Recognition of Anions by Protonated Methylazacalixpyridines

Abstract

Methylazacalixpyridines are a unique kind of macrocyclic molecules that are able to self-regulate their conformations to best fit the guests. They had shown good recognition to both neutral molecules such as diols and fullerenes and cations. After protonation, the conformation of methylazacalixpyridines became more flexible and could serve as receptors for anions. In the solution, the protonated methylazacalix[2]pyridine[2]arene formed complexes with halides yielding biding constants of 79 (mol/L)^−1 for chloride, 10 (mol/L)^−1 for bromide, and 79 (mol/L)^−1 for iodide, respectively. The crystal structures of the complexes between protonated methylazacalix[4]pyridine (MACP-4), methylazacalix[2]pyridine[2]arene (MACP-2-A-2), and iodide anion showed a multiple interaction mode including electrostatic attraction, hydrogen bonding, and anion-p interactions.

Keywords

anion recognition / methylazacalixpyridine / protonation