Enhancing Proton Conductivity of a 3D Metal–Organic Framework by Attaching Guest NH3 Molecules

By reaction of a newly designed organic ligand, [3-(naphthalene-1-carbonyl)-thioureido] acetic acid (C10H7C(O)NHC(S)NHCH2COOH; H3L), with Cu(OAc)2, a metal–organic framework [(CuI4CuII4L4)·3H2O]n (1) containing unique mixed-valence [CuI4Cu4IIL4] 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 [CuI4CuII4L4]n-NH3 (2) is procured upon exposure of 1 to NH3 vapors from 28 wt % aqueous NH3 solution, which bears 2 NH3 and 4 H2O 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 × 10–2 S cm–1, which is 2 orders of magnitude larger than that of MOF 1 (4.90 × 10–4 S cm–1) under 100 °C and 98% RH. On the basis of the structural data, Ea values, H2O and ammonia vapor absorptio...