Macrocyclic and acyclic supramolecular elements for co-precipitation of square-planar gold(III) tetrahalide complexes

Macrocyclic hosts have long been used for guest encapsulation, and recently a new application has emerged; employment as supramolecular elements for capture and recovery of gold through host/guest co-precipitation. The guests are square-planar tetrahaloaurate anions, practically important gold complexes with a capacity to engage in non-covalent interactions such as hydrogen bonding and Au–! interactions. The successful macrocyclic hosts for co-precipitation include cyclodextrins, cucurbiturils, and cyclophanes, with recent expansion of the structural scope to include acyclic amides.