Each year, C&E News runs a poll for their “ Molecule of the year “. I occasionally comment with some aspect of one of the molecules that catches my eye (I have already written about cyclo[18]carbon, another in the list). Here, it is the Incredible chloride cage , a cryptand-like container with an attomolar (10 17 M -1 ) affinity for a chloride anion.[cite]10.1126/science.aaw5145[/cite] The essence of
A C–H bonding trap for chloride Part of the reason salt dissolves so well in water is that the polarized O–H bonds attract the negatively charged chloride ions. It has therefore been common to include O–H or N–H bonds in molecular receptors designed to capture anions such as chloride. Liu et al. report the surprising finding that sufficiently polarized C–H bonds can work even better (see the Perspective by Bowman-James). They designed a cage with triazole rings that directed C–H bonds inward to encapsulate chloride with a remarkable attomolar affinity in dichloromethane. Science , this issue p. 159 ; see also p. 124