Proton Conductivity via Trapped Water in Phosphonate-Based Metal-Organic Frameworks Synthesized in Aqueous Media

Unjila Afrin, Mohammad Rasel Mian, Ken Ichi Otake, Riki J. Drout, Louis R. Redfern, Satoshi Horike, Timur Islamoglu, Omar K. Farha*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

10 Scopus citations

Abstract

Metal-organic frameworks (MOFs) are promising candidates for proton-conducting applications. Herein, we report the aqueous synthesis of two new phosphonate-based MOFs comprising glyphosate linkers, [Mg(dpmp)]·2H2O (Mg-NU-225) and [Fe(dpmp)]·2H2O (Fe-NU-225), (dpmp = N,N′-diphosphonomethyl-2,5-piperazinedione), and explore their proton conductivities. Single crystal X-ray diffraction measurements revealed that both frameworks display a two-dimensional layered structure with a cyclic ring ligand which forms in situ from the condensation of two glyphosate molecules. Under humid conditions and over a wide temperature range, water molecules are trapped between adjacent layers and facilitate rapid proton conduction. Mg-NU-225 and Fe-NU-225 recorded proton conductivities of 1.5 × 10-5 and 1.7 × 10-5 S cm-1, respectively, along the plane direction and 1.6 × 10-3 and 9.1 × 10-5 S cm-1 perpendicular to the plane direction at 55 °C and 95% relative humidity, as confirmed by two-contact probe impedance methods. The mechanism of proton transport was found to be that of the Grotthuss model from the low activation energy for proton hopping.

Original languageEnglish (US)
Pages (from-to)1086-1091
Number of pages6
JournalInorganic chemistry
Volume60
Issue number2
DOIs
StatePublished - Jan 18 2021

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Inorganic Chemistry

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