Nonspherical anion sequestration by C-H hydrogen bonding

• Published in: Chemical science (Cambridge) Vol. 13; no. 7; pp. 226 - 232
• Main Authors: Mirzaei, Saber, Espinoza Castro, Victor M, Hernández Sánchez, Raúl
• Format: Journal Article
• Language: English
• Published: England Royal Society of Chemistry 16-02-2022; The Royal Society of Chemistry
• Subjects: Affinity; Anions; Aromatic compounds; Atomic properties; Chemistry; Electropositivity; Fluorine; Hydrogen bonding; Hydrogen bonds; Ions
• ISSN: 2041-6520; 2041-6539
• DOI: 10.1039/d1sc07041j

Macrocyclic arenes laid the foundations of supramolecular chemistry and their study established the fundamentals of noncovalent interactions. Advancing their frontier, here we designed rigidified resorcin[4]arenes that serve as hosts for large nonspherical anions. In one synthetic step, we vary the host's anion affinity properties by more than seven orders of magnitude. This is possible by engineering electropositive aromatic C-H bond donors in an idealized square planar geometry embedded within the host's inner cavity. The hydrogen atom's electropositivity is tuned by introducing fluorine atoms as electron withdrawing groups. These novel macrocycles, termed fluorocages, are engineered to sequester large anions. Indeed, experimental data shows an increase in the anion association constant (
K
a
) as the number of F atoms increase. The observed trend is rationalized by DFT calculations of Hirshfeld Charges (HCs). Most importantly, fluorocages in solution showed weak-to-medium binding affinity for large anions like [PF
6
]
−
(10
2
<
K
a
<10
4
M
−1
), and high affinity for [MeSO
3
]
−
(
K
a
>10
6
).
Fluorocages: new class of rigidified host utilizing nontraditional C-H hydrogen bonds to capture the nonspherical anions.