Selective total encapsulation of the sulfate anion by neutral nano-jars

Nano-sized toroidal copper(II)-hydroxide/pyrazolate assemblies, lined by H-bond donors on the inside and hydrophobic on the outside, selectively extract sulfate from mixtures with nitrate or perchlorate. Tetrabutylammonium lids seal the nano-jars and render the encapsulated sulfate anion completely buried and inaccessible, so that it is not precipitated by Ba2+ ions.