Enhancing Proton Conductivity of a 3D Metal-Organic Framework by Attaching Guest NH Molecules.

By reaction of a newly designed organic ligand, [3-(naphthalene-1-carbonyl)-thioureido] acetic acid (CHC(O)NHC(S)NHCHCOOH; HL), with Cu(OAc), a metal-organic framework [(CuCuL)·3HO] (1) containing unique mixed-valence [CuCuL] subunits has been successfully synthesized and structurally characterized. MOF 1 displays a three-dimensional open framework bearing one-dimensional channels. Consequently, a new derivative MOF [CuCuL] -NH (2) is procured upon exposure of 1 to NH vapors from 28 wt % aqueous NH solution, which bears 2 NH and 4 HO molecules in accordance with the elemental and thermal analyses. Both 1 and 2 exhibit relatively high water stability, whose proton conduction properties under water vapor have been researched. Notably, 2 shows an ultrahigh proton conductivity of 1.13 × 10 S cm, which is 2 orders of magnitude larger than that of MOF 1 (4.90 × 10 S cm) under 100 °C and 98% RH. On the basis of the structural data, E values, HO and ammonia vapor absorptions, and PXRD measurements, the proton transfer mechanisms were suggested. This is an efficient and convenient way to obtain suitable and highly proton-conducting materials by attaching NH molecules.