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

TitleSelective isolation of gold facilitated by second-sphere coordination with α-cyclodextrin.
Publication TypeJournal Article
Year of Publication2013
AuthorsLiu Z, Frasconi M, Lei J, Brown ZJ, Zhu Z, Cao D, Iehl J, Liu G, Fahrenbach AC, Botros YY, Farha OK, Hupp JT, Mirkin CA, Fraser Stoddart J
JournalNature communications
Date Published2013

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(OH₂)₆][AuBr₄](α-cyclodextrin)₂}n chain superstructure formed during the rapid co-precipitation of α-cyclodextrin and KAuBr₄ 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 α-, β- and γ-cyclodextrins with KAuBr₄ and KAuCl₄, we hypothesize that a perfect match in molecular recognition between α-cyclodextrin and [AuBr₄](-) leads to a near-axial orientation of the ion with respect to the α-cyclodextrin channel, which facilitates a highly specific second-sphere coordination involving [AuBr₄](-) and [K(OH₂)₆](+) 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 α-cyclodextrin-an inexpensive and environmentally benign carbohydrate.

Alternate JournalNat Commun