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DOE OSTI · 3533190

Multi-Ion Complexes and Competition from Bulky BArF – Anions for Chloride Binding in Ion Pairing Conditions

Morgan, Amanda R. [Indiana University, Bloomington, IN (United States)]·Holleworth, Janine M. [Indiana University, Bloomington, IN (United States)]·Bhattacharjee, Nabarupa [Indiana University, Bloomington, IN (United States)] (ORCID:000000024759135X)·Flood, Amar H. [Indiana University, Bloomington, IN (United States)] (ORCID:0000000227649155)
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Abstract

Cationic charges have long been used to enhance anion binding. Embedding charge introduces strong ion pairing for target anions but also for off-target ions, ultimately generating a mixture of multi-ion species that are hard to identify and quantify. While many sidestep this problem using polar solvents and weakly coordinating ions, these approaches exclude a substantial cross-section of conditions found in applications spanning recognition, assembly, separations, templation, and catalysis. To confront this complexity, we study the binding of an anion to a cationic receptor featuring low shape complementarity in a low-polarity solvent to maximize ionic interactions. We prepared the receptor as a salt of the weakly coordinating tetrakis­[3,5-bis­(trifluoromethyl)­phenyl]­borate (BArF – ) anion and studied the binding of small chloride (Cl – ) and medium-sized iodide (I – ) anions. Surprisingly, the use of the bulky BArF – anion does not suppress ion pairing interactions, with 65% of the receptor being paired at 0.5 mM in dichloromethane. We observe multi-ion receptor-Cl – complexes (2:1, 1:1, 1:2), reinforcing the complexity that emerges when working in low-polarity media. Here, we reveal the dependence of affinity on anion charge density and size and that bulky BArF – counteranions compete for chloride binding. These studies reveal the noninnocence of BArF – anions and strategies to quantify multi-ion species.

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Morgan, Amanda R. [Indiana University, Bloomington, IN (United States)], Holleworth, Janine M. [Indiana University, Bloomington, IN (United States)], Bhattacharjee, Nabarupa [Indiana University, Bloomington, IN (United States)] (ORCID:000000024759135X), Flood, Amar H. [Indiana University, Bloomington, IN (United States)] (ORCID:0000000227649155). 2025-10-09. Multi-Ion Complexes and Competition from Bulky BArF – Anions for Chloride Binding in Ion Pairing Conditions. https://doi.org/10.1021/acs.joc.5c01750

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