title: Selective isolation of gold facilitated by second-sphere coordination with α-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(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.
authors.affiliation: Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208-3113, USA.
authors.forename: Zhichang
authors.initials: Z
authors.lastname: Liu
authors.forename: Marco
authors.initials: M
authors.lastname: Frasconi
authors.forename: Juying
authors.initials: J
authors.lastname: Lei
authors.forename: Zachary J
authors.initials: ZJ
authors.lastname: Brown
authors.forename: Zhixue
authors.initials: Z
authors.lastname: Zhu
authors.forename: Dennis
authors.initials: D
authors.lastname: Cao
authors.forename: Julien
authors.initials: J
authors.lastname: Iehl
authors.forename: Guoliang
authors.initials: G
authors.lastname: Liu
authors.forename: Albert C
authors.initials: AC
authors.lastname: Fahrenbach
authors.forename: Youssry Y
authors.initials: YY
authors.lastname: Botros
authors.forename: Omar K
authors.initials: OK
authors.lastname: Farha
authors.forename: Joseph T
authors.initials: JT
authors.lastname: Hupp
authors.forename: Chad A
authors.initials: CA
authors.lastname: Mirkin
authors.forename: J
authors.initials: J
authors.lastname: Fraser Stoddart