Porphyrinylphosphonate-Based Metal-Organic Framework: Tuning Proton Conductivity by Ligand Design

Abstract

A novel metal-organic framework [Zn₃ (Ni-H₂ TPPP)(Ni-H₄ TPPP)(Ni-H₅ TPPP)⋅7(CH₃ )₂ NH₂ ⋅DMF⋅7 H₂ O] (where Ni-H_x TPPP (x=2,4,5) are partially deprotonated [5,10,15,20-tetrakis(3-(phosphonatophenyl)-porphyrinato(2-))]nickel(II) species), IPCE-2Ni, with outstanding proton conductivity (1.0×10^-2 S cm^-1 at 75 °C and 95 % relative humidity) has been obtained. The high concentration of free phosphonate groups and compensating dimethylammonium cations bound by hydrogen bonds in the unique crystal structure of IPCE-2Ni is a key factor responsible for the observed high proton conductivity, which is one order of magnitude higher than for the corresponding MOF based on 5,10,15,20-tetrakis(4-(phosphonatophenyl)porphyrinato(2-))]nickel(II) IPCE-1Ni and comparable with that of leaders among MOFs.

Keywords: X-ray analysis; conducting materials; metal-organic frameworks; porphyrinylphosphonate; proton conductivity.