title: Coordination-chemistry control of proton conductivity in the iconic metal-organic framework material HKUST-1.
abstract: HKUST-1, a metal-organic framework (MOF) material containing Cu(II)-paddlewheel-type nodes and 1,3,5-benzenetricarboxylate struts, features accessible Cu(II) sites to which solvent or other desired molecules can be intentionally coordinated. As part of a broader investigation of ionic conductivity in MOFs, we unexpectedly observed substantial proton conductivity with the "as synthesized" version of this material following sorption of methanol. Although HKUST-1 is neutral, coordinated water molecules are rendered sufficiently acidic by Cu(II) to contribute protons to pore-filling methanol molecules and thereby enhance the alternating-current conductivity. At ambient temperature, the chemical identities of the node-coordinated and pore-filling molecules can be independently varied, thus enabling the proton conductivity to be reversibly modulated. The proton conductivity of HKUST-1 was observed to increase by ~75-fold, for example, when node-coordinated acetonitrile molecules were replaced by water molecules. In contrast, the conductivity became almost immeasurably small when methanol was replaced by hexane as the pore-filling solvent.
authors.affiliation: Department of Chemistry and International Institute for Nanotechnology, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208, USA.
authors.forename: Nak Cheon
authors.initials: NC
authors.lastname: Jeong
authors.forename: Bappaditya
authors.initials: B
authors.lastname: Samanta
authors.forename: Chang Yeon
authors.initials: CY
authors.lastname: Lee
authors.forename: Omar K
authors.initials: OK
authors.lastname: Farha
authors.forename: Joseph T
authors.initials: JT
authors.lastname: Hupp