi.org/10.1016/j.talanta.2024.126581  

   Chaudhary, Chandan K; Dasgupta, Purnendu K (November 2024, Talanta)

   Cation exchange membranes (CEMs) are widely used in many applications. The fixed anionic groups e.g., COO􀀀 , –SO3 - , etc. in the polymer matrix ideally allows the passage only of oppositely charged cations, driven by a potential or a concentration gradient. Anions, charged negative, the same as the membrane matrix, cannot pass through the membrane due to electrostatic repulsion. Such “Donnan-forbidden” passage can, however, occur to some degree, if the electrical or concentration gradient is high enough to overcome the “Donnan barrier”. Except for salt uptake/transport in concentrated salt solutions, the factors that govern such Forbidden Ion Transport (FIT) have rarely been studied. In most applications of transmembrane ion transport, whether electrically driven as in electrodialysis, or concentration-driven, it is the transport of the counterion to the fixed charged groups, such as that of the proton through a CEM, that is usually of interest. Nevertheless, CEMs are also of interest in analytical chemistry, specifically in suppressed ion chromatography. As used in membrane suppressors, both transport of permitted ions and rejection of forbidden ions are important. If the latter is indeed governed by electrostatic factors, other things being equal, the primary governing factor should be the charge density of the membrane, tantamount to its ion exchange capacity (IEC). In fabricating microscale suppressors, we found useful to synthesize a new ion exchange polymer that can be easily molded to make tubular microconduits. Despite a high IEC of this material, FIT was also found to be surprisingly high. We measured several relevant properties for thirteen commercial and four custom-made membranes to discover that while FIT is indeed linearly related to 1/ IEC for a significant number of these membranes, for very high water-content membranes, FIT may be overwhelmingly governed by the water content of the membrane. In addition, FIT through all CEMs differ greatly among strong acids, they may still be transported as the molecular acids and the extent is in the same order as the expected activity of the molecular acid in the CEM. These results are discussed with the perspective that even for strong acids, the transport does take place as un-ionized molecular acids. 

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