Decorated crown ethers as selective ion traps: Solvent's role in crown's preference towards a specific ion

Abstract

Deviation of sodium and potassium concentrations from their optimal values in living organisms is associated with severe health conditions, thus their precise determination in blood samples requires design of sensitive sensors. Additionally, excess of the two alkali cations should be removed from drinking water. Crown ethers are well-known metal ion traps, as careful choice of crown's size and its substituents might tune it towards favoring a specific ion. It has been proved experimentally that dibrominated bithiophene crown ethers with five and six oxygen atoms selectively capture the Na+ and the K+ ion, respectively (Giovannitti et al., Adv. Funct. Mater. 26, 2016, 514) in acetonitrile solution. In the present contribution, we analyzed the nature of ion–crown, ion–solvent, and crown–solvent interactions, and demonstrated that the solvent molecules are responsible for the decorated crown's preference for a particular alkali cation. While past research focused on the ring size and the ion radius compatibillity, which is important for a formation of a stable ion–crown complex, our findings highlight the decisive role of solvent molecules in the selectivity of crown ethers toward particular cations.