Selective isolation of gold facilitated by second-sphere coordination with ?-cyclodextrin.

ABSTRACT: Gold recovery using environmentally benign chemistry is imperative from an environmental perspective. Here we report the spontaneous assembly of a one-dimensional supramolecular complex with an extended {[K(OH?)?][AuBr?](?-cyclodextrin)?}n chain superstructure formed during the rapid co-precipitation of ?-cyclodextrin and KAuBr? in water. This phase change is selective for this gold salt, even in the presence of other square-planar palladium and platinum complexes. From single-crystal X-ray analyses of six inclusion complexes between ?-, ?- and ?-cyclodextrins with KAuBr? and KAuCl?, we hypothesize that a perfect match in molecular recognition between ?-cyclodextrin and [AuBr?](-) leads to a near-axial orientation of the ion with respect to the ?-cyclodextrin channel, which facilitates a highly specific second-sphere coordination involving [AuBr?](-) and [K(OH?)?](+) and drives the co-precipitation of the 1:2 adduct. This discovery heralds a green host-guest procedure for gold recovery from gold-bearing raw materials making use of ?-cyclodextrin-an inexpensive and environmentally benign carbohydrate.

SUBMITTER: Liu Z 

PROVIDER: S-EPMC3674257 | biostudies-literature | 2013

REPOSITORIES: biostudies-literature