title: Unique Proton Dynamics in an Efficient MOF-Based Proton Conductor.
abstract: Recently, research on metal-organic frameworks (MOFs) serving as a new type of proton conductive material has resulted in many exciting achievements. However, direct observation of a well-established proton-transfer mechanism still remains challenging in MOFs and other crystalline compounds, let alone other conductive materials. Herein we report the solvothermal synthesis of a new proton-conducting MOF, (Me2NH2)[Eu(L)] (H4L = 5-(phosphonomethyl)isophthalic acid). The compound consists of a layered anionic framework [Eu(L)]-and interlayer-embedded counter cations (Me2NH2)+, which interact with adjacent uncoordinated O atoms of phosphonate groups to form strongly (N-H···O) hydrogen-bonded chains aligned parallel to the c-axis. Facile proton transfer along these chains endows the compound with single-crystal anhydrous conductivity of 1.25 × 10-3S·cm-1at 150 °C, and water-assisted proton conductivity for a compacted pellet of microcrystalline crystals attains 3.76 × 10-3S·cm-1at 100 °C and 98% relative humidity (RH). Proton dynamics (vibrating and transfer) within N-H···O chains of the compound are directly observed using a combination of anisotropic conductivity measurements and control experiments using large single-crystals and pelletized samples, in situ variable-temperature characterization techniques including powder X-ray diffraction (PXRD), single-crystal X-ray diffraction (SCXRD), diffuse reflectance infrared Fourier transform spectrum (DRIFTS), and variable-temperature photoluminescence. In particular, a scarce single-crystal to single-crystal (SCSC) transformation accompanied by proton transfer between an anionic structure (Me2NH2)[Eu(L)] and an identical neutral framework [Eu(HL)] has been identified.
authors.affiliation: College of Chemistry and Molecular Engineering, Zhengzhou University , Zhengzhou 450001, China.
authors.forename: Yong-Sheng
authors.initials: YS
authors.lastname: Wei
authors.affiliation: College of Chemistry and Molecular Engineering, Zhengzhou University , Zhengzhou 450001, China.
authors.forename: Xiao-Peng
authors.initials: XP
authors.lastname: Hu
authors.affiliation: College of Chemistry and Molecular Engineering, Zhengzhou University , Zhengzhou 450001, China.
authors.forename: Zhen
authors.initials: Z
authors.lastname: Han
authors.affiliation: College of Chemistry and Molecular Engineering, Zhengzhou University , Zhengzhou 450001, China.
authors.forename: Xi-Yan
authors.initials: XY
authors.lastname: Dong
authors.affiliation: College of Chemistry and Molecular Engineering, Zhengzhou University , Zhengzhou 450001, China.
authors.forename: Shuang-Quan
authors.identifier: 0000-0002-6728-0559
authors.initials: SQ
authors.lastname: Zang
authors.affiliation: College of Chemistry and Molecular Engineering, Zhengzhou University , Zhengzhou 450001, China.|Department of Chemistry and Center of Novel Functional Molecules, The Chinese University of Hong Kong , Shatin, New Territories, Hong Kong SAR, China.
authors.forename: Thomas C W
authors.identifier: 0000-0002-4316-2937
authors.initials: TC
authors.lastname: Mak